JP2005346865A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium having excellent dimensional stability without generating track deviation to environmental change such as temperature, humidity and tension and useful especially for a high density magnetic recording medium. <P>SOLUTION: The magnetic recording medium has a layer (a metal layer) containing metals or a metal based inorganic compound on one side of a polyester layer, a magnetic layer as an outer layer on the one side and a back coat layer as an outer layer on the opposite side. The magnetic recording medium has 0 to 10 ppm/°C temperature expansion coefficient in the width direction, 0 to 7 ppm/%RH humidity expansion coefficient and 0 to 1,200 ppm width dimensional change in a tape running environment. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnetic recording medium that can be suitably used for high-density recording of digital data and the like.

  Magnetic recording media in which a magnetic recording layer is provided on a biaxially oriented polyester film are used for digital video tapes, computer backup tapes (hereinafter referred to as data tapes), and the like. In recent years, in magnetic tapes, especially data tapes that perform magnetic recording at high density, the track has become very small, which can cause slight thermal and mechanical dimensional changes during tape running and storage, and data recording. The difference in the temperature and humidity environment at the time of reading has caused a problem that causes poor data reproduction.

  Therefore, a magnetic recording medium compatible with high-density recording is required to have high dimensional stability against stresses such as changes in temperature and humidity environment and heat and tape tension. In a linear recording type data tape, high dimensional stability in the tape width direction is particularly required. Needless to say, high productivity is required to supply products to the market at a low price in accordance with the recent price reduction of recording media in general.

  In order to improve the dimensional stability against temperature and humidity changes in the tape width direction, it is effective to increase the strength in the width direction of the film used as a base material (hereinafter referred to as a base film) to reduce the temperature and humidity expansion. . However, when the strength in the width direction is increased, the strength in the longitudinal direction is inevitably lowered, and the tape is easily stretched in the longitudinal direction with respect to the tape tension, resulting in the accompanying creep in the width direction. Thus, it is difficult to achieve both dimensional stability against changes in temperature and humidity and dimensional stability against tension by changing the strength of the base film.

  As a base film capable of meeting the above dimensional stability requirements, a magnetic recording medium support in which a reinforcing film made of a metal material such as a metal or a semimetal is provided on a polyester film, or a magnetic recording medium using this support is available. It is known (patent documents 1 to 3).

However, even if the magnetic recording medium support or the magnetic recording medium disclosed in Patent Documents 1 to 3 is used, the properties such as the rigidity and the coefficient of humidity expansion are good, but the tape width against changes in temperature and humidity environment and tension. The total balance, such as the deformation of the tape and the shrinkage of the width due to long-term creep, is not good, and there is still a problem that when used as a data tape, if the environment changes, track deviation is likely to occur. I understood.
JP 2002-319122 A JP 2001-256636 A JP 2000-11364 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium that has excellent dimensional stability that is unlikely to cause a track shift even in response to environmental changes such as temperature and humidity and tension, and is particularly useful for a high-density magnetic recording medium. It is in.

To achieve the above object, the present invention provides:
A layer (M layer) containing a metal or a metal-based inorganic compound is provided on at least one surface of the polyester layer, and a magnetic layer is provided on the outer layer of this layer (M layer), and a back coat layer is provided on the opposite outer layer. The temperature expansion coefficient in the width direction of the magnetic recording medium is 0 to 10 ppm / ° C., the humidity expansion coefficient is 0 to 7 ppm /% RH, and the width dimension changes in the tape running environment shown below are as follows: It is characterized by a magnetic recording medium of 0 to 1,200 ppm.

[Width dimension change in tape running environment]
The sum of the following a, b, and c is defined as a width dimension change in the tape running environment.

  a: Absolute value of the dimensional change rate in the width direction when the load is changed from 10 ° C. and 10% RH to 30 ° C. and 80% RH with a load of 1 N applied in the longitudinal direction.

  b: Absolute value of the dimensional change rate when the longitudinal load is changed from 0.5 to 1.5 N in an environment of 40 ° C. and 60% RH.

  c: Absolute value of contraction rate in the width direction before and after holding for 48 hours in a state where a load of 1 N was applied in the longitudinal direction under an environment of 40 ° C. and 60% RH.

  According to the present invention, as described below, by defining the temperature expansion coefficient of the magnetic recording medium, the humidity expansion coefficient, and the temperature change in the width direction dimension when a load is applied in the longitudinal direction of the medium, to a specific range, A magnetic recording medium having excellent dimensional stability can be obtained in all temperature and humidity ranges of low temperature and low humidity, low temperature and high humidity, high temperature and low humidity, and high temperature and high humidity.

  The magnetic recording medium of the present invention has a magnetic layer in one outer layer of a support having a layer (M layer) containing a metal or a metal-based inorganic compound in at least one of a polyester layer (B layer) made of a polyester film. The magnetic recording medium preferably has a backcoat layer on the outer layer opposite to the magnetic layer. It is difficult to obtain the effects of the present invention with a conventional magnetic recording medium having no M layer (strengthening layer).

  The polyester layer of the magnetic recording medium of the present invention is preferably a biaxially oriented polyester film. In the case of a laminated film having two or more film layers, it is sufficient that at least one layer constituting the film layer is biaxially oriented. When all layers are non-oriented or uniaxially oriented polyester films, it is difficult to satisfy the characteristics of the present invention.

  The polyester layer of the present invention is preferably a polyester film containing 70% by weight or more of polyester. More preferably, it is a polyester film containing 90% by weight or more of polyester. It may consist of a single polyester or two or more polyesters, or may be a polymer alloy with another thermoplastic resin. The polymer alloy here refers to a polymer multi-component system, which may be a block copolymer by copolymerization or a polymer blend by mixing or the like.

  The polyester used in the polyester layer of the present invention may be a polymer composed of an acid component such as aromatic dicarboxylic acid, alicyclic dicarboxylic acid or aliphatic dicarboxylic acid and a diol component.

  As the aromatic dicarboxylic acid, for example, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid and the like can be used. As alicyclic dicarboxylic acid, cyclohexane dicarboxylic acid etc. can be used, for example. As the aliphatic dicarboxylic acid, for example, adipic acid, sebacic acid, dodecanedioic acid and the like can be used. Of these, terephthalic acid, 2,6-naphthalenedicarboxylic acid and the like can be preferably used, and terephthalic acid can be particularly preferably used. These acid components may be used alone or in combination of two or more.

  Examples of the diol component include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, Triethylene glycol, 2,2′-bis (4′-β-hydroxyethoxyphenyl) propane and the like can be used, and ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol are particularly preferable. Diethylene glycol or the like can be used, and ethylene glycol can be used particularly preferably. These diol components may be used alone or in combination of two or more.

  Preferred examples of the polyester include polyethylene terephthalate (PET) and poly (ethylene-2,6-naphthalenedicarboxylate) (PEN) from the viewpoints of performance and cost. Among these, PET is excellent from the viewpoint of cost and creep characteristics (the values of b and c of the present invention to be described later are easily controlled within a preferable range), and PEN has heat resistance and temperature / humidity deformation characteristics (a of the present invention to be described later). From the viewpoint of easy control of the value of the value within a preferable range.

  When the polyester is a polyester having ethylene terephthalate as a main constituent, the polyester may be either a direct weight method or a DMT method, but calcium acetate is preferably used as a transesterification catalyst in the DMT method. In the polymerization stage, although not particularly limited, it is preferable to use a germanium compound as a polymerization catalyst in order to reduce coarse protrusions due to foreign matters. Examples of germanium catalysts include (1) amorphous germanium oxide, (2) crystalline germanium oxide of 5 μm or less, and (3) germanium oxide dissolved in glycol in the presence of an alkali metal, an alkaline earth metal, or a compound thereof. And a solution of germanium oxide prepared by dissolving (4) germanium oxide in water, adding glycol to the solution and distilling off the water, and the like.

  Polyesters include trimellitic acid, pyromellitic acid, glycerol, pentaerythritol, polyfunctional compounds such as 2,4-dioxybenzoic acid, monofunctional compounds such as lauryl alcohol and phenyl isocyanate, p-hydroxybenzoic acid, Copolymerization of aromatic hydroxycarboxylic acid such as m-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid, p-aminophenol, p-aminobenzoic acid, etc., in an amount that does not impair the effects of the present invention. May be.

  As described above, the polyester layer of the present invention may be a polymer alloy of polyester and another thermoplastic resin. In this case, the thermoplastic resin preferably has good affinity with the polyester and preferably has melt moldability, and has a glass transition temperature higher than that of the polyester from the viewpoint of improving thermal dimensional stability. A thermoplastic resin is preferred. Examples of such a thermoplastic resin include polyimide (including polyetherimide), polysulfone, polyethersulfone and the like, and polyimide is particularly preferable from the viewpoint of affinity. Here, having good affinity (compatibility) means, for example, using a polymer alloy made of polyester and a thermoplastic resin, creating an unstretched or biaxially stretched film, When observed with a microscope at a magnification of 30,000 to 500,000 times, it means that a structure having a diameter of 200 nm or more (for example, a polymer domain having poor dispersion) that is not caused by additives such as organic and inorganic particles is not observed. However, the method for determining affinity is not particularly limited to this, and if necessary, there is good affinity by observing a single glass transition point by a temperature modulation type DSC (MDSC). May be determined.

  As said polyimide, what contains a structural unit as shown by the following general formula is preferable, for example.

However, R ₁ in the formula is

Represents one or more groups selected from an aliphatic hydrocarbon group such as, an alicyclic hydrocarbon group, an aromatic hydrocarbon group,
R ₂ in the formula is

Represents one or two or more groups selected from an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, and an aromatic hydrocarbon group.

  Such polyimide dehydrates one or more compounds selected from the group consisting of tetracarboxylic acid and / or its anhydride and an aliphatic primary monoamine, aromatic primary monoamine, aliphatic primary diamine and aromatic primary diamine. It can be obtained by condensation.

  From the viewpoints of melt moldability and affinity with polyester, a polyetherimide containing an ether bond in the polyimide component as shown by the following general formula is particularly preferred.

(Wherein R ₃ is a divalent aromatic or aliphatic residue having 6 to 30 carbon atoms, R ₄ is a divalent aromatic residue having 6 to 30 carbon atoms, From the group consisting of alkylene groups having 2 to 20 carbon atoms, cycloalkylene groups having 2 to 20 carbon atoms, and polydiorganosiloxane groups chain-terminated with alkylene groups having 2 to 8 carbon atoms Selected divalent organic group.)
Examples of R ₃ and R ₄ include aromatic residues represented by the following formula group:

Can be mentioned.

  In the present invention, 2,2-bis [4- (2,3-dicarboxyphenoxy) phenyl] propane dianhydride and m-phenylenediamine from the viewpoint of affinity with polyester, cost, melt moldability, and the like, or A polymer having a repeating unit represented by the following formula, which is a condensate with p-phenylenediamine, is preferred.

Or

(N is an integer of 2 or more, preferably an integer of 20 to 50)
This polyetherimide is available from GE Plastics under the trade name “Ultem” (registered trademark).

  When the polymer which comprises the polyester film of this invention is a polymer alloy, it is preferable that content of a thermoplastic resin exists in the range of 1-30 weight% in a polymer alloy. More preferably, it is 2 to 15% by weight, and most preferably 3 to 10% by weight. If the content of the thermoplastic resin is more than 30% by weight, the moldability deteriorates, it becomes difficult to perform extrusion molding and stretching, and film formation and processing such as film breakage and die lines during extrusion It may cause the above trouble. In addition, when a very small amount of the thermoplastic resin is added in an amount of less than 1% by weight, poor kneading tends to occur, which may cause coarse protrusions.

  In order to control the dispersion diameter, a compatibilizer may be used in combination with the polymer alloy as necessary. In this case, although the kind of compatibilizer varies depending on the kind of polymer, the addition amount is preferably 0.01 to 10% by weight.

