Gypsum board and method of manufacturing gypsum board

Abstract

A gypsum board having a gypsum core, wherein the gypsum core is a hardened body of a gypsum slurry containing water and a gypsum raw material containing recycled gypsum recovered from gypsum board waste, and wherein the gypsum core has an organic fiber content of 3.0 mass% or less.

Description

Technology Field

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

[0002] Patent Document 1 discloses a method for manufacturing a gypsum board, comprising a process of adjusting a slurry by mixing a gypsum raw material containing 70% by weight or more of recycled gypsum, a water reducing agent of 0.1% to 1.0% by weight relative to the gypsum raw material, a foaming agent of 0.01% to 0.10% by weight relative to the gypsum raw material, and water, and a process of curing the slurry, wherein the gypsum raw material is 90% by weight or more of the amount excluding the water content from the total amount of the slurry. Prior art literature

[0003] Japanese Patent Publication No. JP2020-63165 The problem to be solved

[0004] Gypsum board waste has been discharged as waste for a long time.

[0005] Gypsum board waste includes scraps generated during gypsum board production or interior construction. Most of the scraps generated during production and other processes are recycled by gypsum board manufacturers and other entities.

[0006] In addition, gypsum board waste includes waste generated from building renovations and demolition projects. The majority of gypsum board waste produced during such projects is not recycled but disposed of in landfills. Furthermore, gypsum board waste generated from building renovations and demolition projects accounts for a significant proportion of the total gypsum board waste generated.

[0007] In the future, as the demolition of buildings increases, the amount of gypsum board waste is expected to rise further; therefore, there is a need to reduce the amount of gypsum board waste disposed of in landfills from the perspectives of protecting the natural environment and controlling costs.

[0008] Accordingly, as disclosed in Patent Document 1, etc., there has been ongoing research on gypsum boards, such as gypsum boards manufactured using gypsum board waste.

[0009] However, since manufacturing recycled gypsum used in the gypsum board disclosed in Patent Document 1 requires multiple processes, there were problems in terms of manufacturing costs and productivity.

[0010] Therefore, one can consider manufacturing gypsum boards using recycled gypsum produced by crushing and calcining waste gypsum boards as a gypsum source.

[0011] Since gypsum boards are used as building materials, they are required to possess non-combustible properties. However, there is a risk that components other than gypsum may be mixed into recycled gypsum. Therefore, there have been concerns regarding whether gypsum boards manufactured using recycled gypsum as a source would be able to exhibit sufficient non-combustible properties.

[0012] Taking into account the problems of the prior art described above, one aspect of the present invention aims to provide a gypsum board having non-combustible properties while using recycled gypsum recovered from gypsum board waste as a gypsum raw material. means of solving the problem

[0013] To solve the above problem, according to one embodiment of the present invention, a gypsum core is provided, and

[0014] The above gypsum core is a hardened body of a gypsum slurry containing water and gypsum raw materials containing recycled gypsum recovered from gypsum board waste, and

[0015] The above gypsum core provides a gypsum board having an organic fiber content of 3.0 mass% or less. Effects of the invention

[0016] According to one embodiment of the present invention, a gypsum board having non-combustible properties can be provided by using recycled gypsum recovered from gypsum board waste as a gypsum raw material. Brief explanation of the drawing

[0017] FIG. 1 is an explanatory diagram of a plasterboard according to an embodiment of the present invention. Specific details for implementing the invention

[0018] The embodiments for carrying out the present invention will be described below with reference to the drawings, but the present invention is not limited to the following embodiments, and various modifications and substitutions may be added to the following embodiments without departing from the scope of the present invention.

[0019] [Plaster]

[0020] (1) About plasterboard

[0021] Hereinafter, the gypsum board of the present embodiment will be described using the drawings.

[0022] Figure 1 shows a schematic diagram of the plasterboard (10) of the present embodiment.

[0023] As shown in FIG. 1, the gypsum board (10) of the present embodiment has a gypsum core (11).

[0024] The plaster board (10) of the present embodiment may have a plate shape as shown in FIG. 1. The plaster core (11) has an upper surface (11A) and a lower surface (11B) located opposite to the upper surface (11A). The upper surface (11A) and the lower surface (11B) are surfaces located at both ends according to thickness.

[0025] And, a side surface (11C) is positioned between the upper surface (11A) and the lower surface (11B).

[0026] In FIG. 1, the gypsum board (10) and gypsum core (11) are shown in a rectangular shape, but the gypsum board (10) containing the gypsum core (11) can be used as a building material, and is not limited to this shape, and can be made into an appropriate shape depending on the use.

[0027] In FIG. 1, an example is shown in which the gypsum board (10) is made only of a gypsum core (11), but it is not limited to this form. The gypsum board (10) of the present embodiment may be any one selected from, for example, a gypsum board specified in JIS A 6901 (2014), a gypsum board that is lighter or heavier than the gypsum board specified in JIS A 6901 (2014) (hereinafter, the gypsum board specified in the above JIS and the gypsum board that is lighter or heavier than the gypsum board specified in the above JIS are collectively referred to as 'gypsum board'), a glass mat gypsum board, a gypsum containing glass fiber nonwoven fabric, etc.

