WO2014000820A1 - Insulating composition for electrical power applications - Google Patents

Insulating composition for electrical power applications Download PDF

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Publication number
WO2014000820A1
WO2014000820A1 PCT/EP2012/062758 EP2012062758W WO2014000820A1 WO 2014000820 A1 WO2014000820 A1 WO 2014000820A1 EP 2012062758 W EP2012062758 W EP 2012062758W WO 2014000820 A1 WO2014000820 A1 WO 2014000820A1
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WIPO (PCT)
Prior art keywords
nucleating agent
weight
calculated
amount
copolymer
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Application number
PCT/EP2012/062758
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French (fr)
Inventor
Gustavo Dominguez
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Abb Research Ltd
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Publication date
Application filed by Abb Research Ltd filed Critical Abb Research Ltd
Priority to PCT/EP2012/062758 priority Critical patent/WO2014000820A1/en
Publication of WO2014000820A1 publication Critical patent/WO2014000820A1/en

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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
    • H01B3/44—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 vinyl resins; acrylic resins
    • H01B3/441—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 vinyl resins; acrylic resins from alkenes

Definitions

  • the present invention refers to an insulating composition and a method for preparing said insulating composition and a use of the insulating composition for reducing conductivity in insulation material.
  • Electrical power applications such as cables and joints, etc. that are used for the transmission of power generally comprise of a metallic conductor surrounded by an insulating coating.
  • the insulation material of the coating is preferably flexible, strong and non-conductive.
  • Olefins polymers such as polyethylene have been used as insulation materials for low, medium and high voltage cables. These polymers have advantageous processability and electrical properties.
  • WO2010/076242 describes the problem of power loss at increasing operational temperatures.
  • the solution is found in the use of a mixture of hetero- phasic polymers.
  • Cross-linked polyolefins can be prepared by mixing polyolefins with a cross-linking agent. During cooling nucleation occurs by the formation of focal centres. Crystals grow from the focal centres to form a crystalline structure.
  • nucleati ng agents in the preparation of polyolefins has been descri bed . By the addition of a nucleati ng agent a foreign surface (the nucleati ng agent) is introduced on which crystal growth can occur. The addition of nucleating agent during the preparation of cross-linked polyolefins increases the crystal fraction of the plastic material obtained .
  • Horrocks et al (Milliken and Company) describe the use of nucleating agents for the preparation of polyethylene polymers to improve some physical properties of the polymer such as gloss, haze, surface roughness, elasticity and tear strength .
  • Conductivity is not addressed i n this paper, neither are any details described about the chemical composition of the nucleating agents. Thus, little is known about how the conductivity of insulation material can be reduced .
  • the conductivity of insulation material is important because the conductivity for electrical applications determines the leakage current and the heat generated for such a leakage. Preferably the conductivity is as small as possible.
  • the i nsulation material must be strong , flexi ble and have low temperature impact strength . There is a need for providing improved insulation material .
  • the object of the present invention is to provide insulation material for electrical power applications that has a reduced or no conductivity. It is another objective of the present i nvention to provide insulation material for electrical applications, which has a required strength , flexi bility and low temperature impact strength. A further object of the invention is to provide insulation material that can be easily manufactured and handled.
  • an insulating composition compris- ing
  • the amount of cross-linking agent is between 0.1 and 2.0 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the amount of nucleating agent is between 0.01 and 0.5 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the nucleating agent comprises 40-80 wt% calcium cyclo-dicarboxylate calculated on weight of the nucleating agent and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent and the filler is present in the amount of up to 10 wt% calculated on the weight of the total of the composition.
  • the nucleating agent may comprise 40-80 wt% calcium cyclohexanedicarboxylate (1R.2S) and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent. Further, in another embodiment, the nucleating agent may comprise 50-70 wt% calcium cyclohexanedicarboxylate (1R.2S) and 30-50 wt% zinc stearate calculated on the weight of the nucleating agent, or 55-65 wt% calcium cyclohexanedicarboxylate (1R.2S) and 35-45 wt% zinc stearate.
  • the composition may be used as insulation material for coating electrical conductors.
  • the advantage of the novel composition is a reduction in DC conductivity between 30 and 60% compared to the use of a composition that does not comprise a nucleating agent.
  • the new composition may decrease the current loss through power applications such as cables. A decrease in cur- rent leakage will also prevent heat generation related to such leakage.
  • the use of the insulating composition in insulating material is expected to result in savings in energy, which clearly has an environmental advantage as well as the advantage of cost reduction for energy transmission.
  • the polyethylene polymer or copolymer thereof is selected from the group comprising low density polyethylene, ultra low density polyethylene, linear low density poly- ethylene, high density polyethylene and ultra high density polyethylene, or mixtures thereof, or copolymers of ethylene with one or more alkanes selected from propylene, butane, pentane, hexane, octane and polypropylenes.
  • the polyethylene polymer is low density polyethylene.
  • the amount of filler may be between 0.3 and 8 wt% of the total weight of the composition.
  • the filler is selected from the group compris- ing polyhedral olgomeric silesquioxanes (POSS) or metal oxides, such as oxides, dioxides or trioxides of calcium, zinc, silicon, aluminium, magnesium and titanium, CaC0 3 and nanoclay, or mixtures thereof.
