JPH03194720A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enable production of such a magnetic coating material having excellent dispersibility for superfine Co-contg. gamma-Fe2O3 particles and metal powder, excellent thermal stability and low viscosity by forming a magnetic layer composed of ferromagnetic fine powder dispersed in copolymers of specified structural units on a nonmagnetic supporting body. CONSTITUTION:The copolymer consists of vinyl chloride unit, ester unit expressed by formula I, hydroxyl group-contg. unit, epoxy group-contg. unit, carboxylic group-contg. unit expressed by formula II, and phosphate unit expressed by formula III. The magnetic layer where ferromagnetic fine powder is dispersed in the copolymer is formed. In formula I, R<1> represents hydrogen atom or methyl group, R<2> represents univalent hydrocarbon group. In formula II, (n) is integer from 1 to 8. In formula III, R<1> is hydrogen atom or methyl group, R<3> is bivalent group expressed by CpH2p(OCpH2p)q (p and q are integers, p=2 to 4, q= 0 to 10), R<4> is hydrogen atom or alkyl group of 1-6C. By this method, the dispersibility to the superfine Co-contg. gamma-Fe2O3 particles and metal power is improved and viscosity of the coating material can be reduced since it has good solubility for various kinds of org. solvents.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to magnetic recording media, and in particular to a special copolymer characterized by vinyl chloride that exhibits excellent performance as a binder for ferromagnetic fine powder. This invention relates to an improved magnetic recording medium using.

[Prior Art] Magnetic recording media such as magnetic tapes are generally held together by providing a coating film made of magnetic powder and a binder (synthetic resin) on the surface of a support such as a polyester film.

In recent years, as the performance of video tapes and audio tapes has improved, high signal density and high playback output in short wavelength recording are required. To cope with these trends, magnetic powders have become finer particles than ever before, and because they have a very large magnetic moment, the particles tend to agglomerate with each other (as a result, they can be dispersed uniformly into the binder resin). Diversification is becoming more difficult than ever.

Furthermore, when dispersing ferromagnetic fine powder, a method is used in which a high shear force is applied, but this process increases the viscosity and temperature of the paint, and increases the temperature when using a magnetic recording tape, causing the vinyl chloride binder to This method has the drawbacks of inducing thermal decomposition of the resin, deteriorating the magnetic powder due to hydrogen chloride gas, reducing the durability of the magnetic recording medium, and corroding the magnetic head.

As a means of preventing this thermal decomposition, the method of adding stabilizers for vinyl chloride resin has long been well known, but since these are low molecular weight compounds, if they are present in large quantities in the magnetic recording medium, they will bleed from the magnetic recording medium. Since this phenomenon causes a decrease in durability and staining of the magnetic head, the amount of its use is naturally limited, and therefore its effectiveness is also limited.

In order to solve this technical problem, extensive studies are being conducted from the viewpoint of improving the affinity for magnetic powder as a binder resin.
As shown in the publication, a vinyl chloride-carboxylic acid vinyl ester-unsaturated carboxylic acid and unsaturated carboxylic acid anhydride copolymer has been proposed, but the Co-containing ultrafine particles, which are important as magnetic powders, have been proposed. -The dispersibility of various magnetic powders, including Fears, is poor (furthermore, the reactivity with urethane resin is poor, so when a magnetic paint using this is applied to a substrate, the paint film peels off, making it difficult to use as a magnetic recording medium). It is not practical. Also, this product has insufficient thermal stability.

Also, JP-A-61-117729, JP-A-61-2
No. 43934 proposes a vinyl chloride copolymer in which hydroxyl groups, carboxyl groups, etc. are introduced into the molecular structure, but none of them have sufficient dispersibility in ultrafine CO-containing -FexOs and metal powders. Furthermore, since the solution viscosity of this product is high, a large amount of organic solvent is required when preparing the magnetic coating, and furthermore, because of its poor thermal stability, it has the disadvantage that the released hydrogen chloride corrodes the magnetic head.

In addition, JP-A-61-199220, JP-A-6
Although the copolymer disclosed in Japanese Patent No. 2-132226 has improved dispersibility for magnetic powder, it is insufficient in terms of thermal stability.

[Problems to be Solved by the Invention] Therefore, the present invention provides 20 g of Co-containing ultrafine particles,
This was done in order to develop a binder resin that has excellent dispersibility in metal powders and thermal stability, and which is also capable of manufacturing a magnetic paint with low viscosity, and to provide a high-performance magnetic recording medium.

