US2330810A

US2330810A - Plasterboard faced with lightweight paper

Info

Publication number: US2330810A
Application number: US423642A
Authority: US
Inventors: Dean D Crandell
Original assignee: National Gypsum Co
Current assignee: National Gypsum Co
Priority date: 1941-12-19
Filing date: 1941-12-19
Publication date: 1943-10-05
Anticipated expiration: 1960-10-05

Description

Oct. 5, 1943. D. D. CRANDELL -PLASTER BOARD FACED WITH LIGHTWEIGHT PAPER Filed Dec. 19, 1941 Dcm-S). @EEiEm,

ATTORNEYS Patented Oct. 5, 1943 V UNITED STAT ,PLASTERBOARD'FACED WITH LIGHT- WEIGHT PAPER Dean 1). Crandell, Buflalo, N. Y., assignor to National Gypsum Company, Buflalo, N. Y.

Application December 19,- 1941, Serial No. 423,642

5 Claims. (Cl. 154-454 The present invention relates to an improved plaster board and more particularly a plaster board in which the core of set cementitious material' is faced with lightweight paper having. relatively high crosswise strength and relatively high porosity.

In the manufacture of wall board from cementitious materials, such as calcined gypsum, it has been the practice heretofore to prepare a mix of calcined gypsum and water and to run this mix between upper and lower facing sheets producing,

upon setting or crystallization of the calcined gypsum, .a wall board or plaster board having a set core with facing sheets enclosing the core and bonded thereto in order to decrease the frangibility of the cementitious core.

Due to the fact that these facing paper sheets possess a greater lengthwise than crosswise strength and are fed lengthwise of the board making machine: the crosswise strength of the board with the paper facing sheet attached is less than the lengthwise strength. It has been general practice, therefore, to provide a facing paper having a crosswise strength of at least 25 pounds per square inch as'determined on Standard Scott tensile strength machine in order 'to produce set plaster board that is sufliciently resistant to fracture to be employed for usual purposes of such wall board.

It has been the general practice to employ, as facing sheets for gypsum lath, the weakest type of gypsum wall board, paper made of so-called chip stock made on a cylinder machine and having a weight of about62 pounds per thousand square feet of paper and athickne'ss of about 0.020 inch in order to obtain paper possessing the requisite 25 pounds crosswise strength. Such paper, since it is made on a cylinder machine, possesses a lengthwise strength, that is, strength measured in the machine direction, of about 80 pounds, a figure much higher than is necessary to produce satisfactory board. Such a paper produces a gypsum lath which when tested by procedure well known in the industry and outlined in Federal Specification SSW 51 A will have a transversejstrength lengthwise with the fibers of approximately 100 pounds and crosswise of 40 pounds. Thinner and lighter paper made of bait stock has not been foundsatisfactory as facing sheets-due to the tendency of the paper to pull away from the board and form corrugations and due to difficulty encountered in drying the flnishedboard.

It is obvious that the wide difference between the two directional stre h accomplishes no}- satisfactory results. Therefore it'is advanta geous to produce and employ a facing-sheet on which the crosswise strength is maintained up to, or is superior to, the present acceptable minimum. This is accomplished, in accordance with the present invention, by the use of a Fourdrinier sheet made at 55 pounds lengthwise and 35 pounds crosswise strength which produces a lath possessing a crosswise strength of 50-55 pounds and a lengthwise strength of -80 pounds.

Recently suggestions have been made to use combinations of plies of chip and kraft paper in order to obtain a facing sheet with the requisite crosswise strength and having a unit weight considerably below the 62 pounds normally employed. However, since such paper is made in plies it is subject to the disadvantage of all cylinder paper, namely, to split and separate into the constituent lamellae. j.

It is an object of the present invent-ion to provide a wallboard faced with paper of a Weight considerably below that heretofore thought necessary to provide the requisite crosswise strength and which is not subject to splitting into plies.

It is a further object of the invention to provide a wall board faced with paper made of combined chip and kraft stock and having suflicient porosity to permit of eflicient and rapid drying.

In the drawing:

Fig. 1 is an enlarged sectional view of wall board of the present invention, and

Fig. 2 shows the forming end of a wall board machine and illustrates diagrammatically the feed of the plastic core between facing sheets.

