Yi Shiming, Zheng Qi, Liu Zhanchuan, Liu Yanfei (Hebei Chenyang Industrial & Trade Group Co., Ltd., Baoding,Hebei 072550，China)
Abstract: Different commercialized dispersants are used to prepare coating films based on waterborne alkyd as main film-forming material in order to carry out a comparative study of film properties. Specifically, different fillers/pigments, additives and ratios thereof are applied to evaluate the testing results, analyze the dispersing mechanism and point out the specific difference between various dispersants in waterborne alkyd paints.
0 Introduction In the
past 30 years, China’s coatings industry has been undergoing reform and opening up. Promoted, environmentally friendly water-based coatings gradually entered every household. The traditional solvent-based coatings have gradually decreased their market share due to the large amount of organic volatile substances. Environmental pollution, air pollution, toluene and other auxiliary agents are becoming more and more familiar to people. Environmental protection has become a growing trend, and the research and development of water-based coatings has received more and more attention. It is a market trend that water-based coatings replace solvent-based coatings, and the concept of health and environmental protection is gradually becoming the main factor for people to choose water-based coatings.
Traditional coatings and inks require a large amount of organic solvents. With the depletion of petroleum resources, the prices of organic solvent products are getting higher and higher, and people’s awareness of environmental protection has increased, leading domestic and foreign researchers to pay more attention to water. Instead of organic solvents, prepare water-based coatings and inks (such as water suspending agents and water dispersible granules). As an important raw material of water-based coatings, the quality of dispersants determines the yield value of coatings and the gloss and hiding power of coatings.
Dispersant is also known as wetting dispersant. In addition to the same wetting effect of wetting agent, one end of its active group can be adsorbed on the surface of the pigment crushed into fine particles, and the other end solvates into the paint base to form an adsorption layer (adsorption The more bases, the longer the chain links, and the thicker the adsorption layer), the charge repulsion (water-based paint) or entropy repulsion (solvent-based paint) is generated, so that the pigment particles are dispersed and suspended in the paint base for a long time to avoid re-flocculation. The stable color paint system is stable. Most of the commercially available wetting and dispersing agents are anionic and non-ionic. Their principle is low surface tension, quickly wetting the pigment particles, and then using high shear forces, such as dispersers, grinding machines, etc. to form a semi-flocculated (or controlled flocculation) dispersion of the pigment particles . There are many types of dispersants. Preliminary estimates indicate that there are more than 1,000 substances in the world that have a dispersing effect. According to their structure, they can be divided into: ① anionic, ② cationic, ③ non-ionic, ④ amphoteric, ⑤ electrically neutral, ⑥ polymer (including high, medium and low relative molecular weight) hyperdispersants.
In this study, water-based alkyd resin was used as the film-forming carrier, and different dispersants were used to make the paint. Then its performance was verified and an experimental scheme was formulated. The resin has a low VOC content in the coating system prepared by using water and a small amount of a co-solvent as an aid, which meets the requirements of modern green industrial coating and environmental protection. Water-based alkyd paint is based on water-based alkyd resin. It has good wettability and dispersibility to pigments and fillers. The paint film has high gloss and good fullness. Because the alkyd resin is a condensate of an alcohol and an acid, it contains ester bonds that are easily hydrolyzed. The degradation causes the relative molecular weight to decrease, and the acid value to rise, leading to a decrease in dispersion stability and even delamination. So choosing the right dispersant is very important in waterborne alkyd paint system. In particular, polymer dispersants have significant effects on pigment dispersion, especially in terms of wettability and stability, and have greatly improved the application performance of pigments. They have become a new generation of highly effective dispersants.
1 Experimental part
According to the performance characteristics of different dispersants, equal amounts are added to the water-based alkyd decorative paint, a single variable experiment is performed, the chemical properties are tested, and a suitable dispersant is selected.
1.1 Experimental raw materials
TEGO Dispers 760W (approximately 35% active content): Deco; BYK-194: BYK, Germany; Water-based alkyd resin (solid content of 70%): Homemade; ethylene glycol butyl ether (BCS) : Commercially available; antirust fillers (composite zinc phosphate, aluminum tripolyphosphate), titanium dioxide, precipitated barium sulfate (1,500 mesh), neutralizer 1, neutralizer 2, defoamer, anti-settling agent, drier Agent, substrate wetting agent: commercially available.
1.2 Experimental instruments The
experimental instruments are shown in Table 1.
2 Experimental process
2.1 Selection of raw material selection
resin: Waterborne alkyd resin developed by the independent research and development team of Chenyang Industry and Trade Group as the carrier, its solid content is 70%, the resin has high gloss, good fullness, and has a relatively good effect on pigments and fillers. Good wetting and dispersing properties, and excellent water and weather resistance.
Solvent selection: BCS (ethylene glycol butyl ether) is used as a co-solvent, which mainly dissolves the resin and improves the surface leveling of the paint film. Its volatility is also one of the determining factors for the drying speed of the paint film.
Powder selection: Anti-rust filler (composite zinc phosphate, aluminum tripolyphosphate) is an important part of water-based coatings to obtain good anti-rust effect, which can improve the compactness of the paint film, enhance the mechanical properties of the coating, and improve water resistance The resistance to salt spray is also greatly improved. Aluminum tripolyphosphate can dissociate tripolyphosphate ions in coatings. Tripolyphosphate ions have a strong ability to capture metal ions, can effectively block metal ions to form inorganic polymer complexes, and passivate metal surfaces. , Play the role of chemical rust. Then it slowly decomposes into a dense orthophosphoric acid film, which isolates moisture, oxygen, and other metals from contact with it, and has the effect of blocking rust. Therefore, it has the dual functions of chemical corrosion protection and rust prevention.
Composite zinc phosphate is mainly composed of zinc phosphate, iron phosphate, alumina, and silica. The free phosphate ions contained in it form a passivation film and crosslink with other pigment ions to form a complex, which plays a protective role.
1. TEGO Dispers 760W: suitable for water-based formulations, especially for carbon black and organic pigments. Free of solvents and ethoxynonylphenol.
2. BYK-194: It mainly reduces the surface tension between molecules and thus accelerates the film formation and cross-linking physically. Has excellent storage performance and excellent viscosity reduction effect. Adding amount of dispersant: 0.3% (added during stirring).
2.2 Experimental formula The
basic formula is shown in Table 1.
3.3 Performance test The comparison of
performance is shown in Table 2.
2.4 Experimental results and retained
sample photos See Table 3 for experimental results and retained sample photos.
3 Concluding remarks
Water-based alkyd resin is used as a film-forming substance, supplemented with additives, powder paint test, and the single variable (dispersant) is changed to test various properties, including drying speed, water resistance, salt spray resistance, and heat storage And physical properties. Experiments show that TEGO (Digo) 760 w in water-based alkyd paint is superior to BYK194 except that it is slightly inferior in water resistance test. Therefore, TEGO760 w is more suitable for water-based alkyd decorative paint according to a large number of experiments.
Water-based alkyd paints include water-based alkyd steel structure paints, decorative paints, protective paints, and other types. They are inexpensive, have high gloss and fullness, and are suitable for different fields and coating surfaces. In the future, health, environmental protection, low VOC and high corrosion resistance will be water-based The development direction of alkyd paint, water-based coatings will definitely be the future development trend, and environmentally friendly coatings will be the new pattern in the future.