DE102023004759A1 - Curable epoxy compositions, their use and polythiol hardener mixtures - Google Patents

Abstract

Described are curable epoxy compositions containing a) epoxy resin, b) selected mixtures of polythiol hardeners and c) selected curing accelerators.
The epoxy compositions can be processed into molded articles or adhesive bonds with excellent hydrolysis resistance.

Description

The invention relates to epoxy compositions with selected polythiol hardener mixtures and to the use of these compositions as adhesives, sealants, casting resins, potting compounds, or for the production of molded articles. Furthermore, novel polythiol hardener mixtures are described.

Epoxy resins are synthetic resins containing epoxy groups. These are reactive resins that, when mixed with a hardener, react to form a thermoset. The hardener acts as a reaction partner and, together with the epoxy resin, forms a macromolecular polyether. Depending on the application, a resin formulation may contain additives.

After curing, epoxy resins possess good mechanical properties as well as good temperature and chemical resistance. Epoxy resins are used, among other things, as reactive and stoving varnishes, adhesives, for the production of laminates, as embedding materials in metallography, or as molding compounds for components in electrical engineering and electronics.

To produce cured epoxy compounds, the epoxy resin is mixed with a hardener. This triggers the polymerization of the epoxy compound, creating a three-dimensional polymer network. Hardeners come from a wide variety of substance classes. Examples include polyvalent aromatic or aliphatic amines, dicarboxylic anhydrides, or polythiols.

Epoxy compositions can be presented as one-component or two-component formulations. In one-component formulations, the curable resin, hardener, and optionally other additives are used in a ready-to-use state and are stimulated to cure by activation, for example, by heating and/or irradiation. In two-component formulations, the curable resin and hardener are stored separately and mixed together immediately before curing. The curable resin and/or hardener may optionally contain other additives.

In addition to hardeners, epoxy adhesive formulations often contain curing accelerators. These are usually compounds with amino groups.

Epoxy adhesives containing polythiol hardeners are known from the patent literature.

In the JP 2009-051954 A accordingly WO 2009/028271 A1 discloses curable compositions consisting of a) compounds containing glycidyl and (meth)acryloyloxy groups in one molecule, b) compounds containing more than one thiol residue per molecule, and c) a curing accelerator. The proportion of component b) is 1 to 60 parts per 100 parts of component a). A wide variety of compounds are mentioned as polythiols, including 1,1,1-tris-(hydroxymethyl)propane-tris-(3-mercaptopropionate).

The CN 103282401 A accordingly WO 2012/093510 A1 discloses resin compositions containing a) epoxy resin without benzene rings, b) polythiol compound, and c) latent hardener, e.g., an imidazole. The composition is characterized by rapid curing at low temperatures and by the fact that the cured product has a low glass transition temperature that does not change even upon prolonged storage. A wide variety of polythiol compounds are mentioned, including 1,1,1-tris(hydroxymethyl)propane tris(3-mercaptopropionate) and dipentaerythritol hexa(3-mercaptopropionate).

In the WO 2018/085546 A1 discloses curable compositions containing a) polythiol, b) polyepoxide, c) a photolatent base that releases a first amine upon irradiation, and d) a second amine that is in a separate phase. The composition is radiation- and heat-curable and is characterized by long shelf life. A wide variety of compounds are mentioned as polythiols. In the examples, a liquid poly(bis(ethyleneoxy)methane) with mercaptan end groups is used.

In the US 2013/0128435 A Curable resin compositions are disclosed which contain a) an epoxy resin which is liquid at 23°C, b) a hardener which is liquid at 23°C and which may be, inter alia, a polythiol, c) a secondary or tertiary amine which is solid at 23°C, and d) fillers in an amount of 50 to 150 parts by weight per 1,000 parts by weight of components a) to c). The composition has a low viscosity of 0.5 to 50 Pas at 25°C. The cured products are characterized by good resistance resistant to moisture. A wide variety of compounds are mentioned as polythiols, including 1,1,1-tris-(hydroxymethyl)propane tris-(3-mercaptopropionate) and dipentaerythritol hexa-(3-mercaptopropionate). The examples do not describe compositions using polythiols as hardeners.

The JP 2021-03834 A relates to curable compositions containing a) epoxy resin, b) thiol curing agent, and c) a selected curing accelerator having a primary and an amino group bonded to an alkylene radical. The compositions cure at low temperatures and exhibit good stability upon heating. A wide variety of compounds are mentioned as polythiols, including 1,1,1-tris-(hydroxymethyl)propane tris-(3-mercaptopropionate) and dipentaerythritol hexa-(3-mercaptopropionate). The latter compounds are also used in the examples.

The CN 104797623 A accordingly WO 2014/084292 A1 Describes hardeners for epoxy resins. The hardeners contain at least one hydroxyl group and at least two thiol groups per molecule and have a molecular weight in the range of 100 to 2,000 g/mol. The hardeners allow rapid curing at low temperatures, and one-component formulations containing these hardeners have good storage stability. In addition to these hardeners, other polythiols can also be used. Specifically mentioned compounds include 1,1,1-tris-(hydroxymethyl)-propane tris-(3-mercaptopropionate) and dipentaerythritol hexa-(3-mercaptopropionate), which are also used in the examples.

Although a large number of different epoxy resins with different properties are known, there is still a need for such resins with improved properties.

One problem that underscores the need for the present invention concerns the lack of hydrolytic stability of molded parts or adhesive bonds. This instability poses a significant challenge for manufacturers of molded parts or adhesive bonds, as it negatively impacts the quality of the molded parts or the quality and adhesion strength of the bond.

For example, comparative samples with poor hydrolytic stability show that the bond strength of bonds decreases significantly after only 100 hours in a test with 85% relative humidity at 85°C. This problem is critical because a minimum stability of at least 250 hours under these test conditions is currently required to meet user requirements. Hydrolytic stability is crucial because molded bodies and adhesives are exposed to humid environments in many applications and therefore must exhibit high resistance to moisture and hydrolytic degradation.

Another problem that underscores the need for the present invention concerns the high viscosities of liquid hardeners, which complicate their incorporation into the epoxy compound and their homogeneous distribution within it. An uneven distribution of the hardener in the curable mixture can also have a negative impact on the quality of molded articles or on the quality and adhesion strength of the bond.

The present invention aims to solve these urgent problems of the lack of hydrolytic stability and the high viscosity of the hardener and to provide epoxy compositions, particularly in the form of one-component formulations, with a significantly improved stability that meets the high requirements of end users.

Surprisingly, it has now been found that selected mixtures of polythiol hardeners in combination with selected curing accelerators can be processed into curable epoxy formulations which are characterized by a homogeneous distribution of the hardeners in the curable mixture as well as by a good storage stability of the formulations with epoxy resins and which, on the other hand, result in cured products with excellent hydrolysis stability.

The object of the present invention is to provide curable epoxy formulations with a homogeneous distribution of the hardeners in the curable mixture.

A further object of the present invention is to provide curable epoxy formulations with very good storage stability.

Yet another object of the present invention is to provide cured epoxy resins with very good hydrolysis resistance.

