JPH04364222A - Magnetic recording medium and production thereof - Google Patents

Abstract

PURPOSE:To obtain a video tape having a tough magnetic layer less in drop out by scrape or scratch when travelling by making a magnetic layer tough for the reason that since free water is decreased by reaction of water in the magnetic coating material with organic acid anhydride to organic acid, urethane reaction of hydroxyl group of polyurethane resin with polyisocyanate is not obstructed by water adsorbed on a magnetic powder of a magnetic coating material or by water in a solvent. CONSTITUTION:In the magnetic recording medium made by applying the magnetic coating material obtained by dispersing a strong magnetic powder in a binder, the magnetic coating material contains an organic acid anhydride. Since adequate water adsorbed on the magnetic powder facilitates dispersion of the magnetic powder into the binder, addition and dispersion of the organic acid anhydride is executed after dispersion of the magnetic powder into the binder.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated magnetic recording medium used as a video tape, audio tape, computer tape, etc., and a method for manufacturing the same.

0002

BACKGROUND OF THE INVENTION Conventionally, coated magnetic recording media in which a magnetic layer in which ferromagnetic powder is dispersed in a binder is provided on a nonmagnetic support have been widely used as video tapes, audio tapes, and the like. In order to produce these coated magnetic recording media, fine particles of ferromagnetic powder are dispersed in a mixture of a conventionally known vinyl chloride copolymer or the like and a polyurethane resin having active hydrogen such as hydroxyl groups as a binder. After blending and dispersing various additives such as carbon black abrasives or lubricants as necessary, a polyisocyanate compound is blended as a hardening agent to prepare a magnetic paint, and this is applied to a non-magnetic support such as polyethylene. After being coated on a terephthalate film, oriented and dried, the surface is smoothed by thermal calendaring, and then thermally cured as required to obtain a magnetic layer.

0003

In recent years, in order to achieve higher density recording, that is, to improve electromagnetic conversion characteristics in the high frequency range, there has been a trend towards increasing the amount of fine particles of ferromagnetic powder. As a result, there is a substantial shortage of binder, the binding force between the magnetic powder and the binder weakens, and the magnetic layer tends to become fundamentally brittle. As a result, for example, in video tapes, the magnetic layer is scraped or scratched during running, resulting in dropouts. Under these circumstances, it is an object of the present invention to provide a magnetic recording medium having a strong magnetic layer that can effectively prevent the occurrence of dropouts caused by abrasion and scratches.

0004

[Means for Solving the Problems] In order to achieve this object, the present invention provides a magnetic recording medium coated with a magnetic paint in which ferromagnetic powder is dispersed in a binder. Construct by containing things. Since a suitable amount of water adsorbed on the magnetic powder facilitates the dispersion of the magnetic powder into the binder, the addition and dispersion of the organic acid anhydride is carried out after the magnetic powder is dispersed into the binder.

[0005]

[Function] According to the structure of the present invention, the water in the magnetic paint reacts with the organic acid anhydride to become an organic acid, and free water is reduced, so the water and solvent adsorbed to the magnetic powder in the magnetic paint are removed. The moisture contained therein does not inhibit the urethanization reaction between the hydroxyl groups of the polyurethane resin and the polyisocyanate, and as a result, the magnetic layer becomes tough and a videotape with fewer dropouts due to scratches or scratches during running can be obtained.

[0006]

EXAMPLES The present invention will be explained in detail below.

