JP5964655B2 - Laminated polyester film - Google Patents

Description

  The present invention relates to a laminated polyester film used for a base film of a coating type magnetic recording tape such as data storage.

Polyester films have been used as base films for magnetic recording tapes because they are relatively inexpensive and have excellent mechanical properties. And when using for the base film of a magnetic-recording tape, it is calculated | required that a polyester film has a flat surface without a rough protrusion and a fault. On the other hand, in a coating type magnetic recording tape formed by applying a magnetic layer to a polyester film, a uniform magnetic layer cannot be efficiently produced if the winding property and running property of the base film are unstable. It is required that the polyester film contains a lubricant such as particles to form protrusions on the surface. These two requirements are contradictory, and in order to satisfy these requirements, Patent Document 1 proposes a laminated film that suppresses aggregation of particles contained in the film layer. Patent Document 2 proposes that inert particles having a specific average particle diameter are included in the surface on which the magnetic layer is formed and the surface on which the magnetic layer is not formed.
However, recent demands not only increase storage capacity, but also improve productivity and reduce cost per unit storage capacity.

Japanese Patent Laid-Open No. 9-201926 International Publication No. 2000/76749

  The object of the present invention is to improve the slitting property at a higher speed while providing sufficient electromagnetic conversion characteristics even in a high-density recording region in the obtained magnetic recording tape when used as a base film of a coating type magnetic recording tape. Is to provide a laminated polyester film for a coating type magnetic recording tape.

  The present inventors have eagerly studied to solve the above-mentioned problems, and have so far flattened the base film as the magnetic recording capacity has increased, but in the opposite direction, the surface on the side not particularly forming the magnetic layer In addition, it has been found that by adding a very small amount of particles having a large average particle diameter in a specific range with respect to the thickness of the film layer to be contained, the slit property can be highly improved without deteriorating electromagnetic conversion characteristics. The present invention has been reached.

Thus, according to the present invention,
1. A polyester film used as a base film of a coating type magnetic recording tape, comprising at least two layers of an A layer and a B layer,
The layer A on the side forming the magnetic layer contains particles A having an average particle size of 0.05 to 0.15 μm in a range of 0.01 to 0.5% by weight, and the thickness (tA) of the layer A and the particles The ratio (tA / dA) of A to the average particle diameter (dA) is in the range of 4 to 20,
Side of the layer B is not formed and the other magnetic layer, the particles B1 having an average particle size of 0.40-0.90μm 0.001- 0.018 wt% and an average particle size 0.03-0.17μm particles B2 The ratio (tB / dB1) between the thickness (tB) of the B layer and the average particle diameter (dB1) of the particles B1 is 4.0 to 9.0. A laminated polyester film for coating type magnetic recording tape that falls within the range.
2. 2. The laminated polyester film for coating type magnetic recording tape as described in 1 above, wherein the ratio (tA / dB1) of the thickness of layer A (tA) to the average particle diameter (dB1) of particles B1 is 2.0 or more.
3. The ratio (tA / dA) of the thickness of the A layer (tA) to the average particle diameter (dA) of the particles A is in the range of 4 to 15 , and the average particle diameter of the particles A is 0.05 to 0.14 μm. 2. The laminated polyester film for coating type magnetic recording tape according to 1 above, which is a range .
4). 2. The laminated polyester film for coating type magnetic recording tape as described in 1 above, wherein the thickness is 2.8 to 7.5 μm.
5. 2. The laminated polyester film for coated magnetic recording tape as described in 1 above, wherein the particles A, B1 and B2 are any of spherical silica particles, crosslinked polystyrene particles, silicone particles and silica-acryl composite particles.
6). 2. The laminated polyester film for coating type magnetic recording tape as described in 1 above, wherein the polyester is mainly composed of ethylene terephthalate or ethylene-2,6-naphthalenedicarboxylate.
7). A coated magnetic recording tape comprising the laminated polyester film according to any one of 1 to 6 above and a magnetic layer coated on the surface of the A layer side.
Is also provided.

  The laminated polyester film of the present invention can exhibit necessary electromagnetic conversion characteristics when formed into a coating type magnetic recording tape, and is excellent in slitting properties, so that it can be produced at a higher speed.

