JPS6176573A - Magnetic coating - Google Patents

Abstract

PURPOSE:The titled coating that is obtained by adding a low molecular nitrocellulose, a vinyl chloride-vinyl acetate-vinyl alcohol terpolymer and a polyurethane rethane to the binder, thus being suitable for production of magnetic recording media with good electromagnetic transduction. CONSTITUTION:A magnetic powder, a dispersant and (A) a low molecular nitrocellulose (preferably of less than H1/16 particle size index) are kneaded. Then, (B) a vinyl chloride-vinyl acetate-vinyl alcohol copolymer (preferably of 250-600 average polymerization degree) and (C) a polyurethane are added to the product and kneading is repeated to give the objective coating. The amounts of components B and C are 50-300pts.wt. and 50-300pts.wt. per 100pts.wt. of a component A and the total amount of the 3 binders is preferably 15-50pts.wt. per 100pts.wt. of the magnetic powder.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a magnetic material. More specifically, the present invention relates to a magnetic coating material that can produce magnetic recording media with excellent electromagnetic conversion characteristics and coating film properties.

[Prior art]

According to J.P. 7-1, a coating-type magnetic recording medium is widely used, which is formed by coating a magnetic powder in a binder with a magnetic coating on a support made of a non-magnetic material such as a polyester film. It is being

In recent years, the magnetic powder used in magnetic paints has been moving toward finer particles in order to record the crystal density of recording media. As a result, it has often been difficult to achieve high dispersion of magnetic powder using the binders and dispersion methods used in conventional magnetic paints.For this reason, magnetic recording media made from such magnetic paints have It has been proposed to use a binder with a lower molecular weight than the conventional binder because it is difficult to obtain good electromagnetic conversion characteristics and to improve the dispersibility of magnetic powder. When a magnetic paint is applied to a support, the magnetic surface becomes orange skin-like or sticky after drying, and a blocking phenomenon occurs after the magnetic recording medium has been manufactured and rolled up. Another drawback was likely to occur.

[Problem that the invention seeks to solve]

The present invention has been made in view of the above problems, and an object of the present invention is to provide a magnetic recording medium in which magnetic powder is mixed and dispersed with high dispersibility in a binder, and a magnetic recording medium having 4H electromagnetic conversion characteristics can be formed. The goal is to provide a comparison.

Another object of the present invention is to provide a magnetic coating material that can form a magnetic recording medium in which the magnetic layer does not become cylindrical or block after being rolled up.

[State of invention [℃]

The present invention provides a magnetic paint for forming a magnetic recording medium.
Ij1 The magnetically receptive paint is characterized in that the binder contains low molecular weight nitrocellulose, a vinyl chloride-vinyl acetate-vinyl alcohol copolymer, and a polyurethane resin.

Hereinafter, the magnetic field of the present invention will be explained in detail.

Traditional magnetic paints generally include magnetic powder and binder.

The magnetic coating composition of the present invention is composed of components such as a dispersant, an abrasive agent, and a hardening agent, but conventionally known components other than the binder can be used in the magnetic paint of the present invention. Furthermore, the composition ratios of these components may be the same as those conventionally used.

The binder of the magnetic paint of the present invention contains at least a total of three types of compounds: low molecular weight nitrocellulose, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, and polyurethane resin.

The guideline for usable nitrocellulose is JIS K.
6?03 (1975) As a result of a drop test, a viscosity symbol of H1/16 or less is preferable. Vinyl chloride-vinyl acetate-vinyl alcohol copolymers having various polymerization molar ratios can be used.

Further, the average degree of polymerization of this copolymerization is not particularly limited either (but about 250 to 600 can be preferably used).

Various types of polyurethane resins can be used with respect to the tumor average molecular weight. Examples include [N-2304, N-5032゜N-508 manufactured by Nippon Horikretan Co., Ltd.]
3, Take [Bffi product industry ifl E-550, Nisten 5702 manufactured by Gutdrich. Examples include Nisten 5703J.

The total amount of the binder for the three heel types mentioned above is 10% of the magnetic powder.
It is preferable to add 15 to 50 parts to 0 part of vinyl chloride-vinyl acetate-vinyl alcohol copolymer to 100 parts of nitrocellulose.
It is preferable to use about 50 to 300 parts of polyurethane.

The most preferred method for manufacturing the porcelain of the present invention will be described below.

First, a magnetic powder 9 dispersant having a predetermined composition.

The abrasive, solvent, etc. and low molecular weight nitrocellulose are sufficiently kneaded using a sand mill, kneader, etc. Next, vinyl chloride-vinyl acetate-vinyl alcohol and polyurethane resin are added to the above mixture, and the mixture is further kneaded.

Next, a known curing agent such as a polyisocyanate crosslinking agent is added to the composition mixed as described above, and the mixture is thoroughly stirred to complete the production of a green paint.

As explained above, in the first stage, a low molecular weight binder is added and kneaded, and then the remaining binder is added and kneaded.
The purpose of the present invention can be achieved more effectively by preparing the magnetic screams by dividing the preparation among everyone, and this is the most preferable method. However, the object of the present invention can also be achieved by adding and kneading three types of binders at once to produce a magnetic paint.

The magnetic paint of the present invention has high dispersibility of magnetic powder in the binder, and the magnetic layer of a magnetic recording medium formed with the magnetic paint of the present invention is neither sticky nor cylindrical. The reason why the above effects are obtained is not necessarily clear, but it is thought to be as follows. That is, it is thought that the reason why the dispersibility of the magnetic powder in the binder is improved is that the low molecular weight nitrocellulose has good adhesion with the magnetic powder.

