GB1594737A - Method for producing insect-combating device - Google Patents

Description

(54) METHOD FOR PRODUCING INSECT COMBATTING DEVICE (71) We, A. H. ROBBINS COMPANY, INCORPORATED, a Corporation organised and existing under the laws of the State of Virginia, United States of America, of 1407 Cummings Drive, Richmond, Virginia 23220, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process for the preparation of an insecticidecontaining device such as a pet collar for the control of fleas or ticks on warm blooded animals or a pest strip or the like for the control of common houseflies (Musca domestica), fruit flies (Drosphila melanogaster), mosquitoes (Culex pip lens) or the like. In particular, this invention relates to a novel process for the manufacture of a shaped body comprised of a synthetic resin having dispersed therein the insecticide 1,2-dibromo-2,2-dichloroethyl dimethyl phosphate, commonly known as naled, alone or in combination with one or more other insecticides.

Heretofore, insect-combatting devices, such as pet collars, pest strips and the like, comprised of a polyvinyl chloride (PVC) resin having a dispersion of the insecticide dimethyl 2,2,-di-chlorovinyl phosphate, commonly known as DDVP or by its trade mark VAPONA, have been widely used for the purpose of controlling fleas and flying insects such as houseflies, mosquitoes and the like in the vicinity of the device. However, DDVP has been reported to have an objectionable depressing effect on the plasma and red cell cholinesterase at least in animals, which effect is particularly acute at the high concentrations which are produced during the first few days after a pest strip has been exposed to the atmosphere. This is believed due to the fact that the liberation rate of DDVP from presently available DDVP.containing pest strips is not uniform but rather is higher during the first few days after activation, i.e. removal of the pest strip from the packing and exposing it to the atmosphere. There are also indications that DDVP may be harmful to humans and pest strips containing DDVP have been banned in Holland. Moreover, the aforementioned initial high liberation rate represents an unduly rapid loss of insecticide and shortens the period over which DDVP is liberated at a rate sufficient to control pests effectively. DDVP has also been found to possess a high degree of residual toxicity in the area of the device, apparently from adsorption of the DDVP vapours in walls, floors, ceilings, curtains, rugs and the like. Even after a DDVP-containing device is removed from a room, residual DDVP vapours can often be detected for several days.

It has also been suggested to utilize other insecticides such as naled in an insect-combatting device. The preparation of naled is described in U.S. patent No.

2,971,882 (Osmonson et al) and PVC resin-naled combinations have been proposed for use as an insecticide of a general nature in French patent No. 1,568,198, and British patent No. 955,350. Netherlands published application No. 6,610,279 discloses fly strips composed of PVC-naled as well as PVC-DDVP combinations which are stated to have such high insecticide release rates as to require an outer laminate layer to retard the insecticide release. U.S. patent No. 3,344,021 discloses PVC-naled combinations for use as an anthelmintic composition.

A number of problems have been encountered in providing a commercially satisfactory PVC resin-naled combination for use in an insect-combatting device.

First, there must be a sufficient amount of naled released to provide effective control of the insects in the vicinity of the device. Contrary to statements in prior art disclosures, it has been found that release rates for naled are very much lower than the release rates for DDVP. Naled has a low vapour pressure of about 2x 10-4 mm. Hg. at 200C. as compared to that for DDVP of 1.2x10-2. Naled vapour pressure is thus only about 1.7% of the vapour pressure of DDVP.

It has further been found that the inclusion of an insecticide such as naled in a synthetic resin matrix in amounts sufficient to control insects for a commercially acceptable time leads to exudation of liquid insecticide (or "spew") on the surface of the device. These liquid droplets pose serious environmental and aesthetic problems as well as significantly decreasing the effective life of the device.

The applicants copending application No. 44883/76 (Serial No. 1563497) relates to an improved insect-combatting device for use against houseflies, gnats, mosquitoes and the like of a shaped solid body having a porous surface capable of gradually and continually releasing naled insecticide in an amount sufficient to provide an insecticidally active concentration of naled over a prolonged period of time, the device comprising a synthetic resinous matrix material, from about 15 to about 35 weight percent of naled and a minor amount effective to retard spewing of the insecticide of finely divided silica and at least one C,4 to C20 saturated aliphatic carboxylic acid or a salt or ester thereof. The device is formed from a mixture of the synthetic resin, naled, finely divided silica particles, C,4 to C20 aliphatic saturated carboxylic acid or salt or ester thereof and a surface porosity control component. The surface porosity control component is non-reactive in the mixture and has a boiling point at or below the curing temperature such that it produces surface openings in communication with pores in the body by vaporization and provides for release of naled gas at a rate effective to control insects in the vicinity of said body, but insufficient to form as spew on the body.

