US3558540A

US3558540A - Plastic impression compositions

Info

Publication number: US3558540A
Application number: US775489A
Authority: US
Inventors: Eugene J Molnar
Original assignee: EUGENE J MOLNAR
Current assignee: EUGENE J MOLNAR
Priority date: 1968-11-13
Filing date: 1968-11-13
Publication date: 1971-01-26
Anticipated expiration: 1988-01-26
Also published as: GB1232808A; DE1769736B2; DE1769736A1

Abstract

NEW PLASTIC COMPOSITIONS ARE DISCLOSED WHICH CAN BE USED FOR TAKING IMPRESSIONS WHILE THE COMPOSITION IS INITS PLASTIC STAGE, SAID COMPOSITION INCLUDING A SOLID RESIN AND A SOLVENT SYSTEM WHICH INCLUDES AN EXTENDER AND A BENZYL RADICAL COMPOUND SUCH AS BENZYL ALCOHOLS, BENZYL ETHERS, BENZYL KETONES, BENZYL ALDEHUDES, AND BENZYL ESTERS. THE SOLVENT SYSTEM LEADS TO A CONTROLLED EARLY SETTING, AND INPARTS IMPROVED PROPERTIES TO THJE PLASTIC COMPOSITION FOR TAKING IMPRESSIONS, PARTICULARLY OF LIVING ANATOMICAL STRUCTURES.

Description

3,558,540 PLASTIC IMPRESSION COMPOSITIONS Eugene J. Molnar, 713 S. Stone Ave., La Grange, Ill. 60525 No Drawing. Continuation-impart of application Ser. No.

607,883, Jan. 9, 1967. This application Nov. 13, 1968,

Ser. No. 775,489

Int. Cl. C08f 21/04, 45/34 US. Cl. 260-23 6 Claims ABSTRACT OF THE DISCLOSURE The present invention is in the field of plastic impression compositions, particularly plastic compositions used to make anatomical impressions for making later reproductions. This application is a continuation-in-part of copending US. application, Ser. No. 607,883, filed Jan. 9, 1967, now abandoned, and by the same applicant.

The plastic compositions of this invention will be particularly directed to the use of the compositions for taking impressions of the ear. It should be understood that such a description and discussion relative to the ear may likewise be extended to taking other anatomical impressions or other equivalent uses, for example, mouth impressions, or use as dental issue conditioners and temporary denture liners.

The art has devised methods for taking ear impressions, for example, as parts for hearing aid devices; and the art has generally used the materials developed in the dental art for taking impressions of the mouth. Special techniques and training have been developed in the dental art for taking dental impressions, and these techniques and training do not successfully meet all the problems in taking ear impressions. Special problems are encountered in taking dental impressions which are not necessarily the same or may be altogether different in the ear impression art. For example, the dental practitioner never contacts the mouth parts which are to be later copied with the impression material alone. The dental practitioner uses trays or similar devices to introduce the plastic impression material into the mouth, therefore, the plastic impression material is confined during the impression taking step. The use of the tray is important for taking mouth impressions because the practitioner is able to evenly distribute the material, and to employ an equalized pressure in the distribution of the impression material against the parts of the month which will be reproduced. These procedures are required in order to obtain an accurate reproduction of any part of the mouth.

The average practitioner in the hearing aid field has limited training in such impression techniques and limited knowledge of the nature and physical properties of the impression materials which are required for successful practice.

In the hearing aid field, the plastic impression material is generally worked into the ear canal and against the outer areas of the ear with the fingers while in the plastic deformable or mold making stage. Such plastic impression material is not confined with a tray and, consequently, the pressure on the impression material is not evenly dis- United States Patent Olfice Patented Jan. 26, 1971 tributed. After the practitioner obtains his ear impression, he generally surrounds it with an investment which is usually a mixture of modified plaster and water. This mixture is allowed to set or harden and] the impression is then withdrawn from the mold cavity which has been formed by the investment material around the impression. The negative mold is then used for reproducing the positive hearing aid or other insert called the ear mold, for example.

