JP2858136B2 - Application method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for applying a coating solution to a continuously running belt-like support (hereinafter referred to as a web), and more particularly, to a multi-layer simultaneous coating method using a curtain coating method. About.

[Background of the Invention]

The coating method using a free-fall curtain method is a method in which a coating solution is formed into a thin film and applied to a web at a certain speed or higher to apply the coating solution. For example, Japanese Patent Publication Nos. 49-14130 and 49-24133.
The techniques are disclosed in, for example, JP-A Nos. 49-35447 and 50-76151.

This coating method is capable of simultaneous multi-layer coating, and has come into practical use for coating very precise and thin layers such as photographic light-sensitive materials, in addition to the slide bead coating method.

FIG. 1 shows an example of a curtain coating method, and FIG.
2 is a side sectional view, and FIG. 2B is a perspective view. Two layers of coating liquid 3 (upper layer) flowing down the slide surface from liquid injection device 2
The coating liquid 4 (lower layer) naturally flows down between the edge guides 5 in the form of a thin film curtain, and is applied onto the running web 1.

In this case, in FIG. 1 (a), when the web is traveling in the direction A, the upper layer is on the web, but when it is traveling in the direction B, the upper layer is on the lower side.

Normally, in the case of multi-layer coating, a surfactant is added to the uppermost layer to stabilize the coating film after coating, Wilhelmy type,
The static or quasi-static surface tension measured by the method of Dunui's method or capillary rise is made lower than that of other layers, but in the case of curtain coating, the surface tension difference between the front and back free interfaces is large in the free fall section. Then, the end portion becomes unstable, causing a contraction of the flow from the surface having the higher surface tension, which causes the film to break. Specifically, two liquids having a difference in the dynamic surface tension in the free-falling liquid film are laminated on the slide surface to form a curtain liquid film. Causes a contraction and becomes an extremely thin film portion.

If the coating is performed in such a state, not only a portion where a normal film thickness distribution is not obtained at the end portion, but also the strength of the free-falling liquid film is remarkably deteriorated, which may lead to destruction of the entire liquid film. There is.

Unless the dynamic surface tension is properly set, there is a problem that stable coating cannot be performed in curtain coating.

[Object of the invention]

In view of the above problems, an object of the present invention is to provide a curtain coating method capable of eliminating the instability at the end of the multilayer coating by curtain coating and performing stable multilayer coating.

[Configuration of the invention]

The object of the present invention is to provide a method of applying a plurality of liquids on a support by a slide hopper type curtain coating method, wherein the difference between the dynamic surface tension of the uppermost layer and the lowermost layer is 0.05 to 0.2 in a free fall section. This is achieved by a multi-layer simultaneous coating method characterized by being within 10 dyne / cm in the range of sec.

By setting the traveling direction of the web to the direction B, the uppermost layer on the slide surface becomes the lowermost layer on the support, and the lowermost layer on the slide surface becomes the uppermost layer on the support. In this case, the difference between the dynamic surface tension of the minimum layer and the dynamic surface tension of the lowermost layer may be within 15 dyne / cm within the fall time of 0.05 to 0.2 sec in the free fall section.

 Hereinafter, the present invention will be described specifically.

A method for measuring the dynamic surface tension in a coating film in curtain coating is described in a report by SPLin in Journal of Fluid Mechanism (J. Fluid Mech) 1981, Vol.112.pp.443-458. Has been established by Also, P. Joos and others have published the Journal of Colloid and Interface Science (J. Colloid and In
terface Sciense), Vol. 115, No. 2, Feb. 1987, discusses the behavior of surfactants in curtain films.

We analyzed the stability of the edge of the falling film in the actual multi-layer curtain coating, and found that the stability here is the difference in dynamic surface tension of each layer measured by the above measurement method, especially the difference between the top layer and the bottom layer. However, the fall time in the free fall section is 0.05-0.
It was found that it was sufficiently secured when it was within 10 dyne / cm within the range of 2 sec.

Also, considering the orientation of the surfactant, the condition is more relaxed when the coating liquid, which is the uppermost layer after coating with a large amount of the surfactant, is on the solid wall side on the slide surface. In that case, it was found that the difference between the dynamic surface tensions of the uppermost layer and the lowermost layer should be within 15 dyne / cm.

The general application conditions of curtain coating to which the present invention is applied are as follows: coating solution viscosity: 1 to 200 cp flow rate: 0.1 cc / cm · sec or more for each layer, and the total flow rate is
It is within 0.5-5cc / cm · sec.

