WO2016193032A1

WO2016193032A1 - Diglycidyl ethers of tetrahydrofuran diglycol derivatives and oligomers thereof as curable epoxy resins

Info

Publication number: WO2016193032A1
Application number: PCT/EP2016/061541
Authority: WO
Inventors: Ulrich Karl; Monika CHARRAK; Hans-Josef Thomas
Original assignee: Basf Se
Priority date: 2015-06-02
Filing date: 2016-05-23
Publication date: 2016-12-08
Also published as: TW201704229A

Abstract

Cured epoxy resins are widespread on account of their outstanding mechanical and chemical properties. It is common to use epoxy resin based on bisphenol A diglycidyl ether or bisphenol F diglycidyl ether, but for many sectors these are problematic because of their endocrine effect. The present invention relates to tetrahydrofuran diglycol diglycidyl ether derivates and to curable epoxy resin compositions based thereon, as alternatives to the bisphenol A or bisphenol F diglycidyl ethers and to the epoxy resin compositions based thereon.

Description

Diglycidyl ethers of tetrahydrofuran diglycol derivatives and oligomers thereof as curable epoxy

Description

The present invention relates to tetrahydrofuran diglycol diglycidyl ether derivatives, to processes for preparing them, and to the use thereof for producing adhesives, composite materials, moldings, 3D-Printed parts, or coatings. The present invention further relates to curable epoxy resin compositions comprising a curing component and a resin component which comprises at least one tetrahydrofuran diglycol diglycidyl ether derivative or an oligomer based thereon as polyepoxide compound, and also to methods for curing a composition of this kind and to epoxy resins that are obtainable or obtained by curing a composition of this kind.

Epoxy resins is a designation customary for oligomeric compounds having on average more than one epoxide group per molecule, which are converted by reaction with suitable curing agents (hardeners) or by polymerization of the epoxide groups into thermosets, or cured epoxy resins. Cured epoxy resins, on account of their outstanding mechanical and chemical properties, such as high impact strength, high abrasion resistance, good heat and chemicals resistance, more particularly a high level of resistance toward alkalis, acids, oils and organic solvents, and high weathering resistance, excellent adhesiveness to a large number of materials, and high electrical insulation capacity, are widespread. They serve as a matrix for fiber composites and are often a major constituent in electrical laminates, structural adhesives, casting resins, coatings, 3D-Printing resins, and powder coating materials. 3D-Printing resins are generally photosensitive formulations used in stereolithography or photopolymer jetting applications.

The majority of commercial (uncured) epoxy resins are prepared by coupling epichlorohydrin to compounds which possess at least two reactive hydrogen atoms, such as polyphenols, monoamines and diamines, aminophenols, heterocyclic imides and amides, aliphatic diols or polyols or dimeric fatty acids. Epoxy resins which derive from epichlorohydrin are referred to as glycidyl-based resins. Generally speaking, bisphenol A diglycidyl ether or bisphenol F diglycidyl ether, or the corresponding oligomers, are used as epoxy resins.

Exacting requirements are imposed especially on coatings of containers for the storage of foods and drinks. The coating accordingly is to resist strongly acidic or salty foods (e.g., tomatoes) or drinks, so that no corrosion occurs to the metal, which might in turn lead to contamination of the contents. Moreover, the coating must not impact the flavor or appearance of the foods. Since the production of the containers often involves further forming of containers that have already been coated, the coating must be flexible. Many contents, such as foods, are not pasteurized until they are in the can; the coating therefore, is required to withstand heating at 121 °C for at least 2 hours without damage and without migration of ingredients. The use of epoxy resins based on bisphenol A or bisphenol F diglycidyl ethers is becoming seen as problematic in an increasing number of sectors on account of the endocrine effect of the corresponding diols. To solve this problem, a variety of proposals have been made:

US 2012/01 16048 discloses a bisphenol A (BPA) and bisphenol F (BPF) free polymer, which as well as ester bonds also comprises hydroxyether bridges, with use being made of di-epoxides which are based on open-chain aliphatic diols such as neopentyl glycol (NPG), on simple cycloaliphatic diols such as 1 ,4-cyclohexanedimethanol or on aromatic diols such as resorcinol. From experience, however, the aliphatic and cycloaliphatic diols described produce coatings which are very soft and have low temperature and chemicals resistance.

WO 2012/089657 discloses a BPA-free preparation comprising a film-forming resin and an adhesion promoter. The resin is an epoxidized resin prepared for example from the diglycidyl ethers of NPG, ethylene glycol, propylene or dipropylene glycol, 1 ,4-butanediol or

1 ,6-hexanediol. Here, the same restrictions on the properties of the coating are anticipated as in the previous example. WO 2010/100122 proposes a coating system which is obtainable by reaction of an epoxidized vegetable oil with hydroxy-functional compounds such as, for example, propylene glycol, propane-1 ,3-diol, ethylene glycol, NPG, trimethylol propane, diethylene glycol, etc.

US 2004/0147638 describes a 2-layer (core/shell) system, wherein the core is formed from a BPA- or BPF-based epoxy resin, and the outer layer from, for example an acrylate resin. The critical issue here is whether the outer layer is truly able fully to prevent the migration of BPA or bisphenol A diglycidyl ether (BADGE) into the contents.

WO 2012/091701 proposes various diols and their diglycidyl ethers as a substitute for BPA or BADGE for epoxy resins, including derivatives of BPA and ring-hydrogenated BPA, alicyclic diols based on cyclobutane and diols having a furan ring as their parent structure.

The object on which the present invention is based is that of providing monomeric and/or oligomeric diglycidyl ether compounds for use in epoxy resin systems, especially as an at least partial substitute for BADGE in corresponding epoxy resin systems, particularly for use in the coating of containers.

