Study on the Factors Affecting the Size and Shape of the Color Particles of Multicolor Coatings Containing Sand

Huang Zuwei,Shi Xiaolong,Qi Bo
(Asia Paint(Shanghai)Co.,Ltd.,Shanghai,201717,China)

Abstract :The action mechanism of protective colloid of multicolor coatings containing sand,and the factors affecting color particle shape and storage stability were studied. The effects of protective colloid amount,type and amount of cellulose on the size and storage stability of color particles,as well as the effects of different grades of sand on the colorful particles of multicolor coatings containing sand and dry film were discussed.

0 Introduction
As a new type of imitation stone finish coating on the market, the sand-containing multicolor coating has a unique rough surface imitating stone effect that is realistic and beautiful; while the real stone paint with similar concave-convex surface effect has a base texture and sprays a flat water-in-water effect. The process is complicated and the cost is high. In comparison, sand-containing colorful coatings not only meet the environmental protection requirements of low VOC (volatile organic compound) content, but also have unique stone-like characteristics in decorative effects. They are increasingly used in exterior wall coatings.
Sand-containing multicolor coatings are developed on the basis of water-in-water multicolor coatings. Although there are many lessons for reference, due to the addition of relatively dense sands, they have always existed in terms of particle morphology, storage stability, and construction smoothness. Many questions. This study focuses on the factors that affect the size and morphology of the colored particles of sand-containing colorful coatings, as well as subsequent stability factors, such as the concentration of protective glue, the type and content of cellulose in the base paint, and the gradation of sand molds. .

1 Experimental Section
1.1 raw
acrylic emulsion RS-2788, BATF; acrylic emulsion BLJ-9385, Poly good; DP-80, Dupree; hydroxyethylcellulose HBR250, Ashland; associative ethyl Hydroxyethylcellulose EHM500, AkzoNobel; Titanium Dioxide R-699, Long Mang Bai Lilian; Protective Glue S-482, Zhejiang Fenghong; Sand, other water-based additives, commercially available.


1.2 Equipment
SFJ-400 high-speed disperser, STM-V Stormer viscometer, Shanghai Modern Environment Engineering Technology Co., Ltd .; multicolor coating spray gun W-77, Shanghai Iwata Industrial Co., Ltd.


1.3 Preparation of sand-containing multicolor coating
1.3.1
Formula See Table 1 for the formula of sand-containing multicolor coating.

Formulation of sandy multicolor coating

1.3.2 Preparation process
Preparation of basic paint: According to the formula of basic paint, add raw materials to the reactor in sequence to the end of the powder, and disperse for 30 minutes at high speed; adjust to medium speed, add the remaining additives and emulsion, and disperse evenly for 10 minutes, add defoamer and thickener Protective glue S-482 (7%), after dispersing at low speed for 5 minutes, control the viscosity of the base paint to 120 ~ 130 KU, add sand with different particle sizes, and disperse evenly before use.
Preparation of protective glue: Control the temperature of deionized water not lower than 25 ℃, put in a fixed amount of S-482, add bactericide, disperse for 30 minutes at high speed, completely dissolve and set aside.
Continuous phase emulsion preparation: Add deionized water, emulsion, and various additives in order according to the formula, stir at medium speed, and test the viscosity of the continuous phase to 110 ~ 120 KU, and store it for future use.
Preparation of the finished paint: the base paint is adjusted to different colors according to the proportion of the color point, and the ratio of m (toning base paint): m (granulated protective glue): m (continuous phase emulsion) = 48:22:30 will be adjusted The color base paint is added to the granulating protective glue, the dispersing disc is cut into granules, and then the continuous phase emulsion of the remaining proportion is added to obtain a sand-containing multicolor coating.

2 Results and discussion
2.1 Effect of granulated protective gel concentration on sand-containing colorful particles
Colorful protective gel is a nano-scale synthetic lithium lithium silicate with good dispersion stability. Its molecular formula is Na0.3 + xLi0.3 + yMg2.7-ySi4O10 (OH) 2, where 0 ≤ x ≤ 0.4 and 0 ≤ y ≤ 0.2.
The structure diagram of the protective glue is shown in Figure 1. It is a cylindrical nanostructure with a diameter of about 25 nm and a thickness of 1 nm. It has a negative charge on the round surface and a positive charge on the edge of the column.

Structural diagram of protective glue

The protective glue S-482 used in this research is an organically modified lithium lithium silicate, in which a monovalent cation is added, and hydration occurs during the dispersion process. The sheet of lithium magnesium silicate penetrates a large amount of water. Under the action, the distance between the layers becomes larger, and a large amount of the sheet lithium lithium silicate is free in the water. At the same time, because the upper and lower layers of the sheet are negatively charged, and the end faces are positively charged, they attract and overlap each other. Form a new three-dimensional structure-“card house structure”. The hydration process is shown in Figure 2.

