JP2020189407A - Laminated polyester film and coat-type magnetic recording tape using the same - Google Patents

Abstract

To provide a laminated polyester film enabling highly well-balanced surface smoothness and productivity and a coat-type magnetic recording tape using the same.SOLUTION: The laminated polyester film is a base film for a coat-type magnetic recording tape comprising at least 2 layers composed of A layer forming a surface on a side forming a magnetic layer and B layer forming a surface not forming a magnetic layer, wherein a rate of a thickness tA (μm) of A layer to a total layer thickness t (μm) of the film, (tA/t), is 0.38 or over and 0.50 or under; A layer has Ra of less than 5 nm and B layer has Ra in a range of 5-10 nm, Ra being a surface roughness measured by using a non-contact type three-dimensional surface roughness meter and measured at magnification of 25-fold; when A layer and A layer, B layer and B layer, and A layer and B layer are respectively brought into contact with each other and allowed to run with a shuttle tester, and peak values obtained by high speed Fourier transformation of spectra in a range of 10000 ms to 30470 ms since the film has started to move are respectively shown as PAA, PBB and PAB, PBB-PAA is 30 Hz or over and PAB is 200 Hz or over.SELECTED DRAWING: None

Description

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

Polyester films have been used as base films for magnetic recording tapes because they are relatively inexpensive and have excellent mechanical properties. When used as a base film for a magnetic recording tape, the polyester film is required to have a flat surface without coarse protrusions or defects. On the other hand, in a coating type magnetic recording tape formed by coating a magnetic layer on a polyester film, if the winding property and running performance of the base film are unstable, a uniform magnetic layer cannot be efficiently produced. , It is required that the polyester film contains particles as a lubricant to form protrusions and the like on the surface. These two requirements are contradictory, and in order to satisfy these requirements, Patent Documents 1 to 6 specify the catalyst species to be specific in order to reduce surface defects, and the particles contained in the film. As a result, it has been proposed to use a film having a small amount of coarse particles and a film having such a treatment and having few surface defects. Further, Patent Documents 7 to 8 propose biaxially oriented polyester films that are excellent in stabilization of the original fabric shape and electromagnetic conversion characteristics as a magnetic recording medium by reducing the swell component of the base film focusing on the spatial frequency. It has been done.

However, recent base films for coated magnetic recording tapes have the flatness of the film surface to further increase the recording density and the productivity such as film forming property and winding property of the film to be manufactured at low cost. There is a demand for a more highly compatible film, and it has become impossible to fully answer as a base film for coated magnetic recording tapes in recent years.

Japanese Unexamined Patent Publication No. 2004-114492 JP-A-2002-363311 JP-A-2002-363310. JP-A-2002-059520 Japanese Unexamined Patent Publication No. 2011-165266 Japanese Unexamined Patent Publication No. 2014-189717 Japanese Unexamined Patent Publication No. 2001-341265 Japanese Unexamined Patent Publication No. 2004-091753

An object of the present invention is to provide a film that does not stick to a transport roll in the film forming process and can be wound in the film winding process without causing appearance defects such as wrinkles and defects. It is productive and has excellent electromagnetic conversion characteristics and flatness of the film surface that can reduce error rate and dropout when used as a base film for coated magnetic recording tapes, especially data storage. It is an object of the present invention to provide a laminated polyester film capable of highly achieving both productivity and a coating type magnetic recording tape using the same.

From the viewpoint of productivity, the film winding process needs to be wound as fast as possible, and for that purpose, it is necessary to increase the contact pressure of the winding and efficiently remove the air between the films. Therefore, low-height protrusions are tightly formed on the surface to prevent the films from sticking to each other even if the contact pressure is high, and relatively high-height protrusions are provided at appropriate intervals so that air can easily escape. It has been proposed to provide it. However, even if the protrusions on the surface of the film are controlled at the nanometer level, there is a difference in take-up property, and it is difficult to achieve both flatness and productivity, which are the problems of the present invention.

Therefore, as a result of diligent research on films having the same surface shape but different take-up properties, the present inventors have found that, in a specific laminated film, at least the A layer forming the magnetic layer and the B layer which is the non-magnetic layer are formed. Differences in peak values PAA, PBB, and PAB obtained by the fast Fourier transform of the spectrum when the A-layers, B-layers, and A-layers and B-layers of the laminated polyester film are in contact with each other and run on a shuttle tester. In particular, when PBB-PAA is 30 Hz or higher and PAB is 200 Hz or higher, it is found that the flatness can be maintained at a high level without causing defects such as wrinkle entrainment, and the present invention has been reached. did.

Thus, according to the present invention, there are two base films used for the coating type magnetic recording tape, at least the A layer forming the surface on the side where the magnetic layer is formed and the B layer forming the surface on the side not forming the magnetic layer. A laminated polyester film consisting of layers
The ratio (tA / t) of the thickness tA (μm) of the A layer to the total thickness t (μm) of the film is 0.38 or more and 0.50 or less.
The surface roughness (Ra) when measured at a measurement magnification of 25 times using a non-contact three-dimensional surface roughness meter is less than 5 nm for the A layer and 5 to 10 nm for the B layer.
The peak value obtained by the fast Fourier transform of the spectrum in the range of 10000 ms to 30470 ms after the film starts to move when the film is run on the shuttle tester by contacting the A layer and the A layer, the B layer and the B layer, and the A layer and the B layer, respectively. , PAA, PBB and PAB, respectively, a laminated polyester film having a PBB-PAA of 30 Hz or higher and a PAB of 200 Hz or higher is provided.

The laminated polyester film of the present invention has excellent productivity as a film, but when used as a coating type magnetic recording tape, especially as a base film for data storage, it has excellent electromagnetic conversion characteristics and excellent flatness that can reduce error rates and dropouts. It is possible to provide a laminated polyester film having a property and a coating type magnetic recording tape using the same.

Hereinafter, the present invention will be described in detail. For convenience of explanation, the film-forming direction of the film may be referred to as a mechanical axis direction, a longitudinal direction, a longitudinal direction, and an MD direction, and the directions orthogonal to the film-forming direction and the thickness direction are the width direction, the lateral direction, and the like. Sometimes referred to as the TD direction.

As the polyester in the present invention, a polyester known per se can be adopted as long as it can form a film on a film. For example, an aromatic polyester obtained by polycondensation of a diol component and an aromatic dicarboxylic acid component is preferable. Examples of such aromatic dicarboxylic acid components 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 such diol components include ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol, and 1,6-hexanediol.

