Abstract:
A stain resistant grout composition comprises a mixture of an acrylic latex, an aliphatic urethane and a paraffin. Preferably, the composition is an aqueous composition and is a low volatile organic compound (VOC) composition.

Description:
FIELD OF THE INVENTION 
     The invention relates to a stain resistant grout composition. More particularly, the invention relates to a stain resistant ceramic tile grout composition which includes a mixture of an acrylic latex, an aliphatic urethane and a paraffin. Preferably, the composition is an aqueous composition and is a low volatile organic compound (VOC) composition. 
     BACKGROUND OF THE INVENTION 
     The tendency of ceramic tile grout to stain easily requires a high level of maintenance. Overcoming this deficiency has been a high priority for the ceramic tile industry for many years. While heat and chemical resistant grouts, such as epoxy and furan grouts, exist on the commercial market, these grouts contain hazardous ingredients and require the expertise of a professional installer. 
     The present invention results in a grout product for ceramic tile that is highly resistant to a wide variety of staining agents. The composition takes two forms: a liquid admix for standard portland cement grout and a one component, pre-mixed paste. 
     Discho U.S. Pat. No. 5,387,644 discloses a hardenable monomer composition useful for grouts. The Disoho composition comprises a mixture of a crosslinkable acrylic monomer, carbon black and/or a polyester- or polyethermethane oltgomer having at least two polymerizable double bonds and a paraffin oil. The oltgomer is an aliphatic or aromatic, bifunctional or polyfunctional polyester- or polyether-urethane acrylate. Therefore, the Discho composition is not a mixture of an acrylic latex, an aliphatic urethane and a paraffin, but the reaction product of a crosslinkable acrylic monomer and a reactive acrylic end-capped polyester- or polyether urethane. Further, the Discho composition is a liquid and the urethane oligomer has a molecular weight of no more than 2,000. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, the stain resistant grout composition comprises a mixture of an acrylic latex, an aliphatic urethane and a paraffin. Preferably, the composition is 5% to 40% by weight of acrylic latex, 0.5% to 15% by weight of aliphatic urethane and 0.5% to 6% by weight of paraffin. 
     More preferably, the acrylic latex is 10% to 30% by weight of the composition, and still more preferably about 15% to about 20% by weight. More preferably, the aliphati c  urethane is 0.5% to 10% by weight of the composition, and still more preferably about 1% to about 4% by weight. More preferably, the paraffin is 0.5% to 3% by weight of the composition, and still more preferably 0.5% to 1% by weight. The minimum amounts of the components are needed for improved stain resistance. The components increase cure time of the composition, therefore less water is trapped under the skin which forms on the surface of the composition. 
     If the aliphatic urethane is greater than 15%, the composition is too hard and tough, and the workability and desired properties are reduced. If the paraffin is greater than 6%, adhesiveness of the composition is reduced. 
     The preferred aliphatic urethane is a fully reacted, thermoplastic urethane and has a molecular weight greater than 10,000. The allphatic urethane is preferably dispersed in a blend of water, N-methylpyrrolidone and amine. The preferred paraffin is a paraffin wax. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The acrylic latex serves as the vehicle which carries the other components of the composition and dries by evaporation. The acrylic latex provides alkali resistance and promotes adhesion. The quick release of volatile components in the acrylic latex, compared to other latexes, promotes early hardness development. 
     The paraffin provides water resistance by &#34;floating&#34; to the surface of the composition and forming a shield on the surface of the grout. The paraffin provides immediate stain resistance while the acrylic resin and urethane cure over the first few hours to three days. 
     The urethane enhances volatilization of the latex water, repels external water, improve the continuity of the filler, and improves adhesion, abrasion resistance, chemical resistance and stain resistance. The combination of these components yields a product which dries hard and is impervious to penetration by stain carrying agents. 
     The grout of the present invention is not only impervious, but also is harder than existing cement grouts. Therefore, the present grout also improves abrasion resistance. 
     The preferred aliphatic urethane is a fully reacted, thermoplastic urethane such as Spensol L41-MPW-32, Spensol L44-MPW-32, Spensol L51-MPW-35, Spensol L52-MPW-30, Spensol L53-MPW-30, Spensol L54-MPW-32, Spensol L55-MPW-35 and Spensol L56-MPW-36, all of which are manufactured by Reichhold Chemicals, Inc. Spensol L-MPW-32 and Spensol L44-MPW-32 are less expensive resins which can be used when color stability is not critical. Spensol L51-MPW-35 has a higher hardness. Spensol L52-MPW-30 has a low impact resistance. Spensol L53-MPW-30 has the best abrasion resistance. Spensol L54-MPW-32 is suitable for both air dry and force dry application. Spensol L55-MPW-35 and Spensol L56-MPW-36 can be used for flexible substrates. 
     The urethane is preferably a water dispersible polyurethane elastomer; more preferably it is dispersed in a blend of water, N-methylpyrrolidone and amine. The preferred amine is triethylamine and the preferred weight ratio of urethane/water/N-methylpyrrolidone/amine is about 
     While the aliphatic urethane dispersion has a small percentage of organic solvent, the grout composition is a low VOC composition. Because the composition does not include epoxy components, the grout can be exposed to UV light without yellowing, i.e. has UV resistance. 
     Numerous additives, well known in the art, can be included in the grout composition for their known purposes. Such additives include anti-settling agents, humectants, pH control agents, biocides, freeze/thaw stabilizers, surfactants, fillers/extenders, drying rate controllers, defoamers, shrinkage controllers, anti-oxidants and pigments. Examples 1 to A set forth one-part grout compositions of the present invention which can be used directly as a ceramic tile grouts. 
     
