Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1119334
Background of the Invention
This inYention is directed to resin-coated sand compositions and a
process for the preparation thereof, and more particularly, to a process
for producing resin-coated sand compositions substantially free of
nitrogen by the dry hot coating method. The compositions thus prepared
are suitable for manufacturing foundry sand cores and ~olds.
Conventional resin-coated sand compositions have been typically
prepared by the dry hot coating method by mixing heated sand particles
with a novolac phenolic resin (hereinafter referred to as a novolac resin)
in the form of an agitated aqueous solution, adding hexamethylenetetramine
(hereinafter referred to as hexamine) as a hardening agent, in an amount
of 10 to 15 parts by we;ght with respect to 100 parts by weight of resin,
and further adding calcium stearate.
Such resin-coated sand compositions produced with novolac resins and
lS hexamine exhibit fast curing and excellent flow, but are also often as-
sociated with certain drawbacks such as pollution problems and defects in
the cast products, such as pinholes or blow holes resulting from the
presence of nitrogen compounds, such as ammonia or formaldehyde, generated
- by the pyrolysis of hexamine when the resin-coated sand compositions are
~ used in iron or steel casting or when forming molds.
In order to avoid such problems, various attempts have been made to
. employ a shell molding resin with a very low nitrogen content when using
dry hot coating methods. A representative attempt in this direction is
the use of a sotid resole phenolic resin obtained with an ammonia catalyst
(hereinafter referred to as a solid ammonia resole resin).
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1119334
This method is, however, associated with certain drawbacks such as
slower hardening as compared to novolac resins cured with hexamine, and
unsatisfactory flow (insufficient hot flow) resulting from premature local
curing before the sand particles become well-coated in the course of mulling.
As a result, the cured articles frequently exhibit significantly lower
physical strength than those obtained with a novolac resin and hexamine,
and, therefore, this method has not been extensively employed in practice.
A method has also been proposed for controlling the degree o~ reaction
of a solid ammonia resole resin in the earlier stages of reaction in order
to accelerate the hardening. However, this method still results in insuff-
icient hot flow and ~hus in insufficient strength of the molded articles.
In addition, a method has been proposed for using a solid ammonia
resole resin as a curing agent for novolac resins. This method, though
effective for improving the physical strength of the molded article,is
associated with the serious drawback of slow curing.
The present inventors have found that these problems can be solved by
using, as a curing agent for novolac resins, a lubricant-containing solid
resole phenolic resin having a higher content of methylol radicals (here-
inafter referred to as a lubricant-containing solid resole resln). The
presence of a lubricant in the resin elevates the apparent melting point
and thus improves its resistance against blocking.
As this method provides a solid resole resin having a high degree
of reactivity (with a higher content of methylol radicals), it is possible
to obtain a coated sand composition with a fast curing speed and with a
h;gher crosslinking density. Also, the uniform distribution of lubricant
~- in the solid resole resin assures an improvement in hot flow and uniform
mixing with the novolac resin.
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Accordingly, it is an object o~ the present invention to provide a
process for producing a resin-coated sand composition having good physical
strenyth and rapid curing by means of the dry hot coating method.
Another object of the present invention is to provide a process for
producing a resin-coated sand composition capable o~ substantially elimin-
ating gas defects in cast products and also capable of preventing the
various associated pollution problems.
A still further object of the present invention is to provide a
process which utilizes a stable supply of a reactive binder substantially
free of blocking characteristics and which provides for the simpli~ied
preparation of a more reactive solid resole resin.
