JP2006347004A - Laminated polyester film for metal thin film type magnetic recording medium and magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated polyester film which is little in the precipitation of a cyclic trimer and exhibits excellent electromagnetic conversion characteristics when made into a metal thin film type magnetic recording medium. <P>SOLUTION: The laminated polyester film for the metal thin film type recording medium comprises a polyester layer A located in the side of a surface A where a magnetic layer is provided, and a polyester layer B located in the side of a surface B where a back coat layer is provided. The polyester layer A contains a polyester A having a cyclic trimer content of ≤0.7 wt% and an intrinsic viscosity of 0.4-0.65, the surface roughness Ra of the surface A is 0.5-4 nm, and the surface roughness of the surface B is 5-20 nm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laminated polyester film, and more specifically, a magnetic recording medium excellent in electromagnetic conversion characteristics and running durability, particularly a metal thin film type magnetic recording medium for recording / reproducing digital signals, such as a digital video cassette tape, a data storage tape, etc. The present invention relates to a laminated polyester film for a metal thin film type magnetic recording medium useful as a base film.

  In recent years, the progress of high-density recording of magnetic recording media has been remarkable. For example, a ferromagnetic metal thin film type magnetic film in which a ferromagnetic metal thin film is formed on a nonmagnetic support by a physical deposition method such as vacuum deposition or sputtering or a plating method. Recording media are being developed and put to practical use.

  The metal thin film (magnetic layer) of the ferromagnetic metal thin film type magnetic recording medium has a thickness of 0.2 μm or less and is very thin, realizing high-density recording. For the purpose of realizing further high-density recording, the magnetic layer is becoming thinner, and the development of recording media having a thickness of 100 nm or less is progressing. For this reason, the degree to which the surface state of the base film, which is a nonmagnetic support, affects the surface properties of the magnetic layer is increasing. That is, in the case of a ferromagnetic metal thin film type magnetic recording medium, the surface state of the nonmagnetic support appears as it is as the surface irregularities of the metal thin film, which causes noise in recording / reproducing signals. Therefore, it is desirable that the surface of the nonmagnetic support is as smooth as possible.

  On the other hand, there is a strong demand for polyethylene terephthalate (PET), which is inexpensive to manufacture, as a base film support. However, cyclic trimers can be formed from the inside of the PET film due to long-term storage of the base film and heat load processes during metal deposition. Bleeding out to the film surface and crystallizing, forming protrusions on the surface of the base film, deteriorating the flatness of the base film, causing noise in recording / playback signals and tape dropout was there. This problem becomes more pronounced as the thickness of the metal thin film becomes thinner.

  In order to prevent the precipitation of the cyclic trimer, a method of providing a coating layer for preventing oligomer precipitation on the surface of the base film on which the magnetic layer is provided, or a method of using Ti as a polymerization catalyst for the polymer on the side on which the magnetic layer is provided ( Patent Document 1), and a method (Patent Document 2) in which the cyclic trimer contained in the polyester layer on the side where the back coat layer is provided is 0.8 wt% or less has been proposed. In particular, it does not prevent the precipitation of the cyclic trimer on the surface of the base film on which the magnetic layer is provided.

Solid state polymerization of polymers is known as a technique for reducing cyclic trimers, but the intrinsic viscosity of polymers with reduced cyclic trimers by solid phase polymerization is as high as about 0.74, reducing foreign substances in the polymer. Therefore, there is a problem that the filtration pressure increases, film formation cannot be performed, and the film cannot be used as a support for a ferromagnetic metal thin film type magnetic recording medium.
JP 2004-265551 A JP 2002-248723 A

  An object of the present invention is to provide a laminated polyester film that eliminates the disadvantages of the prior art and exhibits excellent electromagnetic characteristics when it is used as a metal thin film type magnetic recording medium with little cyclic trimer precipitation. It is in.

  The present invention for solving the above problems is a metal thin film comprising a polyester layer A located on the surface A side on which the magnetic layer is provided, and a polyester layer B located on the surface B side on which the backcoat layer is provided. Type polyester film A, wherein the polyester layer A contains a polyester A having a cyclic trimer content of 0.7 wt% or less and an intrinsic viscosity of 0.4 to 0.65, The laminated polyester film for metal thin film type magnetic recording media is characterized in that the surface roughness Ra of A is 0.5 to 4 nm and the surface roughness of the surface B is 5 to 20 nm.

  Here, it is also preferable that the polyester layer B contains polyester B having a cyclic trimer content of 0.7 wt% or less and an intrinsic viscosity of 0.4 to 0.65.

  Moreover, it is also preferable that at least one surface of the surface A or the surface B is formed of a coating layer.

  Further, a magnetic recording medium in which a ferromagnetic metal thin film layer is provided on the surface A of the laminated polyester film for metal thin film type magnetic recording medium is also preferable.

  According to the present invention, there is provided a laminated polyester film for a metal thin film type magnetic recording medium that exhibits excellent electromagnetic conversion characteristics when it is made into a metal thin film type magnetic recording medium without precipitation of a cyclic trimer and has few dropouts. Can be provided.

  The laminated polyester film for metal thin film type magnetic recording media of the present invention (hereinafter sometimes simply referred to as a laminated polyester film) has a laminated structure of two or more layers, and the polyester layers in the outermost layer of the laminated polyester film are respectively Polyester layer A and polyester layer B are formed.

