JPH01302527A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the various characteristics and reliability of the magnetic recording medium by using a specific vinyl chloride copolymer, rubber binder and polyisocyanate as a binder resin and specifying the glass transition temp. of a magnetic layer to <=80 deg.C. CONSTITUTION:The vinyl chloride copolymer contg. vinyl chloride, vinyl alcohole, amine-modified vinyl compd. and epoxy group-contg. vinyl compd. as essential constituting components is used as the binder resin of the coating type magnetic glass transition temp., by which the surface characteristic of the dispersible coated film of magnetic powder is improved and the good magnetic characteristics and electromagnetic conversion characteristics are obtd.; in addition, the reliability at and under a high temp. and high humidity are improved. The traveling property, wear resistance, etc., of the magnetic coated film are improved by adding a rubber binder and polyisocyanate further to the above-mentioned copolymer and the calendering of the magnetic layer is facilitated and the surface characteristics of the magnetic coated film are improved by confining the glass transition temp. of the magnetic layer to <=80 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to magnetic recording media used as magnetic tapes and floppy disks, and in particular improves the dispersibility of magnetic powder and the surface properties of magnetic coatings, and improves electromagnetic conversion characteristics. The present invention relates to a magnetic recording medium that has good reliability under high temperature and high humidity environments.

BACKGROUND OF THE INVENTION Generally, coated magnetic recording media are made by coating a magnetic coating material mainly consisting of magnetic powder, binder resin, and solvent onto a support such as a polyester film. The properties of the magnetic coating film formed on the support are closely related not only to physical properties such as running properties, but also to magnetic properties and electromagnetic conversion properties from the dispersibility of magnetic powder, etc., and this is mainly due to bonding. It is largely controlled by the agent resin and various additives. Therefore, various binder resins have been proposed so far.
As one of them, vinyl chloride-vinyl acetate-vinyl alcohol copolymer has been widely used. The characteristics of this copolymer are that it is relatively inexpensive, easily soluble in solvents, has good compatibility with other resins, and has a high affinity with magnetic powder due to the hydroxyl group in its molecules. , has advantages such as improved dispersibility, and provides excellent magnetic properties and electromagnetic conversion properties.

However, as the performance of magnetic recording devices has improved in recent years, magnetic recording media are required to have even higher recording densities and higher reproduction output in short wavelength recording. In response to this,
The magnetic powder used is becoming more finely divided, and it is becoming increasingly difficult to obtain satisfactory characteristics using only the above-mentioned resins.

In order to solve the above problems, there is a method to increase the affinity with the magnetic powder and improve the dispersibility of the magnetic powder by introducing various hydrophilic groups into the molecular structure of the binder resin. . When vinyl chloride-vinyl acetate-vinyl alcohol copolymer is used as the binder goza, the molecule P:'
Hydrophilic groups introduced during the process include carboxyl groups (JP-A-58-137133), sulfonic groups, sulfonic acid groups, or sodium sulfonate groups (JP-A-62-2).
11822) etc. are known. However, binder resins into which hydrophilic groups have been introduced generally have a high glass transition temperature, and therefore have the drawback that surface processing is difficult and it is difficult to improve the surface properties of the magnetic layer after calendering.

On the other hand, vinyl chloride-vinyl acetate-vinyl alcohol copolymers tend to undergo a dehydrochloric acid reaction under high temperature and high humidity environments, resulting in deterioration of the magnetic coating.

Furthermore, the generated hydrogen chloride causes problems such as deterioration of blocking characteristics (a phenomenon in which the magnetic layer is transferred to the head cylinder) and an increase in dropouts.

Problems to be Solved by the Invention In view of the problems associated with the above-mentioned atomization of magnetic powder and dehydrochloric acid reaction, the present invention has better dispersibility of magnetic powder, better surface properties of magnetic coating, and electromagnetic conversion characteristics. In addition, the present invention provides a magnetic recording medium with improved reliability under high temperature and high humidity environments.

Means for Solving the Problems In order to solve the above problems, the magnetic recording medium of the present invention includes:
(i) a vinyl chloride-based copolymer containing vinyl chloride, vinyl alcohol, an amine-modified vinyl compound, and an epoxy group-containing vinyl compound as essential components; (11)
A rubber-based binder and (iii) polyisocyanate are used as binder resin components, and a magnetic powder is dispersed therein, and then applied onto a support to form a magnetic layer, and the glass transition temperature of the magnetic layer is set to 80°C or lower. That is.

