U.S. patent application number 11/222042 was filed with the patent office on 2006-03-09 for polymer latex suitable for the preparation of dip-molded articles.
Invention is credited to Soren Butz, Volker Erb, Katja Siepen, Hans-Gunter Vogt.
Application Number | 20060052513 11/222042 |
Document ID | / |
Family ID | 35997089 |
Filed Date | 2006-03-09 |
United States Patent
Application |
20060052513 |
Kind Code |
A1 |
Butz; Soren ; et
al. |
March 9, 2006 |
Polymer latex suitable for the preparation of dip-molded
articles
Abstract
The present invention relates to a polymer latex made by
free-radical emulsion polymerization comprising polymer particles
containing structural units derived from at least one conjugated
diene component, whereby said polymer particles comprise at least
one hard phase segment having a glass transition temperature (Tg)
of at least 50.degree. C. and at least one soft phase segment
having a glass transition temperature (Tg) of 10.degree. C. at
most, the total amount of hard phase segments being 2 to 40 wt-%
and the total amount of the soft phase segments being 60 to 98 wt-%
based on the total weight of the polymer particles, whereby the Tg
is measured by DSC according to ASTM D3418-03 and said polymer
latex having an electrolyte stability determined as critical
coagulation concentration of less than 30 mmol/l CaCl2 (determined
for a total solids content of the latex of 0.1% at pH 10) that is
particularly suitable for the production of dip-molded articles.
Furthermore, the present invention relates to a process for making
such a polymer latex, to the use of said polymer latex for the
production of dip-molded articles, to a compounded polymer latex
composition that is suitable for the production of dip-molded
articles, to a method for making dip-molded latex articles, as well
as to the latex articles obtained thereby.
Inventors: |
Butz; Soren; (Dulmen,
DE) ; Erb; Volker; (Dusseldorf, DE) ; Siepen;
Katja; (Kurten, DE) ; Vogt; Hans-Gunter;
(Dormagen, DE) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
35997089 |
Appl. No.: |
11/222042 |
Filed: |
September 8, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60609094 |
Sep 9, 2004 |
|
|
|
Current U.S.
Class: |
524/555 ;
524/556 |
Current CPC
Class: |
Y10T 442/20 20150401;
Y10T 428/31931 20150401; C08L 53/02 20130101; C08L 2666/02
20130101; C08L 2666/02 20130101; C08F 293/00 20130101; C08F 293/005
20130101; C08L 53/02 20130101; C08L 53/00 20130101; C08L 53/00
20130101 |
Class at
Publication: |
524/555 ;
524/556 |
International
Class: |
C08F 8/30 20060101
C08F008/30 |
Claims
1. A polymer latex made by free-radical emulsion polymerization
comprising polymer particles containing structural units derived
from at least one conjugated diene component, whereby said polymer
particles comprise at least one hard phase segment having a glass
transition temperature (Tg) of at least 50.degree. C. and at least
one soft phase segment having a glass transition temperature (Tg)
of 10.degree. C. at most, the total amount of hard phase segments
being 2 to 40 wt-% and the total amount of the soft phase segments
being 60 to 98 wt-% based on the total weight of the polymer
particles, whereby the Tg is measured by DSC according to ASTM
D3418-03 and said polymer latex having an electrolyte stability
determined as critical coagulation concentration of less than 30
mmol/l CaCl.sub.2 (determined for a total solids content of the
latex of 0.1% at pH 10).
2. The polymer latex of claim 1, wherein the total amount of hard
phase segments is between 5 and 30 wt-% and the total amount of the
soft phase segments is between 70 and 95 wt-%, the weight
percentages being based on the total weight of the polymer
particles.
3. The polymer latex of claim 1, wherein the total amount of hard
phase segments is 10 to 25 wt-% and the total amount of the soft
phase segments is 75 to 90 wt-%, the weight percentages being based
on the total weight of the polymer particles.
4. The polymer latex of claim 1, wherein the soft phase segments
contain independently from each other structural units derived from
monomers selected from the group consisting of conjugated dienes;
ethylenically unsaturated mono-carboxylic acids; ethylenically
unsaturated di-carboxylic acids, anhydrides, mono-esters and
mono-amides thereof; (meth)acryl nitrile; styrene; substituted
styrenes; alpha-methyl styrene; C1 to C10 esters of (meth)acrylic
acid; amides of (meth)acrylic acid; ethylenically unsaturated
compounds comprising N-methylol amide groups, and ester and ether
derivatives thereof.
5. The polymer latex of claim 1, wherein the hard phase segments
contain independently from each other structural units derived from
monomers selected from the group consisting of ethylenically
unsaturated mono-carboxylic acids; unsaturated di-carboxylic acids,
anhydrides, mono-esters and mono-amides thereof; ethylenically
unsaturated compounds comprising N-methylol amide groups, and ester
and ether derivatives thereof; and mixtures thereof; (meth)acryl
nitrile; styrene; substituted styrenes; alpha-methyl styrene; C1 to
C8 esters of (meth)acrylic acid; amides of (meth)acrylic acid; and
mixtures thereof.
6. The polymer latex of claims 1 having an electrolyte stability
determined as critical coagulation concentration of less than 25
mmol/l CaCl.sub.2 determined for a total solids content of the
latex of 0.1% at pH 10.
7. The polymer latex of claim 6, having an electrolyte stability
determined as critical coagulation concentration of less than 20
mmol/l CaCl.sub.2 determined for a total solids content of the
latex of 0.1% at pH 10.
8. The polymer latex of claim 1, wherein the polymer particles
comprise groups that are capable of self-crosslinking.
9. Polymer latex of claim 8, wherein the groups capable of
self-crosslinking are selected from N-methylol amide groups and
their ester and ether derivatives thereof; and mixtures
thereof.
10. The polymer latex of claim 9, wherein said groups capable of
self-crosslinking are selected from N-methylol acrylamide,
N-methylol methacrylamide, N-methoxymethyl-(meth)acrylamide,
N-n-butoxy-methyl-(meth)acrylamide,
N-acetoxymethyl-(meth)acrylamide, and
N(-2,2-dimethoxy-1-hydroxyethyl)acrylamide.
11. The polymer latex of claim 1, wherein said polymer latex is
carboxylated.
12. The polymer latex of claim 11, wherein the soft phase segment
or the hard phase segment or both are carboxylated.
13. The carboxylated polymer latex of claim 11, wherein the polymer
particles comprise groups that are capable of
self-crosslinking.
14. The polymer latex of claim 13, wherein said groups capable of
self-crosslinking are selected from N-methylol amide groups and
their ester and ether derivatives thereof; and mixtures
thereof,
15. The polymer latex of claim 14, wherein said groups capable of
self-crosslinking are selected from N-methylol acrylamide,
N-methylol methacrylamide, N-methoxymethyl-(meth)acrylamide,
N-n-butoxy-methyl-(meth)acrylamide,
N-acetoxymethyl-(meth)acrylamide, and
N(-2,2-dimethoxy-1-hydroxyethyl) acrylamide.
16. A compounded polymer latex composition suitable for the
production of dip molded articles comprising the polymer latex of
claim 1.
17. The compounded polymer latex composition of claim 16 being free
of sulfur and accelerators for the sulfur vulcanization.
18. The compounded polymer latex composition of claim 17 being
substantially free of polyvalent cations and cross-linkers.
