EP0197493A2

EP0197493A2 - Vertical drawing curtain coating method and apparatus

Info

Publication number: EP0197493A2
Application number: EP86104449A
Authority: EP
Inventors: Wang Zhongjun
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-04-01
Filing date: 1986-04-01
Publication date: 1986-10-15
Also published as: JPS61292140A; CN85100851B; CN85100851A; EP0197493A3

Abstract

This invention develops a new kind of vertical drawing curtain coating method and apparatus, which contains three main parts: a higher uniform equal-flow distributing coater, a vertical drawing short-curtain, a parallel rotated coating roller and moving webs. This coating method can simultaneously coat one or more than one layer with high uniformity, and is suitable for silver salt or non-silver salt photo-sensitive materials production. It can use a liqud viscosity from 2 to 1,000 mPas at a coating velocity 30 to 300 mm/in to get a coating weight from 20 to 240 ml/m²; and can avoid coating defects such as those usually found in the bead coating and vertical free-falling curtain coating methods.

Description

Field of The Invention

This invention can simultaneously coat one or more than one layer on a moving web with high uniformity, and is suitable for silver salt or non-silver salt photo- sensitive materials production. It is also suitable for other productions, which require one layer or more than one coating layer such as double coating non-carbon tissue-paper.

Background Of The Art

In the photographic industry, there are used black-and white and colour films or papers. All those products need a coating method, which can coat various liquid components continuously on the paper, film, or cloth with high uniformity. Some products need coating one layer, others need coating two layers, three layers, four layers, or more layers. For example, the negative colour films need coating twelve or sixteen layers. According to the different products requirement, the minimum thickness of the wet coating layer is 0.010 millimetre, and the maximum thickness is 0.200 millimetre. It is a kind of high precise coating technique, so that the standard deviation of the non-uniformity should be less than ±1%, when the width of the coating web is more than 1,000 millimetres.
In the old dip-coating method, the thickness of wet coating layer h, the viscosity of the liquid η, the surface tension of the liquid σ, the coating velocity U and the radius of curvature R have the mathematical relation as following:
which has been described by DERYAGIN B. T. AND LEVI S. M., FILM COATING THEORY, p.47, FOCAL PRESS, LONDON, 1964.
The velocity of this coating method is usually controled at 4 to 18 metres per minute, and gets the thickness of wet coating layer from 0.120 to 0.260 millimetre. However, this coating method can coat only one layer by one pass, and it is difficult to control the accurate coating thickness. Therefore, it has those shortcomings such as: the mono-coating layer, the thicker layer, the lower speed, and flow-down of the coating liquid, and can not satisfy to produce colour films and papers.
T. A. Russell et al. had developed a kind of bead coating method, which had been published in US Pat. No. 2,761, 419 and U.S.Pat. No. 2,761,791. In these so-called bead coating, slide hopper, or cascade coating systems, the liquid composition is accurately fed by the metric pump through the distributing chamber and the delivery gap. Then the coating liquid is over-flown on the slope of the slide hopper, and is contineously coated on the highspeed moving web through the bead, which is suspended between . the lip of the slide hopper and the moving web. As a plurality of liquid coating composition flows under the laminar-flow condition,there is no mixing phenomenon between each two layers. This bead coating method can simultaneously coat at least more than one layer, and get more thiner wet coating layers. The velocity of this coating method is usually controled at 40 to 150 metres per minute, and gets the wet coating thickness from 0.090 to 0.160 millimetre. Therefore this bead coating method has notable advantages such as: the multiple coating layer, the thiner layer, the higher coating speed, and the accurate control coating thickness; and has been widely used to produce colour films and papers with high-quality.
However, the coating bead is suspended between the lip of the slide hopper and the moving web, and there are two independent radius of curvature R₁, R₂, existing on the upper and lower surface of the bead. Similarly to the old dip- coating method, the upper radius of curvature R₁, the thickness of wet coating layer h, the viscosity of the liquid η, the surface tension of the liquid δ, the coating velocity U have the mathematical relation as following:
Otherwise, the upper and lower radius of curvature R₁, R₂₁ the pressure of upper space P₁, the pressure of lower space P₂₁ the density of the liquid p, the acceleration of gravity g, the surface tension of liquid σ, and the thickness of suspending bead h₀, have the mathematical relation as following:
which has been described by Wang Zhongjun, CURRENT THEORY AND PRACTICE OF COATING AND DRYING TECHNIQUE, p.32 to 41, First Film Factory, The Ministry Of Chemical Industry, 1973.
However, as can be seen from the above description and the mathematical relation, the bead coating method has some unavoidable shortcomings as following:

