WO2009153274A1 - Epoxy-based adhesive or sealant comprising inorganic nanoparticles with acrylic acid ester-containing casing - Google Patents

Abstract

Epoxy-based composition that can be used as an adhesive or sealant or as structural foam and that comprises 0.5 to 40 wt.% of inorganic particles that are encased in organic polymers, wherein said organic polymers are selected from polystyrene or from homopolymers or copolymers of esters of acrylic acid and/or methacrylic acid which consist of at least 30 wt.% of esters of acrylic acid and/or methacrylic acid; use of such a composition as a structural adhesive or structural foam in automobile or equipment construction; product comprising components that are glued, sealed, strengthened or stiffened with such a cured composition.

Description

Epoxy-based adhesive or sealant comprising inorganic nanoparticles with acrylic acid ester-containing casing

The present invention relates to an epoxy-based adhesive or sealant, which comprises inorganic nanoparticles that possess a casing of organic polymers. The casing consists of polystyrene or of at least 30 wt.% of acrylic acid esters. In the scope of the present invention, the term "Adhesive or Sealant" also includes those sealants that on heating can expand and cure to a foam, in particular to a structural foam. A "Structural foam" is understood to mean a foam that is inside a hollow component and due to its strength and/or stiffness stiffens and/or reinforces the component. The adhesive or sealant according to the present invention preferably finds use as a structural adhesive or structural foam in automobile or appliance construction, particularly in the automotive construction industry.

Epoxy-based adhesives are hard and brittle in the cured state. Generally, the bonded joints obtained with them indeed exhibit a very high tensile shear strength. With chipping, impact or impact peeling stresses, especially at temperatures below 0 ⁰C and in particular below -20 ⁰C however, these flake off, such that with these types of stresses the bonded joint easily loses adherence. Accordingly, numerous proposals have been made to modify epoxy resins by flexible additives in order to significantly reduce their brittleness. A common method concerns the use of specific rubber adducts in epoxy resins, which are contained as the heterodisperse phase in the epoxy resin matrix.

US-A-5 290 857 describes an epoxy resin adhesive composition comprising an epoxy resin as well as a powdered core/shell polymer and a heat activation type hardener for the epoxy resin. The powder core/shell polymer is composed of a core comprising an acrylate polymer or a methacrylate polymer having a glass transition temperature of -30 ⁰C or lower and a shell comprising an acrylate polymer or a methacrylate polymer comprising crosslinking monomer units having a glass transition temperature of 70 ⁰C or higher, wherein the weight ratio of the core to the shell is in the range of 10: 1 to 1 : 4. It is stated that these compositions have excellent adhesive properties such as impact resistance, tensile shear strength and T-peel strength as well as a good semi-gelling property. Information concerning the properties of bonded joints with these adhesives at low temperatures was not given.

Inorganic particles can also be used to improve the impact resistance of epoxy adhesives. This is known for example from the study "Toughening mechanisms of nanoparticle-modified epoxy polymers" by B. B. Johnsen, A.J. Kinloch, R. D. Mohammed, A.C. Taylor and S. Sprenger in Polymer 48 (2007), pages 530 to 541. This article reports that inorganic particles, for example glass, silicon oxide or aluminum oxides can improve the toughness of epoxy resins. However, when relatively large particles (particle size between 4 and 100 μm) are used, they increase the viscosity of the resin, thereby deteriorating the processability. This undesirable increase in viscosity can be lessened by using inorganic nanoparticles. In the cited article the use of colloidal silicic acid coated with an organo silane was investigated as an example.

Epoxy-based adhesives or sealants are known from DE 10 2006 042 796 A1 and comprise 5 to 30 wt.% inorganic particles whose surface was coated by reaction with organic molecules. Organic molecules were selected which carry at least two terminal functional groups, wherein each functional group comprises at least one heteroatom having at least one free pair of electrons.

EP 1 715 003 A1 discloses one-component, heat curable adhesive compositions comprising a) at least one room temperature liquid epoxy resin based on diglycidyl ethers of bisphenol A, b) at least one copolymer with a glass transition temperature of less than or equal to -30 ⁰C and groups that are reactive towards epoxides, c) at least one heat activatable curing agent and/or accelerator and d) at least one silicon dioxide sol modified by organo silane. The sol is preferably modified with an epoxy-functional silane.

WO 2004/1111136 A1 discloses a nanoparticulate redispersible zinc oxide powder and a process for its manufacture, wherein the zinc oxide particles are coated with an alkylene ether carboxylic acid, whose molecules possess a carbon-carbon double bond. EP 1 469 020 A1 discloses a granulate that comprises core-shell particles, whose core consists of an inorganic material and whose shell consists of a polyacrylate, preferably polyethyl acrylate, polybutyl acrylate, polymethyl methacrylate and/or a copolymer thereof. According to this document it is important that there exists a difference between the refractive index of the core material and that of the coating material. These particles are added in particular for their optical effects, for example in moldings or films. The use in epoxy-based adhesives or sealants to improve the fracture properties is not described.

The present invention achieves the object of providing epoxy-based adhesives or sealants that exhibit better mechanical properties after curing, such as for example impact resistance, fatigue resistance and compression strength, and a low viscosity before curing, in order to be more easily processable. The present invention relates to an epoxy-based adhesive or sealant that, based on the total adhesive or sealant, comprises 0.5 to 40 wt.%, preferably 1 to 30 wt.% and particularly 2 to 15 wt.% of inorganic particles that are encased in organic polymers, wherein said organic polymers are selected from polystyrene or from homopolymers or copolymers of esters of acrylic acid and/or methacrylic acid which consist of at least 30 wt.% of polymerized esters of acrylic acid and/or methacrylic acid. In the scope of the present invention, the term "adhesive or sealant" also encompasses so-called structural foams.

