GB2029416A

GB2029416A - Epoxy Resin Composition

Info

Publication number: GB2029416A
Application number: GB7911873A
Authority: GB
Original assignee: Texaco Development Corp
Current assignee: Texaco Development Corp
Priority date: 1978-09-11
Filing date: 1979-04-04
Publication date: 1980-03-19
Also published as: GB2029416B; DE2930326A1

Abstract

The invention provides epoxy resin compositions comprising a vicinal polyepoxide, and an oligomeric poly(ethylene-piperasine), which can act as a curing agent itself, or as an accelerator for a known curing agent which is not by itself able to effect a complete cure of the composition, (e.g. en anhydride or dicyandiamide). Generally the oligomeric poly(ethylenepiperazine) has the formula <IMAGE> where n is 1-20, preferably 2-6.a

Description

SPECIFICATION Epoxy Resin Composition This invention relates to curable epoxy resins. More particularly, it relates to compositions comprising a novel curing agent, oligomeric poly(ethylenepiperazine).

Epoxy resins constitute a broad class of polymeric materials having a wide range of physical characteristics. The resins have epoxide groups which are cured by reaction with certain catalysts or curing agents to provide cured epoxy resin compositions with certain desirable properties. Carboxylic acid anhydrides provide one such class of curing agents. The most commonly used anhydride curing agents are those of dicarboxylic acids, such as maleic anhydride or phthalic anhydride, or of tetracarboxylic acids, such as pyromellitic dianhydride.

Epoxy resin formulations using prior art curing agents usually comprise two components, one containing the epoxy resin and the other containing the curing agent. These must be mixed only at the time a cured product is desired, often by persons unfamiliar with formulating techniques.

A novel epoxy resin curing agent is disclosed herein which. can be mixed with the epoxy resin and stored as a one component system. This system can then be cured by the application of heat.

This novel curing agent also accelerates the cure of certain prior art curing agents.

The cured epoxy resin compositions of the invention are useful as coatings, castings, and sealants.

This invention provides a curable epoxy resin composition which comprises: (a) a vicinal polyepoxide having an average of at least 1.8 reactive, 1 ,2-epoxy groups per molecule, and (b) an oligomeric poly(ethylenepiperazine) or derivative thereof.

This invention also provides a composition as defined above comprising a curing agent known per se.

This invention also provides a method for curing such compositions comprising heating said compositions, and cured epoxy resin compositions cured by such a process.

Generally the vicinal polyepoxide containing compositions are organic materials having an average of at least 1.8 reactive 1,2epoxy groups per molecule. These polyepoxide materials can be monomeric or polymeric, saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic, and may be substituted if desired with other substituents besides the epoxy groups, e.g., hydroxyl groups, ether radicals, or aromatic halogen atoms.

Preferred polyepoxides are glycidyl ethers prepared by epoxidizing the corresponding allyl ethers or redacting, by known procedures, a molar excess of epichlorohydrin and an aromatic polyhydroxy compound, e.g. isopropylidene bisphenol, a novolak or resorcinol. The epoxy derivatives of methylene or isopropylidene bisphenols are especially preferred.

A widely used class of polyepoxides which are useful according to the invention includes the resinous epoxy polyethers obtained by reacting an epihalohydrin, such as epichlorohydrin, with either a polyhydric phenol or a polyhydric alcohol. An illustrative, but by no means exhaustive, listing of suitable dihydric phenols includes 4,4'-isopropylidene bisphenol; 2,4'-dihydroxydiphenylethylmethane; 3,3' dihydroxydiphenyldiethylmethane; 3,4'-dihydroxydiphenylmethylpropylmethane; 2,3'- dihydroxydiphenylethylphenylmethane; 4,4'-dihydrnxydiphenylprnpylphenylmethane; 4,4'dihydroxydiphenylbutylphenylmethane; 2,2'-dihydroxydiphenylditolylmethane; and 4,4'dihydroxydiphenyltolylmethylmethane.Other polyhydric phenois which may also be co-reacted with an epihalohydrin to provide these epoxy polyethers are such compounds as resorcinol, hydroquinone and substituted hydroquinones, e.g., methylhydroquinone.

