The present invention is directed to a curable composition comprising (1) a solid epoxy composition prepared by reacting (a) a solid epoxy resin prepared by reacting a normally liquid epoxy resin with a polyhydric phenol in the presence of an etherification catalyst with (b) a small amount of tris(hydroxymethyl) aminomethane and (2) at least one epoxy curing agent.

BACKGROUND OF THE INVENTION 
The preparation of glycidyl polyethers of polyhydric phenols, particularly 
dihydric phenols is well-known. For example, such glycidyl polyethers of 
dihydric phenols may be prepared by reacting the required proportions of 
the dihydric phenol and epichlorohydrin in an alkaline medium. The desired 
alkalinity is obtained by adding basic substances, such as sodium or 
potassium hydroxide, preferably in stoichiometric excess to the 
epichlorohydrin. The reaction is preferably accomplished at temperatures 
within the range of from 50.degree. C. to 150.degree. C. The heating is 
continued for several hours to effect the reaction and the product is then 
washed free of salt and base. 
By adjusting the relative amounts of the reactants and the process 
conditions, the resulting glycidyl polyethers will range from liquids to 
solid epoxy resins. See, for example, U.S. Pat. No. 2,633,458, wherein the 
preparation of various glycidyl polyethers of dihydric phenols is 
described. Polyether A is a liquid, whereas Polyether E is a solid epoxy 
resin. This technique for the preparation of solid epoxy resin requires 
constant process and control changes to accommodate the great variety of 
molecular weight ranges demanded by the various users of epoxy resins. 
Accordingly, there is a growing trend to utilize a so-called "fusion" 
technique wherein a liquid polyether similar to Polyether A of U.S. Pat. 
No. 2,633,458 is prepared. Then, using this liquid epoxy resin as a base 
resin, solid resins having a wide range of molecular weights may be 
subsequently prepared by reacting said liquid resin with an appropriate 
amount of a dihydric phenol in the presence of an etherification catalyst. 
This fusion process is described in U.S. Pat. No. 3,477,990, U.S. Pat. No. 
3,547,881, and U.S. Pat. No. 3,978,027. In some respects; however, solid 
epoxy resins prepared by this fusion technique do not exhibit the same 
physical properties as the solid resins prepared by the process described 
in U.S. Pat. No. 2,633,458, especially in pipe coatings. 
The use of tris(hydroxymethyl) aminomethane to inhibit the crystallization 
of liquid diglycidyl ethers of Bisphenol A is known. See, for example, 
U.S. Pat. No. 3,477,981. Prepolymers of tris(hydroxymethyl) aminomethane 
and liquid epoxy resins are also known. See, for example, U.S. Pat. No. 
3,607,833. These prepolymers contain a relatively large amount of 
tris(hydroxymethyl) aminomethane, e.g., from about 5 to 14%. 
It has now been found that the physical properties of cured solid epoxy 
resins prepared via the fusion technique can be significantly improved by 
reacting the solid fusion epoxy resin with a small amount of 
tris(hydroxyalkyl) aminomethane, generally less than 1%. 
SUMMARY OF THE INVENTION 
The present invention is directed to a curable composition comprising (1) a 
solid epoxy composition prepared by reacting (a) a solid epoxy resin 
prepared by reacting a normally liquid epoxy resin with a polyhydric 
phenol in the presence of an etherification catalyst with (b) a small 
amount of tris(hydroxymethyl) aminomethane and (2) at least one epoxy 
curing agent. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention is particularly directed to a curable composition 
especially suitable for pipe coatings comprising (1) a solid epoxy 
composition prepared by reacting (a) a solid epoxy resin prepared by 
reacting a normally liquid epoxy resin containing more than one vicinal 
epoxy group in the molecule with a polyhydric phenol, preferably Bisphenol 
A, in the presence of an etherification catalyst (e.g., "onium" salt) with 
(b) less than 1% by weight based on the solid epoxy resin of 
tris(hydroxymethyl) aminomethane and (2) at least one epoxy curing agent, 
preferably an amino compound. 
As stated hereinbefore, the preparation of solid epoxy resins via the 
fusion process is well known. Accordingly, such resins prepared by 
processes described in U.S. Pat. No. 3,477,990, U.S. Pat. No. 3,547,881 
and U.S. Pat. No. 3,978,027, among others, are suitable for use in the 
present invention. 
