JP7722739B2 - Method for producing gypsum composition, gypsum composition, mineral raw material for gypsum composition, and method for producing hardened body - Google Patents

Description

The present invention relates to a gypsum composition that is used to form a hardened body by adding water and mixing minerals, calcined gypsum, and a polycarboxylate-based water-reducing agent to form a calcined gypsum slurry.The calcined gypsum slurry has a low viscosity and exhibits good fluidity (moldability).The present invention relates to a useful technology that enables the formation of hardened bodies such as gypsum-based building materials with improved functionality, such as fire resistance, strength, and sound insulation, using this slurry.

In recent years, the proportion of recycled gypsum in the materials used to form gypsum-based building materials, such as gypsum boards, has increased due to societal demands for reducing the volume of industrial waste. As the proportion of recycled gypsum in the materials used to form gypsum-based building materials increases, the amount of water mixed in to impart fluidity to the calcined gypsum slurry used in the formation of the building materials increases. This increases the amount of water mixed in, which in turn increases the drying energy required. To address this issue, it has been proposed to reduce the amount of water mixed in by adding a water-reducing agent (called a water-reducing agent) to the gypsum composition that makes up the calcined gypsum slurry. For example, Patent Document 1 proposes a dicarboxylic acid-based gypsum water-reducing agent for use in dental gypsum slurries. Furthermore, Patent Document 2, a prior art document, describes the recent trend toward switching to polycarboxylic acid-based water-reducing agents, which do not generate formaldehyde, in gypsum-water slurries used in gypsum boards.

Meanwhile, it has been proposed to add a mineral (colemanite) to the gypsum composition that constitutes the calcined gypsum slurry in order to improve the fire resistance of the resulting gypsum-based building material (see Patent Document 3). Patent Document 4 discloses that by adding colemanite to the gypsum-based molded body, it is possible to improve not only the fire resistance but also the neutron shielding performance. In this way, adding a mineral to the gypsum composition makes it possible to enhance the functionality of the resulting gypsum-based building material. For this reason, there is a need for the development of a gypsum composition that can be used to form building materials with desired improved functions by adding various minerals.

International Publication No. 2018/230028 Patent No. 6293584 Special Publication No. 57-11864 Patent No. 5596933

However, the inventors have discovered that when preparing a calcined gypsum slurry containing a mineral, using a water-reducing agent to reduce the amount of mixed water may result in the desired water-reducing performance not being achieved. Specifically, the inventors have discovered that when water is added to a gypsum composition containing a mineral, calcined gypsum, and a polycarboxylate-based water-reducing agent to form a calcined gypsum slurry, the viscosity increases, resulting in poor fluidity of the calcined gypsum slurry and affecting moldability, and this needs to be improved.

Therefore, the object of the present invention is to solve, by a simple means, the technical problem discovered by the inventors that increases the viscosity of a calcined gypsum slurry when water is added to a gypsum composition containing a mineral, calcined gypsum, and a polycarboxylate-based water-reducing agent to form the slurry. Generally, by adding a mineral to a calcined gypsum slurry for forming a hardened body of a gypsum-based building material or the like, the hardened body of the building material or the like formed using the slurry has improved functionality, such as fire resistance, strength, and sound insulation. Therefore, if a gypsum composition that solves the above-mentioned technical problem in a simple manner and can produce a mineral-containing calcined gypsum slurry with low viscosity and excellent fluidity (moldability) is provided, it would be extremely useful industrially.

The above object can be achieved by the following method for producing a gypsum composition of the present invention.
[1] A method for producing a gypsum composition containing a mineral, calcined gypsum, and a polycarboxylate-based water-reducing agent, the method comprising a pretreatment step of the mineral, in which a liquid polyamide polyamine and/or an alkylene oxide adduct of a polyamide polyamine is applied to the mineral in advance in the pretreatment step so that the ratio of the liquid polyamide polyamine and/or the alkylene oxide adduct to the calcined gypsum is within a range of 0.1 to 10 wt % on a mass basis, calculated as a solid content.

Preferred embodiments of the method for producing the gypsum composition of the present invention are as follows.
[2] The method for producing a gypsum composition according to the above [1], wherein in the pretreatment step, the liquid polyamide polyamine and/or alkylene oxide adduct of polyamide polyamine is sprayed onto the mineral, and then the mineral is dried.

