JPH0867855A - Binder for magnetic recording material and magnetic recording material - Google Patents

Abstract

PURPOSE: To obtain a binder for magnetic recording media, excellent in magnetic powder dispersibility and capable of forming a magnetic film excellent in abrasion and heat resistances. CONSTITUTION: This binder for magnetic recording media comprises a copolymer of a vinyl monomer having an acidic group, a styrenic monomer and/or an acrylic or a methacrylic ester as a principal component and the acid value of the copolymer is >=0.1 to <=50KOHmg/g. Otherwise,, the binder comprises a copolymer of a vinyl monomer having a basic group and the styrenic monomer and/or the acrylic or methacrylic ester as a principal component and 0.5-20wt.% vinyl monomer having the basic group is contained in the copolymer. The viscosity of the copolymer when dissolved in a solvent of methyl ethyl ketone (MEK)/ toluene at 50/50 weight ratio arid 10wt.% concentration is >=2 to <=50cp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder for a magnetic recording material and a magnetic recording material using the binder, and in particular, it has excellent dispersibility of magnetic powder and has excellent wear resistance and heat resistance. The present invention relates to a binder for a magnetic recording body capable of forming a magnetic coating film having excellent properties and a magnetic recording body using the binder.

[0002]

2. Description of the Related Art A magnetic recording material such as a magnetic tape or a magnetic disk is generally prepared by applying a magnetic paint obtained by mixing magnetic powder and a binder onto a substrate such as polyester.
It is manufactured by drying to form a magnetic coating film.

The above magnetic recording medium is required to have excellent electromagnetic characteristics and durability such as resistance to contact with a magnetic head. Therefore, the binder for a magnetic recording material can form a magnetic coating film having excellent dispersibility of magnetic powder in the case of forming a magnetic coating, and having excellent abrasion resistance and heat resistance. Various characteristics such as being present are required.

Conventionally, a vinyl chloride-vinyl acetate-vinyl alcohol polymer has been widely used as a binder satisfying the above requirements (Japanese Patent Publication No. 55-34493).

On the other hand, with the recent increase in the density of magnetic recording, it has become necessary to use magnetic powder having a smaller particle size. As a result, when the above vinyl chloride-vinyl acetate-vinyl alcohol polymer is used as a binder,
There is a problem that the dispersibility of fine magnetic powder is not sufficient.

Therefore, in place of the above-mentioned polymer, a polyvinyl acetal resin has been proposed as a binder resin having excellent affinity with magnetic powder and exhibiting good dispersibility for fine magnetic powder. (JP-A-61-2722)
4 and JP-A-1-236290).

It is also proposed to use a copolymer composed of an aliphatic lower unsaturated acid, acrylonitrile, and an aliphatic lower unsaturated acid ester as a binder for a magnetic recording material having excellent abrasion resistance. Has been done. (Japanese Patent Publication Sho 48-5483
Issue)

[0008]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a magnetic recording material which can form a magnetic coating film having more excellent magnetic powder dispersibility and excellent abrasion resistance and heat resistance. It is intended to provide a binder and a magnetic recording body using the binder for the magnetic recording body.

[0009]

A binder for a magnetic recording medium according to the present invention comprises a vinyl monomer having an acid group, a styrene-based monomer and / or a (meth) acrylic acid ester. It contains a copolymer as a main component, the acid value of the copolymer is 0.1 KOHmg / g or more and 50 KOHmg / g or less, and methyl ethyl ketone (MEK) / toluene = 50/50 (weight ratio) 10 in a solvent. It is characterized in that the viscosity when dissolved at a concentration of wt% is 2 cp or more and 50 cp or less.

The binder for a magnetic recording medium according to the second aspect of the present invention is mainly a copolymer of a vinyl monomer having a basic group, a styrene monomer and / or a (meth) acrylic acid ester. 0.5 to 20 wt% of the vinyl monomer having the basic group is contained in the copolymer as a component, and
Methyl ethyl ketone (MEK) / toluene = 50/50
(Weight ratio) The viscosity when dissolved in a solvent at a concentration of 10 wt% is 2 cp or more and 50 cp or less.

