Note: Descriptions are shown in the official language in which they were submitted.
:~ll49Z~
- 1 -
The invention relates to a flocked, foam-coated water
vapor permeable, bacterial barrier.
Background Of The Invention
There is a need for bacterial barriers that are also water
vapor permeable, from which surgical drapes and gowns and
similar articles can be fabricated. The desired
properties of such barriers would include:
1) ability to prevent passage of bacteria, even under
moderate pressure such as woulcl be encountered by a '
surgeon leaning against a sharp edge or corner;
2) comfortable to wear, which re~uires a certain minimum
moisture vapor transmission rat:e. Of secondary importance
is the amount of skin contact;
3) sterilizability;
4) absence of linting;
5) low cost so that the ,article can be used once and then
discarded (to eliminate the need for the hospital to
launder and sterilize the article);
-2- CHIC-61~
6) appropriate aesthetics, including a fabric-like
appearance. This is especially important for surgical
gown material; and
7) sufficient strength to withstand (a) fabrication into
finished products, (b) normal handling, and (c) the
stresses and strains incurred in use.
The present invention is directed to the provision of a
bacterial barrier that has the above-enumerated
properties. As far as is known, no earlier material has
all of these properties.
Broad Statement Of The Invention
The invention provides a water vapor permeable bacterial
barrier having the appearance of fabric, and being capable
of filtering bacteria. The barrier comprises a
microporous plastic film, said film being coated on at
least one side thereof with a foamed latex polymer, and
flocked fibers on the exterior surface of the foamed latex
polymer. Optionally, the barrier may contain fibrous
reinforcement to enhance certain mechanical properties
such as tear strength and/or puncture resistance.
The Prior Art
Loft et al., in U.S. Patent No. 3,745,057, disclose the
use of microporous plastic film in sterilizable packaging
as a bacterial barrier.
Absorbent medical dressings having microporous plastic
film backings are disclosed by Bierenbaum et al., U.S.
Patent No. 3,426,754, Riely, U.S. Patent No. 3,709,221,
and Elton et al., U.S. Patent No. 3,870,593. Elton et al.
also state that their microporous film can be used to
-3- CHIC-~19
fabricate surgical drapes (Col. 10, line 47), but no
structure of such a drape is disclosed.
Strauss, in U.S. Patent No. 3,214,501, discloses
nonadhesive bandages made from a microporous film composed
of butyl rubber and polyethylene.
Westfall et al., in U.S. Patent No. 4,056,646 and Klein,
in U.S. Patent Nos. 3,903,331 and 3,961,116, disclosed
flocked, foamed latex polymer on a fibrous substrate.
Palmer et al., in U.S. Patent No. 3,956,553, disclose a
flocked fabric produced by adhesively bonding flocking to
a base fibrous web. At Col. 4, lines 57-58, the patentees
state that the flocked fabric is sui-ted for hospital
drapes and surgical gowns.
A surgical drape composed of a nonporous plastic film,
nonwoven fabric, and latex adhesive is disclosed by
Hansen, U.S. Patent No. 3,809,077.
Outdoor garments (e.g., parkas) made from "Gore-Tex" (a
microporous polytetrafluoroethylene film) sandwiched
between nylon taffeta and nylon tricot, are sold
commercially (see page 21 of L. L. Bean's Spring 1978
catalogue).
Detailed Description of the Invention
The invention employs microporous plastic films which are
capable of filtering bacteria, but which are sufficiently
water vapor permeable to be comfortable to wear. By
"capable of filtering bacteria" is meant that water that
has been inoculated with bacteria can be forced through
the film under moderate pressure (e.g., about 5-20 psi),
with sterile water being recovered on the other side of
~IL4~2~
4 CHIC-619
the film. The requisite filtering capabilities are
ordinarily achieved when the maximum pore size is about
0.2 micron, as determined by the bubble point method using
isopropyl alcohol as the wetting liquid. The bubble point
method for pore size determination is the procedure of
ASTM F316-70.
The water vapor permeability requirements for comfort
cannot be stated with exact precision because conditions
of end-use vary widely. When the body is at rest, normal
skin exudes moisture at a rate of the order of 60 grams
per 100 square inches per 24 hours. Thus, adding a factor
for perspiration, the minimum moisture vapor transmission
rate (MVTR) required for comfort is about 100, and
preferably about 250, grams per 100 square inches per 24
hours. tMVTR is measured by ASTM E96-66, Procedure E.)
Of course, the higher the MVTR value is, the more
comfortable the barrier will be.