Among these, from the viewpoint of dimensional stability during processing at high temperature, it is preferable to use ethylene terephthalate or ethylene-2,6-naphthalenedicarboxylate as the main repeating unit, and particularly ethylene-2,6-naphthalenedium. It is preferable that carboxylate is the main repeating unit. The term "main" as used herein preferably means 60 mol% or more, 70 mol% or more, 80 mol% or more, and further 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 the pamphlet of International Publication No. 2008/09661, 6,6'-( 6,6'-(alkylenedioxy) di-2-naphthoic acid components such as trimethylenedioxy) di-2-naphthoic acid component and 6,6'-(butyreneoxy) di-2-naphthoic acid component Copolymerized ones can also be mentioned. The amount of copolymerization of the preferred (alkylenedioxy) di-2-naphthoic acid component is in the range of 5 to 40 mol% and further in the range of 6 to 35 mol%, particularly 7 to 7 to 40 mol% based on the number of moles of the total dicarboxylic acid component. It is in the range of 30 mol%. When the 6,6'-(alkylenedioxy) di-2-naphthoic acid component is copolymerized, ethylene terephthalate or ethylene-2,6-naphthalenedicarboxylate component and 6,6'-(alkylene dioxy) are used. The total amount of oxy) di-2-naphthoic acid component is preferably 90 mol% or more of the total acid component.

The polyester in the present invention contains 6,6'-(alkylenedioxy) di-2-naphthoic acid component in ο-chlorophenol at 35 ° C. when it does not contain 6,6'-(alkylenedioxy) di-2-naphthoic acid component. When 2-naphthoic acid component is contained, the intrinsic viscosity as measured at 35 ° C. in a mixed solvent of P-chlorophenol / 1,1,2,2-tetrachloroethane (40/60 weight ratio) is 0. It is preferably 40 dl / g or more, and 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 molding may be insufficient. On the other hand, when the intrinsic viscosity exceeds 1.0 dl / g, the productivity at the time of polymerization decreases.

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 at the time of melt-kneading becomes extremely high, and thermal deterioration or the like is likely to occur.

In addition, the polyester in the present invention further copolymerizes other copolymerization components known per se, for example, 10 mol% or less, further 5 mol% with respect to the number of moles of the repeating unit, as long as the effect of the present invention is not impaired. It may be copolymerized in the following range, or another thermoplastic resin or the like may be blended in a range of, for example, 20% by weight or less, further 10% by weight or less.

By the way, although the laminated polyester film of the present invention can be produced from the above-mentioned polyester, it is magnetic from the viewpoint of maintaining a high degree of electromagnetic conversion characteristics when it is used as data storage while maintaining the range in which winding can be performed at high speed. The average particle size of the particles added to the film layer A forming the surface on the side where the layer is formed is preferably 0.04 to 0.2 μm, more preferably 0.06 to 0.18 μm, and 0.07 to 0.17 μm. Is more preferable, and 0.08 to 0.16 μm is particularly preferable. The content thereof is preferably 0.001 to 0.20% by mass, more preferably 0.003 to 0.18% by mass, and 0.005 to 0.16% by mass based on the mass of the film layer A. More preferably, 0.007 to 0.14% by mass is particularly preferable.

Further, the particles added to the B layer forming the surface on the side where the magnetic layer is not formed contain at least two kinds of particles from the viewpoint of improving the winding property, and the average particle diameter thereof is 0.04 to 0.2 μm, respectively. Is preferable, 0.06 to 0.18 μm and 0.07 to 0.45 μm are more preferable, 0.07 to 0.17 μm and 0.10 to 0.42 μm are further preferable, and 0.08 to 0.16 μm and 0. .13 to 0.39 μm is particularly preferable. The content thereof is preferably 0.03 to 0.9% by mass and 0.05 to 0.5% by mass, and 0.05 to 0.7% by mass and 0.07, respectively, based on the mass of the film layer B. ~ 0.45% by mass is more preferable, 0.07 to 0.6% by mass and 0.08 to 0.40% by mass are further preferable, 0.09 to 0.5% by mass and 0.09 to 0.35. Mass% is particularly preferred. When the average particle size is smaller than this range or the content is less than this range, the electromagnetic conversion characteristics are good, but it tends to be difficult to wind up at high speed. Further, when the average particle size and the content exceed these ranges, for example, when the base film of a data storage having a high recording density such as a storage capacity of 3 TB or more is used, the electromagnetic conversion characteristics tend to deteriorate.

In order to achieve good electromagnetic conversion characteristics, the surface roughness (Ra) of the film layer A is preferably 5.0 nm or less, more preferably 4.8 nm or less, further preferably 4.6 nm or less, and 4.4 nm or less. Especially preferable. Further, in order to realize both good electromagnetic conversion characteristics and high-speed winding property, the surface roughness (Ra) of the film layer B is preferably 5.0 to 10.0 nm, and is in the range of 5.2 to 9.5 nm. Is more preferable, the range of 5.4 to 9.0 nm is further preferable, and the range of 5.6 to 8.5 is particularly preferable.

As the particles to be contained, it is preferable that the particles originally do not contain coarse particles or contain very few coarse particles. Therefore, particles that tend to have a sharp particle size distribution curve and easily exist in the state of primary particles are preferable, and organic polymer particles such as silicone particles, crosslinked acrylic resin particles, crosslinked polyester particles, and crosslinked polystyrene particles, and spherical silica particles. , At least one type of particles selected from the group consisting of composite particles of silica and an organic polymer, particularly a group consisting of silicone particles, crosslinked polystyrene particles and spherical silica particles, and silica-acrylic composite particles. It is preferable that the particles are at least one selected from the above. Of course, when these particles are contained, it is preferable to perform filtration with a filter, treat the surface of the particles with a dispersant, or strengthen kneading with an extruder in order to further eliminate coarse particles.

The types of these particles may be the same or different on the surface on which the magnetic layer is formed and the surface on which the magnetic layer is not formed, but the same type is preferable from the viewpoint of ease of recovery and suppression of transfer. In addition, the same average particle diameter in the present invention means that the values up to two decimal places calculated by rounding off the third decimal place when calculating the average particle diameter (μm) of the particles are the same. That is, it means that the average particle size does not differ when the size is 0.01 μm or more. For example, when particles having the same average particle diameter are added to the surface on which the magnetic layer is formed and the surface on which the magnetic layer is not formed, the protrusions due to the particles formed on the surface have the same height, so that the surface on which the magnetic layer is not formed is formed. It is possible to suppress the transfer to the surface formed from the film, and when the film is collected and reused, it can be reused in either layer.

