WO2009023449A1

WO2009023449A1 - Electrically conductive liquid crystal polymers

Info

Publication number: WO2009023449A1
Application number: PCT/US2008/071880
Authority: WO
Inventors: Joseph Huang; Cory L. Prestangen
Original assignee: Polyone Corp
Current assignee: Avient Corp
Priority date: 2007-08-14
Filing date: 2008-08-01
Publication date: 2009-02-19
Anticipated expiration: 2010-02-14

Abstract

An electrically conductive polymer compound is disclosed. The compound comprises a matrix comprising liquid crystal polymer and electrically conductive particles consisting essentially of carbon nanotubes dispersed in the matrix. The compound is useful for making extruded and molded plastic articles that need electrical conductivity.

Description

ELECTRICALLY CONDUCTIVE LIQUID CRYSTAL POLYMERS

CLAIM OF PRIORITY

[0001] This application claims priority from U.S. Provisional Patent

Application Serial Number 60/955,785 bearing Attorney Docket Number 12007013 and filed on August 14, 2007, which is incorporated by reference.

FIELD OF THE INVENTION

[0002] This invention concerns liquid crystal polymer compounds which are electrically conductive.

BACKGROUND OF THE INVENTION

[0003] Thermoplastic articles can be superior to metal because they do not corrode and can be molded or extruded into any practical shape.

Thermoplastic articles are also superior to glass because they do not shatter when cracking.

[0004] Thermoplastic articles can be made to be electrically conductive if sufficient amounts of electrically conductive particles are dispersed in the articles. Many types of articles need to be electrically conductive, and neither metal nor glass articles is practical.

SUMMARY OF THE INVENTION

[0005] Therefore, what the art needs is an electrically conductive thermoplastic compound that can be used to make thermoplastic articles for use in electrically conductive circumstances, particularly where the surface of the thermoplastic article needs to have at least low surface electrical resistivity or even electrical conductivity.

[0006] The art also needs an electrically conductive thermoplastic compound that is durable and has a high melting point, so that the thermoplastic article can function in temperatures above ambient temperature and in circumstances where the article encounters friction against other materials. [0007] The present invention has solved that problem by relying on liquid crystal polymer to provide the high temperature and durability, with electrically conductive particles dispersed therein. Moreover, the present invention has found that carbon nanotubes should be the only type of electrically conductive particle dispersed in the liquid crystal polymer. [0008] Thus, one aspect of the invention is an electrically conductive thermoplastic compound, comprising (a) liquid crystal polymer; and (b) a carbonaceous electrically conductive additive dispersed in the liquid crystal polymer, wherein the additive consists essentially of carbon nanotubes in an amount ranging from about 0.1 to about 10 weight percent of the compound; and wherein the compound has a surface resistivity of less than 10¹² ohm/square. [0009] Features of the invention will be explained below.

EMBODIMENTS OF THE INVENTION

[00010] Thermoplastic Polymer Matrix

[00011] Liquid Crystal Polymer

[00012] Any commercially available liquid crystal polymer (LCP) is a candidate to serve as the matrix of the compound of the present invention. The choice of LCP depends on the ultimate processing and performance properties desired by one of ordinary skill in the art, who can make a selection without undue experimentation, because it is known that LCP is a highly crystalline, thermotropic (melt-orienting) thermoplastics that can deliver exceptionally precise and stable dimensions when making thermoplastic articles. LCP is particularly suitable for high temperature performance and chemical resistance in very thin-walled injection molded applications.

[00013] Non-limiting examples of commercially available LCP include the Zenite brand product line of LCP from DuPont (Wilmington, DE) and the Vectra brand product line of LCP from Ticona (Wilmington, DE). Of the product line, injection molding grades are preferred.

[00014] One commercially available LCP is Vectra A950 brand LCP from Ticona.

[00015] Optional Second Polymer

[00016] Optionally, any polymer which is compatible and preferably miscible with LCP can be used in a blend with LCP to achieve particular processing or performance properties when making thermoplastic articles. Without undue experimentation, one skilled in the art can determine which polymers are suitable for blending with LCP and select from them. Non- limiting examples of such polymers include polyphenylene sulfide (PPS), syndiotactic polystyrene (s-PS), and combinations thereof. [00017] Electrically Conductive Particles

[00018] The electrically conductive particles for the present invention are carbon nanotubes, expressly to the exclusion of other types. The reason for the selection of carbon nanotubes is based on the tremendous electrically conductivity that can be achieved with them, as compared to other types of electrically conductive particles, whether metallic or non-metallic or both. Relatively small amounts of carbon nanotubes, with their considerably large aspect ratios, provide a surface resistivity of less than 10¹² ohms/square in compounds of the present invention. It is viewed that any other type of electrically conductive particle would interfere with the use of carbon nanotubes as the sole means of providing electrical conductivity. [00019] Carbon nanotubes have aspect ratios ranging from 10:1 to

10,000:1 and are particularly suitable for dispersion within a thermotropic thermoplastic polymer such as LCP. This is because carbon nanotubes are also susceptible to orientation or alignment.