Function The present invention is characterized in that the three-component resin described above is used as the binder resin of the coated magnetic recording medium, and the glass transition temperature of the magnetic layer is 80° C. or lower. Vinyl chloride as binder resin.

By using a vinyl chloride copolymer containing vinyl alcohol, an amine-modified vinyl compound, and an epoxy group-containing vinyl compound as essential components, the dispersibility of the magnetic powder and the surface properties of the magnetic coating are improved, resulting in good magnetic properties. characteristics and electromagnetic conversion characteristics can be obtained, and reliability under high temperature and high humidity environments is improved. Furthermore, by adding a rubber binder and polyinsyanate to the vinyl chloride copolymer, it is possible to improve the physical properties of the magnetic coating, such as running properties and abrasion resistance. Furthermore, it has been found that by setting the glass transition temperature of the magnetic layer to 80° C. or less, the magnetic layer can be easily calendered and the surface properties of the magnetic coating film can be improved.

In the present invention, the vinyl chloride-based copolymer which is used as one of the binder resin components and whose essential constituents are vinyl chloride, a vinylalcohol-modified vinyl compound, and an epoxy group-containing vinyl compound has an amino group in its molecular structure. By having a hydrophilic group, the affinity with magnetic powder which also has many hydrophilic groups such as hydroxyl groups on the surface increases.

As a result, the dispersibility of the magnetic powder is improved, and good magnetic properties and electromagnetic conversion properties can be obtained. Furthermore, by having an epoxy group in the molecular structure, hydrogen chloride generated by the dehydrochlorination reaction reacts with the epoxy group and is captured. As a result, free hydrogen chloride no longer exists in the magnetic coating film, and the dehydrochloric acid reaction of the vinyl chloride copolymer is inhibited. Therefore, the magnetic coating film is less likely to deteriorate even in high temperature and high humidity environments.
In addition, blocking of the magnetic coating occurs when hydrogen chloride corrodes the head cylinder surface, and dropouts occur when trace amounts of metal ions in the magnetic coating react with hydrogen chloride and sludge onto the magnetic coating surface. Such phenomena can also be greatly reduced.

Examples of the vinyl chloride copolymer include vinyl chloride 60-95% by weight, c% r vinyl alcohol 2-16t%, and amine-modified vinyl compound 0.06% by weight.
It is preferable to use one having an average degree of polymerization of 200 to 800, consisting of 6% by weight, some amount of an epoxy group-containing vinyl compound, and some amount of other vinyl compounds as necessary. If the amount of vinyl chloride is too small, the physical strength will decrease, and if it is too large, the solubility in a solvent will decrease, which is disadvantageous in use. Furthermore, if the amount of vinyl alcohol is too small, the dispersibility of the magnetic powder will decrease, and the compatibility with the rubber binder used in combination will decrease. On the other hand, if it is too large, physical strength and thermal stability will decrease. If the amount of the amine-modified vinyl compound is too small, the dispersibility of the magnetic powder will decrease and the surface properties of the magnetic coating will decrease. On the other hand, if the amount is too high, the dispersibility and surface properties will deteriorate, and the solubility in solvents will further decrease, making it impossible to use it as a binder resin.

If the amount of the epoxy group-containing vinyl compound is too small, the ability to inhibit the dehydrochlorination reaction will be reduced, while if it is too large, the polymerization reaction will be inhibited, making it difficult to obtain a high molecular weight binder resin.

If the average degree of polymerization of a copolymer composed of such unit components is too low, the magnetic coating film will become brittle and its physical strength will decrease, and the durability of the magnetic coating film will also decrease. On the other hand, if the average degree of polymerization is too high, the viscosity of the paint at a given concentration will increase, resulting in significantly poor workability and difficulty in handling.
It is desirable that the average degree of polymerization is in the range of 200 to 800.

