Method of joining, potting or coating substrates using a curable compound

Abstract

A method of joining, potting or coating substrates using a curable compound comprises the following steps: a curable compound is provided, wherein the curable compound comprises the following components: (A) a thiol-reactive component, (B) an at least difunctional thiol, (C) a nitrogen-containing compound as latent accelerator, and (D) a stabilizer. The curable compound is metered onto a first substrate. The curable compound is activated by heating the curable compound to an activation temperature T1 of 50°C or higher and a wait time for curing of the curable compound is observed, in which the curable compound is kept at a curing temperature T2. After activation at the activation temperature T1, the curable compound has an open time of at least 30 seconds and cures fully within 7 days. The activation temperature T1 is higher than the curing temperature T2.

Description

[0001] Process for joining, casting or coating substrates using a curable mass

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a method for joining, casting or coating substrates using a thermally pre-activatable mass.

[0004] TECHNICAL BACKGROUND

[0005] One-component compounds based on epoxy-thiol systems are known for their low-temperature curing. The use of latent accelerators allows for the formulation of storage-stable compounds with rapid curing behavior.

[0006] Corresponding epoxy-thiol-based adhesives are described, for example, in US Pat. No. 5,430,112 A. The addition of a solid, dispersed amine hardener as a latent accelerator, consisting of an epoxy-amine adduct or an amine blocked with isocyanate groups, makes it possible to formulate compounds with processing times of up to one week that cure at temperatures below 120 °C. The compounds should have the longest possible shelf life to allow sufficient time for processing steps such as mixing, defoaming, and application.

[0007] Storage stability can be further improved by adding a suitable stabilizer. US Pat. No. 6,232,426 B1 demonstrates the use of borate esters, which interact advantageously with a solid, dispersed accelerator. The compounds can be cured at 80 °C and retain their flowability for at least one month after storage at 25 °C.

[0008] Due to their ability to cure reliably at low temperatures, the adhesives are particularly used for the production of temperature-sensitive components such as semiconductor devices, camera modules, and lenses. Furthermore, the compounds can be made light-fixable by appropriately blending them with radically curable components in combination with radical photoinitiators. This makes them particularly suitable for use in applications requiring rapid fixation of joining partners. For example, in the manufacture of LIDAR or camera systems, optical elements and imaging sensors must be aligned and fixed to one another with high positional accuracy. This so-called "active alignment" process enables high-quality components to be manufactured at the required high cycle rates.

[0009] Storage-stable one-component compounds that can be fixed with light and cure at low temperatures are described, for example, in WO 2019 / 115203 A1. They comprise a stabilizer mixture of a sulfonyl isocyanate and an organic acid. The compounds are first fixed with actinic radiation to achieve contour stability sufficient for subsequent process steps and then heat-cured in a subsequent oven process.

[0010] WO 2016 / 143777 A1 describes epoxy-thiol systems with a (meth)acrylate component. The compounds can be cured by heat and light. The addition of a photoinitiator is optional. The combination of radical and anionic inhibitors with an ester-free thiol results in particularly storage-stable and media-resistant adhesives.

[0011] A disadvantage of the processes described in the prior art using thiol-curing resin systems is that continuous heat input, for example, from an oven, is required for the final curing of the compounds. Joined, coated, or cast components are therefore constantly exposed to high thermal stress.

[0012] There is therefore a continued need for single-component compounds that can be dosed at room temperature, particularly for joining, coating, or encapsulating electronic components, which enable a process suitable for bonding particularly temperature-sensitive components. SUMMARY OF THE INVENTION

[0013] The object of the present invention is to provide a method using a curable mass, in particular a one-component mass, which is suitable for processing temperature-sensitive components and in particular enables temporally and spatially decoupled process steps during an open time.

[0014] This object is achieved according to the invention by a method according to claim 1.

[0015] Further embodiments of the invention are specified in the subclaims, which can optionally be combined with one another.

[0016] The method according to the invention for joining, casting or coating substrates using a curable mass comprises the following steps: a) Providing the curable mass, wherein the curable mass comprises the following components:

[0017] (A) a thiol-reactive component,

[0018] (B) a thiol which is at least difunctional,

[0019] (C) a nitrogen-containing compound as a latent accelerator, and

[0020] (D) a stabilizer; b) dosing the curable mass onto a first substrate; c) activating the curable mass by heating to an activation temperature Ti of 50°C or higher; and d) maintaining a waiting time for curing the curable mass, during which the curable mass is kept at a curing temperature T2; wherein the curable mass, after activation at the activation temperature Ti, has an open time of at least 30 seconds and cures completely within 7 days, and wherein the activation temperature Ti is higher than the curing temperature T2. The invention is based on the fundamental idea of ​​thermally preactivating the curable mass by heating the curable mass to the activation temperature Ti, thus initiating the curing process.At the same time, the open time of the curable mass is selected such that after activation at the activation temperature Ti, a sufficiently long open time of at least 30 seconds remains, during which further processing steps can be carried out on or with the pre-activated mass. In this way, the heat input for activating the curable mass can be spatially and temporally separated from further processing steps, so that the thermal stress on the substrate and / or other components that come into contact with the curable mass only after activation can be minimized or even completely avoided.

[0021] The process according to the invention is thus characterized by a flexible and resource-efficient activation of the curable mass. The type of heat input is not restricted in any way and can be carried out, for example, in an oven, by induction, or by radiation, in particular infrared radiation or radiation generated by a laser.

[0022] The method is further characterized in that the heat input is short and thus suitable for preactivating the curable mass, wherein the mass further has, after the preactivation, an open time during which, for example, another substrate can be added to the liquid, preactivated mass.

[0023] "Activating" the compound is understood here and below to mean that the curable compound, after heating to the activation temperature Ti, has an open time of at least 30 seconds at the curing temperature T2 and cures after a specified time, namely within 7 days. The specified time is, in particular, a maximum of 24 hours. Within this time period, the compound exceeds the gel point and transforms into the solid state.

[0024] The "open time" refers to the time after heat application at the activation temperature T 1 during which the activated compound has not yet exceeded its gel point. During this time, the compound only slightly changes its properties with regard to viscosity and adhesion. Joining a second substrate is possible within the open time.

[0025] The duration of the open time is determined by haptic measurement of the flow behavior over a specified period. Within the open time, the process according to the invention can be carried out reliably.

[0026] However, it is also possible that the activated masses remain at least partially joinable beyond the specified open time before they solidify to such an extent that no further flow or pressing onto another substrate is possible.

[0027] In addition to the composition of the curable mass, the open time can also be influenced by the choice of the activation temperature Ti and the curing temperature T2, as well as the holding time at the respective temperature.

[0028] The masses are considered “workable” if the viscosity of the respective ready-mixed mass increases by less than 100% during storage at room temperature for a period of at least 24 hours.

[0029] "Final curing" refers to a state at which the maximum strength buildup of the mass is complete. This means that the mechanical properties of the mass essentially no longer change. In particular, the residual enthalpy of the cured mass is less than 15%. According to the invention, final curing is completed within a maximum of seven days, preferably within three days, particularly preferably within one day, i.e., within 24 hours.

[0030] Surprisingly, it has now been discovered that the multi-stage process is made possible by a hardenable mass that includes the following components:

[0031] (A) a thiol-reactive component,

[0032] (B) a thiol which is at least difunctional,

[0033] (C) a nitrogen-containing compound as a latent accelerator, and

[0034] (D) a stabilizer. The use of the curable mass ensures that it initially remains liquid after pre-activation at the activation temperature Ti. At the same time, it ensures that the curable mass reliably cures at the curing temperature T2, which is lower than Ti, after the open time has elapsed.

