U.S. patent application number 16/848181 was filed with the patent office on 2020-07-30 for ziegler-natta catalyzed polyisoprene articles.
The applicant listed for this patent is LifeStyles Healthcare Pte. Ltd.. Invention is credited to Catherine Tang Kum Choo, Chayapon Ngowprasert, KC Nguyen.
Application Number | 20200239607 16/848181 |
Document ID | 20200239607 / US20200239607 |
Family ID | 1000004780962 |
Filed Date | 2020-07-30 |
Patent Application | download [pdf] |
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United States Patent
Application |
20200239607 |
Kind Code |
A1 |
Nguyen; KC ; et al. |
July 30, 2020 |
Ziegler-Natta Catalyzed Polyisoprene Articles
Abstract
A polymeric article comprises an elastomeric layer comprising
cured synthetic polyisoprene particles that comprise a
Ziegler-Natta catalyzed polyisoprene.
Inventors: |
Nguyen; KC; (Dothan, AL)
; Ngowprasert; Chayapon; (A. Phunphin Suratthani, TH)
; Choo; Catherine Tang Kum; (Melaka, MY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LifeStyles Healthcare Pte. Ltd. |
Singapore |
|
SG |
|
|
Family ID: |
1000004780962 |
Appl. No.: |
16/848181 |
Filed: |
April 14, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16115750 |
Aug 29, 2018 |
10662269 |
|
|
16848181 |
|
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62552859 |
Aug 31, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 6/04 20130101; C08F
36/08 20130101 |
International
Class: |
C08F 36/08 20060101
C08F036/08 |
Claims
1. A polymeric article comprising: an elastomeric layer comprising
cured synthetic polyisoprene particles that comprise a
Ziegler-Natta catalyzed polyisoprene material comprising: a cis-1,4
isomer content of greater than or equal to 95% by weight to less
than or equal to 97% by weight; a trans-1,4 isomer content of 1% by
weight or less; and a 3,4 isomer content of 5% by weight or
less.
2. The polymeric article of claim 1, wherein the synthetic
polyisoprene particles are pre-vulcanized.
3. The polymeric article of claim 1, wherein the Ziegler-Natta
catalyzed polyisoprene material comprises a cis-1,4 isomer content
of about 96% to 97% by weight.
4. The polymeric article of claim 1, wherein the article has a
thickness in the range of from 0.030 to 0.065 mm.
5. The polymeric article of claim 1, wherein the elastomeric layer
comprises a post-vulcanized structure having a molecular weight
between crosslinks (M.sub.c) of less than 11,000 g/mol.
6. The polymeric article of claim 1, wherein the synthetic
polyisoprene particles have a median particle diameter in the range
of approximately from 0.2 to 2 micrometers.
7. The polymeric article of claim 1, wherein the synthetic
polyisoprene particles are bonded to each other through
intra-polyisoprene particle crosslinks and inter-polyisoprene
particle crosslinks.
8. The polymeric article of claim 7, wherein the intra-polyisoprene
particle crosslinks and inter-polyisoprene particle crosslinks
comprise sulfur-crosslinks.
9. The polymeric article of claim 1 in the form of a condom, a
finger cot, or a glove.
10. A prophylactic device comprising: an elastomeric layer
comprising cured synthetic polyisoprene particles that are
pre-vulcanized, wherein the synthetic polyisoprene particles
comprise a Ziegler-Natta catalyzed polyisoprene material that
comprises: a cis-1,4 isomer content of greater than or equal to 95%
by weight to less than or equal to 97% by weight; a trans-1,4
isomer content of 1% by weight or less; and a 3,4 isomer content of
5% by weight or less.
11. The prophylactic device of claim 10 in the form of a condom,
wherein the elastomeric layer forms an open end, a closed end, and
a tubular sheath extending from the closed end to the open end.
12. The prophylactic device of claim 10, wherein the elastomeric
layer comprises a post-vulcanized structure having a molecular
weight between crosslinks (M.sub.c) of less than 11,000 g/mol.
13. The prophylactic device of claim 10, wherein the synthetic
polyisoprene particles have a median particle diameter in the range
of approximately from 0.2 to 1.5 micrometers.
14. The prophylactic device of claim 10, wherein the elastomeric
layer further comprises intra-polyisoprene particle
sulfur-crosslinks, and inter-polyisoprene particle
sulfur-crosslinks.
15. A method for producing a polymeric article, comprising:
disposing an elastomeric coating of a Ziegler-Natta catalyzed
polyisoprene material comprising: a cis-1,4 isomer content of
greater than or equal to 95% by weight to less than or equal to 97%
by weight; a trans-1,4 isomer content of 1% by weight or less; and
a 3,4 isomer content of 5% by weight or less on a former; and
curing the elastomeric coating to form an elastomeric layer of the
polymeric article.
16. The method of claim 15, wherein the disposing of the
elastomeric coating on the former comprises dipping the former into
an emulsion of the Ziegler-Natta catalyzed polyisoprene
material.
17. The method of claim 15, wherein the Ziegler-Natta catalyzed
polyisoprene material is pre-vulcanized in the presence of a
pre-vulcanization composition before dipping the former, wherein
the pre-vulcanization composition comprises: soluble sulfur, a
dithiocarbamate accelerator, and a surfactant.
18. The method of claim 15, wherein the polymeric article comprises
a prophylactic device.
19. The method of claim 15, wherein the elastomeric layer comprises
a post-vulcanized structure having a molecular weight between
crosslinks (M.sub.c) of less than 11,000 g/mol.
