Basic knowledge of sealants

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Silicone sealant is a paste that solidifies into a tough rubber-like organic elastomer once it comes into contact with moisture in the air. It has strong bonding force and high tensile strength, and is also weather-resistant, shock-resistant, moisture-proof, odor-resistant, and adaptable to large changes in temperature. In addition, it has a wide range of applicability and can be bonded to most building materials, curtain wall weathering, and structural assembly (structural adhesive), so its application value is very high.

Classification of sealants

1. According to chemical composition:

1) Silicone RSi: has good weather resistance, durability and displacement ability, but poor decorability.

2) Polyurethane PU: has good cold resistance and wear resistance, but its heat resistance is worse than that of silicone, and is mainly used for automobile windshields, etc.;

3) Polysulfide PS: a two-component product, used for the second sealing of insulating glass, and its weather resistance is worse than the previous two;

4) Acrylic acid: solidifies after removing moisture, and is relatively hard after solidification, mainly used for door and window sealing;

5) Butyl glue: It needs to be heated by a machine to reduce its viscosity before it can be applied to the substrate. After solidification, it is sticky, has no flow, and has weak adhesion, but has good airtightness, and is mainly used for the first sealing of insulating glass.

2. According to the curing type:

1) Acidic glue; deacidification type

2) Neutral glue: dealcoholization type and deoxime type; condensation product of hydroxylamine and ketone – oxime,

3) Deamidation type: ammonia odor, ultra-low modulus, good elongation, but poor adhesion, suitable for highways and runways;

4) Deacetone type: odorless, fast curing, long storage period, high temperature resistance (300℃), but the production process is complicated and the cost is high, mainly used in the electronics industry.

3. According to packaging:

1) Single component and double component

2) Hard and soft

Composition of sealant

1) Base glue: 107 glue (polysiloxane), determines the comprehensive performance of the glue (weather resistance, etc.)

2) Reinforcement agent: SiO2 (silicon powder), calcium carbonate, white carbon black, etc., determines the strength and hardness of the sealant;

3) Cross-linking agent: MOS (methyl tributylidene oxime siloxane), VOS (vinyl tributylidene oxime siloxane), forming a three-dimensional network structure to make the structure of the colloid itself compact;

4) Coupling agent: adhesive, promotes bonding;

5) Plasticizer: silicone oil, which can make the surface of the rubber strip smooth, the feel of the glue application is good, the workability is good, and the consistency of the glue is adjusted.

Curing mechanism of sealant

1. Single component:

1) Curing by absorbing moisture in the air;

2) Gradually curing from the outside to the inside (curing rate);

3) The curing mechanism of single component products is related to the environmental climate. The higher the temperature and humidity, the faster the curing;

2. Two components:

Part A is the base glue and Part B is the curing agent. They are mixed in the prescribed proportion and cured simultaneously. The applicable period is 20 minutes to half an hour (curing is related to temperature, but mainly depends on the ratio of Part A to Part B).

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