JPH0367622B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a magnetic recording base film and a method for producing the same, and more specifically, it is an excellent base film useful as a base material for audio magnetic tape, video magnetic tape, computer magnetic tape, floppy disk, etc. The present invention relates to a magnetic recording base film having adhesive properties and solvent resistance, and a method for manufacturing the same. Prior Art It is known to melt extrude thermoplastic polyesters, such as polyethylene terephthalate or its copolymers, polyethylene naphthalate or its copolymers, or blends thereof with small proportions of other resins, to form films. It is also known that the resulting biaxially stretched and heat-set polyester film has better heat resistance, gas barrier properties, electrical properties, and chemical resistance than films made of other resins. However, since the surface is highly crystal oriented, the surface has high cohesion and poor receptivity to paints, adhesives, inks, and the like. Therefore, when a synthetic resin layer is provided on the surface of such a polyester film, the film surface is subjected to corona discharge treatment in order to strengthen the adhesion between the two.
A method is used in which the surface is activated by ultraviolet irradiation treatment, plasma treatment, or flame treatment and then coated with a synthetic resin coating. however,
Although these methods of activating the film surface can be expected to improve adhesion to the coating layer by increasing the secondary bonding force due to wetting, the activity decreases over time. Therefore, these means of activating the film surface are not necessarily satisfactory. As another method for increasing the receptivity of the polyester film surface, an etching method has been proposed in which the surface is swollen or partially dissolved with various chemicals. This involves etching the film surface by contacting the film surface with a chemical such as acid, alkali, amine aqueous solution, trichloroacetic acid, or phenols, and
This method attempts to decompose, dissolve, relax, etc. the crystal orientation near the surface, and at the same time reduce cohesiveness and increase adhesion with the binder resin. The adhesion of the layer provided, for example, a synthetic resin coating layer, becomes strong. However, some of the chemicals used in this method are harmful, and there is a risk that they may be dangerous to handle, or that volatile substances from the chemicals may be released into the atmosphere. There are various disadvantages in practical terms, such as the need for extreme caution. As a method similar to this method, a primer layer (undercoat layer) is provided on the surface of the film in advance, a thin surface layer that is different from the base film is formed, and then a desired layer, such as a synthetic resin layer, is coated. be. When forming the undercoat layer, a coating process is usually performed in a process different from the polyester film forming process. However, in applications where delicate quality must be maintained, such as audio magnetic tape, video magnetic tape, computer magnetic tape, and floppy disks, even if an easily adhesive surface is successfully formed, If the resulting film has surface defects due to dust, it cannot be used as a base film for these purposes, but this defect is more likely to occur in this other process. Therefore, it is desirable to perform the undercoating process in an atmosphere as free from dust as possible. There is a polyester film forming process that satisfies these conditions, and if undercoating is performed in this process, a product that can be fully used for the above-mentioned advanced film processed products can be obtained. On the other hand, in the prior art, methods for modifying the surface of a polyester film into an easily adhesive surface by treating the surface with a primer are often achieved by applying a composition dissolved in an organic solvent to the surface layer of the film. I came. When such a method is carried out during film production, contamination of the surrounding environment by fugitive organic solvents,
resulting in unfavorable safety and hygiene conditions,
The use of organic solvents should be kept to a minimum as much as possible since they adversely affect the film forming process. Therefore, when performing in-line subbing treatment in the film forming process, it is preferable to use a composition using water as a solvent from the viewpoints of process, economy, and safety. Therefore, many primer compositions using water as a solvent have been proposed, and in particular, many proposals have been made for aqueous solutions or dispersions of polyurethane or polyester. For example, Japanese Patent Publication No. 46-10193 discloses the use of polyurethane having solvent resistance to acetone and water dispersibility. However, these primer compositions swell or dissolve in solvents used in magnetic paints, such as methyl ethyl ketone, cyclohexanone, tetrahydrofuran, etc., and are insufficient in terms of solvent resistance. When a highly polar paint such as a magnetic paint is applied on such a primer layer, mixing of the primer layer and the magnetic layer occurs, which not only reduces the adhesion effect of the primer layer but also causes streaks on the surface of the applied layer. A good coated surface cannot be obtained.
