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SPECIALTY PLASTICSLiquid Crystal Polymers

(LCP)

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LCP

History

Liquid crystal polymers, also known as self-reinforced polymers were first introduced in 1965 (@Kevlar from Du Pont de Nemours).

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

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LCP

• This was followed in 1972 by Ekkcel 1-2000 from Carborundum which was Thermotropic (melt-processable) in nature

• Development work commenced in 1975 by Celanese led in the mid eighties to Vectra (now a Hoechst product) based on thermotropic polyester.

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LCP• BASF (Ultrax) and Bayer (KU 1-90 range)

have also now commenced production of LCPs. The highly ordered state in solution or in the melt contrasts with the randomly ordered macromolecules of conventional polymers.

• 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- flexible unit

a

a

b

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LCP

LCPs are characterized by two superimposed structural principles:

- main chain polymers in which the rigid molecular units (mesogens) are arranged in the polymer chain &

- side chain polymers in which the mesogens are attached as side groups.

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LCP

• Main chain polymers are not suitable for use at high temperatures.

• The side chain polymers are distinguished by particularly good electrical and optical properties which are exploited in optical storage or liquid crystal displays (LCD).

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LCPLCPs are based mainly on polyesters

but polyestercarbonates, polyesteramides, polyesterimides &

polyazomethines

can also be used in their production.

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LCP – General Properties

Besides the properties typical of each type of LCP, they all share the following characteristics:• melt-processable• ordered structures in the melt• highly oriented in the solid state (self-reinforcement)• anisotropic property profile• wide variation in properties possible

by selecting the appropriate LCP type

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LCP properties -1In addition they exhibit the following properties:

–medium density–high tensile strength –high notched impact strength–high tensile modulus of elasticity, up to–wide melting range

–high continuous service temperature

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LCP properties -2• 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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LCP properties -3

• 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.

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LCP

Disadvantages are

- anisotropic physical properties,

- low strength of joints,

- low elongation at break (1.2 to 6.9%).

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LCP

A recently introduced amorphous LCP exhibits less variation in properties at high temperatures. The processing range is wider and the material can thus be blow molded and thermoformed.

Processable LCPs cannot be obtained from rigid linear macromolecules alone because they melt only above their decomposition temperature. This difficulty has been overcome by incorporating flexible linkages in the main chain.

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LCPMany properties, favorable and unfavourable, can be significantly influenced by the choice of processing conditions and molding design, e.g.:

At large wall thicknesses, LCPs lose their peak properties 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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LCP

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 and opaque grey, dark and black colorations.

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

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LCP• The physical properties of self-reinforced

polymers do not differ significantly from those of filled or reinforced engineering plastics.

• The ability to align the orientation tendency in molded or semi-finished material with the direction of the greatest stress to obtain high performance moldings is unmatched

• The cost/performance ratio is also favorable – low shrinkage, low processing temp.

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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 achieved by orientation of flow.

• The usual flat shaped design of injection moldings leads, however, to a multi-axial stress state which oriented LCP cannot cope with isotropically.

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LCP ProcessingInjection Moldings

• The unavoidable shear and stretching flow lead to different localised orientations. This behavior can be compensated only to a limited extent by suitable choice of the position and shape of the gate.

• Instead of stiffness and strength, the main motives nowadays for using LCPs as engineering materials are flowability, flame retardance, dimensional stability at high temperatures, low thermal expansion, resistance to chemicals and rigidity with low wall thickness.

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LCPLCP resins have • Low outgassing even at extreme

temperatures, a factor that's critical for sensitive electronics and optical applications.

• When it comes to precision, LCP resins have excellent molding properties, provide the design freedom for extremely small and intricate parts with cross sections as thin as 0.25 mm.

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LCP – Machining & Fabrication

• LCPs can be machined and joined with conventional tools 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 virgin material.

• Material which has absorbed moisture must be predried.

• Plasticizing cylinders can be purged with PE-HD.

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LCP – Typical Applications• Electrical & Electronic:

– Substrates for chips and printed circuits, – Coil cores, sockets, encapsulations, Sensors, – switches and other electronic components requiring

outstanding performance at elevated temperatures, – Buffer films, couplings and connectors for fiber

optics, – Precision high temperature applications such as

optical 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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LCP – Typical Applications• Drive belt pulleys, packings, bearings,

seals, • Accessories for oil drilling, pumps, • Packings for distillation columns and

scrubbing towers,• Measuring instruments, • Surface mount devices • Dual ovenable cookware • Heat sinks containing graphite fibers

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LCP -Tradenames

• Ekce1, 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

Table -1 Guide values of properties of LCP

Properties Units LCP

Density g/cm3 1.4 -1.9

Water absorption (23°C, 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 275-330

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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 cm 1015-1016

Dielectric constant 2.6-3.3

Dissipation factor, tan 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

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