Gypsum board manufacturing method, gypsum slurry and gypsum board

Abstract

Provided is a method for producing gypsum board that can use a gypsum raw material containing a high proportion of gypsum derived from waste gypsum board and can reduce energy consumption. [Solution] A method for manufacturing gypsum board using waste gypsum, comprising a granulation step of granulating waste gypsum powder to prepare waste gypsum granules, a slurry preparation step of preparing a gypsum slurry containing the waste gypsum granules and calcined gypsum powder as gypsum materials, and a slurry hardening step of hardening the gypsum slurry, wherein in the granulation step, the waste gypsum powder is granulated so that the average particle size of the waste gypsum granules is 1 mm or more and is 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%.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a gypsum board, a gypsum slurry, and a gypsum board. [Background technology]

[0002] Gypsum board is an architectural interior material made of a core of gypsum, covered on both sides with gypsum board base paper. It is fireproof, soundproof, dimensionally stable, easy to install, and is also economical, so it is widely used for the walls and ceilings of buildings.

[0003] Gypsum is classified into gypsum dihydrate, gypsum hemihydrate, and gypsum anhydrite depending on the form of its crystal water. Naturally occurring gypsum is gypsum dihydrate and gypsum anhydrite, but gypsum hemihydrate (commonly known as calcined gypsum) can be obtained by calcining gypsum dihydrate.

[0004] The gypsum (gypsum dihydrate) used as a raw material for gypsum boards can be either chemical gypsum or natural gypsum. Chemical gypsum includes by-product gypsum from various industries (by-product gypsum), gypsum obtained by capturing sulfurous acid gas in the flue gas from thermal power plants with lime (flue gas desulfurization gypsum), and gypsum obtained by neutralizing sulfuric acid with lime (neutralized gypsum). In recent years, the amount of recovered gypsum derived from recovered gypsum board waste (waste gypsum board) has been increasing.

[0005] The typical manufacturing method for gypsum board uses a streamlined continuous production system from receiving the gypsum raw material to completing the gypsum board product. Generally, there is a firing process in which gypsum (gypsum dihydrate) is calcined in a furnace to produce gypsum hemihydrate (calcined gypsum), which has the property of solidifying when it reacts with water; a molding process in which the gypsum hemihydrate is mixed with water to form a slurry, which is then poured onto a line (belt) along which base paper flows and the gypsum is sandwiched between the base paper; a drying process in which the board with the gypsum sandwiched between the base paper is sent into a dryer to remove excess moisture; and a finishing process in which the board is cut to the desired dimensions.

[0006] The amount of waste gypsum board generated annually is approximately 1.1 x 10 6 t, of which approximately 0.3 × 106 t is scrap material from production and interior construction work in new buildings, and is recycled by gypsum board manufacturers. However, the remaining approximately 0.8 × 10 6 Gypsum is generated during the 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), and because it reacts with water under anaerobic conditions to generate hydrogen sulfide (H2S), it had to be buried in a controlled final disposal site. As a result, securing disposal sites and the management costs have become problems.

[0007] Most of the gypsum derived from waste gypsum board (hereinafter also referred to as "waste gypsum") is discarded without being recycled, and the cost and space required for disposal itself are problems, so there is a demand for the establishment of a method for recycling waste gypsum board.

[0008] Patent Document 1 discloses a method for manufacturing gypsum board, which includes the steps of preparing a slurry by mixing a gypsum raw material containing 70% or more by mass of recycled gypsum, 0.1 to 1.0% by mass of a water-reducing agent relative to the gypsum raw material, 0.01 to 0.10% by mass of a foaming agent relative to the gypsum raw material, and water, and the step of hardening the slurry, in which the gypsum raw material accounts for 90% or more by mass of the total amount of the slurry excluding the water content. Here, "recycled gypsum" refers to gypsum containing crystals with an average particle size of 20 μm or more (typically an average particle size of 60 μm or less), which is produced by recycling "scrap gypsum" and has a larger particle size than "scrap gypsum." The crystal particle size of "scrap gypsum" is generally 1 to 5 μm. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 6529205 Summary of the Invention

[0010] The gypsum board manufacturing method disclosed in Patent Document 1 is advantageous in that it can manufacture gypsum boards using gypsum raw material made entirely from recycled gypsum produced from gypsum derived from waste gypsum boards (waste gypsum). The waste gypsum is gypsum dihydrate, which is converted into gypsum hemihydrate by heating and calcining at 150 to 185°C. The hemihydrate gypsum powder is then recrystallized into gypsum dihydrate crystals in a reaction layer after particle size adjustment. By promoting crystallization and increasing the particle size, large-crystal recycled gypsum (gypsum dihydrate) is obtained. Therefore, before recycled gypsum can be produced from waste gypsum boards, calcination and crystallization (large crystallization) processes 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 large specific surface area requires a large amount of water to be added when the gypsum becomes calcined, which increases drying costs and becomes rate-limiting, slowing down production speed.As a result, the waste gypsum content that does not interfere with the production of gypsum boards was less than 10% by mass.

