Curable mass, method for joining, casting and coating substrates and use of the mass

Abstract

The invention relates to a one-component curable mass containing (A) at least one at least difunctional, solid isocyanate having a passivated surface, (B) at least one first, liquid isocyanate-reactive component selected from the group of alcohols, amines and thiols and their mixtures; and (C) at least one second, solid isocyanate-reactive component having a melting point of at least 50°C. The invention further relates to a method for joining, casting and / or coating substrates and to a use of the mass.

Description

[0001] Curable mass, process for joining, casting and / or coating substrates and use of the mass

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a heat-curable one-component composition based on isocyanates.

[0004] Furthermore, the invention relates to a method for joining, coating or encapsulating substrates, in particular electronic components, using the compound.

[0005] TECHNICAL BACKGROUND

[0006] The use of polyisocyanates in combination with polyamines or polyols in curable compounds is generally known. Due to their high reactivity, such compounds have a limited processing time, and the components must be mixed promptly before use. Storage-stable compounds can be obtained by using blocked polyisocyanates, which release the blocking agent at elevated temperatures. Alternatively, surface-passivated polyisocyanates are used. Solid, finely dispersed polyisocyanates are reacted with an isocyanate-reactive compound, thus modifying the surface with a passivating coating. By applying heat, such compounds can undergo a rapid polyaddition reaction with the isocyanate, thus curing the compound.Such adhesives can be particularly suitable as an alternative to silicones with excellent flow properties and high flexibility at low temperatures of the cured masses.

[0007] Reflow soldering is primarily used for the conductive fixation of surface-mounted components on printed circuit boards. One of the advantages of this method is that the components are initially bonded by the solder paste during assembly and are only then finally soldered, for example, in a reflow soldering oven. The use of adhesives can additionally fix, pot, or seal the components. A disadvantage of this process is that the adhesive masses are sometimes exposed to temperature peaks of more than 240 °C for a duration of more than one minute, which can lead to a drastic drop in the adhesion level. The prior art does not describe any solutions that enable the widespread use of polyisocyanate-based formulations for such applications.

[0008] EP 0 100 508 B1 describes heat-curing compounds based on polyisocyanates. The polyisocyanate, which has particle diameters between 0.1 pm and 150 pm, is first deactivated with an isocyanate-reactive compound, whereby 0.1 to 20 equivalent percent of the isocyanate groups are converted. The resulting compounds have a storage stability of at least 3 months.

[0009] EP 0 103 323 B1 describes a process for the production of solid, surface-passivated polyisocyanates and their use in storage-stable, heat-curable compositions. High-molecular-weight polyols and / or polyamine compounds, as well as low-molecular-weight chain extenders, are described as curing agents. Additional components from the aforementioned groups can optionally be added. The targeted use of high-melting amines to increase thermal stability and adhesion is not disclosed.

[0010] EP 0 153 579 B1 describes the use of polyisocyanate-based adhesives. Polyamines, hydrazines, amidines, and / or guanidines are used to passivate the finely dispersed polyisocyanates. The reaction takes place in a liquid component that also acts as a hardener. Higher molecular weight polyols and / or polyamines are also used here. Furthermore, additional polyols and / or polyamines with molecular weights below 400 g / mol can be used.

[0011] EP 0 671 423 B1 describes one-component, heat-curing polyurethane compounds with increased resistance to temperature and humidity. Polyisocyanates with a diphenylurea backbone are preferred starting materials for temperature-stable formulations. Other polyisocyanates tend to soften, decompose, or foam. The targeted addition of high-melting amines is not disclosed. Due to the structural limitations of the polyisocyanates, the achievable property profile of the cured compounds is limited.

[0012] EP 3749700 A1 discloses one-component, storage-stable compositions based on surface-passivated polyisocyanates. The addition of a radically radiation-curable component and a photoinitiator renders the compositions dual-curing. The curing agents can be selected from the group of alcohols, amines, and thiols, as well as mixtures thereof. The compositions are also light-fixable to prevent flow during curing. The addition of high-melting amines to increase temperature stability and adhesion is not described.

[0013] There is therefore still a need for single-component compounds that can be dosed at room temperature, particularly for joining, coating or encapsulating electronic components, which, in addition to high flexibility of the cured compound, also have high temperature stability, in particular a high tolerance to temperature peaks, such as those that occur in reflow soldering processes, and which show improved adhesion.

[0014] SUMMARY OF THE INVENTION

[0015] The object of the present invention is to avoid the disadvantages of the compositions known from the prior art and to provide thermosetting one-component masses which are characterized in particular by their temperature stability and adhesion in the cured state.

[0016] This object is achieved according to the invention by a one-component, curable composition according to claim 1. Advantageous embodiments are specified in the subclaims, which can optionally be combined with one another.

