Preparation and Supporting Research of Waterborne Self-cleaning Color Coatings with High Weather Resistance

LIU Xiao-jing, AN Wen-dong, LING Qin, ZHAO Chang-yong, ZHANG Xiao-man, XING Xiao (Shijiazhuang Paint Company, Shijiazhuang 050051, Hebei, China)

Abstract: A kind of full-life-cycle green environmentally friendly waterborne self-cleaning color coatings with high weather resistance is developed according to the requirements of raw materials for green environmentally friendly coatings. This paper mainly describes the course and process of preparing waterborne self-cleaning color coatings with high weather resistance and the process of latex, pigment, filler and additive screening for such coatings and discusses their reaction mechanisms to select the most compatible supporting coatings layer.

0 Introduction
Water-based colorful paint is a new type of decorative paint, and Compared with real stone paint, granite marble has many advantages such as realistic simulation, excellent performance, simple construction technology, and relatively low cost. It can replace granite and other stones and reduce the extraction of natural stones. With the increasingly strict environmental protection laws and regulations and the gradual increase of people’s environmental awareness, environmentally friendly products have begun to occupy a dominant position. In addition, due to the environmental characteristics of dryness, low rainfall, windy dust, and relatively strong ultraviolet rays in the north, in order to improve the service life of exterior wall products, reduce the frequency of renovation, and save resources, the performance requirements of exterior wall coatings must be increased accordingly. Especially in terms of self-cleaning and anti-ultraviolet aging of the wall, it should meet the requirements of northern environmental characteristics.
This experiment is based on T / CPCIF 0001-2017 “Technical Specification for Evaluation of Green Design Products for Water-based Architectural Coatings”, DB13 / 3005-2017 “Standards for Limits of Volatile Organic Compound Content in Architectural Coatings and Adhesives”, and HJ 2537-2014 “Environmental Labeling Products” Technical requirements Waterborne coatings, GB 24408-2009 “Limits of harmful substances in exterior wall coatings for buildings” and HJ / T 4343-2012 “Water-based colorful architectural coatings” standard requirements, developed a suitable for northern environment and meet people’s wall Highly weather-resistant self-cleaning water-based colorful coating products that pursue the decorative effect of the body and meet the requirements of green environmental protection.

1 Experimental part
1.1 Main experimental raw material
protective rubber, industrial grade, imported; hydroxyethyl cellulose, industrial grade, Ashland; silicone acrylic latex, industrial grade, domestically produced; pure acrylic latex, industrial grade, domestically produced; titanium dioxide, R706 DuPont; water-based colorant (iron oxide black, iron oxide red, iron oxide yellow): industrial grade, domestically produced; preservatives, industrial grade, imported.

1.2 Experimental instruments
Contact angle measuring instrument (CA-100D): Shanghai Yingnuo Precision Instrument Co., Ltd .; high-speed disperser (WJ-1.1), thermal storage drying box (TIK), scrub resistance instrument (PS2730): Shanghai Pushen Chemical Machinery Co., Ltd .; Xenon lamp aging tester (Q-LAB): imported; Stormer viscometer (STM-2): Biaogeda Precision Instrument Co., Ltd .; granulator (JD-2.1): Foshan Jieding Machinery Equipment Co., Ltd .; colorful spray gun (TT-871): Zhejiang Chengyu; Electrothermal Blast Dryer (101-1AD): Shanghai Kuntian Laboratory Instrument Co., Ltd.

1.3 Preparation of high weather-resistant self-cleaning water-based colorful paint
1.3.1 Preparation of
protective glue solution The basic formula of protective glue solution is shown in Table 1.

Table 1 Basic Formula of Protective Glue Solution

Weigh a certain amount of deionized water into the mixing tank, adjust the speed of the disperser to 800 ~ 1 200 r / min, and then slowly add the weighed protective glue (to avoid caking), and disperse for 20 ~ 30 The protective gum solution is obtained in min.

1.3.2 Preparation of
tinted base coatings The formulation of tinted base coatings is shown in Table 2.

Table 2 Basic Formula of Basic Toning Coatings

Add hydroxyethyl cellulose to water at a mixing rate of 200 to 300 r / min, and disperse for 2 to 3 minutes, then add dispersant, wetting agent, antifoaming agent, pigment, filler, and multifunctional auxiliary. Stirring rate increased to 1 200 ~ 1 500 r / min, stirring for 20 ~ 30 min until completely dissolved, adding protective rubber solution, latex, film-forming aid, propylene glycol, defoamer, preservative in order at 600 ~ 800 r / min 2. Protect the glue solution, and continue to disperse for 5-10 minutes to obtain the tinted base coating.

