Environmental protection and cost reduction techno

2022-08-16
  • Detail

Environmental protection and cost reduction technology of automotive coatings and coatings since entering the 21st century, the world-wide important topic in the field of automotive coatings and coatings is to meet the requirements of the times: environmental protection, energy saving and resource saving, and reducing coating costs on the basis of high quality. From the perspective of preventing air pollution, it is required to reduce the emission of VOC (volatile organic compounds); From the point of view of preventing global warming, it is required to reduce CO2 emissions; From the perspective of preventing water pollution and overcoming global water shortage, it is required to save water consumption, improve water recycling efficiency, and achieve zero discharge; At the same time, for sustainable development, we must improve the utilization rate of resources; In order to realize cleaner production and with the increasingly fierce competition in the domestic and foreign automobile market, the profit margin has been greatly reduced. It is necessary to optimize the process and reduce the cost on the basis of ensuring high quality

the three coat coating system (3C3B) of car body: pre paint phosphating → cathodic electrophoretic primer → solvent based intermediate coating → solvent based topcoat (and the later topcoat coating process of primer + gloss varnish has become 4c3b coating system), which has a history of 30 years. In order to realize the above requirements of the times of environmental protection, energy conservation, resource saving and cost reduction, automotive coating has once again entered an era of renewal and revolutionary change; Relying on technological progress and updating concepts, the innovative situation of "major surgery" on the current 4c3b process has arrived. Foreign experience is that automobile factories, coating material companies and coating equipment and coating equipment companies work closely together to solve key problems, establish topics and divide responsibilities. In addition, Japan is characterized by an overall consideration of environmental protection (reducing VOC and CO2 emissions) and economy (reducing investment and operating costs). Japan's technical and economic indicators in terms of energy conservation, resource saving and coating cost reduction are at the world's leading level

at present, the painting process of car body in China is still a three coat painting process mainly consisting of cathodic electrophoretic primer, solvent based intermediate coat and topcoat. Since 2004, the new body coating line of Toyota, general motors, Honda and Mercedes Benz joint ventures in China has used water-based primer since it was put into production. Recently, the new line has begun to use water-based intermediate coat and water-based primer, which will promote the hydration of automotive coatings and coatings in China

in recent years, China's automobile production and sales have shown a leap forward development. In 2006, the automobile production exceeded 7million, and has become the third largest automobile production country in the world. If we do not pay attention to the emission of three wastes in the process of automobile coating, the consequences of damage to environmental protection and people's living environment will be unimaginable. The state should speed up the formulation of strict environmental protection laws and regulations, promulgate strict laws and regulations in line with international standards, and enterprises should treat and limit the discharge of three wastes independently

this paper uses the experience of foreign countries for reference, especially the environmental protection and economic overall consideration of Japan, whose climatic conditions and automobile production conditions are similar to those of China, and uses the experience of the original coating equipment as much as possible to introduce the environmental protection and cost reduction technology of automobile coating, so as to expand the thinking of Chinese people

progress in environmental protection and cost reduction technology of surface treatment before coating

nowadays, the phosphating process of three cation (Zn Ni Mn) type is widely used before cathodic electrophoretic coating of car body. In recent years, in order to implement the cleaner production standard, many new treatment agents and technologies have been developed, such as phosphorus free and nitrogen free biodegradable degreaser, new liquid surface conditioner, low temperature and low slag phosphating agent, organic accelerator without nitrite The goal of chromium free passivation and lubricant application: no passivation technology, cleaning water recycling technology (ultrafiltration, nano filtration and RO Technology) and closed cleaning "O" discharge technology, etc., so that the traditional phosphating pretreatment process has made great technological progress in energy saving, water saving, reducing the discharge of wastewater and waste residue, etc. However, due to the nature of zinc salt phosphating agent, the following problems are difficult to solve

① discharge wastewater containing substances harmful to the environment (Ni, Mn, P, etc.)

② phosphating slag generated when generating zinc salt phosphating film needs to be treated as waste

③ the surface adjustment process is required, and the surface adjustment process is automatically drained, and sewage treatment is required

in order to meet the requirements of the times of higher environmental protection, energy conservation and resource saving and the need to simplify the process and reduce costs, foreign countries have successfully developed phosphate free pre coating surface treatment technology, which has brought revolutionary changes to the traditional phosphating treatment technology. Relevant reports are as follows:

the phosphate free pretreatment technology introduced by Toyota Motor Company: the conversion film is amorphous zirconia (ZrO2), with a film weight of 100mg/m2 and a film thickness of 40nm; In terms of technology, the surface adjustment process is canceled, and the film-forming treatment time is shortened (120s → 90s); Thus, the equipment length and process time can be shortened; In terms of environmental protection: sediment is reduced by more than 90%, and P, Ni and Mn are eliminated; F ion is reduced to 70% of the original phosphating treatment process), which is one of the environmental protection coatings with excellent energy saving and appearance decoration. Ultraviolet (UV) curing and thermal curing can be used together, and the inner surface and shaded parts without UV curing also have sufficient film properties. Its curing process is as follows:

automatic electrostatic or manual spraying → drying at room temperature for 5min → heating I (heating to 110 ℃ for 10min, evaporation of solvent) → UV irradiation process → heating II holding temperature at 140 ℃ for 10 ~ 12min and having the potential of low temperature drying (90 ℃). The existing equipment can be used, and the length of drying room can be shortened, The transformation cost is less

uv and thermal double curing varnish have been used for motorcycle gasoline tank gloss coating. The motorcycle gasoline tank rotates in the process of coating and curing, so that the UV light exposed to all parts of the tank is uniform, without shadow, and to prevent defects such as vertical flow, uneven coating, flow marks and so on. Compared with the heat curing gloss coating line, the processing cost (including coating cost) of unit coating (oil tank) can be reduced by more than 50%