The dental impression materials now available do not adequately serve for the above purposes for several reasons. These reasons include the problem of tackiness of the dental impression materials which makes hand manipulation difiicult, and which presents a problem of the plastic impression material adhering to the dry ear surface. In general, the dental impression materials require more exacting handling techniques and a greater demand on the training and skill of the practitioner which is not commonly encountered among practictioners who are not dentally oriented. A further objection of some of the dental impression materials for this use is the problem of the development of exothermic heat which occurs during setting of some dental impression materials. Heat is likely to cause discomfort to the subject or even injury to the ear tissues. A further disadvantage of using dental impression materials relates to the undercuts which exist in the ear. Impressions of such undercuts are likely to be distorted or fractured when using many of the dental impression materials during the step of withdrawal from the ear. The use of some dental impression materials also results in problems when separating the impression from the investment mold.

It will be understood that impression materials which are generally used for sensitive areas, such as the ear canal, would desirably enjoy other advantages such as the ability to take a quick accurate impression, provide little or no discomfort to the subject, pose no problem of infection or physiological incompatibility, and even actively reduce the likelihood of infection. Such materials should form a non-tacky gel within a short time to take an impression, and also set within a reasonably short time so that the material may be removed. On the other hand, they should not set too quickly so as to hamper handling thereof. It is therefore one general object of the invention to provide new plastic compositions which can be successfully used ot take anatomical impressions, such as the ear. k

Another object of this invention is a plastic impression taking material which has improved properties to permit practitioners of limited training and skill to successfully take anatomical impressions, particularly impressions of the ear, to make ear molds for hearing aids, medical stethescope ear pieces, sound receiver units for radio, telephone and other transcription reception, swimming ear plugs, noise blocking ear plugs, and the like.

A still another object of the invention is to provide a plastic composition which can be quickly and simply mixed and manipulated while the plastic composition goes through its various viscosity stages without encountering disadvantages which would present problems in handling such as a too rapid loss of the impression taking or plastic stages.

In view of the foregoing objects, it is a still further object to provide a plastic composition for taking impressions in which a highly successful gel forming agent is employed which has controlled evaporation so that undesirable dimensional changes do not occur in the plastic composition, and the tissue is not irritated.

It is a further object to provide a plastic impression composition where the gel forming agent has other desirable properties such as low water adsorption so as not to dehydrate human tissue. Another feature of this object is to obtain a plastic impression composition wherein the successful gel forming agent does not present problems of irritation to the tissue and is not esthetically objectionable with respect to odors or handling properties.

A still further object of the invention is to provide a plastic composition in which a resin is combined with a solvent system which provides a mixture having a quick but controlled setting time, said solvent system including an extender to provide the desired feature of controlled setting time, as well as providing other desirable features and properties.

The foregoing objects are attained together with other objects which will occur to practitioners from considering the following disclosure of the invention.

The plastic compositions of this invention include a resin which may be any soluble room temperature soluble synthetic resin such as alkyl methacrylates, vinyl acetate and vinyl chloride, copolymers such as vinyl acetate-vinyl chloride, and the like. Various additives may be added to the solid resin such as pigments for coloring, fillers, modifiers, or the like. The resin is soluble in the sense that a solvent system successfully gelatinizes the resin composition. The plastic impression compoitions of the invention therefore include a solvent system which is capable of forming with the solid resin a deformable or plastic impression taking gel. During this stage, the composition is an elastomeric mass. The solvent system and the resin composition may be mixed in various ratios which are easily determinable by practitioners. In the practice of the present invention, the solvent system includes extenders like secondary plasticizers, such as the alkyl aryl hydrocarbons; fixed, edible vegetable oils, and the like, to provide controlled setting time and non-tackiness. The solvent system may include other additives which may be coupling agents to prevent separation of the extender, cohesion adjuvants to enhance or improve the cohesiveness of the plastic composition following the setting stage, and primary plasticizers which flexibilize the composition as well as acting as coupling agents.-

In general, when the resin composition and the solvent system are mixed, the mixture passes through transient viscosity stages which include an initial wetting stage wherein the solid resin is totally wetted with the solvent system; a following plastic or impression taking or mold making stage during which the non-tacky mixture can be shaped or molded into desired contours (during this impression taking stage, the plastic impression material may be considered as being in a condition where the dissolution of the polymer in the solvent system is only partially completed); and a later molding stage, wherein the limited solvation is completed and the mixture may be considered as having reached essentially equilibrium conditions which are characteristic of the gel forms of these compositions. This gel-like formation is a preliminary step to the set of a later stage of the plastic impression material. If the gel forms and sets in the ear, for example, it forms in a solid elastomeric mass which takes an accurate reproduction or impression of the ear canal, and this impression is dimensionally stable for the purposes of this invention. After this set stage, the mold forming or impression taking property of the composition is no longer present. The set elastomeric or elastic material is also referred to as an elastic impression material.