A binder for a magnetic recording medium according to a third aspect of the present invention comprises a vinyl monomer having an acid group and a basic group, a styrene-based monomer and / or a (meth) acrylic acid ester. The vinyl monomer containing a polymer as a main component, the copolymer having an acid value of 0.1 KOHmg / g or more and 50 KOHmg / g or less, and having the basic group in the copolymer is 0.1. 5 to 20% by weight and methyl ethyl ketone (MEK) / toluene = 50/50 (weight ratio)
The viscosity when dissolved in a solvent at a concentration of 10% by weight is 2 cp or more and 50 cp or less.

The magnetic recording medium of the present invention comprises magnetic powder and
The magnetic recording medium binder according to claim 1, 2, or 3 is included.

The details of the present invention will be described below. The acid group used in the present invention is one or more kinds of acid groups such as carboxylic acid, sulfonic acid, sulfinic acid, phosphonic acid and boric acid. Of these, carboxylic acids and sulfonic acids are preferably used from the viewpoint of acid strength and ease of copolymerization. Specific examples of the vinyl monomer having a carboxylic acid include (meth) acrylic acid such as acrylic acid, methacrylic acid, α-ethylacrylic acid and crotonic acid, and α- or β-alkyl derivatives thereof; fumaric acid and maleic acid. Unsaturated dicarboxylic acids such as acid, citraconic acid, itaconic acid; unsaturated succinic acid monoacryloyloxyethyl ester, succinic acid monomethacryloyloxyethyl ester, phthalic acid monoacryloyloxyethyl ester, phthalic acid monomethacryloyloxyethyl ester, etc. Examples include dicarboxylic acid monoester derivatives. Among these, acrylic acid, methacrylic acid, succinic acid monoacryloyloxyethyl ester, and succinic acid monomethacryloyloxyethyl ester are preferably used. Specific examples of the vinyl monomer having sulfonic acid include sulfonic acid and sulfonate compounds such as styrene sulfonic acid, sodium styrene sulfonate, and sodium vinyl sulfonate; 2-acrylamido-2-methylpropane sulfonic acid, Examples thereof include sulfonic acid-containing acrylamide compounds such as 2-methacrylamido-2-methylpropanesulfonic acid. Among these, sodium styrenesulfonate and 2-acrylamido-2-methylpropanesulfonic acid are preferably used.

The basic group used in the present invention is one kind or two or more kinds such as an amino group, a pyridyl group and a quinolyl group. Of these, an amino group is preferably used because of the strength of the base and the ease of copolymerization. Specific examples of the vinyl monomer having an amino group include dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl methacrylate, diethylaminoethyl acrylate, dimethylaminopropyl methacrylamide, dimethylaminopropyl acrylamide and allylamine.

Specific examples of the above-mentioned styrene type monomer include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene and p-methylstyrene.
-Ethylstyrene, 2,4-dimethylstyrene, pn
-Butylstyrene, p-ter-butylstyrene, p-
n-hexyl styrene, pn-octyl styrene, p
-N-nonylstyrene, pn-decylstyrene, p-
Examples thereof include n-dodecyl styrene, p-methoxy styrene, p-phenyl styrene, p-chloro styrene, and 3,4-dichloro styrene. Of these, styrene is the most preferable.

Specific examples of the above-mentioned acrylic acid ester and methacrylic acid ester include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, (Meta)
Isobutyl acrylate, n-octyl (meth) acrylate, dodecyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate,
Examples include stearyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, and methyl α-chloroacrylate. Among these, methyl methacrylate, n-butyl (meth) acrylate, and 2-ethylhexyl acrylate are preferred.

As a method for polymerizing the above-mentioned copolymer, any of conventionally known methods such as a solution polymerization method, a suspension polymerization method, an emulsion polymerization method and a bulk polymerization method may be adopted, but the solution polymerization method is preferable. Used.

In the copolymer according to claim 1 and the invention according to claim 3, the content of the styrene-based monomer component is 40 to 95% by weight, more preferably 60 to 90% by weight, (meth). Acrylic ester component content is 4-4
0% by weight, more preferably 10 to 40% by weight, and copolymerized so that the content of the vinyl monomer component having an acid group is 0.5 to 20% by weight, more preferably 1 to 10% by weight. Preferably.

