JP2013025847A - Polyester film for magnetic recording tape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester film to be used as a base suitable for a data recording tape, which is excellent in productivity and electromagnetic conversion characteristics of a base film with fewer errors and particularly, achieves high-density magnetic recording, as a polyester film for a magnetic recording tape with a large capacity allowing high-density recording.SOLUTION: The polyester film for a magnetic recording tape is a laminate film including a polyester layer A and a polyester layer B, a coating layer I on a surface A of the polyester layer A in the opposite side to the polyester layer B, and a surface B as the surface of the polyester layer B in the opposite side to the polyester layer A, and satisfies the following conditions (a) to (d). (a) The coating layer I provided on the surface A contains inert particles I having an average particle diameter of 5 to 60 nm; the average surface roughness on the coating layer I is 2 to 6 nm; and dents having a depth of 7 nm or more are present by 5,000/mmor less on the coating layer I. (b) The polyester layer A is a polyester layer containing substantially no inert particles and having a layer thickness of 3.0 μm or more. (c) The polyester layer B is a polyester layer containing inert particles B having an average particle diameter of 0.1 to 1.0 μm. (d) The surface B shows an average surface roughness Ra of 8 to 20 nm and a ten-point average roughness Rz of 300 nm or less.

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. Biaxially oriented polyester films are used for digital video tapes, computer backup tapes (hereinafter referred to as data tapes), and the like.

  As an example represented by a magnetic recording medium, a consumer digital video tape put into practical use in 1996 has a Co metal magnetic thin film on a base film and a surface coated with a diamond-like carbon film for Hi8. Despite the smoothness of the surface properties compared to vapor deposition (ME) tape, it has good durability. As the base film, (1) a composite film in which a layer A made of a thermoplastic resin and a layer B made of a thermoplastic resin containing fine particles are laminated (see, for example, Patent Document 1), (2) a smooth film A film made of a polyester film and having a non-magnetic surface-side coating layer mainly composed of a lubricant (see, for example, Patent Document 2) is used, and the surface roughness of the metal magnetic film formation is smaller than that of the Hi8ME tape base. Base film is used.

  However, such a smooth digital video tape for consumer use is obtained by the influence of the foreign matter adhering to the cooling can in the vapor deposition process because the electromagnetic conversion characteristics change greatly due to the surface waviness of the magnetic surface. The dropout (DO) characteristics of this change greatly.

  The tape produced from the above (1) had a large variation in surface waviness of the magnetic surface of the tape, and a large variation in electromagnetic conversion characteristics. Further, the technique (2) has a drawback that the coating layer mainly composed of the lubricant on the surface of the non-magnetic surface tends to be scraped or peeled off by a vapor deposition process, in particular, a vacuum evaporation cooling can, thereby increasing DO. there were.

  In order to solve this problem, (3) a ferromagnetic metal thin film layer is provided on one surface A of the polyester film, the SRa value of the ferromagnetic metal thin film layer is 2 to 5 nm, the SRz value is 40 to 70 nm, the surface undulation A magnetic tape characterized by a thickness of less than 30 nm (see, for example, Patent Document 3) is used, and the tape with good electromagnetic conversion characteristics can be obtained by improving the shaving with a cooling can and reducing the surface waviness. can get.

  However, in data tapes that perform magnetic recording at a higher density in recent years, the surface state of the base film greatly affects the surface properties of the magnetic layer of the magnetic tape due to the very small size of the track. As a result, the recording / reproduction signal is noisy, which causes a problem in data reproduction failure. For this reason, in the above high-density magnetic recording medium, it is desirable that the surface of the base film on which the magnetic layer is formed is as smooth as possible from the viewpoint of electromagnetic conversion characteristics. As a smooth base film, (4) a ferromagnetic metal thin film type used in a perpendicular magnetization recording system in which a film layer is provided on at least the surface I on the side of forming a magnetic surface of a polyester layer containing substantially no inert particles. A polyester film for magnetic recording media (see, for example, Patent Document 4) and a magnetic recording tape in which a coating layer is provided on the surface I of the polyester layer on the side where the magnetic surface is to be formed. A polyester film for surface, wherein the coating layer of surface I comprises a water-soluble polymer or a water-dispersible polymer as a constituent component, and the coating layer contains at least two kinds of inert particles having different average particle sizes A film (see, for example, Patent Document 5) has been proposed.

  On the other hand, it is desirable that the surface of the base film is as rough as possible from the viewpoint of handling such as film formation of the base film, conveyance in the film forming process, scratching, winding and unwinding. This is because if the film surface is too flat, the slipping property between the film and the film deteriorates, blocking phenomenon occurs, and the shape (roll formation) when wound on a roll deteriorates, resulting in a decrease in product yield. This increases the manufacturing cost of the product. In this way, conflicting characteristics are required from the viewpoint of electromagnetic conversion characteristics and handling characteristics. Therefore, as represented by (3) above, in the design of the base film, the surface on the side on which the magnetic layer is formed is a smooth surface, while the surface on the side opposite to the surface on which the magnetic layer is formed has a rough surface. A formed base film is generally used.

