WO2013139390A1

WO2013139390A1 - Curable epoxy resin composition

Info

Publication number: WO2013139390A1
Application number: PCT/EP2012/055010
Authority: WO
Inventors: Cherif Ghoul; Jean-Claude Mauroux; Leopold Ritzer; Rico Gasparini; Vincent Tilliette; Willi Gerig; Julie SIEURAC
Original assignee: ABB Research Ltd Switzerland
Current assignee: ABB Research Ltd Switzerland
Priority date: 2012-03-21
Filing date: 2012-03-21
Publication date: 2013-09-26
Anticipated expiration: 2014-09-21

Description

Curable Epoxy Resin Composition Field of Invention

The present invention refers to a curable epoxy resin composi- tion comprising an epoxy resin component, a hardener component, a filler component, an impact modifier component and optionally further additives, wherein said curable epoxy resin composition has been produced by intensively mixing together in a separate step at least a part of the impact modifier component with at least a part of the epoxy resin component and optionally with some or all of the additives and/or by intensively mixing together in a separate step at least a part of the impact modi^¬ fier component with at least a part of the hardener component and optionally with some or all of the additives, under defined conditions, previously to mixing the components mixed in said separate step or separate steps with the remaining component (s) which are contained in the curable epoxy resin composition. Upon curing, said curable epoxy resin composition yields a cured epoxy resin composition which has a high glass transition temperature and at the same time improved mechanical properties, especially high fracture toughness, combined with excellent electrical properties. The curable epoxy resin composition according to the present invention is specially suited for casting electrical insulations.

State of the Art

Epoxy resin compositions are commonly used as insulating materials for electrical applications because the compositions generally have a comparatively low price, are easy to process and, upon curing, yield electrical insulator systems with good electrical and mechanical properties. In order to enhance spe^¬ cific properties, such as mechanical and electrical properties or the thermal conductivity or to reduce cost epoxy resins are often filled with inorganic filler materials known to be used in electrical applications. For specific applications cured filler containing epoxy resin compositions are often too brittle. Cured - - epoxy resin compositions are inherently brittle, especially when they exhibit a high glass transition temperature (Tg) .

In order to improve the mechanical properties and especially to reduce the brittleness of cured epoxy resin compositions, impact modifiers, also named tougheners, are often added to the curable epoxy resin composition. However, the incorporation of such impact modifiers generally negatively influences the glass tran^¬ sition temperature of the cured product and thereby impairs its thermal and thermo-mechanical properties.

The usual way to prepare epoxy resin compositions is to mix all the components of said composition at a temperature not higher than the casting temperature of the final epoxy resin compo- sition. The obtained mixture is then poured into a mould and the mould is put into an oven for curing, yielding the cured electrical insulator. To mix all the components at a temperature not higher than the casting temperature of the final epoxy resin composition is critical, especially for avoiding premature crosslinking and polymerization of the curable epoxy resin composition .

The combination of high glass transition temperature with high toughness properties is of special importance for example for electrical gas-insulated switchgear (GIS) applications and electrical generator circuit breaker (GCB) applications, for example gas-insulated metal enclosed electrical applications, such as pressurized gas-insulated switchgear stations or spacer insulators and related applications. High glass transition tem- peratures ensure mechanical integrity at high temperatures. Good mechanical properties in general and high fracture toughness in particular ensure a good stability against bursting when the switch operates. Therefore, there is a need for providing a curable epoxy resin composition which upon curing yields a cured product having a - - high glass transition temperature (Tg) and at the same time improved mechanical properties, especially with respect to brittleness, whereby said curable epoxy resin composition is suitable for producing therefrom electrical insulators and is compatible with conventional vacuum casting or Automated

Pressure Gelation (APG) manufacturing processes.

Summary of the Invention

It has now surprisingly been found that curable epoxy resin compositions comprising an epoxy resin component, a hardener component, a filler component, an impact modifier component and optionally further additives, yield a cured product having a high glass transition temperature (Tg) and at the same time improved mechanical properties, particularly with respect to fracture toughness, when the components of said curable epoxy resin composition are mixed together in a selected mixing sequence and under defined conditions, i.e. selected components of said curable epoxy resin composition are mixed together in a separate mixing step previously to mixing said selected compo- nents with all the other remaining components contained in said curable epoxy resin composition.

