U.S. patent application number 11/882742 was filed with the patent office on 2008-10-16 for dip-forming latex, dip-forming composition and dip-formed article.
Invention is credited to Shunjin Aihara, Kazumi Kodama, Hisanori Ota.
Application Number | 20080255314 11/882742 |
Document ID | / |
Family ID | 27767758 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080255314 |
Kind Code |
A1 |
Ota; Hisanori ; et
al. |
October 16, 2008 |
Dip-forming latex, dip-forming composition and dip-formed
article
Abstract
A dip-forming latex obtained by copolymerization of (a) 50-89.5
weight parts of a conjugated diene monomer, (b) 10-40 weight parts
of an ethylenically unsaturated nitrile monomer, (c) 0.5-10 weight
parts of an ethylenically unsaturated acid monomer and (d) 0-20
weight parts of other copolymerizable ethylenically unsaturated
monomer (the total of these monomers is 100 weight parts), wherein
the copolymerization is initiated with a monomer mixture comprising
at least 80 wt. % of (a), at least 50 wt. % of (b), 10-90 wt. % of
(c) and least 80 wt. % of (d), and thereafter, the remainders of
monomers are added to a polymerization system to continue
copolymerization. This latex gives a dip-formed article exhibiting
good softness of touch, high tensile strength and good retention of
close fittingness.
Inventors: |
Ota; Hisanori; (Tokyo,
JP) ; Aihara; Shunjin; (Tokyo, JP) ; Kodama;
Kazumi; (Tokyo, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
27767758 |
Appl. No.: |
11/882742 |
Filed: |
August 3, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10505734 |
Aug 26, 2004 |
7273906 |
|
|
11882742 |
|
|
|
|
Current U.S.
Class: |
525/343 ;
525/374; 526/317.1; 526/335 |
Current CPC
Class: |
C08F 2/22 20130101; C08L
13/02 20130101; C08F 236/12 20130101; C08F 236/12 20130101; A61B
42/00 20160201 |
Class at
Publication: |
525/343 ;
526/335; 526/317.1; 525/374 |
International
Class: |
C08F 236/08 20060101
C08F236/08; C08F 236/06 20060101 C08F236/06; C08F 220/42 20060101
C08F220/42; C08F 220/04 20060101 C08F220/04 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2002 |
JP |
2002-053491 |
Mar 19, 2002 |
JP |
2002-075326 |
May 17, 2002 |
JP |
2002-142621 |
Claims
1. A dip-forming composition comprising a dip-forming latex
obtained by copolymerization of 50 to 89.5 parts by weight of a
conjugated diene monomer, 10 to 40 parts by weight of an
ethylenically unsaturated nitrile monomer, 0.5 to 10 parts by
weight of an ethylenically unsaturated acid monomer and 0 to 20
parts by weight of other copolymerizable ethylenically unsaturated
monomer, provided that the total of these monomers is 100 parts by
weight, wherein said copolymerization is initiated with a monomer
mixture comprising at least 80% by weight of the amount of
conjugated diene monomer used, at least 50% by weight of the amount
of ethylenically unsaturated nitrile monomer used, 10 to 90% by
weight of the amount of ethylenically unsaturated acid monomer used
and at least 80% by weight of the amount of other copolymerizable
ethylenically unsaturated monomer used, and thereafter, the
remainders of monomers are added to a polymerization system to
continue copolymerization.
2. The dip-forming composition according to claim 1, which is
obtained by copolymerization of 55 to 84 parts by weight of a
conjugated diene monomer, 15 to 36 parts by weight of an
ethylenically unsaturated nitrile monomer, 1 to 9 parts by weight
of an ethylenically unsaturated acid monomer and 0 to 15 parts by
weight of other copolymerizable ethylenically unsaturated monomer,
provided that the total of these monomers is 100 parts by
weight.
3. The dip-forming composition according to claim 1, which is
obtained by copolymerization of 65 to 81 parts by weight of a
conjugated diene monomer, 18 to 27 parts by weight of an
ethylenically unsaturated nitrile monomer, 1 to 8 parts by weight
of an ethylenically unsaturated acid monomer and 0 to 10 parts by
weight of other copolymerizable ethylenically unsaturated monomer,
provided that the total of these monomers is 100 parts by
weight.
4. The dip-forming composition according to claim 1, wherein the
copolymerization is initiated with a monomer mixture comprising at
least 80% by weight of the amount of conjugated diene monomer used,
at least 80% by weight of the amount of ethylenically unsaturated
nitrile monomer used, 10 to 90% by weight of the amount of
ethylenically unsaturated acid monomer used and at least 80% by
weight of the amount of other copolymerizable ethylenically
unsaturated monomer used, and thereafter, the remainders of
monomers are added to a polymerization system to continue
copolymerization.
5. The dip-forming composition according to claim 1, wherein the
copolymerization is initiated with a monomer mixture comprising at
least 90% by weight of the amount of conjugated diene monomer used,
at least 90% by weight of the amount of ethylenically unsaturated
nitrile monomer used, 30 to 85% by weight of the amount of
ethylenically unsaturated acid monomer used and at least 90% by
weight of the amount of other copolymerizable ethylenically
unsaturated monomer used, and thereafter, the remainders of
monomers are added to a polymerization system to continue
copolymerization.
6. The dip-forming composition according to claim 4, wherein, after
the copolymerization of the monomer mixture is initiated, the
remainder of ethylenically unsaturated acid monomer is added while
the polymerization conversion of the total monomers added is within
a range of 5 to 90%, and the remainders of conjugated diene
monomer, ethylenically unsaturated nitrile monomer and other
copolymerizable ethylenically unsaturated monomer are added at any
time before the termination of copolymerization.
7. The dip-forming composition according to claim 4, wherein, after
the copolymerization of the monomer mixture is initiated, the
remainder of ethylenically unsaturated acid monomer is added while
the polymerization conversion of the total monomers added is within
a range of 20 to 80%, and the remainders of conjugated diene
monomer, ethylenically unsaturated nitrile monomer and other
copolymerizable ethylenically unsaturated monomer are added at any
time before the termination of copolymerization.
8. The dip-forming composition according to claim 1, wherein the
copolymerization is initiated with a monomer mixture comprising at
least 80% by weight of the amount of conjugated diene monomer used,
50 to 90% by weight of the amount of ethylenically unsaturated
nitrile monomer used, 40 to 90% by weight of the amount of
ethylenically unsaturated acid monomer used and at least 80% by
weight of the amount of other copolymerizable ethylenically
unsaturated monomer used, and thereafter, the remainders of
ethylenically unsaturated nitrile monomer and ethylenically
unsaturated acid monomer are added while the polymerization
conversion of the total monomers added is within a range of 5 to
95%, and the remainders of conjugated diene monomer and other
copolymerizable ethylenically unsaturated monomer are added at any
time before the termination of copolymerization.
9. The dip-forming composition according to claim 8, wherein the
copolymerization is initiated with a monomer mixture comprising at
least 90% by weight of the amount of conjugated diene monomer used,
55 to 85% by weight of the amount of ethylenically unsaturated
nitrile monomer used, 50 to 85% by weight of the amount of
ethylenically unsaturated acid monomer used and at least 90% by
weight of the amount of other copolymerizable ethylenically
unsaturated monomer used.
10. The dip-forming composition according to claim 8, wherein,
after the copolymerization of the monomer mixture is initiated, the
remainders of ethylenically unsaturated nitrile monomer and
ethylenically unsaturated acid monomer are added while the
polymerization conversion of the total monomers added is within a
range of 10 to 90%, and the remainders of conjugated diene monomer
and other copolymerizable ethylenically unsaturated monomer are
added at any time before the termination of copolymerization.
11. The dip-forming composition according to claims 8, wherein,
after the copolymerization of the monomer mixture is initiated, the
remainder of ethylenically unsaturated nitrile monomer is added
while the polymerization conversion of the ethylenically
unsaturated nitrile monomer is within a range of 40 to 95%.
