U.S. patent application number 16/894251 was filed with the patent office on 2020-09-24 for antistatic gloves and process for making same.
The applicant listed for this patent is Allegiance Corporation. Invention is credited to Seong Fong CHEN, Chii Yih LOW, Wei Cheong WONG.
Application Number | 20200299532 16/894251 |
Document ID | / |
Family ID | 1000004872215 |
Filed Date | 2020-09-24 |
United States Patent
Application |
20200299532 |
Kind Code |
A1 |
CHEN; Seong Fong ; et
al. |
September 24, 2020 |
ANTISTATIC GLOVES AND PROCESS FOR MAKING SAME
Abstract
The present invention is directed to antistatic elastomeric
articles and methods of making the same. The articles can be single
layered or multilayered. The single layered articles possess
desirable antistatic properties and desirable properties of comfort
and feel. The multilayered articles have an outermost layer/surface
that possesses desirable antistatic properties and an innermost
layer/surface that exhibits desirable properties of comfort and
feel. In preferred embodiments, the elastomeric articles are made
form a nitrile/natural rubber blend. Articles of the present
invention have antistatic properties measured as having a surface
resistivity below about 10.sup.14 .OMEGA./sq and a static decay
time of less than about 60 seconds.
Inventors: |
CHEN; Seong Fong; (Gelugor,
MY) ; WONG; Wei Cheong; (Kulim, MY) ; LOW;
Chii Yih; (Bayan Lepas, MY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Allegiance Corporation |
Waukegan |
IL |
US |
|
|
Family ID: |
1000004872215 |
Appl. No.: |
16/894251 |
Filed: |
June 5, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14963764 |
Dec 9, 2015 |
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16894251 |
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11811641 |
Jun 11, 2007 |
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14963764 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09D 107/02 20130101;
B32B 25/14 20130101; C09D 109/04 20130101; B29C 41/22 20130101;
C08L 7/02 20130101; C08J 5/02 20130101; C08L 13/02 20130101; C08J
2313/02 20130101; A41D 31/26 20190201; B29C 41/14 20130101; B32B
2307/21 20130101; C08J 2307/02 20130101; A41D 19/015 20130101 |
International
Class: |
C09D 107/02 20060101
C09D107/02; B29C 41/14 20060101 B29C041/14; C08L 13/02 20060101
C08L013/02; C08L 7/02 20060101 C08L007/02; B29C 41/22 20060101
B29C041/22; B32B 25/14 20060101 B32B025/14; C08J 5/02 20060101
C08J005/02; C09D 109/04 20060101 C09D109/04 |
Claims
1-45. (canceled)
46. A process for making an antistatic multilayered elastomeric
article having a first layer and a second layer comprising: a)
preparing a first latex composition by mixing natural rubber latex
with nitrile rubber latex, wherein the natural rubber latex in said
first latex composition is in a lesser amount than the nitrile
rubber latex in said first latex composition, b) preparing a second
latex composition by mixing nitrile rubber latex with natural
rubber latex, wherein the nitrile rubber latex in said second latex
composition is in a lesser amount than the natural rubber latex in
said second latex composition, and c) forming the first layer from
said first latex composition and the second layer from said second
latex composition.
47. The process of claim 46, wherein step a) further comprises
mechanically mixing the natural rubber latex with the nitrile
rubber latex, and wherein step b) further comprises mechanically
mixing the nitrile rubber latex with the natural rubber latex.
48. The process of claim 47, wherein step a) further comprises
adjusting the first latex composition to a pH of about 9.5.
49. The process of claim 47, wherein step c) further comprises
forming a first latex gel from the first latex composition and a
second latex gel from the second latex composition.
50. The process of claim 46, wherein step c) further comprises
dipping a latex article former a first time into a coagulant
solution, dipping the former a second time into the first latex
composition, and dipping the former a third time into the second
latex composition.
51. The process of claim 46, wherein step c) further comprises
vulcanizing the article.
52. The process of claim 46, further comprising a step d)
chlorinating the article.
53. The process of claim 52, wherein the chlorinating step further
comprises: inverting the article a first time, exposing the article
to a chlorine solution a first time inverting the article a second
time, and exposing the article to a chlorine solution a second
time.
54-55. (canceled)
56. A process for making an antistatic multilayer elastomeric
article having a first layer and a second layer comprising: a)
preparing a first latex composition by mixing synthetic rubber
latex with nitrile rubber latex, wherein the synthetic rubber latex
in said first latex composition is in a lesser amount than the
nitrile rubber latex in said first latex composition, b) preparing
a second latex composition by mixing nitrile rubber latex with
synthetic rubber latex, wherein the nitrile rubber latex in said
second latex composition is in a lesser amount than the synthetic
rubber latex in said second latex composition, and c) forming the
first layer from the first latex composition and the second layer
from the second latex composition.
Description
FIELD OF THE INVENTION
[0001] The invention relates to the field of elastomeric articles
such as gloves. In particular, the invention pertains to
elastomeric gloves that can be used in industrial and medical
applications wherein the elastomeric gloves exhibit desirable
static resistivity or antistatic properties while retaining
desirable softness and feel properties.
BACKGROUND OF THE INVENTION
[0002] Elastomeric articles, such as gloves, are well known in the
industrial and medical fields for their ability to form a
protective chemical, microbial, and physical barrier between the
external environment and the user's skin. Various physical and
chemical properties of gloves, and the elastomers they are made
from, are desirable for a variety of applications. In certain
fields where articles such as gloves and finger cots are widely
used, such as electronic assembly, desirable properties include
comfort and softness of feel, maintenance of tactile sensitivity
and surface static resistivity.
[0003] The advantages of elastomeric articles such as gloves with
antistatic properties are also known. In certain fields such as
handling sensitive electronic equipment, the use of gloves and/or
finger cots with antistatic properties is mandatory to avoid static
discharge that can damage electronic components. Polyvinyl chloride
(PVC), acrylonitrile-butadiene (nitrile) and polyurethane rubbers
have been used for antistatic gloves.
