Method of coating and apparatus thereby

Abstract: By a coating method in which a coating solution is supplied from a coating solution supply inlet of a solution injector, the coating solution is distributed in the width direction of the solution injector by means of a manifold, and then is discharged from the solution injector through a slot having an even interval from the manifold to thereby perform coating. The coating method is characterized in that an end portion of the manifold to which the coating solution touches has a curvature with which the portion introduces the coating solution in the direction to discharge the coating solution.

Description: BACKGROUND OF THE INVENTION The invention relates to a method and an apparatus as indicated in the precharacterizing parts of claims 1 and 2, respectively. These method and apparatus serve for making a coating on a continuously running elongated flexible support, such as a photographic material, for example, a photographic paper or the like, a photograving material, photosensitive paper, thermosensitive paper, magnetic material, etc. In a prior art method and apparatus as disclosed in CH-A-530032 and as indicated in the precharacterizing parts of claims 1 and 2 the manifold has a curved surface only in the width direction of the manifold. As for a coating method and a coating apparatus, conventionally known is a device in which a flowing path of a coating solution stream is curved over the entire length thereof as shown in Fig. 1 so as to make the coating solution distribution even from a coating solution supply inlet of a solution injector to a slot outlet of the solution injector in order to avoid thick coating at coating end portions and increase in coating amount at a center portion. (Reference is made to Yuji Harazaki, "Progress of Coating Technique", Extension Technology Service Center Inc., 1988, p. 359.) In the case of using a solution injector constituted by a coating solution supply inlet, a manifold in the direction of width of the solution injector and communicated with the coating solution supply inlet, a slot communicated with the whole of the manifold in the direction of width of the solution injector and communicated with a coating solution discharge outlet, the working to produce such a solution injector is very difficult in view of design and work, and therefore, generally, the manifold is passed through and the opposite ends of the manifold are formed of plugs which are worked linearly. In the case where the end portion of the solution injector is worked linearly, however, the coating solution which contacts the end portion of the manifold partially stays so that the macromolecules in the coating solution are bridged to produce an insoluble material to cause a problem of generation of slag, streak, etc. The object of the invention is to provide a coating method and a coating apparatus in which a solution injector is capable of maintaining good quality of coated products. The above object of the invention is solved by the features as claimed in claims 1 and 2. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a front section of an example of a conventional solution injector having a curved flow path. Fig. 2 is schematic front view of an embodiment of the coating apparatus according to the present invention. Fig. 3(a) shows a cross section of an embodiment of the manifold according to the present invention. Fig. 3(b) shows a front section of the end portion of the manifold. Fig. 3(c) shows a plan section of the same. Fig. 4(a) shows front sections of a conventional technique. Fig. 4(b) shows the technique according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, with referring to Fig.2, the coating method in which a coating solution is supplied from a coating solution supply inlet 4 of a solution injector 1, then distributed in the width direction of the solution injector 1 by means of a manifold 5, and then discharged from the solution injector 1 through a slot 2 having an even distance from the manifold 5 to thereby perform coating, includes slide beads coating, extrusion coating, curtain coating, etc., and other coating methods using such a solution injector 1. Although it is generally considered preferable to make circular the cross section shape of the manifold 5 of the solution injector 1 used in the present invention because of easiness in manufacturing the same, those having a cross section like an ellipse or approximate thereto may be used. In order to make the manifold 5 act to distribute the coating solution in the width direction of the solution injector 1 and to make the total pressure (dynamic pressure and static pressure) of the coating solution flowing in the manifold 5 even as possible, it is preferable to make the manifold 5 have a uniform sectional area to a certain extent, and in order to make the residence time of the coating solution as little as possible, it is desirable to make the end portion of the manifold 5 be curved. The feature of the present invention is in that the slot length is made even, while only end portion(s) of the manifold is (are) made to have a curved surface. As a method in which the end portion of the manifold to which the coating solution contacts is made to introduce, with a curvature, the coating solution in the direction to the coating solution discharge outlet of the slot, specifically, the manifold portion may be worked so that the solution injector is halved along the center line of the slot. As a simplest working method, however, there is a method in which the manifold portion is formed as a through hole which passes left/right through the solution injector and plugs are provided at the end portions to which the coating solution contacts and the inner surfaces of the plugs are finished to be curved surfaces. According to the present invention, the coating solution supply inlet 4 of the solution injector 1 is provided either at a center portion of the solution injector 1, as shown in Fig. 2, or at one end portion of the manifold 5, not shown in the drawings. In the former case, the flow of the coating solution strikes against the both end portions of the manifold, while in the latter case, the flow strikes against the opposite end portion (counter-supply side) of the manifold 5. The feature that an end portion of the manifold to which the coating solution contacts is constituted by a plug, and a front sectional shape of an inner surface of the plug has a curved surface tangentially connected to opposite ends of the slot is specifically realized as follows. In Fig. 3(a) the cross section of the plug portion 3 of the manifold 5 assuming that the cross section of the manifold 5 and the plug 3 are cylindrical and the slot portion 2 exists on top of the manifold portion 5, is shown. The (Y - Y) vertical section of the plug portion 3 has a profile of a two-dimensional curved surface, as shown in Fig. 3(b). When the vertical height of the plug portion 3 is represented by h it is desirable to set the radius of the curvature in vertical plane to be R 1 = (0.5 to 4.0)h. The present invention is effective even if the end surface of the plug 3 is formed of such a two-dimensional curved surface. Further, if such a curved surface as in the horizontal (X - X) section having the horizontal width 1, as shown in Fig. 3(c), is added, the surface of the plug portion 3 becomes a three-dimensional curved surface. It is desirable to set the radius of curvature in horizontal plane to be R 2 = (0.5 to 4.0)1. Provided with such a three-dimensional curved surface, that is, R 1 and R 2 , the effect of the present invention is made higher. As a material of the plug according to the present invention, any material can be used, for example, such as metal, rubber, synthetic resin, or the like, however, it is particularly preferable to use Teflon (TM), polyvinyl chloride, resin, rubber, or the like. In the present invention, the "coating solution" may include those of various solution components corresponding to usages. For example, it includes: coating solutions for a photographic emulsion layer, an under coating layer, a protection layer, a back layer, etc. in a photographic material; coating solutions for a magnetic layer, an under coating layer, a lubrication layer, a protection layer, a back layer, etc. in a magnetic recording medium; and other coating solutions for an adhesive layer, a colored layer, a rust prevention layer, etc., those coating solutions containing a soluble binder or an organic binder. In order to clarify the effect of the present invention, examples of the invention will be shown under. [ Example-1 ] By using a gelatin coating solution shown below as the coating solution, and by using the solution injector according to the present invention, the coating solution was supplied from the center portion of the solution injector. The manifold was filled first with the coating solution containing dyes while the coating solution was supplied at a predetermined flow rate, then the coating solution of the above solution composition containing no dyes (transparent solution) was supplied at the same flow rate, and the time taken for substitution was measured. The test was carried out with respect to three kinds of the plugs provided at the opposite end portions of the manifold, one being a kind in which the inner surface of each plug is a flat surface (Comparative Example), another one being in which the inner surface of each plug has a two-dimensional curved surface, the remainder one being a kind in which the inner surface of each plug has a three-dimensional curved surface. The results were as shown in Table 1. Composition of the coating solution: alkali gelatin + sodium dodecylsulfonate + sodium polystyrenesulfonate + dyes 2 dm 3 /minute 4 dm 3 /minute Comparative Example 56 min 31 min Two-dimensional Curved Surface 37.5 min 17 min Three-dimensional Curved Surface 11.8 min 6.1 min In the above examples, h=50 mm, 1=25 mm, R 1 =1.0 x h, R 2 =2.0 x 1. As seen in Table 1, it is understood that although the stay of the solution is remarkably reduced by making the end surface of the plug be a two-dimensional curved surface, this effect is made to be more extremely preferable when the end surface of the plug uses a three-dimensional curved surface. In both the cases of using a two-dimensional curved surface and a three-dimensional curved surface, it became that no slag, streak, etc. occurred. [ Example-2 ] With respect to a case where the manifold is provided with a coating solution supply inlet at its one end, the test was made on the two cases in which in the 40 mm manifold, the shape of the plug at the other end of the manifold has a flat surface cut at a taper of 45°, (shown in Fig. 4(a)) as Comparative Example and has a two-dimensional curved surface with R 1 =2 x 40 as Example of the present invention, respectively. As the coating solution, water in which red/yellow/blue dyes are added (viscosity of 1 mPa·s) was used. The coating solution was supplied into the solution injector at a predetermined flow rate so that the manifold was filled with the coating solution, and then 7 weight % solution (100 mPa·s) of sodium polystyrenesulfonate was supplied at the same flow rate. The time taken for the substitution of this solution for the coating solution was measured. The results are shown in Table 2. 2 dm 3 /minute 5 dm 3 /minute Comparative Example (45° taper) 12 min 5 min Example of the Invention 3.6 min 1.5 min As apparent from Table 2, it is understood that by using the coating apparatus according to the present invention, the stay of the coating solution in the solution injector can be remarkably improved. By the coating method and coating apparatus according to the present invention, the stay of the coating solution at the end surface portion of the manifold is eliminated so that faults of slag and streak can be prevented.