Specifically, it has been found that cured epoxy resin compo^¬ sitions having a high glass transition temperature (Tg) and at the same time improved mechanical properties are obtained from curable epoxy resin compositions, as defined in the foregoing chapter, when said curable epoxy resin compositions have been produced by mixing together in a separate step at least a part of the impact modifier component with at least a part of the epoxy resin component and optionally with some or all of the additives under defined conditions and/or by mixing together in a separate step at least a part of the impact modifier component with at least a part of the hardener component and optionally with some or all of the additives under defined conditions, and subsequently mixing said components as obtained from the separate mixing step or said separate mixing steps with the - - other remaining component or components which are present in the curable epoxy resin composition. For this mixing process a standard mixing procedure can be used. According to the present invention a specific mixing sequence is applied to prepare the curable epoxy resin composition compri^¬ sing at least an epoxy resin component, a hardener component, a filler component and an impact modifier component. Said impact modifier component preferably has a core-shell structure, i.e. is preferably a core-shell impact modifier, and preferably has an average particle size distribution d₅₀ (i.e. at least 50% of the particles) within the nano-range . Such impact modifiers generally comprise a crosslinked polymer core and a grafted polymer shell, for example a crosslinked poly (butyl acrylate) core with a grafted polymethyl methylacrylate shell.

Description of the Invention

The present invention is defined in the claims. The present invention specifically refers to a curable epoxy resin composi- tion comprising an epoxy resin component, a hardener component, a filler component, an impact modifier component and optionally further additives, characterized in that (a) said impact modifier component has a core-shell structure and an average particle size distribution within the nano-range; (b) said curable epoxy resin composition has been obtained by previously mixing together in a separate step at least a part of the impact modifier component with at least a part of the epoxy resin com^¬ ponent and optionally with some or all of the additives and/or by previously mixing together in a separate step at least a part of the impact modifier component with at least a part of the hardener component and optionally with some or all of the additives, and subsequently mixing the mixture or the mixtures as obtained from said previous mixing step or previous mixing steps with the remaining component or components which are present in the curable epoxy resin composition, whereby (c) said mixing together of at least a part of the impact modifier - - component with at least a part of the epoxy resin component and optionally with some or all of the additives and/or said mixing together of at least a part of the impact modifier component with at least a part of the hardener component and optionally with some or all of the additives as defined in step (b) has been carried out at a temperature higher than the casting temperature of the curable epoxy resin composition.

Said curable epoxy resin composition yields a cured product having a high glass transition temperature (Tg) and at the same time improved mechanical properties, particularly with respect to fracture toughness.

The present invention further refers to a method of producing a curable epoxy resin composition comprising an epoxy resin component, a hardener component, a filler component, an impact modifier component and optionally further additives, and wherein said impact modifier component has a core-shell structure and an average particle size distribution within the nano-range;

characterized in that said method comprises the steps of mixing together in a separate step at least a part of the impact modifier component with at least a part of the epoxy resin com^¬ ponent and optionally with some or all of the optional additives and/or mixing together in a separate step at least a part of the impact modifier component with at least a part of the hardener component and optionally with some or all of the optional additives, at a mixing temperature which is higher than the casting temperature of the curable epoxy resin composition and subsequently mixing the mixture or the mixtures as obtained from the separate mixing step or mixing steps with the remaining component or components which are present in the curable epoxy resin composition.

The present invention further refers to the use of said curable epoxy resin composition for the production of insulation systems in electrical articles. The present invention further refers to said cured epoxy resin composition, which is present in the form of an electrical insulation system, resp. in the form of an electrical insulator. The present invention further refers to the electrical articles comprising an electrical insulation system made according to the present invention.

The present invention further refers to an epoxy resin component useful for producing the curable epoxy resin composition of the present invention, characterized in that said epoxy resin compo^¬ nent comprises at least a part of the impact modifier component and at least a part of the epoxy resin component and optionally some or all of the optional additives contained in the curable epoxy resin composition which is to be produced from said epoxy resin component, said components and optional additives having been mixed together at a temperature higher than the casting temperature of the curable epoxy resin composition which is to be produced from said epoxy resin component.

The present invention further refers to a method of producing an epoxy resin component useful for producing the curable epoxy resin composition of the present invention, characterized in that at least a part of the impact modifier component and at least a part of the epoxy resin component and optionally some or all of the optional additives contained in the curable epoxy resin composition which is to be produced from said epoxy resin component, are separately mixed together at a temperature higher than the casting temperature of the curable epoxy resin

composition which is to be produced with said epoxy resin component .

The present invention further refers to a hardener component useful for producing the curable epoxy resin composition of the present invention, characterized in that said hardener component comprises at least a part of the impact modifier component and - - at least a part of the hardener component and optionally some or all of the optional additives contained in the curable epoxy resin composition which is to be produced from said hardener component, said components and optional additives having been mixed together at a temperature higher than the casting

temperature of the curable epoxy resin composition which is to be produced from said hardener component .

The present invention further refers to a method of producing a hardener component useful for producing the curable epoxy resin composition of the present invention, characterized in that at least a part of the impact modifier component and at least a part of the hardener component and optionally some or all of the optional additives contained in the curable epoxy resin compo- sition which is to be produced from said hardener component, are separately mixed together at a temperature higher than the casting temperature of the curable epoxy resin composition which is to be produced with said hardener component. "At least a part of the impact modifier component" means that at least 50% by weight, preferably 65% by weight, preferably 80% by weight, preferably 90% by weight and preferably 100% by weight of the impact modifier component is separately mixed together with at least a part of the epoxy resin component or the harde- ner component and optionally with some or all of the further additives .