Hereinafter, the present invention will be described in detail.
The laminated polyester film of the present invention is a polyester film used for a base film of a coating type magnetic recording tape, and comprises at least two layers of an A layer and a B layer.
The A layer on the side forming the magnetic layer needs to contain particles A having an average particle size of 0.05 to 0.15 μm in a range of 0.01 to 0.5% by weight. When the average particle diameter of the particles A is less than the lower limit, the effect of improving the slit property is poor even when the particles B1 described later are contained, and when the upper limit is exceeded, the electromagnetic conversion characteristics are impaired. The lower limit of the average particle diameter of the preferred particles A is 0.06 μm, further 0.08 μm, and the upper limit is 0.14 μm, further 0.12 μm. Further, when the content of the particle A based on the weight of the A layer is less than the lower limit, even if the particle B1 described later is contained, the effect of improving the slit property is poor, and when the other upper limit is exceeded, the electromagnetic conversion characteristics are impaired. . The lower limit of the content of the preferred particles A is 0.02% by weight, further 0.04% by weight, while the upper limit is 0.4% by weight, further 0.3% by weight.

  Next, the layer B on the side where the magnetic layer is not formed is composed of particles B1 having an average particle size of 0.40-0.90 μm and particles having an average particle size of 0.03-0.17 μm. It is necessary to contain B2 in the range of 0.15-0.8% by weight. When the average particle diameter of the particles B1 is less than the lower limit, the effect of improving the slit property is poor, and when it exceeds the upper limit, the electromagnetic conversion characteristics are impaired. The lower limit of the average particle diameter of the preferred particle B1 is 0.45 μm, further 0.50 μm, and the upper limit is 0.8 μm, further 0.7 μm. Moreover, if content based on the weight of B layer of particle | grains B1 is less than a minimum, a slit property improvement effect will be scarce, and when it exceeds the other upper limit, electromagnetic conversion characteristics will be impaired. The lower limit of the content of the particles B1 is preferably 0.003% by weight, further 0.004% by weight, and the upper limit is 0.018% by weight, further 0.015% by weight. Further, when the average particle diameter of the particles B2 is less than the lower limit, even if the particles B1 are contained, the effect of improving the slit property is poor, and when the other upper limit is exceeded, the electromagnetic conversion characteristics are impaired. The lower limit of the average particle diameter of the preferred particle B2 is 0.04 μm, further 0.05 μm, and the upper limit is 0.16 μm, further 0.15 μm. In addition, when the content of the particle B2 based on the weight of the B layer is less than the lower limit, the effect of improving the slit property is poor even when the particle B1 is contained, and when the other upper limit is exceeded, the electromagnetic conversion characteristics are impaired. . The lower limit of the content of the particles B2 is preferably 0.20% by weight, further 0.25% by weight, and the upper limit is 0.7% by weight, further 0.6% by weight.

  By the way, in the laminated polyester film of the present invention, the ratio (tB / dB1) of the thickness (tB) of the B layer and the average particle diameter (dB1) of the particles B1 is in the range of 4.0 to 9.0. is necessary. When tB / dB1 is in the above range, the electromagnetic conversion characteristics can be maintained at a high level while suppressing dropout of particles when slitting at high speed. The lower limit of tB / dB1 is preferably 4.3 and further 4.5, while the upper limit is 8.5 and further 8.2.

Furthermore, the preferable aspect of the laminated polyester film of this invention is demonstrated.
In the laminated polyester film of the present invention, the ratio (tA / dB1) of the thickness (tA) of the layer A and the average particle diameter (dB1) of the particles B1 is 2.0 or more. It is preferable because it is highly maintainable. The preferable lower limit of tA / dB1 is 2.2 and further 2.4, and the other upper limit is not particularly limited. However, it is preferably thin from the viewpoint of securing a sufficient winding length when it is used as a magnetic recording tape, and 5.0 and 4 .0.

  In the laminated polyester film of the present invention, the ratio (tA / dA) of the thickness of the A layer (tA) and the average particle diameter (dA) of the particles A is preferably in the range of 4-20. By being in the said range, an electromagnetic conversion characteristic can be expressed more highly. The preferred lower limit of tA / dA is 7, and the other upper limit is 18, and 15.