By the way, as described in Japanese Patent Application Laid-Open No. 2015-39801, agglomerated protrusions formed by five or more particles are known as one of the causes of deteriorating thermal aspiration. In order not to deteriorate the thermal asperity, the number of agglutinating protrusions in the A layer is preferably 5 pieces / cm ² or less, and more preferably 3 pieces / cm ² or less. In the same way, it is preferable that the number of agglutinating protrusions in the B layer is 10/9 cm ² or less. The upper limit of agglutinating protrusions having 5 or more particles in the preferred layer A is 2/9 cm ² or less, and further 1/9 cm ² or less. Further, the upper limit of agglutinating protrusions having 5 or more particles in the preferable B layer is 6 particles / 9 cm ² or less, and further 4 particles / 9 cm ² or less.

The method for suppressing such agglomerated protrusions is not particularly limited, but it is necessary to make the dispersibility of the particles to be contained extremely high, and it is necessary to select particles having good dispersibility as the particles to be contained, and polyester to disperse the particles. For example, selecting a polyester in which particles are easily dispersed, adding particles at the time of polymerization in order to improve the dispersibility of the particles, and separately performing melt-kneading to further improve the dispersibility of the particles, etc. It is preferable to do so.

Next, a method for producing the laminated polyester film will be described. First, the method for producing a polyester in the present invention comprises, for example, a first reaction in which an aromatic dicarboxylic acid or an ester-forming derivative thereof is subjected to an esterification reaction or a transesterification reaction to synthesize a polyester precursor, and the precursor. It consists of a second reaction in which the body is transesterified, and a method known per se can be adopted.

As for the preferable conditions of the first reaction, it may be carried out under normal pressure, but it is preferable to carry out under a pressure of 0.05 MPa to 0.5 MPa because the reaction rate can be more easily increased. The temperature of the first reaction is preferably in the range of 210 ° C to 270 ° C. By setting the reaction pressure within the above range, it is possible to facilitate the progress of the reaction and suppress the generation of by-products typified by dialkylene glycol. At this time, it is preferable to use the alkylene glycol component 1.1 to 6 mol times as much as the acid component present in the reaction system in which the first reaction is carried out, from the viewpoint of the reaction rate and the maintenance of the physical properties of the resin. It is more preferably 2 to 5 mol times, still more preferably 3 to 5 mol times.

Further, in order to increase the reaction rate of the first reaction, it is preferable to use a catalyst known per se, for example, a metal compound having a metal component such as Li, Na, K, Mg, Ca, Mn, Co, Ti. Of these, Mn and Ti compounds are preferable from the viewpoint of easiness of reaction when the reaction is carried out under pressure. In particular, the Mn compound is preferable because it is easy to improve the dispersibility of the inert particles contained therein.

The amount of the catalyst to be added is preferably in the range of 10 to 150 mmol% in terms of metal element, based on the number of moles of the total acid component present in the first reaction, and further 20 to 100 mmol%, particularly 30. It is preferable that the content is in the range of about 70 mmol% because the reaction rate can be promoted, the formation of coarsely insoluble foreign matter caused by the catalyst can be suppressed, and the heat resistance of the obtained copolymer aromatic polyester can be highly maintained. When the titanium compound is added, it is preferable to add the titanium compound so that it exists from the start of the esterification reaction of the first reaction, and continue to use it as a polycondensation reaction catalyst as described above. Of course, it may be added in two or more portions for the purpose of controlling the polycondensation reaction rate.

Next, the second reaction in which the precursor obtained in the first reaction is polycondensed will be described.

In the present invention, for the purpose of imparting a high degree of thermal stability to the obtained polyester, it is preferable to add a thermal stabilizer composed of a phosphorus compound to the reaction system before the start of the polycondensation reaction in the second reaction. The specific phosphorus compound is not particularly limited as long as it contains a phosphorus element in the compound, and for example, phosphoric acid, phosphite, phosphoric acid trimethyl ester, phosphoric acid tributyl ester, phosphoric acid triphenyl ester, and phosphorus. Examples thereof include acid monomethyl ester, phosphoric acid dimethyl ester, phenylphosphonic acid, phenylphosphonic acid dimethyl ester, phenylphosphonic acid diethyl ester, ammonium phosphate, triethylphosphonoacetate, methyldiethylphosphonoacetate, and these phosphorus compounds. May be used in combination of two or more. It is preferable that the phosphorus compound is added during the initial stage of the polycondensation reaction, which is the second reaction, after the first reaction is substantially completed, and the phosphorus compound may be added at once or twice or more. It may be divided into.

By the way, the temperature of the polycondensation reaction is preferably in the range of 270 ° C. to 300 ° C., and the pressure during the polycondensation reaction is preferably carried out under a reduced pressure of 50 Pa or less. If the pressure during the polycondensation reaction is higher than the upper limit, the time required for the polycondensation reaction becomes long, and it becomes difficult to obtain a copolymerized aromatic polyester having a high degree of polymerization. As the polycondensation catalyst, metal compounds such as Ti, Al, Sb, and Ge known per se can be preferably used, and among these, when Mn—Sb is used, the dispersibility of the particles can be improved, which is preferable.

Regarding the method of containing particles, the coarse particles are further reduced by a filter or the like in a slurry state of alkylene glycol, and the particles are added in the polymerization step to have a particle content of 0.02 to 1.0% by weight. It is preferable to prepare a containing master polyester and dilute the master polyester with a polyester containing no particles in order to reduce coarse protrusions due to agglomeration of particles.

The polyester thus obtained contains stabilizers such as ultraviolet absorbers, antioxidants, plasticizers, lubricants such as waxes, flame retardants, mold release agents, and nucleating agents as long as the effects of the present invention are not impaired. It may be blended if necessary. In order to achieve good electromagnetic conversion characteristics, it is preferable not to contain other thermoplastic polymers, pigments, fillers, glass fibers, carbon fibers, layered silicates, etc. that are incompatible with polyester.

