JP5036362B2 - Urethane curable organic binder for mold, foundry sand composition and mold obtained using the same - Google Patents

Description

  The present invention relates to an organic binder for a mold used for molding a phenol urethane mold used in sand mold casting, and a foundry sand composition and a mold obtained using the same.

  As is well known, phenolic urethane molds (gas-curing molds and self-hardening molds), one of the typical organic molds applied to sand casting, are the active ingredients of two-part organic binders. Is a gas-curing mold that is mass-produced by the so-called cold box method, which is molded using a polyaddition reaction (urethane reaction) between a phenolic resin and a polyisocyanate compound, and does not require heating during molding. In addition, self-hardening molds that are not mass-produced by the room temperature self-hardening method are widely used.

  More specifically, the gas curing mold is usually a urethane curable organic binder (generally a two-component binder composed of a phenol resin solution and a polyisocyanate solution using an organic solvent as a solvent) and After kneading the foundry sand with a mixer to produce a foundry sand composition in which the surface of the foundry sand is coated with an organic binder, this is blown into a mold and shaped. It is manufactured by passing a curing catalyst gas such as an amine-based gas through this and curing it instantaneously. On the other hand, the self-hardening mold is prepared by adding a molding sand composition obtained by adding an appropriate curing catalyst at the same time when kneading the urethane curable organic binder and casting sand to a molding mold immediately after kneading. It is manufactured by shaping by hand filling or pouring and allowing it to stand at room temperature for a long time to cure.

  Such phenol-urethane molds have been widely used for casting products made of various metals such as aluminum alloys, magnesium alloys, cast iron, cast steel, etc. Compared to a shell mold (a thermosetting mold produced by the shell mold method) that is one of the system molds, it is more susceptible to heat during casting and has poor heat resistance. For example, when the pouring temperature is high, There is a problem that sand on the mold surface flows during pouring, and casting defects such as squaring are likely to occur, and improvement in heat resistance is strongly demanded in the field of phenol urethane molds.

  For this reason, in order to improve the heat resistance of the mold, although measures such as using synthetic cast sand with excellent fire resistance such as synthetic mullite sand have been taken, it cannot be said that it is still sufficient, and further improvement Is demanded.

  In addition, the phenol-urethane-based mold has a greater “priced property” (flexibility of the mold; the ability of the mold to deform with the shrinkage when the molten metal solidifies and shrinks) than the shell mold, For example, when casting a casting product having a relatively large shrinkage rate, it is possible to prevent the mold from flexing following the shrinkage of the molten metal and causing defects such as cracks in the casting. When casting a cast product of size, the casting mold may bend greatly from where a large amount of molten metal is poured, and the resulting cast product may warp, making it impossible to ensure good dimensional accuracy of the product. . Therefore, depending on the size, shape, material, casting method and the like of the target casting product, in other words, it is also required to control the nature according to the application of the mold.

  However, depending on the application of the mold and the like, if it is attempted to control the nature, the strength in the hot state is lowered, and the heat resistance (thermal stability) is further deteriorated. Specifically, when the molecular weight of the phenol resin, which is the active ingredient of the organic binder, is increased (polymerized) in order to reduce the nature, the resulting mold becomes rigid and the mold is bent. Although the amount is reduced, generally the strength of the mold is lowered, so that the strength in the hot state is also lowered. On the other hand, if the amount of the organic solvent constituting the organic binder is increased or the molecular weight of the phenol resin is reduced in order to increase the properties, the resulting mold will bend easily, but the degree of polymerization of the phenol resin will increase. As a result, the mold itself becomes thermally weak.

  Therefore, in designing the mold, it is extremely difficult to control the quality of the mold required according to the size, shape, material, casting method, etc. of the target casting product and to improve the heat resistance. In general, in the phenol-urethane mold, the heat resistance was sacrificed more or less when controlling the sex.

  By the way, Japanese Patent Laid-Open No. 61-255925 (Patent Document 1) discloses blocked isocyanate for casting and resin-coated sand for casting using the same. However, such resin-coated sand for casting is urethane. Disintegration of cast molds used for the manufacture of castings with relatively low casting temperatures, such as aluminum castings and alloy castings, not for phenol molds but for thermosetting molds (shell molds) The goal is to improve sex.