[0004] The use of natural rubber is associated with good softness
and tactile sensitivity properties. However, natural rubber does
not exhibit good static resistivity. To compensate for this
deficiency, conductive carbon black could be added to natural
rubber latex. However, a concern with such a black-colored article
is shedding of the conductive black particles which can cause
contamination problems. Moreover, carbon black would darken and
blacken the resulting article which is aesthetically unappealing
and potentially visually distracting to the user and may interfere
with the precision of handling instruments.
[0005] U.S. Pat. No. 6,794,475 to Bialke et al. (hereinafter
"Bialke et al.") describes antistatic polymers, blends and
articles. Bialke et al. describes polymeric blends containing a
macromer-modified latex and a secondary latex. The
macromer-modified latex may be an acrylonitrile-based co-polymer
and the secondary latex may be natural rubber. Articles formed from
these polymeric blends allegedly demonstrate improved electrostatic
properties. Specifically, Bialke et al. provides examples of
co-polymers of methoxypolyethylene glycol methacrylate and
acrylonitrile used in blended compositions containing one or more
latex components having static resistive properties. However,
Bialke et al. achieves antistatic properties by modifying a latex
component with a macromer and thereby forming co-polymers
containing macromers such as methoxypolyethylene glycol
methacrylate. Bialke et al. does not describe blending unmodified
latex components, specifically the combination of nitrile rubber
latex with natural rubber latex. Nor does Bialke et al. recognize
the antistatic properties of such a combination.
[0006] U.S. Pat. No. 5,459,880 to Sakaki et al. (hereinafter
"Sakaki et al.") describes gloves having a plurality of different
types of rubbers successively laminated together. Sakaki et al.
describes the lowermost layer as being a natural rubber layer and a
top surface layer as being an oil-resistant rubber layer, such as a
acrylonitrile-butadiene rubber layer. Each of these layers contains
only one particular type of latex. Sakaki et al. does not disclose
latex layers consisting of a blend of more than one type of latex
(e.g., nitrile rubber latex combined with natural rubber latex). In
addition, the process described by Sakaki et al. includes forming a
lower layer and immersing the lower layer into an additional latex
composition immediately thereafter or while the lower layer still
contains water so as to improve the adhesion between the layers of
different types of latex.
[0007] Problems associated with the manufacture of multilayered
articles with different elastomer layers laminated to one another
include chemical incompatibility resulting in delamination between
layers and difficulty in controlling the amount of water in the
latex gel and the degree of latex gelling. When these factors are
not properly controlled, the layers may delaminate. To reduce
delamination of the layers, Sakaki et al. relies on the ability of
the rubber components of both layers to mix with each other at the
interface so that the rubber molecules are entangled with one
another. Such interfacial mixing could only occur if the first
layer is not fully gelled or set (i.e., it is dependent on the
degree or extent of gelling or setting of the first layer). The
degree of gelling is dependent on the concentration of coagulant,
the solids content of the latex, temperature and time, and is
therefore difficult to control. Sakaki et al. does not describe
increasing the chemical compatibility of two different layers by
blending the two different types of latex prior to forming an
article and thus reducing delamination.
[0008] There is a need in the field of elastomeric articles for an
improved manufacturing technique which can produce a
rubber-containing article that exhibits good antistatic or surface
resistivity properties. There is a further need for multilayered
rubber-containing articles wherein additional natural rubber
layer(s) can be formed that afford the advantage of softness of
feel and comfort on the skin-contacting layer while maintaining
good adherence between the layers.
SUMMARY OF THE INVENTION
[0009] The present invention encompasses rubber elastomeric
articles with desirable static resistivity or antistatic properties
and methods of making same. It has been surprisingly discovered
that rubber-containing elastomeric articles, e.g., gloves, can be
manufactured which exhibit desirable antistatic properties without
requiring the addition or incorporation of secondary additives into
the process. The present invention provides a balance between
maintaining effective and desirable antistatic properties of the
outermost surface/layer of the elastomeric article while at the
same time affording the user desirable comfort and feel properties
on the innermost surface/layer.
[0010] In one embodiment, the elastomeric article comprises a
single layer of rubber. In such embodiments, a non-leachable
polymeric antistatic agent with desirable antistatic properties is
blended with an elastomeric material with desirable comfort and
feel properties. It is the inventors' surprising discovery that an
elastomeric article made from such a blend exhibits surface
resistivity and static decay properties that are more similar to
those of an article made from a non-leachable polymeric antistatic
agent than a weighted average would predict. In a preferred
embodiment, the non-leachable polymeric antistatic agent comprises
about 80% w/w and the elastomeric material comprises about 20% w/w.
In another preferred embodiment, the non-leachable polymeric
antistatic agent is nitrile rubber or polyurethane and the
elastomeric material is natural rubber or polyisoprene.
[0011] In another embodiment, the elastomeric article comprises
more than one layer of rubber. In such embodiments, the outermost
layer of the article is composed of a majority of a non-leachable
polymeric antistatic agent with desirable antistatic properties.
The innermost layer of the article is composed of a majority of an
elastomeric material with desirable comfort and feel properties.
Each layer comprises a minor amount of the polymer that is the
major component in the adjacent layer. In a preferred embodiment,
the non-leachable polymeric antistatic agent is nitrile rubber or
polyurethane and the elastomeric material is natural rubber or
polyisoprene.
[0012] The invention also provides for an improved manufacturing
process for multilayered rubber-containing elastomeric articles
such as gloves. It has further surprisingly been discovered that
advantageous interlayer adherence based on chemical compatibility
can be accomplished by mutually combining minor amounts of latex of
adjacent layers into the predominant latex of each. It has also
been found that strong interlayer adherence results can be
accomplished for antistatic rubber-containing articles while at the
same time achieving good tactile sensitivity of the article. The
present invention provides a balance between chemical compatibility
and adherence between multiple layers of differing compositions of
rubbers and substantially maintains the effective and desirable
antistatic properties of the outermost layer while at the same time
affording the user the desirable comfort and feel properties
associated with the innermost layer.
[0013] In a specific embodiment, a multilayered elastomeric article
of the invention is made by the process comprising: a) preparing a
first blended latex composition for the outermost layer by mixing a
major amount of the non-leachable polymeric antistatic agent with a
minor amount of the elastomeric material; b) preparing a second
blended latex composition for the innermost layer by mixing a minor
amount of the non-leachable polymeric antistatic agent with a major
amount of the elastomeric material; wherein said mixing is
performed prior to the latex gelling; and c) forming a molded
article wherein one layer is formed from said first blended latex
composition and a directly adjacent layer is formed from said
second blended latex composition. In more specific embodiments, the
major polymer component in each layer comprises about 80% w/w and
the minor polymer component comprises about 20% w/w.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 illustrates an exemplary embodiment of a process for
making a multilayered latex molded article.
