JP2019133725A - Polyester film for coating-type magnetic recording medium and magnetic recording medium - Google Patents

Abstract

To provide a polyester film for coating-type magnetic recording medium, which can form a satisfactory magnetic layer while handling ability is kept and is superior in an error rate and preservation durability when the film is processed to a magnetic recording medium.SOLUTION: A polyester film for coating type magnetic recording medium has a layer structure of two layers or more, and it satisfies following (1) to (3) when a layer positioned in an outermost layer on a side where a magnetic layer is applied is set to an A layer, and a layer positioned in the other outermost layer is set to a B layer. (1) The A layer includes inert particles A, and three-dimensional center line surface roughness sRa-A of an A layer side surface (surface A) is 2 to 20nm. (2) The B layer includes inert particles B2 whose average particle diameter is larger than the inert particles A, and includes inert particles B1 whose average particle diameter is larger than the inert particles B2, and the three-dimensional center line surface roughness sRa-B of a B layer side surface(surface B) is 3 to 40nm. (3) An aspect ratio (major axis/minor axis) of the inert particles B1 is 1.1 to 5.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a polyester film that can be suitably used for a coating type magnetic recording medium.

  In recent years, magnetic recording media for data storage, digital video tape, and the like have been increasing in density and capacity. For example, linear recording magnetic recording media such as LTO (Linear Tape Open) and SDLT (Super Digital Linear Tape) have been developed that have a high capacity of 7 TB per roll.

  Many studies have been made to increase the capacity, such as increasing the strength of the base film by increasing the draw ratio, optimizing the temperature expansion coefficient and humidity expansion coefficient in the tape width direction, and reducing the additive particle size. (Patent Documents 1 to 5). However, even if these techniques are used, sufficient characteristics cannot be obtained for a magnetic recording medium having a capacity higher than 7 TB per roll.

JP, 2006-192247, A Japanese Patent Laying-Open No. 2015-202602 Japanese Unexamined Patent Publication No. 2015-3408 JP 2012-153100 A JP 2012-56157 A

  In these magnetic recording media, it is essential to minimize defects on the magnetic surface of the recording medium in order to realize a high capacity. As a typical example of the magnetic surface defect, there is a depression generated on the magnetic surface due to transfer of the uneven shape of the backcoat layer. The back coat layer is provided on the surface opposite to the magnetic layer, and mainly plays a role of improving the running property of the tape. This layer is a coating film formed by applying a coating material for forming a backcoat layer on the surface opposite to the surface on which the magnetic layer is provided and drying it.

  If the magnetic layer of the magnetic tape is rough, it directly leads to magnetic surface defects and data errors, so that the magnetic layer side of the base film is particularly difficult to smooth. Therefore, it is preferable that the back coat layer side is rough to some extent in order to improve handling in the production process, but if it is too rough, the protrusions of the back coat layer are formed on the surface of the magnetic layer in the post-treatment process after winding on a roll. To cause a data error such as a missing pulse (MP). On the other hand, when the base film is excessively smoothed, there is a problem that handling properties are deteriorated and the yield of the base film production process is likely to deteriorate.

  Furthermore, with an increase in recording capacity of magnetic recording media, there is an increasing demand for storage durability as well as data error suppression. In particular, the importance of storage durability related to reliability during long-term use has attracted attention. A factor that lowers the storage durability is that a foreign substance of a level that cannot be removed even by the self-cleaning mechanism adheres to the head that reads the recording data. In addition to minute dirt and dust on the magnetic layer or the base film, the foreign matter may have protrusions caused by particles added to the base film to provide handling and winding properties. is there.

  If the magnetic layer of the magnetic tape is rough, it directly leads to magnetic surface defects and data errors, so that the magnetic layer side of the base film is particularly difficult to smooth. Therefore, it is preferable that the back coat layer side is rough to some extent in order to improve handling in the production process, but if it is too rough, the protrusions of the back coat layer are formed on the surface of the magnetic layer in the post-treatment process after winding on a roll. Or the storage durability is lowered as a starting point of shaving by the head. On the other hand, if the base film is excessively smoothed, the handling property is lowered, the yield of the base film production process is deteriorated, and the storage durability is also lowered due to the abrasion by the head due to the friction between the magnetic tape and the head. was there. In particular, since the protruding portion of the backcoat layer is easily scraped by contact with the head, there is a problem that it becomes difficult to make the surface rough to ensure handling properties as the requirement for storage durability becomes stricter.

  When the polyester film for a coating type magnetic recording medium of the present invention to be described later is used, the aspect ratio of the inert particle B1 having the largest average particle diameter contained in the B layer is obtained even if the surface of the base film has the same roughness as before. As a result, it has been found that data error improvement and storage durability are satisfied in a well-balanced manner, or that when one characteristic is improved, the deterioration of the other characteristic can be suppressed to a minimum, and the present invention has been completed. .

  That is, the present invention for solving the above problems has the following characteristics.

  When having a layer structure of two or more layers, the layer located on the outermost layer on the side where the magnetic layer is applied is the A layer, and the layer located on the other outermost layer is the B layer, the following (1) to (3) Polyester film for coating type magnetic recording media satisfying

  (1) The A layer contains inert particles A, and the three-dimensional centerline surface roughness sRa-A of the surface of the A layer (surface A) is 2 to 20 nm.

  (2) The layer B contains inert particles B2 having an average particle size larger than that of the inert particles A, and further contains inert particles B1 having an average particle size larger than that of the inert particles B2, and the layer B side surface (surface B ) Three-dimensional centerline surface roughness sRa-B is 3 to 40 nm.

  (3) The aspect ratio (major axis / minor axis) of the inert particles B1 is 1.1-5.

  According to the present invention, when processed into a magnetic recording medium, it is possible to form a good magnetic layer while maintaining handling properties. Furthermore, a polyester film for a coating type magnetic recording medium excellent in error rate and storage durability is provided.

1 is a schematic view of an apparatus for measuring width dimensional stability. FIG.

  Hereinafter, an embodiment of the polyester film for coating type magnetic recording medium of the present invention will be described. A coating-type magnetic recording medium is a magnetic material having a process of forming a coating film by drying a coating material (for example, a dispersion containing magnetic powder for magnetic recording) applied on a support in the manufacturing process. It is a recording medium.

  The polyester film for coating type magnetic recording medium of the present invention (hereinafter sometimes simply referred to as “the film of the present invention”) is preferably used as a support for the coating type magnetic recording medium. That is, the film of the present invention has a surface roughness and particle structure on both sides, and the aspect ratio of the inert particles B1 having the largest average particle diameter contained in the B layer. However, the improvement in data error and the storage durability are satisfied in a well-balanced manner, or when one characteristic is improved, the deterioration in the other characteristic can be suppressed to the minimum, and a good electromagnetic conversion characteristic with few data errors can be obtained.

  The film of the present invention has a layer structure of two or more layers. When the layer located on the outermost layer on the side to which the magnetic layer is applied is A layer and the layer located on the other outermost layer is B layer, the following (1 It is a polyester film for coating type magnetic recording media that satisfies () to (3).