The applicants U.K. patent specification No. 1444038 relates to an improved flea control collar for a warm blooded animal which comprises a strip of a length sufficient to encircle the neck of the animal and clamping means at or near one end of the strip for engaging a portion of the strip spaced from the clamping means to prevent loss of the collar from the animal, the strip comprising a mixture of a flexible synthetic resin and between 5 and 25 percent by weight of the strip of naled and the strip having surface openings in communication with pores in the strip whereby, upon use of the strip as a collar, the strip releases naled vapour at a rate effective to control fleas on the animal but insufficient to form as droplets on the strip or to be toxic to the animal.

As is shown by the foregoing, insect-combatting devices may be formed by a variety of techniques. However, an unexpected problem found with a PVC-naled composition is the tendency of the resin to decompose during the shaping process.

For example, unsatisfactory results were obtained in early tests where naled was substituted for DDVP in PVC combinations employed in extrusion apparatus used for making PVC-DDVP pet collars known in the art. Burning and charring of the extrudate were found to occur during curing of the collars, and the finished collar underwent an unexplainable reduction in the naled concentration as compared with the naled concentrate in the original mixture.

According to the present invention, a process for forming a shaped solid body having a porous surface capable of gradually and continually releasing naled insecticide in an amount sufficient to provide an insecticidally active concentration of naled over a prolonged period of time, comprises extruding a mixture of a synthetic resinous matrix material, from 5 to 35% by weight of naled (based on the weight of the mixture) and a surface porosity control component that is nonreactive in the mixture and has a boiling point at or below the curing temperature to produce surface openings in communication with pores in the said body by vaporization of the porosity control component to provide for release of naled gas at a rate effective to control insects in the vicinity of said body, but insufficient to form as spew on the body, the mixture being extruded in an extruder of which all of the surfaces which contact the mixture are formed of an acid resistant material.

According to a further aspect of the invention is a process for forming a shaped body of a mixture of from 20 to 80 weight percent of a polyvinyl chloride matrix material; from 5 to 35 weight percent of naled and from 0.8 to 5 weight percent of a surface porosity control component that is non-reactive in the mixture and has a boiling point at or below the curing temperature to produce surface openings in communication with pores in said body by vaporisation of said porosity control component to provide for release of naled gas a rate effective to control insects in the vicinity of said body, but insufficient to form as spew on the body and finely divided silica particles, in which the mixture is extruded in an extruder of which all of the surfaces which contact the mixture are formed of an acid-resistant material. The invention also extends to shaped naled containing bodies formed by the method of the present invention.

The term "extrusion surfaces" is used to define those surfaces of an extruder which in normal operation are contacted by the resin/naled mixture being extruded.

As noted above, extrusion of PVC-naled compositions in extrusion apparatus used for making PVC-DDVP pet collars known in the art has resulted in burning and charring of the extrudate and degration of the naled contained therein. It has been found that in the presence of heat and moisture, naled becomes acidic and extremely corrosive, especially to carbon steel which is the standard material for most parts of polymer extruders. In addition, under these conditions, naled can initiate autocatalytic degradation of PVC resin. However, the extrusion of naledcontaining compositions as disclosed herein in an extrusion apparatus having all of its surfaces in contact with the naled-containing composition formed of an acidresistant material results in a uniform, highly satisfactory extruded product with minimal indications of any burning, charring or naled degradation. The process of the present invention is also useful for the extrusion of mixtures containing not only naled but also other insecticides to obtain an extruded product which is uniform, reproducable and relatively constant in naled content.

The successful extrusion of naled-containing compositions offers a number of advantages as compared to other types of polymer-forming techniques, for example, casting of a plastisol dispersion. Extrusion is relatively fast and is adapted to be used with both dry and liquid (plastisol) blends. Rapidity of formation is advantageous not only because of the greater yield of acceptable product in a particular unit of time but also because the longer a naled-containing composition is maintained at an elevated temperature, the greater the likelihood that some of the naled will degrade. In addition, extrusion may be used to produce a variety of sizes and shapes which are unsuitable for production by casting. A number of other advantages of extrusion will be apparent to those skilled in the art.

