Heat-curable polyurethane compositions with wide temperature window

Abstract

A hydrazide with a melting point of at least 65°C is used as a curing agent for the heat-curing in a heat-curable polyurethane composition that comprises a prepolymer with isocyanate end groups, obtained from at least one polyisocyanate and at least one polyol, and at least one epoxy resin. As a result of this combination, heat-curing polyurethane compositions are obtained that have better storage stability and can be cured with constant mechanical properties over a wide temperature range.

Description

[0001] HEAT-CURING POLYURETHANE COMPOSITIONS WITH A WIDE TEMPERATURE WINDOW

[0002] Technical area

[0003] The invention relates to the use of a hardener for heat curing in a heat-curable polyurethane composition. Furthermore, the invention relates to a heat-curable polyurethane composition and a process for curing such a composition.

[0004] State of the art

[0005] Polyurethane compositions have long been known and are used in many areas, for example, as adhesives, sealants, or coatings in the construction and manufacturing industries. A distinction is made between one-component (1K) and two-component (2K) polyurethane (PUR) compositions. In 1K polyurethane compositions, where all components are contained in a single component, a further distinction can be made between moisture-curing compositions, which cure under the influence of atmospheric moisture, and heat-curing compositions, in which curing is induced by heating.

[0006] WO 2009 / 080738 A1 (Sika Technology AG), for example, describes a moisture-curing polyurethane composition comprising a polyisocyanate and an amine blocked by an aldehyde or ketone as a moisture-activated crosslinker. These compositions cure with moisture at room temperature or slightly elevated temperatures, particularly below 40°C, forming aldehydes and / or ketones. To significantly reduce undesirable outgassing of the aldehydes and ketones in the cured state, the composition contains hydrazides, which react with the aldehydes and / or ketones at temperatures above 80°C to form low-volatility components.

[0007] Heat-curing polyurethane compounds are primarily used as adhesives and sealants in industrial manufacturing. This is particularly true as sealants in automotive construction. These heat-curing polyurethane compounds are applied after the components have been painted, for example, along with the paint curing process in appropriate curing ovens, typically at temperatures of > 110°C.

[0008] For heat-curing polyurethane compositions, thermolabile hardeners or heat-activated hardeners are used, which start the curing process of the composition at a defined temperature.

[0009] EP 0 255 572 A1 (Sika AG), for example, describes a one-component adhesive and / or sealant compound containing a polyurethane-based prepolymer and a heat-activated hardener. The stoichiometric ratio of prepolymer to hardener is selected so that only partial crosslinking is possible upon heating to temperatures of 60 to 180°C, resulting in a product with highly viscous to plastic properties. Dicyandiamides or the sodium chloride complex salt of 4,4'-diaminodiphenylmethane are mentioned as hardeners.

[0010] However, the problem with currently available heat-curable polyurethane compositions is that they must be cured within a relatively narrow temperature window. At temperatures that are too low, there is usually a risk of incomplete conversion of the hardener, which can lead to the hardener leaching from the cured product as an oily liquid. At temperatures that are too high, however, there is a risk of undesirable, severe discoloration. Furthermore, polyurethane compositions are not usually stable at high temperatures and begin to decompose at temperatures above 180°C or at the latest above 200°C. This manifests itself in a significant loss of mechanical properties such as tensile strength.

[0011] Furthermore, known heat-curable polyurethane compositions are often based on problematic substances, such as 4,4'-methylenedianiline, which is classified as a substance of very high concern (SVHC) under the REACH regulation, or they are not sufficiently stable in storage.

[0012] There is therefore still a need for improved solutions that do not have the aforementioned disadvantages or that have them to a lesser extent.

[0013] Description of the invention

[0014] The object of the invention is therefore to provide improved solutions for heat-curable polyurethane compositions which overcome the aforementioned disadvantages and are particularly suitable as one-component adhesive and / or sealant compositions. The compositions should preferably be curable in the widest possible temperature window. This should be done in such a way that the mechanical properties of the cured product can be reliably guaranteed essentially or at least largely independent of the curing temperature. Furthermore, the aim is for the compositions to show as little discoloration as possible at high curing temperatures and not to significantly lose their mechanical properties, and for the compositions to be as stable as possible with regard to demixing or segregation of components. The latter is particularly important in the case of only a partial or incomplete heat-curing reaction, as occurs, for example, inThis can occur at too low curing temperatures. Finally, the compositions should be as stable as possible even at higher ambient temperatures.

[0015] Surprisingly, it was found that the task was solved by a

[0016] Use according to claim 1 can be achieved. The core of the invention is therefore the use of a hydrazide having a melting point of at least 65°C as a hardener for heat curing in a heat-curable polyurethane composition which comprises a prepolymer with isocyanate end groups, obtained from at least one polyisocyanate and at least one polyol, and at least one epoxy resin.

[0017] It has been shown that hydrazides can be used as hardeners in 1-component polyurethane compositions containing at least one prepolymer with isocyanate end groups in combination with an epoxy resin, leading to unexpected advantages. This allows for the creation of storage-stable 1-component polyurethane compositions suitable as adhesives and / or sealants. These compositions can be specifically cured by heat curing within a wide temperature range, particularly in the range of 100-220°C. They exhibit excellent mechanical properties and are not prone to discoloration across the entire temperature range. Storage stability is maintained from room temperature up to 60°C.

[0018] It is assumed that this is due to the fact that the hydrazides used as hardeners achieve effective curing even at comparatively low curing temperatures, starting above the melting point of the hydrazide, without the epoxy resin used negatively influencing this process. The epoxy resin is likely to contribute to curing particularly at higher temperatures, for example, above 150°C, by reacting with other components of the composition, such as the hydrazide, to form a crosslinking reaction. One of the surprising features is that the inventive use of the combination of hydrazides and epoxy resin when cured at high temperatures leads to far less severe discoloration and far better temperature stability of the mechanical properties in the cured products than with previously known heat-curable polyurethane compositions.In addition, compositions are available that are stable against component separation even in the case of incomplete heat-curing reactions, such as those that occur at excessively low curing temperatures. In particular, the problem of oily fluids escaping from the cured product can be effectively prevented.

[0019] This is likely due to the relatively high melting point of the hydrazide, which ensures that any unreacted hardener remains in the cured product in an unreacted state. Even if a certain portion of the prepolymer in the heat-curing composition cures due to moisture before the actual heat curing, shifting the ratio of available prepolymer to hardener, the excess hardener does not pose a problem in terms of segregation.

[0020] The discolorations typical of polyurethane compositions are already very low in this case, even at high curing temperatures of up to 220°C, and can be largely avoided by using stabilizers, especially phosphite stabilizers.

[0021] The polyurethane compositions obtainable according to the invention have, in particular, stable mechanical properties over the entire application range and in particular at curing temperatures up to 220°C, especially with regard to the modulus of elasticity.

[0022] A further advantage of the present invention is that problematic substances, such as 4,4'-methylenedianiline, which is classified as a substance of very high concern (SVHC) according to the REACH regulation, can be dispensed with or unexpectedly advantageous alternatives are provided.

[0023] In addition, the available polyurethane compositions adhere very well to metal substrates and a wide variety of coatings, especially to coatings such as those applied in vehicle construction, for example by cathodic dip painting.

[0024] The polyurethane compositions obtainable by the use according to the invention can be used, among other things, as adhesives and sealants in industrial production, in particular as sealants in vehicle construction, where they can be cured, for example, on freshly painted components together with the paint curing in the corresponding curing oven.

