U.S. patent application number 17/125369 was filed with the patent office on 2021-06-24 for polymer compositions and products formed therewith.
This patent application is currently assigned to Church & Dwight Co., Inc.. The applicant listed for this patent is Church & Dwight Co., Inc.. Invention is credited to Steven T. Adamy, Carmen Guzman, Rajesh Ranjan, Muthiah Thiyagarajan, Jon Toliver.
Application Number | 20210189104 17/125369 |
Document ID | / |
Family ID | 1000005326717 |
Filed Date | 2021-06-24 |
United States Patent
Application |
20210189104 |
Kind Code |
A1 |
Thiyagarajan; Muthiah ; et
al. |
June 24, 2021 |
POLYMER COMPOSITIONS AND PRODUCTS FORMED THEREWITH
Abstract
The present disclosure provides compositions and products formed
therefrom. In particular, the disclosure provides elastomeric latex
articles, such as gloves and condoms, that can be prepared
utilizing a styrene-polyisoprene-styrene (SIS) latex. The
elastomeric articles can exhibit desired tensile properties while
being substantially or completely free of undesired components,
such as sulfur and zinc oxide, which can be allergens. The
disclosure further provides methods of preparing elastomeric latex
articles.
Inventors: |
Thiyagarajan; Muthiah;
(Flemington, NJ) ; Ranjan; Rajesh; (Princeton,
NJ) ; Guzman; Carmen; (Ewing, NJ) ; Toliver;
Jon; (Franklin Park, NJ) ; Adamy; Steven T.;
(Lawrenceville, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Church & Dwight Co., Inc. |
Princeton |
NJ |
US |
|
|
Assignee: |
Church & Dwight Co.,
Inc.
Princeton
NJ
|
Family ID: |
1000005326717 |
Appl. No.: |
17/125369 |
Filed: |
December 17, 2020 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62951856 |
Dec 20, 2019 |
|
|
|
63018311 |
Apr 30, 2020 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08J 5/02 20130101; C08K
5/005 20130101; C08L 7/02 20130101; C08L 25/16 20130101; C08K 5/40
20130101; C08J 2325/16 20130101; C08J 2309/08 20130101; A61F 6/04
20130101; C08J 2307/02 20130101 |
International
Class: |
C08L 7/02 20060101
C08L007/02; C08L 25/16 20060101 C08L025/16; C08K 5/40 20060101
C08K005/40; C08K 5/00 20060101 C08K005/00; C08J 5/02 20060101
C08J005/02; A61F 6/04 20060101 A61F006/04 |
Claims
1. An elastomeric article comprising one or more layers of a
polystyrene-polyisoprene-polystyrene (SIS) latex composition,
wherein the elastomeric article at a thickness of about 0.1 mm or
less exhibits a tensile strength of about 20 MPa or greater when
measured in accordance with ASTM D412 and exhibits a tensile
modulus at 500% elongation of less than 2.75 MPa when measured in
accordance with ASTM D412.
2. The elastomeric article of claim 1, wherein the SIS latex
composition is substantially free of one or more of the following:
elemental sulfur or free sulfur; zinc oxide; and diphenyl
guanidine.
3. The elastomeric article of claim 1, wherein the elastomeric
article exhibits an elongation at break of about 1000% or
greater.
4. The elastomeric article of claim 1, wherein the elastomeric
article exhibits a tear strength of at least 2 N/mm when measured
in accordance with ASTM D624-00.
5. The elastomeric article of claim 1, wherein the elastomeric
article exhibits a Young's modulus (E') that is less than 1 MPa at
a frequency of 1 Hz and that is greater than 1 MPa at a frequency
of 21.5 Hz.
6. The elastomeric article of claim 1, wherein the SIS latex
composition further comprises a dithiocarbamate.
7. The elastomeric article of claim 1, wherein the SIS latex
composition further comprises a thiuram.
8. The elastomeric article of claim 1, wherein the SIS latex
composition further comprises one or more of a surfactant, an
antioxidant, a viscosity modifier, a filler, and a smoothing
agent.
9. The elastomeric article of claim 8, wherein the SIS latex
composition comprises a viscosity modifier including at least a
hydrophobically modified alkali soluble emulsion.
10. The elastomeric article of claim 1, wherein the elastomeric
article is a condom.
11. An elastomeric article formed from a composition comprising:
polystyrene-polyisoprene-polystyrene (SIS) latex; an amphoteric
surfactant; at least one sulfur donor; and at least one
dithiocarbamate.
12. The elastomeric article of claim 11, wherein the composition
comprises the amphoteric surfactant in an amount of 0.01 to about
2.0 phr.
12. The elastomeric article of claim 11, wherein the composition
comprises the dithiocarbamate in an amount of about 0.1 to about
2.0 phr.
14. The elastomeric article of claim 11, wherein the composition
comprises the at least one sulfur donor in an amount of about 0.1
to about 2.0 phr.
15. The elastomeric article of claim 11, wherein the at least one
sulfur donor comprises a thiuram compound.
16. The elastomeric article of claim 11, wherein the composition
further comprises one or more of an antioxidant, a viscosity
modifier, a filler, and a smoothing agent.
17. The elastomeric article of claim 11, wherein the elastomeric
article at a thickness of about 0.1 mm or less exhibits a tensile
strength of about 20 MPa or greater when measured in accordance
with ASTM D412 and exhibits a tensile modulus at 500% elongation of
less than 2.75 MPa when measured in accordance with ASTM D412.
18. The elastomeric article of claim 11, wherein the composition is
substantially free of one or more of the following: elemental
sulfur or free sulfur; zinc oxide; and diphenyl guanidine
19. A method for preparing an elastomeric article, the method
comprising forming a film on a former using two separate
formulations having different overall compositions, each of the two
separate formulations comprising a
polystyrene-polyisoprene-polystyrene (SIS) polymer.
20. The method of claim 19, wherein one of the two separate
formulations includes one or more cure accelerators and one or more
surfactants, and wherein another of the two separate formulations
expressly excludes any cure accelerators.
21. The method of claim 19, wherein the method comprises sequential
dipping of the former into separate containers that separately
contain the two separate formulations to form the film on the
former.
22. The method of claim 21, wherein the method further comprises
separating the sequential dipping of the former into the separate
containers with a drying period that is carried out at a
temperature of about 50.degree. C. or greater for a time of about 1
minute or greater.
23. The method of claim 21, wherein the method further comprises
curing the film formed by the sequential dipping of the former into
the separate containers, and the curing is carried out at a
temperature of about 100.degree. C. or greater for a time of about
5 minutes or greater.
24. A method for preparing an elastomeric article, the method
comprising: preparing a compounded latex composition include a
polystyrene-polyisoprene-polystyrene (SIS) latex, at least one
sulfur donor, and at least one dithiocarbamate; prevulcanizing the
compounded latex composition to form a prevulcanized compounded
latex composition; dipping a former into the prevulcanized
compounded latex composition to form at least one layer of the
prevulcanized compounded latex composition thereon; and curing the
at least one layer of the prevulcanized compounded latex
composition on the former to provide the elastomeric article.
25. The method of claim 24, wherein the at least one sulfur donor
is a thiuram compound.
26. The method of claim 24, wherein the at least one sulfur donor
includes one or both of dipentamethylenethiuram tetrasulfide (DPTT)
and dipentamethylenethiuram hexasulfide (DPTTH).
27. The method of claim 24, wherein the compounded latex
composition further includes at least one amphoteric
surfactant.
28. The method of claim 24, wherein the compounded latex
composition further includes at least one antioxidant.
29. The method of claim 24, comprising prevulcanizing the
compounded latex composition in a temperature range of about
25.degree. C. to about 40.degree. C. for a time of about 12 hours
to about 48 hours.
30. The method of claim 24, comprising prevulcanizing the
compounded latex composition until achieving a relaxed modulus of
about 0.50 to about 0.61.
31. An elastomeric article prepared according to the method of
claim 24.
32. The elastomeric article of claim 31, wherein the elastomeric
article is a condom.
33. The elastomeric article of claim 31, wherein the elastomeric
article at a thickness of about 0.1 mm or less exhibits one or both
of a tensile strength of about 20 MPa or greater when measured in
accordance with ASTM D412 and a tensile modulus at 500% elongation
of less than 2.25 MPa when measured in accordance with ASTM D412.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional
Pat. App. No. 62/951,856, filed Dec. 20, 2019, and U.S. Provisional
Pat. App. No. 63/018,311, filed Apr. 30, 2020, the disclosures of
which are incorporated herein by reference in their entireties.
FIELD OF THE DISCLOSURE
[0002] The present disclosure relates to polymer compositions and
products that are formed from the polymer compositions, such as
elastomeric articles (e.g., thin-walled products, such as gloves
and condoms). The present disclosure further relates to methods of
making such products.
BACKGROUND
[0003] Natural rubber, which is comprised primarily of
cis-1,4-polyisoprene, is well known for use in making thin-film,
elastomeric articles, such as surgical gloves, balloons, condoms,
and the like. However, articles formed from natural rubber latex
are associated with a number of health problems, such as allergic
reactions. As a result, some have turned to synthetic polyisoprene
as a replacement for natural rubber in such articles. Because of
the desire to achieve articles with excellent tensile properties,
however, polyisoprene articles have typically been vulcanized
similarly to natural rubbers using sulfur-based curing agents and
zinc oxide cure activators. While avoiding some of the problems
associated with the use of natural rubber, the requirement for
using sulfur and zinc oxide can nevertheless also present health
concerns arising from allergic reactions as well. Accordingly,
there remains a need in the field for compositions and articles
formed therefrom that are thin-film forming materials and that can
provide articles with the desired tensile properties without the
health concerns noted above.