20. The method of claim 17, further comprising adding a
post-vulcanization composition to the emulsion after the
Ziegler-Natta catalyzed polyisoprene material is pre-vulcanized,
wherein the post-vulcanization composition comprises amorphous
sulfur or polysulfur and an accelerator.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of and claims the benefit
of priority of pending U.S. application Ser. No. 16/115,750, filed
on Aug. 29, 2018, which claims priority under 35 U.S.C. .sctn.
119(e) to U.S. Provisional Application No. 62/552,859, filed Aug.
31, 2017, the disclosures of which are incorporated herein by
reference in their entireties.
FIELD
[0002] The present disclosure is directed to personal protective
articles and, more specifically, to condoms comprising polyisoprene
catalyzed by Ziegler-Natta catalysts.
BACKGROUND
[0003] Prophylactic devices, such as condoms, finger cots, and
gloves, such as examination and surgical gloves, are typically made
of polymeric materials to provide protection against chemicals,
abrasions, germs, viruses, and microbes among many uses. Polymeric
materials include natural rubber latex (natural polyisoprene),
synthetic polyisoprene, or various polyurethanes. Prophylactic
devices made of natural rubber are strong. Natural rubber, sourced
from Hevea Brasiliensis and/or guayule, has a high level of
stereo-regularity, meaning that the polymer molecules of which it
is comprised consist almost exclusively of cis-1,4 isoprene units.
Natural rubber latex is also a highly branched polymer with a high
molecular weight and a wide molecular weight distribution. These
characteristics of the natural rubber result in vulcanized rubber
products having a unique combination of strength and elasticity.
However, natural rubber also contains proteins that produce dermal
allergic reactions in some susceptible individuals.
[0004] Synthetic polyisoprene resins have been developed to provide
the benefits of natural rubber and to eliminate the potential for
protein allergy. However, some synthetic polyisoprenes, such as
that produced by Kraton Inc., by anionic addition polymerization,
typically consist of lower levels of stereo-regularity (i.e., less
than 90% cis 1,4 isoprene) and reduced molecular weight.
Consequently, articles produced from such synthetic polyisoprenes
have inferior properties compared with natural rubber articles. In
addition, synthetic polyisoprene latex with lower levels of
stereo-regularity unfavorably flocks and agglomerates in
suspension, which results in defects in dipped articles, A latex
dip tank of such a synthetic polyisoprene correspondingly has a
limited available processing window for dipping articles.
Furthermore, addition of anti-flocculants interferes with
cross-linking, resulting in anisotropic cure properties, e.g., poor
strength and elongation properties, such as voids and cracks due to
the formation of fractures in inter-particle and intra-particle
regions.
[0005] There is an ongoing need to produce prophylactic devices,
such as condoms, finger cots, and polymeric gloves that are thin,
strong and non-allergenic.
SUMMARY
[0006] Embodiments according to the present disclosure include
polymeric articles, and methods for manufacturing polymeric
articles, that comprise synthetic polyisoprene materials catalyzed
using Ziegler-Natta catalysts, substantially as shown in and/or
described in connection with at least one of the figures, as set
forth more completely in the claims, are disclosed. Various
advantages, aspects, and novel features of the present disclosure
will be more fully understood from the following description and
drawings.
[0007] The foregoing summary is not intended, and should not be
contemplated, to describe each embodiment or every implementation
of the present disclosure. Other and further embodiments are
described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] So that the manner in which the above recited features of
the present disclosure can be understood in detail, a more
particular description of the disclosure, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this disclosure and are therefore not to be considered limiting of
its scope, for the disclosure may admit to other equally effective
embodiments. It is to be understood that elements and features of
one embodiment may be in other embodiments without further
recitation. It is further understood that, where possible,
identical reference numerals have been used to indicate comparable
elements that are common to the figures.
[0009] FIG. 1 depicts a first transmission electron microscopy
(TEM) image, according to embodiments of the disclosure;
[0010] FIG. 2 depicts a second TEM image, according to embodiments
of the disclosure;
[0011] FIG. 3 depicts a third TEM image, according to embodiments
of the disclosure;
[0012] FIG. 4 depicts a fourth TEM image, according to embodiments
of the disclosure; and
[0013] FIG. 5 is a perspective schematic view of a condom according
to an embodiment.
DETAILED DESCRIPTION
[0014] Embodiments described in this disclosure, briefly summarized
above and discussed in greater detail below, comprise polymeric
articles, such as condoms, including thin-walled condoms and
gloves. Embodiments may comprise condoms or gloves that are formed
using coagulants. Embodiments may comprise condoms and gloves that
are formed using Ziegler-Natta catalyzed synthetic polyisoprene
materials. Embodiments may comprise condoms and gloves that are
made using Ziegler-Natta catalyzed synthetic polyisoprene materials
and coagulants.
[0015] The inventors have unexpectedly observed that condoms made
from the Ziegler-Natta catalyzed polyisoprene resins described
herein have enhanced tensile strength, allowing thinner condoms to
be manufactured. Thinner condoms allow greater sensitivity to
wearers. Thinner gloves are more flexible yet unexpectedly retain
puncture resistance and abrasion resistance. Any, all or some of
the embodiments according to the disclosure comprise condoms and/or
polymeric gloves having a thickness of, for example, 0.030-0.065 mm
in cross-sectional thickness. Exemplary embodiments according to
the disclosure comprise condoms or polymeric gloves that are
0.040-0.055 mm in cross-sectional thickness.