[0028] Accordingly, the gypsum board (10) of the present embodiment may, depending on the shape of the gypsum board, further place a surface material such as a board base paper or a glass mat on the upper surface (11A) or lower surface (11B) of the gypsum core (11). In addition, a glass fiber nonwoven fabric (glass tissue) may be embedded on the upper surface (11A) or lower surface (11B). As shown in FIG. 1, the gypsum board (10) may be made of only the gypsum core (11) without placing a surface material on the upper surface (11A) or lower surface (11B) of the gypsum core (11).

[0029] (1-1) About the plaster core

[0030] In the gypsum board (10) of the present embodiment, the gypsum core (11) may be a hardened body of a gypsum slurry containing water and a gypsum raw material containing recycled gypsum recovered from gypsum board waste.

[0031] (1-2) Regarding the components contained in the gypsum slurry

[0032] The gypsum core (11) contained in the gypsum board (10) of this embodiment is a hardened body of gypsum slurry. The components that may be contained in the gypsum slurry are described below.

[0033] (1-2-1) Gypsum Raw Materials

[0034] Gypsum raw materials refer to raw materials containing gypsum, such as calcined gypsum, used in the preparation of gypsum slurries.

[0035] As mentioned above, the gypsum raw material may include recycled gypsum.

[0036] One method for reusing waste gypsum board is to use recycled gypsum obtained by crystallizing the gypsum in the waste gypsum board as a raw material. However, to produce recycled gypsum, the waste gypsum board must be crushed and calcined to form a gypsum slurry, and crystallization must be carried out on the gypsum slurry, which requires numerous processes for manufacturing. Therefore, there are problems in terms of manufacturing costs.

[0037] Therefore, the inventor of the present invention conducted an investigation into a gypsum board using recycled gypsum recovered from gypsum board waste. Recycled gypsum is gypsum converted into hemihydrate gypsum by crushing and calcining gypsum board waste. In other words, recycled gypsum is a calcined product of crushed gypsum board waste.

[0038] Since recycled gypsum is obtained by crushing and calcining waste gypsum boards, it requires fewer manufacturing steps and can reduce the energy consumed during production compared to recycled gypsum. Therefore, recycled gypsum can suppress manufacturing costs and other expenses compared to recycled gypsum.

[0039] As previously described, recycled gypsum is a calcined product of crushed waste gypsum board. Therefore, recycled gypsum may contain calcined gypsum, specifically calcium sulfate hemihydrate. Regarding the gypsum component, recycled gypsum may consist solely of calcined gypsum, but dihydrate gypsum may also be present. Since recycled gypsum is derived from waste gypsum board, it may contain components other than gypsum, such as paper derived from the waste gypsum board.

[0040] Recycled gypsum may contain dry-ground waste gypsum board. Recycled gypsum may consist of dry-ground waste gypsum board. However, even in this case, the incorporation of unavoidable impurities during the manufacturing process is not excluded. Compared to wet-ground waste gypsum board, dry-ground waste gypsum board can suppress the attachment and incorporation of moisture to the ground material during grinding. Therefore, by including dry-ground waste gypsum board in recycled gypsum, the incorporation of dihydrate gypsum can be suppressed. Furthermore, dry-ground waste gypsum board refers to a material obtained by firing dry-ground waste gypsum board, i.e., a fired product.

[0041] Although the content ratio of recycled gypsum in the gypsum raw material is not particularly limited, according to the inventor's review of the present invention, it is possible to produce a gypsum board having non-combustible properties even when the content ratio of recycled gypsum in the gypsum raw material is high. Therefore, from the perspective of environmental protection and cost reduction, it is desirable to have a high content ratio of recycled gypsum in the gypsum raw material. Accordingly, the content ratio of recycled gypsum in the gypsum raw material is, for example, preferably 30 mass% or more, more preferably greater than 60 mass%, and even more preferably 65 mass% or more.

[0042] In addition, as described herein, a gypsum board having non-combustible properties refers to a board having a total heat output of 8 MJ / m² over 20 minutes when a heat generation test is conducted. 2 It means that it is less than or equal to.

[0043] The gypsum raw material may consist solely of recycled gypsum. Therefore, the content of recycled gypsum in the gypsum raw material can be 100 mass% or less.

[0044] Accordingly, for example, the content ratio of recycled gypsum in the above gypsum raw material is preferably 30 mass% or more and 100 mass% or less, more preferably 60 mass% or more and 100 mass% or less, and more preferably 65 mass% or more and 100 mass% or less.

[0045] In addition to recycled gypsum, the gypsum raw material may also contain virgin gypsum raw material, that is, new gypsum raw material that is not recycled.

