JPH0354698B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a polyester film with improved surface properties, particularly slipperiness, by providing a coating layer.

Biaxially oriented polyester films, especially biaxially oriented polyethylene terephthalate films, have excellent transparency, dimensional stability, mechanical properties, electrical properties, gas barrier properties, heat resistance, chemical resistance, etc., and are used as packaging materials and electrical insulation materials. It is used as a base material for photosensitive materials, drafting materials, electrophotographic materials, magnetic recording materials, etc. that use silver salts, diazo compounds, photosensitive resins, etc.

As the recording density of magnetic recording media increases and the capacitance of capacitors increases, polyester films that are used are increasingly required to be flat and have good slip properties. The requirements are similar for optical and electrophotographic applications.

Conventionally, methods for improving the slipperiness of polyester films include adding fine organic or inorganic particles to polyester (additional particle method), and precipitating transesterification catalyst residue during polyester polymerization ( Methods using a polyester composition, such as the precipitated particle method), a method using a polymer blend, and a method using an organic lubricant, are used. However, with methods such as the additive particle method, precipitated particle method, and polymer blending, if one of slipperiness and flatness improves, the other decreases, and it is difficult to improve both of them, and they are not suitable for optical applications. Furthermore, there are problems such as the need to satisfy transparency. Although the method of blending lubricants can achieve smoothness to a certain extent, it may cause contamination of the process or product due to lubricant transfer, difficulty in achieving and maintaining a high degree of vacuum during vapor deposition, and problems between layers when forming a laminate. There are many problems such as decreased adhesion.

In contrast to conventional methods using compositions, a technique for smoothing films by applying a coating layer to the film and forming mountain-like protrusions on the surface has recently been developed in JP-A-Sho.
It has been proposed in JP-A No. 56-10455, JP-A-57-18254, JP-A-58-62826, etc.

The present inventors have previously discovered that a biaxially oriented polyester film having a coating layer made of an acrylic resin and a polyester resin has excellent surface properties (Japanese Patent Laid-Open Publication No. 124651/1982). As a result of further investigation regarding the slipperiness of films with coating layers, it was found that films with coating layers mainly composed of polyester resins, polyurethane resins, butadiene-based elastomer resins, etc. had poor slipperiness. Films containing acrylic resin as a component of the coating layer generally had good slip properties. this is,
It is presumed that this is related to the polarity or flexibility of the resin, and as a result of further studies on coating layers mainly composed of acrylic resins, we found that films with coating layers composed of acrylic resins and specific resins have smoothness. The inventors have found that the present invention is based on the findings that the present invention has excellent properties such as durability of the coated layer, transparency of the film, and interlayer adhesion when formed into a laminate.

That is, the present invention includes a water-dispersible or water-soluble acrylic resin, a water-dispersible or water-soluble polyester resin having a sulfonic acid group, and a polyester film having a low elongation at break on at least one side of the polyester film.
This invention relates to a biaxially stretched polyester film provided with a coating layer consisting of 200% or less of a water-soluble resin.

The polyester film constituting the substrate in the present invention is preferably a polyethylene terephthalate film in which 80 mol% or more of its constituent units are ethylene terephthalate, and copolymer components other than the ethylene terephthalate component include, for example, diethylene glycol, propylene glycol, neopentyl glycol, Diol components such as polyethylene glycol, polytetramethylene glycol, 1,4-cyclohexanedimethanol; isophthalic acid, 2,6-naphthalene dicarboxylic acid, 5-sodiosulfoisophthalic acid, adipic acid, azelaic acid, sebacic acid and their esters Dicarboxylic acid components such as forming derivatives; oxymonocarboxylic acids such as oxybenzoic acid and its ester forming derivatives, etc. can be used.

In the polyester composition constituting the substrate in the present invention, additive particles, precipitated particles, and other catalyst residues that form protrusions on the film surface, and resins other than polyethylene terephthalate are high-density magnetic recording materials whose magnetic layer is vapor-deposited metal. Although it is preferable to reduce the amount as much as possible depending on the intended use, it may be contained in an amount conventionally used by those skilled in the art depending on the intended use. That is, the film of the present invention imparts slipperiness to a film that has almost no surface protrusions and could not be put to practical use in the past, and also provides even better slipperiness to a film that has surface protrusions and is appropriately slippery. In this sense, a protrusion-forming agent for polyester film may be included as appropriate depending on the purpose. As additives other than the protrusion-forming agent, antistatic agents, stabilizers, lubricants, crosslinking agents, etc. can be used as necessary.