[00020] Carbon nanotubes are categorized by the number of walls. The present invention can use both single-wall nanotubes (SWNT) or multi-wall nanotubes (MWNT) or both. [00021] To achieve such aspect ratios, nanotubes can have a length ranging from about 1 μm to about 10 μm, and preferably from about 1 μm to about 5 μm and a width or diameter ranging from about 0.5 nm to about 1000 nm, and preferably from about 0.6 nm to about 100 nm. [00022] Also, such conductive media should have resistivities ranging from about 1 x 10^"8 Ohm»cm to about 3 x 10² Ohm»cm, and preferably from about 1 x 10^"6 Ohm»cm to about 5 x 10^"1 Ohm»cm.

[00023] More information about MWNT can be found at U.S. Pat No.

4,663,230 (Tennent). More information about SWNT can be found in U.S. Pat. No. 6,692,717 (Smalley et al.)

[00024] Non-limiting examples of carbon nanotubes are SWNT made and sold by Carbon Nanotechnologies of Houston, Texas and MWNT made and sold by Hyperion Catalysis International of Cambridge, Massachusetts. [00025] The carbon nanotubes can be added at the time of melt compounding of the LCP or can be made into a masterbatch to facilitate a two- step process of dispersion into the ultimate thermoplastic compound. Preferably, the masterbatch route is used, because carbon nanotubes are extraordinarily small particles need special equipment to be dispersed into a matrix. The polymer carrier for the masterbatch can be LCP or an optional polymer mentioned above. The amount of MWNT in a masterbatch can range from about 5 to about 30 weight percent, and preferably from about 10 to about 20 weight percent. The concentration of MWNT in the masterbatch depends, in part, on the amount of masterbatch to be used at the time of melt compounding, using a so-called "let-down" ratio.

[00026] Hyperion Catalysis International offers the service of dispersing

MWNT it makes into a variety of thermoplastic polymer resins. In this instance, Hyperion Catalysis International made masterbatch MB9515-06 for use in the present invention. One skilled in the art can request similar commercial services from Hyperion Catalysis International. [00027] Optional Other Additives

[00028] While carbon nanotubes serve as the only electrically conductive particles, the compound of the present invention can include conventional plastics additives in an amount that is sufficient to obtain a desired processing or performance property for the compound. The amount should not be wasteful of the additive nor detrimental to the processing or performance of the compound. Those skilled in the art of thermoplastics compounding, without undue experimentation but with reference to such treatises as Plastics Additives Database (2004) from Plastics Design Library (www.williamandrew.com), can select from many different types of additives for inclusion into the compounds of the present invention.

[00029] Non-limiting examples of optional additives include adhesion promoters; biocides (antibacterials, fungicides, and mildewcides), anti-fogging agents; anti-static agents; bonding, blowing and foaming agents; dispersants; fillers and extenders; fire and flame retardants and smoke suppresants; impact modifiers; initiators; lubricants; micas; pigments, colorants and dyes; plasticizers, impact modifiers; processing aids; release agents; silanes, titanates and zirconates; slip and anti-blocking agents; stabilizers; stearates; ultraviolet light absorbers; viscosity regulators; waxes; catalyst deactivators, and combinations of them. [00030] Ingredients

[00031] Table 1 shows the acceptable, desirable, and preferred amounts of each of the ingredients discussed above, recognizing that the optional ingredients need not be present at all. All amounts are expressed in weight percent of the total compound.

[00032] Processing

[00033] The preparation of compounds of the present invention is uncomplicated. The compound of the present can be made in batch or continuous operations. As mentioned above, it is preferable to have the carbon nanotubes be initially dispersed into a concentrated masterbatch by experts who work with carbon nanotubes regularly and have the equipment and expertise to provide an excellent dispersion.

[00034] Mixing in a continuous process typically occurs in a single or twin screw extruder that is elevated to a temperature that is sufficient to melt the polymer matrix with addition of other ingredients either at the head of the extruder or downstream in the extruder. Extruder speeds can range from about 50 to about 500 revolutions per minute (rpm), and preferably from about 100 to about 300 rpm. Typically, the output from the extruder is pelletized for later extrusion or molding into polymeric articles.

