Gypsum board, method for manufacturing gypsum board

Abstract

The gypsum board of the present application has a gypsum core which is a hardened body of a gypsum slurry containing a gypsum raw material, water, and a foam in which a foaming agent is previously foamed, the gypsum raw material containing recycled gypsum recovered from gypsum board waste, the average diameter of the air bubbles contained in the gypsum core being 50 μm or more and 650 μm or less.

Description

Technical Field

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

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

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2020-63165. Summary of the Invention

[0006] The problem to be solved by the present invention

[0007] In the past and present, gypsum board waste has been disposed of as waste.

[0008] As waste materials from gypsum board production, scraps generated during gypsum board manufacturing or interior decoration projects in new buildings can be cited as examples. Most of these scraps are reused by gypsum board manufacturers.

[0009] In addition, gypsum board waste can also be cited as an example, generated during building renovation and demolition projects. Most of this gypsum board waste is not reused and is disposed of in landfills. Therefore, gypsum board waste generated during building renovation and demolition projects constitutes a large proportion of all discarded gypsum board waste.

[0010] With the increasing number of building demolitions in the future, it is foreseeable that the amount of gypsum board waste will further increase. From the perspective of protecting the natural environment and controlling costs, it is necessary to reduce the amount of gypsum board waste disposed of in landfills.

[0011] As disclosed in Patent Document 1, research has been conducted on gypsum boards, such as gypsum plywood made from gypsum plywood waste.

[0012] However, manufacturing the recycled gypsum for gypsum board disclosed in Patent Document 1 requires numerous processes, which leads to problems in manufacturing costs and production efficiency.

[0013] In this regard, gypsum board made by crushing and firing gypsum plywood waste could be considered as a gypsum source. However, gypsum plywood waste also contains components other than gypsum, so the calcined gypsum product, which is a gypsum plywood waste product, may also contain components other than gypsum.

[0014] Gypsum board is used as a building material, and therefore, from the viewpoint of improving the holding force of screws used to fix gypsum board, it is required to have sufficient compressive strength. However, when using recycled gypsum as a gypsum source to manufacture gypsum board, there is a concern about whether it is possible to manufacture gypsum board with sufficient compressive strength to withstand actual use.

[0015] In view of the above-mentioned problems of the prior art, one aspect of the present invention aims to provide a gypsum board that has sufficient compressive strength while using recycled gypsum recovered from gypsum board waste as a gypsum raw material.

[0016] means for solving problems

[0017] To address the aforementioned problems, one aspect of the present invention provides a gypsum board having a gypsum core, the gypsum core being a hardened body of gypsum slurry comprising gypsum raw material, water, and foam pre-foamed with a foaming agent, the gypsum raw material comprising recycled gypsum recovered from gypsum board waste, and the average diameter of the air bubbles contained in the gypsum core being 50 μm or more and 650 μm or less.

[0018] The effects of the invention

[0019] According to one aspect of the present invention, it is possible to provide a gypsum board that has sufficient compressive strength while using recycled gypsum recovered from gypsum board waste as the gypsum raw material. Attached Figure Description

[0020] Figure 1 This is an explanatory diagram of the gypsum board in an embodiment of the present invention.

[0021] Figure 2 This is an illustration of the relationship between the proportion of recycled gypsum in the gypsum raw material and the compressive strength of the obtained hardened gypsum body.

[0022] Figure 3A These are cross-sectional SEM images of the gypsum core of the gypsum board obtained in Examples 1-4.

[0023] Figure 3B These are cross-sectional SEM images of the gypsum core of the gypsum board obtained in Examples 1-4.

[0024] Figure 4A This is a cross-sectional SEM image of the gypsum core of the gypsum board obtained in Comparative Example 1.

[0025] Figure 4B This is a cross-sectional SEM image of the gypsum core of the gypsum board obtained in Comparative Example 1. Detailed Implementation

[0026] Hereinafter, the embodiments for carrying out the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments. Various modifications and substitutions may be made to the following embodiments without departing from the scope of the present invention.

[0027] [Gypsum board]

[0028] Hereinafter, the gypsum board of this embodiment will be described with reference to the accompanying drawings.

[0029] Figure 1 A schematic diagram showing the plasterboard 10 of this embodiment.

[0030] like Figure 1 As shown, the gypsum board 10 of this embodiment has a gypsum core 11.

[0031] The gypsum board 10 in this embodiment is as follows: Figure 1 As shown, it can have a plate-like shape. 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 in the thickness direction.

[0032] Furthermore, a side surface 11C is disposed between the upper surface 11A and the lower surface 11B.

[0033] Figure 1 In this text, gypsum board 10 and gypsum core 11 are represented as cuboids, but gypsum board 10 containing gypsum core 11 is not limited to the shape as long as it can be used as building material, and can be adopted in an appropriate shape according to its use.

[0034] Figure 1 The example shown is a gypsum board 10 consisting only of a gypsum core 11, but it is not limited to this embodiment. The gypsum board 10 of this embodiment may be, for example, any one of the following selected from gypsum plywood as specified in JIS A 6901 (2014), gypsum plywood that is lighter or heavier than gypsum plywood as specified in JIS A 6901 (2014) (hereinafter, gypsum plywood as specified in the above JIS and gypsum plywood that is lighter or heavier than gypsum plywood as specified in the above JIS are collectively referred to as "gypsum plywood"), glass mat gypsum plywood, glass fiber nonwoven fabric gypsum-containing board, etc.

[0035] Therefore, in this embodiment, depending on the shape of the gypsum board 10, for example, board base paper or glass pads may be disposed as surface materials on the upper surface 11A or lower surface 11B of the gypsum core 11. Furthermore, glass fiber nonwoven fabric (glass veneer) may be embedded in the upper surface 11A or lower surface 11B. Figure 1 As shown, it is also possible to omit the surface material on the upper surface 11A or the lower surface 11B of the gypsum core 11 and form the gypsum board 10 solely from the gypsum core 11.

[0036] One method for reusing gypsum board waste is to use gypsum from the waste as a raw material and then crystallize it to obtain recycled gypsum. However, to produce recycled gypsum, the gypsum board waste needs to be crushed, calcined, and then made into gypsum slurry, which is then crystallized. This process requires multiple steps, thus presenting challenges in terms of manufacturing costs.

[0037] In response, the inventors of this invention have researched gypsum boards using recycled gypsum recovered from gypsum board waste. Recycled gypsum is a hemihydrate gypsum produced by crushing and firing gypsum board waste. In other words, recycled gypsum is a fired product of crushed gypsum board waste.

