Guide to the use of defoamers for shoe coatings: scientific application helps upgrade quality

In the field of shoe manufacturing, the quality of coatings directly affects the appearance, durability and functionality of shoes. However, during the production, mixing, spraying and other processes of coatings, a large amount of foam is often generated due to various reasons. These foams will not only cause defects such as pinholes, pitting, and orange peel on the coating surface, but may also affect the adhesion and wear resistance of the coating, reducing the overall quality of the shoe. As a key auxiliary agent to solve the foam problem, the correct use of defoamers for shoe coatings is particularly important.

1. Analysis of the causes of foaming in shoe coatings

(I) Raw materials and formula factors

The composition of shoe coatings is complex, including resins, solvents, pigments, fillers and other substances. Some raw materials such as surfactants and dispersants, although they help to improve the performance of coatings, also have certain foaming properties. In addition, improper proportions of the components in the formula, such as too fast evaporation of the solvent, will cause the gas in the system to be unable to be discharged in time, thus forming foam.

(II) Production process and environmental impact

During the production process of paint, operations such as stirring and grinding will introduce a large amount of air. If it cannot be discharged in time, foam will be formed. In the shoe coating process, improper operations such as excessive spraying pressure and too close spray gun distance will also cause air to mix into the paint. At the same time, changes in ambient temperature and humidity, such as accelerated solvent volatilization in a high temperature environment, can also easily cause foam to form.

(III) Hazards of foam

The presence of foam not only affects the appearance quality of shoe materials, but also has a negative impact on their performance. Bubbles on the surface of the coating will leave pinholes after drying, reducing the waterproofness and anti-fouling properties of the coating; foam may also weaken the adhesion between the coating and the shoe substrate, causing the coating to peel off.

2. Principle of action of defoaming agent for shoe coating

The defoaming agent for shoe coating mainly achieves defoaming by reducing the surface tension of the foam and destroying the elasticity and stability of the foam film. The active ingredients of the defoaming agent can be quickly dispersed into the foam system, replacing the surfactant molecules on the surface of the foam and reducing the surface tension of the foam. Since the surface tension of the defoaming agent is lower than that of the foam liquid film, the foam liquid film will break due to surface tension imbalance. At the same time, defoamers can also destroy the elasticity of the foam film, making it impossible for the foam to return to its original state when disturbed by external factors, thereby accelerating the collapse of the foam.

3. Recommendations for the use of defoaming for shoe coatings

(I) Choose a suitable defoamer

Different types of shoe coatings, such as water-based coatings and solvent-based coatings, have different requirements for defoamers. Water-based coatings should use water-based defoamers, which have good water solubility and dispersibility; solvent-based coatings need to use solvent-based defoamers to ensure compatibility with the coating system. In addition, the formulation, application process and performance requirements of the coating should also be considered, and a defoamer with good defoaming effect, strong durability and no effect on other properties of the coating should be selected.

(II) Determine a reasonable dosage

The dosage of defoamer is not the more the better. Excessive use may cause new problems such as shrinkage cavities and fish eyes in the coating, and will also increase production costs. Generally speaking, the amount of defoamer added is between 0.1% and 0.5% of the total amount of the coating, and the specific dosage needs to be determined through experiments. During the test, the amount of defoamer can be gradually increased to observe the foam elimination and coating performance changes to find the best amount of addition.

(III) Correct addition method

The timing and method of adding defoamers will also affect their effect. In the coating production process, defoamers can be added in the grinding stage, paint mixing stage or finished product stage. Adding in the grinding stage helps to suppress the generation of foam in the early stage of coating preparation; adding in the paint mixing stage can eliminate the foam generated during the stirring process; adding in the finished product stage is suitable for coatings that are sensitive to foam. When adding, the defoamer should be added to the coating slowly and stirred thoroughly to ensure that it can be evenly dispersed in the coating system.

(IV) Precautions during construction

During the shoe coating construction process, attention should be paid to controlling the construction environment and operating process. Keep the construction site well ventilated to avoid high temperature and high humidity environment; adjust the spraying pressure and spray gun distance to avoid excessive mixing of air into the coating. At the same time, the coating after using the defoamer should be constructed as soon as possible to avoid long-term storage that may cause the defoamer to fail or the coating performance to change.

4. Storage and management of defoamers for shoe coatings

(I) Storage conditions

Defoamers should be stored in a cool, dry, ventilated warehouse, away from direct sunlight and high temperature environment. The storage temperature is generally controlled between 5℃ - 35℃. Too high or too low temperature may affect the performance of the defoamer. At the same time, prevent the defoamer from contacting with water, acid, alkali and other substances to avoid chemical reactions.

(II) Shelf life management

Different types of defoamers have different shelf lives, generally around 6-12 months. Before use, check the shelf life of the defoamer to avoid using expired products. For unopened defoamers, they should be stored in accordance with the requirements of the product manual; for opened defoamers, they should be sealed in time to prevent them from volatilizing or being contaminated.

(III) Safety precautions

Some defoamers may be toxic and irritating. During use and storage, pay attention to personal protection and wear protective equipment such as gloves, masks and goggles. If it accidentally comes into contact with the skin or eyes, rinse immediately with plenty of water and seek medical attention in time. In addition, the discarded defoamer should be handled in accordance with relevant regulations to avoid pollution to the environment.

The correct use of defoamers for shoe coatings is a key link in ensuring the quality of shoe coatings. By understanding the causes of foaming, mastering the working principle of defoamers, and rationally selecting, using and storing defoamers, the foam in the coating can be effectively eliminated and the quality and performance of shoe materials can be improved. In the actual production process, shoe manufacturers should continuously optimize the production process and strengthen the application research of defoamers to meet the market demand for high-quality shoe materials.