US3824998A

US3824998A - First aid dressing for wounds or burns

Info

Publication number: US3824998A
Application number: US00188317A
Authority: US
Inventors: G Snyder
Original assignee: Celanese Corp
Current assignee: Celanese Corp
Priority date: 1971-10-12
Filing date: 1971-10-12
Publication date: 1974-07-23
Anticipated expiration: 1991-07-23
Also published as: CA1011206A

Abstract

A first aid dressing for wounds or burns to prevent gross infection of the burns or wounds from air or water-borne bacteria, dust, dirt, etc. which comprises a microporous breathable thermoplastic film of sufficient size to cover the burn or wound and preferably an uninjured perimeter around the burn or wound and means around the perimeter of the microporous film, such means being able to provide a closure of the microporous film dressing to the perimeter around the burn or wound, the closure being sufficiently secure to prevent gross entry of air between the dressing and the skin. In use, when so applied, the first aid dressing, which is usually non-adherent to the wound or burn, is inflated away from the wound or burn by means of positive pressure created by moisture vapor issuing from the burn or wound or the uninjured parts of the body which are covered by the first aid dressing or entrapped air heated by the skin. The first aid dressing is permeable to air and moisture vapor, but impermeable to liquid water and other liquids which do not wet the hydrophobic film and also to air-or water-borne bacteria, etc.

Description

United States Patent 11 1 Snyder 1 11 3,324,998 [451 July 23, 1974 FIRST AID DRESSING FOR WOUNDS OR BURNS [75] Inventor: George W. Snyder, Hudson, NJ.

[73] Assignee: Celanese Corporation, New York,

[22] Filed: Oct. 12, 1971 [21] Appl. No: 188,317

[52] US. Cl. 128/157, 128/132 R [51] Int. Cl. A611 13/00 [58] Field of Search 128/157, 132, 83, 165, 128/184, 260, 400, 82, 154, 156, 159

[56] References Cited UNITED STATES PATENTS 1,980,486 11/1934 King etal 128/132 R 3,324,580 6/1967 Baxter 128/165 UX 3,329,143 7/1967 Gordon 128/82 3,610,238 10/1971 Rich 128/184 FOREIGN PATENTS OR APPLICATIONS 648,733 1/1951 Great Britain 128/156 1,163,130 4/1958 France 128/132 R 641,061 8/1950 Great Britain 128/132 R 7/1962 France 128/132 R Primary ExaminerLawrence W. Trapp Attorney, Agent, or FirmThomas J. Morgan; Linn 1. 9999M??? 13m [5 7] ABSTRACT A first aid dressing for wounds or burns to prevent gross infection of the bums or wounds from air or water-home bacteria, dust, dirt, etc. which comprises a microporous breathable thermoplastic film of sufficient size to cover the burn or wound and preferably an uninjured perimeter around the burn or wound and means around the perimeter of the microporous film, such means being able to provide a closure of the microporous film dressing to the perimeter around the burn or wound, the closure being sufficiently secure to prevent gross entry of air between the dressing and the skin. In use, when so applied, the first aid dressing, which is usually non-adherent to the wound or burn, is inflated away from the wound or burn by means of positive pressure created by moisture vapor issuing from the burn or wound or the uninjured parts of the body which are covered by the first aid dressing or entrapped air heated by the skin. The first aid dressing is permeable to air and moisture vapor, but impermeable to liquid water and other liquids which do not wet the hydrophobic film and also to air-or water-borne bacteria, etc.

1.129119%. Prair naFisu PATENIED 3.824.998

INVENTOR.

660/96 W Snyder WZM ATTORNEY FIRST AID DRESSING FOR WOUNDS OR BURNS This invention relates to a first aid dressing for the prevention of gross contamination and infection by airor water-borne bacteria of burns or wounds.

When in the course of human events, tragedy in the form of severe wounds or burns befalls either an individual or groups of people engaged in dangerous pursuits such as war, many times the wounds or burns sustained are not the major cause of concern but rather secondary contamination of the wound or more serious infection of the wound or burn caused by air-borne bacteria or Water-borne bacteria, etc. For example, if

, someone is severely burned in an automobile accident where a gasoline tank explodes, there is a major chance of infection occurring from the time of the burn to the time when the patient is admitted to a hospital and treatment is begun. Similarly, where in jungle combat, a soldier or groups of soldiers are wounded by mortar rounds which tear gaping wounds in the torso exposing the viscera, secondary infection or contamination of the wound often times provides greater cause for concern than the wounds themselves.

Ordinary bandages of sterile gauze and the like are of limited use in combatting contamination and gross infection because they are grossly permeable to all manner of air-borne and also water-borne contamination and sources of infection. Similarly, ordinary nonporous plastic films are of little or no utility because,

while they might tend to keep out air-borne and water-' borne contamination and sources of infection, they also deprive the wounded or burned area of oxygen; and if left on for sufficiently long periods of time, instead of inhibiting sources of infection, they would tend to promote an anaerobic infection. Non-porous films render the covered area hot and sweaty. The first aid dressings of the present invention combat the foregoing and other disadvantages of the prior art.