12. The dip-forming composition according to claim 8, wherein,
after the copolymerization of the monomer mixture is initiated, the
remainder of ethylenically unsaturated acid monomer is added while
the polymerization conversion of the total monomers added is within
a range of 20 to 80%.
13. The dip-forming composition according to claim 8, wherein,
after the copolymerization of the monomer mixture is initiated, the
remainder of ethylenically unsaturated nitrile monomer is added at
two or more times.
14. The dip-forming composition according to claim 1, wherein the
conjugated diene monomer is at least one monomer selected from the
group consisting of 1,3-butadiene and isoprene.
15. The dip-forming composition according to claim 1, wherein the
ethylenically unsaturated nitrile monomer is at least one monomer
selected from the group consisting of acrylonitrile and
methacrylonitrile.
16. The dip-forming composition according to claim 1, wherein the
ethylenically unsaturated acid monomer is at least one monomer
selected from the group consisting of ethylenically unsaturated
carboxylic acid monomers.
17. The dip-forming composition according to claim 1, which further
comprises a vulcanizer selected from the group consisting of sulfur
and polyamines, and a vulcanization accelerator.
18. A dip-formed article made by dip-forming the dip-forming
composition as claimed in claim 1.
19. The dip-formed article according to claim 18, which has a
tensile stress at 300% elongation of not larger than 2.5 MPa, a
tensile strength of at least 15 MPa, and a tensile stress retention
of at least 70% as measured when 6 minutes elapses from the time of
100% elongation.
20. The dip-formed article according to claim 19, which has a
swelling degree in methyl ethyl ketone of not larger than 200%.
21. The dip-formed article according to claim 19, which is a glove.
Description
[0001] This application is a Divisional of co-pending application
Ser. No. 10/505,734 filed on Aug. 26, 2004, and for which priority
is claimed under 35 U.S.C. .sctn. 120; and this application claims
priority of Application No. 2002-053491, 2002-075326, and
2002-142621 filed in Japan on Feb. 28, 2002, Mar. 19, 2002, and May
17, 2002 respectively under 35 U.S.C .sctn. 119; the entire
contents of all are hereby incorporated by reference.
TECHNICAL FIELD
[0002] This invention relates to a dip-forming latex, a dip-forming
composition, and a dip-formed article. More particularly, it
relates to a dip-forming latex made by copolymerization of a
conjugated diene monomer, an ethylenically unsaturated monomer and
an ethylenically unsaturated acid monomer; a dip-forming
composition comprising the dip-forming latex; and a dip-formed
article made by dip-forming the dip-forming composition.
[0003] The dip-formed article exhibits good softness of touch, high
tensile strength and preferably good retention of tight fitness,
and is useful as, for example, gloves.
BACKGROUND ART
[0004] Rubber gloves are widely used for household uses, industrial
uses in, for example, food industry and electronic part industry,
and surgical and other medical uses. It is generally required for
rubber gloves that (1) they have good softness of touch and are
well-fitting and comfortable to wear, namely, they are capable of
being easily stretched in conformity with movement of fingers so
that fatigue does not itself felt even when they are worn for long
hours, (2) they are not easily broken, namely, they have a high
tensile strength, and (3) they exhibit good retention of close
fittingness, namely, they are not easily slackened nor crumpled
when fingers are moved, and they keep a well-fitted state for a
long time.
[0005] Rubber gloves made by dip-forming natural rubber latex have
widely been used, but, allergies to natural rubber sometimes cause
rashes or itching due to protein contained in a slight amount in
natural rubber.
[0006] Rubber gloves made by dip-forming a synthetic rubber latex,
for example, an acrylonitrile-butadiene copolymer latex, are known.
Allergy does not develop to rubber gloves made from an
acrylonitrile-butadiene copolymer latex, but these gloves exhibit
poor balance between the softness of touch or comfortable
fittingness, and the tensile strength.
[0007] For example, U.S. Pat. No. 5,014,362 discloses gloves
dip-formed from a composition comprising a carboxyl-modified
acrylonitrile-butadiene copolymer latex having incorporated therein
minor amounts of zinc oxide, sulfur and a vulcanization
accelerator, which are characterized as exhibiting a tensile stress
retention of almost zero % as expressed by the formula of
(A/B).times.100 wherein B is tensile stress as measured immediately
after 100% elongation and A is tensile stress as measured when 6
minutes elapses from the measurement of B. These gloves are easily
stretched, well-fitting and comfortable to wear, but their
retention of close fittingness is poor.
[0008] International publication WO 97/48765 discloses gloves
dip-formed from a composition comprising a carboxyl-modified
acrylonitrile-butadiene copolymer latex, ammonium casein, sulfur
and a vulcanization accelerator, and not containing zinc oxide.
These gloves have high tensile strength, but they are not easily
stretched and do not exhibit comfortable fittingness, and their
retention of close fittingness is poor.
[0009] U.S. Pat. No. 5,910,533 discloses a dip-formed article made
from a copolymer latex prepared by copolymerization of 80 to 99% by
weight of a conjugated diene monomer, 0 to 10% by weight of an
unsaturated acid monomer and 0 to 20% by weight of other
unsaturated monomers such as acrylonitrile and methyl methacrylate.
As a specific example of the copolymer latex, a copolymer latex
comprised of 87 weight parts of butadiene, 10 parts of
acrylonitrile and 3 weight parts of methacrylic acid is mentioned.
Gloves made from this copolymer latex can easily be stretched, have
good softness of touch and are comfortable to wear, but the tensile
strength is low and they are liable to be broken during
wearing.
[0010] International publication WO 00/21451 discloses gloves made
by dip-forming a composition comprising an acrylonitrile-butadiene
copolymer latex containing a specific amount of a carboxyl group,
an extremely slight amount of zinc oxide, sulfur and a
vulcanization accelerator, which are characterized as exhibiting a
tensile stress retention in a range of 50 to 70%. These gloves
exhibit good retention of close fittingness, but the balance
between the softness of touch or comfortable fittingness and the
tensile strength is occasionally poor.
DISCLOSURE OF THE INVENTION
[0011] In view of the foregoing, an object of the present invention
is to provide a dip-formed article having good softness of touch
and comfortable fittingness, and high tensile strength.
[0012] Another object of the present invention is to provide a
dip-formed article having good softness of touch, comfortable
fittingness, high tensile strength, and an enhanced retention of
close fittingness.
[0013] Other objects of the present invention are to provide a
dip-forming composition giving the above-mentioned dip-formed
article; and a dip-forming latex used for the dip-forming
composition.
[0014] In one aspect of the present invention, there is provided a
dip-forming latex obtained by copolymerization of 50 to 89.5 parts
by weight of a conjugated diene monomer, 10 to 40 parts by weight
of an ethylenically unsaturated nitrile monomer, 0.5 to 10 parts by
weight of an ethylenically unsaturated acid monomer and 0 to 20
parts by weight of other copolymerizable ethylenically unsaturated
monomer, provided that the total of these monomers is 100 parts by
weight, wherein said copolymerization is initiated with a monomer
mixture comprising at least 80% by weight of the amount of
conjugated diene monomer used, at least 50% by weight of the amount
of ethylenically unsaturated nitrile monomer used, 10 to 90% by
weight of the amount of ethylenically unsaturated acid monomer used
and at least 80% by weight of the amount of other copolymerizable
ethylenically unsaturated monomer used, and thereafter, the
remainders of monomers are added to a polymerization system to
continue copolymerization.
[0015] In another aspect of the present invention, there is
provided a dip-forming composition comprising the above-mentioned
dip-forming latex.
[0016] In another aspect of the present invention, there is
provided a dip-formed article made by dip-forming the
above-mentioned dip-forming composition.