  (1) The A layer contains inert particles A, and the three-dimensional centerline surface roughness sRa-A of the surface of the A layer (surface A) is 2 to 20 nm.

  (2) The layer B contains inert particles B2 having an average particle size larger than that of the inert particles A, and further contains inert particles B1 having an average particle size larger than that of the inert particles B2, and the layer B side surface (surface B ) Three-dimensional centerline surface roughness sRa-B is 3 to 40 nm.

  (3) The aspect ratio (major axis / minor axis) of the inert particles B1 is 1.1-5.

  In the manufacturing process of the magnetic recording medium, the magnetic layer and the back coat layer are applied to both sides of the film as the support, and then the coating film is cured. In that case, since it heats in the state wound by the roll, the wound film is wound up by stress relaxation and a stress generate | occur | produces in the radial direction of a roll. Due to the stress in the roll radial direction, the magnetic layer and the back coat layer (B surface) are strongly compressed, particularly on the roll core side. At this time, if the surface on the back coat layer (B surface) side has an uneven shape, the unevenness is transferred to the surface of the magnetic layer. The transferred irregularities make the gap between the read head and the magnetic layer unstable when used as a magnetic recording medium, leading to a decrease in output called a missing pulse (MP), resulting in a decrease in performance of the magnetic recording medium.

  For MP, it is effective to reduce the unevenness of the backcoat layer in order to prevent the unevenness from being transferred to the magnetic layer. Since the unevenness of the backcoat layer is greatly affected by the surface shape of the film used as the support, it is effective to smooth the surface of the film. However, if the film surface is made too smooth, the handling property is lowered, the yield in the film manufacturing process is lowered, and the storage durability is also lowered due to the abrasion by the head due to the friction between the magnetic tape and the head. Therefore, the B surface side (surface B) is preferably a moderately rough surface within a range where transfer to the magnetic layer is allowed. However, if the surface is too rough, not only the magnetic tape characteristics, such as the error rate, are reduced, It may become a starting point for shaving by the head, and the storage durability may decrease. However, in recent years, there has been an increasing demand for higher capacity recording media, and it has become difficult to achieve both yield maintenance and surface smoothness in the film manufacturing process, and both the error rate and storage durability of magnetic tape. .

  Therefore, the polyester film of the present invention is effective in that the surface B is rough enough to maintain the handling property, but the deterioration of the storage durability is suppressed at the time of processing into a magnetic recording medium. That is, in the polyester film of the present invention, it is important that the inert particles B1 have an aspect ratio (major axis / minor axis) of 1.1 to 5. When the aspect ratio is smaller than 1.1, suppression of transfer to the magnetic layer and storage durability are likely to be lowered. On the other hand, when it is larger than 5, the storage durability is likely to be lowered along with the running property of the magnetic tape. In addition, 1.15 to 4.5 is preferable, and 1.2 to 4 is more preferable from a comprehensive viewpoint such as transfer suppression, storage durability, magnetic tape running property, and film-forming property. The method for adjusting the aspect ratio of the particles used in the polyester film of the present invention will be described in more detail in the specific examples of inert particles described later and further in the specific examples of the film production method.

  The polyester that can be used in the present invention is not particularly limited as long as it is a polyester that becomes a high-strength film by molecular orientation, but polyethylene terephthalate or polyethylene-2,6-naphthalate is preferably a constituent.

  In the present invention, the main component of the polyester is particularly preferably polyethylene terephthalate from the viewpoints of appearance, heat resistance, dimensional stability and economy. Here, the main component means 50% by mass or more of the whole polyester. Furthermore, 60% by mass or more is preferably polyethylene terephthalate. More specifically, it is preferable that 60 mol% or more of the glycol units constituting the polyester are structural units derived from ethylene glycol, and 60 mol% or more of the dicarboxylic acid units are structural units derived from terephthalic acid. Here, the dicarboxylic acid unit (structural unit) or the diol unit (structural unit) means a divalent organic group from which a portion to be removed by polycondensation has been removed. It is represented by

Dicarboxylic acid unit (structural unit): —CO—R—CO—
Diol unit (structural unit): —O—R′—O—
(Where R and R ′ are divalent organic groups)
In addition, when a trivalent or higher carboxylic acid or alcohol such as trimellitic acid unit or glycerin unit or a derivative thereof is included, the trivalent or higher carboxylic acid or alcohol unit (structural unit) is similarly obtained by polycondensation. The trivalent or higher valent organic group from which the part to be removed is removed is meant.

  Examples of glycols or derivatives thereof that give the polyester used in the present invention include diethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, and 1,5-pentane. Diol, 1,6-hexanediol, aliphatic dihydroxy compounds such as neopentyl glycol, diethylene glycol, polyethylene glycol, polypropylene glycol, polyoxyalkylene glycol such as polytetramethylene glycol, 1,4-cyclohexanedimethanol, spiroglycol, etc. Examples thereof include alicyclic dihydroxy compounds, aromatic dihydroxy compounds such as bisphenol A and bisphenol S, and derivatives thereof. Among them, diethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol are heat resistant and easy to handle. Preferably used.

  Examples of the dicarboxylic acid or its derivative that gives the polyester used in the present invention include isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfone dicarboxylic acid, diphenoxyethanedicarboxylic acid, and 5-sodium sulfone. Aromatic dicarboxylic acids such as dicarboxylic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, maleic acid, fumaric acid and other aliphatic dicarboxylic acids, 1,4-cyclohexanedicarboxylic acid and other alicyclic dicarboxylic acids And oxycarboxylic acids such as paraoxybenzoic acid, and derivatives thereof. Examples of dicarboxylic acid derivatives include dimethyl terephthalate, diethyl terephthalate, 2-hydroxyethyl methyl terephthalate, dimethyl 2,6-naphthalenedicarboxylate, dimethyl isophthalate, dimethyl adipate, diethyl maleate, and dimethyl dimer. An esterified product can be mentioned. Of these, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and esterified products thereof are preferably used from the viewpoint of heat resistance and handleability.

  In the present invention, it is preferable to contain a thermoplastic resin different from polyester (hereinafter sometimes referred to as heat-resistant thermoplastic resin) in order to prevent a decrease in dimensional stability or to adjust the degree of orientation. Examples of the heat resistant thermoplastic resin include polyimide resins (including polyetherimide), polysulfone, polyethersulfone, polyamideimide, polyetheretherketone, and polyarylate. Among these, from the viewpoint of affinity with polyester and melt moldability, polyimide resins, particularly polyetherimide, are preferably exemplified.

  For the heat-resistant thermoplastic resin, in order to easily obtain the effects of dimensional stability and storage durability when processed into a magnetic recording medium, inert particles B1 and B2 to be contained in the below-described inert particles, particularly the B layer, Are preferably different components. Furthermore, the content of the heat-resistant thermoplastic resin is preferably 0.3% by mass or more and 10% by mass or less, and more preferably 0.4% by mass or more and 8% by mass or less. If it is less than 0.3% by mass, the dimensional stability tends to be lowered. On the other hand, when it is more than 10% by mass, it tends to be broken during film formation.