The present invention comprises a microporous polymeric film as more particularly described hereinafter together with a means of fasteningthe perimeter of the microporous film to preferably an uninjured perimeter of the body which surrounds the wounded or burned area which is desired to be protected from gross contamination and sources of infection.

The appended figures illustrate but a few of the different embodiments of the present-invention.

FIG. 1 illustrates a human arm which has a wound (w). The arm including the wounded portion is enclosed in an elongated tubular microporous film struc ture sealed across one end (10). The arm, of course, is inserted into the structure at the open end. That end is substantially tightly attached to the arm above the wound area by means such as adhesive tape, a draw string (11, illustrated) or a fiat elastic band attached to the open end of the bag.

FIG. 2 shows a bag, which may be considered a sort of duffel bag arrangement, again an elongated tubular structure sealed across one end (10). The patient who is wounded (w) or burned in the lower extremities and possibly the lower portion of the torso is inserted into the bag and means (11) such as described above for FIG. 1 are used to substantially tightly close the open end of the bag to the patient around the midsection, for example, which is above the wounded area. A longer bag might be utilized which would enclose the patient up to a higher portion of the anatomy; for example, it might be closed about the neck sufficiently tight for purposes of this invention and yet not so tight that it would restrict breathing or swallowing of the patient.

FIG. 3 illustrates a human torso with a wounded (w) or burned area in the abdomen. In this case, it may be preferable to employ the first aid dressing of this invention in the form of a rather large film which has about its perimeter a continuous or substantially continuous band of adhesive. The film (12) is positioned so that the central non-adhesive area is over the wound or burn. Adhesive perimeter (13) is continuous and seals the film securely around the wound, preferably to the uninjured area sorrounding it.

FIG. 4 shows a structure basically similar to that illustrated in FIG. 1; however, it differs in that it has a simple valve comprised of (14) and (l5). (14) is a tubular member attached to and open to structure (10); and (15) is a pinch clamp, shown clamping off (14).

FIGS. 5 and 6 are two views of a small dressing (20). FIG. 5 is a view of the part that is toward the skin when in use. FIG. 6 is a cross sectional view, the dressing being sectioned 'as shown in FIG. 5. In FIGS. 5 and 6,

(21) is the microporous breathable thermoplastic film;

(22) is a ring of suitable material (preferably same polymer as film) of appropriate thickness to space the film away from a burn or wound, one surface of the ring being attached to the film; and (23) is a coating of adhesive on the opposite surface of the ring.

In whatever form, the first aid dressing depicted in FIGS. 1 to 4 should be sufficiently large that they can balloon away from the injured area under the action of the positive pressure caused by moisture vapor issuing from the covered area. In the dressing depicted in FIGS. 5 and 6, the ring serves to space this relatively small dressing away.

As pointed out above, the first aid dressing of this invention has a combination of unique properties not found in any other heretofore known dressing which enable it to be used in the first aid of wounds or burns, etc. to prevent the entry into such wounds or burns of air-borne or water-borne contamination or sources of infection. The first aid dressings do not adhere to the wounded or burned area. They are essentially inert and in addition are readily sterilized by known means. They permit the relatively free passage of air from outside the dressing through the microporous wall of the dressing and into contact with the wounded area or burned area. They permit the relatively free egress from the wounded area or burned area of moisture vapor issuing from the uninjured skin area or from the wounded or burned area itself. This is important since it renders the dressing relatively comfortable, which would not be the case where a non-porous polymeric film had been used. That would keep the skin clammy and moist. In such a case, the build-up of sweat or body fluids on the wounded or burned area might not be in the best interest of prevention of contamination or infection. This, as pointed out, is alleviated or prevented through use of the first aid dressings of this invention. The film is permeable to moisture vapor issuing from the skin, but permeable to such an extent that there results in the space between the dressing and the wound a positive pressure caused by the moisture vapor, which causes the dressing to balloon away from the wound to a greater or lesser degree depending on the area covered and the size of the dressing.

Porous or cellular films can be classified into two general types: one type in which the pores are not interconnected, i.e., a closed-cell film, and the other type in which the pores are essentially interconnected through tortuous paths which may extend from one exterior surface orsurface region to another, i.e., open-celled film. The microporous films useful in the present invention are of the latter type.

The microporous films useful in the present invention are also characterized by a reduced bulk density, sometimes hereinafter referred to simply as a low density. That is, these microporous films have a bulk or overall density lower than the bulk density of corresponding films composed of identical polymeric material, but having no open-celled or other voidy structure. The term bulk density as used herein means the weight per unit of gross or geometric volume of the film, where gross volume is determined by immersing a known weight of the film in a vessel partly filled with mercury at 25C. and atmospheric pressure. The volumetric rise in the level of mercury is a direct measure of the gross volume. This method is known as the mercury volumenometer method, and is described in the Encyclopedia of Chemical Technology, Vol. 4, page 892 (Interscience 1949). v

Porous films have been produced which possess a microporous, open-celled structure, and which are also characterized by a reduced bulk density. Films possessing this microporous structure are described, for example, in U.S. Pat. No. 3,426,754. The preferred method of preparation described therein involves drawing or stretching at ambient temperatures, i.e., cold'drawing, a crystalline, elastic starting film in an amount of about to 300 percent of its original length, with subsequent stabilization by heat setting of the drawn film under a tension such that the film is not free to shrink or can shrink only to a limited extent.

