JP2010225249A - Polyester film for magnetic recording tape - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyester film having excellent electromagnetic transducing characteristics and improved running durability with a magnetic head as a polyester film for a large capacity magnetic recording tape wherein high density recording is made possible and suitable for a use in which high image quality and high reliability are required such as a DVCAM use. <P>SOLUTION: In the polyester film for the magnetic recording tape wherein a film layer is provided on a surface I on the magnetic surface forming side of a polyester layer, the film layer on the surface I has a water soluble polymer or a water dispersion polymer as a constituent, at least two kinds of inert particles having average particle diameters different from each other are contained in the film layer, D<SB>S</SB>, N<SB>S</SB>, D<SB>L</SB>and N<SB>L</SB>satisfy all of formula (1): 25<D<SB>L</SB><70, formula (2): 1.5<D<SB>L</SB>/D<SB>S</SB><6 and formula (3): 100<N<SB>S</SB>/N<SB>L</SB><10,000 when an average particle diameter of particles (particles L) having the largest average particle diameter of the inert particles is defined as D<SB>L</SB>(nm), protrusion density caused by the particles L is defined as N<SB>L</SB>(pieces/mm<SP>2</SP>), an average particle diameter of particles (particles S) having the smallest average particle diameter is defined as D<SB>S</SB>(nm) and protrusion density caused by the particles S is defined as N<SB>S</SB>(pieces/mm<SP>2</SP>), surface roughness Ra of the film layer on the surface I is 1.5 to 6.0 nm and the aggregation rate of protrusions caused by particles S is lower than 20%. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a polyester film for magnetic recording tape.

  Polyester films typified by polyethylene terephthalate film are used in a wide range of applications due to their excellent physical and chemical properties, particularly as a base film for magnetic recording media.

As one of metal thin film type magnetic recording media, consumer digital video tape and digital video cassette (DVC) tape put into practical use in 1995 are made of Co metal on the surface of one side of a base film with a thickness of 6-7 μm. A magnetic thin film is provided by vacuum deposition, and a diamond-like carbon film is coated on the surface. In the case of a camera-integrated video using a DV minicassette, the basic specification (SD specification) has a recording time of 1 hour. Also, using this consumer DV format, the tape running speed is increased by 1.5 times and the recording track width is increased from 10μm to 15μm of DV, realizing high image quality and high reliability required for business use. The same tape width (1/4 inch) DVCAM format was developed in 1996. The DVCAM format is a professional VTR with high image quality, high sound quality, small size, and light weight, and is excellent for business use such as excellent damping characteristics and high-quality editing performance. It is among companies, productions, cable TV, and video journalists. It has an extremely high reputation. The base film comprises (1) a polyester film, a discontinuous film mainly composed of fine particles having a particle diameter of 5 to 50 nm, and a polymer blend adhered to at least one surface of the film. Is a polyester film containing a water-soluble polyester copolymer and having protrusions formed on a discontinuous film by fine particles (see, for example, Patent Document 1), (2) One surface of the polyester layer A is made of an aqueous polyester resin. A polyester film coated with a continuous film C comprising 0.5 to 30 wt% of inert particles C having an average particle size of 10 to 50 nm and a volume shape factor of 0.1 to π / 6, The thickness of C is 3 to 50 nm, the aqueous polyester resin forming the coating C has a number average molecular weight of 10,000 to 1,000,000, and the coating C of the film Polyester film surface roughness WRa of a 0.1～4Nm, and the number of foreign matters deposited on the surface of the film C when the film was held for 30 minutes at 120 ° C. is 1000 / mm ² or less (See, for example, Patent Document 2).

  In addition, in the fall of 2001, a video standard appeared that had a recording time of 1 hour with a volume ratio of 30% compared to the MICRO MV standard DV mini cassette. This new video standard is digital recording using the same vapor deposition tape as DVC, but the image compression method is not the DV compression of the DVC standard but MPEG2 compression, the tape width is from 6.35 mm to 3.8 mm, and the shortest recording wavelength is The track pitch is changed from 0.49 μm to 0.29 μm, from DV 10 μm and DVLP 6.7 μm to 5 μm, and the density is greatly increased. The magnetic layer of the vapor deposition tape is greatly reduced in thickness from 160 to 220 nm of the Co oxide film thickness of DVC to 50 nm in the MICRO MV tape. This high density recording and reproduction is possible because a magnetoresistive head (MR head) is used for reproduction. Since this MR head has a characteristic that it can detect a minute leakage magnetic flux from a magnetic recording medium with high sensitivity, it is possible to reduce noise by making the magnetic recording layer thinner. Thus, it is possible to improve the surface recording density.

  However, in applying this MR head, it is possible to use a base film as in the above (1) and (2) of the digital recording system, but it was prepared from a base film having a continuous film as in (2). In the magnetic tape, it is difficult to satisfy both the durability of the magnetic tape surface by the recording head and the durability of the reproducing MR head by the magnetic tape surface magnetic layer. In other words, the film thickness of the MR head metal thin film is very thin, about 20 nm, and it is very easy to scrape. Therefore, the MICRO MV tape made from the conventional base (2) used in the DVC tape has a running life of the MR head. It becomes extremely short (about 100 hours of continuous reproduction), and frequent MR head replacement is required. Further, in the magnetic tape manufactured from the base film as described in (1) above, the number of fine particles on the surface of the base film is reduced or the size of the fine particles is reduced so that the electromagnetic conversion characteristics of the magnetic tape are improved. When the surface roughness is reduced by using the above method, the electromagnetic conversion characteristics are greatly improved, but the friction with the MR head is increased and the running durability is remarkably lowered.

