The effect of film-forming additives in latex paint is analyzed.

film-forming additives in latex paint to analyze the . Shen Huifang Fu and Qing Huanghong Chen Huanqin
(South China University of Technology Institute of Chemical Engineering, Guangzhou, Guangdong 510640)latex paint is a large category of water-based paint, containing very low VOC, belongs to the "green paint". Latex paint is mainly a mixture of water dispersion of polymer particles and water dispersion of pigment particles. But they do not have good construction performance, difficult to get a good paint film, must add a variety of additives to achieve the required construction performance and film quality, film additives are one of the most important additives in latex paint.1 film-forming process of latex paint
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 fuse with each other to form a continuous coating film. Latex paint film into the following processes
(1) particles gradually close
sperome particles in latex paint with a double electroclite layer and shielding stability to maintain a dispersed state, after the construction of the film, the water gradually evaporated, relying on its driving force, scattered particles gradually close together, when close to a certain degree, adjacent particles are tightly squeezed together and reached a dense state, lost the freedom of movement and form a gel.
(2) particle stability
further evaporation of water, 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 the particles, particle stability is destroyed, so that particles contact each other, attract each other, flow to each other, and form a continuous coating film.
(3) Polymer chain segments penetrate each other
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.. 2. Film-forming additive concept and commonly used film-forming additives
latex paint polymer for thermoplastic polymer, only at a certain temperature can be filmed, can form a continuous coating of the minimum temperature, called the minimum film-forming temperature of the emulsion, so the film-forming temperature must be above the minimum film-forming temperature. Latex paint in order to achieve a certain function, the addition of a large proportion of hard monosome, the minimum film temperature higher than room temperature can not be filmed, must be added into a membrane additive to make it into a film. Membrane additives, also known as film agents, coagulants, polysorbents, often high boiling point solvents, slowly volatile after the formation of the coating film, to promote the plastic flow of latex particles and elastic deformation, improve their cohesion properties. Film-forming additives in latex paint soften the surface of the particles due to the solubility of latex particles, making polymer particles susceptible to pressure deformation, and the addition of film-forming additives reduces the minimum film-forming temperature of emulsion and latex paint. Commonly used film-forming additives are ethylene glycol, propylene glycol, hexanol, methyl glycol, 12 carbon acetic alcohol, ethylene glycol, propylene glycol ether, ethylene glycol butyl ether, ethylene glycol ether and acetate vinegar, pine fuel, dipropylene pine oil, dihydrogen ze and so on.3 film additives
(1) film additives must be strong solvents for polymers. To reduce the glass temperature of the polymer, and has a good compatible, otherwise it will affect the appearance of the paint film and its luster
(2) in the water solubility is small, for latex particle adsorption and has excellent polymeric properties
(3) film-forming additives have a suitable volatilization speed, before the film remains in the latex paint coating, its volatilization speed should be lower than water and ethanol. After the film must be completely volatile
(4) plus human latex system adsorption on the surface of latex particles, does not affect the stability of latex particles.4 The role and influence of film-forming additives
the role of film-forming additives is like a "temporary" plasticizer to reduce the glassy temperature (Tg) of the polymer, once the particle deformation and film-forming process is completed, the film-forming additives will evaporate from the coating film, so that the polymer Tg value is restored to the initial value. Typically, most film-forming additives are 112h behind water at room temperature, so film-forming additives should consist of solvents that are less volatile. The biggest prerequisite for film-forming additives is that during the drying process, moisture evaporates, and the film-forming additive remains in the coating, which eventually evaporates itself from the coating. Propylene glycol butyl ether as a membrane additive for water-based coatings, the study shows that propylene glycol butyl ether on ethyl propylene latex paint, phenyl-propylene latex paint effect is better, plus 4% of the emulsion can make the minimum film temperature of water-based coatings from 20 degrees C to about 4 degrees C., Chen Yongjun and others believe that film-forming additives directly determine the degree to which polymer latex particles conjugenate into a complete continuous coating film, which in turn affects the long-term anti-corrosion effect of the coating film. Film-forming additives also affect the drying speed of the coating film to a certain extent. Film-forming additives significantly affect the minimum film-forming temperature and corrosion resistance of the coating film. Film-forming additives, such as and at low temperatures, can also deform polymer latex particles and fuse them to form a complete continuous film, reducing the migration of water and corrosive ions to the steel substrate surface. If polymer latex particles congenate into a non-continuous film under capillary pressure, the permeability of the coating film increases, thus reducing corrosion resistance. The addition of film-forming additives is generally 3% to 11% is appropriate, otherwise the polymer latex particles gather prematurely, making the coating surface porous and loose. Excessive film-forming additives are also important factors affecting the stability of coating freeze-thaw.
