Binder composition for production of molds and method of producing mold

The binder composition for the production of molds of the present invention comprises a binder obtained by polycondensation of polycondensable components comprising as major components furfuryl alcohol, urea, and an aldehyde. In the binder contained in the binder composition for the production of molds, the difference A-B! between the weight % of charged furfuryl alcohol (A) based on the weight of the binder and the weight % of unreacted furfuryl alcohol (B) based on the weight of the binder is 5.0 to 60.0. When the binder composition for the production of molds of the present invention is used, the curing of the binder is further accelerated without deteriorating the working atmosphere.

TECHNICAL FIELD 
The present invention relates to a binder composition for the production of 
molds which is used to be added to a refractory granular material when a 
mold is produced, and a (binder/curing agent for the production of molds) 
composition comprising a binder composition for the production of molds 
and a curing agent composition. The present invention also relates to a 
sand composition for the production of molds which comprises a refractory 
granular material and the binder composition for the production of molds, 
or a sand composition for the production of molds which comprises a 
refractry granular material, the binder composition for the production of 
molds and the curing agent composition. The present invention further 
relates to a method for producing a mold by using the sand composition for 
the production of molds. 
BACKGROUND ART 
Conventionally, as a binder for foundry sand for the production of molds, 
an acid curing resin, such as a phenolic resin, a furan resin, and 
furfuryl alcohol, is used, and a method of producing a mold wherein these 
binders are cured by adding a curing agent thereto is usually carried out. 
A furan resin having good properties as an organic self-curing resin for 
foundry sand has long been used (Japanese Patent Publication No. 
39-1543/1964, etc.), and such a furan resin has been improved in various 
ways to develop, depending on its application, for example, a binder which 
is weaken in odor by adding thereto glyoxal, tetraoxane or the like and a 
binder is lowered in cost by modifying it with a phenolic resin, a urea 
resin or the like. 
However, there has recently been a demand for an improvement in working 
efficiency through improvements in machinery, facilities, processes, and 
the like for the production of castings and in association with it, as a 
binder for foundry sand, a self-curing organic binder of a quick curing 
type has been strongly desired. To meet the demand, for example, a method 
wherein the sand temperature is elevated in order to accelerate the curing 
of a binder, a method wherein water is removed under reduced pressure, and 
a method wherein use is made of a large quantity of a curing agent have 
been adopted. 
However, for such a purpose, to elevate the temperature is economically 
disadvantageous because extra energy is required. Further to remove water 
under reduced pressure can accelerate the curing to a certain extent but 
cannot fundamentally solve the problem. Further the use of a large 
quantity of a curing agent can improve the curing speed to accelerate the 
curing, but results in such disadvantages that the working atmosphere is 
deteriorated by the decomposed gases and that the strength of castings was 
lowered. 
In view of the above, as a curing agent composition that makes the working 
atmosphere difficultly deteriorated even if the curing agent composition 
is used in a relatively large quantity, one wherein a phosphoric acid 
compound and a sulfonic acid compound are mixed in a specified ratio is 
suggested (Japanese Patent Application Laid-Open No. 5-237587). That is, 
by mixing a phosphoric acid compound low in toxicity with a sulfonic acid 
compound capable of promoting curing in a specified ratio, it is intended 
to accelerate the curing speed and to prevent the working atmosphere from 
being deteriorated. Although such a curing agent composition was very 
useful, it is needless to say that if the usage was too much, the working 
atmosphere was deteriorated disadvantageously. Further the above official 
gazette does not describe at all the use of a furan resin together with a 
curing accelerator and the adjustment of the degree of polycondensation of 
that furan resin. 
DISCLOSURE OF THE INVENTION 
Therefore, an object of the present invention is to provide a binder 
composition for the production of molds which does not deteriorate the 
working atmosphere and whose curing is promoted. 
Further, an object of the present invention is to provide a (binder/curing 
agent for the production of molds) composition comprising the binder 
composition for the production of molds and a curing agent composition. 
Still another object of the present invention is to provide a sand 
composition for the production of molds which comprises a refractory 
granular material and the binder composition for the production of molds, 
or a sand composition for the production of molds which comprises a 
refractry granular material, the binder composition for the production of 
molds and the curing agent composition. 
Still another object of the present invention is to provide a method for 
producing a mold by using the sand composition for the production of 
molds. 
The inventors of the present invention have studied keenly to attain the 
above objects and have found that, in a binder composition for the 
production of molds which comprises a binder obtained by polycondensation 
of polycondensable components comprising as a major component furfuryl 
alcohol, by adjusting the degree of polycondensation of the binder to a 
specified range, the curing of the binder composition for the production 
of molds can be further accelerated without deteriorating the working 
atmosphere. 
Further, the inventors of the present invention have found that, in a 
binder composition for the production of molds which comprises a binder 
obtained by polycondensation of polycondensable components comprising as 
major components furfuryl alcohol, urea, and an aldehyde, by adjusting the 
degree of polycondensation of the binder to a specified range, by 
adjusting the water content in the binder composition for the production 
of molds to a specified value or below, and by adjusting the nitrogen atom 
content attributed to the urea in the binder composition for the 
production of molds, the curing of the binder composition for the 
production of molds can be further accelerated without deteriorating the 
working atmosphere. 
The present invention has been made on the basis of the above findings to 
attain the above objects by providing a self-curing binder composition for 
the production of molds (hereinafter referred to as "a first binder 
composition for the production of molds") comprising a binder obtained by 
polycondensation of polycondensable components comprising as a major 
component furfuryl alcohol, and one or more curing accelerators 
represented by the following general formula (1): 
##STR1## 
(wherein X.sub.1 and X.sub.2, which may be the same or different, each 
represent H, CH.sub.3 or C.sub.2 H.sub.5), wherein, in the binder 
contained in the binder composition for the production of molds, the 
difference A-B! between the weight % of charged furfuryl alcohol (A) 
based on the weight of the binder and the weight % of unreacted furfuryl 
alcohol (B) based on the weight of the binder after the polycondensation 
is 5.0 to 60.0, and the curing accelerator is contained in an amount of 
0.5 to 63.0% by weight. 
Further, the present invention has also attained the above objects by 
providing a self-curing binder composition for the production of molds 
(hereinafter referred to as "a second binder composition for the 
production of molds") comprising a binder obtained by polycondensation of 
polycondensable components comprising as major components furfuryl 
alcohol, urea, and an aldehyde, wherein, in the binder contained in the 
binder composition, the difference A-B! between the weight % of charged 
furfuryl alcohol (A) based on the weight of the binder and the weight % of 
unreacted furfuryl alcohol (B) based on the weight of the binder after the 
polycondensation is 5.0 to 60.0, the water content in the binder 
composition for the production of molds is 6.0% by weight or less, and the 
nitrogen atom content in the binder composition for the production of 
molds is 0.5 to 4.0% by weight. Preferably the polycondensable components 
comprise furfuryl alcohol and urea. It is also preferable that the 
polycondensable components comprise furfuryl alcohol and an aldehyde. 
Particularly preferably the polycondensable components comprise furfuryl 
alcohol, urea, and an aldehyde. 
