Thermosetting polyurethane composition with wide temperature window

Abstract

A hydrazide having a melting point of at least 65 DEG C is used as a curing agent for thermocuring in a thermocuring 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. A heat-curable polyurethane composition is obtained by said combination, which has improved storage stability and can be cured over a wide temperature range and has constant mechanical properties.

Description

Technical Field

[0001] The present invention relates to the use of a curing agent in a heat-curing polyurethane composition for heat curing. The present invention also relates to a heat-curing polyurethane composition and a method for curing the composition. Background Art

[0002] 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 can be made between one-component (1K) and two-component (2K) polyurethane (PUR) compositions. For 1K polyurethane compositions, in which all components are contained in one component, a further distinction can be made between moisture-curing compositions, which cure under the influence of air moisture, and heat-curing compositions, which cure by heating.

[0003] For example, WO 2009 / 080738 A1 (Sika Technology AG) describes a moisture-curing polyurethane composition comprising polyisocyanates and amines blocked with the aid of aldehydes or ketones as moisture-activatable crosslinkers. The composition cures with moisture at room temperature or slightly elevated temperatures (especially below 40° C.) to form aldehydes and / or ketones. In order to significantly reduce undesirable outgassing of aldehydes and ketones in the cured state, the composition contains hydrazides which react with aldehydes and / or ketones at temperatures above 80° C. to form less volatile components.

[0004] Heat-curing polyurethane compositions are primarily used as adhesives and sealants in industrial production. They are used in particular as sealants in vehicle construction, wherein the heat-curing polyurethane compositions are cured, for example after the painting of the components together with the paint curing, usually at temperatures >110° C. in corresponding curing ovens.

[0005] In heat-curing polyurethane compositions, thermally unstable curing agents or heat-activatable curing agents are used which initiate the curing process of the composition at a defined temperature.

[0006] For example, EP 0 255 572 A1 (Sika AG) describes a one-component adhesive and / or sealant comprising a polyurethane-based prepolymer and a heat-activatable hardener, wherein the stoichiometric ratio between prepolymer and hardener is selected such that only partial crosslinking occurs upon heating to temperatures of 60 to 180° C. and a product having highly viscous to plastic properties is obtained. Mention may be made of dicyandiamide or a sodium chloride complex salt of 4,4′-diaminodiphenylmethane as hardener.

[0007] However, a common problem with the currently known heat-curing polyurethane compositions is that these compositions must cure within a relatively narrow temperature window. If the temperature is too low, there is generally a risk that the curing agent will not react completely, which can lead to the curing agent oozing out of the cured product in the form of an oily liquid. Conversely, if the temperature is too high, there is a risk of undesirable strong discoloration. In addition, polyurethane compositions are generally unstable at high temperatures and begin to decompose at temperatures above 180° C. (up to 200° C. at the latest). This manifests itself as a significant loss of mechanical properties (e.g. tensile strength).

[0008] Furthermore, known heat-curing polyurethane compositions are often based on problematic substances, such as 4,4′-methylenedianiline, which is classified as a substance of very high concern (SVHC) according to the REACH regulation, or they have insufficient storage stability.

[0009] There is therefore a constant need for improved solutions which have none or only a few of the above-mentioned disadvantages. Summary of the invention

[0010] Therefore the object of the present invention is to provide a kind of improvement scheme of heat-curing polyurethane composition, it can overcome the above-mentioned shortcomings and is particularly suitable as one-component adhesive and / or sealant composition.Described composition should be curable in the temperature window as wide as possible.This especially makes it possible to reliably guarantee the mechanical properties of the cured product basically or at least independently of the curing temperature to a great extent.In addition, be committed to making the composition show as little discoloration as possible under high curing temperature, and will not obviously lose its mechanical properties, and the composition is as stable as possible in terms of separation or segregation of components.Especially, even in the case of only partial heat curing reaction or incomplete heat curing reaction, for example, when the curing temperature is too low, separation or precipitation of components may also occur.Finally, even at higher ambient temperature, composition should also be stored stably for as long as possible.

[0011] Surprisingly, it has been found that this object can be achieved by the use according to claim 1. 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-curing 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.

[0012] It has been found that hydrazides can be used as curing agents in one-component polyurethane compositions, which contain at least one prepolymer having isocyanate end groups in combination with an epoxy resin, and produce unexpected advantages. Thus, storage-stable one-component polyurethane compositions can be provided, which are suitable as adhesives and / or sealants and can be cured in a wide temperature window, in particular in the range of 100-220° C., by heat curing in a targeted manner, and have excellent mechanical properties and are not prone to discoloration when cured over the entire temperature range. The storage stability is storage stability at room temperature to 60° C.

[0013] It is presumed that this is because the hydrazide used as curing agent can lead to effective curing even at relatively low curing temperatures starting from above the melting point of the hydrazide, while the epoxy resin used at the same time does not have an adverse effect on this process. In particular, at higher temperatures, for example above 150° C., the epoxy resin may promote curing by reacting with other components of the composition (such as hydrazide) and crosslinking. It is particularly surprising that the use of a combination of hydrazide and epoxy resin during curing at high temperatures according to the present invention leads to less noticeable discoloration in the cured product and better temperature stability of the mechanical properties compared to the currently known heat-curing polyurethane compositions.

[0014] Also obtainable is a composition which is stable in terms of component separation even in the case of an incomplete heat curing reaction, such as occurs at too low a curing temperature. In particular, the problem of oily liquid seeping out of the cured product can be effectively avoided.

[0015] This is probably because hydrazide has a relatively high melting point, which ensures that any unreacted curing agent remains in the cured product in an unreacted state. Therefore, even when a certain proportion of the prepolymer in the heat-curable composition is cured by moisture before the actual heat curing so that the ratio of available prepolymer to curing agent changes, the excess curing agent does not cause segregation problems.

[0016] Even at high curing temperatures of up to 220° C., discoloration, which is common in polyurethane compositions, rarely occurs and can be largely avoided by stabilizers, in particular phosphite stabilizers.

[0017] The polyurethane compositions obtained according to the invention have particularly stable mechanical properties, in particular with regard to the modulus of elasticity, over the entire range of use (and in particular at curing temperatures of up to 220° C.).

[0018] 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 avoided or unexpectedly advantageous alternatives can be provided.

[0019] Furthermore, the polyurethane compositions obtained adhere very well to metallic substrates and to various coatings, in particular to coatings which are applied, for example, by cathodic dip coating, for example in vehicle construction.

[0020] The polyurethane compositions obtained by the use according to the invention are particularly useful as adhesives and sealants in industrial production, in particular as sealants in vehicle construction, which compositions can be cured in corresponding curing ovens, for example on freshly painted parts, together with the curing of the paint.

