JPH04147424A - Polyester film for magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve adhesion property of a magnetic coating film and back coating film, and surface smoothness by forming a specified coating layer comprising polyester urethane resin on a polyester film. CONSTITUTION:At least one surface of a base film comprising polyester resin is coated with a polyester polyurethane polymer which can be dispersed in water but insoluble in water. This polymer is obtained from a source component containing a polyol component containing at least polyester polyol and a polyisocyanate component. This polymer gives rough projections by <=10 per 100 cm<2> when formed into a film. Thereby, the film causes no problem such as blocking, and shows excellent adhesion property with a magnetic coating film and a back coating film.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a polyester film used as a base film for magnetic recording media, and more specifically, the present invention relates to a polyester film used as a base film for magnetic recording media. A thin layer of polyurethane polymer is formed,
The present invention relates to a polyester film for a magnetic recording medium that has improved adhesion to a magnetic recording layer and a back coat layer formed thereon, has high smoothness, and provides a magnetic recording medium with good electromagnetic conversion characteristics.

[Prior Art] Biaxially stretched films made of polyester resin have excellent heat resistance, dimensional stability, strength, etc.
It is widely used as a film base material for magnetic recording media. However, biaxially oriented polyester film is highly crystal oriented and has poor adhesion to the magnetic recording layer and back coat layer. (2) A method in which the surface is subjected to corona discharge treatment, corona discharge treatment in various gas atmospheres, ultraviolet irradiation treatment, plasma treatment, flame treatment, etc., or (2) A method in which the surface of the substrate is subjected to acid, alkali, or amine treatment. Methods of improving adhesion include chemical etching treatment using an aqueous solution, trichloroacetic acid, phenols, etc., and a combination of the above-mentioned treatments (1) to (2). Among these methods, the method of forming a primer layer on a polyester film base material has been widely put into practical use because it is superior in terms of ease of processing, work safety, cost, and effect on improving adhesion. . Many compositions have been proposed as brimer treatment agents to be used here. Among them, brimer treatment agents whose main component is polyurethane resin have excellent applicability to polyester film substrates, adhesion of the coated layer, and anti-blocking properties. It is attracting attention as being excellent in sex etc.

However, even if conventional brimer treatment agents are effective against a specific type of magnetic paint, the same effect may not be obtained when the type of paint changes, so they are not satisfactory for many types of magnetic paint. It is not possible to obtain a stable brimer effect. Furthermore, it has been pointed out that when a primer layer is formed on a base film and then wound up into a roll, the films tend to block each other.

[Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a magnetic recording layer and a back coat layer without causing problems such as blocking. The object of the present invention is to provide a polyester film for magnetic recording media that exhibits excellent adhesive properties.

[Means for Solving the Problems] The structure of the polyester film for magnetic recording media according to the present invention that can solve the above problems is as follows: At least one side of a base film made of a polyester resin contains at least a polyester polyol. A water-dispersible but Kinoshita-soluble polyester polyurethane polymer obtained from raw materials containing a polyol component and a polyisocyanate component, and when the polymer is made into a film, it can be determined by the following method of Funai. The gist is that it is coated with a polyester polyurethane polymer having a number of coarse projections of 10 or less per 100 cm2.

(Method for measuring the number of coarse protrusions) In a clean room, a 0.1 μm thick film made of polyester polyurethane polymer was formed on a smooth glass plate, and a 10 μm thick smooth film was superimposed on top of it. After close contact, irradiate Na D-ray from above,
The number of interference rings formed by protrusions originating from undispersed matter or foreign matter contained in the polymer and having an order of 3 or more is determined as the number of coarse protrusions.

[Function] Examples of the base film used in the present invention include thermoplastic polyester resin films, such as films of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and the like. Among these, particularly preferred are mono- or copolymerized polyester films in which 80% or more of the resin component is polyethylene terephthalate, or polyester films containing 80% or more of polyethylene terephthalate.
It is a polyester blend film containing 0% or more.