As the aldehyde, a conventionally known aldehyde compound can be used, such 
as formaldehyde, glyoxal, and furfural. In particular, in the present 
invention, formaldehyde is preferably used in view of the economy and 
odor. 
When the polycondensation is carried out using as the polycondensable 
components furfuryl alcohol and/or urea and/or an aldehyde, a mixture 
(binder) comprising a condensate of furfuryl alcohol, a polycondensate of 
furfuryl alcohol and an alkylol urea, a condensate of urea and an 
aldehyde, a polycondensate formed by polycondensation of these 
condensates, unreacted reactants of the respective components, water, etc. 
is obtained, which will be varied depending on the mixing proportion of 
the components. 
Preferably the binder is contained in an amount of 37.0 to 99.5% by weight 
in the first binder composition for the production of molds. 
The mixing ratio and polycondensation conditions of the polycondensable 
components are suitably adjusted so that A-B! may be within the above 
range. For example, if the binder is prepared by using polycondensable 
components made up of furfuryl alcohol, urea, and an aldehyde, they are 
preferably mixed in amounts of 50.0 to 98.0% by weight, 1.0 to 9.0% by 
weight, and 0.5 to 9.0% by weight respectively, subsequently they are 
reacted for a prescribed time under basic conditions, and then they are 
subjected to polycondensation under acid conditions. 
An important point in the present invention is that the degree of 
polycondensation of furfuryl alcohol in the binder is adjusted to a 
specified range. Since it is difficult, however, to measure the degree of 
polycondensation of furfuryl alcohol directly, in the present invention, 
the difference between the weight % of charged furfuryl alcohol based on 
the weight of the binder and the weight % of unreacted furfuryl alcohol 
based on the weight of the binder after the polycondensation is taken as 
an index of the degree of polycondensation of furfuryl alcohol. That is, 
in the present invention, the degree of polycondensation of furfuryl 
alcohol is adjusted so that the difference, A-B!, between the weight % of 
charged furfuryl alcohol (A) and the weight % of unreacted furfuryl 
alcohol (B) after the polycondensation will be 5.0 to 60.0. If the 
difference A-B! is less than 5.0, the degree of polycondensation of 
furfuryl alcohol is too low to increase satisfactorily the curing speed of 
the first binder composition for the production of molds and therefore the 
initial strength of the resulting mold is not improved. On the other hand, 
if the difference A-B! is more than 60.0, the degree of polycondensation 
of furfuryl alcohol is too high and therefore the viscosity of the first 
binder composition for the production of molds is increased, which lowers 
the mixing capability of the below-described sand composition (mixed sand) 
for the production of molds, resulting in the lowering of the strength of 
the mold. The difference A-B! is preferably 10.0 to 50.0, and more 
preferably 15.0 to 40.0. 
To obtain an index of the degree of polycondensation of furfuryl alcohol, 
the weight % of charged furfuryl alcohol and the weight % of unreacted 
furfuryl alcohol must be measured and the measurement can be carried out, 
for example, by the following method. 
In the above binder contained in the first binder composition for the 
production of molds, the weight % of unreacted furfuryl alcohol based on 
the weight of the binder after the polycondensation can be measured by gas 
chromatography. In that case the conditions of gas chromatography are as 
follows; the apparatus to be used: GC-14A manufactured by Shimadzu 
Corporation; the column to be used: PEG-20M chromosorb WAW DMCS 10% 60/80 
MESH 0.5 m.times.3 mm (.phi.); the detector: FID; and the carrier gas: He. 
Further, in the first binder composition for the production of molds, the 
method of measuring the weight % of charged furfuryl alcohol based on the 
weight of the binder is as follows. By allowing the reaction of potassium 
bromide, potassium bromate, and hydrochloric acid to produce bromine in 
excess to the furfuryl alcohol in the binder contained in the first binder 
composition for the production of molds, the produced bromine is added to 
the double bonds of the furfuryl alcohol, thereafter potassium iodide is 
added in excess to the excess bromine remaining in the system to produce 
iodine and potassium iodide, and the produced iodine is titrated with 
sodium thiosulfate to measure the weight % of charged furfuryl alcohol in 
the binder contained in the first binder composition for the production of 
molds. In this method of measuring charged furfuryl alcohol, detected 
aromatic compounds and aliphatic compounds having the double bonds in the 
molecules are measured separately by other method to calculate the weight 
% of charged furfuryl alcohol in the binder contained in the first binder 
composition for the production of molds. 
The first binder composition for the production of molds of the present 
invention comprises a binder which is obtained by polycondensation of 
polycondensable components comprising as a major component furfuryl 
alcohol and has a degree of polycondensation in a specified range adjusted 
in the above manner, and one or more curing accelerators represented by 
the above general formula (1). As the curing accelerator, for example, 
2,5-bishydroxymethylfuran, 2,5-bismethoxymethylfuran, 
2,5-bisethoxymethylfuran, 2-hydroxymethyl-5-methoxymethylfuran, 
2-hydroxymethyl-5-ethoxymethylfuran, and 
2-methoxymethyl-5-ethoxymethylfuran can be mentioned, which can be used 
singly or as a mixture. Particularly, as the curing accelerator, 
2,5-bishydroxymethylfuran is preferably used. This is because, in 
comparison with 2,5-bismethoxymethylfuran and 2,5-bisethoxymethylfuran, 
2,5-bishydroxymethylfuran is high in reactivity to further accelerate the 
curing reaction of the binder obtained by polycondensation of the 
polycondensable components comprising as a major component furfuryl 
alcohol. The reason why 2,5-bishydroxymethylfuran is high in reactivity is 
that the hydroxyl groups in the molecule contribute to the curing 
reaction. In contrast, in the case where 2,5-bismethoxymethylfuran or the 
like is used, since it contributes to the curing reaction after the 
methoxymethyl ether is hydrolyzed to produce hydroxyl groups, the action 
of promoting the curing reaction becomes a little poor. In the case where 
furfuryl alcohol is reacted with formaldehyde to produce a furan resin, it 
is known that 2,5-bishydroxymethylfuran is produced as an initial 
condensate (see "Kobunshi Yakuzai Nyumon" published by Sanyo Chemical 
Industries, Ltd.). However, it has not been known that 
2,5-bishydroxymethylfuran plays an action of promoting curing a binder 
obtained by polycondensation of polycondensable components comprising as a 
major component furfuryl alcohol. 
The curing accelerator is added and contained in the first binder 
composition for the production of molds in an amount of 0.5 to 63.0% by 
weight. If the amount of the added curing accelerator is less than 0.5% by 
weight, the curing reaction of the first binder composition for the 
production of molds is not accelerated satisfactorily to improve the 
initial strength of the mold to a satisfactory extent. On the other hand, 
if the amount of the added curing accelerator is more than 63.0% by 
weight, the amount of the binder obtained by polycondensation of 
polycondensable components comprising as a major component furfuryl 
alcohol is relatively reduced whereby causing the curing accelerator to be 
difficultly dissolved in the binder and as a result a precipitation is 
produced in the first binder composition for the production of molds. The 
amount of the curing accelerator to be added is preferably 1.8 to 50.0% by 
weight, more preferably 2.5 to 50.0% by weight, further more preferably 
5.0 to 40.0% by weight, and most preferably 7.0 to 40.0% by weight. 