JP-A 61-255925

  Here, the present invention has been made in the background of such circumstances, and the problem to be solved is not only excellent heat resistance but also the expected property of the phenol-urethane mold. The urethane curable organic binder for molds that can also provide the properties, the molding sand composition obtained by using the urethane curable organic binder for molds, and the casting sand composition It is to provide a mold.

  As a result of intensive studies on the organic binder, the present inventor has found that the above-mentioned problems can be solved by incorporating a specific blocked isocyanate compound, and the present invention has been completed. It was.

  That is, the present invention is a urethane-curing organic binder for molds used for the molding of phenol-urethane molds, and reacts an isocyanate compound with a monoalcohol together with a phenol resin, a polyisocyanate compound, and an organic solvent. The gist of the present invention is a urethane-curable organic binder for molds, which contains the blocked isocyanate compound obtained in this manner.

  The present invention also provides a casting sand composition obtained by coating a molding sand with the urethane curable organic binder for a mold as described above, and a mold obtained by molding and curing the casting sand composition ( Gas curing molds and self-hardening molds) also have their gist.

  Thus, in the urethane curable organic binder for molds according to the present invention, in addition to the phenol resin, polyisocyanate compound and organic solvent that have been widely used conventionally as a constituent of the organic binder, In the case of a mold formed using this urethane curable organic binder for molds, it contains a blocked isocyanate compound obtained by reacting an isocyanate compound with a monoalcohol. The heat resistance (thermal stability) can be improved extremely effectively without impairing the mold, and this improvement in heat resistance eliminates the occurrence of casting defects such as squaring and is advantageous for casting products that have no casting surface defects. Can be manufactured.

  In addition, the blocked isocyanate compound not only improves the heat resistance of the template, but also affects the properties of the template. Depending on the type of the blocked isocyanate compound used, the properties of the template are improved. It grows and shrinks. For this reason, by selecting a specific blocked isocyanate compound as appropriate, it becomes possible to obtain better properties depending on the application of the template. In other words, depending on the size, shape, material, casting method, and the like of the target casting product, the required properties of the mold are different, but according to the present invention, the blocked isocyanate compound is appropriately selected. This makes it possible to control the nature of the mold.

  Therefore, in the mold obtained by using the urethane curable organic binder for mold according to the present invention, not only excellent heat resistance but also desired flexibility can be realized. A casting product without defects can be advantageously produced.

  By the way, in the urethane curable organic binder for molds according to the present invention (hereinafter simply referred to as “organic binder”), the phenol resin used as one of the active ingredients is not particularly limited. Conventionally, various known phenol resins that are conventionally used when molding a phenol-urethane mold are appropriately used. Specifically, in the presence of the reaction catalyst, the phenols and aldehydes are adjusted so that the aldehydes are in a ratio of, for example, about 0.5 to 3.0 moles with respect to 1 mole of the phenols. At least one of benzyl ether type phenol resin, resol type phenol resin, novolac type phenol resin, modified phenolic resin thereof, and mixtures thereof obtained by addition / condensation reaction and soluble in an organic solvent. Are appropriately selected and used.

  The reaction catalyst used in the production of the phenol resin is not particularly limited, and various catalysts such as an acidic catalyst, a basic catalyst, and a combination catalyst thereof are appropriately selected according to the desired phenol resin. To be used. Specifically, in the production of a benzyl ether type phenol resin, for example, it has a divalent metal element such as lead naphthenate, zinc naphthenate, lead acetate, zinc chloride, zinc acetate, zinc borate, lead oxide and the like. In addition to the metal salt, a combination of an acidic catalyst and a basic catalyst capable of forming such a metal salt can be mentioned. Such a metal salt is generally 0.01% with respect to 100 parts by mass of phenols. It is used at a ratio of ˜5 parts by mass. Moreover, as a reaction catalyst used in manufacture of another phenol resin seed | species, sodium hydroxide, potassium hydroxide, ammonia, oxalic acid, a sulfuric acid, hydrochloric acid etc. can be illustrated, for example.

