Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-11-07
2004-08-24
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S432000, C524S449000, C524S445000, C524S431000, C524S425000
Reexamination Certificate
active
06780926
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a process for the manufacture of organopolysiloxane compositions, and in particular organopolysiloxane compositions which cure to elastomeric solids.
BACKGROUND AND PRIOR ART
Organopolysiloxane 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 an organosilane cross-linking agent for the polydiorganosiloxane, for example an alkoxy silane, an acetoxy silane, an oximo silane, alkenyloxy silane or an amino silane. These materials are frequently curable upon exposure to atmospheric moisture at room temperature.
One important application of the above-described curable compositions is their use as sealants in which there is formed an elastomeric mass between surfaces which is adherent to at least two such surfaces.
Fillers used in these compositions may be divided into two types, reinforcing fillers and extending fillers. Reinforcing fillers are usually of small particle size and typically are surface active in that they contain reactive groups on their outer surface. Examples of reinforcing fillers include fumed silica, calcined silica, precipitated silica, titania, zinc oxide, clay and mica all of which are used for the purpose of imparting mechanical strength to the cured products.
Extending fillers include ground calcium carbonate, magnesium carbonate, quartz, diatomaceous earth, barium sulphate, and calcium sulphate. It is also to be noted that some fillers, such as precipitated calcium carbonate, can be considered as semi-reinforcing in that they provide compositions with a degree of reinforcement.
One important requirement of such sealant materials is the ability to adhere well to a variety of substrates. For example, the use of plastics in various industries, particularly the construction industry, is increasing. This is especially true for plastics such as polyvinyl chloride (PVC), used for window frames, polymethylmethacrylate (PMMA), used for bathtub and bathroom accessories, and polycarbonate (PC) such as Lexan, used as transparent sheeting material or for the manufacture of safety glass laminates and insulating glass units. Other substrates to which sealants are expected to adhere include, for example, polyvinylidene fluoride or polyesters which tend to be used to coat metal surfaces.
Whilst many sealants containing extending fillers such as calcium carbonate are known to develop sufficient adhesion to the plastics discussed above, sealants containing silica reinforcing filler materials typically show poorer plastic adhesion properties.
Some reinforcing fillers have a tendency to “structure” (i.e. form an elastic mass before cure, impeding the normal processing operations such as moulding and extrusion) and to agglomerate in the sealant composition which can lead to premature crepe hardening. To reduce this tendency, reinforcing fillers can be surface treated with hydrophobing agents prior to use. Suitable hydrophobing agents include, for example, organochlorosilanes, organopolysiloxanes, and hexamethyldisilazanes. Whilst such surface treated fillers “give” good plastic adhesion, they are expensive and cause negative rheological effects to resulting sealant compositions.
Consequently, a common practice in sealant manufacture is to include adhesion promoters in the sealant compositions in order to enhance adhesion to various substrates, and in particular plastics, especially PVC, PMMA and PC. Commonly used adhesion promoters include, for example, alkoxy silanes such as aminoalkylalkoxy silane, epoxyalkylalkoxy silane, mercaptoalkylalkoxy silane, and derivatives thereof.
Another group of compounds which have been used as adhesion promoters for some considerable time are silicon containing isocyanurates as described, for example, in U.S. Pat. Nos. 3,517,001, 3,708,467 and 4,100,129 (General Electric Company). Typically these comprise:
wherein one D substituent is —R
y
—Si—(R″
x
)(OR″
3−x
), in which R is a divalent hydrocarbon radical selected from alkylenearylene, alkylene, cycloalkylene and halo-substituted derivatives thereof, R″ is an alkyl or haloalkyl radical with up to 8 carbon atoms, x is from 0 to 3 and y is 1. The remaining D substituents are selected from —R
y
—Si—(R″
x
)(OR″
3−x
) as described above, styryl, vinyl, allyl, chloroallyl or cyclohexenyl.
However, we have found that the mere presence of adhesion promoters is not always sufficient to provide reliable adhesion on plastics. This has been found to be particularly the case in compositions containing alkoxy silane cross-linkers, especially when they contain silica as filler.
Surprisingly, the inventors have found that the position at which the adhesion promoter is added relative to the other components of the organosiloxane composition in the process of manufacture of organosiloxane compositions suitable as sealants can significantly effect adhesion properties, especially to plastic substrates, of the compositions.
U.S. Pat. No. 3,517,001 describes the preparation of a variety of silicon containing isocyanurates of the type indicated above and indicates their use as adhesion promoters within silicone compositions. U.S. Pat. No. 3,708,467 and U.S. Pat. No. 4,100,129 both describe sealant compositions containing a silanol-terminated polydiorganosiloxane, a silane cross-linking agent, a titanate catalyst and optionally fillers such as silicas and isocyanurate adhesion promoters. Preferred uses for such compositions including being sealants and caulking compounds.
The preferred process for making such sealants in the presence of an adhesion promoter is combining all the ingredients other than the silane cross-linker, the titanate catalyst and the adhesion promoter to form a base blend, removing moisture and adding the silane cross-linker, titanate catalyst and adhesion promoter just prior to packaging the resulting composition. U.S. Pat. No. 4,102,852 describes a one component self extinguishing cured silicone composition using dimethyl and phenyl-methyl hydroxy polysiloxane polymers in combination with a selection of reinforcing and extending fillers as well as carbon black. The catalyst is a dialkoxy chelated titanium and an adhesion promoter, preferably 1,3,5-tris (trimethoxysilylpropyl) isocyanurate, may be used. The composition is prepared by mixing all the ingredients in any order desired, however a preferred process consists of adding the carbon black and then the other fillers into the polymer, then the cross-linker and finally the titanate catalyst “and/or any additional optional additives are mixed into the composition”. It is indicated that a drying cycle must occur prior to the addition of the cross-linker and catalyst. In the examples, the adhesion promoter is added via a premix made of the catalyst, cross-linker and adhesion promoter so that all the silanes and the titanate catalyst are added in 1 step at the end of the manufacturing process.
The above process may be appropriate in certain circumstances but it is often found that such a method can lead to a poor sealant rheology and slumping, particularly if the catalyst and cross-linker are added into the reaction mixture after the addition of the filler.
The inventors have identified an improved process for the preparation of an organopolysiloxane composition suitable for use as a sealant which provides a resulting sealant with significantly improved adhesive properties.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, there is provided a process for making an organopolysiloxane composition comprising mixing the following components:
i) a polymer having not less than two groups bonded to silicon which are hydroxyl or hydrolysable groups or a partial condensate thereof;
ii) a surface active filler;
iii) an organosilane comprising at least two silicon bonded reactive groups;
iv) a catalyst; and
v) an adhesion promoter characterised in that organosilane (iii) is mixed with surface active
De Buyl Francois
Deglasse Patrick
Leempoel Patrick
Dow Corning S.A.
McKellar Robert L.
McKellar Stevens, PLLC
Moore Margaret G.
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