[0025] Further aspects of the invention are the subject of further independent claims. Particularly preferred embodiments of the invention are the subject of the dependent claims.

[0026] Ways to implement the invention

[0027] A first aspect of the present invention relates to the use of a hydrazide having a melting point of at least 65°C in combination with an epoxy resin as a hardener for heat curing in a heat-curable polyurethane composition comprising a prepolymer having isocyanate end groups of at least one polyisocyanate and at least one polyol.

[0028] Compound names beginning with "poly" refer to substances that contain two or more of the functional groups mentioned in their name per molecule. The compounds can be monomeric, oligomeric, or polymeric. A polyol, for example, is a compound with two or more hydroxyl groups. A polyisocyanate is a compound with two or more isocyanate groups.

[0029] Isocyanate-reactive compounds are compounds that contain at least one isocyanate-reactive group that can react with isocyanate groups to form a chemical bond. A one-component polyurethane composition refers to a composition in which the constituents are present in a single component. As a rule, a one-component composition is stable at room temperature (e.g., 23°C) and, if a moisture-curable system is present, in the absence of atmospheric moisture, for at least a certain period of time (e.g., at least 1 day or at least 1 month).

[0030] The term “storage-stable” refers to the property of a substance or composition that it can be stored at room temperature in a suitable container for several weeks up to 6 months or more without its application or usage properties changing as a result of storage to an extent relevant to its use.

[0031] The average molecular weight here means the number average molecular weight (Mn), which can be determined by gel permeation chromatography (GPC) against a polystyrene standard.

[0032] Heat curing is understood to mean curing at an elevated temperature of, for example, at least 80°C, in particular at least 100°C, and especially more than 120°C. Heat curing is carried out, in particular, at a temperature above the melting point of the hydrazide.

[0033] During heat curing, the polyurethane composition is cured simultaneously throughout after application. In contrast, during moisture curing, the polyurethane composition is diffusion-controlled curing from the outside in after application. Moisture curing is understood to mean curing under moisture, in particular atmospheric humidity. Moisture curing is generally carried out at a temperature of no more than 40°C, with moisture curing usually being carried out at room temperature, i.e., for example, at temperatures below 35°C, e.g., at approximately 23°C. All of the following information, in particular regarding the polyurethane composition, the process, and the uses, naturally applies equally to the inventive use, the inventive process, the products obtainable therefrom, and the inventive adhesive and / or sealant compositions, even if this is not specifically stated.

[0034] The polyurethane composition according to the invention comprises a prepolymer with isocyanate end groups composed of at least one polyisocyanate and at least one polyol. Mixtures of two or more such prepolymers can also be used. Prepolymers with isocyanate end groups are known to those skilled in the art. The prepolymer has at least two isocyanate end groups and preferably exactly two isocyanate end groups. Via the isocyanate end groups, the prepolymer can be chain-extended or crosslinked by reaction with compounds containing isocyanate-reactive groups, such as water, hydroxyl groups, or amino groups, which causes the curing of the polyurethane composition. The terms "curing" or "crosslinking" hereinafter also include chain-extension reactions.

[0035] The prepolymer with isocyanate end groups composed of at least one polyisocyanate and at least one polyol is a polyurethane prepolymer produced by reacting at least one polyisocyanate and at least one polyol. Such prepolymers are readily available to those skilled in the art.

[0036] The reaction of the at least one polyol with at least one polyisocyanate can be carried out, for example, by reacting the polyol component and the polyisocyanate component using conventional methods, e.g., at temperatures of 50 to 100°C, optionally in the presence of a suitable catalyst, with the polyisocyanate being used in stoichiometric excess. Additives such as solvents and / or plasticizers can be added to the reaction mixture as required. The prepolymer with isocyanate end groups is formed as the reaction product. Solvents, if used, can be removed again after the reaction. Plasticizers, if used, can preferably remain in the resulting product.

[0037] The polyisocyanate used to form the prepolymer with isocyanate end groups is preferably a polyisocyanate, in particular a diisocyanate, selected from aliphatic polyisocyanates and / or aromatic polyisocyanates. One such polyisocyanate or two or more such polyisocyanates can be used. An aliphatic polyisocyanate is preferred.

[0038] An aliphatic polyisocyanate is an aliphatic compound containing at least two isocyanate groups. An aliphatic diisocyanate is preferred. It can be an acyclic or cyclic aliphatic polyisocyanate, with a cyclic aliphatic polyisocyanate being preferred. It is preferably a saturated aliphatic polyisocyanate. These polyisocyanates are well known and commercially available.

[0039] Examples of suitable aliphatic polyisocyanates are 1,6-hexamethylene diisocyanate, 2,2,4- and 2,4,4-trimethyl-1,6-hexamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, cyclobutane-1,3-diisocyanate, cyclohexane-

[0040] 1,3- and 1,4-diisocyanate and mixtures of these isomers, isophorone diisocyanate (IPDI, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane),

[0041] 2,4- and 2,6-hexahydrotoluene diisocyanate, hexahydro-1,3- and -1,4-phenyl diisocyanate, perhydro-2,4'- and -4,4'-diphenylmethane diisocyanate, and mixtures of the aforementioned isocyanates. Isophorone diisocyanate (IPDI) and hexamethylene 1,6-diisocyanate (HDI) are particularly preferred.

[0042] Examples of suitable aromatic polyisocyanates are 4,4'-

[0043] Diphenylmethane diisocyanate, optionally with proportions of 2,4'- and / or 2,2'-diphenylmethane diisocyanate (MDI), 2,4-tolylene diisocyanate or mixtures thereof with 2,6-tolylene diisocyanate (TDI), 1,4-phenylene diisocyanate (PDI), and / or naphthalene-1,5-diisocyanate (NDI).

[0044] Particularly preferred polyisocyanates are 4,4'-diphenylmethane diisocyanate, optionally with proportions of 2,4'- and / or 2,2'-diphenylmethane diisocyanate (MDI), 2,4-tolylene diisocyanate or mixtures thereof with 2,6-tolylene diisocyanate (TDI) and / or isophorone diisocyanate (IPDI).

[0045] To form the prepolymer with isocyanate end groups, at least one polyisocyanate is reacted with one or more polyols. All polyols commonly used in polyurethane chemistry can be used.

[0046] A wide variety of suitable polyols are commercially available.

[0047] The polyol preferably has an average molecular weight or, if it is a non-polymeric polyol, a molecular weight of 250 to 30,000 g / mol and preferably of 400 to 20,000 g / mol.

[0048] The polyol further preferably has an average OH functionality in the range of 1.6 to 3. It is understood that polymeric compounds may also contain substances formed from side reactions, for example, which have only one or no hydroxyl group.

[0049] Preferably, the polyol is a diol or triol having an OH number in the range of 8 to 185 mg KOH / g, in particular in the range of 10 to 120 mg KOH / g.

