HK1246768B - Gypsum hardened body and gypsum-based building material - Google Patents

Description

Gypsum hardener and gypsum-based building materials

This invention patent application is a divisional application filed for an application filed on May 21, 2013, with application number 201380047586.0 and invention name “Gypsum composition, gypsum slurry, gypsum hardened body, gypsum-based building materials, gypsum board, and method for manufacturing gypsum-based building materials”.

Technical Field

The present invention relates to a gypsum composition, gypsum slurry, gypsum hardened body, gypsum-based building materials, gypsum board, and a method for producing the gypsum-based building materials.

Background Art

Traditionally, gypsum-based building materials such as gypsum board, reinforced gypsum board, ordinary hard gypsum board, glass mat gypsum board, gypsum board with added glass fiber non-woven fabric, and slag gypsum board have been widely used due to their excellent properties such as fire resistance, sound insulation, construction efficiency, and cost-effectiveness.

This type of gypsum-based building materials is usually manufactured by adding water and the like to a gypsum composition that is pre-mixed with cooked gypsum and various additives, kneading the mixture with a mixer to form a gypsum slurry (gypsum mud), and then forming the gypsum slurry into a predetermined shape with board base paper, glass mat, or glass fiber non-woven fabric, followed by drying and cutting.

The lightness (or weight) of gypsum-based building materials is determined by the amount of gypsum and the amount of foam voids in the hardened gypsum, which is primarily used as the core material. Therefore, by reducing the amount of gypsum, and in other words, increasing the proportion of foam voids, the overall specific gravity of the gypsum-based building material can be reduced, thus achieving weight reduction.

However, if the specific gravity of the hardened gypsum that constitutes gypsum-based building materials decreases, its physical strength also decreases. Therefore, even for gypsum boards that use hardened gypsum as the core material and use board base paper as the surface material, or use hardened gypsum as the core material and use glass mat as the surface material, or use hardened gypsum as the core material and embed glass fiber nonwoven fabric (glass tissue) in the surface, if the specific gravity of the hardened gypsum as the core material is reduced, the strength of the gypsum board will also be weakened.

Patent Document 1 discloses an example in which, when foam is added to a gypsum slurry obtained by kneading a gypsum composition with water, the diameter of the added foam is increased and uniformed, and the shape is made into a good spherical shape, thereby forming a gypsum cured body with a low specific gravity.

However, even with the method disclosed in Patent Document 1, the strength of the gypsum cured body cannot be sufficiently improved.

Furthermore, studies have been conducted on the use of starch in order to improve the strength of hardened gypsum. For example, Patent Document 2 discloses an example in which the strength of hardened gypsum, which has a low specific gravity, is significantly improved by using pregelatinized starch.

However, when using pregelatinized starch, the foam added when producing a hardened gypsum with a low specific gravity becomes a mixture of larger and smaller foams, with the larger foams becoming deformed. This deformed foam is known to be a precursor to partial separation between the surface base paper and the hardened gypsum when forming a gypsum board, for example. This can lead to swelling on the gypsum board surface.

In addition, there is also the problem that the amount of water required for preparing the gypsum composition using water increases significantly due to the addition of pregelatinized starch, and the drying cost of the hardened gypsum increases.

Furthermore, even if the amount of α-starch added is increased, the strength-enhancing effect reaches a limit when the added amount exceeds a certain amount, and the starch cannot be fully applied to applications requiring both lightweighting and strength.

<Prior Art Literature>

<Patent Document>

Patent Document 1: (Japanese) Patent Application Publication No. 04-505601

Patent Document 2: (Japanese) Patent Publication No. 2008-543705

Summary of the Invention

<Technical Problems to be Solved by the Invention>

In view of the above-mentioned problems of the prior art, the present invention aims to provide a gypsum composition that can obtain a high-strength hardened gypsum without significantly increasing the amount of water added when preparing the gypsum slurry.

<Solutions for solving technical problems>

The present invention, for solving the above-mentioned problems, provides a gypsum composition comprising: plaster of Paris; and urea phosphate-esterified starch.