Water-dispersible or water-soluble acrylic resin (hereinafter abbreviated as "acrylic resin") in the present invention
is preferably one containing alkyl acrylate or alkyl methacrylate as a main component,
The vinyl monomer component is 30 to 90 mol%, copolymerizable with these components, and has a functional group.
It is a water-soluble or water-dispersible resin containing mol%.

A vinyl monomer that can be copolymerized with alkyl acrylate or alkyl methacrylate and has a functional group can be used to impart hydrophilicity to the resin and improve its water dispersion, or to provide it between the resin and the polyester film or on the undercoat layer. It is preferable to have a functional group that improves the adhesion with other coating layers or the affinity with the polyester resin blended as a coating agent. Preferred functional groups include a carboxyl group or a salt thereof, Acid anhydride groups, sulfonic acid groups, or salts thereof, amide groups, alkylolated amide groups, amino groups (including substituted amino groups) or alkylolated amino groups, or salts thereof, hydroxyl groups, epoxy groups etc. Particularly preferred are carboxyl groups or salts thereof, acid anhydride groups, epoxy groups, and the like. Two or more types of these groups may be contained in the resin.

The reason why it is preferable that the alkyl acrylate or alkyl methacrylate in the acrylic resin is 30 mol% or more is because of the coating formability, the strength of the coating film,
This is because blocking resistance becomes better. The reason why the alkyl acrylate or alkyl methacrylate content in the acrylic resin is preferably 90 mol% or less is that by introducing a compound having a specific functional group into the acrylic resin as a copolymerization component, it can be made water-soluble or water-dispersible. This is to make it easier to use and to stabilize its state over a long period of time.Furthermore, it improves the adhesion between the coating layer and the polyester film layer, and improves the strength, water resistance, and chemical resistance of the coating layer due to reactions within the coating layer. Furthermore, it is possible to improve the adhesion between the film of the present invention and other materials.

Examples of alkyl groups in alkyl acrylates and alkyl methacrylates include methyl group, ethyl group, n-propyl group, isopropyl group, n-
Examples include butyl group, isobutyl group, t-butyl group, 2-ethylhexyl group, lauryl group, stearyl group, and cyclohexyl group.

As the vinyl monomer having a functional group copolymerizable with alkylia acrylate or alkyl methacrylate, the following compounds having functional groups such as a reactive functional group, a self-crosslinking functional group, and a hydrophilic group can be used.

Examples of compounds having a carboxyl group or a salt thereof, or an acid anhydride group include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid,
Examples include crotonic acid, metal salts of these carboxylic acids with sodium, ammonium salts, and maleic anhydride.

Examples of compounds having a sulfonic acid group or a salt thereof include vinyl sulfonic acid, styrene sulfonic acid,
Examples include metal salts and ammonium salts of these sulfonic acids with sodium and the like.

Examples of compounds having an amide group or an alkylolated amide group include acrylamide, methacrylamide, N-methylmethacrylamide,
Examples include methylolated acrylamide, methylolated methacrylamide, ureido vinyl ether, β-ureido isobutyl vinyl ether, and ureido ethyl acrylate.

Examples of compounds having an amino group or an alkylolated amino group or a salt thereof include diethylaminoethyl vinyl ether, 2-aminoethyl vinyl ether, 3-aminopropyl vinyl ether, 2-aminobutyl vinyl ether,
Dimethylaminoethyl methacrylate, dimethylaminoethyl vinyl ether, methylolated amino groups thereof, alkyl halides;
Examples include those converted into quaternary chlorides with dimethyl sulfate, sultone, etc.

Examples of compounds having a hydroxyl group include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, β-hydroxypropyl acrylate, β-hydroxypropyl methacrylate,
Examples include β-hydroxy vinyl ether, 5-hydroxypentyl vinyl ether, 6-hydroxyhexyl vinyl ether, polyethylene glycol monoacrylate, polyethylene glycol monomethacrylate, polypropylene glycol monoacrylate, and polypropylene glycol monomethacrylate.