  Moreover, when preparing the said polymer alloy, you may add the timing which adds a thermoplastic resin to polyester before and after superposition | polymerization of polyester. Further, mixing and pelletizing may be performed before melt extrusion. Furthermore, as another method for adjusting the polymer alloy to a more preferable dispersion state, for example, a method of mixing using a tandem extruder, a method of finely dispersing a thermoplastic resin using two or more polyesters, and a pulverizer Examples include a method of mixing after pulverizing a thermoplastic resin, a method of mixing by dissolving both in a solvent and coprecipitation, a method of mixing one into a solution after dissolving one in a solvent, and the like. This is not the case. Particularly preferably, once a master pellet containing a high concentration of thermoplastic resin (for example, 35 to 65% by weight, more preferably 40 to 60% by weight) is prepared, it is further diluted with polyester before melt extrusion. When the method of adjusting to a predetermined concentration is used, the dispersibility between polymers is improved and a preferable dispersion state may be exhibited.

  The polyester film of the present invention may be a single-layer film, but when used as a magnetic tape, it preferably has a laminated structure of at least two layers. By having a laminated structure of two or more layers, the surfaces on both sides of the film have different characteristics such as a certain degree of roughness for improving transportability and runnability and smoothness for improving electromagnetic conversion characteristics. be able to. Furthermore, you may have the coating layer which consists of a 1-50 nm-thick water-soluble polymer etc. on the film surface.

  The polyester film of the present invention preferably contains inert particles in order to improve the running durability of the magnetic recording medium, the running property with the magnetic head, or the handling property such as the winding property. . The inert particles referred to in the present invention are inorganic or organic particles that do not cause a chemical reaction in the polymer of the present invention and do not adversely affect magnetic recording due to electromagnetic influences. Inactive particles include titanium oxide, calcium carbonate, kaolin, talc, wet or dry silica, colloidal silica, calcium phosphate, barium sulfate, alumina, zirconia, and other inorganic particles, acrylic acids, styrene, silicone, imide, etc. Organic particles, particles precipitated by a catalyst added during the polyester polymerization reaction (so-called internal particles), surfactants, and the like.

  The preferable average particle diameter and content of the inert particles contained in the polyester film of the present invention vary depending on the laminated structure of the film.

  When the polyester film has a laminated structure of two or more layers, the average particle size of the particles contained in the film layer on the magnetic layer side is preferably 0.005 to 0.5 μm, more preferably 0.01 to It is 0.1 μm, most preferably 0.05 to 0.08 μm. The content is preferably 0.01 to 1% by weight, more preferably 0.05 to 0.5% by weight. The average particle size of the particles contained in the film layer on the back coat layer side is preferably 0.05 to 2 μm, more preferably 0.1 to 1 μm. The content is preferably 0.01 to 1% by weight, more preferably 0.05 to 0.5% by weight. In addition, when taking the laminated structure of 3 layers or more, inactive particles do not need to contain in inner layers other than the outermost layer of both sides.

  When the polyester film has a single layer configuration, the average particle diameter of the inert particles is preferably 0.01 to 1 μm, and more preferably 0.05 to 0.5 μm. The content is preferably 0.01 to 1% by weight, more preferably 0.05 to 0.5% by weight.

  Note that only one kind of inert particles may be used, or two or more kinds of particles may be used. When using 2 or more types of particle | grains, it is preferable that the average particle diameter of each particle | grain satisfy | fills said preferable range, and the sum total of content of all the particles satisfy | fills said preferable range.

  In addition, heat stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, flame retardants, pigments, dyes, fatty acid esters, waxes and other organic lubricants are added to the polyester film as long as the present invention is not inhibited. May be.

  The intrinsic viscosity of the polymer constituting the polyester film of the present invention is preferably in the range of 0.55 to 3.0 (dl / g) from the viewpoint of controlling the stability of the film forming process and the terminal carboxyl group concentration. More preferably, it is 0.60 to 2.0 (dl / g). In addition, the intrinsic viscosity of the film after film formation is preferably in the range of 0.50 to 2.0 (dl / g), more preferably from the viewpoint of film forming stability and dimensional stability. 0.55 to 1.0 (dl / g). When the intrinsic viscosity is smaller than the above range, the terminal carboxyl group concentration becomes high, and it becomes easy to cause expansion due to humidity, or the viscosity is too low and extrusion failure such as bubbles may occur and productivity may be lowered. On the other hand, when it is larger than the above range, due to high viscosity, extrusion failure such as streaks may occur, the surface of the magnetic recording medium becomes rough, and electromagnetic conversion characteristics and the like may deteriorate.

In the magnetic recording medium of the present invention, at least one of the polyester layers has a layer (M layer) containing a metal or a metal-based inorganic compound. In a magnetic recording medium composed only of a polyester layer, a magnetic layer, and a backcoat layer, it is difficult to satisfy the preferable range of the width dimension change of the present application. Here, the metals represent so-called simple metals, metalloids, alloys, and intermetallic compounds. Specifically, for example, simple metals such as Mg, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Mo, Pd, Ag, Sn, Pt, Au, Pb, and semi-metals include C, Si, Ge, Sb, Te, etc. It may be an intercalation compound. As the metal-based inorganic compound, for example, oxides, nitrides, carbides, borides, sulfides, and the like of the above metals can be used. Specifically, for example, oxides such as CuO, ZnO, Al ₂ O ₃ , SiO ₂ , Fe ₂ O ₃ , Fe ₃ O ₄ , Ag ₂ O, TiO ₂ , MgO, SnO ₂ , ZrO ₂ , and InO ₃ . And nitrides such as TiN, ZrN, GaN, TaN, and AlN, and carbides such as TiC, WC, SiC, NbC, ZrC, and Fe ₃ C. Moreover, said metal type inorganic compound may be used individually, respectively, and of course, multiple types may be mixed and used. Among them, the metal material constituting the M layer preferably contains an aluminum element from the viewpoints of water vapor shielding properties, productivity, and environmental properties, and particularly preferably contains an aluminum element as a main component, more preferably It is preferable to use a single metal of aluminum.

  As a method for forming the M layer (hereinafter sometimes referred to as a metal layer), physical vapor deposition or chemical vapor deposition can be used. Physical vapor deposition methods include vacuum vapor deposition and sputtering, and vacuum vapor deposition is common. In particular, in order to make the crystal grain size of the metal layer small and precise, it is necessary to increase the kinetic energy of the deposited material. Therefore, electron beam evaporation or sputtering is preferable.

  The thickness of the metal layer is preferably 5 to 200 nm, more preferably 10 to 100 nm, and most preferably 30 to 70 nm. By setting it within this range, the crystal grain size of the metal layer can be made finer, and it is easy to satisfy conditions such as no adverse effects on water vapor shielding properties, reinforcing effects, and surface smoothness, which is preferable. If the thickness is smaller than 5 nm, the water vapor shielding property is small and the effect of increasing the strength is small, so the effect of improving the dimensional stability of the present invention may be small. When it is larger than 200 nm, cracks and grain boundaries are likely to be formed, and the surface of the magnetic recording medium becomes rough and electromagnetic conversion characteristics may be deteriorated or dimensional stability may be deteriorated. Further, repeated running tends to cause peeling and dropping, and the possibility and productivity may decrease. The thickness of the metal layer is more preferably 5 to 70 nm, and still more preferably 10 to 65 nm.

  The crystal grain size of the metal material of the metal layer is preferably 50 nm or less. An amorphous state having no crystal grains is most preferable from the viewpoint of water vapor shielding properties, and the smaller the crystal grain size, the larger the water vapor shielding properties are. When it is larger than 50 nm, the water vapor shielding property is deteriorated and the dimensional stability may be deteriorated. The crystal grain size is more preferably 40 nm or less, still more preferably 30 nm or less. The crystal grain size can be controlled by the formation method of the metal layer and the thickness of the metal layer.

  In the magnetic recording medium of the present invention, the metal layer may be provided only on one side of the polyester layer or on both sides. When the magnetic layer of the present invention is a ferromagnetic metal thin film, it is preferable to provide a metal layer on the backcoat layer side of the magnetic layer, and it is not necessary to provide a metal layer on the magnetic layer side. When the magnetic layer of the present invention is a coating type, it is preferable to provide a metal layer on both sides of the polyester layer from the viewpoint of suppressing cupping.

  When two or more metal layers are provided, the same metal may be used for all metal layers, or different metals may be used for each layer. Also, the layer thickness and crystal grain size may be different for each layer.

  The magnetic recording medium of the present invention is formed by providing a magnetic layer and a backcoat layer on a support composed of the above polyester layer and metal layer.

  Suitable examples of the magnetic layer of the magnetic recording medium of the present invention include a magnetic layer formed by dispersing a ferromagnetic metal thin film and fine powder of ferromagnetic metal in a binder, and a magnetic layer coated with a metal oxide.

  Various ferromagnetic metal thin films can be used, and iron, cobalt, nickel and alloys thereof are preferable. When the magnetic layer is a metal thin film, the thickness of the magnetic layer is preferably 50 to 300 nm. Examples of the method for forming the magnetic layer include vapor deposition, sputtering, and ion plating.

Examples of the ferromagnetic metal fine powder used in the magnetic layer formed by dispersing the ferromagnetic metal fine powder in a binder include γ-Fe ₂ O ₃ , FeO _x (4/3 ≦ x <3/2), Co Ferromagnetic iron oxide powders such as γ-Fe ₂ O ₃ and Co-coated FeO _x (4/3 ≦ x <3/2), ferromagnetic metal powders mainly composed of iron, and ferromagnetic hexagonal ferrites Examples of the powder include a ferromagnetic metal powder mainly composed of iron and a ferromagnetic hexagonal ferrite powder in order to achieve high density recording.

Examples of the ferromagnetic metal powder include ferromagnetic metal powders having a metal content of 50% by weight or more and 60% or more of the metal content being iron. Specific examples of the ferromagnetic metal powder include, for example, Fe—Co, Fe—Ni, Fe—Al, Fe—Ni—Al, Fe—Co—Ni, Fe—Ni—Al—Zn, and Fe—Al—Si. Etc. The ferromagnetic metal powder mainly composed of iron preferably has a needle shape or a spindle shape. And the long axis length becomes like this. Preferably it is 0.05-0.25 micrometer, More preferably, it is 0.05-0.2 micrometer. Moreover, a preferable acicular ratio is 3 to 20, and a preferable BET specific surface area is 30 to 80 m ² / g.

In addition, the ferromagnetic hexagonal ferrite powder includes fine tabular barium ferrite and strontium ferrite, and ferromagnetic powder in which a part of Fe atoms is substituted with atoms such as Ti, Co, Ni, Zn, and V. Etc. The ferromagnetic hexagonal ferrite powder has a preferable plate diameter of 0.02 to 0.09 μm, a preferable plate ratio of 2 to 7, and a preferable BET specific surface area of 30 to 70 m ² / g.

  The ferromagnetic powder preferably has a coercive force of 120 to 240 kA / m (1,508 to 3,015 Oe), particularly preferably 130 to 200 kA / m (1,634 to 2,513 Oe). If it is within the above range, the RF output in the entire wavelength region can be obtained without excess or deficiency, and the overwrite characteristics are also good.

It is preferable that the saturation magnetization of the ferromagnetic metal powder is ^{100~180Am 2 / kg (100~180emu / g} ), is especially preferred ^{110~160Am 2 / kg (110~160emu / g} ). On the other hand it, the saturation magnetization of the ferromagnetic hexagonal ferrite powder is preferably from ^{30~70Am 2 / kg (30~70emu / g} ), particularly ^{45~70Am 2 / kg (45~70emu / g} ) Is preferred. If it is within the above range, sufficient reproduction output can be obtained.

  The ferromagnetic powder may contain a rare earth element or a transition metal element as necessary. Specifically, Al, Si, S, Sc, Ti, V, Cr, Mn, Cu, Zn, Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, Ta, W, Re, Au , Hg, Pb, Bi, La, Ce, Pr, Nb, Sm, Eu, Gd, Tb, Dy, Ho, Yb, Lu, B, and P.

In the present invention, the ferromagnetic powder may be subjected to surface treatment in order to improve the dispersibility of the ferromagnetic powder. The surface treatment can be performed by a method similar to the method described in “Characterization of Powder Surfaces” (TJWiseman et al., Academic Press, 1976). For example, the surface of the ferromagnetic powder is coated with an inorganic oxide. A method is mentioned. Examples of the inorganic oxide that can be used at this time include Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , ZnO, and the like. Two or more kinds may be mixed and used. The surface treatment can be performed by organic treatment such as silane coupling treatment, titanium coupling treatment, and aluminum coupling treatment in addition to the above method.

