JPS6034166B2 - magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording medium with excellent wear resistance.

Magnetic recording tapes have made remarkable progress in recent years, and are now used in large quantities for applications such as electronic computers, video tapes, and magnetic sheets.

And video tape. When used for commercial purposes, the contact speed between the magnetic coating surface of the recording tape and the recording head is high, so repeated use may cause problems with the abrasion resistance of the recording tape's magnetic coating, and at the same time generate frictional heat. Therefore, heat resistance is also an issue. Conventionally, vinyl chloride-vinyl acetate copolymers, acrylic resins, methacrylic resins, polyurethane resins, butyral resins, etc. have been used as binders for magnetic tapes. It has been difficult to obtain magnetic recording tapes with wear resistance.

In view of the above points, the present invention has been made as a result of various researches aimed at providing a magnetic recording medium with excellent heat resistance and wear resistance.
Looking at binders for magnetic recording media with excellent performance,
It was done by putting out. That is, the gist of the present invention is a modified polyvinyl alcohol obtained by acetalizing a modified polyvinyl alcohol containing an unsaturated dicarboxylic acid, an alkyl ester of the unsaturated dicarboxylic acid, or an alkali metal salt of the unsaturated dicarboxylic acid as a copolymerization component. A magnetic recording material characterized in that a mixture of a polyvinyl acetal resin, a polyurethane resin having an active isocyanate group in its molecule, and a magnetic powder is coated on a substrate as a magnetic paint.

The modified polyvinyl acetal resin used in the present invention is obtained by acetalizing the following modified polyvinyl alcohol, and the degree of acetalization is 60 to 7.
8 mol %, particularly 70 to 75 mol % is preferable, and acetalization can be carried out by reacting an aldehyde compound such as butyraldehyde with polyvinyl alcohol in a conventional manner. In the present invention, the modified polyvinyl alcohol refers to polyvinyl alcohol in which an unsaturated dicarboxylic acid, an alkyl ester of the carboxylic acid, or an alkali metal salt of the carboxylic acid is contained in the copolymerization component, and the ester or The metal salts may be mono- or gestational or metal salts, or may be one in which one of the carboxyl groups of the dicarboxylic acid is an ester and the other is an alkali metal salt.

Further, the content of the modifying component such as unsaturated dicarboxylic acid in the modified polyvinyl alcohol is preferably 0.1 to 3 mol%, particularly preferably 0.1 to 0.5 mol%. In addition, in the above, unsaturated dicarboxylic acid refers to a compound having a double bond contributing to polymerization and two carboxyl groups, such as maleic acid and fumaric acid, and alkyl ester refers to a compound having two carboxyl groups, such as maleic acid and fumaric acid. It refers to a compound esterified with an alkyl hydroxide such as methanol, ethanol, and propanol, and an alkali metal salt of a carbosic acid is a compound in which the above carboxyl group is converted into a carboxylic acid by reaction with an alkali metal base such as lithium, sodium, or potassium. Refers to compounds that have become salts. Next, the polyurethane resin used in the present invention has an active isocyanate group in its molecule.

And what has this active isocyanate group is
The structure is not limited to one in which an isocyanate group is bonded to the end of the molecule. Also included are polyurethanes whose isocyanate end groups are blocked with phenol or the like, whose activity is suppressed under normal conditions, but whose isocyanate groups can become active under activation conditions such as heating. In the present invention, a mixture of the above-mentioned modified polyvinyl acetal resin and the above-mentioned polyurethane resin is used as a binder in a magnetic recording medium, and the mixing ratio is 8:2 to 8:2 by weight of the modified polyvinyl acetal resin to polyurethane resin. It is best to have a ratio of 4 to 6.

This is because the isocyanate groups in the polyurethane react with the hydroxyl groups and -COO- groups in the modified polyvinyl acetal resin in a mixture of the two types of resins mentioned above at room temperature or under heated conditions, forming a three-dimensional network structure and integrating them. This is because the resin has excellent heat resistance, hardness, high elasticity, and excellent abrasion resistance, but if the amount of polyurethane resin is too large or too small, the abrasion resistance tends to decrease.
Next, as the magnetic powder used in the present invention, powdered magnetic substances conventionally used for imparting magnetism to magnetic recording bodies can be used, and for example, y-Fe203 powder is suitable.

To manufacture the magnetic recording medium of the present invention, first, the modified polyvinyl acetal resin, polyurethane resin, and magnetic powder are added to form a mixture and a magnetic paint is prepared.

In order to prepare this magnetic paint, it is generally preferable to add the above components to a suitable solvent to form a resin solution in which magnetic powder is dispersed, and in the above solution, colorants and other additives are added as appropriate. May be added. Next, the magnetic coating material prepared as described above is applied onto a suitable magnetic recording material substrate such as a polyester film and dried to form a coating film, thereby obtaining the magnetic recording material of the present invention.

