Interpreting the "code" of thickeners and wetting dispersants for water-based coatings (3)

. 3. The characteristics of water-based coating thickeners and wetting dispersants and their applications
Cellulose thickener cellulose thickeners have high thickening efficiency, especially for water phase thickening; However, there are poor leveling, more splash appearance when roller coating, poor stability, susceptible to microbial degradation and other defects. Because it is low viscosity under high shear, static and low shear has high viscosity, so after coating, the viscosity is increased agilely, can avoid hanging, but on the other hand constitutes poor leveling. Studies have been conducted to find that the relative molecular mass of thickeners increases, and the splashing of latex coatings also increases. Cellulose thickeners are prone to splashing because of their relative molecular mass. Such thickeners are through the "fixed water" to reach the thickening effect, pigments and latex particles rarely adsorption, thickener volume overflowing the entire water phase, suspended pigments and latex particles to one side, simple flocculation, and therefore poor stability. Because it is a natural polymer, susceptible to microbial indecology. Polyacrylic thickener polyacrylic thickeners have strong thickening and better leveling, good biological stability, but poor pH sensitivity and water resistance.
-type polyurethane thickener this joint layout is damaged under the effect of shear force, the viscosity decreases, when the shear force does not see viscosity and can be restored, can avoid the construction process to present a flow-hanging appearance. And its viscosity rehabilitation has a certain lag, is conducive to film leveling. The relative molecular mass (thousands to tens of thousands) of polyurethane thickeners is much lower than that of the two types of thickeners (hundreds of thousands to millions) and does not grow splashing. The high water-solubility of cellulose thickeners will affect the water resistance of the coating film, but the polyurethane thickener molecules together have hydrophobic and hydrophobic groups, hydrophobic groups and coating substrates have a strong affinity, can enhance the water resistance of the coating film. Because latex particles participate in the bonding, no flocculation occurs, so that the coating film lubrication, has a high gloss. The combined polyurethane thickener has many functions better than other thickeners, but because of its common glue thickening process, the ingredients in the coating formulation that affect the adhesive beam are bound to have an effect on the thickening. When using such thickeners, the effects of various factors on thickening function should be fully taken into account, and it is not easy to replace emulsions, defystants, dispersants, film-forming aids, etc. used in coatings.
inorance thickener is represented by benthic soil, usually water-based bento-free soil absorbent water expansion after the formation of a denatured gel mineral, after absorbing water volume is several times the original volume. It not only plays a thickening role, but also can prevent sinking, anti-flow hanging, anti-floating color hair flower, its thickening effect is better than the same amount of alkali-soluble acrylic and polyurethane thickeners. In addition, it has a wide range of pH adaptability, good freeze-thaw stability and biological stability. Because it does not contain water-soluble surfactants, fine particles in dry film have the characteristics of preventing water transfer and diffusion, and can enhance the water resistance of the coating film. Inororgent thickener water-based bentonish thickener has strong thickening, good tentacles, pH habits of a wide scale, good stability and other advantages. However, because bento is an inorderable powder, good light absorption, can significantly decrease the coating surface gloss, play a similar effect of anti-light agent. Therefore, in the light latex coating guess in the use of benthic soil, pay attention to the amount of control. Nanotechnology completes the nano-chemicalization of inorgic particles and also gives inorgic thickeners some new functions. Organic thickeners have water-soluble or water-soluble swelling, which remains in the coating after film forming, which has a negative effect on the water resistance of the coating. Therefore, taking into account the special features of waterproof coatings, under the premise of ensuring the thickening effect of coatings should be used as little organic thickeners as possible, and more water-resistant series of inorganic thickeners.
coating thickener is a very important additive for water-based coatings with low viscosity. In thick-slurry coatings, high-viscosity hydroxyethyl cellulose with high denaturation and methylene thickeners with flowing carb-based should be selected; You can choose to use low-viscosity and high-viscosity hydroxyethyl cellulose, or you can choose acrylic emulsion thickeners; In fact, paint thickener mixing and use is better than using alone. For example, phenyl propylene and pure propylene emulsions are used for flat light, light medium and high-grade latex paint, you can use two fluid characteristics of thickener combination to achieve high and low shear viscosity balance.