  The binder contained in the magnetic layer can be used without particular limitation as long as it is variously used for a magnetic recording medium. Examples thereof include thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof.

  Specifically, copolymers of vinyl chloride and modified products thereof, copolymers of acrylic acid, methacrylic acid and esters thereof, copolymers of acrylonitrile (rubber resins), polyester resins, polyurethane resins, epoxy resins, A fiber-based resin, a polyamide resin, or the like can be used.

  The number average molecular weight of the binder is preferably 2,000 to 200,000.

In order to improve the dispersibility, the binder includes hydroxyl group, carboxyl group or salt thereof, sulfonic acid group or salt thereof, phosphoric acid group or salt thereof, nitro group or nitrate ester group, acetyl group, sulfate ester group or salt thereof. A polar functional group (so-called polar group) such as a betaine structure such as an epoxy group, a nitrile group, a carbonyl group, an amino group, an alkylamino group, an alkylammonium base, sulfobetaine, or carbobetaine may be contained.

  Solvents contained in the magnetic coating used to form the magnetic layer include ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents, and chlorinated hydrocarbon solvents. Specifically, the solvents described in JP-A 57-162128, page 3, lower right column, line 17 to page 4, lower left column, line 10 can be used. The amount of the solvent used is preferably 80 to 500 parts by weight, more preferably 100 to 350 parts by weight with respect to 100 parts by weight of the ferromagnetic powder.

  In addition, the magnetic paint used for forming the magnetic layer requires additives used for ordinary magnetic recording media such as a dispersant, a lubricant, an abrasive, an antistatic agent, a rust inhibitor, and an antifungal agent. Can be added accordingly. Specific examples of the additive include Japanese Patent Application Laid-Open No. 57-162128, page 2, lower left column, line 6 to page 2, lower right column, line 10 and page 3, lower left column, line 6 to page 3, upper right column, line 18. And various additives described in the above.

  The thickness of the magnetic layer is preferably 0.03 to 3 μm, more preferably 0.05 to 2 μm, and particularly preferably 0.05 to 1 μm. When the thickness of the magnetic layer is within this range, it is easy to increase the recording density, and it is also easy to design a high density.

  If necessary, an intermediate layer formed by dispersing inorganic powder and / or organic powder in a binder can be provided between the magnetic layer and the support. The intermediate layer may be a magnetic layer or a nonmagnetic layer. When the intermediate layer is a magnetic layer, the intermediate layer is a magnetic layer containing magnetic powder (hereinafter referred to as a magnetic intermediate layer), and includes a magnetic powder, a binder, and a solvent as main components. It is formed using paint. On the other hand, when the intermediate layer is a non-magnetic layer, the intermediate layer is a layer containing non-magnetic powder (hereinafter referred to as a non-magnetic intermediate layer), and contains the non-magnetic powder, a binder and a solvent as main components. It is formed using a nonmagnetic paint.

  Ferromagnetic powder is preferably used as the magnetic powder contained in the magnetic paint used for forming the magnetic intermediate layer. Examples of the ferromagnetic powder include iron oxide magnetic powder, ferromagnetic metal powder mainly composed of iron, and ferromagnetic hexagonal ferrite powder. As the ferromagnetic powder, those similar to the iron oxide magnetic powder, ferromagnetic metal powder, and ferromagnetic hexagonal ferrite powder contained in the magnetic coating used for forming the magnetic layer are used. The physical properties of the ferromagnetic powder such as coercive force, saturation magnetization, shape, and BET specific surface area are the same as those of the ferromagnetic metal powder and the ferromagnetic hexagonal ferrite powder used for forming the magnetic layer.

  The magnetic powder contained in the magnetic coating used for forming the magnetic intermediate layer can contain a rare earth element or a transition metal element as necessary. Further, the magnetic powder may be subjected to the same surface treatment as the ferromagnetic metal powder of the magnetic layer.

  As the solvent contained in the magnetic paint used for forming the magnetic intermediate layer, the same solvent as that contained in the magnetic paint used for forming the magnetic layer is used. The amount of the solvent used is preferably 80 to 500 parts by weight, more preferably 100 to 350 parts by weight, based on 100 parts by weight of the magnetic powder.

  Moreover, the additive added to the magnetic coating material used for formation of the said magnetic layer can be added to the magnetic coating material used for formation of the said magnetic intermediate layer as needed. Moreover, the nonmagnetic powder contained in the nonmagnetic coating material used for formation of the nonmagnetic intermediate layer mentioned later can also be added to the magnetic coating material used for forming the magnetic intermediate layer.

  Next, the nonmagnetic intermediate layer will be described. Examples of the nonmagnetic powder contained in the nonmagnetic paint used for forming the nonmagnetic intermediate layer include carbon black, graphite, titanium oxide, barium sulfate, zinc sulfide, magnesium carbonate, calcium carbonate, zinc oxide, calcium oxide, Magnesium oxide, magnesium dioxide, tungsten disulfide, molybdenum disulfide, boron nitride, tin dioxide, silicon dioxide, nonmagnetic chromium oxide, alumina, silicon carbide, cerium oxide, corundum, artificial diamond, nonmagnetic iron oxide, garnet Silica, silicon nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, diatomaceous earth, dolomite, resinous powder, and the like. Among these, nonmagnetic iron oxide, titanium oxide, carbon black, alumina, silicon oxide, boron nitride and the like are preferably used. These nonmagnetic powders may be used alone or in combination of two or more.

  The non-magnetic powder may be spherical, plate-like, needle-like or amorphous, and the size is preferably 5 to 200 nm in the case of spherical, plate-like or amorphous. The needle-shaped material preferably has a major axis length of 20 to 200 nm and a needle ratio of 3 to 20.

  In the present invention, in order to improve the dispersibility of the non-magnetic powder, the non-magnetic powder may be subjected to the same surface treatment as the ferromagnetic powder contained in the magnetic paint used for forming the magnetic layer. it can.

  As the solvent contained in the nonmagnetic paint used for forming the nonmagnetic intermediate layer, the same solvent as that contained in the magnetic paint used for forming the magnetic layer is used. The amount of the solvent used is preferably 80 to 500 parts by weight, particularly preferably 100 to 350 parts by weight with respect to 100 parts by weight of the nonmagnetic powder. Moreover, the additive added to the magnetic coating material used for formation of the said magnetic layer can be added to the nonmagnetic coating material used for formation of the said nonmagnetic intermediate layer as needed.

  The thickness of the intermediate layer (magnetic or nonmagnetic) is preferably 0.2 to 3 μm, and particularly preferably 0.5 to 2 μm. If the thickness of the intermediate layer is within this range, the magnetic recording medium is less likely to be wrinkled or bent, and a high recording capacity is facilitated.

  As the backcoat layer of the magnetic recording medium of the present invention, a coating type backcoat layer having a thickness of about 0.2 to 1.0 μm mainly composed of carbon black or a binder may be used, or a vapor deposition method, a direct current sputtering method, Metal thin film type formed by attaching metal or metalloid to the support in vacuum by dry plating means such as AC sputtering, RF sputtering, DC magnetron sputtering, RF magnetron sputtering, and ion beam sputtering. A back coat layer may be used.

  The former coating type backcoat layer can be formed from a backcoat paint according to a conventional method. As the back coat paint, an appropriate amount of a binder, a curing agent, an inorganic powder or the like similar to the magnetic paint used for forming the magnetic layer is used. The thickness of the back coat layer is preferably 0.05 to 1.0 [mu] m, and particularly preferably 0.1 to 0.8 [mu] m from the viewpoint of both running durability and high recording capacity.

  In the case of the latter metal thin film type backcoat layer, various metals can be used as the backcoat layer, and Al, Cu, Zn, Sn, Ni, Ag, Co, etc., and alloys thereof are used. Co and Cu—Al alloys are preferred. Moreover, Si, Ge, As, Sc, Sb etc. are used as a semimetal which forms a backcoat layer, and Si is suitable. Furthermore, ceramics such as an oxide film or a carbonized film obtained by subjecting the metal or semimetal to an oxidation reaction, a carbonization reaction, or the like during vapor deposition are also suitable. Further, it is preferable to further add an additive to improve conductivity. The thickness of the metal thin film type back coat layer is about 0.05 to 1.0 μm. Such a backcoat layer is preferably composed of the reinforcing film itself of the support used in the present invention or at least one metal thin film formed on the reinforcing film of the support used in the present invention. In particular, the reinforcing film of the support is preferably used as a backcoat layer.

  In addition, a protective layer having a thickness of 1 to 50 nm can be provided on the metal thin film type back coat layer as necessary. As a material constituting the protective layer, in addition to oxides, nitrides, and carbides of metals such as Al, SiC and the like, and compounds containing the same can be considered. In particular, a carbon film, particularly diamond-like carbon is preferable. The protective layer made of diamond-like carbon is formed by a physical vapor deposition (PVD) method or a chemical vapor deposition (CVD) method. In particular, it is formed by an ECR plasma CVD apparatus. That is, the ECR plasma CVD apparatus is operated on the magnetic layer on the support disposed in the vacuum chamber, and plasma of hydrocarbon gas is sprayed on the magnetic layer. Thereby, a protective layer (diamond-like carbon layer) is formed on the surface of the magnetic layer.

Further, if necessary, it is preferable from the viewpoint of running property to form a lubricant layer made of a suitable lubricant on the protective layer. In particular, a fluorine-based lubricant such as perfluoropolyether is preferable, and the thickness of the lubricant layer is about 0.5 to 10 nm. As a lubricant, for example,
- [C (R) F- CF 2 -O] p - ( wherein, R is F, CF _3, groups such as CH ₃₎ (p is an integer of 1 or more), particularly HOOC-CF ₂ (OC ₂ F _{4) p (OCF 2) q} -OCF 2 COOH, F- (CF 2 CF 2 CF 2 O) n-CF 2 CF 2 COOH (p, q, n is an integer of 1 or more) carboxyl group-modified par such _{fluoropolyethers, HOCH 2 -CF 2 (OC 2} F 4) p (OCF 2) q-OCF 2 -CH 2 OH, HO- (C 2 H 4 O) m-CH 2 - (OC 2 F 4) p _{(OCF 2) q-OCH 2} - (OCH 2 CH 2) n-OH, F- (CF 2 CF 2 CF 2 O) n-CF 2 CF 2 CH 2 OH (p, q, m, n is 1 And alcohol-modified perfluoropolyethers such as the above integers). The molecular weight is preferably 500 to 50,000. Specifically, there are trade names “FOMBLIN Z DIAC” and “FOMBLIN Z DOL” from Montecatini, and “demnum SA” from Daikin Industries. In particular, in terms of durability, it is preferable to use a lubricant having both a fluorine-based alkyl group and an alkyl group. It is also preferable to use a mixture of these lubricants.

  The thermal shrinkage rate at 100 ° C. for 30 minutes in the width direction of the magnetic recording medium of the present invention is preferably −0.3 to 0.3%, more preferably −0.1 to 0.1%. When the thermal shrinkage rate is out of the preferred range, the tape may be deformed when the temperature condition for handling the magnetic recording medium is changed, causing a track deviation or causing wrinkles.

  The thermal contraction rate in the width direction of the magnetic recording medium of the present invention can be controlled by the thermal contraction rate of the polyester layer, the thickness of the metal layer, the thermal history during processing, and the like. The thermal shrinkage rate at 100 ° C. for 30 minutes in the width direction of the polyester layer is preferably −0.1 to 0.5%, more preferably 0 to 0.3%. Further, in order to control the heat shrinkage rate of the polyester layer in the magnetic recording medium within the above preferred range, the heat shrinkage rate at 100 ° C. for 30 minutes in the width direction of the polyester film before processing is −0.1. -1% is preferable, More preferably, it is 0-0.5%. If the thermal shrinkage rate is larger than the above range, it may cause troubles such as “wrinkles” when processing into a magnetic recording medium, or it may be difficult to control the thermal shrinkage rate of the magnetic recording medium within a preferable range. is there. Moreover, the polyester film smaller than the said range has progressed too much relaxation of an amorphous part, a temperature-humidity expansion coefficient becomes high too much, and quality may fall.