While the above described microporous or voidcontaining film of the prior art is useful in certain applications, the search has continued for new processes able to produce open-celled microporous films having a greater number of pores, a more uniform pore concentration or distribution, a larger total pore area, and better thermal stability of the porous film. These properties are significant in applications such as filter media where a large number of uniformly distributed pores are necessary or highly desirable; and in applications such as breathable medical dressings subject to high temperatures, e.g., sterilization termperatures, where thermal stability is necessary or highly desirable.

An improved process for preparing open-celled microporous polymer films from non-porous, crystalline, elastic polymer starting films includes 1) cold stretching, i.e. cold stretching the elastic film until porous surface regions or areas which are elongated normal or perpendicular to the stretch direction are formed, (2) hot stretching the cold stretched film until fibrils and pores or open cells which are elongated parallel to the stretch direction are formed, and thereafter (3) heating or heat setting the resulting porous film under tension, i.e., at substantially constant length, to impart stability to the film. Yet another process is similar to this process but consolidates steps (2) and (3) into a continuous, simultaneous, hot stretching-heat setting step, said step being carried out for a time sufficient to render the resulting microporous film substantially shrink resistant (less than about 15 percent).

The elastic starting film or precursor film useful in this invention is preferably prepared from crystalline polymers such as polypropylene by melt extruding the polymer into a film, taking up the extrudate at a drawdown ratio giving an oriented film, and thereafter heating or annealing the oriented film, if necessary, to improve or enhance the initial crystallinity.

The essence of the improved microporous process is the discovery that the sequential cold stretching and hot stretching steps impart to the elastic film a unique open-celled structure which results in advantageous properties, including porosity and improved thermal stability. A further enhancement of porosity occurs when the film is treated with certain organic liquids such as perchloroethylene.

As determined by various morphological techniques or tests such as electron microscopy, the microporous films are characterized by a plurality of elongated, nonporous, interconnecting surface regions or areas which have their axes of elongation substantially parallel. Substantially alternating with and defined by these nonporous surface regions which are a plurality of elongated, porous surface regions which contain a plurality of parallel fibrils or fibrous threads. These fibrils are connected at each of their ends to the non-porous regions, and are substantially perpendicular to them. Between the fibrils are the pores or open cells of the films utilized by the present invention. These surface pores or open cells are substantially interconnected through tortuous paths or passageways which extend from one surface region to another surface area or region.

With such a defined or organized morphological structure, the films which are treated according to the improved process may have a greater proportion of surface area that the pores cover, a greater number of pores, and a more uniform distribution of pores, than previous microporous films. Further, the fibrils present in the films of the improved invention are more drawn or oriented with respect to the rest of the polymer material in the film, and thus contribute to the'higher thermal stability of the film. I

The total surface area per cubic centimeter of the films used in this invention is in the range of from 2 to about 200 square meters per cc. Preferably the range is from about 5 to about 100 square meters per cc. and most preferably from about 10 to about square meters per cc. These values can be compared with normal pin-holed film which has a total surface area per gram of about 0.1 square meters; paper and fabric which have values per gram of about 1.0 square meters and leather which has a value of about 1.6 square meters per cc. Additionally, the volume of space per volume of the films used in this invention ranges from about 0.05 to about 1.5 cubic centimeters per gram, preferably from about 0.1 to about 1.0 cubic centimeters per gram and most preferably from 0.2 to about 0.85 cubic centimeters per gram. Additional data to define the films used in this invention relates to nitrogen flux measurements, wherein the microporous films have Q (or nitrogen) Flux values in the range of from about 5 to 400 perferably about 50 to 300. These values give an indication of porosity, with higher nitrogen flux values indicating higher levels of porosity.

Nitrogen flux may be calculated by mounting a film having a standard surface area of 6.5 square centimeters in a standard membrane cell having a standard volume of 63 cubic centimeters. The cell is pressurized to a standard differential pressure (the pressure drop across the film) of 200 pounds per square inch with nitrogen. The supply of nitrogen is then closed off and the time required for the pressure to drop to a final differential pressure of 150 pounds per square inch as the nitrogen premeates through the film is measured with a stop watch. The nitrogen flux, Q, in gram moles per square centimeter minute, in then determined from the equation:

Q (27.74 X /At X T) where At is the change in time measured in seconds and T is the temperature of nitrogen in degrees Kelvin. The above equation is derived from the gas law, PV ZnRT, wherein P is pressure; V is volume; Z is the compressibility factor; n is the number of moles of gas; R is the gas constant per mole; and T is the absolute temperature.

