Gypsum slurry, gypsum board, and method of manufacturing a gypsum board

Abstract

Provided is a method of manufacturing a gypsum board using waste gypsum, the method comprising the steps of:　granulating waste gypsum powder to prepare waste gypsum granules;　preparing a gypsum slurry containing the waste gypsum granules and calcined gypsum powder as gypsum materials; and　hardening the gypsum slurry;　wherein the waste gypsum powder is granulated in the step of granulating so that the average particle size of the waste gypsum granules is 1 mm or more and 1 / 2 or less of the thickness of the gypsum board; and　a proportion of the waste gypsum granules in the gypsum material is 10 to 65 mass%.

Description

GYPSUM SLURRY, GYPSUM BOARD, AND METHOD OF MANUFACTURING A GYPSUM BOARDCross-Reference to Related Applications

[0001] The present application claims priority from Japanese Patent Application No. 2024-148672 filed on August 30, 2024, which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a gypsum slurry, a gypsum board, and a method of manufacturing a gypsum board.

[0003] Gypsum board is a construction interior material that has a core of gypsum covered on both sides with gypsum board base paper, and has characteristics such as fire resistance, sound insulation, dimensional stability, and ease of construction, and is also economical. Therefore, gypsum boards are widely used for the walls and ceilings of buildings.

[0004] Gypsum includes gypsum dihydrate, gypsum hemihydrate, and anhydrous gypsum, depending on the form of crystal water thereof. Naturally occurring gypsums include gypsum dihydrate and anhydrous gypsum, but gypsum hemihydrate (commonly known as calcined gypsum) is obtained by calcining gypsum dihydrate.

[0005] The gypsum (gypsum dihydrate) used as a raw material for gypsum board can be either chemical gypsum or natural gypsum. Chemical gypsum includes gypsum that is a by-product of various industries (by-product gypsum), gypsum made by capturing sulfurous acid gas in the exhaust gas from thermal power plants using lime (flue gas desulfurization gypsum), and gypsum made by neutralizing sulfuric acid with lime (neutralization gypsum). Moreover, in recent years, the amount of recycled gypsum derived from recycled gypsum board waste (waste gypsum board) has been increasing.

[0006] A typical method of manufacturing a gypsum board uses a streamlined continuous production system from receiving the gypsum raw material to completing the gypsum board product, and generally includes a firing step in which gypsum (gypsum dihydrate) is calcined in a furnace to obtain gypsum hemihydrate (calcined gypsum), which has the property of reacting with water and solidifying; a molding step in which the hemihydrate gypsum is mixed with water to make a slurry, which is then poured onto a line (belt) on which base paper flows, such that the gypsum is interposed between base papers; a drying step in which the board with the gypsum interposed between base papers is sent to a dryer to remove excess moisture; and a finishing step in which the board is cut to the dimensions of the final product.

[0007] The amount of waste gypsum board generated is approximately 1.1 × 106tons per year. Of this, approximately 0.3 × 106tons is waste material from production or interior construction work on new buildings, and is recycled by gypsum board manufacturers. However, the remaining approximately 0.8 × 106tons is generated during renovation and demolition of buildings, and is disposed of in landfills without being recycled. However, gypsum is a mineral whose main component is calcium sulfate (CaSO4) which reacts with water under anaerobic conditions to produce hydrogen sulfide (H2S), so burying in a managed final disposal site is required. As a result, securing disposal sites and the costs of managing these sites is a problem.

[0008] Most of the gypsum derived from waste gypsum boards (hereinafter referred to as “waste gypsum”) is discarded without being recycled, and the cost and space required just for disposal is a problem, so there is demand for establishment of a method for recycling waste gypsum board.

[0009] Patent Document 1 discloses a method of manufacturing a gypsum board, which includes: a step of preparing a gypsum slurry by mixing gypsum raw material containing 70 mass% or more of recycled gypsum, 0.1 to 1.0 mass% of a water reducing agent relative to the gypsum raw material, 0.01 to 0.10 mass% of a foaming agent relative to the gypsum raw material, and water; and a step of hardening the slurry; wherein the gypsum raw material accounts for 90 mass% or more of the total amount of the slurry, excluding the water content. Here, “recycled gypsum” refers to gypsum that contains crystals with an average particle size of 20 μm or more (typically, the average particle size is 60 μm or less), is produced by recycling “waste gypsum”, and has a larger particle size than “waste gypsum”. It should be noted that the crystal particle size of “waste gypsum” is generally 1 to 5 μm.

[0010] [PTL 1]Japanese Patent No. 6529205

[0011] The method of manufacturing a gypsum board disclosed in Patent Document 1 is advantageous in that gypsum board can be manufactured using a gypsum raw material that is 100% recycled gypsum produced from gypsum derived from waste gypsum board (waste gypsum). The waste gypsum is gypsum dihydrate, which is converted into gypsum hemihydrate by heating and calcining at 150 to 185°C. The particle size of the hemihydrate powder is then adjusted to form gypsum dihydrate crystals in a reaction layer where recrystallization occurs. By promoting crystallization and increasing the size of the particles, large crystals of recycled gypsum (gypsum dihydrate) are obtained. Therefore, before recycled gypsum can be produced from waste gypsum boards, a calcination process and a crystallization process (large crystallization) must be performed, which poses a problem of high energy consumption. 　　　　　　　Furthermore, when waste gypsum powder is mixed directly into the gypsum raw material, the crystal size of the raw gypsum is small, resulting in insufficient strength of the gypsum board, and the specific surface area is large, requiring a large amount of water to be added when the gypsum is converted into calcined gypsum, which in turn increases the drying costs and becomes a rate limiting factor, slowing down the manufacturing rate. Therefore, the amount of waste gypsum that does not interfere with the production of gypsum board was less than 10 mass%.

[0012] One object of the present invention is to provide a method of manufacturing a gypsum board, which can use a gypsum raw material containing a high proportion of gypsum derived from waste gypsum board and that can reduce energy consumption.

[0013] The above object can be achieved by the following means. 　　　　　　　A method of manufacturing a gypsum board using waste gypsum, comprising the steps of: 　　　　　　　granulating waste gypsum powder to prepare waste gypsum granules; 　　　　　　　preparing a gypsum slurry containing the waste gypsum granules and calcined gypsum powder as gypsum materials; and 　　　　　　　hardening the gypsum slurry; 　　　　　　　wherein the waste gypsum powder is granulated in the step of granulating so that the average particle size of the waste gypsum granules is 1 mm or more and 1 / 2 or less of the thickness of the gypsum board; and 　　　　　　　a proportion of the waste gypsum granules in the gypsum material is 10 to 65 mass%.

