JPH04261848A - Easily adherent polyester film and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve adhesiveness between a magnetic layer and a base film and to provide a flat and easily adherent polyester film for use in medium for magnetic recording whose flat base film has improved slip properties and handling characteristics and a method for manufacture thereof. CONSTITUTION:A polyester film having an average roughness on the center line (Ra) of 0.01mum or less, an average roughness at ten points (Rz) of 0.1mum or less and a thickness of 20mum, wherein a primer layer comprising an ester- acryl copolymer (A) having a transformation temperature (Tg) of 10 deg.C or higher and polyurethane (B) having an anionic group is provided on at least one surface of said polyester. A method for manufacturing this polyester film according to the in-line coating method also is disclosed herein.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION The present invention relates to a flat, easily adhesive polyester film for magnetic recording media and a method for producing the same, and more particularly to a flat, easily adhesive polyester film for use in magnetic recording media, and more particularly, it is extremely flat and has excellent slip properties, and has excellent adhesive properties for magnetic layers, and is used for video tapes, The present invention relates to a polyester film useful as a base material for magnetic recording media such as audio tapes, and a method for producing the same.

0002

BACKGROUND OF THE INVENTION Polyester films, particularly biaxially oriented films made of polyethylene terephthalate, have excellent mechanical properties, heat resistance, chemical resistance, surface flatness, etc., and are therefore used in various fields. In particular, the demand for materials used as base materials for magnetic recording media such as video tapes and audio tapes has increased dramatically in recent years.

Generally, magnetic recording media are made by dispersing and kneading magnetic powder, a resin binder called a binder, a dispersant, a lubricant, etc. in an organic solvent on a non-magnetic material (base film) such as a polyester film. It is manufactured by applying a magnetic paint and drying it to form a magnetic layer that becomes a recording layer.

However, in recent years, in order to improve electromagnetic properties and recording density, as seen in video tapes in particular, efforts have been made to make magnetic powder particles finer and more densely packed, as well as to flatten the surface of the magnetic layer. be.

[0005] Conventionally, in magnetic recording media, it is known that increasing the adhesiveness between the base film and the magnetic layer is effective in improving the yield during tape slitting and the durability during tape running. However, especially in the case of the recent high filling of magnetic powder, the adhesion of the magnetic layer to the base deteriorates significantly, so some measure to improve the adhesion is essential.

On the other hand, in order to improve the electromagnetic properties, it is necessary to further flatten the surface of the magnetic layer, and for this purpose, it is necessary to flatten the surface of the polyester film that is the base material as well as flatten the magnetic layer itself. is required.

[0007] However, such a flat film has poor slipperiness and poor air escape during winding, so it poses a serious hindrance to operations such as winding, unwinding, coating, or slitting. This results in undesirable phenomena such as the occurrence of wrinkles, uneven end surfaces of the rolls, and the adsorption of dust due to generated static electricity. Such a phenomenon becomes more pronounced as the film becomes thinner, and furthermore, the phenomenon becomes more noticeable as the film becomes wider and longer.

By the way, methods for improving the adhesiveness of polyester films include physical treatments such as corona treatment, ultraviolet treatment, plasma treatment, EB treatment, flame treatment, etc., or treatment agents such as alkali, amine aqueous solution, trichloroacetic acid phenols, etc. It is known that the process is However, these methods have practical disadvantages such as deterioration of adhesive strength over time and contamination of the working environment due to volatilization of chemicals.

Another known method is to apply an easily adhesive coating agent to the surface of the film to form a primer layer in a process other than the usual polyester film forming process. However, with this method, organic solvents are usually used as coating solvents, and the coating atmosphere is not sufficiently clean. There are safety and hygiene problems such as deterioration of

[0010] Therefore, if this primer treatment is performed during the polyester film forming process using a water-based coating agent, there will be no adhesion of dust in a clean environment, and since it is a water-based solvent, there will be no risk of explosion or environmental deterioration. film performance, economics,
It has been proposed to use a water-soluble or water-dispersible polyester resin, polyurethane resin, or the like as a primer because it is advantageous in terms of safety.