Precursor films useful in the processes for making microporous films are elastic films of crystalline, filmforming polymers. These elastic films have an elastic recovery at zero recovery time (hereinafter defined) when subjected to a standard strain (extension) of 50 percent at 25C. and 65 percent relative humidity of at least about 40 percent preferably at least about 50 percent, and most preferably at least about 80 percent.

Elastic recovery as used herein is a measure of the ability of a structure or shaped article such as a film to return to its original size after being stretched, and may be calculated as follows: 7 A

Elastic Recovery (ER) length added when stretched strain is merely exemplary. In general, such starting films will have higher elastic recoveries at strains less than 50 percent, and somewhat lower recoveries at strains substantially higher than 50 percent, as compared to their elastic recovery at a 50 percent strain.

Thesestarting elastic films will also have a percent crystallinity of at least percent, preferably at least 30 percent and most preferably at least 50 percent, e.g., about 50 to 90 percent, or more. Percent crystallinity is determined by the x-ray method described by R. G. Quynn et al. in the Journal of Applied Polymer Science, Vol. 2, No. 5, pp. 166-173 1959). For a detailed discussion of crystallinity and its significance in polymers, see Polymers and Resins, Golding (D. Von Nostrand, 1959).

Preferred suitable starting elastic films, as well as the preparation thereof, are further defined in British Pat. No. 1,198,695, published July 15, 1970. Other elastic films which may be suitable for the practice of the present invention are described in British Pat. No. 1,052,550, published Dec. 21, 1966, and are well known in the art.

The starting elastic films utilized in the preparation of the permeable films used in the present invention should be differentiated from films formed from classical elastomers such as the natural and synthetic rubbers. With such classical elastomers the stress-strain behavior, and particularly the stress-temperature relationship, is governed by an entropy-mechanism of deformation (rubber elasticity). The positive temperature coefficient of the retractive force, i.e., decreasing stress with decreasing temperature and complete loss of elas- Although a standard strain of 50 percent is used to identify theelastic properties of the starting films, such tic properties at the glass transition temperature, are consequences of entropy-elasticity. The elasticity of the starting elastic films utilized in preparing microporous films, however, is of a different nature. In qualitative thermodynamic experiments with these elastic starting films, increasing stress with decreasing temperature (negative termperature coefficient) may be interpreted to mean that the elasticity of these materials is not governed by entropy effects but dependent upon an energy term. More significantly, the starting elastic films have been found to retain their stretch properties at temperatures where normal entropy-elasticity could no longer be operative. Thus, the stretch mechanism of the starting elastic films is thought to be based on energy-elasticity relationships, and these elastic films may then be referred to as non-classical elastomers.

As stated, the starting elastic films employed in preparing the microporous films used in this invention are made from a polymer of a type capable of developing a significant degree of crystallinity, as contrasted with more conventional or classical elastic materials such as the natural and synthetic rubbers which are substantially amorphous in ther unstretched or tensionless state.

A significant group of polymers, i.e., synthetic resinous materials, which may be used are the olefin polymers, e.g., polyethylene, polypropylene, poly-3-methyl butene-l, poly-4-methyl pentene-l, as well as copolymers of propylene, S-methyl butene-l, 4-methyl pentene-l, or ethylene with each other or with minor amounts of other olefins, e.g., copolymers of propylene and ethylene, copolymers of a major amount of 3- methyl butene-l and a minor amount of a straight chain n-alkene such as n-octene-l, hexadecene-l, noctadene-l or other relatively long chain alkenes, as well as copolymers of 3-methyl petene-l and any of the same n-alkenes mentioned previously in connection with 3-methyl butene-l. These polymers in the form of film should generally have a precent crystallinity of at least 20 percent, preferably at least 30 percent, and most preferably about 50 percent to percent or higher.

For example, a film-forming homopolymer of polypropylene may be employed. When propylene homopolymers are used, it is preferred to employ an isotactic polypropylene having a percent crystallinity as indicated above, a weight average molecular weight ranging from about 100,000 to 750,000, preferably about 200,000 to 500,000 and a melt index (ASTM- 8D-l238-57T, Part 9, page 38) from about 0.1 to about 75, preferably about 0.5 to 30, so as to give a final film product having the requisite physical properties.

While the present disclosure and examples are directed primarily to use of the aforesaid olefin polymers, the invention also contemplates the high molecular weight acetal, e. g., oxymethylene polymers. While both acetal homopolymers and copolymers are contemplated, the preferred acetal polymer is a random oxymethylene copolymer, one which contains recurring oxymethylene, i.e., --CH --O-, units interspersed wtih -OR groups in the main polymer chain where R is a divalent radical containing at least two carbon atoms directly linked to each other and positioned in the chain between the two valences, with any substituents on said R radical being inert, that is, those which do not include interfering functional groups and which will not induce undesirable reactions, and wherein a major amount of the OR units exist as single units attached to oxymethylene groups on each side. Examples of preferred polymers include copolymers of trioxane and cyclic ethers containing at least two adjacent carbon atoms such as the copolymers disclosed in US. Pat. No. 3,027,352 of Walling et a1. These polymers in film form should also have a crystallinity of at least 20 percent, preferably at least 30 percent, and most preferably at least 50 percent, e.g., 50 to 60 percent or higher. Further, these polymers have a melting point of at least 150C., and a number average molecular weight of at least 10,000. For a more de- .tailed discussion of acetal and oxymethylene polymers,

see Formaldehyde, Walker, pp. 175191 (Reinhold Many of the microporous films useful to make the first aid dressings of this invention are readily disposable after use by incineration. Acetal polymers are superior in this regard.

