US2590013A - Plasterboard - Google Patents

Description

Patented Mar. 18, 1952 'PLASTERBOARD, SCUFF RESISTANT PAPER LINER, AND PROCESS Harry N'. Huntz'icker and John K. Wise, Evanston,

'Ill., assignors to United States Gypsum Com.-

pany, Chicago, 111., a corporation of Illinois No Drawing. Application June 22; 1948, Serial No. 34,555

6 Claims.

This invention relates to scuff resistant paper and a process for producing same and more particularly to a building element, such as gypsum wallboard, having scuff resistant'paper applied to one surface thereof. I

Processes and apparatus for the manufacture of gypsum wallboard including a set-hardened gypsum core between a pair of paper liners are well known inthe art. One such process comprises the steps of covering a high rosin size paper sheet with an aqueous slurry of gypsum to a predetermined depth, applying thereover a second paper sheet, and then permitting the slurry to set. The gypsum may contain a small quantity of starch which assists in the formation and maintenance of a strong bond between the paper sheets and the gypsum core in the final product. After the gypsum has set, the board iscut to size and kiln dried.

Gypsum wallboards prepared as indicated above are standard articles of commerce and are sold in large quantities. These boards are customarily erected bynailing them to conventional wood studs. However, in building construction, the joints between successive boards, that is, the places at which an edge ofone board abuts against a correspondingedge of'anotherboard, have a tendency to be unsightly in the finished wall. Many different methods have been attempted. in aneffort to provide a cheapyfeasible means of rendering the joints invisible in the final wall structure. The most widely used method has been to cover the joint with a filled aqueous adhesive cement, usually of the protein type, and embed therein a paper tape. After the adhesive cementhas dried,.an additional coat of the same or another adhesive is applied to smooth ofi the completed assembly. When this last mentioned adhesive has dried, the cemented area, which usually extends over each board face for. several inches :on either side of the joint, is sanded smooth. The result is a smooth, level, monolithic wall construction which is ready to be decorated.

The above mentioned system of Wall construction has certain disadvantages when employing paper-lined plasterboards that are now available in commerce. When the final coat of the joint cement is sanded, it is; practically impossible for the mechanic to avoid touching and sanding the adjacent paper surfaces ofthe wallboard with the sandpaper. Wherever suchcontact occurs, .the surface of the paper of-the--wallboard is scuffed. This is very undesirable since subsequent painting tends to accentuate rather than to, cover the scuff marks. A further undesirable feature is that the paper surface of the Wallboard exhibits, when painted with oil paints, a marked QThis. also causes an unsightly appearance.

Factory sizing of1finished'plasterboardsz. is impractical because the cost of handling the boards would be prohibitive. Furthermore, plasterboards emerge from the dryingkilns at such a high rate of speed in lineal feet per-minute that equipment necessary to size them at thispoint in the operation would be prohibitive in cost. The obvious expedient of applyingxaconventional size coat to the paper'before the board is'formed has proven to be a practical'impossibility.. This is so since at least a part of the water. present in the initial aqueous plaster slurry mustr be removed from the core during the drying. operation, thus necessitating that the I vapors pass directly through the paper liners For this reason the porosity of the paper must be very closely and carefully controlled prior to and during manufacture of the plasterboard. Experience has shown that application of conventional size coatings to the paper tends to seal-the sheet' and render it less porous. Thus when a gypsum wallboard is made from such a sheet, the water vapor in the core will have a tendency to blow the paper loose from the core during the drying cycle.- in the kilns. v It is, thereforeone object of this invention to provide .an inexpensive, easy to apply. sizing material capable of imparting to gypsum wallboard paper resistance to scuffing and fiber raising without substantially changing the porosityof the sheet.

A further object of this invention is thetprovision of a porous paper sheet having scuff resistant properties which is particularly useful in the manufacture of paper-lined gypsum boards.

A further object of this invention isthe provision. of a process ofpreparing paper having increased scuff. resistance without imparting excessiveembrittlement properties to the. paper.

A still further-object. of this invention is the provision of a paper-lined building element, such as plasterboard, which is. resistant to scuffing when treated with sandpaper and which iscapable of decoration, even on the sanded portions, with oil paints or water-thinned. paints. without bleeding or other adverse effect.

Further andadditional objects. will appearfrom the following description .and .theappended claims.