1. a) mindestens ein Epoxidharz,
2. b) ein Gemisch aus Polythiolhärtern mit den Komponenten A und B, worin Komponente A ausgewählt wird aus der Gruppe der Umsetzungsprodukte der über eine Ethergruppe dimerisierten oder der über zwei Ethergruppen trimerisierten vier- bis achtwertigen Alkohole mit Mercaptocarbonsäuren, worin Komponente B ausgewählt wird aus der Gruppe der Umsetzungsprodukte der zwei- bis vierwertigen monomeren Alkohole mit Mercaptocarbonsäuren und worin der Anteil der Komponenten A und B im Gemisch 100 % beträgt, und
3. c) mindestens einen Härtungsbeschleuniger aus der Gruppe der sekundären aliphatischen, aromatischen, araliphatischen oder heterocyclischen Amine, der tertiären aliphatischen, aromatischen, araliphatischen oder heterocyclischen Amine, der aliphatischen, aromatischen, araliphatischen oder heterocyclischen Verbindungen mit mindestens einer sekundären und mindestens einer tertiären Aminogruppe, der aliphatischen, aromatischen, araliphatischen oder heterocyclischen Verbindungen mit einer Hydroxylgruppe und mindestens einer sekundären und/oder tertiären Aminogruppe, der Guanidine, der Amidine, der Cyanamide, der photolatenten Basen oder Gemischen von zwei oder mehreren davon.

The present invention relates to curable compositions containing

1. a) at least one epoxy resin,
2. b) a mixture of polythiol hardeners with components A and B, wherein component A is selected from the group of reaction products of four- to eight-valent alcohols dimerized via one ether group or trimerized via two ether groups with mercaptocarboxylic acids, wherein component B is selected from the group of reaction products of two- to four-valent monomeric alcohols with mercaptocarboxylic acids and wherein the proportion of components A and B in the mixture is 100%, and
3. c) at least one curing accelerator from the group of secondary aliphatic, aromatic, araliphatic or heterocyclic amines, tertiary aliphatic, aromatic, araliphatic or heterocyclic amines, aliphatic, aromatic, araliphatic or heterocyclic compounds having at least one secondary and at least one tertiary amino group, aliphatic, aromatic, araliphatic or heterocyclic compounds having a hydroxyl group and at least one secondary and/or tertiary amino group, guanidines, amidines, cyanamides, photolatent bases or mixtures of two or more thereof.

In principle, any epoxy compound is suitable as component a). These are monomeric or polymeric organic compounds with at least one, preferably at least two, epoxy groups. Mixtures of different epoxy resins can also be used.

Examples of monomeric epoxides are alkylene, arylene, alkylarylene, arylalkylene, or alkylenearylalkylene groups containing at least two epoxide groups. These alkylene, alkylarylene, arylalkylene, or alkylenearylalkylene radicals may optionally be interrupted in the alkylene group by one or more non-directly adjacent ether bridges -O-, thioether bridges -S-, or amine bridges -NH- and may optionally be substituted by one or more alkoxy radicals, hydroxyl groups, or halogen atoms, preferably chlorine or bromine.

Polyepoxides are preferred, especially those having two, three or four epoxide groups in the molecule.

Epoxy resins used according to the invention can also be obtained by chain extension of polyepoxides.

Most commercially used epoxy resins are produced by reacting hydroxyl-containing compounds with epichlorohydrin. Such epoxy resins are called glycidyl-based epoxy resins or glycidyl epoxy resins. The hydroxyl-containing compounds can be polyols or polyphenols.

Examples of polyphenols are bisphenols and novolaks. Examples of polyols are dihydric alcohols such as 1,2-ethanediol, 1,3-propanediol, or 1,4-butanediol. The reaction of polyols with epichlorohydrin leads to diglycidyl polyethers.

Instead of polyols, polycarboxylic acids, polyamines, or polyamides can also be reacted with epichlorohydrin. Dicarboxylic acids such as adipic acid, sebacic acid, or hexahydrophthalic acid can be used for diglycidyl ester resins.

A second possibility for producing epoxy resins is the reaction of aliphatic or cycloaliphatic alkenes with peroxide compounds, such as peracids. This process converts a double bond into an oxirane ring.

Epoxy resins preferably used as component a) are diglycidyl ethers of bisphenols, particularly bisphenol A. These are produced by reacting epichlorohydrin with bisphenol A. Epichlorohydrin is first added to bisphenol A, forming bis(3-chloro-2-hydroxypropoxy)bisphenol A. This is then reacted with a stoichiometric amount of alkali metal hydroxide in a condensation reaction, forming the bis-epoxide. Higher molecular weight bisphenol A diglycidyl ethers can be obtained by reacting monomeric bisphenol A diglycidyl ether with additional bisphenol A.

Depending on the chain length, viscous, clear liquids are formed, so-called liquid epoxy resins, or if there are several repeating units in the molecule, colorless solids are formed, so-called solid epoxy resins.

Preferred components a) are aromatic polyepoxides. These are typically epoxy resins that, in addition to the epoxy groups, contain at least one, in particular at least two, and very particularly preferably one to four aromatic radicals, for example phenylene radicals, per molecule. The aromatic radicals may optionally be mono- or polysubstituted, for example by halogen, such as chlorine or bromine, by alkyl having 1 to 4 C atoms, such as methyl or ethyl, or by hydroxyalkyl having 1 to 4 C atoms, such as hydroxymethyl.

In epoxy resins with repeating units containing two or more aromatic rings, the rings can be in condensed form or, in particular, linked to one another via a covalent bond or a divalent bridging group. Examples of divalent bridging groups are branched or straight-chain alkylene groups with 1 to 4 carbon atoms, which may be substituted by halogen atoms, such as chlorine or bromine.

Further preferred aromatic polyepoxides are bisphenol diglycidyl ethers. The bisphenols can, for example, be divalent compounds in which two phenylene radicals, each having a hydroxyl group, are linked to one another via a divalent bridging group, for example via -CH ₂ - (bisphenol F), via -C(CH ₃ ) ₂ - (bisphenol A), or -SO ₂ - (bisphenol S). The hydroxyl groups are preferably located in the 4,4'-position. The phenylene radicals are preferably unsubstituted or substituted by one to four halogen atoms, preferably by chlorine or bromine, per phenylene ring. The bisphenols can also be phenylene radicals which have two hydroxyl groups. The phenylene radical is preferably unsubstituted or substituted by one to four halogen atoms, preferably by chlorine or bromine.

Epoxy resins preferably used as component a) are diglycidyl ethers of bisphenols, which are derived in particular from bisphenol A, bisphenol F, bisphenol S or from brominated bisphenols A, F or S.

The epoxy resins usable as component a) according to the invention can be aromatic polyepoxides derived from a novolak. In such epoxy resins, most or all of the phenolic hydroxyl groups of the novolak are etherified with a glycidyl group. The novolak can be a phenol novolak, an ortho-, meta-, or para-cresol novolak, or a combination thereof.

Other epoxy resins preferably used as component a) are polyglycidyl ethers of novolaks. These highly viscous to solid epoxy resins typically contain 2 to 6 epoxy groups per molecule. Due to the high functionality of these resins, curing results in the formation of highly cross-linked polymers with high temperature and chemical resistance, but low mechanical flexibility.

