JPH0367623B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a base film for magnetic recording media, and more particularly to a polyester base film for metal thin film magnetic recording media that is flat, has excellent running properties, and is capable of long-term recording. <Prior art> In recent years, as a high-density magnetic recording medium, a ferromagnetic metal thin film has been formed as a magnetic recording layer on a nonmagnetic support by a vacuum deposition method such as vacuum evaporation or sputtering, or a plating method without using a binder. Therefore, a thin film magnetic recording material using this ferromagnetic metal has been proposed. For example, Co vapor-deposited tape
147010), a perpendicular magnetization film made of a Co-Cr alloy (Japanese Patent Application Laid-open No. 134706/1983), etc. have been proposed. A metal thin film formed by such thin film forming means such as vapor deposition, sputtering, or ion plating is expected to have performance equivalent to or better than that of a conventional coated recording medium having a thickness of 3 μm or more. By the way, US Pat. No. 3,787,327 is based on the idea that magnetic properties such as the coercive force Hc, which is a static property, or the squareness ratio of the hysteresis loop do not depend much on the surface condition of the non-magnetic support used. Examples include vacuum-deposited Co-Cr multilayer structures as disclosed in . However, the metal thin film formed is thin;
The disadvantage is that the surface condition (surface irregularities) of the nonmagnetic support directly manifests itself as irregularities in the magnetic film, which causes noise. Therefore, from the viewpoint of noise, it is preferable that the surface condition of the nonmagnetic support is as smooth as possible. On the other hand, from the viewpoint of handling such as winding and unwinding of the film, if the film surface is flat, the sliding property between the films will be poor, and blocking phenomenon will occur, making it impossible to use as a product. It is required that the film surface be rough. Furthermore, from the viewpoint of electromagnetic conversion characteristics, the surface of the nonmagnetic support is required to be flat, while from the viewpoint of handling properties, it is required to be rough. Base films are required to simultaneously satisfy these two contradictory properties. Furthermore, when a metal thin film magnetic recording medium is actually used, a serious problem is the runnability of the metal thin film surface. In the case of conventional coated magnetic recording media,
Although it is possible to improve the running performance of a magnetic surface by adding a lubricant to the binder of magnetic powder, it is very difficult to maintain stable running performance in the case of metal thin film magnetic recording media, especially at high temperatures. It had drawbacks such as particularly poor running performance in high humidity conditions. Furthermore, when recording for a long time, the difference between the output waveform of the head (hereinafter referred to as envelope) from the initial state is extremely large, the output decreases, and long-time recording is difficult. <Objective of the Invention> An object of the present invention is to provide a polyester base film for a metal thin film magnetic recording medium that is flat and capable of forming a metal thin film with excellent running properties and capable of long-term recording. <Configuration and Effects of the Invention> According to the present invention, an object of the present invention is to achieve the following characteristics (a):
On one side of a biaxially oriented polyester film that satisfies ~(e), (a) Young's modulus in the longitudinal direction: 500 Kg/mm ² or less (b) Young's modulus in the lateral direction: 650 kg/mm ^{2 or} more (c) 150°C in the lateral direction Thermal shrinkage rate at 1~5% (d) Center line average roughness (Ra) 0.001~0.003μ on the surface (e) Number of protrusions with a height (h) of 0.27~0.54μ
0.2 pieces/mm ² or less Consists of a composition whose main components are polyurethane, acrylic resin, low molecular weight polyolefin wax, and a roughening substance with an average particle size of 0.15μ or less, and the center line average roughness Ra of the surface is 0.002~ This is achieved by using a base film for a magnetic recording medium in which a thin film having a thickness of 0.01μ and having no mountain-like irregularities is formed on the surface, and the surface of the polyester film on which the thin film is not formed is the surface on which the metal thin film is formed. In the present invention, polyester is a linear saturated polyester synthesized from an aromatic dibasic acid or its ester-forming derivative and a diol or its ester-forming derivative. Specific examples of such polyesters include polyethylene terephthalate, polyethylene isophthalate, polybutylene terephthalate, poly(1,4-cyclohexylene dimethylene terephthalate), polyethylene-
Examples include 2,6-naphthalene dicarboxylate, and also include copolymers thereof or blends of these with small proportions of other resins. The biaxially oriented polyester film of the present invention is a film that satisfies the following properties (a) to (e). (a) Young's modulus in the longitudinal direction 500Kg/mm ² or less (b) Young's modulus in the lateral direction 650Kg/mm ² or more (c) Heat shrinkage rate at 150℃ in the lateral direction 1 to 5% (d) Center line of the surface Average roughness (Ra) 0.001 to 0.003μ (e) Number of protrusions with protrusion height (h) of 0.27 to 0.54μ
0.2 pieces/mm ² or less This biaxially oriented polyester film can be produced based on a method of melt-extruding polyester, rapidly cooling it to form an unstretched film, and then sequentially biaxially stretching the unstretched film. For example, a biaxially oriented polyethylene terephthalate film that satisfies the above characteristics (a) to (e) can be obtained by melt-extruding polyethylene terephthalate containing a lubricant through a die, rapidly cooling it on a casting drum to form an unstretched film, and then forming the unstretched film. The film is made by sequentially stretching and heat-treating the film in two axial directions, and at that time, the film forming conditions are adjusted to the longitudinal stretching ratio so that the film has the above characteristics.
