JP3152912B2 - Magnetic recording media - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic tape and a magnetic disk in which a magnetic layer containing a magnetic powder and a binder is formed on a non-magnetic support.

[Conventional technology]

2. Description of the Related Art In recent years, there has been a demand for further improving the recording density, electromagnetic conversion characteristics, durability, and the like of a magnetic recording medium such as a video tape with the improvement in performance of a recording / reproducing device.

To meet the above demands in a magnetic recording medium having a coating type magnetic layer, in terms of recording density and electromagnetic conversion characteristics, the packing density and orientation ratio of the magnetic powder in the magnetic layer are increased and the surface of the magnetic layer is smoothed. It is important to improve the properties, and from the viewpoint of durability, it is necessary to increase the coating strength of the magnetic layer. These properties are greatly affected by the type of binder used in the magnetic layer and the combination thereof.

Conventionally, as the above binder, a magnetic resin is used together with a cellulose resin such as nitrocellulose, which is considered to have good dispersibility, or a vinyl chloride copolymer such as a vinyl chloride-vinyl acetate-vinyl alcohol copolymer. A composition in which a polyurethane resin which is considered to give a good result on the durability of the layer is used in combination, and a polyisocyanate compound is further added as a cross-linking agent is most commonly employed.

Further, together with the binder and the magnetic powder in the magnetic paint used to form the magnetic layer, the packing density, orientation ratio,
Add a dispersant to improve surface smoothness, etc.
Abrasives have also been blended for the purpose of increasing the strength of the coating film.

[Problems to be solved by the invention]

However, when a combination of the above-mentioned conventional cellulose resin / polyurethane resin / polyisocyanate compound is employed as the binder, the packing density and the orientation ratio of the magnetic powder are insufficient, and the vinyl chloride copolymer The combination of the coalesced / polyurethane resin / polyisocyanate compound is difficult in terms of the surface smoothness of the magnetic layer and the strength of the coating film, and none of them can cope with the recent demand for higher performance of magnetic recording media. is there.

On the other hand, it is necessary to increase the amount of both the dispersant and the abrasive in order to achieve a sufficient effect. However, if the amount is large, the former causes a decrease in the durability of the magnetic recording medium, and the latter causes an electromagnetic wave. There is a problem that the conversion characteristics are deteriorated.

An object of the present invention is to provide a magnetic recording medium which has excellent electromagnetic conversion characteristics, can sufficiently cope with recent high-density recording, and has high durability.

[Means for solving the problem]

The present inventors have conducted intensive studies in order to achieve the above object, and as a result, as a binder, instead of a conventional general-purpose vinyl chloride copolymer such as a vinyl chloride-vinyl acetate-vinyl alcohol copolymer. When a specific quaternary copolymer is used, the dispersibility of the magnetic powder is remarkably improved, and a magnetic layer excellent in packing density, orientation ratio, and surface smoothness of the magnetic powder can be formed. The combined use of the coalescable, polyurethane resin and polyisocyanate compound greatly enhances the coating strength of the magnetic layer, and has high electromagnetic conversion characteristics and durability that can sufficiently respond to recent demands for high performance. Thus, the present inventors have found that a magnetic recording medium capable of achieving a high recording density can be obtained, and have accomplished the present invention.

That is, the present invention relates to a magnetic recording medium in which a magnetic layer containing a magnetic powder and a binder is formed on a nonmagnetic support, wherein the binder has a monomer composition of vinyl chloride 85 to 85.
90% by weight, 1 to 4% by weight of vinyl acetate, 8 to 12% by weight of hydroxypropyl acrylate, 0.1 to 0.5% by weight of maleic acid, a vinyl chloride-vinyl acetate-hydroxypropyl acrylate-maleic acid copolymer, polyurethane resin and poly Including an isocyanate compound as an essential component,
In addition, the present invention relates to a magnetic recording medium, wherein the polyurethane resin comprises 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 described above, the magnetic recording medium of the present invention, which is used as a binder of a magnetic powder together with a vinyl chloride-vinyl acetate-hydroxypropyl acrylate-maleic acid copolymer, a polyurethane resin and a polyisocyanate compound, can be used for conventional magnetic recording media. Electromagnetic conversion characteristics and durability are much higher than those of a magnetic recording medium using a vinyl chloride copolymer as a binder component. The reason is considered as follows.