19. A compounded polymer latex composition suitable for the
production of dip molded articles comprising the carboxylated
polymer latex of claim 11.
20. The compounded polymer latex composition of claim 19 being free
of sulfur and accelerators for the sulfur vulcanization.
21. The compounded polymer latex composition of claim 20 being
substantially free of polyvalent cations and cross-linkers.
22. A compounded polymer latex composition suitable for the
production of dip molded articles comprising the carboxylated
polymer latex of claim 13.
23. The compounded polymer latex composition of claim 22 being free
of sulfur and accelerators for the sulfur vulcanization.
24. The compounded polymer latex composition of claim 23 being
substantially free of polyvalent cations and cross-linkers.
25. A method for making dip molded latex films comprising: (a)
immersing a mold having the desired shape of the final article in a
coagulant bath comprising a solution of a metal salt; (b) removing
the mold from the bath and optionally drying the mold; (c)
immersing the mold as treated in step (a) and (b) in the compounded
latex composition of claims 16 or 19; (d) removing the mold from
the latex composition and optionally immersing the latex coated
mold in a water bath; (e) heat treating the latex coated mold
obtained from step (d) at a temperature of 80 to 180.degree. C.;
and (f) removing the latex article from the mold.
26. A film made from a polymer latex of claim 1.
27. The film according to claim 26 exhibiting an increase in
tensile strength of at least 2 MPa after heat treatment at
120.degree. C. for 30 minutes compared to the identical polymer
latex film kept at 25.degree. C.
28. The film according to claim 26 being heat treated and having a
tensile strength of at least about 7 MPa and an elongation at break
of at least about 300% measured according to ISO 37:1994.
29. A film made from a carboxylated polymer latex of claim 11.
30. The film according to claim 29 exhibiting an increase in
tensile strength of at least 2 MPa after heat treatment at
120.degree. C. for 30 minutes compared to the identical polymer
latex film kept at 25.degree. C.
31. The film according to claim 29 being heat treated and having a
tensile strength of at least about 7 MPa and an elongation at break
of at least about 300% measured according to ISO 37:1994.
32. A film made from a polymer latex of claim 13, wherein the
polymer particles comprise groups that are capable of
self-crosslinking.
33. The film according to claim 32 exhibiting an increase in
tensile strength of at least 2 MPa after heat treatment at
120.degree. C. for 30 minutes compared to the identical polymer
latex film kept at 25.degree. C.
34. The film according to claim 32 being heat treated and having a
tensile strength of at least about 7 MPa and an elongation at break
of at least about 300% measured according to ISO 37:1994.
35. A latex article comprising a latex film according to claims 26
or 29 being selected from surgical gloves, examination gloves,
condoms, catheters and industrial and household gloves.
36. A method for making a polymer latex comprising polymerizing in
an emulsion polymerization process in presence of a free-radical
initiator, stabilizers and water a first ethylenically unsaturated
monomer or mixture of monomers that results in a hard phase segment
having a glass transition temperature (Tg) of at least 50.degree.
C., and thereafter polymerizing a second monomer or mixture of
monomers that results in a soft phase segment having a glass
transition temperature (Tg) of 10.degree. C. at most or vice versa
in amounts so that the total amount of hard phase segments is 2 to
40 wt-% and the total amount of the soft phase segments is 60 to 98
wt-% based on the total weight of the polymer, whereby the Tg is
measured by DSC according to ASTM D3418-03 with the proviso that at
least one conjugated diene is employed in the polymerization
process and the amount of stabilizers is adjusted to obtain an
electrolyte stability determined as critical coagulation
concentration of less than 30 mmol/l CaCl.sub.2 determined for a
total solids content of the latex of 0.1% at pH 10.
37. The method of claim 36, further comprising polymerizing at
least one hard phase and/or soft phase segment.
38. The method of claim 37, wherein the first segment is
polymerized in the presence of a seed latex for adjusting the
particle size.
39. A method for making an impregnated substrate comprising
impregnating a substrate with the polymer latex according to claims
1, 11, or 13.
40. A method for making a coated substrate comprising coating a
substrate with the polymer latex according to claims 1, 11, or
13.
41. Article comprising a substrate coated or impregnated by the
polymer latex according to claims 1, 11, or 13.
42. Article according to claim 41 wherein the substrate is a
textile material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of US Provisional patent
Application No. 60/609,094, filed Sep. 9, 2004, the entire
disclosure of which is hereby expressly incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a polymer latex that is
particularly suitable for the production of dip-molded articles.
Furthermore, the present invention relates to a process for making
such a polymer latex, to the use of said polymer latex for the
production of dip-molded articles, to a compounded polymer latex
composition that is suitable for the production of dip-molded
articles, to a method for making dip-molded latex articles, as well
as to the latex articles obtained thereby.
[0004] 2. Description of the Related Art
[0005] Thin wall extensible articles, such as gloves and other
medical products have long been made from a natural latex polymer.
Typically such articles are formed from natural rubber latex,
naturally occurring emulsion of polymer and water with added
stabilizing agent and vulcanizing chemicals. Additionally, in order
to achieve the desired mechanical properties products made from
natural rubber latex are vulcanized using a sulfur-base
vulcanization system that also includes accelerators.
[0006] Such sulfur-based cure systems have been also employed for
vulcanizing synthetic polymer lattices thereby introducing
sulfur-based links during the crosslinking of the polymer
composition. In these sulfur-based cure systems in addition to
sulfur accelerators, such as amines, thiazoles, sulphenamides,
dithiocarbamates and thiuram are utilized.
[0007] EP-A-1 063 258 relates to a latex composition for dip
molding wherein C8-22 fatty acids or salts thereof are incorporated
as bubble breakers. This latex composition is vulcanized using
additional sulfur based vulcanization systems in order to produce
the dip molded products.
[0008] Similarly EP-A-559 150 discloses a copolymer latex suitable
for dip molding whereby the latex is vulcanized by a traditional
sulfur vulcanization system.
[0009] EP-A-753 530 relates to a different technology. Herein a
polymer latex is described having segments of different glass
transition temperature. This polymer latex is used for making
mattresses whereby traditional sulfur containing vulcanization
systems are used. This application does not relate to dip
molding.
[0010] Recently it has been discovered that latex articles made
either of natural rubber lattices or of synthetic rubber lattices
using sulfur-based cure systems may induce allergenic reactions of
the type IV.
[0011] Since one important field of application for natural and
synthetic rubber articles is, for example, medical gloves or
condoms that inevitably will come in contact with the skin of the
wearer and due to the increasing susceptibility to allergenic
reactions of people in modern society it has been a long-felt need
in industry to provide synthetic rubber compositions that can be
formed into dip-molded articles, like medical gloves, that do not
induce allergenic reactions or liberate compounds that may induce
other health risks, like for example nitrosamine without
compromising the desired and necessary properties of these
products, like mechanical strength, elasticity. Furthermore, it is
especially or medical gloves desired that they possess adequate
esthetic properties with respect to drape, softness and tactility.
Furthermore it is most important for these products that they
provide a good barrier to microbial penetration and are
substantially impermeable to a variety of liquids and gases.
Therefore, in addition to the desired mechanical properties it is
also important that the final product has a uniform film
thickness.
[0012] In the prior art several approaches to substitute a
sulfur-based curing system containing accelerators were discussed
in order to avoid allergenic reactions caused by the rubber
articles.