. In accordance with this invention it has been discovered that scuff resistant properties may be imparted to paper by treating a paper sheet with a product prepared by heating together Water, a polysaccharide from the group consisting of starches and dextrins, an aliphatic aldehyde and a nitrogen compound capable of reacting with the aldehyde to form a resin or the amine-aldehyde type. In accordance. With'one embodiment of this invention, an aqueousdispersion of starch or dextrin is. heated, preferably abovexthesgelat- 3 inization temperature, in the presence of urea and formaldehyde to form a reaction product which is thereafter used to treat a paper sheet, as will be hereinafter more fully described. The nature of the reaction between the starch or dextrin and the urea and formaldehyde is not clearly understood and it is not definitely known whether a well defined chemical reaction product actually forms during this heating treatment. However, it has been discovered that the heat treatment of these substances together in aqueous solution is necessary prior to the time that the solution is applied to the paper whereby to produce a paper having the desired scuff resistant properties and porosity. Simple mixtures of starch or dextrin and a previously formed urea-formaldehyde resin applied to a paper sheet exhibit insufficient penetration into the sheet, excessive embrittlement of the sheet, and markedly reduced porosity. Likewise treatment of a paper sheet with unreacted starch, urea and formaldehyde does not give the desired penetrability or the necessary degree of porosity that are obtained by the process and product disclosed and claimed herein.

In order more fully to explain the invention, reference will be made to the following examples which illustrate several particular embodiments thereof. However, it will be clear to one skilled in the art that this invention is not to be limited by the examples given but only by the scope of the claims appended hereto.

Example 1 The following ingredients in the amounts indicated in parts by weight were thoroughly mixed:

Dextrin 120 Urea 40 Formalin (37%) 216 Water 290 The acidity of the resulting solution was adjusted to pH 5 to 5.5 and the batch was heated to 85? C. and held between 85 and 90 C. for minutes. Thereafter the acidity was adjusted to about pH 7 and the heating continued for an ad ditional 45 minutes. The resulting solution containing the reaction product or condensate of dextrin, urea and formaldehyde was applied in several concentrations (by diluting with water where necessary) to one surface of a chip paper of the type ordinarily employed in making gypsum wallboard. This paper was a highly rosin sized paper. The excess solution was then removed by a doctor blade and the sheet dried. The dried sheet was then baked to cure the condensate contained therein under conditions which simulate the high temperature drying of plasterboard in a commercial manufacturing process, minutes at 250 F. being adequate. The resulting sheet was found to be remarkably resistant to scuffing and fiber raising when sanded with paper or emery cloth. Tests were made on the several papers with the results indicated in the following table:

The porosities reported in this example and in the succeeding examples were determined ac- -cording to the standard Tappi method T-460m-44.

The porosity values refer to the number of sec onds for cc. of air to pass through a porous sheet under standard conditions. Accordingly the lower numbers in the table indicate a higher porosity.

Example 2 The following ingredients in parts by weight were thoroughly mixed:

Oxidized starch 40 Urea 30 Formalin (37%) 162 Water 168 Per cent Per cent Solids in ggg gg' g Condensate treating solution 5 9 re in final t1 eatment treatment sheet 25 s 170 260 Z. 8 185 190 1. 5 160 160 l. 2

Although the porosity of the sheet treated with the 25% solution decreased from 170 to 260, this latter value is still well within the range required for gypsum board paper. The sheets were highly resistant to scuffing and fiber raising.

Example 3 The following ingredients in parts by weight were thoroughly mixed:

Dextrin 90 Urea 5 Formalin (37 27 Water 278 Per cent Per cent Solids in ff g Condensate treating solution S as e ore ee er in final treatment treatment sheet The sheets were found to be resistant to scuiiing and fiber raising.

Example 4 The following ingredients in parts by weight were thoroughly mixed:

Starch (90 fluidity) Urea 40 Formalin (37%) 216 Water 580 The acidity of the mixture was adjusted-to pH 5 to 5.5 and it was heated at 85 to 90 C. for one hour. Thereafter the acidity was adjusted mea ow 25? CI. The solution is stirred. for three minutes andiallowed to stand forf27' minutes, after'whi'ch the. volume of solution which-flows from a standard orifice. in 70 seconds at 25 C. is measured. This volume is regarded as the fluidity of the starch (see Kerr; Chemistry and" Industry of Starch, 1944, at page 95).

Example In this example the following ingredients in parts by weight were employed:

Acid hydrolyzed cornstarch of 90 fluidity; 150

Urea 40 Formalin' (37%) 216 Water Q. 580

Asmooth paste was formed of the starch with some. of the water and. thereafter the remaining ingredients were added thereto in the amounts specified. .The acidity was adjusted to pH 4.9 with dilute aceticacid and the batch washeated with stirring to 85 to. 90 C. and held at that temperature for 60 minutes. Thereafter the acidity .wasadjusted to about pH 6.6 and the'heating was continued for another 60 minutes wherea-fter the batch was allowed to cool. A portion of the resultingcondensate wasapplied to a piece; of

high rosin size'chipboardpaper. 'After removal of the excess of the condensate by a doctor blade and baking, the surface of the sheet was found to be highly resistant to scuifing when rubbed with sandpaper or emery cloth. As a matter of fact, the abrasive actually smoothed rather than roughened the surface. The porosity and flexibility of the sheet were changed only slightly.