  Here, the polyester layer A is located on the surface (surface A) on the side where the magnetic layer will be provided later, and this surface A may be formed directly by the polyester layer A or by a coating layer described later. Sometimes. Similarly, the polyester layer B is located on the surface (surface B) on the side where the backcoat layer is provided (surface on the opposite side of the surface A), and this surface B may be directly formed by the polyester layer B. For example, it may be formed by a coating layer described later.

  The polyester layer A preferably contains a polyester A having a cyclic trimer content of 0.7 wt% or less and an intrinsic viscosity of 0.4 to 0.65. The polyester B preferably contains a polyester B having a cyclic trimer content of 0.7 wt% or less and an intrinsic viscosity of 0.4 to 0.65 (the names of polyester A and polyester B are for convenience) Both may be the same polyester or different polyesters).

  In addition, when it is set as the layer structure of three or more layers, it is a layer between the polyester layer A and the polyester layer B, Comprising: When the polyester layer directly laminated | stacked with the polyester layer A is made into the layer C, inclusion of layer C When the amount of the cyclic trimer is more than 0.7% by weight, the thickness of the polyester layer A is preferably 0.5 μm or more in order to prevent the precipitation of the cyclic trimer bleed out from the layer C. More preferably, it is 0.7 μm or more. In addition, when the amount of the cyclic trimer contained in the polyester layer B is 0.7% by weight or less, the polyester layer is a layer between the polyester layer A and the layer B and is directly laminated on the layer B. When layer D is a layer D (the polyester layer D is the same as the polyester layer C in the case of a three-layer laminate), the layer D contains more than 0.7% by weight of the cyclic trimer. In order to prevent precipitation of the cyclic trimer bleed out from the polyester layer B, the thickness of the polyester layer B is preferably 0.5 μm or more, more preferably 0.7 μm or more.

  As the polyesters A and B contained in the polyester layer A and the polyester layer B, aliphatic polyesters and aromatic polyesters can be used, and aromatic polyesters are particularly preferable. Polyesters A and B may be the same type or different types. When the laminated polyester film is a multilayer laminated film having more than two layers, aliphatic polyester, aromatic polyester, etc. can be used as the polyester contained in layers other than polyester layer A and polyester layer B. Polyester is preferable, and polyester A and B may be the same type or different types.

  Examples of the polyester in the present invention include terephthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, aromatic dicarboxylic acid such as isophthalic acid, aliphatic dicarboxylic acid such as adipic acid and sebacic acid, hexahydroterephthalic acid, hexahydro Polyesters obtained from dicarboxylic acid components such as alicyclic dicarboxylic acids such as isophthalic acid and glycol components such as ethylene glycol, butanediol, and cyclohexanedimethanol can be used. Specifically, polyethylene terephthalate, poly Examples include butylene terephthalate and polyethylene naphthalate. Among these, polyethylene terephthalate, which is industrially inexpensive, is particularly preferable.

  Further, the polyester may be a homopolymer or a copolymer, and one or more of the above-mentioned dicarboxylic acids and diols can be used as the copolymer component. Furthermore, polyalkylene glycols such as polyethylene glycol and polybutylene glycol, oxycarboxylic acids such as 5-sodium sulfoisophthalic acid, and hydroxyethoxybenzoic acid can also be used.

  The intrinsic viscosity of the polyester A in the present invention is preferably 0.4 to 0.65. More preferably, it is 0.5-0.63, Most preferably, it is 0.55-0.6. When the intrinsic viscosity of polyester A is less than 0.4, film breakage tends to occur during film formation, and productivity tends to decrease. Moreover, when the intrinsic viscosity of polyester A exceeds 0.65, the melt viscosity of the polymer becomes high, and filter filtration for removing foreign matters in the polyester resin tends to be difficult. The polyester A in the present invention preferably has a cyclic trimer content of 0.7 wt% or less. More preferably, it is 0.7-0.2 wt%, More preferably, it is 0.6-0.3 wt%, More preferably, it is 0.5-0.4 wt%. When the amount of the cyclic trimer contained in the polyester A exceeds 0.7 wt%, the cyclic trimer is transferred from the inside of the polyester to the film surface due to a long-term storage of the film roll and a process of receiving a heat load during metal deposition. It tends to bleed out and form protrusions on the surface of the base film to deteriorate the flatness of the base film. If the amount of the cyclic trimer is less than 0.2 wt%, the heat treatment time in the process of polymerizing the polyester A becomes longer, the deterioration of the polymer proceeds, and the generation of foreign matters may be increased during film formation. .

  The polyester A is a polyester resin obtained by various esterification reactions, transesterification reactions, and subsequent polycondensation reactions, in an inert gas atmosphere having a moisture content of 1,000 ppm or less and an oxygen concentration of 1,000 ppm or less. In addition, by carrying out heat treatment for 2 hours to 60 hours at a temperature in the range of 80 ° C. or lower than the melting point of the melting point in the absence of an inert gas, the cyclic trimer has an optimum intrinsic viscosity. It can be obtained as a reduced polyester.

  The surface roughness Ra of the surface A of the laminated polyester film in the present invention is 0.5 to 4 nm, preferably 1 to 3 nm, more preferably 1.5 to 2.5 nm. If the surface roughness Ra value of the surface A is less than 0.5 nm, the ferromagnetic metal thin film layer formed by vacuum deposition on the surface A becomes smooth and slipperiness decreases, and the magnetic metal thin film is worn and magnetic. The durability of the recording medium tends to be low. On the other hand, when the surface roughness Ra of the surface A exceeds 4 nm, the ferromagnetic metal thin film layer becomes a rough surface, and the electromagnetic conversion characteristics of the magnetic recording medium tend to deteriorate. The surface roughness Rz of the surface A in the present invention is preferably 5 to 50 nm because the film winding property is improved, and more preferably 10 to 30 nm.

