An LCD Plant Tackles Global Warming - Toshiba Matsushita Display Technology Co., Ltd.

JFS Newsletter No.54 (February 2007)
Toward a Sustainable Japan--Corporations at Work Article Series No.58
http://www.tmdisplay.com/tm_dsp/en/index.html

Personal computers, mobile phones, car navigation systems, televisions, DVD players, and digital cameras -- all these information-related devices use liquid crystal displays (LCDs) for their screens. The LCD business has been growing into one of Japan's key industries, and the demand for LCDs is expected to continue expanding even further. However, compared to the final assembly of digital devices and home appliances, the manufacture of LCDs, semiconductors and other electronic device parts consumes massive amounts of energy, and the industry has been called upon to promote in-house global warming measures.

As a global corporation that produces digital and electronic devices, social infrastructure, and home appliances, the Toshiba Group is committed to tackling global warming, and is focusing its efforts on its electronic device business because this sector accounts for about 70 percent of the group's total energy consumption (CO2 equivalent), while accounting for only 20 percent of total sales.

This article introduces Toshiba Matsushita Display Technology Co. (TMD), part of Toshiba Group's electronic device manufacturing team, focusing on its LCD plant's efforts to tackle global warming.

TMD was established in 2002 after a merger of LCD businesses that served Toshiba Corporation and Matsushita Electric Industrial Co. The company enjoys a reputation for its technological excellence in the area of small- and medium-sized mobile displays. Along with four domestic plants, TMD has manufacturing subsidiaries both in and outside Japan and 15 sales offices. It has roughly 2,700 employees and sales are estimated at 320 billion yen (U.S.$ 2.7 billion) for fiscal 2006.

TMD incorporated a wide range of anti-global warming initiatives in a new LCD manufacturing line that was installed in its Ishikawa Plant in November 2005 and started operations in April 2006. Compared with conventional manufacturing lines, the new line is expected to achieve a 53 percent reduction in greenhouse gas emissions.

The new line incorporates three types of anti-global warming strategies, including one that was introduced into LCD manufacturing for the first time.

The first strategy was to conserve energy in cooling water used in air conditioning. The LCD manufacturing process requires a highly clean environment in order to maintain product quality, and air conditioning is always used to control cleanliness, temperature and humidity in cleanrooms.

To regulate room temperature, 14-degree C (Celsius) water suffices, but 6-degree C water is needed to regulate humidity. Formerly, 6-degree water was used to regulate both room temperature and humidity, but the new line uses two systems with different water temperatures: 6-degree water for controlling humidity and 14-degree C water for controlling temperature to increase cooling efficiency with less energy input.

Ishikawa Prefecture where the plant is located has severe winters, and another way the company attempts to reduce total energy consumption is to use cold air from outside to cool down the air conditioning coolant water from December to March. Many other factories belonging to the Toshiba Group and located in areas with cold winters have adopted this system.

Another strategy was to build a "ballroom" type cleanroom, and to make effective use of under-floor air-conditioning/recirculation passages. A "ballroom" means a large room without support pillars, like a room for social dancing or large parties. Conventional manufacturing lines consume a huge amount of energy because they consist of many small cleanrooms for individual work processes.

The new line improved space efficiency by eliminating room partitions and completing the manufacturing process in a single cleanroom. They also aimed to reduce power consumption by cleaning not the entire room but only individual pieces of manufacturing equipment and the transfer system that moves the substrate boards between machines.

Ordinary cleanrooms are two-storied: the second floor is used for production and the first floor for the passage of dirty air pulled down from the ceiling to the floor by the air conditioning system. The new line attempts to also use the first floor for production. If this idea can be realized, they can substantially reduce cleanroom floor space, allowing for further reductions in electricity consumption by air-conditioners, etc.

Ballroom-type cleanrooms have been adopted at some semi-conductor plants. However, it was thought difficult to do so in LCD plants, because LCD manufacture uses substrate boards larger than those used for semiconductors. The unprecedented production design of these cleanrooms, which incorporated less space for air recirculation passages, was the largest challenge in building the new line.

The design project team consisted of people from a variety of related departments, such as technical and product development, manufacturing and facility management. They worked together, carefully discussing and studying the design. The team completed a new cleanroom design that occupies about 44 percent less floor space compared with conventional designs by incorporating many innovations such as the installation of a cleaning unit on each piece of equipment, a system to control airflow during the transferring and loading of substrate boards, and cleanliness adjustment mechanisms for each process. As a result, the new design successfully reduced the use of building materials and cleaning units, minimizing initial construction cost as well as reducing the amount of energy consumed.

The third strategy was to reduce Perfluorocarbon (PFC) gas emissions. PFC gas, a kind of chlorofluorocarbon, has a greenhouse effect that is thousands to tens of thousands times greater than carbon's. PFC gasses, including CF4, SF6 and NF3, are indispensable in manufacturing LCDs. However, the resulting exhaust gas is resistant to decomposition with water. This gas was emitted directly to the surrounding environment.

In the new TMD line, PFC gas emissions were reduced by 90-95 percent by introducing cutting-edge equipment that renders PFC gas harmless by burning and decomposing the gas before adding water to it.

TMD also decided to replace NF3 gas with a type of fluorine that does not have greenhouse effect, and equipped the new line with Japan's first fluorine gas generator. The use of fluorine was known to reduce environmental impacts, but practical use of fluorine on a massive scale, as in mass production of LCDs, has been difficult due to constraints on the pressure and concentration of the fluorine in the process of putting it into a gas cylinder. TMD examined various ways to avoid using NF3, and finally employed a method developed by a British equipment manufacturer that applies electrolysis to fluorinated acid to generate the fluorine. The manufacturing line has operated smoothly and brought about substantial results.

The LCD industry set a worldwide goal to reduce PFC gas emissions to the year 2000's level by 2010. As LCD production is expected to experience a 3- to 5-fold increase by 2010, this target value appears extremely ambitious.

In order to meet this target value, TMD is planning to expand to other lines the PFC gas reduction technology demonstrated in the new line. TMD also hopes to develop new technology to utilize used PFC gas without releasing anything to the surrounding environment.

According to preliminary calculations, the new line incorporating all these innovations will reduce greenhouse gas emissions to 28,258 tons of CO2 equivalent annually, while a comparable conventional line would emit 60,082 tons annually. This achievement is imminent. The engineers who participated in launch of the new line are striving to solve issues in order to achieve further reduction of greenhouse gasses.

(Written by Eriko Saijo)