Select from the following ranges: 3.0 to 3.8 times, transverse stretching ratio 3.5 to 4.5 times, stretching temperature 80 to 120°C, and heat setting temperature 150 to 240°C. Further, the heat shrinkage rate in the lateral direction can be set to a desired value by relaxing or tensioning the material in the lateral direction. The biaxially oriented polyester film preferably has a thickness of 4 to 15 microns, more preferably 5 to 13 microns. Further, the Young's modulus in the transverse direction is preferably 700 Kg/mm ² or more, and the heat shrinkage rate at 150°C in the transverse direction is preferably 2 to 4%.
The centerline average roughness Ra of the surface is preferably 0.0015 to 0.0025μ, and the protrusion height (h) on the surface is 0.27 to
The number of 0.54μ protrusions is preferably 0 pieces/mm ² . The centerline average roughness Ra and the number of protrusions on the surface can be adjusted by adjusting a lubricant dispersed in the polyester. This lubricant has an average particle size of 20~
Silicon oxide with a diameter of 100 mμ, particularly 30 to 80 mμ is preferably mentioned, and the silicon oxide contains 0.005 to 0.1% by weight,
In particular, it is preferable to disperse and contain the polyester in a proportion of 0.008 to 0.05% by weight. It is preferable that the lubricant does not contain coarse particles such as agglomerated particles. For example, when silicon oxide is added in the polyester manufacturing process, the silicon oxide is once made into a water-dispersed sol and then water is replaced with glycol (e.g. ethylene glycol) to form glycol. It is preferable to use it as a dispersion. Directly dispersing silicon oxide in glycol is not preferable because agglomeration occurs upon addition, resulting in the formation of coarse protrusions on the film surface.
If the average particle size of silicon oxide used as a lubricant is less than 20 mμ, the film surface will become completely flat, resulting in poor running durability.On the other hand, if it exceeds 100 mμ, protrusions on the film surface will become large, resulting in a decrease in output as an electromagnetic conversion characteristic. is large and undesirable. Furthermore, if the content of the lubricant is too small, the film surface will become too flat, while if it is too large, the protrusions on the film surface will become too high, which is not preferable. In the present invention, polyurethane,
It consists of a composition whose main components are an acrylic resin, a low molecular weight polyolefin wax, and a roughening substance with an average particle size of 0.15μ or less, and the centerline average roughness of the surface is
A film having Ra of 0.002 to 0.01 μ and a surface state of minute irregularities without mountain-like irregularities is formed. The coating liquid that forms a thin film on the surface of this polyester film is preferably an aqueous coating liquid, and the polyurethane in the coating liquid is preferably an aqueous polyurethane, which is converted into water by a carboxylic acid group, a sulfonic acid group, or a sulfuric acid half ester base. It is a polyurethane with enhanced affinity for water, and such a water affinity-imparting group is usually introduced during or after polyurethane synthesis. The amount of bases such as carboxylic acid groups, sulfonic acid groups, and sulfuric acid half-ester bases is preferably 0.5 to 15% by weight. If the proportion of the base is too small, the water affinity of the polyurethane will be insufficient, making it difficult to prepare a coating solution, and if it is too large, the inherent properties of the polyurethane will be impaired, which is not preferable. Such aqueous polyurethane forms a stable aqueous dispersion or aqueous solution using a dispersion aid if desired. Examples of polyhydroxy compounds used in the synthesis of polyurethane include polyethylene glycol,
Polypropylene glycol, polyethylene/polypylene glycol, polytetramethylene glycol, hexamethylene glycol, tetramethylene glycol, 1,5-pentanediol, diethylene glycol, triethylene glycol, polycaprolactone, polyhexamethylene adipate, polyhexamethylene sebacate, poly Examples include tetramethylene adipate, polytetramethylene sebacate, trimethylolpropane, trimethylolethane, pentaerythritol, and glycerin. Examples of the polyisocyanate compound include hexamethylene diisocyanate, diphenylmethane diisocyanate, tolylene diisocyanate, isophorone diisocyanate, an adduct of tolylene diisocyanate and trimethylolpropane, an adduct of hexamethylene diisocyanate and trimethylolethane, and the like. be able to. Examples of the carboxylic acid-containing polyol include dimethylolpropionic acid, dimethylolbutyric acid, dimethylolvaleric acid, and trimellitic acid bis(ethylene glycol) ester. Examples of the amino group-containing carboxylic acid include β-aminopropionic acid, γ-aminobutyric acid, and P-aminobenzoic acid. As the hydroxyl group-containing carboxylic acid, for example, 3-
