Two-component polyurethane structural adhesive with improved properties

Abstract

1) A PU2K structural adhesive composition characterized by: the -NCO component and the hardener component each comprise 0.1% to 40% (by weight) of a thixotropic composition (A) comprising a bis-urea obtained by the reaction of a primary aliphatic amine with a diisocyanate, suspended in a continuous phase consisting of a plasticizer selected in particular from alkyl phthalates and pentaerythritol tetravalerate; and At least one of the -NCO component and the hardener component comprises 5% to 40% (by weight) alumina. 2) Application as a structural adhesive in the fields of construction, transport manufacturing, preferably the automotive, railway and aerospace industries, and shipbuilding.

Description

Technical Field

[0001] The subject of the present invention is a two-component polyurethane structural adhesive composition (PU2K) that exhibits improved properties regarding sagging and heat dissipation. The present invention also relates to the use of the curable composition.

Background Art

[0002] Structural adhesives are well known for the manufacture of assemblies by adhesive bonding of the most diverse substrates (for example, metal substrates), which can withstand stresses comparable to those of assemblies obtained by mechanical means, such as screwing or welding. The adhesive seal that joins two substrates in such an assembly enables it to withstand very high mechanical tensile stresses, for example above 7 MPa, preferably above 20 MPa.

[0003] Such mechanical performance qualities of the adhesive seal can be obtained with two-component polyurethane structural adhesive compositions.

[0004] The latter compositions are provided in the form of the following two compositions (or components): - On the one hand, it contains a chemical entity having isocyanate - NCO end groups (known as the -NCO component), and - On the other hand, it contains a chemical entity having groups that react with the NCO groups, for example a chemical entity having hydroxyl or amino end groups (known as the hardener component).

[0005] These two components are often packaged separately in two compartments of a dual cartridge for their use. Therefore, dispensing of the adhesive composition is carried out by extruding the two components, for example using a dual cartridge gun, and obtaining a homogeneous mixture of them by, for example, attaching a static mixer to the dual cartridge. The reaction between the -NCO reactive group and, for example, the -OH group (known as a crosslinking reaction) resulting from the mixing of the two components has the effect of forming a solid three-dimensional polymer network, which imparts the desired mechanical properties to the adhesive seal formed between the assembled substrates.

[0006] Among the practical properties required for two-component polyurethane structural adhesive compositions, there are some that are actually very important regarding their anti-sagging behavior.

[0007] This is because the adhesive, which is directly produced from a mixture of the -NCO component and the curing agent component, is deposited (by an operator or by an automated device) onto a first clearly defined surface of a first substrate in the form of beads, which may range in diameter up to 2 cm. This surface, thus treated with the adhesive, then comes into contact with a second clearly defined surface of a second substrate after a certain period of time, which may vary depending on the adhesive's release time.

[0008] However, it is possible that, even though the crosslinking of the adhesive is not yet complete, the first surface on which the adhesive beads are initially deposited, or both substrates immediately after they come into contact, may be in a non-horizontal position, particularly a vertical position. This has the effect of exposing the still-uncrosslinked adhesive beads to gravity, and as a result, to the risk of deformation, creep, or even sagging (also known as "slump") under the action of stress resulting from the force.

[0009] Such changes in the shape of the beads are referred to in the remainder of this specification by the general term "slack." Consequently, there may be variations in the thickness of the adhesive during crosslinking between the two substrates, and therefore, in the final assembly obtained after complete crosslinking, there may be non-uniformity, particularly dimensional non-uniformity, in the adhesive seal that firmly bonds the two substrates.

[0010] This non-uniformity in adhesive seals is particularly likely to affect the mechanical properties of adhesive seals that must withstand the very high mechanical stresses expected of structural adhesives.

[0011] Therefore, under its usage conditions, it is particularly desirable to limit, and even eliminate, the sagging of the two-component polyurethane structural adhesive composition.

[0012] Bostik's application FR 3063915 describes a sagging inhibitor comprising diurea in the form of a suspension of solid diurea particles obtained by the reaction of aromatic diisocyanates with aliphatic amines in a specific plasticizer as a continuous phase. This patent application also describes a one-component mastic adhesive composition based on a polyurethane prepolymer having -NCO-terminated groups, comprising 5% to 25% (by weight) of the aforementioned agent. However, the tensile strength properties of the adhesive seal obtained by crosslinking the composition with moisture in the atmosphere are not suitable for resistance to stresses that may be applied to structural adhesives, such as mechanical tensile stresses exceeding 7 MPa. Furthermore, the crosslinking rate of one-component polyurethane adhesives is generally much slower than that of PU2K.

[0013] Bostik's FR 3079840 describes a specific two-component polyurethane structural adhesive composition in which the -NCO component has a weight content of 0.1% or less of diisocyanate monomers that are potentially hazardous to user handling and health. The -NCO component and the curing agent component of this composition each contain a rheological agent consisting of a micronized amide wax.

[0014] However, it remains highly desirable to provide other two-component polyurethane structural adhesive compositions that exhibit other improved properties with respect to crosslinked adhesive seals, which are actually important, while enabling the limitation or even elimination of sagging during use.

[0015] Therefore, PU2K type structural adhesives are increasingly being used in the transportation sector, for example, to assemble battery components for electric and hybrid vehicles, or to assemble metal components near heat engines. Consequently, with regard to batteries where recharging involves a rise in temperature, it is important to limit as much as possible such rise, which may degrade certain electronic circuits or shorten the battery life. To do this, any improvement in heat dissipation of the battery components, particularly the heat dissipation of the adhesive seals used to assemble the components, is important.

[0016] As a result, there is a need to improve the heat dissipation of the adhesive seals included in the related assemblies.

[0017] Therefore, the object of the present invention is to provide a two-component polyurethane structural adhesive composition that can solve the following two problems: -Improvement of heat dissipation of adhesive seals obtained by the reaction of the curing agent component and the -NCO component, and - Resistance to sagging during application to the surface of the substrate being assembled.

[0018] Another object of the present invention is to provide a two-component polyurethane structural adhesive composition that can form an adhesive seal exhibiting a tensile breaking stress of more than 10 MPa, preferably more than 20 MPa, after a crosslinking reaction between the two components.

[0019] Another object of the present invention is to provide a two-component polyurethane structural adhesive composition that exhibits rheological behavior suitable for adhesive extrusion by coating equipment such as dual-cartridge guns and static mixers.

[0020] Here, it has been found that these objects can be achieved in whole or in part by the two-component polyurethane structural adhesive composition described below.