However, if a soft resin material is used for the primer to improve adhesion, the films with the primer layer may block each other due to changes in temperature and humidity during storage.
It has the disadvantage that it can stick (sticking). Furthermore, with such a primer, it is difficult to improve the smoothness of the flat base and the ease of handling such as rolling up.

[0012] In order to resolve the blocking resistance, slipperiness, and handling properties, it may be possible to use a resin with a high Young's modulus at the expense of some adhesion, but in this case, the surface smoothness of the primer layer This tends to cause problems such as damage to the primer layer or abrasion of the primer layer during the magnetic paint application process or calendering process.

[0013]

[Object of the Invention] An object of the present invention is to provide a flat, easily adhesive polyester film for magnetic recording media, which has improved adhesiveness between a magnetic layer and a base film, as well as improved slipperiness and handling properties of the flat base film. It's about doing.

Another object of the present invention is to provide a preferred method for producing such a flat, easily adhesive polyester film.

[0015]

[Structure of the Invention] In order to achieve the above object, the present invention consists of the following structure. 1. A polyester film having a centerline average roughness (Ra) of 0.01 μm or less, a ten-point average roughness (Rz) of 0.1 μm or less, and a thickness of 20 μm or less has a glass transition temperature (Tg) on at least one side. A flat, easily adhesive polyester film for magnetic recording media, characterized in that it is provided with a primer layer consisting of an ester/acrylic copolymer (A) at a temperature of 10° C. or higher and a polyurethane (B) having an anionic group. 2. An aqueous primer solution containing an ester-acrylic copolymer (A) having a glass transition temperature (Tg) of 10° C. or higher and a polyurethane having an anionic group (B) is applied to at least one side of the polyester film before crystal orientation is completed. The method for producing a flat, easily adhesive polyester film for magnetic recording media according to item 1 above, characterized in that the film is then dried, stretched, and heat treated to complete crystal orientation.

In the present invention, the 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-2,6-naphthalene dicarboxylate, etc. Copolymers of these or blends of these with small proportions of other resins are also included.

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. For this polyester film, 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/min.
It is preferable that the crystals are oriented to such an extent that it exhibits a particle size of 100 g or more.

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 that is oriented to (stretched film), etc.

[0019] In the present invention, the polyester film is
It is necessary that the center line average roughness (Ra) is 0.01 μm or less and the ten point average roughness (Rz) is 0.1 μm or less. Preferably, the center line average roughness (Ra) is 0.01 to 0.0
Within the range of 0.01 μm and ten point average roughness (Rz) of 0.1
It is within the range of ~0.01 μm.

Such surface roughness can be achieved by incorporating fine fillers such as silicon oxide, kaolin, talc, calcium carbonate, alumina, etc. into the polyester and adjusting the particle size and content thereof. The preferred filler particle size is in the range of 0.02 to 1 μm. Especially 0.02~0
．． It is preferable to combine a filler with a small particle size of 2 μm and a filler with a large particle size of 0.2 to 1 μm. The preferred content is 0.005 to 0.5% by weight.

In the present invention, the ester/acrylic copolymer (A) which is a component forming the primer layer is an aqueous polymer, such as an aqueous polyester/polyacrylic block polymer, or an aqueous polymer in which the backbone polymer is polyester and polyacrylic is grafted onto it. Examples include polyester/polyacrylic graft copolymers and aqueous polyacrylic/polyester graft copolymers in which the backbone polymer is polyacrylic and polyester is grafted onto it. The most preferred is an aqueous polyester/polyacrylic graft copolymer in which the core polymer is polyester and polyacrylic is grafted thereto.

