Medical gloves abstract
A process for making powder-free medical gloves that are nevertheless
easy to don involves first forming a glove on a form by successively
dip-coating layers of a coagulant containing acid-soluble powder
dispersed throughout, an elastomer, and an antiblocking composition
with particles distributed throughout. After curing the elastomer
and applying a silicone coating, the glove is removed from the form
and treated successively with acid, to dissolve the powder, and
with bleach, to reduce blocking. Using this process, high quality
natural rubber medical gloves can be produced.
Medical gloves claims
I claim:
1. A process for making a powder-free medical glove comprising
the steps of:
a) forming the glove by
(i) dip-coating a first layer onto a glove form, the first layer
comprising a coagulant with a first acid-soluble powder dispersed
throughout,
(ii) dip-coating over the first layer a second layer of an elastomer,
(iii) dip-coating over the elastomer layer a third layer that comprises
an antiblocking composition with particles distributed throughout,
the majority of particles having a size greater than the thickness
of the antiblocking composition in the third layer,
(iv) heating the layers to cross-link the elastomer and to bond
the elastomer layer to the antiblocking layer, and
(v) dip-coating a silicone emulsion over the underlying layers;
(b) removing the glove from the form and reversing the glove, so
that the first layer is on the outside of the glove;
(c) treating the glove with an acid to dissolve the acid-soluble
powder;
(d) rinsing the glove with a first aqueous liquid;
(e) treating the glove with a bleach to reduce blocking;
(f) rinsing the glove with a second aqueous liquid;
(g) treating the glove with a silicone emulsion; and
(h) drying the glove.
2. The process of claim 1 in which the elastomer comprises natural
rubber latex.
3. The process of claim 1 in which the antiblocking composition
is selected from the group consisting of carboxylated styrene butadiene
lattice, carboxylated butadiene lattice, vinyl acrylate lattice,
and polyurethane aqueous dispersions.
4. The process of claim 1 in which the antiblocking compound comprises
a cationic polyurethane of molecular weight at least about 100000.
5. The process of claim 1 in which the particles comprise a material
selected from the group consisting of cornstarch, polyurethane,
nylon, and mixtures thereof.
6. The process of claim 5 in which the particles comprise a polyester
based polyurethane powder.
7. The process of claim 1 in which the size of the particles is
in the range from about 5 to about 50 micrometers.
8. The process of claim 1 in which the average particle size is
about 30 to about 40 micrometers.
9. The process of claim 1 in which the acid-soluble powder comprises
calcium carbonate.
10. The process of claim 1 in which the silicone emulsion has a
silicone concentration in the range from about 0.05% to 1.5%.
11. The process of claim 10 in which the silicone concentration
in the emulsion is in the range from about 0.2% to 0.65%.
12. The process of claim 1 in which the silicone emulsion further
comprises a second acid-soluble powder, which is subsequently dissolved
by the acid.
13. The process of claim 1 in which the acid comprises nitric acid.
14. The process of claim 13 in which the nitric acid concentration
is in the range from about 0.5% to 10%.
15. The process of claim 1 in which the bleach comprises sodium
hypochlorite.
16. The process of claim 1 further comprising leaching the first
two layers in water to remove soluble impurities before dip-coating
the third layer.
17. The process of claim 1 further comprising pre-washing the glove
in a dilute acid before treating the glove with acid.
18. The process of claim 17 in which the dilute acid for the pre-wash
comprises acid that has been used previously to treat earlier gloves.
Medical gloves description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for making medical gloves that
are substantially free of loose powder but are nevertheless easy
to don.
2. Description of the Related Art
Medical gloves generally have to conform tightly to the hand of
the wearer. That requirement makes it hard to don the gloves, unless
they have a lubricant on their inner (skin-contacting) surface.
Powder of one form or another has traditionally served this lubricating
function; however, post-operative complications, such as adhesions,
peritonitis, and granuloma formation have been attributed to the
use of loose powder on surgical gloves and other items used in surgery.
To avoid the potential complications, there have long been efforts
to reduce or eliminate the need to use powder to facilitate donning
of medical gloves. A number of approaches have been tried, including
halogenating the gloves, blending rubber and resin latex, and depositing
granular material on the inner surface of the gloves. These attempts,
and their drawbacks, have been summarized in U.S. Pat. No. 4143109
issued on Mar. 6 1979 to Stockum, and the disclosure of that patent
is incorporated herein by reference. Stockum's patent discloses
yet another approach to avoiding the need to use loose dusting powder
to permit easy donning of gloves. His approach involves having an
inner layer of the glove that is bonded to the outer, elastomeric
layer. The inner layer has embedded in it particles that are distributed
throughout and that are greater in size than the thickness of the
inner layer. Thus, the particles protrude from the inner surface,
while remaining secured to the surface and not being easily abraded
off. A problem with that approach is that the number of particles
to be contained in the inner layer has to be carefully controlled.