In the laminated polyester film of the present invention, for example, a step of preparing a polyester polymer for a magnetic layer and a polyester polymer for forming an opposite surface, laminating them in a molten state, and co-extruding them from a die into a sheet. It can be produced by a step of forming a laminated unstretched polyester film by cooling and solidifying the obtained sheet-like material, and by stretching the obtained laminated unstretched polyester film in the film forming direction and the width direction. The temperature in the process of extruding in the molten state is not particularly limited as long as there is no unmelted material and the temperature does not cause excessive thermal deterioration of the polyester. For example, the melting point of the polyester (hereinafter referred to as Tm: ° C.) or ( It is preferable to carry out at a temperature of Tm + 70) ° C. Next, for cooling, in order to maintain the flatness of the obtained laminated unstretched polyester film and reduce thickness unevenness, a rotating cooling drum installed below the die along the film forming direction was used. , It is preferable to bring a sheet-like material into close contact with it for cooling. Next, regarding stretching, the laminated unstretched polyester film was uniaxially (longitudinal or horizontal) at a temperature of (polyester glass transition temperature (hereinafter referred to as Tg) -10) ° C to (Tg + 60) ° C. It is stretched at a magnification of .5 times or more, preferably 3 times or more, and then stretched at a temperature of Tg to (Tg + 60) ° C. in a direction orthogonal to the stretching direction at a magnification of 2.5 times or more, preferably 3 times or more. Is preferable. At this time, in order to keep the above-mentioned skin index within a desired range, it is desirable that the transverse stretching temperature is in the range of (Tg + 25) to (Tg + 60 ° C.). More preferably, (Tg + 30) to (Tg + 60 ° C.), particularly preferably (Tg + 30) to (Tg + 55 ° C.), and most preferably (Tg + 35) to (Tg + 55 ° C.). At this time, the transverse stretching temperature is preferably raised stepwise, and all temperatures are preferably within the above range. If the transverse stretching temperature is too low with respect to Tg, excessive stretching stress is concentrated on the particles, and as a result, the voids around the particles become large, so that the protrusions become high and large. On the other hand, when the surface is mildly laterally stretched in the above-mentioned temperature range, the rough surface layer side can be flattened by simultaneously increasing the lateral stretching ratio than usual, and as a result, it has a desired height and size. It becomes possible to form protrusions.

Further, if necessary, it may be stretched again in the vertical direction and / or the horizontal direction. The total stretch ratio when stretched in this way is preferably 9 times or more, more preferably 12 to 35 times, and particularly preferably 15 to 30 times as the area stretch ratio (longitudinal stretch ratio x horizontal stretch ratio). .. Furthermore, the biaxially oriented film can be heat-fixed at a temperature of (Tm-70) to (Tm-10) ° C., and is preferably heat-fixed at, for example, 180 to 250 ° C. The heat fixing time is preferably 0.1 to 60 seconds. Further, although the above-mentioned stretching has been described by sequential biaxial stretching, simultaneous biaxial stretching that simultaneously stretches in the longitudinal direction and the lateral direction may be used.

Further, the laminated polyester film of the present invention may be relaxed in the width direction while being heat-fixed or after heat-fixing. By relaxing in the width direction in this way, the heat shrinkage rate in the width direction of the film can be maintained in an appropriate range. This relaxation itself can also be performed in the vertical direction. On the other hand, when the film is relaxed, the Young's modulus of the film is lowered, a desired Young's modulus cannot be secured, and tension cannot be applied during processing, which may cause a problem. Therefore, the appropriate relaxation rate strongly depends on the polymer type of the film and the film forming conditions. For example, in the film forming of polyethylene-2,6-naphthalate film, the temperature at the time of relaxation is set to 210 ° C., and the relaxation rate is 1. It is preferable to form a film at 0.0%.

The laminated polyester film of the present invention preferably has a Young's modulus in the longitudinal direction of 5 GPa or more in order to exhibit excellent dimensional stability when used as a base film of a high-density magnetic recording medium. If the Young's modulus in the longitudinal direction is lower than the above, it becomes easy to stretch when tension is applied in the longitudinal direction in the handling of the film, which causes a problem. On the other hand, the upper limit is not limited, but it is preferably higher from the viewpoint of the above handling. The Young's modulus in the width direction is preferably in the range of 4 to 15 GPa, further 5 to 14 GPa, particularly 6 to 13 GPa, most preferably 7 to 11 GPa, from the viewpoint that the coefficient of thermal expansion in the base film can be easily set in the range described later. preferable. If the Young's modulus in the width direction is less than the lower limit, it becomes difficult to reduce the coefficient of thermal expansion of the magnetic recording tape, and the film tends to wrinkle due to the transport tension in the coating process. If the upper limit is exceeded, the coefficient of thermal expansion of the magnetic recording tape becomes excessively small. From such a viewpoint, the laminated polyester film of the present invention is preferably a biaxially oriented laminated polyester film oriented by stretching in the film forming direction and the width direction.

The total thickness of the laminated polyester film of the present invention is preferably 2.0 μm or more and 8.0 μm or less. The preferred lower limit of the total thickness is 2.3 μm, further 2.6 μm. The preferred upper limit of the total thickness is 7 μm, further 6 μm, especially 5.5 μm. If the thickness is smaller than the lower limit, the tape has no stiffness, so that the electromagnetic conversion characteristics are deteriorated and wrinkles are likely to occur in the coating process. When the thickness exceeds the upper limit, the length of the tape per roll of the tape becomes short, so that it tends to be difficult to reduce the size and increase the capacity of the magnetic tape.

In order to provide a cheaper laminated polyester film, a non-product film generated during film formation may be recovered and used as a recovery chip or the like. When a recovery chip is used, it is preferably added to the B layer that does not form a magnetic layer.

By the way, if the thickness ratio of the B layer is too large, the large particles contained in the B layer side may be pushed up to the A layer side, which may cause deterioration of the electromagnetic conversion characteristics and a missing pulse. Therefore, the ratio (tA / t) of the thickness tA (μm) of the A layer to the total layer thickness t (μm) of the film is preferably in the range of 0.383 or more and 0.497 or less, preferably 0.386 or more and 0.494 or less. The range is more preferable, and the range of 0.388 or more and 0.492 or less is particularly preferable.

In the present invention, in order to evaluate whether or not a laminated polyester film can be wound at high speed while having good electronic conversion characteristics, it is obtained by fast Fourier transform of the spectrum when the films are brought into contact with each other with a shuttle tester. The peak value obtained was found to be useful. Here, the peak values obtained when the A-sides, the B-sides, and the A-side and the B-side are brought into contact with each other are referred to as PAA, PBB, and PAB, respectively. That is, it has been found that the feature of the present invention is that excellent flatness and productivity can be achieved at the same time by setting PAA-PBB to 30 Hz or higher and PAB to 200 Hz or higher. The preferred ranges of PAA, PBB and PAB are as follows: PBB-PAA is preferably 35 Hz or higher and PAB is preferably 230 Hz or higher, PBB-PAA is more preferably 40 Hz or higher, PAB is more preferably 260 Hz or higher, PBB-PAA is 45 Hz or higher and PAB is 290 Hz or higher is particularly preferable. If each peak value deviates from the lower limit, wrinkles are likely to occur when winding at high speed. On the other hand, if the upper limit is exceeded, the electromagnetic conversion characteristics deteriorate, the error rate, and the dropout cannot be reduced.

