Industry | Research on Influencing Factors of Stain Resistance of Inorganic Exterior Wall Coatings

Inorganic exterior wall coatings with inorganic potassium silicate or silica sol as the main film-forming substances have good physical properties, but they require excellent stain resistance when applied to exterior wall coatings, and truly achieve better stain resistance Reasonable material compatibility needs to be considered.
In this study, starting from the formulation design of inorganic silicate coatings, the combination of powder structure, and the selection of additives, the influence of various factors on the stain resistance performance is explored.
0 Introduction
With the rapid development of industrialization, it has caused serious damage to the earth's environment, and serious pollution threatens people's living space.
"Green" and "environmental protection" are the requirements put forward to the coating industry after people attach great importance to environmental protection, and they are also the future development direction of the coating industry.
Compared with organic coatings, inorganic coatings are directly derived from the abundant minerals in nature.
The production and use process of the base material fully meets the requirements of energy saving and emission reduction, and has technical indicators that most organic coatings with the same cost cannot reach.
.
In recent years, the domestic construction engineering market has promoted the development of inorganic interior wall coatings due to the national mandatory requirements for fireproof and non-combustible interior wall coatings for underground confined spaces.
Major domestic architectural coating manufacturers are conducting research and development of inorganic architectural coatings.
And continue to launch their own new products, so that inorganic silicate coatings find rare development opportunities in our country.
Inorganic coatings have good outdoor weather resistance and adhesion, but their stain resistance is equally important to their service life.
There are many references for the preparation of inorganic coatings, regarding the stain resistance of organic coatings.
There are also many research documents.
However, there are few domestic reports on the factors affecting the stain resistance of inorganic coatings.
Tian Hebao and others explored the basis of the blending stability of potassium silicate and silica sol by characterizing the particle size of the potassium silicate and silica sol compound solution; Qian Huai and Zhang Wei et al.
believed that the air permeability of silicate coatings is One of its strengths, but the porous surface will inevitably lead to a higher water absorption rate of the coating, which causes the fly ash to easily accumulate in the paint film during the stain resistance test and it is difficult to wash it off.
Due to the special structure of silicate and silica sol, there is a big difference from acrylic emulsion, and the mechanism of stain resistance will not be exactly the same.
This article analyzes the influence 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%): Peiteng; Silica sol (MOS-2012): Peiteng; 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; PTFE Wax Powder (TF1778): Lubrizol; Rutile Titanium Dioxide (R996): Sichuan Dragon Mang; 800 mesh silica powder: Guangdong Yufeng; 1 000 mesh heavy calcium (GF110): Guangfu; 800 mesh talc (CMS-666); Liaohua; 1 250 mesh wet sericite (GA-4): Ruige.

1.
2 Experiment and testing equipment
High-speed dispersion machine (GFJ-0.
4): Shanghai Modern Environmental Engineering Technology Co.
, Ltd.
; Coating Contamination Resistance Tester (QWX): Tianjin Jinke Material Testing Machine Co.
, Ltd.
; Reflectance Tester (C84-III) ): Shanghai Modern Environment Co.
, Ltd.
; scrub resistance tester (BGD526): Guangzhou Biaogeda Experimental Equipment Co.
, Ltd.

1.
3 Coating preparation and performance test
1.
3.
1 Inorganic binding substance and emulsion compatibility test
Select several emulsion products with excellent calcium ion stability, and do the compatibility test with two optional potassium silicate, according to the emulsion : Stabilizer: Potassium silicate=9:1:22 to mix, observe whether there is demulsification or flocculation.

1.
3.
2 The
experimental formula for the preparation of inorganic coating samples is shown in Table 1.

0 Introduction 1 Experimental part
1.
1 Experimental raw material ChangxingBASF
1.
2 Experiment and test equipment 1.
3 Coating preparation and performance test
1.
3.
1 Inorganic binding substance and emulsion compatibility test 1.
3.
2 Preparation of inorganic coating samples 1.
3.
3 Preparation process of inorganic exterior wall coating
(1) Pre-mixing: in Add water to the dispersion tank, and then add additives, stir and mix at 300～500 r/min to form a gelatinous substance;
(2) Grinding and dispersion: Add titanium dioxide and fillers to the dispersion tank at a speed of 2 000～3 000 r/min Down beating and grinding for 20-25 minutes until the fineness is less than 60 μm;
(3) Add styrene-acrylic emulsion and quaternary ammonium salt stabilizer
in the dispersing tank, mixing uniformly at 800-1 200 r/min; (4) In the dispersing tank Add potassium silicate solution and the remaining water in sequence, mix well at 800～1 200 r/min, and get it.
1.
3.
3 Preparation process of inorganic exterior wall coatings 1.
3.
4 Performance test method
According to JG/T26-2002 "Exterior Inorganic Architectural Coatings", the thermal storage stability, viscosity, contrast ratio, low temperature storage stability, water resistance and resistance were tested respectively.
Alkaline, drying time, scrub resistance, temperature change resistance, aging resistance, stain resistance, coating appearance, etc.

