One component water reduced epoxy adhesives

An epoxy resin composition is disclosed. The epoxy resin is useful as a flexible adhesive. The composition comprises a modified epoxy base resin with a curing agent. The resin is modified by partial reaction with a polyoxyalkylene monoamine. No solvent is present in the formulation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to curable epoxy resins. More particularly it 
relates to one and two component epoxy resin compositions which are useful 
as flexible adhesives and which do not rely upon a solvent for their low 
viscosity. 
2. Prior Art 
Epoxy resins constitute a broad class of polymeric materials having a wide 
range of physical properties. The resins are characterized by epoxide 
groups which are cured by reaction with certain catalysts or curing agents 
to provide cured epoxy resin compositions with certain desirable 
properties. 
The most common epoxy resins are a condensation product of epichlorohydrin 
and bisphenol A. This system can be cured with any of the conventional 
curing agents such as polyamines, polycarboxylic acids, anhydrides and 
Lewis acids. Bisphenol A based epoxy compositions when cured have good 
adhesive properties but many are inherently stiff and brittle and hence 
their use is limited to applications where tensile shear forces do not 
come into play. 
It has been found that plasticizers can be added to the epoxy resin 
adhesive system to improve flexural strength. Typical methods of 
plasticization include the addition of flexibilizing aliphatic amines to 
the curing agent, addition of aminated or carboxylated rubbers to the 
system, addition of carboxy-terminated polyesters, addition of organic 
hydroxyl containing compounds and the addition of epoxidized oils. 
In H. N. Vazirani Adhesives Age 23, No. 10, p. 31 is described reaction 
products of liquid epoxy resins with a polyoxypropylene diamine which are 
useful in flexibilizing adhesive systems. 
It is well known in the art that there is a need for an epoxy system that 
will produce a flexible cured resin with good adhesive properties. 
SUMMARY OF THE INVENTION 
The invention comprises a two part epoxy resin composition which relies on 
its inherent low viscosity and hence requires no solvent for use. In one 
embodiment, the two parts are kept separate and mixed immediately before 
use. In another embodiment a latent curative agent is used and the two 
parts are mixed to form a stable emulsion which may be stored for periods 
of time prior to use. 
The first part of the composition, hereinafter referred to as Part A or 
base resin, is a polyepoxide which has been reacted with from about 50 wt 
% to about 70 wt % of a polyoxyalkylene monoamine of molecular weight of 
about 900 to about 2000. Part B is a curative agent. The one component 
system is mixed with a latent curative agent. The two component system is 
mixed with an effective amount of any of the typical epoxy curative agents 
immediately prior to use. The system contains no solvent. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Part A of the two part composition of the present invention comprises an 
epoxy base resin. The preferred epoxy base resin is a a vicinal 
polyepoxide containing compound. Generally the vicinal polyepoxide 
containing compounds which are amine cured 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 heterocyclic, and may 
be substituted if desired with other substituents besides the epoxy 
groups, e.g., hydroxyl groups, ether radicals, aromatic halogen atoms and 
the like. These vicinal polyepoxide containing compounds typically are of 
an epoxy equivalent weight of 150 to 250. Preferably the base resin, which 
has an epoxide equivalent weight of from 175 to 195, is derived from 
condensing epichlorohydrin with 2,2-bis(p-hydroxyphenyl propane) to form 
2,2-bis[(p-2,3 epoxy propoxy) phenyl] propane, a derivative of bisphenol 
A. 
Preferred polyepoxides are those of glycidyl ethers prepared by epoxidizing 
the corresponding allyl ethers or reacting, by known procedures, a molar 
excess of epichlorohydrin and an aromatic polyhydroxy compound, i.e., 
isopropylidene bisphenol, novolac, resorcinol, derivatives of aromatic 
amines, etc. 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, and the like, with 
either a polyhydric phenol or a polyhydric alcohol. Typically the epoxy 
resins have an average of at least 1.8 reactive, 1,2-epoxy groups per 
molecule. 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'-dihydroxydiphenylpropylphenylmethane, 
4,4-dihydroxydiphenylbutylphenylmethane, 
2,2'-dihydroxydiphenylditolylmethane, 
4,4'-dihydroxydiphenyltolylmethylmethane and the like. Other polyhydric 
phenols which may also be co-reacted with an epihalohydrin to provide 
these epoxy polyethers are such compounds as resorcinol, hydroquinone, 
substituted hydroquinones, e.g., methylhydroquinone, and the like. 
Among the polyhydric alcohols which can be coreacted 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, 
1,2,6-hexanetriol, trimethylolpropane, mannitol, sorbitol, erythritol, 
pentaerythritol, their dimers, trimers and higher polymers, e.g., 
polyethylene glycols, polypropylene glycols, triglycerol, 
dipentaerythritol and the like, polyallyl alcohol, polyhydric thioethers, 
such as 2,2'-, 3,3'-tetrahydroxydipropylsulfide and the like, mercapto 
alcohols such as monothioglycerol, dithioglycerol and the like, polyhydric 
alcohol partial esters, such as monostearin, pentaerythritol monoacetate 
and the like, and halogenated polyhydric alcohols such as the 
monochlorohydrins of glycerol, sorbitol, pentaerythritol and the like. 
Another class of polymeric polyepoxides which can be amine cured and are in 
accordance with the present invention includes the epoxy novolac 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 novolac 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. 
Because of the typically rigid epoxy systems, polyglycidyl ethers of 
novolac resins, polyglycidyl derivatives or aromatic amines, i.e. 
tetraglycidyl methylene dianiline and other normally rigid epoxy 
structures may be modified with polyoxyalkylene monoamines in order to 
promote flexibility. 
The epoxy base resin is modified by partially reacting it with a 
polyoxyalkylene monoamine of molecular weight of about 900 to about 2000. 
That is, with from about 50 wt % to about 70 wt % and preferably about 55 
wt % to about 65 wt % of polyoxyalkylene monoamine. The polyoxyalkylene 
monoamine is preferably a block copolymer of ethylene oxide and propylene 
oxide terminated with a primary amino group. 
Compositions which use less than 50 wt % polyoxyalkylene monoamine 
demonstrate less flexibility with high viscosity. Compositions wherein 
greater than 70 wt % polyoxyalkylene monoamine is incorporated demonstrate 
lowered adhesive strength and decreased viscosity in solutions. 
Flexibility and viscosity are most beneficially balanced when from about 
55 wt % to about 65 wt % of polyoxyalkylene monoamine are reacted with the 
epoxy base resin. The polyoxyalkylene monoamine is preferably a block 
copolymer of ethylene oxide and propylene oxide terminated with a primary 
amino group. It is seen from the Examples that diamines in general produce 
unsatisfactory results. 
In the one component system, epoxy base resins reacted with less than 50 wt 
% of polyoxyalkylene monoamine produce adhesives with low peel strength. 
Those modified with greater than 70 wt % display decreased viscosities. 
It has been found that polyoxyalkylene monoamines of molecular weight from 
about 900 to about 2000 produce a group of flexible epoxy resins 
demonstrating superior qualities for an adhesive. 
Monoamines and diamines of molecular weight less than about 900 produce 
highly viscous epoxy systems without the desired adhesive properties. 
Amines of molecular weight greater than 2000 produce adhesives displaying 
high peel strength but so viscous that they cannot be mixed and applied 
without solvent thinner and therefore are useless in applications where a 
solvent free adhesive is required. 
A group of polyoxyalkylene monoamines has been found that demonstrates 
beneficial properties and which is characterized by the general formula: 
EQU CH.sub.3 O(CH.sub.2 CH.sub.2 O).sub.A [CH.sub.2 CH(CH.sub.3)O].sub.B 
CH.sub.2 CH(CH.sub.3)NH.sub.2 
wherein A ranges from about 16 to about 25 and B ranges from about 1 to 
about 5. 
This group of polyoxyalkylene monoamines has a molecular weight of from 900 
to 2000 and preferably from 900 to 1100. 
This group of monoamines is also a block copolymer of oxyethylene groups 
(--CH.sub.2 CH.sub.2 O--) and oxypropylene groups [--OCH.sub.2 
CH(CH.sub.3)--]. 
Monoamines of this type are marketed by Texaco Chemical Co., Inc. under the 
trademark JEFFAMINE.RTM. M-series. 
Part B of the two part composition of the present invention comprises a 
curative agent and optionally an accelerator. The epoxy base resin is 
cured with any of the anhydrides, aliphatic amines and polyamides 
typically used and known in the art for curing epoxy base resins. 
One embodiment the epoxy resin composition of the present invention is a 
two component adhesive composition comprising: 
(A) a polyepoxide which has been reacted with from about 55 wt % to about 
65 wt % of a polyoxyalkylene monoamine of the general formula: 
EQU CH.sub.3 [CH.sub.2 CH.sub.2 O].sub.A [CH.sub.2 (CH.sub.3)CH.sub.2 O].sub.B 
CH.sub.2 (CH.sub.3)CHNH.sub.2 
wherein A ranges from 16 to 20 and B ranges from 1 to 5; and 
(B) a curative agent. 
The amine curative agents which can be utilized in accordance with the two 
component embodiment of the present invention are generally any of those 
amine curative agents which are well known to be useful for the curing of 
vicinal epoxides. Generally, those curative agents having at least three 
reactive amino hydrogens are useful. Exemplary of those amines which can 
be utilized are alkylene polyamines such as diethylene triamine, 
triethylene tetramine and the like; oxyalkylene polyamines such as 
polyoxypropylene, di- and triamine and diamino derivatives of ethylene 
glycol, such as 1,13-diamino 4,7,10-trioxatridecane. 