[0038] Recycled gypsum is obtained by crushing and firing waste gypsum board. Therefore, compared with recycled gypsum, it requires fewer manufacturing steps, thereby reducing the energy required in the manufacturing process. Thus, compared with recycled gypsum, recycled gypsum can reduce manufacturing costs. However, according to the inventors' research, when using gypsum raw materials containing recycled gypsum to manufacture gypsum boards, the compressive strength of the gypsum boards sometimes decreases.

[0039] (1) Study on the compressive strength of gypsum board

[0040] In response, the inventors of this invention investigated the reasons for the decrease in compressive strength in gypsum boards using recycled gypsum.

[0041] (1-1) Study on the effect of organic fiber incorporation on the compressive strength of hardened gypsum (Experimental Example 1)

[0042] First, the inventors of this invention investigated the effect of organic fibers, such as paper, attached to the recycled gypsum on the compressive strength of the gypsum board.

[0043] To properly study the effect of organic fibers, the compressive strength of the hardened gypsum body was evaluated using recycled gypsum from which paper as an organic fiber was completely removed, after the gypsum paste was hardened by varying the amount of paper added.

[0044] Specifically, as Experimental Examples 1-1 to 1-4, gypsum paste was prepared by mixing reused gypsum, paper, and water according to the mixing ratio shown in Table 1 below.

[0045] Here, regarding the water added when preparing gypsum slurry, the goal is to add water so that the specific gravity of the hardened gypsum body obtained after the gypsum slurry hardens is 0.65.

[0046] Furthermore, by injecting plaster slurry into a cubic mold with one side length of 40 mm and drying it at a constant temperature of 40°C, a hardened plaster body was prepared as the test subject.

[0047] The recycled gypsum was made by drying and pulverizing gypsum board waste to a degree sufficient to remove any attached paper, and then firing the material after completely removing the paper through sieving and other processes. Additionally, paper recycled from the recycled gypsum was used as the paper.

[0048] (Methods for evaluating the compressive strength of hardened gypsum bodies)

[0049] Regarding the hardened plaster specimens obtained as test pieces, the compressive strength was measured using an Autograph testing machine (Shimadzu AG-X plus) at a load speed of 1 mm / min. The compressive strength of each experimental example listed in the table below is the average (arithmetic mean) of the compressive strength of six test pieces prepared under the same conditions, obtained by dividing the total measured value of the six test pieces by the number of test pieces, 6. In the other experiments below, the compressive strength of the hardened plaster specimens was also evaluated under the same conditions.

[0050] The evaluation results are shown in Table 1.

[0051] [Table 1]

[0052] Based on the results shown in Table 1, a tendency to increase the compressive strength of the hardened gypsum body is confirmed by reducing the paper content. However, even with a paper content of 2.5% by mass (i.e., 2.5% by mass relative to the gypsum raw material), the compressive strength is still 25 kgf / cm². 2 The above compressive strength confirms that it possesses sufficient compressive strength. Furthermore, the hardened gypsum body has a compressive strength of 25 kgf / cm². 2 The above compressive strength prevents screws from being over-driven into the gypsum hardened body and damaging it, while providing sufficient force to hold the screw in place. This means that the gypsum hardened body, with a compressive strength of 25 kgf / cm², can withstand such force. 2 The above compressive strength is practically sufficient when using gypsum board.

[0053] (1-2) Study on the effect of the proportion of recycled gypsum in gypsum raw materials on the compressive strength of hardened gypsum bodies (Experimental Example 2)

[0054] Secondly, the inventors of this invention have studied the compressive strength of the hardened gypsum body when the proportion of recycled gypsum in the gypsum raw material is changed.

[0055] The compressive strength of hardened gypsum bodies prepared by varying the mass ratio of recycled gypsum in gypsum raw materials was evaluated.

[0056] Specifically, as Experimental Examples 2-1 to 2-10, gypsum paste was prepared by mixing new gypsum, recycled gypsum, and water according to the mixing ratios shown in Table 2 below. The water added during the preparation of the gypsum paste was increased to achieve a specified specific gravity in the hardened gypsum body obtained from the gypsum paste. Furthermore, in addition to using the aforementioned gypsum paste, hardened gypsum bodies were prepared under the same conditions as in Experimental Example 1, and their compressive strength was evaluated.

[0057] As a recycled plaster, the recycled plaster containing the attached paper is used at a ratio of 2.5% by mass. Furthermore, as a new plaster, new plaster raw materials are used instead of recycled plaster.

[0058] The evaluation results are shown in Table 2. Here, Figure 2 This shows the relationship between the proportion of recycled gypsum in the gypsum raw material and the compressive strength of the obtained cured gypsum.

[0059] [Table 2]

[0060] Based on the results shown in Table 2, it can be confirmed that the compressive strength of the hardened gypsum body tends to decrease with increasing proportion of recycled gypsum. However, even in Experimental Example 2-10, where the proportion of recycled gypsum in the gypsum source is 100% by mass, a compressive strength of 25 kgf / cm² is achieved. 2 The above compressive strength indicates sufficient compressive strength.

[0061] (1-3) Research on the reasons for the change in compressive strength of hardened gypsum bodies due to the increased proportion of recycled gypsum in gypsum raw materials

[0062] However, as Figure 2As shown, it can be confirmed that when the proportion of recycled gypsum in the gypsum raw material exceeds 30% by mass, the compressive strength of the hardened gypsum body decreases sharply. The reason for this might be the increased proportion of paper in the gypsum raw material. However, since recycled gypsum contains a fixed proportion of paper, it is difficult to imagine that this would be the cause of the sharp decrease in compressive strength of the hardened gypsum body when the proportion of recycled gypsum in the gypsum raw material exceeds 30% by mass.

[0063] In response, the inventors of this invention have studied the reason why the compressive strength of the hardened gypsum body decreases sharply when the proportion of recycled gypsum in the gypsum raw material exceeds 30% by mass.

[0064] Specifically, the proportion of recycled gypsum in the gypsum raw material was set to 100% by mass, and a gypsum plywood production line was used to manufacture gypsum plywood with board base paper on the surface of the gypsum core.

[0065] When examining the cross-section of the gypsum core of the manufactured gypsum board, multiple air bubbles with a diameter of approximately 2 mm or more were observed, whereas this phenomenon was not observed in the 40 mm square hardened gypsum body.

[0066] Furthermore, for the manufactured gypsum board, test pieces were cut from multiple locations, and the compressive strength was measured. The results showed a large deviation in the compressive strength values, with the minimum value being less than half of the maximum value, and some reaching 25 kgf / cm². 2 The following section.