The components making up a satisfactory insecticide-containing insectcombatting device include a synthetic resin that is compatible with the relatively high amounts of insecticide and of a strength sufficient to maintain the integrity of the shaped device throughout the period during which the insecticide is released in amounts effective to combat insects and arachnids, e.g. fleas/ticks, flies or mosquitoes. The shaped insect-combatting device includes the synthetic resin in a concentration sufficiently large to give the device physical properties such as strength, flexibility, and freedom from tackiness so as to make it suitable for use as an insect-combatting device. Generally, the shaped device contains from 20 to 80, preferably from 25 to 60, weight percent of the synthetic resin.

The various known synthetic resins which can be used in the insect-combatting device include materials such as polyethylene, polypropylene, copolymers of ethylene and propylene, nylon, Cellophane (Registered Trade Mark), Polyacrylates, such as polymers and copolymers of methylacrylate, ethylacrylate, methylmethacrylate and ethylmethacrylate; polymers of vinyl compounds, such as polystyrene, polymerized divinylbenzene; polyvinyl halogenides, such as polyvinylchloride, polyvinyacetals, such as polyvinylbutyral; polyvinylidene compounds, such as polyvinylidenechloride; polyvinylacetate; ethylvinylacetatevinylacetate copolymers; copolymers of vinylchloride and vinylacetate; polyurethanes, polyaldehydes; and other thermoplastics.

Polyvinylchloride (PVC) homopolymers and copolymers with other polymers such as polyvinyl acetate (PVA) are preferred synthetic resin materials. Suitable PVC resins are commercially available and include, for example, PVC homopolymer dispersion resin Firestone (Registered Trade mark) FPC-6337TM and FPC-9290TM available in U.S.A. from Firestone Plastics Co., PVC homopolymer dispersion resin Diamond (Registered Trade Mark) PVC-7502TM and PVC homopolymer extender resin Diamond PVC7A46TM, both available in U.S.A. from The Diamond Shamrock Co., PVC homopolymer extender resin Borden 2605TM available in U.S.A. from the Borden Co. and FLO-WEL 405 resin available in U.S.A. from Air Products and Chemicals Co., and mixtures thereof. Other suitable commercially available PVC resins are known in the art. Suitable PVC-PVA copolymers are also commercially available in U.S.A. and include, for example, Geon (Registered Trate Mark) 135 (Goodrich Corp.), PVC-74 (Diamond Alkali Co.) and XR-6338 (Exxon-Firestone) (Registered Trade Mark). Other PVC-PVA copolymers are also known in the art.

The improved insect-combatting device of the present invention contains naled (1,2-dibromo-2,2-dichloroethyl dimethyl phosphate) insecticide in an amount sufficient to provide an insecticidally active concentration of the insecticide over a prolonged period of time, which amount can be from 5 to 35, preferably 15 to 30, weight percent insecticide.

One or more other insecticides compatible with the naled-containing composition may also be included. For example, the composition may also contain from 2 to 12 weight percent of a carbamate insecticide (further defined below).

Carbamate insecticides which may be utilised are disclosed in U.S. Patent 3,852,416. Neither insecticide adversely affects the mode of emission of the other from the resin matrix. The carbamates are emitted from the surface of the device primarily as powders and are substantially free of naled. The carbamate does not interfere with release of vaporous naled.

Carbamates useful in combination with naled in the present invention are represented by the formula:

wherein; R' is aryl, substituted aryl, heterocyclic or substituted heterocyclic groups, R2 is hydrogen or lower alkyl, and R3 is lower alkyl.

The term "lower alkyl" as used herein refers to an alkyl group, branched, or straight chain, having a chain length of one to six carbon atoms. The term "aryl" as used herein refers to an aryl group such as phenyl or naphthyl. The term "substituted aryl" as used herein refers to a phenyl or naphthyl group substituted with one or more groups such as lower alkyl, halogen, lower alkoxy, lower alkylamino, lower dialkylamino or lower alkylthio. The term "heterocyclic" as used herein refers to an organic cyclic group having an oxygen atom, sulphur atom or one or two nitrogen atoms in the nucleus thereof and containing up to twelve carbon atoms. The term "substituted heterocyclic" as used herein refers to a heterocyclic group substituted with one or more groups such as lower alkyl, lower alkoxy, lower alkythio, lower alkylamino, lower dialkylamino carbamoyl or alkyl substituted carbamoyl or halogen.

