recycling lcd screen

7/29/2019 Recycling LCD screen

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How can we recycle LCD monitor

Ana-Marija (Mia Viki)


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LCD (liquid-crystal-display) monitors


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Liquid crystalls

Liquid crystalls can be found in nature aroundus, but also in many electronic devices andapplications

It represents a state of materie whichcombines properties form both liquid andcrystalls

We can divide liquid crystalls into threegroups: thermotropic, liotropic andmetallotropic


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Liquid crystalls

Thermotropic liquid crstalls are build from

organic molecules and depending on

temperature can exchibit in different phases


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Thermotropic liquid crystalls

Molecules are in so called nematic phase

Combines from cilinder organic moleculeswhich can move freely

Although they do not posses arranged crystall

structure , the cilinders are merging andtrying to hold on arranged system in one

direction


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Smectic phase of liquid crystalls

In smectic phase , crystalls poses higher level of

inner arrangment then in nematic phase

It combines of layer that can slide across one

another

Phases between layers haves properties of liquid


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Smectic phase


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Chiral phase

Chiral molecules are turning in parallel in one

direction and in that way they are saving

longterm arrangement

The consiquences of turning angle from center

of rotation is optical propertie like Bragg

reflexion


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Chiral phase


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Usage of liquid crystall

The usage of liquid crystalls comes from the

fact that we have permanent electrical dipoles

whose orientation in space is determened by

orientation of molecules

Using outside electrical field we can influence

on inner arrangement of crystalls and

consiquentually on their optical preferences


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Main components of LCD monitor

Liquid crystall

Glass

Thin transistor film

Conducting electrodes

Color filters

Polarizators

Background light Reflective background

Plastical components


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Components of LCD screen


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LCD

LCD-display is based on liquid crystalls that arebound between two glasses substrates withpolarizator form outer side

On inner side of the glass substrate there is athin transistor film on one part glass substrateand color filter on another glass substrate

Exeption transistor and color filter on innerside , we also have conducting electrodes andand orientation films


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Making of picture

Depending about presence or nonpresenceof electric currence , the liquid crystalls arearranging themselves in such matter that they

combine with polarizators making light topass or not to pass

The light that comes from background lightsource is regulated when passing throughsample of color filter on inner side od thefront glass substrate


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Materials and chemical composits

1. Liquid crystalls

LCD display usually combines 10 -25 components

because only one doesnt fulfill complex

properties that LCD demands

From first discovery of liquid crystalls , we have a

knowledge for about more than 20 000

compounds that have nematic phase: some ofthem are anisilidenparaaminophenylacetate

(APAPA) and 4-n-penthyl -4-ciano-biphenyl(PCB)


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Materials and chemical composits

2008. , about 69 % of LC was made by german

company Merck KggA which patented about

2500 LC mixtures

Compounds that have been used in LC

mixtures are usually poliaromatic polimers

with 14 to 30 carbon atoms on which we

selectively add atoms of O, N, F, Br or Cl.


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LCDElectrodes

Conductive electrodes are from inner part of

glass substrates

Electrodes are made from transparent

conducting layer made from indium-tin oxides

(ITO) .ITO is a mixture of indium(III) oxide

(In2O3) and tin(IV) oxide (SnO2) in relate to

90:10


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LCDElectrodes

The position of electrodes in shematics for LCD screen


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Color filters

Color filter are made from black matrix,

surface layer,RGB pattern and conductive

electrode (ITO)


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Color filter

Color filter


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Polarizators

Polarizators are settled on outer side of glasssubstrate

These are special filters which allow onlypolarized light to pass, to be more acurate ,

fotons who are vibrating in only one plane They are made from layer films , begining from

layer of polyethilen tereftalate (PET) , then layerof celulose threeacetate, then layer of polyvinylalcohole impregnated with iodine or nonspecificcolors, then another layer of celulosethreeacetate and ends up with PET layer


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Polarizators

PET layer


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Polarizators

Celulose threeacetate


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Polarizators

Polarizators with polyvinyl alcohole and

impregnated iodine are also called H-cells

In later time , it is common to use polyvinyl

chains which can be derived from

dehydratation of polyvinyl alcoholethose are

called K-cells

In LCD screens there is one vertical and one

horizontal polarizator


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Background lighthing

In all LCD monitors there are fluorescentlamps, which are used to light up thebackground of screen and they represent the

only active light source Fluorescent light source is a glass tube which

produces white light . In the inner part of glasstube there is a mercury sample under lowpressure who is emitting UV radiance whenbeing in ionized form


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Background lighthing

The inner part of flourescent source is painted

by phosphor

Phosphore is capable of apsorbing energy and

to emitt one in a form of visible radiance


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Glass

Glass is combined with many sodium and

other alkali ions which can move freely on the

surface of the glass

To avoid those kind of efects , we are using

borsilicium glass or glass painted by a layer of

silicium oxide

Silicium oxide is preventing ions to react with

moisture from air


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Plastical components

The most simple solution is to use transparent

plastical surfaces for lighter LCD

Plastical components will make screen easier ,

but cheap plastical components will disperse

light more then glass and can react chemicaly

with molecules of liquid crystalls

Plastical components are also used for making

of outer screen frame


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Recycle of LCD materials

With growing production of LCD screens we

also have growing amount of their disposal

,and to taking care of represents a large

ecological issue

Liquid crystalls which are made of aromatic

rings supstituited with halogen atoms produce

very toxical products dangerous forenviroment (dioxanes, furans..etc..)