The polyester that becomes the backbone polymer of this aqueous polyester/polyacrylic graft copolymer is a substantially linear polymer synthesized from a polybasic acid or its ester-forming derivative and a polyol or its ester-forming derivative. . Polybasic acid components of this polymer include terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, 2,6-naphthalene dicarboxylic acid, 1,4
-Cyclohexanedicarboxylic acid, adipic acid, sebacic acid, trimellitic acid, pyromellitic acid, dimer acid, etc. can be exemplified. Two or more types of these components can be used. Furthermore, in addition to these components, unsaturated polybasic acids such as maleic acid, fumaric acid, itaconic acid, etc., and hydroxycarboxylic acids such as p-hydroxybenzoic acid, p-(β-hydroxyethoxy)benzoic acid, etc. may be used in small proportions. can. The proportion of the unsaturated polybasic acid component and the hydroxycarboxylic acid component is at most 10 mol%, preferably 5 mol% or less.

[0023] Polyol components include ethylene glycol, 1,4-butanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, xylylene glycol, and dimethylol. propionic acid, glycerin, trimethylolpropane,
Examples include poly(ethylene oxide) glycol and poly(tetramethylene oxide) glycol. Two or more types of these can be used.

The backbone polymer is preferably an aqueous polyester, and for example, an aqueous dispersion is prepared by copolymerizing a hydrophilic group-containing compound such as an organic sulfonate, a carboxylate, diethylene glycol, polyethylene glycol, or polytetramethylene glycol in the molecule. It is advantageous and preferable for making. A trifunctional or higher-functional carboxylic acid is usually used to introduce this carboxylic acid salt, but since this carboxylic acid branches during the polymerization process and tends to gel, it is desirable to reduce the copolymerization ratio. In this respect, the introduction of hydrophilic groups using sulfonate salts, diethylene glycol, polyalkylene ether glycol, etc. is more advantageous since the problems that occur when using carboxylate salts do not occur.

In order to introduce a sulfonate group into the polyester molecule, for example, 5-Na sulfoisophthalic acid, 5-ammonium sulfoisophthalic acid, 4-Na sulfoisophthalic acid, 4-methylammonium sulfoisophthalic acid, 2 - Sulfonic acid alkali metal salts or sulfonic acid amine salt compounds such as Na sulfoterephthalic acid, 5-K sulfoisophthalic acid, 4-K sulfoisophthalic acid, 2-K sulfoterephthalic acid, and Na sulfosuccinic acid can be used. preferable. The polyhydric carboxylic acid or polyhydric alcohol having a sulfonate group preferably accounts for 0.5 to 20 mol%, more preferably 1 to 18 mol%, of the total polycarboxylic acid component or the total polyhydric alcohol component.

In order to introduce a carboxylic acid group into the polyester molecule, for example, trimellitic anhydride, trimellitic acid, pyromellitic anhydride, pyromellitic acid,
Compounds such as trimesic acid, cyclobutanetetracarboxylic acid, and dimethylolpropionic acid can be used. Further, a carboxylic acid salt can be obtained by neutralizing a carboxylic acid with an amino compound, ammonia, an alkali metal, or the like.

[0027] When introducing a hydrophilic group-containing compound into a polyester molecule, various known methods can be employed. To further explain the case of introducing a carboxylate or organic sulfonate group, for example, (1) a method of synthesizing polyester using a compound having a carboxylate or organic sulfonate group in the molecule as one of the starting materials; ■ A method in which a polyester is synthesized using a compound having three or more carboxylic acid salts in the molecule as a starting material as one component, and then free carboxyl groups in the polyester are neutralized in a medium with ammonia, amines, alkali metal compounds, etc. There are other methods.

To further explain the method (2), for example, trimellitic anhydride is used as a component of the polyester raw material to produce a polymer having free carboxyl groups in the side chains.
After the reaction is completed, aqueous ammonia is added to neutralize the reaction mixture to produce a water-based polyester. Preferably, the polyester is produced by a melt polymerization method.

