EP4150023A1

EP4150023A1 - Method for structurally connecting electrically conductive plastic substrates using heat-curing adhesives, more particularly in combination with metal substrates

Info

Publication number: EP4150023A1
Application number: EP21724681.8A
Authority: EP
Inventors: Dusko PARIPOVIC; Ilona SIMON
Original assignee: Sika Technology AG
Current assignee: Sika Technology AG
Priority date: 2020-05-14
Filing date: 2021-05-10
Publication date: 2023-03-22
Also published as: CN115551963A; WO2021228785A1

Abstract

The present invention relates to a method for bonding heat-stable substrates, comprising the following steps: i) applying a heat-curing adhesive composition KL to the surface of a first substrate S1, ii) bringing the applied heat-curing adhesive composition KL into contact with the surface of a second substrate S2, wherein one or both substrates, more particularly only one substrate, is an electrically conductive plastic substrate KS; iii) heating the at least one electrically conductive plastic substrate KS by means of resistance heating. The invention provides a curing method with lower energy consumption and lower investment costs, which method more particularly permits substrates having different thermal longitudinal expansion coefficients to be structurally connected by means of heat-curing adhesive compositions and enables lower tension in the cured adhesive compositions.

Description

PROCESS FOR THE STRUCTURAL JOINING OF ELECTRICALLY CONDUCTIVE PLASTIC SUBSTRATES WITH HEAT-CURING ADHESIVES, IN PARTICULAR IN COMBINATION WITH METALLIC

SUBSTRATES

Technical area

The invention relates to the field of thermosetting adhesive compositions, especially for connecting substrates with different thermal expansion coefficients, especially in the shell of Trans port means or white goods.

State of the art

Thermosetting adhesive compositions have long been known. An important area of application of heat-curing adhesive compositions is found in vehicle construction, especially when bonding in the shell construction of means of transport or white goods. In both cases, after the application of the adhesive compositions, the bonded object is heated in an oven, as a result of which the thermosetting adhesive composition is also cured.

The heating of the bonded objects is connected with a considerable energy consumption and large investment costs for suitable shell ovens. Another problem arises in particular when two substrates with different coefficients of thermal expansion are connected to one another by structural bonding. The curing step in the oven at temperatures of 120 - 220 ° C causes the two substrates to expand to different lengths. During the subsequent cooling process, the cured adhesive composition, especially in the case of adhesive compositions based on epoxy resin, creates a high tension, which either leads to failure of the adhesive connection, deformation of the substrates or what is known as “freezing” of the tension in the adhesive connection leads. Such “freezing” causes the adhesive bond to react significantly during its service life more sensitive to static, dynamic and shock loads, which can lead to a weakening of the adhesive bond.

There is therefore a need for curing processes which manage with lower energy consumption and lower investment costs. There is also a need for methods of structurally joining substrates with different thermal coefficients of linear expansion by means of heat-curing adhesive compositions which, on the one hand, ensure sufficient mechanical properties for structural bonding and, on the other hand, lead to bonds that reduce the high stresses that occur during conventional heat-curing in ovens.

Presentation of the invention

The object of the present invention is therefore to provide a curing process with lower energy consumption and lower investment costs, which in particular allows structural bonding by means of heat-curing the adhesive compositions of substrates with different thermal coefficients of linear expansion and enables reduced stress in the cured adhesive compositions.

Surprisingly, it was possible to achieve this object by a method according to the invention in accordance with claim 1.

Further aspects of the invention are the subject of further independent claims. Particularly preferred embodiments of the invention are the subject matter of the dependent claims.

Ways of Carrying Out the Invention

The present invention relates to a method for bonding heat-stable substrates, which comprises the steps: i) applying a thermosetting adhesive composition KL to the surface of a first substrate S1, ii) contacting the applied thermosetting adhesive composition KL with the surface of a second substrate S2 - kind that the applied thermosetting adhesive composition KL is arranged between the two substrates S1 and S2, one or both substrates, in particular only one substrate, being an electrically conductive plastic substrate KS, and the thickness of the applied thermosetting adhesive composition KL after step ii) is> 0.1 mm, preferably> 0.3 mm, preferably> 0.5 mm, in particular> 1 mm; iii) heating the at least one electrically conductive plastic substrate KS by resistance heating.

In this document, the use of the term “independent of one another” in connection with substituents, radicals or groups is to be interpreted in such a way that the identically designated substituents, radicals or groups with different meanings can occur simultaneously in the same molecule.

In this document, a “toughness improver” is understood to mean an additive to an epoxy resin matrix which results in a significant increase in toughness even with small additions of> 5% by weight, in particular> 10% by weight, based on the total weight of the epoxy resin compositions acts and is therefore able to withstand higher bending, tensile, impact or shock loads before the matrix tears or breaks.

The prefix “poly” in substance names such as “polyol”, “polyisocyanate”, “polyether” or “polyamine” indicates in this document that the respective substance formally contains more than one of the functional groups per molecule that appear in its name.

In the present document, “molecular weight” means the molar mass (in grams per mole) of a molecule. “Average molecular weight” is the number-average molecular weight M _{n of} an oligomeric or polymeric mixture of molecules, which is usually determined using GPC against polystyrene as the standard.

A “primary hydroxyl group” is an OH group that is bonded to a carbon atom with two hydrogens. In the present document, the term “primary amino group” refers to an NH2 group that is bonded to an organic radical, while the term “secondary amino group” refers to an NH group attached to two organic radicals which can also be part of a ring together , is bound. Accordingly, an amine which has a primary amino group is referred to as a “primary amine”, an amine with a secondary amino group is correspondingly referred to as a “secondary amine” and one with a tertiary amino group is referred to as a “tertiary amine”.