Other polyepoxides preferably used as components a) do not contain any aromatic radicals. These non-aromatic epoxy compounds can be branched or straight-chain alkylene radicals having 1 to 20 carbon atoms, which are etherified with two or more glycidyl groups. The alkylene radicals may optionally contain one or more non-adjacent hetero bridge atoms, for example -O-, -S-, or -NH-. The alkylene radicals may optionally be substituted at one or more carbon atoms, for example by hydroxyl groups or by halogen atoms, such as chlorine or bromine.

Epoxy resins preferably used as component a) are aliphatic or cycloaliphatic epoxy resins. These can be obtained by the epoxidation of double bonds in aliphatic or cycloaliphatic compounds or by the reaction of aliphatic or cycloaliphatic polyols or polycarboxylic acids with epichlorohydrin.

Aliphatic or cycloaliphatic epoxides contain one or more aliphatic or cycloaliphatic residues with one or more oxirane residues in the molecule. An example of this is 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate. Aliphatic and cycloaliphatic epoxides are characterized by a high oxirane content and the absence of chlorine, which results in low viscosity and, after curing, good weather resistance, low dielectric constants, and high glass transition temperatures. temperatures. Due to their low dielectric constants and the absence of chlorine, aliphatic and cycloaliphatic epoxies are frequently used to encapsulate electronic systems. They are also preferred for radiation-cured paints and varnishes.

Another group of aliphatic or cycloaliphatic epoxy resins preferably used as component a) are epoxidized vegetable oils. These can be produced by epoxidizing unsaturated carboxylic acids, preferably unsaturated fatty acids, using peroxide compounds. These epoxy resins often have very low viscosities and are therefore often used as reactive diluents.

Another group of aliphatic or cycloaliphatic epoxy resins preferably used as component a) are low-molar mass glycidyl epoxy resins, which are formed by the reaction of epichlorohydrin with aliphatic or cycloaliphatic polyols to form polyglycidyl ethers; or which are formed by the reaction of epichlorohydrin with aliphatic or cycloaliphatic polycarboxylic acids to form polyglycidyl esters. Aliphatic or cycloaliphatic glycidyl epoxy resins also generally have a low viscosity.

Examples of suitable epoxy resins of this type are ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerol diglycidyl ether, butanediol diglycidyl ether and hexanediol diglycidyl ether.

Examples of particularly suitable aliphatic polyepoxides with more than two epoxy groups are glycerol triglycidyl ether and polyglycidyl ethers of 1,1,1-trimethylolpropane, pentaerythritol and sorbitol.

Examples of suitable cycloaliphatic polyepoxides are glycidyl ethers of cycloaliphatic alcohols, such as 1,4-cyclohexanedimethanol, bis(4-hydroxycyclohexyl)methane or 2,2-bis(4-hydroxycyclohexyl)propane; furthermore cycloaliphatic epoxy resins, such as bis(2,3-epoxycyclopentyl) ether, 2,3-epoxycyclopentyl glycidyl ether, 1,2-bis(2,3-epoxycyclopentyloxy)ethane and 3,4-epoxycyclohexylmethyl 3',4'-epoxycyclohexanecarboxylate) and hydantoin diepoxide.

Further examples of suitable polyepoxides are polyepoxides with amino groups, such as poly(N-glycidyl) compounds, which are obtainable by dehydrochlorination of reaction products of epichlorohydrin with amines containing at least two amino hydrogen atoms. These amines can be, for example, aniline, n-butylamine, bis(4-aminophenyl)methane, m-xylylenediamine, or bis(4-methylaminophenyl)methane.

Further examples of suitable polyepoxides are polyepoxides with thioether groups. Examples include di-S-glycidyl derivatives of dithiols, such as ethane-1,2-dithiol or bis(4-mercaptomethylphenyl) ether.

Another group of epoxy resins preferably used as component a) are halogenated epoxy resins, for example diglycidyl ethers of brominated bisphenols, such as brominated bisphenol A, bisphenol F or bisphenol S. Such halogenated epoxy resins are often used when flame-retardant properties are required, such as in electrical applications, e.g. for the production of printed circuit boards.

Epoxy resins can be characterized using various parameters, including molecular weight, molecular weight distribution, hydroxyl number, or epoxy equivalent weight.

Further preferred components a) are chain-extended polyepoxides whose molecular weight has been increased to achieve the desired epoxy equivalent weight. Chain-extended epoxy resins can be obtained by reacting monomeric diepoxides with, for example, a diol in the presence of a catalyst, thereby forming a linear polymer. The resulting epoxy resin, e.g., an aromatic or non-aromatic epoxy resin, can, for example, have an epoxy equivalent weight of at least 150 or at least 200 grams per equivalent.

Other preferred aromatic epoxy resins have an epoxy equivalent weight of up to 2,000 or up to 1,000 grams per equivalent.

Particularly preferred components a) are aromatic epoxy resins having an epoxy equivalent weight in the range from 150 to 2,000, in particular from 150 to 1,000 and most preferably from 170 to 900 grams per equivalent.

The epoxy equivalent weights can be selected so that the epoxy resin is present as a liquid.

The proportion of component(s) a) in the epoxy composition according to the invention is usually 20 to 95 wt. %, preferably 30 to 90 wt. % and in particular 40 to 80 wt. %, based on the total amount of the epoxy composition.

Epoxy resins preferably used as component a) are aromatic polyepoxides, in particular diglycidyl ethers of bisphenols, and very particularly preferably diglycidyl ethers derived from bisphenol A, bisphenol F, bisphenol S or from brominated bisphenols A, F or S.

Component A of the polythiol hardener mixtures used according to the invention as component b) are reaction products of the four- to six-valent alcohols dimerized via one ether group with mercaptocarboxylic acids or of the four- to eight-valent alcohols trimerized via two ether groups with mercaptocarboxylic acids.

Dimerized tetra- to hexavalent alcohols include dimers of tri- to tetravalent aliphatic or cycloaliphatic alcohols. These are aliphatic or cycloaliphatic compounds with three to four hydroxyl groups in the molecule. Examples of such alcohols are glycerol, trimethylolpropane, and pentaerythritol. These alcohols are dimerized via an ether group. Two of these monomeric alcohol residues are thus connected via an ether residue to form tetra- to hexavalent alcohols.

Trimerized tetra- to octahedral alcohols include trimers of trihydric or tetrahydric aliphatic or cycloaliphatic alcohols. These are aliphatic or cycloaliphatic compounds with three to four hydroxyl groups in the molecule. Examples of such alcohols are glycerol, trimethylolpropane, and pentaerythritol. These alcohols are trimerized via two ether groups. Three of these monomeric alcohol residues are thus connected via two ether residues as tetrahydric to octahedral alcohols.

Preferred dimerized or trimerized tetra- to octhydric alcohols are derived from triols or tetrols, in particular from glycerol, trimethylolpropane and pentaerythritol.

