Method for improving adhesion of polyurethane coating on stainless steel substrate

Abstract
Through the analysis of the causes of poor adhesion of polyurethane magnetic paint on stainless steel surface, and by improving the wetting effect of the coating film, reduce the surface pressure of the coating film, improve the amount of pigment, reduce the internal polymerization of the coating film, improve the amount of adhesion promoter, reduce the amount of low molecule (plasticizer), reduce the thermoal expansion coefficient of the coating and other effective means to improve the adhesion of the polyurethane coating on the stainless steel surface.
Foreword
Polyurethane magnetic paint by short lysolate resin preparation of the substrate, additives, pigments, organic solvents, such as the composition of the A component, group B is divided into pre-polymer containing toluene isocyanate as a curing agent, when used in a proportional modulation. Polyurethane magnetic paint has high hardness, good gloss, fast drying, good adhesion, good protection function, good decoration, good plumpness, excellent resistance to chemicals, acid, alkali, saline and other characteristics .
for the problem of poor adhesion of polyurethane magnetic paint on stainless steel substrate, this experiment improved the polyurethane magnetic paint, so that the product has a greater range of use.
factors that affect the adhesion of the coating film: there are
mechanisms for the attachment of the coating film: mechanical attachment and chemical attachment. Mechanical adhesion depends on the roughness of the substation and the material of the substation, rough through the small adhesion difference, rough through the large coating film easy to crack, and easy to wrap the gas, later may cause the coating film foaming and other ills. The different materials of the substation cause different sizes of surface stress, resulting in different coating adhesion.
chemical adhesion refers to the interface between the coating film and the substrate coating film and substrate molecules mutual attraction, polyurethane magnetic paint is containing 2 or more kinds of official energy groups react with each other into a film. The factors affecting the adhesion of the coating film are shown in Figure 1.
1.1 Effect of wetting efficiency
Effect of wetting effect on adhesion
Wetting is a necessary standard when examining adhesion, and only works when the substrate and coating reach effective wetting. The wetting of the surface can be described from a thermodynamic point of view, the surface stress of the coating at liquid state and the surface energy of the substrate and solid coating film are important parameters affecting the strength of the interface connection and the formation of adhesion. It is generally believed that the adhesion of the coating film depends on the polar group of the polymer in the film-forming substance, such as the binding with the polar group on the surface of the substrate. In order to combine well, it is necessary to require the polymer to have a certain amount of fluidity, so that the polymer molecules better wet the substrate surface, so that the polymer's polar group close to the applied surface of the polar group, when the distance between the two molecules becomes very small (up to 0.1 nm), polar groups due to the role of Vanderwal force or hydrogen bonds to produce an attachment balance. Reduce the thickness of the film, reduce the cohesion force, improve the adhesion strength of the coating film to the object. However, the coating film is too thin easy to lead to the coating can not form a film or can not play a protective role. Add the appropriate amount of pigment, reduce cohesion, improve the adhesion strength of the coating film to the object, so the color paint is better than varnish adhesion. 1.2 Thermal expansion coefficient affects because the expansion coefficient is different, any substance temperature is different, they shrink and expand to different degrees, so when the coating is applied to the surface of the object, affected by thermal expansion and cold contraction, the coating and substrate contraction or expansion is different. Therefore, the smaller the change of the coating in the process of heat expansion and cold contraction, the better the adhesion of the coating film. For example, epoxy resin has a small coefficient of thermal expansion, so epoxy resin adhesion is good. 1.3 The effect of the substrate surface blasting and sandpaper polishing or chemical treatment can increase the adhesion of the coating film, because the surface becomes rough and uneven, so that the effective adhesion area increases. Remove dirt from the surface to obtain a polar surface. So the more thoroughly the surface is treated, the better the adhesion. However, the treated surface must be applied immediately and should not be placed too long, otherwise it will affect the adhesion of the coating film. The material of the substrate also has an effect on adhesion.
