LSR VS Solid Silicone Rubber

What is the difference with LSR ( liquid silicone rubber )and solid silicone rubber?

Liquid silicone rubber and solid silicone rubber can be distinguished by making process, appearance, smell , molding process, industry useful and cost.

Making process:

Liquid silicone rubber

Solid silicone industry based on sodium silicate (sodium silicate) as raw material, hydrolysis produce gel in the acid medium, and then made from silica gel by aging, washing, drying process, according to the water content is different, for the translucent or white solid. Goods sold are irregular granular, globular, micro spherical silica gel, which has good wear resistance, used as the catalyst carrier in fluidized bed operation.

Liquid Silicone is liquid shape before being formed, and has fluidity, fast vulcanization, environmental protection and safety. It can meet the requirements of food grade certification, and has the advantages of tearing strength, resilience, heat yellowing and thermal stability. Liquid silicone is divided into encapsulated silicone rubber, silicone rubber mold, sealant and other types of liquid silicone, divided into A glue and B glue, using quantitative device to control both of 1:1 ratio, and then through the static mixer to fully mixing, injection injection feeding pipe after injection molding production. The liquid silica gel was injected into the hot runner mold and made of silica gel products, which can achieve the advantages of one molding, no waste and automation.

The main point of Liquid silicone rubber:

Resistance to steam and humidity
Flame retardancy
Low creep and compression set
Weatherability
Vibration absorption
Corrosion resistance
Resistance to mold, mildew, and bacteria growth
UL component recognition

Liquid silicone can be cured at room temperature and can be cured at high temperature. The curing process can be completed in a few seconds by high temperature curing. Liquid silicon rubber is a typical liquid silicon rubber, which is soft, nontoxic, tasteless and transparent. Medical safety is the high safety of food.

Solid silicone rubber

silica sol liquid silicon sol is important carrier of the material, industry usually by ion exchange method makes the silica sol sodium silicate sodium off system. It is translucent milky liquid, the content of silica in the sold goods is commonly 20% ~ 30%, and the most high is 50%, the colloidal particles diameter of 100 ~ 200 a, some items of 1300 a. A high concentration of silica sol is usually with the aid of trace amounts of sodium oxide to maintain its stability. Colloidal silica drying after into porous solids. For example, in production by oxidation of propylene ammoniation of acrylonitrile (oxygen) phosphorus molybdenum – bi – / silicon oxide catalyst, is to contain active component solution mixed with silica sol, the spray drying method into micro spherical catalyst.

The main properties of solid silicone Rubber:

1. excellent transparency

2. excellent tear strength (35N / mm)

3. excellent springback, yellowing resistance and heat-resistant aging

4. good thermal stability and weatherability (using temperature -60 C ~ 250 C)

5. after mixing A / B at 20 C, the safe operation time in the sealed state is 5 days, and the safe operation time is shortened when the temperature rises.

Appearance:

Liquid silicone rubber is in a liquid state and has fluidity;

Solid silicone rubber  is in a solid state and has no fluidity.

Smell:

Liquid silicone rubber has high transparency, no peculiar smell, and the injection molded silicone products has a glue injection port. The LSR molded silicone products is odorless.

Solid silicone rubber have to use  the flavor of curing agent or other curing agents, and the product has no glue injection port.  With different odor accroding to the difference grade. 

Molding process:

Liquid silicone is a food-grade/Medical Grade material with high transparency and high safety. No auxiliary materials such as vulcanizing agent are added during molding, and it is sealed and fed for injection molding;

Liquid silicone is injection molding liquid silicone rubber (LSR): its full name is injection molding liquid silicone rubber, and vulcanization equipment is an injection molding machine.

The injection molding machine has a very simple process (no need for manual processes such as batching, rubber mixing, cutting, and placing in the high-temperature glue process, only one worker needs to take the product), and the product has high accuracy (all manual procedures before molding All are replaced by machines), high output (A / B glue mixed at a temperature of 130 degrees for a few seconds), many advantages such as saving labor, electricity, and materials, can produce all products produced by high-temperature glue.

LSR molding process:

  • 1. LSR A + B components typically come in suitable injection molding equipment and then heat-cured into a molded rubber part. A process controlled pumping kit presses down on the buckets to force the material into static mixer and feed into the injection unit.
  • 2. Then, streams of pigment can be added and controlled. In the injection, press material will be mixed together additionally with a screw and pushed forward to create a “shot” of material, or the amount needed to fill the mold.
  • 3. After the material is injected into the mold, it will then stay clamped together to cure the LSR. Then, either an operator or a robot will remove the cured product from the mold and the cycle repeats. It is a very quick efficient process.
  • 4.Secondary steps like post bake can help reduce volatilities and improve compression set. And the deflashing process removes unwanted flashing. It’s then cleaned to remove foreign material and packaged for shipment.

Solid silicone rubber is a transparent material, and a vulcanizing agent needs to be added during molding to speed up the vulcanization molding time.  Solid silicone part is compression-molded, and after being kneaded by raw materials, it is cut into a size and thickness suitable for molding, and then placed in silicone mold, manual demoulding.

The solid silicone rubber compression molding: This enables the silicone to cure once introduced to heat. To add pigment to the silicone, the silicone must be mixed using a two-mill roll. This is a labor-intensive process that has the possibility for contamination of the silicone. Once the material is pre-catalyzed and pigment is added it is weighed and often shaped to the approximate size and configuration of the desired part. It is then placed directly into the mold cavity. The rubber is then compressed between the top and bottom plates. These plates are heated to melt the silicone and vulcanize (cure) the silicone.

After the cutted silicon rubber ready the compression molding process:

  • 1.The mold is prepared by being heated and sealed
  • 2.Uncured Silicone (preform) is placed in the mold cavity
  • 3.The mold is closed
  • 4.Heat and pressure are applied (according to programmable logic controls and in accordance with temperature and pressure parameters)
  • 5.The mold is opened and the cured rubber is removed
  • 6.Post-molding processes include deflashing, inspection, postcuring, etc.

Industry use:

Liquid silicone rubber is generally used in baby products, kitchen products and medical products, and it can directly contact food and human body;

Solid silicone rubber is generally used in daily necessities, industrial miscellaneous parts, and auto parts.

Cost

Liquid, The cost for raw material and production, is higher than solid.

Conclusion

According to the above information, you can see there are much difference of the LSR (liquid sillicone rubber) and Solid silicone rubber.

You also can see the following sheet to know them more simply.

The Fumed silicone rubber can pass the FDA in Eu request = LFGB Standard.

In ZSR Group has rich experience in producing Custom silicone products with LSR and solid silicone rubber. We also can help selet the right material (LSR or Solid silicone rubber) according to your project.

Any Silicone products or Silicone project need technical support, you also can custom Silicone products at ZSR Group. We will support your Silicone products from idea to life

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