Gypsum board and method for producing gypsum board

Abstract

A gypsum board includes a gypsum core, wherein the gypsum core is a cured body of a gypsum slurry including water and a gypsum raw material containing recycled gypsum recovered from gypsum board waste; and wherein the gypsum core contains organic fibers in a proportion of 3.0 mass% or less.

Description

Gypsum board, manufacturing method of gypsum board

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

[0002] Patent Document 1 discloses a method for producing a gypsum board, which includes the steps of preparing a slurry by mixing a gypsum raw material containing 70% by weight or more of recycled gypsum, 0.1% by weight to 1.0% by weight of a water-reducing agent relative to the gypsum raw material, 0.01% by weight to 0.10% by weight of a foaming agent relative to the gypsum raw material, and water, and hardening the slurry, in which the gypsum raw material accounts for 90% by weight or more of the total amount of the slurry excluding the water content.

[0003] Japanese Patent Application Publication No. 2020-63165

[0004] BACKGROUND ART Gypsum board waste has been conventionally discharged as waste.

[0005] Gypsum board waste includes scraps generated during gypsum board production and new building interior construction. Most of the scraps generated during gypsum board production are recycled by gypsum board manufacturers.

[0006] Another example of gypsum board waste is waste gypsum board generated during building renovations, demolition work, etc. Most of the waste gypsum board generated during building renovations, demolition work, etc. is not recycled, but is disposed of in landfills. Furthermore, waste gypsum board generated during building renovations, demolition work, etc. accounts for a large proportion of all waste gypsum board generated.

[0007] It is expected that the amount of gypsum board waste generated will continue to increase in the future as building demolition increases, but from the perspective of protecting the natural environment and reducing costs, there is a need to reduce the amount of gypsum board waste that is disposed of in landfills.

[0008] Therefore, as disclosed in Patent Document 1 and the like, studies have been conducted on gypsum boards, such as gypsum boards, manufactured using waste gypsum boards.

[0009] However, in order to produce the recycled gypsum used in the gypsum board disclosed in Patent Document 1, many steps are required, which poses problems in terms of production cost and productivity.

[0010] Therefore, it is conceivable to produce gypsum boards using recycled gypsum produced by crushing and burning waste gypsum boards as the gypsum source.

[0011] Gypsum boards are used as building materials and are therefore required to have non-combustible properties. However, recycled gypsum may contain components other than gypsum. For this reason, there has been concern about whether gypsum boards manufactured using recycled gypsum as a gypsum source can exhibit sufficient non-combustible properties.

[0012] In view of the problems of the above-mentioned conventional technology, one aspect of the present invention aims to provide a gypsum board that has non-flammable properties while using recycled gypsum recovered from waste gypsum board materials as the gypsum raw material.

[0013] In order to solve the above problems, according to one embodiment of the present invention, there is provided a gypsum board having a gypsum core, wherein the gypsum core is a hardened body of a gypsum slurry containing a gypsum raw material including recycled gypsum recovered from gypsum board waste and water, and the gypsum core has an organic fiber content of 3.0 mass% or less.

[0014] According to one embodiment of the present invention, a gypsum board having non-combustible properties can be provided while using recycled gypsum recovered from waste gypsum board materials as the gypsum raw material.

[0015] FIG. 1 is an explanatory diagram of a gypsum board according to an embodiment of the present invention.

[0016] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments, and various modifications and substitutions can be made to the following embodiments without departing from the scope of the present invention. [Gypsum Board] (1) Regarding the Gypsum Board Hereinafter, the gypsum board of this embodiment will be described with reference to the drawings.

[0017] FIG. 1 shows a schematic diagram of a gypsum board 10 of this embodiment.

[0018] As shown in FIG. 1 , a gypsum board 10 of this embodiment has a gypsum core 11 .

[0019] The gypsum board 10 of this embodiment can have a plate-like shape as shown in Fig. 1. The gypsum core 11 has an upper surface 11A and a lower surface 11B located opposite the upper surface 11A. The upper surface 11A and the lower surface 11B are surfaces located at both ends along the thickness.

[0020] A side surface 11C is disposed between the upper surface 11A and the lower surface 11B.

[0021] In Figure 1, the gypsum board 10 and the gypsum core 11 are shown in a rectangular parallelepiped shape, but the gypsum board 10 including the gypsum core 11 can be used as a building material, etc., and is not limited to such a shape, but can be made into an appropriate shape depending on the application.

