JPH0287320A - magnetic recording medium - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording medium used in a magnetic recording/reproducing device, and more particularly to a magnetic recording medium having a long running durability, especially a long still life.

BACKGROUND OF THE INVENTION In recent years, in magnetic recording media such as audio tapes and video tapes, iron oxide magnetic materials such as r-Fe203゜Co-containing-Fe203 are used as magnetic recording powder to reduce the noise level. Powder, Fe.

There is a tendency to make ferromagnetic alloy powders mainly composed of Ni and Co into fine particles. However, there is a drawback that the finer the particles of the magnetic powder, the lower the abrasion resistance of the magnetic layer containing it, and the worse the durability of the magnetic recording medium.

Therefore, in the past, while the magnetic powder used was made into fine particles, eight I! , 2o3. Cr2O3,a-F
The durability of the magnetic recording medium is improved by reinforcing the magnetic layer by adding and increasing the amount of an abrasive made of hard non-magnetic powder such as E203. Furthermore, in relation to the so-called still characteristic in which the same part of the magnetic coating film repeatedly slides into contact with the magnetic head in video tapes, etc., liquid lubricants are used to satisfy both the lubricity and strength of the magnetic layer. However, fatty acids and fatty acid esters with excellent lubrication performance are mixed into the magnetic layer, or a protective layer made of a lubricant is formed on the surface of the magnetic layer (for example,
Japanese Patent Publication No. 59-23008, Japanese Patent Application Publication No. 6972650
Publication No.).

Problems to be Solved by the Invention However, when using an abrasive as described above, increasing the amount used will extend the still life due to the coating reinforcement effect of the abrasive, but on the contrary, the filling properties of the magnetic powder will be reduced. The amount of abrasive used cannot be increased too much because problems such as deterioration of orientation and deterioration of surface properties of the magnetic layer tend to occur.

Furthermore, when attempting to improve lubricity by mixing fatty acids or fatty acid esters into the magnetic layer, using a large amount of liquid lubricant is particularly effective, but liquid lubricants generally do not constitute the magnetic layer. It has good compatibility with the binder contained in the magnetic layer, and therefore dissolves in a large amount into the magnetic layer, resulting in an excellent lubricity. In particular, fatty acid esters are effective in improving still properties, but on the other hand, the binder traps many lubricant molecules, resulting in a so-called swollen state, which weakens the binding force of the original ferromagnetic powder and causes significant deterioration of the magnetic layer. As with abrasives, there is a limit to the amount used, and it is not possible to add too much.

In addition, the protective layer made of a lubricant has poor durability and its lubricating effect cannot be maintained for a long period of time, and its mechanical strength as a protective layer is not very good, so it cannot provide sufficient protection. It was difficult to demonstrate.

In view of the above problems, the present invention provides an abrasive and a fatty acid.

It provides a magnetic recording medium that has a magnetic layer with excellent running durability without changing the amount of fatty acid ester added, has a long still life, and has good electromagnetic conversion characteristics such as output and C/N ratio. be.

Means for Solving the Problems In order to solve the above problems, the magnetic recording medium of the present invention has a magnetic layer mainly composed of ferromagnetic powder and a binder on one side of a non-magnetic support, and a magnetic layer mainly composed of ferromagnetic powder and a binder. It has a back coat layer mainly composed of non-magnetic inorganic fine powder and a binder on its surface, and the amount of residual solvent contained in the magnetic layer is 0.1% by weight or less.

Function The inventors have discovered that the amount of residual solvent contained in the magnetic layer has a significant relationship with still life characteristics. In other words, normally manufactured magnetic recording media have a
The residual solvent contained in the coating was about 0.3% by weight, and it was found that this had a very large effect on the decrease in the mechanical strength of the coating film. Based on these results, in the present invention, the total amount of residual solvent contained in the magnetic layer is reduced to 0.
．． By reducing the amount to 1% by weight or less, the still life is significantly improved compared to conventional lubricants without increasing the amount of lubricant more than conventional ones, and extremely excellent durability is imparted to the magnetic recording medium.

That is, in the production of magnetic recording media, a magnetic paint strain-adjusted by dispersing ferromagnetic powder in a binder solution is coated onto a non-magnetic support to a thickness of approximately 2 to 5 μm using, for example, gravure coating. Apply to.

By such a method, the magnetic layer coated on the nonmagnetic support is subjected to a treatment for orienting the ferromagnetic powder in the magnetic layer, if necessary, and then the formed magnetic layer is dried. Furthermore, the surface is smoothed and hardened, and a back coat layer is provided.

In the production of the above-mentioned magnetic recording media, the magnetic layer coated on the non-magnetic support is subjected to several heat treatments, and the organic solvent used to prepare the magnetic paint evaporates and scatters, leaving the non-magnetic support. A magnetic coating film is formed on the magnetic support.

