Curable composition of halogen-containing polymer and crosslinking agent therefor

A curable composition consisting essentially of PA1 (1) 100 parts by weight of a halogen-containing polymer, PA1 (2) 0.1 to 10 parts by weight of a 3,5-dimercapto-1,2,4-triazole compound defined in claim 1 as a crosslinking agent, PA1 (b) 0.5 to 50 parts by weight of a compound of a metal of group II or IVa of the periodic table as an acid acceptor.

This invention relates to a curable composition of a halogen-containing 
polymer, and to a crosslinking agent therefor which can readily and 
effectively induce curing of the halogen-containing polymer. 
More specifically, this invention pertains to a curable composition 
consisting essentially of 
(1) 100 parts of weight of a halogen-containing polymer, 
(2) 0.1 to 10 parts by weight of a 3,5-dimercapto-1,2,4-triazole compound 
as a crosslinking agent which is selected from compounds of the following 
formulae 
##STR1## 
wherein 
R.sub.1 represents a member selected from the class consisting of a 
hydrogen atom, alkyl groups containing 1 to 18 carbon atoms, cycloalkyl 
groups containing 5 to 18 carbon atoms, alkenyl groups containing 2 to 18 
carbon atoms, aryl groups containing 6 to 18 carbon atoms and aralkyl 
groups containing 7 to 18 carbon atoms; 
R.sub.2 and R.sub.3 are identical or different, and each represents a 
member selected from the class consisting of a hydrogen atom, a sodium 
atom, a potassium atom, groups of the formula 
##STR2## 
and groups of the formula 
##STR3## 
in which 
R.sub.4 and R.sub.5 are identical or different and each represents a member 
selected from the class consisting of a hydrogen atom, alkyl groups 
containing 1 to 12 carbon atoms, cycloalkyl groups containing 5 to 12 
carbon atoms, aryl groups containing 6 to 12 carbon atoms and aralkyl 
groups containing 7 to 18 carbon atoms, or R.sub.4 and R.sub.5 may form a 
heterocyclic ring in combination with each other or through another 
heteroatom, and R.sub.6 represents a member selected from the class 
consisting of alkyl groups containing 1 to 18 carbon atoms, cycloalkyl 
groups containing 5 to 18 carbon atoms, alkenyl groups containing 2 to 18 
carbon atoms, aryl groups containing 6 to 18 carbon atoms, aralkyl groups 
containing 7 to 18 carbon atoms and groups of the formula 
##STR4## 
in which 
R.sub.7 represents a member selected from the class consisting of alkylene 
groups containing 1 to 8 carbon atoms, alkenylene groups containing 1 to 8 
carbon atoms, cycloalkylene groups containing 6 to 12 carbon atoms and 
arylene groups containing 6 to 12 carbon atoms; 
and SR.sub.2 and SR.sub.3 may be bonded within the same molecular or among 
a plurality of molecules, forming a group of the formula 
##STR5## 
in which R.sub.7 is as defined above, and 
(3) 0.5 to 50 parts by weight of a compound of a metal of group II or IVa 
of the periodic table as an acid acceptor. The invention also relates to 
the use of the aforesaid compounds of formula (I) and (I') as a 
crosslinking for halogen-containing polymers. 
Halogen-containing polymers such as polychloroprene, polyepichlorohydrin, 
an epichlorohydrin/ethylene oxide copolymer, chlorine-containing acrylic 
rubber, chlorinated polyethylene, brominated butyl rubber, fluorine rubber 
and polyvinyl chloride in the cured state find extensive use as materials 
having superior thermal stability, oil resistance and chemical resistance. 
It has been difficult however to cure the halogen-containing polymers 
effectively because the carbon-halogen bond in these polymers is 
chemically stable. 
Numerous curing agents for halogen-containing polymers have been suggested 
heretofore, but none have shown a satisfactory curing effect. 
2-Mercaptoimidazoline, a typical curing agent now in commercial use, too, 
has the defect that it cannot cure polymers having relatively low 
reactivity, such as chlorinated polyethylene or polyvinyl chloride, at a 
feasible speed. In addition, it has been pointed out that 
2-mercaptoimidazoline may be carcinogenic (P. R. Johnson, Rubber Journal, 
pages 37-44, April 1973). 