Other relatively crystalline polymers to which the invention may be applied are the polyalkylene sulfides such as polymethylene sulfide and polyethylene sulfide, the polyarylene oxides such as polyphenylene oxide, the polyamides such as polyhexamethylene adipamide (nylon 66) and polycaprolactam (nylon 6), and polyesters such as polyethylene terephthalate, all of which are well known in the art and are not described further herein for the sake of brevity.

The types of apparatus suitable for forming the starting elastic films to be used to make microporous films for the first aid dressings of this invention are well known in the art.

For example, a conventional film extruder equipped with a shallow channel metering screw and coat hanger die, is satisfactory. Generally, the resin is introduced into a hopper of the extruder which contains a screw and a jacket fitted with heating elements. The resin is melted and transferred by the screw to the die from which it is extruded through aslot in the form of a film from which it is drawn by a take-up or casting roll. More than one take-up roll in various combinations or stages may be used. The die opening or slot width may be in the range, for example, of about 10 to 200 mils.

Using this type of apparatus, film may be extruded at a drawdown ratio of about 20:1 to 200:1, preferably 50:1 to 150:1.

The terms drawndown ratio or, more simply, draw ratio, as used herein is the ratio of the film wind-up or take-up speed to the speed of the film issuing at the extrusion die.

The melt temperature for film extrusion is in general no higher than about 100C. above the melting point of the polymer and no lower than about 10C. above the melting point of the polymer.

For example, polypropylene may be extruded at a melt temperature of about 180C. to 270C preferably 1 200C. to 240C. Polyethylene may be extruded at a melt temperature of about 175C. to 225C., while acetal polymers, e.g., those of the type disclosed in US. Pat. No. 3,027,352 may be extruded at a melt temperature of about 185C. to 235C, preferably 195C. to 215C.

The extrusion operation is preferably carried out with rapid cooling and rapid drawdown in order to obtain maximum elasticity. This may be accomplished by having the take-up roll relatively close to the extrusion slot, e.g., within two inches and, preferably, within one inch. An air knife operating at temperatures between, for example, 0C. and 40C., may be employed within one inch of the slot to quench, i.e., quickly cool and solidify the film. The take-up roll may be rotated, for example, at a speed of 10 to ft/min., preferably 50 to 500 ft/min.

While the above description has been directed to slot die extrusion methods, an alternative method of forming the starting elastic films for the microporous films used in this invention is the blown film extrusion method wherein a hopper and an extruder are employed which are substantially the same as in the slot extruder described above. From the extruder, the melt enters a die from which it is extruded through an annulus to form a tubular film having an initial diameter D Air enters the system through an inlet into the interior of said tubular film and has the effect of blowing up the diameter of the tubular film to a diameter D Means such as air rings may alsobe provided for directing air about the exterior of the extruded tubular film so as to provide quick and effective cooling. Means such as a cooling mandrel may be used to cool the interior of the tubular film. After a short distance during which the film is allowed to completely cool and harden, it is wound up on a take-up roll.

Using the blown film method, the drawdown ratio is preferably 20:1 to 200:1, the slot opening 10 to 200 mils, the D /D ratio, for example, is from 0.5 to 6.0 and preferably about 1.0 to about 2.5, and the take-up speed, for example is 30 to 700 ft/min. The melt temperature may be within the ranges given previously for slot extrusion.

The extruded film may then be initially heat treated or annealed in order to improve crystal structure, e.g., by increasing the size of the crystallites and removing imperfections therein.

In order to render the precursor, or starting, film microporous, it is subjected to a process generally comprising the steps of stretching until micropores are formed and heat setting to stabilize the thus formed pores of the starting film. Preferably the process comprises either the consecutive steps of cold stretching, hot stretching and heat setting or the steps of cold stretching and simultaneously hot stretching and heat setting the precursor film. Other variations on this process (such as elimination of the hot stretching step) can be carried out, resulting in microporous films which, although slightly inferior to those films made by the cold stretch hot stretch a heat set process, still find utility in the microporous first aid dressings of this invention.

The term cold stretching as used herein is defined as stretching or drawing a film to greater than its original length and at a stretching temperature, i.e., the temperature of the film being stretched, less than the temperature at which the melting of the film begins when the film is uniformly heated from a temperature of 25C. at a rate of 20C. per minute. The term hot stretching" or hot stretching-heat setting as used herein is defined as stretching above the temperature at which melting begins when the film is heated from a temperature of 25C. at a rate of 20C. per minute, but below the normal melting point of the polymer, i.e., below the temperature at which fusion occurs. For example, using polypropylene elastic film, cold stretching is carried out, preferably, below about 120C. while hot stretching or hot stretching-heat setting is carried out utive stretching steps occur is in the range of about to about 300 percent of the original length of the film prior to stretching.