  The surface roughness Ra of the surface A is controlled by a method of adjusting the particle size and amount of inert particles contained in the polyester A or a method of providing a coating layer (hereinafter referred to as coating layer A) on the outermost surface of the polyester layer A. However, a method of providing a coating layer is particularly preferable because the cyclic trimer that bleeds out from the polyester layer A can be blocked. The coating layer A preferably contains 0.1 to 30 wt% of inert particles made of an inorganic substance or an organic substance having an average particle diameter of 5 to 50 nm, more preferably 10 to 20 nm.

  Preferred examples of the resin forming the film layer A include cellulose derivatives such as polyvinyl alcohol, tragacanth gum, gum arabic, casein, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, polyester ether copolymers, water-soluble polyester copolymers, and the like. However, a polymer blend of a cellulose derivative and a water-soluble polyester copolymer is particularly preferable. 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 copolymerizing 2-70 wt% of polyalkylene ether glycol components 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. In particular, the cellulose derivative contributes to prevention of precipitation of the cyclic trimer, and the water-soluble polyester copolymer contributes to improvement in adhesion between the cellulose derivative and the polyester film surface.

  When the polyester layer A contains inert particles, preferred inert particles contained in the polyester A include, for example, (1) heat-resistant polymer particles (for example, crosslinked silicone resin, crosslinked polystyrene resin, formaldehyde resin, aromatic polyamide). Particles made of resin, polyimide resin, polyamideimide resin, cross-linked polyester, etc.), (2) metal oxide (for example, 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, include fine particles of inorganic compounds such as bentonite, etc.). 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, Alternatively, fine particles made of kaolin are preferred. More preferred are fine particles comprising crosslinked silicone resin particles, crosslinked polystyrene resin particles, 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 surface B of the laminated polyester film in the present invention preferably has a surface roughness Ra of 5 to 20 nm. More preferably, it is 7-15 nm. When the surface roughness Ra of the surface B is less than 5 nm, the film winding property and blocking resistance tend to be poor. On the other hand, if the surface roughness Ra exceeds 20 nm, the adhesion to the cooling can is lowered in the metal thin film forming step, and the problem of heat loss of the film is likely to occur. The surface roughness Rz of the surface B is preferably 100 to 400 nm because the roll-up property of the film is further improved, and more preferably 150 to 300 nm.

  The surface roughness Ra of the surface B can be adjusted by the particle size and amount of the inert particles contained in the polyester B. The preferable average particle diameter of the inert particles is 50 to 1,000 nm, more preferably 100 to 500 nm. The preferable content of the inert particles contained in the polyester B is 0.01 to 1.0 wt%, more preferably 0.1 to 0.6 wt%.

  Examples of preferable inert particles to be contained in polyester B include (1) heat-resistant polymer particles (for example, crosslinked silicone resin, crosslinked polystyrene resin, formaldehyde resin, aromatic polyamide resin, polyimide resin, polyamideimide resin, 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.) Microparticles consisting of UNA inorganic compounds. 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, Alternatively, fine particles made of kaolin are preferred. 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 polyester B used for the polyester layer B preferably has an intrinsic viscosity of 0.4 to 0.65 in order to remove foreign substances in the polyester resin, and is more preferable because it makes it easier to filter the molten polymer. It is polyester 0.55-0.6.

  Further, the content of the cyclic trimer of the polyester B is 0.7 wt% or less, the cyclic trimer precipitated from the polyester layer B bleeds out, and the film is wound on the surface A when it is wound into a roll. It is preferable from the point which can suppress transferring, More preferably, it is 0.6 wt% or less. The lower limit is not particularly limited, but from the viewpoint of ease of production, cost, etc., the content of the cyclic trimer of polyester B is preferably 0.2 to 0.7 wt%. More preferably, it is 3 to 0.6 wt%.

  As a manufacturing method of the polyester B contained in the said polyester polyester layer B, the manufacturing method of the polyester A used for the above-mentioned polyester layer A can be used.

  It is preferable to provide a coating layer (coated polyester layer B) on the outermost surface of the polyester layer B because it is possible to suppress the cyclic trimer bleed out from the polyester layer B from being deposited on the surface B.

  The coated polyester layer B preferably contains no particles from the viewpoint of preventing the particles from falling off due to friction with a cooling can during metal thin film forming.

  The coated polyester layer B may be any material as long as it is slippery between the cooling can and hard to be scraped, and has a function of not allowing the degradation product from the polyester film to pass through. Or it is comprised from a water-dispersible polymer, Preferably it forms from the composition which added the silicone and the silane coupling agent to the water-soluble polymer and / or the water-dispersible polymer.

Examples of water-soluble polymers used in the coated polyester layer B include polyvinyl alcohol, tragacanth rubber, gum arabic, casein, cellulose derivatives such as methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyester ether copolymers, water-soluble polyester copolymers, and the like. Can be used. In addition, as a water-dispersible polymer emulsion, a polymethyl methacrylate emulsion, a polyacrylate emulsion, etc. can be used. As a silicone, an organosilicon compound having a siloxane bond in the molecular skeleton such as polydimethylsiloxane is a covalent bond. Many connected polymers can be used. Silicone improves the slipperiness of the coating layer and ensures running performance with a cooling can and abrasion resistance. 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 the release of the silicone from the lubricant layer, and also contributes to an improvement in adhesion between the coating layer and the polyester.

  The total thickness of the laminated polyester film in the present invention is preferably 2 μm or more and less than 10 μm, more preferably 4 μm to 8 μm.

