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Proceedings of the 19 Waste Management Conference of the IWMSA (WasteCon2008).
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6 – 10 October 2008. Durban, South Africa. ISBN Number: 978-0-620-40434-1
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ReLCD: RECYCLING AND
RE-USE OF LCD PANELS
KOPACEK B
SAT, Austrian Society for Systems Engineering and Automation, Austria (bernd.kopacek@satresearch.at)
ABSTRACT
Nowadays more and more consumers substitute their conventional TV-sets and computer
monitors with LCD panels. In the near future huge amounts of LCDs will start coming back to
recycling. As LCDs with hazardous mercury backlight lamps are used an appropriate recycling
technology has to be implemented.
KEYWORDS
LCD, Recycling, Re-Use
INTRODUCTION
Liquid Crystal Displays (LCDs) are widely used in notebooks, organizers, mobile phones, pocket
calculators, measuring and control instruments, electronic games, hand-held miniature TVs,
audio-video equipment, large signboards, automotive displays and more and more for PC
monitors and TVs.
According to a study from Stanford Resources (San Jose, California) the annual value of
LCD-products reached 35 billion EUR in 2002, about 30% of this within the European Union,
representing a total area of 2,1 million m² Liquid Crystal Displays. An annual increase rate of
about 15% is estimated for the next years (up to 4,1 million m² in 2005).
As LCDs are already on the market for several years, larger quantities of the more than 2,5
billion LCDs are coming into their End-of-Life stage for treatment. In 2005 this figure will become
even more dramatic - 40.000 tons of LCD-modules contained in 2 million tons of waste electrical
and electronic equipment (WEEE) or about 30% of total WEEE within EU. An amount which is
representing 400 million EUR costs for incineration.
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Currently the only method used to deal with redundant LCD units is incineration or landfill.
Both are expensive and cause emissions into the atmosphere (global warming) respectively
water contamination (Class II) and difficulties in biodegradation. Up to now there is no recycling
solution for LC-Displays available.
As a consequence European Commission requests the disassembly of LCDs with an area
bigger than 100 cm² in the Directive 2002/96/EC of the European Parliament and of the Council
on Waste Electrical and Electronic Equipment (WEEE Directive) of February 13, 2003.
Structure and material composition of LCD
The definition of “LCD“ describes the sandwich composed of the two glass plates with
connected polymers (for example polarizers, colour filters) and the sealed liquid crystal mixture
in between the two glass plates. This definition does not include the backlight unit, the printed
circuit board, cables and frame which are part of the LCD module. Figure 1Error! Reference
source not found. shows the structure of a liquid crystal display.
Figure 1. Structure of LCD
Glass plates
The plate at LCD panel is a glass substrate with a transparent metal coating for the electrodes
of the display. In LCDs usually soda lime type glass is used, but in some cases it can be a more
expensive borosilicate type. The thickness of glass substrate is 0,4 - 1,1 mm.
Polarizer and orientation layers
The outer surface of both glass substrates are coated with polarizer layers made of
polycarbonate with the thickness of 0,2 mm. On the top of electrodes, the orientation layer can
be found. The orientation layer ensures the specific starting orientation in the unstressed state.
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Usually hydrocarbon polymers, such as polyvinyl alcohol or heat resistant polyimide are applied.
The thickness of this layer is 30 to 100 nm.
Electrode
The transparent conductive coating is a thin layer of a metal, such as gold, silver, or tin.
Generally tin-oxide, indium-oxide, or their alloys are used because these materials constitute a
hard layer. In the industry the most preferred electrode material is the indium-tin oxide (ITO,
In2O3.SnO2) because of reasonable costs and eligible transparency. Accessible information
about Indium Tin Oxide electrode layer used in Liquid Crystal Displays and other applications
(e.g. solar cells) are the following:
• Thickness: 30-80 nm;
• Density: ~7,1-7,2 g/cm³;
• Typical In2O3:SnO2 ratio (by weight): 95:5-85:15, depends on application
Liquid crystals
Liquid crystals are used as mixtures typically containing between 10 and 25 single compounds.
These mixtures are composed of chemically quite similar compounds. Some of the compounds
only differ in their alkyl or alkoxy side chains by varying number of carbon atoms (homologous
compounds). The thickness of liquid crystal layer is about 5 μm, and the volume of it is about
350 mg in a 15” display. One the most important manufacturer, Merck KgaA, has confirmed that
the liquid crystals supplied by them don’t contain any of the substances mentioned in the EU
Directive 200/95/EC of 27 January 2003 on Restriction of the use of certain hazardous
substances in electrical and electronic equipment. Despite this, liquid crystals are known to be
hazardous to water (water contamination class II) and very difficult to biodegrade (0 – 30%
within 28 days).
Colour filter layer
The light passes through a colour filter layer, which is a key component for making colour
images. Colour filters’ pixel has red, green, and blue colour elements, and black matrix is
located between the colours to avoid leakage of light. The colour filter layer must be as smooth
as possible for maximal colour purity. The black matrix is usually made of chromium, chromeoxide, or black resins. Colour filter is usually an organic or inorganic polymeric material
(gelatine, casein, polyvinyl alcohol, acrylic, epoxy, polyester and polyimide) with pigments.
