Improvement of preparation and vulcanization process of room temperature vulcanized liquid silicone rubber for LED display potting

[Source: "High - tech LED - Technology and Applications" December issue ]

The two-component condensation type room temperature vulcanization silicone rubber is classified into four types: a dealcoholization type, a dehydrogenation type, a dehydroxylamine type, and a dehydration type. Among them, dealcoholized RTV-2 is the most commonly used, commercial two-component room temperature vulcanized rubber is mostly dealcoholized; dehydrogenated room temperature vulcanized silicone rubber is mainly used as foamed silicone rubber; dehydroxyamine type room temperature vulcanized silicone rubber is mainly used as high Low modulus silicone rubber with elongation; dehydration type room temperature vulcanized silicone rubber has a slow vulcanization reaction, and has less practical application.

The basic composition of the two-component room temperature vulcanized silicone rubber includes the following three main components: 1 base rubber polymer - hydroxyl terminated polydiorganosiloxane; 2 vulcanizing agent system - crosslinking agent, catalyst, accelerator, inhibition Agent / stabilizer, etc.; 3 filler - reinforcing filler (silica, etc.), semi-reinforcing filler (quartz powder, diatomaceous earth, etc.), incremental filler (quartz powder, calcium carbonate powder, talcum powder, etc.); There are also pigments, dyes and the like.

Among the above components of silicone rubber, the proportion of the vulcanizer system is small, and the proportion of the production cost is small, but it has an important influence on the comprehensive performance of the silicone rubber product. Therefore, research and improvement of silicone rubber The matching vulcanizing agent is of great significance for improving product quality and improving economic benefits.

1. Vulcanization reaction and performance requirements and test standards for room temperature vulcanized silicone rubber for LED display screen

Under the action of the catalyst, the base polymer of the two-component room temperature vulcanized silicone rubber undergoes a chemical crosslinking reaction with the crosslinking agent, and at the same time, the low molecular substance formed by the condensation reaction is removed.

There are various explanations for the vulcanization mechanism of two-component room temperature vulcanized silicone rubber. Taking the dealcoholized RTV-2 gel as an example, HOBHKOB believes that the OR in the polymer HO(Me2Sio)n and the crosslinker Si(OR)4 under the catalysis of the catalyst R2Sn(OCOR)2 The transition complex state is formed, and a three-dimensional network structure is formed by stepwise condensation; Nagy considers that Si(OR)4 forms a cyclic compound with R2Sn(OCOR)2, and then condenses the structure with HO(Me2SiO)nN, and releases ROH. The above explanation about the vulcanization mechanism does not indicate that the crosslinking reaction requires a small amount of water. In fact, the vulcanization reaction of the general condensation type silicone rubber in the normal environment is gradually extended from the surface to the inside, and the water content of the silicone rubber material is gradually increased. Up to 0.1%, the vulcanization time is a constant. Li Guangliang explained the mechanism of water participation in the vulcanization reaction: the first step of the silicone rubberization reaction is the hydrolysis of the most easily hydrolyzed ester group (-OOCR) on the Sn atom of the catalyst, the formation of OH on the Sn, and the second reaction of the vulcanization reaction. The step is that OH on Sn reacts with Si(OEt)4, and Si is connected to Sn, and the resulting intermediate has high reactivity, and is cross-linked with Si-OH of the silicone rubber polymer, and finally the sulfurization reaction is completed. .

Unfinished

For more information, please refer to "High - tech LED - Technology and Applications" December issue