  In the laminated structure of the film of the present invention, the upper limit of the thickness of the polyester layer B is preferably 8 to 25% of the total thickness, more preferably 10 to 20%. When the thickness of the polyester B is less than 8% of the total thickness, the inert particles in the polyester B are likely to fall off. When the thickness of the polyester layer B is greater than 25% of the total thickness, the shape of the inert particles in the polyester layer B may be transferred to the surface A.

  The laminated polyester film in the present invention can be produced by various methods. For example, the laminated structure of the polyester layer A and the polyester layer B is preferably manufactured by a co-extrusion method, and the coating layer A and the coating layer B are preferably laminated by a coating method. Of course, the coating layer should just be formed in at least any one surface.

Hereinafter, a biaxially oriented polyester film will be described by way of example.
Polyester A containing inert particles as necessary in an extruder is melted and further subjected to high-accuracy filtration with a filter as it is, and polyester B containing inert particles in another extruder. In a molten state, after high-precision 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 A and polyester B can be adjusted to the above-described preferred lamination thickness ratio by adjusting the extrusion amount of the extruder of each layer. In addition to an extruder that extrudes polyester A and polyester B, in addition to extruding polyester A and polyester B, the polyester C is melt-extruded by an extruder and filtered through a filter if necessary. And can be laminated between the polyester layer A and the polyester layer B. After melt-laminating in this manner, the film is coextruded from the die at a melting point (Tm) to (Tm + 70) ° C., and then rapidly cooled and solidified on a casting drum at 10 to 50 ° C. to obtain an unstretched laminated film sheet. 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, if necessary, a coating liquid for forming the coating layer A or the coating layer B is applied to the film surface and dried, and then, in the direction perpendicular to the stretching direction (in a 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 and heat-set.

  The solid content concentration of the coating liquid applied to form the film layer A formed on the surface on the polyester layer A side is 0.01 to 1 wt%, more preferably 0.04 to 0.5 wt%. 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.

  The solid content concentration of the coating liquid applied to form the coating layer B formed on the surface on the polyester layer B side is 0.01 to 1 wt%, more preferably 0.04 to 0.5 wt%. 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 A on the polyester layer A, as described above, a method of applying a coating solution having a predetermined composition and concentration on the base layer 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. Ra of the surface A can be controlled by adjusting fine particles and components of the coating layer and fine particles inside the polyester layer A. The same method may be used for forming the coating layer B on the polyester layer B, and the coating layer thickness can be controlled to a desired value by adjusting the solid content concentration of the coating solution and the coating solution thickness.

In the present invention, in order to improve various performances including head touch as a magnetic recording medium, running durability, and at the same time to achieve a thin film, the Young's modulus of the laminated film is set in the vertical and horizontal directions, respectively. Usually 4,000 N / mm ² or more and 5,500 N / mm ² or more, preferably 4,500 N / mm ² or more and 6,000 N / mm ² or more, more preferably 5,000 N / mm ² or more and 6,500 N / mm ² or more. The degree of crystallinity of the polyester layers A and B is desirably 30 to 50% when the polyester is polyethylene terephthalate and 28 to 38% when the polyester is polyethylene-2,6-naphthalate. If both are below the lower limit, the heat shrinkage rate is increased, while if the upper limit is exceeded, the abrasion resistance of the film is lowered, and white powder is liable to occur when sliding with the roll or guide pin surface.

  According to the present invention, a laminated polyester film in which a polyester layer B is laminated on one side of the polyester layer A, and further a laminated polyester film in which a film layer A is further laminated on the surface of the polyester layer A of the laminated film, Further, a magnetic recording medium is also provided in which each of the laminated polyester films in which the coating layer B is further laminated on the surface of the polyester layer B is used as a base film.

  An embodiment for producing a magnetic recording medium from the above-described laminated polyester film of the present invention is as follows.

  The laminated polyester film of the present invention has a ferromagnetic metal thin film layer formed of iron, cobalt, nickel, chromium or an alloy or oxide containing these as a main component on the surface A by a method such as vacuum deposition, sputtering, or ion plating. And, if necessary, a back coat layer can be provided on the surface B by various methods to obtain a magnetic recording medium. The thickness of the ferromagnetic metal thin film layer is preferably 20 to 300 nm.

  In addition, the laminated polyester film of the present invention is further provided with a protective layer such as diamond-like carbon (DLC) and a fluorine-containing carboxylic acid-based lubricating layer in order on the surface of the ferromagnetic metal thin film layer, if necessary. In addition, if necessary, by providing a backcoat layer on the surface B by various methods, the output in the short wavelength region, the electromagnetic characteristics such as S / N, C / N, etc. are excellent, and the dropout and error rate are excellent. A low-density vapor-deposition type magnetic recording medium can be obtained. This vapor deposition type magnetic recording medium is extremely useful as a magnetic tape medium for Hi8 for analog signal recording, digital video cassette recorder (DVC) for digital signal recording, data 8 mm, DDSIV, and particularly excellent when used for digital video tape applications. It is possible to obtain the results. Further, excellent results can be obtained even for data storage tape applications, which is preferable. In addition, an image data recording alloy film made of photoreactive Ge, Sb, Te or the like is formed, and can be suitably used as a base film of an optical recording tape capable of recording image data and the like.

  The measurement method used in this example is as follows.

[Measurement method]
(1) 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 on the surface of the film in a 40 μm square area in a damping mode. From the surface profile curve obtained, Ra value was determined from the arithmetic average roughness corresponding to JIS · B0601 · Ra, and Rz value was obtained from the ten-point average roughness.
The details of the measurement conditions are as follows.