Another portion of the condensate formed as above indicated in this example was acidified to pH .4with alum. This acidified solution was appliedto another piece of chipboardpaper. in the manner indicated above with substantially the same results. A film cast from the acidified solution became hard and insoluble in water upon baking.

Example 6 The following ingredients in parts by weight The acidity was adjusted to pH'5.2 with acetic "acid and sodium hydroxide. heated for one hour'at' 85 to 90C. whereafter the acidity'was adjusted to pH 7.44With sodium hydroxideand the heating continued for an addi-- The batch was tional hour." Chipboard paper treated: with the condensate in the manner previously indicated was foundto be highly resistant to scuffing and fiber raising. and the porosity of'the paperx'was substantially unchanged; The condensate inzthis example. penetrated the: paper. a, 1 little .more readily than; the: condensate of. Example 5.

' Example 7 a l-he. following. ingredients in: parts by weight were mixed together:

Oxidized starch. Urea 5 "10 Formalin (37%) "-27 Water 685 The resulting. mixture hadan unadjusted acidity of pI-I 7.8. It was heated for one hour at to C. during which time theacidity drifted to pH 6.74. When. applied to chipboard paper in the manner previously indicated, .this condensate gave excellent sculi resistance with little change in sheet porosity.

Example 8 .The following ingredients in parts by weight were mixed together:

Dextrin 50 Urea 30 Formalin (37 92 Water 400 The mixture was heated for 90 minutes at 85 to. 90 C'., the acidity being about pH 6. The condensate was applied ,to. paper in the manner previously indicatedand when the excess was removed and the sheet baked, it showed excellent scuff resistance and. partioally .no change in porosity.

Example 9 The following ingredients in parts "by weight were mixed together:

Enzyme converted starch Urea '75 .Formalin (37%) 200 Water 700 The acidity of the resulting batch was adjusted to. about. pH 7 and the batch was then heated for two hours at 85 to 90. C. Paper treated with this condensate and baked was resistant to scuffing and substantially unchanged in porosity.

It will be apparent from the foregoing examples. that the amount of condensate applied to the surface of the paper may vary within wide limits. It is preferred, however, that the conditions be controlled so that the final paper sheet product contains between about 0.5 and about 5.0 per cent by weight of condensate, preferably between about 1.0 and.3.0 per cent. It is pre ferred for proper porosity control that the condensate penetrate into the surface of the sheet at least to some extent. Penetration may be expedited by rolling or calendering the sheet. Obviously the bulk of the condensate is close to the surface and in the case of manila papers the manila liner may contain 35 per cent or so of.

sheet onecalendermg. However; it: wi1'l :-be.apparent that the other; methodsiof: application .will occur to those. skilled in the, art.

analogous fashion with aldehydes.

I'he paper that has been treated in the manner indicated in the previous paragraph is ready for application as aliner to ypsum board. This may be effected in any desired manner such as those commonly in practice now in the industry and as indicated in the foregoing. After the paper-lined gypsum sheet has set, the gypsum board is then dried out in suitable kilns maintained at high temperature. The heat treatment in the kilns serves in a measure to bake or cure the condensate directly within the paper sheet, thereby rendering the sheet scuff resistant. This corresponds to the baking step indicated in the previous examples. It is at this point in the manufacture of the gypsum board that it is most desirable for the porosity of the paper sheet to be maintained since in the drying kilns or ovens water vapor must escape through the paper liners. If the liners are insufiiciently porous, then they will have a tendency to be blown loose from the gypsum core during the drying cycle. In the commercial kilns now in use, the air intake temperature may range between 250 and 500 F. and accordingly the paper liners must permit of the ready escape of steam or water vapor therethrough during the drying period.

As previously indicated, it is an important feature of this invention that the polysaccharide (i. e. starch or dextrin) be heat-treated in the presence of water and the urea and formaldehyde prior to application to the paper sheet. In connection with this cooking procedure, there do not appear to be any critical factors other than those which will permit the proper reaction between the several ingredients to take place. As is well known in the resin art, the speed and extent of reaction will depend upon the interrelationship of time, temperature, acidity and concentration factors. However, it is preferred to heat or cook the several ingredients at a temperature which is above the gelatinization temperatures of the starch or dextrin employed. The range of 85 to 90 C., as indicated in' all of the examples, is suitable. As previously indicated, if the several ingredients are not precooked or otherwise prereacted prior to the time that they are applied to the paper, it is substantially impossible to obtain proper penetration. The preheating or prereacting of the several ingredients breaks down the gel characteristics of the starch or dextrin, and a viscous flow is permitted'which'will permit at least a portion of the composition to penetrate into the surface of the paper.