"At least a part of the epoxy resin component or at least a part of the hardener component" means that at least 50% by weight, preferably 65% by weight, preferably 80% by weight, preferably 90% by weight and preferably 100% by weight of the epoxy resin component or the hardener component is separately mixed together with at least a part of the impact modifier component and optio^¬ nally some or all of the further additives. - -

Preferred is mixing together in a separate step at least a part of the impact modifier component with at least a part of the hardener component and optionally with some or all of the optional additives, at a mixing temperature which is higher than the casting temperature of the curable epoxy resin composition.

Preferably 100% by weight of the impact modifier component present within the epoxy resin composition is mixed with at least a part of the hardener component present within the epoxy resin composition and most preferably 100% by weight of the impact modifier component present within the epoxy resin compo^¬ sition is mixed together with 100% by weight of the hardener component present within the epoxy resin composition, optionally together with some or all of the further additives present.

According to the present invention, said mixing process is carried out at a temperature higher than the casting temperature of the curable epoxy resin composition to be produced with said hardener component . At "a temperature higher than the casting temperature of the curable epoxy resin composition to be produced" means that said temperature is within the range of 60°C to 180°C, preferably within the range of 70°C to 170°C, preferably within the range of 80°C to 160°C, preferably within the range of 90°C to 140°C, and preferably within the range of 100°C to 140°C.

Said mixing process is preferably, but not necessarily, carried out under vacuum, preferably at a pressure of less than 100 mbar

(<100 mbar), preferably less than 50 mbar (<50 mbar), preferably less than 20 mbar (<20 mbar) and preferably less than 10 mbar

(<10 mbar) .

Said mixing process is preferably carried out for a time period within the range of 10 minutes to twenty-four hours, preferably for a time period within the range of 30 minutes to six hours, and more preferably within the range of one hour to three hours. - -

Impact modifiers with a particle size within the nano-range are known and commercially available. These impact modifiers are made so that the special core-shell structure allows the product to disperse as discrete particles within the matrix, without dissolving or melting. According to the mixing sequence and the mixing parameters of the present invention, surprisingly, distinctly improved values for the glass transition temperature of the cured epoxy resin composition are obtained and no impairment of its thermal and thermo-mechanical properties has been found. This may have different reasons.

The core-shell impact modifier component has an average grain size distribution (d₅₀) within the range of 50 nm (nanometer) up to 1.0 μπι (Mikrometer) and preferably within the range of 100 nm (nanometer) up to 900 nm (nanometer) . Preferably at least 50% of the grains, preferably at least 70% of the grains, preferably at least 80% of the grains, preferably at least 90% of the grains, are within the ranges given.

Preferred impact modifiers with a particle size within the nano- range which are commercially available are for example Paraloid® EXL 2300, Paraloid® EXL 2330 und Paraloid® EXL 3330 (from Dow Chemical Company) . These are acrylic core-shell impact modifiers having a crosslinked poly (butyl acrylate) core with a grafted polymethyl methacrylate shell and are available as free flowing powders or as tablets. Such acrylic core-shell impact modifiers are described e.g. in US 3,859,389. Preferred are core-shell impact modifiers with a poly(alkyl acrylate) and/or a poly(alkyl methacrylate) core component such as polymers made from methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, tert. -butyl acrylate, 2-ethylhexyl acrylate and the corresponding methacrylate polymers. Most preferred is poly (n-butyl methacrylate) as core material. Preferred shell-material polymers are made from methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate. Most preferred is poly(methyl acrylate ) .

There exist further commercial core-shell impact modifiers which can be used in the present invention, such as Kraton®G (Shell Co.), Metablene®-S (Mitsubishi Rayon), Novolen 1100 L (Novolen Technology Holdings C.V.), which are based on different poly- mers, such as SBS, SIS, Latex-copolymers and/or polyolefins, etc. These commercial core-shell impact modifiers are known to the expert in the art who is able to choose a desired core-shell impact modifier for optimizing the present invention. The core-shell impact modifier component is present within the epoxy resin composition within the range of 0.5% by weight to 6.0% by weight, preferably within the range of 1.0% by weight to 5.0% by weight, preferably within the range of 1.0 % by weight to 4.0 % by weight, calculated to the total weight of the epoxy resin composition.