  • Fillers which may be advantageously used are polyhedral olgomeric silesquioxanes (POSS), MgO, SiO x , AI 2 O 3 , TiO 2 , CaO, CaO 3 , and nanoclays or mixtures thereof.
  • the cross-linking agent is dicumyl peroxide.
  • the cross-linking agent may be present in an amount of 0.5 - 2.0 wt%. Further, the cross-linking agent may be present in an amount of 0.5 - 1.5 wt%, or in an amount of 0.6 - 1.2 wt%.
  • the nucleating agent may be present in an amount of 0.05 to 0.5 wt%. Further, the nucleating agent may be present in an amount of 0.1 - 0.32 wt%, or in an amount of 0.1 - 0.25 wt%. Further, the cross-linking agent may be present in an amount of 0.5 - 1.5 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the nucleating agent is present in an amount of 0.05 to 0.5 wt% calculated on the weight of the polyethylene polymer or copolymer thereof.
  • the cross-linking agent is present in an amount of 0.6 or 1.2 wt% and the nucleating agent is present in an amount of 0.1, 0.2 or 0.32 wt%. In another embodiment, the cross-linking agent is present in an amount of 0.6 wt% and the nucleating agent is present in an amount between 0.05 wt% and 0.25 wt%, or the cross-linking agent is present in an amount of 1.2 wt% and the nucleating agent is present in an amount between 0.05 wt% and 0.5 wt%, on the weight of the polyethylene polymer or copolymer thereof.
  • the object is also achieved by a use of the insulating composition described above, for reducing conductivity in insulation material.
  • the invention further relates to insulation material containing the insulating composition as described above.
  • One embodiment relates to an electrical power application characterized in comprising an electrical conductor coated with insulation material containing the insulating composition as described above.
  • composition comprising a polyethylene polymer or copolymer thereof, a cross-linking agent, and a nucleating agent, and optionally a filler,
  • the amount of cross-linking agent is between 0.1 and 2.0 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the amount of nucleating agent is between 0.01 and 0.5 wt% calculated on the weight of the polyeth- ylene polymer or copolymer thereof and the nucleating agent comprises 40-80 wt% calcium cyclo-dicarboxylate calculated on weight of the nucleating agent and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent and the filler is present in the amount of up to 10 wt% calculated on the weight of the total of the composition,
  • the cross-linking agent may be provided separately or the crosslinking agent may be included in the polyethylene polymer or the copolymer thereof.
  • the nucleating agent could be in the form of a master batch or could be the components separated.
  • the composition may be de-gassed at a temperature between 15 and 80°C.
  • One embodiment relates to a method for reducing conductivity in insulation material, characterized in that the insulation material comprises the insulating composition prepared by the method described above.
  • the nucleating agent may comprise 40-80 wt% calcium cyclohexanedicarboxylate (1R.2S) calculated on the weight of the nucleating agent and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent.
  • the nucleating agent may comprise 50-70 wt% calcium cyclohexanedicarboxylate (1R.2S) and 30-50 wt% zinc stearate.
  • the amount of filler may be between 0.3 and 8 wt% of the total weight of the composition.
  • the polyethylene polymer or copolymer thereof is selected from the group comprising low density polyethylene, ultra low density polyethylene, linear low density polyethylene, high density polyethylene and ultra high density polyethylene, or mixtures thereof, or copolymers of ethylene with one or more alkanes selected from propylene, butane, pentane, hexane, octane and polypropylenes and the cross-linking agent is a peroxide.
  • the cross-linking agent may be present in an amount of 0.5 - 2.0 wt%. Further, the cross-linking agent may be present in an amount of 0.5 - 1.5 wt%, or in an amount of 0.6 - 1.2 wt%.
  • the nucleating agent may be present in an amount of 0.05 to 0.5 wt%. Further, the nucleating agent may be present in an amount of 0.1 - 0.32 wt%, or in an amount of 0.1 - 0.25 wt%.
  • the nucleating agent may comprise 50-70 wt% calcium cyclohexanedicarboxlyate (1R.2S) and 30-50 wt% zinc stearate calculated on the weight of the nucleating agent or 55-65 wt% calcium cyclohexanedicarboxylate (1R.2S) and 35-45 wt% zinc stearate.
  • the cross-linking agent is present in an amount of 0.6 wt% and the nucleating agent is present in an amount between 0.05 wt% and 0.25 wt%, or the cross-linking agent is present in an amount of 1.2 wt% and the nucleating agent is present in an amount between 0.05 wt% and 0.5 wt%, the weight of the polyethylene polymer or copolymer thereof.
  • Fig 1 shows the weight percentage of the cross-linking agent versus the normalized conductivity of the insulating material.
  • Fig 2 shows the weight percentage of the nucleating agent versus the normalized conductivity of the insulating material.
  • An insulating composition used for reducing the conductivity of electrical power applications according to the present invention may comprise;
  • nucleating agent comprising 40-80 wt% calcium cyclo- dicarboxylate and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent.
  • the composition may optionally comprise a filler of up to 10 wt% of the total composition.
  • the polyethylene polymer or copolymer thereof is se- lected from the group comprising low density polyethylene, ultra low density polyethylene, linear low density polyethylene, high density polyethylene and ultra high density polyethylene, or mixtures thereof.
  • the polyethylene polymer may be a copolymer of ethylene with one or more alkanes selected from propylene, bu- tane, pentane, hexane, octane and polypropylenes.