Measurement surface Surface A Surface B
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%)

(2) Amount of cyclic trimer in polyester 10 mg of polyester resin shaved from polyester layer A or polyester layer B was heated in 1 ml of 1,1,2,2-tetrachloroethane at 200 ° C. for 10 minutes in a glass ampoule. After cooling, the content was diluted with chloroform to 25 ml, and the resulting solution was analyzed using Toyo Soda Co., Ltd. high performance liquid chromatograph HLC-802UR using chloroform as a developing solvent.

(3) Average particle diameter of fine particles A fine particle powder is dispersed on an electron microscope (electron microscope) test stand so that these particles do not overlap as much as possible, and an electron microscope (preferably a transmission electron microscope) has a magnification of 1,000,000. The area equivalent circle diameter was determined for at least 100 particles, and the number average value was used as the average particle diameter.

  In addition, when calculating | requiring this particle size from a film, it calculates | requires by the following a) method.

  a) A gold thin film deposition layer is provided on the film surface A of the film with a gold sputtering device at 20 to 30 nm (χ nm), and observed with an electron microscope (preferably a scanning electron microscope) at a magnification of about 100,000 times, and at least 100 The equivalent circle diameter is obtained for each particle, and the value obtained by subtracting 2χ nm from the number average value is defined as the particle size.

(4) Average particle diameter of particles In the case of particles contained in polyester B, the polyester resin is removed from the surface B side 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 D obtained thereby is defined as the average particle diameter.

D = ΣDi / N
Here, Di is the equivalent circle diameter of the particles, and N is the number. However, when the coating layer B contains fine particles, the ashing treatment is performed after the coating layer B is removed.

  In the case of particles contained in polyester A, the average particle size is determined by the same method. However, when the coating layer A contains fine particles, the ashing treatment is performed after the coating layer A is removed.

(5) Thickness of polyester layers A and B, and thickness of the entire film The thickness of the entire film is measured at 10 points randomly 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.

  The measurement conditions are as follows.

(A) Measuring device Secondary ion mass spectrometer (SIMS); “6300” manufactured by PERKIN ELMER INC.
(B) Measurement conditions Primary ion species: Cs ²⁺
Primary ion acceleration voltage: 3KV
Primary ion incident angle: 60 °
Primary ion current: 150 nA
Raster area: 300 μm × 400 μm
Analysis area: Gate 9%
Measurement vacuum: 6.0 × 10 ⁻⁹ Torr
E-GUNN: 0.5KV-3.0A
(6) Young's modulus Measured at 25 ° C. and 65% RH using an Instron type tensile tester according to the method defined in JIS-Z-1702.

(7) Intrinsic viscosity IV of polyester
Using the polyester resin cut out from the polyester layer A or layer B, measurement was performed at 25 ° C. using orthochlorophenol as a solvent.

(8) Manufacture of magnetic tape and characteristics (electromagnetic conversion characteristics) evaluation On the surface A of the laminated polyester film, a 100% cobalt thin ferromagnetic film (thickness 150 nm) is formed in the presence of a small amount of oxygen by continuous vacuum oblique deposition Let it form. The oxygen concentration is adjusted so that the oxygen content of the ferromagnetic metal thin film is 5% in terms of the number ratio of atoms to the metal. A diamond-like carbon (DLC) film is provided on the surface of the formed ferromagnetic thin film by a CVD method, a fluorine-containing carboxylic acid-based lubricating layer is sequentially provided, and a back coat layer is provided on the surface B by a known method. Thereafter, it is slit to 8 mm width to obtain a magnetic tape. A 50 m length of this tape was incorporated into a Sony high-weight cassette to obtain a VTR cassette tape. A 100% chroma signal was recorded on this tape using a Sony VTR for household use (trade name EDV-6000) by a TV test waveform generator (TG7 / U706) manufactured by Shiba-Soku, and color video noise made by Shiva-Soku was measured from the reproduced signal. Chroma S / N was measured with a vessel (925D / 1).

  Next, based on an Example, this invention is demonstrated.

[Example 1]
(Method for producing polyester A)
100 parts by weight of dimethyl terephthalate, 70 parts by weight of ethylene glycol, and 0.09 part by weight 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 weight of phosphoric acid and 0.03 part by weight 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, and then extruded into water from a discharge nozzle to form a cylindrical chip having a diameter of about 5 mm and a length of about 7 mm (the equivalent spherical diameter of the polymer is 6.4 mm).

The obtained polymer had an intrinsic viscosity of 0.650, a carboxy end group concentration of 25 equivalents / 10 ⁶ g polymer, and the amount of cyclic trimer in the polymer was 1.3 wt%.

The obtained polymer was dried at 150 ° C. under reduced pressure, and then the inside of the system was slightly pressurized at 1.20 kg / cm ² with nitrogen gas. The oxygen concentration in the reaction system is 50 ppm and the water content is 12 ppm. The inside of the system was maintained at this pressure (non-circulating), and after heat treatment at a temperature of 240 ° C. for 20 hours, the polymer was taken out. The resulting polymer had an intrinsic viscosity of 0.60 and a carboxy end group concentration of 28 equivalents / 10 ⁶ g polymer. The amount of cyclic trimer in the polymer was 0.30 wt%. Polyester A was obtained by adding 0.02 wt% of silica having an average particle diameter of 60 nm to the polymer thus obtained.

