Alicante, Spain (PressExposure) March 29, 2010 -- Introduction
Current electronics are developed in such a way that the constant progress can hardly be followed. As a usual rule, electronic devices are made and commercialized on glass substrates (TVs, PC computers, portable computers, mobiles, etc.). Current research projects are focused, nevertheless, on using plastic devices as a support due to functional performance and economic issues.
Thus, plastic electronics represent a new range of electronics whose main aim is the production of devices on plastic substrates from organic and hybrid materials. This new technology will help in the development of lighter, more flexible devices, making it easier for them to be inserted in certain articles or even allowing the development of devices that coil up or fold on themselves. On the other hand, it is an economic technology due to both the type of materials used as well as the ease of the production techniques.
The experimental development of these devices is the aim of the consortium members of the PLASeTOY project, which is made up of AIJU, CIDETEC (Electrochemical Technologies Centre) and CETEMMSA. This programme, supported by the Spanish Science and Innovation Ministry and co-financed by FEDER (Regional Development European Fund) funds within the framework of the National Plan of Experimental Development DEX-560540-2008-3, is being coordinated by AIJU, the technological institute for toys.
The plastic electronic devices to be developed in this project can be split into the following categories:
- Electro-optical Devices. Three different types will be developed, to say, electrochromic, PDLC (Polymer Dispersed Liquid Crystals) and Electroluminescent (EL). All of them use an electrical field to provoke a different optical effect.
The introduction of these devices will give added value to the final product and comply with the electrical standards applicable to toys.
- Flexible Tactile Devices. These will be developed with the aim of substituting all kinds of keys and bellboys by contact areas on the same piece, allowing the homogenization of the toy, making its design easy and avoiding the production of traditional moulds. Moreover, it offers higher safety guarantees as small pieces that could come off will be avoided.
- Flexible Plastic Electronic Tracks. The development of these kinds of circuits will save having to use wires and welding, facilitate the article design, decrease the electrical and electronic waste and help with the compliance of the Directive RoHS, which is difficult to obey with current techniques.
Polymer Dispersed Liquid Crystals (PDLC)
The technology called "Polymer Dispersed Liquid Crystals" or PDLC, is based on the dispersion of micro drops of liquid crystal in a polymeric matrix. The difference between the refraction rates of liquid crystal and the polymer causes a high light dispersion (Scattering) that makes the material take on a translucent aspect. When a film of this kind of material is deposited between two transparent electrodes and a field of alternating current is applied, the aspect changes from translucent (OFF) to transparent (ON) as the orientation of liquid crystal molecules is parallel to the electrical field.
One of the main advantages of this technology is the low commutation time (in the order of a millisecond), however the fact that it has no memory effect must be mentioned and consequently it not only requires a current to provoke the commutation to the transparent state but to maintain this state as well. On the other hand, the employment of a polymer as a matrix, gives it certain mechanical properties, allowing the preparation of films of bigger surfaces. Moreover, this polymeric nature makes possible the employment of plastic substrates, allowing the production of flexible and lightweight devices.
In reference to the applications of PDLC technology, its electro-optical characteristics make it an excellent option for the development of intelligent windows, mainly for application in the residential and automotive sectors. Another of the widest applications is as a divider or private window electrically controlled in offices, hospitals, shop windows, etc.
Taking advantage of CIDETEC's experience in the development of electro-optical devices, new research tasks have been started in order to obtain materials and devices based on the PDLC technology, not only on glass substrate but on plastic substrate as well due to the advantages and possibilities the latter offers. Until now composites have been made using a mixture of pneumatic liquid crystal and a polymeric matrix of a different nature, and by varying parameters such as the composition and the phase separation process, the production of small devices as big as 5x5 cm2 has been possible.
Within the PLASeTOY project the development of devices working in a reverse mode has been started, that is to say, transparent in the OFF state and translucent in the ON state, modifying the composite's composition. Usually, the construction of this kind of device that operates in a "reserve mode", is possible by using liquid crystal with a negative dielectric constant, which is orientated in a perpendicular direction to the applied electrical field. It is a much less frequent and less researched system, as the liquid crystal systems with these characteristics are few. On the other hand, the preparation of such devices is more complex, as it requires an additional phase previous to the planar orientation of the material in reference to the substrate, which uses pre-treated surfaces or applies a powerful magnetic field (> 7 T), among other techniques. It is a kind of device which is in development, which still requires the optimization of several aspects and therefore more research is being undertaken.
Electrochromism is the term for the property that some organic and inorganic natured materials have for changing colour under the action of an electrical field in a reversible way due to a redox reaction. This property allows these materials to be used as filter systems in the visible light area and that of IR (Infrared) decreasing the amount of light and solar radiation that passes through. This allows the use of these kinds of materials in such applications as intelligent windows or eye filters where it is important to filter both, luminosity and solar radiation. Other applications of electrochromic materials include displays and rear-view mirrors that are darkened when light falls upon them with a certain intensity avoiding the dazzling of drivers. This application is the only one being commercialized at this moment.
