US3110612A

US3110612A - Method and apparatus for cast coating paper

Info

Publication number: US3110612A
Application number: US77083A
Authority: US
Inventors: Bruce C Gottwald; John M Haigh
Original assignee: Albemarle Paper Manufacturing Co
Current assignee: Albemarle Paper Manufacturing Co
Priority date: 1960-12-20
Filing date: 1960-12-20
Publication date: 1963-11-12
Anticipated expiration: 1980-11-12
Also published as: GB955747A

Description

Nov. 12, 1963 B. c. GOTTWALD EI'AL 3,110,612

METHOD AND APPARATUS FOR CAST COATING PAPER Filed Dec. 20. 1960 N COATING RECEIVING G LAYER PAPER DRI DR COATING .4 PAPER) Ezx'xx on l6 Q i ;;;ii;; u W

VA R REC NG COATING ls BA 5 R EIEfiSUR INVENTORS BRUCE C. GOTTWALD 8 VAPOR RECEIVING N M. HAIGH BACKING LAYER here to the drum dryer.

United States Patent O 3,110,612 METHOD AND APPARATUS FOR CAST COATENG PAPER Bruce C. Gottwald and John M. Haigh, Henrico County, Va., assignors to Albemarle Paper Manufac turiug Company, Richmond, Va., a corporauon of Virginia Filed Dec. 20, 1960, Ser. No. 77,083 13 Claims. ((31. 117-6 1) This invention relates generally to a method and apparatus for the high speed coating of paper with an extremely smooth surface. More particularly, this invention is concerned with a process and apparatus for coating a Web of paper with a cast surface or other smooth surface at a speed heretofore unobtainable.

The manufacturer today, as is well known, utilizes a colorful and attractive pack-aging or wrapping for his product, which is appealing to the prospective purchaser, for the reason that such eye catching packagings are a significant factor in the sale of any individual product. This is particularly true when competitive products are often side by side on the retail shelf, each vying for the attention of the consumer. Thus, more attractive Wrappings or packages have been sought by manufacturers, to sell their product without adding appreciably to the cost of the product.

One of the most desirable type of packages from the standpoint of attractiveness is a cast coated paper such as was disclosed in the basic Bradner Patent 1,719,166. A paper so produced has a very smooth surface which is the image of the chromium plated highly polished dryer drum used. While the patented apparatus and process has produced a smooth product, there are inherent disadvantages which attend such prior means and method. Among these disadvantages is the fact that the paper produced was often distorted and spotty, due to the fact that the coating was forced away from the drum before drying, by reason of the liquid boiling at the surface between the coating and the drum; In an attempt to eliminate this undesirable situation, the temperature of the drum was maintained below the boiling point of the liquid in the coating, which in most cases was water. Thus, the temperature of the drum was limited to a temperature below 212 F.

While the distorted or spotty product was to some extent avoided by reducing the temperature of the drum, it is obvious that the production rate was considerably reduced because of the resulting slower drying rate. As a matter of fact, the average speed of prior cast coating operations was limited to about 50-80 feet per minute, due to the necessity of assuring proper drying of the wet coating. Obviously, this slow production rate greatly increased the cost of the coated paper product.

Attempts to raise the temperature of the drum above the boiling temperature of the liquid in the coating, to speed up the drying and thus the production rate, resulted in the boiling of the liquid and the blowing of the coating away from the drum immediately after its release from the pressure nip. This blowing causes a splitting of the coating and the distortion mentioned above. In addition, part of the coating will adhere to the dryer and part will remain on the paper, One of the reasons for the splitting of the coating is that the usual aqueous coating, such as starch or starch and clay, has higher adhesive properties than cohesive properties while wet. However, the reverse is true after the coating has dried. Thus, the blowing which occurs before the coating surface has dried, will cause the coating at least partially to ad- Further use of this dryer with the adhering portions of the coating on its surface, only compounds the problem.