There is also a class of the latest types of silicone non-ion surfactants on the market, also known as wetting agents, its molecular weight is low, multi-hydrophobic base is an umbrella-shaped symmetrical structure, compared with traditional active agents, wetting, permeability performance is extremely excellent, efficient, is a revolutionary new representative of the surface active agent. Dynamic, static surface pressure is very low, containing double hydroxyl, reactive active agent, chemical properties are inert, generally do not participate in the system of chemical reactions, good acidity and alkalinity resistance, chemical properties are stable. Wetting agents have anionic and non-ionic surfactants, anionic surfactants include alkyl sulfates, sulfates, fatty acids or fatty acids sulphates, acetate soaps, phosphates, etc.;
An excellent dispersant should meet the following requirements: good dispersion performance, to prevent filler particles from gathering with each other;
In the process of coating production, pigment dispersion is a very important production link, it is directly related to the storage of paint, construction, appearance and the performance of paint film, so the reasonable choice of dispersant is a very important production link. However, the dispersion of coating slurry is not only related to dispersants, and the formulation of coating formulation and the selection of raw materials have a relationship. Dispersant is to spread all kinds of powders in solvents reasonably, through a certain principle of charge rejection or polymer bit resistance effect, so that all kinds of solids are very stable suspended in solvents (or dispersion). Considering its compatibility with the main resin and other additives of the coating is essential for the selection of wetting dispersants, poor compatibility can have a great impact on the performance of the coating: light will affect the transparency of the coating, heavy will cause many properties of the coating to be destroyed. In particular, polymer-type dispersants, if compatible with the resin substitline is not good, its long-chain extension base in the dispersant curled into a line clump, stretch can not open, even if the adsorption base adsorption on the surface of the pigment can not form a spatial bit resistance effect, and even lead to high paint viscosity, poor color spread, back thickening, coating gloss decreased.
two key indicators for the selection of wetting agents: the turbidity point of the wetting agent and the ability of the wetting agent to reduce surface pressure. At present, many anion and non-ionic moisturizers are used. Good dispersion performance of pigment fillers, to prevent pigment particles from gathering with each other, with resin, pigments have appropriate compatibility, do not affect the performance of the main body of the coating, non-toxic, inexpensive is as a paint dispersant should have the basic conditions.the addition of
wetting dispersants in it plays its due role at the same time, sometimes will also produce certain side effects on the system, such as polyether modified polymethylsiloxane, has the control of the coating surface state, reduce interface pressure, improve the wetting of the substrate, enhance adhesion and spread capacity. But it also has stable foam, is not conducive to the flow of paint, affecting inter-layer adhesion, over-temperature baking easy to decompose into long-chain sioxane and other negative effects caused by surface defects. Traditional low molecular weight dispersants are helpful for moisturizing and dispersing pigments, but they have a negative effect on foaming.. 4. Advances in the development of thickeners for water-based coatings
Since the 1980s, the demand for coating additives in China has increased rapidly. Many international additive multinational companies have entered the Chinese market, domestic additive companies also have a series of goods to the market. However, compared with multinational companies, domestic companies in the series of goods and commodity functions there is still a certain distance, some commodity development is still in the imitation period, in the future probably concentrate on the development of our characteristics of goods. In order to meet the needs of environmental protection, the market share of water-based coating additives should be expanded, and the combined thickener has been successfully used in water-based coating for decades. However, traditional commodities often introduce some organic solvents into water-based systems, so the recent development direction is liquid-concluded solvent-free thickeners. The co-fusion and correction of polyacrylic thickeners to increase certain substances, and the compounding with other thickeners is also an important part of current research and development. The new modified cellulose thickener, which has low relative molecular mass and low splashing, can be used in cooperation with pigment fillers in latex coatings to form a three-dimensional mesh structure to ensure the stability of latex coatings. The water-soluble polyacrylic thickener can be modified to further improve its performance. Recently, hydrophobic thickeners have been developed due to higher water resistance and construction properties of latex coatings. RheovisCR, a british company such as Allied Colliod, is one of these thickener varieties. It is in the traditional alkali-activated acrylic emulsion thickener molecular branch chain connected to the reactive surfactant, its longer hydrophobic end base in the water to form a glue beam with each other, so that the thickening form from a linear structure into a mesh structure. The construction, cover, leveling, antiflow hanging, electrolyte resistance and post-thickening of acrylic thickeners are superior to ethylene acetate-acrylic and non-connectiv thickeners; The longer the hydrophobic base of the reactive surfactant, the smaller the use of thickener, the longer the hydrophobic base is about twelve carbon, the best electrolyte resistance, and the stability of the hydrophobic-based polyether-type reactive surfactant is very poor. The interaction between the ligation thickener and the surfactant, both of which work by adsorption to the particle surface of the coating component, so excessive amount of surfactant in the formulation will cause the compounding thickener to be replaced from the surface of the latex grain into a continuous phase, thereby inhibiting the connectivity of the compounding thickener, resulting in a decrease in the flatness, gloss and cover power of the coating. There is also an interaction between the dispersant and the conceding thickener, and the compatibleness of the two has a great influence on the stability of latex paint. The modified ethylene oxide polyurethane inlay copolymer thickener will occur salt analysis when the polyic acid is both polypolymer dispersants are present, and should be used in conjunction with polyic acid copolymer dispersants.