[0035] The difference between the activation temperature Ti and the curing temperature T2 is preferably 30 °C or more. In other words, the relationship between the activation temperature Ti and the curing temperature T2 is determined by the equation:

[0036] Ti > T2+ 30 °C

[0037] A difference of at least 30 °C between the activation temperature Ti and the curing temperature T2 ensures that components that come into contact with the curable compound after activation only need to be exposed to significantly lower temperatures than during activation. This significantly minimizes thermal stress. Furthermore, the energy required to cure the curable compound is reduced.

[0038] According to the invention, the activation temperature Ti required for activation is at least 50 °C, preferably 60 °C or more. At an activation temperature Ti below 50 °C, the risk of unintentional activation of the curable mass increases, which can adversely affect its processing time.

[0039] In particular, however, the activation temperature Ti is not more than 200 °C, preferably not more than 180 °C, particularly preferably not more than 120 °C. In this way, the effort required to activate the curable mass can be minimized, and components can be used in the curable mass that would not be able to withstand higher temperatures to a sufficient degree.

[0040] Further process steps after activation are carried out according to the invention at a curing temperature T2 that is preferably 50 °C or less, more preferably 40 °C or less. Moderately elevated holding temperatures T2 of, for example, 40 °C or 50 °C can be advantageously used to accelerate the final curing of the activated materials in step d). Substrates and components are exposed to only minimal thermal stress at these temperatures.

[0041] Preferably, the curing temperature T2 is at least 20 °C. Particularly preferably, the curing temperature T2 is no higher than room temperature. This eliminates the need for any, or at least no significant, cooling of the curable mass during the waiting period, which significantly simplifies handling and process control.

[0042] The curable compound is kept at the activation temperature Ti for a maximum activation time of 15 minutes, preferably no more than 1 minute. A short activation time shortens the process time and thus enables high cycle rates in manufacturing processes. Furthermore, the thermal stress on the substrate is minimized.

[0043] The accelerator (C) can be solid at room temperature and dispersed throughout the mass. This increases the storage stability of the curable mass while ensuring the most uniform activation possible.

[0044] In one variant, the accelerator (C) has a melting point of 50 °C or more. In other words, the accelerator (C) can have a melting point that is matched to the activation temperature Ti, for example, corresponding to the activation temperature Ti.

[0045] The accelerator (C) may also contain one or more blocked amine groups, which are converted into the corresponding free amine compound upon heating to the activation temperature Ti.

[0046] In one variant, the activation of the curable mass according to step c) takes place before the dosing of the curable mass according to step b). This process is particularly advantageous when the curable mass is applied using a flow-through activation device.

[0047] The method may further comprise a further step: c1) supplying a second substrate to the curable mass on the first substrate to produce a substrate composite.

[0048] Step c1) can be performed either before or after activation of the curable mass, but preferably after activation of the curable mass. By temporally and spatially decoupling the activation of the curable mass from the creation of the substrate composite, the thermal stress on the second substrate is minimized, allowing even thermally sensitive components to be used as the second substrate.

[0049] In principle, the second substrate can be added before or after the curable composition has reached its open time. To enable a particularly robust process, however, it is preferred to add the second substrate in step c1) of the process according to the invention, if this is carried out, within the open time.

[0050] Furthermore, the curable composition may further comprise a free-radical photoinitiator (E), and the process may further comprise the following step: c2) fixing the curable composition by actinic radiation; wherein step c2) occurs after activation according to step c). In other words, the already activated composition may be fixed by means of an additional irradiation step.

[0051] In step c2), a rapid buildup of strength of the compound is thus enabled. For the purposes of the method according to the invention, "fixation" or "fixing" refers to the buildup of a strength of the compound beyond which no further flow of the compound can occur, or the degree of strength beyond which joined parts, in particular substrates, can be handled in subsequent processes without causing destruction of the adhesive bond, in particular the substrate bond.

[0052] Depending on the formulation of the curable composition, the photoinitiator (E) can react with the thiol-reactive component (A) and / or with the at least difunctional thiol (B) to fix the composition. For example, component (A) contains an ethylenically unsaturated compound (A2) used for fixation. In another variant, the curable composition further contains an additive (F) comprising an inductively heatable component (F1), wherein the curable composition is inductively heated to the activation temperature Ti.

[0053] By adding an inductively heatable component (F1), it is possible to introduce the energy required for activation into the curable mass via an external alternating field. Heating the curable mass to the activation temperature Ti suitable for activation can occur after dosing and / or joining, for example, by passing through an induction coil. Alternatively, the activation of the curable mass can occur before or during the dosing process, for example, in a flow-through activation device with an induction coil, with an infrared radiator, or with an external heat source that is at least partially in thermal contact with part of the flow-through activation device.

[0054] Due to the particularly economical energy input and the possibility of flow activation, the method according to the invention is particularly suitable for bonding thermally sensitive components such as optoelectronic components and camera modules.

[0055] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0056] The invention is described in detail below by way of example with reference to preferred embodiments, which, however, are not intended to be limiting, and with reference to the drawings. In the drawings:

[0057] Fig. 1 is a side view of an exemplary embodiment of a device for thermally preactivating and dosing a curable mass in the process according to the invention,

[0058] Fig. 2 shows the device from Fig. 1 in a sectional view, and

[0059] Fig. 3 shows the device from Fig. 1 in an exploded view.

[0060] The following definitions are used in the description: “One-component” or “one-component mass” means in the sense of the invention that the said components of the mass are present together in one packaging unit.

[0061] In the context of the invention, “liquid” means that at 23 °C the loss modulus G” determined by viscosity measurement is greater than the storage modulus G' of the mass in question.

[0062] “At least difunctional” means that each molecule contains two or more units of the respective functional group.

[0063] Where the indefinite article “ein” or “eine” is used, this also includes the plural form “ein or mehr” unless this is expressly excluded.

[0064] All weight proportions listed below refer to the total weight of the curable mass, unless otherwise stated.

[0065] According to the invention, the curable composition used comprises a thiol-reactive component (A), an at least difunctional thiol (B), a nitrogen-containing compound as a latent accelerator (C) and a stabilizer (D).

[0066] In a first preferred embodiment, the curable composition for carrying out the process according to the invention contains components (A) to (D).

[0067] In a second preferred embodiment, the curable composition for carrying out the process according to the invention comprises at least one epoxide (A1) and one ethylenically unsaturated compound (A2) as component (A), as well as components (B) to (D) and a radical photoinitiator (E).

[0068] In a third preferred embodiment, the curable composition for carrying out the process according to the invention contains, in addition to components (A) to (D), an additive (F) which comprises an inductively heatable component (F1).

[0069] The individual components of the curable mass for use in the process according to the invention are described in more detail below.

[0070] Component (A): Thiol-reactive component

[0071] The curable composition comprises at least one thiol-reactive component (A). The thiol-reactive component (A) is preferably selected from the group of epoxides (A1), ethylenically unsaturated compounds (A2), and combinations thereof.

[0072] Epoxies (A1)

[0073] The epoxide (A1) is not further restricted in its chemical structure and includes aromatic or aliphatic compounds with at least one epoxide group in the molecule, such as cycloaliphatic epoxides, glycidyl ethers, glycidylamines and mixtures thereof.

