In the present invention, formaldehyde is particularly preferably used. The urea in the furan resin composition of the present invention is urea not having undergone any condensation reaction with formaldehyde or furfuryl alcohol, and may be either urea remaining as unreacted or a separately added urea. By regulating the ph value in this range, the turbidity and precipitation of urea can be suppressed.
Regulation of the pH can be conducted with an alkali such as potassium hydroxide or sodium hydroxide or an acid such as acetic acid or oxalic acid. Although the reason that the effect of the present invention is demonstrated is not evident. The furan resin composition of the present invention can provide a binder for mold production containing the same. Further, the furan resin composition of the present invention can be used in combination with a hardener, to constitute a binder for mold production.
When the furan resin composition of the present invention is used to produce a mold, a hardener such as a conventionally known phosphoric acid compound or a sulfonic acid compound can be used as the hardener for curing the resin composition.
The content of the hardener in the binder is preferably 10 to 60 parts by weight, more preferably 15 to 40 parts by weight, based on parts by weight of the furan resin composition. As the phosphoric acid compound, use is made of phosphoric acid, condensed phosphoric acid, phosphates such as methyl phosphate and ethyl phosphate, and phosphates such as potassium phosphate and potassium hydrogen phosphate.
As the sulfonic acid compound, use is made of aliphatic sulfonic acid such as methane sulfonic acid and ethane sulfonic acid, aromatic sulfonic acid such as benzene sulfonic acid, toluene sulfonic acid, xylene sulfonic acid and phenol sulfonic acid, and inorganic acids such as sulfuric acid. The furan resin composition of the present invention can be used in combination with a hardener in order to serve as a binder, and can provide a binder for mold production not deteriorating curing properties such as mold strength and curing rate by further using at least one curing accelerator selected from the group consisting of a compound represented by the following general formula 1 [referred to hereinafter as curing accelerator 1 ] and a phenol derivative having a substituent group increasing the charge density in the ortho- or para-position relative to a hydroxyl group [referred to hereinafter as curing accelerator 2 ],.
The curing accelerator 1 includes 2,5-bishydroxymethyl furan, 2,5-bismethoxymethyl furan, 2,5-bisethoxymethyl furan, 2-hydroxymethylmethoxymethyl furan, 2-hydroxymethylethoxymethyl furan, and 2-methoxymethylmethoxymethyl furan.
In particular, 2,5-bishydroxymethyl furan is preferably used. This is because 2,5-bishydroxymethyl furan is more highly reactive than 2,5-bismethoxymethyl furan or 2,5-bisethoxymethyl furan and accelerates the curing reaction of a binder comprising furfuryl alcohol polycondensed as a major component. The reason for the high reactivity of 2,5-bishydroxymethyl furan is that its hydroxy group constitutes to the curing reaction. From the viewpoint of an effect of improving the initial strength of a mold and the solubility of the curing accelerator 1 in the furan resin composition, the curing accelerator 1 is used preferably in an amount of 0.
The curing accelerator 2 is a compound having a substituent group increasing the charge density in the ortho- or para-position relative to a hydroxyl group of phenol, and examples include resorcinol, cresol, hydroquinone, phloroglucinol, methylene bisphenol etc. In particular, resorcinol and phloroglucinol are preferable. From the viewpoint of an effect of improving the initial strength of a mold and the solubility of the curing accelerator 2 in a binder, the curing accelerator 2 is contained preferably in an amount of 1.
Further, a binder constituted by incorporating the furan resin composition of the present invention, the specific curing accelerator described above and the hardener described above can be obtained. The respective components of the binder described above are admixed with a refractory granular material to give kneaded sand sand composition for mold production. As the refractory granular material, it is possible to employ a conventionally known refractory granular material, for example new sand or reclaimed sand such as silica sand based on quartz, chromite sand, zircon sand, olivine sand, alumina sand, mullite sand and synthetic mullite sand.
As the reclaimed sand, sand obtained by usual a mechanical attrition or calcine system is used, but sand reclaimed by the attrition system is preferable because it is produced in higher yield, is economically excellent and is generally used. For obtaining the mulled sand the sand composition for mold production , a silane coupling agent in addition to the binder of the present invention may be added for the purpose of further improving the strength of the resulting mold.
The silane coupling agent may be used after incorporation into the binder. The sand composition for mold production obtained in this manner can be used to produce a mold by a general method of producing a self-curing mold. That is, the sand composition for mold production is charged into a predetermined wooden patterns, and the compounded and mulled furan resin composition for mold production, preferably used in combination with the specific curing accelerator described above, is cured by the action of a hardener or a curing composition, whereby a mold can be obtained.
For mulling mod production, curing temperature etc. The present invention is described in more detail by reference to the Examples. The Examples illustrate the present invention and are not intended to limit the present invention. The results of the compression strength MPa of the test piece, as determined after 30 minutes and after 24 hours by a method described in JIS Z are shown in Table 1.