[0015] FIG. 2 illustrates an exemplary embodiment of a process for
forming a multilayered latex molded article.
[0016] FIG. 3 illustrates an exemplary embodiment of a process for
chlorinating a multilayered latex molded article.
[0017] FIG. 4 illustrates an exemplary embodiment of a process for
washing a chlorinated multilayered latex molded article.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The elastomeric articles of the present invention display
desirable antistatic properties while also having desirable comfort
and feel. In one embodiment, the elastomeric articles of the
present invention display desirable antistatic properties on the
outermost surface and/or layer of the article while having
desirable comfort and feel properties on the innermost
skin-contacting surface/layer of the article. This is accomplished
by using blends of polymers that each have desirable properties,
e.g., good surface resistivity and static decay times (i.e.,
non-leachable polymeric antistatic agent) and good comfort and feel
properties (i.e., elastomeric material). In one embodiment, the
blended polymers are used to make a single layer elastomeric
article. In another embodiment, the blended polymers are used to
make a multilayer elastomeric article. In such embodiments, the
outermost surface/layer is comprised of a majority of the
non-leachable polymeric antistatic agent with a minor amount of the
elastomeric material. The innermost surface/layer is comprised of a
majority of the elastomeric material with a minor amount of the
non-leachable polymeric antistatic agent.
[0019] As used herein, the term "antistatic" as used to define the
properties associated with the inventive elastomeric articles
refers to a material having a surface resistivity of about 10.sup.9
.OMEGA./sq to about 10.sup.14 .OMEGA./sq (as measured according to
ASTM D257-99) and a static decay time of less than about 60 seconds
(as measured by MIL-STD-3010A Test Method 4046--Electrostatic
Properties). Surface resistivity and volume resistivity are as
defined in ASTM D257 and are measured at a relative humidity of
12+/-3% and a temperature of 22+/-2.degree. C. Static decay time
(SDT) is as defined in MIL-PRF-81705D. The surface resistivity,
volume resistivity, and SDT of each glove sample were determined by
averaging the values measured for three pieces (specimens) of each
glove sample.
[0020] Ultimate elongation and modulus at 500% elongation are
defined and measured in accordance with ASTM D412-98a.
[0021] As used herein, the term "major" or "majority" with respect
to the overall composition of rubber is meant to indicate an
ingredient that is present in an amount greater than the
combination of remaining ingredients within the given composition.
As used herein, the terms "minor" or "minority" with respect to the
overall composition of rubber is meant to indicate an ingredient
that is present in an amount that is less than the amount of at
least one other ingredient within the given composition.
[0022] The antistatic elastomeric articles of the present invention
with desirable surface resistivity and static decay times are
particularly useful in applications where control of static
electricity is important, such as in computer and electronic
assembly techniques. While any elastomeric article can be made
using the methods of the present invention, in preferred
embodiments, the elastomeric articles are gloves or finger
cots.
[0023] The elastomeric articles of the invention are made from
blends of non-leachable polymeric antistatic agents with desirable
surface resistivity and static decay times and elastomeric
materials with desirable comfort and feel properties in either a
single layer or multilayer form. Non-leachable polymeric antistatic
agents can be both ionic (e.g., polybetaine and quaternary
polysalts) and nonionic (e.g., nitrile rubber and polyvinyl
chloride). Examples of non-leachable polymeric antistatic agents
with desirable surface resistivity and static decay times include,
but are not limited to, nitrile rubber, polyurethane, polyvinyl
chloride, epichlorohydrin rubber, EPDM-polyaniline copolymer,
polyether, polyalkylene oxide, polyalkylene glycol, polybetaine,
polyacetylene, polyaniline, copolyesteramide, polyetheramide,
polyetheresteramide block copolymer, polythiophene,
polyparaphenylene, polyvinyl carbazole, polyglycol diglycidyl
ether, polypyrrole, polyfuran, polybenzene, polyphenylene sulfide,
salts of polyacrylic acid, polymer electrolyte/ionomers, quaternary
polysalts, and ammonium polyphosphate. Examples of elastomeric
materials with desirable comfort and feel properties include, but
are not limited to, natural rubber, polyisoprene, polychloroprene,
plasticized polyvinyl chloride, polybutadiene, butyl rubber, EPD,
polyacrylic rubber, polyurethane, halogenated butyl rubber, and
styrene-containing block copolymers (e.g., SIS, SEBS). In preferred
embodiments, the non-leachable polymeric antistatic agent is
nitrile rubber or polyurethane and the elastomeric material is
natural rubber or polyisoprene.
[0024] The art will appreciate that "nitrile rubber" is a broad
class of polymers, and that nitrile rubber compositions may be
greatly varied. One embodiment of the present invention
contemplates the use of carboxylated nitrile rubber latex. Another
embodiment of the present invention contemplates the use of
carboxylated nitrile rubber latex composed of between about 25% and
about 40% acrylonitrile, between about 54% and about 73% butadiene
and between about 2% and about 6% carboxylic acid. In another
embodiment of the present invention, the carboxylic acid is
methacrylic acid. In yet another embodiment of the present
invention, the carboxylated nitrile rubber latex is composed of
about 39% acrylonitrile, about 58% butadiene, and about 3%
carboxylic acid. In yet another embodiment of the present
invention, the carboxylated nitrile rubber latex is composed of
about 39% acrylonitrile, about 55% butadiene, and about 6%
carboxylic acid. These illustrative embodiments are in no way
intended to limit to the recited compositions the scope of nitrile
rubber contemplated for use in the present invention.