Mode for Carrying Out the Invention

[0021] Therefore, the subject matter of the present invention is firstly a two-component polyurethane structural adhesive composition (PU2K) consisting of an -NCO component and a curing agent component, wherein the -NCO component and the curing agent component each contain 0.1% to 40% (by weight) of a thixotropic composition (A) based on the total weight of the corresponding component, and the thixotropic composition (A) is based on its total weight, - 1% to 40% (by weight) of bisurea (a) obtained by the reaction of a primary aliphatic amine (a1) and a diisocyanate (a2) having a molar mass of less than 500 g / mol, - the following: - alkyl phthalate, - pentaerythritol tetravalerate, - an ester of an alkyl sulfonic acid and phenol, - diisononyl 1,2-cyclohexanedicarboxylate, - 3,3’-[methylenebis(oxymethylene)]bis[heptane], and - dioctyl carbonate and 60% to 99% (by weight) of a plasticizer (b) selected from, where the thixotropic composition (A) is provided in the form of a suspension (or dispersion) of solid particles of bisurea (a) in a continuous phase consisting of the plasticizer (b), and at least one of the -NCO component and the curing agent component contains 5% to 40% (by weight) of alumina (B) based on the total weight of the component, characterized in that it is a two-component polyurethane structural adhesive composition (PU2K).

[0022] Tests carried out by the applicant's company have shown that by incorporating the thixotropic composition (A) into each of the -NCO and hardener components, in combination with the presence of alumina (B), it is possible to limit, and in fact even eliminate, the undesirable effect of sagging of the PU2K structural adhesive composition during the preparation of assemblies of substrates at least one of which is in a non-horizontal position, particularly a vertical position. Such an effect is further obtained while not reducing the tack of the adhesive seal and its ability to withstand very high levels of stress expected in the structural adhesive, and while providing an increase in thermal conductivity (or electrical conductivity) in response to improved heat dissipation.

[0023] Such PU2K structural adhesives also retain the ability to be extruded using a standard gun suitable for a dual cartridge equipped with a static mixer (in which they are packaged), and are thus, in fact, overall very advantageous products in all industrial fields such as the transportation field where there is a need to improve the heat dissipation of adhesive seals for assemblies of metal parts intended for the manufacture of batteries designed for electric or hybrid vehicles.

[0024] -NCO component: The -NCO component contains one or more chemical entities having isocyanate end groups.

[0025] According to one embodiment, the -NCO component may be aliphatic (linear, branched or cyclic) or aromatic and may include a (one or more) polyisocyanate which may be substituted.

[0026] Preferably, the polyisocyanate contained in the -NCO component is selected from diisocyanates, triisocyanates and mixtures thereof.

[0027] According to one preferred embodiment, the diisocyanate is isophorone diisocyanate (IPDI), pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), heptane diisocyanate, octanedi diisocyanate, nonane diisocyanate, decanedi diisocyanate, undecane diisocyanate, dodecane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate) (4,4'-HMDI), norbornane diisocyanate, norbornene diisocyanate, cyclohex Xan-1,4-diisocyanate (CHDI), methylcyclohexane diisocyanate, ethylcyclohexane diisocyanate, propylcyclohexane diisocyanate, methyldiethylcyclohexane diisocyanate, cyclohexane dimethyl diisocyanate, 1,5-diisocyanato-2-methylpentane (MPDI), 1,6-diisocyanato-2,4,4-trimethylhexane, 1,6-diisocyanato-2,2,4-trimethylhexane (TMDI), 4-(isocyanatomethyl)octane-1,8- Diisocyanates (TIN), 2,5-bis(isocyanatomethyl)bicyclo[2.2.1]heptane (2,5-NBDI), 2,6-bis(isocyanatomethyl)bicyclo[2.2.1]heptane (2,6-NBDI), 1,3-bis(isocyanatomethyl)cyclohexane (1,3-H6-XDI), 1,4-bis(isocyanatomethyl)cyclohexane (1,4-H6-XDI), xylylene diisocyanate (XDI) (especially m-xylylene diisocyanate (m-XDI)), toluene diisocyanate (especially toluene En-2,4-diisocyanate (2,4-TDI) and / or toluene-2,6-diisocyanate (2,6-TDI)), diphenylmethane diisocyanate (especially diphenylmethane-4,4'-diisocyanate (4,4'-MDI) and / or diphenylmethane-2,4'-diisocyanate (2,4'-MDI)), tetramethylxylylene diisocyanate (TMXDI) (especially tetramethyl-metaxylylene diisocyanate), for example, HDI or PDI allophanates having the following formulas (Y1) and (Y2): TIFF0007885221000001.tif91170[In the formula, -i is an integer in the range of 1 to 2. -j is an integer in the range of 0 to 9, preferably 2 to 5. -R represents a saturated or unsaturated, cyclic or acyclic and linear or branched hydrocarbon chain containing 1 to 20 carbon atoms, preferably 1 to 12 carbon atoms, more preferably 6 to 14 carbon atoms. -R 3 [This represents a straight-chain or branched-chain divalent alkylene group having 2 to 4 carbon atoms, preferably a divalent propylene group.] Selected from the group consisting of and mixtures thereof.

[0028] MDI may be in the form of isomers or mixtures of isomers such as 4,4'-MDI and / or 2,4'-MDI.

[0029] TDI may be in the form of isomers or mixtures of isomers such as 2,4'-TDI and / or 2,6'-TDI.

[0030] Diisocyanates that can be used are widely available on the market. Examples include Scuranate® TX, sold by Vencorex, which corresponds to 2,4-TDI with a purity of approximately 95%; Scuranate® T100, sold by Vencorex, which corresponds to 2,4-TDI with a purity of over 99% (by weight); Desmodur® I, sold by Covestro, which corresponds to IPDI; or Isonate® M125, sold by Dow, which corresponds to MDI containing at least 97% 4,4'-MDI.

[0031] According to another embodiment, the triisocyanate contained in the -NCO component can be selected from diisocyanate isocyanurate, diisocyanate and triol adducts, and biuret.

[0032] In particular, isocyanurates can be used in the form of a technical mixture of (poly)isocyanurates having a purity of 70% (by weight) or more of the isocyanurate.

[0033] The diisocyanate isocyanurates that can be used in accordance with the present invention can correspond to the following general formula (W). TIFF0007885221000002.tif48170[where, R 2 This represents a linear or branched, cyclic, aliphatic, arylaliphatic, or aromatic alkylene group containing 4 to 9 carbon atoms. However, the NCO group is not covalently bonded to a carbon atom that forms part of an aromatic hydrocarbon ring, such as a phenyl group.

[0034] Examples of diisocyanate isocyanurates that can be used in accordance with the present invention include the following: -Hexamethylene diisocyanate (HDI) isocyanurate: TIFF0007885221000003.tif39170 - Isophorone diisocyanate (IPDI) isocyanurate: TIFF0007885221000004.tif61170 - Pentamethylene diisocyanate (PDI) isocyanurate: TIFF0007885221000005.tif43170 - Metaxylylene diisocyanate (m-XDI) isocyanurate: TIFF0007885221000006.tif42170 - Hydrogenated form of m-XDI isocyanurate: TIFF0007885221000007.tif38170

[0035] Diisocyanate isocyanurates are also commercially available. For example, HDI isocyanurates are sold by Bayer under the names Desmodur® N3300, N3600 and N3790BA, or by Vencorex under the names Tolonate® HDT, HDT-LV and HDT-LV2.