Examples of compounds having an epoxy group include glycidyl acrylate and glycidyl methacrylate.

Furthermore, in addition to the above compounds, the following compounds may be used in combination. namely, acrylonitrile, methacrylonitrile, styrenes, butyl vinyl ether, maleic acid mono- or dialkyl esters, fumaric acid mono- or dialkyl esters,
Examples include, but are not limited to, itaconic acid mono- or dialkyl esters, methyl vinyl ketone, vinyl chloride, vinylidene chloride, vinyl acetate, vinyl pyridine, vinyl pyrrolidone, and vinyl trimethoxysilane.

The acrylic resin may contain a surfactant. However, when the ratio of acrylic resin to components other than acrylic resin is high, the low molecular weight surfactant contained in the acrylic resin is concentrated during the film forming process, and the interface between particles This may cause problems with the mechanical strength, water resistance, and adhesion of the coating film to the laminate if it accumulates on the surface of the coating or migrates to the interface of the coating layer. In such a case, a polymer obtained by so-called soap-free polymerization that does not contain a surfactant can be used.

The method for producing acrylic resins that do not contain surfactants is described in "Water-soluble Polymers/Water-Dispersible Resins Comprehensive Technical Data Collection" No. 309, edited by Management Development Center Publishing Department, published by Management Development Center Publishing Department, January 1981. It is possible to use the methods shown in the lecture text (December 1982) titled "~Prospecting the future from the latest research results~ New developments in emulsions and future technical issues" sponsored by the Industrial Technology Research Institute. can. For example, use of oligomers or polymeric surfactants instead of low molecular weight surfactants, introduction of hydrophilic groups into polymers by using polymerization initiators such as potassium persulfate or ammonium persulfate, and polymers containing hydrophilic groups. Copolymerization of monomers, use of reactive surfactants,
So-called shell-core type polymers in which the compositions of the inner layer and outer layer of dispersion particles are changed can be used as a technique for producing water-dispersible acrylic resins that do not contain so-called surfactants.

The water-soluble or water-dispersible polyester resin having a sulfonic acid group used in the present invention (hereinafter abbreviated as polyester resin) has excellent coating properties on a polyester film and interlayer adhesion between the coating layer and the polyester film. , is effective in improving the cohesive failure properties and frictional abrasion properties of the coating layer. As polyester resin, Tokuko No. 47-40873,
Polyesters known in JP-A-50-83497, JP-A-50-121336, JP-A-52-155640, etc., or polyesters similar thereto can be used.

For example, the dicarboxylic acid component of polyester is
Examples of aromatic dicarboxylic acids include terephthalic acid,
Isophthalic acid, 2,6-naphthalene dicarboxylic acid and their ester-forming derivatives are used. Examples of aliphatic dicarboxylic acids include adipic acid, azelaic acid, sebacic acid and their ester-forming derivatives. Examples of monocarboxylic acids include oxybenzoic acid and its ester-forming derivatives.

Further, as the glycol component of polyester, aliphatic, alicyclic, aromatic diols, etc. can be used, and examples thereof include ethylene glycol, 1, 4
-Butanediol, diethylene glycol, triethylene glycol, 1,4-cyclohexanedimethanol, p-xylene diol, etc. are used, and examples of poly(oxyalkylene) glycols include so-called polyethylene glycol, polypropylene glycol, polytetramethylene glycol, etc. used.

Polyesters include not only saturated linear polyesters consisting of the above-mentioned ester-forming components, but also
A polyester made of a compound having an ester-forming component having a valence of 3 or more or a polyester having a reactive unsaturated group can also be used.

A polyester having a sulfonic acid group can be produced using a compound having a sulfonic acid group that can be used as a polyester component together with the above-mentioned polyester forming component.

Examples of compounds having sulfonic acid groups include:
Metal salts include sulfoisophthalic acid, sulfoterephthalic acid, sulfonaphthalene-2,6-dicarboxylic acid and ester-forming derivatives thereof. Preferred metals for the metal salt include lithium, sodium, potassium, and magnesium. Among these, a highly preferred compound is 5-sodiosulfoisophthalic acid or 5-sodiosulfodimethylisophthalate.