Methyl and/or ethyl esters preferably illustrate the esters of acrylic acid and/or methacrylic acid, wherein particularly preferably at least a part of the esters is present as the methyl ester. Moreover, the polymers can also comprise non-esterified acrylic acid and/or methacrylic acid; this can improve the coupling of the organic polymer onto the surface of the inorganic particles. Consequently, it is particularly preferred in this case if the monomer units of non-esterified acrylic acid and/or methacrylic acid are at or near to that end of the polymer chain that is bonded to the surface of the inorganic particle.

Preferably the organic polymers consist of at least 80 wt.% of esters of acrylic acid and/or methacrylic acid. In particular, they can consist of 90 wt.%, 95 wt.% or completely of esters of acrylic acid and/or methacrylic acid. In so far as the organic polymers comprise other monomers than these esters of acrylic acid and/or methacrylic acid or non-esterified acrylic acid and/or methacrylic acid, then these are preferably selected from comonomers that possess epoxy, hydroxyl and/or carboxyl groups.

In an alternative embodiment the organic polymers consist completely of polystyrene.

The organic polymers of the casing are preferably non-crossl inked or so weakly crosslinked that not more than 5 % of monomer units of one chain are crosslinked with monomer units of another chain. It can also be advantageous that the polymers in the proximity of the surface of the inorganic particles are more strongly crosslinked than those closer to the exterior of the casing. In particular, the casing is preferably formed in such a way that at least 80 %, particularly at least 90 % and particularly preferably at least 95 % of the polymer chains are linked with one end onto the surface of the inorganic particles.

Prior to the deposition of the casing of organic polymers, the organic particles preferably exhibit an average particle size in the range 1 to 1000 nm, especially in the range 5 to 100 nm or 5 to 30 nm. The particle size can be determined by the known methods of light scattering and by electron microscopy.

The casing of organic polymers has a lower density than that of the inorganic particles. The thickness of the casing of organic polymers is such that the weight ratio of the inorganic core to the casing of organic polymers is in the range from 2: 1 to 1 : 5, particularly in the range from 3: 2 to 1 : 3. This can be controlled by the choice of reaction conditions when forming the casing of organic polymers on the inorganic particles.

In general, the inorganic particles can be selected from among metals, oxides, hydroxides, carbonates, sulfates and phosphates. Here, the oxides, hydroxides and carbonates can also be present in mixed form, for example basic carbonates or basic oxides. If the inorganic particles are metallic, then preferably iron, cobalt, nickel or alloys are considered, which consist of at least 50 wt.% of one of these metals. Oxides, hydroxides or mixed forms thereof are preferably selected from those of silicon, cerium, cobalt, chromium, nickel, zinc, titanium, iron, yttrium, zirconium and/or aluminum. Mixed forms thereof are also possible, such as for example particles of alumosilicates or of silicate glasses. Zinc oxide, aluminum oxides or hydroxides as well as SiO2 or the oxide forms of silicon known as silicic acid or as silica are particularly preferred. Moreover, the inorganic particles can consist of carbonates, such as for example calcium carbonate, or of sulfates, such as for example barium sulfate. Naturally, it is also possible for particles having differently composed inorganic cores to be present side by side.

The inorganic particles that have a casing of organic polymers can be manufactured for example by the method described in WO 2004/111136 A1 in the example for coating zinc oxide with alkylene ether carboxylic acids. According to this procedure, monomeric or prepolymeric constituents of the casing are added to a suspension of the untreated inorganic particles in a non-polar or weakly polar solvent, the solvent is removed and the polymerization is initiated, for example radically or photochemically. In addition, a process analog to that in EP 1 469 020 A1 can be used, wherein monomers or prepolymers of the filler material can be added as the organic coating components for the particles.

The mechanical properties of the cured adhesives or sealants, such as especially the break behavior, can be further improved if the adhesives or sealants possess particles or domains of rubber in addition to the previously described inorganic particles with a casing of organic polymers. Butadiene rubbers and especially acrylonitrile-butadiene rubbers for example are suitable for this.

Numerous polyepoxides, which have at least two 1 ,2-epoxy groups per molecule, are suitable epoxy resins for the adhesives or sealants according to the invention. The epoxide equivalent of these polyepoxides can vary between 150 and 4000. Fundamentally, the polyepoxides can be saturated, unsaturated, cyclic or acyclic, aliphatic, alicyclic, aromatic or heterocyclic polyepoxide compounds. Exemplary suitable polyexpoxides include the polyglycidyl ethers that are manufactured by the reaction of epichlorohydrin or epibromohydrin with a polyphenol in the presence of alkali. Exemplary suitable polyphenols are resorcinol, pyrocatechol, hydroquinone, bisphenol A (bis-(4-hydroxyphenyl)-2,2-propane), bisphenol F (bis(4-hydroxyphenyl)methane), bis(4-hydroxyphenyl)-1 ,1 -isobutane, 4,4'-dihydroxybenzophenone, bis(4- hydroxyphenyl)-1 ,1 -ethane, 1 ,5-hydroxynaphthalene.

Further polyepoxides that are in principle suitable are the polyglycidyl ethers of polyalcohols or diamines. These polyglycidyl ethers are derived from polyalcohols such as ethylene glycol, diethylene glycol, thethylene glycol, 1 ,2-propylene glycol, 1 ,4- butylene glycol, 1 ,5-pentane diol, 1 ,6-hexane diol or trimethylolpropane.

Polyglycidyl ethers of diamines can be manufactured for example by the dehydrochlorination of the reaction products of epichlorohydrin with amines that comprise at least two amino groups. Examples of amines, on which such epoxides are based, are aliphatic amines, such as hexamethylene diamine, cycloaliphatic amines, such as 1 ,4-diaminocyclohexane, bis-aminomethylene-1 ,4-cyclohexane, aromatic amines such as bis-(4-aminophenyl)-methane, bis(4-aminophenyl) ether, bis(4- aminophenyl) sulfone, 4,4'-diaminobiphenyl or 3,3'-diaminobiphenyl, or araliphatic amines, such as m-xylylene diamine. Further, poly-(N-glycidyl) compounds such as triglycidyl isocyanurate, N,N'-diglycidyl derivatives of cycloalkylene ureas, such as of ethylene urea or of 1 ,3-propylene urea, and N,N'-diglycidyl derivatives of hydantoins, such as of 5,5-dimethylhydantoin can be used.

