JPH01232523A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the magnetic recording medium which is improved in reliability and durability at the time of use over a long period of time by using a binder into which respectively specific two vinyl chloride resins are incorporated as the binder of magnetic powder. CONSTITUTION:The specific vinyl chloride resin A has at least one kind of the strong acid base selected from SO3M, SO4M and PO4M2 (where M is an alkali metal or NH4) and an epoxy group. The specific vinyl chloride resin has at least one kind of the acidic group selected from COOH, SO3H and PO4HM' (where M' is H or org. group). The desired magnetic recording medium is obtd. by making combination use of the resins A and B as the binder of the magnetic powder.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improved magnetic recording medium, and more particularly to a magnetic recording medium with excellent monodispersity and durability.

(Prior Art) Magnetic recording media such as magnetic tapes and magnetic cards are generally manufactured by applying a magnetic paint containing magnetic powder and its binder as a magnetic layer onto a substrate such as a polyester film. In order to increase the near-wind coercive force and maximum saturation magnetization, and improve the signal-to-noise ratio and recording density, finer magnetic powders with large coercive force and a large specific surface area have been used as the above-mentioned magnetic powder. Ta.

However, as a binder for such fine magnetic powder, vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-maleic acid copolymer resin, vinyl chloride-vinyl acetate-maleic acid-vinyl alcohol copolymer resin When magnetic paint is prepared using vinyl chloride copolymer resin such as resin.

There are disadvantages such as thickening of the paint and insufficient dispersibility. In addition, low molecular weight surfactants are used as dispersants to improve dispersibility, but using large amounts of these dispersants can reduce the durability of magnetic recording media and cause head stains, so their use is prohibited. There is a limit to the amount.

On the other hand, in order to improve the durability and reliability of magnetic recording media,
Polyurethane resin, polyester resin.

It is particularly useful to add a cross-linking agent to the magnetic paint to form a cross-linking bond with a flexible material such as acrylonitrile-butadiene rubber and part or all of the binder to form a cross-linking bond (forming the magnetic layer into a film). This is a common method for recording magnetic recording tapes.Therefore, the binder is required to be compatible with these flexible materials and to have appropriate reactivity with the crosslinking agent.Furthermore, In order to improve tape reliability, tapes are now required to have excellent chemical stability and to be less likely to generate decomposition products that can cause deterioration of magnetic powder or corrosion of heads. It's coming.

In order to improve the performance of such magnetic recording media, SO3M
, 804M, PO4M2 (where M is an alkali metal or NH4), it is effective to use as a binder a vinyl chloride resin having at least one kind of strong acid base and an epoxy group; By utilizing the reactivity of epoxy groups, vinyl chloride resins can be used to crosslink coatings with polyamine compounds and polycarboxylic acid compounds.

It has been found that when these crosslinking agents are used, the crosslinking speed is faster and the crosslinking progresses more effectively than when using ordinary epoxy group-containing vinyl chloride copolymer resins that do not have strong acid groups. (JP-A-60-2383 (16° JP-A-60-
238371. However, among these crosslinking agents, low molecular weight ones are used,
If a material that is incompatible with the vinyl chloride resin is used, there are no concerns that the crosslinking agent that remains in the magnetic layer without reacting may reduce the durability of the magnetic recording medium or cause head corrosion. I can't do it.

(Problems to be Solved by the Invention) The purpose of the present invention is to solve the problems that stand in the way of improving the performance of magnetic recording media, and in particular, to solve the problems that stand in the way of improving the performance of magnetic recording media. The goal is to provide recording media.

(Means for Solving the Problems) The object of the present invention is to solve SO3M, SO4M, PO4M
2 (where M is an alkali metal or NH4), a vinyl chloride resin having at least one kind of strong acid base and an epoxy group, and COOH, SO3H, and SO4H.

This can be achieved by using a vinyl chloride resin having at least one acidic group selected from P○4HM' (where M' is H or an organic group) as a binder for the magnetic powder.

SO3M, SO4M and PO4 used in the present invention
Vinyl chloride resin having at least one strong acid base selected from M2 and an epoxy group (hereinafter sometimes referred to as resin A) is composed of (1) a radically polymerizable monomer having the corresponding strong acid base and an epoxy group; (2) A method of copolymerizing a monomer having an epoxy group with vinyl chloride together with other copolymerizable monomers as necessary; A method of copolymerizing with vinyl chloride using a radical generator having a corresponding strong acid and base together with a polymer.

(6) Obtained by a method in which a copolymer of a monomer having an epoxy group, vinyl chloride, and other monomers used as necessary is partially reacted with a corresponding compound having a strong acid base. be able to. It is also possible to combine these methods.