[0036] Diisocyanate and triol adducts can preferably be prepared from aromatic or aliphatic diisocyanate monomers and mixtures thereof, more preferably from diisocyanates selected from aliphatic diisocyanate monomers. The diisocyanate monomers may be in the form of pure isomers or mixtures of isomers.

[0037] Examples of triols that can be used to prepare adducts between diisocyanates and triols include glycerol, trimethylolmethane (TMM), trimethylolethane (TME), and trimethylolpropane (TMP). Preferably, TMP is used.

[0038] As shown below, examples of diisocyanate and triol adducts that can be used in accordance with the present invention include adducts of metaxylylene diisocyanate and trimethylolpropane. This adduct is sold, for example, by Mitsui Chemicals under the name Takenate® D-110N. TIFF0007885221000008.tif18170

[0039] The biuret that can be used in accordance with the present invention is a monomer, oligomer, or polymer biuret of hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), pentamethylene diisocyanate (PDI), metaxylylene diisocyanate (m-XDI), or hydrogenated metaxylylene diisocyanate (m-HXDI).

[0040] Examples of HDI biuret products include the following formula: TIFF0007885221000009.tif42170

[0041] HDI biuret is marketed, for example, by Bayer under the names Desmodur® N100 and N3200, or by Vencorex under the names Tolonate® HDB and HDB-LV.

[0042] According to a very particularly preferred alternative embodiment of the present invention, the triisocyanate contained in the -NCO component of the PU2K structural adhesive composition is hexamethylene diisocyanate (HDI) biuret.

[0043] Hardening agent components: The curing agent component comprises at least one chemical entity having a group that reacts with the isocyanate-NCO group, for example, a hydroxyl or amino-terminated group, or a mixture of such entities.

[0044] According to the first preferred embodiment, the curing agent component comprises a polyol or a mixture of polyols.

[0045] The polyols that can be used can be selected from those having a number-average molar mass or molecular weight (Mn) in the range of 60 g / mol to 22,000 g / mol, preferably 600 g / mol to 18,000 g / mol, preferably 1,000 g / mol to 12,000 g / mol, preferably 1,000 to 8,000 g / mol, and more preferably even more preferably in the range of 1,000 g / mol to 4,000 g / mol.

[0046] The number-average molecular weight of a polyol can be calculated from its hydroxyl value (OHN) expressed in mg KOH / g and from the functionality of the polyol, or it can be determined by methods well known to those skilled in the art, such as size exclusion chromatography (or SEC) using a PEG (polyethylene glycol) standard.

[0047] Polyols can have hydroxyl functionality in the range of 2 to 6, preferably 2 to 4, and more preferably 2 to 3. In the context of the present invention, unless otherwise specified, the hydroxyl functionality of a polyol is the average number of hydroxyl functions per mole of polyol.

[0048] The polyols that can be used can be selected from polyester polyols, polyether polyols, polydiene polyols, polycarbonate polyols, poly(ether-carbonate) polyols, prepolymers having -OH terminal groups, and mixtures thereof.

[0049] The polyols that can be used can also be selected from aliphatic polyols, aryl aliphatic polyols, aromatic polyols, carbonate polyols, and mixtures of these compounds.

[0050] According to the present invention, the polyester polyol can have a number-average molecular weight in the range of 500 g / mol to 22000 g / mol, preferably 700 g / mol to 10000 g / mol, and more preferably 900 to 6000 g / mol.

[0051] Among polyester polyols, the following are examples: - Naturally derived polyester polyols, such as castor oil; -Polyester polyols produced from condensation: -One or more aliphatic (linear, branched, or cyclic) or aromatic polyols, such as ethanediol, 1,2-propanediol, 1,3-propanediol, glycerol, trimethylolpropane, 1,6-hexanediol, 1,2,6-hexanetriol, butenediol, cyclohexanedimethanol, sucrose, glucose, sorbitol, glycerol, trimethylolpropane, pentaerythritol, mannitol, triethanolamine, N-methyldiethanolamine, and mixtures thereof, -One or more polycarboxylic acids or their esters or anhydride derivatives, e.g., 1,6-hexanedioic acid, dodecanedioic acid, azelaic acid, sebacic acid, adipic acid, 1,18-octadecanedioic acid, phthalic acid, succinic acid and mixtures thereof, unsaturated anhydrides, e.g., maleic acid or phthalic anhydride, or lactones, e.g., caprolactone.

[0052] The polyester polyols mentioned above can be prepared by conventional methods, and most are commercially available.

[0053] Among polyester polyols, for example, the following products with a hydroxyl function equal to 2 can be cited. - A polycaprolactone with a number-average molecular weight of approximately 2000 g / mol and a melting point of approximately 50°C, Tone® 0240 (sold by Union Carbide). - Dynacoll® 7381 (sold by Evonik) has a number-average molecular weight of approximately 3500 g / mol and a melting point of approximately 65°C. - Dynacoll® 7360 (sold by Evonik), derived from the condensation of adipic acid and hexanediol, has a number-average molecular weight of approximately 3500 g / mol and a melting point of approximately 55°C. - Dynacoll® 7330 (sold by Evonik) has a number-average molecular weight of approximately 3500 g / mol and a melting point of approximately 85°C. -Dynacoll® 7363 (sold by Evonik), also derived from the condensation of adipic acid and hexanediol, has a number-average molecular weight of approximately 5500 g / mol and a melting point of approximately 57°C. -Dynacoll(registered trademark) 7250 (sold by Evonik): A polyester polyol having a viscosity of 180 Pa.s at 23°C, a number-average molecular weight Mn equal to 5500 g / mol, and a Tg equal to -50°C. -Kuraray(registered trademark) P-6010 (sold by Kuraray): A polyester polyol having a viscosity of 68 Pa.s at 23°C, a number-average molecular weight equal to 6000 g / mol, and a Tg equal to -64°C. -Kuraray® P-10010 (sold by Kuraray): A polyester polyol having a viscosity of 687 Pa.s at 23°C and a number-average molecular weight equal to 10,000 g / mol.

[0054] According to a preferred embodiment, the polyester polyol is selected from polycaprolactone; castor oil; polyester polyols obtained from the condensation of ethylene glycol, propylene glycol, 1,3-propanediol and / or 1,6-hexanediol with various isomers of adipic acid and / or phthalic acid; and mixtures thereof.