[Means for Solving the Problems 1] The present invention relates to a magnetic recording medium that solves the problems described above, and comprises the following constituent units (a) vinyl chloride units, (b) vinyl chloride units, ) A monomer unit (hereinafter referred to as an ester unit) represented by the formula (wherein R' is a hydrogen atom or a methyl group, and R2 is a monovalent hydrocarbon group), (c) the side chain contains a hydroxyl group -vinyl monomer units that are organic groups (hereinafter simply referred to as hydroxyl group-containing units), (d) vinyl monomer units that have epoxy groups (hereinafter simply referred to as epoxy group-containing units), ) Monomer unit ′ (hereinafter simply referred to as carboxyl group-containing unit) represented by the formula % formula % (where n = an integer of 1 to 8)
and (f) Formula [wherein R' is a hydrogen atom or a methyl group, R3 is the formula CpH*p(OCJ*p)q (where p=2 to 4.
q=an integer from Q to lO), R
4 represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms]
This invention relates to a magnetic recording medium in which a magnetic layer is formed by dispersing ferromagnetic fine powder in a copolymer composed of monomer units represented by (hereinafter simply referred to as phosphate ester units).

The present inventors have researched a binder resin for magnetic recording media consisting of a copolymer of vinyl chloride, a monomer containing an ester unit, and a vinyl monomer containing a hydroxyl group. When a specific amount of half ester of a specific dibasic acid is used as a component for copolymerization, and a phosphate ester-containing monomer is combined with this, ultrafine Go-containing -F particles are formed.
ears, and metal powder, and these copolymer resins have extremely good solubility in various organic solvents used as coating media, making it possible to lower the viscosity of magnetic paints, making them easier to coat. I found out that it can greatly improve your sexual performance.

The present inventors further discovered that by using an epoxy group-containing monomer as a copolymerization component, the thermal stability of the stabilizer for vinyl chloride resin could be improved over a long period of time without causing the bleeding phenomenon, and the present invention was completed. This is what I did.

The binder resin used in the present invention also has the advantage that it has sufficient compatibility with polyurethane resins used in combination as appropriate, and that it can be easily crosslinked by reaction with urethane polymers containing isocyanate groups. Therefore, by using this as a binder, a high-performance magnetic recording medium with improved long-term durability can be obtained.

The present invention will be explained in detail below.

The copolymer as the binder resin used in the present invention is characterized by being composed of each of the units (a) to (f) described above, and in particular, the (a) unit 60～
95% by weight, (b) units 0-15% by weight.

(c) unit 5-15% by weight, (:) unit 0.1-8% by weight, (ne) unit (11-10% by weight, (f) unit 0.0
The proportion is 1 to 3% by weight, and the average degree of polymerization is 200 to 50.
It is desirable that the value has 0.

If the amount of the vinyl chloride unit (a) is too small, the physical strength will decrease, while if it is too large, the solubility will decrease, which is disadvantageous in use. A particularly preferable range is 65
~88% by weight.

The (b) ester unit is used to improve the solubility, flexibility, etc. of the copolymer.
The monomer corresponding to the unit is [I]
[nl is mentioned. R' in the formula is a hydrogen atom or a methyl group,
R8 is a monovalent hydrocarbon group.

Examples of preferable vinyl esters corresponding to the above formula [R1 include vinyl acetate, vinyl propionate, vinyl versatate (manufactured by Shell Chemical Co.), vinyl stearate, and vinyl benzoate. Further, examples of desirable (meth)acrylic esters corresponding to the formula [R1 include ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and propyl methacrylate.

As the ester unit (b), any one of formulas [I] to [R1] described above may be used alone or in combination of two or more thereof, but the polymerization ratio in the copolymer may be large. If it is too high, the resin becomes soft and the durability of the magnetic recording medium (magnetic tape, etc.) decreases, so as mentioned above, the range is from 0 to 15% by weight. In particular, 3 to 7% by weight
It is desirable that it be within the range of .

Examples of the monomer corresponding to the hydroxyl group-containing unit (c) include the following.

0 00HII
II 1CH,=CH-
C-OCH, C1, OH, CH, =CH-QC-CHC
H.

CH,=CH-0(C1,),OH If the weight ratio of the hydroxyl group-containing unit introduced by these monomers in the copolymer is too small, the dispersibility of the ferromagnetic powder will not only decrease ( On the other hand, if the isocyanate prepolymer is blended with too much isocyanate, the compatibility with the polyurethane resin used will decrease, and if the isocyanate prepolymer is added, the viscosity will increase significantly, causing difficulties in pot life, and the physical strength will decrease, making magnetic recording difficult. The durability of the media (magnetic tape, etc.) decreases.
As mentioned above, it is desirable that the content be in the range of 5 to 15% by weight, particularly in the range of 7 to 10% by weight.