1. The suspending bead between the lip of slide hopper and the moving web is unstable. Especially at the lower coating speed condition, it is easily to result the lateral streak defects on the coating webs by those factors such as: the vibration of circumstance, the unevenness of motion, and the pressure variation of suction chamber.
2. At the higher coating speed condition, this bead coating method is usually to reduce the viscosity of the coating liquid by diluting it with water, that means to require more drying capacity or more energy consumption. The modern colour film or paper requires more thiner coating layer, and the thickness of each wet composition is between 0.010 to 0.035 millimeter. Even at a plural coating condition, the sum of wet thickness of several coating composition is also less than the minimum limit of the bead coating method.
3. The most troublesome problem in the bead coating method is the narrow gap between the moving web and the lip of the slide hopper, the limit range of the gap width is 0.150 to 0.450 millimeter, and is usually controled in 0.200 to 0.350 millimeter. Obviously, in order to avoid any splitting of the web or interruption of the coating operation, the thickness of the splice must be less than the width of the gap. So it is always required to provide a butt splice, or splicing on the inclined position, or'withdrawing the slide hopper when a splice is passing by the coating point. For the same reason, the bead coating method should stop the moving of the web to splice with a special treated adhesive tape and require a voluminous accumulator.
4. In the bead coating operation, any bubble and fine particles of fiber, slug, lump, dust etc. will destroy the stability of the bead to form the "pencil lines" defects at a long distance and to result an enormous waste of product. On the other hand, the unevenness of the surface of the film and paper can also interrupt the stability of the bead to result the waste of product.

D. J. Hughes and J. K. Greiller had developed a new kind of free-falling vertical curtain coating method, which resembles the bead coating method to get a plurality of surperposed layers under the laminar-flow condition, and is similar to the curtain coating method to apply in the painting field. This coating method is allowed to use a liquid composition of higher viscosity from 5 to 100 mPas (1 mPas - 1 c^p). The liquid curtain will be accelerated by gravity at a rate less than acceleration in free falling, and the web is moving on the horizontal direction at the coating speed as far as 0.3 to 3 folds of the velocity of free-falling vertical curtain near the surface of coating web. When the height of free-falling curtain is set at 50 to 200 millimetres and the coating web speed at 1.5 to 5 metres per minute, it will provide the extreme thinness of wet coating layer about 0.020 to 0.080 millimetre. On the other hand, this coating method can avoid those defects such as: "streak", "pencil line", and "interruption by splice" frequently found in the bead coating method, and it is more suitable for the production of the colour film and paper.
However, the free-falling vertical curtain coating method also has some shortcomings as following:

1. The structure of the multiple curtain coater and the air shields both limiting the height of free-falling curtain must be more than 100 to 120 millimeters. Therefore, in the U.S.Pat. No. 3,632,403, U.S.Pat. 4,233,346 and GB.Pat. 1,429,260, there are some different methods to eliminate the thicker edges in this coating method. On the other hand, the U.S.Pat. 4,287, 240 suggests to use the double layer of screening or perforated plate material as a shield to protect the flow of free-falling curtain against disturbance by ambient air currents.
2. In practical photographic industry, there are various products and a variety of coating liquid compositions with different coating wet thickness. Some products require the lower ratio of gelatin to the silver halide, and some other products require simultaneously to coat six to seven liquid compositions forming a plurality of distinct layers and geting the wet thickness of 0.150 to 0.160 millimetre, which exceeded the limited range of free-falling coating method. Some medium factories, which do not require excessive high-speed, but expect to manufacture various products by the same coating machine would face troubles.