  The film of the present invention has a layer structure of two or more layers. This is because when used as a support for a magnetic recording medium, one surface (A layer side surface, A surface) has smoothness for obtaining excellent electromagnetic conversion characteristics, and the other surface (B layer side). This is because it is easy to achieve both a suitable roughness for imparting excellent transportability and tape runnability in the film formation and processing steps to the surface (surface B).

  Note that having a layer configuration of two or more layers means that there are at least two layers, and may be a multilayer stack configuration of three layers, four layers, or more. The layer that controls the surface shape of one surface (surface A) is the A layer, and the layer that controls the surface shape of the other surface (surface B) is the B layer, and the surface A, surface B, A layer, or B layer. Are defined in the present invention. These layers may be constituted by a coating layer, but are preferably layers formed by coextrusion.

  For example, when the present invention is composed of two layers, one layer is the A layer and the other layer is the B layer. In the case of a three-layer configuration or a four-layer configuration in which a coating layer is formed on one surface or both surfaces of the two-layer configuration, the coating layer is defined as a C layer or a D layer, and a C layer / A layer / B layer, The layer structure is C layer / A layer / B layer / D layer. When the C layer or D layer does not affect the surface shape or the influence is slight, the C layer or D layer is the A layer. The surface of the C layer is the surface A and the surface of the D layer is the surface B.

  As described above, when the film of the present invention is used as a support for a coating type magnetic recording medium, the surface A (A surface) is the surface on the side where the magnetic layer is provided, and the opposite surface B (B surface). Is a surface on the running surface side where a back coat layer or the like is provided.

  When the magnetic layer is provided on the surface A side (A surface side, A layer side surface), the surface roughness sRa-A of the polyester film is 2 to 20 nm. If surface A (A surface) sRa-A is 2 nm or more, it is preferable in the film production, processing step, and the like because process troubles associated with an increase in the coefficient of friction with a transport roll and the like are suppressed. Further, if sRa-A is 20 nm or less, it is preferable because appropriate electromagnetic conversion characteristics can be maintained when used as a magnetic tape for high-density recording. When the magnetic layer is provided on the surface A side, the lower limit of sRa-A is more preferably 2.5 nm, still more preferably 3 nm, and the upper limit of sRa-A is more preferably 15 nm, still more preferably 10 nm.

  On the other hand, when the backcoat layer is provided on the surface B side (B surface side, B layer side surface), the surface roughness sRa-B is 3 to 40 nm. If sRa-B of the surface B (B surface) is 3 nm or more, the friction coefficient with the transport roll or the like becomes small, and the occurrence of process troubles is suppressed, which is preferable. Moreover, if sRa-B is 40 nm or less, when storing as a film roll or a pancake, it is preferable because a decrease in electromagnetic conversion characteristics due to transfer of surface protrusions to the opposite surface can be suppressed. When the backcoat layer is provided on the surface B side, the lower limit of sRa-B is more preferably 4 nm, still more preferably 5 nm, and the upper limit of sRa-B is more preferably 30 nm, still more preferably 20 nm.

  In order to make sRa within the above range, it is preferable to add inert particles in the layer. In the present invention, when the inert particles A are used for the A layer constituting the surface A, the average particle diameter dA is 0. It is preferably 0.01 to 0.6 μm, more preferably 0.04 to 0.4 μm, and the content thereof is preferably 0.005 to 0.5% by mass, 0.01 to More preferably, it is 0.3 mass%. In the magnetic recording medium support, it is preferable to use particles having an average particle size of 0.6 μm or less because deterioration of electromagnetic characteristics can be suppressed. Generally, sRa decreases as the average particle size and addition amount of the inert particles to be added decreases, and sRa increases as the average particle size and addition amount of the inert particles to be added increase.

  When the particles are contained in the B layer constituting the surface B, the B layer contains the inert particles B2 having an average particle size larger than that of the inert particles A, and further the inert particles B1 having an average particle size larger than that of the inert particles B2. It is important to contain. When the inert particle having the largest average particle size contained in the B layer is the inert particle B1, the average particle size dB1 is preferably 0.1 to 2 μm, and preferably 0.2 to 1 μm. More preferably, the content is preferably 0.001 to 0.1% by mass, and more preferably 0.002 to 0.05% by mass. As described above, when the layer B further contains the inert particles B2, the average particle diameter dB2 is preferably 0.02 to 0.5 μm, more preferably 0.05 to 0.4 μm. The content is preferably 0.08 to 2% by mass, and more preferably 0.1 to 1% by mass.

  In the present invention, dB1 is preferably 0.2 to 1.0 μm larger than dB2 from the viewpoint of facilitating handling when processed into a magnetic recording medium, and dB2 is 0.05 to 0 greater than dA. It is preferable that it is 4 μm larger.

  Inactive particles added to the film of the present invention include inorganic particles such as spherical silica, titanium dioxide, calcium carbonate, aluminum silicate, mica, magnesium oxide, calcium phosphate, talc, barium sulfate, or crosslinked polystyrene particles and crosslinked silicone. Preferable examples include organic polymer particles that are heat-resistant polymer particles such as resin particles, crosslinked acrylic resin particles, crosslinked styrene-acrylic resin particles, crosslinked polyester particles, polyimide particles, and melamine resin particles. These can be used alone or in combination of two or more. Among these, the inert particles B1 and B2 are easy to adjust the aspect ratio, that is, excellent in error rate or storage durability. Inorganic particles include calcium carbonate, aluminum silicate, mica, magnesium oxide, calcium phosphate. , Talc and barium sulfate are preferred. On the other hand, as the organic polymer particles that are heat resistant polymers, crosslinked polystyrene particles, crosslinked silicone resin particles, and crosslinked styrene-acrylic resin particles are preferable. Among these, the inert particle B1 is an inorganic particle because it is easy to balance the error rate and storage durability, and any one of calcium carbonate, aluminum silicate, mica, magnesium oxide, calcium phosphate, talc, and barium sulfate. A preferred combination is a seed or two or more, and the inert particles B2 are heat-resistant polymer particles. Furthermore, as the heat resistant polymer, crosslinked polystyrene particles are most preferable from the viewpoint of film forming property and transportability.

  In addition, the inert particles A and the inert particles B2 added to the film of the present invention preferably have a uniform particle diameter and particle distribution, and the volume shape factor f is 0.3 to π / 6. It is preferable that it is 0.4-π / 6. The volume shape factor f is expressed by the following equation.

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

  The volume shape factor f is the maximum π / 6 (= 0.52) when the particle is a sphere. The inert particles are preferably subjected to filtration or the like to remove coarse particles and inclusions as necessary. Among the inert particles, spherical silica is excellent in monodispersity, so that the formation of surface protrusions on the film can be easily controlled, and is preferably used in the present invention.