The epoxy resin component as used according to the present invention within the curable epoxy resin composition contains at least two 1,2-epoxy groups per molecule. Cycloaliphatic and aromatic epoxy resin compounds useful for the present invention comprise unsubstituted glycidyl groups and/or glycidyl groups substituted with methyl groups . These glycidyl compounds have an epoxy value (equiv./kg) preferably of at least three, preferably at least four and especially at about five or higher, preferably about 5.0 to 6.1. Preferred are for example optionally substi^¬ tuted epoxy resins of formula (I) :

D = -0 - , -S 0 2 - , -C O - , -C H 2 - , -C (C H 3 )2 - , -C (C F 3 )2 - n = z e ro o r 1 or optionally substituted epoxy resins of formula (II) :

D = -0 -, -S 0 2 -, -C O - , -C H 2 -, -C (C H 3 )2- , -C (C F 3 )2 - n = ze ro o r 1

Compounds of formula (I) or formula (II) wherein D is [-(CH₂)-] or [-C(CH₃)₂-] are preferred. Preferred further are compounds of formula (II) wherein D is [-(CH₂)-] or [-C(CH₃)₂-], and prefe^¬ rably [-C(CH₃)₂-], i.e. diglycidylether of 2 , 2-bis- ( 4-hydroxy- phenyl ) -propane [diglycidylether of bisphenol A (DGEBA) ] . DGEBA is commercially available. DGEBA as preferably used in the present invention has an epoxy value (equiv./kg) of at least three, preferably at least four and especially at about five or higher, preferably about 5.0 to 6.1.

Preferred cycloaliphatic epoxy resin compounds are for example Araldite® CY 184 (Huntsman Advanced Materials Ltd. ) which is a cycloaliphatic diglycidylester epoxy resin compound having an epoxy content of 5.80-6.10 (equiv/kg) .

Further epoxy resins to be used within the scope of the present invention are for example hexahydro-o-phthalic acid-bis-glycidyl ester, hexahydro-m-phthalic acid-bis-glycidyl ester or hexa- hydro-p-phthalic acid-bis-glycidyl ester. Preferred epoxy resin compounds are liquid at room temperature or when heated to a temperature of up to about 100 °C.

Numerous hardeners are known to be used as hardener component in epoxy resin compositions. The preferred hardener component is an acid anhydride. Such anhydrides are preferably aliphatic and cycloaliphatic or aromatic polycarbonic acid anhydrides. Pre^¬ ferred is phthalic anhydride, a tetrahydrophtalic anhydride - -

(THPA) , a hexahydrophtalic anhydride (HHPA) , a methylhydro- phthalic anhydride, a methyltetrahydrophthalic anhydride

(MTHPA) , a methyl-hexahydrophtalic anhydride (MHHPA) , or a methyl-nadic anhydride (MNA) or a mixture thereof.

MTHPA, for example, is commercially available and exists in different forms, e.g. as 4-methyl-l , 2 , 3 , 6-tetrahydrophthalic an^¬ hydride or as 4-methyl-3 , 4 , 5 , 6-tetrahydrophthalic anhydride. Although the different forms are not critical for the appli- cation in the present invention, 4-methyl-l , 2 , 3 , 6-tetrahydro^¬ phthalic anhydride and 4-methyl-3, 4, 5, 6-tetrahydrophthalic an^¬ hydride are the preferred compounds to be used.

Methyltetrahydrophthalic anhydride (MTHPA) is often supplied commercially as a mixture containing MTHPA isomers as the main component, together with other anhydrides, such as tetrahydro- phthalic anhydride (THPA) , methylhexahydrophthalic anhydride (MHHPA) and/or phthalic anhydride (PA) . Such mixtures may also be used within the scope of the present invention. The content of MTHPA within such a mixture is preferably at least 50% by weight, preferably at least 60% by weight, preferably at least 70% by weight, preferably at least 80% by weight, and preferably at least 90% by weight, calculated to the total weight of the mixture .

The hardener component within the epoxy resin composition is present preferably in concentrations within the range of 0.8 to 1.2 reactive group equivalents of the hardener component, calcu^¬ lated per one epoxy equivalent present in the epoxy resin component; preferably one reactive group equivalent of the hardener component, per one epoxy equivalent present in the epoxy resin component.

The filler component is preferably selected from conventional filler materials as are generally used as fillers in electrical insulations. Preferably said filler is selected from the group - - of filler materials comprising inorganic oxides, inorganic hydroxides and inorganic oxyhydroxides , preferably silica, quartz, known silicates, aluminium oxide, aluminium trihydrate [ATH] , titanium oxide or dolomite [CaMg ( C0₃ ) ₂ ] , wollastonite, glass beads, metal nitrides, such as silicon nitride, boron nitride and aluminium nitride or metal carbides, such as silicon carbide as well as cut or continuous reinforcing fibers of known composition, length and diameters. Also a mixture of different fillers may be used. Preferred are silica and quartz, specifi- cally silica flour, with a Si0₂-content of about 95-98% by weight .