The present invention relates accordingly to tetrahydrofuran diglycol diglycidyl ether derivatives (THF DGE derivatives) of the formula I

(I), where

R1 and R2 independently of one another are each a hydrogen atom, an alkyl group having 1 to

4 C atoms, a halogen atom (F, CI, Br, I), or a nitro group, preferably a hydrogen atom or an alkyl group having 1 to 4 C atoms,

R3 is a hydrogen atom or a glycidyl group, and

n is 0 to 100, preferably 0 to 30.

In the case of THF DGE derivatives of the formula I which have 2 or more R3 radicals (n = 2 to 100), R2 in each case independently of any other is a hydrogen atom or a glycidyl group.

Alkyl groups for the purposes of the invention possess 1 to 20 C atoms. They may be linear, branched, or cyclic. They preferably have no substituents with heteroatoms. Heteroatoms are all atoms apart from C and H atoms.

One embodiment of the invention relates to oligomeric THF DGE derivatives of the formula I where n is 1 to 100, preferably 1 to 30. An oligomeric THF DGE derivative of the formula I for the purposes of the invention also includes a mixture of oligomeric THF DGE derivatives having different ns and different substitution patterns for R3 (hydrogen atom or glycidyl group).

One embodiment of the invention relates to monomeric THF DGE derivatives of the formula I with n = 0.

One embodiment of the invention relates to mixtures of monomeric and oligomeric THF DGE derivatives of the formula I.

One embodiment of the invention relates to tetrahydrofuran diglycol diglycidyl ether derivatives of the formula I, in which R1 and R2 are each hydrogen atoms, n is 0 to 100, preferably 0 to 30, and R3 is as defined above (monomeric or oligomeric tetrahydrofuran diglycol diglycidyl ethers and monomeric or oligomeric diglycidyl ethers, respectively).

Preferred embodiments of the invention are monomeric tetrahydrofuran diglycol diglycidyl ethers (THF DGE) corresponding to the formula I wherein R1 and R2 are each a hydrogen atom and n is 0, and also oligomeric THF DGE corresponding to the formula I wherein R1 and R2 are each a hydrogen atom, n is 1 to 100, preferably 1 to 30, and R3 is a hydrogen atom or a glycidyl group (independently of one another), and also mixtures of monomeric and oligomeric

THF DGE.

The present invention further relates to a process for preparing THF DGE derivatives of the formula I, comprising reacting the corresponding tetrahydrofuran diglycol derivatives (THF derivatives) of the formula II

(II), where

R1 and R2 have the same definition as for the THF DGE derivatives of the formula I, with epichlorohydrin.

The reaction generally produces a mixture of monomeric and oligomeric THF DGE derivative. The higher the excess of epichlorohydrin used, the greater the fraction of monomeric THF DGE derivative. Monomeric THF DGE derivatives can be separated from the oligomeric THF DGE derivatives by means of separation techniques known to the skilled person, such as

chromatographic, extractive or distillative methods, for example. In one particular embodiment, 1 to 20 equivalents, preferably 2 to 10 equivalents, of

epichlorohydrin are used for preparing the THF DGE derivatives of the formula I. The reaction typically takes place in a temperature range from -10°C to 120°C, preferably 20°C to 60°C. To accelerate the reaction it is possible to add bases such as aqueous or alcoholic solutions or dispersions of inorganic salts, such as LiOH, NaOH, KOH, Ca(OH)2 or Ba(OH)2, for example. Furthermore, suitable catalysts such as tertiary amines can be used.

In another particular embodiment, the reaction of the THF derivatives of the formula II to give the corresponding THF DGE derivatives of the formula I, in accordance with the invention, takes place with 0.9 to 20, preferably with 1 to 10, equivalents of epichlorohydrin at a temperature in a range from 20°C to 180°C, preferably from 70°C to 150°C, in the presence of a Lewis acid catalyst, preferably in the presence of tin(IV) chloride or boron trifluoride adducts such as boron trifluoride etherates. The reaction mixture is then admixed with a base (dilute sodium hydroxide solution, for example) and heated for a further period (1 to 5 hours, for example) (at reflux, for example). Thereafter the product can be isolated by phase separation and washing steps with water. The present invention further relates to processes for preparing THF DGE derivative-based oligomers by reacting monomeric THF DGE derivatives of the formula I with diols (chain extension). This is done by reacting monomeric THF DGE derivative of the formula I (n = 0) or a mixture of two or more THF DGE derivatives of the formula I with different ns, where

predominantly n is 0, with one or more diols. This mixture of two or more THF DGE derivatives of the formula I preferably comprises the monomeric THF DGE derivative (n = 0) to an extent of at least 60 weight%. For this purpose it is preferred to use 0.01 to 0.95, more preferably 0.05 to 0.8, more particularly 0.1 to 0.4 equivalent of the diol, based on the THF DGE derivative used. A substoichiometric amount of the diol or diols is preferably used to bring about an average of more than 1 , preferably more than 1.5, more preferably more than 1.9 epoxide group(s) per molecule in the resultant THF DGE derivative-based oligomer. The reaction takes place typically in a temperature range from 50°C to 200°C, preferably 60°C to 160°C. Suitable diols are customarily aromatic, cycloaliphatic or aliphatic dihydroxy compounds, examples being furandimethanol, ring-hydrogenated bisphenol A, ring-hydrogenated bisphenol F, neopentyl glycol, bisphenol A, bisphenol F or bisphenol S, preferably furandimethanol, ring-hydrogenated bisphenol A or ring-hydrogenated bisphenol F.