[0017] The one-component, curable composition according to the invention comprises

[0018] (A) at least one at least difunctional, solid isocyanate having a passivated surface and a melting point of at least 40 °C; (B) at least one first, liquid isocyanate-reactive component selected from the group of alcohols, amines and thiols and mixtures thereof; and

[0019] (C) at least one second solid isocyanate-reactive component having a melting point of at least 50 °C.

[0020] The compound is liquid at room temperature and, after curing, is characterized by high strength and temperature stability. The tendency of the cured compound to soften, decompose, or foam at temperatures above 180°C is significantly reduced. The composition of the compounds according to the invention can be varied within a wide range, particularly with regard to the selection of the resin component. This provides the user with a multitude of options for adjusting the property profile of the cured compounds to suit their needs.

[0021] The invention is based on the surprising finding that the addition of solid, isocyanate-reactive components can significantly improve the temperature stability and adhesion of heat-curing one-component compounds based on surface-passivated, solid isocyanates.

[0022] This makes the compositions according to the invention particularly suitable for reflow soldering, where such thermal stresses can occur over a longer period of time. Furthermore, the adhesion level is significantly increased, particularly on metal surfaces, making the compositions suitable for magnetic bonding or for use in automotive sensors, for example.

[0023] Furthermore, a method for joining, coating or casting substrates using the composition according to the invention is proposed.

[0024] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0025] The invention is described in detail below by way of example using preferred embodiments, which, however, are not intended to be limiting. The following definitions are used in the description: "One-component" or "one-component composition" means, for the purposes of the invention, that the aforementioned components are present together in a common formulation, i.e., they are not stored separately from one another.

[0026] The masses are considered “workable” if the viscosity of the respective ready-mixed mass increases by less than 25% during storage at room temperature for a period of at least 72 hours.

[0027] In the context of the invention, “liquid” means that at room temperature the loss modulus G” determined by rheological measurement is greater than the storage modulus G' of the mass in question.

[0028] "At least difunctional" means that the respective compound or mixture of substances has a functionality of at least 2, based on a specific functional group. At least difunctional or polyfunctional isocyanates therefore have at least two isocyanate groups (-NCO) in the molecule.

[0029] Where the indefinite article “ein” or “eine” is used, this also includes the plural form “ein or mehr” unless this is expressly excluded.

[0030] All weight proportions listed below refer to the total weight of the curable mass, unless otherwise stated.

[0031] Component (A): at least difunctional, solid isocyanate

[0032] In principle, any at least difunctional isocyanate having a melting point of at least 40°C can be used as the solid, at least difunctional isocyanate (A). Preferably, the at least difunctional isocyanate has a melting point of at least 60°C. The melting point of the at least difunctional isocyanate is preferably at most 170°C.

[0033] The isocyanate is preferably an aliphatic, cycloaliphatic, heterocyclic, or aromatic polyisocyanate. The polyisocyanate may be present at least partially, preferably entirely, in dimeric form. Examples of suitable polyisocyanates include: dimeric 2,4-diisocyanatotoluene, dimeric 4,4'-diisocyanatodiphenylmethane, 3,3'-diisocyanato-4,4'-dimethyl-N,N'-diphenylurea, the isocyanurate of isophorone diisocyanate, 1,4-phenylene diisocyanate, naphthalene-1,5-diisocyanate, and addition products of diisocyanates with short-chain diols having 2 to 6 carbon atoms, such as 1,4-butanediol or 1,2-ethanediol. Particularly preferred are dimeric 2,4-diisocyanatotoluene, dimeric 4,4'-diisocyanatodiphenylmethane, 3,3'-diisocyanato-4,4'-dimethyl-N,N'-diphenylurea and / or the isocyanurate of isophorone diisocyanate.

[0034] To provide storage-stable compounds, the solid polyisocyanate is passivated on its surface. To this end, the solid polyisocyanate is reacted with a passivating agent to prevent immediate reaction of the solid isocyanate with the liquid isocyanate-reactive component (B) present in the one-component compound.

[0035] Preferably, the solid polyisocyanate is reacted on its surface with a passivating agent, as described, for example, in EP 0 153 579 A2, EP 0 100 508 B1 or EP 3 749 700 A1.

[0036] By reacting the solid polyisocyanate with the passivating agent, an essentially inert shell forms on its surface, which prevents further reaction of the isocyanate groups underneath the shell until the shell is broken up by the application of heat, so that the one-component mass hardens.

[0037] Preferred passivating agents are compounds from the group of polyamines, amidine and / or guanidine compounds, hydrazines, alkylhydrazines and / or hydrazide compounds, which react with the isocyanate groups on the surface of the solid polyisocyanate to form urea groups.

