JP2006274113A - Biaxially oriented polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially oriented polyester film hardly suffering from permanent deformation in the thickness direction of the film even under a high-temperature high-humidity condition. <P>SOLUTION: In a first embodiment, the film deformation amount in the thickness direction is at most 6.0% of the whole thickness of the film when the film is subjected to a 24-hr transfer treatment at 40°C and 90% RH under a load of 15 MPa in the longitudinal direction. In a second embodiment, the film has a heat shrinkage factor S<SB>MD</SB>in the longitudinal direction of 0.0-1.8% at 100°C, and S<SB>MD</SB>and a creep C<SB>ZD</SB>in the thickness direction satisfy a relationship: 0≤5S<SB>MD</SB>+3C<SB>ZD</SB>≤24. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

    The present invention has little permanent deformation of the film in the thickness direction under high temperature and high humidity, and is useful when used as a magnetic recording material, electronic material, plate-making film, sublimation ribbon, packaging material, and particularly suitable as a magnetic recording material base film. The present invention relates to a polyester film.

    In recent years, magnetic recording media for data storage and digital video tape have been increasing in density and capacity. Generally, there are a helical recording system and a linear recording system as recording systems used for such a magnetic recording medium. The helical recording system pulls out the tape from the cartridge with two reels, scans the cylindrical head that rotates at high speed, and reads and writes to the tape diagonally, whereas the linear recording system has a cartridge with one reel. Then, the tape is guided to the head, and the tape is read and written in a straight line in the longitudinal direction. Although the linear recording method has a lower recording density than the helical recording method, it is said to have high reliability for data storage due to less damage to the tape because the tape is gently wound around the head.

Recently, the LTO employing such a linear recording system (L inear T ape O pen) and SDLT (S uper D igital L inear T ape), those having a high capacity of more than 100GB in Volume 1 of the tape is developed ing. In general, there are three methods for increasing the capacity: increasing the number of tracks, decreasing the recording wavelength, and increasing the tape length. First, if the number of tracks is increased, the width of one track becomes narrower, so that control of dimensional stability in the tape width direction is important. In addition, surface smoothness is required to realize sufficient electromagnetic conversion characteristics after shortening the recording wavelength. Further, since the size of the magnetic recording medium cartridge is basically unchanged, in order to increase the tape length per roll, it is essential to reduce the thickness of the tape and increase the strength associated therewith. From these three viewpoints, many studies have been made so far, such as optimization of the temperature expansion coefficient and humidity expansion coefficient in the tape width direction, reduction of the diameter of the additive particles, and enhancement of the base film by increasing the draw ratio.

  However, even if these techniques are used, sufficient electromagnetic conversion characteristics cannot be obtained for a linear recording magnetic recording medium having a high capacity of 100 GB or more per roll. As a result of investigation, it has been clarified that minute deformation in the film thickness direction that occurs under high temperature and high humidity conditions affects the characteristics of the magnetic recording medium.

In general, the linear recording method is more susceptible to spacing loss than the helical recording method because the tape is loosely wound and the head does not push the tape in the vertical direction. Spacing loss is a gap in the order of nanometers formed between the head and the tape. If the spacing loss is large, electromagnetic conversion characteristics deteriorate. In order to keep the head contact stable and reduce the spacing loss, in addition to the thickness uniformity over a long period such as thickness unevenness that has been studied in the past, the surface flatness in the micro area of micron level It has been found that control is important. Up to now, although there has been a study on dimensional stability in the longitudinal or width direction and reversible deformation in the thickness direction (Patent Document 1), no improvement has been studied on irreversible deformation in the thickness direction.
JP2003-132524A (page 2)

    The problem to be solved by the present invention is to provide a biaxially oriented polyester film with little permanent deformation of the film in the thickness direction under high temperature and high humidity.

A first aspect for achieving the object of the present invention is that a film deformation amount in the thickness direction is 6.0% or less when a transfer treatment is performed for 24 hours at 40 ° C. and a humidity of 90% RH with a load of 15 MPa in the longitudinal direction. A biaxially oriented polyester film characterized in that

A second aspect to achieve the object of the present invention, the longitudinal direction of 100 ° C. thermal shrinkage rate _{S MD} is from 0.0 to 1.8%, and the relationship between the creep _{C ZD} in the thickness direction is 0 ≦ _{5S MD Biaxial} , characterized by + 3C _ZD ≦ 24, is an oriented polyester film.

    According to the present invention, a biaxially oriented polyester film useful when used as a base film for a high-density magnetic recording medium can be obtained with little permanent deformation of the film in the thickness direction when a transfer treatment is performed under high temperature and high humidity.

    The biaxially oriented polyester film of the first aspect of the present invention has a film deformation amount in the thickness direction when a load of 15 MPa is applied in the longitudinal direction and a transfer treatment is performed at 40 ° C. and 90% RH for 24 hours. Is 6.0% or less, preferably 5.0% or less, and more preferably 4.0% or less. If the film deformation amount in the thickness direction is larger than 6.0%, when the tape is stored or run under high temperature and high humidity, it is deformed by receiving a transfer from a hub or the like, and data cannot be read. Further, for example, in a linear recording tape, a leader tape not provided with a magnetic material is connected to the tip of a magnetic tape provided with a magnetic recording layer, and the leader tape is connected to a drive unit to run. The joining of the leader tape and the magnetic tape is generally performed by overlapping the two, and a thickness step at the joint is inevitable. The joint is overlapped on the outside of the magnetic tape, but it receives a winding load and gives stress in the thickness direction to the magnetic tape wound on the inside. A minute thickness unevenness will be given.

  As described above, the present invention suppresses minute thickness fluctuations on the magnetic tape and the tape support due to local stress in the thickness direction of the tape caused by the transfer of the hub and the like, and the joint with the leader tape. Has found that improvement of irreversible deformation in the thickness direction of the film is necessary.