Examples of monomers having epoxy groups used in the production of these resins A include glycidyl ethers of unsaturated alcohols such as allyl glycidyl ether and methallyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, and glycidyl-p- Glycidyl esters of unsaturated acids such as vinyl benzoate, methyl glycidyl itaconate, glycidyl ethyl maleate, glycidyl vinyl sulfonate, glycidyl (meth)allylsulfonate, butadiene monoxide, vinylcyclohexene monoxide, 2-methyl-5,6 - Examples include epoxide olefins such as epoxyhexene.

Among the examples of the monomer having a strong acid base in the method (1) above in the production of resin A in the present invention.

Examples of SO3M include vinylsulfonic acid, methylvinylsulfonic acid, (meth)allylsulfonic acid, styrenesulfonic acid, ethyl (meth)acrylate-2-sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 5 Examples include alkali metal salts and ammonium salts of acids such as -aryloxy-2-hydroxypropanesulfonic acid. An example of 804M is (meth)acrylic acid-
Examples of PO4M2 include alkali metal salts or ammonium salts of acids such as 2-ethyl sulfate and 3-allyloxy-2-hydroxypropane (IILT[R).
There are alkali metal salts or ammonium salts of acids such as propyl (meth)acrylate-3-chloro-2-phosphate, ethyl (meth)acrylate-2-phosphate, and 6-allyloxy-2-hydroxypropane phosphate. .

Among the radical generators having a strong acid base in the method (2), those having SO4M include potassium persulfate, ammonium persulfate, and the like.

Potassium superphosphate has PO4M2.

Examples include sodium superphosphate.

Furthermore, in the method (3) above, among the compounds used to react with the copolymer of a monomer having an epoxy group and vinyl chloride to introduce a strong acid base into the resin,
Examples of SO3M include sulfite, ammonium sulfite, sodium bisulfite, potassium bisulfite, ammonium thiosulfate, sodium taurate, sodium sulfanilate, and sodium sulfamate.
E+04M includes sodium bisulfate, ammonium bisulfate, sodium 2-aminoethyl sulfate, etc.
As O4M2.

Examples include dipotassium hydrogen phosphate and disodium hydrogen phosphate.

In addition, examples of monomers that may be used as necessary other than monomers having an epoxy group, vinyl chloride, and monomers having a strong acid/base include carboxylic acid vinyl esters such as vinyl acetate and vinyl propionate: methyl Vinyl ether, isobutyl vinyl ether, vinyl ether of cetyl vinyl ether: vinylidene such as vinylidene chloride, vinylidene fluoride; diethyl maleate, butyl benzyl maleate, di-2-hydroxyethyl maleate, dimethyl itaconate, methyl (meth)acrylate.

Unsaturated carboxylic acid esters such as ethyl (meth)acrylate, lauryl (meth)acrylate, and 2-hydroxypropyl (meth)acrylate; Olefins such as ethylene and propylene; Unsaturated nitriles such as (meth)acrylonitrile: styrene .

Examples include aromatic vinyls such as α-methylstyrene and p-methylstyrene. These monomers are used not only to improve the solubility of the resin while controlling the compatibility and softening point of the resin A and other resins when mixed together, but also to improve the properties of the coating film and the coating properties. Appropriate selection is made depending on the need for improving the manufacturing process.

Copolymerization of a monomer having an epoxy group and vinyl chloride, or copolymerization of a monomer having an epoxy group, a monomer having a strong acid base, and vinyl chloride.

It can be carried out by ordinary polymerization methods, including cases where other monomers are further copolymerized. In addition, the reaction between a copolymer of a monomer having an epoxy group, vinyl chloride, and other monomers used as necessary, and a compound having a strong acid base may also be affected depending on the properties of the raw materials and the separation of the product. 1 due to process reasons
This can be done by a conventional method.

The amount of strong acid/base bonded to the resin A obtained as described above is 0.1 to 4.
It is necessary that it be 0% by weight. If it is less than 0.1% by weight, the dispersibility of the magnetic powder will be insufficient, and if it exceeds 400% by weight, the hydrophilicity of the resin will become strong, resulting in insufficient solubility in solvents or the moisture resistance of the coating film. Moreover, agglomeration of the magnetic powder occurs, which actually worsens the dispersibility.

Further, resin A needs to have 0.1% by weight or more of epoxy groups. If it is less than 0.1% by weight, the reactivity with the acidic group-containing vinyl chloride resin will be insufficient.

On the other hand, C! used in combination with resin A! OOH, 5O3H, S○
4H.

Vinyl chloride resin having at least one acidic group selected from PO4HM' (hereinafter sometimes referred to as resin B)
(4) A method of copolymerizing vinyl chloride with a radically polymerizable monomer having a corresponding acidic group and, if necessary, other monomers that can be copolymerized; (5) having an acidic group corresponding to til. It can be obtained by a method in which a compound is reacted with a vinyl chloride resin to introduce a corresponding acidic group. Among the examples of monomers having acidic groups in the method (4), 5O3H and 1904H.

