JP2003071373A - Application method - Google Patents

Abstract

(57) [Problem] To provide a curtain coating method for stabilizing a multilayer curtain film by preventing curtain film distortion due to a teapot phenomenon and preventing occurrence of coating defects. In a slide curtain coating method in which a thin film liquid material in a laminated state is freely dropped and simultaneously coated on a continuously running support, an average flow velocity of all layers on a coating die slide surface is 9 cm or more and 15 cm or less, and A curtain coating method, wherein the difference between the dynamic surface tensions of the uppermost layer and the lowermost layer is within 25 dyn / cm.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of silver halide photographic materials, magnetic recording materials, pressure- and heat-sensitive recording papers, art papers, coated papers, and ink-jet recording sheets. , A belt-shaped support that runs continuously (hereinafter referred to as a web)
The present invention relates to a method of applying a liquid thin film (hereinafter, referred to as a curtain film) to a liquid. 2. Description of the Related Art A slide bead method or an extrusion method is generally known as a multi-layer simultaneous coating method, but in recent years, a curtain coating method has been frequently used with the demand for high-speed coating. Have been. The curtain coating method is a method in which a curtain film is applied by freely falling onto a continuously running web, and is disclosed as a basic technique in Japanese Patent Publication Nos. 49-24133 and 49-35447. [0003] When coating on a web with a curtain coating device, the instability of the free-falling curtain film has a significant effect on product quality. A typical phenomenon that hinders the stability of the curtain film is a phenomenon behind the curtain film (hereinafter, referred to as a teapot phenomenon). A book on the teapot phenomenon by SFKistler and Schweizer "
1997, LIQUID FILM COATING ”. [0004] The teapot phenomenon is a phenomenon in which the curtain film does not fall vertically downward and tries to wrap around the lip. The teapot phenomenon is remarkable when the viscosity of the coating solution decreases or the coating amount increases, that is, when the Reynolds number of the coating solution is relatively large. [0005] Such a teapot phenomenon is liable to cause a streak failure due to the unevenness of the wetting line, and to make it impossible to obtain a good coated surface quality because the coating amount in the width direction of the curtain film becomes uneven. For example, to reduce the momentum of the coating solution on the slide surface, the viscosity of the lowermost coating solution is increased to 40 cP or more. Coating method which is characterized in that is is Hei 1-131549
Japanese Patent Application Laid-Open No. 10-309506 discloses a coating method in which the range of the average flow velocity of the entire coating liquid layer on the slide surface is adjusted in order to adjust the momentum of the coating liquid. An apparatus for linearizing a wetting line and stabilizing a curtain film is disclosed in JP-A-1-381.
Japanese Patent Application Laid-Open No. Sho. 51-66 and Japanese Patent Publication No. 6-509505 disclose a coating method in which the shape of an edge guide is devised to reduce curtain film distortion due to a teapot phenomenon.
-57734 and JP-A-9-253552. [0006] Even though the teapot phenomenon can be suppressed to some extent by these disclosed methods, it has not been a sufficient countermeasure for a wide variety of coating liquid properties, flow rates, and the like. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to prevent a curtain film from being distorted due to a teapot phenomenon so that a multilayer film can be formed. An object of the present invention is to provide a coating method for stabilizing a curtain film and preventing the occurrence of coating defects. [0008] The object of the present invention is to provide a slide curtain coating method for free-falling a thin film liquid material in a laminated state and simultaneously coating it on a continuously running support. This is achieved by a curtain coating method, wherein the layer average flow rate is 9 cm or more and 15 cm or less per second, and the difference in dynamic surface tension between the uppermost layer and the lowermost layer is 25 dyn / cm. Hereinafter, the present invention will be described in detail.
FIG. 1 shows a perspective view of a curtain coating apparatus. As described in JP-B-49-24133, curtain coating is performed by uniformly supplying a coating liquid from the slit 5 to form a coating liquid in a laminated state on the slide surface 4 and to apply the coating liquid to the pair of edge guides 6. Along the way, the coating film is dropped freely from the lip tip 1 as a curtain film 7 and collides with the continuously running web 2 to perform coating. [0010] From the great experimental results by the present inventor, it was found that the average flow velocity of all layers of the multilayer coating solution on the slide surface 4 and the difference between the dynamic surface tension differences between the uppermost layer coating solution and the lowermost layer coating solution were simultaneously balanced. It has been found that the curtain film distortion due to the phenomenon can be completely prevented. The dynamic surface tension difference in the present invention is the difference between the surface tension of the uppermost layer coating solution and the surface tension of the lowermost layer coating solution between 5 msec and 20 msec from the start of free fall of the curtain film.
It is preferably at most 25 dyn / cm, more preferably at most 10 dyn / cm. The adjustment of the dynamic surface tension difference is performed by changing the type and amount of the surfactant. In the present invention, the dynamic surface tension difference is important in the multilayer structure, and there is no restriction on the magnitude relationship between the dynamic surface tension values of the respective layers. However, in the case of three or more layers, the dynamic surface tension value of the uppermost layer needs to be set equal to or slightly smaller than the surface tension value of the layer adjacent to the uppermost layer. It is preferable that the gradient of decrease in the dynamic surface tension of the lowermost layer coating solution whose interface is renewed at the tip of the lip is larger than the dynamic surface tension of the uppermost layer coating solution as a free surface. It is preferable that the temperature falls to 60 dyn / cm or less within 20 msec. More preferably, 5 msec to 20 msec