based on the above introduction: excellent coating appearance (as smooth as mirror, fresh pgd=1.0); The scratch resistance and acid rain resistance of the film are outstanding; Energy saving and reducing VOC emission are beneficial to environmental protection; It can also greatly reduce the coating cost; The reconstruction investment cost of the existing equipment is the least, and so on. The double curing gloss coating will be a highly competitive high solid and environment-friendly coating for automobiles, which deserves the attention of the automotive coating industry

progress in energy saving and CO2 emission reduction technology

according to the data of Japan atmosphere news agency, the annual production of 240000 car body coating equipment has an electric consumption of 6000 ~ 7000kw and an average annual heat consumption of 80000 ~ 90000mj/h. Converted into a line of CO2 emissions, the annual emissions of more than 40000 tons (169.6kg, co2/set). Among them, paint spraying room and drying room (including cooling room) are the main equipment that consumes energy (CO2 emissions), accounting for 42% and 6.8% respectively in terms of electricity, 49.7% and 27.3% respectively in terms of heat energy, and their CO2 emissions account for 64.8% of the total CO2 emissions. Therefore, 5754, etc., the paint spraying room and drying room have become the main innovation objects of the coating line to save energy and reduce CO2 emissions

◆ technological progress trend of saving energy and reducing CO2 emission in drying

nowadays, the typical painting process of car body is to paint electrophoretic primer, intermediate coat and finishing coat (primer and varnish). Generally, after painting a layer of paint, it is dried once and cooled once (4c3b), and the treatment temperature is about 140 ℃. The measures to save energy and reduce CO2 emissions are as follows:

① improve the drying performance of the coatings used (low temperature, rapid, self drying instead of drying)

② in the development of a complete set of automotive coatings suitable for the "wet touch wet" process, the drying process is cancelled or merged

③ select or develop innovative curing methods and energy-saving drying equipment for film, such as UV and thermal double curing methods and equipment

the "wet touch wet" process has been applied in practice, including the 3C1B intermediate coating and finish coating process in which the intermediate coating drying process is cancelled, and the three coatings of intermediate coating, primer and finish are dried together; And the 2c1b "wet touch wet" process of drying the electrophoretic primer together with the intermediate coat

although the "wet touch wet" process of two coatings of electrophoretic primer and intermediate coating can improve the degree of freedom of finish coating design, it must be dried above 150 ℃. If the interface of electrophoretic primer/intermediate coating is not fully controlled, rust resistance, yellowing resistance and cracking resistance may be reduced. There is also the coating of stone impact resistant underbody paint and other auxiliary materials, which needs to be comprehensively solved from the engineering surface

in recent years, foreign companies are developing self drying (air drying) PVC free underbody paint and weld sealant to replace the current PVC series underbody paint and weld sealant. Toyota is developing moisture cure polyurethane series underbody coating, which is a rubber type elastic deformation material without PVC, heavy metals and solvents, and is self drying without drying room. Apply after the body coating is qualified. It has crack resistance and sound damping function

◆ technical trends of energy saving and CO2 emission reduction in the paint booth

the average CO2 emission of coating equipment is 169.6/kg CO2/set, of which the CO2 emission of the paint booth accounts for 46.3% (78.6kg CO2/set)

the technical measures to reduce the CO2 emission of the paint booth are:

① selection of heating and cooling energy. If you turn the electrical switch on the panel and use natural gas as the heating source, the CO2 emission is less, which is more than 8% less than that of liquefied petroleum gas (butane)

② reduce the air volume in the paint booth. The CO2 emission of the paint booth increases or decreases with the proportion of the air supply volume of the paint booth, so reducing the air volume of the paint booth is the primary measure to reduce the CO2 emission

shortening the process length of the spray booth, reducing the width of the spray booth and reducing the wind speed of the spray booth are the three elements to reduce the air supply and exhaust volume of the spray booth. The above factors should be fully discussed in the aspects of coating process design, coating machine selection and air flow control technology

③ control the air conditioning temperature (the relationship between the set value of air supply temperature and humidity and CO2 emission)

keep constant temperature and humidity throughout the year without changing with meteorological conditions. The energy consumption and CO2 emission of the paint booth are the largest. Setting the temperature and humidity value range separately with the season can greatly reduce CO2 emission. If the range of annual management temperature is expanded according to the characteristics of water-based coatings (the dependence of water evaporation and saturation), the effect is greater. This is related to the spraying construction window of water-based coatings, and it is necessary to develop and adopt water-based coatings with a wide temperature range

④ improve the equipment by selecting energy-saving accessories and heat and kinetic energy recovery devices. Such as designing low-pressure loss cleaners and air conditioning devices, selecting high-efficiency motors, fans and lighting appliances, total heat exchangers and exhaust recycling

⑤ strengthen maintenance management during operation. If the paint booth stops running or reduces the air volume during the rest period, do not light the area stop light; Flexible application of frequency conversion technology, etc

my summary

* most of the environmental protection and cost reduction technologies of the above industrial coating are mature technologies that have been produced and applied abroad

* in recent ten years, the construction performance of automotive waterborne coatings has been greatly improved; It can be predicted that in the next decade, it will catch up with the level of organic solvent automotive coatings

* comprehensively innovate the coating process of automobile body. Toyota's 2010 goal of coating is no longer a dream. It will be achieved: reduce the coating cost by 50%, reduce the VOC emission by 87%, and pursue the goal of 10g/m2; Reduce CO2 emissions by 52%

* the top priority of the third largest auto producing country is to catch up in environmental protection and cost reduction. (end)

Copyright © 2011 JIN SHI