Cross-linkable mixtures and method for producing same

Details Cross-linkable mixtures and method for producing same Cross-linkable mixtures and method for producing same

1999-08-19

2001-10-09

Moore, Margaret G. (Department: 1712)

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

Synthetic resins

From silicon reactant having at least one...

C528S015000, C528S032000, C524S862000, C524S710000, C524S151000

Reexamination Certificate

active

06300455

ABSTRACT:

The present invention relates to crosslinkable mixtures and a process for preparing them.
When using addition crosslinking silicone rubber systems, the problem generally arises that the reactive mixture, once prepared, has a finite rate of curing even at room temperature. This can be a nuisance, in particular when the machines have to be shut down for a relatively long time due to technical difficulties or for other reasons. In this case, reactive silicone rubber mixtures left in the machines crosslink even at room temperature which means that very costly cleansing procedures have to be performed before the process can be started up again.
For this reason, there has long been a market need for addition crosslinking silicone rubber systems which ideally do not cure at room temperature at all and have the highest possible rate of reaction under the processing conditions.
In order to achieve this objective, so-called inhibitors are normally added to the rubber systems. One group of inhibitors comprises organophosphorus compounds. Thus, for example, in DE-A-3 635 236, the use of cyclometallised platinum phosphite complexes for increasing the storage-stability at room temperature is described. The catalyst inhibitor complexes mentioned there do increase the pot life at room temperature, but they have the disadvantage that they are complicated to prepare, which is associated with additional production costs. EP-A-662 490 describes general organophosphorus compounds as inhibitors in addition crosslinking silicone systems. The aliphatic and aromatic phosphines mentioned there, however, have the disadvantage that they cause a clear reduction in the rate of reaction under the processing conditions (T=120 to 170° C.). DE-P 19532316.5 describes crosslinkable addition crosslinking mixtures which contain, in addition to a hydrosilylation catalyst, an organophosphorus compound and an inhibitor. The adjustment described there, using a 2-component system, however, is complicated. Mixtures which are fully inhibited at room temperature and in which there is no effect on the rate of reaction under the conditions of curing with an additive, have not hitherto been disclosed.
There is therefore the object of providing suitable mixtures for lowering the activity of the catalyst at room temperature, even in rapid, addition crosslinking silicone systems, without extending the curing times under the reaction conditions.
In addition, the mixture should be as simple as possible, i.e. it should comprise the smallest possible number of components.
It has now been found, that the problems in addition crosslinking polysiloxane mixtures can be solved if these contain Pt compounds or elemental Pt or any other hydrosilylation catalysing substance and at least one sterically complicated substituted triaryl phosphite of the type described in more detail below. The mode of action of the organophosphorus compound as inhibitor becomes closer to that of an ideal inhibitor (switch function, threshold characteristic) the more sterically complicated is the aromatic group R.
The invention therefore provides crosslinkable mixtures containing the following components
a) at least one polysiloxane, which contains at least two olefinically or acetylenically unsaturated multiple bonds,
b) at least one polyhydrogensiloxane, which contains at least two hydrogen atoms bonded directly to the silicon atom,
c) at least one substance for catalysing the hydrosilylation,
d) at least one phosphorus compound of the general formula (I): P(OR)
3
where R=C
7
-C
31
-alkylaryl,
wherein R may have different definitions within one molecule, and
e) optionally further auxiliary substances.
Component a) in the context of the invention is preferably a cyclic, linear or branched polysiloxane which is built up from units of the general formula (II)
