Abstract:
The present invention relates generally to paints and paint bases, and, more specifically to a process and composition for providing a stable gel-free dispersion of zinc pyrithione plus cuprous oxide biocide in paint. In accordance with the process of the present invention, the paint or paint base contains a metal salt of wood rosin in order to impart desired gelation-inhibition to the paint.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to paints and paint bases, and, more specifically to a process for providing a stable, gel-free dispersion of zinc pyrithione plus cuprous oxide biocide in paint. 
     BACKGROUND OF THE INVENTION 
     Combinations of zinc pyrithione and cuprous oxide are known to be excellent antifouling agents when formulated into Paints and paint bases (i.e., the paint before pigment addition) also containing rosin, as disclosed, for example, in U.S. Pat. No. 5,057,153. Unfortunately, however, such paints have now been found to thicken or gel unacceptably within a few days, at best, or a few hours, at worst, when formulated with typical commercial grades of zinc pyrithione in combination with cuprous oxide. 
     Heretofore, the only solutions to the problem of gellation of paints containing rosin and zinc pyrithione in combination with cuprous oxide, known to the present inventors, have been to use rigorously purified zinc pyrithione, as disclosed in co-pending U.S. application Ser. No. 07/644,015, or to add amines or esterified rosin, as disclosed in co-pending U.S. application Ser. No. 07/716,415. Since these solutions may have drawbacks such as increased cost or lack of compatibility with some paints, a new, economical solution to the problem would be highly desired by the paint manufacturing community in order to maximize flexibility in using this combination of biocides in view of its excellent biocidal activity. 
     SUMMARY OF THE INVENTION 
     In one aspect, the Present invention relates to a process for providing a gellation-inhibited solvent-based paint or paint base containing zinc pyrithione and cuprous oxide which comprises the steps of: 
     (a) incorporating said zinc pyrithione and also incorporating cuprous oxide into a solvent-based paint or paint base to provide a biocide-containing paint or paint base, said zinc pyrithione being present in an amount of between about 1% and about 25% (preferably 5-25% more preferably 10-25%), and said cuprous oxide being present in an amount of between about 20% and about 70%, the total amount of said pyrithione salt plus said cuprous oxide being between about 20% and about 80%, said weight percents being based upon the total weight of the biocide-containing paint or paint base, and 
     (b) incorporating a metal salt of rosin or a mixture of metal salt of rosin plus underivatized rosin into said biocide-containing paint or paint base, said metal salt being the reaction product of a carboxylic acid-containing rosin (also referred to herein as &#34;underivatized&#34; rosin) with a metal-containing base (preferably a metal oxide or metal hydroxide), said mixture having a total acidity as measured by acid number of not greater than 70 (preferably between 0.1 and 50, more preferably between 0.1 and 30), and said metal salt of rosin or mixture of metal salt of rosin plus underivatized rosin being present in a total amount of between about 1% and 20% (preferably 2-15%, more preferably 4-10%), based upon the total weight of the paint or paint base, in order to form a paint or paint base characterized by enhanced biocidal efficacy and resistance to gellation. 
     In another aspect, the Present invention relates to the above process wherein steps (a) and (b) are conducted simultaneously to provide the desired paint or paint base stabilized against gellation. 
     In another aspect, the present invention relates to a paint or paint base composition characterized by enhanced biocidal efficacy and gellation resistance wherein the paint or paint base contains a biocide consisting essentially of cuprous oxide and zinc pyrithione and wherein the paint or paint base is stabilized against gellation by virtue of the presence therein of the above-described metal salt of rosin or mixture of metal salt of rosin and underivatized rosin. 
     These and other aspects of the invention will become apparent upon reading the following detailed description of the invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with the present invention, it has now been surprisingly found that the use of a metal salt of rosin provides stability against gellation of a solvent-based paint or solvent-based paint base containing a biocide consisting essentially of cuprous oxide and zinc pyrithione. The metal preferably is selected from the group consisting of the alkali metals, the alkaline earth metals, the transition metals, and aluminum, that is aluminum plus the members of groups IA, IB, IIA, IIB, IIIB, IVB, VB, VIB, VIIB, and VIIIB in the periodic table of the elements. More preferably, the metal is selected from the group consisting of calcium, zinc, copper, iron, nickel, aluminum, magnesium, and combinations thereof. As used herein, the term &#34;rosin&#34; refers to the natural product corresponding to the residue left after distilling off the volatile oils from resin obtained from various species of pine trees. It is offered commercially as &#34;wood rosin&#34; when obtained from stumps of such trees and as &#34;gum rosin&#34; when obtained from incisions in the living tree. It is also known as colophony or yellow resin. It consists substantially of isomers of abietic acid. 