[0021] Further aspects of the invention are the subject matter of further independent claims. Particularly preferred embodiments of the invention are the subject matter of the dependent claims. DETAILED DESCRIPTION

[0022] A first aspect of the present invention relates to the use of a hydrazide-bonded epoxy resin having a melting point of at least 65° C. as a heat-curing curing agent in a heat-curing polyurethane composition comprising a prepolymer having isocyanate end groups obtained from at least one polyisocyanate and at least one polyol.

[0023] Compound names beginning with "poly" denote substances containing two or more of the functional groups that appear in their names per molecule. Such compounds may be monomeric, oligomeric or polymeric compounds. Polyols are, for example, compounds having two or more hydroxyl groups. Polyisocyanates are compounds having two or more isocyanate groups.

[0024] Isocyanate-reactive compounds are compounds having at least one isocyanate-reactive group which can react with an isocyanate group to form a chemical bond.

[0025] A one-component polyurethane composition refers to a composition in which the components are present in one component. Generally speaking, a one-component composition is storage stable at room temperature (e.g. 23° C.) and when a moisture curing system is present, at least for a certain period of time (e.g. at least 1 day or at least 1 month) under conditions of excluding air moisture.

[0026] The term "storage-stable" refers to the property of a substance or composition that it can be stored in a suitable container at room temperature for several weeks to 6 months or more without its application properties or use properties changing due to storage to an extent relevant to its use.

[0027] The average molecular weight here denotes the number average molecular weight (Mn), which can be determined by gel permeation chromatography (GPC) relative to polystyrene standards.

[0028] Thermal curing is understood to mean curing at elevated temperatures, for example of at least 80° C., in particular of at least 100° C., especially of more than 120° C. Thermal curing is particularly carried out at temperatures above the melting point of the hydrazide.

[0029] In the case of thermal curing, the polyurethane composition is cured in its entirety at the same time after application. In contrast, in the case of moisture curing, diffusion-controlled curing of the polyurethane composition takes place after application from the outside inwards. Moisture curing is understood to be curing by moisture, in particular air moisture. Moisture curing is generally carried out at a temperature of not more than 40° C., with moisture curing usually taking place at room temperature, i.e., for example, at a temperature below 35° C. (e.g., about 23° C.).

[0030] All statements made below, in particular with respect to the polyurethane composition, the process and the use, of course, also apply to the use according to the invention, the process according to the invention, the products obtainable therefrom and the adhesive and / or sealant composition according to the invention, even if not indicated otherwise.

[0031] The polyurethane composition of the present invention comprises a prepolymer having isocyanate end groups formed from at least one polyisocyanate and at least one polyol. A mixture of two or more such prepolymers may also be used. Prepolymers having isocyanate end groups are known to those skilled in the art. The prepolymer has at least two isocyanate end groups, preferably exactly two isocyanate end groups. Through the isocyanate end groups, the prepolymer can be chain-extended or cross-linked by reacting with a compound having an isocyanate-reactive group (e.g., water, hydroxyl or amino group), which results in the curing of the polyurethane composition. The term "curing" or "cross-linking" hereinafter also includes chain-extending reactions.

[0032] Prepolymers having isocyanate end groups formed from at least one polyisocyanate and at least one polyol are polyurethane prepolymers, which are prepared by reaction of at least one polyisocyanate and at least one polyol. Those skilled in the art can easily prepare such prepolymers.

[0033] The reaction of at least one polyol with at least one polyisocyanate can be carried out, for example, by reacting the polyol component and the polyisocyanate component by conventional methods, for example at a temperature of 50 to 100° C., optionally in the presence of a suitable catalyst, wherein the polyisocyanate is used in a stoichiometric excess. Admixtures, such as solvents and / or plasticizers, can be optionally added to the reaction mixture as required. The resulting reaction product is a prepolymer with isocyanate end groups. If a solvent is used, the solvent can be removed again after the reaction. If a plasticizer is used, it can preferably be retained in the product obtained.

[0034] The polyisocyanate used to form the prepolymer with isocyanate end groups is preferably a polyisocyanate selected from aliphatic polyisocyanates and / or aromatic polyisocyanates, in particular a diisocyanate. One such polyisocyanate or two or more such polyisocyanates can be used. Aliphatic polyisocyanates are preferred.

[0035] Aliphatic polyisocyanates are aliphatic compounds having at least two isocyanate groups. Aliphatic diisocyanates are preferred. They may be acyclic or cyclic aliphatic polyisocyanates, with cyclic aliphatic polyisocyanates being preferred. Saturated aliphatic polyisocyanates are preferred. These polyisocyanates are known and commercially available.

[0036] 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-1,3- and 1,4-diisocyanate and mixtures of these isomers, isophorone diisocyanate (IPDI, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane), 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 above isocyanates. Particularly preferred are isophorone diisocyanate (IPDI) and hexamethylene-1,6-diisocyanate (HDI).

[0037] Examples of suitable aromatic polyisocyanates are 4,4′-diphenylmethane diisocyanate, optionally with a content of 2,4′- and / or 2,2′-diphenylmethane diisocyanate (MDI), 2,4-toluene diisocyanate or mixtures thereof with 2,6-toluene diisocyanate (TDI), 1,4-phenylene diisocyanate (PDI) and / or naphthalene-1,5-diisocyanate (NDI).

[0038] Particularly preferred polyisocyanates are 4,4′-diphenylmethane diisocyanate, optionally with a content of 2,4′- and / or 2,2′-diphenylmethane diisocyanate (MDI), 2,4-toluene diisocyanate or mixtures thereof with 2,6-toluene diisocyanate (TDI) and / or isophorone diisocyanate (IPDI).

[0039] To form the prepolymer with isocyanate end groups, at least one polyisocyanate is reacted with one or more polyols. All polyols common to polyurethane chemistry can be used. A wide variety of suitable polyols are commercially available.

[0040] The polyol preferably has a medium molecular weight or, if it is a non-polymeric polyol, has a molecular weight of 250 to 30 000 g / mol, preferably 400 to 20 000 g / mol.

[0041] The polyols also preferably have an average OH functionality in the range from 1.6 to 3. It will be appreciated that the polymer compounds may also contain substances formed by side reactions which, for example, have only one hydroxyl group or have no hydroxyl groups.

[0042] The polyol is preferably a diol or triol having an OH value of 8 to 185 mg KOH / g, in particular 10 to 120 mg KOH / g.