Further suitable polyepoxides are polyglycidyl esters of polycarboxylic acids, for example reaction products of glycidol or epichlorohydrin with aliphatic or aromatic polycarboxylic acids such as oxalic acid, succinic acid, glutaric acid, terephthalic acid or dimer fatty acid. Additional epoxides are derived from the epoxidation products of olefinically unsaturated cycloaliphatic compounds or of natural oils and fats.

The epoxy resins obtained by the reaction of Bisphenol A or Bisphenol F with epichlorohydrin are quite particularly preferred. Room temperature (22 ⁰C) liquid or solid epoxy resins or mixtures of liquid and solid epoxy resins can be employed, wherein the liquid epoxy resins are preferably based on Bisphenol A and exhibit a sufficiently low molecular weight. Room temperature-liquid epoxy resins are employed for example that generally have an epoxide equivalent weight of 150 to about 220, an epoxide equivalent weight range of 182 to 192 being particularly preferred. Guanidines, substituted guanidines, substituted ureas, melamine resins, guanamine derivatives, cyclic tertiary amines, aromatic amines and/or their mixtures can be employed as the heat activatable or latent curing agents for the epoxy resin binding agent system. The curing agents may both be stoichiometrically incorporated into the curing reaction, but they may also be catalytically active. Examples of the substituted guanidines are methyl guanidine, dimethyl guanidine, trimethyl guanidine, tetramethyl guanidine, methyl isobiguanidine, dimethyl isobiguanidine, tetramethyl isobiguanidine, hexamethyl isobiguanidine, heptamethyl isobiguanidine and most particularly cyanoguanidine (dicyandiamide). Alkylated benzoguanamine resins, benzoguanamine resins or methoxymethyl ethoxymethyl benzoguanamine may be mentioned as representatives of suitable guanamine derivatives. The selection criterion for the one- component inventive heat curable hot melt adhesives is naturally the low solubility of said substances at room temperature in the resin system, with the result that solid, finely ground curing agents have preference here, in particular dicyandiamide is suitable. This ensures a good storage stability of the composition.

Catalytically active substituted ureas may be used in addition to or instead of the aforementioned curing agents. These are in particular p-chlorophenyl-N,N-dimethylurea (monuron), 3-phenyl-1 ,1 -dimethylurea (fenuron) or 3,4-dichlorophenyl-N,N-dimethylurea (diuron). In principle, catalytically active tertiary acryl or alkyl amines, such as e.g. benzyl dimethyl amine, ths(dimethylamino)phenol, piperidine or pipehdine derivatives may also be used, but in many cases these have an excessively high solubility in the adhesive system, such that a useful storage stability of the one-component system is not achieved here. In addition, various, preferably solid, imidazole derivatives may be used as the catalytically active accelerator. There may be mentioned as representatives 2-ethyl-2-methylimidazole, N-butylimidazole, benzimidazole, as well as N-Ci to C12 alkyl imidazoles or N-aryl imidazoles.

Besides the epoxy resin as the component a), the adhesive or sealant can comprise as component b) a copolymer containing groups that are reactive to epoxides or a reaction product of such a copolymer with a stoichiometric excess of epoxide compounds containing at least 2 epoxide groups per molecule. Then, copolymers with a glass transition temperature of less than or equal to -30 ⁰C are particularly preferred. Examples of the copolymers of component b) are 1 ,3-diene polymers containing carboxyl groups and additional polar ethylenically unsaturated comonomers. Butadiene, isoprene or chloroprene can be employed as the diene, butadiene being preferred. Examples of polar, ethylenically unsaturated comonomers are acrylic acid, methacrylic acid, lower alkyl esters of acrylic acid or methacrylic acid, for example their methyl or ethyl esters, amides of acrylic acid or methacrylic acid, fumaric acid, itaconic acid, maleic acid or their lower alkyl esters or half esters, or maleic anhydride or itaconic anhydride, vinyl esters such as for example vinyl acetate or in particular acrylonitrile or methacrylonithle. Quite particularly preferred copolymers b) are carboxyl terminated butadiene-acrylonithle copolymers (CTBN) that are offered in liquid form under the trade name Hycar by Noveon Inc. (earlier B. F. Goodrich). They have molecular weights between 2000 and 5000 and acrylonitrile contents between 10 % and 30 %. Examples are Hycar CTBN 1300 X 8, 1300 X 13 or 1300 X 15.

Core/shell polymers known from US-A-5 290 857 or from US-A-5 686 509 can also be employed as component b). In this case the core monomers should have a glass transition temperature of less than or equal to -30 ⁰C, these monomers can be selected from the group of the abovementioned diene monomers or suitable acrylate or methacrylate monomers; optionally the core polymer can comprise minor amounts of crosslinking monomer units. The shell is predominantly composed of copolymers that have a glass transition temperature of at least 60 ⁰C. The shell is preferably composed of styrene or lower alkyl acrylate or methacrylate monomer units (methyl or ethyl esters) as well as polar monomers such as (meth)acrylonitrile, (meth)acrylamide, styrene or radically polymerizable unsaturated carboxylic acids or carboxylic anhydrides, optionally with a minor amount of styrene.