Accordingly, the present invention also provides THF DGE derivative-based oligomers, which are obtainable or obtained by reacting a monomeric THF DGE derivative of the formula I (n = 0) or a mixture of two or more THF DGE derivatives of the formula I with different ns, where predominantly n is 0, with one or more diols. This mixture of two or more THF DGE derivatives of the formula I preferably comprises the monomeric THF DGE derivative (n = 0) to an extent of at least 60 weight%. In one particular embodiment, the one or more diols used are not identical with the THF derivative of the formula II that corresponds to the THF DGE derivatives of the formula I, and so, as a result, THF DGE derivative-based co-oligomers are obtainable or obtained.

In one particular embodiment, the present invention relates to processes for preparing

THF DGE derivative-based oligomers starting from monomeric THF DGE derivatives of the formula I, where the monomeric THF DGE derivative of the formula I (n = 0) or a mixture of two or more THF DGE derivatives of the formula I with different ns, where predominantly n is 0, is reacted with the corresponding THF derivative of the formula II. This mixture of two or more THF DGE derivatives of the formula I preferably comprises the monomeric THF DGE derivative (n = 0) to an extent of at least 60 weight%. For this purpose, it is preferred to use 0.01 to 0.95, more particularly 0.1 to 0.4, equivalent of the THF derivative of the formula II, based on the

THF DGE derivative of the formula I used. A substoichiometric amount of the THF derivative of the formula II is preferably used to produce an average of more than 1 , preferably more than 1.5, more preferably more than 1 .9 epoxide groups per molecule in the resultant THF DGE derivative-based oligomer. The reaction takes place typically in a temperature range from 50°C to 200°C, preferably 60°C to 160°C. In an analogous way it is also possible to carry out specific preparation of higher molecular mass oligomeric THF DGE derivatives of the formula I, starting from oligomeric THF DGE derivatives of the formula I with a lower degree of oligomerization. The present invention also relates to curable epoxy resin compositions comprising a curing component, which comprises at least one curing agent, and a resin component, which comprises at least one THF DGE derivative-based polyepoxide compound selected from the group consisting of THF DGE derivatives of the formula I (monomeric and/or oligomeric) and THF DGE derivative based co-oligomer.

The present invention preferably relates to curable epoxy resin compositions comprising a curing component, which comprises at least one curing agent, and a resin component, which comprises at least one THF DGE derivative-based polyepoxide compound selected from the group consisting of THF DGE derivatives of the formula I (monomeric and/or oligomeric).

In one particular embodiment the present invention relates to curable epoxy resin compositions comprising a curing component, which comprises at least one curing agent, and a resin component, which comprises at least one oligomeric THF DGE derivative of the formula I (n = 1 to 100, preferably 1 to 30), the epoxide equivalent (EEW) of the oligomeric THF DGE derivatives of the formula I used being on average between 130 and 3000 g/mol, more particularly between 140 and 1000 g/mol.

In one particular embodiment, the curable epoxy resin composition of the invention contains less than 40 weight%, more preferably less than 10 weight%, very preferably less than 5 weight%, more preferably less than 1 weight% of bisphenol A or F-based compounds, based on the overall resin component. The curable epoxy resin composition of the invention is preferably free from bisphenol A or F based compounds. Bisphenol A or F based compounds for the purposes of the present invention are bisphenol A and F themselves, their diglycidyl ethers, and also oligomers or polymers based thereon.

In one particular embodiment of the curable epoxy resin composition of the invention, the THF DGE derivative-based polyepoxide compounds account in total for a fraction of at least 40 weight%, preferably at least 60 weight%, more particularly at least 80 weight%, based on the overall resin component.

In one particular embodiment the curable epoxy resin composition of the invention is a photosensitive formulation and may comprise also acrylate components like generally used in typical hybrid formulation for 3D Printing applications as for example described in US5476748 The compounds of the formula I of the invention are also suitable for use as reactive diluents, more particularly as reactive diluents for BADGE-, bisphenol F diglycidyl ether-, tetraglycidyl- methylenedianiline-, cresol-, novolak- or triglycidylaminophenol-based epoxy resins, on account of their suitability for lowering the viscosity of other epoxy resins, especially BADGE-, bisphenol F diglycidyl ether-, tetraglycidylmethylenedianiline-, cresol-, novolak- or triglycidylaminophenol- based epoxy resins, in the resin component and in the curable composition. The addition of the compounds of the formula I of the invention as reactive diluents has the advantageous effect of a comparatively small reduction in the glass transition temperature.

Accordingly, in one particular embodiment, the present invention relates to curable

compositions comprising a curing component which comprises at least one curing agent, and a resin component which comprises at least one THF DGE derivative-based polyepoxide compound selected from the group consisting of THF DGE derivatives of the formula I

(monomeric), and at least one epoxy resin selected from the group consisting of diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F (BFDGE), diglycidyl ether of ring-hydrogenated bisphenol A, diglycidyl ether of ring-hydrogenated bisphenol F, tetraglycidylmethylenedianiline, cresol epoxy resin, novolak epoxy resin, and triglycidylaminophenols and oligomers thereof. The at least one THF DGE derivative-based polyepoxide compound here accounts in total for a fraction of preferably up to 30 weight%, more preferably up to 25 weight%, more particularly of 1 to 20 weight%, especially of 2 to 20 weight%, very particularly of 5 to 15 weight%, based on the resin component (epoxy resin(s) and THF DGE derivative-based polyepoxide compound(s)) of the curable composition.