[0011] One non-limiting object of the present invention is to provide a method for producing gypsum board that can use a gypsum raw material containing a high proportion of gypsum derived from waste gypsum board and can reduce energy consumption.

[0012] The above object can be achieved by the following means. A method for manufacturing gypsum board using waste gypsum, a granulation step of granulating the waste gypsum powder to prepare waste gypsum granules; A slurry preparation step of preparing a gypsum slurry containing the waste gypsum granules and calcined gypsum powder as gypsum materials; A slurry hardening step of hardening the gypsum slurry. Equipped with In the granulation step, the waste gypsum powder is granulated 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, The ratio of the waste gypsum granules in the gypsum material is 10 to 65% by mass. method. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a graph showing the evaluation results of fluidity of the gypsum slurry of Example 4. [Figure 2] 1 shows scanning electron microscope images of the waste gypsum powder and waste gypsum granules of Example 4. A, waste gypsum powder (×50 observation, bar represents 500 μm); B, waste gypsum powder (×300 observation, bar represents 50 μm); C, waste gypsum granules (×50 observation, bar represents 500 μm); D, waste gypsum granules (×300 observation, bar represents 50 μm). DETAILED DESCRIPTION OF THE INVENTION

[0014] In the present invention, "A to B" indicating a range of values ​​includes the values ​​A and B written before and after "to" as the lower and upper limits, respectively. For example, "1 to 10" means a range of values ​​from 1 to 10.

[0015] In the present invention, the phrase "substantially free of" a specific compound means that the content of the specific compound is below the measurement limit.

[0016] Although the embodiments of the present invention will be described in detail below, 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.

[0017] [Gypsum board manufacturing method] The method for manufacturing a gypsum board of the present invention is a method for manufacturing a gypsum board using waste gypsum, and includes a granulation step 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"); a slurry preparation step of 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 a slurry hardening step of hardening the gypsum slurry, wherein in the granulation step, the waste gypsum powder is granulated so that the average particle size of the waste gypsum granules is 1 mm or more and ½ 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%.

[0018] In the gypsum board manufacturing method of the present invention, the gypsum dihydrate is granulated without producing recycled gypsum (gypsum hemihydrate) from the waste gypsum (gypsum dihydrate). Furthermore, after granulation, the waste gypsum granules are not fired to convert the dihydrate gypsum into hemihydrate gypsum, and the waste gypsum particles are not crystallized (large crystallized). Therefore, the gypsum board manufacturing method of the present invention is more energy-efficient than the gypsum board manufacturing method disclosed in Patent Document 1.

[0019] <Granulation process> In the granulation process, the waste gypsum powder is granulated to prepare waste gypsum granules. The above-mentioned waste gypsum is gypsum derived from 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 crystallization water of calcium sulfate dihydrate may be lost, and calcium sulfate monohydrate, 0.5 hydrate, or anhydrous may be included. Note that the "main component" here refers to the component that is most abundant by mass, and if there are two or more components that are most abundant, any of them may be treated as the main component.

[0020] Waste gypsum board is gypsum board that has been discarded, regardless of whether the original gypsum board is unused or already used. Used gypsum board is, for example, gypsum board that was used as a building material and is generated when a building is demolished. Unused gypsum board is, for example, offcuts cut off from gypsum board used as a building material, surplus gypsum board, etc.

[0021] The waste gypsum powder is preferably obtained by crushing and classifying the above-mentioned waste gypsum board. The method for crushing the waste gypsum board is not particularly limited, but it is preferable to use a crusher, such as a jaw crusher, a gyratory crusher, an impact crusher, a roll 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, or a cutter mill.

[0022] There are no particular limitations on the method for classifying the pulverized waste gypsum, but dry classification is preferred, and either sieving or air classification can be used. In sieving, the classification diameter is determined by the mesh size of the wire mesh or mesh plate, and the dimensions of test sieves are specified in JIS Z 8801-1:2019 "Test Sieves - Part 1: Metal Wire Sieves" and JIS Z 8801-2:2022 "Test Sieves - Part 2: Metal Plate Sieves." Air classification, also known as wind classification, is broadly divided into gravity classification, inertia classification, and centrifugal classification. In gravity classification, the classification diameter is determined by the balance between the gravitational settling velocity of the particles and the ascending air velocity, and an example of a classifier is a zigzag classifier. In centrifugal classification, the classification diameter is determined by the condition where the centrifugal settling velocity of the particles is equal to the inward radial velocity of the airflow, and an example of a classifier is a cyclone classifier. As a cyclone classifier, a forced rotation vortex type cyclone classifier is preferred because it can increase the raw material supply amount.