[0074] The epoxide (A1) can be mono- or higher functional.

[0075] The epoxide (A1) preferably comprises at least one di- or higher-functional epoxide.

[0076] Examples of monofunctional epoxides (A1) include butyl glycidyl ether, (2-ethylhexyl) glycidyl ether, phenyl glycidyl ether, 2,3-epoxypropyl-o-tolyl ether, 4-tert-butylphenyl glycidyl ether, styrene oxide, a-pinene oxide, cresol glycidyl ether, polyethylene glycol monoglycidyl ether, polypropylene glycol monoglycidyl ether, polytetramethylene monoglycidyl ether, fatty acid glycidyl esters, norbornene oxide, glycidyl ether of cardanol and glycidyl neodecanoate.

[0077] Cycloaliphatic epoxides (A1) are known in the art and include compounds that carry both a cycloaliphatic group and an oxirane ring.

[0078] Examples of representatives are 3-cyclohexenylmethyl-3-cyclohexylcarboxylate diepoxide, 3,4-epoxycyclohexylalkyl-3',4'-epoxycyclohexanecarboxylate, 3,4-epoxy-6-methylcyclohexylmethyl-3',4'-epoxy-6-methylcyclohexanecarboxylate, vinylcyclohexene dioxide, bis(3,4-

[0079] Epoxycyclohexylmethyl)adipate, dicyclopentadiene dioxide, limonene dioxide, 1,2-epoxy-6-(2,3-epoxypropoxy)hexahydro-4,7-methanindane.

[0080] Aromatic epoxides (A1) can also be used in the compositions according to the invention. Examples of aromatic epoxides (A1) are bisphenol A epoxy resins, bisphenol F epoxy resins, phenol novolak epoxy resins, cresol novolak epoxy resins, biphenyl epoxy resins, 4,4'-biphenyl epoxy resins, divinylbenzene dioxide, 2-glycidylphenyl glycidyl ether, naphthalenediol diglycidyl ether, glycidyl ether of tris(hydroxyphenyl)methane, glycidyl ether of tris(hydroxyphenyl)ethane, and glycidyl ether of allylphenol novolaks. Furthermore, all fully or partially hydrogenated analogues of aromatic epoxides (A1) can also be used. Low-halogen or halogen-free bisphenol A and bisphenol F epoxy resins are preferred.

[0081] Isocyanurates substituted with epoxide-containing groups and other heterocyclic compounds can also be used as component (A1) in the compositions of the invention. Examples include triglycidyl isocyanurate and monoallyldiglycidyl isocyanurate.

[0082] In addition, polyfunctional epoxy resins of all the resin groups mentioned, tough, elasticized epoxy resins and mixtures of various epoxy compounds can also be used in the compositions according to the invention.

[0083] A combination of several epoxy-containing compounds, of which at least one is tri- or higher-functional, is also within the meaning of the invention.

[0084] Suitable epoxies (A1) are commercially available under the trade names CELLOXIDE™ 2021 P, CELLOXIDE™ 8000 from Daicel Corporation, Japan, or EPI KOTE™ RESIN 828 LVEL, EPI KOTE™ RESIN 166, EPI KOTE™ RESIN 169 from Westlake Epoxy, or Epilox™ resins of the product series A, T and AF from Leuna Harze, Germany, or EPICLON™ 840, 840-S, 850, 850-S, EXA850CRP, 850-LC from DIG KK, Japan.

[0085] Ethylenically unsaturated compounds (A2)

[0086] The ethylenically unsaturated compound (A2) is not further restricted structurally as long as it contains an ethylenically unsaturated double or triple bond.

[0087] Suitable examples include (meth)acrylates, allyl compounds, vinyl compounds, methallyl compounds, isoprenes, butadienes and propargyls.

[0088] The ethylenically unsaturated compound (A2) can be mono- or higher functional.

[0089] The ethylenically unsaturated compound (A2) preferably comprises at least one difunctional or higher-functional compound (A2). Ethylenically unsaturated compounds (A2) based on (meth)acrylates are preferably used.

[0090] For example, both aliphatic and aromatic (meth)acrylates can be used.

[0091] Here and in the following, “(Meth)acrylates” refers to both the derivatives of acrylic acid and methacrylic acid as well as combinations and mixtures thereof.

[0092] Suitable examples are the following ethylenically unsaturated compounds (A2): isobornyl acrylate, stearyl acrylate, tetrahydrofurfuryl acrylate, cyclohexyl acrylate, 3,3,5-trimethylcyclohexanol acrylate, behenyl acrylate, 2-methoxyethyl acrylate and other mono- or polyalkoxylated alkyl acrylates, isobutyl acrylate, isooctyl acrylate, lauryl acrylate, tridecyl acrylate, isostearyl acrylate, 2-(o-phenylphenoxy)ethyl acrylate, acryloylmorpholine, N,N-dimethylacrylamide, 4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,10-decanediol diacrylate, tricyclodecanedimethanol diacrylate, dipropylene glycol diacrylate,

[0093] Tripropylene glycol diacrylate, polybutadiene diacrylate, cyclohexanedimethanol diacrylate, diurethane acrylates of monomeric, oligomeric, or polymeric diols and polyols, trimethylolpropane triacrylate (TMPTA), and dipentaerythritol hexaacrylate (DPHA), and combinations thereof. Higher-functional acrylates derived from multiply branched or dendrimeric alcohols can also be used advantageously.

[0094] The analogous methacrylates are also within the meaning of the invention.

[0095] Urethane acrylates based on polyesters, polyethers, polycarbonate diols and / or (hydrogenated) polybutadiene diols can be used as higher molecular weight ethylenically unsaturated compounds (A2).

[0096] Ethylenically unsaturated compounds (A2) with allyl groups are also suitable, such as 1,3,5-triallyl-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione, which is commercially available as TAICROS®. Unhydrogenated polybutadienes with free double bonds, such as the Poly BD(ß^) types, can also be used as ethylenically unsaturated compounds (A2). A combination of several ethylenically unsaturated compounds (A2) is also within the scope of the invention.

[0097] Furthermore, hybrid compounds which, in addition to at least one epoxy function, have at least one ethylenically unsaturated group can be advantageously used in the curable composition.

[0098] By suitable selection of components (A1) and / or (A2), the reactivity and thus the open time of the curable mass can be advantageously adjusted and adapted to the process requirements.

[0099] Component (A) is present in the curable composition according to the invention, based on the total weight of the reactive components (A) to (E), in particular in a proportion of 5 to 85 wt.%, preferably in a proportion of 20 to 75 wt.%.

[0100] Component (B): at least difunctional thiol

[0101] The at least difunctional thiol (B) serves as a hardener in the composition according to the invention and comprises compounds having at least two thiol groups (-SH) in the molecule.

[0102] Component (B) is not further restricted in its chemical structure and preferably comprises aromatic and aliphatic thiols and combinations thereof.

[0103] Preferably, the at least difunctional thiol (B) is selected from the group consisting of ester-based thiols, polyethers with reactive thiol groups, polythioethers, polythioether acetals, polythioether thioacetals, polysulfides, thiol-terminated urethanes, thiol derivatives of isocyanurates, biaryls, diaryls and glycoluril, and combinations thereof.