That is, the above quaternary copolymer has a hydroxyl group contained therein derived from the monomer component hydroxypropyl acrylate, and is converted into a conventional general-purpose vinyl chloride copolymer such as a vinyl chloride-vinyl acetate-vinyl alcohol copolymer. Shows stronger activity than the contained hydroxyl group, and also contains a carboxyl group that is more hydrophilic than the hydroxyl group, so it shows a strong affinity for magnetic powder that has a generally hydrophilic surface in magnetic paint. It is assumed that the adsorption property to the body is improved to achieve a very high dispersion state, and the presence of the above-mentioned hydroxyl group and carboxyl group increases the crosslink density of the binder by the polyisocyanate compound in the magnetic coating film. .

For this reason, 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 high degree of dispersibility of the magnetic powder described above, thereby being excellent. As well as providing electromagnetic conversion characteristics, it is possible to increase the recording density, and the magnetic layer exhibits extremely tough and large abrasion resistance due to the high crosslink density and moderate elasticity based on polyurethane resin, resulting in excellent durability. It is considered to be effective.

The vinyl chloride-vinyl acetate-hydroxypropyl acrylate-maleic acid copolymer includes a random copolymer, a block copolymer and a graft copolymer, and various types having different monomer ratios are used. In particular, 85 to 90% by weight of vinyl chloride, 1 to 4% by weight of vinyl acetate, and 8 to 12% of hydroxypropyl acrylate.
Those having a composition range of 0.1% to 0.5% by weight of maleic acid are preferred. The average molecular weight is usually
It is good to be about 30,000 to 40,000.

As the polyurethane resin used in combination with the above quaternary copolymer, a general polyurethane resin comprising a polymer having a hydroxyl group only at both ends of the main chain (hereinafter, referred to as polyurethane resin A) is used instead of the polyurethane resin. A polyurethane resin (hereinafter, referred to as a polyurethane resin B) comprising a polymer having at least one of a hydroxyl group and a carboxyl group in addition to both ends (including a polymer having a hydroxyl group or a carboxyl group at both ends of the main chain) It is better to use

The polyurethane resin B is used in combination with the quaternary copolymer and the polyisocyanate compound,
It has been found that a magnetic recording medium having better electromagnetic conversion characteristics and durability can be obtained as compared with the case where a general polyurethane resin A is used.

This is because polymers containing hydroxyl groups or carboxyl groups at other than both ends of the main chain have higher affinity with magnetic powder in magnetic paint and higher crosslinkability than polymers containing only both ends of the main chain. From these facts, it is presumed that the polyurethane resin B improves the surface smoothness and the durability of the magnetic layer more because the polyurethane resin A has an improved adsorption action and a cross-linking rate to the magnetic powder in the magnetic paint than the polyurethane resin A. You.

Such a polyurethane resin B is, for example, when synthesizing a polyurethane from a polyester polyol and a polyisocyanate, a trihydric or higher valent as at least a part of a polyhydric alcohol or a polycarboxylic acid as a raw material of the polyester polyol. 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 the present invention, it is preferable that the average molecular weight of both the polyurethane resins A and B is usually in the range of 10,000 to 100,000.

In the present invention, the use ratio of the quaternary copolymer and the polyurethane resin is 65/35 to 35/35 by weight ratio of the former / the latter.
If the ratio is too low, the electromagnetic conversion characteristics and high-density recording performance of the magnetic recording medium will be insufficient, and if the ratio is too high, the magnetic recording medium will be mainly used. Satisfactory results cannot be obtained in terms of the durability of the medium.

