as used herein , “ a ” and “ an ” mean one or more , unless otherwise indicated . the “ fatty acid ” or “ solid fatty acid ” useful in the present invention is any fatty acid of from about 16 to about 36 carbon atoms and being a solid at room temperature . such fatty acids include , but are not limited to , stearic , palmitic , margaric , nonadecanoic , arachidic , heneicosanoic , dehenic , tricosanoic , tetracosanoic , pentacosanoic , and cerotic fatty acids . the solid fatty acid is present in the formulation of the invention in an amount of from about 5 wt % to about 50 wt %, preferably from about 15 wt % to about 30 wt %. the “ low melting polymer or copolymer ” is selected from those polymers or copolymers having a melt temperature of below 250 ° f ., preferably below 200 ° f . examples of polymers and copolymers useful in the present invention include , but are not limited to , polyethylene , polyvinyl acetate , polyethylene , ethylene acid copolymers , ethylene acrylates , polyurethanes , styrene - butadiene , polyvinyl acetate , polyvinyl butyral , and mixtures and copolymers thereof . in order to obtain compatibility with the solid fatty acid and to improve processing of the formulation in conventional equipment , the polymer or copolymer is used , partially or wholly , in the form of granules , small irregularly shaped particles or powder . conventional pellets of polymers are very difficult to work with in this invention and can only constitute a small percentage ( no greater than about 15 wt % and preferably below about 10 wt %) of the total amount of polymer or copolymer , if they are used at all . the low melting polymer or copolymer is present in the formulation of the invention in an amount of from about 40 wt % to about 80 wt %, preferably from about 50 wt % to about 70 wt %, of which at least about 40 wt % is in the form of granules , small irregularly shaped particles or powder . the pest control active agent may be an insecticide , bactericide , fungicide , acaricide , attractant , repellent , or any other biologically active ingredient that is compatible with the other components of the pest control system . in one presently preferred embodiment , the active agent is chosen from any active agent known to be useful in the control of insect or acarid pests . exemplary pesticides and repellents which are effective against horn flies , face flies , stable flies , house flies , mosquitoes , lice , ticks , and mites are bioresmethrin , permethrin , tetramethrin , cypermethrin , decamethrin , pyrethrins , resmethrin , cyhalothrin , allethrin , dichlorvos , carbaryl , naled , citrus oils , citronella oil , pine oil , stirofos , fenvalerate , stabilene , benzyl benzoate , methyl nonyl ketone , n - butylacetanilide , di - n - propyl isocinchomeronate , 2 - octylthioethanol , dimethyl carbate , dimethyl phthalate , n , n - diethyl - m - toluamide , and 2 , 3 : 4 , 5 - bis ( 2 - butylene )- tetrahydro - 2 - furfural . many of these active ingredients are effective both as a pesticide and as a repellent , and the activity of many is enhanced by the inclusion of a synergist . especially preferred synergists include piperonyl butoxide and n - octyl bicycloheptene dicarboximide . the active agent may be a liquid or a solid at room temperature . to prepare pest control systems according to the invention , the pest control active agent and the solid fatty acid are mixed together at a predetermined ratio , with the proviso that the fatty acid is present at a high level . generally , the amount of fatty acid in the formulation should be at least about 5 wt %, preferably at least about 15 wt %. the active agent / fatty acid mixture is then heated to a liquid state and added to granules of , small irregularly shaped particles of , or powder form of a low melting polymer or copolymer to make a dry blend . this dry blend formulation may then be processed into a shaped article , such as a pet collar or an ear tag or the like , on a conventional extruder or molding machine at low temperatures ( that is , at temperatures that will melt the low melting polymer or copolymer , which is generally below about 250 ° f .) by methods known in the art . if processing of the shaped article takes place at higher temperatures , the article should be cooled to room temperature as quickly as possible . in some cases when the article is not quickly cooled , there is excessive bloom on the surface , which can flake off . when this happens , the article can be annealed at 140 ° f . as a post operation to prevent the excessive bloom . additional components may optionally be included in the pest control system of the invention . such optional ingredients can include , but are not limited to , plasticizers , synergists , fragrances , coloring agents , preservatives , antioxidants , light