This copolymer can be produced using general suspension polymerization method, emulsion polymerization method,
It is produced by solution polymerization, bulk polymerization, etc., but when introducing vinyl alcohol, lower fatty acid vinyl such as vinyl acetate or vinyl propionate is copolymerized, and the resulting copolymer is catalyzed with an acid in an appropriate solvent. The method is carried out by saponifying the product and purifying it by a conventional method. Vinyl acetate, vinyl propionate, etc. may be present in small amounts as unsaponified moieties, or vinyl versatate, alkyl esters of acrylic acid or methacrylic acid, esters of maleic acid or itaconic acid, vinylidene chloride, Some amount of various vinyl ethers may be copolymerized.

Since the introduction of vinyl alcohol is in the above-mentioned range of 2 to 16% by weight, the copolymerization amount of lower fatty acid vinyl and the saponification rate (mo)v%) need to be adjusted so as to maintain this range. be.

On the other hand, the amine-modified vinyl compound can be introduced simultaneously with the saponification reaction. That is, by adding various amine compounds described below to the saponification reaction system and heating and stirring at 1°C to 80°C for a certain period of time until the desired degree of saponification is obtained, vinyl alcohol is introduced, and at the same time, the chlorine atoms of vinyl chloride and An amine is introduced into the side chain by reaction with an amine compound. In this amine modification, the amount of amine compound used is such that the amount of amine modified vinyl compound in the copolymer is 0.
．． It is necessary to set the amount within the range of 0.05 to 5% by weight.

The amine compounds used include primary, secondary or tertiary amines such as aliphatic amines, cycloaliphatic amines, aromatic amines, and specifically ethylamine, propylamine, butylamine, cyclohexylamine, etc. l Reamine, ethanolamine, naphthylamine, aniline, O-
/L/Idine, diethylamine, dioctylamine,
Diisobutylamine, jetanolamine, N-methylaniline, trimethylamine, triethylamine.

Triisobutylamine, tridecylamine, N-methyldiphenylamine, hexamethylenetetramine, triethanolamine, tributylamine.

Examples include pyridine, α-picoline, β-picoline, γ-picoline, 2,4-lutidine, quinoline, and morpholine.

Regarding the introduction of epoxy group-containing vinyl compounds,
This is carried out by copolymerizing epoxy group-containing monomers such as glycidyl methacrylate and glycidyl acrylate. When introducing this epoxy group, it is necessary to adjust the amount of the epoxy group-containing vinyl compound in the copolymer to be in the range of 1 to 6% by weight.

In the present invention, the glass transition temperature of the magnetic layer is 80° C. or lower. If the glass transition temperature is higher than 800, it becomes difficult to calender the magnetic layer, the surface properties of the magnetic coating deteriorate, and as a result, it becomes difficult to obtain good electromagnetic conversion characteristics.

The ratio of the binder resin components used in the present invention is 80 to 20% by weight of the vinyl chloride copolymer, 20 to 80% by weight of the rubber binder, and 5 to 30% by weight of the polyisocyanate. % is desirable. If the ratio of the vinyl chloride copolymer is too low or the ratio of the rubber binder is too high, the dispersibility of the magnetic powder will decrease and the surface properties of the magnetic coating will decrease. On the other hand, if the ratio of the vinyl chloride copolymer is too high or the ratio of the rubber binder is too low, the physical strength of the magnetic coating will decrease, the glass transition temperature of the magnetic layer will increase, and the calendaring of the magnetic layer will increase. Since processing becomes difficult, the surface properties of the magnetic coating deteriorate. Also, if the amount of polyisocyanate is too small, the physical strength of the magnetic coating will be insufficient, and if it is too large, unreacted polyisocyanate will float to the surface of the magnetic coating, causing calendar adhesion.
This causes problems such as reduced running performance.

The rubber binder used in the present invention is a polyurethane resin, a polyester resin, or a combination of both. As these polyurethane resins or polyester resins, among the known binder resins conventionally used as binder resins for magnetic recording media, those having a glass transition temperature of the magnetic layer of 80° C. or lower can be used.

Examples of the polyisocyanate used in the present invention include bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and inphorone diisocyanate, and trifunctional isocyanates such as trimethylolpropane tolylene diisocyanate. Further, among polyisocyanates that can be used as a curing agent, any polyisocyanate can be used as long as the glass transition temperature of the magnetic layer is 80° C. or lower. These polyisocyanates are
It is added in an amount of 5 to 30% by weight based on the total binder resin component.