[0104] Examples of commercially available ester-based thiols based on 2-mercaptoacetic acid include trimethylolpropane trimercaptoacetate, pentaerythritol tetramercaptoacetate and glycol dimercaptoacetate, which are available under the brand names Thiocure™ TMPMA, PETMA and GDMA from Bruno Bock, Germany.

[0105] Other examples of commercially available ester-based thiols include

[0106] Trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(3-mercaptobutylate), glycol di(3-mercaptopropionate) and tris[2-(3-mercaptopropionyloxy)ethyl]isocyanurate, available under the brand names Thiocure™ TMPMP, PETMP, GDMP and TEMPIC from Bruno Bock, Germany.

[0107] Examples of commercially available thioethers include DMDO (1,8-dimercapto-3,6-dioxaoctane), available from Arkema SA, France, DMDS (dimercaptodiethyl sulfide) and DMPT (2,3-di((2-mercaptoethyl)thio)-1-propanethiol), both available from Bruno Bock, Germany.

[0108] With regard to increased resistance of the cured compounds to temperature and humidity, the use of ester-free thiols is particularly preferred. Examples of ester-free thiols can be found in JP 2012 153 794 A, which is incorporated into the description by reference.

[0109] US 11 807 596 B2 describes ester-free thiol hardeners having a dithioacetal backbone, which can also be used advantageously in the compositions according to the invention.

[0110] Further ester-free polythiols, as disclosed in WO 2023 / 065802 A1 and suitable for use in the compositions according to the invention, can be synthesized, for example, starting from 5,5'-diallyl-2,2'-dihydroxybiphenyl (magnolol).

[0111] Particularly preferred in the composition according to the invention is the use of tris(3-mercaptopropyl)isocyanurate (TM PI) as a trifunctional ester-free thiol. These thiols have been shown to ensure both good hydrolytic stability and improve adhesion to various substrates. According to a particularly preferred embodiment, the at least difunctional thiol of component (B) therefore comprises tris(3-mercaptopropyl)isocyanurate alone or in a mixture, as well as in a mixture with other at least difunctional thiols.

[0112] Ester-free thiols based on a glycoluril compound are known from EP 3 075 736 A1. These can also be used in the compositions of the invention as component (B), alone or in a mixture with other at least difunctional thiols. Higher-functional thiols, which are obtainable, for example, by oxidative dimerization processes of at least difunctional thiols, can also be used in component (B).

[0113] Monofunctional thiols can also be advantageously used in the curable composition in addition to the at least difunctional thiol (B).

[0114] The above list is to be seen as exemplary and not exhaustive.

[0115] In particular, the proportion of the at least difunctional thiol (B) in the curable composition according to the invention is from 15 to 90 wt.%, preferably from 20 to 75 wt.%, based on the total weight of the reactive components (A) to (E).

[0116] Component (C): Accelerator

[0117] The compositions according to the invention contain as further component (C) an accelerator for curing.

[0118] Preferably, the accelerator is a heat-latent accelerator which is activated by heating to the temperature of hot curing, i.e. when heated to the activation temperature Ti, and releases a basic compound.

[0119] Both solid and liquid accelerators can be used.

[0120] All compounds that are also known as latent hardeners for epoxy compounds and that are suitable for addition crosslinking with the epoxy compound at the activation temperatures are suitable as accelerators.

[0121] The accelerator is preferably in solid form at room temperature and dispersed in the composition.

[0122] Furthermore, heat-latent, liquid accelerators can also be used, in particular liquid accelerators with blocked amine groups, which are converted into the free amine compound when heated to the activation temperature T 1.

[0123] The accelerator is preferably a nitrogen-containing compound, particularly preferably a compound selected from the group consisting of amines, ureas, imidazoles, triazine derivatives, polyamidoamines, and / or guanidines. Furthermore, adducts and / or reaction products of epoxides or isocyanates with the aforementioned nitrogen compounds can be used as accelerators, in particular reaction products with amines, as already described in US Pat. No. 5,430,112.

[0124] Examples of commercially available accelerators are Ajicure PN-H, Ajicure MY-24, Ajicure MY-25, Ajicure PN-23 (available from Ajinomoto Co., Ltd., Tokyo, Japan); Fujicure FXR1081, FXR1020, FXR1030 (available from Sanho Chemical Co. Ltd); Aradur 9506 (available from Huntsman International LLC., USA) and Curezol (available from Shikoku Chemicals Corporation, Japan).

[0125] Furthermore, encapsulated hardeners can be advantageously used as accelerators (C) in the curable compositions, i.e., accelerators (C) in encapsulated form. Commercial products are available under the name Novacure from Asahi-Kasei, Japan. Examples of commercially available products include HX-3613, HX-3722, HX-3741, HX-3742, HX-3088, HX-3921 HP, HX-3922HP, HX-3941 HP, HXA-3932HP, HXA-5911 HP, HXA-9322HP, and HXA-9382HP, or Technicure® LC-80 and Technicure® LC-100 from ACCI Specialty Materials, USA.

[0126] In addition to the aforementioned compounds, the use of photolatent bases as latent accelerators (C) is also possible. Examples of possible substance classes include 4-(ortho-nitrophenyl)-dihydropyridine, triethylammonium salts as disclosed in WO 2017 / 160810 A1, alpha-aminoacetophenones, or amines blocked with photolatent groups. These can release basic compounds upon actinic radiation and thus also act as accelerators (C).

[0127] In the curable composition according to the invention, the accelerator (C) is present in particular in a proportion of 0.1 wt.% to 30 wt.%, preferably 1 to 25 wt.%, based on the total weight of the reactive components (A) to (E).

[0128] Component (D): Stabilizer

[0129] The curable compositions for use in the process according to the invention further comprise a stabilizer (D). By adding the stabilizer (D), storage stability and processing time can be improved, for example.

[0130] Numerous stabilizers (D) are known in the prior art; for example, boric acids or aluminum chelates can be used. Sulfonyl isocyanates and organic acids can also be used alone or as a stabilizer mixture, as described in WO 2019 / 115203 A1.

[0131] Furthermore, aluminates, titanates, zirconium acid esters and isocyanates, as described in CN 110 054 760 B, can be used as stabilizer (D).

[0132] By using a stabilizer (D), it is possible to ensure a processing time of the curable compositions of at least 24 hours, preferably at least 72 hours, at room temperature. The compositions remain fully activatable according to the process steps of the invention.

[0133] Boric acids as component (D) can carry linear alkyl radicals, branched alkyl radicals, cyclic alkyl radicals and / or aromatic radicals.

[0134] Examples of boric acids are trimethyl borate, triethyl borate, tri-n-propyl borate, triisopropyl borate, tri-n-butyl borate, tris-(2-ethylhexyl) borate, tricyclohexyl borate, 2,2'-oxybis(5,5-dimethyl-1,3,2-dioxaborolane), triphenyl borate, tribenzyl borate, tri-ortho-tolyl borate, tri-meta-tolyl borate and triethanolamine borate.

[0135] An example of an aluminum chelate is aluminum tris-acetylacetonate.

[0136] Sulfonyl isocyanates used as component (D) can be bonded to an aliphatic or aromatic radical.

[0137] The aliphatic sulfonyl isocyanate may comprise a linear or branched alkyl radical having 1 to 18 C atoms, preferably having 4 to 8 C atoms.

[0138] The sulfonyl isocyanate preferably comprises an aromatic sulfonyl isocyanate, particularly preferably a monofunctional arylsulfonyl isocyanate. The aryl radical can be an optionally alkyl-substituted or unsubstituted phenyl radical, naphthyl radical, or biphenyl radical. The sulfonyl isocyanate particularly preferably comprises para-toluenesulfonyl isocyanate.