[0050] As polyols, for example, the following commercially available polyols or mixtures thereof can be used: a) Polyoxyalkylene polyols, also called polyether polyols or oligoetherols, which are polymerization products of ethylene oxide, 1,2-propylene oxide, 1,2- or 2,3-butylene oxide, oxetane, tetrahydrofuran or mixtures thereof, possibly polymerized with the aid of a starter molecule with two or more active hydrogen atoms such as, for example, water, ammonia or compounds with several OH or NH groups such as, for example, 1,2-ethanediol, 1,2- and 1,3-propanediol, neopentyl glycol, diethylene glycol, triethylene glycol, the isomeric dipropylene glycols and tripropylene glycols, the isomeric butanediols, pentanediols, hexanediols, heptanediols, octanediols, nonanediols, decanediols, Undecanediols, 1,3- and 1,4-cyclohexanedimethanol, bisphenol A, hydrogenated bisphenol A, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, glycerol, aniline,as well as mixtures of the aforementioned compounds. Both polyoxyalkylene polyols with a low degree of unsaturation (measured according to ASTM D-2849-69 and expressed in milliequivalents of unsaturation per gram of polyol (mEq / g)), produced, for example, using so-called double metal cyanide complex catalysts (DMC catalysts), and polyoxyalkylene polyols with a higher degree of unsaturation, e.g., produced using anionic catalysts such as NaOH, KOH, CsOH, or alkali metal alcoholates, can be used.

[0051] Polyoxyalkylenediols or polyoxyalkylenetriols, especially polyoxyethylene and polyoxypropylenediols and triols, are particularly suitable. Polyoxyalkylenediols and triols with a degree of unsaturation of less than 0.02 mEq / g and an average molecular weight in the range of 1,000 to 30,000 g / mol, as well as polyoxypropylenediols and triols with an average molecular weight of 400 to 8,000 g / mol, are particularly suitable.

[0052] Also particularly suitable are so-called ethylene oxide-terminated ("EO-endcapped") polyoxypropylene polyols. The latter are special polyoxypropylene polyoxyethylene polyols obtained, for example, by further alkoxylating pure polyoxypropylene polyols, especially polyoxypropylene diols and triols, with ethylene oxide after completion of the polypropoxylation reaction, thus giving them primary hydroxyl groups. b) Styrene-acrylonitrile or acrylonitrile-methyl methacrylate-grafted polyether polyols. c) Polyester polyols, also called oligoesterols, produced by known processes, in particular the polycondensation of hydroxycarboxylic acids or the polycondensation of aliphatic and / or aromatic polycarboxylic acids with di- or polyhydric alcohols.

[0053] Particularly suitable polyester polyols are those which are prepared from di- to trihydric, in particular dihydric, alcohols, such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, neopentyl glycol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-hexanediol, 1,6-hexanediol, 1,8-octanediol, 1,10-decanediol, 1,12-dodecanediol, 1,12-hydroxystearyl alcohol, 1,4-cyclohexanedimethanol, dimer fatty acid diol (dimerdiol), hydroxypivalic acid neopentyl glycol ester, glycerol, 1,1,1-trimethylolpropane or mixtures of the aforementioned alcohols, with organic di- or tricarboxylic acids, in particular dicarboxylic acids, or their anhydrides or esters such as succinic acid, glutaric acid, adipic acid, trimethyladipic acid, suberic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, maleic acid, fumaric acid, dimer fatty acid, phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, dimethyl terephthalate, hexahydrophthalic acid,Trimellitic acid and trimellitic anhydride, or mixtures of the aforementioned acids, as well as polyester polyols made from lactones such as s-caprolactone and starters such as the aforementioned di- or trihydric alcohols. d) Polycarbonate polyols, such as those obtainable, for example, by reacting the above-mentioned alcohols used to synthesize the polyester polyols with dialkyl carbonates, diaryl carbonates, or phosgene. e) Block copolymers bearing at least two hydroxyl groups, which have at least two different blocks with a polyether, polyester, and / or polycarbonate structure of the type described above, in particular polyetherpolyester polyols. f) Polyacrylate and polymethacrylate polyols. g) Polyhydroxy-functional fats and oils, for example natural fats and oils, in particular castor oil; or so-called oleochemical polyols obtained by chemical modification of natural fats and oils.for example, the epoxy polyesters or epoxy polyethers obtained by epoxidation of unsaturated oils and subsequent ring opening with carboxylic acids or alcohols, or polyols obtained by hydroformylation and hydrogenation of unsaturated oils; or polyols obtained from natural fats and oils by degradation processes such as alcoholysis or ozonolysis and subsequent chemical linking, for example by transesterification or dimerization, of the degradation products thus obtained or derivatives thereof. Suitable degradation products of natural fats and oils are, in particular, fatty acids and fatty alcohols as well as fatty acid esters, in particular the methyl esters (FAME), which can be derivatized, for example, by hydroformylation and hydrogenation to hydroxy fatty acid esters. h) polyhydrocarbon polyols, also called oligohydrocarbonols, such as, for example, polyhydroxy-functional polyolefins, polyisobutylenes, polyisoprenes; polyhydroxy-functional ethylene-propylene,Ethylene-butylene or ethylene-propylene-diene copolymers; polyhydroxy-functional polymers of dienes, in particular of 1,3-butadiene, which can in particular also be prepared from anionic polymerization; polyhydroxy-functional copolymers of dienes such as 1,3-butadiene or diene mixtures and vinyl monomers such as styrene, acrylonitrile, vinyl chloride, vinyl acetate, vinyl alcohol, isobutylene and isoprene, for example polyhydroxy-functional acrylonitrile / butadiene copolymers, as can be prepared, for example, from epoxides or amino alcohols and carboxyl-terminated acrylonitrile / butadiene copolymers; and hydrogenated polyhydroxy-functional polymers or copolymers of dienes. Preferably, the NCO / OH ratio in the reaction between polyisocyanate and the polyol is in the range from 2 / 1 to 10 / 1, particularly preferably in the range from 3 / 1 to 8 / 1, in particular in the range from 4 / 1 to 7 / 1.

[0054] The prepolymer preferably has an NCO content in the range of 0.5 to 10% by weight, preferably 0.6 to 8.4% by weight, in particular 0.8 to 7% by weight.

[0055] In particular, the prepolymer with isocyanate end groups made of at least one polyisocyanate and at least one polyol has a content of monomeric polyisocyanates, in particular monomeric diisocyanates, of at most 0.5% by weight, preferably at most 0.3% by weight, in particular at most 0.2% by weight, in particular at most 0.1% by weight.

[0056] Preferred prepolymers are those formed with isophorone diisocyanate (IPDI) and / or 2,2'-diphenylmethane diisocyanate (MDI); the prepolymer has a content of monomeric polyisocyanates, especially monomeric diisocyanates, of at most 0.5% by weight, preferably at most 0.3% by weight, in particular at most 0.2% by weight, especially at most 0.1% by weight.

[0057] Such a prepolymer is particularly suitable for the manufacture of preparations, such as elastic adhesives, sealants and coatings, which have a content of monomeric polyisocyanates, in particular monomeric diisocyanates, of less than 0.1% by weight; these are safe to handle even without special protective measures and can therefore be sold in many countries without hazard labelling.

[0058] It has also been shown that prepolymers with a low proportion of monomeric polyisocyanates, when used with the curing agents used according to the invention, result in particularly advantageous polyurethane compositions in which the advantages of the invention are particularly evident. Particularly in the case of MDI-based prepolymers, it is advantageous to remove the excess MDI monomers after production, as these can otherwise influence the curing of the isocyanate-containing polymer with the hydrazide by slowing it down, particularly in embodiments in which the hydrazide is already coated with MDI, as described below. However, in the case of IPDI- or TDI-based prepolymers, the presence of residual monomeric diisocyanates has no influence on the curing.

[0059] The reaction between the polyisocyanate and the polyol is preferably carried out in the absence of moisture at a temperature in the range from 20 to 160 °C, in particular from 40 to 140 °C, optionally in the presence of suitable catalysts.