[0014] FIG. 1 is a graph depicting the evaluation results of fluidity of the gypsum slurry of Example 4.FIG. 2 is a scanning electron microscope image of the waste gypsum powder and waste gypsum granules of Example 4. A: Waste gypsum powder (50X observation, bar represents 500 μm); B: Waste gypsum powder (300X observation, bar represents 50 μm); C: Waste gypsum granules (50X observation, bar represents 500 μm); D: Waste gypsum granules (300X observation, bar represents 50 μm).

[0015] In the present invention, the numerical range “A to B” includes the numerical value A and the numerical value B written before and after “to” as the lower limit and upper limit, or the upper limit and lower limit. For example, “1 to 10” means a numerical range of 1 or more and 10 or less.

[0016] In the present invention, the term “substantially free of” a specific compound means that the amount of the specific compound is below a measurement limit.

[0017] Although the embodiments of the present invention will be described below in detail, the present invention is not limited to the embodiments described below, and various modifications are possible without departing from the gist of the present invention.Method of manufacturing a gypsum board

[0018] The method of manufacturing a gypsum board of the present invention is a method of manufacturing a gypsum board using waste gypsum, the method comprising the steps of: 　　　　　　　granulating waste gypsum powder (hereinafter also referred to as “waste gypsum powder”) to prepare waste gypsum granules (hereinafter also referred to as “waste gypsum granules”); 　　　　　　　preparing a gypsum slurry containing the waste gypsum granules and calcined gypsum powder (hereinafter also referred to as “calcined gypsum powder”) as gypsum materials; and 　　　　　　　hardening the gypsum slurry; 　　　　　　　wherein the waste gypsum powder is granulated in the step of granulating so that the average particle size of the waste gypsum granules is 1 mm or more and 1 / 2 or less of the thickness of the gypsum board; and 　　　　　　　a proportion of the waste gypsum granules in the gypsum material is 10 to 65 mass%.

[0019] In the method of manufacturing a gypsum board of the present invention, the gypsum dihydrate is granulated without producing recycled gypsum (gypsum hemihydrate) from the waste gypsum (gypsum dihydrate). In addition, after granulation, a calcination step of the waste gypsum granules is not required in order to convert the dihydrate gypsum into hemihydrate gypsum, and a crystallization (large crystallization) step is not required for the waste gypsum particles. Therefore, the method of manufacturing a gypsum board of the present invention is more energy efficient than the method of manufacturing a gypsum board as disclosed in Patent Document 1.

[0020] <Granulating Waste Gypsum Powder > 　　　　　　　In the step of granulating waste gypsum powder, the waste gypsum powder is granulated to prepare waste gypsum granules. 　　　　　　　The waste gypsum is a gypsum derived from a waste gypsum board, and is a material whose main component is calcium sulfate dihydrate (also known as gypsum dihydrate). However, at least a portion of the water of crystallization of calcium sulfate dihydrate may be lost, and calcium sulfate monohydrate, hemihydrate or anhydrous may be contained. Herein, the term “main component” refers to a component that is included most abundantly on a mass basis, and when there are two or more components that are included most abundantly, any of the components may be treated as a main component.

[0021] Waste gypsum board is gypsum board that has become waste, and the original gypsum board can be unused or used. Used gypsum board is, for example, gypsum board that was used as a building material, and is generated when a building is demolished. Furthermore, unused gypsum boards include, for example, waste pieces cut off from gypsum boards used as building materials, surplus gypsum boards, and the like.

[0022] The waste gypsum powder is preferably obtained by crushing and classifying the waste gypsum board. 　　　　　　　The method for crushing the waste gypsum board is not particularly limited, but a crusher is preferably used. The crusher can be selected from, for example, a jaw crusher, a gyratory crusher, an impact crusher, a roller crusher, an edge runner, a disintegrator, a semi-autogenous grinding (SAG) mill, an autogenous grinding mill, a bead mill, a ball mill, a rod mill, a jet mill, a hammer mill, a cutter mill, and the like.

[0023] The method for classifying the pulverized waste gypsum is not particularly limited, but dry classification is preferred, and either sieving or air classification can be used. During sieving, the classification diameter is determined by the opening size of the wire mesh or mesh plate, and the dimensions of the test sieves are specified in JIS Z 8801-1: 2019 “Test sieves - Part 1: Metal mesh sieves” and JIS Z 8801-2: 2022 “Test sieves - Part 2: Metal plate sieves”. Air classification is also referred to as forced air classification, and is broadly divided into gravity classification, inertial classification, and centrifugal classification. In gravity classification, the classification size is determined by the balance between the gravitational settling speed of the particles and the ascending air speed, and a zigzag classifier is an example of this type of classifier. In centrifugal classification, the classification size is determined by the condition where the centrifugal settling velocity of the particles is equal to the inward radial velocity of the airflow. An example of this type of classifier is a cyclone classifier. The cyclone classifier is preferably a forced rotation vortex type cyclone classifier because a large amount of raw material can be supplied.

[0024] A pulverizer and classifier are preferably used in a coupling. In this case, the pulverizer is expected to play a role in breaking down agglomerated particles in addition to pulverizing coarse particles. 　　　　　　　The particle size distribution of the waste gypsum powder is not particularly limited, but as a result of particle size distribution measurement by a laser diffraction / scattering method, the volume-based cumulative 50% particle size (D50) is preferably in a range of 50 to 300 μm, and more preferably in a range of 100 to 250 μm. The volume-based cumulative 10% particle size (D10) is preferably within a range of 5 to 30 μm, and more preferably within a range of 5 to 20 μm. Furthermore, the volume-based cumulative 90% particle size (D90) is preferably within a range of 350 to 800 μm, and more preferably within a range of 400 to 550 μm.

[0025] The particle size distribution of the waste gypsum powder can be measured using a commercially available laser diffraction / scattering type particle size distribution measuring device, for example, Partica LA-960V2 (manufactured by Horiba, Ltd.).