  By the way, from the viewpoint of sufficiently securing the winding length when the magnetic recording tape is formed while providing the relationship between the inert particles A and the inert particles B1 as described above and the thicknesses of the A layer and the B layer. The laminated polyester film of the invention preferably has a thickness of 2.8-7.5 μm. The lower limit of the thickness of the preferred laminated polyester film is 3.0 μm, further 3.5 μm, and the other upper limit is 7.0 μm, further 6.0 μm. From the same viewpoint, the lower limit of the thickness of the A layer is preferably 0.8 μm, further 1.0 μm, and the other upper limit is preferably 3.0 μm, and further 2.5 μm. The lower limit of the thickness of the B layer is It is preferable that the upper limit is 2.0 μm, further 2.5 μm, and the other upper limit is 4.5 μm, and further 4.0 μm.

  In the present invention, the particles A, particles B1 and particles B2 to be contained are preferably very small particles even if they do not originally contain or contain coarse particles. Therefore, particles having a sharp particle size distribution curve are preferred, and particles that are likely to exist in the form of primary particles are preferable. Organic polymer particles such as silicone resin, crosslinked acrylic resin, crosslinked polyester, crosslinked polystyrene, and spherical silica, silica and organic Preferably, it is at least one kind of particles selected from the group consisting of polymer composites, and in particular, at least one kind selected from the group consisting of silicone resin, crosslinked polystyrene and spherical silica, and silica-acrylic composite particles. Particles are preferred. Of course, when these particles are contained, it is preferable to filter with a filter, to treat the surface of the particles with a dispersant, or to enhance kneading with an extruder in order to eliminate coarse particles.

These particles are preferably of the same particle type in the A layer and the B layer, and it is particularly preferable from the viewpoint of recovery that the particles A and the particles B2 have the same average particle diameter.
By the way, it is preferable that the particle A, the particle B1, and the particle B2 each have a single peak when the particle size distribution curve is viewed. Whether or not there is a single peak is determined by creating a particle size distribution curve with the particle diameter on the horizontal axis and the particle frequency on the vertical axis, and when the measurement pitch of the particle diameter on the horizontal axis is 0.01 μm, there is only one peak. Even if there are a plurality of peaks, it means that there is no dent that is 50% or less with respect to the height of the lower peak between the peaks. From the same viewpoint, it is preferable that the relative standard deviation of the particle size of all the particles when viewing the particle size distribution curve is 0.19 or less, and further 0.14 or less.

  As the polyester in the present invention, a known polyester can be adopted as long as it can be formed into a film. For example, an aromatic polyester obtained by polycondensation of a diol component and an aromatic dicarboxylic acid component is preferable. Examples of the aromatic dicarboxylic acid component include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, and the like. 6,6 ′-(alkylenedioxy) di-2-naphthoic acid. Examples of the diol component include ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and 1,6-hexanediol.

  Among these, ethylene terephthalate or ethylene-2,6-naphthalenedicarboxylate is the main repeating unit from the viewpoint of dimensional stability during processing at high temperature, and ethylene-2,6-naphthalene is particularly preferable. Those having carboxylate as the main repeating unit are preferred. The term “main” as used herein means preferably 80 mol% or more, and more preferably 90 mol% or more.

  Further, from the viewpoint of further improving the dimensional stability against environmental changes, the 6,6 ′-(ethylenedioxy) di-2-naphthoic acid component described in International Publication No. 2008/096612 pamphlet, 6,6 ′-( 6,6 ′-(alkylenedioxy) di-2-naphthoic acid components such as trimethylenedioxy) di-2-naphthoic acid component and 6,6 ′-(butylenedioxy) di-2-naphthoic acid component The thing copolymerized is also mentioned. The copolymerization amount of the preferred (alkylenedioxy) di-2-naphthoic acid component is in the range of 5 to 40 mol% based on the number of moles of all dicarboxylic acid components.

  When the polyester in the present invention does not contain a 6,6 ′-(alkylenedioxy) di-2-naphthoic acid component, it is 6,6 ′-(alkylenedioxy) di- in o-chlorophenol at 35 ° C. When the 2-naphthoic acid component is contained, the intrinsic viscosity when measured in a mixed solvent of P-chlorophenol / 1,1,2,2-tetrachloroethane (40/60 weight ratio) at 35 ° C. is 0. It is preferably 40 dl / g or more, more preferably 0.40 to 1.0 dl / g. If the intrinsic viscosity is less than 0.4 dl / g, cutting may occur frequently during film formation, or the strength of the product after forming may be insufficient. On the other hand, when the intrinsic viscosity exceeds 1.0 dl / g, productivity during polymerization is lowered.