(Method for producing polyester B)
100 parts by weight of dimethyl terephthalate, 70 parts by weight of ethylene glycol, and 0.09 part by weight 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 weight of phosphoric acid and 0.03 part by weight 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, and then extruded into water from a discharge nozzle to form a cylindrical chip having a diameter of about 5 mm and a length of about 7 mm. (The equivalent spherical diameter of the polymer is 6.4 mm) The resulting polymer has an intrinsic viscosity of 0.650, the carboxy end group concentration is 25 equivalents / 10 ⁶ g polymer, and the amount of cyclic trimer in the polymer Was 1.3 wt%. The polymer thus obtained was made to contain 0.50 wt% of polystyrene spheres having an average particle size of 320 nm to obtain polyester B.

  The obtained polyester A and polyester B were each dried at 170 ° C. for 3 hours, adjusted to a ratio of 5: 1 to two extruders and supplied by co-extrusion, and a melting temperature of 280 to 800 After melting at 300 ° C and high-accuracy 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 coextrusion die on a casting drum at a temperature of 25 ° C Was quickly cooled to obtain an unstretched laminated polyester film having a thickness of 84 μm. During extrusion, both polyester A and polyester B could be extruded without increasing the filter pressure. Next, the unstretched film thus obtained was preheated, longitudinally stretched 3.0 times at 110 ° C. by a roll stretching method, and rapidly cooled to obtain a longitudinally stretched film. The amount of cyclic trimer therein was 0.60 wt%.

  In order to provide the film layer A on this longitudinally stretched film, an aqueous solution having the following composition and concentration was applied to the outside of the polyester layer A by a Mayer bar method with a coating thickness of 4.0 μm.

Aqueous solution applied to the outside of the polyester layer A:
Methylcellulose 0.10wt%
Water-soluble polyester 0.30wt%
0.03wt% spherical silica with an average particle size of 12nm
Further, in order to provide the coating layer B, a water-soluble station having the following composition and concentration was applied to the outside of the polyester layer B by a Mayer bar method with a coating thickness of 4.0 μm.

Methylcellulose 0.12wt%
Water-soluble polyester 0.30wt%
Aminoethylsilane coupling agent 0.01wt%
Then, it supplied to the stenter and extended | stretched 4.2 times in the horizontal direction at 110 degreeC. The obtained biaxially stretched film was heat-fixed with hot air of 220 ° C. for 4 seconds to obtain a laminated biaxially oriented polyester film having a total thickness of 6.4 μm and a polyester layer B thickness of 1.0 μm. Young's modulus of the film is machine direction 4,500N / mm ^2, it was transverse 6,500N / mm ^2. Table 1 shows other characteristics of the laminated film and characteristics of a ferromagnetic thin film vapor deposition type magnetic tape using the film.

[Example 2]
(Method for producing polyester A)
Polyester A was obtained in the same manner as in Example 1 except that silica particles having an average particle diameter of 60 nm were not added to the polymer.

(Method for producing polyester B)
100 parts by weight of dimethyl terephthalate, 70 parts by weight of ethylene glycol, and 0.09 part by weight 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 weight of phosphoric acid and 0.03 part by weight 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, and then extruded into water from a discharge nozzle to form a cylindrical chip having a diameter of about 5 mm and a length of about 7 mm (the equivalent spherical diameter of the polymer is 6.4 mm).

The obtained polymer had an intrinsic viscosity of 0.650, a carboxy end group concentration of 25 equivalents / 10 ⁶ g polymer, and the amount of cyclic trimer in the polymer was 1.3 wt%.

The obtained polymer was dried at 150 ° C. under reduced pressure, and then the inside of the system was slightly pressurized at 1.20 kg / cm ² with nitrogen gas. The oxygen concentration in the reaction system is 50 ppm and the water content is 12 ppm. The inside of the system was maintained at this pressure (non-circulating), and after heat treatment at a temperature of 240 ° C. for 20 hours, the polymer was taken out. The resulting polymer had an intrinsic viscosity of 0.60 and a carboxy end group concentration of 28 equivalents / 10 ⁶ g polymer. The amount of cyclic trimer in the polymer was 0.30 wt%. The polymer thus obtained was made to contain 0.50 wt% of polystyrene spheres having an average particle size of 320 nm to obtain polyester B.

  A laminated polyester film was obtained in the same manner as in Example 1 except that polyester A and polyester B thus obtained were used. Table 1 shows the obtained film characteristics and the characteristics of the ferromagnetic thin film vapor deposition type magnetic tape using the film.

[Example 3]
(Method for producing polyester A)
100 parts by weight of dimethyl terephthalate, 70 parts by weight of ethylene glycol, and 0.09 part by weight 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 weight of phosphoric acid and 0.03 part by weight 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, and then extruded into water from a discharge nozzle to form a cylindrical chip having a diameter of about 5 mm and a length of about 7 mm (the equivalent spherical diameter of the polymer is 6.4 mm).

The obtained polymer had an intrinsic viscosity of 0.650, a carboxy end group concentration of 25 equivalents / 10 ⁶ g polymer, and the amount of cyclic trimer in the polymer was 1.3 wt%.

The obtained polymer was dried at 150 ° C. under reduced pressure, and then the inside of the system was slightly pressurized at 1.20 kg / cm ² with nitrogen gas. The oxygen concentration in the reaction system is 50 ppm and the water content is 15 ppm. The inside of the system was maintained at this pressure (non-circulating), and after heat treatment at a temperature of 240 ° C. for 10 hours, the polymer was taken out. The resulting polymer had an intrinsic viscosity of 0.5 and a carboxy end group concentration of 28 equivalents / 10 ⁶ g polymer. The amount of cyclic trimer in the polymer was 0.65 wt%. In this way, polyester A was obtained.

