JPS58117263A - Production of magnetic paint - Google Patents

Abstract

PURPOSE:To produce a magnetic paint having improved dispersibility, by kneading a nitrile rubber with a kneaded material composed of a polyurethane resin and a ferromagneic metallic iron or its alloy to disperse them in each other. CONSTITUTION:A polyurethane resin is kneaded with the powder of a ferromagnetic metallic iron or its alloy to disperse them in each other. This kneaded material and a nitrile rubber are kneaded to disperse them in each other, thereby obtaining a magnetic paint. Pref. polyurethane resins are those having a softening temp. of 150 deg.C or lower, an average MW of 10,000-200,000 and the degree of polymn. of 200-2,000. Examples of nitrile rubbers are polymers contg. acrylonitrile unit in the molecule and having an average MW of 10,000-150,000 and the degree of polymn. of 100-1000, such as a butadiene/acrylonitrile copolymer and an acrylate ester/acrylonitrile copolymer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a magnetic paint that is effective for manufacturing magnetic recording media such as magnetic tapes and magnetic disks, and aims to improve the method for dispersing magnetic paint. That is.

Many binders for magnetic recording media have been proposed in the past, but as the demand for high-density recording media increases, magnetic powders become finer particles, and the magnetic powders used also shift from iron oxide to metallic iron or alloys. However, the dispersibility of magnetic paint has come to have a great influence on the characteristics of the recording medium in which it is used.

The inventor studied the dispersibility of ferromagnetic metallic iron or alloy powder, and recognized that a system containing polyurethane resin and nitrile rubber as the main binders had excellent dispersibility.
This is what led to the discovery of the present invention. That is, in the present invention, when making polyurethane, after first dispersing the polyurethane resin and magnetic powder (hereinafter referred to as -order dispersion),
This is based on the discovery that the method of dispersing nitrile rubber (hereinafter referred to as 5-secondary dispersion) has excellent dispersibility, and conventional methods for dispersing magnetic powder have clearly been based on force, The degree of dispersion was evaluated by measuring the squareness ratio and orientation ratio of the magnetic tape.

The polyurethane resin used in the present invention has a softening temperature of 160°C or less and an average molecular weight of 10.000 to 20.
0,000. The degree of polymerization is about 200-2. OOOfMF may be used. Specifically, Niraporan 3113°5032 (Jd High Quality product name etc. manufactured by Nippon Polyurethane Co., Ltd.) can be used singly or as a mixture. Also, -='
) En-acrylonitrile copolymer, butadiene-acrylonitrile-styrene copolymer, acrylic acid ester-acrylonitrile copolymer, etc. are used as the lyl rubber. Specifically, Squid-14 manufactured by Nippon Zeon Co., Ltd.
32J (product name) is suitable.

Various types of crosstalk machines are used to disperse magnetic paint crosstalk. For example, three-roll mill, ball mill, pebble mill, sand grinder, high-speed roller/flatter disperser, high-speed stone mill, high-speed impact mill, disperser, kneader.
1. A high-speed mixer, homogenizer, ultrasonic disperser, etc. are used alone or in combination.

In the present invention, the term "main binder" means that the binder contains polyurethane resin and nitrile rubber with a content of 70 to 100%.
96 occupies. In addition, polyester resins, phenoxy resins, polyvinyl butyral resins, etc. can be mixed with nitrile rubber as plasticizers or reinforcing agents to achieve secondary dispersion δ.
It is also possible to do so. As magnetic powder, metal iron, Fe-Co, Fe-Ni, Go-N
i, Fe-Co-Ni.

Various alloy powders such as Fe-Co-B and Fe-Go-Cr-B are used.

Examples and comparative examples of the present invention will be described below.

(Example) Ferromagnetic metal iron powder dispersant 3 parts polyurethane resin 10 parts by weight Silicone oil Q5 MEK-) Luene-cyclohexanone 300 parts The above composition was mixed and dispersed in a ball mill for 24 hours to obtain a primary dispersion.

Next, 10 parts by weight of nitrile rubber was added to this mixture,
The mixture was mixed and dispersed again using a ball mill for 24 hours to complete the secondary dispersion. Coronet) L (polyisocyanate manufactured by Nippon Polyurethane Co., Ltd., trade name) was added to the obtained magnetic paint as a curing agent.
After adding and mixing, a magnetic tape with a film thickness of 3 μm was obtained through the following steps: coating, orientation, drying, and calendering.

(Comparative Example 1) In the example, nitrile rubber was used as the -order dispersion,
A magnetic tape was obtained in the same manner using polyurethane resin as the secondary dispersion.

(Comparative Example 2) A magnetic tape was obtained in the same manner as in Example except that the same polyurethane resin and nitrile rubber were mixed and dispersed in a ball mill for 48 hours.

The squareness ratio and orientation ratio of each of the magnetic tapes obtained in Examples and Comparative Examples 1 and 2 were measured and the results are shown in the following table.

In the table.

(a) The squareness ratio (Br/Bm) is expressed as the ratio of the residual magnetic flux density Br to the maximum magnetic flux density [Bm] when the obtained magnetic tape is measured in an external magnetic field of 500006.
A VSM-Ill model manufactured by Toei Kogyo Co., Ltd. was used as the measuring device.

The larger this value is, the better the dispersion is.

(b) Orientation ratio (Br'/Br) is the residual magnetic flux density Br' when an external magnetic field is applied perpendicular to the orientation direction of the obtained magnetic layer, and the residual magnetic flux density when an external magnetic field is applied parallel to it. FB
, r. The smaller this value, the better the dispersion.O As is clear from the above explanation and table, the magnetic paint obtained by the method of the present invention has excellent dispersibility, and as a result, The magnetic recording medium produced using
The squareness ratio and orientation are improved compared to conventional products.

In the above embodiments, the case where metallic iron was used as the magnetic powder was explained, but it goes without saying that the same effect can be obtained when using 1-alloy powder.

Claims (1)

[Claims] When producing a magnetic paint used as an agent, after cross-dispersing the polyurethane resin and the ferromagnetic metal iron or alloy powder, adding the above-mentioned 2) IJ rubber to this kneaded mixture and cross-dispersing again. Features: A manufacturing method for magnetic paint.