The magnetic powder used in the present invention includes γ-Fe2
o3. Fe3O4 and those obtained by adsorbing or doping cobalt ions, oxide-based magnetic powder such as Or 02, furthermore, Fe, Co, Ni, or metal-based magnetic powder containing these as components, and other conventionally known materials. Examples include: Good results can be obtained if the mixing ratio of the magnetic powder and the binder resin is 10 to 40 parts by weight of the binder resin per 100 parts by weight of the magnetic powder.

Incidentally, when preparing magnetic paint by uniformly dispersing magnetic powder and binder resin, abrasives, antistatic agents, dispersants, and lubricants have been conventionally used.

Adding plasticizers, etc., as well as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone.

Various organic solvents such as toluene may be used in the same manner as conventional ones, and there are no particular restrictions on these points.

As the support, conventionally known materials such as polyester, polyimide, synthetic resins such as polyvinyl chloride, other magnetic metals, and ceramics can be used. Furthermore, conventionally known processes for producing magnetic recording media can be used.

Example The present invention will be further explained below with reference to Examples and Comparative Examples.

[Example 1] First, the ball mill A magnetic paint was prepared with the following composition.

Vinyl chloride copolymer C, which contains vinyl chloride, vinyl alcohol, an amine-modified vinyl compound, and an epoxy group-containing vinyl compound as essential constituents, is hereinafter referred to as vinyl chloride copolymer 1. ) 10 parts by weight Polyurethane resin 1 10 parts by weight Co-adhesion 7
Fe 203 (BET specific surface area 35〃〆/r) 100 parts by weight Alumina 3 parts by weight Carbon black 5 parts by weight n-buty stearate 1'Aikm stearic acid
1 part by weight polyisocyanate (
Trimethylolpropane tolylene diisonanate) Type 5 needle Methyl ethyl ketone 150 parts by weight Toluene
100 parts by weight/chlorhexanone
The composition etc. of the 50 parts by weight vinyl chloride co-claw assembly 1 are shown in Table 1, and the composition etc. of the polyurethane resin 1 are shown in Table 2.

Table 1 (Binder Resin 2 Composition and Degree of Polymerization) Table 2 The magnetic paint prepared with the above composition was coated on a polyethylene terephthalate film having a final film thickness of 6 μm with a thickness of 14 μm.
The magnetic tape was coated to a width of about 12.65 inches, dried, smoothed, and cured, and then cut to a width of about 12.65 inches.

[Example 2] In Example 1, the vinyl chloride copolymer 1 was changed to 8 parts by weight and the polyurethane resin 1 was changed to 12 parts by weight to form a coating, and a magnetic tape was produced in the same manner as in Example 1.

[Comparative Example 1] A magnetic tape was produced in the same manner as in Example 1 except that the vinyl chloride copolymer 1 was changed to 12 parts by weight and the polyurethane resin 1 was changed to 8 parts by weight to form a coating.

[Comparative Example 2] In Example 1, polyurethane resin 1 was changed to polyurethane resin 2 (composition etc. are shown in Table 2) to form a paint, and a magnetic tape was produced in the same manner as in Example 1.

[Comparative Example 3] In Example 1, vinyl chloride copolymer 1 was replaced with a vinyl chloride copolymer (hereinafter referred to as vinyl chloride copolymer) containing vinyl chloride, vinyl alcohol/v-supported amine-modified vinyl compound as an essential component. It is abbreviated as Polymer 2.

The composition etc. are shown in Table 1. ) was changed into a paint, and a magnetic tape was prepared in the same manner as in Example 1.

[Comparative Example 4] In Example 1, vinyl chloride copolymer 1 was replaced with vinyl chloride-vinyl acetate-vinyl alcohol copolymer (hereinafter abbreviated as vinyl chloride copolymer 3).The composition etc. are shown in Table 1. .) and turned it into a paint, and produced a magnetic tape in the same manner as in Example 1.

Table 3 shows the measurement results of the magnetic properties (2) surface smoothness and the glass transition temperature of the magnetic layer for the magnetic tapes of Examples and Comparative Examples prepared as described above.
Table 4 shows the measurement results for N) and durability, and Table 5 shows the measurement results for the amount of dechlorinated ions after being left in a high-temperature, high-humidity environment.

