US3019130A

US3019130A - Fluid cushioned coating method and apparatus

Info

Publication number: US3019130A
Application number: US764891A
Authority: US
Inventors: Hornbostel Lloyd
Original assignee: Beloit Iron Works Inc
Current assignee: Beloit Iron Works Inc
Priority date: 1958-10-02
Filing date: 1958-10-02
Publication date: 1962-01-30
Anticipated expiration: 1979-01-30

Description

Jan. 30, 1962 HORNBOSTEL 3,019,130

FLUID CUSHIONED COATING METHOD AND APPARATUS Filed Oct. 2, 1958 Ill M H m EXCESS COATING Lloyd Hornbosfe/ United States Patent 3,019,130 FLUID CUSHIONED COA'IING METHOD AND APPARATUS Lloyd Hornbostel, Beloit, Wis, asslgnor to Beloit Iron Works, Beloit, Wis., a corporation of Wisconsin Filed Oct. 2, 1958, Ser. No. 764,891 11 Claims. (Cl. 117-111) This invention relates to a method of and apparatus for coating sheet material. More particularly, this invention relates to such a method and apparatus wherein a mobile coating composition is smoothed upon a portion of a flexible web or sheet which is supported for the smoothing operation by maintaining a positive gas pressure which acts as a cushion for the web. The invention is applicable to the coating of woven or felted fabrics, paper, sheets of rubber or other resinous material, cellulose films, and other sheet material of similar nature.

Various methods of smoothing a coating composition on a web have in the past been developed. Some of these methods have utilized an air jet in order to smooth coating compositions on a Web which is supported from its opposite side either by a roller or other solid surface. One such method is, for example, disclosed in US, Patent No. 2,252,345, issued to S. J. Johnson on August 12, 1941. In the prior art methods, on air jet from a nozzle urges the moving web against a blade and is able to apply only the force due to the velocity energy of the air stream. Furthermore, since the air is continuously flowing and escaping to the ambient, it is necessary to expend considerable energy in the continuous air pumping operation.

It is therefore an object of the present invention to provide a method and apparatus for smoothing coating compositions on a web which overcomes the above-noted disadvantages of the known prior art.

It is a further object of this invention to provide a method and apparatus for smoothing coating compositions on a web wherein a positive gas pressure is built up in back of a portion of the web which is displaced from a guide surface and urged toward a smoothing surface by the positive pressure.

It is a further object of this invention to provide a method and apparatus for smoothing coating compositions on a web wherein the coated web is urged against a smoothing surface by gas under pressure which gas may also be heated to simultaneously initiate the drying process during the smoothing step.

It is a further object of this invention to provide a resilient, controllable means whereby a coating applied to a web may be leveled and smoothed either with or without the removal of excess coating and which utilizes a substantially static positive gas pressure so that power need be expended only to overcome gas leakage.

Other objects, features and advantages of the present invention will be more fully apparent from the following detailed description taken in connection with the accompanying drawing wherein:

FIGURE 1 is a diagrammatic showing of a typical apparatus suitable for use in the present method.

FIGURE 2 is a somewhat fragmentary and schematic perspective view of the apparatus shown in FIGURE 1.

Turning to the drawings and in particular to FIGURE 1 thereof, a web 10, for example a web of paper, with its two sides indicated as A and B respectively, is fed from any convenient source and is continuously advanced through the nip of a pair of adjacent rollers 11 and 12. The side A of the web contacts the roller 11 which turns in a vat 13 containing a fluid coating composition. Roller 11 is driven by any convenient means (not shown) at a speed which permits the application to the web of the desired weight of coating composition. This coating is applied to the side A of the web 10.

Patented Jan. 30, 1962 The web 10 is then trained or fed around a perforate roller 14 so that the side B of the web contacts the surface of the roller 14. It will, of course, be understood that in the use of the device coating may be applied to the web in advance of the perforate roller 14 by any convenient means known in the art. The use of rollers 11 and 12 and vat 13 for this purpose is of course shown only by way of example. The uncoated or reverse side B of the web is then trained or wrapped around the perforate roller 14 and the applied coating is leveled or smoothed by a blade or doctor 15 in a manner to be described below. If desired, an excess of coating may be removed by the doctor 15 and received in a vat 16 positioned below the doctor.

