Epson's Industrial Inkjet Technology Improves Quality and Shrinks Environmental Impacts

Inkjet head used in the TFT panel alignment layer deposition process

Epson's proprietary Micro Piezo inkjet technology is used in more than just print heads. It is also employed in the fabrication of high-temperature polysilicon TFT liquid crystal panels for 3LCD projectors. The first trials involving industrial inkjet technology began at Epson's Suwa Minami Plant in 2005. Let's check in on what's happening now, and look at a program that uses this core Epson technology to shrink environmental footprint in manufacturing while simultaneously improving quality.

Shooting for quality with a low environmental impact

In 2005, Epson successfully demonstrated the world's first practical industrial application of inkjet technology, in a system for depositing liquid crystal alignment layers on panels for 3LCD projectors. Alignment layers were conventionally formed by using a flexographic printing process to transfer the material for the alignment layers from a printing plate to the glass substrates. The flexographic process, however, is not conducive to applying alignment layer material in uniform coats, and there were substantial variations in layer thickness. The quality that this process could deliver was nearing its limit. The flexographic process was also risky because it could produce a large volume of defective panels in rapid succession if a foreign body or other contaminant became adhered to the roller that was used to transfer-coat the substrates. It was these shortcomings that prompted the Epson to look to applied industrial inkjet technology for answers, and to develop an inkjet alignment layer deposition system. In the beginning, the primary objective of the development team was to improve production efficiency and quality. Eventually, however, they were also able to reduce the amount of materials and energy used in the manufacturing process. The inkjet deposition system was installed first in a production line at the Suwa Minami Plant, but has since been rolled out to the Chitose Plant. TFT panels can use either of two types of alignment layers, organic or inorganic. The inkjet system produces the organic variety. In the future, however, Epson plans to produce inorganic layers with the inkjet system, too.

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What are alignment layers?

Liquid crystal molecules are loosely ordered molecules. Alignment layers, thin films that are analogous to plates with etched grooves, are used to neatly orient these molecules in a predetermined direction along the grooves. The material polyimide is used for the organic alignment layers produced by an inkjet system.

An Epson robot used in the production system

Pack filled with alignment layer material. As in the case of a printer, the pack is connected to the inkjet head by a tube.

Inkjet system advantages

Higher quality

A high-temperature polysilicon TFT liquid crystal panel for home projectors. The panel's alignment layers are inkjet-deposited.

Projectors are growing brighter by the year, and as brightness increases, unevenness in the thickness of alignment layers is amplified in projected images. Inkjet systems deposit alignment layers that are more uniform in thickness than those formed by flexographic printing because the inkjet method does not physically contact the substrates. Moreover, the inkjet process drastically reduces the risk that a high volume of defective panels could be produced due to the presence of a foreign body, such as can happen relatively easily with the flexographic process. In short, the inkjet process improved quality.

Reduced material consumption, improved eco performance minimizes material use

The inkjet deposition system reduces material use because it directly deposits the material for the alignment layers exactly where it is needed on the substrates, and in the precise amounts it is needed. The flexographic printing process uses a printing plate to form the pattern for the alignment layer, and the plate had to be replaced and cleaned each time a new panel model was introduced. The inkjet system does not use printing plates. Patterns are formed by controlling the driving of the nozzles in the inkjet head, and the only time cleaning is required is during maintenance.

Analyzing the inkjet process using LCA

Compared to flexographic printing systems, inkjet systems mitigate environmental impacts while boosting both quality and production efficiency. The extent to which those environmental impacts were mitigated was analyzed via life cycle assessment* (LCA). In addition to using fewer material resources, compact inkjet systems use one-third less energy and only one-fifth the floor space of flexographic systems. The quality, efficiency, and savings of materials, space, and energy combine to sharply reduce environmental impacts. In fact, CO2 emissions per chip (HTPS panel) were reduced by approximately 75%.

* LCA: A technique for quantifying the environmental impacts of a product across its life cycle, from the manufacture of parts, to product assembly, transport, use, disposal and recycling..