Silicone sealants contain various fillers. These include silicon dioxide, nano calcium carbonate, wollastonite powder, and heavy calcium carbonate. Nano calcium carbonate is the most common one used. In the domestic sealant market, over 60% of silicone sealants contain nano calcium carbonate. This usage is quite significant.
Nano calcium carbonate is a key filler in silicone sealants. It boosts adhesion, weather resistance, and mechanical performance. This includes improvements in elastic modulus and elongation at break. Its small particle size, high surface area, and surface energy are the reasons for these benefits. Modified heavy calcium carbonate undergoes a special process. This improves the shape, dispersibility, and surface activity of the particles. It can partly replace nano calcium carbonate in silicone sealants. It also helps reinforce them to some degree.
Recently, information from the State Intellectual Property Office showed that Hubei Xingfa Chemical Group Co., Ltd. Applied for a patent called “A silicone sealant with modified heavy calcium that partially replaces nano-calcium carbonate and a preparation method.” The invention uses modified heavy calcium in the preparation process. It also reduces the same amount of nano-calcium carbonate for sealant preparation. Modified heavy calcium partially replaces nano-calcium carbonate in silicone sealant. This keeps the mechanical properties, such as colloid strength and elongation at break, mostly unchanged. The operation process is easy. It helps lower the production costs for the sealant factory.
The specific plan is as follows:
Preparation method of modified heavy calcium
Add 800-mesh heavy calcium carbonate to the reactor. Then, mix it with water to make a slurry. The mass fraction should be between 50% and 75%. Start stirring and heating. When the slurry temperature rises to 65-80°C, add the modifier. Under the condition of stirring speed of 800-1000rad/min, react for 50-70min. After the reaction, stop stirring. The slurry is filtered, dried and ground to obtain modified heavy calcium carbonate.
The modifier includes at least one of the following: Peg-7 glyceryl cocoate, sodium octadecenoate, or distearyloxyisopropylaluminate. The dosage ratio for these modifiers ranges from 0.1 to 1.0:1.0 to 1.3.6:1.0 to 3.7.
Preparation method of silicone sealant
The silicone sealant has these components (by weight):
- 200-500 parts of hydroxyl-terminated polydimethylsiloxane
- 300-800 parts of nano calcium carbonate
- 10-250 parts of modified heavy calcium carbonate
- 100-250 parts of heavy calcium carbonate
- 1-10 parts of catalyst
- 50-200 parts of plasticizer
- 8-20 parts of coupling agent
- 25-60 parts of crosslinking agent
Among them:
- The viscosity of hydroxyl-terminated polydimethylsiloxane at 25°C is 20000-100000 mPa·s.
- The plasticizer can be one of these: white oil, methylphenyl silicone oil, vinyl silicone oil, or dimethyl silicone oil.
- The crosslinker includes at least one of the following: methyl triacetone oxime silane, phenyl triacetone oxime silane, methyl vinyl diacetone oxime silane, or dimethyl diacetone oxime silane.
- The coupling agent is at least one of KH-550, KH-560, KH-570, and KH-792.
- Nano calcium carbonate powder has 300-500 parts. Its oil absorption value ranges from 22.0 to 27.0 g dop per 100 g of CaCO3. The specific surface area measures 24 to 35 m²/g.
- The modified heavy calcium carbonate is 10-30% of the mass of nano calcium carbonate.
Specific operation method
Mix hydroxyl-terminated polydimethylsiloxane, nano calcium carbonate, heavy calcium carbonate, and modified heavy calcium carbonate in a kneader. Stir for 5 minutes. After the materials are stirred and mixed evenly, heat and evacuate the materials. The heating temperature of the materials is controlled to be 100-130°C and the vacuum degree is ‑0.09-‑0.1MPa. The materials are dehydrated and stirred at a high temperature of 100°C for 90-150 minutes. After the high-temperature dehydration is completed, stop heating. When the temperature goes below 40°C, add plasticizer. Then, stir in vacuum for 20 to 40 minutes. Stop stirring to get the base rubber.
In a planetary mixer, add the base rubber, crosslinking agent, coupling agent, and catalyst. Keep the temperature below 50°C. Stir at 30-50 rad/min for 3-10 minutes. Then, lower the pressure in the cylinder to below -0.08 MPa. Next, stir at 60-90 rad/min for 25-40 minutes. Stop stirring and quickly discharge the material to get a sealant sample.
To prepare silicone sealant, we activate and modify heavy calcium carbonate. We use fatty acids and coupling agents. This improves the lipophilicity and hydrophobicity of the modified calcium carbonate. It also enhances its compatibility with the organic matrix. These changes help improve processing and mechanical properties in sealant applications. So, we add modified heavy calcium carbonate to replace some nano calcium carbonate powder. This change boosts the overall performance and application value of the silicone sealant. You can maintain properties like colloid strength and elongation at break. Plus, you can lower the production cost of silicone sealant. This method is easy to use. The silicone sealant made this way works well in construction.