US 2901376 A
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Description (OCR text may contain errors)
Aug. 25, 1959 2,901,376
R. J. LEHMAN WEB COATING PROCESS AND SHIELDING APPARATUS TO PREVENT BEADED EDGES Filed Feb. 27, 1957 ROLAND JAMES LEHMAN BY M 6m ATTORNEY United States Patent 2,901,376. Patented Aug. 25, 1959 ice WEB COATING PROCESS AND SI HELDING APPA- RATUS TO PREVENT BEADED EDGES Application February 27, 1957, Serial No. 642,849
8 Claims. (Cl. 117-44) This invention relates to web coating process and apparatus and more particularly to a method and means for permitting the application of a coating material to a moving web while preventing the coating of a particular longitudinal area on the web, e.g., an edge strip. Still more particularly, it relates to a web coating process and a web coating device which eliminates edge bead formation due to surface tension.
In a web coating operation, the edges of the web are frequently irregular and contain imperfections, which may be caused by the web making equipment, e.g., calendering and stretching apparatus. The imperfect edges after coating are trimmed off and discarded. Edge bead formation, i.e., the heavy coating of material at the lateral edges of a coated area due to surface tension is also charactenistic of web coating processes. The area covered by these edge heads is generally nonuniform and likewise must be subsequently trimmed and discharded.
In many instances, the coating material, e.g., a photographic emulsion, is expensive and a costly and complex recovery system is required to salvage the coating material on the trimmed edge portions or valuable ingredients therefrom.
Edge beads (referred to above) do not necessarily occur only on the edges of the web but may also occur on both lateral edges of any coated area, e.g., a stripe, on the web. These edge beads are undesirable, in addition to their nonuniformity, because they result in web damage, e.g., high roll edges, broken or cracked edges, shifted rolls, coated material shrinkage, etc., during subsequent windup and handling.
It is therefore an object of this invention to provide a novel process and apparatus useful in coating processes of the skim, dip or immersion coating types. Another object is to provide such process and apparatus that permits the continuous coating of a preselected longitudinal area on a web. Still another object is to provide such process and apparatus that eliminates surface tension edge bead formation during web coating. Yet-another object is to provide a novel coating device that is economical to construct, not complex, requires substantially no maintenance and has few moving parts. A particular object is to provide such a device that will, during a web coating process, prevent the coating of the edge or edges or other preselected longitudinal area of the web. Another particular object is to provide such a device that is self-aligning. Additional objects will be apparent from the following description of the invention.
The invention is directed to the method of preventing the formation of edge beads due to surface tension during application of a coating of material in a strip to a moving web in a skim, dip or immersion coating process comprising applying said strip of coating in an amount lessat the lateral edge of the strip than at other parts of the strip. In a broad aspect the invention comprises such a process of continuously coating a substantially uniformly thick layer of coating material onto a continuous longitudinal area of a moving web, said area having at least one lateral 2 edge not coincident with a lateral edge of the web, while precluding at said edge of the layer the presence of the coating material in a thickness as great as the desired thickness of the layer.
The process of this invention will be more clearly understood by the following description of several embodiments of the novel web coating apparatus according to this invention, which description will now be given with reference to the accompanying drawing, wherein:
Fig. 1 is a perspective view of one embodiment of the web coating apparatus of this invention;
Fig. 2 is a side elevation of the apparatus of Fig. 1 showing its operational relationship with a coating roller and a web being coated;
Fig. 3 is a partial sectional elevation taken on line 3-3 of Fig. 2 with parts enlarged for clarity; and
Fig. 4 is a view similar to Fig. 3 of an embodiment of the invention useful for preventing the coating of a center strip on a web.
Referring now to the drawing, the principal elements of the apparatus of this invention include a curved portion 1 shaped to conform to the curvature of a coating roll 2, a counterbalance 3 connected with the curved portion 1 by connecting arm 4, and means for supporting the curved portion and counterbalance about a pivot so that the downward weight of the counterbalance eifects an upward pressure of the curved portion on the web 5 being coated about coating roll 2. It is essential to this invention that at least one lateral edge of the curved portion 1 be beveled, i.e., that the lateral edge be non-perpendicu lar to the plane of the web being coated. it is important in order to carry out the novel process of this invention that the inner surface of this beveled edge projects over the area of the web being coated permitting the presence of a successively diminishing amount of coating material at the edge of that area. In order to remove the edge bead completely, the thickness of the curved portion 1 is :at least equal to and preferably slightly greater than the final Wet thickness of the coating applied.