  In the above high density magnetic recording media (3), (4), and (5), the surface on the side on which the smooth magnetic layer is formed is caused by the roughness and protrusions on the opposite side roughened for handling. When rolled into a roll, the effect of transfer appears remarkably. It has been newly found that the surface of the magnetic layer, which is inherently smooth in order to achieve high-density recording, is recessed by several nanometers, which may cause deterioration of electromagnetic conversion characteristics and noise, affecting the smooth magnetic layer surface. No base film surface design was required.

Japanese Patent Publication No. 1-263338 Japanese Examined Patent Publication No. 4-33273 JP-A-10-172126 JP 2010-79995 A JP 2010-225249 A

  An object of the present invention is to solve the above-mentioned conventional problems, have a low noise, excellent electromagnetic conversion characteristics, excellent base film productivity, and high-density recording polyester film for magnetic recording tapes. In particular, it is to provide a polyester film serving as a base suitable for data backup applications of computers.

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

  (1) It has a polyester layer A and a polyester layer B, has a coating layer I on the surface A of the polyester layer A opposite to the polyester layer B, and has a surface of the polyester layer B opposite to the polyester layer A. A polyester film for a magnetic recording tape which is a laminated film having a surface B and satisfies the following (a) to (d).

(A) The coating layer I provided on the surface A includes inert particles I having an average particle diameter of 5 to 60 nm, the average surface roughness Ra on the coating layer I is 2 to 6 nm, and the depth on the coating layer I The number of dents of 7 nm or more is 5,000 / mm ² or less.

  (B) The polyester layer A is a polyester layer containing substantially no inert particles, and has a layer thickness of 3.0 μm or more.

  (C) The polyester layer B is a polyester layer containing inert particles B having an average particle size of 0.1 to 1.0 μm.

  (D) The surface B has an average surface roughness Ra of 8 to 20 nm and a ten-point average surface roughness Rz of 300 nm or less.

(2) The polyester film for magnetic recording tapes according to (1) above, wherein the coating layer II made of an organic compound is provided on the surface B at a solid mass of 10 to 50 mg / m ² .

  (3) The polyester film for magnetic recording tape according to (1) or (2), wherein the average particle diameter dB (μm) of the inert particles B and the thickness tB (μm) of the polyester layer B satisfy the following formula: .

0.2 ≦ dB / tB ≦ 3
(4) The polyester film for magnetic recording tapes according to any one of (1) to (3), wherein the total thickness is 4 to 9 μm.

  (5) The polyester film for magnetic recording tapes according to any one of (1) to (4), 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 is extremely excellent in electromagnetic conversion characteristics.

  In addition, when the polyester film for magnetic recording tape of the present invention is used, it is possible to perform digital recording with ultra-high density, and in particular, it is used as a base film for computer backup applications requiring high-density recording and high reliability. Then, excellent results can be obtained, which is preferable.

  The laminated film in the present invention is a polyester film having a two-layer structure of a polyester layer A and a polyester layer B by a coextrusion method or the like. The polyester layer A is a surface on which a magnetic layer is provided when a magnetic tape is manufactured and magnetic recording is performed (the surface on which the coating layer I is provided, hereinafter referred to as the surface A). On the other hand, the polyester layer B on the side opposite to the surface A of the polyester layer A needs to contain inert particles B from the viewpoint of winding property in order to impart winding property of the film.

  In the present invention, the polymer constituting the polyester layer A (hereinafter referred to as polyester a) and the polymer constituting the polyester layer B (hereinafter referred to as polyester b) may be any 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. . Polyesters a and b may be the same type or different types.

  Polyester a contains substantially no inert particles. The phrase “substantially containing no inert particles” means that no catalyst residue is actively deposited or inert particles are not added. Specifically, an inert particle having a particle size of 0.05 μm or more is used. The content of the active particles is preferably less than 0.001% by mass based on the mass of the polyester a. When the inert particles are substantially contained, coarse protrusions due to aggregation of the inert particles in the polyester a may interfere with the precise surface design of the magnetic tape, or deformation of the surface A by the inert particles may cause the magnetic tape. When this is done, the electromagnetic conversion characteristics will be greatly reduced and noise will increase.

  Preferred inert particle B components to be included in polyester b include, for example, (1) heat-resistant polymer particles (for example, crosslinked silicone resin, crosslinked polystyrene resin, formaldehyde resin, aromatic polyamide resin, polyimide resin, polyamideimide resin, crosslinked) Particles made of polyester), (2) metal oxides (for example, aluminum oxide, titanium dioxide, silicon dioxide (silica), magnesium oxide, zinc oxide, zirconium oxide, etc.), (3) metal carbonates (for example, carbonic acid) Magnesium, 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.) It includes particles of inorganic compounds 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 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.