Another method for introducing sulfonic acid groups into polyester is to sulfonate the unsaturated groups of polyester containing an ester-forming aliphatic unsaturated compound as a copolymerization component with a sulfonating agent such as sodium bisulfite or sodium metabisulfite. Methods can also be exemplified.

The amount of aromatic dicarboxylic acid in the dicarboxylic acid component of the polyester resin is preferably in the range of 50 mol% to 100 mol%. This is to increase the softening point of the polyester resin and improve its adhesion.

The sulfonic acid group in the polyester resin must be present in an amount necessary to make the resin water-soluble or water-dispersible, and the dicarboxylic acid having the sulfonic acid group must be present in an amount of 2 mol% to 20 mol% of the dicarboxylic acid.
It is preferable to use it within the range of .

If the amount of sulfonic acid base is less than 2 mol%, water solubility or water dispersibility will be insufficient, and if the amount of sulfonic acid group is more than 20 mol%, the water resistance of the undercoat layer after coating may be poor, or the film may absorb moisture. This is because they tend to stick together.

Furthermore, as the polyester resin, not only the saturated linear polyester consisting of the above-mentioned ester-forming component, but also polyester consisting of a compound having an ester-forming component of trivalent or higher valence or polyester having a reactive unsaturated group can be used. can.

The water-soluble resin having a breaking elongation of 200% or less (hereinafter referred to as "water-dispersible resin") used in the present invention forms minute protrusions on the surface of the coating layer and imparts slipperiness to the film. As a water-soluble resin,
Compounds shown in the classification of water-soluble polymers in Table 1-1 on page 2 of "Water-Soluble Polymers: Their Markets and Actual Industrial Applications", published by CMC, December 1974, can be used. For example, natural and plant-based products include seaweed extracts such as alginic acid and carrageenan, plant exudates such as gum arabic, plant extracts such as pectin, starches from seeds or tubers, and animal-based proteins such as gluten. Examples include, but are not limited to, proteins such as gelatin, glue, casein, and albumin. Semi-synthetic systems include alginate propylene glycol ester from seaweed extracts, low methoxy pectin from plant extracts, dextran from microbially fermented gums, carboxymethyl starch and hydroxyethyl starch from modified starches, and sodium carboxymethyl cellulose from cellulose derivatives. , methylcellulose, hydroxypropylmethylcellulose, methylethylcellulose, hydroxypropylcellulose, etc., but are not limited to these. Examples of synthetic resins include, but are not limited to, vinyl resins such as polyvinyl alcohol and polyvinylpyrrolidone, and acrylic resins such as polyacrylamide.
The elongation at break of these water-soluble resins is 200% or less, more preferably 100% or less and 5% or more. If the elongation at break of the water-soluble resin is greater than 200%, the water-soluble resin is also likely to be stretched when the polyester film provided with the coating layer is stretched, and the protrusions of the coating layer due to the water-soluble resin will not be clearly defined. In particular, synthetic water-soluble resins are difficult to phase separate from the acrylic resin or polyester resin in the coating layer of the present invention, are easily stretched in a hydrated state or at high temperatures, and have clear protrusions on the surface of the coating layer. may not form. For example, commercially available general grades of polyethylene glycol and polyvinyl alcohol have a breaking elongation of over 250%, and the protrusions on the coating layer are unclear, so we recommend using a grade with a lower breaking elongation through copolymerization or partial crosslinking. You need to choose. It is also possible to reduce the elongation at break by utilizing the properties of different water-soluble resins or water-soluble polymers and low-molecular water-soluble compounds forming complexes (for example, edited by the Polymer Complex Study Group, Academic Society publication center
(published in January 1983, “Polymer Assemblies”). The elongation at break of the water-soluble resin is preferably 5% or more because the hardness and brittleness of the water-soluble resin are related to the impact strength, bending strength, frictional abrasion resistance, etc. of the coating layer. Naturally, the elongation at break of the acrylic resin and polyester resin of the present invention is 200% or more.

The water-solubility of a water-soluble resin refers to the property of not substantially causing turbidity due to light scattering when the resin is dissolved in an aqueous medium. Resins that become colloidal (particle size of 0.1 μm or less) and cause light scattering due to modification or complex formation may also be used as water-soluble resins.