[0013] WO 00/11980 describes synthetic rubber lattices and aqueous
polyurethane dispersions having very low glass transition
temperatures that are crosslinked by means other than sulfur
vulcanization of double bonds. Particularly the synthetic rubber
should be substantially free of carbon-carbon unsaturation. Thus no
diene component shall be used. However, diene monomers can be used
as long as sulfur vulcanization is not applied for crosslinking the
resultant rubber. The polymers described therein are capable to be
crosslinked using external crosslinkers. Suitable crosslinking
functionalities in the polymers are hydroxyl or carboxyl groups.
But nevertheless external crosslinkers are necessary that have a
potential not to be bound to the polymer and therefore to bloom out
to the surface of the polymer in the final product, and therefore
in itself may cause health risks, especially in view of the
selections of crosslinking agents disclosed in that reference.
[0014] An alternative solution to avoid sulfur-based vulcanization
systems containing also accelerators has been described in WO
02/50177. Herein metal oxide crosslinking agents are used for
crosslinking the synthetic polymers. Suitable examples are zinc
oxide, magnesium oxide or cadmium oxide.
[0015] A similar solution has been suggested in WO 02/38640
disclosing rubber compositions containing chelating monomers that
can be crosslinked with polyvalent metal ions. A suitable chelating
monomer is an acetoacetoxy functionalized monomer.
[0016] EP-A-1 631 247 discloses a polymer latex composition for dip
molding comprising a carboxylated conjugated diene based rubber
latex having according to the examples a single glass transition
temperature whereby crosslinking is achieved by the presence of
multivalent cations.
[0017] WO 03/006513 discloses latex formulations comprising a base
polymer having carboxylate groups, a divalent or trivalent metal,
an amine or amino compound and a neutralizing agent in an amount
sufficient to neutralize at least a portion of the carboxylate
groups in the base polymer.
[0018] WO 03/062307 discloses a polymer latex composition. The
polymer particles thereof can be made of different segments having
different glass transition temperatures. These compositions are
either used as coating composition or as a component of a coagulant
for a dip molding process. But in both cases this composition only
forms a coating and the bulk material of the dip molded article is
a conventional sulfur vulcanized polymer latex. It is essential to
the invention described in WO 03/062307 that the polymer latex
having segments of different glass transition temperature is
stabilized using polyvinyl alcohol. Such systems are extremely
stable against electrolytes which also can be seen from the
embodiments where this latex is used in combination with a
coagulant. Even in this coagulation composition the latex remains
stable which is a clear indication that the latex has extremely
high resistance to coagulation due to the presence of polyvinyl
alcohol as stabilizer. For the bulk material of the dip molded
articles a conventional sulfur cured polymer latex is used. The
objective solved by the approach disclosed in WO 03/062307 is to
reduce the stickiness of the inner and outer surface of the glove.
Therefore it is also only necessary to use the particular polymer
latex described in WO 03/062307 as a coating whereas the bulk
material of the dip molded article is still a conventional sulfur
vulcanized polymer latex. Therefore also the latex used for the
coating does not need to fulfill the tensile strength requirement
for dip molded articles.
[0019] Other solutions to avoid sulfur-based vulcanization systems
containing accelerators for crosslinking synthetic or natural
rubber lattices in order to produce health care products still
employ additional crosslinking agents. These are either organic
molecules having a functionality adapted to react with the
crosslinking functionality in the rubber component or polyvalent
metal salts. Thus the rubber compositions still have to be
compounded with the crosslinking agent which results in a
complicated process for making the latex compound. In this process
the relative amounts have to be carefully adjusted in order to
achieve the desired crosslinking density, and if possible to bind
all the additional crosslinkers into the final molecule to avoid
blooming out of crosslinker component that in itself again may
create a health risk. Furthermore, especially when using polyvalent
metal ions as crosslinking agent latex instability during the
compounding process may occur which makes the compounding process
particularly difficult. Furthermore the crosslinking agents,
especially the polyvalent ions, reduce the stability of the latex
compound and therefore the ability to store the already compounded
latex composition prior to its use in a dip-molding process for
making the medical care product. Furthermore, especially the
introduction of polyvalent metal ions as crosslinking system in
rubber compositions may increase environmental hazards.
[0020] WO 02/18490 discloses a different approach wherein a
hydrogenated tri-block copolymer containing, for example,
styrene-ethylene/propylene-styrene segments which do not contain
double bonds, is mixed with a cyclic unsaturated polyolefin
crystalline polymer. This polymer composition is not a latex and
the articles made of this composition have to be extruded.
Furthermore still crosslinking is necessary to obtain the desired
mechanical properties of the final product. Crosslinking can be
achieved either by physical means, like radiation, or by chemical
means, like peroxides and usual vulcanization systems, as disclosed
above.
[0021] From WO 01/30876 substitutes for natural or synthetic rubber
lattices are disclosed that can be used to make medical care
products. Thermoplastic elastomeric tri-block polymers comprising
two polystyrene hard domains and one polyolefin rubber domain are
prepared by using living anionic polymerization. The resultant
polymer, due to the use of butadiene or isoprene, in the polyolefin
rubber domain, still have double bonds available for crosslinking.
Typical crosslinking processes disclosed in WO 01/30876 are
radiation or chemical vulcanization processes using well-known
sulfur/accelerator systems.
[0022] Consequently the elastomeric polymers to be used or making
medical care products according to the teaching of both latter
prior art documents have the disadvantage that still crosslinking
is necessary. Either a complex radiation curing has to be employed
which in itself is a health hazard, or traditional vulcanization
systems that suffer from the drawbacks as discussed above, have to
be applied. Finally conventional dip-molding processes cannot be
applied using these polymer systems in order to make the desired
products.
[0023] U.S. Pat. No. 5,500,469 describes a thermally gellable
artificial latex composition useful for preparing articles such as
gloves, condoms or balloons that are free of vulcanizing agents and
proteins. The polymer of the artificial latex is a preformed
multiblock copolymer prepared by anionic polymerization in
solvents. Due to the anionic polymerization process the number of
monomers which can be used for block copolymerization is very
limited. U.S. Pat. No. 5,500,469 describes only multiblocks
consisting of a combination of type A block consisting of alkenyl
aromatic hydrocarbons and type B block consisting of a conjugated
diene. The block copolymers are dissolved in non polar hydrocarbon
solvents up to a total solids of 20 to 50% of the organic phase.
After adding a sulfate of an ethoxylated phenol as surfactant and
water the hydrocarbon has to be completely removed by distillation.
This means high volumes of organic solvents in relation to the
polymer weight have to be handled. The limited versatility in
respect of suitable monomers for the anionic block copolymerization
process is another disadvantage of the teaching in U.S. Pat. No.
5,500,469.
[0024] In other fields of technology that do not relate to dip
molded articles polymer latex lattices having segments of different
Tg's are known. These lattices can, for example, be used as coating
material whereby in these applications coagulation should be
avoided under any circumstances since this would be detrimental to
the desired coating properties.
[0025] For example, U.S. Pat. No. 5,872,189 discloses
water-redispersible powders based on a polymer latex having
"core/shell" structure with different glass transition
temperatures. The key point of this invention is the
redispersibility in water which can only be achieved if the latex
is stabilized against coagulation. Consequently such a latex cannot
be used in dip molding, and it is explicitly disclosed that these
redispersible powders can be suitably used in the building industry
as additives for hydraulic mineral binders for the production of
protective and decorative coatings and of adhesive mortars and
adhesive cements. Consequently vulcanization of these systems is no
issue at all.