In view of the state of the art, it has been desired to develop other 
curing agents of industrial value which can easily and effectively cure 
halogen-containing polymers relatively low reactivity. 
We have worked extensively in order to develop such curing agents, and 
found that 3,5-dimercapto-1,2,4-triazoles of formula (I) or (I') given 
hereinabove are very useful as crosslinking agents which readily and 
effectively exert a curing action on a wide range of halogen-containing 
polymers including those of relatively low reactivity as exemplified 
hereinabove. 
It is known that a certain compound which may be included within formula 
(I') representing the crosslinking agent of the present invention is an 
effective additive for a photographic silver halide emulsion prepared by 
forming silver halide in the presence of a bismuth ion (Japanese Laid-Open 
Patent Publication No. 96719/74). 
It was reported that a compound corresponding to formula (I') in which 
R.sub.1 is phenyl and R.sub.2 and R.sub.3 are hydrogens was investigated 
for utilization as a vulcanization accelerator in vulcanizing natural 
rubber using sulfur as a vulcanizer (Journal of the Society of Rubber 
Industry, Japan, Vol. 35, pages 166-170 (1962)). The report shows that in 
a Mooney scorch test at 250.degree. F., the increase of Mooney value was 
less than 5 points with this particular compound within 120 minutes after 
the start of the test. This suggests the unacceptability of the compound 
as an accelerator for sulfur-vulcanization of natural rubber. 
Unexpectedly, we have found that the 3,5-dimercapto-1,2,4-triazole compound 
selected from compounds of formulae (I) and (I'), optionally in 
combination with a vulcanization accelerator, exhibits superior 
performances as a crosslinking agent for a wide variety of 
halogen-containing polymers. It has also been found that cured products 
obtained by curing halogen-containing polymers together with a 
vulcanization accelerator have good properties, and the curing time 
changes little with changes in the amount of the crosslinking agent, thus 
ensuring a good reproducibility of quality. 
It is an object of this invention therefore to provide an improved curable 
composition of a halogen-containing polymer. 
Another object of this invention is to provide a crosslinking agent useful 
for such a curable composition. 
The above and other objects and advantages of this invention will become 
more apparent from the following description. 
The halogen-containing polymer in the curable composition of this invention 
includes a variety of polymers such as chlorinated polyethylene, a 
chlorinated ethylene-propylene copolymer, a chlorinated 
ethylene/propylene/nonconjugated diene terpolymer, chlorosulfonated 
polyethylene, polyvinyl chloride, chlorine-containing acrylic rubber, 
chlorinated butyl rubber, brominated butyl rubber, fluorine rubber, 
polychloroprene, polyepichlorohydrin, an epichlorohydrin/allyl glycidyl 
ether copolymer, an epichlorohydrin/ethylene copolymer, and an 
epichlorohydrin/ethylene oxide/allyl glycidyl ether terpolymer. 
The crosslinking agent used in this invention is 
3,5-dimercapto-1,2,4-triazole or its derivatives of formulae (I) and (I'). 
In these formulae, R.sub.1 is selected from the class consisting of alkyl 
groups containing 1 to 18 carbon atoms, preferably 1 to 7 carbon atoms, 
such as methyl, ethyl, isopropyl or heptyl; cycloalkyl groups containing 5 
to 18 carbon atoms, preferably 6 to 14 carbon atoms, such as cyclohexyl, 
4-ethylcyclohexyl or 4-(2-ethyl)hexyl-cyclohexyl; alkenyl groups 
containing 2 to 18 carbon atoms, preferably 3 to 18 carbon atoms, such as 
allyl or oleyl; aryl groups containing 6 to 18 carbon atoms, preferably 6 
to 8 carbon atoms, such as phenyl, tolyl or p-ethylphenyl; and aralkyl 
groups containing 7 to 18 carbon atoms, preferably 7 to 10 carbon atoms, 
such as benzyl or phenethyl. 
