HK1192762A - Epoxy resins with high thermal stability and toughness - Google Patents

Description

Epoxy resins with high thermal stability and toughness

Technical Field

The present invention relates to epoxy resin compositions that exhibit preferred chemical and physical properties when cured. In particular, the cured epoxy resin compositions of the present invention exhibit high glass transition temperatures and high fracture toughness.

Background

Epoxy resins are known for treating surfaces (e.g., concrete, metal, electrical components, and gypsum board) to prevent corrosion and other forms of wear and tear caused by everyday use and the environment. Epoxy resins typically contain a plurality of epoxy or oxirane groups that react with a curing agent to form a network or a significantly crosslinked system.

Curing agents are distinguished from compounds referred to herein as chain extenders. As used herein, "chain extender" is intended to mean a compound having two (2) sites capable of reacting with an epoxy group. During polymerization, the chain extender is typically embedded between the epoxy chains and chain extended with little crosslinking occurring. In contrast, "curing agent" refers to a compound that is capable of catalyzing the polymerization of an epoxy resin with significant networking or crosslinking.

In many applications, it is desirable that the cured epoxy product exhibit a relatively high glass transition temperature (T)_g). One common method of achieving higher glass transition temperatures is through the use of multifunctional epoxy resins such as those described in U.S. patent nos.4559395, 4645803, 4550051, 4529790, 4594291, 2947726, 2971942, and 2809942. However, multifunctional epoxy resins are generally not very tough or ductile and are therefore undesirable in some applications. Further, if a large concentration of polar groups is incorporated into the resin in order to achieve high heat resistance, the cured product may exhibit poor moisture resistance.

One method of improving toughness and flexibility is through the use of chain extenders, such as bisphenol a, which may be incorporated into the epoxy resin prior to curing. Although the resulting cured products generally exhibit a relatively high degree of cure and toughness or ductility, the cured products also tend to exhibit a relatively low glass transition temperature due to low crosslink density. Epoxy resins based on diglycidyl ether of 9, 9-bis (4-hydroxyphenyl) fluorene described in U.S. patent No.4,980,234 are said to provide materials having high glass transition temperature and flexural modulus and low moisture resistance when cured.

It is an object of the present invention to provide a novel epoxy resin composition useful for obtaining a cured epoxy product having a higher glass transition temperature as well as excellent mechanical properties and low hygroscopicity.

Summary of The Invention

The present invention relates to an epoxy resin composition comprising:

(a) a polyepoxide resin;

(b) a chain extender comprising at least one compound of formula (III) or (V):

OH-A-OH (III)

R²O-A-OR² (V)

wherein A is a group of formula (IV)

Wherein Z is hydrogen, methyl or phenyl; and A is₁Represents an organic group required to complete an aromatic residue and R²Is an epoxy functional alkyl group having 1 to 6 carbon atoms; and

(c) and (3) a curing agent.

The above components, when provided in a composition, unexpectedly produce a cured epoxy resin exhibiting a high glass transition temperature and improved fracture toughness upon curing.

Detailed Description

If appearing herein, the term "comprising" and its derivatives are not intended to exclude the presence of any additional component, step or procedure, whether or not the same is disclosed herein. For the avoidance of any doubt, all compositions claimed herein through use of the term "comprising" may include any additional additive, adjuvant, or compound, unless stated to the contrary. Rather, the term "consisting essentially of, if present herein, excludes in any subsequently listed range any other components, steps or procedures other than those not necessary for operability, and if the term" consisting of "is used, excludes any components, steps or procedures not specifically described or recited. Unless otherwise specified, the term "or" means the listed members individually as well as in any combination.

The articles "a" and "an" are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. For example, "mono-epoxy" refers to one epoxy group or more than one epoxy group.

The phrases "in one embodiment," "according to one embodiment," and the like generally refer to a particular element, structure, or feature after the phrase that is included in at least one embodiment of the invention and possibly in more than one embodiment of the invention. Importantly, such phrases are not necessarily referring to the same embodiment.

If the specification states a component or element "may", "might", or "could" be included or have a certain characteristic, that particular component or element need not necessarily be included or have that characteristic.