A preferred embodiment of the apparatus of this invention will now be described with reference to Figures 1 through 3 of the drawing. This preferred embodiment is adapted to prevent the application of coating material during a web coating operation to the side (lateral edge) of the web, and simultaneously to preclude the formation of an edge bead at the lateral edge of the coated area.
The curved portion 1 of the device is connected to the counterbalance 3 by connecting arm 4. The curved portion 1 is provided along its entire length with a flange 6. This flange prevents what is known in the art as back coating, i.e., it prevents the coating material 7 in the coating pan 8 from reaching and Wetting the web on its back surface, which is not desired to be coated. In addition to preventing back-coating, the flange 6 also serves as a guide to insure alignment of the device with the edge of the moving web which may shift laterally somewhat as it passes through the coating station.
The connecting arm 4 may be given added rigidity by any suitable means such as flanges 9. Similarly, the connecting arm 4 and flange 6 connection may be made stronger by any suitable means such as flange 13. Addi tionally, handle 14 may be fastened to arm 4 to provide convenient means for handling and positioning the coating device.
The counterbalance may be made of one or more counterweights 10 which may be secured to connecting arm 4by any suitable means such as bolt 11 and nut 12. The bolt passes through a suitable aperture inthe connect ing arm 4, which aperture may for convenience be oblong to facilitate adjustment of the counterbalance.
Positioned under the connecting arm 4 at a right angle to the arm 4 and the curved portion 1 is a bridge 15 having at each end depending flanges 16. These flanges 16 and flange 13 have holes therein to receive supporting rod 17 which is threaded at one end, as indicated by reference numeral 18. A compression spring 19 is positioned around the supporting rod 17 tocontinuously urge flange 13 and the rest of the coating device in a direction such that flange 6 is pressed against the lateral edge of the web 5, as shown in Fig. 3. The amount of force exerted by spring 19 may be adjustably varied by any suitable means, e.g., wing nut 20, the position of which may be held temporarily immovable by any suitable means, e.g., a lock nut (notshown).
The coating-device (curved portion 1, counterbalance and associated elements) is supported adjacent the coating roll 2 by having supporting rod 17 held in any convenient manner, e.g., secured to the coating pan or other suitable member. In the preferred construction, the rod 17 is inserted through holes in brackets (not shown) attached to the frame of the coating machine. The rod 17 is secured in the brackets with the aid of collar 21 at one end and a second wing nut 22 which may have a cooperating lock nut (not shown) at the other end. It will be. understood that in operation the apparatus of Figures 1, 2 and 3 is positioned as illustrated in Figures 2 and 3 under and at one side of the coating roll, with the curved portion 1 below the liquid level of the coating material 7 in the coating pan 8. Flange 6 is urged by spring 19 laterally against the side of web and projects above the level of material sufliciently to prevent the flow of material over the flange and onto the upper surface of Web 5. The curved portion 1 adjacent the moving web is held upwardly against the web by the weight of the counterbalance pivoted about rod 17 to mask the web surface and prevent the application of coating material to the edge strip along the side of the web.
The beveled edge aspect of this invention is shown most clearly in Fig. 3, wherein there can be seen the curved portion 1 having beveled edge 23 adjacent the lateral edge of the Web area being coated. The amount of bevel, i.e., the amount that the lateral edge 23 varies from a direction perpendicular to the'plane of the web, is indicated by the angle having reference numeral 24 and may vary from 1 to 89 inclusive to obtain a reduction or elimination of edge bead. Unexpectedly superior results have been found possible using a bevel angle between and 20, and preferably 11.
