US3420231A - Thermoplastic cast forming material including an inversely water soluble resin - Google Patents

Description

United States Patent THERMOPLASTIC CAST FORMING MATERIAL INCLUDING AN INVERSELY WATER SOLUBLE RESIN Martin I. Edenbaum, Somerset, N.J., assignor to Johnson & Johnson, a corporation of New Jersey No Drawing. Filed July 18, 1966, Ser. No. 565,705

US. Cl. 12890 Claims Int. Cl. A61f 13/00 This invention relates to sheet materials for forming immobilization casts and more particularly to thermoplastic cast forming sheet material.

It has heretofore been proposed to use thermoplastic sheets for the preparation of casts in the immobilization of various parts of the human body. Thus, for example, in US. Patent 2,616,418 to Eberl there is disclosed material for forming casts which comprises a fabric impregnated with a compounded thermoplastic material and provided in roll form so as to be compact and thus occupy a minimum amount of storage space and so as to be immediately dispensible and severable into suitable lengths when the time has come to use the same.

These thermoplastic cast forming sheets are flexible to some degree but the thermoplastic material in the same is normally relatively hard, nonmoldable and noncohesive at room temperature and at temperatures encountered during normal use, i.e., up to about 100 F., at which temperatures the thermoplastic material is in the crystalline state. When heated to a temperature somewhat above 100 F., the thermoplastic material becomes amorphous in which state it is soft :andlrnoldable and in which state it is generally externally cohesive. When the rolled sheet is removed from the heat source, it may be wrapped about the body part to be immobilized, the material being overlapped in the conventional helical pattern to form a multilayered cast in which the layers cohere together. As the sheet cools, the amorphous thermoplastic material begins to recrystallize and the sheet hardens into a rigid cast, the various layers of the cast forming material remaining cohered together.

In order to form a hard and rigid cast by building one layer of the thermoplastic cast forming material upon another, it is necessary that the sheet have the aforesaid described property of external coherence when in the heated amorphous state; thus when the sheet cools, the various layers of the cast will continue to cohere. However, if the thermoplastic cast forming material is to be provided in roll form and then heated to a temperature at which it becomes soft and moldable and cohesive, and then removed from the heat source and dispensed from the roll in sufiicient length to form a cast, some means must be provided to prevent the various convolutions of the heated roll of cast forming material from cohering together and thus preventing the roll of material from being unwound for use.

It has been suggested to provide a paper interliner, which is nonadhesive with respect to the heated amorphous thermoplastic material, the paper interliner being interposed between the roll convolutions, and being removed when the sheet material is unwound for use. However, the heating of the roll of thermoplastic cast forming material to render the same amorphous and moldable is most suitably done by immersing the same in hot water since the hot water is usually more readily available in the doctors Patented Jan. 7, 1969 oflice than is an oven. If the interliner provided is made of paper, the heating of the roll of cast forming material in water would be undesirable.

It is therefore an object of this invention to provide a normally hard, nonmoldable and noncohesive thermoplastic cast forming material wound on itself in roll form which may be heated by immersion in hot water to render the same soft and moldable but in which the adjacent roll convolutions remain essentially noncohesive with respect to each other; and which when removed from the hot water, unwound from the roll, applied to the patient, and allowed to cool somewhat, will remain soft and moldable but also becomes or may be rendered cohesive.

According to this invention, there is provided a thermoplastic cast forming sheet material wound on itself in roll form, the cast forming material comprising a compounded base thermoplastic material which is normally relatively stiff, hard and crystalline at room temperature and at temperatures up to at least F. and which becomes amorphous and soft and cohesive at temperatures somewhat above about 100 F and a water soluble resin having an inverse solubility function in water in the range of temperatures between room temperature and about R, which when heated becomes relatively insoluble in water at a temperature below 165 F. and which when thereafter cooled becomes relatively soluble in Water at a temperature above the temperature at which the base resin hardens, the inversely water soluble resin being interposed between the roll convolutions to separate portions of the base thermoplastic resin in adjacent roll convolutions.

