RTV 128 - High Initial Tear Strength Moulding Silicone
2 component, room temperature condensation curing silicone compound.
Mix ratio = 20:1 (100 grams Part A : 5 grams Part B).
Available as: 21.0Kg, 5.25Kg, or 1.05Kg.
Fast or Slow cure available.
 
Can be mixed in any ratio desired with RTV120 to adjust Shore A hardness.
 
RTV 128 is used as mould making material (production of
negatives).  The cured product is an exceptionally flexible
rubber with very high mechanical properties and good shelf-life stability. 
It's suitable for mould making of intricate patterns with extremely good pick up of fine details. 
Softer grades are better suited for where there are deep undercuts.
There is no release agent required for de-moulding. 
For the production of multipart moulds and to avoid the adhesion of RTV 128 to itself, use release agents.
 
Key Features
High resistance to initial tearing and tear propagation
Very good flow properties
Can be made thixotropic
Available with either Fast or Slow catalyst.
 
Applications
Mould making
Suitable for polyester, epoxides, wax
 
Thixotropic Adjustment
By addition of the component BS4 Thixo additive, the silicone
rubber can be made thixotropic for special applications,
i. e. the compound is then no longer liquid and castable, but
brushable to pasty.  For this, add approx. 0.5 to 1.5% of Thixo
additive to the already mixed compound of RTV 128 including
Regular Catalyst. The thixotropic effect already occurs after a
short period of time.
 
RTV128: 95-100 parts by weight
Catalyst: 5 parts by weight (Fast or Slow)
BS4 Thixo: 0.5-1.5 parts by weight

Viscosity @20°C (mPa·s):
RTV128 60,000, Fast 30, Slow 100, Thixo 300
Pot life (1000g): Fast 20 minutes, Slow 90 minutes
Mixed viscosity(mPa·s): Fast 48,000, Slow 37,000
 
Cured Elastomer
Colour: white
Tack-free: Fast 20 hours, Slow 10 hours
Hardness (24h) Shore A DIN 53505:  Fast 18, Slow 20
Hardness (7d) Shore A DIN 53505:  Fast 28, Slow 26, Thixo 25
Service temperature (°C):  Fast 180, Slow 180
Tensile strength (N/mm2) DIN 53504:  Fast 2.5, Slow 3.0
Elongation at break (%) DIN 53504:  Fast 420, Slow 420
Resistance to tear (N/mm) ASTM D 624 B:  Fast 20, Slow 20
Linear dimensional change (%):  Fast 1, Slow 1