Typical of the carbamates which can be used in the present invention are: 2-isopropylphenyl-N-methyl carbamate 2-isopropoxyphenyl-N-methyl carbamate 3-( 1 -methylbutyl)phenyl-N-methyl carbamate 3-( 1 ethylpropyl)phenyl.N-methyl carbamate 6-chloro-3,4-xylenyl-N-methyl carbamate 4-methylthio-3,5-xylenyl-N-methyl carbamate l-naphthyl-N-methyl carbamate l-naphthyl-N-ethyl carbamate l-naphthyl-N-isopropyl carbamate l-naphthyl-N-butyl carbamate l-naphthyl-N-hexyl carbamate l-(4-chloronaphthyl)-N-methyl carbamate 1 -(5,6-dihydronaphthyl)-N-methyl carbamate 1 -(5,8-dihydronaphthyl)-N-methyl carbamate 4-benzothienyl-N-methyl carbamate 2,2-dimethyl-1,3-benzodioxol-4-ol methylcarbamate 1 -phenyl-3-methylpyrazol-5-yl-N,N-dimethyl carbamate 2.(N,N-dimethylcarbamyl)-3-methyl-pyrazol-5-yl-N,N-dimethyl carbamate 3,4-xylyl methylcarbamate n-cym-5-yl methylcarbamate o-chlorophenyl methylcarbamate The preparation of carbamates of the above formula has been previously described, for example in U.S. Patents 2,903,478 and 3,203,853.

The preferred carbamates are 2-isopropoxyphenyl-N-methyl carbamate known as propoxur (or SendranTM) and l-naphthyl-N-methyl carbamate known as carbaryl (or Sevin) (Registered Trade Mark).

As noted before, the naled-containing composition fed to the extruder may be in the form of either a liquid (plastisol) dispersion or a dry powder blend with the latter being preferred. Synthetic resins, e.g., PVC, are generally available in the form of dry powders while naled, the porosity control component and resin plasticizer are generally available in liquid form. The carbamate insecticides, when utilized, are generally available in liquid form or as a powder with the carbamate being absorbed on or mixed with porous inert carrier particles, e.g., silica particles.

Plastisol formulations of these components may be prepared in a manner wellknown to those skilled in the art. Generally, the liquid components are first mixed together and then the powder component (or mixture of powder components if more than one is used) is stirred into the liquid mixture gradually until a uniform plastisol dispersion results.

The dry powder blend for extrusion may be prepared by forming a uniform plastisol as above, homogenizing the plastisol into a paste in a suitable mixing device (e.g., a Hobart mixer) and drying the paste in an oven at a moderately elevated temperature, e.g., from about 140 to 1750, preferably from about 1500 to about 170",F., to form free-flowing powder which may be directly fed into the extruder. As will be apparent to those skilled in the art, the amount of naled in a particular extruded shaped body will vary depending upon the particular use for that body. That is, when the extruded shaped body is to be utilized as a collar for cats, the naled concentration is generally in the lower portion of the range (e.g., from 5 to 15 weight percent naled). Similarly, the concentration of the carbamate insecticide, if utilized, will be in the lower portion of the range (e.g., from 2 to 3.5 weight percent) for cat collars. Dog collars generally contain a higher amount of naled (e.g., from 15 to 25 weight percent naled) and similarly higher amounts of carbamate, if utilized, e.g., from 3.5 to 12 weight percent while pest strips generally contain the highest amounts of naled (e.g., from 20 to 35 weight percent naled).

Generally, the utilization of naled insecticide in amounts of from about 15 weight percent, more usually from 25 to 35 weight percent, in a synthetic resin matrix leads to liquid naled droplets or "spew" formation on the surface of the insect-combating device. Liquid droplets of naled insecticide forming on the surface of the shaped device pose a substantial health and safety hazard as well as diminished insecticidal efficiency. The insect-combatting device of the present invention can also include a minor amount effective to retard spewing of the insecticide of finely divided silica particles and at least one C,4 to C20 saturated aliphatic carboxylic acid or a salt or ester thereof and with those exhibits a substantially lessened tendency towards formation of liquid droplets of naled insecticide on its surfaces when the naled is contained in these generally higher amounts.