In the preferred embodiment of the invention, the inversely water soluble resin is mixed with the base resin in an amount between about 0.5 and 5, and preferably between about 2.0 and 4.0, parts by weight per 100 parts by weight of base resin. When the roll of thermoplastic cast forming material is heated to a temperature substantially above room temperature and above about 100 F., usually to temperatures near the upper limits of human tolerance, i.e., 165 F., the base thermoplastic resin becomes soft thus rendering the sheet moldable. When removed from the water, the sheet may still be unwound easily from the roll; however, when the same is wrapped about a limb of a patient in the usual overlapping fashion and allowed to cool, the various adjacent cast layers strongly cohere and when the base thermoplastic resin hardens, a hard rigid cast is formed.

The water soluble resin having an inverse solubility function in water is, as described above, preferably intimately mixed with the base resin. However, it may also be in the form of a surface coating covering all or a portion of one or more surfaces of the cast forming material or in the form of a free film interliner. If the inversely soluble resin is in the form of a surface coating, it is preferably in a dot pattern covering from about 1 to about 10% of the total surface area of the sheet. When the inversely soluble resin is in the form of a free film interliner or a coating covering most or all of the surface area of the material or is admixed wtih the base resin in amounts much greater than about 5 parts by weight per 100 parts by weight of base resin and the inversely soluble resin is not itself cohesive or is not adhesive with respect to the base thermoplastic material, it may be necessary to wipe a portion of the inversely soluble resin from the surface of the sheet in order to obtain a cast in which the various adjacent layers adequately adhere to each other.

Referring again to the preferred embodiment of the invention where the inversely soluble resin is mixed with the base resin or in an amount of from about 0.5 to about 5 parts by weight per 100 parts by weight of base resin, while it is not desired to limit the invention to any theory, the water soluble resin having an inverse solubility function is thought to become relatively insoluble in the hot water as the water contacts the inversely soluble resin at the surface of the various convolutions of the roll and thus an insoluble gel or film is thought to form over a substantial enough portion of the exposed surface of the highly cohesive base thermoplastic resin to effectively separate the adjacent roll convolutions and prevent them from cohering to each other. As the sheet material begins to cool, the solubility of the inversely soluble water soluble resin increases and at some point the same is thought to go into solution in the adsorbed water present on the surface of the sheet. This solution is thought to cover little enough of the surface of the sheet to effectively permit intimate contact between the still moldable and cohesive base thermoplastic base resin in adjacent convolutions of the cast. It is thought that the same phenomenon occurs when the inversely soluble resin is present as a surface coating, preferably in a pattern of small spaced dots, covering from about 1 to about of the total surface area of the sheet.

When the inversely soluble resin is present mixed with the base resin or as a coating in amounts above the limits pointed out above or is present as a free film interliner, it is thought that when the sheet cools and the inversely soluble resin goes into solution on the adsorbed water on the surface of the sheet, a sufficient proportion of the surface area is covered by the solution to still effectively separate the base resin in adjacent convolutions as previously mentioned. In such a case, it may be necessary to wipe a portion of the inversely soluble resin from the sheet as the cast is applied, whether or not this is necessary depending on the relative properties of the base resin and inversely soluble resin. For example, the inversely soluble resin may when in solution become cohesive and/ or adhesive with respect to the base thermoplastic material. In such a case, the adsorbed solution of inversely soluble resin may actually act as a glue, and if its cohesion or adhesion is greater than that of the base resin, the inversely soluble resin actually somewhat reinforces the natural cohesion of the base thermoplastic resin. However, the adhesion or cohesion of the inversely soluble resin is usually low compared to that of the base I resin, and therefore when present in large amounts, it will uusally be desirable to wipe a portion of the inversely soluble resin from the surface of the sheet.

