WO2011023430A1

WO2011023430A1 - Inductively curable adhesive composition

Info

Publication number: WO2011023430A1
Application number: PCT/EP2010/058971
Authority: WO
Inventors: Reiner Wartusch; Harald Herzog; Martina Ortelt
Original assignee: Evonik Degussa Gmbh
Priority date: 2009-08-27
Filing date: 2010-06-24
Publication date: 2011-03-03
Also published as: DE102009028942A1; EP2470613A1

Abstract

Inductively curable adhesive composition comprising core-shell particles having an average primary particle diameter of 2 to 100 nm, the shell comprising amorphous silicon dioxide and the core comprising one or more magnetic metal oxides. It can be used for adhesively bonding rotor vanes of wind turbines.

Description

Inductively curable adhesive composition

The invention relates to an inductively curable adhesive composition which comprises core-shell particles whose shell comprises amorphous silicon dioxide and whose core comprises one or more magnetic metal oxides. A frequent drawback of prior-art adhesives is that the processing life (pot life) before parts become bonded is not long enough, whereas the cure time takes too long a duration. This drawback becomes noticeable in particular when bonding large areas, such as in the construction of vehicles, aircraft or watercraft. Another field in which adhesives are required to withstand high mechanical loads is the construction of wind turbines, and more particularly the construction of vanes for wind turbine rotors.

Methods of producing the mouldings of the vanes of wind turbine rotors are known in the prior art. They involve first producing mouldings of two half-shells from a thermoset polymer, which are then bonded adhesively on the side facing away from the mould.

The prior art has disclosed adhesive compositions which comprise superparamagnetic particles. These adhesive compositions can be cured inductively by magnetic or electromagnetic fields. Thus, for example, DE-A-10163399 discloses an adhesive composition which has dispersed superparamagnetic particles of mixed metal oxide.

The particles have an average diameter of 2 to 100 nm. Through agglomeration or accretion of the superparamagnetic particles, it is difficult to ensure uniform distribution of the particles in the adhesive composition. Moreover, the agglomeration or accretion leads to a change in the magnetic properties of the particles and hence to a lower efficiency on inductive curing.

It was an object of the present invention to provide an adhesive composition which permits a long enough processing life when bonding relatively large areas, but at the same time can be rapidly cured.

The invention provides an inductively curable adhesive composition comprising core- shell particles having an average particle diameter of 2 to 100 nm, the shell comprising or consisting of amorphous silicon dioxide and the core comprising or consisting of one or more magnetic metal oxides. The core-shell particles have an average diameter of 2 to 100 nm. This diameter may relate to isolated individual particles, to aggregated particles or to hybrid forms of the aforementioned particles. The average particle diameter may be determined by methods known to the person skilled in the art, such as laser diffraction or evaluation of TEM micrographs, for example. In one particular embodiment of the adhesive composition of the invention, the core-shell particles comprise or are composed of particles which form intergrown cores and in which the intergrown cores are surrounded by a shell comprising silicon dioxide.

The cores of the particles are magnetic. This means that they are ferrimagnetic, ferromagnetic and/or superparamagnetic. Preference may be given to particles having superparamagnetic properties. Superparamagnetic materials possess no permanent (equidirectional) arrangement of the elementary magnetic dipoles in the absence of external, acting magnetic fields. They may have a slight residual magnetization.

The cores of the particles comprise or consist of magnetic metal oxides. Suitability is possessed more particularly by the oxides of iron, of cobalt, of nickel, of chromium, of europium, of yttrium, of samarium, or of gadolinium. The metal oxides may be present in a single modification or in different modifications.

Preferably, iron oxide may be in the form of gamma-Fe₂O₃ (γ-Fe₂O₃), Fe₃O₄, and mixtures of gamma-Fe₂O₃ (γ-Fe₂O₃) and/or Fe₃O₄.

The metal oxides may further be present in the form of mixed oxide of at least two metals, with the metal components iron, cobalt, nickel, tin, zinc, cadmium, magnesium, manganese, copper, barium, lithium or yttrium.