[0055] According to a preferred embodiment, the polyol (or mixture of polyols) contained in the curing agent component of the PU2K structural adhesive composition according to the present invention is a polyether polyol (or mixture of polyether polyols). According to the present invention, the polyether polyol may have a number average molecular weight in the range of 200 g / mol to 22000 g / mol, preferably 600 g / mol to 18000 g / mol, preferably 1000 g / mol to 12000 g / mol, and more preferably even more preferably 1000 to 4000 g / mol.

[0056] Preferably, the polyether polyol has hydroxyl functionality in the range of 2 to 4, more preferably 2 to 3.

[0057] The polyether polyols that can be used according to the present invention are preferably selected from polyoxyalkylene polyols, and the linear or branched alkylene portion thereof contains 1 to 4 carbon atoms, preferably 2 to 3 carbon atoms.

[0058] More preferably, the polyether polyols that can be used according to the present invention are selected from polyoxyalkylenediols or polyoxyalkylentriols, more preferably polyoxyalkylenediols, wherein the linear or branched alkylene portion comprises 1 to 4 carbon atoms, preferably 2 to 3 carbon atoms.

[0059] Examples of polyoxyalkylenediols or triols that can be used in accordance with the present invention include, for example, the following: - A polyoxypropylene diol or triol (also called polypropylene glycol (PPG) diol or triol) having a number average molecular weight in the range of -400 g / mol to 22000 g / mol, preferably in the range of 400 g / mol to 12000 g / mol, -Polyoxyethylene diols or triols (also called polyethylene glycol (PEG) diols or triols) having a number average molecular weight in the range of -400 g / mol to 22000 g / mol, preferably in the range of 400 g / mol to 12000 g / mol, Polyoxybutylene glycol (also called polybutylene glycol (PBG) diol or triol) having a number-average molecular weight in the range of -200 g / mol to 12000 g / mol, - A PPG / PEG / PBG copolymer or terpolymer diol or triol having a number average molecular weight in the range of -400 g / mol to 22000 g / mol, preferably in the range of 400 g / mol to 12000 g / mol, -Polytetrahydrofuran (polyTHF) diols or triols having a number-average molecular weight in the range of -250 g / mol to 12000 g / mol, Polytetramethylene glycol (PTMG) having a number-average molecular weight in the range of -200 g / mol to 12000 g / mol, -and mixtures thereof.

[0060] Preferably, the polyether polyols that can be used are selected from polyoxypropylene diols or triols. The above polyether polyols can be prepared by conventional methods and are widely available commercially. They can be obtained, for example, by polymerization of the corresponding alkylene oxide in the presence of a catalyst based on a complex metal / cyanide complex.

[0061] Examples of polyetherdiols include polyoxypropylene diols sold by Covestro under the name Acclaim®, such as Acclaim® 18200 with a number average molecular weight of around 18,700 g / mol, Acclaim® 12200 with a number average molecular weight of around 11,335 g / mol, Acclaim® 8200 with a number average molecular weight of around 8,057 g / mol, and Acclaim® 4200 with a number average molecular weight of around 4,020 g / mol, or polyoxypropylene diols sold by Dow under the name Voranol P2000 with a number average molecular weight of around 2004 g / mol.

[0062] An example of a polyethertriol is the polyoxypropylene triol sold by Dow under the name Voranol CP3355, which has a number-average molecular weight of around 3554 g / mol.

[0063] The polydiene polyols that can be used according to the present invention can preferably be selected from polydienes containing hydroxyl-terminated groups and their corresponding hydrogenated or epoxidized derivatives.

[0064] Preferably, the polydiene polyols that can be used according to the present invention are selected from polybutadienes containing optionally hydrogenated or epoxidized hydroxyl-terminated groups. More preferably, the polydiene polyols that can be used according to the present invention are selected from optionally hydrogenated or epoxidized butadiene homopolymers and copolymers containing hydroxyl-terminated groups.

[0065] In the context of the present invention, unless otherwise specified, the term “hydroxyl-terminated group” of a polydiene polyol is understood to mean a hydroxyl group located at the end of the main chain of the polydiene polyol.

[0066] The above hydrogenated derivatives can be obtained by the complete or partial hydrogenation of the double bond of a polydiene containing a hydroxyl-terminated group, and are therefore saturated or unsaturated.

[0067] The above epoxidized derivatives can be obtained by chemoselective epoxidation of the double bond in the main chain of a polydiene containing a hydroxyl-terminated group, and therefore contain at least one epoxy group in their main chain.

[0068] Examples of polybutadiene polyols include saturated or unsaturated butadiene homopolymers containing hydroxyl-terminated groups, which may be epoxidized, such as those marketed by Cray Valley under the names Poly bd® or Krasol®.

[0069] Examples of polycarbonate diols include Converge Polyol 212-10 and Converge Polyol 212-20, sold by Novomer (having number-average molecular weights (Mn) equal to 1000 and 2000 g / mol, respectively, and hydroxyl values ​​of 112 and 56 mg KOH / g, respectively); Desmophen® C XP 2716, sold by Covestro (having a number-average molecular weight (Mn) equal to 326 g / mol, and a hydroxyl value of 344 mg KOH / g); and Polyol C-590, C-1090, C-2090, and C-3090, sold by Kuraray (having number-average molecular weights (Mn) in the range of 500 to 3000 g / mol and hydroxyl values ​​in the range of 224 to 37 mg KOH / g).

[0070] According to a particularly advantageous alternative embodiment of the present invention, the curing agent component contained in the two-component polyurethane structural adhesive composition (PU2K), preferably in combination with the above-described -NCO component, - At least two polyether polyols P1, each having a number-average molecular weight of exactly less than 500 g / mol, -At least one polyether polyol P1 comprises at least three hydroxyl functional groups, preferably at least four hydroxyl functional groups; and -At least one polyether polyol P1 contains at least two hydroxyl functional groups; - Containing at least one polyether polyol P2 having a number average molecular weight strictly exceeding 1000 g / mol.

[0071] Polyether polyol P1: Preferably, the curing agent component includes the following: -At least one polyether polyol P1 comprising at least three hydroxyl functional groups, preferably at least four hydroxyl functional groups; and - At least one polyether polyol P1 comprising two hydroxyl functional groups, preferably comprising at least one arylene radical.

[0072] According to one embodiment, each polyether polyol P1 has a number average molecular weight in the range of 100 g / mol to less than 500 g / mol, preferably 200 g / mol to less than 500 g / mol, more preferably 300 g / mol to less than 500 g / mol, advantageously 400 g / mol to less than 500 g / mol, and more advantageously further 400 g / mol to 490 g / mol.

[0073] Preferably, each polyether polyol P1 has an average hydroxyl value (OHN) in the range of 224 to 2244 milligrams of KOH (mg KOH / g) per gram of polyol, preferably 224 to 1122 mg KOH / g, more preferably 224 to 748 mg KOH / g, and more preferably 229 to 561 mg KOH / g.