[0043] As polyols, for example, the following commercially available polyols or mixtures thereof may be used:

[0044] a) Polyoxyalkylene polyols (also known as polyether polyols or oligoether alcohols), which are polymerization products of ethylene oxide, 1,2-propylene oxide, 1,2- or 2,3-butylene oxide, oxetane, tetrahydrofuran or mixtures thereof, optionally with the aid of starter molecules having two or more active hydrogen atoms, for example water, ammonia or compounds having a plurality of OH- or NH-groups, for example 1,2-ethanediol, 1,2- and 1,3-propylene glycol, neopentyl glycol, diethylene glycol, triethylene glycol, the isomeric dipropylene glycols and tripropylene glycols, the isomeric butanediols, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, undecanediol, 1,3- and 1,4-cyclohexanedimethanol, bisphenol A, hydrogenated bisphenol A, 1,1,1-trimethylolethane, 1,1,1-trimethylolpropane, glycerol, aniline, and mixtures thereof. It is possible to use polyoxyalkylene polyols having a low degree of unsaturation (measured in accordance with ASTM D-2849-69 and expressed in milliequivalents of unsaturation per gram of polyol (mEq / g)), prepared, for example, with the aid of so-called double metal cyanide complex catalysts (DMC catalysts), but also polyoxyalkylene polyols having a higher degree of unsaturation, prepared, for example, with the aid of anionic catalysts such as NaOH, KOH, CsOH or alkali metal alcoholates.

[0045] Particularly suitable are polyoxyalkylene diols or triols, in particular polyoxyethylene and polyoxypropylene diols and triols. Particularly suitable are polyoxyalkylene diols and triols having an unsaturation of less than 0.02 mEq / g and an average molecular weight in the range of 1000 to 30000 g / mol, and polyoxypropylene diols and triols having an average molecular weight of 400 to 8000 g / mol.

[0046] Likewise particularly suitable are so-called ethylene oxide-terminated ("EO-endcapped") polyoxypropylene polyols. The latter are in particular polyoxypropylene polyoxyethylene polyols which are obtained, for example, by further alkoxylating pure polyoxypropylene polyols, in particular polyoxypropylene diols and triols, with ethylene oxide after the polypropoxylation reaction has ended, thus providing them with primary hydroxyl groups.

[0047] b) Styrene-acrylonitrile- or acrylonitrile-methyl methacrylate-grafted polyether polyols.

[0048] c) Polyester polyols, also called oligoesterols, prepared by known processes, in particular the polycondensation of hydroxycarboxylic acids or of aliphatic and / or aromatic polycarboxylic acids with diols or polyols.

[0049] Particularly suitable polyester polyols are those prepared from dihydric to trihydric (especially 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, dimerized fatty glycols (dimer glycol), neopentyl glycol hydroxypivalate, glycerol , 1,1,1-trimethylolpropane or a mixture of the above alcohols, the organic dicarboxylic acid or tricarboxylic acid or its anhydride or ester is, for example, succinic acid, glutaric acid, adipic acid, trimethyl adipic 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 a mixture of the above acids, and a polyester polyol prepared from a lactone and an initiator, the lactone is, for example, ε-caprolactone, and the initiator is, for example, the above diol or triol.

[0050] d) Polycarbonate polyols, such as those obtainable, for example, by reaction of the abovementioned alcohols (used for the synthesis of the polyester polyols) with dialkyl carbonates, diaryl carbonates or phosgene.

[0051] e) Block copolymers carrying at least two hydroxyl groups, which have at least two different blocks having a polyether, polyester and / or polycarbonate structure of the abovementioned type, in particular polyether polyester polyols.

[0052] f) Polyacrylate polyols and polymethacrylate polyols.

[0053] 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 epoxy polyesters or epoxy polyethers obtained by epoxidation of unsaturated oils and subsequent ring opening with carbonic acid or alcohols, or polyols obtained by hydroformylation and hydrogenation of unsaturated oils; or polyols obtained from natural fats and oils by decomposition processes (for example alcoholysis or ozonolysis) and subsequent chemical bonding (for example by transesterification or dimerization) of the decomposition products obtained or their derivatives. Suitable decomposition products of natural fats and oils are in particular fatty acids and fatty alcohols and fatty acid esters, in particular methyl esters (FAME), which can be derivatized to hydroxy fatty acid esters, for example by hydroformylation and hydrogenation.

[0054] h) Polyolefin polyols, also known as oligomeric hydrocarbon alcohols, such as polyhydroxy-functional polyolefins, polyisobutenes, polyisoprenes; polyhydroxy-functional ethylene-propylene copolymers, ethylene-butylene copolymers or ethylene-propylene-diene copolymers; polyhydroxy-functional polymers of dienes, in particular 1,3-butadiene, which can also be prepared in particular by 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, such as polyhydroxy-functional acrylonitrile / butadiene copolymers, such as those which can be prepared, for example, by epoxide- or amino alcohol- and carboxyl-terminated acrylonitrile / butadiene copolymers; and hydrogenated polyhydroxy-functional diene polymers or copolymers.

[0055] In the reaction between polyisocyanate and polyol, the NCO / OH ratio is preferably in the range of 2 / 1 to 10 / 1, particularly preferably in the range of 3 / 1 to 8 / 1, in particular in the range of 4 / 1 to 7 / 1.

[0056] Preferably, the NCO content of the prepolymer is in the range from 0.5 to 10% by weight, preferably from 0.6 to 8.4% by weight, in particular from 0.8 to 7% by weight.

[0057] In particular, the prepolymer having isocyanate end groups, which is formed from 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 and especially at most 0.1% by weight.

[0058] Prepolymers preferably used are those formed with isophorone diisocyanate (IPDI) and / or 2,2′-diphenylmethane diisocyanate (MDI); the prepolymers having a content of monomeric polyisocyanates (especially monomeric diisocyanates) of up to 0.5% by weight, preferably up to 0.3% by weight, in particular up to 0.2% by weight and especially up to 0.1% by weight.

[0059] Such prepolymers are particularly suitable for preparing preparations having a monomeric polyisocyanate content of less than 0.1% by weight, in particular monomeric diisocyanates, such as, in particular, elastic adhesives, sealants and coatings; these preparations can be handled safely even without special protective measures and can therefore be sold in many countries without hazard identification.

[0060] It has also been found that prepolymers with a low proportion of monomeric polyisocyanates, when used with the curing agents used according to the invention, give rise to particularly advantageous polyurethane compositions in which the advantages of the invention are realized to a certain extent. In particular, in the case of prepolymers based on MDI, it is advantageous to remove excess MDI monomers after preparation, since otherwise these monomers may affect the curing of the isocyanate group-containing polymer with hydrazide by slowing down the curing, especially in embodiments in which the hydrazide has been coated with MDI, as described below. However, in the case of prepolymers based on IPDI or TDI, the presence of residual monomeric diisocyanates has no effect on the curing.

[0061] The reaction between polyisocyanate and polyol is preferably carried out with exclusion 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 a suitable catalyst.

[0062] After the reaction, the monomeric polyisocyanate remaining in the reaction mixture (in particular the monomeric diisocyanate remaining) can be removed by suitable separation methods until the stated residual content is reached.

[0063] Preferred separation methods are distillation methods, in particular thin-layer distillation or short-path distillation, preferably under applied vacuum.