[0026] Similarly JP-A-2002-226508 relates to a paper coating
composition wherein also electrolyte stability is of uppermost
importance since otherwise no stable coating composition for paper
coating can be obtained. Furthermore, like in U.S. Pat. No.
5,872,189 vulcanization of the latex is no issue for a latex used
in paper coating compositions.
SUMMARY OF THE INVENTION
[0027] Thus it is the object of the present invention to provide a
polymer latex that can be compounded into latex compositions that
have a long-term stability and can be used for conventional
dip-molding processes for making latex articles whereby no
crosslinking either by radiation or by crosslinking agents in the
compounded composition is necessary to achieve the desired
mechanical properties of the final latex product thereby avoiding
the above described deficiencies of the prior art.
[0028] This object has been solved by a polymer latex made by free
radical emulsion polymerization comprising polymer particles
containing structural units derived from at least one conjugated
diene component whereby said polymer particles comprise at least
one hard phase segment having a glass transition temperature
(T.sub.g) of at least 50.degree. C. and at least one soft phase
segment having a glass transition temperature (T.sub.g) of
10.degree. C. at most, the total amount of hard phase segments
being 2 to 40 wt-% and the total amount of the soft phase segments
being 60 to 98 wt-% based on the total weight of the polymer
particles, whereby the T.sub.g is measured by DSC according to ASTM
D3418-03 and said polymer latex having an electrolyte stability
determined as critical coagulation concentration of less than 30
mmol/l CaCl.sub.2 (determined for a total solids content of the
latex of 0.1% at pH 10).
[0029] Furthermore the present invention relates to a method for
making a polymer latex comprising polymerizing in an emulsion
polymerization process in presence of a free-radical initiator,
stabilizers and water a first ethylenically unsaturated monomer or
mixture of monomers that results in a hard phase segment having a
glass transition temperature (T.sub.g) of at least 50.degree. C.
and thereafter polymerizing a second monomer or mixture of monomers
that results in a soft phase segment having a glass transition
temperature (T.sub.g) of 10.degree. C. at most or vice versa in
amounts so that the total amount of hard phase segments is 2 to 40
wt-% and the total amount of the soft phase segments is 60 to 98
wt-% based on the total weight of the polymer, whereby the T.sub.g
is measured by DSC according to ASTM D3418-03 with the proviso that
at least one conjugated diene is employed in the polymerization
process and the amount of stabilizers is adjusted to obtain an
electrolyte stability determined as critical coagulation
concentration of less than 30 mmol/l CaCl.sub.2 (determined for a
total solids content of the latex of 0.1% at pH 10).
[0030] Furthermore, the present invention relates to a compounded
polymer latex composition that is suitable for the production of
dip-molded articles and comprises the polymer latex as defined
above.
[0031] Although the compounded polymer latex composition may
comprise usual crosslinking and vulcanization systems it is
particularly preferred if the polymer latex composition is free of
sulfur and accelerators for sulfur vulcanization. It is even more
preferred if the polymer latex composition in addition is also
substantially free of polyvalent cations and other chemical
crosslinkers.
[0032] The present invention also relates to a method for making
dip-molded latex articles by:
[0033] (a) immersing a mold having the desired shape of the final
article in a coagulant bath comprising a solution of a metal
salt;
[0034] (b) removing the mold from the bath and optionally drying
the mold;
[0035] (c) immersing the mold as treated in step (a) and (b) in the
compounded latex composition of the present invention;
[0036] (d) removing the mold from the latex composition and
optionally immersing the latex coated mold in a water bath;
[0037] (e) optionally drying the latex coated mold;
[0038] (f) heat treating the latex coated mold obtained from step
(d) or (e) at a temperature of 80 to 180.degree. C.; and
[0039] (g) removing the latex article from the mold,
[0040] and to latex articles that are made of the polymer latex
according to the present invention.
[0041] In addition to dip-molding applications the polymer latex of
the present invention can also be used for coating and impregnating
of all kind of substrates. The present polymer latex is
particularly suitable for impregnating and coating of textile
substrates.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] FIG. 1. Dipped polymer films. Increase of tensile strength
as function of heat treating. Definition of .DELTA.F max see in
Example 1.
[0043] FIG. 2. Comparison of physical film properties. The polymer
films of Examples 1 to 4 were dipped without any curing agents
according to the description. Curing paste of the conventional
vulcanization: 1 phr ZnO, 1 phr Sulfur, 1 phr LDA, pH: 9.7
(NH.sub.3).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0044] It is a surprising result of the present invention that a
polymer latex made by free radical emulsion polymerization can be
formulated into a compounded latex composition that is
substantially free of usual crosslinking and vulcanization
compounds but nevertheless after forming and heat-treating the
latex articles exhibits all the desired properties that are
necessary for medical applications. The final products have the
desired mechanical properties like tensile strength and elongation
and the desired esthetic properties described above very similar to
the products obtained by using typical crosslinking or
vulcanization systems.
[0045] Furthermore the polymer latex according to the present
invention can be successfully used in usual dip-molding processes
of making latex products in that in the dip-molding process a
continuous film of the polymer latex composition can be deposited
onto the mold immersed into the compounded latex composition,
thereby resulting in substantially uniform film thickness of the
final product which is also an important requirement, especially
for medical applications.
[0046] An important feature in order to achieve the above discussed
desired result according to the present invention is that the
polymer latex of the present invention comprises polymer particles
having at least one hard phase segment having a glass transition
temperature (T.sub.g) of at least 50.degree. C. and at least one
soft phase segment having a glass transition temperature (T.sub.g)
of 10.degree. C. at most. In the context of the present invention
the term "segment" shall be understood as a polymer block that is
an integral part of the entire polymer molecule. Consequently the
polymer molecule(s) forming the polymer particles of the latex has
hard segments and soft segments that are to some extent bonded to
each other, for example, by means of a covalent bond. Thus the
polymer particles of the present invention are not mixtures of
polymers having different T.sub.g's but according to a preferred
embodiment of the present invention, for example the soft segment
is grafted by means of covalent bonds onto the hard segment, or
vice versa.
[0047] According to preferred embodiments of the present invention
the T.sub.g of the hard phase segment in the polymer particles is
at least 70.degree. C., preferably at least 80.degree. C., and most
preferred at least 90.degree. C.
[0048] The soft phase segment of the polymer particles according to
the present invention may have a T.sub.g of 0.degree. C. at most,
preferably -10.degree. C. at most, more preferred -20.degree. C. at
most, and most preferred -30.degree. C. at most.
[0049] The T.sub.g of the at least two different segments of the
polymer particles of the present invention can be easily determined
using differential scanning calorimetry (DSC) according to ASTM
D3418-03.
[0050] The polymer latex according to the present invention
comprises a total amount of hard phase segments of 2-40 weight
percent and a total amount of soft phase segments of 6-98 weight
percent, based on the total weight of the polymer particles.
According to a preferred embodiment the total amount of hard phase
segments is 5-30 weight percent and the total amount of the soft
phase segments is 70-95 weight percent. It is most preferred if the
total amount of hard phase segments is 10-25 weight percent and the
total amount of soft phase segments is 75-90 weight percent,
whereby the weight percentages are based on the total weight of the
polymer particles.
