JPS6252365B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to magnetic recording media. More specifically, the present invention relates to a magnetic recording medium with excellent signal recording and reproduction characteristics. A magnetic layer is applied to the surface of the polyester film,
When using a polyester film as a magnetic tape, it is said that wrinkles and scratches should not occur on the surface of the film. For this purpose, it is necessary that the base film has good slipperiness, that is, a low coefficient of friction. This is because films with poor slipperiness may be difficult to coat during film manufacturing or magnetic layer coating.
In addition, when handling the film, the surface of the film is easily damaged or wrinkled, so that it cannot be used as a base film, or even if it is used forcibly, the product yield is extremely poor. Furthermore, even after being processed into a magnetic tape or the like, it is necessary to have good slip properties in order to run the tape smoothly when it is pulled out from a reel or cassette or wound up. In order to improve the slipperiness of a film, it is sufficient to add irregularities to the film surface, and for this purpose, inorganic fine particles may be added to the polymer used as the film raw material,
This may result in the formation of insoluble catalyst residues in the polymer. However, base films for magnetic tapes, especially base films used for video tapes, etc., not only require such excellent slip properties, but also must have excellent abrasion resistance to withstand long-term use. . Magnetic tapes often come into contact with recording devices and playback devices when recording on the tape or reproducing recordings, and the tape is likely to wear out due to this contact, thus giving the tape extremely excellent wear resistance. It is hoped that The problem of wear in magnetic tapes can be broadly divided into two types. The first is the fatigue wear type and the second is the friction wear type. The former is caused by continuous running of a magnetic tape based on polyester film. A magnetic layer is applied to the side of the magnetic tape where information is stored. On the other side, which is not coated with a magnetic layer, contact with the equipment as the tape runs generates powdered polyester fragments, which can cause temporary or permanent signal drop-out when reading the information stored in the magnetic layer. ) to cause This occurs as a result of tape winding, as debris from the uncoated side of the tape settles on the coated side of the magnetic layer, causing separation from the information reading head. These fragments can be removed by cleaning, etc., so they appear to be only a temporary error, but in many cases, they enter the magnetic layer during winding, creating jagged dents on the tape surface. The jagged depressions cause separation between the read head and the magnetic layer coating surface, causing dropout. On the other hand, frictional wear occurs during the film manufacturing process.
This phenomenon occurs when the film is exposed to considerable frictional resistance during the process before the magnetic layer coating process or when reproducing information. When the film is run, polyester fragments are generated in the form of white powder on the surface of the film that has not been coated with the magnetic layer.For example, when applying the magnetic layer, if the coated surface contains polyester fragments,
The magnetic layer is not coated on the portions of the film surface covered with debris, but is coated on the debris. This creates an uneven tape surface, and bumps caused by the magnetic layer being applied to debris on an otherwise smooth surface can cause dropouts. Therefore, fatigue loss wear and friction wear must be reduced. In order to reduce fatigue wear and friction wear between films, and especially between films and metals, it is necessary to lower the coefficient of friction. By causing the presence of , unevenness is imparted to the film surface. However, even if the film has the same coefficient of friction, the degree of wear and runnability will be significantly different between those with large and small surface roughness, and depending on the degree of wear, the film may stop running. do. Furthermore, a phenomenon in which images are distorted occurs when electronically editing a videotape or when starting or stopping a tape. High-end recording and reproducing equipment used for television broadcasting solves these drawbacks with automatic adjustment equipment, but this equipment is complex and expensive. The above-mentioned drawbacks have not been solved in recording and reproducing apparatuses commonly used for home, business, and educational purposes, and it has been desired to improve the base film used. According to the inventor's study, the image disturbance described above is related to the expansion and contraction of the magnetic recording tape due to tension fluctuations at the time of starting and stopping, and the ability to recover from distortion. The conclusion was that it depends on the As a result of intensive research into base films for magnetic recording media that do not have many of the drawbacks mentioned above, the inventors of the present invention found that the film has an intrinsic viscosity and a Young's modulus in the longitudinal direction exceeding a certain value, and that at least one side of the film has an intrinsic viscosity and a longitudinal Young's modulus of The present invention was achieved by discovering that a biaxially oriented polyester film having a surface roughness within a specific range has excellent properties as a base film for a magnetic recording medium without the above-mentioned drawbacks. That is, the present invention provides a magnetic recording medium in which a magnetic layer is provided on the surface of a base film, in which the base film is made of polyester having an intrinsic viscosity of 0.70 or more and containing inert fine particles, and the longitudinal Young's modulus of the film is 700 Kg/mm ² or more, and at least one surface of the biaxially oriented polyester film has a surface roughness of PV value of 0.50 μ or less and CLA value of 0.015 μ or more. It is. The polyester forming the polyester film of the present invention mainly includes terephthalic acid as an acid component, but terephthalic acid 90 (preferably