[0064] Particularly preferred is a multistage process in which the monomeric polyisocyanate or diisocyanate is removed in a short-path evaporator at a jacket temperature in the range from 120 to 200° C. and a pressure of 0.001 to 0.5 mbar.

[0065] In the case of the preferred IPDI as monomeric diisocyanate, the jacket temperature is preferably in the range of 140 to 180°C.

[0066] The reaction of the monomeric polyisocyanate, in particular the monomeric diisocyanate, with the polyol and the subsequent removal of the residual monomeric polyisocyanate in the reaction mixture are preferably carried out without the use of solvents or entrainers.

[0067] Preferably, the monomeric polyisocyanate removed after the reaction is subsequently reused, ie, re-used for preparing the isocyanate group-containing polymer.

[0068] In this reaction, the OH groups of the polyol react with the isocyanate groups of the monomeric polyisocyanates, in particular the monomeric diisocyanates. This also leads to so-called chain extension reactions, in which the OH groups and / or isocyanate groups of the reaction products between the polyol and the monomeric polyisocyanates react. The higher the selected NCO / OH ratio, the fewer chain extension reactions occur, and thus the polydispersity and the viscosity of the resulting polymer are lower. A 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 relative to the theoretical NCO content calculated from the reaction of each OH-group with the monomeric polyisocyanate.

[0069] Preferably, the isocyanate group-containing polymer having a low content of monomeric polyisocyanates 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 here is determined using a cone-plate viscometer with a cone diameter of 25 mm, a cone angle of 1°, a distance from the cone tip to the plate of 0.05 mm, a shear rate of 10 s -1 .

[0070] The use of the preferred isocyanate group-containing polymers or prepolymers makes it possible to obtain high-quality, easily processable heat-curing polyurethane compositions.

[0071] 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 up to 0.3% by weight, and is obtained from the reaction of IPDI with a polyether triol having an average OH functionality in the range of 2.2 to 3, preferably 2.2 to 2.8, in particular 2.2 to 2.6 and an OH value in the range of 10 to 42 mg KOH / g, in particular 20 to 35 mg KOH / g.

[0072] 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% propylene oxide groups, a content of up to 0.3% by weight of monomeric polyisocyanates, and is obtained by reacting IPDI with at least one polyether diol having an OH number in the range of 44 to 120 mg KOH / g.

[0073] The proportion of prepolymers having isocyanate end groups formed from at least one polyisocyanate and at least one polyol in the polyurethane composition can be, for example, in the range from 10 to 90% by weight, in particular 15-70% by weight, preferably 20-50% by weight, in particular 25-45% by weight.

[0074] In the present invention, hydrazide is specifically used as a curing agent in combination with an epoxy resin.

[0075] Hydrazide is a class of compounds with functional groups, wherein two nitrogen atoms are connected by covalent bonds. Especially, hydrazide is an organic hydrazide in this article. It is normally a derivative of an organic acid (such as carboxylic acid and / or sulfonic acid). Carboxylic hydrazide also carries at least one acyl group as a substituent except at least one hydrazide group, and sulfonyl hydrazide also carries at least one sulfonyl group as a substituent except at least one hydrazide group.

[0076] In particular, the hydrazide used is in granular form, preferably in powder form. According to an advantageous embodiment, the hydrazide is present in the form of a powder, the particle size D50 value of the powder being ≤50 μm, in particular ≤20 μm, in particular ≤10 μm, particularly preferably ≤7.5 μm, most preferably ≤5 μm. The data for the particle size D50 here indicate that 50% by weight of the particles have a size equal to or less than a given value. The particle size D50 can usually be determined by laser scattering according to the ISO 13320:2020 standard, for example using a CILAS 920 device from the company CILAS.

[0077] In the use of the present invention, the hydrazide is mixed with the prepolymer, preferably so that the hydrazide is evenly distributed in the prepolymer. In particular, the prepolymer forms a continuous phase in which particulate hydrazide is dispersed before curing.

[0078] Based on 1 part by weight of isocyanate groups in the prepolymer contained in the heat-curing polyurethane composition, the amount of hydrazide used is preferably 1.5 to 10 parts by weight, preferably 2.0 to 7.5 parts by weight, in particular 2.5 to 5.5 parts by weight. This means, for example, that when using 100 g of a prepolymer having an NCO content of 2% by weight, preferably between 3 and 20 g of hydrazide are used.

[0079] The hydrazide is preferably used in a proportion of 0.5 to 15% by weight, preferably 1 to 10% by weight, in particular 1.5 to 23.0% by weight, based on the total weight of the heat-curing polyurethane composition.

[0080] In a preferred embodiment, the hydrazide is coated with an isocyanate monomer, in particular a diisocyanate monomer, especially a diphenylmethane diisocyanate monomer. In particular, the isocyanate monomer is 4,4'-diphenylmethane diisocyanate, which optionally has a portion of 2,4'- and / or 2,2'-diphenylmethane diisocyanate. The coating of the isocyanate monomer forms an encapsulation of the hydrazide in particular. The activation temperature and the storage stability of the polyurethane composition can be controlled (in particular increased) by means of the isocyanate monomer.

[0081] If used, the isocyanate monomer used for the coating is in particular chemically bound to the hydrazide. It is therefore not a free isocyanate monomer. The coating can be carried out, for example, by mixing the hydrazide with the isocyanate monomer. This is particularly carried out before mixing with the other components of the heat-curing polyurethane composition.

[0082] The proportion of isocyanate monomers is in particular 0.01 to 1.0% by weight, preferably 0.02 to 1.0% by weight and in particular 0.1 to 0.3% by weight, based on the total weight of the heat-curing polyurethane composition.

[0083] The weight ratio of isocyanate monomer to hydrazide is in the range of 0.01-0.20, particularly 0.03-0.15, especially 0.05-0.12.

[0084] These parts and ratios have proven to be particularly advantageous for controlling the activation temperature and the storage stability of the polyurethane compositions within practically relevant ranges.

[0085] However, the isocyanate monomers can also be omitted. In this case, the hydrazide is preferably in direct contact with the prepolymer in the polyurethane composition. Therefore, in this case, the hydrazide is present in free and / or unencapsulated form. The advantage of direct contact between the hydrazide and the prepolymer is that the liquefaction of the hydrazide can directly activate the thermal curing, thereby enabling targeted rapid curing.

[0086] The melting point of the hydrazide is particularly preferably at least 75° C., preferably at least 100° C., in particular at least 110° C., in particular at least 120° C., particularly preferably at least 150° C. Thus, a particularly high storage stability can be achieved while effectively reducing segregation in the case of only partially reacted curing agents.

[0087] According to a particularly preferred embodiment, the hydrazide comprises or consists of a dihydrazide.

