Organopolysilozane compositions crosslinkable with...

Details Organopolysilozane compositions crosslinkable with... Organopolysilozane compositions crosslinkable with...

1999-12-01

2001-07-03

Dawson, Robert (Department: 1712)

Plastic and nonmetallic article shaping or treating: processes

Forming structural installations in situ

Uniting preform member with molding material

C528S034000, C528S039000, C528S023000, C556S458000, C556S459000, C052S742160

Reexamination Certificate

active

06254811

ABSTRACT:

TECHNICAL FIELD
The invention relates to alkoxy RTV-1 compositions which give low-modulus vulcanizates, to the preparation of these compositions, and to their use as sealing compounds for filling joints in natural stone.
BACKGROUND ART
Unplasticized RTV-1 (room temperature vulcanizable, one part) compositions have unsatisfactory stress-strain behavior for use as permanently flexible sealing materials, since the stress values at, for example, 100% strain (“modulus at 100% strain”) are too high. A high 100% modulus (e.g. 0.6 N/mm
2
) is associated with a marked increase in stress in the event of widening of the joint, caused for example by changes in temperature, which markedly increases the danger of adhesion failure, i.e. detachment of the flexible sealing material from the respective joint substrate. It has been found in practice, that a 100% modulus of from 0.2 to 0.4 N/mm
2
is desirable for this type of joint.
The stress-strain behavior of a silicone rubber vulcanizate is a function of the type and amount of the filler and especially of the number of crosslinking nodes per unit of volume. The modulus of RTV-1 systems can be reduced by increasing the chain length of the hydroxyl-terminated diorganopolysiloxane component. However, the use of very long-chain polymers compromises the consistency of the RTV-1 system. Thus, if the consistency of the filled paste is to be soft and paste-like but also self-supporting, the viscosity of the organopolysiloxane cannot be too high, otherwise the result is a stiff, putty-like paste which is difficult to use.
For this reason, compositions are frequently made using blends of long-chain polymers and low-viscosity silicone plasticizers. This procedure is common practice in order to prepare a low-modulus product, and the use of such plasticizers for reducing viscosity is vital if the material is to be adequately processable. In addition, the use of a trimethylsilyl-terminated, short-chain organopolysiloxane as a plasticizer also reduces the number of crosslinking nodes per unit of volume, and therefore lowers the modulus.
The fundamental disadvantage of a plasticizer is that it is not chemically bound to the vulcanizate network. It can therefore migrate out onto adjacent surfaces and form deposit, either by being dissolved out from the vulcanizate by contact with a solvent, or by spontaneous migration. This phenomenon becomes particularly noticeable with joints in porous natural stone, such as marble, granite or altoquartzite, since the periphery of the joint becomes hydrophobicized and darkens therefore permanently, and this is of course undesirable. Products comprising plasticizers should therefore in principle not be used for filling joints in natural stone.
To avoid the addition of plasticizer in alkoxy RTV-1 compositions, EP-A-763 556 condenses a short-chained OH-terminated organopolysiloxane with catalysis by an acid phosphoric ester, e.g., di-2-ethylhexyl phosphate, forming a long-chained OH-terminated organopolysiloxane. The condensation is terminated by, for example, incorporating chalk after 14 minutes, which evidently brings about neutralization and thus deactivation. This is followed by the alkoxy end-capping of the long-chained OH-terminated organopolysilane with methyltrimethoxysilane, with catalysis by a titanium catalyst. Low-modulus vulcanizates can be prepared in this way. However, this process requires an excessive number of operations and gives unvulcanized compositions which are undesirably stiff.
U.S. Pat. No. 4,755,578 describes an alkoxy RTV-1 composition which comprises a blend of alkyldialkoxysilyl- and trialkoxysilyl-terminated polymers with dialkylmonoalkoxysilyl-terminated polymers. The dialkylmonoalkoxy end groups are not active in crosslinking. The preparation from hydroxyl-terminated diorganopolysiloxane and dialkoxysilanes, and also trialkoxysilanes, takes place over a relatively long period at relatively high temperatures, such as from 60 to 80° C. The incorporation of other constituents into the RTV-1 composition has to take place separately afterward. The disadvantages of such preparation need not be stated.
