US3296014A

US3296014A - Method and apparatus for pressure cast coating

Info

Publication number: US3296014A
Application number: US349219A
Authority: US
Inventors: Robert C Williams
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-03-04
Filing date: 1964-03-04
Publication date: 1967-01-03
Anticipated expiration: 1984-01-03

Description

Jan. 3, 1967 R. c. WILLIAMS 3,296,014

METHOD AND APPARATUS FOR PRESSURE CAST COATING 2 Sheets-Sheet 1 Filed March 4, 1964 Jan. 3, 1967 R. cv WILLIAMS 3,296,014

METHOD AND APPARATUS FOR PRESSURE CAST COATING 2 Sheets-Sheet 2 Filed March 4, 1964 FIG. 3

United States Patent 3,296,014 METHOD AND APPARATUS FOR PRESSURE CAST CDATING Robert C. Williams, 9902 River Road, Richmond, Va. 23229 Filed Mar. 4, 1964, Ser. No. 349,219 12 Claims. (Cl. 11764) This invention relates to a method and apparatus for cast coating paper. More specifically, this invention relates to an improved method and apparatus for pressure cast coating paper webs in a very simple and expeditious manner.

Since the inception of cast coating (US. Patent 1,719,166) numerous improvements have been made in the art. Many of these improvements have been directed to solution of the problem known as blowing which is caused by vaporization of the liquid component in the coating formulation whereby the coating is forced away from the heated dryer drum before it is cast. For this reason, early cast coating operations were limited to the use of temperatures less than 212 F. A significant recent improvement in the art of cast coating paper whereby temperature-s greater than 212 F. can be employed is that known as pressure cast coating, e.g. see US Patent 3,110,612. That technique comprises heating a wet coated paper web to the vaporization temperature or above of the volatile component of the coating formulation while concomitantly compressing the paper web by pressure belt means sufficient to maintain the paper Web in contact with the casting surface. By operating in this manner, viz. employing operating temperature-s greater than 212 F., greater production rates are achieved. While elegant results are realized by way of the latter technique, a method and means for pressure cast coating without necessitating the use of pressure belt means would be a welcomed contribution to the art.

An object of this invention is to provide a method for pressure cast coating which does not require the use of belt pressure means.

Another object of this invention is to provide an appara tus for pressure cast coating which does not require belt pressure means for casting a coating upon the paper web.

A more specific object of the instant invention is to provide a method and apparatus for pressure cast coating paper webs without pressurizing the paper web itself during the casting operation whereby belt pressure means are dispensed with.

These and further objects will come to light as the discussion proceeds.

FIGURE 1 depicts one embodiment of the apparatus of this invention wherein the process of this invention can be practiced.

FIGURE 2 is a more detailed arrangement of another embodiment of the apparatus of this invention.

FIGURE 3 depicts yet another apparatus arrangement wherein the process of this invention can be practiced.

It has now been found that high temperature pressure cast coating utilizing a hardenable coating formulation comprising a volatile liquid component can be conducted by contacting a wet coating of said coating formulation applied to a paper web with a casting surface; heating said coating to a temperature above the vaporization temperature of said volatile liquid component so as to generate vapors thereof; while simultaneously compressing said coating on said web against said heated casting surface by pressurized air until said coating is cast; and thereafter releasing said cast coated web from said heated casting surface by releasing the air pressure and allowing any moisture in the web to flash therefrom. Operating pursuant to this method prevents the vapors generated in the coatice ing from blowing the oating away from the heated casting surface. The air pressure uniformly presses between the pores in the sheet so as to keep the coating tightly pressed against the drum. Consequently, operating temperatures exceeding 212 F. can be employed. The gen erated vapors are forced to flow away from the casting surface toward and through the base web. Moisture re maining in the base web is removed by flashing upon exit of the coated web from the high pressure casting zone.

Among the chief advantages and features of the instant invention is that a pressure belt means as heretofore employed in the art of pressure cast coating is dispensed with. This results not only in equipment savings, but additionally in cost of operation since there are less parameters and equipment for the machine operator to control. Moreover, since the base sheet is porous, air pressure is applied to the coating itself thus eliminating transfer of sheet and felt imperfections to the coating when pressure is applied via belt.