  Examples of the phenols used in the production of the phenol resin include, in addition to phenol, alkylphenols such as cresol, xylenol, p-tert-butylphenol, and nonylphenol, polyhydric phenols such as resorcinol, bisphenol F, bisphenol A, and the like. A mixture of these may be used, and one of them may be used alone or in combination of two or more. On the other hand, examples of aldehydes include formaldehyde, formalin, paraformaldehyde, polyoxymethylene, glyoxal, furfural, and mixtures thereof. One of them is used alone, or two or more are combined. Used.

  Furthermore, when a modified phenol resin is used as the phenol resin, examples of the modifier (modifier) used in the production thereof include alkyd resins, epoxy resins, melamine resins, urea resins, xylene resins, vinyl acetate resins, Polyamide resins, urea compounds, melamine compounds, epoxy compounds, furfuryl alcohol, polyvinyl alcohol, urea, amides, linseed oil, cashew nut shell liquid, rosin, starches, monosaccharides, etc. One of the agents (denaturing agents) may be used alone or in combination of two or more.

  On the other hand, in the organic binder according to the present invention, the polyisocyanate compound used as another active ingredient is chemically added to the foundry sand by a polyaddition reaction with the active hydrogen of the phenol resin as described above. It is a compound having two or more isocyanate groups in the molecule that can be bonded to develop strength. Specific examples of such polyisocyanate compounds include aromatic polyisocyanates such as diphenylmethane diisocyanate (pure MDI), polymethylene polyphenylene polyisocyanate (polymeric MDI), tolylene diisocyanate (TDI), hexamethylene diisocyanate, and the like. In addition to alicyclic polyisocyanates such as aliphatic polyisocyanates and 4,4′-dicyclohexylmethane diisocyanate, prepolymers having two or more isocyanate groups obtained by reacting these polyisocyanate compounds with polyols are conventionally known. The various polyisocyanates can be mentioned. These may be used alone or in combination of two or more.

  In the organic binder according to the present invention, the mixing ratio of the phenol resin and the polyisocyanate compound is not particularly limited, but generally, the phenol resin and the polyisocyanate compound which are active ingredients are in mass. It is used so that it may be in the range of phenol resin: polyisocyanate compound = 80: 20 to 20:80 on the basis.

  And, from the viewpoints of lowering the viscosity of the organic binder, compatibility with the polyisocyanate compound or the phenol resin, covering property to molding sand, physical properties of the mold, etc. Used by dissolving in an organic solvent. Specifically, the phenol resin is generally dissolved and diluted in an organic solvent that is a combination of a polar organic solvent and a nonpolar organic solvent, and has a concentration of about 30 to 80% by mass (hereinafter referred to as “phenol”). It is prepared and used in “resin solution”). The polyisocyanate compound is generally dissolved in a nonpolar organic solvent and prepared and used in a solution having a concentration of about 40 to 90% by mass. It is not necessary to dissolve in a solvent, and it can be used as it is. Therefore, hereinafter, a polyisocyanate compound stock solution and a solution obtained by dissolving a polyisocyanate compound in an organic solvent are referred to as a “polyisocyanate solution”.

  Here, the organic solvent is not particularly limited as long as it is non-reactive with the polyisocyanate compound and is a good solvent for the solute (phenol resin or polyisocyanate compound) to be dissolved. However, in general, a phenolic resin is used in combination with a polar solvent for dissolving the phenolic resin and an amount of a nonpolar solvent that does not cause separation of the phenolic resin. On the other hand, a nonpolar solvent is used for the polyisocyanate compound.