DISCLOSURE OF INVENTION
An object of the invention is to provide a simple way of manufacturing alkoxy RTV-1 compositions which are easy to use and which, without adding plasticizer, can be adjusted to have a low modulus. For the purposes of the present invention, the term organopolysiloxanes is intended to include dimeric, oligomeric and polymeric siloxanes.
BEST MODE FOR CARRYING OUT THE INVENTION
The invention provides alkoxy RTV-1 compositions comprising the reaction product of
(A) an HO-terminated organopolysiloxane,
(B1) an alkoxysilane which has at least three alkoxy groups and/or its partial hydrolysates, and
(B2) an alkoxysilane which has two alkoxy groups and/or its partial hydrolysates, in the presence of
(C) an acid phosphoric ester of the general formula (I)
(HO)
a
OP(—O—[(CR
1
2
)
b
—O]
c
[(CR
2
2
)
d
]
e
—L—M)
(3−a)
  (I),
where
a is 1 or 2,
R
1
and R
2
are a hydrogen radical, methyl radical or hydroxyl radical,
b and d are 2 or 3,
c is an integer from 2 to 15,
e is 0 or 1
L is an —O—, —COO—, —OOC—, —CONR
3
—, —NR
4
CO— or —CO— radical,
R
3
and R
4
are a hydrogen radical or C
1
-C
10
-alkyl radical, and
M is a monovalent, unsubstituted or hydroxyl-, fluorine-, chlorine-, bromine-, C
1
-C
10
-alkoxyalkyl- or cyano-substituted C
1
-C
20
-hydrocarbon radical,
with the proviso that on any carbon atom only one radical R
1
and R
2
may be a hydroxyl radical.
The process proceeds at temperatures as low as room temperature with a high rate of reaction and high selectively, and therefore shortly after mixing components (A), (B1), (B2) and (C), for example after 10 minutes, the alkoxy-terminated organopolysiloxane formed, which is the product of the reaction of component (A) with (B1) and (B2) with elimination of an alkanol, can be used as an alkoxy RTV-1 composition, if desired after admixing with other constituents. No supply of energy, for example heating of the mixture, is required. There is no need to check whether the reaction has run to completion.
Another advantage of this process is that no side-reactions occur and, for example, no formation of T units or Q units is observed on linear HO-terminated organopolysiloxanes (A). The acid phosphoric esters (C) do not have to be deactivated immediately after the reaction.
Using the blends of bifunctional (B2) and tri- and/or tetrafunctional alkoxysilanes (B1), monoalkoxy-, dialkoxy- and trialkoxysilyl end groups are prepared. The monoalkoxysilyl end groups are not active in crosslinking and therefore do not contribute to increasing the node concentration in the network. This achieves a lower modulus without the need to accept the disadvantage of the migration susceptibility of an admixed plasticizer.
The invention also provides a process for preparing the alkoxy RTV-1 compositions, in which
(A) an HO-terminated organopolysiloxane,
(B1) an alkoxysilane which has at least three alkoxy groups and/or its partial hydrolysates, and
(B2) an alkoxysilane which has two alkoxy groups and/or its partial hydrolysates, are reacted in the presence of
(C) an acid phosphoric ester of the general formula (I).
The weight ratio of the alkoxysilanes (B1):(B2) is preferably from 99:1 to 0.5:1, in particular from 5:1 to 1:1.
c is preferably an integer from 2 to 10, in particular 2, 3, 4 or 5.
L is preferably an —O— radical.
M is preferably an unsubstituted or C
1
-C
10
-alkoxyalkyl-substituted
C
1
-C
20
-hydrocarbon radical, in particular an unsubstituted C
5
-C
18
-hydrocarbon radical.
R
1
and R
2
are preferably a hydrogen radical.
b and d are preferably 2.
The HO-terminated organopolysiloxanes (A) are preferably linear &agr;,&ohgr;-dihydroxypoly(diorganosiloxanes) of the general formula (II)
HO—[R
2
SiO]
m
—H  (II),
where
R is a monovalent, unsubstituted or fluorine-, chlorine-, bromo-C
1
-C
4
-alkoxyalkyl- or cyano-substituted C
1
-C
8
-hydrocarbon radical, and
m has a value which corresponds to a visco

Affiliated with

Also associated with

Rating

Organopolysilozane compositions crosslinkable with... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Organopolysilozane compositions crosslinkable with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Organopolysilozane compositions crosslinkable with... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2522159