In this document, a temperature of 23 ° C is referred to as “room temperature”.

“Heat-stable materials” are understood to mean, in particular, materials which are dimensionally stable at a curing temperature of 100-220 ° C., preferably 120-200 ° C., at least during the curing time.

If two substrates, for example metals or fiber-reinforced plastics, with different thermal coefficients of linear expansion {) are connected to one another through structural bonding, especially in the body shell, the curing step in the oven at temperatures of 120 - 220 ° C, for example when passing through a convection oven, leads to this that the two substrates expand to different lengths. During the subsequent cooling, for example when passing through cooling zones, a high level of tension arises in the cured adhesive composition, which either leads to failure of the adhesive bond, deformation of the substrates or what is known as “freezing” of the tension in the adhesive bond.

With resistance heating, heat is generated by applying a voltage to a conductive mate rial and current flowing through it and heating it up with Joule heat. The higher the specific resistance of the material used, the shorter the heating conductors that can be used. One or both substrates S1 and S2, in particular only one substrate, are an electrically conductive plastic substrate KS.

Electrically conductive fiber-reinforced plastics are particularly preferred as electrically conductive plastic substrates KS.

They are preferably conductive plastic substrates KS which, at the time of step i), have a proportion of thermosetting resins, in particular thermosetting epoxy resins, of less than 5% by weight, preferably less than 1% by weight, preferably less than 0.1% by weight .-%, in particular less than 0.01% by weight, based on the total weight of the conductive plastic substrate KS. Such plastic substrates containing resins in the uncured state are disadvantageous in that they have lower structural properties and are more difficult to handle because of their stickiness.

These electrically conductive fiber-reinforced plastics preferably consist of a flat carrier material, in particular fleeces or mats, made of fibers embedded in a plastic matrix. It is preferably an already hardened plastic matrix.

The flat carrier material made of fibers and / or the plastic matrix can be electrically conductive.

Electrically conductive flat carrier materials made of fibers are preferably metal fibers, carbon fibers and conductive textile fibers (in particular textile fibers coated with metal), in particular carbon fibers.

Electrically conductive plastic matrices, in particular thermosets or thermoplastics, in particular thermosets, preferably contain electrically conductive polymers and / or electrically conductive particles, in particular -electrically conductive particles based on metal, particularly preferably based on copper, and / or

-electrically conductive particles based on glass, plastic, ceramics, metal ceramics, alloys, minerals and rocks, which either themselves are electrically conductive or are made conductive by a suitable coating of noble metals or non-noble metals, in particular electrically conductive carbon black or graphene.

They are preferably electrically conductive fiber-reinforced plastics selected from the list consisting of glass fiber, aramid fiber, Ba salt fiber and carbon fiber reinforced plastics, carbon fiber reinforced plastics are particularly preferred.

These carbon fiber-reinforced plastics preferably consist of the electrically conductive carbon fibers and a conductive or non-conductive plastic matrix, in particular a non-conductive plastic matrix, particularly preferably an epoxy resin matrix.

The electrically conductive plastic substrate KS is preferably a material which can be heated by resistance heating at 20 ° C. by more than 30 Kelvin, in particular more than 50 Kelvin.

The electrically conductive plastic substrate KS is preferably a material with a specific electrical resistance of 1-150, 5-100, in particular 10-75 W mm ² / m. The specific electrical resistance is preferably the specific electrical resistance at 20 ° C.

The metallic substrate MS is preferably a metal selected from the list consisting of steel, in particular electrolytically galvanized, hot-dip galvanized, oiled steel, Bonazink-coated steel and subsequently phosphated steel, and aluminum, in particular aluminum.

The difference in the coefficient of thermal expansion (AO) between the two substrates S1 and S2 is preferably ^{8-30 * 10 -6} [K ^_1 ], especially especially 10-25 ^* 10 ⁶ [K ^_1 ], ^{15-25 *} 10 ^-6 [K ¹ ], particularly preferably 20-25 ^* 10 ⁶ [K ¹ ]. The previously mentioned coefficients of linear expansion (AO) are preferably coefficients of linear expansion

(Da) at 20 ° C. The coefficient of thermal expansion (ώa) is preferably determined using a dilatometer.

The thermosetting adhesive composition KL is preferably a thermosetting adhesive composition KL selected from the group consisting of acrylate adhesive compositions, polyurethane adhesive compositions and epoxy adhesive compositions, preferably polyurethane adhesive compositions and epoxy adhesive compositions, in particular epoxy adhesive compositions.

Possible heat-curing polyurethane adhesive compositions are, for example, one-component polyurethane adhesive compositions comprising surface-deactivated polyisocyanates and at least one isocyanate-reactive component, one component preferably being of a polymeric nature. A surface-inactivated polyisocyanate can be a polyisocyanate inactivated by the formation of a polyadduct with H-active compounds, by inclusion in cage components (molecular sieves) or by encapsulation.

The thermosetting adhesive composition KL is preferably a thermosetting epoxy adhesive composition, particularly preferably a one-component thermosetting epoxy resin composition comprising: a) at least one epoxy resin A with an average of more than one epoxy group per molecule; and b) at least one latent hardener for epoxy resins B.

The epoxy resin A with an average of more than one epoxy group per mole is preferably a liquid epoxy resin or a solid epoxy resin. The loading griff “solid epoxy resin” is well known to the epoxy specialist and is used in contrast to “liquid epoxy resins”. The glass transition temperature of solid resins is above room temperature, ie they can be comminuted into free-flowing powders at room temperature. Preferred epoxy resins have the formula (II)

The substituents R 'and R' stand independently of one another either for Fl or CFh.