According to prior practices, to produce the cast effect on the coating, the coating must initially adhere to the dryer surface. This is accomplished by means of a single pressure roller at the nip in the prior constructions. In order to avoid sticking of the coating to the drum after the drying, the surface of the dryer was coated with an oleaginous material. This is disclosed in the Montgomery Patent 2,568,288. However, the production rate still could not be safely raised above approximately feet per minute.

A later attempt to increase the speed of production of a cast coated paper is shown in Hart 2,919,205. Although the production rate is increased by this process to about 200 feet per minute, it requires a special gellable coating which must be gelled before the coating is contacted by the dryer drum. i

Consequently, it is the primary object of this invention to produce a method and apparatus which will permit the production of a smooth coated paper at a high rate of speed.

Another object of this invention is the production of a cast coated paper with a dryer drum heated to above the boiling temperature of the liquid coating vehicle.

Another object of this invention is to produce a cast coated paper at high speed, without permitting the coating to blow from the dryer drum.

Another object of this invention is the provision of method and means for receiving and absorbing the vaporizing from the coating to be cast on a paper, without permitting the coating to separate from the dryer drum.

This invention also has for its object the provision of a means and method for continuously maintaining the coating against the dryer drum to dry the coating sufiiciently, such that the cohesive strength of the coating will resist any distortion due to further drying.

An additional object of this invention is to provide a means and method for drying and casting a liquid coated paper at a temperature higher than the boiling temperature of the liquid without the necessity of using a pressure sufficient to overcome the vapor pressure of the liquid at the dryer temperature while continuously maintaining the. coating against the casting surface and preventing the separation of the coating from the dryer surface until the coating is sufiiciently dry, whereby the cohesive strength of the coating will resist any distortion due to further drying.

A further and more limited object of this invention is to produce at high speed a cast coated paper by receiving the vapor from the vaporizing liquid in the coating be- I fore it has an opportunity to separate the coating from the drum and additionally maintaining the coating continuously against the dryer drum.

Other objects and advantages of the present invention will become apparent to those skilled in the art, from the following description when read in conjunction with the accompanying drawing, wherein:

FIGURE 1 is a schematic side elevational view of the present invention;

FIGURE 2 is a schematic side elevational view of another embodiment of the present invention showing the use of a soft flexible roller as the pressure means;

FIGURE 3 is a fragmentary sectional View of the area between the dryer drum and the pressure applying means.

Briefly, this invention comprises a method and apparatus for drying a liquid coating on a paper into a smooth surface such as a cast surface at high speed, by the use of a drum heated toa temperature above the,boiling point of the liquid in the coating, the blowing of the coating being prevented by providing a vapor receiving void behind the paper surface having the coating, and by continuously maintaining the coating pressed against the dryer drum with a pressure means until the cohesiveness of the coating is such that further drying will not distort the coating.

It has been discovered that the blowing of the coating away from the surface of the dryer drum can be avoided by providing a means of escape for the vaporized liquid in the wet coating rather than reducing the temperature of the drum. Thus, it is proposed to heat the dryer drum to temperatures as high as 325 F. or even higher, and permit the vapor to escape through the coating and into a vapor receiving void or backing layer which is pressed against the back of the paper surface having the coating thereon.

As can be seen, the vapor from the boiling liquid will not force the coating from the drum surface, but rather, with the proposed construction can pass through both the coating and the normally porous paper surface into the vapor receiving void in back of the paper surface. The only pressures necessary are those that will hold the coating on the drum surface. The best determination of these pressures are those that will overcome the resistance offered by the coating, the paper and the vapor receiver to the passage of the vapor in other words the pressures necessary to hold the coating on the drum are those sufficient to overcome the vapor pressure of the liquid at the drying temperature less the loss in pressure due to the vapor passing through the coating, the paper and into the porous backing. These pressures that may be around 20 psi. are less than the vapor pressures of the liquid at the drying temperature and considerably less than the pressures suggested in the Hart 2,919,205 patent, which are in the neighborhood of 300-380 pounds. per linear inch.