[0026] The average particle size of the waste gypsum powder is not particularly limited, but is preferably 500 μm or less, and more preferably within a range of 100 to 500 μm. 　　　　　　　The average particle size of the waste gypsum powder can be measured using a commercially available laser diffraction / scattering type particle size distribution measuring device, for example, Partica LA-960V2 (manufactured by Horiba, Ltd.).

[0027] The waste gypsum granules are obtained by granulating the waste gypsum powder.

[0028] The waste gypsum particles are preferably granulated using a granulation aid. The granulation aid is also called a granulation promoter or bonding agent (binder), and has the effect of promoting the aggregation of the waste gypsum powder. 　　　　　　　Examples of the granulation aid include water, methylcellulose, carboxymethylcellulose, polyvinyl alcohol, polyacrylamide, paraffin, silicone, starch, blackstrap molasses, Steffen wastewater concentrate, alcohol fermentation wastewater concentrate, lignin sulfonate, konjac powder, sodium alginate, and bentonite. 　　　　　　　The above granulation aids may be used alone or in a combination of two or more. 　　　　　　　The granulation aid is preferably at least one aid selected from the group consisting of these aids, more preferably at least one aid selected from the group consisting of water, starch, silicone, paraffin, and polyvinyl alcohol, and even more preferably silicone.

[0029] The amount of the granulation aid added when granulating the waste gypsum powder is not particularly limited, but when water is used as the granulation aid, the amount of water used is preferably 30 to 60 mass% of the total mass of the waste gypsum powder. If the amount of water used during granulation is within a range of 30 to 60 mass% of the total mass of the waste gypsum powder, the waste gypsum powder can be moistened to a necessary and sufficient degree so that the waste gypsum granules grow appropriately and tend to have an appropriate average particle size.

[0030] When a granulation aid other than water is used as the granulation aid, the amount of the granulation aid is preferably 0.05 to 5.0 mass% of the total mass of the waste gypsum powder. The granulation aid is preferably water and a granulation aid other than water in combination.

[0031] The silicone is not particularly limited as long as it is a synthetic polymeric compound having a main skeleton formed by siloxane bonds, but the silicone preferably contains an organopolysiloxane having an alkenyl group such as an ethenyl group (vinyl group) or a 2-propenyl group (allyl group) at the terminal. The repeating units of the organopolysiloxane are preferably at least one selected type from the group consisting of dialkylsiloxanes, alkylarylsiloxanes, and diarylsiloxanes, more preferably at least one type selected from the group consisting of dimethylsiloxanes, methylphenylsiloxanes, and methylphenylsiloxanes, and even more preferably dimethylsiloxane. The repeating units may be a single type or a combination of two or more types. When two or more types of repeating units are combined, the arrangement may be random or block.

[0032] One suitable example of a silicone is methylhydrogenpolysiloxane having the following structural formula: In the formula, n represents the number of methylhydrogensiloxane units.

[0033]

[0034] The amount of the methylhydrogenpolysiloxane used is preferably 0.05 to 5.0 mass%, more preferably 0.1 to 1.0 mass%, of the total mass of the waste gypsum powder. In the above formula, the number n of methylhydrogensiloxane units is preferably an integer from 1 to 100.

[0035] In order to enhance the effectiveness as a waterproofing material, the methylhydrogenpolysiloxane is preferably used in combination with at least one catalyst selected from cement (Portland cement), calcium silicate hydrate, magnesium oxide, and magnesium hydroxide (hereinafter also referred to as “catalyst”).

[0036] When the methylhydrogenpolysiloxane is used in combination with the catalyst, the amount of the catalyst used is preferably 20 to 100 mass%, and more preferably 40 to 80 mass%, based on the amount of methylhydrogenpolysiloxane.

[0037] The methylhydrogenpolysiloxane may be used as is, or may be used as an emulsion in which the methylhydrogenpolysiloxane is emulsified in water. Use in the form of an emulsion is preferred because this allows the methylhydrogenpolysiloxane to be added and mixed more uniformly with the waste gypsum powder. There are no particular limitations regarding the catalyst (emulsifier) used to emulsify the methylhydrogenpolysiloxane in water to form an emulsion, and examples include nonionic surfactants, anionic surfactants, polyvinyl alcohols, and the like.

[0038] Examples of the nonionic surfactant include glycerol monostearate, glycerol monooleate, sorbitan monopalmitate, sorbitan monostearate, sorbitan tristearate, sorbitan monooleate, sorbitan trioleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene higher alcohol ethers, polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenyl ether, and the like.

[0039] Examples of the anionic surfactant include sodium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium alkylnaphthalenesulfonate, sodium dialkylsulfosuccinate, mixed fatty acid soda soap, sodium stearate soap, potassium oleate soap, sodium higher alcohol sulfate, and the sodium salt of β-naphthalenesulfonic acid formalin condensate.

[0040] The polyvinyl alcohol is preferably one having a degree of saponification of 75 mol% or more, and more preferably one having a degree of saponification of 76 to 90 mol%. Furthermore, the polyvinyl alcohol preferably has a viscosity as a 4% aqueous solution at 20°C of 1 to 80 cP, more preferably 3 to 50 cP.

[0041] When methylhydrogenpolysiloxane is used in combination with an emulsifier, the amount of the emulsifier used is preferably 20 to 100 mass%, and more preferably 40 to 80 mass%, based on the amount of methylhydrogenpolysiloxane.

[0042] The method for granulating the waste gypsum powder can be either a wet granulation method or a dry granulation method. The granulation method is preferably a wet granulation method such as a stirring granulation method, fluidized bed granulation method, or rolling granulation method. Among these, a pan granulation method or drum granulation method using a pan or drum as a granulation vessel is preferred, with the pan granulation method being more preferred. 　　　　　　　Granulation is preferably carried out using a granulator such as a pan type granulator or a drum type granulator.

[0043] The average particle size of the waste gypsum granules is not particularly limited so long as the size is 1 mm or more and 1 / 2 or less of the thickness of the gypsum board. By making the average particle size of the waste gypsum granules less than half the thickness of the gypsum board, the smoothness of the surface of the base of the gypsum board can be maintained, and by making the particle size 1 mm or more, the granule content in the gypsum slurry can be increased. 　　　　　　　Since thickness standards for gypsum boards are 9.5 mm, 12.5 mm, 15 mm, 21 mm, and 25 mm, half the thickness of the above gypsum boards would be 4.75 mm, 6.25 mm, 7.5 mm, 10.5 mm, or 12.5 mm.

