Cold set phenol-formaldehyde resin

A phenol-aldehyde resin useful in such applications as a cold-set binder for cores and molds used in the foundry industry and reactive prepolymers used in reaction injection molding compositions produced by the steps of reacting a phenol and aldehyde in a mole ratio of 1 to 1-2.3 in the presence of catalytic amounts of an organic compound of aluminum, zirconium or titanium.

BACKGROUND OF THE INVENTION 
This invention relates to a phenol-aldehyde resin. 
In a particular aspect this invention relates to a resin useful as a 
cold-set binder for cores and molds used in the foundry industry. 
It is known from J. Robins, U.S. Pat. Nos. 3,676,392; 3,409,579; and 
3,485,797 to provide rapid curing binders for foundry aggregates. The 
binders are phenol-aldehyde resins which are reactive with isocyanates or 
prepolymers or polyurethanes. According to Robins, the foundry aggregate 
is mixed with the resin to which has been added a weak amine curing agent. 
This mixture is mixed with the isocyanate or polyurethane, then placed in 
a molding box or core box and after a short curing time, the mold or core 
is firm enough to be removed. This process makes possible a high 
production rate from a limited number of molds or core boxes, which are 
often very expensive and difficult to make. 
In U.S. Pat. No. 3,485,797, Robins discloses a resin made by reacting an 
aldehyde with a phenol at a mole ratio greater than 1 in the presence of a 
catalyst selected from organic carboxylic salts of lead, zinc, stannous 
tin, iron, lithium, manganese, cobalt, copper and calcium. Of these salts, 
lead and zinc produced a resin containing between 5 and 10% of free 
formaldehyde (based on the original) whereas the remaining (except for tin 
for which no data are disclosed) produced a resin containing from 11 to 
34% of the original formaldehyde in unreacted form. These resins are 
described as being a mixture of dimethylol compounds having dimethylene 
ether linkages and methylene linkages, the former being predominant. 
During the reaction, water is removed continuously as an azeotrope with, 
e.g. aliphatic, aromatic and halogenated hydrocarbons, ethers, esters and 
ketones. These resins can be cross-linked by heating or by the addition of 
acidic compounds such as BF.sub.3, ZnCl.sub.2, SnCl.sub.4 or hydrogen 
acids such as sulfuric and sulfonic acids. 
These binders have been very successful, but there have been some problems 
associated with them. The principal problems involve poor solubility of 
the resins in organic solvents and the lead catalyst, which is generally 
preferred for preparing them, remains in the resin where it forms a toxic 
residue, thus becoming an industrial hygiene problem. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide an improved phenol-aldehyde 
resin. 
It is another object of this invention to provide a reactive 
phenol-aldehyde prepolymer having improved solubility characteristics. 
It is a third object of this invention to provide a reactive 
phenol-aldehyde prepolymer free from lead residues. 
It is a fourth object of this invention to provide an improved cold set 
resin useful as a binder for foundry aggregate for preparing cores and 
molds for the foundry industry. 
It is a fifth object of this invention to provide phenolaldehyde resins 
useful as adhesives and thermosetting plastics. 
Other objects will be apparent to those skilled in the art from the 
description herein. 
It is the discovery of this invention to provide a phenolaldehyde resin 
produced by the steps of reacting a phenol with an aldehyde in a mole 
ratio of 1 to 1-2.3 in the presence of catalytic amounts of an organic 
derivative of aluminum, zirconium or titanium. 
The resin so obtained is a prepolymer useful as a cold-set binder for 
foundry aggregate for preparing cores and molds and can be used singly or 
in multi-component binder systems, including those which can be cured 
chemically, thermally, or by radiation techniques. The resin is soluble in 
polar organic solvents and in polar-nonpolar solvent mixtures. Other uses 
will also be apparent to those skilled in the art, e.g. as an adhesive. 