     The mixture of metal salt of rosin plus underivatized rosin useful in the present invention has an acid number as specified hereinabove. As used herein, the term &#34;acid number&#34; refers to the total acidity of the metal salt of rosin expressed in milligrams of Potassium hydroxide per gram of sample as determined by titration of free acid groups in the sample with standard base. This analysis and analytical technique are well known to those skilled in the art. 
     Although the improved biocidal efficacy and gellation resistance advantages associated with the present invention are expected to provide advantages when used in a wide variety of paints, including indoor and outdoor household paints, industrial and commercial paints, particularly advantageous results are obtained when the process and composition of the present invention are utilized in conjunction with marine paints for use, for example, on ship&#39;s hulls. In addition, the composition and process of the present invention provides highly desirable results in the context of exterior paints of both the latex and alkyd types. 
     Typically, a paint composition will contain a resin, an organic solvent (such as xylene or methylisobutylketone), a pigment, and various optional additives such as thickening agent(s), wetting agents, and the like, as is well-known in the art. The resin is preferably selected from the group consisting of vinyl, alkyd, epoxy, acrylic, polyurethane and polyester resins, and combinations thereof. The resin is preferably employed in an amount of between about 20% and about 80% based upon the weight of the paint or pPaint base. 
     In addition, the paint composition of the present invention optionally additionally contains optional additives which have a favorable influence on the viscosity, the wetting power and the dispersibility, as well as on the stability to freezing and electrolytes and on the foaming properties. If a marine paint is being fabricated, the paint preferably contains a swelling agent to cause the paint to gradually &#34;slough off&#34; in its marine environment, thereby causing renewed biocidal efficacy of newly exposed biocide (i.e., the pyrithione salt Plus paint copper salt) at the surface of the paint in contact with the water medium of the marine environment. Illustrative swelling agents are naturally-occurring or synthetic clays, such as kaolin, montomorillonite bentonite), clay mica (muscovite), and chlorite (hectonite), and the like. In addition to clays, other swelling agents, including natural or synthetic polymers, such as that commercially available as POLYMERGEL, have been found to be useful in the compositions of the present invention to provide the desired &#34;sloughing off&#34; effect. Swelling agents can be used singly or in combination. The total amount of optional additives is preferably no greater than 20% by weight, more preferably between about 1% and about 5% by weight, based upon the total weight of the paint composition. 
     Illustrative thickening agents include cellulose derivatives, for example methyl, hydroxyethyl, hydroxypropyl and carboxymethyl cellulose, poly(vinyl alcohol), poly (vinylpyrolidone), poly(ethylene-glycol), salts of poly(acrylic acid) and salts of acrylic acid/acrylamide copolymers. 
     Suitable wetting and dispersing agents include sodium polyphosphate, aryl or alkyl phosphates, salts of low-molecular-weight poly(acrylic acid), salts of poly(ethane-sulfonic acid), salts of poly (vinyl-phosphonic acid), salts of poly(maleic acid) and salts of copolymers of maleic acid with ethylene, 1-olefins with 3 to 18 carbon atoms and/or styrene. 
     In order to increase the stability to freezing and electrolytes there may be added to the paint composition various monomer 1,2-diols, for example glycol, propylene-glycol-(1,2 , and butylene-glycol-(1,2) or polymers thereof, or ethoxylated compounds, for example reaction products of ethylene oxide with long-chain alkanols, amines, carboxylic acids, carboxylic acid amides, alkyd phenols, poly(propylene-glycol) or poly(butylene-glycol). 
     The minimum temperature of film formation (white point) of the paint composition may be reduced by adding solvents, such as ethylene-glycol, butyl-glycol, ethyl-glycol acetate, ethyl-diglycol acetate, butyl-diglycol acetate, benzene or alkylated aromatic hydrocarbons. As defoaming agents there are suitable for example poly(propylene-glycol) and polysiloxanes. 
     The paint composition of the present invention may be used as a paint for natural or synthetic materials, for example wood, paper, metals, textiles and plastics. It is particularly suitable as an outdoor paint, and is excellent for use as a marine paint. 
     The invention is further illustrated by the following Examples. Unless otherwise stated, the &#34;parts&#34; and &#34;%&#34; are &#34;parts by weight&#34; and &#34;percent by weight&#34;, respectively. 
     While the invention has been described above with references to specific embodiments thereof, it is apparent that many changes, modifications and variations can be made without departing from the inventive concept disclosed herein. Accordingly, it is intended to embrace all such changes, modifications and variations that fall within the spirit and broad scope of the appended claims. All Patent applications, patents and other publications cited herein are incorporated by reference in their entirety. 
    