<Effects of the Invention>

According to the present invention, a gypsum composition can be provided that can obtain a high-strength hardened gypsum without significantly increasing the amount of water added when preparing a gypsum slurry.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is an explanatory diagram of a method for producing a gypsum board according to a third embodiment of the present invention.

FIG2 shows the relationship between the amount of starch added and the compressive strength in Example 2.

FIG3 is a SEM photograph of a cured gypsum body in a low-specific-gravity portion of the gypsum board of Example 3 (Sample No. 3-3).

FIG4 is a SEM photograph of a cured gypsum body in a low-specific-gravity portion of the gypsum board of Example 3 (sample No. 3-9).

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to the following embodiments, and various modifications and substitutions may be made to the following embodiments without departing from the scope of the present invention.

[First embodiment]

The gypsum composition and gypsum slurry (gypsum mud) according to this embodiment will be described.

The gypsum composition of this embodiment includes plaster of Paris and urea phosphate-esterified starch.

The gypsum slurry (gypsum mud) of the present embodiment is obtained by kneading the above-mentioned gypsum composition with water.

Plaster of Paris, also known as calcium sulfate 1/2 hydrate, is a hydraulically setting inorganic composition. Plaster of Paris can be made by calcining natural gypsum, byproduct gypsum, flue gas desulfurization gypsum, or other gypsums, either singly or in combination, in air, using β-hemihydrate gypsum; or α-hemihydrate gypsum, either singly or in combination, using calcination in water. Note that calcination in water includes calcination in steam.

The mixing ratio of the plaster of Paris and the urea phosphate-esterified starch is not particularly limited and can be selected based on the strength required when the gypsum composition is used as a hardened gypsum.

For example, in a gypsum composition, urea-phosphate starch is preferably included in a ratio of 0.2 parts by mass to 10 parts by mass per 100 parts by mass of gypsum. This is because if the ratio of urea-phosphate starch is less than 0.2 parts by mass, sufficient strength may not be achieved. In addition, since sufficient strength is achieved when the ratio of urea-phosphate starch is within the range of 10 parts by mass or less, including urea-phosphate starch in a ratio greater than 10 parts by mass may be unfavorable in terms of cost.

Furthermore, the gypsum composition preferably contains urea-phosphate starch in a ratio of 0.2 parts by mass to 5 parts by mass per 100 parts by mass of the plaster. This is because if the ratio of urea-phosphate starch exceeds 5 parts by mass, for example, a 12.5 mm thick gypsum board may not meet the requirements of Class 1 heat generation specified in JIS A 6901. When the gypsum composition is used as a gypsum-based building material, non-combustibility is often required as a performance factor, in addition to strength. Therefore, the amount of urea-phosphate starch added can be selected according to the needs.

In addition to gypsum and urea phosphate starch, various additives such as adhesive additives, reinforcing fibers and lightweight aggregates, refractory materials, setting regulators, water reducers, and foam diameter regulators may be added to the gypsum composition.

Next, gypsum slurry (gypsum mud) is prepared by kneading the gypsum composition described above in this embodiment with water. When preparing the gypsum slurry, the amount of water added to the gypsum composition is not particularly limited and can be selected based on the required fluidity, etc. Furthermore, various additives such as adhesive additives or foams may be added as needed.

The amount of water required to mix the gypsum composition with water to form a gypsum slurry (gypsum mud) does not change regardless of the presence or absence of urea phosphate starch. Consequently, the amount of heat required for drying does not change regardless of the presence or absence of urea phosphate starch, allowing for the production of a high-strength hardened gypsum without increasing drying costs.

When water, foam, or the like is added to the above-mentioned gypsum composition, kneaded, and hardened to produce a cured gypsum, the urea-phosphate-esterified starch contained in the gypsum composition has the function of increasing the strength of the cured gypsum. Therefore, the strength of the cured gypsum obtained using the gypsum composition can be increased.

Furthermore, when producing a gypsum cured body by adding foam to a gypsum slurry (gypsum mud), the urea-phosphated starch contained in the gypsum composition has the function of maintaining the shape of the foam in the gypsum slurry and the gypsum cured body.

Therefore, by adding bubbles having a substantially uniform diameter, the bubbles in the gypsum slurry (gypsum mud) are well spherical, and the shape of the bubbles in the gypsum hardened body can be kept in a good shape and can be made substantially uniform in diameter.

Furthermore, when the bubbles in the hardened gypsum body are well spherical in shape and have a substantially uniform diameter, in addition to the effect of reducing weight, the strength of the hardened gypsum body can be improved.

Furthermore, increasing the amount of urea-phosphate starch added tends to increase the strength of the resulting cured gypsum. Therefore, by adjusting the amount of urea-phosphate starch added, it is possible to achieve a lightweight yet high-strength cured gypsum.

As described above, the gypsum composition of the present embodiment can produce a gypsum slurry (gypsum mud) having target fluidity without significantly increasing the amount of water added, compared to a gypsum composition not containing urea phosphate starch.

Furthermore, when a hardened gypsum body is produced using the gypsum composition of the present embodiment, the strength of the hardened gypsum body can be improved due to the function of urea phosphate-esterified starch in the gypsum composition.

Furthermore, when foam is added during the production of cured gypsum, the urea-phosphate-esterified starch in the gypsum composition has the function of maintaining the shape of the added foam. Therefore, the shape and size of the foam contained in the cured gypsum can be well maintained, and the strength of the cured gypsum can be improved.

Therefore, according to the gypsum composition of this embodiment, a gypsum cured body that is both lightweight and high-strength can be obtained.

[Second embodiment]

In this embodiment, a gypsum cured body using the gypsum composition described in the first embodiment will be described.

The hardened gypsum body of the present embodiment is obtained by kneading the gypsum composition described in the first embodiment with water and then hardening the kneaded mixture.

Alternatively, a cured gypsum body may be obtained by kneading the gypsum composition described in the first embodiment with foam and water and then curing the mixture.

The foam here means fine foam to the extent that the quality of the gypsum-based building board is not impaired.

When adding foam, a foaming agent is pre-added to water, and air is injected while stirring to form foam. Furthermore, the foam can be mixed with a gypsum composition or water. Alternatively, a gypsum composition can be pre-mixed with water to produce a gypsum slurry (gypsum mud), and the foam can be added to the gypsum slurry. The foaming agent used to form the foam is not particularly limited, and examples thereof include sodium alkyl sulfate, alkyl ether sulfate, sodium alkylbenzene sulfonate, and polyoxyethylene alkyl sulfate.

Here, the mixing ratio of the gypsum composition, water, and foam when preparing the gypsum slurry (gypsum mud) by mixing the gypsum composition with water and, in some cases, foam as described in the first embodiment, is not particularly limited. The mixing ratio of the various components contained in the gypsum slurry (gypsum mud) can be selected based on the specific gravity and strength required for the hardened gypsum, the fluidity required for the gypsum slurry when manufacturing gypsum board, etc.

Furthermore, when producing gypsum slurry (plaster mud), in addition to the above-mentioned gypsum composition, water, and foam, various additives such as adhesive additives may be added as described in the first embodiment. These additives may be added based on the performance required for the gypsum slurry (plaster mud) or the hardened gypsum.

Examples of the adhesive auxiliary agent include known substances such as oxidized starch and polyvinyl alcohol (poval).

Examples of other additives include various water reducing agents, hardening regulators, foam diameter regulators, reinforcing fibers, and lightweight aggregates.

It should be noted that, among the various additives, solid additives may be added to the gypsum composition in advance, and liquid additives may be added to the water added to the gypsum composition in advance.

In this manner, the gypsum slurry (gypsum mud) obtained by kneading the gypsum composition, water, and, if necessary, foam can be formed into a predetermined shape and then hardened to produce a gypsum hardened body.

The specific gravity of the resulting cured gypsum can be selected based on, for example, the weight required for the gypsum-based building material, and is not particularly limited. However, since the lower the specific gravity of the cured gypsum, the lower the strength of the cured gypsum, the specific gravity of the cured gypsum is preferably 0.4 to 0.65. Furthermore, a specific gravity of 0.4 to 0.55 is more advantageous because the effects of the present invention, which achieve both lightweighting and increased strength, are more significantly achieved.