         __________________________________________________________________________           EXAMPLE 1                  EXAMPLE 2                         EXAMPLE 3                                EXAMPLE 4Component       Parts by wt.                  Parts by wt.                         Parts by wt.                                Parts by wt.__________________________________________________________________________Acrylic latex   527.sup.1                  527.sup.1                         1125.sup.3                                1000.sup.2Aliphatic urethane dispersion           100.sup.4                  100.sup.4                         240.sup.6                                130.sup.4Paraffin wax emulsion.sup.7           20     20     100    20Water           73     73     73     73Calcium carbonate           144    544    216    1000Silica          2171   1571   1200   1400Ammonium hydroxide              0.25                     0.25                            0.25                                   0.25Hydroxypropyl methyl cellulose            1      1     1       1Biocide           12.5   12.5   12.5   12.5Propylene glycol           73     73     73     73Surfactant       5      5      5      5Diluent          5      5      5      5Glycol ether    10     10     10     10Defoamer           1.25                     1.25                            1.25                                   1.25Shrinkage controller           195    195    200    195Titanium Dioxide           34     34     34     34Anti-oxidant    24     24     24     24           3396   3196   3320   3984__________________________________________________________________________ .sup.1 Ucar 422 manufactured by Union Carbide Corp. .sup.2 Unocal 1018 manufactured by Rohm and Haas .sup.3 Acronal S705 manufactured by BASF .sup.4 Spensol L54-MPW-32 .sup.5 Neorez R9409 manufactured by Zencca .sup.6 Spensol L512 manufactured by Reichhold .sup.7 Aqua Bead 325E manufactured by Micro Powders, Inc. of New York 
    
     Although a specific acrylic latex, aliphatic urethane and paraffin wax have been identified, other acrylic latexes, aliphatic urethanes and paraffins including paraffin oils can be used. 
    
    
     EXAMPLE 5 
     Example 5 sets forth a liquid admix of the present invention which has been formulated for use with standard portland cement grout compositions. The admix is added to a typical grout formulation, such as a portland cement composition, in a ratio of 1 to 20 by weight to 1 to 30 by weight. 
     
         ______________________________________Component           Parts by wt.______________________________________Acrylic latex.sup.1 70Aliphatic urethane dispersion.sup.4               16.8Paraffin wax emulsion.sup.7               6Water               70Surfactant          1.4Biocide             0.3               164.5______________________________________ .sup.1, .sup.4 and .sup.7 as identified above. 
    
     EXAMPLE 6 
     
         ______________________________________Component            Parts by wt.______________________________________Acrylic latex.sup.2  1292Aliphatic urethane dispersion.sup.5                380Paraffin wax emulsion.sup.7                120Water                73Calcium carbonate    1071Ammonium hydroxide   0.25Hydroxypropyl methyl cellulose                1Biocide              12.5Propylene glycol     73Surfactant           5Diluent              5Glycol ether         10Defoamer             1.25Shrinkage controller 200Titanium dioxide     34Anti-oxidanr         24                3302______________________________________ .sup.2,5 and .sup.7 as identified above.