  • the polyethylene polymer is low density polyethylene (LDPE).
  • Low density polyethylene may also be mixed with one or more polyethylene polymer selected from the group comprising ultra low density polyethylene, linear low density polyeth- ylene, high density polyethylene and ultra high density polyethylene.
  • Low density polyethylene may further be a copolymer of ethylene with one or more alkanes selected from propylene, butane, pentane, hexane, octane and polypropylenes.
  • the cross-linking agent is preferably a peroxide such as for ex- ample dicumyl peroxide (DCP).
  • DCP dicumyl peroxide
  • cross-linking may be performed by radiation.
  • the nucleating agent is preferably a mixture of different ingredients comprising 40-80 wt% calcium cyclohexanedicarboxylate (1R.2S) and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent.
  • the preferred nucleating agent comprises 50-70 wt% calcium cyclohexanedicarboxylate (1R.2S) and 30-50 wt% zinc stearate calculated on the weight of nucleating agent.
  • one or more fillers may be added to the insulating composition in an amount of up to 10 wt% of the total weight of the insulating composition.
  • the amount may be between 0.1 and 9 wt%, or between 0.3 and 8 wt%, or between 0.4 and 6 wt%.
  • the filler may be micro- or nano-fillers, i.e. fillers with an aver- age particle diameter in nano-meters or micrometers. Preferably nano-fillers are used. Examples of such fillers are polyhedral oligomeric silsesquioxanes (POSS), or metal oxides such as oxides, dioxides or trioxides of calcium, zinc, silicon, aluminium, magnesium and titanium. Other filler are CaCO 3 and nanoclay. Mixtures of one or more fillers may also be used.
  • Preferred fillers are polyhedral oligomeric silsequioxanes (POSS ® ), MgO, SiO x , AI 2 O 3 , TiO 2 , CaO, CaCO 3 and nanoclay, or mixtures thereof.
  • Another preferred filler is silicon dioxide.
  • the fillers may be crystalline or amorphous or mixtures thereof.
  • the fillers may be present in an amount between 0.1 and 10 wt% of the total weight of the composition.
  • the insulating composition may further comprise additives such as anitoxidants and the like.
  • additives such as anitoxidants and the like.
  • an antioxidant is 1 ,1 '-thiobis(2-methyl-4-hydroxy-5-tert-butylbenzene), which may be present in an amount between 0.02 and 0.3 wt% of the weight of the polyethylene polymer or copolymer thereof.
  • Another additive may be scortch retardant agent, which may be present in an amount between 0.01 and 0.3% of the weight of the polyethylene polymer or the copolymer thereof.
  • the amount of cross-linking agent is between 0.1 and 2 wt%, or between 0.5 and 1.5 wt%, or between 0.55 and 1.3 wt%.
  • the amount of nucleating agent may be between 0.01 and 0.5 wt%, or between 0.05 and 0.4 wt%, or between 0.1 wt% and 0.4 wt%, or 0.1 , or 0.2, or 0.25, or 0.3, or 0.4 wt%.
  • the amount of cross-linking agent may be 0.6 wt% when the amount of nucleating agent is between 0.05 and 0.25 wt%.
  • the amount of cross-linking agent is 1.2 wt% when the amount of nucleating agent is between 0.05 and 0.5 wt%.
  • the weight percentages for the cross-linking agent and the nu- cleating agent are the percentages of the polyethylene polymer or copolymer thereof and the percentages of the filler are of the total weight of the composition.
  • Fig 1 shows the reduction in conductivity in relation to the amount of cross-linking agent (0.6 and 1.2 wt%) for insulating compositions comprising nucleating agent (0.1, 0.2 and 0.32 wt%).
  • the nucleating agent comprises about 60 wt% calcium cy- clohexanedicarboxylate (1R.2S) and about 40 wt% zinc stearate.
  • Conductivity measurements were carried out at 70°C and 30 kV/mm on samples prepared from LDPE with a 1 mm thickness over 24 h. The plot shows the values of the conductivity normalized by the value of the conductivity for the sample with the same amount of DCP (dicumyl peroxide) but without nucleating agent (NA).
  • Fig 2 shows the reduction in conductivity in relation to the amount of the nucleating agent (0.1 , 0.2 and 0.32 wt%) for insulating compositions comprising 0.6 and 1.2 wt% cross-linking agent.
  • the nucleating agent comprises about 60 wt% calcium cyclohexanedicarboxylate (1R.2S) and about 40 wt% zinc stea- rate and the cross-linking agent is DCP (dicumyl peroxide).
  • the plot shows the results of the DC conductivity at 24 h measured at 70 °C and 30 kV/mm on samples prepared from LDPE with a 1 mm thickness plates and over a ⁇ *25 cm 2 area, normalized for the value of the conductivity measured in a sample without nucleating agent.
  • results show a decrease in conductivity with the addition of nucleating agent. It has been shown that the conductivity is reduced for insulating compositions comprising the nucleating agent together with the cross-linking agent, wherein the amount of nucleating agent is between 0.1 and 0.32 wt% and the amount of cross-linking agent is between 0.6 and 1.2 wt%.
  • the insulating composition of the present invention may be used for reducing conductivity in insulation material such as material used to insulate electrical power applications.
  • the applications may include any electrically insulated material or apparatus. Ex- amples of applications are electrical power cables, electric cable joints, and the like.