The apparatus of the present invention wherein the above method can be practiced is that as shown in the embodiments depicted in the drawings. In FIGURE 1, a paper web 10 to be cast coated is conveyed over

rollers

11 and 12 into position to receive a wet coating of the coating formulation 13 contained in means 14. The coating formulation 13 is applied to the web 10 by the applicator rolls 15 and 16. The wet coating on the web 10 is smoothed out and excess removed therefrom by the air knife doctor 17, residual coating material being collected in means 18 and recycled for subsequent reuse. The wet coated paper web is then fed to the casting unit which comprises the dryer drum 19. The drum 19 has a polished chromium casting surface over which the web 10 is conveyed and positioned by the conveyance means 20 and 21.

The air pressurizing means 22 is constructed so as to form a shroud and essentially air-tight compartment with respect to the casting or dryer drum means 19. A certain amount of air leakage from the casting zone defined by the drum means 19 and the air pressurized means 22 is desirable since it prevents buildup of moisture within the system. Air under pressure is injected into the air pressurizing means 22 by suitable inlet ports, for example at 23 and 24.

Upon exit from the high temperature pressure casting zone, moisture in the cast coated web 10 will flash at the exit nip 25. Such flashing does not disrupt the coating since it is fully cast and strong enough at this point to resist the forces that come into play. The cast coated web 10 is then fed off the drum means 19 over the roller 26 to windup.

The design of the air pressurizing means can vary considerably without departing from the true spirit of this invention.

A more detailed design of a similar embodiment of the apparatus of this invention is that as depicted in FIGURE 2. The paper web 30 is fed into position to receive a coating by the

applicator rollers

32 and 33 of the coating formulation 34 contained Within means 35. The wet coating on the web 30 is smoothed out and excess material removed by the air knife doctor 36, the residual material being collected in means 37 and recycled for subsequent reuse.

The Wet coated web is then fed to the casting unit which comprises the dryer drum 38. The Wet coated web 30 is coveyed and positioned over the casting surface of the drum 38 by the conveyor means comprising the

rollers

39 and 40.

The dryer or casting drum 38 further comprises steam injection and distribution means 41 and condensate removal means 42. The wet coated web 30 is compressed upon the casting surface of the dryer drum 38 by pres- {B surized air fed through

ports

43 and 44 to the air pressurizing means 45. The inside peripheral surface 46 of the air pressurizing means 45 is foraminous.

The air injected into the member 45 passes through the foraminous surface 46 and the paper Web 30 and thereby compresses the coating on the paper web 30 upon the casting surface of the drum means 38. The clearance between the foraminous surface 46 and the casting surface of the drum means 38 is very small so as to minimize air usage. Upon exit from the high temperature pressure casting zone, most of the moisture absorbed by the paper W603i) flashes therefrom at the exit nip 47. The final product cast coated paper web 30 is then conveyed to windup.

In the apparatus arrangement of FIGURE 3, the paper web 50 having previously received a wet coating is fed to the heated casting drum 51. The coating on the web 50 is pressed against the circumferential surface of the drum by the air pressure means comprising the

rollers

52, 53, and 54. The pressure means further comprises the end closure plates means 55 (one on each side) which together with the rollers 52-54 form an essentially air tight high pressure and temperature casting chamber or zone. Pressurized air is injected into the zone through the inlet port 56. The

rollers

52, 53, and 54 are provided with

suitable means

57, 58, and 59 respectively (e.g., a hydraulic system) for urging the rollers toward each other and the drum 51 so as to provide the desired essentially air tight chamber. The chamber defined as above is not intended to be fully air tight inasmuch as vapors of moisture generated during the casting operation are preferably allowed to escape. However, the vapors can be removed via suitable exhaust means.

Upon exit from the high temperature pressure casting zone, most of the moisture absorbed by the paper Web 50 flashes therefrom at the exit nip 60. The web can be further dried upon exit from the casting zone by allowing it to remain in contact with the heated drum 51 for an additional period of time as shown in the drawing. It is to be understood that the number of rollers and their positions with respect to the dryer drum can vary without departing from the spirit of this invention.