BEST MODE FOR CARRYING OUT THE INVENTION
[0017] The dip-forming latex of the present invention is obtained
by copolymerization of 50 to 89.5 parts by weight of a conjugated
diene monomer, 10 to 40 parts by weight of an ethylenically
unsaturated nitrile monomer, 0.5 to 10 parts by weight of an
ethylenically unsaturated acid monomer and 0 to 20 parts by weight
of other copolymerizable ethylenically unsaturated monomer,
provided that the total of these monomers is 100 parts by weight.
The copolymerization is carried out in a manner such that the
copolymerization is initiated with a monomer mixture comprising at
least 80% by weight of the amount of conjugated diene monomer used,
at least 50% by weight of the amount of ethylenically unsaturated
nitrile monomer used, 10 to 90% by weight of the amount of
ethylenically unsaturated acid monomer used and at least 80% by
weight of the amount of other copolymerizable ethylenically
unsaturated monomer used, and thereafter, the remainders of
monomers are added to a polymerization system to continue
copolymerization.
[0018] In a first preferable embodiment of the dip-forming latex,
the dip-forming latex is obtained by a copolymerization procedure
such that the copolymerization is initiated with a monomer mixture
comprising at least 80% by weight of the amount of conjugated diene
monomer used, at least 80% by weight of the amount of ethylenically
unsaturated nitrile monomer used, 10 to 90% by weight of the amount
of ethylenically unsaturated acid monomer used and at least 80% by
weight of the amount of other copolymerizable ethylenically
unsaturated monomer used, and thereafter, the remainders of
monomers are added to a polymerization system to continue
copolymerization. Preferably, after the copolymerization of the
monomer mixture is initiated, the remainder of ethylenically
unsaturated acid monomer is added while the polymerization
conversion of the total monomers added is within a range of 5 to
90%, and the remainders of conjugated diene monomer, ethylenically
unsaturated nitrile monomer and other copolymerizable ethylenically
unsaturated monomer are added at any time before the termination of
copolymerization. This first embodiment of the dip-forming latex is
hereinafter referred to "first dip-forming latex" when appropriate.
The first dip-forming latex gives a dip-formed article having good
softness of touch, comfortable fittingness, and high tensile
strength.
[0019] In a second preferable embodiment of the dip-forming latex,
the dip-forming latex is obtained by a copolymerization procedure
such that the copolymerization is initiated with a monomer mixture
comprising at least 80% by weight of the amount of conjugated diene
monomer used, 50 to 90% by weight of the amount of ethylenically
unsaturated nitrile monomer used, 40 to 90% by weight of the amount
of ethylenically unsaturated acid monomer used and at least 80% by
weight of the amount of other copolymerizable ethylenically
unsaturated monomer used, and thereafter, the remainders of
ethylenically unsaturated nitrile monomer and ethylenically
unsaturated acid monomer are added while the polymerization
conversion of the total monomers added is within a range of 5 to
95%, and the remainders of conjugated diene monomer and other
copolymerizable ethylenically unsaturated monomer are added at any
time before the termination of copolymerization. This second
embodiment of the dip-forming latex is hereinafter referred to
"second dip-forming latex" when appropriate. The second dip-forming
latex gives a dip-formed article having an enhanced retention of
close fittingness, as well as good softness of touch, comfortable
fittingness and high tensile strength.
[0020] By the term "the polymerization conversion of the total
monomers added" as used in this specification, we mean the ratio
(A/B) of the amount (A) of total monomers which have been converted
to a copolymer to the amount (B) of total monomers which have been
added to a polymerization system. For example, in the case when,
after the initiation of polymerization of an initially charged
monomer mixture, a first part of the remainder of a monomer is
added to a polymerization system, the above-mentioned term as of
the addition of the first part of monomer means the polymerization
conversion of the monomers in the initially charged monomer
mixture. In the case when, after the initiation of polymerization
of an initially charged monomer mixture and further after addition
of the first part of the remainder of a monomer, a second part of
the remainder thereof is added to a polymerization system, the
above-mentioned term as of the addition of the second part of
monomer means the polymerization conversion of the sum of the
monomers in the initially charged monomer mixture and the first
part of the remainder of monomer.
[0021] The amount (A) of total monomers which have been converted
to a copolymer is determined, for example, by calculation thereof
by deducting the amount of total unreacted monomers from the amount
(B) of total monomers which have been added to a polymerization
system.
[0022] The conjugated monomer includes, for example, 1,3-butadiene,
isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene,
1,3-pentadiene and chloroprene. Of these, 1,3-butadiene and
isoprene are preferable. 1,3-Butadiene is especially preferable.
These conjugated diene monomers may be used either alone or as a
combination of at least two thereof.
[0023] The amount of conjugated diene monomer is in the range of 50
to 89.5 parts by weight, preferably 55 to 84 parts by weight, more
preferably 65 to 81 parts by weight, and especially preferably 70
to 80 parts by weight, based on 100 parts by weight of the total
amount of monomers. If the amount of conjugated diene monomer is
too small, the dip-formed article is not satisfactory in softness
of touch and comfortable fittingness. In contrast, if the amount of
conjugated diene monomer is too large, the dip-formed article has
low tensile strength.
[0024] As specific examples of the ethylenically unsaturated
nitrile monomer, there can be mentioned acrylonitrile,
methacrylonitrile, fumaronitrile, .alpha.-chloroacrylonitrile and
.alpha.-cyanoethylacrylonitrile. Of these, acrylonitrile and
methacrylonitrile are preferable. Acrylonitrile is especially
preferable. The ethylenically unsaturated nitrile monomer may be
used either alone or as a combination of at least two thereof.
[0025] The amount of ethylenically unsaturated nitrile monomer is
in the range of 10 to 40 parts by weight, preferably 15 to 36 parts
by weight, more preferably 18 to 27 parts by weight, and especially
preferably 18 to 24 parts by weight, based on 100 parts by weight
of the total amount of monomers. If the amount of ethylenically
unsaturated nitrile monomer is too small, the dip-formed article
has low tensile strength. In contrast, if the amount of
ethylenically unsaturated nitrile monomer is too large, the
dip-formed article is not satisfactory in softness of touch and
comfortable fittingness.
[0026] The ethylenically unsaturated acid monomer includes
ethylenically unsaturated monomers having an acidic group such as a
carboxyl group, a sulfonic acid group or an acid anhydride group.
As specific examples of the ethylenically unsaturated acid monomer,
there can be mentioned ethylenically unsaturated monocarboxylic
acid monomers such as acrylic acid and methacrylic acid;
ethylenically unsaturated polycarboxylic acid monomers such as
itaconic acid, maleic acid and fumaric acid; ethylenically
unsaturated polycarboxylic acid anhydride monomers such as maleic
anhydride and citraconic anhydride; ethylenically unsaturated
sulfonic acid monomers such as styrenesulfonic acid; and
ethylenically unsaturated polycarboxylic acid partial ester
monomers such as monobutyl fumarate, monobutyl maleate and
mono-2-hydroxypropyl maleate. Of these, ethylenically unsaturated
carboxylic acid monomers are preferable. Ethylenically unsaturated
monocarboxylic acid monomers are more preferable. Methacrylic acid
is especially preferable. These ethylenically unsaturated acid
monomers may be used in the form of a salt such as an alkali metal
salt or an ammonium salt. The ethylenically unsaturated acid
monomers may be used either alone or as a combination of at least
two thereof.
[0027] The amount of ethylenically unsaturated acid monomer is in
the range of 0.5 to 10 parts by weight, preferably 1 to 9 parts by
weight, more preferably 1 to 8 parts by weight, and especially
preferably 2 to 6 parts by weight, based on 100 parts by weight of
the total amount of monomers. If the amount of ethylenically
unsaturated acid monomer is too small, the dip-formed article has
low tensile strength. In contrast, if the amount of ethylenically
unsaturated acid monomer is too large, the dip-formed article is
not satisfactory in softness of touch, comfortable fittingness, and
retention of close fittingness.