 The coating conditions are: curtain height: 0.5 to 20 cm, coating speed: 60 to 300 m / min.

The main solvent is water, which is used for simultaneous coating of 2 to 20 layers.

The coating solution and web to which the coating method of the present invention is applied are not particularly limited. For example, when applied to the production of photographic light-sensitive materials described in the following examples, any materials and techniques known to those skilled in the art can be used.

〔Example〕

 Hereinafter, the effects of the present invention will be illustrated by examples.

Example 1 With the apparatus shown in FIG.
Two layers of a black and white photographic light-sensitive material were simultaneously coated.

Coating speed: 90 m / min, curtain height: 5 cm As the support, a polyethylene terephthalate film subjected to an undercoat treatment was used.

Coating solution conditions Protective film solution: viscosity 30 cp, wet thickness 20 μm Emulsion layer: viscosity 60 cp, wet thickness 60 μm Static surface tension (σS), dynamic surface tension (σD) of each layer
The unit: dyne / cm was changed as shown in Table 1 below, and the effect on coatability was examined.

From the results in Table 1, in the case of Comparative Example 1, a phenomenon was observed in which only the emulsion layer shrunk at the edge of the falling liquid film, and the film was cut off from the film simultaneously with the start of coating, and uniform coating could not be performed.

In the case of the present invention 1: the surfactant was added to the protective layer, and uniform application was possible.

In the case of the invention 2: The surfactant was added to the emulsion layer, and uniform coating was achieved.

In the case of the present invention, the dynamic surface tension difference ΔσD is 10dy.
ne / cm.

Example 2 The same conditions as in Example 1 except that only the web traveling direction is the direction of FIG. 1B, that is, the case where the upper and lower layers on the slide surface and the web are reversed, the surface tension conditions in Table 2 below. Was applied.

In the case of Comparative Example 2: Although the degree is lighter than that of Example 1,
A similar phenomenon was observed, and uniform coating could not be performed.

In the case of the present invention 3, uniform application was possible by reducing the surfactant in the protective layer.

In the case of Invention 4: Uniform coating was achieved by adding a surfactant to the emulsion layer.

In the case of the present embodiment, the dynamic surface tension of each of the present inventions 3 and 4 is 15 dyne / cm or less, and in the case of the present invention 3, it is 10 dyne / cm or more, but as described above, on the slide surface and on the web. When the upper and lower layers are reversed, it can be seen that uniform application is possible if the thickness is 15 dyne / cm or less.

Example 3 Using the same apparatus as in Example 1, five layers were simultaneously coated.

 The conditions of each layer are as follows.

Curtain height: 7cm Coating speed: 150m / min Support: Double-sided polyethylene laminated paper Note that the protective layer is the uppermost layer.

 The results were as follows.

In the case of Comparative Example 3: At the time when the liquid film was formed, a uniform film was formed, but the free interface of the liquid between the lower end of the edge guide and the support rocked up and down unstable at the same time as the start of coating. As a result of the application, this swing appeared as a change in the application width, and the thick film portion was large.

In the case of the present invention 6: By changing the surfactant of the protective layer, the above-mentioned phenomenon was not observed, and the coating could be performed stably.

〔The invention's effect〕

According to the present invention, it was possible to provide a curtain coating method capable of performing stable multilayer coating by eliminating instability at an end portion in multilayer coating by curtain coating.

[Brief description of the drawings]

FIG. 1A is a side sectional view showing an example of curtain coating according to the present invention, and FIG. 1B is a perspective view. 1: Web 2: Liquid injection device 3: Upper layer liquid, 4: Lower layer liquid 5: Edge guide

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B05D 1/30 B05C 5 / 00,5 / 02 G03C 1/74

Claims (2)

(57) [Claims] 1. A method of coating a plurality of liquids on a support by a slide hopper type curtain coating method, wherein a difference between dynamic surface tensions of an uppermost layer and a lowermost layer is 0.05 to 0.2 sec in a free fall section. A multilayer simultaneous coating method characterized by being within 10 dyne / cm within the range. 2. A method of coating a plurality of liquids on a support by a slide hopper type curtain coating method, wherein the uppermost layer on the slide surface is the lowermost layer on the support, and the lowermost layer on the slide surface is the supporter. Arrange the slide hopper so that it is the uppermost layer on the body, and the difference between the dynamic surface tensions of the uppermost layer and the lowermost layer is within 15 dyne / cm within the range of 0.05 to 0.2 sec for the free fall section. A coating method characterized by the above-mentioned.