[0038] Particular preference is given to using primary, aliphatic, at least difunctional amines with a molecular weight of 60-600 g / mol as passivating agents, and very particularly preferably polyetheramines, such as those commercially available, for example, under the name Jeffamine® D-400 or Jeffamine® T-403 from Huntsman Corporation. For passivation, 0.1-25 mol% of all isocyanate groups present in the solid polyisocyanate can be reacted with the passivating agent, preferably 0.5-15 mol% and particularly preferably 1-10 mol%. The reaction preferably takes place with the formation of urea groups. In a preferred embodiment, the solid polyisocyanate, present in the form of micronized particles, is reacted with the passivating agent at a temperature below the melting point of the solid polyisocyanate in a liquid medium that is not itself a good solvent for the polyisocyanate.In particular, higher molecular weight polyols or polyamines with a molecular weight of up to 20,000 g / mol can serve as the liquid medium, which can themselves be used as isocyanate-reactive components in the compositions according to the invention.

[0039] According to a preferred embodiment, the surface-passivated, solid polyisocyanate is dispersed in finely divided form. This allows a homogeneously cured mass to be obtained upon application of heat.

[0040] The solid polyisocyanate is preferably in the form of particles with a volumetric particle diameter d95 of at most 100 pm, preferably at most 40 pm, and particularly preferably at most 10 pm. By selecting various polyisocyanates and the associated curing systems, both hard and very soft systems can be formulated with the compositions of the invention, which exhibit a virtually unchanged elastic modulus profile over wide temperature ranges.

[0041] According to a further aspect of the invention, the mass has a proportion of 5 to 40 wt.% of the at least difunctional isocyanate, based on the total weight of the mass.

[0042] Component (B): first, liquid isocyanate-reactive component

[0043] In addition to component (A), the compositions according to the invention contain as component (B) at least one first, liquid isocyanate-reactive component which is selected from the group of alcohols, amines and thiols and mixtures thereof.

[0044] In principle, the selection of component (B) from the group of alcohols, amines, and thiols, as well as mixtures thereof, is not restricted, as long as at least one of the first isocyanate-reactive components (B) is liquid at room temperature. Upon heating the mass, component (B) reacts with the polyisocyanate.

[0045] (A) with formation of a network and hardening of the mass.

[0046] Component (B) is not further restricted with regard to its chemical constitution. Component (B) preferably carries isocyanate-reactive groups with an average functionality greater than 1. Particular preference is given to using polyols, polyamines, and / or polythiols with a functionality of at least 2 as isocyanate-reactive compounds. Mixtures of different isocyanate-reactive compounds are also within the scope of the invention.

[0047] The average functionality of component (B) and thus also the crosslinking density can be adjusted almost arbitrarily by combining monofunctional, difunctional, and higher-functional isocyanate-reactive compounds, as long as a polymeric network forms upon application of heat through the addition reaction to the at least difunctional isocyanate (A). The average functionality is preferably at least 1.4 and particularly preferably at least 1.7; but preferably also not greater than 5 and especially not greater than 4.

[0048] The cured masses can be specifically formed with hard and soft segments. To form hard segments, isocyanate-reactive components (B) with a molecular weight of up to 400 g / mol are preferably used as so-called chain extenders. These components, together with the at least difunctional isocyanate, form a high density of linking groups such as (thio)urethane or urea groups, which then link together via a dense network of hydrogen bonds. To form soft segments, component (B) preferably comprises long-chain isocyanate-reactive compounds with a molecular weight of 400 g / mol to 20,000 g / mol.

[0049] The isocyanate-reactive compounds can also be pre-extended with liquid, non-passivated isocyanates to form prepolymers.

[0050] Preferably, component (B) comprises an amine. The amine in component

[0051] (B) Polyetheramines with a molecular weight of 600 g / mol or greater, such as those available as Jeffamine® D-2000 or Jeffamine® T-5000, can be used. Higher molecular weight aromatic amines with an average molecular weight of 400 g / mol to 12,000 g / mol, which can be obtained according to EP 0 071 834 A1 by alkaline hydrolysis of compounds with terminal isocyanate groups, in particular from isocyanate prepolymers, can also be used. Suitable aromatic diamines are commercially available under the names Versalink® P-650 and Versalink® P-1000. Aromatic diamines such as diethylenetoluenediamine, available as Ethacure 100, can also be used as chain extenders.

[0052] Furthermore, a polyol can be used as component (B), particularly preferably a long-chain polyol with an average molecular weight M nfrom 400 g / mol to 20,000 g / mol. Examples of suitable long-chain polyols are polyols based on polyethers, commercially available as Acclaim® grades, polyesters and polycarbonates, available as Kuraray® or Priplast™ grades, as well as polyols based on polybutadienes and hydrogenated polybutadienes, available as Krasol®, Polyvest®, or Nisso-PB® grades.

[0053] Long-chain polyols with an average molecular weight of 2000 g / mol to 20,000 g / mol are particularly suitable for the production of masses that, after curing, exhibit high flexibility at low temperatures and a low glass transition temperature.

[0054] As a chain extender, component (B) may comprise at least one low molecular weight polyol having a molecular weight of up to 400 g / mol, such as glycol, glycerol, 1,4-butanediol or 2-ethyl-1,3-hexanediol.

