Effect of pigment fillers on the hiding power of latex paint
Latex paint is a kind of coating prepared by water dispersing system, synthetic resin as the base material, and adding pigments and fillers, supplemented by various additives. As one of the important indexes to measure the quality of latex paint, covering power is the focus of attention in the design formula and actual production.
Covering power, also known as opacity, is the result of producing scattering and absorption that pigments affects on light. It is generally affected by the crystal shape and type of fillers. The expression of covering power refers to the minimum amount of paint required to achieve complete cover per square centimeter of the surface area of the coated material. In the daily experiment, the method of black and white plate is used to test; Field operation with the same weight products under the same construction conditions, the better the covering power, the more area can be brushed.
The effect of titanium dioxide crystal on the hiding power: titanium dioxide is the most widely used white pigment, and also provides the most important component of hiding power. Titanium dioxide molecules are TiO2, commonly used there are two types of crystal, respectively: anatase type, rutile type, crystal type of different lead to different hiding power, as shown in the following figure rutile titanium dioxide hiding power is obviously higher than anatase titanium dioxide.
The effect of the filler on the hiding power: the general covering power of the coating is determined by the difference between the refraction rate of the coating and the refraction rate of the material around the coating, the greater the difference, the stronger the hiding power; The more common fillers in latex paint are Lide powder, which has a better covering effect. The refractive index and coverage data of fillers commonly used in latex paints are shown below.
Because the surrounding medium is consistent (air: 1, water: 1.33, resin: 1.55), so the refractive index of the medium is the same, so the difference between the refractive index and the surrounding medium depends on the size of its own refractive index; The refractive index of rutile type is larger than that of anatase titanium dioxide, and it is concluded that the covering power of rutile titanium dioxide is better. The comparison chart of the covering power of rutile type and anatase titanium dioxide also verifies the conclusion, and the low refractive index of silica itself, so the covering power is poor. Therefore, it can be seen that the larger the refractive index of the pigment itself, the better the covering effect.
For the general pigment’s fillers, such as calcium carbonate, talc and kaolin, its refractive index is basically equivalent to emulsion, but the finer pigment’ fillers, by adjusting titanium dioxide in the coating film space position, so that titanium dioxide is not together, to achieve the maximum light scattering value, so as to get the highest cover power, generally the effect of this fine filler called isolation, The fine filler is called spacer filler, titanium dioxide spacer; In particular, such as calcined kaolin, etc., using this principle to improve the coverability after mixing with titanium dioxide.
At the same time, when a higher ratio calcium powder is added to latex paint, there is a certain degree of covering property difference among different mineral sources. For this reason, by comparing the covering property difference between our company’s porcelain white calcium powder and the commonly used calcium powder in the market, the black and white grid method is used to represent its covering property. The porcelain white calcium in the left picture below shows low black and white grid color change, that is, the covering property is better than that of ordinary calcium powder. The following figure on the right is the comparison between the porcelain white calcium and ordinary heavy calcium masking cardstock after selection, obviously showing that it has a better dry covering ability than the general heavy calcium, and at the same time, the excellent particle size and titanium dioxide compound can also play better role of separation, improve the overall covering power of the product.
Latex paint is a higher class of PVC products, and the selection and dosage of pigments and fillers in its formula will have a certain impact on the final coverability of the product. Reasonable use and collocation of different fillers will make the formula product show more excellent characteristics.