The filler material has an average grain size as known for the use in electrical insulation systems and is generally within the range of 100 nm (nanometer) up to 3 mm. Preferred, however, is an average grain size (at least 50% of the grains) within the range of about 1 μπι to 300 μτη, preferably from 5 μτη to 100 μτη, or a selected mixture of such average grain sizes. Preferred also is a filler material with a high surface area.

The filler component is present in the epoxy resin composition, depending on the final application of the epoxy resin compo^¬ sition, preferably within the range of about 50% by weight to about 80% by weight, preferably within the range of about 55% by weight to about 75% by weight, preferably at about 60% by weight to about 70% by weight, preferably at about 65% by weight to about 70% by weight, calculated to the total weight of the epoxy resin composition. The filler material optionally may be present in a „porous" form. As porous filler material, which optionally may be coated, is understood, that the density of said filler material is within the range of 60% to 80%, compared to the real density of the non-porous filler material. Such porous filler materials have a higher total surface area than the non-porous material. Said surface area is higher than 0.3 m²/g (BET m²/g) and prefe- - - rably higher than 0.4 m /g (BET) and preferably is within the range of 0.4 m²/g (BET) to 100 m²/g (BET), preferably within the range of 0.5 m²/g (BET) to 80 m²/g (BET) . The filler material may be incorporated into the epoxy resin composition by mixing the filler material into any component of the epoxy resin composition in any desired sequence. The usual way is to add the filler material at a temperature not higher than the casting temperature of the final epoxy resin compo- sition.

According to the present invention the filler material may be added to the epoxy resin component and/or to the hardener component in separate mixing steps, i.e. the filler material is added to the epoxy resin component and/or to the hardener component and treated at a temperature higher than the casting temperature of the curable epoxy resin composition.

For this embodiment, preferably the filler material is

separately added to the epoxy resin component and the impact modifier is separately added to the hardener component,

optionally each time together with optional additives contained in the epoxy resin composition, whereby each mixture is

separately treated at defined elevated temperatures, treating times and reduced pressures. Said elevated temperatures are preferably within the range of 50 to 160°C, preferably within the range of 80 to 120°C; said treating times are preferably within the range of 1 to 12 hours, preferably within the range of 4 to 6 hours; and said reduced pressures are preferably within the range of 0.001 to 1 bar, preferably within the range of 0.01 to 0.5 bar. The obtained mixtures are then cooled to the casting temperature and processed further to produce the cured product. Said specific elevated temperatures, said specific treating times, and said specific reduced pressures applied within the given ranges, substantially depend on the viscosity of the mixture and on the quantity of impact modifier separately - - added to the epoxy resin and/or the hardener component, and can be easily determined by the expert in the art.

The curable epoxy resin composition according to the present invention may comprise further a curing agent for enhancing the polymerization of the epoxy resin with the hardener. Further additives may be selected from hydrophobic compounds including silicones, wetting/dispersing agents, plasticizers, antioxi^¬ dants, light absorbers, pigments, flame retardants, fibers, tougheners and other additives generally used in electrical applications. These are known to the expert.

Preferred curing agents are for example tertiary amines, such as benzyldimethylamine or amine-complexes such as complexes of tertiary amines with boron trichloride or boron trifluoride; urea derivatives, such as N-4-chlorophenyl- ' , ' -dimethylurea (Monuron) ; optionally substituted imidazoles such as imidazole or 2-phenyl-imidazole . Preferred are tertiary amines, especially 1-substituted imidazole and/or N, -dimethylbenzylamine, such as 1-alkyl imidazoles which may or may not be substituted also in the 2-position, such as 1-methyl imidazole or l-isopropyl-2- methyl imidazole. Preferred is 1-methyl imidazole. The amount of catalyst used is a concentration of about 0.1% to 2.0% by weight, calculated to the weight of the epoxy resin component present in the composition and is conventional.

Suitable hydrophobic compounds or mixtures of such compounds, especially for improving the self-healing properties of the electrical insulator may be selected from the group comprising flowable fluorinated or chlorinated hydrocarbons which contain -CH₂-units, -CHF-units, -CF₂-units, -CF₃-units, -CHCl-units, -C (CI ) 2-units, -C ( CI ) 3-units , or mixtures thereof; or a cyclic, linear or branched flowable organopolysiloxane . Such compounds, also in encapsulated form, are known per se. - -

Suitable polysiloxanes are known and may be linear, branched, cross-linked or cyclic. Preferably the polysiloxanes are com^¬ posed of -[Si(R) (R) 0] -groups, wherein R independently of each other is an unsubstituted or substituted, preferably fluorina- ted, alkyl radical having from 1 to 4 carbon atoms, or phenyl, preferably methyl, and wherein said substituent R may carry reactive groups, such as hydroxyl or epoxy groups.