[0139] In principle, any acidic compound capable of transferring protons can be used as the organic acid. The acid preferably has a pKa value of 12 or less, particularly preferably 10 or less. In particular, the pKa value of the acid is below the pKa value of the corresponding acid of the latent accelerator (C).

[0140] Suitable acids include barbituric acid, 3,4-dihydroxybenzoic acid, 3,4,5-trihydroxybenzoic acid, embonic acid,

[0141] Citric acid, phenylboronic acid, Meldrum's acid, phloroglucinol, fumaric acid, ascorbic acid, salicylic acid, 3,4-dihydroxycinnamic acid, quinone derivatives of enolizable acids, mercapto acids, acid anhydrides, acidic phenols, and / or organophosphorus acids. The above list is intended only as examples and is not exhaustive.

[0142] More preferably, the acid comprises or consists of an acidic phenol with a pKa value of 9.0 or less. Most preferably, the acid comprises pyrogallol, alone or in a mixture with another acidic phenol and / or another of the aforementioned acids.

[0143] A combination of several stabilizers (D) is also within the meaning of the invention.

[0144] In the curable composition according to the invention, the stabilizer (D) is present in particular in a proportion of 0.01 wt.% to 1 wt.%, based on the total weight of the reactive components (A) to (E), preferably in a proportion of 0.01 wt.% to 0.5 wt.%.

[0145] Component (E): radical photoinitiator

[0146] The curable composition may further comprise a radical photoinitiator (E).

[0147] The radical photoinitiator (E) enables the light fixation of the curable composition, particularly using the ethylenically unsaturated compound (A2). In addition to component (A2), other radically curable formulation components can also be incorporated into the light fixation network. For example, the reaction of the at least difunctional thiol (B) with component (A2) is possible using a photoinitiator (E) via a radical mechanism. Furthermore, the amount of the at least difunctional thiol (B) available for the addition reaction can be advantageously influenced via a light reaction.

[0148] All common, commercially available compounds can be used as photoinitiator (E), such as a-hydroxyketones, benzophenone, a,a'-diethoxyacetophenone, 4,4-diethylaminobenzophenone, 2,2-dimethoxy-2-phenylacetophenone, 4-isopropylphenyl-2-hydroxy-2-propylketone, 1-hydroxycyclohexylphenylketone, isoamylparadimethylaminobenzoate, methyl 4-dimethylaminobenzoate, methylorthobenzoylbenzoate, benzoin, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2-hydroxy-2-methyl-1-phenylpropan-1-one,

[0149] 2-isopropylthioxanthone, dibenzosuberone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide and bisacylphosphine oxides, wherein the said compounds can be used alone or in combination of two or more of the said compounds as photoinitiator (E).

[0150] As a photoinitiator (E), which can be activated by UV radiation, the IRGACURE TM-Types from BASF SE, Germany, are used, such as the types IRGACURE 184, IRGACURE 500, IRGACURE 1179, IRGACURE 2959, IRGACURE 745, IRGACURE 651, IRGACURE 369, IRGACURE 907, IRGACURE 1300, IRGACURE 819, IRGACURE 819DW, IRGACURE 2022, IRGACURE 2100, IRGACURE 784, IRGACURE 250, IRGACURE TPO, IRGACURE TPO-L. Furthermore, the DAROCUR TM -Types from BASF SE, Germany, such as the types DAROCUR MBF, DAROCUR 1173, DAROCUR TPO and DAROCUR 4265.

[0151] The above lists are to be seen as examples for the photoinitiator (E) and should not be understood as limiting.

[0152] The photoinitiator used as component (E) in the compositions according to the invention is preferably activatable by actinic radiation having a wavelength in the range from 200 to 400 nm, particularly preferably from 250 to 365 nm. If required, the photoinitiator (E) can be combined with a suitable sensitizer.

[0153] The photoinitiator (E) is present in the curable composition in particular in a proportion of 0 to 5 wt.%, for example 0.01 to 5 wt.%, preferably 0.5 to 3 wt.%, based on the total weight of the reactive components (A) to (E).

[0154] Component (F): Additives

[0155] In addition to components (A) to (E), the curable compositions of the invention may contain further additives (F). Examples of additives (F) 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, antioxidants, plasticizers, fillers, flame retardants, corrosion inhibitors, water scavengers, diluents, flow control and wetting additives, adhesion promoters, and combinations thereof.

[0156] The additives may further comprise an inductively heatable component (F1). This component can effectively convert the introduced energy into heat in an external magnetic or electromagnetic alternating field.

[0157] The inductively heatable component (F1) is preferably selected from the group of ferro- and ferrimagnetic particles.

[0158] The temperature required for activation can be controlled, for example, by adjusting the energy applied via the external alternating field, for example using a pyrometer in conjunction with a suitable controller, such as a PID controller.

[0159] The Curie temperature of the particles can also be selected to be within the range of the desired activation temperature Ti of the mass. Above the Curie temperature, the particles lose their magnetic properties and can absorb little to no further energy via induction. This allows for particularly precise control of the temperature of the hardenable mass during activation, thus minimizing the thermal stress on the first substrate. Suitable inductively heatable components (F1) include magnetic metals such as iron, cobalt, and nickel, as well as their ferromagnetic and ferrimagnetic alloys and oxides, and mixtures thereof.

[0160] Particularly suitable are alloys with iron and iron-containing oxides such as iron oxide, magnetite, ferrite, or manganese-zinc-iron oxides and other Ni-Zn alloys.

[0161] Selected examples of suitable iron oxides are FeSiO4, Fe2O3, Fe3O4, MnFe2O4 and SrFe2Oi9.

[0162] Mixed iron oxides and alloys containing barium or strontium are also suitable as ferromagnetic components.

[0163] The inductively heatable component (F1) is present in the masses in particular in a proportion of 1 to 60 wt.%, preferably 10 to 40 wt.%, in each case based on the total weight of the mass.

[0164] The curable composition may further contain a dye (F2). This can be used to create an optical color impression in the visible light range or to formulate an opaque adhesive.

[0165] The dye (F2) can also be used to absorb thermal radiation, especially infrared radiation. In this case, the dye also preferentially absorbs in the longer wavelength range (> 780 nm), beyond the visible spectrum. Examples of black dyes (F2) that absorb over a broad wavelength range are carbon black and titanium black.

[0166] Furthermore, it is possible that the inductively heatable component (F1) absorbs over a broad wavelength range and can replace the dye (F2) completely or partially.

[0167] Dyes (F2) that absorb almost or exclusively in the NIR and / or IR range can also be used advantageously. In particular, IR absorbers such as those described in EP 3 943 534 A1 can be used as dyes (F2) and include, for example, (phthalo)cyanines, squaraine or squarylium dyes, BODIPYs or pyrromethene dyes, as well as porphyrins and dithiolene complexes.

[0168] The combination of several dyes (F2) is also within the scope of the invention. The dye (F2) is present in the compositions in particular in a proportion of 0.01 to 5 wt.%, preferably 0.5 to 4 wt.%, based in each case on the total weight of the composition.

[0169] The additives are present in the curable mass in particular in a proportion of 0 to 80 wt.%, for example from 1 to 80 wt.%, preferably in a proportion of 0 to 50 wt.%, for example from 1 to 50 wt.%, based on the total weight of the mass.

