Research and Application of Water-based Environmental Protection Coating System for Engineering Vehicles

Introduction:
with the increasingly serious industrial pollution and environmental damage, China pays more and more attention to reducing and controlling the emission of organic matter such as VOC in coatings. At present, several provinces have promulgated VOC consumption tax regulations, aimed at rapidly promoting the development of environmentally friendly coatings. Water-based coatings, because of their low toxicity, environmental protection and safety and other excellent performance has become a hot topic in domestic and foreign

. The use of domestic water-based coatings mainly concentrated in the construction and wood industry, and automotive coatings use is very small, and mostly dependent on imported paint brands, which is mainly due to the technical comparison with foreign countries there is a large gap, the development of domestic water-based coatings is very slow. Automotive coatings as the highest performance requirements of the coating varieties, its coating process is also very demanding, automotive coatings and coating technology represents the highest level of contemporary coating industry development.
based on the development of water-based environmental protection coatings to replace traditional solvent-based coatings market needs, according to the only industry standard of water-based automotive coatings HG/T 4570-2013 "automotive water-based coatings" requirements, this research and development of engineering vehicles Water-based environmental protection coating supporting system, including water-based epoxy primer, water-based polyurethane paint and water-based polyurethane paint, all performance indicators meet the requirements of the standard technical indicators, can completely replace the traditional solvent-based supporting system, with great market potential.
1, engineering vehicle water-based epoxy primer preparation
can be applied to the primer water-based paint resin many, but because the water-based epoxy resin molecular structure contains epoxy, hydroxyl and ether bonds and other characteristic groups, the final performance of the primer plays an important role, so most as the first choice. Water-based epoxy primers have excellent adhesion to a variety of substrates (carbon steel, stainless steel, aluminum alloy, etc.), good water and acid resistance, alkaline, paint film shrinkage is small, high hardness, excellent electrical insulation, which is the incomparable advantages of other resin coatings.
water-based epoxy emulsion is the use of internal emulsification technology to particle epoxy resin, and evenly dispersed in the water dispersion, with a long application period, fast drying, can meet the construction characteristics of the engineering vehicle water-based epoxy base raw materials water-based epoxy paint construction. H01 is polyamine-epoxy plus, compared to the market commonly used dipolycic acid and polyamine co-combination of polyamide curing agent, with fast drying, high hardness, good solvent resistance and so on, suitable for engineering car primer fast drying, good solvent resistance performance requirements.
Pigment Volume Concentration (PVC) on the performance of water-based epoxy primers
Pigment Volume Concentration (PVC) affects the adhesion, flexibility and corrosion-resistant properties of water-based epoxy primer film, etc., suitable PVC is the key to the preparation of high-quality coatings.
PVC is too low, pigment particles can not be tightly accumulated, film occupies an excessive volume, PVC is too high, film can not effectively coat pigment particles, paint film tightness is not high, thus affecting corrosion resistance. When PVC is 30%, the experimental preparation of water-based epoxy primers have the best performance, with excellent mechanical and anti-corrosion properties.
2, engineering vehicle water-based polyurethane paint preparation
engineering vehicle paint is used for engineering vehicle primer and paint between the paint. Its main function is to improve the flatness of the finished finish by filling and correcting the surface of the work surface of the finished primer, greatly increasing the gloss, plumpness and freshness of the paint.
general performance requirements for medium paint are:
(1) and primer, paint has a good matching, strong binding force within the coating, moderate hardness;
(2) good fill, can fill, eliminate the surface defects of the primer layer,
(3) good polishing, sanding non-stick sandpaper, good dryness, after polishing paint film flat, smooth,
(4) good stone strike, paint film has excellent elasticity, can absorb a certain amount of shock energy.
present, the car coating line used in the paint more use of ammonia-polyester system, part of the use of ammonia-acrylic acid system, are 130 to 150 degrees C high temperature curing system. However, the engineering vehicles are mostly large vehicles, larger volume, and the use of vehicle spraying method, the existing engineering vehicle manufacturers can only meet the baking conditions of 80 degrees C, therefore, good flexibility of water-based two-part polyurethane is the ideal coating for engineering vehicles film substrate. In order to ensure the smoothness of the paint film in the water-based two-component polyurethane and the aesthetic aesthetics of the paint formula in the water-based two-component polyurethane engineering vehicle, the temperature and relative humidity of the spraying workshop should be strictly controlled, and the temperature and relative humidity control of the spray chamber temperature at (23±2) degrees C and relative humidity (60±5 percent) should be appropriate. After the vehicle has been sprayed, enter the flash dry area to allow slow evaporating of moisture to enter the oven at 80 degrees C baking 0.5 h.
