Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
  • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F290/00—Macromolecular compounds obtained by polymerising monomers on to polymers modified by introduction of aliphatic unsaturated end or side groups
  • C08F290/08—Macromolecular compounds obtained by polymerising monomers on to polymers modified by introduction of aliphatic unsaturated end or side groups on to polymers modified by introduction of unsaturated side groups
  • C08F290/14—Polymers provided for in subclass C08G
  • C08F290/147—Polyurethanes; Polyureas
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/70—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the isocyanates or isothiocyanates used
  • C08G18/81—Unsaturated isocyanates or isothiocyanates
  • C08G18/8141—Unsaturated isocyanates or isothiocyanates masked
  • C08G18/815—Polyisocyanates or polyisothiocyanates masked with unsaturated compounds having active hydrogen
  • C08G18/8158—Polyisocyanates or polyisothiocyanates masked with unsaturated compounds having active hydrogen with unsaturated compounds having only one group containing active hydrogen
  • C08G18/8175—Polyisocyanates or polyisothiocyanates masked with unsaturated compounds having active hydrogen with unsaturated compounds having only one group containing active hydrogen with esters of acrylic or alkylacrylic acid having only one group containing active hydrogen

Definitions

• These coatings require both UV cure, and a post-cure at a temperature of 130°C for 4- 17 hr .
• the process for making transformer coils with these coatings is unattractive in particular because of the post-cure required.
• insulating coatings for high power transformer coils should exhibit several properties.
• the coating should be flexible so that it can withstand bending of the coated conductor as it is wound into a coil.
• the coating should be able to withstand immersion in oil for 28 days at 150°C as described in US-A- 4481258.
• the coating should remain adherant at elevated temperature that is encountered when the transformer is under load.
• the coating should have a dielectric constant smaller than 5% at 60 Hz (24°C), -
• the coating should have a dielectric dissipation factor smaller than 0.05 at 24°C before and after hot oil exposure and smaller than 0.2 at 150°C, both at 60 Hz.
• the invention relates to a metal conductor with a cured coating of about 10-500 ⁇ m thickness which coating has a dielectric dissipation factor (60Hz, 24°C) of lower than about 0.05 and is a radiation-cured coating formulated from components comprising: a) an acrylate functional urethane oligomer having a hydrocarbon backbone b) one or more mono- or polyfunctional diluents, and optionally, c) one ore more light sensitive radical generating compounds.
• the invention relates to a radiation curable coating composition
• a radiation curable coating composition comprising a) an acrylate functional urethane oligomer having a hydrocarbon backbone b) one or more mono- or polyfunctional diluents and optionally, and optionally c) one or more light sensitive radical generating compounds which coating when cured with radiation has a dielectric dissipation factor at 60 Hz at 24°C of lower than about 0.05, a dissipation factor at 60 Hz at 150°C of lower than about 0.2, and an elongation at 25°C of a 25 ⁇ m thin coating of at least about 50%.
• the insulating coating layer on the metal conductor has outstanding insulating properties, both at low and high temperature.
• the insulating coating layer appears to have a low dielectric constant, e.g. lower than about 5 (60Hz, 24°C) and a good dielectric breakdown value.
• the coating is flexible as to allow bending of the metal conductor.
• the metal conductor preferably is an iron, copper, aluminum or silver conductor. In particular aluminum, copper or silver are preferred.
• the metal conductor can be in the form of a wire or a strip.
• the coated metal conductor can be used in capacitors, transformers, motors and the like.
• the coated metal conductor can be used in hot oil environments because of the outstanding properties of the coating.
• the invention is most suitable for coating aluminum or copper strip or wire used in forming power distribution transformer coils.
• the cross-section of the strips commonly ranges from about 0.1-1.7 mm thick and 7-60 cm wide. The strips are wound into coils which are then assembled with cores to form transformers.
• the metal wire or strip is coated as a straight continuous web and the coated metal wire or strip may be wound for storage or for direct use.
• the coating when cured should be cured well at the surface so that no blocking occurs in case the metal conductor is stored.