Further, as a recent example, (3) a base film for magnetic recording tape that is digitally recorded linearly with respect to the longitudinal direction of the magnetic recording tape, and a film containing fine particles and an organic compound on one surface of one side of a polyester film The number of surface scratches with a height of 120 nm or more on the film side surface is 10/100 cm ² or less, the Young's modulus in the film longitudinal direction is 6000 MPa or more, and the refractive index in the film longitudinal direction and the width direction is There is a polyester film for magnetic recording tape (see, for example, Patent Document 3), wherein the difference (Δn) is 30 × 10 ⁻³ or more. Although it is possible to use the base film of (3) for DVCAM applications and the like, it is necessary to contain more lubricant particles in order to improve the running durability of the film. Many coarse protrusions are generated due to. Therefore, the spacing loss with the magnetic head becomes too large, resulting in a problem that the electromagnetic conversion characteristics are remarkably deteriorated.
By the way, in recent years, the recording capacity of hard disks has been increasing at a very high speed. Therefore, it is desired to further increase the recording capacity of magnetic recording media used for backing up these hard disks. In magnetic recording media, higher density and higher capacity are being promoted, and the surface of the base film is required to be as smooth as possible from the viewpoint of electromagnetic conversion characteristics. However, when used as a magnetic recording tape, the friction with the magnetic head increases and the running durability decreases. That is, in order to obtain an ultra-high density magnetic recording tape, it is necessary to have means that achieves both conflicting characteristics of improved electromagnetic conversion characteristics and improved running durability.

Japanese Patent Publication No. 63-57238 JP 2002-160336 A JP 2004-234825 A

  The object of the present invention is to solve the above-mentioned conventional problems, and as a polyester film for a large-capacity magnetic recording tape capable of recording at high density, has excellent electromagnetic conversion characteristics and durability with a magnetic head. In particular, the present invention provides a polyester film that is a base suitable for applications requiring high image quality and high reliability such as DVCAM applications.

  To achieve the above object, the present invention has the following features.

[1] Polyester film for magnetic recording tape having a coating layer on the surface I of the polyester layer on the side where the magnetic surface is formed, and the coating layer on the surface I is composed of a water-soluble polymer or a water-dispersible polymer. In this coating layer, at least two kinds of inert particles having different average particle diameters are contained, and the average particle diameter of particles having the largest average particle diameter (particle L) among these inert particles is defined as D _L (nm) , The protrusion density due to particle L is N _L (pieces / mm ² ), the average particle diameter of the smallest average particle diameter (particle S) is D _S (nm), and the protrusion density due to particle S is N _{When S} (pieces / mm ² ), D _S , N _S , D _L and N _S satisfy all the following formulas (1), (2) and (3), and the surface roughness of the coating layer of surface I Polyester film for magnetic recording tapes having a thickness Ra of 1.5 to 6.0 nm and an aggregation rate of protrusions due to the particles S of less than 20% .

(1) 25 <D _L <70
(2) 1.5 <D _L / D _S <6
(3) 100 <N _S / N _L <10,000
[2] The polyester film for a magnetic recording tape according to the above [1], wherein the protrusion density N _L (pieces / mm ² ) due to the particles L is 5,000 <N _L <300,000.

  [3] The polyester film for magnetic recording tape according to [1] or [2] above, wherein the particles L and / or particles S are spherical silica particles.

  [4] A particle L and / or particle S is a polymer or copolymer of at least one monomer selected from the group consisting of styrene, alkyl acrylate ester, alkyl methacrylate ester and divinylbenzene as a constituent component The polyester film for magnetic recording tapes according to the above [1] or [2], which is a polymer particle.

  [5] The polyester film for magnetic recording tape according to any one of [1] to [4], wherein the total thickness is 4 to 9 μm.

  [6] The polyester film for magnetic recording tape according to any one of [1] to [5], wherein the polyester film contains polyethylene terephthalate or polyethylene-2,6-naphthalate as a constituent component.

  According to the present invention, it is possible to manufacture an ultra-high density magnetic recording tape that has excellent electromagnetic conversion characteristics and good running durability with a magnetic head.

  Also, by using the polyester film for magnetic recording tape of the present invention, it is possible to produce a magnetic recording tape compatible with MR heads that can perform digital recording with ultra-high density and has good running durability even when repeatedly run. can do. In particular, excellent results can be obtained when used as a base film for applications requiring severe running durability in order to achieve high image quality and high reliability such as DVCAM applications.

  In the present invention, the polymer (constituent component) constituting the polyester layer (polyester film) may be a polyester that forms a high-strength film by molecular orientation. Among them, it is preferable that polyethylene terephthalate or polyethylene-2,6-naphthalene dicarboxylate (polyethylene-2,6-naphthalate) is contained as a constituent component. In the polyethylene terephthalate and polyethylene-2,6-naphthalene dicarboxylate, it is preferable that 80 mol% or more of all the constituent components is ethylene terephthalate or ethylene-2,6-naphthalene dicarboxylate. Examples of copolymer components other than ethylene terephthalate and ethylene-2,6-naphthalenedicarboxylate include diol components such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol, p-xylene glycol, and 1,4-cyclohexanedimethanol. Adipic acid, sebacic acid, terephthalic acid (for polyethylene-2,6-naphthalenedicarboxylate), phthalic acid, isophthalic acid, 5-sodium sulfoisophthalic acid, 2,6-naphthalenedicarboxylic acid (for polyethylene terephthalate) And dicarboxylic acid components such as 2,7-naphthalenedicarboxylic acid, trifunctional or higher polyvalent carboxylic acid components such as trimellitic acid and pyromellitic acid, and p-oxyethoxybenzoic acid. The polyester may be mixed in a range in which at least one of an alkali metal salt derivative of a sulfonic acid that is non-reactive with the polyester and a polyalkylene glycol substantially insoluble in the polyester does not exceed 5% by mass. .

  In the present invention, the surface of the polyester layer on the side where the magnetic surface is formed (hereinafter referred to as surface I) is the surface on which the magnetic layer is provided and magnetic recording is performed when the magnetic tape is manufactured.

  The polyester film in the present invention may be a film having a single layer structure or a film having a multilayer structure of two or more layers by a coextrusion method or the like. For example, in the case of a two-layer structure film, it consists of a magnetic layer forming surface side polyester (hereinafter referred to as polyester P) and a polyester on the opposite side (running surface side, hereinafter referred to as polyester Q). Active particles may or may not be contained, but from the viewpoint of aggregation of the inert particles in the polyester P, it is preferable not to contain inert particles. When inert particles are included, electromagnetic conversion characteristics may be deteriorated when the magnetic tape is formed due to the influence of coarse protrusions due to aggregation of inert particles in the polyester P. The polyester Q preferably contains inert particles from the viewpoint of the rollability of the film. Polyesters P and Q may be the same type or different types.