In producing cast coated paper pursuant to the practice of this invention, it is preferred to operate Within a temperature range of from about 220 F. to about 350 F., especially within about 240 F. to 260 F. Moreover, it is preferred to exert a pressure upon the web within the range of from about psi. to about 50 p.s.i., particularly from about p.s.i. to about 35 p.s.i. Operating under these conditions, cast coated paper having optimum properties is produced at lowest cost.

A typical coating formulation for use in the instant invention comprises a pigment, an adhesive, and water. The pigment can be clay, blanc fixe, satin white, talc, calcium carbonate, titanium dioxide, and the like, plus mixtures thereof. Suitable adhesives are casein, glue, starches, gums, alpha-proteins, and the like, as well as mixtures thereof. It is understood of course that other materials can be added, such as waxes; carnauba, beeswax, and the like; water proofing agents: shellac, formaldehyde, and the like; as well as special materials such as: dyes, powdered metals, defoamers, wetting agents, release agents, and the like. The coating formulation is preferably applied at about 8 to about 25 pounds per 3000 square feet of base stock.

The following examples are presented wherein all parts are by weight unless otherwise specified.

Example 1 Base stock Dryer temperature300 F. Air pressure33 p.s.i.g. Results-very smooth finish and high gloss characteristic of cast coatings.

Example II Base stock 18 mil thick uncalendered board 7 lbs./ream/mil density 60 percent kraft and 40 percent groundwood Coating20 lbs/ream, composed of parts clay, 18 parts protein and sufiicient water to make 50 percent solids. Dryer temperature350 F. Air pressure-6O p.s.i.g. Resultsultra smooth finish and high gloss characteristic of cast coatings.

Example III Base stock- 28 mil thick uncalendered board 7 lbs./ream/mil density 60 percent kraft and 40 percent groundwood Coating-2 lbs/ream, oxidized starch from 20 percent solids aqueous solution. Dryer temperature300 F. Air pressure33 p.s.i.g. Resultsvery smooth finish and high gloss characteristic of cast coatings.

Example IV Base stock 23 mil thick calendered board 7 lbs./ream/mil density 100 percent kraft Coating20 lbs/ream, composed of 100 parts clay, 12 parts protein, and 6 parts latex (butadiene-styrene) and sufficient water to make 55 percent solids. Dryer temperature-300 F. Air pressure-63 p.s.i.g. Resultsvery smooth finish and high gloss characteristic of cast coatings.

Example V Base stock 18 mil thick uncalendered board 7 lbs./ream/mil density 60 percent kraft and 40 percent groundwood Coating-3 lbs/ream, oxidized starch from 20 percent solids aqueous solution. Dryer temperature-260 F. Air pressure18 p.s.i.g. Resultsvery smooth and glossy finish.

Cast coated paper produced as above is found to have not only an elegant appearance, but additionally excellent mechanical properties inasmuch as bonding between the coating and the base web is exceptionally good.-

I claim:

1. A high temperature pressure cast coating method utilizing a hardenable coating formulation comprising a volatile liquid component, said method comprising:

(1) contacting a wet coating of said coating formulation, applied upon a paper web, with a casting surface,

(2) heating said coating to a temperature above the vaporization temperature of said volatile liquid component so as to generate vapors thereof, while simultaneously (3) compressing said coating on said web against said heated casting surface by pressurized air until said coating is cast, and thereafter (4) releasing said cast coated web from said heated casting surface by releasing said air pressure and allowing moisture in said web to flash therefrom.

2. The process of claim 1 further characterized in that said casting surface is maintained at a temperature within the range of from about 220 F. to about 350 F.

3. The process of claim 1 further characterized in that said casting surface is maintained at a temperature within the range of from about 240 F. to about 280 F.

4. The process of claim 1 further characterized in that said coating on said web is compressed against said heated casting surface at a pressure within the range of from about 5 p.s.i.g. to about 50 p.s.i.g.

5. The process of claim 1 further characterized in that said coating on said web is compressed against said heated casting surface at a pressure within the range of from about p.s.i.g. to about 35 .p.s.i.g.