[0028] As specific examples of the other copolymerizable
ethylenically unsaturated monomers which are optionally used, there
can be mentioned vinyl aromatic monomers such as styrene,
alkylstyrenes and vinyl naphthalene; fluoroalkyl vinyl ether
monomers such as fluoroethyl vinyl ether; ethylenically unsaturated
amide monomers such as acrylamide, N-methylolacrylamide,
N,N-dimethylolacrylamide, N-methoxymethylacrylamide,
N-propoxymethylacrylamide, methacrylamide,
N-methylolmethacrylamide, N,N-dimethylolmethacrylamide,
N-methoxymethyl-methacrylamide and N-propoxymethylmethacrylamide;
ethylenically unsaturated carboxylic acid ester monomers such as
methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl
acrylate, trifluoroethyl acrylate, tetrafluoropropyl acrylate,
methoxymethyl acrylate, ethoxyethyl acrylate, methoxyethoxyethyl
acrylate, cyanomethyl acrylate, 2-cyanoethyl acrylate,
1-cyanopropyl acrylate, 2-ethyl-6-cyanohexyl acrylate,
3-cyanopropyl acrylate, hydroxyethyl acrylate, hydroxypropyl
acrylate, glycidyl acrylate, dimethylaminoethyl acrylate, methyl
methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl
methacrylate, trifluoroethyl methacrylate, tetrafluoropropyl
methacrylate, methoxymethyl methacrylate, ethoxyethyl methacrylate,
methoxyethoxyethyl methacrylate, cyanomethyl methacrylate,
2-cyanoethyl methacrylate, 1-cyanopropyl methacryalte,
2-ethyl-6-cyanohexyl methacrylate, 3-cyanopropyl methacrylate,
hydroxyethyl methacrylate, hydroxypropyl methacrylate, glycidyl
methacrylate, dimethylaminoethyl methacrylate, dibutyl maleate,
dibutyl fumarate and diethyl maleate; and crosslinking monomers
such as divinylbenzene, polyethylene glycol diacrylate,
polyethylene glycol dimethacrylate, polypropylene glycol
diacrylate, polypropylene glycol dimethacrylate, trimethylolpropane
triacrylate, trimethylolpropane trimethacrylate, pentaerithritol
acrylate and pentaerithritol methacrylate. These optional
ethylenically unsaturated monomers may be used either alone or as a
combination of at least two thereof.
[0029] The amount of the optional ethylenically unsaturated monomer
is not larger than 20 parts by weight, preferably not larger than
15 parts by weight, more preferably not larger than 10 parts by
weight, and especially preferably not larger than 8 parts by
weight, based on 100 parts by weight of the total amount of
monomers. If the amount of the optional ethylenically unsaturated
monomer is too large, the balance between the softness of touch and
comfortable fittingness, and the tensile strength is poor.
[0030] The dip-forming latex of the present invention is obtained
by copolymerization of the above-mentioned monomers, preferably by
an emulsion copolymerization procedure.
[0031] In the copolymerization for the production of dip-forming
latex, the time at which the monomers are added to a polymerization
system is important. That is, the copolymerization is initiated
with a monomer mixture comprising at least 80% by weight of the
amount of conjugated diene monomer used, at least 50% by weight of
the amount of ethylenically unsaturated nitrile monomer used, 10 to
90% by weight of the amount of ethylenically unsaturated acid
monomer used and at least 80% by weight of the amount of other
copolymerizable ethylenically unsaturated monomer used, and
thereafter, the remainders of monomers are added to a
polymerization system to continue copolymerization.
[0032] For the production of the above-mentioned first dip-forming
latex, the copolymerization is initiated with a monomer mixture
comprising at least 80% by weight of the amount of conjugated diene
monomer used, at least 80% by weight of the amount of ethylenically
unsaturated nitrile monomer used, 10 to 90% by weight of the amount
of ethylenically unsaturated acid monomer used and at least 80% by
weight of the amount of other copolymerizable ethylenically
unsaturated monomer used, and thereafter, the remainders of
monomers are added to a polymerization system to continue
copolymerization. Preferably, after the copolymerization of the
monomer mixture is initiated, the remainder of ethylenically
unsaturated acid monomer is added while the polymerization
conversion of the total monomers added is within a range of 5 to
90%, and the remainders of conjugated diene monomer, ethylenically
unsaturated nitrile monomer and other copolymerizable ethylenically
unsaturated monomer are added at any time before the termination of
copolymerization.
[0033] For the production of the above-mentioned second dip-forming
latex, the copolymerization is initiated with a monomer mixture
comprising at least 80% by weight of the amount of conjugated diene
monomer used, 50 to 90% by weight of the amount of ethylenically
unsaturated nitrile monomer used, 40 to 90% by weight of the amount
of ethylenically unsaturated acid monomer used and at least 80% by
weight of the amount of other copolymerizable ethylenically
unsaturated monomer used, and thereafter, the remainders of
ethylenically unsaturated nitrile monomer and ethylenically
unsaturated acid monomer are added while the polymerization
conversion of the total monomers added is within a range of 5 to
95%, and the remainders of conjugated diene monomer and other
copolymerizable ethylenically unsaturated monomer are added at any
time before the termination of copolymerization.
[0034] The ethylenically unsaturated nitrile monomer is initially
added in a polymerization vessel in an amount of at least 50% by
weight of its total amount used for polymerization, and, after the
initiation of polymerization, the remainder thereof is added to
continue copolymerization.
[0035] More specifically, for the production of the first
dip-forming latex, the ethylenically unsaturated nitrile monomer is
initially added in a polymerization vessel preferably in an amount
of at least 80% by weight, more preferably at least 90% and
especially preferably 100% of its total amount used for
polymerization, and, after the initiation of polymerization, the
remainder thereof is added to continue copolymerization.
[0036] For the production of the second dip-forming latex, the
ethylenically unsaturated nitrile monomer is initially added in a
polymerization vessel preferably in an amount of 50 to 90% by
weight, more preferably 55 to 85% by weight and especially
preferably 60 to 85% by weight of its total amount used for
polymerization. If the amount of ethylenically unsaturated nitrile
monomer initially added in a polymerization vessel is too small,
the dip-formed article has low tensile strength. In contrast, if
the amount of ethylenically unsaturated nitrile monomer initially
added is too large, the balance among the softness of touch,
comfortable fittingness, tensile strength and retention of close
fittingness tends to be poor.
[0037] After the initiation of polymerization for the production of
the second dip-forming latex, the remainder of ethylenically
unsaturated nitrile monomer is added while the polymerization
conversion of the total monomers added is preferably within a range
of 5 to 95%, more preferably 10 to 90% by weight and especially
preferably 20 to 90% by weight. After the initiation of
polymerization, if the remainder of ethylenically unsaturated
nitrile monomer is added while the polymerization conversion of the
total monomers added is too small, the dip-formed article tends to
have poor softness of touch, poor fittingness and low tensile
strength. In contrast, if the remainder of ethylenically
unsaturated nitrile monomer is added while the polymerization
conversion of the total monomers added is too large, the dip-formed
article tends to have low tensile strength. The remainder of
ethylenically unsaturated nitrile monomer is added preferably while
the polymerization conversion of the ethylenically unsaturated
nitrile monomer added is in the range of 40 to 95% by weight, more
preferably 45 to 92% by weight and especially preferably 45 to 85%
by weight for enhancement of tensile strength.
[0038] After the initiation of polymerization, the remainder of
ethylenically unsaturated nitrile monomer is added preferably at
two or more times. In this case, the amount of ethylenically
unsaturated nitrile monomer added in each time is preferably equal
to each other for more enhancement of balance between the softness
of touch and comfortable fittingness, and the tensile strength. The
number of times for the addition of ethylenically unsaturated
nitrile monomer is not particularly limited, and may be infinite.