[0055] Suitable thiols for use in component (B) include, for example, ester-based thiols such as trimethylolpropane tris-(3-mercaptopropionate) or pentaerythritol tetrakis-(3-mercaptobutylate). Furthermore, thiol-terminated polyethers can be used as isocyanate-reactive components, as can thiol-bearing polythioethers or tris-(3-mercaptopropyl)isocyanurate.

[0056] The first, liquid isocyanate-reactive component (B) is preferably present in the composition of the invention in a proportion of 5 to 90 wt. %, more preferably in a proportion of 40 to 85 wt. %, based on the total weight of the composition. The proportions can vary widely depending on the functionality and molecular weight of the isocyanate-reactive component. A mixture of polyols, amines, and / or thiols can also be advantageously used in the curable compositions.

[0057] Component (C): second, solid isocyanate-reactive component

[0058] In addition to the first, liquid isocyanate-reactive component (B), the compositions contain at least a second, solid isocyanate-reactive component (C) with a melting point of at least 50 °C. The second, solid isocyanate-reactive component (C) can be selected from the group of alcohols, amines, and thiols, as well as mixtures thereof. Component (C) is preferably selected from the group of alcohols and amines. Particular preference is given to using amines, in particular at least difunctional amines.

[0059] As component (C) it is possible in principle to use any solid isocyanate-reactive compound which has a melting point of 50 °C or more, preferably 60 °C or more, in particular 65 °C or more, and more preferably not higher than 200 °C.

[0060] Component (C) explicitly does not include any compounds of the above-mentioned first isocyanate-reactive component (B). These are liquid at room temperature and are not suitable as component (C).

[0061] The second, solid isocyanate-reactive component (C) is present in the curable mass, particularly in finely divided, dispersed form, and is not dissolved in component (B).

[0062] The second, solid isocyanate-reactive component (C) is preferably in the form of particles having a volumetric particle diameter d95 of at most 100 pm, particularly preferably up to 40 pm, and very particularly preferably up to 10 pm.

[0063] More preferably, component (C) consists of at least 40 wt.% of an amine, more preferably at least 50 wt.%, particularly preferably at least 60 wt.%, based on the weight of component (C). Component (C) is particularly preferably an at least difunctional amine.

[0064] The structure of the amine is not further restricted and includes primary, secondary, and tertiary amines. The amine can also contain aliphatic, cycloaliphatic, and / or aromatic residues, or be cyclically bridged in the form of a heterocyclic or aromatic amine. The different amine functionalities can be present in any combination within a compound.

[0065] The amine can be difunctional or more highly functional and can contain any number of additional isocyanate-reactive groups. In the case of a mixed-functional amine, a thiol or hydroxyl function is preferably present in addition to the amine function. Amine and hydroxyl functions are particularly preferred in combination. Examples of this include epoxy-amine adducts, which contain at least one additional hydroxyl group in addition to an amine function.

[0066] Preferably, compounds having a molecular weight of less than 5000 g / mol, more preferably less than 2000 g / mol, particularly preferably less than 1000 g / mol are used as the solid, second isocyanate-reactive component (C).

[0067] Examples of the solid, second isocyanate-reactive component (C) are 4,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylmethane, 4,4'-diamino-3,3'-dichlorodiphenylmethane, 4,4'-oxydianiline, bis-(4-amino-3,5-diethylphenyl)methane, pentaerythritol, trimethylolpropane or trimethylolethane.

[0068] Commercially available products include Aradur 9664-1 and Aradur 9719-1 from Huntsman and Charmor PM15 from Perstorp.

[0069] Commercial epoxy-amine adducts are available, for example, under the names EH-5011S, EH-5046S, EH-5015SS and EH-5057P from ADEKA, Ancamine 2014FG or Ancamine 2442 from Evonik or Fujicure FXR-1020, Fujicure FXR-1030, Fujicure FXR-1081 or Fujicure FXR-1121 from Sanho Chemical.

[0070] The second, solid isocyanate-reactive component (C) is preferably present in the composition according to the invention in a proportion of 1 to 35 wt.%, more preferably in a proportion of 2 to 25 wt.%.

[0071] Based on the weight of components (B) and (C), the proportion of the solid, isocyanate-reactive component (C) is preferably in a range from 1 to 40 wt. %, more preferably in a range from 2 to 30 wt. %. Component (D): Additives

[0072] In addition to components (A) to (C), the compositions of the invention may contain further additives (D). Examples of additives (D) that may be used include, but are not limited to, catalysts, toughness modifiers such as core-shell particles or block copolymers, dyes, pigments, fluorescent agents, thixotropic agents, thickeners, thermal stabilizers, stabilizers, antioxidants, plasticizers, fillers, flame retardants, corrosion inhibitors, water scavengers, diluents, flow control and wetting additives, adhesion promoters, and combinations thereof.

[0073] Components with radically curable double bonds, as well as radical generators, can also be used as additives (D). This allows for light fixation of the composition in accordance with EP 3 749 700 A1.