Hydroxypropionic acid, γ-hydroxybutyric acid,
Examples include P-(2-hydroxyethyl)benzoic acid and malic acid. Examples of compounds having an amino group or a hydroxyl group and a sulfonic group include aminomethanesulfonic acid, 2-aminoethanesulfonic acid, 2-amino-5-methylbenzene-2-sulfonic acid, sodium β-hydroxyethanesulfonate, aliphatic Examples include propane sultone and butane sultone adducts of di-primary amine compounds, and preferably propane sultone adducts of aliphatic di-primary amine compounds. Further, examples of compounds containing an amino group or a hydroxyl group and a sulfuric acid half-ester group include aminoethanol sulfuric acid,
Examples include ethylenediamine ethanol sulfate, aminobutanol sulfate, hydroxyethanol sulfate, γ-hydroxypropanol sulfate, α-hydroxybutanol sulfate, and the like. Polyurethane can be synthesized using these compounds by conventionally well-known methods. The acrylic resin as a thin film forming component in the present invention is preferably an aqueous acrylic resin containing 40 to 80 mol% of a methyl methacrylate component and 20 to 60% of other vinyl monomer components copolymerizable therewith. If the methyl methacrylate component in the acrylic resin is less than 40 mol %, the strength of the coating film tends to decrease, the coating tends to soften, and the handling property deteriorates due to deterioration of blocking resistance, which is not preferable. On the other hand, the methyl methacrylate component is 80 mol%
If it exceeds this range, the coating film tends to harden, the coating film becomes brittle, the adhesion to the substrate decreases, and the film-forming property deteriorates, which is not preferable. Other vinyl monomers copolymerizable with the above methyl methacrylate include, for example, alkyl acrylate (alkyl groups include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl group). , 2-ethylhexyl group, cyclohexyl group, benzyl group, phenylethyl group, etc.); Alkyl methacrylate (the alkyl group includes an alkyl group other than the methyl group of the above-mentioned alkyl acrylate); 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, - Hydroxy-containing monomers such as hydroxypropyl acrylate, 2-hydroxypropyl methacrylate; acrylamide, methacrylamide, N-methylmethacrylamide,
N-methylacrylamide, N-methylol acrylamide, N-methylol methacrylamide,
Amide group-containing monomers such as N,N-dimethylolallylamide, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-phenylacrylamide; N,N-diethylaminoethyl acrylate, N,N-diethylaminoethyl methacrylate Amino group-containing monomers such as glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether; Sulfonic acid groups such as styrene sulfonic acid, vinyl sulfonic acid and their salts (sodium salt, potassium salt, ammonium salt, etc.) or a monomer containing a salt thereof; crotonic acid,
Itaconic acid, acrylic acid, maleic acid, fumaric acid and their salts (sodium salt, potassium salt,
Monomers containing carboxyl groups or their salts such as ammonium salts, etc.; Monomers containing acid anhydrides such as maleic anhydride and itaconic anhydride; Others, vinyl isocyanate, allyl isocyanate, styrene, vinyl methyl ether, vinyl ethyl ether , vinyl tris alkoxysilane, alkyl maleic acid monoester, alkyl fumaric acid monoester, acrylonitrile, methacrylonitrile, alkyl itaconic acid monoester, vinylidene chloride, vinyl acetate, vinyl chloride and the like. The above-mentioned monomers to be copolymerized with methyl methacrylate may be freely selected, preferably in combination of two or more, but they are effective in imparting hydrophilicity to the acrylic resin, dispersion stability of aqueous liquids, adhesion to polyester films, etc. From the viewpoint of
Those having a functional group such as ammonium salt (ammonium salt, etc.) are preferred. In addition, thermosetting types are suitable for improving the heat resistance, strength, water resistance, etc. of coating films; for example,