As another embodiment, the present invention provides the following gypsum composition.
[3] A gypsum composition for preparing a calcined gypsum slurry, comprising a mixture of a mineral with water, calcined gypsum, and a polycarboxylate-based water-reducing agent, wherein the mineral has been previously provided with a polyamide polyamine and/or an alkylene oxide adduct of a polyamide polyamine in an amount, calculated as a solid content, that is within a range of 0.1 to 10 wt % by mass relative to the calcined gypsum.

Preferred embodiments of the gypsum composition of the present invention are as follows.
[4] The gypsum composition according to the above [3], wherein the mineral is at least one selected from the group consisting of bentonite, colemanite, diatomaceous shale, vermiculite, shirasu, and natural gypsum.
[5] The gypsum composition according to [3] or [4] above, wherein the ratio of the mineral to the calcined gypsum is within the range of 0.01 to 60 wt% on a mass basis.

In another embodiment, the present invention provides a mineral raw material for a gypsum composition as described below.
[6] A mineral raw material constituting a gypsum composition used in a calcined gypsum slurry containing a mineral, calcined gypsum, and a polycarboxylate-based water-reducing agent, which is obtained by adding and mixing with water, wherein the mineral raw material for a gypsum composition is characterized in that a polyamide polyamine and/or an alkylene oxide adduct of a polyamide polyamine is added to the raw material in a ratio to the mineral in the range of 0.02 to 120 wt % by mass, calculated as a solid content.

As another embodiment, the present invention provides the following method for producing a building material.
[7] A method for producing a hardened body, comprising using the gypsum composition according to any one of [3] to [5] above, mixing the gypsum composition with water to form a calcined gypsum slurry, and using the slurry to mold a hardened body.

A preferred embodiment of the method for producing the building material of the present invention is as follows.
[8] The method for producing a hardened body according to the above [7], wherein the viscosity of the slurry (25 ° C.) is 150 dPa s or less when the amount of water mixed is 15 to 60 wt % on a mass basis with respect to the gypsum composition.

The inventors discovered a technical problem of high viscosity in calcined gypsum slurries prepared by adding water to a gypsum composition containing a mineral, calcined gypsum, and a polycarboxylate-based water-reducing agent. The present invention solves this problem with an extremely simple approach: simply adding polyamide polyamine and/or an alkylene oxide adduct of polyamide polyamine (hereinafter also referred to as polyamide polyamine, etc.) to the mineral used. According to the present invention, this simple method makes it possible to provide a mineral-containing calcined gypsum slurry with low viscosity and excellent fluidity (moldability). As a result, adding a mineral to the calcined gypsum slurry makes it easy and stable to provide gypsum hardened bodies, such as useful gypsum-based building materials, that offer improved functionality, such as fire resistance, strength, and sound insulation.

The present invention will be described in detail below with reference to preferred embodiments. The inventors have investigated calcined gypsum slurries containing colemanite, which has been proposed in the prior art cited above and is believed to be capable of further improving the fire resistance of building materials. Colemanite is a calcium borate compound containing five molecules of crystal water, a natural mineral containing boric acid, and has the chemical formula 2CaO.3B ₂ O 3.5H _{2 O.} In recent years, the neutron shielding effect of colemanite has been attracting attention.

During the course of the above-mentioned investigations, the inventors discovered that when water is added to a gypsum composition containing colemanite, calcined gypsum, and a polycarboxylate-based water-reducing agent to form a calcined gypsum slurry, the viscosity of the slurry increases to approximately 300 dPa·s, making the slurry hard and resulting in poor moldability, a technical issue. In contrast, when water is added to a gypsum composition to form a calcined gypsum slurry and the slurry is used to form a hardened gypsum body, taking into account its moldability and handleability, the viscosity of the calcined gypsum slurry is desired to be 150 dPa·s or less, preferably approximately 20 to 100 dPa·s, and more preferably approximately 20 to 50 dPa·s.

The inventors are not certain as to why the viscosity increases when water is added to a gypsum composition containing colemanite, calcined gypsum, and a polycarboxylate-based water-reducing agent to form a calcined gypsum slurry, as described above, but speculate as follows. As described in the patent documents cited above, polycarboxylate-based water-reducing agents are used in gypsum compositions. The inventors believe that the reason for the increased viscosity of the slurry is that when a mineral such as colemanite is present in the gypsum composition, when water is added and mixed to prepare a calcined gypsum slurry, the polycarboxylate-based water-reducing agent is adsorbed to the mineral before the gypsum, resulting in the formation of borate esters and other factors that increase the viscosity of the slurry.

