JPH04241220A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve dispersion property of a magnetic powder and electric characteristics and durability by using a polyurethane resin having sulfobetaine as a binder component of a magnetic layer, and further to improve durability by using vinyl chloride resin as well and polyalkyleneoxidorine ester. CONSTITUTION:The magnetic recording medium has a magnetic layer containing a polyurethane resin having sulfobetaine as a binder component. Also the magnetic recording medium of this invention contains vinyl chloride resin as well and polyalkyleneoxazoline ester as a binder component.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to magnetic recording media.
More specifically, the present invention relates to a magnetic recording medium having good dispersibility of magnetic powder and excellent electrical properties and durability.

0002

2. Description of the Related Art Magnetic recording media are usually made by applying a magnetic paint consisting of magnetic powder, a binder component, an organic solvent and other necessary components onto a substrate such as a polyester film and drying the coating. As the binder component used in this case, it is desired that the binder component has excellent dispersibility of the magnetic powder, can impart excellent electrical properties to the magnetic recording medium, and has excellent durability.

For this reason, polyurethane resins have traditionally been widely used as binder components with excellent properties. Furthermore, in order to improve the dispersibility of magnetic powder, carboxyl groups and sulfone groups are added to the main chain of polyurethane resins. acid group,
Polar groups such as phosphate groups or salts thereof have been introduced. (JP-A-55-38693, JP-A-57-92422, JP-A-59-30235)

0
004]

[Problems to be Solved by the Invention] However, when these polar groups are introduced into the main chain of polyurethane resin, it is not possible to increase the molecular weight of the polyurethane resin, and it also reacts with curing agents such as isocyanate compounds. As a result, the mechanical strength of the magnetic layer decreases and the durability is impaired.

[0005]

[Means for Solving the Problems] This invention was made as a result of various studies in view of the current situation, and aims to improve the dispersibility of magnetic powder by using a polyurethane resin containing sulfobetaine as a binder component. It has been sufficiently improved in electrical characteristics and durability.

[0006] Furthermore, by using vinyl chloride resin as a binder component, the electrical characteristics and durability are further improved, and by using polyalkylene oxide phosphate ester in combination, the durability is further improved. This is what I did.

In the present invention, the polyurethane resin containing sulfobetaine used as a binder component has excellent affinity with magnetic powder because sulfobetaine is not a simple polar group but a zwitterionic group. In addition, it can be made to have a high molecular weight, and the reaction with curing agents such as isocyanate compounds is not inhibited.In fact, since it has a functional group similar to a tertiary amine, the reaction with isocyanate compounds is accelerated. Ru. Therefore, when polyurethane resin containing sulfobetaine is used as a binder component, the dispersibility of magnetic powder is sufficiently improved, the electrical properties are improved, and a strong magnetic layer is formed, further improving durability. be done.

[0008] Such a polyurethane resin having sulfobetaine is produced by producing a polyurethane resin having tertiary nitrogen such as a tertiary amine, and combining this polyurethane resin having tertiary nitrogen with cyclopropane sultone, 1,3- It is obtained by reacting with sultones such as propane sultone and 1,4-butane sultone.

[0009] In the polyurethane resin containing sulfobetaine thus obtained, sulfobetaine may be present at any of the terminal, main chain, or side chain of the molecule. In addition, the content of sulfobetaine in polyurethane resin is
If it is less than 0.005 mmol/g, the desired effect cannot be obtained, and if it is more than 0.1 mmol/g, it may aggregate, so it is recommended to keep it within the range of 0.005 to 0.1 mmol/g. Preferably 0.01 to 0.05 mmol/
It is more preferable to keep it within the range of g. Furthermore, polyurethane resins containing sulfobetaine have poor mechanical properties when the number average molecular weight is less than 8,000;
If it is larger than 0, the solubility will be poor and the dispersibility will be poor, so those with a number average molecular weight of 8,000 to 100,000 are preferably used, and those with a number average molecular weight of 10,000 to 50,000 are more preferably used.