[0088] The hydrazide is preferably a hydrazide of a carboxylic acid and / or a sulfonic acid. In particular, it is a hydrazide of formula (Ia) or (Ib) or formula (Ic):

[0089]

[0090]

[0091] in:

[0092] W represents the p-valent group of a carboxylic acid after removing p carboxylic acid groups;

[0093] X represents a q-valent group of sulfonic acid after removing q sulfonic acid groups;

[0094] m represents 0 or 1;

[0095] p represents 1, 2, 3 or 4, preferably 2; and

[0096] q represents 1, 2, 3, or 4.

[0097] In particular, the hydrazide is a carboxylic acid hydrazide, in particular a carboxylic acid dihydrazide, preferably selected from carbodihydrazide, oxalic acid dihydrazide, succinic acid dihydrazide, adipic acid dihydrazide, suberic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide and isophthalic acid dihydrazide, most preferably adipic acid dihydrazide.

[0098] Using such hydrazides, which are commercially available from various suppliers, it is possible in particular to prepare polyurethane compositions having a use range within a broad temperature window.

[0099] Suitable and preferred commercially available hydrazides are, for example, VDH (from Venture Chemical Ltd.) or ADH (from A&C Catalysts).

[0100] It is also preferred that the polyurethane composition does not contain amines blocked with the aid of aldehydes and / or ketones. In particular, the polyurethane composition does not contain aldimines, ketimines, enamines and / or oxazolidines. In particular, the risk of undesirable degassing of aldehydes and / or ketones can thus be reduced.

[0101] Suitable epoxy resins are the customary industrial epoxy resins, which are obtained in a known manner, for example by oxidation of the corresponding olefins or by reaction of epichlorohydrin with the corresponding polyols, polyphenols or amines.

[0102] Epoxy resins are particularly polyepoxides.

[0103] Particularly suitable epoxy resins are so-called liquid polyepoxide resins, referred to below as “liquid resins”. These have a glass transition temperature below 25° C. Likewise possible epoxy resins are so-called solid resins which have a glass transition temperature above 25° C. and can be comminuted to a free-flowing powder at 25° C. However, liquid epoxy resins are preferred.

[0104] Suitable epoxy resins are in particular epoxy resins of the formula (I):

[0105]

[0106] Here, the substituents R′ and R″ independently of one another represent H or CH 3 . The index s represents a value from 0 to 20.

[0107] Compounds of the formula (I) having an index s>1.5, in particular 2 to 12, are known as solid epoxy resins. Such solid epoxy resins are commercially available, for example, from Dow Chemical or Huntsman or Hexion.

[0108] 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. Such semisolid epoxy resins are likewise regarded as solid epoxy resins for the purposes of the present invention. The term "solid epoxy resin" is well known to those skilled in the art in the field of epoxides and is used in contrast to "liquid epoxy resins".

[0109] Compounds of the formula (I) having an index s between 0 and 1 are liquid epoxy resins. s preferably represents a value of less than 0.2.

[0110] Suitable epoxy resins are in particular aromatic epoxy resins, in particular the glycidylation products of:

[0111] - bisphenol-A, bisphenol-F or bisphenol-A / F, where A is acetone and F is formaldehyde, which serve as reactants for the preparation of the bisphenols. In the case of bisphenol-F, positional isomers, in particular derived from 2,4′- or 2,2′-hydroxyphenylmethane, may also be present.

[0112] - dihydroxybenzene derivatives such as resorcinol, hydroquinone or catechol;

[0113] - other bisphenols or polyphenols such as bis(4-hydroxy-3-methyl-phenyl)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)propane, 2,2-bis(4-hydroxyphenyl)butane (bisphenol-B), 3,3-bis(4-hydroxyphenyl)pentane, 3,4-bis(4-hydroxyphenyl)hexane, 4,4-bis(4-hydroxyphenyl)heptane, 2,4-bis(4-hydroxyphenyl)-2-methylbutane, 2,4-bis(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutane , 1,1-bis(4-hydroxyphenyl)-cyclohexane (bisphenol-Z), 1,1-bis-(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (bisphenol-TMC), 1,1-bis-(4-hydroxyphenyl)-1-phenylethane, 1,4-bis[2-(4-hydroxyphenyl)-2-propyl]benzene (bisphenol-P), 1,3-bis[2-(4-hydroxyphenyl)-2-propyl]benzene (bisphenol-M), 4,4'-dihydroxybiphenyl (DOD), 4,4'-dihydroxybenzophenone, bis(2-hydroxynaphthalen-1-yl)methane, bis(4-hydroxynaphthalen-1-yl)methane, 1,5-dihydroxynaphthalene, tris(4-hydroxyphenyl)methane, 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane, bis(4-hydroxyphenyl)ether or bis(4-hydroxyphenyl)sulfone;

[0114] - condensation products of phenols with formaldehyde obtained under acidic conditions, for example phenol-novolacs or cresol-novolacs, also known as bisphenol-F-novolacs;

[0115] Aromatic amines, for example aniline, p-toluidine, 4-aminophenol, 4,4′-methylenediphenyldiamine, 4,4′-methylenediphenyldi-(N-methyl)amine, 4,4′-[1,4-phenylene-bis(1-methylethylidene)]diphenylamine (diphenylamine-P) or 4,4′-[1,3-phenylene-bis(1-methylethylidene)]diphenylamine (diphenylamine-M).

[0116] Other suitable epoxy resins are aliphatic or cycloaliphatic polyepoxides, in particular:

[0117] - saturated or unsaturated, branched or unbranched, cyclic or open-chain, difunctional, trifunctional or tetrafunctional, C2- to C 30 - glycidyl ethers of alcohols, in particular ethylene glycol, propylene glycol, butylene glycol, hexylene glycol, octanediol, polypropylene glycol, dimethylolcyclohexane, neopentyl glycol, dibromoneopentyl glycol, castor oil, trimethylolpropane, trimethylolethane, pentaerythritol, sorbitol or glycerol, or alkoxylated glycerol or alkoxylated trimethylolpropane;

[0118] - hydrogenated bisphenol-A-, -F- or -A / F-liquid resins, or glycidylation products of hydrogenated bisphenol-A-, -F- or -A / F;

[0119] -amides or N-glycidyl derivatives of heterocyclic nitrogenous bases, for example triglycidyl cyanurate or triglycidyl isocyanurate, or the reaction products of epichlorohydrin and hydantoin.

[0120] Epoxy resins obtained from the oxidation of olefins, such as, in particular, vinylcyclohexene, dicyclopentadiene, cyclohexadiene, cyclododecadiene, cyclododecatriene, isoprene, 1,5-hexadiene, butadiene, polybutadiene or divinylbenzene.

[0121] Preferred epoxy resins are liquid resins, in particular liquid resins based on bisphenols.

[0122] Most preferred epoxy resins are liquid resins based on bisphenol-A, bisphenol-F or bisphenol-A / F diglycidyl ether. Such liquid resins are commercially available, for example from Dow, Huntsman or Momentive. These epoxy resins have a viscosity that is easy to handle and can achieve very high strength and resistance. Such liquid resins can also contain a certain amount of bisphenol A solid resin or novolac.