The branch polymer of the aqueous polyester/polyacrylic graft copolymer is polyacrylic, and the monomers used for producing the polyacrylic include, for example, alkyl acrylate, alkyl methacrylate (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, phenyl group, benzyl group, phenylethyl group, etc.); hydroxy-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate; acrylamide , methacrylamide, N-methylmethacrylamide, N-methylacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N,N-dimethylolacrylamide, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-phenyl Amide group-containing monomers such as acrylamide; amino group-containing monomers such as N,N-diethylaminoethyl acrylate and N,N-diethylaminoethyl methacrylate; epoxy group-containing monomers such as glycidyl acrylate and glycidyl methacrylate;
Examples include monomers containing a carboxyl group or a salt thereof, such as acrylic acid, methacrylic acid, and salts thereof (sodium salt, potassium salt, ammonium salt). These can be used in combination with other types of monomers. Examples of other monomers include epoxy group-containing monomers such as allyl glycidyl ether; styrene sulfonic acid, vinyl sulfonic acid, and their salts (sodium salt, potassium salt,
Monomers containing sulfonic acid groups or their salts such as ammonium salts; carboxyl groups or their salts such as crotonic acid, itaconic acid, maleic acid, fumaric acid and their salts (sodium salts, potassium salts, ammonium salts, etc.) Monomers containing acid anhydrides such as maleic anhydride and itaconic anhydride; vinyl isocyanate, allyl isocyanate, styrene, vinyl methyl ether, vinyl ethyl ether, vinyl tris alkoxysilane, alkyl maleic acid monoester, alkyl Examples include fumaric acid monoester, acrylonitrile, methacrylonitrile, alkyl itaconic acid monoester, vinylidene chloride, vinyl acetate, and vinyl chloride. The above-mentioned monomers can be copolymerized singly or in combination of two or more. Hydroxyl groups, amide groups, carboxyl groups, or their salts (sodium salts, potassium salts, ammonium salts, etc.), etc. from the viewpoint of imparting hydrophilicity to the acrylic polymer, dispersion stability of aqueous liquids, adhesion to polyester films, etc. Preferably, those having a functional group of

[0030] As a method for grafting polyacrylic to polyester (stem polymer), a known graft polymerization method can be used. There are three main methods: (A) A method in which a reaction initiation point such as a radical, cation, or anion is generated in the backbone polymer, and an acrylic monomer is graft-polymerized. (B) A method of graft polymerizing an acrylic monomer in the presence of a backbone polymer using a chain transfer reaction to the polymer. (C) A method of reacting a trunk polymer having a functional group in its side chain with a branch polymer having a group at its end that reacts with the functional group.

A more specific method of (A) above includes, for example, a radical polymerization method in which radicals are generated in the backbone polymer by light, heat, or radiation, and then the monomers are graft-polymerized; using a catalyst such as AlCl3, TiCl4, etc. Examples include cationic polymerization or anionic polymerization methods in which cationic groups are generated in the backbone polymer, or anionic groups are generated in the backbone polymer using metal Na, metal Li, etc., and then monomers are graft-polymerized.

Further, as a more specific method of (B) above, for example, a polyester having a carboxyl group or a hydroxyl group in its side chain is reacted with glycidyl methacrylate, 2-hydroxyethyl acrylate, acrylic acid, etc. to form a side chain of the polyester. A method of introducing an unsaturated group into the chain and polymerizing this with a monomer; a method in which an unsaturated group is introduced into the polymer main chain using an unsaturated compound such as fumaric acid as a component of the synthetic raw material, and an acrylic monomer. Examples include a method of reacting.

Furthermore, as a specific method for the above (C), for example, hydrogen donating groups such as -OH, -SH, -
A polyester (stem polymer) having NH2, -COOH, -CONH2, etc., and a hydrogen accepting group at one end, e.g.

[0034]

A method of reacting an acrylic polymer (branched polymer) such as [Chemical 1]; ) and the like. Other combinations of functional groups include -COOH and -CO
Cl, -COOH and -OH, -COOH and NH2, -
An example is a combination of NH2 and -OH.

The backbone polymer in the graft copolymer (
The weight ratio of polyester) and branched polymer is 5:
The ratio is preferably 95 to 95:5, more preferably 10:90 to 90:10. The molecular weight of the backbone polymer is 5,000 to 2
The molecular weight of the branched polymer is preferably 500,000 to 50,000, more preferably 10,000 to 10,000.