• the coating of the present invention is flexible so that winding for either storage, and/or bending of the coil or wire in the manufacture of articles like transformers does not cause damage to the coating.
• the coating measured at 25 ⁇ m thickness preferably has an elongation of at least about 50%.
• the coating has at least one Tg of below 20°C (as measured by the peak of the tan ⁇ curve in a DSM analysis at 1 Hz).
• the coating has a dissipation factor at 60 Hz at 150°C of lower than about 0.2. Furthermore, the coating preferably has a dissipation factor at 60 Hz at 24°C before and after a hot oil aging test of lower than about 0.05. The coating exhibits its insulating properties even as very thin films.
• the coating preferably has a thickness of about 10-500 ⁇ m, and more in particular between of about 10-100 ⁇ m.
• the first component of the radiation curable coating is an acrylate functional urethane oligomer (a) having a hydrocarbon backbone.
• the word backbone is used to denote the oligomer or polymer to which the acrylate urethane groups are attached.
• This acrylate functional urethane oligomer preferably is used in an amount of about 20-80 wt.% with respect to the total coating composition. More preferably, the amount is about 30-65 wt.%.
• the oligomer (a) utilized in the present invention preferably is the reaction product of (i) a hydrocarbon compound with groups reactive with an isocyanate; (ii) a polyisocyanate; and (iii) an hydroxy functional endcapping monomer.
• the hydrocarbon compound with groups reactive with an isocyanate (i) is provided by a linear or branched hydrocarbon containing a plurality of said reactive end groups, and providing a hydrocarbon backbone to the oligomer.
• the isocyanate reactive groups may be thiol, amine or hydroxy. Particularly preferred are hydroxy groups. Because of the amine and thiol groups, the urethane oligomer may comprise urea or thio-urea groups.
• the hydrocarbon portion is preferably from about 400 to about 4,000 molecular weight. Molecular weight in this case is determined by gel permeation chromotography (GPC), using a methylene chloride solvent, as measured against polystyrene molecular weight standards.
• hydrocarbon is meant a non-aromatic compound containing a majority of methylene groups (-CH 2 -) and which may contain internal unsaturation and/or pendent unsaturation. Fully saturated (i.e., hydrogenated) hydrocarbons are preferred because the electric dissipation factor of the cured coating increases as the degree of unsaturation increases.
• Suitable hydrocarbon polyols include hydroxyl-terminated, fully or partially hydrogenated 1 , 2-polybutandiene; 1,4- and 1,2- polybutadiene copolymers; 1 , 2-polybutadiene polyol hydrogenated to an iodine number of from 9 to 21; fully or partially hydrogenated polyisobutylene polyol; mixtures thereof, and the like.
• the hydrocarbon polyol is substantially fully hydrogenated, and thus a preferred polyol is hydrogenated 1,2- polybutadiene, and hydrogenated 1 , 4-, 1 ,2-polybutadiene copolymers with about 50-80% 1 , 4-butadiene and 50-20% 1,2-butadiene copolymerized monomers.
• Suitable hydrocarbon polyamines or polythiols include the above described polyols with thiol or amino groups in stead of the hydroxy groups.
• the polyisocyanate component (ii) is aromatic or non-aromatic, and preferably is non-aromatic.
• a suitable aromatic polyisocyanate is toluene diisocyanate.
• Non-aromatic polyisocyanates of from 4 to 20 carbon atoms may be employed.
• Suitable saturated aliphatic polyisocyanates include isophorone diisocyanate; dicyclohexylmethane-4,4 '-diisocyanate; 1 , 4-tetramethylene diisocyanate; 1, 5-pentamethylene diisocyanate; 1 , 7-heptamethylene diisocyanate; 1,8- octamethylene diisocyanate; 1 , -nonamethylene diisocyanate; 1 , 10-decamethylene diisocyanate; 2,2,4- trimethyl-1, 5-pentamethylene diisocyanate; 2,2'- dimethyl-1 , 5-pentamethylene diisocyanate; 3-methoxy- 1, 6-hexamethylene diisocyanate; 3-butoxy-l, 6- hexametalyene diisocyanate; omega, omega '-dipropylether diisocyanate; 1 , 4-cyclohexyl diisocyanate; 1,3- cyclohexyl di
• the reaction rate between a hydroxyl- terminated hydrocarbon and the diisocyanate may be increased by use of a catalyst in the amount of 100 to 200 ppm.