[0067] To investigate this, a cross-sectional observation of the gypsum core of the manufactured gypsum board was performed using a scanning electron microscope. The results confirmed that even without the addition of a foaming agent, in addition to air bubbles with a diameter of approximately 2 mm or larger visible to the naked eye, there were also microbubbles with a diameter of less than 50 μm and other air bubbles of various diameters. It was also confirmed that randomly distributed air bubbles of uneven size were present within the gypsum core, forming an uneven gypsum core and gypsum board. Therefore, it was believed that the localized reduction in compressive strength occurred in areas with dense air bubbles.

[0068] Furthermore, the air bubbles of various diameters contained in the gypsum core of the manufactured gypsum board are believed to be caused by foaming of the foaming agent adhering to the recycled gypsum when the raw materials are mixed in the mixer to prepare the gypsum slurry.

[0069] In response, the inventors of this invention further investigated gypsum boards in which the effect of foaming caused by the foaming agent contained in the recycled gypsum on strength reduction was suppressed.

[0070] Initially, an attempt was made to reduce the bubbles caused by the foaming agents contained in the recycled plaster in the plaster slurry (hereinafter also referred to as "bubbles caused by recycled plaster") by adding defoamers to the plaster slurry. However, the method of adding defoamers to the plaster slurry failed to eliminate the bubbles with uneven diameters.

[0071] Secondly, an experiment was conducted whereby pre-formed foam, pre-foamed by a foaming agent, was added to the plaster slurry during the preparation of the plaster core. Furthermore, the foam addition conditions, such as the amount of foaming agent used, were adjusted to ensure that the foam, after the plaster slurry hardens, consists of bubbles with an average diameter of 50 μm or more and 650 μm or less. As a result, it was found that adding pre-formed foam reduced the impact of foam caused by recycled plaster, thus completing this invention.

[0072] The inventors of this invention speculate as follows: By adding foam pre-foamed with a foaming agent to the gypsum slurry, the effect of foam caused by recycled gypsum can be reduced.

[0073] Compared to the larger foam generated by the foaming agent contained in recycled gypsum, foam pre-foamed with a foaming agent is considered a stable foam that is less prone to breakage. The relatively unstable and easily broken large foam generated by the foaming agent in recycled gypsum is dispersed in the gypsum slurry through mixing with the pre-foamed foam. Furthermore, it is believed that during the mixing of the gypsum slurry, the relatively unstable and easily broken large foam generated by the foaming agent in recycled gypsum, through repeated contact with the relatively stable pre-foamed foam, aggregates smaller foam particles and grows larger, thus causing foam breakage.

[0074] Therefore, by adding pre-foamed foam to the gypsum slurry, the large foam caused by the foaming agent contained in the recycled gypsum can be broken down, thus retaining the main added foam. As a result, it is believed that gypsum boards containing a gypsum core obtained by hardening the gypsum slurry can be made using recycled gypsum recovered from gypsum board waste as the gypsum raw material, while obtaining gypsum boards with sufficient compressive strength.

[0075] As mentioned above, the deviation in compressive strength within gypsum board can sometimes increase, and the average compressive strength of the entire gypsum board can sometimes decrease. Therefore, when evaluating the compressive strength of gypsum board, if it is possible to cut multiple test specimens for evaluation, it is preferable to cut, for example, two to ten test specimens from the gypsum board for evaluation. Furthermore, the compressive strength of all evaluated test specimens should be 25 kgf / cm². 2 Under the above conditions, it can be said that the gypsum board has particularly sufficient compressive strength.

[0076] (2) About gypsum board

[0077] Based on the above research results, in the gypsum board 10 of this embodiment, the gypsum core 11 may be a hardened body of gypsum slurry containing gypsum raw materials, water and foam pre-foamed by a foaming agent, wherein the gypsum raw materials include recycled gypsum recovered from gypsum plywood waste.

[0078] As the gypsum core 11, a hardened body of gypsum paste containing gypsum raw material, water, and foam pre-foamed by a foaming agent is used, thereby enabling the use of recycled gypsum recovered from gypsum board waste as gypsum raw material in gypsum board and obtaining gypsum board with sufficient compressive strength.

[0079] (2-1) Regarding the components contained in gypsum mortar

[0080] The gypsum board 10 of this embodiment includes a gypsum core 11, which is a hardened form of gypsum slurry. The components of the gypsum slurry are explained below.

[0081] (Gypsum raw material)

[0082] Gypsum raw materials refer to the raw materials of gypsum such as calcined gypsum used in the preparation of gypsum slurry.

[0083] The gypsum raw material, as described above, may include recycled gypsum.

[0084] Recycled gypsum, as described above, is a calcined product of pulverized gypsum board waste. Therefore, recycled gypsum can contain calcined gypsum, i.e., calcium sulfate hydrate (1 / 2 hydrate). As a gypsum component, recycled gypsum can consist solely of calcined gypsum or may contain residual gypsum dihydrate. Since recycled gypsum uses gypsum board waste as a raw material, it can therefore contain components other than gypsum components such as paper derived from gypsum board waste.

[0085] Reclaimed gypsum can include dry-crushed gypsum board waste. However, in this case, the possibility of unavoidable impurities contaminating the material during manufacturing cannot be ruled out. Compared to wet-crushed materials, dry-crushed gypsum board waste can suppress the adhesion and contamination of moisture during crushing. Therefore, by including dry-crushed gypsum board waste in reclaimed gypsum, the contamination of dihydrate gypsum can be suppressed. Furthermore, dry-crushed gypsum board waste refers to a material obtained by firing the dry-crushed gypsum board waste, i.e., a fired product.

[0086] There is no particular limitation on the proportion of recycled gypsum in the gypsum raw material, but conventional gypsum boards using recycled gypsum have failed to achieve sufficient strength. However, the gypsum board according to this embodiment improves strength regardless of the proportion of recycled gypsum. Therefore, the gypsum board of this embodiment achieves particularly high performance, and thus a high proportion of recycled gypsum in the gypsum raw material is preferred. Therefore, the proportion of recycled gypsum in the gypsum raw material is preferably 30% by mass or more, more preferably 50% by mass or more, and even more preferably 65% ​​by mass or more.

[0087] Gypsum raw materials can also consist solely of recycled gypsum. Therefore, the proportion of recycled gypsum in gypsum raw materials can be less than 100% by mass.

[0088] Therefore, for example, the proportion of recycled gypsum in the above-mentioned gypsum raw materials is preferably 30% by mass or more and 100% by mass or less, more preferably 50% 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.