95) mol% or more and difunctional acids such as isophthalic acid, phthalic acid, adipic acid, sebacic acid, succinic acid, oxalic acid, malonic acid, P-hydroxybenzoic acid, ω-hydroxycaproic acid, etc. 10 (preferably 5) mol% of one or more types
It may be a copolymer consisting of the following, and the glycol component is mainly ethylene glycol, but ethylene glycol 90 (preferably 95) mol% or more and trimethylene glycol, hexamethylene glycol, cyclohexane, etc. Dimethanol (1,4) 10 mol% (preferably 5 mol%) or less of one or more diol compounds such as 2,2,4,4-tetramethylcyclobutanediol (2,4) and hydroquinone, etc. It may be a copolymer using these polymers, or it may be a mixture of these polymers. Furthermore, other polymers of up to 10% by weight (preferably 5% by weight) may be mixed with such polyester. The polyester may contain, for example, stabilizers such as phosphoric acid, phosphorous acid and their esters, and matting agents such as titanium dioxide. The lower limit of the intrinsic viscosity of the polyester film of the present invention is 0.70, and the upper limit is not particularly limited, but is usually 1.5 or less from the viewpoint of film forming operations. The lower limit is preferably 0.75, particularly preferably 0.80. By setting the film's intrinsic viscosity within this range and specifying the Young's modulus and surface roughness as shown below, abrasion resistance was improved, dropouts were reduced, and image distortion was prevented. Obtaining a magnetic recording medium is an unexpected and surprising effect. The polyester constituting the film contains inert fine particles as a film surface roughness imparting agent (lubricant). The inert fine particles include plate-like fine particles such as kaolin, spherical fine particles such as calcium carbonate, titanium dioxide, etc., and spherical amorphous fine particles such as silica. The particle size, particle size distribution, content, etc. of the inert fine particles must be such that the film surface roughness PV value is 0.5 μ or less and
It is determined by satisfying a CLA value of 0.015μ or more. In the film of the present invention, Young's modulus in the longitudinal direction is
The reason why it is specified as 700 kg/mm ² or more is to prevent the tape from expanding and contracting during electronic editing of the videotape or when starting and stopping the tape, and to speed up tape distortion recovery. The longitudinal Young's modulus is preferably
It is 750 Kg/mm ² or more, particularly preferably 800 Kg/mm ² or more. In the film of the present invention, the longitudinal direction is the extrusion direction, and usually means the longitudinal direction of the film. The film of the present invention has excellent runnability and abrasion resistance when the surface roughness PV value and CLA value of at least one surface thereof are within the range specified by the present invention.
A film suitable for magnetic recording media with little dropout can be obtained. Generally, as the PV value increases, the CLA value also tends to increase, but the trends do not always match and may be reversed. Film abrasion resistance and running properties are thought to depend on the film surface condition (film surface roughness), Young's modulus of the film, film running speed, etc., but especially when the running speed is relatively low (1 to 40 cm/sec) ), the runnability and abrasion resistance of a high Young's modulus film such as the film of the present invention depends on the PV value of the surface roughness.
It was found that those with a CLA value of 0.50μ or less and a CLA value of 0.015μ or more have excellent characteristics. PV value is 0.50
When μ is exceeded, both running performance and wear resistance deteriorate. When the CLA value is lower than 0.015μ, wear resistance becomes particularly poor and dropout increases. PV
The value is preferably below 0.40μ, particularly preferably
It is 0.35μ or less. Also, the CLA value is preferably
It is 0.020μ or more, particularly preferably 0.025μ or more. The method for producing the polyester film of the present invention is arbitrary, but for example, the CLA value can be adjusted by adjusting the particle size distribution of the added inert inorganic particles, and the PV value can be adjusted by adjusting the maximum peaks and valleys on the rough surface of the film. Therefore, the particle size of the added inert inorganic particles can be adjusted. More specifically, for example, there is a method in which several types of inorganic particles with different particle size distributions are added and made to exist in the film, and a phosphorus component is added during polymerization to generate a particle source, and classified inorganic particles are added to form a film. Preferably used methods include a method in which a phosphorus component and other additives are added during polymerization, and a method in which the phosphorus component and other additives are added and polymerized, and then the two are blended. When adding inert particles to the polyester that is the polyester film material of the present invention, the addition timing may be before polyester polymerization, during the polymerization reaction, or by kneading in an extruder when pelletizing after completion of polymerization. Furthermore, it may be added during melt extrusion into a sheet, dispersed in an extruder, and extruded, but it is preferable to add it before polymerization.