  The heat shrinkage rate at 100 ° C. for 30 minutes in the longitudinal direction of the magnetic recording medium of the present invention is preferably 0 to 2.0%, more preferably 0.2 to 1.0%. The effect of heat shrinkage in the longitudinal direction on the track deviation is smaller than that in the width direction. However, if it exceeds 2.0%, it will cause a track deviation or “clamping” of the tape during storage. The tape may be deformed.

  The heat shrinkage rate in the longitudinal direction of the magnetic recording medium of the present invention can be controlled by the heat shrinkage rate of the polyester layer, the thickness of the metal layer, the heat history during processing, and the like. The thermal shrinkage rate at 100 ° C. for 30 minutes in the longitudinal direction of the polyester layer is preferably 0 to 2%, more preferably 0.2 to 1%. Further, in order to control the thermal shrinkage rate of the polyester layer in the magnetic recording medium within the above preferred range, the thermal shrinkage rate at 100 ° C. for 30 minutes in the width direction of the polyester film before processing is 0.3 to 2.5% is preferable, and more preferably 0.5 to 1.5%. If the thermal shrinkage rate is larger than the above range, it may cause troubles such as “wrinkles” when processing into a magnetic recording medium, or it may be difficult to control the thermal shrinkage rate of the magnetic recording medium within a preferable range. is there. In addition, a polyester film smaller than the above range does not have sufficiently advanced molecular orientation, leading to a decrease in tape strength, and may cause tape “elongation” during use.

  The temperature expansion coefficient in the width direction of the magnetic recording medium of the present invention is in the range of 0 to 10 ppm / ° C, preferably 2 to 8 ppm / ° C, more preferably 4 to 7 ppm / ° C. Generally, the temperature expansion coefficient of a magnetic head used in a magnetic recording apparatus is around 7 ppm / ° C. When the temperature expansion coefficient in the film width direction is greater than 10 ppm / ° C, the temperature expansion of the film is too much larger than the temperature expansion of the magnetic head, so the environment for recording and reproducing magnetic data changes from low to high. In addition, the film expands in the width direction of the tape, and regenerative defects are likely to occur. In addition, when the temperature expansion coefficient is smaller than 0 ppm / ° C., the temperature expansion of the film is too small than the temperature expansion of the magnetic head. It tends to cause defects.

  In order to control the temperature expansion coefficient in the width direction of the magnetic recording medium of the present invention in a preferable range, the thickness of the metal layer is controlled in a preferable range, and the temperature expansion coefficient in the width direction of the polyester layer is controlled in a preferable range. It is also preferable to control the processing conditions of the magnetic recording medium. Since metals such as aluminum generally have a relatively high temperature expansion coefficient, if the thickness of the metal layer is too thick, the temperature expansion coefficient of the magnetic recording medium deviates from the scope of the present invention. Sometimes. Further, if the heat is excessively applied during the processing conditions of the magnetic recording medium, the amorphous chain portion of the polyester layer may be relaxed and the temperature expansion coefficient may be increased.

  In order to control the temperature expansion coefficient of the magnetic recording medium of the present invention within a preferable range, the temperature expansion coefficient in the width direction of the polyester layer is preferably −4 to 10 ppm /% RH, and more preferably 0 to 7 ppm. /% RH. In the processing step of the magnetic recording medium, the molecular orientation of the polyester layer is easily relaxed. Therefore, when the humidity expansion coefficient of the polyester layer is outside the above range, it is difficult to control the humidity expansion coefficient of the magnetic recording medium within a preferable range. It may become.

  The humidity expansion coefficient in the width direction of the magnetic recording medium of the present invention is in the range of 0 to 7 ppm /% RH, preferably 0 to 5 ppm / ° C. Since the polyester swells when humidity, that is, moisture is added, generally, the humidity expansion coefficient is often a positive value in a magnetic recording medium. In addition, when the orientation is so high that the humidity expansion takes a negative value, the temperature expansion coefficient becomes too small (shrinkage), and when the temperature changes from low to high, the film shrinks in the tape width direction and regenerates. It tends to cause defects. Further, when the humidity expansion coefficient is larger than 7 ppm /% RH, when the environment for recording / reproducing magnetic data is changed from low humidity to high humidity, it expands in the tape width direction and is liable to cause reproduction failure.

  In order to control the humidity expansion coefficient in the width direction of the magnetic recording medium of the present invention to a preferable range, in addition to providing a metal layer, the thickness of the metal layer is controlled to a preferable range. Controlling to a preferable range and controlling the processing conditions of the magnetic recording medium are preferable methods. In general, since metal does not substantially expand in humidity, it is considered that the effect of suppressing humidity expansion in the polyester layer, the magnetic layer, and the back coat layer is exhibited. In addition, when a metal layer is provided on both sides of the polyester layer, it is considered that the effect of preventing water vapor from entering is also exhibited. When the thickness of the metal layer is thin, the above effect is reduced, and the humidity expansion coefficient may fall outside the scope of the present invention. Further, if the heat is excessively applied under the processing conditions of the magnetic recording medium, the amorphous chain portion of the polyester layer may be relaxed and the humidity expansion coefficient may be increased.

  In order to control the humidity expansion coefficient of the magnetic recording medium of the present invention within a preferable range, the humidity expansion coefficient in the width direction of the polyester layer is preferably 0 to 10 ppm /% RH, more preferably 0 to 7 ppm /. % RH. In the processing step of the magnetic recording medium, the molecular orientation of the polyester layer is easily relaxed. Therefore, when the humidity expansion coefficient of the polyester layer exceeds 10 ppm /% H, the humidity expansion coefficient of the magnetic recording medium is controlled within a preferable range. May be difficult.

  The “width dimension change in the tape running environment” of the magnetic recording medium of the present invention is 0 to 1,200 ppm, preferably 0 to 900 ppm, more preferably 0 to 600 ppm. The “width dimension change in the tape running environment” is the sum of the following a, b, and c. a is the absolute value of the dimensional change rate in the width direction when changing from 10 ° C. and 10% RH to 30 ° C. and 80% RH with a load of 1 N in the longitudinal direction, and b is 40 ° C. and 60% RH. Under the environment, the absolute value of the dimensional change rate when the longitudinal load is changed from 0.5 to 1.5 N, c is a state where a load of 1 N is applied in the longitudinal direction under an environment of 40 ° C. and 60% RH. The absolute value of the shrinkage rate in the width direction before and after holding for 48 hours. The “width dimension change in a tape running environment” is a value that serves as an index for stably reading data even if various environmental changes occur in the process of reading after recording and storing data. If the “width dimension change in the tape running environment” exceeds 1,200 ppm, it becomes easy to cause “track deviation” due to the environmental change, and it becomes difficult to use as a high-density magnetic recording medium.

  The a value (absolute value of the dimensional change rate in the width direction when changing from 10 ° C. and 10% RH to 30 ° C. and 80% RH with a load of 1 N in the longitudinal direction) is recorded in the data. This is a value indicating a reversible deformation component of the tape width with respect to changes in the temperature and humidity environment during reproduction. In order for the “width dimension change in the tape running environment” to satisfy the preferable range of the present invention, the a value is preferably 0 to 900 ppm, more preferably 0 to 500 ppm. When the a value exceeds 900 ppm, the width deformation of the tape due to temperature and humidity changes becomes too large, and therefore it may be difficult for the “width dimension change in the tape running environment” to satisfy the preferred range of the present invention. high.

  The b value (absolute value of the dimensional change rate when the longitudinal load is changed from 0.5 to 1.5 N in an environment of 40 ° C. and 60% RH) is the tape at the time of data recording / reproduction. It is a value indicating a reversible deformation component of the tape width with respect to a change in running tension. The b value is preferably 0 to 300 ppm, more preferably 0 to 150 ppm. When the b value exceeds 300 ppm, the width deformation due to the change in the tape tension becomes too large, and therefore it may be difficult for the “width change in the tape running environment” to satisfy the preferred range of the present invention.

  The c value (absolute value of shrinkage in the width direction before and after holding for 48 hours under a load of 1N in the longitudinal direction under an environment of 40 ° C., 60% RH) It is a value indicating creep deformation (irreversible deformation) during storage. The c value is preferably 0 to 200 ppm, more preferably 0 to 50 ppm. When the c value exceeds 200 ppm, the width deformation after repeated running and storage for a long time becomes too large, and therefore it is difficult for the “width dimension change in the tape running environment” to satisfy the preferred range of the present invention. Probability is high.

  As a method for controlling the “width dimension change in the tape running environment” of the magnetic recording medium of the present invention within a preferable range, a metal layer is provided, the thickness of the metal layer is controlled, and the longitudinal direction and width of the polyester layer are controlled. Examples thereof include a method of controlling the orientation in the direction within a preferable range, and controlling the heat history in the film production process and the tape processing step within a preferable range. When the thickness of the metal layer is thin, the effect of reducing the humidity expansion coefficient is reduced, and deformation with respect to the tension in the longitudinal direction is likely to occur. Since the surface property is deteriorated, it is necessary to control to a preferable thickness. When the orientation in the longitudinal direction and the width direction of the polyester layer is high in the longitudinal direction, deformation with respect to tension is reduced, but the temperature and humidity expansion coefficient in the width direction may be increased.

  The a value of the polyester layer of the magnetic recording medium of the present invention is preferably 0 to 1,200 ppm, more preferably 0 to 900 ppm. When the a value of the polyester layer exceeds 1,200 ppm, even if a metal layer is provided, the a value of the magnetic recording medium may be difficult to control within the preferred range of the present application.

  The b value of the polyester layer of the magnetic recording medium of the present invention is preferably 0 to 300 ppm, more preferably 0 to 150 ppm. When the b value of the polyester layer exceeds 300 ppm, even if a metal layer is provided, the b value of the magnetic recording medium may be difficult to control within the preferred range of the present application.

  The c value of the polyester layer of the magnetic recording medium of the present invention is preferably 0 to 300 ppm, more preferably 0 to 100 ppm. When the c value of the polyester layer exceeds 300 ppm, the c value of the magnetic recording medium may be difficult to control within the preferred range of the present application even if a metal layer is provided.

  The surface roughness Ra (m) of the surface on the magnetic layer side of the magnetic recording medium of the present invention is preferably 2 to 5 nm, more preferably 3 to 4.5 nm. When Ra (m) is larger than 5 nm, there may be a case where sufficient electromagnetic conversion characteristics as a high-density magnetic recording medium cannot be obtained. In addition, when Ra (m) is smaller than 2 nm, troubles of conveyance failure are caused during the conveyance process or tape traveling, protrusions on the traveling surface are transferred, and dust is easily damaged during traveling. Or

  The roughness of the magnetic recording medium can be controlled by the surface roughness of the polyester layer and the thickness of the metal layer. In order to control Ra (m) within a preferable range, the surface roughness of the polyester layer on the magnetic layer side is preferably 2 to 7 nm, and more preferably 3 to 5 nm. When it is out of the above range, it may cause poor transportability and deterioration of electromagnetic conversion characteristics. The thickness of the metal layer is as described above, and the thicker the thickness, the easier the surface becomes.

  The surface roughness Ra (b) of the surface on the backcoat layer side of the magnetic recording medium of the present invention is preferably 5 to 20 nm, more preferably 7 to 15 nm. When Ra (m) is larger than 20 nm, transfer may occur to the magnetic surface side during storage, and the surface roughness on the magnetic surface side may become rough. On the other hand, when Ra (m) is smaller than 5 nm, the running property of the tape is lowered, and running failure may occur in the drive.

  The roughness of the magnetic recording medium can be controlled by the surface roughness of the polyester layer and the thickness of the metal layer. In order to control Ra (m) within a preferable range, the surface roughness of the polyester layer on the back coat layer side is preferably 5 to 15 nm, and more preferably 6 to 10 nm. When it is out of the above range, poor transportability and poor flatness may be caused. The thickness of the metal layer is as described above, and the thicker the thickness, the easier the surface becomes.