[0089] Gypsum raw materials, in addition to recycled gypsum, can also include virgin gypsum raw materials, that is, new gypsum raw materials that are not recycled.

[0090] As a raw material for primary gypsum, β-type calcined gypsum or α-type calcined gypsum can be used alone, or a mixture of both. β-type calcined gypsum is obtained by firing a mixture of any single type or combination of gypsum, including natural gypsum, by-product gypsum, and flue gas desulfurization gypsum, in the atmosphere. α-type calcined gypsum is obtained by firing a mixture of any single type or combination of gypsum, including natural gypsum, by-product gypsum, and flue gas desulfurization gypsum, in water (including steam).

[0091] (Foaming agent)

[0092] There is no particular limitation on the type of foaming agent used to generate foam for addition to gypsum grout. For example, the foaming agent preferably includes one or more selected from alkyl ether sulfates and alkyl sulfates.

[0093] By including one or more selected from alkyl ether sulfates and alkyl sulfates in the foaming agent, the large foams caused by the foaming agent contained in the recycled gypsum, which are relatively unstable and prone to defoaming, can be made to defoam more easily, thereby particularly improving the compressive strength of the gypsum board 10. The foaming agent may also be composed of one or more selected from alkyl ether sulfates and alkyl sulfates.

[0094] There is no particular limitation on the content of foaming agent in the gypsum slurry. For example, the amount of foaming agent used when generating foam can be selected with the goal of ensuring that the average diameter of the air bubbles contained in the gypsum core 11 falls within the range described later, and the foaming agent is included in the gypsum slurry.

[0095] Gypsum mortar can contain a foaming agent in a proportion, for example, of 0.01% by mass or more and 0.1% by mass or less. The reason for this is that by including a foaming agent for foam generation in the gypsum mortar at a proportion of 0.01% by mass or more, air bubbles of the desired size can be generated in the hardened gypsum body, such as the gypsum core, obtained after the gypsum mortar has hardened, thereby particularly improving the compressive strength of the gypsum board. However, even if a large amount of foaming agent is used to increase the amount of foaming agent contained in the gypsum mortar during foam generation, the effect of improving the compressive strength of the gypsum board will not change significantly. Therefore, it is preferable that the gypsum mortar contains a foaming agent in a proportion of 0.1% by mass or less.

[0096] (additive)

[0097] Plaster mortar can also contain various additives.

[0098] As additives, one or more can be selected from inorganic fibers such as glass fiber, organic fibers, lightweight aggregates, refractory materials such as vermiculite, setting delay agents, setting accelerators, water-reducing agents, foam diameter adjusters such as sulfosuccinic acid surfactants, waterproofing agents such as silicone or paraffin, organic carboxylic acids, organic carboxylate salts, organophosphate compounds, etc.

[0099] For example, by including a foam diameter adjuster in the plaster slurry, it is easier to adjust the size of the foam and air bubbles contained in the plaster slurry and plaster core 11.

[0100] When gypsum board has a surface base paper such as gypsum plywood, adhesive enhancers such as starch or polyvinyl alcohol can also be used as additives to improve the adhesion between the gypsum core 11 and the base paper for gypsum plywood.

[0101] (2-2) Regarding the average diameter of air bubbles contained in the gypsum core

[0102] The average diameter of the air bubbles contained in the gypsum core 11 is preferably 50 μm or more and 650 μm or less.

[0103] By setting the average diameter of the air bubbles contained in the gypsum core 11 to be 50 μm or more, the compressive strength of the gypsum board 10 can be improved in particular.

[0104] By setting the average diameter of the air bubbles contained in the gypsum core 11 to 650 μm or less, large voids can be prevented from forming on the surface of the gypsum core 11, such as the upper surface 11A or the lower surface 11B. Therefore, when the gypsum board is gypsum plywood, the adhesion between the gypsum core 11 and the base paper of the gypsum plywood can be improved. Furthermore, by setting the average diameter of the air bubbles contained in the gypsum core 11 to 650 μm or less, the amount of gypsum contained in the gypsum core 11 can be sufficiently ensured, thereby improving the compressive strength of the gypsum board 10.

[0105] From the viewpoint of further improving the compressive strength of the gypsum board 10 and preventing large voids from forming on the surface of the gypsum core 11, the average diameter of the air bubbles contained in the gypsum core 11 is preferably 150 μm or more and 400 μm or less.

[0106] The average diameter of the air bubbles contained in the plaster core 11 can be calculated based on a cross-sectional image of the plaster core 11. Specifically, the average diameter of the air bubbles contained in the plaster core 11 can be calculated, for example, in the following order.

[0107] (Method for determining the average diameter of bubbles)

[0108] First, a cross-section of the plaster core 11 is photographed using a scanning electron microscope at a magnification that shows between 25 and 35 air bubbles in a single image. Alternatively, a microscope or similar device can be used instead of a scanning electron microscope.

[0109] For each bubble in the captured image, bubbles with a length of 30 μm or more along a predetermined measurement direction are extracted. Furthermore, there is no particular limitation on the measurement direction; for example, since the captured image is typically rectangular, the direction along the long side of the rectangle can be used as the measurement direction. Additionally, the plaster core obtained after the plaster slurry with added bubbles hardens contains bubbles generated by drainage and bubbles generated by adding foam to the plaster slurry, but the bubbles generated by drainage are smaller, with a length of less than 30 μm along the measurement direction. Therefore, by extracting and evaluating bubbles with a length of 30 μm or more along the measurement direction, the bubbles generated by the foam added to the plaster slurry can be evaluated.

[0110] Then, for all bubbles extracted from the captured image, the maximum length along the measurement direction, i.e., the diameter of the bubble, is measured, and the average (arithmetic mean) of the diameters of all bubbles measured in the image is taken as the average diameter of the bubbles in the captured image.

[0111] Following the same sequence, for one plaster core 11, the observation position was changed and a total of three cross-sectional images were taken, and the average diameter of the bubbles in each image was calculated. Then, the average (arithmetic mean) of the average bubble diameters of the three images was calculated, and this was used as the average diameter of the bubbles contained in the plaster core 11 being evaluated.

[0112] (2-3) Regarding the organic fibers contained in the gypsum core

[0113] The gypsum core 11 may also contain organic fibers.

[0114] Organic fibers mainly originate from paper and other materials contained in recycled gypsum. To adjust the content of organic fibers in the gypsum core 11, organic fibers can be added to the gypsum slurry during preparation as needed. Furthermore, for recycled gypsum, the proportion of organic fibers can be adjusted by removing paper according to the degree of crushing or by sieving as needed.

[0115] The gypsum core 11 preferably contains organic fibers in a proportion of more than 0.1% by mass and less than 2.5% by mass.