[0044] More specifically, when the thickness of the gypsum board to be manufactured is 9.5 mm, the average particle size of the waste gypsum granules is preferably 1 to 4.75 mm, more preferably 1 to 4 mm, and even more preferably 1 to 2 mm. When the thickness of the gypsum board to be manufactured is 12.5 mm, the average particle size of the waste gypsum granules is preferably 1 to 6.25 mm, more preferably 1 to 6 mm, even more preferably 1 to 4 mm, and even more preferably 1 to 2 mm. When the thickness of the gypsum board to be manufactured is 15 mm, the average particle size of the waste gypsum granules is preferably 1 to 7.5 mm, more preferably 1 to 6 mm, even more preferably 1 to 4 mm, and even more preferably 1 to 2 mm. When the thickness of the gypsum board to be manufactured is 21 mm, the average particle size of the waste gypsum granules is preferably 1 to 10.5 mm, more preferably 1 to 9 mm, even more preferably 1 to 6 mm, even more preferably 1 to 4 mm, and even more preferably 1 to 2 mm. When the thickness of the gypsum board to be manufactured is 25 mm, the average particle size of the waste gypsum granules is preferably 1 to 12.5 mm, more preferably 1 to 10 mm, even more preferably 1 to 6 mm, even more preferably 1 to 4 mm, and even more preferably 1 to 2 mm. 　　　　　　　The average particle size of the waste gypsum granules can be measured using a commercially available laser diffraction / scattering type particle size distribution measuring device, for example, Partica LA-960V2 (manufactured by Horiba, Ltd.).

[0045] The strength of the waste gypsum granules is preferably high because this also affects the strength of the gypsum board to be manufactured. For example, if the granules disintegrate when the waste gypsum granules are mixed with water, or if the granules have a strength that can be crushed by a person's fingers, the strength of the produced gypsum board may not be sufficient. Although it is not possible to give a specific numerical value for the strength of the waste gypsum granules themselves, the result of a compressive strength test of the gypsum solidified body conducted in accordance with JIS A 1108:2018 “Test method for compressive strength of concrete” is preferably 2.5 N / mm2or more.

[0046] <Preparing Gypsum Slurry> 　　　　　　　A gypsum slurry comprising waste gypsum granules and calcined gypsum powder as gypsum materials is prepared in the step of preparing a gypsum slurry.

[0047] The gypsum slurry may be prepared by a method of preparing a gypsum slurry in a conventionally known method of manufacturing a gypsum board, except that the gypsum material contains waste gypsum granules in addition to the calcined gypsum powder. Herein, gypsum material refers to a gypsum component added to the gypsum slurry.

[0048] Examples of the calcined gypsum powder include regenerated particles of calcined gypsum obtained by calcining gypsum dihydrate powder obtained by crushing and classifying gypsum (gypsum dihydrate) recovered from waste gypsum boards, and virgin particles of calcined gypsum obtained by calcining gypsum dihydrate powder obtained by crushing and classifying natural gypsum or chemical gypsum.

[0049] The particle size distribution of the calcined gypsum powder is not particularly limited, but can be measured by a laser diffraction / scattering method. The calcined gypsum powder preferably has an average particle size of about 10 to 20 μm, as measured by a laser diffraction / scattering method. The particle size distribution can be measured by the laser diffraction / scattering method using a commercially available laser diffraction / scattering type particle size distribution measuring device, for example, Partica LA-960V2 (manufactured by Horiba, Ltd.).

[0050] The ratio of the waste gypsum granules in the gypsum material of the gypsum slurry is 10 to 65 mass%, preferably 15 to 50 mass%, and more preferably 20 to 30 mass%.

[0051] The proportion of the waste gypsum granules in the solid content of the gypsum slurry is preferably 15 to 50 mass%, more preferably 20 to 30 mass%. Herein, the solid content refers to a component remaining after removing free water other than crystal water from the gypsum slurry.

[0052] The gypsum slurry may further contain commonly used additives. Such an additive is preferably at least one selected from the group consisting of water reducing agents, foaming agents, adhesion promoters, and hardening accelerators.

[0053] The water reducing agent is not particularly limited, but examples thereof include naphthalenesulfonic acid-based water reducing agents and polycarboxylic acid-based water reducing agents. The amount of the water reducing agent to be added is not particularly limited, but is preferably 1.0 mass% or less, and more preferably 0.1 to 0.5 mass%, calculated as solid content, based on the mass of the gypsum board to be produced.

[0054] The foaming agent is not particularly limited, but a surfactant can be suggested. The amount of the foaming agent to be added is not particularly limited, but is preferably 0.1 mass% or less, and more preferably 0.01 to 0.1 mass%, calculated as solid content, relative to the mass of the gypsum board to be produced.

[0055] The adhesion promoter is not particularly limited, but examples thereof include oxidized starch. The amount of the adhesion promoter to be added is not particularly limited, but is preferably 0.5 mass% or less, and more preferably 0.2 to 0.5 mass%, calculated as solid content, based on the mass of the gypsum board to be manufactured.

[0056] The hardening accelerator is not particularly limited, but may be pulverized gypsum dihydrate. The pulverized gypsum dihydrate is obtained by pulverizing gypsum dihydrate into fine particles, and is also referred to as fine gypsum dihydrate powder, which has conventionally been used as a hardening accelerator. The median diameter of the ground gypsum dihydrate is not particularly limited, but is preferably 5 to 10 μm. The amount of the pulverized gypsum dihydrate added is not particularly limited, but is preferably 0.1 to 1.0 mass%, and more preferably 0.2 to 0.8 mass%, calculated as solid content based on the mass of the gypsum board to be manufactured.

[0057] The amount of water blended in the gypsum slurry is not particularly limited, but is preferably 50 to 100 mass%, more preferably 65 to 85 mass%, and even more preferably 70 to 80 mass%, based on the total mass of the gypsum slurry.