In the case of solid epoxy resins, the index s stands for a value of> 1.5, in particular from 2 to 12. Such solid epoxy resins are commercially available, for example from Dow or Fluntsman or Flexion.

Compounds of the formula (II) with an index s from 1 to 1.5 are referred to by the person skilled in the art as semisolid epoxy resins. For the present invention, they are also considered solid resins. However, preferred solid epoxy resins are epoxy resins in the narrower sense, i.e. where the index s has a value of> 1.5.

In the case of liquid epoxy resins, the index s stands for a value of less than 1. Be preferably s stands for a value of less than 0.2.

They are therefore preferably diglycidyl ethers of bisphenol-A (DGEBA), of bisphenol-F and of bisphenol-A / F. Such liquid resins are available, for example, as Araldite® GY 250, Araldite® PY 304, Araldite® GY 282 (Fluntsman) or D.E.R. ™ 331 or D.E.R. ™ 330 (Dow) or Epikote 828 (Flexion).

So-called epoxy novolaks are also suitable as epoxy resin A. In particular, these have the following formula: or CH2, R1 =

H or methyl and z = 0 to 7.

In particular, these are phenol or cresol-epoxy novolaks (R2 = CH ₂ ). Such epoxy resins are commercially available under the trade names EPN or ECN and Tactix® from Huntsman or under the DEN ™ product series from Dow Chemical.

The epoxy resin A is preferably a liquid epoxy resin of the formula (II). In a particularly preferred embodiment, the thermosetting epoxy resin composition contains both at least one liquid epoxy resin of the formula (II) with s <1, in particular less than 0.2, and at least one Solid epoxy resin of the formula (II) with s> 1.5, in particular from 2 to 12.

The proportion of epoxy resin A is preferably 10-60% by weight, in particular 30-50% by weight, based on the total weight of the epoxy resin composition.

It is also advantageous if 60-100% by weight, in particular 60-80% by weight, of the epoxy resin A is an aforementioned liquid epoxy resin. It is also advantageous if 0-40% by weight, in particular 20-40% by weight, of the epoxy resin A is an aforementioned solid epoxy resin.

The thermosetting epoxy resin composition contains at least one latent hardener B for epoxy resins. This is activated by an elevated temperature, preferably at temperatures of 70 ° C. or more. This is preferably a hardener which is selected from the group consisting of dicyandiamide; Guanidines; Anhydrides of polybasic carboxylic acids; Dihydrazides and aminoguanidines.

The hardener B, dicyandiamide, is particularly preferred.

The amount of latent hardener B for epoxy resins is advantageously 0.1-30% by weight, in particular 0.2-10% by weight, preferably 1-10% by weight, especially preferably 5-10% by weight, based on the weight of the epoxy A.

The thermosetting epoxy resin composition preferably additionally contains at least one accelerator C for epoxy resins. Such accelerating hardeners are preferably substituted ureas, such as 3- (3-chloro-4-methylphenyl) -1, 1-dimethylurea (chlorotoluron) or phenyl-dimethylureas, especially p-chlorophenyl-N, N-dimethylurea (Monuron ), 3-phenyl-1,1-dimethylurea (fenuron) or 3,4-dichlorophenyl-N, N-dimethylurea (diuron). Furthermore, compounds of the class of imidazoles, such as 2-isopropylimidazole or 2-hydroxy-N- (2- (2- (2-hydroxyphenyl) -4,5-dihydroimidazol-1-yl) ethyl) benzamide, imidazolines and amine Complexes are used.

The accelerator C for epoxy resins is preferably selected from the list consisting of substituted ureas, imidazoles, imidazolines and amine complexes.

The accelerator C for epoxy resins is particularly preferably selected from the list consisting of substituted ureas and amine complexes, in particular when the latent hardener B is a guanidine, in particular special dicyandiamide.

The one-component heat-curing epoxy resin composition preferably contains at least one toughness improver D. The toughness improver D can be solid or liquid.

In particular, the toughness improver D is selected from the group consisting of terminally blocked polyurethane polymers D1, liquid rubbers D2 and core-shell polymers D3. The toughness ratio is preferred better D is selected from the group consisting of terminally blocked polyurethane polymers D1 and liquid rubbers D2. Particularly before given it is a terminally blocked polyurethane polymer D1. If the toughness improver D is a terminally blocked polyurethane polymer D1, it is preferably a terminally blocked polyurethane prepolymer of the formula (I).

Here, R ¹ stands for a p-valent radical of a linear or branched polyurethane prepolymer terminated with isocyanate groups after the terminal isocyanate groups have been removed, and p stands for a value of 2 to 8. Furthermore, R ² independently of one another stand for a substituent which is selected from the group consisting of

1 and

Here, R ⁵ , R ⁶ , R ⁷ and R ⁸ each independently represent an alkyl or cycloalkyl or aralkyl or arylalkyl group, or R ⁵ forms together with R ⁶ , or R ⁷ together with R ⁸ , form part of a 4- to 7-membered ring which is optionally substituted.

Furthermore, R ^{9 '} and R ¹⁰ each independently stand for an alkyl or aralkyl or arylalkyl group or for an alkyloxy or aryloxy or aralkyloxy group and R ¹¹ for an alkyl group.

R ¹² , R ¹³ and R ¹⁴ each independently represent an alkylene group having 2 to 5 carbon atoms, which optionally has double bonds or is substituted, or a phenylene group or a hydrogenated phenylene group.

R ¹⁵ , R ¹⁶ and R ¹⁷ each independently represent H or an alkyl group or an aryl group or an aralkyl group and R ¹⁸ represents an aralkyl group or a mononuclear or polynuclear substituted or unsubstituted aromatic group, which may be an aromatic hydroxyl group having pen.

