US 3518141 A
Description (OCR text may contain errors)
June 30, 1970 T, BQURNS ETAL 3,518,141
METHOD OF APPLYING P'HOI'OGRAPHIC COATINGS TO A MOVING WEB WITH A SPLIGED JOINT Filed 001;. 28, 1968 Y AK LAWRENCE G M00NALD RICHARD Z' BOUR/VS A 7' TOR/VEYS United States Patent O Int. Cl. B31f 5/00 US. Cl. 156-157 1 Claim ABSTRACT OF THE DISCLOSURE A method for reducing coating disturbances at splices in a web being coated by treating the splicing tape and the adjacent web surface with a material to prevent air entrainment in the coating.
RELATED APPLICATION This application is a continuation-in-part of our copending application Ser. No. 679,083, filed Oct. 30, 1967.
BACKGROUND OF THE INVENTION In many manufacturing operations a substantially continuous web is coated with a liquid material, such as aqueous solutions or dispersions of hydrophilic colloids, see US. Pats. 2,681,294 and 2,739,891, which may then be dried to form the desired product. Such manufacturing processesar'e used in the manufacture of adhesive tapes, magnetic recording tapes and photographic films and papers, among others. In order to increase the efficiency, and consequently lower the cost of manufacturing these products, the coating process generally is carried out in a substantially continuous manner. Inasmuch as the web or support for the coating can only be obtained in finite lengths, a new supply roll of the web must be periodically spliced to the end of the preceding supply roll so that the coating process may continue uninterruptedly.
It has been found that the most desirable way of splicing such webs is to utilize a splice tape extending across the web and joining the two adjacent pieces of the web together. It has also been found that applying the splice tape to the surface being coated provides fewer coating flaws than does the application of the splice tape to the back side of the web. However, even though the application of the splice tape to the coated side of the web results in fewer coating problems than do other methods of splicing, streaks and other defects have still been found in the coating downstream from the splice tape. Normally, the spliced section of the continuous web is cut from the finished product and is scrapped so that the defects in the coating occurring at the splice joint are not found in the final product. However, it has been found that under certain conditions, the splice joint may affect substantial lengths of the coated web following the splice. In many products, it is possible to cut out the affected portion of the web without substantially affecting the usability of adjacent portions. However, in many products this is not possible, and the entire web containing such defects must be scrapped.
As the speed of coating webs is increased and as the width of the web products is also increased, the value of the product being scrapped due to splice-imparted defects downstream from the splice have become excessive. This is even more true in high-cost products utilizing an expensive coating material which cannot be ice easily recovered from scrapped portions of the web. As a result, it has become increasingly important to minimize, if not eliminate, defects resulting from the splice from the coated web products. Moreover, the elimination of these defects must be accomplished without materially increasing the cost of the product.
Furthermore, the elimination of the splice-imposed defects must not in any way result in other, potentially less desirable defects in the coated product. Additionally, the method of eliminating the splice-imposed defects must be readily accomplished without affecting the production rates now possible in high-speed coating machines.
SUMMARY OF THE INVENTION Accordingly, the present invention provides a method of treating a splice joint in a web to be coated, whereby the splice does not cause coating defects downstream of the spliced joint.
Many of the defects in coated webs appear to result from the entrainment of air in the coating deposited on the Web or from the adherence of a small bubble of air to the coating nozzle, which then affects further portions of the coating deposited on the web. It has been found that such entrained air is picked up and such bubbles are generated as the coating passes over the splice tape. The air entrained appears to come from that trapped in the angle formed between the edge of the tape and the surface of the web.
Accordingly, the present invention provides a method of continuously coating a moving web with a layer of a substantially liquid material comprising the steps of moving the web past a coating head and depositing a layer of a substantially liquid material on a surface of the web. At spaced longitudinal intervals, a splicing member or tape is applied to the surface of the web being coated, with the splicing member forming a discontinuity in the web surface. Defects in the web coating are substantially reduced by preventing the entrainment of air from the edge of the splice member.