[0022] 1 shows an example in which the gypsum board 10 is composed only of a gypsum core 11, but is not limited to such a form. The gypsum board 10 of the present embodiment can be any one selected from, for example, a gypsum board defined in JIS A 6901 (2014), a gypsum board that is lighter or heavier than the gypsum board defined in JIS A 6901 (2014) (hereinafter, the gypsum board defined in the above JIS and the gypsum board that is lighter or heavier than the gypsum board defined in the above JIS are also collectively referred to as "gypsum board"), a glass mat gypsum board, a gypsum-containing board with glass fiber nonwoven fabric, etc.

[0023] Therefore, in the gypsum board 10 of this embodiment, depending on the shape of the gypsum board, for example, board base paper, glass mat, or the like can be further disposed as a surface material on the upper surface 11A or the lower surface 11B of the gypsum core 11. Furthermore, glass fiber nonwoven fabric (glass tissue), or the like, can be embedded in the upper surface 11A or the lower surface 11B. As shown in FIG. 1 , the gypsum board 10 can also be formed solely from the gypsum core 11 without disposing a surface material on the upper surface 11A or the lower surface 11B of the gypsum core 11. (1-1) Regarding the Gypsum Core In the gypsum board 10 of this embodiment, the gypsum core 11 can be a hardened body of gypsum slurry containing water and a gypsum raw material including recycled gypsum recovered from gypsum board waste. (1-2) Regarding the Components Contained in the Gypsum Slurry The gypsum core 11 contained in the gypsum board 10 of this embodiment is a hardened body of gypsum slurry. The components that can be contained in the gypsum slurry are described below. (1-2-1) Gypsum Raw Material The gypsum raw material means a raw material containing gypsum, such as calcined gypsum, used to prepare a gypsum slurry.

[0024] The gypsum feedstock can include recycled gypsum, as described above.

[0025] One method for reusing waste gypsum boards is to use recycled gypsum obtained by crystallizing the gypsum in the waste gypsum boards as a raw material. However, to produce recycled gypsum, the waste gypsum boards must be crushed and fired to form a gypsum slurry, and then crystallization must be carried out in the gypsum slurry, which requires many steps for production. This creates problems in terms of production costs, etc.

[0026] Therefore, the inventors of the present invention have studied gypsum boards made from recycled gypsum recovered from waste gypsum boards. The recycled gypsum is gypsum obtained by crushing and calcining waste gypsum boards to produce hemihydrate gypsum. In other words, the recycled gypsum is a calcined product of crushed waste gypsum boards.

[0027] Recycled gypsum is made by crushing and burning waste gypsum board, so it requires fewer manufacturing steps and less energy than recycled gypsum, which means that recycled gypsum can reduce manufacturing costs compared to recycled gypsum.

[0028] As described above, recycled gypsum is a calcined product of crushed gypsum board waste. Therefore, recycled gypsum can contain calcined gypsum, i.e., calcium sulfate hemihydrate. Regarding the gypsum component, recycled gypsum can be composed only of calcined gypsum, but dihydrate gypsum may also remain. Since recycled gypsum is made from gypsum board waste, it may contain components other than the gypsum component, such as paper derived from the gypsum board waste.

[0029] The recycled gypsum may contain dry-ground gypsum board waste. The recycled gypsum may be composed of dry-ground gypsum board waste. However, even in this case, it does not exclude the possibility of unavoidable impurities being mixed in during the manufacturing process. Compared to wet-ground gypsum board waste, dry-ground gypsum board waste can suppress the adhesion and mixing of moisture to the ground material during grinding. Therefore, when the recycled gypsum contains dry-ground gypsum board waste, the mixing of gypsum dihydrate can be suppressed. Note that dry-ground gypsum board waste refers to a material obtained by firing ground material obtained by dry-grinding gypsum board waste, i.e., a fired product.

[0030] Although the content of recycled gypsum in the gypsum raw material is not particularly limited, according to the study of the inventors of the present invention, even when the content of recycled gypsum in the gypsum raw material is high, a gypsum board having non-combustible properties can be obtained. Therefore, from the viewpoints of environmental protection and cost reduction, it is preferable that the content of recycled gypsum in the gypsum raw material is high. Therefore, the content of recycled gypsum in the gypsum raw material is preferably, for example, 30% by mass or more, more preferably more than 60% by mass, and even more preferably 65% ​​by mass or more.

[0031] In this specification, a gypsum board having non-combustible properties is a board having a total heat generation rate of 8 MJ / m for 20 minutes when a heat generation test is carried out. ２ This means that:

[0032] The gypsum raw material may be composed solely of recycled gypsum. Therefore, the content of recycled gypsum in the gypsum raw material can be 100 mass % or less.

