Gypsum-based composition and wall structure

Abstract

This gypsum-based composition containing hemihydrate gypsum, polyvinyl alcohol, and guar gum, the polyvinyl alcohol being contained in a proportion of 0.1% by mass to 0.6% by mass, the guar gum being contained in a proportion of 0.02% by mass to 0.1% by mass.

Description

Gypsum composition, wall structure

[0001] The present invention relates to a gypsum-based composition, a wall structure.

[0002] Gypsum-based compositions have been used in the past to be placed on the surface of a base material for the purpose of smoothing the surface of the base material, etc.

[0003] For example, Patent Document 1 discloses a hemihydrate gypsum plaster composition characterized by containing 0.01 to 10 parts by weight of a natural gum containing galactomannose as a main component per 100 parts by weight of hemihydrate gypsum.

[0004] Japanese Patent Publication No. 53-74527

[0005] Gypsum-based compositions are required to have excellent water retention properties in order to ensure the time required for construction after the slip mixed with water is applied to the base material.

[0006] Furthermore, since gypsum-based compositions are also used to adhere architectural facings to base materials, they are required to have sufficient adhesive strength to exert a sufficient initial adhesive force between the base material and the architectural facings even immediately after adhesion.

[0007] In view of the problems of the conventional techniques described above, an object of one aspect of the present disclosure is to provide a gypsum-based composition having excellent water retention and adhesive properties.

[0008] A gypsum-based composition according to one embodiment of the present disclosure contains gypsum hemihydrate, polyvinyl alcohol, and guar gum, and contains the polyvinyl alcohol in an amount of 0.1% by mass or more and 0.6% by mass or less, and the guar gum in an amount of 0.02% by mass or more and 0.1% by mass or less.

[0009] According to one embodiment of the present disclosure, a gypsum-based composition having excellent water retention and adhesiveness can be provided.

[0010] Fig. 1 is an explanatory diagram of a wall structure according to one embodiment of the present disclosure. Fig. 2 is an explanatory diagram of a method for evaluating adhesive strength. Fig. 3 is an explanatory diagram of a method for evaluating water retention. Fig. 4 is an explanatory diagram of a method for evaluating adhesiveness.

[0011] 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-based composition] The gypsum-based composition of the present embodiment can contain gypsum hemihydrate, polyvinyl alcohol, and guar gum.

[0012] The gypsum-based composition of the present embodiment can also be used to bond a base material to a building surface material, etc. Therefore, the gypsum-based building material of the present embodiment can also be referred to as a gypsum-based adhesive, etc.

[0013] The inventors of the present invention have conducted research into gypsum-based compositions that are excellent in water retention and adhesiveness.

[0014] In this specification, water retention means the property of being able to maintain a moisture-retaining state for a long period of time in a slurry obtained by kneading a gypsum-based composition with water.

[0015] The higher the water retention, the longer the construction time can be, and the greater the degree of freedom in setting the construction period.

[0016] Furthermore, in this specification, adhesiveness refers to the property that, when two gypsum boards are bonded using the gypsum-based composition of the present embodiment, the two gypsum boards can be bonded with sufficient strength before the gypsum-based composition of the present embodiment solidifies. In other words, adhesiveness refers to the adhesive strength (adhesion force) of the gypsum-based composition of the present embodiment to the two gypsum boards before the gypsum-based composition of the present embodiment solidifies.

[0017] Higher adhesiveness means that a building surface material such as a gypsum board can be fixed to a base material with sufficient strength immediately after application, thereby preventing the occurrence of application defects, etc. Furthermore, gypsum-based compositions are often applied to base materials that are vertical surfaces, etc., and higher adhesiveness also means that the slurry containing the gypsum-based composition itself adheres strongly to the base material, preventing dripping.

[0018] The adhesiveness can be evaluated by the adhesive strength before the gypsum-based composition of the present embodiment solidifies when two gypsum boards are bonded together using the gypsum-based composition of the present embodiment. However, a gypsum-based composition with a high adhesiveness rating can also exhibit high adhesiveness when bonding various base materials other than gypsum boards to building surface materials. In other words, a highly adhesive gypsum-based composition can have sufficient adhesive strength before the gypsum-based composition solidifies, even when bonding various building surface materials to a base material such as a concrete base.