The preferred plastics from which to produce the
microporous film are olefin polymers such as film grade
isotactic polypropylene and film grade high density
polyethylene. Polypropylene having a melt ~low rate (by
ASTM D-1238, Method L, I2 at 230C.) of from about 0.5
to about 8 grams per 10 minutes, and high density
polyethylene having a melt index (by ASTM D-1238-65,
Method E, I2 at 190C.) of from about 0.05 to about 1,
are generally suitable.
The preferred olefin polymer microporous films, and
microporous films made from other stretch orientable
plastics such as thermoplastic polyurethanes, used in the
invention can be made by stretching a film containing
minute fracture sites or pore-nucleating agents such as
finely divided filler filler and/or minute crystalline
domains~ The use of a finely divided, inorganic,
~1~92~6
-5~ CHIC-619
water-insoluble, inert filler such as calcium carbonate
having an average particle size of less than 3 microns
is preferred. It is generally preferred to use a filler
that has been surface treated to impart hydrophobic (or
oleophilic) properties in order to facilitate dispersion
and mixing with the olefin polymer. As a general rule,
the filler is employed in amounts of from about 40 to
about 70 weight per cent, based on weight of total polymer
plus filler. At proportions below about 40 weight per
cent, porosity tends to become insufficient, and at
proportions above about 70 weight per cent, the strength
properties of the film tend to be adversely affected (in
particular, the film becomes brittle). The above-stated
proportions reflect experience with calcium carbonate
having an average particle size of about 3 microns. The
practical range of proportions may differ somewhat with
fillers whose specific gravities differ significantly Erom
calcium carbonate, and with fil:Lers having significantly
different particle size. For instance, it is anticipated
that less filler can be used, perhaps as little as about
20 weight per cent, while still achieving the desired
porosity, if it has much smaller particle size, e.g., an
average of 0.1 micron or less.
It is desirable in many cases to employ a small proportion
of a polymeric modifier in an olefin polymer film in order
to improve the tear resistance, impact strength, and the
asthetic properties (hand, drape, etc.) of the film. The
polymeric modifier also serves to facilitate dispersion of
the filler in the olefin polymer.
Such polymeric modifiers include ethylene-propylene
rubbers, ethylene-vinyl acetate copolymers, ethylene-
acrylic ester (e.g. r ethyl acrylate) copolymers, poly-
butene, thermoplastic polyurethane, and thermoplasticrubbers. The thermoplastic rubbers are preferred.
9~4gii
-6- CHIC-619
The polymeric modifier is ordinarily employed in propor-
tions of up to about 10-15 weight per cent, based on total
weight of the film. The maximum amount of polymeric
modifier that can be employed is that amount which
substantially impairs the orientability, and hence ability
to form pores, of the film. This maximum amount will vary
somewhat from one formulation to another, and can readily
be determined by routine experimentation.
The thermoplastic rubbers, which are the preferred
polymeric modifiers, are block copolymers oE styrene and
butadiene or isoprene. They constitute a known class of
materials, which is described in an article by S. L.
Aggarwal, entitled "Structure And Properties Of Block
Polymers And Multi-Phase Polymer Systems: An Overview Of
Present Status And Future Potential", in Polymer, Volume
17, November 1976, pages 938-956.
It is desirable to thoroughly mix the polymer(s) and
~0 filler prior to film formation. A twin screw extruder/
pelletizer has been found to be very useful for this
purpose.
Films based on the above-described formulations are made
by known methods. Illustrations include tubular blown
film methods and cast film (i.e., slot die extrusion)
methods.
The film is made microporous by stretching. The film is
preferably stretched as much as possible in both machine
and cross directions, in order to achieve maximum
porosity. As a practical matter, however, highly filled
films cannot be stretched beyond a certain point that is
dependent, in part, upon factors such as nature and
proportion of polymer(s) and filler, gauge or thickness of
46
_7_ CHIC-619
the unstretched film, method of making the film (e.g.,
case, tubular blown, etc.) and stretching temperature. To
illustrate, 5-mil cast polypropylene or high density poly-
ethylene film containing about 50 per cent filler can be
hot stretched about 3X in both directions to produce a
l-mil microporous film. Tubular blown polypropylene or
high density polyethylene film having a gauge of from 1.5
to 2.5 mils can be stretched in the machine direction at
room temperature about 3X to produce about 1 to 1.5 mil
microporous film.
Film produced as described above, containing about 50
weight per cent filler having an average particle size of
about 3 microns, will usually have a maximum pore size not
greater than about 0.2 micron and a moisture vapor
transmission rate of about 100 to 150 grams per 100 s~uare
inches per 24 hours.