Examples of monomers corresponding to the epoxy group-containing unit (:) include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methallyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, methylglycidyl itaconate, and glycidyl ethyl. Examples include glycidyl esters of unsaturated acids such as malate. The weight proportion of these in the copolymer is preferably in the range of 0.1 to 8% by weight, particularly in the range of 1 to 5% by weight; if this amount is too small, dehydrochlorination during heating will be significant, or If the amount is too large, the resin will not dissolve in various organic solvents used as coating media.

Monomers corresponding to the carboxyl group-containing unit ((e) unit) are half esters of polymerizable unsaturated dibasic acids, such as maleic acid monoalkyl esters and fumaric acid monoalkyl esters (both have methyl as an alkyl group). ,
ethyl, propyl, butyl, hexyl, octyl, etc.)
can be mentioned.

The weight proportion of these in the copolymer is desirably in the range of 0.1 to 10% by weight, particularly in the range of 0.5 to 5% by weight; if this amount is too small, the dispersibility will decrease; and the magnetic powder will aggregate.

The monomer corresponding to the phosphate ester unit (f) unit is mono[(meth)acryloyloxyethyl]
Acid phosphate, [Here, (meth)acryloyloxyethyl represents acryloyloxyethyl or methacryloyloxyethyl, and the same applies hereinafter.

1 Mono[(meth)acryloyloxypropyl]acid phosphate, mono[(meth)acryloyloxybutyl]acid phosphate, mono[(meth)acryloyloxyethoxyethyl]acid phosphate,
Mono[(meth)acryloyloxypolyoxyethylene glycol] acid phosphate, mono[(meth)acryloyloxybrobooxybrobyl] acid phosphate, mono[(meth)acryloyloxypolyoxypropylene glycol] acid phosphate, mono[( (meth)acryloyloxypolyoxybutylene glycol] acid phosphate, (meth)acryloyloxyethyl methyl acid phosphate, (meth)acryloyloxyethyl butyl acid phosphate,
Examples include (meth)acryloyloxypropylethyl acid phosphate, (meth)acryloyloxyethoxyethylmethyl acid phosphate, (meth)acryloyloxypolyoxyethylene glycol butyl acid phosphate, (meth)acryloyloxypolyoxypropylene glycol ethyl acid phosphate, etc. Ru.

The weight proportion of these in the copolymer is preferably in the range of 0.01 to 3% by weight, particularly in the range of 0.1 to 2% by weight. If this amount is too small, magnetic powder (especially BET)
The dispersibility of the specific surface area (more than 35 ■”/g) is insufficient,
If the amount is too large, the solubility in the solvent will be poor, which is not preferable.

In a copolymer composed of such unit components, if the average degree of polymerization is too low, the physical strength of the magnetic layer will decrease, and the durability of the magnetic tape will also decrease; If it is too high, the solution viscosity at a predetermined concentration will be high (and the workability will be extremely poor), so it is desirable that the average degree of polymerization is in the range of 200 to 500.

This copolymer can be produced using general suspension polymerization method, emulsion polymerization method,
It can be produced by a solution polymerization method, a bulk polymerization method, or the like.

When using the above copolymer as a binder resin, other resins may be used in equal or less amounts if necessary. Examples of resins that can be used in combination include polyurethane resins, nitrocellulose, epoxy resins, and polyamides. resin, phenolic resin, acrylic ester, methacrylic ester, styrene, acrylonitrile, butadiene, ethylene, propylene, vinylidene chloride, acrylamide,
Examples include various polymers such as vinyl ethers and copolymers. Among these, polyurethane resins and nitrocellulose are particularly preferred.

In addition to this, it is desirable to use a polyisocyanate-based curing agent, such as bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, Coronate L (trade name manufactured by Nippon Polyurethane Industries), and Disco Examples include trifunctional incyanates such as Module L (trade name, manufactured by Bayer AG) and urethane prepolymers containing isocyanate groups at both ends.

As the ferromagnetic powder used in the present invention, γ-FezO
In addition, Fe5048 and cobalt ions adsorbed or doped therein, CrO2, etc., as well as Fe, Go, Fe-Co, or N in some cases.
Various other conventionally known magnetic powders such as acicular fine particle materials containing i and the like are exemplified. The mixing ratio of the ferromagnetic powder and the binder resin is preferably 8 to 30 parts by weight of the binder resin per 100 parts by weight of the ferromagnetic powder.

