US2252345A

US2252345A - Coating sheet material

Info

Publication number: US2252345A
Application number: US213275A
Authority: US
Inventors: Stanley J Johnson
Original assignee: Warren SD Co
Current assignee: Warren SD Co
Priority date: 1938-06-11
Filing date: 1938-06-11
Publication date: 1941-08-12
Anticipated expiration: 1958-08-12

Description

Aug. 12, 1941- 5. J. JOHNSON 2,252,345

COATING SHEET MATERIAL Filed June 11, 1938 Fig: 5.

Patented Aug. 12,1941

COATING SHEET MATERIAL Stanley J. Johnson, Portland, Maine, minor to S. D. Warren Company, Bosto n, Man, I 001'- poratlon of Massachusetts Application June 11, 1938, Serial No. 213,275

14 Claims.

This invention relates to methods of and apparatus for coating sheet material. The invention is applicable to the coating of woven or felted fabrics, paper, sheets of rubber or other resinous material, films of regenerated cellulose or of cellulose esters or ethers, and other sheet material of similar nature.

A widely used method of coating flexible-sheet material is that disclosed by Lebel in U. S. Patent No 1,980,923. That method, in brief, comprises applying a fluid coating composition to one side of a flexible web, and then supporting the reverse side of the coated web while it is carried past an air jet or air brush" which extends across the width of the web and is directed at the coated surface directly opposite the point of support;

The air jet smooths the layer of fluid coating composition. It may actually cut away part of the coating, which has been applied in excess,

leaving a predetermined residual quantity which it redistributes, evens and smooths on the web in a uniform layer. This method yields a very excellent coated product but it is limited to coating only one side of the web at a time, owing to the fact that the back of the web must be supported while th air jet is acting on the freshly coated side. The smoothing of a coating by means of an air jet without the use of rigid means for supporting the web against the jet is not regarded as feasible at present. Otherwise it would be a simple matter to coat both sides of a web and then smooth both sides in a single pass by means of air jets. The use of one air jet as the supporting means for another air jet also is not regarded as being feasible at present.

By coating only one side of the paper at a time I mean coating only one side of the paper in a single pass of the web from a source such as a reel, through the coating operation and a drying operation.

Another method of coating paper which is ca-- pable of yielding an excellent coated product is one in which fluid coating composition is smoothed on the surface of the web by a driven roll which contacts the coated surface with a wiping action. In this method the coating may be, both applied to and smoothed upon the web ing the web around it under tension.

per in contact with the smoothing roll by bend- In such a case it is practically necessary that the paper shall have a considerable arc of contact with the smoothing roll in order to insur that every spot on the paper surface shall actually be contacted. Otherwise skips or uneven spots may occur on the coated surface. Thus it is seen that there is unavoidable a considerable frictional drag on the paper, since the latter must be held firmly against the roll but yet at the same time must slip over a considerable portionof the roll surface. Nevertheless, paper of fair strength can be smoothed or coated and smoothed satisfactorily by this method, particularly if the pull between the smoothing roll and the first succeeding tension means is comparatively short. It

by the wiping roll or it may be applied in some would appear feasible, and it has been proposed, to coat and smooth both sides of a web in a single operation by using two such wiping or smoothing rolls without backing rolls placed on opposite sides of the web one ahead of the other so that both rolls do not contact the web at the same point. It is apparent, however, that such practice doubles the frictional drag on the paper and consequently, while it is possible to carry out the method experimentally in the case of strong paper, the method has not proved to be generally practicable for production use at ordinary commercial operating speeds. Hence, for practical purposes, roller-coating of this nature still remains a one-side coating process. Coating both sides of the web in a single pass by providing smoothing rolls on opposite sides of the web, each holding the web against th other is, so far as I am aware, not practically possible with equipment available at present.