During this time, it should be reduced to 40 dyn / cm or less. In the present invention, the average flow velocity of all layers is a value obtained by weighting the flow velocity distribution of each layer on the slide surface 4 with the liquid film thickness of each layer on the slide surface 4. The flow velocity distribution and the liquid film thickness of each layer can be obtained by solving Navier-Stokes equation (hereinafter referred to as NS equation) which is a basic equation of the viscous fluid. By finding the solution of the NS equation, for example, in the case of a two-layer flow, the liquid film thickness is expressed by Equation 1, the average flow velocity of each layer is expressed by Equation 2 (average flow velocity of the lower layer coating liquid), and Equation 3 (the upper layer coating liquid). (Average flow rate of liquid). Three
A similar calculation can be made for a multi-layer flow of more than one layer. In Formulas 1, 2, and 3, X is the liquid film thickness ratio obtained by dividing the upper liquid film thickness by the lower liquid film thickness, ρ is the coating liquid density [g / cm ³ ], and μ is the coating liquid viscosity [ g / cm / sec], and q is the coating amount [g / cm
cm ² ], δ is the liquid film thickness [cm], g is the gravitational acceleration [cm / sec ² ], θ
Is the angle that the slide surface 4 makes with the vertical direction, suffix 1,
2 represents a lower layer and an upper layer, respectively. [Equation 1] ## EQU2 ## [Equation 3] The average flow velocity of the whole layer is 9 cm or more per second and 15 c
m, more preferably within a range of 10 cm or more and 12 cm or less per second, the coating amount q, the coating solution viscosity μ, and the angle θ formed by the slide surface 4 with the vertical direction are adjusted. In the present invention, the number of intermediate layers may be one or two or more. Further, the intermediate layer may be omitted to have a two-layer configuration including the uppermost layer and the lowermost layer. In the present invention, the flow rates and viscosities of the uppermost layer, the intermediate layer, and the lowermost layer coating solution are each arbitrarily determined as long as the above-mentioned condition of the average velocity of all layers is satisfied. Examples of the surfactant in the present invention include anionic surfactants such as sodium alkyl sulfate and sodium alkylbenzene sulfonate, and cationic surfactants such as alkylammonium chloride and alkylpyridinium chloride. An activator, a nonionic surfactant represented by polyoxyethylene alkyl phenyl ether, an alkyl ester or the like, or an amphoteric surfactant such as an alkyl amino acid can be appropriately selected and used. The thickener used in the present invention may be any of known and known thickeners. Particularly, the thickener has a remarkable thickening effect and is liable to cause a failure during coating (for example, a solidified product or a deteriorated coated surface quality). Thickeners, for example, water-soluble polymers having a sulfate group described in JP-B-36-21574, JP-B-35-11989 and JP-B-45-12822.
Dextran and its sulfate ester described in
Sulfonic acid groups described in JP-B-53-18687,
Polymer having a carboxylic acid group or a phosphoric acid group, Japanese Patent Publication No. Sho 4
A styrene / maleic anhydride copolymer or a condensate of styrene / maleic anhydride copolymer and polyvinyl alcohol described in JP-A-8-43135 is used, but is not limited thereto. EXAMPLES Coating was performed by a curtain coating apparatus described in Japanese Patent Publication No. 49-24133 under the following conditions. Web: 140 μm thick polyethylene resin-coated paper Curtain film width: 500 mm Curtain height: 80 mm Coating speed: 300 m / min Angle θ between the slide surface and the vertical direction: 67 degrees Coating solution: Temperature setting: 40 ° C. Alkaline treatment The viscosity was adjusted by changing the amount of the thickener (sodium polystyrene sulfonate) added to the aqueous solution of 7% by weight of gelatin so that the average flow rate in all layers became each value shown in Table 1. In this embodiment, the average flow velocity of all layers is changed by adjusting the viscosity of the coating solution. However, the present invention is not limited to this. Alternatively, it is also possible to adjust the average velocity of all layers to a desired value by changing the combination of these conditions. The type and amount of the surfactant differ depending on the degree to which the dynamic surface tension difference should be set. For example, when the dynamic surface tension difference is set to 8 dyn / cm,
0.1 g / L of sodium di-2-ethylhexylsulfosuccinate was added to the lower coating solution, and 2.5 g / L of sodium POE (4) nonylphenyl ether sulfate was added to the upper coating solution. Layer composition: 2 layers Flow rate Lower layer: 2.0 [ml / sec / cm] (coating amount: 40 g / m ² ) Upper layer: 0.5 [ml / sec / cm] (coating amount: 10 g / m ² ) (BM type manufactured by TOKIMEC). Dynamic surface tension is measured by the membrane fracture method (SPLin, J. Fluid
Mech (1981)). The state of forming a curtain film during coating was evaluated according to the following criteria. Table 1 shows the results. Evaluation criteria for curtain film distortion due to the teapot phenomenon. ：: No film distortion was observed. Δ: Weak film distortion was observed, and weak wrinkles occurred at both edges of the curtain film. ×: Strong film distortion was observed, and wrinkles occurred in the curtain film. The number of occurrences of muscle failures in Table 1 is 4 per reel.
The total number of reels in which a streak failure occurred when 25 webs of 00 m length were continuously applied. [Table 1] According to the present invention, in a method for simultaneously applying a coating liquid in a laminated state by a slide curtain coating device, a coating film defect is prevented by stabilizing a multilayer curtain film by avoiding a curtain film distortion due to a teapot phenomenon. It was possible to provide a coating method for preventing occurrence.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a curtain coating apparatus described in Japanese Patent Publication No. 49-24133. [Description of Signs] 3 Coating die 4 Slide surface 5 Slit 7 Curtain film

Claims (1)

Claims 1. A thin film liquid material in a laminated state is allowed to fall freely,
In the slide curtain coating method of simultaneously coating on a continuously running support, the average flow velocity of all layers on the coating die slide surface is 9 cm or more and 15 cm or less, and the difference in dynamic surface tension between the uppermost layer and the lowermost layer is 25 dyn / Curtain coating method characterized by being within cm.