[0016] Embodiments of the disclosure further comprise gloves, such
as examination gloves, surgical gloves, and gloves for household
use, and finger cots. Embodiments further comprise gloves that are
formed using coagulants. Embodiments comprise a polymeric glove
that includes a thumb having a front surface and a back surface; a
plurality of fingers, a palm region; and a backhand region.
[0017] Embodiments of the disclosure further comprise condoms.
Embodiments further comprise condoms that are formed using
coagulants. Embodiments comprise a condom that includes an open
end, a closed end, and a tubular sheath extending from the closed
end to the open end. FIG. 5 is a perspective schematic view of a
condom according to an embodiment. The ZN catalyzed PI condom 100
disclosed herein comprises a closed end 104 and an open end 108. A
tubular shaft 106 extends from the closed end 104 to the open end
108, which has an opening 110 opposite a teat end 102 of the closed
end 104. Optionally, the condom further comprises a bead 114. The
tubular shaft of the condom comprises the ZN catalyzed PI
particles, which may be provided by an aqueous ZN catalyzed PI
latex composition. The aqueous latex compositions may have a solids
content in the range of 60% to 65% by weight. The compositions may
further comprise additional water, preferably deionized water, to
result in a composition solids content in the range of 55% to 60%
by weight. Optionally, the aqueous latex compositions may further
comprise one or more thickeners and/or stablizers/surfactants.
Colorants and/or pigments may optionally be added to the aqueous
latex compositions.
[0018] Before describing embodiments of the present disclosure in
detail, the terminology used herein is for the purpose of
describing particular embodiments only, and is not intended to be
limiting. The embodiments described herein should not necessarily
be limited to specific compositions, materials, designs or
equipment, as such may vary. All technical and scientific terms
used herein have the usual meaning conventionally understood by
persons skilled in the art to which this disclosure pertains,
unless context defines otherwise. Also, as used in this
specification and the appended claims, the singular forms "a,"
"an," and "the" include plural referents unless the context clearly
dictates otherwise.
[0019] The term "flexing" or "flex" refers to finger movements,
such as bending fingers, making a fist, gripping, grasping,
clenching or otherwise folding the fingers.
[0020] The terms "emulsion," "dispersion," "latex" and "suspension"
are generally analogous and indicate a system in which small
particles of a substance, such as rubber particles, are mixed with
a fluid solvent (such as water and/or alcohols and/or other organic
fluids) but are at least partially undissolved and kept dispersed
by agitation (mechanical suspension) and/or by the molecular forces
in a surrounding medium (colloidal suspension). Emulsions
contemplated herein may further comprise typical and suitable
components for rubber or elastomeric formulations and compounds,
such as accelerators, such as guanidines, thiazoles, thiurams,
sulfenamides, thioureas, dithiocarbamates, and xanthanates.
Emulsions contemplated herein may further comprise activators, such
as zinc oxides, cross-linking agents and curatives, such as
elemental sulfur, mono-sulphidic donors, di-sulphidic donors, such
as tetramethyl thiuram disulphide and tetraethyl thiuram
disulphide; and/or polysulphidic donors, such as xanthogen
polysulphide and dipentamethylene thiuramtetrasulfide. Emulsions
contemplated herein may further comprise anti-oxidants and/or
anti-ozonants. At least one suitable anti-oxidant is Wingstay L.
Emulsions contemplated herein may further comprise, surfactants,
such as sodium dodecyl sulfates and polyvinyl alcohols. Emulsions
contemplated herein may further comprise rheology-modifiers, such
as various clays and aluminosilicates, pH adjusters, such as
hydroxides, such as potassium hydroxide, pigments, processing
agents, and/or fillers as are known to those in the art.
[0021] The term "polymer" generally includes, but is not limited
to, homopolymers, copolymers, such as for example, block, graft,
random and alternating copolymers, terpolymers, etc. Furthermore,
unless otherwise specifically limited, the term "polymer" includes
all possible geometrical configurations of the molecule. These
configurations include, but are not limited to isotactic,
syndiotactic and random symmetries.
[0022] The term "thermoplastic" generally includes polymer
materials that become reversibly pliable, moldable, and heatable
above a specific temperature and solidify upon cooling. The term
"thermoset" generally includes polymer materials that strengthen
following heating and solidification, and cannot be reheated and
re-formed after an initial forming. The term "thermoplastic
elastomer" (TPE) denotes a class of copolymers comprising both
thermoplastic and thermoset moieties, producing materials having
properties of both moieties. The term "rubber" generally indicates
elastomers produced from natural rubber latexes or synthetic
elastomers.
[0023] A method for producing synthetic polyisoprene articles
comprises using emulsions of synthetic polyisoprene resins
catalyzed using Ziegler-Natta catalysts. Generally, synthetic
polyisoprene particles of Ziegler-Natta catalyzed polyisoprene
material comprise 96% cis-1,4-polyisoprene or more. The synthetic
polyisoprene particles may comprise a median particle diameter in
the range of approximately from 0.2 to 2 micrometers. Preferably
from 0.2 to 1.5 micrometers. Exemplary synthetic polyisoprene
materials are supplied by BST Elastomer Co., Ltd, located in
Thailand. The method may further comprise a pre-vulcanization
composition and post-vulcanization composition along with
conventional emulsion additives, such as stabilizers, pH control
agents, antioxidants, and preservatives, etc. A typical synthetic
polyisoprene latex composition is provided in terms of 100 parts by
weight of dry rubber (PHR). During compounding, the components of
the latex composition may be suspended in aqueous and/or organic
solvents.