In order to adequately dry the coating so that it will not stick to the dryer drum, it is usually sufficient, as

with a starch adhesive, to dry the surface of the coating whereby the cohesiveness of the coating is greater than the adhesiveness to the dryer drum. However, regardless of the amount of drying, it is important that pressure be applied continuously to the coating, such as will overcome the resistance of the vapor to flow into the vapor receiving layer for a long enough time until the cohesiveness of the coating is such that further drying will not distort the coating. This can only be accomplished if there is a means for applying continuous pressure to the coating, thereby forcing it against the drum along a substantial portion of the drum surface. A feature of this invention, therefore, is the method and means for applying the necessary pressure over a substantial circumferential portion of the drum for sufficient time to dry the surface of the coating sufficiently so that the cohesivenessof the coating is such that further drying of the coating will not distort the coating.

The apparatus for carrying out this invention is shown in FIGURE 1, wherein the numeral generally designates the high speed apparatus for providing an ultrasmooth coating C on a web of paper P.

The paper P may be rough kraft type of paper, which is frequently used for making cartons for articles that may, for example, be placed on the usual retail grocery or drug shelf. This type of paper has a rough surface which does not present as as attractive a package as it could if the surface were smooth. To provide this smooth surface, the paper before entering the apparatus is coated in any conventional manner as by a wet roller and air knife, not shown, with the usual adhesive or mineral-adhesive containing aqueous coating. The mineral may be any of the fine particle type, such as calcium carbonate, clay, etc., while the adhesive may be selected fromthe group such as a protein, starch or a starch derivative, such as acetylated, oxidized, chlorinated, enzyme converted, corn or potato starch, rubber or acrylic latex and polyvinyl alcohol, thermosetting plastics, etc.

Conveying roller 12 conducts the paper P with the wet coating C to the nip of the dryer drum 14, which is heated to a temperature which may be as high as 275-325 F. by a convenient means, such as high pressure steam, within the drum. The drum 14 preferably has the usual 10-12 foot diameter and a highly polished chromium coated surface, which acts as a casting surface in the known manner, but also, it has been found that a machine finishing of the drum will permit the obtaining of a paper surfaced with a smooth coat.

Wrapped around the conveying roller 12 also is the vapor receiving void or backing layer 16 composed of any relatively thick (approximately inch thick) layer, such as the continuous felt belt shown. The type of felt is that commercially used and known. For the purposes of this invention, any other smooth surfaced continuous belt-like layer may be used, and may be composed of wool, cotton, fiberglass or like closely knit, woven or pressed material. The drum 18 is a dryer roll for the felt, and increases the water removing capacity of the apparatus.

As is clearly shown in FIGURE 1, the layer 16 is urged against the drum 14 around a substantial portion of the circumference of the drum. By means of this feature of the invention, sufficient drying time is achieved. This wrapping which may be up to 270 around the drum, but generally at least 5 is accomplished by means of the adjustable tensioning roller 20 having suitable jack means, such as shown at 22. Due to the fact that the layer 16, when made of wool felt for instance, does not have sufilcient tensile strength to withstand even the reduced pressures that can be used in this invention, a pressure means such as the flexible pressure belt 24 may be utilized. It should be understood, however, that if the vapor receiving layer 16 were strong enough to apply the needed pressure and also capable of absorbing the vapor from the coating, the flexible pressure belt 24 would not be necessary. The belt 24 may be made of any flexible material that is smooth, such as a rubber or plasticv material, or evenmay be constructed of wire that may, for example, be of the woven type. The belts may also be porous or nonporous. However, the use of a porous pressure belt provides an unlimited void or vapor receiving volume, inasmuch as the vapor can pass out of the layer 16 through the pores or openings that exist in the porous belt.