    
     COMPARATIVE EXAMPLE A 
     Demonstration of Gellation Results in a Paint Containing Cuprous Oxide Plus Zinc Pyrithione and Wood Rosin 
     A paint was Prepared using the following formulation: 
     The solvent mixture used was a 2:1 mixture of MIBK and xylene (called mixed solvent). 
     The zinc pyrithione used was standard commercial grade and assayed 97.8% pure by iodometric titration. 
     
         ______________________________________Material            Parts   %______________________________________VAGH resin (1)      9.3     2.8DISPERBYK 163 (2)   5.1     1.5Tributyl Phosphate  6.45    2.0Cuprous Oxide       136.5   41.4TITANOX (3)         7.5     2.3Zinc pyrithione powder               25.5    7.7Wood Rosin (4)      6.3     1.9Solvent Mixture     133.0   40.0______________________________________ (1) vinyl chloridevinyl acetatevinyl alcohol terpolymer, a product of Union Carbide Corporation. (2) a high molecular weight block copolymer, a product of BYKChemie. (3) titanium dioxide, a product of DuPont Company. (4) a product of Hercules, Incorporated 
    
     The procedure employed for preparing the paint was as follows: 
     (1) A one pint paint can was charged with 41.93 g of a 22.2% VAGH resin solution in a 2:1 mixture by volume of MIBK and xylene. 
     (2) A mixture of 5.1 g Disperbyk 163 and 5.1 g mixed solvent was added. 
     (3) Tributyl phosphate was added to the paint can and mixed with a high speed disperser at 1000 RPM for 10 minutes. 
     (4) The cuprous oxide, zinc pyrithione, titanox, and 10.8 g carbitol acetate were added to the paint can and mixing was continued at 7000 RPM for 1 hr. 
     (5) The mixing speed was reduced to 2500 RPM and 35 g of mixed solvent was added. 
     (6) Once the temperature dropped from 45° C. to below 35°, a solution of 6.3 g of wood rosin in 50 g of mixed solvent was added to the can and the mixture was mixed for 1.0 hr. at 2500 RPM. 
     The paint formulation made according to this procedure was of suitable viscosity for application by brush immediately after preparation, but thickened to an unpourable paste after approximately 6 hours. 
     GENERAL PROCEDURE FOR MAKING ROSIN DERIVATIVE PAINTS 
     Mill Base (MB) 
     (1) A one pint paint can was charged with 35.2 g of a 22.2% VAGH resin solution in a 2:1 mixture by volume of MIBK and xylene. 
     (2) A mixture of 5.4 g Disperbyk 163 and 4.0 g mixed solvent was added to the can, along with 7.2 g of tricresyl phosphate. 
     (3) The above materials were mixed with a high speed disperser at 1000 RPM for 10 minutes. 
     Pigment Grind (PG) 
     (4) The cuprous oxide, zinc pyrithione, and 20.0 g solvent mixture (as needed) were added to the paint can and mixing was continued at 7000 RPM for 1 hour. The sample temperature was kept below 45° C. using a water bath. 
     Letdown Stage (LD) 
     (5) Next a solution of 14.5 g of the rosin derivative in 25 g of mixed solvent was added to the can and the mixture was mixed for 1.0 hr at 4000 RPM. 
     (7) The solvent mixture which was lost during work-up was added back to the paint and mixed for 5 minutes. Solvent mixture used was a 40% mixture of xylene and 60% MIBK. 
     EXAMPLE I 
     
