JPH0344820A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a medium having excellent electromagnetic conversion characteristics and high durability, suitable for high-density recording by using a specified four-component vinyl chloride copolymer, polyurethane resin and polyisocyanate compd. as the components of a binder in a magnetic layer. CONSTITUTION:By using a four-component copolymer comprising vinyl chloride- vinyl acetate-hydroxypropyl acrylate-maleic acid copolymer, dispersibility of the magnetic powder can be significantly improved and the obtd. magnetic layer is superior in packing density of the powder, orientation ratio and surface smoothness compared to a magnetic layer containing an all-purpose vinyl chlo ride copolymer conventionally used as a binder such as vinyl chloride-vinyl acetate-vinyl alcohol copolymer. This four component copolymer is used with polyurethane resin and a polyisocyanate compd. Thereby, the coating film strength of a magnetic layer is largely improved, and the obtd. medium has high electromagnetic conversion characteristics and durability which satisfy the requirement for high performances, and is suitable for high-density recording.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic recording medium such as a magnetic tape or a magnetic disk in which a magnetic layer containing magnetic powder and a binder is formed on a non-magnetic support.

[Conventional technology]

BACKGROUND ART In recent years, as recording and reproducing equipment has improved in performance, it has been desired to further improve the recording density, electromagnetic conversion characteristics, durability, etc. of magnetic recording media such as video tapes.

In order to meet the above requirements for magnetic recording media having a coating-type magnetic layer, in terms of recording density and electromagnetic conversion characteristics, it is necessary to increase the packing density and orientation ratio of the magnetic powder in the magnetic layer, as well as increase the magnetic layer's packing density and orientation ratio. It is important to improve the surface smoothness, and in terms of durability, it is necessary to increase the coating strength of the magnetic layer. These properties are largely influenced by the type and combination of binders used in the magnetic layer.

Conventionally, the above-mentioned binders include cellulose resins such as nitrocellulose, which are said to have good dispersibility for magnetic powder, and vinyl chloride copolymers such as vinyl chloride-vinyl acetate-vinyl alcohol copolymers, as well as magnetic materials. The most commonly used composition is a combination of a polyurethane resin, which is said to give good results for the durability of the layer, and a polyisocyanate compound added thereto as a crosslinking agent.

In addition, in addition to the above-mentioned binder and magnetic powder, dispersants are added to the magnetic paint used to form the magnetic layer to improve the packing density, orientation ratio, surface smoothness, etc., and to increase the strength of the coating film. It is also practiced to add abrasives for the purpose of

[Problem to be solved by the invention]

However, as a binder, the above conventional cellulose resin/
When a combination of polyurethane resin/polyisocyanate compound is used, the packing density and orientation ratio of the magnetic powder are insufficient, and when a combination of vinyl chloride copolymer/polyurethane resin/polyisocyanate compound is used, the magnetic layer is insufficient. There are problems in terms of surface smoothness and coating strength, and the current situation is that neither of these can meet the recent demands for higher performance of magnetic recording media.

On the other hand, it is necessary to increase the amount of both the dispersant and abrasive mentioned above in order to obtain sufficient effects, but if they are added in large amounts, the former will cause a decrease in the durability of the magnetic recording medium, and the latter will cause an electromagnetic There was a problem in that the conversion characteristics deteriorated.

In light of the above-mentioned circumstances, it is an object of the present invention to provide a magnetic recording medium that has excellent electromagnetic conversion characteristics, can fully cope with the recent increase in high-density recording, and also has a high degree of durability.

[Means to solve the problem]

As a result of extensive studies to achieve the above object, the inventors discovered that they could use vinyl chloride-based copolymers such as vinyl chloride-vinyl acetate-vinyl alcohol copolymers as a binder instead of conventionally used vinyl chloride-based copolymers. When a specific quaternary copolymer is used, the dispersibility of the magnetic powder is significantly improved, and a magnetic layer with excellent packing density, orientation ratio, and surface smoothness of the magnetic powder can be formed. By combining the combination of polyurethane resin and polyisocyanate compound, the coating strength of the magnetic layer is greatly improved, resulting in high electromagnetic conversion characteristics and durability that can fully meet recent demands for higher performance. It was discovered that a magnetic recording medium capable of achieving high recording density can be obtained, and this invention was completed.

