Silicone glue for construction is commonly known as “glass glue†on the market. It is the main structural bonding and sealing material for glass curtain wall construction. It is a moisture curing product. Generally, the first process is the kneading and mixing process: 107 rubber, white oil or silicone oil and nano calcium carbonate are added to the biaxial kneader in a certain proportion and premixed, and taken after a certain time. Vacuum tightly for 3-6 hours. Some companies pre-dry and dehydrate solid fillers such as nano-calcium carbonate to reduce vacuum mixing time. The base material is obtained after the process is completed. After testing the viscous properties, volatiles, etc. of the base material, the second process, the glue is formed, and the base material and the cross-linking agent, the coloring material, the other functional additives are further thoroughly mixed under vacuum conditions. Sealed and preserved neutral silicone rubber products. Nano calcium carbonate has the following problems in the application process: Moisture The moisture content of the product (the silicone rubber enterprise is based on the volatile matter) is higher, and the hydroxyl group (-OH) on the surface of the calcium carbonate particles is increased, and the aggregates tend to cohesive, forming a three-dimensional network under the action of liquid polysilane. The viscosity of the rubber compound is increased, and 1-3 mm particles are formed in the base material, which causes prolonged mixing time, and can be treated by grinding or screen filtration, but most of the grinding process is open, so the moisture in the pellet The position can be removed even if it is removed, but it is difficult to eliminate. It is feasible to filter the base material with an 80-120 mesh screen. 2. Secondary particle size The secondary particle size is large, and it is generally easy to appear in the nanometer calcium carbonate product with a small particle size. Since the particle size range of the nano calcium carbonate is as small as 40-60 nm, the specific surface area of ​​the particle is increased (22 to 34 m 2 /g). ), the cohesion is enhanced, it is easy to form a tight hard agglomeration, and it is relatively difficult to disperse and depolymerize. The hard agglomerated particles cannot be dispersed during the kneading process of the silicone rubber, so it can only be dispersed by one or more grindings, which is bound to increase manufacturing. cost. If there are more crystals of about 40 nm in the product, the particle size of the agglomerates (secondary particles) will reach 30 μm or more. It is difficult to disperse the hard agglomerates in the two-roll mill during use. When the number of particles is sufficient, The surface of silicone rubber products is prone to particles, even "pocky" or "matte" phenomenon. 3. Surface treatment When the surface treatment is insufficient, since the surface of the calcium carbonate particles is polar and has a hydrophilic cross section, it is difficult to be compatible in a non-polar organic substance such as silicone rubber, which causes difficulty in dispersion, and it is difficult to "powder" when mixing. Prolonging the kneading time, even after thorough mixing, the surface of the calcium carbonate coating is significantly increased due to the lack of sufficient organic surfactant coating on the surface of the calcium carbonate, and the hydroxyl groups have more hydroxyl groups on the surface of the calcium carbonate. It can form a hydrogen bond (physical adsorption) with the Si-O bond in the molecular chain of the liquid silicone rubber, and the result will have two different effects: on the one hand, the physical and mechanical properties of the vulcanizate are improved, and on the other hand, The result of the internalization of the system leads to a decrease in the storage stability of the rubber compound. When the surface treatment agent is excessive, it also has an adverse effect on the production of silicone rubber. Because silicone rubber is a kind of viscose product, it has to have good adhesion to the surface of the construction medium. In order to improve the adhesion performance, silicon The ketone rubber formulation is more modified by silane coupling agent. The adhesive property is formed by the two groups in the silane coupling agent and the surface of the construction medium by van der Waals force or hydrogen bond to form physical adsorption or reaction by group. Forming chemical bonds, when the surface treatment agent of calcium carbonate is excessive, the number of organic groups is significantly increased (especially, the nano calcium carbonate product having an organic hybrid as a main surface treatment agent is more obvious), and some groups in the silane coupling agent It will bond with the organic groups in the calcium carbonate surfactant molecules, thus affecting the bonding properties at the construction interface. On the other hand, the excessive amount of surface treatment agent reduces the probability of direct hydrogen bonding of the surface of