Examples of PO4HM' include M, a monomer having a strong acid base used in method (1) of the method for producing resin A above
Examples include monomers in which H is replaced with
4 etc. Examples of COOH include unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid, unsaturated dicarboxylic acids such as fumaric acid, maleic acid, and itaconic acid, and monoesters thereof. As an example of a ternary copolymer resin of vinyl chloride-vinyl acetate-maleic acid, VMCH manufactured by UCC is known, and as an example of copolymerization with a hydroxyl group-containing monomer, JP-A-60-1
There is No. 85226, etc. Various reactions can be used for method (5), but a known example is a reaction using a chloride having a part of the hydroxyl group of a vinyl chloride-vinyl acetate-vinyl alcohol terpolymer and the corresponding acidic group. JP-A-57-4422
7), Vinyl chloride-vinyl acetate-vinyl alcohol ternary copolymer whose hydroxyl group is converted into phosphoric acid ester with phosphoric anhydride etc. (Japanese Patent Application Laid-Open No. 61-172214), epoxy group-containing vinyl chloride copolymer There is a method of reacting a polycarboxylic acid compound with a polycarboxylic acid compound (JP-A-61-53368, JP-A-61-106605).

In addition, as other monomers used as necessary in the production of resin B, the same monomers as those for resin A can be mentioned.

The amount of acidic groups in the vinyl chloride resin having acidic groups prepared by the above fitting is preferably 0.1 to 4% by weight, and less than 0.1% by weight has an effect of improving durability. is insufficient, and if the weight exceeds 40, the magnetic paint tends to thicken.
The decrease in dispersibility increases.

Both resins A and B in the present invention have an average degree of polymerization of 10
0 to 900, preferably 200 to SO0, and the vinyl chloride content is 60 or more by weight. Degree of polymerization is 100
If it is less than υ, the abrasion resistance of the magnetic layer will be insufficient, and if it exceeds 900, the viscosity of the paint will be high and the dispersion of the magnetic powder will likely be insufficient. Also.

If the content of vinyl chloride is less than 60% by weight, disadvantages may occur, such as a decrease in compatibility with the flexible binder or a significant decrease in solvent removal from the coating film.

Of the two vinyl chloride resins used in the present invention, resin A has excellent magnetic powder dispersibility and thermal stability, and resin B promotes the crosslinking reaction by the epoxy groups in resin A, and also has its own acidity. It also causes a reaction between the group and the epoxy group, increasing the durability of the magnetic recording medium. Of course, these two resins are both vinyl chloride resins, and are completely compatible with each other, and because they are polymerized, they are free from phase separation of unreacted substances and plasticization, which occurs when using low-molecular-weight compounds. There is no problem of deterioration of durability over time due to oxidation, oozing, etc. moreover.

Conventionally, when a polyincyanate compound, which has been commonly used as a crosslinking agent for magnetic recording media, is used together, a reaction occurs with the hydroxyl group generated by the reaction between the epoxy group and the acid, so it is necessary to further increase the crosslinking speed and density. can.

Both of the two vinyl chloride resins used in the present invention have the ability to disperse magnetic powder, but in order to obtain higher dispersibility than when each is used alone, one of the two resins must be used. It is effective to use seeds to mix in another resin that remains after dispersion. The mixing ratio of both resins is preferably such that the equivalent ratio of epoxy groups to acidic groups in each resin is in the range of epoxy groups/e group=α1 to 100. Outside this range, the effect of improving durability is small.

In the present invention, in addition to the above-mentioned two vinyl chloride resins, flexible resins such as known polyurethane resins, polyester resins, and acrylonitrile-butadiene copolymer resins are used as binders for the purpose of improving adhesiveness and imparting durability. There is no problem even if it is contained in

Note that these flexible resins may contain epoxy groups, and for the purpose of improving the dispersibility of magnetic powder, 00
0M, SO3M, 804M, PO3M2
, PO4M2 (M is hydrogen, alkali metal, or ammonium).

Magnetic powders that can be used in the present invention include Fe and Co.

Fe alloy system + CO-containing γ-Fe203 system, CO-containing Fe
Any powder such as 3O4 thread, γ-Fe203 type, Fe2O4 type, or barium-ferrite type may be used.

Also, if necessary, conventional materials such as lubricants, dispersants, antistatic agents and abrasives, as well as conventional magnetic coating resins such as phenoxy resins, cellulose resins, amine resins, butyral resins and acrylic resins, can be added. It is also possible to use it within a range that does not impair achievement of the purpose of the invention.

