(Carpoly Chemical Group Co., Ltd., Jiangmen, Guangdong 529000, China)
Abstract: Inorganic exterior wall coatings with inorganic potassium silicate or silica sol as main film-forming material have good physical properties, but need excellent stain resistance if applied to the exterior wall coatings. Reasonable material compatibility should be considered to achieve better stain resistance. In this paper, the formulation of inorganic silicate coatings, the design of powder structure and the additive choice are provided to evaluate the effects of various factors on the antifouling performance.
With the rapid development of industrialization, the global environment has been severely damaged, and serious pollution threatens people’s living space. “Green” and “environmental protection” are the requirements put forward on the coatings industry by people now attaching great importance to environmental protection, and also the future development direction of the coatings industry. Compared with organic coatings, inorganic coatings are directly taken from the rich minerals in nature. The production and use of its base materials fully meet the requirements of energy saving and emission reduction, and have the most difficult technical indicators for organic coatings of the same cost. . In recent years, the domestic construction engineering market has promoted the development of inorganic interior wall coatings due to the country’s mandatory requirements for fireproof and non-combustible interior wall coatings for underground confined spaces. Major domestic architectural coatings manufacturers are conducting research and development of inorganic architectural coatings. And continue to launch their own new products, so that inorganic silicate coatings have found rare development opportunities in China. Inorganic coatings have better outdoor weathering resistance and adhesion, but the impact of their stain resistance on their service life is equally important. There are many literatures on the preparation of inorganic coatings for reference. For the stain resistance of organic coatings The research literature is also more. However, there are few reports on the factors affecting the stain resistance of inorganic coatings in China. Tian Hebao et al. Explored the basis of the stability of the blending of potassium silicate and silica sol by characterizing the particle size of the compound solution of potassium silicate and silica sol; Qian Huai, Zhang Wei, etc. considered that the permeability of silicate coatings was One of its strengths, but the porous surface will inevitably lead to a higher water absorption of the coating, which will cause the fly ash to easily accumulate in the paint film during the stain resistance test and it will be difficult to wash it down. Due to the special structure of silicates and silica sols, there are large differences from acrylic emulsions, and the mechanism of their stain resistance is not exactly the same. This article analyzes the effects of silicate content, silica sol content, powder structure, and additives in the formulation to explore how to achieve high stain resistance inorganic coatings.
1 Experimental part
1.1 Experimental materials
Potassium silicate (AH-K1: modulus 3.75 ~ 4.15, silica content> 16%): Aohan; potassium silicate (GHSK: modulus 4.09, silica content 20.63%): Guolian; stabilized silicic acid Potassium (MOS-1010: Modulus 3.6, silica content 16% ~ 18%): Peito; Silica sol (MOS-2012): Peito; Styrene-acrylic emulsion (6516-2): Changxing; Pure acrylic emulsion ( 7016G): BASF; styrene-acrylic emulsion (791ap): BASF; styrene-acrylic emulsion (296ds): BASF; styrene-acrylic emulsion (559ap): BASF; styrene-acrylic emulsion (R64): Dow; quaternary ammonium salt stabilizer (SPS) : Clariant; Silicone Hydrophobic Agent (BS1306): WACKER; Polytetrafluoroethylene Wax Powder (TF1778): Lubrizol; Rutile Titanium White (R996): Sichuan Long Manganese; 800 mesh fine silicon powder: Guangdong Yufeng; 000 mesh heavy calcium (GF110): Guangfu; 800 mesh talc (CMS-666); Liaohua; 1 250 mesh wet sericite (GA-4): Ruige.
1.2 Experimental and testing instruments
High-speed dispersing machine (GFJ-0.4): Shanghai Modern Environment Engineering Technology Co., Ltd .; Coating Contamination Tester (QWX): Tianjin Jinke Material Testing Machine Co., Ltd .; Reflectivity Tester (C84-III) ): Shanghai Modern Environment Co., Ltd .; Scrub Tester (BGD526): Guangzhou Biaogeda Experimental Equipment Co., Ltd.
1.3 Coating preparation and performance test
1.3.1 Compatibility test of inorganic binding substance and emulsion
Select several emulsion products with better calcium ion stability, and perform compatibility test with two alternative potassium silicates. : Stabilizer: Potassium silicate = 9: 1: 22 and observe whether demulsification or flocculation occurs.
1.3.2 Preparation of inorganic coating samples
The experimental formulation is shown in Table 1.
1.3.3 Preparation process of inorganic exterior wall coatings
(1) Pre-mixing: Add water to the dispersion tank, then add auxiliary agents, and stir and mix to form a gelatinous substance at 300 ～ 500 r / min;
(2) Grinding and dispersing: Add titanium dioxide and filler to the dispersing tank, beat and grind at a speed of 2 000 to 3 000 r / min for 20 to 25 minutes to a fineness of less than 60 μm;
(3) Add styrene-acrylic to the dispersing tank. Emulsion and quaternary ammonium salt stabilizer, 800 ～ 1 200 r / min, mix well;
(4) Add potassium silicate solution and remaining water in order in the dispersing tank, mix 800-1200 r / min, and get.