Finally, R ⁴ stands for a radical of an aliphatic, cycloaliphatic, aromatic or araliphatic epoxide containing a primary or secondary hydroxyl group after the removal of the hydroxyl and epoxide groups, and m stands for a value of 1, 2 or 3.

As R ¹⁸ , on the one hand, phenols or polyphenols, in particular bisphenols, are to be considered in particular after removal of a hydroxyl group. Preferred examples of such phenols and bisphenols are in particular phenol, creole, resorcinol, pyrocatechol, cardanol (3-pentadecenylphenol (from cashew nut shell oil)), nonylphenol, phenols reacted with styrene or dicyclopentadiene, bis-phenol- A, bis-phenol-F and 2,2'-diallyl-bisphenol-A. On the other hand, hydroxybenzyl alcohol and benzyl alcohol after removal of a hydroxyl group are to be considered as R ^18.

If R ⁵ , R ⁶ , R ⁷ , R ⁸ , R ⁹ , R ^{9 '} , R ¹⁰ , R ¹¹ , R ¹⁵ , R ¹⁶ or R ^{17 is} an alkyl group, this is in particular a linear or branched Ci-C2o- Alkyl group. If R ⁵ , R ⁶ , R ⁷ , R ⁸ , R ⁹ , R ^{9 '} , R ¹⁰ , R ¹⁵ , R ¹⁶ , R ¹⁷ or R ¹⁸ stand for an aralkyl group, this grouping is in particular an aromatic group bonded via methylene, especially a benzyl group. If R ⁵ , R ⁶ , R ⁷ , R ⁸ , R ⁹ , R ^{9 '} or R ^{10 stands} for an alkylaryl group, this is in particular a C1 to C2o alkyl group bonded via phenylene, such as, for example, tolyl or xylyl.

The radicals R ² are preferably the substituents of the formulas

As a substituent of the formula e-caprolactam is preferred after removal of the NH proton.

_ v_ p ^IO

As a substituent of the formula ^ ^ monophenols or polyphenols, in particular bisphenols, are preferred after removal of a phenolic hydrogen atom. Particularly preferred examples of such radicals R ² are radicals which are selected from the group consisting of and

The radical Y here stands for a saturated, aromatic or olefinically unsaturated hydrocarbon radical with 1 to 20 carbon atoms, in particular with 1 to 15 carbon atoms. As Y are in particular allyl, methyl, nonyl, dodecyl, Phenyl, alkyl ethers, carboxylic acid esters or an unsaturated cis-alkyl radical with 1 to 3 double bonds are preferred.

Most preferably R ^{2 is} Ό ^{- R.}

The terminally blocked polyurethane prepolymer of the formula (I) is prepared from the isocyanate-terminated linear or branched polyurethane prepolymer with one or more isocyanate-reactive compounds R ² H. If several such isocyanate-reactive compounds are used, the reaction can be sequential or with a mixture of these compounds.

The reaction is preferably carried out in such a way that the one or more isocyanate-reactive compounds R ² H are used stoichiometrically or in a stoichiometric excess in order to ensure that all of the NCO groups have converted.

The polyurethane prepolymer with isocyanate end groups, on which R ¹ is based, can be prepared from at least one diisocyanate or triisocyanate and from a polymer QPM with terminal amino, thiol or hydroxyl groups and / or from an optionally substituted polyphenol Qpp. Suitable diisocyanates are aliphatic, cycloaliphatic, aromatic or araliphatic diisocyanates, in particular commercially available products such as methylene diphenyl diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), tolidine diisocyanate (TM), diisocyanate IP-diisocyanate (TODI), isophorone diisocyanate (TODI), isophorone diisocyanate (TODI), isophorone diisocyanate (TODI) ), 2,5- or 2,6-bis- (isocyanatomethyl) - bicyclo [2.2.1] heptane, 1,5-naphthalene diisocyanate (NDI), dicyclohexylmethyl diisocyanate (H12MDI), p-phenylene diisocyanate (PPDI), m- Tetramethylxylylene diisocyanate (TMXDI), etc. and their dimers. HDI, IPDI, MDI or TDI are preferred.

Suitable triisocyanates are trimers or biurets of aliphatic, cycloaliphatic, aromatic or araliphatic diisocyanates, in particular the isocyanurates and biurets described in the previous paragraph. benen diisocyanates. Suitable mixtures of di- or triisocyanates can of course also be used.

Particularly suitable polymers QPM with terminal amino, thiol or hydroxyl groups are polymers QPM with two or three terminal amino, thiol or hydroxyl groups.

The polymers QPM advantageously have an equivalent weight of 300-6000, in particular 600-4000, preferably 700-2200 g / equivalent of NCO-reactive groups.

Preferred polymers QPM are polyols with average molecular weights between 600 and 6000 Daltons selected from the group consisting of polyethylene glycols, polypropylene glycols, polyethylene glycol-polypropylene glycol block polymers, polybutylene glycols, hydroxyl-terminated polybutadienes, hydroxyl-terminated butadiene-acrylonitrile copolymers and mixtures thereof.

Particularly preferred polymers QPM are α, w-dihydroxypolyalkylene glycols with C2-C6-alkylene groups or with mixed C2-C6-alkylene groups which are terminated with amino, thiol or, preferably, hydroxyl groups. Polypropylene glycols or polybutylene glycols are particularly preferred. Also particularly preferred are hydroxyl group-terminated polyoxybutylenes.