Amino terminated polyalkylene glycols, especially difunctional or trifunctional amino terminated polypropylene glycols, polyethylene glycols or copolymers of propylene glycol and ethylene glycol are also suitable as the component b). They are also known by the name "Jeffamine" (trade name of the Huntsman company). In addition, the amino terminated polyoxytetramethylene glycols, also known as poly-THF, are particularly suitable. Moreover, amino terminated polybutadienes are suitable as building components. The molecular weights of the amino terminated polyalkylene glycols or polybutadienes are between 400 and 5000. The amino terminated polyalkylene glycols or polybutadienes can optionally be treated with a stoichiometric excess of epoxy compounds containing at least two epoxide groups per molecule, prior to their blending with the usual epoxy constituents. Optionally, the component b) can also comprise further additional flexibilizing copolymer additives, for example acrylate group- terminated urethane flexibilizers that can also be modified with epoxy resins based on Bisphenol A.

Generally, the adhesives according to the invention also comprise, in addition to the core/shell particles described above, further colorants and/or fillers known per se, such as, e.g., the various ground or precipitated chalks, carbon black, calcium magnesium carbonates, barytes and in particular silicate fillers of the aluminum-magnesium-calcium silicate type, e.g., wollastonite, chlorite.

In addition, the adhesive or sealant compositions according to the invention may comprise further conventional auxiliaries and additives such as e.g., plasticizers, reactive diluents, rheological aids, wetting agents, antioxidants, stabilizers and/or pigments; preferably the compositions are exempt from plasticizers however. Pyrogenic silicas, bentonites or fibrillated or pulped short fibers for example can be employed in the range between 0.1 and 5 % as the rheological aids.

In the context of this invention, reactive diluents are low-viscosity substances (glycidyl ethers or glycidyl esters) with an aliphatic or aromatic structure, which comprise epoxy groups. Said reactive diluents on the one hand serve to reduce the viscosity of the binder system above the softening point, on the other hand they control the pre-gelling process in injection molding. Typical examples of reactive diluents to be used according to the invention are mono-, di- or triglycidyl ethers of Ce- to Ci₄ monohydric alcohols or alkyl phenols, as well as the monoglycidyl ethers of cashew nut shell oil, diglycidyl ethers of ethylene glycol, of diethylene glycol, of triethylene glycol, of tetraethylene glycol, of propylene glycol, of dipropylene glycol, of tripropylene glycol, of tetrapropylene glycol, of 1 ,4-butylene glycol, of 1 ,5-pentane diol, of 1 ,6-hexane diol, of cyclohexanedimethanol, triglycidyl ethers of thmethylol propane, and the glycidyl esters of C₆- to C₂₄ carboxylic acids or their mixtures. If the adhesive or sealant is to be used as a structural foam then they preferably comprise blowing agents. In principle all known blowing agents are suitable as blowing agents, such as, e.g., the "chemical blowing agents", which release gases by decomposition, or "physical blowing agents", i.e. expanding hollow beads. Examples of the first-mentioned blowing agents are azobisisobutyronitrile, azodicarbonamide, di- nitrosopentamethylene tetramine, 4,4'-oxybis(benzenesulfonic acid hydrazide), diphenylsulfone-3,3'-disulfohydrazide, benzene-1 ,3-disulfohydrazide, p-toluene sulfonyl semicarbazide. The expandable plastic hollow microspheres are particularly preferably based on polyvinylidene chloride copolymers or acrylonitrile/(meth)acrylate copolymers. These are commercially available for example under the names "Dualite" or "Expancel" from Pierce & Stevens and Casco Nobel respectively.

For the purposes of weight reduction, the adhesives or sealants in addition to the abovementioned "normal" fillers, can comprise so called light fillers, selected from the group of the metal hollow spheres, such as e.g. steel hollow spheres, glass hollow spheres, fly ash (fillite), plastic hollow spheres based on phenol resins, epoxy resins or polyesters, expanded hollow micro spheres with wall materials of (meth)acrylate copolymers, polystyrene, styrene (meth)acrylate copolymers and in particular polyvinylidene chloride, as well as copolymers of vinylidene chloride with acrylonithle and/or (meth)acrylates, ceramic hollow spheres or organic lightweight materials of natural origin such as ground-up nut shells, for example the shells of cashew nuts, coconuts or peanut shells, as well as cork powder or coke dust.

The adhesives according to the invention can be formulated on the one hand as one- component adhesives, wherein these can be formulated both as high viscous warmly applied adhesives as well as thermally or radiation initiated curable adhesives or sealants. They can also be hot melt adhesives. In addition, these adhesives or sealants can be formulated as one-component pre-gellable adhesives or sealants. In this case, the compositions comprise either finely dispersed thermoplastic powder such as e.g. polymethacrylates, polyvinyl butyral or other thermoplastic (co)polymers, or the curing system is adapted such that a two-step curing takes place, wherein the gelation step causes only a partial curing of the adhesive or sealant and the final curing in automobile construction occurs e.g. in one of the paint ovens, preferably in the cathodic electrodeposition oven.

On the other hand, an adhesive or sealant according to the invention can be a two- component system, wherein one component A consists of one or more epoxides or comprises them, and a second component B consists of one or more curing agents for epoxides or comprises them. Polymers that possess groups that are reactive towards epoxides can be employed for example as the curing agent in the component B. The inorganic particles with the organic polymer casing can be present in the component A, in the component B or in both components. The inorganic particles with the organic polymer casing are preferably comprised in the component A. When formulating two- component adhesives or sealants, both of the reaction components are blended together only shortly before the application, wherein the curing then takes place at room temperature or at slightly higher temperature. Known reaction components for two- component epoxy resins can be employed for example as the second reaction component B, for example diamines or polyamines, amino terminated polyalkylene glycols (e.g. Jeffamines, amino poly-THF) or polyamino amides. Additional reactive partners can be mercapto-functional prepolymers such as e.g. the liquid Thiokol polymers. Fundamentally, the epoxy compositions can also be cured with carboxylic acid anhydrides as the second reaction component in two-component adhesive or sealant formulations.

