JPH01122021A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility of magnetic powder and to improve the durability of the title medium by incorporating an acryl/butadiene copolymer contg. >=1 kinds among an epoxy group, hydroxyl group, carboxyl group, and amino group and having 200,000-1,000,000 average mol.wt. into the binder of the magnetic powder. CONSTITUTION:The acryl/butadiene copolymer is composed of 0.1-10mol.% functional group of the monomer having the epoxy group, hydroxyl group, carboxyl group, and amino group and 10-50% bonding acrylonitrile to maintain the good dispersibility of the magnetic powder and resilience of the magnetic layer. The average mol.wt. of the copolymer is selected at 200,000-1,000,000 to maintain good durability of the magnetic layer, compatibility with other polymers and solubility in solvents. A nonmagnetic base consisting of polystyrene, etc., is used for the magnetic recording medium. A magnetic layer material contg. the magnetic powder and the binder formed of the above-mentioned constitution is coated on this base and is dried by heating to form the magnetic layer, by which the magnetic recording medium is completed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium having a magnetic layer comprising magnetic powder and a binder.

This type of media is constructed as a so-called coated magnetic recording medium, in which a magnetic layer is formed by coating a non-magnetic support with a magnetic paint containing magnetic powder and a binder as main components. It is used in

A particular object of the present invention is to improve the dispersibility of magnetic powder, impart flexibility to the magnetic layer, and improve durability.

[Conventional technology]

In recent years, there has been a demand for high-density recording and high reproduction output in various magnetic recording media such as video and audio, and as a measure to achieve this, there is a strong tendency to increase the packing density of magnetic powder in the magnetic layer.

In order to improve this packing density, it is necessary to improve the dispersibility of the magnetic powder, and the selection of a resin as a binder has become an important issue.

Conventionally, copolymers mainly composed of vinyl chloride have been used as binders for magnetic recording media, but vinyl chloride copolymers made of vinyl chloride, vinyl acetate, vinyl alcohol, etc. have poor dispersibility for magnetic powder. However, it has reached its limits and is no longer able to meet the demands for high-density filling.

The present inventors have developed a co-condensate of synthetic rubber and phenolic resin (
JP-A-59-55619) has provided a magnetic recording medium in which the dispersibility of magnetic powder is improved, flexibility is imparted to the magnetic layer, and abrasion resistance is improved.

However, the molecular weight of the synthetic rubber used above is one of the most important factors in maintaining compatibility with the phenolic resin, and the number average molecular weight of synthetic rubber is up to about 200,000.

However, at this stage, sufficient consideration had not necessarily been given to the durability of magnetic recording media.

[Problem that the invention seeks to solve]

As described above, there are many points that need to be improved with conventionally used copolymers mainly composed of vinyl chloride, such as the dispersibility of magnetic powder, and with synthetic rubber and phenolic resin, the dispersibility of magnetic powder and the flexibility of the magnetic layer. could be improved, but there was a problem with durability.

[Failure to solve the problem]

As a result of intensive research to solve the drawbacks of the conventional methods as described above, the present inventors have added epoxy groups as functional groups to an acrylic-butadiene copolymer that has good flexibility even without containing a phenolic resin. We have discovered that by containing one or more functional groups selected from hydroxyl groups, carboxyl groups, and amino groups, the dispersibility of magnetic powder can be improved due to its polarity, and the durability can be improved by regulating the molecular weight. The present invention has now been completed.

A magnetic recording medium comprising a magnetic powder and a binder, characterized in that the mixture contains as a binder an acrylobutadiene/based copolymer having a certain functional group and a number average molecular weight. In the present invention, examples of the acrylic-butadiene copolymer used as a binder for the magnetic layer include butadiene/-acrylonitrile rubber, which is a copolymer of butadiene and acrylonitrile. Furthermore, a copolymerizable monomer may be included as a third component.

As the acrylic-butadiene copolymer, the following can be suitably used.

An acrylic-butadiene copolymer in which the monomer having an epoxy group, a hydroxyl group, a carboxyl group, or an amino group has a functional group content of 0.1 to 10 mole and a bound acrylonitrile content of 10 to 50 mole.

Here, if the amount of functional groups of the monomer having an epoxy group, hydroxyl group, carboxyl group, or amino group is less than 0.1 molty, the dispersibility of the magnetic powder will be poor, and if it exceeds 10 molty, the magnetic layer will become soft. Sexuality decreases. If the amount of bound acrylonitrile is less than 10%, the compatibility with other polymers will be poor, and if it exceeds 1% of 5C, the flexibility of the magnetic layer will decrease.

If the average molecular weight of the acrylic-butadiene copolymer according to the present invention is less than 200,000, the durability of the magnetic layer will be poor; If the ODD is exceeded, the compatibility with other polymers will deteriorate and the solubility in solvents will also be extremely reduced.

In addition, as the magnetic powder in the magnetic coating film, γ-Fe2O3
, Fe5o4, or those doped with Co, those coated on the surface as a Co compound, ferromagnetic chromium dioxide (Cr02), or Fe, Fe-
Co-.

Synthetic magnetic powder such as Fe-Co-Ni can be used alone or in combination.