Particularly in recent years, recording densities have been increasing in coated magnetic recording media, and there is a trend toward flattening of base films and thinning of magnetic layers. In particular, the flattening and thinning of the base of floppy disks has progressed rapidly, and the thickness has decreased to about 1 μm. When the magnetic layer becomes thin in this manner, the above-mentioned flow lines generated on the surface of the magnetic layer make it difficult to obtain a good magnetic surface and cause deterioration of electromagnetic conversion characteristics, which is not preferable. Purpose of the Invention The purpose of the present invention is to have excellent adhesion to the magnetic paint applied thereon, to prevent run streaks from occurring when applying these coatings, and to be compatible with the drying conditions of the coating liquid. An object of the present invention is to provide a polyester magnetic recording base film coated with a primer layer having stable solvent resistance that is not affected. Another object of the present invention is to provide a preferable method for manufacturing such a base film for magnetic recording. Structure of the Invention According to the present invention, at least one side of a polyester film containing titanium oxide with an average particle size of 0.5 μm or less and having a centerline average surface roughness (Ra) of 0.02 μm or less a base film for magnetic recording, comprising a primer layer formed by crosslinking an aqueous polyurethane containing at least one of a carboxylic acid group, a sulfonic acid group, and a sulfuric acid half-ester base with an epoxy compound having two or more epoxy groups; In addition, at least one side of the polyester film containing titanium oxide with an average particle size of 0.5 μm or less and before the crystal orientation is completed, a carboxylic acid base,
An aqueous primer coating solution containing an aqueous polyurethane having at least one of a sulfonic acid group and a sulfuric acid half ester base and an epoxy compound having two or more epoxy groups is applied, and then dried, stretched, and heat treated to achieve crystal orientation. This is achieved by a method for manufacturing a base film for magnetic recording, which is characterized in that the center line average surface roughness (Ra) of the coated surface is finally 0.02 μm or less. 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 titanium oxide particles contained in this polyester have an average particle diameter of 0.5 μm or less. If the average particle diameter exceeds 0.5 .mu.m, the surface protrusions of the base film due to the coarse particles become high, making the surface of the magnetic layer rough, and the electromagnetic conversion characteristics are deteriorated, which is not preferable. The method for incorporating titanium oxide into polyester is usually at any time during the reaction to form polyester, for example, during the transesterification reaction or polycondensation reaction when using the transesterification method, or at any time during the polycondensation reaction when using the direct polymerization method. A method is used in which titanium oxide fine particles (preferably as a slurry in glycol) are added to the reaction system at any time, preferably at the beginning of the polycondensation reaction, for example, until the intrinsic viscosity reaches about 0.3. Titanium oxide fine particles are added to the reaction system. The polyester film of the present invention is obtained by melt-extruding such a linear saturated polyester resin, forming it into a film by a conventional method, and subjecting it to oriented crystallization and heat treatment crystallization. This polyester film is crystal oriented to such an extent that the heat of crystal fusion measured by a scanning calorimeter in a nitrogen stream (at a heating rate of 10°C/min) is usually 4 cal/g or more. preferable. The centerline average surface roughness (Ra) of the polyester film is 0.02μ to maintain the smoothness of the magnetic layer.
It must be less than m. This Ra is JIS B
Measure according to 0601. In other words, Tokyo Seimitsu Co., Ltd.