In the pevious arts, there are several hundred patents including various kind of coating methods such as: the kiss-roller-coating, the poly-roller-coating, the knife-coating, the extrude-coating method; but those used mainly and widely in the photographic industry and developed in historical sequence are the dip-coating, the bead-coating, and the free-falling curtain coating methods.
It is an object of the present invention to provide a coating method and an apparatus for coating one or more layers on a moving web which overcomes the disadvantages of the prior art.
This invention develops a new kind of vertical drawing curtain coating method, which can simultaneously coat one or more than one layer on the moving web with high uniformity, and is suitable for silver salt or non-silver salt photosensitive materials production. It is also suitable for other production, which requires one layer or more than one coating layer. This new coating method can suit with the coating thickness of covered range both of the bead-co: Ling and the free-falling curtain method, and can avoid those defects such as: "pencil line", "streak", and "interruption by splice" or those troubles such as: "thicker edges" and "disturbance by air current" in the free-falling curtain coating method.
The new coating method and device contain three main parts: the higher uniform equal-flow distributing coater, the vertical drawing short-curtain, and the parallel rotated coating roller and moving webs; therefore this new coating method may be named as "vertical drawing curtain coating method", which is described as following:

The vertical drawing curtain coating method usually requires a number of precision metric pumps and flowmeters to feed various of liquid compositions into a high uniform equal-flow distributing coater with a deviation less than ±0.5 to 1.0%, then the coating liquid flows down on the sliding slope with the inclination of 20° to form an uniform fluid at a flow rate from 50 to 300 milliliters per second per metre. Before the free-falling, the thickness of fluid is reduced to about 40%, then the liquid curtain falls down with an inertia velocity V_o of 0.065 to 0.226 meters per second. The falling velocity of the liquid curtain V is less than the velocity of a free-falling body due to the fluid viscosity with the mathematical relation as following:

The coater is not situated above the coating web and roller but is situated at the upper flank space of the coating roller and web, which is the main difference of this invention as compared with the free-falling curtain coating method. Therefore, the height of liquid curtain may be reduced to the more or less than 50 millimetres forming a more stable short-curtain, which may be adjusted in the height range from 0.5 millimetre to more or less than 50 millimetres. The short-curtain impinges upon the coating roller and web surface at an angle of elevation β = 0-60° , which will promote the adhesion of coating liquid on the web surface.
If the coating roller and the web are rotated at the same direction and the liner speed of the rotation is greater than the free-falling velocity, the short-curtain will be drawn and much reduced in thickness. According to the different product's requirement, it may be adjusted that the drawing ratio is from 1 fold to 20 folds to get the wet coating thickness h from 0.020 millimetre to 0.240 millimeter. This coating method can coat the liquid to the uneven surface, such as: cloth, screen, and embossed paper.
The vertical drawing curtain is the key of this coating technique in this invention. In an extreme condition, when the height of the curtain is more or less than 50 millimeters, the falling velocity of the curtain is approximate to 1 metre per second. If setting the drawing ratio is to be 3 folds, the liner speed of the coating roller and web will be 5 metres per second, which is equal to 300 metres per minute contenting the requirement of the major factories. In practice, the coating speed is usually less than 180 metres per minute, which is equal to 3 metres per second. If assuming the drawing ratio is to be less 5 to 10 folds, the height of the curtain may be reduced to 5 millimetres to 20 millimetres, and the coating speed is at 0.3 to 3 metres per second, which is equal to 18 to 180 metres per minute. Obviously, the drawing short-curtain has higher stability, which can avoid thoses troubles such as: "thicker edges" and "disturbance by air current" in the free-falling curtain coating method. And it has the sufficient height to pass through any splice such as: flying splice, butt splice , welding splice, or mechanical splice, to avoid those defects such as: "pencil line", "streak", and "interruption by splice" in the bead coating method. Therefore, this new coating machine may be equiped with an automatic splicer of any type, which omits the voluminous accumulator, simplifies the web cleaning system, and makes for the traditional coating machine a great advance.
As compared with the bead coating and the free-falling curtain coating method, this new coating method can use a more larger variation of liquid viscosity in the range from 2 mPas to 1,000 mPas. When coating silver salt photo-sensitive materials, the suitable viscosity of coating liquid may be varied from 5 mPas to 50 mPas usually not exceeding 100 mPas. When coating non-silver salt photo- sensitive materials, the suitable viscosity of coating liquid may be varied from 5 m?as to 500 mPas usually not exceeding 1,000 mPas. Obviously, this new coating method can use a more viscous and more concentrated liquid composition, which will get a thiner coating layer, drying under a lower temperature, requiring less drying capacity , saving the energy and reducing the cost of production.
Outside above described differences, this new coating method is also different from the hot-melting coating and the extrusion coating method, used for manufacturing the adhesive tape, the resin coated paper, or described in the European Pat. 31,301 A. In those coating methods, the melting liquid composition is extruded from a coater to form a liquid curtain which is drawing and gelling between the polished cooling roller and the moving web, so that the hot-melting coating and the extrusion coating methods can not coat those liquid compositions with low viscosity, low gelling strength, or without gelling property. But in this invention, the liquid curtain impacts and adhesives on the surface of the moving web, after drawing and reducing the thickness of liquid coating layer, and then slowly gelling in a chilling chamber, otherwise the new coating method can coat those liquid compositions without gelling property such as used in the non-silver salt photo- sensitive materials production.
The main properties of this vertical drawing curtain coating method are detailed as following:

1. The height of short liquid curtain is adjusted in the range from 0.5 millimetre to more or less than 50 millimetres, and the drawing ratio may be controled in the range from 1 fold to 20 folds.
2. The equal-flow distributing coater can simultaneously coat one layer or more than six layers under the laminar-flow condition, and the standard deviation of the non-uniformity should be less than ±0.5% to ±1%.
3. The suitable viscosity of coating liquid may be varied from 5 mPas to 50 mPas usually not exceeding 100 mPas in the silver salt photo-sensitive materials production, and the suitable viscosity of coating liquid may be varied from 5 mPas to 500 mPas usually not exceeding 1,000 mPas in the non-silver salt photo-sensitive materials production.
4. The sum of the suitable flow rate per unit width of the coater is controled in the range' from 50 ml/s/m to 300 ml/s/m, which requires the drying capacity of 200 to 1,200 kilogram water per hour as the coating width in 1,120 millimeters.
5. The moving speed of the web may be exceeded to 5 metre_per second, usually is controled in the range from 0.3 to 5 metre per second, which is equal to the coating speed from 18 to 300 metre per minute. Under proper conditions, the wet thickness of the plural coating layer may be controled in the range from 0.020 millimetre to 0.240 millimetre, which is equal to the wet coverage of 20 to 240 millilitres per square metre.
6. The more concentrated and viscous liquid will get a thiner coating layer, which may require less drying capacity, save energy and reduce the cost of production at higher coating speed under lower drying temperature.
7. The new coating machine may be equiped with automatic splicer, omits the accumulator, simplifies the web cleaning system, and controls the optimum coating conditions by micro- processor such as: the coating speed, the wet coverage, the flow rate and the height of liquid curtain, which will make the traditional coating machine a great advance.

Owing to those marked characteristics, the vertical drawing curtain coating method is suitable for various coating layers of the silver salt photo-sensitive materials production such as: subbing layer, antihalation layer, filter layer, black and colour film or paper, cine- film, X-ray film, aerial-film, lithographic film, micro-film, holographic micro-film etc.; and is also suitable for non-silver salt photo-sensitive materials production such as: diazo-type micro-film, diazo-type printing paper, red-mask stripping film, electrographic paper (or Electrofax), pressure sensitive copying paper etc.
In the following the invention will be described in connection with embodiments of the present invention in connection with the accompanying drawing.
In the drawing:

Fig. 1 is a vertical sectional view of the dipcoating method according to the state of the art;
Fig. 2 is a vertical sectional view of the bead coating method with a six-layer slide hopper according to the state of the art;
Fig. 3 is a vertical sectional view of the free-falling vertical curtain coating method referring to US Pat. 3,508,947;
Fig. 4 is a vertical sectional view of another type of a free-falling vertical curtain coating method referring to US Pat. 3,508,947;
Fig. 5 is a vertical sectional view of an apparatus for performing a mono-layer vertical drawing curtain coating method according to the present invention;
Fig. 6 is a front view of the apparatus shown in Fig. 5;
Fig. 7 is a vertical sectional view of an apparatus for performing a four-layer vertical drawing curtain coating method according to the present invention;
Fig. 8 is a vertical sectional view of an apparatus for performing a six-layer cascade type vertical drawing curtain coating method according to the present invention;
Fig. 9 is a diagrammatic side elevation of an embodiment of a coating machine for performing the vertical drawing curtain coating method according to the present invention.

