JPH10309506A - Coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating method in which coating defects due to various phenomena are prevented from occurring by restraining a teapot, a contraction, a heel and an air entraining phenomenon and by stabilizing a coating liquid film at the time of a curtain coating. SOLUTION: In a curtain coating method in which a thin film liquid material consisting of at least two kinds of coating liquids is made to fall freely and is applied on a supporting body continuously traveling, all the layer average velocity on a coating die head slide surface is made from 9 cm to 15 cm per second, the viscosity of the utmost upper layer coating liquid at the time of low shearing is made from 80 cps to 20 cps and the viscosity of the utmost lower layer coating liquid at the time of high shearing is made from 5 cps to 20 cps.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of a silver halide photographic light-sensitive material, and a thin liquid material (hereinafter, referred to as a coating liquid film) on a continuously running belt-like support (hereinafter, referred to as a web). To a multi-layer coating by a curtain coating method.

[0002]

2. Description of the Related Art As a multi-layer simultaneous coating method, a slide bead method or an extrusion method is generally known. The curtain coating method is a method in which a coating liquid film is applied by freely falling onto a continuously running web and is applied as a basic technology.
Nos. 9-24133 and 49-35447.

In recent years, with the demand for higher-speed coating to improve productivity, various problems have been taken up and countermeasures have been taken. JP-A-3-
Japanese Patent No. 146172 discloses a phenomenon in which fine bubbles are trapped between a web and a coating liquid film (hereinafter, referred to as an air entrainment phenomenon), and a contact line between a web and a coating liquid film (hereinafter, referred to as a phenomenon). A phenomenon in which a liquid pool occurs in the liquid contact portion (hereinafter, referred to as a heel phenomenon),
A phenomenon in which a coating liquid film does not adhere to a web and jumps (hereinafter, referred to as a dripping phenomenon) is described.

[0004] In addition to these three phenomena, other phenomena peculiar to curtain coating are phenomena behind a coating liquid film (hereinafter referred to as a teapot phenomenon) and a phenomenon in which the coating liquid film is separated from an edge guide (hereinafter referred to as a contraction phenomenon). ). The theoretical treatment of these phenomena is described in detail in SFKistler and Schweizer's book "1997, Liquid Film Coating".

[0005] With the application of high-speed coating, it has been required to concentrate the coating solution for the purpose of reducing the drying load. Concentration of the coating solution increases the viscosity of the coating solution. In the curtain coating method, since the coating liquid film naturally falls vertically downward along the edge guide, a velocity gradient is generated in the vicinity of the edge guide due to the action of viscous resistance, and contraction occurs. If the contraction proceeds, the coating liquid film may eventually be destroyed.

Various methods and devices have been disclosed to avoid such phenomena. For example, Japanese Patent Publication No. 49-354
No. 47 and JP-A-1-199668 describe a method of supplying a low-viscosity auxiliary liquid along an edge guide. Although a stable coating liquid film can be obtained with a low coating amount according to the present disclosure method, a means for separately removing the excessive liquid is required because the excess liquid forms a thick coating portion on both edges of the coating liquid film. Further, there is a problem that the pulsation caused by the supply of the auxiliary liquid propagates to the coating liquid film and causes uneven coating.

[0007] As the coating speed increases, the amount or speed of air entrained on the web surface increases, and the replacement of the web-air solid-gas interface with the web-coating liquid solid-liquid interface is not sufficiently performed. A phenomenon called companion has come to be seen. The coating liquid film fluctuates due to the air entrainment phenomenon, causing coating unevenness. In addition, with an increase in the amount of entrained air, the coating liquid film may eventually scatter without being crosslinked on the web.

A method and an apparatus for removing air entrained in a web for the purpose of suppressing such a phenomenon and performing coating at a high speed without coating failure are disclosed. For example,
Japanese Patent Publication No. 24133 discloses an entrained air suction device having a slit-shaped suction nose disposed upstream of a coating liquid film. Japanese Patent Application Laid-Open No. 3-65266 discloses a coating method and a coating apparatus characterized by uniformly blowing air in a direction opposite to a running direction of a web over a width direction of a web onto a web coating surface immediately before coating. Have been.