The solvent system is used to advantage because it contains a benzyl radical containing compound which is liquid at room temperature. These include the benzyl alcohols, benzyl aldehydes, benzyl chlorides, benzyl ketones, benzyl ethers, benzyl amines, benyl cyanides and benzyl esters. These benzyl radical compounds have been discovered to be solvent gel formers. It has further been found that room temperature aliphatic liquid esters of the benzoic acids and the salicylic acids are also operable gel forming solvents for the purposes of this invention, among which may be mentioned alkyl benzoate and alkyl salicylate. Among the operable room temperature liquid gel formers are benzyl alcohol and its derivatives, benzyl benzoate, benzyl acetate, benzyl butyrate, benzyl, formate, benzyl propionate, benzyl salicylate, dibenzyl ether, phenyl methyl carbinol, benzyl isoamyl ether, phenyl ethyl alcohol, methoxy benzyl alcohol (anisic alcohol), phenyl propyl alcohol, phenyl ethyl isobutyrate (benzyl carbinol isobutyrate), dimethyl benzyl carbinol, benzyl phenyl acetate, phenyl ethyl butyrate, dibenzyl ketone, phenyl ethyl isovalerate, benzyl acetaldehyde (phenyl propyl aldehyde), phenyl ethyl benzoate (benzyl carbinil benzoate), benzyl ethanol amine, benzyl thiol, benzyl butyl ether, methyl benzyl ether, benzyl cinnamate, and the like.

It has been found that the benzyl radical gel former need comprise only a minor portion of the solvent system, say about from 10% up to about 50% by volume of the liquid component. It has also been found that the liquid component should contain an extender which may be a secondary plasticizer such as an aryl alkyl hydrocarbon oil, or a fixed edible vegetable oil, or both. Other extenders may be used, such as a naphthenic oil. The petroleum oil extenders are more economical than the vegetable oils. The hydrocarbon petroleum oil extenders have no solvating powers, and they include Jayflex 205 supplied by the Enjay Chemical Co., Mobilsol L supplied by the Mobil Oil Company, Shell-Flex supplied by the Shell Oil Company and others. The use of the oil extenders leads to several advantages, namely, they extend the reaction time to a desired control level to attain adequate handling and molding time before the composition sets, while still realizing a relatively quick set of less than about one hour. The oil extender further leads to economies in using the resin component. Another important feature of the oil extenders is detackification, that is, they impart anti-tackiness to the plastic composition which is desirable when the compositions are brought into contact with dry tissue surfaces.

On occasion, the alkyl aryl hydrocarbon oils may be partly incompatible and separate or sweat out from the composition because such oils may not mix with ingredients such as benzyl alcohol or glycol diacetate. This does not necessarily blunt the successful practice of the invention, and such separation may be reduced or eliminated by adding coupling agents to the liquid component. It has been found that some benzyl alcohols, butyl benzoates and liquid alkyl phenols such as amyl phenol and nonyl phenol operate as coupling agents as well as solvents, gel formers, and flexibilizers. Other coupling agents are not solvents, such as hexadecyl alcohol, and other higher alcohols. Primary plasticizers such as dibutylphthalate have very slow solvent properties at room tempearture, but they are usefully added as coupling agents and flexibilizers. Smaller amounts of the primary plasticizers do contribute some solvation at room temperature, and further impart the property of flexibility, that is, they improve the plastic handling of the composition. The solvent type coupling agents are preferred even though they may lead to some tackiness. In particular, it has been found that the alkyl phenols very successfully prevent separation of the alkyl aryl hydrocarbon oils when benzyl alcohol, and the like is present in the solvent system.

The alkyl aryl hydrocarbon oils are recognized secondary plasticizes, that is, extenders for primary plasticizers. Their essential characteristic is that of a diluent rather than as a solvent. The preferred alkyl aryl hydrocarbons are oily liquids of a substantially clear color, and substantially free of objectionable odor. They have a molecular weight range of between about 240-320. The alkyl aryl hydrocarbon may be an aromatic, such as toluene, alkylated with an aliphatic compound, such as propylene, as taught in U.S. 3,211,690. The alkyl aryl hydrocarbon may also be a petroleum fraction having a major amount of a saturated hydrocarbon such as a parafiin or a cycloparafiin, and a minor amount of an aromatic hydrocarbon.

