JPH03162A - Coating method - Google Patents

Abstract

PURPOSE:To obtain satisfactory coating property by bringing part of the surface of the front edge of a coating head into contact with a web and specifying the pressure of a coating liq. at a position at which the surface of the back edge is closest to the web. CONSTITUTION:A web 1 is coated with a coating liq. 10 for a lower layer fed from a first coating head 5A on the upper stream side of a coating line placed between a first support roll 2 and a second support roll 3. While the coating liq. 10 is in an undried state, the coated web is further coated with a coating liq. 20 for an upper layer fed from a second coating head 5B on the downstream side placed between the second support roll 3 and a third support roll 4. The pressure P of the coating liq. is regulated to 0.05-0.5kg/cm<2> at a position at which the surface 51a of the back edge is closest to the web. The occurrence of streaks and ununiformity in film thickness can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a coating method in which a coating liquid is extruded onto a web from an extrusion-type coating head.

[Conventional technology]

When applying magnetic paint, photographic light-sensitive materials, heat-sensitive recording materials, etc. when manufacturing magnetic recording media, extrusion coating methods (extrusion coating methods) are used, in which the coating liquid is applied to the web while extruding it from a narrow slot in the coating head. coating method) is known to be used.

This extrusion coating method has advantages such as superior film thickness controllability compared to roll coating, gravure coating, slide coating, or methods including doctor coating.

Various proposals have been made regarding extrusion coating methods, and Japanese Patent Laid-Open No. 117666/1983 discloses that it is preferable to maintain a pool of coating liquid between the end of the front edge surface and the web.

[Problem to be solved by the invention]

However, although JP-A-62-117666 states that it is preferable to keep the liquid pool by separating the front edge surface from the web, in practice, even when coating under the conditions specified in the publication, Good coating properties cannot be obtained.

In other words, if the front edge surface is not in contact with the web, the air accompanying the web will be caught up in the coating liquid, causing bubble failure, or the liquid pool will not be stable due to web chatter, resulting in poor coating properties. Not.

Therefore, the main purpose of the present invention is to extrude coating,
It is an object of the present invention to provide a coating method that can obtain good coating properties without streak failure or uneven film thickness.

[Means to solve division problems]

The above problem is solved in a method of coating a continuously running flexible web from a push-out coating head disposed between support rolls; bringing at least a portion of the front edge surface into contact with the web; The coating liquid pressure P at the part where the backing surface is closest to the web of coating liquid applied from this coating head is 0.05≦P≦0.5 (kg/a) per coating width of 50 cm. This can be solved.

[Effect]

According to the present invention, since at least a portion of the front edge surface is in contact with the web, there is no air entrainment and bubble failure can be prevented, the running performance of the web is stabilized, and chatter can be eliminated. is set to the above conditions, good coating properties can be obtained.

[Specific structure of the invention]

The present invention will be explained in more detail below.

FIG. 1 is an overall view of the coating apparatus of the first embodiment, in which both the lower layer and the upper layer are coated by an extrusion type coating head.
A flexible support (web) 1 passes through a guide roll (not shown) to a first support roll 2 and a second support roll 3.
Then, it is guided to the third support roll 4 and led to the drying process through the guide roll.

An upstream application head 5A is arranged to push the web 1 between the first support roll 2 and the second support roll 3, and a downstream application head 5A is arranged between the second support roll 3 and the third support roll 4. The side coating head 5B is arranged so as to be pushed into the web on which the lower layer has been coated.

Each application head 5A or 5B has a front edge member 5.
0 and a backing member 51, and has a slot 53 therebetween communicating with a liquid reservoir 52. The coating liquid is
The liquid is pumped into the reservoir 52 and applied through the slot 53 onto the web 1 whose back surface is not supported.

In the above example, the lower layer coating liquid is applied to the continuously running flexible web 1 from the upstream first coating head 5A disposed between the first support roll 2 and the second support roll 3. A lower layer is applied by applying lO, and then, in an undried state, the coating liquid 10 is applied to a second downstream side disposed between the second support roll 3 and the third support roll 4.
A so-called wet-on-wet coating method is used in which the upper layer coating liquid 20 is applied from the coating head 5B and layered coating is performed.