The ratio of acrylic resin to the total amount of acrylic resin, polyester resin, and water-soluble resin is preferably 30 to 90% by weight, more preferably
40 to 80% by weight, the proportion of polyester resin is preferably 3 to 60% by weight, more preferably 5 to 50% by weight, and the proportion of water-soluble resin is
Preferably 3 to 60% by weight, more preferably 5 to 60% by weight
50% by weight. If the acrylic resin content is less than 30% by weight, the slipperiness and strength of the coating layer will decrease.
When the amount is more than 90% by weight, the friction and wear properties decrease. If the polyester resin content is less than 3% by weight, the coating properties and adhesion of the coating agent to the base polyester film will decrease, and the friction abrasion and cohesive failure properties of the coating layer will deteriorate, and if it is more than 60% by weight. In this case, a decrease in slipperiness and a deterioration in adhesion at high temperatures occur. If the water-soluble resin is less than 3% by weight, the protrusions on the surface of the coating layer are not clear, and if it is more than 60% by weight, the adhesion of the coating layer to the base polyester film and the mechanical properties of the coating layer are poor. descend.

The coating agent can be applied to polyester film by using a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or other coating equipment as shown in "Coating Method" by Yuji Harasaki, published by Maki Shoten in 1979. can.

The coating step is performed before sequential biaxial stretching, before simultaneous biaxial stretching, after biaxial stretching and before re-stretching, etc. That is, a method (coating and stretching method) in which a coating layer is applied to a polyester film, followed by appropriate drying or stretching without drying (coating and stretching method) is essential for forming protrusions on the surface of the coating layer. Particularly preferably, an aqueous dispersion or aqueous solution is applied to a uniaxially stretched polyester film by a roll stretching method, and the polyester film is immediately stretched perpendicular to the previous stretching direction, with or without drying. This method involves stretching the material in the same direction and heat-treating it.
According to this method, the coating layer can be dried simultaneously with stretching, and the thickness of the coating layer can be reduced in accordance with the stretching ratio.

The shape of the protrusions on the surface of the coating layer varies depending on the stretching method, stretching ratio, stretching speed, etc., but when a film coated after being longitudinally stretched by the sequential biaxial stretching method is laterally stretched, it becomes longer in the longitudinal direction; A so-called mountain range-like protrusion with a narrow width in the lateral direction is formed. The size of the protrusion shape is influenced by the type of water-soluble resin, degree of polymerization, blending amount, thickness of the coating layer, etc. For example, the higher the degree of polymerization of the water-soluble resin, the larger the blending amount, and the thicker the coating layer, the larger the protrusion shape. Furthermore, the shape of the protrusion varies depending on the drying rate and degree of drying of the coated layer after coating and before stretching. This is presumed to be due to phase separation of the water-soluble resin in the coating agent or a difference in stretchability in a water-containing state.

The thickness of the coating layer of the biaxially stretched polyester film of the present invention is preferably in the range of 0.01μ to 1μ, more preferably in the range of 0.01μ to 0.1μ. If the thickness of the coating layer is less than 0.01 μm, it is difficult to apply it uniformly, so uneven coating tends to occur on the product, and if it is thicker than 1 μm, the slipperiness decreases.

The coating layer of the biaxially oriented polyester film of the present invention may optionally contain adhesion improvers, antifoaming agents, coating improvers, thickeners, ultraviolet absorbers, antioxidants, antistatic agents, and lubricants. , inorganic fine particles, dyes,
It may also contain pigments and the like. Furthermore, since the coating agent is water-based, the coating layer can contain water-soluble or water-dispersible epoxy resins, silicone resins, vinyl resins, urethane resins, polyamide resins, butadiene resins, and the like. Also,
To improve the adhesion, water resistance, solvent resistance, and mechanical strength of the coating layer, we use methylol- or alkylol-based urea-based, melamine-based, acrylamide-based, polyamide-based resins, epoxy compounds, and aziridine as crosslinking agents. compound, block polyisocyanate, or vinyl compound may be contained in the coating layer.

The biaxially oriented polyester film of the present invention has good windability and appearance in the film forming process, and has excellent surface properties, especially slipperiness, and can be used as a 1μ to 500μ film for packaging materials, photosensitive materials, drafting materials, etc. It is useful as a base material for electrophotographic materials, magnetic recording materials, etc., and is particularly useful as a base material for high-density magnetic recording materials that require smoothness.