[0033] For this reason, for example, the content of recycled gypsum in the gypsum raw material is preferably 30% by mass or more and 100% by mass or less, more preferably more than 60% by mass or more and 100% by mass or less, and even more preferably 65% ​​by mass or more and 100% by mass or less.

[0034] In addition to recycled gypsum, the gypsum raw material may also contain virgin gypsum raw material, that is, a new gypsum raw material that is not a recycled product.

[0035] As the virgin gypsum raw material, β-type calcined gypsum or α-type calcined gypsum alone, or a mixture of both, can be used. β-type calcined gypsum is obtained by calcining in the atmosphere gypsum obtained by mixing any one of natural gypsum, by-product gypsum, and flue gas desulfurization gypsum, etc., alone or in combination. α-type calcined gypsum is obtained by calcining in water (including in steam) gypsum obtained by mixing any one of natural gypsum, by-product gypsum, and flue gas desulfurization gypsum, etc., alone or in combination. (1-2-2) Additives The gypsum slurry can further contain various additives.

[0036] Examples of additives include one or more selected from foaming agents, adhesion improvers, inorganic fibers such as glass fibers, organic fibers, lightweight aggregates, fire-resistant materials such as vermiculite, set retarders, set accelerators, water-reducing agents, bubble size adjusters such as sulfosuccinate surfactants, water repellents such as silicone and paraffin, organic carboxylic acids, organic carboxylates, organic phosphate compounds, etc. The adhesion improver is an additive that improves the adhesion between the gypsum core 11 and the gypsum board base paper, and examples thereof include starch and polyvinyl alcohol.

[0037] The foaming agent may be mixed with water or the like to foam and then added to the gypsum slurry, or may be added to the gypsum slurry and then foamed during kneading, etc. The foaming agent preferably includes, for example, one or more types selected from alkyl ether sulfates and alkyl sulfates.

[0038] When a foaming agent is added to the gypsum slurry, for example, by including a bubble diameter adjuster in the gypsum slurry, the size of the bubbles contained in the gypsum slurry and the gypsum core 11 can be easily adjusted. (1-2-3) Organic Fibers Gypsum board waste contains components other than gypsum, and there is a risk that components other than gypsum may be mixed into recycled gypsum. For this reason, there has been concern about whether a gypsum board produced using recycled gypsum as a gypsum source can exhibit sufficient non-combustible properties.

[0039] Therefore, the inventors of the present invention conducted a study and found that organic fibers have a significant effect on the non-combustible properties of the gypsum board 10. They then found that a gypsum board with non-combustible properties can be obtained by setting the organic fiber content in the gypsum core within a predetermined range, and completed the present invention.

[0040] Specifically, the organic fiber content of the gypsum core 11 can be 3.0% by mass or less. By setting the organic fiber content of the gypsum core 11 to 3.0% by mass or less, a non-flammable gypsum board 10 can be obtained. By setting the organic fiber content of the gypsum core 11 to 3.0% by mass or less, the fluidity of the gypsum slurry can be increased when a gypsum board is manufactured, thereby increasing the productivity of the gypsum board.

[0041] The content of organic fibers in the gypsum core 11 is preferably 2.8% by mass or less, and more preferably 2.5% by mass or less.

[0042] The gypsum core 11 may also contain organic fibers. The content of organic fibers in the gypsum core 11 may be 0.1 mass% or more.

[0043] When the gypsum core 11 contains 0.1% by mass or more of organic fibers, the shear strength and bending fracture load of the gypsum core 11 and the gypsum board 10 can be increased.

[0044] Therefore, the content 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.

[0045] The organic fibers are mainly derived from paper and the like contained in the recycled gypsum, and are mainly derived from the recycled gypsum. However, in order to adjust the content ratio of the organic fibers contained in the gypsum core 11, organic fibers can also be added to the gypsum slurry when preparing the gypsum slurry, as needed.

[0046] Furthermore, the proportion of organic fibers contained in the recycled gypsum can be adjusted by adjusting the degree of pulverization (crushing) of the recycled gypsum and, if necessary, removing paper by sieving or the like.

[0047] The influence of the organic fiber content contained in the gypsum core 11 of the gypsum board 10 on the total heat generation amount will be described below.

[0048] Specifically, in Experimental Examples 1-1 to 1-7, new gypsum or recycled gypsum, paper, and water were mixed to prepare gypsum slurries in the proportions shown in Table 1 below. The water added when preparing the gypsum slurry was added so that the specific gravity of the gypsum hardened body obtained by hardening the gypsum slurry would be 0.65. The gypsum slurry was then placed between sheets of base paper for board and molded to a thickness of 12.5 mm to prepare gypsum boards, which are gypsum boards 10. The base paper for boards had a basis weight of 200 g / m ２ It was.

