I. What is the difference between liquid silicone and solid silicone?

1. Liquid silicone
   Liquid silicone is relative to solid high-temperature vulcanized silicone rubber. It is a liquid adhesive with good fluidity and fast vulcanization. It is safer and more environmentally friendly and can fully meet food-grade requirements.
2. Solid silicone
   Solid silicone is a saturated polymer elastic material. It has characteristics such as high temperature resistance, cold resistance, solvent resistance, toughness, anti-adhesion, electrical insulation, and chemical resistance. It has a wide range of applications.

II. Comparison between liquid silicone and solid silicone

1. Appearance
   a. As the name suggests, liquid silicone is in a liquid state and has fluidity.
   b. Solid silicone is in a solid state and has no fluidity.
2. Safety
   a. Liquid silicone is a highly transparent and highly safe food-grade material. No vulcanizing agent or other auxiliary materials are added during molding, and it is molded by sealed feeding.
   b. Solid silicone is a transparent environmental protection material. Vulcanizing agents need to be added during molding. It is molded by open mold feeding.
3. Molding methods
   a. Liquid silicone is injection molded liquid silicone rubber (LSR): The full name is injection molded liquid silicone rubber. The vulcanization equipment is an injection molding machine. The injection molding machine has many advantages, such as a very simple process flow (no need for manual processes such as batching, refining, cutting, and arranging materials in the high-temperature adhesive process. Only one worker is needed to take the product), high product accuracy (all manual procedures are replaced by machines before molding), high output (A/B glue is molded into a solid in a few seconds at a certain temperature), saving manpower, electricity, and materials. It can produce all products produced by high-temperature adhesives.
   b. Solid silicone molding: The raw materials are solid blocks. After being mixed by a mixer, they are cut into appropriate sizes and thicknesses for the product and mold by a cutting machine. Then they are placed into the mold and molded under a certain temperature by a pressure molding machine. When demolding, it is similar to plastic products and the mold also needs to be cleaned. There are mainly six molding methods for silicone products:
   • Compression molding: This production process is the most common. It is mainly completed with the cooperation of molds. The shape of the mold determines the shape of the silicone product. Compression-molded silicone products usually use high-temperature molds. After adding solid silicone raw materials with vulcanizing agents, they are molded into solids by applying pressure on a vulcanizing machine. The hardness of compression-molded silicone is usually between 30° and 80°. This production process is relatively simple and is suitable for all silicone products.
   • Injection molding: This process has relatively high quality requirements and is a combination of liquid silicone and plastic. Its products show good thermal stability, cold resistance, excellent electrical insulation properties, and will not produce toxic substances when burned. Therefore, it has become an irreplaceable material in the production and design of health products, automotive products, baby products, medical products, diving products, kitchen utensils, and sealing parts.
   • Solid-state transfer injection: In the processing of solid silicone products, the transfer injection process has a similar processing method to that of liquid silicone, but it is the same as the production method of solid silicone. It uses the same machine and raw materials, but the mold is the same as that of liquid silicone. Mainly, the material is extruded to the root of the product. This method can use the same hardness of solid silicone. After being strongly extruded into the mold cavity by the pressure of the machine, it is molded. However, compared with liquid silicone materials, naturally it does not have such good fluidity. The advantages of this processing method are that the product can avoid many appearance defects and have good control of parting lines. It is mainly aimed at some customers to avoid some appearance parting aesthetics and product quality issues. However, it also has many disadvantages, such as large glue consumption, high cost, complex processing, the need to add a middle plate to the mold and manually lift the mold core, which requires a lot of manpower, and the processing efficiency of the product is low. Therefore, this is one of the reasons why very few silicone product manufacturers use this processing technology at present!
   • Extrusion: Extruded silicone products are usually extruded and molded by an extrusion machine. Generally, the extruded silicone shape is long and tubular and can be cut at will. The products made by the extrusion process have a relatively single shape and are mostly strip-shaped. Silicone tubes are widely used in the fields of medical treatment and mechanical equipment. It can also be used as a buffer material in packaging materials.
   • Calendering: After adding white carbon black, silicone oil, etc. and kneading and mixing to make a compound rubber, it is calendered to produce sheet materials. The film obtained by calendering has obvious differences in the longitudinal and transverse physical and mechanical properties. This phenomenon is called calendering effect. Specifically, the longitudinal tensile strength of the film is greater than the transverse tensile strength. The transverse elongation at break of the film is greater than the longitudinal elongation at break. The longitudinal shrinkage rate of the film is greater than the transverse shrinkage rate. The calendering effect is the result of the orientation of macromolecules and needle-like and flake-like compounding agents in the rubber compound along the calendering direction during the calendering process. The magnitude of the calendering effect is related to the composition of the rubber compound, calendering temperature, speed, speed ratio, etc. It is used for larger products, such as silicone sheets and silicone plates.
   • Pouring: The operation method of pouring mold or perfusion mold: Pouring mold or perfusion mold is used for relatively smooth or simple products. It saves labor and time without mold lines. That is, surround the product or model you want to copy with rubber plates or glass plates, and directly pour the vacuumed silicone into the product. After the silicone dries and forms, take out the product, and the mold is formed. (Note: Pouring molds generally use softer silicone to make molds, so it is easier to demold and will not damage the product inside the silicone mold.) It is a combination of solid and liquid. Applied products such as mobile phone cases and adult products.
   • Coating: Fast vulcanization; strong adhesion; good fluidity and easy defoaming. Using platinum complex catalysis, it is non-toxic and odorless; excellent thermal stability and cold resistance (operating temperature -60°C to 200°C). After molding, it has good air permeability, heat resistance, and a certain tensile strength; extremely good anti-slip performance; no pollution; low hardness; strong bonding for flocking. High tear strength; high transparency; good tensile properties. Wear-resistant, washable, and high temperature resistant; high three-dimensional texture, smooth, soft, and flexible fabric with excellent texture and excellent elasticity. Washable and dry cleanable. Applied to cloth, it has an anti-aging effect. For example, silicone gloves, rain boots, etc.

III. How to distinguish between liquid silicone products and solid silicone products?
Liquid silicone products: High transparency, no peculiar smell, and the product has an injection port.
Solid silicone products: Low transparency, with the smell of vulcanizing agent or other substances covering the vulcanizing agent, and the product has no injection port.

IV. Application fields
Liquid silicone: Generally used in baby products, kitchen products, and medical products, and can directly contact food and the human body.
Solid silicone: Generally used in daily necessities, industrial miscellaneous parts, and automotive parts, etc., and has a relatively wide range of applications.