[0074] As catalysts (D1), preference is given to using compounds known to the person skilled in the art that catalyze the reaction of the isocyanate-reactive groups with the polyisocyanate. Examples of suitable catalysts include, in particular, metal catalysts based on tin, zinc, lead, mercury, or bismuth, or tertiary amines such as triethylenediamine or DBU.

[0075] Inert organic solvents can also be used as diluents, as long as they do not dissolve the solid polyisocyanate. However, the composition is preferably free of inert organic solvents, as the use of such solvents is environmentally harmful and therefore not preferred. In principle, water can also be used as a dispersion medium. However, this requires a complex drying step during processing, which also makes the use of an aqueous dispersion unsuitable.

[0076] Pyrogenic silicas, which may have been surface-modified, are preferred as thixotropic agents.

[0077] The additives are preferably present in the curable composition in a proportion of 0 to 80 wt.%, particularly preferably in a proportion of 0 to 50 wt.%, based on the total weight of the composition. Composition of the compositions according to the invention

[0078] The composition according to the invention preferably comprises or consists of the aforementioned components (A) to (C). Advantageously, the composition may contain at least one of the aforementioned additives (D).

[0079] According to a first preferred embodiment, the composition according to the invention comprises the following components:

[0080] (A) at least one solid, at least difunctional isocyanate having a melting point of at least 40 °C, preferably of at least 60 °C, which is passivated on its surface by reacting 0.5 to 15% of the isocyanate groups with polyamines, amidine and / or guanidine compounds, hydrazine, alkylhydrazines and / or hydrazide compounds;

[0081] (B) at least one first liquid isocyanate-reactive component having an average functionality of 1.7-4; and

[0082] (C) at least one second solid isocyanate-reactive component having a melting point of at least 50 °C.

[0083] In a further preferred embodiment, the isocyanate-reactive component (C) is an at least difunctional amine and has a melting point of at least 60 °C, in particular at least 65 °C.

[0084] Based on the weight of components (B) and (C), the second, solid isocyanate-reactive component is preferably present in a proportion of 1 to 40 wt.%.

[0085] More preferably, the composition contains as component (D) at least one thixotropic agent and / or a catalyst.

[0086] Properties of the compositions according to the invention:

[0087] The compositions according to the invention are liquid at room temperature and formulated as a single-component. The selection of components (A) to (C) and the passivation of the isocyanate-containing component (A) make the compositions processable even at room temperature for a certain period of time. After heat curing, the compositions according to the invention are characterized by high temperature stability and adhesion. This means, for example, that for the cured compositions, only a limited decrease in adhesion in the compressive shear strength and / or tensile strength is observed at temperatures greater than 180°C for 90 minutes or temperatures greater than 240°C for one minute, as occur particularly in the reflow soldering process. In the prior art, this can only be achieved by severely restricting the formulation scope, particularly with regard to the structural diversity of component (A).In the present invention, by adding an additional, high-melting isocyanate-reactive component (C), the thermal stability of the cured compositions could be achieved while maintaining or even improving their mechanical properties. Compared to other addition-curing compositions based on isocyanates, the compositions of the invention thus allow the use of various isocyanate-functional resin components. This provides a broad formulation scope for advantageously adjusting the mechanical properties of the cured compositions. Furthermore, by appropriately selecting the second, solid isocyanate-reactive component (C), the linear-elastic behavior can be varied over a wide range.

[0088] Processing methods using the compositions according to the invention

[0089] The compositions of the invention, which comprise at least components (A) to (C), are characterized by their ability to cure at low temperatures. The resulting joint maintains a consistently high level of adhesion even at high operating temperatures and temperature peaks exceeding 180°C.

[0090] A corresponding process for joining, casting or coating substrates using the compositions according to the invention comprises the following steps:

[0091] (a) providing the composition according to the invention;

[0092] (b) dosing the mass onto a first substrate; (c) optionally adding a second substrate to the mass to form a substrate composite; and

[0093] (d) Hot curing of the mass on the substrate and / or in the substrate composite by heating to a temperature of at least 60 °C.

[0094] Heat curing is preferably carried out at a temperature at which the solid isocyanate dissolves or melts, breaking up the urea or polyurethane shell. Heat curing is preferably carried out at a temperature of no more than approximately 160 °C.

[0095] According to a preferred application, the compound is used in a reflow soldering process. The compounds can be advantageously used, for example, for additional fixing or for encapsulating and sealing components on printed circuit boards. In a corresponding joining process, steps (a) to (d) are carried out. Following heat curing, an additional heating step follows, during which temperatures above 240 °C can be reached. The temperature and duration of the additional heating step are selected such that the substrate composite is heated sufficiently to melt the solder and achieve a material-to-material bond between the components.

[0096] Due to the properties of the compounds according to the invention, the adhesion level is maintained despite the strong thermal stress that occurs during the reflow soldering process. In some cases, the adhesion level of the cured compounds can even be further increased.

