Epoxy floor primer coating construction - whitening

There are many reasons that can cause paint film to turn white, mainly including:

（1） When the moisture content of the substrate is high or the construction environment humidity is high, after the paint is sprayed, the moisture will slowly penetrate outward. When it reaches the topcoat layer, due to the good density of the topcoat, the moisture cannot continue to evaporate outward, and the refractive index of water and paint film is different, resulting in whitening phenomenon. The thicker the topcoat is sprayed, the more obvious it becomes, and the longer it is sprayed, the more obvious it becomes.

（2） If the diluent is not used properly, there may be residual substances such as acid or alkali, which will slowly corrode the paint film and turn white over time.

The following issues with diluents in the market can cause paint to turn white:

1. Due to cost reasons, some more economical substances may be added to local solvents. For example, solvent oil, benzene, dichloromethane, or some recycled solvents contain residual substances that are difficult to evaporate and cannot dissolve the resin. After spraying, it will slowly precipitate, leading to whitening;

2. Some solvent components, such as alcohol solvents, react much faster with curing agents, consuming a portion of the curing agent, resulting in incomplete resin reaction and (- OH) absorbing water, leading to whitening;

3. Alcohol solvents can be mixed with a lot of water, even up to a 1:1 ratio, which dealers cannot detect. The most direct consequence of excessive water content is the whitening of the paint;

4. Due to varying degrees of differences in the product systems of different companies, the use of ammonia based drying agents requires a high water content in the solvent. If the solvent has a high water content, it is easy to experience whitening. In addition, the amount of trimer added to the fast drying curing agent is also relatively large, and trimer curing agents have very high requirements for solvent solubility and moisture content. Therefore, improper selection of diluent can easily lead to whitening phenomenon.

（3） If the amount of primer curing agent is too large, excess curing agent (- NCO) will slowly precipitate and oxidize in the paint film, resulting in whitening. This whitening phenomenon often occurs during seasonal changes. Due to the large temperature difference, the polishing performance of the primer will be affected, so more curing agent will be added.

（4） The curing agent used is not compatible, and some aspects of its performance do not meet the requirements.

In order to achieve the best effect of PU transparent primer and effectively prevent the paint film from turning white, some key points that must be paid attention to during construction are now proposed:

（1） Usage:

1. According to the specified ratio on the label (paint: curing agent), adjust the paint to the appropriate construction viscosity;

2. Construction viscosity: Iwata 2 # cup 12~18s (spray coating);

3. Useful time (after painting): ≤ 4 hours (25 ℃);

4. Must use our company's supporting products (paint, curing agent, diluent);

5. Paint and curing agents can react with water and moisture. If they cannot be used up in one go after opening, they must be resealed in a timely manner; If the viscosity of the curing agent has significantly increased, it cannot be used anymore;

6. The prepared paint must be used up within the usable time (4 hours), and unused paint cannot be added to the next prepared paint for use.

（2） Substrate processing:

1. For boards with a high moisture content (greater than 12%), they must be sealed with DiDebao first;

2. For areas with high environmental humidity, the board must also be sealed with DiDebao;

3. Special sealing primer for Changrun must be used for sealing, and ordinary transparent primer cannot be used for sealing (unable to achieve sealing effect)

（3） Construction conditions and methods:

1. Suitable construction environment: temperature 5-35 ℃, humidity ≤ 80%;

2. According to different construction environments, precautions must be taken during construction:

A、 Construction in high temperature and high humidity environments is prone to foaming, pinholes, and whitening (on-site whitening or later whitening);

B、 Construction in a low temperature and high humidity environment results in slow drying of the paint film, slow and incomplete solvent evaporation, and is prone to later whitening;

C、 To avoid the problems that are prone to occur during construction in the above two environments, thin spraying must be used instead of thick coating. It is important to distinguish between winter and summer diluents;

3. The time between two reapplication: more than 5 hours in summer and more than 10 hours in winter;

4. Before applying interlayer coating, it must be carefully polished to avoid poor adhesion;

5. Before applying the topcoat, the primer must be thoroughly dried for at least 24 hours in summer and at least 48 hours in winter (if the temperature is too low, the drying time needs to be extended);

6. During the work process, ventilation must be maintained to reduce the concentration of solvents in the air, which is conducive to drying;

7. The surface of the paint film after construction should be exposed to the air as much as possible to allow the paint film to dry completely.

Attention: The difference between the environment in which furniture paint is applied and the environment in which it is placed. Furniture coated with high moisture content boards in high humidity environments and placed in low humidity environments are prone to deformation, cracking, and whitening of the paint film.