Component B of the polythiol hardener mixtures used according to the invention as component b) comprises reaction products of di- to tetrahydric monomeric alcohols with mercaptocarboxylic acids. The monomeric di- to tetrahydric alcohols are aliphatic or cycloaliphatic alcohols with two to four hydroxyl groups in the molecule. In contrast to the dimeric or trimeric alcohols of component A, which have alcohol residues linked via ether bridges, the monomeric alcohols of component B have only one alcohol residue and no ether bridges. Examples of such monomeric alcohols are ethylene glycol, propylene glycol, di-, tri-, or tetraethylene glycol, di-tri- or tetrapropylene glycol, glycerol, trimethylolpropane, and pentaerythritol.

Component B of the polythiol hardener mixtures used according to the invention as component b) is preferably a reaction product of tri- to tetravalent monomeric alcohols with mercaptocarboxylic acids.

One or more hydroxyl groups, preferably all hydroxyl groups of these monomeric, dimerized or trimerized alcohols are esterified with mercaptocarboxylic acids. Mercaptocarboxylic acids include aliphatic monocarboxylic acids with a total of two to twenty carbon atoms, which are substituted on one carbon atom with a mercapto group. Preference is given to using aliphatic mercaptocarboxylic acids with a total of two to six carbon atoms, which contain a primary and/or secondary and/or tertiary mercapto group -SH, i.e. which have a radical -CH ₂ -SH, -CH(-SH)- or >C(-SH)-. Particular preference is given to using aliphatic mercaptocarboxylic acids with a total of two to six carbon atoms, which contain a primary and/or secondary mercapto group -SH.

Preferred examples are 2-mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, 3-mercaptobutanoic acid, 4-mercaptobutanoic acid, 3-mercaptopentanoic acid, 5-mercaptopentanoic acid, 5-mercaptohexanoic acid, and 6-mercaptohexanoic acid. 3-mercaptopropionic acid is particularly preferred.

As a rule, more than 50% of the hydroxyl groups, preferably at least 80% and particularly preferably at least 95% and most preferably at least 99% of all hydroxyl groups of these monomeric, dimerized or trimerized alcohols are esterified with mercaptocarboxylic acids.

The proportion of component A in the polythiol hardener mixtures used according to the invention as component b) is typically 10 to 90 wt. %, preferably 30 to 80 wt. %, and particularly preferably 50 to 80 wt. %. The percentages are based on the sum of the amounts of components A and B.

The polythiol hardener mixture used according to the invention as component b) may also contain different components A or B or different components A and B.

The proportion of component B in the polythiol hardener mixtures used according to the invention as component b) is typically 90 to 10 wt. %, preferably 70 to 20 wt. %, and particularly preferably 20 to 50 wt. %. The percentages are based on the sum of the amounts of components A and B.

The proportion of component b) in the epoxy composition according to the invention is usually 4 to 75 wt. %, preferably 10 to 60 wt. % and in particular 15 to 50 wt. %, based on the total amount of the epoxy composition.

The polythiol hardeners preferably used as component A include tetrakis-diglycerol mercaptoalkanoic acid esters, pentakis-triglycerol mercaptoalkanoic acid esters, tetrakis-ditrimethylolpropane mercaptoalkanoic acid esters, hexakis-dipenthaerythritol mercaptoalkanoic acid esters and octakis-tripenthaerythritol mercaptoalkanoic acid esters.

Particularly preferred as component A are reaction products of di-trimethylolpropane, diglycerol, triglycerol, di-pentaerythritol and tri-pentaerythritol with mercaptoalkanecarboxylic acids, preferably with 2-mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, 3-mercaptobutanoic acid or with 4-mercaptobutanoic acid.

Dipentaerythritol hexakis-(3-mercaptopropionate) is particularly preferably used as component A.

The polythiol hardeners preferably used as component B include glycerol bis- or trismercaptoalkanoic acid esters, trimethylolpropane bis- or trismercaptoalkanoic acid esters and penthaerythritol bis-, tris- or tetrakismercaptoalkanoic acid esters.

Particularly preferred as component B are reaction products of trimethylolpropane, glycerol and pentaerythritol with mercaptoalkanecarboxylic acids, preferably with 2-mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, 3-mercaptobutanoic acid or with 4-mercaptobutanoic acid.

Particular preference is given to using polythiol hardener mixtures b) whose component A is dipentaerythritol hexakis-(3-mercaptopropionate) and whose component B is pentaerythritol tetrakis-(3-mercaptopropionate) or in particular trimethylolpropane tri-(3-mercaptopropionate).

Polythiol hardener mixtures containing components A and B are novel and are also a subject of this invention.

The invention therefore also relates to polythiol hardener mixtures containing components A and B, wherein component A is selected from the group of reaction products of tri- to octahedral alcohols dimerized via one ether group or trimerized via two ether groups with mercaptocarboxylic acids, and wherein component B is selected from the group of reaction products of di- to hexahydric monomeric alcohols, in particular tri- to hexahydric monomeric alcohols with mercaptocarboxylic acids.

In preferred polythiol hardener mixtures, the proportion of component A is 10 to 90 wt. %, preferably 30 to 80 wt. %, and particularly preferably 50 to 80 wt. %, and the proportion of component B is 90 to 10 wt. %, preferably 70 to 20 wt. %, and particularly preferably 20 to 50 wt. %, the percentages being based on the total amount of the mixture.

The polythiol hardener mixtures according to the invention are characterized by a low viscosity. These mixtures preferably have a viscosity at 20°C of less than 3,100 mPas, in particular less than 2,100 mPas, and most preferably between 500 and 1,950 mPas. Viscosity is measured using an Esnatec CP-4000 Plus rheometer.

Suitable curing accelerators as component c) are those selected from the group consisting of secondary aliphatic, aromatic, araliphatic, or heterocyclic amines; tertiary aliphatic, aromatic, araliphatic, or heterocyclic amines; aliphatic, aromatic, araliphatic, or heterocyclic compounds containing at least one secondary and at least one tertiary amino group; aliphatic, aromatic, araliphatic, or heterocyclic compounds containing a hydroxyl group and at least one secondary and/or tertiary amino group; guanidines, amidines, cyanamides, or photolatent bases. Mixtures of two or more of these components may also be used.

Amines used as curing accelerators of component c) contain at least one, preferably one to four, secondary and/or tertiary amino groups and optionally a hydroxyl group. The curing accelerator of component c) does not contain a primary amino group.

The curing accelerator of component c) can be secondary or tertiary amines with cyclic radicals or with straight-chain or branched alkyl radicals. Cyclic radicals can have one or more rings, which can be aromatic or non-aromatic. One or more of the nitrogen atoms of the amine can be part of a cyclic radical or part of a carbon-nitrogen double bond.

Guanidines, amidines or cyanamides can also be used as curing accelerators for component c).

Guanidines are nitrogen analogues of carbonic acid. The parent substance, guanidine, has the structural formula (H ₂ N) _{) 2} -C=NH. Guanidines are very strong bases.

Amidines are organic compounds that can formally be considered derivatives of carboxylic acid amides in which the carbonyl group is replaced by a carbimino group. Non-cyclic amidines have the general structural formula R-C(=NR)-NRR, where the R groups within a molecule can be different and can be hydrogen or organyl groups. Amidines are also very strong bases. These include, in particular, the bicyclic amidines DBN and DBU, in which both nitrogen atoms are part of the ring system.