When the content of the styrene-based monomer component is less than 40% by weight, the copolymer becomes hard and pulverization becomes difficult and it may not be possible to make fine powder. If the content of the (meth) acrylic acid ester component is less than 4% by weight, the wear resistance and durability of the magnetic recording material may be deteriorated. If the content of the vinyl-based monomer component having an acid group is less than 0.5% by weight, the dispersibility of the magnetic powder may deteriorate.

The acid value of the copolymer of the invention of claim 1 and the copolymer of the invention of claim 3 is 0.1 KOHmg / g or more, 5 or more.
It should be 0 KOHmg / g or less. If the acid value is less than 0.1 KOHmg / g, the dispersibility of the magnetic powder may deteriorate, and if it is greater than 50 KOHmg / g,
The acid groups may be condensed to increase the viscosity of the binder, or the magnetic powder may have poor dispersibility.

The copolymers of the invention of claim 2 and the invention of claim 3 must contain 0.5 to 20% by weight of a vinyl monomer having a basic group. If the vinyl monomer having a basic group is less than 0.5% by weight, the dispersibility of the magnetic powder may deteriorate, and if it is more than 20% by weight, the binder deteriorates and the heat resistance deteriorates. The dispersibility of the magnetic powder may deteriorate. In this case, the content of the styrene-based monomer component is 40 to 95% by weight, more preferably 60 to 90% by weight, and the content of the (meth) acrylic acid ester component is 4 to 40% by weight, more preferably 10%. ~
It is preferable to copolymerize so as to be 40% by weight. When the content of the styrene-based monomer component is less than 40% by weight, the copolymer becomes hard and pulverization becomes difficult and it may not be possible to make fine powder. When the content of the (meth) acrylic acid ester component is less than 4% by weight,
The wear resistance and durability of the magnetic recording material may be reduced.

In the invention of claim 1, the copolymer of claim 2 and the copolymer of claim 3, a methyl ethyl ketone (MEK) / toluene = 50/50 (weight ratio) concentration of 10% by weight in a solvent. Viscosity when dissolved in 2c
It is necessary that it is p or more and 50 cp or less. Methyl ethyl ketone (MEK) / toluene = 50/50 (weight ratio) The viscosity when dissolved in a solvent at a concentration of 10% by weight is 2c.
If it is less than p, it may be difficult to obtain a certain thickness when applying a magnetic coating material in which magnetic powder and a binder are mixed to the substrate, and if it is greater than 50 cp, the viscosity is high and it is difficult to apply, and the film It may not be.

The binder for magnetic recording media according to the present invention may be used alone, but in general, it is also used as a binder for magnetic recording media. The polyurethane resin, polyester resin, acrylonitrile-butadiene copolymer, epoxy resin or the like used may be used in combination.

Also in the magnetic recording medium according to the invention of claim 4, as the binder, only the binder for the magnetic recording medium of claim 1, 2 or 3 may be used. One or more binders for magnetic recording media may be mixed and used. A magnetic coating material is prepared using the above binder for magnetic recording medium, and is applied on the surface of a substrate according to a commonly used method such as a roll coater to orient the magnetic powder contained in the magnetic coating material, and the magnetic coating material is applied. By drying to form a magnetic coating film on the surface of the substrate, the magnetic recording medium according to the invention of claim 4 can be produced.

The above-mentioned magnetic paint is prepared, for example, by first adding a magnetic powder mixture comprising magnetic powder and a binder for the magnetic recording medium,
It is carried out by mixing an organic solvent such as methyl ethyl ketone, toluene and cyclohexanone and then kneading with a kneader or the like.

The substrate that can be used is not particularly limited, but, for example, a substrate made of polyester, triacetyl cellulose, polyamide, polyimide, polyamide imide, polystyrene, polyvinyl alcohol, nitrocellulose or the like is usually used, and particularly, Preferably, polyester is used.

In the magnetic recording medium according to the fourth aspect of the present invention, a back coat layer mainly composed of non-magnetic powder and a binder is formed on the surface of the substrate opposite to the surface on which the magnetic layer is formed. The binder according to the invention described in claim 1, 2 or 3 can be used as the binder for the back coat layer.

