Remix each of the two components (parts A and B) every time before using.
1. Mixing of the two components
Mix the two product parts BLUESIL RTV A and BLUESIL RTV B according to following mix ratios:

Mixing ratio: ​ ​

RTV 3120 A&BRTV 3128 A&B
A : B = 1 : 1A : B = 10 : 1

The two components may be intimately mixed either by hand or by means of a lowspeed electric or pneumatic mixer to minimize the introduction of air into the mixture.

2. Degassing
After mixing BLUESIL RTV 31xx A&B, it is recommended to eliminate entrapped air. If the mixing is done with the help of a machine both parts are degassed before mixing.
The BLUESIL RTV 3120 A&B and BLUESIL RTV 3128 A&B are degassed under a vacuum of 30 to 50 mbar. Under vacuum, the product expands 3 times its initial volume and forms bubbles on its surface. These bubbles will disappear gradually and the mixture will sink back down to its initial volume within 5 minutes. Release the vacuum and repeat the operation a few minutes later.
Remark: release the vacuum several times imes the degassing. For easier degassing only fill a recipient to 1/3 of its height.

3. Cross linking
The best curing conditions are at 23°C. When using the products at higher temperatures, the pot life is shorter and the setting rate faster. As opposed to this, lower temperatures increase the pot life and decrease the setting rate.
Room temperature curing assures the lowest possible shrinkage, if accelerated cure is desired, mild heat should be preferred. To minimize shrinkage cure the elastomer at maximum temperature of 60°C , higher temperatures will cause higher shrinkage.
At 23°C, the moulds can be demoulded after the time indicated as "demolding time" (see § 2.Polymerization).In order to achieve the best possible performance levels from the moulds, it is preferable to wait for 24 hours before using them.
Be aware that contact with certain materials can inhibit the curing of this RTV:

  • Natural rubbers vulcanized with sulphur
  • Polycondensation RTV catalysed with metal salts
  • PVC stabilizing agents
  • Amine cured epoxies
  • Sulphur containing clays.

If doubts exist it’s recommendable to run a quick test with a small quantity of material in order to assess compatibility. Take duly note that cross contamination due to not well cleaned tools or devices is frequently the main cause of inhibition. The best way is to use only dedicated gear when processing polyaddition RTVs.

4. Processing aids
4.1 Adhesion promoters ("primers")
In order to achieve adhesion of BLUESIL RTV 3120 A&B and BLUESIL RTV 3128 A&B on the pad support, it is recommended to prime the support with an adhesion promoter. Bluestar Silicones recommends the use of primer PM 820 and primer PM 811 A&B according to the instructions below.

SubstrateMetal (steel, aluminum), plastic (polyester), reinforced resins
Pot-life A+B​N.a. (monocomponent)>3 days
Usage levelVery thin layer (30÷60 g/m2)
Use guideline
  1. Application of PM 820
  2. Wait 30 minutes
  3. Application of PM 811
  4. Wait 30 minutes up to 7 days
  5. Application of RTV-2 Silicone​
Application bySpray, brush, cloth

For more detailed information, please refer to the Technical Data Sheets of the Primers.

4.2 Pot-life accelerator / retardant
Should it be desired to change the polymerization time of BLUESIL RTV 3120 A&B and BLUESIL RTV 3128 A&B, following additives allow a customization by increasing the pot-life (retarder PA 40) or by shortening it (accelerator PA 39). Information on their use is shown in the table below.

Usage level0.1 ÷ 3 %0.1 ÷ 5 %
UseMix PA 39 into Pt catalyst partMix PA 40 into base part

4.3 Oil dilution
The hardness of BLUESIL RTV 3120 A&B and BLUESIL RTV 3128 A&B can be adjusted by means of a non reactive silicone oil, that plasticizing the silicone network lowers the material hardness. BLUESTAR SILICONES offers the low viscosity silicone BLUESIL FLD 47 V 50, that can be added to the BLUESIL RTV 3120 A&B and BLUESIL RTV 3128 A&B.

BLUESIL RTV 3120 B may be stored at a temperature below 40 °C/ 104 °F for up to 12 months from its date of manufacturing.Please consult the Safety Data Sheet of this product.


The BLUESIL RTV 3120 A&B and BLUESIL RTV 3128 A&B are two component silicone elastomers which cure at room temperature by a polyaddition reaction.
This reaction can be accelerated by heat.


2 Part RTV


  • High purity products particularly designed for printing pads production.
  • Good mechanical properties.
  • Excellent heat stability.
  • Adjustable hardness by diluting with silicone oils.

These products are specifically formulated for the production of printing pads.

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Viscosity30000PairedCompRH 0174mPa.s




Viscosity40000PairedCompRH 0174mPa.s






hardness_cd523e03-72a3-4261-93f9-36f7bbeeafb1hardness_cd523e03-72a3-4261-93f9-36f7bbeeafb1Hardness20PairedMixRH 0110sh.A
pot-life_0d649a54-7503-4c7c-a047-9d0c4b3e9f6apot-life_0d649a54-7503-4c7c-a047-9d0c4b3e9f6aPot life10PairedMixRH 0114min





BLUESIL RTV 3120 ABLUESIL RTV 3120 A/our_offer/Product/90033724/90033725/BLUESIL-RTV-3120-A