One such alkyl aryl hydrocarbon is known as Jayflex 205 and is supplied by the Enjay Chemical Co. Jayflex 205 has about 88% of saturated hydrocarbons of which about 6% is a paraffin and the balance is naphthene. The aromatic portion is present in about 12% by weight of which less than one-half is of a one ring benzene type and the balance is of different types of indenes. Another alkyl aryl hydrocarbon is known as Elastex 88-S and is supplied by Allied Chemical Corporation. The alkyl aryl hydrocarbons which are particularly useful as extenders have a generally clear color, no objectionable odor, have relatively low specific gravities of from 0.86 to about 0.88, and have a boiling range (-95%) of in excess of 500 R, up to about 700 F.

The edible, fixed vegetable oils which are useful as extenders include safflower oil, linseed oil, cottonseed oil, corn oil, sunflower oil, rape oil, peanut oil, and soybean oil. Such oils also impart lubricity, have the property of detackification nad desirably extend the reaction or molding time before the composition set into an elastomeric mass. The vegetable oils are compatible or miscible with the benzyl compound, whereas the petroleum oil extenders generally are not. It has been further found that mirtures of vegetable and petroleum oils tend to prevent separation, even without a coupling agent. Coupling agents in amounts suflicient to prevent separation, however, are preferred as included ingredients.

The plastic composition may also include a minor amount of a cohesion adjuvant to enhance the cohesive properties of the composition during the handling in taking a mold impression and removing a set elastomeric mass from contact with an anatomical pattern or the like. Such cohesion adjuvants are preferably tris ,8 chloroethyl phosphate, partially hydrogenated terphenyls and primary phthalate plasticizers such as butyl benzyl phthlate. Others may also be operable to serve this feature of the invention.

The solid component includes one or more resins. It is preferred to include a low molecular weight methacrylate polymer or copolymer in small bead or granular form. Useful methacrylate polymers are ethyl methacrylate and isobutyl methacrylate, but a copolymer may be used with like success, such copolymer being the product of ethylmethacrylate and butylmethacrylate. Other resins may be included in the solid components such as an ethylene derived resin, namely, vinylchloride, vinylacetatevinylchloride copolymers and the like. It has been found that the solid components may be more successfully manipulated if a minor amount of an anti-tack solid or powder is added to the solid component, such anti-track powders include calcium carbonate, ultrafine silica, zinc stearate and the like.

Oter gel formers may be added to the liquid component which by themselves would be inadequate or possess disadvantages. Such gel formers are compounds containing both alcohol and other groups, slow evaporating esters, higher molecular weight glycols, and benzyl radical containing plasticizers.

The liquid components are formulated so that the oil extenders comprise about 20% to about 65% by volume of the liquid component. In general, greater amounts provide more lubricity and dilution, which also extends the reaction or setting time. It is therefore preferred not to add extenders in excess of 45% by volume of the liquid component in most applications. The balance of liquid components may include the benzyl compound gel formers or solvents and the coupling agents. Of the balance, the major amount comprises the benzyl compound solvent, and the minor amount being the coupling agent. The liquid component preferably contains a primary plasticizer such as dibutyl phthalate, benzyl butyl phthalate, or the like, in small amounts of from about 5% by volume to about 30% by volume. The primary plasticizers impart flexibility or resiliency, and further impart cohesiveness to the composition. Cohesion adjuvants may also be added to enhance the cohesive properties of the composition,

particularly after a primary plasticizer is added. Such a cohesion adjuvant may be added up to about 5% by volume of the liquid component.

It will be noted that some benzyl containing compounds lead to desired properties of cohesiveness and flexibility without requiring inclusion of a conventional primary plasticizer. Among such benzyl compounds are esters such as benzyl phenyl acetate, butyl benzoate, benzyl acetate, and others.