6. The process of claim 1 further characterized in that said coating formulation comprises a pigment, an adhesive, and water.

7. The process of claim 1 further characterized in that said coating formulation is applied at about 8 to about pounds per 3000 square feet of base stock.

8. A high temperature pressure cast coating method utilizing a hardenable coating formulation comprising a volatile liquid component for cast coating a continuous and moving paper web, said method comprising:

(1) applying a wet coating of said coating formulation to said moving paper web,

(2) contacting said coating with a heated casting surface, said surface being at a temperature sufficient to vaporize said volatile liquid component,

(3) compressing said coating against said heated casting surface by pressurized air suflicient to force said vapors through said coating,

(4) maintaining said heat and said pressure until said coating is cast, and thereafter (5) releasing said cast coated paper web from said casting surface in a reduced pressure zone whereby any moisture in said paper web is allowed to flash therefrom.

9. A high temperature pressure cast coating apparatus for casting a hardenable coating formulation comprising a volatile liquid component upon a continuous and moving paper web, said appaartus comprising:

(1) rotatably mounted casting drum means having a circumferential casting surface,

(a) said drum means being further defined in that it further comprises heating means whereby the casting surface of said drum means is heated to a temperature sufiicient to cast said coating formulation upon said paper Web,

(2) means for conveying said wet coated paper web into contact with the casting surface of said drum means, the extent of contact between said wet coated paper web and the casting surface of said drum means being prescribed by the position of said conveying means with respect .to said drum means, and

(3) pressurizing means positioned relative to said rotatably mounted drum means so as to form an enclosed casting chamber, and

(a) said pressurizing means further defining means for injecting a pressurized gas into said chamber whereby said coating on said web is pressed against the circumferential surface of said drum means as said Web passes through said casting chamber.

10. The apparatus of claim 9 further defined in that said pressurizing means has a foraminous surface in juxtaposition to said paper Web.

11. A high temperature pressure cast coating apparatus for casting a hardenable coating formulation comprising a volatile liquid component upon a continuous and moving paper web, said apparatus comprising:

(1) rotatably mounted casting drum means having a circumferential casting surface (a) said drum means being further defined in that it further comprises heating means whereby the casting surface of said drum means is heated to a temperature sufficient to cast said coating formulation upon said paper web,

(2) air pressurizing means comprising (a) multiple roller means rotatably mounted in series contact with each other, the first and last rollers of which are positioned relative to said drum means so as to be in contact with said paper web,

(b) closure means in combination with said roller means and said drum means so as to form an enclosed casting chamber, and

(c) means for injecting a pressurized gas into said casting chamber whereby said coating on said Web is pressed against the circumferential surface of said drum means as said web passes through said casting chamber.

12. The apparatus of claim 11 further defined in that said multiple roller means comprises three roller means.

3,110,612 11/1963 Gottwald et a1. 11764 MURRAY KATZ, Primary Examiner,

9/1947 Grupe 11764I

Claims

1. A HIGH TEMPERATURE PRESSURE CAST COATING METHOD UTILIZING A HARDENABLE COATING FORMULATION COMPRISING A VOLATILE LIQUID COMPONENT, SAID METHOD COMPRISING: (1) CONTACTING A WET COATING OF SAID COATING FORMULATION, APPLIED UPON A PAPER, WEB, WITH A CASTING SURFACE, (2) HEATING SAID COATING TO A TEMPERATURE ABOVE THE VAPORIZATION TEMPERATURE OF SAID VOLATILE LIQUID COMPONENT SO AS TO GENERATE VAPORS THEREOF, WHILE SIMULTANEOUSLY (3) COMPRESSING SAID COATING ON SAID WEB AGAINST SAID HEATED CASTING SURFACE BY PRESSURIZED AIR UNTIL SAID COATING IS CAST, AND THEREAFTER (4) RELEASING SAID CAST COATED WEB FROM SAID HEATED CASTING SURFACE BY RELEASING SAID AIR PRESSURE AND ALLOWING MOISTURE IN SAID WEB TO FLASH THEREFROM.