Based on the above reasoning, the inventors conducted extensive research into a method for preventing the polycarboxylate-based water-reducing agent present in the gypsum composition from adsorbing onto the minerals that make up the gypsum composition before the gypsum adsorbs, thereby addressing the technical issue of high viscosity of the calcined gypsum slurry made from the gypsum composition described above. As a result, they arrived at the present invention. Specifically, the inventors discovered that by pre-applying a specific amount of polyamide polyamine or the like to the mineral used to prepare a calcined gypsum slurry containing a mixture of mineral, calcined gypsum, and a polycarboxylate-based water-reducing agent with water, it is possible to achieve a low viscosity without the problem of high viscosity of the calcined gypsum slurry.

More specifically, the inventors have discovered that the excellent effects of the present invention can be achieved by configuring the mineral used to obtain a calcined gypsum slurry containing a mineral, calcined gypsum, and a polycarboxylate-based water-reducing agent so that the mineral is provided with a polyamide polyamine or the like in an amount, calculated as solids, relative to the calcined gypsum of 0.1 to 10 wt%. Furthermore, in order to consistently obtain a low-viscosity calcined gypsum slurry, it is preferable for the mineral used as a raw material to have a polyamide polyamine or the like pre-added in an amount, calculated as solids, relative to the mineral of approximately 0.02 to 120 wt% by mass.

[Gypsum composition]
First, each raw material constituting the gypsum composition of the present invention will be described.
<Minerals>
The minerals constituting the present invention are not particularly limited. For the purpose of enhancing the desired functionality of a building material formed using a calcined gypsum slurry containing a mineral, or for the purpose of imparting a desired new functionality, any of the minerals listed below may be appropriately selected and used. In the present invention, for example, a mineral having a mean particle size by volume (MV) of about 10 μm to 3 mm, more preferably about 20 μm to 1 mm, may be used, and minerals whose particle size has been adjusted by pulverization or the like may also be used. Furthermore, the amount of mineral used will vary depending on the type of mineral and the purpose for which the mineral is used, but according to the inventors' studies, it is preferable to use each mineral in an amount within the range shown below.

Examples of minerals that constitute the present invention include bentonite, colemanite, diatomaceous shale, vermiculite, shirasu, and natural gypsum. They can be appropriately selected from the above list depending on the application and desired function. While colemanite has been described as a representative example of a mineral in the specification of the present invention, the "mineral" that constitutes the present invention is not limited to colemanite and can be appropriately selected from minerals with a variety of properties, as described below, depending on the purpose. Furthermore, by using these minerals with a unique composition in which polyamide polyamines and the like have been added in advance, the useful effects of the present invention can be obtained regardless of the mineral used.

Bentonite is a general term for clays primarily composed of montmorillonite. It possesses high viscosity and adhesive properties, and is widely used as a functional material, such as a moisturizer or thickener. It is also widely used in the field of building materials, which is the subject of this invention. The amount of bentonite used (blended) is preferably such that, when a calcined gypsum slurry is prepared, the mass ratio to the calcined gypsum is, for example, 0.01 to 30 wt%. Colemanite is a natural mineral containing boron and is used as a weed control agent and secondary steel material, among other things. In recent years, for example, mixing boron into concrete walls to shield against highly penetrating neutron radiation has been proposed, and the use of colemanite is being investigated. The amount of colemanite used is preferably such that, when a calcined gypsum slurry is prepared, the mass ratio to the calcined gypsum is, for example, 0.1 to 60 wt%. Diatomaceous shale is a porous natural mineral composed of fossilized diatom shells. Due to its unique properties, it is widely used in humidity-regulating building materials, health building materials, and everyday items. The amount of diatomaceous shale used is preferably such that, when made into a calcined gypsum slurry, the mass ratio with the calcined gypsum is, for example, 0.1 to 50 wt%. Vermiculite is a porous and very light mineral with water-retentive properties and breathability, and is used as a soil conditioner and an aggregate for fire-resistant building materials. The amount of vermiculite used is preferably such that, when made into a calcined gypsum slurry, the mass ratio with the calcined gypsum is, for example, 0.01 to 30 wt%. Shirasu is a fine-grained pumice or volcanic ash distributed as a thick layer throughout southern Kyushu. Due to its unique properties, it is used as a concrete aggregate and health building material. The amount of shirasu used is preferably an amount such that, when a calcined gypsum slurry is prepared, the mass ratio to the calcined gypsum is, for example, 0.1 to 50 wt%. Natural gypsum is a naturally occurring raw material of gypsum dihydrate, and can be used as a mineral constituting the present invention. Natural gypsum is used as a bulking agent, etc., but it is often heated to become hemihydrate gypsum (calcined gypsum) and used as a material for building materials and gypsum molds. When gypsum dihydrate is used as a bulking agent, it can be applied to the minerals constituting the present invention, and not only natural gypsum but also by-product gypsum and recycled gypsum can be applied. In this case, the amount of gypsum dihydrate used is preferably an amount such that, when a calcined gypsum slurry is prepared, the mass ratio to the calcined gypsum is, for example, 0.1 to 50 wt%. Note that, as described below, gypsum dihydrate can also be used as a hardening accelerator added as needed to the gypsum composition of the present invention. The mineral constituting the present invention can also be used as a hardening accelerator, and in this case, not only natural gypsum but also by-product gypsum and recycled gypsum can be used. In this case, the amount used is about 0.1 to 5 wt % by mass relative to the calcined gypsum, which is a small amount compared to when used as an extender.