The metal oxides may further be substances having the general formula M¹¹Fe₂O₄, in which M" is a metal component which comprises at least two different divalent metals. Preferably, one of the divalent metals may be manganese, zinc, magnesium, cobalt, copper, cadmium or nickel. Furthermore, the metal oxides may be composed of ternary systems of the general formula (M^a _1-x-y M^b _xFe_y)"Fe₂'"θ₄ where M^a and M^b respectively are the metals manganese, cobalt, nickel, zinc, copper, magnesium, barium, yttrium, tin, lithium, cadmium, calcium, strontium, titanium, chromium, vanadium, niobium or molybdenum, with x = 0.05 to 0.95, y = 0 to 0.95 and x+y < 1. With preference these may be ZnFe₂O₄, MnFe₂O₄, Mn₀6Fe₀₄Fe₂O₄, Mn₀₅Zn₀₅Fe₂O₄, Zn₀ ^ Fei ₉O₄, Zn₀₂Fei ₈O₄, Zn₀₃Fei,₇O₄, Zn₀₄Fei ₆O₄ or Mn₀₃₉Zn_{o 27}Fe₂₃₄O₄, MgFe₂O₃, Mg_{1 2}Mn₀₂Fei ₆O₄, Mg_{1 4}Mn₀₄Fe_{1 2}O₄, Mg_{1 6}Mn₀₆Fe₀₈O₄, Mg_{1 8}Mn_{0 8}Fe₀₄O₄.

In one particular embodiment, in the core-shell particles, there may be compounds present between shell and core that are composed of the elements silicon, iron and oxygen, an example being iron silicate.

In one particularly preferred embodiment of the invention, the core is composed of one or more iron oxides comprising hematite, magnetite and maghemite. In certain cases, small amounts of beta-Fe₂O₃ may be detected. The fraction - as determinable from X- ray diffraction diagrams - of hematite is preferably 1% to 10% by weight, more preferably 4% to 8% by weight, that of magnetite preferably 20% to 50% by weight, more preferably 35% to 40% by weight, and that of maghemite preferably 40% to 75% by weight, more preferably 50% to 60% by weight, with the fractions adding to 100% by weight. Core-shell particles which have this distribution are particularly suitable for inductive heating in a middle-frequency magnetic field of 3-100 kHz, preferably 20 to 60 kHz.

In another particular embodiment of the invention, the fraction - as determinable from the X-ray diffraction diagrams - of hematite is preferably 5% to 40% by weight, more preferably 10% to 30% by weight, that of magnetite preferably 50% to 90% by weight, more preferably 60% to 85% by weight, and that of maghemite preferably 5% to 30% by weight, more preferably 10% to 20% by weight, the fractions adding to 100%. Core- shell particles which have this distribution are particularly suitable for inductive heating in a high-frequency magnetic field of more than 100 kHz, preferably 400 to 1000 kHz.

Particular preference may be given to core-shell particles having a BET surface area of 10 to 80 m²/g, a shell thickness of 2 to 30 nm, and an iron oxide content of 60% to

90% by weight and a silicon dioxide content of 10% to 40% by weight, based in each case on the shell-encased particles.

Especially preferred for inductive curing in a middle-frequency magnetic field are core- shell particles in which

a) the BET surface area is 40 to 70 m²/g,

b) the shell thickness is 5 to 20 nm,

c) the iron oxide content is 80% to 90% by weight and the silicon dioxide content is 10% to 20% by weight, based in each case on the shell-encased particles, and where

d) the core comprises

d 1 ) 1 % to 10% of hematite,

d2) 20% to 50% of magnetite,

d3) 40% to 75% of maghemite,

the sum of these constituents being standardized to 100%.

Especially preferred for inductive curing in a high-frequency magnetic field are core- shell particles in which

a) the BET surface area is 40 to 70 m²/g,

b) the shell thickness is 5 to 20 nm,

d) the core comprises

d1 ) 15% to 40% of hematite,

d2) 50% to 70% of magnetite,

d3) 5% to 30% of maghemite,

the sum of these constituents being standardized to 100%. In the adhesive compositions of the invention, it can be advantageous to have the core-shell particles present in surface-modified form. This may facilitate incorporation into an organic medium. It further improves the physical properties of the adhesive composition, and the heating rates that can be attained. The surface modifiers used for this purpose have at least one functional group which is able to interact or react chemically with reactive groups present on the surface of the core-shell particles, resulting in attachment. This attachment may be by chemical bond, such as covalent bonds, including coordinative bonds (complexes), or ionic bonds, of the functional group to the surface groups of the particles, whereas interactions include, for example, dipole-dipole interactions, polar interactions, hydrogen bonds and van der Waals' interactions. Preference is given to the formation of a chemical bond.