Claims: A coating method in which a coating solution is supplied from a coating solution supply inlet (4) provided at a center portion or at one end portion of a solution injector (1), then distributed in the width direction of said solution injector (1) by means of a manifold (5), and then discharged from said solution injector (1) through a slot (2) having an even distance from said manifold (5) to thereby perform coating characterized in that: in case of the inlet (4) at the center portion both end portions and in case of the inlet at one end portion the opposite end portion in the width direction of said manifold (5) which are (is) constituted by a plug (3), and in the longitudinal section (Y-Y) through the slot the shape of an inner surface of said plug (3) has a curved surface tangentially connected to one or both ends of said slot (2). A coating apparatus comprising a solution injector (1) which has a coating solution supply inlet (4) provided at a center portion or at one end portion of the solution injector (1), a manifold (5) in the direction of width of said solution injector (1) and communicating with said coating solution supply inlet (4), a slot (2) having an even distance from said manifold (5) for discharging said coating solution and thereby perform coating characterized in that in case of the inlet (4) at the center portion both end portions and in case of the inlet at one end portion the opposite end portion in the width direction of said manifold (5) which are (is) contacted by said coating solution are (is) constituted by a plug (3), and in the longitudinal section (Y-Y) through the slot the shape of the inner surface of said plug (3) has a curved surface tangential connected to one or both ends of said slot (2). A coating apparatus according to claim 2, characterized in that in the horizontal section (X-X) the shape of inner surface of said plug (3) has a curved surface.

Inventors: CHINDA KUNIYASU, CHINDA, KUNIYASU, Chinda, Kuniyasu, c/o Fuji Photo Film Co., Ltd.
Applicants: FUJI PHOTO FILM CO LTD, FUJI PHOTO FILM CO., LTD.
Application year: 1991
Main classification: G03C1
IPC codes: G03F7, G03C1, B05C5, B05D1