[0170] Formulation of the curable masses

[0171] A formulation of the curable composition according to the invention for use in the process according to the invention comprises the components (A) to (D) described above.

[0172] According to a first embodiment, the mass preferably consists of the following components, each based on the total weight of the reactive components (A) to (E):

[0173] (A) 5 to 85 wt.% of the thiol-reactive component,

[0174] (B) 15 to 90 wt.% of the at least difunctional thiol,

[0175] (C) 0.1 to 30 wt.% of the nitrogen-containing compound as a latent accelerator,

[0176] (D) 0.01 to 1% by weight of the stabilizer

[0177] In the first embodiment, component (E) is not included.

[0178] According to a second embodiment, the mass preferably comprises or consists of the following components, each based on the total weight of the reactive components (A) to (E):

[0179] (A) 5 to 85 wt.% of the thiol-reactive component comprising at least one epoxide (A1) and one ethylenically unsaturated compound (A2),

[0180] (B) 15 to 90 wt.% of the at least difunctional thiol, (C) 0.1 to 30 wt.% of the nitrogen-containing compound as a latent accelerator,

[0181] (D) 0.01 to 1% by weight of the stabilizer,

[0182] (E) 0.01 to 5 wt.% of the radical photoinitiator.

[0183] By combining an ethylenically unsaturated compound (A2) with a radical photoinitiator (E), the compositions of the invention can be fixed with light. This allows for particularly good positioning of joined components until final curing. Conventional fixation aids, which are unsuitable for processing miniaturized components or would entail unreasonable additional effort, can thus be dispensed with.

[0184] According to a third embodiment, the mass preferably comprises or consists of the following components:

[0185] (A) 5 to 85 wt.% of the thiol-reactive component, based on the total weight of the reactive components (A) to (E).,

[0186] (B) 15 to 90 wt.% of the at least difunctional thiol, based on the total weight of the reactive components (A) to (E),

[0187] (C) 0.1 to 30 wt.% of the nitrogen-containing compound as latent accelerator, based on the total weight of the reactive components (A) to (E),

[0188] (D) 0.01 to 1 wt.% of the stabilizer, based on the total weight of the reactive components (A) to (E),

[0189] (F) 1 to 60 wt.% of the inductively heatable component (F1), based on the total weight of the mass.

[0190] By adding an inductively heatable component (F1), the metered curable masses can be preactivated by applying an external magnetic or electromagnetic alternating field. Alternatively, the energy input can also take place during the metering process, for example, in a flow-through activation device. According to a fourth embodiment, the mass preferably comprises or consists of the following components:

[0191] (A) 5 to 85 wt.% of the thiol-reactive component (A), based on the total weight of the reactive components (A) to (E),

[0192] (B) 15 to 90 wt.% of the at least difunctional thiol, based on the total weight of the reactive components (A) to (E),

[0193] (0) 0.1 to 30 wt.% of the nitrogen-containing compound as latent accelerator, based on the total weight of the reactive components (A) to (E),

[0194] (D) 0.01 to 1 wt.% of the stabilizer, based on the total weight of the reactive components (A) to (E),

[0195] (F) 0.01 to 5% by weight of the dye (F2), based on the total weight of the mass.

[0196] By adding a dye (F2), the metered curable compositions can be preactivated by actinic radiation, particularly NIR and / or IR radiation. Alternatively, the energy input can also take place during the metering process, for example, in a flow-through activation device.

[0197] The curable compositions according to the invention of all embodiments are preferably provided as one-component compositions.

[0198] Properties and use of the hardenable mass

[0199] The curable compound described above is particularly suitable for joining, casting, or coating substrates. This also includes bonding, molding, or sealing substrates.

[0200] It is particularly suitable for joining thermally sensitive components, especially those that are unsuitable for a curing process of up to one hour at temperatures above 60 °C, for example, due to paint coatings or sensitive electronics. Another application is in areas where bonds or encapsulations with as little stress as possible are required. Examples include circuit board encapsulations, which are exposed to changing temperature conditions during operation, or bonds to reinforce solder joints.

[0201] The curable composition of the present invention can be preactivated at moderate activation temperatures Ti and in a short time. The curable composition is therefore particularly suitable, in combination with light-curability, for bonding applications where short cycle times are required. Furthermore, the possibility of eliminating the need for oven heating enables a space- and energy-saving process.

[0202] According to the invention, the activation temperature Ti required for activation is at least 50 °C, preferably 60 °C or more, but in particular not more than 200 °C, preferably not more than 180 °C, particularly preferably not more than 120 °C.

[0203] The activation time can be varied over a wide range and depends on the composition of the curable mass, the type of energy input, and the selected activation temperature Ti. The curable mass is kept at the activation temperature Ti for a maximum activation time of 15 minutes, preferably for a maximum of 1 minute.

[0204] Longer activation times may be preferable if the heat input takes place indirectly, for example in a convection oven.

[0205] In the case of direct heat input, for example through actinic radiation, infrared radiation or induction, activation times of a few seconds can be used advantageously.

[0206] Furthermore, activation using a flow-through activation device may require short activation times. To prevent undesired curing during activation using such a dosing device, it is advantageous to dose the curable mass at a constant volume flow during the pre-activation step. An exemplary device 10, which can serve as a flow-through activation device, for use in the process according to the invention is described below.

[0207] The device 10 shown in Fig. 1 comprises a dispensing needle 12, which is partially enclosed by a heating element 14. The heating element 14 is made of a material with high thermal conductivity, for example, copper.

[0208] The area of ​​the dispensing needle 12 encompassed by the heating element 14 provides an effective heating area in which a heat input suitable for pre-activation can take place during the dispensing process on the hardenable mass passing through the dispensing needle 12.

[0209] The dispensing needle 12 can also be advantageously combined with a dispensing unit (not shown) for adjusting the volume flow of the curable mass. In this case, the dispensing needle 12 is connected to the dispensing unit in the flow direction, with the flow direction running from a needle inlet 16 to a needle outlet 18.

[0210] The heating element 14 is heated by heating cartridges 20, which are positively received in suitable receptacles 22 of the heating element 14 (see Figs. 2 and 3). The receptacles 22 are designed, for example, as bores that are complementary to the outer circumference of the heating cartridges 20.

[0211] The heating cartridges 16 can be heated via heating cables 24 and provide a power of, for example, 30 W to heat the radiator 14.

[0212] The temperature of the radiator 14 is regulated by a control unit (not shown) and measured by a temperature sensor 26 located inside the radiator 14.

[0213] The temperature sensor 26 can be connected to the control unit via sensor cable 28 in a signal-transmitting manner, so that the control unit can regulate the power of the heating cartridges 20 via the heating cables 24 based on temperature values ​​measured by the temperature sensor 26 and transmitted to the control unit. In the embodiment shown, the dispensing needle 12 has a needle volume of 0.057 mL, which is calculated from the inner diameter of the dispensing needle 12 (d = 1.2 mm) and its length (I = 50 mm). The area of ​​the dispensing needle 12 (I = 40 mm) that is positively enclosed by the heating element 14 results in a heating volume of 0.045 mL, where the heating volume refers to the portion of the needle volume that must be heated to the desired activation temperature Ti to activate the hardenable mass.

[0214] The volume flow during the dosing process of the curable mass in the process according to the invention is preferably at least 0.05 mL / min, particularly preferably at least 0.1 mL / min. Taking into account the effective heating range of 0.045 mL in the embodiment shown, this results in a preferred activation time of at most 1 min, particularly preferably at most 30 s.

