Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-09-14
2004-03-02
Wilson, D. R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S123000, C525S375000, C523S410000, C523S415000
Reexamination Certificate
active
06699942
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to powder coating compositions, particularly powder coating compositions with improved mar resistance properties.
BACKGROUND
Solid particulate coating formulations referred to in the industry as “powder coatings” can be applied over various substrates. A major benefit of powder coatings is that little, if any, volatile material is given off to the surrounding environment when powder coatings are cured. Due to increasing restrictions on volatile organic content (VOC), powder coatings are preferred for many applications.
One problem with conventional powder coatings is that they exhibit poor mar resistance properties. “Mar resistance” refers to the ability of a coating composition to maintain its appearance when the coating comes in contact with an abrasive material.
To improve mar resistance, microparticulate materials such as silica, metal sulfides, and crosslinked styrene-butadiene are sometimes added to powder coating compositions. Because the addition of microparticulate materials adversely affects the gloss and the distinctness of image (DOI) of a coated surface, this is a less than ideal solution to the problem.
The present invention provides a curable powder coating composition which exhibits improved mar resistance properties.
SUMMARY OF THE INVENTION
The present invention is a curable powder coating composition comprising a polymer containing reactive functional groups, a curing agent having functional groups reactive with the functional groups of said polymer, the curing agent being present in an amount sufficient to cure said polymer, and less than 10 percent based on total resin solids of the powder coating composition of a tricarbamoyl triazine compound represented by the following chemical formula: C
3
N
3
(NRCOXY)
3
where Y is an alkyl group or substituted alkyl group having 1 to 12 carbon atoms, X is NR′, O, S, PR′, and —C—, and R and R′ are hydrogen and alkyl or a substituted alkyl having 1 to 12 carbon atoms.
DETAILED DESCRIPTION OF THE INVENTION
Various numerical ranges are disclosed in this patent application. Because these ranges are continuous, they include every value between the minimum and maximum values. Unless expressly indicated otherwise, the various numerical ranges specified in this application are approximations. It is implied that the minimum and maximum values within the stated ranges are preceded by the word “about”. Therefore, slight variations above and below the stated ranges can be used to achieve substantially the same results.
The powder coating composition of the present invention comprises a polymer having reactive functional groups. The polymer having reactive functional groups can be chosen from a variety of materials, including but not limited to, acrylic polymers, polyurethane polymers, and polyester polymers. The reactive functional groups on the polymer are selected from carboxylic acid, epoxy, hydroxyl, amino, carbamate, and urea. The polymer is present in the powder coating composition in amounts ranging from about 10 to 90 percent by weight, based on the total weight of resin solids in the powder coating composition.
In an embodiment of the invention, the polymer having reactive functional groups is an acrylic polymer. Acrylic polymers containing the appropriate functional groups can be formed by reacting polymerizable alpha, beta-ethylenically unsaturated monomers containing the functional groups mentioned above with one or more other polymerizable, unsaturated monomers.
Suitable carboxylic acid group-containing monomers include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, citraconic acid, and monoalkylesters of unsaturated dicarboxylic acids. Acrylic acid and methacrylic acid are the preferred carboxylic acids.
Suitable epoxy group-containing monomers include glycidyl acrylate and glycidyl methacrylate.
Suitable amino group-containing monomers include aminoethyl methacrylate and aminopropyl methacrylic.
Pendant carbamate functional groups can be incorporated into the acrylic polymer by copolymerizing the acrylic monomers with a carbamate functional vinyl monomer. Examples of suitable carbamate functional monomers include: (a) carbamate functional alkyl esters of methacrylic acid; (b) the reaction product of hydroxyethyl methacrylate, isophorone diisocyanate, and hydroxypropyl carbamate; (c) the reaction product of hydroxypropyl methacrylate, isophorone diisocyanate, and methanol; and (d) the reaction product of isocyanic acid with a hydroxyl functional acrylic or methacrylic monomer like hydroxyethyl acrylate.
Pendant urea groups can be incorporated into the acrylic polymer by copolymerizing the acrylic monomers with urea functional vinyl monomers. Examples of urea functional monomers include: (a) urea functional alkyl esters of acrylic acid or methacrylic acid and (b) the reaction product of hydroxyethyl methacrylate, isophorone diisocyanate, and hydroxyethyl ethylene urea.
The acrylic polymers typically have number average molecular weights of about 1,000 to 10,000 or 1,000 to 5,500 based on gel permeation chromatography using a polystyrene standard. The acrylic polymers have equivalent weights (based on the functional groups mentioned above) of about 200 to 400 or 250 to 355 gram/equivalent. The glass transition temperature (T(g)) of the polymer is typically about 30° C. to 60° C. or 35° C. to 55° C. The T(g) is determined by Differential Scanning Calorimetry (DSC) at a rate of heating equal to 18° F. (10° C.) per minute.
In another embodiment of the present invention, the polymer having reactive functional groups is a polyurethane polymer containing the functional groups mentioned above for the acrylic polymers. Polyurethane polymers can be prepared by reacting polyols and polyisocyanates. Examples of suitable polyols include low molecular weight aliphatic polyols such as ethylene glycol, propylene glycol, butylene glycol, 1,6-hexylene glycol, neopentyl glycol, cyclohexanedimethanol, trimethylolpropane and the like. Typically, high molecular weight polymeric polyols such as polyether polyols and polyester polyols are used with the lower molecular weight polyols. Examples of polyether polyols are those formed from the oxyalkylation of various polyols like glycols or higher polyols. Suitable glycols include ethylene glycol, 1,6-hexanediol, and Bisphenol A. Suitable higher polyols include trimethylol propane and pentaerythritol. Suitable polyester polyols can be prepared by the polyesterification of organic polycarboxylic acids or anhydrides thereof with organic polyols. Usually, the polycarboxylic acids and polyols are aliphatic or aromatic dibasic acids and diols.
Suitable polyisocyanates include aromatic and aliphatic polyisocyanates. Aliphatic polyisocyanates are preferred because of their exterior durability. Exemplary polyisocyanates include 1,6-hexamethylene diisocyanate, isophorone diisocyanate and 4,4′-methylene-bis-(cyclohexyl isocyanate).
Carboxylic acid functionality can be introduced into the polyurethane by reacting the polyurethane polyol with polycarboxylic acids. Exemplary polycarboxylic acids include succinic acid, adipic acid, azelaic acid, sebacic acid, terephthalic acid, isophthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, trimellitic acid and anhydrides of such acids. Alternatively, the polyisocyanate can be reacted with a mixture of the polyols mentioned above and a polyol containing carboxylic acid groups such as dimethylol propionic acid.
Hydroxyl functionality can be introduced into the polyurethane by reacting the polyisocyanate with a stoichiometric excess of the polyol component to form a polyurethane polyol.
Epoxy functionality can be incorporated into the polyurethane by including a hydroxy functional epoxy compound like glycidol with the polyol component.
Amino functionality can be introduced into the polyurethane by including a polyamine in the monomer charge. Suitable amines include primary and secondary diamines and polyamines in which the radicals attach
Barkac Karen A.
Nakajima Masayuki
Rechenberg Karen S.
Miles Jacques B.
PPG Industries Ohio Inc.
Uhl William J.
Wilson D. R.
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