The surface roughness of the film also depends on the film forming conditions, and tends to become smoother as the stretching ratio is increased. The thickness of the film of the present invention is not particularly limited, but
Usually 2 to 50μ. Films thicker than 50μ have a large cross-sectional area, which reduces the requirements for Young's modulus and residual elongation. Further, a biaxially oriented film is a film that is oriented in the longitudinal and lateral directions by a method such as stretching or rolling. As a base film for a magnetic recording medium, its surface properties are important, and a stretched film is preferred. The film of the present invention has 4 to 7
It can be manufactured by selecting an appropriate combination in the range of 2 to 4 times in the transverse direction. As for the stretching method,
Known methods such as sequential biaxial stretching, simultaneous biaxial stretching, and stretching the biaxially oriented film in the longitudinal direction again can be employed. In addition, when only one side of the film is in contact with the metal roll, only the contact surface can have the surface condition defined by the present invention, and the other side can be made rough or smooth depending on the purpose. The magnetic recording medium of the present invention has a magnetic layer provided on the surface of the above-mentioned polyester film, and the magnetic layer may be of any known type. The magnetic layer usually contains a ferromagnetic powder such as γ-iron oxide, Co-containing iron oxide, chromium oxide, iron powder, etc., and a polymer binder such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, etc. Polymers, vinyl resins such as polyvinyl butyral, vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butyl acrylate-2-hydroxyethyl methacrylate copolymer, rubber resins such as acrylonitrile-butadiene copolymer, nitrocellulose, acetyl It consists of cellulose-based resins such as cellulose, crosslinkable resins such as epoxy, phenoxy, urethane, etc. If desired, an abrasive agent, a light shielding agent, a dispersant, an antistatic agent, etc. may be added thereto. The coated magnetic layer is formed by applying magnetic paint. The magnetic recording medium of the present invention is particularly useful in the low speed range (1 to 40
It is excellent for recording and reproducing signals at a speed of 1.5 cm/sec. The method for measuring each characteristic value defined in the present invention will be explained below. <Intrinsic Viscosity> In the present invention, the intrinsic viscosity calculated from the solution viscosity is used as a measure of the molecular weight of polyester. The measurement method uses O-chlorophenol as the solvent, the measurement temperature is 25°C, and the calculation is performed using the following formula. ηsp/C=[η]+K[η] ² C [where ηsp=solution viscosity/solvent viscosity-1 [η]: Intrinsic viscosity (dl/g) C: Dissolved polymer mass per 100ml of solvent (g/
100ml)...Here it is 1.2. K: Huggins constant (set to 0.247) Solution viscosity and solvent viscosity were measured using an Ostwald viscometer. ] <Young's Modulus> The film was cut into samples with a width of 10 mm and a length of 15 cm, and was stretched using an Instron type universal tensile testing device at a chuck distance of 100 mm and a tensile speed of 10 mm/min and a chart speed of 500 mm/min. Young's modulus was calculated from the tangent to the rising part of the obtained load-elongation curve. <PV value and CLA value> PV [Peak-to-Valley] value and CLA that indicate surface roughness in the present invention
[Center Line Average
Average)] values are those measured by the following methods. PV value: Using a stylus surface roughness tester (SURFCOM 3B) manufactured by Tokyo Seimitsu Co., Ltd., measure the roughened film at a standard film length of 2.6 mm under the conditions of a stylus radius of 3 μ and a load of 0.1 g. , the reference length direction is 50
Magnify the surface roughness direction by 20,000 times, draw a chart, and extract the standard length from the cross-sectional curve. Among the straight lines parallel to the average line, 1 from the higher side.
Select the line that passes through the 2nd peak and the 1st valley bottom from the deepest one, divide the distance between these two lines by the vertical magnification, express it in microns, and express it as the average value of these 10 PV values. Note that the measurement is performed in the vertical direction. CLA value: Cut out a part of measurement length L (reference length 2 mm) from the roughened film roughness curve in the direction of its center line, and draw the center line of this cut out part by
The roughness curve is defined as Y = axis, with the vertical magnification direction as the Y axis.