The water content in the first binder composition for the production of 
molds is preferably 6.0% by weight or less. The water content is more 
preferably 4.0% by weight or less, and most preferably 2.0% by weight or 
less. Since the first binder composition for the production of molds is 
cured by a dehydration condensation reaction, if the water content is more 
than 6.0% by weight, the progress of the dehydration condensation reaction 
is retarded to lower the curing speed of the first binder composition for 
the production of molds, and the initial strength of the mold is tend to 
be unfavorably lowered. Accordingly, from the point of view of the curing 
speed, the smaller the water content is, the more preferable it is. 
However, if the water content is too small, the viscosity of the first 
binder composition for the production of molds is increased excessively in 
some cases and sometimes it becomes difficult to handle. Therefore, in 
such a case, it is preferable that a small amount (that is, 6.0% by weight 
or less) of water should be contained in the first binder composition for 
the production of molds. To adjust the water content in the first binder 
composition for the production of molds, for example, water may be added 
subsequently to the obtained first binder composition for the production 
of molds, or alternatively, use may be made of the condensed water which 
is generated in the course of the production of the first binder 
composition for the production of molds, and if the content of the 
condensed water is excessive, the water may be removed by means of 
dehydration under reduced pressure or the like while if the content of the 
condensed water is too low, water may be added subsequently. The content 
(in % by weight) of water of the first binder composition for the 
production of molds is measured by the Karl Fischer's method. 
If a nitrogen-atom-containing compound (generally urea) is used as the 
polycondensable component in addition to furfuryl alcohol, the nitrogen 
atom content attributed to the nitrogen-atom-containing compound in the 
binder composition for the production of molds is preferably 0.5 to 4.0% 
by weight. If the nitrogen atom content is less than 0.5% by weight, the 
amount of the urea used in the polycondensation of the polycondensable 
component is too small and therefore the strength of the resulting mold is 
not apt to improve satisfactorily while if the nitrogen atom content is 
more than 4.0% by weight, a gas attributed to nitrogen atoms is evolved at 
the time of pouring and therefore casting defects, such as pinholes, are 
apt to be unfavorably formed in the obtained casting. More preferably the 
above nitrogen atom content is 0.5 to 3.0% by weight, and most preferably 
0.5 to 2.0% by weight. 
Many of nitrogen atoms in the first binder composition for the production 
of molds are attributed to urea and even if other nitrogen-atom-containing 
compound than urea is used in obtaining the binder, the nitrogen atom 
content in the first binder composition for the production of molds is 
preferably adjusted to 0.5 to 4.0% by weight. The nitrogen atom content 
(in % by weight) is measured by the Kjeldahl method. 
In the first binder composition for the production of molds, a binder 
obtained by polycondensation of polycondensable components comprising as a 
major component furfuryl alcohol is used as described above, and in 
particular a binder obtained by polycondensation of polycondensable 
components comprising furfuryl alcohol, urea, and an aldehyde is 
preferably used. In addition to these polycondensable components, at least 
one or more of conventionally known various modifiers may be mixed to 
prepare the binder. As those conventionally known various modifiers, can 
be used, for example, polymers and oligomers, such as phenolic resins, 
melamine resins, cumarone/indene resins, petroleum resins, polyesters, 
alkyd resins, polyvinyl alcohols, epoxy resins, ethylene/vinyl acetate, 
polyvinyl acetates, polybutadiene, polyethers, polyethyleneimines, 
polyvinyl chlorides, polyacrylates, polyvinyl butyrals, phenoxy resins, 
cellulose acetate, xylene resins, toluene resins, polyamides, styrene 
resins, polyvinyl formals, acrylic resins, urethane resins, and nylons; 
natural substances, such as lignin, lignin sulfonic acids, rosins, ester 
gums, vegetable oils, bitumens, fuel oils, cashew nut shell liquid, and 
vanillin; saccharides and their derivatives, such as starches, corn 
starch, glucose, and dextrins; polyhydric alcohols, such as resorcin, 
resorcin residue, cresol residue, a reaction by-product between 
2,2,4-trimethyl-4(hydroxyphenyl)cumarone and isopropenylphenol, a reaction 
by-product between terephthalic acid and ethylene glycol, and polyethylene 
glycols; ketones, such as acetone, cyclohexane and acetophenone; 
condensates of these ketones with aldehydes; amino and imino compounds, 
such as dicyandiamide, acrylamide, and thiourea; condensates of these 
amino or imino compounds with aldehydes; and ester compounds, such as 
isocyanuric acid esters and unsaturated fatty acid esters. When these 
modifiers are additionally used together with the above-described 
polycondensable components, the amount thereof to be added is preferably 
20% by weight or less based on the total weight of the above first binder 
composition for the production of molds. 
In the first binder composition for the production of molds, in addition to 
the binder and curing accelerator, a silane coupling agent may be added as 
an optional component. As the silane coupling agent, for example, 
.gamma.-(2-amino)aminopropylmethyldimethoxysilane, 
.gamma.-aminopropyltrimethoxysilane, .gamma.-aminopropyltriethoxysilane, 
.gamma.-glycidoxypropyltrimethoxysilane, or the like can be preferably 
added in an amount of 0.03 to 1.0% by weight in the total amount of the 
composition. 
Next, the second binder composition for the production of molds is 
described. 
As described above, the second binder composition for the production of 
molds comprises a binder obtained by polycondensation of polycondensable 
components comprising as major components furfuryl alcohol, urea, and an 
aldehyde, wherein, in the binder contained in the binder composition for 
the production of molds, the difference A-B! between the weight % of 
charged furfuryl alcohol (A) based on the weight of the binder and the 
weight % of unreacted furfuryl alcohol (B) based on the weight of the 
binder after the polycondensation is 5.0 to 60.0, the water content in the 
binder composition for the production of molds is 6.0% by weight or less, 
and the nitrogen atom content in the binder composition for the production 
of molds is 0.5 to 4.0% by weight. 
As the aldehyde in the polycondensable components, the same aldehydes as 
those which are used in the first binder composition for the production of 
molds can be used. 
An important point in the second binder composition for the production of 
molds is that, similarly to the first binder composition for the 
production of molds, the degree of polycondensation of furfuryl alcohol in 
the binder is adjusted to a specified range. Moreover, in the case of the 
second binder composition for the production of molds, since it is also 
difficult to measure directly the degree of polycondensation of furfuryl 
alcohol, similarly to the first binder composition for the production of 
molds, the difference between the weight % of charged furfuryl alcohol 
based on the weight of the binder and the weight % of unreacted furfuryl 
alcohol based on the weight of the binder after the polycondensation is 
taken as an index of the degree of polycondensation of furfuryl alcohol. 