Cyanamides are amides of cyanic acid. It can also be considered a nitrile of carbamic acid, and in its equilibrium form, carodiimide, it can also be considered a diimide of carbon dioxide.

The cyanamides suitable as component c) include dicyandiamide.

The nitrogen atoms of the curing accelerator c) can be bonded to alkyl groups, aryl groups, arylalkylene groups, alkylarylene groups, alkylarylenealkylene groups, or a combination of these groups. The nitrogen atoms of the curing accelerator c) can also be part of a nitrogen heterocycle.

The curing accelerator of component c) can be photolatent bases. These are radiation-activated catalysts that initiate the curing process.

Examples of photolatent bases e) are ketoprofen salts or borate salts of aliphatic amidines, in particular ketoprofen salts or borate salts of DBU, DBN or DABCO, or N-benzylated aliphatic amines, in particular benzylated DBU, DBN or DABCO. The use of photolatent bases is described, for example, by M. Sangermano et al. in Polymer 55 (2014), 1628-1635 or by B. Blickenstorfer et al. in Radtec Report, July/August 2010, 10-16 described. Other preferred photolatent bases e) are the products CGI 90 and CGI 277 from BASF.

Preferably, the curing accelerators used as component c) contain only carbon, nitrogen and hydrogen atoms or only carbon, nitrogen, hydrogen and oxygen atoms.

The curing accelerators used as component c) may be unsubstituted or may contain one or more substituents. Examples include hydroxyl groups or alkoxy radicals.

The curing accelerators c) preferably used include secondary and tertiary aliphatic or cycloaliphatic amines, secondary and tertiary alkanolamines, secondary and tertiary aromatic or araliphatic amines, nitrogen heterocycles with one or two secondary or tertiary ring nitrogen atoms and optionally one ring oxygen atom, bicyclic systems with one or two nitrogen atoms in the ring system, dicyandiamide, alkyl- or aryl-substituted guanidines, aliphatic amidines or photolatent bases.

Examples of preferred secondary aliphatic amines are diethylamine or dibutylamine.

Examples of preferred tertiary aliphatic amines are triethylamine (TEA), tributylamine, pentamethyldiethylenetriamine (PMDETA), bis(2-dimethylaminoethyl)ether (BDMAEE), pentamethyldipropylenetriamine (PMDPTA), N'-(3-(dimethylamino)propyl)-N,N-dimethyl-1,3-propanediamine, 2,6,10-trimethyl-2,6,10-triazaundecane, N,N-dimethyl-N-ethylamine, N-N-dimethyldecylamine (DMDA), N,N-dimethyloctylamine, N,N,N',N'-tetramethylethylenediamine (TMEDA) or N,N,N',N'-tetramethylpropanediamine.

An example of a preferred secondary cycloaliphatic amine is N-methylcyclohexylamine.

Examples of preferred tertiary cycloaliphatic amines are N,N-dimethylcyclohexylamine or N-cyclohexyl-N-methylcyclohexanamine.

An example of a preferred secondary alkanolamine is N-methylethanolamine.

An example of a preferred tertiary alkanolamine is N,N-dimethylethanolamine (DMEA).

Examples of preferred secondary aromatic amines are N,N'-dimethyl-diethyltoluenediamine or N,N'-dimethyl-diethylmethylbenzenediamine.

Examples of preferred tertiary aromatic amines are N,N-dimethylaniline or triphenylamine.

An example of a preferred secondary araliphatic amine is N-methylbenzylamine.

Examples of preferred tertiary araliphatic amines are tribenzylamine, N,N-dimethylaminomethylphenol, tris(N,N-dimethylaminomethyl)phenol or N,N-dimethylbenzylamine (DMBA).

Examples of preferred nitrogen heterocycles having one or two secondary or tertiary ring nitrogen atoms and optionally one ring oxygen atom are imidazoles, such as imidazole, N-methylimidazole, 1,2-dimethylimidazole, 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole or 1-benzyl-2-methylimidazole; or morpholines, such as N-methylmorpholine, N-ethylmorpholine or 2,2-dimorpholine diethyl ether; or piperazines, such as aminoethylpiperazine, dimethylpiperazine; or pyridines, such as N,N-dimethylaminopyridine (DMAP); or 2,2,5,5-tetraalkylpiperidines, such as N-methyl or N-ethyl-2,2,5,5-tetramethylpiperidine.

Examples of preferred bicyclic systems with one or two nitrogen atoms in the ring system are 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo-[4.3.0]non-5-ene (DBN), 1,4-diazabicyclo[2.2.2]octane (DABCO) or quinuclidine (1-azabicyclo[2.2.2]octane).

Examples of preferred alkyl- or aryl-substituted guanidines are tetramethylguanidine (TMG) or diphenylguanidine (DPG),

Examples of preferred aliphatic amidines are 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo-[4.3.0]non-5-ene (DBN) or 1,4-diazabicyclo[2.2.2]octane (DABCO).

The proportion of component(s) c) in the epoxy composition according to the invention is usually 0.1 to 5 wt. %, preferably 0.2 to 4 wt. % and in particular 0.5 to 3 wt. %, based on the total amount of the epoxy composition.

Particularly preferred curing accelerators c) are nitrogen heterocycles with one or two secondary or tertiary ring nitrogen atoms and optionally one ring oxygen atom, in particular These include imidazoles, morpholines, piperazines, pyridines or 2,2,6,6-tetraalkylpiperidines, or photolatent bases.

In addition to the polythiol hardener mixture b), the composition according to the invention may also contain other hardeners d) used for curing epoxides. These hardeners are known to the person skilled in the art.

Examples of further hardeners d) are polyvalent amines which differ from component c), so-called “acidic hardeners” or polythiols which differ from components A and B of the polythiol hardener mixture b).

The proportion of component(s) d) in the epoxy composition according to the invention is usually 0 to 30 wt. %, preferably 0 to 25 wt. % and in particular 1 to 20 wt. %, based on the total amount of the epoxy composition.

Examples of polyhydric amines are 1,3-diaminobenzene or aliphatic amines with primary amino groups, such as diethylenetriamine or 4,4'-methylene-bis-(cyclohexylamine).

Examples of “acidic hardeners” d) are dicarboxylic acids or dicarboxylic anhydrides, e.g. hexahydrophthalic anhydride.

Examples of polythiols d) are polythiols with an SH functionality between 2 and 8, in particular between 2 and 5, which differ from components A and B of the polythiol hardener mixture b).

Preferred hardeners d) are polythiols. These include in particular phenyldithiols, phenyltrithiols, toluenedithiols, toluenetrithiols, diphenylmethanedithiols, diphenyl ether dithiols, alkylenedithiols such as di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-, undeca- and dodecamethylenedithiol, alkylenetri- and tetrathiols such as terpenethiols, myrcenethiol, farnesenetetrathiol, alkylene ether dithiols, xylylenedithiols, mono-, di-, tri- or tetramethylxylylenedithiols, dicyclohexylmethanedithiols, dicyclohexyl ether dithiols, cyclohexyldithiols, mono-, di-, tri- or tetraalkylcyclohexyldithiols, triphenylmethanetrithiols, biphenyldithiols, isocyanurate tris-N-alkylenethiols, Naphthalenedithiols, naphthalenetrithiols, di-, tri-, or tetraesters of mercaptoalkanoic acids with di-, tri-, or tetrahydric alcohols, in particular di-, tri-, or tetraesters of 3-mercaptopropionic acid, 2-mercaptopropionic acid, or thioglycolic acid with di-, tri-, or tetrahydric aliphatic alcohols, such as ethylene glycol, diethylene glycol ether, propylene glycol, dipropylene glycol ether, butylene glycol, dibutylene glycol ether, ethoxylated or propoxylated derivatives of trimethylolpropane or pentaerythritol. Mixtures of two or more of these hardeners d) can also be used.

