U.S. patent application number 09/760297 was filed with the patent office on 2001-06-21 for process for producing dip-formed rubber article.
Invention is credited to Ohta, Hisanori, Ozawa, Yutaka.
Application Number | 20010004653 09/760297 |
Document ID | / |
Family ID | 16590272 |
Filed Date | 2001-06-21 |
United States Patent
Application |
20010004653 |
Kind Code |
A1 |
Ozawa, Yutaka ; et
al. |
June 21, 2001 |
Process for producing dip-formed rubber article
Abstract
A vulcanizable dip-forming rubber latex composition comprising
an unsaturated nitrile-conjugated diene copolymer rubber latex, a
sulfur-containing vulcanizer, and a vulcanization accelerator
comprising at least one compound selected from (i) dithiocarbamic
acid compounds of the formula: 1 and (ii) zinc dithiocarbamate
compounds of the formula: 2 wherein R.sub.1 and R.sub.2 are
hydrocarbon groups having at least 6 carbon atoms which may be the
same or different, and an optional thiazole compound. A rubber
article dip-formed from the rubber latex composition has no crack
occurrence, good surface luster and good vulcanization properties,
and does not contain a nitrosamine, and therefore, is suitable for
medical use.
Inventors: |
Ozawa, Yutaka; (Tokyo,
JP) ; Ohta, Hisanori; (Kawasaki-shi, JP) |
Correspondence
Address: |
BIRCH, STEWART, KOLASCH AND BIRCH
P.O. Box 747
Falls Church
VA
22040-0747
US
|
Family ID: |
16590272 |
Appl. No.: |
09/760297 |
Filed: |
January 16, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09760297 |
Jan 16, 2001 |
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09230257 |
Jan 22, 1999 |
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6187857 |
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09230257 |
Jan 22, 1999 |
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PCT/JP97/02547 |
Jul 23, 1997 |
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Current U.S.
Class: |
524/565 ;
525/332.7 |
Current CPC
Class: |
C08L 9/04 20130101; C08K
5/39 20130101; C08K 5/39 20130101; A61L 29/042 20130101; B29C 41/14
20130101 |
Class at
Publication: |
524/565 ;
525/332.7 |
International
Class: |
C08F 136/20; C08F
008/34 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 23, 1996 |
JP |
8/210493 |
Claims
1. A vulcanizable dip-forming rubber latex composition
characterized as comprising an unsaturated nitrile-conjugated diene
copolymer rubber latex, a sulfur-containing vulcanizer, at least
one vulcanization accelerator selected from (i) dithiocarbamic acid
compounds represented by the formula (1): 5wherein R.sub.1 and
R.sub.2 are hydrocarbon groups having at least 6 carbon atoms which
may be the same as or different from each other, and (ii) zinc
dithiocarbamate compounds represented by the formula (2): 6wherein
R.sub.1 and R.sub.2 are hydrocarbon groups having at least 6 carbon
atoms which may be the same as or different from each other.
2. The rubber latex composition according to claim 1, which
comprises a thiazole compound in addition to at least one compound
selected from the dithiocarbamic acid compounds of the formula (1)
and the zinc dithiocarbamate compounds of the formula (2) as the
vulcanization accelerator.
3. The rubber latex composition according to claim 1 or 2, which
comprises 0.10 to 10 parts by weight of the sulfur-containing
vulcanizer and 0.1 to 10 parts by weight of the vulcanization
accelerator, based on 100 parts by weight of the unsaturated
nitrile-conjugated diene copolymer rubber.
4. The rubber latex composition according to claim 2, wherein the
vulcanization accelerator is a mixture comprising (A) at least one
compound selected from the dithiocarbamic acid compounds of the
formula (1) and the zinc dithiocarbamate compounds of the formula
(2), and (B) the thiazole compound at a ratio(A:B) of 9.5:0.5 to
3:7 (weight ratio).
5. The rubber latex composition according to any of claims 1 to 4,
wherein the unsaturated nitrile-conjugated diene copolymer rubber
is a copolymer composed of 9 to 50% by weight of an ethylenically
unsaturated nitrile monomer, 30 to 90% by weight of a conjugated
diene monomer, 0 to 20% by weight of an ethylenically unsaturated
acid monomer and 0 to 20% by weight of other ethylenically
unsaturated monomer.
6. The rubber latex composition according to any of claims 1 to 4,
wherein the unsaturated nitrile-conjugated diene copolymer rubber
is a copolymer composed of 20 to 45% by weight of an ethylenically
unsaturated nitrile monomer, 35 to 80% by weight of a conjugated
diene monomer, 1 to 15% by weight of an ethylenically unsaturated
acid monomer and 0 to 20% by weight of other ethylenically
unsaturated monomer.
7. The rubber latex composition according to any of claims 1 to 6,
wherein the unsaturated nitrile-conjugated diene copolymer rubber
has a weight average molecular weight of 50,000 to 500,000 as in
terms of those of standard polystyrene.
8. The rubber latex composition according to any of claims 1 to 7,
wherein the unsaturated nitrile-conjugated diene copolymer rubber
is prepared by using as a polymerization terminator at least one
compound selected from diethylhydroxylamine, hydroxylaminesulfonic
acid and its alkali metal salts, hydroxylamine sulfate, aromatic
hydroxydithiocarboxylic acids and their alkali metal salts,
hydroquinone derivatives and catechol derivatives.
9. The rubber latex composition according to any of claims 1 to 8,
wherein the vulcanization accelerator of the formula (1) is
dibenzyldithiocarbamic acid, and the vulcanization accelerator of
the formula (2) is zinc dibenzyldithiocarbamate.