Further, in order to wind the film without defects such as wrinkles, the static friction coefficient and the dynamic friction coefficient when the films are brought into contact with each other so that the surface on the side where the magnetic layer is formed and the surface on the side where the magnetic layer is not formed are in contact with each other are determined. It is preferably in the range of 0.25 to 0.50 and 0.25 to 0.45, respectively. The lower limit of the static friction coefficient and the dynamic friction coefficient of the base film of the data storage with high recording density exceeding 3TB is 0.25 and 0.20, respectively, but the upper limit is 0.45 or less in the case of the static friction coefficient. Is preferable, 0.42 or less is more preferable, and 0.40 or less is particularly preferable. The coefficient of kinetic friction is preferably 0.43 or less, more preferably 0.40 or less, and particularly preferably 0.38 or less.

Further, it is preferable that the skewness Rsk of the surface roughness curve of the layer A, which is the layer on the side forming the magnetic layer of the laminated polyester film of the present invention, is in the range of 2.0 to 9.5. Here, Rsk is obtained in accordance with JIS B 0601. When Rsk is 0, it means that the concave part and the convex part are in a symmetrical relationship. When the value is positive, the shape is distorted in the concave part, and when the value is negative, the shape is distorted in the convex part. Indicates that you are doing. The Rsk of the A layer of the laminated polyester film of the present invention is preferably in the range of 2.5 to 9.0, particularly preferably in the range of 3.0 to 8.5, and particularly preferably in the range of 3.5 to 8.0. If Rsk is below the lower limit, it becomes too smooth, and it tends to be difficult to wind up at high speed. On the other hand, when Rsk exceeds the upper limit, the protrusions are too steep and tend to impair smoothness.

The laminated polyester film of the present invention is preferably used as a base film for high-density magnetic recording tapes, particularly digital recording type magnetic recording tapes. 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-mentioned laminated polyester film. In addition, on the surface of the laminated polyester film of the present invention, in order to improve the adhesiveness with the magnetic layer or the like, a coating layer or the like having a known easy-adhesion function itself is provided as long as the effect of the present invention is not impaired. It may be formed.

In the magnetic layer of the magnetic recording tape of the present invention, needle-like fine magnetic powder or barium ferrite containing iron or iron as a main component is uniformly dispersed in a binder such as polyvinyl chloride, vinyl chloride / vinyl acetate copolymer, and the like. It is formed by applying a coating liquid, and as described above, by using the laminated polyester film of the present invention, it is possible to obtain a magnetic recording tape having excellent dimensional stability, electromagnetic conversion characteristics and error rate performance. it can.

By the way, as mentioned above, in order to increase the recording density, it is necessary to make the magnetic material finer, which makes it difficult to remove the solvent etc. from the coating liquid, and when trying to maintain the processability, the drying etc. becomes hotter. It became necessary to do it in. Then, when trying to process a film having an extremely flat surface at a high temperature, a new problem such as wrinkles was found, and the present invention was reached.

It should be noted that the magnetic layer is excellent in output in a short wavelength region and electromagnetic conversion characteristics such as S / N and C / N when it is applied so that its thickness is 1 μm or less and further 0.1 to 1 μm. It is preferable from the viewpoint of forming a coating type magnetic recording tape for high-density recording with low dropout and error rate. Further, if necessary, it is also preferable to disperse a non-magnetic layer containing fine titanium oxide particles or the like in an organic binder similar to the magnetic layer and apply it as a base layer of the coating type magnetic layer.

Further, on the surface of the magnetic layer, a protective layer such as diamond-like carbon (DLC) and a fluorine-containing carboxylic acid-based lubricating layer are sequentially provided for the purpose, application, and if necessary, and a known backcoat layer is further 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 applications such as 8 mm data, DDSIV, DLT, S-DLT, and LTO.

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

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

(2) Average particle size of particles in the film (2-1) Average particle size of inorganic particles The polyester in the film surface layer is removed by a plasma low temperature ashing treatment method (for example, manufactured by Yamato Scientific Co., Ltd., PR-503 type) to remove the particles. To expose. Select the treatment conditions under which the polyester is incinerated but the particles are not damaged. Observe the particles with a SEM (scanning electron microscope) at a magnification of about 10,000 times, and connect the image of the particles (the shade of light produced by the particles) to an image analyzer (for example, QTM900 manufactured by Cambridge Instrument). The area equivalent circle diameter (Di) of at least 5,000 particles is obtained by changing the observation location. From this result, a particle size distribution curve was created, and the number average was taken as the average particle size. The particle type can be identified by using SEM-XMA, quantitative analysis of metal elements by ICP, or the like. The average particle size of the particles to be added was also calculated by performing the same measurement.

(2-2) Average Particle Diameter of Organic Particles About 100 g of each film layer was scraped off and sampled, a solvent was selected in which polyester was dissolved and particles were not dissolved, the sample was dissolved, and then the particles were centrifuged from polyester. A dispersion in which particles were dispersed so as to be 0.1% by mass in water or a suitable organic solvent was drop-cast onto a glass substrate. After evaporating the solvent, the particles on the substrate are observed with an SEM (scanning electron microscope) at a magnification of about 10,000 times, and the image of the particles (shading of light produced by the particles) is captured by an image analyzer (for example, Cambridge). It is linked to QTM900) manufactured by Instrument, and the area equivalent circle diameter (Di) of at least 5,000 particles is obtained by changing the observation location. From this result, a particle size distribution curve was created, and the number average was taken as the average particle size. The particle type can be identified by using SEM-XMA, quantitative analysis of metal elements by ICP, or the like.

(3) Particle content (3-1) Total content of particles in each layer A solvent in which about 100 g of each of polyester A layer and polyester B layer is scraped from a laminated polyester film and sampled, and polyester is dissolved and particles are not dissolved. Is selected to dissolve the sample, then the particles are centrifuged from the polyester, and the ratio of the particles to the weight of the sample (% by mass) is taken as the total particle content in each layer.
(3-2) Total content of inorganic particles in each layer When inorganic particles are present in the laminated polyester film, the polyester A layer and the polyester B layer are each scraped off and sampled at about 100 g, which is placed in a platinum crucible. It is burned in a furnace at about 1,000 ° C. for 3 hours or more, and then the combustible material in the crucible is mixed with terephthalic acid (powder) to prepare a 50-gram tablet-shaped plate. In this plate, the count value of each element is converted from a calibration curve for each element prepared in advance using wavelength dispersive fluorescent X-rays, 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 a 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 there are no inorganic particles in the layer, the weight ratio of the particles existing in each peak region is calculated from the number ratio of each particle constituting the peak obtained in (2) above, the average particle diameter, and the density of the particles. From this and the total content of particles in each layer obtained in (3-1) above, the content (mass%) of particles existing in each peak region is obtained.
The density of typical fine particles is as follows.
Density of crosslinked silicone resin: 1.35 g / cm3
Density of crosslinked polystyrene resin: 1.05 g / cm3
Density of crosslinked acrylic resin: 1.20 g / cm3
The density of the resin is measured by the method described in "Particle Handbook: Asakura Shoten, 1991 Edition, p. 150", for example, by further separating the particles centrifuged from the polyester by the method (3-1) and using 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 based on the total content of particles in each layer determined in (3-1) above and the total content of inorganic particles in each layer determined in (3-2) above. The contents of the organic particles and the inorganic particles in the particles are calculated respectively, and the content of the organic particles is the content of the above method (3-3) and the content of the inorganic particles is the content of the above method (3-2). Find (% by mass).