That is, the present invention provides a magnetic recording medium in which a magnetic layer containing magnetic powder and a binder is formed on a non-magnetic support, in which the binder is a vinyl chloride-vinyl acetate-hydroxypropyl acrylate-maleic acid copolymer. The present invention relates to a magnetic recording medium characterized by containing a polyurethane resin, a polyisocyanate compound, and a polyisocyanate compound as essential components.

Further, in the present invention, a preferred embodiment is such that the polyurethane resin is made of a polymer containing at least one of a hydroxyl group and a carboxyl group in addition to both ends of the main chain.

[Structure and operation of the invention]

As mentioned above, the magnetic recording medium of the present invention is made of vinyl chloride.
By using a vinyl acetate-hydroxypropyl acrylate-maleic acid copolymer together with a polyurethane resin and a polyisocyanate compound as a binder for magnetic powder, a magnetic recording medium using a conventional general-purpose vinyl chloride copolymer as a binder component can be created. The reason for this is thought to be as follows.

In other words, the hydroxyl groups contained in the above-mentioned quaternary copolymer are derived from the monomer component hydroxypropyl acrylate and are not included in conventional general-purpose vinyl chloride-based copolymers such as vinyl chloride-vinyl acetate vinyl alcohol copolymer. It exhibits stronger activity than the hydroxyl group that is present in the world, and also contains a carboxyl group that is more hydrophilic than the hydroxyl group.
In magnetic coatings, it generally exhibits a strong affinity for magnetic powders that have a hydrophilic surface, improves adsorption characteristics to magnetic materials, and achieves an extremely high degree of dispersion. It is assumed that the crosslinking density of the binder by the polyisocyanate compound is increased in the membrane.

Therefore, in the magnetic recording medium of the present invention, the packing density, orientation ratio, surface smoothness, etc. of the magnetic powder in the magnetic layer are significantly improved based on the above-mentioned high dispersibility of the magnetic powder, resulting in excellent electromagnetic properties. In addition to providing conversion characteristics, it also enables high recording density, and the magnetic layer has a high crosslinking density and moderate elasticity based on polyurethane resin, making it extremely tough and highly abrasion resistant, resulting in excellent durability. It is considered that

The above-mentioned vinyl chloride-vinyl acetate-hydroxypropyl acrylate-maleic acid copolymer includes not only random copolymers but also block copolymers and graft copolymers, as well as various copolymers with different monomer ratios. However, especially vinyl chloride 85-90% by weight, vinyl acetate 1-4% by weight, hydroxypropyl acrylate 8-8% by weight.
Preferably, the composition range is 12% by weight and 0.1 to 0.5% by weight of maleic acid. As for the molecular weight, it is preferable that the average molecular weight is usually about 30,000 to 40,000.

The polyurethane resin used in combination with the above-mentioned quaternary copolymer may be a general polyurethane resin (hereinafter referred to as polyurethane resin A) consisting of a polymer having hydroxyl groups only at both ends of the main chain, but it is more preferable. is a polyurethane resin (hereinafter referred to as polyurethane resin) consisting of a polymer containing at least one of a hydroxyl group or a carboxyl group in addition to both ends of the main chain (including those having a hydroxyl group or a carboxyl group at both ends of the main chain). It is better to use B).

By using the above polyurethane resin B together with the above quaternary copolymer and polyisocyanate compound, -
It has been found that a magnetic recording medium that is superior in both electromagnetic characteristics and durability can be obtained when compared to the case where polyurethane resin A is used.

This is because polymers that contain hydroxyl groups and carboxyl groups in areas other than both ends of the main chain have a greater affinity with the magnetic powder in magnetic paints than polymers that contain them only at both ends of the main chain, and have higher crosslinking properties. Therefore, it is presumed that polyurethane resin B has a better adsorption effect and crosslinking rate for magnetic powder in magnetic paint than polyurethane resin A, so that the surface smoothness and durability of the magnetic layer are further improved. Ru.