Height 0.3μm or more coarse protrusions number of the magnetic layer of the magnetic recording medium of the present invention is preferably from 0 to 10/100 cm ^2, more preferably from 0-5 / 100 cm ^2. If the coarse protrusion exceeds the preferable range, it may cause dropout, and may cause detachment during the processing process or running on the magnetic recording device, resulting in failure, or damage to the magnetic head (especially MR head). It may become.

In order to control the number of coarse protrusions of the magnetic recording medium within a preferable range, it is natural to control the number of coarse protrusions of the polyester layer, but the thickness of the metal layer and the formation method of the metal layer are within the preferable range. It is preferable to control. The number of coarse protrusions of the polyester layer is preferably 0 to 30 pieces / 100 cm ² , more preferably 0 to 10 pieces / 100 cm ² .

  The breaking load (per 1/2 inch width) of the magnetic recording medium of the present invention is preferably 25 to 40N, more preferably 28 to 35N. When the breaking load is less than 25N, the magnetic recording medium is often broken during manufacturing and processing, resulting in a decrease in productivity and cost competitiveness. When the breaking load exceeds 40N, the strength in the longitudinal direction becomes too high, and the dimensional stability in the width direction may be lowered.

  In order to control the breaking load within a preferable range, it is preferable to control the strength in the longitudinal direction of the polyester layer and the thickness of the polyester layer. The preferable breaking load of the polyester layer is 22 to 35N, preferably 25 to 30N.

  The thickness of the polyester layer that is preferable for controlling the breaking load within the above range is preferably 4 to 8 μm, more preferably 6 to 8 μm, although it depends on the strength of the polyester layer. When the thickness exceeds 8 μm, the volume per tape roll becomes too large, which hinders miniaturization. When the thickness is less than 4 μm, the breaking load tends to be low.

  The total thickness of the magnetic recording medium of the present invention is 6 to 10 μm. Preferably it is 7.8-9.2 micrometers. When the thickness is smaller than 6 μm, the tape becomes dull and electromagnetic conversion characteristics deteriorate. When the thickness exceeds 10 μm, since the tape length per one tape is shortened, it is difficult to reduce the size and increase the capacity of the magnetic tape.

  The cupping (the warp in the tape width direction) of the magnetic recording medium of the present invention is preferably 0 to 1 mm, more preferably 0 to 0.5 mm with respect to the 1/2 inch width. The cupping is positive when convex on the magnetic layer side. When the cupping exceeds 1 mm, the edge may be damaged by repeated running or the magnetic head may be damaged. When the cupping is less than 0 mm (that is, convex toward the back coat side), the contact state with the magnetic head (per head) may be deteriorated and may not be used as a high-density magnetic recording medium. In order to control the cupping within a preferable range, it is preferable to control the thermal shrinkage rate of the polyester film before being processed into a magnetic recording medium within the above preferable range. This is because cupping is caused by a difference in shrinkage due to heat between the metal layer and the polyester film during processing. In addition, it is preferable to provide a metal layer on both sides of the polyester layer because it is easy to control cupping. In this case, the thickness of the metal layer provided on both sides of the polyester layer is preferably the same on both sides. When the thicknesses on both sides are different, it is preferable that the magnetic layer side is thicker than the back coat layer side within the above preferred range. Furthermore, when providing metal layers on both sides of the polyester layer, it is preferable to provide both metal layers at the same time. However, in industrial manufacturing methods, it is often difficult to provide metal layers on both sides at the same time. It is preferable to provide it first on the layer side. If the metal layer is first provided on the back coat layer side, the cupping tends to take a negative value.

  The preferred range of Young's modulus in the longitudinal direction of the magnetic recording medium of the present invention varies depending on the type of polyester used in the polyester layer. For example, when polyester is polyethylene terephthalate (PET), 4.5-10 GPa is preferable, More preferably, it is 6-8 GPa. Although it is the same polyester, poly (ethylene-2,6-naphthalenedicarboxylate) (PEN) is more susceptible to deformation in the longitudinal direction than PET, so the Young's modulus in the longitudinal direction is 6-12 GPa, more preferably 7.5-9 GPa. If the Young's modulus in the longitudinal direction is smaller than the above range, the elastic deformation elongation and creep elongation when applying a load in the longitudinal direction are likely to increase, and the dimensional stability in the width direction when applied in the longitudinal direction is reduced, Storage stability is reduced. If the Young's modulus in the longitudinal direction is larger than the above range, tearing frequently occurs in the production process and the productivity decreases, the strength in the width direction decreases, and the dimensional stability in the width direction decreases, When used as a magnetic tape, it tends to be bent with respect to the traveling guide roll.

  The preferred range of Young's modulus in the width direction of the magnetic recording medium of the present invention varies depending on the type of polyester used in the film. Generally, the higher the Young's modulus, the easier it is to cause temperature and humidity expansion. When polyester used for the polyester layer is PET, 4.5 to 9 GPa is preferable, and 5.5 to 7 GPa is more preferable. When the polyester is PEN, the Young's modulus in the width direction is preferably 6 to 10 GPa, more preferably 7.5 to 9 GPa because the temperature and humidity expansion coefficient cannot be reduced unless the Young's modulus for PET is increased. . If the Young's modulus in the width direction is smaller than the above range, temperature and humidity expansion is likely to occur in the width direction, and it becomes difficult to control to the preferred range of the present application, and dimensional stability and storage stability may be reduced. is there. In addition, when the Young's modulus in the width direction is larger than the above range, the temperature expansion coefficient becomes too small and it becomes difficult to control to the preferred range of the present application, and the width is changed when the environment changes from low temperature to high temperature. The shrinkage occurs, the tear frequently occurs in the manufacturing process, and the productivity is lowered, or the creep properties are deteriorated due to the strength reduction in the longitudinal direction.

  The glass transition start temperature (Tg) of the polymer of the polyester layer of the present invention is preferably 80 to 150 ° C, more preferably 82 to 130 ° C, and still more preferably 85 to 120 ° C. Moreover, it is preferable that Tg of the film of a polyester layer is 100-150 degreeC, More preferably, it is 105-130 degreeC. When Tg is higher than the above range, productivity may be reduced. When Tg is lower than the above range, dimensional stability and storage when used as a magnetic tape may be wrinkled by the thermal history of the processing step. Stability may be reduced.

  It is preferable that the terminal carboxyl group density | concentration of the polyester layer of this invention is 0.1-10 equivalent / t, More preferably, it is 1-5 equivalent / t. When the terminal carboxyl group concentration is higher than 10 equivalent / t, the moisture absorption rate and the humidity expansion of the film are increased, and the preferred range of the present invention is not satisfied, and the dimensional stability against changes in the temperature and humidity environment may be reduced. Moreover, when the terminal carboxyl group concentration is less than 0.1 equivalent / t, not only is it difficult to produce industrially, but a gel-like defect caused by a crosslinking reaction may easily occur in the film production process. .

  The magnetic recording medium of the present invention is preferably used as a digital recording magnetic recording medium requiring high dimensional stability. Among them, it is particularly suitable for a base film such as a high density magnetic recording tape for data storage or a digital video tape.

  Hereinafter, the example of the manufacturing method of the biaxially-oriented polyester film of this invention is demonstrated. Here, an example of a coating type magnetic recording medium in which a polymer alloy made of PET and polyetherimide “Ultem” is used as the polyester layer and a metal layer made of aluminum is provided on both sides of the polyester layer will be mainly shown.

(Method for producing polyester layer)
First, bis-β-hydroxyethyl terephthalate (BHT) is obtained by esterifying terephthalic acid and ethylene glycol or by transesterifying dimethyl terephthalate and ethylene glycol according to a conventional method. Next, while transferring this BHT to the polymerization tank, the polymerization reaction is advanced by heating to 280 ° C. under reduced pressure. Here, a polyester having an intrinsic viscosity of about 0.5 is obtained. The obtained PET is pelletized and placed under reduced pressure to undergo solid phase polymerization. In the case of solid phase polymerization, pelletized PET is pre-crystallized in advance at a temperature of 180 ° C. or less, and then solid phase polymerization is performed at 190 to 250 ° C. under reduced pressure of about 1 mmHg for 10 to 50 hours. Further, when the inert particles are contained, a method in which the inert particles are dispersed in the form of a slurry in a predetermined ratio in ethylene glycol, and this ethylene glycol is added during the polymerization is preferable. When the inert particles are added, for example, when the water sol or alcohol sol obtained at the time of synthesis is added without drying, the particles have good dispersibility. Also effective is a method in which a water slurry of inert particles is directly mixed with PET pellets and kneaded into PET using a vented twin-screw kneading extruder. As a method for adjusting the content of the inert particles, a master of a high concentration of inert particles is prepared by the above method, and this is diluted with PET that does not substantially contain inert particles at the time of film formation. A method of adjusting the content of the particles is effective.

Next, PET pellets and polyetherimide pellets are mixed and supplied to a vented twin-screw kneading extruder heated to 270 to 300 ° C. for melt extrusion. The shear rate at this time is preferably 50 to 300 sec ⁻¹ , more preferably 100 to 200 sec ⁻¹ , and the residence time is preferably 0.5 to 10 minutes, more preferably 1 to 5 minutes. The mixing ratio is preferably 20 to 80%, more preferably 40 to 60%. If the mixing ratio of the polyetherimide is too high or too low, the two may not be sufficiently compatible by kneading. Furthermore, when both are not compatible on the said conditions, the obtained chip | tip may be thrown into a biaxial extruder again, and extrusion may be repeated until it is compatible.

  The obtained polyetherimide-containing PET pellets, inert particle master pellets, and polyester pellets were mixed at a predetermined ratio and dried under reduced pressure at 180 ° C. for 3 hours or more. An unstretched film is obtained by supplying to an extruder heated to 280 to 320 ° C. under a nitrogen stream or under reduced pressure so as not to decrease, extruding from a slit-shaped die, and cooling on a casting roll.

  At that time, it is preferable to use various filters, for example, a filter made of a material such as sintered metal, porous ceramic, sand, and wire mesh, as a method for removing foreign substances, altered polymer, unmelted material, etc. in the polymer. . In particular, it is preferable to filter the polymer with a fiber-sintered stainless steel filter having a cut of 1.2 μm or less because coarse protrusions can be easily controlled within the preferred range of the present application. More preferably, the filter is 0.8 μm or less. The filter of 1.2 μm cut here means a filtration accuracy of 1.2 μm, and the filtration accuracy is the maximum glass bead particle size that has passed through the filter media by the method of JIS-B8356-8 (2002). means.

  Moreover, it is preferable to provide a gear pump in order to improve the quantitative supply as required.

  In the case of laminating films, the method is preferably a method of melt laminating a plurality of different polymers using two or more extruders and a manifold or merging block.

  Next, this unstretched film is biaxially stretched and biaxially oriented. As the stretching method, a sequential biaxial stretching method or a simultaneous biaxial stretching method can be used, but in order to control the surface roughness and the number of coarse protrusions to a preferable range of the present application, the simultaneous biaxial stretching method may be used. preferable.

  Further, in order to sufficiently align the molecular chain to sufficiently suppress the temperature and humidity expansion and to control the (width dimension change in the tape running environment) within a preferable range of the present invention, at least 2 in both the longitudinal direction and the width direction. It is preferable to stretch in stages.

  For example, in the case of the sequential biaxial stretching method in which stretching is first performed in the longitudinal direction and then in the width direction, the unstretched film is heated with a heating roll group, and stretched 3 to 8 times in one or more stages in the longitudinal direction (re-longitudinal stretching). Is used, it is 2.5 to 5 times) and cooled by a cooling roll group of 20 to 50 ° C. The longitudinal stretching speed is preferably in the range of 1,000 to 50,000% / min. Subsequently, stretching in the width direction is performed. As a stretching method in the width direction, a method using a tenter is common. The stretching ratio in the width direction is preferably 3 to 8 times (in the case of performing relateral stretching, the first stage stretching is 2 to 4 times), and the stretching speed is preferably in the range of 1,000 to 20,000% / min. .

  When the simultaneous biaxial stretching method is used, the unstretched film is guided to a simultaneous biaxial stretching tenter, and biaxial stretching is performed simultaneously in the longitudinal and width directions. When simultaneous biaxial stretching is performed, the stretching speed is preferably in the range of 1,000 to 20,000% / min in both the longitudinal and width directions. The draw ratio is the same as the sequential biaxial drawing.