• Suitable catalyst include dibutyl tin dilaurate, dibutyl tin oxide, dibutyl tin di-2- hexanoate, stannous oleate, stanous octoate, lead octoate, ferrous acetoacetate, and amines such as tr iethylamine, diethylmethlamine, triethylenediamine, dimethyl-ethylamine, morpholine, N-ethyl morpholine, piperazine, N,N-dimethyl benzylamine, N,N-dimethyl laurylamine, and mixtures thereof.
• a preferred catalyst is dibutyl tin dilaurate.
• the endcapping monomer (iii) is a hydroxyl- terminated aliphatic acrylate or methacrylate, preferably an alkoxylated (meth)acrylate wherein 1-10 molecules of ethylene, propylene at butylene oxide are reacted with acrylic or methacrylic acid.
• Suitable hydroxyl-terminated monoacrylates which may be used as the endcapping monomer include hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate and hydroxypropyl methacrylate. Hydroxyethyl acrylate is preferred because it imparts a faster cure rate to the polyurethane oligomer.
• the molar ratio of the hydrocarbon compound, diisocyanates and endcapping monomer is preferably approximately 1:2:2.
• the second component (b) is constituted by one or more mono- or polyfunctional diluents.
• the diluents are acrylate or methacrylate functional. However, minor amounts of other type of monomer can be used as well.
• the amount of component (b) preferably is about 20-80 wt.% of the total coating composition, more preferred about 20-70 wt.%.
• Particularly preferred is the use of about 10-50 wt.% of monofunctional diluent (s), and 5-40 wt.% of polyfunctional diluent (s).
• the second component (b) of the composition comprises preferably a monofunctional alkyl acrylate or methacrylate-based diluent for monomer.
• the alkyl portion of the monomer has between 6 and 18 carbon atoms, and preferably between 8 and 15, and therefore is hydrocarbon in character.
• This monomer may be either straight chain, branched or cyclic.
• This component comprises from about 5 percent to about 50 percent by weight of the composition, based upon the total weight of the coating composition. Preferably, it comprises from about 5 percent to about 50 percent, and more preferably from about 10 percent to about 40 percent by weight of the composition.
• the monomer is selected to be one that is compatible with the oligomer discussed above.
• C 6 to C ⁇ e alkyl acrylate or methacrylate- based monomers include hexyl acrylate; hexyl methacrylate; cyclohexylacrylate; cyclohexyl- methacrylate; 2-ethylhexyl acrylate; 2-ethylhexyl methacrylate; isooctyl acrylate; isooctyl methacrylate; octyl acrylate; octyl methacrylate; decyl acrylate?
• the second component further comprises preferably an alkylacrylate polyfunctional diluent (or monomer) in an amount of about 5-50 wt.%, preferably about 5-40 wt.%.
• alkylacrylate polyfunctional diluent or monomer
• Suitable examples of these polyfunctional monomers are C 4 -C 15 hydrocarbon diol acrylates; C 4 -C 15 hydrocarbon diol methacrylates; and mixtures of the above.
• hydrocarbon includes cycloalkylgroups.
• Other suitable polyfunctional acrylates are (alkoxylated) polyolpolyacrylates.
• suitable polyfunctional monomers include butanediol dimethyacrylate, butanediol diacrylate, propanediol dimethacrylate, propanediol diacrylate, pentanediol dimethacrylate, pentanediol diacrylate, hexanediol dimethacrylate, hexanediol diacrylate, neopentylglycol dimethacrylate, neopentylglycol diacrylate, tr imethylolpropane triacrylate, tr imethylolpropane tr imethacrylate, polypropylene glycol diacrylate, polypropylene glycol dimethacrylate, cyclohexanedi-methanoldiacrylate or -methacrylate and, tricyclodecane dimethanol di (meth)acrylate.