Among the polyhydric alcohols which can be co-reacted with an epihalohydrin to provide these resinous epoxy polyethers are such compounds as ethylene glycol; propylene glycols; butylene glycols; pentane diols; bis(4-hydroxycyclohexyl)dimethylmethane; 1 ,4-dimethylolbenzene; glycerol; 1,2,6hexanetriol; trimethylolpropane; mannitol; sorbitol; erythritol; pentaerythritol; their dimers, trimers and higher polymers, e.g., polyethylene glycols, polypropylene glycols, triglycerol or dipentaerythritol; polyallyl alcohol; polyhydric thioethers, such as 2,2'-,3,3'-tetrahydroxydipropylsulfide; mercapto alcohols such as monothioglycerol or dithioglycerol; polyhydric alcohol partial esters, such as monostearin or pentaerythritol monoacetate; and halogenated polyhydric alcohols such as the monochlorohydrins of glycerol, sorbitol or pentaerythritol.

Another class of polymer polyepoxides which can be used in accordance with the invention includes the epoxy novolak resins obtained by reacting, preferably in the presence of a basic catalyst, e.g., sodium or potassium hydroxide, an epihalohydrin, such as epichlorohydrin, with the resinous condensate of an aldehyde, e.g., formaldehyde, and either a monohydric phenol, e.g., phenol itself, or a polyhydric phenol. Further details concerning the nature and preparation of these epoxy novolak resins can be obtained in Lee, H. and Neville, K., Handbook of Epoxy Resins, McGraw Hill Book Co., New York, 1967.

It will be appreciated by those skilled in the art that the polyepoxide compositions which are useful according to the practice of the present invention are not limited to those containing the above described polyepoxides, but that these polyepoxides are to be considered merely as being representative of the class of polyepoxides as a whole.

The novel epoxy curing agent of this invention is oligomeric poly(ethylenepiperazine), having the general formula

where n can be 1-20, but is preferably 2-6. It is a crystalline, hard, insoluble solid, readily reduced to a fineiy divided powder, melting at about 230 or. It is prepared by heating 1 -(2-hydroxyethyl)piperazine in an inert liquid at an elevated temperature in presence of an acidic catalyst, such as an aromatic carboxylic acid.

This novel curing agent may be used alone or in combination with another curing agent or agents.

Due to the highly insoluble nature of the oligomeric poiy(ethylenepiperazine) in most liquids, including epoxy resins, it performs as a latent catalyst, permitting formulation of one-component systems. That is, the uncured epoxy resin and the oligomeric poly(ethylenepiperazine) may be mixed and stored until needed. At room temperature, no curing will take place. The mixture may then be applied and heated, whereupon curing will take place. This offers many advantages, including more accurate formulating and easier handling, over the two-component systems of the prior art.

The oligomeric poly(ethylenepiperazine) used according to the invention, may also be used in a two-component system where another curing agent is used. When used in combination with certain other curing agents, the oligomeric poly(ethylenepiperazine) acts as an accelerator.

The oligomeric poly(ethylenepiperazine) can be used according to the invention as an accelerator in a two-component system, where a curing agent is used which will not cure epoxy resins rapidly or at all when used alone. When such a curing agent is used in combination with the oligomeric poly(ethylenepiperazine) the curing of the epoxy resin is greatly speeded up.

A class of curing agents which benefit from the accelerating properties of oligomeric poly(ethylenepiperazine) are the anhydlides. For example, the most commonly used anhydride curing agents are dicarboxylic acid anhydrides, such as maleic anhydride or phthalic anhydride, and tetracarboxylic acid dianhydrides, such as pyromellitic dianhydride.

Anhydride curing agents which can be utilized in accordance with the invention include alkyl substituted bicyclic vicinal anhydrides, such as the Diels-Alder adduct of maleic anhydride and a substituted cyclopentadiene of the formula:

wherein R is alkyl, more preferably, alkyl of from 1 to 4 carbon atoms. Preferred alkyl groups include methyl, ethyl, propyl, and n-butyl. The most preferred alkyl is methyl. The most preferred anhydride is methyl-bicyclo[2,2,1 ]heptene-2,3-dicarboxylic anhydride.