The two comparatively new coating methods, 1. e., the air brush method and the roll-coater method, are both generally considered to yield coated paper of a quality superior to that produced by the older, double brush-coaters of conventional type. Moreover, both new methods are capable of operating at considerably higher speedsthan the old brush-type coaters can attain. Consequently the newer types of coaters applied as one-side coaters are able to, and do,

compete successfully with the older type doublecoaters. It is apparent, however, that a modification of either the air brush method or the rollcoater method or some combination of them which would achieve satisfactory coating of both sides of the web in a single operation and at the speeds now commonly used for those methods in one side operation, would result in an advantageous increase in speed of production with a corresponding decrease in production cost. The present invention accomplishes this desirable result.

It is an object of the present invention to provide improvements in methods of manufacturing sheet material coated on both sides in a single operation.

Another object is to provide a method of coating sheet material on both sides in a single operation which involves the use of two rectilinear substantially non-divergent air jets.

Another object is the provision of a method of holding a web of sheet material bearing a layer of mobile coating composition against a rigid smoothing device by means ofair pressure.

Another object is the provision of a method of holding one side of a web of sheet material bear-- ing a coating on both sides against a rigid smoothing device by means of an air jet which also serves to smooth the other side.

Another object is to provide, in a method of coating sheet material on both sides in a single operation, the improvement comprisingsmoothing the coating on one side by means of an air jet and on the other side by means of a roll, the air jet serving to hold the web against the roll and the roll serving to support the web against the Jet.

Another object is to spread coating on one side of a sheet by an air jet and on the other side by a rigid scraper or blade.

Another object is to provide new combinations of apparatus for the accomplishment of the aforesaid objects.

Other objects and advantages will appear hereinafter.

Broadly, the invention resides in the use of an air jet for holding a coated web of sheet material against a rigid device, either a roll or scraper, which serves to smooth the coating and may also serve to apply coating and more specifically the rigid device may also serve to support the web against the air jet while the latter serves to smooth a coating on its side of the web.

The coated sheet is dried in any suitable manner, as on an air-floater or in a tower or tunnel and the sheet is then finished as desired.

Fig. 1 is a diagrammatic showing of the essential parts of one embodiment of the invention.

Fig. 2 is a diagrammatic showing of a second embodiment of the invention.

Fig. 3 is a diagrammatic showing of a modification of the apparatus illustrated in Fig. 2 in which the scraper 2| of Fig. 2 is replaced by a roller.

Fig. 4 is a diagrammatic showing of a portion only of the apparatus illustrated in Fig. 1 in which the air jet I0 is replaced by a roller.

In Fig. 1 a web for example a web of paper, with its two sides indicated as A and B respectively, is unwound from reel 2, passed over guide and tensioning rolls 3, 3 and passed with side A in contact with roll 4 which turns in a' vat 5 containing fluid coating composition. Roll 4 is driven, by means not shown, at a speed which permits the application of the web of the desired weight of coating composition, usually an amount somewhat in excess of that desired on the finished paper. The web then passes with side B, in contact with guide-roll 6 and past air-nozzle l which emits a rectilinear, substantially non-divergent jet of air against coated side A, thus smoothing the coating on side A and removing the excess coating, if any. Roll I, contacting side 3 of the web, acts as a backing-roll to support the sheet while the air jet from nozzle ii is acting on side A. Roll i also carries a film of coating composition which it transfers to side 3 oi the web at the point of contact therewith. Fluid coating composition is applied to roll l, preferably in excess, by roll 8 which turns in vat d, containing the coating mixture. The coating on roll 'l is spread and smoothed, the excess if any being removed in the process, by a rectilinear, substantially non-divergent air jet from nozzle iii. The web, now coated and the coating spread and smoothed on both sides, is carried to a suitable drier E2 in which the coating is dried sufiiciently not to be marked before it contacts guide roll l3. The web is dried further in its passageto guide-roll i i, and is then wound up on reel l5.