It has been found that the amount of void or vapor receiving volume necessary is dependent upon the amount of vapor generated by the wet coating, and upon the type of coating. For instance, with a coating that sets quickly and sufiiciently at the surface, so that its cohesiveness exceeds its :adhesiveness to the dryer drum, the subsequent flashing of the remaining liquid in the coating or paper will not afiect the smooth surface. In such an instance, there is no need for a large enough volume of void space to receive the additional vapor flashed from the coating after the initial drying, but only that which evolved while the coating passed through this initial drying.

ininstances where a relatively low coat weight is used, for example, /25 pounds per ream, as in the case of an unpigmented coating such as starch, there of course, would be less need for as great a vapor receiving void in this [low liquid containing wet coating, as in the case of a heavier pigmented coating havin a weight range of 12-20 pounds per ream, which would normally contain a greater amount of liquid. Therefore, the layer 16 may be considerably thinner, in the range of 4 inch in thickness. It is also possible to omit the use of the layer 16 entirely, when the low weight coating is placed upon a porous bulky low density paper board having a density of up toabout 10 pounds per ream per mil. In such a case, the void volume presented by the board behind the paper surface upon which the low weight coating is placed, can be sufiicient to receive all the vapor evolved while the paper is pressurized against the dryer drum. The paper board behind the paper surface, therefore, acts as'the equivalent of the backing layer 16, to absorb the relatively small amount of liquid vaporized from the wet coating. It is emphasized that the omission of the layer 16 is only permitted during the practice of this invention when 1) the coating is unpigmented, (2) of a solids coating weight less than 5 pounds per ream applied at not less than 20% solids, (3) placed upon a paper board having a density of up to about pounds per ream per mil, and a minimum thickness of 5 mils.

As best shown in FIGURE 1, there is provided at the nip N a pressure roller 26, which has pressure adjusting means 28 which is similar to means 26 on roller 20". The purpose of roller 26 is to form an accurately defined nip, wherein the coated paper enters the nip tangential to the dryer drum surface. The pressure need not be in excess of the pressure applied by the pressure belt 24 throughout its wrap around the drum 14.

In FIGURE 3, there is shown the usual practice of the invention, in which the paper P has a coating C backed up by a vapor receiving void or layer 16, all of which are continuously pressed by the pressure belt 24 against the dryer drum 14, heated up as high as 325 F. As previously stated, the pressure need only be sufficien-t to overcome the resistance of the passage of the vapor through the coating of the paper and into the layer 16.

Instead of using the pressure belt 24, as shown in FIGURE 1, the necessary pressure may be applied by means of a soft rubber roller 30 rotating about an axis 32. The roller must be soft enough to cover a substantial area of the dryer drum, considerably in excess of the contact that would be provided with the normally used pressure roller. Such a roller can be inflated with air and pressed against the drum to achieve the desired pressure. In order to maintain the pressure of the coating against the drum for sufiicient time to dry the coating, and yet retain the desired production rate, less pressure can be used to inflate the roller 30. Thus, there will be a greater pressured wrap of the paper around the drum.

By utilization of the teaching of this invention, speeds of production as high as 400 feet per minute have been reached on only a 6 foot diameter dryer and a satisfactory product obtained. With a larger drum diameter, considerably higher speeds are possible.

The wrapping of the pressure means about the dryer drum, as stated, is to afiord sulficient drying time for the coated paper between the pressure means and the drum. It should be clear that if a smaller drum than the usual 10-12 feet diameter drums is used, a greater wrapping in terms of degrees of wrap must be accomplished to achieve the necessary pressurized drying. Conversely, if a larger drum is used, less degrees of wrapping are necessary.

The following examples illustrate the present invention, and are not to be considered as limiting the scope of the invention:

' Examples (1) Base stock1 sheet of uncalendered board, density 7#/ream/mil, weight 126 lbs/ream, 18 mil thickness, 60% kraft, 40% groundwood.

Coatin-g20 lbs/ream, composed of 100 parts clay, 18 parts protein and water to make 55% solids.

Dryer temperature-300 F.

Belt pressure33 p.s.i.g., applied continuously over entire sheet.

Felt thickness% inch.

Dryer surfaceChrome plated mirror finish.-

Results: Paper had very smooth finish and high gloss characteristic of cast coatings.

Base stock1 sheet of uncalendetred board, density 7#/ream/mil, weight 126 lbs/ream, 1-8 mil thickness, 60% kraft, 40% groundwood.