[0058] <Hardening Gypsum Slurry> 　　　　　　　The gypsum slurry prepared in the step of preparing a gypsum slurry is hardened in the step of hardening the gypsum slurry. 　　　　　　　The process is the same as a conventionally known gypsum board manufacturing process except for using the aforementioned gypsum slurry. 　　　　　　　Specifically, the gypsum board of the present invention is obtained by supplying the aforementioned gypsum slurry to a base paper and hardening the gypsum slurry. The gypsum slurry supplied to the base paper hardens due to a reaction between the gypsum and water. 　　　　　　　The amount of gypsum slurry supplied onto the base paper can be appropriately set depending on the thickness and width of the resulting gypsum board. 　　　　　　　The environmental conditions such as temperature and humidity when hardening the gypsum slurry on the base paper can be appropriately set. When the calcined gypsum (hemihydrate gypsum) in the gypsum slurry reacts with water to form gypsum dihydrate, needle-like crystals are produced, which then penetrate into the fibers of the base paper and become integrated. Furthermore, if an adhesion promoter (such as oxidized starch) is added, the adhesion promoter gelatinizes and moves to the interface between the paper and the gypsum, and dries as the board dries, causing adhesion. Therefore, the hardened body formed by hardening the gypsum slurry and the base paper are not easily separated.

[0059] The thickness of the gypsum slurry supplied to the base paper is preferably 75 mm or more, more preferably 80 mm or more, even more preferably 85 mm or more, even more preferably 90 mm or more, and even more preferably 100 mm or more, based on the results of a fluidity test described later. Generally, a larger numerical value in the fluidity test results indicates enhanced fluidity of the gypsum slurry, and more efficient production of the gypsum board of the present invention. 　　　　　　　For the fluidity test, a test slurry is prepared by mixing 237 g of gypsum material calculated as gypsum dihydrate and 123 g of water as excess water above the amount of water used in the hydration reaction of the calcined gypsum powder. The test slurry is charged into a mold having a diameter of 50 mm and a height of 50 mm, and the mold is immediately lifted up and the diameter of the spread slurry is measured.

[0060] The compressive strength of the hardened body obtained by hardening the gypsum slurry is preferably 2.5 N / mm2or more, as the results of the compressive strength test described later. The compressive strength test is performed in accordance with JIS A 1108:2018 “Test method for compressive strength of concrete”.

[0061] The gypsum slurry is supplied to a gypsum board base paper (top paper), and a gypsum board base paper (back paper) is supplied to the surface opposite to the top paper, so that the gypsum slurry is interposed between the gypsum board base papers. 　　　　　　　The hardened gypsum slurry and the base papers that sandwich the gypsum slurry are cut with a cutter, and then excess moisture is removed in a dryer. Finally, the board is cut to the desired size to complete the gypsum board. The completed gypsum board is inspected before shipping, and only non-defective products are shipped.Gypsum slurry

[0062] The present invention also provides a gypsum slurry (hereinafter also referred to as “the gypsum slurry of the present invention”). The gypsum slurry of the present invention is the gypsum slurry used in the aforementioned method of manufacturing a gypsum board, and has the same characteristics as the gypsum slurry used in the aforementioned method of manufacturing the gypsum board of the present invention. In other words, the gypsum slurry of the present invention is a gypsum slurry for gypsum boards containing waste gypsum granules obtained by granulating waste gypsum powder and calcined gypsum powder as gypsum materials, wherein the average particle size of the waste gypsum granules is 1 mm or more and 1 / 2 or less of the thickness of the gypsum board, and the proportion of the waste gypsum granules in the gypsum material is 10 to 65 mass%.

[0063] The waste gypsum granules contained in the gypsum slurry of the present invention are similar to the waste gypsum granules used in the aforementioned gypsum board manufacturing method of the present invention, and are prepared by granulating the waste gypsum powder. Hereinafter, the waste gypsum granules contained in the gypsum slurry of the present invention are also referred to as “waste gypsum granules”, and the waste gypsum powder used to prepare the waste gypsum granules is also referred to as “waste gypsum powder”.

[0064] Details of the gypsum slurry of the present invention are the same as those of the gypsum slurry used in the aforementioned method of manufacturing a gypsum board of the present invention.Use of gypsum slurry in the manufacture of gypsum board

[0065] The present invention also provides a use of the gypsum slurry in the production of gypsum board (hereinafter also referred to as “use of the present invention”). 　　　　　　　More specifically, the use of the present invention is the use of the gypsum slurry of the present invention in the manufacturing method of the gypsum board of the present invention.Gypsum board

[0066] The present invention also provides a gypsum board (hereinafter also referred to as the “gypsum board of the present invention”). The gypsum board of the present invention is a gypsum board manufactured by the aforementioned manufacturing method of a gypsum board of the present invention.

[0067] The gypsum board of the present invention is a laminate in which gypsum board base papers are laminated onto both sides of a gypsum hardened body formed into a plate shape. 　　　　　　　The gypsum hardened body contains waste gypsum granules formed by granulating waste gypsum powder and gypsum dihydrate as gypsum materials, wherein the waste gypsum granules have an average particle size of 1 mm or more and 1 / 2 or less of the thickness of the gypsum board, and the proportion of the waste gypsum granules in the gypsum material are 10 to 65 mass%.

[0068] The average particle size (arithmetic mean) of the waste gypsum granules is a value as measured by a laser diffraction / scattering method, and can be measured using a commercially available laser diffraction / scattering type particle size distribution measuring device, for example, Partica LA-960V2 (manufactured by Horiba, Ltd.).

[0069] The gypsum hardened body is obtained by interposing the aforementioned gypsum slurry of the present invention between the gypsum board base papers, hardening, and drying. When the calcined gypsum contained in the gypsum slurry of the present invention reacts with water to form gypsum dihydrate, needle-like crystals are produced, and these needle-like crystals penetrate into the fibers of the base paper and become integrated. Furthermore, if an adhesion promoter (such as oxidized starch) is added, the adhesion promoter gelatinizes and moves to the interface between the paper and the gypsum, and dries as the board dries, causing adhesion. Therefore, the gypsum hardened body and the gypsum board base paper are firmly bonded and do not easily separate.

[0070] The specific gravity of the gypsum board of the present invention is preferably 0.30 to 1.30.

[0071] The product standards and dimensions of the gypsum board of the present invention are not particularly limited, but preferably comply with the standards of JIS A 6901:2014 “Gypsum board products”. Examples

[0072] The present invention will be described below in more detail, with reference to the examples, but the present invention is not limited to the examples described below.