The relative amounts of liquid and solid components are not critical and generally enough liquid component should be used to easily wet the amount of solid components that are employed. Suflicient liquid component should be added to a given amount of solid so the resulting mixture has a soft plastic consistency with sufiicient flow to provide good details and good handling when the soft plastic mixture is brought into contact with the par ticular anatomical structure. In general, from about 5 cc. to about 12 cc. of liquid component may be mixed with about 10 grams of the solid component, but this may be varied by the practitioner who will readily perceive when a sufiicient amount of liquid component is added to obtain the desired soft plastic consistency and handling. While the benzyl radical compounds, which are liquids at room temperature, operate within the scope of the invention, it is preferred to employ benzyl alcohols as the solvent gel former. Linear straight chain alcohols, as such, are not all operable and many of them present problems even when they attain various degrees of operability.,

Linear primary alcohols having chains of 10 or more carbon atoms do not act as solvent gel formers with the polymers used in this invention. Benzyl alcohol has excellent properties in addition to its dispersing and gel forming attributes. Benzyl alcohol is a surface anesthetic and antiseptic, and these properties are decided advantages for plastic impression materials intended to be used in contact with various anatomical structures. The benzyl alcohols are additionally high boiling materials and have low water vapor transmissions or vapor pressures. This permits the plastic impressions, which include the benzyl alcohols and the like, to be dimensionally stable at room temperatures even when the impression molds have thin cross-sections. The benzyl alcohol does not rapidly leave the plastic impression by evaporation or other loss to adversely affect the dimensional stability. The benzyl alcohols are hydrophobic, therefore, they do not dehydrate human tissues, they are non-irritating to tissues, they have a very low order of toxicity, they are all resistant to fungal attacks, and they have a pleasant odor.

The following examples are presented to teach various advantages and embodiments of the present invention, but it should be understood that the disclosed embodiments are intended to be only illustrative.

EXAMPLE 1.

A number of plastic gel forming materials were prepared by mixing 2 grams of a solid ethyl methacrylate powder with 1.5 cc. of thirty three various solvent gel formers. The setting time was recorded for each plastic composition, that is, the time when the gel loses its tackiness.

Solvent: Time Benzyl chloride 1'30" Benzyl cyanide 2'30" Benzyl formate 2'30" Benzyl alcohol 2'30" Benzyl thiol 2'30" Benzyl acetate 3' Phenyl methyl carbinol 4' Benzyl iso amyl ether 5' Benzyl propionate 7' Phenyl ethyl alcohol 8' Benzyl butyrate 9' Anisic alcohol 10' Phenyl propyl alcohol 11 Solvent: Time Benzyl carbinol isobutyrate l3 Dimethyl benzyl carbinol 14' Dibenzyl ether Benzyl phenyl acetate Dibenzyl ketone Benzyl acetaldehyde Benzyl n-butyl ether 16' Methyl o-chlorobenzoate 15 Cinnamic aldehyde 15 u-Propyl benzyl alcohol 20' Phenyl ethyl methylethyl carbinol 20 p-Isopropyl benzyl alcohol 35' Benzyl benzoate Benzyl salicylate Methyl benzyl ether 1 hr., 40 Benzyl cinnamate 2 hrs, 30" Ethanol 1'30 Isopropanol 13' Decyl alcohol No gel C12C13 alcohols NO gel Hexadecyl alcohol No gel The foregoing shows that all the benzyl containing compounds are gel formers with the solid resin component. Substantially all of the benzyl compounds exhibit preferably shorter setting times of under one hour. Those gel formers which have longer setting times, say above about 10 minutes, may be combined with the shorter setting time gel formers to reduce their setting time. The setting time may therefore be tailored in this respect to meet particular requirements of a given plastic impression composition.

Benzyl alcohol does not have the disadvantage of fast evaporation which would make it undesirable for use in plastic impression materials. The relative evaporation rates of benzyl alcohol and some other solvents or gel formers are seen from the following list of vapor pressures measured in mm. of mercury.

Solvent C. Mm. Hg

Ethanol 20 44 Isopropanol 20 33 Methyl benzyl alcohol 20 0. 01 Glycol diacetate 0. 3 Benzaldehyde. 1 Benzyl alcohol--. 1 Benzyl amine 29 1 Phenyl ethyl alcohol. 58. 2 1 Benzyl ethyl ether- 26 1 n-Butyl benzoate 20 0. 13 Hexylene glycol 20 0. 05 oz-Methyl benzylether 20 0. 01 a-Methyl benzyl mcnoethanol amine 20 0. 01

Ethyl alcohol has the disadvantage of a too rapid setting time and a too rapid rate of evaporation for successful handling. Consequently, the dimensional stability of the set product is adversely affected.