[0051] Although according to the present invention single soft
phase and/or hard phase segments may be constituted by homo-polymer
blocks it is preferred that at least the soft phase segment(s)
is(are) constituted by copolymer blocks, particularly copolymer
blocks that contain in addition to structural units derived from at
least one conjugated diene structural units that are derived from
at least one other ethylenically unsaturated co-monomer. In a
particularly preferred embodiment the soft phase and the hard phase
segments are constituted by copolymer blocks. Most preferably, if
copolymer blocks are present either as soft phase segment or hard
phase segment or both these copolymer blocks are random copolymer
blocks. These copolymer blocks can be easily prepared by
free-radical emulsion polymerization in a great versatility. Thus,
it is a particular advantage of the present invention that the
latex polymer can by easily tailored to the specific needs of the
particular end use.
[0052] It is well known to a person skilled in the art how to
adjust the T.sub.g of the hard phase segment or the soft phase
segment by selecting a monomer or a mixture of monomers that result
in the desired T.sub.g in the polymerization process. For example,
the T.sub.g's of the homopolymers of a wide range of monomers are
disclosed in J. Brandrup, E. H. Immergut (eds.), Polymer Handbook,
Second Edition, Wiley, New York,1975
[0053] For random copolymers the T.sub.g depends on the weight
fractions of the component monomers and the T.sub.g's of the
component homopolymers. A rough correlation is described by the Fox
equation: 1/T.sub.g=w/T.sub.g1+w.sub.2/T.sub.g2+ . . .
[0054] where w.sub.1, w.sub.2, . . . are the weight fractions of
the component monomers and T.sub.g1, T.sub.g2, . . . are the
T.sub.g's of the component homopolymers in .degree. K. The Fox
equation allows a first orientation for the T.sub.g of a copolymer.
For the resulting real T.sub.g's also further parameters of the
used monomers and the process have an important influence.
Therefore physical methods for the determination of the T.sub.g
like the DSC method are still necessary.
[0055] It is within the routine of a person skilled in the art to
select in the copolymerization process, as will be discussed below,
certain monomers or mixture of monomers that give rise to a hard
segment or a soft segment in the appropriate amounts in order to
obtain a polymer particle within the ranges of T.sub.g for the hard
segments and the soft segments as well as the relative amounts of
both segments, as specified above for the present invention.
[0056] The polymer particles of the present invention contain
structural units derived from conjugated dienes.
[0057] Particularly preferred dienes are butadienes, isoprene and
chloroprene having a T.sub.g of -83.degree. C., -72.degree. C. and
-45.degree. C., respectively. Examples for other soft monomers are
ethylene (T.sub.g -80.degree. C.), octyl acrylate (T.sub.g
-65.degree. C.), butyl acrylate (T.sub.g -54.degree. C.), ethyl
acrylate (T.sub.g -24.degree. C.).
[0058] Examples of hard monomers are isobutyl methacrylate (T.sub.g
+55.degree. C.), acrylonitrile (T.sub.g +100.degree. C.), styrene
(T.sub.g +100.degree. C.), methyl methacrylate (T.sub.g
+105.degree. C.).
[0059] Furthermore, for the soft segment a mixture of soft and hard
monomers can be used as long as the T.sub.g of the entire soft
segment is within the given ranges. The same applies for the hard
segment.
[0060] In addition to the above exemplified monomers also all other
monomers known to a person skilled in the art having an
.alpha.,.beta.-unsaturated group can be used according to the
present invention.
[0061] Since the conjugated dienes, as exemplified above, have a
very low T.sub.g the conjugated dienes are preferably used in the
soft phase segment of the polymer particles according to the
present invention.
[0062] According to a preferred embodiment of the present invention
the soft phase segments contain independently from each other
structural units derived from the group consisting of conjugated
dienes; ethylenically unsaturated mono-carboxylic acids;
ethylenically unsaturated di-carboxylic acids, anhydrides,
mono-esters and mono-amides thereof; (meth)acryl nitrile; styrene;
substituted styrenes; alpha-methyl styrene; C1 to C10 esters of
(meth)acrylic acid; amides of (meth)acrylic acid; ethylenically
unsaturated compounds comprising N-methylol amide groups, and ester
and ether derivatives thereof; and mixtures thereof.
[0063] Likewise, according to a preferred embodiment of the present
invention the hard phase segments contain independently from each
other structural units derived from monomers selected from the
group consisting of ethylenically unsaturated mono-carboxylic
acids; unsaturated di-carboxylic acids, anhydrides, mono-esters and
mono-amides thereof; (meth)acryl nitrile; styrene; substituted
styrenes; alpha-methyl styrene; C1 to C4 esters of (meth)acrylic
acid; amides of (meth)acrylic acid; and mixtures thereof.
[0064] According to a particularly preferred embodiment of the
present invention the polymer particles of the inventive latex are
carboxylated whereby the carboxyl-functional structural units may
be either present in the soft phase segment or in the hard phase
segment, or both.
[0065] By adjusting the carboxylation grade of the polymer
particles of the present invention an optimum balance between
tensile strength and elasticity of the final product can be
achieved.
[0066] Without wanting to be bound by theory it is believed that
the carboxyl groups in the polymer particles may function as
possible crosslinking sites whereby the amount of metal cations in
the coagulation bath the dip-mold is immersed prior to immersing
into the compounded polymer latex composition is already sufficient
in order to induce crosslinking in order to increase the tensile
strength of the final product. But contrary to the teaching of the
prior art, as discussed above, the presence of additional
polyvalent metal cations in the compounded polymer latex
composition is not necessary. The desired degree of tensile
strength in the final product can be even achieved without the
presence of carboxylic groups in the polymer particles.
[0067] Suitable carboxyl-functional monomers that can be used
according to the present invention are the monocarboxylic acids,
like acrylic acid or methacrylic acid, crotonic acid, vinyl acetic
acid, sorbic acid or ethylenically unsaturated dicarboxylic acids,
like fumaric acid or maleic acid, or the anhydride monoesters or
monoamides thereof, like acrylamide and methacrylamide.
[0068] According to another embodiment of the present invention the
polymer particles may contain functional groups that are capable of
self-crosslinking upon heat treatment. Examples of groups capable
of self-crosslinking are selected from N-methylol amide groups, and
ester and ether derivatives thereof; and mixtures thereof. These
groups can be introduced into the polymer particles of the present
invention by using ethylenically unsaturated monomers containing
these functional groups. Preferred monomers are N-methylol
acrylamide, N-methylol methacrylamide,
N-methoxymethyl-(meth)acrylamide,
N-n-butoxy-methyl-(meth)acrylamide,
N-acetoxymethyl-(meth)acrylamide, N(-2,2-dimethoxy-
1-hydroxyethyl)acrylamide.
[0069] Furthermore ethylenically unsaturated monomers with sulfonic
acid or sulfonate groups can be used. Examples are styrene sulfonic
acid, vinyl sulfonic acid, allyl sulfonic acid, methallyl sulfonic
acid, (meth)acrylic acid-3-sulfopropylester,
2-acrylamido-2-methylpropane sulfonic acid. Beside these sulfonic
acids also their water soluble salts can be used. Preferred are
(meth)acrylic acid-3-sulfopropylester, 2-acrylamido-2-methylpropane
sulfonic acid
[0070] Another important property of the polymer latex of the
present invention is that it can be compounded to a polymer latex
composition that is suitable for dip-molding processes. For this
application it is important that the polymer latex has a certain
maximum electrolyte stability determined as critical coagulation
concentration of less than 30 mmol/l CaCl.sub.2 (determined for a
total solids content of the latex of 0.1% at pH 10).