The following di- or higher-functional thiols are particularly preferably used as hardeners d): hexanedithiol, dodecanedithiol, limonenedithiol, myrcenedithiol, farnesene tetrathiol, pentaerythritol tetrakis(3-mercaptopropionate), trimethylolpropane tri-(3-mercaptopropionate), tris-[2-(3-mercaptopropionyl-oxy)ethyl]isocyanurate, ethylene glycol di-(3-mercaptopropionate), diethylene glycol ether di-(3-mercaptopropionate), ethoxylated trimethylolpropane tri-(3-mercaptopropionate), propoxylated trimethylolpropane tri-(3-mercaptopropionate), pentaerythritol tetrakis(2-mercaptopropionate), trimethylolpropane tri-(2-mercaptopropionate), Tris-[2-(2-mercaptopropionyl-oxy)ethyl]isocyanurate, ethylene glycol di-(2-mercaptopropionate), diethylene glycol ether di-(2-mercaptopropionate), ethoxylated trimethylolpropane tri-(2-mercaptopropionate), propoxylated trimethylolpropane tri-(2-mercaptopropionate)

In addition to components a), b), c, and optionally d), the epoxy compositions according to the invention may contain further additives e) that are typically used together with epoxides. These may be processing aids or additives that impart specific properties to the cured epoxides. Examples include dyes, pigments, reinforcing fibers such as glass or carbon fibers, fillers, antioxidants, UV stabilizers, flame retardants, antistatic agents, lubricants, solvents, or biocides.

Epoxy resin compounds can be enriched with fillers such as fumed silica to make them thixotropic. This thickened resin can be used as a filler or adhesive. Other fillers, such as hollow spheres made of glass, ceramic, or plastic, serve as fillers to reduce the density of the resin. To improve the grip or abrasion resistance of the surface, quartz sand or ceramic powders can be used. Metallic fillers, for example, can be used to increase the maximum continuous operating temperature.

Additional additives such as aluminum hydroxide can improve the fire-retardant properties of the cured epoxy resin.

The compositions according to the invention can be formulated as two-component or one-component compositions.

Two-component formulations typically contain the epoxy resin in component A and the hardener(s) in another component B. The remaining components, such as curing accelerators and other additives, can be contained in components A and/or B. These formulations are storage-stable and are combined immediately before processing to initiate and complete the curing of the epoxy resin.

The composition according to the invention is preferably in the form of a one-component formulation, hereinafter referred to as a "1K mixture." This 1K mixture belongs to the category of reactive adhesives, in which two components, namely resin and hardener, typically react with each other to achieve the desired curing. In contrast to conventional two-component epoxy formulations, in which resin and hardener must be mixed separately, the preferred 1K epoxy adhesive mixture is characterized by the presence of these two components in a single package or container, which significantly facilitates its application.

The epoxy compositions according to the invention can be processed in any manner known to the person skilled in the art.

The cured epoxy compositions are characterized by excellent hydrolytic stability. Thus, the mechanical strength of a molded article or bond after 360 hours of storage at 85 °C and 85% relative humidity decreases by no more than 30%, based on the initial value immediately before storage.

In two-component mixtures, resin and hardener are carefully mixed in the desired ratio before processing or molding. During mixing, the stoichiometric resin-to-hardener ratio should preferably be maintained; otherwise, portions of resin or hardener remain without reactants, which can lead to the retention of unreacted functional groups and incomplete crosslinking. Some epoxy systems, however, are less sensitive and, within certain limits, are expressly designed for varying the mixing ratio. This can influence hardness, elasticity, and other properties. Inhomogeneous mixing of the two components also has the same negative effect as an incorrect ratio.

With 1-component mixtures, there is no need to mix different components before the mixture cures.

Curing can occur at room temperature or at elevated temperature. Photocuring is also possible if the epoxy composition contains a photolatent base. The curing reaction is usually highly exothermic.

The processing time of epoxy compositions is called pot life. It depends on the processing temperature, the epoxy-to-hardener ratio, and the batch size. Typical pot lives range from a few minutes to several hours. During the pot life, the viscosity of the resin increases continuously in a nonlinear curve until eventually, processing is no longer possible.

Heating the mixed epoxy resin reduces its viscosity and thus generally improves its workability, but also shortens its pot life. Increasing the processing temperature by 10 °C significantly reduces the pot life or curing time. Low-reactivity epoxies require long curing times and, if possible, an elevated curing temperature. The presence of curing accelerators shortens the reaction time. Some epoxies can be heat-cured after curing to achieve complete crosslinking and higher heat distortion temperature.

Epoxy resin compounds are often modified with low-viscosity additives. The lower viscosity of the epoxy resin compound allows for better penetration into porous materials, such as the impregnation of fabrics or the coating of concrete, or improves processability by injection molding. (RTM process). On the other hand, such epoxy resin compositions allow for a higher filler loading, resulting in lower volume shrinkage during curing. The mechanical properties of the cured resin can also be improved, as can its economics. Glycidyl ethers are preferred for this purpose because, unlike non-reactive thinners, they are covalently bonded to the polymer and therefore cannot migrate.

Curing can also be initiated by adding photolatent bases or by exposure to UV radiation, which allows curing times in the range of seconds. In addition to the photolatent bases, the curable epoxy mixture can also contain photoinitiators. Examples include α-hydroxy, α-alkoxy, or α-amino aryl ketones, or acylphosphine oxides.

The epoxy compositions according to the invention can be used in a wide variety of fields.

They are suitable as construction adhesives, for example in boat building, household and model making, as metal adhesives, as plastic-based mortar, as casting resins for the production of components by casting processes and in the field of electronics and display production.

They can also be used in conjunction with reinforcing fibers in the construction of aircraft or rotor blades for wind turbines.

The production of mineral cast frames for mechanical engineering, industrial floors or concrete coatings is also possible.

The epoxy compositions according to the invention can also be used for the production of paints or varnishes and for the production of water-soluble synthetic resins for cathodic dip painting, for pipe rehabilitation and as road or path markings.

Another area of application concerns the encapsulation of electrical components or other objects for the purpose of insulation and corrosion protection as well as the production of printed circuit boards.

The application areas of 1K epoxy adhesives are diverse, especially in the electronics industry, where they are widely used in products such as mobile phones, tablets, and televisions. Their outstanding bonding strength and mechanical stability make them a preferred choice for the demanding bonding applications in this industry.

The curable compositions of the present invention are particularly preferably used as adhesives, sealants, casting resins, potting compounds or for the production of molded articles, electronic components or displays.