[0073] [Example 1] Example of manufacturing waste gypsum powder 　　　　　　　The following two types of gypsum boards (manufactured by Chiyoda Ute Co., Ltd.) were prepared. The abbreviations in parentheses are from JIS (JIS A 6901:2014). 　　　　　　　Gypsum board (GB-R): A board made by covering both sides and the longitudinal sides of a gypsum core with board base paper. 　　　　　　　Reinforced gypsum board (GB-F): a board where inorganic fibers are mixed into the core of GB-R to improve fire resistance and impact resistance.

[0074] Gypsum board was crushed and classified to produce the following waste gypsum powder. 　　　　　　　Waste gypsum powder 1: Waste gypsum powder produced from gypsum board (GB-R). 　　　　　　　Waste gypsum powder 2: Waste gypsum powder produced from reinforced gypsum board (GB-F).

[0075] The particle size distribution of the produced waste gypsum powder was measured using a laser diffraction / scattering type particle size distribution measuring device (manufactured by Horiba, Ltd.). The measurement results are shown in Table 1.

[0076]

[0077] In Table 1, D10, D50, and D90 refer to the volume-based cumulative 10% particle size, the volume-based cumulative 50% particle size, and the volume-based cumulative 90% particle size, respectively.

[0078] In addition, gypsum board (GB-R) was crushed and classified to produce waste gypsum powder (hereinafter also referred to as “waste gypsum powder 3”) having a particle size in a range of 1 to 2 mm.

[0079] [Example 2] Example of manufacturing waste gypsum granules 　　　　　　　Waste gypsum powder 1 produced in Example 1 was used to produce waste gypsum granules. 　　　　　　　Specifically, the waste gypsum powder 1 was granulated using a granulator (pan-type granulator, Chiyoda Ute Co., Ltd.). 　　　　　　　The granulation aid for waste gypsum granule 1 was 50 mass% of water based on the total mass of the waste gypsum powder 1; and the granulation aid for waste gypsum granule 2 contained 50 mass% of water, 0.5 mass% of silicone (methyl hydrogen polysiloxane), and 0.4 mass% of a catalyst (Portland cement), based on the total mass of the waste gypsum powder 1. 　　　　　　　The average particle size (arithmetic mean) of the produced waste gypsum granules was measured using a laser diffraction / scattering type particle size distribution measuring device (manufactured by Horiba, Ltd.). The measurement results are shown in Table 2.

[0080]

[0081] [Example 3] Manufacturing example of gypsum board 　　　　　　　Gypsum boards were manufactured using the gypsum board manufacturing equipment of Chiyoda Ute Co., Ltd. (Muroran City, Hokkaido) and compared with GB-R12.5 according to the standard (JIS A 6901:2014). 　　　　　　　Example 1: Calcined gypsum powder and waste gypsum granules 1 were used as gypsum materials. 　　　　　　　Example 2: Calcined gypsum powder and waste gypsum granules 2 were used as gypsum materials. 　　　　　　　Comparative Example 1: Only calcined gypsum powder was used as the gypsum material.

[0082] (1) Manufacturing conditions Gypsum board manufacturing conditions are presented in Table 3.

[0083]

[0084] (2) Performance evaluation of gypsum board 　　　　　　　The performance of the gypsum board manufactured in accordance with JIS A 6901:2014 was evaluated. 　　　　　　　Table 4 shows the results of performance evaluation of the produced gypsum boards.

[0085]

[0086]

[0087]

[0088] It was confirmed that the gypsum boards of the present invention (Examples 1 and 2) also conform to the performance items required for gypsum board products according to JIS A 6901:2014.

[0089] [Example 4] Evaluation of fluidity of gypsum slurry 1 (Effect of gypsum material) 　　　　　　　Calcined gypsum powder, waste gypsum powder 1 produced in Example 1, and waste gypsum granules 1 and waste gypsum granules 2 produced in Example 2 were used as gypsum materials, and as indicated in Table 5, 237.0 g of gypsum material, calculated as gypsum dihydrate, and 123.0 g of water, which was surplus water above the amount of water used in the hydration reaction of the calcined gypsum powder, were mixed to prepare a gypsum slurry, and the fluidity of the gypsum slurry was evaluated.

[0090]

[0091]

[0092] The fluidity test was performed by loading the prepared gypsum slurry into a frame having a diameter of 50 mm and a height of 50 mm, immediately lifting the frame, and measuring the diameter of the spread slurry. The measurement results are shown in FIG. 1. 　　　　　　　As depicted in FIG. 1, the fluidity of the gypsum slurry of No. 2 (addition rate of waste gypsum powder 1: 5%) was 70 mm, which is not considered sufficient, but the fluidity of the other gypsum slurries was 90 mm or more, which is considered favorable.

[0093] FIG. 2 depicts scanning electron microscope photographs of waste gypsum powder 1 and waste gypsum granules 1. FIG. 2A is a 50X observation image of waste gypsum powder 1, and the bar at the bottom right represents 500 μm. FIG. 2B is a 300X observation image of the waste gypsum powder 1, and the bar at the bottom right represents 50 μm. FIG. 2C is a 50X observation image of the waste gypsum granules 1, and the bar on the bottom right represents 500 μm. FIG. 2D is a 300X observation image of the waste gypsum granules 1, and the bar at the bottom right represents 50 μm. 　　　　　　　The waste gypsum powder 1 has fine waste gypsum powder, produced during the pulverizing of the gypsum board, adhering to the surface (FIGS. 2A and 2B). It is thought that these particles accelerate hardening of the gypsum slurry and reduce the fluidity of the gypsum slurry. On the other hand, unlike the waste gypsum powder 1, the waste gypsum granules 1 do not have fine waste gypsum powder adhering to the surface, and therefore it is thought that the fluidity of the gypsum slurry was favorable.

[0094] [Example 5] Evaluation of fluidity of gypsum slurry 11 (effect of gypsum material and granulation aid) (1) Manufacturing of waste gypsum granules (waste gypsum granules) 　　　　　　　The waste gypsum powder 1 produced in Example 1 was granulated using a pan-type granulator (manufactured by Chiyoda Ute Co., Ltd.) such that the average particle size of the granules was within a range of 1 to 3 mm in order to produce waste gypsum granules A to P.

