Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-02-17
2002-12-10
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
active
06492450
ABSTRACT:
This invention relates to the use of polymers in gypsum wallboard. The polymers contain hydrophobically modified monomers as polymerized units and are prepared by emulsion polymerization.
Gypsum wallboard is a material which is commonly used in buildings for walls and ceilings. It is usually a flat board of gypsum material which is lined on both external surfaces with paper.
Gypsum wallboard typically contains calcium sulfate hemihydrate as a major ingredient, and so is very hydrophilic. When placed on gypsum, a drop of water will be absorbed almost immediately. This may lead to problems in that the gypsum may become weakened or the water may cause stains in the walls or ceilings.
Gypsum wallboard may be utilized in places where it is exposed to high moisture levels, such as areas with humid climates. Exposure to water is common in rooms such as bathrooms or kitchens, where steam from showers may build up in the room or water from the sink may splash onto the wall. Alternatively, gypsum wallboard may be exposed to water through leaks in roofs or pipes. Due to the problems associated with water, there is a need for a water resistant gypsum wallboard.
One approach to solving this problem has been to treat the paper liner with a latex of resin solids mixed with water. This approach has been demonstrated in U.S. Pat. No. 5,397,631. Gypsum wallboard which has paper liner treated in this manner can usually be easily identified, as the paper liners tend to be blue or green to indicate that they have been treated. Even though this approach provides some protection against water, water is able to slowly penetrate the treated paper liner and get into the gypsum. Waxes have been used to provide some water resistance to gypsum by admixing the wax with the gypsum, but polymers have not been taught to be useful in this manner.
When polymers have been admixed with gypsum, the purpose has been to increase the strength of the gypsum. WO 98/30515 discloses the use of polymers of lower alkyl acrylate esters, such as butyl acrylate and methyl methacrylate as additives for gypsum to improve the strength of gypsum board. Although the polymers utilized improve the strength of the gypsum wallboard, they do not provide water resistance.
Therefore, there is a continuing need for a water resistant gypsum wallboard. It would also be useful if the treament which provides water resistance does not weaken the gypsum wallboard.
I have found that this need can be met by treating the gypsum with a polymer, which contains as polymerized units a hydrophobically modified monomer. By hydrophobically modified monomer is meant a C
12
to C
40
alkyl ester of (meth)acrylic acid.
The present invention provides a composition including from 80 to 99.5 parts by weight calcium sulfate, and from 0.5 to 20 parts by weight of a polymer including as polymerized units: a) from 1 to 100 parts by weight of at least one C
12
to C
40
alkyl ester of (meth)acrylic acid, b) from 0 to 99 parts by weight of at least one ethylenically unsaturated monomer, and c) from 0 to 15 parts by weight of at least one ethylenically unsaturated acid containing monomer or salts thereof.
In a second aspect, the present invention provides a method of protecting gypsum wallboard including: 1) admixing from 0.5 to 20 parts by weight of a polymer with from 80 to 99.5 parts by weight calcium sulfate and water; 2) molding the admixture to form a gypsum wallboard; and 3) drying the gypsum wallboard; wherein the polymer includes as polymerized units: a) from 1 to 100 parts by weight of at least one C
12
to C
40
alkyl ester of (meth)acrylic acid, b) from 0 to 99 parts by weight of at least one ethylenically unsaturated monomer, and c) from 0 to 15 parts by weight of at least one ethylenically unsaturated acid containing monomer or salts thereof.
The polymer used in this invention may be prepared by a single stage or multi-stage process. The process for making the polymer may be solution polymerization or emulsion polymerization utilizing methyl-&bgr;-cyclodextrin (“CD”). See U.S. Pat. No. 5,521,266 for a detailed description of the emulsion polymerization process. The emulsion polymerization process utilizing CD is preferred.
The morphology of the polymer utilized in this invention may be designed to optimize certain properties of the polymer. For example, the polymer may be made in a core-shell morphology wherein the core polymer is designed to have a lower glass transition temperature than the polymer that creates the shell. Alternatively, the polymer that makes up the core may be designed to have a higher glass transition temperature than the polymer that makes up the shell. In this case, the core may act as a filler and the shell may bind the harder cores together to aid in film formation. The core-shell polymers may be prepared by methods well known in the art.
In the process utilized for preparing the samples within this application, a first stage was prepared by adding a monomer emulsion and sodium persulfate to a solution containing CD, deionized water, and surfactant. The first stage was reacted at 85° C. A second stage was prepared by making a second monomer emulsion and feeding the second monomer emulsion and a sodium persulfate solution to the reacted first stage. The second stage was reacted at 85° C.
The polymer used in this invention contains as polymerized units from 1 to 100 parts by weight, preferably from 20 to 95 parts by weight, more preferably 40 to 95 parts by weight of at least one C
12
to C
40
alkyl ester of (meth)acrylic acid. It is further preferred that the polymer used in this invention contains as polymerized units from 60 to 95 parts by weight, preferably 70 to 94 parts by weight, more preferably 80 to 93 parts by weight of at least one C
12
to C
40
alkyl ester of (meth)acrylic acid. It is preferred that the alkyl ester of (meth)acrylic acid be a C
12
to C
30
alkyl ester of (meth)acrylic acid. It is more preferred that the alkyl ester of (meth)acrylic acid be a C
12
to C
18
alkyl ester of (meth)acrylic acid. Suitable alkyl esters of (meth)acrylic acid include, but are not limited to lauryl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, behenyl (meth)acrylate, and eicosyl (meth)acrylate. Beneficial properties may be obtained by utilizing more than one C
12
to C
40
alkyl ester of (meth)acrylic acid.
The polymer used in this invention may also contain as polymerized units from 0 to 99 parts by weight, preferably 4 to 79 parts by weight, more preferably 4 to 59 parts by weight of at least one ethylenically unsaturated monomer. It is further preferred that the polymer used in this invention contains as polymerized units from 4 to 39 parts by weight, preferably 5 to 29 parts by weight, more preferably 6 to 19 parts by weight of at least one ethylenically unsaturated monomer. Suitable ethylenically unsaturated monomers for use in the preparation of the polymer compositions of this invention include, but are not limited to (meth)acrylic ester monomers including methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, methyl methacrylate, butyl methacrylate, hydroxyethyl methacrylate, and hydroxypropyl acrylate; acrylamide or substituted acrylamides; styrene or substituted styrene; vinyl acetate or other vinyl esters; vinyl monomers such as vinyl chloride, vinylidene chloride, N-vinyl pyrolidone; and acrylonitrile or methacrylonitrile. Butyl acrylate, methyl methacrylate, and styrene are preferred.
The polymer used in this invention may also contain as polymerized units from 0 to 15 parts by weight, preferably 1 to 10 parts by weight, more preferably 1 to 5 parts by weight ethylenically unsaturated acid containing monomer or salts thereof. Suitable ethylenically unsaturated acid containing monomers include, but are not limited to acrylic acid, methacrylic acid, crotonic acid, phosphoethyl methacrylate, 2-acrylamido-2-methyl-1-propanesulfonic acid, sodium vinyl sulfonate, itaconic acid, fumaric acid, maleic acid, monomethyl itaconate, monomethyl fumarate, monobutyl fumarate, and
Cain Edward J.
Greenblatt Gary D.
Rohm and Haas Company
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