What Is High Cured Silicone Rubber

  • By:TBL
  • Date:2022/07/26

Silicone rubber is a high-performance elastomer characterized by an unusual combination of properties. These properties range from high-temperature performance to durability, excellent electrical insulation properties as well as its transparency. Heat Cured Rubber are silicone elastomers formed from straight chains with extremely high molecular weights. The system will cure using organic peroxide curing agents or platinum catalysts. HCR has excellent resistance to temperature and aging.


Chemical Structure

Heat cured rubber elastomers are also known as high temperature vulcanized (HTV) silicone rubbers. They consist of reactive, ie linear, silicone gums with very high molecular weight macromolecules containing various reactive groups. The most commonly used gums are partially phenylated or perfluorinated vinyl gums. Various raw materials are added to impart additional properties to the HCR, such as fumed or precipitated silica with high specific surface area to improve mechanical properties, heat stabilizers and various other additives such as plasticizers or anti-structuring agents. Crosslinking is achieved using organic peroxides in polycondensation systems or platinum catalysts in polyaddition systems.


Heat cured rubber elastomers have excellent properties far superior to traditional organic elastomers. They have excellent mechanical temperature resistance and can be used in the temperature range from -50°C to +300°C. The aging resistance of these elastomers highlights their fundamental properties, such as their chemical inertness, their photo-oxidative stability and the absence of residual reactive groups after curing. Rich colors are possible. By using sufficiently fine silica fillers, it is even possible to produce transparent articles for food and paramedical applications. The addition of various additives opens unlimited doors for customizing HCRs, creating solutions for all existing and new applications in aerospace, automotive, healthcare, oil and gas, construction, electronics , etc. Recent examples are heat transfer additives for electric vehicles, conductive materials for power or consumer electronics, and antimicrobial solutions for healthcare applications.


What Is Curing ?

According to Wikipedia's definition, "silicone curing" is the fundamental chemical process in polymer chemistry used to crosslink polymer chains. It is a key process in the elastomer industry for curing or curing uncured synthetic or natural rubber materials into the desired shape and size. Curing is usually achieved by adding chemical additives (hardeners or hardeners) or by using heat or UV systems without chemical additives.


Silicone Rubber Curing

Since silicone elastomers are also made up of polymer chains, similar curing is required before manufacturing the finished silicone rubber. Silicone rubber is a thick, viscous liquid when uncured or uncured. In order for it to harden, it must undergo a cross-linking and hardening mechanism (hardening mechanism), which takes place through a catalytic reaction, i.e. the cross-linking of the liquid polymer system, where it builds up and hardens . Silicone is mostly made in a two-step process to the desired shape and size. This is done at manufacturing and then continues during the post-curing process. The operating elements during curing are widely varied to provide end results with various properties. This process is irreversible. For silicone heat cured rubber, there are two most commonly used curing systems. Platinum curing system and peroxide curing system.


Platinum Curing System 

Platinum hardening technology has been around for a long time, especially for applications requiring high purity products, such as medical devices, food and beverage processing industries, and pharmaceutical applications. In platinum-cured silicone systems, two different chemical groups react in the presence of platinum. It is also known as "addition hardening" or a two-part system. Compared to peroxide compounds, the details are more complicated. The base silicone polymer should contain vinyl functionality. Unlike peroxide curing systems, platinum is a true catalyst. It is not ingested by the process. In fact, in platinum curing systems, platinum-catalyzed reactions occur even at normal temperature and pressure, so the activity must be technically reduced. The first request-response occurs much faster than that initiated by peroxide because it does not depend on the rate determining step.


Peroxide Curing Systems

The use of peroxides to cure silicone elastomers has long been a routine method. The peroxide curing procedure is well defined, using free radicals for the crosslinking generated by the organic peroxide. There are basically two parts: different types of peroxides and silicone resins. Although the term "catalyst" is used when the peroxide hardens, it is not really a catalyst reaction because it is absorbed in the process. Peroxide-induced methods are classified as side reactions. Generally divided into three stages. When the silicone elastomer is exposed to a heating process, the peroxide thermally degrades to generate free radicals. These free radicals hit methyl or vinyl groups, depending on the polymer and peroxide used, to form active sites for crosslinking. At this point, the active sites on the silicone polymer are connected, forming carbon-carbon bonds.




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