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
structure Curing speed
Humid 5. ty
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
Urethane resin vulcanized rubber
Soldering flux Fat clay _ 19 _ ...
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