  • the insulating composition of the present invention may be prepared by any known method used for making insulated electrical power applications. However, it has been found that the conductivity of the insulating composition can be further reduced if the product obtained from the preparation method is de-gassed in the end of the preparation method. This de-gassing may be done in an oven at a temperature, whereby gasses trapped in the composition evaporate from the composition, while the structure of the insulating composition remains in-tact. Examples of de-gassing temperatures are between 10 and 70°C, or between 15 and 60°C, or 25 and 70°C. De-gassing may be performed under vacuum.
  • a method for preparing insulating material with reduced conductivity may comprise any known method for the preparation of any insulating material, characterized in that the insulating material is being de-gassed at the end of the preparation method.
  • One method for the preparation of an insulating composition may comprise step a) of mixing a polyethylene polymer or copolymer thereof (optionally containing cross-linking agent) with a masterbatch of the nucleating agent described above.
  • adding one or more additives such as antioxidants to the mix- ture.
  • the cross-linking agent can also be added separately.
  • the mixture is melted and extruded.
  • steps may be performed at a temperature between 120 and 300°C, or 140 and 210°C, or 150 and 200°C.
  • the temperature for method steps of melting and extrusion may be between 120 and 220°C, or 140 and 210°C.
  • step e the product obtained is de-gassed in step e) at a tem- perature between 15 and 80°C.
  • the insulating composition comprises low density polyethylene, the nucleating agent comprising about 50-70 wt% calcium cyclohexanedicarboxylate (1R.2S) and about 30-50 wt% zinc stearate calculated on the weight of the nucleating agent and optionally a filler between 0.3 and 8 wt%, such as silicon dioxide, of the total weight of the composition, and cross-linking agent dicumyl peroxide, whereby the amount of cross-linking agent is between 0.5 and 1.5 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the amount of nucleating agent is between 0.05 and 0.5 wt% calculated on the weight of the polyethylene polymer or copolymer thereof.
  • the nucleating agent comprising about 50-70 wt% calcium cyclohexanedicarboxylate (1R.2S) and about 30-50 wt% zinc stearate calculated on the weight of the nucleating agent and optionally a filler between 0.3 and

Abstract

The present invention relates to an insulating composition comprising a polyethylene polymer or copolymer thereof, a cross-linking agent, and a nucleating agent and optionally a filler. The amount of cross-linking agent is between 0.1 and 2.0 wt% and the amount of nucleating agent is between 0.01 and 0.5 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the nucleating agent comprises 40-80 wt% calcium cyclo-dicarboxylate and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent and the filler is present in the amount of up to 10 wt% calculated on the total weight of the composition. The invention further relates to a method for preparing said insulating composition. The invention also relates to a use of the insulating composition for reducing conductivity in insulation material and to insulation material and electrical power application comprising the insulating composition.

Description

Insulating composition for electrical power applications
THE FIELD OF THE INVENTION
The present invention refers to an insulating composition and a method for preparing said insulating composition and a use of the insulating composition for reducing conductivity in insulation material.
BACKGROUND OF THE INVENTION AND PRIOR ART Electrical power applications such as cables and joints, etc. that are used for the transmission of power generally comprise of a metallic conductor surrounded by an insulating coating. The insulation material of the coating is preferably flexible, strong and non-conductive.
Olefins polymers such as polyethylene have been used as insulation materials for low, medium and high voltage cables. These polymers have advantageous processability and electrical properties.
Many attempts have been made to improve different qualities of insulation materials. For example, WO2010/076242 describes the problem of power loss at increasing operational temperatures. The solution is found in the use of a mixture of hetero- phasic polymers.
US2009/0145627 describes the use of a silane cross-linker in the polyethylene polymer to improve the strength of the insulation material. Conductivity of the insulation material is however not considered in this application. Cross-linked polyolefins can be prepared by mixing polyolefins with a cross-linking agent. During cooling nucleation occurs by the formation of focal centres. Crystals grow from the focal centres to form a crystalline structure. The use of nucleati ng agents in the preparation of polyolefins has been descri bed . By the addition of a nucleati ng agent a foreign surface (the nucleati ng agent) is introduced on which crystal growth can occur. The addition of nucleating agent during the preparation of cross-linked polyolefins increases the crystal fraction of the plastic material obtained .
Horrocks et al , (Milliken and Company) describe the use of nucleating agents for the preparation of polyethylene polymers to improve some physical properties of the polymer such as gloss, haze, surface roughness, elasticity and tear strength . Conductivity is not addressed i n this paper, neither are any details described about the chemical composition of the nucleating agents. Thus, little is known about how the conductivity of insulation material can be reduced . The conductivity of insulation material is important because the conductivity for electrical applications determines the leakage current and the heat generated for such a leakage. Preferably the conductivity is as small as possible. At the same time, the i nsulation material must be strong , flexi ble and have low temperature impact strength . There is a need for providing improved insulation material .
SUMMARY OF THE I NVENTION
The object of the present invention is to provide insulation material for electrical power applications that has a reduced or no conductivity. It is another objective of the present i nvention to provide insulation material for electrical applications, which has a required strength , flexi bility and low temperature impact strength. A further object of the invention is to provide insulation material that can be easily manufactured and handled.
