Formula evaluation and application of additives for water-based coatings (3)

1. 2. 6 Surface Stress Test Instrument
The most famous way to test liquid surface stress is to du Nouy lift the Tour de France, place a platinum silver ring in a certain amount of test liquid, and then slowly lift the ring, at which point the ring pulls up the liquid to form a film in the air interface. The force required to pull the film is the surface pressure of the liquid in mN/m. This method is particularly suitable for comparing surface stress in different surfactant solutions or solvent-based varnishes. For pigment-containing systems, the data measured are inaccurate because pigments impede the stability of the film. There is no doubt that the liquid must be in equilibrium in this test method. All surfactants have sufficient time to gather into the gas/liquid interface to ensure low test values. However, due to significant differences in coating construction, the rapid formation of new interfaces, and the fact that substrate moisturizers have little time to move to the interface and orientation, this dynamic migration capability of surfactants cannot be tested by the Du Nouy Tour de France. The measurement of dynamic surface stress can be obtained by the "maximum bubble pressure method". The higher the pressure required to form bubbles at the other end of the capillary tube, the higher the pressure required, the more energy is needed to produce a new interface, i.e. higher dynamic surface pressure, by blowing air through the capillary (usually air bubbles). Bubbles can be formed at different speeds, for example, 1 bubble per second or 1O bubbles per second, when the bubble production speed is high to a certain extent, many surfactants can not move and direct fast enough, and effectively reduce dynamic surface pressure.in high-speed construction, such as in the printing industry, the significance of these tests is obvious. Many coatings containing fast-directional "dynamic" surfactants achieve better results during construction. The balance of static and dynamic surfactant questions is usually required. Static surface stress play a major role in avoiding shrink holes in contaminated substrates. Therefore, measuring dynamic surface stress using bubble pressure is only a supplement, not a substitute for the Du Nouy Tour de France.the ideal pigment dispersion method, it is best to understand the basic principles of the dispersion process, which is the theoretical basis for discussing new wetting and pigment stabilization aids.1. 3 Dispersion processif the color spread as a function of time, you can evaluate the process of measuring dispersion. The dispersion process consists of three closely linked steps.(1) the air on the pigment surface is replaced by abrasivemixture liquid during the wetting and wetting process of the pigment particle surface. Especially in water-like systems, the use of wetting aids is essential when pigments or filler surfaces are non-polar.(2) Disintegation of pigment adhesionPigment adhesion is disintegration under the action of mechanical energy, high-speed dispersion or sanding can provide the shear force required for pigment adhesion disintegration. The process of pigment defeatication mainly depends on the size of the added mechanical energy and the time it lasts, and the additives play a relatively small role here. In fact, in practice pigments are rarely dispersed into situations where they are completely primitive particles or aggregates.(3) Pigment stability modePigment stability is to maintain pigment particles have been in the final stage of dispersion to achieve the degree of dispersion, and can be in the process of painting, storage and construction to control and maintain this more ideal dispersion state. So it's a complicated process. The stability of the pigment can be achieved by adsorbing the polymer on the surface, as the refractive force between the polymers prevents pigment particles from gathering into flocculations due to the mutual attraction of Van der Worrest. Static stability occurs when the same charge is distributed on the surface of the pigment and close to each other, pigment particles are asked because of the same charge to produce rebuke force, charged particles of the Coulomb rebuke force to keep the system stable. However, the surface potential between pigment particles can not be measured directly, the zeta potential measurement method can be used to calculate the surface potential (the potential of the double layer of the shear surface). When the surface of a pigment solid particle is completely covered by a polymer, contact between the particles is avoided, which can be considered as a bit resistance stabilization. Strong interactions between polymers and solvents (organic solvents or water) prevent the tendency of polymers to get too close (flocculation).. 1. 4 Wetting and dispersing pigmentsand dispersing additives improve the mixing of pigments and fillers in coating systems. Good pigment dispersion determines the optical properties and cover power of the coating film. The most suitable pigment dispersion requires consistent particle size, not only in newly prepared coatings, but also in storage and application. Many common disadvantages are related to the performance of pigments: (1) adding pigments that are difficult to wet;) Floating color (finger rub experiment) ;(7) hair flower (Benaud's nest) ;(8) uneven gloss; (9) poor covering force; (10) insufficient pigment coloring force; (10) poor color reproduction.of these problems can be solved by using suitable wetting and dispersants.. 