Accordingly the present invention also relates to a resin component comprising at least one THF DGE derivative-based polyepoxide compound selected from the group consisting of THF DGE derivatives of the formula I (monomeric), and at least one epoxy resin selected from the group consisting of diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F (BFDGE), diglycidyl ether of ring-hydrogenated bisphenol A, diglycidyl ether of ring-hydrogenated bisphenol F, tetraglycidylmethylenedianiline, cresol epoxy resin, novolak epoxy resin, and triglycidylaminophenols and oligomers thereof. The at least one THF DGE derivative-based polyepoxide compound here accounts in total for a fraction of preferably up to 30 weight%, more preferably up to 25 weight%, more particularly of 1 to 20 weight%, especially of 2 to 20 weight%, very particularly of 5 to 15 weight%, based on the resin component (epoxy resin(s) and THF DGE derivative-based polyepoxide compound(s)) of the curable composition.

In one preferred embodiment of the curable epoxy resin composition of the invention, the overall resin component accounts for at least 10 weight%, more particularly at least 25 weight%, based on the overall curable epoxy resin composition.

For the purposes of the present invention all epoxide compounds and only the epoxide compounds, of the curable epoxy resin composition are to be assigned to the resin component. Epoxide compounds for the purposes of the present invention are compounds having at least one epoxide group - hence including, for example, corresponding reactive diluents. The epoxide compounds of the resin component preferably contain on average at least 1 .1 , more preferably at least 1.5, more particularly at least 1.9 epoxide groups per molecule.

Curing agents for the purposes of the invention are compounds suitable for producing crosslinking of the THF DGE derivative-based polyepoxide compounds of the invention.

Reaction with curing agents can be used to convert polyepoxide compounds into infusible, three-dimensionally "crosslinked", thermoset materials. In the curing of epoxy resins, a distinction is made between two types of curing. In the first case, the curing agent has at least two functional groups which are able to react with the oxirane groups and/or hydroxyl groups of the polyepoxide compounds, with formation of covalent bonds (polyaddition reaction). In the course of curing, a polymeric network is then formed, made up of units which originate from the polyepoxide compounds and units originating from the curing agent molecules, these units being linked covalently to one another, and the degree of crosslinking being controllable via the relative amounts of the functional groups in the curing agent and in the polyepoxide compound. In the second case a compound is used which brings about the homopolymerization of polyepoxide compounds with one another. Such a compound is often also termed an initiator or catalyst. Homopolymerization inducing catalysts are Lewis bases (anionic homopolymerization; anionically curing catalysts) or Lewis acids (cationic homopolymerization; cationically curing catalysts). They bring about the formation of ether bridges between the epoxide compounds. It is assumed that the catalyst reacts with a first epoxide group, accompanied by ring opening, with formation of a reactive hydroxyl group, which reacts in turn with a further epoxide group with formation of an ether bridge, so leading to a new reactive hydroxyl group. On account of this reaction mechanism, the substoichiometric use of such catalysts is sufficient for curing. Imidazole is an example of a catalyst which induces the anionic homopolymerization of epoxide compounds. Boron trifluoride is an example of a catalyst which triggers a cationic homopolymerization. Additionally, mixtures of different curing agents which enter into a polyaddition reaction, and mixtures of curing agents which induce

homopolymerization, and also mixtures of curing agents which undergo polyaddition reaction and curing agents which induce homopolymerization, can be used for the curing of polyepoxide compounds.

Suitable functional groups which are able to enter into a polyaddition reaction with the oxirane groups of polyepoxide compounds (epoxy resins) are, for example, amino groups, hydroxyl groups, thioalcohols and derivatives thereof, isocyanates, and carboxyl groups and/or derivatives thereof, such as anhydrides. Accordingly, curing agents used for epoxy resins typically include aliphatic, cycloaliphatic and aromatic polyamines, carboxylic anhydrides, polyamidoamines, amino resins such as, for example, formaldehyde condensation products of melamine, urea, benzoguanamine or phenolic resins such as novolaks, for example. Oligomeric or polymeric, acrylate-based curing agents with hydroxy functions or glycidyl functions in the side chain, and also epoxyvinyl ester resins, are also used. The skilled person is aware of those applications for which a fast- or slow-acting curing agent is used. For example, for storage- stable one-component formulations, he or she will use a curing agent which is very slow-acting (or which acts only at a relatively high temperature). Optionally, a curing agent will be used which is liberated as an active form only under application conditions, examples being ketimines or aldimines. Known curing agents possess a linear or no more than slightly crosslinked structure. They are described, for example in Ullmann's Encyclopedia of Industrial Chemistry, 5th edition on CD-ROM, 1997, Wiley-VCH, chapter "Epoxy Resins", hereby incorporated in full by reference. Examples of suitable curing agents for the curable epoxy resin composition of the invention include polyphenols, polycarboxylic acids, polymercaptans, polyamines, primary monoamines, sulfonamides, aminophenols, aminocarboxylic acids, carboxylic anhydrides, carboxylic acids containing phenolic hydroxyl groups, sulfanilamides, and also mixtures thereof. In the context of this invention, the respective poly compounds (e.g. polyamine) also include the corresponding di compounds (e.g. diamine).