[0024] In general, a pre-vulcanizing composition includes sulfur in
the range of 0.6 to 1.8 PHR. An accelerator package includes zinc
diethyldithiocarbamate (ZDEC) and/or zinc dibutyldithiocarbamate
(ZDBC) accelerator, and/or sodium dibutyldithiocarbamate (SDBC)
accelerator, a diisopropyl xanthogen polysulphide (DIXP)
accelerator and/or a dipentamethylene thiuramtetrasulfide (DPTT)
accelerator. The pre-vulcanizing composition may comprise a total
accelerator content is in the range of 0.6 to 2.5 PHR. The
pre-vulcanizing composition may comprise a zinc oxide activator.
The pre-vulcanization composition may comprise a surfactant, i.e.,
a wetting agent. The surfactant may be a salt of a fatty acid, such
as sodium stearate, sodium oleate, or potassium caprylate. Some
embodiments comprise more than one surfactant, e.g., potassium
caprylate, also known as potassium salt of octanic acid and sodium
dodecyl benzene sulphonate (SDBS). Exemplary embodiments comprise a
surfactant package having potassium caprylate, sodium dodecyl
benzene sulphonate (SDBS) and polyoxyethylene cetyl/stearyl ether
in the range of 0.3 to approximately 1.5 PHR. An anti-oxidant and
preservative package includes a butylated reaction product of
p-cresol and, optionally, dicyclopentadiene in the range of 0.3 to
approximately 1.0 PHR.
[0025] The sulfur in the pre-vulcanizing package is, for example,
elemental sulfur having a high soluble sulfur content, typically of
the S.sub.8 ring structure. The pre-vulcanization composition
further comprises an accelerator. For example, an accelerator that
can break or disrupt the S.sub.8 sulfur ring structure is zinc
dithiocarbamate. Reference to "high soluble sulfur content" means
having enough soluble sulfur present to form sufficient to permeate
into latex particles in the aqueous latex emulsion and crosslink
during curing to achieve commercially acceptable articles, such as
condoms and/or gloves. The pre-vulcanization of the synthetic latex
particles in the latex occurs over a period of time, e.g., 9 hours
to 2 days depending on the temperature of the latex, which is
generally in the range of 20.degree. C. to 30.degree. C. The degree
of pre-vulcanization at different points after initial compounding
of the synthetic latex particles may be monitored by at least one
of four tests. An equilibrium-swelling test, which uses any
suitable solvent, measures the equilibrium swelling of films dried
down from the synthetic latex. A relaxed modulus test gauges the
vulcanization of the relaxed modulus at 100% extension (MR100) of
films dried down from the dissolved latex. Similarly, a
pre-vulcanized relaxed modulus test (PRM) measures the relaxed
modulus at 100% extension of the pre-vulcanized films.
[0026] A Toluene Swell Index (TSI) test may be used to measure the
level of crosslinking by immersing the dried casted film sample in
the toluene and calculate the swollen rate. TSI may be substituted
with an isopropanol index test. Cast film of the compounded latex
to produce film thickness of 0.10-0.15 mm and dry the film at
50+/-3 degree Celsius for 10 minutes and/or leave the film at
ambient temperature until it is fully dried. Peel off the film with
the powder such as corn starch or CaCO.sub.3 to prevent the film
surface being stick to itself. Cut a disc sample with a die cutter.
Submerge the disc film into the toluene for 60 minutes. Measure the
diameter of the swollen film. Calculate the % swollen by subtract
the original disc diameter from the swollen film diameter and
divided by the original film diameter. The latex particles progress
from a non-crosslink stage (index >220%), to a partial crosslink
stage (index <220%), then to a semi-crosslink stage (index
<180%) and finally to a fully crosslink stage (index <100%)
as pre-vulcanizing sulfur is incorporated within the particle.
[0027] Compounding methods according to embodiments of the
disclosure include dissolving a latex composition in an aqueous
solvent and stirring periodically and examining for permeation of
pre-vulcanization agents into the synthetic polyisoprene particles
for example, by using an isopropanol index test. Polyisoprene latex
has an inherent tendency to flock and `case harden` due to a
peripheral reaction with sulfur catalyzed by ZDBC or ZDEC, i.e., an
outside surface hardens, preventing crosslinking of internal
molecules. The presence of surfactants and creation of opened out
S.sub.8 chains of sulfur enables the diffusion of sulfur into the
particles. In other words, the diffusion of sulfur into the
particles, i.e., `through-hardening` can occur, allowing the
crosslinking of internal molecules. A latex article or product
comprising a through-hardened structure is stronger than an
otherwise similar latex article or product having a case-hardened
structure.
[0028] The pre-vulcanization composition provides sulfur to
synthetic polyisoprene latex particles in the aqueous synthetic
polyisoprene emulsion for pre-vulcanizing the intra-particle
regions. During pre-vulcanization, the ring structure of the sulfur
is broken by the catalytic action of the accelerator, e.g., zinc
dithiocarbamate, which penetrates the polyisoprene particles and
initially interacts with the isoprene double bonds therein.
[0029] Without intending to be bound by theory, it is believed that
the penetration of the components of the pre-vulcanizing
composition into the polyisoprene particles is a function of the
diffusion process, which may be a linear function of time. The
penetration of the components comprises an exponential function of
temperature, reflecting a thermally activated process. Therefore,
increasing the temperature by a few degrees during the
pre-vulcanization step increases the pre-vulcanization rate. For
example, pre-vulcanization at room temperature may be about 3-5
days or as much as about 9 days, while pre-vulcanization at, for
e.g., about 50-70.degree. C., may take about 3-7 hours. In the
absence of pre-vulcanization of the synthetic polyisoprene
particles, crosslinking predominantly occurs in the periphery
(i.e., case-hardening) of the synthetic polyisoprene particles,
resulting in weak particles. Attempts to crosslink the
inter-particle region within the particles only during
post-vulcanization, discussed below, results in over crosslinking
of the intra-particle regions, which, in turn, results in a latex
product with poor stretch properties.