[0019] In the following description of this specification, the term "adhesion" may also be used. In this specification, "adhesion" refers to the property of adhering the gypsum-based composition of this embodiment to a base material and, after the gypsum-based composition of this embodiment has solidified, being able to adhere the gypsum-based composition of this embodiment to the base material with sufficient strength. Therefore, adhesion can also be expressed as adhesive strength or the like.

[0020] Higher adhesiveness means that after application, when the gypsum-based composition of the present embodiment exhibits adhesive strength, the gypsum-based composition of the present embodiment and the base material can be bonded with sufficient strength.

[0021] By including polyvinyl alcohol in a gypsum-based composition, adhesiveness and tackiness can be improved. However, increasing the amount of polyvinyl alcohol to improve adhesiveness and tackiness can cause a decrease in water retention. This is thought to be because polyvinyl alcohol has foaming (swelling) properties, and increasing the amount of polyvinyl alcohol absorbs water, increasing the amount of foaming of polyvinyl alcohol.

[0022] However, reducing the amount of polyvinyl alcohol reduces the adhesiveness and tackiness of the gypsum-based composition.

[0023] Therefore, the inventors of the present invention conducted further studies and found that by blending guar gum into a gypsum-based composition, the adhesiveness of the gypsum-based composition can be increased without excessively increasing the amount of polyvinyl alcohol blended. Therefore, the gypsum-based composition of the present embodiment, in which guar gum and polyvinyl alcohol are selected and blended in combination, can increase water retention while also sufficiently increasing adhesiveness and adhesion. (1) Components Contained in the Gypsum-Based Composition The components contained in the gypsum-based composition of the present embodiment are described below. (1-1) Gypsum Hemihydrate The gypsum-based composition of the present embodiment can contain gypsum hemihydrate as a main ingredient. "Contained as a main ingredient" means that it is contained in the largest amount by mass.

[0024] The gypsum-based composition of the present embodiment may contain gypsum hemihydrate as a main component, and the content ratio is not particularly limited, but may be, for example, 80% by mass or more and 95% by mass or less.

[0025] Note that the content ratio of each component related to the gypsum-based composition in this specification refers to the content ratio of each component in a gypsum-based composition that is not kneaded with water, i.e., to which water is not added, and refers to the content ratio of each component in the total of gypsum hemihydrate, polyvinyl alcohol, guar gum, and additives.

[0026] Hemihydrate gypsum (calcined gypsum), also known as calcium sulfate hemihydrate, is an inorganic composition having hydraulic properties. As the hemihydrate, β-type hemihydrate gypsum or α-type hemihydrate, or a mixture of the two, can be used. β-type hemihydrate gypsum can be obtained by calcining in the atmosphere any one of natural gypsum, by-product gypsum, flue gas desulfurization gypsum, recycled gypsum such as waste gypsum board, or a mixture of any of these. α-type hemihydrate gypsum can be obtained by calcining in water (including steam) any one of natural gypsum, by-product gypsum, flue gas desulfurization gypsum, recycled gypsum such as waste gypsum board, or a mixture of any of these.

[0027] The hemihydrate used as a raw material for the gypsum-based composition preferably contains β-type hemihydrate, and the main component of the hemihydrate used as a raw material is more preferably β-type hemihydrate. Note that the main component of the hemihydrate used as a raw material being β-type calcined gypsum means that the β-type hemihydrate accounts for more than 50% by mass of the hemihydrate used as a raw material. The hemihydrate used as a raw material may be composed solely of β-type calcined gypsum.

[0028] To produce α-type gypsum hemihydrate, gypsum dihydrate such as natural gypsum must be calcined under pressure in water or steam using an autoclave. In contrast, β-type gypsum hemihydrate can be produced by calcining gypsum dihydrate such as natural gypsum in the atmosphere under atmospheric pressure, and β-type gypsum hemihydrate can be produced more productively than α-type gypsum hemihydrate.