Zhang Feilong and other studies on the effects of two film-forming additives B1 and B2 on the process of film-forming reaction, and found that when the concentration of B1 as a membrane additive increased, the reaction speed of raw-painted film was accelerated, the curing time of the paint film was shortened, while gloss and adhesion decreased.the film additive B1 excessive, may make the lacquer liquid structure changes, causing milk breaking, transphalmation, so that the paint liquid shape is not a complete coating film, coating film performance is poor, so film additives should not be excessive. Film-forming additive B2 is also a kind of conceding solvent, can make raw paint become an average liquid, but the water holding capacity is weak, so can not shorten the film reaction time of raw paint, but can reduce the freezing point of water, reduce the film temperature. It works better when the two additives are used together. Wang Xinmin believes that the role of film additives is to make latex particles dissolve and soften, so that its glassy temperature fly temporarily down, to promote its concentration at lower temperatures into a film, and then gradually escape from the coating, so that the dry film to restore the original fly, so as to maintain the polymer high-flying value of the performance, but also to achieve the latex particles at lower temperatures into the membrane purposes. He examined the effects of propylene glycol ether and alcohol vinegar on emulsion performance in different amounts of film-forming additives. With the increase in the amount of film additives, the MFT of emulsion decreased, Hu Lingxia and other studies found that film additives promote the plastic flow and elastic deformation of latex particles, change the properties of co-ombo, can be filmed in a wide range of construction temperature. To choose the best quantity, we should consider that latex paint can have excellent film-forming, better leveling and anti-hanging resistance, but also make latex paint good frozen solubility. In addition to helping film-forming properties, film-forming additives also have the function of reducing the freezing temperature of latex paint, which is beneficial to the normal construction of latex paint at lower temperatures.. Texanol chemical structure is, 2,2,4, one-three methyl one, 1,3-glycol monoto butylate and almost insoluble with water 12 carbon alcohol esters 112 is a very good effect of film-forming additives, it can not only effectively reduce the film temperature, but also to improve the fluidity of latex paint, improve the uniformity and stability of pigments are good. Film-forming additives help to improve the scrub resistance and decontamination of coatings by increasing the degree of denseness of the paint film. Film-forming additives promote effective film-forming agents, in the composition of film-forming additives must have both hydrophobic film-forming additives and hydrophobic film-forming additives, because the use of these two film-forming aids has the synergy of promoting film-forming. Hydro-hydroplasty aids migrate to the hydro-hydroelectral shell of emulsion particles, playing the role of plasticizers, promoting the first effective binding of hydro-hydroelectral crusts of emulsions, and triggering the initial poly-forming membrane. After that, the process of polyfilm formation is promoted by hydrophobic film-forming additives. Because hydrophobic film-forming additives have a greater affinity to the hydrophobic nuclei of emulsion particles and migrate to the nuclear part, thus effectively plasticizing the nucleation part, so that emulsion particles further variant, forming a structure. When a single hydro-hydroelectral film aid is used, only the shell part of the emulsion particle is plasticized, although it begins to form a membrane, but cannot be carried out to the second stage. And when the use of insufficient amount of a single hydrophobic film aid, only make the particle's nucleation process can not start normally, but if the use of excessive single hydrophobic film aid, then the nucleation of emulsion particles can reach a higher degree of plasticization, although the initial clustering membrane is bad, but the second stage of the film process can still occur, can also form a good water barrier emulsion film. However, hydrophobic film-forming additives have a greater impact on the stability of emulsions, with the increase in their dosage effect increased, easy to cause emulsion milk breaking, condensation and other phenomena. This is because the dehydration of hydrophobic film aids destroys the hydration protection layer of emulsion particles, reducing the stability of the emulsion.antifreeze is generally a small molecular weight of organic compounds, such as glycol, propylene glycol, benzoyl alcohol, pine alcohol, diacetonol, glycol sylene ether, diopropyl butyl diacetate vinegar, glycol butyl ether acetate vinegar and so on. These compounds have a high boiling point, have proper hydroelesty, and are good for the solubility of emulsions. After the addition of human emulsion, can appropriately reduce the viscosity of the emulsion, improve the fluidity of latex particles, and thus reduce the MFT of the emulsion. Obviously, this kind of antifreeze is a membrane additive. The large amount of film-forming additives is not conducive to the freezing and thawing stability of latex paint. In phenyl propylene emulsions, antifreeze and film-forming aids are usually added: benzoyl alcohol, glycol, propylene glycol. Such as the use of benzoyl alcohol, its addition generally accounted for 6% of the emulsion, can make phenyl propylene emulsion at about 5 degrees C construction. Film-forming additives can reduce the minimum film-forming temperature of latex paint, make emulsion particle deformation easier, improve the degree of emulsion particle condensation, emulsion polymer and pigment between wetting, mechanical properties of latex paint film, latex paint film density, latex paint wash resistance. When the amount of film additives is less, increasing the amount of latex paint can significantly improve the wash-resistant brush performance of latex paint, with the increase of film-forming additives, latex paint wash-resistant performance improvement effect is reduced.5 Notation
Film additives play an extremely important role in latex paint, there are few reports on film-forming additives, especially the study of the role of film-forming additives is particularly important..