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RT416 - 1 Condensation reaction and addition reaction The...

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Unformatted text preview: 1) Condensation reaction and addition reaction The functional groups which are adopted in the two-pack RTV rubber are classified into two types. According to their group. the curing system are divided into the condensation reaction and the addition reaction. Sn catalyst Condensation ReactionsSiDHoROSiE+—————assiosk~ROH T P: catalyst (Alcohol) Addition REECtionasiCH-CH;+HS$—————————fiSiCH;CHZSis In the condensation reaction, in curing, a secondary product(A1cohol) generates after reaction, then, the shrinkage rate in the condensation reaction becomes bigger than that in the addition reaction. The'addition reaction is excellent in the dimentional accuracy and stability of the pysical properies of rubber. because there is no secondary products in the addition reaction. The model production by Vacuum casting requires high accuracy, consequently, silicone RTV rubber is almost cured by the addition reaction. However, there sometimes might happen curing inhibition in the addition reaction. If the curing inhibition is found in the curing check, in which small quantity of RTV is preliminally n. pplied on the master mold and checked, the master model should be painted or as a substitutiVe mean. the condensation reaction which has no curing inhibition should be adopted. Comparison of reaction types Types Item Chemical structure Curing speed Humid 5. ty Temperature Secondary products Shrinkage rate Curing inhibition due to contamination x x xx x-xx XX)? W-‘A/V/ ‘ // Basic material Q - . Condelation Addition asiOH+ROSis ESiCHSCszflsiE Sn . Pt - ——b iSiOSfivROH #ESiCHz CH; Si; A ———r C) . ‘ Below GO'C No restriction o /,z x ‘77’ Alcohol None Big ' 0 in theory Existence cure can be thered by P.N.S.,Sn,Pb compound For example Epoxy resin Amintcuring agent Hydrochloride resin Urethane resin vulcanized rubber Condésated Silicone Soldering flux Fat clay _ 19 _ ...
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