It will be noted that the roller 14 is a hollow cylindrical roller the outer cylindrical wall 17 of which is provided with a plurality of perforations or apertures 18 which are preferably uniformly spaced over the entire surface thereof. Inside the roller 14, a gland or housing 19 is reconnected to any convenient source of a gas such as air maintained under a controllable pressure. The gland 19 is shown in cross-section in FIGURE 1 and preferably extends the entire axial length of the roller 14. In crosssection, gland 19 may conveniently be of generally U or horseshoe shape and is thus provided with an air outlet channel 20 formed by the

gland side members

21 and 22 which respectively extend into contacting relation with the inner surface of the wall 17 of the roller 14. In practice, it is preferred to make the diameters of apertures 18 less than the thickness of

gland wall members

21 and 22. The chamber 23 formed between the outer wall surface of the gland 19 and the inner wall 17' of roller 14 may in certain applications conveniently be provided with an additional gland or glands connected to a vacuum source so that the portion of the roller 14 exposed to the said gland or glands may function as a suction roll to maintain the web firmly in contact with it. The use of a moderate vacuum in suction chamber 23 is, for example, desirable where the angle of wrap of the web about the roller 14 must be less than or with light sheets or webs which may be lifted by the air pressure from chamber 19 entirely away from the roller 14.

As the web 10 is fed around the roller 14, a bubble 24 is formed in the portion of the web in front of the air outlet 20 from pressure chamber 19. This: results from the fact that the air under pressure from chamber 19 displaces the web 10 from the guide surface afforded by the outer surface of roller 14 and urges the web outwardly therefrom into contact with the blade or doctor 15. In order to prevent any substantial escape of air from the ends of the bubble 24 thus formed, stationary blocks or dams 25 and 26 are provided close to each. of the edges of the travelling web. These blocks may conveniently be mounted in closely spaced relationship to the ends of roller 14 and protrude outwardly beyond the roller past the position of the blade 15 in order to insure a complete closure of the ends of the bubbles. The positive air prasure maintained in the bubble by the pressure chamber 19 urges the bubble portion 24 of the web 10 against the doctor 15 and affords an air cushion for the web during the smoothing operation. The web is then conducted to any known dryer arrangement such as the dryer drums of the paper machine or tunnel dryers or the like. In FIGURE 1, this is illustrated schematically by the roller 27 over which the web 10 is fed to a dryer 28.

There is thus provided a resilient, controllable means whereby an applied coating may be leveled and smoothed either with or without the removal of any excess coating as desired. The force with which the web 10 is urged against the blade 15 is of course determined by and may be controlled by adjustment of the air pressure in the pressure chamber 19. The perforate roller 14 and gland 19 are similar to a suction roll in arrangement but in practice may be lighter in construction. The consumption of air is small because only leakage losses must be pumped. The perforate roll may be light since it is required essentially to support only its own weight. The air pressure which may be used is limited only by the permissible tension in the web being coated and since the applied forces are essentially in balance there is no significant applied load to the roll itself. I

With certain coatings and paper combinations, the use of heated air may be desired in order to begin the set of the coating during the smoothing operation. This may readily be achieved by interposing any suitable heating means in the line feeding air to pressure chamber 19. As noted above, the use of a moderate vacuum in the suction chamber 23 is frequently desirable but is not necessary in many applications. If a vacuum is not maintained in the suction chamber the web may be held against the roller 14 by the normal tension in the feeding loop.

It will of course be apparent that the present method and apparatus may be used either in a paper making machine or on independent coating machines of any known type. The use of a positive gas pressure to urge the web against a smoothing surface or into a smoothing position for any suitable type of smoothing operation affords a controllable air cushion to support the web during the smoothing operation without requiring that large volumes of air be pumped. At the same time, it affords the possibility of initiating the drying action during the smoothing action by using heated as well as pressurized air to form the above discussed cushion.

While air is in fact used to form the cushion in the presently preferred embodiment of the invention, it will be understood that any suitable gas or fluid could equivalently be used. The term gas as used in the specification and claims is therefore intended to mean any pumpable fluid including air which may be maintained under positive pressure, that is, under pressure greater than ambient atmospheric pressure.

While a particular preferred exemplary embodiment of the invention has now been described, it will be understood that modifications and variations may be effected therein without departing from the spirit and scope of the novel concepts of the present invention as defined by the following claims.

I claim as my invention:

1. A method of smoothing mobile coating composition on one side of a flexible web comprising, continuously engaging a moving surface with the opposite side of said coated web to advance said web along a path defined thereby, yieldably moving a limited length of said advancing web away from said moving surface and held with its coated one side pressed against a rigid smoothing element by gas pressure acting across said limited length of said web to thereby smooth said coating composition on said one side of said web while it is yieldably supported by said gas pressure.

2. A method of coating an elongated flexible web with a mobile coating material comprising, applying said coating material to a side of said web, continuously advancing said web while the major portion of the opposite side thereof is in contact with a perforate guide surface, urging a minor portion of said web away from said guide surface by maintaining a positive gas pressure only on said opposite side of said web, and smoothing said coating composition on said side of said web in its said minor portion while thus yieldably supported by said positive gas pressure on the opposite side thereof.

