High temperature vulcanized silicone rubber sealing strip is a new kind of sealing strip made of new materials, which is mainly made of methyl vinyl rubber as the base material, adding reinforcing filler, infiltrating agent (structure control agent), other additives, crosslinking agent and color master glue to prepare mixing rubber, and extruded by rubber extruder through high temperature baking vulcanization. The production process is shown in Figure 1. Raw rubber: polymerization degree of 5000 ~ 8000, vinyl content of 0.03% ~ 0.3%; Fillers: vaporous silica, precipitated silica, diatomaceous earth, quartz powder, etc. Structure control agent: hydroxyl silicone oil, silazane, diphenylsilanediol, etc. The SI-O bond energy of methyl vinyl siloxane main chain is 444KJ/mol, which is larger than the C-C bond energy of common organic polymer main chain (356 KJ/mol) and C-O bond energy (339KJ/mol). The high temperature vulcanized silicone rubber seal has better aging resistance, high resilience and high and low temperature resistance than other traditional seals.


1 Reaction mechanism of high temperature vulcanized silicone rubber


The crosslinking reaction of high temperature vulcanized silicone rubber can be divided into two ways according to the type of crosslinking agent: peroxide initiation reaction and silane addition reaction. Peroxide-triggered reaction is the thermal decomposition of organic peroxides to produce free radicals, which attack methyl groups or vinyl groups on the siloxane side and cause a chain reaction, resulting in crosslinking. The reaction mechanism is as follows:


Silohydroaddition reaction is the cross-linking of vinyl and silohydride on the siloxane side group under the catalysis of platinum complex. The reaction mechanism is as follows:


2 Excellent characteristics of high temperature vulcanized silicone rubber seals
Excellent weather resistance and aging resistance. The bond energy of silicone rubber is higher than the ultraviolet radiation energy (370KJ/mol), so the silicone rubber keeps the main chain unbroken under the action of sunlight and ozone for a long time, and the performance is not significantly reduced. The silicone rubber seal has a longer service life.
Excellent resistance to high and low temperatures. Silicone rubber can be used in a temperature environment of -60 ~ 200℃ for a long time. The wide use temperature range allows the silicone rubber seal to maintain good performance in cold areas at high latitudes and hot areas at low latitudes.
Good resilience. The Si-O bond rotation energy in silicone rubber is low, and the siloxane is a spiral chain structure, so the silicone rubber has good resilience, which makes the silicone rubber seal return to the original shape after being deformed by external force to ensure its sealing performance.
Safety and environmental protection. Silicone rubber is physiologically inert, non-toxic and tasteless, and does not release volatile gases during use. It is widely used in food and pharmaceutical industries. In the United States FDA certification, so far, silicone rubber is the most harmless material to the human body in all new environmentally friendly materials.
Selective gas permeability. According to research, the oxygen transmission rate of silicone rubber is 25 times that of natural rubber and 428.6 times that of butyl rubber. Silicone rubber has lower permeability to harmful gases such as sulfur dioxide than other rubbers. This performance can make the room maintain fresh air, the most suitable for people's life.
Smooth surface, variety of colors. The surface of silicone rubber is hydrophobic and smooth, adjustable in various colors, and has a good decorative effect.


3 Application of high temperature vulcanized silicone rubber seals
In recent years, silicone rubber, as a new type of rubber material, has shown unparalleled superior performance in many fields, playing the role of dustproof, waterproof, fixed, sound insulation, heat insulation, shock absorption, sealing and decoration, and is widely used in construction, automotive, aerospace, medical and health, communication and power, transportation, household appliances and other fields.


4 Prospect of high temperature vulcanized silicone rubber seals
Silicone rubber seals have not been widely used due to price and market awareness. Compared with other rubber seals, the excellent performance indicators of silicone rubber seals are more suitable for low-carbon building energy-saving doors and Windows vigorously advocated by the state, and are also more in line with the green environmental protection needs of modern life. Other plastic rubber seals are derived from petroleum cracking products, while silicone rubber is derived from silicon ore, which is more sustainable. With the progress of science and technology and the reduction of the cost of use, it is a general trend for silicone rubber seals to replace other rubber seals.