Next, the polyester and acrylic polymer components of the aqueous polyacrylic/polyester graft copolymer whose backbone polymer is polyacrylic may be the same as those for the above-mentioned aqueous polyester/polyacrylic graft copolymer. Such a copolymer can be produced by using polyacrylic as a backbone polymer and grafting polyester as a branch polymer onto this, but this manufacturing method is not particularly limited. Some examples of this manufacturing method include a method of introducing an unsaturated group to one end of polyester and copolymerizing it with an acrylic monomer;
Polyester is made by introducing functional groups such as carboxyl groups, hydroxyl groups, methylol groups, etc. into the side chains of polyacrylic, and reacting with polyester having introduced epoxy groups, isocyanate groups, hydroxyl groups, methylol groups, etc., which react with the above functional groups, at one end. There are methods that use molecular reactions.

The molecular weight of the trunk polymer (polyacrylic) in this graft copolymer is preferably 5,000 to 200,000, more preferably 10,000 to 100,000, and the molecular weight of the branch polymer is 500 to 50,000, more preferably 1,000 to 100,000. 10,000 is preferable. The ratio of trunk polymer to branch polymer is 5:95 by weight.
-95:5, more preferably 10:90-90:10.

Furthermore, each component of the aqueous polyester/polyacrylic block copolymer can be the same as the above-mentioned aqueous polyacrylic/polyester graft copolymer.

Such a block copolymer can be synthesized by a known method. For example, a method of introducing an acrylic unsaturated group at both ends of polyester and block polymerizing this with polyacrylic, or a method of introducing a group capable of polymeric reaction at the end of polyacrylic (e.g., an isocyanate group, an epoxy group, a hydroxyl group, There is a method of synthesis by introducing a carboxyl group (such as a carboxyl group) and reacting this with the hydroxyl group or carboxyl group at the end of the polyester.Furthermore, there is a method of transesterifying the polyol and polycarboxylic acid ester, followed by a temperature of 250 to 300°C. The polycondensation reaction is started under normal pressure, and the reaction is finally carried out under vacuum to obtain a polyester with a predetermined degree of polymerization. After dissolving the polyester and polyacrylic in an organic solvent, a block copolymer is formed by a polymer reaction, etc. There is a way to make liquid. The molecular weight of polyacrylic in the block copolymer is 1,
000 to 50,000, more preferably 2,000 to 10,000, and the molecular weight of the polyester is 2,000 to 50,000, more preferably 30,000 to 50,000.
,000 to 10,000, and the total molecular weight is preferably 5,000.
~200,000 is preferable. The ratio of the above-mentioned polyacrylic and polyester is 95:5 to 5:95 in terms of polymerization ratio, and more preferably 80
:20 to 20:80 is preferable.

[0040] These ester-acrylic copolymers have a glass transition temperature (Tg) of 10°C or higher,
More preferably, the temperature is 20°C or higher. If Tg is too low, the effect of improving slipperiness will not be recognized, and the blocking resistance will also be poor.

[0041] The urethane (B) used as a component for forming the primer layer in the present invention is a polyurethane having an anionic group, particularly preferably a polyurethane having a carboxylic acid group, a sulfonic acid group, or a sulfuric acid half ester group; It is preferable to have a carboxylic acid ammonium salt or amine salt group.

Usually, such a water affinity-imparting group is introduced during or after polyurethane synthesis.

For example, introduction of a carboxylic acid group can be carried out by using a polyhydroxy compound having a carboxylic acid group as one of the raw material polyhydroxy compounds during polyurethane synthesis, or by introducing a hydroxyl group into the isocyanate group of a polyurethane having unreacted isocyanate groups. This can be carried out by reacting a carboxylic acid having an amino group or a carboxylic acid having an amino group, and then adding the reaction product to an aqueous alkali solution under high-speed stirring and neutralizing it. In addition, the introduction of a sulfonic acid group or a sulfuric acid half-ester group is usually carried out by forming a prepolymer from a polyhydroxy compound, a polyisocyanate, and a chain extender, and adding an amino group or a hydroxyl group capable of reacting with the terminal isocyanate group and a sulfonic acid group or This can be carried out by adding and reacting a compound having a sulfuric acid half ester base in its molecule, and finally obtaining an aqueous polyurethane having a sulfonic acid group or a sulfuric acid half ester base in its molecule. In this case, it is preferable to carry out the formation reaction in an organic solvent, then add water and then remove the solvent.