Moreover, the present invention includes the use of an adhesive or sealant according to the present description as a structural adhesive or structural foam in automobile or appliance construction. When used as a structural adhesive or as a structural foam, the adhesive, after bonding the parts to be assembled, is thermally cured at a temperature between 100 to 150 ⁰C for a period of 30 to 120 minutes. In particular, curing can be carried out for a period of 50 to 70 minutes at a temperature in the range 110 to 130 ⁰C.

Finally, the present invention includes a subject matter that comprises components that are bonded, sealed, strengthened or reinforced with an inventive adhesive or sealant or structural foam after its curing. The components can be components made of metal, in particular metal sheets that can be shaped into hollow bodies and jointed. In particular, the subject matter can represent an automobile. The adhesives and sealants according to the invention can comprise, for example (data in wt.%):

Epoxy resin 25 - 70, preferably 30- 60,

Polymers containing groups that are reactive to epoxy groups 0 - 40, preferably 10 - 30,

Curing agent 0 - 15, preferably 1 - 10,

Accelerator 0 - 5, preferably 0.1 - 3,

Core-shell nanoparticles 0.5 to 40, preferably 1 t- 30, Thixotrope 0 - 15, preferably 1 - 10,

Colorants and/or fillers 0 - 5, preferably 0.1 - 2, Reactive diluent 0 -.30, preferably 1 - .20, wherein at least either, the polymers containing groups that are reactive to epoxy groups, or curing agents, must be present.

A structural foam according to the invention can comprise, for example (data in wt.%):

Epoxy resin 2 - 70, preferably 15 - 60,

Polymers containing groups that are reactive to epoxy groups 0 - 40, preferably 10 - 30,

Curing agent 0 - 15, preferably 1 - 10,

Accelerator 0 - 5, preferably 0.1 - 3,

Core-shell nanoparticles 0.5 - 40, preferably 1 - 30, Colorants and/or fillers (including fibres) 0 - 50, preferably 5 - 40,

Light fillers 0 - 30, preferably 1 - 20,

Reactive diluent 0 - 15, preferably 0 - 10,

Propellants 0.5 - 20, preferably 1 - 10, wherein at least either, the polymers containing groups that are reactive to epoxy groups, or curing agents, must be present.

The present invention can be realized for example in the following adhesive compositions (data in wt.%). Silica encased in methyl acrylate is added for example as the "Core-shell nanoparticles". Example 1 :

Epoxy resin (Epon^R 828) 55%

Rubber modified resin 23%

Curing agent (DICY) 6%

Accelerator (Fenuron) 0.7%

Core-shell nanoparticles 10%

Thixotrope (Cab-O-Sil^R TS720) 5%

Carbon black 0.3%

Example 2:

Epoxy resin/core-shell rubber particles (Zeon^R F351 ) 50%

Rubber modified resin 30%

Curing agent (DICY) 4%

Accelerator (Fenuron) 0.7%

Core-shell nanoparticles 10%

Thixotrope (Cab-O-Sil^R TS720) 5%

Carbon black 0.3%

Example 3:

Epoxy resin/core-shell rubber particles (Zeon^R F351 ) 50%

Epoxy resin/amino terminated polyether (US 6 015 865) 30%

Curing agent (DICY) 4%

Accelerator (Fenuron) 0.7%

Core-shell nanoparticles 10%

Thixotrope (Cab-O-Sil^R TS720) 5%

Carbon black 0.3%

Example 4:

Epoxy resin 55%

Epoxy resin/amino terminated polyether (US 6 015 865) 23% Curing agent (DICY) 6' % Accelerator (Fenuron) 0 .7% Core-shell nanoparticles 10% Thixotrope (Cab-O-Sil^R TS720) 5 % Carbon black 0 .3%

Example 5:

This example describes the materials used in the synthesis of silica nano-particles onto which are grafted or grown esters of acrylic or methacylic acid, or polystyrene, and the synthesis and performance of those nano-particles in an adhesive composition.

MATERIALS

Colloidal nanosilica dispersions were purchased under the trade name

ORGANOSILICASOL™ from Nissan Chemical America Corporation (Houston, TX).

MEK-ST and MEK-ST-L are dispersion grades of nano-silica in methyl ethyl ketone. The ST grade contains 10nm silica particles and the ST-L grade contains 50nm silica particles.

MIBK-ST is a dispersion of 10nm silica particles in methyl isobutyl ketone (MIBK). These materials were used directly for subsequent chemical reactions and processing.

IPA-ST-ZL is a dispersion of ~70nm silica particles in isopropyl alcohol. The particles in IPA-ST-ZL were removed from isopropyl alcohol (IPA) and re-dispersed into MEK, MIBK, toluene or another organic solvent appropriate for subsequent chemistry and processing using a wet solvent exchange process. The solvent exchange process is described later in this section.

Methyl ethyl ketone and hexane were obtained from Fisher Scientific. Methylsiobutylketone, hexane, heptane and octane were obtained form Sigma-Aldrich (St. Louis, MO). Toluene was obtained from VWR International LLC. All solvents used were reagent grade with the exception of toluene, which was anhydrous.

All silanes used in this work were obtained from Gelest Inc. (Morrisville, PA). Silanes used in the work reported here include; Methacryloxypropyltrimethoxysilane (Gelest Product # SIM6487-4) Mercaptopropyltrimethoxysilane (Gelest Product # SIM6476.0) Allyltrimethoxysilane (Gelest Product # SIA0540.0) Aminophenyltrimethoxysilane (Gelest Product # SIA0599.2)

Hexamethyldisilazane (CAS # 99-97-3) was obtained from Sigma-AIdrich (St. Louis, MO)

Spherical fused silica, grade SO-E2 under the trade name Admafine™ was obtained from Admatechs Company Limited (Aichi, Japan). These particles have a d50 of 0.5 micron and are not surface treated as supplied.

40000 Dalton poly(methacrylate) in toluene (50 wt%) was obtained from Sigma-AIdrich and used as the source material for the free polymer used in control samples.

