subject: Analysis: Introduction and the role of temporary plasticizer - plasticizer, coalescent - Plastic industry [print this page] Analysis: Introduction and the role of temporary plasticizer - plasticizer, coalescent - Plastic industry
HC plastic mesh News: Due to the special nature of polymer emulsions, film-forming resin dissolved in solvent in the process and the general paint a different nature, and water-soluble paint is different. Because the latex polymer particles from the ball instead of having separate polymer molecules, so drying film must relate to the integration of larger particles. This process can be divided into several steps: starting as water evaporation, coating reduced the overall volume of the polymer particles close to each other. In order to achieve direct contact between particles, must first overcome the electrostatic repulsion between particles, electrostatic repulsion is the original force to maintain a stable dispersion. Particles contact with each other, the film required the arrangement of particles, deformation and fusion is not so effective, only when the capillary force between particles and the surface tension greater than the particles and when the resistance to deformation. The following steps can be polymer glass transition temperature Tg well described, Tg it with paint is another important indicator of MFFT (minimum film forming temperature) are closely related. Dispersion in the polymer particles only above Tg, the exact time on the MFFT to form the coating. So people have to under the molding temperature Tp to find what you want, find the corresponding monomers in the synthesis, or by adding external Plasticizer Make Tp MFFT
Because of this restriction, it is necessary to lower the glass transition temperature but also guarantee a certain hardness, so the needs of many applications can not meet. The addition of the so-called film-forming additives and flocculants, so this theory can be broken. Such material can also be called a temporary Plasticizer It can soften the polymer particles, and in film after film in will evaporate from. So that we can use the Tg> Tp hard polymer film at room temperature, and get hard coating.
A product to be used as a film-forming additives must meet certain requirements. First of all, as a temporary plasticizer used in this product must have sufficient chemical stability, for example, will not be saponified in alkaline formulations. Second, the odor should be small, in the indoor use of the coating has such a request. Another is to ask the coalescent with these sensitive polymer dispersions compatible, would not join the instability phenomenon. This instability can be observed a substantial increase in viscosity, or the most serious cases there is the occurrence of gel for the same reason, carry out operations must be careful to prevent the vibration of the local reaction (gel). Well beyond the general preparation of the final product, but also place for some time, so that distribution of film additives to achieve a balance. Also requested that the temporary plasticizer on the polymer plasticized with the best possible results, in order to reduce their dosage. In the volatile context, calls the process of film-forming additives in the membrane remain in the film role played by plastic, and once completed film, film-forming additives evaporate immediately. If the film-forming additives remain in the film in a long time, can lead to sticky and agglomerated, and pollution. So we can think of, good film-forming additive does not exist, we must find a best compromise, in combination with a variety of products.
A three-phase model can describe the nature of film-forming additives. This model is a departure from the fact that the use of such aids as film-forming substance, the water in the system, grains and grain distribution of shell in this phase there is a certain relationship. Certainly exist in the particle shell effects is the best, because the film is here. Particularly good if the water soluble film-forming additives, then it is mainly distributed in the water plasticization effect was not natural. If the film-forming additives in the polymer particles greater distribution within the film's impact on the general. In addition, you can use this operation method: is the use of small water-soluble film-forming additives, the operation is in the aqueous phase. This will gradually forming additives into the polymer particles from the water. But this operation also problematic, because the coalescent is the form of droplets in water phase, not enough time if placed in it will cause the coating opacity. One of the solutions is to be incorporated in the polymerization temporary plasticizer (integration into the monomer).
To know whether a product is suitable for film-forming additives, must know its dispersion in the distribution of its plasticizing effect of the polymer and its evaporation rate. This evaluation of the different dispersion is different for different applications are different, there is no general coalescent.