When expressed as (x), the value given by the following formula is expressed in μ units. "CAL=1/ ^L∫L _O |f(x)|dx" This measurement is performed on 8 samples, the 3 samples with the largest values are excluded, and the average value of the 5 samples is expressed. Note that the measurement is performed in the vertical direction. Examples will be given below to further specifically explain the present invention. In addition, "dynamic friction coefficient" in the examples
The measurement method and the evaluation value of "abrasion resistance" were performed as follows. <Dynamic friction coefficient μk> As shown in Figure 1, in an atmosphere of 25℃ and 60% relative humidity, the rough side of the polyester film was angled to a SUS27 fixing rod (surface roughness 0.3S) with an outer diameter of 20mmφ. They are brought into contact at Θ (unit: radian) and moved at a speed of 95 mm/sec. Population tension at this time
The dynamic friction coefficient μk was calculated from the exit tension T ₂ g when T ₁ is 30 g using the following formula (in the present invention, the dynamic friction coefficient when running for 30 m is defined as μk). μk=2.303/ΘlogT ₂ / _T1 In the examples, measurements were made at Θ=180°. <Abrasion resistance> Abrasion resistance was evaluated by measuring the coefficient of dynamic friction μk described above.
2000 under the same conditions.
The paper was run for 100 m, and the degree of adhesion of white powder to the tissue paper was classified into 1 to 5 below. No. 1 has no white powder and exhibits excellent frictional resistance. Sample No. 2 has a slight amount of white powder, but can be used satisfactorily. Sample No. 3 contained more white powder than No. 2, and was present on the entire surface of the tissue paper, making it unusable. Sample No. 4 produced more white powder than Sample No. 3 and was not usable. No. 5 has white powder adhered to the entire surface of the tissue paper and shows the worst friction and wear. <Screen disturbances when starting/stopping> The tape was subjected to a recording/playback test using Sony's Umatake video equipment, and the presence or absence of initial screen disturbances when tape running was stopped and restarted. was evaluated using the following criteria 1, 2, and 3. 1...No disturbance is observed. 2... A little disturbance is observed, but there is no problem in practical use. 3...The disorder is so large that it cannot be used as a practical product. As a comprehensive evaluation, those with good running performance, wear resistance, and screen disturbance during start/stop were given as ○, those with no practical problems were given △, and those that were unusable were given as ×. Examples 1 to 5, Comparative Examples 1 to 6 As shown in Table 1, inert fine particle-containing polyethylene terephthalate (added during polymerization) with various intrinsic viscosities, various particle sizes, and contents was used.
Films were formed at the heat setting temperature and stretching ratio shown in the table. The conditions are as follows: melt extrusion, quench cooling, and create an amorphous unstretched film in the longitudinal direction.
It was stretched at 75°C and then laterally stretched at 100°C. Then, it was heat-set for 10 seconds so that the free heat shrinkage rate at 150°C was 5 to 6%. The various properties of the film obtained under these conditions were
Shown in the table. These films were coated with magnetic paint to a thickness of 4 μm according to a known method, and mirror-finished using a calendar to prepare video tapes. This videotape was subjected to a recording/playback test using a Umatake video device manufactured by Sony Corporation. Video tapes using the films produced under the conditions of Comparative Examples 2, 4, 5, and 6 as base films had the disadvantage that many dropouts occurred and the screen flickered. From the results shown in Table 1, it is clear that the film of the present invention is good in terms of runnability, abrasion resistance, dropout, and screen disturbance. Examples 6 to 10, Comparative Examples 7 to 8 During polymerization of polyester, the amounts shown in Table 1,
Polyethylene terephthalate with different intrinsic viscosities to which inert fine particles of different types and particle sizes have been added is melt-extruded and rapidly cooled to produce an amorphous unstretched film, which is sequentially stretched at 90°C in the longitudinal and transverse directions. axially stretched, then stretched 1.5 times in the longitudinal direction again at 140°C,
Heat fixation was performed at 230°C for 10 seconds. This film was also evaluated in the same manner as in Examples 1 to 5, and the results are shown in Table 1. 【table】

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a tape base inspection machine that measures the coefficient of dynamic friction μk of a film rough surface. In the figure, number 1 is the unwinding reel, 2 is the tension control, 3, 5, 6, 8, 9, 11 are the free rollers, 4 is the tension detector (inlet), and 7 is the tension control.
A SUS27 fixed rod (20 mmφ outer diameter), 10 a tension detector (outlet), 12 a guide roller, and 13 a take-up reel.

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer provided on the surface of a base film, in which the base film is made of polyester having an intrinsic viscosity of 0.70 or more and containing inert fine particles, and the longitudinal Young's modulus of the film is 700 Kg/mm ² or more. , and at least one surface has a PV value of 0.50 μ or less and a CLA value of 0.015.
A magnetic recording medium characterized by being a biaxially oriented polyester film having a surface roughness of μ or more.