  In the film of the present invention, the Young's modulus in the longitudinal direction is preferably 4 to 13 GPa. If the Young's modulus in the longitudinal direction is 4 GPa or more, the film is stretched in the longitudinal direction due to the tension in the longitudinal direction in the tape drive, and the recording track shift due to the shrinking of the film in the width direction due to this elongation deformation can be suppressed. preferable. The lower limit of the Young's modulus in the longitudinal direction is more preferably 4.3 GPa, and even more preferably 4.5 GPa. Moreover, it is preferable if the Young's modulus in the longitudinal direction is 13 GPa or less because edge damage can be suppressed by obtaining a sufficient Young's modulus. The upper limit of the Young's modulus in the longitudinal direction is more preferably 10 GPa, and even more preferably 8 GPa.

  In the film of the present invention, the Young's modulus in the width direction is preferably 4 to 13 GPa. A Young's modulus in the width direction of 4 GPa or more is preferable because edge damage can be suppressed. The lower limit of the Young's modulus in the width direction is more preferably 5 GPa, and even more preferably 6 GPa. Further, it is preferable that the Young's modulus in the width direction is 13 GPa or less because a sufficient Young's modulus in the longitudinal direction can be obtained. The upper limit of the Young's modulus in the width direction is preferably 11 GPa, more preferably 10 GPa.

  In addition, in this invention, a longitudinal direction is a direction generally called MD direction, Comprising: The same direction as the longitudinal direction at the time of a polyester film manufacturing process is pointed out. In the present invention, the width direction is a direction generally referred to as a TD direction and refers to the same direction as the width direction during the polyester film manufacturing process (a direction orthogonal to the MD direction in the plane).

  Moreover, it is preferable that the thickness of the film of this invention is 2-10 micrometers. It is preferable that the thickness of the film is 2 μm or more because the necessary strain as a magnetic recording medium can be obtained. The lower limit of the thickness of the film is preferably 3 μm, and more preferably 4 μm. In addition, since the film thickness is 10 μm or less, the tape length per tape can be sufficiently secured, which is preferable because the magnetic tape can be reduced in size and increased in capacity. The upper limit of the thickness of the film is preferably 8 μm, and more preferably 6 μm.

  The thickness ratio of the A layer and the B layer is preferably 1 to 30%, more preferably 2 to 28%, and most preferably 4 to 25% when the total thickness is 100%. . When the B layer thickness ratio is less than 1%, it is difficult to form a uniform laminate, and the slip properties of the film and the magnetic tape are lowered at a place where the number of inert particles B1 and B2 is small. The slit property of the magnetic tape tends to deteriorate. In addition, the yield of films and magnetic tapes tends to decrease due to scratches from the process roll. On the other hand, when the ratio of the B layer is larger than 30%, the surface B becomes rough, and the magnetic tape is electromagnetically converted together with the smoothness of the surface A due to the transfer marks when the film or the magnetic tape is wound into a roll. The characteristic is deteriorated or the error rate is likely to increase. In addition, when it is set as the structure of 3 layers or more, it is preferable that B layer thickness ratio is in the said range, after making the total thickness including layers other than A layer and B layer into 100%.

  The film of the present invention is produced, for example, as follows. Hereinafter, examples using polyethylene terephthalate (PET) as the polyester will be described as representative examples, but the present invention is not particularly limited thereto.

  As a method for producing the inert particles, the inorganic particles are preferably prepared by pulverizing and classifying natural products such as calcium carbonate, aluminum silicate, mica, magnesium oxide, calcium phosphate, talc, and barium sulfate. More specifically, it can be adjusted by performing the pulverization process for a long time or in multiple stages and not performing classification, or by performing the classification process for a short time or reducing the filter accuracy. In addition, synthetic products by chemical reaction may be grown using the above-mentioned natural products on the core seed particles, or fine primary particles may be combined or agglomerated by reaction, or a dispersion technique such as a dispersant may be used in combination. Is preferable in that a desired average particle diameter and aspect ratio can be easily obtained.

  As for the heat-resistant polymer, for example, polystyrene is the seed polymer particle, among the polymerizable monomers, the crosslinkable monomer is divinylbenzene, the copolymerizable monomer is ethylvinylbenzene, and the mass ratio of the crosslinkable monomer and the copolymerizable monomer [ The crosslinkable monomer / copolymerizable monomer] is set to (60 parts by mass / 40 parts by mass) or more, and after divinylbenzene / ethylvinylbenzene is absorbed into polystyrene, it is polymerized and crosslinked to produce divinylbenzene / styrene copolymer crosslinked particles. It is preferable to adjust (DVBS). As a method for adjusting the aspect ratio, for example, it is possible to cope with the seed polymer particles before polymerization or by applying pressure deformation at the stage after polymerization (before crosslinking), or by applying an action such as stirring at the polymerization stage.

  As a method of incorporating inert particles into polyester, for example, inert particles A or inert particles B are dispersed in a predetermined proportion in ethylene glycol, which is a diol component, and the ethylene glycol slurry is completely polyester-polymerized. It may be added at an optional stage before. Here, when the particles are added, for example, when the water sol or alcohol sol obtained when the particles are synthesized is added at any stage before the completion of polyester polymerization without drying, the dispersibility of the particles is good. The slipperiness and electromagnetic conversion characteristics of the film can be improved. Another effective technique is to mix a water slurry of particles with a predetermined polyester pellet, supply the mixture to a vent type twin-screw kneading extruder, and knead it into the polyester. By these methods, polyester pellets containing particles are prepared.

  Prepared as described above, polyester pellets containing particles and polyester pellets substantially free of particles and the like are mixed at a predetermined ratio, dried, and then supplied to a known melt laminating extruder to produce a polymer. Is filtered through a filter.

  Further, in a coating type high density magnetic recording medium application in which a very thin magnetic layer is applied, a very small foreign matter may cause DO (dropout) which is a magnetic recording defect. It is effective to use a highly accurate fiber-sintered stainless steel filter capable of collecting 95% or more of the above foreign matters. Subsequently, the polymer is extruded into a sheet form from a slit-shaped slit die, and this polymer is cooled and solidified on a casting roll to obtain an unstretched film. That is, a plurality of extruders, a plurality of manifolds, or a merge block (for example, a merge block having a rectangular merge section) is used to stack the required number of layers, the sheet is extruded from the die, cooled by a casting roll, and unstretched film Get. In this case, it is effective to install a static mixer or a gear pump in the polymer flow channel from the viewpoint of stabilizing the back pressure and suppressing the thickness variation.

  Subsequently, the unstretched film is stretched biaxially in the longitudinal direction and the width direction and then heat treated. Although a extending process is not specifically limited, It is preferable to extend | stretch in 2 steps or more in each direction. That is, it is preferable to perform re-longitudinal and re-lateral stretching because a high-strength film optimal as a magnetic tape for high-density recording is easily obtained.

  The stretching method may be simultaneous biaxial stretching or sequential biaxial stretching. Since simultaneous biaxial stretching does not involve stretching by a roll, local heating of the film surface does not occur, the surface property is easy to control, and the stretching method is more preferable.