The present disclosure relates generally to novel epoxy resin compositions including benzofuran units therein and articles or substrates coated with such compositions. It has been surprisingly found that the incorporation of benzofuran units as chain extenders results in glass transition temperatures that exhibit improvements, for example glass transition temperatures of at least about 120 ℃, preferably greater than about 150 ℃, without substantial loss of through fracture toughness (i.e., K)_1c/G_1c) A difunctional epoxy resin having a measured toughness. In some embodiments, the compositions of the present disclosure exhibit a glass transition temperature of at least 120 ℃ and at least 100Joules/m²And in other embodiments exhibit an improvement in glass transition temperature of at least 25 ℃ without substantial loss of fracture toughness as compared to conventional compositions that do not contain benzofuran units therein. Such properties can be used to generally identify significantly improved compositions according to the present invention.

According to a particular embodiment, a benzofuran diol component, a benzofuran diepoxide component, or a mixture thereof is provided in an epoxy resin composition along with a polyepoxide resin and a curing agent to form, upon curing, a cured epoxy resin exhibiting improved glass transition temperature and toughness. The term "improved glass transition temperature" as used herein is intended to mean a cured epoxy resin that has been increased in its glass transition temperature using the present disclosure as compared to conventional resins. The term "improved toughness" is intended to mean a cured resin that exhibits improved fracture toughness as compared to conventional resins using the present disclosure. The term "polyepoxide resin" refers to a compound containing or containing more than one epoxy group prior to reaction. Furthermore, the term "epoxy resin composition" is intended to mean an uncured composition which, upon curing, cures into a "cured epoxy resin" or "cured product". In the present disclosure, the benzofuran diol component and/or the benzofuran diepoxide component is used to increase epoxy resin chain length without introducing increased crosslinking. On the other hand, curing agents are used to introduce sufficient crosslinking. In some embodiments, the benzofuran diol component is used in an amount such that about 5% to 90%, preferably about 9% to 70%, of the reactive epoxy groups provided by the polyepoxide resin will react with the reactive hydroxyl groups provided by the benzofuran diol component, while in other embodiments, the benzofuran diepoxide component is used in an amount such that about 2% to 78%, preferably about 4% to 60%, by weight of the resulting resin contains benzofuran units. The amount of curing agent used depends on the concentration of its functional groups and its molecular weight. In some embodiments, the curing agent is used in an amount sufficient to react with a significant amount of the remaining reactive epoxy groups in the epoxy resin composition. The term "substantial amount" is used herein to refer to an amount sufficient to generate sufficient crosslinking to produce a cured epoxy resin having a desired glass transition temperature and toughness.

In one embodiment, the epoxy resin composition contains from about 5% to about 95%, preferably from about 10% to about 90%, and more preferably from about 15% to about 85% by weight of the polyepoxide resin, based on the total weight of the epoxy resin composition.

The polyepoxide resin may include one or a mixture of aliphatic, cycloaliphatic, or aromatic epoxy compounds having from about 1.5 to about 2.5 epoxy groups, preferably about 2 epoxy groups. In some embodiments, the epoxy compound has an EEW of about 180 to about 20,000. In other embodiments, the epoxy compound has a weight average molecular weight of about 400 to about 50,000.

Although the epoxy compound may be used in its commercially available form, it may also be derivatized to a low molecular weight epoxy compound using standard methods known to those skilled in the art, for example, by derivatizing an epoxy compound having an EEW of about 180 to about 500 with bisphenol A to produce an epoxy compound having an EEW of about 500 to about 12,000.

According to one embodiment, the epoxy compound is an epoxy resin represented by structural formula (I) or (II):

wherein each R is independently a divalent hydrocarbon group having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms; each R¹Independently hydrogen or alkyl having 1 to 4 carbon atoms; each X is independently hydrogen or a hydrocarbyl or hydrocarbyloxy group having from 1 to 12, preferably from 1 to 6, carbon atoms or a halogen; each t is independently 0 or 1; and n is an integer having a value of 0 to about 150. As used herein, "hydrocarbyl" refers to hydrocarbyl groups including, but not limited to, aryl, alkyl, cycloalkyl, alkenyl, cycloalkenyl, cycloalkadienyl, alkynyl, aralkyl, aralkenyl, aralkynyl, and the like, and including all substituted, unsubstituted, branched, straight chain, heteroatom-substituted derivatives thereof. Similarly, the term "hydrocarbyloxy" refers to a hydrocarbyl group having an oxygen bond between it and the object to which it is attached.

