JPH08217995A - Coating material for magnetic recording medium and production of magnetic recording medium - Google Patents

Abstract

PURPOSE: To ensure good applicability without occurrence of overflow even in high-speed coating. CONSTITUTION: A coating fluid is extruded from the tip of a slot provided close to the surface of a continuously traveling support to coat the support therewith by a direct extrusion coater, wherein the viscosity of a solution consisting mainly of a solvent and a resin not adsorbed on particles is at least 3cP.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating material for a magnetic recording medium suitable for coating by an extrusion coater and a method for producing the magnetic recording medium, and more particularly to improvement of high speed coating property.

[0002]

As a method for applying a coating solution such as a magnetic coating material onto a non-magnetic support, there are various methods such as roll coating, gravure coating, slide pede coating, curtain coating and extrusion coating. Although the coating method is used according to the purpose of use, the extrusion coating has an excellent advantage that a uniform coating layer can be obtained.

On the other hand, the magnetic recording medium itself has been rapidly improved in recent years, and electromagnetic conversion characteristics have been improved in order to achieve high recording density and high image quality. With this,
Oxidized magnetic powders having a high BET value, barium ferrite powders, and the like have been widely used as magnetic powders. For this reason, the coating liquid has a high viscosity, and in order to improve the productivity, there is an increasing demand for a thin film and a high-speed coating.

From these requirements, it has been considered to use an extrusion coating instead of the conventional direct gravure coating when applying a coating liquid such as a magnetic coating or a back coating. According to this extrusion coating, when the direct gravure coating is used, the coating speed is 400 m / min or less, while the coating speed is sufficiently high (for example, coating speed 60
0 m / min) can be secured.

However, with this extrusion coating, good coating can be performed only in a relatively narrow range, and a desired coating state can be obtained under the conditions of high viscosity, thin film and high speed coating as described above. Things are very difficult. That is, especially when performing thin film coating such as a film thickness of 30 μm or less (film thickness during wet coating), film thickness unevenness occurs in the obtained film. This is complicatedly related to various factors such as the dimensional accuracy of the coater head, the edge shape, the liquid pool shape, the base tension, and the physical properties of the coating liquid.

Therefore, when this extrusion coating is carried out, there are some restrictions on the composition. However, even if such thin film coating is possible, high-speed coating causes a phenomenon called overflow which has not been seen before. This phenomenon is considered to occur because the base film is attracted to the coater head with high-speed coating.

[0007]

Therefore, the present invention has been proposed in view of such circumstances, and it is possible to obtain a uniform coating film thickness without overflow even at high speed coating. Another object of the present invention is to provide a coating material for a magnetic recording medium and a method for manufacturing the magnetic recording medium.

[0008]

Means for Solving the Problems The inventors of the present invention have earnestly studied that the above-mentioned object cannot be achieved, and as a result, the viscosity of the coating material at the time of application is a solution composed of a resin not adsorbed on particles and a solvent. Can be estimated by the viscosity of, and the higher the viscosity of this solution,
It was found that overflow does not easily occur when high-speed coating is performed, and the present invention has been completed.

That is, the coating material for a magnetic recording medium of the present invention is composed of particles, a resin and a solvent, and is extruded from the tip of a slot which is brought close to the surface of a continuously running support and is supported by the extrusion coater. A coating material for a magnetic recording medium, which is applied on the body, wherein the viscosity of a solution composed of a resin not adsorbed on particles and a solvent is 3c.
It is characterized by being ps or more.

Further, in the method for producing a magnetic recording medium of the present invention, a coating solution comprising particles, a resin and a solvent is extruded by pushing the coating solution from the tip of the slot which is brought close to the surface of the continuously running support. It is characterized in that, when it is applied onto the above-mentioned support by a rouge coater, the viscosity of a solution mainly composed of a resin not adsorbed on particles and a solvent is 3 cps or more.

[0011]

When a coating material comprising particles, a resin and a solvent is applied by an extrusion coater, the viscosity of the solution composed of the resin and the solvent which are not adsorbed on the particles is 3c.
By setting it to ps or more, the occurrence of overflow during high-speed coating can be suppressed.

[0012]

EXAMPLES The present invention will be described below with reference to specific examples, but it goes without saying that the present invention is not limited to these examples.

Experiment 1 Audio tapes (trade name,
CV) and VHS video tape (trade name, KN-II
I) is applied at a high speed by an extrusion coater,
The flow curve of the coating material at the time of application was determined. The results are shown in FIGS. 1 and 2.