When such a polyurethane resin containing sulfobetaine is used in combination with a vinyl chloride resin, it has good mutual compatibility, and the vinyl chloride resin further improves the dispersibility of the magnetic powder and improves its mechanical strength. is strengthened, further improving electrical properties and durability.

Examples of such vinyl chloride resins include vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, and vinyl chloride-vinyl acetate-maleic acid copolymer. Polymers and the like are preferably used, and examples of commercially available products include those available in the United States. C. Manufactured by C company; VAGH, VYHH, VM
CH, manufactured by Sekisui Chemical Co., Ltd.; S-LEC A; manufactured by Denki Kagaku Co., Ltd.; 1000G, and the like.

[0012] It is also used in combination with an isocyanate compound with good compatibility, and when used in combination with this isocyanate compound,
Since it has sulfobetaine, which is a functional group similar to a tertiary amine, the reaction with an isocyanate compound is accelerated, the degree of crosslinking is improved, and the durability is further improved.

As such isocyanate compounds, trifunctional low molecular weight isocyanate compounds are preferably used, and specific examples of commercially available products include, for example, Coronate, manufactured by Nippon Polyurethane Industries, Ltd. L, manufactured by Bayer; Desmodule L, etc. can be mentioned.

Furthermore, it can be used in combination with polyalkylene oxide phosphate ester with good compatibility, and when used in combination with polyalkylene oxide phosphate ester, the effect of polyalkylene oxide phosphate ester, which has excellent dispersibility of magnetic powder, is exhibited. As a result, the dispersibility of the magnetic powder is further improved, and the electrical properties are further improved.

As such a polyalkylene oxide phosphate ester, for example, a commercially available product such as Garfac RE-610 manufactured by Toho Chemical Industry Co., Ltd. is preferably used.

[0016] The magnetic recording medium of the present invention may be manufactured according to a conventional method, for example, the above-mentioned polyurethane resin containing sulfobetaine may or may not be used in combination with another vinyl chloride resin and a dispersant. A magnetic paint is prepared by mixing and dispersing magnetic powder, an organic solvent, and other additives, and this magnetic paint is applied onto a substrate such as a polyester film by any method such as spraying or roll coating. , just dry it.

[0017] Examples of the magnetic powder used here include γ-Fe2O3 powder, Fe3O4 powder,
Iron oxide powder in intermediate oxidation state between γ-Fe2 O3 and Fe3 O4, Co-containing γ-Fe2 O3 powder, Co
In addition to containing Fe3O4 powder and CrO2 powder, various conventionally known magnetic powders such as metal powders such as Fe powder, Co powder, and Fe-Ni-Cr alloy powder, barium ferrite powder, and nitride-based magnetic powder such as iron nitride can be used. Broadly encompassing.

[0018] As the organic solvent, those commonly used in magnetic recording media, such as methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dioxane, and dimethyl formamide, can be used alone or in combination of two or more. be done.

It should be noted that various commonly used additives such as lubricants, abrasives, antistatic agents, dispersants, etc. may be optionally added to the magnetic paint.

[0020]

[Example] Next, an example of the present invention will be described. Example 1 1,4-butanediol

5 parts by weight Poly 1,6-hexane carbonate diol
100 Triethanolamine
0.5 〃
4,4'-diphenylmethane diisocyanate
10〃
tin octylate

0.01 Tetrahydrofuran

400 Toluene

400 This composition was reacted at 40° C. for 6 hours in a nitrogen atmosphere to obtain a polyurethane resin having tertiary nitrogen.

Next, using the polyurethane resin containing tertiary nitrogen obtained in this way, the polyurethane resin containing tertiary nitrogen is prepared.
100
Part by weight cyclopropane sultone

0.2 Tetrahydrofuran

A polyurethane resin containing sulfobetaine was obtained by reacting the 300 〃 composition at 40°C for 6 hours. The polyurethane resin containing sulfobetaine thus obtained had a number average molecular weight of 40,000 and a sulfobetaine content of 0.03 mmol/g.