  In sequential biaxial stretching, the stretch ratio of the unstretched film in the longitudinal direction is, for example, 2.5 to 5 times, preferably 2.8 to 4.5 times, and the stretching temperature is, for example, 80 to 130 ° C., preferably 85 to 125. It extends | stretches as 0 degreeC, More preferably 90-120 degreeC. It is preferable because the stretching unevenness of the film can be suppressed by setting the stretching ratio in the longitudinal direction to 4 times or less and the stretching temperature to 80 ° C. or higher. The stretching ratio is 2.5 times or more, and the stretching temperature is 130 ° C. or lower to make it magnetic. This is preferable because sufficient strength can be obtained when used as a recording medium.

  Next, the uniaxially stretched film has a stretching ratio in the width direction of, for example, 3 to 5.5 times, preferably 3.3 to 5 times, and a stretching temperature of, for example, 80 to 140 ° C, preferably 85 to 130 ° C, more preferably 85. Stretched at ~ 120 ° C. The film can be prevented from being broken by setting the draw ratio in the width direction to 5 times or less and the draw temperature to 80 ° C. or more. As the magnetic recording medium, by setting the draw ratio to 3 times or more and the draw temperature to 140 ° C. or less. It is preferable because sufficient strength can be obtained when used.

  On the other hand, in the simultaneous biaxial stretching, the unstretched film is stretched simultaneously in the longitudinal direction and the width direction at a stretching temperature of, for example, 80 to 160 ° C, preferably 85 to 130 ° C, more preferably 90 to 110 ° C. Setting the stretching temperature to 80 ° C. or higher is preferable because breakage of the film can be suppressed, and setting the stretching temperature to 160 ° C. or lower is preferable because sufficient strength can be obtained when used as a magnetic recording medium.

  Moreover, from the viewpoint of preventing uneven stretching in both sequential biaxial stretching and simultaneous biaxial stretching, the total stretching ratio in the longitudinal direction and the width direction is, for example, 8 to 30 times, preferably 9 to 25 times, and more preferably 10 to 20 times. It is preferable to double. It is preferable to set the draw ratio to 8 times or more because sufficient strength can be obtained for a high-density magnetic recording medium. Moreover, it is preferable to set the draw ratio to 30 times or less because the film can be prevented from being broken during the production process. From the viewpoint of obtaining the necessary strength for the high-density magnetic recording medium, the temperature is preferably 120 to 210 ° C., more preferably 125 to 200 ° C., and again in the longitudinal direction and / or the width direction as necessary. The stretching is preferably performed at 1.05 to 1.8 times, more preferably 1.1 to 1.6 times. A stretching ratio of 1.05 times or more is preferable because sufficient strength can be obtained, and a stretching ratio of 1.8 times or less is preferable because the film can be prevented from being broken during the manufacturing process.

  Thereafter, heat setting is performed at 180 to 235 ° C., preferably 190 to 220 ° C., for example, for 0.5 to 20 seconds, preferably 1 to 15 seconds. It is preferable that the heat setting temperature is 180 ° C. or higher because the crystallization of the film proceeds and the structure can be stabilized. Further, by setting the heat setting temperature to 235 ° C. or lower, it is possible to suppress a decrease in Young's modulus accompanying the progress of relaxation of the polyester amorphous chain portion, which is preferable from the viewpoint of obtaining sufficient strength as a magnetic recording medium application. . Thereafter, for the purpose of relaxing the strain of plane orientation and improving the dimensional stability, it is preferably 0.5 to 7.0%, more preferably 0.5 to 6.5 in the longitudinal direction and / or the width direction. % Relaxation treatment.

  The film of the present invention is sufficiently rough on the side B to which the back coat is applied, so that the running property and slipperiness of the film and tape are sufficiently secured, and the handling property is excellent. Therefore, improvement in the yield in the manufacturing process of the base film is expected. On the other hand, by defining the aspect ratio of the inert particles B1 having the largest average particle diameter contained in the B layer corresponding to the B surface side, the unevenness of the backcoat layer is prevented from being transferred to the magnetic layer side. be able to. For this reason, the film of this invention can be preferably used as a support body of a coating type magnetic recording medium.

  The polyester film of the present invention is particularly excellent in characteristics as a magnetic recording medium and processability to a coating type magnetic recording medium, and can be suitably used as a base substrate for the application.

  As a particularly preferable application, it is suitably used for a base film for magnetic tape of a digital data recording system such as digital video cassette, data storage, DLT, LTO, digital AIT, AIT turbo, etc. In particular, it is most preferably used as a base material for data storage, in which a magnetic metal thin film such as a metal magnetic material is applied as a recording layer.

[Methods for measuring physical properties and methods for evaluating effects]
The characteristic value measurement method and effect evaluation method in the present invention are as follows.

(1) Thickness of the whole film (total thickness) and thickness of A layer and B layer The thickness of the whole film was measured at 10 points at random with a micrometer, and the average value was used. In the measurement of one point, the measurement was performed in a state where all the test pieces collected from 10 pieces were stacked. Finally, the value obtained by dividing the average value by the number of stacked test pieces (10) was taken as the total film thickness.

  Moreover, about the thickness of A layer and B layer, the thickness of a relatively thin polyester layer is measured by the method described below, and the thickness of the relatively thick polyester layer is relatively less than the total thickness of the polyester layer. The thickness was subtracted.

  That is, the film cross section was observed at 20,000 times with a transmission electron microscope (TEM). The section thickness of TEM was about 100 nm, and the thickness of each layer was evaluated from the observation result of the interface based on the contained particle diameter and particle concentration.

  In addition, when observation by the above was difficult, it evaluated using the secondary ion mass spectrometer (SIMS). While etching from the surface, the depth profile of the element concentration resulting from the particles or the heat-resistant thermoplastic resin was measured, and the thickness of each layer was evaluated. When measurement by SIMS is difficult (for example, polymer particles other than silicone resin), Fourier transform microinfrared spectroscopy (microscopic FT-IR method) or X-ray photoelectric spectroscopy (XPS method) while etching the surface Etc.

(2) Average particle diameter of inert particles A, B1, B2 (dA, dB1, dB2)
The polyester resin is removed from the surface A (A layer side surface) and the surface B (B layer side surface) of the polyester film by a plasma low-temperature ashing method (for example, PR-503 type manufactured by Yamato Kagaku) to expose the particles. The treatment conditions are selected so that the polyester resin is ashed but the particles are not damaged. This was subjected to an ion coating treatment of platinum / palladium = 85/15 (mass ratio) and then observed at 10,000 times using a SEM (S-3400N scanning electron microscope manufactured by Hitachi High-Technologies Corporation). Images were taken so that the total number of particles was 1,000 or more by changing the observation location. An OHP film was overlaid on the image photograph of the obtained particles, and the particle portion of the photograph was painted with black magic and marked. The OHP film was subjected to numerical processing with an image analyzer (image analysis software manufactured by Seaon Co., Ltd.), and the obtained area data (μm ² ) of each particle was converted to an equivalent circle equivalent diameter. Further, the number average diameter of all particles was defined as the average particle diameter.