However, although the amount of air entrained in the web can be reduced to some extent by the above-described apparatus, the properties of the coating liquid are closely related to the air entrainment phenomenon, so the removal of entrained air is insufficient depending on the physical properties. There is a problem that it becomes. This was written by Gutov (EDGA
This is illustrated by the coating operation limit diagram in the curtain coating method presented by Kistler (1984, SFKistler) cited in RB. GUTOFF (1995, Coating and Drying Defects).

The coating operation limit diagram shows the coating liquid density ρ (g / g
cm ³ ), the coating solution viscosity at low shear μ (g / cm / sec), the Reynolds number Re (= ρq / μ) defined by the coating solution flow rate per unit width q (cc / sec / cm), and web transport Speed U
The occurrence of the heel phenomenon is indicated by the relationship of the ratio (U / V) to the free fall velocity V (cm / sec) of the coating liquid film (cm / sec), and the heel phenomenon is indicated by the relation between the web transport speed and the minimum film formation flow rate. The phenomenon and air entrainment are described. Here, the minimum film forming flow rate is a coating liquid flow rate per unit width which is minimum required for stably forming a coating liquid film. Specifically, it is shown that as the Re number is increased, that is, the lower the viscosity is, the more the heel is generated, and the higher the viscosity is, the more the air entrainment phenomenon occurs. Is shown to decrease.

On the other hand, the teapot phenomenon is a phenomenon in which the coating liquid film does not fall vertically downward and tries to go around the rear of the lip, and the momentum due to the flow velocity difference between the uppermost coating liquid and the lowermost coating liquid at the lip is reduced. It is due to imbalance. The teapot phenomenon is remarkable when the viscosity of the lowermost layer decreases, that is, when the Re number is large, causing unevenness of the wetting line at the lip and causing distortion in the coating liquid film, and the coating amount in the width direction of the coating liquid film is reduced. It is not uniform, and good coating surface quality cannot be obtained.

An apparatus for stabilizing a coating liquid film by linearizing a wetting line by designating a lip shape in order to reduce such a teapot phenomenon is disclosed in Japanese Patent Application Laid-Open No. 1-3816.
No. 6 and Japanese Patent Publication No. 6-509505. Although the unevenness of the wetting line due to the teapot effect can be reduced to some extent by improving the shape of the lip, it has not been a complete measure because it largely depends on the properties of the coating solution as described above.

Japanese Patent Laid-Open Publication No. 1-131549 discloses measures for suppressing the heel phenomenon and the teapot phenomenon. Specifically, the viscosity of the lowermost layer coating liquid is 40 cps or more, the viscosity of the uppermost layer coating liquid is 30 cps or less, and the viscosity ratio of the coating liquid between the two layers that are stacked and in contact with each other is 2 or less based on the low viscosity side. It is a coating technique. In any of the disclosed viscosities, the shear rate is 10 ³ sec
Value at ^-1 .

However, with the recent demand for high-speed coating, in high-speed coating such as exceeding 250 m / min, the shearing speed in the liquid contact portion becomes at least 10 ⁵ sec ⁻¹ or more. Accordingly, the method disclosed in Japanese Patent Application Laid-Open No. 1-131549 has a problem that the teapot phenomenon and the heel phenomenon can be avoided at the same time, but the air entrainment phenomenon cannot be suppressed.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to provide a teapot phenomenon, a contraction phenomenon, and a phenomenon peculiar to a curtain coating method. An object of the present invention is to provide a coating method for stabilizing a coating liquid film by simultaneously avoiding an air entrainment phenomenon and a heel phenomenon, thereby preventing occurrence of coating defects.