[0116] By including more than 0.1% by mass of organic fibers in the gypsum core 11, the shear strength and bending fracture load of the gypsum core 11 and gypsum board 10 can be improved.

[0117] By reducing the organic fiber content of the gypsum core 11 to 2.5% by mass or less, the fluidity of the gypsum slurry can be improved during the manufacture of gypsum board, thus increasing the productivity of the gypsum board. Furthermore, by reducing the organic fiber content of the gypsum core 11 to 2.5% by mass or less, the non-combustible properties of the gypsum board 10 can be improved.

[0118] The inventors of this invention have studied the effect of the content of organic fibers contained in the gypsum core 11 of the gypsum board 10 on the total heat generation.

[0119] Specifically, as Experiments 3-1 to 3-6, new or recycled plaster, paper, and water were mixed according to the mixing ratios shown in Table 3 below to prepare plaster slurry. Furthermore, water was added to achieve a specific gravity of 0.65 for the hardened plaster body obtained from the plaster slurry. The plaster slurry was then prepared with a basis weight of 200 g / m³. 2 The plywood is formed by mixing the base paper with a thickness of 12.5 mm to create a gypsum board 10.

[0120] The recycled gypsum was made by drying and pulverizing gypsum board waste to a degree sufficient to remove any attached paper, then sieving and burning the material to completely remove the paper. Additionally, paper recycled from the recycled gypsum was used as the paper.

[0121] (Fever test)

[0122] The total heat output of the gypsum board used as the test subject was measured using the calorimetric test as shown in ISO 5660-1 cone calorimetry for 20 minutes.

[0123] The evaluation results are shown in Table 3.

[0124] [Table 3]

[0125] Based on the results shown in Table 3, it was confirmed that when the paper content is below 3.0% by mass, the total calorific value over 20 minutes is 8 MJ / m³. 2 Therefore, it has been confirmed that by setting the content of organic fiber in the gypsum core 11 to 3.0% by mass or less, excellent non-combustible properties can be obtained, and in particular, by setting it to 2.5% by mass or less, the non-combustible properties can be improved.

[0126] For example, the proportion of organic fibers contained in the gypsum core 11 can be measured and calculated in the following order.

[0127] First, the plaster core 11 is heated to 150°C and then pulverized to obtain pulverized material. There is no particular limitation on the degree of pulverization; the pulverization can be carried out on a sieve that can inhibit the dissolution time of the plaster components during water washing.

[0128] Next, the obtained pulverized material is washed with water through a 100-mesh sieve. Since the residue on the sieve is the organic fiber contained in the gypsum core, its dried mass is measured and taken as the organic fiber mass. Furthermore, the mass ratio of the organic fiber mass to the mass of the pulverized material provided on the sieve can be calculated as the mass ratio of the organic fiber contained in the gypsum core 11.

[0129] Furthermore, if 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 containing the surface material.

[0130] (2-4) Regarding the total heat generation of gypsum board

[0131] In this embodiment, the gypsum board 10 preferably has a total heat generation of 8 MJ / m² over 20 minutes. 2 the following.

[0132] By setting the total heat generation of plasterboard 10 over 20 minutes to 8 MJ / m 2 The following method yields gypsum board with excellent non-combustible properties. The total calorific value of the gypsum board 10 can be selected by adjusting the content of organic components in the gypsum board 10, for example, by adjusting the degree of paper removal during the manufacture of recycled gypsum.

[0133] For example, as described in "(2-3) Regarding the organic fibers contained in the gypsum core", by setting the content of organic fibers contained in the gypsum core 11 to less than 3.0% by mass, the total heat generation of the gypsum board 10 over 20 minutes can be made to be 8 MJ / m³. 2 The following is a summary of the benefits of using gypsum core 11. By setting the content of organic fibers contained in the gypsum core 11 to 2.5% by mass or less, it is particularly effective in suppressing total heat generation.

[0134] (2-5) Regarding the specific gravity of gypsum board

[0135] There is no particular limitation on the specific gravity of gypsum board; for example, it can be set to 0.65 or higher. Setting the specific gravity of gypsum board to 0.65 or higher can particularly improve its strength.

[0136] While there is no specific upper limit on the specific gravity of gypsum board, from the perspective of improving operability on the construction site, it can be less than 1.1 or even below 1.0.

[0137] The specific gravity of gypsum board can be evaluated according to the method specified in JIS A 6901 (2014).

[0138] [Manufacturing method of gypsum board]

[0139] The method for manufacturing gypsum board according to this embodiment may include a gypsum slurry preparation process, a forming process, and a hardening process.

[0140] According to the gypsum board manufacturing method of this embodiment, a gypsum board of one form of the present invention can be manufactured. Therefore, some descriptions of matters already described regarding the gypsum board will be omitted.

[0141] (Plaster slurry preparation process)

[0142] In the gypsum slurry preparation process, gypsum raw materials containing recycled gypsum recovered from gypsum board waste, water, and foam pre-foamed with a foaming agent are mixed to prepare gypsum slurry.

[0143] For example, these raw materials can be mixed using a mixer to prepare gypsum slurry. Various additives can also be added to the gypsum slurry as needed. The raw materials suitable for use in gypsum slurry have already been described and will not be repeated here.

[0144] The raw materials for gypsum slurry can be mixed in one step or in multiple stages. For example, only the solid components can be mixed to obtain a gypsum composition, and then the gypsum composition can be mixed with the remaining liquid components to obtain gypsum slurry.

[0145] There are no particular restrictions on the timing of adding or mixing foam into plaster slurry. For example, the raw materials for plaster slurry containing foam can be mixed all at once. Alternatively, foam can be added to the plaster slurry after the plaster slurry containing ingredients other than foam has been prepared.

[0146] In the gypsum slurry preparation process, foam can be added with the aim of achieving an average bubble diameter of 50 μm or more and 650 μm in the gypsum core 11 of the gypsum board 10 obtained after the hardening process. Therefore, for example, it is possible to conduct a preliminary test to manufacture gypsum board by using foam generated by varying the amount of foaming agent added, and select the foam generation and addition conditions based on the results of the preliminary test.

[0147] Furthermore, in the gypsum slurry preparation process, various gypsum slurries with different foam generation and addition conditions, such as bubble diameter and foam addition amount, can be prepared. In this case, in the molding process, a multilayer of gypsum slurries can be formed. In the molding process, the thickness of each layer can be selected with the goal of ensuring that the average diameter of the bubbles in the gypsum core 11 of the gypsum board 10 obtained after the hardening process is within a specified range.