Ooating2(l lbs/ream, composed of 100 parts clay, 18 parts protein and water to make 55% solids.

Dryer temperature35 0 F.

Belt pressure60 p.s.i.g., applied continuously over entire sheet.

'Felt thicknessinch.

Dryer surfaceChrorn'e plated mirror finish.

Base stock-l sheet uncalenedered board, density 7#/ream/mil, weight 200 lbs/ream, 28 mil thickness, 60% kraft, 40% groundwood.

-Coating2 lbs/ream, oxidized starch from 20% solids aqueous solution- Temperature-300 F.

Pressure-33 p.s.i.g.

Felt-None.

Dryer surface-Chrome plated mirror finish.

Base stock-Calendered board, density 11#/ream/ mil, weight 250 lbs/ream, 23 mil thickness, kraft.

Coating20 lbs/ream; solids composed of 100 parts Another run with a board of density 10#/ream/mil was made under identical conditions as Example #5, with satisfactory results. This would seem to substantiate the position that for the lower density board used in Example #5, a higher temperature or lower pressure is possible if the felt were retained, or the felt could be eliminated entirely, because the less dense board would have sufiicient void space to receive the released vapor.

As used herein, the term ream refers to 500 sheets of paper, each sheet being 24 inches by 36 inches.

From the foregoing detailed description, it will be evident that there are a number of changes, adaptations, and modifications of the present invention which come within the province of those skilled in the art. However, it is intended that all such variations not departing from the spirit of the invention, be considered as within the scope thereof as limited solely by the appended claims.

What is claimed-is:

1. The method of cast coating paper and the like corn prising coating a paper web surface with a hardenable liquid coating containing a volatile liquid and an adhesive which coating is conformable to a smooth forming surface, pressing said coating paper surface with a continuous pressing surface against a smooth forming surface heated to a temperature suiiicient to boil said liquid and under a pressure sufiicient to continuously maintain said coating against said smooth forming surface, maintaining a vapor receiving web between the coated paper sur-.

face and said pressing surface, continuously maintaining said pressure for a sufficient time until sufficient volatile liquid has been vaporized and been driven from the surface of the coating. whereby the cohesive strength of the coating will resist any distortion due to further drying.

2. The method of cast coating paper and the like comprising coating a paper web surface with a hardenable liquid coating containing a volatile liquid and an adhesive which coating is conformable to a smooth forming surface, pressing said coating paper surface with a continuous pressing surface against a chromium plated drum having a smooth forming surface heated to a temperature suiiicient to vaporize said liquid, said temperature being above the boiling temperature of the liquid, said pressing being at a pressure sufficient to continuously maintain said coating against said smooth forming surface, maintaining a vapor receiving web between the coated paper surface and said pressing surface, continuously maintaining said pressure for a sufficient time until sufficient volatile liquid has-been vaporized and been driven from the surface of the coating whereby the cohesive strength of the coating will resist any distortion due to further drying.

3. The method of cast coating paper and the like comprising coating a paper web surface with a vhardenable liquid coating containing a volatile liquid and an adhesive which coating is conformable to a smooth forming surface, pressing said coated paper surface with a continuous pressing surface against a chromium plated drum having a smooth forming surface heated to a temperature sufiicient to vaporize said liquid, said temperature eing above the boiling temperature of the liquid, said pressing being at a pressure sufficient to continuously maintain said coating against said smooth forming surface, maintaining a vapor receiving void formed by a felt belt between the coated paper surface and said pressing surface, continuously maintaining said pressure for a suflicient time until sufficient volatile liquid has been vaporized and been driven from the surface of the coating whereby the cohesive strength of the coating Will resist any distortion due to further drying.

4. The method of cast coating a rough thick paper board having a paper surface and a porous substantially thick vapor receiving backing with a hardenable liquid coating containing a volatile liquid which coatingis conformable to a smooth forming surface, pressing said coated paper surface with a continuous pressing surface against asmooth forming surface heated to a temperature sufiicient to boil said liquid and under a pressure sufficient to continuously maintain said coating against said smooth forming surface, continuously maintaining said pressure for a sufiicient time until sufiicient volatile liquid has been vaporized and been driven from the surface of the coating whereby the cohesive strength of the coating will resist any distortion due to further drying.

