Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
  • H01B1/20—Conductive material dispersed in non-conductive organic material
  • H01B1/24—Conductive material dispersed in non-conductive organic material the conductive material comprising carbon-silicon compounds, carbon or silicon
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
  • H01C7/02—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having positive temperature coefficient
  • H01C7/027—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material having positive temperature coefficient consisting of conducting or semi-conducting material dispersed in a non-conductive organic material

Definitions

• This invention relates to conductive polymer compositions and devices containing them, especially circuit protection devices.
• Conductive and semi-conductive compositions comprising carbon black dispersed in a polymer are known. They may have room temperature resistivities ranging from less than 1 ohm.cm to 10 8 ohm.cm or more, and may exhibit positive temperature coefficent (PTC) behavior, zero temperature coefficient (ZTC or constant wattage) behavior or negative temperature coefficient (NTC) behavior.
• PTC positive temperature coefficent
• ZTC zero temperature coefficient
• NTC negative temperature coefficient
• the invention provides a conductive polymer composition which has a resistivity at 23°C of less than 10 6 ohm. cm and which comprises
• the invention provides an electrical device, especially a circuit protection device, which comprises:
• compositions may exhibit PTC, ZTC, or NTC behavior; for example any of the compositions disclosed in the prior art and the earlier applications referred to above may be modified by the inclusion of at least one arc-controlling additive.
• the invention is especially valuable in relation to PTC compositions, particularly those having low resistivities at 23°C, eg. below 20 ohm. cm, preferably below 10 ohm. cm, especially below 2 ohm. cm, which are useful in circuit protection devices.
• the preferred arc-controlling additives for use in the present invention are particulate materials, particularly inorganic materials, especially hydrated inorganic materials. Particularly good results have been obtained using alumina trihydrate, Al 2 0 3 3N 2 O. Other inorganic materials include magnesia hydrate, magnesia and alumina.
• the conductive filler and the arc-controlling additive preferably have a total surface area of at least 1,800, especially at least 3,000, particularly at least 4,000, m 2 /cc of composition, with higher values, eg. at least 8,000 m 2 /cc, at least 10,000 m2/cc and at least 12,000 m 2 /cc being particularly preferred.
• the composition should contain an effective amount of the arc-controlling additive, typically 5 to 65%, preferably 10 to 35%, by volume of the composition.
• the composition can also contain further additives which are known to enhance the effectiveness of anti-tracking additives in insulating compositions.
• additives include the phosphorus-containing compounds disclosed in British Patent No. 1,575,465 and the oxides of elements of the transition series, lanthanide series or non-transuranic actinide series disclosed in British Patents Nos. 1,337,951 and 1,337,952.
• the conductive filler in the composition preferably consists essentially of at least one carbon black.
• the carbon black is selected with a view to the electrical characteristics desired in the composition, as taught by the various patents and applications referred to above.
• the carbon black preferably has a particle size, D, which is from 20 to 50 millimicrons and a surface area, S in m 2 /g such that S/D is not more than 10.
• D particle size
• S in m 2 /g such that S/D is not more than 10.
• the polymer component in the composition which may comprise one or more polymers, preferably has a crystallinity of at least 1%, especially at least 5%, particularly at least 10%.
• the polymer component consists essentially of one or more crystalline polymers selected from polyolefins and copolymers of at least one olefin and at least one polar comonomer copolymerisable therewith, eg. polyethylene or polypropylene.
• suitable polymers are referred to in the patents and applications referred to above.
• compositions may be substantially free of cross-linking or may be cross-linked, eg. to a gel fraction of at least 0.4 or 0.6.
• compositions free of cross-linking are preferred, because the presence of cross-linking tends to increase the likelihood of formation of carbonaceous conductive paths when arcing takes place.
• the composition can be prepared by dispersing the carbon black or graphite, the arc-controlling additive and any other additives in the polymer component in any suitable way.
• the composition can be shaped by molding or extrusion or another melt-shaping technique into an element of the desired shape, any cross-linking thereof being carried out after such shaping.
• Conductive polymer compositions comprising a crystalline polymer component, at least 4% by volume of carbon black and at least 4% by volume of a nonconductive particulate filler, the total surface area of the carbon black and filler being at least 1800 m 2 /cc of composition, are described and claimed in the contemporaneously filed application corresponding to U.S. Serial Nos. 141,984 and 141,988 (MP0712 and MP0714).
• the ingredients for the master batch were dry blended and then mixed for 8 minutes in a Banbury mixer turning at high gear. The mixture was dumped, cooled and granulated. The final mix was prepared by dry blending 948 g of the Hydral 705 with 2439 g. of the master batch mixture, and then mixing the dry blend for 4-5 minutes in a Banbury mixer turning at high gear. The mixture was dumped, cooled, granulated and dried (at 70°C, 1 Torr for 16 hours).
• the granulated final mix was melt extruded in the form of a strip about 1.27 cm wide and about 0.27 cm thick, using a cross-head die, around a pair of pre-heated 20 AWG (diameter 0.095 cm) 19/32 stranded nickel-plated copper wires whose centers were 0.6 cm apart.
• the extruded product was cut into 2.5 cm lengths, and the polymeric composition removed from half of each length to produce a circuit control device as shown in Figure 4 of the contemporaneously filed application corresponding to U.S. Serial No. 142,053 (MP0724).
• Example 2 the Master Batch ingredients were blended in a pre-heated Banbury mixer, and the mixture dumped, cooled and granulated. 67 g. of the granulated mixture was banded on a 7.6 cm electric roll mill, and the Hydral was added in portions to give a uniform mixture; mixing was continued for several more minutes and the mixture was then removed from the mill, cooled, granulated and compression-molded into slabs.
• Example 3 the Master Batch ingredients were blended in a pre-heated Banbury mixer, and the mixture dumped, cooled and granulated. 67 g of the granulated mixture was banded on a 3 inch electric roll mill, and the Hydral was added in portions to give a uniform mixture; mixing was continued for several more minutes and the mixture was then removed from the mill, cooled, granulated and compression-molded into slabs.
• Example 4 the procedure described for Example 2 was followed, using the different ingredients shown in Table 2, except that 50 g. of the granulated Master Batch was used and 50 g. of the filler (Maglite D) added to it.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Dispersion Chemistry (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Ceramic Engineering (AREA)
• Electromagnetism (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Thermistors And Varistors (AREA)
• Conductive Materials (AREA)

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Cited By (19)

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• 1981
  • 1981-04-21 EP EP81301764A patent/EP0038713B1/fr not_active Expired
  • 1981-04-21 AT AT81301764T patent/ATE29329T1/de not_active IP Right Cessation
  • 1981-04-21 JP JP6053681A patent/JPS56161463A/ja active Granted
  • 1981-04-21 DE DE8181301764T patent/DE3176415D1/de not_active Expired
  • 1981-04-21 CA CA000375879A patent/CA1176453A/fr not_active Expired
  • 1981-04-21 GB GB8112310A patent/GB2074169B/en not_active Expired
• 1989
  • 1989-10-19 HK HK830/89A patent/HK83089A/xx not_active IP Right Cessation

Patent Citations (4)

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