Using a stylus-type surface roughness tester (SURFCOM 3B) manufactured by J.D. Co., Ltd., apply a film surface roughness curve to the chart under the conditions of a stylus radius of 2μ and a load of 0.07g, and calculate the center of the film surface roughness curve from the obtained film surface roughness curve. When a part of measurement length L is extracted in the direction of the line, the center line of this extracted part is taken as the X axis, the direction of vertical magnification is taken as the Y axis, and the roughness curve is expressed as Y=f(x), the following The value given by the formula (Ra: μm) is defined as the film surface roughness. Ra=1/L∫ ^L _O |f(x)|dx In the present invention, eight measurements are taken with a reference length of 0.25 mm, and Ra is expressed as the average value of five measurements, excluding three from the largest value. In the present invention, the polyester film before crystal orientation is completed is an unstretched film obtained by thermally melting the polymer and forming it into a film as it is;
A uniaxially stretched film in which an unstretched film is oriented in either the vertical or horizontal direction; a film that is further stretched at a low magnification in both the vertical and horizontal directions (finally re-stretched in the vertical or horizontal direction) At least the biaxially stretched film before oriented crystallization is completed). The aqueous primer coating solution used in the present invention contains an aqueous polyurethane having at least one of a carboxylic acid group, a sulfonic acid group, and a sulfuric acid half-ester base, and an epoxy compound having two or more epoxy groups. This aqueous polyurethane has an increased affinity for water by a carboxylic acid group, a sulfonic acid group, or a sulfuric acid half-ester base, and such water affinity-imparting groups are usually introduced during or after the synthesis of the polyurethane. For example, the introduction of a carboxylic acid group can be achieved by using a polyhydroxy compound containing a carboxylic acid group as one of the raw material polyhydroxy compounds during polyurethane synthesis;
The isocyanate groups of polyurethane having unreacted isocyanate groups are reacted with a hydroxyl group-containing carboxylic acid or an amino group-containing carboxylic acid, and then the reaction product is added to an alkaline aqueous solution under high speed stirring,
This can be done by neutralizing, etc. Also,
The introduction of a sulfonic acid group or a sulfuric acid half ester base usually results in the formation of a prepolymer from a polyhydroxy compound, a polyisocyanate and a chain extender;
A compound having an amino group or hydroxyl group capable of reacting with the terminal isocyanate group and a sulfonic acid group or a sulfuric acid half ester base is added to this and reacted, and finally a sulfonic acid group or a sulfuric acid half ester base is formed in the molecule. This can be done by obtaining an aqueous polyurethane having the following properties. In this case, it is preferable to carry out the formation reaction in an organic solvent, then add water and then remove the solvent. Another method is to synthesize a polyurethane having a sulfonic acid group using a compound having a sulfonic acid group as one of the raw materials, and then add the polyurethane to an alkaline aqueous solution under high speed stirring to neutralize it. , the following sultone compound is added to the primary or secondary amino group of the main chain or side chain of polyurethane in the presence of an alkali to form an alkali sulfonic acid salt (e.g. -
Examples include methods of introducing SO ₃ Na, etc.). As the alkaline aqueous solution, it is preferable to use an aqueous solution of sodium hydroxide, potassium hydroxide, ammonia, alkylamine, etc., but the alkali does not remain in the coating film (undercoating film), such as ammonia, and amines that volatilize under drying conditions. Particularly preferred. 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/propylene glycol, polytetramethylene glycol, hexamethylene glycol, tetramethylene glycol, 1,5-pentanediol, diethylene glycol, triethylene glycol, polycaprolactone, polyhexamethylene adipate, polyhexamethylene sebacate, polytetra Examples include methylene acypate, 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. . Examples of the carboxylic acid-containing polyol include methylolpropionic acid, dimethylolbutyric acid, dimethylolvaleric acid, and trimellitic acid bis(ethylene glycol) ester. As amino group-containing carboxylic acids,
Examples 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, and 2-amino-5-methylbenzene-2-
Examples include sulfonic acid, sodium β-hydroxyethanesulfonate, propane sultone adducts of aliphatic di-primary amine compounds, butane sultone adducts, and preferably propane sultone adducts of aliphatic di-primary amine compounds. can give. Furthermore, 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. Examples of epoxy compounds having two or more epoxy groups that crosslink with aqueous polyurethane include and water-soluble or water-dispersible epoxy compounds such as addition condensates of bisphenol A and epichlorohydrin. Examples of compounds that promote the reaction between aqueous polyurethane and epoxy compounds (reaction promoting compounds) include tertiary amino group-containing compounds and salts thereof, compounds having a nitrogen-containing ring structure and salts thereof, quaternary ammonium salt compounds, etc. I can do it. More specifically, examples of tertiary amino group-containing compounds include trimethylamine, triethylamine, tri-n-butylamine, dimethylaminobenzene, benzyldimethylamine, and 2,4,6-tris(dimethylaminomethyl)phenol. ,