There are no particular restrictions on the polyester components other than the polyethylene terephthalate component in the copolymerized polyester or polyester blend, and any polyester components can be combined. As the dicarboxylic acid component constituting such a polyester, aromatic, aliphatic, and alicyclic dicarboxylic acids can all be used. Examples of aromatic dicarboxylic acids include isophthalic acid, orthophthalic acid, and 2,6-naphthalene dicarboxylic acid; examples of aliphatic dicarboxylic acids include succinic acid, adipic acid, sebacic acid, and oxalic acid; Group dicarboxylic acids include 1,3-cyclopentanedicarboxylic acid, 1,4
-Cyclohexanedicarboxylic acid and the like are exemplified. It is also effective to use an oxyacid such as p-hydroxybenzoic acid in place of the aromatic dicarboxylic acid.

The glycol component constituting the above polyester is as follows:
Aliphatic glycol having 2 to 8 carbon atoms or 6 to 1 carbon atoms
Two alicyclic glycols are preferred. Such glycols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, 1,2-cyclohexane dimetatool. , 1.
Examples include 3-cyclohexane dimetatool, 1,4-cyclohexane dimetatool, p-xylene glycol, diethylene glycol, triethylene glycol, and the like. In addition, it is also possible to use polyether glycols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol as the aliphatic glycol.

The above acid component and glycol component are polyesterized by polycondensation using a conventional method. This polyester may be used alone or in combination with 2ff1 or more if necessary, or may be copolymerized with a small amount of other copolymerizable components during the polyester manufacturing process, or may be blended with a small amount of resin other than polyester. Furthermore, appropriate amounts of antioxidants, heat stabilizers, lubricants, pigments, ultraviolet absorbers, etc. may be added as necessary. These resins are usually made into a base film by a melting/extrusion method or a casting method in which the resin is dissolved in a solvent and cast. This base film may be used in an unstretched state, or may be uniaxially or biaxially stretched as necessary.

Next, the polyester polyurethane polymer formed as an adhesion improving layer on at least one side of the base film is composed of a polyester polyol, a polyisocyanate, and optionally a low molecular compound having two or more active hydrogen atoms. Manufactured by reacting with a chain extender.

The above-mentioned polyester polyol is obtained by a reaction between a dicarboxylic acid and a glycol, and any aromatic, aliphatic, or alicyclic dicarboxylic acid can be used as the dicarboxylic acid component. Aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-
Examples include naphthalene dicarboxylic acid, and in place of some of them, oxyacids such as p-hydroxybenzoic acid can also be used in combination. As the aliphatic dicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, oxalic acid, etc. are used. In addition, as the alicyclic dicarboxylic acid, 1.3-
Cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid,
Examples include 1,4-cyclohexanedicarboxylic acid.

As the glycol component constituting the polyester polyol, both aliphatic glycols and alicyclic glycols having 2 or more carbon atoms can be used, but in the present invention, alkylene glycols having 4 or more carbon atoms (for example, butanediol) , hexanediol) and alicyclic glycols (for example, cyclohexane dimetatool) or bisphenol compounds are preferably used together.

Using the above dicarboxylic acid component and polyhydric alcohol component,
When polycondensation is carried out by a melt polycondensation method, a solution polycondensation method, an interfacial polycondensation method, etc., a polyester polyol is obtained.

For example, a direct esterification method in which each of the above components is directly reacted, water is distilled off, and polycondensation is performed while esterification is performed.Alternatively, the dialkyl ester of the dicarboxylic acid component and the glycol component are reacted, and the resulting alcohol is distilled off. A transesterification method is employed in which transesterification is carried out while polycondensation is carried out.

