JPH0651158B2 - Application method - Google Patents

Description

The present invention relates to a curtain coating method for viscous liquids, and more particularly to a multilayer curtain coating method for a photographic layer of a silver halide photographic light-sensitive material.

[Prior art]

Photographic materials generally include hydrophilic colloids that suspend silver halide grains and / or contain additives that control photographic properties and productivity, such as flexible long webs such as ethylene terephthalate or baryta paper. It is manufactured by continuously coating and drying.

As a method of coating a photographic layer constituting a photographic material on a web, an immersion method, a double roll method, an air doctor method, etc. are initially used, and a curtain coating method, a slide hopper method, etc. are required under the request of multiple simultaneous high speed coating. Is being developed.

The above-mentioned curtain coating method is disclosed in JP-B-49-24133, JP-B-49-35447 and JP-B-53-31005 as a basic technique.

In the disclosed technique, the liquid curtain stretched between the guide means of the hanging liquid curtain proposed therein causes a curtain tear near the guide means, or a thick film pulse is formed on both edges of the liquid curtain. There is a problem such as generation of stripes, and in order to guarantee the stability of the liquid curtain, it is necessary to set the supply liquid amount to at least 1.4 to 1.5 cm ³ / cm · sec, which makes it difficult to apply a thin film. Furthermore, when the liquid is released from the lip-shaped eaves at the end of the slide surface of the coater where the liquid curtain is formed, an unfavorable phenomenon such as a tea pot effect is accompanied,
Or, in the area where the liquid curtain is attached to the support, problems such as laying, inclusion of air bubbles between the applied liquid layer and the support, and formation of heel-shaped liquid aneurysm have been pointed out.

An improved proposal for the lip-shaped eaves or the landing condition is disclosed in JP-A-51-57734.
No. 52-69946, No. 52-114636, No. 52-117936,
55-134668, 59-136162 or 61-292140, the shape, curvature, landing angle of the liquid curtain on the lower surface of the lip has been studied.

Regarding the improvement of the stability of the liquid curtain, JP-A-50-76151,
53-4053, 54-50542, 55-56867, 59-100435
A proposal for improvement has been made in the issue.

On the other hand, Japanese Patent Application Laid-Open Publication No.
Nos. 50-88138, 55-73365 and 59-132966 propose a method of supplying a gelatin solution, water or a low viscosity gelatin solution along both edges of the liquid curtain.

Further, Japanese Patent Application Laid-Open No. 54-68847 proposes to move a guide means (a guide wire in this case) while conforming to the liquid curtain.

The technical efforts described above have been pursued in order to cultivate and extend the excellent qualities of the curtain coating method-comparable to the slide popper method (beat coating method) in the relatively high viscosity and the thin film coating property. However, from the viewpoint of practical detection, (1) there is a large deviation in the flow rate range that allows high viscosity and thin film coating, (2) uniform film thickness at the center of the liquid curtain by improving the lip However, (3) Stabilize both edges of the liquid film, take measures such as making the liquid curtain width wider than the support width to prevent thick film striae. Instead, the backside of the liquid support will occur in the landing area, and the liquid loss will be large while the process equipment is contaminated, leading to cost disadvantages. (4) In the landing area, foaming will be trapped between the liquid layer and the support. Easy to increase the coating speed. (5) Each of the above measures complicates the general coater shape and makes the manufacturing accuracy and maintenance. And hid impractical plane to various factors.

[Object of the Invention]

The object of the present invention is to pay attention to the excellent qualities of the curtain coating method and the obstacles lying in front of it, to form a stable liquid curtain even at a small flow rate without causing unnecessary liquid loss. It is an object of the present invention to provide a curtain coating method in which thickening of both edges of the liquid curtain is at least reduced.

[Constitution of the invention, its effect]

The above-mentioned object of the present invention is to stack at least two kinds of liquid layers on an inclined slide surface and hang them down from a curved lip-shaped ridge at the end of the slide surface to run a free-falling laminated liquid curtain formed. In the multi-layer curtain coating method of landing on the support and laying on the support, the inclination angle α of the sliding surface with respect to the horizontal plane is 30 to 70 °, and the surface of the curved lip-shaped eaves in contact with the laminated liquid has a radius of curvature of 40 mm. The coating method is characterized by the above cylindrical surface.

As an aspect of the present invention, it is preferable that an angle β formed between the downward direction of the laminated liquid curtain and the direction of travel of the support at the landing point of the liquid curtain is 120 to 150 °.

Next, the present invention will be described with reference to the drawings.

In FIG. 1, 1 is a coder and 11 is a slide surface. The sliding surface has an inclination of α with respect to the horizontal plane. Reference numeral 12 designates a lip-shaped eave at the end of the slide surface 11, and the surface of the lip-shaped eave that contacts the laminated liquid is a cylindrical surface having a radius R. 3 is a liquid curtain that falls freely from the labial eaves and 2 is a back roll that stretches the web 4.
P is a landing point on the web 4 where the liquid curtain 3 is stretched around the back roll 2. β is an angle formed by the liquid curtain hanging direction at the point P and the traveling direction of the web 4 (the tangential direction of the roller 2 at the point P).

Further, on the slide surface 11, there is provided a liquid width regulating plate which forms a bank on both sides of the laminated flowing liquid, and the lip-shaped eaves take over both edges of the laminated liquid flow with a predetermined width. A liquid curtain guide for hanging the guide is addressed and extends to the landing area of the liquid curtain,
The contraction of the liquid curtain is prevented and a liquid curtain with a predetermined width is landed on the web, and the laminated liquid is laid on the web.

In the above coating system, the laminated liquid flows down at the center of the slide surface at the flow velocity v ₁ , and the liquid curtain hangs at the center of the liquid curtain at the center of the liquid curtain at the free fall speed v ₂ and the transport speed v on the web. Laid in ₃ .