<Polyamide polyamines and alkylene oxide adducts of polyamide polyamines>
A technical feature of the present invention is that a mineral that has been pretreated with a specific compound is used as a constituent mineral of a gypsum composition used in preparing a calcined gypsum slurry containing a mixture of a mineral with water, calcined gypsum, and a polycarboxylate-based water-reducing agent. Specifically, the present invention is characterized in that a liquid polyamide polyamine or the like is added to the above-mentioned mineral that constitutes the present invention in advance so that the ratio of the calcined gypsum to the mineral in terms of solid content is within a range of 0.1 to 10 wt % by mass.

The "polyamide polyamines and alkylene oxide adducts of polyamide polyamines" used in the mineral pretreatment of this invention are used as forming components in obtaining gypsum dispersants (water-reducing agents), as described, for example, in Japanese Patent Nos. 4,844,878 and 6,095,644. For example, Japanese Patent No. 6,095,644 describes a gypsum dispersant (water-reducing agent) containing a polyamide polyamine and/or its alkylene oxide adduct having a weight-average molecular weight of 500 to 4,800, obtained by reacting (A) a polycarboxylic acid polymer with (B) a polyalkylene polyamine and a dibasic acid as essential components, and in which the mass ratio of component (A) to component (B) is (A):(B) = 1:1 to 30:1. The publication also describes an effect that by using the component (A) and the component (B) in combination, even when raw gypsum of different qualities is used, sufficient fluidity can be stably imparted to the gypsum slurry regardless of the type of raw gypsum.

As previously mentioned, the inventors discovered a technical problem: when water is added to a gypsum composition containing a mineral, calcined gypsum, and a polycarboxylate-based water-reducing agent to prepare a calcined gypsum slurry, the viscosity of the slurry increases to approximately 300 dPa·s, making the slurry hard. To address this problem, the inventors, referring to the prior art described above, attempted to premix a polyamide polyamine with the calcined gypsum that constitutes the gypsum composition, thereby using a carboxylate-based water-reducing agent and a polyamide polyamine in combination. However, the calcined gypsum slurry containing the mineral prepared in this manner ended up being highly viscous, and they were unable to obtain the low-viscosity calcined gypsum slurry that consistently provides sufficient fluidity, as aimed at by the present invention.

In response to the above, the inventors conducted further research into how to easily and stably impart sufficient fluidity to a calcined gypsum slurry containing minerals and achieve a low viscosity. As a result, as mentioned above, they discovered that it is possible to obtain a low-viscosity calcined gypsum slurry that is stably imparted sufficient fluidity by the extremely simple means of using a mineral that has been pre-treated in advance to have a specific amount of polyamide polyamine or the like attached (imparted) to it as a calcined gypsum slurry material.

As will be described in more detail below, the mineral treatment that characterizes this invention is carried out by first applying (adhering) a liquid polyamide polyamine or the like to the mineral so that the ratio of the polyamide polyamine or the like to the calcined gypsum is within the range of 0.1 to 10 wt% by mass, calculated as solids. More preferably, the polyamide polyamine or the like is applied (adhered) to the mineral so that the ratio of the polyamide polyamine or the like to the calcined gypsum is within the range of 0.2 to 5 wt% by mass, or even within the range of 0.5 to 1 wt% by mass, calculated as solids.

The amount of polyamide polyamine or the like applied to the mineral is preferably in the range of 0.02 to 120 wt % by mass, calculated as solid content, relative to the mineral. It is even more preferable that the amount applied in advance be in the range of 0.2 to 20 wt %.