  Specifically, as the polar solvent, for example, aliphatic carboxylic acid ester, among them, particularly from the viewpoint of environmental safety, dicarboxylic acid methyl ester mixture (for example, trade name: DBE, manufactured by DuPont, glutaric acid Dicarboxylic acid alkyl esters such as dimethyl, dimethyl adipate and dimethyl succinate), vegetable oils such as rapeseed oil methyl ester, ethyl oleate, ethyl palmitate, mixtures thereof, esters such as fatty acid monoesters, etc. Other examples include ketones such as isophorone, ethers such as isopropyl ether, and furfuryl alcohol. Examples of the nonpolar solvent include petroleum hydrocarbons such as paraffins, naphthenes, and alkylbenzenes. Specific examples include ipsol 100 and ipsol 150 (trade name, manufactured by Idemitsu Kosan Co., Ltd.), HAWS ( Trade names, manufactured by Shell Chemicals Japan Co., Ltd., Solvesso 100 (trade name, manufactured by ExxonMobil Corp.) and the like can be exemplified.

  And in the organic binder according to the present invention, in addition to the above-mentioned phenol resin, polyisocyanate compound and organic solvent, further contains a blocked isocyanate compound obtained by reacting an isocyanate compound with a monoalcohol. However, by using such a blocked isocyanate compound, the heat resistance (thermal stability) of the mold is extremely effectively improved without losing the mold strength. Thus, the occurrence of casting defects such as squaring can be prevented, and a casting product free from casting surface defects can be advantageously manufactured. Moreover, since such a blocked isocyanate compound affects not only the heat resistance but also the properties of the template, by appropriately selecting a specific blocked isocyanate compound, it is possible to obtain a desired one according to the intended use of the template. It becomes possible to realize more sex.

  Here, the blocked isocyanate compound is preferably an isocyanate compound having one or more isocyanate groups (NCO groups) in the molecule and monoalcohols having one hydroxyl group (OH group) in the molecule. Is a compound having a urethane bond obtained by reacting an OH group of a monoalcohol with a ratio of about 1 mol (NCO group / OH group = about 1) to 1 mol of NCO group of the isocyanate compound, in other words, This is a compound in which the NCO group of the isocyanate compound is blocked (protected) by the OH group of the monoalcohol. In addition, although unreacted isocyanate compound (unreacted NCO group) and unreacted monoalcohol (unreacted OH group) may remain in the compound, in particular, unreacted monoalcohol has a molding sand composition. It is desirable to reduce it as much as possible because it may adversely affect the pot life of the item. In addition, when the reaction between the isocyanate compound and the monoalcohol is slow, it can be used as a reaction catalyst for a known divalent metal salt such as dibutyltin dilaurate. When the catalyst remains, it accelerates the hardening of the foundry sand composition to be described later and adversely affects the pot life. Therefore, it is desirable to remove it before use.

  Here, monoalcohols used for the production of the blocked isocyanate compound as described above are not particularly limited, and specific examples thereof include methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso -Butanol, 2-butanol, t-butanol, n-amyl alcohol, iso-amyl alcohol, diethyl carbinol, n-hexanol, 2-methyl-1-pentanol, 2-ethyl-1-butanol, n-heptanol, Examples include octyl alcohol, nonyl alcohol, decyl alcohol, lauryl alcohol, oleyl alcohol, stearyl alcohol, methoxymethanol, ethoxymethanol, methyl cellosolve, ethyl cellosolve, and butyl cellosolve. In a blocked isocyanate compound produced from a monoalcohol having one hydroxyl group in the molecule and an isocyanate compound, which will be described later, although it varies depending on the type of isocyanate compound to be combined, When a blocked isocyanate compound produced from alcohols is used, the displacement of the template at the time of heat load tends to be larger than that of a conventional one not containing a blocked isocyanate compound, which is greater. While a template can be obtained, when a blocked isocyanate compound generated from monoalcohols having a large number of carbon atoms is used, the template displacement during thermal load tends to be small, and the template is less prone. That is, a mold having rigidity can be obtained (see FIG. 3).Therefore, by appropriately selecting monoalcohols and isocyanate compounds constituting the blocked isocyanate compound, it becomes possible to control the properties of the template. In short, if a blocked isocyanate compound is selected in accordance with the properties required for the mold, not only the heat resistance is improved, but a mold having more desired properties can be obtained.