Another embodiment of the apparatus of this inven- 'tion is illustrated by Fig. 4 wherein is shown a coating device for preventing the application of coating material 7 in a pan 8 to a longitudinal area, strip or stripe on the surface of the web 5 as it passes around coating roll 2. The device may include the curved portion 1 with as sociated connecting arm, counterbalance and related elements and is constructed similar to the embodiment of Figures 1-3, lacking only the flange 6 and handle 14. The device in operating position may be held by any suitable means, e.g., by two wing nuts on a threaded supporting rod if no automatic lateral adjustment is desired. In the embodiment of Fig. 4, each lateral edge is beveled, i.e., varies from the vertical by amounts indic'ated by angles 25 and 26, comparable to angle 24 of Fig. 3.
It will be understood that the coating device for precluding the coating of a side strip on a web (the preferred embodiment of Figures 13) may be either righthanded or left-handed, depending on which side of the web is to be masked and left uncoated. Thus, for use on the other edge of the web, a device which is transversely a mirror replica of the Fig. 1 device may be used. It is only necessary to transpose the flange 6 and handle 14 for an operable device. Of course, coating devices may be used simultaneously at each side as well as '4 at one or more central areas on a web in a single coating operation if desired.
The invention will be further explained but is not intended to be limited by the following examples:
Example I A gelatino silver iodobromide photographic emulsion havinga viscosity of 27 centistokes and a solids content of 7.6% by weight is dip coated onto one surface of a cellulose acetate web about 7 mils thick. The coating apparatus of Fig. 2 is used having a coating controller device according to this invention positioned at each edge of the web. The controller devices each have a masking surface (that part of curved portion 1 that contacts the web) that is inch in width, and a bevel as illustrated in Fig. 3 of 7. After coating, it is observed that no emulsion has been applied to the web where masked, leaving an uncoated strip at each edge measuring inch. The surface tension head is also reduced by about as is noted when a sample coated according to this example is compared with a sample similarly coated usinga controller device having a bevel of Example 11 Example I is repeated except that each of the edge coating controllers has a A inch wide masking surface with an 11 beveled edge. Coating material is effectively eliminated where masked for edge strips each inch wide. Material coated according to this example has no surface tension bead on each lateral edge of the coated area, whereas a web sample similarly coated using a controller device having a bevel of 90 has corresponding beads measuring 0.0053 in thickness.
' Example III Example 11 is repeated except that the devices each have a masking surface /2 inch wide with a 45 bevel. The results are similar with a 55% reduction in surface tension bead thickness.
Example IV Example V Example I is repeated except that the emulsion has a viscosity of 8.4 centistokes and a solids content of 5.5%, the web is a cellulose triacetate film 10 mils thick, the coating devices each has a masking surface A inch wide and an 11 bevel, each uncoated edge measures 75 inch Wide and the surface tension bead is completely eliminated.
Example VI A gelatino silver bromide photographic emulsion having a viscosity of 22.5 centistokes and a solids content of 7.6% is coated onto a baryta coated paper which has been given a slight tubsize. The coating apparatus of Fig. 4 is used having a masking surface (that part of curved portionl that contacts the web) 1 inch wide with a resultant uncoated longitudinal strip 1 inch Wide. The curved portion 1 has lateral edges beveled 80 and 16 with edge. bead improvements of 10% and 97% respectively when compared with a 90 device.
The various parts of the apparatus according to this invention may be readily constructed from one or more parts secured together to form the essential features hereinafter set forth in the claims. For example, the curved portion 1 of this device may be fabricated from a flat piece of metal strip stock, plastic, wood or other material which can be formed or shaped into a curve whose center of curvature lies in the axis of the coating roll. The height of the flange, which may be of similar material, is not critical and may be as low as M; or inch or as high as a chord joining the ends of the curved portion. The thickness of the curved portion is likewise not critical; a strip of stainless steel 0.0312 inch thick has been found entirely satisfactory.
The proper weight of, i.e., force required from, the counterbalance is readily determinable by persons in the art and will depend on such factors as the material of which the curved portion is made, the Width and thickness of the curved portion, the coating roll diameter, the viscosity of the material being coated, etc. Generally, the upward force of the curved portion must be slightly greater than the force exerted by the surface tension bead. Weights of from 30 to 60 grams have been found satisfactory in carrying out the above examples. Spring tension or other suitable means may be used in place of the weights. It has also been found advantageous in the preferred embodiment to vary the force exerted by the compression spring 19 proportionally with the weight of the counterbalance in order to maintain the most satisfactory alignment of the coating device with the edge of the web.
