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.

What is silicone Rubber?

Silicone is a highly active adsorption material, the main component of which is silicon dioxide (SiO₂) and contains a certain amount of water (H₂O). The chemical formula can be expressed as mSiO₂·nH₂O. Silicone has many unique physical and chemical properties, including adsorption, thermal stability, chemical stability, etc., and is widely used in various fields. Silicone raw materials are mainly divided into two types: liquid silicone rubber (LSR) and solid silicone rubber.

Liquid silicone rubber

Liquid silicone is relative to solid high temperature vulcanized silicone rubber. It is a liquid rubber with good fluidity, fast vulcanization, safer and more environmentally friendly, and can fully meet food grade requirements. Liquid silicone, also known as liquid silicone, is a liquid rubber relative to solid high-temperature vulcanized silicone rubber. It has the characteristics of good fluidity, fast vulcanization, safer and more environmentally friendly, and can fully meet food grade requirements.

Liquid silicone has excellent tear resistance, resilience, anti-yellowing, thermal stability, heat resistance and anti-aging. It is a highly transparent and safe food-grade material. No auxiliary materials such as vulcanizers are added during molding, and the molding is done by sealed feeding.

The advantage of liquid silicone rubber

Solid silicone rubber

Solid silicone rubber is a saturated polymer elastic material with the characteristics of high temperature resistance, cold resistance, solvent resistance, crack resistance, anti-adhesion, electrical insulation, chemical resistance, etc. It has a wide range of applications.

Solid silicone is in solid state and has no fluidity. It is also a transparent environmentally friendly material. During molding, vulcanizing agent needs to be added to speed up the vulcanization molding time and open mold casting is used for molding.

The advantage of solid silicone rubber

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

Appearance

Making process

Liquid silicone rubber Making process

Liquid silicone is mainly composed of siloxane (chemical formula R3SiO1/2), which is made by heating reaction after adding crosslinking agent and catalyst. Among them, the raw materials of siloxane are mainly silicon dioxide and dimethyl silicon hydroxide. After high-temperature reaction, these substances form polymers, namely siloxane.

The production process steps of liquid silicone are as follows:

1. Add raw materials such as silicon dioxide and dimethyl silicon hydroxide to the reactor.
2. Add crosslinking agent and catalyst and start heating reaction.
3. Control the reaction temperature and time according to different requirements.
4. After the reaction, various treatments are performed on the product as needed.

Through the above steps, liquid silicone with different hardness and viscosity can be obtained.

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 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

Liquid silicone is a transparent, elastic, high and low temperature resistant and aging resistant material with the following

Characteristics:

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

High and low temperature resistance: Liquid silicone can be used in a temperature range of -60℃ to +200℃, and will not deform, crack or stick due to heat or cold.

Aging resistance: Liquid silicone is not easily affected by oxygen, ultraviolet rays, moisture and other factors in the natural environment, and will not harden or deform due to aging.

Tensile strength: Liquid silicone has high tensile strength and can maintain its shape and elasticity under tension and pressure.

Food grade certification: Liquid silicone material can pass food grade certification and is suitable for use in food packaging and other related fields.

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.

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 Making process

Solid silicone is industrially made of water glass (sodium silicate) as raw material, which is hydrolyzed in an acidic medium to form a gel, and then aged, washed, dried and other processes to form silica gel. Depending on the water content, it is a translucent or white solid. Commercially available products include irregular granular, spherical and microspherical silica gel, which are often used as catalyst carriers in fluidized bed operations.

When used as a catalyst carrier, silica gel is usually impregnated in a solution containing catalytically active components, so that the solution is absorbed into the pores of silica gel, and after drying, activation and other procedures, the active components are distributed on the surface of silica gel. The pore structure of silica gel has an important influence on the properties of the prepared supported catalyst, such as the pore volume and pore size distribution of silica gel. Conventionally, silica gel with an average pore size of less than 15-20 is called fine-pore silica gel; and silica gel with an average pore size of more than 40-50 is called coarse-pore silica gel.

However, the fine pore structure is not conducive to the diffusion of reactant molecules, but it can reduce the utilization rate of the inner surface of the catalyst, and the product molecules generated deep in the pores are not easy to escape from the pores, which is easy to cause deep side reactions. The pore structure of silica gel is related to the manufacturing method and conditions, such as gelation, aging, pH, temperature, time during washing, etc. The commercial silica gel can be expanded by pore expansion treatment. The commonly used method is to place it in an autoclave and add water or a salt-containing aqueous solution (such as sodium carbonate, sodium acetate) for hot pressing treatment. For example, hot pressing treatment at 320℃ and 10MPa can change the specific surface area and average pore size of silica gel from 135m2/g and 123 to 26.9m2/g and 508 respectively.

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

Excellent transparency：Solid silicone is usually milky white, and can be colored during the processing and mixing stage, suitable for a variety of color requirements‌.

Excellent tear strength (35N / mm)：Solid silicone has good elasticity and physical strength, can remain intact when subjected to large deformations, and is not easy to break‌

excellent springback, yellowing resistance and heat-resistant aging

Good thermal stability and weatherability (using temperature -60 C ~ 250 C)  Solid silicone performs well in a wide temperature range. It can maintain excellent physical properties, including cold resistance and heat resistance, in a temperature range of -60°C to +250°C‌

Physical and chemical stability‌: Solid silicone is a porous, polymer-structured material with high adsorption and chemical stability. It can remain stable in various chemical environments and is suitable for a variety of application scenarios‌

Smell

Liquid silicone rubber

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.

Liquid silicone is usually odorless or has a very light odor before curing. Liquid silicone is environmentally friendly, non-toxic and odorless before curing, but masterbatch ingredients and vulcanizers are added during the curing process, and a little odor will be produced during high-temperature molding. This odor will disappear naturally after two or three days under natural ventilation and will not affect the quality of silicone products.

Solid Silicone Rubber

During the production process of solid silicone materials, some additives such as masterbatch ingredients and vulcanizers are usually added. These additives may produce some odor during the high-temperature molding process. The silicone raw material itself is non-toxic and odorless, but after adding masterbatch ingredients and vulcanizers, it will produce some odor through high-temperature molding by hydraulic presses, but this odor usually does not affect the product quality and can be eliminated by itself.

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 according 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 compression molding

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 demolding.

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 silicone rubber ready the compression molding process:

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

The unit price of liquid silicone is usually higher than that of solid silicone. The production cost of liquid silicone is relatively high, mainly because its processing technology is complicated and the equipment requirements are high, so its market price is also relatively high. Specifically, the price of liquid silicone is usually nearly double that of solid silicone.

When will you choose the liquid silicone rubber?

When will you choose the Solid silicone rubber?

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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