The organic acid anhydrides of the present invention include phthalic anhydride, hexahydrophthalic anhydride, methylnadic anhydride,
Examples include, but are not limited to, succinic anhydride, dodecynylsuccinic anhydride, maleic anhydride, and adipic anhydride. Also, the amount used is 0.5 to 0.5 to ferromagnetic powder.
10% by weight is suitable, more preferably 1 to 5% by weight. In addition, the binder used in the present invention includes vinyl chloride/vinyl acetate copolymer, vinyl chloride/vinyl acetate copolymer,
It may be vinyl acetate/maleic acid copolymer, vinyl chloride/vinylidene chloride copolymer, or even vinyl chloride/acrylonitrile copolymer, and at least one of these and
For example, mixtures of polyurethane resins having active hydrogen such as hydroxyl groups are used. A polyisocyanate is used as the curing agent, and a conventionally known trimethylolpropane (TMP) adduct of tolylene diisocyanate is commonly used, such as Coronate L manufactured by Nippon Polyurethane Kogyo Co., Ltd. Further, the ferromagnetic powder used in the present invention is not particularly limited, and may include ferromagnetic metal powder, γ-Fe2O3
, Fe3O4, Co-coated γ-Fe2O3, and barium ferrite powder. In the present invention, after the ferromagnetic powder is dispersed in a binder, an organic acid anhydride is added and further dispersed to form a magnetic coating. There is no problem in adding commonly used additives such as stearic acid, myristic acid, oleic acid, n-butyl stearate, butoxyethyl stearate, and α-Al2O3 and Cr02 as polishing agents. The obtained magnetic paint is applied onto a non-magnetic support, and the non-magnetic support used is generally a polyester film such as polyethylene terephthalate or polyethylene naphthalate, but is not limited to these. . Generally, after coating, orientation, and drying, a magnetic layer is formed by smoothing the surface and thermally curing by thermal calendaring, but a back coat layer may be provided on the opposite side of the support from the magnetic layer. It is provided for the purpose of running stability, and a binder with abrasives and carbon black dispersed therein is used.

By adding an organic acid anhydride to the magnetic coating material as in the present invention, it is possible to suppress the occurrence of dropouts in video tapes. This result (Table 1
).

[0009]

[Table 1]

According to Table 1, the magnetic layer to which an organic acid anhydride is added has no scratches or scratches on the magnetic layer during running of the video tape, and has fewer dropouts. This means that the moisture adsorbed to the magnetic powder in the magnetic paint and the moisture in the solvent generally inhibit the urethanization reaction between the hydroxyl groups of the polyurethane resin and the polyisocyanate, making the resulting magnetic layer brittle. When an organic acid anhydride is added to a magnetic paint as in the present invention, water in the magnetic paint reacts with the organic acid anhydride to become an organic acid, reducing free water and inhibiting the urethanization reaction. It becomes difficult to be treated. As a result, the magnetic layer becomes tougher, and it is believed that a videotape with fewer dropouts due to scratches or scratches during running can be obtained. In addition, since a suitable amount of water adsorbed on the magnetic powder facilitates the dispersion of the magnetic powder into the binder, the addition and dispersion of the organic acid anhydride should be carried out after the magnetic powder has been dispersed into the binder. is effective.

[0011] Specific examples will be shown and explained below. (Example 1) A magnetic paint was prepared with the following composition.

Ferromagnetic powder

100 parts by weight Vinyl chloride/vinyl acetate copolymer (average degree of polymerization 300) 10 parts by weight Polyurethane resin (weight average molecular weight 30,000)
10 parts by weight phthalic anhydride

1 part by weight Al
2O3

9 parts by weight carbon black

1 part by weight stearic acid

2 parts by weight myristic acid
1
Part by weight n-butyl stearate

1 part by weight Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) 4 parts by weight
solvent

235 parts by weight (MEK/toluene/cyclohexanone = 3/2/1, weight ratio) The ferromagnetic powder used in this example was surface-oxidized Fe powder, specific surface area: 56 m2 /g, coercive force: 1565×103/(4
π) A/m, saturation magnetization: 125 emu/g. First, 20 parts by weight of a solvent was added to ferromagnetic powder, and the mixture was wetted and crushed using a planetary mixer. To this, 10 parts by weight each of vinyl chloride/vinyl acetate copolymer and polyurethane resin were added and kneaded. Next, after adding 1 part by weight of phthalic anhydride, 9 parts by weight of α-Al2O3, 1 part by weight of carbon black, and 215 parts by weight of a solvent were blended and dispersed using a sand mill to prepare a magnetic paint stock solution. 2 parts by weight of stearic acid, 1 part by weight of myristic acid, and 1 part by weight of n-butyl stearate were added to the obtained magnetic paint stock solution.
A magnetic paint was prepared by stirring with a disper and adding 4 parts by weight of Coronate L. This magnetic paint is applied onto a 10 μm thick polyethylene terephthalate film using a gravure roll, and after orientation, drying, and heat calender surface smoothing, it is heat cured to form a magnetic layer, and a back coat layer is formed on the opposite side. After that, the film was slit into 1/2 inch width to create a videotape.