10. The rubber latex composition according to any of claims 2 to 8,
wherein the thiazole compound vulcanization accelerator is at least
one compound selected from 2-mercaptobenzothiazole, dibenzothiazyl
disulfide and a zinc salt of 2-mercaptobenzothiazole.
11. A rubber article dip-formed from the rubber latex composition
as claimed in any of claims 1 to 10.
12. The dip-formed rubber article according to claim 11, which has
an extracted nitrosamine content of not larger than 1 ppm.
13. The dip-formed rubber article according to claim 11, which has
an extracted nitrosamine content of not larger than 0.1 ppm.
14. The dip-formed rubber article according to claim 11 or 12,
which is a medical article, a glove for home use or industrial use,
a nipple or a balloon.
15. The dip-formed rubber article according to claim 13, wherein
the medical article is a glove for operation, a glove for medical
examination or detection, a balloon sac or a catheter.
Description
TECHNICAL FIELD
[0001] This invention relates to a dip-forming, vulcanizable rubber
latex composition comprising a sulfur-containing vulcanizer an a
vulcanization accelerator, which is used for making a vulcanized
unsaturated nitrile rubber article without production of a
nitrosamine which is restricted by regulation, and further relates
to a rubber article dip-formed therefrom.
BACKGROUND ART
[0002] Certain N-nitrosamines (hereinafter abbreviated to
"nitrosamines") are carcinogenic, and a problem arises in that it
is possible that nitrosamines are produced in vulcanized rubber
articles made from a solid polymer rubber or a polymer rubber
latex.
[0003] For example, as examples of the vulcanized rubber articles
made from a polymer rubber latex, there can be mentioned those
which are used in contact with the human body, such as a nipple, a
balloon, gloves for operation, or medical examination or detection,
a balloon sac, and other medical articles. It is possible that
nitrosamines are detected in these vulcanized rubber articles.
Especially a serious problem is caused in medical rubber articles
which are used in direct contact with mucous membranes or
organs.
[0004] At present, the restriction of nitrosamines contained in
vulcanized rubber articles by regulation is an urgent problem in
Japan and many other countries. Already in German, the maximum
permissible amount of specific nitrosamines is 10 ppb or below. As
such nitrosamines which are restricted by regulation, there can be
mentioned seven species, which include, for example,
N-nitrosodimethylamine, N-nitrosodiethylamine,
N-nitrosodi-n-butylamine and N-nitrosomethylphenylamine.
[0005] It is known that the occurrence of nitrosamines in
vulcanized rubber articles is due to the fact that a dithiocarbamic
acid compound used as a polymerization terminator for emulsion
polymerization or as a vulcanization promoter emulsifier remains in
a solid polymer rubber or polymer rubber latex. Namely, the
dithiocarbamic acid compound is hydrolyzed to produce a secondary
amine which in turn reacts with NO.sub.x in the environment or
nitrites or other NO.sub.x contained in food or the saliva to
produce nitrosamines.
[0006] Thus it has been studied to use dithiocarbamic acid
compounds as a vulcanization accelerator for rubber, which produce
only a negligible amount of a nitrosamine or a secondary amine,
i.e., a precursor of nitrosamine. As an example of such
dithiocarbamic acid compounds, there can be mentioned zinc
dibenzyldithiocarbamate. However, it is reported that when this
vulcanization accelerator is used for a natural rubber latex, the
resulting vulcanized rubbers generally have poor vulcanization
properties as compared with vulcanized rubbers made with other
conventional vulcanization accelerators (Polymer Digest, 1987, 12,
p12-). The present inventors have also confirmed that when zinc
dithiocarbamates are incorporated in a natural rubber latex, rubber
articles dip-formed from the natural rubber latex have cracks and
poor surface luster.
[0007] A vulcanization accelerator incapable of producing a
nitrosamine, which is different from the dithiocarbamic acid
compound vulcanization accelerator, such as zinc
isopropylxanthogenate, has also been reported. This vulcanization
accelerator is however little or no practicality because it has a
low storage stability and an offensive smell, and results in rubber
vulcanizates with poor vulcanization properties.
[0008] Other types of vulcanization accelerators such as
thiophosphate compounds, thiazole compounds,
benzothiazolesulphenamide compounds and guanidine compounds are
known, but desired vulcanization properties cannot be obtained with
these vulcanization accelerators (Polymer Digest, 1991, 1,
p65-).
[0009] Thus there is an increasing demand for a vulcanization
accelerator which is incapable of producing a nitrosamine or a
secondary amine and giving a vulcanized rubber having good
vulcanization properties.
DISCLOSURE OF INVENTION
[0010] To solve the problems encountered with the conventional
vulcanization promoters, the present inventors have conducted
researches into vulcanization accelerators and found that, when
specified dithiocarbamic acid compounds are used as a vulcanization
accelerator for an unsaturated nitrile rubber (NBR) latex, a
vulcanized rubber article dip-formed therefrom has no crack
occurrence, excellent surface luster and good vulcanization
properties. Based on this finding, the present invention has been
completed.
[0011] Thus in accordance with the present invention there is
provided a vulcanizable dip-forming rubber latex composition
characterized as comprising an unsaturated nitrile-conjugated diene
copolymer rubber latex, a sulfur-containing vulcanizer, at least
one vulcanization accelerator selected from (i) dithiocarbamic acid
compounds represented by the formula (1): 3
[0012] wherein R.sub.1 and R.sub.2 are hydrocarbon groups having at
least 6 carbon atoms which may be the same as or different from
each other, and (ii) zinc dithiocarbamate compounds represented by
the formula (2): 4
[0013] wherein R.sub.1 and R.sub.2 are hydrocarbon groups having at
least 6 carbon atoms which may be the same as or different from
each other, and an optional thiazole compound vulcanization
accelerator.