However falling speed for the viscous resistance in the vicinity of both edges of the laminated liquid and Ekimaku slide surface _{v 1 '~v 1 (v 1} '<v 1) falling speed _{v '2 ~v 2 (v'} 2 < There is a transition zone d of v ₂ ), and the influence of surface tension further causes thick film veins to occur on both edges, and in the liquid curtain, a curtain tear from around both edges may occur.

The tendency is that the higher the viscosity of the liquid and the smaller the amount of the liquid, the wider the transition zone, and between v ₁ ′ and v ₁ (△ v ₁ ) and between v ₂ ′ and v ₂
The difference in (△ v ₂ ) is remarkable.

In the present invention, looking at the relationship between the inclination angle α of the slide surface and the velocity transition area d in both images of the laminated liquid and the liquid curtain, α <30 °
I learned that v ₁ ′ and v ₂ ′ are small, and Δv ₁ , Δv ₂ and d are large, and the liquid curtain breaks relatively easily. When α ≧ 30 ° or more, the situation of lamination and liquid curtain becomes good, and stable coating is possible even when the liquid flow rate is reduced. When 60 ° ≦ α ≦ 90 °, the stabilizing effect is saturated, and when α> 90 °, a turbulent turbulence occurs on the surface of the stack and the liquid curtain.

From the above knowledge, in the present invention, select 30 ° ≦ α ≦ 70 °,
Also, preferably, 45 ° ≦ α ≦ 60 ° is adopted. FIG. 2 shows the relationship between α and the minimum flow rate that can bring about stable coating. The liquid viscosity is 30 cp at the coating temperature and the liquid curtain height is 10 cm.

The above knowledge means that the flow time of the laminated liquid on the slide surface can be short, but the laminated liquid flows down on the slide surface at v ₁ and separates from the lip to become a liquid curtain and becomes free at v ₂ . There is a rapid velocity transition when moving to the drop, and since the liquid width is kept constant, a large stretching force is applied to the liquid lamination, and in the section where turbulence easily occurs between the lamination liquids in multi-layer coating. is there.

In the present invention, the sliding surface having the inclination α is v ₁
In seeking the relationship between acceleration and lip eaves transitioning falling speed of the laminating solution and v ₂ flowing down from v ₁ without causing turbulence in the lamination with the liquid intermission with the v _2, the lip eaves curved at a minimum We have found that the practical use is sufficiently satisfied if the acceleration is generated by a cylindrical surface having a radius of 40 mm or more. More preferably, the radius of curvature was 40 to 100 mm. A curved surface other than a circle may be used as long as it provides a smooth acceleration.

Further, the angle formed by the contact surface with the lip-shaped eave curved surface at the eaves (FIG. 1L) at which the laminated liquid separates from the slide surface is 70 to 11
0 ° is preferable, and 80 to 95 ° is more preferable. Further, it is preferable that the kicking angle from the eaves l to the inside of the lip-shaped eaves (the angle between the lip-shaped eaves-cut including l and the contact surface at the l) is 90 ° or less.

In the present invention described above, it was possible to enhance the coating stability at a small liquid flow rate, but by reducing the flow rate, the impact force on the web landing area of the liquid curtain is small and the fixed air layer on the support surface is destroyed, Insufficient removal force may cause air bubbles to be trapped between the laying liquid layer and the support, significantly impairing the coating quality.

In order to eliminate this difficulty, the liquid curtain was obliquely driven into the fixed air layer of the support to eliminate inclusion of bubbles.
At this time, when the angle β of the driving angle in the hanging direction of the liquid curtain and the running direction of the support is β, 120 ° ≦ β ≦ 150 ° is preferable. The landing area of the liquid curtain on the web may be other than the area wound on the back roll.

Fig. 3 shows the relationship between β and the flow rate (cm ³ / cm · sec) per unit width of the liquid curtain when the liquid viscosity is 30 cp and the coating speed is 100 m / min.
Curve a in the figure is a critical curve for bubble inclusion. The curve b is an allowable critical curve due to other factors, and the region that gives good coating quality is the part between the curves a and b that includes the hatch.

(Example) Next, the effect of the present invention is shown by an example.

Comparative Example A polyethylene terephthalate film was coated with the following three coaters at a coating speed of 100 m / min. β = 120 °
The viscosity was adjusted to 30 cp at the coating temperature.

Example-1 Coating was performed with the following three coaters under the same coating conditions as above.

Example-2 Coating was carried out with a coater of α = 70 ° R = 40 mm while changing β under the same coating conditions as above.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining the coating system of the present invention. FIG. 2 is a relationship diagram between the angle α and the allowable minimum flow rate, and FIG. 3 is a relationship diagram between the angle β and the liquid curtain flow rate. 1 ... Coater, 2 ... Back roll 3 ... Liquid curtain, 4 ... Support web 11 ... Sliding surface, 12 ... Lip eaves α ... Sliding surface inclination angle β ... Liquid curtain driving angle R ... Lip eave curvature radius, l ... Eaves

Claims (2)

[Claims] 1. A support body for laminating at least two kinds of liquid layers on a slanted slide surface, which is hung down from a curved lip-shaped eave at the end of the slide surface, and which runs a free-falling laminated liquid curtain formed. In the multilayer curtain coating method of landing and laying on a support, the inclination angle α of the sliding surface with respect to the horizontal plane is 30 to 70.
The coating method is characterized in that the surface of the curved lip-shaped eaves that contacts the laminating liquid is a cylindrical surface having a curvature radius of 40 mm or more. 2. An angle β between the downward direction of the laminated liquid curtain and the traveling direction of the support at the landing point of the liquid curtain is 12
The coating method according to claim 1, which is 0 to 150 °.