The biaxially oriented polyester film of the second aspect of the present invention, the longitudinal direction of 100 ° C. thermal shrinkage rate _{S MD} is from 0.0 to 1.8%, and 0 ≦ between the creep _{C ZD} in the thickness direction 5S _MD + _{3C ZD} ≦ 24, preferably a _{0 ≦ 5S MD + 3C ZD ≦} 21 between the _{S MD} is 0.0 to 1.5%, and the thickness direction creep _{C ZD.} When the heat shrinkage _SMD is greater than 1.8%, the winding tightening when wound in a reel shape becomes large, and therefore, for example, the film in the thickness direction tends to be permanently deformed by transfer of the hub. When the thermal shrinkage rate is smaller than 0.0%, the film is easily stretched due to the heat load during processing, and therefore, uniform tension is difficult to be applied and uneven coating may occur. On the other hand, if 5S _MD + 3C _ZD is larger than 24, film deformation in the thickness direction tends to occur when stored at a high temperature.

In general, in the linear recording method, the tape is gently wound, and the force with which the head pushes the tape in the vertical direction is weak. Therefore, spacing loss is more likely to occur than in the case of the helical recording method, and the control of the microplanarity of the film surface is an important characteristic. In particular, in order to maintain excellent microplanarity after heat load in the film processing step, it is necessary to reduce micro heat shrinkage unevenness of the film. For that purpose, when the polyester film is a polyethylene terephthalate film, the microscopic Raman crystallization index Ic in the film thickness direction is 8 ^{−1 to} 20 cm ⁻¹ , preferably 10 ^{−1 to} 18 cm ⁻¹ , more preferably 12 ^{−1 to} 16 cm. ^-1 . The microscopic Raman crystallization index indicates that the crystallinity of the film can be analyzed in micron units, and the smaller the value, the more stable the structure. If the Ic of the polyethylene terephthalate film is greater than 20 cm ⁻¹ , the structure is not stable, shrinkage due to heat treatment may occur, and the microplanarity may deteriorate. On the other hand, in order to stabilize the structure until Ic is smaller than 8 cm ^−1, it is necessary to considerably increase the draw ratio, and tearing may occur.

When the polyester film is a polyethylene naphthalate film, the microscopic Raman crystallization index is preferably 18 ^{−1 to} 28 cm ⁻¹ , preferably 20 ^{−1 to} 25 cm ⁻¹ . When Ic of polyethylene naphthalate is larger than 28 cm ⁻¹ , the structure is not stable, shrinkage due to heat treatment may occur, and microplanarity may deteriorate. On the other hand, in order to stabilize the structure until Ic is smaller than 18 cm ^−1, it is necessary to considerably increase the draw ratio, and tearing may occur.

The difference between the maximum value and the minimum value of Ic in the thickness direction is 1 cm ⁻¹ or less, preferably 0.5 cm ⁻¹ or less, and more preferably 0.3 cm ⁻¹ or less. If there is a variation in the microscopic Raman crystallization index greater than 1 cm ^{−1, the} degree of minute thermal shrinkage in the film thickness direction during heat treatment is not uniform, and the microplanarity of the film surface tends to deteriorate.

From the viewpoint of preventing shrinkage unevenness during heat treatment, the difference between the maximum value and the minimum value of the microscopic Raman crystallization index in the film plane direction is also 1 cm ⁻¹ or less, preferably 0.5 cm ⁻¹ or less, more preferably 0.3 cm. ^-1 or less.

  One of the features of the present invention is that it is difficult to analyze with macro measurement methods such as Young's modulus and crystallinity that have been used in the prior art, the problem of spacing loss and electromagnetic conversion characteristics deterioration in the linear recording method However, it has been found that it can be expressed by a microscopic Raman crystallization index, which is a very microscopic measurement. Accordingly, even if the Young's modulus and crystallinity are the same, the effect may not be obtained if the microscopic Raman crystallization index exceeds the above range.

    The biaxially oriented polyester film in the present invention is not particularly limited as long as it is a polyester that becomes a high-strength film by molecular orientation, but is preferably mainly composed of polyethylene terephthalate and polyethylene-2,6-naphthalate. Particularly preferred is polyethylene terephthalate having good creep characteristics. Examples of polyester copolymer components other than ethylene terephthalate include diol components such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, p-xylylene glycol, and 1,4-cyclohexanedimethanol, adipic acid, sebacic acid, and phthalate. Dicarboxylic components such as acid, isophthalic acid and 5-sodiumsulfoisophthalic acid, polyfunctional dicarboxylic acid components such as trimellitic acid and pyromellitic acid, p-oxyethoxybenzoic acid and the like can be used.

  The biaxially oriented polyester film of the present invention may be a single layer or a laminated structure of two or more layers. The two-layer structure is more preferable because it can easily control the formation of surface protrusions on the layer (B) opposite to the layer (A) to which the magnetic layer is applied when used as a magnetic recording medium.

The surface roughness WRa ^A of the layer (A) of the two-layer structure biaxially oriented polyester film measured with a non-contact type three-dimensional roughness meter is preferably 0.01 to 8 nm, more preferably 0.1. It is -4 nm, More preferably, it is 0.2-2 nm. When WRa ^A is made smaller than 0.01 nm, the sliding between the head and the tape may be deteriorated. If the thickness exceeds 8 nm, the surface becomes too rough and sufficient electromagnetic conversion characteristics for a high-density magnetic recording medium may not be obtained. On the other hand, the surface roughness WRa ^B of the layer (B) on the opposite side is preferably 1 to 10 nm, more preferably 3 to 6 nm. If it is smaller than 1 nm, wrinkles or the like may occur during winding of the film, resulting in poor winding. On the other hand, if WRa ^B is larger than 10 nm, the surface becomes too rough, so that when it is wound as a film roll, it may easily cause an adverse effect such as transfer to the layer (A) to which the magnetic layer is applied.

    Next, in order to satisfy the above surface roughness, it is preferable to add inert particles in the layer. In the present invention, the inert particles I used for the layer (A) have an average particle size dI of preferably 0. 0.04 to 0.30 μm, preferably 0.05 to 0.15 μm, and the content is preferably 0.001 to 0.30 wt%, more preferably 0.01 to 0.25 wt%. In a magnetic recording medium, if particles having an average particle size larger than 0.30 μm are used, electromagnetic conversion characteristics may be deteriorated.