[0060] After the reaction, the monomeric polyisocyanate remaining in the reaction mixture, in particular the remaining monomeric diisocyanate, can be removed down to the described residual content by means of a suitable separation process.

[0061] The preferred separation process is a distillative process, in particular thin-film distillation or short-path distillation, preferably under vacuum.

[0062] Particularly preferred is a multi-stage process in which the monomeric polyisocyanate or diisocyanate is removed in a short-path evaporator at a jacket temperature in the range of 120 to 200 °C and a pressure of 0.001 to 0.5 mbar.

[0063] In the case of the preferred IPDI as monomeric diisocyanate, the jacket temperature is preferably in the range of 140 to 180°C. The reaction of the monomeric polyisocyanate, in particular the monomeric diisocyanate, and the polyol and the subsequent removal of the monomeric polyisocyanate remaining in the reaction mixture preferably takes place without the use of solvents and / or entraining agents.

[0064] Preferably, the monomeric polyisocyanate removed after the reaction is subsequently reused, ie used again for the production of polymer containing isocyanate groups.

[0065] During the reaction, the OH groups of the polyol react with the isocyanate groups of the monomeric polyisocyanate, particularly the monomeric diisocyanate. This also leads to so-called chain extension reactions, in which OH groups and / or isocyanate groups of reaction products between polyol and monomeric polyisocyanate react. The higher the NCO / OH ratio, the fewer chain extension reactions take place and the lower the polydispersity and thus the viscosity of the resulting polymer. One measure of the chain extension reaction is the average molecular weight of the polymer or the width and distribution of the peaks in the GPC analysis. Another measure is the effective NCO content of the monomer-free polymer in relation to the theoretical NCO content calculated from the reaction of each OH group with a monomeric polyisocyanate.

[0066] Preferably, the isocyanate group-containing polymer with a low content of monomeric polyisocyanate has a viscosity at 20 °C of at most 50 Pa s, in particular at most 40 Pa s, particularly preferably at most 30 Pa s. The viscosity is determined using a cone-plate viscometer with a cone diameter of 25 mm, cone angle of 1 °, cone tip-plate distance of 0.05 mm at a shear rate of 10 s' 1 . With the preferred isocyanate group-containing polymers or

[0067] Prepolymers can be used to obtain high-quality, easily processable thermosetting and polyurethane compositions.

[0068] A particularly preferred prepolymer with a low content of monomeric polyisocyanates has an NCO content in the range of 1 to 2.5% by weight, preferably 1.1 to 2.1% by weight, based on all repeating units in the polyether segment; 80 to 100% by weight, in particular 80 to 90% by weight, of 1,2-propyleneoxy groups and 0 to 20% by weight, in particular 10 to 20% by weight, of 1,2-ethyleneoxy groups; a monomeric polyisocyanate content of at most 0.3% by weight and is obtained from the reaction of IPDI with a polyether triol having an average OH functionality in the range from 2.2 to 3, preferably 2.2 to 2.8, in particular 2.2 to 2.6 and an OH number in the range from 10 to 42 mg KOH / g, in particular 20 to 35 mg KOH / g.

[0069] Another particularly preferred prepolymer with a low content of monomeric polyisocyanates has an NCO content in the range of 2.8 to 7% by weight, based on all repeating units in the polyether segment; 100% propyleneoxy groups, a content of monomeric polyisocyanate of at most 0.3% by weight, and is obtained from the reaction of I PDI with at least one polyether diol having an OH number in the range of 44 to 120 mg KOH / g.

[0070] The proportion of prepolymer with isocyanate end groups from at least one polyisocyanate and at least one polyol in the polyurethane composition can, for example, be in the range from 10 to 90 wt.%, in particular from 15 to 70 wt.%, preferably 20 to 50 wt.%, in particular 25 to 45 wt.%.

[0071] In this case, a hydrazide is specifically used as a hardener in combination with the epoxy resin. Hydrazides are a class of compounds that have a functional group in which two nitrogen atoms are linked via a covalent bond. In particular, the hydrazides in this case are organic hydrazides. These are typically derivatives of organic acids, such as carboxylic acids and / or sulfonic acids. Carboxylic acid hydrazides carry at least one acyl group as a substituent in addition to at least one hydrazide group, while sulfonic acid hydrazides carry at least one sulfonyl group as a substituent in addition to at least one hydrazide group.

[0072] In particular, the hydrazide used is particulate, preferably powdered. According to an advantageous embodiment, the hydrazide is present as a powder with a particle size D50 of <50 pm, in particular <20 pm, preferably <10 pm, particularly preferably <7.5 pm, and most preferably <5 pm. The specified particle size D50 refers to 50 wt.% of the particles having a size equal to or smaller than the specified value. The particle size D50 can typically be determined by laser light scattering according to the ISO 13320:2020 standard, for example, using the CILAS 920 device from CILAS.

[0073] When used according to the invention, the hydrazide is mixed with the prepolymer, preferably such that the hydrazide is evenly distributed throughout the prepolymer. In particular, the prepolymer forms a continuous phase in which the particulate hydrazide is dispersed before curing.

[0074] The hydrazide is preferably used in a proportion of 1.5-10 parts by weight, preferably 2.0-7.5 parts by weight, especially 2.5-5.5 parts by weight, based on one part by weight of isocyanate groups contained in the prepolymer in the thermosetting polyurethane composition. This means, for example, that when using 100 grams of a prepolymer with an NCO content of 2 wt.%, preferably between 3 and 20 grams of hydrazide are used.

[0075] The hydrazide is preferably used in a proportion of 0.5 - 15 wt.%, preferably 1 - 10 wt.%, in particular 1.5 - 23.0 wt.%, based on the total weight of the thermosetting polyurethane composition.

[0076] In a preferred embodiment, the hydrazide is coated with an isocyanate monomer, in particular with a diisocyanate monomer, specifically with diphenylmethane diisocyanate monomer. In particular, the isocyanate monomer is 4,4'-diphenylmethane diisocyanate, optionally with proportions of 2,4'- and / or 2,2'-diphenylmethane diisocyanate. The coating of the isocyanate monomer forms, in particular, an encapsulation for the hydrazide. The isocyanate monomer can be used to control, and in particular increase, the activation temperature and storage stability of the polyurethane compositions.

[0077] If used, the isocyanate monomer used for the coating is chemically bonded to the hydrazide. Accordingly, it is not a free isocyanate monomer. The coating can be applied, for example, by mixing the hydrazide with the isocyanate monomer. This is especially important before mixing with the other components of the thermosetting polyurethane composition.

[0078] The isocyanate monomer has in particular a proportion of 0.01 - 1 wt.%, preferably 0.02 - 1 wt.%, in particular 0.1 - 0.3 wt.%, based on the total weight of the thermosetting polyurethane composition.

[0079] The weight ratio of isocyanate monomer to hydrazide is preferably in the range of 0.01 - 0.20, particularly 0.03 - 0.15, and most preferably 0.05 - 0.12. These proportions and ratios have proven particularly advantageous for controlling the activation temperature and storage stability of polyurethane compositions within the ranges relevant for practical use.

[0080] However, isocyanate monomers can also be omitted. In this case, the hydrazide in the polyurethane composition is preferably in direct contact with the prepolymer. Accordingly, the hydrazide is present in free and / or unencapsulated form. Direct contact between the hydrazide and prepolymer has the advantage that heat curing can be activated immediately upon liquefaction of the hydrazide, enabling targeted and rapid curing.