Although silica is known in the art, along with a number of other minerals and glasses, as a filler for various synthetic resins, it has unexpectedly been found that -finely divided silica particles generally having a particle size of from about 1 to about 50, preferably from about 2 to about 10, microns, exhibit a high degree of relative efficiency in retarding insecticide spewing when utilized in sufficient amounts, which spew-retarding amounts are generally in the range of from 10 to 35, preferably from about 15 to about 25, weight percent of the insect-combatting device. It has been found that utilization of finely divided silica particles in an amount of less than about 10 percent by weight is generally ineffective to provide any significant retardation of the insecticide spew while utilization of finely divided silica particles in an amount above about 35 percent by weight does not result in any further reduction in spew formation.

While the addition of the finely divided silica particles exhibit a high degree of relative efficiency in retarding naled insecticide spewing, a small amount of the naled insecticide may nonetheless sometimes exude from the insecticide containing device. It has also been found that the utilization of the C,4 to C20 saturated aliphatic carboxylic acid alone (i.e., without the finely divided silica particles) with the resin and insecticide in the insect-combatting device of the present invention is insufficient to retard effectively spewing of the naled insecticide from the device. The utilization of a minor amount of both the finely divided silica particles and the C14 to C20 saturated aliphatic carboxylic acid has however been found to possess a high efficiency for insecticide spew retardation and effectively to maintain the surface of the device free of liquid droplets of the insecticide.

The C,4 to C20 saturated aliphatic carboxylic acid, which can be a mixture of such acids, is generally utilized in an amount of from .0.25 to 3, preferably from 0.5 to 1.5, weight percent in the device. Stearic acid and palmitic acid are preferred.

In the embodiments where polyvinyl resins are used, plasticizers and other additives commonly used for providing the flexibility, strength and surface characteristics desired for an insect-combatting device are well known to those. skilled in this art, and no further discussion is deemed necessary here. Suitable plasticizers include esters of phosphoric acid such as tricresyl phosphate and esters of phthalic acid such as dioctyl phthalate. Other esters such as those of adipic acid, azelaic acid, maleic acid, ricinoleic acid, myristic acid, and trimellitic acid as well as complex linear polyesters, polymeric plasticizers and epoxidized soybean oils may be used. In addition, colouring and odour control agents may also be employed to enhance consumer acceptance.

As noted above, naled has a low vapour pressure. The naled release rate from a PVC-naled device is comparatively low and may be inadequate for a commercially acceptable insect-combatting device. The use of an additive in the mixture can be very helpful in increasing the naled release rate and makes possible both effective insect control at lower initial naled concentrations and an insect-combatting device having an increased effective life.

The additive, also referred to as a surface porosity control component, is present in the final mix used in forming the device, and hence must be non-reactive with the other components.of the dispersion or mix. The main function of the additive is to provide a surface porosity which preferably includes pores extending part way into the body of the device. The desired surface characteristics are obtained by the vaporization of the additive during the curing period. Hence the additive should comprise one or more compounds having a boiling point at or below the curing temperature of the resin.

Compounds which are suitable as the surface porosity control component in PVC resins which are cured at a temperature in the range of between about 260 to 400"F. include aldehydes and their lower alkyl acetals containing bromine or chlorine, generally having a boiling point of from about 1700 to about 400 , preferably from about 185 to about 350",F. The porosity control component may thus include one or more of the following which have approximate boiling point temperature as set forth: Name B.P. F. chloroacetaldehyde 185 dichloroacetaldehyde 192 chloral 218 bromoacetaldehyde 176-221 dibromoacetaldehyde 346 bromal 320 bromodichloroacetaldehyde 258 chlorodibromoacetaldehyde 299 bromochloroacetaldehyde 233 2-bromopropanol 229 The surface porosity control component is included in the naled-containing synthetic resin composition in an amount sufficient to produce sufficient surface porosity by its vaporization during curing of the dispersion to effectively increase the release rate of naled gas from the formed device. While the amount of the porosity control component to be used depends on the density of surface openings desired and somewhat on the particular procedure used for curing the resin, it is generally from 0.8 to 5, preferably from 1 to 3, weight percent of the dispersion.