[0030] The post-vulcanization composition includes amorphous or
polysulfur, which is insoluble at latex emulsion temperature, e.g.
20-40.degree. C., but is soluble at a vulcanization or cure
temperature, e.g., 110-150.degree. C. Generally, the
post-vulcanization composition comprises accelerators such as, but
not limited to, zinc diethyldithiocarbamate (ZDEC), zinc
dibutyldithiocarbamate (ZDBC), sodium diethyldithiocarbamate
(SDEC), sodium dibutyldithiocarbamate (SDBC), a thiuram compound
and a xanthogen. Examples of suitable xanthogens include, but are
not limited to, diisopropyl xanthogen polysulphide (DIXP),
diisopropyl xanthogen, tetraethylthiuram disulfide, and xanthogen
sulfide. DIXP is a suitable xanthogen owing to its polysulphidic
donor properties. The post-vulcanization composition may further
comprise a thiuram accelerator. An example of a polysulphidic
thiuram accelerator is dipentamethylene thiuramtetrasulfide (DPTT).
Another example of a thiuram compound is tetrabenzyl thiuram
disulfide. Zinc oxide may also be added as an activator.
[0031] The post-vulcanization composition provides the ability to
crosslink regions between the particles of synthetic polyisoprene
or inter-particle regions thereby assuring a high quality
substantially uniformly cured synthetic polyisoprene product.
[0032] The post-vulcanization composition activates inter-particle
cross-linking at a temperature of, e.g., 100-150.degree. C. In
addition, post-vulcanization processes also crosslink the synthetic
polyisoprene particles with sulfur. Such post-vulcanization results
in a more homogeneous latex coating having greater strength and
elongation properties. The composition produced is stable for up to
approximately 5 days at 20.degree. C. to 25.degree. C. and is
useful for a production line.
[0033] Table 1 shows at least one exemplary embodiment of a
Ziegler-Natta (ZN) catalyzed synthetic polyisoprene resin latex
composition for producing a polymeric article. The latex
composition is preferably aqueous.
TABLE-US-00001 TABLE 1 Formulation - ZN Catalyzed Quantity per
hundred dry rubber Component (PHR) Synthetic Polyisoprene Resin ZN
(e.g., see Table 2) 100 Alkyl Aryl Sulphonate 0.1-0.3 Potassium
Caprylate/Potassium Oleate 0.1-0.46 Polyoxyethylene cetyl/Stearyl
Ether 0.1-0.5 Sulfur 0.8-1.8 Reactive Zinc Oxide 0.05-0.5 ZDEC/ZDBC
0.4-1.0 SDBC/SDEC 0.05-0.5 DIXP/Diisopropyl Xanthogen/Xanthogen
Sulfide 0.2-0.6 Anti-oxidant 0.5-1.0
[0034] Table 2 below shows a comparison of pre-vulcanization
behavior of an exemplary anionic polyisoprene and an exemplary
Ziegler-Natta catalyzed synthetic polyisoprene resin.
TABLE-US-00002 TABLE 2 PI Resins Ziegler-Natta Anionic IR (ZN)
Microstructure Median particle size (.mu.m) Max 1.8 Max 1.5 Cis-1,4
(% wt) 92 96-97 Trans-1,4 (% wt) 1.50 0.50 3,4-isomers (% wt) 6.50
2.5-3.5 Macrostructure Linear Branched Molecular weight
distribution Narrow Narrow Avg molecular weight (*10.sup.6 g/mol)
2-3 1 Gel (% wt) Intrinsically nil 10.0-20.0 Ash (% wt) 0.05-0.1
0.15-3.0 Trace metal content (ppm) 70 400-3000 Stabiliser content
(% wt) 0.05-0.3 1 TSC (%) 63 60-64 Viscosity (cps) 150 50-150 pH
9.5-12.0 10.0-12.0 Specific gravity 0.91 0.91 Color Amber Light
yellow Residual solvent (ppm) 1500 (0.15%) 1000 (0.10%)
[0035] The present disclosure further provides a method of forming
a synthetic polyisoprene polymeric article. The method comprises
disposing an elastomeric coating of a Ziegler-Natta catalyzed
polyisoprene material on a former and curing the elastomeric
coating to form an elastomeric layer of the polymeric article. The
disposing step may comprise dipping a coagulant-free or coagulant
coated former in an emulsion of the Ziegler-Natta catalyzed
polyisoprene material, which may be an aqueous latex composition
according to Table 1 having pre-vulcanized particles, at least once
to form a thin layer of latex or elastomeric coating with
individual particles of pre-vulcanized synthetic polyisoprene on
the surface of the former. The former can be any suitable former as
is known in the art. The present inventive composition is
particularly useful for layering onto formers for condoms and
gloves.
[0036] Embodiments of the Ziegler-Natta catalyzed formulations
disclosed in Table 1, which may use ZN PI resins of Table 2, as
well as other Ziegler-Natta catalyzed formulations, are capable of
making condoms that have a lighter color than natural rubber
condoms, allowing a greater range of colored condoms to be
manufactured, while maintaining similar hardness and tensile
strength properties. Furthermore, any residual solvent content in
condoms made therefrom is lower, lending to lesser allergenicity.
