U.S. patent number 3,824,998 [Application Number 05/188,317] was granted by the patent office on 1974-07-23 for first aid dressing for wounds or burns.
This patent grant is currently assigned to Celanese Corporation. Invention is credited to George W. Snyder.
United States Patent |
3,824,998 |
Snyder |
July 23, 1974 |
FIRST AID DRESSING FOR WOUNDS OR BURNS
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.
Inventors: |
Snyder; George W. (Hudson,
NJ) |
Assignee: |
Celanese Corporation (New York,
NY)
|
Family
ID: |
22692661 |
Appl.
No.: |
05/188,317 |
Filed: |
October 12, 1971 |
Current U.S.
Class: |
128/888; 128/856;
47/84; 602/58 |
Current CPC
Class: |
A61F
13/00021 (20130101); A61F 2013/0017 (20130101); A61F
2013/00846 (20130101); A61F 2013/00093 (20130101); A61F
2013/00106 (20130101); A61F 2013/00157 (20130101); A61F
2013/00182 (20130101); A61F 2013/00519 (20130101); A61F
2013/00272 (20130101) |
Current International
Class: |
A61F
13/00 (20060101); A61f 013/00 () |
Field of
Search: |
;128/157,132,83,165,184,260,400,82,154,156,159 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
648,733 |
|
Jan 1951 |
|
GB |
|
1,163,130 |
|
Apr 1958 |
|
FR |
|
641,061 |
|
Aug 1950 |
|
GB |
|
1,303,238 |
|
Jul 1962 |
|
FR |
|
Primary Examiner: Trapp; Lawrence W.
Attorney, Agent or Firm: Morgan; Thomas J. Grim; Linn I.
Bressler; Marvin
Claims
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 100 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 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.
Description
This invention relates to a first aid dressing for the prevention
of gross contamination and infection by air-or 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
non-porous 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
fastening the 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 structure 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
flat 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 (15). (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 or surface 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 25.degree.C. 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).
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 10 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 void-containing 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, non-porous, interconnecting surface regions
or areas which have their axes of elongation substantially
parallel. Substantially alternating with and defined by these
non-porous 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.
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 80 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 .times. 10.sup.3 /.DELTA.t .times. T)
where .DELTA.t 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, film-forming 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 25.degree.C. 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: ##SPC1##
Although a standard strain of 50 percent is used to identify the
elastic properties of the starting films, such 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.
These starting elastic films will also have a percent crystallinity
of at least 20 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 elastic 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-1, poly-4-methyl
pentene-1, as well as copolymers of propylene, 3-methyl butene-1,
4-methyl pentene-1, 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-1 and a
minor amount of a straight chain n-alkene such as n-octene-1,
hexadecene-1, n-octadene-1 or other relatively long chain alkenes,
as well as copolymers of 3-methyl petene-1 and any of the same
n-alkenes mentioned previously in connection with 3-methyl
butene-1. 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 90 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-1958D-1238-57T, 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.sub.2 --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 U.S. Pat. No. 3,027,352 of Walling et al.
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
150.degree.C., and a number average molecular weight of at least
10,000. For a more detailed discussion of acetal and oxymethylene
polymers, see Formaldehyde, Walker, pp. 175-191 (Reinhold
1964).
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 a slot 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 100.degree.C. above the melting point of the polymer and
no lower than about 10.degree.C. above the melting point of the
polymer.
For example, polypropylene may be extruded at a melt temperature of
about 180.degree.C. to 270.degree.C., preferably 200.degree.C. to
240.degree.C. Polyethylene may be extruded at a melt temperature of
about 175.degree.C. to 225.degree.C., while acetal polymers, e.g.,
those of the type disclosed in U.S. Pat. No. 3,027,352 may be
extruded at a melt temperature of about 185.degree.C. to
235.degree.C., preferably 195.degree.C. to 215.degree.C.
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, 0.degree.C. and 40.degree.C.,
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 100 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.sub.1. 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.sub.2.
Means such as air rings may also be 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.sub.1 /D.sub.2
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 - 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
25.degree.C. at a rate of 20.degree.C. 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 25.degree.C. at a
rate of 20.degree.C. 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 120.degree.C. while hot
stretching or hot stretching-heat setting is carried out above this
temperature.
When a separate heat setting step is employed, it follows the cold
stretching -- heat stretching steps and is carried out from about
125.degree.C. up to less than the fusion temperature of the film in
question. For polypropylene the range preferably is about
130.degree.C. to 160.degree.C.
The total amount of stretching or drawing which should occur when
either a single stretching or consecutive stretching steps occur is
in the range of about 10 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.sup.R 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 adhesive-coated 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
spaced-apart 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 pressure-sensitive
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 water-insoluble 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.
In a preferred embodiment for the fabrication of the dressings of
this invention, the viscoelastic pressure-sensitive 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 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 passing the 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 coated on a moving
endless casting belt or drum having a polished antistick surface,
such as are known to the film casting art. After preliminary
partial drying of the adhesive coating, the microporous dressing
film is laid on the adhesive layer and further drying is employed
to produce the porous adhesive film product. The dry product is
then stripped from the belt or drum and is 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 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 self-inflating 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 material 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 the perimeter
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 10 inches .times. 10 inches .times. 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 III
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
90.degree. to each other. Other means of reinforcing may also be
used.
* * * * *