[0148] (Forming process)

[0149] In the molding process, plaster slurry prepared in the plaster slurry preparation process is molded to produce plaster slurry molded bodies.

[0150] Specifically, for example, in the case of manufacturing gypsum board as gypsum board 10, gypsum paste can be manufactured by placing gypsum paste between the base paper of gypsum board and shaping it by a molding machine.

[0151] In the gypsum slurry preparation process, when there are multiple gypsum slurries with different foam addition conditions, the forming process can also provide each gypsum slurry with the goal of forming a desired layering sequence to form a gypsum slurry layer.

[0152] (Hardening process)

[0153] The hardening process enables the gypsum paste molded body obtained in the molding process to harden.

[0154] The hardening process is achieved by relying on the hydration reaction of calcined gypsum (hemihydrate gypsum) in the gypsum slurry to produce dihydrate gypsum, which forms needle-like crystals that solidify. Therefore, in the gypsum slurry mold formed in the molding process, the calcined gypsum in the gypsum slurry reacts with water, and the hardening process is achieved by promoting the hydration reaction of the calcined gypsum.

[0155] The method for manufacturing gypsum board according to this embodiment may also include any steps. Specifically, it may include, for example, the following cutting steps, drying steps, and gypsum recycling steps.

[0156] (Cutting process)

[0157] In the cutting process, a cutting device can be used to cut the gypsum slurry molded body.

[0158] After the plaster slurry is formed in the molding process, it gradually hardens. Therefore, the cutting process can be performed, for example, during or after the hardening process. However, it is preferable to perform the cutting process when the hardening process has progressed to a point where the plaster slurry can be cut.

[0159] The cutting process can be performed multiple times. Therefore, the method for manufacturing gypsum board according to this embodiment may also include, for example, a first cutting process, which can be referred to as a rough cutting process. In addition, a second cutting process may also be included.

[0160] In the first cutting process, for example, the plaster slurry molded body can be cut to the desired size according to the size of the dryer used in the drying process described later.

[0161] In addition, the second cutting process can be performed, for example, after the drying process, and can be cut into the desired product size.

[0162] (Drying process)

[0163] In the drying process, the plaster slurry molded body can be dried. In the drying process, any remaining moisture contained in the plaster slurry molded body can be dried. Furthermore, in the drying process, it is preferable to provide the plaster slurry molded body after the hardening process is completed. The drying process can be carried out by forcibly drying the plaster slurry molded body using a dryer.

[0164] There are no particular limitations on the method of using a dryer to forcibly dry gypsum slurry molded bodies. For example, a dryer can be installed in the conveying path of the gypsum slurry molded bodies, allowing them to pass through the dryer continuously for drying. Alternatively, the gypsum slurry molded bodies can be moved into the dryer for batch drying.

[0165] (Reuse of plaster manufacturing process)

[0166] In the process of manufacturing recycled gypsum, recycled gypsum is produced by crushing and firing waste gypsum board. The resulting recycled gypsum can then be supplied to the gypsum slurry preparation process.

[0167] In the process of reusing gypsum, there are no particular limitations on the method of crushing gypsum board waste; for example, dry crushing is acceptable. Compared with wet crushing, dry crushing of gypsum board waste can suppress the adhesion and mixing of moisture during crushing. Therefore, by dry crushing gypsum board waste, the energy during firing can be controlled, and the mixing of dihydrate gypsum can be suppressed.

[0168] Therefore, the recycled gypsum provided to the gypsum slurry preparation process can include dry pulverized gypsum board waste, and the recycled gypsum can also be composed of dry pulverized gypsum board waste.

[0169] In the process of reusing gypsum manufacturing, screening and magnetic separation can be performed as needed to remove components other than gypsum, such as metal or paper.

[0170] According to the gypsum board manufacturing method of this embodiment, gypsum board with sufficient compressive strength can be obtained while using recycled gypsum recovered from gypsum plywood waste as gypsum raw material.

[0171] [Example]

[0172] The following are specific embodiments for illustration, but the present invention is not limited to these embodiments.

[0173] [Refer to Examples 1-1 to 1-6]

[0174] The following steps were taken to manufacture gypsum board as a gypsum board, and its compressive strength and adhesion were evaluated.

[0175] (1) Manufacturing conditions

[0176] Specifically, as in Reference Examples 1-1 to 1-6, regarding gypsum raw materials and paper, new gypsum, water, foam, and starch as an adhesive enhancer were mixed according to the mixing ratio shown in Table 4 below to prepare a gypsum paste (gypsum paste preparation process). Furthermore, water was added with the aim of achieving a specific gravity of 0.65 for the hardened gypsum body obtained after the gypsum paste hardens.

[0177] As a new type of plaster, it uses new plaster raw materials, rather than recycled materials.

[0178] When adding foam to gypsum slurry, the amount of foaming agent used to generate the foam is adjusted to achieve the average diameter of the air bubbles contained in the gypsum core as shown in Table 5, and then added to the gypsum slurry. No foam was added in Reference Example 1-1.

[0179] Then, by placing the obtained gypsum paste between the base paper for gypsum board and forming it into a 12.5 mm thick plate, a gypsum paste molded body is manufactured (forming process).

[0180] Then, the plaster slurry is hardened (hardening process).

[0181] After the hardening process, the gypsum slurry is cut and dried to manufacture gypsum board (cutting process and drying process).

[0182] (2) Evaluation Methods

[0183] (2-1) Compressive strength

[0184] To evaluate the compressive strength of the obtained gypsum board, ten test specimens, each 40 mm long × 40 mm wide × 12.5 mm thick, were cut from different locations within the same gypsum board. The specimens were dried at a constant temperature of 40°C, and then the compressive strength of each specimen was measured using an Autograph testing machine (Shimadzu AG-X plus) at a load speed of 1 mm / min. The average value and standard deviation were calculated.

[0185] The compressive strength of each test specimen is shown in the columns for test specimens 1 to 10 of Table 4. The average value is expressed in the "Average" column, and the standard deviation is expressed in the "σ" column.

[0186] (2-2) Average diameter of the bubble

[0187] The average diameter of the bubbles was measured and calculated in the same order as described in "(2-2) Regarding the average diameter of bubbles contained in the plaster core" ("Method for determining the average diameter of bubbles"), except for observation and photography using a microscope. Furthermore, the direction along the long side of the photographed image was used as the measurement direction. This was also the case in the following examples and comparative examples.

[0188] (2-3) Specific gravity

[0189] The specific gravity of gypsum board was evaluated according to the method described in JIS A 6901 (2014).