  The stretching temperature varies depending on the type of polymer used, but can be determined using the glass transition temperature Tg of the polymer as a guide. In the case of sequential biaxial stretching, it is preferably performed in the range of Tg to Tg + 50 ° C. in the longitudinal direction and in the range of Tg + 10 ° C. to Tg + 30 ° C. in the width direction. In the case of simultaneous biaxial stretching, it is preferable to stretch in the range of Tg to Tg + 30 ° C. in both the longitudinal and width directions. When the stretching temperature is lower than the above range, film breakage frequently occurs and productivity decreases, re-stretchability decreases, orientation cannot be sufficiently increased, and temperature and humidity expansion coefficient becomes large. , A, b, and c values become large, and it may be difficult to control the (width dimension change in the tape running environment) within the preferable range of the present invention. In addition, when the stretching temperature is higher than the above range, the molecular orientation is not sufficiently obtained, and the values of a, b, and c are increased, and it may be difficult to control to the preferable range of the present invention. .

  In order to produce the polyester layer of the present invention, it is preferable to perform re-longitudinal stretching and re-lateral stretching. As the stretching conditions in that case, when performing the second stage by sequential biaxial stretching, the stretching in the longitudinal direction is a heating roll group having a temperature of Tg to Tg + 100 ° C., and a stretching ratio of 1.1 to 2.5 times. As the stretching method in the width direction, a method using a tenter is preferable, and the stretching is preferably performed at a temperature Tg + 50 ° C. to Tg + 150 ° C. and a stretching ratio of 1.1 to 2.5 times. In the case of simultaneous biaxial stretching, it is preferable to perform the stretching at a stretching temperature Tg + 50 ° C. to Tg + 150 ° C. in both the longitudinal direction and the width direction at a stretching ratio of 1.1 to 2.5 times. When the stretching temperature is lower than the above range, film breakage frequently occurs, the productivity is lowered, the orientation cannot be sufficiently increased, and the values of a, b, and c are increased, which is preferable in the present invention. It may be difficult to control the range. In addition, when the stretching temperature is higher than the above range, the molecular orientation is not sufficiently obtained, and the values of a, b, and c are increased, and it may be difficult to control to the preferable range of the present invention. .

  Subsequently, the stretched film is heat-treated while being stretched under tension or in the width direction. Preferably, it is preferable to perform heat treatment while performing fine stretching at a magnification of 1.05 to 1.2 times, because relaxation is suppressed, the values of a and b are reduced, and the range of the present invention is easily controlled. For example, in the case of PET, the heat treatment temperature is preferably 190 ° C. to 230 ° C., and the heat treatment time is preferably 3 to 10 seconds. On the other hand, for example, in the case of a polymer alloy in which polyimide is added to PET, the relaxation of the molecular chain is accelerated, so that the heat treatment temperature is preferably 180 ° C. to 220 ° C., and the heat treatment time is preferably 2 to 7 seconds. In addition, for example, in the case of PEN, since the creep characteristics are poor as the polymer characteristics and it is better to sufficiently fix the structure, the heat treatment temperature ranges from 200 ° C. to 250 ° C., and the heat treatment time ranges from 5 seconds to 12 seconds. It is preferable to carry out with. When the heat treatment temperature is made higher than the above range or the heat treatment time is made longer than the above range, the molecular chain is relaxed and the values of a and b become large, which may be difficult to control within the preferred range of the present invention. In addition, when the heat treatment temperature is made lower than the above range or the heat treatment time is made shorter than the above range, the structure of the molecular chain is insufficiently fixed and the creep characteristics are deteriorated. Since a value becomes large, it may become difficult to control within a preferable range of the present invention.

(Manufacturing method of M layer (metal layer))
Next, a metal layer is provided on the polyester layer. Here, an example of a method for producing a metal layer using a vacuum deposition method will be given.

A polyester film is set on a film running device installed in a vacuum deposition apparatus, and vacuum deposition is performed. Vapor deposition is preferably performed at a high vacuum of 1.00 × 10 ^{−5 to} 1.00 × 10 ⁻¹ Pa. It is made to travel through a cooling metal drum of 0 to 50 ° C., the deposited material is heated and evaporated, and is formed and wound on both surfaces of the film. The film running speed is preferably 10 to 200 m / min, and more preferably 50 to 150 m / min. When the traveling speed is out of the above range, it may be difficult to set the thickness of the metal layer within a preferable range, or productivity may be inferior. When the metal layer is provided on both sides of the polyester layer, it is preferable to provide two heating vapor deposition devices and a cooling drum in the same vacuum layer and vapor deposit both sides in one pass. After the removal, two passes may be performed in which a metal layer is provided on the other surface again. Of course, in the case of two passes, even in the case of one pass, the order of providing the metal layers is preferably the magnetic layer side and the back coat layer side because cupping can be suppressed.

(Manufacture of magnetic layer and back coat layer)
Furthermore, a magnetic layer and a back coat layer are provided on a support in which a metal layer is provided on the polyester layer. Here, an example of a manufacturing method of a magnetic layer and a back coat layer using a coating method will be given.

  First, a support for a magnetic recording medium slit to a width of 0.1 to 3 m (preferably 0.5 to 1.5 m) is conveyed with a tension of 1 to 30 kg / m (preferably 2 to 10 kg / m). Then, a magnetic coating and a non-magnetic coating are applied on one surface of the support by a multilayer coating with an extrusion coater, magnetically oriented, and then dried. The conveyance speed at this time is preferably 50 to 400 m / min, more preferably 150 to 250 m / min, from the viewpoints of productivity and workability. The drying temperature is preferably 80 to 120 ° C, more preferably 100 to 110 ° C. When the drying temperature is lower than 80 ° C., the drying is not sufficiently performed. When the drying temperature is higher than 120 ° C., relaxation of the molecular chain is promoted, and the a, b, and c values may be deteriorated. Next, a back coat is applied to the nonmagnetic layer surface side under the same conditions. An example of the composition of the magnetic layer and the back coat layer is shown below.

  Furthermore, using a calender device, the calender treatment is performed at a temperature of 80 to 130 ° C. (more preferably, 100 to 120 ° C.) and a linear pressure of 100 to 300 kg / cm, and then wound up. The conveyance speed and process tension at this time are the same as described above.

  Further, aging and curing are performed. The temperature at this time also varies depending on the type of polyester used in the polyester layer. Since PET has a low Tg, when it is processed at a high temperature, orientation relaxation is likely to proceed, and in particular, the a value of the present application tends to deteriorate. When PEN is insufficiently aged, the creep characteristics deteriorate and the b and c values are likely to deteriorate. Therefore, it is better to treat PEN at a higher temperature than PET. If it is PET, 60-80 degreeC is preferable, More preferably, it is 65-75 degreeC, If it is PEN, 60-100 degreeC is preferable, More preferably, it is 70-90 degreeC. The treatment time is also the same. In the case of PET, it is preferably 10 to 80 hours, more preferably 20 to 50 hours. In the case of PEN, 20 to 100 hours are preferable, and 40 to 70 hours are more preferable. In addition, when a thermoplastic resin such as polyimide is mixed with polyester to form an alloy, aging may be shortened.

  Among the preferable conditions for the aging process, it is preferable to increase the processing time when the processing temperature is short, and it is preferable that the processing time is short when the processing temperature is relatively high. The processing conditions related to both temperature and time can be expressed by using the peak area of enthalpy relaxation of the magnetic recording medium obtained by differential scanning calorimetry (DSC) as an index.

  The peak area ΔH for enthalpy relaxation of the magnetic recording medium of the present invention is preferably 0.5 J / g to 1 J / g. When the peak area of enthalpy relaxation is less than 0.5 J / g, the amorphous chain is not sufficiently densified, and the b and c values of the present invention are large. Since the relaxation proceeds too much, the a value of the present invention increases, and in any case, it becomes difficult to control (change in the width dimension in the tape running environment) within the preferable range of the present invention.

(Composition of magnetic paint)
-Ferromagnetic metal powder: 100 parts by weight-Modified vinyl chloride copolymer: 10 parts by weight-Modified polyurethane: 10 parts by weight-Polyisocyanate: 5 parts by weight-Stearic acid: 1.5 parts by weight-Oleic acid: 1 part by weight Carbon black: 1 part by weight α-alumina: 10 parts by weight Methyl ethyl ketone: 75 parts by weight Cyclohexanone: 75 parts by weight Toluene: 75 parts by weight (composition of nonmagnetic paint)
-Modified polyurethane: 10 parts by weight-Modified vinyl chloride copolymer: 10 parts by weight-Methyl ethyl ketone: 75 parts by weight-Cyclohexanone: 75 parts by weight-Toluene: 75 parts by weight-Polyisocyanate: 5 parts by weight-Stearic acid: 1.5 Part by weight-Oleic acid: 1 part by weight (back coat composition)
Carbon black (average particle size 20 nm): 95 parts by weight Carbon black (average particle size 280 nm): 10 parts by weight α-alumina: 0.1 parts by weight Modified polyurethane: 20 parts by weight Modified vinyl chloride copolymer: 30 parts by weight-Cyclohexanone: 200 parts by weight-Methyl ethyl ketone: 300 parts by weight-Toluene: 100 parts by weight (Methods for measuring physical properties and methods for evaluating effects)
The characteristic value measurement method and effect evaluation method in the present invention are as follows.

(1) Temperature expansion coefficient The film was sampled to a width of 4 mm, and set to TMA TM-3000 manufactured by Vacuum Riko Co., Ltd. and a heating control unit TA-1500 so that the test length was 15 mm. The atmospheric condition is 23 ° C. and 65% RH. A load of 0.5 g was applied to the film, the temperature was raised from the ambient temperature (23 ° C.) to 50 ° C., and then cooled to 25 ° C. Thereafter, the temperature was increased from 25 ° C. to 50 ° C. at a rate of temperature increase of 1 ° C./min. The displacement amount ΔL (mm) of the film from 30 ° C. to 40 ° C. at that time was measured, and the temperature expansion coefficient (ppm / ° C.) was calculated from the following formula.
Thermal expansion coefficient (ppm / ° C.) = {(ΔL / 15) / (40-30)} × 1,000,000
(2) Humidity expansion coefficient The film was sampled to a width of 10 mm and set in a tape elongation tester made by Okura Industry installed in a constant temperature and humidity chamber so that the test length was 200 mm (load of 0.5 g was applied) ing). Atmosphere conditions were set to a temperature of 30 ° C. and a humidity of 40% RH, and after standing for 2 hours, the film length was measured (L ₄₀ ). Thereafter, at a constant temperature, by varying the humidity from 40% RH to 80% RH, after standing for 2 hours, (and L ₈₀₎ the film length was measured. The displacement (L ₈₀ -L ₄₀ ) between these two points was ΔL (mm), and the humidity expansion coefficient (ppm /% RH) was calculated from the following equation.

Humidity expansion coefficient (ppm /% RH) = {(ΔL / 200) / (80-40)} × 1,000,000
(3) a value (absolute value of the dimensional change rate in the width direction when changing from 10 ° C. and 10% RH to 30 ° C. and 80% RH with a load of 1 N applied in the longitudinal direction)
A magnetic recording medium slit to a width of 12.65 mm (1/2 inch) is used as a sample. This sample is set in a film dimension measuring apparatus (FIG. 1) installed in a constant temperature and humidity chamber.

  After applying a 1N load to the sample, using a constant temperature and humidity chamber, the atmospheric condition is 10 ° C. and 10% RH, and the sample is allowed to stand for 1 hour, and then the film width (mm) is measured. Next, the atmospheric condition is changed to 30 ° C. and 80% RH, and the film is allowed to stand for 1 hour, and then the film width (mm) is similarly measured. The absolute value of the two differences was divided by 12.65 (mm) and converted to ppm units to obtain the a value (ppm).

(4) b value (absolute value of dimensional change rate when the load in the longitudinal direction is changed from 0.5 to 1.5 N in an environment of 40 ° C. and 60% RH)
A magnetic recording medium slit to a width of 12.65 mm (1/2 inch) is used as a sample. This sample is set in a film dimension measuring apparatus (FIG. 1) installed in a constant temperature and humidity chamber.

