Introduction of film-forming additives - temporary plasticizers and their role analysis.

the particularity of polymer emulsions, the film-forming process is fundamentally different from the general coating in solvents and different from water-soluble coatings. Because emulsions are made up of polymer particle pellets rather than independent polymer molecules, drying the film must involve fusion between these larger particles. This process can be divided into several steps: starting with the overall volume of the coating shrinks due to evaporation of water, and polymer particles are close to each other. In order to achieve direct contact between particles, it is necessary to first overcome the electrostational repulsion between particles, which is the force that previously maintained the stability of the dispersion. After the particles come into contact with each other, the arrangement and deformation between the particles required for the film is not effective, only if the capillary force and surface pressure between the particles are greater than the deformation resistance of the particles. The following steps can be well described with polymer glsification temperature, and Tg is closely related to MFFF (minimum film-forming temperature), another important indicator of coatings. Dispersion particles can only form coatings when they are above the polymer, or rather on top of MFFT. So people have to press Tussauds according to the molding temperature TP, find the corresponding monosome for synthesis, or add an external plasticizer, so that TP.MFFT.
because of this limitation, both low glass temperature and to ensure a certain degree of hardness, so many applications can not meet the needs. The addition of so-called film-forming additives and coagulants to the system allows this theory to be broken. These substances can also be called temporary plasticizers, which soften polymer particles and then evaporate from the coating film after they are formed. This allows us to use the hard polymer of Tg-Tp to form a film at room temperature and get a hard coating.a product to be used as a film-forming additive, must meet certain requirements. First of all, this product used as a temporary plasticizer must have sufficient chemical stability, for example, not to be saponified in alkaline formulations. Second, the smell should be small, in the indoor use of coatings have such requirements. Then there is the requirement that membrane additives to be compatible with these sensitive polymer dispersants, added without instability. This instability can be observed from a significant increase in viscosity, or the most serious of cases is the same reason for the gel, and care should be taken to prevent local vibration reactions (gels). Generally after the final product is prepared, but also to be placed for a period of time, so that film-forming additives to achieve distribution balance. This temporary plasticizer is also required to have the best possible plasticization effect on the polymer in order to reduce its addition. In terms of volatility, membrane additives are required to remain in the coating film in the film process to play a plasticizer role, and once the film is completed, the film additives immediately evaporate. If the film-forming aid remains in the coating film for a long time, it can cause adhesion, clinging and contamination. So we can think that the ideal film-forming additive does not exist, we must find an optimal compromise, with a variety of products combined.a three-phase model can well describe the properties of membrane additives. This model is based on the fact that the substance used as a membrane additive has a certain relationship in the distribution of water, particle interior and particle shell in the system. The effect of existing in the particle shell is certainly best, because film-forming is carried out here. If the film additive water solubility is particularly good, then it is mainly distributed in water, plasticization effect is naturally small. If film-forming additives are more distributed within polymer particles, the effect on film-forming is also general. In addition, this method of operation can be used: is the use of small water-soluble film-forming additives, and the operation is in the water phase. In this way, the film-forming additive slowly enters the polymer particles from the water. However, this operation is also a problem, because film-forming additives are present in the water phase in the form of droplets, if not placed for enough time will cause the coating film turbidity. One solution is to add a temporary plasticizer (dissolved into the monosome) to the polymerization reaction. To know whether a product is suitable for use as a film-forming aid, it is important to know its distribution in the dispersion, its plasticization effect on the polymer, and its volatilization rate. This evaluation is different for different dispersants and different applications, so there is no universal film-forming additive., there are no fixed rules for the selection of membrane additives, but only some basic points to consider the problem. The formulation is the best adhesive for its use, the best for this formulation and the best film-forming additive for this application..