[0023] It is preferable to use a crusher and a classifier in combination. In this case, the crusher is expected to play a role in breaking down agglomerates in addition to crushing coarse particles.

[0024] 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 the range of 50 to 300 μm, more preferably in the range of 100 to 250 μm. Furthermore, the volume-based cumulative 10% particle size (D10) is preferably in the range of 5 to 30 μm, more preferably in the range of 5 to 20 μm. Furthermore, the volume-based cumulative 90% particle size (D90) is preferably in the range of 350 to 800 μm, more preferably in the range of 400 to 550 μm. The particle size distribution of the waste gypsum powder can be measured using a commercially available laser diffraction / scattering particle size distribution measuring device, for example, Partica LA-960V2 (manufactured by Horiba, Ltd.).

[0025] The average particle size of the waste gypsum powder is not particularly limited, but is preferably 500 μm or less, and more preferably within the 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 particle size distribution measuring device, for example, Partica LA-960V2 (manufactured by Horiba, Ltd.).

[0026] The waste gypsum granules can be obtained by granulating the above-mentioned waste gypsum powder.

[0027] When granulating particles of waste gypsum, it is preferable to use a granulation aid. Granulation aids are also called granulation promoters or binders, and have the effect of promoting the aggregation of waste gypsum powder. Examples of the granulation aid include water, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyacrylamide, paraffin, silicone, starch, blackstrap molasses, stephen wastewater concentrate, alcohol fermentation wastewater concentrate, lignin sulfonate, konjac flour, sodium alginate, and bentonite. The above granulation aids can be used alone or in combination of two or more. The granulation aid is preferably at least one selected from the group consisting of these, more preferably at least one selected from the group consisting of water, starch, silicone, paraffin, and polyvinyl alcohol, and even more preferably silicone.

[0028] 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 the range of 30 to 60 mass% of the total mass of the waste gypsum powder, the waste gypsum powder can be moistened as necessary and sufficiently, and the waste gypsum granules tend to grow just right and have an appropriate average particle size.

[0029] When a granulation aid other than water is used as the granulation aid, it is preferably 0.05 to 5.0 mass% of the total mass of the waste gypsum powder. As the granulation aid, it is preferable to use water and a granulation aid other than water in combination.

[0030] The silicone is not particularly limited as long as it is a synthetic polymer compound having a main skeleton formed by siloxane bonds, but preferably includes 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 unit of the organopolysiloxane is preferably at least one selected from the group consisting of dialkylsiloxanes, alkylarylsiloxanes, and diarylsiloxanes, more preferably at least one selected from the group consisting of dimethylsiloxane, methylphenylsiloxane, and methylphenylsiloxane, and even more preferably dimethylsiloxane. The repeating unit may be one type alone or two or more types may be combined. When two or more types of repeating units are combined, the arrangement may be random or block.

[0031] A suitable example of a silicone is a methylhydrogenpolysiloxane having the following structural formula: where n is the number of methylhydrogensiloxane units.

[0032] [ka]

[0033] The amount of the methylhydrogenpolysiloxane used is preferably 0.05 to 5.0 mass % of the total mass of the waste gypsum powder, and more preferably 0.1 to 1.0 mass %. In the above formula, the number n of methylhydrogensiloxane units is preferably an integer of 1 to 100.

[0034] In order to enhance its effectiveness as a waterproofing material, the above-mentioned methylhydrogenpolysiloxane is preferably used in combination with at least one selected from cement (Portland cement), calcium silicate hydrate, magnesium oxide, and magnesium hydroxide (hereinafter also referred to as "catalyst").

[0035] When the methylhydrogenpolysiloxane is used in combination with the catalyst, the amount of the catalyst used is preferably 20 to 100% by mass, more preferably 40 to 80% by mass, based on the methylhydrogenpolysiloxane.

[0036] The methylhydrogenpolysiloxane may be used as is, or may be used as an emulsion in which the methylhydrogenpolysiloxane is emulsified in water. Use as an emulsion is preferred because it allows the methylhydrogenpolysiloxane to be more uniformly added and mixed with the waste gypsum powder. The catalyst (emulsifier) ​​used to emulsify the methylhydrogenpolysiloxane in water to form an emulsion is not particularly limited, and examples include nonionic surfactants, anionic surfactants, polyvinyl alcohol, etc.

[0037] Examples of the nonionic surfactants 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 ether, polyoxyethylene octylphenyl ether, and polyoxyethylene nonylphenyl ether.

[0038] 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, higher alcohol sodium sulfate, and sodium salt of β-naphthalenesulfonic acid formalin condensate.

[0039] The polyvinyl alcohol is preferably one having a saponification degree of 75 mol % or more, more preferably one having a saponification degree of 76 to 90 mol %. The viscosity of a 4% aqueous solution of the polyvinyl alcohol at 20°C is preferably 1 to 80 cP, more preferably 3 to 50 cP.