Further still, the allergenicity of condoms made from Ziegler-Natta
catalyzed formulations is lower compared with natural rubber and
anionic formulations, owing to lesser amounts of accelerators and
sulfur. The branched molecular structure of the Ziegler-Natta
catalyzed synthetic polyisoprene provides greater strength than
linear molecular structure of an anionic catalyst produced latex.
The Ziegler-Natta catalyzed synthetic polyisoprene also comprises a
greater amount of cis character, e.g., cis-1,4 isomer, of the
polyisoprene molecules than the anionic catalyzed polyisoprene,
improving the strength properties of products made with
Ziegler-Natta catalyzed synthetic polyisoprene.
[0037] Also, the exemplary Ziegler-Natta catalyzed formulation of
Table 1 has potentially lower total solids content, allowing the
manufacture of thinner condoms. And, the exemplary Ziegler-Natta
catalyzed formulation of Table 1 has potentially lower viscosities
during the dipping processes, allowing thinner condoms to be
produced therefrom. Lower viscosities also allow a faster line
speed during manufacturing. In at least some embodiments, unlike
other condom manufacturing, coagulants may be disposed on condom
formers prior to the disposition of a Ziegler-Natta catalyzed
polymeric coating on the formers, allowing a stronger condom to be
manufactured at similar thicknesses compared with anionic
polymerized condom formulations.
[0038] Furthermore, the Ziegler-Natta catalyzed formulation of
Table 1 produces smaller particle sizes, which allows a thinner
film and improve user sensitivity during sexual intercourse and/or
glove use. Smaller particles also exhibit improved crosslinking,
which improves the process-ability of thinner products. For
example, preventing the condom or glove collapse during washing
processes and allows powder to coat evenly on both inside and
outside and, therefore, reducing defects.
[0039] Table 3 lists a typical dipping method for producing a
condom using a Ziegler-Natta catalyzed polyisoprene resin that is
pre-vulcanized, as described above. A similar method can be created
for a synthetic polyisoprene surgical glove.
TABLE-US-00003 TABLE 3 First dip (thickness of coating may be
controlled by latex viscosity and/or former speed in the dip tank
Drying of the latex coating (60-80.degree. C.; 1-3 min). Second dip
(optional) Drying of the latex coating (60-80.degree. C.; approx
1-3 min). Beading/ring formation on the open end of the condom
Drying of the ring and latex coating (70-100.degree. C.; approx 1-3
min) Curing (110-130.degree. C.; approx 11-15 min) Leaching
(70-80.degree. C.; approx 1-2 min) Stripping of the condoms from
the formers
[0040] The method of dipping for the condoms using the
surfactant-stabilized, pre-vulcanized synthetic polyisoprene latex
composition is typically within the 5-day period, e.g., an average
lifetime of synthetic polyisoprene latex emulsion tank. A condom
former is dipped in the composition in a first dip. The wall
thickness of the latex coating is controlled by the viscosity of
latex, which is a function of the total solids content of the
composition in the dip tank. The speed of movement of the formers
while dipping also affects the wall thickness. The latex coating
that coats the formers is dried at approximately 60-100.degree. C.
for approximately 1-3 minutes. The latex coating on the former is,
optionally, dipped again into the composition to apply a second dip
coating. The latex coating after the second dip is dried at
approximately 60-80.degree. C. for approximately 1-3 minutes. The
open end of the condom is rolled to create a bead ring, which is
distal to a tip of a closed end of the condom.
[0041] The coating can be post-vulcanized by heating the coating,
e.g., to about 110 to 150.degree. C. for approximately 8 to 15
minutes, to form an elastomeric layer of a condom. Exemplary
embodiments include post-vulcanization that is achieved by heating
in an oven at approximately 120.degree. C. for approximately 12
minutes. During this period, the inter-particle regions are
cross-linked. The intra-particle regions also undergo further
crosslinking, producing a more homogeneous latex product. The
condom is optionally leached in water at approximately
70-80.degree. C. for about 1-2 minutes to remove residual
surfactants and cross-linking agents from the condom. The condom is
then stripped from the former. The latex articles, such as condoms,
produced display higher strength and improved stretch, even when a
low stereo-regularity synthetic polyisoprene is used. The synthetic
polyisoprene articles are free from irritation-causing proteins
that cause latex sensitivity issues.
[0042] Embodiments according to the disclosure comprise the use of
a coagulant solution to wet the former and may include an exemplary
aqueous solution of 5% calcium nitrate, although other
concentrations are possible as are known to those in the art, such
as an aqueous solution ranging in concentration from 6-40% calcium
nitrate. Other salts, such as calcium chloride, calcium citrate,
aluminum sulfate, and the like and/or mixtures thereof may be used.
Furthermore, the coagulant solution may be aqueous, alcoholic, or a
mixture of aqueous and alcoholic solutions/solvents. Weaker acid
solutions may also be used as coagulants, such as formic acid,
acetic acid, and other low pKa acids as are known to those in the
art.
[0043] Embodiments according to the disclosure comprise the use of
pre-vulcanizing and post-vulcanizing methods, the technology of
which is disclosed in commonly-assigned U.S. Pat. Nos. 8,087,412;
8,464,719; 9,074,027; and 9,074,029 which are incorporated by
reference in entirety. Methods for determining the molecular weight
between crosslinks M.sub.c is disclosed in U.S. Pat. Nos.
8,087,412; 8,464,719; 9,074,027; and 9,074,029.