Referring specifically to an embodiment where the inversely soluble resin should not be wiped from the surface of the sheet, certain base thermoplastic resins, such as the vinyl resins, have a relatively low external c0- hesiveness in the amorphous state, although this cohesiveness is high enough to cause roll unwind problems. On the other hand, certain of the inversely water soluble resins, such as methyl cellulose, when in solution have a somewhat higher external cohesiveness than the vinyls. In the case of such a combination, it will not only be desirable to allow the adsorbed solution of the inversely water soluble resin to remain between the cast layers to aid in cohering the cast convolutions together but it will also be desirable to maximize the surface area covered by the solution by utilizing the inversely water soluble resin mixed with the base resin at higher concentrations or in the form of a continuous coating or free film interliner to thereby maximize the cohesion between cast layers. If the cast forming material is to be coated with the inversely soluble resin, the coating may be of any thickness. If the inversely soluble resin is present in the form of a free film interliner, films having a thickness of between 2 and 5 mils have been found to be particularly suitable.

The base thermoplastic resin may be any of the thermoplastic resins which have the characteristics earlier described, namely, that they are normally relatively hard and noncohesive at room temperature but when heated to a temperature substantially above room temperature, they become soft and moldable and somewhat cohesive. These resins fall into three main categories. Some thermoplastic resins such as those described in US. Patent 2,301,426 to Lovell have a hysteresis softening curve, that is, they become amorphous at a temperature somewhat above the temperature at which they recrystallize, the melting and recrystallizing occurring relatively rapidly at these temperatures. Some resins such as neoprene become amorphous and recrystallize at the same temperature but recrystallize rather slowly. Still other resins, such as the vinyls, soften and harden at the same temperature and do so quite rapidly in which case they must be heated substantially above the softening point and used before the temperature returns to the softening point.

Thermoplastic resins, such as neoprene, which when cooled to room temperature have a delayed recrystallization and thus remain soft, moldable and cohesive for a substantial amount of time, on the order of 5 minutes or more, before hardening into a hard, rigid material are preferred for a cast forming material, so as to provide adequate time for the doctor to properly apply the cast to the patient. Thermoplastic materials having a highly regular polymeric structure usually have rates of crystallization in the preferred range, and, of these materials, polymers such as Neoprene HC consisting essentially of trans 1,4 chloroprene polymeric units and polymers similar to Neoprene HC such as balata and gutta-percha consisting essentially of trans 1,4 isoprene polymeric units have been found to be particularly suitable, the same crystallizing in about 6 to 10 minutes at room temperatures.

Any water soluble material having the inverse solubility characteristics earlier described may potentially be used to alter the external cohesive characteristics of the thermoplastic cast forming sheets. The particular inversely soluble resin chosen depends on the softening characteristics of the base thermoplastic resin. In those cases where the cohesive characteristics of the cast convolutions are to be provided primarily by the base thermoplastic resin, the inversely soluble resin when cooled must become soluble in water at a temperature above the temperature at which the base resin becomes noncoh-esive so that the cast convolutions become firmly cohered together. In the case of base resins having a sharp point of recrystallization, this temperature is the limiting solubility temperature, while in the case of the delayed crystallization resins, such as neoprene, the room temperature at which the cast is applied, i.e., usually about F., is essentially the limiting solubility temperature.

On the other hand, in all cases, the inversely soluble resin when heated must become insoluble in water at temperatures well below F., the upper limits of human tolerance, since the cast forming material must be unwound from the roll, and therefore, for all practical purposes, applied to the body, while essentially noncohesive.

It is desirable that the point of insolubility of the inversely soluble resin in water as it is heated and the point of solubility as the same is cooled be as low as possible so that a substantial period of time is available to apply the entire roll of material to the body after it is removed from the heat source and before it becomes externally cohesive. In other words, in the case of a base resin, such as neoprene, having a delayed crystallization at room temperature, it is preferable that the thermoplastic resin having the inverse solubility characteristics be relatively insoluble in water at all temperatures much above room temperature but be relatively soluble in water at room temperature. Obviously, some compromise must be made in that the solubility function will not be discontinuous but will generally follow a relatively gentle curve between relative solubility at lower temperature and relative insolubility at higher temperatures.