Methyl acrylate monomer (CAS # 96-33-3), styrene monomer (CAS #100-42-5) and 2,2'-azobis(2-methylpropionitrile) (AIBN) (CAS # 78-67-1 ) were all obtained from Sigma- AIdrich (St. Louis, MO).

Acrylate terminated poly(methyl methacrylate) with a molecular weight of 4800 Daltons was obtained under the trade name ELVACITE 1010 from Lucite International America (Parkesburg, WV).

Acrylate terminated polystyrene (ATPS) with a molecular weight of 6300 Daltons was obtained under the product name BX-ATPS from BIMAX (Cokeysville, Maryland).

Bisphenol based epoxy resins with tradenames Epon 826 and Epon 863 were obtained from Hexion Specialty Chemicals (Columbus, OH).

Cycloaliphatic epoxy resin, 3,4-epoxycyclohexylmethyl-3,4- epoxycyclohexanecarboxylate (CAS # 2386-87-0) (CAE) was obtained from Sigma- AIdrich (St. Louis, MO).

Samples of nanosilica dispersions were obtained under the trade name Nanopox from NanoResins AG (Geesthacht, Germany).

Liquid imidazole curing agent was obtained under the trademark CUREZOL® 1 B2MZ from AirProducts (Allentown, PA) and the cationic, thermal initiator was obtained under the product name CXC-1612 from King Industries (Norwalk, CT). CHARACTERIZATION TECHNIQUES & INSTRUMENTATION

The success of silane and polymer grafting reactions was determined using a combination of size exclusion chromatography (SEC) and thermal gravimetric analysis (TGA).

Particles were separated from free species by repeated precipitation from MEK using hexane, heptane or octane. TGA was conducted after extensive washing to confirm and quantify silane on the surface. All TGA experiments were run using a TA Instruments 2950 system under high purity air to ensure full decomposition of organic species. The temperature was ramped at 5⁰C per minute from 2O⁰C to 900⁰C.

All size exclusion chromatography (SEC) measurements were made using a Shimadzu 717 GPC plus autosampler equipped with both UV-VIS and refractive index detectors. Molecular weights are reported with respect to polystyrene standards with MEK as solvent mobile phase.

Progress of the polymer grafting reactions was monitored by SEC using the conditions described above. The elution peaks of the nanoscale silica and free polymer were easily resolved. The disappearance of the free polymer peak, over the course of the reaction, by mass balance indicated the success of the grafting reaction. Precipitation techniques followed by TGA analysis were used to confirm the presence of polymer on the surface of the particles.

SOLVENT EXCHANGE PROCESS TO EXTRACT SILICA PARTICLES FROM DISPERSIONS One part by weight of an isopropanol silica dispersion was mixed with at least 1.5 parts by weight of hexane, heptane or octane to destabilize the silica dispersion. The destabilized silica dispersion was massed into sealed containers suitable for centrifuge processing. The liquids were centhfuged until the silica particles formed a compacted cake. The supernatant solvent mixture was decanted and a predetermined amount of the new solvent was placed into each container. The silica cake was not allowed to dry during this step to avoid inducing irreversible aggregation. The silica was easily re- suspended by mild agitation.

As an example of one run, 1000g of IPA-ST-ZL was combined with 150Og of hexane and centrifuged as described above to precipitate 30Og of silica. To this 70Og of methyl ethyl ketone was added to generate 100Og of nanosilica in MEK at 30 wt%.

DISPERSION, RESIN EXCHANGE PROCESS

The solvent containing the surface modified silica particles was combined directly with the liquid epoxy resin. The resin was poured into a glass kettle reactor (1.5 L to 3L) containing the silica dispersion. The kettle reactor was equipped with at four ports to enable simultaneous vacuum, air/nitrogen flow, mechanical mixing, and addition.

Pre-emptive selection of the solvents used in the grafting reaction was made to ensure compatibility of the solvent with the liquid resin. Incompatibility of the solvent-resin system will induce particle aggregation. Single solvents or mixtures of solvents were used to ensure, induce, or maintain compatibility. The solvent, resin, silica mixture was mixed under low shear until all of the resin completely dissolved. The dispersions were transparent, although some were colored depending on the silica size, silane and resin color.

The solvent was removed from the mixture by evaporation through application of vacuum (1000 to 4000 mTorr) at ambient temperature (15 to 4O⁰C) maintained by a water bath or jacket surrounding the reactor. The solvent/resin pair determined the combination of pressure, temperature and time that were needed to remove the solvent. Removal of higher boiling solvents such as MIBK was facilitated by additional air flow through the head space in the reactor. As the mixture was concentrated, low shear mechanical mixing was used to agitate the dispersion and facilitate solvent removal.

Residual solvent content and final dispersion silica composition were measured using TGA.

Depending on the concentration and the viscosity of the initial liquid resin, the dispersion was poured, or removed with silicone spatulas, from the reactor. Dispersions, depending on the particle size, silane, resin index of refraction, and loading, varied from transparent to opaque.

SAMPLE PREPARATION & CURING

Surface treated nanosilica dispersions in reactive resins were massed into polypropylene cups fitted for FLACKTEK INC SPEEDMIXER™ (Landrum, SC) dual axis centrifuge mixer, model DAC-150.

Liquid imidazole (1 B2MZ) was added to the glycidal epoxy based formulations at 2 wt% (resin basis) and the solid cationic initiator (CXC-1612) was added to the cycloaliphatic resin based formulations at 0.5 wt% (resin basis).

The formulations were then mixed using the SPEEDMIXER™ in a sequence of steps of 1000 RPM for 120 seconds and 2700 RPM for 30 seconds to incorporate the catalyst and remove bubbles.

The samples were then poured into silicone molds constructed of a RTV rubber (Dow Chemical RTV 3112) to form bars (for mechanical testing) 60mm in length, 3mm in thickness and 6mm in width. Mold release agents were not used.