[0046] As a raw material for virgin gypsum, β-type calcined gypsum or α-type calcined gypsum, either alone or as a mixture of both, may be used. β-type calcined gypsum can be obtained by calcining in the atmosphere a mixture of natural gypsum, byproduct gypsum, and flue gas desulfurization gypsum, either alone or as a combination of any one of them. α-type calcined gypsum can be obtained by calcining in water (including in steam) a mixture of natural gypsum, byproduct gypsum, and flue gas desulfurization gypsum, either alone or as a combination of any one of them.

[0047] (1-2-2) Additives

[0048] Gypsum slurry may also contain various additives.

[0049] As additives, for example, foaming agents, adhesion enhancers, inorganic fibers such as glass fibers, organic fibers, lightweight aggregates, refractory materials such as vermiculite, setting retardants, setting accelerators, water reducers, foam diameter adjusters such as sulfosuccinate-type surfactants, water repellents such as silicone or paraffin, and one or more selected from organic carboxylic acids (or organic carboxylic acids), organic carbonates (or organic carboxylates), and organic phosphate compounds. The adhesion enhancer is an additive that improves the adhesion between the gypsum core (11) and the base paper for the gypsum board, and may include starch, polyvinyl alcohol, etc.

[0050] The foaming agent may be mixed with water, etc., to foam it, and then added to the gypsum slurry, or the foaming agent may be added to the gypsum slurry and then foamed during mixing, etc. As for the foaming agent, it is preferable to include one or more types selected from, for example, alkyl ether sulfates and alkyl sulfates.

[0051] When a foaming agent is added to the gypsum slurry, for example, the gypsum slurry contains a foam diameter adjusting agent, so that the size of the bubbles contained in the gypsum slurry or the gypsum core (11) can be easily adjusted.

[0052] (1-2-3) Organic fiber

[0053] Gypsum board waste contains components other than gypsum, raising concerns that non-gypsum components may be mixed into recycled gypsum. Therefore, there were concerns regarding whether gypsum boards manufactured using recycled gypsum as a source would be able to exhibit sufficient non-combustible properties.

[0054] Therefore, as a result of the inventor of the present invention conducting a review, it was confirmed that organic fibers have a significant influence on the non-combustible properties of the gypsum board (10). And, by keeping the content ratio of organic fibers in the gypsum core within a predetermined range, it was discovered that a gypsum board with non-combustible properties could be produced, and the present invention was completed.

[0055] Specifically, the gypsum core (11) can have an organic fiber content of 3.0 mass% or less. By having the organic fiber content of the gypsum core (11) 3.0 mass% or less, it is possible to make a gypsum board (10) that has non-combustible properties. By having the organic fiber content of the gypsum core (11) 3.0 mass% or less, the fluidity of the gypsum slurry can be increased when manufacturing the gypsum board, thereby increasing the productivity of the gypsum board.

[0056] The content of organic fibers in the gypsum core (11) is preferably 2.8 mass% or less, and more preferably 2.5 mass% or less.

[0057] The gypsum core (11) may contain organic fibers. The gypsum core (11) may have an organic fiber content of 0.1 mass% or more.

[0058] By having the gypsum core (11) contain at least 0.1 mass% of organic fibers, the shear strength or bending fracture load of the gypsum core (11) or the gypsum board (10) can be increased.

[0059] Accordingly, the content ratio of organic fibers in the gypsum core (11) is preferably, for example, 0.1 mass% or more and 3.0 mass% or less, more preferably 0.1 mass% or more and 2.8 mass% or less, and even more preferably 0.1 mass% or more and 2.5 mass% or less.

[0060] Organic fibers are mainly derived from recycled gypsum, such as paper contained in recycled gypsum. However, in order to adjust the content ratio of organic fibers contained in the gypsum core (11), organic fibers may be added to the gypsum slurry when preparing the gypsum slurry as needed.

[0061] In addition, regarding the recycled gypsum, the proportion of organic fibers contained in the recycled gypsum can be adjusted by removing paper through the degree of crushing (shattering) or, if necessary, sieving.

[0062] The effect on the total heat generation due to the content of organic fibers included in the gypsum core (11) of the gypsum board (10) is explained below.

[0063] Specifically, in Experimental Examples 1-1 to 1-7, a gypsum slurry was prepared by mixing new or recycled gypsum, paper, and water to achieve the mixing ratio shown in Table 1 below. Additionally, the water added when preparing the gypsum slurry was added such that the specific gravity of the hardened gypsum body obtained by hardening the gypsum slurry was 0.65. Then, the gypsum slurry was placed between base papers for boards and molded to a thickness of 12.5 mm to prepare a gypsum board, which is a gypsum board (10). The base papers for boards had a basis weight of 200 g / m² 2 was.

[0064] For the recycled gypsum, waste gypsum board was dry-crushed to the point where the attached paper could be removed, and the paper was completely removed through sieving and other methods before being calcined. Additionally, the paper used was the paper recovered during the manufacturing of the recycled gypsum.

