A complete guide to the use of water-based plastic paint wetting agents: a practical guide from addition to construction

A complete guide to the use of water-based plastic paint wetting agents: a practical guide from addition to construction

In plastic coating, water-based plastic paint wetting agents are the core additives to ensure the quality of the coating. However, if used improperly, not only can its performance advantages not be brought into play, but it may also cause coating defects such as shrinkage and poor adhesion.

1. Accurately calculate the amount of addition: the golden ratio to meet different needs

The amount of water-based plastic paint wetting agent is not a fixed value, and factors such as plastic material, paint liquid formula and performance requirements must be considered comprehensively. Generally speaking, the amount of addition ranges from 0.1% to 2% of the total amount of paint liquid, but in actual application, the optimal amount must be determined through scientific experiments.

(I) Adjust the amount according to the plastic material

The surface properties of different plastic materials vary significantly, and the demand for wetting agents is also different. For example, non-polar plastics such as polyolefins (PP, PE) have low surface energy and are difficult to wet, so the amount of wetting agent usually needs to be controlled at 0.5% - 2%; while for ABS and PC plastics with relatively high polarity, the amount of wetting agent can be appropriately reduced to 0.1% - 0.8%. Taking automotive interior PP material parts as an example, if the amount of wetting agent added is less than 0.5%, problems such as paint sag and shrinkage holes are prone to occur; excessive addition of more than 2% may cause the paint to dry more slowly, affecting production efficiency.

(II) Optimizing the amount based on the paint formula

The resin type, pigment type and filler content of water-based plastic paint will affect the appropriate amount of wetting agent. For paint systems with high solid content and high viscosity, the proportion of wetting agent needs to be appropriately increased to ensure the wetting effect; and for paints containing a large amount of pigments and fillers, due to the large specific surface area of the particles, the amount of wetting agent also needs to be increased to ensure dispersibility. It is recommended to use the "gradient test method": configure 5 groups of samples with different addition amounts (such as 0.3%, 0.6%, 0.9%, 1.2%, and 1.5%) in the laboratory, and screen out the addition ratio with the best comprehensive performance by observing the surface tension of the paint liquid, the leveling and adhesion of the coating.

2. Grasp the timing of addition: the key nodes of different processes

The timing of adding water-based plastic paint wetting agents directly affects its dispersion efficiency and final effect. Common addition stages include pre-mixing stage, grinding and dispersion stage, and paint mixing stage.

(I) Addition in the pre-mixing stage

Applicable to most conventional production scenarios. In the early stage of paint preparation, the wetting agent is pre-mixed with the water-based resin and part of the water, and stirred for 10-15 minutes to make it evenly dispersed. This method allows the wetting agent to reduce the surface tension of the resin solution in advance, creating favorable conditions for subsequent pigment dispersion. For example, when producing paint for the plastic shell of 3C products, adding a wetting agent in the pre-mixing stage can effectively prevent pigment agglomeration and improve the color uniformity of the coating.

(II) Addition in the grinding and dispersion stage

When dealing with pigments that are difficult to disperse or when the coating fineness is extremely high, a wetting agent can be added in the grinding stage. Through the mechanical force of equipment such as sand mills and ball mills, the wetting agent can penetrate deeper into the pigment aggregates and enhance the dispersion effect. Taking the production of metallic plastic paint as an example, adding wetting agents in batches during the grinding process can make metallic pigments such as aluminum powder evenly dispersed, avoiding problems such as flowery and floating colors.

(III) Addition in the paint mixing stage

If the wetting properties of the paint liquid need to be temporarily adjusted, the wetting agent can be added in the paint mixing stage. However, it should be noted that the amount added at this stage should not exceed 0.3% of the total amount, and it needs to be fully stirred (the recommended stirring time is ≥20 minutes), otherwise local poor wetting is likely to occur. For example, when shrinkage cavities are found in the paint liquid during trial coating, a small amount of wetting agent can be added to remedy the situation.

III. Choose the right method of addition: ensure uniform dispersion

The choice of the method of addition needs to be combined with the production equipment and the characteristics of the paint liquid. Common methods include direct addition, dilution and batch addition.

(I) Direct addition

Applicable to laboratory tests or small production equipment. Pour the calculated wetting agent directly into the mixing tank, turn on high-speed stirring (speed ≥ 800rpm), and quickly disperse the additive within 5-10 minutes. Be careful to avoid pouring a large amount of wetting agent at one time to prevent local concentration from being too high and causing agglomeration.

(II) Add after dilution

In large-scale industrial production, in order to ensure uniform dispersion of the wetting agent, it is often diluted into a 5%-20% aqueous solution before addition. Inject it into the mixing tank at a constant flow rate through a metering pump, while maintaining medium-speed stirring (speed 400-600rpm), and continue stirring for more than 30 minutes. This method is particularly suitable for paint systems with higher viscosity, and can effectively avoid coating defects caused by uneven dispersion of the wetting agent.

(III) Add in batches

For special plastic materials with extremely low surface tension, or products with extremely high requirements for wetting effects, it is recommended to add in batches. For example, add 60% of the wetting agent for initial wetting, stir for 15 minutes, and then add the remaining 40% of the wetting agent and continue to disperse for 20 minutes. This method allows the wetting agent to fully act on the plastic surface and improve the adhesion of the coating.

4. Construction precautions: Avoid common problems

(I) Surface pretreatment cannot be ignored

No matter what kind of wetting agent is added, the plastic surface must be thoroughly cleaned to remove impurities such as oil and release agent. It is recommended to use a combination of alcohol wiping + deionized water rinsing to ensure that the surface is clean and dry, providing a good foundation for the wetting agent to work.

(II) Control the construction environment conditions

The temperature and humidity of the construction environment have a significant impact on the wetting effect. The ideal construction temperature is 20-25℃, and the relative humidity is controlled at 40%-60%. Too high humidity can easily cause the coating to turn white, while too low temperature will prolong the drying time and affect the penetration effect of the wetting agent.

(III) Use other additives in combination

To achieve the best coating effect, water-based plastic paint wetting agents can be used in combination with additives such as leveling agents and defoamers. However, attention should be paid to the compatibility between the additives. It is recommended to conduct a small test evaluation first to avoid chemical reactions or performance conflicts.

Mastering the correct use of water-based plastic paint wetting agents is the key to achieving high-quality plastic coatings. From accurately calculating the amount of addition to scientifically controlling the construction details, every link requires rigorous operation. With the improvement of environmental protection requirements and the development of plastic coating technology, the use of wetting agents will continue to innovate.