5. The method of cast coating paper and the like comprising coating a paper web surface with a hardenable liquid coating containing an adhesive selected from the group consisting of starch, a starch derivative polyvinyl alcohol, rubber and acrylic latex, and a protein and a volatile liquid which coating is conformable to a smooth forming surface, pressing said coated paper surface with a continuous pressing surface against a smooth forming surface heated to a temperature sufficient to boil said liquid and under a pressure sufficient to continuously maintain said coating against said smooth forming surface, main taining a vapor receiving Web between the coated paper surface and said pressing surface, continuously maintaining said pressure for a sufficient time until sufficient volatile liquid has been vaporized and been driven fromthe surface of the coating whereby the cohesive strength of the coating will resist any distortion due to further drying.

6. The method of cast coating paper and the like comprising coating a paper web surface with a hardenablc liquid coating containing a pigment and an adhesive selected from the group consisting of starch, a starch derivative polyvinyl alcohol, rubber and acrylic latex and a protein, and a volatile liquid, said volatile liquid being water, which coating is conformable to a smooth forming surface, pressing said coated paper surface with a continuous pressing surface against a smooth forming surface heated to a temperature sufficient to boil said liquid, said pressing being at a pressure sufficient to continuously maintain said coating against said smooth forming surface, maintaining a vapor receiving web between the coated paper surface and said pressing surface, continuously maintaining said pressure for a sufficient time until sufficient volatile \ilqllld has been vaporized and been driven from the surface of the coating whereby the cohesive strength of the coating will resist any distortion due to further drying.

7. The method of cast coating paper and the like comprising coating a paper web surface with a hardenable liquid coating containing a volatile liquid which coating is conformable to a smooth forming surface, pressing said coated paper surface with a continuous pressing surface against a smooth forming surface heated to a temperature sufficient to vaporize said liquid, said temperature being above the boiling temperature of the liquid, said pressing being at a pressure less than the vapor pressure of the liquid being vaporized, said pressure being sufficient to continuously maintain said coating against said smooth forming surface, maintaining a vapor receiving web between the coated paper surface and said pressing surface, continuously maintaining said pressure for a suflicient time until suflicient volatile liquid has been vaporized and been driven from the surf-ace of the coating whereby the cohesive strength of the coating will resist any distortion due to further drying.

8. The apparatus of claim 9, wherein said pressure member for applying pressure includes a drum conforming roller which conforms to the shape of the drum through a substantial circumferential arc of said drum.

9. Apparatus for casting a wet coating on a paper wherein the coating includes solids and a liquid comprising; rotatable casting drum having a smooth polished surface heated to a temperature in excess of the boiling tem- Jerature of the liquid, means for conveying said Wet coating on said wet paper into contact with said heated surface over an arcuate casting zone of said drum surface, backing means in contact with the paper on a side opposite to said coated side for receiving vapor from said coating, a pressure member disposed against said backing means at said casting zone for applying pressure to said backing means urging the latter towards said drum surface, said pressure member being wrapped around said heated surface through a substantial circumferential arc of said drum and exerting pressure uniformly over said are in excess of the magnitude of the vapor pressure of the boiling liquid minus the pressure loss due to the passage of vaporized liquid through the coating and the paper until the cohesive strength of the coating will resist any distortion due to further drying.

10, Apparatus for casting a Wet coating on a paper wherein the coating includes solids and a liquid comprising: a rotatable casting drum having a smooth polished surface heated to a temperature in excess of the boiling temperature of the liquid, means for conveying said Wet coating on said paper into contact with said heated surface over an arcuate casting zone of said drtun surface, backing means in contact with the paper on a side opposite to said coated side for receiving vapor fro-m said coating, a pressure member disposed against said backing means at said "casting zone for applying pressure to said backing means urging the latter towards said drum surface, said pressure member comprising a flexible continuous belt in contact with said backing means, said pressure member being wrapped around said heated surface through a substantial circumferential are of said drum and exerting pressure uniformly over said are in excess of the magnitude of the vapor pressure of the boiling liquid minus the pressure loss due to the passage of vaporized liquid through the coating and the paper until the cohesive strength of the coating will resist any distortion due to further drying.