Non-cyclic siloxane compounds preferably on average have about from 20 to 5000, preferably 50-2000, - [Si (R) (R) 0] -groups . Pre^¬ ferred cyclic siloxane compounds are those comprising 4-12, and preferably 4-8, -[ Si (R) (R) 0] -units .

The hydrophobic compound is added to the epoxy resin composition preferably in an amount of from 0.1% to 10%, preferably in an amount of from 0.25% to 5% by weight, preferably in an amount of from 0.25% to 3% by weight, calculated to the weight of the weight of the epoxy resin component present. Suitable processes for casting curable epoxy resin compositions, including the curable epoxy resin composition of the present invention, are for example the Vacuum Casting Process and the Automated Pressure Gelation (APG) Process. These processes are carried out at a casting temperature within the range of room temperature to 150°C, preferably within the range of 50°C to 150°C, typically at a temperature of about 65°C.

This means that each component of the present epoxy resin composition, which has been obtained by a separate mixing step at a temperature higher than the casting temperature of the curable epoxy resin composition to be produced, preferably is cooled down after the separate mixing step to at least the casting temperature of the final curable epoxy resin composition before further processing it to the curable epoxy resin

composition. - -

The uncured epoxy resin composition is cured at a temperature of room temperature to about 280°C, preferably within the range of 50°C to 280°C, preferably within the range of 100°C to 200°C, preferably within the range of 100°C to 170°C, and preferably at about 130°C and during a curing time within the range of about 30 minutes to about 10 hours. Curing generally is possible also at lower temperatures, whereby at lower temperatures complete curing may last up to several days depending on the catalyst present and its concentration. The Vacuum Casting Process and the Automated Pressure Gelation (APG) Process when being applied to a composition of the present invention also typically include such a curing step in the mold for a time sufficient to shape the epoxy resin composition into its final infusible three dimensional structure.

Preferred uses of the electrical insulation systems produced with epoxy resin compositions according to the present invention are electrical gas-insulated switchgear (GIS) applications and electrical generator circuit breaker (GCB) applications, for example gas-insulated metal enclosed electrical applications, such as pressurized gas-insulated switchgear stations or spacer insulators as well as dry-type transformers, cable terminations, cast coils for dry type distribution transformers, especially vacuum cast dry distribution transformers, which within the resin structure contain electrical conductors, and in the casting of electrical components such as bushings, switches, insulators, sensors, converters, cable end seals and insulators.

These may be produced also for medium and high-voltage insu- lations for indoor and outdoor use, like breakers or switchgear applications; medium and high voltage bushings; as long-rod, composite and cap-type insulators, and also for base insulators in the medium-voltage sector, in the production of insulators associated with outdoor power switches, measuring transducers, leadthroughs , and overvoltage protectors, in switchgear con^¬ structions, in power switches, and electrical machines, as coa- - - ting materials for transistors and other semiconductor elements and/or to impregnate electrical components. The following examples illustrate the invention without limiting the scope of the claimed invention.

Examples 1-3

Components of the epoxy resin composition:

- Resin DER 331, from Dow Chemical Corp. The resin DER 331 is a classic DGEBA epoxy resin.

- Hardener HY 1102, from Huntsman. The hardener HY 1102 is a cycloaliphatic anhydride hardener (MHHPA) .

- Catalyst DY070, from Huntsman ( 1-methy-imidazole )

- Filler Martoxid MDLS-6 from Albemarle Corp., which is an

aluminum oxide filler (A1₂0₃) .

- Nano core-shell impact modifier: Paraloid® EXL-2300G from DOW Chemical Corp. (pure acrylic)

The standard mixing method is to mix the components together and then cast the insulator part . The mixing method and mixing sequence according to Examples 1-3 is carried out by premixing the epoxy resin component and the filler (Martoxid MDLS-6) in a separate step and by premixing the hardener and the core-shell impact modifier (Paraloid® EXL-2300G) in a separate step.

Subsequently all the components of the final epoxy resin composition are mixed together.

Detailed mixing method: The hardener and the impact modifier, both, are preheated to 80°C and are then mixed together at this temperature for one hour in a IKA Eurostar mixing apparatus under vacuum at 0.05 bar, at 1200 rpm (rounds per minute) . The epoxy resin component and the filler are separately mixed together for six hours at 100°C in an IKA Eurostar mixing apparatus under vacuum at 0.5 bar, at 1200 rpm. The hardener/- impact modifier mixture and the epoxy resin/filler mixture are then cooled to 55°C. Both mixtures are then mixed together under vacuum at 0.5 bar for one hour after having added the catalyst - -

(Catalyst DY070) . Finally, the resin is cast into the desired shape and cured for 2 hours at 80°C, then for 4 hours at 140°C and then for 1 hour at 150°C.

Table 1 shows the components used in Example 1-3.