Bis-, tris- and tetraphenols are particularly suitable as the polyphenol Qpp. This is understood to mean not only pure phenols, but also, if appropriate, substituted phenols. The type of substitution can be very diverse. In particular, this is understood to mean a substitution directly on the aromatic nucleus to which the phenolic OH group is attached. Phenols are also understood to mean not only mononuclear aromatics, but also polynuclear or condensed aromatics or heteroaromatics which have the phenolic OH group directly on the aromatic or heteroaroma.

In a preferred embodiment, the polyurethane prepolymer is produced from at least one diisocyanate or triisocyanate and from a polymer QPM with terminal amino, thiol or hydroxyl groups. The polyurethane prepolymer is produced in a manner known to the person skilled in the polyurethane, in particular by adding the diisocyanate or triisocyanate is used in a stoichiometric excess with respect to the amino, thiol or hydroxyl groups of the polymer QPM.

The polyurethane prepolymer with isocyanate end groups preferably has elastic character. It preferably shows a glass transition temperature Tg of less than 0 ° C.

The toughness improver D can be a liquid rubber D2. This can be a carboxyl or epoxy terminated polymer, for example.

In a first embodiment, this liquid rubber can be a carboxyl- or epoxy-terminated acrylonitrile / butadiene copolymer or a derivative thereof. Such liquid rubbers are commercially available, for example, under the names Hypro / Hypox® CTBN and CTBNX and ETBN from Emerald Performance Materials. As derivatives are in particular elastomer-modified prepolymers containing epoxy groups, such as those under the Struktol® product line, in particular from the Polydis®, Polycavit®, Polyvertec® product line, from the Struktol® company (Schill + Seilacher Group, Germany) or under the product line Albipox (Evonik, Germany) are commercially available, suitable.

In a second embodiment, this liquid rubber can be a polyacrylate liquid rubber which is completely miscible with liquid epoxy resins and only separates into microdroplets when the epoxy resin matrix cures. Such polyacrylate liquid rubbers are available, for example, under the designation 20208-XPA from Dow.

It is of course also possible to use mixtures of liquid rubbers, in particular mixtures of carboxyl- or epoxy-terminated acrylonitrile / butadiene copolymers or of derivatives thereof.

In a third embodiment, the toughness improver D can be a core-shell polymer D3. Core-shell polymers consist of an elastic core polymer and a rigid shell polymer. Particularly suitable core-shell polymers consist of a core (core) made of elastic acrylate or butadiene polymer, which is a rigid shell (shell) of a rigid thermoplastic see Polymers enveloped. This core-shell structure is either formed spontaneously through the segregation of a block copolymer or is specified by the polymerization process as latex or suspension polymerization with subsequent grafting. Preferred core-shell polymers are so-called MBS polymers, which are commercially available under the trade name KaneAce ™ from Kaneka, Clearstrength ™ from Arkema, Paraloid ™ from Dow or F-351 ™ from Zeon.

The proportion of toughness improver D is preferably 5-50% by weight, 10-40% by weight, particularly preferably 15-30% by weight, based on the total weight of the epoxy resin composition.

In a further preferred embodiment, the composition additionally contains at least one filler F. This is preferably mica, talc, kaolin, wollastonite, feldspar, syenite, chlorite, bentonite, montmorillonite, calcium carbonate (precipitated or ground), dolomite, quartz , Silica (pyrogenic or precipitated), cristobalite, calcium oxide, aluminum hydroxide, magnesium oxide, hollow ceramic spheres, hollow glass spheres, organic hollow spheres, glass spheres, color pigments.

The total proportion of the total filler F is advantageously 5-40% by weight, preferably 10-30% by weight, based on the total weight of the epoxy resin composition.

A particularly preferred one-component epoxy resin composition comprises:

-10-60% by weight, in particular 20-50% by weight, based on the total weight of the epoxy resin composition, epoxy resin A with an average of more than one epoxy group per molecule; 60-100% by weight, in particular 60-80% by weight, of the epoxy resin A is preferably a liquid epoxy resin and 0-40% by weight, in particular 20-40% by weight, the epoxy resin A is a solid epoxy resin ;. At least one latent hardener for epoxy resins B, preferably selected from dicyandiamide, guanidines, anhydrides of polybasic carboxylic acids, dihydrazides, and aminoguanidines, and their derivatives, dicyandiamide being preferred;

-Preferably at least one accelerator C, selected from the list consisting of substituted ureas, imidazoles, imidazolines and amine complexes, in particular selected from the list consisting of substituted ureas and amine complexes, especially preferably substituted ureas;

At least one aforementioned toughness improver D, preference being given to those which were previously described as preferred toughness improver D, preferably the proportion of toughness improver D is 20-60% by weight, 25-55% by weight, particularly preferably 30 -50% by weight, based on the total weight of the epoxy resin composition;

-preferably 5-40% by weight, preferably 10-30% by weight, based on the total weight of the epoxy resin composition, of a filler F selected, preferably from the group consisting of wollastonite, calcium carbonate, calcium oxide, colored pigments, especially carbon black, and pyrogens Silicas, in particular calcium carbonate, calcium oxide and pyrogenic silicas;

It can furthermore be advantageous if the preferred thermosetting epoxy resin composition is more than 80% by weight, preferably more than 90% by weight, in particular more than 95% by weight, particularly preferably more than 98% by weight, most preferably more than 99% by weight, based on the total weight of the epoxy resin composition, consists of the aforementioned components.

An example of a particularly preferred composition is, for example, the composition in Table 1. It is advantageous if the thermosetting epoxy resin composition has a viscosity at 25 ° C. of 100-10,000 Pa * s, in particular 500-5000 Pa * s, preferably 1000-3000 Pa * s. This is advantageous in that it ensures good applicability. The viscosity measurement is preferably carried out on a rheometer of the type MCR 101 from the manufacturer Anton Paar in an oscillatory manner using a plate-plate geometry at a temperature of 25 ° C with the following parameters: 5 Hz, 1 mm gap, plate-plate distance 25 mm, 1 % Deformation.