[0081] The hydrazide particularly preferably has a melting point of at least 75°C, preferably at least 100°C, especially at least 110°C, in particular at least 120°C, particularly preferably at least 150°C.

[0082] This allows particularly high storage stability to be achieved and at the same time segregation is effectively reduced when the hardener is only partially reacted.

[0083] According to a particularly preferred embodiment, the hydrazide comprises or consists of a dihydrazide.

[0084] The hydrazide is preferably a hydrazide of a carboxylic and / or sulfonic acid. In particular, it is a hydrazide of formula (Ia) or (Ib) or (Ic): where:

[0085] W represents the p-valent residue of a carboxylic acid after removal of p carboxylic acid groups;

[0086] X represents the q-valent radical of a sulfonic acid after removal of q sulfonic acid groups; m represents 0 or 1; p represents 1, 2, 3 or 4, preferably 2; and q represents 1, 2, 3 or 4.

[0087] In particular, the hydrazide is a carboxylic acid hydrazide, in particular a carboxylic acid dihydrazide, preferably selected from the group consisting of carbodihydrazide, oxalic acid dihydrazide, succinic acid dihydrazide, adipic acid dihydrazide, suberic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, dodecanoic acid dihydrazide and isophthalic acid dihydrazide, most preferably adipic acid dihydrazide.

[0088] Such hydrazides, which are commercially available from various suppliers, can be used to produce, among other things, polyurethane compositions with applications in a wide temperature range.

[0089] Suitable and preferred commercially available hydrazides include AJICURE® VDH (from Venture Chemical Ltd.) or Technicure® ADH (from A&C Catalysts). Furthermore, it is preferred if the polyurethane composition is free of amines blocked by aldehydes and / or ketones. In particular, the polyurethane composition is free of aldimines, ketimines, enamines, and / or oxazolidines. This can, in particular, reduce the risk of undesirable outgassing of aldehydes and / or ketones.

[0090] Conventional technical epoxy resins are suitable as epoxy resins. These are obtained in known ways, for example, by oxidizing the corresponding olefins or by reacting epichlorohydrin with the corresponding polyols, polyphenols, or amines.

[0091] In particular, the epoxy resin is a polyepoxide.

[0092] Particularly suitable as epoxy resins are so-called liquid polyepoxide resins, hereinafter referred to as "liquid resins." These have a glass transition temperature below 25°C. Also suitable as epoxy resins are so-called solid resins, which have a glass transition temperature above 25°C and can be ground into pourable powders at 25°C. However, liquid epoxy resins are preferred.

[0093] Suitable epoxy resins are in particular epoxy resins of the formula (I):

[0094] Here, the substituents R' and R" independently of one another represent either H or CH3. The index s stands for a value from 0 to 20. Compounds of the formula (I) with an index s of > 1.5, in particular from 2 to 12, are referred to as solid epoxy resins. Such solid epoxy resins are commercially available, for example, from Dow Chemical or Huntsman or Hexion.

[0095] Compounds of formula (I) with an index s between 1 and 1.5 are referred to by those skilled in the art as semisolid epoxy resins. For the purposes of the present invention, they are also considered solid epoxy resins. The term "solid epoxy resin" is well known to those skilled in the art and is used in contrast to "liquid epoxy resins."

[0096] Compounds of formula (I) with an index s between 0 and 1 are liquid epoxy resins. Preferably, s represents a value of less than 0.2.

[0097] Suitable epoxy resins are in particular aromatic epoxy resins, in particular the glycidylation products of:

[0098] - Bisphenol-A, bisphenol-F, or bisphenol-A / F, where A stands for acetone and F for formaldehyde, which served as starting materials for the production of these bisphenols. In the case of bisphenol-F, positional isomers may also be present, particularly those derived from 2,4'- or 2,2'-hydroxyphenylmethane.

[0099] - Dihydroxybenzene derivatives such as resorcinol, hydroquinone or pyrocatechol;

[0100] - other bisphenols or polyphenols such as bis(4-hydroxy-3-methylphenyl)methane, 2,2-bis(4-hydroxy-3-methylphenyl)propane (bisphenol C), bis(3,5-dimethyl-4-hydroxyphenyl)methane, 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane, 2,2-bis(4-hydroxy-3-tert.butylphenyl)propan, 2,2-Bis(4-hydroxyphenyl)butan (Bisphenol-B), 3,3-Bis(4- hydroxyphenyl)pentan, 3,4-Bis(4-hydroxyphenyl)hexan, 4,4-Bis(4- hydroxyphenyl)heptan, 2,4-Bis(4-hydroxyphenyl)-2-methylbutan, 2,4- Bis-(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutan, 1, 1-Bis(4- hydroxyphenyl)-cyclohexan (Bisphenol-Z), l,l-Bis(4-hydroxyphenyl)- 3,3,5-trimethylcyclohexan (Bisphenol-TMC), l,l-Bis(4- hydroxyphenyl)- 1-phenylethan, l,4-Bis[2-(4-hydroxyphenyl)-2- propyl]benzol (Bisphenol-P), l,3-Bis[2-(4-hydroxyphenyl)-2- propyl]benzol (Bisphenol-M), 4,4'-Dihydroxydiphenyl (DOD), 4,4'- Dihydroxybenzophenon, Bis(2-hydroxynaphth-l-yl)methan, Bis(4- hydroxynaphth-l-yl)methan, 1,5-Dihydroxynaphthalin, Tris(4- hydroxyphenyl)methan, l,l,2,2-Tetrakis(4-hydroxyphenyl)ethan, Bis(4-hydroxyphenyl)ether oder Bis(4-hydroxyphenyl)sulfon;.

[0101] - condensation products of phenols with formaldehyde obtained under acidic conditions, such as phenol novolaks or cresol novolaks, also called bisphenol F novolaks;

[0102] - aromatic amines, such as aniline, toluidine, 4-aminophenol, 4,4'-methylenediphenyldiamine, 4,4'-methylenediphenyldi-(N-methyl)amine, 4,4'-[l,4-phenylene-bis(l-methylethylidene)]bisaniline (bisaniline-P) or 4,4'-[l,3-phenylene-bis(l-methylethylidene)]bisaniline (bisaniline-M).

[0103] Other suitable epoxy resins are aliphatic or cycloaliphatic polyepoxides, in particular

[0104] - Glycidyl ethers of saturated or unsaturated, branched or unbranched, cyclic or open-chain di-, tri- or tetrafunctional Cz- to Cso-alcohols, in particular ethylene glycol, propylene glycol, butylene glycol, hexanediol, octanediol, polypropylene glycols, dimethylolcyclohexane, neopentyl glycol, dibromoneopentyl glycol, castor oil, trimethylolpropane, trimethylolethane, pentaerythrol, sorbitol or glycerol, or alkoxylated glycerol or alkoxylated trimethylolpropane;

[0105] - a hydrogenated bisphenol A, F or A / F liquid resin, or the glycidylation products of hydrogenated bisphenol A, F or A / F;

[0106] - an N-glycidyl derivative of amides or heterocyclic nitrogen bases, such as triglycidyl cyanurate or triglycidyl isocyanurate, or reaction products of epichlorohydrin with hydantoin.

[0107] - Epoxy resins from the oxidation of olefins, such as in particular vinylcyclohexene, dicyclopentadiene, cyclohexadiene, cyclododecadiene, cyclododecatriene, isoprene, 1,5-hexadiene, butadiene, polybutadiene or divinylbenzene.