[0014] Further, in accordance with the present invention, there is
provided a rubber article dip-formed from the above-mentioned
vulcanizable dip-forming rubber latex composition.
BEST MODE FOR CARRYING OUT THE INVENTION
[0015] The embodiments of the present invention will now be
described in detail.
[0016] The main point of the present invention lies, for the
production of a vulcanized rubber article by dip-forming a
sulfur-vulcanizable polymer rubber latex, in the use of an
unsaturated nitrile-conjugated diene copolymer rubber as the
polymer rubber, and a sulfur-containing vulcanizer and, in
combination therewith, a dithiocabamic acid compound of the formula
(1) and/or a zinc dithiocarbamate compound of the formula (2) as
the vulcanization accelerator.
Vulcanizable Dip-Forming Rubber Latex Composition
[0017] The unsaturated nitrile-conjugated diene copolymer rubber
latex used in the dip-forming rubber latex composition is a latex
of a copolymer rubber prepared by copolymerizing a conjugated diene
monomer, an ethylenically unsaturated nitrile monomer, and optional
copolymerizable ethylenically unsaturated acid monomer and/or other
ethylenically unsaturated monomer.
[0018] The conjugated diene monomer used for the preparation of the
unsaturated nitrile-conjugated diene copolymer rubber is not
particularly limited and includes, for example, 1,3-butadiene,
isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene,
1,3-pentadiene and chloroprene. Especially 1,3-butadiene and
isoprene are preferable. These conjugated diene monomers may be
used either alone or as a combination of at least two thereof. The
amount of the conjugated diene monomer is usually in the range of
30 to 90% by weight and preferably 35 to 80% by weight, based on
the total weight of the monomers. If the amount of the conjugated
diene monomer is smaller than 30% by weight, the vulcanized rubber
article dip-formed from the latex composition has rigid feeling. In
contrast, if the amount thereof is larger than 90% by weight, the
vulcanized rubber article dip-formed from the latex has a poor oil
resistance and low tensile strength and tear strength.
[0019] The ethylenically unsaturated nitrile monomer is not
particularly limited and includes, for example, acrylonitrile,
methacrylonitrile, fumaronitrile, .alpha.-chloroacrylonitrile and
.alpha.-cyanoethylacryloni- trile. These ethylenically unsaturated
nitrile monomers may be used either alone or as a combination of at
least two thereof. The amount of the ethylenically unsaturated
nitrile monomers is usually in the range of 9 to 50% by weight and
preferably 20 to 45% by weight, based on the total weight of the
monomers. If the amount of the unsaturated nitrile monomer is
smaller than 9% by weight, the vulcanized rubber article dip-formed
from the latex composition has a poor oil resistance. In contrast,
if the amount thereof is larger than 50% by weight, the vulcanized
rubber article dip-formed from the latex has a rigid feeling.
[0020] The ethylenically unsaturated acid monomer optionally used
includes ethylenically unsaturated monomers having an acid group
such as a carboxyl group, a sulfonic acid group and an acid
anhydride group. As specific examples thereof, there can be
mentioned ethylenically unsaturated carboxylic acids such as
acrylic acid, methacrylic acid, itaconic acid maleic acid and
fumaric acid; polycarboxylic acid anhydrides such as maleic
anhydride and citraconic anhydride; ethylenically unsaturated
sulfonic acid monomers such as styreneslulfonic acid; and partial
ester monomers of an ethylenically unsaturated polycarboxylic acid
such as monobutyl fumarate, monobutyl maleate and
mono-2-hydroxypropyl maleate. These ethylenically unsaturated
polycarboxylic acid monomers may also be used as an alkali metal
salt or an ammonium salt. These ethylenically unsaturated acid
monomers may be used either alone or as a combination of at least
two thereof. The amount of the ethylenically unsaturated acid
monomers is usually not larger than 20% by weight, preferably in
the range of 1 to 15% by weight and more preferably 2 to 10% by
weight, based on the total weight of the monomers. If the amount of
the acid monomer is larger than 20% by weight, the vulcanized
rubber article dip-formed therefrom has a poor tear strength and a
rigid feeling.
[0021] As specific examples of the other copolymerizable
ethylenically unsaturated monomer optionally used for
copolymerization, there can be mentioned vinyl aromatic monomers
such as styrene, alkylstyrenes and vinylnaphthalenes; fluoroalkyl
vinyl ethers such as fluoroethyl vinyl ether; ethylenically
unsaturated amide monomers such as acrylamide, methacrylamide,
N-methylolacrylamide, N-methylolmethacrylamide,
N,N-dimethylolacrylamide, N,N-dimethylolmethacrylamide,
N-methoxymethylacrylamide, N-methoxymethylmethacrylamide,
N-propoxymethylacrylamide and N-propoxymethylmethacrylamide;
vinylpyridine; vinylnorbornene; non-conjugated diene monomers such
as dicyclopentadiene and 1,4-hexadiene; and ethylenically
unsaturated carboxylic acid esters such as methyl acrylate, methyl
methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate,
butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl
methacrylate, trifluoroethyl acrylate, trifluoroethyl methacrylate,
tetrafluoropropyl acrylate, tetrafluoropropyl methacrylate, dibutyl
maleate, dibutyl fumarate, diethyl maleate, methoxymethyl acrylate,
methoxymethyl methacrylate, ethoxyethyl acrylate, ethoxyethyl
methacrylate, methoxyethoxyethyl acrylate, methoxyethoxyethyl
methacrylate, cyanomethyl acrylate, cyanomethyl methacrylate,
2-cyanoethyl acrylate, 2-cyanoethyl methacrylate, 1-cyanopropyl
acrylate, 1-cyanopropyl methacrylate, 2-ethyl-6-cyanohexyl
acrylate, 2-ethyl-6-cyanohexyl methacrylate, 3-cyanopropyl
acrylate, 3-cyanopropyl methacrylate, hydroxyethyl acrylate,
hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl
methacrylate, glycidyl acrylate, glycidyl methacrylate,
dimethylaminoethyl acrylate and diemthyl-aminoethyl methacrylate.
