By Alchin Wang, General Manager

Once you’ve read a document on electronic paper (e-paper), you’ll never want to go back to traditional liquid crystal (LCD), light-emitting diode (LED) or organic light-emitting diode (OLED) displays.

The only problem is that e-paper has still not reached the level of market maturity that makes it capable of being sufficiently commoditized. That’s because most manufacturers feeding the market aren’t able to create e-paper displays (EPDs) that can operate under the toughest environmental conditions and achieve the highest possible levels of reliability and performance.

 

The demands of e-paper

Users of e-paper justifiably put significant demands on the technology. They expect it to perform exactly the way paper does, including the fact that with paper there’s no need to make compromises when it comes to operating conditions.

Just like paper, e-paper is expected to reflect light rather than emit light as conventional flat panel displays do. Just like paper, e-paper is expected to be less of a strain on the eyes and to offer wider viewing angles than are possible with LCD, LED or OLED displays. This means that e-paper manufacturers must ensure their designs are capable of offering a scalable solution that can operate under any of the environmental conditions that paper can be exposed to.

The problem with traditional displays is that they have been designed to mimic paper but they don’t behave like paper and there is a growing demand from customers for a technology that makes this possible.

Traditional displays tend to be capable of operating at temperature ranges of between 0°C and +70°C. Those that are constructed for more demanding industrial environments – and are, therefore, much more costly – operate at between -40°C and +85°C. Even then, the ability to customize these displays is extremely limited and users might have to install enclosures or take other measures to provide environmental protection. Compare this with EPDs which tend to be supplied to a customized format and be capable of being used over a much wider temperature range.

 

How to manufacture an e-paper display

Figure 1 shows the make-up of an EPD which incorporates such unique features as edge glue, an e-ink film and a protective sheet. These combine to make up the front plane laminate (FPL), shown in Figure 2.

Figure 1: The make-up of an e-paper display

 

Figure 2: The front plane laminate (FPL) of an EPD

When manufacturing an e-paper display, a roller attaches the FPL to the TFT substrate and compresses the materials which are stuck together with silver glue (ensuring conductivity between the e-ink and the substrate). It’s important during this process that there are no cavities created should the silver glue not make optimum contact. Figure 3 shows how this can lead to defects in the screen and poor image quality. It is also essential that a protective sheet used on EPDs offers not just excellent environmental protection but also high levels of light transmission.

Figure 3: Surface defects can be created in EPDs during the rolling process

 

The Pervasive Displays solution

With many years of experience backed by extensive research and development in the science behind the technology, Pervasive Displays has put itself at the forefront of the design and manufacture of e-paper displays.

For example, we have created a proprietary silver glue which does away with defects by suspending the silver particles in a paste and using a double dot design. Likewise, the glue used by Pervasive Displays to attach the protective film to the board has been designed to achieve 4.5 times the level of moisture resistance of similar glues while minimizing shrinkage during the curing phase. This makes the product far more reliable and durable when operating under a number of demanding conditions.

At the same time, we have developed a protective sheet material that is at least 10 times more resistant to moisture than other materials on the market. Finally, special surface treatments, including 3H hardness, make EPDs from Pervasive Displays substantially more resistant to acetone, detergents, alcohol, perfumes and many other chemicals. The end result is an EPD that offers superior optical performance and readability under a wide range of environmental operating conditions. For example, while the contrast ratio for 2- and 3-color products is increased by 15%, the chromaticity index for 3-color products is boosted by 5%.

 

Market maturity

As the market matures thanks to technology developed by Pervasive Displays, we have ramped up production of e-paper display products and now sell more than 20 million displays per annum. With our unrivalled expertise and experience, we are forging ahead with technological developments that will ensure e-paper finally takes its place in the market as a genuine replacement for paper.