If too few particles are embedded, donning remains difficult. If
too many particles are used, some loose particles could remain and
could possibly cause the undesirable medical effects.
Another approach to facilitating medical glove donning is disclosed
in U.S. Pat. No. 4499154 issued on Feb. 12 1985 to James et
al. That approach makes use of a skin-contacting coating of a lubricating
hydrogel bonded to the inner surface of the glove and treated with
a surfactant to improve its lubricity. However, it is not capable
of providing gloves that are as easy to don as powdered gloves.
SUMMARY OF THE INVENTION
In accordance with the present invention, a process for making
a powder-free medical glove comprises:
a) forming the glove by
(i) dip-coating a first layer onto a glove form, the first layer
comprising a coagulant with an acid-soluble powder dispersed throughout,
(ii) dip-coating over the first layer a second layer of an elastomer,
(iii) dip-coating over the elastomer layer a third layer that comprises
an antiblocking composition with particles distributed throughout,
the majority of particles having a size greater than the thickness
of the antiblocking composition in the third layer,
(iv) heating the layers to cross-link the elastomer and to bond
the elastomer layer to the antiblocking layer, and
(v) dip-coating a silicone emulsion over the underlying layers;
(b) removing the glove from the form and reversing the glove, so
that the first layer is on the outside of the glove;
(c) treating the glove with an acid to dissolve the acid-soluble
powder;
(d) rinsing the glove with a first aqueous liquid;
(e) treating the glove with a bleach to reduce blocking;
(f) rinsing the glove with a second aqueous liquid;
(g) treating the glove with a silicone emulsion; and
(h) drying the glove.
The powder-free medical glove made by this process can be donned
without difficulty and has substantially no free powder.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a cross section of a tank with a glove form being
coated.
FIG. 2 depicts a flow diagram of the process of the present invention.
FIG. 3 depicts a finished glove.
FIG. 4 shows an enlarged cross section of the glove of FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a process for making medical gloves
that have the combination of properties that are required for these
gloves--thin, soft, strong, etc.--and that, in addition, can be
donned easily, despite their being powder-free. As used in this
specification and the appended claims, "powder-free" means
that the gloves contain substantially no loose powder on the completion
of the glove-making process.
FIG. 1 illustrates part of an apparatus for practicing the present
process. It is of a type that has long been used for making elastomeric
gloves and includes a glove form 10 which generally has the shape
of a hand, and a tank 12 into which the form is dipped. The complete
apparatus includes a series of tanks, each similar to tank 12 into
which the form is dipped successively. Of course, the liquid 14
would be different in the different tanks. For dipping purposes,
the form 10 the tank 12 or both may be moved. When all the dipping
steps are completed, a finished glove is removed, or "stripped",
from the form and reversed, so that the first layer is on the outside.
The form 10 is generally made of glazed or bisque porcelain or plastic.
Of course, the size of the form determines the size of the glove.
Although a variety of elastomers may be used for medical gloves,
including natural rubber latex, nitrile rubber latex, coagulable
polyurethane aqueous dispersion, and the like, natural rubber latex
is preferred because it has superior properties and lower cost.
For brevity and convenience, we will describe the process of this
invention in the context of natural latex rubber gloves, recognizing
that the modifications necessary to produce gloves of other common
materials will be clear to the artisan. Conventional methods for
preparing latex rubber gloves are described in a bulletin "Dipping
With Natural Rubber Latex", The Malaysian Rubber Producers'
Research Association, Hertford, England, 1980 and the disclosure
of that bulletin is incorporated herein by reference.
In order to provide reproducible latex layers on the form, a coagulant
layer is first dipped onto the form. The coagulant may be of any
composition well known in the art and described in the above-mentioned
bulletin, such as alcohol solutions of calcium salts. The coagulant
includes an acid soluble powder, such as calcium carbonate, which
will facilitate stripping the glove from the form and will subsequently
be dissolved in acid.
The coagulant-coated form is then dipped into latex, after which
the latex layer gels. Preferably, the gelled layer is leached in
water to extract a large percentage of the water-soluble impurities
in the latex and coagulant.
An antiblocking composition with particles distributed throughout
is then dip-coated over the latex. "Blocking" refers to
the tendency of glove surfaces to stick together. The antiblocking
composition, which will be on the interior surface of the glove
after stripping, keeps the interior surfaces of the glove from sticking
together and making it difficult or impossible to get air and liquids
into the fingers for post-strip processing. The antiblocking composition
also serves as a binder to bind the particles to the rubber. It
should have tensile strength, elongation, tear strength, and modulus
that are comparable to that of the natural rubber. Suitable compositions
include carboxylated styrene butadiene lattice, carboxylated butadiene
acrylonitrile lattice, vinyl acrylate lattice, polyurethane aqueous
dispersions, and the like. Polyurethane aqueous dispersion is preferred,
because it provides the best combination of mechanical parameters.