These ethylenically unsaturated monomers may be used either alone
or as a combination of at least two thereof. The amount of these
ethylenically unsaturated monomers is usually not larger than 20%
by weight based on the total weight of the monomers.
[0022] The molecular weight of the unsaturated nitrile-conjugated
diene copolymer is not particularly limited, but is usually in the
range of 50,000 to 500,000 and preferably 80,000 to 200,000 as a
weight average molecular weight expressed in terms of that of
standard polystyrene (hereinafter merely referred to as molecular
weight). If the molecular weight is too small, a rubber article
dip-formed therefrom has a low tensile strength. In contrast, if
the molecular weight is too large, a rubber article dip-formed
therefrom has a rigid feeling.
[0023] The unsaturated nitrile-conjugated diene copolymer rubber
latex is prepared usually by an emulsion polymerization procedure.
The temperature at which the emulsion polymerization is effected is
not particularly limited, but is preferably not higher than about
40.degree. C. because the latex can be produced stably and a rubber
article dip-formed therefrom has a high mechanical strength and a
soft feeling.
[0024] The manner in which the monomers are added is not
particularly limited. Any manner can be employed in which the
monomer mixture is charged into a polymerization reactor at once or
continuously, or part of the monomer mixture is charged in a
polymerization reactor and the remainder is continuously introduced
therein.
[0025] A polymerization initiator used is not particularly limited,
but a redox polymerization initiator is preferable. Preferable
peroxides used in the redox initiator are those which have a
half-life of 10 hours at a temperature of at least 100.degree. C.,
and, specific examples of the peroxides, there can be mentioned
hydroperoxides such as diisopropylbenzene hydroperoxide, cumene
hydroperoxide, t-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl
hydroperoxide and 2,5-dimethylhexane-2,5-dihydroperoxide.
Especially those which have a half-life of 10 hours at a
temperature of at least 130.degree. C., such as, for example,
1,1,3,3-tetramethylbutyl hydroperoxide, are preferable because the
rubber latex can be stably produced and a rubber article dip-formed
therefrom has a high mechanical strength and a soft feeling. The
amount of the peroxide varies to some extent depending upon the
particular peroxide, but is preferably in the range of 0.01 to 0.6%
by weight based on the monomer mixture.
[0026] The reducing agent component used in the redox
polymerization initiator is not particularly limited, and includes,
for example, compounds containing a metal ion in a reduced state
such as ferrous sulfate and cuprous naphthenate; sulfonic acid
compounds such as sodium methanesulfonate; and amine compounds such
as dimethylaniline. These reducing agents may be used either alone
or as a combination of at least two thereof. The amount of the
reducing agent varies to some extent depending upon the particular
reducing agent, but is preferably in the range of 0.03 to 10 parts
by weight based on 1 part by weight of the peroxide.
[0027] An emulsifier used for the preparation of the unsaturated
nitrile-conjugated diene copolymer rubber is not particularly
limited. As specific examples of the emulsifier, there can be
mentioned nonionic emulsifiers such as polyoxyethylene alkylether,
polyoxyethylene alkylphenolether, polyoxyethylene alkylester and
polyoxyethylenesorbitan alkylester; anionic emulsifiers such as
fatty acids, for example, myristic acid, palmitic acid, oleic acid
and linolenic acid, and their salts, higher alcohol sulfate esters
and alkylsulfosuccinic acids; cationic emulsifiers such as ammonium
chlorides, for example, trimethylammonium chloride and
dialkylammonium chlorides, benzylammonium salts and quaternary
ammonium salts; and copolymerizable emulsifiers such as sulfoesters
of .alpha., .beta.-unsaturated carboxylic acids, sulfate esters of
.alpha., .beta.-unsaturated carboxylic acids and
sulfoalkylarylethers of .alpha., .beta.-unsaturated carboxylic
acids. Of these, anionic emulsifiers and nonionic emulsifiers are
preferable. These emulsifiers may be used either alone or as a
combination of at least two thereof. The amount of the emulsifier
is not particularly limited, but is preferably in the range of 0.1
to 9.0% by weight based on the monomer mixture.
[0028] In the course of polymerization, when the predetermined
conversion is reached, a polymerization terminator is added into
the polymerization system to stop polymerization. The
polymerization terminator used is not particularly limited and
conventional terminators having an amine structure such as
hydroxylamine and sodium dimethyldithiocarbamate can be used.