In addition, examples of binders that can be used with the acrylonitrile-butadiene copolymer in the present invention include conventionally known thermoplastic resins, thermosetting resins, and reactive resins.

Examples of the thermoplastic resin include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, acrylic acid ester-acrylonitrile copolymer, vinylisochloride/-acrylonitrile copolymer, polyamide resin,
One type of polyvinyl butyral resin, a cellulose derivative, a polyester resin, or a mixture thereof may be used.

Examples of thermosetting resins or reactive resins include thermosetting polyurethane resins, phenol resins, urea resins, melamine resins, silicone resins, acrylic reaction resins, and mixtures of high-molecular polyester resins and incyanate prepolymers. Alternatively, a mixture thereof can be used.

Further, in the magnetic layer, that is, in the magnetic coating film, various suppressive additives such as a dispersant, a lubricant, an abrasive, an antistatic agent, etc. may be used as necessary.

Also, as a dispersant, Capri/#! , lauric acid, myristic acid, stearic acid, oleic acid, linoleic acid, etc., metal soap lecithin made of an alkali metal or alkaline earth aliphatic acid having 12 to 18 carbon atoms, etc. can be used.

Further, the amount of these dispersants added is in the range of 1 to 20 parts by weight per 100 parts by weight of the binder.

As the lubricant, solid lubricants such as molypide disulfide/tungsten disulfide, various silicone oils, various fatty acid esters made of fatty acids and alcohols, etc. can be used, but the amount added is 100% by weight of the binder. 1.0 to 20 parts by weight.

As the abrasive, those with relatively high hardness such as fused alumina, silicon carbide, chromium oxide, and cola/dam can be used. The average particle size of these materials is preferably selected to be 2 μm or less. Further, antistatic agents include natural surfactants such as carbon black and saponin, anionic surfactants such as alkylene oxide and glycerin, and higher alkyl amino,
Quaternary ammonium salts, cationic surfactants such as pyridine and other heterocycles, anionic surfactants containing acidic groups such as carbo/acids, sulfonic acids, phosphoric acid, sulfate ester groups, phosphate ester groups, amino acids Ampholytic surfactants such as , aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, etc. are used, and these surfactants can be added alone or in combination.In addition, these surfactants are used as antistatic agents. However, it is sometimes used, for example, to improve dispersion and lubricity.

Further, as the non-magnetic base material of the magnetic recording medium according to the present invention, polyethylene terephthalate, polyethylene,
Polyesters such as 2.6-naphthalate, polyolefins such as polypropylene, cellulose conductors such as cellulose triacetate and cellulose diacetate, polycarbonate, polyamide, polyimide, etc. can be used.

It goes without saying that the magnetic recording medium according to the present invention can also be modified in various ways, such as by coating the magnetic layer with a top coat to impart lubricity or by providing an antistatic back layer. Probably.

[Examples] Specific examples of the present invention will be described below, but it goes without saying that the present invention is not limited to these examples.

The formulation is shown in Table-1.

Table-1 Material name Example Comparative example r-Fe
203 (parts by weight) ioo
1 o.

Polyurethane resin (parts by weight) 13
15 PVC/vinyl acetate copolymer (parts by weight)
12. 15 Acrylic-butadiene copolymer (parts by weight) 5 - Thermosetting resin (parts by weight)
0.5 0.5 Dispersant (parts by weight)
11 Methyl ethyl ketone CM parts) 100
100 Toluene (parts by weight) 100100 Table-2! EXAMPLE After mixing and dispersing each composition in the above-mentioned coating-1 except for the polyurethane resin in a ball mill for 24 hours, the polyurethane resin was added and passed through a sand mill to form a paint. This paint was applied to a polyethylene terephthalate film as a support to a dry thickness of 5.0 μmK, and after drying by heating, the magnetic surface was subjected to supercalender treatment. This was slit into 3.18 mm width and made into a cassette tape.

Below are the test results of the Pioneer cassette deck key: △ Yes ○ Large magnetic flux density Bm Durability: Observation of the magnetic layer after running test for 1000 times at 355Rz and 10KHz [Effects of the invention] As is clear from the above explanation, By incorporating one or more functional groups selected from epoxy groups, hydroxyl groups, carboxyl groups, and amino groups into the acrylic-butadiene copolymer, the dispersibility of the magnetic powder becomes good. .

Moreover, by controlling the molecular weight, durability is improved, and therefore electromagnetic conversion characteristics are extremely excellent.

Claims (2)

[Claims] (1) In a magnetic recording medium having a magnetic layer comprising magnetic powder and a binder, the binder contains at least one functional group selected from epoxy groups, hydroxyl groups, carboxyl groups, and amino groups. , and the average molecular weight is 2
1. A magnetic recording medium comprising an acrylic-butadiene copolymer having a molecular weight of 00,000 to 1,000,000. (2) Monomers constituting the acrylic-butadiene copolymer include epoxy groups, hydroxyl groups, carboxyl groups,
Or the amount of functional groups of the monomer having an amino group is 0.1 to 1
0 mol% and the amount of bound acrylonitrile is 10 to 50
% of the magnetic recording medium according to claim 1.