[0028]

The binder for a magnetic recording medium according to claim 1 or 3 and the magnetic recording medium according to claim 4 using the binder include the vinyl monomer having the specific acid group and the styrene-based monomer. Polymers and / or copolymers with (meth) acrylic acid esters are used. The specific copolymer has an acid value of 0.1 K
It is set to be OHmg / g or more and 50 KOHmg / g or less, which makes the dispersibility of the magnetic powder very good.

The binder for a magnetic recording medium according to claim 2 or 3 and the magnetic recording medium according to claim 4 using the same are the vinyl monomer having the specific basic group and the styrene-based monofunctional monomer. A copolymer with a monomer and / or a (meth) acrylic acid ester is used. The specific copolymer contains 0.5 to 20% by weight of a vinyl monomer having a basic group, which makes the dispersibility of the magnetic powder very good.

In the inventions of claims 1 to 4, the viscosity when dissolved in a solvent of methyl ethyl ketone (MEK) / toluene = 50/50 (wt%) at a concentration of 10 wt% is 2 c.
Since it is p or more and 50 cp or less, the dispersibility of the magnetic powder is good, and when the magnetic coating material is applied to the substrate,
It is easy to apply and can be applied with a uniform thickness. further,
The magnetic coating after drying the magnetic coating also has excellent abrasion resistance and heat resistance.

[0031]

EXAMPLES The present invention will be clarified by giving non-limiting examples and comparative examples of the present invention. First, examples according to the invention of claim 1 and comparative examples thereof will be described.

Example 1 70 parts by weight of styrene, 3 parts by weight of methyl methacrylate, 20 parts by weight of n-butyl acrylate and 7 parts by weight of monomethacryloyloxyethyl succinate were used, and the degree of polymerization was 30.
0 and a copolymer having an acid value of 10 KOHmg / g were dissolved in a mixed solvent [methyl ethyl ketone / toluene = 50/50 (weight ratio)] to obtain a binder solution for a magnetic recording material having a concentration of 10% by weight. The viscosity of this solution was 5.2 cp.

In the binder solution obtained as described above,
A magnetic powder (particle size 0.8 μm) of cobalt-γ-iron oxide was added in an amount 2.5 times by weight, and the mixture was kneaded for 4 hours with a paint conditioner.

The magnetic paint prepared as described above was added to
It was applied on a polyethylene terephthalate (PET) film having a thickness of 14 μm so that the thickness after drying would be 5 μm. Next, after subjecting the coating film to a magnetic field orientation treatment, the coating film was dried, and a PET film having a coating film formed on one surface was wound up. Further, the PET film on which the magnetic coating film was formed was subjected to a calendar treatment and cut into a 1/2 inch width to prepare a magnetic recording material.

The measurement of the degree of polymerization in the above was carried out as follows. First, 0.5 g of a sample is precisely weighed and dissolved in 50 ml of toluene at 30 ° C. The solution was put into an Ostwald viscometer set in a constant temperature bath kept at 30 ° C., the dropping seconds were measured, and calculated by the following formula.

[0036]

[Equation 1]

The above-mentioned acid value was measured as follows. First, 2.0 g of a sample is precisely weighed and dissolved with 30 ml of methyl ethyl ketone. The solution
1% by weight phenolphthalein solution as an indicator
Titration was performed with a 50N potassium hydroxide / isopropyl alcohol solution (KOH / IPA solution), and calculation was performed using the following formula.

[0038]

[Equation 2]

The solution viscosity in the above was measured with a BM type viscometer for a sample solution kept at 20 ° C. in a thermostatic chamber at 20 ° C.

Examples 2 to 5 As shown in Table 1 below, the binders for magnetic recording bodies of Examples 2 to 5 were prepared in the same manner as in Example 1 except that the monomer composition was changed. A magnetic recording body was obtained in the same manner as in Example 1. Table 1 also shows the polymerization degree, acid value, and solution viscosity of each binder for magnetic recording media.