[0215] To enable sufficient activation of the curable mass, the volume flow is preferably at most 1.0 mL / min, particularly preferably at most 0.8 mL / min. In this case, the preferred activation time is at least 2.5 s, particularly preferably at least 3 s.

[0216] The activation temperature is preferably from 80 to 180 °C, particularly preferably from 100 °C to 150 °C.

[0217] It is understood that the previously specified values ​​for the dimensions of the dispensing needle, the heating volume, and the volume flow are only examples and can be adapted according to the requirements of the respective application scenario.

[0218] After activation of the curable mass by suitable heat input, the activated mass exhibits an open time during which it remains liquid and does not yet exceed the gel point. Within this open time, the subsequent process steps, in particular the optional addition and joining of an additional substrate in step c1), can be carried out reliably.

[0219] However, it is also possible for the activated mass to remain at least partially joinable beyond the specified open time before solidifying to such an extent that no further flow or pressing onto another substrate is possible. To enable a robust process, the optional addition of a second substrate in step c1) of the method according to the invention is preferred within the open time.

[0220] The open time of the activated masses is preferably at least 30 seconds. Short open times of 30 seconds to 1 minute are particularly suitable for rapid industrial manufacturing processes. When using a flow-through activation apparatus, however, a longer open time may be advantageous for reasons of process reliability, particularly an open time in the range of 2 minutes or more, preferably 5 minutes or more.

[0221] The duration of curing, and therefore the open time, preferably does not exceed 24 hours.

[0222] There is usually a correlation between the open time and the curing time, which means that a shorter open time is not a disadvantage per se, but can offer advantages for the overall process due to the faster curing of the compound.

[0223] However, curable materials with very short open times of less than 30 seconds can only be processed to a limited extent in a joining process after activation and are also not suitable for flow activation.

[0224] Optionally, the curable compound can be fixed after activation with actinic radiation, providing what's known as "green strength," or handling strength. This means that no further flow occurs after curing. Components in joints remain fixed relative to each other and can thus be transferred to further production steps, even manually, for example.

[0225] Light fixation strengths are typically above 1 MPa on glass / glass.

[0226] The compound activated by the process according to the invention typically cures completely within 7 days at room temperature, preferably within 3 days, particularly preferably within one day, i.e., within 24 hours. For faster curing or to accelerate the final curing of the compound, it can optionally be maintained, after activation at the activation temperature Ti, at a curing temperature T2 that is above room temperature, but preferably not higher than 50°C, particularly preferably not higher than 40°C.

[0227] Preferably, the mechanical properties of the cured mass, i.e. after complete curing, are in the range of conventional thiol-cured epoxy resins.

[0228] In particular, the cured mass has a glass transition temperature in the range of 15 to 85 °C and achieves compressive shear strengths of at least 1 MPa, preferably at least 4 MPa, on substrates such as aluminum, FR4, nickel or PA.

[0229] Measurement methods and definitions used

[0230] Room temperature

[0231] Room temperature is defined as 23 °C ± 2 °C.

[0232] Curing

[0233] Curing of the adhesive is achieved as soon as the compressive shear strength exceeds 1 MPa or the achieved compressive shear strength is equal to that of the heat cure.

[0234] DSC measurements

[0235] DSC measurements of reactivity were performed in a dynamic differential scanning calorimeter (DSC) type DSC3+ from Mettler Toledo according to the standards of the DIN EN ISO 11357 group.

[0236] For this purpose, 6 to 10 mg of the liquid sample were weighed into a 40 pL aluminum crucible, tightly sealed with a lid, and subjected to a measurement from 30 to 220 °C at a heating rate of 10 K / min (first heating run) and a measurement from 0 to 220 °C at a heating rate of 20 K / min (second heating run). The process gas was air (flow rate 30 mL / min). The reaction enthalpy was evaluated as an integral of the first heating run, as well as the glass transition temperature in the second heating run, using the half-step method based on DIN EN ISO 11357-2.

[0237] To determine the residual enthalpy, the aluminum crucibles were prepared in the same way and then preactivated in the furnace according to the conditions specified in Table 1. After seven days, the measurement was taken from 30 to 220 °C and at a heating rate of 10 K / min. The process gas was air (flow rate 30 mL / min). The residual enthalpy is the quotient of the measured enthalpy seven days after preactivation and the measured enthalpy of the unactivated adhesive, expressed as a percentage.

[0238] Compressive shear strength after activation

[0239] Two FR4 test specimens (dimensions 20 mm x 20 mm x 5 mm), annealed at 120 °C for 3 hours, were bonded together with a 5 mm overlap using the respective compound according to the invention. For this purpose, a bead of the compound was applied to the first test specimen. The compound was pre-activated in an oven under the conditions defined for each compound in Table 1. A second test specimen was then joined. The adhesive layer thickness of 0.1 mm and the overlap were adjusted using spacer wires and a bonding device. The test specimens were then measured after the specified time.

[0240] Compressive shear strength (DSF) after oven curing

[0241] Two test specimens (dimensions 20 mm x 20 mm x 5 mm) made of tempered FR4 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 80 °C for 60 minutes.

[0242] Open time

[0243] The determination is carried out using a haptic test using a toothpick on a drop of adhesive (diameter: 11 mm, height: 1.4 mm) on an aluminum tensile shear test specimen (width: 25 mm, length: 100 mm, thickness: 1.6 mm). The open time is determined in triplicate, and the arithmetic mean of the measured values ​​is determined. The adhesive drops are activated under predefined conditions depending on the intended application. The activation conditions such as temperature, duration, and heat input can be found in the following tables. A stopwatch is started at the end of the heating process.

[0244] Using a toothpick, the expected viscosity increase is assessed haptically. At intervals of 5 seconds, the geometry of the activated adhesive droplet is manipulated with the toothpick in a vertical movement by pulling the tip of the toothpick upward from the center of the adhesive droplet, holding the toothpick at an angle of approximately 45° to the slide. If the activated adhesive droplet does not return to its original geometry within 1 second of manipulation with the tip of the toothpick, the stopwatch is stopped, and the end of the adhesive's open time is reached.

[0245] In the event that a mass remains liquid or has an open time of less than 30 s and / or can no longer be reliably determined using the method described, it is marked as undetermined with “nb”.

[0246] Viscosity and processing time

[0247] To determine the processing time, the viscosity of the curable compound was measured at a shear rate of 10 / s using an Anton Paar MCR-302 rheometer. A PP20 die was used, with a gap of 500 pm and a temperature of 23 ± 1 °C. A sufficient processing time is achieved if the measured viscosity increases by less than 100% during storage at room temperature for at least 24 hours.

[0248] Manufacturing examples

[0249] To prepare the curable compositions according to the invention, solid and soluble components (D) and (E) were first dissolved in component (A) at room temperature. Subsequently, the remaining liquid components (B), (D), and (E) were added. Finally, component (C) and optionally further additives (F) were added.

[0250] The components were blended according to the weight percentages specified in the tables. Mixing was performed in a Labotop with butterfly mixing tools under vacuum (PC laboratory system). Appropriate cooling of the compound during production ensures that the curing process does not begin at this stage. The resulting compounds were then filled into cartridges.

[0251] The energy input for hot curing to the activation temperature Ti can be achieved by convection, for example in a circulating air oven, by heat conduction, for example by means of a hot plate or thermode, or by means of electromagnetic radiation, for example by means of infrared radiation sources, a laser, microwaves or induction.

