Soft Tin Cured Liquid Silicone Rubber for Mold Making

soft pour-on brush-on 5-15 A condensation tin catalyst
Lead Time
Quantity(kilograms)1-10001000-5000≥5000
Est. Time(days)2-34-7To Be Negotiated

1. Description

This series of condensation-cure (tin-catalyzed) silicone rubber is a low hardness, relatively soft mold rubber. It consists of a white or translucent Part A base and a clear to slightly yellowish Part B curing agent. When mixed in a weight ratio of 100A:3B, they will cure at room temperature into a soft, elastic silicone material. However, it should be noted that this series of silicone rubber has limited tear strength and is better suited for making small, simple molds.

white tin cure liquid silicone

Based on the properties of tin-catalyzed silicone, it is recommended to work with it within a temperature range of 20 to 30°C (68 to 86°F). Curing becomes challenging below 10°C (50°F), so it is important to maintain suitable temperatures. If you decide to apply heat to accelerate curing, it is not advisable to exceed 45°C (113°F). Additionally, you can adjust the operation time and curing time suitable for your project by adjusting the ratio of part A and part B (100:2-100:4).

2. Feature

  1. Low hardness, soft, good elasticity.
  2. Viscosity is relatively low, easy to vacuum defoam.
  3. Excellent demolding performance for most materials.
  4. Suitable for pouring or brushing applications.
  5. Simple operation, quick curing at room temperature.
translucent tin cure liquid silicone

3. Application

These low-durometer tin-cured silicones are ideal for applications that require softness and elongation. It is widely used in candle and soap molds, miniature crafts, architectural and historical restoration molds, and other applications where flexible molds are needed.

In addition to being suitable for pour-on applications, this series of silicones can also be used for brush-on applications by adding thickeners (thixotropic agents) to reduce their flow rate.

soap silicone mold

Soap Silicone Mold

candle silicone mold

Candle Silicone Mold

bear craft silicone mold

Bear Craft Silicone Mold

handicraft silicone mold

Handicraft Silicone Mold

4. Attention

  1. It is recommended to use Part A and Part B of the same model and lot number. If a different model or lot number is used, its suitability should be determined by testing.
  2. Parts A and B should be mixed properly and in the correct proportions. Using too much tin curing agent to accelerate curing may shorten the mold's service life, leading to brittleness and deterioration.
  3. If the tin-cured silicone material appears gummy or uncured after the recommended curing time, it is necessary to investigate the cause, which may include temperature, mixing ratio, whether it was stirred evenly, and whether other substances were added.
  4. Tin-cured silicone molds may exhibit higher shrinkage over time, depending on the material being cast into the mold, mold configuration, and other variables.

5. Safety

  1. When using tin-cured liquid silicone, it is important to ensure adequate ventilation. During curing, the following gases are generated depending on the cure type: acetic acid type (acetic acid), alcohol type (methanol), oxime type (methyl ethyl ketone oxime - MEKO), and acetone type (acetone). If ventilation is inadequate, respiratory protection should be worn. Avoid continuous inhalation of vapors and spray mist, and take precautions to prevent skin and eye contact. Wear safety glasses with side shields and use liquid-tight gloves, such as butyl rubber, neoprene, or PVC, to minimize the risk of contamination. Remember to wash your hands thoroughly after use.
  2. Over time, tin-cured silicone appliances and molds may leach and become brittle due to the catalyst's instability. As a result, these products are intended for industrial use only and should not be used in applications that require a long shelf life or direct contact with the skin. For food contact applications, platinum-cured silicone rubber should be used instead.
  3. Under normal storage and handling conditions, these products are stable in airtight containers at room temperature and will not undergo hazardous reactions.
  4. Please keep these products out of the reach of children.
  5. First Aid Measures:
    • Skin Contact: If the product comes into contact with the skin, wash thoroughly with soap and water.
    • Eye Contact: In case of contact with the eyes, flush them with plenty of water while lifting the upper and lower eyelids. If irritation persists, seek medical attention.
    • Inhalation: Remove the individual from the contaminated area and provide fresh air. If breathing has stopped, administer artificial respiration and seek immediate medical attention.
    • Ingestion: If ingested, do not induce vomiting unless instructed by a physician. Never give anything by mouth to an unconscious person.

Please note that these measures are general guidelines. In case of an emergency, always consult a medical professional or seek immediate medical attention.

6. Storage

The shelf life of the product is 12 months from the date of production. Storing the material at higher temperatures can also reduce the available shelf life of unused materials. These products have a limited shelf life and should be used as soon as possible.

Containers that have been opened must be carefully sealed to prevent leakage. Store the material in a cool, dry, well-ventilated place, away from heat, direct sunlight, strong oxidizers, and any incompatible substances such as strong bases and acids.