The resulting microporous film exhibits a final cyrstallinity of preferably at least 30 percent, more preferably about 50 to 100 percent as determined by the aforementioned x-ray method and as previously defined an elastic recovery from a 50 percent extension of at least 50 percent, preferably 60 to 85 percent. Furthermore, this film exhibits an average pore size of about 100 to 12,000 Angstroms more usually 150 to 5,000 Angstroms, the values being determined by mercury porosimetry as described in an article by R. G. Quynn et al., on pages 21-34 of Textile Research Journal, Jan. 1963.

Additional description, of the different methods for the preparation of microporous films is contained in copending U.S. application, Ser. No. 835,367 filed on June 23, 1969,-copending U.S. application, Ser. No. 876,511 filed on Nov. 13, 1969, copending U.S. application Ser. No. 84,712 filed on Oct. 28, 1970, and copending U.S. application, Ser. No. 104,715 filed on Jan. 7, 1971.

The means for fastening the first aid dressing of this invention to the victims are of such nature that a seal is formed between the victim and the dressings that will permit the positive pressure generated by moisture vapor issuing from the covered area of the patient to at least partially inflate the dressing away from the injured area which is covered by the dressing. Any suitable means may be used. Examples of such means are drawstrings about the open perimeters of, for example, dressings of the sort illustrated in FIGS. 1 and 2, elastic bands affixed to those perimeters which have a series of gripper snaps to allow for correct adjustment, or tapes affixed to those perimeters which have a Velcro closure device so positioned as to allow correct adjustment to the victim.

The first aid dressings which are flat, rather than tubular with a closed end, may be affixed over the wounded or burned area by means of an adhesivecoated perimeter, preferably on the microporous dressing itself. The adhesive is preferably a continuous but microporous pressure sensitive adhesive coating. This adhesive is preferably a rubbery-based adhesive which is water-insoluble and viscoelastic, and the coating is aggressively tacky in its normal dry state. This adhesive coating is firmly anchored to provide a unitary integrated structure that will not be delaminated or split when the tape is unwound.

The present invention contemplates the use of any highly gas and moisture permeable adhesive coating for the film herein. Preferably, the process of forming the continuous adhesive'coating around the perimeter of the film is of such a nature that, during the drying of the coating, innumerable, pore-like apertures spontaneously develope therein and these pores result in a viscoelastic porous adhesive membrane covering the porous backing. These pores are so minute that they are not visible to the human eye upon casual inspection of the film-the adhesive coating thus being of a visibly continuous nature. They are, however, of sufficient size and closeness together to permit of ample transpiration of skin moisture and wound vapors. and to permit of absorption of liquid material therethrough into the porous film backing. The effect is essentially uniform over the entire contacted body area; as distinguished from the effects produced by tapes which have relatively large holes or apertures therein, or which have been perforated by needles, or which have discontinuous spacedapart strips or spots of ordinary impermeable adhesive on a porous backing, to obtain a so-called breathable" tape, as suggested in the prior art. The continuous uniform microporous recticular nature of the continuous adhesive perimeter around the film is a decided advantage.

If desired, use can be made of rubber-base pressuresensitive adhesive coating compositions that are free from extraneous or undesirable non-volatile components or ingredients, and from liquid plasticizers, thereby avoiding the presence in the dried adhesive coating of substances which impair adhesion or cohesion or which may cause or promote skin irritation. For instance, use can be made of pure viscoelastic polymers which are inherently aggressively tacky and highly cohesive and which are relatively non-irritating to the human skin, such as the pressure-sensitive acrylate polymers. This latter adhesive is not only waterinsoluble but it is hydrophobic as indicated by the fact that drops of water deposited on the surface do not flow out and wet the surface. The microporosity of the adhesive coating obviates the need of including any moisture-absorptive material in the adhesive composition. 1

In a preferred embodiment for the fabrication of the dressings of this invention, the viscoelastic pressuresensitive adhesive is applied to the porous backing film in such a way as to provide thereon a continuous soft sticky viscid coating containing a volatile vehicle which is in small enough proportion to avoid wicking or penetration of the adhesive through the body of the porous film backing when it is-promptly dried after application. Further drying of the semi-dry adhesive coating results in progressive loss of the residual volatile vehicle and a shrinkage of the coating. These capillary and shrinkage effects produce a strain in each tiny portion of the viscoelastic adhesive film which bridges a backing passageway and in yielding to this strain one or more minute openings (pores) are autogenously formed therein. In this way the entire adhesive coating, during drying autogenously develops a vast number of closely spaced pores per square inch producing a microporous reticulated structure in an adhesive film that remains visibly continuous and provides a unitary microporous film-adhesive web.

The necessary degree of adherency of the dressing is not prevented by the presence of these pores. The viscoelastic property of the adhesive prevents the pores from closing up even during prolonged pressing of the adhesive in storage.