The present invention will be explained below with reference to Examples. Note that the evaluation in the examples is based on the method described below.

(1) Workability: Approximately 30 sheets of A4 size film are stacked, and the overall flexibility, peelability and pullability of each film,
Observe charging properties (2) Coefficient of friction: Value when stacked films are moved in parallel at 20 mm/min under a load of 100 g/cm ² at 23°C and 60% RH (3) Coefficient of high temperature friction: 20 g at one end 8 with load applied
A mm-wide film was wound around a 6 mmφ, 0.2S fixed metal pin at an angle of 45 degrees to 180 degrees, and the tension speed was 200 degrees.
Value measured in mm/min (4) Adhesion between coating layer and base film: Observation of surface condition by rapid peel test using cellophane tape (5) Adhesion: 40℃, 80%RH, 10Kg/cm ² , 20 hours Peel strength of films stacked under the conditions of ASTM D1893 method (6) Transferability of coating agent: film to film, film to chrome-plated metal plate, film and polyester film with the cobalt-nickel magnetic layer surface deposited on top of each other, Microscopic observation of the surface of the test material after the pressure test under the same conditions as the adhesion test (7) Stylus type surface roughness: Kosaka Institute Co., Ltd., thin film step meter ET-10 type, stylus tip radius 0.5μ , stylus load 1
Comparative example: Polyethylene terephthalate with an intrinsic viscosity of 0.62, which contains almost no surface protrusion forming agent based on polymerization catalyst residues, was melted at about 285°C and extruded onto a cooling drum at about 60°C while applying an electrostatic charge. . Further, the film was stretched 3.5 times in the machine direction at 83°C with rolls, then stretched in the transverse direction at 110°C, and heat treated at 220°C to obtain a biaxially stretched film with a thickness of 12.1μ. This film had extremely poor winding properties, making it difficult to obtain a long film roll, and the resulting film roll had a poor winding appearance, making it impossible to ship as a product. Just to be sure, I cut it out as an A4 size sheet and observed the workability, but the films stuck together and became one whole, making it difficult to handle the film. The coefficient of friction of this film could not be measured because the film did not slip.
In other words, this film cannot be put to practical use due to its lack of slipperiness.

Example 1 Shell-core structure self-crosslinking hydrosol type containing methyl methacrylate, isobutyl methacrylate, acrylic acid, methacrylic acid, and glycidyl methacrylate as main components, with carboxylic acid groups neutralized with ammonia, and containing no surfactant. Acrylic resin (Dyurimer manufactured by Nippon Pure Chemical Industries, Ltd.)
SEX-725, trade name) 70 parts (hereinafter sometimes abbreviated as solid content), 7 mol% in dicarboxylic acid is 5-
A water-dispersible polyester resin (polyester WR901 manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd., trade name ) 20 copies,
Comparative example except that an aqueous coating agent with a concentration of 3% by weight consisting of 10 parts of methylcellulose with a breaking elongation of about 15% and 0.5 parts of lithium salt of perchloroalkyl sulfonic acid was applied to one side of the film after longitudinal stretching and before transverse stretching. A biaxially stretched polyester film was obtained in the same manner as above. The thickness of the coating layer was approximately 0.04 g/m ² in terms of solid content.

The workability of this film was good, and the adhesion between the coating layer and the base film was strong. The winding property and winding appearance in the film forming process were also good.
The coefficient of friction between the coated layer surface and the coated surface of this film was 0.83 in static friction coefficient and 0.61 in dynamic friction coefficient. The coefficient of high-temperature friction was measured at 80°C with a winding angle of 45 degrees, and the coefficient of dynamic friction on the non-coated layer surface was 1.67, while on the coated layer surface it was 0.56, which was good. The adhesion was 19 g on the coated layer side and the non-coated layer side, which was a value that would not cause any problem in the occurrence of adhesion between the films during storage and distribution of the film roll. There is no transferability of the coating agent, and the shape of the protrusions on the surface is
It is elongated and homogeneous in the vertical direction, with no fine and abnormal protrusions.
The protrusion height was approximately 150 Å, making it suitable for precision applications.

Example 2 The same water-based coating agent as in Example 1 was used except that the amount of acrylic resin used was 60 parts and 10 parts of methylolmelamine was added, and a coating layer was formed on one side in the same manner as in Example 1. A biaxially stretched polyester film was obtained.