  When the polyester P includes inert particles, preferable inert particles to be included in the polyester include, for example, (1) heat-resistant polymer particles (for example, crosslinked silicone resin, crosslinked polystyrene resin, formaldehyde resin, aromatic polyamide resin, Particles made of polyimide resin, polyamideimide resin, cross-linked polyester, etc.), (2) metal oxide (eg, aluminum oxide, titanium dioxide, silicon dioxide (silica), magnesium oxide, zinc oxide, zirconium oxide, etc.), (3) Metal carbonates (eg, magnesium carbonate, calcium carbonate, etc.), (4) metal sulfates (eg, calcium sulfate, barium sulfate, etc.), (5) carbon (eg, carbon black, graphite, diamond, etc.), and (6) Clay mineral (for example, Olin, clay, bentonite), and is made of inorganic compound particles such as. Among these, crosslinked silicone resin particles, crosslinked polystyrene resin particles, melamine-formaldehyde resin particles, polyamideimide resin particles, other aluminum oxide (alumina), titanium dioxide, silicon dioxide, zirconium oxide, synthetic calcium carbonate, barium sulfate, diamond, Or the particle | grains which consist of kaolin are preferable. More preferred are crosslinked silicone resin particles, crosslinked polystyrene resin particles, and other particles made of aluminum oxide (alumina), titanium dioxide, silicon dioxide, or calcium carbonate. These inert particles may be used alone or in combination of two or more. Different components such as a surfactant, an antistatic agent and various ester components may be added.

Examples of preferable inert particles contained in the polyester Q include (1) heat-resistant polymer particles (for example, a crosslinked silicone resin, a crosslinked polystyrene resin, a formaldehyde resin, an aromatic polyamide resin, a polyimide resin, a polyamideimide resin, a crosslinked polyester, etc. Particles), (2) metal oxides (eg, aluminum oxide, titanium dioxide, silicon dioxide (silica), magnesium oxide, zinc oxide, zirconium oxide, etc.), (3) metal carbonates (eg, magnesium carbonate, Calcium carbonate, etc.), (4) metal sulfates (eg, calcium sulfate, barium sulfate, etc.), (5) carbon (eg, carbon black, graphite, diamond, etc.), and (6) clay minerals (eg, kaolin, Clay, bentonite, etc.) Like particles consisting of UNA inorganic compound. Among these, crosslinked silicone resin particles, crosslinked polystyrene resin particles, melamine-formaldehyde resin particles, polyamideimide resin particles, other aluminum oxide (alumina), titanium dioxide, silicon dioxide, zirconium oxide, synthetic calcium carbonate, barium sulfate, diamond, Or the particle | grains which consist of kaolin are preferable. More preferred are fine particles made of crosslinked silicone resin particles, crosslinked polystyrene resin particles, and other aluminum oxide (alumina), titanium dioxide, silicon dioxide, or calcium carbonate. These inert particles may be used alone or in combination of two or more. Different components such as a surfactant, an antistatic agent and various ester components may be added.
In the present invention, a coating layer is provided on the surface I, and the coating layer contains a water-soluble polymer or a water-dispersible polymer as a constituent component.

  Preferred examples of the water-soluble polymer include cellulose derivatives such as polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose, polyester ether copolymers, water-soluble polyester copolymers, and the like. A polymer blend of polymers is particularly preferred. The water-soluble polyester copolymer is a polyester obtained by polycondensation of a dicarboxylic acid component and a glycol component. For example, a functional acid component such as a dicarboxylic acid component having a sulfonic acid group is contained in an amount of 5 mol% or more of the total carboxylic acid component. Although what gave water solubility by copolymerizing and / or 2-70 mass% copolymerizing a polyalkylene ether glycol component as a glycol component is preferable, it is not limited to these. As the dicarboxylic acid having a sulfonic acid group, 5-sulfoisophthalic acid, 2-sulfoterephthalic acid and the like, metal salts thereof, phosphonium salts and the like can be preferably used, and 5-sodium sulfoisophthalic acid is particularly preferable. As the other dicarboxylic acid component when 5-sodium sulfoisophthalic acid is copolymerized, isophthalic acid, terephthalic acid and the like are preferable, and as the glycol component, ethylene glycol, diethylene glycol and the like are preferable. The cellulose derivative particularly contributes to the formation of a fine concavo-convex structure on the film surface, and the water-soluble polyester copolymer contributes to an improvement in adhesion between the cellulose derivative and the polyester film surface.

  As the water dispersible polymer, polymethyl methacrylate emulsion, polyacrylic ester emulsion and the like can be used.

  In the present invention, the coating layer on the surface I contains at least two kinds of inert particles having different average particle sizes.

  As the material of the inert particles contained in the coating layer on the surface I, the same material or different materials may be used.

  The material is selected from the group consisting of polystyrene, polyacrylic acid methyl ester, polyacrylic acid ethyl ester, polymethacrylic acid methyl ester, polymethacrylic acid ethyl ester, and divinylbenzene. Organic materials such as tetrafluoroethylene, polyacrylonitrile, benzoguanamine, and silicone, and inorganic materials such as silica, alumina, titanium dioxide, kaolin, calcium carbonate, talc, and graphite may be used. In general, particles made of an inorganic material have high hardness and are not easily deformed, so that the magnetic head is excellent in cleaning properties, and it is easy to produce fine particles of various sizes. On the other hand, organic particles are excellent in dispersibility and have little aggregation between particles.

In the present invention, among the above-described inert particles, the average particle size of particles having the largest average particle size (particle L) is D _L (nm), and the protrusion density due to the particle L is N _L (number / piece mm ² ), D _S , where D _S (nm) is the average particle size of the smallest average particle size (particle S), and N _S (particles / mm ² ) is the protrusion density due to particle _S , N _S , D _L and N _S satisfy all of the following formulas (1), (2) and (3), and the agglomeration rate of the protrusions caused by the particles S is less than 20%.