Microporous plastic films made by other processes can also
be employed. Such other processes include the technique
of preparing a plastic film containing a Einely divided,
soluble filler, and leaching out the filler with a
solvent. This method is less preferred because it is
generally more expensive than the stretching process
described above in detail.
In one desirable aspect of the invention, the microporous
film is produced from two layers of film. In this aspect,
two separate films (or an unslit tubular blown film) are
superimposed on one another and are then fed through hot
rolls maintained near the melting point of the film to
form a laminate that cannot be pulled apart without
destroyin~ the films. The laminate is then stretched as
taught above to form a microporous film. The advantage of
using the double layer construction is that the proba-
bility of having pin holes or other defects that extend
~1~9;246
-~- CHIC-619
all the way through the film is greatly reduced. Gel
specs, impurities, or other foreign materials that might
cause such defects would be found in only half the
thickness of the double layer film product, thereby
substantially reducing the probability of pin hole
formation from these causes.
The desirable effects of a double layer film may also be
produced by coextrusion wherein two separate streams of
polymer melt are joined in laminar flow just upstream of
the die. By so doing, gel specs, etc., would be isolated
in half the extruded film thickness, thereby reducing the
probability of pin hole formation.
The microporous film described above is coated with a
Eoamed latex polymer on at least one side, and flocked
fibers are applied to the external surface of the foam.
The latex polymers employed are known materials. They are
generally film-forming grade materials, including
aqueous-based acrylic latexes, styrene-butadilatexes,
polyvinyl acetate latexes, natural or synthetic rubber
latexes, and any other aqueous-based latex made from a
water-insoluble polymer. The acrylic latexes are
preferred.
The foaming of the latex is effected by beating air into
the latex so that the volume of the latex is increased
from about 2 to about 18 times its original volume. (The
latex employed will ordinarily contain conventional addi-
tives such as surfactants, foam stabilizers, thickeners,cross-linking agents, colorants and/or opacifying agents,
and the like, employed in the usual amounts.)
The foamed latex is then applied to the surface of the
microporous plastic film by knife coating, reverse roll
coatingl or other conven-tional procedure~ Flocked fibers
~92~6
-9- CHIC-619
are then applied to the external surface of the foam by
spraying, dusting, sieving, or the like. The flock is
preferably applied only in the amount required to coat the
latex. This minimizes linting. Short cut cotton flock is
preferred, although other types of flock can be used The
flocked and foamed film is then dried to remove the water
from the foamed latex, as by passing through a heated
tunnel maintained at a temperature of about 80C. to about
150C. for a period of about 5 to about 90 seconds. If
desired, the foamed and flocked film can be passed through
a pair of rolls under moderate pressure to crush the foam.
This can be done either before or after curing. Loose
flock, if any, is then removed by vacuum, brushing, beater
bars, or a combination thereof. The flock is an important
contributor to the textile-like appearance of the
bacterial barrier of the invent:ion.
If desired, a coating of foamecl latex polymer and flocked
fibers can be applied to the ot:her surface of the
microporous film. This will usually be done before the
crushing and final drying or curing steps. The final
drying and curing step is carried out by subjecting the
late~ polymer to a temperature within the ran~e of from
about ~0C. to about 150C. for a period o~ from about 10
to 90 seconds. The temperatures in both the initial
drying step and final drying and curing step are selected
to avoid excessive shrinking of the microporous film.
Thus, temperatures used for high density polyethylene
microporous film are usually lower than those used for
polypropylene microporous film.
If desired, fibrous reinforcement may be included in the
water vapor permeable bacterial barrier of the invention
to enhance certain mechanical properties such as tear
strength. The fibrous reinforcement can be in the form of
a scrim, an open~weave gauze, a nonwoven web such as a
9;246
-10- CHIC-619
spunbonded web, or the like. The fibrous reinforcing web
can be made of fibers such as rayon, cotton, nylon,
polyester, polypropylene, bicomponent fibers, or mixtures
thereof. The reinforcing web will usually weigh from
about 0.15 to about 1 ounce per square yard.
The preferred fibrous reinforcing webs include nylon
spunbond including partially bonded and point bonded nylon
spunbond, polypropylene spunbond, polyester spunbond,
woven scrim, or cross-layed scrim.
The fibrous reinforcing web can be incorporated in the
water vapor permeable bacterial barrier by placing the
reinforcing web on top of the microporous film, and then
applying the foamed latex on top of the fibrous web.
