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

Abstract
: In the face of the severe environmental protection situation, according to the only industry standard of water-based automotive coatings HG/T 4570-2013 "Automotive water-based coating" requirements, research and development of engineering vehicles with environmentally friendly
water-based two-part epoxy primer
/
water-based two-part polyurethane coating
/
water-based dual-group polyurethane system
matching. The supporting system has good comprehensive performance, with excellent adhesion, water resistance, chemical resistance and weather resistance, all performance indicators meet or far exceed the standard requirements. Engineering vehicle water-based environmental protection coating products have been the whole vehicle coating, with a high gloss and fullness, can completely replace the traditional solvent-based similar products, with a huge market potential

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Introduction
With the increasingly serious industrial pollution and environmental damage, China is paying 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 have become the focus of domestic and foreign coating research because of their low toxicity, environmental protection and safety. 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.
2.1 Engineering vehicle water-based epoxy primer preparation
can be applied to the primer water-based paint resin many, but because the hydro-oxycodone 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 primer has 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 advantages of other resin coatings incomparable.
this study through a large number of domestic and foreign water-based epoxy coating literature and materials, and learn from the experience of domestic and foreign well-known water-based paint resin manufacturers paint, to determine the engineering vehicles with two-group water-based epoxy primer using imported H01 water-based epoxy multiple Amine curing agent, at the same time choose suitable pigments and water-based paint additives, prepared paint Group A distribution party see Table 1;
experiments to add pigments to water-like epoxy polyamine curing agents can avoid the phenomenon of abrasive emulsion in water-like epoxy emulsions.
E01 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 applicable period, fast drying, can meet the construction characteristics of the engineering vehicle water-based epoxy base raw materials water-based epoxy paint construction characteristics
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H01 is polyamine-epoxy plus, compared to the market commonly used dipolyacid acid and polyamine shrink into a polyamide curing agent, with fast drying, high hardness, good solvent resistance and so on, suitable for engineering vehicles with primer fast drying, good solvent resistance performance requirements
.The effect of pigment volume concentration (
PVC
) on the performance of water-based epoxy primers

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. As can be known from Table 2, when PVC is 30%, the experimental preparation of water-based epoxy primers have the best performance, with excellent mechanical and anti-corrosion properties.2.2
Preparation of paint in water-based polyurethane for engineering vehicles In-paint for engineering vehicles is used between engineering vehicle primers and finishes. 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. Generally the performance requirements of medium paint are: (1) with primer, paint has a good matching, strong binding force within the coating, moderate hardness; (3) good sanding, sanding non-stick sandpaper, good dryness, after polishing paint film flat, smooth; At present,
car coating line used in the paint more use of ammonia
-polyester system, part of the use of amino-acrylic system, are 130 to 150 degrees C high temperature curing system.
However, 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 the water-based two-part polyurethane is the ideal coating for engineering vehicles film substrate. According to the performance index of medium paint and the requirements of the composite coating supporting system, the design formula of water-based hydroxypropyl acrylic dispersion S01 was selected for the preparation of paint in water-based two-component polyurethane of engineering vehicles.
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 of the coating technology engineering vehicle,
should strictly control the temperature and relative humidity of the spraying workshop
, and control the temperature of the spray chamber by temperature and relative humidity regulation device at (23±2) degrees C, relative humidity (60±5 percent). 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.2.3
The preparation of water-based polyurethane paint for engineering vehicles
paint as the outermost layer of the supporting composite coating for engineering vehicles, mainly plays a protective and decorative role, determining the weather resistance and appearance of the coating
. Car paint needs to have the following characteristics: (1) good matching with medium paint, good adhesion, high gloss, high plumpness, high freshness, good weather 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, resistance to stone strike, 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; The engineering vehicle water-based two-part polyurethane paint formula S02, -OH content of 4.2%, solid content of 45%. 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. Therefore, the experiment finally selected sulfonate modified HDI type isocyanate curing agent Y01, with excellent water dispersion, high NCO content, ecological environmental protection, zero VOC emissions.
Engineering car paint coating appearance requirements are higher, need to solve the problem between flow hanging and leveling, leveling aid 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-shrinkable holes and orange lines and other surface defects,
this experiment selected TEGO482 leveling aid can significantly improve the flow of the paint when the film. 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. Through a large number of comparative experiments, combining cost, dispersion efficiency and media resistance, this experiment determined that it is more appropriate to add 1% TEGO757W dispersant.
Water-based two-part polyurethane coating dry is slow, can add a suitable catalyst to accelerate the reaction of isocyanate and active hydrogen compounds, thereby shortening the drying time, but need to pay attention to the catalyst on the water-based two-part polyurethane application period, need to be weighed between dry and adaptation period. Through a large number of experimental studies, it is shown that adding 2% organo tin catalyst LH-10 can effectively improve the dryness of water-based two-part polyurethane paint, which has no effect on the applicable period.
3 Conclusion
(1) Select the long-term, fast-drying internal emulsification E01 water-based epoxy dispersant and H01 water-based epoxy polyamine curing agent, prepare the application process requirements of the supporting system of water-based environmental protection coatings for engineering vehicles shown in the preparation of adhesion, using air spray construction methods For sand blasting after rust treatment of steel plate sprayed water-based epoxy primer / water-based polyurethane paint / water-based polyurethane paint, 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 two-component epoxy primer. When PVC is 30%, the prepared water-based epoxy primer has the best performance, with excellent mechanical performance and anti-corrosion performance;
(2) water-based two-component polyurethane coating has good flexibility, moderate hardness and good abrasion, etc. , this paper selects S01 hydroxypropyl acrylic dispersion design formulation preparation engineering vehicle water-based two-component polyurethane paint, each performance index meets the standard requirements;
(3) selected cost-effective domestic S02 water-based hydroxypropyl acrylic dispersion and yellow-resistant good HDI type isocyanate curing agent Y01, prepared a high hardness, high gloss, high plumpness and weather resistance outstanding engineering vehicle water-based two-pack polyurethane finish;
(4) developed the 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 or far exceed the HG/T 4570-2013 "automotive water-based coating" standard requirements.
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