Example 1 (comparative Example): shows the fracture toughness

(MPA.m^A0.5) of a cured composition obtained from a curable composition made by mixing the components as described above, but without the addition of an impact modifier.

Example 2 (comparative Example): shows the fracture toughness

(MPA.m^A0.5) of a cured composition obtained from a curable composition containing an impact modifier, but obtained by conventionally mixing all the components together.

Example 3 : shows the fracture toughness (MPA.m^A0.5) of cured composition obtained from a curable composition containing an impact modifier, obtained by mixing the components according to the present invention.

Table 1

Discussion

Example 1 (comparative Example) shows that the composition obtained by mixing the components according to the present invention but without the addition of an impact modifier, ha low fracture toughness. - -

Example 2 (comparative Example) shows that the composition con^¬ taining an impact modifier, but obtained by conventionally mixing all the components together has low fracture toughness.

Example 3 shows that the composition containing an impact modifier and obtained by mixing the components according to present invention has superior high fracture toughness.

Claims

1. Curable epoxy resin composition comprising an epoxy resin component, a hardener component, a filler component, an impact modifier component and optionally further additives,

characterized in that (a) said impact modifier component has a core-shell structure and an average particle size distribution within the nano-range; (b) said curable epoxy resin composition has been obtained by previously mixing together in a separate step at least a part of the impact modifier component with at least a part of the epoxy resin component and optionally with some or all of the additives and/or by previously mixing together in a separate step at least a part of the impact modi- fier component with at least a part of the hardener component and optionally with some or all of the additives, and subse^¬ quently mixing the mixture or the mixtures as obtained from said previous mixing step or previous mixing steps with the remaining component or components which are present in the curable epoxy resin composition, whereby (c) said mixing together of at least a part of the impact modifier component with at least a part of the epoxy resin component and optionally with some or all of the additives and/or said mixing together of at least a part of the impact modifier component with at least a part of the hardener component and optionally with some or all of the additives as defined in step (b) has been carried out at a temperature higher than the casting temperature of the curable epoxy resin

composition .

2. Curable epoxy resin composition according to claim 1, wherein at least 50% by weight, preferably 65% by weight, pre^¬ ferably 80% by weight, preferably 90% by weight and preferably 100% by weight of the impact modifier component has been separately mixed together with at least a part of the epoxy resin component or the hardener component and optionally with some or all of the further additives.

3. Curable epoxy resin composition according to claim 1 or 2, wherein at least 50% by weight, preferably 65% by weight, pre^¬ ferably 80% by weight, preferably 90% by weight and preferably 100% by weight of the epoxy resin component or the hardener component has been separately mixed together with at least a part of the impact modifier component and optionally some or all of the further additives.

4. Curable epoxy resin composition according to claim 1, wherein at least a part of the impact modifier component with at least a part of the hardener component and optionally with some or all of the optional additives, has been mixed in a separate step at a mixing temperature which is higher than the casting temperature of the curable epoxy resin composition.

5. Curable epoxy resin composition according to any one of the claims 1-4, wherein said temperature higher than the casting temperature of the curable epoxy resin composition to be produced is within the range of 60°C to 180°C, preferably within the range of 70°C to 170°C, preferably within the range of 80°C to 160°C, preferably within the range of 90°C to 140°C, and preferably within the range of 100°C to 140°C.

6. Curable epoxy resin composition according to any one of the claims 1-5, wherein said mixing process was carried out under vacuum, preferably at a pressure of less than 100 mbar, prefe^¬ rably less than 50 mbar, preferably less than 20 mbar and preferably less than 10 mbar (<10 mbar) .

7. Curable epoxy resin composition according to any one of the claims 1-6, wherein said impact modifier component has an average grain size distribution (d₅₀) within the range of 50 nm (nanometer) up to 1.0 μπι (Mikrometer) and preferably within the range of 100 nm (nanometer) up to 900 nm (nanometer) .

8. Curable epoxy resin composition according to claim 7, wherein said impact modifier has a poly(alkyl acrylate) and/or a poly(alkyl methacrylate) core component, preferably made from methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, tert. -butyl acrylate, 2-ethylhexyl acrylate and the corresponding methacrylate polymers and a shell-material polymer made from methyl acrylate, ethyl acrylate, n-propyl acrylate, n- butyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate.

9. Curable epoxy resin composition according to claim 7 or 8, wherein said impact modifier component is present within the epoxy resin composition within the range of 0.5% by weight to 6.0% by weight, preferably within the range of 1.0% by weight to 5.0% by weight, preferably within the range of 1.0 % by weight to 4.0 % by weight, calculated to the total weight of the epoxy resin composition.