(4) Thickness of film and each polyester layer (4-1) Thickness of film Stack 10 films to prevent dust from entering, measure the thickness with a dot-type electronic micrometer, and calculate the film thickness per sheet. To do.
(4-2) Thickness of each polyester layer Using a secondary ion mass analyzer (SIMS), the element caused by the highest concentration of particles in the film in the range from the surface layer to the depth of 3,000 nm. The concentration ratio of carbon elements (M ⁺ / C ⁺ ) of polyester is used as the particle concentration, and analysis is performed in the thickness direction 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. Then, the particle concentration once reached the maximum value begins to decrease again. Based on this concentration distribution curve, the depth at which the surface particle concentration becomes 1/2 of the maximum value (this depth is deeper than the depth at which the maximum value is obtained) is obtained, 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 accelerating voltage: 12KV
Primary ion current: 200 nA
Raster area: 400 μm □
Analysis area: Gate 30%
Measurement vacuum: 0.8 Pa (6.0 x 10 ^-3 Torr)
E-GUN: 0.5KV-3.0A
If the particles contained most in the range from the surface layer to a depth of 3000 nm are organic polymer particles, it is difficult to measure with SIMS, so XPS (X-ray photoelectron spectroscopy) and IR (infrared spectroscopy) while etching from the surface. The same depth profile as described above may be measured by the method) or the like 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, the chuck distance is 100 mm, and the film is pulled by 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 part of the obtained load-elongation curve.

(6) Surface roughness (Ra)
Measured using a non-contact three-dimensional surface roughness meter (manufactured by ZYGO: New View7300) under the conditions of a measurement magnification of 25 times and a measurement area of 283 μm × 213 μm (= 0.0603 mm ² ), and built into the roughness meter. The central surface average roughness (Ra) was determined by the surface analysis software Metro Pro, and this was used as the surface roughness (Ra). The measurement was performed 10 times at different measurement points, and the average value thereof was taken as the central surface average roughness (Ra). Further, the surface roughness of the flat side (A layer side) of the laminated polyester film was defined as RaA, and the surface roughness of the rough side (B layer side) was defined as RaB.

(7) Static friction coefficient and dynamic friction coefficient of the film The laminated polyester film sample was slit into tapes of 2.54 cm × 50 cm and 1.27 cm × 35 cm, respectively. A film running tester (HOYO ELECTRONICS CORP. FRICTION TESTER SFT) is used to make a film running tester (HOYO ELECTRONICS CORP. It was set on the guide roller of -1200S) so that the holding angle was 90 degrees. A sample having a width of 1.27 cm was allowed to stand for 5 minutes with a load of 200 g applied, and then the sample side having a width of 1.27 cm was run. The tension was taken in every 10 ms with a data logger, and the static friction coefficient was measured as the tension when the film started to move, and the dynamic friction was measured as the average value of the tension in the range of 20000 ms to 50,000 ms after the film started to move. From Euler's belt theory below, the static friction coefficient and the dynamic friction coefficient were obtained from the average values of three times.
μ = 2 / π × ln (T2 / T1)
T1: Tension with load = 200g T2: Tension of static friction or dynamic friction Holding angle: 90 degrees Mileage: 10cm
Running speed: 1 mm / sec
Guide roller diameter: 1.3 cm

(8) FFT analysis of the dynamic friction region The FFT analysis of the tension of the dynamic friction region obtained in (7) above was performed. Data is captured at intervals of 10 ms in the range from 10000 ms to 30470 ms after the film starts to work, and the obtained 2048 data are FFT analyzed, and the absolute value of the complex number is used as the amplitude. Of the obtained waveforms, the waveform from which the data of 1 to 9 Hz with extremely large amplitude is removed is removed by a cosine roll pass filter (roll-off section = 0.5) to remove waves having a frequency of 0.03 Hz or higher. .. The value of the frequency showing the maximum amplitude between 100 Hz and 600 Hz of the waveform was taken as the peak value.

(9) Number of agglomerated protrusions The polyester of the film surface layer is removed by a plasma low temperature ashing treatment method (for example, manufactured by Yamato Scientific Co., Ltd., PR-503 type) to expose the particles. Select the treatment conditions under which the polyester is incinerated but the particles are not damaged. The particles are observed with an SEM (scanning electron microscope) at a magnification of about 10,000 times. Voids are generated around the particles of the protrusions on the film surface due to stretching. If there is one particle in the void, it is not agglomerated. When there are 5 or more particles in the void, the protrusions are formed by aggregation, and the protrusions are agglomerated with 5 or more particles. Then, 100 voids were confirmed, and the number of agglutinating protrusions of 5 or more particles existing per 9 cm ² was calculated from the measurement area required for the voids.

(10) Preparation of Magnetic Tape A backcoat layer paint having the following composition is applied to the rough surface layer (A layer) side surface of the laminated polyester film having a width of 1000 mm and a length of 1000 m obtained in each Example and Comparative Example by a die coater (processing). After applying and drying at a tension of 20 MPa, a temperature of 120 ° C., and a speed of 200 m / min), a non-magnetic paint or magnetic paint having the following composition is applied to the flat layer (B layer) side surface of the film with a die coater. At the same time, the film is applied with a different film thickness, magnetically oriented, and dried. Further, a small test calendar device (steel roll / nylon roll, 5 stages) is used for calendering at a temperature of 70 ° C. and a linear pressure of 200 kg / cm, and then curing is performed at 70 ° C. for 48 hours. The tape was slit to 12.65 mm and incorporated into a cassette to form a magnetic recording tape. The coating amounts were adjusted so that the thicknesses of the backcoat layer, the non-magnetic layer, and the magnetic layer after drying were 0.5 μm, 1.2 μm, and 0.1 μm, respectively.
<Composition of non-magnetic paint>
-Titanium dioxide fine particles: 100 parts by weight-Eslek A (Sekisui Chemical's vinyl chloride / vinyl acetate copolymer: 10 parts by weight-Nipporan 2304 (Polyurethane elastoma made by Nippon Polyurethane): 10 parts by weight-Coronate L (Polyurethane made by Japan Polyurethane) 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: 2 parts by weight, lauric acid: 1.5 parts by weight <magnetic Paint composition>
-Iron (major axis: 0.037 μm, needle-like ratio: 3.5, 2350 Elstead): 100 parts by weight-Eslek A (Sekisui Chemical's vinyl chloride / vinyl acetate copolymer: 10 parts by weight-Nipporan 2304 (Nippon Polyurethane) Polyurethane elastoma): 10 parts by weight, Coronate L (Polyisocyanate made by Nippon Polyurethane): 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: 2 parts by weight, lauric acid: 1.5 parts by weight <Composition of backcoat layer paint:>
Carbon black: 100 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