[0049] The recycled gypsum was prepared by dry-pulverizing waste gypsum board to the extent that any attached paper could be removed, and then calcining the gypsum after completely removing the paper by sieving or the like. The paper used was paper collected during the production of recycled gypsum. (Heat generation test)

[0050] The obtained gypsum board specimen was subjected to a heat generation test in accordance with the ISO 5660-1 cone calorimeter method, and the total heat generation amount after a heating time of 20 minutes was measured.

[0051] The evaluation results are shown in Table 1.

[0052] According to the results shown in Table 1, when the content of organic fiber paper is 3.0 mass % or less, the total heat generation rate for 20 minutes is 8 MJ / m ２Therefore, it was confirmed that the gypsum core 11 has excellent non-combustibility by setting the organic fiber content to 3.0% by mass or less, and in particular, the non-combustibility can be improved by setting the organic fiber content to 2.8% by mass or less or 2.5% by mass or less.

[0053] The proportion of organic fibers contained in the gypsum core 11 can be measured and calculated, for example, by the following procedure.

[0054] First, the gypsum core 11 is heated to 150°C and then pulverized to obtain a pulverized product. The degree of pulverization is not particularly limited, and the pulverization size can be selected so as to reduce the time required for dissolving the gypsum component during the water washing on a sieve described below.

[0055] Next, the obtained pulverized material is washed with water on a 100-mesh sieve. Since the material remaining on the sieve is the organic fiber contained in the gypsum core, the mass is measured after drying and used as the organic fiber mass. Then, the mass ratio of the organic fiber mass to the pulverized material supplied on the sieve is calculated, which can be used as the mass ratio of the organic fiber contained in the gypsum core 11.

[0056] In addition, when the gypsum board 10 has a surface material, the above evaluation can be performed on the gypsum core 11 after removing the portion of the gypsum board 10 that includes the surface material.

[0057] Therefore, the organic fibers contained in the gypsum core of the gypsum board of this embodiment can be the 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 this embodiment may contain various organic fibers with different lengths. (2) Total heat generation amount of the gypsum board The gypsum board 10 of this embodiment has a total heat generation amount of 8 MJ / m for 20 minutes. ２ Preferably, it is 6 MJ / m or less. ２ More preferably, it is:

[0058] The total heat generation amount of the gypsum board 10 for 20 minutes is 8 MJ / m ２ By setting the value to 6 MJ / m or less, a gypsum board with excellent non-combustibility can be obtained. ２ By doing so, non-flammable properties can be maintained even when a paint containing an organic component is applied or placed on the surface of the gypsum board 10.

[0059] 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, and can be adjusted, for example, by the degree of paper removal when producing recycled gypsum. For example, as described in "(Organic fibers)" of "(1-2) Regarding components contained in the gypsum slurry," by setting the content ratio of organic fibers contained in the gypsum core 11 to 3.0 mass% or less, the total calorific value of the gypsum board 10 can be set to 8 MJ / m ２ The following can be achieved. In particular, by setting the content of organic fibers in the gypsum core 11 to 2.8 mass% or less, the total heat generation can be particularly suppressed. (3) Specific Gravity of the Gypsum Board The specific gravity of the gypsum board is not particularly limited, but may be, for example, 0.65 or more. By setting the specific gravity of the gypsum board to 0.65 or more, the strength of the gypsum board can be particularly increased.

[0060] The upper limit of the specific gravity of the gypsum board is not particularly limited, but from the viewpoint of improving the ease of handling at the construction site, it may be less than 1.1 or may be 1.0 or less.

[0061] The specific gravity of the gypsum board can be evaluated according to the method described in JIS A 6901 (2014). (4) Configuration Example of Gypsum Board The gypsum board 10 of the present embodiment can also be, for example, a gypsum board.

[0062] That is, the gypsum board 10 of this embodiment can also be a gypsum board having board base paper on the upper surface 11A and the lower surface 11B of the gypsum core 11.

[0063] In this case, the base paper for the board is not particularly limited, but the basis weight of the base paper for the board is preferably 200 g / m ２ It is preferable that:

[0064] The basis weight of the board base paper is 200 g / m ２ This is because the non-combustible properties of the gypsum board can be improved by satisfying the following conditions.