That is, the remainder of ethylenically unsaturated nitrile monomer
can be continuously added.
[0039] The ethylenically unsaturated acid monomer is initially
added in a polymerization vessel in an amount of 10 to 90% by
weight of its total amount used for polymerization, and, after the
initiation of polymerization, the remainder thereof is added to
continue copolymerization.
[0040] More specifically, for the production of the first
dip-forming latex, the ethylenically unsaturated acid monomer is
initially added in a polymerization vessel in an amount of 10 to
90% by weight, preferably 30 to 85% by weight and more preferably
50 to 80% by weight of its total amount used for polymerization,
and, after the initiation of polymerization, the remainder thereof
is added to continue copolymerization. If the amount of
ethylenically unsaturated acid monomer initially added is too
small, the dip-formed article has low tensile strength. In
contrast, if the amount thereof initially added is too large, the
dip-formed article is not satisfactory in softness of touch,
comfortable fittingness and tensile strength.
[0041] After the initiation of polymerization for the production of
the first dip-forming latex, the remainder of ethylenically
unsaturated acid monomer is added while the polymerization
conversion of the total monomers added is preferably within a range
of 5 to 90%, more preferably 20 to 80% by weight and especially
preferably 40 to 80% by weight. When the remainder of ethylenically
unsaturated monomer is added while the polymerization conversion of
the total monomers added is within this range, the dip-formed
article has well balanced softness of touch, comfortable
fittingness and tensile strength. The remainder of ethylenically
unsaturated acid monomer may be added either in one lot, or in two
or more lots. It can also be added in a continuous manner. The
addition in one lot is preferable.
[0042] For the production of the second dip-forming latex, the
ethylenically unsaturated acid monomer is initially added in a
polymerization vessel in an amount of 40 to 90% by weight,
preferably 50 to 85% by weight and more preferably 60 to 80% by
weight of its total amount used for polymerization. If the amount
of ethylenically unsaturated acid monomer initially added in a
polymerization vessel is too small, the dip-formed article has poor
tensile strength and poor retention of tight fitness. In contrast,
if the amount of ethylenically unsaturated acid monomer initially
added is too large, the dip-formed article is not satisfactory in
softness of touch, comfortable fittingness and tensile
strength.
[0043] After the initiation of polymerization for the production of
the second dip-forming latex, the remainder of ethylenically
unsaturated acid monomer is added while the polymerization
conversion of the total monomers added is within a range of 5 to
95% by weight, preferably 10 to 90% by weight, more preferably 20
to 80% by weight and especially preferably 40 to 70% by weight. If
the remainder of ethylenically unsaturated acid monomer is added
while the polymerization conversion of the total monomers added is
within this range, the dip-formed article has well-balanced and
good softness of touch, comfortable fittingness and tensile
strength. The remainder of ethylenically unsaturated acid monomer
may be added either in one lot, or in two or more lots. It can also
be added in a continuous manner. The addition in one lot is
preferable.
[0044] The conjugated diene monomer is initially added in a
polymerization vessel in an amount of at least 80% by weight,
preferably at least 90% by weight of its total amount used for
polymerization, and, after the initiation of polymerization, the
remainder thereof is added to continue copolymerization.
Preferably, the entire amount of conjugated diene monomer used for
polymerization is initially added before the initiation of
polymerization.
[0045] The optional other copolymerizable ethylenically unsaturated
monomer is initially added in a polymerization vessel in an amount
of at least 80% by weight, preferably at least 90% by weight of its
total amount used for polymerization, and, after the initiation of
polymerization, the remainder thereof is added to continue
copolymerization. Preferably, the entire amount of the monomer used
for polymerization is initially added before the initiation of
polymerization.
[0046] The procedures for copolymerization may be conventional
provided that the time at which the monomers are added to a
polymerization system is satisfied with the above requirements. For
example, in the case of an emulsion polymerization, a monomer
mixture is polymerized by using a polymerization initiator in the
presence of water and an emulsifier, and, when the polymerization
conversion reaches a predetermined value, a polymerization stopper
is added to terminate polymerization.
[0047] The emulsifier used for emulsion copolymerization is not
particularly limited, and, as specific examples thereof, there can
be mentioned nonionic emulsifiers such as polyoxyethylenealkyl
ethers, polyoxyethylene alkyl phenol ethers, polyoxyethylene alkyl
esters and polyoxyethylene sorbitan alkyl esters; anionic
emulsifiers such as salts of fatty acids, for example, myristic
acid, palmitic acid, oleic acid and linolenic acid,
alkylbenzenesulfonic acid salts, for example, sodium
dodecylbenzenesulfonate, and higher alcohol sulfuric acid ester
salts and alkylsulfosuccinic acid salts; cationic emulsifiers such
as alkyltrimethylammonium chloride, dialkylammonium chloride and
benzylammonium chloride; and copolymerizable emulsifiers such as
sulfoesters of .alpha., .beta.-unsaturated carboxylic acids,
sulfate esters of .alpha., .beta.-unsaturated carboxylic acids and
sulfoalkyl aryl ethers. Of these, anionic emulsifiers are
preferable. These emulsifiers may be used either alone or as a
combination of at least two thereof. The amount of emulsifier is in
the range of 0.1 to 10 parts by weight based on 100 parts by weight
of the total monomers added.
[0048] The amount of water used for emulsion copolymerization is in
the range of 80 to 500 parts by weight, preferably 100 to 300 parts
by weight, based on 100 parts by weight of the total monomers
added.
[0049] The polymerization initiator used is not particularly
limited, and, as specific examples thereof, there can be mentioned
inorganic peroxides such as sodium persulfate, potassium
persulfate, ammonium persulfate, potassium perphosphate and
hydrogen peroxide; organic peroxides such as diisopropylbenzene
hydroperoxide, cumene hydroperoxide, tert-butyl hydroperoxide,
1,1,3,3-tetramethylbutyl hydroperoxide,
2,5-dimethylhexane-2,5-dihydroperoxide, di-tert-butyl
hydroperoxide, di-.alpha.-cumyl peroxide, acetyl peroxide,
isobutyryl peroxide and benzoyl peroxide; and azo compounds such as
azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile and methyl
azobisisobutyrate. These polymerization initiators may be used
either alone or as a combination of at least two thereof. Peroxide
polymerization initiators are preferable because a latex can be
stably produced and a dip-formed article having enhanced softness
of touch and high tensile strength can be obtained from the latex.
The amount of polymerization initiator is preferably in the range
of 0.01 to 1.0 part by weight based on 100 parts by weight of the
total monomers added.
[0050] The peroxide polymerization initiator can be used in
combination with a reducing agent, as a redox polymerization
initiator. The reducing agent used 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 methanesulfonic acid; and
amine compounds such as dimethylaniline. These reducing agents may
be used either alone or in combination. The amount of reducing
agent is preferably in the range of 0.03 to 10 parts by weight
based on 1 part by weight of peroxide.
[0051] As a polymerization stopper, there can be used, for example,
hydroxylamine, hydroxylamine sulfate salt, diethyl hydroxylamine,
hydroxylaminesulfonic acid and its alkali metal salts; sodium
dimethyldithiocarbamate, hydroquinone derivatives and catechol
derivatives; and aromatic hydroxydithiocarboxylic acids such as
hydroxydimethylbenzenethiocarboxylic acid,
hydroxydiethylbenzenethiocarboxylic acid and
hydroxydibutylbenzenethiocarboxylic acid, and alkali metal salts
thereof. The amount of polymerization stopper is not particularly
limited, but is usually in the range of 0.1 to 2 parts by weight
based on 100 parts by weight of the total monomers added.
[0052] Polymerization auxiliaries can be used for emulsion
copolymerization according to the need, which include, for example,
a molecular weight modifier, a particle size modifier, a chelating
agent and an oxygen scavenger.
