in accordance with the present invention , it has now been surprisingly found that storage - stable dispersions of solid biocides in swellable polymer resins are provided by causing carrier absorption into the polymer to occur under elevated temperature conditions . the resulting dispersions are storage - stable against settling and against &# 34 ; setting - up &# 34 ; that would otherwise typically occur during warehousing of the dispersions prior to use . carriers useful in the process of the present invention include , for example , plasticizers and other resin - compatible additives . useful plasticizer - type carriers include , for example , adipic acid derivatives such as diisobutyl adipate , di - n - hexyl adipate , heptyl nonyl adipate , bis ( 2 - ethylhexyl ) adipate , diisodecyl adipate and bis ( 2 - butoxyethyl ) adipate ; azelaic acid derivatives such as bis ( 2 - ethylhexyl ) azelate ; benzoic acid derivatives such as diethylene glycol dibenzoate , dipropyleneglycol dibenzoate , and 2 , 2 , 4 - trimethyl - 1 , 3 - pentanediol - isobutyrate benzoate ; citric acid derivatives such as tri - n - butyl citrate and tri - n - butyl acetylcitrate ; epoxy derivatives such as epoxidized soybean oil , epoxidized linseed oil , 2 - ethylhexyl epoxy tallate and bisphenol a diglycidyl ether ; glycol derivatives such as diethlyene glycol dipelargonate , triethylene glycol di - 2 - ethylbutyrate , and poly ( ethylene glycol ) ( 200 ) di - 2 - ethylhexanoate ; glycolates such as methyl phthalyl ethyl glycolate and butylphthalyl ethyl glycolate ; hydrocarbons such as hydrogenated terphenyls hb - 40 , poly ( alkyl naphthalenes ) panaflex , aliphatic aromatics leromoll ! and chlorinated paraffin ( 52 % wt % c1 ) cereclor s - 52 ! ; isophthalic acid derivatives such as di - 2 - ethylhexyl isophthalate ; oleic acid derivatives such as butyl oleate ; phosphoric acid derivatives such as tributyl phosphate , tri - 2 - ethylhexyl phosphate , tributoxyethyl phosphate , chlorinated diphosphate ( phosgard 2xc - 20 !, cresyl diphenyl phosphate , tricresyl phosphate , isopropylphenyl diphenyl phosphate krotinex 100 !, t - butylphenyl diphenyl phosphate santicizer 154 !, 2 - ethylhexyl diphenyl phosphate and isodecyl phosphate ; phosphoric acid derivatives such as chlorinated polyphosphonate phosgard c - 22 - r ! ; phthalic acid derivatives such as dimethyl phthalate , dibutyl phthalate , butyl octyl phthalate , diisohexyl phthalate , heptyl nonyl phthalate , heptyl nonyl undecyl phthalate , diisooctyl phthalate , dialkyl ( c 7 - c 11 ) mixed linear phthalates santicizer 711 or platinol 711p !, bis ( 2 - ethylhexyl ) phthalate , ( n - hexyl , n - octyl , n - decyl ) phthalate , ( n - octyl , n - decyl ) phthalate , diisodecyl phthalate , diundecyl phthalate , ditridecylphthalate , butyl cyclohexyl phthalate , butyl benzyl phthalate , diisononyl phthalate , 7 -( 2 , 6 , 6 , 8 - tetramethyl - 4 - oxa - 3 - oxo - nonyl ) benzyl phthalate , bis ( 2 - butoxyethyl ) phthalate and dicylclohexyl phthalate ; polyesters such as adipic acid polyester ( mol wt 6000 ) paraplex g - 40 !, adipic acid polyester ( mol wt 2000 ) santicizer 334f !, azelaic acid polyester ( mol wt 850 ) plastolein 9720 !, azelaic acid polyester ( mol wt 2200 ) plastolein 9750 ! and sebacic acid polyester ; ricinoleic acid derivatives such as methyl ricinoleate , n - butyl acetylricinoleate and castor oil ( 90 wt % glyceryl ricinoleate ); sebacic acid derivatives such as bis ( 2 - ethylhexyl ) sebacate ; stearic acid derivatives such as butyl acetoxystearate ; sucrose derivatives such as sucrose acetate - isobutyrate ; sulfonic acid derivatives such as n - thyl -( o , p )- toluenesulfonamide and alkylsulfonic acid ester of phenol and cresol mesamoll ! ; terephthalic acid derivatives such as bis ( 2 - ethylhexyl ) terephthalate ; and trimellitic acid derivatives such as tris ( 2 - ethylhexyl ) trimellitate , heptyl nonyl trimellitate , heptyl nonyl undecyl trimellitate and triisodecyl trimellitate . other useful carriers include additives not normally classified as plasticizers , such as polyols . an important criterion for the additive ( s ) useful as carriers within the scope of the present invention is that the additive ( s ) interacts with the selected swellable polymer resin upon heating to cause swelling of the polymer particles . in order for the carrier to be useful in a specific application , swelling of the polymer particles must occur at an elevated temperature below the degradation temperature of the polymer and of the carrier . heat stabilizers can optionally be employed in order to avoid elevated degradation temperatures . the amount of carrier employed in the processes of the present invention suitably ranges between about 20 and about 95 , preferably between about 50 and about 85 , weight percent based upon the total weight of the dispersion . suitable heat swellable polymer resins useful in the present invention include , for example , the following resins and combinations thereof : cellulosics such as cellulose acetate , cellulose acetate - butyrate , cellulose nitrate , and ethylcellulose ; polyacrylates such as poly ( methyl methacrylate ) and acrylic copolymers , polystyrenes ; polyolefins such as polyethylene and polypropylene ; polycarbonates ; rubbers and synthetic elastomers ; vinyl polymers such as polyvinyl acetate ), poly ( vinyl butyral ), poly ( vinyl alcohol ) and poly ( vinylchloride ); and polyacrylonitrile and modified copolymers thereof ; and combinations thereof . the degree of crystallinity of any particular polymer may affect the extent of carrier absorption into the polymer for the specific carrier selected , as would be readily apparent to those of ordinary skill in the art . the amount of swellable polymer resin ( s ) employed in the processes of the present invention suitably ranges between about 1 and about 60 , preferably between about 5 and about 40 , weight percent based upon the total weight of the dispersion . suitable biocides useful in the present invention include , for example , the following biocides and combinations thereof : the above biocides are suitably employed individually or in combinations of two or more biocides , as may be desired . the preferred biocides are sodium pyrithione , zinc pyrithione , copper pyrithione , chitosan pyrithione , pyrithione disulfide , and combinations thereof . the biocide ( s ) is typically employed in an amount of between about one and about 50 , preferably between about 5 and about 30 , weight percent based upon the total weight of the dispersion . the processes of the present invention are suitable for the preparation of resin concentrates , if desired , containing high levels of biocide . the concentrates are subsequently diluted with additional polymer resin , which can be the same or different resin from that used in the preparation of the concentrate , to provide a working composition containing at least a &# 34 ; biocidally effective amount &# 34 ; of biocide , i . e ., an amount of biocide sufficient to provide the desired level of biocidal efficacy in the working composition . selection of the carrier for use in the preparation of a concentrate advantageously takes into account additives that are desirably present in the working composition . alternatively , the working composition is suitably prepared directly using the processes of the present invention without the necessity for preparing a concentrate . the processes of the present invention are suitably effected in a few minutes or less up to ten hours or more , depending upon the specific starting materials and processing conditions employed . other additives are suitably optionally employed in the processes of the present invention , including for example pigments such as titanium dioxide , fillers and reinforcing agents such as glass fibers , heat stabilizers such as calcium sterate , uv stabilizers , surfactants such as polyalkyleneoxide ethers , dispersing agents , suspending agents , and the like , and combinations thereof . if used , the optional