In the present invention, during coating in the first coating head 5A, coating is performed with the front edge surface 50a in contact with the web 1, and coating liquid pressure P at the portion of the back edge surface 51a closest to the web 1. is defined as above.

This coating liquid pressure P can be defined by being measured as follows, similar to the above-mentioned Japanese Patent Application Laid-Open No. 62-117666.

That is, a pressure gauge is provided between the pump and the liquid reservoir 52, preferably near the coating head 5A, and the coating liquid is allowed to flow out from the slot 53 while the coating head 5A and the web 1 are not in contact with each other. , the value indicated by the pressure gauge when the coating liquid is not applied to the web L is P, kg/al
Then, with the application head 5A in contact with or close to the web 1, when applying the same application liquid to the web 1 by extruding it from the slot 53 at the same flow rate as when no application is being performed, The value indicated by the pressure gauge is P
okay/a! When r, these differential pressures can be defined as the coating liquid pressure P according to the present invention. Therefore, it can be expressed by the following equation.

P=P, -P, (1) The coating liquid pressure P per coating width of 50ω is required to satisfy the condition of equation (2).

0.05≦P≦0.5 (kg/cd) --------
(2) If the coating liquid pressure P is large, a sufficient coating liquid layer will not be formed between the exit portion of the slot 53 and the backing surface 51a and the web 1, making it difficult to obtain a desired film thickness. Moreover, when the coating liquid pressure P is small, the web 1 is
It is easy to separate from a, there is a risk of air entrainment, and the film thickness fluctuates greatly, making it impossible to perform good coating.

The upper limit of the coating liquid pressure P is more preferably 0.2) cg/
Less than cd is preferred.

The coating liquid for the lower layer and the coating liquid for the upper layer may be the same or different. For example, when obtaining a magnetic recording medium,
The lower layer is a subbing layer and the upper layer is a magnetic layer, or the lower layer is a magnetic layer and the upper layer is a protective layer. When both layers are magnetic layers, the properties of each magnetic paint may be different.

〔Example〕

Next, examples of the present invention will be shown to clarify the effects of the present invention.

Each of the following magnetic paints was coated on a support made of polyethylene terephthalate with a thickness of 14 μm at a coating speed of 200 m/min.
When the dry film thickness was 3.5 μm for the lower layer and 1.0 μm for the upper layer as shown in Fig. 2, the streak failure and coating unevenness after coating were investigated at the first coating head. As a result, the results shown in Table 1 were obtained. In the composition, all parts are by weight.

<Upper layer> ★Co-containing magnetic iron oxide (Hc=9000e.

BET value 45i/g) 150 parts★Polyurethane resin IO part★Vinyl chloride-vinyl acetate resin 20 parts★Alumina powder
10 parts★Myristic acid 2 parts★Butyl stearate 1 part★Polyisocyanate 10 parts★Toluene
200 parts★Methyl ethyl ketone★Carbon black lower layer> y Fe2es powder (Hc=7000 e.

BET value 25 resistance/g) ★α-A 1303 ★Carbon black★Vinyl chloride copolymer★Polyurethane resin★Butyl stearate★Myrstic acid★Stearic acid★Methyl ethyl ketone★Toluene★Oleic acid★Polyisocyanate 200 parts 10 parts 100 parts 8 parts 5 parts 20 parts 7 parts 1 part 0.65 parts 0.35 parts 150 parts 150 parts 0.65 parts 10 parts Table 1 O: Best O: Good Δ: Unevenness ×: Due to scraping, air mixing, etc. [Effect of the Invention] As described above, according to the present invention, during extrusion coating,
Good coating properties can be obtained without streak failure or uneven film thickness.

[Brief explanation of drawings]

Fig. 1 is an overall schematic diagram of an example of a coating apparatus for carrying out the method of the present invention, and Fig. 2 is a diagram showing an example of a coating apparatus for carrying out the method of the present invention. 4... Third support rolls 5A, 5B... Coating head 10... Lower layer coating liquid 20... Upper layer coating liquid

Claims (1)

[Claims] (1) In a method of coating a continuously running flexible web from an extrusion type coating head disposed between support rolls; The coating liquid pressure P at the part where the back edge surface is closest to the web of coating liquid applied from the coating head is 0.05≦P≦0.5 (kg/cm^2) per coating width of 50 cm. A coating method characterized by: