CA1136601A

CA1136601A - Non-crystallizing epoxy resin accelerator

Info

Publication number: CA1136601A
Application number: CA000335608A
Authority: CA
Inventors: Harold G. Waddill
Original assignee: Texaco Development Corp
Current assignee: Texaco Development Corp
Priority date: 1978-10-19
Filing date: 1979-09-12
Publication date: 1982-11-30
Also published as: GB2032436A; SE7908655L; FR2439216B1; FR2439216A1; DE2941727A1; GB2032436B

Abstract

ABSTRACT

The invention provides a novel accelerator combination for amine-cured epoxy resins. The accelerator combination com-prises N-aminoethylpiperazine and an alkanolamine, preferably triethanolamine. Optionally, the accelerator combination also includes piperazine. The presence of the N-aminoethylpiperazine greatly reduces the tendency of the accelerator toward crystalliz-ation. The accelerator combination also shows a synergistic effect on the curing rates of epoxy resins.

Description

113~

NON-CRYSTALLIZING EPOXY RESIN ACCELERATOR
This invention relates to curable epoxy resins.
More particularly, to a novel curing accelerator.
Epoxy resins constitute a broad class of polymeric materials having a wide range of physical characteristics.
The resins comprise epoxide groups and are cured by reaction with certain catalysts or curing agents to provide cured epoxy resin compositions with certain desirable properties.
One class of such curing agents comprises generally the amines. The most commonly used amine curing agents are ali-phatic amines such as diethylenetriamine or triethylene-tetramine, and/or polyoxyalkylene polyamines; such as polyoxypropylenediamines and triamines.
Epoxy resin compositions having improved physical properties are obtained by employing polyoxyalkyleneamines, and polyalkylenediamines in particular, as curing agents.
It is common to employ, with such epoxy resin compositions, a co-curing agent such as those described in U.S. Patent No.
3,549,592.
Also known to be effective as epoxy curing agents or co-curing agents are various ureas and substituted ureas, such as those disclosed in U.S. Patents No. 3,294,749;

2,713,569; 3,386,956; 3,386,955; 2,955,372 and 3,639,338.
The ureas disclosed in the above references are useful as either curing agents or as curing accelerators.
Aliphatic or aromatic compounds having a single terminal ureido group are well known. It has been disclosed in U.S. Patent No. 2,145,242 that diureido-terminated aliphatic compounds can be produced by reacting urea with an aliphatic diamine wherein each terminal amine has at least one labile hydrogen. Other substituted ureas are disclosed in U.S.
Patent No. 3,965,072.
Diureide-terminated polyoxyalkylene material provides cured epoxy resin compositions exhibiting outstanding strength of adhesion as disclosed in U.S. Patent No. 4,110,309 which issued 8/29/78.

--1-- ' ~13~i601 In several applications, accelerated curing of epoxy resins at ambient temperatures is necessary. A typical example is the use of an epoxy resin as an adhesive in a flammable environment. Curing with many prior art amines may be too slow for this and other specific situations.
U.S. Patents No. 3,875,072 and 3,943,104 disclose an accelerator comprising piperazine and an alkanolamine.
This accelerator combination has one disadvantage. It tends to crystallize at low termperatures, thus reducing its usefulness in some cases.
The present invention is an accelerator which does not crystallize at low temperatures.
According to one embodiment, the present invention provides an accelerator combination for accelerating the curing of an amine-cured polyglycidyl ether of a polyhydric phenol which comprises N-aminoethylpiperazine and an alkanol-amine. Preferably, the alkanolamine is triethanolamine (TEA).
According to another embodiment, the accelerator combin-ation of aminoethyl piperazine ~AEP) and the alkanolamine also includes piperazine.
The invention also provides a curable epoxy resin composition which comprises a vicinal polyepoxide, an amine curing agent and an accelerator combination as defined above.
The invention also provides a process for curing a vicinal polyepoxide by reaction with an amine curing agent, wherein said curing is accelerated by addition of an acceler-ator combination as defined above.
The resulting cured epoxy resins have excellent properties.
Generally-the vicinal polyepoxide containing compositions are organic materials having an average of at least 1.8 reactive 1,2-epoxy groups per molecule. These polyepoxide.
materials can be monomeric or polymeric, saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or hetero-cyclic, and may be substituted if desired with other substituents besides the epoxy groups, e.g., hydroxyl groups, ether radicals, and aromatic halogen atoms.
Preferred polyepoxides are those of glycidyl ethers - 113t;601 prepared by epoxidizing the corresponding allyl ethers or reacting, 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 present 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'-dihydroxydiphenylethyl-methane; 3,3'-dihydroxydiphenyldiethylmethane; 3,4'-dihydroxydiphenylmethylpropylmethane; 2,3'-dihydroxydiphenyl-ethylphenylmethane; 4,~'-dihydroxydiphenylpropylphenyl-methane; 4,4'-dihydroxydiphenylbutylphenylmethane; 2,2'-dihydroxydiphenylditolylmethane, and 4,4'-dihydroxy-diphenyltolylmethylmethane. Other polyhydric phenols which may also be co-reacted with an epihalohydrin to provide these epoxy polyethers are such compounds as resorcinol, hydro-quinone, and substituted hydroquinones, e.g., methylhydro-quinone.
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-hydroxy-cyclohexyl)dimethylmethane; 1,4-dimethylolbenzene; glycerol;
1,2,6-hexanetriol; trimethylolpropane; mannitol; sorbitol;
eryt~itol; 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'-tetra-hydroxydipropylsulfide; mercapto alcohols such as mono-thioglycerol or dithioglycerol; polyhydric alcohol partialesters, such as monostearin, or pentaerythritol monoacetate;
and halogenated polyhydric alcohols such as the monochloro-hydrins of glycerol, sorbitol, or pentaerythritol.
Another class of polymeric polyepoxides which are in 113~60~

accordance with the present 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, ~. 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 whGle.
The amine curing agents which can be utilized in accordance with the present invention are generally any of those amine curing agents which are well known to be useful for the curing of vicinal epoxides. Generally, those curing agents having at least three reactive amino hydrogens are useful.
Exemplary of those a~ines which can be utilized are alkylene polyamines such as diethylene triamine and triethylene tetramine; oxyalkylene polyamines such as polyoxypropylene diamine and triamine; and diamino derivatives of ethylene glycol, such as l,13-diamino-4,7,10-trioxatridecane.
Additionally, aromatic amine curing agents are useful, such as the alkylene-linked polyphenyl amines, phenylene diamines and polycyclic or fused aromatic primary amine compounds. Additionally the corresponding cyclo-aliphatic compounds can be used.
Likewise, the polyamide curing agents such as the condensation products of polyamines and polycarboxylic acids are useful. Suitable such amide compounds are, for example, the condensation product of a polyamine and a dimerized fatty acid produced in accordance with V.S. Patent No. 2,379,413.
Of the amine curing agents known to be effective in curing a vicinal epoxy resin, preferred curing agents in ,:

1~3~6C~3~

accordance with the present invention are the polyoxyalkylene containing amine compounds. A preferred class of polyoxy-alkylene polyamines is depicted by the formula:
tH2N-( I CH2)n]r (I) X
wherein X is hydrogen, methyl or ethyl, Z is a hydrocarbon radical having 2 to 5 carbon atoms and a valence of r; n is from 1 to 15, and r is 2, 3 or 4. The most preferred polyoxyalkylene polyamines are the polyoxypropylene diamines wherein X is methyl, n is from 1 to 10, Z is a 1,2-propylene radical, and r is 2. These polyoxyalkylene polyamines can be prepared by known methods as disclosed in U.S. Patents No. 3,236,895 and 3,654,370. The most preferred poly-oxyalkylene polyamine is a polyoxypropylene diamine having a molecular weight of about 230.
Another preferred class of polyoxyalkylene polyamines can be depicted by the formula:
z-[(OCH2-CH)nNH(cH2)yNH2]r (II) wherein X, Z, n and r are defined as above and y is 2 or 3.
These poly(aminoalkylamino)polyethers are the hydrogenated product of the cyanoalkylated adduct of a polyoxyalkylene polyamine as above described. The preparation of the cyano-alkylated adducts is described in U.S. Patent No. 3,666,788.
The accelerator combination of N-aminoethylpiperazine and an alkanolamine may have a combined weight ratio which varies widely, as long as a finite amount or each compound is present. It is within the skill of the art to adjust the ratio of the components to suit a specific need.
Therefore, there is no intent to set an arbitrary ratio range. However, it has been found preferable that the accelerator combination has a weight ratio of 90:10 to 10:90 N-aminoethylpiperazine to alkanolamine.
Examples of preferred alkanolamines useful in the invention include monoethanolamine, diethanolamine, triethanol-amine, hydroxy ethoxyethylamine, N-aminoethylethanolamine, N,N-bis-(hydroxypropyl)- N-hydroxyethylamine, or a mixture thereof. Triethanolamine is especially preferred.
According to one embodiment of the present invention, 1~3~;60~

the accelerator compositions also include piperazine.
U.S. Patents No. 3,875,072 and 3,943,104 disclose an accelerator combination comprising piperazine and an alkanolamine. An improvement in crystallizing tendency over the above will take place once any amount of N-aminoethyl-piperazine is present with a piperazine, alkanolamine mixture.
It has been found that the accelerator combinations of piperazine, N-aminoethylpiperazine and an alkanolamine preferably comprise the following weight percentages:
Most Broad, wt.% Preferred, wt.%
Piperazine 5 to 30 15 to 20 AEP 5 to 50 5 to 20 Alkanolamine 50 to 85 60 to 75 The particular order of mixing of the above described components is not critical in the practice of the present invention. For example, the amine curing agent, N-amino-ethylpiperazine and alkanolamine components (and piperazine if employed) may be blended in any desired order or manner to provide a homogenous mixture of accelerated curing agents.
The mixture may then be incorporated into or mixed with the above described resin component at time of use to give an accelerated self-curing resin at ambient temperature.
In a preferred method of practicing the invention, the N-aminoethylpiperazine and alkanolamine components (and piperazine if employed) are first blended. The blend is then added to the amine curing agent component and this overall mixture is finally mixed with the above-described resin component at time of use. The blend of N-aminoethylpiperazine and alkanolamine component (and optionally piperazine) is capable of being stored for long periods of time, even at low temperatures.
It has been found that the utilization of the components of the accelerator combination within the described combined weight ratio is highly synergistic for accelerating the self-curing of the above-described epoxy resin types cured with said amine curing agents at ambient temperature. Accordingly, experiments have shown that where N-aminoethylpiperazine or an alkanolamine is utilized alone, or where the weight ratio ll366al of the components is outside the prescribed range, the rate of curing at ambient temperature is drastically reduced.
The combined weight of N-aminoethylpiperazine and alkanolamine components (and optionally piperazine) present when mixed with the polyoxyalkylenepolyamine may range from 1 to 100 parts by weight per 100 parts by weight of the polyoxyalkylenepolyamine. The optimum amount may vary somewhat for a given application depending upon the particular epoxy resin, polyoxyalkylenepolyamine and alkanolamine being utilized, and is best determined empirically for the most effective amount.
In the curing of epoxy resins, the curing-hardening agent is usually added in an amount that will provide one reactive -NH in the combined hardener-curing components for each epoxy group in the epoxy resin component. These are known in the art as stoichiometric quantities. Usually the stoichiometric quantities can be calculated from a knowledge of the chemical structure and analytical data for the particular components being utilized, but the stoichiometric quantity is often found empirically. A particular example of such a method is measuring the maximum exotherm temperature during the curing of the epoxy resin at different hardening-curing agent concentrations. A graph of the exotherm temperature vs. the concentration of hardening-curing agent w~ll exhibit a maximum at or near the stoichiometric quantity.
For the purposes of the present invention, the stoichiometric amount of the hardening-curing agent is calculated by adding together the number of equivalents on the basis of weight per replaceable -NH group in the amine curing agent, N-aminoethylpiperazine, alkanolamine and optionally piperazine. Preferably, these components are utilized in amounts that will provide up to 10 percent excess of the stoichiometric amount.
Should fire retardance be required for the epoxy resins cured by the process and composition of the present invention, it will be understood that various fire retardants for epoxy resins in compositions known in the art can be utilized without departing from the intended scope of the invention. Experiments have shown that well known epoxy 1~3~6(~1 resin fire retardants, for example, various halogenated compounds, phosphate compounds, even including piperazine phosphate, can be utilized in effective amounts in the above-described process without affecting the synergistic effect of the accelerator combination of N-aminoethylpipera-zine and alkanolamine components (and optionally piperazine) upon the accelerated curing rate. Preferably, where fire retardance is desirable, an effective amount of piperazine phosphate is incorporated into the above-described mixture.
Accordingly, the piperazine phosphate may be added at any time during the mixing of the components without affecting the described synergistic effect.
The above-described mixture of epoxy resin, amine curing agent, and accelerator combination of N-aminoethyl-piperazine and alkanolamine (and optionally piperazine) is also preferably allowed to self-cure at ambient temperatures of O to 45C. However, the mixture can be cured or post-cured at elevated temperatures up to 175C., if desirable and convenient.
The following Examples and Tables illustrate the practice of the invention in more detail but are not to be construed as limitative.