additives are suitably employed in a minor amount of less than fifty weight percent based upon the weight of the polymer resin . while the invention has been described above with reference 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 . part a -- preparation of a preliminary zinc pyrithione / plasticizer dispersion referred to herein as (&# 34 ; the concentrate &# 34 ;) dioctyl phthalate ( dop ) ( 1000 grams ) was added to zinc pyrithione powder ( 600 grams ) in a steel beaker and mixed on a high speed disperser at 6000 rpm until smooth ( approx . two hours ). the concentrate temperature did not exceed 100 ° c . part b -- preparation of a 5 % zinc pyrithione dispersion containing 20 % pvc prepared at an elevated temperature zinc pyrithione dispersion ( 110 . 9 grams ; 37 . 5 % active in dop ), prepared in accordance with part a above , was combined with bf goodrich geon 125a pvc ( 160 . 0 grams ) and dop ( 529 . 1 grams ). stirring was continued throughout the reaction . the mixture was warmed to 80 ° c . using an oil bath . the temperature was maintained for 3 . 5 hours . the heat was removed , the mixture was allowed to air cool overnight to room temperature with continued stirring . the resulting dispersion containing 5 % zinc pyrithione and 20 % pvc was stable at room temperature and had a static viscosity of approx . 6 , 400 cps at 25 ° c . epoxidized soybean oil ( eso ) ( 406 grams ) was added to dry zinc pyrithione powder ( 200 grams ) in a stainless steel beaker and mixed on a high speed disperser at 3500 rpm for 2 hours . part b -- preparation of a 5 % zinc pyrithione dispersion containing 23 % pvc prepared at an elevated temperature zinc pyrithione dispersion ( 100 . 7 grams ; 31 % active in eso ) prepared in accordance with part a above , was combined with bf goodrich geon 125a pvc ( 138 grams ) and eso ( 361 . 4 grams ). stirring was continued throughout the reaction . the mixture was warmed to 80 ° c . using an oil bath . the temperature was maintained for 4 hours . the heat was removed , and the mixture was allowed to air cool with continued stirring until it reached room temperature . the resulting dispersion containing 5 % zinc pyrithione and 23 % pvc was stable at room temperature and had a viscosity of 13000 centipoise at 23 ° c . with stirring . heating effect on the viscosity of a 5 % zinc pyrithione dispersion containing 28 . 5 % pvc a dispersion was prepared following the procedure of example 1 by combining zinc pyrithione preliminary dispersion ( 111 . 2 grams ; 37 . 4 % active in 711 ) with bf goodrich geon 125a plastisol grade pvc and 711 . stirring was continued throughout the reaction . the mixture was warmed to 80 ° c . using an oil bath . aliquots of the sample were taken at half hour intervals to follow the sample &# 39 ; s viscosity profile . the dispersion viscosity was found to increase with time for 2 . 5 hours , and then the viscosity became constant . ______________________________________time ( hours ) viscosity ( cps ) ______________________________________0 34100 . 5 50101 . 0 68001 . 5 72102 . 0 74002 . 5 95203 . 0 96003 . 5 9520______________________________________ viscosity was found to be a direct function of temperature and polymer concentration . preparation of 5 % zinc pyrithione dispersions in a dioctyl phthalate carrier a series of dispersions were prepared following the procedure of example 1 by combining zinc pyrithione preliminary dispersion ( 35 % active in dop dioctyl phthalate !) with bf goodrich geon 125a plastisol grade pvc and dop . these formulations were heated using an oil bath and varying amounts of pvc for 4 hours . the amounts of pyrithione concentrate ( 35 % active ), pvc and dop for each formulation are as follows : ______________________________________formulation ( grams ) pvc dop______________________________________sample a 89 . 14 120 390 . 89sample b 89 . 14 126 384 . 86sample c 89 . 14 123 387 . 86sample d 89 . 14 108 402 . 