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Recycle of LCD materials

The background light source posses largeamount of mercury , and batteries of smallLCD often have mercury and cadmium

Both elements , mercury and cadmium haveacumulative effect in human body andenviroment , and posses toxicity

Glasses used in LCD screen posses cadmiumand arsenic compounds so their recyclebecomes very important


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Recycling flourescent lamps

Flourescent lamps are made of 94% glass, 4%

metals and 2% phosporus pouder

Mercury is settled inside phosporus pouder

Mercury element is suffiecient to create

toxicity of 30 000 liters of water


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Comparison between flourescent tube from laptop and plain pencil


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Mercury can be depleted on specific mercury

deposits , but those places are very few

We can recycle mercury using vacuum

destillation

Unpure mercury can be destillated in twohead

pots and dried on 360 C , and using condenser

we can extract , condense and assemble pure

mercury in round pots


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Simple aparature for mercury destillation


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Glass recycling

The amount of glass deposits which is

collected on deposits in Taiwan in 2009. has

reached 0,52 million tons

Glass deposits can be recycled to produce

glass ceramics


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Glass recycling

Kitchen assemblance made from glass ceramics


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Glass recycling

Deposit glass is drilled ,homogenized and setin chasement under pressure

Dust particles are assembled in solid mass

using thermal process (the process ofsinteration)

Heating glass deposits we are removingorganic components and stabilize inorganiccomponents incorporating oxidescharacteristic for glass ceramics


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Glass recycling

On temp. from 800-950 OC , in 6 hours and

increasing temperature by 5C O /min we can

get very qualitative glass ceramics


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Recycling plastical components

Most of plastical components are not

biodegradible , but all plastical components

can be recycled

We can recycle plastical components using

pyrolithic procesess in pyrolithic reactors


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Pyrolithic reactor


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The process of pyrolise is a proces where we havedestillation of organic part from deposit withripping of chemical bounds (crecking) of largemolecules of material like plastics, rubber ,leather and similar materials

With the same process we can gain gas andliquid fuels

Gases gained from pyrolithic processes aremixture of :hydrogen , methane, carbonmonoxide and carbon dioxide


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Liquid phase from process of pyrolize has

condensed burning oil whose composition

depends from different deposit material


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Recycling wires of electrical net

Like any other electronic devices we can also

recycle electric circle wires

Materials are first grinded to dust and then we

use chemical and physical processes to dissolvenobel metals in process called smeltingvery

similar to dissolving mineral composits

Using temperature and reductive chemicalagenses we can remove all components

exception metals like copper, gold and silver


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Rycling of liquid crystalls

Liquid crystalls are not easly biodegradible

We dont know much about recycling liquid

crystalls because most of them are under

patent protection and recycling tehniques are

still developing

Merck company recomends industrial burning

process for ecological measurment

l i l b k d f d i


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Ecological background of producing

LCD

Main ecological problem is process of making

LCD materials and their usage (they use lot of

electrical energy)

Factories manufacture several million tons of

waste waters

Those waste waters consists of large

spectrum of organic solvents like :DMSO,MEA, TMAH and chrome residues..

E l i l b k d f d i


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Ecological background of producing

LCD

Chrome is extremly cancerogenetic supstance

We have many methods which can resolveorganic solvents and can isolate dissolved

chromium in a form of chromium oxide fromwaste waters

In the process of production we use largeamount of SF6 (sulfur-flouride) gas andnatural gases which also contributes to globalwarm effect...

H h LCD i l


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How to change LCD materials

ecological issue

Main problem is mercury in flourescent lamps

We have new generation of LCD monitors who

doesnt have mercury , they are energetically

more effective and higher quality

Monitors that are using LED lamps as

background light source are capable off

creating much cleaner white light


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LIGHT EMITTING DIODE(LED)

LED is a semiconducting light source

They are available in many sizes and colors

Very restistant and long life

Recycling LED diode would mean to: induce more money for making glass

Reduce the amount of toxic metals in glass

New form of glasses donz have arsenic , antimonand barium resiudes , their are ligher and havebetter heat properties

recycling lcd screen

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