[0065] In addition, when used as gypsum board, it is preferable that the above-mentioned total heat generation requirement is satisfied. For example, the total heat generation requirement for 20 minutes is 8 MJ / m ２(5) Study on the effect of mixing organic fibers on the compressive strength of the gypsum hardened body (Experimental Example 2) The inventors of the present invention have studied the properties of a gypsum hardened body made from recycled gypsum, other than its non-combustibility. Here, the results of the study on the effect of organic fibers, such as paper, attached to the recycled gypsum on the strength of the gypsum board will be described.

[0066] To accurately examine the influence of organic fibers, the researchers used recycled gypsum, from which the organic fiber paper had been completely removed, and evaluated the compressive strength of gypsum hardened bodies made by hardening gypsum slurries produced by varying the amount of paper added.

[0067] Specifically, in Experimental Examples 2-1 to 2-4, recycled gypsum, paper, and water were mixed together to prepare gypsum slurries in the blending ratios shown in Table 2 below.

[0068] The water added when preparing the gypsum slurry is added so that the specific gravity of the gypsum hardened body obtained by hardening the gypsum slurry becomes a predetermined value.

[0069] The gypsum slurry was then poured into a cubic formwork with a side length of 40 mm, and dried to a constant weight at 40°C to prepare a gypsum hardened body as a test specimen.

[0070] The recycled gypsum was prepared by dry-pulverizing waste gypsum board to the extent that any attached paper could be removed, and then completely removing the paper by sieving or the like, followed by calcining. The paper used was paper recovered during the production of recycled gypsum. (Method for evaluating the compressive strength of gypsum hardened bodies)

[0071] The compressive strength of the obtained gypsum hardened body specimens was measured at a loading rate of 1 mm / min using an autograph (AG-X plus, manufactured by Shimadzu Corporation). The compressive strength of each experimental example listed in Table 2 below was measured for six specimens prepared under the same conditions, and the average value of the compressive strengths of the six specimens was used. In the other experimental examples below, the compressive strength of the gypsum hardened body was evaluated under the same conditions.

[0072] The evaluation results are shown in Table 2.

[0073] According to the results shown in Table 2, it was confirmed that the compressive strength of the gypsum hardened body tends to improve by decreasing the paper content. However, even when the amount of paper mixed was 2.5 parts by mass, i.e., 2.5% by mass relative to the gypsum raw material, the compressive strength of the gypsum hardened body was 25 kgf / cm ２ It was confirmed that the gypsum hardened body had a compressive strength of 25 kgf / cm or more, and had sufficient strength. ２ By having a compressive strength of 25 kgf / cm or more, when screws are driven into the gypsum hardened body, the gypsum hardened body is prevented from being damaged by excessively driving the screws, and the gypsum hardened body has sufficient strength to hold the driven screws. ２ Having the above compressive strength means that when used in a gypsum board, the board has a compressive strength that is sufficient for practical use.

[0074] For example, when a gypsum hardened body containing 2.5% by mass of paper mixed with the gypsum raw material is applied to a gypsum board, the content of paper, which is an organic fiber, in the gypsum core of the gypsum board is 2.5% by mass. (6) Study on the effect of the specific surface area of ​​recycled gypsum on the compressive strength of the gypsum hardened body (Experimental Example 3) Recycled gypsum can be produced, for example, by crushing waste gypsum board material, followed by sieving and firing. By selecting the degree of crushing and sieving of the waste gypsum board material, the degree of separation of organic fiber from the recycled gypsum can be selected, and the amount of organic fiber mixed into the recycled gypsum can be adjusted. Crushing and sieving can also be performed in multiple stages.

[0075] The crushing device used to crush the gypsum board waste is not particularly limited and can be selected depending on the desired organic fiber content and the particle size after crushing that corresponds to the desired content. For example, when crushing the gypsum board waste, a screen crusher or the like can be used as the crushing device. Furthermore, when crushing the gypsum board waste to a fine powder in order to reduce the organic fiber content, a roll crusher, a hammer mill, or the like can be used as the crushing device. Crushing can also be carried out in multiple stages, and a crushing device can be selected depending on the desired particle size of the gypsum board waste at each stage.

[0076] The mesh size during sieving is not particularly limited and can be selected depending on the degree of separation of organic fibers, the type of organic fibers to be separated, the particle size distribution of the gypsum board waste after pulverization, etc. Sieving can also be carried out in multiple stages.

[0077] However, depending on the degree of pulverization when producing recycled gypsum, the strength of the gypsum board may be affected. Therefore, the inventors of the present invention investigated the relationship between the specific surface area of ​​recycled gypsum and the compressive strength of the gypsum hardened body.

[0078] Specifically, in Experimental Examples 3-1 to 3-5, gypsum slurries were prepared using only recycled gypsum as the gypsum raw material. The gypsum slurries were prepared by kneading the gypsum raw material, paper, and water to obtain the blending ratios shown in Table 3 below. Water was added when preparing the gypsum slurry so that the specific gravity of the gypsum hardened body obtained by hardening the gypsum slurry would be a predetermined value. Then, a gypsum hardened body was produced under the same conditions as in Experimental Example 2, except that the above gypsum slurries were used, and the compressive strength was evaluated.

[0079] The recycled gypsum was prepared by dry-pulverizing and sieving waste gypsum board, followed by calcination, and the paper was completely removed. The recycled gypsum used in Experimental Examples 3-1 to 3-5 was prepared by adjusting the degree of pulverization, and the BSA values ​​(hereinafter also referred to as "BSA"), which were the results of measuring the specific surface area using a Blaine air permeability fineness meter, were as shown in Table 3.

[0080] The paper used was paper collected during the production of recycled gypsum.

[0081] According to the results shown in Table 3, regardless of the BSA value of the recycled gypsum, the gypsum hardened body had a strength of 25 kgf / cm ２ It was confirmed that the compressive strength was above the above level and that the strength was sufficient.

[0082] According to the study by the inventors of the present invention, BSA has a peak at 18,200 cm ２In order to produce the recycled gypsum of Experimental Example 3-5, which has a BSA of 0.1 / g, it is necessary to perform multi-stage pulverization and sieving. Furthermore, if the gypsum is pulverized finely to further increase the BSA, clogging is likely to occur during sieving.

[0083] Therefore, it can be said that the recycled gypsum of Experimental Examples 3-1 to 3-5 shown in Table 3 covers the entire range of BSA for recycled gypsum produced by crushing waste gypsum boards. (7) Examination of the effect of the proportion of recycled gypsum in the gypsum raw material on the compressive strength of the gypsum hardened body (Experimental Example 4) Next, the inventors of the present invention examined the compressive strength of the gypsum hardened body when the proportion of recycled gypsum in the gypsum raw material was changed.

[0084] The mass ratio of recycled gypsum in the gypsum raw material was changed to produce gypsum slurries, and the compressive strength of the gypsum hardened bodies obtained by hardening the gypsum slurries was evaluated.

[0085] Specifically, in Experimental Examples 4-1 to 4-6, gypsum slurries were prepared by mixing new gypsum, recycled gypsum, and water to obtain the blending ratios shown in Table 4 below. Note that water was added when preparing the gypsum slurry so that the specific gravity of the gypsum hardened body obtained by hardening the gypsum slurry would be a predetermined value. Then, a gypsum hardened body was produced under the same conditions as in Experimental Example 2, except that the above gypsum slurries were used, and the compressive strength was evaluated.

[0086] The recycled gypsum was prepared by dry-pulverizing waste gypsum board, sieving it, and then calcining it. The paper was completely removed from the recycled gypsum 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. Paper recovered during the production of the recycled gypsum was used.

[0087] The recycled gypsum used in Experimental Examples 4-1 to 4-6 had a BSA of 1700 cm ２ / g. The BSA shown in Table 4 is the BSA of the entire gypsum raw material. As for the new gypsum, a new gypsum raw material that is not a recycled product is used.

[0088] The evaluation results are shown in Table 4.

[0089] According to the results shown in Table 4, regardless of the content ratio of recycled gypsum in the gypsum raw material, the compressive strength of the gypsum hardened body was 25 kgf / cm ２ As a result, it was confirmed that the gypsum board had sufficient strength. [Method for Manufacturing Gypsum Board] The method for manufacturing a gypsum board of the present embodiment can include a gypsum slurry preparation step, a molding step, and a hardening step.

[0090] The gypsum board according to one aspect of the present disclosure can be manufactured by the gypsum board manufacturing method of the present embodiment. Therefore, some of the matters already explained in the gypsum board will not be explained again. (Gypsum Slurry Preparation Process) In the gypsum slurry preparation process, a gypsum raw material containing recycled gypsum recovered from gypsum board waste is mixed with water to prepare a gypsum slurry.

[0091] In the gypsum slurry preparation step, the proportion of recycled gypsum in the gypsum raw material is not particularly limited, but is, for example, preferably 30% by mass or more and 100% by mass or less, more preferably more than 60% by mass and 100% by mass or less, and even more preferably 65% ​​by mass or more and 100% by mass or less.

[0092] For example, these raw material components can be kneaded using a mixer or the like to prepare a gypsum slurry. Various additives such as a foaming agent can also be added to the gypsum slurry as needed. Since the raw materials that can be suitably used for the gypsum slurry have already been described, a description thereof will be omitted here.