EXAMPLE 2 A solid resin component is prepared from the following materials and amounts.

Material Amount Ethylmethacrylate polymer 90 lbs. Vinylchloride-vinylacetate copolymer 11 lbs., 9 oz. Zinc stearate 6 lbs., 5 oz.

The above materials are mixed for 1 hour. The vinyl resins operate as extenders for the solid resin compositions, that is, themethacrylate polymer. The zinc stearate operates as an anti-tack additive.

The examples of the following Table *I show various solvent stystems which are prepared by mixing volumes of the listed ingredients. A plastic composition is prepared in each instance by combining 8 grams of the solid resin component of Example 2 with 5 cc. of a liquid component which represents the following solvent systems. The alkyl aryl hydrocarbon ingredients is Jayflex 20 5, and the edible vegetable oil ingredient is corn oil.

Components, cc.

Ingredient 1 2 3 4 5 6 7 8 Alkyl aryl hydrocarbon.-. 15 15 5 15 20 Plienyl methyl carbinol 15 Phenyl ethyl isobutyrate 15 Benzyl cyanide l5 Bcnzylpropiouate 15 Benzyl phenyl acetate Dibenzyl ether Dibenzyl ketone Phenyl ethyl alcohol Sec. amyl phenol. Butyl benzoate Benzyl ethanol amine Benzyl acetate Butyl benzoate Phenyl propyl a dehyde 15 Phenyl ethyl benzoate 15 Phenyl ethyl isobntyrate 10 Benzyl alcohol 10 Dibntyl sebecate. Butyl benzyl phthalate Anisio alcohol Dibutyl phthalatc Dinonyl phenol Gelling time, minutes. Setting time, minutes Benzylalcohol 20 50 28 30.3 30.3 50 10 Alkylarylhydrocarhon. 22 50 30.6 33.5 33.5

Butyl benzoa Ethyl glycol Glycol diacetate Dibutyl phthalate. Hexo deeyl alcohol* Hexylene glycol Ethoxylated lauryl alcohol" 36. 2 Edible vegetable oil 50 18 Benzyl benzoate Benzyl salicylate. Gelling time, minutes. Setting time, minutes 8 4 6 8 TABLE II Liquid components, parts by volume Ingredient A B C D E F Benzyl alcohol 10 10 1O 1O 10 10 Dibutylphthalate 10 5 5 5 (Enjay 205) alkyl aryl hydrocarb 10 5 5 Safllower oil 10 5 5 Component A is a miscible mixture of the benzyl compound and the primary plasticizer, which sets quickly but which is very tacky, and not moldable for that reason. Component B sets quickly under controlled molding time but there is some separation of ingredients and the composition has little cohesion. Component C is a miscible mixture of the benzyl compound and a vegetable oil which sets quickly, is non-tacky, but does not have the desired cohesion. The plastic composition, however, is useful as a plastic impression material, especially for some applications. Component D sets quickly and has good cohesiveness, but there is some separation because the primary plasticizer is present in an insufficient amount. Component E sets too quickly and is not moldable after 2 minutes. This is due to the slight lower amount of extenders which, however, are sufficient to detackify the composition. This composition is not sufficiently cohesive and pulls apart, as a result of the somewhat lower amount of primary plasticizer. Component F leads to a moldable composition of good cohesiveness which sets quickly, and in which the ingredients do not separate. The fixed vegetable oil appears to cooperate with the primary plasticizer to operate as a coupling agent, apparently because of the miscibility with the benzyl compound.

EXAMPLE 4 A liquid component of a primary plasticizer in a volume of cc. was mixed at room temperature with grms. of the solid resin of Example 2. Each plastic composition required from 4 to 10 hours to set. The primary plasticizers used in the various liquid components were:

Tricresyl phosphate Tris-B-chloroethyl phosphate Dibutyl phthalate Butyl benzyl phthalate Dipropylene glycol dibenzoate Methyl phthalyl ethyl glycolate Each plastic composition required from 4 to 10 hours to set. All the foregoing primary plasticizers are therefore inadequate to comprise a useful solvent system as such for the plastic impression composition in accordance with the purposes of the present invention.