Examples of compounds having a nitrogen-containing ring structure and salts thereof include imidazoles such as 2-methylimidazole, 2-methyl-4-ethylimidazole, 2-ethylimidazole, 2-isopropylimidazole, and 2-phenyl-4-methylimidazole. Compound, 1,8-diazo-bicyclo(5,
4,0) Undecene-7 and their hydrochlorides, carbonates, etc. can be mentioned. Examples of the quaternary ammonium salt compound include triethylbenzylammonium chloride and tetramethylammonium chloride. Among these, compounds containing a tertiary amino group and compounds having a nitrogen-containing ring structure are more preferred. The aqueous primer coating liquid used in the present invention may be an aqueous solution or an aqueous dispersion,
There are no particular restrictions. The ratio of the aqueous polyurethane to the epoxy compound is preferably 1 to 40 parts by weight, more preferably 2 to 30 parts by weight, per 100 parts by weight of the former. If the ratio of the epoxy compound is too high, the adhesion performance will be reduced, and if it is too low, the solvent resistance will be lowered, making it difficult to obtain a good coated surface when applying the coating, which is the object of the present invention, so it is preferable. do not have. In addition, the ratio of the epoxy compound to the reaction accelerating compound is 100 parts by weight of the former, 1 to 60 parts by weight of the latter,
Preferably it is 5 to 50 parts by weight. If it is too small, the effect of promoting the reaction will not be sufficient, and if it is too large, it will be difficult to control the reaction, reducing the stability of the coating liquid. The aqueous primer coating solution is made by dissolving or dispersing the two or more components mentioned above in an aqueous medium, and further contains a required amount of surfactant such as an anionic surfactant or nonionic surfactant. Can be used. Such a surfactant can lower the surface tension of an aqueous coating solution to 40 dyne/cm or less,
Those that promote wetting to polyester films are preferred, such as polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, glycerin fatty acid ester, fatty acid metal soap, alkyl sulfate, alkyl sulfonate, alkyl Sulfosuccinates and the like can be mentioned. Furthermore, other additives such as antistatic agents, ultraviolet absorbers, pigments, organic fillers, inorganic fillers, lubricants, and antiblocking agents may be mixed within a range that does not impair the effects of the present invention. The aqueous primer coating solution may be applied to the polyester film in a normal coating process, that is, in a process in which the biaxially stretched and heat-set polyester film is coated separately from the film manufacturing process. However, this process tends to introduce dirt, dust, etc., and it is desirable to apply the coating in a clean atmosphere for advanced products such as magnetic tapes and floppy disks. From this point of view, coating during the polyester film manufacturing process is preferable. In particular, it is preferable to apply an aqueous primer coating liquid to one or both sides of the polyester film before the crystal orientation is completed during this step. At that time, the solid content concentration of the aqueous primer coating solution is usually 30% by weight or less,
More preferably, it is 10% by weight or less. The amount of coating is 0.5 to 20 g ^per square meter of running film, and more preferably 1 to 10 g.
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 polyester film coated with the aqueous coating solution is dried and subjected to processes such as stretching and heat setting. For example, vertical 1 coated with water-based primer coating liquid.
The axially stretched polyester film is guided into a stenter, where it is laterally stretched and heat set. During this time, the coating solution dries and further undergoes a crosslinking reaction, forming a continuous film on the film. Heat for the crosslinking reaction is usually supplied by heat during stretching or heat setting. For example, 200℃ for about 10 seconds, 150℃ for about 1 minute, 120℃
You can heat it for about 15 minutes at 220℃ for about 8 seconds, etc.
It may also be heated under more severe conditions or less severe conditions. The coating liquid may be dried by heating at 100°C for about 5 seconds, at 110°C for about 5 seconds, and at 90°C for about 20 seconds. It may also be air-dried. Conditions for oriented crystallization of the polyester film, such as stretching, heat setting, etc., can be carried out under conditions conventionally accumulated in the art. The centerline average surface roughness Ra of the coated side of the obtained polyester film must be 0.02 μm or less. Effects of the Invention The polyester film having the primer layer obtained in this manner exhibits high adhesion to magnetic paints, and exhibits high adhesion to magnetic paints such as methyl ethyl ketone, toluene, ethyl acetate, butyl acetate, ethanol, dioxane, tetrahydrofuran, cyclohexanone, cyclohexane, etc. Shows excellent solvent resistance to organic solvents. Examples Hereinafter, the present invention will be further explained with reference to Examples.