[0025] The art will appreciate that "polyurethane" is a broad class
of polymers, and that polyurethane compositions may be greatly
varied to achieve varying physical properties. Thus, polyurethanes
may broadly be characterized as "polymeric antistatic agents"
and/or "elastomeric materials", depending on their chemical
composition and desired physical properties. For example, a
polyurethane made from a polyester diol, an amine-based chain
extender, and a neutralized ionomer may be expected to possess
antistatic properties. One of ordinary skill in the art would be
able to vary the composition of a polyurethane to achieve a polymer
with antistatic properties and/or desirable comfort and feel
properties, although the inventors believe that the same
polyurethane will likely not serve as both components of a single
embodiment of the composition. That is, one of ordinary skill in
the art would be able to select a particular polyurethane either as
a suitable polymeric antistatic agent based on its conductivity or
as a suitable elastomeric material based on its desirable comfort
and feel properties. The above example in no way limits the scope
of polyurethanes contemplated for use in the present invention.
[0026] When making a single layer elastomeric article of the
invention or the outer layer of a multilayer elastomeric article of
the invention, a polymer blend containing a major amount of a
non-leachable polymeric antistatic agent and a minor amount of
elastomeric material is used. The blend is used to manufacture the
entire single layer article or to manufacture the outermost layer
of the multilayered article. Any means of blending can be used,
including, but not limited to, solvent-based blending, melting
block blending and latex blending. In one embodiment, the latex
composition for the blend comprises a non-leachable polymeric
antistatic agent in an amount from about 51% to about 95%, and an
elastomeric material in an amount of from about 49% to about 5% of
the total blended latex composition. Preferably, the latex
composition for the blend comprises a non-leachable polymeric
antistatic agent in an amount from about 60% to about 90%, and an
elastomeric material in an amount of from about 40% to about 10% of
the total blended latex composition. More preferably, the latex
composition for the blend comprises a non-leachable polymeric
antistatic agent in an amount from about 65% to about 85%, and an
elastomeric material in an amount of from about 35% to about 15% of
the total blended latex composition. In a specific embodiment, the
latex composition for the blend comprises a non-leachable polymeric
antistatic agent in an amount of about 80%, and an elastomeric
material in an amount of about 20% of the total blended latex
composition. The non-leachable polymeric antistatic agent component
may be a single polymer or may itself be a blend of more than one
non-leachable polymeric antistatic agent. Similarly, the
elastomeric material component may be a single polymer or a blend
of more than one elastomeric material.
[0027] In embodiments where a multilayered elastomeric article is
made, the innermost skin-contacting layer of the article may be
comprised of a majority of an elastomeric material with desirable
comfort and feel properties. Thus, the latex composition used to
prepare the innermost layer may be comprised of an elastomeric
material in an amount from about 51% to about 95%, and a
non-leachable polymeric antistatic agent in an amount of from about
49% to about 5% of the total blended latex composition. Preferably,
the innermost layer latex composition may be comprised of an
elastomeric material in an amount from about 60% to about 90%, and
a non-leachable polymeric antistatic agent in an amount of from
about 40% to about 10% of the total blended latex composition. More
preferably, the innermost layer latex composition may be comprised
of an elastomeric material in an amount from about 65% to about
85%, and a non-leachable polymeric antistatic agent in an amount of
from about 35% to about 15% of the total blended latex composition.
In a specific embodiment, the innermost layer latex composition may
be comprised of an elastomeric material in an amount of about 80%,
a non-leachable polymeric antistatic agent in an amount of about
20% of the total blended latex composition. The non-leachable
polymeric antistatic agent component may be a single polymer or may
itself be a blend of more than one non-leachable polymeric
antistatic agent. Similarly, the elastomeric material component may
be a single polymer or a blend of more than one elastomeric
material.
[0028] It is desirable that the antistatic elastomeric articles of
the invention have a surface resistivity preferably less than about
10.sup.14 .OMEGA./sq, more preferably less than about
8.times.10.sup.13 .OMEGA./sq, and most preferably less than about
5.times.10.sup.13 .OMEGA./sq. It is also desirable that the
antistatic elastomeric articles of the invention have a static
decay time preferably less than about 60 seconds, more preferably
less than about 40 seconds, and most preferably less than about 30
seconds. It is also desirable that the antistatic elastomeric
articles of the invention have a modulus at 500% elongation
preferably less than about 10 MPa, more preferably less than about
7 MPa, and most preferably less than about 5 MPa.
Process of Making Antistatic Gloves
[0029] In embodiments where the elastomeric article is a single
layer glove, any known method known in the art can be used to make
the glove providing that the polymer blends described above are
used. For example, the single latex dip used for single layer
gloves is described in D. C. Blackley, Chapter 17 "Latex-dipping
processes" in Polymer Latices: Science and Technology 2.sup.nd
edition Volume 3, Chapman & Hall London 1997 (incorporated by
reference in its entirety).
[0030] In embodiments where the elastomeric article is a
multilayered glove, a standard coagulant dipping process well known
to be used in the manufacture of medical examination and surgical
gloves can be used. The standard process can be readily modified to
apply multiple latex dips as compared to the ordinary single latex
dip used for single layer gloves (D. C. Blackley, supra).
[0031] The process may be illustrated according to the following
non-limiting example of preparing an antistatic glove. To prepare
an antistatic glove according to the invention, a first latex blend
composition of a majority of a non-leachable polymeric antistatic
agent (e.g., nitrile rubber) and a second latex blend composition
of a majority an elastomeric material (e.g., natural rubber) are
prepared. The first latex blend composition comprises a blend of a
non-leachable polymeric antistatic agent (e.g., nitrile rubber) and
an elastomeric material (e.g., natural rubber), wherein the former
polymer comprises a majority of the first latex blend composition.
The second latex blend composition comprises a blend of the same
polymers described above, however, the elastomeric material
comprises a majority of the second latex blend composition. A clean
latex article former (e.g., a mold) is dipped into a coagulant
solution and heat dried. Subsequently, the coagulant-coated former
is dipped into the first latex blend composition. The latex film on
the former is then coagulated by the coagulant to form a gel and
complete setting of the gel is aided by heat (heat gellation) which
also partially dries the gel. The gelled rubber covered former is
dipped into the second latex blend composition and subsequently
heat gelled and dried.
[0032] In embodiments where the elastomeric article has more than
two layers, it is made by successively laminating one layer on top
of another by dipping into the latex composition (and coagulant if
necessary).