Preferred curing agents for the curable epoxy resin composition of the invention are amino hardeners and phenolic resins. In one particular embodiment the curable epoxy resin composition of the invention comprises an amino hardener as curing agent. Amino hardeners suitable for the polyaddition reaction are compounds which possess at least two secondary or at least one primary amino group(s). The linking of the amino groups of the amino hardener with the epoxide groups of the polyepoxide compound forms polymers whose units originate from the amino hardeners and from the polyepoxide compounds. Amino hardeners are therefore used generally in a stoichiometric ratio to the epoxide compounds. If, for example, the amino hardener has two primary amino groups, and can therefore be coupled with up to four epoxide groups, crosslinked structures may be formed. The amino hardeners of the curable epoxy resin composition of the invention possess at least one primary amino group or two secondary amino groups. Starting from polyepoxide

compounds having at least two epoxide groups, curing can be accomplished by a polyaddition reaction (chain extension) using an amino compound having at least two amino functions. The functionality of an amino compound here corresponds to its number of NH bonds. A primary amino group therefore has a functionality of 2, while a secondary amino group has a

functionality of 1 . The linking of the amino groups of the amino hardener with the epoxide groups of the polyepoxide compound produces polymers from the amino hardener and the polyepoxide compound, the epoxide groups being reacted to form free OH groups. It is preferred to use amino hardeners having a functionality of at least 3 (for example, at least 3 secondary amino groups or at least one primary and one secondary amino group), more particularly those having two primary amino groups (functionality of 4). Preferred amino hardeners are Dimethyl Dicykan (DMDC), dicyandiamide (DICY), isophoronediamine (IPDA), diethylenetriamine (DETA), triethylenetetramine (TETA), bis(p- aminocyclohexyl)methane (PACM), methylenedianiline (e.g. 4,4'-methylenedianiline), polyetheramines, e.g. polyetheramine D230, diaminodiphenylmethane (DDM),

diaminodiphenylsulfone (DDS), 2,4-toluenediamine, 2,6-toluenediamine, 2,4-diamino-1 - methylcyclohexane, 2,6-diamino-1 -methylcyclohexane, 2,4-diamino-3,5-diethyltoluene, 2,6- diamino-3,5-diethyltoluene, 1 ,2-diaminobenzene, 1 ,3-diaminobenzene, 1 ,4-diaminobenzene, diaminodiphenyl oxide, 3,3',5,5'-tetramethyl-4,4'-diaminobiphenyl and 3,3'-dimethyl-4,4'- diaminodiphenyl, and also aminoplast resins such as, for example, condensation products of aldehydes such as formaldehyde, acetaldehyde, crotonaldehyde or benzaldehyde with melamine, urea or benzoguanamine, and also mixtures thereof. Particularly preferred amino hardeners for the curable composition of the invention are Dimethyl Dicykan (DMDC), dicyandiamide (DICY), isophoronediamine (IPDA) and methylenedianiline (e.g.

4,4'-methylenedianiline) and also aminoplast resins such as, for example, condensation products of aldehydes such as formaldehyde, acetaldehyde, crotonaldehyde or benzaldehyde with melamine, urea or benzoguanamine.

In the context of the curable epoxy resin composition of the invention, polyepoxide compound and amino hardener are preferably used in an approximately stoichiometric ratio in terms of the epoxide and amino functionalities. Particularly suitable ratios of epoxide groups to amino functionality are 1 :0.8 to 0.8:1.

In one particular embodiment the curable epoxy resin composition of the invention comprises a phenolic resin as curing agent. Phenolic resins suitable for the polyaddition reaction possess at least two hydroxyl groups. Linking of the hydroxyl groups of the phenolic resin with the epoxide groups of the polyepoxide compound forms polymers whose units originate from phenolic resins and from the polyepoxide compounds. Phenolic resins can generally be used both in a stoichiometric ratio and in a substoichiometric ratio to the epoxide compounds. When substoichiometric amounts of the phenolic resin are used the reaction of the secondary hydroxyl groups of the existing epoxy resin with epoxide groups is promoted by the use of suitable catalysts.

Examples of suitable phenolic resins are novolaks, phenolic resoles, condensation products of aldehydes (preferably formaldehyde and acetaldehyde) with phenols in general. Preferred phenols are phenol, cresol, xylenols, p-phenylphenol, p-tert-butylphenol, p-tert-amylphenol, cyclopentylphenol, and p-nonyl- and p-octylphenol.

The curable epoxy resin composition of the invention may also comprise an accelerator for the curing. Suitable curing accelerators are, for example, imidazole or imidazole derivatives or urea derivatives (urons), such as, for example, 1 ,1-dimethyl-3-phenylurea (fenuron). The use of tertiary amines such as, for example, triethanolamine, benzyldimethylamine,

2,4,6-tris(dimethylaminomethyl)phenol and tetramethylguanidine as curing accelerators has also been described (US 4,948,700). It is known, for example, that the curing of epoxy resins with DICY can be accelerated by addition of fenuron.

The curable epoxy resin may be formulated as a photosensitive formulation generally used for stereolithography or photopolymer jetting applications. In particular these photosensitive epoxy resins may also contain amounts of acrylate components as described in for example

US5476748 and are generally used in 3D-Printing applications.

The curable epoxy resin composition of the invention may also comprise a diluent.

Diluents for the purposes of this invention are conventional diluents or reactive diluents. The addition of diluent to a curable epoxy resin composition typically lowers its viscosity.

Conventional diluents are, customarily, organic solvents or mixtures thereof, examples being ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone (MIBK), diethyl ketone or cyclohexanone, esters of aliphatic carboxylic acids such as ethyl acetate, propyl acetate, methoxypropyl acetate or butyl acetate, glycols such as ethylene glycol, diethylene glycol, triethylene glycol or propylene glycol etc., glycol derivatives such as ethoxyethanol,

ethoxyethanol acetate, ethylene or propylene glycol monomethyl or dimethyl ethers, aromatic hydrocarbons such as toluene or xylenes, aliphatic hydrocarbons such as heptane, for example, and also alkanols such as methanol, ethanol, n- or isopropanol or butanols. In the course of the curing of the epoxy resin, they evaporate from the resin composition. This can lead to an unwanted reduction in resin volume (contraction) or to the formation of pores, and so may adversely affect mechanical properties of the cured material such as, for example, the fracture resistance, or even the surface properties.

