JPS6233329A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the dispersibility of magnetic powder by contg. the polyurethane having the specified polyol number in a magnetic layer. CONSTITUTION:The polyurethane of which the number average mol.wt. of the polyol constituting the polyurethane is about 1,000-25,000 is incorporated as a binder into the magnetic layer. The electromagnetic conversion characteristic and magnetic characteristic are deteriorated if the number average mol.wt. of the polyol is exessively small like 800. The dispersibility of the magnetic powder is poor if the number average mol.wt. of the polyol is as large as 3,000. Since the dispersibility of the magnetic powder in the magnetic powder in the magnetic coating compd. is thereby improved, the dispersion operation is smoothly executed, the cost is reduced and further the electromagnetic conversion characteristic and magnetic characteristics such as Y-S/N and squareness ratio are improved. Wear resistance, etc. are improved as well.

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 for use in video, audio, computers, etc., for example.

[Prior art and its problems]

BACKGROUND ART Binders used in coated magnetic recording media have conventionally been required to have good abrasion resistance, adhesion, surface smoothness, and dispersibility of magnetic powder.

From this point of view, polyurethane is widely used as a binder. That is, polyurethane, which has been used conventionally, has excellent abrasion resistance and is therefore more widely used than other binder resins.

However, this polyurethane is not completely satisfactory as a material for the magnetic coating layer, and has the disadvantage that the dispersibility of the magnetic powder is not particularly good.

Therefore, research is being conducted to solve the above drawbacks by introducing polar groups into polyurethane, that is, to improve the dispersibility of magnetic powder. However, there is no method to improve the dispersibility of magnetic powder by introducing polar groups. However, there is the problem of gelation of magnetic paints, and for this reason, the method of introducing polar groups into polyurethane is by no means desirable.

[Disclosure of the invention]

As a result of research into what causes the disadvantages of polyurethane, which has excellent properties such as abrasion resistance, that is, the decrease in the dispersibility of magnetic powder, the inventor found that the dispersion of magnetic powder in magnetic paint It has been found that the properties are greatly influenced by the molecular weight of the polyol constituting the polyurethane.

In other words, since the urethane bonding group of polyurethane has greater polarity than other alkyl groups, it was revealed that this urethane bonding group is a dominant factor in the dispersibility of magnetic powder in magnetic paint. Based on this revelation, researchers suggested that it would be possible to improve the dispersibility of magnetic powder by adjusting the density of urethane bonding groups in polyurethane by increasing or decreasing the molecular weight of the polyol that makes up the polyurethane. I got an idea.

As a result of repeated experiments based on this idea, the number average molecular weight of the polyol that makes up polyurethane was approximately 1.
The dispersibility of magnetic powder in a magnetic paint containing polyurethane of 000 to 2500 as a binder is good, and Y-3/N of a magnetic recording medium constructed by applying this magnetic paint.
It has been found that the electromagnetic conversion characteristics shown by the squareness ratio and the like are good, and the properties such as abrasion resistance, adhesiveness, and surface smoothness are also good.

If the number average molecular weight of the polyol constituting the polyurethane is considerably smaller than 1,000, the density of the urethane bonding groups will become relatively too large, resulting in gelation of the magnetic paint. If it becomes too large, the dispersibility of the magnetic powder in the magnetic coating material is significantly reduced.

[Example 1] 100 parts by weight of Co-containing γ-FetOs magnetic powder with a BET value of 30 m”/g, and a polyol with a number average molecular weight of 120
0 polyurethane, 5 parts by weight of vinyl chloride-vinyl acetate copolymer, 5 parts by weight of polyisocyanate hardener, 5 parts by weight of alumina, 2 parts by weight of lubricant, and 60 parts by weight of methyl ethyl ketone were cross-dispersed for a predetermined time. A magnetic paint is obtained, which is applied to a base film of polyethylene terephthalate, and then undergoes predetermined steps such as drying, curing, and cutting to obtain a magnetic recording medium such as a magnetic tape for video.

[Example 2] A magnetic recording medium is obtained by carrying out the same procedure as in Example 1 using a polyol having a number average molecular weight of 2000 constituting polyurethane.

[Comparative Example 1] A magnetic recording medium is obtained by carrying out the same procedure as in Example 1 except for using polyurethane having a number average molecular weight of 800 as a polyol.

[Comparative Example 2] A magnetic recording medium is obtained by carrying out the same procedure as in Example 1 using polyurethane having a number average molecular weight of 3000 as a polyol.

〔Characteristic〕

Regarding the magnetic recording media on each side, Y-3/N.

The squareness ratio and the state of the magnetic paint at the time of application are as shown in the table.

Table: If the number average molecular weight of the polyol constituting the polyurethane used is too small, such as 800, the density of polar groups such as urethane bonding groups becomes too large, and the gelation of the magnetic paint starts early. Not only is the coating process difficult, but the electromagnetic properties and magnetic properties are degraded as shown by the Y-5/N and squareness ratios, and conversely, the number average of polyol is When the molecular weight is large, such as 3000, gelation of the magnetic paint is difficult to begin, but because the dispersibility of magnetic powder in the magnetic paint is poor, electromagnetic conversion as shown by Y-5/N and squareness ratio It has good characteristics and magnetic properties.

On the other hand, in Examples in which the number average molecular weight of the polyol constituting the polyurethane is within the range of about 1000 to 2500, the magnetic paint is difficult to gel, and the magnetic paint application work is difficult. In addition, the dispersibility of the magnetic powder in the magnetic paint is good, and cross-talk dispersion work can be carried out smoothly.Therefore, the production efficiency of magnetic recording media is high, and it can be provided at a correspondingly low cost. , Y-5/N, and squareness ratio, the electromagnetic conversion characteristics and magnetic characteristics are also good.

〔effect〕

In the magnetic recording medium according to the present invention, since the polyurethane used as the binder and the polyol as its constituent component have a number average molecular weight of approximately 1000 to 2500, gelation of the magnetic paint constituting the magnetic layer is difficult to begin. Therefore, there is no problem even if the magnetic paint is prepared in large quantities in advance, and the application work of the magnetic paint can be carried out smoothly.Furthermore, the dispersibility of the magnetic powder in the magnetic paint is good, so the dispersion work can be carried out smoothly. Therefore, the manufacturing efficiency of magnetic recording media is good, and it can be provided at a correspondingly low cost.Furthermore, the electromagnetic conversion characteristics such as Y-S/N and squareness ratio, magnetic properties are also good, and wear resistance etc. It also has excellent features.

Claims (1)

[Claims] A magnetic recording medium characterized in that a magnetic layer contains polyurethane in which the polyol constituting the polyurethane has a number average molecular weight of approximately 1,000 to 2,500.