The mixture is formed into a shaped body by extrusion through an extruder in which all of the surfaces which may come in contact with the naled-containing synthetic resin mixture (e.g., the feed hopper, barrel, screw, die and the like) are formed of or coated with an acid-resistant material. When the shape of the extruded body is solid, i.e., without defined internal hollows or passages, the extruder apparatus can be of any conventional type known to those skilled in the art for extruding synthetic resin mixtures. If the extruded body contains any internal hollows or passages, a cooling chamber should be provided at the exit end of the die to rapidly cool the extruded material which has a relatively low hot strength at conventional extrusion temperatures. In any case, it is critical that the extrusion be conducted in the presence of acid-resistant materials.

The acid-resistant material can be any conventional metal, metal alloy or nonmetallic material which is resistant to the acidic nature of the naled material.

Typically, the acid-resistant material will be aluminium, nickel or stainless steel or various alloys thereof (e.g., Xaloy, Hastelloy, Stellite (Registered Trade Marks) or the like), nickel-plated alloys, ceramics or glass. Nickel-based alloys such as Xaloy 101 or nickel alloys containing tungsten carbide particles are especially suitable for the construction of parts such as the barrel where high abrasion resistance is required. The component parts of the extruder apparatus may be formed entirely of this material or the naled-contacting parts may be coated or plated with this material.

Extrusion may be performed under pressure and temperature conditions sufficient. to produce an extruded, cured body from the synthetic resin-naled mixture. Extrusion may be carried out, for example, at a temperature of from 200 to 350, preferably from 240 to 310,OF. and a die pressure of from 200 to 900, preferably from 400 to 750, psig.

The invention is additionally illustrated in the following Examples: EXAMPLE I A mixture (in parts by weight) of 40 p.b.w. polyvinyl chloride homopolymer dispersion resin 15 p.b.w. polyvinyl chloride homopolymer blending resin 20.5 p.b.w. dioctyl phthalate (DOP) 2.5 p.b.w. epoxidized octyl tallate (EPO) 1 p.b.w. calcium-zinc stabilizer 21 p.b.w. naled (1,2-dibromo-2,dichloroethyl dimethyl phosphate) 2 p.b.w. bromodichloroacetaldehyde is thoroughly triturated to form a plastisol dispersion. The plastisol dispersion is fed to a conventional type plastics extruder which has a one inch barrel with an Xaloy 800 (a commercially available nickel-based alloy containing tungsten carbide particles) liner, an aluminium die and a nickel plated screw with stellite flights such that the plastisol dispersion is fed into and extruded through the extruder in contact only with surfaces of acid-resistant material. The dispersion is extruded at a die temperature of about 265"F and a die pressure of about 600 psig to form a solid, essentially rectangular cross-section shape. The colour of the extrudate is light brown and discernably lighter than similar shapes produced with similar mixtures by casting or injection molding. The lighter colour of the extruded shape indicates 9.0 p.b.w. di-2-ethylhexylphthalate 2.5 p.b.w. epoxidized octyl tallate 1.0 p.b.w. Bentone (Registered Trade Mark) 28.0 p.b.w. naled 2.0 p.b.w. surface porosity control component (e.g., bromodichloroacetaldehyde) 25.0 p.b.w. amorphous silica particles, average particle size, 2.35 microns 1.5 p.b.w. palmitic acid is formed into a uniform plastisol dispersion by first mixing the liquid components, adding the stabilizer and then generally mixing a mixture of the other dry components. The plastisol is extruded in the extruder and under the conditions as used in Example I.

Analysis of the resulting extruded shape shows the naled content to be 26% by weight and the extrudate is suitable for use as a dog collar.

EXAMPLE III A mixture (in parts by weight) of 36.0 p.b.w. polyvinyl chloride homopolymer dispersion resin 15.0 p.b.w. polyvinyl chloride homopolymer extender resin 19.0 p.b.w. dioctyl phthalate 3.0 p.b.w. epoxidized octyl tallate 1.0 p.b.w. calcium-zinc stabilizer 19.0 p.b.w. naled 2.0 p.b.w. bromodichloroacetaldehyde 5.0 p.b.w. propoxur (a powder of 90% 2-isopropoxyphenyl N-methyl carbamate and 10% amorphous silica) is formed into a uniform plastisol dispersion by first mixing the liquid components, adding the stabilizer and then gradually mixing a mixture of the other dry components. The plastisol is extruded in the extruder and under the conditions as used in Example I.

Analysis of the resulting extruded shape shows the naled content to be 18% by weight and the propoxur content to be 4.5% by weight. The extrudate is suitable for use as a dog collar.