    In the polyester film having a two-layer structure, the thickness tB of the layer (B) is preferably 0.1 to 2.0 μm, more preferably 0.2 to 1.5 μm. When this thickness is smaller than 0.1 μm, the particles are likely to drop off, and when it is larger than 2.0 μm, the protrusion forming effect of the added particles may be reduced.

  In the polyester film having a two-layer structure, the particle contained in the layer (B) may be one type or two or more types. The average particle diameter dII of the largest inert particles II added to the polyester layer (B) is preferably 0.1 μm to 1.0 μm, more preferably 0.4 μm to 0.9 μm, and the content is preferably 0.00. The average particle diameter of the inert particles III is smaller than that of the particles II, and the average particle diameter is preferably 0.05 μm to 0%. 0.5 μm, more preferably 0.2 μm to 0.4 μm, and the content is preferably 0.1 wt% to 1.0 wt%, more preferably 0.2 to 0.4 wt%.

  In the two-layer polyester film, the inert particles contained in the layer (A) and the layer (B) are inorganic particles such as spherical silica, aluminum silicate, titanium dioxide, calcium carbonate, and other organic polymer particles. Are preferably crosslinked polystyrene resin particles, crosslinked silicone resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, crosslinked polyester particles, polyimide particles, melamine resin particles, and the like. One or more of these are selected and used.

  In the polyester film having a two-layer structure, the inert particles contained in the layer (A) and the layer (B) preferably have a uniform particle shape and particle distribution, and the volume shape factor is preferably f = 0.3 to π. / 6, more preferably f = 0.4 to π / 6. The volume shape factor f is expressed by the following equation.

f = V / Dm ³
Here, V is the particle volume (μm ³ ), and Dm is the maximum diameter (μm) on the projection plane of the particles.

  The volume shape factor f takes the maximum π / 6 (= 0.52) when the particle is a sphere. In order to remove coarse particles and inclusions as necessary, filtration or the like is preferably performed. Among them, spherical silica is preferable because it is excellent in monodispersity, can easily control the formation of protrusions, and the effects of the present invention become better. If necessary, α-type alumina, γ-type alumina, δ-type alumina, θ-type alumina, zirconia having a primary particle size of 0.005 to 0.10 μm, preferably 0.01 to 0.05 μm from the viewpoint of reinforcing the background. In addition, inert particles selected from silica, titanium particles and the like may be contained within a range that does not affect the formation of surface protrusions.

    Moreover, the biaxially oriented polyester film in the present invention has a Young's modulus in the longitudinal direction of the film of 5000 MPa or more, preferably 5500 MPa or more, and more preferably 6000 MPa or more from the viewpoint of improving the creep characteristics. On the other hand, the Young's modulus in the width direction is 3500 MPa or more, preferably 4000 MPa or more, and more preferably 4500 MPa or more from the viewpoint of improving dimensional stability. In order to achieve both dimensional stability in the longitudinal direction and the width direction, the Young's modulus in the longitudinal direction is preferably 6000 MPa or more and the Young's modulus in the width direction is 4500 MPa or more.

    In general, in the linear recording method, it is preferable that the dimensional change rate in the width direction when the tension is applied in the longitudinal direction is small from the viewpoint of preventing track deviation. When a load of 32 MPa is applied in the longitudinal direction of the film and the film is treated at a temperature of 49 ° C. and a humidity of 90% RH for 72 hours, the dimensional change in the width direction before and after the treatment is preferably 0.40% or less, more preferably 0.38%. Hereinafter, it is further preferably 0.35% or less. If it is larger than 0.40%, track deviation may occur when used as a magnetic tape.

    Moreover, the thermal shrinkage rate in the width direction of the polyester film in the present invention is 0.0 to 2.0%, preferably 0.0 to 1.0%. When the thermal shrinkage rate is larger than 2.0%, film shrinkage during high-temperature storage or heat treatment is severe, and microplanarity may be deteriorated. The heat shrinkage rate in the width direction can be appropriately adjusted by a known method such as relaxation treatment.

In the biaxially oriented polyester film of the present invention, the temperature expansion coefficient in the width direction of the film is preferably −10 × 10 ^{−6 to} 20 × 10 ⁻⁶ / ° C., more preferably −5 × 10 ⁻⁶ to 15 × 10 ⁻⁶ / ° C., more preferably 0 to 8 × 10 ⁻⁶ / ° C. Furthermore the humidity expansion coefficient in the transverse direction of the film is preferably 0~20 × ¹⁰ -6 /% RH, more preferably ^{5 × 10 -6 ~15 × 10 -6} /% RH, more preferably 6 × ^{10 -6} ~ 10 × 10 ⁻⁶ /% RH. If the temperature expansion coefficient and the humidity expansion coefficient exceed these ranges, the fixed head may not be able to correctly read the magnetic information written on the tape if the temperature difference or humidity difference between data writing and data reading is large. In order to read the data correctly even if there is a change in the temperature and humidity environment, it is preferable to set each expansion coefficient within the above range.

  The biaxially oriented polyester film in the present invention may be provided with an easy-adhesion layer by applying a water-soluble coating or an organic solvent-based coating on at least one side within a range that does not impair the effects of the present invention.

  The total thickness of the polyester film used in the present invention is becoming thinner as the capacity increases, and is preferably 2.0 to 8.0 μm, more preferably 4.0 to 7.0 μm. If it is thicker than 8.0 μm, the tape length entering the cassette becomes short, and a sufficient recording capacity may not be obtained. If the thickness is less than 2.0 μm, sufficient strength may not be obtained when a tape is used.

  Next, the preferable manufacturing method of the biaxially oriented polyester film of this invention is demonstrated. As a method of incorporating the inert particles into the polyester, for example, the inert particles I are dispersed in the form of a slurry at a predetermined ratio in ethylene glycol, which is a diol component, and this ethylene glycol slurry is added at an arbitrary stage before the completion of polyester polymerization. To do. Here, when adding the particles, for example, when the water sol or alcohol sol obtained at the time of synthesis is added without drying, the dispersibility of the particles is good, and both the slipping property and the electromagnetic conversion property are good. It can be. Also effective for the effect of the present invention is a method in which an aqueous slurry of particles is directly mixed with predetermined polyester pellets, supplied to a vent type twin-screw kneading extruder and kneaded into polyester.

