JPH01205154A - Process for forming multiple coating layer simultaneously - Google Patents

Abstract

PURPOSE:To enable formation of multiple coating layers stably also at high speed under conditions for forming thin film by regulating the viscosity of a lowermost layer to <20cP and that of the next layer to below the viscosity of the lowermost layer. CONSTITUTION:Coating liquid 13, 14 flowing down along a slide is formed to thin films by deflecting the coating liquid in the radial direction at a bead part 12 and lifting up on a web 10. The shearing velocity of the coating liquid is low when flowing down along the slide surface 5 but increases gradually as it flows downward and attains a high shearing velocity at the bead part 12. The viscosity of the coating liquid 14 which forms the lowermost layer is regulated to <=20cP at a stage of low shearing velocity, but higher than the viscosity of the coating liquid 13 which forms a layer next to the lowermost layer. The coating liquid 14 for the lowermost layer is prepd. in such a manner that its viscosity is higher than the viscosity of the next layer even at a stage of high shearing velocity. By this constitution, defect of generating streaks is prevented even in a stage of executing coating at high speed under conditions for forming thin film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a multilayer simultaneous coating method using a slide hopper device.

[Prior Art] An example of coating a photographic light-sensitive material on a long flexible support commonly referred to as a web using a slide hopper device is an example of coating a photographic light-sensitive material. In this method, multiple layers flow simultaneously over a slide surface, forming a bead at the point where it meets the moving web at the end of the slide, and applying the multiple coating layers onto the web simultaneously via this bead. Bead stability is very important in this coating method, and techniques are often used to stabilize the bead, for example, by creating an air pressure difference between the top and bottom of the bead and creating a negative pressure on the bottom side. ing. In such a coating method, especially in the case of simultaneous multi-layer coating, the physical properties of the coating liquid of each coating layer and their mutual relationships are very important for stable coating.

In recent years, photographic materials have become thinner and there is a strong demand for high-speed coating, and in such cases it is becoming increasingly difficult to perform stable coating.

Conventionally, as a countermeasure to this, the viscosity of the bottom layer has been lowered. For example, in Japanese Patent Publication No. 56-20534, the wet film thickness of the bottom layer 2 to 12 μm (hereinafter referred to as hw)
The viscosity is 1-8 cp, and the next layer is hw 15-20 p.
A method is disclosed in which the viscosity is 10 to 100 cp. In this case, since the viscosity of the bottom layer is low, the bead portion becomes unstable and glabellar mixing occurs between the bottom layer and the next layer.

Japanese Patent Publication No. 60-12107 discloses a method in which the viscosity of the bottom layer is 20 to 200 cp at low shear rates (10'5 ec-') and 10 cp or less at high shear rates (10'5 ec-'). However, setting only the bottom layer may cause interlayer mixing.

JP-A-56-108566 discloses a method in which the viscosity difference between the bottom layer and the adjacent layer is set to ±10 (!) at low shear rates, and the bottom layer has a lower viscosity than its adjacent layer at high shear rates. are doing.

Furthermore, Japanese Patent Laid-Open No. 174970/1983 discloses a method in which the same method as above is applied to the uppermost layer and its adjacent layer.

In JP-A No. 59-100434, an acceleration layer is provided below a relatively high viscosity layer, and an extension layer is provided above it, and this acceleration layer has a viscosity of 1 to 20 (!I) when hw is 2 to 30 μm. A method is disclosed in which the extension layer has a hw of 5 to 20 μm and 1=10 cp.

All of the above patents basically involve making the viscosity of the bottom layer lower than the viscosity of the next layer, but lowering the viscosity under thin film coating conditions is advantageous for bead formation, but it also causes streaks. tends to deteriorate. In fact, we found that the higher the viscosity of the bottom layer, the less streaks occur.

[Problems to be Solved by the Invention] In order to solve the above-mentioned problems, an object of the present invention is to provide a coating method that is unlikely to cause streak failure even under high-speed, thin-film conditions when performing multilayer simultaneous coating using a slide hopper device. That's true.

Means for Solving Problem E] The above object of the present invention is to solve the problem by using a slide hopper device,
In a multilayer simultaneous coating method in which a large number of coating liquids are simultaneously applied to a moving web, the viscosity of the coating liquid forming the bottom layer is 20 cp or less at a low shear rate, and the coating liquid forming the next layer after the bottom layer is The coating liquid forming the bottom layer is prepared and applied so that the viscosity is higher than that of the coating liquid used for forming the bottom layer, and the viscosity of the bottom layer is higher than the viscosity of the next layer even at high shear rates. This is achieved by a multilayer simultaneous coating method.