Other curing agents which are aided by the accelerator of this invention are guanamines, cyanurates, imidazoles, acrylamides and non-polymeric am ides such as dicyandiamide.

In general, any curing agent which will not cure epoxy resins at an acceptable rate will benefit from the accelerator of this invention.

Derivatives of the poly(ethylenepiperazine), such as those prepared by reacting the oligomeric poly(ethylenepiperazine) with compounds which react with the terminalOH and/or -NH groups, are also useful as curing agents according to this invention. For example, carboxylic acids and alkylene oxides, to name only two, can be reacted to form derivatives of oligomeric poly(ethylenepiperazine) which are useful as curing agents in accordance with this invention.

The cured resins in accordance with the invention, may be prepared in a conventional manner.

The oligomeric poly(ethylenepiperazine) curing agent is mixed with the polyepoxide in amounts according to the functional equivalent weight of the curing agent employed. Generally the number of equivalents of reactive groups is from 0.8 to 1.2 times the number of epoxide equivalents present in the curable epoxy resin composition, with from 0.9 to a stoichiometric amount being preferred. The exact amount of constituents in accordance with the above general requirements will depend primarily on the application for which the cured resin is intended.

The novel curing agent is incorporated into the resin by mixing. The constituents forming the curable material are intimately mixed by standard methods, and preferably degassed in the presence of a commercial defoamer and minute amounts of silicone oils to prevent voids and bubbles.

In accordance with a preferred embodiment, a curable resin comprises a diglycidyl ether of 4,4'isopropylidene bisphenol and an effective amount of the oligomeric poly(ethylenepiperazine) curing agent. According to a greatly preferred embodiment, from 10 to 30 parts by weight of curing agent is used per 100 parts of resin. Generally, the mixture of epoxy resin and the oligomeric poly(ethylenepiperazine) is allowed to self-cure at elevated temperatures up to 2000C.

It will further be realized that various conveniently employed additives can be mixed with the polyepoxide containing composition of the present invention final cure. For example, conventional pigments, dyes, fillers and flame retarding agents, which are compatible, and natural or synthetic resins can be added.

Furthermore, known solvents for polyepoxide materials such as toluene, benzene, xylene, dioxane and ethylene glycol monomethylether, can be used. The polyepoxide resins of the invention can be used in any of the above applications for which polyepoxides are customarily used.

The compositions of the invention can be used as impregnants, surface coatings, pottings, capsulating compositions and laminates.

The following Examples illustrate the nature of the present invention but are not intended to be limitative thereof.

Example 1 Curing with Oligomeric Poly(Ethylenepiperazine)=E/P Polymer This Example demonstrates that satisfactorily cured epoxy resins are obtained using oligomeric poly(ethylenepiperazine) as the sole curing agent.

Formulation: A B C Epoxy resin (EEW 185) 100 100 100 E/P Polymer 15 20 25 The properties of 1/8 inch (0.3175 cm) castings, after curing for 1 hr. at 80"C; 1 hr. at 1 200C and 3 hrs. at 1 600C are set out in Table 1 below. Smaller amounts of E/P polymer, when used as a curing agent resulted in incomplete curing.

Table 1 Formulation: A B C Izod impact strength (J/m) 13.88 14.42 6.94, Tensile Strength (mPa) 51.02 41.37 36.54 Tensile Modulus (mPa) 2923 2992 2799 Elongation at Break (%) 1.9 1.4 1.3 Flexural Strength (mPa) 95.15 86.18 77.22 Flexural Modulus (mPa) 31 72 3213 3130 Heat Distortion Temperature (OC, 1.82 mPa/0.455 mPa) 74/83 78/86 74.5/83 Shore D Hardness, 0--10 sec 88-86 89-87 89-87 Example 2 Curing with Methyl-bicyclo[2,2,1]heptene-2,3-dicarboxylic Anhydride and E/P Polymer This Example demonstrates that oligomeric poly(ethylenepiperazine) performs successfully as an accelerator epoxy resins cured with a known curing agent, i.e. methyl-bicyclo[2,2,ljheptene-2,3- dicarboxylic anhydride. Formulations containing only epoxy resin and the anhydride remained an uncured liquid after being subjected to the same curing cycle. Benzyldimethylamine is a known accelerator.