Referring to the _Fig. 1 there is shown an apparatus of the known dip-coating method, 1 is a moving web, 2 is a coating roller, 3 is a coating layer, 4 is a coating liquid, 5 is a coating trough, h is the wet thickness of the coating layer, and R is the radious of curvature of the liquid surface in the coating trough.
Fig. 2 shows an apparatus of the bead coating method with a six-layer slide hopper, 1 is the moving web, 2 is a coating roller, 3 is the coating layer, 4 is the coating liquid flowing down the slide surface, 6 is the plate of slide hopper, 7 is the passage of the hot water, 8 is the delivery gap, 9 is the uniform flowing chamber, 10 is the pressure gap, 11 is the equal-flow distributing chamber, h is the wet thickness of coating layer, h₁ is the thickness of suspending bead, t is the coating gap between the moving web and the lip of the slide hopper, P₁ is the pressure of upper space, P₂ is the pressure of the lower space, R, is the upper radius of curvature, and R₂ is the lower radious of curvature. Referring to: Wang Zhongjun and Song Fuhai, "The Design Of Cascade Coater To Improve The Uniformity", THE COLLECTED REPORTS OF THE SILVER SALT AND NON-SILVER SALT PHOTO-SENSITIVE MATERIALS, p.121 to 123, (1983), editor by The Society Of China Photo-sensitive Research, China.
Fig. 3 shows an apparatus of the free-falling vertical curtain coating method referring to U.S.Pat. 3,508,947, 1 is a moving web, 2 is a coating roller, 3 is a coating layer, 4 is a coating liquid flowing down the slide surface, 6 is a plate of coater, 12 is a distributing chamber, 13 is a rod-like edge guiders, 14 is a curved air shield, 15 is a main catch tray, 16 is a curtain deflector, h is the wet thickness of coating layer, and H₁ is the height of free-falling curtain.
Fig. 4 shows an apparatus of another type free-falling vertical curtain coating method referring to the U.S. Pat. No. 3,508,947. 1 is a moving web, 3.is a coating layer, 4 is a coating liquid flowing down the slide surface, 12 is a distributing chamber, h is the wet thickness of coating layer, and H₂ is the height of free-falling curtain.
Fig. 5 shows an apparatus of a mono-layer vertical drawing curtain coating method according to the present invention, 1 is a moving web, 2 is a coating roller, 3 is a coating layer, 6 is a plate of coater, 7 is a passage of hot water, 8 is a delivery gap, 11 is a equal-flow distributing chamber, 13 is a plate-like edge guides, 17 is a chilling chamber, 18 is a cover of the coater, h is the wet thickness of coating layer, H₃ is the height of vertical drawing curtain, and the short-curtain falls down to the moving web surface on the coating roller at an angle of elevation β = 0° to 60°.
Fig. 6 is a front view of the apparatus of Fig. 5. 1 is the moving web, 2 is the coating roller, 3 is the coating layer, 6 is the plate of coater, 13 is a plate-like edge guide, 1₇ is the chilling chamber, 19 is side plate of coater, 20 is an inlet or outlet of hot water, 21 is an inlet of coating liquid, 22 is a fixed screw and 23 is a vertical drawing short-curtain. Sometimes the coating width of the coater 6 may be larger or smaller than the width of the moving web 1, or the length of the coating roller should be shorter or longer than the width of the moving web 1 for the same reason.
Fig. 7 shows an apparatus for performing a four-layer vertical drawing curtain coating method according to the present invention. 1 is the moving web, 2 is the coating roller, 3 is the coating layer, 4 is the coating fluid, 6 is the plate of coater, 7 is the passage of hot water, 8 is the delivery gap, 9 is the uniform flowing chamber, 10 is the pressure gap, 11 is the equal-flow distributing chamber, 13 is the plate-like edge guide , 17 is the chilling chamber, 18 is the cover of the coater, h is the wet thickness of coating layer, H₄ is the height of vertical drawing curtain, and the short-curtain falls down to the moving web surface on the coating roller at the angle of elevation β = 0° to 60 .
Fig. 8 shows an apparatus for performing a six-layer cascade type vertical drawing curtain coating method according to the present invention. 1 is the moving web, 2 is the coating roller, 3 is the coating layer, 4 is the coating liquid flowing down the slide surface, 6 is the plate of coater, is the passage of hot water, 8 is the delivery gap, 9 is the uniform flowing chamber, 10 is the pressure gap, 11 is the equal-flow distributing chamber, 13 is the plate-like edge guides, 17 is the chilling chamber, h is the wet thickness of coating layer, h₂ is the thickness of flowing fluid on the slide surface, h₃is the thickness of flowing fluid before free-falling, H₄is the height of vertical drawing curtain, and the short-curtain falls down to the moving web surface on the coating roller at the angle of elevation β = 0° to 60°.
Fig. 9 is a sketch of an embodiment of a new coating machine for performing the vertical drawing curtain coating method according to this invention 1 is the moving web, 2 is thecoating roller, 3 is the coating layer, 4 is the coating fluid, 17 is the chilling chamber, 19 is the side plate of coater, 21 is the inlet of coating liquid, 24 is the turning roller, 25 is the supporting rollers, α is the angle of elevation of the chilling chamber, and the angle of elevation d may be situated from 30 degrees to 90 degrees.