[0095] The following granulation aids were used. 　　　　　　　Water 　　　　　　　Starch (oxidized starch) 　　　　　　　Paraffin 　　　　　　　Polyvinyl alcohol (PVA1, PVA2, PVA3) 　　　　　　　Silicone (methylhydrogenpolysiloxane) 　　　　　　　Catalyst (Portland cement)

[0096] The waste gypsum granules and the granulation aids used in granulating were as follows. ・ Waste gypsum granule A: Water (50 mass% of waste gypsum powder 1) ・ Waste gypsum granule B: Water (50 mass% of waste gypsum powder 1), oxidized starch (0.1 mass% of waste gypsum powder 1) ・ Waste gypsum granule C: Water (50 mass% of waste gypsum powder 1), oxidized starch (1.0 mass% of waste gypsum powder 1) ・ Waste gypsum granule D: Water (50 mass% of waste gypsum powder 1), silicone (methyl hydrogen polysiloxane) (1.0 mass% of waste gypsum powder 1), catalyst (Portland cement) (0.4 mass% of waste gypsum powder 1) ・ Waste gypsum granule E: Water (50 mass% of waste gypsum powder 1), silicone (methyl hydrogen polysiloxane) (0.5 mass% of waste gypsum powder 1), catalyst (Portland cement) (0.4 mass% of waste gypsum powder 1) ・ Waste gypsum granules F: Water (50 mass% of waste gypsum powder 1), silicone (methylhydrogenpolysiloxane) (0.25 mass% of waste gypsum powder 1), catalyst (Portland cement) (0.4 mass% of waste gypsum powder 1) ・ Waste gypsum granules G: Water (50 mass% of waste gypsum powder 1), silicone (methylhydrogenpolysiloxane) (0.25 mass% of waste gypsum powder 1), catalyst (Portland cement) (0.2 mass% of waste gypsum powder 1) ・ Waste gypsum granules H: Water (50 mass% of waste gypsum powder 1), silicone (methylhydrogen polysiloxane) (0.25 mass% of waste gypsum powder 1) ・ Waste gypsum granule I: Water (50 mass% of waste gypsum powder 1), silicone (methyl hydrogen polysiloxane) (0.125 mass% of waste gypsum powder 1), catalyst (Portland cement) (0.4 mass% of waste gypsum powder 1) ・ Waste gypsum granule J: Water (50 mass% of waste gypsum powder 1), paraffin (2 mass% of waste gypsum powder 1) ・ Waste gypsum granule K: Water (50 mass% of waste gypsum powder 1), PVA 1 (0.1 mass% of waste gypsum powder 1) ・ Waste gypsum granule L: Water (50 mass% of waste gypsum powder 1), PVA 1 (0.5 mass% of waste gypsum powder 1) ・ Waste gypsum granule M: Water (50 mass% of waste gypsum powder 1), PVA2 (0.1 mass% of waste gypsum powder 1) ・ Waste gypsum granule N: Water (50 mass% of waste gypsum powder 1), PVA2 (0.5 mass% of waste gypsum powder 1) ・ Waste gypsum granule O: Water (50 mass% of waste gypsum powder 1), PVA3 (0.1 mass% of waste gypsum powder 1) ・ Waste gypsum granule P: Water (50 mass% of waste gypsum powder 1), PVA3 (0.5 mass% of waste gypsum powder 1)

[0097] (2) Fluidity test 　　　　　　　For the fluidity test, a test slurry was prepared by mixing 237 g of gypsum material calculated as gypsum dihydrate and 123 g of water as excess water above the amount of water used in the hydration reaction of the calcined gypsum powder. The test slurry was charged into a mold having a diameter of 50 mm and a height of 50 mm, and the mold is immediately lifted up and the diameter of the spread slurry was promptly measured. 　　　　　　　The gypsum materials include calcined gypsum powder, waste gypsum powder 1 produced in Example 1, waste gypsum powder 3, and waste gypsum granules A to P produced as described above. Table 6 shows the formulation of the gypsum slurry and the results of the fluidity test.

[0098]

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105]

[0106] As can be seen from the results of the fluidity test shown in Table 6, the gypsum slurry of the present invention had excellent fluidity and had excellent productivity when manufacturing a gypsum boards even when the content ratio of waste gypsum granules was increased.

[0107] Gypsum slurry No. 2 using only the waste gypsum powder 3 (particle size 1 to 2 mm) had poor fluidity. This is in contrast to the excellent fluidity of the gypsum slurry made from waste gypsum granules of the same average particle size, which shows that the average particle size alone is not important for solving the problem. Although the reason for such a result cannot be determined with certainty, the present inventors hypothesized that this may be due to the fact that the particles of the waste gypsum powder 2 have an uneven and porous surface, and that fine waste gypsum powder adheres to the surface.

[0108] [Example 6] Strength evaluation of gypsum granules 　　　　　　　Gypsum dihydrate (calcium sulfate dihydrate) powder sold as a reagent was granulated in the same manner as waste gypsum granules 1 in Example 2 to produce gypsum granules (hereinafter also referred to as “gypsum granule 3”). 　　　　　　　The state of the waste gypsum granules 1 and the gypsum granules 3 produced as described above was observed when coming in contact with water. When gypsum granules 3 came into contact with water, the water turned cloudy and white, and after stirring under the stirring conditions described below, the granules disintegrated to such an extent that the shape could no longer be visually confirmed. In contrast, waste gypsum granules 1 did not disintegrate even when stirred under the stirring conditions described below. 　　　　　　　(Stirring conditions) 　　　　　　　Shape: One-sided disk turbine type 　　　　　　　Diameter: 75mm 　　　　　　　Mixing speed: 1400 rpm 　　　　　　　Mixing time: 60 seconds

