There are many differences between condensed silicone rubber and addition silicone rubber in product packaging form, use mode and performance (Fig. 2), such as curing speed, bulk strength, adhesion, etc., but each has its own advantages.

1. Packaging form

The condensed silicone rubber can be packaged in either one component or two components. The addition silicone rubber is a temperature sensitive product, so it is necessary to separate the catalyst from the crosslinking agent. The two-component packaging is usually used to avoid reaction during storage. Of course, there are also single component addition silicone rubber products in the market, which are mainly divided into two types: one is low-temperature storage type, that is, it needs to be stored and transported under the condition of freezing / refrigeration, which is inconvenient to use; The other is room temperature storage type. The product uses special structure of catalyst and inhibitor, which does not have reaction activity at room temperature. At high temperature, the catalyst activity is released to realize cross-linking curing. However, the cost is high and the curing temperature is high.

2. Curing rate
Due to the difference of curing mechanism, there is a great difference in curing speed between condensed and addition silicone rubber. Condensation type silicone rubber (mainly refers to one component) is a kind of silicone rubber which reacts from the surface with the help of moisture in the air and vulcanizes gradually from the surface to the inside. Deep curing is slow, and it usually takes 24 hours or even a week to complete vulcanization. Addition silicone rubber can be vulcanized at room temperature or at high temperature. At room temperature, the internal and external vulcanization of the compound is more consistent, and there is no obvious order. At high temperature, the curing rate can be adjusted with the temperature. Under baking condition, the compound can be cured rapidly in 5 min or even 1 min. It should be noted that, under heating conditions, the curing speed of addition silicone rubber has a certain relationship with sizing thickness, heat transfer of substrate, and air blowing effect of baking equipment.

3. Body strength
The mechanical properties of both condensed and addition silicone rubber can be improved by reinforcing fillers such as nano calcium carbonate and fumed silica, among which fumed silica has the most obvious reinforcing effect. Due to the difference of systems, condensed silicone rubber usually uses nano calcium carbonate as the main reinforcing filler, and the addition of fumed silica is limited, so the tensile strength is low, generally not more than 3Mpa, while addition silicone rubber generally uses fumed silica as the reinforcing filler, and the addition amount can be increased to more than 30% through the treatment of hexamethyldisilazane and other modifiers, and the tensile strength can be improved To achieve more than 10 MPa, far more than the condensed silicone rubber.

4. Adhesiveness
By adding silane coupling agent, condensed silicone rubber can achieve the bonding of a variety of materials, so at present, condensed silicone rubber is mostly used in the fields of construction, household appliances, lighting, rail transit, photovoltaic and so on, which is based on its good adhesion and bonding universality. However, the adhesiveness of the addition silicone rubber is far less than that of the condensation silicone rubber, which is related to the low polarity of the molecular chain and the absence of polar groups in the molecular chain that can react with the coupling agent. Generally, the adhesiveness of addition silicone rubber can be improved by the following three ways: (1) using primer to treat the surface of the substrate; (2) adding tackifier with special structure, which usually needs high temperature baking to achieve good adhesion.

In addition, there are differences in reaction by-products and catalyst poisoning between addition and condensation silicone rubber. In the curing process of condensed silicone rubber, small molecules such as acetic acid, alcohols or ketoximes are usually released, which has a certain odor, while addition silicone rubber has no reaction by-products and low odor. Because the platinum catalyst of addition silicone rubber is easy to be poisoned and inactivated, it can not contact the organic compounds containing N, P, s and other elements, and the ionic chemicals containing Sn, Pb, Hg, Bi, as and other heavy metals.