  The melting point of the polyester in the present invention is preferably 200 to 300 ° C, more preferably 210 to 290 ° C, and particularly preferably 220 to 280 ° C. If the melting point is less than the lower limit, the heat resistance of the biaxially oriented film may be insufficient, and if the melting point exceeds the upper limit, the temperature during melt kneading becomes very high, which tends to cause thermal degradation.

  The polyester in the present invention is further copolymerized with other copolymer components known per se within a range not impairing the effects of the present invention, for example, 10 mol% or less, further 5 mol% with respect to the number of moles of repeating units. Copolymerization may be carried out in the following range, and other thermoplastic resins and the like may be blended in a range of, for example, 20% by weight or less, and further 10% by weight or less. Further, the polyester in the present invention requires a stabilizer such as an ultraviolet absorber, a lubricant such as an antioxidant, a plasticizer, and a wax, a flame retardant, a release agent, and a nucleating agent as long as the effects of the present invention are not impaired. You may mix according to. From the viewpoint of reducing the waviness index on the surface on which the magnetic layer is formed, other thermoplastic polymers, pigments, fillers, glass fibers, carbon fibers, layered silica that are incompatible with polyesters that tend to increase the waviness index. It is preferable not to contain acid salts.

  The laminated polyester film of the present invention is prepared, for example, by preparing a polymer for the polyester A layer and a polymer for the polyester B layer forming the opposite surface, and laminating these in a molten state and coextruding them from a die into a sheet. It can manufacture by extending | stretching the process of making a lamination | stacking unstretched polyester film and the obtained lamination | stacking unstretched polyester film in a film forming direction and the width direction by cooling and solidifying the obtained sheet-like material. The temperature in the process of extruding in a molten state is not particularly limited as long as there is no unmelted material and the temperature of the polyester does not excessively deteriorate. For example, the melting point of the polyester (Tm: ° C.) to (Tm + 70) ° C. It is preferable to carry out at temperature. Next, for cooling, in order to reduce the thickness unevenness while maintaining the flatness of the obtained laminated unstretched polyester film, a rotating cooling drum installed below the die along the film forming direction is used. It is preferable to cool the sheet-like material in close contact with it. Next, for stretching, the laminated unstretched polyester film is uniaxially (longitudinal or transverse) (polyester glass transition temperature (Tg) −10) ° C. to (Tg + 100) ° C. to 3.5 times or more. The film is preferably stretched at a magnification of 4 times or more, and then stretched at a temperature of Tg to (Tg + 100) ° C. in a direction perpendicular to the stretching direction at a magnification of 3 times or more, preferably 3.5 times or more.

  Further, if necessary, the film may be stretched again in the machine direction and / or the transverse direction. The total draw ratio when stretched in this manner is preferably 14 times or more, more preferably 17 to 35 times, and particularly preferably 21 to 30 times as an area draw ratio (longitudinal draw ratio x transverse draw ratio). . Furthermore, the biaxially oriented film can be heat-set at a temperature of (Tm-70) to (Tm-10) ° C., and is preferably heat-set at, for example, 180 to 250 ° C. The heat setting time is preferably 0.1 to 60 seconds. Moreover, although the above-mentioned extending | stretching was demonstrated by sequential biaxial stretching, you may use simultaneous biaxial stretching which extends | stretches simultaneously in the vertical direction and a horizontal direction.

  The laminated polyester film of the present invention has a longitudinal Young's modulus of 3 to 10 GPa, more preferably 3.5 to 9 GPa, particularly in order to develop excellent dimensional stability when used as a base film of a high-density magnetic recording medium. It is preferably 4 to 8 GPa. On the other hand, the Young's modulus in the width direction is 4 to 15 GPa, more preferably 5 to 14 GPa, particularly 6 to 13 GPa, most preferably 7 to 11 GPa, from the viewpoint of easily setting the temperature expansion coefficient of the base film to the range described later. It is preferable. If the Young's modulus in the width direction is less than the lower limit, it is difficult to reduce the temperature expansion coefficient when the magnetic recording tape is used. On the other hand, if the upper limit is exceeded, the temperature expansion coefficient when the magnetic recording tape is used becomes excessively small. End up.

  The laminated polyester film of the present invention is preferably used as a base film of a high-density magnetic recording tape, particularly a digital recording magnetic recording tape. Therefore, the magnetic recording medium using the laminated polyester film of the present invention will be further described.