[0033] The multilayered latex article is then leached in water,
heat dried and vulcanized to cure the article. After the curing
step, the multilayered latex article is leached in water a second
time. Lastly, the multilayered latex article is cooled and removed
from the former. The gloves are inverted when removed from the
former so as to orient the layer containing a majority of the
elastomeric material toward the inner skin-contacting surface of
the wearer and the layer containing a majority of the non-leachable
polymeric antistatic agent toward the exterior environment.
Variations of the basic process can be made. For example, the
gloves may be beaded in an additional step after latex gelling and
before the leaching step.
[0034] The donnability of the gloves may be enhanced by a
chlorination step. The chlorination step may be used to produce a
powder-free article. A powder-free glove as used herein is as
defined in ASTM 6319-00a and has a powder residue limit of 2.0
mg/glove tested according to ASTM D6124. The chlorination step is
interposed between the post-cure leaching and removal of the gloves
from the former. In one particular embodiment, the removed gloves
are turned inside out in a clean room environment to orient the
skin-contacting layer toward the exterior of the gloves. The gloves
are washed, chlorinated, and thorough washed again with clean
water. The gloves are then dried, manually inverted, and dried a
second time. Once the gloves have been dried a second time, they
are then packaged. The techniques and equipment for the process are
conventional and readily available to one skilled in the glove
manufacturing field.
[0035] The antistatic gloves of the present invention provide the
desirable properties of both of the polymers in the polymer blend
(e.g., the antistatic properties of the non-leachable polymeric
antistatic agent and the desirable comfort and feel properties of
the elastomeric material). The desirable static decay time and
surface resistivity values associated with the non-leachable
polymeric antistatic agent are substantially maintained in the
outermost layer/surface of gloves prepared according to the process
described herein. The multilayer latex antistatic gloves also
demonstrate improved delamination resistance due to chemical
compatibility between the layers, and also provide the desirable
soft feel simulating natural rubber for the innermost
skin-contacting layer/surface.
[0036] Another advantage of the antistatic gloves and the process
for making multilayered articles described herein is that
lamination of the layers is based on the chemical compatibility of
the first latex composition and the second latex composition and
does not rely on the extent of gellation and the amount of water
present in an intermediate latex gel. This allows for an easily
controlled and more reliable lamination of the multilayered gloves
and provides an improvement over the difficult and uncertain
methods previously available.
[0037] An important aspect of the process described herein includes
pre-blending the latex compositions, i.e., mechanically mixing the
ingredients prior to latex coagulation or gelling. The pre-blending
step further homogenizes the latex blend composition. Any blending
method can be used for the pre-blending including, but not limited
to, solvent-based blending, melting block blending, and latex
blending. Furthermore, in the case of multilayered articles, the
pre-blending of the latex ingredients enhances the chemical
adherence between the different rubber layers formed according to
the process, and reduces the likelihood of delamination.
[0038] Without being bound by any theory or mechanism, in one
embodiment of the invention, the combination of desirable
antistatic properties (i.e., surface resistivity and static decay
times) and desirable comfort and feel properties of the gloves
result from a migration of the non-leachable polymeric antistatic
agent to the surface due to the immiscibility of the polymeric
antistatic agent with the elastomeric material. It is understood
that this combination of desirable antistatic and comfort
properties may be achieved by other mechanisms.
EXAMPLES
[0039] The following non-limiting examples illustrate particular
embodiments of the invention. The examples are not meant to be
comprehensive of the entire scope of the invention.
Example 1: Comparative Static Testing of Gloves
[0040] Three types of glove samples were tested for static
resistance properties and compared. The gloves were composed
of:
[0041] 1) 100% natural rubber;
[0042] 2) 100% nitrile rubber; and
[0043] 3) two layers, the outermost layer comprising 80% nitrile
rubber and 20% natural rubber, laminated directly to an innermost
layer comprising 80% natural rubber and 20% nitrile rubber prepared
using the process described below.
[0044] For the two-layered glove, one glove sample was tested for
static resistance properties. For 100% nitrile rubber gloves, eight
different commercially available gloves and six different lab
dipped gloves were each tested for static resistance properties
(see Table 1). For 100% natural rubber gloves, different gloves
were tested for static resistance properties. Each glove sample was
tested for surface resistivity, volume resistivity and static decay
time (SDT) as set forth above. For each glove sample, three
specimens (prepared from three pieces of gloves) were tested and
the results averaged. The surface resistivity and volume
resistivity of each specimen was measured once. The SDT for each
specimen was measured a total of six times. The SDT for each
specimen was calculated averaging the SDT observed upon charging
the specimen to +5000V three times, and to -5000V three times. As
relative humidity affects the static resistance properties in an
inversely proportional manner, the glove specimens were conditioned
in a chamber at relative humidity of 12.+-.3% and a temperature of
22.+-.2.degree. C. prior to taking and recording the measurements.
The resistivity and SDT measurements were taken using the outer
surface of the glove specimen.
[0045] A description of the 100% nitrile rubber gloves studied, and
the static resistance properties of each, are detailed in Table
1.
TABLE-US-00001 TABLE 1 100% Nitrile Rubber Gloves and Static
Resistance Properties Surface Resistance, Volume Static ohms/
Resistance, Decay Sample Manufacturer Catalog sq cm ohms Time, s
Remarks Powder free Nitrile Omigrace for 2Y1812/ 6.12 .times.
10.sup.12 7.38 .times. 10.sup.11 4.28 -- Allegiance N88001-041 CR10
Nitrile Smart Glove 2Y1840T 2.24 .times. 10.sup.13 1.63 .times.
10.sup.13 16.13 Clean Room Gloves for Allegiance CR10 Nitrile Smart
glove 2Y1841T 1.65 .times. 10.sup.13 9.10 .times. 10.sup.12 15.35
Clean Room Gloves for Allegiance CR10 Nitrile Smart glove 2Y1842T
1.44 .times. 10.sup.13 8.26 .times. 10.sup.12 13.78 Clean Room
Gloves for Allegiance CR10 Nitrile Smart Glove 2Y1842T 1.93 .times.