[0029] The physical properties of the gypsum hemihydrate used in the gypsum-based composition of the present embodiment are not particularly limited. For example, the gypsum hemihydrate may have a Blaine specific surface area of ​​3000 cm ２ / g or more 12000cm ２ / g or less, and ２ / g or more 10000cm ２ It is more preferable that the SiO2 content is 1 / g or less.

[0030] The Blaine specific surface area of ​​hemihydrate gypsum is 3000 cm ２ / g or more, the water retention and adhesiveness of the gypsum-based composition can be particularly improved. The Blaine specific surface area of ​​hemihydrate gypsum is 5000 cm ２ / g or more.

[0031] In addition, the Blaine specific surface area of ​​hemihydrate gypsum is 12000 cm ２ / g or less, the handleability of the gypsum hemihydrate can be improved and the production cost can be reduced. ２ (1-2) Polyvinyl alcohol (PVA) The gypsum-based composition of the present embodiment may contain polyvinyl alcohol in a proportion of 0.1% by mass or more and 0.6% by mass or less, or may contain polyvinyl alcohol in a proportion of 0.3% by mass or more and 0.5% by mass or less, or may contain polyvinyl alcohol in a proportion of 0.4% by mass or more and 0.5% by mass or less.

[0032] Polyvinyl alcohol has the function of enhancing the adhesiveness and cohesion of the gypsum-based composition of this embodiment. Therefore, by setting the polyvinyl alcohol content to 0.1% by mass or more, the adhesiveness and cohesion of the gypsum-based composition of this embodiment can be enhanced. As described above, the polyvinyl alcohol content may be 0.3% by mass or more, or may be 0.4% by mass or more.

[0033] However, if the blending ratio of polyvinyl alcohol is too high, the water retention capacity decreases. Therefore, by setting the polyvinyl alcohol content to 0.6% by mass or less, the water retention capacity of the gypsum-based composition of this embodiment can be increased. The polyvinyl alcohol content may be set to 0.5% by mass or less. (1-3) Guar Gum The gypsum-based composition of this embodiment can contain guar gum in a ratio of 0.02% by mass or more and 0.1% by mass or less.

[0034] Guar gum has the function of increasing the adhesiveness and tackiness while preventing a decrease in the water retention property of the gypsum-based composition of this embodiment. Therefore, by setting the guar gum content to 0.02 mass% or more, the water retention property, adhesiveness, and tackiness of the gypsum-based composition of this embodiment can be increased.

[0035] However, guar gum has a smaller effect of enhancing adhesiveness and tackiness than polyvinyl alcohol, and therefore, by using guar gum in combination with polyvinyl alcohol and keeping its content at 0.1% by mass or less, water retention, adhesiveness, and tackiness can be enhanced in a balanced manner.

[0036] Furthermore, by setting the content of guar gum to 0.1% by mass or less, when preparing a slurry of the gypsum-based composition of this embodiment, it is possible to maintain the proportion of excess water that has not reacted with the components of the gypsum-based composition of this embodiment. Therefore, the fluidity of the slurry of the gypsum-based composition can be maintained at an appropriate level, and good workability can be maintained. (1-4) Other Additives The gypsum-based composition of this embodiment can further contain any additives.

[0037] The other additives include one or more selected from the group consisting of extenders, aggregates, and setting time adjusters.

[0038] Therefore, the gypsum-based composition of the present embodiment may further contain one or more selected from an extender, an aggregate, and a setting time adjuster.

[0039] Examples of the extender include one or more fillers selected from talc, magnesium silicate, magnesium carbonate, calcium carbonate, magnesium hydroxide, silica, anhydrous gypsum, etc. When the gypsum-based composition of the present embodiment contains an extender, the content thereof may be, for example, 1% by mass or more and 5% by mass or less.

[0040] Examples of the aggregate include one or more types selected from mica, vermiculite, diatomaceous earth, silica balloons (including shirasu balloons, perlite, etc.), glass microbeads, and polymer microspheres. When the gypsum-based composition of the present embodiment contains an aggregate, the content thereof may be, for example, 1% by mass or more and 5% by mass or less.

[0041] Examples of setting time adjusters include organic acids such as citric acid and tartaric acid, salts thereof, and higher fatty acids. That is, the setting time adjuster can be one or more selected from organic acids, organic acid salts, and higher fatty acids. When the gypsum-based composition of the present embodiment contains a setting time adjuster, the content thereof may be, for example, 0.05% by mass or more and 0.4% by mass or less.