Use of an adhesive which is agressively tacky but is more rubbery and firmer than conventional surgical tape adhesive (which are loaded with softeners and pigments) is desirable, and is provided by the previously a 1 I mentioned acrylate polymer adhesive. Such a dressing can be removed more readily and comfortably from the skin after prolonged contact and yet is readily applied and immediately adhere. to the skin with adequate adhesion when pressed into place. Furthermore, the elasticity of the film backing utilized herein can be maintained, e.g., at 50 percent extension a recovery of 80 percent can be obtained, so that the tape or dressing will retain and hold the skin in its initial position.

Application of the adhesive to the porous film backing may be accomplished by a variety of methods. One convenient way to carry out this process is first to prepare in the usual way a solution of the adhesive in sufficient solvent (volatile vehicle) to provide a coatable viscosity. This adhesive solution is then coated in the desired perimeter shape and size on a liner web having a dense nonporous, shiny-smooth surface of an antistick nature that will permit of ready separation from the adhesive coating in its subsequent semi-dried and fully dried states. This adhesive coating is partially dried by passingthe web into a hot air drying oven or over a heated drum, and is brought into laminar bonding contact with a superimposed web of the porous backing. The resulting sandwich web is then promptly further heated to eliminate the residual solvent from the adhesive coating, during which interval the adhesive coating acquires the desired porous state (which is retained in the fully dried product) and upon completion of the drying operation to fully remove the solvent, it is wound up in a jumbo roll. Drying of the applied adhesive coating perimeter layer is conducted with sufficient 'promptness to prevent the adhesive from soaking or striking through the body of the porous film backing. The evaporating solvent is free to escape through the porous backing web. Drying of the adhesive coating while at all stages in contact with the impermeable, smooth, shiny surface of the liner, results in the dried adhesive coating having a smooth dense outer surface characteristic. During the porosity-inducing phase of the drying, the adhesive contact to the liner is disrupted at the points where the pores are formed. This is permitted by the anti-stick surface which allows the adhesive to pull away from it where the pores develop, leaving the surrounding adhesive surfaces in continued contact with the liner surface.

This dried composite sheeting is subsequently unwound from the jumbo roll and the adhesive-coated films and liner are slit between perimeters of adjoining dressings. For use the liner is stripped from the dressing and discarded. While in place during storage, however, it keeps the dressing side that will subsequently be toward the wound free from contamination.

Instead of using a liner web in the manufacture of the tape (as just described), the adhesive solution can be combined with a smooth-surfaced anti-stick liner web and handled as previously described. It will be evident that these procedures also result in a tape having a smooth adhesive surface.

Other methods of forming an adhesive perimeter may 7 also be used.

The transpiration porosity of the tape is such as to provide a moisture vapor transmission rate that exceeds the perspiration emission rate of the human skin under ordinary conditions. The permeable or porous adhesive coating is hydrophobic but is (in common with other such adhesives) capable of softening and swelling upon prolonged contact with liquid perspiration. However, due to transpiration of perspiration through the pores, there is much less tendency for the adhesive to soften or lose tackiness upon prolonged contact with perspiring skin than is the case where the ordinary non-porous type of adhesive is used. Perspiration from the underlying skin can pass through the adhesive coating either as vapor, or as liquid which is absorbed by the porous capillary structure of the backing and thence evaporated, so that in any case the skin is maintained in a dry state under ordinary conditions. These features result in retention of the tape and the skin in the initial position.

The flat film dressing which is selfinflating as hereinbefore described should have sufficient free area to allow sufficient room to inflate the dressing. Usually the free area which will become inflated should be at least about 10 square inches.

For flat film first aid dressings of smaller area, it is preferred that a walled adhesive-coated perimeter be utilized, which will space the dressing away from the wound. Such a dressing is shown in FIGS. 5 & 6. The walled perimeter may be of any sufficiently flexible ma terial which will contour itself to the area of the body to be covered. Those polymers mentioned above for preparation of the microporous dressing, as well as others, may be used for the walled perimeters, which need not be microporous. It will usually be practical to employ the same class of polymers for theperimeter walls as was used to make the microporous dressing. The walls should be of sufficient height to space the microporous dressing away from the wound. Generally, heights of one-sixteenth inch to about three-sixteenths inch are useful. The widths of the walls are generally not critical. They should be wide enough, however, to

permit the application of sufficient adhesive, which will maintain the dressing securely covering the wound.

In any of the dressings of this invention but particularly the larger tubular ones illustrated in FIGS. 1 and 2, there may be incorporated in the dressing a valve with means for opening and closing access to the enclosed dressing by gases, liquids, or solids so that they can be introduced into or extracted from the atmosphere in the closed dressing. Such a dressing is shown in FIG. 4. Gases liquids, or solids, which can be introduced can either promote healing, or be bacteriostatic or bactericidal, or anesthetic, or perform combinations of these and other functions. Oxygen is known to promote healing and may be introduced in proper mixtures for that purpose. Gaseous or vaporous bactericides, bateriostats and anesthetics are well known.