(1) 25 <D _L <70
(2) 1.5 <D _L / D _S <6
(3) 100 <N _S / N _L <10,000
Here, when the particles L are used as a magnetic tape, the particles L play a role of reducing the friction with the magnetic head and maintaining running durability and improving the cleaning performance of the magnetic head. The average particle diameter of the particles L is 25 to 70 nm, more preferably 30 nm to 50 nm. When the average particle diameter D _L of the particles L exceeds 70 nm, falling occurs in particles, friction with the magnetic head becomes large, the running durability scraped surface may be reduced. Further, if the average particle size of the particles L is less than 25 nm, the cleaning effect of the magnetic head is lowered, and the running durability may be lowered. The number density of protrusions resulting from the particles L is 5,000 to 300,000 pieces / mm ² , and preferably 10,000 to 100,000 pieces / mm ² . When the projection density exceeds 300,000 pieces / mm ² , particles fall off, and the surface tends to be shaved and the dropout of the magnetic tape tends to increase. In addition, the spacing with the magnetic head increases, making it difficult to provide a high-density magnetic recording medium. If the number density of the protrusions caused by the particles L is less than 5,000 / mm ² , the cleaning effect of the magnetic head is lowered and the running durability tends to be lowered. Further, the particle size ratio (D _L / D _S ) between the particles L and the particles S is larger than 1.5 and smaller than 6. When the particle size ratio is larger than 6, the spacing with the magnetic head becomes large when the magnetic tape is used, and the electromagnetic conversion characteristics tend to deteriorate. In addition, particles fall off, and the surface of the magnetic tape tends to be scraped. Further, the number density ratio of projections (N _S / N _L ) by particles is 100 to 10,000, more preferably 160 to 1,000. If the projection number density ratio (N _S / N _L ) is greater than 10,000, the cleaning effect of the magnetic head is lowered and the running durability tends to be lowered. On the other hand, if the number density ratio (N _S / N _L ) is smaller than 100, the spacing with the magnetic head increases and it becomes difficult to provide a high-density magnetic recording medium. In particular, in DVCAM applications, the average particle diameter D _L of the particles _L is 35 to 45 nm, the number density of the protrusions is 10,000 to 100,000 / mm ² , and the average particle diameter of the particles S having the smallest average particle diameter D _S is 20nm or less, the number density of protrusions is in the range of 10 million / mm ² of 50 million / mm ² is considered preferable electromagnetic conversion characteristics in view of the running durability.

  Further, the aggregation rate of the protrusions caused by the particles S in the coating layer is less than 20%, more preferably less than 10%. When the aggregation rate of the protrusions is 20% or more, the spacing loss with the magnetic head is increased due to the coarse protrusions, so that the electromagnetic conversion characteristics may be deteriorated.

  From the viewpoint of easily satisfying the above-mentioned characteristics, the particles L and / or particles S are preferably spherical silica particles, and the particles L and / or particles S are styrene, alkyl acrylate ester, methacrylic acid. It is also preferred that the polymer particles comprise a polymer or copolymer of at least one monomer selected from the group consisting of alkyl esters and divinylbenzene.

  In the present invention, the surface roughness Ra value on the coating layer of the surface I is 1.5 to 6 nm, more preferably 2.5 nm or more and less than 5 nm. When the Ra value exceeds 6 nm, the running durability of the magnetic tape with the magnetic head improves, but the electromagnetic conversion characteristics tend to deteriorate. Further, if the Ra value is less than 1.5, friction with the magnetic head increases and running durability tends to decrease.

  In the present invention, the surface opposite to surface I (hereinafter referred to as surface II) is provided with a coating layer rougher than surface I containing a lubricant such as silicone, or contains more inert particles. It is particularly preferable to use a two-layer structure in which polyester Q layers to be laminated are laminated, or further provided with a rough coating layer thereon. When a coating layer is provided on the surface II, the slipperiness between the films is improved, and handling properties such as winding and unwinding of the film in the processing step are improved.

  As the coating layer provided on the surface II, any coating layer may be used as long as it is slippery and difficult to be scraped, and has a function of not allowing degradation products from the polyester film to pass through. It is preferably formed from a composition in which silicone and a silane coupling agent are added to a water-soluble polymer and / or a water-dispersible polymer. As the water-soluble polymer used for the coating layer, cellulose derivatives such as polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyester ether copolymers, water-soluble polyester copolymers, and the like can be used. As the water-dispersible polymer emulsion, polymethyl methacrylate emulsion, polyacrylate emulsion, and the like can be used.

  As the silicone, a polymer in which a large number of organosilicon compounds having a siloxane bond in the molecular skeleton such as polydimethylsiloxane are connected by a covalent bond can be used. Silicone improves the slipperiness of the coating layer, and ensures the runnability and abrasion resistance of the film on the surface II side. Moreover, blocking between films when a polyester film is wound is prevented. A fluorine compound may be used as a lubricant.

  Examples of silane coupling agents include organosilicon monomers having two or more different reactive groups in the molecule, and one of the reactive groups is a methoxy group, an ethoxy group, a silanol group, etc. One reactive group is a vinyl group, an epoxy group, a methacryl group, an amino group, a mercapto group, or the like. The reactive group is selected from those that bind to the side chain, terminal group and polyester of the water-soluble polymer. As the silane coupling agent, vinyltrichlorosilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, γ- Glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, etc. Applicable. The silane coupling agent contributes to prevention of release of the silicone from the lubricant layer, and further contributes to improvement in adhesion between the coating layer and the polyester.

  The total thickness of the polyester film in the present invention including the polyester film and the coating layer is preferably 4 to 9 μm, and more preferably 5 to 7 μm.

  The polyester film in the present invention can be produced by various methods. For example, in order to obtain a laminated polyester film having a two-layer structure, it is preferably produced by a coextrusion method, and the formation of a coating layer or a coating layer on the surface I and the surface II is preferably carried out by a coating method.

  Hereinafter, the example of the manufacturing method of the polyester film in this invention is demonstrated.