Air-nozzles i0 and II may be constructed according to the disclosure of the co-pending application of K. E. Terry, Serial No. 78,235, now Patent No. 2,139,628. In the above described embodiment any suitable means may be substituted for roll 4 for applying coating to side A of the web and instead of applying coating to the side B of the web by means of roll I, coating may be applied by any other suitable means and roll I may serve merely as a smoothing means or application of coating to side A may be omitted in which event jet I I would serve merely to hold the web against the smoothing roll 7. Roll 1 may rotate in a direction opposite to the direction of the web travel or it may rotate in the same direction but with a peripheral speed different from the lineal speed of the web.

According to the modification of the invention shown in Fig. 2. a web I with sides A and B is passed between squeeze rolls "5 and I8 which leave a limited quantity of fluid coating composition on both sides of the web. The coating composition is supplied to side A by roll l6 which turns in vat containing the coating mixture.

Coating composition is supplied to side B by ipe l9, near the entrance to the nip between l6 and I8. The web is carried past air-nozzle 20 which emits a rectilinear substantially non-divergent air jet that smooths the coating on side A, preferably removing the excess therefrom, and that I likewise pushes the sheet into firm contact with the rigid blade or scraper 2|. Blade 2| smooths the coating on side B, preferably removing excess coating therefrom, and likewise serves to support the web while the air jet from 20acts thereon. The web, coated and smoothed on both sides, is then dried and finished in any conventional way.

In this modification it is apparent that if coating is not applied to side A, the jet 20 will serve merely to hold the web against the scraper 2| while it serves to smooththe coating on side B. It is likewise apparent that rolls l6 and I8 may be replaced by any other suitable means for appurpose, 1. e. to support the web against the jet 20 and to smooth coating on side B of the web. When a roll is used both, as applicator and smoothing means as in the case of the roll 1 in Fig. 1, it is-preferre'd to use an air brush to spread the coating upon the said roll. Nevertheless, in many cases fairly satisfactory results may be obtained by use of'a rigid doctor meana e. g., a blade or another roll, in place of the air brush it. The substitution of a roller, 1. e. the roller 23, for the air brush I is illustrated in Fig. 4.

a the roll I, making the web follow the contour of In the set-up shown in Fig. 1, the air jet from firmly against the rigid smoothing device. The latter function of the air brush is found to be very useful, even in cases where the side of the web contacted by the air jet is not coated. The pressure of'the air jet pushes the web firmly against the opposed smoothing means, making unnecessary extra tension to hold the sheet in contact with the smoothing means. The air jet makes it possible for the opposed smoothing means, to spread and smooth the coating satisfactorily even when the web makes substantially only a line contact with the smoothing means. Thus may be avoided all frictional drag caused by a sharp bend of the web about the smoothing means and contact of the web with excessive area of the smoothing means.

The rigid smoothing means I in Fig. 1, or 2| in Fig. 2, likewise has two distinct functions to fulfill. First it smooths the mobile coating on the side of the web which it contacts; secondly it also serves as the supporting means required to back up the web while the air brush is acting on the other side.

Thus it is seen that in either the arrangement of Fig. 1, orthe arrangement of Fig. 2, there is double cooperation between the, air smoothing means and the rigid smoothing means. For instance, air brush ll of Fig. 1, and air brush 20 of Fig. 2, each has a primary function and a secondary function, and coating-roll I of Fig. 1, and scraper 2| of Fig. 2, also each has a primary function and a secondary function. The primary function of each smoothing means, of course, is to smooth the coating on the side of the web on which it acts. Each means, however, is assisted in the accomplishment of its primary smoothing function, by the cooperating action of the opposed means as the latter performs its secondary supporting function. Specifically, in Fig. 1, the air fromnozzle II has for its main purpose the smoothing of the coating on side A of the web; the air jet isenabled to accomplish this purpose, however, only because of the support given by roll I on the opposite side of the web. Conversely, coating roll 1 spreads and smooths the coating on side B of the web as its chief function, but it is assisted in this action by the air pressure from nozzle H which pushes the web firmly against roll I. 1

The particular arrangement of apparatus shown in-Fig. 1, produces a practical equivalent of a web coated and smoothed on both sides by the use of an air brush. One of the outstanding advantages of the air brush method of coating is that a coating of uniform thickness can be applied irrespective of considerable possible variation in thickness or uniformityof surface of the base stock. In the same way it is found that a uniform layer of coating composition can be spread upon the surface of an applicator roll by use of an perfections in the roll itself. Hence a uniform layer of coating may be spread on coating-roll I of Fig. 1, and the coating may be transferred uni.- formly to a web contacting the roll, sincethe air jet from nozzle ll acts to push the web against the roll even if considerable variation in diameter may exist therein at various points along its length.