Such polyurethane resin B is used, for example, when synthesizing polyurethane from polyester polyol and polyisocyanate. It can be produced by a method such as using a polyol obtained using a compound.

Regarding the molecular weight of the polyurethane resin used in this invention, the average molecular weight of both the above-mentioned polyurethane resins A and B is usually 10,000 to ioo, oo.

It is preferable that it is in the range of .

In this invention, the proportion of the quaternary copolymer and polyurethane resin used is from 65/35 to 65/35 by weight of the former/latter.
It is best to set the ratio to be about 35/65; if the former ratio is too low, the magnetic recording medium will be insufficient mainly in terms of electromagnetic conversion characteristics and high-density recording performance, while if the ratio is too high, It becomes difficult to obtain satisfactory results in terms of the durability of the magnetic recording medium.

In this invention, the polyisocyanate compounds used in combination with such quaternary copolymers and polyurethane resins include low molecular weight monomers, dimers, and trimers having two or more isocyanate groups in the molecule. In addition to polymers, examples include a reaction product of 3 moles of diisocyanate such as tolylene diisocyanate and hexamethylene diisocyanate and 1 mole of trimethylolpropane, and polyfunctional isocyanate compounds such as polyphenylmethane polyisocyanate.

Commercially available products of these polyisocyanate compounds include Nippon Polyurethane's product names "Coronate LJ, rCoronate HL, I,""Coronate2030,""CryonateMRJ,""MillionateMTL," and Sumitomo Bayer Urethane products. Names: "Desmodule L", "Desmodule N", "Desmodule ILJ", "Desmodule HLJ", Narita Pharmaceutical Co., Ltd.'s product name "Takenate D-1"
02", "Takenate D-11ONJ", "Takenate D
202" etc.

The amount of such a polyisocyanate compound to be used is set so that the isoneanate group is equivalent to the hydroxyl group and carboxyl group in the above-mentioned quaternary copolymer and polyurethane resin, or slightly more than this. good.

In addition, in this invention, other binder components may be added as a binder to the three components of the above-mentioned quaternary copolymer, polyurethane resin, and polyisocyanate compound, if necessary.

To manufacture the magnetic recording medium of this invention, according to a conventional method,
A magnetic paint containing a binder containing the above-mentioned quaternary copolymer, a binder containing the three components of a polyurethane resin, and a polyisocyanate compound, magnetic powder, and an appropriate solvent is prepared, and this paint is applied onto a non-magnetic support such as a polyester film. Thereafter, a magnetic layer is formed by magnetic field orientation and drying, followed by surface treatment such as calendering and cutting into a desired shape and size.

As the magnetic powder, any of those conventionally known as recording elements for magnetic recording media can be used, such as γF ez 03 , Fe304, intermediate oxides thereof, Co-containing TFezOz, Co-containing Fe3O4, etc. In addition to acicular iron oxide powder, barium ferrite, hexagonal plate-shaped ferrite powder such as strontium ferrite, and other oxide-based magnetic powders, Fe, Co, Ni, alloys of these, other metals, or small amounts of non-metals. Metal magnetic powders made of alloys containing elements can also be used.

In addition, various commonly used additives such as dispersants, lubricants, abrasives, antistatic agents, etc. may be appropriately blended into the above-mentioned magnetic paint.

〔Effect of the invention〕

According to this invention, since the binder structure of the magnetic layer uses a specific vinyl chloride quaternary copolymer, polyurethane resin, and polyisocyanate compound as the RFC component,
The dispersibility of the magnetic powder is extremely good, and as a result, the packing density, orientation ratio, and surface smoothness of the magnetic powder in the magnetic layer are significantly improved, and the crosslinking density of the binder is high and the elasticity is moderate. Since the magnetic layer becomes strong and strong, it is possible to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and a high degree of durability that can fully cope with the recent trend towards high-density recording.

In addition, in this invention, if the above-mentioned polyurethane resin is configured to contain at least one of a hydroxyl group and a carboxyl group in addition to both ends of the main chain, the above-mentioned electromagnetic conversion characteristics and durability can be improved. There is an advantage of further improvement.

〔Example〕

Next, examples of the present invention will be specifically described in comparison with comparative examples. In addition, parts in the following are parts by weight and %.
% means weight %.

