Film-forming additives and their applications in latex paint coatings (3)

3 Film-forming process in latex paint coating
latex paint in the coating operation, latex particles closely accumulated, latex particles melt, polymer chain end diffused with each other. Latex paint coated on the substrate, the paint volatile points (mainly water) outside steaming internal suction, coating solid content is increasing, particles close to each other finally reached the closest accumulation. Drying continues, the adsorption layer covering the surface of the latex particles is destroyed, the surface of the exposed polymer particles is in direct contact, and under the solubility and dissolution of the polymeric solvent, the particles soften and deform and melt into a continuous film. Latex particles melt at the same time, the polymer surface of the chain end molecules penetrate each other, diffusion, coating film further homogenization. Latex paint film and weather conditions have a great relationship, high temperature, high wind, low humidity, low temperature, excessive humidity, etc. will lead to latex particles film-forming bad, affecting the performance of coating film. Unlike solvent-based coatings, the film-forming process of latex paint is generally divided into the following processes:
is the filling process. After latex paint construction, with the gradual evaporation of water, the polymer particles and pigment particles, filler particles, which were originally dispersed by static refractive refractive force and spatial resistance stabilization, gradually close together, but still can move freely. At this stage, the volatilization of water is similar to the volatilization of pure water, which is constant volatilization. When latex particles account for 74% (volume) of the membrane layer, the particles are close to each other and reach a dense filling state. Emulsizers and other water-soluble additives in the group are left in water with particle gaps.
is the fusion process. With the further evaporation of water, polymer particles and pigments, filler particles surface adsorption layer damage, exposed particles become irreversible mutual contact, to achieve close accumulation, its gap is getting smaller and smaller, to capillary diameter, due to capillary action, its capillary pressure is higher than the polymer particles anti-deformation force, particle deformation, and finally condensation, fusion into a continuous coating film. It is generally believed that the theoretical volume solid content is 74%, that is, the accumulation constant is 0.74. The water volatilization rate of this stage is about the initial 5% to 10%, this process is the key to whether the emulsion can form a membrane, if the emulsion particles Tg is high (in order to make the coating film has good mechanical properties, weather resistance and resistance to contamination, Tg value generally can not be too low), at lower ambient temperature, it is difficult to deform, so that the fusion process is blocked, resulting in film, when often need to use film additives to assist the film.
is the diffusion process. Under the force of shrinking surface, it is also believed that under the effect of capillary force or surface pressure, if the temperature is higher than the minimum film temperature (MFT), emulsion polymer particles deform, polymer particles deform, polymer formation film, while the polymer interface molecular chain diffuses, penetrates and wraps with each other, so that the coating film performance is further improved, forming a uniform coating film with good performance. At this stage the moisture is mostly volatile by internal diffusion to the surface, so the volatilization rate is very slow.
the film-forming process of latex paint is more complex, going through a process from dispersing polymer particles to gathering into a whole. After its construction, the water evaporates, and the speral particles must be fused with each other to form a continuous coating film. Sphere particles in latex paint with dual electron layer and shielding stability to maintain a decentralized state, after the construction of the film gradually volatile moisture, relying on its driving force, scattered particles gradually close together, when close to a certain extent, adjacent particles are tightly squeezed together to achieve a dense state, lost the freedom of movement and form a gel-like. Moisture evaporates further and the volume of the paint film shrinks. When the water volatility will be exhausted, its driving force will also disappear, at this time capillary force obviously works, volume contraction and capillary absorption gravity is much greater than the dispersion and stability of particles, particle stability is destroyed, so that particles contact each other, attract each other, flow to each other, conjuration to form a continuous coating film. Over time, residual additives gradually evaporate, polymer molecular bands penetrate each other, membrane properties gradually improve, and finally form a uniform and good performance coating film. During the film-forming process of latex paint, the entire formulation composition of latex polymers, dispersants and surfactants affects the film-forming process.
with the development of society, the restrictions on the industrial application of solvents and even high boiling point cluster additives will be more and more, while new surfactants will continue to appear, the latex used in coatings will inevitably change. These changes can lead to changes in the latex coating process, as well as changes in the structure and viscosity of the lacquer film. In order for water-based latex paint to play its greatest role in the coating industry, technological innovation is needed, so its film-forming system needs to be studied in greater depth.4 The performance detection and testing of film-forming additives in
coatings depend entirely on the chemical properties of polymers. The film-forming properties of polymeric polymers can be indicated by testing the minimum film-forming temperature (MFFT). The level of MFFT determines whether a membrane additive needs to be added to the final coating. Film-forming additive analysis and testing of latex paint mainly includes: film-forming additive performance testing, film-forming additive composition analysis, film-forming additive formulation analysis and so on. Specific testing items are: formulation analysis, composition analysis, appearance: color, density, boiling point, melting point, viscosity, fineness, covering force, drying time, adhesion, dispersion, gloss, electrical properties: high temperature resistance, water resistance, chemical resistance, oil resistance, solvent resistance, chemical inertness and so on.