[0053] The polymerization temperature is not particularly limited,
but is usually in the range of 0 to 95.degree. C., preferably 5 to
70.degree. C.
[0054] The polymerization conversion at which the polymerization
reaction is terminated is preferably at least 90%, more preferably
at least 93%.
[0055] After the polymerization reaction is terminated, unreacted
monomers are removed from a polymerization mixture and the solid
content and pH value thereof are adjusted according to the need to
give a desired copolymer latex.
[0056] Additives such as an antioxidant, a preservative, an
anti-fungus agent and a dispersant can be incorporated in the
thus-obtained latex according to the need.
[0057] The copolymer latex preferably has a number average particle
diameter in the range of 60 to 300 nm, more preferably 80 to 150
nm. The particle diameter can be adjusted to a desired value by
varying the amounts of an emulsifier and polymerization
initiator.
[0058] The dip-forming composition of the present invention
comprises the above-mentioned dip-forming latex.
[0059] Preferably a vulcanizing agent and a vulcanization
accelerator are incorporated in the dip-forming composition of the
present invention. If desired, zinc oxide can be further
incorporated in the dip-forming composition.
[0060] As the vulcanizing agent, those which are conventionally
used in dip-forming are mentioned. As specific examples thereof,
there can be mentioned sulfur such as powdery sulfur, flower of
sulfur, precipitated sulfur, colloidal sulfur, surface-treated
sulfur and insoluble sulfur; and polyamines such as
hexamethylenediamine, triethylenetetramine and
tetraethylenepentamine. Of these, sulfur is preferable.
[0061] The amount of vulcanizing agent is preferably in the range
of 0.5 to 10 parts by weight, more preferably 2 to 5 parts by
weight and especially preferably 3.5 to 4.5 parts by weight based
on 100 parts by weight of the solid content of latex.
[0062] As the vulcanization accelerator, those which are
conventionally used in dip-forming are mentioned. As specific
examples thereof, there can be mentioned dithiocarbamic acids such
as diethyldithiocarbamic acid, dibutyldithiocarbamic acid,
di-2-ethylhexyldithiocarbamic acid, dicyclohexyldithiocarbamic
acid, diphenyldithiocarbamic acid and dibenzyldithiocarbamic acid,
and zinc salt thereof; and 2-mercaptobenzothiazole, zinc salt of
2-mercaptobenzothiazole, 2-mercaptothiazoline,
dibenzothiazyldisulfide, 2-(2,4-dinitrophenylthio)-benzothiazole,
2-(N,N-diethylthiocarbaylthio)benzothiazole,
2-(2,6-dimethyl-4-morpholinothio)benzothiazole,
2-(4'-morpholino-dithio)benzothiazole, 4-morphonylyl-2-benzothiazyl
disulfide and 1,3-bis(2-benzothiazyl-mercaptomethyl)urea. Of these,
zinc dibutyldithiocarbamate, 2-mercaptobenzothiazole and zinc salt
of 2-mercaptobenzothiazole are preferable. These vulcanization
accelerators may be used either alone or as a combination of at
least two thereof.
[0063] The amount of vulcanizing accelerator is preferably in the
range of 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts
by weight and especially preferably 1 to 3 parts by weight based on
100 parts by weight of the solid content of latex.
[0064] The amount of zinc oxide is preferably not larger than 5
parts by weight, more preferably not larger than 1 part by weight
and especially preferably not larger than 0.5 part by weight based
on 100 parts by weight of the solid content of latex.
[0065] Conventional ingredients such as a pH adjuster, a thickener,
an antioxidant, a dispersant, a pigment, a filler and a softener
may be incorporated in the dip-forming composition of the present
invention, according to the need. Provided that the object of the
present invention is achieved, other latex such as natural rubber
latex or isoprene rubber latex can be incorporated with the
dip-forming latex.
[0066] The dip-forming composition of the present invention has a
solid content in the range of 20 to 40% by weight, preferably 25 to
35% by weight.
[0067] The dip-forming composition of the present invention has a
pH value in the range of 8.5 to 12, preferably 9 to 11.
[0068] The dip-formed article of the present invention is made by
dip-forming the above-mentioned dip-forming composition. A
conventional dip-forming method can be adopted, which includes, for
example, a direct dip-forming method, an anode cohesion dip-forming
method, a Teague cohesion dip-forming method and a combination of
these methods. Of these, an anode cohesion dip-forming method is
preferable because a dip-formed article having a uniform thickness
is easily obtained.
[0069] The anode cohesion dip-forming method is carried out by a
process comprising the steps of dipping a dip-forming form in a
solution of a coagulant to form a layer comprised of the coagulant
solution on the form; and dipping the form having the coagulating
solution layer thereon in a dip-forming composition to form a
coagulated layer comprised of the dip-forming composition.
[0070] As specific examples of the coagulant, there can be
mentioned metal halides such as barium chloride, calcium chloride,
magnesium chloride, zinc chloride and aluminum chloride; nitric
acid salts such as barium nitrate, calcium nitrate and zinc
nitrate; acetic acid salts such as barium acetate, calcium acetate
and zinc acetate; and sulfuric acid salts such as calcium sulfate,
magnesium sulfate and aluminum sulfate. Of these, calcium chloride
and calcium nitrate are preferable.
[0071] The coagulant is usually used as a solution in water, an
alcohol or a mixture thereof. The concentration of coagulant in the
solution is usually in the range of 5 to 70% by weight, preferably
20 to 50% by weight.
[0072] The coagulated layer of the dip-forming composition, formed
on the surface of a dip-forming form is usually heat-treated to
cure.
[0073] The form having formed thereon the coagulated dip-forming
composition layer can be dipped in water, preferably warm water
maintained at a temperature of 30 to 70.degree. C., for 1 to 60
minutes to remove water-soluble impurities such as, for example,
excessive emulsifier and coagulant, from the coagulated dip-forming
composition layer. This water washing can be carried out either
before or after the heat-treatment of the coagulated dip-forming
composition layer, but, the water washing is preferably carried out
before the heat-treatment because water-soluble impurities can be
more effectively removed.
[0074] The water-washed coagulated composition layer is
heat-treated usually at a temperature of 100 to 150.degree. C. for
10 to 120 minutes to cure the coagulated composition layer. The
heating can be carried out by an external heating method using
infrared rays or heated air, or an internal heating method using
high frequency. Of these, an external heating method using heated
air is preferable.
[0075] The cured, coagulated dip-forming composition layer is
released from the form to obtain a dip-formed article. The release
can be carried out manually or by applying water pressure or
compressed air.
[0076] After the release from the form, the dip-formed article can
be further heat-treated at a temperature of 60 to 120.degree. C.
for 10 to 120 minutes.
[0077] The dip-formed article may have a surface-treated layer
formed on the inner surface and/or the outer surface.
[0078] By using the dip-forming latex of the present invention, a
dip-formed article having a tensile stress at 300% elongation of
not larger than 2.5 MPa, a tensile strength of at least 15 MPa,
preferably at least 20 MPa, and a tensile stress retention of at
least 70%, preferably larger than 70%, as measured when 6 minutes
elapses from the time of 100% elongation, can be easily obtained.
Further, a dip-formed article having these characteristics and a
swelling degree in methyl ethyl ketone (hereinafter abbreviated to
"MEK" when appropriate) of not larger than 200%, preferably not
larger than 180%, can also be obtained. The smaller the swelling
degree in MEK, the more excellent the oil resistance.
EXAMPLES
[0079] The invention will now be described by the following
examples wherein % and parts are by weight unless otherwise
specified.
[0080] Polymerization conversion of acrylonitrile in a
polymerization mixture and properties of a dip-formed article were
evaluated by the following methods.