SUMMARY OF THE DISCLOSURE
[0004] The present disclosure provides compositions of polymeric
materials and products made therefrom. The products may include any
material that is useful when provided in the form of a thin film
that is elastomeric and exhibits substantially high tensile
strength, such as gloves, condoms, and similar articles. The
present disclosure further provides methods of preparing polymeric
compositions and products.
[0005] In one or more embodiments, the present disclosure provides
elastomeric articles comprising one or more layers of a compounded
polystyrene-polyisoprene-polystyrene (SIS) latex composition. More
particularly, the elastomeric articles can be configured to exhibit
specific properties. For example, at a thickness of about 0.1 mm or
less, the elastomeric articles can be configured to exhibit a
tensile strength of about 20 MPa or greater when measured in
accordance with ASTM D412 and exhibit a tensile modulus at 500%
elongation of less than 2.25 MPa when measured in accordance with
ASTM D412. The elastomeric articles may be further defined in
relation to one or more of the following statements, which can be
combined in any order or number.
[0006] The SIS latex composition can be substantially free of one
or more of the following: elemental sulfur or free sulfur; zinc
oxide; and diphenyl guanidine.
[0007] The elastomeric article can exhibit an elongation at break
of about 1000% or greater.
[0008] The elastomeric article can exhibit a tear strength of at
least 2 N/mm when measured in accordance with ASTM D624-00.
[0009] The elastomeric article can exhibit a Young's modulus (E')
that is less than 1 MPa at a frequency of 1 Hz and that is greater
than 1 MPa at a frequency of 21.5 Hz.
[0010] The SIS latex composition further can comprise a
dithiocarbamate accelerator.
[0011] The SIS latex composition further can comprise a thiuram
accelerator.
[0012] The SIS latex composition further can comprise one or more
of a surfactant, an antioxidant, a viscosity modifier, a filler,
and a smoothing agent.
[0013] The SIS latex composition can comprise a viscosity modifier
including at least a hydrophobically modified alkali soluble
emulsion.
[0014] The elastomeric article can be a condom.
[0015] In some embodiments, the present disclosure can provide
elastomeric articles formed from composition comprising specific
combinations of materials. In particular, such elastomeric articles
may be formed from compositions comprising:
polystyrene-polyisoprene-polystyrene (SIS) latex; an amphoteric
surfactant; at least one sulfur donor; and at least one
dithiocarbamate accelerator. The elastomeric articles may be
further defined in relation to one or more of the following
statements, which can be combined in any order or number.
[0016] The composition can comprise the amphoteric surfactant in an
amount of 0.01 to about 2.0 phr.
[0017] The composition can comprise the dithiocarbamates
accelerator in an amount of about 0.1 to about 2.0 phr.
[0018] The composition can comprise the at least one sulfur donor
in an amount of about 0.1 to about 2.0 phr.
[0019] The at least one sulfur donor can comprise a thiuram
compound.
[0020] The composition further can comprise one or more of an
antioxidant, a viscosity modifier, a filler, and a smoothing
agent.
[0021] The elastomeric article at a thickness of about 0.1 mm or
less can exhibit a tensile strength of about 20 MPa or greater when
measured in accordance with ASTM D412 and can exhibit a tensile
modulus at 500% elongation of less than 2.25 MPa when measured in
accordance with ASTM D412.
[0022] The composition can be substantially free of one or more of
the following: elemental sulfur or free sulfur; zinc oxide; and
diphenyl guanidine
[0023] In further embodiments, the present disclosure can provide
methods for preparing an elastomeric article. In particular, the
methods can comprise forming a film on a former using two separate
formulations having different overall compositions, each of the two
separate formulations comprising a
polystyrene-polyisoprene-polystyrene (SIS) polymer. Such methods
may be further defined in relation to one or more of the following
statements, which can be combined in any order or number.
[0024] One of the two separate formulations can include one or more
cure accelerators and one or more surfactants, and wherein another
of the two separate formulations expressly excludes any cure
accelerators or cure agents.
[0025] The method can comprise sequential dipping of the former
into separate containers that separately contain the two separate
formulations to form the film on the former.
[0026] The method further can comprise separating the sequential
dipping of the former into the separate containers with a drying
period that is carried out at a temperature of about 50.degree. C.
or greater for a time of about 1 minute or greater.
[0027] The method further can comprise curing the film formed by
the sequential dipping of the former into the separate container,
and the curing is carried out at a temperature of about 100.degree.
C. or greater for a time of about 5 minutes or greater.
[0028] In other embodiments, the present disclosure can provide
methods for preparing an elastomeric article that do not
necessarily require the use of multiple, different formulations.
For example, such methods can comprise: preparing a compounded
latex composition include a polystyrene-polyisoprene-polystyrene
(SIS) latex, at least one sulfur donor, and at least one
dithiocarbamate accelerator; prevulcanizing the compounded latex
composition to form a prevulcanized compounded latex composition;
dipping a former into the prevulcanized compounded latex
composition to form at least one layer of the prevulcanized
compounded latex composition thereon; and curing the at least one
layer of the prevulcanized compounded latex composition on the
former to provide the elastomeric article. Such methods may be
further defined in relation to one or more of the following
statements, which can be combined in any order or number.
[0029] The at least one sulfur donor can be a thiuram compound.
[0030] The at least one sulfur donor can include one or both of
dipentamethylenethiuram tetrasulfide (DPTT) and
dipentamethylenethiuram hexasulfide (DPTTH).
[0031] The compounded latex composition further can include at
least one amphoteric surfactant.
[0032] The compounded latex composition further can include at
least one antioxidant.
[0033] The method further can comprise prevulcanizing the
compounded latex composition in a temperature range of about
25.degree. C. to about 40.degree. C. for a time of about 12 hours
to about 48 hours.
[0034] The method further can comprise prevulcanizing the
compounded latex composition until achieving a relaxed modulus of
about 0.50 to about 0.61.
[0035] In still further embodiments, the present disclosure can
relate to elastomeric articles that are prepared according to one
or more of the methods described herein. In particular, the
elastomeric article can be a condom. Moreover, the elastomeric
article at a thickness of about 0.1 mm or less can exhibit one or
both of a tensile strength of about 20 MPa or greater when measured
in accordance with ASTM D412 and a tensile modulus at 500%
elongation of less than 2.25 MPa when measured in accordance with
ASTM D412.
BRIEF DESCRIPTION OF THE DRAWING
[0036] FIG. 1 is a graph showing Young's modulus (E') values for
various elastomeric articles according to the present disclosure
compared with known elastomeric articles.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0037] The invention now will be described more fully hereinafter
through reference to various embodiments. These embodiments are
provided so that this disclosure will be thorough and complete, and
will fully convey the scope of the invention to those skilled in
the art. Indeed, the invention may be embodied in many different
forms and should not be construed as limited to the embodiments set
forth herein; rather, these embodiments are provided so that this
disclosure will satisfy applicable legal requirements. As used in
the specification, and in the appended claims, the singular forms
"a", "an", "the", include plural referents unless the context
clearly dictates otherwise.
[0038] The present disclosure relates to polymer compositions, more
specifically to synthetic latex compositions. The present
disclosure further relates to products that are formed from the
polymer compositions as well as methods of making such products.
The polymer compositions are particularly useful in preparing
articles that can exhibit excellent physical properties even in the
absence of additives that are often found in convention elastomeric
articles and that can be a potential source of allergens.
[0039] The compositions provided herein and the products that may
be prepared therefrom can comprise primarily a styrene-modified
polyisoprene rubber material. More particularly, a
poly(styrene-isoprene-styrene) material may be used, which may also
be referred to as a polystyrene-polyisoprene-polystyrene material
or "SIS" material or SIS polymer. The SIS polymer in particular can
be a block copolymer that can be provided in the form of an aqueous
latex dispersion. For example, suitable SIS polymer is available
from Kraton Polymers under the name 2GL in their Cariflex.RTM.
polymer line. The SIS latex material used according to the present
disclosure can have a solids content of about 40% to about 65%,
such as about 45% to about 65% or about 45% to about 55%.
[0040] In some embodiments, the SIS polymer may be characterized in
relation to the relative content of the styrene and isoprene
monomer blocks. Test data confirmed that all types of SIS polymers
will not necessarily achieve an elastomeric article meeting the
performance requirements described herein. In particular, both of
tensile strength and modulus tend to increase with an increase in
styrene content in the SIS polymer, but the relative increases are
not of the same magnitude. Thus, styrene content in a SIS polymer
can have a significant impact on the usefulness of an article
prepared with the SIS polymer, particular in instances, as
described herein, where high tensile strength but low modulus are
preferred. Preferably, a SIS polymer useful according to the
present disclosure includes a styrene content that is within a
range that is defined by the weight percentage of styrene in the
polymer block polymer backbone structure as compared to the overall
molecular weight of the polymer (e.g., a wt/wt % of styrene in the
overall polymer). For example, in some embodiments, the SIS polymer
used according to the present disclosure can comprise at least 12%,
at least 12.6%, or at least 13% styrene based on the total weight
of the SIS polymer. The term "at least" in this instance can be
defined, in some embodiments, as having a maximum of about 25%.