[0042] The gypsum-based composition of the present embodiment may contain any additive other than the above-described extender, aggregate, and setting time adjuster. For example, the composition may contain one or more additives selected from a pH adjuster, a water repellent, a coloring pigment, a foaming agent, an antifoaming agent, an antifungal agent, a viscosity adjuster, a plasticizer, a lubricant, a slipping agent, and the like.

[0043] The gypsum-based composition of the present embodiment can enhance adhesiveness, cohesion, and water retention by combining polyvinyl alcohol and guar gum and incorporating them in an appropriate range. Therefore, the content of organic fibers such as methylcellulose, which have been added to conventional gypsum-based compositions to adjust their cohesion, can be sufficiently reduced. For example, the content of organic fibers such as methylcellulose can be reduced to 0.1% by mass or less. When the gypsum-based composition contains multiple types of organic fibers, the total content can be reduced to 0.1% by mass or less.

[0044] The gypsum-based composition of the present embodiment can exhibit sufficient adhesion and water retention properties even without containing organic fibers, so the gypsum-based composition of the present embodiment does not need to contain organic fibers. (2) Use form of the gypsum-based composition The gypsum-based composition of the present embodiment can be used by mixing with water to form a slurry. The blending ratio of water when forming the slurry is not particularly limited and can be selected taking into consideration workability, etc.

[0045] When the gypsum-based composition of this embodiment is made into a slip, for example, water can be blended and kneaded in a ratio of 30 parts by mass or more and 75 parts by mass or less per 100 parts by mass of the gypsum-based composition. Water may also be blended and kneaded in a ratio of 35 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the gypsum-based composition. (3) Characteristics of the Gypsum-Based Composition (3-1) Adhesion The gypsum-based composition of this embodiment can enhance adhesion by containing polyvinyl alcohol and guar gum in a predetermined content ratio. Adhesion can be evaluated as adhesive strength. Specifically, for example, the gypsum-based composition of this embodiment has an adhesive strength of 0.9 N / mm when bonded to a base material. ２ It may be more than that.

[0046] The upper limit of the adhesive strength of the gypsum-based composition of the present embodiment when adhered to a base material is not particularly limited, but is, for example, 2.0 N / mm ２ Therefore, the gypsum-based composition of the present embodiment has an adhesive strength of 0.9 N / mm when bonded to a base material. ２ 2.0N / mm or more ２(3-2) Regarding Water Retention, the gypsum-based composition of the present embodiment may have a water retention of 2.0% or less, or 0.0% or less, which is the rate of decrease in the diameter of the smallest encompassing circle of the region where water spreads from the slip onto the filter paper, when the slip is placed on filter paper after 0 minutes and 90 minutes have elapsed since being kneaded with water.

[0047] The lower limit of the water retention is not particularly limited, but may be, for example, −20.0% or more. Therefore, the water retention of the gypsum-based composition of the present embodiment may be −20.0% or more and 2.0% or less, or −20.0% or more and 0.0% or less.

[0048] The slip of the gypsum-based composition preferably has an appropriate fluidity to improve workability. Since the slip of the gypsum-based composition has an appropriate fluidity, the slip of the gypsum-based composition preferably contains excess water that has not reacted with components contained in the gypsum-based composition. The amount of such excess water can be evaluated by the water retention at 0 minutes after mixing the gypsum-based composition with water. Therefore, the water retention (0 min), which is the diameter of the smallest encompassing circle of the area where water spreads from the slip onto the filter paper at 0 minutes, may be 11 mm or more. (3-3) Regarding Adhesion: When two gypsum boards are bonded using the gypsum-based composition of this embodiment using a slip kneaded with water, the adhesive strength at 15 minutes after bonding is 0.50 N / cm ２ It may be 0.60 N / cm or more. ２ It may be more than that.