[0016]

The object of the present invention is to allow a thin film liquid comprising at least two or more coating liquids to fall freely,
In the curtain coating method of coating on a continuously running support, the average flow velocity of all layers on the slide surface of the coating die head is 9 cm or more and 15 cm or less, and the viscosity of the uppermost layer coating solution at low shear is 8 cps or more and 20 cps or less. And the viscosity at the time of high shear of the lowermost layer coating solution is 5 cps or more and 20
The problem is solved by a coating method characterized by being cps or less.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the average flow velocity of all layers is a value obtained by calculating the flow velocity distribution of each layer on the slide surface of the coating head by a weighted average weighted by the liquid film thickness of each layer on the slide surface. is there. 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 obtaining the solution of the NS equation, for example, in the case of a two-layer flow, the liquid film thickness can be obtained by Equation 1 and the flow velocity distribution of each layer can be obtained by Equations 2 and 3.
The same calculation can be performed for a multilayer flow of three or more layers. 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, and ρ is the coating liquid density [g / c.
m3] and μ are the viscosity of the coating solution at low shear [g / cm / se
c] and q are the coating amount [g / cm2], δ is the liquid film thickness [cm], g is the gravitational acceleration [cm / sec2], θ is the angle between the slide surface and the vertical direction, and subscripts 1 and 2 are They represent the lower and upper layers, respectively.

[0019]

(Equation 1)

[0020]

(Equation 2)

[0021]

(Equation 3)

As a result of experiments by the present inventors, it has been found that the teapot phenomenon is strongly influenced by the average flow velocity of the whole layer on the slide surface, and that the teapot phenomenon can be avoided if the average flow velocity is in the range of 9 cm to 15 cm per second. Was.

[0023] In the present invention the viscosity at low shear, the viscosity shear rate at 10 sec ^-1, and viscosity at high shear, shear rate definitive to 10 ⁵ sec ^-1 or 10 ⁶ sec ^-1 or less It is viscosity. Thickeners or non-Newtonian additives (polymeric substances) to give the coating liquid a so-called non-Newtonian property in which the viscosity changes with the shear rate.
Is well known in the art. In the present invention, the shear viscosity was measured using a facing jet extensional viscometer (RFX manufactured by Rheometrics).

In the present invention, the viscosity of the uppermost layer coating solution at low shear is preferably in the range of 8 cps to 20 cps, more preferably 10 cps to 15 cps.
ps or less. When the viscosity is less than 8 cps, the contraction phenomenon is avoided, but the coating liquid film is easily influenced by the surrounding air flow of the coating liquid film, so that the coating liquid film swings with a slight change in the air flow. Further, the liquid-contacting portion is also sensitive to vibration, and the vibration may cause a coating failure. On the other hand, if the viscosity exceeds 20 cps, the viscous resistance acting on the edge guide increases, and the contraction phenomenon becomes remarkable. By setting the viscosity of the uppermost layer coating liquid at the time of low shear within the above range, the viscous resistance acting near the edge guide can be reduced, so that the supply of the auxiliary liquid as disclosed in JP-A-1-199668 is No means is required.

In the present invention, the viscosity of the lowermost layer coating solution at high shear is preferably 5 cps to 20 cps, more preferably 8 cps to 12 cps. When the viscosity is less than 5 cps, coating failure occurs due to a heel phenomenon. If the viscosity exceeds 20 cps, the air entrainment phenomenon and the dripping phenomenon become remarkable.

In the present invention, the viscosity at the time of low shear of the lowermost layer coating solution is arbitrarily determined as long as the above-mentioned condition of the average velocity of all layers is satisfied.

In the present invention, the number of intermediate layers may be one or two or more. Further, a two-layer structure including the uppermost layer and the lowermost layer without the intermediate layer may be employed. The viscosity of the intermediate layer at the time of low shear is appropriately determined within the range of the viscosity of the adjacent layer at the time of low shear as long as the above-mentioned condition of the average flow velocity of all layers is satisfied.