[0109] Aspects of the present invention are described below. [1]　　　　　　A method of manufacturing a gypsum board using waste gypsum, comprising the steps of: 　　　　　　　granulating waste gypsum powder to prepare waste gypsum granules; 　　　　　　　preparing a gypsum slurry containing the waste gypsum granules and calcined gypsum powder as gypsum materials; and 　　　　　　　hardening the gypsum slurry; 　　　　　　　wherein the waste gypsum powder is granulated in the step of granulating so that the average particle size of the waste gypsum granules is 1 mm or more and 1 / 2 or less of the thickness of the gypsum board; and 　　　　　　　a proportion of the waste gypsum granules in the gypsum material is 10 to 65 mass%. [2]　　　　　　The method according to [1], wherein the calcined gypsum powder, the waste gypsum granules, and water are mixed to prepare the gypsum slurry. [3]　　　　　　The method according to [1] or [2], further including: mixing at least one additive selected from the group consisting of water reducing agents, foaming agents, adhesion promoters, hardening accelerators, and hardening retarders with the gypsum slurry. [4]　　　　　　The method according to [3], wherein when a water reducing agent is mixed into the gypsum slurry, the water reducing agent is mixed in an amount of 1.0 mass% or less, calculated as solid content, with regard to the mass of the gypsum board. [5]　　　　　　The method of [4], wherein the water reducing agent includes a naphthalene sulfonic acid water reducing agent or a polycarboxylic acid water reducing agent. [6]　　　　　　The method according to any one of [3] to [5], wherein when a foaming agent is mixed into the gypsum slurry, the foaming agent is mixed in an amount of 0.1 mass% or less, calculated as solid content, with regard to the mass of the gypsum board. [7]　　　　　　The method according to any one of [1] to [6], wherein in the step of granulating, the waste gypsum powder is mixed with a granulation aid containing at least one aid selected from the group consisting of water, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyacrylamide, paraffin, silicone, starch, molasses, Steffen wastewater concentrate, alcohol fermentation wastewater concentrate, lignin sulfonate, konjac powder, sodium alginate, and bentonite to perform granulation. [8]　　　　　　The method according to [7], wherein the waste gypsum powder has an average particle size of 500 μm or less. [9]　　　　　　The method according to [7] or [8], wherein in the step of granulating, 30 to 60 mass% of water is mixed with the waste gypsum powder based on the total mass of the waste gypsum powder.

[0010] A gypsum slurry for a gypsum board comprising waste gypsum granules obtained by granulating waste gypsum powder and calcined gypsum powder as gypsum materials, wherein 　　　　　　　the average particle size of the waste gypsum granules is 1 mm or more and 1 / 2 or less of the thickness of the gypsum board, and 　　　　　　　the proportion of the waste gypsum granules in the gypsum material is 10 to 65 mass%.

[0011] The gypsum slurry according to

[0010] , further comprising at least one additive selected from the group consisting of water reducing agents, foaming agents, adhesion promoters, hardening accelerators, and hardening retarders.

[0012] A gypsum board formed by laminating gypsum board base paper on both sides of a gypsum hardened body formed into a plate shape, wherein 　　　　　　　the gypsum hardened body contains waste gypsum granules formed by granulating waste gypsum powder and gypsum dihydrate as gypsum materials; 　　　　　　　the average particle size of the waste gypsum granules is 1 mm or more and 1 / 2 or less of the thickness of the gypsum board; and 　　　　　　　the proportion of waste gypsum granules in the gypsum material is 10 to 65 mass%.

[0013] The gypsum board according to

[0012] , having a specific gravity of 0.30 to 1.30.

[0014] Use of a gypsum slurry comprising waste gypsum granules obtained by granulating waste gypsum powder and calcined gypsum powder as gypsum materials for manufacturing a gypsum board, wherein 　　　　　　　the average particle size of the waste gypsum granules is 1 mm or more and 1 / 2 or less of the thickness of the gypsum board, and 　　　　　　　the proportion of the waste gypsum granules in the gypsum material is 10 to 65 mass%.

Claims

1. A method of manufacturing a gypsum board using waste gypsum, comprising the steps of: 　　　　　　　granulating waste gypsum powder to prepare waste gypsum granules; 　　　　　　　preparing a gypsum slurry containing the waste gypsum granules and calcined gypsum powder as gypsum materials; and 　　　　　　　hardening the gypsum slurry; 　　　　　　　wherein the waste gypsum powder is granulated in the step of granulating so that the average particle size of the waste gypsum granules is 1 mm or more and 1 / 2 or less of the thickness of the gypsum board; and 　　　　　　　a proportion of the waste gypsum granules in the gypsum material is 10 to 65 mass%.

2. The method according to claim 1, wherein the calcined gypsum powder, the waste gypsum granules, and water are mixed to prepare the gypsum slurry.

3. The method according to claim 2, further comprising: mixing at least one additive selected from the group consisting of water reducing agents, foaming agents, adhesion promoters, hardening accelerators, and hardening retarders with the gypsum slurry.

4. The method according to claim 3, wherein when a water reducing agent is mixed into the gypsum slurry, the water reducing agent is mixed in an amount of 1.0 mass% or less, calculated as solid content, with regard to the mass of the gypsum board.

5. The method of claim 4, wherein the water reducing agent includes a naphthalene sulfonic acid water reducing agent or a polycarboxylic acid water reducing agent.

6. The method according to claim 3, wherein when a foaming agent is mixed into the gypsum slurry, the foaming agent is mixed in an amount of 0.1 mass% or less, calculated as solid content, with regard to the mass of the gypsum board.

7. The method according to any one of claims 1 to 6, wherein in the step of granulating, the waste gypsum powder is mixed with a granulation aid containing at least one aid selected from the group consisting of water, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyacrylamide, paraffin, silicone, starch, molasses, Steffen wastewater concentrate, alcohol fermentation wastewater concentrate, lignin sulfonate, konjac powder, sodium alginate, and bentonite to perform granulation.

8. The method according to claim 7, wherein the waste gypsum powder has an average particle size of 500 μm or less.

9. The method according to claim 7, wherein in the step of granulating, 30 to 60 mass% of water is mixed with the waste gypsum powder based on the total mass of the waste gypsum powder.

10. A gypsum slurry for a gypsum board containing waste gypsum granules obtained by granulating waste gypsum powder and calcined gypsum powder as gypsum materials, wherein the average particle size of the waste gypsum granules is 1 mm or more and 1 / 2 or less of the thickness of the gypsum board, and the proportion of the waste gypsum granules in the gypsum material is 10 to 65 mass%.

11. .　　　　　　The gypsum slurry according to claim 10, further comprising at least one additive selected from the group consisting of water reducing agents, foaming agents, adhesion promoters, hardening accelerators, and hardening retarders.

12. A gypsum board formed by laminating gypsum board base paper on both sides of a gypsum hardened body formed into a plate shape, wherein the gypsum hardened body contains waste gypsum granules formed by granulating waste gypsum powder and gypsum dihydrate as gypsum materials; the average particle size of the waste gypsum granules is 1 mm or more and 1 / 2 or less of the thickness of the gypsum board; and the proportion of waste gypsum granules in the gypsum material is 10 to 65 mass%.

13. The gypsum board according to claim 12, having a specific gravity of 0.30 to 1.30.

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