[0097] According to a further embodiment, the composition can be additionally fixed with light prior to heat curing. Formulation components required for light fixation can be found in EP 3 749 700 A1. In particular, a radiation-curing component such as (meth)acrylates and a photoinitiator for radical polymerization are used for light fixation, which are incorporated into the composition as additional components. A corresponding process for casting, coating, or joining substrates using the compositions according to the invention with light fixation preferably comprises the following steps:

[0098] (a) providing the curable mass; (b) dosing the mass onto a first substrate;

[0099] (c) irradiating the mass with actinic radiation;

[0100] (d) optionally supplying a second substrate to form a substrate assembly, wherein the second substrate is brought into contact with the irradiated mass; and

[0101] (e) heat curing the irradiated mass on the substrate and / or in the substrate composite by heating to a temperature of at least 60 °C.

[0102] If the process is carried out as a joining process including step (d), steps (c) and (d) can also be performed in reverse order. This process sequence offers the advantage that the components can be additionally fixed in position by irradiation with actinic radiation before the heat-curing step.

[0103] Using the described process and the compounds according to the invention, a high degree of positioning accuracy of the joined components can be achieved until final curing. Conventional fixing aids, which are not practical for miniaturized components or would entail unreasonable additional effort, can thus be dispensed with.

[0104] A component joined and fixed by the process using the compositions of the invention can be securely held in place even when mounted at an angle. Even in components that cannot be penetrated by actinic radiation, the described process using the compositions of the invention can be used to fix the fillet welds using actinic radiation.

[0105] Measurement methods and definitions used

[0106] Room temperature

[0107] Room temperature is defined as 23 °C ± 2 °C. Curing

[0108] "Crosslinking" or "curing" is defined as a polymerization, addition, or condensation reaction beyond the gel point. The gel point is the point at which the storage modulus G' becomes equal to the loss modulus G".

[0109] Thermal DSC measurements

[0110] The melting point was determined as an endothermic peak in a differential scanning calorimeter (DSC) (Mettler Toledo DSC822e).

[0111] 6–10 mg of the sample were weighed into a 40 pL aluminum crucible, sealed with a perforated lid, and subjected to a measurement from 30–220 °C at a heating rate of 2 K / min. The process gas was nitrogen at a flow rate of 30 mL / min.

[0112] Particle size distribution

[0113] The particle size distribution was determined using a Microtrac S3500 particle size analyzer by laser light diffraction in accordance with ISO 13320. The distribution indicated by the size d95 refers to the volumetric particle diameter.

[0114] Tensile strength

[0115] Tensile properties such as tensile strength and elongation at break were determined in accordance with DIN EN ISO 527-2:2012-06. Type 5A specimens were used. The test was conducted at room temperature on a Zwick Roell Allround-Line 20 kN universal testing machine with a test speed of 200 mm / min. Heat curing was performed in a preheated convection oven at 120 °C for 30 minutes. After the test specimen mold had cooled, the cured specimen was removed from the mold and conditioned at room temperature for 24 hours.

[0116] Compressive shear strength

[0117] Two specimens (dimensions 20 mm x 20 mm x 5 mm) made of clad aluminum were bonded together with a 5 mm overlap using the respective compound. A bead of the compound was applied to the first specimen. A second specimen was then bonded. The adhesive layer thickness of 0.1 mm and the overlap were adjusted using spacer wires and a bonding device. The bonded specimens were cured in a preheated convection oven at 120 °C for 30 minutes.

[0118] Manufacturing examples

[0119] To prepare the compositions according to the invention, the first, liquid isocyanate-reactive component (B) was first mixed with the passivating agent, and the micronized, solid isocyanate (A) was added. Subsequently, the second, solid isocyanate-reactive component (C) and optionally further additives (D) were added.

[0120] The components were blended according to the weight percentages specified in the tables. Mixing was performed in a Labotop mixer with sickle-shaped kneading arms (PC Laborsysteme). The mixtures were then degassed and filled into cartridges.

[0121] Curing of the compositions of the invention and the comparative compositions by applying heat is initiated by the solid isocyanate dissolving or melting at elevated temperature, breaking up the urea or polyurethane shell. Curing of the compositions of the invention and comparative examples was carried out by heating to 120°C for 30 minutes. Depending on the type and amount of passivating agent in the solid isocyanate, an adjustment of the curing temperature may be necessary.

[0122] The energy input for heat curing can be achieved by convection, for example in a circulating air oven, by heat conduction, for example using a heating plate or thermode, or by electromagnetic radiation, for example using IR radiation sources, lasers, microwaves or induction.

[0123] The following list contains all the compounds used to produce the curable masses and their abbreviations.