In order to uniformly disperse the ferromagnetic powder and the binder resin, it is necessary to add commonly used lubricants, abrasives, antistatic agents, dispersion aids, rust preventives, etc. Various other organic solvents such as methyl ethyl ketone, methyl isobutyl ketone, and toluene can be used in the same manner as in the past (although there are no particular restrictions on these points).

Supports include synthetic resins such as polyester, polyolefin, cellulose acetate, and polycarbonate;
Other magnetic metals and ceramics are used, and they are used in the form of films, tapes, sheets, plates, etc.

The coating means for forming the magnetic layer on the support may be any conventionally known method, and by appropriately applying smoothing treatment such as calendaring treatment, the high-performance magnetic recording medium that is the object of the present invention can be obtained. can get.

[Example] Next, the present invention will be specifically explained based on examples.

In addition, all parts in the examples represent parts by weight, and all percentages represent weight %.

Example 1 After replacing nitrogen in an autoclave equipped with a stirring device, 210 parts of methanol, 210 parts of ion-exchanged water, and 11 parts of vinyl chloride were placed in an autoclave equipped with a stirring device.
9 parts vinyl acetate, 8 parts 2-hydroxypropyl acrylate, 3 parts allyl glycidyl ether, 5 parts mono(2-ethylhexyl) maleate, mono(
1 part of methacryloyloxyethyl) acid phosphate; 5 parts of di(2-ethylhexyl) peroxydicarbonate as a polymerization initiator; and 1 part of methyl cellulose.
After starting the reaction by raising the temperature to 55°C with stirring, the following mixture (278 parts of vinyl chloride, 17 parts of vinyl acetate, 35 parts of 2-hydroxypropyl acrylate) was added.
parts, allyl glycidyl ether 7 parts, maleic acid mono(
Continuously pressurized 449 parts of 2-ethylhexyl) ester, 3 parts of mono(methacryloyloxyethyl) acid phosphate, and 100 parts of methanol over a period of 7 hours.
A copolymerization reaction was carried out.

The internal pressure of the autoclave was 2 kg/cm after 12 hours.
The residual pressure is released, cooled, filtered, washed, deliquified,
After drying, 450 parts of copolymer powder (polymer ①) was obtained.

Example 2 Copolymer powders (polymers ① to ①) were obtained in the same manner as in Example 1, except that the types and amounts of monomers were varied as shown in Table 1.

Table 1 In Table 1, a is vinyl acetate b is vinyl laurate C is 2-hydroxypropyl acrylate d is 2-hydroxybutyl methacrylate e is allyl glycidyl ether f is glycidyl methacrylate g is mono(2-ethylhexyl maleate) Ester h is maleic acid monobutyl ester l is mono(methacryloyloxyethyl) acid phosphate m is mono(acryloyloxypolyoxypropylene glycol) acid phosphate, and the numerical values are Example 3 An autoclave equipped with a stirring device was purged with nitrogen. After that, 520 parts of ion exchange water, 197 parts of vinyl chloride, 26 parts of vinyl acetate
10 parts of allyl glycidyl ether, 5 parts of di(2-ethylhexyl) peroxydicarbonate as a polymerization initiator, and 1 part of methyl cellulose, and after starting the reaction by raising the temperature to 65°C with stirring, the following mixture was added. [198 parts of vinyl chloride, 50 parts of 2-hydroxypropyl acrylate, mono(2-ethylhexyl) maleate
15 parts of ester, mono(methacryloyloxyethyl)
Four parts and 1,267 parts of acid phosphate were continuously compressed over a period of 5 hours to carry out a copolymerization reaction.

After 11 hours, the internal pressure of the autoclave became 2 kg/cm'', so the residual pressure was released, the autoclave was cooled, filtered, washed, dehydrated, and dried to obtain 420 parts of copolymer powder (Polymer ■).

Comparative Example 1 After replacing nitrogen in an autoclave equipped with a stirring device, 210 parts of methanol, 210 parts of ion-exchanged water, and 12 parts of vinyl chloride were placed in an autoclave equipped with a stirring device.
4 parts, vinyl acetate 8 parts, 2-hydroxypropyl acrylate 15 parts, maleic acid 5 parts, mono(methacryloyloxyethyl) acid phosphate 2 parts, as a polymerization initiator, di(2-ethylhexyl) peroxydicarbonate 5 parts , and 1 part of methylcellulose were charged and heated to 55°C with stirring to start the reaction, and then the following mixture [vinyl chloride 283 parts, vinyl acetate 17 parts, 2
-35 parts of hydroxypropyl acrylate, 9 parts of maleic acid, 3 parts of mono(methacryloyloxyethyl) acid phosphate, 100 parts of methanol] 447 parts
It took a long time to continuously pressurize and cause a copolymerization reaction.