As surface modifiers it is possible with preference to use halosilanes, alkoxysilanes, silazanes and/or siloxanes. Examples thereof are:

a) Organosilanes (RO)₃Si(C_nH_2n+I) or (RO)₃Si(C_nH_2n-I )

R = alkyl, such as, for example, methyl-, ethyl-, n-propyl-, isopropyl-, butyl- n = 1 - 20 b) Organosilanes R'_x(RO)ySi(C_nH2n+i ) or R'_x(R0)_ySi(C_nH_2n-1)

R = alkyl, such as, for example, methyl-, ethyl-, n-propyl-, isopropyl-, butyl- R' = alkyl, such as, for example, methyl-, ethyl-, n-propyl-, isopropyl-, butyl- R' = cycloalkyl

n = 1 - 20; x+y = 3; x = 1 ,2; y = 1 ,2 c) Haloorganosilanes X₃Si(C_nH_2n+-_] ) Or X₃Si(C_nH_2n-1)

X = CI, Br; n = 1 - 20 d) Haloorganosilanes X2(R')Si(C_nH2_n+i ) or X₂(R')Si(C_nH_2n-1)

X = Cl, Br; R' = alkyl, such as, for example, methyl-, ethyl-, n-propyl-,

isopropyl-, butyl-; R'=cycloalkyl; n = 1 - 20 e) Haloorganosilanes X(R')2Si(C_nH2_n+i ) or (R')₂Si(C_nH_2n-1)

X = Cl, Br; R' = alkyl, such as, for example, methyl-, ethyl-, n-propyl-, isopropyl-, butyl-; R'=cycloalkyl; n = 1 - 20 f) Organosilanes (RO)3Si(CH2)_m-R'

R = alkyl, such as, for example, methyl-, ethyl-, propyl-; m = 0.1 - 20

R' = methyl-, aryl (for example -CgHs, substituted phenyl radicals), -C4Fg, OCF₂-

CHF-CF₃, -C₆F₁₃, -0-CF₂-CHF₂₁ -NH₂, -N₃, -SCN, -CH=CH₂, -NH-CH₂-CH₂- NH₂, -N-(CH₂-CH₂-NH₂)₂, -0OC(CH₃)C = CH_2] -OCH₂-CH(O)CH_2]

-NH-CO-N-CO-(CH₂)_5, -NH-COO-CH₃, -NH-COO-CH₂-CH₃, -NH- (CH₂)₃Si(OR)_3] -S_x-(CH₂)₃Si(OR)_3, -SH, -NR¹R¹¹R'" (R' = alkyl, aryl; R" = H, alkyl, aryl; R'" = H, alkyl, aryl, benzyl, C₂H₄NR"" R with R"" = H, alkyl and R =

H, alkyl) g) Organosilanes of the type (R")_x(R0)_ySi(CH₂)_m-R'

R" = alkyl; x+y = 2; cycloalkyl x= 1 ,2; y = 1 ,2; m = 0.1 to 20

R' = R' = methyl-, aryl (for example -CgHs, substituted phenyl radicals), C₄F₉, OCF₂-CHF-CF₃, -C₆F₁₃, -0-CF₂-CHF₂₁ -NH₂, -N₃, -SCN, -CH=CH₂, - NH-CH₂-CH₂-NH₂, -N-(CH₂-CH₂-NH₂)₂, -0OC(CH₃)C = CH_2] -OCH₂-CH(O)CH_2] - NH-CO-N-CO-(CH₂)_5, -NH-COO-CH₃, -NH-COO-CH₂-CH₃, -NH-(CH₂)₃Si(OR)_3] -S_x-(CH₂)₃Si(OR)_3, -SH, -NR¹R¹¹R'" (R' = alkyl, aryl; R" = H, alkyl, aryl; R'" = H, alkyl, aryl, benzyl, C₂H₄NR"" R with R"" = H, alkyl and R = H, alkyl) h) Haloorganosilanes X₃Si(CH₂)_m-R'

