Water-based coatings: thinking of formulation design and application of additives.

: China from the paint power to paint power transformation, not only to improve product quality to strengthen brand meaning, but also to environmental protection, energy conservation and carbon reduction direction. Water-based coating is the main measure of environmental protection, energy saving and carbon reduction. There are many differences between the formulation design of water-based coatings and solvent-based coatings, and the thinking in formulation design should be different from solvent-based coatings., the difference between water-based coatings and solvent-based coatings
(1), solvents are different: water-based coatings with water as solvents. Solvent-based coatings use organic solvents as solvents. The biggest difference is that the surface is different, pure water is 72.5mN/m. Organic solvents vary by type and surface stress (roughly 18-35mN/m). As a result, many differences in the manufacture and application of water-based coatings and solvent-based coatings are caused.
(2), solvent different resin structure is also different. Water as a solvent, the resin must be hydro-hydro-hydro, market-supplied water-based resin, water-soluble, water dispersion and water dilution (emulsified) three categories. According to the variety of acrylic, acrylic modified polyurethane, water-based polyurethane (PUD), two-group PUD, water-based UV, water-based epoxy, water-based polyester, water-based ammonia paint and so on. The first five categories are mostly used in wood paint, and the last few are mostly used in industrial paint. Their common characteristics are hydro-hydro-hydro. Dissolvedin water or dispersed in water or diluted emulsified in water. The resin of solvent-based coatings is a solution for organic solvents. It is dissolved in the same or similar organic solvent in the molecular state according to the dissolution parameters and the hydrogen bond force respectively.
(3), wetting spread is different, water due to surface strength on the general substrate wetting spread is not good, organic solvent wetting spread is good, but not exactly the same. Whether the coating can be spread on the substrate can be represented by a spread factor (S): S s rSG-rLs-rLG. Only when S is positive is the spread of wetting can it occur. One of the key is rLs, to reduce rLs, it is necessary to use substrate moisturizer, otherwise the coating will not have a good spread wetting.
(4), flow and leveling effects are different, the flow and leveling of the coating depends on the surface strength of the coating and its ability to spread and wet the substrate. Water surface stress leveling is good, but if the substrate wetting ability is poor, coating film is very easy to appear the phenomenon of shrinking non-spreading, so the overall performance of the leveling is poor. The surface pressure of organic solvent is slightly lower than that of the substrate, but its wetting ability on the substrate is strong, and the coating film is spread well, so the overall performance is good leveling.
(5), the surface state is different, water-based paint surface pressure is high, very easy to appear surface state defects, but the control is not difficult, solvent-based coatings due to low surface pressure, not easy to appear surface defects, but surface state control than water-based coatings difficult.
(6), dynamic surface stress balance ability is different, the dynamic surface stress of water-based coatings is prone to imbalance, solvent-based coatings rarely appear dynamic surface force problems. This is due to the low surface pressure of the solvent and the use of surfactants in less quantities and types than water-based coatings. Therefore, in the state of motion, the chances of surfactant re-discharge imbalance are quite small.
(7), foaming and de-foaming are difficult, water-based coatings are easy to foam, solvent-based coatings are relatively good. Foam elimination is difficult and easy, especially high viscosity micro-bubbles are particularly difficult to remove. Overall, water-based foams are easier to eliminate than solvent-based foams. However, some water-based paint dark bubbles, and two-part solvent-based PU coatings due to water-containing foam is as difficult to eliminate.(8), pigment dispersion and storage stability is different, in the water-like system pigment wetting difficulties, water-like system is generally relatively low viscosity easy to produce precipitation, most rely on thickening and anti-sinking. Solvent system pigment wetting is better than water-based system, storage stability is also better than water-based system, pigment wetting efficiency can be referenced down W s k s rcos sr3/ηι Yang the therm: rsG s rsL s rLGcos s. The pigment wetting efficiency is expressed in Yang's the therology: rsG-rsL , rcos. The actual front formula is a formal fix to Yang's the therology when the pigment is dispersed in the coating.(9), paint coating conditions are different, solvent-based coating coating equipment, can be used for water-based coatings.
but there are many differences. Particularly obvious is the temperature and humidity, solvent-based coating application temperature is relatively wide,hair speed can be adjusted with solvents, but different water-based paint, low temperature can not be applied (about 10 degrees C), 0 degrees C or less will freeze,dissolved paint performance will be affected. High temperature (above 35 degrees C) can seriously affect the leveling, prone to dry spray phenomenon (especially water-based PU coatings). Humidity large drying speed is slow, humidity small temperature high level is not good.
