Curable composition of elastomeric vinylidene fluoride copolymer

A curable composition comprising an elastomeric vinylidene fluoride copolymer, a polyhydroxy compound and a vulcanization accelerator, characterized in that said copolymer contains from 2 to 50 mol % of vinylidene fluoride units and unsaturated bonds introduced by reacting an untreated elastomeric vinylidene fluoride copolymer dispersed in an aqueous medium, with an aqueous alkaline solution containing an onium compound.

The present invention relates to a curable composition, and more 
particularly, to an elastomeric fluorine-containing copolymer composition 
having improved curability. 
A combination of a hydroxy compound and a suitable vulcanization 
accelerator has been known for the curing of elastomeric vinylidene 
fluoride copolymers (Japanese Examined Patent Publications No. 11138/1976 
and No. 38072/1977). This combination is effective for usual copolymers 
having a high content of vinylidene fluoride particularly with respect to 
the scorch resistance and the permanent set of the cured products. 
However, it is inferior in the ability for curing copolymers having a low 
content of vinylidene fluoride. 
It is an object of the present invention to overcome such a problem 
inherent to the prior art, and to provide a composition which contains an 
elastomeric copolymer having a low content of vinylidene fluoride, and 
which has excellent curability and is capable of presenting a vulcanized 
elastomer having excellent properties. 
The present invention provides a curable composition comprising an 
elastomeric vinylidene fluoride copolymer, a polyhydroxy compound and a 
vulcanization accelerator, characterized in that said copolymer contains 
from 2 to 50 mol % of vinylidene fluoride units and unsaturated bonds 
introduced by reacting an untreated elastomeric vinylidene fluoride 
copolymer dispersed in an aqueous medium, with an aqueous alkaline 
solution containing an onium compound. 
Now, the present invention will be described in detail with reference to 
the preferred embodiments. 
In the present invention, the untreated elastomeric vinylidene fluoride 
copolymer may be a copolymer of vinylidene fluoride with at least one 
comonomer which is capable of forming an elastomeric copolymer when 
copolymerized with vinylidene fluoride. For instance, there may be 
mentioned copolymers of vinylidene fluoride with at least one comonomer 
selected from the group consisting of tetrafluoroethylene, 
chlorotrifluoroethylene, trifluoroethylene, vinyl fluoride, 
hexafluoropropylene, a perfluoro(alkylvinyl ether), a 
perfluoro(alkoxyalkylvinyl ether), ethylene, propylene, isobutylene and 
the like. More specifically, there may be mentioned a vinylidene 
fluoride-tetrafluoroethylenepropylene terpolymer, a vinylidene 
fluoride-tetrafluoroethylene-ethylene-isobutylene four-component 
copolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene 
terpolymer, a vinylidene fluoride-tetrafluoroethylene-perfluoro 
(alkylvinyl ether) terpolymer, and a vinylidene 
fluoride-tetrafluoroethylene-perfluoro(alkoxyalkylvinyl ether) terpolymer, 
and such copolymers to which other comonomer units are further 
incorporated. It is preferred to employ a copolymer having a glass 
transition temperature of not higher than room temperature. 
The proportions of the respective monomer units in such copolymers are 
optionally selected taking into account various properties such as the 
mechanical properties, heat resistance, low temperature resistance, 
chemical resistance, oil resistance, etc. For instance, the vinylidene 
fluoride-tetrafluoroethylene-propylene terpolymer preferably comprises 
from 2 to 50 mol % of vinylidene fluoride units, from 20 to 60 mol % of 
tetrafluoroethylene units and from 20 to 50 mol % of propylene units. 
Further, in such copolymers, the proportion of the vinylidene fluoride 
units is preferably from 2 to 50 mol %, more preferably from 10 to 40 mol 
%. If the proportion is too high, there will be drawbacks with respect to 
the physical properties, such as a decrease in the alkali resistance or in 
the amine resistance of the copolymer. On the other hand, if the 
proportion is too low, the formation of unsaturated bonds will be 
inadequate, and the effectiveness for the improvement of the curability 
deteriorates. 
In the present invention, it is important that such a copolymer contains 
unsaturated bonds which have been introduced by reacting an untreated 
copolymer dispersed in an aqueous solution, with an aqueous alkaline 
solution containing an onium compound. 
The method for dispersing the untreated elastomeric vinylidene fluoride 
copolymer in an aqueous medium is not critical. However, it is 
advantageous to employ a method wherein the copolymer is formed in an 
aqueous medium by means of e.g. emulsion polymerization or suspension 
polymerization, and the latex or aqueous dispersion thereby obtained is 
used as it is. Of course, it is also possible to use an aqueous dispersion 
prepared by dispersing a copolymer prepared by solution polymerization or 
bulk polymerization, by means of a suitable means. In any case, the 
average particle size of the copolymer dispersed in the aqueous medium is 
preferably at most 10 mm in order to conduct the reaction smoothly. 
Further, the aqueous dispersion may contain t-butanol or an organic 
solvent such as trichlorotrifluoroethane or dichlorotetrafluoroethane for 
the purpose of facilitating the reaction. 
In the present invention, the onium compound is preferably the one which 
reacts with a nucleophilic agent and thus serves to promote the solubility 
in an organic medium by the action of the lipophilic cation, or to improve 
the affinity to an organic substance, and which has a function to 
facilitate the reaction of the nucleophilic agent with an organic 
substrate. For instance, there may be employed an ammonium compound with 
its cation center element being nitrogen and various other compounds such 
as a phosphonium compound, an arsonium compound, a sulfonium compound, an 
oxonium compound, a selenonium compound, a stannonium compound and an 
iodonium compound. A quaternary ammonium compound and a quaternary 
phosphonium compound are preferred from the viewpoint of the availability. 
As such a compound, a chloride, a bromide, an iodide, a hydroxide and a 
hydrosulfate are preferred. Among them, a compound having a well balanced 
hydrophilic and lipophilic nature is preferably employed from the 
viewpoint of the activity. As such a suitable compound, there may be 
mentioned tetrabutylammonium bromide, tetrabutylammonium chloride, 
benzyltributylammonium chloride, benzyltriethylammonium bromide, 
tetrabutylammonium hydrogen sulfate, tetrabutylammonium hydroxide, 
benzyltriethylammonium chloride, tetrabutylphosphonium bromide and 
tetrapropylphosphonium bromide. The amount of the onium compound is not 
critical. However, in order to have the dehydrofluorination reaction 
conducted smoothly, it is preferred to adjust the amount depending upon 
the proportion of the vinylidene fluoride units in the copolymer to be 
treated. When the proportion is represented by V (unit: mol %), the amount 
(parts by weight) of th onium compound is preferably selected within a 
range of from 20/V to 400/V, more preferably from 40/V to 200/V per 100 
parts by weight of the untreated copolymer i.e. the copolymer to be 
treated. 
In the present invention, as the alkali source of the aqueous alkaline 
solution containing the onium compound, an amine, ammonia, an alkali metal 
hydroxide, an alkaline earth metal hydroxide or the like is basically 
useful. However, from the viewpoints of the workload of the waste water 
treatment and the coagulating properties of the copolymer, it is preferred 
to employ sodium hydroxide or potassium hydroxide. The alkali 
concentration in the aqueous solution is usually from 0.5 to 40% by 
weight, preferably from 2 to 20% by weight. 
In the present invention, it is preferred to take a due care not to cause 
gelation of the unreacted copolymer when the unreacted elastomeric 
vinylidene fluoride copolymer is reacted with the aqueous alkaline 
solution containing the onium compound, in view of the blending properties 
or curing properties thereby obtainable. Further, from the viewpoints of 
both the curing properties and the physical properties of the vulcanizate, 
the concentration of unsaturated bonds in the copolymer treated for the 
dehydrofluorination, is preferably from 0.1 to 15 per 100 units of the 
monomer, and this value is preferably at a level of from 0.5 to 10, 
particularly from 1 to 5. From such viewpoints, the temperature is 
preferably from 50.degree. to 120.degree. C., more preferably from 
70.degree. to 100.degree. C., and the reaction time is preferably from 10 
minutes to 10 hours, particularly from 30 minutes to 3 hours. 
In the present invention, as the polyhydroxy compound, it is preferred to 
employ a polyhydroxy aromatic compound such as hydroquinone, bisphenol A, 
bisphenol AF or salts thereof. Further, a fluorinecontaining fatty acid 
diol may also be employed. Such a polyhydroxy compound is incorporated 
usually in an amount of from 0.1 to 20 parts by weight, preferably from 1 
to 10 parts by weight, per 100 parts by weight of the elastomeric 
vinylidene fluoride copolymer. 
In the present invention, as the vulcanization accelerator, it is preferred 
to employ a quaternary ammonium compound such a methyltrioctylammonium 
chloride, benzyltriethylammonium chloride or tetrahexylammonium 
tetrafluoroborate; a quaternary immonium compound such as 
8-methyl-1,8-diaza-cyclo(5,4,0)-7-undecenium chloride; or a quaternary 
phosphonium compound such as benzyltriphenylphosphonium chloride, 
m-trifluoromethylbenzyltrioctylphosphonium chloride or 
benzyltrioctylphosphonium bromide. 
Such a vulcanization accelerator is used usually in an amount of from 0.2 
to 10 parts by weight per 100 parts by weight of the elastomeric 
vinylidene fluoride copolymer. 
To the composition of the present invention, there may be incorporated 
various additives which are commonly used for the preparation of the 
conventional vulcanized elastomers. These additives include metal oxides 
such as magnesium oxide and lead oxide; metal hydroxides such as calcium 
hydroxide; reinforcing fillers such as carbon black, fine silica, clay and 
talc; other fillers; pigments; antioxidants; and stabilizers. 
For the preparation of the composition of the present invention, it is 
desirable to sufficiently uniformly blend the elastomeric copolymer, the 
polyhydroxy compound, the vulcanization accelerator and other additives. 
Such blending is conducted by a conventional means such as a rubber 
kneading roll or a Bumbury's mixer. The operation for the blending is not 
critical. Usually, the additives can adequately be dispersed in the 
elastomeric vinylidene fluoride copolymer by kneading the mixture at a 
temperature of from 30.degree. to 80.degree. C. for from about 10 to 60 
minutes. 
It is also possible to add the additives in a form of a suspension by 
dissolving and dispersing the additives in a suitable medium. It is also 
possible to employ a wet blending whereby the blending is conducted in a 
medium from the beginning. In such a case, a composition in the form of a 
suspension can be prepared by using a mixer such as an open roll, a ball 
mill or a homogenizer. It is desirable to select the optimum condition and 
operation for the blending process depending upon the particular purpose 
and upon the types of the starting materials and the additives. 
The composition of the present invention can be fabricated into a shaped 
product such as a sheet, a pipe, a rod, a tube, an angle, a channel, a 
coated fabric and a coated board by a continuous fabrication process such 
as an extrusion, a transfer molding process, a roll-coating process, a 
brush-coating process or a dipping process. It is also possible to 
fabricate it into articles having complexed shapes or into special molded 
products such as sponge rubber by various molding and processing methods. 
The fabricated composition of the present invention is vulcanized by a 
suitable vulcanizing means whereby a vulcanized elastomer is obtained from 
the composition of the present invention. 
In the present invention, the vulcanization can be conducted by an 
operation which has been commonly employed in the conventional 
vulcanization. For instance, it is possible to employ an operation in 
which a shaped product is heated under pressure in a mold, or a method in 
which the composition is molded by extrusion, calender rolling or 
injection molding, and then the molded product is heated in a heating 
furnace or in a steamed oven. The conditions for the operation of the 
vulcanization are selected to be the optimum conditions for the starting 
materials or the blend composition. The temperature for the vulcanization 
is usually from 80.degree. to 250.degree. C., preferably from 120.degree. 
to 200.degree. C. The heating time is not critical, and it is usually 
selected within a range of from 1 minute to 3 hours, preferably from 5 
minutes to 2 hours depending upon the types of the polyhydroxy compound 
and the vulcanization accelerator. The heating time can be shortened by 
increasing the heating temperature. Further, it is possible to conduct a 
post cure treatment of the vulcanizate thereby obtained, which often 
serves for an improvement of the physical properties. For instance, it is 
possible to conduct the post cure treatment at a temperature of from 
150.degree. to 250.degree. C., preferably from 180.degree. to 230.degree. 
C., for from 2 to 25 hours. 
Now, the present invention will be described in further detail with 
reference to Examples and Comparative Examples. However, it should be 
understood that the present invention is by no means restricted to these 
specific Examples. In the Examples and Comparative Examples, the curing 
properties of the compositions and the physical properties of the 
vulcanizates were measured as follows: 
Curing properties 
By using a Curelastometer (JSR II Model, manufactured by Imanaka Kikai 
Kogyo K.K.), a vulcanization curve was obtained at 170.degree. C., and the 
effective torque .DELTA.TR corresponding to the vulcanization density and 
the optimum curing time t.sub.90 were calculated from the vulcanization 
curve. 
Physical properties of vulcanizates 
A curable composition was molded and vulcanized in a shape of a test piece 
having a thickness of 2 mm and the one for the measurement of permanent 
set, under a pressure of 100 kg/cm2G at a temperature of 190.degree. C. 
for 20 minutes, and then subjected to second curing at 230.degree. C. for 
24 hours to obtain a test piece, which was subjected to the measurement of 
various physical properties. 
The tensile properties, low temperature resistance and chemical resistance 
were measured in accordance with JIS K-6301, and the permanent set was 
measured in accordance with ASTM D-395-78.

EXAMPLE 1 
A latex containing 13.1% by weight of a terpolymer comprising vinylidene 
fluoride/tetrafluoroethylene/propylene in the molar ratio of 
34.8/38.9/26.3 was prepared by emulsion polymerization. 
On the other hand, into a 2 liter three-necked flask equipped with a 
condenser and a stirrer, 500 g of an aqueous solution containing 10% by 
weight of sodium hydroxide was charged and heated to 90.degree. C. To this 
solution, 380 g of the latex obtained above was dropwise added under 
stirring, and the resulting copolymer was permitted to coagulate to obtain 
a dispersion of the copolymer. The dropping rate and the stirring rate 
were controlled to adjust the particle size of the coagulated particles to 
be at most 10 mm. 
Then, 1.5 g of tetra-n-butylammonium bromide was added to the above 
dispersion, and the mixture was maintained at 90.degree. C. for 3 hours. 
As the time passes, both the particle phase and the liquid phase colored 
brown. After cooling the dispersion to room temperature, the particle 
phase was separated, washed and dried, whereby 49.6 g of the treated 
copolymer was obtained. 
By the treatment, new absorption peaks were observed at 3130 cm.sup.-1, at 
1722 cm.sup.-1 and at 1690 cm.sup.-1 in the infrared spectrum, and thus 
the introduction of unsaturated bonds was confirmed. 
40 g of the treated copolymer obtained above, 0.8 g of 
benzyltriphenylphosphonium chloride, 2 g of bisphenol AF, 2.4 g of calcium 
hydroxide and 10 g of MT carbon were kneaded by a 4 inch roll mill to 
obtain a curable composition. The curing properties of the curable 
composition and the physical properties of the vulcanizate are shown in 
Table 1. 
COMATIVE EXAMPLE 1 
380 g of the same latex as in Example 1 was dropwise added to an aqueous 
sodium chloride solution, followed by coagulation, washing and drying, 
whereby 49.8 g of a white polymer was obtained. 
The copolymer thus obtained was directly blended and kneaded in the same 
manner as in Example 1 to obtain a curable composition. 
The curing properties of such a composition were as poor as .DELTA.TR being 
only 1.4 kg-cm and t.sub.90 being as long as 11.7 minutes, thus not 
suitable for practical application. 
COMATIVE EXAMPLE 3 
A latex containing 13.1% by weight of a four component copolymer comprising 
vinylidene 
fluoride/tetrafluoroethylene/propylene/perfluoro-(2-bromoethylvinyl ether) 
in a molar ratio of 40.1/34.8/23.2/1.9 and having a composition similar to 
the one used in Example 1 except that a small amount of 
perfluoro-(2-bromoethyl vinyl ether) units are contained as curing sites, 
was prepared by emulsion polymerization. 
The intrinsic viscosity of the four component copolymer separated from the 
above latex was 0.63 dl/g as measured in tetrahydrofuran. 
This copolymer was directly blended and kneaded in the same manner as in 
Example 1 to obtain a curable composition. The curing properties of the 
composition and the physical properties of the vulcanizate are shown in 
Table 1. 
EXAMPLE 2 
The same treatment and operation as in Example 1 were conducted except that 
a terpolymer comprising vinylidene fluoride/tetrafluoroethylene/propylene 
in a molar ratio of 25.9/39.8/34.4 was used as the elastomeric vinylidene 
fluoride copolymer, whereby a curable composition was obtained. 
The curing properties and the physical properties of the vulcanizate are 
shown in Table 1. 
EXAMPLE 3 
The same operation as in Example 1 was conducted except that 
benzyltriethylammonium chloride was used instead of the 
benzyltriphenylphosphonium bromide as the vulcanization accelerator, 
whereby a curable composition was obtained. 
The curing properties and the physical properties of the vulcanizate are 
shown in Table 1. 
TABLE 1 
______________________________________ 
Exam- Exam- Exam- 
ple ple ple Comparative 
1 2 3 Example 1 
______________________________________ 
Curing properties 
Effective torque 
4.6 4.8 4.2 1.4 
.DELTA.TR (kg-cm) 
Optimum curing time 
9.0 9.2 8.9 11.7 
t.sub.90 (min) 
Physical properties 
Tensile breaking 
164 181 171 154 
strength (kg/cm.sup.2) 
Breaking elongation (%) 
153 162 182 364 
100% Modulus 82 83 75 37 
Hardness (JIS A) 
79 79 78 72 
Permanent set (%) 
29 28 29 46 
______________________________________ 
*Permanent set: 25% Compression, 200.degree. C. .times. 70 hrs 
EXAMPLE 4 
The same operation as in Example 1 was conducted except that 
tetra-n-butylphosphonium bromide was used instead of the 
tetra-n-butylammonium bromide as the onium compound for the reaction of 
the aqueous alkaline solution containing an onium compound, whereby a 
curable composition was obtained. 
The curing properties of the composition were substantially the same as 
those in Example 1 with .DELTA.TR being 4.2 kg-cm, and t.sub.90 being 9.3 
minutes, and the physical properties of the vulcanizate were substantially 
the same as those in Example 1. 
The compositions of the present invention have remarkably improved 
curability and thus are useful as a starting material for vulcanized 
elastomers having excellent physical properties, and they also have 
industrial advantages that they can be produced by a simple process in 
good reproducibility. 
Further, by virtue of various excellent physical properties of the 
vulcanizates, they are useful for a wide range of applications to e.g. 
automobile parts such as radiators or engine parts including O-rings, 
gaskets, sealing materials or tubes, food plant machinery such as heat 
exchanger gaskets or diaphragms, chemical plant machinery such as gaskets, 
sealing materials or hoses, or other sealing materials for automatic 
vending machines.