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White Silicone Rubber

Parameter Item Test Method RTV-3105 A/B RTV-3110 A/B RTV-3115 A/B
Unvulcanized Physical Properties @ 24 Hrs 25°C/77°F
Physical State - Liquid / Fluid Liquid / Fluid Liquid / Fluid
Form - Viscous Viscous Viscous
Odor - Slight Odor Slight Odor Slight Odor
Part A (Base) Color ASTM E 1767 White White White
Part B (Catalyst) Color ASTM E 1767 Clear to Light Yellow Clear to Light Yellow Clear to Light Yellow
Part A Viscosity, mPa.s ASTM D 4287 13,000 15,000 18,000
Part B Viscosity, mPa.s ASTM D 4287 250 250 250
Part A Specific Gravity, g/cm3 ASTM D 792 1.08-1.10 1.08-1.10 1.10-1.12
Part B Specific Gravity, g/cm3 ASTM D 792 0.98 0.98 0.98
Part A and Part B mixed @ 25°C/77°F
Mix Ratio by Weight (A:B) - 100:3 100:3 100:3
Working Time, Minutes - 35 35 35
Curing Time, Hours - 10 10 10
Typical Properties of Cured Rubber @ 24 Hrs 25°C/77°F
Hardness, Shore A Durometer ASTM D 2240 5 10 15
Tear Strength, N/mm ASTM D 624 C 8.0 12.0 15.0
Tensile Strength, Mpa ASTM D 412 1.2 1.8 2.0
Elongation, % ASTM D 412 550 500 450
Shrinkage, % - ≤0.40 ≤0.40 ≤0.35
Heat Resistance, °C (°F) - 200 (392) 200 (392) 200 (392)

Translucent Silicone Rubber

Parameter Item Test Method RTV-3205 A/B RTV-3210 A/B RTV-3215 A/B
Unvulcanized Physical Properties @ 24 Hrs 25°C/77°F
Physical State - Liquid / Fluid Liquid / Fluid Liquid / Fluid
Form - Viscous Viscous Viscous
Odor - Slight Odor Slight Odor Slight Odor
Part A (Base) Color ASTM E 1767 Translucent Translucent Translucent
Part B (Catalyst) Color ASTM E 1767 Clear to Light Yellow Clear to Light Yellow Clear to Light Yellow
Part A Viscosity, mPa.s ASTM D 4287 13,000 15,000 18,000
Part B Viscosity, mPa.s ASTM D 4287 250 250 250
Part A Specific Gravity, g/cm3 ASTM D 792 1.05-1.07 1.05-1.07 1.05-1.07
Part B Specific Gravity, g/cm3 ASTM D 792 0.98 0.98 0.98
Part A and Part B mixed @ 25°C/77°F
Mix Ratio by Weight (A:B) - 100:3 100:3 100:3
Working Time, Minutes - 35 35 35
Curing Time, Hours - 10 10 10
Typical Properties of Cured Rubber @ 24 Hrs 25°C/77°F
Hardness, Shore A Durometer ASTM D 2240 5 10 15
Tear Strength, N/mm ASTM D 624 C 9.0 13.0 16.0
Tensile Strength, Mpa ASTM D 412 1.4 2.0 2.2
Elongation, % ASTM D 412 555 520 470
Shrinkage, % - ≤0.40 ≤0.40 ≤0.35
Heat Resistance, °C (°F) - 200 (392) 200 (392) 200 (392)

Step 1: Preparing the Master Pattern

The master pattern must be clean and dry. If the master models is friable, weak, or porous, one may need to apply a consolidant or sealant, and possibly plug deep holes or crevices.

Step 2: Applying the Release Agent

This series of silicones has excellent mold release properties, and typically does not require a mold release agent for most materials. However, if the master pattern is highly porous or rough, has numerous crevasses and undercuts, or not prone to spalling, it is recommended to apply a thin layer of mold release agent to facilitate mold release and prolong the life of the mold.

The release agent should be applied evenly over the entire master pattern, ensuring that it is distributed into all crevices and undercuts. However, it should only be applied thinly to avoid compromising the surface detail of the master pattern. If a brush is used to apply the agent, any excess should be buffed away afterwards, and any brush strokes erased. Since silicone rubber captures even microscopic details, the surface of the release agent will be recorded rather than the master pattern.

Common mold release agents include acrylic sprays, Vaseline, silicone oil and soapy water, among others.

Step 3: Measuring and Mixing

For the white tin-cured silicone, it is important to note that a small amount of powder may settle over time during storage. Therefore, it is recommended to stir Part A and shake Part B before mixing. The sediments are not reactants, so there is no issue in using them while stirring.