EXAMPLE IV Example III is repeated using a mixture (in parts by weight) of 42.0 p.b-.w. polyvinyl chloride homopolymer dispersion. resin 16.0 p.b.w. polyvinyl chloride homopolymer extender resin 21.0 p.b.w. dioctyl phthalate 3.0 p.b.w. epoxidized octyl tallate 1.0 p.b.w. calcium-zinc stabilizer 12.5 p.b.w. naled 1.5 p.b.w. bromodichloroacetaldehyde 3.0 p.b.w. propoxur The plastisol is extruded as described in Example I. The extrudate contains 12 weight percent naled and 2.5 weight percent propoxur.

EXAMPLES V-XII Mixtures are made of the formulations shown in Table I. In each case, the liquid components (plasticizers, naled and surface porosity control component) are uniformly mixed with the stabilizer, stearic acid, carbamate powder (propoxur) and silica. The polyvinyl chloride resins, which in these Examples are dry powders, are uniformly mixed and added to the liquid mixtures. The total mixture is then homogenized into a paste in a hobart mixer. The paste is dried into free-flowing powder particles in an over at 1600F. The particles are then fed directly into the extruder of Example I or cooled for later use in such an extruder. The powder is extruded under the conditions of Exampie I.

In Examples V, VI, XI and XII, a low molecular weight homopolymer resin is added, as the blending resin, to reduce fusion temperature. In Examples VII, VIII, and IX, propylene-vinyl chloride copolymers are added to increase the melt flow of the mixture. The small amounts of silica and stearic acid are added to reduce the difflsionat resistance of naled in the pdlyvinyl chloride matrix and as a lubricant, respectively.

Each of the extruded samples shows a porous surface and when assayed shows a very-little loss in naled content (i.e., about 1% or less in each case) from that originally added. The extruded samples are suitable for use as pet collars.

Bromodichloro Polyvinyl Chloride Acetaldehyde Finely Resin p.b.w. Vinyl Chloride- Surface Porosity Divided Example Dispersion Blending Propylene Co- Plasticizers Naled Propoxur Control Agent Stabilizer, Stearic Silica No. Resin Resin polymer p.b.w. p.b.w. p.b.w. p.b.w. Compound, pbw Acid pbw Particles V 34.9 23.0 - 22 16.2 - 1.8 Magnesium Zinc 1.9 0.2 VI 35.0 22.3 - 22.5 16.2 - 1.8 " 0.5 0.2 1.5 VII 38.4 - 21.0 22.0 16.2 - 1.8 Calcium Zinc 0.5 0.1 VIII 37.5 - 17.5 24.0 16.2 - 1.8 Barium Cadmium 1.0 - 2 IX 35.9 - 23.0 20 17.1 - 1.9 Magnesium Zinc 2 0.1 X 20 11 - 12.5 28 - 2 1.5 25 XI 35.5 20.4 - 21.0* 16 5.0** 1.6 Calcium Zinc 0.5 - XII 42.0 21.0 - 24.0* 8.5 3.0** 1.0 " 0.5 - * Includes 3.0 p.b.w. epoxidized octyl tallate stabilizer ** Includes 10 weight percent (of the total amount of propoxur) of silica particles EXAMPLE XIII The mixture and procedure of Example X is repeated except that 30 weight percent of a technical grade of naled (l,2-dibromo-2,2-dichloroethyl dimethyl phosphate) commercially available from the Chevron Company is used. This product is known to contain certain impurities such as bromodichloroacetaldehyde, chloral, carbon tetrachloride and various forms of phosphates. These impurites constitute about 9 weight percent of the product and in large part are sufficiently volatile as to be released during the extrusion of the mixture and hence not to interfere with the functioning of the collar.

The device formed in the manner indicated contains about 26 weight percent naled.

COMPARATIVE EXAMPLE A mixture similar to that used in Example V with about 54 weight percent polyvinylchloride resin, 19 weight percent dioctyl phthalate, 3 weight percent epoxidized octyl tallate stabilizer, 1 weight percent of antioxidant and 23 weight percent technical grade of naled (as in Example XIII) is extruded in a conventional extruder used for making pet collars of polyvinyl chloride and DDVP (dimethyl 2,2dichlorovinyl phosphate), which extruder is formed primarily in its mixturecontacting surfaces of plain carbon steel which is not acid-resistant. Burning and charring of the extrudate are found to occur and the extruded collar contains significantly less naled (about 18 weight percent) than originally present. In the presence of heat and moisture, the naled becomes acidic and extremely corrosive, especially to carbon steel thus resulting in naled and steel degradation. Also, the naled initiates autocatalytic degradation of the PVC resin.

