Liquid crystal polymer film

Details Liquid crystal polymer film Liquid crystal polymer film

1991-12-12

1994-02-22

Robinson, Ellis P.

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

With charge transferring layer of specified composition

25229901, 264108, 2641761, 2641771, 26417716, 425325, 425224, 428480, C09K 1900

Patent

active

052885291

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the invention
The invention relates to methods and apparatus for forming a mechanically isotropic liquid crystal polymer film. It relates more particularly to producing a film which inherently maintains its flat shape and has a more uniform coefficient of thermal expansion than has been obtainable previously. It also relates to methods and apparatus for forming a film structure comprising two relatively thin outer layers which are controllably oriented in one direction, and one or more relatively thick inner layers controllably oriented in one or more different directions.
2. Description of Related Art
The invention relates in general to the formation of multiaxially oriented films from high-molecular-weight liquid crystalline lyotropic or thermotropic polymers (homopolymers, copolymers, and the like), under processing conditions whereby the films have a controlled molecular orientation. The films of the present invention are preferably prepared from rod-like, extended-chain, aromatic-heterocyclic polymers. These polymers generally fall into two classes, those that are modified in solution form, i.e., lyotropic liquid crystalline polymers, and those that are modified by temperature changes, i.e., thermotropic liquid crystalline polymers. For a shorthand expression covering both types of polymers, the present disclosure will use the term "ordered polymers" or "liquid crystal polymers."
The ordered polymers concerned herein are believed to have a fixed molecular shape, e.g. linear, or the like, due to the nature of the monomeric repeating units comprising the polymeric chain. Linear ordered polymers are also known as "rod-like" polymers. These rod-like polymers can be blended with the more common, typical "coil-like" polymers in which the molecular chain does not have a relatively fixed shape. Some of these blends have processing and functional characteristics similar to liquid crystal polymers, and to that extent, these blends are to be considered as being included in the invention disclosed herein.
Liquid crystal polymer films have desirable qualities in a number of applications, but significant drawbacks related to their mechanical anisotropy. They are useful in particular for forming circuit substrates. Circuits can be formed on such a film by plating and etching, and then a plurality of such circuits can be laminated, to form a circuit board having multiple circuits accommodated within the board. Flexible circuits can also be formed on liquid crystal polymer films,
However, the mechanical properties of liquid crystal polymer films have been inadequate for these applications. They cannot be blown and drawn after extrusion as coil polymers can, since they become too highly oriented in the die. They are too weak in the non-orientation directions to be stretched after extrusion, even while in semi-flowable form. To improve their strength, liquid crystal polymer films are typically extruded between a pair of concentric counter-rotating cylindrical dies to form a tube. This process causes the inner and outer surface layers of the tube to have different respective directions of fibrillar orientation, and this gives the tube biaxial strength and permits blowing and drawing, if desired.
FIGS. 2A-2C are schematic representations of extruder films showing the morphology of the oriented polymer material layers therein. In FIG. 2A, with no transverse or circumferential shear, the film has a uniaxial orientation, with all molecules oriented in the machine direction, that is, longitudinally with respect to the direction of flow through the die. In FIG. 2B the film has a biaxial orientation. The molecules in the top portions of the film are oriented at an angle of +theta with respect to the machine direction while the portions of the film in the lower part of FIG. 2B are oriented at an angle of -theta to the machine direction. FIG. 2C shows a planar isotropic film wherein the polymer rods lie randomly in the film plane, not strongly oriented at any specific angle with respect to

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