Summary of the Invention
The present inventors have now succeeded in developing an improved
foundry sand composition comprising sand, a solid novolac resin, a lubricant-
containing solid resole resin reactive with said novolac resin, and op-
tionally, hexamine present in an amount of up to about ~ parts by weight
based on 100 parts by weight of the total amount of resin. The use of a
lubricant-containing solid resole resin as a curing agent for the novolac
resin in the preparation of resin-coated sand compositions provides satis-
factory hot flow without substantial adverse blocking effects, and also
provides the following significant advantages:
1) The substantial absence of defective castings and disagreeable
odors due to gas formation;
2) Satisfactory hot flow and uniform ~ixing of the lubricant-
containing resole with the novolac due to the presence of the lubricant,
and satisfactory cure speed due to a higher content of reactive radicals
in the solid resole resin;
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3) A higher crosslinking density, and a resulting increase in
strength of the molded articles, due to the use of a novolac resin in
combination with a solid resole resin having a higher content ~f reactive
radicals; and
4) The lack of, or very limited need for, the addition of a lub-
ricant, such as calcium stearate, in the blending process for the preparation
of resin-coated sand compositions thus facilitating the blending operation.
Descr;ption of the Preferred Embodiments
The lubricant-containing solid resole resin employed in the present
invention may be obtained by incorporating a lubricant into the base resin
prepared by reacting l mole of phenol with at least l mole of formaldehyde
in the presence of an alkaline catalyst.
Suitable solid resole resins include ammonia solid resole resins,
prepared by using an amine catalyst such a ammonia or an amine compound,
solid resole resins prepared by the combined use of an amine catalyst and
an alkali metal catalyst, and solid resole resins prepared by using an
alkali metal catalyst alone.
The phenolic reactant employed in the present invention to prepare
the novolac or resole resin can be phenol, an alkylphenol such as m-cresol,
p-cresol, xylenol or mixtures thereof.
As source of formaldehyde, in addition to formalin, forma1dehyde
polymers such as paraformaldehyde or trioxane, or mixtures thereof, can
be advantageously employed. In addition, hexamine can be employed not
only as a catalyst, but also in combination with ammonia as a source of
formaldehyde.
Examples of ami~e compounds applicable as amine catalysts are mono-
methylamine, triethylamine, ethanolamine, aniline, etc.
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11193~4
Typical examples of suitable alkali metal catalysts are
hydroxides and oxides of alkali metals such as sodium, potassium
and lithium, and hydroxides and oxides of alkali earth metals
such as barium, calcium and magnesium.
Typical examples of suitable lubricants are carnauba wax,
montan wax, paraffin wax, polyethylene wax, aliphatic amides such
as ethylene bis-stearamide, methylene bis-stearamide, oxystear-
amide, stearamides, linoleic amide, etc., aliphatic acid salts
such as calcium stearate, rosin, "Vinsol" resin (a complex ther-
moplastic mixture derived from southern pinewood comprising phen-
olic constituents in the form of substituted phenolic ethers,
polyphenols and phenols of high molecular weight), polyethylene-
glycol, polystyrene, talc, etc. The preferred lubricant is an
aliphatic amide or polyethylene wax.
Such a lubricant can be added prior to, during, or after the
preparation of the solid resole resin to obtain a lubricant-
containing solid resole resin. In order to achieve a homogeneous
dispersion, the lubricant is added preferably prior to or during
the reaction and preferably in the form of a dispersion. The
amount of lubricant employed may vary within a range of about 0.5
to about 10 parts by weight based on 100 parts by weight of the
solid resole resin, and preferably within a range of about 1 to
about 7 parts by weight to achieve a more satisfactory hot flow
and cure speed.
The following examples will serve to illustrate the process
for producing the lubricant-containing solid resole resin of the
present invent;on:
1) One mole of phenol and 1-3 moles of formaldehyde are
placed in a reactor, and an alkaline catalyst is added thereto
prior to the addition of a lubricant. The mixture thus obtained
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11~933~
is subjected to a condensation reaction for about 30 minutes to
2 hours at a temperature of 50C to 100C. (The lubricant is
preferably added after completion of the condensation reaction
or subsequently during the course of dehydration.) The reaction
mixture is then subjected to dehydration under reduced pressure
and at a temperature not exceeding 100C. to obtain a highly vis-
cous yellow or brownish-yellow resin, which is removed from the
reactor, rapidly cooled and crushed to obtain a lubricant-contain-
ing solid resole resin in solid state.