  On the other hand, the isocyanate compound used in the production of the blocked isocyanate compound as described above may be an isocyanate compound having one or more NCO groups, and is one of the active ingredients in the organic binder according to the present invention as described above. In addition to the polyisocyanate compound, a monoisocyanate compound such as an alkyl monoisocyanate can be used. Among these, hexamethylene diisocyanate, tolylene diisocyanate (TDI), diphenylmethane diisocyanate (pure MDI), polymethylene polyphenylene polyisocyanate (polymeric MDI) and the like are particularly preferable from the viewpoint of availability of raw materials and ease of synthesis. Used for.

  In the organic binder according to the present invention, one kind of blocked isocyanate compounds obtained by reacting the monoalcohols and isocyanate compounds as described above is used alone, or two or more kinds are used in combination. It is done. At that time, the blocked isocyanate is added to and mixed with one or both of the phenol resin solution and the polyisocyanate solution, depending on the type and presence / absence of an unreacted group (NCO group, OH group), Alternatively, it is dissolved or dispersed in an appropriate organic solvent, added to a phenol resin condensation product, or directly added to the foundry sand during the production of the foundry sand composition described below. It is used. Among these, the blocked isocyanate compound has a high affinity for the polyisocyanate solution, so that it is desirable that the blocked isocyanate compound be added to and mixed with the polyisocyanate solution and, if necessary, dissolved by heating or the like. Moreover, although such a blocked isocyanate compound is blended at a ratio of 0.001 part by mass or more with respect to 100 parts by mass of the polyisocyanate compound contained in the polyisocyanate solution, the effect is expressed. Effectively, the blending amount is preferably set in a range of 0.1 to 10 parts by mass with respect to 100 parts by mass of the polyisocyanate compound. Further, from the viewpoint of cost, 0.3 to 5 is preferable. It is even more preferable that the amount is set within a range of mass parts.

  Thus, the organic binder according to the present invention is formed by the specific blocked isocyanate compound as described above, the phenol resin solution and the polyisocyanate solution forming phenol urethane. In addition, if necessary, the agent may be a known long-life extender, silane coupling agent, mold release agent, anti-drying agent and the like conventionally used for urethane curable organic binders for molds. Various additives can be appropriately selected and blended in a quantitative range that does not impair the effects of the present invention.

  For example, among the various additives as described above, the pot life extender (curing retarder) is used to suppress the urethanization reaction and extend the pot life of the foundry sand composition. Specific examples include isophthalic acid chloride, salicylic acid, benzoic acid, phosphoric acid, acidic phosphate ester, phosphorus chloride, boric acid and the like.

  Further, the silane coupling agent is used for preventing deterioration of the mold strength in a humid environment and for improving the adhesion between the resin component of the organic binder and the foundry sand. N-β (aminoethyl) -γ-aminopropyltrimethoxysilane, amino-based silanes such as γ-aminopropyltriethoxysilane, and epoxy-based silanes such as γ-glycidoxypropyltrimethoxysilane. it can. As a usage-amount of this silane coupling agent, generally the ratio used as 0.01-5 mass parts with respect to 100 mass parts of a phenol resin, Preferably it is about 0.05-2.5 mass parts is employ | adopted.

  Thus, the organic binder according to the present invention is constituted by the various components as described above, and a phenolurethane mold (a gas curing mold or a self-hardening mold) is formed using this organic binder. is there.

  First, the gas curing mold will be described. When molding a gas-curing mold, first, an organic binder is kneaded into the foundry sand, whereby an organic binder is coated on the surface of the foundry sand (binder-coated sand). ) Will be manufactured. That is, a phenol resin solution, a polyisocyanate solution, a specific blocked isocyanate compound, and, if necessary, other various additives are sufficiently kneaded and mixed with the foundry sand as an organic binder. As a result, a foundry sand composition having an organic binder coated on the surface is produced. At this time, the kneading operation is desirably performed at a temperature in the range of −10 to 50 ° C. using a continuous or batch mixer similar to the conventional one.