Filled molds were transferred to a convection oven and the temperature was ramped from ambient to 100⁰C over the period of two hours to allow samples to level and bubble migration to occur. The oven temperature was raised to 12O⁰C for two hours, then to 15O⁰C for two hours. The cycloaliphatic epoxy and bis-F epoxy samples were treated using the same curing conditions (despite the different rates of curing and cure temperatures).

MECHANICAL TESTING

The cured sample bars were removed from the molds and sanded to remove burrs and topological imperfections. The exact sample dimensions were recorded before testing each individual sample.

Force versus displacement curves were measured using a TEXTURE ANALYZER TA-XT2i manufactured by Stable Micro Systems (Godalming, Surrey, UK) fitted with a 25kg transducer and a 3-point bending fixture of custom design. The samples were strained at a rate of 0.2 mm per second to their failure point.

Force versus displacement curves were converted to stress-strain curves using the appropriate beam moment equations [L. S. Marks, "Mechanical Engineers Handbook, 5^th Edition", McGraw-Hill, New York, 1951 pg. 425-447]. The modulus, maximum strength elongation and integral toughness were determined from the resulting stress-strain curves using standard methods. Data analysis was conducted using Microsoft Excel. STOICHIOMETRIC CALCULATIONS

The calculation of the proper amount of silane to use in grafting processes depends on the particle size and mass of the silica nano-particles on which grafting will be performed and on the silanol surface density of the silica particles on which the grafting will be performed. The silanol surface density of the silica nano-particles used to calculate stoichiometry depends on the molecular volume of the silane that is to be grafted as well as the surface density of silanol groups on the native silica particles.

An example calculation of the amount of methyl acryloxy silane needed to treat 50 grams of 50nm silica is provided below to demonstrate how such calculations were carried out.

Input Parameter Units Value particle density kg/m³ 2250 particle diameter Nm 50 surface site density SiOH groups / nm² 3.5 target coverage Ratio 1.00 silane molecular weight g/mol 248.35 silane density g/cm³ 1 reaction stoichometry SiOH groups per silane 3 mass of particles 50

Output Parameter Units Value particle radius Nm 25.0

Area per particle Nm² 7854.0 volume per particle Nm³ 65449.8 mass per particle Kg 1.47262E-19 mass per particle G 1.47262E-16 area per particle m² 7.85398E-15 specific surface area m²/g 53.3 surface sites per particle MoI 4.56399E-20 specific site density mol/g 0.000309923 specific site density micro mol/g 309.9 SILICA SURFACE TREATMENT PROCEDURES

The procedures for surface modification of nanosilica particles used in this work followed the anhydrous wet method. This enabled stoichiometric control and colloidal stability of the nanoparticles to be maintained thorough the entire process.

Surface modified nanosilica dispersions were prepared on a 50 gram scale with respect to silica.

The appropriate amount of dispersion was massed to yield 50 grams of silica. In one sample, for example, 50 grams of 10nm nanosilica were obtained from 166.7g of MEK-

ST or MIBK-ST. The selection of the dispersion solvent depended on the target reflux temperature as well as resin compatibility and particle stability before and after the grafting process. Nanosilica, 50nm, in MEK was obtained from MEK-ST-L and 50nm silica in MIBK was obtained from IPA-ST-L that has been exchanged into MIBK using the solvent exchange process described above. Dispersions prepared by the solvent exchange process are 30 wt%.

All reactions were carried out in a 3-neck round bottom flask immersed in a temperature controlled oil bath. One neck was fitted with a reflux column, one with a stopcock to regulate gas/vacuum, and the third with a glass stopper to serve as an addition port.

Upon completion of grafting reactions the contents of the reactor were transferred to polyethylene containers for storage and transport. In some cases, the contents of the reactor were transferred directly to a glass kettle reactor for the resin exchange process described above.

REACTION 1 : Amino benzyl trimethoxy silane was grafted onto the surface of 50nm nanosilica in a mixture of MEK and MIBK by adding 1.102g of the silane to 5Og of the nanosilica contained in the reaction flask and then stirring under reflux for 18 hours. After 20 minutes, 50 ml of MIBK was added to the reactor to dilute the silica particles and avoid aggregation.

REACTION 2: Allyl-thmethoxysilane was grafted to nanosilica using the following process. The reaction was conducted at a 100 gram scale of silica. Nanosilica particles with diameters of 70 and 50nm in MEK were obtained either directly from dispersions provided by Nissan Chemical or from samples prepared via the solvent exchange process described above. Silane, 8.381 g, was added to the reactor and stirred for 18 hours at 8O⁰C. The lower temperature and longer time were used because of the low boiling point of the silane.

REACTION 3, PMMA GRAFTED TO SILICA: Poly(methyl methacrylate) was grafted to the surface of nanosilica by the following procedure. Amino-surface-modified 50nm silica, 30 grams, in MEK or MIBK was combined with 1.27 grams of acrylate terminated poly(methyl methacrylate) (AT-PMMA) and reacted for 18 hours under reflux.

REACTION 4, PS GRAFTED TO SILICA: Polystyrene (PS) was grafted to the surface of nanosilica by the procedure described here: 5Og of amino-modified nanosilica (Scheme 1 , 50 nm) in MEK was introduced into the reaction vessel. To this was added 1.65g of Bimax Bx-ATPS added in one portion, and the mixture stirred for 18 hours at reflux (115°C).

REACTION 5, PS GROWN FROM SILICA: Polystyrene was grown from the surface of nanosilica particles using a free radical polymerization procedure as described here. Vinyl modified nanosilica (50 nm, 12.5g), styrene (1.00 g), MEK-ST (17.82 g), AIBN (0.102 g,), were introduced in a tricol flask. After three freeze-thaw-pump cycles, the flask was heated to 75°C in an oil bath. Polymerization proceeded in the dark under an argon atmosphere with magnetic stirring.