[0093] The recycled gypsum to be subjected to the gypsum slurry preparation step has a BSA of, for example, 1500 cm ２ / g or more 20000cm ２ / g or less is preferable.

[0094] Recycled gypsum BSA 1500cm ２ By making the content of the gypsum board liner paper of the waste gypsum board material 100% or more, organic fibers derived from the board base paper can be easily removed, and the non-combustible properties of the resulting gypsum board can be particularly improved.

[0095] By increasing the BSA of recycled gypsum, organic fibers can be easily removed, and the inclusion of organic fibers in recycled gypsum can be particularly reduced. However, if the BSA of recycled gypsum is excessively high, clogging may occur during sieving, making it more difficult to remove organic fibers. For this reason, the BSA of recycled gypsum is set to 20,000 cm ２ / g or less. (Forming Step) In the forming step, the gypsum slurry prepared in the gypsum slurry preparation step is formed to produce a gypsum slurry formed body.

[0096] When foam is added to the gypsum slurry in the gypsum slurry preparation step, and multiple types of gypsum slurries with different foam addition conditions are prepared, the gypsum slurries may be supplied in a desired layering order in the molding step to form a gypsum slurry laminate.

[0097] Furthermore, for example, when manufacturing a gypsum board as the gypsum board 10, a gypsum slurry can be placed between board base papers and molded by passing it through a molding machine to produce a gypsum slurry molded body.

[0098] When manufacturing a gypsum board as the gypsum board 10, the base paper for the board is not particularly limited, but the basis weight is 200 g / m ２ It is preferable to use the following board base paper.

[0099] This is a board base paper basis weight of 200 g / m ２ This is because the non-combustible properties of the gypsum board can be improved by the following: (Hardening Step) In the hardening step, the gypsum slurry molded body obtained in the molding step can be hardened.

[0100] The hardening process can be carried out by the hydration reaction of calcined gypsum (hemihydrate gypsum) contained in the gypsum raw material in the gypsum slurry, which generates needle-like crystals of gypsum dihydrate and coagulates and solidifies. Therefore, within the gypsum slurry formed body formed in the molding process, a reaction occurs between the calcined gypsum and water in the gypsum raw material added to the gypsum slurry, and the hydration reaction of the calcined gypsum progresses, thereby carrying out the hardening process.

[0101] The organic fiber content in the gypsum core of the gypsum board obtained after the hardening step can be 3.0 mass% or less.

[0102] The method for manufacturing a gypsum board according to the present embodiment may further include any steps. Specifically, the method may include, for example, the following cutting step and drying step. (Cutting Step) In the cutting step, the gypsum slurry molded body can be cut by a cutting device.

[0103] After the gypsum slurry molded body is formed in the molding step, the gypsum slurry gradually hardens. Therefore, the cutting step can be performed, for example, during the hardening step or after the hardening step is completed. However, it is preferable to perform the cutting step after the hardening step has progressed to an extent that the gypsum slurry molded body can be cut.

[0104] The cutting step can be performed multiple times. Therefore, the method for manufacturing a gypsum board of this embodiment can also have a first cutting step, which can be called a rough cutting step, for example. It can also have a second cutting step.

[0105] In the first cutting step, the gypsum slurry molded body can be cut to a desired size depending on, for example, the size of a dryer used in the drying step described below.

[0106] Furthermore, the second cutting step can be performed, for example, after the drying step, and the gypsum slurry molded body can be cut to a desired product size. (Drying Step) In the drying step, the gypsum slurry molded body can be dried. In the drying step, excess moisture contained in the gypsum slurry molded body can be dried. Note that it is preferable to supply a gypsum slurry molded body that has completed the hardening step to the drying step. The drying step can be performed by force-drying the gypsum slurry molded body using a dryer.

[0107] The method for forcibly drying the gypsum slurry molded body using a dryer is not particularly limited. For example, a dryer can be provided on the transport path of the gypsum slurry molded body, and the gypsum slurry molded body can be continuously dried by passing the gypsum slurry molded body through the dryer. It is also possible to transport the gypsum slurry molded body into the dryer and dry the gypsum slurry molded body in batches. (Recycled Gypsum Manufacturing Process) In the recycled gypsum manufacturing process, recycled gypsum can be produced by crushing and firing gypsum board waste. The produced recycled gypsum can be subjected to a gypsum slurry preparation process.

