RTV-2 silicone is a highly versatile elastomeric material used to fabricate molds, special effects, prototyping applications, and various other products. It is known for its pliability, flexibility, durability, and resistance to extreme temperatures. RTV-2 silicone rubber is categorized into two series: condensation-cure (tin catalyst) silicone and addition-cure (platinum catalyst) silicone. Although both have similar characteristics, their curing processes and final properties differ, making them suitable for different applications. In this article, we will compare the two types of silicone rubber and discuss their properties and applications to help you choose the right type for your needs.
1. Curing Principle
The curing mechanism is the primary difference between tin-cured silicone and platinum-cured silicone. In condensation-cure silicone, also known as tin-catalyzed silicone, the cross-linking agent undergoes hydrolysis reaction with moisture in the air, cross-linking with polydimethylsiloxane (-OH hydroxyl terminated) under the action of a tin-based catalyst. During the curing process, acetic acid is released as a byproduct.
On the other hand, platinum-cured silicone, also known as addition-cured silicone, undergoes cross-linking with a curing agent and vinyl (-CH=CH-) silicone oil under the influence of a platinum catalyst. No byproducts are generated during the curing process, resulting in the final product exhibiting minimal shrinkage and ensuring higher dimensional accuracy.
2. Performance
The difference in curing mechanisms can affect the final properties of silicone. Tin-cured silicone has higher tear strength compared to platinum-cured silicone. However, the stability of tin-cured silicone decreases over time as byproducts released during curing can lead to silicone degradation. Additionally, tin-cured silicone is more prone to shrinkage and aging with time.
Platinum-cured silicone has lower tear strength than tin-cured silicone, but it is more stable over time. This is because the curing process does not release any byproducts that may affect the performance of the silicone. Additionally, platinum-cured silicone exhibits higher heat resistance, making it suitable for applications that require exposure to high temperatures.
3. Mixing Ratio
Tin-cured silicone and platinum-cured silicone are both RTV-2 silicone rubber compounds, but their ratios of Part A to Part B are different. The ratio of condensation-cured silicone is 100:2-100:4, while the ratio of addition-curing silicone (translucent) is 1A:1B and the ratio of addition-curing silicone (transparent) is 10A:1B.
4. Exterior Color
The default color of tin-cured silicone is white or translucent. The Part A base is white or translucent, and the Part B tin catalyst is clear to light yellow in color. If other colors need to be customized, the manufacturer usually adds pigments for coloring in Part B.
The default color of platinum-cured silicone is translucent or transparent. Both Part A and Part B are translucent in the case of translucent platinum-cured silicone. If other colors are needed, the manufacturer usually adds pigments to Part B for coloring. In the case of transparent platinum-cured silicone (10A:1B), the Part A base is transparent, while the Part B platinum-curing agent is colorless.
white liquid silicone
translucent liquid silicone
transparent liquid silicone
5. Application
No single material is suitable for every process, and the properties of tin-cured and platinum-cured silicone make them suitable for different applications. Tin-cured silicone is commonly used for making molds for casting materials such as resins, concrete, sculptures, plaster, wax, and low-melting point metals. High-hardness tin-cured silicone is also used for rapid prototyping. Additionally, tin-cured silicone is suitable for applications that require high tear strength and flexibility.
concrete mold
plaster mold
sculpture mold
Platinum-cured silicone is commonly used for manufacturing food-grade molds, soap, candles, and other products where it does not release any byproducts that could contaminate the final product. It is also used in the production of realistic dolls, special effects, and adult sex products because it is more stable over time and has higher heat resistance. Additionally, platinum-cured silicone is suitable for applications that require a smooth surface finish and minimal shrinkage.
cake silicone mold
candle silicone mold
clear silicone mold
6. Shelf Life
Compared to platinum-cured silicone, tin-cured silicone has a shorter shelf life, typically 10 to 12 months. Addition-curing silicone (translucent) has a shelf life of 24 months, while addition-curing silicone (transparent) has a shelf life of 12 months.
7. Compatibility
Tin-cured silicone is compatible with most substances and is not affected by them during the curing process. However, platinum-cured silicone cannot be mixed with tin-cured silicone because addition-curing silicone is sensitive to pollutants such as sulfur, latex, and certain types of clay. These pollutants can inhibit the curing process of platinum-cured silicone. Platinum-cured silicone is commonly used in medical devices, food-grade applications, and high-performance products due to its biocompatibility, resistance to environmental factors, and ability to meet strict regulatory requirements.
8. Cost
This is a factor to consider when selecting the appropriate material for your project. Tin-cured silicone is typically more affordable than platinum-cured silicone, making it a good choice for cost-conscious projects. Platinum-cured silicone is generally more expensive than tin-cured silicone, but it offers several advantages that may make it worth the extra cost.
Summarize
Compare Items | Tin-Cured (condensation cure) Silicone | Platinum-Cured (addition cure) Silicone |
---|---|---|
Mixing Ratio (A:B) | 100:2 to 100:4 | 1:1 or 10:1 |
Default Color | White or translucent | Translucent or transparent |
Hardness Range | 5-40 Shore A | 0-50 Shore A |
Heat Resistance | 200°C (392°F) | 250°C (482°F) |
Shrinkage | 0.3%-0.5% | 0.1%-0.2% |
Shelf Life | 10 to 12 Months | 12 to 24 Months |
Cost | Lower Priced | Higher Priced |
Curing Principle | Condensation cure – catalyzed using tin salts | Addition cure - catalyzed using platinum |
Curing Method | From surface to interior, affected by the thickness | Simultaneous curing inside and outside, not affected by thickness |
Curing Conditions | Need to absorb air moisture | Sealed environment can also be cured |
Odor | Slightly smelly | No smell, Fda certified |
By-Product | Yes | No |
Viscosity | Medium | Translucent silicone is lower, clear silicone is higher |
Compatibility | Almost unaffected | Acids and bases will inhibit curing |
Heat Curing | ≤45°C (113℉) | ≤200°C (392℉) |
Usage Method | Pour-on or brush-on | Pour-on or brush-on |
pouring silicone
brushing silicone
In conclusion, tin-cured and platinum-cured silicones each have their unique advantages and disadvantages. The choice of silicone rubber depends on the specific requirements of your application. For example, tin-cured silicone is a good choice for cost-conscious projects, while platinum-cured silicone is a good choice for high-performance applications. By understanding the differences between the two, you can make an informed decision on which type of silicone rubber to use in your project.