The specific embodiments of this invention illustrated in the drawing are of course capable of modification Without departing from the scope of the present invention. For example, it is not absolutely essential that the bevel described above of from 1 to 89 exist solely and strictly as a straight line when viewed in cross section as in Figures 3 and 4. Thus, the lateral edge 23 may be somewhat curved, either convex or concave or combination of both, or the edge 23 may be irregular in shape, for example, stepped or partly straight and partly curved and/or irregular. It can be seen that the bevel angle is, as illustrated, equal to the angle subtended by the web surface and the lateral edge, and it is essential to the present invention only that this latter angle be less than a right angle whereby coating material is applied to the lateral edge of an area being coated in an amount more or less uniformly decreasing in thickness at the lateral edge. Other modifications will be apparent to persons skilled in the art.
The novel process and apparatus of this invention are useful in controlled non-edge coating and selective striping of webs. For example, in one useful application, a plurality of the devices of this invention are positioned on a single shaft to coat a web with a photographic maf terial to obtain successive coated and uncoated striped areas. The uncoated areas are then coated with a magnetic material by apparatus similar to that just described. The web is slit longitudinally at the median of each magnetic coated stripe and perforated by known methods.
The invention is also useful in applying a magnetic sound track to perforated film and in coating between the margin and the perforations of photographic motion picture films. Other uses Will readily be apparent.
An advantage of the invention resides in the reduction in waste of coating material or, alternatively, in the elimination of costly reclamation procedures. Another advantage is that the process is not dependent on specially constructed water-tight seals between the web and the coating material. An'additional advantage is that complex adjustments are not required during operation as in prior art methods and apparatus. Further advantages are that the device is economical to construct, not complex, easy to clean maintain, and self-aligning during operation. A particular advantage is the reduction or elimination of surface tension edge bead during coating operations.
The invention claimed is:
1. The method of continuously dip coating a substantially uniformly thick layer of coating material onto a width of a moving flexible web, which method comprises positively applying said coating material across the entire said width, while applying said coating material in a lesser amount on the edge of said width than at the central portion of said width, said lesser amount. tapering toward the edge of said width.
2. In apparatus for coating a layer of coating material onto a web, said apparatus comprising a container for coating material, and located above said container a coating roll so positioned as to pass a web around, under and upwardly away from said roll so that the lower surface of said web contacts said coating material in said container to apply a coating of said material to said lower surface of said web, the improvement comprising a shielding device positioned on the underside of said roll so that said device contacts said web as said web contacts and moves around and under said roll and as said web contacts said coating material in said container, said device comprising a curved structure adapted to confine itself to the curvature of said roll in juxtaposition to said roll so as to allow only the thinness of said web to pass therebetween, said structure having a limited width portion which extends over only a not-tobe-coated width of the traveling web, said portion sloped at its edge in a direction to provide a sloping surface which is non-perpendicular to the plane of said web and which projects over the edge of the coating material being applied to said web, said sloping surface sloping from a position in contact with said web downwardly and outwardly away from said notto-be-coated width of said web so as to provide during coating the application of a thickness of coating material tapering toward the edge of said width being coated.
3. Apparatus in accordance with claim 2 additionally having means for providing upward pressure of said curved structure on said web as said web passes around and under said coating roll.
4. Apparatus in accordance with claim. 3 wherein said means is a counterbalance connected with said curved structure, said counterbalance and said curved structure so located about a pivot that the downward weight of said counterbalance effects an upward pressure of said curved structure on said web as said web passes around and under said coating roll.
5. Web stripe-coating apparatus comprising a lateral arrangement of a plurality of said shielding devices set forth in claim 2.
6. Apparatus as set forth in claim 2 wherein said sloping surface and said lower surface of said web define an angle within the range from 10 to 20.
7. Apparatus as set forth in claim 6 wherein said angle is about 11.
8. Apparatus in accordance with claim 2, said apparatus additionally having a flange on one side of said curved structure for preventing back-coating, and spring means for forcing said shielding device laterally and maintaining lateral alignment of said apparatus.
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