After 12 hours, the autoclave internal pressure was 2 kg/Cm2.
The residual pressure was released, and the mixture was cooled, filtered, washed, deliquified, and dried to obtain 440 parts of copolymer powder (Polymer ■).

Comparative Example 2 Copolymer powders (polymers ① to @l) were obtained in the same manner as in Comparative Example 1, except that the types and amounts of monomers were varied as shown in Table 2.

Table 2 In Table 2, i is maleic acid, j is acrylic acid for maleic anhydride (others are the same as above), and the numerical values are for the copolymer powder obtained above (polymer ■ ~ [phase ]) The analysis results of the polymer composition and average degree of polymerization, and the results of measuring various physical properties (solution viscosity, thermal stability, dispersibility, and magnetic performance) by preparing samples using the following method using each polymer are presented in this section. It was as shown in Table 3.

(1) Solution viscosity 40 parts of the copolymer resin was dissolved in 160 parts of a solvent (methyl ethyl ketone/methyl isobutyl ketone/toluene = 1/1/1), and the viscosity of the solution was adjusted to 25°C using a B-type viscometer. It was measured using

(2) Precisely weigh 1 g of thermostable copolymer resin into a 15 cc test tube, plug the opening with absorbent cotton sandwiched with Congo red test paper, and place in an oil bath at 150°C to generate salt. The time taken for Congo Red test paper to change color was measured using Shun.

(3) Dissolve 10 parts of the dispersible copolymer resin in a solvent consisting of 30 parts of methyl ethyl ketone, 30 parts of methyl isobutyl ketone, and 30 parts of toluene at 50°C for 1 hour, and then mix with an Eiger mill while polyurethane resin N-2304 (Japanese) 5 parts (manufactured by Polyurethane Co., Ltd.) and 40 parts of the following magnetic powders A to C were added thereto and kneaded for an additional hour. Furthermore, 2 parts of Coronate L (manufactured by Nippon Polyurethane Co., Ltd.) were added and kneaded for 5 minutes to obtain a magnetic paint.

This was placed on a 21 micron thick polyester film.
It was coated to a thickness of μ, subjected to magnetic field orientation treatment, and dried.

Magnetic powder A: 45. Om”/g of CO-containing T-Fe
ars magnetic powder B: 50. Om”/g CO content Y
-Fe2rs magnetic powder C: 67.5 m”/g metal powder Gloss (%) of the magnetic tape made in this way
was measured.

The gloss is 60 by Crossmeter (manufactured by Murakami Color Giken).
The reflectance was compared with a standard glass plate. This value represents the dispersibility of the magnetic powder in the magnetic coating film, and it is determined that the larger the value, the better the dispersibility.

(4) Magnetic performance Using the magnetic tape made above, a vibrating sample magnetometer (
(manufactured by Toei Kogyo) to measure the squareness ratio.

[Effects of the Invention] The binder resin forming the magnetic recording medium of the present invention has excellent dispersibility in ultrafine particles of Co-containing -Fears and metal powder, and has extremely good solubility in various organic solvents used as coating media. Therefore, it has a low viscosity and also exhibits excellent thermal stability, so a high-performance magnetic recording medium with good durability and excellent stability over time can be obtained, and has great practical value.

Claims (1)

[Claims] 1. On a non-magnetic support, there are the following structural units (a) vinyl chloride unit, (b) formula ▲ mathematical formula, chemical formula, table, etc. ▼ (However, R^1 in the formula Hydrogen atom or methyl group, R^
2 indicates a monovalent hydrocarbon group), (c) a vinyl monomer unit whose side chain is a hydroxyl group-containing monovalent organic group, (d) a vinyl monomer having an epoxy group. body unit, (e)
Formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ Monomer units represented by (where n = an integer from 1 to 8) and (f) formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ [However, in the formula R^1 is a hydrogen atom or a methyl group, R^
3 is the formula C_pH_2_q(OC_pH_2_p)_q(
(where p=2 to 4 and q=an integer of 0 to 10), R^4 is a hydrogen atom or a carbon number of 1 to 6
1. A magnetic recording medium comprising a magnetic layer in which fine ferromagnetic powder is dispersed in a copolymer consisting of a monomer unit represented by the following alkyl group. 2. The copolymer contains (a) 60 to 95% by weight of units, (
b) Units 0 to 15% by weight, (c) Units 5 to 15% by weight,
(d) Units 0.1-8% by weight, (e) Units 0.1-10
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium comprises 0.01 to 3 weight % of (f) units and has an average degree of polymerization of 200 to 500.