10.sup.13 2.59 .times. 10.sup.12 24.5 Clean Room Gloves for
Allegiance CR10 Nitrile Allegiance 2Y1841 1.80 .times. 10.sup.13
8.29 .times. 10.sup.12 8.71 Clean Room Gloves Powder free Nitrile
Ansell Nitrilite 93- 1.42 .times. 10.sup.14 1.77 .times. 10.sup.12
36.65 Clean Room Gloves Edmont 112 Powder free Nitrile Ansell
Nitrilite 93- not not 27.51 Clean Room Gloves Edmont 112L measured
measured Lab dipped Powder N/A N/A 2.22 .times. 10.sup.13 6.24
.times. 10.sup.12 11.86 Nitrile Latex: free Nitrile #1 (ca. 39%
acrylonitrile/ ca. 58% butadiene/ ca. 3% carboxylic acid) Lab
dipped Powder N/A N/A 4.17 .times. 10.sup.13 5.06 .times. 10.sup.12
7.62 Nitrile Latex: free Nitrile #2 (ca. 39% acrylonitrile/ ca. 58%
butadiene/ ca. 3% carboxylic acid) Lab dipped Powder N/A N/A 1.79
.times. 10.sup.13 5.31 .times. 10.sup.12 8.57 Nitrile Latex: free
Nitrile #3 (39% acrylonitrile/ 58% butadiene/ca. 3% carboxylic
acid) Lab dipped Powder N/A N/A 4.32 .times. 10.sup.13 4.49 .times.
10.sup.12 9.93 Reichhold Tylac free Nitrile #4 68073-06 (ca. 26%
acrylonitrile) Lab dipped Powder N/A N/A 7.78 .times. 10.sup.13
6.56 .times. 10.sup.12 15.12 Nitrile Latex: free Nitrile #5 (39%
acrylonitrile/ 55% butadiene/ 6% carboxylic acid) Lab dipped Powder
N/A N/A 6.65 .times. 10.sup.13 6.88 .times. 10.sup.12 17.64
Reichhold Noion free Nitrile #6 68083-00
[0046] The static resistance properties of the 100% natural rubber
glove(s), the 100% nitrile rubber gloves, and the multilayered
glove, are detailed in Table 2. The range of values for the 100%
nitrile rubber gloves from Table 1 are summarized in Table 2. The
resistivity values of the 100% natural rubber glove(s) were always
higher than the maximum range of the measuring equipment, which is
greater than 10.sup.14 .OMEGA./sq and 10.sup.14.OMEGA..
TABLE-US-00002 TABLE 2 Resistivity and Static Decay Data Surface
Volume Static Glove Sample Resistivity Resistivity Decay Time
Composition (.OMEGA./sq) (.OMEGA.) (sec) 100% Natural Rubber
>10.sup.14 >10.sup.14 >3,600 100% Nitrile Rubber 6.1
.times. 10.sup.12 to 7.4 .times. 10.sup.11 to 4-37 1.4 .times.
10.sup.14 1.6 .times. 10.sup.13 Outer Layer 80%/20% 1.7 .times.
10.sup.13 2.3 .times. 10.sup.12 27.2 Nitrile Rubber/Natural Rubber
Inner 80%/20% Natural Rubber/Nitrile Rubber
[0047] As can be seen from the data in Table 2, the gloves of the
present invention exhibit antistatic properties comparable to those
of the 100% nitrile rubber gloves. This result is surprising
because, as set forth below, the calculated theoretical values for
SDT and surface resistivity for a layer composition composed of 80%
nitrile rubber and 20% natural rubber are not these values.
[0048] 100% pure nitrile rubber gloves exhibit a SDT of 4 to 37
seconds with 4 seconds as the best case scenario. A glove material
containing 80% nitrile rubber would therefore be expected to have
an SDT of 3.2 seconds. 100% natural rubber gloves exhibit a SDT of
greater than 3,600 seconds with 3600 seconds as the best case
scenario. A glove material containing 20% natural rubber would
therefore be expected to have SDT of 720 seconds. Based on these
calculations, the expected SDT value for 80% nitrile rubber and 20%
natural rubber would be 3.2 seconds+720 seconds, or 723.2 seconds.
Instead, the actual demonstrated SDT for this rubber layer was 27.2
seconds--significantly lower than expected.
[0049] The surface resistivity theoretical calculations differ from
the actual measured values as well. 100% nitrile rubber gloves
exhibited surface resistivity values ranging from
6.1.times.10.sup.12 to 1.4.times.10.sup.14 .OMEGA./sq. Assuming a
best case of 6.1.times.10.sup.12 .OMEGA./sq, an 80% nitrile rubber
surface layer composition would be expected to contribute
4.88.times.10.sup.12 .OMEGA./sq. 100% natural rubber exhibited a
surface resistivity value of greater than 10.sup.14 .OMEGA./sq.
Assuming a best case scenario, a 20% natural rubber surface layer
would be expected to contribute more than 2.times.10.sup.13
.OMEGA./sq. The calculated surface resistivity for a surface layer
on a glove composed of 80% nitrile rubber and 20% natural rubber
would be greater than 4.88.times.10.sup.12+2.times.10.sup.13
.OMEGA./sq, or 2.488.times.10.sup.13 .OMEGA./sq. However, the
actual received surface resistivity value was 1.7.times.10.sup.13
.OMEGA./sq--lower than the expected best case value.
Examples 2-6: Detailed Preparation of Gloves
[0050] The method 100 used in preparing examples 2-7, comprises:
[0051] (1) preparing a latex composition composed of a majority of
nitrile rubber for a first layer and a latex composition composed
of a majority of natural rubber for a second layer, [0052] (2)
dipping and forming the gloves 200, and [0053] (3) chlorinating the
gloves 300 and making powder-free clean room gloves.
Preparation of Latex Compounds
[0054] Two latex compositions were prepared and blended, each
comprising a nitrile rubber latex and a natural rubber latex. A
first latex composition included a majority of a nitrile rubber
latex and formed a first layer, the outer layer, of the antistatic
glove. A second latex composition included a majority a natural
rubber latex and formed a second layer, the inner donning side, of
the antistatic glove.
First Latex Composition
[0055] Raw nitrile rubber latex (composed of about 39%
acrylonitrile, about 58% butadiene, and about 3% carboxylic acid)
was stirred with a mechanical stirrer (IKA Labortechnik RW20.n) at
about 500 rpm and 0.30 phr of non-ionic surfactant Teric 320 was
added to the stirred nitrile rubber latex to enhance its stability.