results and analysis
2.1 wetting dispersant on the effect of adhesion coating film adhesion is produced between the coating and the applied substrate surface polar group of gravity between the mutual gravity, and the mutual gravity between this polar group is based on the coating on the surface of the coated substrate good moisture conditions. Since the wet condition of the coating on the surface of the coated substrate depends on the surface pressure of the coating, the wet dispersant BYK-P104S is added to reduce the surface pressure of the coating in order to improve the wetting efficiency and enhance the adhesion of the coating film to the substrate surface. Dispersants can reduce the interface between liquids/solids, improve the dispersion efficiency of pigments in the resin, and good dispersion can make the coating surface more flat. 2.2 The force caused by the cohesion between molecules of similar substances caused by the addition of resin on adhesion is called cohesion. The greater the cohesion of the coating, the lower the leveling and wetness, resulting in poor adhesion. In the process of drying and curing the film, with the degree of the volatile and cross-linking reaction of the solvent, the cohesion between the molecules of the film material slowly increases, and the coating film produces contraction, which eventually leads to the reduction of the adhesion of the coating film. Therefore, we through the DYS-637 resin addition of different amounts to change the method of coating film polymerization to achieve the purpose of improving adhesion, commonly used methods are: to the coating appropriately increase the amount of pigment, reduce the film polymer force, improve the adhesion of the coating film on the substrate (polymer film has a certain contraction), in the polyurethane magnetic paint formula design, reduce the amount of resin, improve pigment quality score, can improve the adhesion of the coating film. 2.3 Effects of different adhesion promoters on adhesion
The structure of the coupled agents
when resins and additives in coatings have low molecular weight substances (e.g. stingrates, plasticizers, etc.), they create a weak interface layer between the coating and the coating, affecting the wetting of the coating to the substrate and reducing adhesion. Select adhesion promoters suitable for polyurethane resins to enhance coating adhesion to substrates. 2.4 The difference between the thermal expansion coefficient of the coating coating and the thermal expansion coefficient of the substrate affects the adhesion properties of the coating film, and with the change of temperature conditions, all materials will shrink and expand in different degrees. When the coating is applied to the substrate surface, the bonding point between the coating and the applied surface will be damaged to varying degrees due to the effect of thermal expansion and cold shrinkage. Generally speaking, the coefficient of thermal expansion of the coating film is significantly greater than the coefficient of thermal expansion of the substrate, so when the temperature changes, the expansion or contraction of the coating film is larger than that of the sheet, thus causing the corresponding deformation of the coating film, resulting in wrinkles, turtle lines, etc., reducing the adhesion of the coating film. The smaller the thermal expansion coefficient of the coating, the better the adhesion of the coating film, add inorder fillers to the formula, reduce the thermal expansion coefficient of the coating. 2.5 The effect of substrate surface treatment and roughness on adhesion substrate surface treatment and surface roughness: the substrate surface is treated by blasting, blasting, sanding, etc. to obtain surface roughness in accordance with specific requirements, increase the effective adhesion area, and improve adhesion. When the surface of the substrate adheres to water, dust, acid, alkali and other impurities, it will cause the appearance of weak interface layer between the coating film and the substrate, hinder the wetting effect of the coating on the substrate, reduce the polarity point, and lead to the decrease of coating adhesion. Stainless steel has unique strength, high wear resistance, superior corrosion resistance and not easy to rust and other excellent characteristics. When treating stainless steel surfaces, the choice of treatment methods and the improvement of surface roughness of substrates can affect the adhesion between coating layers. The surface of the substrate is not treated or the treatment is not clean, which has a great influence on the adhesion of the coating film. 2.6 The impact of the construction process on adhesion construction process: the coating film in the drying furnace because the furnace temperature is too high or stay too long, light will lead to the coating film color change, heavy will lead to the coating film become brittle, poor adhesion. Reasonable construction process and standard operating order have a great impact on the performance of coating film, therefore, it is necessary to reasonably regulate the operation. Through the above experimental data analysis, the following conclusions are obtained: (1) the addition of wetting dispersants to the formulation design of polyurethane magnetic paint can improve the adhesion of the coating film. (2) In the polyurethane magnetic paint formulation design to reduce the amount of resin, improve pigment quality score, can improve the film adhesion. (3) In the polyurethane magnetic paint formula to add inorgable fillers, artificial aging performance has no effect, can improve the adhesion of the coating film. (4) The addition of castor oil to the polyurethane magnetic paint enhances the adhesion between the matching coatings.
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