[0071] If the electrolyte stability is too high then it is
difficult to coagulate the polymer latex in a dip-molding process
with the result that either no continuous film of the polymer latex
on the immersed mold is formed or the thickness of the resulting
product is non-uniform.
[0072] It is within the routine of the person skilled in the art to
appropriately adjust the electrolyte stability of a polymer latex.
The electrolyte stability will depend on certain different factors,
for example, amount and selection of monomers to be used for making
the polymer latex, especially monomers containing polar-functional
groups, as well as the selection and amount of the stabilizing
system, for example, the emulsion polymerization process for making
the polymer latex. The stabilizing system may contain
surface-active agents and/or protective colloids.
[0073] A person skilled in the art is able, depending on the
selected monomers and their relative amounts for making the polymer
latex of the present invention, to adjust the stabilizing system in
order to achieve an electrolyte stability according to the present
invention.
[0074] Since there are so many different influences on the
electrolyte stability the adjustment has to be made by trial and
error experiments. But this can be easily done without any
inappropriate efforts using the test method for electrolyte
stability, as disclosed above.
[0075] Furthermore the working examples below provide examples how
the appropriate electrolyte stability of the polymer latex of the
present invention can be adjusted.
[0076] The polymer latex of the present invention can be prepared
by a conventional emulsion polymerization process using multistep
or multisequential polymerization in order to obtain the segments
of different T.sub.g.
[0077] In the process according to the present invention first a
selected monomer or mixture of monomers in order to obtain either a
hard phase segment or a soft phase segment are polymerized in
presence of a free radical-forming activator, an emulsifier and in
presence of water. Thereafter a second monomer or mixture of
monomers that results in a hard phase if the first segment was a
soft phase, or vice versa, is polymerized in the same reaction
mixture. Thereby a multistep or multisequential copolymerization
takes place. It is also possible to introduce into the polymer
particles more than one hard and/or more than one soft segment.
Thereby it is not important in which sequence the hard and soft
segments are polymerized. For example, it is also within the
present invention to first polymerize two or more soft or hard
segments and thereafter at least one of the respective other
segments. It is, of course, also possible to polymerize hard and
soft segments in an alternative sequence.
[0078] It is only important that there is at least one hard and at
least one soft segment in the relative amounts, as discussed above
with respect to the present invention.
[0079] According to one preferred embodiment first a hard phase
segment is polymerized, followed by a soft phase segment and then
again a hard phase segment is polymerized.
[0080] It is also possible in the polymerization process of the
present invention to use a seed latex for polymerization of the
first segment, irrespective of whether it is a hard or a soft
segment, in order to adjust the desired particle size. The seed
suitable according to the invention consists of, for example,
lattices based on the lattices to be produced according to the
present invention. Alternatively, also the seed may be a latex
containing only monomers that would constitute either a hard
segment or a soft segment of the latex of the present invention.
But it is also possible to use a seed latex that is totally
different from the latex according to the present invention, as
long as the desired particle size is obtained.
[0081] The particle size of the initially introduced seed is
preferably in the range from 10-80 nm, even more preferred in the
range from 20-50 nm.
[0082] Inorganic pigments whose particles can act as seeds for the
subsequent polymerization can also be used as seed in the process
according to the invention. Pigments having an average particle
size of 5-100 nm, such as silica sole, are for example
suitable.
[0083] The quantity of the seed to be used depends on the size of
the latex to be produced and is usually 0.01-5 weight percent,
preferably 0.1-2 weight percent, based on the total amount of
monomers used in the polymerization process.
[0084] Free radical initiators which may be used in the process
according to the present invention are, for example, inorganic
peroxy compounds, such as hydrogen peroxide, sodium, potassium and
ammonium peroxydisulfate, peroxycarbonates and peroxyborates, as
well as organic peroxy compounds, such as alkyl hydroperoxides,
dialkyl peroxides, acyl hydroperoxides, and diacyl peroxides, as
well as esters, such as tertiary butyl perbenzoate and combinations
of inorganic and organic initiators. The quantities of initiators
are usually within the range of 0.01-5 weight percent, based on the
total amount of monomers used, preferably in the range of 0.05-2.0
weight percent. The above mentioned inorganic and organic peroxy
compounds may also be used in a known manner in combination with
one or more suitable reducing agents. Examples of such reducing
agents which may be mentioned are sulfur dioxide, alkali metal
disulfites, alkali metal and ammonium hydrogen sulfites,
thiosulfates, dithionites and formaldehyde sulfoxylates, as well as
hydroxylamine hydrochloride, hydrazine sulfate, iron (II) sulfate,
glucose and ascorbic acid. The quantity of the reducing agent is
0.01-1.0 weight percent, based on the total weight of monomers.
[0085] The most suitable initiator or initiator system may be
determined by means of preliminary tests. Suitability is in
particular dependent upon the nature of the used monomers and the
polymerization reaction temperature.
[0086] It is frequently advisable to perform the emulsion
polymerization additionally in the present of buffer substances and
chelating agents. Suitable substances are, for example, alkali
metal phosphates and pyrophosphates (buffer substances) and the
alkali metal salts of ethylenediaminetetraacetic acid (EDTA) as
chelating agents. The quantity of buffer substances and chelating
agents is usually 0.01-1 weight percent, based on the total
quantity of monomers.
[0087] Furthermore, it may be advantageous to use chain transfer
agents (regulator) in emulsion polymerization. Typical agents are,
for example, organic sulfur compounds, such as C.sub.1-C.sub.12
alkyl mercaptans, n-dodecylmercaptan and t-dodecylmercaptan being
preferred. The quantity of chain transfer agents, if present, is
usually 0.05-3.0 weight percent, preferably 0.2-2.0 weight percent,
based on the total weight of the used monomers.
[0088] It is also significant in the emulsion polymerization
according to the invention that the addition of the necessary
stabilizer and/or emulsifier is controlled to achieve the desired
particle size and sufficient stabilization to avoid agglomeration
during the polymerization process, but also to achieve a
electrolyte stability as required by the present invention. The
emulsifiers are known and are commonly used in emulsion
polymerization (D. C. Blackley, Emulsion Polymerization, Chapter 7,
Applied Science Publishers Ltd. London 1975).
[0089] Emulsifiers which may be used according to the invention are
in particular so-called anionic emulsifiers, such as high fatty
alcohol sulfates, higher alkyl sulfonates, alkyl aryl sulfonates,
aryl sulfonates together with the condensation products thereof
with formaldehyde, salts of sulfosuccinic acid esters and sulfate
ethylene oxide adducts. Preferably the polymer latex of the present
invention is free of sulfates of an ethoxylated phenol.
[0090] So-called non-ionic emulsifiers may also be mentioned, such
as for example, the known reaction products of ethylene oxide with
fatty alcohols, such as lauryl, myristyl, cetyl, stearyl and oleyl
alcohols with fatty acids such as lauric, mauristic, palmitic,
stearic and oleic acid and amides thereof, and with alkyl phenyl
such as isooctyl, isononyl and dodecyl phenol.