  When there are two or more kinds of particles having different particle diameters such as the inert particles B1 and B2, the particle number distribution with the equivalent circle equivalent diameter is a distribution having two or more peaks. Therefore, the data obtained by equivalent circle equivalent diameter conversion is the first peak in which the Y axis is the maximum value in the particle size distribution plotted with the X axis as the particle size (0.01 μm unit) and the Y axis as the number. The corresponding X-axis particle size was defined as the average particle size dB2 of the inert particles B2. Next, the particle diameter corresponding to the second peak on the side having a larger particle diameter than the first peak was defined as the average particle diameter dB1 of the inert particles B1.

(3) Aspect ratio (major axis / minor axis) of inert particles B1
Using a microtome, ultra-thin sections were prepared in the longitudinal direction and width direction of the polyester film, and observed at 25,000 times using a SEM (S-3400N scanning electron microscope manufactured by Hitachi High-Technologies Corporation). Images were taken for 10 particles (20 in total) in the longitudinal direction and width direction by changing the location. About the image photograph of each obtained particle | grain, the major axis and the minor axis were measured, and it computed from the average value of the aspect-ratio (major axis / minor axis) for 20 pieces.

(4) Three-dimensional centerline surface roughness sRa-A, sRa-B
Using a three-dimensional roughness meter (ET-4000A manufactured by Kosaka Laboratory Ltd.) and stylus mode (needle contact type roughness measurement), sRa-A on the smooth surface (surface A, surface of the A layer side) of the film It measured about sRa-B of the rough surface (surface B, B layer side surface) (unit: nm). The measurement conditions were as follows, and the average values measured at five locations arbitrarily selected from the film A layer side surface (surface A) and the B layer side surface (surface B) were sRa-A and sRa-B, respectively. did.
Scanning speed 0.02mm / sec
Measuring length 0.2mm
cut off 0.08mm
Needle pressure 6 mgr
Needle diameter 2μm
Running pitch (X pitch) 0.40μm
Feed pitch (Y pitch) 2μm
Longitudinal magnification (Z measurement magnification) 100,000 times Number of measurement 100 100 (5) Young's modulus Young's modulus was measured based on JIS-K7161 (1994). In the measurement, an Instron type tensile tester was used, and the conditions were as follows. The average value of five measurement results was defined as the Young's modulus in the present invention.

Sample size: width 10 mm x sample length 100 mm
Tensile strength: 200 mm / min Measurement environment: Temperature 23 ° C., humidity 65% RH
Number of measurements: measured 5 times and calculated from the average value (6) Production of magnetic tape After slitting the biaxially oriented laminated polyester film obtained in Examples and Comparative Examples to a width of 1 m, it was conveyed with a tension of 200 N as a support. A magnetic paint and a non-magnetic paint having the following composition are applied to the smooth surface (surface A, A layer side surface) of the film with an extrusion coater (the upper layer is a magnetic paint and the coating thickness is 0.1 μm after drying, and the lower layer is a non-magnetic paint) The coating thickness was 1.0 μm), magnetically oriented, and dried at a drying temperature of 100 ° C. Next, a back coat having the following composition was applied to the surface on the opposite side of layer B (surface B) (coating thickness after drying: 0.4 μm), dried at a drying temperature of 100 ° C., and then a small test calender device (steel / nylon) The film was calendered at a temperature of 85 ° C. and a linear pressure of 2.2 × 10 ⁵ N / m with ⁵ rolls, and then wound up. The original tape was slit to a width of 1/2 inch (12.65 mm) to prepare a pancake, and then a portion of 200 m in length from this pancake was incorporated into a cassette to obtain a cassette tape.
(Composition of magnetic paint)
Ferromagnetic metal powder: 100 parts by mass [Fe: Co: Ni: Al: Y: Ca = 70: 24: 1: 2: 2: 1 (mass ratio)]
[Long axis length: 0.09 μm, axial ratio: 6, coercive force: 153 kA / m (1,922 Oe), saturation magnetization: 146 Am ² / kg (146 emu / g), BET specific surface area: 53 m ² / g, X-ray Particle size: 15 nm]
Modified vinyl chloride copolymer (binder): 10 parts by mass (average polymerization degree: 280, epoxy group content: 3.1% by mass, sulfonic acid group content: 8 × 10 ⁻⁵ equivalent / g)
-Modified polyurethane (binder): 10 parts by mass (number average molecular weight: 25,000, sulfonic acid group content: 1.2 × 10 ⁻⁴ equivalent / g, glass transition point: 45 ° C.)
Polyisocyanate (curing agent): 5 parts by mass (Coronate L (trade name) manufactured by Nippon Polyurethane Industry Co., Ltd.)
2-ethylhexyl oleate (lubricant): 1.5 parts by mass Palmitic acid (lubricant): 1 part by mass Carbon black (antistatic agent): 1 part by mass (average primary particle size: 0.018 μm)
Alumina (abrasive): 10 parts by mass (α alumina, average particle size: 0.18 μm)
-Methyl ethyl ketone: 75 parts by mass-Cyclohexanone: 75 parts by mass-Toluene: 75 parts by mass (composition of non-magnetic paint)
Modified polyurethane: 10 parts by mass (number average molecular weight: 25,000, sulfonic acid group content: 1.2 × 10 ⁻⁴ equivalent / g, glass transition point: 45 ° C.)
-Modified vinyl chloride copolymer: 10 parts by mass (average polymerization degree: 280, epoxy group content: 3.1% by mass, sulfonic acid group content: 8 × 10 ⁻⁵ equivalent / g)
-Methyl ethyl ketone: 75 parts by mass-Cyclohexanone: 75 parts by mass-Toluene: 75 parts by mass-Polyisocyanate: 5 parts by mass (Coronate L (trade name) manufactured by Nippon Polyurethane Industry Co., Ltd.)
・ 2-ethylhexyl oleate (lubricant): 1.5 parts by mass Palmitic acid (lubricant): 1 part by mass (backcoat composition)
Carbon black: 95 parts by mass (antistatic agent, average primary particle size 0.018 μm)
Carbon black: 10 parts by mass (antistatic agent, average primary particle size 0.3 μm)
Alumina: 0.1 part by mass (α alumina, average particle size: 0.18 μm)
Modified polyurethane: 20 parts by mass (number average molecular weight: 25,000, sulfonic acid group content: 1.2 × 10 ⁻⁴ equivalent / g, glass transition point: 45 ° C.)
-Modified vinyl chloride copolymer: 30 parts by mass (average polymerization degree: 280, epoxy group content: 3.1% by mass, sulfonic acid group content: 8 × 10 ⁻⁵ equivalent / g)
Cyclohexanone: 200 parts by mass Methyl ethyl ketone: 300 parts by mass Toluene: 100 parts by mass (7) Error rate Using a commercially available LTO drive 3580-L11 manufactured by IBM, Recording / reproduction (recording wavelength: 0.55 μm) was repeated 60 times in an environment of 25 ° C. and 65% RH, and then evaluated according to the following criteria.

A: Error rate is less than 1.0 × 10 ⁻⁶ (most desirable)
○: Error rate is 1.0 × 10 ⁻⁶ or more and less than 1.0 × 10 ⁻⁵ (desirable)
Δ: Error rate is 1.0 × 10 ⁻⁵ or more and less than 1.0 × 10 ⁻⁴ (can be used practically)
×: Error rate is 1.0 × 10 ⁻⁴ or more (unusable)
The error rate is calculated from the error information (number of error bits) output from the drive by the following formula.