DETAILED DISCUSSION 
According to the process of the present invention, a phenol and an 
aldehyde, preferably unsubstituted phenol and formaldehyde, are reacted in 
the presence of the catalyst in a mole ratio of about 1 to 1-2.3, 
preferably about 1 to 1.3, at a temperature of from about 100.degree. C. 
to 130.degree. C. for a period of time sufficient to result in a cloud 
point of from 40 to 60% (cloud point determinations are known in the art; 
a 1% solution of the resin in tetrahydrofuran is prepared and is titrated 
with water until a cloud appears; the percentage of water tolerated is 
reported as the cloud point), and a neat viscosity of 100-2000 cps at 
75.degree. C. At the end of the heating period, residual aldehyde is 
present in an amount of 1-9%, preferably about 3%, and free phenol is 
present in an amount of 4-10%, preferably about 8%. The water content is 
approximately 1% . During the reaction period, water of reaction plus the 
conjugate alcohol of the aldehyde, and solvent, if any, are separated by 
distillation. After the reaction is judged to be complete as determined by 
cloud point and viscosity measurements, the temperature is reduced to 
about 75.degree. C. and a vacuum is applied to remove residual water and 
alcohol or solvent. The resin is then further cooled and diluted with a 
suitable solvent or solvent mixture such as butoxyethanol, alone or with 
aromatic solvents, to any desired concentration, usually to about 60% for 
use in a no-bake process or to about 50% for use in a cold box. 
More particularly, it is an embodiment of this invention to provide a 
2-stage process for the production of a resin prepolymer comprising the 
steps of reacting phenol and formaldehyde in a mole ratio of about 1 to 
1-2.3 at a temperature of up to about 120.degree. C., for a period of time 
sufficient to provide a cloud point of 50-60% thereby forming water of 
reaction and methanol, then separating a major portion of the water of 
reaction and methanol by distillation at 115.degree.-120.degree. C. for a 
period of time sufficient to provide a cloud point of 47-50% and a 
viscosity of 100-130 centipoise at 75.degree. C. and separating residual 
water and methanol at reduced pressure at about 80.degree. C. or less 
thereby producing a prepolymer having a cloud point of about 45-50% and a 
neat viscosity of 200-1000 centipoise at 75.degree. C. 
The phenol-aldehyde resin prepolymer so produced is essentially an 
ortho-substituted, aldehyde-terminated, oligomer having an average degree 
of polymerization of between 2 and 15 phenol units. The resin prepolymer 
is further characterized in that the phenol units are connected by 
benzylic ether and methylene bridges which are present in a ratio of about 
1:5. 
Acetal and aldehydic terminated polymers are present along with the usual 
methylol groups. This provides the observed improved properties, such as 
solubility, of this resin system. 
The distillate obtained during the condensation reaction of the phenol and 
aldehyde contains water of reaction, residual reactants and, surprisingly, 
the conjugate alcohol of the aldehyde reactant. For example, when the 
reactants are phenol and formaldehyde in a 1.3 mole ratio, there will be 
about 10% of methanol in the distillate. 
The presence of the conjugate alcohol in the distillate is a characterizing 
feature of the phenol-aldehyde reactions catalyzed by alkoxides and 
carboxylates of aluminum, zirconium and titanium. Another characterizing 
feature of this reaction is the presence of salicylaldehyde as a component 
of the resin. 
It is also a characterizing feature of these phenol-aldehyde reactions that 
the reaction mixture is unusually acidic. For example, the pH of a 1:1 by 
volume slurry in water is about 2.5 or less, depending on catalyst type 
and concentration. 
The phenol used in the practice of this invention generally will be the 
unsubstituted compound. However, substituted phenols are regarded as the 
practical equivalent thereof and can be substituted in place of phenol. 
Since the resins tend to be principally ortho-substituted on the phenol 
ring, ortho-substituted phenols are generally considered to be 
undesirable. However, any one, all, or none of the remaining carbon atoms 
of the phenol ring can be substituted. The nature of the substituent can 
vary widely and it is only necessary that the substituent not interfere in 
the polymerization of the aldehyde with the phenol at the ortho-position. 
Substituted phenols which can be employed in the formation of the phenolic 
resins include: alkyl-substituted phenols, aryl-substituted phenols, 
cycloalkyl-substituted phenols, the foregoing substituents containing from 
1 to 26 and preferably from 1 to 6 carbon atoms. Specific examples of 
suitable phenols, aside from the preferred unsubstituted phenol include: 
m-cresol, p-cresol, 3,5-xylenol, 2,3,4-trimethylphenol, 3-ethylphenol, 
3,5-diethylphenol, p-butylphenol, 3,5-dibutylphenol, p-amylphenol, 
p-cyclohexylphenol, p-octylphenol, 3,5-dicyclohexylphenol, p-phenylphenol, 
p-crotylphenol, 3,5-dimethoxyphenol, 3,4,5-trimethoxyphenol, 
p-ethoxyphenol, p-butoxyphenol, 3-methyl-4-methoxyphenol, and 
p-phenoxyphenol. 
The aldehyde used in the practice of this invention can be any aliphatic or 
aromatic aldehyde. It can be introduced to the reaction as a solid, such 
as a paraformaldehyde, as a liquid such as salicylaldehyde or paraldehyde, 
as a solution such as an alcohol, e.g., methanol or butanol, etc., or as a 
gas from a generator. Aqueous solutions are unsatisfactory since the 
presence of water is detrimental to catalyst activity. Alcoholic solutions 
should be avoided if the formation of the oxidized species is preferred. 
If an alcoholic aldehyde solution is used, then butanol is the preferred 
solvent. 
The catalysts suitable for the practice of this invention are the organic 
derivatives of aluminum, zirconium and titanium. The preferred organic 
derivatives are the alkoxides, alkyls and carboxylate salts. The alkyl and 
alkoxy groups are generally of from 1 to 10 carbon atoms and the 
carboxylate is generally of 1 to 20 carbon atoms. 
Of the aluminum compounds, the preferred compounds are triethyl aluminum 
and aluminum isopropoxide. Of the carboxylate aluminum salts, the oleate 
is a preferred catalyst. 
The preferred organic titanates include but are not limited to tetra-alkyl 
substituted titanates, e.g. tetrakis-ethylhexyl titanate, tetraphenyl 
titanate, tetrabutyl titanate and tetraisopropyl titanate; 
tetrakis-ethylhexyl titanate is a preferred catalyst. Other organic 
titanates include titanate salts of carboxylic acids of from 1 to 20 
carbon atoms, e.g. titanium oleate and titanium naphthenate. 
Of the zirconium compounds, the alkoxides are preferred, especially 
zirconium isopropoxide. 
The amount of catalyst to be used varies somewhat according to the 
catalyst. In general, an amount sufficient to provide from about 100 to 
about 5000 ppm or more based on the phenol content, of aluminum, titanium 
or zirconium ion. About 3000 ppm is generally preferred. 
It is an embodiment of this invention to modify the phenolaldehyde reaction 
end product with from 1-20% of a third component or mixture thereof which 
can include natural polymers such as soy protein; polyhydric compounds 
such as cellulosics and starches; polyols such as glycols or polyglycols, 
polyvinyl alcohol, and erythritols; amines such as aniline, substituted 
aniline and polyamines such as hexamethylenediamine; amides such as ureas, 
polyamides, polyacrylamides, urethanes, polyurethanes; and monohydric 
alcohols such as furfuryl alcohol. The third component can also be 
additional or different aldehydes or phenols and can be included with the 
other reactants at the beginning of the process or at any stage during the 
reaction period or the third component can be added to the finished resin. 
Adhesion promoters can also be incorporated into the resin to modify resin 
structure as well as performance properties. Examples would include 
functional silanes. It is another embodiment of this invention to react 
the finished resin with alkanols of 1-5 carbon atoms, preferably butanol, 
to provide etherified products, or to react the finished resin with 
acylating agents, preferably acetic anhydride, to provide esterified 
products. Such reactions are well known in the art. Alternatively, the 
reaction can be conducted in situ since the conjugate alcohol of the 
aldehyde is present as a byproduct of the reaction. The establishment and 
conduct of such reactions are well known to those skilled in the art. 
For cold box applications, the resin is mixed with a foundry aggregate, 
e.g. sand, in an amount of about 0.5 to 5.0%, preferably about 0.5 to 1.0% 
based on sand. Then a reactive prepolymer 0.5 to 1.0% based on sand is 
added to the sand-resin mixture which is then delivered to a mold or a 
core box. A gaseous catalyst such as phosphine or BF.sub.3 and complexes 
is then passed through the sand mixture which results in chemically curing 
the resin. Strong base amine catalysts known in the art can also be used. 
In no-bake applications, about 0.1 to 2.0% (based on total binder) catalyst 
is mixed with the resin portion and this mixture is then mixed with the 
aggregate. The reactive prepolymer is then added and after thorough 
mixing, the coated sand is delivered to a molding box or core box. Within 
minutes the reactive prepolymer and the resin react and cure, and the mold 
or core can be removed from the box. The catalysts used in the practice of 
this invention include organo-phosphine derivatives of which 
triphenylphosphine is preferred. Combinations of these with metal driers, 
such as lead naphthenate are also effective. Amine bases can also be used 
in the practice of this invention. Those with pK.sub.b from 4 to 7 are 
preferred, e.g. N-ethylmorpholine and dimethylbenzylamine. These catalysts 
can also be used with other known catalyst, e.g. naphthenates of lead, 
tin, cobalt and the like. Amine catalysts known in the art can also be 
used. 