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113~iÇ;0~

. EXAMPLE 4 Storage of accelerator mixtures at 5C.

Components: A B C D
_ AEP 3.0 4.0 5.0 6.0 TEA 7.0 6.0 5.0 4.0 Appearance aftOr Storage at 5 C for:
72 hours 1) 1) 1) 1) 10 days 1) 1) 1) 1) 1) No crystals formed 113660~

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E X 14 0 O X 0 0 ~ z s ~ o l~ o ~ ~ ~E ~ 0 113~6~1 -The following data demonstrate that a three (3) component accelerator comprising piperazine, triethanolamine and N-aminoethylpiperazine has less tendency to crystallize at low temperatures than a two (2) component accelerator comprising 5 piperazine and triethanolamine.
A B C
Composition Piperazine 30 25 20 Triethanolamine 70 70 75 10 N-aminoethylpiperazine - 5 5 CrystallizatOon-Storage at 5 C., glass or metal 24 hours. None None None

4 days 1 1 None 157 days 1 1 None 14 days 1 1 None 21 days 2 1 None 28 days 2 1 None Storage at -20C., glass 2024 hours. 1 1 None 4 days 1 1 4 7 days 1 1 4 14 days 2 2 4 21 days 2 2 4 2528 days 3 2 4 Storage at -20C., metal 24 hours. None None None 4 days 1 1 4 7 days 1 1 4 3014 days 2 2 4 -21 days ' 2 2 4 28 days 2 2 4 lFew crystals 2Numerous crystals 3Large amount crystals Very few crystals 113~61~

This Example shows the lessened tendency to crystallize of the three (3) component accelerator system (as in Example 2) but here mixed with an epoxy curing agent, JEFFAMINE D-230, (65% D-230, 35% accelerator).
A B C
Composition of Accelerator Piperazine 30 25 20 Triethanolamine 70 70 75 N-aminoethylpiperazine - 5 5 Storage at 25C., glass 24 hours. 4 None None 4 days 4 None None 7 days 1 None None 14 days 1 None None 1521 days 2 None None 28 days 2 None None Storage at 5C., glass 24 hours. 1 None None 4 days 2 2 None 207 days 2 2 None 14 days 3 3 None 21 days 3 3 None 28 days 3 3 None Storage at -20C., glass 2524 hours. 1 1 None 4 days 1 1 4 7 days 2 2 4 14 days 3 3 21 days 3 3 3028 days 3 3

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An accelerator combination for accelerating the curing of an amine-cured polyglycidyl ether of a polyhydric phenol which comprises N-aminoethylpiperazine and an alkanolamine.

2. An accelerator combination as claimed in Claim 1 wherein the alkanolamine is monoethanolamine, diethanolamine, triethanolamine, hydroxy ethoxyethylamine, N-aminoethylethanolamine, N,N-bis(hydroxypropyl)- N-hydroxyethylamine, or a mixture thereof.

3. An accelerator combination as claimed in Claim 1 wherein the weight ratio of N-aminoethylpiperazine to alkanolamine is about 90:10 to 10:90.

4. A composition as claimed in Claim 1, 2 or 3 which additionally comprises piperazine.

5. A composition as claimed in Claim 1, 2 or 3 which comprises from 5 to 30 weight % of piperazine, 5 to 50 weight %
of N-aminoethylpiperazine and 50 to 85 weight % of alkanolamine.

6. A process for curing a vicinal polyepoxide by reaction with an amine curing agent wherein said curing is accelerated by addition of an accelerator combination as claimed in Claim 1.

7. A process as claimed in Claim 6 wherein the accelerator combination is added in an amount of 1 to 100 parts by combined weight per 100 parts by weight of said amine curing agent.

8. A process as claimed in Claim 6 or 7 wherein said amine curing agent is a polyoxypropylenediamine.

9. A process as claimed in Claim 6 or 7 wherein said amine curing agent is a polyoxypropylenediamine which has an average molecular weight of 230 to 400.

10. A curable epoxy resin composition which comprises a vicinal polyepoxide, an amine curing agent, and an accelerator combination as claimed in Claim 1, 2 or 3.