US3300371A

US3300371A - Gypsum plaster board

Info

Publication number: US3300371A
Application number: US158411A
Authority: US
Inventors: Harry E Hart
Original assignee: Celotex Corp
Current assignee: Celotex Corp
Priority date: 1961-12-11
Filing date: 1961-12-11
Publication date: 1967-01-24
Anticipated expiration: 1984-01-24

Description

Jan.' 2'4, 1967 l H. E. HAR-f 3,300,371

GYPSUM PLJASTER BOARD 'Filed D60. ll 1961 United States Patent O 3,300,371 GYPSUM PLASTER BOARD Harry E. Hart, Hinsdale, Ill., assignor to The Celotex Corporation, a corporation of Delaware Filed Dec. 11, 1961, Ser. No. 158,411 8 Claims. (Cl. IGI- 229) The present invention pertains to a gypsum core plaster board which can be used conventionally as wallboard or as a plaster base, and more particularly to an improved gypsum plaster board to which plaster or a water base paint may be adhered.

It is customary in finishing the interior walls and oeilings of a building to provide a plaster surf-ace which is applied to a backing. A preferable type of backing is a -gypsum plaster board or gypsum lath comprising a core of set gypsum and paper cover sheets enclosing the core. A major problem in the use of such paper covered sheets is the provision of rapid and uniform water absorption from the plaster applied to the surface thereof. Without such rapid and uniform water absorption there is a lowering of the strength in the plaster facing. Furthermore, rapid and uniform water absorption is necessary t-o lreduce slippage of the plaster on the wall when it is rodded or darbied.

Another factor of great importance is the strength of the bond between the gypsum core and the paper cover sheets, so that the paper cover sheets will not peel or delaminate from the ygypsum core. A weakness of the interface bond may produce a totally unacceptable wall iinish. Additionally, it is necessary that the paper cover sheets, which :are conventionally manufactured, do not delaminate between their adjacent plies.

With reference to the paper cover sheets themselves, they must be of uniform strength throughout with strong bonds between the plies. Additional wet and dry strength in the paper cover sheets make it possible t-o reduce the caliper or thickness of the sheets, thus reducing the lweight of the paper used. A reduced weight is `reflected in a reduced freight rate and a cost `savings on the paper stock brought to the gypsum board plant.

Also, increased strength in the paper cover sheets with a reduction in its thickness vastly improves t-he scoring properties of the gypsum lath as well as improving its nailing characteristics.

There is presently available a type of lath in which at least one ply of the paper cover sheet incorporates ta urea or melamine type resin to supplement the conventional rosin and alum size. However, this additional resin which is compatible with the rosin and alum size does not preh vent the migration of the size in the cover sheet to the interface between the gypsum core and the cover sheet. At times the presence of the size at the surface of the gypsum core produces a slick bond, which means the crystals of gypsum at the interface do not penetrate the paper cover sheets and the paper to gypsum bond is greatly impaired.

It is, therefore, an object of the present invention to provide a gypsum board which has uniform and rapid water absorption over its surface.

It is yet another object of the present invention to provide a novel gypsum board or lath in which the strength of the Wet bond between the plies of the paper and the bond between the paper cover sheets and the gypsum core is greatly improved.

It is a further object of the present invention to provide a novel gypsum board in which the paper is of reduced caliper compared to more conventional board paper and thus, lighter in weight.

These and other objects and advantages of the present invention will become more apparent when the following more detailed description of the invention is considered with the accompanying drawing, and in which:

Mice

The drawing is a cross-sectional view of the plaster 'board of the present invention.

Referring now to the drawing, there i-s therein shown a plaster board or lath 10 comprising a gypsum core 11 and facing sheets 15 and 16. Each of the facing sheets 15 and 16 is made up of seven plies 1824 and 27-33, respectively. Of course, it should be understood that since only one side of the plaster lath will ordinarily receive a plaster coat, only one of the sheets 15 tand 16 need be used. In this latter case, the other sheet may be of such conventional paper as is now available.