The pH of the nitrile rubber latex was adjusted to about 9.5 using
a 3% w/v potassium hydroxide solution and the nitrile rubber latex
was additionally stirred for about 10 minutes.
[0056] Similarly, raw low ammonia natural rubber latex was stirred
with a mechanical stirrer (IKA Labortechnik RW20.n) at about 500
rpm. A potassium hydroxide solution (0.5 phr) and an ammonium
caseinate solution (0.20 phr) were sequentially added to the
stirred natural rubber latex to enhance its stability. The natural
rubber latex was further stirred for about 10 minutes.
[0057] The stabilized natural rubber latex was gradually added to
the nitrile rubber latex while stirring the stabilized nitrile
rubber latex. The percentage of nitrile rubber latex and the
percentage of natural rubber latex as compared to the total
composition are provided in Table 3. Subsequently, the nitrile
rubber and natural rubber latex mixture was stirred with a
mechanical stirrer for about 30 minutes. Other ingredients were
added one at a time at about 10 minutes intervals in the order
listed in Table 3. (i.e., sulfur dispersion followed by zinc
dibutyldithiocarbamate (ZDBC) dispersion followed by zinc oxide
(ZnO) dispersion, then Wingstay L dispersion and finally titanium
dioxide (TiO.sub.2) dispersion). Lastly, water was added to the
mixture to dilute the latex to a total solids content (TSC) of
about 20%.
Second Latex Composition
[0058] The second latex composition was prepared according to the
formulation described in Table 3. In contrast to the process
utilized to prepare the first latex composition, the stabilized
nitrile rubber latex (minor component) was added to the stabilized
natural rubber latex (major component) before the addition of other
ingredients listed in Table 3. Water was added to this mixture to
adjust the TSC to about 27%.
TABLE-US-00003 TABLE 3 Latex Compound Formulation First Second
Formulation dip compound dip compound Nitrile Rubber Latex
(composed 51-95 5-49 of about 39% acrylonitrile, about 58%
butadiene, and about 3% carboxylic acid) Teric 320 0.30 0.15 KOH
adjust pH Raw Natural Rubber Latex 5-49 51-95 KOH 0.50 0.50
Ammonium Caseinate 0.20 0.20 Sulphur Dispersion 2.00 1.00 ZDBC
Dispersion 1.00 0.75 ZnO Dispersion 1.50 0.75 Wingstay L Dispersion
0.50 0.50 TiO.sub.2 Dispersion 1.00 1.00 TSC (%) 20 27
[0059] Both the first and second latex compositions were matured at
ambient temperature for about 24 hours, prior to dipping a latex
article former and forming a multilayered latex article (e.g.,
gloves).
[0060] Five different gloves were prepared using combinations of a
first dip composition and a second dip composition with different
ratios of natural rubber and nitrile rubber latex blends (Examples
2-6). The compositions of Examples 2-6 are summarized in Table
4.
TABLE-US-00004 TABLE 4 Composition of the Examples Example 2 3 4 5
6 1st dip composition Nitrile rubber 100 95 80 60 51 Natural rubber
0 5 20 40 49 2nd dip composition Nitrile rubber 0 5 20 40 49
Natural rubber 100 95 80 60 51
[0061] A two-layer powder-free antistatic glove with an outermost
majority nitrile rubber layer and an innermost majority natural
rubber layer was prepared as illustrated in FIG. 1. This process
100 involved making the gloves by a double dip coagulant dipping
process 200 followed by chlorinating 300 and washing 400 the gloves
as set forth below.
Dipping Procedure
[0062] A round ambidextrous glove former was washed thoroughly with
detergent and water 202. The cleaned former was heated in an oven
at 70.degree. C. 204 until the former reached a temperature between
59-66.degree. C. The heated former was dipped into a coagulant
composition 206 (Table 5), which was maintained at a temperature
between 53-59.degree. C. The coagulant coated former was dried in
the oven at 70.degree. C. for 3-5 minutes 208, until the former
reached a temperature between 53-58.degree. C. The coagulant coated
former was dipped into the first latex composition 210 for a dwell
time of about 12-18 seconds. The dwell time in the first latex
composition may be varied depending on the desired thickness of the
first layer. Subsequently, the former was dried in the oven at
135.degree. C. for 1 minute 212. The former was then dipped into
the second latex composition 214 for a dwell time of about 5-10
seconds. Similar to forming the first layer, the dwell time in the
second latex composition may be varied depending on the desired
thickness of the second layer. The former covered with a wet gelled
latex film was dried in the oven at 70.degree. C. for 2 minutes 216
and then leached with hot tap water at 40.degree. C. for 3 minutes
218. The leached latex film was manually beaded. The beaded latex
film was dried and cured in the oven at 135.degree. C. for 20
minutes 220. After curing the latex film in the oven, the former
was cooled to ambient temperature 222. The formed glove was then
removed from the former. Starch powder may be added to aid the
removal of the glove from the former 224.
TABLE-US-00005 TABLE 5 Coagulant Composition Ingredients % (wt/wt)
Water, Soft 82.95 Cellosize QP52,000 0.05 Calcium nitrate 12.00
Calcium carbonate 4.80 Surfynol Tg 0.20 Total 100.00 Specific
gravity of coagulant = 1.080-1.090.
Chlorination Procedure
[0063] The formed gloves were chlorinated 300 under class 10 clean
room environments to remove the powder (i.e., calcium carbonate and
starch), thus producing powder-free clean room gloves, and to
improve the donning characteristics of the gloves. First, the
gloves were manually inverted 302 so that the majority natural
rubber layer (i.e., the donning side of gloves) was on the exterior
and exposed. The inverted gloves were loaded into a chlorinator and
pre-rinsed with tap water for 15 minutes 304. The pre-rinsed gloves
were then placed in a chlorine solution having a concentration of
about 300 ppm for 35 minutes 306. The chlorinated gloves were
rinsed with water for 15 minutes and rinsed again with water five
(5) more times 308. The gloves were then manually inverted 310 so
that the majority nitrile rubber layer was on the exterior.