[0108] A liquid resin, in particular a liquid resin based on a bisphenol, is preferred as the epoxy resin.

[0109] The most preferred epoxy resin is a liquid resin based on bisphenol A, bisphenol F, or bisphenol A / F diglycidyl ether. Such liquid resins are commercially available from companies such as Dow, Huntsman, or Momentive. These epoxy resins have an easily manageable viscosity and enable high strength and durability. Such liquid resins can also contain portions of bisphenol A solid resin or phenol novolaks.

[0110] The epoxy equivalent weight (EEW) of the epoxy resin is typically 100 g / eq - 500 g / eq, especially 130 g / eq - 250 g / eq. The epoxy equivalent weight is measured according to ASTM D1652-11 (2019). Such epoxy resins react at higher temperatures, e.g., above 150°C, and thereby lead to further crosslinking of the polyurethane composition.

[0111] The epoxy resin is used in particular in a proportion of 0.1 - 15 wt.%, preferably 1 - 10 wt.%, in particular 1.5 - 5 wt.%, most preferably 2 - 4 wt.%, based on the total weight of the thermosetting polyurethane composition.

[0112] In particular, no epoxy-amine adduct is used in the polyurethane composition, especially no epoxy-amine adduct obtainable by reacting a bisphenol diglycidyl ether with an aliphatic polyamine, and / or the polyurethane composition does not contain such an epoxy-amine adduct. The aliphatic polyamine is in particular a diamine, especially a diamine with a primary amine group and a secondary amine group and / or a diamine with a primary amine group and a tertiary amine group. In particular, the epoxy-amine adduct not used is one as described in EP 0 365 984 A2, page 5, lines 8-16. Such adducts are unsuitable for the present inventive composition.

[0113] The polyurethane composition according to the invention may optionally further contain one or more other auxiliaries and additives commonly used in the polyurethane industry as additives.

[0114] Examples of such additives are plasticizers; solvents; inorganic and organic fillers, e.g. ground or precipitated calcium carbonates, carbon blacks, kaolins, aluminum oxides, silicas and / or PVC powder; fibers, e.g. made of polyethylene; pigments; rheology modifiers, e.g. thixotropic agents, thickeners such as urea compounds, polyamide waxes, bentonites or pyrogenic silicas; adhesion promoters, in particular silanes such as epoxysilanes, vinylsilanes and isocyanatosilanes; drying agents, e.g. p-tosyl isocyanate and other reactive isocyanates, orthoformic acid esters, calcium oxide or molecular sieves; stabilizers against heat, light and UV radiation; flame-retardant substances; surface-active substances such as wetting agents, leveling agents, deaerating agents or defoamers; and fungicides or substances that inhibit fungal growth.

[0115] The additives can be added in suitable amounts as needed and depending on the intended application. As a rule, it is preferred that the polyurethane composition contains at least one plasticizer and / or at least one filler.

[0116] The plasticizer is selected, for example, from carboxylic acid esters such as phthalates, in particular diisononyl phthalate (DINP), diisodecyl phthalate (DIDP) and / or di(2-propylheptyl)phthalate (DPHP); hydrogenated phthalates, in particular hydrogenated diisononyl phthalate (DINCH); terephthalates, in particular dioctyl terephthalate; trimellitates, in particular trioctyl trimellitate; adipates, in particular dioctyl adipate; azelates; sebacates; polyols, in particular polyoxyalkylene polyols and / or polyester polyols; benzoates; glycol ethers; glycol esters; organic phosphoric, phosphonic and / or sulfonic acid esters; polybutenes, polyisobutenes; and / or plasticizers derived from natural fats or oils, in particular epoxidized soybean and / or linseed oil.

[0117] The plasticizer preferably has a vapor pressure of less than 0.1 mbar at 20°C and / or the plasticizer has a boiling point of at least 250°C, preferably at least 300°C, especially at least 350°C, at atmospheric pressure of 101,325 kPa. This prevents, in particular, the plasticizer from excessively outgassing at higher curing temperatures, e.g., above 180°C.

[0118] The plasticizer is particularly preferably selected from phthalates and / or trimellitates, in particular diisodecyl phthalate (DIDP) and / or trioctyl trimellitate. These have proven particularly advantageous for the present thermosetting polyurethane composition. The plasticizer is preferably used in a proportion of 0.1-30 wt.%, preferably 5-25 wt.%, in particular 10-20 wt.%, based on the total weight of the thermosetting polyurethane composition.

[0119] The thermosetting polyurethane composition further preferably contains one or more stabilizers against heat, oxygen, moisture, light, and / or UV radiation. Suitable stabilizers include, for example, hindered amines (HALS stabilizers), hindered phenols, phosphites, and / or aromatic amines. Such stabilizers are commercially available, for example, under the product names IRGANOX, KINOX, DOVERNOX, WESTON, IRGAPHOS, DOVERPHOS, and / or IONOL.

[0120] Phosphites, especially organophosphites, are particularly preferred as stabilizers. Organophosphites, also known as phosphite esters, in particular contain one or more groups of the formula (II):

[0121] R 1 , R 2 and R 3Each independently represents an organic residue, for example, with 1-25 carbon atoms. The organic residues can contain one or more heteroatoms or consist exclusively of carbon and hydrogen atoms.

[0122] Preferably, at least one of the radicals R 1 , R 2 and R 3 an aromatic group.

[0123] In particular, the stabilizer is an organodiphosphite which has two groups of formula II.

[0124] Such phosphite stabilizers are commercially available, for example, under the name DOVERPHOS®. Surprisingly, it has been shown that phosphites can further reduce any discoloration of polyurethane compositions, which in this case is typically very slight even at curing temperatures of 200°C and above. In contrast, stabilizers in the form of phenols are less suitable for stabilization at such high curing temperatures.

[0125] The proportions of the components in the polyurethane composition can vary widely depending on the components used and the intended use. The following quantities for practical and preferred embodiments refer to the total weight of the polyurethane composition.

[0126] The thermosetting polyurethane composition particularly preferably comprises the following components based on the total weight of the thermosetting polyurethane composition: a) 0.5 - 15% by weight, preferably 1 - 10% by weight, in particular 1.5 - 3.0% by weight, of the hydrazide; b) 0.1 - 15% by weight, preferably 1 - 10% by weight, in particular 2 - 5% by weight, of the epoxy resin; c) 15 - 70% by weight, preferably 20 - 50% by weight, in particular 25 - 40% by weight, of the prepolymer; d) 0 - 1% by weight, preferably 0.02 - 1% by weight, in particular 0.1 - 0.3% by weight, of the isocyanate monomer; e) 0 - 70 wt.%, preferably 10 - 60 wt.%, in particular 40 - 50 wt.%, of inorganic and / or organic fillers, in particular as described above; f) 0 - 30 wt.%, preferably 5 - 25 wt.%, in particular 10 - 20 wt.%, of plasticizers, in particular as described above; g) 0 - 5 wt.%; preferably 0.5 - 4 wt.%, in particular 1 - 3 wt.-%, stabilizers, in particular as described above, preferably phosphites; h) 0 - 1 wt.%, preferably 0.01 - 0.8 wt.%, in particular 0.05 - 0.6 wt.%, catalysts; i) Optionally one or more additional additives, the proportions of which add up to 100 wt.%.