It will be apparent from the foregoing that any type of starch or dextrin may be employed in accordance with this invention. It is preferred to usea converted starch to improve penetration so that the proper amount of condensate will be carried into the sheet. As previously indicated, the amounts of condensate present in v. the final sheet may be as high as 5 per cent of the total weight of the sheet, the preferred range being between about 1 and 3 per cent. It will also be apparent that the urea may be replaced in whole or in part with other nitrogen-containing organic compounds known to react in an Such materials may include thiourea, melamine, dicyan- -diamide, biuret, formamide, acetamide ethanoI- amine, diethylamine, sulfamates and the like. As a matter of fact, while urea is preferred, any amine or amide may be employed which is capable of reacting with an aldehyde to form a resin commonly referred to as one of the amine-alde hyde type. Likewise this invention is not limited to the use of formalin as specified in the foregoing examples. Other sources of formaldehyde, such as paraformaldehyde, trioxymethylene, hexamethylenetetramine, etc. may be employed. Also other aldehydes which may react with the amine and/or amide, such as acetaldehyde, butyraldehyde, glyoxal, furfural, etc. may be employed as complete or partial replacements for formaldehyde.

As will be apparent from the foregoing examples, the treated paper may be prebaked' to set the resin and thereafter the paper may be applied to a gypsum board as a top cover sheet.

While several particular embodiments of this invention are shownabove, it will be understood, of course, that the invention is not to be limited thereto, since many modifications may be made, and it is contemplated, therefore, by the appended claims, to cover any such modifications as fall within the true spirit and scope of this invention.

We claim:

1. A decoratable plasterboard having secured to at least one surface thereof a porous, highly sized calendered paper sheet having scuff-resistant properties, said sheet containing in gradually diminishing quantities from the exposed surface thereof in an amount between about 0.5

and about 5 per cent by weight of the sheet, a heat-cured pre-formed heat reaction product of water, a polysaccharide selected from the group consisting of starches and dextrins, a compound selected from the group consisting of aliphatic amines and amides, and an aldehyde, the molar ratio of said aldehyde to said compound being within the range of about two to one and about four to one. 7

2. The plasterboard recited in claim 1 wherein said compound is urea and wherein said aldehyde is formaldehyde.

3. A porous, highly sized calendered paper sheet suitable for use as a gypsum wallboard paper liner and having scuff-resistant properties which contains in gradually diminishing quantities from one surface thereof in an amount between about 0.5 and about 5 per cent by weight of the sheet, a, heat-cured pre-formed heat reaction product of water, a polysaccharide selected from the group consisting of starches and dextrins, a compound selected from the group consisting of aliphatic amines and amides, and an aldehyde, the molar ratio of said aldehyde to said compound being within the range of about two to one and about four to one.

4. The porous paper sheet recited in claim 3 wherein said compound is urea and wherein said aldehyde is formaldehyde. Y

5. A process of treating a highly sized porous paper suitable for use in the manufacture of paper-lined gypsum wallboard to impart scuffresistant properties to said paper without essentially changing the porosity thereof which comprises applying to one surface of said sized paper an aqueous solution of a heat reaction product of water, a polysaccharide selected from the group consisting of starches and dextrins, a compound selected from the group consisting of aliphatic amines and amides, and an aldehyde, the molar ratio of said aldehyde to said compound being within the range of about two to one and about four to one, the amount of said solutionapplied to said paper being sufficient to deposit on said surface solid'reaction product 9 in an amount equal to between about 0.5 and about 5 per cent by weight of said paper, and thereafter calendaring said paper whereby said reaction product is distributed in the paper in a gradually decreasing concentration from the surface thereof.

6. The process recited in claim 5 wherein said compound is urea and wherein said aldehyde is formaldehyde.

HARRY N. HUNTZICKER. JOHN K. WISE.

REFERENCES CITED UNITED STATES PATENTS Name Date Bauer et a1 Aug. 20, 1940 Number 10 Number Name Date 2,246,635 Moller June 24, 1941 2,338,602 Schur Jan. 4, 1944 2,352,553 Lefebure June 27, 1944 2,452,054 Jones Oct. 26, 1948 2,496,440 Caesar et a] Feb. 7, 1950 FOREIGN PATENTS Number Country Date 539,331 Great Britain Sept. 5, 1941 57,967 Netherlands Aug. 15, 1946 OTHER REFERENCES The Use of Urea-Formaldehyde Resin for Waterproofing Starch Used in Corrugated and Solid Fiberboard Production, by Philip B. Taft, published in the Paper Trade Journal, Oct. 15, 1942, pages 30-32 or Tappi Sections 206-208.