[0049] The upper limit of the adhesive strength is not particularly limited, but is, for example, 1.50 N / cm ２ Therefore, when the gypsum-based composition of the present embodiment is used to bond two gypsum boards together using a slip kneaded with water, the adhesive strength after 15 minutes from bonding may be 0.50 N / cm ２ 1.50N / cm or more ２ It may be 0.60 N / cm or less ２ 1.50N / cm or more ２ It may be the following:

[0050] Specific evaluation methods for the properties of adhesiveness, water retention, and pressure-sensitive adhesiveness will be described in the evaluation methods in the Examples. [Wall Structure] The gypsum-based composition according to one embodiment of the present disclosure can be used for a wall structure. Therefore, a configuration example of a wall structure including the gypsum-based composition according to one embodiment of the present disclosure will be described.

[0051] The wall structure of this embodiment can have, for example, the structure shown in Fig. 1. Fig. 1 is a side view of the wall structure 10 of this embodiment.

[0052] The wall structure 10 of this embodiment can have a base material 11, an architectural surface material 12 covering at least a portion of the surface 11A of the base material 11, and a gypsum-based composition 13 arranged between the base material 11 and the architectural surface material 12.

[0053] When manufacturing the wall structure of this embodiment, the gypsum-based composition according to one aspect of the present disclosure can be mixed with water to form a slip, and then applied to the surface 11A of the base material 11, such as a mortar or concrete structure. In this case, the slip of the gypsum-based composition may be applied so as to cover the entire surface 11A of the base material 11, or may be applied to the surface 11A of the base material 11 in the form of multiple balls, for example.

[0054] A primer may be applied to the surface 11A of the base material 11 of the wall structure 10 of this embodiment. That is, the primer may be disposed between the surface 11A of the base material 11 and the slip of the gypsum-based composition 13. Examples of the primer include one or more types selected from aqueous vinyl acetate emulsions, aqueous acrylic emulsions, and the like.

[0055] Then, by placing architectural facing 12 on the slurry of gypsum-based composition 13 applied to surface 11A of base material 11, architectural facing 12 is fixed onto base material 11, and wall structure 10 can be manufactured. Note that the slurry of gypsum-based composition 13 applied to surface 11A of base material 11 will dry and solidify over time after application.

[0056] The architectural facing 12 has a first surface 12A facing the base material 11 and a second surface 12B located opposite the first surface 12A. The second surface 12B can be placed, for example, on the indoor side, and the wall structure 10 can also be used as a member for dividing a room. A finishing material such as wallpaper can also be placed on the second surface 12B.

[0057] The architectural facing material 12 used in the wall structure 10 is not particularly limited, and examples thereof include fiber-reinforced cement boards, glass mat gypsum boards, gypsum-containing boards with glass fiber nonwoven fabrics, gypsum boards, gypsum boards, etc. The gypsum boards may be either gypsum boards defined in JIS A 6901 (2014) or gypsum boards that are lighter or heavier than gypsum boards defined in JIS A 6901 (2014).

[0058] Examples of the fiber reinforced cement board include slate boards, calcium silicate boards, and slag gypsum boards specified in JIS A 5430 (2004).

[0059] Glass mat gypsum board is a gypsum board in which at least the upper or lower surface of the gypsum core is covered with a glass mat as a covering material, for example.

[0060] The gypsum-containing board with nonwoven glass fiber fabric is, for example, a gypsum board in which nonwoven glass fiber fabric (glass tissue) as a covering material is embedded near at least the upper or lower surface of the gypsum core.

[0061] The gypsum board is, for example, a gypsum board in which at least the upper surface or the lower surface of a gypsum core is covered with a covering material, gypsum board base paper.

[0062] The wall structure of this embodiment uses a gypsum-based composition according to one aspect of the present disclosure. Therefore, when the architectural facing 12 is placed on the base material 11, the adhesiveness of the architectural facing 12 to the base material 11, i.e., the initial adhesive strength, can be sufficiently increased. Therefore, even after construction, the architectural facing 12 can be prevented from detaching, even until the gypsum-based composition solidifies. Furthermore, by increasing the adhesiveness of the gypsum-based composition, dripping of the gypsum-based composition slurry can be prevented during construction.