In order to obtain the polyester polyurethane polymer of the present invention, a preferable polyester polyol is a hard polyester polyol, especially one in which the dicarboxylic acid component constituting the polyester polyol is mainly composed of an aromatic dicarboxylic acid, and the glass transition temperature (Tg) is A polyester polyol having a temperature of 10°C or more and 60°C or less is preferable. For those with a Tg of less than 10°C, when the laminated film is wound into a roll,
Coating layers made of polyester polyurethane polymers tend to block and become unstable, while those with a Tg of over 60°C may cause poor adhesion between the coating layer and the base polyester film, magnetic recording layer and/or back coat layer. Sexuality may be insufficient.

As the polyisocyanate to be reacted with the polyester polyol thus obtained, aromatic, aliphatic, and alicyclic polyisocyanates can all be used, but aromatic diisocyanates such as toluylene diisocyanate are preferred. A polyurethane bond-containing composition obtained using such an aromatic diisocyanate has high strength when formed into a film, and exhibits excellent adhesion to a magnetic recording layer and a back coat layer.

The polyester polyurethane polymer can be obtained by reacting the polyester polyol with the polyisocyanate according to a conventional method. It is also effective to allow the chain to extend. The diol used here is 1.8-
Preferred examples include hexanediol, and examples of diamines include ethylenediamine, hexamethylenediamine, and piperazine. Diamine is more preferred in terms of increasing film strength.

Among the polyester polyurethane polymers thus obtained, in the present invention, a water-dispersible but Kinoshita-soluble polymer is used. Here, "Kinoshita solubility" refers to the property that even when the target polyester polyurethane polymer is immersed in hot water at 80°C and stirred, the polymer does not dissolve in the hot water, and is more specific. For example, when a polyester polyurethane polymer is chipped and placed in a large excess of hot water (80°C) and stirred for 24 hours, the weight loss due to dissolution of the polymer is 5% by weight or less. are considered to be Kinoshita-soluble. However, this polyester polyurethane polymer has moderate polarity, and for example, ① a method of vigorously stirring the fine particles of the combined prototype in water together with an emulsifier; ③ When synthesizing the polyester polyurethane polymer, it is possible to A method in which a polyurethane (prepolymer) containing a group (chain extender if necessary) and an emulsifier are reacted by strong stirring in water, and dispersion and polymerization by mechanical shearing force are proceeded in parallel. ■Polyester polyurethane polymer It can be dispersed in water by introducing an ionic group such as a hydroxyl group, an amine group, or a carboxyl group into the side chain or end of the compound to impart self-emulsifying properties. However, in consideration of the water resistance of the film, it is desirable to adopt a water dispersion method that does not use an emulsifier. Note that a water-dispersible polyurethane or other water-dispersible resin compound having a different component composition may be added to this aqueous dispersion, if necessary. Examples of other water-dispersible resin components used here include water-dispersible polyester resins, water-dispersible acrylic resins, and the like. However, in consideration of the water resistance of the coating, it is preferable to introduce ionic groups such as hydroxyl groups, amino groups, and carboxyl groups into the side chains or terminals of the polymer to impart self-emulsifying properties and disperse the polymer.

In addition, as additives, various additives such as lubricants, pigments, preservatives, ultraviolet absorbers, and antistatic agents may be added, or these additives may be added as appropriate during the water dispersion process described above to create a uniform aqueous dispersion. It can be done.

Additives and additives used here include, for example, silica, calcium carbonate, kaolinite, alumina,
Examples include inorganic inert particles such as talc and barium sulfate; organic inert particles such as benzoguanamine resin and polystyrene resin (all particle sizes of about 0.01-10 μm); by adding these, slipping properties and This is expected to further improve blocking resistance. Furthermore, it is also possible to add appropriate amounts of pigments, organic or inorganic antistatic agents, preservatives, ultraviolet absorbers, etc., as necessary.