1.3.3 Preparation of continuous phase

The basic formulation of the continuous phase is shown in Table 3.

 Table 3 Basic Formula of Continuous Phase

Weigh a certain amount of deionized water into a mixing tank, and add latex, multifunctional auxiliary, film-forming auxiliary, propylene glycol, defoaming agent, preservative, and thickener in order under low speed 600-800 r / min. , Stir for 10-20 minutes until uniform.

1.3.4 Preparation of highly weather-resistant self-cleaning water-based colorful paint
See Table 4 for the preparation of highly weather-resistant self-cleaning water-based colorful paint.

Table 4 Basic Formula of Waterborne Self-cleaning Color Coatings with High Weather Resistance

Weigh a certain amount of protective glue into a mixing tank, divide the base paint into several parts according to a certain proportion, and color each separately; after the coloring is completed, add each color of the base paint to the protective gum solution according to the proportion and disperse it at a low speed. Egg-shaped color blocks; then granulate with a granulator, select the appropriate screen and rotation speed according to the particle size; finally add a certain amount of continuous phase to the colored particles, mix well, and check the viscosity. The final finished product of water-based colorful paint is obtained.

1.4 Preparation and production process of high weather-resistant self-cleaning water-based colorful paint

Figure 1 shows the production process of high-weather self-cleaning water-based colorful paint.

Fig. 1 Production Process of Preparing Waterborne Self-cleaning Color Coatings with High Weather Resistance

1.5 Preparation of high weather-resistant self-cleaning water-based colorful paint overcoat varnish

See Table 5 for the basic formula of high-weather-resistant self-cleaning water-based colorful paint overcoat varnish.

Table 5 Basic Formula of Varnish

High weather-resistant self-cleaning water-based colorful paint products are designed with environmental protection from the four life-cycle attributes: resource attributes, energy attributes, environmental attributes, and product attributes. Formed a truly green environment-friendly, highly weather-resistant, self-cleaning product. Based on the requirements of the above four attributes, the raw materials used in the preparation of high weather-resistant self-cleaning water-based colorful paint products meet the requirements of green environment-friendly paint raw materials.

1.6 Performance test
According to the above-mentioned basic formula and preparation process, the highly weather-resistant self-cleaning water-based colorful paint is prepared in accordance with T / CPCIF 0001-2017 “Technical Specifications for Green Design Product Evaluation Water-based Architectural Coatings”, DB13 / 3005-2017 “Architectural Coatings and Adhesives” Volatile Organic Compound Content Limit Standard “, HJ 2537-2014” Technical Requirements for Environmental Labeling Products, Water-based Coatings “, GB 24408-2009” Limits of Harmful Substances in Exterior Wall Coatings for Buildings “, the four most demanding standards The standard spine detects the content of harmful substances in the product. The test indicators, test results and test basis are shown in Table 6.

Table 6 Limits of Harmful Substances in Coatings

The coating film performance test of the coating is performed in accordance with the requirements of HJ / T 4343-2012 “Water-based Colorful Architectural Coatings”. The coating film performance test is a composite coating (primer coating + water-based colorful coating + overcoat varnish). The specific testing indicators and testing The results and detection basis are shown in Table 7.

Table 7 Performance Test Indicators of Coatings Film

2 Results and discussion
2.1 Influence of the types of water-based colorful continuous phase latex on film performance

In combination with the characteristics of water-based colorful paint tinting base coatings, a domestic silicon-acrylic latex was used as the film-forming material for the tinting base coatings. The emulsifier in the latex or the functional groups in the emulsion structure will react with the protective gum, causing the color particles to swell and deform, destroying the stability of the finished product, resulting in poor compatibility between the latex and the protective gum, resulting in foaming of the coating film in water. White, affecting the decorative effect, destroying the flexible protective film. Silicone acrylic latex has good compatibility with the mainstream protective rubber systems on the market and has a wide range of application prospects. This experiment will not discuss this in detail.
The continuous phase latex of water-based colorful paint is very important to the performance of the final coating film. Its role is to make the colorful paint firmly adhere to the wall of the building, and to beautify and protect the appearance of the building. Its effect on artificial aging is particularly prominent. At present, high weather resistance is one of the development trends of water-based colorful coatings. Therefore, the following factors should be considered in the preparation process: (1) continuous phase latex and the selected protective gum solution are better. Compatibility, that is, to maintain “relative inertness” with the protective gel to prevent the phenomenon of sudden increase in viscosity or even gelation during storage. (2) Excellent weather resistance, improve product life, reduce refurbishment frequency, and save resources. (3) Appropriate film formation temperature and small particle size ensure the compactness and stain resistance of the coating film on the premise of ensuring good film formation. (4) Good physical and mechanical properties and chemical resistance to meet standard requirements. In this experiment, five kinds of colorful continuous phase latexes commonly used in the market are selected for comparison test. The test results are shown in Table 8.