The objects are achieved by an insulating composition compris- ing
- a polyethylene polymer or copolymer thereof,
- a cross-linking agent, and characterized by further comprising
- a nucleating agent, and
- optionally a filler,
whereby the amount of cross-linking agent is between 0.1 and 2.0 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the amount of nucleating agent is between 0.01 and 0.5 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the nucleating agent comprises 40-80 wt% calcium cyclo-dicarboxylate calculated on weight of the nucleating agent and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent and the filler is present in the amount of up to 10 wt% calculated on the weight of the total of the composition.
In an embodiment the nucleating agent may comprise 40-80 wt% calcium cyclohexanedicarboxylate (1R.2S) and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent. Further, in another embodiment, the nucleating agent may comprise 50-70 wt% calcium cyclohexanedicarboxylate (1R.2S) and 30-50 wt% zinc stearate calculated on the weight of the nucleating agent, or 55-65 wt% calcium cyclohexanedicarboxylate (1R.2S) and 35-45 wt% zinc stearate.
The composition may be used as insulation material for coating electrical conductors. The advantage of the novel composition is a reduction in DC conductivity between 30 and 60% compared to the use of a composition that does not comprise a nucleating agent. The new composition may decrease the current loss through power applications such as cables. A decrease in cur- rent leakage will also prevent heat generation related to such leakage. The use of the insulating composition in insulating material is expected to result in savings in energy, which clearly has an environmental advantage as well as the advantage of cost reduction for energy transmission.
In one embodiment, the polyethylene polymer or copolymer thereof is selected from the group comprising low density polyethylene, ultra low density polyethylene, linear low density poly- ethylene, high density polyethylene and ultra high density polyethylene, or mixtures thereof, or copolymers of ethylene with one or more alkanes selected from propylene, butane, pentane, hexane, octane and polypropylenes. In another embodiment, the polyethylene polymer is low density polyethylene.
The amount of filler may be between 0.3 and 8 wt% of the total weight of the composition.
In one embodiment, the filler is selected from the group compris- ing polyhedral olgomeric silesquioxanes (POSS) or metal oxides, such as oxides, dioxides or trioxides of calcium, zinc, silicon, aluminium, magnesium and titanium, CaC03 and nanoclay, or mixtures thereof. Fillers which may be advantageously used are polyhedral olgomeric silesquioxanes (POSS), MgO, SiOx, AI2O3, TiO2, CaO, CaO3, and nanoclays or mixtures thereof.
In yet another embodiment, the cross-linking agent is dicumyl peroxide.
The cross-linking agent may be present in an amount of 0.5 - 2.0 wt%. Further, the cross-linking agent may be present in an amount of 0.5 - 1.5 wt%, or in an amount of 0.6 - 1.2 wt%.
The nucleating agent may be present in an amount of 0.05 to 0.5 wt%. Further, the nucleating agent may be present in an amount of 0.1 - 0.32 wt%, or in an amount of 0.1 - 0.25 wt%. Further, the cross-linking agent may be present in an amount of 0.5 - 1.5 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the nucleating agent is present in an amount of 0.05 to 0.5 wt% calculated on the weight of the polyethylene polymer or copolymer thereof.
In another embodiment, the cross-linking agent is present in an amount of 0.6 or 1.2 wt% and the nucleating agent is present in an amount of 0.1, 0.2 or 0.32 wt%. In another embodiment, the cross-linking agent is present in an amount of 0.6 wt% and the nucleating agent is present in an amount between 0.05 wt% and 0.25 wt%, or the cross-linking agent is present in an amount of 1.2 wt% and the nucleating agent is present in an amount between 0.05 wt% and 0.5 wt%, on the weight of the polyethylene polymer or copolymer thereof.
The object is also achieved by a use of the insulating composition described above, for reducing conductivity in insulation material.
The invention further relates to insulation material containing the insulating composition as described above. One embodiment relates to an electrical power application characterized in comprising an electrical conductor coated with insulation material containing the insulating composition as described above.
The objects of the invention is also achieved by a method for the preparation of an insulating composition, wherein the method comprises the steps of
a) providing a composition comprising a polyethylene polymer or copolymer thereof, a cross-linking agent, and a nucleating agent, and optionally a filler,
whereby the amount of cross-linking agent is between 0.1 and 2.0 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the amount of nucleating agent is between 0.01 and 0.5 wt% calculated on the weight of the polyeth- ylene polymer or copolymer thereof and the nucleating agent comprises 40-80 wt% calcium cyclo-dicarboxylate calculated on weight of the nucleating agent and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent and the filler is present in the amount of up to 10 wt% calculated on the weight of the total of the composition,
b) optionally adding additives to the composition;
c) melting and extruding said composition, at a temperature between 120 and 300°C.
The cross-linking agent may be provided separately or the crosslinking agent may be included in the polyethylene polymer or the copolymer thereof. The nucleating agent could be in the form of a master batch or could be the components separated.
The composition may be de-gassed at a temperature between 15 and 80°C.
One embodiment relates to a method for reducing conductivity in insulation material, characterized in that the insulation material comprises the insulating composition prepared by the method described above.
In an embodiment the nucleating agent may comprise 40-80 wt% calcium cyclohexanedicarboxylate (1R.2S) calculated on the weight of the nucleating agent and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent.