[00035] Mixing in a batch process typically occurs in a Banbury mixer that is capable of operating at a temperature that is sufficient to melt the polymer matrix to permit addition of the solid ingredient additives. The mixing speeds range from 60 to 1000 rpm. Also, the output from the mixer is chopped into smaller sizes for later extrusion or molding into polymeric articles. [00036] Subsequent extrusion or molding techniques are well known to those skilled in the art of thermoplastics polymer engineering. Without undue experimentation but with such references as "Extrusion, The Definitive Processing Guide and Handbook"; "Handbook of Molded Part Shrinkage and Warpage"; "Specialized Molding Techniques"; "Rotational Molding Technology"; and "Handbook of Mold, Tool and Die Repair Welding", all published by Plastics Design Library (www.williamandrew.com), one can make articles of any conceivable shape and appearance using compounds of the present invention.

[00037] The compounds of the present invention are particularly suitable for thin- wall injection molding for use in making intricate or complex molded shapes.

USEFULNESS OF THE INVENTION

[00038] Compounds of the present invention can be molded into any shape which benefits from having electrically conductive or static dissipative surfaces, high stiffness in thin wall sections, and a low coefficient of thermal expansion. Compounds of the present invention can be used by anyone who purchases Stat-Tech brand conductive polymer compounds from PolyOne Corporation (www.polyone.com) for a variety of industries, such as the medical device industry or the electronics industry where disposable or recyclable plastic articles are particularly useful in laboratory or manufacturing conditions. [00039] Examples of electronics industry usage includes media carriers, process combs, shipping trays, printed circuit board racks, photomask shippers, carrier tapes, hard disk drive components, sockets, bobbins, switches, connectors, chip carriers and sensors, etc. LCP compounds can withstand surface mount soldering temperatures, including those needed with lead-free solder.

[00040] Examples of medical industry usage includes electromagnetic interference shielding articles, tubing, drug inhalation devices, laboratory pipette tips, implantable medical device components, biomedical electrodes, and other devices that need protection from electrostatic discharge, static accumulation, and electromagnetic interference. LCP compounds can replace stainless steel in medical applications and certain grades of commercial LCP are compliant with USP Class VI guidelines and ISO 10993-1. Compounds of the present invention are both electrically conductive and resistant to gamma radiation, steam autoclaving and most chemical sterilization methods. [00041] As an example of the usefulness of the invention, a formulation having the ingredients shown in Table 2 was made according to the procedure and conditions of Table 3 and Table 4.

[00042] In the form of a plastic article having the shape of a molded plaque, the compound had a surface resistivity of 10⁹ as measured using ASTM D-257. This is within the desired range of 10⁶ -10⁹ ohms/square for an electronic product that needs to be electrically conductive. [00043] The invention is not limited to the above embodiments. The claims follow.

Claims

What is claimed is:

1. An electrically conductive thermoplastic compound, comprising:

(a) liquid crystal polymer; and

(b) a carbonaceous electrically conductive additive dispersed in the liquid crystal polymer, wherein the additive consists essentially of carbon nanotubes in an amount ranging from about 0.1 to about 10 weight percent of the compound; and wherein the compound has a surface resistivity of less than 10¹² ohm/square.

2. The compound of Claim 1, wherein the carbon nanotubes are single- wall nanotubes.

3. The compound of Claim 1, wherein the carbon nanotubes are multi-wall nanotubes.

4. The compound of any of Claims 1-3, further comprising an optional second polymer selected from the group consisting of polyphenylene sulfide, polystyrene, and combinations thereof.

5. The compound of any of Claims 1-4, further comprising an optional functional additive selected from the group consisting of adhesion promoters; biocides (antibacterials, fungicides, and mildewcides), anti-fogging agents; antistatic agents; bonding, blowing and foaming agents; dispersants; fillers and extenders; fire and flame retardants and smoke suppresants; impact modifiers; initiators; lubricants; micas; pigments, colorants and dyes; plasticizers, impact modifiers; processing aids; release agents; silanes, titanates and zirconates; slip and anti-blocking agents; stabilizers; stearates; ultraviolet light absorbers; viscosity regulators; waxes; catalyst deactivators, and combinations of them.

6. The compound of any of Claims 1-5, wherein the carbon nanotubes have an aspect ratio ranging from 10:1 to 10,000:1.

7. The compound of any of Claims 1-5, wherein the carbon nanotubes have a diameter ranging from about 0.5 nm to about 1000 nm.

8. The compound of any of Claims 1-7, wherein the amount of liquid crystal polymer ranges from about 91 to about 94 weight percent of the compound and wherein the electrically conductive particles ranges from about 4 to about 9 weight percent of the compound.

9. A molded plastic article made from the compound of any of Claims 1-8.

10. A method of making a compound of any of Claims 1-8, comprising the steps of

(a) dispersing the carbon nanotubes in a carrier of liquid crystal polymer in a concentration ranging from about 5 to about 30 weight percent to form a carbon nanotube masterbatch, and

(b) melt mixing the carbon nanotube masterbatch with additional liquid crystal polymer, wherein the masterbatch is about 30 to about 35 weight percent of the compound.