The core 11 is conventional and comprises the usual ingredients of a set slurry of calcium sulfate hemihyd-rate, water, starch, foam, etc. The specific process for making gypsum plaster board is well known, and for this reason a detailed explanation of this process will not be repeated.

The paper cover sheets 15 and 16 are bonded to the core 11 by the penetration of gypsum crystals which, when the excess water of the gypsum slurry is driven ot by drying, interlock with the paper fibers in the sheet t-o form a stable and a strong bond. As indicated, the paper cover sheet 15 is made with seven plies. This paper can be made on any conventional cylinder paper making machine having seven wells or compartments for holding the paper stock individually for each ply. The three innermost plies 20, 21 and 22, are made with conventional paper fiber stock that has been sized. In refining t-he paper stock for all the plies ground wood, sulfate or sulphite stock should be used.

The two plies 19 and 23, lying immediately outside of the three central plies 20-22, are made lwithout any sizing at all, but contain an alkaline salt or alkaloid t-o -act as a buffer and prevent migration of the size from the central plies. As will become more .apparent later, this buffer zone is of extreme importance in :achieving the novel lath of the invention. While many suitable alkaline salts and alkalies may be used, soda ash -or caustic soda have been found -to be preferable. An organic alkaloid may be used, if desired.

The two

outermost plies

18 and 24 contain a polyamide resin which 4is compatible with ian alkaline pH. Preferably, the pH of the stock in the outer plies is held at a pH of 7.10, or higher. The pH may be maintained by adding sui-licient -alkaline salts or alkaloid compounds. The resin is added to the furnish in the cylinder wells in an amount of about 0.1 to 5.5%. Resin in an amount of 5.5% has been added `to the furnish, but experiments indicate that more resin may be added without imparing the desired characteristics of the paper. The wet strength of the paper will vary depending upon the amount of resin added.

While the specific example has referred to a cylinder machine :having seven wells, other paper making machines may be used. Thus, the inverformer, which does not use Wells, may be used with equal effectiveness.

Also, the resin and other ingredients may be added to the furnish at places other than the wells. For example, the ingredients may be added to the paper stock at the head box or Jordans.

Furthermore, while a seven ply paper has been found to be practical, the number of plies may be reduced to as low as three. In this latter case, the center ply contains the alkaline buffer and the two outer plies contain the polyamide resin.

The specific resin added to the outermost plies is an uncured thermosettng cationic resin comprising a water soluble polymeric reaction product of epichlorohydrin and a polyamide derived from a polyalkylene polyamine and a saturated aliphatic diba-sic carboxylic acid containing about 3 to 10 carbon atoms. Such a resin is commercially available from the Hercules Powder Company of Wilmington, Delaware, and sold under the trade name of Kymene 557. Additionally, complete information as to the characteristics of the resin and its manner of manufacture may be found in U.S. Patent No. 2,926,154, issued to Gerald I. Keim on February 23, 1960. Further information with regard to the use of this resin in the production of a wet strength sheet may be found in U.S. Patent No. 2,926,116, issued to Gerald I. Keim, on February 23, 1960.

The actual manufacture of the gypsum lath, as previously indicated, is conventional. A proper gypsum slurry with calcium sulfate hemihydrate, water starch, foam, accelerator, etc., is made and dropped on a paper cover sheet in a conventional gypsum wallboard machine. The paper sheet is folded so that its outer edges are slightly retroverted and are spaced inwardly from the edge of the lath. A top cover sheet is applied to the upper exposed surface of the gypsum slurry and glued to the retroverted edges of the bottom sheet. The sandwich of gypsum core with its enclosing paper cover sheets is conveyed on a belt until the gypsum core sets. After this, the sandwich is cut to appropriate length and is conveyed through a drier where the excess water is driven from the gypsum core after final set takes place.