It will be seen that the invention makes possible the production in a single operation of twoside] coated paper of the highest quality at speeds comparable to those now used for making one-side coated papers. Besides this obvious advantage, it is believed that the fact that both sides are coated before drying, makes the penetration of the coating composition the same on both sides of the sheet, and tends to decrease likelihood of trouble from curling of the finished sheet.

The invention likewise provides a new arrangement of apparatus, employing two air brushes, by which paper or other sheet material 1 may be coated on both sides simultaneously. An

important feature of the invention is a method of holding a coated web against a rigid smoothing device by means of air pressure.

Iclaim:

- 1. A method of coating a web of fiexible'sheet material on both sides in a single operation comprising continuously advancing the web; applying mobile coating composition to one side of the web, rigidly supporting the reverse side of the web against a solid surface while subjecting the mobile coating on the first side directly opposite said surface to the action of a rectilinear, substantially non-divergent air stream, whereby the coating composition is spread and smoothed on said first side; simultaneously applying mobile coating composition to the surface and spreading and smoothing said coating thereon by means of a second rectilinear, substantially n0n-diver gent air stream and moving the surface in contact with the web whereby the layer of coating thereon, is transferred to the second side of said web, and drying the coated web.

2. A method of coating flexible webs on both sides comprising continuously advancing the web, applying mobile coating composition to the two sides of the web; substantially simultaneously smoothing the coating on thetwo sides by subv jecting the coated web on one side to the action of a rigid smoothing surface and on the other side to the action of an air jet, the surface and the air jet being substantially directly opposed to each other on opposite sides of the web, and drying the so-coated web.

3. In a method of smoothing mobile coating composition upon a flexible web by means of a rigid smoothing surface the improvement comprising urging the web against said smoothing surface by means of an air jet.

4. A method of coating paper on both sides in which a paper web is continuously advanced, mobile coating composition is applied to the two sides of the web, the mobile coating composition is spread and smoothed substantially simultaneously on the two sides, on one side by an air jet and on the other by 3. rigid surface.

5. Apparatus for coating flexible sheet material comprising means for continuously advancing a web of the material, means for applying coating to at least one side of the web, rigid means contacting said side of the web for smoothing said air brush in spite of minor possible imcoating, and an air jet positioned to urge the web toward said smoothing means.

6. Apparatus as defined in claim 5 in which the smoothing means is a scraper.

7. Apparatus as defined in claim 5 in which the smoothing means is a roll.

8. Apparatus for coating a flexible sheet matev a free air jet.

10. Apparatus for coating flexible sheet material comprising means for continuously advanc ing a web 01' the material, means for applying,

coating to both sides of the web, rigid means contacting the web for smoothing the coatin on one side thereof, and an air jet positioned to urge the web against said rigid means and also to smooth the coating on the other side 0! the web.

11. Apparatus as defined in claim 10 in which the rigid smoothing means is a scraper.

12. Apparatus as defined in claim 10 in which the rigid smoothing means is a roller.

13. Apparatus for coating flexible sheet material comprisingmeans for continuously advancing a web of the material, a rotating roller contacting one side of the web, means for applying coating to the roller, means for smoothing the coating on the roller, means for applying coating to the other side of the web and an air iet positioned to urge the web against the roller and to smooth the coating on said other side of the web.

14. Apparatus for coating flexible sheet material comprising means for continuously advancing a web of the material, a roller for applying coating to one side of the web and smoothing the coating thereon by a wiping action and an air jet positioned to urge the web against said roller.

STANLEY J. JOHNSON.