The following examples illustrate the invention without limiting it

Production of the test specimens for the 85/85 test

Step 1: Preparation of the aluminum plates

• Stärke: 1,6 mm, Breite: 25 mm, Länge: 102 mm, Material: 2024T3 Bare.

Aluminum plates were used that met the following specifications:

• Thickness: 1.6 mm, width: 25 mm, length: 102 mm, material: 2024T3 Bare.

The surface of one of the aluminum plates was roughened with 60-grit sandpaper.

Step 2: Applying the 1K mixture

The 1-component epoxy adhesive mixture was evenly applied to the roughened aluminum plate.

Step 3: Place the second aluminum plate

An identical aluminum plate was placed on top of the wetted aluminum plate to create an overlap, resulting in an adhesive area of 12.5 mm x 25.0 mm.

Step 4: Adjust the distance

The distance between the two aluminum plates was ensured by adding glass beads with a diameter of 70-110 µm into the 1-component epoxy adhesive.

Step 5: Fixing the bond

The bond was then secured with staples. Excess material was removed with a metal spatula.

Step 6: Curing

The bonds were cured in a drying cabinet (type: FDL 115, company: Binder GmbH) for 30 minutes at 80°C.

Step 7: Aging

After cooling the bonds to room temperature (21 °C), they were stored in the same oven at 50 °C for a further 16 hours to allow artificial aging and thus the achievement of the final strength properties.

In a series of tests, a total of 24 bonded joints were produced using this method. This procedure ensured reproducible production of test specimens for the 85/85 test and enabled the evaluation of the long-term durability and resistance of the 1K mixture under extreme environmental conditions.

Conducting the tensile shear tests and analyzing the results

• Maximalkraft: Die maximale aufgebrachte Kraft, die erforderlich war, um die Verklebung zu brechen, wurde ermittelt.
• Kraft beim Bruch: Die Kraft, die zum Zeitpunkt des Bruchs der Verklebung aufgebracht wurde, wurde ebenfalls gemessen und dokumentiert.
• Dauer des Versuchs: Die Zeitspanne, die benötigt wurde, bis das Versagen der Verklebung auftrat, wurde erfasst.

For each individual measurement point, lap-shear tests were conducted according to ASTM 1002 (2010) using a Zwick testing machine (model: BT1-FB010TN.D30). A total of four bonded joints were tested to failure in each test. During these tests, the following parameters were recorded and analyzed:

• Maximum force: The maximum applied force required to break the bond was determined.
• Force at break: The force applied at the time of bond breakage was also measured and documented.
• Duration of the test: The time required until bond failure occurred was recorded.

• Kohäsiver Bruch: Wenn das Versagen hauptsächlich innerhalb der Klebstoffschicht auftrat, wurde dies als kohäsiver Bruch klassifiziert.
• Adhäsiver Bruch: Ein Bruch, bei dem die Trennung zwischen dem Klebstoff und den verklebten Oberflächen auftrat, wurde als adhäsiver Bruch identifiziert.
• Gemischter Bruch: Bei einem gemischten Bruch traten sowohl kohäsive als auch adhäsive Brüche auf, wodurch eine Kombination der beiden Bruchmuster sichtbar wurde.

After each bond failed, a thorough fracture investigation was conducted to determine the type of fracture. The following fracture patterns were distinguished:

• Cohesive failure: If the failure occurred primarily within the adhesive layer, this was classified as cohesive failure.
• Adhesive fracture: A fracture in which separation occurred between the adhesive and the bonded surfaces was identified as an adhesive fracture.
• Mixed fracture: In a mixed fracture, both cohesive and adhesive fractures occurred, revealing a combination of the two fracture patterns.

In addition, the layer thickness of the broken bonds was measured and documented to enable a comprehensive analysis of the test results.

This test method and the corresponding analyses enabled a thorough investigation of the strength and failure characteristics of the bonded joints, which was of great importance for further development and quality control.

To determine the hydrolysis stability of the bonds, they were tested in a climate chamber (Thermotec; LHL-114) at a constant temperature of 85°C and a relative humidity of 85% stored (85/85 test). The tests were carried out at regular intervals according to the method described above.

The tests were conducted to evaluate the effects of humidity and high temperatures on the bonds over time. This process enabled the evaluation of the long-term stability and durability of the bonds under the specific environmental conditions simulated in the climatic chamber. An initial measurement point was determined for each test series. Subsequent measurements were taken at intervals of 100, 250, 360, and 500 hours. The tests were terminated when a bond had a residual strength of < 2 MPa.

Investigations conducted and results obtained

Tests were conducted with 1-component adhesive formulations. For each, a bisphenol A epoxy resin (Epilox A 19-00 from Leuna Harze) was combined with a curing accelerator (= thermolatent base Ajicure PN23 (imidazole)) to achieve a thermolatent base content of 1% by mass based on the finished 1-component mixture. The polythiol or polythiol mixture was mixed stoichiometrically with the epoxy resin. The ratio varied somewhat depending on the polythiol mixture, but amounted to approximately 58 g of epoxy resin and 40 g of polythiol (mixture). In addition, 1 g of glass beads and 1 g of catalyst were added. The polythiol (mixture) was 1,1,1-tris-(hydroxymethyl)-propane tris-(3-mercaptopropionate) (TMPMP), pentaerythritol tetrakis-(3-mercaptopropionate) (PETMP), dipentaerythritol hexakis-(3-mercaptopropionate) (DiPETMP), or mixtures of these compounds. The polythiol hardeners used in the adhesive formulations tested and the results obtained are listed in Table 1 below. The maximum force MK in MPa was determined after different storage times in the climatic chamber (85°C, 85% relative humidity). The layer thickness of the broken bonds was between 100 and 150 µm. Examples V1, V2, and V3 are comparative examples. Example 1 is an example according to the invention. Table 1: Adhesive formulations tested Example V1 V2 1 V3* ⁾ Polythiol (mixture) TMPMP TMPMP+PETMP TMPMP+DiPETMP DiPETMP MK (0 h) 14.8 17 15 11 MK (100 h) 8.9 16 11 10 MK (250 h) 5.2 14 14 11 MK (360 h) 2.6 8 13 14 MK (500 h) 0.4 2 7 13 * ⁾ The incorporation of DiPETMP into the formulation was difficult due to the high viscosity of this compound.

Discussion of the results

It was found that the addition of DiPETMP to a 1K mixture can significantly improve hydrolytic stability, as shown in the table above. Due to the high viscosity of DiPETMP, it was used in combination with TMPMP.

The improvement in hydrolytic stability correlates positively with the amount of DiPETMP added. With increasing addition of this polythiol hardener in the mixture with TMPMP, the achieved improvement becomes even more pronounced. This is shown in Table 2 below. Table 2: Adhesive formulations tested Example V4 2 3 4 Polythiol (mixture) (wt%) TMPMP (100) TMPMP+DiPETMP (80/20) TMPMP+DiPETMP (70/30) TMPMP+DiPETMP (50/50) Viscosities of polythiol (mixture) mPas 1530 1940 2180 3060 MK (0 h) 14.5 14 12.6 10.9 MK (100 h) 8.8 11.7 11.5 11.7 MK (250 h) 5.7 8.3 9.5 12 MK (500 h) 0.5 1.3 0.8 1.0

The maximum force MK in MPa was determined after different storage times in the climatic chamber (85°C, 85% rel.H.).