[0074] Among polyether polyols P1, examples include Dianol® 330 (propoxylated 4,4'-isopropylidenediphenol with approximately 280 mg KOH / g of OHN) sold by CECA, and Lupranol® 3402 (propoxylated ethylenediamine with functional properties of 4 and approximately 470 mg KOH / g of OHN) sold by BASF.

[0075] Polyether polyol P2: The curing agent component comprises at least one polyether polyol P2 having a number average molecular weight that is strictly greater than 1000 g / mol, preferably 10000 g / mol or less, preferredly 5000 g / mol or less, and advantageously 3000 g / mol or less.

[0076] Polyether diols are more particularly preferred, and among them, polyoxyalkylenediols such as polyoxypropylene diol are preferred.

[0077] Examples of such commercially available products include polyoxypropylene diol sold by Dow under the name Voranol® P 1010, which has a number average molecular weight (Mn) of around 1020 g / mol and a hydroxyl value of approximately 110 mg KOH / g, or Voranol® P2000, also sold by Dow, which has a number average molecular weight of around 2040 g / mol and a hydroxyl value of approximately 55 mg KOH / g.

[0078] According to a second embodiment of the present invention, the curing agent component comprises a compound having an amino-terminated group, preferably a polyamine having two or more amino groups per mole, preferably a polyoxyalkylene polyamine (or polyetheramine). Preferably, the polyoxyalkylene polyamine has 2 to 4 amino groups per mole, more preferably 2 to 3 amino groups per mole. The polyoxyalkylene polyamine generally has a number average molar mass or molecular weight (Mn) of about 140 or more, preferably about 200 or more. The polyoxyalkylene polyamine preferably has a number average molecular weight (Mn) in the range of 200 to 5000 g / mol or less, preferably 200 to 4000 g / mol, and preferably 200 to 2000 g / mol. Among the preferred polyoxyalkylene polyamines, examples include Jeffamine® T403, a polypropylene oxide triamine available from Huntsman with a number-average molecular weight (Mn) of approximately 440 g / mol; Jeffamine® D-400, a polypropylene oxide diamine with a number-average molecular weight (Mn) of approximately 430 g / mol; and Jeffamine® D-2000, a polypropylene oxide diamine with a number-average molecular weight (Mn) of approximately 2000 g / mol.

[0079] Thixotropic composition (A): The two-component polyurethane structural adhesive composition (PU2K) according to the present invention is such that its -NCO component and its curing agent component each contain 0.1% to 40% (by weight) of thixotropic composition (A) based on the total weight of the corresponding components, and thixotropic composition (A) is based on its total weight, - 1% to 40% (by weight) of bisurea (a) obtained by the reaction of a primary aliphatic amine (a1) with a diisocyanate (a2) having a molar mass of less than 500 g / mol, -below: -Alkyl phthalate, preferably diisodecyl phthalate (DIDP); - Pentaerythritol tetravalerate; - Esters of alkyl sulfonic acid and phenol; -Diisononyl 1,2-cyclohexanedicarboxylate; -3,3'-[methylenebis(oxymethylene)]bis[heptane]; and - Dioctyl carbonate It contains 60% to 99% (by weight) of a plasticizer (b) selected from the following.

[0080] Therefore, the thixotropic composition (A) is a suspension (or dispersion) of solid particles of bisurea (a) in a continuous phase consisting of a plasticizer (b).

[0081] Preferably, the thixotropic composition (A) consists of bisurea (a) and a plasticizer (b) in the weight content shown above.

[0082] Bisurea (a) is obtained by the reaction of a primary aliphatic amine (a1) with a diisocyanate (a2) having a molar mass of less than 500 g / mol.

[0083] The selected amine is preferably an n-alkylamine containing 1 to 22 carbon atoms, and more preferably an n-butylamine.

[0084] The diisocyanate (a2) that can be used may be aromatic or aliphatic and have formula (II): NCO-R 6 -NCO (II) [In the formula, R 6 It is selected from one of the following divalent radicals, and its formula below shows the two free valencies: -a) Divalent radicals derived from isophorone; TIFF0007885221000010.tif33170-b) Divalent radical 4,4'-methylenebis(cyclohexyl); TIFF0007885221000011.tif16170-c) Divalent radicals derived from toluene-2,4-diisocyanate (or 2,4-TDI) or toluene-2,6-diisocyanate (or 2,6-TDI) of the following formulas: TIFF0007885221000012.tif39170-d) Divalent radicals derived from diphenylmethylene-4,2'-diisocyanate (or 4,2'-MDI) or diphenylmethylene-4,4'-diisocyanate (or 4,4'-MDI) of the following formulas: TIFF0007885221000013.tif27170-e) -(CH2)6- (or hexamethylene radical); -f) TIFF0007885221000014.tif37170 (or m-xylylene radical); -g) TIFF0007885221000015.tif37170 (or hexahydro-m-xylylene radical)

[0085] Diphenylmethylene-4,4'-diisocyanate (or 4,4'-MDI) corresponding to one of the above formulas d) is particularly preferred.

[0086] The plasticizer (b) is known to those skilled in the art and is advantageously selected from commercially available plasticizers.

[0087] Among alkyl phthalates, the use of diisodecyl phthalate (DIDP) is preferred.

[0088] Regarding pentaerythritol tetravalerate, one example is the product sold by Perstorp under the trademark name Pevalen (registered trademark).

[0089] Regarding esters of alkyl sulfonic acids and phenols, one example is the product Mesamoll®, marketed by Lanxess.

[0090] Regarding diisononyl 1,2-cyclohexanedicarboxylate, one example is the product marketed by BASF under the name Hexamoll Dinch®.

[0091] 3,3'-[methylenebis(oxymethylene)]bis[heptane] can be identified by its CAS number: 22174-70-5 and is also known by the trade name 2-ethylhexylal, available from Lambiotte.

[0092] Finally, dioctyl carbonate (European chemical number or EC number: 434-850-2) is available from BASF.

[0093] According to a very particularly preferred alternative, the plasticizer (b) is diisodecylphthalate (DIDP).

[0094] According to another embodiment, the thixotropic composition (A) comprises, preferably, 10% to 30% (by weight) of bisurea (a) and 70% to 90% (by weight) of a plasticizer (b).

[0095] The thixotropic composition (A) used in the PU2K structural adhesive composition according to the present invention can be prepared as follows.

[0096] The reaction between an aliphatic amine a1) and a diisocyanate a2) is highly exothermic. To prevent the large amount of heat generated by the reaction from leading to the decomposition of the resulting bisurea, compounds a1) and a2) are each dissolved in a plasticizer b) before they react together, and as a result, the plasticizer b) helps to dissipate the heat generated by the reaction. The two solutions of compounds a1) and a2) in plasticizer b) are advantageously introduced into the reactor via injectors under a pressure of 40–200 bar, preferably 80–120 bar, so that the two solutions come into contact in a sprayed liquid state. The amounts of reactants preferably correspond to a ratio of (moles of a1) / (moles of a2) equal to about 2. Bis-urea is produced by a reaction in the form of solid particles dispersed in a continuous phase of plasticizer b), and the Brookfield viscosity of the corresponding suspension is generally 1 to 50 Pa.s, preferably 10 to 25 Pa.s, when measured at a temperature of 23°C.