  In order to obtain a polyester film having a two-layer structure by converting the polyester P containing inert particles as necessary in an extruder into a molten state and further filtering with a filter as it is, another extruder After the polyester Q containing the inert particles is melted and subjected to high-accuracy filtration with another filter, each is led to a feed block and laminated in a molten state. The ratio of the lamination thickness of polyester P and polyester Q can be set to a desired lamination thickness ratio by adjusting the extrusion amount of the extruder of each layer. After melting, preferably laminating in this way, after extrusion or co-extrusion from the die at a melting point (Tm) to (Tm + 70) ° C., it is rapidly cooled and solidified on a casting drum at 10 to 50 ° C. A film sheet is obtained. Thereafter, the unstretched laminated film is stretched in a uniaxial direction (longitudinal direction or lateral direction) at a temperature of (Tg) to (Tg + 80) ° C. (where Tg is the glass transition temperature of the polyester) and a magnification of 2 to 8 times. And preferably, the film is stretched by 3 to 7.5 times. Further, a coating liquid for forming a coating layer or a coating layer on the surface I and, if necessary, the surface II is applied to the surface of the film and dried, and then, in the direction perpendicular to the stretching direction (perpendicular to the uniaxial stretching direction) The film of the present invention can be produced by a production method in which the film is stretched and oriented (in the direction) and heat-set.

  As solid content concentration of the coating liquid applied in order to form a membrane | film | coat layer on the surface I, 0.01-1 mass% is preferable, More preferably, it is 0.1-0.6 mass%. In addition, other components such as other surfactants, stabilizers, dispersants, ultraviolet absorbers, thickeners, antistatic agents and the like may be added to the aqueous coating liquid as long as the effects of the present invention are not hindered. it can. In order to make the aggregation rate of the protrusions caused by the particles contained in the coating layer, particularly the aggregation rate of the protrusions caused by the particles S, less than 20%, the pH of the coating liquid applied to the surface I is adjusted to 8-11. It is preferable to do. More preferably, the pH is 9 to 10.5. If the pH is less than 8, the particles tend to aggregate easily, so it is important to manage the pH. In order to adjust the pH of the coating solution, an appropriate amount of acid / base component such as hydrochloric acid or sodium hydroxide aqueous solution can be used. Moreover, it is preferable that the coating liquid temperature just before apply | coating to a film adjusts to 12 to 28 degreeC, More preferably, it adjusts to 19 to 25 degreeC, and it applies. When the coating liquid is applied to a film at a temperature of 28 ° C. or higher, solids such as water-soluble polymers, water-dispersible polymers, and silane coupling agents may be generated. Further, when the coating liquid temperature is less than 12 ° C., the particles tend to aggregate.

  The solid content concentration of the coating liquid applied to form the coating layer on the surface II is preferably 0.01 to 1% by mass, more preferably 0.3 to 0.8% by mass. In addition, other components such as other surfactants, stabilizers, dispersants, ultraviolet absorbers, thickeners, antistatic agents and the like may be added to the aqueous coating liquid as long as the effects of the present invention are not hindered. it can.

  Biaxial stretching can be performed, for example, by sequential biaxial stretching or simultaneous biaxial stretching, but if desired, further stretching in the longitudinal direction or the transverse direction, or both (longitudinal and transverse directions) before heat setting. The so-called strengthening type with increased mechanical strength can also be used.

  In order to form the coating layer on the surface I, as described above, a method of applying a coating liquid having a predetermined composition and concentration on the base film after the stretching in the uniaxial direction is taken. As a coating method, any of a doctor blade method, a gravure method, a reverse roll method, and a Mayer bar method may be used. The Ra value of the surface I can be controlled by adjusting the amount of particles in the coating layer. A similar method may be used for forming the coating layer on the surface II, and the thickness of the coating layer can be controlled to a desired value by adjusting the solid content concentration of the coating solution and the coating solution thickness.

  When the polyester film of the present invention is used as a base film of a magnetic recording medium, especially for magnetic tape applications in which digital data is recorded and reproduced by an MR head, high-density recording is possible and excellent results are obtained. be able to. In particular, it can be suitably used as a base film for applications requiring high image quality and high reliability such as commercial VTRs.

  The measurement method used in this example is shown below.

(1) Average particle diameter of particles L and particles S (1-1) Measurement of average particle diameter of surface I film layer The average particle diameter of the inert particles contained in the surface I film layer is film Inert particles before applying to the sample were diluted with aqueous ammonia at pH 11 and filtered through a 0.2 μm filter, and the average particle size (with a value measured by “NICOMP model 380 Dynamic Light Scattering” manufactured by Particle Sizing System, Inc. was used. D _L and D _S ).

(1-2) Measurement of number density of protrusions caused by particles on surface I The number density of two or more kinds of particles having different average particle diameters on the film layer provided on surface I is By providing a gold thin film deposition layer with a thickness of 20 to 30 nm by a gold sputtering apparatus, and observing the particles L at an enlargement magnification of 50,000 times with an electron microscope (preferably a scanning electron microscope), and taking 10 photographs. Measure (the area per photo is 3.9 × 10 ⁻⁶ mm ² ), and the particles S are measured by observing at a magnification of 10,000 times and taking 10 photos (1 photo) The area per unit area is 9.7 × 10 ⁻⁵ mm ² ). From the 10 photographs taken, the number of particles having each particle diameter observed in the photograph was counted and converted to the number of particles per 1 mm ² to obtain the number of particles.

(1-3) Measurement of the agglomeration rate of protrusions caused by particles on the surface I When the number density of protrusions in (1-2) is observed, certain protrusions are located in the vicinity (within the distance of the major axis of the protrusions). It is confirmed whether or not there is a projection, and if it exists, the projection is regarded as a projection present in an aggregated state. The number of protrusions present in this aggregated state is divided by the total number of protrusions in the same field of view to determine the aggregation rate (%).

(2) Surface roughness Ra value and Rz value of film The surface roughness Ra value and Rz value of the film surface were measured using an atomic force microscope (scanning probe microscope). Specifically, using a desktop small probe microscope (“Nanopics” 1000) manufactured by Seiko Instruments Inc., an atomic force microscope measurement scan was performed in a damping mode in the range of 40 μm square. From the profile curve of the surface obtained, Ra was calculated from the arithmetic average roughness corresponding to JIS / B0601, 1996 / Ra, and Rz value was calculated from the ten-point average roughness. The details of the measurement conditions are as follows.
Measuring surface Surface I Surface II
Measurement mode Damping mode Damping mode Measurement direction Width direction Width direction measurement area 40 × 40μm 40 × 40μm
Scan speed 380s / FRAME 380s / FRAME
Number of scans 512 lines 512 lines Amplitude mode LL (20%) HH (100%)
(3) Total thickness of the entire film The total thickness of the entire film was measured at 10 points randomly with a micrometer, and the average value was used.