In accordance with the present invention a cementitious mix is prepared in. a conventional way from calcined gypsum and water to which may be added, if desired, paper pulp, starch and foaming ingredients, all. as is well known in the art. The cementitious mix is thereafter fed between the improved facing sheet, more fully described hereinafter, possessing a crosswise strength of about 30 to 35 pounds and a lengthwise strength of about 52 to 57 pounds or higher,

the paper having a weight of about 38 to 45.

length desired and fed to a conventional drying oven where the excess free water not combined as water crystallization is removed.

The product thus formed is a wall board or plaster board having a crosswise strength equivalent to that made from calcined gypsum and water and faced with 62 pound chip paper of a caliper of 0.019 to 0.020, board that has been found eminently satisfactory in industrial uses.

The paper employed as facing sheets II and M for the plaster core 20 is advantageously prepared from about 30 to 50% by weight of chip fibers which may be obtained from waste-newspaper stock, and the like, and about 50 to 70% by weight of kraft fibers. This stock is prepared in the usual way in suitable breaker heaters, deckers, and finish heaters to which latter the appropriate amount of size, alum and coloring,

if desired, may be added and the fiber-water ratio adjusted prior to feeding the stock to the head box of aconventional Fourdrinier machine. Suiiicient stock is run under the slice bar to the wire of the Fourdrinier machine to produce a finished paper of about 40 pounds per thousand square feet in weight and having a caliper of about 0.016". Upon test this paper is found to possess a minimum crosswise strength of about 32 pounds and a lengthwise strength (machine direction) of about 55 pounds. Since the paper is made on a Fourdrinier machine it is not formed as individual plies but represents one single ply not subject to splitting.

Paper made of this composition on a'Fourdrinier machine is especially suitable for facing sheets for wall board since the paper is relatively porous and due tothe low caliper permits of more rapid drying of the completed Wall board in the kiln. The increased rate of drying will become apparent when it is understood that the improved facing paper shows a 20 second densometer test, that is 100 c. c. of air under a constant specified pressure will flow through the paper sheet in 20 seconds as contrasted with a 90 second densometer test'for normal chip sheets made on a cylinder machine.

- From the above it will be seen that the present invention provides. a plaster board that is faced It will further be seen that the porosity of the paper permits'of more rapid drying of the board and therefore of an increase of the machine speed with consequent greater production from a given machine.

What is claimed is:

1. Wall board comprising a set cementitious core and a paper sheet bonded to one face of the core, said sheet comprising paper of the Fourdrinier type of a pulp composition comprising about 30-50% chip stock and about 50-70% kra t stock by weight and having a weight 01' 35 to 4 pounds per thousand square feet, a crosswis strength of about 28-35 poundsand a densom eter test of in the neighborhood of 20 seconds.

2. Wall board comprising a set cementitious core and a paper sheet bonded to one face of the core, said'sheet comprising paper of the Fourdrinier type and having a weight of 35 to 45 pounds per thousand square feet, a crosswise strength of about 28 to 35 pounds and a composition of mixed kraft and chip stock producing a densometer test of in the neighborhood of 20 seconds.

3. Wall board comprising a set cementitious core and a paper sheet bonded to one face of the core, said sheet comprising paper of the Fourdrinier type of a pulp composition comprising about 30-50% chip stock and about -70% kraft stock by weight and having a crosswise strength of above 28 pounds and a weight of 35 to 45 pounds per thousand square feet.

4. Wall board comprising a set cementitious core ands. paper sheet bonded to one face of the core, said sheet comprising paper of a pulp composition comprising about 3050% chip stock and about 50-70% kraft stock by weight and having a crosswise strength of about 28-35 pounds and a thickness of about 0.015 to 0.016 inch.

5. Wall board comprising a set cementitious core and a paper sheet bonded to one face of the densometer test in the neighborhood of 20 secwith a type of paper which will not separate into Y plies when the board is scored preparatory to breaking as is usual on thejob, one which does not scuif easily and one which ,will not pull away into lamellae upon withdrawal of the cutting knife of the board machine.

onds, said paper sheet having a weight of 35 to 45 pounds per thousand square feet, a crosswise strength of 28-35 pounds and a thickness of about 0.015 to 0.016 inch.

DEAN D. .CRAN'DELL.