[0065] (Pyrogenicity test)

[0066] For the obtained test specimen, a test of exothermic reaction was conducted in accordance with the ISO 5660-1 cone calorimeter method, and the total heat output was measured at a heating time of 20 minutes.

[0067] The evaluation results are shown in Table 1.

[0068]

[0069] According to the results shown in Table 1, when the content of organic fiber paper is 3.0 mass% or less, the total heat output over 20 minutes is 8 MJ / m² 2 It was confirmed that the following could be achieved. Therefore, it was confirmed that the gypsum core (11) has excellent non-combustible properties by keeping the organic fiber content at 3.0 mass% or less, and in particular, the non-combustible properties can be improved by keeping it at 2.8 mass% or less or 2.5 mass% or less.

[0070] The proportion of organic fibers included in the gypsum core (11) can be measured and calculated, for example, in the following order.

[0071] First, the gypsum core (11) is heated to 150°C and then crushed to obtain a crushed material. The degree of crushing is not particularly limited, and the size can be selected and crushed so that the time for dissolving the gypsum component when washing with water on the sieve below can be shortened.

[0072] Next, the obtained crushed material is washed with water on a 100-mesh sieve. Since the residue on the sieve is an organic fiber contained in the gypsum core, its mass is measured after drying and is used as the mass of the organic fiber. Then, the mass ratio of the organic fiber mass to the crushed material supplied on the sieve can be calculated and used as the mass ratio of the organic fiber contained in the gypsum core (11).

[0073] In addition, if the gypsum board (10) has a surface material, the portion of the gypsum board (10) containing the surface material can be removed, and then the above evaluation can be performed on the gypsum core (11).

[0074] Accordingly, the organic fibers contained in the gypsum core of the gypsum board of the present embodiment can be reduced to the amount of paper remaining on a 100-mesh sieve when the gypsum core is washed with water on a 100-mesh sieve. The gypsum core of the gypsum board of the present embodiment may contain various organic fibers of different lengths.

[0075] (2) Regarding the total heat output of the gypsum board

[0076] The gypsum board (10) of the present embodiment has a total heat output of 8 MJ / m² over 20 minutes. 2 It is desirable that it be less than or equal to 6 MJ / m² 2 It is more desirable to be less than this.

[0077] The total heat output of the plasterboard (10) over 20 minutes is 8 MJ / m² 2 By making it below this level, it is possible to make a gypsum board with excellent non-combustible properties, and 6 MJ / m²2 By doing this, even when a paint containing organic components is applied and placed on the surface of the gypsum board (10), the non-combustible properties can be maintained.

[0078] The total calorific value of the gypsum board (10) can be selected by adjusting the content ratio of organic fibers in the gypsum core (11), for example, by the degree of paper removal when manufacturing recycled gypsum. For example, as already described in ‘(organic fibers)’ of ‘(1-2) Regarding the components contained in the gypsum slurry,’ by making the content ratio of organic fibers included in the gypsum core (11) 3.0 mass% or less, the total calorific value of the gypsum board (10) is 8 MJ / m² 2 The amount can be reduced to 2.8 mass% or less. In particular, the total heat generation can be particularly suppressed by reducing the content ratio of organic fibers included in the gypsum core (11) to 2.8 mass% or less.

[0079] (3) Regarding the specific gravity of gypsum board

[0080] The specific gravity of the gypsum board is not specifically limited, but, for example, it can be 0.65 or higher. By making the specific gravity of the gypsum board 0.65 or higher, the strength of the gypsum board can be particularly increased.

[0081] The upper limit of the specific gravity of the gypsum board is not specifically limited, but from the perspective of improving handling at the construction site, it may be less than 1.1 or 1.0 or less.

[0082] The specific gravity of the gypsum board can be evaluated according to the method described in JIS A 6901 (2014).

[0083] (4) Regarding the composition of plasterboard

[0084] The plasterboard (10) of this embodiment may be, for example, made of plasterboard.

[0085] That is, the gypsum board (10) of the present embodiment may be a gypsum board having a board base paper on the upper surface (11A) and lower surface (11B) of the gypsum core (11).

[0086] In this case, the base paper for the board is not specifically limited, but the basis weight of the base paper is 200g / m² 2 It is desirable that it be less than or equal to this.

[0087] The basis weight of the base paper for boards is 200g / m² 2 This is because reducing it to this level can increase the non-combustible properties of the gypsum board.

[0088] In addition, even in the case of using gypsum board, it is desirable to satisfy the previously described regulations regarding total heat output; for example, a total heat output of 8 MJ / m² over 20 minutes. 2 It is desirable that it be less than or equal to this.

