JPH0559491B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for sequentially forming multiple layers on a moving support. More specifically, the present invention relates to a multilayer coating method for manufacturing magnetic recording media. [Prior Art] In recent years, magnetic recording media have become denser and thinner, and as a result, the conventional single-layer magnetic layer is now being replaced with a two-layer magnetic layer. Furthermore, in order to improve the adhesion between the magnetic layer or back layer and the support, an undercoat layer is provided, and a multilayer structure of two to three layers is becoming necessary. On the other hand, in order to achieve the above-mentioned multilayer structure, the current practice is to repeat coating and drying one layer at a time. [Problems to be solved by the invention] However, this method has poor productivity;
Furthermore, equipment costs also increase. Therefore, a method (hereinafter referred to as a multilayer coating method) is desired in which multiple layers can be formed in a single coating and drying process (at least without drying each layer one by one). Roll coating, gravure coating, roll coating, or extrusion coating plus doctor coating are used as coating methods for magnetic recording media, but it is obvious that multilayer coating cannot be formed using these coating methods due to the shearing force during coating. It is. Furthermore, various extrusion coating methods have been proposed, but all of these are single layer coating methods. On the other hand, as a multilayer coating method, a slide coating method with slots has been shown as a coating method for photographic light-sensitive materials, but when manufacturing magnetic recording media, the coating liquid is a highly viscous and organic solvent dispersion that tends to aggregate. It is not suitable because it dries easily and is not suitable for high-speed application. Therefore, an object of the present invention is to coat multiple layers of a magnetic recording medium in a single coating/drying process (at least without drying each layer one by one), and to have suitability for high-speed coating.
It is an object of the present invention to provide a multilayer coating method for a magnetic recording medium which is formed with excellent uniformity and without failures such as agglomerated spots. [Means for Solving the Problems] As a result of various studies, the present inventors have found that the above object can be achieved by the present invention described below. That is, in the present invention, a first coating liquid is applied to a moving support in advance, and a second coating liquid is applied to the surface of the support without supporting the back surface of the support before the coating liquid dries. In a magnetic recording medium coating method in which a second coating liquid is applied by pressing an extrusion port of a coating head of a coating liquid, the coating amount of the first coating liquid is 60 c.c./m ² or less, and the second coating liquid is A method for coating a magnetic recording medium, characterized in that the amount of coating liquid applied is 50 c.c./m ² or less. In particular, in the present invention, it is preferable that the time from applying the first coating liquid to applying the second coating is within 5 seconds. The present invention will be explained below with reference to the drawings. FIG. 1 is an explanatory diagram of an embodiment of the second layer coating portion of the present invention, and FIGS. 2 and 3 are explanatory diagrams of a state in which coating is not possible in the second layer coating head. is a running support, and is a first layer or a first coating liquid applied to the support. a and b are support rolls of the support coated with the first coating liquid;
An extrusion type coating head having a slot for applying a second layer of coating liquid is arranged between the support rolls a and b. When applying multiple layers in this state, the following problems occur. First, if the coating amount of the first layer is large, the coating liquid of the first layer is scraped off as if it cannot pass through the coating head, as shown in FIG. Even if the tip shape and tension of the coating head were changed, as long as the coating head was pressed against the support 1, this phenomenon occurred in all cases when the coating amount of the first coating liquid was 60 c.c./m ² or more. Next, if the amount of the second layer or the second coating liquid applied is too large, the first coating liquid and the second coating liquid will flow out together to the inlet side as shown in Figure 3. Put it away. This phenomenon was also tested under various conditions, and this phenomenon occurred in all cases where the coating amount of the second layer exceeded 50 c.c./m ² . Furthermore, if the time between applying the first coating liquid and applying the second coating liquid is long, the surface of the first coating liquid will solidify, and as a result, the second coating head 4 will become dry. It was found that solidified material adhered to the tip and caused streaks, etc. Although it depends on the solid content concentration of the first coating solution and the type of organic solvent, if the time interval between coating the first layer and coating the second layer is within 5 seconds, all results are good. The results were obtained. In the present invention, the first layer coating method (not shown)
We offer roll coating, gravure coating, extrusion coating, slide bead coating, curtain coating, and methods that combine these with a doctor, depending on the liquid properties, coating amount, coating speed, etc.
Can be selected arbitrarily. The coating head for the second layer is an extrusion type coating head, for example, Japanese Patent Application Laid-Open No. 57-84771, 58-
No. 104666, No. 58-109162, No. 59-94657, No.
This is a coating head as shown in publications such as No. 60-78664 and No. 58-202075. Further, any coating liquid used for the magnetic recording medium may be used as the first coating liquid, such as an organic solvent, an organic solvent undercoating liquid containing a binder, a liquid in which carbon black is dispersed in a binder, a magnetic material dispersion liquid, etc. In addition, the second coating liquid is not particularly limited, but may include an overcoat liquid, a magnetic dispersion liquid,
Examples include backing liquid, etc. Furthermore, it is desirable that the solvent of the first coating liquid and the solvent of the second coating liquid have the same composition or be compatible, but this is not a necessary condition. [Examples] Example 1 A polyethylene terephthalate base having a thickness of 15 μm was coated as a support at a coating speed of 200 m/min. Table 1 shows the coating liquid formulation for the first layer, and Table 3 shows the coating liquid formulation for the second layer. Apply the first layer coating liquid by roll coating or
Coating was carried out using the coating head disclosed in Japanese Patent Application Laid-Open No. 57-84771. The coating amounts are 5, 10, 30, 60, and 80 ^c.c./m2 . The coating liquid for the second layer is in the form shown in Figure 1,
As a coating head, for example, Japanese Patent Application Laid-open No. 57-84771,
Coating amounts of 5, 10, 30, 50, and 70 c.c./m ² were applied using the apparatus shown in publications such as No. 58-104666 and No. 59-94657. The time interval from applying the first layer to the second layer is
It was hot in 0.5 seconds. Tension is 5 per 1m width
~30Kg, coating width is 500mm. Table 1 First layer coating liquid prescription Carbon black (Sebalco MICT, average particle size 250 μm) 200 parts Nipporan-7304 (made by Nippon Polyurethane) 80 parts Phenoxy resin (PKH-1) made by Union Carbide 35 parts Copper oleate 1 Part Methyl Ethyl Ketone Part A Cyclohexanone 50 parts Liquids (a), (b), and (c) were prepared by changing the amount of Part A in the above table.The viscosity and solid content concentration of each liquid are shown below.

