JP7606375B2 - Curable composition and method for producing same - Google Patents

Description

The present invention relates to a curable composition.

Patent Document 1 is an invention in the field of application of lumps called concretions found in layers of sedimentary rock. Patent Document 1 proposes a structural material that is characterized by comprising a base material for forming a structure, and an ion supply source that supplies at least one of cations and anions that constitute sparingly soluble salts that are present inside or on the surface of the base material and have a solubility in water of a first value or less at the temperature of the environment in which the base material is disposed. In addition, Non-Patent Document 1 describes the principle of Patent Document 1.

Another invention in the field of inorganic hardening compositions is Patent Document 2. Patent Document 2 describes how a composition containing magnesium oxide, water, and ethylene carbonate (ethylene carbonate) can be molded and cured for 28 days to produce a building material with excellent compressive strength.

International Publication No. 2020/040243 Japanese Patent Application Publication No. 08-143352

Hidekazu Yoshida et al. , Scientific Reports volume 5, Article number: 14123 (2015)

Patent Document 1 describes the application of the mechanism of formation of spherical lumps called concretions in horn shells to fields such as cement-based structural materials. The compressive strength of natural concretions is extremely high, for example, 100 N/ ^mm2 . However, in structures produced by the method described in Patent Document 1, although a layer of calcium carbonate could be formed, it was not possible to reproduce the high compressive strength of natural concretions.

For example, materials for modeling used in 3D printers are required to have not only high strength after curing but also a high curing speed.

Therefore, the present invention has been made in consideration of the above circumstances, and aims to provide a curable composition that has a high curing rate and can produce a cured product with high strength.

The inventors have investigated a method for producing a high-strength hardened body from a hardenable composition by applying the mechanism of concretions. As a result of observing natural concretions, the inventors have discovered that calcium carbonate is arranged in the gaps between rocks, resulting in a morphology in which the constituent components are densely packed. They then infer that the dense morphology is what gives the concretions their high compressive strength.

The inventors considered kneading a carbonate source such as ethylene carbonate, propylene carbonate, or glycerol carbonate with a calcium source such as calcium hydroxide or calcium oxide to fill the gaps in the calcium carbonate and create a dense morphology. After kneading, the carbonate source decomposes to generate carbon dioxide, which is then absorbed by calcium hydroxide or calcium oxide to fill the gaps in the calcium carbonate. They conducted experiments based on this assumption. Initially, the inventors tried a method of generating carbon dioxide by thermally decomposing and hydrolyzing ethylene carbonate. As a result, they discovered that when a specific combination of glycerol carbonate (glycerol-1,2-carbonate) and calcium hydroxide is kneaded, a hardenable composition and structure that can produce a hardened body with high strength can be obtained, and thus the present invention was completed.

The detailed mechanism by which the hardened body of the present embodiment has high strength has not been clarified. The inventors have arrived at the finding from experiments that high strength can be achieved when glycerol carbonate is used as the carbonic acid supply source and calcium hydroxide is used as the calcium supply source.
For example, when calcium hydroxide is used as the calcium source, ethylene carbonate as the carbonic acid source, and calcium carbonate as the aggregate, the compressive strength of the structure is 5 to 10 N/mm2 ^. This is presumably because ethylene carbonate has a melting point of 36°C and is solid at 25°C, so it simply hardens by wrapping around the surrounding materials, and no hardening reaction occurs. When kneading this ethylene carbonate, it is used after it has been made liquid by boiling it in hot water. Note that glycerol carbonate is liquid at 25°C, so there is no need to boil it in hot water.
For example, when calcium oxide was used as the calcium source, glycerol carbonate as the carbonic acid source, and calcium carbonate as the aggregate, the compressive strength of the structure was 30 to 40 N/ ^mm2 , and when the structure was left in the air, it turned into powder and collapsed.
For example, when calcium oxide was used as the calcium source, glycerol carbonate as the carbonic acid source, and calcium carbonate as the aggregate, the hardening reaction occurred in the same way as when glycerol carbonate was used. However, when the hardened body was stored in the air, it turned into powder and collapsed (a dusting-like phenomenon occurred).

When considering the mechanism by which the strength of the cured body of the present embodiment is improved, the inventors considered Patent Document 2 as a system similar to the cured body of the present embodiment. However, although Patent Document 2 describes a system using magnesium oxide, ethylene carbonate, and water, it does not describe the mechanism in detail.
The present inventors have also investigated a system in which calcium hydroxide or calcium oxide is used as a calcium supply source, ethylene carbonate is used as a carbonic acid supply source, and water is further added, with reference to Patent Document 2. Although it depends on the composition of the raw materials, it has been confirmed that although heat is generated, hardening does not proceed from the surface, or even if hardened, the hardened body does not exhibit the same compressive strength as the hardened body of the present embodiment.

From the above, the inventors discovered that by studying the mechanism of concretion, it is possible to obtain a hardened body with high strength, and thus completed the present invention.

That is, the curable composition of the present invention contains a cyclic carbonate having a hydroxy group and calcium hydroxide, and the compressive strength of the curable composition becomes 30 N/mm2 ^{or more} within 1.5 hours from immediately after mixing the cyclic carbonate and calcium hydroxide.

The above mixing is preferably carried out under reduced pressure, at 5°C or less, and for a mixing time of 5 minutes to 1 hour.

（式（Ｉ）中、Ｒ^１は２～６個の炭素原子を含む二価の炭化水素基であり、当該炭化水素基の水素原子のうち少なくとも１つは、ヒドロキシ基により置換されている）。 The cyclic carbonate is preferably a compound represented by the following formula (I).

In formula (I), R ¹ is a divalent hydrocarbon group containing 2 to 6 carbon atoms, at least one of the hydrogen atoms of the hydrocarbon group being substituted with a hydroxy group.

It is preferable that the hardenable composition of the present invention further contains aggregate.

The mixing ratio of the cyclic carbonate is preferably 40 parts by mass or less per 100 parts by mass of the total amount of calcium hydroxide and aggregate.

The mixing ratio of the calcium hydroxide is preferably 80 parts by mass or less per 100 parts by mass of the total amount of calcium hydroxide and aggregate.

The present invention provides a curable composition that has a high curing rate and can produce a cured product with high strength.

1 is a photograph of a test specimen of Example 1. 1 is a SEM photograph of a specimen of Example 1.

The curable composition of the present embodiment contains a cyclic carbonate having a hydroxyl group and calcium hydroxide, and the compressive strength of the curable composition becomes 30 N/ ^mm2 or more within 1.5 hours after mixing the cyclic carbonate and calcium hydroxide. Such a curable composition has a high curing speed and can give a cured product with high strength.

The compressive strength of the curable composition is preferably 40 N/mm2 or ^more , more preferably 50 N/mm2 or more, even more preferably 60 N/mm2 or ^more , even more preferably 70 N/ ^mm2 or ^more , and particularly preferably 80 N/ ^mm2 or more within 1.5 hours after mixing the cyclic carbonate and calcium hydroxide. In terms of workability, it is preferable that high hardness is developed as quickly as possible.

The compressive strength of the curable composition is preferably 30 N/mm ² or more within 1.0 hours from immediately after mixing the cyclic carbonate and calcium hydroxide, more preferably 40 N/mm 2 or more, even more preferably 50 N/mm ² or more, even more preferably 60 N/mm ² or more, very preferably 70 N/mm ² or ^more , and particularly preferably 80 N/mm ² or more. For example, when creating construction materials with a 3D printer, the outer frame is first formed with a material that hardens immediately, and then other materials are filled inside. Therefore, from the viewpoint of forming construction materials at high speed, it is preferable that hardness is quickly developed. In addition, it is preferable that hardness is quickly developed from the viewpoint of being able to withstand when the force applied to the outer frame is increased when the inside is filled with an object.

The compressive strength of the curable composition is preferably 30 N/mm ² or more within 0.5 hours from immediately after mixing the cyclic carbonate and calcium hydroxide, more preferably 40 N/mm 2 or more, even more preferably 50 N/mm ² or more, even more preferably 60 N/mm ² or more, very preferably 70 N/mm ² or ^more , and particularly preferably 80 N/mm ² or more. For example, when creating construction materials with a 3D printer, the outer frame is first formed with a material that hardens immediately, and then the inside is filled with other materials. Therefore, from the viewpoint of forming construction materials at high speed, it is preferable that hardness is quickly developed. In addition, even if it is not used in a 3D printer, when it is used as a molding material, it is preferable from the viewpoint of reducing the time required for manufacturing the product and improving mass productivity.

The hardenable composition of this embodiment may optionally contain other components such as aggregate as raw materials in addition to the cyclic carbonate having a hydroxyl group and calcium hydroxide. An example of the aggregate is calcium carbonate. When other components are added to the hardenable composition, the measurement of the change over time in the compressive strength of the hardenable composition can start immediately after mixing the cyclic carbonate having a hydroxyl group, calcium hydroxide, and other components.

The raw materials are mixed until the cyclic carbonate having a hydroxyl group, calcium hydroxide, and other components such as aggregates added as necessary are mixed substantially uniformly. In other words, the point at which each component of the hardenable composition is mixed substantially uniformly is regarded as immediately after mixing, and is the starting point for measuring the change over time in the compressive strength of the hardenable composition. The mixing method may be changed as appropriate depending on the viscosity of the components used, and may be carried out, for example, under reduced pressure, at a temperature of -5°C or higher and 5°C or lower, and for a mixing time of 5 minutes to 1 hour. Mixing may be carried out using a kneader, which will be described later.

From immediately after the raw materials are mixed to prepare the curable composition until the compressive strength is measured, the curable composition may be left to stand under conditions of, for example, 15 to 25°C (preferably 20°C) and a relative humidity of 50 to 80% (preferably 60%). The compressive strength of the curable composition may be, for example, the compressive strength measured on a test specimen obtained by molding the composition by packing it into a formwork having a width of 1 cm, a depth of 1 cm, and a length of 6 cm.

(Method for producing curable composition)
Hereinafter, a method for producing the curable composition and a method for producing the cured product according to the present embodiment will be described. The method for producing the curable composition according to the present embodiment includes a mixing step of mixing a cyclic carbonate having a hydroxyl group with calcium hydroxide to prepare a curable composition. In this specification, when "to" is used to express a numerical range, the endpoints of the numerical range are included.

<Mixing step>
In the mixing step, the cyclic carbonate having a hydroxyl group and calcium hydroxide are mixed to produce a curable composition. When raw materials other than the cyclic carbonate having a hydroxyl group and calcium hydroxide are used, they are mixed together in the mixing step.
The mixing method is not limited, and examples thereof include mixing using a batch type kneader such as a mixer, kneader, or kneader ruder, or a continuous type kneader such as an extruder equipped with a vent port and a vacuum chamber. In addition, in a system where hardening is unlikely to occur during mixing and there is no need to use a machine, the materials may be stirred by hand. As a method of mixing, for example, it is preferable to use a kneader equipped with a vacuum chamber. Examples of kneaders include PNV-1T (motor: 100V250W, capacity: 1L, rotation speed: 28.8rpm to 62.4rpm, blade shape: Σ type) manufactured by Irie Shokai Co., Ltd. The better the dispersibility of the raw materials, the higher the compressive strength of the hardened body produced tends to be. On the other hand, hardening may progress along with the mixing of the raw materials. As a result, a kneader with a high shear stress that can improve the dispersibility of the raw materials even when hardening begins to progress is preferable.

In the mixing process, when there are multiple raw materials to be mixed, it is preferable to first mix powders with other powders and liquids with other liquids, and then mix the powder mixture and the liquid mixture. This can further improve dispersibility. For example, in a system in which glycerol carbonate, calcium hydroxide, and calcium carbonate (aggregate) are mixed, it is preferable to first mix calcium hydroxide and calcium carbonate to prepare a powder mixture, and then mix glycerol carbonate with the powder mixture.

In the mixing step, for example, it is preferable to remove moisture before mixing the raw materials, which can suppress hardening during mixing and allow a structure having a desired shape to be formed.
Examples of the method of mixing after removing moisture include a method of mixing under reduced pressure, a method of mixing together with a moisture absorbent, a method of mixing in an environment where a moisture absorbent is placed, and a method of mixing while drying by heating. Examples of the method of mixing after removing moisture include mixing under reduced pressure, and more preferably mixing by drawing a vacuum. This allows kneading in a system with less moisture.
The method for reducing the pressure is not limited, and for example, an oil rotary pump, an aspirator, a water seal pump, a rotary pump, or the like can be used.
It is preferable to completely remove moisture, but in the actual manufacturing process, complete removal is difficult, and the inclusion of a small amount of moisture is permissible.

In the mixing step, for example, it is preferable to mix the raw materials while cooling. This makes it possible to suppress hardening during mixing, and to form a structure of a desired shape. The cooling temperature is not limited, but may be, for example, -50°C or higher, preferably -30°C or higher, more preferably -20°C or higher, even more preferably -10°C or higher, even more preferably 0°C or higher, and especially preferably 5°C or higher. In addition, the cooling temperature may be, for example, 25°C or lower, 20°C or lower, or 10°C or lower.
The cooling method is not limited, but may be, for example, a method of cooling the kneading machine itself, such as a kneader.

The phenomenon that occurs in the mixing process will be explained. When the raw materials are mixed, for example, at low temperature and under reduced pressure, granulation occurs in which the particles gradually become larger. If mixing is continued after that, the granulated powder suddenly produces liquid on the surface, and a paste-like hardenable composition is formed. If this paste-like hardenable composition is filled into a mold and left in the air, it becomes a hardened product.
For example, cooling the device to -5°C and evacuating in an environment of 20°C and 60% humidity will result in finer granulation during mixing than cooling the device to -5°C and evacuating in an environment of 23°C and 60% humidity (it is presumed that a small amount of air gets mixed into the device). Also, for example, cooling the device to -5°C and evacuating in an environment of 5°C and 45% humidity will result in finer granulation during mixing than the above-mentioned system.

Regarding the hardening composition according to the present embodiment, the mechanism by which the hardening reaction proceeds is largely unknown. One possibility is that glycerol carbonate is uniformly attached to the surfaces of calcium hydroxide and aggregate particles.
When the curing composition of the preferred composition according to the present embodiment is kneaded, the powder particles are initially observed to grow larger (i.e., granulated). On the other hand, as the kneading continues, light reflection is observed on the surface, as if the powder is wet. The powder then becomes paste-like, becoming a curing composition. This curing composition is then subjected to a molding process.
The reason why the properties of the kneaded state change in this way is unclear. One possibility is that some kind of chemical reaction occurs due to shear heat, causing granulation. This suggests the possibility that, for example, carbon dioxide is produced from glycerol carbonate, which is absorbed by slaked lime to produce calcium carbonate, acting as a binder between calcium hydroxide and aggregate. Alternatively, it is also suggested that no chemical reaction occurs, and that glycerol carbonate is well dispersed on the surface of calcium hydroxide and aggregate, acting as a binder between calcium hydroxide and aggregate.

<Molding process>
The method for producing a cured product according to the present embodiment may further include a molding step of molding the curable composition into a desired shape to obtain a molded product after the mixing step described above. This allows a structure made of a cured product having a predetermined shape to be obtained.

For example, when glycerol carbonate and calcium hydroxide are mixed in the mixing process, if the mixture is left in air at room temperature, heat is generated immediately and hardening progresses. Although the detailed mechanism is not clear, during hardening, calcium hydroxide absorbs carbon dioxide and becomes calcium carbonate, which fills the gaps between the raw materials such as calcium hydroxide. This makes it difficult to mold the mixture into any shape after hardening. It is preferable to mold the hardenable composition into the desired shape by placing it in a mold such as a metal mold or wooden frame.

<Drying process>
The method for producing a cured body according to the present embodiment may further include a drying step for drying the cured body, if necessary. The temperature condition of the drying step is not limited, and may be, for example, 60° C. or higher, 80° C. or higher, or 100° C. or higher. The drying time may be, for example, 1 hour or more, 10 hours or more, 24 hours or more, or 72 hours or more. The drying step may be performed under reduced pressure.
Depending on the formulation, a glycerin-like liquid may seep out from the hardened product, but this can be removed by a drying process. Cyclic carbonates also have the property of generating carbon dioxide through thermal decomposition.
In addition, the case where the drying step is not performed is preferable from the viewpoint of improving toughness compared to the case where the drying step is performed.
Drying may be performed, for example, by heating with a heater or by heating with hot air.

In addition to the drying process described above, the cured composition may be cured, for example. Curing may be performed, for example, by steam curing in high-temperature moisture, or by submerging the cured composition in hot water. For example, if the cured composition is submerged in 100°C hot water, curing will proceed and the composition will turn white.

<Curing process>
The method for producing a cured product according to this embodiment includes a curing step of curing the curable composition or the molded product. The curable composition of this embodiment often has a high curing rate, and often cures simply by leaving it at ambient temperature (about 15 to 35°C, 20°C, 25°C, etc.) without heating, but heating may be performed to further increase the curing rate. The heating temperature is not particularly limited, but may be 110°C or lower, or may be 90 to 100°C. In addition, if the reaction heat during curing is a problem depending on the embodiment, curing may be performed while cooling. The humidity (relative humidity, RH) during the curing step is not particularly limited, but may be, for example, 30 to 80%. The curing step may be performed after the drying step or simultaneously with the drying step (i.e., a step of curing while drying).

<Ingredients>
Next, the raw materials of the curable composition according to this embodiment will be described.
The raw materials used are essentially a cyclic carbonate having a hydroxyl group and calcium hydroxide.

（式（Ｉ）中、Ｒ^１は、２～６個の炭素原子を有する二価の炭化水素基であり、当該二価の炭化水素基の水素原子のうち少なくとも１つはヒドロキシ基により置換されている。） (Cyclic carbonate having a hydroxy group)
The cyclic carbonate having a hydroxyl group may be, for example, one that generates carbon dioxide after mixing, and preferably one that reacts with other raw material components to generate carbon dioxide. The ring size of the cyclic carbonate having a hydroxyl group may be, for example, 8-membered ring or less, preferably 7-membered ring or less, and more preferably 6-membered ring or less. The ring size of the cyclic carbonate having a hydroxyl group may be, for example, 4-membered ring or more, and preferably 5-membered ring or more. This allows stable generation of carbon dioxide during mixing. Specifically, a compound represented by the following formula (I) may be mentioned.

In formula (I), R ¹ is a divalent hydrocarbon group having 2 to 6 carbon atoms, and at least one of the hydrogen atoms of the divalent hydrocarbon group is substituted with a hydroxy group.

R ¹ is preferably a divalent hydrocarbon group having 3 to 5 carbons. The number of hydroxy groups in the cyclic carbonate is preferably 1 to 3, and more preferably 1 or 2. R ¹ may contain a carbon-carbon double bond (i.e., it may be an unsaturated hydrocarbon group).

（式（ＩＩ）中、Ｒ^１１及びＲ^１２は、それぞれ独立に水素原子、ヒドロキシ基又は－ＣＨ_２ＯＨ基であり、式（ＩＩＩ）中、Ｒ^２１、Ｒ^２２及びＲ^２３は、それぞれ独立に水素原子、ヒドロキシ基又は－ＣＨ_２ＯＨ基である。） It is preferable that the cyclic carbonate contains at least one compound represented by the following formula (II) or (III).

(In formula (II), R ¹¹ and R ¹² each independently represent a hydrogen atom, a hydroxyl group, or a —CH ₂ OH group, and in formula (III), R ²¹ , R ²² , and R ²³ each independently represent a hydrogen atom, a hydroxyl group, or a —CH ₂ OH group.)

It is preferable that R ¹¹ and R ¹² are each independently a hydrogen atom or a -CH ₂ OH group, and it is preferable that R ²¹ and R ²³ are each independently a hydrogen atom or a -CH ₂ OH group.

The compounds represented by formula (II) and (III) include the following compounds (IIa) to (IIh) and (IIIa) to (IIId).

Among these, glycerol carbonate (compound of formula (IIa), glycerol 1,2-carbonate) or compound of formula (IIIb) (glycerol 1,3-carbonate) is preferred, with glycerol carbonate being more preferred. Glycerol carbonate is preferred from the viewpoint of reacting with calcium hydroxide at room temperature.

Glycerol carbonate may contain glycerin and other components as impurities.

(Calcium hydroxide)
There is no limitation on the calcium hydroxide, and it may be a natural or synthetic product, and a commercially available product may also be used. An example of commercially available calcium hydroxide is special slaked lime grade manufactured by Ube Material Industries, Ltd. In addition, a product in which calcium hydroxide and calcium carbonate are mixed in advance may also be used, and an example of such a product is a fertilizer grade product manufactured by Tagawa Lime Industries, Ltd.

The amount of the cyclic carbonate having a hydroxyl group added (charge amount, i.e., mixing ratio) is, for example, preferably 100 parts by mass or less, more preferably 70 parts by mass or less, more preferably 65 parts by mass or less, even more preferably 60 parts by mass or less, and especially preferably 55 parts by mass or less, relative to 100 parts by mass of calcium hydroxide. The amount of the cyclic carbonate having a hydroxyl group added is, for example, preferably 30 parts by mass or more, more preferably 40 parts by mass or more, even more preferably 45 parts by mass or more, even more preferably 48 parts by mass or more, and especially preferably 50 parts by mass or more, relative to 100 parts by mass of calcium hydroxide.
It is presumed that by controlling the amount of the cyclic carbonate having a hydroxyl group added within the above range, the carbon dioxide generated from the cyclic carbonate having a hydroxyl group can be appropriately absorbed by the calcium hydroxide, which allows the gaps in the calcium hydroxide, etc. to be filled with calcium carbonate, thereby further improving the compressive strength.

(aggregate)
In addition to the raw materials, cyclic carbonate having a hydroxyl group and calcium hydroxide, for example, it is preferable to further add aggregate. As the aggregate, calcium carbonate is preferable. The calcium carbonate may be a natural product or a synthetic product, and a commercially available product may also be used. As a commercially available calcium carbonate, road grade manufactured by Ube Material Industries, Ltd. may be mentioned.

When aggregate is added, the amount of cyclic carbonate having a hydroxyl group added (charge amount, i.e., mixing ratio) is, for example, preferably 100 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 60 parts by mass or less, even more preferably 40 parts by mass or less, and especially preferably 32 parts by mass or less, relative to 100 parts by mass of calcium hydroxide and aggregate in total, from the viewpoint of ease of mixing and dispersibility of the hardening composition, the amount of cyclic carbonate having a hydroxyl group added is, for example, preferably 10 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 25 parts by mass or more, and especially preferably 28 parts by mass or more, relative to 100 parts by mass of calcium hydroxide and aggregate in total, from the viewpoint of ease of mixing and dispersibility of the hardening composition. Although the detailed mechanism is unclear, it has been confirmed that, when calcium hydroxide and aggregate are added, the smaller the amount of cyclic carbonate having a hydroxyl group added, the easier it is to improve the strength. By setting the amount of cyclic carbonate added within the above range, the mixing process can be carried out smoothly, and it is important to maintain a balance in order to obtain high strength by reducing the amount of cyclic carbonate having a hydroxyl group added.

When aggregate is added, the amount of calcium hydroxide added (charge amount, i.e., mixing ratio) is, for example, preferably 80 parts by mass or less, more preferably 70 parts by mass or less, even more preferably 65 parts by mass or less, even more preferably 63 parts by mass or less, very preferably 50 parts by mass or less, and particularly preferably 40 parts by mass or less, relative to 100 parts by mass of the total of calcium hydroxide and aggregate. The amount of calcium hydroxide added is, for example, preferably 20 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 40 parts by mass or more, even more preferably 50 parts by mass or more, and especially preferably 55 parts by mass or more, relative to 100 parts by mass of the total of calcium hydroxide and aggregate. It is considered important that calcium hydroxide absorbs carbon dioxide and becomes calcium carbonate in order to achieve high strength. In addition, if the amount of calcium hydroxide added is 20 parts by mass or more, the expansion of the hardened body can be prevented, and the strength is improved. For this reason, it is preferable that the amount of calcium hydroxide added is within the above numerical range.

(Water reducing agent)
The raw material may further contain a water reducing agent. This allows the mixing step to be performed while reducing the amount of cyclic carbonate having a hydroxyl group added. The type of water reducing agent is not limited, but examples that can be used include nitrohumate, lignin sulfonate, citric acid, polycarboxylic acid, and naphthalene.

(Other ingredients)
The raw material may further contain a carbonate ester (excluding cyclic carbonates having a hydroxyl group) as another component. Examples of the carbonate ester include ethylene carbonate, propylene carbonate, 1,3-dioxan-2-one, 4-fluoro-1,3-dioxolan-2-one, 4-chloro-1,3-dioxolan-2-one, 4-vinyl-1,3-dioxolan-2-one, 4-methoxy-1,3-dioxolan-2-one, and vinylene carbonate.
The raw material may also contain, as other components, for example, a small amount of alcohol, which can promote ring-opening of the cyclic carbonate having a hydroxyl group.

The hardened body of this embodiment is obtained by hardening the hardenable composition. As described below, the hardened body of this embodiment contains calcium carbonate produced by the reaction of calcium hydroxide with carbon dioxide, and may contain unreacted calcium hydroxide. In addition, when the hardenable composition contains aggregate, the hardened body also contains the aggregate. In other words, the hardened body of this embodiment can be said to be a bonded body in which particles containing calcium carbonate and, optionally, calcium hydroxide or aggregate are bonded together. Each particle contained in the hardened body may contain one or more of calcium carbonate, calcium hydroxide, and aggregate. The hardened body of this embodiment may be a structure formed into a predetermined shape in advance, or may not be formed.

<Structure>
Next, the structure according to this embodiment will be described.
The structure according to this embodiment is obtained by molding and curing the curable composition.

(Inorganic Components)
When the structure is subjected to wide-angle X-ray diffraction measurement to analyze the inorganic components, the content of calcium carbonate in the structure is preferably 5 parts by mass or more, more preferably 20 parts by mass or more, even more preferably 40 parts by mass or more, and even more preferably 60 parts by mass or more, relative to 100 parts by mass of the total of calcium carbonate and calcium hydroxide. This makes it possible to improve the strength of the structure. Furthermore, the content of calcium carbonate in the structure may be 100 parts by mass or less, 99 parts by mass or less, or 90 parts by mass or less.

The particle size of calcium hydroxide and calcium carbonate in the structure is preferably 5 μm or more, more preferably 6 μm or more, more preferably 7 μm or more, and even more preferably 10 μm or more. This makes it possible to reduce the surface area of the interface of the inorganic particles per unit volume. This reduces the frequency of defects and improves the strength of the structure.
The particle size of the inorganic component constituting the structure can be measured, for example, by the following method. First, the structure is broken to prepare a cross section. Next, a 3000x photograph is taken with a scanning electron microscope (SEM). Next, for each particle shown in the photograph, the length in the longest direction is taken as the particle size (hereinafter also referred to as the maximum particle size).

In the hardened body, the elemental concentration of calcium is preferably 20 to 70 atomic %, more preferably 25 to 65 atomic %, and even more preferably 30 to 60 atomic %. In addition, in the hardened body, the elemental concentration of carbon is preferably 20 to 80 atomic %, more preferably 30 to 70 atomic %, and even more preferably 40 to 65 atomic %. When the elemental concentrations of calcium and carbon are each within the above ranges, the compressive strength of the hardened body tends to be superior. The concentration of each element in the hardened body can be measured, for example, by energy dispersive X-ray analysis.

式中、ＺＯＨはＯＨ部分を有する求核体を示す。Ｚは、有機基であっても（例えば、ＺＯＨがアルコールの場合）よいし、水素原子（つまり、ＺＯＨが水の場合）であってもよい。かかる反応は、塩基触媒の存在下で促進されることが知られている。本実施形態の硬化性組成物は、塩基性の強い水酸化カルシウムを含み、骨材も塩基性を有する場合があることから、これらが触媒として機能していると考えられる。
硬化性組成物中では、ヒドロキシ基を有する環状カーボネート化合物のヒドロキシ基、並びに不純物として含まれ得る水、アルコール及び上記求核体として機能すると考えられる。また、上記開環付加反応の生成物もヒドロキシ基を有するため、ヒドロキシ基を有する環状カーボネートに対して求核体として機能し得る。この場合、開環付加反応が逐次的に進み、開環付加重合した化合物（ポリマー又はオリゴマー）が生成し得ると考えられる。
なお、上記化学反応式でＺＯＨがＯＨ^－である場合、反応生成物は水と反応して脱炭酸反応が起こる（環状カーボネート化合物の加水分解反応）。この際に、アルコール（グリセロールカーボネートの場合は、グリセリン）が生じる（加水分解反応）。
また、カーボネート化合物は、以下のとおり、一般に脱炭酸反応を受けることが知られている。

そのため、上記開環付加重合で生じたポリマー又はオリゴマーについても、これらの分子が有するカーボネート基（－Ｏ－Ｃ（＝Ｏ）－Ｏ－）の一部又は全部が脱炭酸反応してエーテル結合（末端のカーボネート基であればヒドロキシ基）に置き換わる。有機成分にはこのようにして生じた高分子量成分も含まれ得ると考えられる。
一連の反応で生じた二酸化炭素の少なくとも一部は、水酸化カルシウムと反応して炭酸カルシウムを生じると考えられる。つまり、硬化性組成物においてヒドロキシ基を有する環状カーボネート化合物は、炭酸供給源として機能し、水酸化カルシウムはカルシウム供給源として機能する。この際に成長する炭酸カルシウム相同士が周辺の反応途中の水酸化カルシウム、骨材等を巻き込みながら複雑に結合（付着）し合い、強固な結合体が形成されるものと考えられる。 (Organic Components)
In the curable composition, it is believed that cyclic carbonates having hydroxyl groups undergo ring-opening polymerization addition and decarboxylation reactions to generate carbon dioxide. In general, cyclic carbonate compounds undergo ring-opening by undergoing nucleophilic substitution reactions at the carbonyl carbon with nucleophiles. The reaction of ethylene carbonate with nucleophile ZOH having an -OH moiety is shown below as an example.

In the formula, ZOH represents a nucleophile having an OH moiety. Z may be an organic group (for example, when ZOH is an alcohol) or a hydrogen atom (i.e., when ZOH is water). It is known that such a reaction is accelerated in the presence of a base catalyst. The curable composition of the present embodiment contains calcium hydroxide, which is highly basic, and the aggregate may also have basicity, so it is believed that these function as a catalyst.
In the curable composition, it is considered that it functions as the hydroxy group of the cyclic carbonate compound having a hydroxy group, as well as water, alcohol, and the above-mentioned nucleophile that may be contained as impurities.In addition, since the product of the above-mentioned ring-opening addition reaction also has a hydroxy group, it can function as a nucleophile to the cyclic carbonate having a hydroxy group.In this case, it is considered that the ring-opening addition reaction proceeds sequentially, and a compound (polymer or oligomer) that is subjected to ring-opening addition polymerization can be produced.
In the above chemical reaction formula, when ZOH is ^OH- , the reaction product reacts with water to cause a decarboxylation reaction (hydrolysis reaction of the cyclic carbonate compound). During this reaction, alcohol (glycerin in the case of glycerol carbonate) is produced (hydrolysis reaction).
Moreover, carbonate compounds are generally known to undergo a decarboxylation reaction as follows.

Therefore, in the polymer or oligomer produced by the ring-opening addition polymerization, a part or all of the carbonate groups (-O-C(=O)-O-) of these molecules undergo a decarboxylation reaction and are replaced with ether bonds (hydroxy groups in the case of terminal carbonate groups). It is considered that the organic components may also include high molecular weight components produced in this way.
It is believed that at least a part of the carbon dioxide produced in the series of reactions reacts with calcium hydroxide to produce calcium carbonate. That is, in the curable composition, the cyclic carbonate compound having a hydroxyl group functions as a carbonic acid supply source, and calcium hydroxide functions as a calcium supply source. It is believed that the calcium carbonate phases that grow at this time are intricately bonded (adhered) to each other while involving the surrounding calcium hydroxide in the middle of reaction, aggregates, etc., to form a strong bond.

（なお、式（１）において、Ｒは、下記式（２）のいずれか１つ）

For example, when glycerol carbonate is used, it is believed that a substance represented by the following formula (1) is produced by ring-opening addition polymerization.

(In the formula (1), R is any one of the following formulas (2):

It is also believed that cyclic carbonates having hydroxyl groups are hydrolyzed to generate carbon dioxide even in the structure (hardened body). For example, as mentioned above, glycerol carbonate is hydrolyzed to generate glycerin and carbon dioxide.

(density)
The apparent density of the structure according to this embodiment is, for example, 3.0 g/m3 ^or less, preferably 2.7 g/m3 or ^less , more preferably 2.5 g/m3 or ^less , and even more preferably 2.3 g/m3 or ^less . The structure according to this embodiment can achieve both low density and high strength that cannot be achieved with existing materials. This makes the structure according to this embodiment preferable as a building material, for example.

<Applications>
The curable composition can be used, for example, as a material for a 3D printer. The curable composition of the present embodiment has excellent modeling properties using a 3D printer from the viewpoints of the curing speed after mixing and the strength after curing.
In addition, the hardenable composition or the hardened body can be used, for example, to absorb carbon dioxide (carbon dioxide absorbent) since unreacted calcium hydroxide contained in a structure can adsorb and remove carbon dioxide from the atmosphere. The hardened body according to the present embodiment can be suitably used as a carbon dioxide absorption material having excellent strength. Using such a material as a substitute for cement and concrete can contribute to the realization of a low-carbon society.
Furthermore, the structure according to the present embodiment can be used, for example, as an alternative material to fiber-reinforced concrete. The structure according to the present embodiment is preferable in that it does not contain materials that are difficult to process, such as metal fibers, and can achieve high strength.

<Other uses>
The cured product of the present embodiment may be obtained by curing the curable composition without going through a molding step. Examples of applications of such a curable composition include injection materials and coating agents.

The present invention is not limited to the above-mentioned embodiment, and any modifications or improvements that can achieve the object of the present invention are included in the present invention.

The above describes embodiments of the present invention, but these are merely examples of the present invention, and various configurations other than those described above can also be adopted.

The present invention will be described in detail below using examples, but the present invention is not limited to the descriptions of these examples.
Details of the components used in each of the Examples and Comparative Examples are given below.

(Raw materials)
Glycerol carbonate (hereinafter referred to as GC. 90% purity, the remaining 10% is glycerin, glycerol carbonate whose hydroxyl groups are converted to methyl carbonate)
(The one that was
・Calcium hydroxide ・Calcium carbonate

<Method of producing curable composition>
First, the curable compositions and raw materials for the structures of Example 1 and Comparative Example 1 were prepared according to the compositions shown in Table 1.

(Mixing process)
A mixing step then took place.
In Example 1 and Comparative Example 1, since the shear stress required for mixing was large, mixing was performed using a kneader capable of cooling and decompression (manufactured by Irie Shokai Co., Ltd., grade: PNV-1T (motor: 100V 250W, capacity: 1L, rotation speed: 28.8 rpm to 62.4 rpm, blade shape: Σ type)). The cooling temperature of the kneader was set to 5°C. In addition, after the raw materials were charged into the kneader, mixing was performed while drawing a vacuum using a vacuum pump. Mixing was performed for 15 to 20 minutes. As a result, a curable composition was obtained.

(Molding process)
Next, a molding step was carried out.
Molding was performed by filling the curable composition into a mold having a width of 1 cm, a depth of 1 cm, and a length of 6 cm. The curable composition was left to stand in the mold under conditions of 20° C. and a relative humidity of 60%. After molding in this manner, the curable composition was demolded to obtain a specimen (structure) of Example 1. The specimen of Example 1 is shown in FIG. 1.
The specimen of Example 1 was subjected to measurements of compressive strength, apparent density, SEM observation, and XRD measurement. Each measurement method will be described below. The compressive strength was measured 0.5 hours and 1.5 hours after the preparation of the curable composition (immediately after mixing the raw materials), and measurements other than the compressive strength were performed 3 hours after filling the mold.
The curable composition of Comparative Example 1 was not sufficiently cured even after 1.5 hours had elapsed since mixing, and therefore could not be demolded, and measurements of compressive strength and the like could not be performed.

<Compressive strength>
The compressive strength was measured according to the method described in JIS R5201:1997 (Physical Testing Methods for Cement). The evaluation results are shown in Table 1. It was confirmed that the hardenable composition of Example 1 already exhibited high compressive strength 0.5 hours after mixing.

<Apparent density>
For the specimens of Example 1 molded to 1 cm width x 1 cm depth x 6 cm length, the masses of each were measured at the age of 3 hours, and the apparent densities were calculated by dividing the masses by the volumes of the molded bodies. As a result, the apparent densities of all the specimens were in the range of 2.1 g/ ^cm3 to 2.2 g/ ^cm3 . As can be seen from these results, the specimens of Example 1 were confirmed to be low-density, high-strength materials.

<SEM Observation>
The cross section of the specimen of Example 1 was observed by SEM. The observation was performed using a Miniscope TM3030 (manufactured by Hitachi High-Technologies Corporation) at a measurement magnification of 3000 times and a voltage of 15.0 kV. FIG. 2 is an SEM photograph of the specimen of Example 1. On the other hand, it was confirmed that Example 5 contained a large number of particles with a maximum particle size of 5.6 μm or more.
Furthermore, for the specimen of Example 1, EDX (Energy Dispersive X-ray spectroscopy) measurement was performed on the black dots (●) in the SEM photograph of Figure 2. As a result, carbon and calcium were detected in the specimen of Example 1.

<XRD Measurement>
Each specimen of Example 1 was subjected to wide-angle XRD (X-ray diffraction, device: D2 PHASER 2nd Generation (Bruker), CuKα ray) measurement. The diffraction pattern identified in the XRD measurement was separated into peaks derived from CaCO ₃ crystals and peaks derived from Ca(OH) ₂ , and the ratio was determined. The abundance ratio of calcium carbonate and calcium hydroxide in the inorganic material is shown in Table 1. As a result, it was confirmed that unreacted calcium hydroxide was present in the specimen of Example 1. As a result, each specimen has room for absorbing carbon dioxide. In addition, it was confirmed that the higher the abundance ratio of calcium carbonate in the inorganic material, the higher the compressive strength. The abundance ratio based on the diffraction intensity of XRD reflects the abundance ratio of electrons, that is, the mass ratio.

Claims (4)

A hardenable composition comprising glycerol-1,2-carbonate , calcium hydroxide , and an aggregate ,
The mixing ratio of the glycerol-1,2-carbonate is
40 to 60 parts by mass per 100 parts by mass of the calcium hydroxide, and
20 to 40 parts by mass per 100 parts by mass of the calcium hydroxide and the aggregate,
The mixing ratio of the calcium hydroxide is:
50 to 70 parts by mass per 100 parts by mass of the calcium hydroxide and the aggregate,
The hardenable composition has a compressive strength of 30 N/mm2 ^or more within 1.5 hours after mixing the glycerol-1,2-carbonate , the calcium hydroxide, and an aggregate . The hardenable composition of claim 1 , wherein the aggregate is calcium carbonate . The method includes a mixing step of mixing glycerol-1,2-carbonate, calcium hydroxide, and aggregate,
In the mixing step,
The mixing ratio of the glycerol-1,2-carbonate is
40 to 60 parts by mass per 100 parts by mass of the calcium hydroxide, and
20 to 40 parts by mass per 100 parts by mass of the calcium hydroxide and the aggregate,
The mixing ratio of the calcium hydroxide is:
50 to 70 parts by mass per 100 parts by mass of the calcium hydroxide and the aggregate,
In the mixing step, mixing is carried out under reduced pressure, at 5° C. or lower, and for a mixing time of 5 minutes to 1 hour;
The method for producing a hardenable composition , wherein the compressive strength of the hardenable composition is 30 N/mm2 or more ^within 1.5 hours immediately after mixing the glycerol-1,2-carbonate, the calcium hydroxide, and the aggregate . The method for producing a hardenable composition according to claim 3, wherein the aggregate is calcium carbonate .