[0252] The following list contains all the compounds used to produce the curable masses and their abbreviations.

[0253] Component (A) - Thiol-reactive component:

[0254] A1-1 : Epikote Resin 166 (mixture of bisphenol A and bisphenol F glycidyl ethers, Hexion, USA)

[0255] A1-2: jER YX 8034 (Mitsubishi Chemical, Japan)

[0256] A2-1: Photomer 4006 (trimethylolpropane triacrylate, IGM Resins, USA)

[0257] A2-2: Sartomer SR833S (Arkema, France)

[0258] A2-3: Sartomer SR420 (Arkema, France)

[0259] Component (B) - at least difunctional thiol:

[0260] B-1: TMPI (Tris(3-mercaptopropyl)isocyanurate)

[0261] B-2: Karenz MTPE-1 (Pentraerythritol tetrakis(3-mercaptobutylate), Showa Denko, Japan) Component (C) - Accelerator:

[0262] C-1: Ajicure PN-23J (Ajinomoto company, Japan)

[0263] C-2: Novacure HXA5911 HP (Company Asahi Kasei, Japan)

[0264] Component (D) - Stabilizer: D-1: Pyrogallol (1,2,3-trihydroxybenzene, Merck, USA)

[0265] D-2: para-toluenesulfonyl isocyanate (Merck company, USA)

[0266] D-3: Tributyl borate (Merck company, USA)

[0267] Component (E) - Radical photoinitiator:

[0268] E-1 : Omnirad 184 (1-Hydroxycyclohexylphenyl ketone, IGM Resins, Germany)

[0269] Component (F) - Additives:

[0270] F-1: Silbond FW 600 EST (Quartzwerke GmbH, Germany)

[0271] F1-1: Iron(II,III) oxide (company Alfa Aesar Thermo Fisher, USA)

[0272] F-2: Cab-O-Sil TS-720 (Cabot Corporation, USA)

[0273] Table 1: Composition and properties of curable compositions according to the invention.

[0274] nb: not determinable

[0275] Table 2:

[0276] nb = not determinable

[0277] * = no measurable deviation from the baseline

[0278] The inventive compositions of Examples E1 to E11 each comprise the required components (A) to (D). The compositions are processable for at least 24 hours and can be preactivated by heating to an activation temperature Ti according to the conditions specified in the tables. The measured open times are at least 30 seconds. After 24 hours, the compositions are solid and fully cured after 168 hours at the latest. The measured residual enthalpies are less than 15%.

[0279] Inventive examples E4 to E11 contain, in addition to components (A) to (D), the optional component (E), which can optionally be used for light-fixing the curable compositions after process step c2).

[0280] In Examples E1 to E5, different components (A) and (B) are used. This clearly shows that both compositions that use only an epoxide (A1) as the thiol-reactive component (A) and compositions that use a combination of epoxide (A1) and ethylenically unsaturated compound (A2) exhibit the desired behavior after preactivation.

[0281] In example E6, the accelerator (C) is an encapsulated hardener that is released by heating the compound to the activation temperature Ti. Under the selected conditions, the compound has an open time of 30 s.

[0282] Example E7 contains an inductively heatable component (F1) as additive (F). The compound is therefore suitable for pre-activation by induction, providing a particularly precise and gentle method for pre-activating the compound.

[0283] In example E8, the additive (F-1) is omitted.

[0284] In Example E9, the stabilizer (D) is varied, using a stabilizer mixture of an acidic phenol (pyrogallol) and an organoborate. The curable compound has a pot life of at least 24 hours. With an open time of 1.33 minutes, the compound is suitable for high-speed production processes.

[0285] In Example E10, a monofunctional acrylate (A2-3) is additionally used as the ethylenically unsaturated compound (A2). In Example E11, the thiol-reactive component (A) consists of an ethylenically unsaturated compound (A2).

[0286] The compositions shown can be thermally preactivated according to the inventive process and then cure within a waiting period. The cured compositions according to the invention meet all mechanical requirements.

[0287] Comparative Examples V1 and V2 do not use component (B). Comparative Example V1 either remained liquid or cured immediately. An open time could be determined for V2, but no significant strength buildup occurred after the open time.

[0288] The compound according to Comparative Example V3 does not contain stabilizer (D). The required processing time was not achieved.

[0289] The compound according to comparative example V4 does not contain accelerator (C). The compound does not cure.

[0290] Further comparative examples include the adhesives GE6515 (cationic, heat-curing), LT3708 (isocyanate-based, heat-curing), and BS3770 (isocyanate-based, heat-curing) available from DELO Industrie Klebstoffe GmbH & Co. KGaA. Depending on the selected pre-activation parameters, these adhesives remained liquid for more than 1 day after heat application or cured without a measurable open time.

Claims

Patent claims 1. A method for joining, casting or coating substrates using a curable mass, the method comprising the following steps: a) providing the curable mass, the curable mass comprising the following components: (A) a thiol-reactive component, (B) a thiol which is at least difunctional, (C) a nitrogen-containing compound as a latent accelerator, and (D) a stabilizer; b) dosing the curable mass onto a first substrate; c) activating the curable mass by heating the curable mass to an activation temperature Ti of 50°C or higher; and d) maintaining a waiting time for curing the curable mass, during which the curable mass is kept at a curing temperature T2; wherein the curable mass, after activation at the activation temperature Ti, has an open time of at least 30 seconds and cures completely within 7 days, and wherein the activation temperature Ti is higher than the curing temperature T2.

2. The method according to claim 1, wherein the difference between activation temperature Ti and curing temperature T is 230 °C or more.

3. The process according to claim 1 or 2, wherein the activation temperature Ti is not more than 200 °C, preferably not more than 180 °C, particularly preferably not more than 120 °C.

4. Process according to one of the preceding claims, wherein the curing temperature T2 is less than 50 °C, preferably less than 40 °C.

5. Process according to one of the preceding claims, wherein the curing temperature T2 is at least 20 °C.

6. Process according to one of the preceding claims, wherein the curable mass is kept at the activation temperature Ti for an activation period of at most 15 minutes, preferably of at most 1 minute.

7. Process according to one of the preceding claims, wherein the thiol-reactive component (A) of the curable composition comprises an epoxide (A1).

8. The process according to claim 7, wherein the thiol-reactive component (A) of the curable composition comprises an epoxide (A1) and an ethylenically unsaturated compound (A2).

9. Process according to one of the preceding claims, wherein the accelerator (C) is solid at room temperature and is dispersed in the mass.

10. Method according to one of the preceding claims, wherein the activation of the curable mass according to step c) takes place before the dosing of the curable mass according to step d).

11. The method according to any one of the preceding claims, wherein the method further comprises the following step: c1) supplying a second substrate to the curable mass on the first substrate to form a substrate composite.

12. The process according to any one of the preceding claims, wherein the curable composition further contains a free-radical photoinitiator (E), and the process further comprises the following step: c2) fixing the curable composition by actinic radiation; wherein step c2) takes place after the activation according to step c).

13. A process according to any one of the preceding claims, wherein the cured mass has a residual enthalpy of 15% or less at T2 after 7 days.

14. The method according to any one of the preceding claims, wherein the mass further contains an additive (F) comprising an inductively heatable component (F1), and wherein the curable mass is inductively heated to the activation temperature Ti.

Images