[0091] The total quantity of emulsifiers or stabilizers to be used
is calculated such that the latex is stabilized during
polymerization in such a manner that no coagulate is formed but
that on the other hand the required electrolyte stability of the
final polymer latex as required by the present invention is
achieved.
[0092] In polymerizing the different segments of the polymer
particles of the present invention the first segment to be
polymerized can be polymerized in a batch or in a semicontinous
modus, irrespective of whether it is a soft phase segment or hard
phase segment. The second segment may be polymerized using a
semicontinous process. Alternatively it is also possible to
polymerize all segments either using a batch process or a
semicontinous process or it is alternatively possible to use a
batch process or a semicontinous process for the polymerization of
the individual segments in any desired sequence.
[0093] The polymer latex of the present invention is particularly
suitable for dip-molding processes. Therefore, according to one
aspect of the present invention the polymer latex is compounded to
produce a polymer latex composition that can be directly used in
dip-coating processes. To get reproducible good physical film
properties, the pH of the compounded polymer latex composition has
to be adjusted by pH modifiers to be in the range of pH 7 to 11,
preferably 8 to 10. The compounded polymer latex composition
contains the polymer latex of the present invention, the pH
modifiers, preferably ammonia or alkali hydroxides and usual
additives to be used in these compositions selected from
antioxidants, pigments, TiO.sub.2, fillers and dispersing
agents.
[0094] It is possible to use in the compounded polymer latex
compositions according to the present invention to be used in
dip-molding processes conventional vulcanization systems, like
sulfur in combination with accelerators, like thiurams and
carbamates and zinc oxide. But since these components are not
necessary according to the present invention to achieve the desired
mechanical and esthetic properties of the final product but may
create problems with respect to allergenic reactions and other
health hazards, and in addition lead to an increased complexity in
the compounding process the compounded latex composition of the
present invention is preferably free of these components.
[0095] Furthermore the compounded polymer latex composition of the
present invention does not need a crosslinker component, like for
example, polyvalent cations or other polyfunctional organic
compounds suitable to react with functional groups on the latex
particles in order to achieve chemical crosslinking. Consequently
the latex compositions according to the present invention are
preferably substantially free of crosslinker components, especially
of polyvalent cations. By the term "substantially free" is meant
that, for example, polyvalent metal cations may be present at an
impurity level, for example that is introduced without intention
due to a possible impurity of other components, to make either the
latex or the latex composition. For example total polyvalent metal
ions at an impurity level may be present in a concentration of less
than 1 mmol/l, preferably less than 0.5 mmol/l, more preferred less
than 0.3 mmol/l and most preferred less than 0.2 mmol/l.
[0096] In the method for making dip-molded latex articles according
to the present invention first a mold having the desired shape of
the final article is immersed in a coagulant bath comprising a
solution of a metal salt. The coagulant is usually used as a
solution in water, an alcohol or a mixture thereof. As specific
examples of the coagulant the metal salts can be metal halides like
calcium chloride, magnesium chloride, barium chloride, zinc
chloride and aluminum chloride; metal nitrates such as calcium
nitrate, barium nitrate and zinc nitrate; metal sulfates like
calcium sulfate, magnesium sulfate, and aluminum sulfate; and
acetic acid salts such as calcium acetate, barium acetate and zinc
acetate. Most preferred are calcium chloride and calcium nitrate.
The coagulant solution might contain additives to improve the
wetting behavior of the former
[0097] Thereafter the mold is removed from the bath and optionally
dried. The such treated mold is then immersed in the compounded
latex composition according to the present invention. Thereby a
thin film of latex is coagulated on the surface of the mold.
Thereafter the mold is removed from the latex composition and
optionally immersed in a water bath in order to extract, for
example, polar components from the composition and to wash the
coagulated latex film.
[0098] Thereafter the latex coated mold is optionally dried at
temperature below 80.degree. C.
[0099] Finally the latex coated mold is heat treated at a
temperature of 80-180.degree. C. in order to obtain the desired
mechanical properties for the final film product. Then the final
latex film is removed from the mold. The duration of the heat
treatment will depend on the temperature and is typically between 1
and 60 minutes. The higher the temperature the shorter is the
required treatment time.
[0100] The final heat treated polymer latex film has a tensile
strength of at least about 7 MPa and an elongation at break of at
least about 300%, preferably a tensile strength of at least about
10 MPa, an elongation at break of at least about 350% and more
preferred a tensile strength of at least about 15 MPa and an
elongation at break of at least about 400%. These mechanical
properties were measured according to ISO 37:1994.
[0101] Preferably, a polymer latex film according to the present
invention exhibits an increase in tensile strength of at least 2
MPa, preferably at least 4 MPa, more preferred at least 5 MPa, most
preferred at least 6 MPa after heat treatment at 120.degree. C. for
30 minutes compared to the identical polymer latex film kept at
25.degree. C. (room temperature).
[0102] This process can be used for any latex article that can be
produced by a dip-molding process known in the art.
[0103] The present invention is especially applicable for
dip-molded latex articles selected from health care devices, like
surgical gloves, examination gloves, condoms, catheters or all
different kinds of industrial and household gloves.
[0104] A particular advantage of the compounded latex composition
of the present invention is that no kind of crosslinkers is
necessary and is preferably not present in the compounded latex
composition. The lack of polyvalent metal cations above the
impurity level, as discussed above, leads to a considerably
increased stability of the compounded latex composition leading to
an increased pot life. This will add flexibility to the preparation
process. Furthermore, since only few components in addition to the
polymer latex are necessary to compound the latex composition of
the present invention, also the preparation of this composition is
much easier compared to prior art compositions, especially it is
not necessary any longer to exactly determine and measure the
amounts of crosslinkers, accelerators, etc.
[0105] The present invention will be further illustrated with
reference to the following examples.
EXAMPLE 1
[0106] 55 g of a 31% seed latex (particle size 36 nm) are heated to
40.degree. C. in a nitrogen-purged autoclave with 750 g of water, 2
g Na dodecyl benzene sulfonate, 0.5 g of Na.sub.4EDTA, 0.05 g of Na
formaldehyde sulfoxylate, 0.8 g of t-butyl hydroperoxide and an
increment of the hard phase monomers mixture consisting of 94.3 g
methylmethacrylate and 4.0 g methacrylic acid was added. After 1 h
of polymerization an increment of following soft phase
monomer/chain transfer agent mixture consisting of 270 g acrylo
nitrile, 36 g methacrylic acid, 579 g butadiene, and 9 g
t-dodecylmercaptan was added. Over a period of 7 hours an
emulsifier/co-activator feed of 22.5 g Na dodecyl benzene
sulfonate, 0.7 g Na formaldehyde sulphoxylate, and 300 g water was
added. After a total polymerization time of 12 hours the total
solids content was 48.0% corresponding to a conversion of 98%. The
polymerization was short stopped by addition of 20 g of a 5%
aqueous solution of diethylhydroxylamine. The pH was adjusted by
ammonia to pH 7.5 and the residual monomers were removed by vacuum
distillation at 60.degree. C.
