LIQUID CRYSTAL POLYMER (LCP)

HISTORY

1.
1972 Carborundum (CBO) marketed (EKKCEL 1-2000 (copolymer of p-hydroxybenzoic acid, terephthalic acid, and 4,4 '-dihydroxy diphenyl).
2.
1976 Eastman Kodak announced X-7G, a liquid crystal type polyester modified with -p-hydroxy benzoic acid (PHB).
3. 1979 Sumitomo Chemical developed Ekonol E2000 series used its own technology.
4. 1984 CBO technology sold to Dart, and its subsidiary Dartco (now Amoco) marketed a heat resistant type I LCP (Xydar).
5. 1985 Celanese (now Ticona) debuted a Type II LCP (VECTRA) with a good balance of heat resistance and processability. Polyplastics starts imports into Japan and marketed in the same year.




PROPERTIES
The chemical structure of LCP is as below::
 

What is liquid crystal polymer? It has liquid crystal behavior with orderly array and the optical refraction phenomenon even in the molten state owing to the forces between the molecules. LCP can be divided into three categories according to heat deflection temperature: 

•Type I LCP: HDT above 300°C.
•Type II LCP(A): HDT between 240°C and 300°C. 
•Type II LCP(B): HDT between 200°C and 240°C. 
•Type III LCP: HDT below 200°C. 

The liquid crystal polymer refers to the plastic molecules containing the structure of , thus LCP of different manufacturers has different functional groups of (R, R’) and structures of (—A—B—)which lead to different processing properties and different heat resistances.

1.
General properties: LCP resin is generally beige, but also a solid opaque white powder. Density is 1.4~1.7 g/cm3.
2.
Mechanical properties: LCP has self-reinforced features, even the mechanical strength and elastic modulus of unfilled LCP can be equal to or beyond that of common engineering plastics with 10% of glass fiber reinforced. Especially when reinforced by glass fiber or carbon fiber, it can reach abnormal high standard which is superior to common engineering plastics. LCP also has good friction and wear properties, while creep can be ignored.
3.
Thermal performance: LCP has dense crystalline structure with a high load deformation temperature (180~260°C) , the continuous use of high temperature (200~240°C), soldering (260°C, 10 seconds~310°C, 10 
seconds) despite of its relatively low melting point.
4.
Electrical properties: LCP has excellent electrical insulation properties, the dielectric strength of which is much higher than that of common engineering plastics. It also has good arc resistance. Its electrical properties will not be affected when used as electrical parts in continuous use temperature of 200 ~300°C and the intermittent use of the temperature is up to 316°C.
5.
Flame retardance: LCP is self-extinguishing, UL94 V-0 without any flame retardants and the flames do not drop with no toxic fumes which is very rare in the plastics. Thus it is one of the best fire safe plastic.
6.
Weather resistance: Much better than most plastics and its performance will not be significantly decreased in the circumstances of carbon arc accelerated by UV irradiation 6700 hours, or 10 trillion Co60 nuclear radiation Mrads.
7.
Resistant chemical substances: LCP can not be affected in a wide temperature range by all industrial solvents, fuel oil, detergent, bleach, hot water and acid with concentration 90%, alkali 50% .Stress cracking will no occur in the solvents.
8.
Non-resistant chemical substances: Acid with concentration over 90%, alkali over 50%.
9.
Hydrolysis resistance: Excellent hydrolysis resistance.
10. Radiation resistance: Excellent radiation resistance.


MOLDING CONDITIONS
LCP can be molded in the following ways:
1. Melt spinning 2. Injection 3. Extrusion 4. Pressing 5. Coating

Injection molding conditions:

1.
Predrying: Though a moisture proof package is adopted, the material is of a polyester type polymer, so it is advised to predry before molding. The drying conditions are: 140~160°C for more than 4 hours (max. 24 hours). For drying, a shelf type air dryer and hopper dryer are suitable. When using either one, the hot air temperature and velocity must be regulated for uniform drying under the conditions described above. Especially when using a hopper dryer, it is necessary to pay attention not to have a short pass and the pellet temperature must not be the set temperature but the temperature described above. A dehumidifying dryer gives good results. It is also advised to use a hopper dryer during the molding in order to avoid reabsorption of moisture.
2.
Use of regrind: Regrinds can be used. But if 100% regrind is used, the mechanical properties and thermal resistance will be decreased owing to the broken glass fibers. Furthermore, it should be noted that repeated regrinding will change the color to a slightly darker shade. Thus it is recommended that the use of regrind be limited to 25% of total volume. 
3.
Thermal stability: LCP has no great increase in viscosity even when it is retained in the cylinder for a long time.
4.
Injection machine: Since the molding temperature and the injection speed of PPS are both very high, a full-electric machine is recommended to acquire a quality product.
5.
Cylinder capacity: Weight of one shot must be 50-75% of the cylinder capacity in general.
6.
Nozzle and locking system: The nozzle may be a commonly used open nozzle, but in order to avoid drooling of the molten material, a shut-off valve is desired.
7.
Screw: The L/D ratio is 20:1.
8.
Cylinder temperature: Type I: 355~400°C; Type II: 330~370°C;Type III: 290~320°C.
9.
Mold temperature: 80~120°C.
10.
Injection pressure: 15~45MPa.
11.
Injection speed: High: 100~300mm/sec.
12.
Back pressure: 0~2MPa.
13.
Screw speed: 100~200 rpm.
14.
Molding shrinkage: Flow direction: 0.02~0.07%; Transverse direction: 0.5~0.7%.
15.
Secondary processing: LCP can be bonding and welding, etc.



MOLD DESIGN

1.
Mold design: As LCP is not corrosive to mold, all standard mold steels are usable. Some fillers are corrosive to mold and in such a case, selection of a suitable mold steel or heat treatment is necessary, as in the case of all other molding materials filled with the similar additives.
2.
Runners: When easiness of machining is compared, the runner shapes are in the order of a semi-round, trapezoid and round, but considering the cross-sectional area and pressure loss, the order will be the round, trapezoid and semi-round. Here, the round or trapezoidal runners are recommended. The optimum runner size depends on the required length and product size when economical advantages are taken into consideration, and the diameter of 2 to 5mm is generally adopted. The runner length should be as short as possible. In multi-cavity molds, the distance between cavities must be made even wherever possible in order to decrease irregular filling between the cavities. LCP by nature is a material of easy mold releasing and at the same time it is a high flow material, therefore, if there is any defect on the mold surface, it will be transferred to the molded parts and the mold releasing is sometimes affected. The sprues and runners must be polished carefully. At the end of the sprue and runner a slug well should be provided to prevent the cold slug from running into the molded parts.
3.
Gate: The gate design is particularly important when designing a mold for LCP. As LCP is anisotropic, the gate location must be decided by considering the mold filling pattern. When molded parts are to take advantages of LCP's outstanding characteristics in a specific direction, such a direction is made the flow direction as a rule. When a product shape is complicated and the flow direction is random during the mold filling, it is not necessary to consider the influences of gate location. For the gate system, the popularly adopted side gate, pin-point gate and submarine gate are all adaptable.
4.
Release taper: The standard release taper is 1 to 20. When dimensional accuracy is particularly required, a release taper of 1/4 to 1/20 can be adopted.
5.
Air vent: LCP generates nearly no gas during molding. Even so, it is good to provide an air vent to remove the air inside the mold cavity for easy filling. The air vent for LCP is 1/100 to 2/100mm deep. The depth of this range has the limited cross-sectional area of air passage, so it is advised to provide air vents not only at air trapping spots but in a wide area.


APPLICATIONS


1.
Automotive industry: Automobile combustion system components, burning pumps, insulation components, precision components and electronic components, etc.
2.
Electrical and Electronics: High-density connector, coil planes, bobbins, the substrate carrier, capacitors case, socket, surface-mount electronic components, electronic packaging materials, printed circuit boards, braking equipment and lighting equipment, etc.
3.
Home-use Electric Appliances: Microwave oven kitchen containers and food containers, etc.
4.
Mechanical industry: Distillation column filler, valves, pumps, oil well equipment, measurement equipment parts, seals and bearings ,etc.
5.
Medical industry: Surgical equipment, intubations, knives, sterilization trays, laparoscopy and dental materials, etc.



COMPUTER PARTS
CONNECTOR




MANUFACTURERS AND BRANDS

MANUFACTURER
BRAND
Ticona Vectra
DuPont Zenite
Polyplastics Vectra
Solvay Xydar
NPC Xydar
Sumitomo Sumikasuper
Ueno Fiber Ueno
Toray Siveras
DIC Octa
Unitika Rodrun
MEP Parapet