These results demonstrate the significant benefits of adding a mixture of DiPETMP and TMPMP to the 1K mixture in improving hydrolytic stability.

Example V3 shows that very good MK values can also be achieved with a pure DiPETMP system. Systems containing DiPETMP and other polythiol hardeners, such as TMPMP, exhibit comparable hydrolysis resistance. However, these mixtures are lower in viscosity than pure DiPETMP and can therefore be more easily incorporated into the curable epoxy composition. The use of additional polythiols with a functionality between 2 and 8 can also lead to a reduction in the viscosity of the overall system.

QUOTES CONTAINED IN THE DESCRIPTION

This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• JP 2009-051954 A [0008]
• WO 2009/028271 A1 [0008]
• CN 103282401 A [0009]
• WO 2012/093510 A1 [0009]
• WO 2018/085546 A1 [0010]
• US 2013/0128435 A [0011]
• JP 2021-03834 A [0012]
• CN 104797623 A [0013]
• WO 2014/084292 A1 [0013]

Cited non-patent literature

• M. Sangermano et al. in Polymer 55 (2014), 1628-1635 or by B. Blickenstorfer et al. in Radtec Report, July/August 2010, 10-16 [0091]

Claims (18)

Curable compositions comprising a) at least one epoxy resin, b) a mixture of polythiol curing agents with components A and B, wherein component A is selected from the group of reaction products of tetra- to octadecyl alcohols dimerized/trimerized via one or two ether groups with mercaptocarboxylic acids, wherein component B is selected from the group of reaction products of di- to tetravalent monomeric alcohols with mercaptocarboxylic acids, and wherein the proportion of components A and B in the mixture is 100%, and c) at least one curing accelerator from the group of secondary aliphatic, aromatic, araliphatic, or heterocyclic amines, tertiary aliphatic, aromatic, araliphatic, or heterocyclic amines, aliphatic, aromatic, araliphatic, or heterocyclic compounds having at least one secondary and at least one tertiary amino group, aliphatic, aromatic, araliphatic, or heterocyclic compounds having a hydroxyl group and at least one secondary and/or tertiary amino group, guanidines, amidines, cyanamides, photolatent bases or mixtures of two or more thereof. Compositions according to Claim 1 , characterized in that the epoxy resin a) is an aromatic polyepoxide. Compositions according to Claim 2 , characterized in that the epoxy resin a) is a diglycidyl ether of bisphenols, preferably a diglycidyl ether derived from bisphenol A, bisphenol F, bisphenol S or from brominated bisphenols A, F or S. Compositions according to at least one of the Claims 1 until 3 , characterized in that component A is selected from the group of reaction products of di-trimethylolpropane, diglycerol, triglycerol, di-pentaerythritol or tri-pentaerythritol with mercaptocarboxylic acids, preferably with 2-mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, 3-mercaptobutanoic acid or with 4-mercaptobutanoic acid, and that component B is selected from the group of reaction products of trimethylolpropane, glycerol or pentaerythritol with mercaptocarboxylic acids, preferably with 2-mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, 3-mercaptobutanoic acid or 4-mercaptobutanoic acid. Compositions according to Claim 4 , characterized in that component A is dipentaerythritol hexa-(3-mercaptopropionate) and that component B is pentaerythritol tetrakis-(3-mercaptopropionate) or in particular trimethylolpropane tri-(3-mercaptopropionate). Compositions according to at least one of the Claims 1 until 5 , characterized in that the proportion of component A is 10 to 80 wt. %, preferably 50 to 70 wt. %, and the proportion of component B is 90 to 20 wt. %, preferably 50 to 30 wt. %, the percentages being based on the sum of the amounts of components A and B Compositions according to at least one of the Claims 1 until 6 , characterized in that the curing accelerator c) is selected from the group consisting of secondary and tertiary aliphatic or cycloaliphatic amines, secondary and tertiary alkanolamines, secondary and tertiary aromatic or araliphatic amines, nitrogen heterocycles with one or two secondary or tertiary ring nitrogen atoms and optionally one ring oxygen atom, bicyclic systems with one or two nitrogen atoms in the ring system, dicyandiamide, alkyl- or aryl-substituted guanidines, aliphatic amidines and photolatent bases. Compositions according to Claim 7 , characterized in that the curing accelerator c) is a nitrogen heterocycle having one or two secondary or tertiary ring nitrogen atoms and optionally one ring oxygen atom, in particular an imidazole, morpholine, piperazine, pyridine or 2,2,6,6-tetraalkylpiperidine. Compositions according to at least one of the Claims 1 until 8 , characterized in that in addition to hardener b) there is present as a further hardener d) a polythiol hardener with an SH functionality between 2 and 8, which differs from components A and B in the polythiol mixture b). Compositions according to Claim 9 , characterized in that the polythiol hardener d) is selected from the group consisting of hexanedithiol, dodecanedithiol, limonenedithiol, myrcenedithiol, farnesene tetrathiol, tris-[2-(3-mercaptopropionyl-oxy)ethyl]isocyanurate, ethylene glycol di-(3-mercaptopropionate), diethylene glycol ether di-(3-mercaptopropionate), ethoxylated trimethylolpropane tri-(3-mercaptopropionate), propoxylated trimethylolpropane tri-(3-mercaptopropionate), ethylene glycol di-(2-mercaptopropionate), diethylene glycol ether di-(2-mercaptopropionate), ethoxylated trimethylolpropane tri-(2-mercaptopropionate), and propoxylated Trimethylolpropane tri-(2-mercaptopropionate). Compositions according to at least one of the Claims 1 until 10 , characterized in that they contain a photolatent base. Compositions according to at least one of the Claims 1 until 11 , characterized in that they contain, in addition to components a), b), c and optionally d), further additives e), preferably processing aids, dyes, pigments, reinforcing fibers, fillers, antioxidants, UV stabilizers, flame retardants, antistatic agents, lubricants, solvents or biocides or mixtures of two or more thereof. Compositions according to at least one of the Claims 1 until 12 , characterized in that they are one-component formulations. Shaped bodies or adhesive joints obtainable by curing the curable compositions according to at least one of the Claims 1 until 13 . Use of the curable compositions according to at least one of the Claims 1 until 13 as adhesives, sealants, casting resins, potting compounds or for the production of molded bodies, electronic components or displays. Polythiol hardener mixtures containing components A and B, wherein component A is selected from the group of reaction products of the four to eight-valent alcohols dimerized via one ether group or trimerized via two ether groups with mercaptocarboxylic acids, and wherein component B is selected from the group of reaction products of the two to four-valent monomeric alcohols with mercaptocarboxylic acids. Polythiol hardener mixtures according to Claim 16 , characterized in that the proportion of component A is 10 to 80 wt. %, preferably 50 to 70 wt. %, and that the proportion of component B is 90 to 20 wt. %, preferably 50 to 30 wt. %, the percentages being based on the total amount of the polythiol hardener mixture. Polythiol hardener mixtures according to Claim 16 or 17 , characterized in that they have a viscosity at 20°C of less than 3,100 mPas, preferably from 500 to 1,950 mPas.