[0064] The gloves were then chlorinated a second time using a
similar process having the same pre-rinse 312, chlorinating 314 and
post-rinse steps 316 as described above. After the second
chlorination, the gloves were placed in a washer. First, the gloves
were washed with water at ambient temperature for 15 minutes 402.
Next, the gloves were washed using hot water at 80.degree. C. for 1
hour 404. Then, the gloves were rinsed with water at ambient
temperature for 15 minutes 406. The gloves were removed from the
washer and dried in a tumbler dryer at 80.degree. C. for 2.5 hours
and cooled in the tumble dryer at ambient temperature for 30
minutes 408.
[0065] The gloves were then placed in a tumbler washer and washed
for six (6) cycles at 40 minutes per cycle using de-ionized water
410. Water remaining in the gloves was extracted by centrifugal
force, i.e., spinning the gloves in a water extraction machine for
15 minutes 412. Finally, the gloves were dried again in a tumbler
dryer at 80.degree. C. for 2.5 hours and cooled in the tumble dryer
at ambient temperature for 30 minutes 414. The extensive washing
protocol described above resulted in clean room gloves having a
particle count of less than 6000 particles per square cm for
particles greater than 0.5 .mu.m. It should be noted cleaner gloves
tend to exhibit higher surface resistivity values and higher static
decay times.
Example 2
[0066] A multilayer nitrile/natural rubber latex laminate glove
with an outer layer comprising 100% nitrile rubber latex and an
inner layer comprising 100% natural rubber latex was prepared in a
manner similar to the procedures described above. The first latex
composition comprised 100% nitrile rubber latex (and 0% natural
rubber latex) and the second latex composition comprised 100%
natural rubber latex (and 0% nitrile rubber latex). This particular
glove showed delamination of the two layers immediately after heat
curing in the oven.
Example 3
[0067] A powder-free nitrile/natural rubber latex laminate glove
comprising an outer layer having a composition of 95% nitrile
rubber latex/5% natural rubber latex and an inner layer comprising
a composition of 95% natural rubber latex/5% nitrile rubber latex
was prepared in a manner similar to the procedures described above.
The glove of Example 3 did not show any delamination of the two
layers immediately after heat curing in the oven. However, some
delamination of the two layers occurred after the glove was
chlorinated. The glove of Example 3 exhibited a surface resistivity
of 3.3.times.10.sup.12 .OMEGA./sq and a static decay time of 22
seconds (Table 6), and thus possessed antistatic properties. In
addition, the glove demonstrated a modulus at 500% elongation of
3.6 MPa and an ultimate elongation of 609% (Table 6).
Example 4
[0068] A powder-free nitrile/natural rubber latex laminate glove
comprising an outer layer having a composition of 80% nitrile
rubber latex/20% natural rubber latex and an inner layer having a
composition of 80% natural rubber latex/20% nitrile rubber latex
was prepared in a manner similar to the procedures described above.
The glove of Example 4 did not show any delamination of the two
layers immediately after heat curing in the oven or after
chlorination. The glove of Example 4 exhibited a surface
resistivity of 1.7.times.10.sup.13 .OMEGA./sq and a static decay
time of 27.2 seconds (Table 6), and thus possessed antistatic
properties. In addition, the glove demonstrated a modulus at 500%
elongation of 3.7 MPa and an ultimate elongation of 569% (Table
6).
Example 5
[0069] A powder-free nitrile/natural rubber latex laminate glove
comprising an outer layer having a composition of 60% nitrile
rubber latex/40% natural rubber latex and an inner layer having a
composition of 60% natural rubber latex/40% nitrile rubber latex
was prepared in a manner similar to the procedures described above.
The glove of Example 5 did not show any delamination of the two
layers immediately after heat curing in the oven or after
chlorination. The glove of Example 5 exhibited a surface
resistivity of 2.8.times.10.sup.13 .OMEGA./sq and a static decay
time of 29.2 seconds (Table 6), and thus possessed antistatic
properties. In addition, the glove demonstrated a modulus at 500%
elongation of 4.2 MPa and an ultimate elongation of 569% (Table
6).
Example 6
[0070] A powder-free nitrile/natural rubber latex laminate glove
comprising an outer layer having a composition of 51% nitrile
rubber latex/49% natural rubber latex and an inner layer having a
composition of 51% natural rubber/49% nitrile rubber was prepared
in a manner similar to the procedures described above. The glove of
Example 6 did not show any delamination of the two layers
immediately after heat curing in the oven or after chlorination.
The glove of Example 6 exhibited a surface resistivity of
3.0.times.10.sup.13 .OMEGA./sq and a static decay time of 34.0
seconds (Table 6), and thus possessed antistatic properties. In
addition, the glove demonstrated a modulus at 500% elongation of
6.6 MPa and an ultimate elongation of 569% (Table 6).
TABLE-US-00006 TABLE 6 Properties of Gloves Surface Volume Static
Ultimate Modulus at 500% Glove Sample Resistivity Resistivity Decay
Time Elongation Elongation Composition Example (.OMEGA./sq)
(.OMEGA.) (sec) (%) (MPa) Outer Layer 3 3.3 .times. 10.sup.12 1.47
.times. 10.sup.14 21.8 609 3.6 95% Nitrile Rubber/ 5% Natural
Rubber Inner Layer 5% Nitrile Rubber/ 95% Natural Rubber Outer
Layer 4 1.7 .times. 10.sup.13 2.3 .times. 10.sup.12 27.2 569 3.7
80% Nitrile Rubber/ 20% Natural Rubber Inner Layer 20% Nitrile
Rubber/ 80% Natural Rubber Outer Layer 5 2.8 .times. 10.sup.13 3.9
.times. 10.sup.12 29.2 569 4.2 60% Nitrile Rubber/ 40% Natural
Rubber Inner Layer 40% Nitrile Rubber/ 60% Natural Rubber Outer
Layer 6 3.0 .times. 10.sup.13 2.5 .times. 10.sup.12 34.0 569 6.6
51% Nitrile Rubber/ 49% Natural Rubber Inner Layer 49% Nitrile
Rubber/ 51% Natural Rubber
[0071] The invention has been described herein above with reference
to various and specific embodiments and techniques. It will be
understood that reasonable variations in said embodiments and
techniques may be made without significantly departing from either
the spirit or scope of the invention defined by the following
claims.
* * * * *