  The average particle diameter of the inert particles B is 0.1 μm to 1 μm, preferably 0.2 μm to 0.5 μm. Further, two or more kinds of inert particles B having different average particle diameters may be used. In that case, the average particle diameter of the particles having the largest average particle diameter must be less than 1 μm. Moreover, when using the inert particle B which has 2 types of average particle diameters, the mass of a particle with a large average particle diameter is compared with the mass W (BS) of the particle | grains with a small average particle diameter among the inert particles B. W (BL) is preferably W (BL) / W (BS) <0.3. When the average particle diameter of the inert particles B exceeds 1 μm, the rollability of the film is improved, but when the polyester film is provided with a magnetic layer and then left in a roll shape, the shape of the inert particles B is By transferring to the magnetic layer provided on the surface A, it appears as a dent, and the magnetic conversion characteristics deteriorate due to frequent dropouts and errors of the magnetic tape. Moreover, when an average particle diameter is less than 0.1 micrometer, when winding a film on a roll, handling property is bad and production efficiency falls.

  In the present invention, the layer thickness of the polyester layer A is 3.0 μm or more. When the film is less than 3.0 μm, when the film is wound into a roll, the shape of the surface A is easily deformed due to the pushing up of the inert particles B in the polyester layer B through the film. The electromagnetic conversion characteristics of the are reduced. The relationship between the average particle diameter dB (μm) of the inert particles B and the thickness tB (μm) of the polyester layer B is preferably 0.2 ≦ dB / tB ≦ 3.0. More preferably, 0.8 ≦ dB / tB ≦ 2.0, and when dB / tB is smaller than 0.2, the inert particles are buried in the polyester layer B, and the effect of improving the winding property of the film is improved. Does not appear. When dB / tB exceeds 3.0, the protrusions of the inert particles B are excessively protruded from the polyester layer B on the surface B side, and when the magnetic film is provided on the polyester film, When the shape of the inert particles B is transferred to the magnetic layer provided on the surface A, it appears as a dent, and the magnetic conversion characteristics deteriorate due to frequent dropouts and errors of the magnetic tape. When the total film thickness is the same, the polyester layer B is preferably thin for the above reasons within the range where the effect of the inert particles B is exerted.

  In the present invention, a coating layer I described in detail below is formed on the surface A of the polyester layer A opposite to the polyester layer B. The coating layer I contains a water-soluble polyester resin and contains other water-soluble polymers or water-dispersible polymers as constituent components.

  The water-soluble polyester resin is a polyester obtained by polycondensation of an acid component and a glycol component, and preferably contains a sulfonic acid group or a salt thereof. For example, the acid component includes not only a dicarboxylic acid component but also a sulfonic acid group. Such a functional acid component is water-soluble by copolymerizing 5 mol% or more of the total carboxylic acid component and / or copolymerizing 2 to 70% by mass of a polyalkylene ether glycol component as a glycol component. However, it is not limited to these. As the sulfonic acid group or dicarboxylic acid, 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. Also included are graft polymers or block copolymers in which an acrylic polymer chain is bonded to a polyester chain, or acrylic modified polyester resins in which two polymers constitute a specific physical configuration (IPN, core-shell) in microscopic particles. .

  As the water-soluble polymer other than the water-soluble polyester resin of the film layer I, cellulose derivatives such as polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose, polyester ether copolymers, water-soluble polyester copolymers, and the like are preferable. Among them, a polymer blend of a cellulose derivative with the water-soluble polyester is particularly preferable. Cellulose derivatives contribute particularly to the formation of fine uneven structures on the film surface, and water-soluble polyester copolymers contribute to improving the adhesion between the cellulose derivative and the polyester film surface and prevent the inert particles from being scraped off. There is.

  Examples of the water-dispersible polymer include, but are not limited to, polymethyl methacrylate emulsion and polyacrylate emulsion.

  In the present invention, the coating layer I contains inert particles I described in detail below.

  As a component of the inert particle I, a polymer of each monomer selected from polystyrene, polyacrylic acid methyl ester, polyacrylic acid ethyl ester, polymethacrylic acid methyl ester, polymethacrylic acid ethyl ester, and divinylbenzene Alternatively, an organic material such as a copolymer, polytetrafluoroethylene, polyacrylonitrile, benzoguanamine, or silicone, or an inorganic material such as silica, alumina, titanium dioxide, kaolin, calcium carbonate, talc, or graphite may be used. In general, inorganic particles are excellent in magnetic head cleaning properties because they are hard and difficult to deform, and spherical silica particles composed of inorganic materials, particularly silica, are preferred because they can easily produce fine particles of various sizes. On the other hand, organic particles are excellent in dispersibility and have little aggregation between particles. Among these, at least one polymer particle selected from the group consisting of styrene, alkyl acrylate ester, alkyl methacrylate ester, a polymer of divinylbenzene, and a copolymer of divinylbenzene is preferable.