the calcium carbonate particles with the silicone gum system, mainly relying on the combination of surfactant organic molecules and the system, because the calcium carbonate surfactant molecules are organic long-chain molecules. Mainly, the bonding force between the organic molecules is relatively flexible, so the cured silicone rubber product has a low modulus. If a proper part of the surface energy of the calcium carbonate surface is hydrogen-bonded to the silicone rubber system, The network structure of the system is stronger and the cohesion is stronger. The tear strength of such products will increase. In addition, the short-chain organic matter in the surface treatment agent is volatile, and when the treatment is excessive, the volatile matter of the product is increased, so that the low-boiling organic matter extracted during the vacuum kneading of the silicone rubber is increased. 4.pH value Storage stability is a very important quality index of silicone rubber products. The storage stability of the dealcoholization type is slightly poor, but the production cost of the dealcoholization type is relatively low, so the enterprises are still mainly based on this type. From the current development of silicone rubber technology, the quality and performance of products are constantly improving, the formulation technology is becoming more and more perfect, and it has become more and more complicated. Some corresponding functional additives have increased, coupled with the continuous popularization of automated production line technology, so that some silicon Ketone rubber enterprises put forward higher requirements on the performance of nano calcium carbonate, and the pH value of the product is required to be below 9.5. In theory, calcium carbonate is a weak base salt with a pH of 8-10. The surface active agent of nano-active calcium carbonate is generally a weak organic acid or an organic acid salt, which has a certain neutralization effect on the surface. Some nano-calcium carbonate products with sufficient surface treatment can be controlled at 8-9. For example, the PH value of Baiyanhua CC of Japan Baishi Company is controlled below 8.8, but the pH value of many domestic enterprises is 9-10. Even reached around 10.5. The pH value is too high for the following reasons: Firstly, the purity of limestone, when MgCO3 ≥ 1.5% in limestone, has an irresistible effect on the pH value of the product, because the solubility of MgCO3 is better than that of CaCO3, and it is easy to electrolyze to produce OH. -. Secondly, in the carbonization process, Mg(HCO3)2 water-soluble salt is formed. Although most of it is excluded during filtration and dehydration, more than 10% remains in the filter cake. This part will remain in the product with the filter cake drying. Promote an increase in pH. 5. Storage stability problems in dealcoholized rubber This problem has been seen in some silicone rubber companies, causing greater confusion for nano-calcium carbonate and silicone rubber companies. Due to the production process and product characteristics of the silicone rubber product, it is determined that the finished product obtained by adding the crosslinking agent to the silicone rubber product must be sealed and stored. Once the finished product has quality problems, it is difficult to rework the finished product, resulting in a large loss. According to relevant data, the dealcoholized silicone gum generally uses a highly hydrolyzable reactive silane coupling agent, which can easily cause a trace amount of moisture in the filler and a free alcohol formed by the reaction of the silane coupling agent without introducing a hydroxyl group and a moisture scavenger. , thereby causing a decrease in the storage stability and vulcanization performance of the system. In particular, products with insufficient surface treatment absorb moisture very quickly during storage, and the secondary particles of nano-CaCO3 are porous, and the water itself is difficult to remove. Therefore, it is reasonable to think that the surface of calcium carbonate particles under this condition is considered. It has more water and hydroxyl groups, and correspondingly forms a local microscopic network structure with calcium carbonate as a node. In severe cases, local microstructuralization and stress concentration occur, and more finely distributed "granules" (actual shrinkage or protrusion) are formed. . Another peculiar phenomenon of this "particle" is that it gradually disappears when the temperature of the system rises. It can be explained as: due to the increase of the temperature of the system, the thermal motion of the molecule is intensified, the microscopic cross-linking is destroyed, and the local stress is weakened. Or disappeared, so the surface and internal molecular structure of the silicone rubber returned to the normal state, and the temporary "particles" disappeared. When the temperature of the system is lowered, the "particles" reappear in their original positions. AUTRENDS INTERNATIONAL LIMITED , https://www.petspetsdoggze.com