Compound weight weight minutes hours molding casting composition Example 1 97 3 9 — 0 50 0. The weight parts of the curing accelerator and the hardener in the table refer to ratios relative to parts by weight of the furan resin composition. The pH of the furan resin composition was regulated with potassium hydroxide and oxalic acid. The invention claimed is: 1. The binder for production of molds according to claim 1 , which further comprises at least one curing accelerator selected from the group consisting of a compound represented by the following general formula 1 and a phenol derivative having a substituent group increasing the charge density in the ortho- or para-position relative to a hydroxyl group of the phenol,.
A method of producing molds, which comprises using the binder for production of molds according to claim 1 or 2. The binder for production of molds according to claim 1 , wherein said urea remaining as unreacted or a separately added urea is an urea not having undergone any condensation reaction with formaldehyde or furfuryl alcohol. The binder for production of molds according to claim 1 , wherein the urea is an unreacted urea. The binder for production of molds according to claim 1 , wherein the pH range is 7.
USB2 en. EPB1 en. At such lower temperatures, phenolic novolak resins frequently do not burn out completely, with the result that cores or portions thereof are frequently left in the casting. It is accordingly an object of the present invention to provide a resin for use in coating foundry sand to provide a resin-coated sand having improved shakeout and collapsibility characteristics.
It is a more specific object of this invention to produce and to provide a method for producing a furan-modified phenolic resin for use in coating foundry sands which is capable of being formed into cores highly susceptible to complete degradation, even at lower casting temperatures. The concepts of the present invention reside in a phenolic novolak resin which has been modified to incorporate in the resin a furan.
It has been unexpectedly found that phenolic novolak resins which incorporate furan therein can be used in coating foundry sands which in turn are ideally suited for use in the shell process to produce cores and molds having significantly improved shakeout and collapsibility characteristics.
The present invention also realtes to a process for forming foundry cores and molds comprising the steps of:. The resin of this invention has been found to provide extremely good tensile strengths, and improved collapsibility and shakeout characteristics, even when used in the casting of lower melting metals. In the practice of this invention, the modified phenolic novolak resins of the invention are produced in one of two processes.
In one type of process, a furan-containing compound, such as furfuryl alcohol or furfural is reacted with a phenolic compound in a first step to produce a furan-phenolic intermediate.
That intermediate is then reacted in a second step with an aldehyde to produce the resin. In the most preferred practice of this invention, the furan-modified phenolic novolak resins are produced by reacting, in a first step, furfuryl alcohol with a phenol at an acid pH, the mole ratio of the furfuryl alcohol to the phenol being within the range of 0.
In the second step, the furfuryl-phenolic intermediate produced in the first step is in turn reacted with a C 1 to C 3 aliphatic aldehyde, the mole ratio in the latter step being 0. The resins produced in this preferred embodiment of the invention are ideally suited for use in the manufacture of resin-coated sands. Such resin coated sands can in turn be used in the manufacture of foundry cores and molds having greatly improved collapsibility and shakeout characteristics.
It is an important concept of the preferred practice of this invention that the reaction between the furfuryl alcohol and the phenol to form the furfurylphenol intermediate and the reaction between that intermediate and the aldehyde be carried out at an acid pH. The resins described in that patent are of the resole type wherein the ratio of formaldehyde to phenol is greater than 1 to produce a thermosetting resin.
As is described in the foregoing patent, it is necessary, to secure adhesion to sand, to contact the resin and the sand with an additional quantity of furfuryl alcohol and an acid curing agent to securely bond the resulting resin to the grains of sand. This additional step is not only complex from the standpoint of foundry operations, but is undesirable for the further reason that it represents an expensive and inefficient operation when used on a commercial scale. In contrast, the resins of the present invention are, of necessity, solid resins which can be placed in the liquid form by dissolution in the appropriate solvent.
They are of the novolak type wherein the ratio of aldehyde to phenol is less than 1. As a result, the resins of this invention are thermoplastic and can be converted to a thermosetting form by addition of a curing agent. In Canadian Pat.
The resulting intermediate can then be further modified by reaction with furfural or formaldehyde. The resin produced, which is other than a novolak resin, is used for different applications. As used herein, the term "acid pH" refers to and includes a reaction mixture in which the pH is below 6, and preferably below 5.
The reaction is therefore usually carried out in the presence of an acid catalyst which serves to adjust the pH of the reaction mixture to the desired level. Such catalysts are, of themselves, very well known in promoting condensation reactions of this type.
Included are sulfuric acid, hydrochloric acid, sulfamic acid, oxalic acid and phenol sulfonic acid, although a variety of other strong acids may be used in their stead. In the practice of this invention, use is preferably made of phenol, although all or a portion of the phenol in the reaction mixture can be replaced by small quantities of substituted phenols such as o-cresol, t-butylphenol, and the like.
