CA1116066A - Gypsum board manufacture - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A paper covered gypsum board a method of manu-facture is disclosed. A water-soluble Werner type chromium complex of a fatty acid having 14 to 18 carbon atoms is placed between the gypsum core and the paper liner, in an amount between 0.035 and 0.15 lb. of the complex per 1000 ft2 of paper liner.

Description

BACKGROUND OF THE INVENTION
Gypsum board is a sandwich o a gypsum core (hydrated calcium sulfate) between two papér liners.
Gypsum board is usually made by spreading an aqueous slurry of calcined gypsum on a paper web and then applying another paper web over the slurry. The sandwich is then formed into a continuous flat sheet, allowed to set, cut into board lengths, and dried in high temperature drying kilns. Often during manufacture starch is added to the gypsum slurry to retard the loss of water into the paper liner during cr~vstallization and process drying. The loss of this water into the liner can cause recalcining of the gypsum during drying. This in turn results in the failure of the bond between the gypsum and the liner.
The gypsum board industry has ~ound that the application of a low level of silicone resin to the paper liner/gypsum core interface prevents the migration of starch into the paper allowing a reduction in starch requirement.
The silicone is usually applied to the paper and cured and thereafter the paper is used to make gypsum board. Dis- -closures on this process and the useful silicones can be ~ -found in U.S. Patents 3,389,042 and 31481,829. Furthermore, other sizing agents have been so employed, e.g., see U.S.
Patent 3,307,987, where wax, acrylonitrile, ammonium oleate and ammonium stearate were used for this purpose.
SUMMARY OF THE INVENTION
The prior art processes for making gypsum board can be improved if water-soluble, Werner type chromium complexes of carboxylic acids are employed as the sizing agent between ~he paper liners and the gypsum core. Such complexes have - ~,,

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been previously used in gypsum board manufacture as a water-repellent coating on the outer surface of the paper liner, see U.S. Patent 2,776,234. They have also been used to im-part water resistance to starch, see U.S. Patent 2,359,858.
When used as the sizing agent between paper liners and the gypsum core, the Werner type chromium complexes provide improved results in that they prevent migration of the starch in the gypsum core into the paper liner. They also provide improved water resistance, thus reducing the wicking o~ the gypsum into the paper while at the same time permitting water vapor to escape from the gypsum core during drying. Further, when the complexes are used in the appro-priate amounts, there is no interference with the bonding of the paper liner to the gypsum core.
The proc~ss of the invention also requires less critical process control than the art processes as no curing step is involved and the composition of the paper liner does not have to be carefully controlled. The process also reduces manufacturing costs as less sizing agent and starch is required and lighter weight paper liners can be used.
DES~RIPTION OF THE INVENTION

. _ The gypsum core can be made from any conventional gypsum slurry. Such slurries typically contain about 75 parts ~ater per 100 parts of calcined gypsum and often con- -tain a water-retention agent such as starch. In the process of the invention the amount of starch added to the core can range from .4~ to .8%. It is one of the advantages of the invention that less starch can be employed than in many art processes.

3~ The paper liners or chipboard paper employed are ; ~ ~ , ;

also not critical, and those conventionally used in the industry can be employed. Thus, they can be made from groundwood and sulite pulps or from waste paper pulps, e.g., greyback papers. The paper liners generally range in thick-ness from 0.010 to 0.030 inch, and they often are made up of several plies.
The si~ing a~ents useful in the process oE the invention are water-soluble, Werner type chromium complexes of fatty acids having 14 to 18 carbon atoms~ r~hese com-plexes are known to be water repellents and release agentsand are described in detail in U.S. Patent 2,273,040. The complexes are usually supplied as a solution in water, an alcohol, usually 2-propanol, and acetone. A typical solu-tion will contain 26-43% (wt) complex, 4-5% (wt) water, 10-16% (wt) acetone and the remainder 2-propanol.
When in solution the complexes have the following structure:
R
~C
~
Cl \ ¦ R,O ` J Cl ~

