Precipitation preventing method for silicone compositions

Abstract: The precipitation of a filler containing silicone composition can be prevented by incorporating a condensation product of D-sorbitol and benzaldehyde.

Description: Background of the Invention The present invention relates to a precipitation preventing method for a silicone composition and more particularly to a method for preventing the precipitation or settling of fillers contained in a silicone composition, the caking of precipitated fillers, the loss of fluidity, etc. Silicone compositions, or polyorganosiloxane compositions, are well known and have heretofore been used in various fields. As polyorganosiloxane compositions there are well known addition reaction type polyorganosiloxane compositions and condensation reaction type polyorganosiloxane compositions. The former, addition reaction type polyorganosiloxane compositions, are of the type wherein a polyorganosiloxane having an alkenyl group and a polyorganosiloxane having a hydrogen atom bonded directly to a silicon atom are cured by using an addition reaction catalyst, e.g. a platinum compound. The latter, condensation reaction type polyorganosiloxane compositions, are of the type wherein a polyorganosiloxane having a hydroxyl group and a hydrolyzable crosslinking agent are cured by using a tin compound for example. Fillers are often added to these silicone compositions for imparting useful properties thereto and for reducing the cost. Various filler-containing silicone compositions are known. For example, the silicone potting agent used for the embedding of electric and electronic parts possesses superior characteristics after curing such as high heat resistance, cold resistance, water resistance and moisture resistance, as as well as excellent shock absorbing property, electrical characteristics and heat conductivity, and is applied to various uses. Such conventional electronic parts as power transistors, diodes, coils and various printer heads generate heat during use, which may lead to deterioration of their characteristics or damage, thus various silicones for heat radiation are used. Also, RTV silicone is used for sealing the flange surfaces in automobiles, construction machines, industrial robots, etc. from fluid. The following are mentioned as examples of fillers highly effective for both addition reaction type and condensation reaction type (one-part, two-part) silicone compositions. Examples of heat-conductive fillers include such metal oxides as zinc oxide, aluminum oxide, ferric oxide, titanium dioxide, and zirconium oxide; such metals as copper, copper alloy, aluminum, and iron. Further, in uses in which corrosion should be avoided, there are known highly heat-conductive ceramics such as graphite and silicon carbide. Examples of other fillers which are used frequently include fumed silica (Aerojil), precipitated silica, which enhances cured physical properties, tensile strength and tear strength, quartz powder, diatomaceous earth, calcium carbide, glass fiber, calcined clay, mica powder, potassium titanate, and chromium oxide. These may be used alone or in combination of two or more. Usually, silicone compositions are available commercially in one- or two-part form containing such fillers, catalyst, etc. Electrical characteristics, shock absorbing property, heat radiating property, as well as resistance to heat, cold moisture an chemicals, of the silicone compositions are enhanced by the fillers. However, since the fillers are incorporated in the silicone stock solution usually in a large amount of 30 to 70 wt%, if a treatment is performed to keep low the viscosity of the silicone composition used, that is, if priority is given to the ease of use by the user, the fillers will be precipitated and so it is necessary to mix and agitate at every use of the composition. Further, if the composition is stored for a long period in a distribution channel, precipitation will proceed and cause caking of the fillers, with the result that it becomes difficult to effect mixing and agitation at the time of use. On the other hand, increasing the viscosity for suppressing the precipitation will lead to the loss of fluidity and of the easiness of use by the user. Summary of the Invention The present invention has been accomplished in view of the above-mentioned circumstances and it is the object of the invention to provide an effective precipitation (incl. caking) preventing method for a filler-containing silicone composition without great increase of viscosity, thereby making it possible to use the same composition in a cartridge or an open can. The present invention resides in a precipitation preventing method for a silicone composition, characterized by incorporating a condensation product of D-sorbitol and benzaldehyde in a filler-containing silicone composition to prepare a precipitation-preventable silicone composition. The condensation reaction product preferably principally comprises dibenzylidene sorbitol. According to a second aspect of the present invention there is provided a filler-containing silicone composition characterised in that it further contains a condensation reaction product of D-sorbitol and benzaldehyde in a precipitation reducing amount. The condensation reaction product preferably principally comprises dibenzylidene sorbitol. Detailed Description of the Invention As the filler-containing silicone composition in the present invention there may be used any of the foregoing known liquid silicone compositions. In other words, any filler-containing polyorganosiloxane composition is employable in the invention provided the filler contained therein is likely to precipitate. Examples of such polyorganosiloxane compositions include both of the foregoing addition reaction type and condensation reaction type, and both one- and two-part types of these compositions are employable. No special limitation is placed on the viscosity of such filler-containing polyorganosiloxane compositions provided they are liquid compositions having a fluidity in which the precipitation of the fillers causes a problem. For example, their viscosity can be selected in the range of 0,02 to 200 Pa·s (20 to 200,000 cP). Also as to the filler, no special limitation is placed thereon, and the amount thereof is optional, depending on the purpose of use of the filler, but usually it is in the range of 30 to 70 wt% relative to the silicone stock solution, as noted previously. The blending ingredient, which constitutes a characteristic feature of the present invention, is a condensation product of D-sorbitol and benzaldehyde, i.e., benzylidene sorbitol. A commercially available product is employable as the blending ingredient. The amount thereof is preferably 1 to 10 parts by weight based on 100 parts by weight of a liquid silicone composition containing a filler (and a catalyst). In the case of a two-part type silicone composition, it is preferable that the blending ingredient be incorporated in both A and B liquids. According to a preferred embodiment of the method of the present invention, a filler-containing liquid silicone composition, or A and B which constitute said composition, and the condensation product referred to above, are compatibilized under heating, agitated and then cooled at room temperature, followed by further agitation into a homogeneously dispersed phase. The silicone composition thus given a precipitation preventing property is used in a suitable form according to the purpose of use thereof. For example, it may be used as a cartridge type sealant. In this case, A and B liquids are each charged into a cartridge, then the cartridges are attached to an automatic mixing system of the type in which mixing and injection are performed automatically as soon as the user presses and opens the cartridges using suitable means. According to the method of the present invention, since the precipitation of fillers can be prevented while suppressing the increase of viscosity, it is no longer required to perform mixing and agitation just before use which have been considered necessary for the conventional sealants of the same type. Besides, the working efficiency is high and there are no variations in equation between lots. The present invention will be described below on the basis of working Examples and Comparative Examples. Examples and Comparative Examples The following are the contents of trade names of ingredients used: " Gel-ol D " a condensation product of D-sorbitol and benzaldehyde (presumed to be a mixture of mono-, di- and tribenzylidene sorbitols in which dibenzylidene sorbitol is predominant) (a product of Shin Nippon Rika K.K.) " Coagulan GP-1 " Lauroyl glutamic dibutylamide (a product of Ajinomoto Co., Inc.) " Aerojil No. 200 " Fine powder of silica (a product of Nippon Aerojil K.K.) The blending ingredients were added each 2 parts by by weight to 100 parts by weight of each of the following commercially available silicone compositions, followed by heating at 100-150°C (preferable 120° to 130°): 1 ○ TB 1230 A/b ... a two-part type, addition reaction type, polyorganosiloxane composition, for potting 2 ○ Toray Silicone SE 4410 A/B ... a two-part, addition reaction type, polyorganosiloxane composition, for heat radiation The mixtures thus treated were cooled to room temperature then agitated and mixed, and 300ml of each placed into a 300 ml graduated cylinder, followed by standing for 3 months, then observed for the state of separation on the basis of the following criterion: ○ ..... no separation, O mm Δ ..... separated supernatant liquid 5-10 mm X ..... separated supernatant liquid 10-20 mm XX .... separated supernatant liquid 90 mm or more (blank) Further, after foaming, a foamed state was checked along the following criterion: ○ ..... good Δ ..... ordinary X ..... bad XX .... very bad The results obtained In Examples 1 and 5 prepared according to the method of the present invention, no precipitation occured and the characteristics after curing are remarkably superior when compared with Examples 2-4 and 6-8 which are comparative. The increase of viscosity after the addition of the blending ingredient was relatively small, and a high working efficiency was obtained.