(4) Young's modulus in the longitudinal direction of the film The Young's modulus is determined according to ASTM-D882-02 (2002) from the rising slope of the start point in the stress-strain curve obtained by tensile test measurement, and is expressed in MPa. The sample width and effective length were 10 mm and 100 mm, respectively. The tensile speed was 100 mm / min.

(5) Characteristics of magnetic tape (MICRO MV tape) The characteristics of the magnetic tape were evaluated as follows.

  A cobalt-oxygen film having a thickness of 50 nm was formed on the surface I of the film of the present invention using a vacuum deposition apparatus. Next, a diamond-like carbon film was formed to a thickness of 10 nm on the cobalt-oxygen film layer by sputtering, and a fluorine-containing fatty acid ester lubricant was applied to a thickness of 3 nm. Subsequently, a back coat layer made of carbon black, polyurethane, and silicone was provided on the surface II with a thickness of 500 nm, slitted to a width of 3.8 mm by a slitter, and wound on a reel to produce a magnetic tape (MICRO MV tape). .

(5-1) Evaluation of running durability The running durability of magnetic tape (MICRO MV tape) is recorded in a quiet room using a commercially available MICRO MV video camera (MICRO MV video camera) and played for 1 minute. This was evaluated by counting the number of block-like mosaics (dropout (DO) number) that appeared on the screen. The number of DO was first examined for initial characteristics (initial number of DO) after tape production at room temperature (25 ° C.). Next, tape reproduction was repeated 200 times over the entire length, and the number of DOs during the 200th reproduction was measured.

Running durability is
(Number of DOs per minute during 200th playback)-(Number of DOs per minute during initial playback)
Was determined as follows.

0 / min: ◎
1-2 pieces / min: ○
3-5 pieces / min: △
6 or more / minute: ×
(5-2) Evaluation of Electromagnetic Conversion Characteristics (C / N) The tape produced above was measured for C / N of 7 MHz ± 1 MHz using a commercially available MICRO MV video camera (MICRO MV video camera). It was. This C / N was compared with a commercially available MICRO MV tape and judged as follows.

+3 dB or more: ◎
+2 dB or more to less than +3 dB: ○
+1 dB or more and less than +2 dB: Δ
Less than +1 dB: ×
Next, based on an Example, this invention is demonstrated.

[Example 1]
(Method for producing polyester P)
100 parts by mass of dimethyl terephthalate, 70 parts by mass of ethylene glycol, and 0.09 parts by mass of calcium acetate were placed in a reactor and subjected to a transesterification reaction at 180 to 210 ° C. to distill methanol. When the transesterification reaction was completed, 0.02 part by mass of phosphoric acid and 0.03 part by mass of antimony trioxide were added, and then the pressure in the system was gradually reduced to 1 mmHg or less in 60 minutes. At the same time, the temperature was gradually raised to 290 ° C. The polycondensation reaction was carried out for 2 hours to obtain polyethylene terephthalate (PET) substantially free of inert particles.

(Production method of polyester Q)
100 parts by mass of dimethyl terephthalate, 70 parts by mass of ethylene glycol, and 0.09 parts by mass of calcium acetate were placed in a reactor and subjected to a transesterification reaction at 180 to 210 ° C. to distill methanol. When the transesterification reaction was completed, 0.02 part by mass of phosphoric acid and 0.03 part by mass of antimony trioxide were added, and then the pressure in the system was gradually reduced to 1 mmHg or less in 60 minutes. At the same time, the temperature was gradually raised to 290 ° C. A polycondensation reaction was carried out for 2 hours, and then a cylindrical chip having a diameter of about 5 mm and a length of about 7 mm was formed by extrusion into water from a discharge nozzle. Polyester Q was obtained by adding 0.50 wt% of polystyrene spheres having a number average particle diameter of 300 nm to the polymer thus obtained.

  The obtained polyester P and polyester Q were each dried at 170 ° C. for 3 hours, adjusted to have a thickness ratio of 6: 1, and supplied to two extruders by coextrusion. After melting at 300 ° C. and high-precision filtration with a steel wire filter with an average opening of 1 μm, polyester B is laminated on one side of polyester A using a multi-manifold type coextrusion die, on a casting drum at a temperature of 25 ° C. To obtain an unstretched film. Next, the unstretched film thus obtained was preheated and longitudinally stretched three times at 110 ° C. by a roll stretching method.

In the step after the longitudinal stretching, an aqueous solution having the following composition and concentration was applied to the outside of the one-side surface I by a Mayer bar method so that the solid content application amount was 25 mg / m ² .

Composition of aqueous solution applied to surface I Water 99.40% by mass
Methylcellulose 0.10 mass%
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.47% by mass
Particle L Spherical silica particles having an average particle diameter of 45 nm 1.2 × 10 ⁻³ mass%
Particle S Spherical silica particles having an average particle diameter of 18 nm 3.6 × 10 ⁻² mass%
Further, in order to provide the coating layer B on the surface II side, an aqueous solution having the following composition and concentration was applied to the outside of the polyester layer B by an air knife method so that the solid content application amount was 45 mg / m ² .

Composition of coating aqueous solution on surface II Water 99.44% by mass
Methylcellulose 0.26% by mass
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.29 mass%
Aminoethylsilane coupling agent 1.1 × 10 ⁻³ mass%
Then, it extended | stretched 4 times at 110 degreeC in the horizontal direction with the stenter. The obtained biaxially stretched film was heat-fixed with hot air of 220 ° C. for 4 seconds to obtain a biaxially oriented polyester film. This was slit into a small width with a slitter and wound into a roll around a cylindrical core to prepare a polyester film having a thickness of 6.3 μm.

  The characteristics of the obtained polyester film are shown in Tables 1 and 2.

[Example 2]
A polyester film having a thickness of 6.1 μm was obtained in the same manner as in Example 1 except that the coating aqueous solution on the surface I side of Example 1 was changed as follows.

Composition of aqueous coating solution on surface I
99.55% by weight of water
Methylcellulose 0.091 mass%
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.47% by mass
Particle L Spherical silica particles having an average particle size of 41 nm 1.1 × 10 ⁻⁵ mass%
Particle S Particle of styrene-methyl acrylate-divinylbenzene copolymer having an average particle diameter of 20 nm 3.8 × 10 ⁻⁴ mass%
The characteristics of the obtained polyester film are shown in Tables 1 and 2.

