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Covering power refers to the ability to completely cover the paint coated, in latex paint is mainly reflected through the contrast ratio, minimum requirements GB GB/T9756-2009 is 0.90. Titanium dioxide is the main raw material to provide wet hiding power of latex paint, after resin emulsion of raw materials on the cost impact is low in latex paint, so how in the situation of titanium dioxide under fixed improve dispersion to improve the hiding power of great significance of titanium dioxide.
The titanium dioxide choice
The pigment particle size has great influence on its hiding power, industrial rutile titanium dioxide particle size is generally in the 0.1 ~ 0.5um, according to the principle of light wave diffraction, at about 0.15um to cover the best titanium dioxide, covering power of a sharp decline in beyond 0.4um.
The selection of dispersing agent
To choose the good adhesion of titanium dioxide and resin compatibility good dispersing agent, titanium dioxide surface with the general A12 (3) treatment, hydrophilic, were slightly alkaline, phosphoric acid, carbonic acid bond easily attached on the surface of titanium white powder. For example, dispersing agent HOO-P- (OR) C18H35R, in which "R" structure, if similar to the structure of resin, good compatibility. Different dispersant to set different "-R" group and resin compatibility, i.e. containing multiple functional groups of dispersant.
The selection of thickeners
Should avoid the use of high molecular weight thickener, due to large molecular weight, easy to build their own space, so that the titanium dioxide emissions, caused by volume flocculation of titanium dioxide. General alkali swelling thickener, contains a lot of cOO-, high molecular weight, which can make the titanium dioxide are connected with each other, thus causing flocculation, thickening agent as far as possible the use of small molecule non ion amount of hydroxy ethyl cellulose A1.
Control of production process
It is also important to the dispersion of titanium dioxide, titanium dioxide, surface treatment of more use of Al2O3, pH value is less than 6, the positively charged surface of titanium white powder, the pH value is greater than 7.5, titanium dioxide is negatively charged, so the best dispersion of titanium dioxide pH value between 6.5 ~ 7, pH value is high, can be well dispersed, but no good adhesion, and the system may be unstable, so the best finish in dispersing titanium dioxide after adding cellulose dispersion until completely dissolved, add the pH value regulator. If conditions permit, the best single dispersed titanium dioxide.
The pigment volume concentration (PVC)
The low-grade latex paint another enhance Zhegeli to increase PVC, improve air porosity of coating, filler and air through the refraction rate difference to improve dry hiding power. The more powder to obtain high PVC, while for the covering force help, but reduce the effect of free water in the formula, brushing area and construction, and the impact of scrub resistance. Therefore in the scrub resistance qualified circumstances, by reducing the content of resin emulsion to improve PVC to increase the hiding power is a good choice. The general low-grade latex paint powder of total amount control in 45% ~ 50%, PVC control in 76% ~ 82% good. In addition can reduce CPVC by matching the thickness of powder, the data shows the pigments and fillers with a thickness control gap 0.3Um in diameter, can play the best cover effect, and reduce the side angle light, can improve the performance of construction.
The hanging color
That is, add a small amount of pigments (the past is generally add ultramarine, now often use purple pulp) to improve the hiding power, white paint by hanging after color visual seems more white, can also be a higher contrast ratio. Is mainly hanging color after the coating brightness reduced, thus the black and white contrast and substrate closer, make the person is not easy to distinguish visually, and thus become more high covering power. You can also use a lower luminance fillers (such as water washed kaolin), or directly adding a small amount of iron oxide yellow or black iron slurry to reduce the brightness of coating to improve the hiding power, bringing it closer to the substrate color, this in the actual construction and the effect is more obvious.
