US2227494A

US2227494A - Method and apparatus for coating paper

Info

Publication number: US2227494A
Application number: US155394A
Authority: US
Inventors: Leon J Gold
Original assignee: PLASTICS FINISHING CORP
Current assignee: PLASTICS FINISHING Corp
Priority date: 1937-07-24
Filing date: 1937-07-24
Publication date: 1941-01-07
Anticipated expiration: 1958-01-07

Description

Jan. 7, 1941. L. J. GOLD METHOD AND APPARATUS FOR COATING PAPER Filed July 24, 1957 L s 0 Y may xm W m N 0 m E Patented Jan. 7, 1941 UNITED STATES PATENT OFFICE Leon .l. Gold, Brooklyn, N. Y., assignor to Plastics Finishing Corporation, Brooklyn, N. Y., a corporation of New York Application July 24, 1937, Serial No. 155,294

Claims. (01. 91-55) This invention relates to the preparation of decorative and protective surface coatings on sheet or strip material, It provides an improved method and apparatus which combine with simplicity and economy of operation the capacity to produce, by a single direct application of liquid coating material, lacquer coatings that are permanently bonded to paper or like materials and possess highly desirable surface characteristics. 10 Prior to my invention printed and lithographed paper for advertising purposes and the like has been prepared with a coating of transparent lacquer, usually a cellulosic material such as cellu-; lose acetate, either by producing a thin sheet of the coating material and then sealing it to the paper or by applying a film of the'coating material while in a liquid state. The former practice results in coated paper of excellent appearance, but it is expensive and a tendency for the coating to split away from the paper is encountered which causes considerable difficulty. The practice of applying a film of liquid coating material to the paper is economical and the dried coating does not peel off from the paper, but unless several films of the material are applied separately to the paper the appearance and value of the final product are inferior when usual coating methods are used, due to non-uniformities in the surface of the coating which greatly reduce its gloss and reflective power, This is partly attributable to absorption of a large part of a single film of coating material by the paper. I have found that the inferior quality of the prior product is also caused by the liquid applying roller and the feed rollers of higher peripheral speed which are used in the usual method.

One of the objects of my invention is to provide a new method, together with apparatus for practicing it, which enable the economical production, by a single application of liquid coating material, of improved lacquer coated sheet material having a glossy appearance closely similar to that of the laminated constructions referred to above.

Another object of the invention is to provide a method and apparatus which are capable of continuous operation on very long strips of the sheet material to be coated and which produce coatings of uniform high surface gloss throughout the length of the strips.

Another object isto provide a method and apparatus of the type above mentioned which are adapted to withstand long periods of continuous use without adding to the bulkiness of the apparatus and in which parts ultimately requiring attention due to accumulation of coating material thereon may be replaced without substantial interruptlons in operation.

Still another object of the invention is to provide a method for coating paper with liquid lacquer or varnish which safeguards the coating against surface contamination from the time it is applied until a product having a dry glossy surface and no longer susceptible of contamination is obtained.

Another object of the invention is to provide a method of coating which attains the objects mentioned above and at the same time produces embossed or engraved indicia or designs on the coated surface.

I have found that the foregoing and other desirable objectives may be accomplished by applying a single film of liquid coating material to a strip of paper or other sheet material undergoing treatment, covering the coating shortly after it is applied and while it is still moist with a band of flexible sheet-like material having a smooth polished surface adjacent the coating, pressing the coated strip and the band together so that the smooth surface of the latter is brought into intimate contact with and molds the surface of the moist film of coating material, maintaining this intimate contact until the coating material has dried and then separating the band from the dried coated strip. In carrying out these operations of the improved method a strip or successive strips of the paper or other similar material to be coated are moved continuously past coating applying means, such as a roller dipping into a bath of the coating material, in order continuously to apply a film of the liquid coating material to one face of the paper. A band of flexible sheet-like material of a width sufficient to cover the coated por tion of the paper strip is maintained in condition for use, for example on a suitable reel, so that it may be brought into face-to-face contact with the coated strip as the latter moves away from the applying means. The covering band is moved at the same speed as the coated strip, and after the strip and band have been brought into contact they are continuously passed together through pressure applying means which forces the smooth surface of the flexible band into intimate contact with the moist coating and thereby spreads the coating uniformly on the strip and imparts to the surface of the coating a smoothness or polish similar to that existing on the adjacent surface of the band. From the pressure applying means the combined materials are passed through a drying Cl u I known examples.

zone, which may include a heating and drying chamber or may consist merely of a zone in which the materials are kept; together for any desired length of time until the coating has become thoroughly dry. Thereafter, the covering band of flexible material is stripped from the coated paper, and a product of high quality is obtained which possesses a uniform coating having a very smooth glossy surface.