[Example 3]
A polyester film having a thickness of 6.1 μm was obtained in the same manner as in Example 1 except that the coating aqueous solution on the surface I side of Example 1 was changed as follows.

Composition of aqueous coating solution on surface I
99.40% by mass of water
Methylcellulose 0.089 mass%
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.32 mass%
Particle L Spherical silica particles having an average particle diameter of 40 nm 9.5 × 10 ⁻⁶ mass%
Particle S Spherical silica particles having an average particle diameter of 25 nm 3.8 × 10 ⁻⁴ mass%
The characteristics of the obtained polyester film are shown in Tables 1 and 2.

[Example 4]
A polyester film having a thickness of 6.4 μm was obtained in the same manner as in Example 1 except that the aqueous coating solution on the surface I side of Example 1 was changed as follows.

Composition of aqueous coating solution on surface I
99.55% by weight of water
Methylcellulose 0.089 mass%
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.32 mass%
Particle L Spherical silica particles having an average particle diameter of 65 nm 2.5 × 10 ⁻⁵ mass%
Particle S Spherical silica particles having an average particle diameter of 18 nm 3.6 × 10 ⁻⁴ mass%
The characteristics of the obtained polyester film are shown in Tables 1 and 2.

[Example 5]
A polyester film having a thickness of 5.9 μm was obtained in the same manner as in Example 1 except that the aqueous coating solution on the surface I side of Example 1 was changed as follows.

Composition of aqueous coating solution on surface I
99.55% by weight of water
Methyl cellulose 0.087 mass%
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.47% by mass
Particle L Spherical silica particles having an average particle diameter of 41 nm 9.4 × 10 ⁻⁶ mass%
Particle S Spherical silica particles having an average particle diameter of 12 nm 3.6 × 10 ⁻⁴ mass%
Other particles Particles of styrene-methyl acrylate-divinylbenzene copolymer having an average particle diameter of 20 nm 1.8 × 10 ⁻² mass%
[Example 6]
A polyester film having a thickness of 6.3 μm was obtained in the same manner as in Example 1 except that the aqueous coating solution on the surface I side of Example 1 was changed as follows.

Composition of aqueous coating solution on surface I
99.41% by mass of water
Carboxymethyl cellulose 0.087% by mass
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.47% by mass
Particle L Spherical silica particles having an average particle diameter of 41 nm 8.7 × 10 ⁻⁶ mass%
Particle S Spherical silica particles having an average particle diameter of 18 nm 3.6 × 10 ⁻⁴ mass%
The characteristics of the obtained polyester film are shown in Tables 1 and 2.

[Example 7]
A polyester film having a thickness of 6.3 μm was obtained in the same manner as in Example 1 except that the aqueous coating solution on the surface I side of Example 1 was changed as follows.

Composition of aqueous coating solution on surface I
99.41% by mass of water
Hydroxymethylcellulose methylcellulose 0.087 mass%
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.47% by mass
Particle L Spherical silica particles having an average particle diameter of 41 nm 9.3 × 10 ⁻⁶ mass%
Particle S Particles of styrene-methyl acrylate-divinylbenzene copolymer having an average particle diameter of 20 nm 3.3 × 10 ⁻⁴ mass%
The characteristics of the obtained polyester film are shown in Tables 1 and 2.

[Example 8]
A polyester film having a thickness of 6.3 μm was obtained in the same manner as in Example 1 except that the aqueous coating solution on the surface I side of Example 1 was changed as follows.

Composition of aqueous coating solution on surface I
99.55% by weight of water
Methylcellulose 0.086% by mass
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.32 mass%
Particle L Spherical silica particles having an average particle diameter of 60 nm 1.3 × 10 ⁻⁴ mass%
Particle S Spherical silica particles having an average particle diameter of 18 nm 3.6 × 10 ⁻⁴ mass%
The characteristics of the obtained polyester film are shown in Tables 1 and 2.

[Example 9]
A polyester film having a thickness of 6.3 μm was obtained in the same manner as in Example 1 except that the aqueous coating solution on the surface I side of Example 1 was changed as follows.

Composition of aqueous coating solution on surface I Water 99.61% by mass
Methylcellulose 0.093 mass%
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.29 mass%
Particle L Spherical silica particles having an average particle diameter of 45 nm 1.6 × 10 ⁻⁵ mass%
Particle S Spherical silica particles having an average particle diameter of 8 nm 8.6 × 10 ⁻⁵ mass%
The characteristics of the obtained polyester film are shown in Tables 1 and 2.

[Example 10]
A polyester film having a thickness of 6.7 μm was obtained in the same manner as in Example 1 except that the aqueous coating solution on the surface I side of Example 1 was changed as follows.

Composition of aqueous coating solution on surface I Water 99.65% by mass
Methyl cellulose 0.087 mass%
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.26 mass%
Particle L Spherical silica particles having an average particle diameter of 41 nm 1.0 × 10 ⁻⁶ mass%
Particle S: Spherical silica particles having an average particle diameter of 12 nm 1.1 × 10 ⁻⁴ mass%
The characteristics of the obtained polyester film are shown in Tables 1 and 2.

[Example 11]
A polyester film having a thickness of 6.3 μm was obtained in the same manner as in Example 1 except that the aqueous coating solution on the surface I side of Example 1 was changed as follows.

Composition of aqueous coating solution on surface I Water 99.64% by mass
Methylcellulose methylcellulose 0.087 mass%
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.26 mass%
Particle L Particle of styrene-methyl acrylate-divinylbenzene copolymer having an average particle diameter of 30 nm 3.5 × 10 ⁻⁶ mass%
Particle S Spherical silica particles having an average particle diameter of 12 nm 1.5 × 10 ⁻⁴ mass%
The characteristics of the obtained polyester film are shown in Tables 1 and 2.

[Comparative Example 1]
A polyester film having a thickness of 6.4 μm was obtained in the same manner as in Example 1 except that the aqueous coating solution on the surface I side of Example 1 was changed as follows.