2) One mole of phenol and 1-3 moles of formaldehyde are
placed in a reactor and an alkaline catalyst is added. The mix-
ture obtained is subjected to a condensation reaction for about
30 minutes to 2 hours at a temperature of 50C. to 100C. A dis-
persion of a lubricant is then added to the reaction mixture with
a silane coupling agent, such as amino-silane or epoxysilane, and
rapidly dried to obtain a lubricant-containing solid resole resin
in flake or granular form.
3) A lubricant-containing solid resole resin can also be
obtained by incorporating a lubricant into a ;olid resole resin
modified by a modifier capable of reacting with formaldehyde such
as resorcin, urea, melamine, cashew nut shell oil, etc.
The novolac resin employed in the presen~ invention is a solid
condensate with a melting point of 70C to 100C prepared by the
reaction of phenol and formaldehyde in the presence of an organic
or inorganic acid catalyst such as oxalic acid, hydrochloric acid,
sulfuric acid, p-toluenesulfonic acid or zinc acetate, followed by
dehydration, said condensate being obtainable in flake, granular
or rod shaped forms. Furthermore, in addition to ordinary novolac
resins, so-called high ortho-novolac resins are also included in
the novolac resins employed in the present invention. ~he prepara-
tion of suitable high ortho-novolac resins is fully described in
US Patent 3,425,989, to Shepard et al.
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1~933~
The novolac resin thus obtained is a thermoplastic. Hexamine
is a representative curing agent for the novolac, but it is asso-
ciated, as explained in the foregoing, with certain disadvantages
such as defects in cast products and with disagreeable odors due
to the formation of gas. Also, as explained in the foregoing, a
solid resole resin is unsatisfactory as a curing agent due to its
slow cure speed, although it is not associated with the above-
mentioned disad~antages.
The amount of novolac employed should preferably be in the
range of about 1 part by weight to about 30 parts by weight based
on 100 parts by weight of the total amount of resin employed. The
upper limit can be increased to about 40 parts by weight if hexa-
mine is employed.
The resin-coated sand compositions of the present invention
can be prepared by placing sand, preheated to 120C. to 140C, i.e.
at an elevated temperature sufficient to fluidize the solid resin
into a muller, adding a novolac resin in flake, granular or rod
shaped form, further adding the lubricant containing solid resole
resin of the present invention, and if necessary, adding a small
amount of hexamine dissolved in the cooling water, and continuing
the mulling until the sand lumps are crushed, with the addition,
when required, of a small amount of cal~ium stearate. The total
resin content of the sand composition will preferably be in the
range of about 2 to about 5 parts by weight based on 100 parts by
weight of sand.
The present invention sill be further elucidated by the
following examples which are not intended to limit the scope there-
of. The amounts and percentages in the specification and claims
are represented by parts by weight and percent by we;ght unless
specifically defined otherwise.
EXAMPLE 1
2000 parts of phenol and 1350 parts of 37~ formalin were placed
in a reactor, and 15 parts of 10% hydrochloric acid was added. The
mixture was heated to 100C. and reacted under reflux for 3 hours.
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The reaction mixture was subjected, successively~ to dehydration
under a reduced pressure of 30-65 cmHg, then removed from the re-
actor when the internal temperature rose to 160C., allowed to
cool, and crushed to obtain a novolac resin in granular form.
EXAMPLE 2
2000 parts of phenol and 2590 parts of 37% formalin were placed
in a reactor, and 160 parts of a 28% ammonia solution was added.
The mixture was gradually heated to 100C and reacted under reflux
for 30 minutes. After the addition and mixing of 100 parts of
methylene bis-stearamide, the reaction mixture was subjected to de-
hydration under a reduced pressure of 30-50 cmHg, then removed from
the reactor when the internal temperature rose to 82C., rapidly
cooled and crushed to obtain a solid resole resin with a melting
point of 97C in granular form. The solid resole resin thus ob-
tained was found to have no blocking characteristics.