In a preferred embodiment, the epoxy compound is a diglycidyl ether of a bisphenol a epoxy resin, i.e., a diglycidyl ether of bisphenol a:

and diglycidyl ether of bisphenol a:

the diglycidyl ether can be prepared by reacting 2 molecules of epichlorohydrin with 1 molecule of bisphenol a in the presence of a base, such as sodium hydroxide. In other embodiments, the reaction is carried out such that the resulting diglycidyl ether molecules react in situ with the bisphenol molecules to produce the epoxy resin.

In this case, the epoxy resin is a mixture comprising polymer species corresponding to different values of n in the following idealized chemical formula:

wherein n is an integer having a value of 0 to about 150.

In addition to bisphenol A, the epoxy compound may be another epoxy resin prepared by the derivatization of the diglycidyl ethers of the following bisphenols with the following illustrative, but not limiting, bisphenols:

the epoxy resin composition further contains a chain extender. The chain extenders of the present disclosure include compounds of the general formula (III):

OH-A-OH (III)

wherein A is a group of formula (IV)

Wherein Z is hydrogen, methyl or phenyl; and A is₁Represents the organic group required to complete the aromatic residue.

By A₁A finished aromatic residue; i.e. by A₁Aromatic residues formed with the linking carbon atoms shown in formula (IV) include phenyl, diphenylmethane (i.e., phenylmethylphenyl), biphenyl (i.e., biphenyl), substituted with one or two C's at the methyl group (i.e., on the methane carbon atom)₁–C₄Alkyl substituted diphenylmethane (i.e. phenyl di (C)₁–C₄Alkyl) methylphenyl), diphenyl ketone (i.e., benzoylphenyl) or diphenyl sulfone (i.e., phenylsulfonylphenyl). In some embodiments, a is a group having the formula:

wherein Z is as defined above; y is a direct bond, CH₂、C(C₁-C₄Alkyl radical)₂-C = O or-S (= O)₂(ii) a And d is an integer having a value of 0 to 3.

The compound of formula (III) can be made by reacting the appropriate diol and diketone in the presence of a strong acid. The compounds of formula (III) are further described on page 4 of EP0595530a1, the content of which is incorporated herein by reference.

In another embodiment, the chain extender of the present disclosure is a compound of formula (V):

R²O-A-OR² (V)

wherein A is as defined above and R²Is an epoxy functional alkyl group having 1 to 6 carbon atoms. In a preferred embodiment, each R is²Is 2, 3-epoxypropyl. In this embodiment, the benzofuran units are incorporated into the polyepoxide resin by reaction of a diepoxy compound rather than by a dihydroxy compound.

In embodiments where the diepoxide compound of formula (V) is utilized to incorporate benzofuran units into a polyepoxide resin, a chain extender that is free of benzofuran may be included to provide certain preferred characteristics in the resulting cured resin. As the chain extender containing no benzofuran, various materials can be used, including the above-mentioned bisphenols. In other embodiments, the benzofuran-free chain extender may be another difunctional active hydrogen compound, such as a diglycidyl ether epoxy resin, a dithiol, a dicarboxylic acid, or a diamine.