[0127] The prepolymer and the other components of the composition used can be mixed together in any order to obtain the polyurethane composition. Some components, such as the hydrazide, which is optionally coated with the isocyanate monomer, can also be added as a mixture with a plasticizer, for example. Mixing can take place at room temperature (e.g. 23°C). It can also be carried out partially or completely at a slightly elevated temperature, for example to facilitate homogenization or dispersion. All mixing devices known in the field can be used as mixing devices. The viscosity can be adjusted as desired, taking the intended use into account; for example, the polyurethane composition can be pasty and preferably have pseudoplastic properties.

[0128] The invention also relates to a heat-curable polyurethane composition as obtained in the use according to the invention.

[0129] In other words, it is a thermosetting polyurethane composition comprising: (i) an isocyanate-terminated prepolymer composed of at least one polyisocyanate and at least one polyol, (ii) a hydrazide, and (iii) an epoxy resin. Optionally, one or more of the other components described above may also be present.

[0130] All above information and explanations regarding the use according to the invention and the thermosetting polyurethane composition, e.g. regarding suitable components, etc., apply accordingly.

[0131] The thermosetting polyurethane composition can be a multi-component, e.g., two-component, thermosetting polyurethane composition. However, it is preferably a single-component thermosetting polyurethane composition.

[0132] The polyurethane composition, preferably the one-component polyurethane composition, is generally suitable for bonding one or more materials of the same or different nature, and in particular for bonding in vehicle construction or vehicle repair. The polyurethane composition is also suitable as a sealant for sealing an element, in particular for sealing in vehicle construction or vehicle repair. The element is, for example, a substrate, a surface, a joint, and / or a cavity.

[0133] The invention also relates to a process for curing a polyurethane composition as described above, wherein the polyurethane composition is cured by the action of heat.

[0134] The temperature used for heat curing can vary widely depending on the polyurethane composition used, the desired degree of crosslinking and the duration of heat curing. Heat curing can be carried out, for example, at temperatures in the range from 100 to 220°C. The duration of heat curing can be, for example, in the range from 1 to 120 minutes. The invention also relates to a process for bonding adherends, in particular vehicle parts, using the heat-curable polyurethane composition according to the invention as described above, comprising: a) applying the heat-curable polyurethane composition to one or both adherend surfaces to be bonded, b) contacting the adherend surfaces to be bonded and c) curing the polyurethane composition by heat curing, in particular at temperatures as described above.

[0135] The invention further relates to a method for sealing an element to be sealed with the thermosetting polyurethane composition according to the invention as described above, comprising: a) applying the thermosetting polyurethane composition onto and / or into the element to be sealed; b) curing the polyurethane composition by heat curing, in particular at temperatures as described above.

[0136] The element to be sealed is, in particular, a substrate, a surface, a joint, and / or a cavity, in particular of a vehicle. In step a), the thermosetting polyurethane composition can be applied to the substrate or surface and / or introduced into the joint and / or cavity.

[0137] The parts to be bonded, or the surfaces to be bonded, and / or the element to be sealed, can be made of any material, and the surfaces to be bonded can be made of the same or different materials. Examples of suitable materials include metal, metal alloys, glass, plastic, ceramics, textiles, or painted elements or parts to be bonded.

[0138] The thermosetting polyurethane composition can be applied to one or both of the surfaces to be bonded or to the element to be sealed in a conventional manner known to those skilled in the art. The surfaces to be bonded are brought into contact, with the surfaces to be bonded being pressed against each other if necessary.

[0139] The curing of the polyurethane composition is then carried out by heat curing, e.g. at temperatures in the range of 100 to 220°C, in particular in the temperature range between 150°C and 220°C.

[0140] The invention also relates to an article comprising joining parts and a cured polyurethane composition as an adhesive bond between the joining parts, which article is obtainable by the process according to the invention. The joining parts are, in particular, components of a vehicle.

[0141] The invention also relates to an element, in particular of a vehicle, with a cured polyurethane composition as described above as a sealing compound.

[0142] In the following, the invention is further explained by examples, which are not intended to limit the invention in any way.

[0143] Examples

[0144] The following examples are intended to further illustrate the described invention. Of course, the invention is not limited to these described examples. Unless otherwise stated, the chemicals used were purchased from Sigma-Aldrich (Switzerland).

[0145] Production of prepolymers:

[0146] Polymer P1 :

[0147] 780.0 g of Desmophen® 5031 BT (glycerol-initiated ethylene oxide-terminated polyoxypropylene triol, OH number 28.0 mg KOH / g, OH functionality approx. 2.3; from Covestro) and 220 g of 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (Vestanat® IPDI, from Evonik) were reacted according to a known process at 80 °C to form a polyetherurethane polymer with an NCO content of 6.4 wt.%, a viscosity of 4.1 Pa s at 20 °C and a monomeric IPDI content of approx. 12 wt.%.

[0148] Subsequently, the volatile components, especially the majority of the monomeric IPDI, were removed by distillation in a short-path evaporator (jacket temperature 160 °C, pressure 0.1 to 0.005 mbar). The resulting polyetherurethane polymer had an NCO content of 1.9 wt.%, a viscosity of 8.2 Pa s at 20 °C, and a monomeric IPDI content of 0.02 wt.%.

[0149] Polymer P1 is a prepolymer (isocyanate group-containing polymer) with a low content of monomeric diisocyanates.

[0150] The viscosity was measured using a thermostatted cone-plate viscometer Rheotec RC30 (cone diameter 25 mm, cone angle 1 °, cone tip-plate distance 0.05 mm, shear rate 10 s -1 ) measured.

[0151] The content of monomeric diisocyanate was determined by HPLC (photodiode array detection; 0.04 M sodium acetate / acetonitrile as mobile phase) after prior derivation using N-propyl-4-nitrobenzylamine. Polyurethane compositions

[0152] The ingredients listed in Table 1 were mixed in the specified amounts (in parts by weight) using a planetary mixer under vacuum and moisture exclusion to form one-component polyurethane

[0153] Compositions R and C1 - C5 are mixed and stored under exclusion of moisture until use.

[0154] Table 1 : Polyurethane compositions (numbers in wt%)

[0155] 1 Adipic acid dihydrazide coated with diphenylmethane diisocyanate

[0156] (Desmodur CD-L from Covestro) by mixing the two components at 23°C and stirring for 10 minutes under vacuum

[0157] 1 aContent of total adipic acid dihydrazide used (before coating)

[0158] 1 b Amount of isocyanate monomer used for coating

[0159] 2 Araldite GY 250 (from Huntsman)

[0160] 3 Omyacarb® 5 GU (from Omya)

[0161] 4 Trioctyl trimellitate

[0162] 5 Diisodecyl phthalate

[0163] 6 Cab-O-Sil TS-720 (hydrophobic silica; Cabot Corp.)

[0164] 7 Titanium dioxide (Kronos 2220 from Kronos) The compositions could be stored without problems for several months at temperatures up to 60°C.

[0165] Test without coating of hydrazide with isocyanate monomer

[0166] An additional composition, C6, was prepared, but in which the hydrazide was not coated with isocyanate monomer. Composition C6 was formulated identically to composition C5, with the differences that 1.73 wt.% pure hydrazide (without prior treatment with isocyanate monomer) was used, and 13.77 wt.% plasticizer was used to compensate for the mass difference due to the missing isocyanate monomer. Thus, C6 differs from C5 essentially only in that the hydrazide is not coated with isocyanate monomer.