Epoxy group-containing monomer and amino group, acid anhydride group, carboxyl group, hydroxyl group or N-
Combination with monomer containing methylol group; N
Examples include a combination of a monomer containing a -methylol or N-methylol ether group and a monomer containing a carboxyl group or an amino group, and monomers that are thermosetting even when used alone, such as a carboxylic acid group or a methylol group. One type or a combination of two or more of these reactive groups can be optionally introduced into one type of acrylic resin or two or more types of acrylic resins. It may be a combination of resins. In addition, low molecular weight substances (for example, alkylolated melamine, etc.) that have groups that can react with the reactive groups in the acrylic resin and with each other when heated are used.
It is also possible to add more than one species. The aqueous liquid of acrylic resin can be produced by any known method. At that time, molecular weight regulators (mercaptans), dispersion aids (polymer protective colloids such as polyvinyl alcohol and hydroxymethylcellulose), etc. may be added as necessary. In addition, applications of low molecular weight surfactants, high molecular weight surfactants, reactive surfactants, etc., and production methods using so-called soap-free polymerization, which do not contain surfactants, may also be adopted. The low molecular weight polyolefin wax, which is a thin film forming component in the present invention, has physical and chemical properties similar to high molecular weight polyolefin resins, but has an extremely low melt viscosity, and is a wax such as paraffin wax, microcrystalline wax, etc. Tsukusu,
It has a higher melting point than carbana wax, montan wax, etc. In particular, low molecular weight polypropylene has a high melting point of 150°C. These polyolefin waxes can be made water-based by known manufacturing methods such as mixing molten polyolefin and hot water containing an emulsifier (surfactant, etc.) to form an O/W emulsion, or by oxidizing. Polyolefins containing carboxyl groups in their molecules can be more easily emulsified with water. Among these low molecular weight polyolefins, polyethylene waxes are preferred, with an average molecular weight of 1000 to
10000, density 0.91 to 0.97 (g/ml), melt viscosity (140℃, cps) on a Burckfield viscometer of approximately 20
Polyethylene waxes in the range of from about 700 to about 700 are preferred. Furthermore, those having a molecular weight in the range of 2,000 to 4,000 are preferred because they are easily water-soluble and satisfy the properties such as lubricity as a polyethylene wax. Note that high molecular weight polyethylene (molecular weight 20,000) has an extremely high melt viscosity of about 80 million cps, making it extremely difficult to make it water-based. In the present invention, the roughening substances to be mixed with the aqueous liquid (aqueous solution, dispersion, or emulsion) of the polyurethane, acrylic resin, and low molecular weight polyolefin wax include polystyrene, polymethyl methacrylate, methyl methacrylate copolymer, and polystyrene. Organic fine powder such as tetrafluoroethylene, polyvinylidene fluoride or polyacrylonitrile, benzoguanamine resin, etc., or silica, alumina, titanium dioxide, kaolin, talc, graphite, calcium carbonate, feldspar, molybdenum disulfide, carbon black or barium sulfate. These may be made into an aqueous dispersion using an emulsifier or the like, and may also be used in fine powder form as a polyurethane aqueous liquid, an acrylic resin aqueous liquid, or a low molecular weight polyolefin wax. It may be one that can be added to an aqueous liquid. This surface roughening substance is fine particles with an average particle size of 0.15μ or less, preferably 0.01 to 0.1μ. Furthermore, these water-insoluble solid substances are preferably ultrafine particles with a specific gravity not exceeding 3 in order to avoid settling in the aqueous dispersion. If the average particle size is larger than 0.15μ, the surface of the thin film becomes too rough, which is not preferable. The surface roughening substance has the effect of promoting the uniform formation of microprotrusions on the thin film itself, and the reinforcing effect of the thin film with the fine powder itself, and also improves the blocking resistance of acrylic resin and low molecular weight polyolefin wax to the thin film.