Note that "parts" in the examples mean "parts by weight." Moreover, each characteristic of the film was measured by the following method. 1 Adhesion The evaluation paint was applied to the primer-coated polyester film, dried at 80℃ for 1 minute, and then
Aged at 60℃ for 24 hours, coating thickness averaged 2μ
Roll coat so that it becomes m. The resulting coated film was abraded with a head load of 50 g using an RCA abrasion tester (RCA Corporation), and the number of abrasions until a hole appeared on the coated surface was used as a measure of adhesion. [Adjustment of paint for evaluation] Nitrocellulose in Lutzker thinner for paint
RS1/2 [Flakes containing 25% isopropanol;
manufactured by Daicel Corporation] to prepare a 40wt% solution,
Add 43.9 parts of the liquid, followed by 32.5 parts of polyester resin (Tesmofen #1700, manufactured by Bayer AG), 2.60 parts of chromium dioxide magnetic powder, soybean oil fatty acid (Reshion P, manufactured by Riken Vitamin Co., Ltd.) as a dispersant and wetting agent, Cationic activator (cation AB: manufactured by NOF Corporation)
1 part, 0.5 part, and 0.8 part of squalene (dumpling liver oil) were respectively put into a ball mill. 282 parts of a mixed solution consisting of methyl ethyl ketone (hereinafter abbreviated as MEK)/cyclohexanone/toluene 3/4/3 (weight ratio) is further mixed and sufficiently pulverized to prepare a mother liquor paint (45 wt%). To 50 parts of this mother liquor, 48 parts of an addition reaction product of trimethylolpropane and toluene diisocyanate (Coronate L: manufactured by Nippon Polyurethane Industry Co., Ltd.) and 6.25 parts of butyl acetate were added, resulting in a final solid concentration of 42.75 wt. %
A magnetic paint for evaluation was obtained. 2 Solvent resistance Apply a drop of tetrahydrofuran (approx.
0.02cc), place gauze on top, and
Place a 100g weight on it and move the gauze at a speed of approximately 1000mm/min. After drying at room temperature, interference micrographs of those not treated with tetrahydrofuran and those treated with tetrahydrofuran are compared at 400x magnification, and the state of surface change of the primer is judged as follows. Items with almost no primer: × Items with almost no change in primer: 〇 Items with slight changes in surface morphology in between
: 〇～△ Those with a considerable change in surface morphology: ×～△ Those with an intermediate change in surface morphology: △ Example 1 Polyurethane aqueous dispersion having a carboxylic acid amine base [manufactured by Toyo Polymer Co., Ltd.: trade name Merci-
585] 80 parts (as non-volatile components), 10 parts of polyoxyethylene nonyl phenyl ether [manufactured by NOF Corporation: trade name NS-240] and a polyfunctional epoxy compound [Toyo Polymer Co., Ltd.: trade name Merci]. AD-C-65〕
Dilute 10 parts with ion-exchanged water to obtain a solid content concentration of 2% by weight.
An aqueous primer coating solution was prepared. This coating solution was applied to a biaxially stretched polyethylene terephthalate film with an Ra of 0.012 μm (average particle size 0.2 μm).