That is, in the second binder composition for the production of molds, 
similarly to the first binder composition for the production of molds, the 
degree of polycondensation of furfuryl alcohol is adjusted so that the 
difference, A-B!, between the weight % of charged furfuryl alcohol (A) 
and the weight % of unreacted furfuryl alcohol (B) after the 
polycondensation will be 5.0 to 60.0. The reason why the difference A-B! 
is specified to be in the range is the same as that of the case of the 
first binder composition for the production of molds. A preferable range 
of the above difference A-B! is the same as that of the case of the first 
binder composition for the production of molds. 
The method of measuring the weight % of charged furfuryl alcohol based on 
the weight of the binder and the weight % of unreacted furfuryl alcohol 
based on the weight of the binder is the same as that of the case of the 
first binder composition for the production of molds. 
The water content in the second binder composition for the production of 
molds is needed to be 6.0% by weight or less. The water content is 
preferably 4.0% by weight or less, and most preferably 2.0% by weight or 
less. The reason why the water content is 6.0% by weight or less is the 
same as that of the first binder composition for the production of molds. 
The methods for adjusting and measuring the water content in the second 
binder composition for the production of molds are the same as those of 
the first binder composition for the production of molds. 
The nitrogen atom content (mainly attributed to urea but also inclusive of 
other nitrogen-atom-containing compounds than urea) in the second binder 
composition for the production of molds is needed to be 0.5 to 4.0% by 
weight. This reason is the same as that of the case of the first binder 
composition for the production of molds. The nitrogen atom content is 
preferably 0.5 to 3.0% by weight, and most preferably 0.5 to 2.0% by 
weight. 
The nitrogen atom content (in % by weight) is measured by the Kjeldahl 
method in the same way as the case of the first binder composition for the 
production of molds. 
In the second binder composition for the production of molds, in addition 
to the polycondensable components, one or more conventionally known 
various modifiers may be mixed to prepare the binder. As the 
conventionally known modifiers, the same as those of the case of the first 
binder composition for the production of molds can be used. Further the 
amount thereof to be added is the same as that of the case of the first 
binder composition for the production of molds. 
The binder in the second binder composition for the production of molds is 
preferably contained in an amount of 40 to 100% by weight in the total 
amount of the composition. 
Further, in the second binder composition for the production of molds, in 
addition to the binder and modifiers which is be used in the first binder 
composition for the production of molds, a silane coupling agent may be 
added as an optional component. As the silane coupling agent, for example, 
.gamma.-(2-amino)aminopropylmethyldimethoxysilane, 
.gamma.-aminopropyltrimethoxysilane, .gamma.-aminopropyltriethoxysilane, 
.gamma.-glycidoxypropyltrimethoxysilane, or the like can be preferably 
added in an amount of 0.03 to 1.0% by weight in the total amount of the 
composition. 
Next, the (binder/curing agent for the production of molds) composition of 
the present invention will be described. 
The (binder/curing agent for the production of molds) composition comprises 
the binder composition for the production of molds and a curing agent (or 
a curing agent composition). 
As the curing agent, a conventionally known any curing agent which is used 
in the production of molds can be used. Particularly preferable one as the 
curing agent is a curing agent composition comprising a phosphoric acid 
type compound and a sulfonic acid type compound mixed in a specified ratio 
which is described in Japanese Patent Application Laid-Open No. 5-237587. 
The curing agent composition will be further described. In the curing agent 
composition, the blending is carried out preferably in such a manner that 
the weight ratio of the phosphorus atom weight (phosphorus atom content) 
attributed to the phosphoric acid type compound to the sulfur atom weight 
(sulfur atom content) attributed to the sulfonic acid type compound 
satisfies the relation 0.01.ltoreq.(the sulfur atom content/(the 
phosphorus atom content+the sulfur atom content)).ltoreq.0.7. In other 
words, the sulfur atom weight in the curing agent composition is 
preferably adjusted to 1/99 to 7/3 of the phosphorus atom weight. If the 
sulfur atom weight is smaller than the above range, the phosphorus atom 
weight becomes relatively excessive (that is, the amount of the phosphoric 
acid type compound becomes excessive), thereby phosphorus atoms are apt to 
accumulate in a large amount in the reclaimed sand that has used a 
refractory granular material repeatedly, leading to a tendency that 
casting defects, such as pinholes, are liable to be formed. Further, the 
phosphorus accumulated in the reclaimed sand absorbs moisture intensely, 
leading to a tendency to hamper the curing of the binder composition for 
the production of molds. On the other hand, if the sulfur atom weight is 
larger than the above range (that is, the amount of the sulfonic acid 
compound exceeds the prescribed range), harmful decomposition products are 
liable to be released at the time of pouring, leading to a tendency to 
deteriorate the working atmosphere. Most preferably the weight ratio of 
the phosphorus atom weight and the sulfur atom weight falls to 
0.03.ltoreq.(the sulfur atom content/(the phosphorus atom content+the 
sulfur atom content)).ltoreq.0.6. The sulfur atom content in the curing 
agent composition is measured by the combustion-neutralization titration 
method and the phosphorus atom content in the above curing agent 
composition is measured by ICP (inductively coupled plasma emission 
spectrometer). 
As the phosphoric acid type compound in the curing agent composition, for 
example, phosphoric acid, a polyphosphoric acid, an ester of phosphoric 
acid, such as methyl phosphate and ethyl phosphate, or a salt of 
phosphoric acid, such as potassium phosphate and potassium 
hydrogenphosphate, is used. 
On the other hand, as the sulfonic acid type compound in the curing agent 
composition, for example, an aliphatic sulfonic acid, such as 
methanesulfonic acid and ethanesulfonic acid; an aromatic sulfonic acid, 
such as benzenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid, 
and phenolsulfonic acid; or an inorganic acid, such as sulfuric acid, is 
used. 
In the (binder/curing agent for the production of molds) composition, there 
are no particular restrictions on the mixing ratio (on the basis of 
weight) of the binder composition for the production of molds and the 
curing agent (or the curing agent composition), but generally the range of 
the mixing ratio is such that preferably the binder composition for the 
production of molds/the curing agent (or the curing agent composition) is 
from 1.0 to 20.0, and more preferably from 1.0 to 5.0. 
In the (binder/curing agent for the production of molds) composition, in 
addition to the binder composition for the production of molds and the 
curing agent (or the curing agent composition), a silane coupling agent 
may be added as an optional component. As the silane coupling agent, for 
example, .gamma.-(2-amino)aminopropylmethyldimethoxysilane, 
.gamma.-aminopropyltrimethoxysilane, .gamma.-aminopropyltriethoxysilane, 
.gamma.-glycidoxypropyltrimethoxysilane, or the like can be added 
preferably in an amount of 0.03 to 1.0% by weight in the total amount of 
the composition. 
Next, the sand composition for the production of molds will be described. 
The sand composition for the production of molds comprises a refractory 
granular material and the binder composition for the production of molds 
or comprises a refractory granular material, the binder composition for 
the production of molds, and the curing agent (or the curing agent 
composition). 
The sand composition for the production of molds can be obtained, for 
example, by kneading the binder composition for the production of molds 
into the refractory granular material or by kneading the binder 
composition for the production of molds and the curing agent (or the 
curing agent composition) into the refractory granular material. 