[0123] The epoxy equivalent weight (EEW) of the epoxy resin is in particular 100 g / eq to 500 g / eq, in particular 130 g / eq to 250 g / eq. The epoxy equivalent weight is in particular measured according to ASTM D1652-11 (2019).

[0124] Such epoxy resins react at higher temperatures, for example starting from 150° C., and lead to further crosslinking of the polyurethane composition.

[0125] The epoxy resin is used in particular in a proportion of 0.1 to 15% by weight, preferably 1 to 10% by weight, in particular 1.5 to 5% by weight and most preferably 2 to 4% by weight, based on the total weight of the heat-curing polyurethane composition.

[0126] In particular, no epoxide-amine adducts are used in the polyurethane composition, in particular no epoxide-amine adducts obtained by reacting bisphenol diglycidyl ether with aliphatic polyamines, and / or the polyurethane composition does not contain such epoxide-amine adducts. Aliphatic polyamines are in particular diamines, in particular diamines having one primary and one secondary amino group and / or diamines having one primary and one tertiary amino group. In particular, epoxide-amine adducts not used are those described in EP 0 365 984 A2, page 5, lines 8-16. These adducts are not suitable for the composition according to the invention.

[0127] The polyurethane compositions of the invention may also optionally contain one or more further auxiliaries and admixtures customarily used in the polyurethane industry as additives.

[0128] Examples of such additives are plasticizers; solvents; inorganic and organic fillers, for example ground or precipitated calcium carbonate, carbon black, kaolin, aluminum oxide, silicon dioxide and / or PVC powder; fibers, for example polyethylene fibers; pigments; rheology modifiers, for example thixotropic additives, thickeners, for example urea compounds, polyamide waxes, bentonites or pyrogenic silicas; adhesion promoters, in particular silanes, such as epoxysilanes, vinylsilanes and isocyanatosilanes; desiccants, for example p-tolyl isocyanate and other reactive isocyanates, orthoformates, calcium oxide or molecular sieves; stabilizers against heat, light and UV radiation; flame retardants; surface-active substances, for example wetting agents, leveling agents, deaerators or defoamers; and bactericides or substances that inhibit the growth of fungi.

[0129] If desired and depending on the target application, additives can be added in a customary manner in suitable amounts. It is generally preferred that the polyurethane composition comprises at least one plasticizer and / or at least one filler.

[0130] 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 phosphates, phosphonates and / or sulfonates; polybutenes; polyisobutenes; and / or plasticizers derived from natural fats or oils, in particular epoxidized soybean oil and / or linseed oil.

[0131] The plasticizer preferably has a vapor pressure of less than 0.1 mbar at 20° C. and / or the boiling point of the plasticizer at a normal pressure of 101.325 kPa is at least 250° C., preferably at least 300° C., in particular at least 350° C. This can prevent the plasticizer from degassing too strongly at higher curing temperatures (e.g. above 180° C.).

[0132] Particularly preferably, the plasticizer is selected from phthalates and / or trimellitates, in particular diisodecyl phthalate (DIDP) and / or trioctyl trimellitate. These have proven to be particularly advantageous for the heat-curing polyurethane composition of the invention. The plasticizer is preferably used in a proportion of 0.1-30% by weight, preferably 5-25% by weight, in particular 10-20% by weight, based on the total weight of the heat-curing polyurethane composition.

[0133] The heat-curing polyurethane composition preferably also contains one or more stabilizers against heat, oxygen, moisture and / or UV radiation. Suitable stabilizers are, for example, hindered amines (HALS stabilizers), hindered phenols, phosphites and / or aromatic amines. These stabilizers are commercially available, for example, under the trade names IRGANOX, KINOX, DOVERNOX, WESTON, IRGAPHOS, DOVERPHOS and / or IONOL.

[0134] Particularly preferred as stabilizers are phosphites, in particular organic phosphites. Organic phosphites are also known as phosphites, in particular having one or more groups of formula (II):

[0135]

[0136] Here, R 1 , R 2 and R 3 are independently of one another an organic radical, for example an organic radical having 1 to 25 carbon atoms. The organic radical may have one or more heteroatoms or consist exclusively of carbon and hydrogen atoms.

[0137] Preferably, the group R 1 , R 2 and R 3 At least one of the compounds comprises an aromatic group.

[0138] In particular, the stabilizer is an organic diphosphite having two groups of the formula II.

[0139] Such phosphite stabilizers are known, for example, under the name Commercially available.

[0140] Surprisingly, it has been found that the use of the phosphites can further reduce possible discoloration of the polyurethane composition, which is generally only slight even at curing temperatures of 200° C. and above. In contrast, phenolic stabilizers are less suitable for stabilization at such high curing temperatures.

[0141] The proportions of the ingredients in the polyurethane composition can vary within wide ranges, depending on the ingredients used and the intended application. The amounts stated below for suitable and preferred embodiments are based on the total weight of the polyurethane composition.

[0142] Particularly preferably, the heat-curing polyurethane composition comprises the following components based on the total weight of the heat-curing polyurethane composition:

[0143] a) 0.5 to 15% by weight, preferably 1 to 10% by weight, in particular 1.5 to 3.0% by weight of hydrazide;

[0144] b) 0.1 to 15% by weight, preferably 1 to 10% by weight, in particular 2 to 5% by weight of epoxy resin;

[0145] c) 15 to 70% by weight, preferably 20 to 50% by weight, in particular 25 to 40% by weight, of prepolymers;

[0146] d) 0-1% by weight, preferably 0.02-1% by weight, in particular 0.1-0.3% by weight, of isocyanate monomers;

[0147] e) 0 to 70% by weight, preferably 10 to 60% by weight, in particular 40 to 50% by weight, of inorganic and / or organic fillers, in particular those as described above;

[0148] f) 0 to 30% by weight, preferably 5 to 25% by weight, in particular 10 to 20% by weight, of plasticizers, in particular those as described above;

[0149] g) 0 to 5% by weight, preferably 0.5 to 4% by weight, in particular 1 to 3% by weight, of stabilizers, in particular those as described above, preferably phosphites;

[0150] h) 0-1% by weight, preferably 0.01-0.8% by weight, in particular 0.05-0.6% by weight of catalyst;

[0151] i) optionally, one or more additional additives, the proportion of which makes up 100% by weight.

[0152] The prepolymer and other components used in the composition can be mixed with each other in any order to obtain the polyurethane composition. Some components, such as hydrazide optionally coated with isocyanate monomers, can also be added, for example, mixed with a plasticizer. Mixing can be carried out at room temperature (e.g. 23° C.). For example, in order to make homogenization or dispersion easier, mixing can also be carried out partially or completely at a slightly elevated temperature. All mixing devices known in the art can be used as mixing devices. The viscosity can be adjusted at will considering the intended application, for example, the polyurethane composition can be in a pasty state and preferably has structural viscosity.