Coupled with the effect of reducing frictional force and the effect of contributing to the scratch resistance of the thin film due to the synergistic effect of both, it imparts an excellent slipperiness effect to the polyester film. The mixing ratio of polyurethane (A), acrylic resin (B), low molecular weight polyolefin wax (C) and roughening substance (D), which are the main components of the thin film, is usually [(A) + (B) +
(C)]/(D)=98/2~40/60, [(A)+(B)]/(C)=
98/2~40/60, and (A)/(B)=90/10~10/90
(Solid content equivalent: weight %) is preferably in the range of [(A)+(B)+(C)]/(D)=95/5 to 60/
40, [(A)+(B)]/(C)=95/5~60/40,(A)/(B)=
It is preferably in the range of 80/20 to 20/80 (weight ratio). If the mixing ratio of acrylic resin and low molecular weight polyolefin wax is too small, the frictional force will increase and the handling properties will be deteriorated, while if it is too large, the adhesion between the thin film and the polyester film will be reduced or the thin film will become brittle. This may cause the film to become less slippery. In addition, if the mixing ratio of the roughening substance is too small, the roughening substance added may
The film's slipperiness is reduced due to a decrease in the uniform protrusion formation effect of the fine protrusion forming substance in the thin film, and a decrease in the reinforcing effect of the fine powder itself on the thin film.
On the other hand, if this ratio is too high, the ratio of surface roughening substances will increase, which will reduce the adhesion between the thin film and the polyester film, make the thin film brittle, etc. Since it is destroyed by frictional force and the thin film is worn away, the sustainability of the smoothing effect is impaired. The polyurethane, acrylic resin, and low molecular weight polyolefin wax (C) may be mixed with the roughening substance (D) after each is in the state of an aqueous dispersion. ), or into an aqueous dispersion of all of (A), (B), and (C), a powdery surface roughening substance, and if necessary, an emulsifier may be added and dispersed by stirring. The thin film on the polyester film in the present invention is preferably formed by applying the above-mentioned coating liquid to the surface of the polyester film before the oriented crystallization process is completed. At this time, in order to ensure smooth application of the coating film, the film surface may be subjected to corona discharge treatment as a preliminary treatment, or a chemically inert surfactant may be used in combination with the thin film-forming composition. preferable. The surfactant is a substance that promotes wetting of the polyester film by lowering the surface tension of the coating liquid to 40 dyne/cm or less, and includes, for example, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid, etc. ester, glycerin fatty acid ester, fatty acid metal soap, alkyl sulfate, alkyl sulfonate,
Examples include anionic and nonionic surfactants such as alkyl sulfosuccinates. Furthermore, within the scope of not eliminating the effects of the present invention,
For example, other additives such as antistatic agents, ultraviolet absorbers, lubricants, etc. can be mixed. Here, the polyester film before the above-mentioned crystal orientation is completed includes an unstretched film, a film stretched in a uniaxial direction, a film stretched in a biaxial direction but with at least one of the stretching orientations being in a predetermined orientation. Examples include films that have not been seasoned. The solid content concentration of the coating liquid is usually 30% by weight or less, preferably 15% by weight or less. The appropriate viscosity is 100 cps or less, preferably 20 cps or less. The amount of coating is approximately 0.5 to 20g per ^1m2 of moving film.
Furthermore, 1 to 10 g is preferable. In other words, in the final biaxially stretched film, about 0.001 to 1 g per 1 m ² on one surface of the film, more preferably about
A solids content of 0.01 to 0.3 g is preferred. Any known coating method can be used as the coating method. For example, a roll coating method, a gravure coating method, a roll brushing method, a spray coating, an air knife coating, an impregnation method, a curtain coating method, etc. may be applied alone or in combination. The above coating liquid is preferably applied to the film immediately after being subjected to longitudinal uniaxial stretching, and then the film is preferably introduced into a tenter for transverse stretching and heat setting. The area of the coated material is expanded as the film is stretched in an unsolidified state, and is heated to volatilize water and firmly adhere to the surface of the biaxially stretched film. The above-mentioned coating liquid in the present invention is converted into a solid coating film having a large number of microprojections, as described above, by the substrate stretching process and the heat treatment process. This heating is preferably at a temperature of about 100 to about 240°C and about 1 to about
It takes place for 20 seconds. In this way, the thin film formed on one side of the polyester film has a center line average roughness of 0.002~
0.01μ and there are no mountain-like irregularities on the surface.