Comparative Example 1 Binder for magnetic recording medium was prepared in the same manner as in Example 1 except that 7 parts by weight of monomethacryloyloxyethyl succinate was not used in Example 1 but was changed to 10 parts by weight of methyl methacrylate. To obtain a magnetic recording medium.

Comparative Example 2 A magnetic recording material was prepared in the same manner as in Example 3 except that 10 parts by weight of acrylic acid was increased to 18 parts by weight and 65 parts by weight of styrene was decreased to 52 parts by weight in Example 3. A binder was obtained and a magnetic recording body was prepared.

Comparative Examples 3 and 4 The binders for magnetic recording bodies of Example 2 have the same monomer composition and a polymerization degree of 90 (Comparative Example 3) and 18000, respectively.
A binder for a magnetic recording medium was obtained in the same manner as in Example 2 except that the one used in Comparative Example 4 was used, and a magnetic recording medium was prepared.

Table 1 shows the monomer composition, the degree of polymerization, the acid value, and the solution viscosity of the binders for magnetic recording materials of Comparative Examples 1 to 4 above.

[0045]

[Table 1]

The monomer abbreviations in Table 1 have the following meanings. ST: Styrene, MMA: methyl methacrylate, BA: butyl acrylate 2EHA: 2-ethylhexyl acrylate, AAc: acrylic acid MAHES: succinic acid monomethacryloyloxyethyl ester AMPS: 2-acrylamido-2-methylpropanesulfonic acid

[Evaluation of Examples and Comparative Examples] The glossiness, abrasion resistance and heat resistance of the magnetic recording bodies of Examples 1 to 5 and Comparative Examples 1 to 4 produced as described above are determined as follows. Was measured and evaluated.

The results are shown in Table 2. Gloss: A gloss meter (Glossmeter, manufactured by Murakami Color Research Co., Ltd.) was used, and both the incident angle and the reflection angle were set to 60 °.

Abrasion resistance: The magnetic recording medium was run at a running speed of 50 cm / sec while being in contact with the magnetic head, and the
The abrasion loss was measured by the running test after running 0 times. In Table 2, the wear loss of Comparative Example 3 is set to 100%,
The wear reductions of Examples 1 to 5 and Comparative Examples 1, 2, and 4 are shown as values relative to the wear reduction of Comparative Example 3.

Heat resistance: evaluated by a heat adhesion test.
That is, a plurality of magnetic recording bodies were prepared, heated at a temperature of 120 ° C. for 15 minutes, and then a plurality of magnetic recording bodies were stacked to examine the block property. The meanings of the evaluation symbols in Table 2 are as follows.

○: good ×: bad

[0052]

[Table 2]

As is clear from Table 2, in Comparative Example 1,
Since the acid value was 0 KOHmg / g, it was considered that the dispersion of the magnetic powder was poor and the glossiness was lowered, which was confirmed to be inferior to the result of Example 1.

In Comparative Example 2, it was considered that the acid value was too large and the glossiness was deteriorated as in Comparative Example 1, and it was confirmed that the result was inferior to the result of Example 3. Comparative Example 3
It was confirmed that the result was inferior to the result of Example 2 because the abrasion resistance and heat resistance were poor because the glossiness was good but the polymerization degree was low.

In Comparative Example 4, although the glossiness and the heat resistance were good, the solution viscosity was high and it was difficult to apply the magnetic paint.
It was confirmed that the abrasion resistance was poor because the applied film thickness was not constant, which was inferior to the result of Example 2. Next, examples according to the invention of claim 2 and comparative examples thereof will be described.

Example 6 A copolymer containing 70 parts by weight of styrene, 5 parts by weight of methyl methacrylate, 20 parts by weight of n-butyl acrylate and 5 parts by weight of dimethylaminoethyl acrylate, and having a degree of polymerization of 400 is mixed with a solvent. [Methyl ethyl ketone / toluene = 50
/ 50 (weight ratio)] to obtain a binder solution for a magnetic recording material having a concentration of 10% by weight. The viscosity of this solution is 6.1c
It was p.

In the binder solution obtained as described above,
A magnetic powder (particle size 0.8 μm) of cobalt-γ-iron oxide was added in an amount 2.5 times by weight, and the mixture was kneaded for 4 hours with a paint conditioner.