In the above method, the chemical compositions of the bottom layer and the next layer may be substantially the same.

Next, a schematic sectional view of the slide hopper device used in the present invention is shown in FIG.

The web 10 runs while being held by the coating backup roll 1, and comes into contact with the coating liquid flowing from the slot 4 of the slide bead coating machine 2 onto the slide surface 5 at the coating machine lip part 6, and forms a ribbon-shaped liquid pool in the lip part. A bead 12 is formed through which the coating liquid is applied onto the web. At this time, a method is generally adopted in which the bead is stabilized by pulling the bead downward with the decompression device 3. The above mechanism is the same whether it is a single layer or two or more layers, and simultaneous multilayer coating can be performed by flowing a plurality of coating liquids onto the slide surface through a plurality of slots. The case in Figure 1 is an example of two-layer coating,
This is an example of simultaneous multilayering in which the emulsion liquid 14 is poured into the lower layer and the protective film liquid 13 is poured into the upper layer. In such slide bead coating, the coating liquid that has flown down the slide is pulled up onto the web by changes in the radial direction at the bead portion and becomes a thin layer. Further, the shear rate of the coating liquid at this time is low as it flows down the slide surface, gradually increases as it flows down, and exhibits a high shear rate at the bead portion.

In the following examples, multilayer coating was performed using such a slide hopper coating device.

[Example] The effects of the present invention will be explained in more detail with reference to Examples below.

Example 1 The bottom layer is a gelatin silver halide emulsion containing silver halide grains, hw 50 μm, and the upper layer is a gelatin protective film solution containing a surfactant, hv 20 μ11. The low shear rate is lo"5ec-', High shear rate 10'5e
It was set as c-'. The support uses a polyester base,
Coating was carried out at a coating speed of 80 m/1/1 inch under the conditions shown in Table 1.

,,6≧Table-1 In Table=1, the numbers in the upper and lower layers represent the viscosity in cp. The results show the number of muscle failures per unit width and length. ☆ caused bead breakage. Low and high indicate shear rates, respectively.

From the results in Table 1, it can be seen that stable coating can be performed under the condition No. 3 of the present invention.

Example 2 A photosensitive material consisting of four layers was coated with the following configuration. The first and third layers from the bottom are gelatin emulsion layers containing silver halides having different color sensitivities, the second layer is a gelatin intermediate layer, and the top layer is a gelatin protective film layer containing a surfactant.

A triacetate base was used as the support, and the coating speed was 150.
m/min, and coating was performed under the conditions shown in Table 2 below. The low shear rate is 102 (sec-'), and the high shear rate is 10'(sec'').

Further, among the following conditions, the viscosity conditions of the third layer and the fourth layer were the same. Thus, the third layer is 20 cp at low shear rates and 11 cp at high shear rates. The fourth layer has a low shear rate of 20
cp, high shear rate 12 cp.

The method of writing Table-2 is the same as Table-1.

The results in Table 2 also show that under condition No. 7 of the present invention, good results with less muscle damage were obtained as in Table 1.

According to other study results, setting the top layer to 20 cp or more actually makes the bead unstable. 20c for the bottom layer
It is important to keep the viscosity of the next layer lower than that of the bottom layer while keeping the viscosity below p.

[Effects of the Invention] According to the present invention, it is possible to provide a coating method that is stable even under high speed and thin film coating conditions when performing simultaneous multilayer coating using a slide hopper device.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a slide bead coating machine. 1: Coating backup roll, 2 Ni slide bead coating machine, 3: Pressure reducing device, 4 Ni slot, 5 Ni slide surface, 6: Lip part, 10: Web, 11: Coating film, 13: Protective film liquid, 14: Emulsion liquid ,

Claims (1)

[Claims] In a multilayer simultaneous coating method in which a large number of coating liquids are simultaneously applied to a moving web using a slide hopper device, the viscosity of the coating liquid forming the bottom layer is less than 20 cp at a low shear rate; The coating liquid forming the bottom layer is prepared so that it has a higher viscosity than the viscosity of the coating liquid forming the next layer after the bottom layer, and further, the viscosity of the bottom layer is higher than the viscosity of the next layer even at high shear rates. A multi-layer simultaneous coating method characterized by coating.