  The particle-containing pellets prepared in this manner and the pellets substantially free of particles and the like are mixed at a predetermined ratio, dried, then supplied to a known melt laminating extruder, and the polymer is filtered through a filter.

  Also, in high-density magnetic recording medium applications where a very thin magnetic layer is applied, very small foreign matter can cause DO (dropout), which is a magnetic recording defect. It is effective to use a highly accurate one that collects 95% or more. Subsequently, the sheet is extruded from a slit-shaped slit die and cooled and solidified on a casting roll to form an unstretched film. In other words, 1 to 3 extruders, 1 to 3 layers of manifolds or merging blocks (for example, merging blocks having a rectangular merging section) are stacked as necessary, sheets are extruded from the die, and cooled by casting rolls. To make an unstretched film. In this case, a method of installing a static mixer and a gear pump in the polymer flow channel is effective from the viewpoint of stabilizing the back pressure and suppressing thickness fluctuation.

  The stretching method may be simultaneous biaxial stretching or sequential biaxial stretching. Since simultaneous biaxial stretching does not involve stretching by a roll, local heating of the film surface does not occur, and it is easy to control the micro Raman crystallization index that affects the micro-planarity during thermal loading, so as a stretching method More preferred. In simultaneous biaxial stretching, an unstretched film is first stretched simultaneously in the longitudinal and width directions at a stretching temperature of, for example, 80 to 160 ° C, preferably 85 to 130 ° C, more preferably 90 to 110 ° C. When the stretching temperature is lower than 80 ° C., the film tends to break, and when the stretching temperature is higher than 160 ° C., it may be difficult to obtain sufficient strength when used as a magnetic recording medium. From the viewpoint of preventing uneven stretching, the total stretching ratio in the longitudinal direction and the transverse direction is, for example, 8 to 30 times, preferably 9 to 25 times, more preferably 10 to 20 times, and stretching over several zones. When performing, it is preferable that the temperature of each zone is the same, or the temperature difference of each zone shall be 10 degrees C or less from a viewpoint of preventing an extending | stretching nonuniformity. When the draw ratio is less than 8, it is difficult to obtain the necessary and sufficient strength for the high-density magnetic recording medium targeted by the present invention. On the other hand, if the magnification is larger than 30 times, the film may be torn and it may be difficult to manufacture. In order to obtain the strength required for the high-density magnetic recording medium, the temperature is preferably 140 to 200 ° C., more preferably 160 to 190 ° C., preferably 1.05 to 1.8, more preferably, as necessary. Is preferably 1.2 to 1.6 times and stretched in the longitudinal and / or width direction again. If it is smaller than 1.05, sufficient strength may not be obtained in the longitudinal or width direction, and if it is larger than 1.8 times, the thermal shrinkage rate may be increased. Thereafter, heat setting is performed at, for example, 200 to 235 ° C., preferably 205 to 220 ° C., for example, for 0.5 to 20 seconds, preferably for 1 to 15 seconds. If the heat setting temperature is lower than 200 ° C., the crystallization of the film does not proceed, so that the structure is not stable, and microplanarity may be deteriorated due to heat shrinkage during high temperature storage or heat load. On the other hand, when the temperature is higher than 235 ° C., relaxation of the polyester amorphous chain portion proceeds, the Young's modulus becomes smaller, and the creep in the thickness direction may worsen. In order to suppress the variation in the microscopic Raman crystallization index, the temperature difference between the upper and lower sides of the film is, for example, 20 ° C. or less, preferably 10 ° C. or less, and more preferably 5 ° C. or less. If the temperature difference between the top and bottom of the film is larger than 20 ° C., the microscopic Raman crystallization index in the thickness direction is not uniform, and microplanarity may be deteriorated during heat treatment. Thereafter, a relaxation treatment of 0.5 to 7.0% is performed in the longitudinal and / or width direction.

   In simultaneous biaxial stretching, unlike sequential biaxial stretching described later, the film is heated by high-temperature air. Therefore, only the film surface is locally heated and no sticking occurs, and the stretching method is preferable to sequential stretching. On the other hand, in simultaneous biaxial stretching, the zones from the initial stretching temperature of about 90 ° C. to the heat setting temperature of about 220 ° C. are all connected in the longitudinal direction. Temperature difference is likely to occur up and down. A method for reducing the temperature difference is not particularly limited, but it is effective to provide a facility such as a shutter for suppressing a free flow of high-temperature air between zones having different temperatures. In particular, in order to prepare a film in which the variation of the microscopic Raman crystallization index is suppressed, the gap between the film and the shutter is, for example, 1 to 250 mm, preferably 2 to 100 mm, and more preferably 3 to 50 mm. If the gap is smaller than 1 mm, the film may come into contact with the shutter and break. On the other hand, if it is larger than 250 mm, the variation in the microscopic Raman crystallization index becomes large, and the microplanarity may deteriorate. By appropriately changing the speed of the air blown from the nozzle, the film and the shutter can be adjusted so as not to contact each other.

    On the other hand, the biaxially oriented polyester film of the present invention can also be produced using sequential stretching. In order to suppress variation in the microscopic Raman crystallization index, the first longitudinal stretching is important, and the stretching temperature is, for example, 90 to 160 ° C, preferably 95 to 150 ° C, more preferably 100 to 120 ° C. is there. When the stretching temperature is lower than 90 ° C., the film is easily broken, and when the stretching temperature is higher than 160 ° C., the film surface may be thermally damaged. Further, from the viewpoint of preventing stretching unevenness and scratches, stretching is preferably performed in two or more stages, and the total magnification is, for example, 2.5 to 8.0, preferably 2.8 to 4.0, Preferably it is 2.8 to 3.3 times. If the draw ratio is less than 2.5 times, it may be difficult to obtain the strength required for a magnetic recording medium. On the other hand, when the magnification is larger than 8.0 times, the film is liable to be scratched, so that it is difficult to use as a magnetic recording medium, and the film may be broken at the time of re-longitudinal stretching. Further, as the stretching roll, a non-adhesive silicone roll whose surface roughness and the like are easily controlled is preferable. The surface roughness Ra of the drawing roll is, for example, 0.005 to 1.0 μm, preferably 0.1 to 0.6 μm. When Ra is larger than 1.0 μm, irregularities on the roll surface may be transferred to the film surface during stretching. When Ra is smaller than 0.005 μm, the roll and the film background may stick to each other, and the film surface may be easily damaged by heat. When ceramic, Teflon (registered trademark) or metal rolls are used as in the prior art, only the film surface is heated locally, causing adhesion, and the microscopic Raman crystallization index varies between the film surface and the inside. Is likely to occur. Further, the total contact time between the roll and the film in the stretching portion is, for example, 0.1 seconds or less, preferably 0.03 seconds or less, which is particularly effective in producing the film. When the contact time between the roll and the film is longer than 0.1 seconds, only the film surface is locally heated by the heat of the stretching roll, causing a variation in the microscopic Raman crystallization index between the film and the inside, which is It may cause micro flatness deterioration during loading. Here, the contact time is the time obtained by dividing the contact distance between the film and the stretching roll by the film speed including the roll, and when stretching is performed over a plurality of rolls, the total time of the stretching. As a method of shortening the contact time, there is a method of stretching the film while holding it on a roll. For example, it is particularly effective to stretch the film only between nip rolls without winding the film around the stretching roll.