  The magnetic recording medium of the present invention can be produced by forming a magnetic layer on the above-described laminated polyester film. In addition, on the surface of the laminated polyester film of the present invention, in order to improve the adhesiveness with a magnetic layer or the like, a coating layer having a well-known easy-adhesion function, etc., as long as the effect of the present invention is not impaired. Although it may be formed, it is preferable that there is no easy-adhesion layer because the easy-adhesion layer is easily broken when blocking or slitting at high speed.

  The magnetic layer in the magnetic recording tape of the present invention is uniformly dispersed in a binder such as polyvinyl chloride, vinyl chloride / vinyl acetate copolymer with acicular fine magnetic powder or barium ferrite magnetic powder mainly composed of iron or iron, It is formed by applying the coating liquid, and as described above, by using the laminated polyester film of the present invention, it can be slit at high speed while being excellent in electromagnetic conversion characteristics. can do.

  In addition, it is excellent in electromagnetic conversion characteristics such as output in a short wavelength region, S / N, C / N, etc., particularly when the magnetic layer is applied so that the thickness is 1 μm or less, and further 0.1 to 1 μm. This is preferable from the viewpoint of a coating type magnetic recording tape for high density recording with low dropout and error rate. If necessary, it is also preferable to disperse and coat a nonmagnetic layer containing fine iron oxide powder or the like in the same organic binder as that of the magnetic layer as an underlayer of the coating type magnetic layer.

Further, a protective layer such as diamond-like carbon (DLC) and a fluorine-containing carboxylic acid-based lubricating layer are sequentially provided on the surface of the magnetic layer as required, and a known backcoat layer is provided on the other surface. May be provided.
The coating type magnetic recording tape thus obtained is extremely useful as a magnetic tape for data use such as data 8 mm, DDSIV, DLT, S-DLT, LTO and the like.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. The characteristics of the polyester, laminated polyester film and data storage in the present invention were measured and evaluated by the following methods.

(1) Intrinsic viscosity As described above, the intrinsic viscosity of the obtained polyester is measured at o-chlorophenol at 35 ° C. When it is difficult to dissolve uniformly with o-chlorophenol, p-chlorophenol / It was determined by measurement at 35 ° C. using a mixed solvent of 1,1,2,2-tetrachloroethane (40/60 weight ratio).

(2) Particle size, average particle size, and relative standard deviation of particle size in the film Polyester on the film surface layer is removed by a plasma low-temperature ashing method (for example, PR-503, manufactured by Yamato Kagaku), and the particles are removed. Expose. The treatment conditions are such that the polyester is ashed but the particles are not damaged. This is observed with a SEM (scanning electron microscope) at a magnification of about 10,000 times, and an image of the particle (light density produced by the particle) is connected to an image analyzer (for example, QTM900, manufactured by Cambridge Instrument) The observation area is changed, and the area equivalent circle diameter (Di) of at least 5,000 particles is obtained. From this result, a particle size distribution curve of the particles was prepared. The identification of the particle type can be performed using SEM-XMA, quantitative analysis of metal elements by ICP, or the like. Moreover, the average particle diameter of the particle | grains to add was measured similarly, calculated | required the particle size of each particle | grain, and made the number average the average particle diameter.

(3) Content of particles (3-1) Total content of particles in each layer The polyester A layer and the polyester B layer were sampled by scraping about 100 g each from the laminated biaxially oriented polyester film, the polyester was dissolved, and the particles were After selecting the solvent not to be dissolved and dissolving the sample, the particles are centrifuged from the polyester, and the ratio of the particles to the sample weight (% by weight) is the total particle content in each layer.

(3-2) Total content of inorganic particles in each layer When inorganic particles of the laminated polyester film are present, the polyester A layer and the polyester B layer are each scraped and sampled about 100 g, and this is sampled in a platinum crucible. Burn in a furnace at about 1,000 ° C. for 3 hours or more, then mix the burned product in the crucible with terephthalic acid (powder) to make a 50 gram tablet plate. This plate is converted using a wavelength-dispersed fluorescent X-ray to calculate the count value of each element from a calibration curve for each element that has been prepared in advance, and the total content of inorganic particles in each layer is determined. The X-ray tube for measuring fluorescent X-rays is preferably a Cr tube and may be measured with an Rh tube. The X-ray output is set to 4 kW, and the spectral crystal is changed for each element to be measured. When there are a plurality of types of inorganic particles of different materials, the content of the inorganic particles of each material is determined by this measurement.