[0040] When the methylhydrogenpolysiloxane is used in combination with the emulsifier, the amount of the emulsifier used is preferably 20 to 100% by mass, more preferably 40 to 80% by mass, based on the methylhydrogenpolysiloxane.

[0041] As a method for granulating the waste gypsum powder, either a wet granulation method or a dry granulation method can be used. As the granulation method, wet granulation methods such as agitation granulation method, fluidized bed granulation method, and rolling granulation method are preferred. Among these, pan granulation method or drum granulation method using a pan or drum as a granulation container are preferred, and pan granulation method is more preferred. Granulation is preferably carried out using a granulator such as a pan granulator or a drum granulator.

[0042] The average particle size of the waste gypsum granules is not particularly limited as long as it is 1 mm or more and 1 / 2 or less of the thickness of the gypsum board. By setting the average particle size of the waste gypsum granules to 1 / 2 or less of the thickness of the gypsum board, the smoothness of the surface of the base of the gypsum board can be maintained, and by setting it to 1 mm or more, the content of granules in the gypsum slurry can be increased. The thickness standards for the above gypsum board are 9.5 mm, 12.5 mm, 15 mm, 21 mm, and 25 mm, so half the thickness of the above gypsum board is 4.75 mm, 6.25 mm, 7.5 mm, 10.5 mm, or 12.5 mm.

[0043] 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 still 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 still 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 particle size distribution measuring device, such as Partica LA-960V2 (manufactured by Horiba, Ltd.).

[0044] The strength of the waste gypsum granules is preferably high, as it also affects the strength of the gypsum board produced. For example, if the strength of the waste gypsum granules is such that the granules disintegrate when mixed with water, or the granulated granules can be crushed with a human finger, the strength of the gypsum board produced may not be sufficient. Although it is not possible to express the strength of the waste gypsum granules themselves in specific numerical values, the results 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" showed a compressive strength of 2.5 N / mm 2 It is preferable that this is the case.

[0045] <Slurry preparation process> In the slurry preparation step, a gypsum slurry containing the waste gypsum granules and calcined gypsum powder as gypsum materials is prepared.

[0046] The gypsum slurry may be prepared by a method for preparing a gypsum slurry in a conventionally known method for producing gypsum board, except that the gypsum material contains the waste gypsum granules in addition to the calcined gypsum powder. Here, the gypsum material refers to a gypsum component added to the gypsum slurry.

[0047] Examples of the calcined gypsum powder include recycled 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.

[0048] The particle size distribution of the calcined gypsum powder is not particularly limited, but can be measured by a laser diffraction / scattering method. The average particle size of the calcined gypsum powder measured by the laser diffraction / scattering method is preferably about 10 to 20 μm. Measurement of the particle size distribution by the laser diffraction / scattering method can be performed using a commercially available laser diffraction / scattering particle size distribution analyzer, such as the Partica LA-960V2 (manufactured by Horiba, Ltd.).

[0049] The proportion of the waste gypsum granules in the gypsum material in the gypsum slurry is 10 to 65 mass %, preferably 15 to 50 mass %, and more preferably 20 to 30 mass %.

[0050] 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 %. Here, the solid content refers to the components remaining after removing free water other than crystal water from the gypsum slurry.

[0051] The gypsum slurry may further contain a commonly used additive, preferably at least one selected from the group consisting of a water-reducing agent, a foaming agent, an adhesion promoter, and a hardening accelerator.

[0052] The water-reducing agent is not particularly limited, but examples 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% in terms of solid content, relative to the mass of the gypsum board to be produced.

[0053] The foaming agent is not particularly limited, but a surfactant can be exemplified. 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% in terms of solid content, relative to the mass of the gypsum board to be produced.

[0054] The adhesion promoter is not particularly limited, but examples thereof include oxidized starch, etc. 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, relative to the mass of the gypsum board to be produced.

[0055] The hardening accelerator is not particularly limited, but pulverized gypsum dihydrate can be exemplified. The pulverized gypsum dihydrate is obtained by pulverizing gypsum dihydrate to produce fine particles, and is also called gypsum dihydrate fine powder. It has conventionally been used as a hardening accelerator. The median diameter of the pulverized gypsum dihydrate is not particularly limited, but is preferably 5 to 10 μm. The blending amount of the pulverized gypsum dihydrate is not particularly limited, but is preferably 0.1 to 1.0 mass% in terms of solid content relative to the mass of the gypsum board to be manufactured, and more preferably 0.2 to 0.8 mass%.

[0056] The amount of water blended into the gypsum slurry is not particularly limited, but is preferably 50 to 100 mass % relative to the total mass of the gypsum slurry, more preferably 65 to 85 mass %, and even more preferably 70 to 80 mass %.

[0057] <Slurry hardening process> In the slurry hardening step, the gypsum slurry prepared in the slurry preparation step is hardened. Except for the use of the gypsum slurry, the process is the same as the conventionally known gypsum board manufacturing process. Specifically, the gypsum board of the present invention is obtained by supplying the gypsum slurry to the 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 to be supplied onto the base paper can be appropriately set depending on the thickness and width of the gypsum board to be obtained. The environmental conditions such as temperature and humidity when hardening the gypsum slurry on the base paper can be set appropriately. When the calcined gypsum (gypsum hemihydrate) in the gypsum slurry reacts with water to form gypsum dihydrate, needle-like crystals are generated, which penetrate the fibers of the base paper and become integrated. Furthermore, if an adhesion enhancer (such as oxidized starch) is added, it gelatinizes and moves to the interface between the paper and the gypsum, where it dries as the board dries, forming an adhesion. Therefore, the hardened product formed by the hardened gypsum slurry and the base paper do not easily peel off.

[0058] The gypsum slurry supplied to the base paper preferably has a diameter of 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, as determined by the fluidity test described below. Generally, the larger the numerical value in the fluidity test, the better the fluidity of the gypsum slurry, and the more efficient the production of the gypsum board of the present invention. For the fluidity test, a test slurry is prepared by mixing 237g of gypsum material (calculated as gypsum dihydrate) with 123g of water (excess water from the amount used in the hydration reaction of the calcined gypsum powder). This test slurry is loaded into a φ50mm x height 50mm mold, which is then immediately removed and the diameter of the spread slurry is measured.

[0059] The compressive strength of the hardened body obtained by hardening the gypsum slurry was 2.5 N / mm 2 The above is preferable. Compressive strength tests are conducted in accordance with JIS A 1108:2018 "Test methods for compressive strength of concrete."

[0060] The gypsum slurry is supplied to a gypsum board base paper (cover), and a gypsum board base paper (backing paper) is supplied to the surface opposite to the cover, and the gypsum slurry is sandwiched between the gypsum board base papers. The hardened gypsum slurry and the base paper sandwiched between them are cut with a cutter, then excess water is removed in a dryer, and the gypsum board is finally cut to the desired size. The finished gypsum board is inspected before shipping, and only non-defective products are shipped.

[0061] [Gypsum slurry] The present invention also provides a gypsum slurry (hereinafter also referred to as "gypsum slurry of the present invention"). The gypsum slurry of the present invention is a gypsum slurry used in the above-described method for producing a gypsum board, and has the same characteristics as the gypsum slurry used in the above-described method for producing a gypsum board of the present invention. That is, the gypsum slurry of the present invention is a gypsum slurry for a gypsum board, which contains, as gypsum materials, waste gypsum granules obtained by granulating waste gypsum powder and calcined gypsum powder, and is characterized in that the waste gypsum granules have an average particle size of 1 mm or more and ½ 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%.

[0062] The waste gypsum granules contained in the gypsum slurry of the present invention are the same as the waste gypsum granules used in the above-mentioned method for manufacturing a gypsum board of the present invention, and are prepared by granulating waste gypsum powder. Hereinafter, the waste gypsum granules contained in the gypsum slurry of the present invention will also be referred to as "waste gypsum granules," and the waste gypsum powder used to prepare the waste gypsum granules will also be referred to as "waste gypsum powder."

[0063] The details of the gypsum slurry of the present invention are the same as those of the gypsum slurry used in the above-described method for producing a gypsum board of the present invention.

[0064] [Use of gypsum slurry in the production of gypsum board] 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 above-mentioned method for producing a gypsum board of the present invention.

[0065] [Gypsum board] 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 above-described method for manufacturing a gypsum board of the present invention.

[0066] The gypsum board of the present invention is a laminate obtained by laminating gypsum board base paper on both sides of a gypsum hardened body formed into a plate shape. The gypsum hardened body contains waste gypsum granules obtained by granulating waste gypsum powder and dihydrate gypsum as gypsum materials, the waste gypsum granules having 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 being 10 to 65 mass%.

[0067] The average particle size (arithmetic mean) of the above waste gypsum granules is a value measured by the laser diffraction / scattering method, and can be measured using a commercially available laser diffraction / scattering particle size distribution measuring device, such as the Partica LA-960V2 (manufactured by Horiba, Ltd.).

[0068] The gypsum hardened body is obtained by sandwiching the gypsum slurry of the present invention described above between the gypsum board base paper, 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 generated, which penetrate the fibers of the base paper and become integrated. Furthermore, if an adhesion enhancer (oxidized starch, for example) is added, these gelatinize and migrate to the interface between the paper and the gypsum, where they adhere by drying as the board dries. Therefore, the gypsum hardened body and the gypsum board base paper are firmly bonded and do not easily peel off.

[0069] The specific gravity of the gypsum board of the present invention is preferably 0.30 to 1.30.

[0070] 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." [Example]

[0071] The present invention will be explained in more detail below using experimental examples, but the present invention is not limited to the experimental examples described below.

[0072] [Example 1] Example of manufacturing waste gypsum powder The following two types of gypsum board (manufactured by Chiyoda Ute Co., Ltd.) were prepared. The abbreviations in parentheses are JIS (JIS A 6901:2014) standards. Gypsum board (GB-R): A board made by covering both sides and the longitudinal sides with board base paper. Reinforced gypsum board (GB-F): Inorganic fibers are mixed into the core of GB-R to improve fire resistance and impact resistance.

[0073] The 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).

[0074] The particle size distribution of the produced waste gypsum powder was measured using a laser diffraction / scattering particle size distribution measuring device (manufactured by Horiba, Ltd.). The measurement results are shown in Table 1.

[0075] [Table 1]

[0076] In Table 1, D10, D50, and D90 are the volume-based cumulative 10% particle size, volume-based cumulative 50% particle size, and volume-based cumulative 90% particle size, respectively.

[0077] Also, gypsum board (GB-R) was crushed and classified to produce waste gypsum powder (hereinafter also referred to as "waste gypsum powder 3") with a particle size in the range of 1 to 2 mm.

[0078] [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.). As a granulation aid for waste gypsum granules 1, 50% by mass of water based on the total mass of waste gypsum powder 1 was used, and as a granulation aid for waste gypsum granules 2, 50% by mass of water, 0.5% by mass of silicone (methylhydrogenpolysiloxane), and 0.4% by mass of catalyst (Portland cement) based on the total mass of waste gypsum powder 1 were used. The average particle size (arithmetic mean) of the produced waste gypsum granules was measured using a laser diffraction / scattering particle size distribution measuring device (manufactured by Horiba, Ltd.). The measurement results are shown in Table 2.

[0079] [Table 2]

[0080] [Example 3] Gypsum board manufacturing example Gypsum board was manufactured using the gypsum board manufacturing equipment of Chiyoda Ute Co., Ltd. (Muroran City, Hokkaido) and compared with the GB-R12.5 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.

[0081] (1) Manufacturing conditions Table 3 shows the manufacturing conditions of the gypsum board.

[0082] [Table 3]

[0083] (2) Performance evaluation of gypsum board The performance of gypsum board manufactured in accordance with JIS A 6901:2014 was evaluated. Table 4 shows the results of performance evaluation of the manufactured gypsum boards.

[0084] [Table 4A]

[0085] [Table 4B]

[0086] [Table 4C]

[0087] 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 in JIS A 6901:2014.

[0088] [Example 4] Evaluation of fluidity of gypsum slurry I (effect of gypsum material) Calcined gypsum powder, waste gypsum powder 1 produced in Example 1, waste gypsum granules 1 and waste gypsum granules 2 produced in Example 2 were used as gypsum materials, and as shown in Table 5, 237.0 g of the gypsum material was used in terms of gypsum dihydrate, and 123.0 g of water was added as excess water from the amount of water used in the hydration reaction of the calcined gypsum powder to prepare a gypsum slurry, and the fluidity of the gypsum slurry was evaluated.

[0089] [Table 5A]

[0090] [Table 5B]

[0091] For the fluidity test, the prepared gypsum slurry was placed in a mold measuring φ50 mm and height 50 mm, and the mold was immediately lifted up to measure the diameter of the spread slurry. The measurement results are shown in Figure 1. As shown in Figure 1, the fluidity of No. 2 gypsum slurry (addition rate of waste gypsum powder 1: 5%) was 70 mm, which was not sufficient, but the fluidity of the other gypsum slurries was 90 mm or more, which was good.

[0092] Figure 2 shows scanning electron microscope images of waste gypsum powder 1 and waste gypsum granules 1. Figure 2A is a 50x magnification image of waste gypsum powder 1, with the bar at the bottom right being 500 μm. Figure 2B is a 300x magnification image of waste gypsum powder 1, with the bar at the bottom right being 50 μm. Figure 2C is a 50x magnification image of waste gypsum granules 1, with the bar at the bottom right being 500 μm. Figure 2D is a 300x magnification image of waste gypsum granules 1, with the bar at the bottom right being 50 μm. The waste gypsum powder 1 had fine waste gypsum powder produced during the crushing of the gypsum board attached to its surface (Figures 2A and 2B), which is thought to have accelerated the hardening of the gypsum slurry and reduced its fluidity.On the other hand, unlike the waste gypsum powder 1, the waste gypsum granules 1 did not have fine waste gypsum powder attached to its surface, which is thought to have resulted in good fluidity of the gypsum slurry.

[0093] [Example 5] Evaluation of fluidity of gypsum slurry II (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.) so that the average particle size of the granules was within the range of 1 to 3 mm, to produce waste gypsum granules A to P.