In the present invention, the flow rates of the lowermost layer, the intermediate layer, and the uppermost layer are each arbitrarily determined as long as the condition of the average velocity of all the layers is satisfied.

The thickener used in the present invention may be any of known and known thickeners. Particularly, the thickener has a remarkable thickening effect and may cause a failure during coating (for example, a coagulated product or a deteriorated coating surface quality). Thickeners, for example, water-soluble polymers having a sulfate ester group described in JP-B-36-21574,
JP-B-35-11989 and JP-B-45-12822.
Dextran and its sulfate ester described in Japanese Patent Publication No. Sho 53-18687, a polymer having a sulfonic acid group, a carboxylic acid group or a phosphoric acid group described in Japanese Patent Publication No. Sho 53-18687,
A styrene / maleic anhydride copolymer or a condensate of styrene / maleic anhydride copolymer and polyvinyl alcohol described in JP-A-43135 is used, but is not limited thereto.

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 typified by polyoxyethylene alkylphenyl ether, an alkyl ester, or the like, or an amphoteric surfactant such as an alkyl amino acid can be appropriately selected and used.

In the present invention, the amount of the surfactant added is adjusted so that the concentration exceeds the critical micelle concentration.

The web used in the present invention includes plastic film, metal, resin-coated paper, synthetic paper and the like. As the material of the plastic film, for example, polyolefin, polyester, cellulose acetate and the like are used. Typical examples of the resin used for the resin-coated paper include polyethylene and polyolefin, but are not necessarily limited thereto. Further, as the metal web, for example, an aluminum web is used. Furthermore, in the case of resin coated paper and plastic film,
In order to improve the wettability, a water-soluble polymer such as gelatin can be applied in advance as an undercoat layer.

The surface roughness of the web used in the present invention is as follows:
0.2 μm or less, more preferably 0.1 μm
It is as follows.

The coating solution in the present invention includes a coating solution for a photosensitive emulsion layer, an undercoat layer, a protective layer, a back layer, etc. as in a photographic material.

[0035]

EXAMPLES Coating was carried out by a curtain coating apparatus described in JP-B-49-24133, according to the following conditions. Operating conditions Coating speed (web transport speed): 300 m / min Web: 100 μm thick polyethylene terephthalate film Web width: 350 mm Application width: 320 mm Curtain height: 75 mm Coating die head slide surface inclination angle: 23 degrees with respect to the horizontal direction

Coating liquid: Temperature setting: 38 ° C. Viscosity of each layer: 1.5% of the gelatin coating amount of each layer as a solid content.
g / m ^2, and the viscosity was adjusted to a predetermined value by appropriately changing the amount of the thickener added. Unless otherwise specified, the viscosity shall indicate the viscosity at low shear. The surface tension was measured by a plate method (CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.). Top layer: protective layer (aqueous gelatin solution) Surface tension: 25 dyne / cm Flow rate: 1.0 cc / sec / cm Middle layer: silver halide emulsion layer Surface tension: 30 dyne / cm Flow rate: 1.0 cc / sec / cm Bottom layer: Undercoat layer (aqueous gelatin solution) Surface tension: 30 dyne / cm Flow rate: 1.0 cc / sec / cm

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

[Table 4]

[0041]

According to the present invention, the coating liquid film is stabilized by simultaneously avoiding the teapot phenomenon, the contraction phenomenon, the heel phenomenon, and the air entrainment phenomenon in the multilayer curtain coating, and the coating defects caused by the various phenomena are prevented. The occurrence could be prevented.

Claims (1)

[Claims] 1. A curtain coating method in which a thin film liquid material comprising at least two or more kinds of coating liquids is freely dropped and coated on a continuously running support. 9cm or more per second 15c
m, the viscosity of the uppermost layer coating solution at low shear is 8 cps to 20 cps, and the viscosity of the lowermost layer coating solution at high shear is 5 cps to 20 cps.