If you are not in a hurry, it is advisable to use the recommended dosage (100A:3B) of the standard catalyst. If you require different colors, you can add the colorant and mix it thoroughly. It is important to ensure that the base and curing agent are thoroughly mixed and stirred evenly to avoid local non-curing.

Never use more than the maximum recommended dose of the catalyst (100A:5B), as doing so may cause the liquid silicone to begin setting up before it can be properly stirred and poured. This will significantly shorten the lifespan of the silicone mold.

Step 4: Vacuum Degassing

After mixing parts A and B, it is recommended to vacuum degas the liquid silicone to eliminate any entrapped air. When subject to a vacuum, the silicone mixture should well up as air pockets rise and burst. You must pay attention to the working time of the silicone and avoid letting the silicone cure before pouring/application.

Vacuum degassing can be carried out either before or after pouring. However, if you choose to vacuum degas after pouring, your vacuum box should have a sufficiently large volume.

Techniques to Reduce Air Bubbles:

  1. One is to apply a thin initial coat of silicone with a fine paintbrush, gently spreading it into all cavities and undercuts (after which more silicone may be poured).
  2. Hold the silicone container high above the master pattern and allow it to flow down slowly in a thin stream. This helps to break up any air bubbles as the silicone flows.
  3. Temporarily incline the master pattern at an angle and pour the liquid silicone onto the higher end, allowing it to flow down over the rest of the pattern. Once the silicone reaches the lower end, lay the pattern flat and/or tilt or rotate it as necessary to achieve even coverage.

These techniques can be used alone or in combination with each other. Additionally, reducing the temperature and decreasing the ratio of curing agent can extend the working time and help to reduce air bubbles.

Step 5: Pouring Silicone

Pour-on Process: The vacuum-degassed liquid silicone is poured carefully over the master pattern, typically covering it to a depth of 0.5-1.5 cm above the highest point. If the layer is too thin, the mold may be prone to tearing. It is also advisable to apply thicker layers of silicone in narrow or intricate sections and along the edges where extra strength is required to prevent tearing.

Brush-on Process: After the first layer of silicone begins to cure, a strip of gauze, cheesecloth, or open-weave cotton cloth can be lightly applied to increase the strength of the mold. If a second batch is applied, it should be applied while the first batch is partly cured but still tacky. Once a layer of silicone is cured completely, it is difficult to make a good bond with a subsequent layer. After the gauze is applied, apply another layer of silicone to thoroughly cover the gauze layer. Typically the finished mold should be at least 3-4mm thick even in the thinnest sections. Be sure not to push the gauze through to the master pattern surface. When selecting gauze, non-elastic types should be used.

Step 6: Demolding the Mold

After the specified curing time has passed, the outer surface of the mold feels hard and dry, and the hardness of the mold does not change after a period of time, and the mold can usually be removed or demolded. When removing the mold, gently peel up all the edges first, and then the middle section. If any portion seems too soft, immediately stop pulling and replace any lifted sections, allowing more time to cure further.

 
  • I was using this rtv-2 silicone product and when I mixed part A and part B together I was getting air bubbles when stirring. is this normal? Will it affect the mold quality?
    Yes, RTV-2 liquid silicone will produce some bubbles when stirring, it is recommended that you use a vacuum pump to defoam is the best solution. If there are air bubbles in the mold, it will indeed cause a shorter service life.
    Helpful (11) Not Helpful (47) Reply
  • Is the mold made of this product soft or hard?
    Soft or hard depends on the hardness chosen, but no matter how hard it is, it is an elastomeric material.
    Helpful (19) Not Helpful (10) Reply
  • I created a sculpture using plasticine... is it possible to make the mold with this liquid silicone material?
    Yes, it is recommended to spray a release agent on the plasticine sculpture model to prevent damage to the soft plasticine model during demoulding.
    Helpful (12) Not Helpful (13) Reply
  • I get a lot of microbubbles as soon as I start mixing, any tips to reduce the bubbles?
    Yes, tin cure liquid silicone is a viscous liquid that will produce air bubbles when mixed and stirred. We recommend using a vacuum pump to defoam is the best solution. If you don't have a vacuum pump, it is recommended to choose an addition cure silicone with a lower hardness or use a brush-on process to reduce air bubbles.
    Helpful (22) Not Helpful (12) Reply
  • I have a delicate piece with some undercuts that I need to cast in resin. I'm concerned about the hardness of the resin once it cures, as I need a mold that is soft and stretchy enough to accommodate the piece. Can you tell me how soft this liquid silicone will be when it cures?
    Silicone has good mold release properties, you can choose low hardness silicone with 5-15 shore A. It is recommended that you spray the release agent for better effect.
    Helpful (12) Not Helpful (11) Reply
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