Paint film or ink film adhesion detection

The paint film or ink film adhesion refers to the ability of the paint film or ink film and the surface of the adhered object to adhere to each other through physical and chemical action. From a practical point of view, adhesion refers to the force required for the paint film or ink film to be removed from the print. This force is the bond of the paint film or the ink film and the base film. The adhesion of the paint film or ink film is one of the important indicators for assessing the performance of the paint film or ink film. Only the paint film or ink film has a certain adhesion, and it can adhere well to the surface of the base body. Will play the role of paint or ink adhesion and protection, to achieve the purpose of applying paint or ink.

First, the film or ink film adhesion mechanism

There are two kinds of adhesion mechanisms of paint film or ink film: mechanical adhesion and chemical adhesion. Mechanical adhesion depends on the nature of the base acquisition (roughness, porosity) and the strength of the paint film or ink film formed. Chemical adhesion refers to the mutual attractiveness of the interface film or ink film molecules and the base-collecting molecules between the paint film or the ink film and the base film, and depends on the physical and chemical properties of the paint film or the ink film and the base film.

When people explain the adhesion mechanism of the paint film or ink film, it is generally believed that the chemical attachment theory is more realistic. Among the cohesive forces that are chemically attached, include electrostatic forces, van der Waals attractive forces, hydrogen bonding forces, and chemical affinities. These forces determine the adhesion of paint or ink to the surface of the base body:

1. The degree of wetting of an object by a liquid film-forming substance;

2. Formation of a directional adsorption layer on a solid surface;

3. A two-electron layer caused by the boundary between the film formation and the solid surface during the formation of the paint film or ink film.

Therefore, in the study of the adhesion of the paint film or ink film, determine the kind of paint film or ink film tear off from the object

Type is very important and can be roughly divided into the following three types.

(1) Adhesion type: The paint film or ink film completely falls off the surface.

(2) Cohesive type: The paint film or ink film is cracked or lifted, and the adhesive force is greater than the cohesive force.

(3) Mixed type: The paint film or the ink film partially falls off from the surface, that is, the paint film or the ink film itself is partially split, and the adhesive force is close to the cohesive force.

It is generally believed that the adhesion of the paint film or ink film depends on the polar group of the polymer (or lower molecular weight prepolymer) in the film-forming substance, such as -OH, or - the polar group of the COOH and the base surface In order to combine these polar groups with each other, polymer molecules must be required to have a certain degree of fluidity, so that the polymer molecules can better wet the base mining surface, so that the polar groups of the polymer are close to being The polar surface of the imprinting surface, when the distance between the two molecules becomes very small (reaches within 1 A), the adhesion equilibrium between the polar groups due to van der Waals forces or hydrogen bonding.

Second, the method of measuring paint film or ink film

We use two kinds of paint film or ink film adhesion measurement methods: one is the direct determination method for the force required to separate the paint film or the ink film from the surface of the print, and the other is the paint film or the ink film in other. Indirect measurement method for performance measurement.

1 . Direct adhesion measurement method

(1) Twist method (peel test method)

(2) Pulling method

(3) Ultrasonic Oscillation Test

(4) Ultracentrifuge adhesion test

(5) B, B Adria adhesion test

(6) Adhesion test method

2. Indirect adhesion assay

(1) Determine the adhesion of paint film or ink film on a press

(2) Method for determining the flexural strength and elasticity of a paint film or ink film

(3) Determination of adhesion of paint film or ink film by knife cutting

Third, the factors affecting the film or ink film adhesion

1. Polarity adaptability of paint film or ink film and printed surface

From the molecular structure, molecular polarity and intermolecular interaction forces. It is known that the adhesion of the paint film or ink film results from the mutual attraction between the molecular polar group orientation of the polymer in the paint or ink and the polar groups of the polar molecules on the printed surface. Only when the polar bases are suitable for the two will get a better adhesion film or ink film. Otherwise, polar paints or inks are printed on non-polar objects, or non-polar paints or inks printed on polar objects do not give good adhesion to the paint film or ink film. For example, vinyl chloride paint on metal plates has poor adhesion. Epoxy paint on vinyl sheets also has poor adhesion. This shows that in order to get a good adhesion must select the object corresponding to the paint or ink polarity.

2. Adhesion of paint film or ink film to printed surface

The degree will increase as the polarity of the film increases. Therefore, adding various polar substances to the film-forming substance will increase the adhesion.

3. The presence of dirt, grease, dust, etc. on the metal plate surface reduces the polarity of the metal surface and causes the adhesion to decrease.

4. The decrease of the polar base on either side of the paint film or the ink film and the base mining surface is a factor that affects the adhesion of the paint film or ink film.

5. The decrease of the polarity point in the film or ink film will also reduce the adhesion. For example, when the amino paint dries to form a film, the -OH of the alkyd resin is further cross-linked with the -CH2OH of the amino resin and is continuously consumed. Causes the constant decrease of the attachment polarity point. This is one reason why adhesion of aminoalkyd paint has dried up. Therefore, the longer the paint dries, the more the paint adhesion decreases.