In another aspect, the fibrous reinforcing web can be
placed on top of the flocked latex foam after the foam has
been dried, but before it has been cured, and the fibrous
web/flocked, foamed microporous film composite can be
passed through a pair of hot, embossed rolls under
moderate pressure (e.g., from about 1 to about 10 pounds
per linear inch). The temperature of the rolls can be
from about 180 to about 250F. The preferred fibrous web
to employ in this aspect of the invention is a lightweight
(e.g., about 0.2 to about 0.6 ounce per square yard) nylon
spunbonded web.
The preferred weights and proportions of the components of
the water vapor permeable bacterial barrier of the
invention are the following:
92~
--11--
Ounces per square yard
Microporous film 1/4 to 1
(0.5 to 1.5 mils)
Latex polymer foam0.2 to 0.5
~per side)
Flocking, 0.3-0.4 mm, cotton0.1 to 0.4
(per side)
Fibrous reinforcing web0.2 to 0.6
(per side)
The bacterial barrier of the invention is composed mostly
of plastic. That is, in most cases, the weight of the
microporous film plus the latex polymer foam, will equal
or exceed the weight of the fiber flocking plus the
optional fibrous reinforcing web. Nevertheless,
especially when the microporous film is coated on both
surfaces with the flocked foam, the bacterial barrier of
the invention resembles fabric in appearance more than
plastic. By this is meant that the bacterial barrier has
visual appearance, hand, and drape properties that are
characteristic of fabric, and the flocked foam surfaces do
not have the shiny visual appearance and the plastic ~eel
that is characteristic of plastic films.
The bacterial barrier of the invention exhibits sufficient
strength to withstand fabrication into finished products,
normal handling, and use. The dimensional stability, tear
strength, puncture and burst resistance, and tensile
strength, are all adequate for the intended purpose,
despite the light weight of the material. Thus, it can be
seen that the bacterial barrier of the invention combines
a number of normally contradictory properties: water
vapor permeable, yet also a bacterial barrier; composed
246
- 12 - CHIC-619
largely of plastic, yet has the appearance of fabric,
light in weight and low cost, yet strength adequate for
its intended purpose, contains fiber flocking, yet is
substantially lint-free.
The following examples illustrate the production of the
bacterial barriers of the invention:
Example 1
Film Preparation
The following components are mixed in a Werner &
Pfleiderer pelletizer:
Parts, by weiqht
Polypropylene(l) 45
Thermoplastic Rubber(2) 5
Calcium Carbonate(3)50
_______~___________________ _________.. __________________
(1) Hercules "Pro-Fax" 6723, mel-t flow of 0.8,
heat stabilized
(2) "Solprene" 41~3, a radial block copolymer; 85/15
(by weight) isoprene/styrene ratio
(3) "Hi-pflex-100", average particle size 3 microns,
with a hydrophobic surface treatment
Pro-Fax, Solprene and Hi-pflex are trademarks.
________________________________________________________
The pelletizer is a twin screw, three start profile,
extruder (screw diameter -- 53 millimeters, L/D = 35). The
materials are metered at the back end of the screw, and
are extruded into several strands, which are chopped to
form pellets. The extruder barrel temperature varies from
about 345 to about 410F.
Blown tubular film is produced from the above-described
pellets using a 1 inch, 24/1 (L/D), single screw extruder
1~L49~'~6
-13- CHIC-619
using a 20-mil gauge, 2-1/2 inch diameter die. The screen
pack behind the die contains 40/60/40 mesh screens; the
back pressure is 2000 to 3500 psi, the screw speed is 50
to 80 RPM, ~he extruder temperature is 410 to 440F., and
the die temperature is 450F. The blow up ratio is 1.3 to
2.8, the gauge of the film is 1.5 to 2.5 mils, and the lay
flat width of the film is 5 to 11 inches.
Film Stretching
The film is longitudinally stretched 3X at room
temperature using two sets of 4-roll godets. Typical
godet speeds are 0.8 feet per minute for the first set and
2.4 feet per minute for the second. For starting gauges
of 1.5 to 2.5 mils, typical finished gauges are 1 to 1.5
mils, with a 10 to 20 per cent width reduction. The film
has a maximum pore size (by the bubble point method, using
isopropyl alcohol as the wetting liquid) of 0.2 micron,
and a moisture vapor transmission of about 100 grams per
100 square inches per 24 hours.