X = Cl, Br; m = 0.1 - 20; R' = methyl-, aryl (for example -CgHs, substituted phenyl radicals), -C₄F₉, -OCF₂-CHF-CF₃, -C₆F₁₃, -O-CF₂-CHF_2] -NH₂, -N₃, -SCN, -CH=CH₂, -NH-CH₂-CH₂-NH₂, -N-(CH₂-CH₂-NH₂)_2, -0OC(CH₃)C = CH_2] - OCH₂-CH(O)CH_{2 :} -NH-CO-N-CO-(CH₂)_5] -NH-COO-CH₃, -NH-COO-CH₂-CH₃,

-NH-(CH₂)₃Si(OR)_3] -S_x-(CH₂)₃Si(OR)₃, -SH, i) Haloorganosilanes (R)X₂Si(CH₂)_m-R'

X = Cl, Br; R = alkyl, such as methyl-, ethyl-, propyl-; m = 0.1 - 20

R' = methyl-, aryl (e.g. -CgHs, substituted phenyl radicals), -C₄F₉, -OCF₂- CHF-CF₃, -C₆F₁₃, -0-CF₂-CHF₂, -NH₂, -N₃, -SCN, -CH=CH₂, -NH-CH₂-

CH₂-NH₂, -N-(CH₂-CH₂-NH₂)₂, -0OC(CH₃)C = CH_2] -OCH₂-CH(O)CH_2]

-NH-CO-N-CO-(CH₂)_5] -NH-COO-CH₃, -NH-COO-CH₂-CH₃,

-NH-(CH₂)₃Si(OR)₃, where R may be methyl-, ethyl-, propyl-, butyl-,

S_x-(CH₂)₃Si(OR)₃, where R may be methyl-, ethyl-, propyl-, butyl-, and

-SH j) Haloorganosilanes (R)₂X Si(CH₂)_m-R'

X = CI, Br; R = alkyl; m = 0.1 - 20

R' = methyl-, aryl (for example -CgHs, substituted phenyl radicals),

-C₄F₉, -OCF₂-CHF-CF₃, -C₆F_{1 3}, -O-CF₂-CHF_2]

-NH₂, -N₃, -SCN, -CH=CH₂, -NH-CH₂-CH₂-NH_2,

-N-(CH₂-CH₂-NH₂),, -0OC(CH₃)C = CH_2] -OCH₂-CH(O)CH₂

-NH-CO-N-CO-(CH₂)_5] -NH-COO-CH₃, -NH-COO-CH₂-CH₃,

-NH-(CH₂)₃Si(OR)_3] -Sχ-(CH₂)₃Si(OR)₃, -SH, k) Silazanes of the type R'F^Si-NH-SiF^R'

R = alkyl, vinyl, aryl

R' = alkyl, vinyl, aryl,

Hexamethyldisilazane I) Cyclic polysiloxanes of type D 3, D 4 or D 5, with D3, D4 and D5 referring to cyclic polysiloxanes having 3, 4 or 5 units of the type -O-Si(CH3)2-. For example, octamethylcyclotetrasiloxane = D 4 m) Polysiloxanes or silicone fluids of type Y-O-[[SiRR')_m-O]-[SiR"R'"-O]_n]_u-Y with

m = 0,1 ,2,3,...., n = 0,1 ,2,3,..., u = 0,1 ,2,3,...

Y = CH₃, H, C_nH_2n+1 with n = 1-20; Si(CH₃)₃, Si(CH₃)₂H, Si(CH₃)₂OH,

Si(CH₃)₂(OCH₃), Si(CH₃)₂(C_nH_2n+1) with n = 1-20

R = alkyl, such as CnH2n+1 , where n = 1 to 20, aryl, such as phenyl radicals and substituted phenyl radicals, (CH₂)_n-NH₂, H

R'= alkyl, such as CnH2n+1 , where n = 1 to 20, aryl, such as phenyl radicals and substituted phenyl radicals, (CH₂)_n-NH₂, H

R^" = alkyl, such as C_nH_2n+1, with n = 1 to 20, aryl, such as phenyl radicals and substituted phenyl radicals, (CH₂)_n-NH₂, H

R^'" = alkyl, such as C_nH_2n+1, with n = 1 to 20, aryl, such as phenyl radicals and substituted phenyl radicals, (CH₂)_n-NH₂, H As silanizing agents it is possible with preference to use trimethoxyoctylsilane

[(CH₃O)₃-Si-C₈H₁₇] (for example DYN ASYLAN® OCTMO, Degussa AG).