Further, in another embodiment, the nucleating agent may comprise 50-70 wt% calcium cyclohexanedicarboxylate (1R.2S) and 30-50 wt% zinc stearate. The amount of filler may be between 0.3 and 8 wt% of the total weight of the composition. In yet another embodiment of the method, the polyethylene polymer or copolymer thereof is selected from the group comprising low density polyethylene, ultra low density polyethylene, linear low density polyethylene, high density polyethylene and ultra high density polyethylene, or mixtures thereof, or copolymers of ethylene with one or more alkanes selected from propylene, butane, pentane, hexane, octane and polypropylenes and the cross-linking agent is a peroxide.
The cross-linking agent may be present in an amount of 0.5 - 2.0 wt%. Further, the cross-linking agent may be present in an amount of 0.5 - 1.5 wt%, or in an amount of 0.6 - 1.2 wt%. The nucleating agent may be present in an amount of 0.05 to 0.5 wt%. Further, the nucleating agent may be present in an amount of 0.1 - 0.32 wt%, or in an amount of 0.1 - 0.25 wt%.
Further, the nucleating agent may comprise 50-70 wt% calcium cyclohexanedicarboxlyate (1R.2S) and 30-50 wt% zinc stearate calculated on the weight of the nucleating agent or 55-65 wt% calcium cyclohexanedicarboxylate (1R.2S) and 35-45 wt% zinc stearate. In a further embodiment of the method, the cross-linking agent is present in an amount of 0.6 wt% and the nucleating agent is present in an amount between 0.05 wt% and 0.25 wt%, or the cross-linking agent is present in an amount of 1.2 wt% and the nucleating agent is present in an amount between 0.05 wt% and 0.5 wt%, the weight of the polyethylene polymer or copolymer thereof.
BRIEF DESCRIPTION OF THE DRAWINGS Fig 1 shows the weight percentage of the cross-linking agent versus the normalized conductivity of the insulating material.
Fig 2 shows the weight percentage of the nucleating agent versus the normalized conductivity of the insulating material.
DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS THE INVENTION
An insulating composition used for reducing the conductivity of electrical power applications according to the present invention may comprise;
1) a polyethylene polymer or copolymer thereof,
2) a cross-linking agent, and
3) a nucleating agent comprising 40-80 wt% calcium cyclo- dicarboxylate and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent.
The composition may optionally comprise a filler of up to 10 wt% of the total composition.
Preferably the polyethylene polymer or copolymer thereof is se- lected from the group comprising low density polyethylene, ultra low density polyethylene, linear low density polyethylene, high density polyethylene and ultra high density polyethylene, or mixtures thereof. The polyethylene polymer may be a copolymer of ethylene with one or more alkanes selected from propylene, bu- tane, pentane, hexane, octane and polypropylenes. Most preferably the polyethylene polymer is low density polyethylene (LDPE). Low density polyethylene may also be mixed with one or more polyethylene polymer selected from the group comprising ultra low density polyethylene, linear low density polyeth- ylene, high density polyethylene and ultra high density polyethylene. Low density polyethylene may further be a copolymer of ethylene with one or more alkanes selected from propylene, butane, pentane, hexane, octane and polypropylenes.
The cross-linking agent is preferably a peroxide such as for ex- ample dicumyl peroxide (DCP). Alternatively, cross-linking may be performed by radiation.
The nucleating agent is preferably a mixture of different ingredients comprising 40-80 wt% calcium cyclohexanedicarboxylate (1R.2S) and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent. The preferred nucleating agent comprises 50-70 wt% calcium cyclohexanedicarboxylate (1R.2S) and 30-50 wt% zinc stearate calculated on the weight of nucleating agent. Optionally one or more fillers may be added to the insulating composition in an amount of up to 10 wt% of the total weight of the insulating composition. The amount may be between 0.1 and 9 wt%, or between 0.3 and 8 wt%, or between 0.4 and 6 wt%. The filler may be micro- or nano-fillers, i.e. fillers with an aver- age particle diameter in nano-meters or micrometers. Preferably nano-fillers are used. Examples of such fillers are polyhedral oligomeric silsesquioxanes (POSS), or metal oxides such as oxides, dioxides or trioxides of calcium, zinc, silicon, aluminium, magnesium and titanium. Other filler are CaCO3 and nanoclay. Mixtures of one or more fillers may also be used. Preferred fillers are polyhedral oligomeric silsequioxanes (POSS®), MgO, SiOx, AI2O3, TiO2, CaO, CaCO3 and nanoclay, or mixtures thereof. Another preferred filler is silicon dioxide. The fillers may be crystalline or amorphous or mixtures thereof. The fillers may be present in an amount between 0.1 and 10 wt% of the total weight of the composition.
The insulating composition may further comprise additives such as anitoxidants and the like. One example of an antioxidant is 1 ,1 '-thiobis(2-methyl-4-hydroxy-5-tert-butylbenzene), which may be present in an amount between 0.02 and 0.3 wt% of the weight of the polyethylene polymer or copolymer thereof. Another additive may be scortch retardant agent, which may be present in an amount between 0.01 and 0.3% of the weight of the polyethylene polymer or the copolymer thereof.
For reducing the conductivity it is important that the amount of cross-linking agent is between 0.1 and 2 wt%, or between 0.5 and 1.5 wt%, or between 0.55 and 1.3 wt%. The amount of nucleating agent may be between 0.01 and 0.5 wt%, or between 0.05 and 0.4 wt%, or between 0.1 wt% and 0.4 wt%, or 0.1 , or 0.2, or 0.25, or 0.3, or 0.4 wt%.