Claims: A precipitation preventing method for a silicone composition, characterised by incorporating a condensation reaction product of D-sorbitol and benzaldehyde in a filler-containing silicone composition to prepare a precipitation preventable silicone composition. A method as set forth in claim 1, wherein said condensation reaction product principally comprises dibenzylidene sorbitol. A method as set forth in claim 1 or claim 2, wherein the amount of said condensation reaction product added is in the range of 1 to 10 parts by weight based on 100 parts by weight of said filler-containing silicone composition. A method as set forth in any one of claims 1 to 3, wherein the silicone is an addition reaction type polyorganosiloxane. A method as set forth in any one of claims 1 to 3, wherein the silicone is a condensation reaction type polyorganosiloxane. A filler-containing silicone composition characterised in that it further contains a condensation reaction product of D-sorbitol and benzaldehyde in a precipitation reducing amount. A composition according to claim 6 wherein said condensation reaction product principally comprises dibenzylidene sorbitol. A composition according to claim 6 or claim 7 wherein the amount of said condensation reaction product added is in the range of 1 to 10 parts by weight based on 100 parts by weight of said filler-containing silicone composition. A composition according to any one of claims 6 to 8 wherein the silicone is an addition reaction or condensation reaction type polyorganosiloxane.

Inventors: MATSUYAMA TAKAO, SATO YOSHINORI, USAMI IKUZO, MATSUYAMA, TAKAO, SATO, YOSHINORI, USAMI, IKUZO
Applicants: THREE BOND CO LTD, THREE BOND CO., LTD.
Application year: 1991
Main classification: C08L83
IPC codes: C08K5, C08L83, C08K13