Using the magnetic coating material prepared as described above, a magnetic recording medium was prepared in the same manner as in Example 1. The degree of polymerization and the solution viscosity were measured as in Example 1. The results are shown in Table 3.

Examples 7 to 10 As shown in Table 3 below, the binders for magnetic recording bodies of Examples 7 to 10 were prepared in the same manner as in Example 6 except that the monomer composition was changed. A magnetic recording material was obtained in the same manner as in Example 6. Table 3 also shows the polymerization degree and solution viscosity of each magnetic recording material binder.

Comparative Example 5 A binder for a magnetic recording medium was prepared in the same manner as in Example 6 except that 5 parts by weight of dimethylaminoethyl acrylate was not used in Example 6 but was changed to 10 parts by weight of methyl methacrylate. Then, a magnetic recording body was prepared.

Comparative Example 6 Dimethylaminoethyl acrylate 16 in Example 8
The amount of styrene was increased to 30 parts by weight, and 59 parts by weight of styrene was added to 4 parts.
A magnetic recording material binder was obtained in the same manner as in Example 8 except that the amount was reduced to 5 parts by weight, and a magnetic recording material was produced.

Comparative Examples 7 and 8 The binders for magnetic recording bodies of Example 7 have the same monomer composition and a polymerization degree of 100 (Comparative Example 7) and 17500, respectively.
A binder for magnetic recording bodies was obtained in the same manner as in Example 7 except that the one used in Comparative Example 8 was used, and further magnetic recording bodies were prepared.

Table 3 shows the composition of each monomer in Comparative Examples 5 to 8, the degree of polymerization of each binder for magnetic recording materials, and the solution viscosity.

[0064]

[Table 3]

The abbreviations of the monomers in Table 3 have the following meanings. ST: Styrene, MMA: methyl methacrylate, BA: butyl acrylate 2EHA: 2-ethylhexyl acrylate, DMAEA: dimethylaminoethyl acrylate DMAEMA: dimethylaminoethyl methacrylate DMAPAA: dimethylaminopropyl acrylamide

[Evaluation of Examples and Comparative Examples] The glossiness, abrasion resistance, and heat resistance of the magnetic recording bodies of Examples 6 to 10 and Comparative Examples 5 to 8 produced as described above were evaluated according to the above examples. It was measured and evaluated in the same manner as in 1. The results are shown in Table 4.

[0067]

[Table 4]

As is clear from Table 4, in Comparative Example 5,
Since the content of the vinyl monomer having a basic group was 0, it was considered that the dispersion of the magnetic powder was poor and the glossiness was lowered, which was confirmed to be inferior to the result of Example 6. .

In Comparative Example 6, the content of the vinyl monomer having a basic group was too high, and it is considered that the glossiness was deteriorated as in Comparative Example 5, which was inferior to the result of Example 8. Was confirmed.

In Comparative Example 7, it was confirmed that the glossiness was good, but the degree of polymerization was low, so the abrasion resistance and heat resistance were poor, and the results were inferior to those of Example 7. In Comparative Example 8,
Although the glossiness and heat resistance are good, the solution viscosity is high, it is difficult to apply the magnetic paint, and the abrasion resistance is poor because the applied film thickness is not constant, which is inferior to the result of Example 7. Was confirmed.

Example 11 74 parts by weight of styrene, 10 parts by weight of methyl methacrylate,
A copolymer consisting of 10 parts by weight of n-butyl acrylate, 3 parts by weight of acrylic acid and 3 parts by weight of dimethylaminoethyl acrylate and having a degree of polymerization of 380 and an acid value of 8 KOHmg / g was mixed solvent [methyl ethyl ketone / toluene 50 /
50 (weight ratio)] to obtain a binder solution for a magnetic recording medium having a concentration of 10% by weight. The viscosity of this solution is 4.8 cp
Met.

In the binder solution obtained as described above,
A magnetic powder (particle size 0.8 μm) of cobalt-γ-iron oxide was added in an amount 2.5 times by weight, and the mixture was kneaded for 4 hours with a paint conditioner.