REACTION 6, HMDZ TREATED SILICA: The surface of nanosilica was treated by trimethylsilyl functional groups by the following procedure: 52g nanosilica (70 nm) from Nissan Chemicals dispersed in MEK were added to a reaction flask; then, 0.265g of hexamethyldisilazane (HMDZ, Aldrich) was added in one portion to the reaction mixture and stirred overnight for 18 hours at 85°C. RESULTS

The tables below summarize the composition and mechanical properties of control samples and polymer treated nano-silica samples dispersed in two model epoxy resins.

Symbols, abbreviations and notation found in the summary table have the following meanings:

(E) is Young's modulus reported in units of MPa (Mega Pascals) with a standard experimental error of 15%;

(dl_) is the elongation to break where elongation is defined as the bending deflection relative to the initial beam thickness; standard error for the elongation is 24%;

(J) is the integral toughness reported in units of MJ/m³ (mega Joules per cubic meter) with a standard error of 35%;

Filler loading and size are reported in weight percent and nanometer respectively unless otherwise indicated;

(^*) indicates the sample did not break using 3 point bend cell and is a very flexible material;

(#) indicates the dispersion was not chemically stable, instantly formed gels, cured to solids within 36 hours, with no-catalyst, and had non-uniform morphology;

The use of " ~ " in the filler loading column indicates an approximate/target composition based on masses used, not confirmed by TGA;

Q(x) indicates target coverage or grafting density of x, where x is a fraction 0 to 1 ; if not stated explicitly otherwise Q is 1 (100% target coverage).

"none" indicates untreated silica;

"unknown" indicates that the treatment is not uniquely specified by supplier;

"grow" indicates a polymer surface treatment that was grown from the surface by reaction of a monomer;

"graft" indicates a polymer chain that was grafted to the surface of the silica particles by reaction of a terminal functional group;

PTMS is phenyl thmethoxy silane treated silica;

HMDZ is hexamethyl disilazane treated silica;

DPDMS is diphenyldimethoxy silane treated silica;

PMA is poly methyl acrylate;

PMMA is polymethyl methacrylate;

PS is polystyrene. PROPERTIES OF POLYMER TREATED NANOSILICA DISPERSIONS IN BIS-F TYPE EPOXY RESIN

COMMENTS RESIN SILICA TREATME LOADIN E dl_ J

SIZE NT G

NM

CONTROL Epon 0 207 0.23 296.3

863 8 1

GRAFT Epon 50 Reaction -30 374 0.28 412.4

Q(0.2) 863 3 PMMA 9 0

GROW Epon 50 Reaction -30 294 0.23 358.7

863 5 3 0

PS

PROPERTIES OF POLYMER TREATED NANOSILICA DISPERSIONS IN CYCLOALIPHATIC EPOXY

RESIN.

COMMENTS RESIN SILICA TREATMENT LOADING E DL J

SIZE NM

CONTROL CAE 0 2606 0.085 131.8

IN HOUSE CAE 20 HMDZ 40 3808 0.058 77.4

PREPARED

NANOPOX CAE 20 unknown 40 3833 0.035 33.6

F630

GRAFT CAE 50 PS -35 3727 0.103 116.4

GROW CAE 70 PS -30 2958 0.096 83.7

GRAFT CAE 50 PMMA -30 3643 0.069 113.7

The results show that the presence of the polymer grafted silica filler improves material toughness

Claims

Claims

1 . An epoxy-based composition that can be used as an adhesive or sealant or as structural foam and that, based on the total composition, comprises 0.5 to 40 wt. % of inorganic particles that are encased in organic polymers, wherein said organic polymers are selected from polystyrene or from homopolymers or copolymers of esters of acrylic acid and/or methacrylic acid which consist of at least 30 wt.% of esters of acrylic acid and/or methacrylic acid.

2. The composition according to claim 1 , wherein the organic polymers consist of at least 80 wt.% of esters of acrylic acid and/or methacrylic acid.

3. The composition according to one or both of claims 1 and 2, wherein the organic polymers of the casing are not crosslinked or so weakly crosslinked that not more than 5 % of monomer units of a chain are crosslinked with monomer units of another chain.

4. The composition according to claim 1 , wherein the organic polymers consist of polystyrene.

5. The composition according to one or more of claims 1 to 4, wherein the inorganic particles, prior to being coated with the casing of organic polymers, have an average particle size in the range from 1 to 1000 nm, particularly in the range 5 to 30 nm or 5 to 100 nm.

6. The composition according to one or more of claims 1 to 5, wherein in the particles, the weight ratio of the inorganic core to the casing of organic polymers is in the range from 2: 1 to 1 : 5, particularly in the range from 3: 2 to 1 : 3.

7. The composition according to one or more of claims 1 to 6, wherein the inorganic particles are selected from metals, oxides, hydroxides, carbonates, sulfates and phosphates.

8. The composition according to claim 7, wherein the inorganic particles are selected from iron, cobalt, nickel or alloys that consist of at least 50 wt.% of one of these metals.

9. The composition according to claim 7, wherein the inorganic particles are selected from oxides or hydroxides of silicon, cerium, cobalt, chromium, nickel, zinc, titanium, iron, yttrium, zirconium and/or aluminum.

10. The composition according to one or more of claims 1 to 9, wherein it additionally includes particles or domains of rubber.

11 . The composition according to one or more of claims 1 to 10, wherein it exists in two components, wherein one component A consists of or comprises one or a plurality of epoxy resins, and a second component B consists of or comprises one or a plurality of curing agents for epoxy resins, and wherein the inorganic particles are present in the component A, the component B or in both components.

12. The composition according to one or more of claims 1 to 1 1 , wherein it is a one-component composition and the curing of which can be initiated by heat or by radiation.

13. A use of a composition according to one or a plurality of claims 1 to 12 as a structural adhesive or structural foam in the automobile or equipment construction industry.

14. A product comprising components that are glued, sealed, strengthened or stiffened with a cured composition according to one or more of claims 1 to 12.