Methyl cellulose has been found to be particularly suitable for the thermoplastic resin having inverse solubility where the base resin has delayed crystallization at room temperature in that it is relatively soluble in water at room temperature but is relatively insoluble in water at temperatures above about 120 F. Other suitable inversely water soluble materials are polyvinyl methyl ether, hydroxy propyl methyl cellulose, and certain copolymers of normal isopropyl acrylamide, among others. The gel point of any of these inversely soluble materials may be depressed, if desired, by adding an inorganic salt to the composition.

The cast forming sheet materials heretofore described may comprise a fibrous substrate impregnated with the thermoplastic compositions disclosed herein or the sheet may comprise a fibrous substrate with calendered thermoplastic films on one or both sides thereof. If it is desired, the fibrous substrate may be eliminated entirely, the sheet being formed, for example, by solvent casting a sheet of the thermoplastic resin.

Although only a few embodiments of the invention have been described above and only certain embodiments will be described specifically in the examples, the invention should not be construed to be limited thereby, the invention being limited only by the scope of the appended claims.

Example I A thermoplastic composition comprising 100 parts by weight of Neoprene HC, a highly refined trans chloro isoprene consisting of about 97% of the trans 1,4 chloroprene polymeric units, and about 2 parts by weight of methyl cellulose is compounded and solvent cast at 15% solids in cyclohexane to form a sheet 20 mils thick. The sheet is wound on itself in roll form with about 25 feet of the material on the roll. The roll is placed in a hot water bath at about 165 F. to heat the same and render the sheet moldable. When the sheet is removed from the hot water, it is found that it may be easily unwound, the various layers not cohering together and when examined closely, it is found that a relatively continuous insoluble film of methyl cellulose has been formed across the face of the material.

The material while wet is wrapped around a leg of a patient in the usual helical pattern and allowed to cool. As the temperature drops below 120 Fjthe thermoplastic material again becomes cohesive with respect to itself and when the surface of the same is examined, it is found that the methyl cellulose has gone into solution in the adsorbed water present on the surface of the thermoplastic material, the solution covering only a portion of the surface. After about minutes, it is found that the overlapped thermoplastic sheet has hardened into a rigid cast, the various convolutions of which are still cohered together.

The same procedures are followed using, in turn, polyvinyl methyl ether, hydroxy propyl methyl cellulose and copolymers of isopropyl acrylamide and similar results are obtained.

Example II A thermoplastic composition consisting of Neoprene HC is formed into a sheet as described in Example I. One surface of the sheet is coated with a 2-mil thick coating of methyl cellulose. The sheet is wound on itself in roll form and when the same is used as described in Example I, it is found that the sheet may be essentially unwound from the roll, however, when the cast is formed, it is found that the cohesion between adjacent cast layers is substantially weaker than the cohesion found to exist between adjacent cast layers in Example I.

The test is repeated except that the methyl cellulose solution is wiped from the surface of the cast forming material as it is applied to the patient. It is found that the cohesion level between adjacent cast convolutions is of the same magnitude as found in Example 1.

Example III A sheet of cast forming material is formed in the same manner as in Example II. A 4% solution by weight of methyl cellulose in water is prepared. A 4-mil thick free film of methyl cellulose is prepared from the solution by casting the solution onto a glass plate. The cast forming material is wound on itself in roll form with the free film of methyl cellulose interposed between the roll convolutions. When the cast forming material is used as previously described, the results obtained are equivalent to those reported in Example H.

Example IV A thermoplastic cast forming material in sheet form is provided as described in Example II. A pattern of small dots of methyl cellulose is printed on one surface of the cast forming material, the dots being 4 mils in diameter, and the printed pattern covering approximately 7% of that surface of the sheet. When the cast forming material is wound on itself in roll form and used as previously described, the results obtained are similar to those reported in Example I.