The aqueous dispersion of the polyester polyurethane resin described above is applied onto the base film by a known method. For example, the above aqueous dispersion is applied onto an unstretched base film obtained by melting/extrusion, or a base film obtained by uniaxially or biaxially stretching, and further stretching and post-heat treatment are performed as necessary. be exposed. Among these methods, a method in which an aqueous dispersion is applied onto an unstretched or uniaxially stretched base film, then uniaxially or biaxially stretched and heat treated is a method that more effectively improves the adhesion and surface strength of the coating layer. Recommended as a way to increase this. In addition, any known method such as a roll coating method (gravure method, reverse method, etc.), knife coating method, rod coating method, nozzle coating method, air knife coating method, etc. can be adopted for applying the above-mentioned aqueous dispersion. Incidentally, prior to application of the aqueous dispersion, it is also possible to subject the surface of the base film to corona discharge treatment or other physical or chemical surface activation treatment.

The amount of the aqueous dispersion applied is appropriately selected depending on the application and purpose, but the most common is the dry weight per unit area (river 2) of the coating film finally obtained through biaxial stretching etc. 0.01-5g, preferably 0.02-1g
is within the range of If the coating amount is less than 0.01 g/m2, it is difficult to obtain a sufficient adhesion improvement effect, and if it exceeds 5 g/m2, blocking tends to occur.

By the way, the polyester polyurethane resin layer formed as a coating layer on the base film increases the adhesion to the magnetic recording layer and back coat layer, but it is difficult to prevent insoluble foreign matter that may be mixed into this coating layer. The resulting coarse protrusions cause signal defects such as dropouts when a magnetic layer is formed thereon. Therefore, the number of coarse protrusions present in the coating layer must be minimized, and therefore, in the present invention, the number of coarse protrusions shown below is defined as a standard for ensuring the smoothness necessary for a film for magnetic recording media. .

That is, in a clean room, a layer of the above polyester polyurethane polymer with a thickness of 0.1 μm was placed on a smooth glass plate.
A smooth film with a thickness of 10 μm was superimposed on the surface of the film, and Na was applied from above.
When irradiated with D-ray, the number of interference rings of order 3 or more formed by coarse protrusions derived from undispersed matter or foreign matter contained in the polyester polyurethane polymer is 10 or less per 100 cm2, More preferably, the number should be 3 or less. If the number of coarse protrusions is larger than this, defects such as dropouts will increase when used as a magnetic recording medium, making it impossible to meet the purpose of the present invention. To obtain such a highly clean aqueous dispersion,
Before coating, the aqueous dispersion may be passed through a filter with a pore size of about 3 μm or less, more preferably about 1.5 μm or less to remove coarse insoluble matter. It should be noted that the microprotrusions with the above-mentioned interference ring of secondary order or less have almost no adverse effect on the magnetic properties, so they are not a particular problem in the present invention, but it is preferable that the number of these microprotrusions be small. Of course.

The thus obtained polyester film for magnetic recording media of the present invention has both interlayer adhesion between the base material and the coating layer, and adhesion between the coating layer and the magnetic recording layer and back coat layer formed on the surface thereof. It has good properties and does not cause blocking even when wound into a roll. Moreover, since the film has few coarse protrusions and a high surface smoothness, by using this as a base film, a magnetic recording medium with excellent electromagnetic characteristics can be obtained.

[Example] The present invention will be specifically described below with reference to Examples.

The performance evaluation method adopted in the examples is as follows. Further, in the following examples, "r parts" means "parts by weight" unless otherwise specified.

Co-y-Fe203 100 parts Vinyl chloride/vinyl acetate copolymer 18 parts Urethane-modified saturated polyester resin 18 parts α-alumina
3 part carbon black
1 part toluene 10
5 parts methyl ethyl ketone 105 parts cyclohexanone 105 parts After mixing and dispersing the above raw materials in a ball mill for about 12 hours, add palmitic acid, 1 part dodecyl stearate, 2 parts oleic acid.
Add 2 parts and mix for an additional 30 minutes.

Next, 14 parts of a 75% solids solution of a triisocyanate compound in ethyl acetate was added and mixed for an additional hour to form a magnetic paint.

