Organosilicon polymers are a type of special polymer material with a semi-organic and semi-inorganic structure, which has unique and excellent properties. Organic silicon products are diverse in form and widely used, so organic silicon materials have earned the reputation of "industrial MSG" and "catalyst for the development of high-tech".

Material properties

1. Good fluidity, slow hardening speed, and a higher molding temperature is required for compression molding.

2. After compression molding, it must be cured at high temperature.

Classification

Organosilicon plastic can be mainly divided into three types according to their molding methods: laminated plastic, molded plastic and foam plastic.

Organosilicon laminated plastic

Organosilicon laminated plastic can be made by high-pressure and low-pressure molding methods, or by vacuum bag molding. The use pressure of the high-pressure molding method is about 6.86MPa; the use pressure of the low-pressure molding method is about 0.20MPa. The main difference between the two lies in the different catalysts and polymerization degrees used: high-pressure laminated plastic usually use triethanolamine as a catalyst; low-pressure laminated plastic use highly active special catalysts, such as a mixture of dibutyltin diacetate and 2-ethylhexanoate lead. High-pressure laminated plastic generally have excellent electrical properties and the lowest water absorption rate.

The molding process of silicone laminated plastic is as follows: the glass cloth is passed through a silicone resin liquid pool to which a catalyst has been added at a certain rate, so that the glass cloth is soaked with a layer of glue containing about 45% solid resin, and then dried in a filtered circulating air flow for 30 minutes, and then pre-cured in a circulating air flow at 110¡ãC for 5 minutes. After cooling, a flexible, non-sticky, moldable and flattened cloth can be obtained. For high-pressure molding, it can be pressed at a pressure of 6.86MPa and a temperature of 175¡ãC for 75 minutes; for low-pressure molding, it can be pressed at a pressure of 0.20MPa and a temperature of 175¡ãC for 15-60 minutes (depending on the size and thickness). In order to improve the performance of the material, the pressed parts need to be heat cured at 250¡æ for 12-24h or longer.

If you want to make laminated plastic with excellent electrical properties, it is important to reduce the alkali content in the glass cloth. In addition, glass cloth with high alkali content will affect the curing and gelling time of the resin. Before molding, all glass cloths must be cleaned and various trace organic slurries are removed from the glass cloth, otherwise it will affect the adhesion of the resin and cause the color of the laminated plastic to be poor.

There are two ways to remove the slurry. One is to burn the glass cloth at 350¡æ, and the other is to put the glass cloth in detergent for fine bleaching. The first treatment method is simple and has better effect. The disadvantage is that it will affect the tensile strength of the glass fiber and the mechanical properties of the glass cloth. However, if it is produced by continuous method, rough glass cloth can be used to improve the mechanical properties of the laminated plastic, but the electrical properties will be reduced. Therefore, generally, finer glass cloth (thickness 127-178¦Ìm) is used, so that a laminated plastic with both excellent electrical properties and medium mechanical strength can be obtained.

Organic silicone molded plastic

Organic silicone molded plastic is a kind of thermosetting plastic made by mixing organic silicone resin, filler, catalyst, dye, release agent and curing agent. Commonly used fillers include glass fiber, asbestos, quartz powder, talcum powder, mica, etc.; the catalyst is lead oxide, triethanolamine and a mixture of triethanolamine and benzoyl peroxide; the commonly used release agent is calcium oleate.

The basic composition of organic silicone molded plastic is as follows (mass fraction): silicone resin 25%; filler 73%; pigment>1%; release agent>1%; catalyst is trace.

The molding process of organic silicone molded plastic can be divided into three stages: mixing, molding and post-curing, which are introduced as follows:

(1) Mixing. In order to obtain silicone molded products with excellent performance, the various components of the molded plastic must be mixed evenly. The processing technology and equipment of general thermosetting molding plastic can be used, such as using a double-drum mixer to fully mix the resin, filler, glass fiber, additives and catalyst at 80-90¡ãC to obtain molded plastic. The molded plastic after mixing has good flow properties. However, due to the large shear force of the double-drum mixer, it is easy to grind the long glass fiber filler into powder, reducing its reinforcement effect. Therefore, the impact strength of the silicone molded plastic processed by this equipment is low.

Using a high-speed stirring mixer (stirring speed up to 2000-4000r/min) to process silicone molded plastic, it only takes 2-4 minutes to ensure that various materials are mixed evenly, and the glass fiber can be kept within a certain length range.

The mixed silicone molding plastic should be sealed and stored in a non-metallic container to prevent moisture absorption or mixing with metal impurities, otherwise it is easy to cause cracking, blistering or poor fluidity of the parts during the molding process.