3, the preparation of water-based polyurethane paint
paint for engineering vehicles as the outermost layer of the supporting composite coating for engineering vehicles, mainly play a protective and decorative role, determines the weather resistance and appearance of the coating.
car paint needs to have the following characteristics:
(1) and medium paint matching good, good adhesion, high gloss, high plumpness, high freshness, good weather resistance;
(2) high hardness, good resistance to scratches and stone strikes,
(3) excellent water, oil, chemical and salt spray resistance,
(4) acid rain resistance, wet heat change and temperature change resistance.
Therefore, the selection of water-based hydroxypropyl acrylic dispersion as the main resin, with isocyanate curing agent of the water-based two-component polyurethane coating not only meets the environmental requirements of automotive coatings, but also has a good adhesion, stone resistance, corrosion resistance and weather resistance, such as a series of excellent performance. The performance of water-based two-component polyurethane coating is mainly determined by the composition and structure of water-based hydroxypropyl acrylic resin, and the amount of reaction cross-link density is affected by the content of the -OH group on the molecular chain segment, which directly affects the adhesion, hardness and chemical resistance of the paint film. -The higher the OH content, the faster the reaction rate with the -NCO group, the faster the paint film drying, and improve the reaction cross-link density, so that the water-based two-part polyurethane paint film has a high hardness, high gloss, good chemical resistance; Another important parameter affecting the performance of water-based hydroxypropyl acrylic resin is the solid content, the lower the solid content, the higher the water content, the slower the paint film drying; Because of the high decorative paint for engineering vehicles, high weather resistance and other special requirements, so water-based hydroxypropyl acrylic dispersant curing agent can only choose weather resistance is particularly prominent, can withstand the sun and night dew, rain and wind conditions are not yellowing fat or lipid ring isocyanate curing agent. At present, the main commonly used are HDI diodes, HDI trimers and IPDI trimers. However, the price of IPDI trimer is high, and HDI trimer compared to HDI is not only fast drying, high hardness advantages, but also because of its self-clustering to form a stable hexaling ring structure, can further improve the lacquer film weather resistance.
Engineering car paint coating appearance requirements are high, need to solve the problem between flow hanging and leveling, leveling additives can reduce the surface pressure of the coating, increase the fluidity of the coating system under low shear stress, so that the paint film to achieve smooth, non-shrinking holes and orange lines and other surface defects. The high decorative requirements of paint coating for engineering vehicles require coatings with uniform dispersion, good stability, bright and bright paint film colors, the need to choose dispersants with high dispersion efficiency to improve storage stability, to prevent floating color, flowering and other problems. Water-based two-group polyurethane coating dryness is slow, can add a suitable catalyst to accelerate the reaction of isocyanate and reactive hydrogen compounds, thereby shortening the drying time, but it is necessary to pay attention to the impact of catalyst on the water-based two-part polyurethane application period, need to be weighed between dryness and adaptation period.
Conclusion
(1) Select the application period of long, dry fast internal emulsified water-based epoxy dispersion and water-based epoxy polyamine curing agent, preparation adhesion shows the engineering vehicle water-based environmental protection coating supporting system coating process requirements, the use of air spray construction methods, sand blasting After rust removal treatment, the steel plate is sprayed with water-based epoxy primer/water-based polyurethane paint/water-based polyurethane finish, the production of engineering vehicle water-based environmental protection coating supporting composite coating model, excellent, suitable for engineering vehicles with fast-drying, solvent-resistant good water-based double-component epoxy primer. When PVC is 30%, the prepared water-based epoxy primer has the best performance, with excellent mechanical and anti-corrosion properties;
(2) water-based two-component polyurethane coating has good flexibility, moderate hardness and good abrasion, etc., select water-based hydroxypropyl acrylic dispersion design design formulation engineering vehicle water-based bi-component polyurethane paint, all performance indicators meet the standard requirements;
(3) select water-based hydroxypropyl acrylic dispersion and yellow-resistant good HDI-type isocyanate curing agent, preparation of high hardness, high gloss, high plumpness and weather resistance outstanding engineering vehicle water-based two-part polyurethane paint;
(4) developed engineering vehicle water-based two-part epoxy primer / water-based two-part polyurethane paint / water-based two-part polyurethane paint matching good, all performance indicators meet the HG/T 4570-2013 "automotive water-based paint" standard requirements.
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