Thus, in some embodiments, a SIS polymer as used herein can have a
styrene content of about 12% to about 25%, about 12.6% to about
18%, about 13% to about 16%, or about 13.5% to about 15% by weight,
based on the total weight of the SIS polymer. As further discussed
herein, a preferred SIS polymer may be defined by a plurality of
separate characteristics that make the polymer particular useful in
forming an elastomeric article with desired properties. It has been
found herein that the styrene content can affect one or more of the
further properties that are desired. For example, it can be
preferable for relaxed modulus of the SIS polymer to be within a
defined range, and use of a SIS polymer with a styrene content
outside of a preferred range can be detrimental to the desired
relaxed modules property of the elastomeric article formed with the
SIS polymer. In particular, it can be beneficial for the styrene
content of the SIS polymer to be within the range of about 12% to
about 16%, and more preferably about 13% to about 16%. Thus, while
the present disclosure contemplates the ability to form an
elastomeric article utilizing a SIS polymer with a styrene content
that is greater than 16% wt/wt, such as a higher range noted above,
the specific range of about 12% to about 16% can be particularly
beneficial for enabling the elastomeric article to exhibit one or
more properties as described herein, and specifically tensile
strength and relaxed modulus.
[0041] SIS latex compositions according to the present disclosure
can be used in forming elastomeric articles that exhibit desirable
strength and softness properties, provide thermoplastic-like
behavior, and also can be prepared without typical curing agents
and/or curing accelerators that may be allergen sources. A SIS
latex composition may comprise substantially only the SIS latex
material in an aqueous dispersion. In some embodiments, the SIS
latex compositions may include one or more additives that are
useful to provide further, desired properties to the articles
prepared therefrom, and such additives are further described below.
Such compositions may be referred to herein as a compounded SIS
latex, and it is understood that the term "compounded SIS latex
composition" can specifically reference compositions including the
SIS latex dispersion combined with one or more further components.
Moreover, if desired, further polymer materials may be combined
with the SIS polymer to provide combination polymer compositions.
For example, in some embodiments, it may be useful to combine a
content of a natural rubber latex ("NRL") with a content of a SIS
polymer to provide a polymer composition for use in forming at
least a part of an elastomeric article. For example, in embodiments
further described herein wherein a binary process is utilized, it
may be useful to utilize a combination of SIS latex and natural
rubber latex as one dipping or coating formulation. In some
embodiments, a ratio of NRL to SIS latex can be about 0.01 to about
0.1, about 0.02 to about 0.08, or about 0.03 to about 0.07, based
on the weight of NRL and the weight of SIS polymer used in the
composition (i.e., a wt/wt ratio). The foregoing ratios may apply
to a single latex composition from which one or more layers may be
formed through dipping. Alternatively, the foregoing ratios may
apply to an end product (i.e., an elastomeric article) where at
least NRL is used in one or more layers forming the product and at
least SIS is used in one or more layers forming the product.
[0042] A wide variety of elastomeric articles may be prepared using
compounded SIS latex compositions according to the preset
disclosure. The compositions may be utilized to form films
comprising one or a plurality of layers, and the films may
particularly be provided in specific forms to provide elastomeric
articles having desired end uses. For example, the compositions may
be utilized in preparing elastomeric gloves, condoms, protective
films for medical instruments, and other like uses where a
substantially thin, elastomeric film is desirable.
[0043] In one or more embodiments, the present disclosure thus can
provide elastomeric articles comprising one or more layers of a
compounded SIS latex composition. The one or more layers may be in
the form of a single film, a plurality of films that are
independent but at least partially adhered or otherwise bonded
together, or a plurality of films that are at least partially
blended together. In some embodiments, multiple films may be
combined in such a manner that the films blend together (at least
partially) at surfaces thereof such that a unitary, single film or
layer results (i.e., a plurality of films or layers are
sufficiently intimately blended together at the film or layer
surfaces such that the films or layers are substantially
inseparable). Such instances are readily envisioned in light of the
processing discussion provided further herein in relation to
dipping or otherwise forming a plurality of films or layers on a
former or similar structure so that sequentially applied films or
layers become blended or bonded together to form substantially a
single film or layer.
[0044] The polymer compositions and/or articles formed therefrom
may be defined in one or more embodiments in relation to the
absence of certain components that are commonly present in similar
articles and compositions but may be undesirable. For example, in
some embodiments, the SIS latex composition and/or an elastomeric
article formed therewith may be substantially free or completely
free of any free sulfur or elemental sulfur. As further discussed
herein, certain composition components may be sulfur-containing
materials (e.g., "sulfur donors"), but the sulfur therein is bound
in a compound form. Conventional vulcanization reactions, however,
typically utilize soluble sulfur (e.g., S.sub.8 rings) that are
easily solubilized to provide free, elemental sulfur in the mixture
to participate in crosslinking. The present compositions may be
substantially free or completely free of such free sulfur or
elemental sulfur. In some embodiments, the SIS latex composition
and/or an elastomeric article formed therewith may be substantially
free or completely free of any zinc oxide. While zinc oxide is
commonly used as a cure activator in known elastomeric articles,
the presently disclosed compositions advantageously can be used to
form elastomeric articles without the need for utilizing such cure
activator. Similarly, the SIS latex composition and/or an
elastomeric article formed therewith may be substantially free or
completely free of any diphenyl guanidine cure accelerator, which
also is commonly used in known elastomeric articles. As used above,
"substantially" free can indicate that no more than a trace amount
of the referenced material or compound is present, such as less
than 0.1%, less than 0.05%, or less than 0.01% by weight.
[0045] A SIS latex composition useful according to the present
disclosure may comprise substantially only the SIS latex
dispersion. For example, as discussed further below, elastomeric
articles may be prepared utilizing a plurality of different
formulations for a plurality of individual dipping or other coating
steps. A suitable formulation for use in forming at least one film
or layer in making an elastomeric article thus may consist
essentially or consist of a SIS latex dispersion or an aqueous SIS
polymer.
[0046] In some embodiments, a compounded SIS latex composition may
include one or more further components in addition to the SIS latex
dispersion. The combination of the SIS latex dispersion and the one
or more further components can be referred to as a compounded latex
composition.
[0047] In one or more embodiments, one or more cure accelerators
may be included in the SIS latex composition. Suitable cure
accelerators can include, for example, one or more
dithiocarbamates. Non-limiting examples of suitable
dithiocarbamates can include zinc dibutyldithiocarbamate (ZDBC),
zinc diethydithiocarbamate (ZDEC), zinc dimethyldithiocarbamate
(ZDMC), zinc dibenzyl dithiocarbamate (ZBED), sodium diethyl
dithiocarbamate (SDEC), and sodium dibutyldithiocarbamate
(SDBC).
[0048] As noted above, the compounded SIS latex composition may
include one or more sulfur donors. In some instances, the sulfur
donor may also be classified as or recognized in the field as being
an accelerator. In some embodiments, useful sulfur donors can
include one or more thiurams, such as dipentamethylenethiuram
hexasulfide (DPTTH), dipentamethylenethiuram tetrasulfide (DPTT),
tetramethylthiuram monosulfide (TMTM), tetramethylthiuram disulfide
(TMTD), tetraethylthiuram disulfide (TETD), and tetrabenzylthiuram
disulfide (TBzTD). Additionally, or alternatively, other types of
sulfur donors may also be utilized. For example,
4,4'-dithiodimorpholine (DTDM), thiocarbamyl sulfonamide, and
N-oxydiethylene thiocarbamyl-N-oxydiethylene sulfenamide (OTOS) may
be utilized in some embodiments. The use of such materials can be
beneficial in that the sulfur included in the sulfur donor
compounds is not free sulfur that can contribute to potential
allergies. Additionally, disulfide (S--S) bonds produced during
curing (i.e., cross-linking) when using curing materials that
include free/elemental sulfur are very weak and are susceptible to
breakage from exposure to heat or stress. By using sulfur donors
that include bulky, alkyl groups, breakage when exposed to heat or
stress can be significantly reduced. The presently disclosed
compositions and methods further reduce the possibility of surface
bloom and also can provide significantly improved heat resistance
and aging stability.
[0049] A single curing accelerator or a mixture of two or more
curing accelerators may be used in the compounded SIS latex
composition in a total amount based upon a composition including
100 parts per hundred rubber (phr) of the SIS latex. For example,
in some embodiments, a single curing accelerator may be used in an
amount of about 0.01 to about 5.0 phr, about 0.02 to about 4.0 phr,
about 0.1 to about 3.0 phr, or about 0.5 to about 2.0 phr. In other
embodiments, a single curing accelerator may be used in an amount
of about 0.1 to about 5.0 phr, about 0.2 to about 4.5 phr, or about
0.4 to about 4.0 phr. In further embodiments, a total amount of all
curing accelerators in the SIS latex composition can be about 0.2
to about 8.0 phr, about 0.3 to about 6.0 phr, about 0.4 to about
5.0 phr, about 0.5 to about 4.0 phr, or about 1.0 to about 3.0 phr.
In some embodiments, a sulfur donor may be considered to be a cure
accelerator, and the amount of a sulfur donor may be within the
above-recited ranges for single cure accelerators and/or for total
cure accelerators. Alternatively, the above-discussed ranges may be
applied individually to components utilized as accelerators and to
components utilized as sulfur donors.