Simply, a normally liquid epoxide is reacted with a dihydric phenol in the 
presence of a suitable catalyst, usually an onium salt. 
THE POLYEPOXIDES 
Although normally liquid epoxides are suitable in the present compositions, 
semi-solid epoxy resins as well as mixtures of liquid resins containing a 
small amount of solid resin are useful. 
The liquid polyepoxides employed in the present invention include those 
compounds possessing more than one vic-epoxy group per molecule, i.e., 
more than one 
##STR1## 
group per molecule. These polyepoxides are saturated or unsaturated, 
aliphatic, cycloaliphatic, aromatic or heterocyclic, and are substituted, 
if desired, with non-interfering substituents, such as halogen atoms, 
hydroxy groups, ether radicals, and the like. Polyepoxides employed are 
monomeric or polymeric. Preferred liquid polyepoxides include the 
so-called liquid glycidyl polyethers of polyhydric phenols and polyhydric 
alcohols. More preferred are the glycidyl polyethers of 
2,2-bis(4-hydroxyphenyl)propane having an average molecular weight between 
about 300 and about 900 and a epoxide equivalent weight of between about 
140 and about 500. Especially preferred are the glycidyl polyethers of 
2,2-bis(4-hydroxyphenyl)propane having an average molecular weight of 
between about 300 and about 900, an epoxide equivalent weight of between 
about 140 and about 500, and containing from about 0.1% to about 1.0% 
weight or higher saponifiable chlorine. As used herein the terms "epoxide 
equivalent weight" and "weight per epoxide" refer to the average molecular 
weight of the polyepoxide molecule divided by the average number of 
oxirane groups present in the molecule. 
Various examples of polyepoxides that may be used in this invention are 
given in U.S. Pat. No. 3,477,990 (e.g., column 2, line 39 to column 4, 
line 75) and it is to be understood that so much of the disclosure of that 
patent relative to examples of polyepoxides is incorporated by reference 
into this specification. 
Other suitable epoxy resins include those compounds derived from polyhydric 
phenols and having at least one vicinal epoxy group wherein the 
carbon-to-carbon bonds within the six-membered ring are saturated. Such 
epoxy resins may be obtained by at least two well-known techniques, i.e., 
by (1) the hydrogenation of glycidyl polyethers of polyhydric phenols or 
(2) by the reaction of hydrogenated polyhydric phenols with 
epichlorohydrin in the presence of a suitable catalyst such as Lewis 
acids. See, for example, U.S. Pat. No. 3,336,241. 
ETHERIFICATION CATALYSTS 
In general, any catalyst which will catalyze the epoxy-phenoxy reaction is 
suitable for use in preparing the fusion resin. Preferred catalyst, 
however, are the so-called "onium" salts, especially the phosphonium and 
ammonium halides. Suitable phosphonium halides are disclosed in U.S. Pat. 
No. 3,477,990, and it is understood that so much of the disclosure 
relative to phosphonium halides is incorporated by reference in this 
specification. 
The amount of etherification catalyst will vary from about 0.001% to about 
10% by weight of the polyepoxide and will preferably range from about 
0.05% to about 5% by weight. Of course, mixtures of catalysts may be 
employed. 
PHENOLS 
Suitable phenols include those compounds possessing at least one hydroxyl 
group attached to an aromatic nucleus. The phenols are monohydric or 
polyhydric and are substituted, if desired, with a great variety of 
different types of substituents. Examples of the phenols include among 
others, phenol, resorcinol, o-cresol, m-cresol, p-cresol, chlorophenol, 
nitrophenol, hydroquinone, 2,2-bis(4-hydroxyphenyl)propane, 
2,2-bis(4-hydroxyphenyl)-pentane, and the like, and polymeric type 
polyhydric phenols obtained by condensing monohydric or polyhydric phenols 
with formaldehyde. 
Preferred phenols to be used are the polyhydric phenols containing from 2 
to 6 OH groups and up to 30 carbon atoms. Coming under special 
consideration are the phenols of the formula 
##STR2## 
wherein X is a polyvalent element or radical and R independently is a 
member of the group consisting of hydrogen, halogen and hydrocarbon 
radicals. The preferred elements or radicals represented by X are oxygen, 
sulfur, --SO--, --SO.sub.2 --, divalent hydrocarbon radicals containing up 
to 10 carbon atoms and oxygen, silicon, sulfur or nitrogen containing 
hydrocarbon radicals, such as 
##STR3## 
radicals wherein R' is a divalent hydrocarbon radical. 
Various examples of phenols that msy be used in this invention are also 
given in U.S. Pat. No. 3,477,990 (e.g., column 5, line 1 to column 6, line 
10) and it is to be understood that so much of the disclosure of that 
patent relative to examples of phenols is incorporated by reference into 
this specification. 
The amount of the epoxide and the phenol to be employed in preparing the 
fusion resin varies over a wide range depending upon the type of reactants 
and the type of product to be produced. In general, these reactants are 
used in approximately chemical equivalent amounts, i.e., a chemical 
equivalent amount of the phenol will be that sufficient to furnish one 
phenolic hydroxyl for every epoxy group to be reacted. For example, if one 
is reacting a diepoxide with a monohydric phenol and both epoxy groups are 
to be reacted, one mole of diepoxide should be reacted with about two 
moles of the monohydric phenol. On the other hand, if one is reacting a 
diepoxide with a dihydric phenol and a monomer product is desired by 
reacting both epoxide groups, one should react one mole of the diepoxide 
with about 2 moles of the polyhydric phenol. If a polymeric product is 
desired smaller ratios should be utilized as desired, such as, for 
example, 4 moles of the diepoxide and 5 moles of the polyhydric phenols. 
Superior results are obtained when the higher molecular weight resins are 
produced and in this case the ratios of reactants are varied depending 
upon the molecular weight desired and upon the type of end groups, i.e., 
whether the product is to be terminated with an epoxide or with a phenol. 
An especially preferred phenolic hydroxy ether resin having an epoxide 
equivalent weight of between about 2000 and about 4000 obtained by 
reacting 2,2-bis(4-hydroxyphenyl)propane with the diglycidyl ether of 
2,2-bis(4-hydroxyphenyl)propane having an epoxide equivalent weight 
between about 140 and about 500. 
The reaction is conducted in the presence or absence of solvents or 
diluents. In most cases, the reactants are liquid and the reaction is 
easily effected without the addition of solvents or diluents. However, in 
some cases, where either or both reactants are solids or viscous liquids 
it is desirable to add diluents to assist in effecting the reaction. 
Examples of such materials include the inert liquids, such as inert 
hydrocarbons as xylene, toluene, cyclohexane and the like. 
If solvents are employed in the reaction and the resulting product is to be 
used for coating purposes, the solvent is typically retained in the 
reaction mixture. Otherwise, the solvent is removed by any suitable method 
such as by distillation or the like. 
When it is desired to produce phenolic hydroxy ethers of higher viscosities 
but not higher epoxide equivalent weights, the polyepoxide and phenol are 
subjected to thermal bodying prior to the addition of the catalyst. 
"Thermal bodying" refers to heating the polyepoxidephenol mixture at 
specified temperatures and times prior to adding the catalyst. A preferred 
thermal bodying treatment comprises heating the polyepoxide mixture to a 
temperature of between about 120.degree. C. and 200.degree. C., preferably 
between about 145.degree. C. and about 165.degree. C., for between about 
15 minutes and 60 minutes. 
The solid fusion epoxy resin obtained by the above process are the desired 
phenolic hydroxy ether compounds. Their physical characteristics depend 
upon the desired reactants and proportions. In general, the products vary 
from liquids to solids, and in the case of the high molecular weight 
resins vary from viscous liquids to hard solids. The products possess at 
least one alcoholic hydroxyl group formed by each reaction of the epoxide 
and phenolic hydroxyl group, and can be further reacted through this group 
or groups. The polyfunctional reactants also give products terminated in 
phenolic hydroxyl groups and/or epoxy groups, and these are available for 
further reaction with the tris(hydroxymethyl) aminomethane to produce 
curable coatings exhibiting excellent physical properties, especially 
improved adhesion and hot-water resistance. 
The tris(hydroxyalkyl)aminomethane may be advantageously added to the 
fusion resin at the end or near the end of the fusion reaction. The 
preferred tris(hydroxyalkyl)aminomethanes are 
tris(hydroxymethyl)aminomethane and tris(hydroxyethyl)aminomethane. 
The tris(hydroxyalkyl) aminomethane is employed in amounts from about 0.01 
to about 1 parts per 100 parts by weight (phr) of the fusion epoxy resin. 
The resulting tris-aminomethane modified solid epoxy fusion resin may be 
cured with conventional epoxy curing agents to produce cured compositions 
having improved physical properties. For example, when these modified 
fusion resins are formulated into typical thick-film epoxy powder coatings 
of the type used in coating pipe for underground service, the resins 
demonstrate an unexpected improvement under the stress of cathodic 
protection and also after exposure to hot water. 
The modified solid fusion epoxy resins obtained by use of the present 
invention are reacted with various conventional curing agents to form hard 
insoluble, infusible products. Examples of suitable curing agents include, 
among others, the poly-basic acids and their anhydrides such as the di, 
tri- and higher carboxylic acids; those acids containing sulfur, nitrogen, 
phosphorus or halogens; amino-containing compounds such as, for example, 
diethylene triamine and pyridine; polyamides containing active amino 
and/or carboxyl groups; and others. 
Suitable such curing agents are disclosed in U.S. Pat. No. 3,477,990. 
The amount of curing agent varies considerably depending upon the 
particular agent employed. For the alkalies or phenoxides, 1% to 4% by 
weight is generally suitable. With phosphoric acid and esters thereof, 
good results are obtained with 1 to 10% by weight added. The tertiary 
amine compounds are preferably used in amounts of about 1% to 15% by 
weight. The acids, anhydrides, polyamides, polyamines, polymercaptans, 
etc. are preferably used in at least 0.8 equivalent amounts, and 
preferably 0.8 to 1.5 equivalent amounts. An equivalent amount refers to 
that amount needed to give one active hydride (or anhydride group) per 
epoxy group. 
Preferred curing agents include amino-containing compounds especially the 
imidazoles and benzimidazoles as well as substituted imidazoles and 
benzimidazoles. Very preferred curing agents include the epoxy adducts of 
imidazole and substituted imidazole compounds as disclosed in U.S. Pat. 
No. 3,756,984. It is sometimes desirable to use a mixture of 
amino-containing compounds such as an adduct of an imidazole compound and 
an epoxy resin in combination with dicyandiamide. 
Solvents or diluents are sometimes added to make the composition more fluid 
or sprayable. Preferred solvents or diluents include those which are 
volatile and escape from the polyepoxide composition before or during cure 
such as ester, chlorinated hydrocarbons and the like. To minimize expense, 
these active solvents are often used in admixture with aromatic 
hydrocarbons such as benzene, toluene, xylene, etc. and/or alcohols such 
as ethyl, isopropyl or n-butyl alcohol. Solvents which remain in the cured 
compositions are used, such as diethyl phthalate, dibutyl phthalate and 
the like, as well as cyano-substituted hydrocarbons, such as acetonitrile, 
propionitrile, adiponitrile, benzonitrile, and the like. It is also 
convenient to employ normally liquid glycidyl compounds, glycidyl 
cyclopentyl ether, diglycidyl ether, glycidyl ether of glycerol and the 
like, and mixtures thereof. 
Other materials are also added to the composition as desired. This includes 
other types of polyepoxides such as described in U.S. Pat. No. 3,477,990. 
This also includes fillers, such as sand, rock, resin particles, graphite, 
asbestos, glass or metal oxide fibers, and the like, plasticizers, 
stabilizers, asphalts, tars, resins, insecticides, fungicides, 
anti-oxidants, pigments, stains and the like. 
The temperature employed in the cure varies depending chiefly on the type 
of curing agent. The amino-containing curing agents generally cure at or 
near temperature and no heat need be applied. The acids, anhydrides, and 
melamine derivatives, on the other hand, generally require heat, such as 
temperatures ranging from about 65.degree. C. to about 210.degree. C. 
Preferred temperatures range from about 90.degree. C. to about 210.degree. 
C. and more preferably from about 120.degree. C. to 195.degree. C. 
To illustrate the manner in which the invention may be carried out, the 
following examples are given. It is to be understood, however, that the 
examples are for the purposes of illustration and the invention is not to 
be regarded as limited to any of the specific materials or conditions 
recited therein. Unless otherwise indicated, parts are parts by weight. 
Polyepoxide A is a glycidyl polyether of 2,2-bis(4-hydroxyphenyl) propane 
having an average molecular weight of about 350 and a weight per epoxide 
(WPE) of about 180. 
Epoxy Curing Agent X is a 50:50 weight blend of dicyandiamide and an adduct 
of Polyepoxide A and 2-methyl imidazole.

EXAMPLE I 
This example illustrates the preparation of the present curable epoxy 
composition. 