  The observed average particle size of the inert particles I is 5 to 60 nm. This reduces the friction with the magnetic head and maintains the running durability when the magnetic tape is used, and also improves the self-cleaning property to the magnetic head in repeated use. The observation average particle diameter is 5 to 60 nm as described above. This observed average particle diameter is an average value of the particle diameters observed on the film on the surface I side, and among the protrusions caused by the inert particles in the film on the surface I side, the individual particle diameter is 5 to 60 nm. It means the average particle size of the protrusions in the range.

  When the observed average particle diameter is less than 5 nm, the cleaning effect in repeated use of the magnetic tape is not improved, and the durability is not improved. On the other hand, when the observed average particle diameter exceeds 60 nm, the surface of the magnetic tape becomes rough, and the electromagnetic conversion characteristics are remarkably deteriorated. In addition, with repeated use, the inert particles may be shaved off and dropout may increase. The observation average particle diameter is particularly preferably 15 to 40 nm.

Also, projections density due to the inert particles I is preferably from 100～8,000 thousands / mm ^2, more preferably is from 1,000 to 5,000 million pieces / mm ^2. When the protrusion density is less than 1 million pieces / mm ² , since the particle density is too small, the cleaning effect cannot be expected. Moreover, when it exceeds 80 million pieces / mm ² , the surface of the magnetic tape becomes rough, the electromagnetic conversion characteristics are remarkably deteriorated, and particles are dropped off by repeated running of the magnetic tape, and the surface is shaved. There is a tendency for dropouts to increase. The agglomeration rate of the protrusions caused by the inert particles I is preferably less than 30%, more preferably less than 15%. If the aggregation rate of the projections is 30% or more, the coarse projections increase the spacing loss with the magnetic head and the electromagnetic conversion characteristics are remarkably deteriorated. In addition, the magnetic tape travels and causes dropout due to dropout of particles. .

  Further, the inert particles I may contain two or more kinds of inert particles having different average particle diameters as required.

  In the present invention, the average surface roughness Ra value on the coating layer I is 2 to 6 nm, and more preferably 2.5 to 4.5 nm. When the Ra value exceeds 6 nm, the running durability of the magnetic tape with the magnetic head is improved, but the electromagnetic conversion characteristics are deteriorated. Further, when the Ra value is less than 2 nm, the electromagnetic conversion characteristics are good, but the friction with the magnetic head in repeated use of the magnetic tape is increased and the running durability is lowered.

  In the present invention, the average surface roughness Ra of the surface of the polyester layer B opposite to the polyester layer A (hereinafter referred to as surface B) is 8 to 20 nm. Preferably it is 10-16 nm. The ten-point average surface roughness Rz is 300 nm or less, preferably 250 nm or less. When Ra is less than 8 nm, it becomes too smooth, and when producing a polyester film, particularly when slitting by a slitter after film formation, the film is slit into a predetermined width and rolled to form a roll. It enters too much and cannot be rolled up. When Ra exceeds 20 nm or Rz exceeds 300 nm, when the magnetic tape is wound into a roll, it appears as a dent by being transferred to the magnetic layer provided on the surface A, and the magnetic tape is dropped out. Electromagnetic conversion characteristics deteriorate due to frequent occurrence of errors. Furthermore, the ratio of Ra and Rz preferably satisfies Rz / Ra ≦ 22. When Rz / Ra exceeds 22, when rolled up by a coarse protrusion on the surface B side, it appears as a dent by transferring to a magnetic layer provided on the surface A, and the electromagnetic conversion characteristics are significantly reduced. .

In the present invention, on the surface B side, a coating layer II made of an organic compound may be provided with a solid content mass of 10 to 50 mg / m ² within a range satisfying the above-described average roughness Ra and Rz of the surface B. . When a coating layer is provided on the surface B, Ra and Rz on the surface B mean measured values from above the coating layer II.

  As the coating layer II, any material may be used as long as it is slippery and hard to be scraped, and has a function of not allowing a degradation product from the polyester film to pass through, and is mainly a water-soluble polymer and / or a water-dispersible polymer. Preferably, it is formed from a composition obtained by adding a silicone and a silane coupling agent to a water-soluble polymer and / or a water-dispersible polymer. As the water-soluble polymer used in the coating layer II, cellulose derivatives such as polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, and 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 B 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.

Preferably solid mass of the coating layer II is 10 to 50 mg / ^{m 2,} more preferably from 25~40mg / ^{m 2.} When the coating layer II is made into a magnetic tape and wound in a roll shape, it has a role of reducing transfer to the magnetic layer provided on the surface A. When the solid content mass is less than 10 mg / m ² , The effect is not obtained. If the solid content mass exceeds 50 mg / m ² , the coating layer II may be scraped off in the film forming process, or the scraped material may be adhered in the magnetic tape manufacturing process.