[0153] The present invention also provides for a heat-curing polyurethane composition obtainable according to the use according to the invention.

[0154] In other words, the composition is a heat-curable polyurethane composition comprising: (i) a prepolymer having isocyanate end groups formed from at least one polyisocyanate and at least one polyol, (ii) a hydrazide, and (iii) an epoxy resin. Optionally, one or more of the above-mentioned other components may also be present.

[0155] All of the above statements and explanations concerning the use according to the invention and the heat-curing polyurethane composition (for example with regard to suitable components etc.) apply correspondingly.

[0156] The heat-curable polyurethane composition may be a multi-component (eg, two-component) heat-curable polyurethane composition, but is preferably a one-component heat-curable polyurethane composition.

[0157] Polyurethane compositions, preferably one-component polyurethane compositions, are generally very suitable for bonding one or more materials having the same or different properties, in particular for bonding in vehicle construction or vehicle repair. The polyurethane compositions are likewise suitable as sealants for sealing elements, in particular for sealing in vehicle construction or vehicle repair. The elements are, for example, substrates, surfaces, seams and / or cavities.

[0158] 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.

[0159] The temperature for heat curing can vary within a wide range 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 a temperature in the range of 100 to 220° C. The duration of heat curing can, for example, be in the range of 1 to 120 minutes.

[0160] The present invention also relates to a method for bonding joint parts (especially vehicle parts) using the heat-curable polyurethane composition of the present invention as described above, comprising:

[0161] a) applying a heat-curing polyurethane composition to one or both surfaces of the parts to be bonded,

[0162] b) contacting the surfaces of the parts to be bonded, and

[0163] c) Curing the polyurethane composition by thermal curing, in particular at the temperatures mentioned above.

[0164] The present invention also relates to a method for sealing a component to be sealed using the heat-curable polyurethane composition of the present invention as described above, comprising:

[0165] a) applying a heat-curing polyurethane composition onto and / or into the component to be sealed;

[0166] b) Curing the polyurethane composition by thermal curing, in particular at the temperatures mentioned above.

[0167] The elements to be sealed are in particular substrates, surfaces, seams and / or cavities, in particular substrates, surfaces, seams and / or cavities of vehicles. In step a), the heat-curing polyurethane composition can be applied to the substrate or surface and / or introduced into the seams and / or cavities accordingly.

[0168] The joint or the joint surface to be bonded and / or the element to be sealed can be made of any material, wherein the joint surfaces to be bonded can be made of the same material or different materials. Examples of suitable materials are metals, metal alloys, glass, plastics, ceramics, fabrics or painted elements or joints.

[0169] The heat-curing polyurethane composition can be applied to one or both surfaces of the parts to be bonded or the elements to be sealed in a conventional manner known to the person skilled in the art. The surfaces of the parts to be bonded are brought into contact, optionally by pressing the surfaces of the parts to be bonded against one another.

[0170] The curing of the polyurethane composition is then carried out under heating, for example at a temperature of 100 to 220° C., in particular in a temperature range between 150° C. and 220° C., by thermal curing.

[0171] The invention also relates to an article obtained by the process according to the invention, comprising a joined part and a cured polyurethane composition as an adhesive connection of the joined part. The joined part is in particular a component of a vehicle.

[0172] The invention likewise relates to a component, in particular a vehicle component, which comprises a cured polyurethane composition as described above as a sealant.

[0173] The present invention is further explained below by examples, but the examples do not limit the present invention in any way.

[0174] Example

[0175] Examples are described below which explain the invention in more detail. The invention is of course not limited to the examples described.

[0176] If not stated otherwise, the chemicals used were obtained from Sigma-Aldrich (Switzerland).

[0177] Preparation of prepolymer:

[0178] Polymer P1:

[0179] 780.0g 5031BT (ethylene oxide-terminated polyoxypropylene triol starting from glycerol, OH value 28.0 mg KOH / g, OH functionality about 2.3; from Covestro) and 220 g of 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane ( IPDI, from Evonik) was reacted at 80° C. according to known methods to form a polyether polyurethane polymer having an NCO content of 6.4% by weight, a viscosity of 4.1 Pa·s at 20° C. and a monomeric IPDI content of about 12% by weight.

[0180] Subsequently, the volatile components, in particular most of the monomeric IPDI, were distilled off in a short-path evaporator (jacket temperature 160° C., pressure 0.1 to 0.005 mbar). The polyether polyurethane polymer thus obtained had an NCO content of 1.9% by weight, a viscosity of 8.2 Pa·s at 20° C. and a monomeric IPDI content of 0.02% by weight.

[0181] The polymers P1 are prepolymers (polymers containing isocyanate groups) having a low content of monomeric diisocyanates.

[0182] The viscometer was Rheotec RC30 (cone diameter 25 mm, cone angle 1°, distance from cone tip to plate 0.05 mm, shear rate 10 s -1 ) to measure viscosity.

[0183] The monomeric diisocyanate content was determined by HPLC (detection by photodiode array; 0.04 M sodium acetate / acetonitrile as mobile phase) after previous derivatization by N-propyl-4-nitrobenzylamine.

[0184] Polyurethane composition

[0185] The components shown in Table 1 were mixed in the specified amounts (by weight) by a planetary mixer under vacuum and under the condition of excluding moisture to form one-component polyurethane compositions R and C1-C5, and stored under the condition of excluding moisture until use.

[0186] Table 1: Polyurethane composition (value unit weight %)

[0187]

[0188] 1 Adipic acid dihydrazide coated with diphenylmethane diisocyanate (Desmodur CD-L von Covestro) was obtained by premixing the two components under vacuum stirring at 23°C for 10 minutes.

[0189] 1aTotal content of adipic acid dihydrazide used (before coating)

[0190] 1b Amount of isocyanate monomer used for coating

[0191] 2 Araldite GY 250 (from Huntsman)

[0192] 3 5GU (from Omya)

[0193] 4 Trioctyl trimellitate

[0194] 5 Diisodecyl phthalate

[0195] 6 Cab-O-Sil TS-720 (hydrophobic silica; Cabot Corp.)

[0196] 7 Titanium dioxide (Kronos 2220, from Kronos)

[0197] These compositions can be stored at temperatures up to 60°C for several months.

[0198] Testing without isocyanate monomer coated hydrazide

[0199] A further composition C6 was prepared, but the hydrazide was not coated with an isocyanate monomer. Composition C6 was formulated in the same manner as composition C5, except that 1.73 wt % of pure hydrazide (not previously treated with an isocyanate monomer) and 13.77 wt % of a plasticizer were used to compensate for the difference in quality due to the lack of an isocyanate monomer. Thus, C6 differed from C5 primarily only in that the hydrazide was not coated with an isocyanate monomer.