Reactive diluents are substances of low molecular mass which, in contrast to conventional solvents, have functional groups, generally oxirane groups, which are able to react with the hydroxyl groups of the resin and/or with the functional groups of the curing agent, with formation of covalent bonds. Reactive diluents in the sense of the present invention are aliphatic or cycloaliphatic compounds. They do not evaporate in the course of curing, but instead are bound covalently, in the course of curing, into the resin matrix as it forms. Examples of suitable reactive diluents are mono- or polyfunctional oxiranes. Examples of monofunctional reactive diluents are glycidyl ethers of aliphatic and cycloaliphatic monohydroxy compounds having in general 2 to 20 C atoms such as, for example, ethylhexyl glycidyl ether and also glycidyl esters of aliphatic or cycloaliphatic monocarboxylic acids having generally 2 to 20 C atoms. Examples of polyfunctional reactive diluents are, in particular, glycidyl ethers of polyfunctional alcohols having in general 2 to 20 C atoms, and containing on average typically 1.5 to 4 glycidyl groups, such as 1 ,4-butanediol diglycidyl ether, 1 ,6-hexanediol diglycidyl ether, diethylene glycol diglycidyl ether or the glycidyl ethers of trimethylolpropane or of pentaerythritol. Reactive diluents described to date do enhance the viscosity properties of the epoxy resin compositions, but in many cases they impair the hardness of the cured resin and result in a relatively low solvent resistance. It is also known that the reactive diluents lower the reactivity of the epoxy resin compositions formulated with them, resulting in longer cure times.

The curable epoxy resin composition of the invention may also include fillers, such as pigments. Suitable fillers are metal oxides such as titanium dioxide, zinc oxide and iron oxide, or hydroxides, sulfates, carbonates, and silicates of these or other metals, examples being calcium carbonate, aluminum oxide, and aluminum silicates. Further suitable fillers are, for example, silicon dioxide, fumed or precipitated silica, and also carbon black, talc, barite or other non-toxic pigments. Mixtures of the fillers can be used as well. The weight fraction of the fillers in the coating, and their particle size and particulate hardness, and also their aspect ratio, will be selected by a skilled person in accordance with the requirements of the application.

The curable epoxy resin composition of the invention may comprise further additives according to the requirements, examples being defoamers, dispersants, wetting agents, emulsifiers, thickeners, biocides, cosolvents, bases, corrosion inhibitors, flame retardants, release agents and/or waxes.

The curable epoxy resin composition of the invention may also comprise reinforcing fibers such as glass fibers or carbon fibers. These fibers may take the form, for example, of short fiber pieces of a few mm to cm in length, or else continuous fibers, fiber windings or woven fiber fabrics.

The present invention further relates to a process for preparing a cured epoxy resin, comprising the curing of the curable epoxy resin composition.

The curing may take place under atmospheric pressure and at temperatures of less than 250°C, more particularly at temperatures less than 235°C, preferably at temperatures less than 220°C, more particularly in a temperature range from 40°C to 220°C. Curing of the curable epoxy resin composition to moldings takes place typically in a mold until dimensional stability has been achieved and the workpiece can be removed from the mold. The subsequent operation for removing inherent stresses in the workpiece and/or for completing the crosslinking of the curable epoxy resin is called heat-conditioning. In principle it is also possible to carry out the heat-conditioning process before the workpiece is removed from the mold, for the purpose of completing the crosslinking, for instance. The heat-conditioning operation typically takes place at temperatures at the limit of dimensional stiffness (Menges et al., "Werkstoffkunde Kunststoffe" (2002), Hanser-Verlag, 5th edition, p. 136). Heat-conditioning takes place typically at temperatures from 120°C to 220°C, preferably at temperatures from 150°C to 220°C. The cured workpiece is exposed to the heat-conditioning conditions typically for a time period of 30 to 240 minutes. Longer heat-conditioning times may also be appropriate, depending on the dimensions of the workpiece. In the curing of the curable epoxy resin composition to form coatings, the substrate to be coated is first of all treated with the curable epoxy resin composition, after which the curable epoxy resin composition on the substrate is cured. The treatment of the curable epoxy resin composition may take place before or after the shaping of the desired article, by dipping, spraying, roller application, spread application, knife coating, or the like, in the case of liquid formulations, or by application of a powder coating material. Application may take place to individual pieces (e.g., can parts) or to fundamentally continuous substrates, such as to strip rolls of steel in the case of coil coating, for example. Suitable substrates are typically those of steel, tinplate (galvanized steel) or aluminum (for beverage cans, for example). Curing of the curable epoxy resin composition following application to the substrate takes place typically in the temperature range from 20°C to 250°C, preferably from 50°C to 220°C, more preferably from 100°C to 220°C. The time is typically 0.1 to 60 min, preferably 0.5 to 20 min, more preferably 1 to 10 min.

A comprehensive description of the common types of metal packaging and their production, metals and alloys used, and coating techniques is given in P.K.T. Oldring and U. Nehring:

Packaging Materials, 7th Metal Packaging for Foodstuffs, I LSI Report, 2007, hereby

incorporated by reference.

The present invention further relates to the cured epoxy resins obtained or obtainable by curing the curable epoxy resin composition of the invention, more particularly in the form of coatings on metallic substrates. The present invention further relates to the use of the compounds of the formula I of the invention and of the curable epoxy resin composition of the invention for producing adhesives, composite materials, moldings, and coatings, more particularly coatings, preferably on containers, more particularly on containers for the storage of food. The present invention further relates to the use of the compounds of the formula I of the invention as reactive diluents, more particularly as reactive diluents for BADGE- or BFDGE- based epoxy resins. The compounds of the formula I of the invention are suitable for lowering the viscosity of other epoxy resins, especially BADGE- or BFDGE-based epoxy resins, in the resin component and in the curable composition. The addition of the compounds of the formula I of the invention as reactive diluents has the advantageous effect of a comparatively low reduction in the glass transition temperature.