However, in the heat treatment described above, the time required for the magnetic coating film to pass through the drying oven is extremely short, and in the curing process, problems such as heat shrinkage of the non-magnetic support occur, so the temperature is There are limits.

From the above, in manufacturing the above-described magnetic recording medium, the organic solvent used for preparing the magnetic paint does not completely evaporate and scatter, but remains in the magnetic layer. Organic solvents such as MEK, toluene, and cyclohexanone are often used to prepare magnetic paints, but the boiling point of each is
(79-80.5℃), toluene (110-111.5
°C), cyclohexanone (163-167 °C),
Under the above heat treatment conditions, as can be seen from the boiling point, most of MEK and luene are volatilized, but a particularly large amount of cyclohexanone remains. Also, the solubility of cyclohexanone in the binder.

Since the adsorption to magnetic powder is particularly large compared to MEK, )/renin, the amount of cyclohexanone added to the magnetic paint increases, and the amount dissolved in the binder and adsorbed to the magnetic powder increases. The amount remaining after drying increases.

MEK, )/renin, and cyclohexanone remaining in the magnetic layer weaken the binding force between the magnetic powder and the binder by adsorbing to the surface of the magnetic powder, and also dissolve in the binder and act as a plasticizer. Decreases the mechanical strength of the coating. These effects become more noticeable as the amount of residual solvent increases.

In the present invention, the amount of residual solvent contained in the magnetic layer is set to 0.1% by weight or less, thereby eliminating the problems caused by the residual solvent as described above, and easily achieving durability of the magnetic layer. It is possible.

Examples The present invention will be described in detail below, but the present invention is not limited to these Examples. In addition, in the following, parts mean parts by weight.

(Example 1) γ-Fe203 magnetic powder 100 parts VAG
H (manufactured by σ, C, C, USA, vinyl chloride 11 parts - vinyl acetate-vinyl alcohol urethane elastomer 11 parts trifunctional low molecular weight incyanate compound (Coronate L manufactured by Nippon Polyurethane) 4.5 parts α-A1203 powder
6-part myristic acid
2-part stearin ifln-buti l
v i part MEK
150 parts toluene
150 parts cyclohexanone
26 parts The above composition was used to prepare a ball millable paint, and this magnetic paint was applied onto a 1471 m thick polyester film to a dry thickness of 5 μm and dried to form a magnetic layer. Next, this was subjected to calender treatment and curing treatment, and then a back coat (H4) was applied, dried, and cut into a predetermined width to produce a magnetic tape.

(Example 2) A magnetic tape was produced in the same manner as in Example 1 except that the amount of cyclohexanone used in the composition of the magnetic coating material in Example 1 was changed to 60 parts and 75 parts.

Comparative Example 1 A magnetic tape was produced in the same manner as in Example 1 except that the amount of cyclohexanone used was 100 parts in the composition of the magnetic coating material in Example 1.

A still life test and the amount of residual solvent in the magnetic layer were performed on the magnetic tapes obtained in each actual mm and comparative example. The still life was determined by using a VTR at -10° C. and measuring the time it took for the output to drop by 20 degrees. The amount of residual solvent in the magnetic layer was measured by peeling off the backcoat layer of the magnetic tape, and then measuring the amount of residual solvent using headspace chromatography, and expressing the amount as a ratio to the unit weight of the magnetic tape. Ordinary magnetic tape (Comparative example 1
), the amount of residual solvent measured by the above method is 0.
It was 15% by weight.

The figure is a graph showing the relationship between the amount of residual solvent in the magnetic layer and the still life. White circles indicate the magnetic tapes obtained in Example 1 and Example 2, and black circles indicate the magnetic tapes obtained in Comparative Example 1. 1 shows the garden air tape.

Effects of the Invention As described above, according to the present invention, the still life can be easily improved simply by controlling the amount of residual solvent contained in the magnetic layer. In other words, in the drying and curing described above based on the boiling point of each solvent, cyclohexanone with a high boiling point remains the most, so the amount of residual solvent can be controlled by adjusting the amount of cyclohexanone blended. It is.

For this reason, conventional methods for improving durability have been to compound and increase the amount of abrasives, as well as to increase the amount of fatty acids and fatty acid esters. This completely eliminates disadvantages such as a decrease in properties and a decrease in the strength of the magnetic layer due to the plasticizing effect of the fatty acid ester.

[Brief explanation of the drawing]

The figure is a diagram showing the relationship between the amount of residual solvent and the still life of the magnetic recording medium obtained by the present invention. O θ, l ° Back melt amount < * + Z) θ, 2

Claims (1)

[Claims] A non-magnetic support has a magnetic layer mainly composed of ferromagnetic powder and a binder on one side, a back coat layer mainly composed of a non-magnetic inorganic fine powder and a binder on the other side of the non-magnetic support, and The amount of residual solvent contained in the magnetic layer is 0.1% by weight.
A magnetic recording medium characterized by the following.