The following substances can be used more particularly as polysiloxanes or silicone fluids of the type Y-O-[[SiRR')_m-O]-[SiR"R'"-O]_n]_u-Y with

R = alkyl, H; R' = alkyl, H; R" = alkyl, H; R'" = alkyl, H; Y = CH₃, H, C_nH_2n+1 with n=1-20; Y = Si(CH₃)₃, Si(CH₃)₂H, Si(CH₃)₂OH, Si(CH₃)₂(OCH₃), Si(CH₃)₂(C_nH_2n+1) with n=1-20; m = 0,1 ,2,3,...oo; n = 0,1 ,2,3,...α>; u = 0,1 , 2,3, ...∞.

The fraction of the particles having a core-shell structure in the inductively curable adhesive composition of the invention is preferably 0.1 % to 20% by weight, and more preferably 0.5% to 10% by weight, based in each case on the adhesive composition. The inductively curable adhesive composition of the invention preferably comprises a resin which is obtainable by mixing at least two reactive components, it being possible for one or more of the reactive components to comprise particles having the core-shell structure.

The reactive groups are preferably selected from the group consisting of an epoxy resin and an amine or an epoxy resin and a carboxylic anhydride or an acrylate and an amine or an isocyanate and a polyol or an epoxy resin, and isocyanate, a polyol and an amine.

The resin in question may preferably be a resin obtainable by mixing an epoxy resin and a hardener preparation. The epoxy resin may be, for example, a resin based on a polyglycidyl ether, a polyhydroxide, a polyol or phenol. Examples include 2,2-bis-4-hydroxyphenylpropane

(bisphenol A),

bis-4-hydroxyphenylpropane (bisphenol F), a phenol-formaldehydenovolak or a cresol- formaldehydenovolak. The hardener preparation may comprise one or more anhydrides and/or amines.

This anhydride is preferably from the group consisting of phthalic anhydride, tetrahydro-, hexahydro-, methyltetrahydro-, endomethylenetetrahydro-,

methylenedimethylenetetrahydro-phthalic anhydride, maleic anhydride/styrene copolymer, dodecenylsuccinic anhydride, tetrachlorophthalic anhydride and hexachloroendomethylenetetrahydrophthalic anhydride.

The amine is preferably selected from the group consisting of aliphatic, cycloaliphatic, aromatic, araliphatic and heterocyclic amines.

Examples include the following:

- tertiary amines selected from the group consisting of N,N,N',N'-tetramethylhexane- 1 ,6-diamine, diazabicyclooctane, N,N-dimethylcyclohexylamine, tris-N,N- dimethylaminomethylphenol, N,N-dimethylamino-4-pyridine, N,N-dimethylamino-4- toluidine, N,N-diethyl-1 ,3-propanediamine, N,N-dimethylpropylenetramine, tris- 2,4,6-dimethylaminomethylphenol and tri-n-butylamine, 3-aminoethyl-3,5,5- trimethylcyclohexylamine, 1 ,4-cyclohexane bis(methylamine);

- alkylenediamines such as ethylenediamine or butane-1 ,4-diamine; polyalkylenepolyamines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, dipropylenetriamine or tripropylenetetramine;

- N-hydroxyalkylderivates of polyalkylenepolyamines, such as N- (hydroxyethyl)diethylenetriamine, or mono-N-2-hydroxypropyl derivates of triethylenetetramine; polyoxyalkylenepolyamines such as polyoxyethylene- and polyoxypropylenediamines and -triamines;

- N,N-dialkylalkylenediamines such as N,N-dimethylpropane-1 ,3-diamine or N, N- diethylpropane-1 ,3-diamine;

- cycloaliphatic amines having an amino group or aminoalkyl group on the ring, such as 3-aminomethyl-3,5,5-trimethylcyclohexylamine (isophoronediamine);

- aromatic amines such as bis(4-aminophenyl)methane or

bis(4-aminophenyl) sulphone;

- N-aminoalkylpiperazines such as N-(2-aminoethyl)piperazine or N-(3- aminopropyl)piperazine;

- polyaminoamides, for example reaction products of polyalkylenepolyamines with polymerized unsaturated fatty acids.