[0094] The following granulation aids were used: water Starch (oxidized starch) paraffin Polyvinyl alcohol (PVA1, PVA2, PVA3) Silicone (methylhydrogenpolysiloxane) Catalyst (Portland cement)

[0095] The waste gypsum granules and the granulation aids used in granulating them are as follows: Waste gypsum granules A: Water (50% by mass of waste gypsum powder 1) Waste gypsum granules B: water (50% by mass of waste gypsum powder 1), oxidized starch (0.1% by mass of waste gypsum powder 1) Waste gypsum granules C: water (50% by mass of waste gypsum powder 1), oxidized starch (1.0% by mass of waste gypsum powder 1) Waste gypsum granules D: water (50% by mass of waste gypsum powder 1), silicone (methyl hydrogen polysiloxane) (1.0% by mass of waste gypsum powder 1), catalyst (Portland cement) (0.4% by mass of waste gypsum powder 1) Waste gypsum granules E: water (50% by mass of waste gypsum powder 1), silicone (methyl hydrogen polysiloxane) (0.5% by mass of waste gypsum powder 1), catalyst (Portland cement) (0.4% by mass of waste gypsum powder 1) Waste gypsum granules F: water (50% by mass of waste gypsum powder 1), silicone (methyl hydrogen polysiloxane) (0.25% by mass of waste gypsum powder 1), catalyst (Portland cement) (0.4% by mass of waste gypsum powder 1) Waste gypsum granules G: water (50% by mass of waste gypsum powder 1), silicone (methyl hydrogen polysiloxane) (0.25% by mass of waste gypsum powder 1), catalyst (Portland cement) (0.2% by mass of waste gypsum powder 1) Waste gypsum granules H: water (50% by mass of waste gypsum powder 1), silicone (methylhydrogenpolysiloxane) (0.25% by mass of waste gypsum powder 1) Waste gypsum granules I: water (50% by mass of waste gypsum powder 1), silicone (methyl hydrogen polysiloxane) (0.125% by mass of waste gypsum powder 1), catalyst (Portland cement) (0.4% by mass of waste gypsum powder 1) Waste gypsum granules J: water (50% by mass of waste gypsum powder 1), paraffin (2% by mass of waste gypsum powder 1) Waste gypsum granules K: water (50% by mass of waste gypsum powder 1), PVA 1 (0.1% by mass of waste gypsum powder 1) Waste gypsum granules L: water (50% by mass of waste gypsum powder 1), PVA 1 (0.5% by mass of waste gypsum powder 1) Waste gypsum granules M: water (50% by mass of waste gypsum powder 1), PVA2 (0.1% by mass of waste gypsum powder 1) Waste gypsum granules N: water (50% by mass of waste gypsum powder 1), PVA2 (0.5% by mass of waste gypsum powder 1) Waste gypsum granules O: water (50% by mass of waste gypsum powder 1), PVA3 (0.1% by mass of waste gypsum powder 1) Waste gypsum granules P: water (50% by mass of waste gypsum powder 1), PVA3 (0.5% by mass of waste gypsum powder 1)

[0096] (2) Fluidity test For the fluidity test, a test slurry was prepared by mixing 237 g of gypsum material (calculated as gypsum dihydrate) with 123 g of water (excess water from the amount of water used in the hydration reaction of the calcined gypsum powder). This test slurry was loaded into a mold measuring φ50 mm x height 50 mm, and the mold was immediately removed to measure the diameter of the spread slurry. The gypsum materials used were 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.

[0097] [Table 6A]

[0098] [Table 6B]

[0099] [Table 6C]

[0100] [Table 6D]

[0101] [Table 6E]

[0102] [Table 6F]

[0103] [Table 6G]

[0104] [Table 6H]

[0105] 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 was excellent in productivity for gypsum boards even when the content ratio of waste gypsum granules was increased.

[0106] The gypsum slurry using only waste gypsum powder 3 (particle size 1-2 mm) in No. 2 had poor fluidity. This is in contrast to the gypsum slurry using waste gypsum granules with a similar average particle size, which had excellent fluidity, and it can be seen that the average particle size alone is not important for solving the problem. Although the reason for this result cannot be determined definitively, the inventors speculate that the particles of waste gypsum powder 2 have an uneven and porous surface, and that the fine waste gypsum powder adhering to the surface may have an effect.