The epoxy resin composition also contains a curing agent for curing the epoxy resin composition and forming a crosslinked polymer network. According to one embodiment, the curing agent is an aliphatic, cycloaliphatic, aromatic or heterocyclic amine, including but not limited to m-and p-phenylenediamine, bis (4-aminophenyl) methane, aniline-formaldehyde resin, bis (4-aminophenyl) sulfone, ethylenediamine, propane-1, 2-diamine, propane-1, 3-diamine, N-diethylethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, N- (2-hydroxyethyl) -, N- (2-hydroxypropyl) -and N- (2-cyanoethyl) -diethylenetriamine, 2, 4-trimethylhexane-1, 6-diamine, 2,3, 3-trimethylhexane-1, 6-diamine, m-xylylenediamine, p-, N, N-dimethyl-and N, n-diethylpropane-1, 3-diamine, ethanolamine, bis (4-aminocyclohexyl) methane, 2-bis (4-aminocyclohexyl) propane, 2-bis (4-amino-3-methylcyclohexyl) propane, 3-aminomethyl-3, 5, 5-trimethylcyclohexylamine (isophoronediamine) and N- (2-aminoethyl) piperazine, 2,4, 6-tris (dimethylaminomethyl) phenol and other mannich bases, N-benzyldimethylamine, triethanolamine, dicyandiamide, carboxylic acid hydrazide, imidazole, aminoplast, polyaminoamides (such as those made from aliphatic polyamines and di-or trimeric unsaturated fatty acids), isocyanates, isothiocyanates; phosphoric acid; a polythiol; or polycarboxylic acids and their anhydrides, for example phthalic anhydride, tetrahydrophthalic anhydride, methylendomethylenetetrahydrophthalic anhydride, nonenylsuccinic anhydride, dodecenylsuccinic anhydride, hexahydrophthalic anhydride, hexachloroendomethylenetetrahydrophthalic anhydride and endomethylenetetrahydrophthalic anhydride and mixtures thereof, maleic anhydride, succinic anhydride, pyromellitic dianhydride, benzophenone-3, 3 ', 4, 4' -tetracarboxylic anhydride, polysebacic anhydride, polyazelaic anhydride, the acids corresponding to the abovementioned anhydrides and also isophthalic acid, terephthalic acid, citric acid and mellitic acid. Other curing agents include alkali metal alkoxides of alcohols, for example, sodium alkoxides of 2, 4-dihydroxy-3-hydroxymethylpentane, stannous salts of alkanoic acids, for example stannous octoate, Friedel-Crafts catalysts, for example boron trifluoride and its complexes, and chelates formed by the reaction of boron trifluoride with 1, 3-diketones.

The amount of curing agent that can be used varies with the resin composition and is generally provided in an amount effective to cause significant curing over a desired length of time. In one embodiment, the amount of curing agent used may range from about 1 to 40 weight percent of the total weight of the epoxy resin composition. In other embodiments, when the curing agent is an amine, the amount of curing agent used may be from about 0.75 to about 1.25 amino-hydrogen equivalents of the amine per 1, 2-epoxy equivalents remaining in the epoxy resin composition. When polycarboxylic acids or their anhydrides are used, typically from about 0.4 to about 1.1 carboxylic acid or carboxylic acid anhydride equivalents are provided per 1, 2-epoxy equivalent remaining in the epoxy resin composition.

If desired, the epoxy resin composition may optionally be mixed with one or more conventional additives, such as stabilizers, extenders, fillers, reinforcing agents, pigments, dyes, plasticizers, tackifiers, accelerators, non-reactive diluents or any mixtures thereof, prior to curing.

Useful stabilizers include: phenothiazine itself or a C-substituted phenothiazine having 1 to 3 substituents or an N-substituted phenothiazine having 1 substituent, for example, 3-methyl-phenothiazine, 3-ethyl-phenothiazine, 10-methyl-phenothiazine; 3-phenyl-phenothiazine, 3, 7-diphenyl-phenothiazine; 3-chlorophenothiazine, 2-chlorophenothiazine, 3-bromophenothiazine; 3-nitrophenothiazine, 3-aminophenothiazine, 3, 7-diaminophenothiazine; 3-sulfonyl-phenothiazine, 3, 7-disulfonyl-phenothiazine, 3, 7-dithiocyanatothiazine; substituted quinine and pyrocatechol, copper naphthenate, zinc dimethyldithiocarbonate and hydrated phosphotungstic acid. Useful extenders, reinforcing agents, fillers, accelerators and pigments include, for example: coal tar, pitch, glass fiber, boron fiber, carbon fiber, cellulose, polyethylene powder, polypropylene powder, mica, asbestos, quartz powder, gypsum, antimony trioxide, bentonite, silica aerogel ("aerosil"), lithopone, barite, titanium dioxide, eugenol, dicumyl peroxide, isoeugenol, carbon black, graphite, and iron powder. Other additives may also be added, for example, fire retardants, flow control agents such as silicones, cellulose acetate butyrate, polyvinyl butyrate, waxes, stearates, and the like.