In successive stretching, for example, 80 to 160 ° C., preferably 85 to 130 ° C., more preferably 90 to 110 ° C., and preferably 2.5 to 6.0 times in the width direction, preferably 2.8 to 4.0. The film is stretched by a factor of 3.0, more preferably 3.0 to 3.5. If the temperature and magnification range are out of the range, problems such as uneven stretching or film breakage may occur, and it may be difficult to obtain a film characterized by the present invention. In order to obtain a microscopic Raman crystallization index as an object of the present invention, it is preferably 130 to 160 ° C., more preferably 135 to 145 ° C., preferably 1.05 to 1.8 times, more preferably as necessary. Re-longitudinal stretching is preferably performed at 1.2 to 1.6 times. In particular, when the stretching temperature is lower than 130 ° C., the film may be easily broken and the production may be difficult. On the other hand, when the stretching temperature is higher than 160 ° C., the film surface is easily damaged by heat.
On the other hand, if it is smaller than 1.05 times, sufficient strength may not be obtained, and if it is larger than 1.8 times, the thermal shrinkage rate may be increased. Thereafter, for example, preferably after re-stretching by 1.0 to 1.5 times, more preferably 1.1 to 1.3 times, preferably 200 to 235 ° C., preferably 205 to 220 ° C., preferably 0 It is heat-fixed for 5 to 20 seconds, more preferably 1 to 15 seconds. In particular, when the heat setting temperature is lower than 200 ° C., the crystallization of the film does not proceed and the structure is not stable, and the microplanarity may be deteriorated during the heat treatment. On the other hand, if the temperature is higher than 235 ° C., relaxation of the polyester amorphous chain portion proceeds, and the Young's modulus may be reduced, or creep in the thickness direction may be deteriorated. Moreover, in order to suppress the dispersion | variation in a micro Raman crystallization index | exponent, the temperature difference of a film upper and lower sides becomes like this. Preferably it is 20 degrees C or less, More preferably, it is 10 degrees C or less, More preferably, it is 5 degrees C or less. If the temperature difference between the top and bottom of the film is greater than 20 ° C., the microscopic Raman crystallization index in the thickness direction is not uniform, and microplanarity may be deteriorated during heat treatment.

  The winding core in the present invention preferably has a surface roughness (Ra) of 0.5 μm or less, more preferably 0.2 μm or less. If the thickness exceeds this range, the unevenness of the surface of the winding core is transferred to the surface of the film to be wound. Therefore, as a base film for a magnetic recording medium in which the flatness of the film is strictly required, the electromagnetic conversion characteristics are remarkably deteriorated. May end up. A method for setting the surface roughness (Ra) of the winding core to such a range is not particularly limited, but a desired surface roughness is obtained by using a hard resin such as an epoxy resin on the core surface and grinding the surface with high accuracy. Is obtained. In particular, it can be finished with higher accuracy by performing a buffing process after grinding.

The axial elastic modulus (Ya) of the winding core is 10 GPa Or more, more preferably 14 GPa That's it. If a winding core that is less than this range is used, the winding core may be deformed by the tension and contact pressure applied when the film is wound. The circumferential elastic modulus (Yr) of the winding core is also 10 GPa It is preferable that it is above, and more preferably 14 GPa or more. If a winding core less than this range is used, the winding core may be deformed as described above. The method for setting the strength of the take-up core to such a range is not particularly limited. For example, in the case of a fiber reinforced plastic core, it can be adjusted by appropriately selecting the amount of carbon fibers in the base material. The desired strength can also be obtained by adjusting the thickness.

  The substrate of the winding core in the present invention is not particularly limited, but it is desirable to use a high-strength material such as fiber reinforced plastic, aluminum, or iron. In particular, since the core based on fiber reinforced plastic is lightweight, it is effective in terms of handling.

    Hereinafter, the present invention will be described in detail with reference to examples.

The characteristic value measurement method and effect evaluation method of the present invention are as follows.
A. Average particle size of particles The polymer was removed from the film by a plasma low-temperature ashing method to expose the particles. The treatment conditions were selected such that the polymer was ashed but the particles were not damaged as much as possible. The particles were observed with a scanning electron microscope (SEM), and the particle images were processed with an image analyzer. The SEM magnification was appropriately selected from about 5000 to 20000 times. The volume average diameter d was obtained by the following formula from the particle diameter and the volume fraction thereof when the number of particles was changed to 5000 or more by changing the observation location. When two or more kinds of particles having different particle diameters were contained, the same measurement was performed for each particle to obtain the particle diameter.
d = Σ (di · Nvi)
Here, di is the particle size, and Nvi is the volume fraction. When the particles were significantly damaged by the plasma low-temperature ashing method, the film cross section was observed at 3000 to 100,000 times with a transmission electron microscope (TEM). The section thickness of the TEM was about 100 nm, 500 places or more were measured from different locations, and the volume average diameter d was determined from the above formula.
B. Particle Volume Shape Factor With a scanning electron microscope, photographs of the particles were taken, for example, 10 fields at a magnification of 5000 times. Furthermore, the maximum diameter of the projection plane and the average volume of the particles were calculated using an image analysis processing apparatus, and a volume shape factor was obtained by the following formula.