The specific gravity of the hardened gypsum can be adjusted to a desired specific gravity by adjusting the amount of foam added when producing the gypsum slurry (gypsum mud).

When foam is added to a cured gypsum body, the size of the foam contained in the cured gypsum body is not particularly limited. However, the average diameter of the foam contained in the cured gypsum body is preferably from 100 μm to 1000 μm. This is because by setting the average diameter of the foam contained in the cured gypsum body within this range, the strength of the cured gypsum body becomes higher than that of a cured gypsum body of the same weight without the addition of foam.

The average diameter of the bubbles contained in the cured gypsum is preferably from 200 μm to 800 μm, and most preferably from 200 μm to 600 μm. This is because the strength of the cured gypsum can be further improved by setting the average diameter of the bubbles within the above range.

Examples of methods for adjusting the diameter of the foam contained in the hardened gypsum to a desired size include a method of selecting the size of the foam using a foaming machine for foaming a foaming agent and a method of controlling the size of the foam using a foam diameter regulator.

Furthermore, the shape of the foam contained in the gypsum cured body is preferably a good spherical shape.

This is because the strength of the cured gypsum body can be improved by making the shape of the foam contained in the cured gypsum body into a good spherical shape.

Furthermore, the shape of the foam contained in the hardened gypsum is preferably a spherical (true spherical) or a shape close to a spherical shape. This is because when the shape of the foam contained in the hardened gypsum is a spherical or a shape close to a spherical shape, the strength of the hardened gypsum can be further improved.

As described in the first embodiment, the urea phosphate-esterified starch contained in the gypsum composition has the function of increasing the strength of the hardened gypsum and the function of maintaining the shape of the added foam.

Therefore, the gypsum hardened body described in this embodiment can be made into a high-strength gypsum hardened body by utilizing the function of urea phosphate-esterified starch itself, and when manufacturing gypsum slurry (gypsum mud), when at least good spherical foam is added, and more preferably, spherical or nearly spherical (roughly spherical) foam is added, the function of the shape of the foam contained in the gypsum hardened body can be utilized to further improve the strength of the gypsum hardened body.

Furthermore, the amount of water added when mixing a gypsum composition with water to form a gypsum slurry (gypsum mud) does not significantly change depending on the presence or absence of urea phosphate starch. Consequently, the amount of heat required for drying does not significantly change depending on the presence or absence of urea phosphate starch, allowing a high-strength hardened gypsum to be obtained without increasing drying costs.

Furthermore, increasing the amount of urea-phosphate starch added tends to increase the strength of the resulting cured gypsum. Therefore, by adjusting the amount of urea-phosphate starch added, a lightweight and high-strength cured gypsum can be produced.

[Third embodiment]

In this embodiment, a gypsum-based building material using the hardened gypsum described in the second embodiment as a core material will be described.

Here, the gypsum-based building material is not particularly limited as long as it is a gypsum-based building material having a hardened gypsum body as a core material as described in the second embodiment. Examples of the gypsum-based building material include plate-shaped gypsum-based building materials such as gypsum board, glass mat gypsum board, gypsum board with glass fiber non-woven fabric, and slag gypsum board, as well as block-shaped gypsum-based building materials.

Gypsum-based building materials can be produced, for example, by a production method including the following steps.

A step of kneading the gypsum composition described in the first embodiment with water to prepare a gypsum slurry (gypsum mud). At this time, the various additives described in the second embodiment may be added as needed.

Next, the step of adding foam to the gypsum slurry is performed. It should be noted that this step can be omitted when foam is not added to the gypsum slurry. Alternatively, this step can be omitted when foam is added, and the foam can be mixed with the gypsum composition and water during the above-mentioned mixing step.

Furthermore, the steps of shaping and hardening the gypsum-based building materials according to their respective shapes can include placing the aforementioned gypsum slurry (gypsum mud) between the surface materials, hardening the gypsum slurry, and using the hardened gypsum body as the core material. For example, if the intended gypsum-based building material is gypsum board, the steps of placing the aforementioned gypsum body (gypsum mud) between the board base papers, and hardening the gypsum body placed between the board base papers, can be included. In this way, a gypsum board can be produced with the hardened gypsum body described in the second embodiment as the core material.