  Moreover, when manufacturing this foundry sand composition, the phenol resin solution and the polyisocyanate solution constituting the organic binder are from the point where the polyaddition reaction (urethanization reaction) gradually proceeds from the stage of mixing them. It is prepared separately and prepared in advance, and is usually mixed at the same time or every other time at the time of kneading with foundry sand. Further, the blocked isocyanate compound is added and used as described above, while the various additives are used by being added to one or both of the separately prepared phenol resin solution and polyisocyanate solution. Or dissolved or dispersed in a suitable organic solvent, or added to a condensation product of a phenol resin.

  Subsequently, the foundry sand composition obtained as described above is filled and shaped with pressurized air in a mold such as a mold giving a desired mold shape. Then, by passing a curing catalyst gas through the shaped product, the curing reaction of the mold (casting sand composition) is promoted, and the mold is cured to a strength at which the mold can be removed. Thereafter, the mold is removed from the mold to produce a gas curing mold. As the curing catalyst gas, for example, tertiary amines such as triethylamine, dimethylethylamine, dimethylisopropylamine are preferably used. In addition to such tertiary amines, cyclic nitrogen compounds, pyridine, N- Ethylmorpholine or the like can also be used, and at least one of them is selected and used in a usual quantitative range.

  Next, the self-hardening mold will be described. When molding a self-hardening mold, as in the case of the gas-curing mold, first, a casting sand composition in which the casting sand surface is coated with an organic binder is produced. The foundry sand composition is premixed with a curing catalyst together with the organic binder, and this is different from the gas-cured foundry sand composition. Therefore, the obtained foundry sand composition is filled by hand or pouring into a molding frame such as a wooden mold that gives a desired mold shape immediately after the curing proceeds rapidly by the contained curing catalyst. After being shaped, curing is promoted by allowing it to stand at room temperature for several hours to 24 hours. Then, a self-hardening mold is manufactured by releasing the forming frame. In this case, examples of the curing catalyst include bases, amines, metal ions and the like that are usually used in the known Ashland method, and at least one of them is selected to obtain a normal quantitative amount. Used in a range.

  In the preparation of the foundry sand composition, the organic binder can be appropriately used mainly in an amount necessary for obtaining a mold having a desired strength. Preferably, the phenol resin which is an active ingredient is used. Alternatively, the phenol resin solution and the polyisocyanate compound are blended so that the blending amount of the polyisocyanate compound is 0.01 to 5.0 parts by mass, more preferably 0.1 to 2.0 parts by mass with respect to 100 parts by mass of the foundry sand. An isocyanate solution is used.

  The casting sand used in the present invention may be natural sand or artificial sand as long as it has fire resistance and particle size that can be used as mold sand, and is particularly limited. is not. Specifically, for example, silica sand, olivine sand, zircon sand, chromite sand, alumina sand, ferrochrome slag, ferronickel slag, converter slag, mullite artificial particles (for example, obtained from ITOCHU CERATECH CORPORATION) In addition to fresh sand such as “Cerabeads”), these recovered sand and reclaimed sand can be mentioned. And one of these can be used alone or in combination of two or more. Among them, in view of the effect of imparting heat resistance to the mold and the regeneration treatment after collecting the mold, it is spherical. Mullite-based artificial particles having excellent crush resistance are more suitably used.

  Thus, gas-cured molds and self-hardened molds manufactured as described above have improved heat resistance and are more suitable than expected, such as aluminum alloys, magnesium alloys, cast iron, cast steel, etc. Therefore, it is advantageously used for casting of casting products of various sizes and shapes made of various metals.

  Some examples of the present invention will be shown below to clarify the present invention more specifically. However, the present invention is not limited by the description of such examples. Needless to say. In addition to the following examples, the present invention includes various changes and modifications based on the knowledge of those skilled in the art without departing from the spirit of the present invention, in addition to the specific description described above. It should be understood that improvements and the like can be added. In this example, the measurement of the mold strength and the hot creep test immediately after cutting and after 24 hours was performed by the following test methods.

(1) Measurement of mold strength After casting sand composition immediately after kneading is put into a sand magazine of a cold box molding machine, this casting sand composition is filled in a mold for bending strength test piece molding, By bending a triethylamine as a curing catalyst, a bending strength test piece having a width of 30 mm, a length of 85 mm, and a thickness of 10 mm was produced. The filling conditions were pressure: 0.3 MPa for 3 seconds, while triethylamine gassing and air purge conditions were respectively pressure: 0.3 MPa for 10 seconds. Then, the obtained bending strength test piece is used immediately after molding or after standing at room temperature for 24 hours, and each bending strength (N / cm ² ) is set to a small compression bending tester SC200D manufactured by Takachiho Seiki Co., Ltd. The former was used as the mold strength immediately after the mold removal, and the latter was used as the mold strength after 24 hours from the mold removal. Then, the mold strength immediately after the mold release and the mold strength after 24 hours from the mold release were measured twice, and the average value was obtained.

(2) Hot creep test First, as shown in FIG. 1, a cylindrical hot creep measurement test piece (30 mmφ × 50 mmH) with a slit was made into a CB machine molding machine (blow: 0.3 MPa × 1) manufactured by Toko Seisakusho. Second, gassing: 0.16 MPa × 1 second, purge: 0.2 MPa × 15 seconds). Then, the obtained test piece is placed in a horizontal casting sand thermal dilatometer manufactured by Ozawa Science Co., Ltd. having a movable tubular electric furnace as shown in FIG. 2 so that the slit opening of the test piece is downward. Mounted horizontally. Thereafter, while constantly applying a load of 520 g to the test piece, the electric furnace previously held at 1000 ° C. was moved (see the two-dot chain line in FIG. 2), and the test piece was introduced into the electric furnace. And from the time of starting heat exposure in the atmosphere of nitrogen stream, the creep displacement (deflection amount: mm) of a test piece was measured until the time (disruption time: second) when a displacement changes rapidly. This measurement was performed 4 times each, and the average value was obtained.

  Moreover, the graph which shows the relationship between the creep displacement measured by this hot creep test and time was shown in FIG. In FIG. 3, the creep curve indicated by a broken line is that of a test piece (blank) made of a casting sand composition coated with an organic binder containing no blocked isocyanate compound, and a plurality of solid lines indicated by solid lines. The creep curve is that of a test piece composed of a molding sand composition coated with an organic binder containing a typical blocked isocyanate compound (isocyanate compound: TDI, monoalcohols: described in the figure). The creep displacement is the maximum amount of displacement before the displacement changes abruptly, and is the displacement of a portion that is a substantially horizontal straight line for about several minutes in FIG.

  Moreover, the blocked isocyanate compound, the phenol resin solution, and the polyisocyanate solution were prepared and prepared as follows. And the foundry sand composition which concerns on Examples 1-10 and Comparative Example 1 was prepared using them.

-Preparation of blocked isocyanate compounds-
In a three-necked reaction flask equipped with a reflux, a thermometer, and a stirrer, a predetermined isocyanate compound and monoalcohol shown in Table 1 below were mixed at a functional group molar ratio of NCO group / OH group = 1. The mixture was charged at a ratio of 05 and reacted at 90 ° C. for 5 hours to produce a blocked isocyanate compound having 0.5% by mass or less of unreacted NCO groups.

-Preparation of phenol resin solution-
In a three-necked reaction flask equipped with a reflux, a thermometer and a stirrer, 100 parts by mass of phenol, 55.5 parts by mass of 92% by mass paraformaldehyde, and 0.32 parts by mass of lead naphthenate as a divalent metal salt After reacting at reflux temperature for 90 minutes, the reaction mixture was concentrated by heating to obtain a benzyl ether type phenol resin having a water content of 1% by mass or less. Next, the obtained phenol resin was used with a polar organic solvent (DBE) and a non-polar organic solvent (Solvesso 100 and HAWS) at a blending ratio (mass basis) of DBE: Solvesso 100: HAWS = 46: 48: 6. Then, γ-glycidoxypropyltrimethoxysilane having a phenol resin content of 0.5% by mass was added thereto to prepare a phenol resin solution having a phenol resin content of 50% by mass.