2 1 \ " ¦ ~H2O
Cl O' Cl :; .
where R is a fatty acid radical of C13 to C17, preferably the radical from stearic or myristic acid, and R' is the alkyl group of the alcohol, preferably 2-propanol.
When the complex is urther diluted with water, ..
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water will replace the coordinated alcohol groups and some of the chlorine atoms.
A preferred complex for use in the process of the invention is the one made by reacting basic chromic chloride with myristic acid in alcohol while first excluding more than 6% (wt) water, and then adding water to 8-50% (wt) and heating to 35~70C for 20 to 75 minutes. This results in a complex having a ratio of coordinated water to chromium atoms in the range of 2:1 to 4:1. Such complexes and their methods of preparation are described in U.S. Patent 3,284,215.
The amount of complex applied is critical. This amount must provide the desired water repellency properties without creating any problem due to the release character-istics of the complex. The amount to be added will be about 0.035 lb to about 0.15 lb complex per 1000 ft2 of paper.
Lower amounts usually do not provide the desired water repellency; and higher amounts do not improve water repel~
lency and can create release problems. It should be under-stood that variations in the absorbency of the paper liner ;~
have an effect on the amount of complex to be applied.Further, the amount of complex to be applied is related to Cobb value and experience has shown that Cobb values of 0.3 to 1.0, preferably 0.3 to 0.7, give good performance. The desired loading can be obtained by dilution with water to a concentration between 0.3 and 5% and adjusting the applica-tion procedure to obtain the desired pickup.
The Werner type complexes normally have a pH in water in the range of 2 to 3. Before being used in the process of the invention the pH is adjusted to 3 to 5 with a weak base. This adjustment promotes hydrolysis and ~ _ 5 _ 69;)~

polymerization o~ the complex by hydroxyl bridges between adjacent chromium atoms. The pH will drift lower as the neutralized solution ages. Suitable bases are dilute ammonia solutlon, morpholine, hexamethylenetetramine, piperidine, melamine, urea and salts of weak acids, e.g., sodium formate, sodium carbonate or sodium silicate. The nitrogen bases are preferred ancl hexamethylenetekramine is the most preferred.
The complex is appliecl to the gypsum contacting surface of the paper liner in any conventional manner, such as spraying, brushiny, txansfer rolls or immersion. The complex can be applied during the paper-making process or as one of the first steps in the gypsum board manufacturing process. Thus, it can be applied at the size press or calender stack of the paper machine.
After the complex solution is applied, the paper liner is dried and then brought into contact with the gypsum core. The drying may take place at 80-120C for a few seconds or in the paper roll using the residual heat of the paper leaving the paper machine. Drying at the elevated ~ ~
temperature is preferred. The sandwich of paper liner/gypsum ~, core is then treated in the conventional manner.
The following Examples are offered to illustrate the process of the invention.

In the following tests a Werner type chromium complex of myristic acid in 2-propanol is employed. This complex has an average analysis of:
chromium as CR 5.7-5.8% (wt) chloride as Cl 7.9-8.0% (wt) , .

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myristic acid 11.5-15% (wt) density (20C) 0.969 g/cc color blue-green This complex is commercially avai,lable rom E. I. du Pont de Nemours and Company as "Quilon"*C chrome complex, and its manner of prepaxation is described in U.S.
Patent,3,284,215. The other comp:Lexes within the scope of the invention can be use~ in the same manner.
, The chromium complex in 2-propanol is first diluted to a 1% solution in water and neutralized with 2.5 grams of hexamethylenetetramine per 100 grams of complex.
The complex is then applied to the paper liner using a laboratory applicator to simulate a surface treat-ment. The applicator consisted of lightweight cotton cloth wound around a wooden rod. The covered rod was dipped into a pan of the solution and rolled on the side of the pan to remove excess solution. The wet applica-tor was then wiped across the surface o the paperboard, lightly wetting the surface. The paperboard was carefully weighed before and after treatment to give a wet pickup. The loading could be controlled over a fairly narrow range by the wetness of the cloth and the pressure and speed of application. The treat~d samples were dried on a drum drier with an internal temperature of 120C and a surface temperature of 105-107C.
The following table lists the results for various loadings of chromium complex. A control sample is also made using the silicone resin and application procedure of U.S. ~ , Patent 3,389,042.
*d~no~es ~rade Ina~
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TABLE
Ch~omium Complex Loading, Cobb Value, Sample lb/1000 ft2 ~m/100 cm2 ~ 0.035 ~.56 2 0.051 0.30 3 0.060 0.34

