Coating composition and process of preparation

专利名称：Coating composition and process of

preparation

发明人：ALLEN LYMAN S.申请号：US42813154申请日：19540506公开号：US2870035A公开日：19590120

摘要：Hydrated silica, polysilicic acid, or partially dehydrated silicic acid having an acidnumber, as defined, above 0.2 but below 0.85, is coated with an organic silicate having atleast two alkoxy-, aryloxy-, aralkoxy-, or alkaryloxy-groups, or at least one each of twosuch groups and having the silicon atom thereof attached to at least one other oxygenatom, and is simultaneously, or subsequently comminuted. The silica should contain 1000or more silanol groups and have a surface area 80-600 sq. m./grm. and bulk density lessthan 10 lbs./cu. ft. The silica may be an aerogel prepared by adding aqueous sodiumsilicate, with stirring to aqueous sulphuric acid, and either cooling the resulting hydrosolto 50 DEG C., adjusting the pH to 5, breaking up the resulting gel, filtering, washing anddrying, or converting the resulting hydrosol to an alcohol with ethyl alcohol, centrifugingout sodium sulphate, adjusting the pH to 3.6 with aqueous sodium bicarbonate, andheating in an autoclave above the critical temperature of the alcohol-water vehicle. Thesilica may be immersed in an anhydrous solution of the silicate and comminuted in an airgrinding mill, or freshly prepared aerogel before removal from the autoclave may betreated with vapour of a silicate, a spray of silicate, or a spray of silicate solution and thencomminuted. Alternatively, silica aerogel undergoing comminution in an air grinding mill

at 100-200 DEG C. may be subjected to the action of silicate vapour, or a spray of silicate,or of a solution thereof. The silica particles, carrying a coating 2-35 per cent of silicate,and comminuted to size 0.01-15 microns are hydrophilic, partially or completely

hydrophobic, and non-organophilic, or organophilic depending on the amount of silicate.The surface film appears to be a polymer of the silicate held by reaction with the silanolgroups. The properties of the coated silica are improved by ageing at room temperature,or by heating under atmospheric, or sub-atmospheric, pressure to 80-300 DEG C. for 5mins.-24 hours. The organic silicates are of general formula where R are alkyl, aryl,alkaryl, or aralkyl groups and x is 1-20, e.g. tetramethyl-, tetraethyl-, tetrabutyl-,tetrapropyl-, tetrabenzyl,- or tetraphenyl-orthosilicates, or polymers thereof, or alkylesters of tetrasilicic, metadisilicic, or metatrisilicic acids. The coated silica may be used as areinforcing filler for silicone rubbers, as flatting agents for lacquers or as oil thickeners.Specifications 649,896, 654,850 and 807,453 are referred to.ALSO:Hydrated silica,

polysilicic acid, or partially dehydrated silicic acid having an acid number, as defined, above0.2 but below 0.85 is coated with an organic silicate having at least two alkoxy-, aryloxy-,aralkoxy-, or alkaryloxy-groups, or at least one each of two such groups and having thesilicon atom thereof attached to at least one other oxygen atom, and is simutaneously, orsubsequently, comminuted, and the coated silica may be used as a reinforcing filler forsilicone rubbers. 10-55 parts coated silica are incorporated into 100 parts silicone gum inthe presence of 1-6 parts benzoyl peroxide or tert.-butyl perbenzoate, and the

composition is aged 5-100 days at 60-100 DEG F., remilled, and vulcanized at 110-225 DEGC. The silicone gum may be a dimethyl polysiloxane prepared by heating a hydrolysate ofdimethyldichlorosilane in the presence of iron chloride, sodium or potassium hydroxides,or sulphuric acid or a copolymer of at least 90 per cent dimethylsiloxane and not morethan 10 per cent diphenylsiloxane. Specifications 649,896, 654,850 [both in Group III], and807,453 are referred to.

申请人：MONSANTO CHEMICAL COMPANY

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