The following examples further illustrate the invention:

Example 1

The mono-layer coating apparatus as illustrated in Fig. 5 might be used to coat the organic solvent type coating liquid. For instance, in manufacturing the diazo-type micro-film, a 6% acrylonitrile-vinylidene chloride copolymer of acetone solution and other components having a viscosity of 72 mPas were coated to a polyethylene terephthalate film of a thickness of 0.100 millimeter. The height of the short-curtain H was 25 millimetres and the flow rate of coating liquid Q/L was 80 ml/s/m, so that the free-falling velocity of liquid curtain V would be less than 0.74 meter per second. If the ratio of drawing speed was 2.7 folds, the wet thickness h of 0.040 millimetre for said layer might be obtained at a coating speed U of 2 metres per second.

Example 2

Any coating apparatus as illustrated in Fig. 5, Fig. 7, or Fig. 8 might be used to coat an aqueous coating liquid. For instance: in the coating of an antihalation layer, a 15% blue-black dyed aqueous gelatin solution having a viscosity of 52 mPas was coated on the back of a cellulose triacetate film base of a thickness of 0.140 millimeter. The height of the short-curtain H was 17 millimetres and the flow rate of coating liquid Q/L was 75 ml/s/m, so that the free-falling velocity of liquid curtain V would be less than 0.6 meter per second. If the ratio of drawing speed was 2 folds, the wet thickness h of 0.063 millimetre (or dry thickness of 7 microns) for said layer might be obtained at a coating speed U of 1.2 metre per second.

Example 3

A coating apparatus as illustrated in Fig. 7 or Fig. 8 might be used to apply a dual colloidal silver antihalation layer to a cellulose triacetate film of a thickness of 0.140 millimetre. A black colloidal silver dis- pe=sion for photographic antihalation layer contained 8% gelatin having a viscosity of 14 mPas and required to obtain a wet thickness of 0.025 millimetre, and a 7% aqueous gelatin solution for the top coating layer having a viscosity of 12 mPas and required to obtain a wet thickness of 0.010 millimetre. If the height of the short-curtain H was 15 millimetres and the sum of the flow rate ΣQ/L was 70 ml/s/m, the free- falling velocity of liquid curtain V would be less than 0.58 metre per second. When the ratio of drawing speed was 3.5 folds, the wet thickness h of 0.035 millimetre for said layer might be obtained at a coating speed U of 2 metres per second.

Example 4

A coating apparatus as illustrated in Fig. 7 or Fig. 8 might be used to apply a dual layer of a X-ray sensitive emulsion and a protective coating to a clear polyester film base with a thickness of 0.190 millimetre. There was 12% gelatin in the coating emulsion having a viscosity of 21 mPas and containing 38 grams of silver per litre of emulsion, which required to obtain a wet coating thickness h' of 0.157 millimetre or a silver coverage of 6.0 grams per square metre. The protective coating liquid was a 9% aqueous gelatin solution with a viscosity of 18 mPas, which required to obtain a wet coating thickness h" of 0.015 millimetre. As the flow rate of the emulsion Q_I/L was 90 ml/s/m, the flow rate of the protective coating liquid Q₂/L was 10 ml/s/m, and the height of short-curtain H was 12 millimetres, the free-falling velocity of liquid curtain V would be less than 0.52 metre per second. If the ratio of drawing speed was 1.12 folds, the sum of the wet thickness of Σh of 0.172 millimetre might be obtained at a coating speed U of 0.58 metre per second.