f = V / Dm ³
Here, V is the average volume (μm ³ ) of the particles, and Dm is the maximum diameter (μm) of the projection surface.
C. Film Lamination Thickness The depth profile of the particle concentration was measured by XPS (X-ray photoelectron optical method), IR (infrared spectroscopy) or confocal microscope while etching from the surface. In the surface layer of the film laminated on one side, the particle concentration is low due to the air-resin interface called the surface, and the particle concentration increases as the distance from the surface increases. In the case of the film laminated on one side of the present invention, the particle concentration once reached the maximum value at the depth [I] starts to decrease again. Based on this concentration distribution curve, the depth [II] (here, II> I), which is ½ of the maximum particle concentration, was defined as the lamination thickness. Furthermore, when inorganic particles etc. are contained, using a secondary ion mass spectrometer (SIMS), the concentration ratio of the element resulting from the highest concentration of the particles in the film and the carbon element of the polyester Using (M + / C +) as the particle concentration, analysis in the depth (thickness) direction from the surface of the layer (A) was performed. The lamination thickness was obtained from the same method as described above.
D. Film deformation amount in the thickness direction A film left for 24 hours at 23 ° C. and a humidity of 65% RH was sampled to a width of 10 mm and a length of 700 mm. A stainless steel cylinder having a diameter of 25 mm was prepared by attaching a transfer step by attaching a stainless tape having a width of 10 mm and a thickness of 100 μm. The sampled film was wrapped around the layer (A) for 5 turns, a load was applied so that the tension was 15 MPa, and the film was left in an oven at 40 ° C. and a humidity of 90% RH for 24 hours.

  The amount of film deformation of the most core side layer (A) was measured using a three-dimensional fine shape measuring instrument (model ET-30HK) and a three-dimensional surface roughness analysis system (model TDA-21) of Kosaka Laboratory. The conditions were as follows, 10 measurements were performed twice at different locations, and the average value of 20 times was taken as the film deformation amount.

-Tip radius of stylus: 2 μm
・ Load of stylus: 10mg
・ Vertical magnification: 50000 times ・ Horizontal magnification: 500 times ・ Cutoff: 0.25 mm
・ Feed pitch: 2μm
・ Measurement length: 2000μm
Measurement speed: 20 μm / second Microscopic Raman crystallization index A sample was embedded in an epoxy resin and polished to obtain a cross section. At five locations different in the plane direction, the microscopic Raman crystallization index was measured every 1 μm in the thickness direction (6 points for a 6 μm film and 4 points for a 4.5 μm film), and the average of the same position in the thickness direction The value was calculated, and the maximum value, the minimum value, and the difference between the maximum value and the minimum value (ΔIc) were calculated from the values. In the plane direction, after cutting the cross section, the area from the film surface to a depth of 1 μm is 6 mm each in the longitudinal and width directions every 2 mm (corresponding to 1/2 inch tape width). A total of 12 points are laser Raman microprobe method (air resolution) 1 μm) under the following conditions to calculate the variation. The half-width of 1730 cm ⁻¹ (carbonyl group stretching vibration) was defined as the microscopic Raman crystallization index Ic, and the difference between the maximum value and the minimum value was defined as ΔIc.

Equipment; Ramanor U-64000 manufactured by Jobin Yvon
Measurement mode: Micro Raman objective lens: × 100
Beam diameter: 1μm
Cross slit: 100 μm
Light source: Ar + Laser / 5145Å
Laser power: 50mW
Diffraction grating; Spectrograph 1800 gr / mm
Dispersion: single 21A / mm
Slit: 100 μm
Detector: CCD / Jobin Yvon 1024 × 256
F. Young's Modulus of Film According to the method of JIS-K7127, Young's modulus was measured at 23 ° C. and humidity 65% RH using an Instron type tensile tester. A sample film having a width of 10 mm and a length of 100 mm cut in the machine direction (MD) and the width direction (TD) of the film was measured by pulling.
G. 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 controller TA-1500 so that the test length was 15 mm. A load of 0.5 g was applied to the film to raise the temperature from room temperature (23 ° C.) to 50 ° C., and then the temperature was once returned to room temperature. Thereafter, the temperature was increased again from room temperature to 50 ° C. The displacement amount (ΔLmm) of the film from 30 ° C. to 40 ° C. at that time was measured, and the temperature expansion coefficient was calculated from the following equation.

Thermal expansion coefficient (/ ° C.) = (ΔL / 15) / (40-30)
H. Humidity expansion coefficient After sampling the film to a width of 10 mm and setting it on a tape elongation tester made by Okura Industry so that the test length is 200 mm, changing the temperature from 30 ° C. and humidity from 40% RH to 80% RH and holding for 30 minutes The displacement (ΔLmm) was measured, and the humidity expansion coefficient was calculated from the following equation.