It has uniform minute irregularities. According to the present invention, the film surface is flat,
Moreover, we can provide a biaxially oriented polyester film for metal thin film magnetic recording media that can form a metal thin film surface with excellent running properties.In particular, the noise is dramatically reduced, the noise level is extremely excellent, and the running performance of the metal thin film surface is improved. It is possible to provide a biaxially oriented polyester film that is useful for manufacturing thin metal film magnetic recording media that have excellent running durability in the case of long-term recording. Examples Hereinafter, the present invention will be further explained with reference to Examples.
In addition, the physical properties of the film were measured by the following method. 1 Center line average roughness Ra According to JIS B0601, using a high-precision surface roughness meter SE-3FAT manufactured by Kosaka Laboratory Co., Ltd., the needle radius was 2 μm,
Measurement load 30mg, magnification 200,000x, cutoff 0.08
The chart is placed under the conditions of mm, and a part of measurement length L is extracted from the film surface roughness curve in the direction of its center line, and the center line of this extracted part is set on the
With the vertical magnification direction as the Y axis, the roughness curve is Y=f
When expressed as (x), the value given by the following formula is μ
Expressed in m units. R _CLA = 1/L∫ ^L ₀ ｜f(x)｜dx In this measurement, the measurement length was 1.25 mm, and 4 pieces were measured.
Expressed as an average value. 2 Number of surface projections Aluminum is uniformly vacuum-deposited on the film surface to a thickness of 400 to 500 Å or less, and collodion is pasted on the opposite non-evaporated surface (film surface). After drying, visible monochromatic light multiple interference reflection method is applied. Using a microscope (for example, manufactured by Carl Zeiss JENA), take pictures of 10 arbitrary locations at 100x magnification, find the number of protrusions corresponding to the protrusion height in each photograph, and convert it to 1 mm ² . At this time, the field of view for 10 photographs is 1.55 mm ² . 3 Electromagnetic conversion characteristics (recording density characteristics) S/N (dB) ratio and
High-density recording characteristics,
In particular, evaluate the magnitude of the noise level. 4. Long-term durability Recording and playback are repeated using a commercially available VHS VTR, and the playback screen after 100 repeated runs is evaluated using the following criteria. 〇: Running smoothly and there is no fluctuation in the playback screen ×: There is fluctuation in the playback screen 5 Young's Modulus Cut the film into a sample width of 10 mm and length of 150 mm.
Tensile with an Instron type universal tensile testing device with a chuck distance of 100 mm, a tensile speed of 10 mm/min, and a chart speed of 500 mm/min. Young's modulus is calculated from the tangent to the rising portion of the obtained load-elongation curve. 6 Heat shrinkage rate Free heat shrinkage is performed for 30 minutes in a hot air circulation furnace (gear aging tester) at 150°C, and calculated using the following formula. Thermal shrinkage rate = original length - length after shrinkage / original length x 100 (%) Use 300 mm as the original length. Examples 1 to 3 and Comparative Examples 1 to 3 Zinc acetate as a catalyst to 100 parts by weight of dimethyl terephthalate and 70 parts by weight of ethylene glycol.
Add 0.023 parts by weight (0.020 mol% to dimethyl terephthalate) and carry out transesterification while distilling off methanol at 150 to 240°C for 4 hours, then add stabilizer (glycol solution of phosphorus compound) to 0.014 parts by weight in terms of trimethyl phosphate. Next, 0.04 parts by weight of antimony trioxide was added as a polycondensation catalyst, and a predetermined amount of silicon oxide having the average particle size listed in Table 1 was added, and the mixture was heated under a high vacuum of 1 mmHg or less. A time polycondensation reaction is carried out, and the intrinsic viscosity (η: O-
Polyethylene terephthalate (chlorophenol solvent, measured at 25°C) of 0.65 was obtained. These polyethylene terephthalates were melt-extruded and rapidly cooled to form an unstretched film according to a conventional method, and then 3.4 times the length in the machine direction at 100°C and 4.3 times the time in the transverse direction at 120°C.
