Crosslinking agents

Details Crosslinking agents Crosslinking agents

2000-05-04

2003-02-11

Moore, Margaret G. (Department: 1712)

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

Synthetic resins

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

C528S014000, C528S015000, C528S032000, C528S031000, C528S039000, C556S458000, C556S479000, C556S451000, C525S477000

Reexamination Certificate

active

06518371

ABSTRACT:

TECHNICAL FIELD
The invention relates to Si—H functional polyorganosiloxanes, to compositions which comprise this polyorganosiloxane, to processes for preparing silicone elastomers employing the Si—H functional polyorganosiloxane, and to crosslinkable compositions having exceptional properties, employing the Si—H functional polyorganosiloxanes together with conventional Si—H polyorganosiloxanes.
BACKGROUND ART
Crosslinking agents for addition-crosslinking polymer compositions having Q units and a hydrogen content of 1% are known from EP-A 0 565 238. A disadvantage of such compositions are slow vulcanization and therefore a long cycle time for injection molding, and unsatisfactory mechanical properties.
DISCLOSURE OF INVENTION
The object of the invention is to improve upon prior art crosslinkers and elastomers, and in particular to provide Si—H functional crosslinking agents and compositions which improve the tear propagation resistance, elongation at break, and ultimate tensile strength of organopolysiloxane elastomer compositions.
BEST MODE FOR CARRYING OUT THE INVENTION
The invention provides a polyorganosiloxane containing the units (HR
2
Si—O
1/2
) HM units, (Si—O
4/2
) Q units, (R
1
Si—O
3/2
) T units and (R
2
Si—O
2/2
) D units in a HM:Q:T:D units ratio of from 2:1:0:0 to 6:4:2:2, or (HR
2
Si—O
1/2
) HM units, (R
1
Si—O
3/2
) T units, (R
2
Si—O
2/2
) D units and (R
2
(R
1
O)Si—O
1/2
) “alkoxyM” units in a HM:T:D:alkoxy-M ratio of from 1:2:0:0 to 3:4:2:2, where R are identical or different, optionally halogenated hydrocarbon radicals having from 1 to 18 carbon atoms per radical, or are OR
1
, where R
1
is a monovalent, unsubstituted or substituted hydrocarbon radical having from 1 to 8 carbon atoms, and in each molecule there are at least 3 Si-bonded hydrogen atoms.
Examples of radicals R are preferably alkyl radicals such as the methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl and tert-pentyl radicals; hexyl radicals such as the n-hexyl radical; heptyl radicals such as the n-heptyl radical; octyl radicals such as the n-octyl radical and isooctyl radicals such as the 2,2,4-trimethylpentyl radical; nonyl radicals such as the n-nonyl radical; decyl radicals such as the n-decyl radical; dodecyl radicals such as the n-dodecyl radical; octadecyl radicals such as the n-octadecyl radical; alkenyl radicals such as the vinyl radical and the allyl radical; and cycloalkyl radicals such as the cyclopentyl, cyclohexyl, cycloheptyl, and methylcyclohexyl radicals.
Examples of substituted radicals R are cyanoalkyl radicals such as the &bgr;-cyanoethyl radical, and halogenated hydrocarbon radicals, for example haloalkyl radicals such as the 3,3,3-trifluoro-n-propyl radical, the 2,2,2,2′,2′,2′-hexafluoroisopropyl radical, and the heptafluoroisopropyl radical.
The methyl and ethyl radicals are preferred as radical R simply because they are more easily accessible.
Radical R
1
is preferably a hydrogen atom or an optionally substituted hydrocarbon radical having from 1 to 8 carbon atoms, more preferably hydrogen and alkyl radicals having from 1 to 3 carbon atoms, and most preferably methyl, ethyl and isopropyl radicals.
Additional preferred polyorganosiloxanes are those having the formula (H(CH
3
)
2
SiO)
4
Si (=HM4Q) or (H(CH
3
)
2
SiO)
3
SiCH
3
(=HM3T).
The viscosity of the novel polyorganosiloxanes is preferably from 10 to 500,000 mPa·s, more preferably from 10 to 100,000 mPa·s, and most preferably from 10 to 10,000 mPa·s. The viscosities of HM4Q and HM3T are between 0.001 and 1000 mPa·s.
The novel polyorganosiloxanes are also used as hardness-reducing constituents.