(3-3) Content of various particles in each layer (when no inorganic particles are present)
When inorganic particles are not present in the layer, the weight ratio of the particles present in each peak region is calculated from the number ratio of each particle constituting the peak determined in (2) above, the average particle diameter and the density of the particles, From this and the total content of particles in each layer determined in (3-1) above, the content (% by weight) of particles present in each peak region is determined.
The typical fine particle density is as follows.
Density of crosslinked silicone resin: 1.35 g / cm ³
Cross-linked polystyrene resin density: 1.05 g / cm ³
Cross-linked acrylic resin density: 1.20 g / cm ³
The resin density is further determined by separating the particles centrifuged from the polyester by the method (3-1), and measured by a method described in “Fine Particles Handbook: Asakura Shoten, 1991 edition, page 150”, for example, with a pycnometer. be able to.

(3-4) Content of various particles in each layer (when inorganic particles are present)
When inorganic particles are present in the layer, the layer is determined from the total content of particles in each layer determined in (3-1) and the total content of inorganic particles in each layer determined in (3-2). The content of the organic particles and the inorganic particles in each is calculated, the content of the organic particles is the method (3-3), and the content of the inorganic particles is the method (3-2). (Wt%) is determined.

(4) Thickness of film and each polyester layer (4-1) Thickness of film 10 films are stacked so that dust does not enter, the thickness is measured with a dot-type electronic micrometer, and the film thickness per sheet is calculated. To do.

(4-2) Thickness of each polyester layer Using a secondary ion mass spectrometer (SIMS), an element caused by the highest concentration of particles in the film ranging from the surface layer to a depth of 3,000 nm The concentration ratio (M + / C +) of the carbon element in the polyester is defined as the particle concentration, and analysis in the thickness direction is performed from the surface to a depth of 3,000 nm. In the surface layer, the particle concentration is low due to the interface of the surface, and the particle concentration increases as the distance from the surface increases. And the particle concentration once reached the maximum value starts to decrease again. Based on this concentration distribution curve, a depth at which the surface layer particle concentration is ½ of the maximum value (this depth is deeper than the depth at which the maximum value is reached) is determined, and this is defined as the surface layer thickness. Then, the thickness of each layer is calculated from the thickness of the film and the thickness of the surface layer.
The conditions are as follows.
(A) Measuring device: secondary ion mass spectrometer (SIMS)
(B) Measurement conditions Primary ion species: O ²⁺
Primary ion acceleration voltage: 12KV
Primary ion current: 200 nA
Raster area: 400 μm
Analysis area: 30% gate
Measurement degree of vacuum: 0.8 Pa (6.0 × 10 ⁻³ Torr)
E-GUN: 0.5KV-3.0A
In addition, when the most contained particles in the range from the surface layer to a depth of 3000 nm are organic polymer particles, it is difficult to measure by SIMS, so XPS (X-ray photoelectron spectroscopy), IR (infrared spectroscopy) while etching from the surface. The depth profile similar to the above may be measured by the method) to obtain the surface layer thickness.

(5) Young's modulus The film is cut into a sample width of 10 mm and a length of 15 cm, and the distance between chucks is set to 100 mm, and the film is pulled with an Instron type universal tensile tester under the conditions of a tensile speed of 10 m / min and a chart speed of 500 mm / min. The Young's modulus is calculated from the tangent of the rising portion of the obtained load-elongation curve.

(6) Surface roughness (Ra)
Measured using a non-contact type three-dimensional surface roughness meter (manufactured by ZYGO: New View 5022) at a measurement magnification of 25 times and a measurement area of 283 μm × 213 μm (= 0.0603 mm ² ), and incorporated in the roughness meter The center surface average roughness (Ra) was determined by the surface analysis software Metro Pro, which was defined as the surface roughness (Ra). The measurement was performed 10 times while changing the measurement location, and the average value thereof was defined as the center plane average roughness (Ra). The surface roughness of the laminated polyester film on the side where the magnetic layer is formed (A layer side) is RaA, and the surface roughness on the side where the magnetic layer is not formed (B layer side) is RaB.