Pigments usually have carboxyl-, amino-, or sulfon groups. For example dianthraquinone (red)
or copper phthalocyanine (green or blue) is used. The thickness of colour filter layer is between
0,7 - 2,5 μm, and the pigments are under 0,1 μm.
Backlight unit
About 90% of LCDs use backlight unit. Backlight unit consists of light source, reflector, light
guide plate, and diffuser. Several technologies are used in backlight units, e.g. there are
electroluminescent, light emitting diode, and cold cathode fluorescent lamps. In most backlight
units the light source is a fluorescent tube because it offers low power consumption and very
bright white light. The reflector is usually a polymer film with a thickness of 25 μm coated with
Ag or Ag-alloys with a thickness of 150 nm. The polymer film is made of PET (polyethylene
terephthalate), and contains UV-ray absorbing agents to prevent UV-ray originating
degradation.
OBJECTIVE
Currently the only way to deal with End-of-Life LCDs is disposing them in waste incinerators or
landfills. Incineration of LCDs causes the same volatile products and residues as incineration of
municipal waste. Among other compounds, these emissions, due to the possible content of
liquid crystals of chlorine, could be made up of dioxins and furans, very toxic substances that
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are currently under discussion. Furthermore, it is assumed that under high thermal conditions
there will be breakdown products that can be toxic. On the other hand, landfilling is not
ecologically efficient since it has been researched that large LCDs possess a backlight
containing mercury and the battery of small LCDs may also contain mercury or cadmium,
substances classified as toxic due to its accumulative effects in both human body and
environment. Therefore an eco-efficient disassembly and recycling technology for end of life
LCDs that fulfils the WEEE-Directive of the European Commission has to be implemented.
ReLCD went in several areas beyond the unsatisfactory state-of-the-art. The objectives
were:
•
To find a cheap and fast test methodology to verify if the obsolete or excess LCDs are
still working
•
To develop a technology to refurbish the working LCDs and re-integrate them into repair
and in exemptions also in production processes
•
To find a test method to detect hazardous substances in LC-mixtures
•
To develop an eco-efficient disassembly and recycling technology for the non-working
LCDs that fulfils the WEEE-Directive of the European Commission
•
To research possible enhancements to the existing LCD design and production in order
to come to a more sustainable life-cycle of LCDs (publication of guidelines)
•
Building up a pilot plant incorporating and testing the developed technologies
By all these measures decrease the amount going to landfill or incineration as well as
decrease the threats to the environment and mankind of today’s state-of-the-art technology.
PROJECT RESULT
Although numerous manufacturers and various different types are available on the market the
characteristics important for dismantling are similar for all types. So a representative sample
was selected to find the most efficient treatment method. The aim was to separate the
hazardous backlight lamps from the panel.
About 90% of LCDs use backlight unit. Apart from manual dismantling some cutting
technologies were investigated.
If the backlight lamp - which represents just 2% of the total mass of the LCD – is not
extracted before, the whole screen has to be treated as hazardous waste. Therefore the goal of
the project has been to find a cheap technology for dismantling the backlight unit because the
remaining 98% of the mass can be easily treated in a conventional shredder for waste
electronics.
For separation of the backlight lamps the following treatment technologies methodologies
have been evaluated:
•
•
•
•
Manual dismantling
Water Jet Cutting
Laser Cutting
Circular Saw
A rough estimation of the processing costs and total treatment costs have been also
investigated.
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The following parameters have been considered:
• Mean processing time
• Maintenance costs
• Personnel costs
• Material revenues
Although some alternative treatment technologies were investigated the best results were
achieved by manual dismantling. Both the costs per item and the quality assessment reach the
best results.
Especially the high investment costs of jet cutting and laser cutting result to an inefficient cost
trend especially for low volumes. After the amortisation time and huge volumes laser cutting can
be competitive to manual dismantling. As the recycling amount of LCDs for the next years is
hard to estimate high investment costs will also cause a high financial risk. Even more that more
and more producers use mercury-free backlight lamps. These do not have to be extracted and
the whole module can be recycled as “normal” WEEE (Waste from Electrical and Electronic
Equipment) in the future.
Sawing technologies like circular sawing or band sawing would be inefficient because of the
material composition of LCD panels. Although a huge variety of special designed saw blades
are available no one fits all requirements which are necessary to cut LCD panels. Especially the
content of glass result to difficulties and the lifetime of the sawing-blade is reduced heavily. The
short lifetime of the sawing equipment will result to very high variable costs. Hence sawing can
never be competitive to manual dismantling.
It can be also stated, that some manufactures already consider requirements for dismantling.
Our investigations show that already 40% of the panels are designed disassembly friendly. As
we expect a rising of the percentage in the future manual dismantling will become efficient
anymore. A percentage of 60% will reduce the mean dismantling time to 1,4 min. A dismantling
time of 1,4 min per panel prefer manual dismantling to other technologies (e.g.: Laser cutting …)
even in countries with high labour costs.
ACKNOWLEDGEMENT
The author would like to thank all partners in the research consortium as well as the European
Commission to enable the project by its funding.