Error rate = (number of error bits) / (number of write bits)
(8) Storage durability The cassette tape produced by the method of (6) was stored for 7 days in an environment of 60 ° C. and 85% RH, and then left for 24 hours in an environment of 25 ° C. and 65% RH. This cassette tape was evaluated in the same manner as in the method (7).

(9) Width stability (width dimension change rate)
The tape is taken out from the cassette tape cartridge produced by the above method (6), the sheet width measuring device produced as shown in FIG. 1 is placed in the following constant temperature and humidity chamber, and the width dimension is measured. The sheet width measuring device shown in FIG. 1 is a device that measures the width dimension using a laser, and fixes the magnetic tape 9 to the load detector 3 while setting it on the free rolls 5 to 8, and the end portion A weight 4 serving as a load is hung on. When this magnetic tape 9 is irradiated with the laser beam 10, the laser beam 10 oscillated linearly in the width direction from the laser oscillator 1 is blocked only by the portion of the magnetic tape 9, enters the light receiving unit 2, and the blocked laser beam The width is measured as the width of the magnetic tape. The average value of the three measurement results is defined as the width in the present invention.

・ Measuring device: Sheet width measuring device manufactured by Ayaha Engineering Co., Ltd. ・ Laser oscillator 1, light receiving unit 2: Laser dimension measuring device LS-5040 manufactured by Keyence Corporation
-Load detector 3: Load cell CBE1-10K manufactured by NMB
・ Constant temperature and humidity chamber: SE-25VL-A manufactured by Kato Corporation
・ Load 4: Weight (longitudinal direction)
・ Sample size: width 1/2 inch x length 250 mm
-Retention time: 5 hours-Number of measurements: 3 measurements.

  Next, the width dimensions (1A, 1B) were measured under the following A and B conditions. That is, lA is measured after 24 hours have elapsed under the A condition, and then lB is measured after 24 hours have elapsed under the B condition. Three points were measured: a sample cut from the 30 m point from the beginning of the tape cartridge, a sample cut from the 100 m point, and a sample cut from the 170 m point, and the average value was taken as the width dimension.

A condition: 10 ° C, 10% RH, tension 0.8N
B condition: 29 ° C, 80% RH, tension 0.5N
Furthermore, based on the obtained width dimension (1A, 1B), the width dimension change rate was calculated by the following formula.

Width change rate (ppm) = 10 ⁶ × ((1B-1A) / 1A)
From the width dimension change rate thus obtained, the width dimension stability was evaluated according to the following criteria. △ is practically usable, and X is rejected.

A: Maximum width change rate is less than 500 (ppm) ○: Maximum width change rate is 500 (ppm) or more and less than 600 (ppm) Δ: Maximum width change rate is 600 (ppm) or more Less than 700 (ppm) ×: The maximum value of the width dimensional change rate is 700 (ppm) or more [Example 1]
194 parts by mass of dimethyl terephthalate and 124 parts by mass of ethylene glycol were charged into a transesterification reactor, and the contents were heated to 140 ° C. and dissolved. Thereafter, 0.3 parts by mass of magnesium acetate tetrahydrate and 0.05 parts by mass of antimony trioxide were added while stirring the contents, and a transesterification reaction was performed while distilling methanol at 140 to 230 ° C. Next, 0.5 parts by mass of a 5% by mass ethylene glycol solution of trimethyl phosphate (0.025 parts by mass as trimethyl phosphate) and 0.3% of a 5% by mass ethylene glycol solution of sodium dihydrogen phosphate dihydrate were obtained. Mass parts (0.015 parts by mass as sodium dihydrogen phosphate dihydrate) were added.

  Addition of trimethyl phosphoric acid in ethylene glycol reduces the temperature of the reaction contents. Therefore, stirring was continued until the temperature of the reaction contents returned to 230 ° C. while distilling excess ethylene glycol. In this way, after the temperature of the reaction contents in the transesterification reactor reached 230 ° C., the reaction contents were transferred to the polymerization apparatus.

  After the transition, the reaction system was gradually heated from 230 ° C. to 290 ° C. and the pressure was reduced to 0.1 kPa. The time to reach the final temperature and final pressure was both 60 minutes. After reaching the final temperature and the final pressure, the reaction was carried out for 2 hours (3 hours after the start of polymerization), and the agitation torque of the polymerization apparatus was a predetermined value (specific values differ depending on the specifications of the polymerization apparatus. The value indicated by polyethylene terephthalate having an intrinsic viscosity of 0.62 was a predetermined value). Accordingly, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into cold water in a strand form, and immediately cut to obtain polyethylene terephthalate pellets having an intrinsic viscosity of 0.62 (raw material-1).

  A pellet of polyethylene terephthalate containing spherical silica particles having an average particle diameter of 0.10 μm and a volume shape factor f = 0.51, and a polyethylene terephthalate pellet (raw material-1) containing substantially no particles are made of spherical silica particles. A thermoplastic resin A was prepared by mixing "Ultem" 1010 manufactured by SABIC Innovative Plastics Co., Ltd. so as to be 4% by mass as a heat-resistant thermoplastic resin having a content of 0.05% by mass.

  Also, polyethylene terephthalate containing divinylbenzene / styrene copolymer crosslinked particles (DVBS) having an average particle size of 0.3 μm and a volume shape factor f = 0.52, divinylbenzene having an average particle size of 0.8 μm and an aspect ratio of 2.1 / Polyethylene terephthalate containing styrene copolymer crosslinked particles and polyethylene terephthalate pellets (raw material-1) substantially free of particles, DVBS particle content of 0.3 μm is 0.26 mass%, 0.8 μm A thermoplastic resin B was obtained by mixing 4% by mass of “Ultem” 1010 manufactured by SABIC Innovative Plastics Co., Ltd. as a heat-resistant thermoplastic resin so that the DVBS particle content was 0.01% by mass.

  Thermoplastic resin A and thermoplastic resin B are each dried under reduced pressure at 160 ° C. for 8 hours, then supplied to separate extruders, melt-extruded at 275 ° C., filtered with high precision, and then laminated in a rectangular two-layer confluence block The thickness ratio (A layer | B layer) = 7 | 1, and the layers were merged and laminated so that the B layer side was the cast drum surface side to form a two-layer laminate. Thereafter, the film was wound around a casting drum having a surface temperature of 25 ° C. by using an electrostatic application casting method on a cooling roll through a slit die kept at 295 ° C., and solidified by cooling to obtain an unstretched laminated film.

  This unstretched laminated film was stretched 3.1 times in the longitudinal direction at 113 ° C. by a roll type stretching machine (MD stretching 1). These stretching operations were performed by utilizing the peripheral speed difference between two sets of rolls.

  2. Grip both ends of the obtained uniaxially stretched laminated film with clips while leading to a 95 ° C. preheating zone in the tenter, and then continuously in the 92 ° C. heating zone in the width direction (TD direction) perpendicular to the longitudinal direction. The film was stretched 4 times (TD stretching 1).

