Specialty Plastics-liquid Crystal Polymers

8/2/2019 Specialty Plastics-liquid Crystal Polymers

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SPECIALITY PLASTICS

Speciality plastics are those plastics whichdisplay high structure and performance

characteristics even at high temperature. Mostlythese plastics have outstanding chemicalresistance, electrical properties and have verygood fire resistance.These plastics are expensive and are used inthose applications where high performance isrequired.


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There are different types of speciality plastics:-

Liquid crystal polymers (LCP)

Polytetrafluoroethylene (PTFE)

Thermoplastics polyurathene (TPU)

Polysulphone (PSO)

Polyethersulphone (PES) Polyphenylene sulphide (PPS)

Polyphenylene Ether (PPE)

Polyetheretherketone (PEEK)

Polyarylates

Polyamide-Imide (PAI)

Polyether-Imide (PEI)


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LIQUID CRYSTAL POLYMERS (LCP)Liquid crystal polymers are a group of polymers that

exhibit regular molecular order both in molten and

solid states.They are rigid, strong and brittle thermoplastics.

The viscosity of these substances can changeunexpectedly in certain ranges of temperature and

pressure, They out perform other plastics in termsof mechanical and thermal properties.


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Commercially the first lyotropic (non-meltprocessable LCP), aromatic polyamide (Kevlar) was

introduced in the market in 1965.

This well-known aramid fiber is a lyotropic (insolution form) macro-molecularly ordered polymer.

The first thermotropic(melt processable) LCP,Ekkel | 2000 was made commercially available in1972.


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Between the liquid and solid states, LCPs may be in

a liquid crystalline intermediate state which is

described as mesomorphous.


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LCP molecular structure

a- linear

rigid unit

b- flexibleunit

a b


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LCP

LCPs are characterized by two superimposed structuralprinciples:

- main chain polymers in which the rigid molecular

units (mesogens) are arranged in the polymerchain &

- side chain polymers in which the mesogens are

attached as side groups.


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Main chain polymers are not suitableforuse athigh temperatures.

The side chain polymers are distinguished byparticularly good electrical and opticalproperties which are exploited in opticalstorage or liquid crystal displays (LCD).


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LCPs are based mainly on polyesters

but

polyestercarbonates,polyesteramides,polyesterimides &polyazomethines

can also be used in their production.


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LCP GENERAL PROPERTIES

In addition they exhibit the following properties:

medium density

high tensile strength

high notched impact strength

high tensile modulus of elasticitywide melting range

high continuous service temperature


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good low temperature properties low coefficient of linear expansion orientation easily achieved by injection molding,

extrusion and blow molding processable on standard machines low shrinkage low melt viscosity, but high strength and

extensibility of melt


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good electrical properties

high resistance to chemicals flammability UL 94 V-0 (0.8 mm) without flame

retardant low moisture absorption

high resistance to stress cracking Transparent to microwaves Resistance to food Hydrolytically stable


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Table -1 Guide values of properties of LCP

Properties Units LCP

Density g/cm3 1.4 -1.9

Water absorption (23C, 24h) % 0.02-0.04

Mechanical

Tensile strength N/mm2 140-240

Elongation at break % 1.2-6.9

Tensile modulus of elasticity N/mm2 10000-40000

Notched impact strength (Izod) J/m 53-530

Thermal

Melting Point C >400

CORPORATE TRAINING AND PLANNING


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Table -1 Guide values of properties of LCP

Properties Units LCP

Service temperature in air without

mechanical loading (long-term)C 185-250

Heat deflection temperature C 180-240

Coefficient of linear expansion between 0 and 50 C K-1 0-25x10-6

Electrical

Volume resistivity Wcm 1015-1016

Dielectric constant 2.6-3.3

Dissipation factor, tan d 50 Hz 0.003-0.004

Dielectric strength kV/mm 31-43

Tracking resistance class C 1500-200

Fire performance to UL 94 class V-0

CORPORATE TRAINING AND PLANNING


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LCP

A recently introduced amorphous LCP exhibitsless variation in properties at high temperatures.

The processing range is wider and the materialcan thus be blow molded and thermoformed.

Processable LCPs cannot be obtained from

rigid linear macromolecules alone because theymelt only above their decompositiontemperature. This difficulty has been overcomeby incorporating flexible linkages in the mainchain.


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Many properties, favorable and unfavourable, can besignificantly influenced by the choice of processingconditions and molding design, e.g.:

At large wall thicknesses, LCPs lose their peakproperties in the longitudinal direction,

shrinkage can become negative in the direction of flow,

anisotropy can be reduced by adding fillers,

filler content can be very high (> 40% w/w).


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AVAILABILITY

Liquid crystal polymers are available as a self-reinforcing, glass, glass/mineral, or mineral carbon

fibre filled resin

LCP is supplied as pellets in transparent andopaque grey, dark and black colorations .

Injection molding grades and extrusion grades forrod, tube, film and for extrusion coating.


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LCP are also available in powder form.

Source of LCPs are:-

Di acyl chlorideDi phenol

Di acid(Terephthalic Acid)

Hydroxy acid (p-Hydroxy Benzoic acid)


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LCP Processing

LCP Injection Moldings

The original point of using LCPs was to exploit

the increase in strength which can be achievedby orientation of flow.

The usual flat shaped design of injectionmoldings leads, however, to a multi-axial stressstate which oriented LCP cannot cope withisotropically.


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LCP resins have Low outgassing even at extremetemperatures, a factor that's critical for sensitiveelectronics and optical applications.

When it comes to precision, LCP resins haveexcellent molding properties, provide thedesign freedom for extremely small andintricate parts with cross sections as thin as 0.25

mm.

Predried at 149oC for 8 hours


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LCP Machining & Fabrication

LCPs can be machined and joined with conventionaltools and machinery.

They can be bonded with the usual adhesives for

polyesters

They can be welded with ultrasonics.

They can be metallized by spraying or electroplating.


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LCP - recycling

Up to 25% w/w scrap can be added to virginmaterial.

Material which has absorbed moisture must bepredried.

Plasticizing cylinders can be purged with PE-HD.


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APPLICATIONS:-

Electrical & Electronic

Substrates for chips and printed circuits

Coil cores, sockets, encapsulations, Sensors

Switches and other electronic componentsrequiring outstanding performance at elevatedtemperatures

Buffer films, couplings and connectors for fiberoptics


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Automobiles

Precision high temperature applications such asoptical lens components, sensors, LED housings,and motor components

Miniaturized moldings (particularly for use in

aggressive environments)Under-bonnet components in contact with fuel,

Numerous components in aircraft cabins, fuel

systems, radomes, electrical components


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Typical Applications

Drive belt pulleys, packings, bearings, sealsAccessories for oil drilling, pumps

Packings for distillation columns and scrubbingtowers

Measuring instruments

Surface mount devices

Dual ovenable cookware

Heat sinks containing graphite fibers

Needle less syringes

Semiconductor handling device


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LCP -Tradenames

Ekcel, Ekonol (Carborundum Co., Metallic Div.,US)

Granlar (Montedison Inst. Guido, IT)

Novoaccurate (Mitsubishi Chem. Ind., lP)Rodron (U nitika, lP)

Ultrax (BASF, DE)

Vectra (Hoechst, DE)Victrex (ICI, GB)

Xydar (Amoco Performance Products )


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Specialty Plastics-liquid Crystal Polymers