[0081] Polymerization Conversion of Acrylonitrile (AN) (%)
[0082] A part of a polymerization liquid was taken, and the content
of unreacted acrylonitrile (AN) was measured. From the amount (a)
of AN initially charged and the measured content (b) of unreacted
AN, the ratio (%) ([(a-b)/a].times.100) of the amount of AN (a-b)
converted to a copolymer to the amount (a) of AN initially charged
was calculated. In the case when, after initiation of
polymerization of an initially charged monomer mixture and further
after addition of a first part of the remainder of AN, a second
part of the remainder of AN is added, the polymerization conversion
of AN as of the addition of the second part thereof is calculated
from the formula:
Polymerization conversion of AN (%)=[(a+a')-b]/(a+a').times.100
where
[0083] a: amount of AN in initially charged monomer mixture
[0084] a': amount of first part of the remainder of AN
[0085] b: amount of unreacted AN
[0086] Tensile Stress at 300% Elongation (MPa)
[0087] A dumbbell specimen (Die-C) was punched out from a
dip-formed article of a glove form, according to ASTM D412.
[0088] Tensile stress at 300% elongation was measured on the
dumbbell specimen at a drawing rate of 500 mm/min by Tensilon
tensile tester ("RTC-1225A" available from Orientec K. K.). The
smaller the tensile stress at 300% elongation, the more excellent
the softness of touch and comfortable fittingness of dip-formed
article.
[0089] Tensile Strength (MPa)
[0090] Tensile strength was measured on the dumbbell specimen at a
drawing rate of 500 mm/min by Tensilon tensile tester (the same as
mentioned above) immediately before breaking.
[0091] Elongation at Break (%)
[0092] Elongation at break was measured on the dumbbell specimen at
a drawing rate of 500 mm/min by Tensilon tensile tester (the same
as mentioned above) immediately before breaking.
[0093] Tensile Stress Retention (%)
[0094] Tensile stress was measured on the dumbbell specimen by
Tensilon tensile tester (the same as mentioned above). Tensile
stress retention was determined from the tensile stress (Md0) as
measured immediately after the elongation reached 100%, and the
tensile stress (Md6) as measured when the specimen at the
elongation of 100% was kept as it was for 6 minutes. The tensile
stress retention (%) was defined as the ratio (%) of
Md0/Md6.times.100. The larger the tensile stress retention, the
more excellent the retention of close fittingness of dip-formed
article.
[0095] Swelling Degree in Methyl Ethyl Ketone (MEK) (%)
[0096] A disc specimen having a diameter (D1) of 2 cm was punched
out from a dip-formed article. The specimen was dipped in a MEK
bath having a large volume at 20.degree. C. for 72 hours, to be
thereby swelled. Diameter (D2) was measured after swelling, and the
swelling degree was calculated from the following equation (1).
Swelling Degree in MEK (%)=(D2/D1).sup.2.times.100 (1)
Example 1
[0097] A pressure polymerization vessel was charged with 18 parts
of acrylonitrile, 3 parts of methacrylic acid, 74 parts of
1,3-butadiene, 0.3 part of tert-dodecyl mercaptan as a molecular
weight modifier, 150 parts of deionized water, 2.5 parts of sodium
dodecylbenzenesulfonate, 0.2 part of potassium persulfate and 0.1
part of sodium ethylenediaminetetraacetate. Then the temperature of
the content was elevated to 39.degree. C. to initiate
polymerization.
[0098] When the polymerization conversion of the total monomers
added reached 60% (at this time, the polymerization conversion of
acrylonitrile reached 66%), 4 parts of acrylonitrile and 1 part of
methacrylic acid were added to a polymerization system. While the
temperature was maintained at 39.degree. C., the polymerization was
continued until the polymerization conversion reached 95%.
Thereafter 0.1 part of diethylhydroxlamine was added to terminate
the polymerization.
[0099] Unreacted monomers were distilled off from the thus-prepared
copolymer latex, and then, the solid content and pH value of the
latex were adjusted to give a copolymer latex A having a solid
content of 45% and a pH value of 8.5.
[0100] An aqueous dispersion of a vulcanizing agent was prepared by
mixing together 3.5 parts of sulfur, 0.1 part of zinc oxide, 2
parts of zinc dibutylcarbamate, 0.03 part of potassium hydroxide
and 5.63 parts of water. 11.26 parts of the aqueous dispersion of a
vulcanizing agent was mixed with 250 parts of the above-mentioned
copolymer latex (solid content: 100 parts), and then, deionized
water was added to the mixture to prepare a dip-forming composition
having a solid content of 30%.
[0101] An aqueous coagulant solution was prepared by mixing
together 20 parts of calcium nitrate, 0.05 part of
polyoxyethyleneoctyl phenyl ether (nonionic emulsifier) and 80
parts of water. A dip-forming glove form was dipped in the aqueous
coagulant solution for 1 minute, and then, the glove form was taken
out and dried at 50.degree. C. for 3 minutes whereby the coagulant
was deposited on the glove form.
[0102] The glove form having the coagulant deposited thereon was
dipped in the above-mentioned dip-forming composition for 6
minutes. The glove form was taken out from the dip-forming
composition, and then, the glove form having thereon a dip-formed
layer was dried at 25.degree. C. for 3 minutes and then dipped in
warm water at 40.degree. C. for 3 minutes to remove water-soluble
impurities. Then the glove form was dried at 80.degree. C. for 20
minutes and subsequently heat-treated at 120.degree. C. for 25
minutes whereby the dip-formed layer was vulcanized. Finally the
vulcanized, dip-formed layer was peeled from the glove form to
obtain a dip-formed article of a glove shape. Properties of the
dip-formed article were evaluated. The results are shown in Table
1.
Examples 2 and 3
[0103] Copolymer latexes B and C were prepared by the same
procedures as described in Example 1 except that the amount of the
initial monomer mixture charged, the amounts of acrylonitrile and
methacrylic acid added after the initiation of polymerization, and
the conditions under which the additional monomers were added were
varied as shown in Table 1.
[0104] Dip-formed articles were made by the same procedures as
described in Example 1 except that copolymer latexes B and C were
used instead of copolymer latex A. Properties of the dip-formed
article were evaluated. The results are shown in Table 1.
Comparative Examples 1 and 2
[0105] Copolymer latexes D and E were prepared by the same
procedures as described in Example 1 except that the amount of the
initial monomer mixture charged, the amounts of acrylonitrile and
methacrylic acid added after the initiation of polymerization, and
the conditions under which the additional monomers were added were
varied as shown in Table 1.
[0106] Dip-formed articles were made by the same procedures as
described in Example 1 except that copolymer latexes D and E were
used instead of copolymer latex A. Properties of the dip-formed
article were evaluated. The results are shown in Table 1.
TABLE-US-00001 TABLE 1 Comparative Example Example 1 2 3 1 2
Monomer Composition (parts) Initial charge: 1,3-butadiene 74 74 73
74 74 Methacrylic acid (MA) 3 3 2 4 -- Acrylonitrile (AN) 18 15 20
22 18 % of initially charged MA to total MA 75 75 66.7 100 0 % of
initially charged AN to total AN 81.8 68.1 83.3 100 81.8 Amount of
AN added after initiation of polymerization *1 at polymerization
conversion of 40% -- 3.5 (48%) -- -- -- at polymerization
conversion of 60% 4 (66%) -- 4 (64%) -- 4 (67%) at polymerization
conversion of 70% -- 3.5 (73%) -- -- -- Amount of MA added after
initiation of polymerization at polymerization conversion of 40% --
1 -- -- -- at polymerization conversion of 60% 1 -- 1 -- 4
Copolymer Latex A B C D E Properties of Dip-Formed Article Tensile
stress at 300% elongation (MPa) 1.9 1.8 2 2.5 3.5 Tensile strength
(MPa) 23.5 25.2 24.8 16.7 17.8 Elongation at break (%) 610 630 610
570 510 Retention of tensile stress (%) 75 76 73 67 56 Swelling
degree in MEK (%) 144 135 156 222 234 *1 Percents within
parentheses indicate polymerization conversion of AN at which AN
was added
[0107] The following will be seen from Table 1.