(7) Slit property The master roll of the laminated biaxially oriented polyester film formed is slit into a width of 1000 mm and a length of 1000 m with a leather blade type slitter while changing the conveying speed, and wrinkles and windings during winding The maximum speed that can be wound up without any deviation was defined as the slit speed, and a relative value was obtained with Example 1 as 100, and evaluated according to the following criteria.
Evaluation criteria ◎: 80 or more
○: 60 or more, less than 80
×: Less than 60

(8) Sharpness The film was cut into a width of 12.7 mm and a length of 100 m, and the tension was 50 g / 12.7 mm, the winding speed was 60 m / min (low speed), and 300 m using a high-speed winding tester manufactured by Yokohama System. / Minute (high speed), after moving (frictioning) a stainless steel SUS304 fixing rod with an outer diameter of 5 mm and a surface roughness Ra of 20 nm at a hugging angle of 90 °, the film was rubbed Aluminum deposition was performed, and the number of dents of particle drop marks was measured with an optical microscope under the conditions of an objective lens 50 times (measurement area 140 μm × 105 μm × 8 sheets = 0.118 mm ² ), and then evaluated according to the following criteria.
Evaluation criteria A: Particle drop marks are less than 40.
○: Particle drop marks are 40 or more and less than 120.
X: Particle drop marks are 120 or more.

(9) Preparation of magnetic tape A back coat layer paint having the following composition was applied to the surface of the rough surface layer (A layer) of the laminated biaxially oriented polyester film having a width of 1000 mm and a length of 1000 m obtained in each Example and Comparative Example. After coating and drying with a die coater (tension during processing: 20 MPa, temperature: 120 ° C., speed: 200 m / min), a non-magnetic paint or magnetic paint having the following composition on the surface of the flat layer (B layer) side of the film Is applied at the same time with a die coater while changing the film thickness, magnetically oriented and dried. Further, after calendering with a small test calender (steel roll / nylon roll, 5 stages) at a temperature of 70 ° C. and a linear pressure of 200 kg / cm, curing is performed at 70 ° C. for 48 hours. The tape was slit to 12.65 mm and incorporated into a cassette to obtain a magnetic recording tape. The coating amount was adjusted so that the thicknesses of the dried backcoat layer, nonmagnetic layer and magnetic layer were 0.5 μm, 1.2 μm and 0.1 μm, respectively.
<Composition of non-magnetic paint>
Iron oxide powder: 80 parts by weight Carbon black: 20 parts by weight Eslek A (Sekisui Chemical vinyl chloride / vinyl acetate copolymer: 10 parts by weight Coronate L (Nippon Polyurethane Polyisocyanate): 5 parts by weight Lecithin: 1 part by weight, methyl ethyl ketone: 150 parts by weight, toluene: 75 parts by weight, lauric acid: 1.5 parts by weight <Composition of magnetic paint>
-Barium ferrite magnetic powder: 100 parts by weight-Esreck A (Sekisui Chemical's vinyl chloride / vinyl acetate copolymer: 10 parts by weight-Nipponran 2304 (Nippon Polyurethane Polyurethane Elastomer): 10 parts by weight-Coronate L (Nippon Polyurethane Poly Isocyanate): 5 parts by weight, lecithin: 1 part by weight, methyl ethyl ketone: 75 parts by weight, methyl isobutyl ketone: 75 parts by weight, toluene: 75 parts by weight, carbon black: 1 part by weight, lauric acid: 1.5 parts by weight <back Composition of coat layer paint:>
Carbon black: 50 parts by weight Thermoplastic polyurethane resin: 60 parts by weight Isocyanate compound: 18 parts by weight (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.)
Silicone oil: 0.5 parts by weight Methyl ethyl ketone: 250 parts by weight Toluene: 50 parts by weight

(10) Electromagnetic conversion characteristics For measuring the electromagnetic conversion characteristics, a 1/2 inch linear system with a fixed head was used. Recording was performed using an electromagnetic induction head (track width 25 μm, gap 0.1 μm), and reproduction was performed using an MR head (8 μm). The relative speed of the head / tape is 10 m / sec, a signal with a recording wavelength of 0.2 μm is recorded, the reproduced signal is analyzed with a spectrum analyzer, the output C of the carrier signal (wavelength 0.2 μm), and the integration over the entire spectrum. The relative value with the noise N ratio as C / N ratio and Example 1 as 0 dB was determined and evaluated according to the following criteria.
◎: +1 dB or more ○: −1 dB or more, less than +1 dB ×: less than −1 dB