(Example 2) A videotape was prepared in the same manner as in (Example 1) except that 1 part by weight of phthalic anhydride in (Example 1) was changed to 2 parts by weight.

(Example 3) A videotape was prepared in the same manner as in (Example 1) except that 1 part by weight of phthalic anhydride in (Example 1) was changed to 1 part by weight of hexahydrophthalic anhydride.

(Example 4) 1 part by weight of hexahydrophthalic anhydride of (Example 3) was added to 2 parts by weight.
A videotape was prepared in the same manner as in Example 3 except that parts by weight were changed.

(Example 5) A videotape was prepared in the same manner as in (Example 1) except that 1 part by weight of phthalic anhydride in (Example 1) was changed to 1.0 part by weight of methylnadic anhydride.

(Example 6) 1 part by weight of phthalic anhydride of (Example 1) was mixed with 1 part by weight of succinic anhydride.
．． A videotape was produced in the same manner as in Example 1 except that the amount was changed to 0 parts by weight.

(Example 7) A videotape was prepared in the same manner as in (Example 1) except that 1 part by weight of phthalic anhydride in (Example 1) was replaced with 1.0 part by weight of dodecynylsuccinic anhydride.

(Example 8) A videotape was prepared in the same manner as in (Example 1) except that 1 part by weight of phthalic anhydride in (Example 1) was replaced with 1.0 part by weight of maleic anhydride.

(Example 9) A videotape was prepared in the same manner as in (Example 1) except that 1 part by weight of phthalic anhydride in (Example 1) was replaced with 1.0 part by weight of adipic anhydride.

Comparative Example 1 A videotape was prepared in the same manner as in Example 1 except that 1 part by weight of phthalic anhydride was not added.

The various characteristics of the videotape shown in Table 1 were evaluated in accordance with the following. (1) Curability: After curing the gloss coating in a drying oven at 60°C for 24 hours, absorbent cotton was soaked with MEK,
After rubbing the same area 100 times with a load of 100 g, the extent to which the coating film had melted was evaluated relative to each other. ○: Hardly soluble, △: Slightly soluble, ×: Completely soluble.

(2) Magnetic layer scraping and scratches: VTR, AU-6
50 (manufactured by Matsushita Electric Industrial Co., Ltd.) at 40℃, 85
After repeatedly running 200 times in an environment of %RH, the degree of scraping and scratches on the surface of the magnetic layer was observed using an optical microscope (×50). ○: None, △: Slightly present, ×: Much present (
3) Dropout: Using a dropout counter, measure 30 seconds per minute at 16dB for 15μ seconds.
Measurements were made for minutes, and the average value per minute was taken.

[0024]

[Effects of the Invention] As is clear from the description of the examples above, the magnetic recording medium obtained by adding the organic acid anhydride according to the present invention to the magnetic paint has a higher running performance than the conventional one. It is possible to realize an excellent magnetic recording medium in which the magnetic layer is free from scratches and scratches, and the occurrence of dropouts is significantly suppressed.

Claims (2)

[Claims] 1. A magnetic recording medium comprising a magnetic paint in which ferromagnetic powder is dispersed in a binder and coated on a non-magnetic support, characterized in that the magnetic paint contains an organic acid anhydride. magnetic recording medium. 2. A method for producing a magnetic recording medium, which comprises dispersing ferromagnetic powder in a binder and then applying a magnetic coating material containing an organic acid anhydride dispersed thereon to a non-magnetic support.