However, it is preferable to use a polymerization terminator which
does not give an offensive smell and is incapable of producing a
nitrosamine or capable of producing only a very minor amount of a
nitrosamine, which is restricted by regulation. As specific
examples of such polymerization terminators, there can be mentioned
diethylhydroxylamine, hydroxylaminesulfonic acid and its alkali
metal salts, hydroxylaminesulfate salts, aromatic
hydroxydithiocarboxylic acids such as
hydroxyldimethylbenezenethiocarboxylic acid,
hydroxyldiethylbenezenethiocarboxylic acid and
hydroxyldibutylbenezenethi- ocarboxylic acid, and their alkali
metal salts, hydroquinone derivatives and catechol derivatives.
[0029] These radical polymerization terminators may be used either
alone or as a combination of at least two thereof. The amount of
the polymerization terminator is not particularly limited but is
usually in the range of 0.1 to 10 parts by weight based on 100
parts by weight of the total monomers.
[0030] By using the polymerization terminator incapable of
producing a nitrosamine or capable of producing only a very minor
amount of a nitrosamine, which gives an offensive smell, in
combination with the specified vulcanization accelerator, the
content of the nitrosamines in a rubber article dip-formed
therefrom can be controlled to zero or an negligible extent. The
amount of the nitrosamines extracted from the rubber article
dip-formed therefrom (said amount can be measured by the method
mentioned hereinafter) is generally not larger than 1 ppm. By more
suitably choosing the polymerization terminator and the
vulcanization accelerator, the amount of the nitrosamines extracted
can be lowered to a level of not larger than 0.1 ppm.
[0031] When the unsaturated nitrile-conjugated diene copolymer
rubber latex is prepared, a molecular weight modifier, a particle
diameter adjuster, an anti-aging agent, a chelating agent, an
oxygen-capturing agent and other polymerization auxiliaries can be
used according to the need.
[0032] The sulfur-containing vulcanizer used in the present
invention includes sulfur and sulfur-containing compounds which are
generally used as a sulfur-containing vulcanizer for polymer rubber
latexes. As specific examples of the sulfur-containing vulcanizer,
there can be mentioned sulfur such as powdery sulfur, flower of
sulfur, precipitated sulfur, colloidal sulfur, surface-treated
sulfur and insoluble sulfur; and sulfur-containing compounds such
as sulfur chloride, sulfur dichloride, morpholine disulfide, an
alkylphenol disulfide, N,N'-dithio-bis(hexahydro- -2H-azepinone-2),
phosphorus-containing polysulfide, high-molecular-weight
polysulfide, tetramethylthiuram disulfide, selenium
dimethyldithiocarbamate and
2-(4'-morpholinodithio)benzothiazole.
[0033] The amount of the sulfur-containing vulcanizer is not
particularly limited, but is usually in the range of 0.10 to 10
parts by weight and preferably 0.1 to 5 parts by weight, based on
100 parts by weight of the unsaturated nitrile-conjugated diene
copolymer rubber.
[0034] In the present invention, in combination with the
sulfur-containing vulcanizer, a vulcanization accelerator selected
from (i) dithiocarbamic acid compounds represented by the formula
(1) and/or (ii) zinc dithiocarbamate compounds represented by the
formula (2) is used optionally with a thiazole vulcanization
accelerator.
[0035] In the formulae (1) and (2), R.sub.1 and R.sub.2are
hydrocarbon groups having at least 6 carbon atoms which may be the
same as or different from each other. As examples of R.sub.1 and
R.sub.2, there can be mentioned an alkyl or cycloalkyl group which
may have a branch, an aryl group which may have a substituent, and
a benzyl group which may have one or two alkyl groups each having 1
to 5 carbon atoms in the .alpha.-carbon atom.
[0036] As specific examples of the dithiocarbamic acid compounds of
the formula (1), there can be mentioned dibenzyldithiocarbamic
acid, di-2-ethylhexyldithiocarbamic acid, diphenyldithiocarbamic
acid and dicyclohexyldithiocarbamic acid. As specific examples of
the zinc dithiocarbamate compounds of the formula (2), there can be
mentioned zinc salts of the above-recited dithiocarbamic acid
compounds. Dibenzyldithiocarbamic acid and its zinc salt are
especially preferable. These compounds have an excellent
dispersibility in water and rubber articles dip-formed therefrom
have no color.
[0037] The dithiocarbamic acid vulcanization accelerators used in
the present invention do not produce a nitrosamine which is
restricted by regulation. The dithiocarbamic acid vulcanization
accelerators can exhibit a vulcanization accelerating activity and
can impart vulvanization properties to rubber articles dip-formed
therefrom, which are similar to those given by the conventional
dithiocarbamic acid vulcanization accelerators which are considered
in the art to be indispensable for making rubber articles by
dip-forming and which produce nitrosamines restricted by
regulation. The rubber articles dip-formed from the latex
composition with the vulcanization accelerator used in the present
invention do not give an offensive smell, are not colored or are
colored only to a negligible extent, do not have cracks or have
very few cracks, and have an excellent surface luster.
[0038] Even if the above-mentioned dithiocarbamic acid and/or zinc
dithiocarbamate vulcanization accelerator is used alone,
vulcanization properties of the desired extent can be imparted to
vulcanized rubber articles. However, when these vulcanization
accelerators are used in combination with a thiazole compound
vulcanization accelerator, mechanical strength and other physical
properties can be varied more widely.