The stain resistance test method is carried out according to the method in Appendix A of JG/T26-2002.
Fly ash is used as the pollution medium to evaluate the change of paint film reflectivity 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 combinations of potassium silicate and emulsion were selected for experiments.
The experimental combinations are shown in Table 2.

1.
3.
4 Performance test method 2 Results and discussion
2.
1 Analysis of compatibility of emulsion and silicateThe first prerequisite for exploring the stain resistance of inorganic coatings is to select a product system that can be stored stably, and then perform subsequent performance tests.
Table 2 shows:
(1) Different silicates/silica sols with different emulsion phases Capacitive properties will have different performances.
In the verification experiment, the author found that the combination of demulsification occurs when the two are mixed.
After the paint is made, there will be different degrees of post-thickening and gelatinization.
Therefore, this method can be used as a simple method to determine the compatibility of silicate and emulsion;
(2) The stabilized potassium silicate is milder than other potassium silicates, and the emulsion is more tolerant.
, The adaptation range is wider, and the Aushan potassium silicate with a certain range of modulus is not sufficiently concentrated in the crystal form, the emulsion is the least tolerant, and the requirements for the emulsion are correspondingly higher;
(3) Compared with silica sol Potassium silicate has better compatibility with various emulsions, and it is not easy to cause flocculation or gelation;
(4) The better the alkali resistance of the emulsion itself, the better the compatibility with silicate.

2.
2 The influence of silicate and emulsion combination on stain resistance
Take the formula 1# in Table 1 and add different emulsion and potassium silicate combinations, and other raw materials are unified, prepare sample paint, and prepare sample board.
Test each performance separately according to the performance test method described in 1.
3.
4.
2.
2 The influence of the combination of silicate and emulsion on stain resistance can be seen from Table 3.
The combination of different silicates and emulsions shows great differences, the balance of various properties and the best performance of stain resistance , Select MOS1010 and 791ap to experiment with 2#, 3#, 4#, 5# formulas, and some of the performances obtained 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 closely related to the proportion of the emulsion in the binding substance.
After increasing the emulsion content and reducing the potassium silicate content, the stain resistance performance appears There is a rising law (see Figure 1), but in order to achieve a lower organic content, the experiment is to compound silica sol in potassium silicate and increase the amount of use, and the stain resistance will also improve, such as 5# in this way.
The stain resistance will be significantly improved compared to 4#.
2.
3 Influence of powder structure on stain resistance
It can also be seen from the data of 5# and 6# in Table 4 that if the proportion of heavy calcium in the formula is reduced, and the amount of silica powder and mica powder is increased, the stain resistance has also been significantly improved.
The reason may be that the silica powder The porosity is low, the filling is good, and the porosity of the paint film is effectively reduced.
The lamella structure of mica powder provides better sealing, making the dust on the surface of the paint film easy to wash away, and excessive addition of heavy calcium It will have a negative effect on the stain resistance of the paint film.

2.
4 The influence 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 Vinyl fluoride wax powder increases the anti-sticking performance of the coating.
See Table 5.

2.
3 The influence of powder structure on stain resistance 2.
4 The influence of additives on stain resistance is visible.
The use of silicone hydrophobing agent alone cannot make the fly ash absorbed into the coating film washed out by water, while PTFE Wax powder reduces the adhesion of fly ash on the surface of the paint film to a certain extent and improves the smoothness of the paint film, so it is beneficial to improve the stain resistance of the inorganic paint film.

3 Conclusion
The experiments conducted on several factors that may affect the stain resistance of inorganic coatings show that the porosity and porosity of the surface of the silicate coating film is the main reason for the poor stain resistance, and the surface energy of the paint film is The impact is relatively limited.
Therefore, to improve 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 The method of compounding silica sol increases the proportion of inorganic binder and reduces the porosity; (3) The porosity is reduced by selecting powders with good filling and sealing properties such as silica powder and mica powder; (4) ) Supplemented with a certain amount of PTFE wax powder can help reduce the surface energy of the paint film to a certain extent and improve the stain resistance.
Through the comprehensive consideration of the above aspects, it can be made to meet the existing standard stain resistance requirements The product.

3 Conclusion