[Table] Table 3 Second layer coating liquid formulation (magnetic dispersion) CO-containing magnetic iron oxide (S _BET 35m ² /g) 100 parts Nitrocellulose 10 parts Polyurethane resin (trade name "Nituporan 2304")
(manufactured by Nippon Polyurethane Co., Ltd.) 8 parts polyisocyanate 8 parts Cr ₂ O ₃ 2 parts carbon black (average particle size 20 μm) 2 parts stearic acid 1 part butyl stearate 1 part methyl ethyl ketone 300 parts It is shown in Table 4.

【table】

[Table] *-1: Application is not possible due to the phenomenon shown in Figure 2 *-2: Figure 3 〃 〃
Regardless of the liquid viscosity of the first layer, the first layer is 80 c.c./m ²
As mentioned above, if the coating amount of the second layer was 60 c.c./m ² or more, good coating could not be achieved. Example 2 Same as Example 1, except that the thickness of the polyethylene terephthalate base was 75 μm as a support.
The coating liquid for the first layer was used as (b), and the test was conducted under the same conditions. The results were identical to those shown in column (b) of Table 4. Example 3 Using the first layers (a) and (c) shown in Example 1, a test was conducted by varying the time from coating the first layer to coating the second layer. The time was changed by changing the distance between the first and second heads. The first layer was 20 c.c./m ² , the second layer was 10 c.c./m ² , the support was a 75 μm polyethylene terephthalate film base, and the coating speed was 100 m/min.

〔Effect of the invention〕

As shown above, in the coating method of the magnetic recording medium of the present invention, the coating amount of the first layer is 60 c.c./m ^{2 or less, and the coating amount of the second layer is 60 c.c./m 2} or less.
As long as the coating amount of the layer is 50 c.c./m ² or less, coating is possible regardless of the liquid formulation. Also, good surface quality can be obtained if the second layer is applied within 5 seconds after the first layer is applied. Therefore, multilayer coating is possible in the same coating zone, which is very effective in reducing manufacturing costs.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of one embodiment of the second layer coating portion of the present invention, and FIGS. 2 and 3 are explanatory diagrams of a state in which coating is not possible in the second layer coating head. DESCRIPTION OF SYMBOLS 1... Support, 2... First layer coating liquid, 3a,
3b...Support roll, 4...Coating head for second layer, 5...Coating liquid for second layer.

Claims (1)

[Scope of Claims] 1. A first coating liquid is applied in advance to a moving support, and before the coating liquid dries, a first coating liquid is applied to the surface of the coating liquid without supporting the back surface of the support. In the magnetic recording medium coating method of applying the second coating liquid by pressing the extrusion port of the coating head for the second coating liquid, the coating amount of the first coating liquid is 60 c.c./m ² or less, and A method for coating a magnetic recording medium, characterized in that the coating amount of the coating liquid in item 2 is 50 c.c./m ² or less. 2. The method for coating a magnetic recording medium according to claim 1, wherein the time from when the first coating liquid is applied to the support to when the second coating liquid is applied is within 5 seconds.