Electricity: conductors and insulators – Conduits – cables or conductors – Insulated
Reexamination Certificate
1999-09-15
2001-06-26
Wu, David W. (Department: 1713)
Electricity: conductors and insulators
Conduits, cables or conductors
Insulated
C174S1100AR, C174S1100SR, C174S1100PM, C174S11000P, C174S1100AR, C174S118000, C524S430000
Reexamination Certificate
active
06252173
ABSTRACT:
This invention concerns the use of bauxite or brucite as flame-retardants in non-aqueous organic polymer formulations, particularly in electric insulation or sheathing or encapsulation compositions, and also in bitumen.
Bauxite ore contains 40-70% aluminium containing minerals consisting mostly of Gibbsite (a crystalline form of aluminium trihydroxide or ATH) and Boehmite. These ores also contain many mineral impurities including silicates, iron and titanium compounds and organic compounds especially humates.
Brucite is a mineral widely used as a source of magnesium hydroxide (Mg(OH)
2
), the second largest selling (after ATH) mineral hydroxide flame-retardant. Its volume use as a flame-retardant is only a fraction of ATH however. It is more thermally stable than ATH, decomposing at temperatures above 300° C.
Aluminium trihydroxide (ATH) is very widely used as a flame-retardant additive in various organic polymer formulations. ATH has the valuable property (which magnesium hydroxide also shares) of decomposing endothermically, at temperatures around those at which organic polymers tend to ignite, with the release of non-toxic gas (steam) which tends to exclude oxygen. ATH is made by the Bayer process from bauxite. As it has other uses, particularly as a raw material to make alumina for use in smelters for the production of metallic aluminium, it commands a premium price. There is a need for a cheaper flame-retardant having the advantageous properties of ATH. This need has existed for several decades.
U.S. Pat. No. 4,126,473 and U.S. Pat. No. 4,390653 mention bauxite as an alternative flame-retardant to ATH. U.S. Pat. No. 4,216,130 describes the use of bauxite as a flame retarding filler in rubber latex compositions for carpet backing. Critical limits are placed on particle size and surface area and pH, in order that the bauxite may perform satisfactorily in the polymer foam compositions. GB 1506154 describes the use of bauxite as a flame-retardant in polyurethane foam formulations; coarse particles or aggregates were used in order to obtain adequate foam stability. Perhaps because of this destablisation problem, bauxite has never achieved commercial success as a flame-retardant in latex or polyurethane foams, nor indeed in any other polymer formulations.
Polymer formulations for use in the electricity and electronics industries need to comply with varied and demanding criteria, e.g. as defined in Underwriters Laboratories Publication UL44. A major use is as insulation and sheathing for electric or fibre optic wires and cables; where such wires and cables are exposed to atmospheric or marine environments, excellent water resistance is required. Excellent mechanical properties are also required for cable sheathing. Another use is in potting compositions used to coat or encapsulate electric or fibre optic components and connections e.g. on circuit boards or as transformer coils; again, excellent water resistance is required for external or marine environments. Of course, excellent flame-retardant properties are also required in all cases.
This invention is based on the discovery that in many instances the relevant properties of bauxite are substantially or at least as good as those of ATH. Since bauxite is much cheaper than ATH, this discovery has significant commercial implications. Since bauxite contains a large proportion of ATH, the reasons for any improvement are not obvious; perhaps it results from a synergistic effect between the ATH and iron oxide or one of the other mineral components of bauxite.
Bauxite typically contains 10% or more of (non-alumina) impurities of composition that depends on where the mineral has been mined. It was surprising (to the inventors) to discover that these impurities do not materially harm the properties of bauxite (viz a viz ATH), even in demanding applications such as electric component insulation and sheathing and encapsulation.
The mineral brucite also contains significant and variable concentrations of various non-magnesia impurities. Again, it would have been expected that those impurities might harm the properties of brucite when used as a flame-retardant in technically demanding electrical applications.
One impurity which is generally absent from both bauxite and brucite is soluble alkali metal compounds generally measured as soda. By contrast, as a result of its production by the Bayer process, ATH contains measurable soda. On account of this difference in soda content, polymer formulations containing bauxite or brucite often have better water resistance than do comparable formulations containing ATH.
In one aspect, this invention provides a non-aqueous organic polymer formulation which contains an effective concentration of bauxite or brucite as a flame-retardant. Preferably the invention consists essentially of the organic polymer and the bauxite or brucite flame-retardant, optionally together with other typical formulation ingredients in usual concentration. Preferably the formulation is of a quality which is suitable for shaping into a solid product for use as electric or fibre optic insulation or sheathing or encapsulation.
In another aspect the invention provides electric or fibre optic wire or cable provided with insulation or sheathing which is an organic polymer containing an effective concentration of bauxite or brucite as a flame-retardant.
In another aspect the invention provides an electric or fibre optic component or connection coated with or encapsulated in an organic polymer containing an effective concentration of bauxite or brucite as a flame-retardant.
In yet another aspect the invention provides bitumen containing an effective concentration of bauxite or brucite as a flame-retardant. As shown in the examples below, the overall performance of bauxite and brucite as flame-retardants in bitumen is substantially superior to that of ATH.
The non-aqueous organic polymer formulation may be suitable for shaping by melting, casting, extruding, moulding, curing and other techniques well known in the field. The formulation is based on an organic polymer which may be natural rubber or a synthetic resin, plastic or elastomeric, thermoplastic or thermosetting. The following are polymers used for wire and cable applications.
ethylene propylene terpolymer rubber (EPDM)
ethylene propylene rubber (EPR)
isoprene isobutylene (butyl) rubber (IIR)
acrylonitrile butadiene copolymer rubber (NBR)
natural rubber (NR)
polychloprene rubber (PCP)
styrene butadiene rubber (SBR)
silicone rubber (SR)
polyisobutylene (PIB)
with the above able to be either thermoplastic rubber or vulcanised rubber;
polyester
polyacrylate
epoxy
polyurethanes (PUR)
polycarbonate
polyolefins
polypropylene (PP)
ethylene tetra fluoroethylene (ETFE)
ethylene vinyl acetate (EVA)
chlorinated polyethylene (CPE)
chlorosulphonated polyethylene (CSP)
polytetrafluoroethylene (PTFE)
polyethylene tetraphthalate (PETP)
high density polyethylene (HDPE)
very high density polyethylene (VHDPE)
low density polyethylene (LDPE)
ultra low density polyethylene (ULDPE)
linear low density polyethylene (LLDPE)
crosslinked polyethylene
polycarbonate
polyvinyl acetate (PVA)
polyvinyl chloride (PVC)
and any of the above polymers produced with metallocene catalyst technology.
Epoxy, polyester, acrylic and phenolic are examples of polymer systems generally used for potting and encapsulation of electric and fibre optic components and connections.
Other typical formulation ingredients are listed below, and would be used in usual concentrations according to manufacturers recommendations.
vulcanising/cross linking systems
stabilisers including UV stabilisers
antioxidants
plasticisers
lubricants
colorants
impact modifiers
other flame retardants
processing aids
carbon black
coupling agents
silanes
fibres
gloss control agents
anti shrink additives
halogen source.
The term “non-aqueous” is intended to exclude water-based latex systems and other formulations containing significant amounts of water for example as a solvent for catalysts or other additives. Formulations according to the invention are gener
Brown Steve
Dayer Andrew John
Evans Ken
Mead Natalie
Rodriguez Consuelo Espejo
Alcan International Limited
Cooper & Dunham LLP
Egwim Kelechi
Wu David W.
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