(R
3
)
a
(R
4
)
b
SiO
(4−a−b)/2
  (II)
Here, R
3
represents a C
2
-C
8
-alkenyl radical, e.g. vinyl, allyl, 1-butenyl, 1-hexenyl etc. The alkenyl radicals may be bonded to silicon atoms within the chain or right at the end. R
4
is a monovalent, saturated hydrocarbon radical with up to 10 carbon atoms from the group of substituted and unsubstituted alkyl, aryl, and arylalkyl radicals. Examples of these monovalent radicals R
4
are methyl, ethyl, propyl, isopropyl, butyl, octyl, etc., cyclobutyl, cyclopentyl, cyclohexyl etc., phenyl, tolyl xylyl naphthyl, etc., benzyl, phenylethyl, phenylpropyl. The following conditions are placed on the integers a and b:0≦a≦3 and 0≦b≦3 and 0≦a+b≦4. The number a is preferably 0 or 1. In the radicals R
4
in the present invention, some or all of the hydrogen atoms may be substituted by fluorine and/or chlorine, bromine, or iodine atoms or cyano groups. This means that R
4
may also represent, for example, a chloromethyl, trifluoropropyl, chlorophenyl, dibromophenyl, cyanoethyl, cyanopropyl or cyanopropyl radical.
Using nomenclature which is familiar to a person skilled in the art:
M:(CH
3
)
3
SiO
1/2
D:(CH
3
)
2
SiO
2/2
T:(CH
3
)SiO
3/2
M
Vi
:(CH
2
═CH)(CH
3
)
2
SiO
1/2
D
Vi
:(CH
2
═CH)(CH
3
)SiO
2/2
the following may be cited as examples of component a):
M
2
D
100
D
3
Vi
M
2
Vi
D
180
M
Vi
MD
100
D
3
Vi
T
5
D
550
M
7
Vi
T
3
D
500
M
2
Vi
M
3
T
6
D
300
D
Vi
M
4
Vi
M
4
M
2
Vi
D
1500
M
2
Vi
D
4000
D
50
Vi and
M
2
D
2000
D
5
Vi
The molar proportion of unsaturated radicals of the type R
3
may be chosen to have any value.
The molar proportion of unsaturated radicals of the type R
3
in component a) should preferably be between 10
−3
and 10 mmol per gram. The expression ‘between’ always includes the particular limiting values cited, both here and in the text which follows. The viscosity of component a) is preferably between 10
−3
and 1.000.000 Pa.s at 25° C.
Component b) in the context of the present invention is a polysiloxane which is built up from units of the general formula (III)
H
c
(R
4
)
d
SiO
(4−c−d)/2
  (III)
wherein R
4
is defined in the same way as above and R
4
may optionally also be defined in the same way as R
3
. The stoichiometric indices c and d are integers where 0≦d≦3 and 0≦c≦2 and 0≦c+d≦4. Preferably, 0≦c≦1.
Using nomenclature which is familiar to a person skilled in the art
Q:SiO
4/2
M
H
:H(CH
3
)
2
SiO
1/2
D
H
:H(CH
3
)SiO
2/2
the following may be cited as examples of component b):
M
2
H
D
10
,
M
2
D
10
D
10
H
,
M
2
H
D
20
D
10
H
,
M
2
Vi
D
11
H
,
M
2
D
3
Vi
D
8
H
, and
QM
1,3-1,8
H
D
0,1
,
(M, D, M
Vi
and D
Vi
are defined in the same way as for component a)).
The molar proportion of hydrogen atoms directly bonded to a silicon atom in component b) may be chosen to have any value at all.
In component b), the molar proportion of hydrogen atoms directly bonded to a silicon atom is preferably between 0.01 and 17 mmol, more preferably between 0.1 and 17 mmol and in particular is between 1 and 17 mmol per gram of component b).
In the overall mixture described, components a) and b) are preferably present in a ratio by amounts such that the molar ratio of hydrogen atoms directly bonded to a silicon atom (SiH) in component b) to unsaturated radicals (Si-vinyl) in component a) is preferably between 0.05 and 20, more preferably between 0.5 and 10 and in particular between 1 and 5.
Component c) in the context of the invention preferably includes the elements platinum, rhodium, iridium, nickel ruthenium and/or palladium, as the element on a support substance or in the form of their compounds. Platinum compounds or platinum complexes such as, for example, H
2
PtCl
6
, platinum/olefin complexes, platinum/alcoholate complexes, platinum/vinylsiloxane complexes or also elemental platinum on a support substance such as e.g. activated carbon, Al
2
O
3
or SiO
2
are preferred. Component c) is, in particular, a platinum/vinylsiloxane complex. Platinum/vinylsiloxane complexes preferably contain at least 2 olefinically unsaturated double bonds in the siloxane, see e.g. U.S. Pat. No. 3 715 334.
The expression siloxane also inc

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