What is claimed is:

1. A thermoplastic cast forming sheet material wound on itself in roll form comprising a "base thermoplastic resin which is normally relatively hard, rigid and noncohesive at room temperature and at temperatures up to about F. but which becomes soft, moldable and cohesive at a temperature above about 100 F. and below about F and an inversely water soluble resin which when heated in water 'becomes relatively insoluble at a temperature below about 165 F and which when thereafter cooled in water becomes relatively soluble at a temperature above the temperature at which the base thermoplastic resin rehardens, at least a portion of said inversely soluble resin being interposed between adjacent roll convolutions to separate portions of said base resin in said adjacent roll convolutions.

2. The cast forming material of claim 1 in which said inversely soluble resin is present admixed with the base resin in an amount of from between about 0.5 to about 5 parts by weight per 100 parts by weight of base thermoplastic resin.

3. The cast forming material of claim 1 in which the inversely soluble resin is present in the form of a coating on at least one surface of the cast forming sheet.

4. The cast forming material of claim 3 in which said coating covers between about 1.0 and about 10% of the surface area of the sheet.

5. The cast forming material of claim 1 in which said inversely soluble resin is present in the form. of a free film interliner.

6. The thermoplastic cast forming material of claim 1 in which said inversely soluble resin is chosen from the group consisting of methyl cellulose, polyvinyl methyl ether, hydroxy propyl methyl cellulose and copolymers of isopropyl acrylamide.

7. A thermoplastic cast forming material of claim 6 in which said base thermoplastic resin is chosen from the group consisting of polymers consisting essentially of polymeric units chosen from the group consisting of trans 1,4-choroprene and trans 1,4-isoprene.

8. A thermoplastic cast forming material of claim 7 in which said base thermoplastic resin is Neoprene HC.

9. The thermoplastic cast forming material of claim 8 in which said inversely soluble resin is methyl cellulose.

10. The thermoplastic cast forming material of claim 9 in which said methyl cellulose is admixed with the Neoprene HC in an amount of from about 2 to about 4 parts 8 FOREIGN PATENTS by Weight per 100 parts by weight of Neoprene HC. 146,050 4/1952 Australia- References Cited RICHARD A. GAUDET, Primary Examine:

UNITED STATES PATENTS 5 R. L. FRINKS, Assistant Examiner;.

2,301,426 11/1942 Lovell 128-90 2,616,418 11/1952 Eberl 12s 9o 2,697,434 12/1954 Rodman 12890

Claims (1)

1. A THERMOPLASTIC CAST FORMING SHEET MATERIAL WOUND ON ITSELF IN ROLL FORM COMPRISING A BASE THERMOPLASTIC RESIN WHICH IS NORMALLY RELATIVELY HARD, RIGID AND NONCOHESIVE AT ROOM TEMPERATURE AND AT TEMPERATURES UP TO ABOUT 100*F. BUT WHICH BECOMES A SOFT, MOLDABLE AND COHESIVE AT A TEMPERATURE ABOVE ABOUT 100*F. AND BELOW ABOUT 165*F.; AND AN INVERSELY WATER SOLUBLE RESIN WHICH WHEN HEATED IN WATER BECOMES RELATIVELY INSOLUBLE AT A TEMPERATURE BELOW ABOUT 165*F. AND WHICH WHEN THEREAFTER COOLED IN WATER BECOMES RELATIVELY SOLUBLE AT A TEMPERATURE ABOVE THE TEMPERATURE AT WHICH THE BASE THERMOPLASTIC RESIN REHARDENS, AT LEAST A PORTION OF SAID INVERSELY SOLUBLE RESIN BEING INTERPOSED BETWEEN ADJACENT ROLL CONVOLUTIONS TO SEPARATE PORTIONS OF SAID BASE RESIN IN SAID ADJACENT ROLL CONVOLUTIONS.