The amount of cross-linking agent may be 0.6 wt% when the amount of nucleating agent is between 0.05 and 0.25 wt%.
Alternatively, the amount of cross-linking agent is 1.2 wt% when the amount of nucleating agent is between 0.05 and 0.5 wt%.
The weight percentages for the cross-linking agent and the nu- cleating agent are the percentages of the polyethylene polymer or copolymer thereof and the percentages of the filler are of the total weight of the composition.
Fig 1 shows the reduction in conductivity in relation to the amount of cross-linking agent (0.6 and 1.2 wt%) for insulating compositions comprising nucleating agent (0.1, 0.2 and 0.32 wt%). The nucleating agent comprises about 60 wt% calcium cy- clohexanedicarboxylate (1R.2S) and about 40 wt% zinc stearate. Conductivity measurements were carried out at 70°C and 30 kV/mm on samples prepared from LDPE with a 1 mm thickness over 24 h. The plot shows the values of the conductivity normalized by the value of the conductivity for the sample with the same amount of DCP (dicumyl peroxide) but without nucleating agent (NA). The results show a reduction in the conductivity val- ue for all the samples in comparison to the same sample without nucleating agent. Fig 2 shows the reduction in conductivity in relation to the amount of the nucleating agent (0.1 , 0.2 and 0.32 wt%) for insulating compositions comprising 0.6 and 1.2 wt% cross-linking agent. The nucleating agent comprises about 60 wt% calcium cyclohexanedicarboxylate (1R.2S) and about 40 wt% zinc stea- rate and the cross-linking agent is DCP (dicumyl peroxide). The plot shows the results of the DC conductivity at 24 h measured at 70 °C and 30 kV/mm on samples prepared from LDPE with a 1 mm thickness plates and over a ττ*25 cm2 area, normalized for the value of the conductivity measured in a sample without nucleating agent.
The results show a decrease in conductivity with the addition of nucleating agent. It has been shown that the conductivity is reduced for insulating compositions comprising the nucleating agent together with the cross-linking agent, wherein the amount of nucleating agent is between 0.1 and 0.32 wt% and the amount of cross-linking agent is between 0.6 and 1.2 wt%.
The insulating composition of the present invention may be used for reducing conductivity in insulation material such as material used to insulate electrical power applications. The applications may include any electrically insulated material or apparatus. Ex- amples of applications are electrical power cables, electric cable joints, and the like.
The insulating composition of the present invention may be prepared by any known method used for making insulated electrical power applications. However, it has been found that the conductivity of the insulating composition can be further reduced if the product obtained from the preparation method is de-gassed in the end of the preparation method. This de-gassing may be done in an oven at a temperature, whereby gasses trapped in the composition evaporate from the composition, while the structure of the insulating composition remains in-tact. Examples of de-gassing temperatures are between 10 and 70°C, or between 15 and 60°C, or 25 and 70°C. De-gassing may be performed under vacuum. A method for preparing insulating material with reduced conductivity may comprise any known method for the preparation of any insulating material, characterized in that the insulating material is being de-gassed at the end of the preparation method. One method for the preparation of an insulating composition may comprise step a) of mixing a polyethylene polymer or copolymer thereof (optionally containing cross-linking agent) with a masterbatch of the nucleating agent described above. Optionally adding one or more additives such as antioxidants to the mix- ture. The cross-linking agent can also be added separately.
In a following step the mixture is melted and extruded. These steps may be performed at a temperature between 120 and 300°C, or 140 and 210°C, or 150 and 200°C.
The temperature for method steps of melting and extrusion may be between 120 and 220°C, or 140 and 210°C.
Finally, the product obtained is de-gassed in step e) at a tem- perature between 15 and 80°C.
Preferably the insulating composition comprises low density polyethylene, the nucleating agent comprising about 50-70 wt% calcium cyclohexanedicarboxylate (1R.2S) and about 30-50 wt% zinc stearate calculated on the weight of the nucleating agent and optionally a filler between 0.3 and 8 wt%, such as silicon dioxide, of the total weight of the composition, and cross-linking agent dicumyl peroxide, whereby the amount of cross-linking agent is between 0.5 and 1.5 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the amount of nucleating agent is between 0.05 and 0.5 wt% calculated on the weight of the polyethylene polymer or copolymer thereof.
The word "between" as used herein, is defined to include the mentioned values as well as any value in between these values. Thus, the expression "between 1 and 2", includes 1, 1.654 and 2.
The present invention is not limited to the embodiments disclosed but may be varied and modified within the scope of the following claims.

Claims

1. An insulating composition comprising
- a polyethylene polymer or copolymer thereof,
- a cross-linking agent, and characterized by further comprising
- a nucleating agent, and
- optionally a filler,
whereby the amount of cross-linking agent is between 0.1 and 2.0 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the amount of nucleating agent is between 0.01 and 0.5 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the nucleating agent comprises 40-80 wt% calcium cyclo-dicarboxylate calculated on the weight of the nucleating agent and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent and the filler is present in the amount of up to 10 wt% calculated on the weight of the total weight of the composition.
The insulating composition according to claim 1, characterized in that the nucleating agent comprises 40-80 wt% calcium cyclohexanedicarboxylate (1R.2S) calculated on the weight of the nucleating agent and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent.