(2) Molding. Silicone molded plastic can be molded using the common molding methods for thermosetting plastic, such as molding. The choice of molding method depends on the performance of the molded plastic, the requirements for the performance of the molded object, and its external geometric dimensions.

Injection molding or transfer molding is suitable for products with complex shapes, small sizes, and large production volumes. The molded plastic is required to have good fluidity and rapid curing characteristics. The molding temperature is high, the pressure is low, and the time is short.

Compression molding is suitable for manufacturing products with large external dimensions, small plastic part molding shrinkage, and high mechanical strength. Due to the large proportion of fibrous fillers in the molded plastic components, the fluidity of this plastic is worse than that of injection molding plastic, the curing speed is slow, the molding pressure is high, and the time is long. The molding temperature of silicone molded plastic is 160-180¡æ, and the pressure and time are related to the external dimensions and thickness of the part.

(3) Post-curing. In order to improve the physical and mechanical properties and high temperature resistance of silicone molded products, they must be post-cured. The determination of the post-curing process should be based on the type of plastic and the size and thickness of the part. Condensation-type silicone molded plastic should be cured at 200¡ãC for more than 2 hours, and the curing time will be extended as the thickness of the part increases. Polymerization-type and addition-type silicone molded plastic can be cured at 150¡ãC for a certain period of time to achieve complete crosslinking.

According to different uses, silicone molding plastic can be divided into two types: silicone molded plastic for structural materials and silicone molded plastic for semiconductor packaging. The characteristics of silicone molded plastic used as structural materials are good heat resistance, small changes in mechanical strength and electrical insulation properties with temperature. They are widely used in rockets, aerospace, aircraft manufacturing industries, radio, electrical engineering and other industries. They can also be used to make high-power DC contactors, terminal blocks, various heat-resistant insulating materials, and instrument housings and electrical device parts that can be used for a long time at or above 200¡ãC, such as brush holder rings, coil frames, etc. Silicone molded plastic used to encapsulate electronic components, semiconductor transistors, integrated circuits, etc. have the characteristics of heat resistance, non-flammability, low water absorption, good moisture resistance and non-corrosion. They can still maintain stable electrical insulation and mechanical properties in a wide range of temperature, humidity and frequency, thereby protecting the encapsulated semiconductor components from moisture, dust, impact, vibration and temperature.

Organic silicon foam plastic

Organic silicon foam plastic are a low-density sponge-like material that can withstand high temperatures of 360¡ãC and are flame-resistant. They are excellent materials for heat insulation, sound insulation, flame retardancy and electrical insulation.

Organic silicon foam plastic can be divided into two categories: one is powdery and foams when heated to about 160¡ãC; the other is liquid two-component and can foam at room temperature. Powdered foam plastic are made of solvent-free silicone resins with low melting points (melting point 60-70¡ãC) and low molecular weight containing silanol groups, mixed with fillers (diatomaceous earth, quartz powder, etc.), foaming agents, and catalysts, and then melted and crushed.

When in use, heat the powder plastic to 160¡æ to start foaming until the foaming is complete, and then place the foam in a 250¡æ oven for heat curing for about 70 hours. The foaming agent used is azobisisobutyronitrile, N,N¡ä-dinitrosomethylenetetramine or 4,4¡ä-oxybisbenzenesulfonylhydrazine, etc.; the catalyst is octanoate, cyclopentaneate or amine.

Two-component room temperature silicone foam plastic is composed of two silicone liquids containing silanol groups and silicon-hydrogen bonds, with quaternary ammonium base (or platinum compound) as a catalyst, and foaming and cross-linking are achieved by releasing hydrogen during the reaction.

Silicone foam plastic is widely used as thermal insulation and electrical insulation materials in the construction and machinery industries, as well as lightweight, high temperature resistant and moisture resistant materials for aircraft, rockets, etc. It can also be used as filler for propellers, wings, cabins and insulation materials for fire walls.

Identification method

1. Use a ballpoint pen to apply on a small area. If it can be easily wiped off with your hands after application without leaving any trace, it is a silicone product. If it needs to be wiped clean with water, it is a rubber or plastic product.

2. If the product itself has a fragrance or a plastic or rubber smell, it is not a silicone product. Silicone products usually have no smell or almost a trace smell (caused by the outer packaging shell or other non-silicone parts of the device itself).

3. Do not get it wet. Get it wet with a proper amount of water. If it can be easily wiped off with a paper towel without leaving any trace, it is a silicone product. If there are still water drops or water traces after wiping with a paper towel, it is a plastic or rubber product.

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