It is particularly preferred to use thermosetting epoxy resin compositions KL, which in the cured state:

-a tensile shear strength, especially measured according to DIN EN 1465, of more than 10 MPa, more than 15 MPa, more than 20 MPa, and / or -a tensile strength, especially measured according to DIN EN ISO 527, of more than 10 MPa, more than 15 MPa, more than 20 MPa, and / or an elongation at break, in particular measured according to DIN EN ISO 527, of more than 10%, more than 20%, more than 30%, in particular 30-200%, especially preferably 30-150%, and / or

-a modulus of elasticity, especially measured in accordance with DIN EN ISO 527, of 300-1000 MPa, in particular 500-800 MPa.

have an impact peel strength, in particular measured according to ISO 11343, of more than 30 N / mm, more than 40 N / mm, more than 60 N / mm at 23 ° C, and / or

- have an angle peel strength, in particular measured according to DIN 53281, of more than 5 N / mm, more than 8 N / mm, more than 10 N / mm.

In step i), the thermosetting adhesive composition KL is preferably applied to the surface of a first substrate S1 in the form of adhesive beads with a thickness of 5 - 50 mm, in particular 7.5 - 30 mm, preferably 10 - 20 mm and a length of 5 - 500 cm, in particular 10-200 cm, preferably 20-100 cm. The heat-curing adhesive composition KL is preferably applied in an automated process, in particular by an application robot. This is for example An advantage over a circular or square application that this leads to a reduction in the contact area between the two substrates S1 and S2 by means of the applied thermosetting adhesive composition KL. On the one hand, this reduces the area of thermal bridges due to the adhesive composition KL, which allow a heat transfer, which can lead to a greater difference in the length expansion of the two subsections S1 and S2. On the other hand, this reduces the amount of hardened adhesive composition and thus the amount of potentially "frozen" stress in the adhesive bond.

It is further preferred if the thickness of the applied thermosetting adhesive composition KL after step ii) and / or step iii) is> 0.3 mm, preferably> 0.5 mm, preferably> 1 mm, in particular> 1.5 mm. The thickness is preferably <5 mm, preferably <4 mm, preferably <3 mm, in particular <2.5 mm. The thickness is preferably determined on the basis of the cross section which runs through the bond of the two substrates with the adhesive composition. The thickness preferably corresponds to the average distance between the two substrates S1 and S2 in contact with the thermosetting adhesive composition.

In step i), the thermosetting adhesive composition KL is preferably applied to less than 30% of the total surface of a first substrate S1, in particular to less than 20%, less than 10%, less than 5%, in particular less than 3% Total surface of a first substrate S1. This is advantageous in that it leads to a reduction in the contact area between the two substrates S1 and S2 by means of the applied thermosetting adhesive composition KL. On the one hand, this reduces the area of thermal bridges due to the adhesive composition KL, which allow a heat transfer, which can lead to a greater difference in the length expansion of the two substrates S1 and S2. On the other hand, this reduces the amount of cured adhesive composition and thus the amount of potentially “frozen” stress in the adhesive bond. It can also be advantageous if in step i) the application of the heat-curing adhesive composition KL to more than 0.01% of the total surface of a first substrate S1, in particular to more than 0.1%, more than 0.5%, more than 1%, in particular more than 2% of the total surface of a first substrate S1 takes place.

Preferably, each of the two substrates S1 and S2, in particular at the point of contact with the applied heat-curing adhesive compositions, has a thickness of> 0.5 mm, preferably> 0.75 mm, in particular> 1 mm, preferably the thickness is <5 mm, preferably < 4 mm, especially <3 mm. The thickness is preferably determined on the basis of the cross section which runs through the composite of the two substrates with the adhesive composition.

The method according to the invention is preferably a method for vehicle construction and sandwich panel construction, in particular for vehicle construction, particularly preferably automobile construction, most preferably in the body shell of automobiles.

In step iii) the at least one electrically conductive plastic substrate KS is heated by resistance heating.

Preferably, in step iii) the at least one electrically conductive plastic substrate KS is heated to a temperature of 100-220 ° C, in particular 120-200 ° C, preferably between 140 and 200 ° C, particularly preferably between 150 and 190 ° C.

It is further preferred if the electrically conductive plastic substrate KS for 5 minutes to 6 hours, preferably 10 minutes to 2 hours, preferably 10 minutes to 60 minutes, preferably 10 minutes to 30 minutes, particularly preferably 10 minutes to 20 minutes aforementioned temperature is left. Surprisingly, it was found that the samples produced by means of electrical resistance heating have higher tensile shear strength values, in particular when the adhesive layer is thicker. In particular, the curing time was at the Resistance hardening takes less than half as long as flitz hardening in the oven, which is a huge time saver. This can be seen, for example, in the results of the tensile shear strength measurement in Table 2. List of reference symbols

In FIGS. 1 and 2, schematic cross-sections of the structure of the mixed composite structures made of an aluminum profile and a CFRP plate are shown, which will be mentioned in the following experimental part. They show:

1 aluminum profile

2 CFR plate

3 insulated screw

4 spacers (1 mm)

5 glue

6 fixing clamp (insulated)

7 gap

8 Electrodes A bonded article results from such a method mentioned above. Such an article is preferably a vehicle or part of a vehicle. A further aspect of the present invention therefore relates to a bonded article obtained from the aforementioned method. It goes without saying that sealing compounds can also be realized with an aforementioned composition in addition to heat-curing adhesives. Furthermore, the method according to the invention is not only suitable for automobile construction but also for other areas of application. Particularly noteworthy are related applications in the construction of means of transport such as ships, trucks, buses or rail vehicles or in the construction of consumer goods such as washing machines.