In the present invention, the number of recesses having a depth of 7 nm or more on the coating layer I is preferably 5,000 / mm ² or less. When the polyester film is wound into a roll, the number of dents tends to be greater in the core portion than in the surface layer, but the maximum value is measured from the surface layer to the core. When the number of dents exceeds 5,000 / mm ² , the electromagnetic conversion characteristics are significantly deteriorated due to deformation of the surface of the magnetic tape. The size of the recess on the coating layer I having a depth of 7 nm or more greatly affects the electromagnetic conversion characteristics. In order to reduce the number of dents to 5,000 / mm ² or less, the layer thickness of the polyester layer A, Ra and Rz of the surface B, and the solid content mass of the coating layer II are set to predetermined conditions. Also, when winding in a roll shape, in order to reduce the winding tension and surface pressure, and to reduce the number of core portions in the roll shape, surface pressure taper and tension taper from the roll core portion to the roll surface layer portion. It is also an effective technique to gradually take up with low surface pressure and low tension using

  The total thickness of the polyester film for magnetic recording tape in the present invention including the polyester layer A, the polyester layer B, and the coating layer is preferably 4 to 9 μm, and more preferably 4.5 to 6.0 μm.

(Production method)
The polyester film (polyester layer) in the present invention can be produced by various methods. In order to obtain a laminated polyester film having a two-layer structure comprising a polyester layer A and a polyester layer B, it is preferable to produce polyester a and polyester b by coextrusion, and the coating layer I and coating layer II on the surface A and surface B Is preferably formed by a coating method.

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

  Polyester a is melted with an extruder and further filtered with high accuracy as it is. Further, polyester b containing inert particles B in a separate extruder is melted and filtered with high accuracy using a separate filter, and each is then led to a feed block, where it is laminated in a molten state. The ratio of the lamination thickness of the polyester a and the polyester b 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. Furthermore, a coating liquid for forming the coating layer I and the coating layer II on the surface A and, if necessary, the surface B is applied to the film surface and dried, and then, in the direction perpendicular to the stretching direction (the uniaxial stretching direction is The film in the present invention can be produced by a production method in which the film is stretched and oriented (in a direction orthogonal to each other) and heat-set.

  The solid content concentration of the coating liquid to be applied to form the coating layer I on the surface A side is preferably 0.1 to 2% by mass, more preferably 0.6 to 1.6% by mass. In addition, other components such as other surfactants, stabilizers, dispersants, ultraviolet absorbers, thickeners, antistatic agents and the like can be added to the coating liquid as long as the effects of the present invention are not impaired. . In order to adjust the dispersion state of the inert particles I contained in the coating layer I, an acid / base component such as hydrochloric acid or a sodium hydroxide aqueous solution may be appropriately 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 applied to a film in a state where the coating liquid temperature exceeds 28 ° C., solid substances such as water-soluble polymers, water-dispersible polymers, and silane coupling agents may be generated. On the other hand, if the coating liquid temperature is less than 12 ° C., coarse protrusions tend to occur due to aggregation of the inert particles I.

  When forming the coating layer II on the surface B side, the solid content concentration of the coating liquid to be applied 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 can be added to the coating liquid as long as the effects of the present invention are not impaired. .

  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 I on the surface A side, as described above, a method of applying a coating solution having a predetermined composition and concentration on the base film after completion of stretching in the uniaxial direction may be employed. 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 A can be controlled by adjusting the amount of inert particles in the coating layer and the material average particle size. A similar method may be used for forming the coating layer II on the surface B. The thicknesses of the coating layer I and the coating layer II can be controlled to desired values by adjusting the solid content concentration of the coating liquid and the coating thickness.

  The polyester film for magnetic recording tape of the present invention can be recorded at a high density and has excellent durability when used as a base film of a magnetic recording medium, particularly for magnetic tape applications in which digital data is recorded and reproduced by an MR head. Results can be obtained. In particular, it can be suitably used as a base film for data backup applications requiring high reliability.

  The measurement method used in this example is shown below.

(1) Measurement of the thickness of the polyester layers A and B and the thickness of the entire film The thickness of the entire film is measured randomly at 10 points with a micrometer, and the average value is used. Regarding the layer thicknesses of the polyester layers A and B, the layer thickness of the relatively thin polyester layer is measured by the method described below, and the layer thickness of the relatively thick polyester layer is relatively smaller than the total thickness. Subtract the thickness of the thin polyester layer.

  Using a secondary ion mass spectrometer (SIMS), a metal element caused by the highest concentration of particles in a film having a depth in the range of 5,000 nm and a particle containing no metal element in the film are contained. In this case, the metal element concentration (M) caused by the catalyst contained in the highest concentration at the time of polyester film polymerization is measured. The metal element concentration M once reaches a stable value 1, and then monotonously increases or decreases to a stable value 2. Based on this distribution curve, in the former case, the thickness (μm) of the thin polyester layer is set to a depth that gives a particle concentration of (stable value 1 + stable value 2) / 2.

