JPS63148251A - Coating method - Google Patents

Abstract

PURPOSE:To stabilize coating of thin films by increasing the flow rate of a coating liquid to the flow rate higher than a normal flow rate at the starting time of coating in the case of coating said liquid onto a traveling web. CONSTITUTION:The flow rate of the coating liquid is increased to the rate higher than the normal flow rate at the starting time of coating in the case of coating said liquid onto the traveling web by a slide bead coating method. The web 10 travels by being wound around a back up roll 1 and contacts the coating liquid passed from a slot 4 of a slide bead coating machine 2 to a sliding surface 5 in a lip part 6 of the coating machine to form a bead 21 which is a ribbon-shaped liquid pool. The coating liquid is coated on the web through said bead 12. A method for stabilizing the bead by pulling downward the bead by a pressure reducing device 3 is generally adopted. The coating of the thin film in particular is thereby stably executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a slide bead coating method, and more particularly to a method for coating thin films.

[Conventional technology]

Photographic materials generally contain hydrophilic colloids (e.g. gelatin) containing additives that suspend silver halide grains and/or adjust photographic properties and productivity, and are made of hydrophilic colloids (e.g. gelatin) that suspend silver halide grains and/or contain additives that adjust photographic properties and productivity. It is manufactured by continuously coating and drying at 122.

Initially, the dip method, double roll method, air doctor method, etc. were used as a method for coating the web with the photographic layers constituting the photographic material, and the curtain coating method and slide bead coating method were used in response to the demand for simultaneous multi-layer coating at high speed. was developed, and the slide bead coating method has now become mainstream.

Regarding the slide bead coating method, US Pat.
No. 81,294, No. 2,761.419, No. 2,76
No. 1,791 and US Pat. No. 837.095.

As described in the above-mentioned patent, the slide and one-drive coating method involves extruding one or more coating liquids as a continuous wide ribbon through a slit provided in a slide hopper, and creating a web that runs close to the lip at the end of the slide surface. A single layer or laminated ribbon of the coating liquid is passed across the surface to form a bead, and the casting speed of the coating liquid is matched with the running speed of the web to remove the ribbon from the bead, so that the ribbon is not coated in a single layer on the web. A laminated coating is applied. Note that the web running in the direction -a is stretched over a coating backup roller provided close to the lip portion.

Therefore, in the slide bead coating method configured in this way, it is essential that the coating liquid supply amount and web running speed (coating distance) be perfectly matched, but there is also a difference between the web and the lip. The shape stability of the bead formed by the passed coating liquid ribbon has a great influence on the uniformity and drying of the coating film.

For example, bead tracking with respect to the running direction of the web! ! If the vibration of the bead occurs in the longitudinal direction of the web, it will simply cause horizontal stripes (ribbed unevenness) and coating breaks, and if the vibration causes mixing between the coating liquid layers at the bead position, it will cause spotting and vertical unevenness. Causes uneven streaks.

These disadvantages cannot be avoided unless the bead itself has an active self-righting force for stabilizing the bead shape.

U.S. Pat. No. 2,681,294 discloses a reduced-pressure type slide bead coating in which a reduced-pressure chamber is attached and the beads are suctioned by reduced pressure in a direction opposite to the running direction of the web to stabilize the bead.

Important factors related to bead stability include flow rate, physical properties of the coating liquid, coating temperature, vacuum conditions, and the gap between the coating machine lip and the web stretched over the coating backup roller (hereinafter referred to as bead gap).

Among these, the higher the flow rate, the higher the coating stability, but the desired dry film thickness and coating properties (viscosity, gelatin concentration, surface tension, etc.)
Because of this relationship, the range of choices is self-limited.

In recent years, in the photographic photophobic materials industry, the need for thin film coating has been greatly increasing, mainly due to demands for improved performance.

When coating a thin film, it is necessary to reduce the coating flow rate, but if you start coating (starting bead formation) with this reduced flow rate, it will be possible to reduce the coating flow rate depending on the degree of thin film, bead gap, and coater vacuum. A phenomenon occurs in which bead formation is difficult in the hand direction.

[Problem that the invention seeks to solve]

In view of the above-mentioned problems, an object of the present invention is to provide a coating method that can stably perform thin film coating by stably forming a bead at the start of coating in slide bead coating.