1.3.4 Performance test method
According to JG / T26—2002 “Inorganic Coatings for Exterior Walls”, test thermal storage stability, viscosity, contrast ratio, low temperature storage stability, water resistance, alkali resistance, drying time, scrub resistance , Temperature resistance, aging resistance, stain resistance, appearance of coating film, etc.
The stain resistance test method is carried out in accordance with the method in Appendix A of JG / T26-2002. Fly ash is used as the pollution medium to evaluate the change of the reflectance of the paint film before and after pollution.
2 Results and discussion
2.1 Analysis of the compatibility of emulsion and silicate
According to the method mentioned in 1.3.1, different potassium silicate and emulsion combinations were selected for experiments. The experimental combinations are shown in Table 2.
The first prerequisite for exploring the stain resistance of inorganic coatings is to choose a product system that can be stored stably, and then perform subsequent performance tests. From Table 2, we can see that:
(1) Different silicates / silica sols with different emulsion phases Capacitive properties will appear differently. In the verification experiment, the author found that the combination of the two showed demulsification. After the paint was made, post-thickening and gelling would occur to varying degrees. Therefore, this method can be used as a simple method to determine the compatibility of silicate and emulsion.
(2) The stabilized potassium silicate is more gentle than other potassium silicates, and the emulsion has a higher tolerance for it. , The range of adaptation is wider, and the potassium silicate in a certain range has a low degree of crystal tolerance due to insufficient concentration of the crystal form, and the tolerance of the emulsion is the lowest, and accordingly the requirements for the emulsion are higher;
(3) compared with silica sol Potassium silicate has better compatibility with various emulsions and is less prone to flocculation or gelation.
(4) The better the alkali resistance of the emulsion itself, the better the compatibility with the silicate compound.
2.2 Effect of silicate and emulsion mix on stain resistance
Adopt formula 1 # in Table 1 to add different combinations of emulsion and potassium silicate, other raw materials are unified, sample paint is prepared, and sample plate is prepared. Test each performance separately according to the performance test method described in 1.3.4.
It can be seen from Table 3 that different combinations of silicates and emulsions show large differences. Based on the balance of various properties and the best performance of stain resistance, MOS1010 and 791ap are selected for 2 #, 3 #, and 4 #. The experimental results of the 5 # formula are shown in Table 4.
It can be seen from the formulas of 2 #, 3 #, and 4 # in Table 4 that the stain resistance is highly related to the proportion of the emulsion in the binding substance. After increasing the emulsion content and reducing the content of potassium silicate, the stain resistance performance is shown The rising rule (see Figure 1), but in order to achieve a lower content of organic matter, the experiment is to mix silica sol in potassium silicate and increase the amount of use, and the stain resistance will be improved, such as 5 # in this way Stain resistance will be significantly improved compared to 4 #.
2.3 Influence of powder structure on stain resistance
From the data of 5 # and 6 # in Table 4, it can also be seen that reducing the proportion of heavy calcium in the formula, increasing the amount of silicon fine powder and mica powder, and its stain resistance It has also been significantly improved, possibly due to the low porosity of silicon micropowder and good filling properties, which effectively reduces the porosity of the paint film, while the lamellar structure of the mica powder provides better sealing, making the ash deposit on the surface of the paint film It is easy to rinse, and excessive addition of heavy calcium will adversely affect the stain resistance of the paint film.
2.4 Effect of additives on stain resistance
For the 5 # formula, try to improve the stain resistance by adding additives. Consider using WACKER silicone hydrophobic agent BS1306 to increase the hydrophobicity of the coating and Lubrizol TF1778 polytetrafluoroethylene. Fluoroethylene wax powder increases the coating’s anti-stick properties. See Table 5.
It can be seen that the use of organic silicon hydrophobic agent alone cannot make the fly ash that has been absorbed in the coating film washed out by water, and the polytetrafluoroethylene wax powder reduces the adhesion of fly ash to the surface of the paint film to a certain extent. Properties, improve the smoothness of the paint film, so it is beneficial for improving the stain resistance of the inorganic paint film.
Experiments on several factors that may affect the stain resistance of inorganic coatings have shown that the loose and porous surface of the silicate coating film is the main reason for the poor stain resistance, and the impact of the surface energy of the film is relatively Limited, therefore, improving the stain resistance of inorganic coatings is not a simple adjustment, but needs to be adjusted from the following aspects: (1) increase the emulsion content and reduce the porosity; (2) use silicate and silica sol The method of compounding and increasing the proportion of inorganic binders to reduce the porosity; (3) reducing the porosity by using powders such as silicon micronized powder and mica powder with good filling and sealing performance; (4) auxiliary With a certain amount of polytetrafluoroethylene wax powder, it helps to reduce the surface energy of the paint film to a certain extent and improve the stain resistance. Only through comprehensive consideration of the above aspects can products be made that meet the requirements of existing standards for stain resistance .