  Using a constant temperature and humidity chamber, the atmospheric conditions are set to a temperature of 40 ° C. and a humidity of 60% RH.

  After applying a load of 0.5 N to the sample, the sample is allowed to stand for 1 hour, and then the film width (mm) is measured. Next, the load was changed to 1.5 N, and after standing for 1 hour, the film width (mm) was measured in the same manner. The absolute value of the two differences was divided by 12.65 (mm) and converted to ppm units to obtain the b value (ppm).

(5) c value (absolute value of contraction rate in the width direction before and after holding for 48 hours under a load of 1 N in the longitudinal direction under an environment of 40 ° C. and 60% RH)
After applying a load of 1 N to the sample, the atmospheric condition was set to 40 ° C. and 60% RH using a constant temperature and humidity chamber. The film width (mm) after standing for 1 hour and the film width (mm) after standing for 24 hours were measured, and the difference between the two was divided by 12.65 (mm) and converted to ppm units. It was set as the dimensional change (ppm) in the width direction when the treatment was performed for 24 hours at 45 ° C. and 30% RH.

(6) Width Dimension Change in Tape Running Environment The total of the a value, b value, and c value obtained in the above (3), (4), and (5) was defined as the width dimension change in the tape running environment.

(7) Young's modulus, breaking load It measured using the Instron type tensile tester according to the method prescribed | regulated to ASTM-D882. The measurement was performed under the following conditions.

  The breaking load was calculated in terms of 12.65 mm width.

Measuring device: Orientec Co., Ltd. film strong elongation automatic measuring device
“Tensilon AMF / RTA-100”
Sample size: width 10 mm x test length 100 mm,
Tensile speed: 200 mm / min Measurement environment: temperature 23 ° C., humidity 65% RH
(8) Surface roughness Ra
The center line average roughness Ra was measured using a high precision thin film level difference measuring device ET-10 manufactured by Kosaka Laboratory. The conditions are as follows, and an average value obtained by scanning 20 times in the film width direction was used as a value: ・ Tip tip radius: 0.5 μm
-Stylus load: 5mg
・ Measurement length: 1mm
・ Cutoff value: 0.08mm
(9) Number of coarse protrusions Three-dimensional roughness meter (SE-3AK, manufactured by Kosaka Laboratory: Measured 50 times by scanning in the film width direction under the following conditions: stylus tip radius 2 μm, stylus load 0.07 g, By measuring the number of protrusions with a height of 0.3 μm or more using a measurement area width of 0.5 mm × length of 15 mm (pitch of 0.1 mm) and a cut-off value of 0.08 mm, it is coarse by converting to 100 cm ^2. Obtain the number of protrusions. Furthermore, if necessary, a known method for measuring the number of protrusions on the film surface such as an atomic force microscope (AFM) or a 4-detection SEM may be used in combination.

However, when measuring the number of coarse protrusions of the polyester layer, the following method may be used. After ^two measurement surfaces (100 cm ² ) are stacked and brought into close contact with each other by electrostatic force (applied voltage 5.4 kV), the height of the coarse protrusion from the Newton ring caused by the interference of the coarse protrusion light between the two films. The number of coarse protrusions of a single ring or more was H1, and the number of coarse protrusions of a double ring or more was H2. The light source used was a halogen lamp with a 564 nm bandpass filter.

However, when measurement is difficult with the measurement area, the measurement area may be changed as appropriate and converted to 100 cm ² . (For example, a measurement area of 1 cm ² is measured for 50 visual fields and converted to 100 cm ^2. )
(10) Thermal contraction rate It measured according to JIS C2318.

Sample size: width 10 mm, marked line interval 200 mm
Measurement conditions: temperature 100 ° C., treatment time 30 minutes, no load state The heat shrinkage rate was determined from the following equation.

Thermal contraction rate (%) = [(L ₀ −L) / L ₀ ] × 100
L ₀ : Marking interval before heat treatment L: Marking interval after heat treatment However, the sample size may be measured by reducing the mark interval depending on the size of the obtained sample.

(11) Average particle diameter of inert particles The cross section of the film is observed with a transmission electron microscope (TEM) at a magnification of 10,000 times or more. The section thickness of TEM is about 100 nm, and the measurement is performed at 100 fields or more at different locations. The measured weight average of equivalent circle equivalent diameters was defined as the average particle diameter d of the inert particles.

  When two or more kinds of particles having different particle diameters exist in the film, the number distribution of equivalent circle equivalent diameters is a distribution having two or more peaks, and the average particle diameter is calculated separately for each of them. To do.

(12) Polyester, thermoplastic resin, content of inert particles in polyester layer Dissolve both polyester and thermoplastic resin in a suitable solvent and measure NMR (nuclear magnetic resonance) spectra of ¹ H nuclei. To do. A suitable solvent varies depending on the type of polymer, for example, hexafluoroisopropanol (HFIP) / deuterated chloroform is used. In the obtained spectrum, the peak area intensity of absorption peculiar to polyester and thermoplastic resin (for example, absorption of aromatic protons of terephthalic acid in the case of PET) is obtained, and the molarity of polyester and thermoplastic resin is determined from the ratio and the number of protons. Calculate the ratio. Further, the weight ratio is calculated from the formula amount corresponding to the unit unit of each polymer. The measurement conditions are, for example, the following conditions, but are not limited to this because they differ depending on the type of polymer.

Equipment: BRUKER DRX-500 (Bruker)
Solvent: HFIP / deuterated chloroform Observation frequency: 499.8 MHz
Standard: TMS (tetramethylsilane) (0 ppm)
Measurement temperature: 30 ° C
Observation width: 10 KHz
Data point: 64K
acquisiton time: 4.952 seconds
Pulse delay time: 3.048 seconds Integration count: 256 times In addition, composition analysis may be performed by a microscopic FT-IR method (Fourier transform microscopic infrared spectroscopy) as necessary. In that case, it calculates | requires from ratio of the peak resulting from the carbonyl group of polyester, and the peak resulting from other than that substance. In order to convert the peak height ratio to the weight ratio, a calibration curve is prepared with a sample whose weight ratio is known in advance, and the polyester ratio relative to the total amount of polyester and other substances is determined. The thermoplastic resin ratio is determined from this and the inert particle content. Moreover, you may use together an X-ray microanalyzer as needed.

  Also, for the content of inert particles, choose a solvent that dissolves polyester and thermoplastic resin but does not dissolve inert particles, dissolve polyester and thermoplastic resin, and centrifuge the inert particles to obtain a weight percentage. Asked.

(13) Glass transition temperature (Tg)
Specific heat was measured with the following equipment and conditions, and determined according to JIS K7121 (1987).

Apparatus: Temperature modulation DSC manufactured by TA Instrument
Measurement condition:
Heating temperature: 270-570K (RCS cooling method)
Temperature calibration: Melting point of high purity indium and tin Temperature modulation amplitude: ± 1K
Temperature modulation period: 60 seconds Temperature rising step: 5K
Sample weight: 5mg
Sample container: Aluminum open container (22 mg)
Reference container: Aluminum open container (18mg)
The glass transition temperature was calculated by the following formula.

Glass transition temperature = (extrapolated glass transition start temperature + extrapolated glass transition end temperature) / 2
(14) Peak area ΔH of enthalpy relaxation
Specific heat was measured with the following equipment and conditions, and the measurement was performed according to JIS K7121 (1987).

Apparatus: DSC manufactured by Seiko Instruments Inc.
Measurement condition:
Heating temperature: 25-300 ° C
Temperature increase rate: 40 ° C / min Sample weight: 5mg
Sample container: Aluminum open container (22mg)
Reference container: Aluminum open container (18mg)
The peak area of the endothermic peak observed on the lower temperature side than the Tg observed in the above item (13) is obtained and used as the peak area of enthalpy relaxation.

(15) Cupping A magnetic recording medium slit to a width of 12.65 mm (1/2 inch) is used as a sample.

  The tape is sampled to a length of 1 m and left for 3 hours at 25 ° C. and 65% RH under no load. Further, after that, a 500 mm length portion at the center is sampled and both ends are fixed on the table in a state where 3.5 g of tension is applied in the longitudinal direction (the interval between the fixed ends is 200 mm). The stage is fixed to a stage of an optical microscope capable of detecting the height position of the stage so that the center part in the longitudinal direction is the center, and observed at a magnification of 40 times. Focus on the surface of the table and the tape edge, and measure the height of the stage. The difference in the height of this stage is taken as cupping (mm).

(16) Intrinsic viscosity Calculated from the following equation from the solution viscosity measured at 25 ° C in orthochlorophenol.

η _sp / C = [η] + K [η] ² · C
Here, η _sp = (solution viscosity / solvent viscosity) −1, C is the weight of dissolved polymer per 100 ml of solvent (g / 100 ml, usually 1.2), and K is the Huggins constant (assuming 0.343). The solution viscosity and solvent viscosity were measured using an Ostwald viscometer.

(17) Terminal carboxyl group concentration of the film The film was obtained by dissolving the film in orthochlorocresol / chloroform (weight ratio 7/3) at 90 to 100 ° C. and measuring the potential difference with alkali. The unit is equivalent / ton.

(18) Tape running test The produced magnetic recording medium is slit into a 1/2 inch width under the condition of 25 ° C. and 65% RH, and a length of 650 m is incorporated into the cassette as a magnetic tape. It was.

  The prepared cassette tape is set in a tape running device installed in a constant temperature and humidity chamber, and first, 0.5N and 1.5N tape widths are measured under standard conditions (25 ° C., 65% RH). Next, the vehicle is caused to travel in the order of the following conditions 1 to 6 at a traveling speed of 5 m / sec. For each condition, run from unwinding to the end of winding. The process of running 6 conditions is performed 10 times. After returning to the standard state and storing for 10 hours, the running test is performed again. This process is repeated 10 times.

Condition 1: 10 ° C, 10% RH Tape tension 0.5N
Condition 2: 10 ° C., 10% RH Tape tension 1.5N
Condition 3: 10 ° C., 60% RH Tape tension 0.5 N
Condition 4: 10 ° C., 60% RH Tape tension 1.5N
Condition 5: 40 ° C., 60% RH Tape tension 0.5 N
Condition 6: 40 ° C., 60% RH Tape tension 1.5N
A laser dimension measuring device LS-5040 manufactured by Keyence Corporation is installed in the tape running device so that the tape width can be read at all times (sampling time 5 seconds). The average value of the tape width values for one condition is taken as the tape width of the condition, and the difference from the tape width of the standard condition divided by 12.65 mm is the tape width change (expansion is positive, shrinkage is Expressed as negative). In addition, a standard metal piece (a width of 12.65 mm at 25 ° C. and 65% RH) is installed in the apparatus, and at the same time, a dimensional change in the environment (referred to as a dimensional change of the standard piece) is read. Similarly, the change rate from the standard condition is obtained. The value obtained by subtracting the width change rate of the standard piece from the tape width change rate is defined as the relative width change rate, and evaluated according to the following criteria.

  In the case of 0 or more and less than 500 ppm: Very excellent characteristics as a high-density magnetic recording medium.

  When it is 500 ppm or more and less than 700 ppm: Excellent characteristics as a high-density magnetic recording medium.

  When it is 700 ppm or more and less than 900 ppm: It can be used as a high-density magnetic recording medium.

  When 900 ppm or more: Unusable as a high-density magnetic recording medium.

  Based on the following examples, embodiments of the present invention will be described.

(Example 1)
50 parts by weight of polyethylene terephthalate (PET) pellets (Tg 80 ° C.) having an intrinsic viscosity of 0.85 obtained by a conventional method and 0.68 intrinsic viscosity of polyetherimide (PEI) “Ultem” manufactured by General Electric (GE) 50 parts by weight of 1010 (Tg 216 ° C.) was supplied to a co-rotating bent type twin-screw kneading extruder heated to 290 ° C. to produce a PET / PEI blend chip containing 50% by weight of PEI.