The materials bonded by means of an aforementioned composition occur at temperatures between typically 120 ° C and -40 ° C, preferably between 100 ° C and -40 ° C, in particular between 80 ° C and -40 ° C.

Examples In the following some examples are given, which further illustrate the invention, but are not intended to limit the scope of the invention in any way. Determination of the Da voltage

In order to simulate the effect of the Da tension with the highest possible Da (different thermal expansion), CFRP and aluminum substrates were glued together. A heat-curing one-component epoxy resin composition according to Table 1 was used as the adhesive.

Table 1 CFRP plate type: Sika CARBODUR S626, width 60 mm x length 600 mm

(or 800 mm), thickness 2.6 mm

-Thermal expansion coefficient: a = 0.2 * 10 ^{6 1} -Thermal conductivity of carbon fiber: 17 W / (m * K) -Specific electrical resistance of carbon fiber: 66 W * mm2 / m

Aluminum profile width 60 mm x depth 80 mm x length 600 mm. Thickness: 3mm

Thermal expansion coefficient: a = 23.8 * 10 ⁶ K ¹ thermal conductivity: 205 W / (m * K)

Specific electrical resistance: 0.027 W * mm2 / m

The following was used as the heating source:

Sika Carbo Heater 2 (CH), Sika Services Switzerland -Maximum output power: 6 kW

-Input current: The fixed maximum input current for the individual phase is: 6A, 10A, 16A.

-Programmable parameters: target temperature profile, heating time, maximum output current (10A were used).

Test methods

To visualize the Da tension, as shown in FIGS. 1 and 2, a simplified composite construction was assembled from an aforementioned aluminum profile (1) and an aforementioned CFRP plate (2) and either in an oven (FIG. 1) or cured by means of Sika Carbo Hea ter 2 (Figure 2). The length of the CFRP plate in the structure in FIG. 1 was 600 mm, in the structure in FIG. 2800 mm (additional space for attaching the electrodes).

The spacers (4) (thickness 1 mm), the screws (3) used and the fixing clamp (6) are materials that are insulated from the flow of heat and current.

The curing in the oven took place at an oven temperature of 175 ° C. for 35 minutes. Curing with the Sika Carbo Heater 2 took place with the following settings:

-Heating time 22 min (temperature curve according to Figure 3), output current 10A.

In the case of the two mixed composite constructions, after the hardening step, the bending of the CFRP plate due to the increase in the gap was compared. The hardening of the adhesive freezes the arrangement of the two substrates in the heated state, which shows in a deformation of the CFRP plate in the cooled state. The greater the deformation / increase in the gap, the higher the tension that has been frozen in / built up in the cured adhesive.

The temperature profile of the heating of the aluminum profile and the CFRP plate during curing by means of the Sika Carbo Heater 2 was recorded with temperature probes, as can be seen in FIG.

3 temperature probes were applied to each of the two substrates:

CFRP-1: On a CFRP plate, close to the adhesive CFRP-2: On a CFRP plate, close to the gap CFRP-3: On a CFRP plate, close to the screws AI-1: On an aluminum profile, close to the adhesive AI-2 : On aluminum profile, near the gap AI-3: On aluminum profile, near the screws

On the basis of the temperature measurement in FIG. 3, it was found that heat was transferred via the adhesive area to the aluminum substrate and the aluminum substrate was also heated, but only up to approx. 95 ° C.

The following calculation shows the theoretical difference in the increase in length of the aluminum profile when hardened at 175 ° C compared to 95 ° C.

The following formula can theoretically be used to calculate the difference in the coefficient of linear expansion (ÄL) at the two curing temperatures. AL = Lo * a * DT

Lo = 600 mm

AL Aiu oven = 600 mm * 23.8 * IO ^ K ¹ * 150K = 2.14 mm AL Aiu Carbo Heater = 600 mm * 23.8 * 10 ⁶ K ^_1 * 70K = 1.0 mm

Surprisingly, it was found that, due to the lower heating of the aluminum, the resulting deformation (increase in gap) after curing and cooling when using electricity-induced heat to cure the adhesive is reduced from 5.5 mm (oven-cured) to only 1.5 mm, which corresponds to an improvement of approx. 72%. The gap width before curing was 2.5 mm, due to the fixation of the substrates with screws (3), despite the use of spacers (4) with a thickness of 1.0 mm.

Drinking resistance measurement

Then tensile shear strength samples were produced using steel (DC04) and CFRP (Carbodur).

Zuoscherfestiakeit (ZSF1 (DIN EN 14651

A test sheet made of steel (DC04) (50 mm x 10 mm x 3 mm) was placed on an adhesive surface of 25 x 10 mm (with glass spheres as spacers) with a layer thickness of 0.3 mm or 3.0 mm, using the adhesive composition according to Table 1 glued to a CFRP plate (CARBODUR S626) (50 mm x 10 mm x 3.2 mm) and cured under the specified curing conditions.

Curing conditions:

-35 min at 175 ° C oven temperature «Heat curing in the oven (35min / 175 °)" -Electric hardening using Carbo Heater 2 with the following settings: heating time 15 min, output current 10A "Electrical curing (15min / 10A))" The tensile shear strength was determined in a triple determination in accordance with DIN EN 1465 on a tractor at a tensile speed of 10 mm / min. The measured values are shown in Table 2. Table 2

Surprisingly, it was found that the samples produced by means of electrical resistance heating have higher tensile shear strength values, in particular when the adhesive layer is thicker. In particular, the hardening time for resistance hardening was less than half as long as for heat hardening in the oven, which represents a major time saver.