         ______________________________________EXAMPLE IStep   Material            Parts   %______________________________________MB     VAGH RESIN (22%)    7.8     2.85MB     DISBERYK 163        5.4     1.98PG     CUPROUS OXIDE       150     54.86PG     ZINC PYRITHIONE     13.5    4.94MB     TRICRESYL PHOSPHATE 7.2     2.63LD     ZIREX (1)           14.5    5.30ALL    SOLVENT MIXTURE     75      27.43  *60% MIBK/40% XYLENE  TOTAL               273.4   100.00______________________________________ (1) Zinc rosinate, a product of Arizona Chemical Company 
    
     The ZIREX was found to have an acid number of zero, meaning that the rosin is completely neutralized to the zinc salt and no underivatized rosin was present. The paint example I was of suitable viscosity for application by brush 8 weeks after its preparation. 
     EXAMPLE II 
     
         ______________________________________EXAMPLE IIStep   Material            Parts   %______________________________________MB     VAGH RESIN (22%)    8.10    2.84MB     DISPERBYK 163       6.0     2.1PG     CUPROUS OXIDE       150     52.53PG     ZINC OMADINE DRIED  15.0    5.25MB     TRICESYL PHOSPHATE  7.2     2.52LD     D-98-SFH (1)        14.25   4.99ALL    SOLVENT MIXTURE     85.0    29.77  *60% MIBK/40% XYLENE  TOTAL               285.55  100.00______________________________________ (1) Calcium rosinate, a product of Empire Varnish Company 
    
     The D-98-SFH calcium rosinate was found to have an acid number of 38-44, meaning that it is not completely neutralized and is a mixture of the calcium salt of rosin and underivatized rosin. The paint of example II thickened slightly but was still of suitable viscosity for application by brush 8 weeks after its preparation. 
     EXAMPLE III 
     
         ______________________________________EXAMPLE IIIStep   Material            Parts   %______________________________________MB     VAGH RESIN (22%)    7.8     2.85MB     DISPERBYK 163       5.4     1.98PG     CUPROUS OXIDE       150     54.86PG     ZINC OMADINE DRIED  13.5    4.94MB     TRICRESYL PHOSPHATE 7.2     2.63LD     ZINAR (1)           14.5    5.30ALL    SOLVENT MIXTURE     75      27.43  *60% MIBK/40% XYLENE  TOTAL               273.4   100.00______________________________________ (1) Mixed zinc and calcium rosinate, a product of Arizona Chemical Company. 
    
     The ZINAR mixed zinc and calcium rosinate had an acid number of approximately ten, meaning that it was nearly completely neutralized but was still a mixture of the calcium and zinc salts of rosin and underivatized rosin. The paint of Example III was of suitable viscosity for application by brush 8 weeks after its preparation. 
     While the invention has been described above with references to specific embodiments thereof, it is apparent that many changes, modifications and variations in the materials, arrangements of parts and steps can be made without departing from the inventive concept disclosed herein. Accordingly, the spirit and broad scope of the appended claims is intended to embrace all such changes, modifications and variations that may occur to one of skill in the art upon a reading of the disclosure. All patent applications, patents and other publications cited herein are incorporated by reference in their entirety.