The glass transition temperature (Tg) can be determined by means of Dynamic Mechanical Analysis (DMA), in accordance for example with standar DIN EN ISO 6721 , or with a differential calorimeter (DSC), in accordance for example with standard DIN 53765. In the case of DMA, a rectangular specimen is subjected to torsional load at an imposed frequency and with prescribed deformation. The temperature here is raised with a defined ramp, and storage modulus and loss modulus are recorded at fixed time intervals. The former represents the stiffness of a viscoelastic material. The latter is proportional to the energy dissipated in the material. The phase displacement between the dynamic stress and the dynamic deformation is characterized by the phase angle δ. The glass transition temperature can be determined by a variety of methods: as the maximum of the tan δ curve, as the maximum of the loss modulus, or by means of a tangential method applied to the storage modulus. When the glass transition temperature is determined using a differential calorimeter, a very small volume of sample (approximately 10 mg) is heated in an aluminum crucible and the heat flux is measured in relation to a reference crucible. This cycle is repeated three times. The glass transition is determined as an average from the second and third measurements. The Tg stage of the heat flux curve can be determined via the inflection point, by a half-width method or by the midpoint temperature method.

The term "pot life" refers to a parameter which is typically utilized in order to compare the reactivity of different resin/curing agent and/or resin/curing agent mixture combinations. Pot life measurement is a method for characterizing the reactivity of laminating systems by means of a temperature measurement. Depending on application, deviations from the parameters described therein (quantity, test conditions, and measurement method) have become established. The pot life here is determined as follows: 100 g of the curable composition comprising epoxy resin and curing agent or curing agent mixture are placed in a vessel

(typically a paper cup). A temperature sensor is immersed into this curable composition, and measures and records the temperature at particular time intervals. As soon as this curable composition has solidified, measurement is ended and the time to attainment of the maximum temperature is ascertained. If the reactivity of a curable composition is too low, this

measurement is carried out at an elevated temperature. When the pot life is stated, the temperature of testing must always be stated as well.

The gelling time (also called gel time) according to DIN 16 945 indicates a reference point over the period of time between the addition of the curing agent to the reaction mixture and the transition of the reactive resin composition from the liquid state to the gel state. The temperature plays an important part here, and the gel time is therefore found in each case for a specified temperature. With the aid of dynamic-mechanical methods, especially rotational viscometry, it is possible to examine even small amounts of sample quasi-isothermally and to record the entire viscosity or stiffness profile thereof. According to standard ASTM D 4473, the point of intersection between the storage modulus G' and the loss modulus G", where the damping tan δ has a value of 1 , is the gel point, and the period of time from addition of the curing agent to the reaction mixture to attainment of the gel point is the gelling time. The gelling time thus determined may be regarded as a measure of the curing rate. The invention is now illustrated by the following nonlimiting examples. Example 1

Preparation of monomeric THF DGE

Tetrahydrofuran diglycol (0.8 mol, 105.8 g) is heated to 90°C and admixed with BF3 etherate (8 mmol, 0.54 g). Then epichlorohydrin (1.6 mol, 148 g) is added dropwise in portions, during which the temperature ought not to exceed 140°C or drop below 85°C. After the end of the addition, stirring takes place at 90°C until there is no longer a measurable epoxide content. The reaction mixture is cooled to room temperature, 25% strength sodium hydroxide solution (1.6 mol, 258 g) is added, and the mixture is heated once to boiling. After cooling, the phases are separated, and the organic phase is washed repeatedly with water and dried under reduced pressure. This gives the product in a yield of 52%. The resulting epoxy resin has an epoxide equivalent weight (EEW) of 198 g/eq (as well as the monomeric diglycidyl ether, the product also includes dimers, trimers, and diglycidyl ethers of higher molecular mass). The monomeric THF DGE can by purified by distillation to remove the oligomers.

Example 2

Preparation of cured epoxy resin from monomeric THF DGE

THF DGE from example 1 (EEW 198 g/eq) was mixed, immediately after preparation and without further purification, with a stoichiometric amount of an aminic curing agent. A curing agent used was I PDA. For comparison, a corresponding stoichiometric mixture of bisphenol A based epoxy resin (BADGE; Epilox A19-03 from Leuna Harze, EEW 182 g/eq) and I PDA was prepared. The mixtures were incubated at 23°C or 75°C. At the different temperatures, the rheological measurements for investigating the reactivity profile were carried out on a shear rate-controlled plate/plate rheometer (MCR 301 from Anton Paar) having a plate diameter of 15 mm and a slot distance of 0.25 mm.

The measurement of the gel time was carried out on the abovementioned rheometer in rotational oscillation at 23°C and 75°C. The point of intersection of loss modulus (G") and storage modulus (G') yields the gel time. The average start viscosity (η₀) during 2 to 5 minutes following preparation of the mixture was measured at 23°C and 75°C, likewise the time (t-ioooo) until a viscosity of 10 000 mPa^*s has been reached. The glass transition temperature (Tg) was measured by means of DSC analysis (Differential Scanning Calorimetry) of the curing reaction in accordance with ASTM D 3418 on the second run. The temperature profile operated for the measurement was as follows: 0°C -> 5 K/min 180°C -» 30 min 180°C -» 20 K/min 0°C -» 20 K/min 220°C. The results of the measurements are compiled in table 1. Table 1 : Start viscosity, increase in viscosity, gel time and glass transition temperature for curing THF DGE

The measurements show that with the THF DGE based resin a much lower glass transition temperature is achieved, which suggests an increased flexibility. Furthermore, a significantly lowered start viscosity and also a reduced reactivity are found in the case of curing.