[0097] According to a preferred embodiment, the -NCO component and the curing agent component each comprise 0.5% to 35% (by weight), more preferably 2% to 15% (by weight), of the thixotropic composition (A) based on the total weight of the corresponding components.

[0098] Alumina (B): The two-component polyurethane structural adhesive composition (PU2K) according to the present invention is such that at least one of its -NCO component and curing agent component contains 5% to 40% (by weight) of alumina (B) based on the total weight of the components, preferably

[0099] In a preferred alternative form, alumina (B) is included in the curing agent component, more preferably in an amount of 10% to 35% (by weight) based on the total weight of the component.

[0100] The alumina (B) used is standard alumina, generally supplied in powder form, with solid particles having a diameter of 0.2 μm to 50 μm, more specifically 0.5 μm to 25 μm, and a median diameter D50 of 2 to 5 μm, for example, around 3 μm.

[0101] Alumina (B) is commercially available, for example, from Huber under the name Martoxid® 200.

[0102] -Other components of NCO and hardener components: The -NCO and curing agent components of the PU2K structural adhesive composition according to the present invention may each contain at least one additive selected from the group consisting of solvents, pigments, microspheres, adhesion promoters (e.g., alkoxysilanes), hygroscopic agents, UV stabilizers (or antioxidants), dyes, fillers, and mixtures thereof.

[0103] According to one embodiment, the -NCO and the hardening agent component each comprise at least one filler selected from mineral fillers, organic fillers, and mixtures thereof.

[0104] Examples of mineral fillers that can be used include any mineral filler conventionally used in the field of adhesive compositions. These fillers are typically provided in the form of particles of various shapes. They may be, for example, spherical or fibrous, or they may have an irregular shape.

[0105] Preferably, the filler(s) are selected from the group consisting of clay, quartz, carbonate fillers, kaolin, gypsum, clay, zeolite, molecular sieves, and mixtures thereof. Preferredly, the filler is selected from zeolite and / or carbonate fillers, such as alkali metal or alkaline earth metal carbonates, and more preferably from calcium carbonate or chalk. An example of a calcium carbonate filler is the product sold by Omya under the name Omya BSH, which has an average particle size of 2.4 μm. Siliporite SA 1720, available from Arkema, is an example of a commercially available synthetic zeolite that can also be used as a filler. It is supplied in the form of a 3-angstrom molecular sieve of type A.

[0106] These fillers may be untreated or treated, and may be treated, for example, with an organic acid, such as stearic acid, or a mixture of organic acids consisting mainly of stearic acid.

[0107] Hollow mineral microspheres, such as hollow glass microspheres, or more specifically those made from calcium sodium borosilicate or aluminosilicate, may be used.

[0108] Examples of organic fillers that can be used include any organic fillers and, in particular, polymeric fillers that are conventionally used in the field of adhesive compositions.

[0109] For example, aramid fibers such as Kevlar®, polyvinyl chloride (PVC), polyolefin, rubber, or ethylene / vinyl acetate (EVA) may be used.

[0110] Hollow microspheres made from expandable or non-expandable thermoplastic polymers may be used. In particular, hollow microspheres made from vinylidene chloride / acrylonitrile may be used.

[0111] The average particle size of the filler that can be used is preferably 100 microns or less, more preferably 30 microns or less, and more favorably 10 microns or less.

[0112] The average particle size is measured for the volume particle size distribution corresponding to 50% (by volume) of the sample of particles being analyzed. If the particles are spherical, the average particle size corresponds to the median diameter (D50 or Dv50), which corresponds to the diameter at which 50% of the particles by volume have a size smaller than the aforementioned diameter. In this patent application, this value is expressed in micrometers and is determined by laser diffraction in a Malvern-type instrument according to standard NF ISO 13320-1 (1999).

[0113] Each of the NCO and curing agent components may contain a total amount of filler(s) ranging from 1% to 40% (by weight), preferably 1% to 30% (by weight), relative to the total weight of the corresponding component.

[0114] Furthermore, according to a preferred embodiment, the curing agent component may include a crosslinking catalyst. The crosslinking catalyst that can be used may be any catalyst known to those skilled in the art for catalyzing the formation of polyurethanes and / or polyureas by the reaction of at least one polyisocyanate with at least one polyol and / or one polyamine.

[0115] For example, one or more crosslinking catalysts selected from the group consisting of the following may be used. -organometallic catalyst; - Amidine; - Tertiary amines; and - A mixture of those.

[0116] Among organometallic catalysts, those that do not contain tin are preferred. Organometallic compounds (compounds containing at least one metal-carbon covalent bond) can include metal alkoxides, metal carboxylates, and metal coordination complexes having one or more organic ligands. The metal atoms are preferably selected from aluminum, zinc, iron, bismuth, titanium, gold, and zirconium. Organometallic catalysts can contain several metal atoms, such as bismuth and zinc, as seen in Borchers' Borchi® Kat VP 0244 (a mixture of zinc neodecanoate and bismuth neodecanoate).

[0117] Among amidines, the following are particularly noteworthy. -1,8-diazabicyclo[5.4.0]undeca-7-en(DBU): TIFF0007885221000016.tif27170-1,5-diazabicyclo[4.3.0]nona-5-ene(DBN): TIFF0007885221000017.tif27170

[0118] Among tertiary amines, the following are particularly noteworthy: -2,2'-dimorpholinodiethyl ether (DMDEE): TIFF0007885221000018.tif22170-1,4-diazabicyclo[2.2.2]octane (DABCO): TIFF0007885221000019.tif26170

[0119] Preferably, the amount of crosslinking catalyst that can be used is in the range of 0.01% to 1% (by weight), more preferably 0.05% to 0.5% (by weight), relative to the weight of the curing agent component.

[0120] The PU2K structural adhesive composition according to the present invention is advantageously substantially solvent-free. These terms are understood to mean that the solvent content of the adhesive does not exceed 1% by weight, preferably 0.05%.

[0121] PU2K structural adhesive composition: Each of the constituent components -NCO and the curing agent component of the PU2K structural adhesive composition according to the present invention is prepared separately by simple mixing of the components.

[0122] - The NCO component and hardener component are packaged, for example, in a dual cartridge. The adhesive is dispensed using a dual cartridge gun. A homogeneous mixture of the two components is obtained by attaching a static mixer to the dual cartridge.