86______________________________________ all dispersions identified as samples a , b , c , and d were found to have acceptable viscosities ranging from 6 , 000 - 15 , 000 cps . as expected , higher polymer levels produced more viscous materials . a dispersion was prepared following the procedure of example 1 by combining zinc pyrithione preliminary dispersion ( 266 . 67 grams ; 30 % active in eso ) with 48 grams bf goodrich geon 125a plastisol grade pvc and 85 . 33 grams eso . this formulation was heated , using an oil bath , to 80 ° c . for four hours . the sample was found to have an acceptable viscosity of approx . 7 , 000 cps . a series of dispersions were prepared following the procedure of example 1 by combining zinc pyrithione preliminary dispersion ( 96 . 36 grams ; 30 % active in ( bbp ) with bf goodrich geon 125a plastisol grade pvc and bbp . these formulations were heated , using an oil bath , to 80 ° c . for 4 hours . the formulations had an acceptable viscosity range from 9 , 000 to 13 , 000 cps . a series of dispersions were prepared following the procedure of example 1 by combining zinc pyrithione preliminary dispersion ( 100 . 65 grams ; 31 % active in didp ) with bf goodrich geon 125a plastisol grade pvc and didp . stirring was continued throughout the reaction . the mixture was warmed to 80 ° c . for four hours using an oil bath . all the samples had acceptable viscosities ranging from 7 , 000 to 10 , 000 cps and were stable dispersions . stability of a 5 % zinc pyrithione dispersion in bbp containing 15 % pvc a dispersion was prepared following the procedure of example 1 by combining zinc pyrithione preliminary dispersion ( 96 . 36 grams ; 33 % active in bbp ) with bf goodrich geon 125a plastisol grade pvc and bbp . the dispersion was heated using an oil bath to 80 ° c . for four hours . this dispersion had an acceptable viscosity of 12 , 000 cps . the amount of zinc was measured at the top and bottom of this sample by x - ray fluorescence to ensure a stable dispersion with no settling . sample a , which was at room temperature for 3 months , had zinc measurements of 0 . 60 and 0 . 60 at the bottom and top of the sample , respectively . sample b , which was stored at an elevated temperature of 50 ° c . for 3 months had zinc values of 0 . 60 and 0 . 60 at the bottom and top of the sample , respectively . these measurements show that the sample is a storage stable dispersion , even at elevated temperatures , and that settling does not occur . a dispersion was prepared following the procedure of example 1 by combining zinc pyrithione preliminary dispersion with gooodrich geon 125a plastisol grade pvc and dop . the sample was found to have a &# 34 ; b &# 34 ; value on a hunter colorimeter of 7 . 56 . this value measures yellowness . the previous method ( i . e ., the method of u . s . pat . no . 5 , 639 , 803 ) used to make a similar formulation entails mixing zinc pyrithione wet cake ( 20 % water ) and a carrier . this mixture is then heated to an elevated temperature , to remove the water , while stirring for approx . 4 hours . mixing together said concentrate , additional carrier and goodrich geon 125a plastisol grade pvc , the mixture is then prepared similarly to part b of example 1 above . a sample of the material prepared in the previous manner , containing the water removal step , was measured using the hunter colorimeter . this sample &# 39 ; s &# 34 ; b &# 34 ; value was measured at 19 . 56 . this second sample ( i . e ., the comparative example ) has almost twice the amount of yellowing as the first sample measured .
this invention relates to a process improvement for preparing a storage - stable dispersion of a biocide which comprises the steps of : dispersing a solid biocide and a carrier to form a biocide concentrate , heating said biocide concentrate to an elevated temperature to provide a storage stable mixture of biocide , resin and carrier , and cooling said mixture under continuous stirring to provide a homogeneous , storage - stable liquid dispersion . also claimed is the storage - stable product produced by this process .