[0089] (5) Examination of the effect of incorporation of organic fibers on the compressive strength of hardened gypsum (Experimental Example 2)

[0090] The inventor of the present invention conducted an examination of properties other than non-combustibility regarding a hardened gypsum body using recycled gypsum. Here, the results of the examination regarding the influence of organic fibers, such as paper, attached to the recycled gypsum on the strength of the gypsum board are described.

[0091] To accurately examine the effect of organic fibers, recycled gypsum from which organic fiber paper had been completely removed was used, and the compressive strength of gypsum cured from gypsum slurries prepared by varying the amount of paper added was evaluated.

[0092] Specifically, as Experimental Examples 2-1 to 2-4, a gypsum slurry was prepared by mixing recycled gypsum, paper, and water in the mixing ratios shown in Table 2 below.

[0093] In addition, water added when preparing the gypsum slurry was added so that the specific gravity of the hardened gypsum body obtained by hardening the gypsum slurry would be a predetermined value.

[0094] Then, a gypsum slurry was poured into a mold having a cube shape with a side length of 40 mm, and a hardened gypsum body was prepared as a test specimen by drying at constant weight at 40°C.

[0095] For the recycled gypsum, waste gypsum board was dry-crushed to the point where the attached paper could be removed, and the paper was completely removed through sieving and other methods before being calcined. Additionally, the paper used was the paper recovered during the manufacturing of the recycled gypsum.

[0096] (Method for evaluating the compressive strength of hardened gypsum)

[0097] For the obtained gypsum hardened specimens, the compressive strength was measured using an Autograph (manufactured by Shimadzu Corporation, AG-X plus) at a loading rate of 1 mm / min. The compressive strength of each experimental example listed in Table 2 below is the average value of the compressive strengths of the six specimens, which were measured under the same conditions. In the other experimental examples below, the compressive strength of the gypsum hardened specimens was also evaluated under the same conditions.

[0098] The evaluation results are shown in Table 2.

[0099]

[0100] According to the results shown in Table 2, it was confirmed that the compressive strength of the hardened gypsum body tended to improve as the paper content was reduced. However, even when the paper content was 2.5 parts by mass, i.e., 2.5 mass% relative to the gypsum raw material, the compressive strength was 25 kgf / cm² 2 It was confirmed that it possesses sufficient strength by having a compressive strength of the above. In addition, the hardened gypsum body was 25 kgf / cm² 2 By possessing the above compressive strength, when a screw is driven into the hardened gypsum, it prevents the hardened gypsum from being damaged due to excessive screwing and has sufficient force to retain and support the driven screw. That is, the hardened gypsum has a compressive strength of 25 kgf / cm² 2Having the above compressive strength means that when used in gypsum boards, it has sufficient compressive strength for practical use.

[0101] For example, when a hardened gypsum body mixed with paper at a ratio of 2.5 mass% with respect to gypsum raw materials is applied to a gypsum board, the content ratio of paper, which is an organic fiber contained in the gypsum core of the gypsum board, becomes 2.5 mass%.

[0102] (6) Examination of the effect of the specific surface area of ​​recycled gypsum on the compressive strength of the hardened gypsum body (Experimental Example 3)

[0103] Recycled gypsum can be manufactured, for example, by crushing waste gypsum board and subsequently performing sieving or calcination. Furthermore, by selecting the degree of crushing or sieving of the waste gypsum board, the degree of separation of organic fibers from the recycled gypsum can be selected, thereby allowing for the adjustment of the amount of organic fibers incorporated into the recycled gypsum. Crushing or sieving may also be performed in multiple stages.

[0104] The crushing device used when crushing gypsum board waste is not particularly limited and can be selected based on the desired organic fiber content or the particle size after crushing. For example, when performing rough crushing of gypsum board waste, a screen crusher or the like can be used as the crushing device. Furthermore, when crushing gypsum board waste until it becomes a fine powder to suppress the organic fiber content, a roll crusher or a hammer mill can be used as the crushing device. Additionally, crushing can be performed in multiple stages, and a crushing device can be selected at each stage to match the desired particle size of the gypsum board waste.

[0105] In addition, the sieve mesh size during sieving can be selected based on the degree of organic fiber separation, the type of organic fiber to be separated, and the particle size distribution of the gypsum board waste after crushing, and is not particularly limited. Sieving can also be performed in multiple stages.

[0106] However, since there is a concern that the strength of the gypsum board may be affected depending on the degree of grinding when manufacturing recycled gypsum, the inventor of the present invention examined the relationship between the specific surface area of ​​recycled gypsum and the compressive strength of the hardened gypsum body.

[0107] Specifically, in Experimental Examples 3-1 to 3-5, a gypsum slurry was prepared using only recycled gypsum as the raw material. The gypsum slurry was prepared by mixing the gypsum raw material, paper, and water according to the mixing ratio shown in Table 3 below. The water added when preparing the gypsum slurry was added such that the specific gravity of the hardened gypsum body obtained by hardening the gypsum slurry would be a predetermined value. Then, a hardened gypsum body was produced under the same conditions as in Experimental Example 2, except for the use of the above-mentioned gypsum slurry, and the compressive strength was evaluated.