Additionally, aromatic amine curative agents are useful, such as the 
alkylene-linked polyphenyl amines, phenylene diamines and polycyclic or 
fused aromatic primary amine compounds. Further, the corresponding 
cycloaliphatic primary amine, i.e., the hydrogenated products of the above 
aromatic compounds, can be utilized. 
Likewise, the polyamide curative 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 U.S. Pat. No. 2,379,413. 
As seen in the Examples, a preferred curative agent for the two component 
system is N-aminoethylpiperazine. 
In another embodiment, the present invention is related to a one component 
epoxy resin composition comprising: 
(A) a polyepoxide which has been reacted with from about 55 wt % to about 
65 wt % of a polyoxyalkylene monoamine of general formula: 
EQU CH.sub.3 [CH.sub.2 CH.sub.2 O].sub.A [CH.sub.2 (CH.sub.3)CH.sub.2 O].sub.B 
CH.sub.2 (CH.sub.3)CHNH.sub.2 
(B) a latent curative agent 
The latent curative agent may be any one of the many curative agents known 
in the art for curing of vicinal epoxides but which are unreactive with 
epoxy base resins until heat cured. 
Latent curatives are agents that when combined with an epoxy base resin, 
provide an extended pot life (up to six months or longer) with little or 
no reaction taking place. Among materials commonly used for this purpose 
are boron trifluoride-amine complexes, amine salts and certain solid 
materials which may be finely dispersed into an epoxy base resin where 
they remain unreacted until the temperature of the system is raised to the 
point sufficient to melt the solid curative and promote curing. Such a 
material is dicyandiamide (DICY; cyanoguanidine). Dicyandiamide is the 
curative of choice for the present invention since experience has shown 
that it does not degrade over prolonged periods of time. 
In the formulation of the epoxy system, the latent curative agent and 
optionally an accelerator are mixed to form a compatible solution. The 
modified epoxy base resin is added and the mixture is stirred until 
homogeneous. The mixture thereby produced is a stable dispersion of solid 
curative in resin which may be stored for prolonged periods prior to use. 
The curative agent is usually added to the formulation in such an amount 
that there is one reactive NH group in the curing component for each epoxy 
group in the epoxy resin component. These are known as stoichiometric 
quantities. The stoichiometric quantity can be calculated from the 
knowledge of the chemical structure and analytical data on the component. 
Stoichiometry unfortunately is not always calculatable. This is especially 
true with many latent systems. For latent systems, the proper amount of 
curative to provide best properties must be determined experimentally. 
For the purposes of the present invention, the stoichiometric amount of 
curative agent is calculated by adding together the number of equivalents 
on the basis of weight percent replaceable NH groups. In general, it is 
advantageous to use up the 10% excess of the curative agent over the 
stoichiometric amount. 
In the two component system the epoxy base resin and curative agent are 
mixed immediately, prior to use whereas as the one component system exists 
as a stable dispersion and is applied directly to the surface before 
curing. 
With many curatives, curing may be accomplished at ambient conditions. For 
development of optimum achieveable properties, however, curing at elevated 
temperature is necessary. The curing temperature range acceptable in this 
invention is from about 120.degree. C. to about 180.degree. C. for about 1 
to 3 hours. Preferably curing is done at about 150.degree. C. for 1 to 2 
hours. 
Optionally, the epoxy resin formulations of the present invention can 
include an accelerator to speed the amine cure of the epoxy resin. In 
several applications, an accelerator is beneficial, especially when an 
epoxy resin is used as an adhesive in flammable environment, thus making 
prolonged elevated temperature cure inconvenient or even hazardous. Lee, 
H. and Neville, K., Handbook of Epoxy Resins, pp. 7-14 describes the use 
of certain amine-containing compounds as epoxy curative 
agent-accelerators. 
Many accelerators are known in the art which can be utilized in accordance 
with the instant invention. Examples include salts of phenols; salicyclic 
acids; amine salts of fatty acids such as those disclosed in U.S. Pat. No. 
2,681,901; and, tertiary amines such as those disclosed in U.S. Pat. No. 
2,839,480. A preferred accelerator in accordance with the instant 
invention is disclosed in U.S. Pat. No. 3,875,072, G. Waddill. That 
accelerator comprises a combination of piperazine and an alkanol amine in 
a weight ratio of about 1:8 to 1:1. The above amount of accelerator is 
admixed with a polyoxyalkylene diamine curative agent in amount of from 
about 10 to 50 parts by weight accelerator to 100 parts by weight of the 
curing agent. 
The following Examples are illustrative of the nature of the instant 
invention but are not intended to be limitative thereof.