(Method for producing polyester B)
In the same manner as in Example 2, polyester B was obtained.

  A laminated polyester film was obtained in the same manner as in Example 1 except that polyester A and polyester B thus obtained were used. Table 1 shows the obtained film characteristics and the characteristics of the ferromagnetic thin film vapor deposition type magnetic tape using the film.

[Example 4]
(Method for producing polyester A)
In the same manner as in Example 2, polyester A was obtained.

(Method for producing polyester B)
In the same manner as in Example 2, polyester B was obtained.

  Using the polyester thus obtained, a laminated polyester film was obtained in the same manner as in Example 2 except that the coating layer B was not provided. Table 1 shows the obtained film characteristics and the characteristics of the ferromagnetic thin film vapor deposition type magnetic tape using the film.

[Example 5]
(Method for producing polyester A)
In the same manner as in Example 1, polyester A was obtained.

(Method for producing polyester B)
In the same manner as in Example 2, polyester B was obtained.

  Using the polyester thus obtained, a laminated polyester film was obtained in the same manner as in Example 2 except that the coating layer A and the coating layer B were not provided. Table 1 shows the obtained film characteristics and the characteristics of the ferromagnetic thin film vapor deposition type magnetic tape using the film.

[Example 6]
(Method for producing polyester A)
Polyester A was obtained in the same manner as in Example 1 except that 0.1 wt% of silica particles having an average particle diameter of 60 nm were contained in the polymer.

(Method for producing polyester B)
In the same manner as in Example 1, polyester B was obtained.

  A laminated polyester film was obtained in the same manner as in Example 1 using the polyester thus obtained. Table 1 shows the obtained film characteristics and the characteristics of the ferromagnetic thin film vapor deposition type magnetic tape using the film.

[Example 7]
(Method for producing polyester A)
In the same manner as in Example 2, polyester A was obtained.

(Method for producing polyester B)
In the same manner as in Example 2, polyester B was obtained.

  Using the polyester thus obtained, a laminated polyester film was obtained in the same manner as in Example 1 except that the coating layer A was applied with the following aqueous coating solution. Table 1 shows the obtained film characteristics and the characteristics of the ferromagnetic thin film vapor deposition type magnetic tape using the film.

Aqueous solution on the outside of layer A:
Methylcellulose 0.01wt%
Water-soluble polyester 0.30wt%
[Example 8]
(Method for producing polyester A)
In the same manner as in Example 2, polyester A was obtained.

(Method for producing polyester B)
Polyester B was obtained in the same manner as in Example 2 except that 0.70% by weight of polystyrene spheres having an average particle size of 320 nm were contained.

A laminated polyester film was obtained in the same manner as in Example 1 using the polyester thus obtained. Table 1 shows the obtained film characteristics and the characteristics of the ferromagnetic thin film vapor deposition type magnetic tape using the film.
[Example 9]
(Method for producing polyester A)
In the same manner as in Example 2, polyester A was obtained.

(Method for producing polyester B)
Polyester B was obtained in the same manner as in Example 2 except that 0.30 wt% of polystyrene spheres having an average particle diameter of 200 nm were contained.

  A laminated polyester film was obtained in the same manner as in Example 1 using the polyester thus obtained. Table 1 shows the obtained film characteristics and the characteristics of the ferromagnetic thin film vapor deposition type magnetic tape using the film.

[Comparative Example 1]
(Method for producing polyester A)
100 parts by weight of dimethyl terephthalate, 70 parts by weight of ethylene glycol, and 0.09 part by weight 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 weight of phosphoric acid and 0.03 part by weight 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, and then extruded into water from a discharge nozzle to form a cylindrical chip having a diameter of about 5 mm and a length of about 7 mm (the equivalent spherical diameter of the polymer is 6.4 mm).

The obtained polymer had an intrinsic viscosity of 0.650, a carboxy end group concentration of 25 equivalents / 10 ⁶ g polymer, and the amount of cyclic trimer in the polymer was 1.3 wt%. In this way, polyester A was obtained.

(Method for producing polyester B)
In the same manner as in Example 2, polyester B was obtained.

  A laminated polyester film was obtained in the same manner as in Example 1 using the polyester thus obtained. The obtained film could not obtain sufficient electromagnetic characteristics due to the oligomer that bleeds out during the metal thin film deposition process. Table 1 shows the obtained film characteristics and the characteristics of the ferromagnetic thin film vapor deposition type magnetic tape using the film.

[Comparative Example 2]
100 parts by weight of dimethyl terephthalate, 70 parts by weight of ethylene glycol, and 0.09 part by weight 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 weight of phosphoric acid and 0.03 part by weight 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, and then extruded into water from a discharge nozzle to form a cylindrical chip having a diameter of about 5 mm and a length of about 7 mm (the equivalent spherical diameter of the polymer is 6.4 mm).

The obtained polymer had an intrinsic viscosity of 0.650, a carboxy end group concentration of 25 equivalents / 10 ⁶ g polymer, and the amount of cyclic trimer in the polymer was 1.3 wt%. The obtained polymer was heat treated in the same manner as in Example 1 except that nitrogen gas was circulated at a rate of 60 liters per kg of the polymer under normal pressure. The amount of cyclic trimer of the obtained polymer was 0.40 wt%. The intrinsic viscosity of the polymer was 0.75, and the carboxy end group concentration was 20 equivalents / 10 ⁶ g polymer.

  The polyester A thus obtained was extruded in the same manner as in Example 1. As a result, the filter filtration pressure increased and it was not possible to form a film.