Using the magnetic coating material prepared as described above, a magnetic recording medium was prepared in the same manner as in Example 1. The degree of polymerization and the solution viscosity were measured as in Example 1. The results are shown in Table 5.

Examples 12 to 15 As shown in Table 5 below, the binders for magnetic recording bodies of Examples 12 to 15 were prepared in the same manner as in Example 11 except that the monomer composition was changed. A magnetic recording material was obtained in the same manner as in Example 11. Table 5 also shows the degree of polymerization, the acid value, and the solution viscosity of each binder for magnetic recording media.

Comparative Example 9 Magnetic recording was carried out in the same manner as in Example 11 except that 3 parts by weight of acrylic acid and 3 parts by weight of dimethylaminoethyl acrylate were not used in Example 11, but 16 parts by weight of methyl methacrylate was used. A binder for body was obtained, and a magnetic recording body was prepared.

Comparative Example 10 A magnetic recording material was prepared in the same manner as in Example 13 except that 10 parts by weight of acrylic acid was increased to 20 parts by weight and 59 parts by weight of styrene was decreased to 49 parts by weight in Example 13. A binder was obtained and a magnetic recording body was prepared.

Comparative Example 11 Magnetic recording was carried out in the same manner as in Example 12 except that 9 parts by weight of dimethylaminoethyl methacrylate was increased to 25 parts by weight and 60 parts by weight of styrene was decreased to 44 parts by weight. A binder for body was obtained, and a magnetic recording body was prepared.

Comparative Examples 12 and 13 The binders for magnetic recording bodies of Example 12 have the same monomer composition and the degree of polymerization is 85 (Comparative Example 12) and 1790, respectively.
Example 1 except that 0 (Comparative Example 13) was used.
A magnetic recording material binder was obtained in the same manner as in 2, and a magnetic recording material was produced.

The respective monomer compositions of Comparative Examples 9 to 13 above,
Table 5 shows the polymerization degree, acid value and solution viscosity of each binder for magnetic recording media.
It was shown to.

[0080]

[Table 5]

The monomer abbreviations in Table 5 have the following meanings. ST: Styrene, MMA: Methyl methacrylate, BA: Butyl acrylate 2EHA: 2-Ethylhexyl acrylate AAc: Acrylic acid AMPS: 2-Acrylamido-2-methylpropanesulfonic acid DMAEA: Dimethylaminoethyl acrylate DMAEMA: Dimethylaminoethyl methacrylate

[Evaluation of Examples and Comparative Examples] The glossiness, abrasion resistance and heat resistance of the magnetic recording bodies of Examples 11 to 15 and Comparative Examples 9 to 13 produced as described above were measured according to the above-mentioned Examples. It was measured and evaluated in the same manner as in 1.

The results are shown in Table 6.

[0084]

[Table 6]

As is clear from Table 6, in Comparative Example 9,
Since the content of the vinyl monomer having an acid group and a basic group was 0, it is considered that the dispersion of the magnetic powder was poor and the glossiness was lowered, which is inferior to the result of Example 11. confirmed.

Further, in Comparative Example 10, the content of the vinyl monomer having an acid group was too high, and it is considered that the glossiness was deteriorated as in Comparative Example 9, which is inferior to the result of Example 13. It was confirmed.

In Comparative Example 11, the content of the vinyl monomer having a basic group was too high, and it is considered that the glossiness was deteriorated as in Comparative Example 9, and the result was inferior to the result of Example 12. Was confirmed.

In Comparative Example 12, the glossiness was good, but the degree of polymerization was low, so that the abrasion resistance and heat resistance were poor.
It was confirmed that it was inferior to the result of. Comparative Example 13
In addition, although the glossiness and heat resistance are good, the solution viscosity is high, the application of the magnetic paint is difficult, and the abrasion resistance is poor because the applied film thickness is not constant. It was confirmed to be inferior.

