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. Sinograce Chemical produces water-based acrylic coatings for various water-based coatings visit us sinograce chemical: https://www.sinogracechem.com Get a Quote Now :sales@sinogracechem.com Telephone               :+86 0551 63459511

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. Sinograce Chemical produces water-based acrylic coatings and Polyurethane resin for various water-based coatings visit us sinograce chemical: https://www.sinogracechem.com Get a Quote Now :sales@sinogracechem.com Telephone               :+86 0551 63459511

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 liquidfilm-formingsubstances 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 thepolymer(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. Sinograce chemical company produces water-based glue, including polyurethane glue and acrylic glue, which are used in various fields. For more information, please click here visit us sinograce chemical: https://www.sinogracechem.com Get a Quote Now :sales@sinogracechem.com Telephone               :+86 0551 63459511

Some surface properties of plastic substrate affect coating, and the properties related to coating mainly include the following aspects: Due to the characteristics of the plastic substrate itself, its smooth and compact, low surface energy is not conducive to the wetting and adhesion of the coating on the substrate. The crystallinity of the plastic affects the adhesion of the film, and its crystallinity is between the fiber and the rubber. High-density, low-molecular-branched resins have a high degree of crystallization, such as polyethylene surfaces, which are difficult to coat. The thermal deformation properties of plastics. Thermoplastics are softened and deformed by heat, and thermosetting plastics are excessively decomposed by heat. Therefore, plastic coating drying is usually low temperature baking and drying. Plastics have poor solvent resistance, and most thermoplastics, such as ABs, Ps, and PCs, are very sensitive to solvents. In the coating process, the coating solvent system is not similar to the plastic substrate, it is difficult to wet, the adhesion is poor, and the solvent is excessively dissolved on the plastic substrate, which may cause the plastic substrate to crack. Certain additives used in the assembly and molding process of plastic products, such as the migration of plasticizers to the surface or the release of the release agent to the surface, affect the adhesion of the coating to the substrate. Plastic is an insulator with a strong static. Therefore, it is more difficult to coat and adhere the coating on the substrate in the coating of plastic products: the surface treatment must be carried out before the plastic coating, the surface state of the plastic is changed, and the wet spreading and adhesion of the coating is improved.Common surface treatments include dust removal, static elimination, and degreasing.Plastic is a poor conductor, easy to generate static electricity, will absorb a lot of dust and debris during storage and transportation, usually use surfactant solution to wash the surface dust, remove static electricity.The plastic product is added with liquid wax during the molding process to facilitate demolding, and the plastic product is added with a plasticizer, and the migration to the surface affects the wet adhesion and the hardness of the coating film, so the surface is degreased with an organic solvent. Sinograce Chemical company produces a variety of functional chemical additives, such as crosslinking agents, wetting agents, used in various fields in various fields, if you want to learn more, please click here. visit us sinograce chemical: https://www.sinogracechem.com Get a Quote Now :sales@sinogracechem.com Telephone               :+86 0551 63459511