[0108] Recycled gypsum was prepared by dry-crushing and sieving waste gypsum boards, and then calcining them, with the paper completely removed. The recycled gypsum used in Experimental Examples 3-1 to 3-5 had their degree of crushing adjusted during preparation, and the BSA values ​​(hereinafter referred to as 'BSA'), which are the results of measuring the specific surface area using a Blaine air permeability fineness meter, were the values ​​shown in Table 3.

[0109] For the paper, paper recovered during the manufacture of recycled gypsum was used.

[0110]

[0111] According to the results shown in Table 3, regardless of the BSA value of the recycled gypsum, the hardened gypsum body was 25 kgf / cm² 2 It was confirmed that it possessed sufficient strength by having a compressive strength of the above.

[0112] In addition, according to the inventor's review of the present invention, BSA is 18,200 cm 2In order to produce the recycled gypsum of Experimental Example 3-5 with a value of / g, it is necessary to perform multi-stage grinding and sieving. In addition, when finely ground to increase the BSA content, sieve clogging is likely to occur during sieving.

[0113] Therefore, the recycled gypsum of Experimental Examples 3-1 to 3-5 shown in Table 3 can be said to guarantee the entire range of BSA of recycled gypsum manufactured by crushing gypsum board waste.

[0114] (7) Examination of the effect of the proportion of recycled gypsum in the gypsum raw materials on the compressive strength of the hardened gypsum body (Experimental Example 4)

[0115] Next, the inventor of the present invention examined the compressive strength of the hardened gypsum body when the proportion of recycled gypsum in the gypsum raw material was varied.

[0116] The compressive strength of a hardened gypsum body was evaluated by hardening a gypsum slurry prepared by varying the mass ratio of recycled gypsum in the gypsum raw material.

[0117] Specifically, as Experimental Examples 4-1 to 4-6, a gypsum slurry was prepared by mixing fresh gypsum, recycled gypsum, and water according to the mixing ratios shown in Table 4 below. In addition, the water added when preparing the gypsum slurry was added such that the specific gravity of the hardened gypsum body obtained by hardening the gypsum slurry would be a predetermined value. Then, a hardened gypsum body was produced under the same conditions as Experimental Example 2, except for the use of the above-mentioned gypsum slurry, and the compressive strength was evaluated.

[0118] Recycled gypsum was prepared by dry-crushing waste gypsum board, sieving it, and then calcining it. For the recycled gypsum, the paper was completely removed during the preparation process, but after calcination, paper was added so that the content of organic fiber paper was 2.5 parts by mass per 100 parts by mass of gypsum. The paper used was the paper recovered during the production of the recycled gypsum.

[0119] The recycled gypsum used in Experimental Examples 4-1 through 4-6 has a BSA of 1700 cm⁻¹ 2 It is in / g. The BSA shown in Table 4 is the BSA from the total gypsum raw material. For the new gypsum, new gypsum raw material was used instead of recycled material.

[0120] The evaluation results are shown in Table 4.

[0121]

[0122] According to the results shown in Table 4, regardless of the content of recycled gypsum in the raw materials, the compressive strength of the hardened gypsum is 25 kgf / cm² 2 Based on the above, it was confirmed that it possesses sufficient strength.

[0123] [Method of manufacturing gypsum board]

[0124] The method for manufacturing a gypsum board of the present embodiment may include a gypsum slurry preparation process, a molding process, and a curing process.

[0125] By the method for manufacturing a gypsum board of the present embodiment, a gypsum board according to one aspect of the present disclosure can be manufactured. Accordingly, some details regarding the gypsum board that have already been described are omitted.

[0126] (Gypsum slurry preparation process)

[0127] In the gypsum slurry preparation process, gypsum raw materials containing recycled gypsum recovered from gypsum board waste and water can be mixed to prepare a gypsum slurry.

[0128] In the process of preparing a gypsum slurry, the proportion of recycled gypsum in the gypsum raw material is not particularly limited, but, for example, it is preferable to have a ratio of 30 mass% or more and 100 mass% or less, more than 60 mass% and more than 100 mass%, and more than 65 mass% and more than 100 mass%.

[0129] For example, these raw material components can be mixed using a mixer or the like to prepare a gypsum slurry. Various additives, such as foaming agents, may be added to the gypsum slurry as needed. Since the raw materials for gypsum slurry that can be suitably used have already been described, they will be omitted here.

[0130] The recycled gypsum supplied to the gypsum slurry preparation process is, for example, BSA 1500 cm 2 / g or more than 20,000cm 2 It is desirable that it be less than / g.

[0131] 1500cm of BSA of recycled gypsum 2 By making it greater than / g, organic fibers originating from the base paper for boards of gypsum board waste can be easily removed, thereby particularly enhancing the non-combustible properties of the resulting gypsum board.