Hereinafter, a production method example will be specifically described by taking a case where the gypsum-based building material is a gypsum board as an example.

FIG. 1 is a side view partially and schematically showing a formed gypsum board.

In the figure, board base paper (surface covering base paper) 11 serving as a surface material is conveyed along the production line from the right side to the left side.

The mixer 12 can be positioned at a predetermined location relative to the conveyor line, such as above or beside the conveyor line. The gypsum composition described in the first embodiment is mixed with water and, if necessary, additives such as a tackifier, a hardening regulator, and a water reducer to produce gypsum slurry (plaster mud). Furthermore, foam is added as needed through the gypsum slurry (plaster mud) dispensing ports 121, 122, and 125.

It should be noted that, in FIG1 , as described below, low-density and high-density gypsum slurries are produced using one mixer 12 , but two mixers may be provided for supplying high-density and low-density gypsum slurries, respectively.

In addition, although the mixer 12 is shown here as an example of a configuration capable of supplying high-density and low-density gypsum slurries, the present invention is not limited to this configuration. For example, one type of gypsum slurry may be produced and supplied to the base paper 1 for board use.

Next, the obtained high-density gypsum slurry 13 is supplied onto the front cover base paper 1 and the back cover base paper 16 on the upstream side in the conveying direction of the roll coater 15 through the delivery pipes 123 and 124 .

Here, 171, 172, and 173 represent the coating roller, the backup roller, and the grit removal roller, respectively. The gypsum slurry on the front-coating base paper 11 and the back-coating base paper 16 respectively reaches the spreading section of the roll coater 15 and is spread there. A thin layer of high-density gypsum slurry 13 and an edge region are formed on the front-coating base paper 11. Similarly, a thin layer of high-density gypsum slurry 13 is formed on the back-coating base paper 16.

The surface covering base paper 11 is conveyed as is, and the back covering base paper 16 is deflected by the deflection roller 18 in the direction of the conveying line of the surface covering base paper 11. In addition, both the surface covering base paper 11 and the back covering base paper 16 arrive at the forming machine 19. Here, low-density gypsum slurry 14 is supplied from the mixer 12 through the pipeline 126 between the thin layers formed on each base paper 11 and 16. A continuous laminated body with a three-layer structure consisting of the surface covering base paper 11, the low-density gypsum slurry 14, and the back covering base paper 16 is formed, and the laminated body reaches the rough cutting knife (not shown) while hardening. The rough cutting knife cuts the continuous laminated body into plate-like bodies of predetermined length, forming plate-like bodies composed of a core material mainly composed of gypsum covered by base paper, that is, semi-finished products of gypsum board. The roughly cut laminated body is further passed through a dryer (not shown) for forced drying, and then cut into products of predetermined length. In this way, gypsum board products can be manufactured.

The method for manufacturing a gypsum board is not limited to the method described above, and a method for manufacturing a gypsum board from one type of gypsum slurry may be employed, for example, by omitting the step of forming a thin layer of high-density gypsum slurry.

Specifically, gypsum slurry (gypsum mud) is supplied and deposited on a continuously conveyed surface-coated base paper (board base paper). The bottom paper is folded in along the score lines marked on its two end edges so that the gypsum slurry is drawn in. At this point, the back-coated base paper (board base paper), conveyed at the same speed, is superimposed on the gypsum slurry layer.

Next, the gypsum board is formed by passing through a forming machine for determining the thickness and width.

After the gypsum board is formed into a predetermined shape through the above steps, the target gypsum board can be manufactured by going through a rough cutting step, a drying step, a cutting step, etc., similar to the above-mentioned gypsum board manufacturing method.

Here, although gypsum board is used as an example, various gypsum-based building materials can be produced by replacing the base paper for the board as the surface material with glass fiber nonwoven fabric (glass face cloth) or glass mat, etc., and arranging them so as to be buried on the surface or near the surface.

Hereinbefore, the gypsum-based building material having the hardened gypsum body described in the second embodiment as a core material, particularly the gypsum board and the method for producing the same have been described.