Claims (17)

WHAT WE CLAIM IS:

1. A process for forming a shaped solid body having a porous surface capable of gradually and continually releasing naled insecticide in an amount sufficient to provide an insecticidally active concentration of naled over a prolonged period of time, comprising extruding a mixture of a synthetic resinous matrix material, from 5 to 35% by weight of naled (based on the weight of the mixture) and a surface porosity control component that is non-reactive in the mixture and has a boiling point at or below the curing temperature to produce surface openings in communication with pores in the said body by vaporization of the porosity control component to provide for release of naled gas at a rate effective to control insects in the vicinity of said body, but insufficient to form as spew on the body, the mixture being extended in an extruder of which all of the surfaces which contact the mixture are formed of an acid resistant material.

2. A process as claimed in Claim 1 wherein the mixture further includes at least one other insecticidally active material.

3. A process as claimed in Claim 2 wherein the mixture further includes at least one carbamate insecticide having the structural formula:

wherein; R' is aryl, substituted aryl, heterocyclic or substituted heterocyclic groups, R2 is hydrogen or lower alkyl (as hereinbefore defined), and R3 is lower alkyl.

4. A process as claimed in Claim 3 wherein the carbamate insecticide is present in an amount of from 2 to 12% by weight, based on the weight of the mixture.

5. A process as claimed in any of the preceding Claims wherein the synthetic resinous matrix material is a polyvinyl chloride.

6. A process as claimed in Claim 5 wherein the surface porosity control component has a boiling point of from about 1700 F up to the curing temperature of the polyvinyl chloride synthetic resinous material.

7. A process as claimed in any of the preceding Claims wherein the surface porosity control component is chloroacetaldehyde, dichloroacetaldehyde, chloral, bromoacetaldehyde, dibromoacetaldehyde, bromal, bromodichloroacetaldehyde, chlorodibromoacetaldehyde, bromochloroacetaldehyde or 2-bromopropanol or a mixture thereof.

8. A process as claimed in any of the preceding Claims wherein said mixture contains from 15 to 35% by weight naled, from 10 to 35% by weight of finely divided silica particles, from 0.25 to 3% by weight of at least one C14 to C20 aliphatic saturated carboxylic acid or a salt or ester thereof and from 0.8 to 5% by weight of the surface porosity control component.

9. A process as claimed in any of the preceding Claims wherein the mixture is extruded at a temperature of from 200 to 3500 F.

10. A process as claimed in Claim 9 wherein the mixture is extruded at a temperature of from 240 to 3100F.

11. A process as claimed in any of the preceding Claims wherein the mixture is formed into a dry powder mixture prior to extrusion.

12. A process as claimed in Claim 11 wherein the dry powder mixture is formed by homogeneously combining the components of the mixture and then drying the homogeneous combination.

13. A process for forming a shaped body of a mixture of from 20 to 80% by weight of a polyvinyl chloride matrix material; from 5 to 35% by weight of naled .and from 0.8 to 5% by weight of a surface porosity control component that is non reactive in the mixture and has a boiling point at or below the curing temperature to produce surface openings in communication with pores in said body by vaporization of said porosity control components to provide for release of naled gas at a rate effective to control insects in the vicinity of said body, but insufficient to form as spew on the body and finely divided silica particles, in which the mixture is extruded in an extruder of which all of the surfaces which contact the mixture are formed. of an acid-resistant material.

14. A process as claimed in Claim 13 wherein the mixture further includes at least one carbamate insecticide having the structural formula:

wherein R' is aryl, substituted aryl, heterocyclic or substituted heterocyclic groups, R2 is hydrogen or lower alkyl (as hereinbefore defined), and R3 is lower alkyl.

15. A process as claimed in Claim 14 wherein the carbamate insecticide is present in an amount of from 2 to 12 weight percent.

16. A process for forming a shaped resinous naled containing body substantially as described in Examples 1 to XIII.

17. A shaped resinous naled containing body formed by the method of any of Claims 1 to 12, 13 to 15 or 16.