In the formulae (I) and (I'), R.sub.2 and R.sub.3 are identical or 
different, and each represents a member selected from the class consisting 
of a hydrogen atom, a sodium atom, a potassium atom, groups of the formula 
##STR6## 
and groups of the formula 
##STR7## 
R.sub.4 and R.sub.5 in the above definition are identical or different, and 
each represents a member selected from the class consisting of a hydrogen 
atom, alkyl groups containing 1 to 12 carbon atoms, preferably 1 to 8 
carbon atoms, cycloalkyl groups containing 5 to 12 carbon atoms, 
preferably 6 to 8 carbon atoms, aryl groups containing 6 to 12 carbon 
atoms, preferably 6 or 7 carbon atoms and aralkyl groups containing 7 to 
18 carbon atoms, preferably 7 or 8 carbon atoms. Or R.sub.4 and R.sub.5 
may together form a heterocyclic ring preferably having 5 to 8 carbon 
atoms, or may form a heterocyclic ring through another heteroatom 
preferably oxygen or nitrogen. 
Specific examples of the alkyl groups for R.sub.4 and R.sub.5 are methyl, 
ethyl, t-butyl and octyl; examples of cycloalkyl group are cyclohexyl and 
4-ethyl-cyclohexyl; examples of the aryl group are phenyl and tolyl; and 
examples of the aralkyl group are benzyl and phenethyl. Examples of the 
heterocyclic ring formed by R.sub.4 and R.sub.5 are piperidino and 
pipecolino, and examples of the heterocyclic ring formed by these groups 
through another heteroatom are morpholino and piperazino. 
In the group 
##STR8## 
R.sub.6 is a member selected from the class consisting of alkyl groups 
containing 1 to 18 carbon atoms, preferably 1 to 17 carbon atoms, such as 
methyl, isopropyl, 2-ethyl-pentyl and heptadecyl; cycloalkyl groups 
containing 5 to 18 carbon atoms, preferably 6 to 8 carbon atoms, such as 
cyclohexyl and 4-ethyl-cyclohexyl; alkenyl groups containing 2 to 18 
carbon atoms, preferably 6 to 17 carbon atoms, such as 2-hexenyl and 
heptadecenyl; aryl groups containing 6 to 18 carbon atoms, preferably 6 or 
7 carbon atoms, such as phenyl and tolyl; and aralkyl groups containing 7 
to 18 carbon atoms, preferably 7 or 8 carbon atoms, such as benzyl and 
phenethyl. 
R.sub.6 may also represent the group 
##STR9## 
R.sub.7 is a member selected from the class consisting of alkylene groups 
containing 1 to 8 carbon atoms, preferably 2 to 8 carbon atoms, such as 
ethylene, tetramethylene, hexamethylene and octamethylene; alkenylene 
groups containing 1 to 8 carbon atoms, preferably 4 to 8 carbon atoms, 
such as 2-butenylene, 3-hexenylene and 4-octenylene; cycloalkylene groups 
containing 6 to 12 carbon atoms, preferably 6 carbon atoms, such as 
1,4-cyclohexylene; and arylene groups containing 6 to 12 carbon atoms, 
preferably 6 carbon atoms, such as o-phenylene, m-phenylene and 
p-phenylene. 
SR.sub.2 and SR.sub.3 in each of formulae (I) and (I'), taken together, may 
form a group of the formula 
##STR10## 
within the same molecule or among different molecules. 