The improved method may be used in preparing coatings of various kinds of lacquers and varnishes. It is of particular value for the production of paper coated with transparent cellulosicmaterials such as cellulose esters and ethers,

of which cellulose acetate and pyroxylin are well Printed and lithographed paper having a decorative and protective coating of cellulose acetate has a wide field of use for advertising purposes and the like. The method and apparatus of my invention produce paper of this type which is definitely superior in quality to the products of methods heretofore used inpractice.

The band of sheet-like material used to cover and mold the moist coating in an essential step of the present process can be made of various flexible materials that may be obtained with a very smooth surface free of numerous minute surface irregularities which would destroy its polish. Contrary to normal expectations, I have found that a flexible band of this type does not permanently adhere to a coating of moist lacquer or varnish nor mar the surface characteristics of the dried coating when the band is separated therefrom. Although there is adhesion between the band and the coating while the coating material is still moist, the coated strip and the band may be separated without difficulty after the coating has dried. This is the case even though the band be composed of material having a composition closely similar to that of the liquid coating material, and in practice I find it preferable to use an elongated strip of preformed cellulose acetate foil as the smooth flexible band when employing the improved method for the production of cellulose acetate coatings on paper. Another material which is suitable for this purpose is a band of flexible sheet metal foil having a highly polished surface.

In another. embodiment of the invention I employ a the covering band of sheet-like material an elongated strip of moisture-proof cellulose acetate or of wax glassine or similar flexible material having a polished wax coating. This type of material is particularly suitable because of its freedom from any tendency to adhere strongly to the applied coating, even when used in the improved method together with cellulosic coating substances having a relatively high content of solvent. When employing such material heat is not used to hasten drying of the combined strips, but instead either the applied coating is permitted to dry without heating or a partial drying is' effected before the covering band is applied to the moist coating. In the latter event, heating means such as a hood is preferably used to heat the uncoated face of the paper after the liquid coating is applied and before the covering band of flexible polished material is pressed against the still moist coating.

In still another embodiment of the invention I provide coated paper and the like with embossed or engraved indicia or designs in the coating by using a flexible band of sheet-like material which itself is engraved or embossed as desired. The pItSSYll? togeth r of such a band and the coated strip of paper in accordance with my method molds the design of the flexible band into the still moist coating on the strip. The molded coating is then dried while in contact with the band. In this way a decorated product is obtained without altering the procedure used in producing a plain coating and without entailing additional operations. No difficulty is experienced in separating the covering flexible band from the dry coated strip when following the improved method according to this embodiment of the invention.

One of the important advantages of my invention is that the application of the liquid coating material may be carried out simply and without undue precautions of the kind heretofore found necessary to ensure that the coated paper leaving the applying means be in a condition suitable for final use. It has been customary in the application of liquid coating materials prior to my invention to revolve the periphery of the applying roller at a speed different from the speed of the paper, in order to spread the coating material properly on the strip. This and other practices of like intent are made unnecessary by my invention, and the application of the liquid coating material according to the improved method may take place in the simplest way adapted to apply the desired quantity of material fairly uniformly on the paper. Furthermore, the tendency of this customary practice to smear inks and coloring matter on the paper being coated may be avoided entirely, since the peripheral speed of the applying roller may be the same as the linear speed of the paper.

Another important feature of my invention is that the practice of pressing a flexible band of cellulose acetate foil or the like on the still moist coating on strips of paper and of maintaining the foil as so pressed until the coating has set overcomes to a large extent the absorption of solids from the coating solution by the paper during the drying period. In usual coating practice, a large proportion of the solids in the coating solution are absorbed in the paper during absorption and evaporation of solids so that a film coating even approximately comparable to laminated products cannot be obtained without applying a plurality of coatings, which is commercially impractical. According to my invention, however, the cellulose acetate foil is applied and pressed on to the moist coating before this absorption of solids can take place and adhesion between the coating and foil while the former remains moist holds the solids on the face of the paper and causes the formation of a dry coating film which is hardly distinguishable from a laminated film.

Another important advantage of the improved method is that the freshly applied coating is completely protected by the overlying flexible band until after the coating has dried and become thoroughly resistant to surface contamina tion.

My method is further advantageous in that the drying of the coating may be carried out in various ways and over any desired period of time without affecting the quality of the product to the slighest extent and without complicating the apparatus used in performing the method. If an extended drying period is practicable the point of separation of the covering band from the strip of coated paper may be located farther from the po int of applying the liquid coating, or the rate of movement of the band and strip may be reduced. If rapid drying or the use of a small plant space is important a drying chamber of any desired action may be interposed between these two points. If it is desired to dispense with special drying facilities and also to conserve plant space the coated strip of paper and the covering band may be wound together on a suitable reel and set aside until the coating has become thoroughly dry, whereupon it is necessary only to unwind the combined materials and strip off the covering band.

