Application and distribution of additives in water-based coatings (2)

3 thickening fluid
continuous phase of water in water-based coatings, characterized by high surface pressure and low viscosity. Because of the low viscosity, high-density pigments are likely to subside, so a certain amount of thickeners are needed to maintain the suspension of inorgable pigment fillers. However, only the viscosity and the tentacles it provides can not meet the coating requirements of the water-based industrial coating production line, so different fluidity requirements are put forward for the coating, not only to pay attention to the viscosity ratio between the stationary state and the highest shear state, but also to pay attention to the viscosity change curve at different shear rates.
3. 1 Acrylic-alkali swelling thickener
common alkali-soluble (ASE) and hydrophobic modified (HASE) thickeners have the characteristics of anion dispersant and water dispersion resin, not neutralized before anion emulsified polymer, solid content of about 30% of the low-viscosity emulsion. When the pH of the system is adjusted to alkaline, the original crouched large molecule acrylic chain segment began to become salt, after the solubility ionization, the electrostatic rejection of the carboxyl and straighten the growth chain, at this time with the surrounding water molecules form a hydrogen bond, viscosity rises. This process is also a process of harmonization, where the asE or HASE solubility has an optimal pH condition that requires a harmonization of the pH of the resin, the pH required by the dispersant, and the pH required for the thickener to avoid an unenrectable competitive situation.
3. 2 Polyurethane or hydrophobic polyether thickening fluid
a small amount of polyurethane or hydrophobic polyether thickening fluid is usually added to latex paint to improve leveling. In water-based industrial coatings, in order to improve the resistance of the coating film, before construction can not be diluted with water, so very few large numbers of cellulose or alkali-soluble acrylic thickeners. Usually to polyurethane-based fluid, so that the low shear viscosity is slightly lower, the range of viscosity decline under high shear conditions can be controlled to meet the requirements of construction fluidity. These fluids are low relative molecular mass hydrophobic modifiers, non-ionized fluids. Hydrophobic at both ends, slightly hydrophobic in the middle, first of all need to have a certain dispersion in the water, because of its main dependence on the principle of hydrophobic connectivity, requires one end to adsorption in a certain hydrophobic latex particles or dispersion particles around, the other end in the water phase to gather each other and contract synthetic beams, in a stationary state of multiple short chains of such thickeners to synthesize the mesh structure, the short chain in the middle of the polyether part and water molecules form a hydrogen bond, thus regulating the overall adhesive system. The principle of thickening is the principle of hydrophobic and hydrogen bonding of non-ion surfactants. If there is a need to stabilize the mesh structure of hydrophobic connectivity, it is necessary to ensure the overall balance of the system, if the system uses a large number of hydrophobic non-ion moisturizers or stabilizers, will certainly improve the HLB value of the system, at this time a large number of non-ion hydrophobic aids will be around resin or emulsion particles, hindering the hydrophobic end of the polyurethane rheumorant and resin or emulsion particles to form a hydrophobic mesh structure. The two hydrophobic ends of the polyurethane fluid can only be flipped inwards in the water phase if they cannot be combined with the resin particles, and the middle hydrotherphic polyether chain is flipped outwards to form a large glue beam, i.e. flocculation. At this time, although there is also a certain thickening effect, but the coating system is easy to layer, construction is far from the design requirements.
If the total amount of non-ion surfactants in the system is appropriate, but the concentration of polyelectrics is too high, the solubility of non-ion fluid in the water phase will be inhibited, can not be dispersed under the low shear conditions of the painting phase, and form translucent flaky or silky flocculants floating to the surface of the coating. This is because the solubility of low EO in the water phase is much lower than the polyelectronics of anions, once there are too many water solutions neutralized into salt, the effect of dissolving in the water phase with the help of non-ions will be reduced, which will seriously damage the stability or construction of the system.