Table 8 Comparison Test Results of Different Latex

The continuous phase latex selected in Table 8 includes 3 types of silicone acrylic latex and 2 types of pure acrylic latex. It can be seen from Table 8 that its performance is significantly different. W3 basically meets the product performance requirements, but it reacts with the protective gum solution and easily thickens afterwards; W2 and W4 have good compatibility with the protective gum, but cannot resist artificial aging. Meet the standard requirements, and W2 film formation is poor; W5 and protective glue compatibility and artificial aging can not meet the requirements. It can also be seen from Table 8 that the artificial aging resistance of W1, W2, and W3 is significantly better than that of W4 and W5. This is because the Si—O bond energy of W1, W2, and W3 is much larger than the C—C bond and C—O. This makes the heat resistance, weather resistance, and oxygen resistance of the silicone-acrylic latex significantly enhanced, which can effectively extend the service life of water-based colorful coatings, especially W1 can better reflect the high weather resistance characteristics of the product. And W1 has good compatibility with the protective glue, and the physical and chemical properties meet the requirements of the standard. Therefore, W1 was finally selected as the emulsion of the aqueous colorful continuous phase in this experiment.

2.2 Effect of pigments and fillers on coating film properties
According to chemical composition, pigments are divided into two categories: organic pigments and inorganic pigments. The main factors that determine the light resistance and weather resistance of pigments are the chemical composition and structure of the pigments. Related to pigment particle size. In general, inorganic pigments have better light resistance and weather resistance than organic pigments, and the smaller particle size of organic pigments will affect the later storage stability of water-based colorful coatings, causing problems such as bleeding and post-thickening. Take carbon black and iron black paste as an example: the same color of carbon black paste and iron black paste are used, and the same formula is used for grinding to test the effect of pigment types on the color bleeding performance of the particles. The results are shown in Figure 2.

Fig. 2 The Effect of Pigment Types on the Bleeding Property of Gel

In this experiment, the inorganic pigments are iron oxide red paste, iron oxide yellow paste, and iron oxide black paste, which can improve the weather resistance of the product and avoid problems such as bleeding and post-thickening. However, the compatibility of color pastes and colorful paints from different manufacturers is also significantly different. In this experiment, iron oxide red, yellow oxide, and black oxide black pastes from 4 different manufacturers were used for experiments. The experimental results are shown in Table 9.

Color Paste Compatibility Experiment

It can be seen from Fig. 2 that the base paint colored with iron black paste has a small absorbance of the dispersion medium after granulation and better anti-bleeding performance; while the base paint colored with carbon black paste has a larger absorbance of the dispersion medium after granulation. The bleeding is severe. This is due to the small particle size of the carbon black paste, which is more likely to penetrate out of the flexible film, leading to the bleeding of the base coating; on the contrary, the particle size of the iron black paste is larger, is more stable in the base coating, and does not easily penetrate the flexible film , Better anti-bleeding performance.
It can be seen from Table 9 that the color pastes of different manufacturers have certain effects on the color bleeding, post-thickening and storage stability of the products. This is because the dispersion wetting agents used by different manufacturers in the preparation of color pastes have a certain effect. The types and dosages are different, and the types and dosages of dispersing wetting agents have a greater impact on the bleeding and post-thickening of colorful coatings. Therefore, in this experiment, three color pastes in scheme X2 were used to prepare a highly weather-resistant self-cleaning water-based colorful paint.

2.3 Screening of auxiliary types
This experiment mainly screens preservatives for multicolor coatings, because cellulose and protective gum will be used in a large amount during the preparation of water-based multicolor coatings, which provides a large number of nutrients for microorganisms. The presence of microorganisms will cause various problems to the product, such as: reduced viscosity, odor, latex demulsification, etc., and eventually lead to product scrap. Therefore, the correct selection of preservatives can effectively avoid the above situations, ensure product quality, improve production efficiency and product storage stability. And this experiment research is a green environment-friendly product that meets the entire life cycle, then the product must meet the T / CPCIF 0001-2017 “Green Design Product Evaluation Technical Specification Water-based Architectural Coatings” standard requirements, so the selection of preservatives should meet the green environment For the requirements of raw materials for friendly coatings, three preservatives were selected for testing. The test results are shown in Table 10.