Reactive prepolymers are well-known in the art and do not form a part of 
this invention. Examples of such prepolymers include polyisocyanates and 
epoxy resins. Any of the reactive prepolymers known in the art can be used 
in the practice of this invention.

The invention will be better understood with reference to the following 
examples. It is understood, however, that the examples are intended only 
to illustrate the invention and it is not intended that they limit the 
invention. 
EXAMPLE 1 
Phenol 376 g (4 moles) was heated to 50.degree. C. to liquify it and was 
charged to a reaction vessel equipped with a stirrer and reflux condenser. 
The phenol was further heated to 80.degree. C. and 91% paraformaldehyde 
171 g (5.2 moles) was added. After the temperature reached 90.degree. C., 
tetrakis-ethylhexyl titanate 13.3 g was added, thus providing a titanium 
ion catalyst concentration of 3000 ppm based on the phenol content. The 
reaction mixture was then heated to 115.degree.-120.degree. C. and held 
under reflux for about 90 minutes or until the cloud point was 57-60% at a 
refractive index of 1.56-1.59. 
At this point, a water trap was put into place to collect the water of 
reaction. The reaction, which had cooled somewhat, was reheated to 
115.degree.-120.degree. C., and held under distillation for about one hour 
until the cloud point reached 47-50% at a refractive index of 1.59-1.60. 
Approximately 50 ml of distillate was recovered and the resin had a 
viscosity (Cone and Plate at 75.degree. C.) of 100 to 130 cps. 
Heat was removed from the reactor and the system was placed under full 
vacuum for about 30 minutes to remove residual water of reaction. 
Approximately 20 ml of additional distillate was recovered. The 
temperature of the vacuum strip was held within 75.degree.-80.degree. C. 
to minimize further advancement of the resin. The properties of the resin 
are given in Table 1. The distillate composite contained approximately 10% 
methanol. 
A. Using the resin prepared as above, a typical no-bake resin solution was 
prepared by dissolving the resin in the following polar-nonpolar solvent 
system: 
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No-Bake Resin Formulation 
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Resin 60 parts 
2-Butoxyethyl acetate 15 parts 
Aromatic Solvent 25 parts 
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To 12 g of this resin formulation was added 0.125 g of N-ethylmorpholine as 
a 25% wt solution in aromatic solvent and this mixture was mixed well with 
1600 g clean silica sand. Then 12 g of an 80% solution of a polyisocyanate 
prepolymer in aromatic solvent (Mondur MR, marketed by Mobay Chemical 
Corporation, Pittsburgh, Pennsylvania) was added, mixed rapidly, and 
placed in a mold. After a latent period, the resin hardened. The course of 
the set was monitored by a Dietert probe to a core strength of 50 psi at 
which time the core was stripped from the mold. In a second experiment, 
0.25 g of N-ethylmorpholine was used in place of 0.125 g. Core tensile 
strengths as a function of time are shown in Table 2. 
B. The experiment described in the foregoing paragraph A was repeated in 
all essential details except that triphenyl phosphine (25% wt in 
2-butoxyethyl acetate) was substituted for N-ethylmorpholine. The results 
are given in Table 2. 
TABLE 1 
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Properties of Resins 
Resin Properties Example 1 Example 2 
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Free formaldehyde, % 
3.5 5 
Free phenol, % 6 12 
Water, % &lt;1.0 &lt;1.0 
Cloud point, % 45 49 
Neat viscosity (75.degree. C.) cps 
420 210 
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TABLE 2 
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Tensile Strength (psi) 
Catalyst 0.5 1.0 2.0 
(total binder) 
Cure Time hrs hrs hrs ON* 
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N-ethylmorpholine 
latent 3-8 min 150 125 270 220 
(0.125 g) cured 12 min 
N-ethylmorpholine 
latent 0-4 min 123 160 200 230 
(0.25 g) cured 6 min 
Triphenylphosphine 
latent 0-7 min 97 -- -- 167 
(0.125 g) cured 11 min 
Triphenylphosphine 
latent 0-2 min 130 -- -- 160 
(0.25 g) cured 5 min 
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*ON = overnight 
EXAMPLE 2 
Phenol 376 g (4 moles) was heated to 50.degree. C. to liquify it and was 
then charged to a reaction vessel equipped with a reflux condenser and 
stirrer. The phenol was further heated to 80.degree. C. and 91% 
paraformaldehyde 198 g (6 moles) was added. After the temperature reached 
90.degree. C., tetrakis-ethylhexyl titanate 13.3 g was added, thus 
providing a titanium ion catalyst concentration of 3000 ppm based on the 
phenol content. The reaction mixture was then heated to 
115.degree.-120.degree. C. until the cloud point measurement was 50-52% at 
a refractive index of 1.58-1.59. The heat was then removed and a vacuum 
was applied for 90 minutes while holding the temperature at 75.degree. C. 