[0107] [Example 6] Strength evaluation of gypsum granules Powder of dihydrate gypsum (calcium sulfate dihydrate) sold as a reagent was granulated in the same manner as in waste gypsum granules 1 of Example 2 to produce gypsum granules (hereinafter also referred to as "gypsum granules 3"). The state of the waste gypsum granules 1 and the gypsum granules 3 produced as described above when they came into contact with water was observed. When gypsum granules 3 came into contact with water, the water turned cloudy and after stirring under the stirring conditions below, the granules had disintegrated to the point where their shape could no longer be visually confirmed. In contrast, waste gypsum granules 1 did not disintegrate even when stirred under the stirring conditions below. (Mixing conditions) Shape: One-sided disc turbine type Diameter: 75mm Stirring speed: 1400 rpm Mixing time: 60 seconds

[0108] Aspects of the present invention are as follows. [1] A method for manufacturing gypsum board using waste gypsum, a granulation step of granulating the waste gypsum powder to prepare waste gypsum granules; A slurry preparation step of preparing a gypsum slurry containing the waste gypsum granules and calcined gypsum powder as gypsum materials; A slurry hardening step of hardening the gypsum slurry. Equipped with In the granulation step, the waste gypsum powder is granulated 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, The proportion of the waste gypsum granules in the gypsum material is 10 to 65% by mass. method. [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 comprising mixing at least one selected from the group consisting of a water-reducing agent, a foaming agent, an adhesion promoter, a set accelerator, and a set retarder 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 in terms of solid content relative to the mass of the gypsum board. [5] The method according to [4], wherein the water-reducing agent contains a naphthalene sulfonic acid-based water-reducing agent or a polycarboxylic acid-based water-reducing agent. [6] The method according to any one of [3] to [5], wherein when a foaming agent is mixed with the gypsum slurry, the foaming agent is mixed in an amount of 0.1 mass% or less in terms of solid content relative to the mass of the gypsum board. [7] The method according to any one of [1] to [6], wherein in the granulation step, the waste gypsum powder is mixed with a granulation aid containing at least one selected from the group consisting of water, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyacrylamide, paraffin, silicone, starch, blackstrap molasses, stephen wastewater concentrate, alcohol fermentation wastewater concentrate, lignin sulfonate, konjac fly 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 granulation step, water is mixed with the waste gypsum powder in an amount of 30 to 60 mass% of the total mass of the waste gypsum powder.

[10] A gypsum slurry for gypsum boards containing waste gypsum granules obtained by granulating waste gypsum powder and calcined gypsum powder 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, The gypsum slurry has a ratio of the waste gypsum granules in the gypsum material of 10 to 65 mass %.

[11] The gypsum slurry according to

[10] , further comprising at least one selected from the group consisting of a water-reducing agent, a foaming agent, an adhesion promoter, a set accelerator, and a set retarder.

[12] A gypsum board in which gypsum board base paper is laminated on both sides of a gypsum hardened body formed into a plate shape, The gypsum hardened body contains waste gypsum granules obtained by granulating waste gypsum powder and dihydrate gypsum 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, The proportion of the waste gypsum granules in the gypsum material is 10 to 65% by mass. Plasterboard.

[13] The gypsum board according to

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

[14] Use of a gypsum slurry containing waste gypsum granules obtained by granulating waste gypsum powder and calcined gypsum powder as gypsum materials in the manufacture of gypsum boards, 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, The proportion of the waste gypsum granules in the gypsum material is 10 to 65 mass %.

Claims

1. A method for manufacturing gypsum board using waste gypsum, a granulation step of granulating the waste gypsum powder to prepare waste gypsum granules; A slurry preparation step of preparing a gypsum slurry containing the waste gypsum granules and calcined gypsum powder as gypsum materials; A slurry hardening step of hardening the gypsum slurry. Equipped with In the granulation step, the waste gypsum powder is granulated 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, The ratio of the waste gypsum granules in the gypsum material is 10 to 65% by mass. method.

2. 2. The method of 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, wherein the gypsum slurry further comprises mixing at least one selected from the group consisting of a water reducing agent, a foaming agent, an adhesion promoter, a set accelerator, and a set retarder.

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

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

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

7. The method according to any one of claims 1 to 6, wherein in the granulation step, the waste gypsum powder is mixed with a granulation aid containing at least one selected from the group consisting of water, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyacrylamide, paraffin, silicone, starch, blackstrap molasses, steffen wastewater concentrate, alcohol fermentation wastewater concentrate, lignin sulfonate, konjac fly 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 granulation step, 30 to 60 mass% of water based on the total mass of the waste gypsum powder is mixed with the waste gypsum powder.

10. A gypsum slurry for gypsum boards containing waste gypsum granules obtained by granulating waste gypsum powder and calcined gypsum powder 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, The gypsum slurry, wherein the ratio of the waste gypsum granules in the gypsum material is 10 to 65% by mass.

11. The gypsum slurry according to claim 10, further comprising at least one selected from the group consisting of a water reducing agent, a foaming agent, an adhesion promoter, a set accelerator, and a set retarder.

12. A gypsum board in which gypsum board base paper is laminated on both sides of a gypsum hardened body formed into a plate shape, The gypsum hardened body contains waste gypsum granules obtained by granulating waste gypsum powder and dihydrate gypsum 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, The ratio of the waste gypsum granules in the gypsum material is 10 to 65% by mass. Plasterboard.

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

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