[0132] By increasing the BSA of recycled gypsum, organic fibers can be easily removed, thereby significantly reducing the incorporation of organic fibers into the recycled gypsum. However, if the BSA of the recycled gypsum is set too high, it may cause sieve clogging during sieving, which can actually make the removal of organic fibers more difficult. Therefore, the BSA of the recycled gypsum is 20,000 cm³ 2 It is desirable that it be less than / g.

[0133] (Molding process)

[0134] In the molding process, a gypsum slurry molded body can be manufactured by molding the gypsum slurry prepared in the gypsum slurry preparation process.

[0135] In the process of preparing a gypsum slurry, foam is added to the gypsum slurry, and when multiple types of gypsum slurries are prepared with different foam addition conditions, each gypsum slurry may be supplied in a desired stacking order during the molding process to form a stack of gypsum slurries.

[0136] In addition, for example, when manufacturing a gypsum board as a gypsum board (10), a gypsum slurry can be placed between base papers for the board and molded by passing it through a molding machine to produce a gypsum slurry molded body.

[0137] When manufacturing a gypsum board as a gypsum board (10), the base paper for the board is not particularly limited, but the basis weight is 200 g / m² 2 It is preferable to use board base paper of the following quality.

[0138] This refers to a basis weight of 200g / m² for board base paper. 2 This is because reducing it to this level can increase the non-combustible properties of the gypsum board.

[0139] (Curing process)

[0140] In the curing process, the gypsum slurry molded body obtained from the molding process can be cured.

[0141] The hardening process can be carried out by causing needle-shaped crystals of dihydrate gypsum to form through a hydration reaction in which the calcined gypsum (hemihydrate gypsum) contained in the gypsum raw material in the gypsum slurry condenses and solidifies. Accordingly, within the gypsum slurry molded body formed in the molding process, the hardening process can be carried out by reacting between the calcined gypsum in the gypsum raw material added to the gypsum slurry and water, thereby allowing the hydration reaction of the calcined gypsum to proceed.

[0142] The content of organic fibers in the gypsum core of the gypsum board obtained after the curing process can be 3.0 mass% or less.

[0143] The method for manufacturing a gypsum board according to the present embodiment may further include any additional processes. Specifically, for example, it may include the following cutting process or drying process.

[0144] (Cutting process)

[0145] In the cutting process, the gypsum slurry molded body can be cut by a cutting device.

[0146] After forming a gypsum slurry molded body in the molding process, the gypsum slurry gradually hardens. Therefore, the cutting process can be performed, for example, while the hardening process is in progress or after the hardening process is completed. However, it is preferable to perform the cutting process after the hardening process has progressed to the point where the gypsum slurry molded body can be cut.

[0147] The cutting process may be performed multiple times. Accordingly, the method for manufacturing a gypsum board according to the present embodiment may include a first cutting process, which can be described as a preliminary cutting process, for example. Additionally, a second cutting process may be further included.

[0148] In the first cutting process, the gypsum slurry molded body can be cut to a desired size depending on, for example, the size of the dryer used in the drying process described later.

[0149] In addition, the second cutting process can be performed, for example, after the drying process, and can be cut to a desired product size.

[0150] (Drying process)

[0151] In the drying process, the gypsum slurry molded body can be dried. In the drying process, excess moisture contained in the gypsum slurry molded body can be dried. Additionally, it is preferable to supply the gypsum slurry molded body, which has completed the curing process, to the drying process. The drying process can be carried out by forcibly drying the gypsum slurry molded body using a dryer.

[0152] The method of forcibly drying a gypsum slurry molded body by means of a dryer is not particularly limited, but for example, a dryer may be installed on the conveying path of the gypsum slurry molded body, and the gypsum slurry molded body may be continuously dried by passing the gypsum slurry molded body through the dryer. In addition, the gypsum slurry molded body may be introduced into the dryer and dried on a batch-by-batch basis.

[0153] (Recycled Gypsum Manufacturing Process)

[0154] In the recycled gypsum manufacturing process, recycled gypsum can be produced by crushing and calcining waste gypsum boards. The produced recycled gypsum can be supplied to the gypsum slurry preparation process.

[0155] In the process of manufacturing recycled gypsum, the means for crushing waste gypsum board is not particularly limited, but, for example, dry crushing may be used. Compared to dry crushed waste gypsum board, dry crushed waste can suppress the attachment and incorporation of moisture to the crushed material during crushing. Therefore, by dry crushing waste gypsum board, energy during firing can be suppressed and the incorporation of dihydrate gypsum can be suppressed.

[0156] Therefore, the recycled gypsum supplied to the gypsum slurry preparation process may include dry crushed gypsum board waste, and the recycled gypsum may consist of dry crushed gypsum board waste.

[0157] In the recycled gypsum manufacturing process, sieving, magnetic separation, etc., may be performed as needed to remove components other than gypsum, such as metal and paper fragments.