• Preferred alkyl acrylate monomers include isobornyl acrylate, 2-ethylhexylacrylate, isooctylacrylate, cyclohexylacr late, hexanedioldiacrylate, tricyclodecanedimethanol- diacrylate.
• Other diluents may be used in amounts of preferably less than about 10 wt.%. Examples of these diluents are N-vinyl functional or vinylether functional compounds with a molecular weight lower than 500. Examples of these diluents are N-vinyl caprolactam, butyl-vinylether , tr iethyleneglycoldi- vinylether , butanediol-divinylether and the like.
• the diluents preferably are used in a quantity sufficient to adjust the total coating composition to a viscosity of lower than about 2000 mPa.s, preferably lower than about 800 mPa.s at 25°C, measured with a couette apparatus (cup-and-bob viscometer at a frequency 100 rpm) .
• the coating composition of the present invention preferably does not comprise substantial amounts of monomers with relatively strong dipole moments such as N-vinylpyrrolidone, phenoxyeth lacr late, polyoxyalkylane- alkylphenolacrylate and the like.
• the coating composition furthermore, preferably does not comprise -in substantial amounts - those monomer for which dipoles can be easily included, such as aromatic group containing acrylates such as phenylacrylates.
• the man skilled in the art can easily determine the amount allowed in the composition by measuring the dissipation factor .
• the coating is radiation curable, and can be cured with electron beam irradiation or with light with a wavelength between about 200-700 mm.
• the composition comprises a light sensitive radical generating compound or mixture of compounds as photoinitiators.
• the photoinitiator when used in a small but effective amount to promote radiation cure, must provide reasonable cure speed without causing premature gelation of the composition.
• Suitable photoinitiators include the following: hydroxycyclohexylphenyl ketone; hydroxymethylphenylpropanone; dimethoxyphenyl- acetophenone; 2-methyl-l , [4- (methyl thio)phenyl ]- 2-morpholino-propanone-l ; l-(4-isopropylphenyl )- 2-hydroxy-2-methylpropan-1-one ; 1- ( 4-dodecylphenyl )-2- hydroxy-2-methylpropan-l-one; 4-(2- hyd oxyethoxy)phenyl- (2-hydroxy-2-propyl )ketone; diethoxyacetophenone ; 2 , 2-di-sec-butoxyacetophenone ; diethoxy-phenyl acetophenone; and mixtures of these.
• the photoinitiator - if used - preferably comprises from about 1.0 percent to about 10.0 percent by weight of the composition, based upon the total composition.
• the amount of photoinitiator is from about 2.0 percent to about 7.0 percent by weight.
• the photoinitiator should be chosen such that a cure speed, as measured in a dose versus modulus curve, of less than about 2.0 J/cm 2 , and preferably less than about 1.0 J/cm 2 , is required, when the photoinitiator is used in the designated amount.
• the composition preferably also contains an adhesion promoter.
• the adhesion promoter is preferably a compound having a groups participating in the radical curing reaction, and a group that adheres to the metal conductor.
• the group that participates in the curing reaction can be preferably, vinyl, (meth) acrylate or thiol.
• the group that adheres to the metal conductor preferably is hydroxy, acid, zirconate, titanate or silane.
• the acid may be for example carboxylic phosphoric or sulphonic. Most preferred is a (meth)acrylate functionalized carboxylic acid or phosphoric acid.
• adhesion promoters include, but are not limited to, hydroxyethyl (meth)acrylate, hydroxypropyl (meth) acrylate, di- or trialkoxy zirconates or titanates, vinyl tr imethoxysilane, mercaptopropyltr imethoxy silane, acrylic acid, methacrylic acid, ⁇ -carboxyethyl acrylate, Ebecryl 170 and Ebercyl 169.
• the Ebercyl products are acrylate ester derivatives, available from Radcure Specialties in Atlanta, Georgia, and are phosphoric acid based adhesion promoters.
