• Wettability of paint to substrate
    Wettability of paint to substrate

    2019-08-16

    Wettability of paint to substrate The adhesion of the paint film is caused by the mutual attraction between the paint and the polar groups on the surface of the coated substrate, and the mutual attraction between the polar groups is based on the premise that the paint is well wetted on the surface of the coated substrate.Since the wet condition of the coating on the surface of the coated substrate depends on the surface tension of the paint liquid, the surface tension of the paint is lowered to improve the wetting efficiency and enhance the adhesion of the paint film to the surface of the substrate. The wetting of the substrate by the coating is achieved by the flow of the coating.The paint liquid must have a good flow dynamics in the application, even if the powder coating must reach the flow dynamics; the coated surface can only be wetted by the flow of the paint liquid, in order to achieve the purpose of good adhesion of the paint film to the substrate.In general, the coating is not wet well, the interface contact is small, and the adhesion is poor; on the contrary, the coating is wet well, the interface contact is large, and the adhesion is good. When low-molecular-weight substances or additives (such as stearates, plasticizers, etc.) are present in the coating, they will form a weak interfacial layer between the coating and the object to be coated, which will affect the flow of the paint to the substrate. Moisture, reducing adhesion.In addition, when the surface of the substrate is adhered with impurities such as water, dust, acid, alkali, etc., it also causes the appearance of a weak interface layer between the paint film and the substrate, hinders the wetting action of the paint liquid on the substrate, and reduces the polarity point. , resulting in a decrease in the adhesion of the paint film. Sinograce Chemical hasproduces  chemical additives,semi-finished varnish coating, Acrylic Industrial Coatings, welcome to consult us.

    read more
  • Cohesion and thermal expansion coefficient of paint film
    Cohesion and thermal expansion coefficient of paint film

    2019-08-15

    Cohesion and thermal expansion coefficient of paint film The force caused by the cohesion of molecules of the same substance is called cohesion.The more cohesive the coating, the worse the adhesion.In the drying process of paint, with the increase of solvent volatilization and crosslinking degree, the cohesion between film forming material molecules increases, the film produces shrinkage phenomenon, and finally leads to the reduction of film adhesion.Therefore, the purpose of improving the adhesion can be achieved by adopting a method of reducing the cohesion of the paint film. Commonly used methods are: 1.Reduce the thickness of the coating, reduce the cohesive force, and improve the adhesion strength of the paint film to the substrate. 2.Add appropriate pigment to the paint to reduce the cohesion of the paint film and improve the adhesion of the paint film to the substrate.This is an important reason why the adhesion of paint to varnish is generally better. The difference in thermal expansion coefficient between the paint film and the substrate also affects the adhesion of the paint film.It is well known that as temperatures change, all materials undergo different degrees of volumetric contraction and expansion.When the coating is applied to the surface of the substrate, the bonding point between the coating and the surface to be coated will be damaged to varying degrees due to the influence of thermal expansion and contraction.Generally speaking, the coefficient of thermal expansion of the paint film is significantly larger than the coefficient of thermal expansion of the substrate. Therefore, when the temperature changes, the degree of expansion or contraction of the paint film is larger than that of the plate, which causes corresponding deformation of the paint film, resulting in wrinkles and moiré. Etc., reducing the adhesion of the paint film.The smaller the thermal expansion coefficient of the coating, the better the adhesion of the coating film. For example, the thermal expansion coefficient of the epoxy resin is smaller than that of other resins, so the adhesion of the epoxy resin paint film is good.

    read more
  • Polarity of paint film and painted surface
    Polarity of paint film and painted surface

    2019-08-06

    From the viewpoints of molecular structure, molecular polarity and molecular interaction force, the adhesion of the paint film results from the polar group orientation of the polymer molecules in the coating, and its polar group with the polar molecules on the surface of the coated object. The mutual attraction between each other.Only when the polar phase of the two is adapted to obtain a good adhesion film; on the contrary, a good polarity coating is applied to a non-polar plate, or a non-polar coating is applied to a polar plate. A paint film with good adhesion will not be obtained. A reduction in the polar basis of either the paint film or the coated surface will result in a decrease in paint adhesion: 1.There is dirt, grease, dust, etc. on the surface of the substrate, which reduces the polarity of the surface of the substrate and causes a decrease in adhesion. 2.A reduction in the polarity of the paint film also reduces adhesion. For example, when the amino alkyd paint is dried into a film. The -OH of the alkyd resin is further cross-linked with -CH2OH in the amino resin and is continuously consumed, resulting in a continuous decrease in the adhesion polarity point, which is an important reason for the decrease in adhesion of the aminoalkyd paint after drying.The reduction of the polar spots in the paint film may be caused by the cross-linking reaction between different components in the paint, or by the self-bonding of polar groups in the polymer molecules.

    read more
  • Adhesion type and adhesion property of paint film on substrate
    Adhesion type and adhesion property of paint film on substrate

    2019-08-05

    Adhesion type and adhesion property of paint film on substrate The adhesion of the paint film to the substrate is divided into two types: mechanical adhesion and chemical attachment.Mechanical adhesion depends on the properties of the coated sheet (roughness, porosity) and the strength of the formed film; chemical adhesion refers to the mutual attraction of the paint film molecules and the plate molecules at the interface between the paint film and the sheet, depending on the paint film And the physical and chemical properties of the board.Compared with the two types, it is generally considered that the chemical adhesion is more realistic and is the most important type of film adhesion. Investigating the adhesion of the paint film to the surface of the object to be coated requires attention to three aspects: 1.Degree of wetting of the board by liquid film-forming substances 2.Formation of oriented adsorption layer on the surface of the substrate 3. Forming a two-electron layer at the interface between the film former and the substrate. The adhesion of the paint film depends on the polar group of the polymer (or lower molecular weight prepolymer) in the film-forming substance, such as -OH, -COOH, and the polar group on the surface of the object to be coated.In order to make such a polar group bond well, it is required that the polymer molecule has a certain fluidity, so that the polymer molecule can better wet the surface of the substrate, so that the polar group of the polymer is close to the polar group of the coated surface; The distance between the two molecules becomes very small (up to 1A), and the adhesion between the polar groups is due to the combination of van der Waals force, chemical affinity, hydrogen bonding and other cohesive forces.

    read more

Copyright © 2015-2019 Anhui Sinograce Chemical Co., Ltd..All Rights Reserved.powered by dyyseo.com

top