EMBODIMENTS
Embodiment 1
[0044] A polymeric article comprising: an elastomeric layer
comprising cured synthetic polyisoprene particles that comprise a
Ziegler-Natta catalyzed polyisoprene material.
Embodiment 2
[0045] The polymeric article of the preceding embodiment, wherein
the synthetic polyisoprene particles are pre-vulcanized.
Embodiment 3
[0046] The polymeric article of any preceding embodiment, wherein
the Ziegler-Natta catalyzed polyisoprene material comprises a
branched macrostructure.
Embodiment 4
[0047] The polymeric article of any preceding embodiment, wherein
the Ziegler-Natta catalyzed polyisoprene material comprises a
cis-1,4 isomer content of 95% by weight or greater.
Embodiment 5
[0048] The polymeric article of any preceding embodiment, wherein
the Ziegler-Natta catalyzed polyisoprene material comprises a
cis-1,4 isomer content of about 96% to 97% by weight.
Embodiment 6
[0049] The polymeric article of any preceding embodiment, wherein
the Ziegler-Natta catalyzed polyisoprene material comprises a
trans-1,4 isomer content of 1% by weight or less.
Embodiment 7
[0050] The polymeric article of any preceding embodiment, wherein
the Ziegler-Natta catalyzed polyisoprene material comprises a 3,4
isomer content of 5% by weight or less.
Embodiment 8
[0051] The polymeric article of any preceding embodiment, wherein
the article has a thickness in the range of from 0.030 to 0.065
mm.
Embodiment 9
[0052] The polymeric article of any preceding embodiment, wherein
the elastomeric layer comprises a post-vulcanized structure having
a molecular weight between crosslinks (Mc) of less than 11,000
g/mol.
Embodiment 10
[0053] The polymeric article of any preceding embodiment, wherein
the synthetic polyisoprene particles have a median particle
diameter in the range of approximately from 0.2 to 2 micrometers,
or the synthetic polyisoprene particles have a median particle
diameter in the range of approximately from 0.2 to 1.5
micrometers.
Embodiment 11
[0054] The polymeric article of any preceding embodiment, wherein
the synthetic polyisoprene particles are bonded to each other
through intra-polyisoprene particle crosslinks and
inter-polyisoprene particle crosslinks.
Embodiment 12
[0055] The polymeric article of any preceding embodiment in the
form of a condom.
Embodiment 13
[0056] A condom comprising: an elastomeric layer comprising cured
synthetic polyisoprene particles that are pre-vulcanized, wherein
the synthetic polyisoprene particles comprise a Ziegler-Natta
catalyzed polyisoprene material that comprises: a cis-1,4 isomer
content of 95% by weight or greater; a trans-1,4 isomer content of
1% by weight or less; and a 3,4 isomer content of 5% by weight or
less.
Embodiment 14
[0057] The condom of the preceding embodiment, wherein the
elastomeric layer forms an open end, a closed end, and a tubular
sheath extending from the closed end to the open end.
Embodiment 15
[0058] The condom of any of embodiment 13 to the preceding
embodiment, wherein the Ziegler-Natta catalyzed polyisoprene
material comprises a branched macrostructure.
Embodiment 16
[0059] The condom of any of embodiment 13 to the preceding
embodiment, wherein the elastomeric layer comprises a
post-vulcanized structure having a molecular weight between
crosslinks (Mc) of less than 11,000 g/mol.
Embodiment 17
[0060] The condom of any of embodiment 13 to the preceding
embodiment, wherein the synthetic polyisoprene particles have a
median particle diameter in the range of approximately from 0.2 to
1.5 micrometers.
Embodiment 18
[0061] The polymeric article of any of embodiment 13 to the
preceding embodiment, wherein the synthetic polyisoprene particles
are bonded to each other through intra-polyisoprene particle
crosslinks and inter-polyisoprene particle crosslinks.
Embodiment 19
[0062] A method for producing a polymeric article, comprising:
disposing an elastomeric coating of a Ziegler-Natta catalyzed
polyisoprene material on a former; and curing the elastomeric
coating to form an elastomeric layer of the polymeric article.
Embodiment 20
[0063] The method of the preceding embodiment, wherein the
disposing of the elastomeric coating on the former comprises
dipping the former into an emulsion of the Ziegler-Natta catalyzed
polyisoprene material.
Embodiment 21
[0064] The method of any of embodiment 19 to the preceding
embodiment, wherein the emulsion of the Ziegler-Natta catalyzed
polyisoprene material is pre-vulcanized before dipping the
former.
Embodiment 22
[0065] The method of any of embodiment 19 to the preceding
embodiment, wherein the polymeric article comprises a condom and
the elastomeric layer forms an open end, a closed end, and a
tubular sheath extending from the closed end to the open end.
Embodiment 23
[0066] The method of any of embodiment 19 to the preceding
embodiment, wherein the synthetic polyisoprene particles are bonded
to each other through intra-polyisoprene particle crosslinks and
inter-polyisoprene particle crosslinks.
EXAMPLES
[0067] Condoms according to a formulation of Table 1 were
produced.
[0068] A method of measuring molecular weight distribution and
calculating crosslink density requires cutting of disks from condom
samples and swelling the disk samples in toluene until equilibrium.
The disks were initially weighed and after swelling they are
weighed again. The equilibrium volume fraction of the swelled
rubber was calculated using equation shown below. In this equation
P.sub.r is the density of rubber (0.92 g/cm.sup.3), P.sub.s is the
density of toluene (0.862 g/cm.sup.3), W.sub.r is the weight of
rubber before swelling and W.sub.s is the weight of swelled
rubber.