[0063] Furthermore, because the gypsum-based composition according to one embodiment of the present disclosure has excellent water retention properties, it is possible to prevent the gypsum-based composition slurry from losing moisture and drying or solidifying, even if a long time passes between when the gypsum-based composition slurry is applied to the base material 11 and when the architectural facing material 12 is fixed. This allows for greater flexibility in construction planning when manufacturing a wall structure using the gypsum-based composition of this embodiment.

[0064] Furthermore, the base material 11 and the building surface material 12 can be bonded together with sufficiently excellent adhesive strength.

[0065] Specific examples will be given below for explanation, but the present invention is not limited to these examples. (1) Evaluation Method First, the evaluation method for the gypsum-based compositions obtained in the following examples and comparative examples will be explained. (1-1) Adhesion Strength A test specimen 20 for an adhesion strength test shown in Figure 2 was prepared and evaluated.

[0066] First, a slurry 22 prepared by kneading a gypsum-based composition prepared in the following Examples and Comparative Examples with water was filled into an acrylic cylindrical container having an inner diameter of 31 mm and a height of 40 mm, and the upper part was scraped off.

[0067] Next, the gypsum-based composition slurry 22 filled in an acrylic cylindrical container was placed on the rectangular parallelepiped mortar test piece 21 having a thickness of 20 mm and a width and depth of 70 mm each. At this time, the gypsum-based composition slurry 22 was placed so that the scraped surface thereof faced the mortar test piece 21. Then, the acrylic cylindrical container was slowly pulled out.

[0068] The gypsum-based composition slip 22 placed on the mortar test piece 21 was crushed to a thickness T22 of 15 mm, and hardened at room temperature (23°C) for 24 hours. Thereafter, it was further dried to a constant weight at 40°C in the air.

[0069] A jig 24 for a tensile tester was bonded with epoxy resin 23 to a second surface 22B of the dried product 220 of the gypsum-based composition slurry 22, the second surface 22B being located opposite to a first surface 22A facing the mortar test piece 21, and the dried product was left to stand until the epoxy resin 23 hardened.

[0070] The adhesive strength of the obtained test specimen 20 was measured by holding the mortar test piece 21 and pulling the jig 24 along the Y axis, i.e., moving the jig 24 away from the mortar test piece 21, using an autograph.

[0071] The measured adhesive strength was 0.9 N / mm ２ In the above cases, it can be said that the gypsum-based composition has excellent adhesiveness. (1-2) Water Retention Test A test specimen 30 for the water retention test shown in Figure 3 was prepared and evaluated. Figure 3 is a cross-sectional view of the test specimen 30 for the water retention test, taken along a plane passing through the central axis of the gypsum-based composition slip 33.

[0072] First, filter paper 32 was placed on first glass plate 31A, and immediately after kneading, slip 33 of a gypsum-based composition was placed on filter paper 32. The slip 33 of the gypsum-based composition was placed on filter paper 32 by filling a slip ring 34, which was a cylindrical body with an inner diameter of 50 mm and a height of 10 mm, up to the level.

[0073] Next, a second glass plate 31B was further placed on the gypsum-based composition slip 33 to prepare a test specimen 30. The test specimen 30 was left standing for one hour, upside down from the case of Fig. 3. That is, the filter paper 32 and the first glass plate 31A were stacked in this order on the gypsum-based composition slip 33, and the test specimen 30 was left standing for one hour.

[0074] After one hour had passed, the filter paper 32 was collected, and the diameter of the smallest encompassing circle of the part of the filter paper 32 where the water had spread and absorbed was subtracted by 50 mm, which was the diameter of the area of ​​the test piece 30 where the slip 33 was placed on the filter paper 32, to obtain the evaluation result of water retention, specifically the evaluation result of water retention (0 min).

[0075] For the gypsum-based composition slip, the evaluation of water retention was performed under the same conditions and procedures as in the case of the water retention (0 min) above, except that the sample was changed to one obtained 90 minutes after kneading, and the evaluation result of water retention (90 min) was obtained.

[0076] The rate of decrease from water retention (0 min) to water retention (90 min) was calculated and taken as the water retention (decrease rate). When water retention (0 min) is W0 and water retention (90 min) is W90, the water retention (decrease rate) can be calculated using the following formula.

[0077] Water retention (loss rate) = [(W0 - W90) ÷ W0] × 100 If the measured water retention (loss rate) is 2.0% or less and the water retention (0 min) is 11 mm or more, it can be said that the gypsum-based composition has excellent water retention. (1-3) Adhesion A test specimen 40 for an adhesion test shown in Figure 4 was prepared and evaluated.

[0078] First, in a thermo-hygrostat chamber set at 35°C and a relative humidity of 60% RH, an acrylic cylindrical container having an inner diameter of 31 mm and a height of 40 mm was filled with a gypsum-based composition slurry 42 prepared in the following Examples and Comparative Examples.

[0079] Next, the gypsum-based composition slurry 42 filled in a cylindrical container was placed on the first gypsum board 41A, and after the cylindrical container was pulled out, it was left to stand for 20 minutes.

[0080] The gypsum-based composition slip 42 was pressed with a 150 mm square second gypsum board 41B so that the thickness T42 of the gypsum-based composition slip 42 was 5 mm, and the gypsum-based composition slip 42 was left to stand for 15 minutes.

[0081] Thereafter, the second gypsum board 41B was pulled along the Y axis in FIG. 4, i.e., so that the second gypsum board 41B moved away from the first gypsum board 41A, using a push-pull gauge, and the adhesive strength, which is the strength at which the second gypsum board 41B peeled from the gypsum-based composition slip 42, was measured.

[0082] The measured adhesive strength was 0.50 N / cm ２ In the above cases, it can be said that the gypsum-based composition has excellent adhesiveness. (2) Production conditions and evaluation results of gypsum-based compositionsThe production conditions and evaluation results of gypsum-based compositions in the examples and comparative examples are described below. [Example 1] Gypsum hemihydrate, polyvinyl alcohol, guar gum, calcium carbonate (extender), perlite (lightweight aggregate), and a setting time adjuster were weighed and mixed in the mass proportions shown in the "mixture" column of Table 1 to produce a gypsum-based composition.

[0083] The Blaine specific surface area of ​​the gypsum hemihydrate used as a raw material was measured using a Blaine air permeation apparatus described in JIS R 5201 (2015), and is shown in the "Blaine specific surface area" column of "Gypsum hemihydrate" in Table 1.

[0084] Water was added to the gypsum-based composition of this example so as to achieve the water mixing ratio shown in Table 1, and the resulting slurry was used to carry out the evaluations described above. The evaluation results are shown in Table 1.

[0085] The water mixing ratio corresponds to the standard water mixing ratio described in "5.2 Sample Mixing and Setting" of JIS A 6904 (1997) Gypsum Plaster.

[0086] Specifically, the water mixing ratio was determined by the following procedure.

[0087] A sample prepared by stirring a gypsum-based composition and water based on the premixed plaster primer described in Table 3 of JIS A 6904 (1997) was filled into a measurement container and the surface was smoothed. A Vicat needle stick (hollow aluminum, weighing 50 g) specified in JIS R 5201 (2015) was gently lowered onto the approximate center of the surface of the sample filled in the measurement container to measure the penetration depth. The standard softness was determined when the measured penetration depth reached a value of 6±1 mm, and the mass ratio of added water to 100 parts by mass of gypsum plaster, i.e., gypsum composition, at which the standard softness was achieved was defined as the water mixing ratio. [Examples 2 to 10] Gypsum-based compositions and slips were prepared under the same conditions as in Example 1, except that the mass ratios of the raw materials and the water mixing ratios when preparing the slips were set to the ratios shown in Table 1.

[0088] The evaluation results are shown in Table 1. [Comparative Examples 1 to 5] Gypsum-based compositions and slips were prepared under the same conditions as in Example 1, except that the mass proportions of the raw materials and the water mixing ratios when preparing the slips were set to the proportions shown in Table 1.

[0089] The evaluation results are shown in Table 1.

[0090] According to the results shown in Table 1, the gypsum-based compositions of Examples 1 to 10, which contain polyvinyl alcohol and guar gum in a predetermined mass ratio, have a water retention (loss rate) of 2.0% or less and an adhesive strength of 0.50 N / cm ２It was confirmed that the water retention (0 min) was 11 mm or more. In other words, it was confirmed that the gypsum-based compositions of Examples 1 to 10 were gypsum-based compositions excellent in water retention and adhesiveness.