[0190] (2-4) Adhesion test

[0191] When conducting the adhesion test, two test pieces measuring 300mm in length, 910mm in width, and 12.5mm in thickness were first cut from the manufactured gypsum board.

[0192] On the back of one cut test piece, on the original paper, make a cut along the length at a distance of 50 mm from the end along the width.

[0193] Then, with the cut as the center, force is applied from the back to the surface, applying force from the back towards the surface to both ends of the test piece along its width, bending the test piece so that it cracks along the cut. Then, the plaster core is completely separated from the board paper located on the surface of the test piece.

[0194] Observe the surface of the gypsum core located on the surface side of the test piece and calculate the area proportion of the original paper used for board.

[0195] In addition, for another test piece, except for making a cut in the board paper on the surface side, a cut along the length is formed under the same conditions as the first test piece. Then, with the cut as the center, a force is applied from the surface to the back side at both ends of the test piece along the width, bending the test piece to cause it to crack along the cut. Then, the plaster core is completely separated from the board paper located on the back side of the test piece.

[0196] Then, observe the plaster core on the back side of the test piece and calculate the area proportion of the original board paper remaining.

[0197] The average of the proportion of the board base paper area with residual gypsum core calculated for the two test pieces is used as the residual proportion of the board base paper of the gypsum plywood.

[0198] A residual proportion of base paper used for board production below 60% is rated C. A residual proportion of base paper used for board production between 60% and 90% is rated B. A residual proportion of base paper used for board production above 90% is rated A.

[0199] The adhesion of the board base paper to the gypsum core is sufficiently high in case A, and decreases in the order of B and C.

[0200] The evaluation results are shown in Table 5.

[0201] [Examples 1-1 to Examples 1-5, Comparative Example 1]

[0202] The following steps were taken to manufacture gypsum board as a gypsum board, and its compressive strength and adhesion were evaluated.

[0203] (1) Manufacturing conditions

[0204] Specifically, as Examples 1-1 to 1-5 and Comparative Example 1, regarding gypsum raw materials and paper, recycled gypsum, paper, water, foam, and starch as an adhesive enhancer were mixed in the mixing ratios shown in Table 4 below to prepare gypsum slurry (gypsum slurry preparation process). Furthermore, water was added to achieve a specific gravity of 0.65 for the hardened gypsum body obtained after the gypsum slurry hardens. Alkyl ether sulfate was used as a foaming agent for forming foam.

[0205] Furthermore, when adding foam to the gypsum slurry, the amount of foaming agent used to generate foam is adjusted to achieve the average diameter of the air bubbles in the gypsum core as shown in Table 5, and then foamed before being added to the gypsum slurry. In any embodiment where foam is added to the gypsum slurry, the gypsum slurry contains foaming agent at a ratio of 0.01% by mass or more and 0.1% by mass or less. No foam was added in Comparative Example 1.

[0206] In addition, the recycled gypsum used was a fired product made by drying and pulverizing gypsum board to a degree sufficient to remove the attached paper, and then completely removing the paper by sieving. Furthermore, the paper used was recycled paper derived from the recycled gypsum.

[0207] Then, by placing the obtained gypsum paste between the base paper for gypsum board and shaping it into a 12.5mm thick plate, a gypsum paste molded body is manufactured (forming process).

[0208] Then, the plaster slurry is hardened (hardening process).

[0209] After the hardening process, the gypsum slurry is cut and dried to manufacture gypsum board (cutting process and drying process).

[0210] The obtained gypsum board was evaluated for compressive strength, average bubble diameter, specific gravity, and adhesion in the same order as in Reference Examples 1-1 to 1-6. The evaluation results are shown in Tables 4 and 5.

[0211] In addition, SEM images were taken of the cross-sections of the gypsum cores of the gypsum plywood obtained in Examples 1-4 and Comparative Example 1. Figure 3A , Figure 3B This represents the SEM images obtained in Examples 1-4. Figure 4A , Figure 4B This represents the SEM image of Comparative Example 1.

[0212] Furthermore, although the gypsum cores of the gypsum boards obtained in Examples 1-1 to 1-5 contain adhesive enhancers, the content is only trace amounts. Therefore, it can be considered that the gypsum core is composed of gypsum from recycled gypsum and paper. In this case, the gypsum from recycled gypsum is dihydrate gypsum, so the content of paper as an organic fiber in the gypsum core is 2.06% by mass.

[0213] [Table 4]

[0214] [Table 5]

[0215] Based on the results shown in Table 4, it can be confirmed that in the gypsum board of Comparative Example 1, which used recycled gypsum without adding air bubbles, the average compressive strength decreased and the standard deviation increased. Furthermore, in test pieces 1, 6, and 8, the compressive strength was confirmed to be less than 25 kgf / cm². 2 .

[0216] In contrast, in the gypsum board products of Examples 1-1 to 1-5, by adding foam and adjusting the amount of foaming agent used during foam generation, the average diameter of air bubbles in the gypsum core was made to be 50 μm or more and 650 μm or less, thus confirming that the average compressive strength was higher than that of Comparative Example 1. Furthermore, in the gypsum board products of Examples 1-1 to 1-5, the compressive strength of all 10 test specimens reached a very high 25 kgf / cm². 2 The standard deviation of compressive strength is also set at 10 kgf / cm². 2 Furthermore, the standard deviation is also sufficiently small. Moreover, the average compressive strength of the gypsum plywood of Examples 1-1 to 1-5 is comparable to the average compressive strength of the gypsum plywood of Reference Examples 1-1 to 1-6 using new gypsum, confirming that it has a sufficiently large value.

[0217] SEM images of the plaster cores used in Examples 1-4 Figure 3A , Figure 3B SEM image of the plaster core as Comparative Example 1 Figure 4A , Figure 4B A comparison was made. The results showed that the bubbles within the plaster core were amorphous in Comparative Example 1, but nearly spherical in Examples 1-4, indicating they were smaller than those in Comparative Example 1. Furthermore, because the shape and size of the bubbles within the plaster core of Comparative Example 1 varied considerably, the average diameter was not measured.

[0218] In addition, it was confirmed that when the average diameter of the air bubbles in the gypsum core is 50 μm or more, the adhesion between the gypsum core and the base paper for the board can be improved.

[0219] Dihydrate gypsum, obtained by pulverizing and calcining waste gypsum and then rehydrating it, contains crystals whose morphology and size remain almost unchanged compared to the fine needle-like crystals found in waste gypsum, retaining the fine needle-like crystals. Since the needle-like crystals and aggregates of the fine dihydrate gypsum obtained through rehydration of recycled gypsum have weak entanglement with paper fibers, it is expected that the adhesion between the gypsum core and the base paper used in the board will be reduced. However, based on the above evaluation results, it was confirmed that by setting the average diameter of the air bubbles in the gypsum core to be between 50 μm and 650 μm, the adhesion can be improved to the same level as when using virgin gypsum.