WrPrWrPr+Ws-WrPs
[0069] The volume fraction was used in the Florey-Rehner equation
shown below to calculate the crosslink density. In this equation n
is the crosslink density, V.sub.s is the molar volume of toluene
the swelling solvent which is 106.3 cm3/mol, V.sub.r is the volume
fraction of the rubber phase in the swollen gel, and .chi. is the
toluene-cis polyisoprene interaction parameter, which is 0.39.
n=-1/Vs multiplied by [ln(1-Vr)+Vr+.chi.Vr2][Vr13-0.5Vr]
[0070] The molecular weight between crosslinks was calculated by
the following equation. Mc=Prn
Example 1
[0071] Table 4 shown below reports measured molecular weight
between crosslinks and corresponding crosslink density for several
of synthetic polyisoprene condoms manufactured according the
embodiments of the subject disclosure. The higher the molecular
weight between crosslinks, the lower the crosslink density
becomes.
[0072] The data presented indicates that the process of the present
disclosure results in synthetic polyisoprene condoms that have very
consistent molecular weight between crosslinks, providing a condom
having adequate mechanical properties. The molecular weight between
crosslinks (M.sub.c) for the condoms according to the present
embodiments is 0.0000845 mol/cm.sup.3, which is comparable to that
of natural rubber, which has a crosslink density of 0.0000159
mol/cm.sup.3.
TABLE-US-00004 TABLE 4 Molecular Weight Average Original Swollen
weight, weight, Average Mc Sample mg mg Vr Vr N g/mol 1 76.1 460.8
0.1564 0.1564 8.452 .times. 10.sup.-5 10886 2 76.3 448.1 0.1613 3
74.9 467.6 0.1516
[0073] FIG. 1 depicts a first transmission electron microscopy
(TEM) image of a surface of a condom, according to embodiments of
the disclosure.
[0074] FIG. 2 depicts a second TEM image of a surface of a condom,
according to embodiments of the disclosure;
[0075] FIG. 3 depicts a third TEM image of a surface of a condom,
according to embodiments of the disclosure; and
[0076] FIG. 4 depicts a fourth TEM image of a surface of a condom,
according to embodiments of the disclosure.
[0077] The condoms studied in the first, second, third, and fourth
TEM images were prepared as follows. Each condom was washed in
propan-2-ol to remove the lubricant and then dipped in propan-2-ol
containing a small amount of talc to prevent adhesion and thus also
facilitate handling. The condom was then air-dried. A number of
rings were cut from the condom using a parallel, twin-blade cutter
with the blades a nominal 10 mm apart. These rings were to be used
for the two methods of analysis: network visualization by TEM and
Vr measurement by equilibrium swelling.
[0078] Network Visualization.
[0079] After extraction overnight in acetone, the sample of condom
was swelled to equilibrium in styrene. The sample was then
transferred to gelatin capsules and polymerized by heating.
Ultra-thin sections were then prepared by ultramicrotomy at room
temperature using glass knives. The sections were collected on a
water-filled though and relaxed with xylene vapor before collecting
on TEM grids. The sections were then stained with osmium tetroxide
vapor for one hour. Osmium tetroxide reacts with carbon-carton
double bonds and therefore shows up the rubber network as darker
than the polystyrene. Representative TEM micrographs are provided
(see TEM16803-6) in FIGS. 1-4.
[0080] The latex particles were fairly closely bonded together but
the boundaries between the particles could often be seen. The
samples also contain many voids, i.e. areas where the styrene has
infiltrated to form a large pale area. Some of these voids contain
small dark particles so it seems likely that most or all of them
are caused by styrene forming pools around these particles which
have not bonded to the rubber. A void which appears to be empty may
actually contain a particle which is not visible because it was
either above or below the section.
[0081] There are also some small dark patches inside some of the
rubber particles. These do not look like particles but seem to be
small areas of the rubber network which have some electron-dense
(i.e. high atomic number) material attached to them.
[0082] The uncertainty on the scalebar dimension is .+-.10% in all
of the TEM micrographs.
[0083] The latex particles, i.e., synthetic polyisoprene particles
catalyzed using Ziegler-Natta catalysts, exhibited close
bonding.
[0084] All numerical values recited herein are exemplary, are not
to be considered limiting, and include ranges therebetween, and can
be inclusive or exclusive of the endpoints. Optional included
ranges can be from integer values therebetween, at the order of
magnitude recited or the next smaller order of magnitude. For
example, if the lower range value is 0.1, optional included
endpoints can be 0.2, 0.3, 0.4 . . . 1.1, 1.2, and the like, as
well as 1, 2, 3 and the like; if the higher range is 10, optional
included endpoints can be 7, 6, and the like, as well as 7.9, 7.8,
and the like.
[0085] To facilitate understanding, identical reference numerals
have been used, where possible, to designate comparable elements
that are common to the figures. The figures are not drawn to scale
and may be simplified for clarity. It is contemplated that elements
and features of one embodiment may be beneficially incorporated in
other embodiments without further recitation.
[0086] It is to be understood that various changes and
modifications to the embodiments described herein will be apparent
to those skilled in the art. Such changes and modifications can be
made without departing from the spirit and scope of the present
disclosure and without demising the attendant advantages. It is,
therefore, intended that such changes and modifications be covered
by the appended claims.
[0087] All references, including publications, patent applications,
and patents, cited herein are hereby incorporated by reference to
the same extent as if each reference were individually and
specifically indicated to be incorporated by reference and were set
forth in its entirety herein.
* * * * *