(2) Measurement of average particle diameter of inert particles B The polyester resin is removed from the surface B side of the polyester film by a plasma low-temperature ashing method (for example, PR-503 manufactured by Yamato Kagaku) to expose the particles. The treatment conditions are selected such that the film and the thermoplastic resin are ashed but the particles are not damaged. This is observed with an SEM (scanning electron microscope), and the image of the particles (light density produced by the particles) is connected to an image analyzer (for example, QTM900 manufactured by Cambridge Instrument), and the number of particles is 10,000 or more by changing the observation location. Then, the following numerical processing is performed, and the number average diameter obtained thereby is defined as the average particle diameter (dB).

(3) Measurement of inert particles I of coating layer I Measurement of the observed average particle diameter of the inert particles I When determining the observed average particle diameter from the surface I, a metal vapor deposition layer is formed on the coating surface I by a metal sputtering apparatus with a thickness of 20 to 30 nm (the vapor deposition film thickness at this time is xnm). And at least 100 protrusions with a diameter equivalent to an area circle of 25 to 60 nm (observed on the particles). The average value is calculated with respect to (caused), and a value obtained by subtracting 2 × nm from this average value is used as the observation average particle diameter.

B. Measurement of Number Density of Protrusions Due to Inactive Particles I The number density of inactive particles on the coating layer I is the above-mentioned A. In this method, the number of protrusions observed from the photographed photograph measured with an electron microscope (preferably a scanning electron microscope) at a magnification of 30,000 and measured by taking 10 or more photographs. Count. The number density was converted to the number of protrusions per 1 mm ² .

(4) Average surface roughness Ra value of film, 10-point average roughness Rz value Average surface roughness Ra value and 10-point average roughness Rz value of the surface (A, B) of the film are measured by an atomic force microscope (scanning). Type probe microscope). Specifically, using a desktop small probe microscope (“Nanopics” 1000) manufactured by Seiko Instruments Inc., scanning the surface of the film with an atomic force microscope in the range of 40 μm square or 100 μm square in the damping mode. Then, from the obtained surface profile curve, the Ra value was calculated from the arithmetic average roughness corresponding to JIS · B0601, 1996 · Ra, and the Rz value was calculated from the ten-point average roughness. The details of the measurement conditions are as follows.

(Measurement surface: Surface A)
Measurement mode Damping mode Measurement direction Width direction Measurement area 40 × 40μm
Scan speed 380s / FRAME
Number of scans 512 Amplitude mode LL (20%)
(Measurement surface: Surface B)
Measurement mode Damping mode Measurement direction Width direction Measurement area 100 × 100μm
Scan speed 380s / FRAME
Number of scans 512 Amplitude mode HH (100%)
(5) Measurement of the number of dents on the coating layer I A cross-sectional profile is obtained from the two-dimensional image obtained in the average surface roughness measurement on the coating layer I in (4) above. With the unevenness of the cross-sectional profile image, the average convex and concave lines are drawn, and the center line is taken as the base line. With respect to this base line, the lowest part of the recessed part is at a distance of 7 nm or more from the base line, and the number is counted. The above-mentioned count was performed from 20 or more cross-sectional profiles in the obtained 40 μm square image, and the number of dents obtained was converted to 1 mm ² to obtain the number of dents on the coating layer I.

(6) Mass of solid content of coating layer II on the surface B side When the coating liquid for coating formation on the surface B of the film is applied, the amount of the coating liquid consumed by the application within a predetermined time is determined. Calculate the area where the aqueous solution was applied within the fixed time from the application width, film speed, and application time, divide the aqueous solution consumption during application by the application area, and then calculate the solid content concentration in the applied aqueous solution. The solid content (unit: mg / m ² ) of the coating layer was calculated.

(7) Winding property After optimizing the winding conditions at the time of slitting, make a slit of 10 rolls with a width of 620 mm x a length of 10,000 m and make a roll that does not generate film wrinkles after standing at room temperature for 10 days as a good product. The winding property is evaluated according to the following criteria.

Number of non-defective rolls Judgment criteria 8 or more ○
4-7 △
3 or less ×
(8) Characteristics of magnetic 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 A of the film of the present invention using a vacuum deposition apparatus. Next, a diamond-like carbon film was formed with a thickness of 10 nm on the cobalt-oxygen film layer by a sputtering method, and a fluorine-containing fatty acid ester-based lubricant was applied with a thickness of 3 nm. Subsequently, a back coat layer made of carbon black, polyurethane and silicone was provided on the surface B 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). .

A. Durability Evaluation 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. Evaluation was performed by counting the number of block mosaics (dropout (DO) number). 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.

B. 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). 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 a)
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 to obtain polyethylene terephthalate (PET; polyester a) substantially free of inert particles.

(Method for producing polyester b)
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 b was obtained by adding 0.50 wt% of polystyrene spheres having a number average particle diameter (material average particle diameter) of 300 nm as inert particles B to the polymer thus obtained.