In addition, as another method, a polyurethane having a sulfonic acid group is synthesized using a compound having a sulfonic acid group as one of the raw materials, and then the polyurethane is added to an alkaline aqueous solution under high speed stirring. , Neutralization method, add the following sultone compound 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. -SO3 Na etc.)
Examples include methods of introducing. 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 carboxylate bases, sulfonate bases, 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 sepacate, polytetramethylene adipate, polytetramethylene sebacate, trimethylolpropane, trimethylolethane,
Examples include 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 dimethylolpropionic acid, dimethylolbutyric acid, dimethylolvaleric acid, and trimellitic acid bis(ethylene glycol) ester.

Examples of the carboxylic acid having an amino group include β-aminopropionic acid, γ-aminobutyric acid, and P-aminobenzoic acid. Examples of the carboxylic acid having a hydroxyl group include 3-hydroxypropionic acid, γ-hydroxybutyric acid, P-(2-hydroxyethyl)benzoic acid, and malic acid. Compounds having an amino group or hydroxyl group and a sulfone group include:
For example, aminomethanesulfonic acid, 2-aminoethanesulfonic acid, 2-amino-5-methylbenzene-2-sulfonic acid, sodium β-hydroxyethanesulfonate, addition of propane sultone and butane sultone to aliphatic diprimary amine compounds. products, preferably propane sultone adducts of aliphatic diprimary amine compounds. Furthermore, examples of compounds having 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.

[0048] The mixing ratio of the ester/acrylic copolymer (A) and polyurethane (B) in the present invention is [A
]/[B]=preferably in the range of 99/1 to 10/90,
Furthermore, the range of 98/2 to 20/80 is preferable. If the amount of polyurethane (B) is too large, the film will become less slippery and will be difficult to handle. On the other hand, polyurethane (
If the amount of B) is too small, the adhesion will decrease.

The primer layer in the present invention can be formed by applying a coating liquid, preferably an aqueous liquid, containing the components for forming the layer onto a polyester film and drying the coating liquid. The coating liquid is preferably an aqueous liquid such as an aqueous solution or a water emulsion liquid. This aqueous liquid may contain some amount of organic solvent to stabilize the dispersion of the solid components. This aqueous primer coating solution is prepared using ester-acrylic copolymer (A) in an aqueous medium.
) and polyurethane (B) are dispersed or dissolved, and a crosslinking agent, catalyst, wetting agent, etc. are added as necessary. Examples of the wetting agent include anionic, cationic, and nonionic surfactants. Such a surfactant is preferably one that lowers the surface tension of the aqueous liquid to 40 dyne/cm or less and promotes wetting of the polyester film. For example, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, glycerin fatty acid ester,
Preferred examples include fatty acid metal soaps, alkyl sulfonates, quaternary amine salts, and betaine type surfactants. Furthermore, antistatic agents, ultraviolet absorbers, pigments, organic fillers, inorganic fillers, lubricants, antiblocking agents, and the like may be used in combination, as long as they do not impede the object of the present invention.

[0050] This primer coating solution is applied to a polyester film before crystal orientation is completed, for example, immediately after melt extrusion and casting of polyester.
Alternatively, it is preferable to perform stretching on the surface of the polyester film immediately after stretching in either the vertical or horizontal direction. A commonly used method is to apply a primer layer on a uniaxially stretched polyester film that has been stretched in the vertical direction, then stretch it horizontally while heating, and then heat-set the film at a high temperature to complete the solidification of the primer layer. There is. Any known method can be used to coat the primer layer on the polyester film. For example, a spray coating method, an air knife method, a reverse coating method, a kiss coating method, a gravure coating method, a Meyer bar method, a roll brushing method, etc. can be applied. The concentration of the coating liquid applied varies depending on the coating method, but is generally between 0.5 and 5.
It is 0% by weight. The final thickness of the primer layer is 0.0
It is preferable that it is 1-1 micrometer.