In addition, the self-association of polar groups in the polymer molecule can also result in a decrease in the polarity point and a decrease in adhesion. For example, the adhesion of an epoxy resin to a metal mainly depends on the hydrogen bond formed between the epoxy resin and the metal, but -OH is dispersed at an appropriate distance and it is difficult to attract each other, and the polar group is not reduced. The good adhesion of the paint film to the metal surface depends not only on the polarity but also on the mobility of the molecules.

For macromolecules in macromolecules, it is difficult to move, and their solutions are coated on the metal surface. Due to the poor orientation of macromolecules, polar groups do not easily act as adsorptive. This is the lacquer, perchloroethylene. The main reason for low paint adhesion. On the contrary, if a lower molecular weight film-forming substance is printed on the metal surface, the low-molecular polar group can easily adsorb on gold.

On the surface, get a good adhesion. Just like the resol phenolic resin paint made of vegetable oil has good adhesion.

In the film-forming substance-pigment-object surface system, there is no possibility of direct contact between the pigment and the surface of the object because the polar groups of the film-forming substance molecules can not only be oriented on the surface of the object but also on the surface of the pigment particles. The top is oriented so that the non-polar part of the molecule does not allow the pigment to come into contact with the surface of the object.

Fourth, the paint film or ink film adhesion and cohesion of the relationship between

The force caused by the cohesion between molecules of the same kind is called cohesion. The greater the cohesion of the printing layer, the worse the adhesion. On the contrary, the better the adhesion. Therefore, the cohesion can be reduced to achieve the purpose of improving adhesion.

1. Reduce the thickness of the film, reduce the cohesion, and increase the adhesion of the paint film or ink film to the object.

2. Add appropriate amount of pigment to reduce the cohesion and increase the adhesion strength of the paint film or ink film to the object, so the paint or color film ink has better adhesion than the clear ink. In the drying process, paint or ink will volatilize with the solvent, and cross-linking will cause shrinkage of the paint film or ink film, resulting in reduced adhesion.

3. Effects of surface tension and wetting on the adhesion of the printing layer.

(1) The adhesion of the paint film or ink film results from the mutual attraction between the paint or the polar groups on the surface of the paint and ink, and the mutual attractiveness of the polar groups depends on the paint or ink on the surface of the base body. Wetting ability, the ability of this lacquer or ink to wet the surface of the base stock is in turn dependent on the surface tension. Therefore, lowering the surface tension can improve the wetting efficiency and increase the adhesion of the paint film or ink film to the surface of the material.

(2) The paint or ink must exhibit good flow dynamics in the application, even if powder paint or ink must also achieve flow dynamics. The printed surface is wetted by the flow of paint or ink for adhesion purposes. It is generally believed that the paint or ink is not wet well, the interface contact is small, and the adhesion is poor. On the contrary, the paint or ink is wet well, the interface contact is large, and the adhesion is good.

(3) The solvent's ability to dissolve the resin is poor, which often causes the polymer to form a coiled structure, which causes poor wettability to the object and causes a decrease in the adhesion of the paint film or ink film.

(4) The presence of low molecular weight substances or auxiliaries (such as stearates, plasticizers, etc.) in the paint or ink will form weak interfacial layers between the printed layer and the substrate, reducing polarity. , reduce adhesion.

In addition, the surface of the material is often not pure, and often there are impurities such as water, dust, acids, and alkalis, which can cause weak interface layers and reduce adhesion.

4. Effect of thermal expansion coefficient on adhesion of paint film or ink film

Any material affected by temperature changes, they shrink and expand to a different extent (because of different expansion coefficients), so when the paint or ink is printed on the surface of the object, due to thermal expansion and contraction, the paint or ink and printed The adhesion points between the surfaces are damaged to varying degrees. Therefore, the smaller the coefficient of thermal expansion of the paint or ink, the better the adhesion of the printing film. For example, the coefficient of thermal expansion of epoxy resin is smaller than other resins, so the epoxy resin has good adhesion. It is generally believed that the coefficient of expansion of the paint film or ink film is significantly greater than the corresponding coefficient of the printed matter, so when the temperature changes, the degree of expansion or contraction of the paint film or ink film is relatively large, causing corresponding deformation of the paint film or ink film. Produces wrinkles, cracks, etc., which reduces the adhesion of the paint film or ink film.

5. Effect of surface treatment of base mining on adhesion of paint film or ink film

(1) Base sandblasting and emery cloth sanding can both increase the adhesion of the paint film or ink film, because the surface becomes rough and uneven, so that the effective adhesion area increases.

(2) Remove surface dirt and obtain a polar surface. Therefore, the more thorough the surface treatment, the better the adhesion. However, the surface to be treated must be applied immediately and it should not be placed too long, otherwise it will affect the adhesion of the paint film or ink film.

(3) The material of base mining also affects the adhesion.

Reprinted from:Trade Forum