The process of hydration of protective glue to form a "card house structure"

After the base paint is tinted, part of the protective rubber is added to play the role of anti-bleeding. In the test, a protective rubber with a concentration of 7% is selected. First, the granulated protective rubber and the base protective rubber are unified to facilitate production; the second is Considering the need for a certain combination of protective rubber and cellulose in the base paint, the amount of protective rubber for different base materials is designed, and its influence on the viscosity of sand-containing multicolor coatings is investigated. The results are shown in Figure 3. It can be seen from Figure 3 that with the increase of the amount of base protective glue, the viscosity of the sand-containing colorful finished paint increased significantly during storage. This phenomenon is more prominent during low-temperature storage. This is due to the continuous phase emulsion at low temperature. The entanglement of thickener segments leads to an increase in the viscosity of the system.

Curves of the viscosity of sandy multicolor coatings with storage time (different storage temperature)

See Table 2 for the effect of different dosages of base protective glue on the color particles of sand-containing multicolor coatings.

Effect of Different Dosage of Base Protective Glue on Color Particles of Sand-containing Colorful Coatings

It can be seen from Table 2 that with the increase of the amount of base protective glue, the “card house” effect formed by the protective glue increases, resulting in a stronger binding with cellulose in the base paint and a denser protective film formed around the particles. The anti-bleeding ability of the colored particles becomes stronger. At the same time, due to the stronger binding effect, the sand-containing colorful particles change significantly after storage, and the spray pattern becomes smaller compared to the original retention sample. When the amount of protective glue is too much, under long-term heating conditions, the protective glue crosslinks with cellulose and some reactive additives, resulting in excessive internal stress in the sand-containing colorful particles, which cannot be unfolded by normal construction pressure. Causes particles to become smaller.
When the amount of the base paint protective glue is 6%, the anti-bleeding property of the sand-containing multicolor coating and the later storage stability, especially the low-temperature storage stability, are better.


2.2 Effect of Sand

Cellulose multicolor coating color particles of cellulose in the granulation molding sand multicolor coating color play key roles in use, mainly for the following two aspects: (1) provide a basis for a high viscosity varnish, for convenient preparation Colored particles; (2) “gelation” reaction with the lithium magnesium silicate in the base protective glue solution, that is, the “card house” structure formed by the hydration of the protective glue is strengthened, and a cross-linking reaction occurs between the cellulose and the protective glue (Figure 4) The original “hydrophilic” tinting base paint is converted into “hydrophobic”, forming a dense water-insoluble film on the outer surface. Therefore, the type and amount of cellulose not only affect the state of the particles by affecting the viscosity of the base paint, but also have a greater impact on the anti-bleeding performance of the particles and the stability of the particles in the later stage.

Process of cross-linking reaction between cellulose and protective gum

In this study, short-chain cellulose HBR250 and long-chain cellulose EHM500 were selected for use. The test results are shown in Table 3.

Effects of different proportions of cellulose on colored particles of sand-containing colorful coatings

After adding EMH500 to the formula, the color point thickness becomes slightly thicker, and the unevenness and sand feeling of the dry film have been improved to a certain extent. However, with the increase of the amount of EMH500, the state of the colored particles after heat storage is more obvious from the initial ” “Thickening” becomes “significantly thickening”, that is, the thermal storage stability becomes worse, and as the amount of EMH500 increases, the workability of the coating becomes worse.
When HBR250 and EHM500 account for 0.8% and 0.2% of the base paint, respectively, the color particles of the sand-containing multicolor coating have better stability and have better post storage stability.


2.3 Impact of sand type gradation on multicolor coating particles containing sand

About the problem of sand feel, try to add 5% ~ 15% SA30 white sand (main particle size is 30 mesh) in the adjusted formula, and recalculate the formula according to the proportion. SA30 accounts for 5% to 15% of the base paint. Observe the color point state and sand feel effect after adding coarse sand (Table 4).

Effect of Different Sand Type Grading on Color Particles of Sand-containing Colorful Coatings

It can be seen from Table 4 that the addition of SA30 in the formula can improve the unevenness and sand feeling of the dry film to a certain extent, but with the increase of the SA30 content, the coating ability of the base paint decreases, resulting in some coarse sand being exposed. The stability of the coating is reduced. In summary, the sand mold ratio w (SA30): w (SA80): w (SA120) = 2: 3: 1 is selected to avoid the rough sand of the sample being too prominent and the feeling of sticking.

3 Conclusion
(1) The research shows that the optimal concentration of S-482 as a base protective glue is 7%, and the optimal amount is 6%.
(2) When HBR250 and EHM500 are selected as the cellulose, which account for 0.8% and 0.2% of the base paint, respectively, the colored particles of the sand-containing multicolor coating are stable and the storage stability is good.
(3) When sand ratio w (SA30): w (SA80): w (SA120) = 2: 3: 1 is selected, the sand-containing multi-color paint obtained has better appearance and appropriate unevenness.

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