The friction coefficient of this film is the static friction coefficient.
0.96 and dynamic friction coefficient of 0.60, which were the same in workability as the film of Example 1, but the adhesiveness and high-temperature dynamic friction coefficient were 12 g and 0.47, respectively, resulting in a more useful film due to the improving effect of the crosslinking agent.

Example 3 A biaxially stretched polyester film was obtained in the same manner as in Example 1, except that the same coating agent used in Example 1 was applied to both sides of the film after longitudinal stretching and before transverse stretching.

Coefficient of friction of this film (coating layer surface/coating layer surface)
had a static friction coefficient of 0.71 and a dynamic friction coefficient of 0.53. This film has coating layers on both sides, so
In the film transport process, etc., it was more useful than a film having a coating layer on one side. In addition, a flat film without a coating layer may have oligomer protrusions formed unevenly over time, which can be a problem in high-density magnetic recording applications. It was also useful as a countermeasure.

Example 4 The same acrylic resin used in Example 1,
Using 60 parts, 20 parts, and 0.5 parts of polyester resin and lithium salt of perfluoroalkyl sulfonic acid, respectively, 20 parts of Nitta Gelatin Co.'s water-soluble gelatin U (trade name) or photographic gelatin P-2225 (trade name) was used. ) A biaxially stretched film was obtained in the same manner as in Example 1, except that 20 parts of the above were blended. These films had good workability and other properties, and were suitable for practical use. Regarding the surface shape, photographic gelatin with a high degree of polymerization had larger protrusions in length, width, and height than water-soluble gelatin.

Example 5 Hydroxyethylcellulose from Daicel Corporation was used instead of methylcellulose used in Example 1.
5 copies each of HEC Unicel QP-3L (product name),
Various biaxially stretched polyester films were obtained in the same manner as in Example 1, except that 10 parts and 20 parts of the acrylic resin were used, and 75 parts, 70 parts, and 60 parts of the acrylic resin were used accordingly. Furthermore, instead of QP-3L, we used QP-4400 (trade name), which has a higher viscosity, and QP-100MH (trade name), which has an even higher viscosity, and made various biaxially oriented polyester films with the same amount. Ta. The shapes of these surface protrusions were longitudinally elongated protrusions similar to those in Example 1. The size of the surface protrusions increased as the viscosity of hydroxyethyl cellulose increased and as the amount of hydroxyethyl cellulose added increased. These films had good workability and were suitable for practical use.

Example 6 In place of the hydroxyethylcellulose in Example 5, hydroxypropylmethylcellulose Metrose 60SH-50, 65SH-50, manufactured by Shin-Etsu Chemical Co., Ltd.
Various biaxially stretched polyester films were obtained in the same manner as in Example 5 using 90SH-100 (trade name). The shape and size trends of the surface protrusions were similar to those in Example 5. These films had good workability and were suitable for practical use.

Example 7 Various biaxially oriented polyesters were prepared in the same manner as in Example 5, using sodium carboxymethyl cellulose from Daicel Corporation, CMC Daicel 1120, 1260, 2100 (trade name) instead of the hydroxyethyl cellulose in Example 5. I got the film. The shape and size trends of the surface protrusions were similar to those in Example 5.
These films had good workability and could be put to practical use.

Example 8 Carrageenan, which is carrageenan from Chugai Boeki Co., Ltd., was used instead of hydroxyethyl cellulose in Example 5.
Various biaxially oriented polyester films were obtained in the same manner as in Example 5 using HL-20, G-50 (trade name), synthetic sodium alginate from Daiichi Kogyo Yakuhin Co., Ltd., and AG gum (trade name). Ta. These films had good workability and were suitable for practical use.

As shown in the above examples, the biaxially stretched polyester film of the present invention has good winding properties and appearance during the film forming process even if it is flat.
It has excellent surface properties, especially slipperiness, and is useful in many practical applications.

Claims (1)

[Claims] 1 A coating layer consisting of a water-dispersible or water-soluble acrylic resin, a water-dispersible or water-soluble polyester resin having a sulfonic acid group, and a water-soluble resin with a breaking elongation of 200% or less is provided on at least one side of the polyester film. Biaxially oriented polyester film.