EXAMPLE I A first aid dressing of the sort mentioned in connection with FIG. 1 and made of microporous polypropylene (produced in accordance with the foregoing description) was pulled up over a human arm and the top of the dressing secured about the upper arm area to form a substantially air-tight seal. After several minutes the first aid dressing, which was initially limp about the arm, became inflated through the action of the positive pressure of the moisture vapor issuing from the arm. The first aid dressing was essentially not in contact with the arm but rather freely floated at some distance from it. At no time was the arm clammy or sweaty from the encasement in the first aid dressing, rather, it felt cool and comfortable in the dressing.

EXAMPLE II A inches X 10 inches X 1 mil microporous polypropylene first aid dressing with a one-half inch wide adhesive perimeter, which is produced in accordance with the foregoing description, is placed over a human abdomen. Within minutes the adhesive-free central portion of the dressing is inflated away from the abdomen by the action of the positive pressure of moisture vapor issuing from the covered skin. The covered area is dry,'and not at all clammy or sweaty, as would be the case with a nonporous plastic film.

EXAMPLE in A walled-perimeter microporous dressing is prepared from microporous polypropylene film 2 inches in diameter and 1 mil thick by heat sealing the edge to the top of a one-eighth inch thick 0 shaped ring of polypropylene with the width of the 0 one-fourth inch. An adhesive coating was coated on the bottom of the 0. The adhesive side of the finished dressing is then placed against a human cheek, where after a short while the microporous dressing becomes slightly domed from the action of the partial pressure of moisture vapor issuing from the skin.

EXAMPLE IV Example I is repeated but with an optional modification of the dressing. The modification comprises the heat sealing of a commercial plastic valve to the dressing. Again the dressing is affixed to an arm, but this time oxygen from a cylinder is introduced through the valve into the atmosphere in the dressing thereby enriching the enclosed air in the dressing. The valve is then closed. Depending on porosity, size of the dressing, etc., the higher concentration of oxygen in the air in the enclosed dressing will slowly equilibrate with the lower concentration of oxygen in the atmosphere outside the dressing by a process of diffusion through the microporous dressing.

Some microporous films may have good tensile strength in one direction (machine) and poor tensile strength in the other direction (transverse). If this proves to be a problem in a particular dressing, the film may be reinforced by cross laminating with another layer of the film with the above directions at to each other. Other means of reinforcing may also be used.

What is claimed is:

1. A first aid dressing comprising an inflatable micorporous polymeric film, said film having an average pore size in the range of between about to 12,000 Angstroms, having a shape adapted to cover and enclose a wound or burn and means about the perimeter of the first aid dressing by which the dressing can be securely affixed around the wound or burn.

2. The first aid dressing of claim 1 in which the microporous film is a microporous polypropylene film.

3. A first aid dressing as claimed in claim 2 in which the microporous polypropylene film dressing has an average pore size in the range of between about and 5,000 Angstroms.

4. The first aid dressing of claim 1 which is in the form of a tubular structure sealed across one end.

5. A first aid dressing as claimed in cliam 4 in which the open end of the tubular structure has a draw string attached thereto.

6. A first aid dressing as claimed in claim 4 wherein the open end of the tubular structure has affixed around its perimeter an elastic closure.

7. A first aid dressing as claimed in claim 6 wherein the elastic closure is a flat elastic band.

8. The first aid dressing of claim 4 in which there is incorporated in the dressing a valve as a means for opening and closing access to the enclosed dressing by gases, liquids, or solids.

9. A first aid dressing as claimed in claim 1 in which the dressing is in the form of a flat film with means about its perimeter to securely affix the dressing about the wound or burn.

10. A first aid dressing as claimed in claim 9 in which on one side of the film and substantially continuously extending about its perimeter there is an adhesive band.

11. A first aid dressing as claimed in claim 9 which is affixed to the top of a wall around its perimeter and the means for affixing the dressing around the wound or burn is an adhesive coating on the bottom of the wall.

Claims

2. The first aid dressing of claim 1 in which the microporous film is a microporous polypropylene film.
3. A first aid dressing as claimed in claim 2 in which the microporous polypropylene film dressing has an average pore size in the range of between about 150 and 5,000 Angstroms.
4. The first aid dressing of claim 1 which is in the form of a tubular structure sealed across one enD.
5. A first aid dressing as claimed in cliam 4 in which the open end of the tubular structure has a draw string attached thereto.
6. A first aid dressing as claimed in claim 4 wherein the open end of the tubular structure has affixed around its perimeter an elastic closure.
7. A first aid dressing as claimed in claim 6 wherein the elastic closure is a flat elastic band.
8. The first aid dressing of claim 4 in which there is incorporated in the dressing a valve as a means for opening and closing access to the enclosed dressing by gases, liquids, or solids.
9. A first aid dressing as claimed in claim 1 in which the dressing is in the form of a flat film with means about its perimeter to securely affix the dressing about the wound or burn.
10. A first aid dressing as claimed in claim 9 in which on one side of the film and substantially continuously extending about its perimeter there is an adhesive band.
11. A first aid dressing as claimed in claim 9 which is affixed to the top of a wall around its perimeter and the means for affixing the dressing around the wound or burn is an adhesive coating on the bottom of the wall.