US2806811A - Paper-covered gypsum board - Google Patents

Description

P 1957 R. s. VON HAZMBURG 2,806,811

PAPER-COVERED GYPSUM BOARD Filed Dec. 31, 1954 INVENTOR.

United States atent Dfihce PAPER-COVERED GYPSUM Basal).

Romulus S. von Hamburg, Wilmette, 111., assignor to United States Gypsum Company, Glncago, 1b., a corporation of Illinois Application December 31 1954, Serial No. 479,190.

7 Claims. (Gl. 154-86)- The present invention relates to an improved form of gypsum-core plaster board, in which the paper cover sheets are of such a nature that they will not split longitudinally of the board.

As is well known inthis art, paper covered gypsum boards are made by enclosing a mass of plastic watergauged gypsum composition between paper sheets and allowing the resulting product to set up; whereafter itis dried and cut up into sheets of the. desired size. One of theessential features of such a board-is a firm adherence of the central gypsum core to the cover sheets, so that the board will not delaminate at the interfacebetween the core and the cover sheets.

This has been quite satisfactorily accomplished in the past by the additionof'farinaceous materials'tothe core. These farinaceous materials contain a certain percentage of a water-soluble starch which, during the drying of the gypsum board, will migrate to the interface between the core and the cover sheets, and will hence be closely associated with the gypsum crystals which interlock with the fibers of the cover sheets, thereby preventing their release. Thepresence of the starchy or farinaceousmaterial also serves to protect the fine gypsum crystals, from becoming calcined during the drying of the board, forv if they did so, they would lose their strength, with resulting destruction ofthebond between the, core and the cover sheets. When such loosening of thebond occurs, the resulting boards are known as peelersfi The gypsum core is thusexposed, and the board, at least to the de. gree that the peeling extends into the board, isrendered useless, and must be trimmed down to obtain pieces of board of'a useful size.

It has now been discovered that another type of defect can make its appearance, and lead to defective boards of the general nature of. peelers, except that in the present case the delamination occurs not at the interface between the core and the cover sheets, but is the result of the delamination of the cover sheets themselves, which split either between the plies of the paper, or, in some cases, involve actual internal splitting of the plies themselves.

The cover sheets usually employed in the production of gypsum core boards consists, in the case of wallboard which is intended to form the internal walls of rooms, of two types. The outer cover sheet is in the form of a paper built up of: a plurality of plies, the two outer plies being usually of a somewhat better grade of paper, such as manila paper, the furnish for which is made of a mix ture of ground-wood and sulfite pulps. The inner plies, including the one which will be in contact with the gypsum core of the'board, is usually made of repulped newsprint, either used papers or over-issue newspapers. The paper used to line the rear side of the board is usually made of a plurality of plies of such repulped newsprint. In any event, the papers are made on what is known as a cylinder machine, the pulp being picked up on rotating screens, so that a plurality of layers or plies will be ob tained, which, by being superimposed upon each other 21 immediately after their formation will bond to eachother and produce a. substantially uniform piece of paper. Under certain circumstances, such paper is subject to separation of the plies from each other, i. e. it may delaminate.

When gypsumboard covered with such a laminated or multiple-ply paper is. dried, there appears to be set up in the paper. rather severe strains, which arebelieved to be the cause of the delamination or, in severe cases, even the longitudinal actual-splitting of the ply which is near.- est. to the core. This. may occur on either the front or the back of, thegypsum board, and is probably attributable to the development of undue strain in the plies. of the paper during the drying of the board.

It is therefore one of the objects. of the presentinvention to.provide a suitable paper cover sheet for gypsum covered wallboards which is of such a nature that; it will neither. delaminate between the plies nor permit splitting off the plydirectly adjacent the core.

This object is attained by the incorporation with the furnish. from which at least the innermost ply of the paper ismade of certain strength-imparting resinous additions, which. give them. such plies, and to some extent impartto the next adjacent plies a greater degree of wet strength, so that the plies adjacent the core will neither delaminate norsplit, whereby all difiicultiesfrom peelers of, this specific type are avoided.

To provide a more clear explanation. of. the application of these concepts to the preferred embodiment of thepresent invention, an illustration hasbeenannexed to formapart of this disclosure.