Humidity expansion coefficient (/% RH) = (ΔL / 200) / (80-40)
I. Heat Shrinkage The film is cut into a length of 10 mm and a length of 250 mm in the longitudinal and width directions, two marked lines are put at an interval of about 200 mm, and the interval is measured at 23 ° C. (this is Xmm). The distance between the marked lines after being left in a 100 ° C. atmosphere for 30 minutes with a 0.15 g load applied to the tip of this sample was measured again at 23 ° C. (this is defined as Ymm), and 100 × (X− Y) / X was defined as the heat shrinkage rate.
J. et al. Dimensional change rate The film was cut into 100 mm in the longitudinal direction and 30 mm in the width direction, and after humidity adjustment for 24 hours under conditions of 23 ° C., humidity 65% RH and no load, on a chrome mask manufactured by Dai Nippon Printing Co., Ltd. The sample is attached by static electricity, and the length in the width direction (L0) is measured using an optical microscope. Then, it was left for 72 hours under a condition of 49 ° C. and a humidity of 90% RH under a load of 32 MPa in the longitudinal direction. After 72 hours, the load was released, and after adjusting the humidity for 24 hours under the conditions of 23 ° C., humidity 65% RH and no load, the length (L1) in the width direction was measured. The dimensional change rate in the width direction was determined by the following formula.
Dimensional change rate in width direction (%) = [(L0−L1) / L0] × 100
K. Surface roughness of drawing roll
Using a surface roughness meter Surf Test 301 manufactured by Mitutoyo Co., Ltd., the center surface average roughness was measured at three points in the roll width direction at a cutoff of 0.25 mm, and the average value was adopted.
L. Surface roughness WRa
Using a non-contact three-dimensional roughness meter TOPO-3D manufactured by WYKO, the measurement area magnification was 41.6 times, and the measurement area was 239 × 239 μm (0.057 mm ² ). WRa was measured by surface analysis software (ver.4.90) incorporated in the roughness meter. The measurement was performed 10 times and the average value was adopted. The measuring device is not limited to WYKO, and a non-contact three-dimensional roughness meter ZYGO capable of performing the same measurement or an atomic force microscope AFM may be used.
M.M. Surface roughness of winding core According to JIS B0601, each of the surface roughness meter Surfcom 111A of Tokyo Seimitsu Co., Ltd. was used and the center line average roughness was divided into three equal parts in the width direction at a cutoff of 0.25 mm. In the central part of the region, the surface roughness was measured and the average value was adopted.
N. Axial elastic modulus of winding core A core having an outer diameter of 167 mm, an inner diameter of 152.5 mm, and a length of 1023 mm is supported so that the distance between the fulcrums is 900 mm, and a load is applied to the center of the core. The axial elastic modulus was determined.
O. Elastic modulus in the circumferential direction of the winding core A core cut to an outer diameter of 167 mm, an inner diameter of 152.5 mm, and a length of 50 mm is placed between two flat plates, a load is applied at the center, and the circumferential elasticity is determined by the load-deflection ratio. The rate was determined.
P. Creep amount in the thickness direction A room temperature creep test was performed using an ultra-micro hardness meter, a creep deformation amount-time diagram was obtained, and creep characteristics were evaluated. In the test, a maximum load of 0.1 mN was applied in 15 seconds, held at about 0.1 mN for 10 minutes, and then unloaded to about 0.01 mN in 15 seconds. The slope of the creep deformation amount-time diagram during 10 minutes holding was defined as the creep amount in the thickness direction.

Measuring device: MTS Systems Co., Ltd. Ultra micro hardness tester Nano Indenter XP
Working indenter: Diamond regular triangular pyramid indenter Holding condition: About 0.1 mN-10 min
Measurement atmosphere: 21 ° C, humidity 60% RH
Q. Evaluation of micro-planarity by thermal treatment Heat treatment was performed by leaving the film in an oven at 100 ° C. for 24 hours under no tension. The microplanarity of the layer (A) before and after the heat treatment was measured at a measurement area magnification of 41.6 times and a measurement area of 239 × 239 μm (0.057 mm ² ) using a non-contact three-dimensional roughness meter TOPO-3D manufactured by WYKO. did. Relative Power at spatial frequencies of 10 cm ⁻¹ and 200 cm ⁻¹ was determined by surface analysis software (ver. 4.90) built in the roughness meter. The measurement was performed 10 times, and the average value was used as the value of the relative power. WRa was measured only for the film before heat treatment.

The relative power is a value representing the power spectrum P (fx, fy) at each spatial frequency in a logarithmic scale (dB), and the surface waviness of P (fx, fy) 1 nm ² is analyzed to be expressed as 0 dB. It is standardized in the software. Measurement was made with x as the film width direction and y as the film longitudinal direction. P (fx, fy) is calculated by the following equation, respectively.

In the equation, P (fx, fy) is a power spectrum, A is a measurement area, FT is a Fourier transform operation represented by ∬h (x, y) exp [i2π (x · fx + y · fy)], h (X, y) is surface shape data, and fx, fy are frequency coordinates in space.

  Zjk is the height on the three-dimensional roughness chart at the j-th and k-th positions in each direction when the measurement direction and the direction orthogonal thereto are divided into M and N, respectively.

The intensity difference between spatial frequencies 10 (1 / mm) and 200 (1 / mm) is read and expressed as I ^10-200 TD. This value indicates the degree of micro-planarity on the film surface, and the smaller the value is on the plus side, the worse the micro-planarity is. The measuring device is not limited to WYKO, and a non-contact three-dimensional roughness meter ZYGO capable of performing the same measurement or an atomic force microscope AFM may be used.

I ^10-200 TD was measured before and after heat treatment, and (I ^10-200 TD after heat treatment) − (I ^10-200 TD before heat treatment) was calculated to evaluate the micro-planarity by thermal heat treatment. For use as a high-density magnetic recording medium, the difference in I ^10-200 TD before and after the heat treatment is 6 dB or less, preferably 4 dB or less, more preferably 2 dB or less.

Example 1
A pellet of polyethylene terephthalate containing spherical silica particles having an average particle size of 0.06 μm and a volume shape factor f = 0.51 and polyethylene terephthalate containing substantially no particles was prepared, and the content of spherical silica particles was 0.2% by weight. The thermoplastic resin A was prepared by mixing two types of pellets so that Further, polyethylene terephthalate containing divinylbenzene / styrene copolymer crosslinked particles having an average particle size of 0.3 μm and a volume shape factor f = 0.52, and divinyl having an average particle size of 0.8 μm and a volume shape factor f = 0.52 A pellet of polyethylene terephthalate containing benzene / styrene copolymer crosslinked particles and polyethylene terephthalate containing substantially no particles has a particle content of 0.3 μm of 0.26% by weight and a particle content of 0.8 μm of 0.8%. The thermoplastic resin B mixed so that it might become 01 weight% was prepared. These thermoplastic resins were each dried under reduced pressure at 160 ° C. for 8 hours, then supplied to separate extruders, melt-extruded at 275 ° C. and filtered with high precision, and then merged and laminated with a rectangular two-layer merge block. Layer lamination was used. Thereafter, the film was wound around a casting drum having a surface temperature of 25 ° C. by using an electrostatic application casting method on a cooling roll through a slit die maintained at 285 ° C., and solidified by cooling to obtain an unstretched laminated film. This unstretched laminated film was stretched 3.5 times in the longitudinal and width directions at 95 ° C and 12.3 times in total by a linear motor type simultaneous biaxial stretching machine, and then 1.4 times in the longitudinal direction again at 190 ° C. The film was stretched 1.2 times in the width direction and heat-treated at 220 ° C. for 3 seconds under a constant length. The distance between the film and the shutter was 20 mm, and the temperature difference between the top and bottom of the film was 1 ° C. Thereafter, a relaxation treatment of 2% in the width direction was performed to obtain a biaxially oriented polyester film having a total thickness of 6.5 μm and a layer (B) thickness of 0.5 μm.