11. The method of cast coating paper and the like comprising coating a paper sunface with a hardenable liquid coating containing a pigment and an adhesive in a volatile liquid, heating a smooth polished drum surface to a temperature above the boiling temperature of the liquid, applying a continuous vapor receiving and absorbing backing layer into continuous contact with said paper, pressing a continuous belt against said backing layer forcing said coating into continuous contact With and around a substantial portion of said drum surface at a pressure at least equal to the vapor pressure of the liquid in contact with the drum surface minus the pressure loss due to the passage orf vaporized liquid through the coating and the paper.

12. The method of cast coating paper and the like comprising coating a paper surface with a hardenable liquid coating containing a pigment and an adhesive in a volatile liquid, heating a smooth polished drum sunface to a temperature above the boiling temperature of the liquid, applying a continuous vapor receiving and absorbing backing layer into continuous contact with said paper, pressing a continuous non-porous belt against said backing layer forcing said coating into continuous contact With and around a substantial portion of said drum surface at a pressure at least equal to the vapor pressure of the liquid in contact with the drum surface minus the pressure loss due to the passage of vaporized liquid through the coating and the paper.

13. The method of cast coating paper and the like comprising coating a paper Web surface with a hardenable liquid coating containing a volatile liquid and an adhesive which coating is conformable to a smooth forming surface, pressing :said coated paper surface With a continuous non-porous pressing surface against a smooth forming surface heated to a temperature sufficient to boil said liquid and under a pressure suflicient to continuously maintain said coating against said smooth forming surface, maintaining a vapor receiving web between the coated paper surface and said pressing surface, continuously maintaining said pressure for a suflicient time until sufficient volatile liquid has "been vaporized and been driven from the surface of the coating whereby the cohesive strength of the coating will resist any distortion due to further drying.

References Cited in the file of this patent UNITED STATES PATENTS 1,944,600 Greene Jan. 23, 1934 2,337,013 Bradner et a1. Dec. 14, 1943 2,457,433 Barrett Dec. 28, 1948 2,510,313 Houth et al. June 6, 1950 2,870,038 MacIntyre Jan. 20, 1959 2,919,205 Hant Dec. 29, 1959 FOREIGN PATENTS 393,740 Great Britain Jime 15, 1933

Claims

1. THE METHOD OF CAST COATING PAPER AND THE LIKE COMPRISING COATING A PAPER WEB SURFACE WITH A HARDENABLE LIQUID COATING CONTAINING A VOLATILE LIQUID AND AN ADHESIVE WHICH COATING IS CONFORMABLE TO A SMOOTH FORMING SURFACE, JPRESSING SAID COATING PAPER SURFACE WITH A CONTINUOUS JPRESSING SURFACE AGAINST A SMOOTH FORMING SURFACE HEATED TO A TEMPERATURE SUFFICIENT TO BOIL SAID LIQUID AND UNDER A PRESSURE SUFFICIENT TO CONTINUOUSLY MAINTAIN SAID COATING AGAINST SAID SMOOTH FORMING SURFACE, MAINTAINING A VAPOR RECEIVING WEB BETWEN THE COATED PAPER SURFACE AND SAID PRESSING SURFACE, CONTINUOUSLY MAINTAINING SAID PRESSURE FOR A SUFFICIENT TIME UNTIL SUFFICIENT VOLATILE LIQUID HAS BEEN VAPORIZED AND BEEN DRIVEN FROM THE SURFACE OF THE COATING WHEREBY THE COHESIVE STRENGTH OF THE COATING WILL RESIST ANY DISTORTION DUE TO FURTHER DRYING.