As the refractory granular material, those conventionally known as foundry 
sand, for example, new sand, such as siliceous sand comprising quartzose 
material as a major component, chromite sand, zircon sand, olivine sand, 
alumina sand, mullite sand, and synthetic mullite sand, reclaimed sand, 
and the like can be used. 
As the reclaimed sand, one obtained, for example, by the ordinal mechanical 
abrading technique or roasting technique can be used and one reclaimed by 
the abrading technique is preferable because the yield is high and it is 
economically excellent and is common. 
In the sand composition for the production of molds, there are no 
particular restrictions on the mixing ratio of the refractory granular 
material, the binder composition for the production of molds, and the 
curing agent (or the curing agent composition), but generally the range is 
such that, based on the total amount of the composition, the refractory 
granular material is preferably contained in an amount of 90.0 to 99.99% 
by weight, the binder composition for the production of molds is 
preferably contained in an amount of 0. 1 to 5.0% by weight, and the 
curing agent (or the curing agent composition) is preferably contained in 
an amount of 0.005 to 5.0% by weight. 
Further, to the sand composition for the production of molds, may be added, 
in addition to the essential components, a silane coupling agent for the 
purpose of further improving the strength of the resulting mold. 
As the silane coupling agent, for example, 
.gamma.-(2-amino)aminopropylmethyldimethoxysilane, 
.gamma.-aminopropyltrimethoxysilane, .gamma.-aminopropyltriethoxysilane, 
.gamma.-glycidoxypropyltrimethoxysilane, or the like can be mentioned. The 
silane coupling agent can be added preferably in an amount of 0.00003 to 
0.05% by weight in the total amount of the sand composition for the 
production of molds. The silane coupling agent may be contained previously 
in the binder composition for the production of molds. 
Next, the method for producing a mold by using the sand composition for the 
production of molds of the present invention will be described. 
According to the present invention, a mold can be produced using the sand 
composition for the production of molds generally by the method for 
producing a self-curing mold. That is, the method of the present invention 
comprises the steps of filling the sand composition for the production of 
molds into a prescribed molding pattern and curing the binder composition 
for the production of molds contained in sand composition for the 
production of molds by the action of the curing agent composition thereby 
obtaining a mold. According to the sand composition for the production of 
molds comprising the binder composition for the production of molds, the 
curing speed of the mold is relatively high and about 30 minutes to 1 hour 
after the filling of the sand composition for the production of molds into 
the molding pattern, the mold can be removed satisfactorily. In addition, 
pouring the molten metal into the mold can produce a high quality casting 
under a good atmosphere. In the kneading of the sand composition for the 
production of molds, in the production of molds, and in the curing, etc., 
heating or cooling is not particularly required and they are carried out 
at ambient temperatures without any trouble. Further, with respect to 
points that have not been particularly described in detail in the method 
of producing a mold, techniques for the conventionally known method of 
producing molds can be suitably applied.

EXAMPLES 
Now, the present invention is described in detail by Examples, but the 
present invention is not limited to these Examples. The percentages quoted 
in the Examples and Comparative Examples represent % by weight. 
(Examples 1 to 19 and Comparative Examples 1 to 8) 
The polycondensable components made up of furfuryl alcohol, urea, and 
formaldehyde are reacted for a prescribed time under basic conditions and 
then are further reacted under acid conditions to effect polycondensation 
with dehydration being effected as required. After the completion of the 
polycondensation, the curing accelerator (2,5-furandimethanol 
(bishydroxymethylfuran) (1883-75-6) (CAS registered number) manufactured 
by Aldrich Fine Chemical Co., Ltd.) shown in Tables 1 and 2 is added, 
followed by mixing, to prepare each of the binder compositions for the 
production of molds wherein the curing accelerator is contained in the 
ratio (% by weight) shown in Tables 1 and 2 and the difference A-B! 
between the weight % (A) of charged furfuryl alcohol and the weight % (B) 
of unreacted furfuryl alcohol is shown in Tables 1 and 2. In these binder 
compositions for the production of molds, the water content is 2.0% by 
weight and the nitrogen atom content is 2.0% by weight. 
Then 1 part by weight of each of the binder compositions for the production 
of molds and 0.4 part by weight of a 70% aqueous toluenesulfonic acid 
solution as a curing agent are added to every 100 parts by weight of 
Kakezu floatation No. 5 siliceous sand as a refractory granular material, 
followed by mixing, to obtain sand compositions for the production of 
molds. Immediately thereafter, each of the sand compositions for the 
production of molds is filled into a test piece frame measuring 50 mm 
(.phi.).times.50 mm (height) and test molds are obtained at 25.degree. C. 
by the self-curing mold shaping method. At that time, after the passage of 
1 hour and 24 hours, the compression strength of the test molds is 
measured by the method described in JIS Z 2604-1976. The results are shown 
in Tables 1 and 2. 
TABLE 1 
______________________________________ 
Compression 
Strength 
(kg/cm.sup.2) 
Curing Accelerator After After 
Examples 
Type Amount A-B! 1 hr 24 hrs 
______________________________________ 
1 Bishydroxymethylfuran 
0.5 5.0 5.7 33.1 
2 Bishydroxymethylfuran 
2.0 5.2 6.6 33.6 
3 Bishydroxymethylfuran 
2.0 7.8 7.3 34.2 
4 Bishydroxymethylfuran 
3.0 7.8 7.9 34.5 
5 Bishydroxymethylfuran 
3.0 12.5 8.8 35.3 
6 Bishydroxymethylfuran 
6.0 12.5 9.7 35.8 
7 Bishydroxymethylfuran 
6.0 17.5 10.6 36.6 
8 Bishydroxymethylfuran 
8.0 17.5 11.6 37.0 
9 Bishydroxymethylfuran 
8.0 25.2 12.9 39.7 
10 Bishydroxymethylfuran 
8.0 35.6 12.4 38.3 
11 Bishydroxymethylfuran 
15.0 20.3 16.9 48.0 
12 Bishydroxymethylfuran 
25.0 26.6 20.3 53.2 
13 Bishydroxymethylfuran 
25.0 35.5 20.0 50.7 
14 Bishydroxymethylfuran 
25.0 42.5 14.1 45.6 
15 Bishydroxymethylfuran 
35.0 32.3 17.1 48.4 
______________________________________ 
TABLE 2 
__________________________________________________________________________ 
Compression Strength 
Curing Accelerator (kg/cm.sup.2) 
Type Amount 
A-B! 
After 1 hr 
After 24 hrs 
__________________________________________________________________________ 
Examples 
16 Bishydroxymethylfuran 
45.0 
32.6 
14.0 45.4 
17 Bishydroxymethylfuran 
55.0 
47.1 
13.9 41.3 
18 Bishydroxymethylfuran 
63.0 
52.2 
13.0 40.8 
19 Bishydroxymethylfuran 
15.0 
20.5 
17.1 48.6 
Bismethoxymethylfuran 
1.0 
Comparative 
1 None 3.0 2.6 28.0 
Example 
2 Bishydroxymethylfuran 
0.3 1.8 2.8 29.2 
3 Bishydroxymethylfuran 
0.3 6.5 3.6 29.5 
4 Bishydroxymethylfuran 
2.1 3.5 3.8 29.8 
5 Bishydroxymethylfuran 
30.8 
65.2 
2.8 29.6 
6 Bishydroxymethylfuran 
50.3 
65.6 
3.0 29.8 
7 Bishydroxymethylfuran 
64.5 
58.0 
*1 
8 Bishydroxymethylfuran 
65.0 
63.5 
*1 
__________________________________________________________________________ 
*1 The measurement could not be conducted since the test mold was not 
homogeneous. 