[0039] The thiazole compound vulcanization accelerator used
includes those which have heretofore conventionally used, and, as
specific examples thereof, there can be mentioned
2-mercaptobenzothiazole and its zinc salt, copper salt, sodium salt
and cyclohexylamine salt; 2-mercaptothiazoline, dibenzothiazyl
disulfide, 2-(2,4-dinitrophenylthio)- -benzothiazole,
2-(N,N-diethylthiocarbaylthio)benzothiazole,
2-(2,6-dimethyl-4-morpholinothio)benzothiazole,
2-(4'-morpholinodithio)be- nzothiazole,
4-morpholinyl-2-benzothiazyl disulfide and
1,3-bis(2-benzothiazylmercaptomethyl)urea. Of these,
2-mercaptobenothiazole and its zinc salt, and dibenzothiazyl
disulfide are preferable.
[0040] The amount of the vulcanization accelerator is suitably
determined so that sufficient vulcanization can be attained and
mechanical strength and other physical properties required for
vulcanized rubber articles are obtained, and is not particularly
limited. Usually the total amount of the vulcanization accelerator
is 0.1 to 10 parts by weight based on 100 parts by weight of the
solid content in the copolymer rubber latex.
[0041] When the above-mentioned two types of vulcanization
accelerators are used in combination, the proportion of the two
vulcanization accelerators is not particularly limited, but the
ratio of the dithiocarbamic acid and/or zinc dithiocarbamate
vulcanization accelerator to the thiazole compound vulcanization
accelerator is preferably in the range of 9.5/0.5 to 3/7 by
weight.
[0042] In addition to the above-mentioned vulcanization
accelerators, zinc oxide can be used in a manner similar to the
conventional sulfur vulcanization method. Active zinc oxide can be
used as the zinc oxide, but is difficult to disperse. The amount of
zinc oxide is suitably determined so that a sufficient
vulcanization can be attained and the mechanical strength and other
physical properties required for vulcanized rubber articles are
obtained, and is not particularly limited.
[0043] According to the need, additives can be incorporated in the
dip-forming rubber latex composition of the present invention for
imparting desired properties to vulcanized rubber articles, which
include, for example, reinforcers such as carbon black, silica and
talc, fillers such as calcium carbonate and clay, plasticizers,
anti-aging agents, and ultraviolet absorbers. Other rubber latexes
such as natural rubber latex and isoprene rubber latex can be
incorporated provided that the object of the present invention can
be achieved.
[0044] The procedure by which the dip-forming rubber latex
composition of the present invention is prepared is not
particularly limited. Usually the rubber latex can be made by
thoroughly mixing and dispersing together an unsaturated
nitrile-conjugated diene copolymer rubber latex, a
sulfur-containing vulcanizer, a vulcanization accelerator and other
additives together with a dispersion stabilizer by using a
conventional mixing and dispersing apparatus. The method by which
the respective ingredients are added is not particularly limited,
and, as a preferable method, a method can be employed wherein the
copolymer rubber latex is mixed with various additives by using a
dispersion stabilizer to prepare a dispersion, and the dispersion
is thoroughly mixed by using a stirrer or dispersing apparatus such
as a kneader or a disper.
Dip-Formed Rubber Articles
[0045] The dip-formed rubber articles of the present invention are
made by dip-forming the above-mentioned vulcanizable unsaturated
nitrile-conjugated diene copolymer rubber latex composition.
[0046] Usually the dip-forming is carried out by a process wherein
a mold is dipped in a bath of a dip-forming rubber latex
formulation whereby a rubber latex is deposited on the mold
surface, the mold having the rubber latex deposit on the surface
thereof is taken-up from the bath, if desired, a coating film on
the mold is dried, and then is separated from the mold to obtain a
rubber article. The dip-forming method includes, for example, a
direct dipping method, an anode coagulant dipping method and a
teague coagulant dipping method.
[0047] In the dip-forming method, a coagulant can be used, if
desired, prior to dipping of the mold in a bath of a rubber latex
formulation or after the dipped mold is taken-up from the bath.
More specifically, for example, a mold can be pre-treated with a
coagulant before the mold is dipped in the rubber latex
formulation, or a solution of a coagulant can be sprayed onto a
mold having a deposited rubber latex coating.
[0048] In the dip-forming method, the mold can be pre-heated before
it is dipped in the rubber latex formulation or, if desired, the
mold can be treated with warm water or heat-treated. By conducting
the warm water-treatment or the heat-treatment, excessive monomers
and additives can be removed. The specific procedure for the warm
water-treatment or the heat-treatment is not particularly limited,
and, as specific examples of the treatment procedure, there can be
mentioned a procedure wherein the mold having a deposited rubber
latex coating is dipped in a warm water bath, a procedure wherein
warm air is blown against the mold having a deposited rubber latex
coating in an oven, and a procedure wherein the mold having a
deposited rubber latex coating is irradiated with infrared
rays.
[0049] The kinds of the vulcanized rubber articles of the present
invention may be the same as vulcanized rubber articles made by the
conventional dip-forming methods. As specific examples of the
vulcanized rubber articles, there can be mentioned gloves for
operation, or medical examination or detection, medical rubber
articles such as a balloon sac and a catheter balloon, a nipple,
gloves for home use, gloves for industrial use, and balloons.
[0050] The invention will now be described by the following
examples and comparative examples, wherein parts are by weight
unless otherwise specified.
EXAMPLES 1-5
Comparative Example 1
[0051] To an NBR (copolymer composed of acrylonitrile 27 wt. %,
1,3-butadiene 67.5 wt. % and methacrylic acid 5.5 wt. %,
polymerization terminator: hydroxylamine sulfate, molecular weight:
200,000) latex, a dispersion of vulcanizer and vulcanization
accelerator (kinds and amounts thereof are shown in Table 1) was
added, and the mixture was thoroughly mixed and dispersed by using
a stirrer to prepare a dip-forming rubber latex composition.