Regardless of the particular practice employed to dry the coating, the dry coated product possesses a uniform high polish throughout its length. The flexible band used as the molding element for producing these desirable surface characteristics is separated from the dry coated strip in substantially as good condition as when first used, and it may be reused in the same manner over and over again until it becomes unsatisfactory due to accumulation of material on its smooth surface or for other reasons. When a sheet of cellulose acetate is used as the flexible band it may be discarded after it becomes unsatisfactory, at no substantial loss. When a band of more expensive material, such as thin sheet metal, is used it may be more desirable to recondition the surface of the band by removing accumulations that may have taken place. In either event, however, the reconditioning of a band or the replacement of an old one may be carried out without interrupting the coating operations, since several bands of flexible material are usually kept available to be fed into contactwlth strip material leaving the coating applying means.

The operation of the improved method and suitable apparatus for carrying it out are indicated in the accompanying drawing, which illustrates diagrammatically a preferred manner of practicing the invention.

Referring to the drawing in greater detail, a strip of paper or other similar sheet material A to be coated is moved along a feed table II) and thence through apparatus for applying a film of liquid coating material and for completing other .operations of the method. From table It! the strip is fed over a coating applying roller I! by feed rollers l4 and I6. Roller l2 dips into a bath of liquid coating material, for example a cellulose acetate solution; maintained in a suitable receptacle it. As the roller revolves it picks up a film of the liquid coating material and carries it to the under surface of the strip A, which preferably is moved at the same speed as the periphery of roller I! by appropriate revolution of rollers 14 and it. In this manner the film of liquid coating material picked up by roller I2 is continuously applied to a surface of strip A, as at B, and immediately after application of the coating the strip passes beyond roller l2 in condition for the next operation. To prevent adhesion between the moist coating B and the applying roller, suitable stripping means, such as a stripper finger 20, is preferably provided adjacent the back side of roller 12.

Shortly after the film B of coating material has been applied to strip A, the coating is covered by a smooth, polished surface of a flexible band C of sheet like material, preferably a band of preformed cellulose acetate foil. This material is kept on a roll 22 from which it is unwound and passed over a guide 24 and brought into contact Wl h the moist coating B on themoving strip A. With the band thus properly located over the moist coating, the strip and band are moved to gether between cooperating

rollers

26 and 28 for applying pressure to the moving materials and bringing the band into intimate contact with the moist coating. As the materials pass between the pressure applying rollers the smooth polished surface on the band continuously overcomes any non-uniformities in the thickness of theapplied coating and molds the surface of the coating so that it conforms generally to the surface of the band. From the pressure applying rollers the contacted materials are then passed onward through a drying chamber 30 having entry and

exit openings

32 and 34, respectively, in which a heated atmosphere is maintained to hasten the drying of the moist coating. The materials then travel onward to a point where they are continuously separated.

In the illustrated form of apparatus, means are provided to break superficial adhesion between the covering band and the dried coating. Such means includes a series of staggered rollers 36, 38' and 4ll,-respectively, which subject the travelling materials to abrupt bending and thus break any adhesion between the coating and the band. Any number of these rollers may be used, but when three are used as illustrated the materials pass over roller 36, beneath roller 38 and over roller 40, and at the latter point they are in condition for final separation and separate handling. A stripper finger 42 is provided at this point to ensure proper continuous operation. The flexible band C is then Wound on a roll 44. The dried coated paper is received by a conveyor 46 and carried onward in condition for further processing or immediate use.

It will be apparent that the form of apparatus used in all of the steps of this improved method may be modified in any way without departing from the essence of the invention. Instead of the roller l2 other forms of applying means can be used, and the strip material to be coated canbe fed to the applying means in various ways. To a like extent the

pressure applying rollers

26 and 28 can be substituted by other equivalent apparatus, as well as the drying means, the means for breaking adhesion between the coated strip and covering band, and the means for separating and handling the separated materials. In the coating of a continuous strip of paper it may be desirable to employ a roll 48 above the path of movement of the materials so that the dry coated paper may be wound on roll 48 while the covering band is continuously wound on roll 44. In the coating of short strips of paper and like materialthis arrangement is obviously unsuitable, and the conveyor 46 with the stripper finger 42 between it and roller 40 forms a more satisfactory arrangement.

As explained hereinabove, I prefer to practice the method of my invention by the use of a flexible band of preformed cellulose acetate foil. This type of material is easily obtainable with a smooth surface which is free from noticeable markings or surface irregularities. When used in the manner described it imparts a highly desirable finish to coatings applied as a single liquid film of cellulose acetate or similar cellulosic material. When using a cellulose acetate band that does not have a polished wax surface in the preparation of cellulose acetate coatings, it is preferable to employ as the coating material a cellulosic solution which possesses a relatively small content of solvent. In this manner I have found that any tendency for the moist coating to penetrate into the surface of the band is overcome, and a clean separation between the moving materials in the final stage of the method is obtained.