Table 3 Table 4 Table 6 However, in Table 3, the magnetic properties are measured using a vibrating sample magnetometer (
The surface gloss was measured using a crossmeter (manufactured by Nippon Gunshoku Kogyo Co., Ltd.), and the 60° reflectance after surface smoothing treatment was compared with a standard glass plate. This is the value. The glass transition temperature of the magnetic layer was determined using a dynamic viscoelasticity automatic measuring device (manufactured by Toyo Baldwin Co., Ltd.) at a temperature that gives the peak of the loss modulus of the magnetic tape at a measurement frequency of 110. Also, in Table 4, S/N
Comparative Example 4
This is the value obtained by calculating the difference between Furthermore, the durability was confirmed by using a VTR (under the desk! NV-8200 manufactured by Sangyo Co., Ltd.)
This is the result of an O-pass running test, and the number of N is 1o. Furthermore, in Table 5, the amount of dechlorinated ions is determined by leaving the magnetic tape in an environment of 601:, 90% RH for 150 hours, peeling off the magnetic layer from the base film, and then extracting free chlorine ions with distilled water. It was determined by quantifying it using mercury thiocyanate absorption spectrophotometry.

As shown above, magnetic recording media (Example 1 and Example 2) using binder resins that meet the requirements of the present invention are as follows:
The surface properties and magnetic properties (especially squareness ratio) of the magnetic coating film are improved,
As a result, electromagnetic conversion characteristics such as S/N are also improved. On the other hand, in the present invention, deterioration in durability, which tends to occur when a hydrophilic group is introduced into the binder resin, is not observed. Furthermore, the amount of dechlorinated ions is also significantly reduced compared to the conventional method.

On the other hand, when the ratio of the rubber binder is low (Comparative Example 1) or the glass transition temperature of the rubber binder is high (
For reasons such as Comparative Example 2), a magnetic recording medium in which the glass transition temperature of the magnetic layer is higher than the requirements of the present invention has poor surface properties and S /N deteriorates. Furthermore, the magnetic recording medium (Comparative Example 3) using a vinyl chloride copolymer that does not contain an epoxy group-containing vinyl compound has a large amount of dechlorinated ions.

Furthermore, in the magnetic recording medium (Comparative Example 4) using a conventionally known vinyl chloride copolymer, a decrease in magnetic properties was observed due to poor dispersibility of the magnetic powder.

Effects of the Invention According to the present invention, (1) vinyl chloride, vinyl alcohol, an amine-modified vinyl compound, and an epoxy group-containing vinyl compound are essential constituents as a sizing agent resin for a coated magnetic recording medium. By using a vinyl chloride copolymer (11), a rubber binder (11), and (110 polyisocyanate), and by setting the glass transition temperature of the magnetic layer to 8o C or lower, the dispersibility and magnetic properties of the magnetic powder can be improved. It is possible to obtain a magnetic recording medium with improved coating film surface properties and electromagnetic conversion characteristics, and with good reliability under high temperature and high humidity environments.

Claims (3)

[Claims] (1) (i) A vinyl chloride copolymer containing vinyl chloride, vinyl alcohol, an amine-modified vinyl compound, and an epoxy group-containing vinyl compound as essential components; (ii) a rubber binder; and (iii) a polyisocyanate. is used as a binder resin component, and magnetic powder is dispersed in these and applied to a support to form a magnetic layer, and the glass transition temperature of the magnetic layer is adjusted to 80°C.
A magnetic recording medium characterized by the following. (2) Vinyl chloride copolymer is vinyl chloride 60-95
% by weight, 2 to 16% by weight of vinyl alcohol, 0.05 to 6% by weight of an amine-modified vinyl compound, 1 to 6% by weight of an epoxy group-containing vinyl compound, and some amount of other vinyl compounds as necessary, and has an average degree of polymerization of 200. 2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a magnetic flux density of .about.800. (3) The rubber binder is a polyurethane resin, a polyester resin, or a combination thereof, and the ratio of the binder resin component is 80 to 20% by weight of vinyl chloride copolymer,
2. The magnetic recording medium according to claim 1, wherein the rubber binder is 20 to 80% by weight, and the polyisocyanate is 5 to 30% by weight.