[Example 1]
Polyethylene-2 for polyester A layer having an intrinsic viscosity of 0.62 containing 0.10 wt% of true spherical silica particles (particle A) having an average particle size of 0.14 μm as particles to be added to the flat layer (magnetic layer) side , 6-Naphthalate pellets, 0.012% by weight of silicone particles (particle B1) having an average particle size of 0.5 μm and 0.43% by weight of true spherical silica particles (particle B2) having an average particle size of 0.14 μm Polyethylene-2,6-naphthalate pellets for polyester B layer having an intrinsic viscosity of 0.62 were prepared. Each pellet was dried at 170 ° C. for 6 hours and then supplied to two extruder hoppers, respectively, at a melting temperature of 310 ° C., and a thickness ratio of A layer: B layer = 3: 7 was placed on the cooling drum from the die. The sheet was coextruded to obtain a laminated unstretched polyester film.
The laminated unstretched polyester film thus obtained was preheated to 120 ° C. and heated from above with an IR heater so that the film surface temperature was 140 ° C., and stretched in the machine direction (manufactured at a stretch ratio of 4.8 times). Stretching in the film direction) was performed. Subsequently, the sheet is supplied into a stenter heated to 155 ° C., stretched 5.1 times in the transverse direction (first stage), and further supplied into a stenter heated to 180 ° C. After stretching twice, it was heat-fixed with hot air at 210 ° C. for 4 seconds to obtain a laminated biaxially oriented polyester film having a thickness of 5.0 μm. The Young's modulus of the obtained laminated biaxially oriented polyester film was 6.3 GPa in the vertical direction and 8.9 GPa in the horizontal direction.
Table 1 shows the characteristics of the obtained laminated biaxially oriented polyester film.

[Examples 2 to 17 and Comparative Examples 1 to 13]
The same operations as in Example 1 were repeated except that the thicknesses of the particles A, particles B1 and B2, and the A layer and B layer to be contained were changed as shown in Table 1 or Table 2.

  In Tables 1 and 2, silica means true spherical silica particles, silicone means true spherical silicone particles, and polystyrene means true spherical crosslinked polystyrene particles.

  The laminated polyester film of the present invention, when used as a magnetic recording medium, is suitable for use as a base film of a coating type magnetic recording tape because it has excellent electromagnetic conversion characteristics and can be slit at high speed. Can do.

Claims (7)

A polyester film used as a base film of a coating type magnetic recording tape, comprising at least two layers of an A layer and a B layer,
The layer A on the side forming the magnetic layer contains particles A having an average particle size of 0.05 to 0.15 μm in a range of 0.01 to 0.5% by weight, and the thickness (tA) of the layer A and the particles The ratio (tA / dA) of A to the average particle diameter (dA) is in the range of 4 to 20,
Side of the layer B is not formed and the other magnetic layer, the particles B1 having an average particle size of 0.40-0.90μm 0.001- 0.018 wt% and an average particle size 0.03-0.17μm particles B2 The ratio (tB / dB1) between the thickness (tB) of the B layer and the average particle diameter (dB1) of the particles B1 is 4.0 to 9.0. A laminated polyester film for coating type magnetic recording tape that falls within the range.   The laminated polyester film for a coated magnetic recording tape according to claim 1, wherein the ratio (tA / dB1) of the thickness of the A layer (tA) and the average particle diameter (dB1) of the particles B1 is 2.0 or more. The ratio (tA / dA) of the thickness of the A layer (tA) to the average particle diameter (dA) of the particles A is in the range of 4 to 15 , and the average particle diameter of the particles A is 0.05 to 0.14 μm. The laminated polyester film for coated magnetic recording tape according to claim 1, which is in a range .   The laminated polyester film for coated magnetic recording tape according to claim 1, wherein the thickness is 2.8 to 7.5 µm.   The laminated polyester film for coated magnetic recording tape according to claim 1, wherein the particles A, particles B1 and B2 are any of spherical silica particles, crosslinked polystyrene particles, silicone particles, and silica-acrylic composite particles.   The laminated polyester film for coated magnetic recording tape according to claim 1, wherein the polyester mainly comprises ethylene terephthalate or ethylene-2,6-naphthalenedicarboxylate as a repeating unit.   A coated magnetic recording tape comprising the laminated polyester film according to any one of claims 1 to 6 and a magnetic layer coated on the surface of the A layer side.