Unvulcanized film was dip-formed from each rubber latex composition
by the following coagulant dipping method.
Making of Film by Coagulant Dipping Method
[0052] A metal mold having a predetermined shape was dipped in an
aqueous calcium nitrate solution having a 35 wt. % concentration
for 10 seconds, and then the mold was dipped in the dip-forming
rubber latex composition having a solid content of 47 wt. % for 5
seconds. The mold having a thus-deposited coating film was dried at
room temperature for 30 minutes.
[0053] Each of the thus-made unvulcanized films was vulcanized
under conditions of 100.degree. C. for 40 minutes or 120.degree. C.
for 40 minutes in an oven to obtain a vulcanized film. The
vulcanized films did not give any offensive smell and had no
color.
[0054] Small modified #2 dumbbell-shaped specimens were cut from
the vulcanized film, and their mechanical strength and other
physical properties were evaluated. The tensile tests were
conducted at a pulling speed of 500 mm/min to measure a tensile
strength (kg/cm.sup.2) and an elongation (%) at break. Surface
luster and occurrence of cracks of the film were visually examined
by naked eye. The results are shown in Table 1. Rating "A" in
surface luster means that the surface luster is good, and rating
"A" in crack occurrence means that crack did not occur.
1 TABLE 1 Additives*1 Vulcanizing conditions 100.degree. C. .times.
120.degree. C. .times. VA*2 40 min. 40 min. Crack Surface Sulfur
Zinc oxide A* B* C* TS*3 El*4 TS*3 El*4 occurrence luster Comp.
Exam. 1 2 2 0.5 -- -- 190 520 230 650 A A Example 1 2 2 -- 0.5 --
215 520 245 630 A A Example 2 2 2 -- 0.5 0.5 175 550 255 620 A A
Example 3 2 2 -- 1 1 285 560 310 600 A A Example 4 1 3 -- 0.5 0.5
210 500 250 520 A A Example 5 3 3 -- 0.5 0.5 120 700 120 740 A A
Comp. Exam.: Comparative Example *1: parts/latex[solid] 100 parts
*2: Vulcanization accelerator *3: Tensile strength (kg/cm.sup.2)
*4: Elongation (%) *A: zinc di-n-butyldithiocarbamate *B: zinc
dibenzyldithiocarbamate *C: 2-mercaptobenzothiazole
[0055] The content of nitrosamine in each of the films vulcanized
at 140.degree. C. for 40 minutes was measured. The results are
shown in Table 2.
[0056] The measurement of the nitrosamine content was carried out
as follows.
[0057] (1) The vulcanized film is washed with a stream of warm
water for 10 minutes and then dried at room temperature.
[0058] (2) 15 g of the dry film is dipped in 85 ml of methanol
under stationary conditions at 90.degree. C. for 8 hours, and then,
is taken-out therefrom.
[0059] (3) The methanol containing the extracted material is
concentrated at 40.degree. C. under a reduced pressure to a volume
of 5 ml.
[0060] (4) The content of nitrosamine in the methanol is measured
by GS/MS-Scan. Previously calibration curves are drawn on standard
materials, i.e., seven nitrosamines including
N-nitrosodimethylamine, which are restricted by regulation.
2 TABLE 2 VA N-nitrosodi-n- Other nitrosamines Sulfur ZnO A B C
butylamine (ppm) restricted by regulations Comp. Exam. 1 2 2 0.5 --
-- 1.68 ND Example 2 2 2 -- 0.5 0.5 ND ND Comp. Exam.: Comparative
Example VA: Vulcanization accelerator ND: Not detected. Detection
limit is 0.1 ppm. A: zinc di-n-butyldithiocarbamate B: zinc
dibenzyldithiocarbamate C: 2-mercaptobenzothiazole
EXAMPLES 6-9
Comparative Example 2
[0061] By the same procedures as employed in Example 1, vulcanized
NBR films were made wherein an NBR (copolymer composed of
acrylonitrile 37 wt. %, 1,3-butadiene 57.5 wt. % and methacrylic
acid 5.5 wt. %, polymerization terminator: hydroxylamine sulfate,
molecular weight: 200,000) latex was used instead of the NBR latex
used in Example 1 with all other conditions remaining the same.
Mechanical properties of the films were measured and the crack
occurrence and surface luster thereof were visually examined. The
results are shown in Table 3.
3 TABLE 3 Additives*1 Vulcanizing conditions 100.degree. C. .times.
120.degree. C. .times. VA*2 40 min. 40 min. Sulfur Zinc oxide A* B*
C* TS*3 El*4 TS*3 El*4 Comp. Exam. 2 2 2 0.5 -- -- 260 500 280 520
Example 6 2 2 -- 0.5 -- 190 500 200 500 Example 7 2 2 -- 0.5 0.5
250 480 330 500 Example 8 1 3 -- 0.5 0.5 265 450 230 420 Example 9
3 3 -- 0.5 0.5 125 600 165 650 Comp. Exam.: Comparative Example *1:
parts/latex[solid] 100 parts *2: Vulcanization accelerator *3:
Tensile strength (kg/cm.sup.2) *4: Elongation (%) A*: zinc
di-n-butyldithiocarbamate B*: zinc dibenzyldithiocarbamate C*:
2-mercaptobenzothiazole
EXAMPLES 10-14
Comparative Examples 3, 4
[0062] In these examples, unsupported globes were made as an
example of the dip-formed rubber articles.