(11) Electromagnetic conversion characteristics A 1/2 inch linear system with a fixed head was used to measure the electromagnetic conversion characteristics. An electromagnetic induction type head (track width 25 μm, gap 0.1 μm) was used for recording, and an MR head (8 μm) was used for reproduction. The relative velocity of the head / tape is 10 m / sec, a signal with a recording wavelength of 0.2 μm is recorded, the reproduced signal is frequency-analyzed with a spectrum analyzer, and the output C of the carrier signal (wavelength 0.2 μm) and the integration of the entire spectrum are integrated. The ratio of noise N was defined as the C / N ratio, and the relative value was obtained with Comparative Example 5 prepared by the method (10) above as 0 dB, and evaluated according to the following criteria.
⊚: + 1 dB or more ○: 0 dB or more and less than + 1 dB Δ: -1 dB or more and less than 0 dB ×: less than -1 dB

(12) Error rate The original tape produced in (10) above is slit to a width of 12.65 mm (1/2 inch), incorporated into a case for LTO, and a data storage with a magnetic recording tape length of 850 m. I made a cartridge. This data storage was recorded using an IBM LTO5 drive in an environment of 23 ° C. and 50% RH (recording wavelength 0.55 μm), and then the cartridges were stored in an environment of 50 ° C. and 80% RH for 7 days. After storing the cartridge at room temperature for one day, the full length was regenerated, and the error rate of the signal during reproduction was measured. The error rate is calculated by the following formula from the error information (number of error bits) output from the drive. Evaluate the error rate based on the following criteria.
Error rate = (number of error bits) / (number of write bits)
⊚: Error rate is less than 1.0 × ^10-6 ○: Error rate is 1.0 × ^10-6 or more, less than 1.0 × ^10-5 Δ: Error rate is 1.0 × ^10-5 or more, 1 .0 × 10 less than ^-4 ×: Error rate is 1.0 × 10 ^-4 or more

(13) Dropout (DO)
The data storage cartridge whose error rate was measured in (12) above was loaded into an IBM LTO5 drive, a data signal of 14 GB was recorded, and the data signal was reproduced. A signal having an amplitude (PP value) of 50% or less of the average signal amplitude was detected as a missing pulse, and four or more consecutive missing pulses were detected as dropouts. For the dropout, one roll having a length of 850 m is evaluated, converted into the number of pieces per 1 m, and judged according to the following criteria.
⊚: Dropout 3 pieces / m or less ○: Dropout 3 pieces / m or more, 9 pieces / m or less ×: Dropout 9 pieces / m or more

(14) Film Windability A film having a width of 300 mm was wound at a winding speed of 80 m / min under constant tension conditions to obtain a roll having a length of 6,000 m. The appearance of this roll after being stored for 72 hours under the conditions of a temperature of 25 ° C. and a humidity of 55% was visually observed and judged according to the following criteria, and C was defined as poor take-up property.
⊚: No wrinkles or end face misalignment 〇: No wrinkles or less and no end face misalignment △: Wrinkles 2 or less and end face misalignment less than 1 mm ×: 3 wrinkles Those with end face deviation of 1 mm or more.

[Example 1]
As the particles to be added to the flat layer side, 0.08% by mass of spherical silica particles (particles A) having an average particle diameter of 0.10 μm are contained, and the intrinsic viscosity is 0.62. As the particles to be added to the phthalate pellets (glass transition temperature: 121 ° C., melting point: 265 ° C.) and the rough surface layer side, spherical silica particles (particles B1) having an average particle diameter of 0.10 μm were added to the average particles of 0.12% by mass. Polyethylene-2,6-naphthalate pellets for polyester B layer having an intrinsic viscosity of 0.62 containing 0.08% by mass of spherical silica particles (particles B2) having a diameter of 0.30 μm (glass transition temperature: 121 ° C., Melting point: 265 ° C.) was prepared. Then, after each pellet was dried at 170 ° C. for 6 hours, it was supplied to each of the two extruder hoppers, and at a melting temperature of 300 ° C., the thickness ratio of layer A: layer B = 40:60 was placed on the cooling drum from the die. It was co-extruded into a sheet to obtain a laminated unstretched polyester film.

The laminated unstretched polyester film thus obtained is preheated to 120 ° C., heated from above with an IR heater so that the film surface temperature becomes 140 ° C., and has a draw ratio of 5.0 times in the longitudinal direction (manufactured). Stretching in the film direction) was performed. Subsequently, the film is supplied into a stenter heated to 155 ° C., stretched 5.3 times in the lateral direction (first stage) while gradually raising the temperature to 165 ° C. and 170 ° C., and then further heated to 180 ° C. After being supplied into the provided stenter and stretched 1.2 times in the lateral direction again, it was heat-fixed with hot air at 215 ° C. for 4 seconds, and then relaxed in the width direction at 190 ° C. with a relaxation rate of 0.27%. A biaxially oriented laminated polyester film having a thickness of 4.0 μm was obtained.
Table 1 shows the characteristics of the obtained biaxially oriented laminated polyester film.

[Examples 2 to 11, Comparative Examples 1 to 6]
The same operation as in Example 1 was repeated except that the thicknesses of the particles A, the particles B1, the particles B2, the particles B3, and the layers to be contained were changed as shown in Table 1. Table 1 shows the characteristics of the obtained biaxially oriented laminated polyester film.

[Example 12]
Polyethylene-terephthalate pellets for polyester A layer (glass transition) containing 0.08% by mass of spherical silica particles (particles A) having an average particle diameter of 0.10 μm as particles to be added to the flat layer side and having an intrinsic viscosity of 0.62. As particles to be added to the rough surface layer side at a temperature of 76 ° C. and a melting point of 255 ° C.), spherical silica particles (particle B1) having an average particle diameter of 0.10 μm are 0.12% by mass and have an average particle diameter of 0.30 μm. Polyethylene-terephthalate pellets for polyester B layer having an intrinsic viscosity of 0.62 (glass transition temperature: 76 ° C., melting point: 255 ° C.) containing 0.08% by mass of spherical silica (particles B2) were prepared. Then, after each pellet was dried at 170 ° C. for 3 hours, it was supplied to two extruder hoppers, respectively, and at a melting temperature of 280 ° C., the thickness ratio of layer A: layer B = 40:60 was placed on the cooling drum from the die. It was co-extruded into a sheet to obtain a laminated unstretched polyester film.

