Polyorganosiloxane RTV compositions

Details Polyorganosiloxane RTV compositions Polyorganosiloxane RTV compositions

2001-10-09

2003-04-08

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...

C528S901000, C528S034000, C528S028000, C528S029000, C525S452000, C556S458000, C556S463000, C556S482000, C524S588000

Reexamination Certificate

active

06545104

ABSTRACT:

This invention is concerned with organosiloxane compositions which are curable to elastomers and also relates to the use of such compositions as sealing materials.
Organosiloxane compositions which cure to elastomeric solids are well known. Typically such compositions are obtained by mixing a polydiorganosiloxane having reactive terminal groups, generally silanol groups, with a silane cross-linking agent for the polydiorganosiloxane, for example an alkoxy silane, an acetoxy silane or oximo silane, a filler and a curing catalyst. These compositions are frequently single part compositions curable upon exposure to atmospheric moisture at room temperature or two part compositions curable upon mixing under room conditions.
One important application of the above-described curable compositions is their use as sealants. In use as a sealant, it is important that the composition has a blend of properties which render it capable of application as a fluid to a joint between substrate surfaces where it can be worked, prior to curing, to provide a smooth surfaced mass which will remain in its allotted position until it has become cured to an elastomeric body adherent to the adjacent substrate surfaces. It is frequently desirable that the composition cures quickly enough to provide a sound seal within several hours but not so quickly that the surface cannot be tooled to desired configuration shortly after application. Among specifically desirable attributes for such compositions are thixotropy to the extent desirable for the composition to remain in its allotted location whilst curing in the joint whether horizontal or upright together with flowability to the extent desirable to enable tooling of the surface by use of a wetted spatula without sticking to the spatula and without beading. Satisfactory adhesion to as many of a variety of materials as possible, especially those used in construction or automotive applications is also required for example glass, polyacrylates, polycarbonates, steel, aluminium, wood and concrete. Furthermore, a relatively fast cure is desirable, including a fast surface cure rate to provide a mass with good elasticity of the skin formed and lack of surface tackiness after curing for about 24 hours. The cured composition should have a strength and elasticity appropriate for the particular joint concerned.
Conventional silicone sealant compositions typically contain a reinforcing filler and possibly an extending filler. The fine particle size silicas and calcium carbonates such as fumed silicas and precipitated calcium carbonates are often used to provide the reinforcing filler and various materials are employed as extending fillers. Generally speaking, those compositions which are required to demonstrate thixotropic properties prior to cure and higher tensile and tear strength properties when cured employ larger quantities of the reinforcing fillers. The silicas are generally employed in those compositions which are intended to be transparent or at least substantially so whereas the calcium carbonates are often employed in compositions where transparency is less required.
It is also a common practice in the formulation of silicone based sealants to incorporate a material which serves as a plasticiser or extender for the composition. Commonly the trimethylsilyl polydiorganosiloxanes are used for this purpose. Whilst they are effective at the time of application of the sealant and subsequently, at least for a time, sometimes they exude from the sealant over time and may give rise to staining of the surrounding substrates onto which the material bleeds.
It is one of the various objects of this invention to provide a curable organosiloxane composition having an improved blend of properties.
Surprisingly we have now found that curable organosiloxane compositions which contain certain polyhydroxyl urethane prepolymer materials may be formulated which have a lower cost or improved combinations of properties.
The present invention provides in one of its aspects a room temperature vulcanisable composition formed by mixing components comprising a polysiloxane having hydroxyl or hydrolysable groups, a crosslinker having silicon bonded hydrolysable groups selected from the group consisting of alkoxy-, acetoxy- and oximo- silanes, and a hydroxyl terminated urethane prepolymer.
The concept of “comprising” where used herein is used in its widest sense to mean and to encompass the notions of “include” and “consist of”.
In a composition according to the invention, the hydroxyl bearing polysiloxane may be according to the general formula X-A-X where A may be any desired siloxane molecular chain for example a polydiorgano-siloxane chain and thus preferably includes siloxane units R
s
SiO
(4-s)
in which R represents an alkyl group having from 1 to 10 carbon atoms (for example, a methyl, ethyl, propyl, butyl, vinyl, cyclohexyl, phenyl or tolyl group) or a halogenated hydrocarbon group having 1 to 10 carbon atoms (for example a chloropropyl or fluorinated alkyl group for example 3,3,3-trifluoropropyl, chlorophenyl, beta-(perfluorobutyl)ethyl or chlorocyclohexyl group) and s has a value of 0, 1 or 2. The organic groups are preferably at least substantially all methyl groups. Preferred materials are linear materials i.e. s=2 for all chain units. Preferred materials have polydiorgano-siloxane chains according to the general formula —(R′
2
SiO)
t
— in which each R′ represents a methyl group and t has a value from about 200 to about 1500. Suitable materials have viscosities of the order of about 100 mPa.s to about 300,000 mPa.s. The groups X of the polymeric material are hydroxyl or hydrolysable groups and may be selected, for example, from —R
2
SiOH, —RSi(OR
2
)
2
, —Si(OR
2
)
3
, —R
2
SiOR
2
or —R
2
SiR″SiR
p
(OR
2
)
3-p
where R represents an alkyl group having from 1 to 6 carbon atoms as aforesaid, (and is preferably methyl), R″ is a divalent hydrocarbon group which may be interrupted by one or more siloxane spacers having up to six silicon atoms, R
2
is an alkyl or oxyalkyl group in which the alkyl groups have up to 6 carbon atoms and p has the value 0, 1 or 2. Preferred polysiloxanes are thus polydiorganosiloxanes having terminal, silicon-bound hydroxyl groups or terminal, silicon-bound organic radicals which can be hydrolysed using moisture. These polydiorganosiloxanes preferably have a viscosity of 0.5 to 200 Pa.s at 25° C. The polydiorganosiloxanes may be homopolymers or copolymers. Mixtures of different polydiorganosiloxanes having terminal condensable groups are also suitable.
In a composition according to the invention the crosslinker is a silicon compound containing hydrolysable groups and preferably comprises one or more silanes. The hydrolysable groups are suitably silicon-bonded hydrolysable groups exemplified by acyloxy groups (for example acetoxy, octanoyloxy, and benzoyloxy); ketoximo groups (for example dimethyl ketoximo, methylethyl ketoximo, diethyl ketoximo, amylmethyl ketoximo, and isobutylmethyl ketoximo); alkoxy groups (for example methoxy, ethoxy, and propoxy) and alkenyloxy groups (for example isopropenyloxy and 1-ethyl-2-methylvinyloxy). The crosslinker can have three or more silicon-bonded hydrolysable groups per molecule. When the crosslinker is a silane and when the silane has three silicon-bonded hydrolysable groups per molecule, the fourth group is suitably a non-hydrolysable silicon-bonded organic group. These silicon-bonded organic groups are exemplified by alkyl groups (for example methyl, ethyl, propyl, and butyl); cyclo alkyl groups (for example cyclopentyl and cyclohexyl); alkenyl groups (for example vinyl and allyl); aryl groups (for example phenyl, and tolyl); aralkyl groups (for example 2-phenylethyl) and groups obtained by replacing all or part of the hydrogen in the preceding organic groups with halogen. The silicon-bonded organic groups are preferably methyl. The crosslinker can be a silane or siloxane and in the case of siloxanes the molecular structure can be straight chained, branched, or cyclic and the silico

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