About 50-60 ml of distillate (ca 10% methanol) was recovered during this 
period. The properties of the resin are given in Table 1. 
EXAMPLE 3 
The resin of Example 1 was evaluated in the following typical cold-box 
formulation. 
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Cold Box Resin Formulation 
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Resin 50 parts 
Diisobutyl phthalate 30 parts 
Aromatic solvent* 15 parts 
Kerosene 4 parts 
Oleic acid 1 part 
100 parts 
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*Panasol An3, marketed by Amoco Chemical Corporation was used. 
Twelve grams (12 g) of this resin solution was thoroughly mixed with 1600 g 
washed silica sand. To this mixture was added 12 g of an 80% solution of 
polyisocyanate prepolymer (Mondur MR). The total binder component was 1.5% 
based on sand. 
The sand-binder mixture was delivered to a mold box and triethylamine gas 
was passed through the box to cure the sand cores. The samples obtained 
showed good tensile strengths as a function of time. The pot-life of the 
sand-binder mixture also was acceptable. Typical results are shown in 
Table 3. 
TABLE 3 
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Properties of Cold-Box Core Samples 
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I. Tensile Strength: 
Core samples prepared and broken as 
function of time 
Core Age (hrs) 0 1/2 1.0 2.0 4 ON 
Tensile (psi) 110 160 170 200 240 280 
II. Pot Life: Sand-binder mixture aged and 
cores made at time intervals 
Pot Life (hrs) -- 1.0 2.0 3.0 4.0 
Tensile (psi) 110 150 130 110 75 
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EXAMPLE 4 
The experiment of Example 1 was repeated in all essential details except 
that urea, 5% based on the phenol, was included in the phenol-formaldehyde 
reaction mixture. The resin thereby obtained was useful in cold-box and 
no-bake applications. 
EXAMPLES 5-7 
The experiment of Example 4 was repeated in all essential details except 
that the following modifying compounds were substituted for urea. The 
resins thereby obtained were useful in cold-box and no-bake applications. 
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Example Modifier 
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5 Soy protein (pro-cote 
products of Ralston 
Purina) 
6 Aniline 
7 Furfuryl alcohol 
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EXAMPLES 8-13 
The experiment of Example 4 is repeated in all essential details except 
that the following modifying compounds are substituted for urea. The 
resins thereby obtained are useful in cold-box and no-bake applications. 
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Example Modifier 
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8 Starch 
9 Ethylene glycol 
10 Polyvinyl alcohol 
11 Pentaerythritol 
12 Hexamethylenetetramine 
13 Polyacrylamide 
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EXAMPLES 14-17 
The experiment of Example 1 was repeated in all essential details except 
that the following catalysts were substituted for tetrakis-ethylhexyl 
titanate. The resins thereby obtained were useful in cold-box and no-bake 
applications. 
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Example Modifier 
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14 Zirconium isopropoxide 
15 Aluminum isopropoxide 
16 Tetrabutyl titanate 
17 Tetraisopropyl titanate 
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EXAMPLES 18-21 
The experiment of Example 1 is repeated in all essential details except 
that the following catalysts are substituted for tetrakis-ethylhexyl 
titanate. The resulting resins are useful in cold-box and no-bake 
applications. 
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Example Modifier 
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18 Titanium laureate naphthenate 
19 Titanium oleate 
20 Titanium naphthenate 
21 Triethylaluminum 
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Determination of Cloud Point 
Cloud point measurements are well known in the art and are commonly 
employed to indicate the degree of polymerization of a resin. In general, 
the procedure involves dissolving a weighed amount of resin in a weighed 
amount of solvent and titrating with a non-solvent until a cloud appears 
in the mixture. The cloud point is that number obtained by dividing the 
weight of the non-solvent by the sum of the weights of the non-solvent, 
the solvent and the resin. This number is multiplied by 100 and is 
expressed as a percentage. The term cloud point as used herein is intended 
to mean that percentage obtained by dissolving one gram of resin in 99 g 
of tetrahydrofuran (the solvent) and titrating with water.