A green and better paint finish at Mazda

Reducing VOCs and CO2 emissions have been contradictory aims in paintshop for many years, but Mazda has come up with a revolutionary solution

Mazda Motor Corporation recently announced the successful launch of the newly developed Aqua-tech Paint System for vehicle body painting at its Ujina Plant No.1, in Japan. This innovative technology achieves the world’s highest standards for limiting the emissions of volatile organic compounds (VOC) contained in the paint as well as for lowering the carbon dioxide (CO2) gas generated from the energy consumed during the vehicle painting process.

The Aqua-tech Paint System maintains the same worldclass low CO2 emissions volume as the Three Layer Wet Paint System — Mazda’s paint system currently installed at all of its production facilities in Japan — and reduces VOC emissions by a further 57 percent. At only 15 grams per square meter of vehicle body surface, the extremely low VOC emissions volume makes Aqua-tech the least polluting water-based paint system in the world. The new system also delivers improved paint quality.

Cleaner plant and brighter finishes

Water-based paints tend to produce far lower VOC emissions than solvent-based paints due to their low VOC content.

However, drying water-based paint consumes much more energy because the water must be evaporated using a forced drying process. The large quantities of carbon dioxide produced during this process have long been an issue.

The Aqua-tech technology includes the introduction of an improved paint shop air conditioning system and a new, highly efficient evaporation system that removes the water contained in the paint. In addition, Mazda has managed to consolidate the coating processes by developing topcoat paints that possess additional properties, properties that are usually provided by the primer paint.

These include brightness, durability and resistance to chipping and light damage. Two new types of topcoat paint were developed for the Aqua-tech Paint System: a water-based colour basecoat and the first urethane clear coat to be fully implemented by any company in Japan.

Heat and humidity – a delicate balancing act

By changing its approach to air-conditioning the paint booth, the team achieved a 34 percent reduction in energy consumption compared to conventional water-based paint booths.

Conventional water-based paint systems use air conditioning to maintain ideal conditions by keeping both the temperature and humidity at a fixed level. However, this consumes a considerable amount of energy, especially in summer and winter, to heat and cool the air inside and maintain humidity at the prescribed level.

After investigating various drying conditions, the team at Mazda found that the evaporation rate could also be controlled by adjusting the humidity level depending on the ambient temperature in the paint booth. This means that it is no longer necessary to maintain a fixed temperature in the booth.

Depending on the temperature of the air, there is a limit to how much water vapour it can absorb. The speed that paint dries depends on the difference between this limit and the amount of water vapour already in the air. This means that, even when the temperature or humidity changes, if this “difference” can be kept constant, it is possible to achieve a constant paint drying speed, and therefore a constant paint drying time.

Based on this theory, Mazda has developed a system that constantly controls the maximum water vapour absorption volume by monitoring the external air conditions and making the smallest necessary adjustments to temperature and humidity inside the paint booth. The system significantly reduces energy consumption.

Energy saving flash off process

With water-based paint systems, a preheating (flash off) drying process is applied between the base and clear topcoats. By evaporating the water contained in the base coat paint before applying the clear coat, the process is designed to improve the finished paint quality.

Usually the process involves raising the temperature to 80ºC until the paint is sufficiently dry. However, before the clear coat can be applied, the temperature must be reduced back down to 40ºC. If the vehicle body is too hot, the clear coat paint will dry before it has time to spread out, and the final finish will be impaired.

Conventional heating systems blow hot air into the paint booth. However, this method heats the steel vehicle body as well as the paint. Cooling the steel afterwards also consumes large amounts of energy.

In order to reduce the large energy demand for heating and cooling, the Aqua-tech paint system flash off process features an infrared heater. This heats only the paint surface, enabling the water solvent to be evaporated without heating the steel body. The heater can also be switched on and off quickly. This means the amount of heating can easily be optimized for each body size and paint colour. The technology means the water can be efficiently removed with the lowest possible electricity consumption.

Mazda’s flash off process also employs hot air as a support system to heat the vehicle body interiors — where it is hard to use the infrared heater — and efficiently ensure an even temperature throughout. This new system also minimizes the amount of energy needed for cooling, and results in a 17-percent reduction in CO2 emissions compared with common flash off processes.