2 Pigment slurry for water-based coatingsIn water-based building coating systems, organic pigments are dispersed in water through non-ion and anion-type wetting dispersants, while also adding low volatile organic solvents with good solubility. The performance of this dispersed slurry, including long-term storage stability, depends mainly on the physical and chemical properties of the pigments used in the system. For example, color slurry containing ethylene glycol and ethylene alkyl phenol is not widely used in industrial coating systems because of its poor compatible with many types of resins. The standardization of color paste depends not only on the content of pigments, but also on the color coloring force and tone. In latex paint, color testing is a major task.in order to comply with environmental regulations, the vast number of industrial paint manufacturers have been trying to find ways to reduce the content of organic solvents in coatings. The challenge of this technology has led to the development of water-based coatings. If the right slurry can be developed, it will be a good opportunity to meet the user's needs for small quantities of water-based slurry/paint. . 2. 1 Evaluation method On the one hand, sophisticated test methods are still being used, such as the use of fluid performance maps of color slurry to assess the stability of the achieve and maintain, on the other hand, many practical methods (non-directness), such as gloss, coloring force, color display and mixed color paste finger rub method, has been widely used. . 2. 2 Influencer In general, the factors affecting pigment dispersion depend mainly on the pigment's own characteristics, such as density, chemical structure, crystal structure and size, shape, surface geometry, production process and surface treatment. Special attention needs to be paid to the non-polar surface treatment of inorganic pigments and the polar surface treatment of organic pigments with smaller particle sizes. There is no good way to "see" the exact interaction between pigment particle surface pigments and polymers, although this is helpful. The most important raw material in the slurry is inorganic or organic pigments, the liquid medium carrying pigment is mainly composed of water. In the grinding process, the pigment should be completely moisturized as soon as possible to ensure maximum color spread. This requires the help of the pigment surface wetting aid. At the same time, since bubbles are accompanied by the use of moisturizers, the selection of desiccants may be necessary. Basic color paste not only requires good storage stability, but must remain stable after being added to the coating system of different resins and does not cause any problems when mixed with coatings containing other different pigments. In order to maintain the stability of pigments in the color paste, dispersion aids are also necessary. Some pigments, although well dispersed, have a tendency to subside due to their high density. The subside of this slurry is not easily re-dispersed. When using such pigments, a denatured thickener must be added to the slurry. In order to eliminate foam from the early stages of the grinding process, organic modified silica defoulants are currently proven to be the most effective defoulants. It is recommended to use a 100% effective deboulant to ensure maximum shear stability during grinding. If thickeners are needed, modified bento-moisturized soil types can be used to achieve excellent thickening properties in very low dosages and have good compatibleity with many resins. . 3 Additive development direction As people become more aware of the use of industrial raw materials that meet ecological and environmental requirements, coating raw material suppliers are being asked to meet more and more environmental and technical regulations, and organic solvents in various coating systems are gradually being replaced by water. This recent trend can be reflected in industrial and transport vehicle paints, which have traditionally used high-gloss acrylic, polyurethane-acrylic and polyurethane-polyester resins, and are now being used by these resin suppliers to replace traditional hardness, chemical resistance and aging properties with high-gloss solvent-based resins. water-based coating system will also appear in the traditional paint manufacturing and construction problems, but some in the traditional system has a good deblblishing performance, dispersion performance and substrate wetting effect of additives, is no longer suitable for the new water-based coating system. Taking deboulants as an example, the ability of traditional desobbists to deblod in the storage process of coatings is gradually reduced. In addition, the luster and clarity of the paint film often change significantly after the desiccant is added. A new anti-foaming agent technology has recently been developed, which maintains a certain degree of incompatibleity with the de-foaming action necessary without the reduction of de-foaming efficiency or surface defects. similar problems occur when using traditional substrate wetting agents, the wetting efficiency gradually decreases with the change of time. This has also led to the development of a new polyether-modified sioxane surfactant, which has excellent stability over a wider pH range. newly synthesized water-based polymers become more sensitive to the introduction of glycol and pigment wetting dispersant additives when applied to coloring slurry systems. This has led to the development of a new solvent-free wetting dispersion aid suitable for the development of a universal slurry without substations. environmental regulations has prompted paint manufacturers to develop more environmentally friendly coatings, while the performance of coatings should be maintained or even improved. In water-based coating systems, the use of de-foaming aids, dispersion aids and substrate wetting aids is essential. The main job of coating additive suppliers is to accurately predict formulation trends and develop the right products to facilitate technological progress. .