The insulating composition according to claim 2, characterized in that the nucleating agent comprises 50-70 wt% calcium cyclohexanedicarboxylate (1R.2S) calculated on the weight of the nucleating agent and 30-50 wt% zinc stearate calculated on the weight of the nucleating agent.
4. The insulating composition according to any one of claims 1- 3, characterized in that the polyethylene polymer or copolymer thereof is selected from the group comprising low density poly- ethylene, ultra low density polyethylene, linear low density polyethylene, high density polyethylene and ultra high density poly- ethylene, or mixtures thereof, or copolymers of ethylene with one or more alkanes selected from propylene, butane, pentane, hexane, octane and polypropylenes.
5. The insulating composition according to claim 4, characterized in that the polyethylene polymer is low density polyethylene.
6. The insulating composition according to any one of claims 1 to 5, characterized in that that the amount of filler is between
0.3 and 8 wt% calculated on the total weight of the composition.
7. The insulating composition according to any one of claims 1 to 6, characterized in that the filler is selected from the group comprising polyhedral oligomeric silsesquioxanes (POSS) or metal oxides such as oxides, dioxides or trioxides of calcium, zinc, silicon, aluminium, magnesium and titanium, CaC03 and nanoclay, or mixtures thereof.
8. The insulating composition according to any one of claims 1 to 7, characterized in that the cross-linking agent is dicumyl peroxide.
9. The insulating composition according to any one of claims 1 to 8, characterized in that the cross-linking agent is present in an amount of 0.5 - 1.5 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the nucleating agent is present in an amount of 0.05 to 0.5 wt% calculated on the weight of the polyethylene polymer or copolymer thereof.
10. Use of the insulating composition according to any one of claims 1 to 9, for reducing conductivity in insulation material.
11. Insulation material characterized in containing the insulating composition according to any one of claims 1 to 9.
12. An electrical power application characterized in comprising an electrical conductor coated with insulation material containing the insulating composition according to any one of claims 1 to 9.
13. A method for the preparation of an insulating composition, characterized in comprising the steps of
a) providing a composition comprising a polyethylene polymer or copolymer thereof, a cross-linking agent, and a nucleating agent, and optionally a filler,
whereby the amount of cross-linking agent is between 0.1 and 2.0 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the amount of nucleating agent is be- tween 0.01 and 0.5 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the nucleating agent comprises 40-80 wt% calcium cyclo-dicarboxylate calculated on the weight of the nucleating agent and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent and the filler is present in the amount of up to 10 wt% calculated on the total weight of the composition,
b) optionally adding additives to the composition;
c) melting and extruding said composition, at a temperature between 120 and 300°C.
14. A method for reducing conductivity in insulation material, characterized in that the insulation material comprises the insulating composition prepared by the method according to claim 13.
15. The method according to claims 13 or 14, characterized in that the nucleating agent comprises 40-80 wt% calcium cyclo- hexanedicarboxlyate (1R.2S) and 20-60 wt% zinc stearate calculated on the weight of the nucleating agent.
16. The method according to claims 15, characterized in that the nucleating agent comprises 50-70 wt% calcium cyclohexanedi- carboxlyate (1R.2S) and 30-50 wt% zinc stearate calculated on the weight of the nucleating agent.
17. The method according to any one of claims 13 to 15, characterized in that the polyethylene polymer or copolymer thereof is selected from the group comprising low density polyethylene, ultra low density polyethylene, linear low density polyethylene, high density polyethylene and ultra high density polyethylene, or mixtures thereof, or copolymers of ethylene with one or more alkanes selected from propylene, butane, pentane, hexane, octane and polypropylenes and the cross-linking agent is a peroxide.
18. The method according to any one of claims 13 to 17, characterized in that the cross-linking agent is present in an amount of 0.5 - 1.5 wt% calculated on the weight of the polyethylene polymer or copolymer thereof and the nucleating agent is present in an amount of 0.05 to 0.5 wt% of the polyethylene polymer or the copolymer thereof.
PCT/EP2012/062758 2012-06-29 2012-06-29 Insulating composition for electrical power applications WO2014000820A1 (en)

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WO2016046479A1 (en) * 2014-09-26 2016-03-31 Nexans Electrical device comprising a cross-linked layer
KR20170041824A (en) * 2014-08-07 2017-04-17 넥쌍 Cable comprising a crosslinked layer
CN108822750A (en) * 2018-04-12 2018-11-16 中天光伏材料有限公司 A kind of polyolefin packaging adhesive film with self-repair function
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EP3435384A1 (en) * 2014-04-24 2019-01-30 Nexans Self-healing materials and cables
WO2015162022A1 (en) * 2014-04-24 2015-10-29 Nexans Self-healing materials and cables
US10354776B2 (en) 2014-04-24 2019-07-16 Nexans Self healing materials and cables
EP2937869A1 (en) * 2014-04-24 2015-10-28 Nexans Self-healing materials and cables
KR20170041824A (en) * 2014-08-07 2017-04-17 넥쌍 Cable comprising a crosslinked layer
KR101974471B1 (en) 2014-08-07 2019-05-02 넥쌍 Cable comprising a crosslinked layer
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CN108822750B (en) * 2018-04-12 2021-03-19 中天光伏材料有限公司 Polyolefin packaging adhesive film with self-repairing function
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CN113402799A (en) * 2021-05-19 2021-09-17 南方电网科学研究院有限责任公司 Crosslinked polyethylene composite material and preparation method and application thereof

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