Furthermore, vinyl chloride copolymers Vl, V2, polyurethane resins A, B1 used in the following examples and comparative examples
The configuration of -83 is as follows.

<Vinyl chloride copolymer Vl> Vinyl chloride-vinyl acetate-hydroxypropyl acrylate-maleic acid copolymer (weight ratio 86:3.5:10
:0.5, average molecular M35゜000) Vinyl chloride copolymer v2> Vinyl chloride-vinyl acetate-vinyl alcohol copolymer (
(Weight ratio 90:4:6, average molecular weight 33,000) <Polyurethane resin A> Polymer having hydroxyl groups only at both ends of the main chain (trade name 2° Tuboran 2304, manufactured by Nippon Polyurethane Co., Ltd., average molecular weight approximately 60,000) <Polyurethane resin Bl> Polymer having hydroxyl groups at both ends of the main chain and carboxyl groups at other ends (average molecular weight approximately 40,000
) <Polyurethane resin B2> A polymer that has hydroxyl groups at both ends of the main chain and also has hydroxyl groups in addition to both ends (average molecular weight approximately 40,000) <Polyurethane resin B3> A polymer that has hydroxyl groups at both ends of the main chain Examples 1 to 4 Zinc stearate 0.5 parts Myristic acid 2 parts N-butyl stearate 1 part Cyclohexanone 96 parts Toluene 96 parts The above components were blended in an appropriate order, thoroughly mixed and dispersed using a dispersion machine such as a high-speed dispersion machine or a sand mill to form a paint, and then filtered through a filter with an average pore size of 0.6 μm to prepare a magnetic paint. . This magnetic paint was applied onto a polyester film with a thickness of 14 μm so that the thickness after drying was approximately 4 μm, magnetically oriented and dried to form a magnetic layer, and then calendered.
Four types of video tapes were prepared by cutting each section into 2-inch width pieces.

Comparative Examples 1 to 4 Four types of videotapes were produced in the same manner as Examples 1 to 4, except that the same amount of vinyl chloride copolymer V2 was used in place of vinyl chloride copolymer 1.

Regarding each videotape of the above examples and comparative examples,
The surface roughness, residual magnetic flux density, orientation ratio, and still characteristics of the magnetic layer were measured, and the results shown in the table below were obtained. The measurement method for each item is as follows.

<Surface Roughness> The center line average roughness (Ra value) of the surface of the magnetic layer was measured using a stylus type surface roughness meter.

Residual magnetic flux density, orientation ratio> Measurement was performed using a vibrating sample magnetometer (VSM-3 manufactured by Toei Kogyo Co., Ltd.) at an applied magnetic field of 10 oersted.

Still characteristics> V) (Using an S72 video tape recorder, 5'C,
A videotape was played back in still mode in an atmosphere of 40% RH, and the time until the playback output signal level decreased by 3 dB from the initial value was measured.

From the results in the table above, it can be seen that the videotape of this invention (actual male side 1 to 4) is better than the conventional videotape (comparative examples 1 to 4).
Compared to the magnetic layer, the surface smoothness and magnetic properties are better, so based on this, excellent electromagnetic conversion characteristics can be obtained, and the coating film strength of the magnetic layer is much greater and exhibits a high degree of durability. is clear.

In addition, in this invention, in video tapes (Examples 1 to 3) using a polymer having at least one of a hydroxyl group and a carboxyl group in addition to both ends of the main chain as the polyurethane resin, the polyurethane resin It can be seen that the magnetic properties and durability are further improved than the videotape using a general polymer having hydroxyl groups only at the end of the main chain (Example 4).

Claims (2)

[Claims] (1) In a magnetic recording medium in which a magnetic layer containing magnetic powder and a binder is formed on a non-magnetic support, the binder is composed of vinyl chloride-vinyl acetate-hydroxypropyl acrylate-maleic acid copolymer and polyurethane. A magnetic recording medium characterized by containing a resin and a polyisocyanate compound as essential components. (2) The magnetic recording medium according to (1), wherein the polyurethane resin is made of a polymer containing at least one of a hydroxyl group and a carboxyl group in addition to both ends of the main chain.