[0050] In one or more embodiments, a compounded SIS latex
composition useful according to the present disclosure can comprise
SIS polymer and optionally a further polymer, an accelerator, and a
sulfur donor. In some embodiments, a compounded SIS latex
composition may consist essentially of or consist of SIS polymer
and optionally a further polymer, an accelerator, and a sulfur
donor. A compounded SIS latex composition according to the present
disclosure, however, can further comprise one or more additional
components that can be useful, for example, to assist in resisting
aging (and thus maintaining stability of the end product) and/or to
provide additional, useful properties to the formed elastomeric
article. As non-limiting examples, further materials such as
surfactant(s), antioxidant(s), rheological stabilizer(s),
filler(s), and smoothing agent(s) may be included in the compounded
SIS latex composition. Accordingly, in one or more embodiments, a
compounded SIS latex composition according to the present
disclosure may comprise, consist essentially of, or consist of SIS
polymer and optionally a further polymer, an accelerator, a sulfur
donor, and an antioxidant; a compounded SIS latex composition
according to the present disclosure may comprise, consist
essentially of, or consist of SIS polymer and optionally a further
polymer, an accelerator, a sulfur donor, and a rheological
stabilizer; a compounded SIS latex composition according to the
present disclosure may comprise, consist essentially of, or consist
of SIS polymer and optionally a further polymer, an accelerator, a
sulfur donor, an antioxidant, and a rheological stabilizer; a
compounded SIS latex composition according to the present
disclosure may comprise, consist essentially of, or consist of SIS
polymer and optionally a further polymer, an accelerator, a sulfur
donor, and a surfactant; a compounded SIS latex composition
according to the present disclosure may comprise, consist
essentially of, or consist of SIS polymer and optionally a further
polymer, an accelerator, a sulfur donor, a surfactant, and an
antioxidant; a compounded SIS latex composition according to the
present disclosure may comprise, consist essentially of, or consist
of SIS polymer and optionally a further polymer, an accelerator, a
sulfur donor, a surfactant, an antioxidant, and a rheological
stabilizer; and/or a compounded SIS latex composition according to
the present disclosure may comprise, consist essentially of, or
consist of SIS polymer and optionally a further polymer, an
accelerator, a sulfur donor, a surfactant, an antioxidant, and one
or more of a rheological stabilizer, a filler, and a smoothing
agent. It is understood that recitation of "a" component above does
not exclude the presence of a plurality of any one or more of the
noted components unless the context specifically indicates that
only a single instance of the noted component is to be utilized.
Moreover, one or more components may be expressly excluded from
such example compositions.
[0051] A variety of surfactants may be utilized in the present
compositions, including cationic surfactants, anionic surfactants,
and amphoteric surfactants. In some embodiments, one or more
amphoteric surfactants in particular may be included with the SIS
latex. Amphoteric surfactants are recognized as being zwitterionic
and thus include both positive and negative charges, and any such
material may be utilized according to the present disclosure.
Useful amphoteric surfactants may include alkyl substituted amino
acids, betaines, and amine oxides. For example, monosodium
N-lauryl-beta-iminodipropionic acid, may be particularly useful in
the present compositions. Non-limiting examples of alternative
types of surfactants that may be utilized include potassium
laurate, sodium salt of sulfated methyl oleate, and sodium
dodecylbenzene sulfonate (SDBS). The amount of surfactant(s)
included in the present SIS latex compositions can be in the range
of about 0.01 to about 4 phr, about 0.05 to about 3.5 phr, about
0.1 to about 3.0 phr, or about 0.2 to about 2.0 phr.
[0052] Various types of antioxidants may likewise be utilized in
the present SIS latex compositions. Non-limiting examples of
antioxidants that may be used include a butylated reaction product
of p-cresol and dicylopentadiene that is available under the name
Bostex 24 and a variety of mercapto-imidazole compounds, such as
2-mercaptobenzimidazole (MBI), 2-mercaptotoluimidazole (MTT),
2-mercapto toluimidazole (MTI), a zinc salt of
2-mercaptobenzimidazole (ZMBI), a zinc salt mercaptotoluimidazole
(ZNTI), and the like. The amount of antioxidant(s) (individually or
in total) included in the present SIS latex compositions can be in
the range of about 0.01 to about 4 phr, about 0.05 to about 3.5
phr, about 0.1 to about 3.0 phr, or about 0.2 to about 2.0 phr.
[0053] A non-limiting example of fillers that may be utilized
includes fumed silicas or dispersions thereof, such as available
under the tradename cab-o-sperse.RTM.. A non-limiting example of
smoothing agents that may be utilized include proteins, such as
casein. The amount of filler(s) and/or smoothing agent(s) included
in the present SIS latex compositions (individually or in total)
can be in the range of about 0.01 to about 4 phr, about 0.05 to
about 3.5 phr, or about 0.1 to about 3.0 phr.
[0054] In various embodiments, elastomeric articles may be prepared
by conventional methods, such as dipping one or more formers into a
liquid polymer composition, such as defined herein, one or more
times to form one or more layers of the polymer composition on the
former. While suitable elastomeric articles may be formed using a
variety of polymer compositions utilizing various combinations of
the possible ingredients described herein, it has been found herein
that addition of one or more rheology modifiers can be particularly
useful to improve the dipping profiled so that the tensile
properties and the overall aesthetics of the formed product are not
solely dependent upon the rheological properties of the liquid
composition arising from the total solids content of the liquid
composition. In other words, while combination of the polymer(s)
components, any surfactants, any antioxidants, and any of the
further compounds described herein (i.e., to provide a compounded
SIS formulation) may be effective to form an elastomeric article
with desired properties, the compounded SIS formulation may not
exhibit properties in the liquid state that allow for consistency
in the manufacturing process so that film properties are
substantially uniform from one item to the next. The present
disclosure can overcome such consistency issues, when needed,
through addition of one or more rheological stabilizers. For
example, while natural rubber and substantially pure synthetic
polyisoprene latex compositions have previously been used because
of their stability, the use of further polymers for forming
elastomeric articles can be challenging due to low stability and/or
inconsistent dipping results, as noted above. Initial testing
according to the present disclosure found that while a compounded
SIS formulation was effective for forming elastomeric articles,
inconsistent film coverage on the film former hindered the ability
to provide articles with consistently achieved properties that are
discussed herein and also led to unacceptable defect occurrence and
unacceptable scrap rates. According to the present disclosure, such
unacceptable results can be overcome in a variety of manners.
[0055] As further described below, such problems with inconsistency
may be addressed in some embodiments through specific control of
process conditions. Likewise, such problems may be addressed, at
least in part, through the specific use of amphoteric surfactants
and/or specific combinations of cure accelerators. In one or more
embodiments, improved dipping profile (and thus consistent
production of elastomeric articles with desired properties) may be
achieved through addition of at least one rheological stabilizer.
Such components may be beneficial to impart stability to the
compounded SIS formulation by, for example, improving pick-up of
the compounded SIS formulation on the surface of the former.
Improved "pick-up" can mean imparting greater uniformity of the
ultimate coating layer, thus avoiding thin spots or even voids in
the coating layer. Useful rheological stabilizers can be any
additive, particularly a polymer additive, that is adapted to or
configured to improve film thickness uniformity without
significantly adversely affecting other film properties, such as
tensile strength and/or tensile modulus. This can be achieved, for
example, by improving the viscosity profile, flow properties, and
similar rheological properties of the liquid, compounded SIS
formulation to be applied to a former. Particularly useful
rheological stabilizers can include one or more materials
categorized as a hydrophobically modified alkali swellable emulsion
("HASE") polymer.
[0056] Known HASE materials that may be utilized according to the
present disclosure include materials which preferably include
structural units of a) an acrylate, for example ethyl acrylate,
butyl acrylate, or ethylhexyl acrylate, preferably ethyl acrylate;
b) an acid, preferably acrylic acid, methacrylic acid, itaconic
acid, or phosphoethyl methacrylate, preferably acrylic acid or
methacrylic acid; and c) an alkylated ethoxylate monomer,
preferably an alkylated ethoxylate acrylate or methacrylate. In
some embodiments, useful HASE polymers include materials comprising
ethyl acrylate, methacrylic acid, and hydrophobically modified
(e.g., with C.sub.22 behenyl pendant groups) methacrylate with 25
moles of ethoxylation. Such materials can function synergistically
with surfactants. In a non-limiting example embodiment, a suitable
HASE material is available under the name Novethix.TM. L-10 and is
an acrylates/beheneth-25 methacrylate copolymer. In one or more
embodiments, a single HASE material or a total HASE material
content in an SIS latex composition can be in the range of about
0.01 to about 1.0 phr, about 0.01 to about 0.50 phr, about 0.01 to
about 0.20 phr, or about 0.02 to about 0.05 phr.