4 0.065 0.27 0.070 0.28 6 0u102 0.33 7 0.1~0 0.29 Silicone treated 0.34 (control) The loadings were calculated from weight of solu-tion pickup, except for Sample 4 which was determined by chromium analysis. The calculated loading for Sample 4 was 0.052 lb/1000 square feet, lower than the actual analysis. ;~
This difference is due in part to some drying during treat-ment and weighing. ~n this respect the other calculated ;~
loading may be low; i.e., as much as 25% low.
~he treated samples were conditioned at 71F and 50% R.~l. and tested for Cobb size using TAPPI test T441, modified to use 150 ml of 120F water for 3 minutes. The -procedure was as follows:
1. Determine the "dry weight" of the paper by weigh-:: :
ing, to the nearest 0.01 gm, a 125 mm X 125 mm . .
sample of the paper.
2~ Clamp the sample in a standard 100 sq cm Cobb ring having an area of 100 square centimeters wlth the paper surface to be tested exposed. The Cobb ring ~ -is preheated to 100~120F prior to conducting the test in order to prevent rapid cooling of the test water.

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6i 3. Pour 150 ml oE clean tap water at 120F into the Cobb ring. Start a timer as soon as the water is poured into the ring.
4. After the water has been in contact with the paper for exactly 3 minutes, pour out the water.

5. As rapidly as possible remove the sample from the ring and blot it "dry" of surface water with a blotter or paper towel.

6. Fold the sample into quarters to reduce we~ght loss from evaporation and reweigh the sample to the nearest 0.01 gm. This is the "wet weight."
(Steps 5 and 6 should not exceed 15-30 seconds.)

7. Determine the Cobb value by subtracting the dry weight from the wet weight.
At chromium complex loadings between 0.05 and 0.14 lbs per 1000 square feet, essentially equivalent Cobb size values were obtained. These values indicate sufficient water repellency càn be obtained at the lower value and extra chromium complex does not improve the water repellency.
A higher Cobb size value was obtained at 0.035 lbs of complex per 1000 square feet, indicating the lower limit of adequate coverage.
The paper liners of Samples 1-7 can be employed to make gypsum board using conventional techniques. Optimum bonding will be achieved in the 0.05 to 0.10 lb/100 ft range.

The complex of Example 1 can be used in a commer- '!
cial application at the calender stack o a paper machine.
The solution is prepared by diluting 25 lbs of the chromium complex solution in 200 gallons o water and adding 0.25 lb . ~ . : . . .

6~j of hexamethylenediamine. The solution is then applied to one side o the cylinder board made from waste paper from a water box on the calender stack at the end of the paper machine. The chromium complex loading is 0.042 lb/1000 ft2 of paper. The treated paper can then be rolled and dried from the residual heat in the paper.
Similar applications using 21 lbs of the chromium complex solution in 200 gallons of water, neutralized with 0.25 lb of hexamethylenetetramine gives a chromium complex loading of 0.035 lb/]000 ft2 of paper.
The treated paper liners can be used to make gypsum board using conventional techni~ues. The bond be-tween the gypsum core and the liners will be good and uniform throughout the roll. Untreated paper liners will give delamination between the core and the liner.

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Claims (7)

CLAIMS:

1. In the method of making gypsum board by form ing into board form a core of gypsum slurry and laminating said core between two paper liners and drying, the improve-ment consisting essentially of, prior to the lamination, applying to the surface of the paper liner which contacts the gypsum core with 0.035 to 0.15 lb/1000 ft2 of paper liner with an aqueous solution of a water-soluble t Werner type chromium complex of a fatty acid having 14 to 18 carbon atoms in an alcohol.

2. The process of Claim 1 wherein the core of gypsum also contains starch.

3. The process of Claim 1 wherein the fatty acid is myristic and the alcohol is 2-propanol.

4. The process of Claim 1 wherein the complex is neutralized to pH 3-5 prior to application.

5. The process of Claim 4 wherein hexamethylene-tetramine is used to neutralize the complex.

6. In a paper-covered gypsum board having a gypsum core and paper liners covering both sides of said core the improvement consisting essentially of having on the surface of the paper liners which contact the gypsum core 0.035 to 0.15 lb/1000 ft2 of paper liner of a water-soluble, Werner type chromium complex of a fatty acid having 14 to 18 carbon atoms.

7. The gypsum board of Claim 6 wherein the fatty acid is myristic.