In a preferred embodiment, the epoxy resin composition comprises a polyepoxide resin represented by a compound of formula (VI) wherein X, R, A and t are as defined above, a is an integer having a value of 1 to 100, preferably 1 to 30, and b is an integer having a value of 0 to 100, preferably 0 to 30, in the presence of a benzofuran diol and/or benzofuran diepoxide component.

Upon curing with a suitable curing agent, the epoxy resin undergoes a ring-opening reaction that may include, but is not limited to, the following reaction mechanisms represented by formulas (VIIa) through (VIIf):

in one embodiment, the polyepoxide resin, the benzofuran diol component, and/or the benzofuran diepoxide component may be combined with a suitable curing agent and may be used as a composite matrix resin. The prepreg can be prepared as follows: continuous reinforcement fiber bundles are dipped into a solution of a composite matrix resin (in monomeric or polymeric form) and then wound onto a drum to form a unidirectional prepreg sheet having a length equal to the circumference of the drum. Other pre-impregnation methods known to those skilled in the art, such as hot melt methods, may also be used. The solvent is then evaporated from the prepreg on a drum or in an oven. The partially or fully dried prepreg sheets may then be cut into small pieces, stacked into the desired configuration, and then consolidated into a laminate by the application of heat and pressure. This lamination process is also used to cure the composite matrix resin. The laminate is generally consolidated (fused and void free) at a temperature lower than the temperature of rapid solidification. Once consolidated, the temperature is increased to effect curing. After lamination, the parts are typically post-cured separately in an oven at a higher temperature.

The novel epoxy resin compositions of the present disclosure are also useful as high temperature adhesives. Typically, the resin composition may be applied to either or both bonding surfaces in the form of a glass cloth prepreg, a resin solution (in monomeric or polymeric form), or a resin film. The assembly is then consolidated and cured under heat and pressure in a manner similar to that used to form the composite material described above.

In addition, there are many uses for the epoxy resin compositions of the present disclosure in the field of electronic applications. For example, they may be applied from solution to form a planarization layer or dielectric layer on a silicon wafer, or they may be used to encapsulate electronic devices. The applied layer or encapsulant can then be dried and cured to form a thermo-oxidative stable thermoset film.

In another embodiment, the total mixture obtainable from the polyepoxide resin, the benzofuran diol component and/or the benzofuran diepoxide component according to the present disclosure in combination with the curing agent may also be heated at 50 ℃ to 300 ℃ for a suitable length of time in order to achieve a faster and/or more complete cure. Heating periods, such as 50 ℃ for about 0.25-1 hour, 150 ℃ to 200 ℃ for about 0.5-2 hours, and 175 ℃ to 250 ℃ for about 1-5 hours, can be used.

In some embodiments, it may be preferred to react all of the chain extender with the polyepoxide resin prior to initiating cure. This depends in part on the percentage of chain extender to be incorporated.

Thus, the epoxy resin compositions of the present invention can be used in various applications, for example in the field of composites, such as in the manufacture of castings or prepregs, in the electronic field, such as potting and moulding compositions, in lamination processes, as adhesives and for surface protection, such as coatings for pipes and containers.

In another embodiment, the present disclosure provides a method of bonding at least two substrates together comprising:

a) providing an epoxy resin composition comprising: (i) a polyepoxide resin; (ii) a benzofuran diol component, a benzofuran diepoxide component, or mixtures thereof, as described above; and (iii) a curing agent;

b) applying the epoxy resin composition to at least one surface of one or more substrates; and

c) the surfaces of the substrates to be bonded together are brought into mating engagement so that the composition cures therebetween to form a bond.