[0051] Oriented crystallization conditions for polyester film,
For example, conditions such as stretching and heat setting can be performed under conditions conventionally accumulated in the art.

[0052]

Effects of the Invention The polyester film having the primer layer of the present invention has excellent adhesion to the magnetic layer of a magnetic recording medium and also has excellent flatness, so it can be used for high-end home video tapes such as 8m/m video and has high reliability. It is suitably used as a base material for professional video tapes, etc., which require high performance and durability. Furthermore, although the polyester film having the primer layer of the present invention is flat, it has excellent slipperiness and handling properties, and has excellent roll-up properties during polyester film manufacturing and subsequent slitting. Furthermore, it has excellent transportability in the coater when applying magnetic paint.

[0053]

[Examples] The present invention will be further explained below 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. Magnetic paint adhesion Ferromagnetic metal magnetic powder (BET value 50m2
/gr) 100 parts Polyurethane resin (
Toyobo UR8300) 8 parts
PVC copolymer (Nippon Zeon MR110)
12 parts α-Al2 O3 (average particle size 0.20 μm) 5 parts
Carbon black (average particle size 25mμ)
2 parts stearic acid-m-
butyl
Part 3 Lecithin

4 parts solvent MEK

130 parts toluene

130 parts cyclohexanone 6
0 parts The above composition was kneaded and dispersed by a conventional method to prepare a magnetic paint. Next, 5 parts of a curing agent (Coronate L, Nippon Polyurethane Co., Ltd.) was added and stirred with a disper. After filtering through a filter with an average opening of 1 μm, it was applied onto a polyester film, followed by orientation, drying, and calendering. The sample was slit to a width of 8 m/m, and Scotch tape No. 1 was placed on top of the magnetic layer. 56 (manufactured by 3M) was adhered without air bubbles, and after smoothing and adhering it with a manual load roll with a load of 2 kg, the peel strength was measured at a peel speed of 200 m/m/min (peeling angle 180°).

2. Surface roughness (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 radius of the needle was 2.
μm, load 30mg, magnification 200,000 times, cutoff 0
．． Hang the chart under the condition of 0.08 mm, extract a part of measurement length L from the film surface roughness curve in the direction of its center line, set the center line of this extracted part as the X axis, and the direction of vertical magnification as the Y axis, When the roughness curve is expressed as Y=f(x), the value given by the following equation is expressed in μm.

[0056]

[Equation 1] In this measurement, four measurements were made with a reference length of 1.25 mm, and the average value is expressed.

(2) Ten point average roughness (Rz) JIS B
According to 0601, draw a chart in the same manner as Ra, and in the part extracted from the cross-sectional curve by the standard length,
The value of the difference between the average elevation of the fifth highest mountain peak and the average elevation of the fifth deepest valley, measured in the direction of vertical magnification from a straight line that is parallel to the average line and does not cross the cross-sectional curve. is expressed in micrometers (μm). In this measurement, the reference length was set to 1.25 m/m, and four measurements were taken, and the average value is expressed.

3. Film Friction Coefficient According to ASTM D1894-63, the static friction coefficient (μ
s) was measured. However, the thread plate was a glass plate, and the load was 1 kg.

4. A polyester film roll with a width of 4,000 m/m produced using a biaxial stretching machine is stretched to 1,200 m/m using a slitting machine.
It was slit into three rolls of m width x 10,000 m. The surface condition of the rolled product roll and the end face of the roll were observed and ranked.

○: No edge displacement/surface defects (wrinkles, protrusions, etc.) are observed △: Some misalignment/surface defects (wrinkles, protrusions, etc.) are observed ×
: Severe edge misalignment and surface defects.

5. After overlapping the primer-coated side and the uncoated back side of the anti-blocking polyester film, cut it into a 10cm x 15cm square, and heat it in an atmosphere of 50°C x 70% RH for 17 hours.
A load of 6 kg/cm2 is applied, and then the peel strength of this 10 cm width is measured. The peeling speed at this time is 100m/
m/min.