[0057] In one or more embodiment, SIS latex compositions useful
herein may include the SIS latex emulsion alone or may include the
SIS latex emulsion in combination with one or more further
components described above. As non-limiting examples, the present
disclosure encompasses at least the following compositions (wherein
the absence of any component otherwise mentioned herein may
encompass the express exclusion of such component): SIS latex
dispersion alone; SIS latex dispersion and one or more amphoteric
surfactants; SIS latex dispersion and one or more cure
accelerators; SIS latex dispersion and one or more sulfur donors;
SIS latex dispersion, one or more amphoteric surfactants, and one
or more cure accelerators; SIS latex dispersion, one or more
amphoteric surfactants, and one or more sulfur donors; SIS latex
dispersion, one or more cure accelerators, and one or more sulfur
donors; SIS latex dispersion, one or more amphoteric surfactants,
one or more cure accelerators, and one or more sulfur donors; SIS
latex dispersion, one or more amphoteric surfactants, one or more
cure accelerators, one or more sulfur donors, and one or more
antioxidants. Optionally, any of the foregoing may include one or
more fillers and/or one or more smoothing agents and/or one or more
viscosity modifiers. Preferably, the SIS latex composition will
have a solid content as noted previously. Likewise, preferably, the
SIS latex composition will utilize SIS polymer having a styrene
content as noted previously. As non-limiting examples, suitable SIS
latex compositions may include one or more of the following
materials in the noted ranges, and it is understood that the noted
ranges are exemplary only, and may be modified in light of the
further ranges otherwise described herein. For example, an SIS
latex composition may comprise approximately 100 phr of the SIS
latex emulsion at the desired solid content, about 0.1 to about 5.0
phr of one or more cure accelerators, about 0.01 to about 2.0 phr
of one or more surfactants, about 0.1 to about 5.0 phr of one or
more sulfur donors, and about 0.01 to about 2.0 phr of one or more
antioxidants. Optionally, an SIS latex composition may comprise
about 0.01 to about 0.5 phr of one or more fillers and/or about
0.01 to about 0.5 phr of one or more smoothing agents and/or about
0.01 to about 0.5 phr of one or more viscosity modifiers. The
foregoing are provided as example embodiments and should not be
construed as excluding combinations of components and
concentrations in ranges otherwise described herein unless
expressly noted.
[0058] SIS latex compositions as described above can be used as
otherwise described herein in preparing one or more products, such
as an elastomeric article (e.g., gloves, condoms, or similar
film-like, elastomeric articles). Beneficially, the formed products
can be substantially streak-free, can be compatible with a wide
range of materials that are commonly combined with such articles
(e.g., powders for gloves and lubricants for condoms), can exhibit
improved ease of removal from formers during production of the
products, and can exhibit reduced or no yellow coloration. Thus,
the compositions and products may exhibit at least a certain level
of whiteness as observable utilizing a colorimeter. In addition,
elastomeric articles prepared according to the present disclosure
utilizing SIS latex compositions as described herein can exhibit a
variety of physical properties at specifically desirable
performance levels.
[0059] An elastomeric article according to the present disclosure
in particular can exhibit a tensile strength of about 20 MPa or
greater, about 22 MPa or greater, about 25 MPa or greater or about
28 MPa or greater (such as in the range of about 20 MPa to about 50
MPa, about 22 MPa to about 40 MPa, or about 25 MPa to about 38
MPa). Likewise, an elastomeric article according to the present
disclosure can exhibit a tensile modulus at 500% elongation that is
less than 2.75 MPa, less than 2.25 MPa, less than 2.0 MPa, less
than 1.75 MPa, or less than 1.50 MPa (such as in the range of about
0.50 to about 2.70, about 0.50 to about 2.20, about 0.75 to about
2.10, about 1.0 to about 2.0, or about 1.1 to about 1.8. Tensile
strength and tensile modulus can be measured in accordance with
American Society for Testing and Materials (ASTM) D412.
[0060] Tear strength (or tear resistance) can also be used as an
indicator of appropriate strength and article integrity. More
particularly, tear strength/tear resistance may be defined as the
average force required to propagate a tear in the article divided
by the thickness of the article. This value thus can incorporate a
measured tear force, which is the average force required for the
article to completely tear. Because the unique properties of
elastomeric articles, such as the SIS articles described herein,
tear force may be recited as an average since the actual values
(highs and lows) will vary across the total article. In some
embodiments, an elastomeric article according to the present
disclosure can have a tear strength of at least 1.5 N/mm, at least
2 N/mm, or at least 2.2 N/mm (e.g., up to a maximum of about 20
N/mm or about 15 N/mm). In further embodiments, tear strength can
be about 2 N/mm to about 20 N/mm, about 2.2 N/mm to about 15 N/mm,
about 2.5 N/mm to about 12 N/mm, or about 3 N/mm to about 10 N/mm.
Tear strength can be evaluated using ASTM D624-000.
[0061] Elastomeric articles according to the present disclosure
further can be defined in relation to the elongation at break. For
example, the present elastomeric articles can exhibit an elongation
at break of about 1000% or greater, about 1050% or greater, or
about 1100% or greater (such as in the range of about 1000% to
about 1500%, about 1050% to about 1400%, or about 1100% to about
1300%). Physical properties exhibited by example embodiments of
elastomeric articles as well as methods of preparing such articles
and example compositions used in preparing such articles are
further provided in the Examples appended hereto.
[0062] Physical characteristics of an elastomeric article described
herein (such as tensile strength, tensile modulus, and elongation
at break) can be derived, in some embodiments, from the specific
combination of materials utilized in forming the articles. In
further embodiments, physical properties may be derived, at least
in part, from the processing steps used in forming the elastomeric
articles. For example, stability of the elastomeric article may
directly relate to the type and amount of surfactant that is
utilized (e.g., the specific utilization of an amphoteric
surfactant) and/or total solids level of the SIS latex composition
and/or the relative styrene concentration in the SIS polymer. Film
strength may be directly related to the combination of accelerators
that are used and the total concentration of accelerators and/or to
the uniformity of the produced film. Film elasticity may be
directly related to the nature of the physical and chemical
crosslinking that is achieved during film formation, including the
level of prevulcanization that is achieved and/or the final cure
level that is achieved. Film clarity may be directly related to the
formulation stability, the uniformity of the film, and the
combination of accelerators and concentration of accelerators that
are used.
[0063] In some embodiments, the elastomeric articles may be
characterized in relation to dynamic mechanical analysis (DMA),
such as the testing described in Example 9 herein. DMA testing can
be utilized to provide a Young's modulus (E') that is indicative of
mechanical properties of the article when under a substantially low
degree of stretch, and this can be indicative of high film quality
that is analogous to strength testing that is carried out at higher
degrees of stretching (e.g., tensile strength). Elastomeric
articles according to the present disclosure may have a Young's
modulus (E') that is less than 1 MPa at a frequency of 1 Hz and
that is greater than 1 MPa at a frequency of 21.5 Hz. For example,
the Young's modulus (E') at 1 Hz may be less than 1 MPa but greater
than 0.8 MPa, and the Young's modulus (E') at 21.5 Hz may be
greater than 1.05 MPa, greater than 1.1 MPa, or greater than 1.15
MPa.
[0064] Physical properties of the elastomeric articles or films
that are produced according to the present disclosure may likewise
relate to the average thickness of the articles/films. The
presently disclosed compositions may be particularly useful in
forming relatively thin-walled structures that still exhibit the
overall strength (e.g., at least a minimum tensile strength and/or
tear strength) and softness (e.g., below a maximum tensile modulus)
that is desired. In one or more embodiments, physical
characteristics defined herein may relate to an elastomeric article
having an average thickness of less than 0.1 mm, less than 0.09 mm,
or less than 0.08 mm (e.g., down to a minimum thickness of about
0.01 mm). Preferably, the elastomeric articles may have a thickness
of about 0.04 mm to about 0.09 mm, about 0.045 mm to about 0.085
mm, or about 0.06 mm to about 0.08 mm.
[0065] In one or more embodiments, the present disclosure further
provides for methods of preparing an elastomeric article. The
methods may include a plurality of steps including mixing of
polymer composition components, one or more steps wherein a former
of other mold is dipped or otherwise coated with one or more
coatings or layers of polymer composition to form a film of a
desired thickness, and a curing step wherein the formed film is
processed to be in a substantially finished form (e.g., crosslinked
or otherwise solidified to form a unitary article of manufacture).
Optionally, one or more drying steps may be utilized. Further,
suitable processing equipment may be used as needed to provide for
the necessary processing steps, including formers, dip tanks,
heating equipment, fans, conveyers, and the like may be
utilized.
[0066] A SIS latex dispersion may be obtained from a supplier in a
higher solid content than is desired for the end products.
Accordingly, a method of manufacture of an elastomeric article can
include diluting a SIS latex dispersion (e.g., using deionized
water or the like) to the desired solid content. The optionally
diluted SIS latex dispersion may be ready for use as a formulation
for forming a film. In some embodiments, where one or more
additives may be desired, the specific additives may be added
sequentially or simultaneously to the SIS latex dispersion to form
the polymer composition. Where surfactants and accelerators are
utilized, these in particular may be added together to the SIS
latex dispersion and stirred for a time to reach a substantially
homogeneous dispersion of the materials. Antioxidant may
specifically be added to the polymer composition after addition of
the further components, such as within a few hours of the start of
any dipping or other coating process. The polymer composition may
be filtered prior to being transferred to a dip tank or storage
tank for storage for a time suitable for de-aeration of the
mixture. For example, the polymer composition may be filtered using
a 200 .mu.m filter (e.g., suitable to filter out particles having a
size greater than 200 .mu.m) or a differently sized filter (e.g.,
suitable to filter out particles having a size that is greater than
150 .mu.m, greater than 175 .mu.m, greater than 200 .mu.m, or
greater than 225 .mu.m).
[0067] In some embodiments, a method for preparing an elastomeric
article may particularly be a binary process, which can indicate
that two separate formulations are utilized or that at least two
separate formulations are utilized. A former or other mold then may
be dipped or otherwise coated at least once with each of the
separate formulations in any order, optionally being at least
partially dried between separate dipping or coating procedures. A
Formulation A, for example, may comprise a SIS polymer (e.g., a SIS
latex dispersion), one or more cure accelerators, one or more
surfactants, and optionally one or more cure agents and/or
activators, and a Formulation B, for example, may comprise a SIS
polymer and one or more surfactants and may expressly exclude any
cure accelerators and/or cure agents. Such binary dipping process
can be particularly useful to provide improved control over the
final cure of the SIS latex film (e.g., the elastomeric article).
