Room temperature vulcanized silicone rubber is a type of silicone rubber widely used in the organic silicone industry at present, referred to as RTV. As early as ten years ago, China's room temperature vulcanized silicone rubber has reached the demand of 300,000 tons. It is mainly used in the construction industry and is used for Glass glue, sealant, interior decoration and door and window seals account for the majority. At present, with the gradual expansion of the industry's use and product innovation and research and development to allow it to develop rapidly, the product's performance specifications remain unchanged. Do you know its material properties?

 

 

(1) Surface drying time

 

 

Refers to the time when a single-component room temperature vulcanized silicone product is exposed to the atmospheric curing process, and the surface is touched with a finger, and the viscosity is lost. Commonly refers to the time distance when the silicone rubber flat sealant is squeezed out to dry under the specified conditions, and the surface does not stick to the hand.

 

 

(2) Curing depth

 

 

 

It refers to the thickness of the silicone rubber flat sealant cured from the outside to the inside within a certain time after the glue is applied in a fixed mold under the specified conditions, such as: 2 ～ 3mm / 24h , 0.6mm / h and so on.

 

 

 

(3) extrudability (defined in accordance with ASTMC1183)

 

 

 

According to ASTM C1183 specification request, under the specified conditions, using Semco pipe and specific glue nozzle (3.2mm diameter), under specific pressure conditions, the extrusion weight per unit time is called extruding.

 

 

 

(4) Instant seal pressure

 

 

 

Refers to the silicone rubber flat sealant with a certain diameter on the flange surface, and then immediately closed, control the adhesive layer has a reasonable thickness, and then apply air pressure according to a certain rate, the maximum pressure it accepts is the instant sealing pressure.

 

 

 

5 (5) Solidification characteristics in oil

 

 

 

It refers to the silicone rubber flat sealant is placed in a fixed mold, and then the mold is placed in the oil. The thickness of the silicone rubber flat sealant cured from outside to inside in a certain period of time is used to characterize the silicone rubber flat sealant. Curing properties in oil.

 

 

 

(6) Shear strength adherence rate during drying time

 

 

 

It means that the sheared test piece that has been glued is placed for a certain period of time under a specific high temperature and high humidity condition, and then it is closed and bonded, and it is left to stand for 168 hours under standard conditions to stop curing. Under the conditions of direct bonding and curing for 168h, the shear strength of the test was stopped, and the strength adherence rate was calculated.

 

 

 

(7) Thermal stability without curing

 

 

 

Means that the uncured silicone flat sealant is placed in a high-temperature environment for a certain period of time, and then can still be cured under the specified conditions, which clarifies that the silicone rubber flat sealant is stable under this temperature condition. If the sealant thermal stability temperature is ≥100 ° C, it means that the uncured sealant can continue to be cured after being heated at 100 ° C.

 

 

According to the phenyl content (phenyl: silicon atom) in silicone rubber, it can be divided into low phenyl, middle phenyl and high phenyl silicone rubber. When the rubber is crystallized or close to the glass transition point or the two conditions overlap, the rubber will appear stiff. The introduction of an appropriate amount of large-volume groups can destroy the regularity of the polymer chain, which can reduce the crystallization temperature of the polymer. At the same time, the introduction of large-volume groups changes the force between the polymer molecules, so the glass can also be changed.化 温度。 The temperature.

 

 

 

Low phenyl silicone rubber (C6H5 / Si = 6 ~ 11%) has excellent low temperature resistance due to the above reasons, and it is independent of the type of phenyl monomer used. The vulcanizate has a brittle temperature of -120 ° C, making it the best low-temperature rubber today. Low phenyl silicone rubber has the advantages of vinyl silicone rubber, and the cost is not high, so there is a tendency to replace vinyl silicone rubber.

 

 

 

When the phenyl content is greatly increased, the rigidity of the molecular chain will be increased, resulting in a decrease in cold resistance and elasticity, but the ablation resistance and radiation resistance will be improved. The phenyl content reaches C6H5 / Si = 20 ~ 34 % Is medium phenyl silicone rubber with ablative resistance, high phenyl silicone rubber (C6H5 / Si = 35 ~ 50%) has excellent radiation resistance.