JP2022125116A - Casting sand for lamination molding and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide casting sand capable of realizing high mold strength and imparting high dimensional accuracy as well.

SOLUTION: Casting sand for lamination molding is used for a method for producing a mold by a lamination molding method including a step in which a step of forming a layer containing casting sand and a step of adding a binder to a prescribed region of the layer to solidify the region are successively repeated, wherein (1) a furan resin organic layer is formed at surfaces of sand grains composing the casting sand and (2) the furan resin organic layer has a solubility (25°C) to methanol of 32% or more.

SELECTED DRAWING: None

COPYRIGHT: (C)2022,JPO&INPIT

Description

The present invention relates to a new foundry sand for additive manufacturing and a method for producing the same. In particular, the present invention relates to casting sand supplied to a three-dimensional layered molding machine (three-dimensional layered molding apparatus) or the like, which is a sand molding machine for casting, and a manufacturing method thereof.

The additive manufacturing method is a technique for producing a compact by stacking sliced two-dimensional layers based on three-dimensional data such as 3D-CAD. In fact, an object with a desired shape can be created by layering three-dimensional additive manufacturing materials with a 3D printer. Various materials such as metals, resins, sand, gypsum, and ceramics are used as materials for the three-dimensional layered manufacturing.

Among these, since sand can be suitably used as a casting mold, the sand mold is also produced by the additive manufacturing method. In particular, in recent years, a three-dimensional lamination technique that can directly realize a three-dimensional shape created by CAD or the like as a sand mold has been attracting attention. In such sand mold manufacturing methods, various manufacturing methods and materials for three-dimensional additive manufacturing have been proposed for the purpose of improving sand mold defects and improving lamination fluidity.

For example, a preparation step of preparing foundry sand having sand grains and a surface-modified layer containing a cured resin covering the sand grains and provided with a curing agent adhering to the surface-modified layer; a solidification step of forming a layer and adding a binder to the molding sand layer to harden the binder added portion of the molding sand layer; and a stacking step of stacking the added portions by repeating the solidification step. is known (Patent Document 1).

Further, for example, foundry sand characterized by having sand grains and a surface-modified layer containing a cured resin covering the sand grains has been proposed (Patent Document 2).

Further, the step of mixing artificial sand with a furan resin composition containing a furan resin precursor, and the step of mixing a curing agent with the artificial sand mixed with the furan resin composition, wherein the curing agent is and xylenesulfonic acid are known (Patent Document 3).

These use casting sand in which the sand grain surface is coated with a hardened body of "furan resin precursor", and "furan resin precursor" is also used as a binder that is sprayed when performing 3D additive manufacturing using it. It is a technique to manufacture a mold with

However, these conventional techniques require further improvement in terms of achieving both high strength of the mold and dimensional accuracy of the mold.

Specifically, since the film covering the surface of the conventional foundry sand as described above is a hardened film, it has low reactivity with the binder and requires a relatively long time to develop strength. Also, if the reactivity with the binder is reduced, the binder will dissolve more readily in the reaction water, resulting in the solution seeping into the untreated sand and hardening in unintended areas. This is the cause of the decrease in dimensional accuracy.

Regarding the speed of strength development, in the actual production of molds, it is required to shorten the time taken to remove the mold, but a certain reaction time is required for curing of the applied binder. Considering mass production, it is desirable to cure in about 3 hours (preferably about 1 hour if possible) from the end of lamination to removal of the mold. Since the boundary is unclear, it is necessary to remove the sand carefully using a brush or the like. In addition, if the sand to which the binder is unintentionally adhered is mixed with the sand in the area where the binder is not applied (hereinafter also referred to as "untreated sand"), it may significantly impair the reusability of the untreated sand. Therefore, significant restrictions are imposed on the work.

Regarding the dimensional accuracy of the above mold, when manufacturing the mold by spraying the binder on the molding sand by the additive manufacturing method, the boundary between the area where the binder is applied and the area where the binder is not applied is the boundary as designed. The major cause is that the interface is not designed to meet the requirements for the surface to be formed.

The fundamental reason why the boundary surface does not conform to the design is the water (hereinafter "reaction water") generated during the dehydration condensation reaction of the binder (which may be contained in the film in some cases) furan resin precursor. ). This reaction water oozes out of the reaction system in the step of curing the furan resin precursor, and ceases to be generated when the furan resin precursor is completely cured. The present inventors have found from experimental results that the igross value of the untreated sand near the mold (hardened body) is higher than that of the untreated sand farther away from the mold (hardened body). We have found that this is the cause of the decrease in accuracy and strength.

In the additive manufacturing method, the viscosity of the applied binder (furan resin precursor) is low. The solution seeps out onto the untreated sand. As a result, the untreated sand that should not be hardened (especially the untreated sand near the mold) is slightly hardened, resulting in a decrease in dimensional accuracy and a decrease in the reuse rate of untreated sand. It is considered to be. Incidentally, if the reuse rate is forcibly increased, untreated sand to which furan resin is adhered will be included in the reused casting sand, so that the resulting mold cannot have high strength. For this reason, the reuse rate cannot be simply increased, resulting in an increase in cost.

In order to solve these problems, it is considered effective to design a binder (furan resin precursor) to increase the curing speed. However, when the amount of the acid catalyst is increased, problems such as the possibility that the sulfur component contained in the acid catalyst may adversely affect the metal structure of the cast product and the possibility of inducing gas defects may occur.

In addition, for example, the undesigned addition of a curing accelerator such as resorcin increases the curing speed of the applied binder too quickly, resulting in a rapid increase in the amount of reaction water produced. lead to the birth of Even if only temporarily, some of the excessively generated reaction water is taken into the resin originating from the film and the binder to cause internal hardening failure, or it spreads through the foundry sand due to its own weight or capillary action. The inventor of the present invention has confirmed that the dimensional accuracy and the like are rather lowered. From this, it can be said that there is a limit to improving the dimensional accuracy and the like only by adjusting the curing speed.

In this way, a design that increases the hardening speed does not provide a fundamental solution for increasing the reuse rate of untreated sand or improving the mold strength, so a new control method is required. However, it is difficult to adopt a method of increasing the viscosity of the binder from the beginning. This is because, in the three-dimensional lamination molding machine, the binder must be ejected from the print head, so the viscosity of the binder must be suppressed to a certain value or less. Furthermore, it is possible to change to a resin that produces less reaction water, for example, a method of using a novolac-type phenolic resin that is used in another casting method called the shell method for the surface modification layer, but the furan resin composition If so, another problem (for example, blocking phenomenon, etc.) occurs that was not a problem. In order to solve the blocking phenomenon, it is known to add a water-absorbing material or an oil such as calcium stearate, which is solid at room temperature, to the foundry sand. Therefore, the characteristics that have been improved with much effort will be lost.

Furthermore, if the amount of binder added is increased in order to increase the strength of the mold, it will lead to an increase in the amount of water produced by reaction, resulting in repeated problems of dimensional accuracy. For this reason, it can be said that it is difficult to achieve both high strength and dimensional accuracy of the mold with the foundry sand of the prior art.

In addition to the above-mentioned documents, for example, a particulate material used in a three-dimensional laminated mold is coated with an acid catalyst that activates and hardens an organic binder for binding the particulate material as a coating film. Coated foundry sand is known (Patent Documents 4-5).

In the foundry sand produced by these methods, the sand and the hardening agent come into direct contact with each other, and the activity of the hardening agent may be lowered due to the components contained in the sand. In this case, even if a binder is added to the foundry sand to which a hardening agent has been added, the binder cannot be sufficiently hardened, resulting in molding defects of the sand mold. In particular, when the binder is applied to the laminated foundry sand, the applied binder and the hardening agent on the surface of the foundry sand come into contact with each other, and a hardening reaction immediately occurs. For this reason, although the initial strength (of the mold) can be obtained to some extent, if the amount of binder is small, the binder will gradually solidify before covering the entire casting sand grain, so no further increase in strength can be expected.

In addition, by applying two types of acid curing agents to the foundry sand for self-hardening mold molding, the curing speed of the furan resin is increased, and at the same time, the reaction water is dispersed in the furan resin to improve the internal hardening failure of the furan resin. , a technique for improving mold strength is known (Patent Document 6).

However, the furan resin produced by this method is also completely cured, so it cannot be used to improve the mold strength in a three-dimensional laminate mold machine. As with the technology described above, initial strength can be obtained to some extent, but no further increase in strength can be expected.

If a large amount of binder is used to improve the strength of the mold using foundry sand produced by these methods, not only will gas defects be induced on the casting side, but also the amount of reaction water generated will increase, resulting in a mold failure. Dimensional accuracy is sacrificed.

In view of the above, in order to achieve both high strength and dimensional accuracy of the mold by these methods, it is necessary to make the environment in which the foundry sand is used considerably low in humidity. In addition, when a hardening agent is present on the outermost surface, it is necessary to prevent blocking between sands due to its deliquescence. Reusability and recycling of casting sand after use are also significantly disadvantageous.

These problems were solved only in the special environment of the additive manufacturing method, where the sand grains need to adhere to each other by simply sprinkling the applied binder only on the areas to be hardened, gently sprinkled on the layered sand. This is a problematic phenomenon. In many cases, this is not a problem in manufacturing methods in which the resin, curing agent, and sand are kneaded mechanically and forcibly, and the kneaded product is forced into a mold. That is, the above-mentioned problems in the additive manufacturing method usually cannot occur in the technique of pressing the kneaded material into a mold.

On the other hand, a liquid curing agent as a catalyst for curing the binder is pre-kneaded with sand grains and layered, and then the coating binder is applied in a three-dimensional layered molding machine and cured. A hard type foundry sand has been proposed (Patent Document 7).

However, the self-hardening type foundry sand typified by the two-liquid mixed type is wet sand at the stage when it is supplied to the three-dimensional layered molding machine, and is not dry sand. Unstable and incapable of producing high-precision molds. In addition, it is necessary to clean the recoater's sand discharge port at regular intervals due to the viscous wet condition (clogging may occur and cause problems). Become. In addition, since the hardening agent is present on the outermost surface of the sand grains, there are also problems similar to those of Patent Documents 4 and 5.

By the way, there is known a technique for improving poor hardening by using reclaimed sand of mullite artificial sand CERABEADS (manufactured by Itochu Ceratec) developed for casting (Non-Patent Document 1). According to Non-Patent Document 1, "In silica sand, the igross component is efficiently removed as the sand is crushed by the load of the regenerator. It is described as "hard to fall."

However, the igross portion of the reclaimed sand is in a more completely hardened state, and simply coating the reclaimed sand with the binder alone cannot harden the reclaimed sand at high speed. In order to obtain a high-strength mold with reclaimed sand, it is necessary to add a hardening agent separately. No improvement is expected.

Furthermore, the difficulty of applying recycled sand to additive manufacturing is also evident from other known documents. For example, in the furan process, the hardening speed is slow and it is difficult to increase the strength. As an example of improving Cerabeads, which has not been widely used as a substitute for silica sand, a method of removing fine powder and basic ion removal treatment such as washing with water has been proposed. (Patent Document 8). However, even in this technique, since the resin component covering the surface of the sand grains is completely cured, it is necessary to attach a new curing agent. As a result, the same problem as in Non-Patent Document 1 occurs, making it difficult to improve dimensional accuracy and strength at the same time. In addition, extra energy is required for drying after removing the fine powder, which affects the production cost.

As another method for solving the problem of reclaimed sand, a method of obtaining reclaimed sand by roasting kneaded sand, which is recovered sand, in an inkjet layered manufacturing method is described (Patent Document 9). However, according to Patent Document 9, the kneaded sand to be roasted is limited to kneaded sand to which no binder is applied (untreated sand). That is, the untreated sand has the same problem as that of Patent Document 4 and the like because the hardening agent is directly coated on the surface of the sand grains.

In addition, as a method for improving the hardening speed of the mold, which decreases when reclaimed sand is used, a method of limiting the types and amounts of the hardening agent remaining in the reclaimed sand and the hardening agent newly added is described. (Patent Document 10). However, Patent Document 10 also has the same problem as Non-Patent Document 1 because the resin component covering the surface of the sand grains in the recycled molding sand itself is in a completely hardened state.

In addition, there is known a method of regenerating recovered sand by mechanically polishing recovered sand and further roasting the ground sand (Patent Document 11). However, in this method, when recovered sand that is not coated with a binder is actually used as a starting material, the surface of the sand grains is directly coated with the hardening agent. will have

JP 2017-100162 JP 2017-100163 JP 2018-140422 Patent No. 6027263 Patent No. 6289648 Patent No. 5119276 Patent No. 5249447 Japanese Patent Application Laid-Open No. 2003-311370 Patent No. 5916789 Patent No. 5537067 JP 2020-104125

"Guidelines and Cases for Introduction of Artificial Sand to Cast Iron Factories" Japan Foundry Association (2012)

SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide a molding sand for additive manufacturing, which can achieve high mold strength and can provide molds with high dimensional accuracy.

As a result of intensive studies in view of the problems of the prior art, the inventors of the present invention have found that particles (particle groups) having specific configurations and physical properties can achieve the above objects, and have completed the present invention. .

That is, the present invention relates to the following laminate manufacturing material and its manufacturing method.
1. A foundry sand for use in a method for manufacturing a mold by an additive manufacturing method, which comprises the steps of forming a layer containing the foundry sand and adding a binder to a predetermined region of the layer to solidify the region. hand,
(1) A furan resin organic layer containing a furan resin precursor and an acid component is formed on the surface of the sand grains constituting the foundry sand,
(2) the furan resin organic layer has a solubility in methanol (25° C.) of 32% or more;
A casting sand for additive manufacturing characterized by:
2. 3. The casting sand for additive manufacturing according to item 1, wherein the igross contained in the casting sand for additive manufacturing is 1.0% by mass or less.
3. 3. The casting sand for additive manufacturing according to item 1 or 2, wherein the pH of the dispersion medium in the dispersion of 10 g of the casting sand for additive manufacturing/50 g of water is 4 or less; 4. The casting sand for additive manufacturing according to any one of items 1 to 3, wherein the casting sand for additive manufacturing has an angle of repose of 42° or less under conditions of a temperature of 25°C and a humidity of 40%.
5. A method for producing foundry sand for additive manufacturing, comprising:
a) mixing starting material sand with a composition comprising a furan resin precursor and a solvent at 100° C. or less to obtain a first mixture;
b) mixing said first mixture with an acid component-containing composition at 100°C or less to obtain a second mixture; and c) drying said second mixture at 120°C or less to form a dry sand casting. A method for producing foundry sand, comprising the step of obtaining sand.
6. 6. The manufacturing method according to item 5, further comprising a step of adding 0.01 to 3 parts by mass of water to 100 parts by mass of sand.
7. 7. The production method according to item 5 or 6, wherein the drying is performed at 50 to 80° C. for 60 to 600 seconds.
8. 7. The production method according to item 5 or 6, wherein the drying is performed until the water content of the second mixture reaches 300 to 1200 ppm by mass.
9. A three-dimensional additive manufacturing kit containing the additive manufacturing foundry sand according to any one of the above items 1 to 4 and a binder.
10. 4. The foundry sand for additive manufacturing according to any one of items 1 to 3, which has a water content of 300 to 1200 ppm by mass.
11. 4. The foundry sand for additive manufacturing according to any one of items 1 to 3, wherein the furan resin precursor contains furfuryl alcohol and a furan resin prepolymer.
12. 4. The foundry sand for additive manufacturing according to any one of items 1 to 3, wherein the acid component contains at least one of ethylbenzenesulfonic acid and cumenesulfonic acid, and xylenesulfonic acid.
13. 4. The foundry sand for additive manufacturing according to any one of items 1 to 3, which is used in combination with a binder containing furfuryl alcohol and a furan resin prepolymer as a binder for additive manufacturing.
14. 7. The production method according to item 5 or 6, wherein the acid component-containing composition contains 50 to 60% by mass of at least one of ethylbenzenesulfonic acid and cumenesulfonic acid, and 40 to 50% by mass of xylenesulfonic acid.
15. 7. The production method according to item 5 or 6, wherein the solvent contains water.
16. 7. The production method according to item 5 or 6, further comprising a step of controlling the second mixture having a water content of 300 to 1200 ppm by mass at a temperature of 15 to 25° C. and a humidity of 45% or less.
17. 10. The three-dimensional additive manufacturing kit according to Item 9, wherein the binder contains furfuryl alcohol and a furan resin prepolymer.

ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide a foundry sand capable of achieving high mold strength and providing molds with high dimensional accuracy. That is, the present invention can provide foundry sand that can provide a mold having high strength and high dimensional accuracy. As a result, the foundry sand of the present invention can be suitably used as a foundry sand for three-dimensional additive manufacturing.

In particular, the foundry sand of the present invention has a solubility in methanol in the furan resin organic layer controlled to a specific range of 32% or more. That is, since the furan resin organic layer is in a so-called semi-cured state, by spraying the binder onto the foundry sand of the present invention, it can be uniformly cured over the entire surface, resulting in high strength and high dimensional accuracy. It is possible to manufacture a mold (molded body) that has both. In particular, in terms of strength, due to the speed of strength development, sufficiently high strength can be obtained even in about a few minutes (e.g., 30 minutes) after the mold is made. As a result of being able to avoid problems due to incorporation of , high dimensional accuracy can also be achieved. Thus, even when a casting mold is produced by the additive manufacturing method using the foundry sand of the present invention, both high strength and high dimensional accuracy can be imparted to the casting mold (molding).

In addition, since the foundry sand of the present invention is apparently in a dry state, there is no risk of inadequate filling of the foundry sand even in the lamination method (laminate manufacturing method) in which sand compaction cannot be performed. It is possible to increase the strength of the mold.

A kit comprising the foundry sand of the present invention having such characteristics and a combination thereof with a binder can be suitably used for producing a sand mold by the additive manufacturing method. The sand mold (mold) obtained in this way can also be used for casting ferrous materials with high melting temperatures, which is difficult with conventional 3D molds. Can be used widely.

The foundry sand of the present invention was developed so as to be suitable for the additive manufacturing method, but it can also be diverted to a so-called self-hardening mold material, in particular, a combination of artificial sand and furan resin. It can also be used as a countermeasure against casting defects such as veining defects.

Further, according to the production method of the present invention, the foundry sand of the present invention can be produced more reliably and efficiently. According to research conducted by the present inventor, it has been found that it is necessary to control the solubility of the furan resin organic layer and the amount of reaction water produced in order to achieve both high mold strength and high dimensional accuracy. In particular, as a means of controlling the solubility of the furan-resin organic layer, it is important to control the water content in the furan-resin organic layer. Furthermore, by devising a method for dispersing the curing agent in the furan resin organic layer, a more desirable effect can be obtained. By introducing these into the production method of the present invention, it is possible to more reliably provide foundry sand that achieves stable mold strength and dimensional stability at the same time with a relatively small amount of curing agent and resin. becomes.

1. Foundry sand for additive manufacturing The foundry sand for additive manufacturing of the present invention (the material of the present invention) is prepared by sequentially performing a step of forming a layer containing the foundry sand and a step of adding a binder to a predetermined region of the layer to solidify the region. A foundry sand for use in a method of manufacturing a mold by an additive manufacturing method comprising repeating steps,
(1) A furan resin organic layer containing a furan resin precursor and an acid component is formed on the surface of the sand grains constituting the foundry sand,
(2) the furan resin organic layer has a solubility in methanol (25° C.) of 32% or more;
It is characterized by

(A) Substances Constituting the Material of the Present Invention Sand grains Sand grains (that is, sand grains before being coated with the furan resin organic layer) are used as the cores of the particles constituting the foundry sand of the present invention. Either natural sand or artificial sand can be used as sand that is an aggregate of sand grains. Examples of natural sand include silica sand, zircon sand, chromite, and olivine. Artificial sand includes mullite, spinel, alumina and the like.

In the present invention, either new sand or reclaimed sand may be used, or mixed sand of new sand and reclaimed sand may be used. In the present invention, new artificial sand is preferable from the viewpoint that igross can be suppressed to a lower level, and among these, artificial sand produced by a sintering method is more preferable. For example, when the CERABEADS are used, it is more preferable to select bone sand with a smaller amount of fine powder because the amount of furan resin can be reduced (for example, product name "CERABEADS X" manufactured by Itochu Ceratech). Generally, it is known that regeneration of furan resin in artificial sand is difficult (igroth becomes larger). When selecting recycled artificial sand for the sand grains of the present invention, in order to achieve low igross (1.0% by mass or less, particularly 0.8% by mass or less) and low pH (4 or less) in the material of the present invention, For example, it is desirable to take measures such as mixing new sand.

Note that the furan resin film remaining on the surface of the sand grains of the reclaimed sand described in Non-Patent Document 1 is completely hardened and therefore does not dissolve in the binder. Therefore, the curing agent present in such furan resin films does not work during additive manufacturing (high strength molds cannot be produced). However, it is difficult to mix and use recycled artificial sand with different surface conditions for each grain of sand because of the nature of the present invention, which aims to homogenously disperse the curing agent and adjust the solubility of the furan resin organic layer. In principle, the use of recycled artificial sand is less suitable for the present invention.

On the other hand, in the case of reclaimed silica sand, it is easily crushed by mechanical grinding, etc. during reclaiming treatment, and the sand grain shape must be improved for casting sand, and the igross content must be sufficiently reduced by reclaiming treatment such as roasting and polishing. Therefore, it can be used in some cases because improvement in wettability with the furan resin organic layer can be expected. However, since the igross contained in the reclaimed silica sand is completely hardened, it does not dissolve in the binder. Therefore, when using reclaimed silica sand, it is preferable to use it as sand grains that are aggregates.

The grain size of the sand grains is not particularly limited, but generally the grain size index is preferably AFS 35 to 120, and more preferably AFS 60 to 115. The particle size can be appropriately adjusted by a known classification method, if necessary.

Furan Resin Organic Layer The furan resin organic layer is a film (resin film) that coats the surface of the sand grain, preferably covering the entire sand grain.

The furan-resin organic layer comprises, inter alia, a) a furan-resin precursor and b) an acid component. In the material of the present invention, the furan resin organic layer does not directly contribute to the bonding of the sand grains forming the foundry sand before being laminated. Therefore, the material of the present invention has a dry powder appearance, and has fluidity as a smooth powder.

(a) Furan Resin Precursor The furan resin precursor is not limited as long as it can form a furan resin by condensation polymerization or the like, and examples thereof include furfuryl alcohol and furan resin prepolymers. In particular, it is desirable to use furfuryl alcohol and a furan resin prepolymer together for the reasons of suppression of heat of reaction and reduction of viscosity of the resin.

The furan resin prepolymer includes, for example, a polymer of furfuryl alcohol homopolymer, a copolymer of furfuryl alcohol and an aldehyde compound, a copolymer of furfuryl alcohol, urea and an aldehyde compound (urea-modified furan resin prepolymer), Examples include copolymers of furfuryl alcohol and furfural. These can be used singly or in combination of two or more.

In the present invention, a copolymer of furfuryl alcohol, urea and an aldehyde compound (urea-modified furan resin prepolymer) is particularly preferred because it facilitates high strength. Examples of the aldehyde compounds include formaldehyde, acetaldehyde, glyoxal, and furfural. In the present invention, formaldehyde is particularly preferred.

When furfuryl alcohol and furan resin prepolymer are used together as furan resin precursors, the total content of furfuryl alcohol is 100 parts by mass, and the content of furfuryl alcohol is in the range of 35 to 60 parts by mass from the viewpoint of viscosity. desirable.

Further, the content of the furan resin precursor is usually 0.05 to 0.7 parts by mass, preferably 0.1 to 0.5 parts by mass, more preferably 0.1 to 0.5 parts by mass per 100 parts by mass of sand grains. It is more preferably 1 to 0.4 parts by mass, more preferably 0.1 to 0.35 parts by mass, and most preferably 0.1 to 0.3 parts by mass. By setting the thickness within such a range, the strength and dimensional accuracy of the resulting mold can be more reliably increased.

The content ratio (solid content) of the furan resin precursor in the furan resin organic layer is not particularly limited as long as it is blended so as to achieve the content shown above, but it is usually about 20 to 90% by mass. It should be within the range. Therefore, it can be set to 30 to 60% by mass, for example.

(b) Acid component The acid component mainly functions as an acid catalyst (curing agent) for curing the binder used in the lamination process. By using these acid components, it is possible to provide a mold capable of exhibiting higher strength. In addition, below, an acid component may be called a "curing agent."

The acid component is not particularly limited, and components that are blended as acid catalysts in known or commercially available foundry sand can also be used. In particular, in the present invention, an acid component with a pKa (25° C.) of 5 or less can be preferably used. More specifically, aliphatic sulfonic acids (eg, methanesulfonic acid, ethanesulfonic acid, etc.), aromatic sulfonic acids (eg, ethylbenzenesulfonic acid, cumenesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, xylenesulfonic acid, etc.) , inorganic acids (eg, sulfuric acid, phosphoric acid, hydrochloric acid, etc.), carboxylic acids (eg, maleic acid, oxalic acid, etc.), and the like.

In the present invention, an aromatic sulfonic acid is preferred, and an aromatic sulfonic acid having an alkyl group with 1 (C1) or more carbon atoms is particularly preferred. Among these, it is preferable to use at least one of ethylbenzenesulfonic acid and cumenesulfonic acid from the viewpoint of easing the storage conditions of the material of the present invention. That is, the acid component preferably contains at least one of ethylbenzenesulfonic acid and cumenesulfonic acid. In this case, the ratio of at least one of ethylbenzenesulfonic acid and cumenesulfonic acid to the total acid components is usually 45% by mass or more, preferably 55% by mass or more. The upper limit of the above ratio is not limited, and can be, for example, 100% by mass.

Moreover, even when ethylbenzenesulfonic acid and cumenesulfonic acid are used, other acid components can be used in combination. As other acid components, xylenesulfonic acid is particularly desirable in the present invention. Examples of xylenesulfonic acid include ortho-xylenesulfonic acid, meta-xylenesulfonic acid, and para-xylenesulfonic acid. These xylenesulfonic acids can be used alone or in combination of two or more. These xylenesulfonic acids are desirably about 50 parts by mass or less (for example, 10 to 50 parts by mass) in the total acid component.

The content of the acid component in the material of the present invention can be appropriately set according to the type of the acid component used, etc., but it is usually 0.05 to 0.5 parts by mass, particularly 0.05 to 0.5 parts by mass per 100 parts by mass of sand grains. It is preferably from 1 to 0.4 parts by mass, more preferably from 0.1 to 0.35 parts by mass, and most preferably from 0.15 to 0.3 parts by mass. By setting it within the above range, higher mold strength can be obtained, and gas defects that can occur when using the mold, as well as adverse effects on the metal structure of the cast product, can be effectively suppressed or prevented.

The content ratio (solid content) of the acid component in the furan resin organic layer is not particularly limited as long as it is blended so as to achieve the content shown above, but it is usually in the range of about 10 to 80% by mass. and should be. Therefore, it can be set to 30 to 60% by mass, for example.

(c) Other Components Other components may be contained in the furan resin organic layer within a range that does not impair the effects of the present invention. For example, one or more of a solvent, a cross-linking agent, a curing accelerator, a filler, a migration inhibitor, a strength improver, and the like can be appropriately contained.

As the curing accelerator, the same curing accelerator as used in the known laminate manufacturing method can be used. Examples include resorcin, bisphenol A, bishydroxymethylfuran and the like. Although the content of the curing accelerator in the furan resin organic layer is not limited, it can usually be appropriately set within the range of about 1 to 30 parts by mass.

Examples of solvents include water, acetone, ethyl acetate, alcohol and the like. In the present invention, the solvent preferably contains water from the viewpoint that the boiling point is relatively high and the solubility of the furan resin organic layer can be easily controlled. The content ratio of the solvent may normally be in the range of about 0 to 1 part by mass with respect to 100 parts by mass of sand. Therefore, the composition may contain no solvent. When a solvent such as water is included, more specifically, it is desirable to set the content in the material of the present invention to 300 to 1200 mass ppm (preferably 300 to 900 mass ppm). Therefore, for example, it can be set to 350 to 800 mass ppm or 550 to 800 mass ppm.

A silane coupling agent can be preferably used as the cross-linking agent. A known or commercially available one can be used for this. The content of the cross-linking agent can be, for example, 0.001 to 0.1 parts by mass, preferably 0.001 to 0.05 parts by mass, per 100 parts by mass of sand grains. Therefore, it can be set to 0.002 to 0.02 parts by mass, for example. In the present invention, aminopropylmethyldimethoxysilane is preferred because it can react with furan resin and is less likely to form silane-derived precipitates. If the amount of the cross-linking agent is too small, the bonding strength between the furan resin organic layer and the sand grains may be reduced, and the strength of the mold may be lowered. On the other hand, if the amount of the cross-linking agent is too large, the adhesiveness between the coating binder and the furan resin organic layer may be hindered, and the strength of the mold may be lowered.

A filler can also be added as an optional component. Thereby, higher mold strength can be obtained. Either an organic filler or an inorganic filler may be used as long as the effects of the present invention are not hindered. Also, the shape of the filler is not particularly limited, and may be spherical, fibrous, scaly, or the like. The fibrous filler may be short fibers or long fibers. Therefore, for example, nanofibers having a fiber diameter of 1000 nm or less and an aspect ratio of about 10 to 5000 can be used. As nanofibers, known or commercially available ones such as carbon fibers, silica fibers, dietary fibers (polysaccharides) such as cellulose, pulp, and glass fibers can be used. In particular, in the present invention, cellulose nanofibers (CNF) are preferred because they can increase the degree of freedom in template design. The amount of the filler to be added is not particularly limited, but it is usually preferably 1×10 ⁻⁴ to 1 part by mass, particularly 1×10 ⁻³ to 0.1 part by mass, based on 100 parts by mass of sand. is more preferable.

Another optional component is a migration inhibitor for suppressing the migration phenomenon described later. The use of migration inhibitors makes it possible to obtain higher strength molds. The migration inhibitor is not limited as long as it can hold the reaction water, and for example, a substance (powder) exhibiting water absorption (hygroscopicity) can be used. In particular, a powdery substance having a melting point or heat resistance temperature of 130° C. or higher (preferably 150° C. or higher) can be used. More specific examples include celluloses such as cellulose nanofibers, dicarboxylic acids such as oxalic acid, and the like. These can be used singly or in combination of two or more. Therefore, at least one of organic powders such as cellulose nanofibers and oxalic acid can be preferably used. By using these together with a curing agent, the degree of freedom in mold design can be further increased.

The amount of the migration inhibitor to be added is not particularly limited, but it is usually about 0.001 to 0.1 parts by mass, particularly 0.005 to 0.05 parts by mass, per 100 parts by mass of sand grains. preferably. Therefore, it can be set to 0.01 to 0.03 parts by mass, for example. In addition, for example, like a cellulose nanofiber, when it has both the function of the said filler and said migration inhibitor, it shall be included in content of a migration inhibitor. Further, for example, when oxalic acid has both functions of the acid component and the migration inhibitor, it is included in the content of the migration inhibitor.

In particular, the inclusion of a migration inhibitor can reduce water, which is a carrier (medium) of the migration phenomenon, so that the migration phenomenon can be effectively controlled. As a result, for example, even under conditions where the amount of reaction water produced is large, it is possible to effectively limit the movement of the furan resin, which tends to collect on the surface layer due to the migration phenomenon. Alternatively, the curing reaction of the furan resin can be delayed even under conditions in which the curing reaction tends to proceed due to rapid dehydration and evaporation. Furthermore, since it can serve as a source of water that is lacking after contact with the applied binder and assist in dissolving the binder, it is possible to adjust the amount of application according to the design of the mold, increasing the degree of freedom in designing the mold. Improvements can also be made.

Further, other optional components include a strength improver that can contribute to improving the strength of the mold. As the strength improver, in addition to being a resin that can be dispersed in furfuryl alcohol (or a binder), any resin that does not dramatically progress in polymerization due to the acid component that is the curing agent may be used. preferably has heat resistance against the explosion heat during casting. At least one phenolic compound can be used as a substance having such a function. More specifically, at least one of novolak, resol, phenol urethane resin and the like is preferred. The amount of the phenolic compound to be added is not particularly limited, but it is usually preferably 0.001 to 0.1 parts by mass, particularly 0.005 to 0.1 parts by mass, based on 100 parts by mass of sand grains. is more preferable.

In particular, in the present invention, the strength of the mold can be further increased by including the strength improving agent in the furan resin organic layer, without abruptly increasing the amount of reaction water produced. Although the reason for this is not clear, it is thought to be mainly due to the ability of the furan resin organic layer to maintain a predetermined solubility in methanol. In other words, rather than contributing to the improvement of mold strength by heating (polymerization), it is speculated that these phenolic compounds increase the strength of the mold by adjusting the solubility of the furan resin organic layer. be done. It is presumed that the retardation of the rate of decrease in the solubility of the furan-resin organic layer would allow time for the curing process of the furan-resin organic layer, and as a result, the poor internal curing of the furan-resin organic layer would be improved. As a result, it is possible to further increase the strength of the mold, so that it is possible to reduce the coating binder or reduce the amount of the coating resin as a whole. As a result, secondary effects such as suppression of dross defects during casting of cast iron and suppression of gas defects during casting of aluminum alloys can be expected.

(B) Physical properties of the material of the present invention In the material of the present invention, the solubility in methanol (25° C.) in the furan resin organic layer is 32% or more, preferably 35% or more, more preferably 45% or more, and Above all, 50% or more is most preferable. If the solubility is less than 32%, the compatibility with the binder is lowered, so that a high-strength mold cannot be produced with a low amount of binder. Although the upper limit of the solubility is not particularly limited, it can usually be about 99%.

In the present invention, the above solubility is an index indicating the degree of curing in the furan resin organic layer, and the higher the value, the lower the degree of curing and the semi-cured state. In other words, the closer the solubility is to 0, the closer to complete curing.

In the material of the present invention, the furan-resin organic layer is not completely cured, and the acid component is homogeneously present in the furan-resin organic layer. It is considered that the strength can be rapidly developed as a result of the fact that the hardening unevenness of the binder can be prevented. In particular, if the migration phenomenon can be well controlled, the acid component on the surface of the furan resin organic layer will be less than the amount of resin, so the risk of deliquescence due to acid can be reduced, and the foundry sand itself is stable in its dry state. Yes, and the lamination property is stable. As a result, it is considered possible to improve the accuracy of the resulting casting or the reproducibility of the mold for the design.

The external appearance of the material of the present invention is usually dry sandy and smooth. That is, since it is foundry sand in a dry powder state, it has fluidity similar to that of granular material. As an indicator of a fluid powder, it is preferable that the angle of repose is 42° or less under conditions of a temperature of 25° C. and a humidity of 40%. Incidentally, in the case of artificial sand, the angle of repose is 35° or less, and in the case of silica sand, the angle of repose is 42° or less. That is, since it has fluidity that allows use of a known or commercially available three-dimensional layered molding machine, it can be applied to these various devices in the same manner as conventional foundry sand. The lower limit of the angle of repose can be, for example, about 24°, but is not limited to this.

Although the Ig loss of the material of the present invention is not limited, it is usually 1.0% by mass or less, preferably 0.8% by mass or less, more preferably 0.75% by mass or less, and more preferably 0.75% by mass or less. The content is preferably 0.7% by mass or less, and most preferably 0.59% by mass or less. If it exceeds 1.0% by mass, there is a risk that unrepairable gas defects may occur in castings during casting of aluminum alloys. Also, the less igross is, the better in terms of suppressing the occurrence of gas defects on the casting side. From this point of view, the lower limit of igross is preferably 0.1% by mass.

Also, a slight gas defect can be dealt with by the casting method or the design of the casting (for example, by increasing the wall thickness for post-processing, etc.). In addition, if the amount of resin in the furan resin organic layer is increased to increase the igross, it takes time for the curing reaction in the additive manufacturing method, and the amount of reaction water increases. etc. In particular, this tendency is particularly noticeable in an environment with a humidity exceeding 45% or in a high-humidity environment such as the rainy season.

Although the pH (25° C.) of the material of the present invention is not particularly limited, it is usually desirably 4 or less, and more desirably 3.5 or less. Therefore, for example, the pH can be 1.5-4. The pH in the present invention refers to the pH of the dispersion medium (water) in the dispersion when 10 g of foundry sand is dispersed in 50 g of water. If the pH of the foundry sand exceeds 4 when the foundry sand is immersed in water, it means that the hardening reaction of the furan resin organic layer of the foundry sand has proceeded too much, and the solubility in the binder and the like is insufficient. It shows that the strength does not increase with time. Table 1 of Patent Document 11 describes the pH of the sinterable artificial sand (reclaimed sand) after use in the lamination method, but due to the influence of the hardening agent remaining in the reclaimed sand, the pH ranges from 4.3 to 4.3. Cases varying up to 9.5 are described. However, as described above, the furan resin composition of the recycled sand is inactivated and does not contribute to the strength improvement of the mold (sand mold). From these events, it can be said that the pH of the foundry sand is just one index for evaluating the performance of the material of the present invention.

When the foundry sand of the present invention is dispersed in water, the semi-cured furan resin (on the surface of the furan resin organic layer) absorbs water and swells. As a result, the hardening agent in the furan resin organic layer can come into contact with water, so the pH of the water, which is the dispersion medium, is thought to indicate the strong acidity of the hardening agent. On the other hand, if the three-dimensional curing reaction of the furan-resin organic layer proceeds too much, the furan-resin organic layer will not be able to swell. According to research by the present inventors, it has also been confirmed that when the pH exceeds 4, the solubility of the furan resin organic layer decreases to less than 32%.

2. Method for producing foundry sand for additive manufacturing The method for producing the material of the present invention is not limited, but for example, a) mix sand grains as a starting material with a composition containing a furan resin precursor and a solvent at 100°C or less. b) obtaining a second mixture by mixing the first mixture with an acid component-containing composition at 100° C. or lower (second step); and c) ) It can be suitably carried out by a manufacturing method including a step (third step) of obtaining dry sand-like foundry sand by drying the second mixture at 120° C. or less.

First Step In the first step, a sand grain as a starting material and a composition (raw material composition) containing a furan resin precursor and a solvent are mixed at 100° C. or lower to obtain a first mixture. The temperature here refers to the sand temperature (hereinafter, the same applies to the second step and the third step). That is, it refers to the temperature of the material itself, not the ambient temperature.

As the sand grains, the same sand as described in the above "1. Casting sand for additive manufacturing" may be used. Moreover, as the raw material composition, in addition to the above-mentioned furan resin precursor and solvent, if necessary, a composition in which various components described in the above “1. As the solvent, those mentioned above can be used, and it is particularly desirable to include water.

The furan resin precursor is not particularly limited, but furfuryl alcohol and a furan resin prepolymer (particularly urea-modified furan resin It is preferable to employ a combination with a prepolymer). In this case, the ratio between the two may be the ratio described above. The ratio in the raw material composition is, for example, about 35 to 85% by mass of furfuryl alcohol and about 15 to 65% by mass of furan resin prepolymer, but is not limited thereto. The content of the furan resin precursor in the raw material composition is usually about 85 to 100% by mass, and can be particularly set to 90 to 98% by mass, but is not limited to this.

In addition, the raw material composition preferably contains a solvent (preferably water). As a result, the furan resin organic layer can be brought into a semi-cured state more reliably. The content of the solvent can be appropriately set depending on the type of furan resin precursor or solvent used, and is usually about 1 to 10% by mass, preferably 3 to 7% by mass, in the raw material composition.

The mixing conditions are not limited as long as the surface of the sand grains can be coated with the raw material composition, but the temperature should be 100°C or less, preferably 70°C or less, and more preferably 35 to 45°C. .

Moreover, the mixing ratio of the sand grains and the raw material composition may be the ratio explained in the above "1. Casting sand for additive manufacturing". The mixing method is not limited, and can be carried out using, for example, a known or commercially available mixer, kneader, or the like.

Second Step In the second step, the second mixture is obtained by mixing the first mixture and the acid component-containing composition at 100° C. or lower.

As for the acid component-containing composition, the acid component content in the acid component composition may be 100% by mass. A mixture containing other components can also be suitably used.

Therefore, in the present invention, the acid component-containing composition preferably contains an aromatic sulfonic acid, and particularly preferably at least one of ethylbenzenesulfonic acid and cumenesulfonic acid. When other aromatic sulfonic acids are used, an acid component composition containing at least one of ethylbenzenesulfonic acid and cumenesulfonic acid and xylenesulfonic acid can be suitably employed. For example, as in Examples below, an acid component-containing composition containing at least one of ethylbenzenesulfonic acid and cumenesulfonic acid: 50 to 60% by mass and xylenesulfonic acid: 40 to 50% by mass can be preferably used. can.

The acid-component-containing composition may contain a solvent, but it is preferable that the composition does not substantially contain a solvent from the viewpoint of controlling the water content.

The mixing conditions are not limited as long as the acid component can be imparted to the furan resin precursor-containing composition on the surface of the sand grains, but the temperature should be 100° C. or less, more preferably 70° C. or less (especially 20° C. to 45° C.). is preferably controlled to Accordingly, by setting the kneading temperature to 100° C. or lower, preferably 70° C. or lower, it becomes possible to more reliably coat the entire sand grains with the raw material composition. As a result, the curing reaction of the furan resin precursor can be controlled more reliably. Also, the mixing ratio of the two may be adjusted to the ratio described in the above "1. Foundry sand for additive manufacturing". As a mixing method, for example, a known or commercially available mixer, kneader, or the like can be used.

Third Step In the third step, the second mixture is dried at 120° C. or lower to obtain dry sand-like foundry sand. As a result, the heat generated by the reaction of the furan resin precursor can be effectively removed along with the drying of the second mixture. By performing the third step, the migration phenomenon can be controlled, and as a result, high casting strength (particularly rapid strength development) and high dimensional accuracy can be reliably achieved. That is, along with the forced removal of reaction water, a state is created in which the curing agent on the surface of the foundry sand is insufficient, and as a result, the furan resin precursor is less likely to be cured on the surface, and as a result, the surface layer of the furan organic layer is in a semi-cured state. It is possible.

The drying method is not particularly limited as long as the moisture content can be controlled. C., most preferably 50-60.degree. Also, the drying time varies depending on the drying temperature and the like, and is usually about 60 to 600 seconds, but is not limited to this. For drying, a known or commercially available mixer, kneader, or the like can be used.

Drying is desirably performed so that the water content of the second mixture is 300 to 1200 mass ppm (preferably 300 to 900 mass ppm). Therefore, for example, it can be set to 350 to 800 mass ppm or 550 to 800 mass ppm. By setting the moisture content in such a manner, the furan resin organic layer can be reliably maintained in a semi-cured state, and an apparently dry powder state can be maintained. That is, the foundry sand of the present invention preferably has a water content of 300 to 1200 mass ppm (preferably 300 to 900 mass ppm). By maintaining such a water content, the semi-cured state of the furan resin organic layer of the foundry sand is more reliably maintained.

From this point of view, if the molding sand after drying is not immediately subjected to the additive manufacturing process, it is usually stored in an environment controlled at a temperature of 15 to 25 ° C. and a humidity of 45% or less, especially at a temperature of 20 to 25 ° C. and It is desirable to store in an environment controlled at a humidity of 40% or less. When stored outdoors, it is preferable to store in a sealed container such as a drum can. In this manner, the furan resin organic layer can retain water receptivity. The amount of reaction water received in the furan resin organic layer can be adjusted by adjusting the balance of the sand temperature immediately before discharge, the kneading time, the materials selected in the first and second steps, the addition amount, and the like.

In this way, a semi-cured furan resin organic layer can be produced on the sand grain surface. Observing the color of the reaction process of the furan resin or furfuryl alcohol, the color changes in the order of colorless to red transparent to yellow transparent to green transparent to brown transparent to dark brown. In this case, since there is a correlation between the solubility in methanol and the color of the furan resin organic layer, which is the resin film, the solubility can be roughly predicted from the color of the resin film. That is, the reaction time, temperature, and amount of each material added are adjusted so that the generated furan resin organic layer has an a* value of −10 or more and 1 or less and a b* value of 1 or more and 20 or less by reflection object color measurement. be able to. It is desirable to use a color diagnosis system using an integrating sphere for the color measurement of reflected objects. Within this range of color difference, the furan resin organic layer can be regarded as having a solubility of 32% or more in methanol.

The state of uniform dispersion of the curing agent in the foundry sand of the present invention can also be evaluated by the color of the sand. If the curing agent is evenly distributed, the color changes to green. On the other hand, when the curing agent is segregated, the segregated portion becomes brown. Since the foundry sand of the present invention has a smooth green color as a whole and no brown portion is observed, it is considered that the curing agent is uniformly dispersed in the furan resin organic layer. In addition to the color, it can also be confirmed from the dimensional stability of layered manufacturing and the high strength of the mold.

<Embodiment of manufacturing method>
An example of the production method of the present invention will be described while showing its possible mechanism of action. Although the specific action mechanism by which the furan resin organic layer of the foundry sand of the present invention can be controlled to a semi-cured state is not clear, it is speculated that it is based on the following actions in relation to the production method of the present invention. be done.

First, a mixture is prepared by adding a furan resin precursor to sand grains. Next, a hardening agent and, if necessary, a solvent (mainly water) are added to the above mixture to obtain initial foundry sand. At this time, when the water content in the film covering the sand grains increases, the curing reaction of the furan resin precursor becomes extremely slow even if it is in contact with the curing agent. This state is equivalent to a state (semi-cured state) in which the furan resin precursor stops in the middle of the curing reaction, and the film exhibits a certain degree of solubility in methanol even at this stage.

The initial foundry sand is then heated while being stirred. At this time, it is considered that the surface of the sand grains can be uniformly wetted with the furan resin precursor and the curing agent by heating by adjusting the heating temperature, the sand temperature, the kneading time, and the like. In particular, if water or the like is used as a solvent at the stage of obtaining the initial molding sand, the sand temperature will not rise sharply, and a time margin for wetting and spreading of the furan resin precursor and the curing agent can be ensured more reliably. Therefore, for example, by adjusting the kneading time with the furan resin precursor while monitoring the sand temperature, the curing reaction of the furan resin precursor can be controlled. This leads to adjustment of the amount of reaction water generated. Therefore, the curing reaction rate can be adjusted by adjusting the amount of reaction water generated without adding a solvent such as water.

Finally, the kneaded sand is dried. In this step, the migration phenomenon can be controlled. In the present invention, the migration phenomenon refers to the fact that when the reaction water is removed from the film, mainly the furan resin precursor, such as unreacted furfuryl alcohol, a part of the acid component, etc., moves through the furan resin organic layer together with the reaction water. It refers to the phenomenon of moving to It is believed that the migration phenomenon causes variations in the concentration of moisture or furan resin precursor in the formed furan resin organic layer in the film thickness direction.

At this time, by adjusting the drying conditions, only the reaction water and the furan resin precursor tend to move to the surface layer of the film. Along with this, the grain side (deep layer portion of the film) becomes a water-rich portion, and the surface layer side becomes a water-poor portion, forming a water concentration gradient. In the process, as described above, the amount of furan resin precursor in the surface layer of the film is greater than that of the acid component, and the acid component is relatively insufficient, and the three-dimensional curing reaction proceeds. It is considered possible to maintain a state of non-existence. At the same time, since there is a large amount of furan resin precursor in the surface layer of the film, it is thought that it can contribute to improvement of compatibility with the binder, improvement of hardening unevenness, and the like.

When ethylbenzenesulfonic acid or cumenesulfonic acid is mainly used as a curing agent, it is possible to realize molding sand that can relax the environmental conditions for use. p-toluenesulfonic acid, xylenesulfonic acid, etc. can be used as a curing agent more reliably if the temperature is 20 to 25° C. and the humidity is 40% or less. In this case, by using at least one of the aforementioned oxalic acid, cellulose nanofibers, etc. as a migration inhibitor, it is possible to provide the material of the present invention with even better performance. In the present invention, the balance adjustment between the amount of reaction water produced from the furan resin and the curing rate of the furan resin is a control index, so the type of acid component is not limited. If there is a material such as oxalic acid that can store moisture in itself, it becomes possible to more reliably form a furan resin organic layer with high solubility. By effectively utilizing the migration phenomenon, the water content in the foundry sand of the present invention can be suppressed to 1200 ppm by mass or less immediately after preparation of the foundry sand.

The foundry sand that has been dried is preferably discharged from the kneading apparatus and stored in an environment controlled at low humidity. It is considered that the furan resin organic layer of the foundry sand obtained in this manner has the property of being able to take in and retain reaction water (hereinafter also referred to as "water acceptability"). Furfuryl alcohol in the furan resin organic layer may undergo a reversible reaction with the water of reaction to return to furfuryl alcohol, even if dehydration condensation has progressed, since the reaction stops during the reaction. If the acid component is also a strong acid, it can take in water by itself. That is, when the binder and the furan resin organic layer of the foundry sand come into contact with each other, even if the reaction water is vaporized and cannot be completely digested, it can be incorporated into the furan resin organic layer to some extent, resulting in improved dimensional stability. It can contribute to improvement. As described above, the amount of moisture that can be retained in the film can be adjusted by adjusting the temperature, etc., when preparing the initial molding sand.

Since the furan resin organic layer of the foundry sand of the present invention is formed in a state where the temperature is suppressed to about 100° C. or lower (especially 70° C. or lower), it is considered that it is polymerized only in chain form. , and is presumed to have high solubility in alcohol. Since it is polymerized in a chain form, relatively many methylol-type hydroxyl groups remain, and it is thought that after the furan resin organic layer is dissolved in the binder furfuryl alcohol, it can be polymerized with the binder. It is also expected that part of the moisture in the film is used for the reverse reaction to furfuryl alcohol. If it is polymerized in a chain shape, its heat resistance is low, but since it can be repolymerized with the applied furan binder, it builds a three-dimensional network and has high heat resistance, making it suitable for molten metal such as cast iron and aluminum alloy. It is thought that it will become tolerable.

The furan resin organic layer, which is a film on the surface of the sand grains, is in a state (that is, in a semi-cured state) having a certain degree of solubility in furfuryl alcohol, furan resin prepolymer, etc. used as a binder. Therefore, it is considered that the furan resin organic layer itself complements the cohesive strength of the binder when it comes into contact with the binder as follows. First, the semi-cured furan resin, from which water has been removed by the migration phenomenon, gathers at a high concentration on the surface of the foundry sand, and swells and then dissolves when it comes into contact with the dispersed binder. In this molten state, the furan resin gathers in the resin neck portion formed between the sand grains of the molding sand, thereby thickening the neck portion. The dissolved furan-resin organic layer comes into contact with the acid component in the furan-resin organic layer with a time lag, and the final curing progresses. In particular, if the furan resin organic layer is a thinner film, this time difference works effectively, and the film can be dissolved to the deep part, and the fragile layer at the interface can be eliminated more reliably. The furan resin organic layer containing the water of reaction proceeds with the curing reaction over time, and the generated water of reaction can be digested by vaporization. There is also no weakened layer to gain, so the molded mold becomes stronger over time. It is presumed that such a mechanism makes it possible to provide a high-strength mold with a relatively small amount of resin.

Incidentally, there is foundry sand coated with a resol resin called resin-coated sand (hereinafter also referred to as "RCS"). Since RCS also has solubility in alcohols, it is considered to be effective in improving dimensional stability. The solubility of this RCS in alcohols is due to the chemical state of the resole resin. That is, in RCS, the resole resin is not cured. However, the resol resin is recured by the addition of acid and loses its solubility in alcohols. Even if a method of post-adding an acid catalyst solution dissolved in a solvent is used as the method of adding the acid catalyst, the resole resin is still cured, so that the solubility of the resole resin in alcohols is lost.

There are other resins that are soluble in alcohols, but since they are classified as thermoplastics, they cannot withstand the heat of molten metals such as cast iron and aluminum alloys. Therefore, it is difficult to manufacture castings with good accuracy.

As described above, it is structurally difficult to simultaneously achieve dimensional stability and high mold strength with the two-liquid adhesive molding method and molding sand having a curing agent applied to the surface, which are the prior art. In other words, the problem is that the amount of water that can be absorbed into the molding sand is small, and that the reaction time of the resin that increases the strength of the mold is small.

In the present invention, the hardening of the coating binder is mainly caused by the acid component in the furan resin organic layer. For this reason, when manufacturing the mold, it is possible to omit the steps of adding water or a solvent, heating, etc., in addition to the foundry sand and the binder.

Generally, when furan resin is used as a binder, due to the nature of the material, it has been common sense to aim for strength improvement through complete curing. On the other hand, in the present invention, the chemical reaction due to forced mixing of the furan resin and the curing agent, which can be provided by making a sand mold by "tegome", which is one of the casting methods using so-called self-hardening resin, is three. Under the special environment of dimensional additive manufacturing, where forced mixing cannot be performed (i.e., under conditions where the resin component and curing agent are not kneaded during molding), complete curing of the furan resin organic layer is not required. . In this respect as well, it can be clearly distinguished from reclaimed sand in a completely hardened state.

In particular, the inventor of the present invention has completed the present invention by paying attention to the fact that furan resin is generally a resin having high solvent resistance and that it is difficult to dissolve it in alcohol and use it after curing. According to "Furan resin" (published in 1960, authored by Toshiyuki Shono), it is explained that when furan resin obtained by condensing furfuryl alcohol alone is used, it is easy to form a solidified product that does not completely harden and dissolves in an organic solvent. It is Further, it is described that when a product obtained by polymerizing furfuryl alcohol alone is used, internal curability is low and adhesiveness is poor. On the other hand, the formaldehyde polycondensate, which is said to have good internal curability, completely cures the furan resin and cannot form a resin film that is easily soluble in alcohols. In fact, common commercially available furan resins use polycondensates such as formaldehyde to improve adhesion, and the manufactured molds may be coated with an alcoholic mold, resulting in hardening. The material is designed so that furan resin has high solvent resistance.

For this reason, if a commercially available furan resin and a curing catalyst are used, only a highly solvent-resistant resin film can be formed. , the internal curability of the resin film (film) deteriorates, and the water content in the resin film increases. In addition, since the migration phenomenon is not properly controlled, the curing catalyst tends to gather on the surface layer. For this reason, when a binder is applied to connect molding sand to another molding sand, the binder hardens and cannot harden to the inside of the resin film, forming a fragile layer at the interface between the sand grains (bone sand) and the resin film. . As a result, the adhesion between the sand grains and the furan resin film becomes low, and only a mold with low mold strength can be obtained.

In contrast, the present invention provides a foundry sand having a furan resin organic layer having both solubility in alcohols and water receptivity by appropriately controlling the hardening reaction and migration phenomenon of the furan resin. can do. As a result, even under the manufacturing method of three-dimensional additive manufacturing (under the constraint that the resin component and the curing agent are not kneaded), the material of the present invention can obtain both high mold strength and high dimensional stability. can.

3. Three-dimensional additive manufacturing kit The present invention includes a three-dimensional additive manufacturing kit containing the material of the present invention and a binder. That is, the material of the present invention (foundry sand) and the binder are stored separately before use, and are provided as a two-component kit in which the two are mixed at the time of use.

The material of the present invention is usually in the form of smooth dry sand, and can be sprinkled (sprinkled) as it is when filled into a three-dimensional layered molding machine. That is, it is also possible to allow each particle of foundry sand to fall naturally.

The material of the present invention may contain additives other than the foundry sand of the present invention as long as the effects of the present invention are not impaired. For example, as described later, various additives such as an anti-slipping agent and a thickening agent can be premixed with foundry sand.

The binder is not particularly limited as long as it has a viscosity (25° C.) of 1 to 15 mPa·s in order to stably eject from the print head, but it is particularly preferable to use a binder containing a furan resin precursor. . The content of the furan resin precursor is, for example, 85 to 100% by weight, particularly 90 to 98% by weight in the binder, but is not limited thereto.

The furan resin precursor is not limited as long as it can form a furan resin by condensation polymerization or the like, and examples thereof include furfuryl alcohol, furan resin prepolymers, and the like. In particular, it is desirable to use furfuryl alcohol and a furan resin prepolymer together for the reasons of suppression of heat of reaction and reduction of viscosity of the resin.

The furan resin prepolymer includes, for example, a polymer of furfuryl alcohol homopolymer, a copolymer of furfuryl alcohol and an aldehyde compound, a copolymer of furfuryl alcohol, urea and an aldehyde compound (urea-modified furan resin prepolymer), Examples include copolymers of furfuryl alcohol and furfural. These can be used singly or in combination of two or more.

In the present invention, a copolymer of furfuryl alcohol, urea and an aldehyde compound (urea-modified furan resin prepolymer) is particularly preferred because it facilitates high strength. Examples of the aldehyde compounds include formaldehyde, acetaldehyde, glyoxal, and furfural. In the present invention, formaldehyde is particularly preferred.

The binder may contain other components as long as the effects of the present invention are not impaired. For example, additives such as solvents, cross-linking agents, and curing accelerators can be contained as necessary. In particular, as the solvent, water is preferable in the present invention because the reaction rate is moderate and the final mold strength tends to be high.

Curing accelerators include, for example, resorcinol, cresol, hydroquinone, phloroglucinol, methylenebisphenol, bishydroxymethylfuran and the like. The amount of the curing accelerator to be added is appropriately adjusted in view of the amount of reaction water generated.

Further, since the molding sand, which is the other material of the kit, has a furan resin organic layer containing an acid component, the binder can strongly bond the molding sands together without a silane coupling agent. Therefore, the content of the silane coupling agent in the binder is usually about 0 to 1% by mass, preferably 0 to 0.1% by mass. Therefore, it may be a composition that does not contain a silane coupling agent. By reducing the content of the silane coupling agent to a small amount or 0% by mass in this way, the binder can be stored for a longer period of time.

Furthermore, an amine compound can be added to the coating binder as required. Addition of the amine compound can effectively suppress changes in the viscosity of the furan resin precursor over time. However, if the amine compound is excessive, there are problems such as slowing the curing speed and inducing gas defects due to nitrogen. Therefore, the content of the amine compound is desirably about 0.001 to 1% by mass in the binder, more desirably 0.001 to 0.5% by mass, more preferably 0.005 to 0.5% by mass. The content is preferably 1% by mass, and most preferably 0.01 to 0.05% by mass. From the above point of view, the amine compound is preferably an alkylamine having 10 or less carbon atoms, and more preferably butylamine.

The amount of the binder to be used is not particularly limited, but it is usually in the range of about 0.5 to 2.5 parts by mass, particularly 0.5 to 2.0 parts by mass, per 100 parts by mass of the material of the present invention. preferable. If the amount of binder is too small, the strength of the mold may not be obtained. Also, if the amount of the binder is too large, the curing speed becomes slow, so that not only is the handling strength not obtained within a predetermined time, but also the dimensional stability may be lowered. Therefore, it is sufficient that the amounts of the foundry sand and the binder are in the above ratio at the time of use, and the kit of the present invention does not necessarily have to be in the above ratio.

In the present invention, the type of furan resin precursor contained in the binder and the type of furan resin precursor contained in the furan resin organic layer of the material of the present invention may be the same or different. good. Thus, for example, when the furan resin organic layer of the material of the present invention contains a combination of furfuryl alcohol and furan resin prepolymer (especially urea-modified furan resin prepolymer), furfuryl alcohol and furan resin prepolymer (especially urea-modified furan resin prepolymer) can be used. Binders including combinations with furan resin prepolymers) can be employed. When the same kind is used, the affinity between the furan resin organic layer of the foundry sand and the binder is improved, and higher casting strength can be achieved. For example, in the material of the present invention in which the furan resin organic layer contains a combination of furfuryl alcohol and a furan resin prepolymer (especially a urea-modified furan resin prepolymer), furfuryl alcohol is used as a binder for lamination molding. and a binder containing furan resin prepolymer.

However, even if the same type is used, it is not always necessary to completely match the composition ratio, additives, etc., and use it while considering the balance between casting strength and dimensional accuracy. It is possible to finely adjust the compounding ratio of furfuryl alcohol, furan resin polymer, etc., the types of additives, etc., taking into account the characteristics of the three-dimensional layered molding machine.

4. Use of Foundry Sand for Additive Manufacturing The material of the present invention can be used for lamination in the same manner as known foundry sand. More specifically, the step of forming a layer containing foundry sand by sprinkling the foundry sand from above (layer forming step) and the step of adding a binder to a predetermined region of the layer to solidify the region (binder addition The material of the present invention can be suitably used as the foundry sand in the method of manufacturing a mold by a three-dimensional additive manufacturing method including the step of repeating step ) in order. As described above, a mold having a desired shape can be manufactured by supplying the material of the present invention to a known or commercially available three-dimensional layered molding machine. In other words, the material of the present invention can be suitably used as foundry sand for use in a three-dimensional layered molding machine.

Such a three-dimensional layered molding machine (three-dimensional layered molding apparatus) has, for example, a unit, a molding sand supply section, a binder supply section, and an operation section, and is capable of producing a sand mold from 3D-CAD data. A casting machine can be used. The foundry sand supply unit is a unit that supplies foundry sand to the unit, and includes a foundry sand tank that stores the foundry sand, a recoater capable of discharging the foundry sand while moving horizontally, and the like. The binder supply section is a unit that supplies a binder to the unit, and includes a binder tank that stores the binder and a print head that ejects the binder. A known or commercially available device can be used for such a device itself.

In the case of manufacturing a mold by the three-dimensional additive manufacturing method, as described above, the step of forming a layer containing foundry sand (layer forming step) and the step of adding a binder to a predetermined region of the layer to solidify the region. A laminate manufacturing method including a step of sequentially repeating the (binder addition step) can be employed. At this time, the curing agent contained in the furan resin organic layer of the foundry sand contributes to the solidification of both the furan resin organic layer and the binder, so that a desired sand mold can be obtained.

Layer Forming Step In the layer forming step, a layer containing foundry sand is formed. More specifically, a layer containing foundry sand can be formed by sprinkling foundry sand from above. Since the material of the present invention is basically in the form of dry sand, it can be allowed to fall smoothly (spray). When a three-dimensional layered molding machine as described above is used, the layers can be reliably formed by discharging molding sand onto a flat surface from a recoater that moves horizontally.

Further, in the layer forming step, the layer may contain components other than foundry sand within a range that does not interfere with smooth layer formation. As such components, components added to known foundry sand can also be employed.

In the present invention, for example, an anti-slip agent can be preferably used. The anti-slip agent is preferably a high-boiling organic compound having a boiling point of 35° C. or higher. Examples include unsaturated fatty acids (eg, linoleic acid, oleic acid, linolenic acid, etc.), saturated fatty acids (eg, lauric acid, myristic acid, stearic acid, etc.), isophorone, xylene, silicone oils, and the like. Anti-slip agents can be used alone or in combination of two or more. Among such anti-slip agents, unsaturated fatty acids are particularly preferred, and linoleic acid is most preferred. The anti-slip agent can be added in the layer forming process, or it can be pre-mixed with the foundry sand. The addition ratio of the anti-slip agent can be, for example, about 0 to 0.1 parts by mass with respect to 100 parts by mass of the material of the present invention. Therefore, anti-slip agents need not be included.

In the conventional additive manufacturing method (wet sand, two-liquid mixing process of hardening agent and binder resin), when artificial sand made by melting method etc. is used as sand grains, the surface smoothness and Due to the roundness of the molding sand, if a liquid agent is added to the molding sand, the molding sand will cause a liquid bridge phenomenon (coagulation), which will impair the fluidity of the sand, which is important in the additive manufacturing method, and the use of small-sized sand grains. becomes difficult. For this reason, there has been proposed a method of adding a drying process to make the sand like dry sand to improve fluidity, but the usable sand grains are limited to sintered artificial sand. By adding a fatty acid such as linoleic acid as an anti-slipping agent to the furan resin organic layer of the foundry sand of the present invention, it is possible to more reliably obtain stable lamination properties regardless of the sand type, particle size, and the like. That is, even if molten artificial sand with high smoothness and roundness is used as sand grains, it becomes possible to retain the foundry sand of the present invention in, for example, a recoater of a three-dimensional multi-layer molding machine without spilling the sand. Also, additional equipment for adding agents such as linoleic acid can be omitted from the three-dimensional layered molding machine. Furthermore, it is possible to prevent the molding sand of the present invention from collapsing after lamination.

In addition, a thickening agent such as wax such as cellulose, sodium alginate, palmitic acid, etc. is used as long as it does not impair the effects of the present invention (especially within a range that does not impair the reaction control of the furan resin or various characteristics as a template). can also The amount of the thickener to be added is not particularly limited, but it is usually 50 parts by mass or less, more preferably 25 parts by mass or less, and most preferably 1 part by mass or less per 100 parts by mass of the material of the present invention. Therefore, it can be set to 0 parts by mass, for example.

In addition, if necessary, a powder capable of giving fine irregularities to the surface of the foundry sand may be added. Thereby, the fluidity and the like of the foundry sand of the present invention can be controlled. Such powders are not particularly limited as long as they have the above functions, and for example, powders of carbon, silica, etc. can be used. The particle size of this powder can be, for example, 1 μm or less, but is not limited to this. Also, the shape of the particles constituting the powder is not limited, and may be, for example, spherical, flake-like (scale-like), needle-like (fibrous), irregular shape, or the like. It may be of any type, such as a simple body.

The thickness of the layer depends on the particle size of the foundry sand, the desired shape of the mold, etc., but it is usually about 100 to 400 μm, preferably 200 to 300 μm. When the layer forming process is repeated, the layer thicknesses formed in each layer forming process may be the same or different.

Binder Addition Step A binder is added (sprayed) to a predetermined region of the layer to solidify the region. A layer containing foundry sand is formed as a single layer by the layer forming step, and the binder is added to the region based on the cross-sectional shape data of the desired compact. For example, when using a three-dimensional layered molding machine as described above, a predetermined area can be solidified by spraying a binder onto the layer from a horizontally moving print head (nozzle). As the binder and the like, for example, those described in the above "3. Three-dimensional additive manufacturing kit" can also be used.

After repeating a series of steps consisting of a combination of the layer forming step and the binder adding step, a molded body (mold) having a predetermined shape can be obtained by removing the portion where the binder is not added.

The compact can then be aged if desired. As a result, curing of the resin component can be accelerated, and a molded article having higher strength can be obtained. The aging conditions are, for example, a temperature of 15-25° C. and a humidity of 45% or less, and particularly a temperature of 20-25° C. and a humidity of 40% or less, but are not limited thereto. For example, the temperature may be 20-25° C. and the humidity 30-45%. Also, the aging time can be, for example, about 1 to 48 hours, but is not limited to this.

A mold thus obtained using suitable foundry sand can realize dimensional stability, high strength, and high design reproducibility. Since the material of the present invention is a dry powder, it can be stably laminated, and since it has excellent dimensional stability, it is possible to further reduce the dimensional tolerance between the 3D-CAD drawing and the resulting mold. In addition, it is also excellent in mass production, and since it is possible to take out the mold (molded body) in about 3 hours normally, and in about 1 hour at the earliest, the additive manufacturing method is also suitable for the production of cast products that require mass production. becomes widely applicable.

EXAMPLES Examples and comparative examples are shown below to describe the features of the present invention more specifically. However, the scope of the present invention is not limited to the examples. "%" indicating the content of the composition in each table means "parts by mass".

Example 1
5 kg of AFS108 mullite-based sintered artificial sand (Cerabeads X#1450 manufactured by Itochu Ceratec Co., Ltd., angle of repose: 31°) (CBX sintered new sand); A curing agent "configuration 2" was prepared. 0.3 parts by mass of the furan resin composition of Structure 1 was added to 100 parts by mass of the artificial sand when the sand temperature of the artificial sand reached 35°C, and the mixture was stirred and mixed in a kneader for 30 seconds. . The sand temperature was 41°C. Next, 0.3 parts by mass of the hardening agent of "Constitution 2" per 100 parts by mass of artificial sand and 0.3 parts by mass of water as a solvent were added to the resulting mixture, and the mixture was mixed with 30 parts by mass in a kneader. Mixed for 2 seconds. Finally, as a drying step, while blowing cold air into the kneader, stirring was continued for 240 seconds until the sand temperature reached 60° C., and then the sand was discharged from the kneader to obtain foundry sand.

Example 2
The same foundry sand as in Example 1 was prepared.

Example 3
A foundry sand was prepared in the same manner as in Example 1 except that the composition and conditions shown in Table 4 were used. In particular, the following changes were made with respect to Example 1. Curing agent was added to the mixture without adding solvent. In the drying process of the mixture, the foundry sand was obtained without introducing air. It took 240 seconds for the sand temperature to reach 60°C at the time of discharge.

Example 4
A foundry sand was prepared in the same manner as in Example 1 except that the composition and conditions shown in Table 4 were used. In particular, the following changes were made with respect to Example 1. 0.1 part by mass of the furan resin composition of Structure 1 was added to 100 parts by mass of artificial sand, and the mixture was stirred and mixed for 30 seconds. The sand temperature was 41°C. Next, 0.03 part by mass of oxalic acid (powder) per 100 parts by mass of artificial sand was added to the resulting mixture and mixed for 10 seconds. The sand temperature was 43°C. Next, 0.15 parts by mass of the hardening agent of "configuration 2" was added to 100 parts by mass of the artificial sand and mixed for 30 seconds. Finally, as a drying step, stirring was continued for 240 seconds until the sand temperature reached 60° C., which is the discharge temperature, and then the sand was discharged from the kneader to obtain foundry sand. No air was introduced in the drying process.

Example 5
A foundry sand was prepared in the same manner as in Example 1 except that the composition and conditions shown in Table 4 were used. In particular, the following changes were made with respect to Example 1. To 100 parts by mass of artificial sand, 0.3 parts by mass of the curing agent of "Configuration 2", 0.005 parts by mass of cellulose nanofiber (CNF), and 0.145 parts by mass of water are added and mixed for 30 seconds. did. In the drying step, stirring was continued for 480 seconds until the sand temperature reached 60° C., which is the discharge temperature, and then the sand was discharged from the kneader to obtain foundry sand. No air was introduced in the drying process.

Example 6
The artificial sand was changed to 25 kg of AFS100 mullite-based molten artificial sand (Espearl #100DAM manufactured by Yamakawa Sangyo Co., Ltd., angle of repose: 24°) (EP molten new sand); A curing agent "Configuration 2" in Table 2 was prepared. When the artificial sand was heated to a sand temperature of 70° C., 0.25 parts by mass of the furan resin composition of “Configuration 1” was added to 100 parts by mass of the artificial sand, and the mixture was stirred and mixed for 90 seconds. . Next, 0.25 parts by mass of the hardening agent of "Configuration 2" per 100 parts by mass of artificial sand was added to the resulting mixture, and the mixture was mixed for 90 seconds while maintaining the sand temperature at 70°C. Finally, the mixture was stirred for an additional 240 seconds while maintaining the temperature at 70° C. until it became dry powder, and then discharged from the kneader to obtain foundry sand. No air was introduced in the drying process.

Example 7
Sand grains were mixed with 5 kg of AFS88 natural silica sand (Albany #90 manufactured by Touchu Co., repose angle 36°) (ALB silica sand new sand), furan resin composition “Constitution 1” in Table 1, and curing agent “Constitution 2” in Table 2. prepared. When the sand temperature of the silica sand reached 35° C., 0.15 parts by mass of the furan resin composition of Structure 1 was added to 100 parts by mass of sand, and the mixture was stirred and mixed for 40 seconds. The sand temperature was 41°C. Next, 0.15 parts by mass of the curing agent of "Constitution 2" per 100 parts by mass of the silica sand and 0.15 parts by mass of water as a solvent were added to the obtained mixture and mixed for 40 seconds. Finally, as a drying step, the sand was stirred for 270 seconds while blowing cold air into the kneader until the sand temperature reached 60° C., and then discharged from the kneader to obtain foundry sand.

Example 8
A foundry sand was prepared in the same manner as in Example 1 except that the composition and conditions shown in Table 4 were used. In particular, the following changes were made with respect to Example 1. To 100 parts by mass of artificial sand, 0.3 parts by mass of the furan resin composition of Configuration 1 and 0.01 parts by mass of liquid resol were added and stirred for 40 seconds. The sand temperature was 41°C. Next, 0.3 parts by mass of the curing agent of "Constitution 2" per 100 parts by mass of artificial sand and 0.3 parts by mass of water as a solvent were added to the resulting mixture and mixed for 40 seconds. Finally, as a drying step, stirring was continued for 300 seconds until the sand temperature reached 60° C., and then the sand was discharged from the kneader to obtain foundry sand. No air was introduced in the drying process.

Example 9
A foundry sand was prepared in the same manner as in Example 1 except that the composition and conditions shown in Table 4 were used. In particular, the following changes were made with respect to Example 1. A mixture obtained by preparing 20 kg of sand grains to obtain foundry sand, adding 0.4 parts by mass of the furan resin composition "Configuration 1" in Table 1, and stirring for 90 seconds. In addition, 0.4 parts by mass of the hardening agent "Constitution 2" was added to 100 parts by mass of the artificial sand, and 0.4 parts by mass of water was added as the solvent to 100 parts by mass of the artificial sand. After mixing for 90 seconds, air was introduced and stirring was continued for 330 seconds until the sand temperature reached 60° C., which was the discharge temperature, to obtain molding sand.

Example 10
A foundry sand was prepared in the same manner as in Example 1 except that the composition and conditions shown in Table 4 were used. In particular, the following changes were made with respect to Example 1. 1 kg of polished and roasted reclaimed artificial sand that was polished and roasted (roasted at 1000° C. after 5 minutes of polishing, angle of repose: 31°) as sand grains, the furan resin composition “Configuration 1” in Table 1, and the curing agent in Table 2. "Composition 2" was prepared. 0.3 parts by weight of the furan resin composition of Structure 1 was added to 100 parts by weight of artificial sand while the temperature of the sand grains was 24° C., and the mixture was stirred and mixed for 40 seconds. The sand temperature was 24°C. Next, 0.3 parts by mass of the curing agent of "Constitution 2" per 100 parts by mass of artificial sand and 0.3 parts by mass of water as a solvent were added to the resulting mixture and mixed for 40 seconds. Finally, as a drying step, the sand was stirred for 240 seconds until the temperature of the sand reached 60° C., and then discharged from the kneader to obtain foundry sand. No air was introduced in the drying process.

Example 11
A foundry sand was prepared in the same manner as in Example 1 except that the composition and conditions shown in Table 5 were used. In particular, the following changes were made with respect to Example 1. To 100 parts by mass of artificial sand, 0.3 parts by mass of the furan resin composition of Configuration 1 and 0.005 parts by mass of liquid resol were added and stirred for 40 seconds. The sand temperature was 44°C. Next, 0.3 parts by mass of the curing agent of "Constitution 2" per 100 parts by mass of artificial sand and 0.3 parts by mass of water as a solvent were added to the resulting mixture and mixed for 40 seconds. Finally, as a drying step, stirring was continued for 300 seconds until the sand temperature reached 60° C., and then the sand was discharged from the kneader to obtain foundry sand. No air was introduced in the drying process.

Example 12
A foundry sand was prepared in the same manner as in Example 11 except that the composition and conditions shown in Table 5 were used. In particular, the following changes were made to Example 11. To 100 parts by mass of artificial sand, 0.3 parts by mass of the furan resin composition of Configuration 1 and 0.1 parts by mass of liquid novolak were added and mixed by stirring for 40 seconds. The sand temperature was 44°C. As a drying step, stirring was continued for 300 seconds until the sand temperature reached 60° C., and then the sand was discharged from the kneader to obtain foundry sand.

Example 13
A foundry sand was prepared in the same manner as in Example 11 except that the composition and conditions shown in Table 5 were used. In particular, the following changes were made to Example 11. To 100 parts by mass of artificial sand, 0.3 parts by mass of the furan resin composition of Structure 1 and 0.03 parts by mass of phenol urethane resin were added and mixed by stirring for 40 seconds. The sand temperature was 44°C. As a drying step, stirring was continued for 300 seconds until the sand temperature reached 60° C., and then the sand was discharged from the kneader to obtain foundry sand.

Example 14
A foundry sand was prepared in the same manner as in Example 11 except that the composition and conditions shown in Table 5 were used. In particular, the following changes were made to Example 11. To 100 parts by mass of artificial sand, 0.3 parts by mass of the furan resin composition of Configuration 1 and 0.05 parts by mass of phenol urethane resin were added and stirred for 40 seconds. The sand temperature was 44°C. As a drying step, stirring was continued for 300 seconds until the sand temperature reached 60° C., and then the sand was discharged from the kneader to obtain foundry sand.

Example 15
A foundry sand was prepared in the same manner as in Example 11 except that the composition and conditions shown in Table 5 were used. In particular, the following changes were made to Example 11. To 100 parts by mass of artificial sand, 0.3 parts by mass of the furan resin composition of Configuration 1 and 0.01 parts by mass of an alkali phenol resin were added and mixed by stirring for 40 seconds. The sand temperature was 44°C. As a drying step, stirring was continued for 300 seconds until the sand temperature reached 60° C., and then the sand was discharged from the kneader to obtain foundry sand.

Example 16
A foundry sand was prepared in the same manner as in Example 1 except that the composition and conditions shown in Table 5 were used. In particular, with respect to Example 1, the following changes were made. To 100 parts by mass of artificial sand, 0.5 parts by mass of the furan resin composition "Constitution 1" shown in Table 1 was added, and the resulting mixture was stirred for 90 seconds. 2" was changed to 0.25 parts by mass with respect to 100 parts by mass of the artificial sand, and water as a solvent was changed to 0.25 parts by mass with respect to 100 parts by mass of the artificial sand and added. After mixing for 60 seconds, air was introduced and stirring was continued for 240 seconds until the temperature of the sand reached 60°C, which was the discharge temperature, to obtain molding sand.

Example 17
A foundry sand was prepared in the same manner as in Example 1 except that the composition and conditions shown in Table 5 were used. In particular, with respect to Example 1, the following changes were made. To 100 parts by mass of artificial sand, 0.7 parts by mass of the furan resin composition "Constitution 1" in Table 1 was added, and the resulting mixture was stirred for 90 seconds. 2” was changed to 0.28 parts by mass with respect to 100 parts by mass of the artificial sand, and water as a solvent was changed to 0.28 parts by mass with respect to 100 parts by mass of the artificial sand. After mixing for 60 seconds, air was introduced and stirring was continued for 240 seconds until the temperature of the sand reached 60°C, which was the discharge temperature, to obtain molding sand.

Comparative example 1
1 kg of regenerated artificial sand (angle of repose: 33°) was prepared by polishing mullite-based sintered artificial sand that had been mechanically polished (Sand Fresher manufactured by Kiyota Casting Co., Ltd.) for 5 minutes.

Comparative example 2
1 kg of mullite-based artificial sand roasted at 500° C. after mechanical polishing (Sand Fresher manufactured by Kiyota Casting Co., Ltd.) for 5 minutes was prepared. The solubility was not measured because it could be determined that the reclaimed sand had been roasted and the resin layer had almost disappeared.

Comparative example 3
The same reclaimed sand as in Comparative Example 1 was used as sand grains. To 100 parts by mass of reclaimed sand, 0.3 parts by mass of the hardening agent "Composition 2" and 0.3 parts by mass of water were added to obtain wet foundry sand. The stirring time was 30 seconds. The angle of repose could not be measured because the foundry sand was wet and could not be passed through the measuring instrument.

Comparative example 4
The same reclaimed sand as in Comparative Example 2 was used as sand grains. To 100 parts by mass of reclaimed sand, 0.3 parts by mass of hardening agent "Composition 2" and 0.3 parts by mass of water were added to obtain wet foundry sand. The stirring time was 30 seconds. The angle of repose could not be measured because the foundry sand was wet and could not be passed through the measuring instrument. Further, the solubility was not measured because it could be determined that the reclaimed sand had been roasted and the resin layer had almost disappeared.

Comparative example 5
A test piece (test example 1 (5) described later) for measuring the pitting strength of the casting sand obtained in Example 1 was pulverized to prepare 1 kg of hardened artificial sand (angle of repose: 32°).

Comparative example 6
200 g of recovered sand (angle of repose: 33°) used for casting was prepared as sand grains. To 100 parts by mass of this recovered sand, 0.3 parts by mass of the hardening agent "Composition 2" and 0.3 parts by mass of water were added to obtain wet foundry sand. The stirring time was 30 seconds. The angle of repose could not be measured because the foundry sand was wet and could not be passed through the measuring instrument.

Comparative example 7
As sand grains, 5 kg of new sand of AFS108 mullite-based sintered artificial sand (Cerabeads X#1450 manufactured by Itochu Ceratec Co., Ltd., angle of repose: 31 °) (CBX sintered new sand) same as in Example 1 and the furan resin composition shown in Table 1 1” and the curing agent “Configuration 2” in Table 2 were prepared. 0.1 part by mass of the furan resin composition of Structure 1 was added to 100 parts by mass of the artificial sand while the temperature of the artificial sand was 24° C., and the mixture was stirred and mixed in a kneader for 30 seconds. The sand temperature was 24°C. Next, 0.15 parts by mass of the hardening agent of "Constitution 2" per 100 parts by mass of artificial sand was added to the resulting mixture, and mixed in a kneader for 300 seconds. The sand was discharged from the kneader without being subjected to a drying step to obtain a dry powder-like foundry sand.

Comparative example 8
A foundry sand was prepared in the same manner as in Comparative Example 7 except that the composition and conditions shown in Table 6 were used. In particular, the comparative example 7 was changed as follows. 0.1 part by mass of the furan resin composition of Structure 1 was added to 100 parts by mass of artificial sand, and the mixture was stirred and mixed for 30 seconds. The sand temperature was 24°C. Next, 0.15 parts by mass of the hardening agent of "Configuration 3" was added to 100 parts by mass of artificial sand, and mixed in a kneader for 300 seconds. In the same manner as in Comparative Example 7, the sand was discharged from the kneader without adding a drying step to obtain a dry powder foundry sand.

Test example 1
The following physical properties were evaluated for the molding sand samples obtained in Examples and Comparative Examples. The results are shown in Tables 4-6.

(1) pH
The pH was measured using a portable pH meter "IM-32P" manufactured by DKK Toa. 10 g of molding sand sample and 50 g of deionized water are weighed out in a beaker, and the electrode of the pH measuring device is immersed in the beaker. I waited in that state for about 5 to 10 seconds. After that, the electrode was used to stir the inside of the beaker (for 10 seconds at a speed of about 2 rotations per second), and then left to stand for 5 minutes. The value on the pH meter was read after 5 minutes. A sample with a pH of 4 or less measured within 10 days after preparation of the sample is accepted. The pH of the sand grains (the sand grains before forming the furan resin organic layer) as the starting material was also measured in the same manner.

(2) Repose angle The repose angle was measured according to JACT test method S-5. About 1 kg of each molding sand sample was used, and a protractor was used to read the angle between the slope formed by the sand pile and the horizontal plate. The angle of repose was measured in a room adjusted to room temperature of 20-25° C. and humidity of 30-40%. Samples with an angle of repose of 42° or less were accepted.

(3) Igross Igross (I) was measured in the following manner. Measurements with a balance were performed in a room adjusted to a temperature of 20-25° C. and a humidity of 30-40%. Igross (I) of 1.0% by mass or less was regarded as acceptable.
1) Weigh 5 g of each foundry sand sample into a glass beaker, heat it at 120° C. for 60 minutes using a dryer, and dry it.
2) Transfer the dried sample into a silica gel-treated (dehumidified) desiccator and allow it to cool to room temperature. (Reduces the effect of water absorption during weighing exhibited by the present invention).
3) Similarly, an alumina crucible is also dried and cooled in a desiccator.
4) Weigh the cooled alumina crucible on a balance and record the crucible weight. Put the molding sand sample of 2) into the crucible after the measurement, and record the total weight of the crucible + the molding sand sample.
5) The crucible containing the sample is fired in an electric furnace at 1000° C. for 1 hour to degrease.
6) After 1 hour, the sample is removed from the oven, transferred into a silica gel-covered (dehumidified) desiccator, and allowed to cool to room temperature.
7) Weigh and record the weight of the cooled sample together with the crucible.
8) Obtain the igross (I) from the following formula.
[(Sample weight before baking - Sample weight after baking) / Sample weight before baking] × 100 (mass%)

(4) Solubility The solubility in methanol (25°C) was measured in the following manner. Since the solubility is affected by temperature and humidity, the experiment was performed in a room adjusted to a temperature of 20-25° C. and a humidity of 30-40%. Measured twice and averaged. A resin film having a solubility in methanol of 32% or more is regarded as acceptable.
1) Measure the igross (I) of various foundry sand samples.
2) Weigh 5 g of various molding sand samples on a circular quantitative filter paper 5B (110 mm in diameter) and set it in a funnel (60 mm in diameter, 8 mm in foot diameter, 65 mm in foot length).
3) Pour 10 mL of methanol (purity>99.8%) into the funnel repeatedly 20 times at 1 minute intervals and filter. During this time, the foundry sand sample in the funnel was kept submerged in methanol. By doing so, the fresh methanol and the foundry sand sample can always come into contact with each other, and at the same time, the oxidation reaction of the resin film due to exposure to air can be prevented.
4) The sample dissolved in methanol is dried together with the filter paper in a dryer at 120°C for 1 hour to remove moisture and methanol.
5) Collect as much of the dried foundry sand sample as possible from the filter paper, and measure the igross (II) after dissolution in the same manner as the igross (I).
6) Solubility was calculated using the following formula.
{Igross (I) - Igross (II)}/Igross (I) x 100 = solubility (%)

(5) Bending strength (TP strength)
A 200 g sample of each foundry sand was weighed into a cooking bowl. The binder for coating shown in Table 3 was added to all the foundry sand samples and stirred for 10 seconds using a stirrer to obtain a mixture. It was left for 30 minutes under conditions of a temperature of 23-25° C. and a humidity of 40-45%, and then removed from the die. Thus, a test piece for bending strength measurement was produced.
After that, using the test piece, the three-point bending strength was measured immediately after (30 minutes), 1 hour and 3 hours after the die was removed. The strength was measured according to JACT test method SM-1. A sample whose strength was measurable after 30 minutes and had a strength of 35 kg/cm ² or more after 3 hours was regarded as acceptable.
As the coating binders used, two types of binders having different curing speeds depending on the presence or absence of a curing accelerator were prepared. Their compositions are shown in Table 3. Each of these ingredients was weighed into a beaker and mixed for 15 minutes at room temperature to prepare each binder. The viscosities of these binders were measured with an E-type viscometer at a constant temperature of 25° C., and the results were 7 mPa·s for Preparation Example 1 and 10 mPa·s for Preparation Example 2.

(5) Exudation Amount As a measure of the dimensional accuracy of the obtained sample, the amount of exudation due to dropping of the binder was evaluated. The seepage amount is an index of dimensional accuracy, and the lower the value, the higher the dimensional accuracy that can be achieved.
The bleeding amount was measured in the following manner. A dish having a diameter of 35 mm and a height of 10 mm is prepared, various molding sand samples shown in Tables 4 to 6 are placed therein, and the surface is smoothed using a ruler. 5 μl of the binder “Preparation Example 1” in Table 3 is sucked up with a micropipette and made into one drop, which is dropped from a height of 5 mm. After being left at room temperature of 24° C. and humidity of 40% for 60 minutes, it is transferred to a dryer at 60° C. and heated for 30 minutes. After heat curing, the solidified portion was collected with a spoon, excess sand was removed with a brush, and the weight of the solidified product was measured. If the weight of the solidified product is 0.170 g or less, it is accepted.

As is clear from the results in Tables 4 to 6, the foundry sands of Examples are excellent in all physical properties. In other words, it can be seen that high dimensional accuracy can be expected because the amount of bleeding is suppressed to a low value of 0.170 g (furthermore, 0.150 g or less) in addition to high strength. In particular, it can be seen that a high strength of 25 kg/cm ² or more (further 30 kg/cm ² or more) can be developed in a short time of 30 minutes after molding.

On the other hand, in Comparative Examples 1 and 2, the igross remaining in the recycled sand could not be used to harden the binder, and the strength could not be measured because the mold could not be removed.

In Comparative Example 3, the target piercing strength could not be obtained only by coating the residual resin layer of the reclaimed sand with the curing agent alone. It is believed that reaction water generated during curing of the coating binder caused internal curing failure. From this point of view, it can be understood that the furan resin organic layer of the present invention complements the strength of the mold and serves as a reservoir for reaction water.

In Comparative Example 4, the target piercing strength could not be obtained only by coating the residual resin layer of the reclaimed sand with the curing agent alone. This is probably because the water added as a solvent, in particular, caused internal curing failure.

In Comparative Example 5, the target piercing strength was not obtained. From this, it can be seen that the furan resin organic layer of the present invention plays an auxiliary role in improving the mold strength.

In Comparative Example 6, the target piercing strength could not be obtained by only adding the curing agent to the residual resin layer of the recovered sand. It is believed that reaction water generated during curing of the coating binder caused internal curing failure.

In Comparative Example 7, since no drying step was added, the migration phenomenon could not be controlled, and the target bending strength could not be obtained. It is presumed that the reason for this is that the curing reaction proceeded too much, so that the solubility of the furan resin organic layer decreased and the reaction with the binder did not proceed so much.

In Comparative Example 8, the migration phenomenon could not be controlled similarly to Comparative Example 7, and the target mold strength could not be obtained. It is presumed that the reason for this is that the curing reaction proceeded too much, so that the solubility of the furan resin organic layer decreased and the reaction with the binder did not proceed so much.

As described above, it is found that controlling the solubility of the furan resin organic layer and controlling the amount of reaction water produced are effective for increasing the strength of the mold. With the material of the present invention, the dimensional stability of the mold can be ensured by producing an appropriate amount of reaction water.

In addition, with respect to the seepage amounts shown in Tables 4 to 6, all the foundry sands according to the examples had a low seepage amount of 0.170 g or less, as described above, and it can be seen that high dimensional accuracy can be exhibited. On the other hand, the samples (Comparative Examples 3 and 4, Comparative Examples 6) to which only the curing agent was added and the samples (Comparative Examples 7 and 8) in which the migration phenomenon could not be controlled were the reaction generated during curing of the coating binder, etc. It can be seen that because the water receptor could not be properly formed in the furan-resin organic layer (or because there was no furan-resin organic layer), the amount of seepage increased, making it difficult to obtain dimensional accuracy. Also, as can be seen from the comparison between Example 3 and Example 4, or from the comparison between Example and Comparative Example, the amount of bleeding and the TP strength by the binder (after 30 minutes), that is, the curing speed It can be seen that there is no correlation.

Test example 2
Foundry sand samples (Samples 1 to 4) were prepared in the same manner as in Example 1 except that the composition was as shown in Table 7, and the water content (mass ppm) of the obtained samples was measured. The moisture content was measured using a Karl Fischer moisture meter "MKV-710" manufactured by Kyoto Electronics Industry Co., Ltd. under the conditions of 150° C., nitrogen flow rate of 200 mL/min, and moisture vaporization method. Each sample was measured within 1 day after fabrication.

As described above, it can be seen that Samples 1 to 4 according to the present invention are in the form of dry powder having an angle of repose of 42° or less and a water content of 1200 ppm or less (especially in the range of 300 to 800 ppm).

Claims (9)

A foundry sand for use in a method for manufacturing a mold by an additive manufacturing method, which comprises the steps of forming a layer containing the foundry sand and adding a binder to a predetermined region of the layer to solidify the region. hand,
(1) A furan resin organic layer containing a furan resin precursor and an acid component is formed on the surface of the sand grains constituting the foundry sand,
(2) the acid component comprises ethylbenzenesulfonic acid and xylenesulfonic acid;
(3) The furan resin organic layer has a solubility in methanol (25° C.) of 32% or more.
A casting sand for additive manufacturing characterized by: 2. The casting sand for additive manufacturing according to claim 1, wherein the igross contained in the casting sand for additive manufacturing is 1.0% by mass or less. 3. The casting sand for additive manufacturing according to claim 1, wherein the pH of the dispersion medium in the dispersion of 10 g of the casting sand for additive manufacturing/50 g of water is 4 or less. The casting sand for additive manufacturing according to any one of claims 1 to 3, wherein the casting sand for additive manufacturing has an angle of repose of 42° or less under conditions of a temperature of 25°C and a humidity of 40%. A method for producing foundry sand for additive manufacturing, comprising:
a) mixing starting material sand with a composition comprising a furan resin precursor and a solvent at 100° C. or less to obtain a first mixture;
b) mixing the first mixture with an acid component-containing composition comprising ethylbenzenesulfonic acid and xylenesulfonic acid at 100°C or less to obtain a second mixture; and c) mixing the second mixture at 120°C or less. A method for producing foundry sand, comprising the step of obtaining dry sand-like foundry sand by drying. The production method according to claim 5, further comprising adding 0.01 to 3 parts by mass of water to 100 parts by mass of sand. The manufacturing method according to claim 5 or 6, wherein the drying is performed at a temperature of 50 to 80°C for 60 to 600 seconds. The production method according to claim 5 or 6, wherein the drying is performed until the water content of the second mixture reaches 300 to 1200 mass ppm. A three-dimensional additive manufacturing kit comprising the additive manufacturing foundry sand according to any one of claims 1 to 4 and a binder.