[Means for solving problems]

It has been found that the above object of the present invention can be achieved by a coating method characterized by increasing the flow rate of the coating liquid from the normal flow rate at the start of coating when coating a running web using the slide bead coating method. Ta. In the case of a multilayer coating of 2M or more, it is reasonable from the viewpoint of cost and cattle production to use a coating liquid that does not contain silver halide.

The present invention will be specifically explained below with reference to the drawings. FIG. 1 is a schematic side sectional view of a slide bead coating machine. web 10
travels while being held by the coating backup roll 1, and comes into contact with the coating liquid flowing onto the slide surface 5 from the slot I/4 of the slide bead coating machine 2 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 a decompression device 3. The above mechanism is the same whether there is one layer or two or more layers, and simultaneous multilayer coating 3 can be performed by flowing a plurality of coating liquids onto the slide surface through a plurality of slots. The case shown in FIG. 1 is an example of two-layer coating, in which the emulsion solution was poured into the lower layer and the protective film solution was poured into the upper layer, thereby performing simultaneous overlaying. In FIG. 1, a flow meter and a flow 1 regulating valve are provided in the piping of the route for sending the protective film liquid to the slot. In FIG. 1, in order to increase the flow rate by using the protective film liquid, a flow meter 7 is installed in the protective liquid collection path. An example in which a control valve 8 is provided is shown.

In general, the bead is unstable, especially at the beginning of coating, and when the coating liquid starts to be applied to the web, even if the coating liquid comes into contact with the running web, the coating liquid is not immediately applied to the web and some It is applied after passing through the induction section. In addition, when the flow rate is small, that is, when coating a thin film (for example, a wet film thickness of 50 μm or less), the coating may not be uniformly applied throughout the entire area, and coating may not be possible.

As a result of intensive research, the present invention has been developed so that even when the flow rate is small,
Once a stable bead is formed all the way through,
It was found that the subsequent breakage of the bead can be reduced by selecting the reduced pressure conditions and the conditions of the pond. Therefore, in the present invention, a stable bead is created by increasing the flow rate of the coating solution only at the start of coating, and after uniform coating throughout the entire coating,
By gradually reducing the flow rate, they succeeded in lowering the thin film coating limit in slide bead coating. An example of such a flow rate change is shown in FIG.

Incidentally, such flow rate control is easily possible by applying the flow meter signal shown in FIG. 1 and the signal from the timer to the flow rate control valve.

〔Example〕

Coating a silver halide-containing gelatin solution with a surface tension of 40 dyne/cm onto a subbed polyethylene terephthalate film using a 30 cI11 coater at a coating speed of 40 m.
/min row-y, vacuum degree 30mmAq, beat r
The rrI gap is 200 am. In coating, the limit of the film thickness that could be coated was determined by changing the viscosity. As a result, viscosity Invention Not implemented (cp) (us) (uaA) As described above, it can be seen that in the case of the present invention, the coating thickness limit is significantly lowered compared to the case not implemented, making it possible to apply a thin film. .

In this case, the leading flow rate of the present invention requires the coating limit flow rate described in the unimplemented section, and the flow rate after bead formation is reduced.

Further, although the above embodiments are examples using a single layer, the same applies to a case where a multilayer is used. In the case of a multi-layer structure, it is advantageous in terms of cost to increase the flow rate by using the membrane residue, intermediate layer liquid, etc.

〔Effect of the invention〕

According to the present invention, it has been possible to provide a coating method that can stably perform particularly thin film coating in slide bead coating.

[Brief explanation of the drawing]

FIG. 2 is a diagram showing how the flow rate changes during coating in the present invention. 1: Coating backup roll, 10: Web 2 varnish slide bead coater, 11: Coating film 4 varnish slot,
12: Bead 5 varnished surface,
13: Protective film liquid 6: Lip part, 14:
Emulsion liquid 7: Flow meter 8: Flow rate control valve Applicant: Konishiroku Photo Industry Co., Ltd. Figure 1

Claims (1)

[Claims] A coating method characterized in that when coating a running web by a slide bead coating method, the flow rate of the coating liquid is increased from the normal flow rate at the start of coating.