In comparing the gypsum lath of the invention made with the novel paper, with more conventional gypsum lath, there has been found to be an unusually strong bonding between the plies of the paper and between the gypsum core and the paper. The fact that the sizing agent is confined to the three interior plies and not permitted to migrate through the alkaline barrier ply avoids the danger of a poor bond between the paper and the gypsum core. A comparison has been made between conventional gypsum lath and the novel gypsum lath of the invention lby wetting the paper and then abrading the moisture laden paper. In the case of regular gypsum lath, the paper was found to delaminate in separate plies. In contrast to this, the novel paper of the invention did not laminate but the plies were strongly bonded together.

A test was made of the nature of the water absorption of conventional gypsum lath and the novel lath of the present invention. In this test, a small glass holding one ounce of water was inverted on the surface of each type of lath. In the case of conventional lath, the water spread over an area about twice the area of the spread of the water on the surface of the novel lath. Thus, indicating that the actual water absorption of the novel lath was about twice that of conventional gypsum lath. This characteristic of enhanced water absorption results in a greater density and higher strength of the plaster applied to the surface of the novel gypsum lath of the invention.

With regard to the paper itself, it has been found advan-I tageous to make it in a balanced condition. By balanced condition is meant that there is a plane of symmetry within the paper at the center running parallel to the surface of the paper. Thus, the center ply 21 is sized with rosin and alum, the next plies 20 and 22 adjacent to the center in each direction from the center ply 21 is also sized with rosin and alum, the next plies 19 and 23 outwardly of plies 20 and 22 contain an alkaline or alkaloid buer system and the two outermost plies 18 -and 24 contain the cationic polyamide resin. In this way, there is uniform strength throughout the paper.

As indicated, the resin employed in the outer plies 18 and 24 is cationic in nature. It has been found that anions in the ply next to the gypsum core prevent proper crystalline formation at the interface of the gypsum core and the paper. The use of a cationic resin obviates this condition and a stronger bond between the gypsum core andthe paper results. In summary, there has been disclosed a novel plaster lath having rapid and uniform water absorption, lighter in weight and producing a strong bond !between the plies of the paper and also between the paper cover sheets and the gypsum core than has heretofore been available.

While there has been shown the best known mode of the invention, other changes and modifications may be made by those skilled in the art, and it is intended to cover such changes and modifications in the appended claims.

I claim:

1. A plaster base for receiving a face coat of plaster comprising a set gypsum core, cover sheets bonded to exposed faces of said core, each of said cover sheets being of multiple ply construction having at least one central ply, said central ply being sized with sufiicient rosin and alum size to prevent tearing of the paper under tension; two plies outwardly adjacent to said central ply having an alkaline buffer therein in an effective amount to prevent migration of the rosin size beyond said two buffer plies, and two additional plies outwardly adjacent to said buffer plies, said outermost plies of each sheet containing a cationic polyamide resin dispersed therein.

2. A plaster base for receiving a face coat of plaster as recited in claim 1, in which said cationic polyamide resin is in an amount of at least 0.1% lby weight of said paper sheet.

3. A paper sheet for lamination to a gypsum core cornprising multiple plies, said paper having at least one central ply, said central ply being sized with suflicient rosin and alum size to prevent tearing of the paper under tension; two plies outwardly adjacent to said central ply having an alkaline buffer therein in an effective amount to prevent migration of the rosin size beyond said two buffer plies, and two additional plies outwardly adjacent to said buffer plies, said outermost plies of each sheet containing a cationic polyamide resin dispersed therein.

4. A paper sheet for lamination to a gypsum core as recited in claim 3, in which said cationic polyamide resin is in an amount at least 0.1% by weight of said paper sheet.