Foam Coating
The following formulation is prepared by adding the
ingredients in the order listed:
~2~4~;;
- 14 - CHIC-619
Inqredient Parts Parts, total
dry weiqht weiqht
Water --- 26.69
Hydroxyethyl-cellulose(4) 0.09 0.09
Acrylic latex( )
ammonia, to p~ = 7 34.23 60.27
Polyethylene glycol(6)
di-2-octoate 4.74 4.74
Ammonium Stearate(7)1.55 7.74
Sodium lauryl sulfate
ammonia, to pH 9.5 0.14 0.47
_ _ _ _ _ _ _ _-- -- :
(4) "Cellosize'` HEC QP 4400 H, viscosity is 4400 cps in
2% aqueous solution
~5) "UCAR" 872 - Ethyl acrylate/2-ethylhexyl
acrylate/N-methylol acrylamide/acrylic acid
(6) "Flexol" 4G0
(7) "Paranol" F-7859 (aqueous solution)
Cellosiæe, UCAR, Flexol and Paranol are all registered
trademarks
___________________.______________________________________
The foregoing formulation is foamed by beating with 8
volumes of air. The foam is applied to the above-
described microporous film by knife coaiing a 5-10 mil
thick wet layer. Cotton flock (0.3-0.4 mil) is dusted on
the surface of the foam using a vibrating sieve. (The
sieve has 900 0.5 mm openings per square inch). The
flocked, foam-coated film is subjected to a temperature of
200F. for about 1 minute, and the excess flock is removed
by vacuuming and brushing. The coating, flocking, drying,
and cleaning process is repeated on the other side, the
æ4~
-15- CHIC-619
foam is then cured by subjecting the product to a
temperature of about 280F. for one minute, after which
the foam is crushed by passing the product through a pair
of nip rolls at a pressure of 1 to 2 pounds per linear
s inch.
The resulting product is fabric-like in appearance, and is
a water vapor permeable bacterial barrier capable of
filtering bacteria.
Example 2
formulation similar to the one described in Example 1,
but which contains 30 parts by weight of polypropylene, 10
parts by weight of thermoplastic rubber, and 60 parts by
weight of calcium carbonate is pelletized as described in
Example 1. This formulation is extruded into film using a
single screw, 2-1/2" Hartig ext:ruder having a L/D ratio of
24/1. The extruder has a 30 inch slot die ha~ing a 20-30
mil gauge. The extruder back pressure is 2200 psi, the
temperature is 360 - 420F., l:he screw turns at 18 to 50
rpm, at a through-put rate of 95-120 pounds per hour. The
extruded film is cast onto rolls maintained at a tempera-
ture of from 140 to 230F., with a line pick up speed of
about 15 feet per minute. The cast film thus produced has
a gauge of about 5 mils.
The above described cast film is stretched in the machine
direction 3X in a heated zone. The film is preheated to
about 275F., is stretched 3X in a zone maintained at
about 280 to 310F., and is taken up on take up rolls
maintained at about 1~5F. There is about a 10 per cent
width reduction during this machine direction stretching.
The film is then subjected to cross direction stretching
in a tenter frame. The stretch is about 3X, and the
._
9~
-16- CHIC-619
temperature in the tenter frame is maintained at about
310F. The film is preheated to about 300 before
stretching, and is heat set at about 302F. after
stretching. The microporous film has a gauge of about 0.7
mil, a good moisture vapor transmission rate ~about 150
grams per 100 square inches per 24 hours), and a maximum
pore size of about 0.14 to 0.18 micron, determined by the
bubble point method.
This film is coated with latex foam and cotton flock as
described in Example 1, to produce a fabric-like, water
vapor permeable, bacterial barrier capable of filtering
bacteria.
Example 3
Using the same equipment and a procedure analogous to that
described in Example 1, tubular blown film is produced
from a 50/50 (by weight) mixture of high density
polyethylene (melt index = 0.58, by ASTM D-1238-65, Method
T) and "Hi-pflex 100" calcium carbonate. The extruder
temperature is 350 to 400F., the die temperature is ~50
F., the back pressure is 5500 psi, the screw speed is 72
rpm, and the take up speed is 15 feet per minute. The
blow up ratio is about 2.6, the lay flat width of the film
is lO`inches, and the gauge of the film is 2 mils.
The film is stretched 3X at room temperature as described
in Example 1 to produce a microporous film having a gauge
of 0.8 mil.
The microporous film is then coated with foamed latex
polymer and cotton flock as described in Example 1 (except
that the drying temperature is about 150F. and the curing
temperature is about 200F.) to produce a fabric-like,
water vapor permeable, bacterial barrier capable of
filtering bacteria.