The adhesive composition of the invention may further comprise one or more unsaturated polyesters or vinyl esters as resins.

The unsaturated polyester resins comprise those based on unsaturated carboxylic acids or acid anhydrides and diols in a blend with unsaturated aromatic monomers.

The unsaturated carboxylic acids and their anhydrides are generally dibasic, unsaturated, preferably alpha, beta-olefinically unsaturated, carboxylic acids.

Examples of these carboxylic acids and their anhydrides are maleic acid, fumaric acid, chloromaleic acid, itaconic acid, citraconic acid, methyleneglutaric acid and mesaconic acid and their esters or, preferably, their anhydrides, and also succinic acid, glutaric acid, methylglutaric acid, adipic acid, sebacic acid, pimelic acid, phthalic anhydride, ortho-phthalic acid, isophthalic acid, terephthalic acid, dihydrophthalic acid, tetrahydrophthalic acid, tetrachlorophthalic acid, dodecanedicarboxylic acids, cis-5- norbornene-2,3-dicarboxylic acid or anhydride, dimethyl-2,6-naphthenedicarboxylate, dimethyl-2,6-naphthenedicarboxylic acid, naphthenedicarboxylic acid or anhydride, and 1 ,4-cyclohexanedicarboxylic acid. In the preparation of the polyester resins it is also possible to use monobasic, tribasic or higher polybasic carboxylic acids, for example ethylhexanoic acid, methacrylic acid, propionic acid, benzoic acid, 1 ,2,4- benzenetricarboxylic acid or 1 ,2,4,5-benzenetetracarboxylic acid.

Suitable polyhydric alcohols include alkanediols and oxaalkanediols, examples being ethylene glycol, 1 ,2-propylene glycol, propane-1 ,3-diol, 1 ,3-butylene glycol, butane- 1 ,4-diol, hexane-1 ,6-diol, 2,2-dimethylpropane-1 ,3-diol, diethylene glycol, triethylene glycol, polyethylene glycol, cyclohexane-1 ,2-diol,

2,2-bis(p-hydroxycyclohexyl)propane, butene-1 ,4-diol,

5-norbornene-2,2-dimethylol, 2,3-norbornenediol, cyclohexanedimethanol, neopentyl glycol, dimethylpropane-1 ,3-diol, 2,2-dimethylheptanediol,

2,2-dimethyloctanediol, 2,2-dimethyl-1 ,3-propanediol, pentaerythritol, dipentaerythritol, tripentaerythritol, trimethylolpropane, ditrimethylolpropane,

2,2,4-trimethyl-1 ,3-pentanediol and 2-butyl-2-ethyl-1 ,3-propanediol.

The unsaturated polyester resin may further comprise a vinyl monomer, examples being styrene, methoxystyrene, divinylbenzene, 4-ethylstyrene,

4-methylstyrene, 4-tert-butylstyrene, p-chlorostyrene or vinyltoluene; esters of acrylic acid and methacrylic acid with alcohols or polyols (such as those described above) having in each case 1 to 18 carbon atoms, examples being methyl methacrylate, butyl acrylate, ethylhexyl acrylate, hydroxpropyl acrylate, lauryl acrylate, stearyl

methacrylate, lauryl methacrylate, butanediol diacrylate and trimethylolpropane triacrylate, allyl esters, for example diallyl phthalate, and vinyl esters, for example vinyl ethylhexanoate, vinyl pivalate, limonene, dipentene, vinyl ethers, indene, allylbenzene and the like. Also suitable are mixtures of these compounds. Preferred components are styrene, alpha-methylstyrene, vinyltoluene and divinylbenzene. The adhesive composition of the invention may further comprise one or more polyols and one or more isocyanates, preferably diisocyanates.