[0062]

[Examples 1 to 3 and Comparative Examples 1 and 2] The acid component consists of terephthalic acid (50 mol%), isophthalic acid (45 mol%) and trimellitic acid (5 mol%), and the glycol component consists of ethylene glycol (80 mol%). polyester (25 mol%) and ethylene glycol (20 mol%)
Intrinsic viscosity measured in O-chlorophenol at °C = 0.
28) Glass transition temperature obtained by polymerizing 3 parts with 6 parts of an acrylic copolymer of methyl methacrylate (48 mol%), ethyl acrylate (47 mol%) and 2-hydroethyl acrylate (5 mol%). 9 parts of the graft polymer having a temperature of 52° C. was dissolved in 90 parts of tetrahydrofuran, and 1 part of a nonionic surfactant [HLB 12.8] was added thereto.

To this solution, 490 parts of water was gradually added while stirring at high speed, followed by heating and distillation to remove the tetrahydrofuran and obtain an aqueous liquid. Furthermore, this liquid contains a polyurethane aqueous dispersion having carboxyl groups [manufactured by Toyo Polymer Co., Ltd.;
Merci 545 (trade name) was added in the proportions shown in Table 1 to obtain an aqueous primer solution for coating.

Next, polyethylene terephthalate containing 0.03% by weight of calcium carbonate with an average particle size of 0.5μ and having an intrinsic viscosity of 0.65 as measured in O-chlorophenol at 25°C was maintained at 20°C. An unstretched film with a thickness of 140 μm was obtained by melt extrusion onto a rotating cooling drum, which was then stretched 5.0 times in the machine axis direction, and then the above aqueous primer solution was applied to one side of the uniaxially stretched film using a kiss coating method. . The average amount applied at this time is 20mg in terms of solid content.
/m2. Continue to 3.9 in the horizontal direction at 105℃
The film was stretched twice and further heat-treated at 210° C. to obtain a primer-coated biaxially oriented polyester film having a thickness of 7.0 μm.

[0065]

[Comparative Example 3] Thickness 7 without primer treatment for comparison
Various evaluations were performed using a μm biaxially oriented polyethylene terephthalate film. The Rz of the film is 0.05
It was μm.

The performance of the polyester films and primer-coated biaxially oriented polyester films obtained in the above Examples and Comparative Examples was evaluated. The results are shown in Table 1.

[0067]

[Table 1] As is clear from Table 1, the primer-coated polyester film of the present invention has excellent adhesion, flatness, slipperiness, handling properties,
Excellent blocking resistance.

Claims (4)

[Claims] Claim 1: Center line average roughness (Ra) is 0.01μ
Ester/acrylic copolymer (A) having a glass transition temperature (Tg) of 10° C. or higher on at least one side of a polyester film having a thickness of 20 μm or less and a ten-point average roughness (Rz) of 0.1 μm or less and a thickness of 20 μm or less. 1. A flat, easily adhesive polyester film for magnetic recording media, characterized in that it is provided with a primer layer made of polyurethane (B) having anionic groups. [Claim 2] Ester/acrylic copolymer (A)
The flat easily adhesive polyester film for magnetic recording media according to claim 1, wherein is an aqueous ester/acrylic graft copolymer in which the trunk polymer is polyester and the branch polymers are acrylic polymers. Claim 3: Polyurethane having an anionic group (
2. The flat easily adhesive polyester film for magnetic recording media according to claim 1, wherein B) is a polyurethane containing at least one of a carboxylic acid group, a sulfonic acid group, and a sulfuric acid half-ester base. 4. At least one side of the polyester film has a glass transition temperature (Tg) of 1 before the crystal orientation is completed.
It is characterized by applying an aqueous primer solution containing an ester-acrylic copolymer (A) and an anionic group-containing polyurethane (B) at 0°C or higher, followed by drying, stretching, and heat treatment to complete crystal orientation. A method for producing a flat, easily adhesive polyester film for magnetic recording media according to claim 1.