[0089]

As described above, in the binder for a magnetic recording medium and the magnetic recording medium using the same according to the first aspect of the present invention, the vinyl monomer having an acid group and the styrene-based monomer Alternatively, it is a copolymer with (meth) acrylic acid ester and has an acid value of 0.1 KOHmg / g or more and 50 KOHmg / g or less, and methyl ethyl ketone (MEK) / toluene = 50/50 (weight ratio) as a solvent. Since a copolymer having a viscosity of 2 cp or more and 50 cp or less when dissolved at a concentration of 10% by weight is contained as a main component, the dispersibility of magnetic powder becomes good. Therefore, the glossiness of the magnetic recording material obtained by dispersing the magnetic powder can be increased. Further, when prepared as a magnetic coating material and applying the magnetic coating material, coating is easy, a film having a uniform thickness is obtained, and the obtained magnetic film is
It has excellent heat resistance and abrasion resistance.

Further, in the binder for a magnetic recording medium and the magnetic recording medium using the same according to the second aspect of the invention, the vinyl monomer having a basic group and the styrene-based monomer and / or (meth) It is a copolymer with an acrylic ester, and the vinyl monomer having the basic group is 0.5 to 2 in the copolymer.
Contains 0% by weight and methyl ethyl ketone (MEK)
/ Toluene = 50/50 (weight ratio) Since the main component is a copolymer having a viscosity of 2 cp or more and 50 cp or less when dissolved in a solvent at a concentration of 10 wt%, the dispersibility of magnetic powder is good. Becomes Therefore, the glossiness of the magnetic recording material obtained by dispersing the magnetic powder can be increased. In addition, when prepared as a magnetic paint and applied with the magnetic paint, a film having a uniform thickness was obtained, and the obtained magnetic film was excellent in heat resistance and abrasion resistance. Will be things.

In the binder for a magnetic recording medium and the magnetic recording medium using the same according to the third aspect of the invention, a vinyl monomer having an acid group and a basic group, a styrene-based monomer and / or a (meth) ) A copolymer with an acrylic ester, and the acid value of the copolymer is 0.1 KOHmg / g or more and 50 KOHm
g / g or less, 0.5 to 20% by weight of the vinyl monomer having the basic group is contained in the copolymer, and methyl ethyl ketone (MEK) / toluene = 50 /
Since a copolymer having a viscosity of 2 cp or more and 50 cp or less when dissolved in a 50 (weight ratio) solvent at a concentration of 10 wt% is contained as a main component, the dispersibility of the magnetic powder becomes good. Therefore, the glossiness of the magnetic recording material obtained by dispersing the magnetic powder can be increased. In addition, when prepared as a magnetic paint and applied with the magnetic paint, a film having a uniform thickness was obtained, and the obtained magnetic film was excellent in heat resistance and abrasion resistance. Will be things.

Claims (4)

[Claims] 1. A main component comprising a copolymer of a vinyl monomer having an acid group and a styrene monomer and / or a (meth) acrylic acid ester, and the acid value of the copolymer is 0.1.
1 KOHmg / g or more and 50 KOHmg / g or less, and methyl ethyl ketone (MEK) / toluene =
A binder for a magnetic recording material, which has a viscosity of 2 cp or more and 50 cp or less when dissolved in a 50/50 (weight ratio) solvent at a concentration of 10% by weight. 2. A copolymer containing a vinyl monomer having a basic group and a styrene-based monomer and / or a (meth) acrylic acid ester as a main component, and the basic component is contained in the copolymer. The vinyl monomer having a group is contained in an amount of 0.5 to 20% by weight, and the viscosity when dissolved in a methylethylketone (MEK) / toluene = 50/50 (weight ratio) solvent at a concentration of 10% by weight is 2 cp or more. A binder for a magnetic recording medium, which is 50 cp or less. 3. A copolymer of a vinyl monomer having an acid group and a basic group and a styrene monomer and / or a (meth) acrylic acid ester as a main component, and the acid of the copolymer. Value is 0.1KOHmg / g or more 50KOHmg / g
It is below, and 0.5 to 20% by weight of the vinyl monomer having the basic group is contained in the copolymer, and methyl ethyl ketone (MEK) / toluene = 50/50.
(Weight ratio) A binder for a magnetic recording material, which has a viscosity of 2 cp or more and 50 cp or less when dissolved in a solvent at a concentration of 10% by weight. 4. A magnetic recording medium comprising magnetic powder and the binder for magnetic recording medium according to claim 1, 2.