JPS6233330A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve wear resistance, adhesiveness, surface smoothness and the dispersibility of magnetic powder by incorporating a polyurethane specified in the total of the carbon atoms of a dicarboxylic acid component, the carbon atoms of a diol component and the carbon atoms of an chain-lengthening diol into a magnetic layer. CONSTITUTION:The polyurethane of which the total of the carbon atoms of the dicarboxylic acid component in the polyester constituting the polyurethane (but the carbon of the carboxyl group is not included in the carbon atoms), the carbon atoms of the diol component and the carbon atoms of the chain-lengthening diol is about 10-18 is incorporated as the binder into the magnetic layer. A polar group density increases excessively and the deteriorated electromagnetic conversion characteristic and magnetic characteristics are caused if the total of the carbon atoms of the polyester and the chain-lengthening diol is too small. The dispersibility of the magnetic powder is poor if the total is excessively large. Since the dispersibility of the magnetic powder in the magnetic coating compd. is thereby improved, the dispersion operation is smoothly executed and the cost is reduced; 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 binder for a magnetic coating layer, and has the disadvantage that it does not particularly have good dispersibility of magnetic powder.

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]

The present inventor conducted research into what causes the disadvantages of polyurethane, which has excellent properties such as abrasion resistance, namely, the decrease in the dispersibility of magnetic powder. We have found that the dispersibility of magnetic powder in magnetic paint is greatly influenced by the number of carbon atoms.

In other words, since both ester groups and urethane groups have greater polarity than other alkyl groups in polyurethane, it was revealed that these groups are the dominant factor in the dispersibility of magnetic powder. Based on this revelation, it is possible to improve the dispersibility of magnetic powder by adjusting the distribution density of these groups, for example, by increasing or decreasing the number of carbon atoms in the alkyl group that connects these groups. This gave me the idea that it might be possible.

As a result of repeated experiments based on this idea, we found that the number of carbon atoms in the dicarboxylic acid component in the polyester constituting polyurethane (however, the carbon number of the carboxyl group is not included in the number of carbon atoms) and the number of carbon atoms in the diol component, The dispersibility of the magnetic powder in the magnetic paint containing polyurethane as a binder, which has a total carbon number of about 10 to 18 in addition to the stretching agent diol, is good, and the Y-5 magnetic recording medium coated with this magnetic paint has good dispersibility. It has been found that the electromagnetic conversion properties shown by /N and squareness ratio are good, and the properties such as abrasion resistance, adhesiveness, and surface smoothness are also good.

If the number of carbon atoms in the above-mentioned elements constituting the polyurethane is considerably smaller than 10, the density of polar groups becomes too large, and as a result, gelation of the magnetic paint is likely to occur.
On the other hand, if it was considerably larger than 18, the dispersibility of the magnetic powder in the magnetic paint would be significantly reduced.

[Example 1] Co-containing FetOi magnetic powder 1 with a BET value of 30.7 g
00 parts by weight, 15 parts by weight of polyurethane with the characteristics shown in the table below, 5 parts by weight of vinyl chloride-vinyl acetate copolymer, 5 parts by weight of polyisocyanate-based curing agent, 5 parts by weight of alumina, 2 parts by weight of lubricant, methyl ethyl ketone A magnetic paint is obtained by cross-dispersing 60 parts by weight for a predetermined period of time, 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] The same procedure as in Example 1 was carried out using polyurethane having the characteristics shown in the table below to obtain a magnetic recording medium.

[Comparative Examples 1 and 2] The same procedure as in Example 1 was carried out using polyurethane having the characteristics shown in the table below to obtain a magnetic recording medium.

〔Characteristic〕

Regarding the magnetic recording media on each side, the Y-5/N, squareness ratio, and state of the magnetic paint at the time of application were investigated, and the results are as shown in the table.

According to this table, if the total number of carbon atoms in the polyester constituting the polyurethane used as the binder component of the magnetic layer and the drawing agent diol is too small, the polar group density becomes too large, causing gelation of the magnetic paint. begins early, which not only makes it difficult to apply the magnetic paint, but also reduces the electromagnetic conversion characteristics and magnetic characteristics as shown by the Y-3/N and squareness ratios. On the other hand, if the total number of carbon atoms is too large, the gelation of the magnetic paint is difficult to begin, but the dispersibility of the magnetic powder in the magnetic paint is poor, which is indicated by the Y-3/N and squareness ratio. As such, the electromagnetic conversion characteristics and magnetic characteristics are not good.

On the other hand, if the total number of carbon atoms in the polyester constituting the polyurethane and the drawing agent diol is as in the above example, gelation of the magnetic paint is difficult to begin, and the application process of the magnetic paint can be smoothly performed. Do it again;
The dispersibility of the magnetic powder in the magnetic paint is good, and crosstalk dispersion work can be carried out smoothly.Therefore, the manufacturing efficiency of magnetic recording media is high, and it can be provided at a lower cost. The electromagnetic conversion characteristics and magnetic characteristics are also good as shown by the squareness ratio.

〔effect〕

The magnetic recording medium according to the present invention has polyurethane used as a binder based on the number of carbon atoms of the dicarboxylic acid (not counting the carbon of the carboxyl group) in the polyester that is a constituent component, the number of carbon atoms of the diol, and the carbon number of the stretching agent diol. Since the sum of the numbers and numbers is approximately 10-18, it is difficult for the magnetic paint constituting the magnetic layer to start gelling, so there is no problem even if the magnetic paint is made in large quantities in advance, and the coating process of the magnetic paint is easy. Do it smoothly, and
Because the magnetic powder has good dispersibility in magnetic paint, the dispersion work can be carried out smoothly, and therefore the production efficiency of magnetic recording media is high, which means that they can be provided at a lower cost.Furthermore, Y-5/N and It has features such as good electromagnetic conversion characteristics such as squareness ratio, good magnetic properties, and excellent wear resistance.

Claims (1)

[Claims] The total number of carbon atoms of the dicarboxylic acid component in the polyester constituting the polyurethane (however, the carbon number of the carboxyl group is not included in the carbon number), the carbon number of the diol component, and the carbon number of the drawing agent diol is about 10 to 1. A magnetic recording medium characterized in that the magnetic layer contains polyurethane having the composition No. 18.