[0124] Component (A): surface-passivated, at least difunctional, solid isocyanate

[0125] A-1 Thanecure T9 SF AD-V - micronized TDI uretdione, melting point 155 °C (Safic-Alcan) A-2 Jeffamine D-400 - liquid polyetheramine passivating agent (Huntsman Corporation)

[0126] Component (B): first, liquid isocyanate-reactive component

[0127] B-1 Jeffamine T-5000 - liquid polyetheramine (Huntsman Corporation)

[0128] B-2 Ethacure 100 - Diethyltoluenediamine (liquid) as a chain extender (Albemarle Corporation)

[0129] B-3 Krasol HLBH-P3000 - liquid polyol (Cray Valley)

[0130] B-42- Ethyl-1,3-hexanediol - liquid polyol (Sigma Aldrich)

[0131] Component (C): solid, second isocyanate-reactive component

[0132] C-1 Dapsone - 4,4'-diaminodiphenylsulfone, melting point 178 °C (Atul Ltd.)

[0133] C-2 Adeka Hardener EH-5046S - Epoxy amine adduct, melting point 110 °C (Adeka Corporation)

[0134] C-3 Ancamine 2014 FG - Epoxy-amine adduct, melting point 69 °C (Evonik Industries)

[0135] C-4 Ancamine 2442 - Epoxy amine adduct, melting point 71 °C (Evonik Industries)

[0136] Component (D): Additives

[0137] D-1 Cab-O-Sil TS-720 - Fumed Silica (Cabot Corporation)

[0138] D-2 Bismuth neodecanoate catalyst (Sigma Aldrich)

[0139] Dispersion of the second, solid isocyanate-reactive component (C)

[0140] According to the invention, the second, solid isocyanate-reactive component (C) is dispersed in component (B). For testing, analogous formulations without the solid isocyanate component (A) were prepared, and the formation of a dispersion was verified by microscopic observation. To detect any temporary dissolution of the second, solid isocyanate-reactive component (C) in the mixture of component (B), microscopic observation was carried out after one and seven days of storage of the mixtures at room temperature. The formulations and results are summarized in Table 1. Table 1: Microscopic examination of the dispersion of component (C).

[0141] Mechanical Properties of the Inventive Materials The materials produced and cured according to the process described above were tested for their temperature and aging resistance. For this purpose, the compressive shear strength was determined as a measure of the initial adhesion and the tensile strength of test specimens bonded with the materials after curing and after aging for 90 minutes at 180 °C. In the materials to be compared, the ratio of the passivated isocyanate (A) to the liquid isocyanate-reactive component (B) was kept constant. The type and proportions of the additional solid isocyanate-reactive component (C) were varied.

[0142] The composition of the investigated masses and the results obtained are given in Table 2. Table 2: Influence of the second, solid isocyanate-reactive component (C) on the mechanical properties of the cured masses.

[0143] The composition according to Example 7 does not contain an additional solid isocyanate-reactive amine as component (C). The composition is therefore not in accordance with the invention. After aging of the cured composition of Example 7, a sharp drop in tensile strength can be observed after aging at 180°C. By adding a solid, isocyanate-reactive component (C), this drop in tensile strength can be significantly reduced, as can be seen in Examples 8 to 11 according to the invention. The cured composition of Example 8 even exhibits a higher tensile strength after aging than the composition immediately after curing.

[0144] The initial adhesion of the joint, measured as the compressive shear strength of a metal-to-metal bond, is not impaired in Examples 8 to 11 according to the invention compared to Comparative Example 7, and in some cases is even improved. After aging, all values ​​are sufficiently stable and increased compared to the initial value.

[0145] Further masses with different solid isocyanate-reactive components (C) and their mechanical properties are shown in Table 3 below.

[0146] Table 3: Variation of the second, solid isocyanate-reactive component (C)

[0147] Compared to the compositions shown in Table 2, the formulations in Table 3 have an increased proportion of the solid isocyanate component (A) and thus a higher strength level. The composition according to Example 13 contains no additional solid isocyanate-reactive amine as component (C) and is therefore not according to the invention. After aging of the cured composition of Example 13, a sharp drop in tensile strength can be observed after aging at 180 °C. In contrast, Examples 14 to 17 according to the invention show a greatly increased tensile strength compared to the initial value. Thus, the aging resistance of the joint at 180 °C is significantly improved by the use of the solid, isocyanate-reactive component (C).

[0148] Inventive Examples 14 to 17 further exhibit high initial compressive shear strength, which is partially improved compared to Comparative Example 13. However, while the compressive shear strength of the cured composition of Comparative Example 13 decreases sharply after aging at 180 °C, the adhesion level of the compositions in Inventive Examples 14 to 17 is significantly increased after aging.

[0149] The influence of the proportion of the second, solid isocyanate-reactive component (C) on the mechanical properties of the cured masses is shown in Table 4 below.