In addition, as mentioned above, magnetic paints manufactured through a two-step kneading process in which the binder is added in two parts exhibit particularly poor dispersibility of the raw magnetic powder due to the following reasons. It will be done. That is, the magnetic i raw powder is mixed in advance into the nitrocellulose with high dispersibility, and the two relatively high molecular weight binders added later and the nido-a cellulose tend to be kneaded together, so the two-step process is carried out. It is believed that the magnetic powder is sufficiently dispersed in the binder by kneading.

In addition, the magnetic layer does not have stickiness and does not become shaped like an apricot cell.
This is thought to be due to the t1 power effect of the high molecular weight vinyl chloride-vinyl acetate-vinyl alcohol and the polyurethane resin.

In particular, polyurethane resin 7C is extremely effective in making the coating film of magnetic paint excellent.

〔Effect of the invention〕

The magnetic paint of the present invention has the highest dispersion of magnetic raw powder into the binder. Therefore, by using the magnetic coating material of the present invention, it has become possible to produce a magnetic recording medium having excellent electromagnetic conversion characteristics.

Furthermore, by using the magnetic image q of the present invention, magnetic "
A! jC It's sticky (and it doesn't give me Yuzu skin either)
It also became possible to manufacture magnetic recording media. Therefore, blocking no longer occurs even after the manufactured magnetic recording medium is wound up.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to typical examples and comparative examples of the present invention. In the following description, "%" and "part" indicating composition are based on weight unless otherwise specified.

Example 1 Ferromagnetic metal powder (Fe-Co-Ni alloy, major axis 0.
25μm axial ratio 8) 100 parts nitrocellulose (trade name Asahi Kasei IH-1/16J)
IS K6703 drop test, viscosity symbol by test: H-1
/16) Part 10 α-AI! 203 (abrasive) 5 parts lecithin (dispersant) 1 part methyl ethyl ketone 60 parts toluene
60 parts of the above composition was mixed and dispersed using a sand grinder. Next, vinyl chloride-vinyl acetate-vinyl alcohol copolymer (polymerization molar ratio 91:3:
6 Average degree of polymerization 400 ) 10 parts, polyurethane elastomer 10 parts, ) f ethyl ketone 60 parts, toluene 6
0 part was further added and mixed and dispersed.

Next, this mixture was transferred to a stirrer, 5 parts of a polyisocyanate crosslinking agent having the chemical formula was added, and the mixture was stirred to form a magnetic image (-[
was manufactured.

Example 2 Example 2 Magnetic production was carried out in the same manner as in Example 1, except that all the compositions mixed and dispersed in Example 1 were mixed and dispersed in a Nando mill at a time in 7 pieces using a sand grinder. (p(This 1 was manufactured.

Example 3 In Example 1, 5 parts of nitrocellulose with JIS K6708 drop test viscosity symbol: Hl/16, which was added first, and vinyl chloride-vinyl acetate-vinyl alcohol copolymer (average degree of polymerization 400 A magnetic paint was produced in exactly the same manner as in Example 1, except that 15 parts of ) were used.

Example In Example 1, 15 parts of H -1/16 nitrocellulose added earlier, vinyl chloride added later,
Vinyl acetate, vinyl alcohol (average degree of polymerization 400)
A magnetic paint was produced in the same manner as in Example 1 except that the amount was 5 parts.

Comparative Example In Example 2, a magnetic [ Produced green paint.

Reference Example A magnetic tape manufactured using a magnetic paint in which magnetic powder has excellent dispersibility exhibits good magnetic properties. From this point of view, a magnetic tape was manufactured as follows using the magnetic paints prepared in Example 1.2.3゜4 and Comparative Example.
Table 1 shows the results of measuring the magnetic properties and evaluating the MF raw material of each magnetic paint. To manufacture a magnetic tape, first, Examples 1+2, 3, 4! Each of the magnetic paints produced in Comparative Example and Comparative Example was applied onto a polyester film having a thickness of 10 μm, and a magnetic field was applied in a predetermined direction to perform a magnetic orientation treatment. Next, after a drying process, a calender treatment is performed to smooth the surface, and the 1γ diameter is approximately 3 μm.
A magnetic layer was formed. After keeping the tape at 50'C for 24 hours, it was cut into a predetermined width (1 piece of tape was produced).

In addition, the glossiness of the magnetic tape manufactured as described above was examined. The higher the gloss, the less sticky the magnetic layer is, and the smoother the magnetic tape is, the better the coating properties.

Therefore, the magnetic paint used as the raw material for magnetic tape has a high gloss level and is of excellent quality. We evaluated the magnetic paint from this perspective as well.

Table 1 shows the results of examining the glossiness of the magnetic tape.

Table 1, < Better than the comparative example ◎ Same level or slightly better ○ As is clear from Table 1 above, the binder is low molecular weight nitrocellulose and vinyl chloride-vinyl acetate-vinyl alcohol copolymer. The magnetic tape produced from the magnetic coating of the present invention using a combination of polyurethane and polyurethane has excellent magnetic properties and gloss.

In particular, a magnetic tape manufactured using a magnetic paint formed by adding a binder in two stages has extremely excellent quality.

Claims (1)

[Claims] (1) A magnetic paint for forming a magnetic recording medium, characterized in that the binder contained in the magnetic paint contains low molecular weight nitrocellulose, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, and polyurethane resin. magnetic paint.