3. In a method of smoothing mobile and dryable coating composition on one side of a flexible web, the steps of continuously advancing the web while maintaining the opposite side thereof in engagement with a guide surface, urging a portion of said web away from said guide surface by maintaining a pressure difference of a gas on opposite sides of said portion of said web, smoothing said coating composition on said one side of said portion of said web, and heating at least part of said gas to help dry said coating composition.

4. In a method of smoothing a mobile and dryable coating composition on one side of a flexible web, the steps of continuously advancing the said web in a fixed path by carrying the opposite side of said coated web on a perforate guide surface, maintaining a partial vacuum in back of a major portion of said moving guide surface to retain said web against said surface, urging a minor intermediate portion of said web away from said moving guide surface by maintaining a cushion of positive gas pressure between said guide surface and said opposite side of said minor portion of said web, smoothing said coating composition on said one side of said minor portion of said web, and heating the gas forming said cushion to simultaneously help dry said coating composition.

5. Apparatus for coating flexible sheet material comprising, a perforate guide surface, smoothing means positioned in closely spaced relationship to said guide surface, means for applying coating to one side of a web of the material, means for continuously advancing the web while its other side is in engagement with said perforate guide surface, means to apply gas having a pressure difference on opposite sides of said web and through a portion of said guide surface to displace a portion of said web away from said guide surface and urge it into yieldable and operative relationship with said smoothing means, and means coacting with said guide surface and said displaced portion of said web to retard the loss of said gas pressure difference.

6. Apparatus for coating flexible sheet material comprising, a perforate guide surface, a smoothing means positioned in closely spaced relationship to said guide surface, means for applying coating to one side of an elongated web of the material, means for continuously advancing the web while its other side is in engagement with said perforate guide surface, means to apply a pressurized gas through a portion of said guide surface under a portion of said web to displace it away from said guide surface and yieldably urge it against said smoothing means, and dam means positioned adjacent each side edge of the traveling web and coacting with said guide surface and said displaced portion of said web to retard the escape of pressurized gas so as to form a pressurized gas cushion under said displaced portion of said web.

7. Apparatus for coating flexible sheet material comprising, a rotating cylinder having sides forming a perforate moving guide surface, a smoothing blade positioned in closely spaced relationship to said guide surface, means for applying coating to one side of a web of material, means for continuously advancing said web while the other side thereof engages and moves with said perforate surface, a pressurized air chamber within said cylinder, said chamber having an outlet positioned to apply pressurized air through a portion of said perforate surface of said cylinder to displace a portion of said web away from said guide surface and urge it against said smoothing blade, and means coacting with said cylinder and said displaced portion of said web to retard the escape of pressurized air from beneath said web so as to form an air cushion under said displaced portion of said web.

8. Apparatus for coating flexible sheet material comprising, a perforate guide surface defining a convexly curved fixed path, smoothing means positioned in closely spaced relationship to said guide surface, means for applying coating to one side of said web material, means for continuously advancing said web while the other side thereof is in engagement with said convexly curved perforate guide surface, means to apply a pressurized gas through a portion of said guide surface to displace a portion of said web away from said guide surface and urge it into operative relationship with said smoothing means,

vacuum means to apply suction through other portions of said guide surface adjacent to, and on both sides of, said pressurized portion to retain the web on said convexly curved guide surface, and means coacting with said guide surface and said displaced portion of said web to retard the escape of pressurized gas so as to form a gas cushion under said displaced portion of said web.

9. Apparatus for coating flexible sheet material comprising, means for applying coating to only one side of a web of the material, moving means for engageably supporting and continuously advancing said web, smoothing means adjacent only said one side, and means to urge a short length of said advancing web away from said moving means and into operative relationship with said smoothing means including gas cushion forming means maintaining a gas pressure difference on opposite sides of said advancing web to yieldably support it in said operative relationship with said smoothing means.

10. Apparatus for coating flexible sheet material comprising, means for applying a dryable coating to one side of a web of material, moving means for continuously engaging and advancing said web, smoothing means adjacent thereto, means to apply a pressure difference of heated gas on opposite sides of said web to urge it away from said moving means and into operative relationship with said smoothing means while helping in the drying of said coating.

11. Apparatus for smoothing a soft deformable coating already on an elongated sheet of flexible web material comprising, moving means for continuously, engaging, guiding, and moving said web, smoothing means adjacent thereto, means including a gas chamber to apply a pressure diflerence of gas to the opposite sides of only a limited length of said moving web adjacent to said smoothing means to yieldably move it away from said moving means and yieldably support said moving web in operative engagement with said smoothing means.

References Cited in the file of this patent UNITED STATES PATENTS