This is achieved, as noted above, by separating the SIS polymer
(and optional combinatory polymer--e.g., NRL) into separate dip
tanks, one including compounded polymer(s) that can cure and
chemically crosslink, and another including only the polymer(s) and
stabilizing agents that can physically crosslink during the final
curing. A such, physical and chemical crosslinking can be balanced
without the need for prevulcanization though heating of the
compounded SIS polymer formulation. This can be particularly useful
since compounded SIS formulations can over-cure without close
monitoring of the prevulcanization temperature, which can adversely
affect the desired properties of the formed, elastomeric
article.
[0068] In an example embodiment, methods for preparing an
elastomeric article can comprise forming a film on a former or
other mold using two separate formulations having different overall
compositions, each of the two separate formulations comprising a
SIS polymer composition or latex dispersion. The two (or at least
two) separate formulations are separate and have different overall
compositions such that the binary process excludes processes
wherein a formed may simply be dipped multiple times in a single
composition. Rather, the separate and different formulations can
vary in the components included therein or excluded therefrom, can
vary in the concentration of components included therein, can vary
in the solid content of the formulation, or in any combination of
such variations. In some embodiments, the separate and different
formulations can differ in that one of the separate and different
formulations can expressly include one or more cure accelerators,
and another of the separate and different formulations can
expressly exclude one or more cure accelerators and/or cure
agents.
[0069] The binary method of forming an elastomeric article can
comprise sequential dipping or coating of a former or other mold
using separate containers that separately contain the two (or more)
separate formulations to form a film on the former or mold. As
such, coating or dipping can be carried out as two or more
individual coating or dipping actions that are performed separately
and sequentially. If desired, the separate and sequential coating
or dipping actions may be separated by a drying period. Thus, a
first coating or dipping action may be carried out to begin forming
of a film, the partial film may be at least partially dried during
the drying period, and a second coating or dipping action may be
carried out to further form or complete forming of the film. While
the individual coating or dipping actions may be characterized as
forming multiple layers, as already described above, it is
understood that the final, elastomeric article to be prepared is
preferably a substantially, thin-film type article having an
average film thickness, wherein the film is a unitary structure,
and individual "layers" are not separable from each other (i.e.,
there can be no de-lamination of layers). Individual coating or
dipping actions thus preferentially are adapted to or configured to
add to an overall average thickness of the film that is formed on
the former or other mold without forming physically separable
layers.
[0070] An individual drying period may be carried out for a defined
time under defined conditions. For example, a drying period may
continue for a time of about 1 minute or greater, about 2 minutes
or greater, or about 3 minutes or greater (such as about 1 minute
to about 10 minutes or about 2 minutes to about 8 minutes). Drying
conditions may be, for example, at a temperature of about
50.degree. C. or greater, about 70.degree. C. or greater, or about
80.degree. C. or greater (such as about 50.degree. C. to about
110.degree. C., about 70.degree. C. to about 110.degree. C., or
about 80.degree. C. to about 110.degree. C.). Drying may be carried
out between individual coating or dipping actions and/or may be
carried out after completion of all coating or dipping actions.
[0071] After all of the coating or dipping actions have been
carried out, the method can further include curing the film. In
some embodiments, curing can be carried out at a temperature of
about 100.degree. C. or greater or about 110.degree. C. or greater
(such as a temperature range of about 100.degree. C. to about
140.degree. C. or about 110.degree. C. to about 130.degree. C.).
The curing time can vary can be, for example, carried out for a
time of about 5 minutes or greater or about 10 minutes or greater
(such as about 5 minutes to about 30 minutes or about 10 minutes to
about 20 minutes).
[0072] In an example embodiment, a method for preparing an
elastomeric article in particular may comprise providing a
Formulation A comprising a SIS polymer, one or more surfactants,
and one or more cure accelerators and providing a Formulation B
comprising a SIS polymer and a surfactant but excluding any cure
accelerators. The method can further comprise dipping a former into
one of Formulation A and Formulation B to form a film of the
respective Formulation on the former, at least partially drying the
film on the former, dipping the forming into the other of
Formulation A and Formulation B to further form a film of the
respective Formulation on the former, and curing the film including
Formulation A and Formulation B.
[0073] In one or more embodiments, a method for preparing an
elastomeric article according to the present disclosure may utilize
a single dipping formulation of the SIS latex composition. As such,
an elastomeric article may be prepared by first forming a
compounded latex composition including the SIS polymer and one or
more further components as described herein. As a non-limiting
example, the compounded latex composition can comprise a
polystyrene-polyisoprene-polystyrene (SIS) latex, at least one
sulfur donor, and at least one dithiocarbamate accelerator.
Optionally, one or more amphoteric surfactants, one or more
antioxidants, one or more fillers, and/or one or more smoothing
agents may be included. The compounded latex composition may be
subjected to conditions suitable for prevulcanization of the
composition to a desired level of prevulcanization or crosslink
density. Thereafter, a former may be dipped into the prevulcanized
compounded latex composition to form at least one layer of the
prevulcanized compounded latex composition thereon. In some
embodiments, the former may be dipped a single time to form a
single layer, or the former may be dipped twice to form two layers,
or the former may be dipped three times to form three layers, or
even more dipping iterations may be carried out. Where multiple
dipping steps are utilized, the formed layer may be at least
partially dried before carrying out the next step in the process.
The layer(s) of the prevulcanized compounded latex composition may
be cured to form the final elastomeric product, which them may be
removed from the former using any suitable method in the field.
[0074] In some embodiments, the present method may be carried out
under defined conditions that are effective to provide desired
properties in the finished, elastomeric article. For example, in
some embodiments, desired properties may be achieved by utilizing
specific prevulcanization conditions. For example, it can be useful
for prevulcanization to be carried out for maturing the composition
through crosslinking. Since the present compositions may be
expressly free of any free sulfur or soluble sulfur and rather
utilizes a sulfur donor, specific prevulcanization conditions may
be useful to ensure that the composition is crosslinked to the
correct crosslink density prior to dipping. For example, maturing
or prevulcanization can be carried out in a temperature range of
about 25.degree. C. to about 40.degree. C. for a time of about 12
hours to about 48 hours. In some embodiments, the temperature for
prevulcanization may be substantially steady throughout the
prevulcanization time (e.g., varying in temperature by no more than
2.degree. C. or no more than 1.degree. C.). In some embodiments,
however, the prevulcanization may be split into a plurality of
temperatures for defined lengths of time. For example,
prevulcanization may be carried out for a first time period at a
first temperature and then for a second time period at a second,
lower temperature. A first, higher temperature range may be about
32.degree. C. to about 38.degree. C., about 33.degree. C. to about
37.degree. C., or about 34.degree. C. to about 36.degree. C. A
second, lower temperature range may be about 26.degree. C. to about
32.degree. C., about 27.degree. C. to about 31.degree. C., or about
28.degree. C. to about 30.degree. C. The "higher" and "lower"
temperature ranges preferably are separated by at least 2.degree.
C., at least 3.degree. C., or at least 4.degree. C. Maturing the
SIS latex composition to achieve prevulcanization may be carried
out such that the time of prevulcanization at the higher
temperature is less than the time of prevulcanization at the lower
temperature. For example, prevulcanization at the higher
temperature may be for a time of about 0.5 hours to about 18 hours,
about 1 hour to about 12 hours, or about 1.5 hours to about 8
hours. Prevulcanization at the lower temperature may be, for
example, for a time of about 2 hours to about 36 hours, about 3
hours to about 30 hours, or about 8 hours to about 24 hours.
[0075] Indication that the desired level of prevulcanization has
been achieved may, in some embodiments, be identified in relation
to one or more measurable properties of the compounded latex
composition prior to dipping. For example, crosslinking density of
the prevulcanized, compounded latex composition may be measured
using the relaxed modulus test. The method for measuring relaxed
modulus was originally published by Gorton and Pendle (Natural
Rubber Technology, 1976, 7(4), 77-84 One method for evaluating
relaxed modulus (or relaxation modulus) can include the following
steps: prepare a tube-shaped film of the latex composition (e.g.,
by dipping a glass tube or similar structure into the latex
composition and then drying the formed film; rolling the tube
shaped film to form a ring and removing the ring from the former;
weighing the formed ring to find its mass (M in grams); placing the
ring on the mounts of a suitable tensile tester and stretching the
ring to 100% extension for one minute; measuring the load in
Newtons exerted by the ring after the one minute; and using the
load reading and the mass of the ring to calculate the relaxed
modulus in MPa according to the following formula:
Relaxed Modulus (MPa)=(F.times.d.times.C)/2M
wherein F is the load in Newtons exerted by the ring after on
minute at 100% extension, d is the density of the latex ring in
grams per cubic centimeter, C is the external circumference of the
dipping tube in centimeters, and M is the mass of the latex ring in
grams. Preferably, relaxed modulus will be measured on a plurality
of samples and the mean taken as the measured value. Such testing
can be carried out, for example, using the a RRIM Relaxed Modulus
Tester, Model M403, available from the Malaysian Rubber Board.
Likewise, such testing may be carried out using a TA. XI Plus
Texture Analyzer equipped with a 5 kilogram load cell.