According to the gypsum-based building material and the method for producing the gypsum-based building material, particularly the gypsum board and the method for producing the gypsum board, as described in the second embodiment, the strength can be improved by utilizing the function of the urea-phosphate-esterified starch contained in the gypsum composition as a raw material.

In addition, when manufacturing a gypsum cured body as a core material, the strength of the gypsum cured body as a core material can be improved by making the shape of the foam added to the gypsum slurry into a good spherical shape, or more preferably into a spherical shape or a shape close to a spherical shape.

Furthermore, when manufacturing gypsum-based building materials, the amount of water required to mix the gypsum composition with water to form the gypsum slurry (gypsum mud) does not significantly change depending on the presence or absence of urea-phosphate starch. Consequently, the amount of heat required for the drying step in manufacturing gypsum-based building materials does not significantly change depending on the presence or absence of urea-phosphate starch. Consequently, a high-strength hardened gypsum core material can be obtained without increasing drying costs. In other words, high-strength gypsum-based building materials can be obtained without increasing drying costs.

As described below, increasing the amount of urea-phosphate starch added increases the strength of the resulting gypsum-based building material. Therefore, by adjusting the amount of urea-phosphate starch added, it is possible to achieve both lightweighting and high-strength cured gypsum. Furthermore, since this cured gypsum serves as the core material, both lightweighting and increased strength can be achieved even for gypsum-based building materials.

<Example>

The following examples are given for illustration, but the present invention is not limited to these examples. (1) Evaluation method

The test methods of the gypsum composition, gypsum slurry (gypsum mud), gypsum hardened body, and gypsum board produced in the following examples are described.

(1-1) Flow test

A fluidity test was conducted on gypsum slurry (gypsum mud) which was a mixture of a gypsum composition and water.

The fluidity test is to allow gypsum slurry (gypsum mud) to flow into a cylinder with a diameter of 8.5 cm and a height of 4 cm until it is full. The cylinder is then quickly lifted vertically upwards to measure the diameter of the gypsum slurry. (1-2) Compressive strength test of hardened gypsum

The compressive strength of the prepared gypsum cured body was measured using an autograph (Model: AG-10KNI, manufactured by Shimadzu Corporation) at a loading speed of 3 mm/min.

(1-3) Compressive strength test of gypsum board

The center portion of a gypsum board produced under the following conditions was cut into a size of 4 cm×4 cm, and three sheets of the cut board were stacked to prepare a test piece.

The measurement conditions were the same as those in the test (1-2). Specifically, an autograph (manufactured by Shimadzu Corporation, model: AG-10KNI) was used and the load speed of the autograph was set to 3 mm/min.

(1-4) Confirmation of foam shape in gypsum board

The gypsum board was cut so that its cross section became a plane, and the cross section was observed using a scanning electron microscope (SEM).

(1-5) Fever test

The heat generation test was conducted in accordance with JIS A 6901:2009, and the total calorific value and the maximum heat generation rate within 20 minutes of heating were measured.

A square with a side size of 99 mm ± 1 mm was cut from the center of the gypsum board as a test piece. The test piece was maintained at a constant temperature of 23°C ± 2°C and a relative humidity of 50 ± 5% before the test.

(2) Experimental content

Experimental Examples 1 to 3 shown below were performed to evaluate the samples obtained by the above-mentioned evaluation method.

(Experimental Example 1)

In this experimental example, the fluidity value of a gypsum slurry using a gypsum composition was studied.

For each sample, gypsum compositions were prepared by mixing plaster of Paris, urea phosphate-esterified starch, or alpha-starch so as to have the compositions shown in Tables 1 and 2. In the table, Samples No. 1-1 to 1-5 are Examples, and Samples No. 1-6 to 1-11 are Comparative Examples.

As the plaster, plaster for drywall was used.

Each of the produced gypsum compositions was further kneaded with water to have the composition shown in Tables 1 and 2 to produce a gypsum slurry.

[Table 1]

[Table 2]

The kneading was performed by using a commercially available blender (model number: SM-R50 manufactured by SANYO) by adding the gypsum composition and then kneading for 15 seconds.