As is apparent from the results in Tables 1 and 2, it can be understood 
that, in the case where the binder compositions for the production of 
molds that contain a curing accelerator are used, the strength of the 
molds after the passage of 1 hour is increased and the strength of the 
molds after the passage of 24 hours is also increased. It can also 
understood that as the content of the curing accelerator is increased 
gradually from 0.5% by weight, the strength of the molds is also 
increased. It can be understood that in that case, at the point where the 
curing accelerator is contained in an amount of 25% by weight, the maximum 
value is attained, and as the curing accelerator is further increased, the 
strength of the molds is lowered gradually, and when the amount exceeds 
63% by weight, the binder composition for the production of molds becomes 
nonuniform. Further, it can be understood that when the amount of the 
curing accelerator is made to be less than 0.5% by weight, the strength of 
the molds is not improved very much. On the other hand, it is understood 
that, in the binder contained in the binder composition for the production 
of molds, when the difference between the weight % of charged furfuryl 
alcohol (A) based on the weight of the binder and the weight % of 
unreacted furfuryl alcohol (B) based on the weight of the binder, that is, 
the value of A-B!, is in the range of 5.0 to 60.0, then after the passage 
of 1 hour, the strength of the molds is increased, and also after the 
passage of 24 hours, the strength of the molds is also increased. Further 
it is understood that as the value of the difference A-B! is increased 
gradually from 5.0, the strength of the molds is also increased gradually. 
It can be understood that, in that case, when the difference A-B! is from 
15.0 to around 40.0, the maximum value is attained, then, when the 
difference A-B! is further increased, the strength of the molds is 
decreased gradually, and when the difference A-B! is more than 60.0, the 
strength of the molds is decreased. On the other hand, it can be 
understood that also in the case where the difference A-B! is less than 
0.5, the strength of the molds is apt to decrease. 
(Examples 20 to 33) 
The polycondensable components made up of furfuryl alcohol, urea, and 
formaldehyde are polycondensed to obtain binders wherein the difference 
between the weight % of charged furfuryl alcohol (A) and the weight % of 
unreacted furfuryl alcohol (B), that is, A-B!, is 25.0. Further, to the 
binders, a curing accelerator comprising 2,5-bishydroxymethylfuran is 
added, followed by mixing, thereby obtaining the binder compositions for 
the production of molds each of which has the water content and the 
nitrogen atom content shown in Table 3. All the contents of the curing 
accelerators in the binder compositions for the production of molds shown 
in Table 3 are 15% by weight. 
Test molds are produced in the same way as in Example 1, except for using 
these binder compositions for the production of molds. Then the 
compression strength of these molds is measured in the same way as in 
Example 1. The results are shown in Table 3. 
TABLE 3 
______________________________________ 
In binder composition for 
production of molds (wt %) 
Compression Strength 
Nitrogen (kg/cm.sup.2) 
Examples 
Water content 
atom content 
After 1 hr 
After 24 hrs 
______________________________________ 
20 1.2 2.5 21.4 51.5 
21 3.8 2.5 18.1 47.9 
22 4.3 2.5 16.0 43.3 
23 5.7 2.5 13.2 40.1 
24 3.8 0.6 12.4 37.8 
25 3.8 1.8 15.2 42.0 
26 3.8 2.8 14.8 44.5 
27 3.8 3.2 14.5 41.3 
28 3.8 3.9 13.0 38.7 
29 6.2 2.5 9.0 33.8 
30 8.5 2.5 6.2 31.5 
31 3.8 0.4 8.2 34.2 
32 3.8 4.2 9.1 35.1 
33 3.8 5.0 7.7 33.0 
______________________________________ 
As is apparent from the results in Table 3, it can be understood that when 
the water content is decreased gradually from 6.0% by weight, the strength 
of the molds is also gradually decreased. It can also be understood that 
when the nitrogen atom content is decreased gradually from 4.0% by weight, 
the strength of the molds is increased gradually. It can be understood 
that, in that case, when the nitrogen atom content is around 1.0 to 3.0% 
by weight, the strength of the molds attains the maximum value, while when 
the nitrogen atom content is decreased further, the strength of the molds 
is decreased gradually, and when the nitrogen atom content is less than 
0.5% by weight, the strength of the molds is also decreased. On the other 
hand, it can be understood that in the case wherein the nitrogen atom 
content is more than 4.0% by weight, the strength of the molds is 
decreased. 
(Examples 34 to 45 and Comparative Examples 9 to 14) 
The polycondensable components made up of furfuryl alcohol, urea, and 
formaldehyde are polycondensed to obtain binder compositions for the 
production of molds containing a binder wherein the difference between the 
weight % of charged furfuryl alcohol (A) and the weight % of unreacted 
furfuryl alcohol (B), that is, A-B!, is 30.0. The water contents and the 
nitrogen atom contents in these binder compositions for the production of 
molds are as shown in Table 4 (18 kinds). 
On the other hand, as a curing agent composition, one obtained by mixing a 
70% aqueous toluenesulfonic acid and 85% phosphoric acid in equal amounts, 
that is, one wherein the (the sulfur atom content/(the phosphorus atom 
content+the sulfur atom content)) is 0.326, is prepared. 
Then, to every 100 parts by weight of Kakezu floatation No. 5 siliceous 
sand as a refractory granular material, are added 1 part by weight of each 
of the binder compositions for the production of molds and 0.45 part by 
weight of the curing agent composition followed by mixing, thereby 
obtaining sand compositions for the production of molds. Test molds are 
produced in the same way as in Example 1, except for using these sand 
compositions for the production of molds. Then the compression strength of 
these molds is measured in the same way as in Example 1. 
The results are shown in Table 4. 
