Adhesion of film to solid surface

The performance (adhesion) that paint film (coating film) can firmly adhere to the painted surface is one of the most important properties of paint coating film.

The concept of so-called adhesion (tackiness) is the performance of mutual bonding between the paint film and the painted surface (bottom surface).

If the paint film does not have good adhesion to the surface, it is impossible to form a coating with corrosion resistance and weather resistance. The better the paint film adheres to the metal it is used for, the better it will protect the metal , so that it is not affected by various destructive factors, which is often the case in tests. The paint film has high physical and mechanical properties (water resistance, hardness, elasticity), but at the same time it cannot adhere well to the metal surface. knots, and are prone to brittleness from the surface, so cannot prevent corrosion. (Related instruments: adhesion Tester)

Adhesion (adhesion) of a paint film to a surface is caused by several factors: 

(1) The wettability of the liquid film-forming substance to the surface; 

(2) The formation of a directional adsorption layer on the solid surface;

(3) During the formation of the paint film, a double electron layer is caused on the boundary between the film former and the solid surface, and these properties depend on:

(1) The difference between the charge of the paint film and the solid surface (metal);

 (2) The presence of polar molecules in the film-forming substance; 

(3) Set force on the surface at the boundary of the liquid film-forming temperature or the paint film and the solid surface; 

( 4 ) the characteristics and state of the solid surface; well depends on ( 5 ) the thickness of the paint film,

Determining the adhesion of the paint film to the surface is of special interest when testing paint films based on polymeric resins, but until now, methods for measuring adhesion have not been widely used in industry. And in most cases it has not been continued into the technical conditions of paint materials.

This is because, until now, there has not been a calculable method for determining the adhesion of any paint film, because each method is firstly limited in application and secondly, the individual methods lead to incomparable results.

Certain methods for testing the adhesion of film removal can still be used to test paint materials, because when selecting a test, it is generally necessary to indicate which method is suitable for measuring the adhesion.

The determination of paint film adhesion can be summarized as follows:

(1) Direct measurement of the force required to separate the paint film from the painted surface, 

( 2 ) The indirect measurement method in the performance test of paint film.

The main methods for determining adhesion can be divided into three categories:

(1) The method is based on the determination of the force required to tear off a certain area of ​​the paint film perpendicular to the surface of the paint film. Paste on the surface of the new paint removal film;

(2) A method based on peeling off the paint film directly from the surface and measuring the work done by peeling off;

(3) Methods based on the determination of resistance. These methods are based on the principle of wedge shape, the principle of side cutting and the principle of moving the paint film with a knife edge. The resistance when force is applied

Indirect methods for determining adhesion can be divided into four categories:

(1) Method for measuring the impact strength of paint film;

(2) The method for measuring the flexural strength and elasticity of the paint film;

(3) The method for measuring the friction resistance strength of the paint film against abrasive materials; 

(4) The method of measuring the hardness of the paint film by scratching. (Related instrument: Hardness Tester)

The mechanical properties of a paint film depend to a large extent on how well the paint film adheres to the substrate. Therefore, when testing these properties, the adhesion of the paint film can be measured from the evolution at any time according to the damage characteristics of the paint film under any kind of mechanical action. If the twists and turns are cut, the paint film is easy to separate from the surface when the adhesion is poor. When the adhesion is good, it is very difficult to remove the paint film from the surface, even under mechanical action. The medium adhesion can be expressed by whether the paint film can be removed at the cutting place by a knife edge, a knife, etc. .

When studying the adhesion of the paint film, it is very important to determine the type of paint film tearing off from the bottom surface. Croto's surname determines three types of paint film tearing according to the paint film; 

(1) The type of adhesion—the paint film is completely peeled off from the surface, and the adhesion force is less than the cohesion force; 

(2) The type of cohesion——the paint film is made to spread out, and the opening force is greater than the cohesion force; 

(3) Mixed type—the paint film is partially peeled off from the surface—the paint film itself is partially drawn, and the adhesion is close to the cohesion.

A better method for measuring the adhesion of paint films is based on tearing off the film from the surface and measuring the work done during the peeling process. A method based on the determination of the resistance of the film against the base is considered to be a good method, either when a stress acting on the wedge principle is applied, or when a cutting film is applied and a strip cut by the knife edge is applied. The principle of moving to the side is carried out when the stress comes into play.