Especially preferred is a cationic polyurethane having a molecular
weight of at least 100000. Cationic compositions are found to provide
desirably softer gloves than anionic or nonionic compositions. The
high molecular weight ensures that blocking is complete. Suitable
antiblocking compositions include Neorez polyurethane emulsions,
such as Neorez XR-9208 (cationic) and Neorez R-962 and R-967 (nonionic/anionic),
available from ICI Resins, Wilmington, Mass.
The particles dispersed through the antiblocking composition are
larger than the thickness of the antiblocking layer and form protrusions
on the inner surface of the glove (after stripping and reversal).
The resulting roughened surface enhances the antiblocking effect
and facilitates fluid flow into and out of the glove during post-stripping
operations. The particles may be any of a variety of acid-resistant
compositions, such as cross-linked cornstarch, polyurethane, nylon,
or mixtures. A polyester based polyurethane powder is preferred.
Such a powder is Vedoc VP180 available from Ferro Corp, Cleveland,
Ohio. Also suitable are Corvel nylon powders, available from Morton
Chemical Div., Reading, Pa.; and epichlorohydrin cross-linked cornstarch
(Vulca 90), available from National Starch and Chemical Corp., Bridgewater,
N.J. The particles should have a size in the range from about 5
to about 50 micrometers, preferably having an average particle size
of about 30 to about 40 micrometers. Reference to size for purposes
of this specification and claims is the diameter, if the particles
are spherical, or the diameter of a sphere having the same volume,
if the particles are not spherical. Additional facts regarding the
particles are described in U.S. Pat. No. 4143109 and that description
is incorporated herein by reference.
After the antiblocking/particle layer has been deposited, the form
with the 3 layers coated on it is heated to cure (i.e., cross-link)
the rubber and to bond the rubber to the antiblocking layer. The
cure time and temperature are known in the art and are not critical;
however, if the temperature is too low, the rubber may be inadequately
bonded to the antiblocking layer.
After the layers have been cured, a silicone emulsion is dip-coated
over the underlying layers to facilitate donning of the finished
glove. The emulsion may also include an acid-soluble powder, which
makes stripping easier and which is ultimately dissolved in acid.
The fully-formed glove is then stripped from the form and reversed,
so that the first layer is on the outside of the glove. The glove
is then treated with an acid to dissolve the acid-soluble powder(s).
This acid treatment, which generally takes about five minutes, serves
to dissolve loose powder to provide a powder-free glove. The acid
treatment, as well as the other post-stripping operations (except
for drying), are performed in a conventional front-loading industrial
washing machine, such as the UDY75 machine, available from Unimac
Co., Inc., Marianna, Fla. The main criterion for an acid suitable
for this step is that its calcium salt be water soluble (if the
powder is calcium carbonate). Nitric acid is preferred, because
all nitrates are water soluble. The preferred nitric acid concentration
is in the range from about 0.5% to about 10%. If the acid is too
concentrated, it can stain the glove; if it is too dilute, it may
not dissolve all the powder. A 2% nitric acid solution is preferred.
Before the acid wash, the glove is preferably "pre-washed"
in a dilute acid (concentration less than about 1%). The source
of the dilute acid may conveniently be spent acid collected from
the acid wash cycle.
After the acid wash, the glove is rinsed in an aqueous liquid,
e.g., water. It is then treated with a bleach (such as 0.5% sodium
hypochlorite) to chlorinate the inner and outer glove surfaces and
prevent blocking--e.g., fingers sticking together on a single glove
or gloves sticking together when brought into contact. The bleach
treatment, which generally takes about fifteen minutes, does not
cause the gloves to have the excessively slippery outer surface
that the prior art chlorine treatments caused.
The glove is then rinsed with an aqueous liquid--water is again
suitable--to remove any residue of bleach, which could otherwise
cause skin irritation. Since the post-stripping processes, including
acid and bleach treatments, may remove the silicone from the glove
surface, there follows a second silicone treatment. This treatment,
which generally takes about five minutes, facilitates glove donning
and reduces blocking between gloves that come into contact. Finally,
the glove is dried in a conventional dryer.
The steps of the present invention are depicted in the flow diagram
of FIG. 2.
The appearance of the finished glove is shown in FIG. 3.
FIG. 4 shows an enlarged representative cross section of the glove
wall, showing particles 20 embedded in antiblocking inner layer
22 which is bonded to elastomer outer layer 24. |