[0200] Thermal curing and properties of samples

[0201] Films of compositions R and C1-C6 with a layer thickness of 2 mm were cured for 30 minutes at different curing temperatures and stored for 7 days in a standard climate (23° C., 50% relative humidity). No oily liquids or the like ooze out of the cured products, either during or after thermal curing.

[0202] The tensile strength, elongation at break and modulus of elasticity were then determined in accordance with DIN 53504 (tensile speed: 200 mm / min). Table 2 summarizes the results.

[0203] Films of compositions C1-C2 containing hydrazide and epoxy resin as curing agents can be cured at temperatures between 100 and 200° C. Over the entire temperature range, the tensile strength, elongation at break and modulus of elasticity remain within practically relevant ranges.

[0204] This is true even at temperatures as high as 220°C for films of compositions C2, C3, C4 and C5.

[0205] In particular, the elastic modulus is relatively constant, with the film of composition C4 having a particularly stable elastic modulus over the entire temperature range, while the tensile strength and elongation at break have relatively high values.

[0206] In contrast, for comparative sample R, the elastic modulus at 200° C. is only 1.5 MPa, while no value (“nm”) can be measured at 220° C. anymore.

[0207] However, the above-described embodiments are to be understood as merely exemplary embodiments that can be modified arbitrarily within the scope of the present invention.

[0208] Table 2: Properties of polyurethane compositions

[0209]

[0210]

[0211] The storage stability of the composition in the container can be determined by the extrusion force.

[0212] In order to determine the extrusion force, the composition is filled in an aluminum cartridge (external diameter 46.9mm, internal diameter 46.2mm, length 215mm, opening 15-M) painted inside and sealed airtightly with a polyethylene stopper (diameter 46.1mm) from Novelis Deutschland GmbH. After adjusting for 24 hours at 23°C, the cartridge is opened and extruded by an extrusion device. For this reason, a nozzle with a 2mm internal diameter opening is screwed onto the cartridge thread. Extrusion equipment (Zwick / Roell Z005) is used to determine the force required for extruding the composition at an extrusion speed of 60mm / min. The values ​​given are the mean values ​​of the forces measured after the extrusion distances of 22mm, 24mm, 26mm and 28mm. The measurement is stopped after the extrusion distance of 30mm.

[0213] To check the storage stability, compositions C5 and C6 were 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.

[0214] Another sealed cartridge of compositions C5 and C6 was each stored in a 60°C oven for seven days to simulate aging in the container.

[0215] After the high temperature storage, the cartridges were cooled again to 23° C. within 24 hours and their extrusion forces were remeasured as described above. Composition C5 exhibited a moderate increase in extrusion force to 1029 N. In contrast, composition C6 exhibited an extrusion force of 3500 N.

[0216] This indicates that coating the hydrazide with the isocyanate monomer achieves a significant improvement in storage stability.

Claims

1. Use of a hydrazide having a melting point of at least 65° C. as a heat-curing curing agent in a heat-curing 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. The method according to claim 1, wherein the hydrazide is a carboxylic hydrazide, in particular a carboxylic dihydrazide, preferably selected from carbodihydrazide, oxalic acid dihydrazide, succinic acid dihydrazide, adipic acid dihydrazide, suberic acid dihydrazide, azelaic acid dihydrazide, sebacic acid dihydrazide, dodecanedioic acid dihydrazide and isophthalic acid dihydrazide, most preferably adipic acid dihydrazide.

3. The method according to claim 1, wherein the hydrazide is coated with an isocyanate monomer, in particular a diisocyanate monomer, especially diphenylmethane diisocyanate.

4. The method according to claim 3, wherein the 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. The method according to claim 1 , wherein the hydrazide is used in an amount of 1.5 to 10 parts by weight, preferably 2.0 to 7.5 parts by weight, in particular 2.5 to 5.5 parts by weight, based on 1 part by weight of isocyanate groups in the prepolymer contained in the heat-curing polyurethane composition.

6. The method according to claim 1, wherein the epoxy resin is a polyepoxide, in particular a diglycidyl ether of bisphenol A, bisphenol F and / or bisphenol A / F.

7. The method according to claim 1, wherein the epoxy resin is used in a proportion of 0.1-15% by weight, preferably 1-10% by weight, in particular 2-5% by weight, based on the total weight of the heat-curing polyurethane composition.

8. The method according to claim 1, wherein a plasticizer is additionally used, which 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. The method according to claim 8, wherein the plasticizer is selected from phthalates and / or trimellitates, in particular diisodecyl phthalate (DIDP) and / or trioctyl trimellitate.

10. The method according to claim 8, wherein the plasticizer is used in a proportion of 0.1-30% by weight, preferably 5-25% by weight, in particular 10-20% by weight, based on the total weight of the heat-curing polyurethane composition.

11. The method according to claim 1 , wherein the prepolymer having isocyanate end groups, which is formed from 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, especially at most 0.1% by weight.

12. The method according to claim 1, wherein the heat-curing polyurethane composition comprises the following components, based on the total weight of the heat-curing polyurethane composition: a) 0.5 to 15% by weight, preferably 1 to 10% by weight, in particular 1.5 to 3.0% by weight of hydrazide; b) 0.1 to 15% by weight, preferably 1 to 10% by weight, in particular 2 to 5% by weight of epoxy resin; c) 15 to 70% by weight, preferably 20 to 50% by weight, in particular 25 to 40% by weight, of prepolymers; d) 0-1% by weight, preferably 0.02-1% by weight, in particular 0.1-0.3% by weight, of isocyanate monomers; e) 0 to 70% by weight, preferably 10 to 60% by weight, in particular 40 to 50% by weight, of inorganic and / or organic fillers; f) 0-30% by weight, preferably 5-25% by weight, in particular 10-20% by weight of plasticizer; g) 0-5% by weight, preferably 0.5-4% by weight, in particular 1-3% by weight, of stabilizers; h) 0-1% by weight, preferably 0.01-0.8% by weight, in particular 0.05-0.6% by weight of catalyst; i) Optionally, one or more additional additives.

13. The method according to claim 1, wherein the polyurethane composition is a one-component composition, in particular a one-component adhesive and / or sealant, particularly preferably for use in vehicle construction.

14. A heat-curing polyurethane composition, in particular a heat-curing polyurethane composition according to any one of the preceding claims and / or a heat-curing polyurethane composition obtained by the use according to any one of the preceding claims, comprising: (i) a prepolymer having isocyanate end groups formed from at least one polyisocyanate and at least one polyol, (ii) a hydrazide and (iii) an epoxy resin.

15. Process for curing a polyurethane composition according to claim 14, wherein the polyurethane composition is cured by the action of heat, in particular in a temperature range between 150°C and 220°C.

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