The laminated unstretched polyester film thus obtained is preheated to 75 ° C., heated from above with an IR heater so that the film surface temperature becomes 90 ° C., and has a draw ratio of 4.8 times in the longitudinal direction. Stretching in the film direction) was performed. Subsequently, the film was supplied into a stenter heated to 90 ° C., stretched 5 times in the lateral direction (first stage) while gradually raising the temperature to 125 ° C. and 130 ° C., and then further heated to 180 ° C. After being supplied into a stenter and stretched 1.2 times in the lateral direction again, it was heat-fixed with hot air at 230 ° C. for 4 seconds, then relaxed at 210 ° C. and a relaxation rate of 1%, and then laminated with a thickness of 4.0 μm. A biaxially oriented polyester film was obtained.
Table 2 shows the characteristics of the obtained biaxially oriented laminated polyester film.

[Examples 13 to 15]
The same operation as in Example 12 was repeated except that the thicknesses of the particles A, the particles B1, the particles B2, the particles B3, and the layers to be contained were changed as shown in Table 2. Table 2 shows the characteristics of the obtained biaxially oriented laminated polyester film.

[Example 16]
Polyethylene-terephthalate pellets (glass) for polyester A layer having an intrinsic viscosity of 0.62, containing 0.08% by mass of spherical silica particles (particle A) having an average particle diameter of 0.10 μm as particles to be added to the flat layer side. A resin composition in which a transition temperature: 76 ° C., a melting point: 255 ° C.) and a polyetherimide pellet (trade name: ULTEM1010) are blended at a mass ratio of 97: 3, and particles to be added to the rough surface layer side have an average particle diameter of 0. A polyester having an intrinsic viscosity of 0.62 containing 0.12% by mass of spherical silica particles (particles B1) having an average particle size of 10.2% by mass and 0.08% by mass of spherical silica particles (particles B2) having an average particle diameter of 0.30 μm. A resin composition obtained by blending polyethylene-terephthalate pellets for layer B (glass transition temperature: 76 ° C., melting point: 255 ° C.) and polyetherimide pellets (trade name: ULTEM1010) at a weight ratio of 97: 3, respectively, in the state of pellets. After drying at 170 ° C. for 3 hours, the particles were supplied to each of the two extruder hoppers, and at a melting temperature of 280 ° C. Extruded to obtain a laminated unstretched polyester film.

The laminated unstretched polyester film thus obtained is preheated to 75 ° C., heated from above with an IR heater so that the film surface temperature becomes 90 ° C., and has a draw ratio of 4.8 times in the longitudinal direction. Stretching in the film direction) was performed. Subsequently, the film was supplied into a stenter heated to 90 ° C., stretched 5 times in the lateral direction (first stage) while gradually raising the temperature to 125 ° C. and 130 ° C., and then further heated to 180 ° C. After being supplied into a stenter and stretched 1.2 times in the lateral direction again, it was heat-fixed with hot air at 230 ° C. for 4 seconds, then relaxed at 210 ° C. and a relaxation rate of 1%, and then laminated with a thickness of 4.0 μm. A biaxially oriented polyester film was obtained. The Young's modulus of the obtained biaxially oriented laminated polyester film was 4.9 GPa in the vertical direction and 7.6 GPa in the horizontal direction.
Table 2 shows the characteristics of the obtained biaxially oriented laminated polyester film.

[Example 17]
The same operation as in Example 16 was repeated except that the particles A, the particles B1, the particles B2, the particles B3, the thickness of each layer, and the amount of polyetherimide to be contained were changed as shown in Table 2. Table 2 shows the characteristics of the obtained biaxially oriented laminated polyester film.

In Tables 1 and 2, PET means polyethylene terephthalate, PEN means polyethylene-2,6-naphthalenedicarboxylate, and PEI means polyetherimide (PEI "Ultem (registered trademark)" 1010 manufactured by SABIC Innovative Plastics Co., Ltd.). ..

The laminated polyester film of the present invention can be suitably used for a coating type magnetic recording tape, particularly a base film for data storage.

Claims (8)

A base film used for a coating type magnetic recording tape, which is a laminated polyester film consisting of at least two layers, an A layer forming a surface on the side where a magnetic layer is formed and a B layer forming a surface on a side not forming a magnetic layer. There,
The ratio (tA / t) of the thickness tA (μm) of the A layer to the total thickness t (μm) of the film is 0.38 or more and 0.50 or less.
The surface roughness (Ra) when measured at a measurement magnification of 25 times using a non-contact three-dimensional surface roughness meter is less than 5 nm for the A layer and 5 to 10 nm for the B layer.
The peak value obtained by the fast Fourier transform of the spectrum in the range of 10000 ms to 30470 ms after the film starts to move when the film is run on the shuttle tester by contacting the A layer and the A layer, the B layer and the B layer, and the A layer and the B layer, respectively. A laminated polyester film having a PBB-PAA of 30 Hz or higher and a PAB of 200 Hz or higher, respectively, when PAA, PBB and PAB are used. The laminated polyester film according to claim 1, wherein the polyester is ethylene terephthalate or ethylene-2,6 naphthalene dicarboxylate as a main repeating unit. The first aspect of claim 1 contains at least one selected from the group consisting of polyimide, polyetherimide, polyetherketone, and polyetheretherketone in the range of 0.5 to 25% by weight based on the mass of the polyester composition. The laminated polyester film described. The laminated polyester film according to claim 1, wherein the skewness Rsk of the surface roughness curve of the layer A is in the range of 2.0 to 9.5. The A layer contains 0.001 to 0.20% by mass of particles having an average particle diameter of 0.04 to 0.2 μm, and the B layer contains at least two or more kinds of particles, and the average particle diameter is 0.04 to 0. The laminated polyester film according to claim 1, which contains 0.03 to 0.9% by mass of 2 μm particles and 0.05 to 0.5% by mass of particles having an average particle diameter of 0.25 to 0.45 μm. Particles 5 or more agglomeration protrusions of the layer A is 3 / 9cm ² or less, the laminated polyester film particles 5 or more agglomeration protrusions of the layer B is 10 pieces / 9cm ² or less. The static friction coefficient is 0.25 to 0.50 and the dynamic friction coefficient is 0.25 to 0.45 when the surface on the side where the magnetic layer is formed and the surface on the side where the magnetic layer is not formed are bonded so as to be in contact with each other. The laminated polyester film according to claim 1, which is in the range of. A coating type magnetic recording tape comprising the laminated polyester film according to any one of claims 1 to 7 and a magnetic layer coated and formed on the surface on the side where the magnetic layer is formed.