Evaluation paint-2 (back coat paint) Carbon black 50 parts Vinyl chloride/vinyl acetate copolymer 30 parts Triisocyanate 30 parts Polyurethane elastomer
30 parts nitrocellulose 3
0 parts Stearic acid amide 5 parts Toluene 120 parts Methyl ethyl ketone 120 parts were milled into 10 parts using a ball mill.
Stir and mix for a while to form a back coat paint. The magnetic paint was applied onto the test film to a dry thickness of 3 μm, subjected to magnetic field orientation treatment, dried at 60°C, and then
Calendar treatment is carried out at 00°C and further cured at 60°C for 72 hours.

The back coat paint was applied onto the test film to a dry thickness of 1 μm, dried at 60°C, calendered at 100°C, and further cured at 60°C for 72 hours.

After coating the test film with the above-mentioned magnetic coating under specified conditions, the coated surface of the obtained film was coated with 5 Ω at 23°C.
Under the atmosphere of 0% RH, "Nichiban LP-12J (
Paste a sheet (width 12 mm x length 10 cm) so that there are no air bubbles, and press a roll on top of it to smooth it out.

The tape was then quickly peeled off by hand in the 80'' direction, and adhesion was visually determined from the amount of magnetic paint remaining on the film.

O: Not peeled off at all △ D Peeling is seen in some parts ×: More than the entire layer peels off Blocking resistance Polyester polyurethane polymer coated on one side 2
The coated and uncoated sides of two films (3 cm x 3 cm) are placed one on top of the other, and this is sandwiched from both sides by silicone rubber measuring 6 cm x 6 am and a glass plate of the same size and 7 mm thick. A load of 2 kg was applied to this, and the temperature was 50°C.
After leaving the film in an atmosphere of ×85%R)l for 48 hours, the adhesive state was observed when the film was peeled off.

O: No adhesion observed Δ: Adhesion of the film occurs in some places ×: Adhesion occurs over the entire surface A tan-based aqueous dispersion was placed on a smooth glass plate in a class 1000 clean room to a dry film thickness. Coat to a thickness of 0.1 μm and dry. Then, on the coating film,
Polyester films with a thickness of 10 μm with as little foreign matter as possible are stacked one on top of the other, and the air in the gaps is pushed out using a roller to bring them into close contact. After that, the D-ray of Na is applied from above to observe the interference ring formed. Then, the number of interference rings having three or more fringes is checked, and the number is calculated as the number per 100 CI112.

K5±Eyu (A) Preparation of polyester polyol In a reactor equipped with a thermometer, a nitrogen gas inlet tube, and a stirrer, add 310 parts of ethylene glycol and 52 parts of neopentyl glycol.
0 parts of dimethyl terephthalate, and 392 parts of dimethyl isophthalate were charged, and while nitrogen gas was introduced, the reaction was carried out at 200° C. for 6 hours while heating, melting, and stirring until the amount of methanol distilled was 252 parts. then 1
After cooling to 20°C, 292 parts of sebacic acid was added.
After further reaction at 200°C for 8 hours, the hydroxyl value was 103.9.
, a polyester polyol (a) having an acid value of 11.1 was obtained. Polyester polyol (b) was also obtained in the same manner except that the raw material composition was changed. The raw material composition and constants for each are shown in Table 1.

(B) Preparation of polyester polyurethane aqueous dispersion Polyester polyol (a) or (b) obtained above 100
After dehydrating a portion at 120°C under reduced pressure and cooling to 80°C,
100 parts of methyl ethyl ketone was added and thoroughly stirred and dissolved. Next, 653 parts of tolylene diisocyanate and 2,2-
17.7 parts of dimethylolpropionic acid (chain extender) was added, and the mixture was reacted at 70°C for 10 hours. 40℃ after completion of reaction
12.3 parts of piperazine was added to carry out a chain extension reaction, and then 13.3 parts of triethylamine and 50 parts of water were added.
0 parts was added to make it water-soluble.

After removing methyl ethyl ketone from the resulting translucent reaction product at 65° C. under reduced pressure, water was added to adjust the concentration to obtain a stable aqueous dispersion with a nonvolatile content of 25%.