EXAMPLE 5 A plastic composition of 10 grrns. of the solid component of Example 2 mixed with 5 cc. of benzyl alcohol set in less than 3 minutes. When a liquid component of 5 cc. benzyl alcohol plus 5 cc. of cottonseed oil is mixed with 10 grms. of the same solid component the setting time is extended to about 8 minutes.

EXAMPLE 6 Ingredient Parts by volume Benzyl alcohol 33 Dibutyl phthalate 37 Al-kyl aryl hydrocarbon (Enjay 205) l5 Safilower oil 12 Cohesion adjuvant, tris-B-chloroethylphosphate 3 The above liquid component is used in mixture with the solid resin component of Example 2, on the basis of 10 grmsl of solid component of 5 cc. of liquid component. The mixture gels within 1 minute and sets within 8 minutes to an elastomeric mass which is non-tacky and which has good cohesiveness. A mold of an outer ear canal is formed with good definition, with ease during the 4 minute period before setting.

The plastic impression compositions which are prepared with solvents such as benzyl alcohol and oil extenders provide easy handling with controlled setting times, they are not tacky, they are desirably plastic during the early viscosity stages for sufiicient times to take impression, they develop a set plastic body which is still elastic, they are dimensionally stable over long periods, they produce no irritation or discomfort to the subject, they do not develop exothermic heat at any viscosity stage, they generally are free from irritation to either the hands of the manipulator or the ear of the subject, and they have a pleasant natural odor. The plastic impression materials of this invention have, in addition, economic advantages because the impression can be quickly and simply 10 retaken in case of an apparent defect. Also, the plastic impression can, be withdrawn from the investment flask intact in preparing the plaster or stone molds. In this way, the finally molded product can be visually compared with the impression material which was used to make the mold.

The invention may now be practiced in the various ways which will occur to practitioners, and such practice will be a part of the invention so long as it comes within the terms of the following claims as given further meaning by the language of the preceding specification.

What is claimed is:

1. A plastic composition to take an elastomeric impression, comprising:

a thermoplastic granular loweralkyl methacrylate copolymer,

a room temperature gel forming solvent system for said resin to form a plastic impression taking gel within about one hour, which solvent system includes from about 10 to about 50 percent by volume of benzyl alcohol, said solvent system being further present from about 5 to about 12 cc. per 10 grams of said resin, and

an oil extender selected from the class of alkyl aryl hydrocarbon secondary plasticizers and fixed edible vegetable oils, said oil extender being in said solvent system from about 20 percent to about 65 percent by volume.

2.. A plastic composition as in claim 1 wherein said solvent system contains from about 5 percent to about 30 percent by volume of a plasticizer to flexibilize the plastic composition.

'3. A plastic composition as in claim 1 wherein said solvent system contains less than about 20 percent by volume of a primary phthalate plasticizer.

4. A plastic composition as in claim 1 wherein said solvent system contains less than about 20 percent by volume of a primary phthalate plasticizer, and wherein said oil extender is a secondary alkyl aryl hydrocarbon plasticizer substantially clear and free of odor, and having a specific gravity from about 0.8 6 to about 0.8-8, comprising a mixture of paraflin and aromatic compounds, and a boiling range in excess of 500 F.

5. A plasticcomposition as in claim 1 wherein said solvent system consists essentially of said benzyl alcohol and a fixed edible vegetable oil.

6. A plastic composition as in claim 1 wherein said solvent system consists essentially of said benzyl alcohol and an alkyl aryl hydrocarbon secondary plasticizer.

References Cited UNITED STATES PATENTS 2,885,378 5/1959 Darby 260-318 2,934,510 4/1960 Crissey et a1 260-31.'8 3,152,096 10/1964 Darby 26030.4 3,211,689 10/1965 Darby 2603l.4

OTHER REFERENCES Buttrey, Rlasticizers, Cleaver-Hume Press Ltd., 2nd ed., 1958, pp. and 192.

ALLAN LIEEBRMAN, Primary Examiner L. T. JACOBS, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0 Dated January 26,

Inventor(s) Eugene J. Molnar It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, after 1i] 4, insert Assignor to Coe Laboratories, Inc., Alsip,

111., a corporation of Illinois Signed and sealed this 16th day of May 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents