Curable fluoroelastomeric compositions

Details Curable fluoroelastomeric compositions Curable fluoroelastomeric compositions

1998-05-19

2001-07-24

Wilson, Donald R. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S326200, C525S140000, C525S102000, C525S340000, C568S615000

Reexamination Certificate

active

06265494

ABSTRACT:

The invention relates to vinylidenefluoride copolymers with other comonomers deriving from fluorinated monomers having an ethylene unsaturation.
More in detail the present invention relates to fluoroelastomeric polymers based on vinylidenefluoride (VDF), hexafluoropropene (HFP), optionally in the presence of one or more ethylenically unsaturated comonomers, preferably tetrafluoroethylene (TFE).
More specifically the invention relates to VDF-based fluoroelastomeric copolymers suitable to the preparation of O-rings, fuel hoses, shaft seals, gaskets, etc.
It is known that for the preparation of these manufactured articles, fluoroelastomeric materials having very good elastic properties combined with an high thermochemical stability are required.
These properties must be combined with good mechanical properties and good processability either in compression or in injection or in extrusion moulding.
It is known to produce VDF, HFP and TFE-based manufactured articles, optionally in the presence of perfluoroalkylvinylethers (PAVE), by using the peroxidic curing. The drawback resides in that generally the obtained compression set are not high and the removal from the moulds is unsatisfactory.
It is known, see for instance EP 525,687, to carry out the ionic curing with accelerants and crosslinking agents. In this case to the polymer suitable crosslinking agents are added, see U.S. Pat. Nos. 4,259,463, 3,876,654, 4,233,421, which comprise aromatic and aliphatic polyhydroxylic compounds. The most common ones are the aromatic compounds including 4,4′-thiodiphenol isopropylene-bis(4-hydroxybenzene), bisphenol A and bisphenol AF, hexafluoroisopropylidene-bis(4-hydroxybenzene).
To the crosslinking agents accelerant systems are added, generally of the class of the phosphonium and amino phosphonium quaternary salts, as described in U.S. Pat. Nos. 3,876,654, 4,259,463. Other compounds behaving as accelerant systems are described in U.S. Pat. Nos. 3,655,727, 3,712,877, 3,857,807, 3,686,143, 3,933,732, 4,233,421 and in EP 335,705, EP 182,299, EP 120.462.
It is also known to add processing additives such as sulphones or sulphoxides to improve the blends processability.
It is moreover known that the fluoroelastomers show a poor processability due to the high viscosity of the compound.
These drawbacks are even more evident in the case of high fluorine content VDF copolymners (fluorine higher than about 67% by weight).
In the case of copolymers or terpolymers, indeed, with a high fluorine content, the crosslinking is still more difficult wherefore mechanical and elastic properties and processability of the manufactured article are poor.
It has been surprisingly and unexpectedly found that it is possible to prepare VDF-based fluoroelastomeric polymers having a very good combination of the following properties:
mechanical properties,
compression set,
low viscosity of the compound such as to allow an easy processing either in compression or in injection or in extrusion.
This became possible by using the ionic curing with a specific curing system.
An object of the present invention are curable fluoroelastomeric compositions comprising
A) 100 phr (parts) of fluoroelastomeric copolymers based on vinylidenfluoride (VDF) and at least a partially or completely fluorinated comonomer having an ethylene unsaturation;
B) 0.5 to 10 phr, preferably 2 to 6, of a curing agent having the general formula
[(R
3
—Si)
m
—(C
y
M
2y
—O—C
z
M
2z
)
p
—(C
t
M
2t−1
)
n
—P
q
—O—]
2
Q
 wherein m, y, z, p, t, n, q, are integers having the following values:
m, q, independently 0 or 1;
p=0, 1, 2, 3;
n=0, 1, 2;
y, z from 1 to 20, preferably from 1 to 10;
t from 3 to 10, preferably from 4 to 8;
R can be:
C
x
M
2x+1
linear or branched aliphatic chain containing hydrogen and/or fluorine (M=H and/or F); or
C
x
M
2x−1
cycloaliphatic structure containing hydrogen and/or fluorine; or
C
x
M
x−1
aromatic structure containing hydrogen or fluorine;
x in said formulas is an integer from 1 to 20, preferably from 1 to 10; or
P
a
wherein P is a bivalent (per)fluoropolyether linking group, a is an integer from 0 to 1;
Q is an aromatic and aliphatic structure containing also fluorine, preferably bisphenol;
or an aromatic structure containing heteroatoms, preferably selected between nitrogen and oxygen;
or a structure having the following formula:
 —S
1
—C(S
2
)—C(S
3
)—Z—C(S
4
)—C(S
5
)—S
6
—
 wherein
S
1
, S
2
, S
3
, S
4
, S
5
, S
6
, equal to or different from each other, are H or C
1
-C
5
alkyls;
Z is a C
1
-C
18
alkylene or cycloalkylene radical, linear or branched, optionally containing oxygen atoms, preferably at least partially fluorinated, or a bivalent (per)fluoropolyoxyalkylene radical P; Z is prefrably a C
1
-C
12
perfluoroalkylene radical, while S
1
, S
2
, S
3
, S
4
, S
5
, S
6
are preferably hydrogen;
with the proviso that when p is different from 0, m=1 and n=q=0;
when n is different from 0, m=p=q=0;
when q is different from 0, m=1 and p=n=0;
the preferred compounds are those wherein m=1 and p=n=q=0; and R is C
x
M
2x+1
wherein x is an integer from 1 to 6; or q=m=1 and n=p=0; and R=C
x
M
2x+1
wherein x is an integer from 1 to 6;
C) the accelerant being an onium-organic compound having a positive charge in amount from 0.05 to 5 phr, preferably from 0.5 to 2.
The (per)fluoropolyoxyether P linking group comprises repeating units statistically distributed along the polymer selected from:
—(CF
2
CF
2
O)—, —(CFYO)— wherein Y is equal to F or —CF
3
, —(C
3
F
6
O)—, —(CF
2
(CF
2
)
z′
O)— wherein z′ is an integer equal to 2 or 3, —(CF
2
CF(OR
f′
)O)—, —(CF(OR
f′
)O)— wherein R
f′
is equal to —CF
3
, —C
2
F
5
, —C
3
F
7
; —CR′
4
R′
5
CF
2
CF
2
O— wherein R′
4
and R′
5
are equal to or different from each other and selected from H, Cl or perfluroalkyl, for instance with 1-4 C atoms.
The number average molecular weight of the (per)fluoroether P is comprised between 300 and 1500, preferably 300 to 600.
Specifically preferred (per)fluoropolyether P are:
—O(CF
2
CF(CF
3
)O)
a′
(CFYO)
b′
—  (a)
wherein Y is F or —CF
3
; a′ and b′ are integers such that the molecular weight is comprised in the above range; a′/b′ is comprised between 10 and 100;
or the repeating units indicated in (a) can be linked as follows:
—O(CF
2
CF(CF
3
)O)
a′
(CFYO)
b′
—CF
2
(R′
f
)
x′
CF
2
—O—(CF
2
CF(CF
3
)O)
a′
(CFYO)
b′
—
wherein R′
f
is a fluoroalkylene group, for instance from 1 to 4 C atoms;
—O(CF
2
CF
2
O)
c′
(CF
2
O)
d′
(CF
2
(CF
2
)
z′
O)
h′
—  (b)
wherein c′, d′ and h′ are integers such that the molecular weight is comprised in the indicated range; c′/d′ is comprised between 0.1 and 10; h′/(c′+d′) is comprised between 0 and 0.05, z′ has the above value, h′ can be also equal to 0;
 —O(CF
2
CF(CF
3
)O)
e′
(CF
2
CF
2
O)
f′
(CFYO)
g′
—  (c)
wherein Y is F or —CF
3
; e′, f′, g′ are integers such that the molecular weight is comprised in the mentioned range; e′/(f′+g′) is comprised between 0.1 and 10, f′/g′ is comprised between 2 and 10;
—O(CF
2
O)
j′
(CF
2
CF(OR
f″
)O)
k′
(CF(OR
f″
)O)
l′
—  (d)
wherein: R
f″
is —CF
3
, —C
2
F
5
, —C
3
F
7
; j′,k′,l′ are integers such that the molecular weight is comprised in the indicated range; k′+l ′ and j′+k′+l ′ are at least equal to 2, k′/(j′+l ′) is comprised between 0.01 and 1000, l′/j′ is comprised between 0.01 and 100;
—O(CF
2
(CF
2
)
z′
O)
s′
—  (e)
wherein s′ is an integer such as to give the indicated molecular weigh

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