[0167] Heat curing of samples and properties

[0168] Films of compositions R and C1-C6 with a layer thickness of 2 mm were cured at various curing temperatures for 30 minutes and stored for 7 days under standard conditions (23°C, 50% relative humidity). No oily liquid or similar leakage occurred from the cured products either during or after heat curing.

[0169] Tensile strength, elongation at break, and Young's modulus were then determined according to DIN 53504 (tensile speed: 200 mm / min). Table 2 provides an overview of the results.

[0170] Films with compositions C1 - C2, which contain hydrazide and epoxy resin as hardeners, can be cured at temperatures between 100 - 200°C. The tensile strength, elongation at break, and modulus of elasticity remain within practical ranges across the entire temperature range. For films with compositions C2, C3, C4, and C5, this is even the case up to 220°C. The modulus of elasticity, in particular, is relatively constant, with the film with composition C4 exhibiting a particularly stable modulus of elasticity across the entire temperature range and, at the same time, relatively high values ​​for tensile strength and elongation at break.

[0171] In contrast, the Young's modulus of comparative sample R is only 1.5 MPa at 200°C, while at 220°C, no measurable values ​​are available («nm»). However, the described embodiments are merely illustrative examples, which can be modified as desired within the scope of the invention.

[0172] Table 2: Properties of polyurethane compositions

[0173] The storage stability of the compositions in the container can be determined by the extrusion force.

[0174] To determine the extrusion force, the compositions were filled into internally coated aluminum cartridges (outer diameter 46.9 mm, inner diameter 46.2 mm, length 215 mm, opening 15-M) and hermetically sealed with a polyethylene plug (diameter 46.1 mm) from Novelis Deutschland GmbH. After conditioning for 24 hours at 23°C, the cartridges were opened and extruded using a dispensing device. For this purpose, a nozzle with a 2 mm inner diameter opening was screwed onto the cartridge thread. Using a dispensing device (Zwick / Roell Z005), the force required to extrude the composition at an extrusion speed of 60 mm / min was determined. The stated value is an average of the forces measured after extrusion travels of 22 mm, 24 mm, 26 mm, and 28 mm. The measurement was stopped after 30 mm of extrusion travel.

[0175] To test storage stability, compositions C5 and C6 were each filled into cartridges as described above. In the fresh state, composition C5 exhibited an extrusion force of 893 N. Composition C6 exhibited an extrusion force of 885 N in the fresh state. Another sealed cartridge each of composition C5 and composition C6 was stored in an oven at 60°C for 7 days to simulate in-container aging.

[0176] After this heat storage, the cartridges were cooled to 23°C for 24 hours and their extrusion force was measured again as described above. Composition C5 showed a moderate increase in extrusion force to 1029 N. Composition C6, in contrast, showed an extrusion force of 3500 N.

[0177] This shows that coating the hydrazide with isocyanate monomer results in a significant improvement in storage stability.

Claims

Patent claims 1 . Use of a hydrazide having a melting point of at least 65°C as a hardener for heat curing in a heat-curable polyurethane composition comprising a prepolymer having isocyanate end groups obtained from at least one polyisocyanate and at least one polyol, and at least one epoxy resin.

2. Use according to claim 1, wherein the hydrazide is a carboxylic acid hydrazide, in particular a carboxylic acid dihydrazide, preferably selected from the group consisting of carbodihydrazide, oxalic acid dihydrazide, succinic acid dihydrazide, adipic acid dihydrazide, suberic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, dodecanoic acid dihydrazide and isophthalic acid dihydrazide, most preferably adipic acid dihydrazide.

3. Use according to at least one of claims 1 or 2, wherein the hydrazide is coated with an isocyanate monomer, in particular with a diisocyanate monomer, especially with diphenylmethane diisocyanate.

4. Use according to claim 3, wherein a weight ratio of isocyanate monomer to hydrazide is in the range of 0.01 - 0.20, in particular 0.03 - 0.15, especially 0.05 - 0.

12.

5. Use according to at least one of claims 1 to 4, wherein the hydrazide is used in a proportion of 1.5 - 10 parts by weight, preferably 2.0 - 7.5 parts by weight, in particular 2.5 - 5.5 parts by weight, based on one part by weight of isocyanate groups in the prepolymer contained in the thermosetting polyurethane composition.

6. Use according to at least one of claims 1 to 5, wherein the epoxy resin is a polyepoxide, in particular a diglycidyl ether of bisphenol A, bisphenol F and / or bisphenol A / F.

7. Use according to at least one of claims 1 to 6, wherein the epoxy resin is used in a proportion of 0.1 - 15 wt.%, preferably 1 - 10 wt.%, in particular 2 - 5 wt.%, based on the total weight of the thermosetting polyurethane composition.

8. Use according to at least one of claims 1 to 7, wherein a plasticizer is additionally used, wherein the plasticizer preferably has a vapor pressure of less than 0.1 mbar at 20°C and / or a boiling point of at least 250°C, preferably at least 300°C, in particular at least 350°C, at normal pressure of 101,325 kPa.

9. Use according to claim 8, wherein the plasticizer is selected from phthalates and / or trimellitates, in particular diisodecyl phthalate (DIDP) and / or trioctyl trimellitate.

10. Use according to at least one of claims 8 or 9, wherein the plasticizer is used in a proportion of 0.1 - 30 wt.%, preferably 5 - 25 wt.%, in particular 10 - 20 wt.%, based on the total weight of the thermosetting polyurethane composition.

11. Use according to at least one of claims 1 to 10, wherein the prepolymer with isocyanate end groups consists of at least one polyisocyanate and at least one polyol and has a content of monomeric polyisocyanates, in particular monomeric diisocyanates, of at most 0.5% by weight, preferably at most 0.3% by weight, in particular at most 0.2% by weight, especially at most 0.1% by weight. Use according to at least one of claims 1 to 11, wherein the thermosetting polyurethane composition has the following components based on the total weight of the thermosetting polyurethane composition: a) 0.5-15% by weight, preferably 1-10% by weight, in particular 1.5-3.0% by weight, of the hydrazide; b) 0.1-15% by weight, preferably 1-10% by weight, in particular 2-5% by weight, of the epoxy resin; c) 15-70% by weight, preferably 20-50% by weight, in particular 25-40% by weight, of the prepolymer; d) 0-1 wt.%, preferably 0.02-1 wt.%, in particular 0.1-0.3 wt.%, of the isocyanate monomer; e) 0-70 wt.%, preferably 10-60 wt.%, in particular 40-50 wt.%, of inorganic and / or organic fillers; f) 0-30 wt.%, preferably 5-25 wt.%, in particular 10-20 wt.%, of plasticizers; g) 0-5 wt.%, preferably 0.5-4 wt.%, in particular 1-3 wt.%, of stabilizers; h) 0-1 wt.%, preferably 0.01-0.8 wt.%, in particular 0.05 - 0.6 wt.%, catalysts; i) Optionally one or more additional additives. Use according to any one of claims 1 to 12, wherein the polyurethane composition is a one-component composition, in particular a one-component adhesive and / or sealant, particularly preferably for vehicle construction. A thermosetting polyurethane composition, in particular as described in any one of the preceding claims and / or obtainable by the use according to any one of the preceding claims, comprising: (i) a prepolymer with isocyanate end groups composed of at least one polyisocyanate and at least one polyol, (ii) a Hydrazide and (iii) an epoxy resin. A process for curing a polyurethane composition according to claim 14, wherein the polyurethane composition is cured by exposure to heat, in particular in the temperature range between 150°C and 220°C.

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