[0123] The adhesive composition is obtained by reacting the -NCO component with the curing agent component in an NCO / (OH+NH) ratio in the range of about 0.90 to 1.20, preferably 1.00 to 1.10, such that the volume ratio of the -NCO component to the curing agent component is preferably close to 1. The NCO / OH+NH ratio is defined as the ratio of the NCO function (meq / g) of the -NCO component to the sum of the reactive OH (meq / g) and NH (meq / g) functions of the curing agent component.

[0124] Another subject of the present invention is the use of the PU2K structural adhesive composition defined above as a structural adhesive for assemblies intended for the manufacture of batteries for electric vehicles or hybrid vehicles, in the fields of construction, the manufacture of means of transport, preferably the fields of the automotive, rail and aerospace industries, and shipbuilding.

[0125] Finally, the subject of the present invention is a method for assembling two substrates by adhesive bonding, -Coating at least one of the two substrates to be assembled with an adhesive composition obtained by mixing the above-described NCO component and curing agent component; then - A method that includes actually bringing two substrates into contact.

[0126] Suitable substrates include, for example, inorganic substrates such as concrete, metal or alloy (aluminum alloy, steel, non-ferrous metal, galvanized metal, etc.); or otherwise organic substrates such as wood, plastics such as PVC, polycarbonate, PMMA, polyethylene, polypropylene, polyester or epoxy resin; and metallic substrates and composite materials coated with paints (for example, those used in the automotive sector).

[0127] The present invention will be described in the following examples, which are given purely as illustrations and should not be interpreted as limiting its scope. [Examples]

[0128] The following ingredients were used: Tolonate® HDB, sold by Vencorex, is a biuret-type HDI-based polyisocyanate with an average functional F=3.7, an NCO percentage in the range of 22.5% to 24.5%, a residual HDI content of less than 0.1%, and a viscosity in the range of 1500 to 2500 mPa.s at 25°C. Voranol® P 2000, marketed by Dow, is a functional F=2 polypropylene glycol (PPG) with 55 mg KOH / g of OHN, i.e., a number-average molecular weight (Mn) of approximately 2040 g / mol. - Dianol® 330, sold by Ceca, is a functional F=2 propoxylated (PPG) 4,4'-isopropylidenediphenol with 280 mg KOH / g of OHN, i.e., a number-average molecular weight (Mn) of approximately 401 g / mol. -Lupranol® 3402, marketed by BASF, is a functional F=4 propoxylated ethylenediamine with a number-average molecular weight (Mn) of approximately 470 mg KOH / g, i.e., 480 g / mol. Omya® BSH, manufactured by Omya, is a hydrophobic calcium carbonate with an average particle size of 2.4 μm. -Siliporite(registered trademark) SA 1720 is a synthetic zeolite sold by Ceca in the form of Type A 3-angstrom molecular sieves. -Aerosil® R202, sold by Evonik, is 100m 2 It is a hydrophobic fumed silica with a specific surface area (BET) around / g. -Borchi(registered trademark) Kat VP 0244 is a catalyst manufactured by Borchers consisting of a mixture of zinc neodecanoate and bismuth neodecanoate. -Martoxid(trademark)200 is alumina manufactured by Huber, and its solid particles have a diameter of 0.5 μm to 25 μm and a median diameter D50 of approximately 3 μm.

[0129] Example A1 (Reference): Preparation of NCO component - The components constituting the NCO component are mixed in proportions shown in Table 1 under nitrogen in a reactor that is continuously stirred.

[0130] After homogenization of the mixture, the content of NCO groups in the -NCO component (expressed as a weight percentage (%NCO) relative to the weight of the -NCO component) is measured according to standard NF T52-132.

[0131] Example A2 (Reference): Preparation of -OH component (curing agent) The components constituting the -OH group are mixed in proportions shown in Table 2 under nitrogen in a reactor that is continuously stirred.

[0132] After homogenization of the mixture (approximately 3 hours), the content of OH groups in the -OH component is measured, expressed as milligrams of KOH per gram of -OH component (mg KOH / g).

[0133] Example A3 (Comparative Example): Preparation and Evaluation of PU2K Adhesive Composition Preparation: The -NCO component prepared in Example A1 and the -OH component prepared in Example A2 were mixed in a ratio where the weight ratio of -NCO component to -OH component was equivalent to 100g of -NCO component for every 95.6g of -OH component, and the -NCO / -OH molar equivalent ratio was equal to 1. The corresponding ratios are shown in Table 3.

[0134] Mixing is performed using a 50ml dual cartridge at a temperature of approximately 23°C. [Table 1] TIFF0007885221000020.tif79170[Table 2] TIFF0007885221000021.tif99170[Table 3] TIFF0007885221000022.tif89170

[0135] evaluation: The comparative PU2K adhesive composition A3 obtained in this manner is subjected to the following tests and measurements.

[0136] a) Flow of the non-crosslinked PU2K composition after extrusion: The purpose of the test used is to evaluate the extrusion through a nozzle of the composition of Example A3, packaged as a dual cartridge, under the influence of pressure applied by a piston integrated with the trigger of a gun operated by an operator. The pressure applied is 3 bar.

[0137] The measured flow velocities are shown in Table 3 in g / min and perfectly match the behavior.

[0138] b) Creep of non-crosslinked PU2K composition: The creep (or slack or slump) of the viscous composition of Example A3 is measured according to standard ASTM D 2202. For this purpose, the composition is introduced into the cavity of a standard measuring fixture positioned horizontally, and a piston is then advanced along the surface of the fixture, which is equipped with a graduated scale, to form a composition cylinder with a diameter of 38.1 mm and a thickness of 4.75 mm, ready to flow downward under the influence of gravity. The fixture is then immediately positioned vertically at 23°C for 15 minutes. At the end of this 15-minute period, a measurement is taken using the graduated scale of the maximum creep point of the initial cylinder formed by the composition.

[0139] Significant creep of the composition was observed corresponding to a distance measured with a 3 cm scale on the instrument, and the results are shown in Table 3.

[0140] c) Intrinsic mechanical performance quality of the crosslinked PU2K composition: The tensile fracture stress and tensile fracture elongation were measured in accordance with the standard ISO 37 (2012).

[0141] The measurement principle involves using a tensile testing apparatus in which a movable jaw moves at a constant speed equal to 10 mm / min. A standard test specimen made of the crosslinked composition of Example A3 is pulled in, and the applied tensile stress (MPa) and elongation (%) of the test specimen are recorded at the moment the specimen breaks. The standard test specimen is dumbbell-shaped, as shown in the international standard ISO 37. The narrow part of the dumbbell used is 20 mm long, 4 mm wide, and 3-4 mm thick.

[0142] The results obtained are shown in Table 3, and correspond to values ​​that highly represent the PU2K structure adhesive.

[0143] d) Thermal conductivity of the crosslinked PU2K composition: Thermal conductivity is measured using a thermal conductivity meter such as the FP2C manufactured by Neotim.