film additives in emulsions and coatings performance test compatible test: is the emulsion and film aids Textanol esterol, benzoyl alcohol, ethylene glycol butyl ether, propylene glycol ether directly mixed, stirred evenly, to observe the characteristics of the emulsion.
the viscosity of the emulsion is to determine its viscosity after adding membrane additives to the compatible emulsion and observe the change of viscosity. Determination of the minimum film temperature of the emulsion: Mix the compatible emulsion with several film-forming aids to determine its minimum film-forming temperature (MFT).
the stability test of emulsion freezing and thawing, Texanol, BA, EB, and PPPH film aids that add a normally compatible lotion (the minimum film temperature of the emulsion is reduced to the minimum dosage of 0 degrees C), place 16h in a refrigerator at -10 degrees C and place 8h under standard conditions (room temperature 23 x 2 degrees C, relative humidity 50 x 5%), so repeat 5 cycles to observe the final state of the emulsion.
Emulsion storage stability test is to add the compatible normal emulsion to the corresponding amount (the minimum film temperature of the emulsion reduced to the minimum dosage of 0 degrees C) of Textanol esterol, benzoyl alcohol, EB, PPH film-forming additives, placed under standard conditions (room temperature 23 to 2 degrees C, relative humidity 50 to 5%), regularly observe the status of the emulsion, determine its viscosity, pH value. The compatible test results of film-forming additives and emulsions show that BA, EB and PPH are compatible in 6512 phenylpropanine emulsions, and PPH is compatible in other emulsions other than pure c-emulsions, but these membrane aids should be slowly added, otherwise they are easy to cause flocculation. For pure propylene emulsions, the addition of these three membrane aids will produce flocculation, and sometimes these film-forming additives can be mixed with alcohol solvents and added to the emulsion, so as not to cause milk breakage. Trexanol ester alcohol compatible is very good, and easy to add, not easy to cause broken milk, the emulsion has universality. After the effect on the mucus of the emulsion is added to the membrane additive, the viscosity of the emulsion is basically increased. This is because the film aid will soften the emulsion particles, emulsion particles dissolve and become large, as long as the addition is appropriate, will not affect the use of emulsion. However, due to the swelling of emulsion particles, the concentration of surfactants and protective collages, which act as protective effects on the surface, decreases accordingly. It is even replaced by a large number of membrane additives, which make the lotion unstable.
for compatible emulsions, to achieve the minimum film-forming temperature of 0 degrees C when the amount of film-forming additives, for phenyl propylene emulsions, the dosage ratio of benzoyl alcohol added. Texanol ester alcohol is small, this may be because of similar compatible principles, benzoyl alcohol can soften phenyl propylene emulsion particles to the maximum extent, so that the minimum film temperature of the emulsion is reduced to 0 degrees C in less amount, but it is more toxic, other types of emulsion compatible is also poor, must be used with alcohol solvents. EB soluble in water, added to the emulsion, not easy to contact with emulsion particles, so its dosing is correspondingly large, but because its volatility speed is comparable to water, or even faster, so adverse to the film, and thus affect the performance of the coating. PPH has a better effect on phenylpropanoules, but because of their slightly more solubility in water, it is not easy to come into contact with emulsion particles. For PPH compatible emulsions, the effect is similar to Trexanol ester alcohol, but for ten pure propylene emulsions or other types of emulsions, Texanol ester alcohol is easier to add than other film-forming aids, and the dosage is not large. The effect on the stability of emulsion freezing and thawing by adding film additives has a certain effect on the stability of emulsion freezing and thawing. After 5 cycles, the emulsion is condensed, the reason is that the film additives make the emulsion particles swell, and make the protective collusion concentration correspondingly reduced, so if the film additive and emulsion are used as a base material for re-use, we should pay attention to not to place storage at low temperature. Membrane additives have no effect on the storage stability of emulsions, and over time, the pH of some lotions decreases slightly, which is due to the volatility of ammonia used in meso-emulsions.
A product to be used as a membrane additive, must meet certain requirements, this product used as a temporary plasticizer must have sufficient chemical stability, for example, will not be saponified in alkaline formula; This instability can be observed from a significant increase in viscosity, or the most serious of cases is the same reason for the occurrence of gels, 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 hair to stick, cling and contaminate. Therefore, the ideal film-forming additive does not exist, we must look for an optimal compromise, with a variety of products used together. Choose products that are efficient, environmentally friendly, low odor and biodegradable..