[0076] Prevulcanization according to the present disclosure
preferably can be carried out until a defined relaxed modulus value
is obtained. In one or more embodiments, the desired relaxed
modulus can be in a range of about 0.50 to about 0.61, about 0.51
to about 0.60, about 0.52 to about 0.59, about 0.53 to about 0.58,
or about 0.54 to about 0.57. Achieving a relaxed modulus value
within these ranges can be a useful indicator that the proper
balance of chemical and physical crosslinking has been achieved for
the compounded SIS polymer formulation. While relaxed modulus
values outside of these ranges may not hinder successful formation
of an elastomeric article, maintaining relaxed modulus values
within these ranges can ensure that the film properties (e.g.,
tensile strength and modulus) will consistently be within the
desired ranges otherwise described herein.
[0077] In one or more embodiments, desired properties may be
achieved by utilizing specific drying conditions during dipping. In
certain embodiments, it can be desirable for drying to be carried
out after a dipping step, prior to a further dipping step and/or
prior to curing. Drying may be carried out in a temperature range
of about 80.degree. C. to about 120.degree. C. or about 85.degree.
C. to about 115.degree. C. Drying in this temperature range can be
for a time of about 1 minute to about 10 minutes, about 2 minutes
to about 8 minutes, or about 3 minutes to about 7 minutes. In some
embodiments, two dipping steps can be utilized, and drying after
the respective dipping steps can be at different temperatures. For
example, drying after a first dipping step can be at a temperature
that is lower than the temperature of a second dipping step. A
first, lower temperature range may be about 80.degree. C. to about
100.degree. C., about 85.degree. C. to about 95.degree. C., or
about 88.degree. C. to about 92.degree. C. A second, higher
temperature range may be about 100.degree. C. to about 120.degree.
C., about 105.degree. C. to about 115.degree. C., or about
108.degree. C. to about 112.degree. C. The "higher" and "lower"
temperature ranges preferably are separated by at least 2.degree.
C., at least 3.degree. C., or at least 4.degree. C.
EXPERIMENTAL
[0078] The present disclosure is more fully illustrated by the
following examples, which are set forth to illustrate certain
embodiments of the present disclosure and are not to be construed
as limiting thereof.
Example 1--Preparation of Synthetic Poly(Styrene-Isoprene-Styrene)
Latex Composition
[0079] An aqueous poly(styrene-isoprene-styrene) latex composition
having a solid content of 65% was obtained from Kraton Polymers and
was diluted to approximately 50% solid content using deionized
water. Surfactant(s) and cure accelerator(s) were added to the
latex mixture and stirred about 100 to 150 rpm at room temperature
overnight. The compounded latex was filtered using a 200 .mu.m
filter and left in a dip tank overnight to remove air bubbles.
Antioxidant(s) were added to the composition approximately two
hours prior to starting of dipping.
Example 2--Preparation of Latex Articles
[0080] Latex articles were prepared utilizing the composition
prepared according to Example 1. The latex articles were prepared
by performing two dipping actions. A first dip in the dip tank was
carried out at a withdrawal speed of about 0.2 to 0.4 inches per
second to obtain the desired film thickness and oven dried at about
90.degree. C. for about 5 minutes. A second dip in the dip tank was
carried out at a withdrawal speed of about 0.2 to 0.4 inches per
second to obtain the desired film thickness and oven dried at about
90.degree. C. for about 5 minutes. The final film was oven cured at
about 120.degree. C. for about 15 minutes. The formed elastomeric
latex article was removed from the former using a corn starch
slurry and air dried.
Example 3--Effect of Accelerators on Physical Properties of
Elastomeric Latex Articles
[0081] Synthetic SIS latex compositions and elastomeric latex
articles were prepared according to the methods of Example 1 and
Example 2 utilizing varying accelerator components and amounts as
seen in Tables 1-3 below. Tensile properties for the different
articles are also shown. As can be seen, the type of accelerator
and the concentration utilized can affect the level of chemical
crosslinking that is achieved.
TABLE-US-00001 TABLE 1 Accelerator Accelerator Accelerator
Formulation (in phr) Control (1.3 phr) (1.5 phr) (1.7 phr) Latex
SIS 100 100 100 100 Surfactant Manawet .TM. 172 0.5 0.5 0.5 0.5
Cure Agent Sulfur 0 0 0 0 Cure Activator Zinc Oxide 0 0 0 0 Cure
ZDEC (Bostex 561) 0 0.52 0.6 0.68 Accelerator DPTTH (Bostex 224) 0
0.78 0.9 1.02 Antioxidant Wingstay .RTM. L 0.5 0.5 0.5 0.5 Tensile
Tensile (MPa) 19.42 24.9 28 25.4 Properties Modulus@500% (MPa) 1.04
1.52 1.59 1.75 Elongation (%) 1419 1335 1358 1288
TABLE-US-00002 TABLE 2 Accelerator Accelerator Accelerator
Accelerator Formulation (in phr) (2.0 phr) (2.5 phr) (3.0 phr) (4.0
phr) Latex SIS 100 100 100 100 Surfactant Manawet .TM. 172 0.5 0.5
0.5 0.5 Cure Agent Sulfur 0 0 0 0 Cure Activator Zinc Oxide 0 0 0 0
Cure ZDEC (Bostex 561) 0.8 1.0 1.2 1.5 Accelerator DPTTH (Bostex
224) 1.2 1.5 1.8 2.5 Antioxidant Wingstay .RTM. L 0.5 0.5 0.5 0.5
Tensile Tensile (MPa) 28.2 26 29.8 21.95 Properties Modulus@500%
(MPa) 1.93 2.3 2.7 3.27 Elongation (%) 1300 1233 1181 1079
TABLE-US-00003 TABLE 3 Bostex Bostex Formulation (in phr) Control
561/224 909 Latex SIS 100 100 100 Surfactant Manawet .TM. 172 0.5
0.5 0.5 Cure Agent Sulfur 0 0 0 Cure Activator Zinc Oxide 0 0 0
Cure ZDEC (Bostex 561) 0 0.6 0 Accelerator DPTTH (Bostex 224) 0 0.9
0 ZDEC + DPTT (Bostex 909) 0 0 1.5 Antioxidant Wingstay .RTM. L 0.5
0.5 0.5 Tensile Tensile (MPa) 19.42 28 26.4 Properties Modulus@500%
(MPa) 1.04 1.59 1.7 Elongation (%) 1419 1358 1273
Example 4--Effect of Cure Agent and Cure Activator on Physical
Properties of Elastomeric Latex Articles
[0082] Synthetic SIS latex compositions and elastomeric latex
articles were prepared according to the methods of Example 1 and
Example 2 with and without the use of sulfur cure agent and zinc
oxide cure activator to evaluate the effect on tensile properties.
The formulations and testing results are shown in Table 4 below. As
seen therein, the presence of sulfur and zinc oxide tended to
increase the tensile modulus while also decreasing the tensile
strength. This result therefore is surprising in that, in
conventional latex compositions (e.g., natural rubber and/or
synthetic polyisoprene), sulfur and zinc oxide are used to increase
crosslinking in order to improve tensile strength. The present
testing, however, showed that it is possible to achieve suitable
tensile properties while excluding sulfur and zinc oxide and thus
being substantially free or completely free of Type I and Type IV
allergens.
TABLE-US-00004 TABLE 4 Without With With Sulfur/ Sulfur/ Sulfur/
Formulation (in phr) Control ZnO ZnO ZnO Latex SIS 100 100 100 100
Surfactant Manawet .TM. 172 0.5 0.5 0.5 0.5 Cure Agent Sulfur 0 0
0.5 0.5 Cure Activator Zinc Oxide 0 0 0.5 0.5 Cure ZDEC (Bostex
561) 0 0.6 0.6 1.2 Accelerator DPTTH (Bostex 224) 0 0.9 0.9 1.8
Antioxidant Wingstay .RTM. L 0.5 0.5 0.5 0.5 Tensile Tensile (MPa)
19.42 28 25.63 29.8 Properties Modulus@500% 1.04 1.59 2.33 2.7
(MPa) Elongation (%) 1419 1358 1267 1181
Example 5--Effect of Viscosity Modifier on Physical Properties of
Elastomeric Latex Articles
[0083] Synthetic SIS latex compositions and elastomeric latex
articles were prepared according to the methods of Example 1 and
Example 2 with and without the use of a viscosity modifier to
evaluate the effect on tensile properties. The formulations and
testing results are shown in Table 5 below. The addition of the
rheological stabilizer is thus effective to improve dipping profile
without adversely affecting the desired properties of the finished
product.
TABLE-US-00005 TABLE 5 Without With Novethix- Novethix- Formulation
(in phr) Control L10 L10 Latex SIS 100 100 100 Surfactant Manawet
.TM. 172 0.5 0.5 0.5 Cure Agent Sulfur 0 0 0 Cure Activator Zinc
Oxide 0 0 0 Cure ZDEC (Bostex 561) 0 0.6 0.6 Accelerator DPTTH
(Bostex 224) 0 0.9 0.9 Antioxidant Wingstay .RTM. L 0.5 0.5 0.5
Viscosity Novethix .TM. L10 0 0 0.05 Modifier Tensile Tensile (MPa)
19.42 28 26.3 Properties Modulus@500% 1.04 1.59 1.9 (MPa)
Elongation (%) 1419 1358 1294
Example 6--Binary Process for Preparation of Synthetic SIS Latex
Articles, and Evaluation of Tensile Properties
[0084] Elastomeric articles can be prepared using a single dip
formulation (as discussed above in Example 2); however, elastomeric
articles with desirable properties likewise can be prepared using a
binary dipping process that utilizes two different polymer
formulations. In the present example embodiment, Formulation A
(including aqueous SIS latex, surfactant, cure accelerators, and
antioxidant) was prepared according to the process of Example 1.