recently developed a liquid fluid variant abroad, which is a solution of pyridoxine, which is modified by the hydrothermical group. When added to the coating, the precipitation is a fine needle-like object, with a very close recrysure rate with the film, so it is almost invisible. These needles can form a three-dimensional structure, its fluidization than organic bentonish soil has a higher low shear rate at the viscosity and lower high shear rate of the viscosity, in storage of the anti-sinking effect is much better than gas phase silicon dioxide, organic bentonic soil and polyamide. At present, the commonly used thickeners are cellulose ether and its derivatives, the combined alkali-soluble expansion thickener and polyurethane thickener. Cellulose ether and its derivative thickeners are mainly hydroxyethyl cellulose, methyl hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose and so on. Hydrophobic modified cellulose is the introduction of a small amount of long-chain hydrophobic alkyl on the cellulose hydrophobic skeleton, thus becoming a joint thickener, and its thickening effect can be comparable to the relative molecular mass of cellulose ether thickener varieties. Alkaline swelling thickeners are divided into two categories: non-contracted alkali-soluble expansion thickeners and contracted alkali-soluble thickeners. Polyurethane thickener is a hydrophobic group modified ethyl ethyl polyurethane water-soluble polymer, which belongs to non-ionized combined thickener. The development of environmentally friendly connective polyurethane thickeners has been widely valued as a contract-type polyurethane thickener without VOC and APEO, in addition to linearly concluded polyurethane thickeners, as well as combed-in polyurethane thickeners. The modified polyurium thickener was developed by BYK. Its thickening process is both hydrogen bonding and end-based co-operation, compared with the general thickener, anti-sinking and anti-flow hanging performance is good.
of the development trend of polyoxyethylene alkyl (benzene) phenol ether (APEO or ACE) moisturizers. Polyoxyethylene alkyl (benzene) phenol ethers are widely used as emulsions when emulsions are polymerized. Twin surfactants are also new developments, are two parent molecules connected by an interval base, the most significant feature of twin surfactants is that the critical beam concentration (CMC) is more than one order of magnitude lower than its "single" surfactants, followed by high efficiency. Traditional surfactants have a hydrophobic tail and a hydrophobic head, while this new surfactant has two hydrophobic and two or three hydrophobics- and is a versatile surfactant called acetylene glycol. In recent years, the study of dispersants has overcome the problem that high molecular weight produces flocculation, and the development to high molecular weight is one of its trends. Such as the use of emulsion polylegis legal production of high molecular weight dispersants are specifically developed for water-based industrial coatings, suitable for organic and inorganic pigment dispersion, good water resistance. Amino has a good affinity for many pigments through acid-base action or hydrogen bonding. The segment co-dispersant with amino acrylic as the anchoring base has been paid attention to. It is based on methyl acrylate and methamphetamine as an anchor-based dispersant. Wet dispersants are used in water-oriented automotive paints not only to direct pigments, but also to prevent aluminum powder from reacting with water.. 5. Conclusion
Water-based paint thickener is a fluidizer, it can not only make the coating thicken, prevent the phenomenon of hanging in the construction, but also can make the coating with excellent mechanical properties and storage stability. Dispersants and thickeners have a great influence on coating gloss, and the reasonable selection of dispersants and thickeners optimizes coating performance. When the toner is added to the base paint, the pigments and fillers in the base paint compete for the dispersants and moisturizer stabilizers in the toner until balance is reached. If there is not enough wetting agent, it will cause the color pigment in the toner to be unstable, flocculation will cause floating color and lead to a decrease in color display. In particular, polyurethane thickeners can not fully conjugate with emulsions and filler particles, will be excessively combined on color pigment particles to form flocculation, resulting in floating flowers, the use of water-resistant dispersants and polyurethane-linked thickeners can be used together to achieve better slurry compatible. High-quality water-resistant dispersants can achieve a considerable dispersion efficiency of water-soluble dispersants, polyurethane-connected thickeners and water-resistant dispersants can be combined with each other to achieve a higher system viscosity, water-soluble dispersants and acrylic thickeners, water-resistant dispersants and polyurethane thickeners can be used in order to achieve the formulation of stable fluid properties, dispersants have a great impact on paint gloss, water-resistant paint. Water-soluble dispersants and acrylic thickeners increase the water absorption rate of the coating film;