-Preparation of polyisocyanate solution-
Polymeric MDI, which is a polyisocyanate compound, is dissolved using a non-polar organic solvent having a blending ratio (mass basis) of ipzol 150: HAWS = 60: 40, and 0.93% by mass of phthalic acid based on the amount of polymeric MDI. Acid chloride was added to prepare a polyisocyanate solution having a polyisocyanate compound content of 75% by mass.

Example 1
First, 0.5 parts by mass of a blocked isocyanate compound that is a reaction product of methanol and TDI is added to 100 parts by mass of a polyisocyanate solution prepared in advance, and the blocked isocyanate compound is obtained by heating and stirring. It was dissolved uniformly. Next, 1000 parts by mass of phthalate silica sand and 10 parts by mass of a phenolic resin solution (active ingredients) that had been allowed to stand for 24 hours in an atmosphere of 25 ° C. × 60% relative humidity in a Dalton product river type tabletop mixer. Amount: 5 parts by mass) and 10 parts by mass of a blocked product-containing polyisocyanate solution (polyisocyanate compound: about 7.5 parts by mass, blocked isocyanate compound: about 0.05 parts by mass), and stirring for 40 seconds. A foundry sand composition coated with an organic binder was prepared by kneading. The obtained molding sand composition was subjected to mold strength measurement and hot creep test according to the above test method, and the results obtained are shown in Table 1 below.

(Examples 2 to 10)
Instead of the blocked isocyanate compound obtained by reacting TDI of Example 1 with methanol, an isocyanate compound as shown in Table 1 below and a monoalcohol are converted into NCO groups / OH in the molar ratio of functional groups. A foundry sand composition was prepared in the same manner as in Example 1 except that various blocked isocyanate compounds obtained by reacting at a ratio of group = 1.05 were used. The obtained molding sand composition was subjected to mold strength measurement and hot creep test, and the results obtained are shown in Table 1 below.

(Comparative Example 1)
A casting sand composition was prepared in the same manner as in Example 1 except that 10 parts by mass of the polyisocyanate solution containing no blocked isocyanate compound was used without using the blocked isocyanate compound. The obtained molding sand composition was subjected to mold strength measurement and hot creep test, and the results obtained are shown in Table 1 below.

  As is clear from the results of Table 1 above, in Examples 1 to 10 using the organic binder containing the blocked isocyanate compound, any organic binder containing no blocked isocyanate compound was used. Compared with the comparative example 1 used, it is recognized that the fracture time is clearly longer and the heat resistance is remarkably improved without impairing the mold strength. Moreover, in Examples 1-10, although different blocked polyisocyanate compounds were used, respectively, it turns out that displacement (deflection amount), that is, the nature differs according to the kind of this blocked polyisocyanate.

  Further, in the graph of FIG. 3, the creep curve of an example using an organic binder containing a typical blocked isocyanate compound (isocyanate compound: TDI, monoalcohol: described in FIG. 3) is drawn with a solid line. However, it can be seen that the break time is longer and the heat resistance is improved than the blank (broken line in FIG. 3) using the organic binder containing no blocked isocyanate compound. In addition, when the carbon number of monoalcohols is 8, 18, the nature is smaller than the blank, and when the carbon number of monoalcohols is 3, 4, 6, it is larger than the blank. It is also recognized that when the monoalcohols have a large number of carbon atoms, the tendency is smaller, and conversely, when the monoalcohols have a small number of carbon atoms, the tendency is likely to be greater.

It is a figure for demonstrating the shape of the test piece used in the hot creep test of an Example. It is a schematic explanatory drawing of the thermal dilatometer used in the hot creep test of an Example. It is a graph showing the relationship between the creep displacement (deflection amount) measured by the hot creep test of an Example, and time.

Claims (3)

  A urethane-cured organic binder for molds used in the molding of phenol-urethane molds, and is a blocked isocyanate obtained by reacting an isocyanate compound with a monoalcohol together with a phenol resin, a polyisocyanate compound, and an organic solvent. A urethane-curing organic binder for molds, comprising a compound.   A foundry sand composition obtained by coating the foundry sand with the urethane curable organic binder for mold according to claim 1. A mold obtained by molding and curing the foundry sand composition according to claim 2.

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