(Production method of polyester film)
The obtained polyester a and polyester b were each dried at 170 ° C. for 3 hours, and then co-extruded by adjusting the thickness ratio of polyester layer A and polyester layer B to 7: 1 in two extruders. , Melt at a melting temperature of 280 to 300 ° C., and after high-precision filtration with a steel wire filter having an average opening of 1 μm, a polyester a is laminated on one side of the polyester a using a multi-manifold coextrusion die. The film was quenched on a casting drum at a temperature of 25 ° C. to obtain an unstretched laminated film having a two-layer structure of polyester layer A and layer B. Next, the unstretched laminated film thus obtained was preheated and longitudinally stretched three times at 110 ° C. by a roll stretching method.

  In the step after longitudinal stretching, an aqueous solution having the following composition and concentration was applied to the surface on the surface A side by the Mayer bar method.

Composition of coating aqueous solution on surface A side (film layer I)
Water 99.3% by mass (rounded to the second decimal place)
Methylcellulose 0.13 mass%
Water-soluble polyester resin (1: 1 polycondensate of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.60 mass%
Spherical silica particles having an average particle diameter of 20 nm 1.3 × 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 4.8 μm.

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

[Example 2]
In the method for producing polyester b of Example 1, the inert particles B were changed to polystyrene spheres having a number average particle size (material average particle size) of 200 nm. In the manufacturing method of the polyester film of Example 1, the ratio of the thickness of the polyester layer A and the polyester layer B is adjusted so as to be 12: 1, and is supplied by coextrusion. An aqueous solution having the following composition and concentration was applied by the Mayer bar method.

Composition of coating aqueous solution on surface A side (film layer I)
Water 99.3% by mass (rounded to the second decimal place)
Methylcellulose 0.13 mass%
Water-soluble polyester resin (1: 1 polycondensate of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.60 mass%
Spherical polystyrene particles having an average particle diameter of 30 nm 1.1 × 10 ⁻³ mass%
Further, in order to provide the coating layer II on the surface B 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 28 mg / m ² .

Composition of aqueous coating solution on surface B side (Coating layer II)
99.44% by mass of water
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%
Otherwise, a polyester film having a thickness of 5.2 μm was produced in the same manner as in Example 1.

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

[Example 3]
In the production of the polyester film of Example 1, a polyester film having a thickness of 3.6 μm was prepared in the same manner as in Example 1 except that the thickness ratio of the polyester layer A and the polyester layer B was adjusted to 5: 1. Produced.

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

[Example 4]
In the method for producing polyester b of Example 1, the inert particles B were changed to polystyrene spheres having a number average particle size (material average particle size) of 900 nm.

  Others were the same as in Example 1, and a polyester film having a thickness of 4.8 μm was produced.

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

[Example 5]
In the production of the polyester film of Example 2, a polyester film having a thickness of 4.9 μm was prepared in the same manner as in Example 2 except that the thickness ratio of the polyester layer A and the polyester layer B was adjusted to 48: 1. Produced.

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

[Example 6]
Polyester having a thickness of 4.8 μm in the same manner as in Example 1 except that the inert particles B were changed to polystyrene spheres having a number average particle size (material average particle size) of 200 nm in the method for producing polyester b of Example 1. A film was prepared.

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

[Example 7]
In the method for producing polyester b of Example 1, the inert particles B were changed to polystyrene spheres having a number average particle size (material average particle size) of 800 nm, and in the production of the polyester film, the thickness of the polyester layer A and the polyester layer B was changed. A polyester film having a thickness of 4.4 μm was produced in the same manner as in Example 1 except that the ratio was adjusted to 21: 1.

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

[Example 8]
In the production of the polyester film of Example 1, the composition of the coating aqueous solution on the surface A side was changed as follows.

Composition of coating aqueous solution on surface A side (film layer I)
Water 99.3% by mass (rounded to the second decimal place)
Methylcellulose 0.13 mass%
Water-soluble polyester resin (1: 1 polycondensate of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.60 mass%
Spherical silica particles with an average particle diameter of 60 nm 1.4 × 10 ⁻³ mass%
Others were the same as in Example 1, and a polyester film having a thickness of 4.8 μm was produced.

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

[Example 9]
In the production of the polyester film of Example 1, the composition of the coating aqueous solution on the surface A side was changed as follows.

Composition of coating aqueous solution on surface A side (film layer I)
Water 99.3% by mass (rounded to the second decimal place)
Methylcellulose 0.13 mass%
Water-soluble polyester resin (1: 1 polycondensate of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.60 mass%
Spherical silica particles with an average particle diameter of 8 nm 1.0 × 10 ⁻³ mass%
Others were the same as in Example 1, and a polyester film having a thickness of 4.8 μm was produced.

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

[Example 10]
In the production of the polyester film of Example 2, a thickness of 5.2 μm was obtained in the same manner as in Example 2 except that the aqueous solution applied to the outside of the polyester layer B was changed so that the solid content coating amount was 11 mg / m ² . A polyester film was prepared.