Using the thus obtained polyurethane resin containing sulfobetaine, Co-containing γ-Fe2 O3 powder was prepared.

80 parts by weight Polyurethane resin containing sulfobetaine
18 〃 Carbon black

1 Alumina

2 〃 Palmitic acid

1.5 〃
liquid paraffin

0.5 〃 Methyl ethyl ketone

100 〃 Cyclohexanone
100
〃 Toluene

After mixing and dispersing the composition of 100 in a sand mill for 10 hours, 2 parts by weight of Coronate L (manufactured by Nippon Polyurethane Industries, Ltd.; trifunctional low molecular weight isocyanate compound) was further added and mixed for 0.2 hours. A magnetic paint was prepared by dispersing it. This magnetic paint is applied onto a polyester film with a thickness of 7 μm to a dry thickness of 4 μm, dried to form a magnetic layer, calendered, cut into a predetermined width, and made into magnetic tape. I made it.

Example 2 In the composition of the magnetic paint in Example 1, the amount of the polyurethane resin containing sulfobetaine used was changed from 18 parts by weight to 8 parts by weight, and VAGH (manufactured by U.C.C.; A magnetic tape was prepared in the same manner as in Example 1, except that 10 parts by weight of vinyl-vinyl acetate-vinyl alcohol copolymer) was added.

Example 3 The composition of the magnetic paint in Example 2 was the same as that of Example 2 except that 1.5 parts by weight of Garfac RE610 (manufactured by Toho Chemical Industries, Ltd.; polyalkylene oxide phosphate ester) was newly added. Magnetic tape was made in the same manner.

Comparative Example 1 In the composition of the magnetic paint in Example 1, Nipporan 23 was used instead of the polyurethane resin containing sulfobetaine.
A magnetic tape was produced in the same manner as in Example 1, except that the same amount of 01 (manufactured by Nippon Polyurethane Kogyo Co., Ltd.; urethane elastomer) was used.

Comparative Example 2 In the composition of the magnetic paint in Example 1, UR8300 (
A magnetic tape was produced in the same manner as in Example 1, except that the same amount of polyurethane resin containing sodium sulfonate (manufactured by Toyobo Co., Ltd.) was used.

Comparative Example 3 In the composition of the magnetic paint in Example 2, UR8300 (
A magnetic tape was prepared in the same manner as in Example 2, except that the same amount of polyurethane resin containing sodium sulfonate (manufactured by Toyobo Co., Ltd.) was used.

[0028] The magnetic tape obtained in each example and comparative example
The residual magnetic flux density and square shape of the disc were measured, and relative sensitivity, durability, and magnetic head contamination were investigated. Relative sensitivity measures output at a frequency of 315Hz, durability is 25
℃ and 60% relative humidity, the number of runs until the output fluctuation became 2 dB was measured. Also, the magnetic head dirt is 10
The sliding contact surface of the head during the 0th run was visually observed to determine whether there was any dirt on the magnetic head. Table 1 below shows the results.

[0029]

[0030]

[Effect of the invention] As is clear from Table 1 above, Example 1
Compared to the magnetic tapes obtained in Comparative Examples 1 to 3, the magnetic tapes obtained in Comparative Examples 1 to 3 all have higher residual magnetic flux density, square shape, and relative sensitivity, are more durable, and have better magnetic properties. There was no head contamination, which indicates that the magnetic recording medium obtained by the present invention has good dispersibility of magnetic powder, excellent electromagnetic conversion characteristics, and further improved durability.

Claims (2)

[Claims] [Claim 1] A magnetic recording medium having a magnetic layer containing a polyurethane resin having sulfobetaine as a binder component. 2. The magnetic recording medium according to claim 1, further comprising a vinyl chloride resin as a binder component. 3. The magnetic recording medium according to claim 1, further comprising a polyalkylene oxide phosphate ester in the magnetic layer. Magnetic recording medium according to 1 and 2