Formulation: A B C D Epoxy resin (EEW 185) 100 100 100 100 Anhydride 85 85 85 85 E/P Polymer - 2 4 2 Benzyldimethylamine 2.5 - - 2 The properties of 1/8 inch (0.3175 cm.) castings, after curing for 2 hrs. at 1000C, 1 hr. at 1 300C and 3 hrs. at 1 500C, are set out in Table 2 below.

Table 2 Formulation: A B C D Izod Impact Strength (J/m) 33.1 19.22 13.88 11.21 Tensile Strength (mPa) 39.30 35.16 34.47 35.85 Tensile Modulus (mPa) 2710 2792 2682 2758 Elongation at Break (%) 1.2 1.2 1.3 1.3 Heat Distortion Temperature (OC, 1.82 mPa/0.455 mPa) 137/144 145/147 147/150 139/145 Shore D hardness, 0--10 sec 92-90 91--90 91-90 91-90 Example 3 Curing with Dicyandiamide (DICY) and E/P Polymer This Example demonstrates the latent accelerating effect of oligomeric poly(ethylenepiperazine) when used with a known curing agent (DICY).Where oligomeric poly(ethylenepiperazine) was used as the accelerator (B) the system remained in an uncured state at room temperature while the same epoxy resin-curing agent system cured with a known accelerator, dimethylbenzylamine (C) was unstable at room temperature, as noted by its large increase in viscosity with time.

Formulation: A B C Epoxy resin (EEW 185) 100 100 100 DICY 6 6 6 E/P Polymer 2 Dimethylbenzylamine 1 Gel time, mins. at 1 200C. 180 20 Brook. visc., cps., initial 8600 10000 6400 after 24 hrs., R.T. 9400 10600 110000 48 hrs., R.T. 8600 9700 2000000 7 days, R.T. 9000 11000 14 days, R.T. 9300 12300 The properties of 1/8 inch (0.3175 cm.) castings, after curing for 1 hr. at 1 200C and 3 hrs. at 1 500C are set out in Table 3 below. Formulation A was uncured after the heat cycle and no properties could be determined.

Table 3 Formulation: B C Izod Impact Strength (J/m) 11.74 18.68 Tensile Strength (mPa) 39.99 61.36 Tensile Modulus (mPa) 2854 2758 Elongation at Break (%) 1.4 3.8 Flexural Strength (mPa) 102.7 129.6 Flexural Modulus(mPa) 3413 3103 Heat Distortion Temperature (OC., 1.82 mPa/0.455 mPa) 105/122 123/133 Shore D hardness (0--1 0 sec) 80-78 77-75

Claims

1. A curable epoxy resin composition which comprises: (a) a vicinal polyepoxide having an average of at least 1.8 reactive, 1,2-epoxy groups per molecule, and (b) an oligomeric poly(ethylenepiperazine) or derivative thereof.

2. A composition as claimed in Claim 1 wherein the oligomeric poly(ethylenepiperazine) is present in an amount comprising at least 10 parts by weight per 100 parts by weight of epoxy resin.

3. A composition as claimed in Claim 1 wherein the polyepoxide is a diglycidyl ether of 4,4'isopropylidene bisphenol.

4. A composition as claimed in any preceding Claim wherein the oligomeric poly(ethylenepiperazine) has the formula:

in which n is 1-20.

5. A composition as claimed in any preceding Claim which comprises a curing agent known per se.

6. A composition as claimed in Claim 5 where the curing agent is an anhydride, guanamine, cyanurate, imidazole, acrylamide or non-polymeric amide.

7. A composition as claimed in Claim 6 wherein the curing agent is methyl bicyclo[2,2,1 ]heptene-2,3-dicarboxylic anhydride.

8. A composition as claimed in Claim 6 wherein the curing agent is dicyandiamide.

9. A composition as claimed in Claim 1 and substantially as hereinbefore described with reference to Example 1.

10. A composition as claimed in Claim 1 and substantially as hereinbefore described with reference to Examples 2 or 3.

11. A method of curing an epoxy resin composition as claimed in any of the preceding Claims which comprises heating said composition.

12. A cured epoxy resin composition when cured by a method as claimed in Claim 9.