 Preservative Test Results

It can be seen from Table 10 that with the increase of the amount of preservatives, the storage performance of the product improves, but the T / CPCIF 0001-2017 “Technical Specification for Evaluation of Green Design Products Water-based Architectural Coatings” standards for heavy metal content and The biocide content is strictly required. The amount of preservatives directly affects the content of heavy metals in the product and whether the biocide content meets the standard requirements. It can be seen from Table 10 that there is no significant difference in the storage stability of the schemes Y2 and Y3, but the GB / T35602-2017 “Green Product Evaluation Coatings” standard requires that the content of chloromethylisothiazolinone / methylisothiazolinone be less than 15 mg / kg, and the isothiazolinone content in the preservative C is 0.6%, and the isothiazolinone content in scheme Y3 exceeds the standard requirements. Therefore, the preservative B was used in this experiment to prepare a highly weather-resistant self-cleaning water-based colorful paint.

2.4 Effect of overcoat varnish on film performance
Water-based colorful paint itself has certain weather resistance and self-cleaning ability, but it is not enough to meet the requirements of the northern environment where the ultraviolet rays in the sun are relatively strong and the wind is dusty. The coating of the coating is covered with a denser protective film to improve the coating’s service life and self-cleaning ability. This dense protective film is a gloss varnish. The introduction of overcoat varnish is mainly to improve the weather resistance and self-cleaning ability of the coating, but under the premise of meeting high weather self-cleaning, other physical and chemical properties of the product must also be taken into account. In this experiment, three kinds of latex were used to prepare the overcoat varnish, and the overcoat varnish and water-based colorful paint were overcoated. The product performance was tested. The test results are shown in Table 11.

Table 11 Properties of Overcoat Varnish Products

It can be seen from Table 11 that the comprehensive performance of the experimental scheme Z1 is superior to the experimental schemes Z2 and Z3, because the latex selected by Z1 is an organosiloxane monomer and acrylate having unsaturated bonds using a chemical copolymerization method Monomer-like copolymerization, modified silicone-acrylic latex with siloxane introduced into the polymer backbone. When it is dried to form a film, the siloxane is hydrolyzed and polycondensed to form a solid cross-linked three-dimensional network (—Si—O—Si—) structure between the polymer molecules and between the polymer and the substrate, so that the coating film is formed. Has strong water resistance and adhesion. In addition, polysiloxane molecules have a helical structure, and the methyl groups are arranged outward and rotate around the Si—O chain. The molecular volume is large and the cohesive energy density is low, so that the latex has strong weather resistance, water repellency and dust resistance. .
Comparing the test results of the experimental scheme Z1 with Table 8, the product’s resistance to artificial aging has been significantly improved, and the stain resistance has reached 0 level. It can be seen that the introduction of the overcoat varnish highlights the design concept of high weather resistance and self-cleaning.

3 Supporting Applications

The application of any product must have a suitable support to reflect its own value, so the comprehensive performance of the support is the complete reflection of the coating film. After more than a year of simulation experiments and practical applications, the best matching system for high weather-resistant self-cleaning water-based colorful paints was obtained, as shown in Table 12.

Table 12 Application and Supporting Parameters of Waterborne Self-cleaning Color Coatings with High Weather Resistance

The choice of flexible putty in this supporting system can to some extent make up for the disadvantages caused by wall cracks. The choice of alkali-resistant sealing primer and matching base color effectively improves the interlayer adhesion of the coating and makes the pattern and texture of the colorful topcoat. Melting into one, merging with each other, the combination of the final varnish makes the product significantly improve the weather resistance and self-cleaning ability. This package has been applied in batches to various types of high-end villas and residential areas such as commercial, public buildings and residences, as shown in Figure 3.

Fig. 3 Cases of Application

4 Concluding remarks
High weather-resistant self-cleaning water-based colorful paints are designed for the entire life cycle of the four major attributes of the product’s resource attributes, energy attributes, environmental attributes, product attributes, etc., and have formed a green product in a true sense. The product complies with T / CPCIF 0001-2017 “Technical Specifications for Evaluation of Green Design Products for Waterborne Architectural Coatings”, DB13 / 3005-2017 “Standards for Limits of Volatile Organic Compound Content in Architectural Coatings and Adhesives”, HJ 2537-2014 “Technical Requirements for Environmental Labeling Products for Waterborne Coatings”, Standard requirements of GB 24408—2009 “Limits of Hazardous Substances in Building Exterior Coatings” and HJ / T 4343—2012 “Water-based Colorful Architectural Coatings”
. At the same time, the supporting application technology of high-weather self-cleaning water-based colorful coatings was beneficially explored, and it was determined that it has both an environmentally friendly and self-cleaning coating supporting system, which provided an important reference for the supporting system of exterior wall products.

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