[0091] In addition, the gypsum-based compositions of Examples 1 to 10 also had an adhesive strength of 0.9 N / mm ２ From the above, it was confirmed that the adhesion was sufficiently high and excellent.

[0092] In contrast, in Comparative Example 1, in which the mass proportion of polyvinyl alcohol exceeded 0.6 mass% and no guar gum was contained, the water retention (loss rate) was extremely high at 20.0%, confirming poor water retention.

[0093] The same tendency was also observed in Comparative Example 2, which did not contain guar gum, although the mass proportion of polyvinyl alcohol was 0.6 mass% or less.

[0094] On the other hand, in Comparative Examples 3 and 4, in which the mass proportion of polyvinyl alcohol was 0.6 mass% or less but an excessive amount of guar gum was added, it was confirmed that the water retention (0 min) was less than 11 mm. This is thought to be because the mass proportion of guar gum exceeded 0.1 mass%, reducing the amount of excess moisture contained in the gypsum-based composition slip that had not reacted with the components contained in the gypsum-based composition. For this reason, the workability of the gypsum-based composition slips of Comparative Examples 3 and 4 was reduced. Furthermore, it was confirmed that adhesion was reduced in Comparative Example 4, in which the amount of guar gum added was increased.

[0095] In Comparative Example 5, in which no polyvinyl alcohol was added, it was confirmed that the adhesive strength was low. [Notes] (1) A gypsum-based composition according to one embodiment of the present disclosure contains gypsum hemihydrate, polyvinyl alcohol, and guar gum, and contains the polyvinyl alcohol in an amount of 0.1 mass% or more and 0.6 mass% or less, and the guar gum in an amount of 0.02 mass% or more and 0.1 mass% or less. (2) In the above (1), when the Blaine specific surface area of ​​the gypsum hemihydrate is 3000 cm ２ / g or more 12000cm ２(3) In the above (1) or (2), it may further contain one or more selected from an extender, an aggregate, and a setting time adjuster. (4) In any of the above (1) to (3), the adhesive strength when bonded to a base material may be 0.9 N / mm ２ (5) A wall structure according to one aspect of the present disclosure includes a base material, a building surface material covering at least a portion of a surface of the base material, and a gypsum-based composition according to any one of (1) to (4) disposed between the base material and the building surface material.

[0096] The gypsum-based composition and the wall structure have been described above in terms of the embodiments, but 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.

[0097] This application claims priority based on Japanese Patent Application No. 2024-125459, filed with the Japan Patent Office on July 31, 2024, the entire contents of which are incorporated herein by reference.

[0098] REFERENCE SIGNS LIST 10 Wall structure 11 Base material 11A Surface 12 Building surface material 12A First surface 12B Second surface 13 Gypsum-based composition 20 Test specimen 21 Mortar test piece 22 Gypsum-based composition slip 220 Dried product 22A First surface 22B Second surface 23 Epoxy resin 24 Jig 30 Test specimen 31A First glass plate 31B Second glass plate 32 Filter paper 33 Gypsum-based composition slip 34 Slip ring 40 Test specimen 41A First gypsum board 41B Second gypsum board 42 Gypsum-based composition slip T42 Thickness

Claims

1. A gypsum-based composition containing gypsum hemihydrate, polyvinyl alcohol, and guar gum, wherein the polyvinyl alcohol is contained in an amount of 0.1% by mass or more and 0.6% by mass or less, and the guar gum is contained in an amount of 0.02% by mass or more and 0.1% by mass or less.

2. The Blaine specific surface area of ​​the hemihydrate gypsum is 3000 cm ２ / g or more 12000cm ２ / g or less.

3. The gypsum-based composition according to claim 1 or 2, further comprising one or more selected from the group consisting of extenders, aggregates, and setting time adjusters.

4. The adhesive strength when bonded to the base material is 0.9 N / mm ２ The gypsum-based composition according to claim 1 or claim 2.

5. A wall structure comprising: a base material; a building surface covering at least a portion of the surface of the base material; and the gypsum-based composition according to claim 1 or 2, disposed between the base material and the building surface.

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