(containing 1.0% by weight of titanium oxide) using the gravure coating method, and then heat-treated for 45 seconds in a drying zone at 140℃, with an average coating amount of 50mg-Dry/m ²
A primer-coated magnetic recording base film was obtained. This base film had sufficient adhesion to the magnetic paint for evaluation, and was also able to form a good coated surface without running streaks. Example 2 Polyurethane aqueous dispersion having a carboxylic acid amine base [manufactured by Toyo Polymer Co., Ltd.: trade name Merci]
585] 77 parts (as non-volatile components), polyoxyethylene nonyl phenyl ether [manufactured by NOF Corporation: trade name NS-240] 10 parts, polyfunctional epoxy compound [Toyo Polymer Co., Ltd.: trade name Merci] AD-C-65〕
Dilute 10 parts and 3 parts of 2,4,6-tris(dimethylaminomethyl)phenol with ion exchange water,
An aqueous primer coating solution having a solid content concentration of 4% by weight was prepared. A base film for magnetic recording was obtained in the same manner as in Example 1 except for using this coating liquid. Examples 3 and 4 Polyethylene terephthalate (containing 0.5% by weight of titanium oxide with an average particle size of 0.3 μm) having an intrinsic viscosity of 0.65 measured in o-chlorophenol at 25°C was melt-extruded onto a rotating cooling drum maintained at 20°C. Thickness
An unstretched film of 950 μm was obtained, then stretched 3.5 times in the machine axis direction, and then a coating solution identical to the coating solution prepared in Example 1 and Example 2 was applied to both sides of the uniaxially stretched film using the kiss coating method. did. The average coating amount at this time was 50 mg/m ² in terms of solid content. Subsequently, it was stretched 3.9 times in the transverse direction at 105℃, and further
Heat treatment was performed at 210° C. to obtain a biaxially oriented magnetic recording base film coated with primers on both sides and having a thickness of 75 μm and an Ra of 0.01 μm. Example 5 In place of the aqueous polyurethane dispersion of Example 2, an OH value consisting of adipic acid, sebacic acid, 1,5-pentanediol and neopentyl glycol components was used.
In the molecule synthesized from 53 aliphatic polyesters, hexamethylene diisocyanate, aminoethanol sulfate half ester and potassium hydroxide -
A magnetic recording base film was obtained in exactly the same manner as in Example 2, except that 80 parts of an aqueous polyurethane dispersion containing 2.2 wt % (solid content) of OSO- ₃ groups (as a non-volatile component) was used. Examples 6 and 7 The procedure was carried out in exactly the same manner as in Example 4, except that triglycerol triglycidyl ether (Example 6) or glycerol polydiglycidyl ether (Example 7) was used instead of the polyfunctional epoxy compound of Example 4. A base film for magnetic recording was obtained. Examples 8 and 9 The reaction was carried out in exactly the same manner as in Example 4, except that 2-methylimidazole (Example 8) or 2-methyl-4-ethylimidazole (Example 9) was used instead of the reaction catalyst in Example 4. A base film for magnetic recording was obtained. Examples 10 and 11 A polyurethane dispersion containing a carboxylic acid amine base instead of the coating solution of Examples 3 and 4 [manufactured by Dainippon Ink Industries, Ltd.: trade name Hydran HW-100]
A base film for magnetic recording was obtained in exactly the same manner as in Examples 3 and 4 except that the following was used. Comparative Example 1 Thickness 75μm without primer treatment for comparison
Various evaluations were conducted using polyethylene terephthalate film. Comparative Example 2 A magnetic recording base film having a primer layer containing no water-based epoxy resin as a crosslinking agent was prepared by the method of Example 1 using only 90 parts of the water-based polyurethane resin and 10 parts of polyoxynonyl phenyl ether. Obtained. The evaluation paint was applied to the magnetic recording base films obtained in Examples 1 to 11 and Comparative Examples 1 to 2 to a dry coating thickness of 1.5 μm and dried, and the adhesion, applicability, and solvent resistance were evaluated. was evaluated. The results are shown in Table 1.

[Table] From Table 1, the primer layer of the magnetic recording base film of the present invention has excellent performance in solvent resistance and adhesion, and enables uniform and stable coating without streaking when applying paint. It is clear that

Claims (1)

[Claims] 1. A polyester film containing titanium oxide with an average particle diameter of 0.5 μm or less and having a centerline average surface roughness (Ra) of 0.02 μm or less, at least on one side of which is a carboxylic acid group or a sulfonic acid group. A base film for magnetic recording comprising a primer layer formed by crosslinking an aqueous polyurethane containing at least one of the following: and a sulfuric acid half ester base with an epoxy compound having two or more epoxy groups. 2. An aqueous polyurethane containing titanium oxide with an average particle diameter of 0.5 μm or less and having at least one of a carboxylic acid group, a sulfonic acid group, and a sulfuric acid half-ester base on at least one side of the polyester film before crystal orientation is completed. A water-based primer containing an epoxy compound having two or more epoxy groups is applied, and then drying, stretching, and heat treatment are performed to complete crystal orientation, and finally the centerline average surface roughness (Ra) of the coated surface is A method for producing a base film for magnetic recording, characterized in that the thickness is 0.02 μm or less.