Phenol is nevertheless preferred as the phenolic reactant. Similarly, a number of lower aliphatic aldehydes, and preferably those containing carbon atoms are employed in the second step of the reaction.
Suitable aldehydes include formaldehyde, acetaldehyde, propionaldehyde and paraformaldehyde. Best results are usually obtained with formaldehyde. The temperature of the reaction which occurs in either the first or the second step is not critical and can be varied within fairly wide limits.
In general, lower reaction temperatures necessitate longer reaction times, while higher reaction temperatures facilitate shorter reaction times. At these temperatures, the reaction is quite rapid, and thus can be carried out in any conventional reaction vessel. While it is not necessary to employ a solvent for the reaction, it is generally desirable to employ aqueous reactants and a catalyst dissolved in water, and thus water serves as an insert reaction medium.
If desired, other inert solvents can be employed, although there is frequently no benefit derived from their use. The second reaction between the aldehyde and the intermediate produced by reaction of furfuryl alcohol and the phenol can likewise be carried out at varying temperatures, depending somewhat on the reaction time. At that temperature, the reaction is rapid and easily controlled. After the reaction is completed, the furan-modified phenolic novolak resin is separated from the reaction mixture.
While not equivalent to the preferred method described in detail, it is also possible to introduce furan into a phenolic novolak resin by reaction of furfural and phenol at an acid pH in a first step, and then, in a second step, adding formaldehyde and continuing the reaction at an acid pH.
While the use of furfural does serve to introduce furan into the resin, it does not react readily, and the first step of the reaction is difficult to control.
As a result, the finished product contains unreacted furfural, and thus has a bad odor and is toxic. In addition, resins produced in this way provide low tensile strengths in foundry applications according to the shell process. One variation on the method described above is that the first step of the reaction can be carried out at a basic pH. In that embodiment, the reaction of the intermediate formed with the aldehyde can be conducted at either an acid or basic pH.
However, the variation has the same disadvantages as described above. In addition, this variation requires the use of high reaction temperatures. Alternatively, it is possible to react phenol and formaldehyde at a basic pH to produce a resole resin, and then react the resole resin with furfuryl alcohol at an acid pH to form a furan-modified resole resin.
In all of the variations described above for incorporating furan into the resin, the overall proportions of the furan-containing compound furfuryl alcohol or furfural , the phenolic compound and the lower aliphatic aldehyde are generally the same as described above.
Generally, the process of coating sand with the resins of this invention utilizes coating methods well known to those skilled in the art.
As noted, the resins produced in accordance with the concepts of this invention are in solid form, but can be rendered liquid by dissolution in a solvent or mixture of solvents such as methanol, ethanol, acetone, methyl ethyl ketone, or mixtures of those solvents in water. There are presently three coating methods currently used to produce resin-coated sands for foundry applications.
In the first of these methods, referred to as the cold coating method, the resin, dissolved in a suitable solvent, is blended with the curing agent and then mixed with sand at room temperature.
The mixing operation is continued until the solvent has evaporated to deposit the solid resin on the grains of sand.
In this particular method, no heating of any of the components is required, and thus this particular method requires somewhat longer mixing times.
In the second method, the so-called warm coating method, the solid resin is dissolved in a solvent and mixed with the curing agent. Since the sand has been heated to an elevated temperature, the time required for evaporation of the solvent is reduced as compared to the cold coating method. The elevated temperature to which the sand has been heated is sufficient to melt the flakes of resin to thereby coat the sand. This method, referred to as the hot coating method, then involves quenching the resin-coated sand with a solution of curing agent dissolved in an appropriate solvent, usually water, to quench the sand and add curing agent to the resulting resin-coated sand.
In each case, the resulting resin-coated sand is free flowing and contains a curing agent to convert the thermoplastic furan-modified phenolic novolak resin to a hard, rigid potentially thermosetting resin. Preferred curing agents are amine curing agents such as hexamethylene tetramine, although a number of other curing agents well known to those skilled in the art may be used instead. As has become common practice in the foundry art, coated sand compositions employed in the practice of this invention preferably are formulated to contain a release agent to facilitate removal of cores and molds produced therefrom from the core base.
Such release agents also improve core density and increase tensile strengths. The coated sand compositions of this invention can be used with or without such release agents. Representative release agents include metal stearates such as calcium stearate, zinc stearate and the like; fatty amides such as the bistearoylamide of ethylene diamine; silicones and other art recognized release agents.
Thye may be added to the muller during the sand coating process, or they may be dissolved or dispersed in the resin prior to coating the resin or sand. In addition to such release agents, the coated sand compositions of this invention can also include other conventional additives frequently used. The use of such additional additives depends largely on the specific casting requirements of a given application.
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