The thickener for latex paint must have good compatibility with the emulsion polymer compound, otherwise the coating film will have a small amount of reticulate, and will produce irreversible particle agglomeration, which will reduce the viscosity and coarsen the particle size. The thickener will change the charge of the emulsion. For example, the cationic thickener will have an irreversible effect on the anionic emulsifier to break the emulsion. The ideal thickener for latex paint must have the following properties:
1. Low dosage and good viscosity
2. Good storage stability, no viscosity reduction due to the action of enzymes, and no viscosity reduction due to changes in temperature and PH value
3, good water retention, no obvious bubble phenomenon
4. No side effects on film properties such as scrub resistance, gloss, hiding power and water resistance
5. No pigment flocculation
The thickening technology of latex paint is an important measure to improve the quality of latex and reduce the cost. Hydroxyethyl cellulose is an ideal thickener, which has multifunctional effects on the thickening, stabilization and rheological adjustment of latex paint.
In the production process of latex paint, hydroxyethyl cellulose (HEC) is used as a dispersant, thickener and pigment suspending agent to stabilize the viscosity of the product, reduce agglomeration, make the paint film smooth and smooth, and also make the latex paint more durable. Good rheology, can withstand high shear strength, and can provide good leveling, scratch resistance and pigment uniformity. At the same time, HEC has excellent workability, and the latex paint thickened with HEC has pseudoplasticity, so the construction methods such as brushing, rolling, filling, and spraying have the advantages of labor-saving, not easy to clean and sag, and less splashing. HEC has excellent color development. It has excellent miscibility with most colorants and binders, making it possible to formulate latex paints with excellent color consistency and stability. The versatility applied in the formulation, it is a non-ionic ether. Therefore, it can be used in a wide pH range (2~12), and can be mixed with the components of general latex paints such as reactive pigments, additives, soluble salts or electrolytes.
There is no adverse effect on the coating film. Because the HEC aqueous solution has obvious water surface tension characteristics, it is not easy to foam during production and construction, and the tendency of volcanic holes and pinholes is less.
Good storage stability. In the long-term storage process, the dispersibility and suspension of the pigment can be maintained, and there is no problem of floating color and blooming. When there is little water layer on the paint surface and the storage temperature changes greatly. Its viscosity is still relatively stable.
HEC can increase the PVC value (pigment volume concentration) solid composition up to 50-60%. In addition, the topcoat thickener of water-based paint can also use HEC.
At present, the thickeners used in domestic high-grade latex paints are imported HEC and acrylic polymers (including polyacrylates, homopolymer or copolymer emulsion thickeners of acrylic acid and methacrylic acid) thickeners.
Hydroxyethyl cellulose can be used for
1. As a dispersant or protective glue
Generally, HEC with a viscosity of 10 to 30 mPaS is used. The HEC of up to 300mPa·S can be used in combination with anionic or cationic surfactants, and the dispersion effect is better. The reference amount is generally 0.05% of the mass of the monomer.
2, as a thickener
Use 15000mPa. The reference dosage of high-viscosity HEC above s is 0.5 to 1% of the total mass of the latex coating, and the PVC value can reach about 60%. In the latex paint, the HEC of about 20Pa,s is used, and the various properties of the latex paint are the best. The cost of simply using HEC above 30O00Pa.s is lower. However, the leveling and other characteristics of latex paint are not good. From the perspective of quality requirements and cost reduction, it is best to use medium and high viscosity HEC together.
3. Incorporation method in latex paint
Surface-treated HEC can be added in dry powder or slurry form. The dry powder is directly added to the pigment grinding. The pH of the addition point should be 7 or lower. Alkaline components such as dispersants can be added after the HEC has been wetted and fully dispersed. Slurry made with HEC should be blended into the slurry before the HEC has had enough time to hydrate and thickened to an unusable condition. HEC slurries can also be prepared with glycol-based coalescing agents.
4. Anti-mildew of latex paint
Water-soluble HEC biodegrades when exposed to molds that are specific to cellulose and its derivatives. Adding preservatives to paint alone is not enough, all components must be enzyme free. The production vehicles of latex paint must be kept clean and tidy, and all equipment must be regularly sterilized with steam 0.5% formalin or 0.1% mercury solution.
Post time: Apr-25-2024