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1、 Preface

Waterborne architectural latex paint is mainly composed of lotion, pigments and fillers, water and various functional additives. Although the amount of additives added is low, it directly determines the production stability, construction performance, and final appearance of the paint film. Wetting and dispersing agents, low foaming wetting agents, and defoamers are the three core types of additives in water-based building coatings. They play different roles in the grinding and painting stages. Improper combination of additives can easily lead to film defects such as shrinkage, pinholes, floating colors, and flower formation.

2、 Mechanism of action of main additives

1. Wetting dispersant

The function is divided into two processes: wetting and dispersion. Wetting is the process of replacing the air and water adsorbed on the surface of pigment fillers, allowing the resin water phase to fully infiltrate the particle surface; Dispersion is the process of breaking down aggregated pigment particles and preventing them from re aggregating through electrostatic repulsion and steric hindrance effects. Inorganic pigments such as titanium dioxide and calcium carbonate are easily dispersed; Carbon black and organic pigments have a larger specific surface area and require higher amounts of dispersants.

2. Low foaming wetting agent

Reduce the surface tension of the system, improve the wetting of the substrate, and solve the problems of missed coating and edge shrinkage in roll coating; Ordinary wetting agent is easy to bring in a large amount of foam. Low foam wetting agent is preferred for architectural coatings, taking into account both wetting ability and foam control.

3. Defoamer

Eliminating bubbles generated during production mixing, grinding, and application of construction rollers can be divided into grinding defoamers and paint defoamers. The two types of defoamers cannot completely replace each other.

3、 Reference for the amount of additives added (based on the total mass of the coating)

1. Inorganic pigments (titanium dioxide, heavy calcium, talc powder): dispersant 0.4% 1.2%

2. Carbon black/high pigment organic color paste: dispersant 1.2% 2.5%

3. Low foaming wetting agent: 0.1% 0.4%

4. Defoamer: 0.15 0.3% in the grinding stage, and 0.1 0.2% in the paint mixing stage. The actual amount needs to be gradient tested according to the total amount of pigments and fillers and the type of lotion. Excess dispersant will cause water resistance decline and gloss loss of the paint film; Insufficient usage can cause the pigment to become rough and float.

4、 Sequence and process of additive addition

1. Grinding stage (high-speed dispersion and pulping): First, add water and neutralizing agent, then add dispersant and grinding defoamer, and finally add pigments and fillers for high-speed grinding. The grinding stage mainly relies on dispersants to stabilize the pigment, combined with shear resistant defoamers to eliminate the large number of bubbles generated during grinding.  

2. Paint mixing stage: add lotion, then add wetting agent, paint mixing defoamer, film forming agent, preservative and thickener. It is not recommended to increase the dosage of dispersants during the paint mixing stage, as it can easily cause system imbalance.

5、 Common paint film defects and solutions for additives

1. Floating color and blooming: mismatched dispersant selection and insufficient dispersion; Can replace dispersants that are compatible with pigments, optimize grinding time, and appropriately mix with wetting agents.  

2. Pinhole: foam is not completely eliminated; Grinding and painting should be done in two stages, and defoamers should be added. Do not add them all at once to avoid excessive concentration of defoamers in certain areas.  

3. Shrinkage: Poor compatibility or insufficient wetting of defoamers; Reduce the amount of defoamer added, use low foaming wetting agents to improve substrate wetting, and prohibit excessive addition of organosilicon defoamers.  

4. Storage and coarse flocculation: Insufficient dosage of dispersant causes secondary agglomeration of pigments and fillers, requiring reassessment of dispersant grade and dosage.

6、 Interference between additives

Wetting agent will weaken the defoaming ability of defoamer. After adding more wetting agent, foam is easy to regenerate repeatedly; Therefore, a balance test should be conducted for both wetting agents and defoamers, and it is not possible to increase the use of a single additive. There is a compatibility conflict between some anionic dispersants and some thickeners, so pay attention to the feeding interval during the paint mixing stage.

7、 Summary

Additives for water-based architectural coatings are not simply added according to the formula dosage, but should be comprehensively adjusted in combination with grinding process, pigment type and lotion system; Distinguishing the division of labor between the grinding section and the paint mixing section, and paying attention to the antagonistic effect between additives, is the key to reducing coating defects.