In those installations where relative movement of the substrates is expected, the substrates to be bonded may be clamped during the curing process. For example, to bond two substrate surfaces, an adhesive amount of the epoxy resin composition is applied to at least one surface, preferably both surfaces and the surfaces are brought into contact with the composition therebetween. The smoothness of the surfaces and their gaps determine the film thickness required for optimal bonding. The epoxy resin composition may be applied to one or more surfaces of a substrate at a desired thickness by methods well known to those skilled in the art, such as spraying, dipping, brushing, painting, rolling, and the like, before, after, or simultaneously with the curing agent. After application, the composition is cured under ambient conditions and/or by application of heat. The surface and intervening epoxy resin composition remain joined until the composition is sufficiently cured to bond the surfaces. Examples of substrates to which the curable composition may be applied include, but are not limited to, steel, galvanized steel, aluminum, copper, brass, wood, glass, paper, composites, ceramics, plastics, and polymeric materials such as polyesters, polyamides, polyurethanes, polyvinyl chloride, polycarbonates, ABS plastics, and plexiglass.

Examples

Examples 1 to 4.Four epoxy resin compositions were prepared according to the following formulation:

¹diglycidyl ether of bisphenol F

²Diglycidyl ether of bisphenol A

³Epoxy cresol novolac resin

These four compositions were then cured at 150 ℃ for 2 hours and then at 180 ℃ for 2 hours, and the cured products exhibited the following properties:

the above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true scope of the present invention. Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.

Claims (9)

1. An epoxy resin composition comprising:

(a) a polyepoxide resin;

(b) a chain extender comprising at least one compound of formula (III) or (V):

OH-A-OH (III)

R²O-A-OR² (V)

wherein A is a group of formula (IV)

Wherein Z is hydrogen, methyl or phenyl; and A is₁Represents an organic group required to complete an aromatic residue and R²Is an epoxy functional alkyl group having 1 to 6 carbon atoms; and

(c) and (3) a curing agent.

2. The epoxy resin composition of claim 1, wherein the polyepoxide resin comprises one or more aliphatic, cycloaliphatic, or aromatic epoxy compounds having about 2 epoxy groups.

3. The epoxy resin composition of claim 2, wherein the epoxy compound is an epoxy resin represented by structural formula (I) or (II):

wherein each R is independently a divalent hydrocarbon group having 1 to 12 carbon atoms; each R¹Independently hydrogen or alkyl having 1 to 4 carbon atoms; each X is independently hydrogen or a hydrocarbyl or hydrocarbyloxy group having from 1 to 12 carbon atoms or a halogen; each t is independently 0 or 1; and n is an integer having a value of 0 to about 150.

4. The epoxy resin composition of claim 1, wherein A¹Is phenyl, diphenylmethane, biphenyl, substituted by one or two C at the methyl radical₁–C₄Alkyl-substituted diphenyl methanes, diphenyl ketones or diphenyl sulphones.

5. The epoxy resin composition of claim 1, wherein a is a group having the formula:

wherein Z is as defined in claim 1 and Y is a direct bond, CH₂、C(C₁-C₄Alkyl radical)₂-C = O or-S (= O)₂(ii) a And d is an integer of 0 to 3.

6. The epoxy resin composition of claim 1, further comprising a toughening agent.

7. The epoxy resin composition of claim 1, wherein the chain extender is a compound of the general formula (V):

R²O-A-OR² (V)

wherein A and R²As defined in claim 1.

8. The epoxy resin composition of claim 7, further comprising a benzofuran-free chain extender selected from the group consisting of bisphenol A, bisphenol F, bisphenol S, resorcinol, catechol, hydroquinone, and mixtures thereof.

9. A method of bonding at least two substrates together comprising:

a) providing an epoxy resin composition comprising: (i) a polyepoxide resin; (ii) a chain extender comprising at least one compound of formula (III) or (V):

OH-A-OH (III)

R²O-A-OR² (V)

wherein A is a group of formula (IV)

Wherein Z is hydrogen, methyl or phenyl; and A is₁Represents an organic group required to complete an aromatic residue and R²Is an epoxy functional alkyl group having 1 to 6 carbon atoms; and (iii) a curing agent;

b) applying the epoxy resin composition to at least one surface of one or more substrates; and

c) mating the substrate surfaces to be bonded together such that the composition cures therebetween to form a bond.