Example 2
Biaxial in the same manner as in Example 1 except that the particle size (f = 0.52) of the particles to be added to the layer (A), the addition amount, the draw ratio in the longitudinal and width directions, and the heat setting temperature were changed to 210 ° C. An oriented polyester film was obtained.

Example 3
The particle size of the particles added to the layer (A) and the layer (B), the added amount, and the thickness of each layer, with the draw ratio in the longitudinal direction of the second stage being 1.6 times and the draw ratio in the width direction being 1.0 times A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the heat setting temperature was changed to 210 ° C.

Example 4
The particle size (f = 0.51), the addition amount of the particles to be added to the layer (A), the stretching ratio in the longitudinal direction of the second stage is 1.0 times, the stretching ratio in the width direction is 1.4 times, and 5 μm. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that a single-layer film was obtained.

Example 5
An unstretched laminated film was prepared in the same manner as in Example 1, and stretched by a sequential biaxial stretching method. First, the film was stretched 3.1 times in the longitudinal direction in two stages at a stretching temperature of 110 ° C. A non-adhesive silicone roll having a surface roughness Ra of 0.40 μm was used for the drawing rolls in contact at this time, and the drawing rolls were further drawn in parallel between the nip rolls. At this time, the contact distance between the film and the roll at the nip portion was 4 mm, and the contact time between the film and the roll was 0.011 second at the first stage, 0.009 second at the second stage, and 0.02 seconds in total. Thereafter, this uniaxially stretched film was stretched 3.2 times in the width direction at a temperature of 95 ° C. with a tenter, then re-longitudinal stretched 1.4 times at 140 ° C., and then stretched 1.2 times in the width direction at 220 ° C., Then, it heat-processed for 3 seconds at 210 degreeC under fixed length. The distance between the film and the shutter was 20 mm. Thereafter, a relaxation treatment of 2% in the width direction was performed to obtain a biaxially oriented polyester film having a total thickness of 6.0 μm and a layer (B) thickness of 0.5 μm.

Example 6
Using a ceramic roll with a stretching temperature of 125 ° C. and a surface roll of 0.6 μm as the stretching roll, and further stretching the film by winding the film around the roll, the contact time between the film and the roll is 0.40 second in the first stage, two stages A biaxially oriented polyester film was obtained in the same manner as in Example 5 except that the mesh was 0.29 seconds and the total was 0.69 seconds.

Example 7
Example 1 except that the stretching ratio in the longitudinal and width directions is changed, the heat setting temperature is 200 ° C., the distance between the film and the shutter is 250 mm, the temperature difference between the top and bottom of the film is 30 ° C., and the thickness of each layer is changed. Thus, a biaxially oriented polyester film was obtained.

Example 8
In Example 1, the polyethylene terephthalate is polyethylene-2,6-naphthalate, the first stage stretching temperature is 130 ° C., the particle diameter of the particles added to the layer (B), the added amount, the thickness of each layer, and the Young's modulus are long. A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the stretching ratio was adjusted so that the direction / width direction = 8000/8000 MPa.

Comparative Example 1
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the heat setting temperature was 240 ° C., and the stretching ratio in the longitudinal and width directions and the amount of particles added to the layer (A) were changed.

Comparative Example 2
A biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the draw ratio in the longitudinal and width directions and the heat setting temperature were 210 ° C.

Comparative Example 3
A biaxially oriented polyester film was prepared in the same manner as in Example 8 except that the stretching ratio was adjusted so that the Young's modulus was longitudinal direction / width direction = 10000/6000 MPa, and the thickness of each layer and the heat setting temperature were changed to 230 ° C. Obtained.

  The evaluation results of the obtained film are as shown in Tables 1 and 2. The relationship between the creep amount in the thickness direction and the thermal shrinkage in the longitudinal direction of each example and comparative example is shown in the table.

Claims (8)

  A film deformation amount in the thickness direction when a load of 15 MPa is applied in the longitudinal direction and a transfer treatment is performed at 40 ° C. and a humidity of 90% RH for 24 hours is 6.0% or less with respect to the total thickness of the film. Biaxially oriented polyester film. Heat shrinkage _{S MD} in the longitudinal direction of 100 ° C. is from 0.0 to 1.8%, and a 0 ≦ _5S MD + _{to 3C ZD} ≦ 24 relation holds between the creep amount _{C ZD} in the thickness direction Characteristic biaxially oriented polyester film. Polyester film is a polyethylene terephthalate film, microscopic Raman crystallization index Ic of the film thickness direction is ^{8 cm} -1 to 20 cm ^-1, and the difference between the maximum value and the minimum value of the thickness direction Ic is ^{1 cm -1} or less The biaxially oriented polyester film according to claim 1, wherein the biaxially oriented polyester film is provided. Polyester film is a polyethylene naphthalate film, microscopic Raman crystallization index Ic of the film thickness direction is ^{18cm -1 ~28cm} -1, and the difference between the maximum value and the minimum value of the thickness direction Ic is ^{1 cm -1} or less The biaxially oriented polyester film according to claim 1 or 2, wherein: The biaxially oriented polyester film according to any one of claims 1 to 4, wherein a difference between a maximum value and a minimum value of Ic in the film plane direction is 1 cm ^-1 or less.   The biaxially oriented polyester film according to any one of claims 1 to 5, wherein the Young's modulus in the longitudinal direction is 6000 MPa or more and the Young's modulus in the width direction is 4500 MPa or more.   The biaxially oriented polyester film according to claim 1, which is used as a base film for a high-density digital magnetic recording medium.   The biaxially oriented polyester film according to any one of claims 1 to 7, which is used as a base film for a linear recording magnetic recording medium.