As shown in FIGS. 1 and 2, it was found that in each of the above-mentioned tapes, the structural viscosity, which is an index of coating instability, was not observed, and the viscosity decreased linearly as the shear rate increased.

Since the shear rate of the coating material at the time of high-speed coating is 10 ⁵ seconds ⁻¹ , it is estimated that the viscosity of the coating material at that time is around 10 nPass (10 cps).

Experiment 2 What is usually used as a solvent for paints when applying a magnetic tape at a high speed by an extrusion coater [ethyl methyl ketone: toluene: cyclohexanone =
5: 3: 2 at a temperature of 25 ° C. and 0.8 mPass (0.8 c
ps)] is dissolved in a binder usually used,
The solution viscosity when the concentration was changed was measured with a Ubbelohde viscometer at a temperature of 25 ° C. The result is shown in FIG.

Therefore, based on these results, various magnetic tapes currently produced are coated and formed at a coating speed of 500 m / min. At that time, the magnetic powder in the coating material and the binder adsorbed on the magnetic powder were removed by a centrifuge, and the solution viscosity of the binder composed of the binder not adsorbed on the magnetic powder and the solvent was determined. The results are shown in Table 1 below.

[0018]

[Table 1]

As shown in Table 1, the solution viscosity at the time of high-speed application was about several mPass in any case, which is almost the same as the estimated value of the coating viscosity at the time of application shown in Experiment 1 above. I found out that The solution viscosity when the magnetic powder was removed from each paint was about 30 mPas.
It was about ss (30 cps).

Further, the likelihood of overflow occurring during the coating was examined, and the results are also shown in Table 1 above.

In Table 1, ⊚ represents that overflow is unlikely to occur, Δ is slightly unlikely to occur, ∘ is slightly likely to occur, and x is most likely to occur.

From Table 1, it has been found that the more the coating solution having a high solution viscosity is used, the more difficult the overflow is and the better the coating can be performed. It is considered that this is because as the solution viscosity increases, the force pressing the base film when the coating material is ejected from the coater head increases, and as a result, the base film separates from the head lip surface.

From the above results, in order to ensure good coatability without overflow during high-speed coating, the solution viscosity of the solution composed of the binder not adsorbed on the magnetic powder and the solvent is 3 mPass (3 cps). As described above, it has been found that it is necessary to be more preferably 5 mPass (5 cps) or more.

In this Example, the magnetic powder and the binder were mixed at the same time when the above-mentioned paint was prepared. However, in order to obtain good high-speed coating property, a binder that does not adsorb to the particles should be added afterwards. The same effect as that of the above method can be obtained also by. Even in this case, the reason why the overflow can be prevented is the same as in the case of the present embodiment.

[0025]

As is apparent from the above description, in the present invention, since the solution viscosity of the paint mainly composed of the resin not adsorbed on the particles and the solvent is increased, the paint from the coater head The force that pushes the base film during ejection is large. As a result, the base film comes to separate from the head lip surface, and overflow can be prevented. Therefore, when high-speed coating with an extrusion coater, which is currently performed at 600 m / min, is performed at a higher coating speed, turbulent flow may occur.
According to the present invention, it is possible to suppress the occurrence of this turbulent flow and realize good high-speed coating properties.

Further, in the present invention, the P / B of the coating material is the same as or lower than the present value, so that the durability can be improved.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a flow curve of a paint used when producing an audio tape according to this example.

FIG. 2 is a characteristic diagram showing a flow curve of a paint used when producing the video tape according to this example.

FIG. 3 is a characteristic diagram showing a relationship between a binder concentration in a paint and a solution viscosity.

Claims (2)

[Claims] 1. A magnetic recording medium composed of particles, a resin and a solvent, extruded from the tip of a slot which is brought close to the surface of a continuously running support, and coated on the support by an extrusion coater. A coating material for a magnetic recording medium, characterized in that the viscosity of a solution composed of a resin not adsorbed on particles and a solvent is 3 cps or more. 2. A paint comprising particles, a resin and a solvent,
When the coating solution is extruded from the slot tip portion which is brought close to the surface of the continuously running support and applied on the above support by the extrusion coater, the resin and the solvent which are not adsorbed on the particles are the main constituents. The viscosity of the solution is 3 cp
and a magnetic recording medium manufacturing method.