Inthedrawings:

Fig. 1 is a partial expanded view of an end of a gypsum board,while .Fig. 2. is, anenlarged diagrammatic view on a somewhat larger scale, showing a split ply which will illustrate the type of commonly occurring difficulty inthe manufacture of-gypsum board.

As indicated hereinabove, a gypsumboard comprises a core 10 encased in a fibrous envelope consisting of a manila sheet 12 and a newsprint sheet 20. Normally, and depending on the characteristics desired in the finished, board, the sheets will consist of a plurality of plies or layers which are formed on a conventional multicylinder, paper-making machine. Themanila sheet-may haye, for. instance, two plies 13 and 14. made from a furnish containing ground wood and. sulfite or any other type of suitable pulp, while plies 15, 16, 17, 18 and 19 known also as filler plies, contain a mixture of waste paper pulps. The furnish for each of theseplies is properly sized with conventional resin and alum, placed-into the vat, formed into a ply and then assembled into a laminated sheet. by means of the multi-cylinder paper forming machine. The assembled sheet is passed through one or more calender stacks, dried and compressed into the sheet to be used as a component of gypsum wallboard.

Theother side of the core 10 is also covered with a fibrous sheet. 20, of a somewhat different composition of furnish, since it is not necessary that the appearance of the; back side of the wallboard need-be asrpleasing as the face side thereof. The back sheet 20 is generally known. as a newsliner or back liner and it likewise is made of arnumber of plies. Plies or fillers 21, 22, 23, 24,, 25-.and. 26 generally consist of a furnish containing a mixture, of waste papers. Ply 27 normally is made from, a, furnish containing percent over-issue newsprint. All furnishes prior to f rmation in paperare sized with. the proper amounts of rosin and alum to attain the, desired degree of waterproofness in the;product.

The cover sheets 12 and 20 are used to enclose-acore 10 containing a cementitious slurry of calcium sulfate hemi-hydrate, water, starch, foam, set-accelerating reagents, fibers, etc. The process of making gypsum wall- 'melamine-aldehyde product.

board has been the subject matter of many patents and is not claimed herein except as related to the application of the fundamental principles of this invention.

The formed board .is produced in one continuous stream; After the cementitious core reaches a satisfactory degree of hardness the stream is cut into desired lengths, which are then passed through a drying kiln to remove the excess of Water, which was needed to render the mass plastic and fiowable before its encasement. The wet board in the course of its drying passes through a high temperature zone of about 500 F., then through an intermediate zone of about 275 F. and finally through dry end zone of about l50-200 F. Normally under conditions enumerated above, a gypsum board inch thick will take about forty-five minutes to pass through the drying kiln zones and emerge as a dry sheet ready for packaging and storage.

.In order to render. the paper sheets, of the type described above used as cover sheets in the making of gypsum board, capable of withstanding delaminating .or splitting within the plies, the teachings of the present invention is brought into play.

For thispurpose it has been found, quite unexpectedly, that the addition of small quantities of resinous materials to the paper will prevent the delamination and splitting of the plies and that paper cover sheets containing such materials can be successfully used in the production of a vastly improved gypsum board without sacrifice of production ,efiiciency and loss of desirable characteristics, as well as physical properties, of the gypsum board;

"More surprising however was the fact that such resins need only be added to the plies at the interface with the core to eliminate entirely the splitting at the ends of the boards as heretofore frequently encountered. Obviously all of the plies could very well contain such resins and still be within the spirit and scope of this invention as claimed.

It has been found that the addition of such resins, in quantities as little as one-half percent, by weight of the paper involved in the particular ply, is all that is needed to obtain the desired results and that resin can be added to the fiber slurry at any stage prior to ply formation with beneficial results, provided however that there is sufiicient time for its substantial and uniform dispersion among the fibers. The resin is preferably added in an emulsion form, or as a solution, either directly to the head box supplying the furnish to the individual cylinder vat, or at some place before the Jordan as the pulp is processed through the paper making plant. Obviously it can be added at any stage, but in case of certain plastics which react within certain time limits, it is advisable to have the reaction take place as close as possible to the vat or sheet forming machine.