[0220] Examples 1-1 to 1-5 show examples where the proportion of recycled gypsum in the gypsum raw material is 100% by mass. However, it is clear from the results of Reference Examples 1-2 to 1-6 that even when a portion of the recycled gypsum is used as new gypsum, by setting the average diameter of the air bubbles contained in the gypsum core within a specified range, it can be confirmed that the compressive strength of the gypsum board can be sufficiently improved. Furthermore, in this case, it was confirmed that the deviation in compressive strength between multiple test specimens cut from the gypsum board can be reduced.

[0221] [Postscript]

[0222] (1) A gypsum board according to one embodiment of the present invention, having a gypsum core, The gypsum core is a hardened gypsum paste comprising gypsum raw materials, water, and foam pre-foamed with a foaming agent. The gypsum raw materials include recycled gypsum recovered from gypsum board waste. The average diameter of the air bubbles contained in the gypsum core is greater than 50 μm and less than 650 μm.

[0223] (2) In (1) above, the bubble may contain one or more selected from alkyl ether sulfates and alkyl sulfates.

[0224] (3) In (1) or (2) above, the gypsum paste may contain the foaming agent in a proportion of more than 0.01% by mass and less than 0.1% by mass.

[0225] (4) In any of (1) to (3) above, the gypsum raw material may contain the recycled gypsum in a proportion of more than 30% by mass and less than 100% by mass.

[0226] (5) In any of (1) to (4) above, the gypsum core may contain organic fibers in a proportion of more than 0.1% by mass and less than 2.5% by mass.

[0227] (6) In any of (1) to (5) above, the recycled gypsum may comprise dry pulverized gypsum board waste.

[0228] (7) In any of (1) to (6) above, the specific gravity is 0.65 or higher.

[0229] (8) Any one of (1) to (7) above can be, where the total heat generated in 20 minutes is 8 MJ / m 2 the following.

[0230] (9) A method for manufacturing gypsum board according to one aspect of the present invention, comprising: a gypsum slurry preparation step, wherein gypsum raw material comprising recycled gypsum recovered from gypsum board waste, water and foam pre-foamed with a foaming agent are mixed to prepare gypsum slurry. The forming process involves shaping the plaster slurry to create a plaster slurry molded body; and The hardening process causes the gypsum paste to harden. In the gypsum slurry preparation process, the foam is added so that the average diameter of the air bubbles contained in the gypsum core obtained after the hardening process is more than 50 μm and less than 650 μm.

[0231] (10) In (9) above, the bubble may contain one or more selected from alkyl ether sulfates and alkyl sulfates.

[0232] (11) In (9) or (10) above, the gypsum paste may contain the foaming agent in a proportion of more than 0.01% by mass and less than 0.1% by mass.

[0233] (12) In any of (9) to (11) above, the gypsum raw material may contain the recycled gypsum in a proportion of more than 30% by mass and less than 100% by mass.

[0234] (13) In any of (9) to (12) above, the gypsum core may contain organic fibers in a proportion of more than 0.1% by mass and less than 2.5% by mass.

[0235] (14) In any of (9) to (13) above, the recycled gypsum may comprise dry pulverized gypsum board waste.

[0236] The above description of gypsum board and its manufacturing method illustrates the embodiments, but the present invention is not limited to the above embodiments. Various modifications and alterations can be made within the scope of the present invention as described in the claims.

[0237] This application claims priority based on Japanese Patent Application No. 2024-012314, filed with the Japan Patent Office on January 30, 2024, and the entire contents of Japanese Patent Application No. 2024-012314 are incorporated herein by reference.

[0238] Explanation of reference numerals in the attached figures

[0239] 10. Plasterboard; 11. Plaster core; 11A Upper surface; 11B Lower surface; 11C Side view.

Claims

1. A type of gypsum board, characterized in that, With plaster core, The gypsum core is a hardened gypsum paste comprising gypsum raw materials, water, and foam pre-foamed with a foaming agent. The gypsum raw materials include recycled gypsum recovered from gypsum board waste. The average diameter of the air bubbles contained in the gypsum core is greater than 50 μm and less than 650 μm.

2. The gypsum board according to claim 1, wherein, The foaming agent comprises one or more selected from alkyl ether sulfates and alkyl sulfates.

3. The gypsum board according to claim 1 or 2, wherein, The gypsum paste contains the foaming agent in a proportion of more than 0.01% by mass and less than 0.1% by mass.

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

5. The gypsum board according to claim 1 or 2, wherein, The gypsum core contains organic fibers in a proportion of more than 0.1% by mass and less than 2.5% by mass.

6. The gypsum board according to claim 1 or 2, wherein, The recycled gypsum comprises dry pulverized material of the gypsum board waste.

7. The gypsum board according to claim 1 or 2, wherein, The specific gravity is above 0.

65.

8. The gypsum board according to claim 1 or 2, wherein, The total heat generated in 20 minutes is 8 MJ / m 2 the following.

9. A method for manufacturing gypsum board, comprising: The gypsum slurry preparation process involves mixing gypsum raw materials, including recycled gypsum recovered from gypsum board waste, water, and foam pre-foamed with a foaming agent to prepare gypsum slurry. The forming process involves shaping the plaster slurry to create a plaster slurry molded body. as well as The hardening process causes the gypsum paste to harden. In the gypsum slurry preparation process, the foam is added so that the average diameter of the air bubbles contained in the gypsum core obtained after the hardening process is more than 50 μm and less than 650 μm.

10. The method for manufacturing gypsum board according to claim 9, wherein, The foaming agent comprises one or more selected from alkyl ether sulfates and alkyl sulfates.

11. The method for manufacturing gypsum board according to claim 9 or 10, wherein, The gypsum paste contains the foaming agent in a proportion of more than 0.01% by mass and less than 0.1% by mass.

12. The method for manufacturing gypsum board according to claim 9 or 10, wherein, The gypsum raw material contains the recycled gypsum in a proportion of more than 30% by mass and less than 100% by mass.

13. The method for manufacturing gypsum board according to claim 9 or 10, wherein, The gypsum core contains organic fibers in a proportion of more than 0.1% by mass and less than 2.5% by mass.

14. The method for manufacturing gypsum board according to claim 9 or 10, wherein, The recycled gypsum comprises dry pulverized material of the gypsum board waste.

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