Claims

1. A method for bonding heat-stable substrates, which comprises the steps: i) applying a thermosetting adhesive composition KL to the surface of a first substrate S1, ii) contacting the applied thermosetting adhesive composition KL with the surface of a second substrate S2 such that the applied thermosetting adhesive composition KL is arranged between the two substrates S1 and S2, one or both substrates, in particular only one substrate, being an electrically conductive plastic substrate KS, and the thickness of the applied thermosetting adhesive composition KL after step ii)> 0.1 mm, preferably> 0.3 mm, preferably> 0.5 mm, in particular> 1 mm; iii) heating the at least one electrically conductive plastic substrate KS by resistance heating.

2. The method according to claim 1, wherein the two substrates S1 and S2 are an electrically conductive plastic substrate KS.

3. The method according to claim 1, wherein only one of the two sub strate S1 and S2 is an electrically conductive plastic substrate KS han delt and the other substrate is a metallic substrate MS, in particular a substrate selected from the list consisting of steel or aluminum, especially aluminum.

4. The method according to any one of the preceding claims, wherein the electrically conductive plastic substrate KS is electrically conductive fiber-reinforced plastics, in particular selected from the list consisting of glass fiber, aramid fiber, basalt fiber and carbon Plastic fiber reinforced plastics, carbon fiber reinforced plastics are particularly preferred.

Method according to one of the preceding claims, wherein the difference in the coefficient of thermal expansion {) between the two substrates S1 and S2 8 - 30 * IO ⁶ [K ¹ ], in particular 10 - 25 * 10- ⁶ [K- ¹ ], 15 - 25 * 10- ⁶ ^[K-1], preferably 20-25 * 10 ⁶ [K ^1].

Method according to one of the preceding claims, wherein the electrically conductive plastic substrate KS is a material with a specific electrical resistance of 1-150, 5-100, in particular 10-75 W mm ² / m.

The method according to any one of the preceding claims, wherein the thermosetting adhesive composition KL is a thermosetting epoxy adhesive composition, particularly preferably a one-component thermosetting epoxy resin composition, comprising: a) at least one epoxy resin A with an average of more than one epoxy group per Molecule; and b) at least one latent hardener for epoxy resins B.

The method according to claim 7, wherein the one-component, thermosetting epoxy resin composition has at least one toughness improver D selected from the group consisting of terminally blocked polyurethane polymers D1, liquid rubbers D2 and core-shell polymers D3, the toughness improver D is preferably selected from the group consisting of terminally blocked polyurethane polymers D1 and liquid rubbers D2, particularly before given it is a terminally blocked polyurethane polymer D1.

9. The method according to any one of the preceding claims, wherein the heat-curing adhesive composition KL in the cured state:

a tensile shear strength, in particular measured according to DIN EN 1465, particularly preferably as described in the example part, of more than 10 MPa, more than 15 MPa, more than 20 MPa, and / or a tensile strength, in particular measured according to DIN EN ISO 527, of more than 10 MPa, more than 15 MPa, more than 20 MPa, and / or

have an elongation at break, in particular measured according to DIN EN ISO 527, of more than 10%, more than 20%, more than 30%, in particular 30-200%, particularly preferably 30-150%, and / or an E- Module, especially measured according to DIN EN ISO 527, of 300-1000 MPa, in particular 500-800 MPa.

-An angle peel strength, especially measured according to DIN 53281, of more than 5 N / mm, more than 8 N / mm, more than 10 N / mm, aufwei sen.

10. The method according to any one of the preceding claims, wherein in step i) the application of the heat-curing adhesive composition KL to the surface of a first substrate S1 in the form of adhesive beads with a thickness of 5-50 mm, in particular 7.5-30 mm, preferably 10-20 mm and a length of 5-500 cm, in particular 10-200 cm, preferably 20-100 cm.

11. The method according to any one of the preceding claims, wherein the thickness of the applied heat-curing adhesive composition KL after step ii) and / or step iii) is> 0.3 mm, preferably> 0.5 mm, preferably> 1 mm, preferably> 1.5 mm, preferably be the thickness <5 mm, preferably <4 mm, preferably <3 mm, in particular <2.5 mm.

12. The method according to any one of the preceding claims, wherein in step i) the application of the thermosetting adhesive composition KL to less than 30% of the total surface of a first substrate S1, in particular to less than 20%, less than 10%, less than 5%, in particular less than 3% of the total surface of a first substrate S1 takes place.

13. The method according to any one of the preceding claims, wherein each of the substrates S1 and S2, in particular at the point of contact with the applied thermosetting adhesive compositions, has a thickness of> 0.5 mm, preferably> 0.75 mm, preferably> 1 mm preferably the thickness is <5 mm, preferably <4 mm, in particular re <3 mm.

14. The method according to any one of the preceding claims, wherein in step iii) the at least one electrically conductive plastic substrate KS to ei ne temperature of 100-220 ° C, in particular 120-200 ° C, preferably given between 140 and 200 ° C especially is preferably heated between 150 and 190 ° C, preferably the electrically conductive plastic substrate KS for 5 min -6 h, preferably 10 min-2 h, preferably 10 min-60 min, preferably 10 min-30 min, particularly preferably 10 min - 20 min, leave at the aforementioned temperature.

15. The method according to any one of the preceding claims, which is a method for vehicle construction and sandwich panel construction, in particular special for vehicle construction, particularly preferably automobile construction.