Typical examples of the crosslinking agent of formula (I) or (I') include 
3,5-dimercapto-1,2,4-triazole, 
1-methyl-3,5-dimercapto-1,2,4-triazole, 
1-allyl-3,5-dimercapto-1,2,4-triazole, 
3,5-dimercapto-1-phenyl-1,2,4-triazole, 
3,5-dimercapto-1,2-triazole monosodium salt, 
3,5-dimercapto-1-methyl-1,2,4-triazole disodium salt, 
3,5-dimercapto-1-ethyl-1,2,4-triazole monopotassium salt, 
1-allyl-3,5-dimercapto-1,2,4-triazole dipotassium salt, 
N-methyl-3(5-mercapto-1-phenyl-1,2,4-triazolyl)sulfenamide, 
N,N-dimethyl-3(5-mercapto-1-phenyl-1,2,4-triazolyl)sulfenamide, 
N,N-dicyclohexyl-3(1-allyl-5-mercapto-1,2,4-triazolyl)sulfenamide, 
1-methyl-3-mercapto-1,2,4-triazolyl-5-thiol acetate, 
1-ethyl-3-mercapto-1,2,4-triazolyl-5-thiol stearate, 
1-allyl-5-mercapto-1,2,4-triazolyl-3-thiol benzoate, 
1-phenyl-1,2,4-triazolyl-3,5-dithiol-di-p-toluylate, 
bis(3-mercapto-1-phenyl-1,2,4-triazolyl)-5-thiol sebacata, 
4-methyl-3,5-dimercapto-1,2,4-triazole, 
4-allyl-3,5-dimercapto-1,2,4-triazole, 
4-phenyl-3,5-dimercapto-1,2,4-triazole, 
4-methyl-3,5-dimercapto-1,2,4-triazole disodium salt, 
4-ethyl-3,5-dimercapto-1,2,4-triazole monosodium salt, 
N-methyl-3(4-ethyl-5-mercapto-1,2,4-triazolyl)sulfenamide, 
N,N-diethyl-3(4-phenyl-5-mercapto-1,2,4-triazolyl)sulfenamide, 
N,N-dicyclohexyl-5(4-allyl-3-mercapto-1,2,4-triazolyl)sulfenamide, 
N-tert.butyl-3(4-methyl-5-mercapto-1,2,4-triazolyl)sulfenamide, 
4-methyl-3-mercapto-1,2,4-triazolyl-5-thiol acetate, 
4-phenyl-5-mercapto-1,2,4-triazolyl-3-thiol benzoate, 
4-ethyl-5-mercapto-1,2,4-triazolyl-5-thiol stearate, 
4-allyl-5-mercapto-1,2,4-triazolyl-3-thiol benzoate, 
4-phenyl-1,2,4-triazolyl-3,5-dithiol-di-p-toluylate, and 
bis(4-phenyl-3-mercapto-1,2,4-triazolyl)-5-thiol sebacate. 
The curable composition of this invention further contains a compound of a 
metal of Group II or IVa of the periodic table as an acid acceptor. The 
metal compounds as an acid acceptor include hydroxides, carbonates, 
carboxylates, silicates, borates, and phosphites of metals of Group II of 
the periodic table, preferably Mg, Ba, Ca and Zn; and oxides, basic 
carbonates, basic carboxylates, basic phosphites, basic sulfites, and 
tribasic sulfates of metals of Group IVa of the periodic table, preferably 
Sn and Pb. Specific examples are magnesia, magnesium hydroxide, barium 
hydroxide, magnesium carbonate, barium carbonate, quick lime, slaked lime, 
calcium carbonate, calcium silicate, calcium stearate, zinc stearate, 
calcium phthalate, magnesium phosphite, calcium phosphite, zinc oxide, tin 
oxide, litharge, red lead, white lead, dibasic lead phthalate, dibasic 
lead carbonate, tin stearate, basic lead phosphite, basic tin phosphite, 
basic lead sulfite, and tribasic lead sulfate. 
The curable composition of this invention consists essentially of 100 parts 
by weight of the halogen-containing polymer (1), 0.1 to 10 parts by 
weight, preferably 0.3 to 6 parts by weight, of 
3,5-dimercapto-1,2,4-triazole or its derivative (2) of formula (I) or (I') 
as a crosslinking agent, and 0.5 to 50 parts by weight, preferably 1 to 20 
parts by weight, of the compound of a metal of Group II or IVa of the 
periodic table as an acid acceptor. 
When the amount of the crosslinking agent (2) is below the specified limit, 
the crosslinking effect is insufficient, and when it exceeds the upper 
limit specified, the resulting cured product is comparatively brittle. 
When the amount of the acid acceptor is below the specified limit, the 
resulting cured product has poor resistance to heat deterioration, and 
when it exceeds the upper limit, the mechanical properties (such as 
tensile strength and elongation) of the resulting cured product are 
degraded. 