This aqueous dispersion was further added to a mixture of water and isopropyl alcohol to obtain a polyester polyurethane aqueous dispersion [coating liquid (al or (b))] with a solid content of 5%.

(C) Preparation of coated polyester film (base film for magnetic recording media) CaCO3 fine particles with an average particle size of 0.8 μm were used at 2500 pp.
Using polyethylene terephthalate dispersed at a concentration of
The film was cooled with a cooling roll to obtain an unstretched film with a thickness of 150 μm. This unstretched film was stretched 3.5 times in the longitudinal direction between a pair of rolls heated to 90°C with different circumferential speeds,
A uniaxially stretched base film was obtained.

Next, the coating solution (a) or (b) containing the polyester polyurethane obtained in the above section (A) was passed through a filter with a pore size of 1.0 μm, and then coated on the base film obtained in the above section (8) using a roll coater. It was applied according to the law. Hot dry at 70°C, then crosswise 3. at 98°C using a tenter.
After stretching 5 times, heat setting at 200 to 210℃ to a thickness of 12
A biaxially stretched polyester film (a) for magnetic recording media of μm.

(b) was obtained. The final coating amount of the coating material (polyester polyurethane resin composition) in each film was about 0.04 g/m2. The resulting film (
Table 2 shows the evaluation of blocking resistance, adhesion, and coarse protrusions of a) and (b).

Comparative Example 1 2500pp of CaCO3 fine particles with an average particle size of 0.8μm
Using polyethylene terephthalate dispersed at a concentration of m, it was melt-extruded into a film at 290°C and cooled with a cooling roll at 25°C to obtain an unstretched film with a thickness of 150 μm. This unstretched film was stretched 35 times in the machine direction between a pair of rolls heated to 90°C at different circumferential speeds, then stretched 3.5 times in the transverse direction at 98°C using a tenter, and then stretched 3.5 times in the transverse direction at 98°C using a tenter. A biaxially stretched polyester film having a thickness of 12 μm was obtained by heat setting at ~210°C. Table 2 shows the evaluation of blocking properties, adhesive properties, and coarse protrusions of the obtained films.

Comparative Example 2 A biaxially stretched coated polyester film was obtained in exactly the same manner as in Example 1 except that a filter with a pore size of 5 μm was used.

Table 2 shows the evaluation of blocking properties, adhesive properties, and coarse protrusions of the obtained films.

As is clear from Table 2, the polyester film of the present invention coated with a polyester polyurethane polymer has good adhesion to the magnetic recording film and back coat film, and has few foreign matter protrusions on the surface. It can be seen that it is suitable as a base film for magnetic recording media.

[Effects of the Invention] The present invention is configured as described above, and by providing a specific coating layer made of a polyester urethane resin on the surface of a polyester film, it can be used in combination with a magnetic coating film or a back coat coating film. It has improved adhesion and surface smoothness, and is extremely excellent as a base film for obtaining high-performance magnetic recording media.

Claims (2)

[Claims] (1) A water-dispersible but Kinoshita-soluble polyester polyurethane polymer obtained from a polyol component containing at least a polyester polyol and a raw material component containing a polyisocyanate component is applied to at least one side of a base film made of a polyester resin. A magnetic material coated with a polyester polyurethane polymer which has a number of coarse protrusions of 10 or less per 100 cm^2 as determined by the method below when the polymer is formed into a film. Polyester film for recording media. (Method for measuring the number of coarse protrusions) In a clean room, a 0.1 μm thick film made of polyester polyurethane polymer was formed on a smooth glass plate, and a 10 μm thick smooth film was superimposed on top of it. After close contact, irradiate Na D-ray from above,
The number of interference rings formed by protrusions originating from undispersed matter or foreign matter contained in the polymer and having an order of 3 or more is determined as the number of coarse protrusions. (2) Claim (1) in which the raw material component contains a low molecular weight compound having two or more active hydrogens as a chain extender.
The film mentioned.