Composition of aqueous coating solution on surface I Water 99.59% by mass
Methylcellulose 0.089 mass%
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.32 mass%
Particle L Spherical silica particles with an average particle size of 80 nm 3.3 × 10 ⁻⁵ mass%
Particle S Spherical silica particles having an average particle diameter of 12 nm 4.3 × 10 ⁻⁵ mass%
The characteristics of the obtained polyester film are shown in Tables 1 and 2.

[Comparative Example 2]
A polyester film having a thickness of 6.1 μm was obtained in the same manner as in Example 1 except that the coating aqueous solution on the surface I side of Example 1 was changed as follows.

Composition of aqueous coating solution on surface I Water 99.54% by mass
Methylcellulose 0.093 mass%
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.32 mass%
Particle L Spherical silica particles having an average particle diameter of 45 nm 6.8 × 10 ⁻⁵ mass%
Particle S Particle of styrene-methyl acrylate-divinylbenzene copolymer having an average particle diameter of 20 nm 4.5 × 10 ⁻⁴ mass%
The characteristics of the obtained polyester film are shown in Tables 1 and 2.

[Comparative Example 3]
A polyester film having a thickness of 6.4 μm was obtained in the same manner as in Example 1 except that the aqueous coating solution on the surface I side of Example 1 was changed as follows.

Composition of aqueous coating solution on surface I Water 99.41% by mass
Methylcellulose 0.10 mass%
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.32 mass%
Particle L Spherical silica particles having an average particle diameter of 41 nm 1.3 × 10 ⁻⁵ mass%
Particle S Spherical silica particles having an average particle diameter of 30 nm 1.7 × 10 ⁻³ mass%
The characteristics of the obtained polyester film are shown in Tables 1 and 2.

[Comparative Example 4]
A polyester film having a thickness of 6.2 μm was obtained in the same manner as in Example 1 except that the aqueous coating solution on the surface I side of Example 1 was changed as follows.

Composition of aqueous coating solution on surface I Water 99.58% by mass
Methylcellulose 0.093 mass%
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.32 mass%
Particle L Spherical silica particles having an average particle diameter of 41 nm 3.5 × 10 ⁻⁵ mass%
Particle S Spherical silica particles having an average particle diameter of 12 nm 7.2 × 10 ⁻⁵ mass%
The characteristics of the obtained polyester film are shown in Tables 1 and 2.

[Comparative Example 5]
A polyester film having a thickness of 6.3 μm was obtained in the same manner as in Example 1 except that the aqueous coating solution on the surface I side of Example 1 was changed as follows.

Composition of aqueous coating solution on surface I Water 99.57% by mass
Methylcellulose 0.093 mass%
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.32 mass%
Particle L Spherical silica particles having an average particle diameter of 20 nm 2.6 × 10 ⁻⁶ mass%
Particle S Spherical silica particles having an average particle diameter of 12 nm 1.4 × 10 ⁻⁴ mass%
The characteristics of the obtained polyester film are shown in Tables 1 and 2.

[Comparative Example 6]
A polyester film having a thickness of 6.3 μm was obtained in the same manner as in Example 1 except that the aqueous coating solution on the surface I side of Example 1 was changed as follows.

Composition of aqueous coating solution on surface I Water 99.56% by mass
Methylcellulose 0.093 mass%
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.32 mass%
Particle L Spherical silica particles having an average particle diameter of 41 nm 1.3 × 10 ⁻⁵ mass%
Particle S Spherical silica particles having an average particle diameter of 12 nm 3.2 × 10 ⁻⁴ mass%
The characteristics of the obtained polyester film are shown in Tables 1 and 2.

[Comparative Example 7]
A polyester film having a thickness of 6.1 μm was obtained in the same manner as in Example 1 except that the coating aqueous solution on the surface I side of Example 1 was changed as follows.

Composition of coating aqueous solution on surface I Water 99.49% by mass
Methylcellulose 0.093 mass%
Water-soluble polyester (1: 1 copolymer of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.32 mass%
Particle L Spherical silica particles having an average particle diameter of 41 nm 1.3 × 10 ⁻⁵ mass%
Particle S: Spherical silica particles having an average particle diameter of 18 nm 9.7 × 10 ⁻⁴ mass%
The characteristics of the obtained polyester film are shown in Tables 1 and 2.

  As is apparent from Table 1, the magnetic recording tape manufactured using the polyester film according to the present invention as a base film is a magnetic recording tape that has excellent electromagnetic conversion characteristics and good running durability even when repeatedly run. there were.

Claims (6)

A polyester film for a magnetic recording tape in which a film layer is provided on the surface I of the polyester layer on the magnetic surface forming side, and the film layer on the surface I comprises a water-soluble polymer or a water-dispersible polymer as a constituent component. The coating layer contains at least two kinds of inert particles having different average particle diameters. The average particle diameter of particles having the largest average particle diameter (particle L) among these inert particles is D _L (nm), and particle L N _S (number of protrusions density projection density due to N _L (number / mm ^2), most having an average particle size less particles having an average particle diameter D _S of the (particles S) (nm), and the particles S due to / Mm ² ), D _S , N _S , D _L and N _S satisfy all of the following formulas (1), (2) and (3), and the surface roughness Ra of the coating layer on the surface I is Polyester film for magnetic recording tapes having a projection aggregation ratio of less than 20% due to particles S of 1.5 to 6.0 nm. Lum.
(1) 25 <D _L <70
(2) 1.5 <D _L / D _S <6
(3) 100 <N _S / N _L <10,000 The polyester film for magnetic recording tape according to claim 1, wherein the protrusion density N _L (pieces / mm ² ) resulting from the particles L is 5,000 <N _L <300,000. The polyester film for magnetic recording tape according to claim 1 or 2, wherein the particles L and / or the particles S are spherical silica particles. Polymer in which particle L and / or particle S is a polymer or copolymer of at least one monomer selected from the group consisting of styrene, alkyl acrylate ester, alkyl methacrylate ester and divinylbenzene The polyester film for magnetic recording tape according to claim 1, wherein the polyester film is a particle. The polyester film for magnetic recording tapes according to any one of claims 1 to 4, wherein the total thickness is 4 to 9 µm. The polyester film for magnetic recording tape according to claim 1, wherein the polyester film contains polyethylene terephthalate or polyethylene-2,6-naphthalate as a constituent component.