More specifically, the elimination of air entrainment from the edge of the spliced member is provided by wetting the splice member and the adjacent web surface with water prior to coating.
The various features of novelty which characterize the present invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and the specific objects obtained by its use, reference should be had to the accompanying drawing and descriptive matter in which the preferred embodiments of the present invention are illustrated and described.
BRIEF DESCRIPTION OF THE DRAWINGS The drawing shows a greatly enlarged schematic section through a spliced joint of a coated web which may be treated in accordance with the teachings of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT A sectional view through a web splice is illustrated wherein the trailing end of one web 10 is spliced to the leading end of a succeeding web 12 by a strip of splicing tape 14 which extends across the point therebetween. In this illustration, the web moves past the coating station in the direction of arrow 16. The layer or coating 18 of a substantially liquid material, such as aqueous solutions (which term is also intended to include dispersions) of hydrophilic colloids and, more specifically, a gelatin-silver halide emulsion, is deposited at the coating section. It will be seen that the splice tape 14 creates a discontinuity in the surface of the web at both the leading and the trailing edges. At relatively low coating speeds it has been found that, as the spliced joint of the Web moves past the coating station, the layer of substantially liquid material generally follows the discontinuous surface at the leading edge of the splice tape. However, a Wedge of air 20 is trapped in the trailing edge of the splice tape and the coated layer does not closely follow the surface of the web at that point. At high coating speeds it has been found that air can be trapped at both the leading and the trailing edges of the splice. The wedge of air 20 trapped between the coating material, the surface of the web, and the edge of the splice tape has been found to become entrained in the liquid coating material as the coating material settles to the surface of the web. The entrained air may then be spread over the succeeding downstream portions of the web, causuing defects in the coating which may result in rejection of the final product, More seriously, some of the trapped air 20 may form small bubbles which adhere to the surface of the coating nozzle and affect the stream of material flowing therethrough. These bubbles may persist for an extended length of time whereby all succeeding coating is affected. As a result, the amount of defective webs may be substantially greater than would be expected due to entrapment of air in the coating alone.
It has been found that the entrainment of air from the splice joint in the coating can be prevented by treating the edge of the splice tape and the adjacent web surface with a film of water prior to the coating operations, and applying the coating while the splice joint is still wet. One theory of operation of this film of water is that it fills the transition from the tape to the web surface to eliminate the wedge of air at the edge of the splice tape. Another theotry is that this treatment changes he wettability of the web by the coating so that no air is entrained to cause subsequent defects in the coating.
Accordingly, in the process of continuously coating the surface of a moving web with a substantially liquid material, the web is transversely spliced at spaced longitudinal intervals, resulting in a discontinuity in the surface being coated. The present invention prevents the formation of disturbances in the coating downstream from the spliced discontinuity by preventing entrainment of air in the coating by wetting the spliced joint prior to coating.
In extremely high speed coating operations it is desirable to treat both edges of the splice tape.
While Water has been referred to throughout this description, it will be understood that pure water is not necessary to the invention. Moreover, some advantages may be obtained by utilizing Wetting agents or other additives in the water.
In addition, while the foregoing discussion has been directed to the formation of splices using a splice tape, the present splicetreatment may be successfully applied to other types of splice joints such as lap joints between the two ends of the web.
1. In the continuous coating of a moving web with a layer of an aqueous solution of hydrophilic colloids, said web having a spliced joint formed by a splice member forming a discontinuity in the surface of the web to be coated, the method of reducing the number of defects in the coated layer downstream from the splice member discontinuity comprising the steps of wetting the splice member and the adjacent web surface immediately downstream from the splice member with water and, before the water dries, coating the aqueous solution onto the web surface.
References Cited UNITED STATES PATENTS 2,657,151 10/1953 Gensel et al. 117-47 2,252,539 8/1941 Adams 156-304 XR PHILIP DIER, Primary Examiner US. Cl. X.R.