Example 5

As stated in the Example 2, in the coating of holographic micro-film, it was necessary first to apply an aqueous gelatin antihalation solution to the back of polyester film base of a thickness of 0.250 millimetre and to obtain a dry thickness of 9 microns of the antihalation layer. Then a coating apparatus as illustrated in Fig. 8 might be used to apply a dual layer of silver halide emulsion and a protective coating liquid to the web. The silver halide emulsion contained 6.5% gelatin with a viscosity of 15 mPas and contained 32 grams silver per litre, which required to obtain a wet coating thickness h' of 0.203 millimetre. The protective coating liquid contained 6% gelatin with a viscosity of 14 mPas, which required to obtain a wet coating thickness h" of 0.010 millimetre. Those two coating liquids were fed into the coater in above proportion, and the sum of liquid flow rate ΣQ/L was 100 ml/s/m. As the height of short-curtain H was 5 millimetres, so the free-falling velocity of liquid curtain V would be less than 0.32 metre per second. If the ratio of drawing speed was 1.4 folds, the sum of the wet thickness Σh of 0.213 millimetre might be obtained at a coating speed U of 0.32 metre per second.

Example 6

In the coating of photo-setting correct-film, as stated in the Example 2, it was necessary first to apply an aqueous gelatin antihalation solution to the back of polyester film base of a thickness of 0.030 millimetre and to obtain a dry thickness of 7 microns of the antihalation layer. Then a coating apparatus as illustrated in Fig. 8 might be used to apply a dual layer of silver halide emulsion and a protective coating liquid to the web. The silver halide emulsion contained 7.5% gelatin with a viscosity of 14 mEas and contained 32 grams silver per litre, which required to obtain a wet coating thickness h' of 0.094 millimetre. The protective coating liquid contained 7% gelatin with a viscosity of 15 mPas, which required to obtain a wet coating thickness h" of 0.010 millimetre. Those two coating liquids were fed into the coater in above proportion, and the sum of liquids flow rate rQ/L was 120 ml/s/m. The inclined angle α of the coater was equal to 20°, and the thickness of flow fluid h₂ was equal to 1.40 millimetre. When the fluid flowed down over the arched head of coater, the thickness of flow fuid would be reduced to 0.98 millimetre before free-falling from the coater. The height of short-curtain H was 20 millimetres and the average inertia velocity of the liquid curtain V₀ was 0.12 metre per second, after free-falling the liquid curtain velocity V was increased to 0.48 metre per second. If the ratio of drawing speed was 2.4 folds, the sum of the wet thickness Σh of 0.104 millimetre might be obtained at the coating speed U of 1.15 metre per second. After processing and drying, this film was rather flat and was suitable for correct photo-setting use.

Example 7

In the coating high-speed photographic film, as stated in the Example 2, it was nessary first to apply an aqueous gelatin antihalation solution to the back of polyester film base of a thickness of 0.100 millimetre and to obtain a dry thickness of 8 microns of the antihalation layer. Then a coating apparatus as illustrated in Fig. 8 might be used to apply those liquid components to the web under the following conditions:
As the height of short-curtain H was 20 millimetres, the free-falling velocity of liquid curtain V would be less than 0.66 metre per second. If the ratio of drawing speed as 1.5 folds, the sum of the wet thickness Σh of 0.170 millimetre might be obtained at a coating speed U of 1 metre per second, or 60 metres per minute.

Example 8

In coating colour paper, a coating apparatus as illustrated in Fig. 8 might be used to apply a plurality of six layers to a resin coated paper of 230 grams weight per square meter under the following conditions:
As the height of short-curtain H was 20 millimetres the free-falling velocity of liquid curtain V would be less than 0.66 metre per second. If the ratio of drawing speed was 1.2 folds, the sum of the wet thickness Σh of 0.150 millimetre might be obtained at a coating speed U of 0.8 metre per second, or 48 metres per minute.