  Next, using two extruders, the extruder A heated to 295 ° C. has 10 parts by weight of the PET / PEI blend chip produced by the pelletizing operation and an intrinsic viscosity of 0.62 substantially containing no inert particles. A mixed raw material of 80 parts by weight of polyethylene terephthalate (PET) pellets and 10 parts by weight of polyethylene terephthalate (PET) pellets having an intrinsic viscosity of 0.62 containing 2% by weight of crosslinked divinylbenzene particles having an average particle diameter of 80 nm is obtained at 180 ° C. It supplied after drying under reduced pressure for 3 hours. In Extruder B heated to 280 ° C., 10 parts by weight of the blend chip obtained by the pelletizing operation, 30 parts by weight of PET chip containing 2% by weight of spherical silica particles having an average particle size of 0.3 μm, and substantially particles 60 parts by weight of PET chip containing no lysate was dried at 180 ° C. under reduced pressure for 3 hours and then supplied. The raw material of Extruder A is filtered using a 1.2 μm cut fiber sintered stainless metal filter, the raw material of Extruder B is filtered using a 3 μm cut fiber sintered stainless steel metal filter, and then merged in a T die. (Lamination ratio 5/1), solidified by cooling and solidification while applying an electrostatic charge to a cast drum having a surface temperature of 25 ° C., to prepare a biaxially oriented two-layer laminated unstretched film (the Tg of the polymer of the unstretched film is 85 ° C).

This unstretched film was biaxially stretched using a simultaneous biaxial tenter having a linear motor clip. Simultaneously in the longitudinal direction and the width direction, the film was stretched 3.3 times x 3.8 times at a temperature of 100 ° C and a stretching speed of 6,000%, and cooled to 70 ° C. Subsequently, the film was redrawn at a temperature of 195 ° C. in the longitudinal direction and the width direction simultaneously by 1.4 × 1.2 times. Further, the film was heat treated at a temperature of 215 ° C. for 2.5 seconds while being stretched 1.1 times in the width direction, and then subjected to a relaxation treatment of 2% in the width direction to produce a biaxially oriented polyester film having a thickness of about 5 μm. The Young's modulus of the film was 7,100 MPa in the longitudinal direction and 5,050 MPa in the width direction. The intrinsic viscosity of the film was 0.65. The temperature expansion coefficient in the width direction is 6.3 ppm / ° C., the humidity expansion coefficient is 9.1 ppm /% RH, the 100 ° C. heat shrinkage rate in the longitudinal direction is 0.9%, and the 100 ° C. heat shrinkage rate in the width direction. Was 0.1%. The number of coarse protrusions on the surface on the side of the extruder A (referred to as A surface) was 15/100 cm ² .

Next, a metal layer was first provided on the A side. The obtained polyester film was set on a film running device installed in a vacuum vapor deposition device, and after making a high vacuum of 1.00 × 10 ⁻³ Pa, it was run through a cooling metal drum at 20 ° C. At this time, Al was heated and evaporated with an electron beam, and an Al metal layer (thickness 60 nm) was formed and wound. Thereafter, the film was set again in a vacuum deposition apparatus, and a metal layer was formed in the same manner on the surface opposite to the A surface to prepare a support film.

  The magnetic coating material (a) having the following composition was applied to the A surface side of the support film obtained above at a line speed of 100 m / min and dried at 110 ° C. for 3 seconds. Using an in-line calendar, calendering was performed under calendar conditions of roll temperature: 105 ° C. and linear pressure: 3.5 kN / cm, and then the back coat paint (I) having the following composition was opposite to the A side of the support film After coating on the surface, the film was dried and wound up at 110 ° C. for 3 seconds. Thereafter, an aging treatment was performed at 70 ° C. for 35 hours to obtain a magnetic recording medium.

<Composition of magnetic paint (a)>
100 parts by weight of acicular ferromagnetic metal powder mainly composed of iron [Fe: Co: Ni: Al: Y: Ca = 70: 24: 1: 2: 2: 1 (weight ratio)]
[Long axis length: 0.09 μm, axial ratio: 6, coercive force: 153 kA / m (1,922 Oe), saturation magnetization: 146 Am ² / kg (146 emu / g), BET specific surface area: 53 m ² / g, X-ray Particle size: 15 nm]
Alumina (abrasive, average particle size: 0.18 μm) 8 parts by weight Carbon black 0.5 part by weight (antistatic agent, average primary particle size: 0.018 μm)
Vinyl chloride copolymer (binder) 10 parts by weight (average polymerization degree: 280, epoxy group content: 3.1% by weight, sulfonic acid group content: 8 × 10 ⁻⁵ equivalent / g)
Polyurethane resin (binder) 7 parts by weight (number average molecular weight: 25,000, sulfonic acid group content: 1.2 × 10 ⁻⁴ equivalent / g, glass transition point: 45 ° C.)
-Palmitic acid (lubricant) 1.5 parts by weight-2-ethylhexyl oleate (lubricant) 2.5 parts by weight-Polyisocyanate (curing agent) 5 parts by weight [Coronate L (trade name) manufactured by Nippon Polyurethane Industry Co., Ltd. ]
・ Methyl ethyl ketone 120 parts by weight ・ Toluene 80 parts by weight ・ Cyclohexanone 40 parts by weight <Composition of back coat paint (I)>
Carbon black 40 parts by weight (antistatic agent, average primary particle size 0.018 μm)
・ Nipporan 2301 (binder) 50 parts by weight [trade name, polyurethane from Nippon Polyurethane Industry Co., Ltd.]
・ 4 parts by weight of polyisocyanate (curing agent) [manufactured by Takeda Pharmaceutical Co., Ltd., trade name (D-250N)]
Nitrocellulose 20 parts by weight Stearic acid 1 part by weight Methyl ethyl ketone 140 parts by weight Toluene 140 parts by weight Cyclohexanone 140 parts by weight As shown in Table 1, this magnetic recording medium satisfies the preferred range of the present invention, It had excellent properties as a density magnetic tape application.

  Further, the cupping of the magnetic recording medium of Example 1 was 0.4 mm, and in the tape running test, the quality was excellent with no powder falling or edge buckling.

(Example 2)
An unstretched film was prepared in the same manner as in Example 1.

This unstretched film was biaxially stretched using a simultaneous biaxial tenter having a linear motor clip. Simultaneously in the longitudinal direction and the width direction, the film was stretched 3.5 × 3.5 times at a temperature of 100 ° C. and a stretching speed of 6,000%, and cooled to 70 ° C. Subsequently, the film was re-stretched at a temperature of 165 ° C. simultaneously in the longitudinal direction and the width direction by 1.4 × 1.4 times. Further, the film was heat-treated at 210 ° C. for 2.5 seconds while being stretched 1.05 times in the width direction, and then subjected to a relaxation treatment of 2% in the width direction to produce a biaxially oriented polyester film having a thickness of about 6 μm. The Young's modulus of the film was 6,000 MPa in the longitudinal direction and 6,200 MPa in the width direction. The intrinsic viscosity of the film was 0.65. The temperature expansion coefficient in the width direction is 4.3 ppm / ° C., the humidity expansion coefficient is 6.1 ppm /% RH, and the number of coarse protrusions on the surface on the side of the extruder A (referred to as A surface) is 8/100 cm ² . there were. The 100 ° C. heat shrinkage rate in the longitudinal direction was 0.7%, and the 100 ° C. heat shrinkage rate in the width direction was 0.4%.

  Subsequently, in the same manner as in Example 1, an aluminum metal layer (layer thickness: 30 nm) was provided on both sides of the polyester film, and after applying a magnetic layer and a backcoat layer, an aging treatment was performed at 75 ° C. for 25 hours. To obtain a magnetic recording medium.

  As shown in Table 1, this magnetic recording medium satisfied the preferable range of the present invention, and had excellent characteristics for high-density magnetic tape applications. Further, the cupping of the magnetic recording medium of Example 2 was 1.0 mm, and in the tape running test, the quality was excellent with no powder falling or edge buckling.

(Examples 3 to 7)
As shown in Table 1, magnetic recording media were prepared by changing the film configuration, strength balance, thickness, and aging treatment.

  The aging treatment conditions are 65 ° C. and 35 hours (Examples 3 and 5), 90 ° C. and 72 hours (Examples 4 and 6), and 80 ° C. and 20 hours (Example 7), respectively.

  As shown in Table 1, these magnetic recording media satisfied the preferred range of the present invention and had excellent characteristics for high-density magnetic tape applications.

  Note that the cupping of the magnetic recording medium of Example 7 was 1.5 mm, and in the tape running test, powder was observed to adhere to the roll of the running test machine.

(Comparative Examples 1 and 2)
A polyester film was obtained in exactly the same manner as in Example 1.

  In Comparative Example 1, a magnetic recording medium was prepared in the same manner as in Example 1 except that a metal layer was not provided and a magnetic layer and a backcoat layer were applied.

  In Comparative Example 2, a magnetic recording medium was obtained in the same manner as in Example 1 by changing the thickness of the metal layer.

  As shown in Table 2, these magnetic recording media did not satisfy the preferred range of the present invention and were inferior in performance as high density magnetic tape applications.

(Comparative Example 3)
In the same manner as in Example 5, the magnetic recording medium was produced by changing the thickness of the metal layer.

  As shown in Table 2, this magnetic recording medium did not satisfy the preferred range of the present invention, and was inferior in performance as a high-density magnetic tape application.

(Comparative Examples 4-6)
A magnetic recording medium was prepared using the conditions of Example 1 of JP 2002-319122 A, Example 4 of JP 2001-256636 A, and Example 1 of JP 2000-11364 A, respectively.

  As shown in Table 2, this magnetic recording medium did not satisfy the preferred range of the present invention, and was inferior in performance as a high-density magnetic tape application.

  The present invention is particularly preferably used for high-density recording magnetic tapes for data storage, but is not limited to this, and can be applied to capacitor applications, insulating films, and the like, and its application range is limited to these. It is not a thing.

It is the schematic of a film dimension measuring apparatus.

Explanation of symbols

1: Laser oscillator 2: Light receiving unit 3: Load detector 4: Load 5: Free roll 6: Free roll 7: Free roll 8: Free roll 9: Magnetic tape 10: Laser light

Claims (7)

A layer (M layer) containing a metal or a metal-based inorganic compound is provided on at least one surface of the polyester layer, and a magnetic layer is provided on the outer layer of this layer (M layer), and a back coat layer is provided on the opposite outer layer. The temperature expansion coefficient in the width direction of the magnetic recording medium is 0 to 10 ppm / ° C., the humidity expansion coefficient is 0 to 7 ppm /% RH, and the width dimension changes in the tape running environment shown below are as follows: A magnetic recording medium of 0 to 1,200 ppm.
[Width dimension change in tape running environment]
The sum of the following a, b, and c is defined as a width dimension change in the tape running environment.
a: Absolute value of the dimensional change rate in the width direction when the load is changed from 10 ° C. and 10% RH to 30 ° C. and 80% RH with a load of 1 N applied in the longitudinal direction.
b: Absolute value of the dimensional change rate when the longitudinal load is changed from 0.5 to 1.5 N in an environment of 40 ° C. and 60% RH.
c: Absolute value of contraction rate in the width direction before and after holding for 48 hours in a state where a load of 1 N was applied in the longitudinal direction under an environment of 40 ° C. and 60% RH. 2. The polyester layer according to claim 1, wherein the polyester layer has a layer (M layer) containing a metal or a metal-based inorganic compound, and the magnetic layer is formed by applying a composition containing a ferromagnetic powder and a binder. Magnetic recording media. The surface roughness Ra (m) of the surface on the magnetic layer side of the magnetic recording medium is 2 to 5 nm, and the surface roughness Ra (b) of the surface on the backcoat layer side is 10 to 20 nm. 2. A magnetic recording medium according to 1. The magnetic recording medium according to claim 1, wherein the number of coarse protrusions having a height of 0.3 μm or more on the surface of the magnetic recording medium on the magnetic layer side is 0 to 10/100 cm ² . The magnetic recording medium according to any one of claims 1 to 4, wherein the breaking load in the longitudinal direction is 25 to 40N. The magnetic recording medium according to claim 1, wherein the polyester layer contains 70 to 99% by weight of polyethylene terephthalate and 1 to 30% by weight of polyimide. The magnetic recording medium according to claim 1, wherein the polyester layer has a thickness of 6 to 8 μm.

Images