  The obtained biaxially stretched laminated film was stretched 1.33 times in the longitudinal direction at 142 ° C. with a roll stretching machine (MD stretching 2). This stretching was performed using the difference in peripheral speed between two sets of rolls.

  Further, the film was led to a tenter and stretched 1.32 times in the width direction in a heating zone at 192 ° C. (TD stretching 2), followed by heat treatment at 207 ° C. for 10 seconds in the heat treatment zone in the tenter, and further at 2.50 ° C. A relaxation treatment was performed in the 7% width direction. Subsequently, after uniformly cooling to 25 ° C., the film edge was removed, and the film was wound on a core to obtain a biaxially stretched laminated polyester film having an overall thickness of 5.0 μm and a B layer thickness of 0.65 μm.

  Regarding the production conditions of this biaxially stretched laminated polyester film, Table 1 shows the raw material composition and thickness relationship, and Table 2 shows the film forming condition relationship. When the obtained biaxially stretched laminated polyester film was evaluated, as shown in Table 2, the surface roughness SRa was 3.8 nm on the layer A side and 7.7 nm on the layer B side, and the Young's modulus in the longitudinal direction was 4.6 GPa. The Young's modulus in the width direction was 6.0 GPa. Further, when used as a magnetic tape, it had excellent error rate, storage durability, width dimension stability, and particularly excellent error rate.

[Examples 2-3]
Biaxially stretched laminated polyester films of Examples 2 to 3 were obtained in the same manner as in Example 1 except that the amount of DVBS particles added in the B layer was changed as shown in Table 1. When the obtained biaxially stretched laminated polyester film was evaluated, it was excellent in each characteristic as shown in Table 2, and was excellent in error rate, storage durability and width dimension stability when used as a magnetic tape. Had.

[Examples 4, 5, and 6]
The biaxially stretched laminated polyesters of Examples 4 to 6 were the same as Examples 1, 2, and 3 except that the DVBS particles in layer B were changed to calcium carbonate particles having an aspect ratio of 1.8 as shown in Table 1. A film was obtained. When the obtained biaxially stretched laminated polyester film was evaluated, it was excellent in each characteristic as shown in Table 2, and was excellent in error rate, storage durability and width dimension stability when used as a magnetic tape. Had.

[Examples 7 to 8]
Biaxially stretched laminated polyester films of Examples 7 to 8 were obtained in the same manner as in Example 2 except that the aspect ratio of DVBS particles in the B layer was changed as shown in Table 1. When the obtained biaxially stretched laminated polyester film was evaluated, it was excellent in each characteristic as shown in Table 2, and was excellent in error rate, storage durability and width dimension stability when used as a magnetic tape. Had.

[Example 9]
A biaxially stretched laminated polyester film of Example 9 was obtained in the same manner as in Example 2 except that the DVBS particles in the B layer were changed to aluminum silicate particles having an aspect ratio of 2.5 as shown in Table 1. When the obtained biaxially stretched laminated polyester film was evaluated, it was excellent in each characteristic as shown in Table 2, and was excellent in error rate, storage durability and width dimension stability when used as a magnetic tape. Had.

[Comparative Examples 1, 2, 3]
Biaxially stretched laminated polyester films of Comparative Examples 1 to 3 were obtained in the same manner as in Examples 1, 2, and 3 except that the aspect ratio of DVBS particles in the B layer was changed as shown in Table 1. When the obtained biaxially stretched laminated polyester film was evaluated, as shown in Table 2, it was inferior in error rate and storage durability when used as a magnetic tape.

[Comparative Example 4]
Biaxially stretched laminated polyester films of Comparative Examples 1 to 3 were obtained in the same manner as in Examples 1, 2, and 3 except that the aspect ratio of DVBS particles in the B layer was changed as shown in Table 1. When the obtained biaxially stretched laminated polyester film was evaluated, as shown in Table 2, it was inferior in storage durability when used as a magnetic tape.

[Comparative Example 5]
As shown in Table 1, a biaxially stretched laminated polyester film was prepared in the same manner as in Example 2 except that the average particle size of the spherical silica particles of the thermoplastic resin A was 0.5 μm and the content was 0.6% by mass. Obtained. When the obtained biaxially stretched laminated polyester film was evaluated, as shown in Table 2, it was particularly inferior in error rate when used as a magnetic tape.

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

Claims (11)

When having a layer structure of two or more layers, the layer located on the outermost layer on the side where the magnetic layer is applied is the A layer, and the layer located on the other outermost layer is the B layer, the following (1) to (3) Polyester film for coating type magnetic recording media satisfying
(1) The A layer contains inert particles A, and the three-dimensional centerline surface roughness sRa-A of the surface of the A layer (surface A) is 2 to 20 nm.
(2) The layer B contains inert particles B2 having an average particle size larger than that of the inert particles A, and further contains inert particles B1 having an average particle size larger than that of the inert particles B2, and the layer B side surface (surface B ) Three-dimensional centerline surface roughness sRa-B is 3 to 40 nm.
(3) The aspect ratio (major axis / minor axis) of the inert particles B1 is 1.1-5. The A layer contains 0.005 to 0.5 mass% of inert particles A having an average particle diameter (dA) of 0.01 to 0.6 μm, and the B layer has an average particle diameter (dB2) of 0.02 to 0.5 μm. The inert particle B2 is 0.08 to 2% by mass, and further contains 0.001 to 0.1% by mass of the inert particle B1 having an average particle diameter (dB1) of 0.1 to 2 μm. 2. A polyester film for coating type magnetic recording medium according to 1. The inert particles B1 and B2 are inorganic particles, and are one or more of calcium carbonate, aluminum silicate, mica, magnesium oxide, calcium phosphate, talc, and barium sulfate. Coating type polyester film for magnetic recording media. The polyester film for coating type magnetic recording media according to claim 1 or 2, wherein the inert particles B1, B2 are heat-resistant polymer particles. The inert particle B1 is an inorganic particle, and is one or more of calcium carbonate, aluminum silicate, mica, magnesium oxide, calcium phosphate, talc, and barium sulfate, and the inert particle B2 is a heat-resistant polymer particle. The polyester film for coating type magnetic recording media according to claim 1 or 2. The polyester film for coated magnetic recording media according to claim 4 or 5, wherein the heat-resistant polymer particles are crosslinked polystyrene particles. The polyester film for a coating type magnetic recording medium according to any one of claims 1 to 6, comprising 0.3 to 10% by mass of a heat-resistant thermoplastic resin having a component different from the inert particles B1 and B2. The polyester film for coating type magnetic recording media according to claim 7, wherein the heat-resistant thermoplastic resin is polyetherimide. The polyester film for coated magnetic recording media according to any one of claims 1 to 8, wherein the main component of the polyester is polyethylene terephthalate. The polyester film for coating type magnetic recording media according to any one of claims 1 to 9, which is used as a base film for coating type digital recording magnetic recording media. A magnetic recording medium using the polyester film for coating type magnetic recording medium according to claim 10.

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