10. Curable epoxy resin composition according to any one of the claims 1-9, wherein said epoxy resin component contains at least two 1,2-epoxy groups per molecule, and is selected from cyclo- aliphatic and aromatic epoxy resin compounds comprising unsub- stituted glycidyl groups and/or glycidyl groups substituted with methyl groups, wherein said glycidyl compounds have an epoxy value (equiv./kg) preferably of at least three, preferably at least four and especially at about five or higher, preferably about 5.0 to 6.1.

11. Curable epoxy resin composition according to any one of the claims 1-9, wherein said epoxy resin component is selected from hexahydro-o-phthalic acid-bis-glycidyl ester, hexahydro-m- phthalic acid-bis-glycidyl ester or hexahydro-p-phthalic acid- bis-glycidyl ester.

12. Curable epoxy resin composition according to any one of the claims 1-11, wherein said hardener is a known hardener component used as hardener component in epoxy resin compositions, prefe^¬ rably an acid anhydride preferably selected from aliphatic and cycloaliphatic or aromatic polycarbonic acid anhydrides.

13. Curable epoxy resin composition according to claim 12, wherein said hardener is selected from phthalic anhydride, tetrahydrophtalic anhydride, hexahydrophtalic anhydride, methyl- hydrophthalic anhydride, methyltetrahydrophthalic anhydride, methyl-hexahydrophtalic anhydride and methyl-nadic anhydride or a mixture thereof.

14. Curable epoxy resin composition according to any one of the claims 1-13, wherein said filler component is selected from con^¬ ventional filler materials as are used as fillers in electrical insulations and is present in the epoxy resin composition within the range of about 50% by weight to about 80% by weight, calcu^¬ lated to the total weight of the epoxy resin composition.

15. Curable epoxy resin composition according to claim 1, wherein said filler component is present in a porous form having a density within the range of 60% to 80%, compared to the density of the non-porous filler material.

16. Curable epoxy resin composition according to claim 1, wherein the filler material has been added to the epoxy resin component and/or to the hardener component in a separate mixing step and has been treated at a temperature higher than the casting temperature of the curable epoxy resin composition, preferably within a temperature range of 50 to 160°C, preferably within the range of 80 to 120°C.

17. Curable epoxy resin composition according to any one of the claims 1-16, wherein the curable epoxy resin composition further comprises additives selected from curing agents, hydrophobic compounds including silicones, wetting/dispersing agents, plasticizers, antioxidants, light absorbers, pigments, flame retardants, fibers, tougheners and other additives generally used in electrical applications.

18. Method of producing a curable epoxy resin composition according to any one of the claims 1-17, characterized in that said method comprises the steps of mixing together in a separate step at least a part of the impact modifier component with at least a part of the epoxy resin component and optionally with some or all of the optional additives and/or mixing together in a separate step at least a part of the impact modifier component with at least a part of the hardener component and optionally with some or all of the optional additives, at a mixing

temperature which is higher than the casting temperature of the curable epoxy resin composition and subsequently mixing the mixture or the mixtures as obtained from the separate mixing step or mixing steps with the remaining component or components which are present in the curable epoxy resin composition.

19. The use of for the production of insulation systems in electrical articles.

20. An electrical insulation system being made from a curable epoxy resin composition according to any one of the claims 1-17.

21. An electrical article comprising an electrical insulation system made according to claim 20.

22. Epoxy resin component useful for producing the curable epoxy resin composition according to any one of the claims 1-17, characterized in that said epoxy resin component comprises at least a part of the impact modifier component and at least a part of the epoxy resin component and optionally some or all of the optional additives contained in the curable epoxy resin composition according to any one of the claims 1-17, said components and optional additives having been mixed together at a temperature higher than the casting temperature of the curable epoxy resin composition which is to be produced from said epoxy resin component.

23. Method of producing an epoxy resin component according to claim 22, characterized in that at least a part of the impact modifier component and at least a part of the epoxy resin com^¬ ponent and optionally some or all of the optional additives contained in the curable epoxy resin composition according to any one of the claims 1-17, are separately mixed together at a temperature higher than the casting temperature of the curable epoxy resin composition which is to be produced with said epoxy resin component.

24. Hardener component useful for producing the curable epoxy resin composition according to any one of the claims 1-17, characterized in that said hardener component comprises at least a part of the impact modifier component and at least a part of the hardener component and optionally some or all of the optional additives contained in the curable epoxy resin compo- sition according to any one of the claims 1-17, said components and optional additives having been mixed together at a

temperature higher than the casting temperature of the curable epoxy resin composition which is to be produced from said hardener component .

25. Method of producing a hardener component useful for producing the curable epoxy resin composition according to any one of the claims 1-17, characterized in that at least a part of the impact modifier component and at least a part of the hardener component and optionally some or all of the optional additives contained in the curable epoxy resin composition according to any one of the claims 1-17, are separately mixed together at a temperature higher than the casting temperature of the curable epoxy resin composition which is to be produced with said hardener component .