The films were sequentially biaxially stretched and heat-set at 225° C. for 30 seconds to obtain biaxially oriented films each having a thickness of 10 μm.
At this time, the coating solution prepared below was uniformly coated on one side of the uniaxially stretched film, which had been subjected to longitudinal stretching, by a kiss coating method at a position immediately before entering the tenter. The average coating amount at this time was about 4 g wet per 1 m ² of the uniaxially stretched film (this amount was 1 m ² for the biaxially stretched film described below).
(equivalent to approximately 0.02g per serving). Next, the uniaxially stretched film coated on one side was heat-set to obtain a biaxially oriented polyester film. <Coating liquid> Polyurethane aqueous dispersion containing carboxylic acid amine base [manufactured by Toyo Polymer Co., Ltd.: trade name Merci 585]
28 parts by weight (as non-volatile components), acrylic resin emulsion [methyl methacrylate/ethyl acrylate/acrylamide = 49/43/8 (mol%)]
28 parts by weight, 7 parts by weight of polyethylene wax emulsion (melting point: approx. 105°C), 27 parts by weight of colloidal silica aqueous dispersion (average particle size: 40-50 mμ), and polyoxyethylene nonyl phenyl ether [manufactured by NOF Corporation] : Trade name NS-208.5] was diluted and dissolved in ion-exchanged water to prepare a coating solution having a solid content concentration of 2% by weight. The film thus obtained had good slipperiness, no blocking occurred, and could be wound up well. The characteristics of the film surface () and () are summarized in Table 1. A cobalt-nickel alloy thin film of 1000Å was deposited on the surface of this polyester film by vacuum evaporation.
It was formed with a film thickness of . The film is then cut into 1/4″ width pieces in the machine direction to form metal thin film magnetic recording tape.
9.5 using a ring head with a gap length of 0.3 μm.
Recording and reproduction were performed at a speed of cm/sec, and the electromagnetic conversion characteristics (digital recording density characteristics) were evaluated. The results are shown in Table-1. From these results, it is understood that the magnetic recording medium based on the film of the present invention has a large S/N ratio, a significantly superior noise level, and excellent long-term durability.

[Table] Examples 4 to 6 and Comparative Examples 4 to 5 Using the same polymer as in Example 2, unstretched films were prepared under the film forming conditions listed in Table 2 (however, the film forming conditions listed in Table 2 were Otherwise, the conditions are the same as in Example 2) A 10 μm film was created,
A coating liquid having the same composition as in Example 2 was applied to the film surface ( ). A cobalt-nickel alloy thin film of 1000Å was deposited on the surface of this polyester film by vacuum evaporation.
It was formed with a film thickness of . The film is then cut into 1/4″ width pieces in the machine direction to form metal thin film magnetic recording tape.
9.5 using a ring head with a gap length of 0.3 μm.
Recording and reproduction were performed at a speed of cm/sec, and the electromagnetic conversion characteristics (digital recording density characteristics) were evaluated. Furthermore, long-term running durability was evaluated. These results are shown in Table-2. It can be seen from Table 2 that Examples 4 to 6 have excellent long-term running durability, a large S/N ratio, and a significantly excellent noise level.

【table】

【table】

Claims (1)

[Claims] 1 (1) On one side of a biaxially oriented polyester film satisfying the following properties (a) to (e), (a) Young's modulus in the longitudinal direction of 500 kg/mm ² or less (b) In the lateral direction Young's modulus: 650Kg/mm ² or more (c) Heat shrinkage rate at 150℃ in the lateral direction: 1 to 5% (d) Surface centerline average roughness (Ra)
0.001~0.003μ (e) Number of protrusions with height (h) of 0.27~0.54μ
0.2 pieces/mm ² or less (2) Consists of a composition whose main components are polyurethane, acrylic resin, low molecular weight polyolefin wax, and a roughening substance with an average particle size of 0.15 μ or less, and has a surface center line average roughness Ra. 1. A base film for a magnetic recording medium, on which a thin film is formed with a thickness of 0.002 to 0.01 μ and has no mountain-like irregularities on the surface, and the surface of the polyester film on which the thin film is not formed is the surface on which the metal thin film is formed. 2 Biaxially oriented polyester film has an average grain size of 20
The base film for a magnetic recording medium according to claim 1, containing 0.005 to 0.1% by weight of silicon oxide having a particle size of ~100 mμ.