stabilizers , and the like . after being processed into the desired shape , the active agent will , together with the solid fatty acid , bloom to the surface of the article , making the active agent available to an environment , such as an animal for example , for pest control purposes , such as , for example , the control of insects and / or acarids on the animal . the fatty acid / active agent combination blooms to the surface and stops until a part of the surface material is removed . when the surface material is removed , it is replaced by more of the combination of the fatty acid / active agent from the inter - matrix of the plastic . the following examples illustrate the practice of the present invention . parts are given as percentages and temperature in degrees fahrenheit unless otherwise noted . “ rt ” is room temperature . the formulation in table 1 is prepared , and is then formed into an insecticidal dog collar , as follows : these collars were subjected to efficacy evaluation against fleas and ticks . the tests consisted of a treated group of three dogs ( one collar per dog ) and a control group of three untreated dogs . the dogs were chosen from random breed adult dogs of mixed sexes and with reasonably uniform haircoat types , and the dogs were individually housed , fed and maintained . the dogs were treated once on day 0 by buckling the test collar around the dogs &# 39 ; necks , leaving at least space for 2 fingers . the dogs were infested with fleas ( ctenocephales felis ) and ticks ( rhipicephalus sanguineus ) on the day before treatment and then re - infested weekly thereafter , each re - infestation to be made approximately 24 hours before the first of the next series of flea and tick counts . flea and tick timed finger counts were performed at 24 and 48 hours after treatment and at 24 hours after each re - infestation . comb counts , by removing and discarding all fleas and ticks , were performed at 72 hours after treatment and after each re - infestation . table i - a three - dog group mean efficacy against fleas day % efficacy 1 53 2 71 3 86 7 79 9 85 14 76 16 87 21 91 23 96 28 79 30 94 35 84 37 91 43 84 45 91 [ 0028 ] table i - b three - dog group mean efficacy against ticks day % efficacy 1 70 2 74 3 76 7 80 9 84 14 90 16 91 21 95 23 96 28 97 30 95 35 91 37 95 43 98 45 99 the formulation in table 2 is prepared , following the procedures of example 1 : the material of the above formulation was subjected to a weigh loss test to ascertain if the non - polymer materials would release from the polymer matrix . the test consisted of extruding the material into dog collars , weighing the collars , wiping the surface of the collars with a clean paper towel and reweighing . the weight difference from each wiping demonstrates the weight loss as it might happen in actual use . a commercial cat pest control collar was similarly tested , as a comparison . while the weight loss of the collar of this invention was lower overall than that of the commercial collar , it followed the same profile of continuous loss over the course of the 25 - day study . also , while it was impossible in this study to ascertain the percent of active agents being released by the wipe test , visual observations show that the released material was a mixture of the oil phase materials and stearic acid . the formulation in table 4 is prepared , and is then formed into an insecticidal dog collar , as follows : 1 . the gokilaht , phosflex , stearic acid and nylar are weighed and added to a heatable mixing vessel . the materials are heated to 165 ° f . and mixed until a honogenous solution is achieved . 2 . the mu 760 - 00 and the elvax 150 polymers are weighed , placed into a mixing vessel and blended to uniformity . 3 . while the polymers are mixing , the heated liquid active agent / stearic acid mixture is sprayed onto the polymers . mixing continued until the mass reached room temperature . 4 . the liquids should be applied to the polymer powder while the polymers are being mixed , so as not to cause large lumps to form . this should be done far enough in advance of extrusion ( generally about 24 hours is sufficient ) so that the liquids can solidify and a free - flowing powder is achieved . the resulting formulation was extruded into dog collars . the extrusion profile is : extruder : prodex 2½ inch ; pe screw 24 / 1 single stage ; screw rpm = 30 zone temperatures : # 1 # 2 # 3 # 4 # 5 gate die off off off 205 205 195 195 screen pack : 1 - 40 2 - 80 collar dimensions and weight : 1 in . × 0 . 513 in . × 0 . 109 in . − 0 . 748 grams ; oval shape
the present invention is directed to a pest control system comprising a low melting point polymer or copolymer , high levels of a solid fatty acid , and active compounds to produce a solid slow release generator of the active compounds .