[Comparative Example 3]
(Method for producing polyester A)
100 parts by weight of dimethyl terephthalate, 70 parts by weight of ethylene glycol, and 0.09 part by weight 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 weight of phosphoric acid and 0.03 part by weight 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, and then extruded into water from a discharge nozzle to form a cylindrical chip having a diameter of about 5 mm and a length of about 7 mm (the equivalent spherical diameter of the polymer is 6.4 mm).

The obtained polymer had an intrinsic viscosity of 0.650, a carboxy end group concentration of 25 equivalents / 10 ⁶ g polymer, and the amount of cyclic trimer in the polymer was 1.3 wt%.

The obtained polymer was dried at 150 ° C. under reduced pressure, and then the inside of the system was slightly pressurized at 1.20 kg / cm ² with nitrogen gas. The oxygen concentration in the reaction system is 1,500 ppm and the moisture is 1,800 ppm. The inside of the system was maintained at this pressure (non-circulating), and after heat treatment at a temperature of 240 ° C. for 20 hours, the polymer was taken out. Although the cyclic trimer in the obtained polymer was 0.45 wt%, the intrinsic viscosity of the polymer was 0.37, the carboxy end group concentration was 80 equivalent / 10 ⁶ g polymer, and the viscosity decreased. It was a large polymer with a high concentration of carboxy end groups. In this way, polyester A was obtained.

(Method for producing polyester B)
In the same manner as in Example 2, polyester B was obtained.

  Using the polyester thus obtained, film formation was carried out in the same manner as in Example 1. However, film breakage occurred frequently during film formation, and a film could not be obtained.

[Comparative Example 4]
(Method for producing polyester A)
Polyester A was obtained in the same manner as in Example 1 except that 0.1 wt% of silica particles having an average particle diameter of 70 nm were added to the polymer.

(Method for producing polyester B)
In the same manner as in Example 2, polyester B was obtained.

  A laminated polyester film was obtained in the same manner as in Example 1 using the polyester thus obtained. The obtained film had a surface roughness Ra of 4.3 nm, and sufficient electromagnetic characteristics were not obtained. Table 1 shows the obtained film characteristics and the characteristics of the ferromagnetic thin film vapor deposition type magnetic tape using the film.

[Comparative Example 5]
(Method for producing polyester A)
In the same manner as in Example 2, polyester A was obtained.

(Method for producing polyester B)
In the same manner as in Example 2, polyester B was obtained.

  Using the polyester thus obtained, a laminated polyester film was obtained in the same manner as in Example 1 except that the coating layer A was applied with the following aqueous coating solution.

Aqueous solution concentration on the outside of layer A:
Water-soluble polyester 0.30wt%
The obtained film had a surface roughness Ra of 0.4 nm and the magnetic surface was smooth and the friction deteriorated, so that the running durability was deteriorated, so that sufficient electromagnetic conversion characteristics could not be obtained. Table 1 shows the obtained film characteristics and the characteristics of the ferromagnetic thin film vapor deposition type magnetic tape using the film.

[Comparative Example 6]
(Method for producing polyester A)
In the same manner as in Example 2, polyester A was obtained.

(Method for producing polyester B)
Polyester B was obtained in the same manner as in Example 2 except that 0.40 wt% of polystyrene spheres having an average particle diameter of 400 nm were contained.

  A laminated polyester film was obtained in the same manner as in Example 1 using the polyester thus obtained. The obtained film has a surface roughness Ra of 22 nm, which is outside the range of the present invention, has a strong degree of shape transfer to the opposite surface of the surface protrusion of the surface B, and does not provide sufficient electromagnetic conversion characteristics. It was. Table 1 shows the obtained film characteristics and the characteristics of the ferromagnetic thin film vapor deposition type magnetic tape using the film.

[Comparative Example 7]
(Method for producing polyester A)
In the same manner as in Example 2, polyester A was obtained.
(Method for producing polyester B)
Polyester B was obtained in the same manner as in Example 2 except that 0.10 wt% of spherical silica particles having an average particle diameter of 200 nm were contained.

  A laminated polyester film was obtained in the same manner as in Example 1 using the polyester thus obtained. The obtained film has a surface roughness Ra of 3 nm which is outside the range of the present invention, the surface B is too flat, and good winding properties cannot be obtained, and the film is wrinkled, and the ferromagnetic thin film The film was broken in the process of vapor-depositing and a ferromagnetic thin film-deposited magnetic tape could not be obtained.

Claims (4)

A laminated polyester film for a metal thin film type magnetic recording medium comprising a polyester layer A located on the surface A side where the magnetic layer is provided and a polyester layer B located on the surface B side where the backcoat layer is provided. The polyester layer A contains polyester A having a cyclic trimer content of 0.7 wt% or less and an intrinsic viscosity of 0.4 to 0.65, and the surface roughness Ra of the surface A is 0.5 to 0.5. A laminated polyester film for metal thin film type magnetic recording media having a surface roughness of 4 nm and a surface roughness B of 5 to 20 nm. 2. The metal thin film type magnetic recording medium according to claim 1, wherein the polyester layer B contains polyester B having a cyclic trimer content of 0.7 wt% or less and an intrinsic viscosity of 0.4 to 0.65. Laminated polyester film. The laminated polyester film for metal thin-film magnetic recording media according to claim 1 or 2, wherein at least one of the surface A and the surface B is formed of a coating layer. A magnetic recording medium comprising a ferromagnetic metal thin film layer on the surface A of the laminated polyester film for a metal thin film type magnetic recording medium according to claim 1.