TABLE 4 
__________________________________________________________________________ 
In binder composition for 
Compression Strength 
production of molds (wt %) 
(kg/cm.sup.2) 
Water content 
Nitrogen atom content 
After 1 hr 
After 24 hrs 
__________________________________________________________________________ 
Examples 
34 6.0 2.5 6.3 43.6 
35 4.2 2.5 7.5 45.3 
36 3.1 2.5 9.0 47.0 
37 2.3 2.5 10.6 48.7 
38 1.5 2.5 12.5 49.5 
39 0.6 2.5 13.2 50.8 
40 3.5 4.0 7.6 45.5 
41 3.5 3.2 7.8 46.8 
42 3.5 2.6 8.0 47.4 
43 3.5 2.1 8.1 46.5 
44 3.5 1.2 8.0 46.4 
45 3.5 0.5 6.8 42.9 
Comparative 
9 6.4 2.5 4.2 37.7 
Examples 
10 9.0 2.5 2.1 32.4 
11 3.5 5.2 3.8 35.6 
12 3.5 4.4 4.7 38.1 
13 3.5 0.3 4.2 37.5 
14 3.5 0.2 3.3 34.0 
__________________________________________________________________________ 
As is apparent from the results in Table 4, it can be understood that when 
the water content in the binder compositions for the production of molds 
is decreased gradually from 6.0% by weight, the strength of the molds is 
also increased gradually. It can also be understood that when the nitrogen 
atom content is decreased gradually from 4.0% by weight, the strength of 
the molds is increased gradually. It can be understood that, in that case, 
when nitrogen atom content is around 1.0 to 2.0% by weight, the strength 
of the mold attains the maximum value, then when the nitrogen atom content 
is decreased gradually, the strength of the molds is decreased gradually, 
and when the nitrogen atom content is made to be less than 0.5% by weight, 
the strength of the molds is decreased. On the other hand, it can be 
understood that in the case wherein the nitrogen atom content is more than 
4.0% by weight, the strength of the mold is also decreased. 
(Examples 46 to 53) 
As curing agent compositions, those containing the components shown in 
Table 5 are prepared. A component other than shown in Table 5 is water. 
On the other hand, polycondensable components made up of furfuryl alcohol, 
urea, and formaldehyde are polycondensed to obtain a binder wherein the 
difference between the weight % of charged furfuryl alcohol (A) and the 
weight % of unreacted furfuryl alcohol (B), that is, A-B!, is 25.0. To 
the binder, is added a curing accelerator made of 
2,5-bishydroxymethylfuran, followed by mixing, thereby preparing a binder 
composition for the production of molds wherein the water content is 2.0% 
by weight and the nitrogen atom content is 2.0% by weight. The binder 
composition for the production of molds contains the curing accelerator in 
an amount of 15.0% by weight. 
To every 100 parts by weight of silicious sand is added 0.33 part by weight 
of each of the curing agent compositions shown in Table 5, followed by 
mixing, and then 0.65 part by weight of the above binder composition for 
the production of molds is added, followed by mixing, thereby obtaining 
sand compositions for the production of molds. After these sand 
compositions for the production of molds are used to produce molds to make 
castings wherein the weight ratio of the mold/molten metal is 2.5, the 
sands recovered by disintegrating the molds are subjected to an operation 
by a crusher to obtain reclaimed sands using an M type rotary reclaimer 
manufactured by Japan Casting Co., Ltd. 
TABLE 5 
__________________________________________________________________________ 
Atom content in 
curing agent 
Curing agent composition composition 
(I)/ 
Sulfonic acid compound 
Phosphoric acid compound 
(I) (II) (I) 
Amount Amount 
Sulfur 
Phosphorus 
+ 
Examples 
Type (%) Type (%) atom 
atom (II)! 
__________________________________________________________________________ 
46 Methanesulfonic acid 
2.7 85% phosphoric acid 
24.9 
Toluenesulfonic acid 
35.0 13.95 
6.7 0.676 
Sulfuric acid 
20.0 
47 Ethanesulfonic acid 
2.0 85% phosphoric acid 
22.3 
Phenolsulfonic acid 
14.5 
Pyrophosphoric acid 
2.0 3.9 6.7 0.368 
Benzenesulfonic acid 
3.2 
48 Phenolsulfonic acid 
6.8 85% phosphoric acid 
44.7 
Toluenesulfonic acid 
38.6 
Methyl phosphate 
5.0 9.25 
13.4 0.408 
Xylenesulfonic acid 
4.8 
49 Xylenesulfonic acid 
8.5 85% phosphoric acid 
47.9 
Phenolsulfonic acid 
7.8 Sodium 2.0 2.9 13.4 0.178 
dihydrogenphosphate 
50 Xylenesulfonic acid 
19.5 
85% phosphoric acid 
65.9 
5.8 18.5 0.239 
Sulfuric acid 
7.5 Metaphosphoric acid 
2.0 
51 Benzenesulfonic acid 
1.0 85% phosphoric acid 
57.8 
Toluenesulfonic acid 
2.1 Sodium 2.0 0.6 16.0 0.036 
dihydrogenphosphate 
52 Tolnenesulfonic acid 
0.5 Phosphorus pentoxide 
39.9 
0.12 
17.42 0.007 
Sulfuric acid 
0.1 
53 Benzenesulfonic acid 
48.5 
85% phosphoric acid 
9.9 
Toluenesulfonic acid 
5.2 16.74 
2.68 0.862 
Sulfuric acid 
18.2 
__________________________________________________________________________ 
Note: 
(I)/(I) + (II)! : Sulfur atom content/(sulfur atom content + phosphorus 
atom content)! in the curing agent composition. 
After 95 parts by weight of each of these reclaimed sands and 5 parts by 
weight of new sand are mixed, the curing agent composition and the binder 
composition for the production of molds are added thereto in the same 
ratio as the above, followed by mixing, to repeat the production of molds, 
casting, reclaiming of the sand, and cycling of the reclaimed sand 20 
times, then to each of the last reclaimed sands are added the curing agent 
composition and the binder composition for the production of molds in the 
same ratio as the above, followed by mixing, and molds are molded 
therefrom. Then the mold is produced, and after the passage of 0.5 hour, 1 
hour, and 24 hours, the compression strength of the mold is measured. 
Further, with respect to the moisture absorption of the reclaimed sands, 
after the reclaimed sands obtained after the 20th cycle are allowed to 
stand for 24 hours in an atmosphere having 90% RH at 25.degree. C., the 
moisture absorption of the reclaimed sands is measured. Further, the 
measurement of the amount of SO.sub.2 released at the time of the 20th 
casting is carried out under the following severe conditions: immediately 
after the completion of filling a molten metal into a mold of 620 
mm.times.770 mm.times.530 mm (height) to mold a casting with a 
casting/molten metal weight ratio of 2.5, the mold is covered with a wood 
box of 900 mm.times.900 mm.times.900 mm (height), and 5 minutes after the 
completion of the casting, SO.sub.2 is measured from the upper part of the 
box by a defection tube. The results are shown in Table 6. 
TABLE 6 
__________________________________________________________________________ 
Moisture absorption 
Amount of Test temperature 
of reclaimed sand 
released 
Compression Strength (kg/cm.sup.2) 
of compression 
Examples 
(% based on sand) 
SO.sub.2 (ppm) 
After 0.5 hr 
After 1.0 hr 
After 24 hrs 
strength (.degree. C.) 