In the present invention, examples of the polyisocyanate compound used in combination with such a quaternary copolymer and a polyurethane resin include low-molecular-weight monomers having two or more isocyanate groups in the molecule, dimers and trimers. In addition to the multimer, a reaction product of 3 moles of diisocyanate such as tolylene diisocyanate or hexamethylene diisocyanate and 1 mole of trimethylolpropane, or a polyfunctional isocyanate compound such as polyphenylmethane polyisocyanate is exemplified.

Commercial products of these polyisocyanate compounds include:
Nippon Polyurethane Co., Ltd. product name "Coronate L",
"Coronate HL", "Coronate 2030", "Millionate MR", "Millionate MTL", trade names of Sumitomo Bayer Urethane Co., Ltd. "Desmodur L", "Desmodur N", "Desmodur IL", "Desmodur H"
L ", trade name of Takeda Pharmaceutical Company Limited" Takenate D-10 "
2, "Takenate D-110N", "Takenate D-202"
and so on.

The amount of such a polyisocyanate compound used is set so that the isocyanate group is equivalent to or slightly larger than the hydroxyl group and the carboxysyl group in the quaternary copolymer and the polyurethane resin. I just need.

In the present invention, the above-mentioned 4 is used as a binder.
If necessary, other binder components may be added to the three components of the base copolymer, the polyurethane resin and the polyisocyanate compound.

In order to produce the magnetic recording medium of the present invention, according to a conventional method, a binder containing three components of the quaternary copolymer and the polyurethane resin and the polyisocyanate compound, and a magnetic paint containing a magnetic powder and an appropriate solvent are prepared. Prepare and apply this paint on a non-magnetic support such as polyester film, then orient it in a magnetic field and dry to form a magnetic layer, and perform surface treatment such as calendering to cut it into the required shape and size. I just need.

As the magnetic powder, any of those conventionally known as recording elements for magnetic recording media can be used. For example, γ-Fe ₂ O ₃ , Fe ₃ O ₄ , an intermediate oxide thereof, and Co-containing γ- Other than oxide magnetic powders such as Fe ₂ O ₃ and ac-containing iron oxide powders such as Co-containing Fe ₃ O ₄ , barium ferrite and hexagonal plate-like ferrite powders such as strontium ferrite,
Metal magnetic powders made of Fe, Co, Ni, alloys of these, or alloys containing these and other metals or small amounts of nonmetallic elements can also be used.

The magnetic paint may contain various additives commonly used, for example, dispersants, lubricants, abrasives, and antistatic agents.

〔The invention's effect〕

According to the present invention, since a specific vinyl chloride-based quaternary copolymer, a polyurethane resin and a polyisocyanate compound are used as components of the binder of the magnetic layer, the dispersibility of the magnetic powder becomes extremely good, Due to this, the filling density of the magnetic powder in the magnetic layer, the orientation ratio, the surface smoothness is significantly improved, and the crosslinking density of the binder is high and the elastic layer has a moderate elasticity, so that a tough magnetic layer is obtained. It is possible to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and high durability that can sufficiently cope with recent high-density recording.

In particular, in the present invention, the use of a polyurethane resin containing at least one of a hydroxyl group and a carboxyl group in addition to both ends of the main chain as the above polyurethane resin further improves the above electromagnetic conversion characteristics and durability. There is an advantage of doing so.

〔Example〕

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

In addition, the vinyl chloride copolymers V1 and V2, polyurethane resins A and B used in the following Examples, Reference Examples and Comparative Examples
The configurations of 1 to B3 are as follows.