While I have described specific procedure and apparatus for carrying out my invention, together with some of the variations which may be made in the form of apparatus and the manner of operation, other modifications within the spirit of the invention will be apparent to persons skilled in the art. I therefore desire that the invention be accorded a scope fully commensurate with the spirit of the specification and the requirements of the claims without restriction to non-essential details.

I claim:

1. The method of producing glossy-surfaced sheet material which comprises applying a film of cellulosic solution to a moving strip of the material, moving the coated strip into contact with a polished surface of an elongated band of flexible foil material of finite length travelling at the same rate as the strip to bring said surface into contact with the moist cellulosic film, continuously pressing the strip and foil together, drying the cellulosic film while in contact with said surface, and thereafter stripping the coated sheet material from said foil.

2. The method of producing glossy-surfaced paper which comprises continuously applying coatings of liquid cellulosic solution to continuously and successively moving strips of paper, continuously moving the coated strips into contact with a polished surface of an elongated band of flexible sheet-like material travelling at the same rate and in the same direction as the strips to bring said surface into intimate contact with the moist cellulosic coatings, said band being of finite length continuously pressing the strips and band together, continuously drying the cellulosic coatings while maintaining the same as pressed in contact with said surface, and continuously stripping the dry coated paper from said band.

3. The method of producing glossy-surfaced coatings on paper and similar sheet material which comprises applying a coating of cellulose acetate solution to a strip of the material, covering the coating while it is moist with asmooth dry surface of a band of preformed flexible cellulosic foil, pressing the coated material and said foil together to bring the moist coating into intimate contact with said foil surface, drying the coating while maintaining said contact, and thereafter separating the coated material and said foil.

4. The method of producing glossy-surfaced paper which comprises continuously applying a coating of liquid cellulosic lacquer having a relatively low content of solvent to the paper, continuously covering the moist coating with a flexible strip of cellulose acetate foil and molding the surface of the coating and holding solids therein on to the face of the paper by pressing it firmly against a smooth surface of said cellulose acetate foil, drying the coating while in contact with said smooth surface and thereafter separating the dry coated paper from said foil.

5. Apparatus for coating sheet material, such as paper, comprising means for applying a coating of liquid cellulosic solution to a surface of moving sheet material, an elongated flexible band of foil material having a polished surface, said band being of finite length, means for continuously bringing the moist coating and said polished surface into intimate contact and for advancing the coated material and foil together away from said applying means, a drying chamber having entry and exit openings for the sheet material and foil, means for passing the sheet material and foil through said chamber, and means beyond said chamber for separating the band from the coated material.

6. Apparatus for coating sheet material, such as paper, comprising means for applying a coating of liquid cellulosic solution to a surface of moving sheet material, an elongated flexible band of foil material having a polished surface, said band being of finite length, means for continuously bringing the moist coating and said polished surface into intimate contact and for advancing the coated material and foil together away from said applying means and through a drying zone, means beyond said zone for flexing said sheet material and foil to break adhesion therebetween and means for separating the foil from the dried coated material.

'7. The method of producing glossy-surfaced coatings on paper and similar sheet material which comprises applying a coating of cellulosic solution to a moving strip of the material, heating the uncoated face of the strip partially to dry the coating, covering the partially dried coating while it is moist with a smooth wax surface of a band of wax-coated flexible foil material of finite length, pressing the coating material and said foil together to bring the moist coating into intimate contact with said surface, drying the coating while maintaining said contact, and thereafter separating the coated material and said foil.

8. The method of producing glossy-surfaced sheet material which comprises applying a film of gloss forming solution to a moving strip of the material, moving the coated strip into contact with a polished surface of an elongated band of flexible foil material of finite length travelling at the same rate as the strip to bring said surface into contact with the moist gloss forming film, continuously pressing the strip and foil together, drying the gloss forming film while in contact with said surface, and thereafter stripping the coated sheet material from said foil.

9. The method of producing glossy-surfaced coatings on paper and similar sheet material which comprises applying a coating of gloss forming solution to a strip of the material, covering the coating while it is moist with a smooth dry surface of a band of preformed fiexible cellulosic foil, pressing the coated material and said foil together to bring the moist coating into intimate contact with said foil surface, drying the coating while maintaining said contact, and thereafter separating the coated material and said foil.

10. Apparatus for coating sheet material, such as paper, comprising means for applying a coating of gloss forming solution to a surface of moving sheet material, an elongated flexible band of foil material having a polished surface, said band being of finite length, means for continuously bringing the moist coating and said pol