__________________________________________________________________________ 
46 0.21 72.3 3.3 9.9 44.8 5 
47 0.25 21.8 5.4 10.2 43.9 35 
48 0.23 47.8 3.6 9.3 45.7 5 
49 0.27 16.1 5.7 11.0 41.4 35 
50 0.25 28.3 5.9 10.9 44.1 5 
51 0.27 3.9 5.8 10.2 42.5 35 
52 0.44 1.2 0 0.7 12.7 35 
53 0.18 102.5 2.0 8.8 41.0 5 
__________________________________________________________________________ 
As is apparent from the results in Tables 5 and 6, it can be understood 
that when the value of (the sulfur atom content/(the phosphorus atom 
content+the sulfur atom content)) is less than 0.01, the moisture 
absorption of the reclaimed sands is high and the compression strength is 
decreased. It can also be understood that when the value of (the sulfur 
atom content/(the phosphorus atom content+the sulfur atom content)) is 
more than 0.7, the working atmosphere is quite deteriorated. Accordingly, 
taking all the aspects together into consideration, it can be understood 
that, in the case wherein the curing agent compositions of Examples 46 to 
51 are used, the moisture absorption of the reclaimed sands is less 
influenced, the compression strength is high, and the working atmosphere 
is good. 
(Examples 54 to 61) 
The binder compositions for the production of molds are prepared in the 
same manner as in the binder composition for the production of molds used 
in Example 34, except that the water content is made to be 0.3% by weight 
and the nitrogen atom content is made to be 2.5% by weight. 
To every 100 parts by weight of siliceous sand, 0.33 part by weight of each 
of the curing agent compositions shown in Table 5 is added, followed by 
mixing, and then 0.65 part by weight of the binder composition for the 
production of molds is added, followed by mixing, thereby obtaining sand 
compositions for the production of molds. Examples 46 to 53 are repeated 
except for the above, thereby measuring the moisture absorption of the 
reclaimed sands, the amount of SO.sub.2 released at the time of the 
casting, and the compression strength of the molds. The results are shown 
in Table 7. 
TABLE 7 
__________________________________________________________________________ 
Moisture absorption 
Amount of Test temperature 
of reclaimed sand 
released 
Compression Strength (kg/cm.sup.2) 
of compression 
Examples 
(% based on sand) 
SO.sub.2 (ppm) 
After 0.5 hr 
After 1.0 hr 
After 24 hrs 
strength (.degree. C.) 
__________________________________________________________________________ 
54 0.23 74.5 2.8 8.3 37.7 5 
55 0.27 22.0 4.5 8.6 36.9 35 
56 0.25 49.0 3.0 7.8 38.4 5 
57 0.29 16.5 4.8 9.3 34.8 35 
58 0.28 29.0 5.0 9.2 37.1 5 
59 0.29 4.0 4.9 8.6 35.1 35 
60 0.48 1.2 0 0.6 10.7 35 
61 0.20 105.0 1.9 7.4 34.5 5 
__________________________________________________________________________ 
As is apparent from the results in Tables 5 and 7, it can be understood 
that when the value of (the sulfur atom content/(the phosphorus atom 
content+the sulfur atom content)) is less than 0.01, the moisture 
absorption of the reclaimed sand is high and the compression strength is 
decreased. It can also be understood that when the value of (the sulfur 
atom content/(the phosphorus atom content+the sulfur atom content)) is 
more than 0.7, the working atmosphere is quite deteriorated. On the other 
hand, it can be understood that, in the case wherein the curing agent 
compositions of Examples 54 to 59 are used, the moisture absorption of the 
reclaimed sands is less influenced, the compression strength is high, and 
the working atmosphere is good. 
(Examples 62 to 71 and Comparative Examples 15 to 17) 
The binder compositions for the production of molds containing binders 
obtained by polycondensation of polycondensable components made up of 
furfuryl alcohol, urea, and formaldehyde are obtained. In the binder 
compositions for the production of molds, the water content is 0.8% by 
weight, the nitrogen atom content is 1.8% by weight, and the difference 
A-B! between the weight % of charged furfuryl alcohol (A) and the weight 
% of unreacted furfuryl alcohol (B) is as shown in Table 8. 
Test molds are produced in the same manner as in Example 34, except for 
using these binder compositions for the production of molds. After the 
passage of 1 hour and the passage of 24 hours, the compression strength of 
the molds is measured. The results are shown in Table 8. 
TABLE 8 
______________________________________ 
In binder composition for 
Compression Strength 
production of molds 
(kg/cm.sup.2) 
A-B! After 1 hr 
After 24 hrs 
______________________________________ 
Examples 
62 5.0 6.0 42.3 
63 7.8 6.4 43.1 
64 10.4 7.8 44.8 
65 12.7 10.7 45.4 
66 15.6 13.2 46.5 
67 23.1 13.5 48.0 
68 30.5 13.3 46.8 
69 43.0 10.5 45.7 
70 52.7 8.3 45.1 
71 60.0 6.1 43.5 
Comparative 
Examples 
15 1.8 3.3 36.0 
16 4.5 4.8 36.4 
17 64.2 4.0 32.6 
______________________________________ 
As is apparent from the results in Table 8, it can be understood that, in 
the above binders contained in the binder compositions for the production 
of molds, when the difference between the weight % of charged furfuryl 
alcohol (A) based on the weight of the binder and the weight % of 
unreacted furfuryl alcohol (B) based on the binder, that is, the value of 
A-B!, is in the range of 5.0 to 60.0, after the passage of 1 hour, the 
strength of the molds is increased and after the passage of 24 hours, the 
strength of the mold is also increased. Further it can be understood that 
when the value of the difference A-B! is increased from 5.0 gradually, 
the strength of the molds is also increased gradually. It can be 
understood that, in that case, when the difference A-B! is around 15.0 to 
40.0, the maximum value is obtained, and when A-B! is increased further, 
the strength of the molds is decreased gradually, and when it is more than 
60.0, the strength of the molds is decreased. Further it can be understood 
that in the case wherein the difference A-B! is less than 5.0, the 
strength of the molds is decreased. 
INDUSTRIAL APPLICABILITY 
When a mold is produced by using the binder composition for the production 
of the present invention, the curing speed of the binder is improved and a 
mold high in initial strength can be obtained. Therefore, when a mold is 
produced using the binder composition for the production of molds of the 
present invention by adopting the method for producing self-curing molds, 
an advanegeous effect that the mold can be removed from the molding block 
at an early stage and therefore that the molding pattern can be used 
effectively can be exhibited. 
Further, in the binder composition for the production of molds of the 
present invention, by using a polycondensate of polycondensable components 
comprising furfuryl alcohol, urea, and an aldehyde, adjusting the water 
content in the binder composition for the production of molds to a 
specified value or below, or by adjusting the nitrogen atom content in the 
binder composition for the production of molds to a specified range, the 
curing of the binder composition for the production of molds can be 
further accelerated and therefore the above-described advantageous effect 
of the present invention can be further improved. 
Further, by using a (binder/curing agent for the production of molds) 
composition comprising the binder composition for the production of molds 
of the present invention and a curing agent composition wherein the sulfur 
atom content and the phosphorus atom content are adjusted to specified 
ranges, even if reclaimed sand is used in a large quantity to produce a 
mold, the advantageous effects that toxic gases, such as SO.sub.2, are 
less released and that a mold having high initial strength as well as high 
final strength can be obtained are exhibited. 
It would be obvious to those skilled in the art that numerous changes and 
modifications of the present invention are possible without departing from 
the spirit and scope of the present invention. Accordingly, the above 
Examples are merely simple illustrations of the present invention and such 
changes and modifications should be embraced in the invention set forth in 
the accompanying claims.