3. 3 Cellulose ether HEC
coatings are more used in hydroxyethyl cellulose ether, in industrial coatings are mainly used in pigment grinding dispersion phase, to improve the suspension of inorganic particles in the water phase, shorten the dispersion time. Powder is usually added directly to the pulp, but HEC still needs to be weakly alkaline to achieve rapid water solubility. So even though HEC is non-ionized, it is still affected by system pH.4 bactericidal preservatives
water-based coatings because of the use of a certain amount of surfactants, in the storage process is easy to metastase, so it is necessary to add preservatives in the tank. Anion preservatives in the slow-release formaldehyde type are usually used, but their use is limited as environmental requirements increase, so cation and non-ion compound preservatives are widely used. However, the efficacy of cation additives is relatively poor, and its stability is not good in anion coating system.5 substrate moisturizers and leveling agents
substrate moisturizers are mainly used in industrial coatings to spread and moisturize the surfaces of metals, plastics and certain wood to improve the adhesion of the coating film, and reduce shrinkage and improve leveling. The substrate moisturizer and pigment moisturizer function is different, and the chemical structure is also very different. Substrate moisturizer belongs to the low HLB value of surfactant substances, in the water-based system is generally not easy to form a glue beam, so unstable foam. However, the water dispersion is poor and the cloud point is low. When the processing heats up, the compatible becomes worse, and the function of deboulant is more tending. Therefore, water-based coatings on shear rate, temperature and relative humidity requirements are high, qualified coating production line these conditions are constant. Substrate wetting agent mainly includes: low relative molecular mass polyether modified polysilicaene (non-ion), but also includes some leveling agents, sterol (non-ion), fatty acid hybrid polymer (non-ion), amber sulfonate (anion). The dispersion of these substrate moisturizers in the water phase can be reliably caused by low boiling point alcohol solvents and reliable hydromassage groups. Its dispersion in water is also affected by the balance or ionity of the two parents in the system.6 desulbant
water-based coatings use a large number of surfactants, which have a strong foaming effect, so it is necessary to add desticants to meet the requirements of paint preparation and construction. Deblisters are composed of different degrees of hydrophobic substances and are insoluble in water. Water dispersion is better deblistering agent is not easy to shrink holes, but the deblistering capacity is poor, not long-lasting. The deblister with poor water dispersion has good durability and is suitable for spraying equipment with high shear rate. Because the high shear force introduces a large amount of air, easy to form bubbles, it is necessary to use high persistence, water dispersion slightly less deblistering agent.
6. 1 Variety of defoulants
defoiling agents mainly include: mineral oil-based defoulants (mainly used in latex paints and high PVC thick coatings), polyether-modified polysilica (for low PVC, high volume solid content, low water coatings), hydrophobic polyethers (coatings for higher water dilution), fatty acid polyester polystyre molecular grade defoulants, ethylene-based modified ethylene.
6. 2 Application of deboulants
The steady foaming effect of latex paint is mainly derived from emulsifying agents in emulsions, the monomers used in polymers and the polymer itself are basically wrapped in adhesive bundles, so de-foaming agents are generally evaluated on the basis of general emulsions. Neutralized salty water-based dispersion side chain of the carbox-based part is neutralized into salt and hydrophobic alkyl main chain dissolved into the water phase, at this time the hydrophobic chain in the coating is not wrapped by the glue bundle, in order to improve the initial water resistance of the coating film, the neutrality of the resin in general Maintained at 80%, at this time the alkyl in the resin on the hydrophobic defocage material has a certain adsorption capacity, while the overall affinity to the air and defoiling agent is equivalent, even if the defoiling agent continues to float to the air surface, but there are still many fine bubble adsorption to the resin around the main chain of hydrophobic. Therefore, high-resistance water-resistant industrial coatings must use a more hydrophobic defocing material than the main chain of resin alkyl to peel off bubbles, because the defoiling agent and water compatible is very poor, if the dispersion difference will cause shrink holes, some in foreign countries use very good defoulant, in the domestic use often produce shrink holes. This is because the production efficiency of coating equipment abroad is very high, high-speed shearing in the air at the same time will also be completely dispersed evenly, thus achieving balance. Deblistering agent in a stationary state, in the water phase of the dispersion is not good, so the paint must be stirred well before use in order to work. In the process of stirring, the non-ionic surfactant substance in the formula plays a role in the dispersion of deboulator. Therefore, if the anionic surfactant in the formulation of the above-mentioned conflict, will affect the dispersion uniformity of desiccant and may lead to shrink holes. In addition, the hydrophobic material is slightly higher than the main chain of dispersant resin, if the hydrophobic gap is too large, the dehydration film after dewatering de-foaming material and the main chain of dispersion is too poor compatible will also lead to shrink holes.7 solvents and main solvents (film additives)
currently water-based coatings can not reach zero VOC, but also must use a small amount of low boiling point alcohol-aided solvents, solvents have a better water-soluble, resin insoluble effect, but to improve the water dispersion of some additives, control freezing and thawing stability, adjust the drying speed when coating film de-liquefaifying. When the solvent is used in a high amount in the formulation, although it can still be diluted with water, the coating should still be solvent-based paint, or called a fake water-based coating. So that many of the above-mentioned water-like additives in the system can not play a normal role. The high boiling point solvent that works on the resin is called a membrane additive, which is insoluble with water and can swell the resin particles in the process of dehydration, which helps to plasticizer the film. Film-forming additives cannot be dispersed in the water phase, which will affect the storage and construction stability of liquefied coatings. A stable formula is not to pre-emulsify or increase the polarity of film additives, but to make film additives moderately dissolved through the overall balance of the anionic surfactants in the formulation. The resin particles cannot be exposed during storage period, and the polymer particles can be dissolved in time during dehydration process, softening them and forming a continuous coating film.8
water-based coatings are more dependent on additives and have more varieties of additives than solvent-based coatings. Water-based paint only as a continuous phase, so water-based paint is not a true solution, almost all the substances in the coating are scattered in the water phase, because the conditions for preparation, storage and construction is a variable, so the paint used by all kinds of additives in the paint after mixing may not be able to reflect the original set function, or even may have negative effects..