[0150] Table 4: Influence of the proportion of component (C) on the mechanical properties of the cured masses Examples 18 to 21 each contain different proportions of the solid isocyanate-reactive component C-2. Comparative Example 7 serves as a reference, in which the same ratio of the passivated isocyanate (A) and the liquid isocyanate-reactive component (B) was used as in the compositions of Examples 18 to 21. While the cured composition according to Comparative Example 7 shows a significant decrease in tensile strength after 90 minutes of aging at 180 °C, the corresponding values ​​for the compositions of Examples 18 to 21 remain at a significantly higher level due to the addition of the solid isocyanate-reactive component (C).

[0151] A decrease in tensile strength after aging can only be observed at a proportion of the isocyanate-reactive component (C) of approximately 30 wt.%. Nevertheless, the initial adhesion is significantly improved compared to Comparative Example 7.

[0152] In the examples described above, the inventive compounds were formulated using a nitrogen-containing compound, in particular an amine, as the liquid isocyanate-reactive component (B). Alternatively or additionally, a polyol that is liquid at room temperature can also be used as component (B). An example of such a composition is given in Table 5 below.

[0153] Table 5: Formulation and properties of a curable composition based on a polyol as component (B).

[0154] In the compositions according to Comparative Example 22 and Example 23, a polyol was used as the liquid isocyanate-reactive component (B). The composition according to the invention according to Example 23, which additionally contains a solid amine as component (C), exhibits high initial adhesion and also improved tensile strength after aging at 180 °C.

[0155] Without the addition of the second, solid isocyanate-reactive component (C), the compressive shear strength decreases significantly after aging at 180 °C, so that the adhesive bond no longer adheres sufficiently. Furthermore, the tensile strength of the cured mass of Comparative Example 22 without the solid isocyanate-reactive component (C) is no longer measurable after aging because the test specimen has decomposed.

Claims

Patent claims 1. A one-component, room-temperature liquid and heat-curable mass comprising (A) at least one at least difunctional, solid isocyanate having a passivated surface and a melting point of at least 40 °C; (B) at least one first liquid isocyanate-reactive compound selected from the group of alcohols, amines and thiols and mixtures thereof; and (C) at least one second solid isocyanate-reactive compound having a melting point of at least 50 °C.

2. Composition according to one of the preceding claims, characterized in that the at least difunctional, solid isocyanate (A) is reacted on its surface with a passivating agent selected from the group of polyamines, amidine and / or guanidine compounds, hydrazine, alkyl hydrazines and / or hydrazide compounds.

3. Composition according to one of the preceding claims, characterized in that the at least difunctional, solid isocyanate (A) is at least partially in dimeric form.

4. A composition according to any one of the preceding claims, characterized in that the molar ratio of the free, non-passivated isocyanate groups of component (A) to the isocyanate-reactive groups of component (B) is 0.4 to 2.

5.

5. Mass according to one of the preceding claims, characterized in that the second, solid isocyanate-reactive component (C) has a particle diameter of at most 100 pm, preferably up to 40 pm, particularly preferably up to 10 pm.

6. A composition according to any one of the preceding claims, characterized in that the solid, second isocyanate-reactive component (C) consists of at least 60% by weight of an amine-functional compound.

7. A composition according to any one of the preceding claims, characterized in that the second, solid isocyanate-reactive component (C) is selected from the group consisting of epoxy-amine adducts, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4-diaminodiphenylmethane, 4,4'-diamino-3,3'-dichlorodiphenylmethane, 4,4'-oxydianiline, bis-(4-amino-3,5-diethylphenyl)methane, pentaerythritol, trimethylolpropane, trimethylolethane and combinations thereof.

8. A composition according to claim 6 or 7, characterized in that the second, solid isocyanate-reactive component (C) is an amine-functional compound.

9. A composition according to any one of the preceding claims, characterized in that the second, solid isocyanate-reactive component (C) is present in a proportion of 1 to 35% by weight, more preferably in a proportion of 2 to 25% by weight, based on the weight of components (B) and (C).

10. Mass according to one of the preceding claims, characterized in that the mass comprises the following components: (A) at least one solid, at least difunctional, solid isocyanate having a melting point of at least 40 °C, preferably of at least 60 °C, which is passivated on its surface by reacting 0.5 to 15% of the isocyanate groups with polyamines, amidine and / or guanidine compounds, hydrazine, alkylhydrazines and / or hydrazide compounds; (B) at least one first liquid isocyanate-reactive component having an average functionality of 1.7-4; and (C) at least one second solid isocyanate-reactive component having a melting point of at least 50 °C.

11. A method for joining, casting and / or coating substrates using a curable mass according to one of the preceding claims, comprising the following steps: a) providing the curable mass according to one of the preceding claims; b) Dosing the mass onto a first substrate; c) Optionally adding a second substrate to the mass to form a substrate composite; d) Heat-curing the mass on the substrate and / or in the substrate composite by heating to a temperature of at least 60 °C.

12. Use of the compositions according to one of claims 1 to 10 in a reflow soldering process for producing electronic components and for bonding magnets, loudspeakers and automotive sensors.

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