Paper having calcium sulfate mineral filler for use in the production of gypsum wallboard
First Claim
1. Gypsum wallboard comprising a core of set calcium sulfate dihydrate and a paper cover sheet bonded to each surface thereof, each of said paper cover sheets comprising:
- (A) a major proportion of cellulose fibers,(B) calcium sulfate as a filler in an amount of from about 10% to about 35% in dry weight,(C) a binder in an amount from about 1% to about 31/2%,(D) a neutral sizing agent in an effective amount to prevent water penetration,(E) a buffering agent comprising a salt of a cation of a strong base and an anion of a weak acid in an amount from about 0.25% to about 10%, and(F) an anionic retention aid in an amount suitable for retaining said filler in said paper.
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Accused Products
Abstract
A composite paper particularly adapted for use as cover sheets in the production of gypsum wallboard, the paper being sufficiently porous to permit better drainage and more rapid drying in the production of the paper, and when applied to the surfaces of a gypsum slurry for forming wallboard, permits less heat to be utilized in the wallboard conversion, thereby saving energy in the board production required for drying the board. The paper comprises in weight percent:
(A) cellulosic fibers in an amount of from about 65% to about 90% and preferably having a fiber freeness of from about 300 ml to about 550 ml Canadian Standard Freeness,
(B) calcium sulfate as a filler in an amount of from about 10% to about 35%,
(C) a binder in an amount from about 1% to about 31/2%,
(D) a flocculant in an amount of from about 0.1% to about 0.2%,
(E) a buffering agent in an amount from about 0.25% to about 10%,
(F) a neutral sizing agent in an effective amount to prevent water penetration,
(G) an anionic polymer in an amount suitable for retaining said filler in said paper, and
(H) a cationic starch when a succinic anhydride is used as the neutral sizing agent.
In a preferred embodiment, after the paper is treated with a neutral internal sizing agent during its formation, it is subsequently treated with a surface sizing agent after formation of the paper, in order to provide certain properties including better adhesion to the gypsum core when used to make gypsum wallboard.
61 Citations
28 Claims
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1. Gypsum wallboard comprising a core of set calcium sulfate dihydrate and a paper cover sheet bonded to each surface thereof, each of said paper cover sheets comprising:
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(A) a major proportion of cellulose fibers, (B) calcium sulfate as a filler in an amount of from about 10% to about 35% in dry weight, (C) a binder in an amount from about 1% to about 31/2%, (D) a neutral sizing agent in an effective amount to prevent water penetration, (E) a buffering agent comprising a salt of a cation of a strong base and an anion of a weak acid in an amount from about 0.25% to about 10%, and (F) an anionic retention aid in an amount suitable for retaining said filler in said paper. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 26)
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18. Gypsum wallboard comprising a core of set calcium sulfate dihydrate and a paper cover sheet bonded to each surface thereof, each of said paper cover sheets comprising a composite paper which comprises in dry weight percent:
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(A) cellulosic fibers in an amount of from about 65% to about 90% and having a fiber freeness of from about 300 ml to 550 ml Canadian Standard Freeness, (B) a particulate mineral filler in an amount of from about 10% to about 35%, (C) a binder in an effective amount to retain said mineral filler, (D) a neutral sizing agent in an effective amount to prevent water penetration, and (E) an anionic polymer as a retention aid for said mineral filler, said paper being sufficiently porous to permit good drainage and rapid drying during its production, and when applied to the surfaces of a gypsum slurry for forming wallboard, permits less heat to be utilized in the wallboard conversion, the use of said paper thereby conserving energy both in paper production and in the board production. - View Dependent Claims (19, 20, 21, 22, 27)
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23. Gypsum wallboard comprising a core of set calcium sulfate dihydrate and a paper cover sheet bonded to each surface thereof, each of said paper cover sheets comprising a composite paper which comprises in dry weight percent:
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(A) fibers in an amount of from about 65% to about 90% and having a fiber freeness of from about 300 ml to 550 ml Canadian Standard Freeness, (B) a particulate mineral filler in an amount of from about 10% to about 35%, (C) a binder in an effective amount to retain said mineral filler, (D) a cationic flocculant in an amount of from about 0.1% to about 0.2%, and (E) a neutral sizing agent in an effective amount to prevent water penetration, and having the following structural formula;
##STR5## wherein each radical R has from 8 to 18 carbon atoms. - View Dependent Claims (24, 25, 28)
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Specification