What factors affect the adhesion of wood furniture

There are many factors affecting the adhesion of wood furniture paint film, which can be summed up mainly as follows: the wettability of the paint on the surface of the painted wood furniture substrate; the surface state and characteristics of the painted wood furniture substrate; the nature of the paint; the finishing process; the environmental conditions of use wait.

Wettability of coatings on the surface of painted wood furniture substrates

Wetting is one of the important factors in producing the adhesion of wood furniture coatings. In order for the paint to fully penetrate into the voids and pits on the surface of the painted wood furniture substrate, fully contact with the surface of the substrate to be painted, and generate interaction force, it is necessary to ensure that the paint can fully infiltrate the surface of the substrate to be painted, because only in close contact Good adhesion between wood and paint is required. If the paint cannot completely infiltrate the surface of the substrate to be painted, resulting in voids, air bubbles, uneven coating, etc., these places will not produce adhesion, and will also cause stress concentration in the coating and reduce the adhesion of the paint film. The wettability is affected by both the surface tension of the paint and the surface tension of the substrate of the finished wood furniture. Complete wetting occurs when the surface tension of the coating is less than that of the finished wood furniture substrate. Therefore, the smaller the surface tension of the paint, the better the wettability, and the higher the surface tension of the painted wood furniture substrate, the more conducive to the complete wetting of the paint. Reducing the viscosity of the paint, improving the fluidity of the paint, and increasing the surface temperature of the painted wood furniture board can all improve the fluidity of the paint, thereby improving its adhesion.

Surface state and characteristics of painted wood furniture substrates

The surface state of the painted wood furniture, such as the surface chemical structure, properties, cleanliness, roughness and surface temperature, etc. all directly have a great influence on the adhesion of the wood furniture paint film. At the same time, the characteristics of the substrate, such as the density and hardness of the substrate, and the moisture content of the substrate also have a certain influence on the adhesion of the paint film.

chemical properties of the surface

The surface tension and polarity of the surface of the coated substrate will affect the wettability of the coating and the formation of chemical bonds. Before finishing, chemical treatment and coupling agent treatment are carried out on the surface of the painted wood furniture substrate, which can significantly improve the adhesion of the paint film.

cleanliness

The surface of the painted wood furniture base material often absorbs moisture, dust, and some have attachments such as oil stains, wood chips, and glue marks. Some wood itself contains oil, for example, the branches of pine contain a lot of oil. These dirt and water-reducing extracts between the paint film and the substrate will hinder the contact between the paint and the real wood surface. Reduce wettability of paint. At the same time, the cohesive force of these attachments is much smaller than that of the coating, and it is easy to detach inside the attachments. These will reduce the paint film adhesion. Therefore, the surface of the substrate to be painted needs to be clean, dry and free from oil.

Sanding quality (usually measured by surface roughness)

The surface of the painted wood furniture substrate has a certain roughness, which can increase the bonding strength of the coating, enhance the mechanical force, and prevent the expansion of tiny cracks in the coating. However, if the surface of the substrate is too rough, it not only affects the wettability of the paint, but also prevents the paint from completely penetrating into the surface of the substrate, which seriously affects the adhesion of the paint film, and is prone to other defects such as air bubbles, which reduces the bonding strength of the coating. All wood furniture needs to be sanded before finishing the base material. Since the wood mainly consists of organic complexes composed of cellulose, hemicellulose and lignin, when subjected to the stress of sanding, it may It causes the breakage of the polymeric molecular bonds on the wood surface to generate some new functional groups. These free radicals have high surface activity within a certain period of time, and can produce a series of chemical reactions with paint molecules to form new connections, which help to improve the surface adhesion of paint films. At the same time, sanding changes the microscopic geometric unevenness of the wood surface, forming unevenness on the surface, making the actual contact area between the coating and the rough surface much larger than its geometric area, and also increasing the adhesion of the paint film. However, the smaller the surface roughness, the better. If the roughness is too small, the surface is too smooth. The force that holds the substrate and the coating together is the interface attraction per unit geometric area, which reduces the adhesion of the paint film. Therefore, the surface roughness of the wood furniture substrate must be moderate.

Substrate moisture content

The moisture content of the wood furniture base material has an important influence on the adhesion of the paint film. Since wood is a porous, anisotropic material, it is hygroscopic and can lose or absorb water from its surroundings. The fiber wall shrinks when water is removed and expands when water is absorbed. Changes in the size of the wood will cause the paint film to crack and fall off, which will seriously affect the adhesion of the paint film. Therefore, the moisture content of the base material of the painted wood furniture should be strictly controlled. When the moisture content of the substrate is higher than 15%, it is not suitable for finishing. Excessive water content will affect the infiltration and diffusion of the paint, reduce the viscosity of the paint, and at the same time cannot make the water in the paint volatilize quickly, making it difficult to cure the paint film and reduce the bonding strength of the paint film. On the other hand, if the water content is high, in the process of wood furniture finishing, due to the loss of water, shrinkage will form internal stress on the coating interface, weakening the adhesion of the paint film.

Density and hardness of substrate

For wood, wood with high density is more rigid than wood with low density, and wood with high density will shrink and expand more than wood with low density within a certain range caused by changes in humidity. Generally speaking, the adhesion of wood with high density is greater than that of wood with low density; the wood with high hardness has greater adhesion than wood with low hardness.

surface temperature

A certain surface temperature can increase the fluidity and wettability of the paint, thereby improving the adhesion of the paint film on wooden furniture. In winter, the temperature is relatively low and it is difficult to adhere. Coatings cured at room temperature have much lower film adhesion than heat cured coatings.

For more details, please refer to the full text of "Factors Affecting Wood Furniture Paint Film Adhesion" (Chen Xiulan, Shen Liming)