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

[Example 11]
In the production of the polyester film of Example 2, a thickness of 5.2 μm was obtained in the same manner as in Example 2 except that the aqueous solution applied to the outside of the polyester layer B was changed so that the solid content coating amount was 48 mg / m ² . A polyester film was prepared.

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

[Comparative Example 1]
In the production of the polyester film of Example 1, a polyester film having a thickness of 3.4 μm was prepared in the same manner as in Example 1 except that the thickness ratio of the polyester layer A and the polyester layer B was adjusted to 14: 3. Produced.

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

[Comparative Example 2]
In the method for producing polyester b of Example 1, the inert particles B were changed to polystyrene spheres having a number average particle size (material average particle size) of 80 nm, and in the production of the polyester film, the thicknesses of the polyester layer A and the polyester layer B were changed. A polyester film having a thickness of 4.4 μm was produced in the same manner as in Example 1 except that the ratio was adjusted to 21: 1.

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

[Comparative Example 3]
In the production of the polyester film of Example 1, the composition of the coating aqueous solution on the surface A side was changed as follows.

Composition of coating aqueous solution on surface A side (film layer I)
Water 99.3% by mass (rounded to the second decimal place)
Methylcellulose 0.13 mass%
Water-soluble polyester resin (1: 1 polycondensate of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.60 mass%
Spherical silica particles with an average particle size of 65 nm 1.4 × 10 ⁻³ mass%
Others were the same as in Example 1, and a polyester film having a thickness of 4.8 μm was produced.

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

[Comparative Example 4]
In the production of the polyester film of Example 1, the composition of the coating aqueous solution on the surface A side was changed as follows.

Composition of coating aqueous solution on surface A side (film layer I)
Water 99.3% by mass (rounded to the second decimal place)
Methylcellulose 0.13 mass%
Water-soluble polyester resin (1: 1 polycondensate of 70 mol% terephthalic acid, 30 mol% 5-sodium sulfoisophthalic acid acid component and ethylene glycol) 0.60 mass%
Spherical silica particles having an average particle diameter of 4 nm 1.0 × 10 ⁻³ mass%
Others were the same as in Example 1, and a polyester film having a thickness of 4.8 μm was produced.

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

[Comparative Example 5]
In the method for producing polyester b of Example 1, the inert particles B were changed to polystyrene spheres having a number average particle diameter (material average particle diameter) of 1,100 nm.

  Others were the same as in Example 1, and a polyester film having a thickness of 4.8 μm was produced.

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

[Comparative Example 6]
In the production of the polyester film of Example 2, a thickness of 5.2 μm was obtained in the same manner as in Example 2 except that the aqueous solution applied to the outside of the polyester layer B was changed so that the solid content coating amount was 52 mg / m ² . A polyester film was prepared.

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

[Comparative Example 7]
In the production of the polyester film of Example 1, a polyester having a thickness of 4.8 μm was obtained in the same manner as in Example 1, except that the tension and surface pressure when wound into a roll were changed to 1.5 times that of Example 1. A film was prepared.

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

  As is apparent from Table 2, the polyester film according to the present invention is excellent in the productivity of the base film, and the magnetic recording tape manufactured from the base film has excellent electromagnetic conversion characteristics and can be run even when repeatedly run. The magnetic recording tape had good durability.

Claims (5)

It has polyester layer A and polyester layer B, has coating layer I on surface A opposite to polyester layer B of polyester layer A, and surface B opposite to polyester layer A of polyester layer B A polyester film for magnetic recording tape, which is a laminated film that satisfies the following (a) to (d).
(A) The coating layer I provided on the surface A includes inert particles I having an average particle diameter of 5 to 60 nm, the average surface roughness Ra on the coating layer I is 2 to 6 nm, and the depth on the coating layer I The number of dents of 7 nm or more is 5,000 / mm ² or less.
(B) The polyester layer A is a polyester layer containing substantially no inert particles, and has a layer thickness of 3.0 μm or more.
(C) The polyester layer B is a polyester layer containing inert particles B having an average particle size of 0.1 to 1.0 μm.
(D) The surface B has an average surface roughness Ra of 8 to 20 nm and a ten-point average surface roughness Rz of 300 nm or less. The polyester film for magnetic recording tapes of Claim 1 with which the coating layer II which consists of an organic compound by the solid content mass of 10-50 mg / m < ² > is provided in the surface B. The polyester film for magnetic recording tape according to claim 1 or 2, wherein the average particle diameter dB (µm) of the inert particles B and the thickness tB (µm) of the polyester layer B satisfy the following formula.
0.2 ≦ dB / tB ≦ 3 The polyester film for magnetic recording tape according to claim 1, wherein the total thickness is 4 to 9 μm. The polyester film for magnetic recording tape according to any one of claims 1 to 4, wherein the polyester film contains polyethylene terephthalate or polyethylene-2,6-naphthalate as a constituent component.