• Mono or diester or phosphoric acid having the following formula are also suitable adhesion promoters:
• R' C, to C 14 alkyl, aryl, alkaryl, or alkyleneoxy.
• organo-phosphate esters having the above formula include, but are not limited to, (1) methylmethacryloyloxyethyl phosphate, where
• the adhesion promoter helps the coating composition adhere to the metal conductor.
• the adhesion promoter may be used in an amount in the range of about 0.2 to 5 wt.% of the composition. Care should be exercised, that the amount of adhesion promotor is not so large that insulating properties are decreased below acceptable level. It is an unexpected advantage of the coating composition of the present invention, that an adhesion promotor can be used in effective amounts and that still very good insulating properties are achieved.
• composition may also contain other components that are known to those skilled in the art including stabilizers, surfactants, plasticizers, chain transfer agents and the like.
• pigment or dye it may be useful to use a small amount of pigment or dye to color the coating. This allows simple visual control of the coated metal conductor. This is in particular useful, in case the metal conductor is only partly coated.
• Suitable pigments or dyes are for example copper phthalocyanine blue, crystal violet lactone (blue), crystal malachite green, sheet fed rubine (red).
• the amount of pigment - if used - will in general be about 0.2-5 wt.% relative to the coating composition.
• the coating may be applied on the metal conductor using known coating method, such as spraying, vacuum coatings dipping and doctoring.
• the coating may be applied under a nitrogen atmosphere to preclude oxygen inhibition, however this is not necessary. If e.g. a relatively large amount of photoinitiator is used, the cure of the surface of the film is adequate as well.
• the invention will be further elucidated by the following, non limiting examples.
• Isophorone diisocyanate (IPDI 429 g) was dissolved in laurylacrylate (420 g) with 1 g BHT (butylated hydroxy toluene) 0.7 g phenolthiazine and 2 g dibutyltindilaurate. To this mixture, 224 g of hydroxyethylacrylate (HEA) was slowly added, and the temperature was kept below 35°C. To the acrylate- isocyanate adduct, 2318 g of a hydrocarbon diol was added (Nisso PB 2000) and it was allowed to react. About 105 g of laurylacrylate was added and the final NCO content was determined to be below 0.1 %. This oligomer A had a theoretical molecular weight of 3089 and was a clear solution of 85% oligomer in 15% laurylacrylate.
• BHT butylated hydroxy toluene
• HOA hydroxyethylacrylate
• an oligomer was made from 400 g IPDI, 139 g HEA, 2876 g Nisso PB 2000 and 380 g laurylacrylate.
• the theoretical molecular weight of the oligomer is 5733.
• oligomer C was prepared from 81 g IPDI, 42 g HEA, 430 g of Nisso PB 2000 and 140 g isobornylacrylate.
• the theoretical molecular weight of the oligomer is 3093.
• Coatings were prepared with the oligomer in 15% diluent mixtures A-C, with further diluents and a photoinitiator as shown in Table 1.
• the coatings were applied on an aluminum plate and cured with 2 J/cm 2 light of a fusion D bulb.
• For measuring the dissipation factor 150 ⁇ m thick films were cast on glass plate and cured with 2 J/cm; the dissipation factor was measured at 24°C and 150°C at 60 Hz with standard equipment with stainless steel electrodes. Results are shown in Table 1 as well.
• Photomer 3016 is: Bisphenol-A-diacrylate
• SA 1002 is: tr icyclododecanedimethanol diacrylate
• SR349 is: ethoxylated bis phenol-A-diacrylate
• compositions and results are summarized in
• the coatings were spin coated on an aluminiumpanel, and cured with 1 J/cm, resulting in a 12.5 ⁇ m film; furthermore, coatings were cast on a glass plate and cured with 2 J/cm 2 .

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• 1997
  • 1997-10-27 WO PCT/NL1997/000588 patent/WO1998019313A1/en not_active Application Discontinuation
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  • 1997-10-27 EP EP97909754A patent/EP0935804A1/de not_active Withdrawn
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