(10), film-forming the same, the above (1) (2) mentioned in the water-based and solvent-based coatings used in different solvents and resins. Solvent-based coatings have physical drying film, oxidation polymerization into film, cross-curing into film, solvent-free type is mostly cross-link polymerization film. The solvent , and the coating film is dried and cured until it is completely cured into a film. Water-based coatings are more complex in their film curing, especially water-dispersed and water emulsified coatings, must be combined with film-forming additives and co-existence solvents. Waterin front, film additives or co-existence solvents in the back, water ran away after membrane additives or co-existence solvent destruction emulsion agent so that the roll into a clump of molybonium molecular compounds dissolved But water-based coatings also have many cross-linked curing into film. Such as water-based paint, two-group PU paint, water-based UV paint.2. Reducing solid/liquid interface stress to improve wetting and spreading capacity to improve the flow and leveling of coatings As can be seen from the table above, surfaceactants with reduced surface strength may not have good surface moistureing capacity: fluorine has the strongest ability to reduce surface pressure, but its ability to spread moisture is the same as the organic compound surfactants that reduce surface pressure is the worst. The reason is whether it can be directed in the solid/liquid interface, reducing rsL. Tego has a range of products that can be quickly scheduled in a liquid/solid interface to reduce rsL. Improves the flow and leveling of coatings. Because it is scheduled under the coating film, it will not affect inter-layer adhesion, but will be beneficial to the improvement of adhesion. Here we should give the substrate moisturizer the next definition: (1), definition, substrate wetting agent refers to the liquid / solid interface directional platoon, reduce its interface pressure of the interface active agent.(2), tego's substrate moisturizers are a strong range of Wet245, 250, 260, 265, 270, 280, Twin4000, 4100. Among them, 245, 260, 270, 280, 4l00, Wet500, ;D 0-75 are recommended. They are all water-oil-like (except D0-75). 245 is the best spread so the most suitable for water-related products. 260 water is also very good but more suitable for solvent-based products. 270 permeability and anti-shrink hole capacity is strong suitable for wood primers and pore materials. 280 atomization is particularly good, suitable for spraying after coating film cover uneven coating system. 4100 in addition to the characteristics of 245 and 260, the most prominent is unstable bubbles, sprayed out of the film less dark bubbles. When using should pay attention to the relationship between rsL and rLg, it is best rLs to rLG, otherwise there will be a hole shrink problem. In particular, there is a powder system, must be used with a leveling agent that can reduce rLg. Failure to do so will cause the surface temperature of the powder particles to be lower than that of the coating to form a shrink-hole cast.500 series and D0-75 are dynamic surface stress balance agents that can also be used as moisturizers for pigments.iii, flow and leveling (1) flow and level definition, flow refers to the coating under the action of external forces, the surface of the substrate to form the whole process of coating. Leveling refers to the process by which a coating becomes a smooth, flat coating film under the action of surface stress. Viscosity is the resistance to paint flow and leveling. Therefore, paint flow and leveling are affected by the properties of paint fluids (cow tons of fluid, plastic fluids, prosthetic fluids, puffing fluids, tactient fluids), viscosity, solvents, leveling agents, pigment dispersion and other factors. That is to say, all the raw materials and design concepts involved in the composition of coatings.(2), leveling agent, is athe liquid/gas interface. (1) Surface state control (silicon, fluorine), (2) promote flow and leveling (acrylic resin, formaldehyde resin), (3) high boiling point mixed solvents, control the coating film open state, extend the flow level time.
applications of water-based fluids, most of the leveling agents used in water-based coatings are polyether-modified polysilica, polyethers or other hydro-based modified fluorocarbons. These are to reduce surface force to control the surface state (ripple-flat waves, shrink holes, prevent Benal vortex-flower orange peel,powder distribution). Reducing surface pressure is equivalent to reducing the ability of the coating film itself to contract, which is detrimental to the level of the coating film. However, it can make the surface pressure tend to balance to prevent shrink holes, ripples and Bernal vortex, which contains the meaning of coating flow, in this respect, it can be said that it has the role of promoting the flow of coating film. However, traces produced by machinery are best not to use such leveling agents (brush marks, rolling marks, printing indentations, etc.). Because of theseare ravine-shaped. Only high surface stress can make it shrink flat, and the use of leveling agents that reduce surface stress is unfavourable. It is best to switch to a leveling agent or substrate wetting agent that does not reduce surface pressure. Wet KL-245 and Wet260 are optional as substrate moisturizers. Glide-100, 425, 450 as leveling agent.