Examples of suitable polyol components include ethylene glycol, propylene glycol, butane-1 ,4-diol, pentane-1 ,5-diol, hexane-1 ,6-diol, heptane-1 ,7-diol, octane-1 ,8-diol, glycerol, trimethylolpropane and pentaerythritol. As polyol component it is additionally possible to use reaction products of low molecular mass polyfunctional alcohols with alkylene oxides, referred to as polyethers. The alkylene oxides have preferably 2 to 4 C atoms. Suitability is possessed for example by the reaction products of ethylene glycol, propylene glycol, the isomeric butanedioles, hexanedioles or 4,4'- dihydroxydiphenylpropane with ethylene oxide, propylene oxide or butylene oxide, or mixtures of two or more thereof. Also suitable, furthermore, are the reaction products of polyfunctional alcohols, such as glycerol, trimethylolethane or trimethylolpropane, pentaerythritol or sugar alcohols, or mixtures of two or more thereof, with the stated alkylene oxides, to form polyether polyols. Particularly suitable polyether polyols are those having a molecular weight of about 100 to about 10 000, preferably of about 200 to about 5000.

There may also be polyester polyols formed by reacting low molecular mass alcohols, more particularly ethylene glycol, diethylene glycol, neopentylglycol, hexanediol, butanediol, propylene glycol, glycerol or trimethylolpropane, with caprolactone.

Likewise suitable as polyfunctional alcohols for the preparation of polyester polyols are 1 ,4-hydroxymethylcyclohexane, 2-methyl-1 ,3-propanediol, butane-1 ,2,4-triol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, dibutylene glycol and polybutylene glycol.

The isocyanates may preferably be 1 ,5-naphthylene diisocyanate, 4,4'- diphenylmethane diisocyanate (MDI), hydrogenated MDI (H12MDI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI),

4,4'-diphenyldimethylmethane diisocyanate, di- and tetraalkylenediphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1 ,3-phenylene diisocyanate,

1 ,4-phenylene diisocyanate, the isomers of tolylene diisocyanate (TDI),

1 -methyl^^-diisocyanatocyclohexane, 1 ,6-diisocyanato-2,2,4-trimethylhexane, 1 ,6- diisocyanato-2,4,4-trimethylhexane, 1 -isocyanatomethyl-S-isocyanato-i ,5,5- trimethylcyclohexane (IPDI), chlorinated and brominated diisocyanates, phosphorus- containing diisocyanates, 4,4'-diisocyanatophenylperfluoroethane, tetramethoxybutane

1 ,4-diisocyanate, butane 1 ,4-diisocyanate, hexane 1 ,6-diisocyanate (HDI), dicyclohexylmethane diisocyanate, cyclohexane 1 ,4-diisocyanate, ethylene diisocyanate, bisisocyanatoethyl phthalate,

1-chloromethylphenyl 2,4-diisocyanate, 1-bromomethylphenyl 2,6-diisocyanate, 3,3- bischloromethyl ether 4,4'-diphenyl diisocyanate, trimethylhexamethylene

diisocyanate, 1 ,4-diisocyanatobutane and 1 ,12-diisocyanatododecane.

The adhesive composition of the invention may further comprise fillers, such as talc, calcium carbonate or silicon dioxide. The silicon dioxide may preferably be precipitated or fumed (pyrogenically prepared) silicon dioxide powder. The silicon dioxide power may also be in surface-modified form.

The invention further provides for the use of the adhesive composition for adhesively bonding rotor vanes of wind turbines. The adhesive composition of the invention leads to uniform distribution of the particles in the adhesive composition, and to a high efficiency on inductive curing.

Examples

Example 1 : Silica coated Iron Oxide

A stream of a vaporous mixture of 0.62 kg/h of SiCI₄ and 0.02 kg/h of monosilane, and a second stream in the form of an aerosol obtained from a 25 percent by weight solution of iron(ll) chloride, corresponding to 1.85 kg/h of iron(ll) chloride, in water, and 5 m³ (STP)/h of nitrogen as an atomizing gas at room temperature (23°C) by means of a two-substance nozzle, are introduced separately into the mixing zone of a reactor.

This mixture is reacted in the combustion zone of the reactor in a flame generated by igniting a mixture of 7.9 m³ (STP)/h of hydrogen and 21 m³ (STP)/h of air. The residence time of the reaction mixture in the combustion zone is approx. 43 ms.