[0108] In the recycled gypsum manufacturing process, the means for pulverizing the gypsum board waste is not particularly limited, but for example, dry pulverization can be used. Compared to wet pulverization, dry pulverization of gypsum board waste can suppress adhesion of moisture to and contamination of the pulverized material during pulverization. Therefore, dry pulverization of gypsum board waste can reduce energy consumption during firing and suppress contamination of gypsum dihydrate.

[0109] Therefore, the recycled gypsum to be subjected to the gypsum slurry preparation step may contain dry-ground waste gypsum board material, or may be composed of dry-ground waste gypsum board material.

[0110] In the recycled gypsum manufacturing process, sieving, magnetic separation, etc. can be performed as needed to remove components other than gypsum, such as metals and paper fragments.

[0111] According to the method for manufacturing a gypsum board of this embodiment, a gypsum board having non-combustible properties can be obtained while using recycled gypsum recovered from waste gypsum boards as the gypsum raw material. [Notes] (1) A gypsum board according to one aspect of the present disclosure has a gypsum core, wherein the gypsum core is a hardened body of a gypsum slurry containing a gypsum raw material containing recycled gypsum recovered from waste gypsum boards and water, and the gypsum core has an organic fiber content of 3.0 mass% or less. (2) In the above (1), the proportion of the recycled gypsum in the gypsum raw material may be 30 mass% or more and 100 mass% or less. (3) In the above (1) or (2), the recycled gypsum may include dry-ground gypsum board waste. (4) In any of the above (1) to (3), the specific gravity may be 0.65 or more. (5) In any of the above (1) to (4), the total heat value for 20 minutes is 8 MJ / m ２ (6) In any one of the above (1) to (5), the gypsum board has base paper on the upper and lower surfaces of the gypsum core, and the basis weight of the base paper is 200 g / m or less. ２ (7) In any one of the above (1) to (6), the gypsum board has board base paper on the upper and lower surfaces of the gypsum core, and the total heat generation amount in 20 minutes may be 8 MJ / m or less. ２ (8) A method for manufacturing a gypsum board according to one aspect of the present disclosure includes a gypsum slurry preparation step of mixing a gypsum raw material containing recycled gypsum recovered from gypsum board waste with water to prepare a gypsum slurry, a molding step of manufacturing a gypsum slurry molded body by molding the gypsum slurry, and a hardening step of hardening the gypsum slurry molded body, wherein the gypsum board obtained after the hardening step has a gypsum core with an organic fiber content of 3.0 mass% or less. (9) In the above (8), in the molding step, the gypsum slurry is disposed between pieces of board base paper and molded, and the basis weight of the board base paper is 200 g / m ２ (10) In the above (8) or (9), the recycled gypsum may include a dry-ground product of the gypsum board waste material.

[0112] Although the gypsum board and the manufacturing method of the gypsum board have been described above in the embodiments, the present invention is not limited to the above embodiments, etc. Various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

[0113] This application claims priority based on Japanese Patent Application No. 2024-012315, filed with the Japan Patent Office on January 30, 2024, the entire contents of which are incorporated herein by reference.

[0114] 10 Gypsum board 11 Gypsum core 11A Top surface 11B Bottom surface 11C Side surface

Claims

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

2. The gypsum board according to claim 1, wherein the proportion of the recycled gypsum in the gypsum raw material is 30% by mass or more and 100% by mass or less.

3. The gypsum board according to claim 1 or 2, wherein the recycled gypsum includes dry-ground waste gypsum board material.

4. A gypsum board according to claim 1 or 2, having a specific gravity of 0.65 or more.

5. Total heat output for 20 minutes is 8MJ / m ２ The gypsum board according to claim 1 or claim 2, wherein:

6. 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 / m ２ The gypsum board according to claim 1 or claim 2, wherein:

7. A gypsum board having board base paper on the upper and lower surfaces of the gypsum core, and a total heat value of 8 MJ / m for 20 minutes ２ The gypsum board according to claim 1 or claim 2, wherein:

8. A method for manufacturing a gypsum board, comprising: a gypsum slurry preparation step of mixing a gypsum raw material containing recycled gypsum recovered from gypsum board waste with water to prepare a gypsum slurry; a molding step of manufacturing a gypsum slurry molded body by molding the gypsum slurry; and a hardening step of hardening the gypsum slurry molded body, wherein the gypsum board obtained after the hardening step has a gypsum core with an organic fiber content of 3.0 mass% or less.

9. In the forming process, the gypsum slurry is placed between board base papers and formed, and the board base papers have a basis weight of 200 g / m ２ The method for manufacturing a gypsum board according to claim 8, wherein:

10. The method for manufacturing a gypsum board according to claim 8 or claim 9, wherein the recycled gypsum includes dry-ground waste gypsum board material.