The invention also provides a composition comprising a silicone polymer bearing unsaturated groups, a catalyst, and the polyorganosiloxane described above. Compositions of this type usually comprise silicone polymers (1) having alkenyl groups, where the alkenyl groups are preferably vinyl or allyl groups, and these are preferably polydimethylsiloxanes having vinyl end groups. Amounts of from 55 to 85% by weight of these are present. Their preparation is described, for example, in EP 208 285. Their viscosity is preferably from 0.5 to 500 Pa·s, preferably from 1 to 100 Pa·s and most preferably 4 to 50 Pa·s at a temperature of 25° C.
The silicone rubber compositions which crosslink to give elastomers optionally also comprise reinforcing or non-reinforcing fillers (2). Examples of non-reinforcing fillers are substances with a BET surface area below 50 m
2
/g, such as powdered quartz, diatomaceous earth, chalk, kaolins and silicates. For the purposes of the present invention, reinforcing fillers are those with a BET surface area of 50 m
2
/g or above, for example fumed silica. Preference is given to reinforcing fillers with BET surface areas of from 150 to 300 m
2
/g. These may also have been hydrophobicized. The amounts used are from 0 to 40% by weight.
The crosslinking agents (3) comprise the novel crosslinking agents, which are present in amounts of from 0.5 to 70% by weight.
Conventional platinum hydrosilylation catalysts may be used as hydrosilylation catalyst (4), catalyzing the addition reaction between the alkylene groups in the polyorganosiloxane (1) described above and the silicon-bonded hydrogen atoms in the novel crosslinking agent (3). In general, any hydrosilylation catalyst for addition-crosslinking silicone rubber compositions may be used. Those preferably used are metal-containing catalysts, such as platinum, palladium, iridium, rhodium and ruthenium, with preference given to platinum and platinum compounds. Particular preference given to is given to polyorganosiloxane-soluble platinum-vinylsiloxane complexes and hexachloroplatinic acid. The amounts of these catalysts which are added to the compositions crosslinkable to give elastomers, are from 0.1 to 500 ppm by weight. It is preferable to use from 5 to 100 ppm by weight of catalyst calculated as platinum metal, and the vulcanization rate can be controlled by varying the amounts used.
Additives (5) which serve to adjust the pot life of the curable rubber compositions may also be present if desired. These are known inhibitors, such as 2-methyl-3-butyn-2-ol, 1,3-divinyl-1,1,3,3-tetramethyldisiloxane and ethynylcyclohexanol. The amounts preferably used of the inhibitor are from 0.01 to 0.2% by weight, based on the total weight of the respective components listed below.
Since the composition is per se reactive and therefore vulcanizes slowly at room temperature, the mixture is generally prepared as two components, of which one may comprise 1, 2, 4 and 5 and the other 1, 2, 3, and 5. The components are mixed by machine shortly before processing and are then processed by injection molding, extrusion, transfer molding or rotational and centrifugal casting processes.
The present invention markedly improves the mechanical properties and the vulcanization properties. For example, tear propagation resistance is increased, and elongation at break for a 30 Shore type elastomer increases from about 700 to just below 1000. Also, surprisingly, the onset temperature decreases from 140° C. in typical prior art elastomers to sometimes below 100° C. with the novel crosslinking agent, while the pot life remains at more than 3 days.
The compounds according to the invention may also be used in a blend with any desired linear or branched polydimethylsiloxane polymer which has at least one SiH group or Si-alkenyl group, preferably an Si-vinyl group.
The silicone polymer used having alkenyl groups may also comprise a polydiorganosiloxane polymer such as polydimethylsiloxane having alkenyl groups, preferably vinyl groups or allyl groups, pendant to the chain in addition to or instead of terminal alkenyl groups. This then gives Shore hardnesses of from 40 to 60. The amount of this polymer used is preferably from 2 to 50% by weight, with preference from 2 to 20% by weight. This polymer may also be used together with polymers which have terminal alkenyl groups, e.g. vinyl groups or allyl groups, or are terminate

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