Background technique
Redividable rubber powder is a white solid powder processed by spraying and drying special latex. It is mainly used as an important additive for “thousand-mix mortar” and other dry-mix mortar additives for external wall insulation engineering construction materials. . The commonly used refractory latex powder is a copolymer of vinyl acetate, which is a white powder that can slide freely and can be well dispersed in water to form a stable emulsion with the same performance as the original latex. As an indispensable additive material in dry-mixed mortar products, redispersible latex powder plays a significant role in cement dry-mixed mortar. It can improve the bond strength and cohesion of the material. Improve the elastic bending strength and flexural strength of the material. Improve the freeze-thaw resistance of the material. Improve the weather resistance, durability, wear resistance of the material. Improve the hydrophobicity of the material and reduce the water absorption. Improve workability and reduce material shrinkage. Can effectively prevent cracking. (I) Improve bonding strength and cohesion
In dry cement mortar products, it is extremely necessary to add redispersible rubber powder. It is very obvious to improve the bonding strength and cohesion of the material. This is due to the penetration of the polymer particles into the pores and capillaries of the cement matrix, and the result of good cohesive strength after hydration with the cement. Due to the excellent adhesion of polymer resin itself, it can improve the adhesion of cement mortar products to substrates, especially the bonding of inorganic binders such as cement to organic substrates such as wood, fiber, PWC, and PS. The improvement of poor performance has a more obvious effect.
Improved bending and tensile resistance
In the rigid skeleton formed after the cement mortar is hydrated, the film of the polymer is elastic and tough, and acts like a movable joint between the cement mortar particles, which can withstand high deformation loads and reduce the stress. Improved tensile and bending resistance
Improve impact resistance
Redispersible latex powder is a thermoplastic resin. The soft film coated on the surface of mortar particles can absorb the impact of external force and relax without breaking, thereby improving the impact resistance of mortar.
Improve hydrophobicity and reduce water absorption
Adding redispersible latex powder can improve the microstructure of cement mortar. Its polymer forms an irreversible network during the cement hydration process, closes the capillary in the cement gel, blocks the absorption of water, prevents the penetration of water, and improves the impermeability.
Improve wear resistance and durability
Adding redispersible 휘 rubber powder can increase the compactness between cement mortar particles and polymer film. The enhancement of cohesive force correspondingly improves the ability of the mortar to withstand shear stress, reduces the wear rate, improves the wear resistance, and prolongs the service life of the mortar
Improve freeze-thaw stability and effectively prevent material cracking
Redispersible latex powder, the plastic effect of its thermoplastic resin can overcome the damage caused by the thermal expansion and contraction of the cement mortar material caused by the change of temperature difference. Overcoming the shortcomings of simple cement mortar, such as large dry shrinkage and easy cracking, can make the material more flexible, thereby improving the long-term stability of the material. However, there are some problems in the production process of the redispersible latex powder in the prior art, resulting in that the latex particles are not uniform and fine enough, and agglomeration is prone to occur during production, transportation and storage. Thereby affecting its use effect.
This process can be realized through the following technical solutions: a production process of redispersible back-dispersed latex powder, the following materials are formulated according to the attached weight percentage polymer emulsion 72-85%; protective colloid 4-9%; release agent 11 -15%; functional additives 0-5%; produced by the following process
a, preparation of protective colloid: in the reaction kettle, the protective colloid powder of the batching amount is not mixed with water and heated to be modulated into glue, and a defoamer is added, heated and kept warm to form a transparent viscous protective colloid, so that the viscosity reaches 2500as, solid The content reaches 19.5-20.5%.
b. Preparation of dispersion: place the prepared protective colloid in the preparation kettle, then add the polymer emulsion of the batching amount, mix evenly, then add defoamer and add water to adjust the viscosity to 70-200Mas, and the solid content reaches 39%- 42%, warming to 50-55°
C, for use;
C, cloud spray drying: open the cloud spray drying tower, when the temperature of the feed inlet at the top of the spray cloud drying tower is heated up to 140-150 DEG C, the prepared dispersion is delivered to the feed inlet at the top of the spray drying tower with a screw pump. In the feed port, the dispersion liquid is atomized into micro-droplets with a droplet diameter of 10-100 microns through the high-speed centrifugal atomization disc in the feed port. At the same time, the micro-droplets are rapidly heated with high-temperature airflow, and at the same time, the release agent is added in the high-temperature airflow. , when the micro-droplets are heated to generate viscosity, the release agent is adhered to the micro-droplets in time, and then the water in the micro-droplets is quickly evaporated to dryness by the high-temperature airflow to form a gas-solid mixture;
d, cooling and separation: keep the temperature of the air outlet of the spray drying tower air outlet at 79°C-81°C, and the gas-solid mixture is rapidly exported from the air outlet at the bottom of the spray drying tower, and then imported into a large bag filter after cooling. The powder in the airflow is separated and the separated powder is classified and sieved to obtain the finished product of redispersed latex powder. Specific Embodiments Add a certain amount of clean water in proportion to a clean reactor, raise the temperature to about 50°C, turn on the stirring mechanism, add protective colloid powder according to 25% of the amount of water added to the reactor, and the process of adding should be slow Add it to prevent the powder from agglomerating in water. Do not add it to the side wall of the reactor. After the addition is complete, add a defoamer equivalent to 1% of the total amount. It is recommended to use a silicone-based defoamer. Cover the feeding hole and heat up to about 95°C. Insulated for 1 hour, the liquid in the reactor is to be formed into a transparent viscous glue, without white particles, sampling, testing viscosity and solid content, requiring viscosity to reach about 2500as, and solid content to reach 19.5～20.5%. Add the prepared protective colloid to the blending kettle, then add the polymer emulsion in proportion, mix the protective colloid and the emulsion evenly, and add defoamer appropriately, generally equivalent to about 0.1% of the total amount, and the defoamer should be used by yourself Emulsified silicone disinfectant
Foaming agent, and add water to adjust the viscosity to 70-200pas, and the solid content to 39%-42%. Raise the temperature to 5055C. Sampling test, ready to use.
The water in the drops will be quickly dried by the high-temperature airflow, and then the gas-solid mixture will be quickly led out of the drying tower, keeping the temperature of the air outlet at the lower air outlet of the drying equipment at 79 ° C -81 ° Co. The gas-solid mixture is guided from the drying equipment After leaving, add dehumidified 5°C dry air to cool down, and the airflow containing powder is introduced into the large bag filter, and the powder in the airflow is separated by two ways of cyclone separation and filtration separation. , The separated powder is classified and sieved to obtain redispersible latex powder islands.
Transport 1,000 kg of dispersion liquid with a solid content of 42% to the drying tower at a certain pressure, and add 51 kg of release agent according to the above method at the same time, dry by spraying and separate solid and gas, and obtain a powder output of 461 kg with suitable fineness .