# US 7,608,347 B2 · Modifiers for gypsum slurries and method of using them

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- Number: US 7,608,347 B2
- Document ID: US7608347B2
- Status: Granted
- Kind: B2
- Application number: 11/450,068
- Filed: 2006-06-09
- Published: 2006-12-14
- Granted: 2009-10-27
- Earliest claimed: 2005-06-14
- Assignees: United States Gypsum Company
- Inventors: Dennis M. Lettkeman; Michael P. Shake; Qingxia Liu; John W. Wilson; Brian Randall; David R. Blackburn
- Web page: https://patentgrep.com/patent/US7608347B2

## CPC

- C04B 28/14: containing calcium sulfate cements {(gypsum-paper plates E04C)}
- Y10T 428/232: Encased layer derived from inorganic settable ingredient
- C04B: LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE {(roofing granules E04D7/005)}; CERAMICS (devitrified glass-ceramics C03C10/00); REFRACTORIES; TREATMENT OF NATURAL STONE
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

An improved gypsum slurry that includes water, calcium sulfate hemihydrate, a polycarboxylate dispersant and a modifier. The modifier is chemically configured to improve the efficacy of the polycarboxylate dispersant. Preferred modifiers include cement, lime, slaked lime, soda ash, carbonates, silicates and phosphates.

## Claims

### Claim 1

A gypsum panel comprising
at least one facing material; and
a gypsum core comprising a hydrated gypsum slurry, said slurry comprising:
water;
calcined gypsum;
a polycarboxylate dispersant; and
at least one modifier chemically configured to increase the efficacy of said polycarboxylate dispersant.

### Claim 2 (depends on 1)

The gypsum panel of claim 1 wherein said modifier is selected from the group consisting of lime, soda ash, carbonates, silicates, phosphates, cement and combinations thereof.

### Claim 3 (depends on 1)

The gypsum panel of claim 1 wherein said modifier is soda ash.

### Claim 4 (depends on 1)

The gypsum panel of claim 1 wherein said modifier is present in concentrations of about 0.05% to about 0.25% by weight based on the dry weight of said calcined gypsum.

### Claim 5 (depends on 1)

The gypsum panel of claim 1 wherein said polycarboxylate dispersant comprises a polyether repeating unit and at least one of acrylic acid, methacrylic acid and maleic acid repeating units.

### Claim 6 (depends on 1)

The gypsum panel of claim 1 wherein said polycarboxylate dispersant has a charge density ratio of about 5 to about 8.

### Claim 7 (depends on 1)

The gypsum panel of claim 1 wherein said polycarboxylate dispersant is present in amounts of about 0.05% to about 0.5% based on the dry weight of said calcined gypsum.

### Claim 8 (depends on 1)

The gypsum panel of claim 1 wherein said water is present in amounts of about 0.5 to about 0.6 based on the dry weight of said calcined gypsum.