EXAMPLE 2
[0107] 55 g of a 31% seed latex (particle size 36 nm) are heated to
40.degree. C. in a nitrogen-purged autoclave with 750 g of water, 2
g Na dodecyl benzene sulfonate, 0.5 g of Na.sub.4EDTA, 0.05 g of Na
formaldehyde sulphoxylate, 0.8 g of t-butyl hydroperoxide. For the
hard phase a feed consisting of 66 g styrene, 28 g acrylonitrile
and 4.0 g methacrylic acid was added within 1 hour. After 2 h of
polymerization a feed of following soft phase monomer/chain
transfer agent mixture consisting of 270 g acrylonitrile, 36 g
methacrylic acid, 579 g butadiene, and 9 g t-dodecylmercaptan was
added within a period of 5 hours. Parallel to the soft phase
monomer feed over a period of 10 hours an emulsifier/co-activator
feed of 22.5 g Na dodecyl benzene sulfonate, 0.7 g Na formaldehyde
sulfoxylate, and 300 g water was added. After a total
polymerization time of 15 hours the total solids content was 48.2%
corresponding to a conversion of 98%. The polymerization was short
stopped by addition of 20 g of a 5% aqueous solution of
diethylhydroxylamine. The pH was adjusted by ammonia to pH 7.5 and
the residual monomers were removed by vacuum distillation at
60.degree. C.
EXAMPLE 3
[0108] The polymerization was carried out like in Example 2 but for
the hard phase a feed consisting of 80 g methylmethacrylate, 14 g
butylacrylate and 4.0 g methacrylic acid was added within 1
hour.
[0109] After a total polymerization time of 15 hours the total
solids content was 47.6% corresponding to a conversion of 97%. The
polymerization was short stopped by addition of 20 g of a 5%
aqueous solution of diethylhydroxylamine. The pH was adjusted by
ammonia to pH 7.5 and the residual monomers were removed by vacuum
distillation at 60.degree. C.
EXAMPLE 4
[0110] 1800 g of a carboxylated NBR latex (Perbunan N Latex VT-LA,
45%, from Polymer Latex) was heated together with 200 g additional
water to 60.degree. C. in a nitrogen purged vessel and an increment
of 190 g methylmethacrylate was added. The mixture was equilibrated
for 1 hour and then the polymerization was started by addition of
0.8 g of t-butyl hydroperoxide and 0.8 g of Na formaldehyde
sulfoxylate dissolved in 20 g of water. After 5 hours the
conversion was nearly 100%. The pH was adjusted by ammonia to pH
7.5 and the residual monomers were removed by vacuum.
[0111] Film preparation (dipped films): The pH was adjusted to 9.7
(NH.sub.3) and the latex was diluted to a TSC of 33%. The dipping
was performed using unglazed porcelain plates as moulds. As
coagulant a calcium nitrate solution with a density of 1.21 g/ccm
at 60.degree. C. was applied. The coagulant dip (3 sec) was
followed by the latex dip (30 sec.) and by air drying (1 minute)
and finally by a leaching of 20 min. After the leaching a heat
treating at 120.degree. C. (30 min) was performed.
[0112] Film preparation (dried Films): The latex films were
prepared by a drying at room temperature. Followed by a heating at
40.degree. C.
[0113] Film Testing/results: The physical film properties of the
dipped polymer films were tested according to the ISO 37:1994. FIG.
1 exemplary the characteristic temperature impact (120.degree. C.
30 min) on the tensile strength. The increase of the tensile
strength is defined as .DELTA.F max according to the drawing. Table
1 summarizes this .DELTA.F max values for the examples 1-4. The
results are compared with one vulcanized dipping latex as control
experiment. The characteristic behavior of the inventive latex
compounds is clearly demonstrated. Only the inventive latex
compounds/latex films shows an significant tensile strength
increase.
[0114] FIG. 2 compares the physical properties of examples 1-4
(heat treated) with a vulcanized Latex film, prepared from a
typical dipping latex. It is obvious, that the inventive latex
compositions/latex films realize the physical film performance of
conventional vulcanisates, but without any curing chemicals.
[0115] TMA/results: Measurement of dried Latex films. The polymer
film is placed between two quartz discs and the penetration of a
needle (1 mm diameter) was followed using a force of 0.5 N at a
heating rate of 5.degree. K/min over a temperature range from -50
to +150.degree. C. The penetration is calculated in % of the used
film thickness. The D 100 values are defined by the needle
penetration in % at 100.degree. C. When the upper temperature of
150.degree. C. was reached, the temperature was kept at 150.degree.
C. for 5 min, then the sample was cooled down to -50.degree. C.,
the needle was placed at a different part of the film surface and a
second temperature run was started under the same conditions. The
.DELTA.D 100 value is calculated by: D 100 of the first temperature
run minus the D 100 of a second temperature run, therefore a
.DELTA.D 100 value>0 represent a increase of the film hardness
as function of the heat treatment. Tab. 2 summarizes the .DELTA.D
100 results of examples 1-4 and of one control experiment. The
characteristic behavior of the inventive latex compositions is
obvious. Only the inventive latex compositions/latex films show the
characteristic film hardening as function of the heat treatment.
TABLE-US-00001 TABLE 1 Quantification of the tensile strength
increase by .DELTA.Fmax Example Example 1 Example 2 Example 3
Example 4 Control .sup.1) .DELTA.Fmax 10.6 11.3 6.0 10.0 0 [MPa]
.sup.1) Perbunan VT-LA using the same film preparation (no
vulcanization)
[0116] TABLE-US-00002 TABLE 2 Decrease of the D.sub.100 value (TMA)
as function of heat treating. The .DELTA.D.sub.100 value is
calculated as difference from the first and the second TMA run.
Example Example 1 Example 2 Example 3 Example 4 Control .sup.2)
.DELTA.D.sub.100 [%] 9 9 11 18 0 .sup.2) Perbunan VT-LA using the
same film preparation (no vulcanization)
[0117] Influence of electrolyte stability: The impact of the
electrolyte stability of the polymer latex of the present invention
is demonstrated by Table 3. The electrolyte stability is determined
as critical coagulation concentration (ccc) for a total solids
content of the latex of 0.1% at pH 10 and room temperature. Under
these conditions the latex is titrated with a 2.0 mol/l solution of
calcium chloride (adjusted to pH 10) and the turbidity of the latex
was followed by photometric measurement using a Mettler Phototrode
DP550 as a function of calcium chloride concentration. The ccc is
taken from the inflection point of the turbidity/electrolyte
concentration curve. The results are shown in Table 3. The film
preparation was performed according to the description using
unglazed porcelain plates as molds and an aqueous calcium nitrate
solution with a density of 1.21 g/ccm at 60.degree. C. as
coagulant.
[0118] Only the examples 1-4 and the control 1 (commercially
available X-NBR with low ccc) can be processed by the described
coagulation process leading to uniform polymer films, while the
control 2 (commercially available X-NBR Latex with high ccc) shows
only an inhomogeneous, partial coagulation leading to non-uniform
polymer films. TABLE-US-00003 TABLE 3 Critical coagulation
concentration and coagulant dipping behavior Example Example 1
Example 2 Example 3 Example 4 Control 1* Control 2** CCC [mmol/l
CaCl.sub.2) 10 9 12 12 6 >100 Results of Uniform Uniform uniform
uniform uniform Incomplete coagulant Polymer Polymer polymer
polymer polymer Coagulation dipping Films Films films films films
none uniform polymer films *Perbunan N Latex VT-LA (from
PolymerLatex) **Perbunan N Latex 3415 M (from PolymerLatex)
* * * * *