[0158] According to the method for manufacturing a gypsum board of the present embodiment, a gypsum board having non-combustible properties can be obtained by using recycled gypsum recovered from gypsum board waste as the gypsum raw material.

[0159] [bookkeeping]

[0160] (1) A gypsum board according to one embodiment of the present disclosure has a gypsum core, and

[0161] The above gypsum core is a hardened body of a gypsum slurry containing water and gypsum raw materials containing recycled gypsum recovered from gypsum board waste, and

[0162] The above gypsum core has an organic fiber content of 3.0 mass% or less.

[0163] (2) In the above (1), the proportion of recycled gypsum in the gypsum raw material may be 30 mass% or more and 100 mass% or less.

[0164] (3) In the above (1) or (2), the recycled gypsum may contain dry crushed gypsum board waste.

[0165] (4) In any one of the above (1) to (3), the specific gravity may be 0.65 or higher.

[0166] (5) In any one of (1) to (4) above, the total heat output over 20 minutes is 8 MJ / m² 2 It may be less than.

[0167] (6) In any one of the above (1) to (5), a gypsum board having a board base paper on the upper and lower surfaces of the gypsum core,

[0168] The basis weight of the above base paper for the board is 200g / m² 2 It may be less than.

[0169] (7) In any one of (1) to (6) above, a gypsum board having a board base paper on the upper and lower surfaces of the gypsum core,

[0170] The total heat output over 20 minutes is 8 MJ / m² 2 It may be less than.

[0171] (8) A method for manufacturing a gypsum board according to one embodiment of the present disclosure comprises a gypsum slurry preparation process in which a gypsum raw material including recycled gypsum recovered from gypsum board waste is mixed with water to prepare a gypsum slurry, and

[0172] A molding process for manufacturing a gypsum slurry molded body by molding the above gypsum slurry, and

[0173] A curing process for curing the above-mentioned gypsum slurry molded body, and

[0174] The content of organic fibers in the gypsum core of the gypsum board obtained after the above curing process is 3.0 mass% or less.

[0175] (9) In the above (8), the above molding process places and molds the gypsum slurry between the base papers for the board, and

[0176] The basis weight of the above base paper for the board is 200g / m² 2 It may be less than.

[0177] (10) In the above (8) or (9), the recycled gypsum may contain dry crushed gypsum board waste.

[0178] Although the gypsum board and the method for manufacturing the gypsum board have been described above through embodiments, the present invention is not limited to the above embodiments. Various modifications and changes are possible within the scope of the gist of the present invention as described in the claims.

[0179] This application claims priority based on Patent Application No. 2024-012315 filed with the Japan Patent Office on January 30, 2024, and incorporates the entire contents of Patent Application No. 2024-012315 into this application. Explanation of the symbols

[0180] 10 plasterboard 11 Gypsum core 11A Top surface 11B underneath 11C side

Claims

Claim 1 A gypsum board having a gypsum core, wherein the gypsum core is a hardened body of a gypsum slurry containing water and a gypsum raw material containing recycled gypsum recovered from gypsum board waste, and wherein the gypsum core has an organic fiber content of 3.0 mass% or less. Claim 2 A gypsum board according to claim 1, wherein the proportion of the recycled gypsum in the gypsum raw material is 30 mass% or more and 100 mass% or less. Claim 3 In claim 1 or 2, the recycled gypsum comprises a gypsum board, wherein the recycled gypsum comprises dry crushed material of the gypsum board waste. Claim 4 A gypsum board having a specific gravity of 0.65 or higher, according to paragraph 1 or 2. Claim 5 In paragraph 1 or 2, the total heat output over 20 minutes is 8 MJ / m² 2 Lee Ha-in, Gypsum board. Claim 6 In claim 1 or 2, a gypsum board having board base paper on the upper and lower surfaces of the gypsum core, wherein the basis weight of the board base paper is 200 g / m² 2 Lee Ha-in, Gypsum board. Claim 7 In claim 1 or 2, a gypsum board having board base paper on the upper and lower surfaces of the gypsum core, wherein the total heat output over 20 minutes is 8 MJ / m² 2 Lee Ha-in, Gypsum board. Claim 8 A method for manufacturing a gypsum board having a gypsum raw material containing recycled gypsum recovered from gypsum board waste and water to prepare a gypsum slurry, a molding process to produce a gypsum slurry molded body by molding the gypsum slurry, and a curing process to cure the gypsum slurry molded body, wherein the organic fiber content in the gypsum core of the gypsum board obtained after the curing process is 3.0 mass% or less. Claim 9 In claim 8, in the molding process, the gypsum slurry is placed and molded between base papers for board, and the basis weight of the base papers for board is 200 g / m² 2 Lee Ha-in, method of manufacturing a gypsum board. Claim 10 A method for manufacturing a gypsum board according to claim 8 or 9, wherein the recycled gypsum comprises dry crushed gypsum board waste.

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