Even when the above-mentioned coating film is left at room temperature, the reaction between the modified polyvinyl acetal resin and the polyurethane resin that produces the aforementioned three-dimensional network structure progresses in the coating film, resulting in heat resistance and abrasion resistance. However, in order to promote the reaction, it is preferable to leave it for several hours to several tens of hours at a temperature of 40 to 60 qo. The magnetic recording medium of the present invention has the above-mentioned structure, and is made by coating a mixture of a specific modified polyvinyl acetal resin, a specific polyurethane resin, and magnetic powder on a substrate as a magnetic paint. The coating film provided on top becomes heat resistant, hard, and highly elastic due to the reaction of the above two types of resins, and therefore becomes a magnetic recording medium with excellent heat resistance and abrasion resistance. It is. Next, examples of the present invention will be described.

Example 1 Maleic acid monomethyl ester monosodium salt was 2.
A modified polyvinyl butyral resin with a degree of butyralization of 75 mol% was prepared by butyralizing modified polyvinyl alcohol with a degree of polymerization of 870 containing 5 mol% using butyraldehyde in a conventional manner.

Next, the following composition containing the modified polyvinyl butyral resin was mixed in a ball mill for about 2 hours.

y-Fe203 powder 30 parts by weight Modified polyvinyl butyral resin 6 parts by weight Carbon black 10 Methyl ethyl ketone 250 Toluene
250'' The following composition was further added to the above mixture and mixed well to prepare a magnetic paint.

4 parts by weight of polyurethane having an active isocyanate group (trade name Takenate XL-1007, manufactured by Takeda Pharmaceutical Co., Ltd.) Methyl ethyl ketone 85 Toluene 85 The magnetic paint obtained above was applied to a polyester base film with a thickness of 12 mm. After coating to a thickness of 10 mm, it was dried and cured by heating at 500 mm. The magnetic recording material obtained above was tested in accordance with ASTM 1242-56 to measure the amount of wear.

The results were as shown in Table 1. Example 2 Maleic acid monomethyl ester monosodium salt 0.5 mol%
Except that a modified polyvinyl butyral resin with a degree of butyralization of 75.2 mol % obtained by butyralizing the contained modified polyvinyl alcohol with a degree of polymerization of 870 was used in place of the modified polyvinyl butyral resin of Example 1. A magnetic recording medium was manufactured in the same manner as in Example 1, and the same tests were conducted to obtain the results shown in Table 1.

Example 3 A magnetic recording medium was manufactured in the same manner as in Example 1, except that a polyurethane having an active isocyanate group (trade name: Desmodur L, manufactured by Badesh) was used as the polyurethane, and the same test was conducted. The results shown in the table were obtained.

Example 4 A modified polyvinyl acetal resin having a butyralization degree of 74.0 was obtained by butyralization of a modified polyvinyl alcohol having a polymerization degree of 870 containing 0.5 mol % of maleic acid monomethyl ester monosodium salt.
A magnetic recording body was produced in the same manner as in Example 1, except that 6 parts by weight of 9 mol% modified polypynylphthyral resin and 2 parts by weight of the polyurethane used in Example 3 were used as the polyurethane. , conducted a similar test and obtained the results shown in Table 1.

Comparative Example 1 Example except that polyvinyl butyral with a degree of butyralization of 74.8 mol % obtained by butyralizing polyvinyl alcohol with a degree of polymerization of 870 without any modification by a conventional method was used instead of the modified polyvinyl butyral resin. 1
A magnetic recording medium was manufactured in the same manner as above, and similar tests were conducted to obtain the results shown in Table 1.

Table 1

Claims (1)

[Scope of Claims] 1 Modification obtained by acetalizing modified polyvinyl alcohol containing an unsaturated dicarboxylic acid, an alkyl ester of the unsaturated dicarboxylic acid, or an alkali metal salt of the unsaturated dicarboxylic acid as a copolymerization component 1. A magnetic recording material comprising a mixture of a polyvinyl acetal resin, a polyurethane resin having an active isocyanate group in its molecule, and magnetic powder, which is coated on a substrate as a magnetic paint. 2. The content of the unsaturated dicarboxylic acid, the alkyl ester of the unsaturated dicarboxylic acid, or the alkali metal salt of the unsaturated dicarboxylic acid, which is a copolymerization component of the modified polyvinyl alcohol, is 0.1 to 3 mol%. The magnetic recording medium according to item 1. 3 Acetalization of modified polyvinyl altal resin is 6
The magnetic recording material according to claim 1, wherein the content is 0 to 78 mol%. 4. The magnetic recording body according to claim 1, wherein a modified polyvinyl butyral resin having a degree of butyralization of 60 to 78 mol % is used as the modified polyvinyl acetal resin. 5. The magnetic recording material according to claim 1, wherein the ratio of modified polyvinyl acetal resin to polyurethane resin is 8:2 to 4:6. 6. The magnetic recording body according to claim 1, wherein the magnetic powder is γ-Fe_2O_3 powder.