(4), Tego water-based leveling agents are quite a lot, the focus is recommended Glidl450, 410, 482. UV coatings can be used reactive leveling agent Rad-2100-2700 series of products or added 432 and so on f4, de-bubble
(1), bubble production, surfactant substances in the coating, especially in the water-based system can form bubbles. Bubbles produced by low-surface molybic actives need to be eliminated with defystants with lower surface pressure. Water-based paint deblistering is difficult and easy. General use of debobbling agent with deboist can be. However, some water-based coatings such as water-based amino paint, water-based epoxy coating system foam is difficult to eliminate. I think it may be due to the following reasons.
With the increase of the concentration ofhair paints of water, the affinity between trace amounts of water in the coating film and the hydrophobic base of the resin is becoming stronger and stronger, but the repulsion of hydrophobic resistance is also enhanced, things must be squeezed upward, but because of its affinity with the resin hydrophobic base, the rising speed will not be too fast. When the surface is reached, the surface concentration is too large to overflow.to create dark bubbles in the coating film, eliminating difficulties. In addition, co-existence solvents mostly use high-boiling solvents of both sexes, which form hydrates with water, water is not easy to release, when the temperature reaches a certain degree, the surface dry can not be released. Solvent coatings are different, organic solvents and resins are soluble, resin release speed is fast, easy to rise to the surface. As long as the control of the solubilitycoating solvent parametersthe hair balance is not easy to produce dark bubbles.
earlier about the foaming caused by the water double-pack PU coating. This is due to the curing agent-NC0 base reacts with water to produce aminomethyric acid. It further decomposes to produce organic amines and C02 gas. During this reaction, the surface of the paint film has already reached the table dry, so the bubble wavein the coating film. This bubble is extremely difficult to eliminate. (2), the degree of difficulty of deblistering (1) the surface strength of the surfactant, (2) the surface viscosity of the foam film (the binding method between the actives), (3) the blocking capacity of the Marnetini phenomenon, (4) the viscosity of the system, (5) the buoyant force of the foam. (3), the classification of desiccant and foaming agent: de-foaming agent, de-foaming agent and de-foaming agent, de-foaming agent is to eliminate the rise to the surface of the bubble, de-foaming agent is to make the system of micro-bubbles become large bubbles quickly rise to the surface. Paints with high viscosity viscosity are best used in conjunction with both. (4), application of foaming agent, good compatible diffusion ability strong deblistering capacity is poor, poor compatible diffusion ability is weak de-bubble ability is strong. High-bounce, high-stick coatings are best used with desticants with strong diffusion compatible and poor diffusion. Improper use of deblisters can have the side effects of shrinking holes and decreasing inter-layer adhesion. . Tego defoamers focus on FoamexN, 810, 815, 822, 825, 843; Airex-901w, 902w, 904w 5, pigment dispersion (1), wetting, is the pigment surface replacement engineering, the key is to reduce solid liquid interface force. Wetting the work of W-rs-rsL. Unlike spread wetting, there are only two interfaces, and spread wetting is three interfaces. (2), dispersion, refers to grinding and crushing good pigment suspension after storage by time not flocculation, not back thick, not precipitation can maintain a stable suspended dispersion state. (3), dispersion, (1) charge stability (water system is particularly important), (2) spatial bit impedance entropy refractive force (solvent system-based), (3) resistance stability (water-based ion-type polymeractant). (4), the application of dispersants, (1) flocculation, high-gloss leveling good (670, 755) ;(2) control flocculation, anti-floating hair flowers, adverse to gloss, but beneficial to anti-sinking anti-flow hanging (610, 630). (5), the amount of addition and the order of addition, (1) according to the pigment surface area (2) according to Daniel flow point calculation, the purpose is to achieve saturation adsorption, to avoid the ad ligation of additives producing nudity points to produce excessive flocculation, the result is thickening, coloring force decline and other adverse phenomena. . Tego water-based dispersants are more, the focus is recommended dispers-715, 735, 740, 750, 755, 752, 760, 762, 6, viscosity adjuster (1), definition, so the name of the adjustment of viscosity additives, many of these additives like moisturizing soil, Si02, hydrogenated oil bentocarbon; acrylic, HEC and joined thickeners: hydrophobic modified HMHEC, HEC, hydrophobic modified alkali solution emulsion (HASE), polyurethane segment copolymer (HEUR) (2), application, thickening efficiency (mostly depending on molecular weight), compatible with other additives of the preparation (surface active agent, dispersant), stability (pH) and flow denaturation control (pH).