Generally, an electrochromic device is made up of 7 layers. On the one hand, the deposition of an electrochromic material on a conductive plastic substrate is required. This electrochromic material can be of an organic (i.e. conductive polymer) or inorganic (i.e. metallic oxide) nature.
For the suitable functioning or an electrochromic device a material capable of being an ions source and receptor is necessary, to compensate for the electrochromic layer charge. Moreover, depending on the colour change obtained by the electrochromic material an appropriate counter electrode based on inorganic oxides or conductive polymers will be used, in such a way that the change is preferable from a transparent state to a coloured state. Finally, both layers are separated by an electrolyte which allows the ions to pass through them.
CIDETEC has made an important innovation in the electrochromism field simplifying the required number of layers for the functioning of an electrochromic device. For this, a formulation has been developed in which the electrochromic material is included, an electrolyte and a pair of re-dox of the electrochromic material, passing from 7 to 5 layers, notably simplifying the manufacturing of such devices and thus reducing the final cost.
The present Project tackles the use of the electrochromic technology combined with the preparation of lithographies on plastic substrates for their further integration in toys, in such a way that specific designs can be made for decorative purposes.
Finally, the preparation of hybrid devices combining electrochromism technology and liquid crystal is being looked at. Thus, it is possible to have a prototype with four different optical effects: colourless transparent, coloured transparent, colourless translucent and coloured translucent.
Flexible tactile switching and flexible circuits
Over the last few years new concepts, in terms of electronic technology, have emerged such as "plastic electronics", "printed electronics" or "organic electronics". These techniques aim to contribute new manufacturing methods which will bring a revolution in the electronic and micro-electronic industry. Basically they consist of using and adapting traditional technologies employed in graphic arts like silk-screen printing, lithography, inkjet printing and roll-to-roll, among others, for the manufacturing of electronic devices usually developed by means of other techniques. The printing of electronic components creates a need for new chemical developments for this technology, for example, conductive inks, resistive inks, insulating inks or semi-conductor inks. Commercial inks designed to be used in "printed electronics" as well as special substrates for printing purposes are already on the market. This is a promising technology, in constant evolution which till now has had satisfactory results on the market.
The main applications of flexible electronics are: pressure sensors, flexible circuits, OLED devices, flexible memories, electroluminescent lamps, flexible batteries, electrophoretic devices, RFID tags, elastic sensors, and flexible photovoltaic panels, among others. Flexible electronics could provide the toy sector with new products with higher flexibility and even the possibility to substitute the current wire track used in conventional electronics.
CETEMMSA has been able to print pressure sensors by means of inkjet technology with the functionality of an on/off switch and the printing of the required circuits for the correct working of the sensor, with the inclusion of several non-hybrid LEDs (conventional) to demonstrate that printed systems work correctly and that "printed electronics" technology has a place within the toy sector.
Electroluminescent technology has been undergoing development for decades but it all started with military research around 30 years ago. Even such a field with some history, has witnessed a high increase in technological advances over the last few years.
The dramatic increase of this technology is due to its versatility enabling it to be used for many applications.
Electroluminescence is a phenomenon in which a material emits light when an electrical field is applied. The electroluminescent devices are of a sandwich structure type and in the interior the luminescent material is deposited.
Electroluminescence has a wide range of applications, from electronic products such as mobile phones, PDA's, watches, toy complements, decoration, advertising, and both conventional and road signs, among others.
CETEMMSA has achieved the assembly of electroluminescent devices on a flexible plastic based substrate. These systems are deposited by means of silk-screen printing, and allow the production of devices of a high variety of sizes and designs. These devices emit different colours according to the phosphorus introduced into the system. They can emit white, blue, green and orange light, among others.
Plastic Electronics in Toys
The toy sector is one of the sectors being widely affected by the import of products from Asian countries. Designs are seemingly copied and the existing commercial rules do not give a real solution to the development of articles that do not obey the standards. Consequently, competency based on cost reduction is not feasible at this point.
Additionally, the design of new toy and childcare articles is being notably slowed down due to the economic crisis that is currently affecting many European and international sectors. The tools available to European enterprises to keep their market share is, invariably, their competitiveness by means of the research and development of new technologies that contribute dynamism and interactivity to the articles developed.
Plastic electronics have the potential to revitalize the economy, to generate new jobs and to contribute to public health, as they allow time and cost savings and give support to increase the functionality of diverse sectors (consumer electronics, building, the automotive sector, several lighting devices, logistics and even fashion). Manufacturers that introduce these devices into their articles, add to their products differing agents to the current market, enhancing innovation, competitiveness and sustainability in the sector.
That is why, the Technological Toy Institute (AIJU) is interested in plastic electronic technologies development, with the aim of introducing important technological innovations, further to the designs created periodically, able to contribute, in the medium term, to a big technological and competitive jump forward in relation to competing countries. During 2010 this research will be continued within this project with the aim of carrying out the established objectives.