In addition to the aforesaid three essential ingredients (1), (2) and (3), 
the curable composition of this invention may further include other 
additives conventionally used in the art. 
Examples of such additives include organic or inorganic fillers such as 
calcium carbonate, clay, talc, diatomaceous earth, ferrite, mica powder, 
barium sulfate, graphite, glass fibers, cork powder and wood flour; 
reinforcing agents such as carbon black, silica, calcium silicate and 
basic magnesium carbonate; plasticizers such as dioctyl phthalate, 
diisodecyl adipate, chlorinated paraffin and process oils for rubbers; 
processing aids such as paraffin wax and stearic acid; antioxidants such 
as polymerized trimethyl dihydroquinoline, 
2,6-di-tert-butyl-4-methyl-phenol and dilauryl thiodipropionate; coloring 
agents such as titanium oxide, red iron oxide and ultramarine; and fire 
retarding agents such as antimony trioxide, aluminum hydroxide, zinc 
borate, tris(chloroethyl)phosphate and tetrabromobisphenols. 
The amounts of these additives per 100 parts by weight of the 
halogen-containing polymer are not more than about 1000 parts by weight 
for the fillers; not more than about 200 parts by weight for the 
reinforcing agent; not more than about 100 parts by weight for the 
plasticizers; not more than about 10 parts by weight for the processing 
aids; not more than about 5 parts by weight for the antioxidants; not more 
than about 50 parts by weight for the coloring agents; and not more than 
about 50 parts by weight for the fire retardants. 
The composition of this invention may further include a vulcanization 
accelerator, the use of which is preferred for halogen-containing polymers 
having a relatively low reactivity such as chlorinated polyethylene, 
polyvinyl chloride, chlorinated butyl rubber and polyepichlorohydrin. 
Examples of the vulcanization accelerator are thiuram sulfides, 
dithiocarbamates, sulfenamides, aliphatic or aromatic amines, salts of 
weak acids such as 2-mercaptobenzothiazole, phthalic acid or benzoic acid 
with these amines, and addition products of these amines with alcohols or 
oximes, for examples adducts with cyclohexyl alcohol, or 
cyclohexanoneoxime. 
Specific exmples of these vulcanization accelerators are 
dipentamethylenethiuram tetrasulfide, tetramethylthiuram disulfide, 
cadmium pentamethylenedithiocarbamate, tellurium dimethyldithiocarbamate, 
piperidine pentamethylenedithiocarbamate, cyclohexylamine, dibutylamine, 
di-ortho-tolyl guanidine, acetaldehyde aniline, 
N-cyclohexyl-2-benzothiazothiazyl sulfenamide, 
N,N'-dicyclohexyl-2-benzothiazyl sulfenamide, and a cyclohexylamine salt 
of 2-mercaptobenzothiazole. 
The amount of the vulcanization accelerator is not particularly critical, 
but is preferably 0.2 to 6 parts by weight per 100 parts by weight of the 
halogen-containing polymer. 
The curable composition of this invention can be prepared by uniformly 
blending 100 parts by weight of the halogen-containing polymer (1), 0.1 to 
10 parts by weight of the 3,5-dimercapto-1,2,4-triazole compound (2) as a 
crosslinking agent, 0.5 to 50 parts by weight of the metal compound (3) as 
an acid acceptor, and optionally the other additives exemplified 
hereinabove. Blending can be effected by using known blending devices such 
as a mixing roll, a Banbury mixer, and various kneaders such as a 
pressure-type kneader. The blending temperature that can be employed is 
about 50.degree. to about 100.degree. C. for the curing agent and 
accelerator, and about 60.degree. to about 200.degree. C. for the other 
compounding agents. 
The composition of this invention can be cured by heating it to a 
temperature of, say, about 100.degree. to about 200.degree. C. The heating 
time can be chosen properly, and may, for example, be about 0.5 to 120 
minutes. Curing of the composition can be performed by any desired methods 
such as press-forming under heat in a mold, injection molding, and heat 
molding using a steam can, an air bath, an infrared ray, or microwaves.