<Vinyl chloride copolymer V1> Vinyl chloride-vinyl acetate-hydroxypropyl acrylate-maleic acid copolymer (weight ratio 86: 3.5: 10: 05, average molecular weight 35,000) <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 (Nipporan 2304, trade name, manufactured by Nippon Polyurethane Co., Ltd., average Molecular weight approx.
60,000) <Polyurethane resin B1> Polymer having hydroxyl groups at both ends of the main chain and having a carboxyl group at both ends (average molecular weight: about 40,000) <Polyurethane resin B2> Having hydroxyl groups at both ends of the main chain Polymer having a hydroxyl group in addition to both ends (average molecular weight: about 40,000) <Polyurethane resin B3> Polymer having a hydroxyl group at both ends of the main chain and having a hydroxyl group and a carboxyl group at both ends other than the both ends (average molecular weight: about 43,000) Examples 1 to 3 and Reference Example 1 The above components were mixed in an appropriate order, mixed and dispersed sufficiently with a disperser such as a high-speed day spa and a sand mill to form a coating material, and then filtered through a filter having an average pore diameter of 0.64 μm to prepare a magnetic coating material. This magnetic paint is applied on a 14 μm-thick polyester film so that the thickness after drying is about 4 μm, and the magnetic layer is formed by magnetic field orientation and drying, and further subjected to a calendering treatment. The video tape was cut into inch widths to produce four types of video tapes.

Comparative Examples 1 to 4 Four types of video tapes were prepared in the same manner as in Examples 1 to 3 and Reference Example 1 except that the same amount of the vinyl chloride-based copolymer V2 was used instead of the vinyl chloride-based copolymer V1. did.

For the video tapes of the above Examples, Reference Examples and Comparative Examples, the surface roughness of the magnetic layer, the residual speed density, the orientation ratio,
When the still characteristics were measured, the results shown in the table below were obtained. In addition, the measuring method of each item is as follows.

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

<Residual magnetic flux density, orientation ratio> Using a vibrating sample magnetometer (VSM-3 manufactured by Toei Kogyo Co., Ltd.), the measurement was performed at an applied magnetic field of 10 K Oersted.

<Still characteristics> 5 ° C, 40% RH using VHS video tape recorder
The video tape was reproduced in the still mode under the atmosphere described above, and the time required for the reproduction output signal level to drop by 3 dB from the initial value was measured.

From the results in the above table, the video tape of the present invention (Example 1)
Nos. To 3) have excellent surface smoothness and magnetic properties of the magnetic layer as compared with the conventional video tapes (Comparative Examples 1 to 4). It is evident that the coating strength of the layer is much higher and shows a high degree of durability.

In addition, in the video tapes of Examples 1 to 3, the use of 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 was particularly advantageous. It can be seen that the magnetic properties and durability are further improved as compared with a video tape using a general polymer having a hydroxyl group only at the chain end (Reference Example 1).

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-63-183906 (JP, A) JP-A-61-117729 (JP, A) JP-A-60-185226 (JP, A) JP-A-60-185 206876 (JP, A) JP-A-61-243934 (JP, A) JP-A-3-44821 (JP, A) JP-A-1-158619 (JP, A) Keiji Iwata "Polyurethane resin handbook" (Showa 62-9-25) Published by Nikkan Kogyo Shimbun p. 480-482 (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 5/702 C09D 5/23 C09D 127/04-127/08 C09D 175/00-175/16 CA (STN) REGISTRY (STN )

Claims (1)

(57) [Claims] 1. A magnetic recording medium comprising a magnetic layer containing a magnetic powder and a binder formed on a nonmagnetic support, wherein the binder has a monomer composition of 85 to 90% by weight of vinyl chloride, ４4% by weight, hydroxypropyl acrylate 8〜12% by weight, maleic acid 0.1〜0.5% by weight, a vinyl chloride-vinyl acetate-hydroxypropyl acrylate-maleic acid copolymer, a polyurethane resin and a polyisocyanate compound as essential components. A magnetic recording medium comprising the polyurethane resin, wherein the polyurethane resin comprises a polymer containing at least one of a hydroxyl group and a carboxyl group in addition to both ends of the main chain.