5. A plaster base for receiving a face coat of plaster comprising a set gypsum core, cover sheets bonded to exposed faces of said core, each of said cover sheets being of multiple ply construction having at least one central ply, said central ply being sized with sufficient rosin and alum size to prevent tearing of the paper under tension; two plies outwardly adjacent to said central ply having an alkaline buffer therein in an effective amount to prevent migration of the rosin size beyond said two buffer plies, and two additional plies outwardly adjacent to said buffer plies, said outermost plies of each sheet containing a cationic polyamide resin dispersed therein, said cationic polyamide resin comprising a water soluble polymeric reaction product of epichlorohydrin and a polyamide derived from a polyalkylene polyamine and a saturated dibasic carboxylic acid containing about 3 to 10 carbon atoms dispersed therein.

6. A paper sheet for lamination to a gypsum core comprising multiple plies, said paper having at least one central ply, said central ply being sized with suflicient rosin and alum size to prevent tearing of the paper under tension; two plies outwardly adjacent to said central ply having an alkaline buffer therein in an effective amount to prevent migration of the rosin size beyond said two buffer plies, and two additional plies outwardly adjacent to said buffer plies, said outermost plies of each sheet containing a cationic polyamide resin dispersed therein, said cationic polyamide resin comprising a water soluble polymeric reaction product of epichlorohydrin and a polyamide derived from a polyalkene polyamine and a saturated dibasic carboxylic acid containing about 3 to 10 carbon atoms dispersed therein.

'7. A plaster board comprising a set gypsum core, cover sheets bonded to exposed faces of said core, each of said cover sheets being of multiple ply construction having at least one central ply, said central ply being sized with suicient rosin and alum size to prevent tearing of the paper under tension; two plies outwardly adjacent to said central ply having an alkaline buffer therein in an effective amount to prevent migration of the rosin size beyond said two buffer plies, and two additional plies outwardly adjacent to said butler plies, said outermost plies of each sheet containing at least 0.1% of a cationic polyamide resin dispersed therein.

8. A paper sheet for lamination to a gypsum core comprising multiple plies, said paper having at least one central ply, said central ply being sized with suflicient resin and alum size to prevent tearing of the paper under tension; two plies outwardly adjacent to said central ply having an alkaline buffer therein in an elective amount to prevent migration of the rosin size beyond said two buffer plies, and two additional plies outwardly adjacent to said buffer plies, said outermost plies of each sheet containing at least 0.1% of a cationic polyamide resin dispersed 15 therein.

References Cited by the Examiner UNITED STATES PATENTS 2,226,553 12/ 1940 Cross.

2,344,600 3/ 1944 Codwise 161-246 2,562,859 7/ 1951 Camp 161-270 2,806,811 9/ 1957 Von Hazmburg 161-246 FOREIGN PATENTS 1,102,628 3/ 1961 Germany.

ALEXANDER WYMAN, Primary Examiner.

EARL M. BERGERT, Examiner.

R. J. ROCHE, Assistant Examiner.

Claims

1. A PLASTER BASE FOR RECEIVING A FACE COAT OF PLASTER COMPRISING A SET GYPSUM CORE, COVER SHEETS BONDED TO EXPOSED FACES OF SAID CORE, EACH OF SAID COVER SHEETS BEING OF MULTIPLE PLY CONSTRUCTION HAVING AT LEAST ONE CENTRAL PLY, SAID CENTRAL PLY BEING SIZED WITH SUFFICIENT ROSIN AND ALUM SIZE TO PREVENT TEARING OF THE PAPER UNDER TENSION; TWO PLIES OUTWARDLY ADJACENT TO SAID CENTRAL PLY HAVING AN ALKALINE BUFFER THEREIN IN AN EFFECTIVE AMOUNT TO PREVENT MIGRATION OF THE ROSIN SIZE BEYOND SAID TWO BUFFER PLIES, AND TWO ADDITIONAL PLIES OUTWARDLY ADJACENT TO SAID BUFFER PLIES, SAID OUTERMOST PLIES OF EACH SHEET CONTAINING A CATIONIC POLYAMIDE RESIN DISPERSED THEREIN.