A delamination-prevention material which has been found particularly effective is a melamine-aldehyde con densation supplied in dry form and sold under a tradename of Parez-607. As mentioned previously, onehalf percent of such a resin based on the dry Weight of the fiber can be used, though it is preferred as a factor of safety to employ three-fourths percent. Quantities up to 3 percent may be used if necessary to obtain the desired elfect. I In adidtion to employing the melamine-aldehyde condensation products, it has been found that urea-aldehyde resins, such as Uforrnite 700, may be used with sub-. stantially equally effective results, though for ease of application and quality control, it is preferred to use the If emulsions are used it is advisable to add suflicient alum to break the emulsion and precipitate the material onto the fibers just as in case of sizing.

There are now available cationically active water-soluble or dispersible aminoplastic resins which, by being substantive to cellulose, quickly and completely become deposited upon the fibers of a pulp furnish.

In practice, the delamination-prevention agent is added to the furnish of the ply involved in the splitting. Figure 2, which is a greatly enlarged fragment of a board core and contacting fibrous cover sheet, shows layers or plies contained in a manila cover sheet, though any other type of cover sheet will serve for illustrative purposes. In Figure 2, ply 19 is shown as having split apart or delaminated, as defined hereinabove, into a two section layer 19a and 1%. By adding the melamine-aldehyde resin to the furnish entering into the vat forming ply 19 in suitable quantities, this ply 19 does not split or delaminate and thus gypsum wallboard can be produced without any rejects from this cause.

Though it is obvious that the delarnination-prevention materials may be varied somewhat in quantities and in action, nevertheless the important factor is that the delamination tendencies are entirely removed by adding to at least the ply adjacent the core, a resinous material having the property of increasing the wet-strength oi the paper of that ply. It may, with advantageous results, also be added to the other plies, but it appears that if it is present in the ply closest to the core, the desired eifect is attained. It is therefore not intended to be limited to the particular illustrated preferred embodiment, but only by the appended claims which define the fundamental concepts underlying this invention.

I claim:

1. Plaster board having paper cover sheets of a multiple ply nature in which the ply directly adjacent the set plaster core of such board contains about one-half to 3% by weight, of a wet-strength imparting aminoplastic resin substantially uniformly distributed throughout said ply.

2. The plaster board of claim 1 in which the wetstrength imparting resin is melamine-formaldehyde.

3. The plaster board of claim 1 in which the wetstrength imparting resin is urea-formaldehyde.

4. Plaster board having paper cover sheets of a multiple ply nature, only the ply directly adjacent the set plaster core of such board containing about /2% to 3% by weight, of a wet-strength imparting aminoplastic resin substantially uniformly distributed throughout said ply.

5. Process of making a paper-covered plaster board which isresistant to intra-ply splitting which comprises forming a multi-ply paper-cover sheet therefor by the steps of incorporating with the'fibers of the pulp forming the lowermost ply of said sheet prior to the formation of said ply from about one-half to three percent by Weight of a wet-strenght-imparting aminoplastic resin, then imposing the other plies thereto to form said sheet,

and using said sheet with said resin-containing layer in contact with the plaster core of said board to form said board.

6. The process as claimed in claim 5, in which the resin is a melamine-formaldehyde resin.

. 7. The process as claimed in claim 5, in which the resin is a urea-formaldehyde resin.

References Cited in the file of this patent UNITED STATES PATENTS Huntzicker et al Mar. 18, 1952

Claims (1)

1. 5. PROCESS OF MAKING A PAPER-COVERED PLASTER BOARD WHICH IS RESISTANT TO INTRA-PLY SPLITTING WHICH COMPRISES FORMING A MULTI-PLY PAPER-COVER SHEET THEREFOR BY THE STEPS OF INCORPORATING WITH THE FIBERS OF THE PLUP FORMING THE LOWERMOST PLY OF SAID SHEET PRIOR TO THE FORMATION OF SAID PLY FROM ABOUT ONE-HALF TO THREE PERCENT BY WEIGHT OF A WET-STTRENGHT -IMPARTING AMINOPLASTIC RESIN, THEN IMPOSING THE OTHER PLIES THERETO TO FORM SAID SHEET, AND USING SAID SHEET WITH SAID RESIN-CONTAINING LAYER IN CONTACT WITH THE PLASTER CORE OF SAID BOARD TO FORM SAID BOARD.

Images