JPS61206920A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having excellent dispersibility of magnetic powder by adding a higher fatty acid as an additive to magnetic powder in a stage for mixing and dispersing simultaneously the magnetic powder and binder the adding an alkyl sulfocarboxylate thereto in a stage for final viscosity adjustment. CONSTITUTION:The effective dispersion is attained by adding the higher fatty acid having 12-18C as the dispersant to the magnetic powder in the stage of simultaneous addition of the magnetic powder then adding the alkyl sulfocarboxylate thereto in the stage for the final viscosity adjustment. The higher fatty acid having 12-18C may be incorporated preferably at 1.0-2.0pts. wt. by the weight of the magnetic powder and is exemplified by a satd. fatty acid such as lauric acid. The alkyl sulfocarboxylate may be incorporated at 0.5-4.0pts.wt. by the weight of the magnetic powder and is exemplified by sodium di-2-ethyl hexylsulfosuccinate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a magnetic recording medium with excellent dispersibility of magnetic powder.

[Prior art and its problems]

Generally, magnetic recording media such as magnetic tapes and flexible magnetic disks are coated with a magnetic paint made by mixing and dispersing magnetic powder, a binder, a volatile solvent, and other necessary additives on a non-magnetic support such as a polyester film. The magnetic layer is formed by coating and drying, but as the density has increased in recent years, there has been a demand for better magnetic properties and electromagnetic conversion properties than ever before, and for this reason, the magnetic powder used is fine particles. Magnetic and coercive force materials are increasingly being used. Therefore, the dispersion of magnetic powder to obtain the magnetic properties and electromagnetic conversion properties required as a medium becomes increasingly difficult and, if exceeded, a significant decrease in dispersibility occurs, and conventional dispersion methods such as higher fatty acids and surfactants As will be explained later, the conventional method in which magnetic powder is added as a dispersant in the process of mixing and dispersing the magnetic powder and the binder at the same time was insufficient.

OBJECT OF THE INVENTION The object of the present invention is therefore to eliminate the above-mentioned drawbacks of the prior art. The present invention aims to provide a method for manufacturing a magnetic recording medium with excellent dispersibility of magnetic powder.

[Configuration of the present invention]

In order to achieve the above object, the present invention is designed to mix two types of dispersants at different times without having to mix them all at once. That is, the present invention manufactures a magnetic recording medium by coating and drying a magnetic paint on a non-magnetic support by mixing and dispersing magnetic powder, a binder, and other necessary additives in a volatile solvent and adjusting the viscosity. In the method, the necessary additive contains at least 12 carbon atoms.
This method is characterized in that the higher fatty acid having a molecular weight of 18 to 18 is mixed and dispersed simultaneously with the magnetic powder and the binder, and then the alkyl sulfocarboxylate is added in the final viscosity adjustment step.

[Effect]

That is, if one or more dispersants are added in the process of mixing and dispersing the magnetic powder and the binder at the same time as in the past, the magnetic powder and other necessary additives such as carbon black or Alh.
BE is adsorbed on the surface of inorganic powder such as Os.
In the case of magnetic iron oxide with a grain size of 40 m and a length of L, the amount of adsorption increases, making it necessary to add even more dispersant. In such cases, a blooming phenomenon occurs after the coating is formed, and excessive dispersant sticks to the head.
This will reduce the durability of the coating film and cannot be put to practical use.

In view of the above problems, the present invention provides carbon black as a magnetic powder and other necessary additives.

It was thought that the dispersion of inorganic powders such as AlhOs could be carried out more effectively by adding the required dispersant in portions. Moreover, even more effective dispersion can be obtained by adding a higher fatty acid having at least 12 to 18 carbon atoms as a dispersant at the same time as the magnetic powder, and adding the alkyl sulfocarboxylic acid salt at the final viscosity adjustment step. They discovered this.

The higher fatty acid having at least 12 to 18 carbon atoms used in the present invention may be contained in 0.2 to 5,0 parts by weight, preferably 1.0 to 2.0 parts by weight based on the magnetic powder. Examples include saturated fatty acids such as lauric acid, myristic acid, and stearic acid.

Further, the alkyl sulfocarboxylate used in the present invention may be contained in an amount of 0.5 to 4.0 parts by weight based on the magnetic powder, and a specific example thereof includes sodium no-2-ethyl sulfosuccinate. .

〔Example〕

The present invention will be explained below with reference to Examples. In this example, antistatic agent carbon black... 4 parts paint film reinforcement agent
α-A120s... 2 parts f11 agent M
BK/) Luz/-1001! a/100 parts 2 parts of stearic acid was added to this composition, mixed for 72 hours in a ball mill, and then mixed at high speed in a mixer with 4 parts of a polyisolaanate compound as a curing agent and fuji-2-ethylhexylsulfoconolinic acid. Add 2 parts of sodium, redisperse for 1 hour while adjusting the viscosity, and pass through a filter with an absolute removal rate of 5 μm.

A magnetic paint was obtained.

The magnetic paint thus obtained has a center line average roughness of 0.02.
It was coated on a polyethylene terephthalate support with a thickness of 75 μm and the orientation magnetic field strength was 200.0 μm.
After being oriented in the direction of travel with Gauss.

It was dried to form a magnetic layer.

On the other hand, in order to clarify the effect of this example, 1. The type of dispersant was the same as in this example, but the timing of mixing was changed.

Magnetic layers were formed by changing the order and weight.

The left half of Table 1 below shows processing conditions for Examples and Comparative Examples. In addition, for paints that cannot pass through a filter with an absolute removal rate of 5 ttm, the diameter is 7 μm and 14 μm.

The magnetic layer was formed using magnetic paint that had passed through a coarse filter, and the column on the far right shows its contents.

The magnetic media of Examples and Comparative Examples obtained as described above were tested for squareness ratio, glossiness, centerline average roughness, and blooming, and the results are shown on the right side of Table 1. The squareness ratio was measured using a vibrating magnetometer with an applied magnetic field of 10.0OOG.
The angle ratio in the strike direction was determined at
The center line average roughness was determined using a surface roughness meter in the direction perpendicular to the running direction, and the blooming temperature was 25°C.

The surface of the magnetic layer was visually observed after being left for 48 hours under an environmental condition of 80% RH, and the presence or absence of two mottled patterns was determined.

As is clear from Table 1, the squareness ratio and glossiness of the samples prepared by the method of the example are much larger than those of the sample prepared by the method of the comparative example.

Also, the centerline average roughness is smaller than either, while the blooming and filter values are similar or smaller. This shows that the sample according to this example is superior to that according to the comparative example.

〔Effect of the invention〕

As can be seen from the above description, the sample prepared by the method of the present invention has excellent dispersibility.

Claims (1)

[Claims] (1) A method of manufacturing a magnetic recording medium by coating and drying a magnetic coating material prepared by mixing and dispersing a magnetic powder binder and other necessary additives in a volatile solvent and adjusting the viscosity onto a non-magnetic support. , in the step of mixing and dispersing a higher fatty acid having at least 12 to 18 carbon atoms as the necessary additive at the same time as the magnetic powder binder, and then adding the alkyl sulfocarboxylate in the step of adjusting the final viscosity. A method for manufacturing a recording medium.