Formulation B was prepared by the same process but only included
aqueous SIS latex, surfactant, and antioxidant. Formulation A was
added to dip tank 1, and Formulation B was added to dip tank 2. As
a comparative, Formulation C was prepared according to the process
of Example 1 using aqueous SIS latex, surfactant, sulfur cure
agent, zinc oxide cure activator, cure accelerators, and
antioxidant. Formulation C was added to dip tank 3. The exact
formulations used in dip tank 1, dip tank 2, and dip tank 3 are
shown in Table 6.
[0085] The binary dipping process using Formulation A and
Formulation B in dip tank 1 and dip tank 2 was carried out as
follows. A former was first dipped into Formulation A in dip tank 1
at a withdrawal speed of about 0.2 to 0.4 inches per second to
obtain the desired film thickness and oven dried at about
90.degree. C. for about 5 minutes. The former with the dried film
was then dipped into Formulation B in dip tank 2 at a withdrawal
speed of about 0.2 to 0.4 inches per second to obtain the desired
film thickness and oven dried at about 90.degree. C. for about 5
minutes. The final film was oven cured at about 120.degree. C. for
about 15 minutes. The formed elastomeric latex article was removed
from the former using a corn starch slurry and air dried. A further
former was used to prepare the control article according to the
process of Example 2 using Formulation C and dip tank 3. The test
results are shown in Table 6.
TABLE-US-00006 TABLE 6 Dip Tank 3 with all Binary Process
components Dip Tank 1 Dip Tank 2 in single tank (Formula- (Formula-
Formulation (in phr) (Control) tion A) tion B) Latex SIS 100 100
100 Surfactant Manawet .TM. 172 0.5 0.5 0.5 Cure Agent Sulfur 0.5 0
0 Cure Zinc Oxide 0.27 0 0 Activator Cure ZDEC (Bostex 0.6 0.6 0
Accelerator 561) DPTTH (Bostex 0.9 0.9 0 224) Antioxidant Wingstay
.RTM. L 0.5 0.5 0 Tensile Tensile (MPa) 25.63 26.34 Properties
Modulus@500% 2.33 1.53 (MPa) Elongation (%) 1267 1367
Example 7--Preparation of Synthetic SIS Latex Articles with Single
Dip Tank
[0086] Condoms were prepared from compounded SIS latex compositions
using varying prevulcanization and drying conditions. The formed
condoms were then subjected to tensile strength testing and tensile
modulus testing. The compounded SIS latex composition is shown in
Table 7. The condom forming parameters and the measured properties
of the formed condoms are provided in Table 8.
TABLE-US-00007 TABLE 7 Component Concentration (phr) SIS polymer
latex dispersion 100 Amphoteric surfactant 0.5 Sulfur donor 0.9
Accelerator 0.6 Antioxidant 0.5
TABLE-US-00008 TABLE 8 Run 1 Run 2 Run 3 Run 4 Run 5 Pre-Vulc.
35.degree. C. for 3 35.degree. C. for 6 hrs/ 29.degree. C. for 23
35.degree. C. for 17 35.degree. C. for 3 hrs/ Conditions
hrs/29.degree. C. for 29.degree. C. for 18 hrs hrs/29.degree. C.
for 29.degree. C. for 18 18 hrs hrs 23 hrs hrs Dry 1/Dry 2
90.degree. C. for 5 90.degree. C. for 5 90.degree. C. for 5
90.degree. C. for 5 90.degree. C. for 5 Conditions min/100.degree.
C. min/100.degree. C. min/110.degree. C. min/100.degree. C. for
min/110.degree. C. for 5 min for 5 min for 5 min 5 min for 5 min
Tensile 15.9 17.04 20.4 20.4 24.5 Strength (MPa) Modulus at 1.31
1.24 1.28 1.13 1.22 500% (MPa) Load at 500% 4.3 4 4.5 3.9 3.9 (N)
Elongation (%) 1260 1270 1290 1290 1310 Relaxed 0.56 0.68 0.70 0.65
0.56 Modulus
[0087] Test sample 5 was also evaluated for tear strength using
ASTM D624-000. Testing indicated that the sample exhibited a tear
strength of 2.23 N/mm.
Example 8--Preparation of Synthetic SIS Latex Articles with Varying
Styrene Content
[0088] Condoms were prepared from compounded SIS latex compositions
using SIS polymer with differing styrene percentages (i.e., 8%,
10%, 11%, 12.6, and 15% wt/wt styrene, based on the total weight of
the SIS polymer). The remaining components of the test compositions
were identical for each sample, and all samples were prepared under
identical pre-vulcanization and drying conditions.
Pre-vulcanization was carried out at 35.degree. C. for 3 hours then
29.degree. C. for 18 hours. The condoms were formed by dipping a
former twice in the composition, drying the first coating
90.degree. C. for 5 minutes, and drying the second coating at
100.degree. C. for 5 minutes. Results of testing for tensile
strength testing and tensile modulus are shown below in Table
9.
TABLE-US-00009 TABLE 9 Sample 1 Sample 2 Sample 3 Sample 4 Sample 5
Styrene content in SIS polymer 8% 10% 11% 12.6% 15% Tensile
Strength (MPa) 4.66 11.1 10.9 11.5 24.5 Modulus at 500% (MPa) 0.98
1.08 1.13 1.17 1.22 Relaxed Modulus 0.28 0.36 0.42 0.49 0.56
Example 9--Dynamic Mechanical Analysis
[0089] Test samples were prepared using the composition provided in
Table 7 above. Prevulcanization was carried out at 35.degree. C.
for a time of 3 hours or 6 hours. Articles were prepared by dipping
the former into the SIS polymer formulation for two iterations.
Drying after the first dipping was carried out for 5 minutes at
90.degree. C., and drying after the second dipping was carried out
for 5 minutes at 110.degree. C. Dynamic mechanical analysis (DMA)
was carried out on the formed articles to measure the properties of
the solid articles in a manner analogous to rheology testing for
liquid compositions. Young's modulus (E) was measured as an
indication of the stiffness of the material as the material was
stretched. Young's modulus (E) is defined as the ratio of the
stress .sigma. (force/area) to the strain .epsilon. (degree of
deformation), wherein E=.sigma./.epsilon.. The modulus (E) can be
defined by a complex expression involving storage modulus (E') and
a loss modulus (E'') as seen below, wherein i=(-1).sup.1/2 (i.e.,
negative to the 1/2 power), and E* is a representation of a vector
quantity in the complex space, and derives from the oscillatory
nature of the stress and strain.
E*=E'+iE''
E=|E*|
[0090] In DMA studies, samples were cut from the above-noted
articles perpendicular to the long axis. The resulting ring was
then folded to produce a sample 8 layers thick, and the sample was
mounted in the DMA using the tensile apparatus. Dimensions were
typically on the order of 9.5 cm long, 7.5 mm long, and 0.55 mm
thick. All studies were run on a Triton Tritec 2000 DMA. Frequency
dependent studies were performed in the frequency range of 0.1 to
75 Hz, using a displacement of 0.1 mm. Run temperatures at
25.degree. C. and 37.degree. C. were regulated by an electric
furnace enclosing the sample holder. Runs at 25.degree. C. were
essentially at the ambient temperature of the laboratory.
Temperature scans were performed by first cooling the sample with
liquid nitrogen to a temperature of approximately -80.degree. C.
The furnace was then used to increase the temperature at a rate of
5.degree. C./minute, up to a maximum temperature of 40.degree. C.
As in the frequency scans, a displacement of 0.1 mm was used, and
the frequency was held constant at 1.0 Hz. In addition to the
above, comparative samples were tested and were taken from
commercial products sold under the tradenames Skyn.RTM. (formed of
polyisoprene) and Trojan.RTM. Enz (formed of natural rubber). Plots
of moduli E' versus frequency indicated that all tested samples
prepared according to the present disclosure exhibited moduli that
were greater than moduli of the comparative samples. The test
results are illustrated in FIG. 1, and the DMA E' data are
particularly useful for illustrating improved film properties when
the film is at a relatively low degree of extension.
[0091] Use of the words "about" and "substantially" herein are
understood to mean that values that are listed as "about" a certain
value or "substantially" a certain value may vary by an industry
recognized tolerance level for the specified value. When an
industry recognized tolerance is unavailable, it is understood that
such terminology may indicate that an acceptable value may be vary
.+-.3%, .+-.2%, or .+-.1% from the specifically listed value. More
particularly, where a temperature is disclosed, "about" or
"substantially" may indicate the specifically listed temperature
.+-.2.degree. C., .+-.1.degree. C., or .+-.0.5.degree. C. Likewise,
in some embodiments, the listed value may be exact, if desired, and
variations above or below the listed value may be expressly
excluded.
[0092] Many modifications and other embodiments of the inventions
set forth herein will come to mind to one skilled in the art to
which these inventions pertain having the benefit of the teachings
presented in the foregoing descriptions. Therefore, it is to be
understood that the inventions are not to be limited to the
specific embodiments disclosed and that modifications and other
embodiments are intended to be included within the scope of the
appended claims. Although specific terms are employed herein, they
are used in a generic and descriptive sense only and not for
purposes of limitation.
* * * * *