<Polycarboxylate-based water-reducing agent>
Next, the polycarboxylate-based water-reducing agent constituting the present invention will be described. A water-reducing agent is a substance that, when water is added to a gypsum composition containing a mineral and calcined gypsum to form a calcined gypsum slurry, facilitates mixing of the gypsum composition with water, thereby reducing the amount of water used during mixing and improving the strength of the formed body after hardening. Adding a water-reducing agent reduces the viscosity of the slurry without increasing the amount of mixed water, improving fluidity and enhancing mixability and workability. Furthermore, suppressing an increase in the amount of mixed water means that the drying energy can be reduced, which is highly desirable from the perspective of industrial applicability.

Known water-reducing agents with surfactant properties include, for example, lignin sulfonates, hydroxycarboxylates, naphthalene sulfonates, melamine sulfonates, polystyrene sulfonates, and polycarboxylates. The present invention aims to resolve the technical issues associated with the use of polycarboxylate-based water-reducing agents, and therefore requires the use of a polycarboxylate-based water-reducing agent. By appropriately selecting usage conditions such as pH, polycarboxylate-based water-reducing agents can exhibit excellent water-reducing performance for gypsum slurries. Furthermore, polycarboxylate-based water-reducing agents are solid under standard conditions, which also makes them effective in the present invention. When obtaining a gypsum composition containing a polycarboxylate-based water-reducing agent, it is preferable to use a powdered polycarboxylate-based water-reducing agent, as this reduces the number of steps required.

Examples of polycarboxylate-based water reducers include the following, any of which can be used in the present invention. Specifically, water-soluble salts of copolymers of chain olefins having 5 or 6 carbon atoms and ethylenically unsaturated dicarboxylic anhydrides, copolymers of polyethylene glycol monoallyl ether and unsaturated dicarboxylic acids, copolymers of polyalkylene glycol mono(meth)acrylate and (meth)acrylic acid, copolymers of sulfonic-terminated (meth)acrylic acid amides, acrylic acid esters, and (meth)acrylic acid, copolymers of sulfonic-terminated monomers such as vinyl sulfonates, aryl sulfonates, and methacrylic sulfonates with (meth)acrylic acid and other monomers, copolymers of maleic acid and monomers with sulfonic-terminated aromatic rings, and quaternary copolymers of sulfonic-terminated monomers with polyalkylene glycol mono(meth)acrylate, polyalkylene glycol mono(meth)acrylate ether, and (meth)acrylic acid can be used.

The amount (mixing amount) of the water-reducing agent used is preferably, for example, in the range of 0.01 to 10 parts by mass per 100 parts by mass of calcined gypsum. Furthermore, it is even more preferable to use the water-reducing agent in the range of approximately 0.3 to 3.0 parts by mass per 100 parts by mass of calcined gypsum. If too little water-reducing agent is used, the viscosity will be too high and the desired fluidity will not be achieved. If too much is used, the desired viscosity and fluidity will be achieved, but the amount will plateau at a certain level, which is undesirable from an economic standpoint.

<Cast plaster>
The calcined gypsum constituting the gypsum composition of the present invention is called gypsum hemihydrate, and there are α-type hemihydrate and β-type hemihydrate depending on the calcination method. α-type hemihydrate is produced by a wet method and is obtained by calcining gypsum dihydrate in water (including in steam). β-type hemihydrate is produced by a dry method and is obtained by calcining gypsum dihydrate in the atmosphere. Either α-type hemihydrate or β-type hemihydrate can be used as the calcined gypsum constituting the present invention, and they may be appropriately mixed and used. Note that α-type hemihydrate has the advantage that less water is required for hardening than β-type hemihydrate, and that the strength increases when hardened.

<Other additives>
The gypsum composition of the present invention may contain, as needed, other conventionally known additives such as setting time adjusters, pH adjusters, and antifoaming agents in addition to the above-mentioned components. For example, as the setting retarder, citrates such as sodium citrate, succinates, acetates, malates, borates such as borax, sucrose, hexametaphosphates, ethylenediaminetetraacetate, diethylenetriaminepentaacetic acid, starch, and protein hydrolysates can be used. As the antifoaming agent, for example, commonly used agents such as polyethers, silicones, alcohols, mineral oils, vegetable oils, and nonionic surfactants can be used as appropriate.

[Method of producing gypsum composition]
The method for producing a gypsum composition of the present invention relates to a technology that can produce a gypsum composition that, when prepared as a mixture with water, contains a mineral, calcined gypsum, and a polycarboxylate-based water-reducing agent, can stably produce a low-viscosity calcined gypsum slurry without increasing the viscosity of the slurry. A key feature of the method for producing a gypsum composition of the present invention is that the mineral constituting the gypsum composition is pretreated by adding a liquid polyamide polyamine or the like to the mineral so that the ratio of the liquid polyamide polyamine to the calcined gypsum falls within a range of 0.1 to 10 wt % by mass, calculated as solids content, and the pretreated mineral is used. For example, by a simple method such as spraying, dripping, or pouring a liquid polyamide polyamine or the like onto the mineral in the pretreatment step, followed by drying the mineral, a mineral raw material having a specific amount of polyamide polyamine or the like attached thereto, which characterizes the present invention, can be easily obtained.

The technical features and effects of the present invention are as described above, and the gypsum composition obtained by the gypsum composition manufacturing method of the present invention may, of course, be provided as a mixture containing a mineral, calcined gypsum, and a polycarboxylate-based water-reducing agent. However, this is not limited to this, and the gypsum composition may also be a product in which these individual materials are mixed together when used on-site. Specific examples include products that combine a mineral that has been pretreated as described above with a mixture of materials other than the mineral.

The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. Note that "%" in the examples and comparative examples is by weight unless otherwise specified.

Different gypsum compositions were prepared, each with a different formulation as shown in Table 1, and water was added to each resulting gypsum composition and mixed to obtain a calcined gypsum slurry. The properties of each resulting calcined gypsum slurry were then examined. First, the basic structure of the gypsum composition used in the examination to obtain the calcined gypsum slurry and the method for obtaining the calcined gypsum slurry are as follows:

<Conditions for each experiment>
In preparation, the blending of the gypsum composition was designed so that the target specific gravity of the gypsum hardened body obtained by hardening the calcined gypsum slurry would be 1.9, and the calcined gypsum slurry was obtained as follows. First, the materials used in the examples and comparative examples and the basic blending will be described.

For the calcined gypsum, 500.0 g of α-type hemihydrate gypsum (abbreviated as "α-St") was used. 254.1 g of powdered colemanite was used as the mineral. The mineral content relative to α-St was 50.8%/α-St. For the colemanite, "Carboron 40M" (trade name, manufactured by Kyoritsu Material Co., Ltd.) was used. The colemanite (2CaO·3B ₂ O ₃ ·5H ₂ O) had a volume average particle size (MV value) of 30 μm. The mineral used in the examples was pretreated to have polyamide polyamine attached. Specifically, liquid polyamide polyamine was sprayed onto the mineral, and then dried in a dryer at 40°C until it reached a constant weight. For the polyamide polyamine liquid, "PCA-0302" (trade name, manufactured by Toho Chemical Industry Co., Ltd., solids content 30%) was used. The polycarboxylate-based water-reducing agent used was powdered "Mighty 21PN" (trade name, manufactured by Kao Corporation). Additionally, gypsum dihydrate was used as a hardening accelerator.

The calcined gypsum slurry was prepared by adding 154.0 g of water (amount to give a 30.8%/α-St ratio) to 500.0 g of alpha-hemihydrate gypsum in the above materials to a mixture appropriately blended with the above materials, and stirring for 5 minutes using a hand mixer (1100 rpm). After preparation, the viscosity of the resulting gypsum slurry was measured, and the measured values are shown in Table 1. As mentioned above, when using the calcined gypsum slurry to form a gypsum hardened body, taking into consideration its formability and handleability, the viscosity of the calcined gypsum slurry should be 150 dPa·s or less, preferably approximately 20 to 100 dPa·s, and more preferably approximately 20 to 50 dPa·s, depending on the application.

[Example 1]
A polyamide polyamine liquid was mixed with colemanite (mineral) in advance, followed by drying to adhere the polyamide polyamine to the colemanite, thereby preparing the mineral used in this example. The amount of polyamide polyamine adhered to the mineral was designed to be the following amount relative to the calcined gypsum after drying. The pretreated colemanite was then blended with other powder samples to obtain the gypsum composition of this example. Furthermore, the obtained gypsum composition was used to prepare a calcined gypsum slurry as described above. In the gypsum composition of this example, 11.8 g of a polycarboxylate-based water-reducing agent was used. This amount was 2.3%/α-St relative to the calcined gypsum. The amount of liquid polyamide polyamine adhered to the colemanite was 1.2%/α-St relative to the calcined gypsum, and the amount adhered to the colemanite after drying was 0.4%/α-St in terms of solid content. The amount of liquid polyamide polyamine used was 2.3% (5.9 g) relative to the colemanite. As another additive, a hardening accelerator was blended in an amount of 2.0%/α-St (10.0 g) relative to the calcined gypsum.

[Example 2]
As in Example 1, colemanite was pretreated in advance to allow polyamide polyamine to adhere to it, and this was used as the mineral for this example. Furthermore, the gypsum composition of this example was obtained in the same manner as in Example 1, except for the points listed below, and a calcined gypsum slurry was prepared using the obtained gypsum composition. In this example, 1.5 g of a polycarboxylate-based water-reducing agent was used. This amount was 0.3%/α-St relative to the calcined gypsum. The amount of liquid polyamide polyamine adhered to the colemanite was 2.3%/α-St relative to the calcined gypsum, and the amount adhered to the colemanite after drying was 0.7%/α-St in terms of solid content. The amount of liquid polyamide polyamine used was 4.6% (11.7 g) relative to the colemanite. As another additive, a hardening accelerator was blended at 1.0%/α-St (5.0 g) relative to the calcined gypsum.

[Example 3]
In the same manner as in Example 1, colemanite was pretreated in advance to allow polyamide polyamine to adhere to it, and this was used as the mineral for this example. Furthermore, the gypsum composition of this example was obtained in the same manner as in Example 1, except for the points listed below, and a calcined gypsum slurry was prepared using the obtained gypsum composition. In this example, 12.5 g of a polycarboxylate-based water-reducing agent was used. This amount was 2.5%/α-St relative to the calcined gypsum. The amount of liquid polyamide polyamine adhered was 0.3%/α-St relative to the calcined gypsum, and the amount adhered to the colemanite after drying was 0.1%/α-St in terms of solid content. The amount of liquid polyamide polyamine used was 0.7% (1.7 g) relative to the colemanite. As another additive, a hardening accelerator was blended at 2.0%/α-St (10.0 g) relative to the calcined gypsum.

[Example 4]
In the same manner as in Example 2, colemanite was pretreated in advance to allow polyamide polyamine to adhere to it, and this was used as the mineral used in this example. Furthermore, a gypsum composition of this example was obtained in the same manner as in Example 2, except for the points listed below, and a calcined gypsum slurry was prepared using the obtained gypsum composition. The amount of liquid polyamide polyamine adhered to the colemanite was 3.3%/α-St relative to the calcined gypsum, and the amount adhered to the colemanite after drying was 1.0%/α-St in terms of solid content. The amount of liquid polyamide polyamine used was 6.6% (16.7 g) relative to the mineral.

[Example 5]
In the same manner as in Example 2, colemanite was pretreated in advance to allow polyamide polyamine to adhere to it, and this was used as the mineral used in this example. Furthermore, a gypsum composition of this example was obtained in the same manner as in Example 2, except for the points listed below, and a calcined gypsum slurry was prepared using the obtained gypsum composition. The amount of liquid polyamide polyamine used to adhere to the colemanite was 33%/α-St relative to the calcined gypsum, and the amount adhered to the colemanite after drying was 10%/α-St in terms of solid content. The amount of liquid polyamide polyamine used was 66% (167 g) relative to the mineral.

Table 1 summarizes the blending of raw material components for the gypsum compositions of Examples 1 to 5. Also shown in Table 1 is the calcined gypsum slurry prepared by adding 30.8% water/α-St relative to the calcined gypsum to the resulting gypsum composition, and the viscosity of the calcined gypsum slurry was measured. Viscosity was measured at room temperature (25°C) using a Lion Visco Tester VT-06 viscometer (trade name, manufactured by Lion Corporation). The viscosity measurement results are summarized in Table 1.

[Comparative Example 1]
In this comparative example, colemanite (mineral) was used without being pretreated with polyamide polyamine. That is, colemanite, calcined gypsum, a polycarboxylate-based water-reducing agent, and a hardening accelerator were mixed to prepare a comparative gypsum composition. In this comparative example, the polycarboxylate-based water-reducing agent was used in an amount of 2.7%/α-St (13.5 g) relative to the calcined gypsum, and the hardening accelerator was used in an amount of 0.2%/α-St (1.0 g) relative to the calcined gypsum. As in the examples, water was added to the obtained comparative gypsum composition to prepare a calcined gypsum slurry, and the viscosity thereof was measured and shown in Table 2.

[Comparative Example 2]
In this comparative example, a polyamide polyamine was mixed with calcined gypsum in advance and dried for pretreatment. The amount of polyamide polyamine attached to the calcined gypsum was the same as the amount attached to the colemanite in Example 2, so that the amount attached to the calcined gypsum after drying was 0.7%/α-St in terms of solid content. This pretreated calcined gypsum was then blended with another powder sample to prepare the gypsum composition of this comparative example. In this comparative example, as in Example 2, a polycarboxylate-based water-reducing agent was blended with the calcined gypsum at 0.3%/α-St (1.5 g) and a hardening accelerator was blended with the calcined gypsum at 1.0%/α-St (5.0 g). As in the examples, water was added to the obtained comparative gypsum composition to prepare a calcined gypsum slurry, and the viscosity was measured and shown in Table 2.

[Comparative Example 3]
A liquid polyamide polyamine was mixed with powders of calcined gypsum, colemanite (mineral), and a polycarboxylate-based water-reducing agent in advance, and then dried. A hardening accelerator was then added to prepare a gypsum composition of this comparative example. The materials used and their amounts were the same as in Example 2. Then, as in the example, water was added to the obtained comparative gypsum composition to prepare a calcined gypsum slurry, and the viscosity was measured and shown in Table 2.

As described above, the viscosity of the calcined gypsum slurries obtained with the gypsum compositions of the Examples was lower than that of the calcined gypsum slurries obtained with the gypsum compositions of the Comparative Examples, all of which were below 100 dPa·s. Therefore, it was confirmed that the calcined gypsum slurries obtained in each Example have superior fluidity and are easier to mold than the Comparative Examples, and that a good hardened body can be obtained with a calcined gypsum slurry of appropriate viscosity. Furthermore, it was confirmed that the gypsum compositions of the Examples can reduce viscosity compared to the gypsum compositions of the Comparative Examples when the amount of water-reducing agent is the same, and are also effective in terms of raw material costs.

Claims (6)

A method for producing a gypsum composition containing a mineral, calcined gypsum, and a polycarboxylate-based water-reducing agent,
The mineral is at least one selected from the group consisting of bentonite, colemanite, diatomaceous shale, vermiculite, shirasu, and natural gypsum, and the ratio of the mineral to the calcined gypsum is within the range of 0.01 to 60 wt% on a mass basis,
The method for producing a gypsum composition includes a pretreatment step for the mineral, wherein in the pretreatment step, a liquid polyamide polyamine and/or an alkylene oxide adduct of a polyamide polyamine is applied to the mineral in advance so that the ratio of the polyamide polyamine and/or the alkylene oxide adduct to the calcined gypsum is within a range of 0.1 to 10 wt % on a mass basis, calculated as a solid content. The method for producing a gypsum composition according to claim 1, wherein in the pretreatment step, the liquid polyamide polyamine and/or alkylene oxide adduct of polyamide polyamine is sprayed onto the mineral, and then the mineral is dried. A gypsum composition for preparing a calcined gypsum slurry, comprising a mixture of a mineral, calcined gypsum, and a polycarboxylate-based water-reducing agent with water,
The gypsum composition is characterized in that the mineral is at least one selected from the group consisting of bentonite, colemanite, diatomaceous shale, vermiculite, shirasu, and natural gypsum, the proportion of the mineral is adjusted so that the ratio to the calcined gypsum is within a range of 0.01 to 60 wt % on a mass basis, and further, a polyamide polyamine and/or an alkylene oxide adduct of a polyamide polyamine is added to the mineral in advance in an amount, calculated as a solid content, such that the ratio to the calcined gypsum is within a range of 0.1 to 10 wt % on a mass basis. A mineral raw material for a gypsum composition used in a calcined gypsum slurry containing a mineral, calcined gypsum, and a polycarboxylate-based water-reducing agent, which is prepared by adding and mixing with water, wherein the raw material is provided with a polyamide polyamine and/or an alkylene oxide adduct of a polyamide polyamine in a ratio to the mineral, calculated as a solid content, within a range of 0.02 to 120 wt % by mass , and the mineral is at least one selected from the group consisting of bentonite, colemanite, diatomaceous shale, vermiculite, shirasu, and natural gypsum . A method for producing a hardened body, comprising: using the gypsum composition according to claim 3 ; mixing the gypsum composition with water to form a calcined gypsum slurry; and molding the hardened body using the slurry. 6. The method for producing a hardened body according to claim 5 , wherein the viscosity (25 ° C.) of the slurry is 150 dPa s or less when the amount of water mixed is 15 to 60 wt % by mass with respect to the gypsum composition.