(Effects of the Invention) Thus, according to the present invention, resin A has the following properties. Due to the excellent magnetic powder dispersibility and thermal stability, it is not only possible to manufacture high-performance magnetic recording media with good conductor conversion characteristics in which fine magnetic powder is uniformly dispersed with high productivity, but also to crosslink resin B. By using it as a crosslinking agent or a crosslinking aid, the magnetic recording medium may change over time due to the residual or poor compatibility of the low molecular weight crosslinking agent.

head stains due to the crosslinking agent oozing out onto the media surface;
A magnetic recording medium is provided which can improve long-term reliability deterioration such as deterioration in runnability, has high recording density, high S/R, and is excellent in durability and reliability.

(Example) The present invention will be described in more detail with reference to Examples below. In addition, parts and parts in Examples, Comparative Examples, and Reference Examples are based on weight unless otherwise specified.

Reference Example 1 By emulsion polymerizing allyl glycidyl ether, vinyl chloride and 2-hydroxypropyl methacrylate with potassium persulfate, the epoxy group was 55%, -804
A vinyl chloride-based resin (A-1) was obtained, which had an average polymerization degree of 300, 0.7 tsumu, 0.7% hydroxyl groups, and 84% vinyl chloride.

Reference Example 2 By emulsion polymerization with vinyl chloride, allyl glycidyl ether, sodium styrene sulfonate, and vinyl acetate total potassium persulfate, the epoxy group was 1.5, -
A vinyl chloride copolymer resin (A-2) having an average degree of polymerization of 400 and 1.04% of 8O3Na and 87% of vinyl chloride was obtained.

Reference Example 6 Vinyl chloride, maleic acid, and vinyl acetate were polymerized with lauroyl peroxide in aqueous methanol to obtain C10
OH 2.5%, vinyl chloride 89%, average degree of polymerization 2
SO vinyl chloride resin (B-1) was obtained.

Reference Example 4 By emulsion polymerizing vinyl chloride, acrylamide-2-methylpropanesulfonic acid, and vinyl acetate with potassium persulfate, 5o3H was 1%, vinyl chloride was 90%,
Vinyl chloride copolymer resin with an average degree of polymerization of 300 (B-2
) was obtained.

Example High-speed shear dispersion was carried out for 90 minutes with the composition shown below.Cobalt celadon magnetic iron oxide 100 (specific surface area 44m27%) Vinyl chloride resin (1) 10 Carbon black 5 Alumina 6 Stearic acid 0.5 Silicone oil 1 .0 Methyl ethyl ketone 45 Cyclohexanone 45 Toluene 45 To the obtained mixture, a mixture having the following composition was added and further mixed and dispersed for 60 minutes.

Vinyl chloride resin (2) 2 Polyurethane resin 8 (Nipporan N-2304 manufactured by Nippon Polyurethane Industries Co., Ltd.) Polyiso 7
Anate 2 (Coronate L manufactured by Nippon Polyurethane Industries) Methyl ethyl ketone
35 cyclohexanone
35 Toluene 35 The thus obtained magnetic paint was coated with a blend coater to a thickness of 20 μm.
It was coated on a polyester film to a dry thickness of 5μ, and the gloss of the coated surface was measured after drying by magnetic field orientation.
Furthermore, the surface was formed using a super calender to form a 40'
After crosslinking for 48 hours in an atmosphere with a relative humidity of 0.0 and SO 2.0, the sample was cut into a 12.65 mm width to prepare a magnetic tape test piece, which was subjected to the following tests.

The reflectance at 600 reflection angle of the coating film before the glossy surface formation treatment was measured using a gloss meter.

(2) A part of the crosslinkable sample was taken and rubbed with absorbent cotton impregnated with methyl ethyl ketone, and the degree of removal of the coating film was expressed in the following three grades.

○: No or almost no shedding Δ: A little shedding ×: A lot of shedding (3) Orientation The sample was cut into SO1111 long pieces and measured using a magnetic property measuring machine (Br/13m).

(4) Durability: In an atmosphere of 40°C and relative humidity of 8°C, a rotating drum covered with abrasive paper was brought into contact with a load of 100y, and rotated at 15 Q rpm. The degree of adhered dirt was displayed in the following three levels, starting from 0.

○: No stains △: Some stains The running resistance was measured using a U gauge in an atmosphere of

○: Low resistance Δ: Low resistance Medium: High resistance The results are shown in the table.

As is clear from the table, according to the present invention, a high-performance magnetic recording medium in which magnetic powder is well dispersed can be obtained, and the medium has good durability and there is no fear of deterioration of characteristics even after long-term use.

Claims (1)

[Claims] At least one selected from SO_3M, SO_4M, PO_4M_2 (where M is an alkali metal or NH_4)
Vinyl chloride resin having a strong acid base and an epoxy group, and COOH, SO_3H, SO_4H, PO_4H
A magnetic recording medium comprising a vinyl chloride resin having at least one acidic group selected from M' (where M' is H or an organic group) as a binder for magnetic powder.