YU Guo-ling1 , WANG Xue-ke2 (1.Nanyang Agricultural Vocational College, Nanyang 473000, Henan, China; 2.Nanyang Wolong Paint Co., Ltd., Nanyang 473000, Henan, China)
Abstract: The function and effect of auxiliaries for waterborne coatings are introduced. The performance and application range of different types of waterborne auxiliaries are compared and analyzed. The selection principle of additives for water -based coatings is clarified: considering the variety of the coatings, the properties of the dispersing medium, the state and characteristics of the pigment surface, the interaction between the auxiliaries, the interaction and preparation of the additives and the components of the water based coatings. It is the premise to choose the suitable additives and the addition amount by the test, and to keep the essential characteristics of the assistants and the stability of the coating system.
With the global implementation of water-based paint, States Regulations have clear restrictions on VO C emissions. Policy pressure and a sense of social responsibility have driven the waterborne revolution in the coatings industry. The development and application of waterborne resins have also made great breakthroughs. The application of various additives to the research and development of waterborne coatings Development is very important.
Common additives for water-based coatings are: wetting and dispersing agents, film-forming auxiliaries, thickeners, substrate wetting agents, defoaming agents, matting agents, surface control agents, anti-corrosion and anti-mold agents, matting agents, corrosion inhibitor Wait. The development of waterborne coating additive industry has a great restrictive effect on the development of waterborne coating industry. The amount of additives in water-based coatings is not much, but it plays a key role in the performance of coating products.
1 Water-based additives and selection
1.1 Wetting and dispersing agents
In the wetting process, the reasons for slow wetting are: small diffusion pressure; small gaps between pigment particles; and high coating viscosity. The types and characteristics of wetting and dispersing agents for water-based coatings are listed in Table 1.
Wetting and dispersing agent selection basis: can effectively reduce surface tension; small amount; good compatibility with other components; unstable foam; no barrier to recoating.
1.2 Substrate wetting agents
The types and characteristics of substrate wetting agents for water-based coatings are listed in Table 2.
The selection basis of substrate wetting agent: small addition amount; no adverse effect on water resistance; fast construction; no adverse effect on interlayer adhesion; good addition; high cost performance.
1.3 Film-forming auxiliaries
Film-forming auxiliaries provide a site for the winding, diffusion, and fusion of latex molecular segments to form a film, usually a high-boiling-point solvent. However, in high-solids coatings, the film-forming aid easily swells the rubber particles, increases the viscosity, and even breaks the latex and gels, resulting in the coating being scrapped. The types and properties of film-forming additives are listed in Table 3.
The method for judging the pros and cons of film-forming additives is to determine the minimum film-forming temperature of the emulsion.
The basis for selecting film-forming aids: must be a strong solvent for the polymer; high film-forming efficiency; no adverse effects on the stability of the emulsion; small odor; small addition; can reduce the minimum film-forming temperature of the aqueous resin; Completely volatilized, does not affect the appearance and gloss of the coating film; good hydrolytic stability; low solubility in water; volatilization speed should be lower than water and ethanol; can be adsorbed on the surface of latex particles, has excellent coalescence properties; and water-based resin The compatibility is good.
The types and characteristics of thickeners are listed in Table 4.
Water-based paints are more prone to air bubbles than solvent-based paints. The reason for the bubbles in water-based coatings is that during the dispersion and construction of water-based coatings, bubbles are generated due to changes in the free energy of the system; the use of emulsifiers and wetting and dispersing agents causes the surface tension to decrease, which helps to generate and stabilize the foam. ; Adding thickener makes the bubble wall thicker and difficult to eliminate. In addition, the foaming tendency of the base material, the compatibility of various additives, the type and amount of the additives have a great impact on the generation and stability of the foam. The types and characteristics of defoamers used in water-based coatings are listed in Table 5.
Methods for evaluating defoamers: bubbling method, roller coating method, shake bubble method, specific gravity method, and the specific gravity method is mainly used in colored paint.
Detection method of defoaming ability: high-speed stirring method.
According to the resin, formula system, construction method, production process and other additives, the defoaming agent is selected through experiments. The general principles are: strong defoaming ability; does not affect other properties; no recoating obstacles; good stability. In low-viscosity latex paints or water-soluble paints, the amount of defoamer is 0.01% to 0.20%, and in high-viscosity latex paints, the amount of defoamer is 0.03% to 1.0%. %, In other water-based coatings, the amount of defoamer is about 0.10%.
Defoamers are generally added when the viscosity is high and dispersed uniformly. The dosage is generally between 0.5% and 1.0%, usually 1/3 ~ 1/2 in the dispersion stage, and 1/2 ~ 2/3 in the paint preparation stage.
The key to selecting a defoamer: if the compatibility is too poor, it may cause surface defects (such as shrinkage), and if the defoamer is completely compatible with the coating, the defoaming effect is not ideal. 1.6 Matting agents Selection criteria for
matting agents for
water-based coatings: refractive index of 1.4 to 1.6; wear resistance, scratch resistance; good dispersion.
Extinction of water-based coatings is mainly based on ultra-fine silica with a refractive index of 1. 4 6. The particle size and porosity of the matting powder are directly related to the matting effect. The particle size range of the commonly used matting powder is 3 ~ 7 μm, and about 5 μm is the best. The porosity is 1.2 ~ 2.0 m L / g between.
The influencing factors of the matting effect are listed in Table 6.
1.7 Surface Control Agent
The surface control agent for water-based coatings can control the surface smoothness, scratch resistance, blocking resistance, anti-sagging, water resistance, gloss, etc. The types and characteristics of surface control agents for water-based coatings are listed in Table 7.
2 Selection of additives
Auxiliaries should consider the properties of the dispersion medium, the state and characteristics of the pigment surface, the interactions between the additives, the interactions and constraints of the additives in the components of the aqueous coating, and the external conditions when selecting water-based additives Effect to minimize the negative effects of the additives. According to the requirements of paint manufacturing, storage, transportation and coating, for different paint varieties, choose the appropriate variety of additives. Under limited conditions, through experiments and comparisons, the types and amounts of additives can be determined, and the positive effects of additives can be exerted in a reasonable manner. Reasonably determine the relationship between the performance of coatings and coatings and the type and amount of additives, and find the best balance between performance and the amount of additives.
When selecting additives, we should overcome the dependence on existing additives, and actively explore the use of new additives, matching additives and environmentally friendly additives. Give full play to the positive effects of the matching additive system, while ensuring the stability of the matching additive system.
3 Development direction of water-based additives
Water-based additives will develop in the direction of performance compounding. While ensuring one property, it can also improve other properties, thereby reducing the overall cost of the formula. Strengthening the development of silicon-modified and fluorine-modified wetting agents and the application of other surfactants, multi-purpose, efficient, long-acting, environmental protection, safety, low cost, easy construction will be the future development direction of water-based additives. Reasonable selection and accurate and proper use of additives are particularly important for the development of water-based coatings industry.
According to the requirements of paint manufacturing, storage, transportation and coating, for different paint varieties, comprehensively consider the nature of the dispersion medium and the state and characteristics of the pigment surface, the interactions between the additives, and the interactions between the additives and the components of the aqueous coating. Actions and constraints, through experiments and comparisons to determine the appropriate varieties and additions of additives, the use of the prominent effects of additives, synergistic effects and characteristics of superimposed effects and other characteristics, the selection of an appropriate matching additive system is the key technology for selecting additives. Exerting the essential characteristics of matching additives and ensuring the stability of the coating system are the prerequisites for the selection of additives.