Claims

A tetrahydrofuran diglycol diglycidyl ether derivative of the formula I

where

R1 and R2 independently of one another are each a hydrogen atom, an alkyl group having 1 to 4 C atoms, a halogen atom (F, CI, Br, I) or a nitro group,

R3 is a hydrogen atom or a glycidyl group, and

n is 0 to 100.

The tetrahydrofuran diglycol diglycidyl ether derivative according to claim 1 , where

R1 and R2 independently of one another are each a hydrogen atom or an alkyl group having 1 to 4 C atoms,

R3 is a hydrogen atom or a glycidyl group, and

n is 0 to 30.

The tetrahydrofuran diglycol diglycidyl ether derivative according to claim 2, where R1 and R2 are each hydrogen atoms.

A process for preparing a tetrahydrofuran diglycol diglycidyl ether derivative according to any of claims 1 to 3 comprising reacting a tetrahydrofuran diglycol derivative of the formula II

where R1 and R2 have the same definition as for the tetrahydrofuran diglycol diglycidyl ether derivative, with epichlorohydrin.

A process for preparing a tetrahydrofuran diglycol diglycidyl ether derivative-based

oligomer, wherein a tetrahydrofuran diglycol diglycidyl ether derivative according to any of claims 1 to 3 with n being 0, or a mixture of two or more tetrahydrofuran diglycol diglycidyl ether derivatives according to any of claims 1 to 3 with different ns, where predominantly n is 0, is reacted with one or more diols.

6. A tetrahydrofuran diglycol diglycidyl ether derivative-based oligomer, which is obtainable by reacting a tetrahydrofuran diglycol diglycidyl ether derivative according to any of claims 1 to 3 where n is 0, or a mixture of two or more tetrahydrofuran diglycol diglycidyl ether derivatives according to any of claims 1 to 3 with different ns, where predominantly n is 0, with one or more diols. 7. The tetrahydrofuran diglycol diglycidyl ether derivative-based oligomer according to claim 6, where the one or more diols are not identical with the tetrahydrofuran diglycol derivatives corresponding to the tetrahydrofuran diglycol diglycidyl ether derivatives.

8. A curable epoxy resin composition comprising a curing component which comprises at least one curing agent, and a resin component which comprises at least one

tetrahydrofuran diglycol diglycidyl ether derivative-based polyepoxide compound selected from the group consisting of tetrahydrofuran diglycol diglycidyl ether derivatives according to any of claims 1 to 3 and tetrahydrofuran diglycol diglycidyl ether derivative-based oligomers according to claim 7.

9. The curable epoxy resin composition according to claim 8, wherein the resin component comprises at least one tetrahydrofuran diglycol diglycidyl ether derivative-based polyepoxide compound selected from the group consisting of tetrahydrofuran diglycol diglycidyl ether derivatives according to any of claims 1 to 3.

10. The curable epoxy resin composition according to claim 8 or 9, wherein the at least one curing agent is selected from the group consisting of amino curing agents and phenolic resin. 1 1 . The curable epoxy resin composition according to any of claims 8 to 10, wherein the

tetrahydrofuran diglycol diglycidyl ether derivative-based polyepoxide compounds account in total for a fraction of at least 40 weight%, based on the overall resin component.

12. The curable epoxy resin composition according to any of claims 8 to 1 1 , wherein the

curable epoxy resin composition includes a fraction of less than 40 weight% of bisphenol

A or F based compounds, based on the overall resin component.

13. The curable epoxy resin composition according to either of claims 9 and 10, wherein the resin component comprises at least one epoxy resin selected from the group consisting of diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, diglycidyl ether of ring- hydrogenated bisphenol A, diglycidyl ether of ring-hydrogenated bisphenol F, tetraglycidyl- methylenedianiline, cresol epoxy resin, novolak epoxy resin, and triglycidylaminophenols, and oligomers thereof.

14. The curable epoxy resin composition according to claim 13, wherein the tetrahydrofuran diglycol diglycidyl ether derivative-based polyepoxide compounds account in total for a fraction of up to 30 weight%.

15. A method for producing a cured epoxy resin, comprising curing the curable epoxy resin composition according to any of claims 8 to 14.

16. A cured epoxy resin obtainable by curing the curable epoxy resin composition according to any of claims 8 to 14.

17. A resin component comprising at least one tetrahydrofuran diglycol diglycidyl ether

derivative-based polyepoxide compound selected from the group consisting of

tetrahydrofuran diglycol diglycidyl ether derivatives according to any of claims 1 to 3, and at least one epoxy resin selected from the group consisting of diglycidyl ether of bisphenol A, diglycidyl ether of bisphenol F, diglycidyl ether of ring-hydrogenated bisphenol A, diglycidyl ether of ring-hydrogenated bisphenol F, tetraglycidylmethylenedianiline, cresol epoxy resin, novolak epoxy resin, and triglycidylaminophenols, and oligomers thereof.

18. The use of the curable epoxy resin composition according to any of claims 8 to 12 for producing adhesives, composite materials, moldings, or coatings. 19. The use of a tetrahydrofuran diglycol diglycidyl ether derivative-based polyepoxide

compound selected from the group consisting of tetrahydrofuran diglycol diglycidyl ether derivatives according to any of claims 1 to 3 as reactive diluent.