EXAMPLE 3
2000 Parts of phenol and 2590 parts of 37% formaline wereplaced in a reactor, and 160 parts of a 28% aqueous ammonia so-
lution and 60 parts of a 50% aqueous solution of sodium hydroxide
were added. The mixture was gradually heated to 100C and reacted
under reflux for 30 minutes. After the addition of 100 parts of
ethylene bis-stearamide and dispersion by admixture, the mixture
was subjected to dehydration under a reduced pressure~ then re-
moved from the reactor when the internal temperature reached 82C,
cooled rapidly and crushed to obtain a solid resole resin with a
melting point of 97C in granular form. The solid resole resin
thus obtained was found to have no blocking characteristics.
REFERENCE EXAMPLE 1
2000 Parts of phenol and 2590 parts of 37% formalin were placed in
a reactor, and 160 parts of a 28% aqueous ammonia solution was added. The
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mixture was gradually heated to 100C. and reacted under reflux for 30
minutes. The mixture was subjected successively, to dehydration under
a reduced pressure of 30-50 cmHg, removed from the reactor when the
internal temperature rose to 95C. cooled rapidly and crushed to obtain
a sol;d resole resin having a melting point of 85C. in granular form.
The conditions for preparation of resin-coated sand compositions,
together with the properties thereof, based on the novolac resin obtained
in Example 1 and the solid resole resin obtained in Examples 2 or 3, or
Reference Example l, in some cases with hexamine, are summarized in Table
l below.
The method of preparation of the resin-coated sand and the methods of
testing were as follows:
l. Preparation of resin-coated sand:
30 Kg of "Ayaragi" silica sand preheated to 130-140C. was placed
in a Whal mixer. A novolac resin (Example l) and a solid resole resin
were added and mulled with the silica sand for 40 seconds. 450 9 of water
(in which a predetermined amount of hexamine, if required, is dissolved)
was added, and mulling was continued until the sand particles were crushed.
After the addition of 20 9 of calcium stearate, the mixture was further
- mulled for 20 seconds, then removed from the mixer and aerated to obtain
the resin-coated sand.
2. Test methods:
Bending strength (kg/cm2) : JACT test method SM-l
Sticking point : JACT test method C-l
Hot tensile strength (kglcm2) : JACT test method SM-lO
From the results in the foregoing and in Table l, it will be observed
that, in order to achieve a higher strength and a faster cure (represented
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by the hot tensile strength value at 30 and 60 seconds), a lubricant-
containing solid resole resin prepared using a mixture of ammonia and an
alkal~ metal catalyst in combination is preferred to that prepared ~ith an
ammonia catalyst alone.
TABLE 7
RUN COtlTROL RU~
1 2 3 4 1 2 3
Cond~tlons of PreparatiOn of resin-cDated sand
Ex. 1 ~novolac) (9) 250250 3S0 350 250350 900
1 0 EX. 2 (solid resole resin
of the present in-
ventlon) (g)6iO
Ex. 3 (solid resole resin
~ of the present in-
1 5 vention) (9) - 650550 550
Ref. Ex. 1 (solid ammonia
resole res~n( (g) - - - - 650 650
Hexam1ne - - 27 45 - 45 135
~ropertles of restn-coated sand
2 0 Bending strength (kgjcm2) 44.9 46.5 43.J 42.5 35.5 33.2 43.3
Stick~ng point (~C.) 103102 104 104 100103 107
Hot tensile strength
(kg~cr )
30 sec. 1.8 2.4 1.7 1.8 1.1 t.4 2.1
2 5 60 sec.6.5 7.3 6.7 6.9 4.3 4.9 6.9
240 sec.19.5 22.1 20.3 19.8 14.5 15.3 20.6
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