In the cooling zone which follows downstream of the combustion zone, the reaction mixture is cooled to 337°C by introducing 7 kg/h of water.

The resulting solid is separated from the gaseous substances on a filter. The solid material displays a BET surface area of 60 m²/g, a mean particle diameter of 16 nm. The thickness of the shell is 3-8 nm. The silica content is 19.3 wt.-%, the iron oxide content is 81.7 wt.-%, in 7:85:7 ratio of maghemite, magnetite and haematite.

Example 2: Adhesive Composition (according to invention)

The silica coated iron oxide of Example 1 is dispersed in Epikote^® 828 Resin

(Resolution Performance Products; based on Bisphenol A) by using a dissolver.

Vestamin^® IPD (Evonik Degussa; isophorone diamine) is added as a curing agent. The mixture was cured inductively by using the high frequency generator Tru Heat HF 5010, made by HUTTINGER Elektronik at a frequency of 607 kHz. Results are shown in Table 1. Table 1 : Inductive curing of adhesive composition of Example 2

Silica coated iron oxide^*

2 wt.-% 3 wt.-% 5 wt.-%

VESTAMINT IPD [g] 100 100

Epikote^® 828 [g] 441 441

Conversion [%] after

2 minutes 99 100 100

3 minutes 100

^* referring to the sum of VESTAM IN^® IPD and Epikote 828

Example 3: Adhesive Composition (according to invention)

The silica coated iron oxide of Example 1 is dispersed in the resin composition by using a dissolver. The curing composition is added. The mixture was cured inductively by using the high frequency generator Tru Heat HF 5010, made by HUTTINGER Elektronik at a frequency of 607 kHz. Results are shown in Table 2.

Table 2: Inductive curing of adhesive composition of Example 3

referring to the sum of resin composition and curing composition; Evonik Degussa;

^& UPPC

The results shown in Tables 1 and 2 demonstrate the efficiency of the inductively curable adhesive composition according to the invention.

Claims

1 . Inductively curable adhesive composition comprising core-shell particles having an average primary particle diameter of 2 to 100 nm, the shell comprising amorphous silicon dioxide and the core comprising one or more magnetic metal oxides.

2. Inductively curable adhesive composition according to Claim 1 , characterized in that the core-shell particles comprise particles which form intergrown cores surrounded by a shell comprising silicon dioxide.

3. Inductively curable adhesive composition according to either of Claims 1 and 2, characterized in that the core is composed of one or more iron oxides comprising hematite, magnetite and maghemite.

4. Inductively curable adhesive composition according to any of Claims 1 to 3, characterized in that the core-shell particles have

a) a BET surface area of 10 to 80 m²/g,

b) a shell thickness of 2 to 30 nm and

c) an iron oxide content of 60% to 90% by weight and a silicon dioxide

content of 10% to 40% by weight, based in each case on the shell-encased particles.

5. Inductively curable adhesive composition according to any of Claims 1 to 4, characterized in that the shell is surface-modified.

6. Inductively curable adhesive composition according to any of Claims 1 to 5, characterized in that the fraction of the particles with core-shell structure is 0.1% to 20% by weight, based on the adhesive composition.

7. Inductively curable adhesive composition according to any of Claims 1 to 6, characterized in that it comprises a reactive resin which is obtainable by mixing at least two reactive components, one or more of the reactive components comprising particles having the core-shell structure.

8. Inductively curable adhesive composition according to any of Claims 1 to 6, characterized in that one reactive component is an epoxy resin and a second reactive component is a hardener selected from one or more carboxylic anhydrides, one or more amines, or a mixture of carboxylic anhydrides and amines.

9. Inductively curable adhesive composition according to any of Claims 1 to 6, characterized in that one reactive component is an unsaturated polyester resin and another reactive component is a polyol.

10. Inductively curable adhesive composition according to any of Claims 1 to 6, characterized in that one reactive component is an isocyanate and another reactive component is a polyol.

1 1. Inductively curable adhesive composition according to any of Claims 1 to 10, characterized in that it comprises fillers.

12. Use of the inductively curable adhesive composition according to any of Claims 1 to 11 for adhesively bonding rotor vanes of wind turbines.