Preparation of Vulcanizer Liquid Dispersion
[0063] The following ingredients were pulverized in a ball mill for
48 hours to prepare a liquid vulcanizer dispersion having a solid
content of 50 wt. %.
4 Parts by weight Colloidal sulfur (Hosoi Kagaku K.K.) 2.0 #1 Zinc
oxide (Seido Kagaku K.K.) 2.0 Vulcanization accelerator A (see
Table 1) 0.5 Titanium oxide (JR 600A supplied by TAYCA K.K.) 0.7
Dispersant (Demol N supplied by Kao Corp.) 0.5 KOH 0.01 Water
5.1
Preparation of Dip-Forming Rubber Latex Composition
[0064] The vulcanizer dispersion prepared by the above-mentioned
method was added to a NBR latex according to the following recipe,
and the mixture was thoroughly stirred to prepare a dip-forming
rubber latex composition.
5 Parts by weight NBR latex* 100 Vulcanizer Dispersion 5.71 *Note,
latex of copolymer composed of acrylonitrile 27 wt. %, butadiene
67.5 wt. % and methacrylic acid 5.5 wt. %, (polymerization
terminator: hydroxylamine sulfate, molecular weight: 200,000)
Preparation of Coagulant Solution
[0065] A coagulant solution was prepared according to the following
recipe.
6 Parts by weight Calcium nitrate 20 Nonionic surface active agent
0.05 (Emulgen 810 supplied by Kao Corp.) Ethyl alcohol 79.95
[0066] A ceramic mold for glove was washed and then dried at
80.degree. C. for 20 minutes. The mold was then dipped in the
coagulant solution for 1 minute, taken out from the coagulant
solution, and dried at 20.degree. C. for 30 minutes, whereby the
coagulant was deposited in the mold.
[0067] Then the coagulant-deposited mold for glove was gently
dipped in the dip-forming rubber latex composition over a period of
5 seconds. When 10 seconds elapsed from the immersion of the entire
mold, the mold was started to take up gently from the rubber latex
composition. The mold was taken up over a period of 5 seconds from
the rubber latex composition, and then, dried at 20.degree. C. for
30 minutes. The dried mold was then subjected to leaching with warm
water at 40.degree. C. for 10 minutes, dried at 80.degree. C. for
40 minutes, and then the deposited rubber coating was vulcanized at
100.degree. C. for 40 minutes in an oven.
[0068] After the mold was cooled, the surface of the deposited
rubber coating was sprinkled with talc and then the rubber coating
of a glove form was separated from the mold to obtain an
unsupported NBR glove. Similarly a deposited rubber coating was
vulcanized at 120.degree. C. for 40 minutes in an oven to obtain an
unsupported NBR glove. Both gloves did not give an offensive smell
and had no color.
[0069] The surface luster and occurrence of cracks in the thus-made
gloves were visually examined by naked eye.
[0070] Small modified #2 dumbbell-shaped specimens were cut from
flat portions of the gloves, and their mechanical strength and
other physical properties were evaluated. The tensile tests were
conducted at a pulling speed of 500 mm/min. The results are shown
in Table 4. Ratings "A" and "B" in surface luster means that the
surface luster is good and poor, respectively, and ratings "A" and
"B" in crack occurrence means that crack did not occur and
occurred, respectively.
[0071] By the same procedures as mentioned above (Example 10),
unsupported gloves were made wherein the kinds and amounts of
sulfur, zinc oxide and vulcanization accelerator were varied as
shown in Table 4 with all other conditions remaining the same
(Examples 11-14). For comparison, an unsupported natural rubber
(NR) glove was made in a similar manner (Comparative Example 4).
The results of evaluation of the respective gloves are shown in
Table 4.
7 TABLE 4 Additives*1 Vulcanizing conditions 100.degree. C. .times.
120.degree. C. .times. VA*2 40 min. 40 min. Crack Surface Sulfur
Zinc oxide A* B* C* TS*3 El*4 TS*3 El*4 occurrence luster C. Ex. 3
NBR 2 2 0.5 -- -- 185 500 210 650 A A Exam. 10 NBR 2 2 -- 0.5 --
205 550 255 610 A A Exam. 11 NBR 2 2 -- 0.5 0.5 180 550 270 620 A A
Exam. 12 NBR 2 2 -- 1.0 1.0 280 550 310 600 A A Exam. 13 NBR 1 3 --
0.5 0.5 220 550 270 530 A A Exam. 14 NBR 3 3 -- 0.5 0.5 135 680 160
730 A A C. Ex. 4 NR 2 2 -- 0.5 0.5 150 800 170 850 B B C. Ex.:
Comparative Example *1: parts/latex[solid] 100 parts *2:
Vulcanization accelerator *3: Tensile strength (kg/cm.sup.2) *4:
Elongation (%) *A: zinc di-n-butyldithiocarbamate *B: zinc
dibenzyldithiocarbamate *C: 2-mercaptobenzothiazole
Industrial Applicability
[0072] Rubber articles dip-formed from the vulcanizable unsaturated
nitrile-conjugated diene copolymer rubber latex composition of the
present invention have no crack occurrence, excellent surface
luster, and good vulcanization properties which compare with those
of rubber articles made with the conventional dithiocarbamic acid
compound vulcanization accelerator. The dip-formed rubber articles
do not contain a nitrosamine and give no offensive smell and have
no color.
[0073] Therefore, as specific examples of the dip-formed rubber
articles, there can be mentioned medical rubber articles such as
gloves for operation, or medical examination or detection, a
balloon sac and a catheter; a nipple; gloves for home use; gloves
for industrial use; and balloons.
* * * * *