[0144] The hot-wire probe is placed between two test specimens of the crosslinked composition of Example A3, which are in the shape of a parallelepiped with dimensions of 80 × 40 × 5 mm, and pre-conditioned at room temperature for one week.

[0145] The measured thermal conductivity is shown in Table 3 in W / mK.

[0146] Example A (Reference): Thixotropic composition (A) consisting of a suspension of bisurea at a concentration of 23.3% by weight in DIDP. First, prepare the following: Solution A of n-butylamine in DIDP, consisting of -17.17% by weight / weight of n-butylamine and 82.83% by weight / weight of DIDP, then Solution B of 4,4'-MDI in DIDP, consisting of 29.46% by weight / weight of 4,4'-MDI in -70.34% by weight / weight of DIDP.

[0147] Two solutions, A and B, are heated to 100°C and then introduced into a reactor under a pressure of 100 bar. Within the reactor, they are continuously sprayed at a weight ratio of A / B = 50.1 / 49.9, corresponding to an n-butylamine / MDI molar ratio equal to 2. The reaction is immediate, and the reactor temperature reaches 140°C at the end of production.

[0148] At the reactor outlet, a stable 23.3% wt / g dispersion of bisurea in DIDP is obtained, and the formula for bisurea is as follows: TIFF0007885221000023.tif19170

[0149] The Brookfield viscosity of the suspension, measured at 23°C, is 15 Pa.s.

[0150] Example 1: Preparation of the -NCO component incorporating the thixotropic composition of Example A: Repeat Example A1 with the components and their contents shown in Table 1.

[0151] Example 2: Preparation of a curing agent component incorporating the thixotropic composition of Example A: Repeat Example A2 with the components and their contents shown in Table 2.

[0152] Example 3 (according to the present invention): Preparation and evaluation of a PU2K adhesive composition comprising the -NCO component of Example 1 and the curing agent component of Example 2: Repeat Example A3 using the -NCO component from Example 1 and the curing agent component from Example 2 in the proportions shown in Table 3.

[0153] The results obtained from the test are shown in Table 3, and the following is clear: - The post-extrusion flow is significantly lower than that of Example A3, but still perfectly acceptable; -Unlike Example A3, there is no creep; -The tensile fracture stress and fracture elongation are similar to those obtained for the adhesive composition of Example A3, and therefore correspond to values ​​that fully represent the PU2K structural adhesive; and -Compared to the thermal conductivity of Example A3, the thermal conductivity increased significantly (60%).

Claims

1. - A two-component polyurethane structural adhesive composition (PU2K) consisting of an NCO component and a curing agent component, - The NCO component and the curing agent component each contain 2% to 15% (by weight) of thixotropic composition (A) based on the total weight of the corresponding components, and thixotropic composition (A) is based on its total weight, A 1% to 40% (by weight) bisurea (a) obtained by the reaction of a primary aliphatic amine (a1) with a diisocyanate (a2) having a molar mass of less than 500 g / mol, wherein the primary aliphatic amine (a1) is an n-alkylamine (a1) containing 1 to 22 carbon atoms, and the diisocyanate (a2) is of formula (II): NCO-R 6 -NCO (II) [In the formula, R 6 is selected from one of the following divalent radicals, and the following formula shows the two free valencies: -a) Divalent radicals derived from isophorone; -b) Divalent radical 4,4'-methylenebis(cyclohexyl); -c) Divalent radicals derived from toluene-2,4-diisocyanate (or 2,4-TDI) or toluene-2,6-diisocyanate (or 2,6-TDI) of the following formulas: -d) Divalent radicals derived from diphenylmethylene-4,2'-diisocyanate (or 4,2'-MDI) or diphenylmethylene-4,4'-diisocyanate (or 4,4'-MDI) of the following formulas: -e) (or m-xylylene radical); -f) (or hexahydro-m-xylylene radical) Therefore, bisurea (a) and below: Alkyl phthalate, Pentaerythritol tetravalerate, Esters of alkyl sulfonic acid and phenol, Diisononyl 1,2-cyclohexanedicarboxylate, 3,3'-[methylenebis(oxymethylene)]bis[heptane], and Dioctyl carbonate It contains 60% to 99% (by weight) of a plasticizer (b) selected from the following, The thixotropic composition (A) is provided in the form of a suspension of solid particles of bisurea (a) in a continuous phase consisting of a plasticizer (b), - A two-component polyurethane structural adhesive composition (PU2K) characterized in that the curing agent component contains 10% to 35% (by weight) of alumina (B) based on the total weight of the above components, and the alumina (B) has a median diameter D50 of 2 to 5 μm.

2. The PU2K structural adhesive composition according to claim 1, characterized in that the -NCO component comprises a polyisocyanate selected from diisocyanates, triisocyanates, and mixtures thereof.

3. The PU2K structural adhesive composition according to claim 2, characterized in that the triisocyanate is selected from diisocyanate isocyanurate, diisocyanate and triol adducts, and biuret.

4. - The PU2K structural adhesive composition according to claim 3, characterized in that the triisocyanate contained in the NCO component is hexamethylene diisocyanate (HDI) biuret.

5. A PU2K structural adhesive composition according to any one of claims 1 to 4, characterized in that the curing agent component contains a polyol or a mixture of polyols.

6. The PU2K structural adhesive composition according to claim 5, characterized in that the polyol is a polyether polyol having a hydroxyl functionality in the range of 2 to 4.

7. The hardening agent component is - At least two polyether polyols P1, each having a number average molecular weight of exactly less than 500 g / mol, - At least one polyether polyol P1 comprises at least three hydroxyl functional groups; and - At least one polyether polyol P1 contains at least two hydroxyl functional groups; - The PU2K structural adhesive composition according to claim 6, characterized by comprising at least one polyether polyol P2 having a number average molecular weight strictly exceeding 1000 g / mol.

8. The PU2K structural adhesive composition according to any one of claims 1 to 7, characterized in that the plasticizer (b) is diisodecyl phthalate.

9. The PU2K structural adhesive composition according to any one of claims 1 to 8, characterized in that the thixotropic composition (A) contains 10% to 30% (by weight) of bisurea (a) and 70% to 90% (by weight) of a plasticizer (b).

10. - The PU2K structural adhesive composition according to any one of claims 1 to 9, characterized in that the NCO and the curing agent component each contain at least one filler selected from mineral fillers, organic fillers, and mixtures thereof.

11. Use of the PU2K structural adhesive composition according to any one of claims 1 to 10 as a structural adhesive in the fields of construction, the manufacture of means of transport, and shipbuilding.

12. A method for assembling two substrates by adhesive bonding, - Coating of at least one of two substrates to be assembled with an adhesive composition obtained by mixing an NCO component and a curing agent component as described in any one of claims 1 to 10; then - A method including actually bringing two substrates into contact.

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