[0108] The dip-formed article (Comparative Example 1) made from
copolymer latex D prepared by copolymerization of the monomers, the
total of which were initially charged, exhibited moderately good
retention of tensile stress, but had slightly poor softness of
touch, and slightly poor tensile strength.
[0109] The dip-formed article (Comparative Example 2) made from
copolymer latex E prepared by copolymerization of the monomers
wherein acrylonitrile and methacrylic acid were added in the midst
of polymerization, but methacrylic acid was not initially charged,
had a tensile strength of approximately the same magnitude as, but
exhibited poor retention of tensile stress and poor softness of
touch as compared with that of Comparative Example 1.
[0110] In contrast to the comparative examples, dip-formed articles
(Examples 1-3) made from copolymer latexes A, B and C prepared by
copolymerization of the monomers wherein part of acrylonitrile and
part of methacrylic acid were initially charged and the remainders
thereof were added in the midst of polymerization, exhibited good
softness of touch, high tensile strength and high retention of
tensile stress.
Example 4
[0111] A pressure polymerization vessel was charged with 23 parts
of acrylonitrile, 3 parts of methacrylic acid, 73 parts of
1,3-butadiene, 0.3 part of tert-dodecyl mercaptan as a molecular
weight modifier, 150 parts of deionized water, 2.5 parts of sodium
dodecylbenzenesulfonate, 0.2 part of potassium persulfate and 0.1
part of sodiumethylenediaminetetraacetate. Then the temperature of
the content was elevated to 37.degree. C. to initiate
polymerization.
[0112] When the polymerization conversion of the total monomers
added reached 60%, 0.1 part of tert-dodecyl mercaptan and 1 part of
methacrylic acid were added to a polymerization system. The
temperature was elevated to 40.degree. C., and, while the
temperature was maintained at 40.degree. C., the polymerization was
continued until the polymerization conversion reached 97%.
Thereafter 0.1 part of diethylhydroxlamine was added to terminate
the polymerization.
[0113] Unreacted monomers were distilled off from the thus-prepared
copolymer latex, and then, the solid content and pH value of the
latex were adjusted to give a copolymer latex F having a solid
content of 40% and a pH value of 8.5.
[0114] An aqueous dispersion of a vulcanizing agent was prepared by
mixing together 3 parts of sulfur, 0.3 part of zinc oxide, 1.5
parts of zinc dibutylcarbamate, 1.5 parts of zinc diethylcarbamate,
0.03 part of potassium hydroxide and 6.33 parts of water. 12.66
parts of the aqueous dispersion of a vulcanizing agent was mixed
with 250 parts of the above-mentioned copolymer latex (solid
content: 100 parts), and then, deionized water was added to the
mixture to prepare a dip-forming composition having a solid content
of 30%.
[0115] An aqueous coagulant solution was prepared by mixing
together 20 parts of calcium nitrate, 0.05 part of
polyoxyethyleneoctyl phenyl ether (nonionic emulsifier) and 80
parts of water. A dip-forming glove form was dipped in the aqueous
coagulant solution for 1 minute, and then, the glove form was taken
out and dried at 50.degree. C. for 3 minutes whereby the coagulant
was deposited on the glove form.
[0116] The glove form having the coagulant deposited thereon was
dipped in the above-mentioned dip-forming composition for 6
minutes. The glove form was taken out from the dip-forming
composition, and then, the glove form having thereon a dip-formed
layer was dried at 25.degree. C. for 3 minutes and then dipped in
warm water at 40.degree. C. for 3 minutes to remove water-soluble
impurities. Then the glove form was dried at 80.degree. C. for 20
minutes and subsequently heat-treated at 120.degree. C. for 25
minutes whereby the dip-formed layer was vulcanized. Finally the
vulcanized, dip-formed layer was peeled from the glove form to
obtain a dip-formed article of a glove shape. Properties of the
dip-formed article were evaluated. The results are shown in Table
2.
Example 5
[0117] Copolymer latex G was prepared by the same procedures as
described in Example 4 except that the composition of the initial
monomer mixture charged, and the amount of methacrylic acid added
after the initiation of polymerization were varied as shown in
Table 2.
[0118] A dip-formed article was made by the same procedures as
described in Example 4 except that copolymer latex G was used
instead of copolymer latex F. Properties of the dip-formed article
were evaluated. The results are shown in Table 2.
Comparative Example 3
[0119] Copolymer latex H was prepared by the same procedures as
described in Example 4 except that the composition of the initial
monomer mixture charged was varied as shown in Table 2 and
methacrylic acid was not added after the initiation of
polymerization.
[0120] A dip-formed article was made by the same procedures as
described in Example 4 except that copolymer latex H was used
instead of copolymer latex F. Properties of the dip-formed article
were evaluated. The results are shown in Table 2.
Comparative Example 4
[0121] Copolymer latex J was prepared by the same procedures as
described in Example 4 except that the composition of the initial
monomer mixture charged and the amount of methacrylic acid added
after the initiation of polymerization were varied as shown in
Table 2.
[0122] A dip-formed article was made by the same procedures as
described in Example 4 except that copolymer latex J was used
instead of copolymer latex F. Properties of the dip-formed article
were evaluated. The results are shown in Table 2.
TABLE-US-00002 TABLE 2 Comparative Example Example 4 5 3 4 Monomer
Composition (parts) Initial charge: 1,3-butadiene 73 71 73 73
Acrylonitrile (AN) 23 26 23 23 Methacrylic acid (MA) 3 2 4 -- % of
initially charged MA to total MA 75 67 100 0 Amount of MA added
after initiation 1 1 -- 4 of polymerization Copolymer Latex F G H J
Properties of Dip-Formed Article Tensile stress at 300% elongation
(MPa) 2.0 2.1 2.3 3.2 Tensile strength (MPa) 22.3 24.1 16.5 15.4
Elongation at break (%) 600 610 590 510
[0123] The following will be seen from Table 2.
[0124] The dip-formed article (Comparative Example 3) made from
copolymer latex H prepared by copolymerization of the monomers,
wherein methacrylic acid was not added after initiation of
polymerization, exhibited moderately good softness of touch, but
had poor tensile strength.
[0125] The dip-formed article (Comparative Example 4) made from
copolymer latex J prepared by copolymerization of the monomers
wherein methacrylic acid was not incorporated in the monomer
mixture initially charged, exhibited poor softness of touch and
poor tensile strength.
[0126] In contrast to the comparative examples, dip-formed articles
(Examples 4 and 5) made from copolymer latexes F and G prepared by
copolymerization of the monomers wherein part of methacrylic acid
was initially charged and the remainder thereof was added in the
midst of polymerization, exhibited good softness of touch and high
tensile strength.
INDUSTRIAL APPLICABILITY
[0127] The dip-formed article of the present invention exhibits
good softness of touch and is characterized by comfortable fit
properties. It also has high tensile strength and preferably
exhibits high retention of close fittingness. This dip-formed
article can have a thickness of about 0.1 mm to about 3 mm. In a
preferred embodiment, a very thin dip-formed article, having a
thickness of only 0.1 to 0.3 mm, is provided by the present
invention.
[0128] Persons skilled in the art will recognize, based upon the
disclosure hereinabove, that the dip-formed article of the present
invention having the above characteristics is suitable for, for
instance, a nipple of nursing bottle, for a medical article such as
a dropper, a duct, and a water pillow, for toys such as a balloon,
a doll, and a ball, and for sporting goods such as a ball, for an
industrial article such as a pressure molding bag and a gas storage
bag; for unsupported gloves and for supported gloves for surgical,
household, agricultural, fishery, and industrial uses; and for a
finger cot. The dip-formed article of this invention is especially
advantageously used to make thin gloves, in particular, thin
surgical gloves.
* * * * *