Example 9

In coating colour negative film, which required to apply fourteen liquid components to the cellulose triacetate film base, and the coating requirements described as following:
A coating apparatus as illustrated in Fig. 8 might be used to apply a plurality of 6 to 8 layers or to apply a plurality of 2 to 4 layers by each passing the coating zone , and illustrated the coating condition as following:
When the height of short-curtain H was fixed at 15 millimetres, the free-falling velocity of liquid curtain V was less than 0.58 metre per second. If the ratio of drawing speed also was fixed at 3.5 folds with the coating speed U of 2.0 metres per second, the sum of the wet thickness Eh from 0.035 to 0.085 millimetre might be obtained by the method of adjusting the amount of the sum of flow rate ΣQ/L from 70 ml/s/m to 170 ml/s/m.
Generally speaking, the above nine examples proved that the vertical drawing curtain coating method and apparatus according to the present invention can coat at various coating speeds to obtain a wide range of wet coverage which exceeded the limited ranges both of the bead coating and the free-falling coating method.

Claims

1. A method for coating silver salt and non-silver salt photo- sensitive materials with a plurality of simultaneously applied one or more than one layer of liquid coating compositions on a travelling web (1), characterized by
the steps of descending a laminar flow from a pouring lip of a coater (6) and forming a uniform liquid short-curtain (23), thereafter impinging and adhering on the travelling web surface partial round a coater roller (2) which is rotated in the same direction as the falling curtain (23) to minimize the thickness by further drawing.

2. A method according to claim 1,
characterized in that
one or more than one layer of liquid compositions fed into the coater (6) by precision metric pump and flow-meter, is descending in a laminar flow from the pouring lip of the coater (6) and is forming a uniform liquid curtain (23), whereas the variation of liquid viscosity is in the range from 2 mPas to 1.000 mPas and whereas a suitable flow rate of the coating liquid per unit width of the coater (6) is controlled in the range from 50 ml/s/m to 300 ml/s/m.

3. A method according to claim 1 or claim 2,
characterized in that
the liner speed of the rotating roller (2) and the web (1) is greater than the free-falling velocity, thereby minimizing the thickness of the short-curtain (23) by the acceleration of gravity and changing the drawing speed ratio from 1 to 20 folds.

4. A method according to one of claims 1 to 3,
characterized in that
the travelling web (1) has either a flat surface such as: paper, baryta paper, resin coated paper, cellulose triacetate film, polyethylene terephthalate film, polycarbonate film, polyethylene film, polypropylene film etc., or an uneven surface such as: cloth, silk, screen, embossing paper etc.

5. An apparatus for performing the method of one of claims 1 to 4,
characterized in that
said apparatus consists of three main parts: the high uniform distributing coater (6), the vertical drawing short-curtain (23), and the travelling web (1) partial around the coating roller (2) which both rotate in the same direction as the falling curtain (23).

6. An apparatus according to claim 5,
characterized in that
said high uniform equal-flow distributing coater (6) can apply one or more than six layers to the travelling web (1) with the standard deviation of the non-uniformity less than + 0.5 % to + 1 %.

7. An apparatus according to claim 4 to claim 6,
characterized by
installing the coater (6) at the upper flank space near by the coating roller (2) and web (1), whereby the height of the pouring lip of the coater (6) to the web surface may be reduced to less than 50 millimeters forming a more stable short-curtain (23) and adjusting the height range from 0.5 millimeter to more or less than 50 millimeters.

8. An apparatus according to one of claims 4 to 7,
characterized in that
the short-curtain (23) falling down from the pouring lip of the coater (6) and impinging upon the web surface and the coating roller (2) are arranged at an angle of elevation (B) from 0 degree to 60 degrees, thereby promoting the adhesion of coating liquid on the web surface.

9. An apparatus according to one of claims 4 to 8,
characterized in that
the short-curtain (23) is guided by two plate-like edge guides (13) fixed on the coater (6) and in that the width between said two edge guides (13) is gradual larger and larger as increasing the height of the short-curtain (23) which facilitates to improve the stability of short-curtain (23) and uniformity adjacent the edge guides (13).