2468 grams of Polyepoxide A was added to 1014 grams of Bisphenol A and the 
mass heated to 230.degree. F. under nitrogen cover. At this temperature, 
1.1 grams of a 50% aqueous solution of tetramethyl ammonium chloride was 
added. An exotherm resulted and the temperature was held at 335.degree. F. 
for one hour at which time 18.4 grams (0.53% of total charge) of 
tris(hydroxymethyl) aminomethane was added, and processing continued at 
335.degree. F. for 30 minutes. The resulting composition was then poured 
out to cool. The product was a light colored clear solid resin with a WPE 
of 902. A 40% solution of this resin in 2-(2-n-butoxyethoxy)ethanol, 
(butyl DIOXITOL.RTM. Glycol Ether), had a Gardner-Holdt viscosity of "U". 
EXAMPLE II 
The same procedure as used in Example I was employed except that the level 
of tris(hydroxymethyl)aminomethane was increased to 0.70%. The product 
from this reaction had a WPE of 891 and a Gardner-Holdt viscosity of "U" 
at 40% non-volatile in butyl DIOXITOL.RTM. Glycol Ether. 
EXAMPLE III 
Each of the resins from Examples I and II, as well as an unmodified control 
resin, were melt-mixed in a BUSS Model K-46 extruder (barrel temperature, 
60.degree. C.) in the formulation shown below: 
______________________________________ 
Epoxy Resin 1239 
Epoxy Curing Agent X 47 
Barium Sulphate (Barytes #1, Pfizer Co.) 
175 
Red Iron Oxide, R-2899 (Pfizer Co.) 
23 
Cabosil M5 (Cabot Corp.) 7 
Modaflow Powder II (Monsanto Chemical Co.) 
7 
1498 
______________________________________ 
The compositions based on the above formulation were thoroughly dry-blended 
and extruded. The extrudates were coarse ground and passed through a 
micorpulverizer to give a free-flowing powder, suitable for fluidized bed 
application. Grit blasted, cold rolled steel panels were dip coated (12 
mil. film) in a fluidized bed with each of the powders. The panels were 
preheated to 475.degree. F., dip coated, post-cured 90 seconds at 
475.degree. F. and water-quenched. The following tests were run on powder 
coatings made from the two modified resins and the control. 
1. Gel time on the uncured powder on a 400.degree. cure plate, in seconds. 
2. Pencil Hardness: Reported as the softest pencil that will actually cut 
the surface of the film. 
3. MIBK Resistance: Time of exposure to MIBK required for the hardness of 
the film to drop two graduations on the pencil harness scale. 
4. Flexibility at 0.degree. F.: A heavy gauge (1".times.8".times.3/8") cold 
rolled steel bar, with a 12 mil. coating of the material is cooled to 
0.degree. F. and bent around a 71/2" diameter mandrel over a 30 second 
time period. 
5. Cathodic Disbonding Test: A 1/8" diameter hole is drilled in the coating 
just down to the metal surface. The coating is then subjected to immersion 
in 3% NaCl at 77.degree. F., with an impressed voltage of six volts 
negative for 30 days. The amount of undercutting (disbonding) at the hole 
is determined by wedging a small penknife blade under the coating, and 
this is reported as the increase in radius from the center of the hole in 
1/64-ths of an inch. 
6. Hot Water Adhesion: A flat probe is immersed in boiling distilled water 
for 15 days. The panel is quickly removed from the water and a 90.degree. 
"V" cut is made in the coating. With the aid of a penknife an attempt is 
made to peel off the coating, while still hot, starting at the point of 
the "V". Adhesion is judged by the ease or difficulty with which the 
coating is removed. 
TABLE I 
______________________________________ 
Compositions 
A B C 
______________________________________ 
% tris(hydroxymethyl) 
0.53 0.70 None 
aminomethane 
Gel Time at 400.degree. F., seconds 
12 12 17 
Pencil Hardness 
F F F 
MIBK Resistance, minutes 
&gt;5&lt;10 &gt;10&lt;15 &gt;30 
Cathodic Disbonding 
(radius of disbonded area) 
30 days @ 77.degree. F. 
11/64 13/64 22/64 
Hot water adhesion 
Good Good Poor 
______________________________________ 
Observation: The modified resins demonstrate faster gel times and better 
disbonding resistance as shown by the lower radii for disbonded area. A 
definite improvement in hot water adhesion was also observed for the 
coatings made with the modified resins.