After the gypsum slurry is manufactured, the above-mentioned (1-1) fluidity test is performed. The results are shown together with Table 1. For the samples No. 1-1 to 1-5 as examples using urea phosphate-esterified starch, the fluidity values are not reduced or are less compared with the sample No. 1-6 to which no starch is added, showing a good fluidity value. On the other hand, the fluidity values of the comparative samples No. 1-7 to 1-11 mixed with alpha-starch are greatly reduced compared with the sample No. 1-6 to which no starch is added. In particular, for the comparative samples No. 1-10 and 1-11, there is no fluidity in the gypsum slurry (gypsum mud) and it is impossible to mix with a stirrer.

(Example 2)

In this example, gypsum cured bodies having various compositions were produced and evaluated.

A gypsum slurry prepared by mixing water and a hardening regulator with a gypsum composition containing plaster of Paris and urea-phosphate-esterified starch or α-starch, with the compositions shown in Tables 3 and 4, was poured into a 2-cm square mold and allowed to harden. After confirming that the gypsum slurry had hardened, it was removed from the mold and dried in a dryer set at 200°C for 20 minutes, then in a dryer set at 40°C until a constant weight was achieved. The specific gravity of the dried hardened gypsum was approximately 0.5.

In Tables 3 and 4, samples No. 2-1 to 2-5 are examples, and samples 2-6 to 2-11 are comparative examples.

Next, the compression strength test described in (1-2) above was performed on each of the obtained samples. The results are shown in Tables 3 and 4.

Samples No. 2-1 to 2-5 using urea phosphate starch also showed improved compressive strength compared to the added amount. On the other hand, Samples No. 2-7 to 2-11 using pregelatinized starch did not show any improvement in strength compared to when urea phosphate starch was added, and the difference became more significant as the added amount increased.

Figure 2 shows the relationship between the amount of starch added and the compressive strength for Samples Nos. 2-1 to 2-5 and 2-7 to 2-11. This indicates that, within the high blending ratio (5% or more relative to the plaster of Paris), the compressive strength of the samples using α-starch approaches its limit. However, the compressive strength of the samples using urea-phosphate starch does not reach its limit within the experimental range, and the compressive strength increases with the addition ratio. This suggests that urea-phosphate starch can be added to achieve the desired compressive strength.

[Table 3]

[Table 4]

(Example 3)

In this experimental example, gypsum boards using gypsum hardened bodies of various compositions as core materials were produced and evaluated.

Gypsum boards were produced using the following steps using a gypsum slurry prepared by mixing water, a hardening regulator, a water reducer, and an adhesion promoter with a gypsum composition containing the predetermined compositions shown in Tables 5 and 6, including plaster of Paris and urea-phosphate-esterified starch or α-starch. In Tables 5 and 6, Samples Nos. 3-1 to 3-5 are examples, and Samples 3-6 to 2-11 are comparative examples.

The manufacturing steps of the gypsum board will be described using FIG1 .

In FIG1 , a board base paper (surface covering base paper) 11 serving as a surface material is conveyed along a production line from the right side to the left side.

As shown in FIG1 , the mixer 12 can be positioned above or beside the conveyor line. In the single mixer 12, the gypsum composition described above is mixed with water, an adhesive enhancer, a hardening regulator, and other additives to produce gypsum slurry (plaster mud) in the composition shown in Tables 5 and 6. At this time, foam is added to the low-density gypsum slurry through the gypsum slurry (plaster mud) dispensing port 125 to adjust the specific gravity to the desired value.

In the mixer 12 , the obtained high-density gypsum slurry 13 is supplied to the front cover base paper 1 and the back cover base paper 16 via the extraction ports 121 , 122 and the delivery pipes 123 , 124 upstream of the roll coater 15 in the conveying direction.

The gypsum slurry on the front cover paper 11 and the back cover paper 16 respectively reaches the spreading section of the roll coater 15 and is spread there. A thin layer of high-density gypsum slurry 13 and an edge region are formed on the front cover paper 11. Similarly, a thin layer of high-density gypsum slurry 13 is formed on the back cover paper 16.

The front cover base paper 11 is conveyed as it is, and the back cover base paper 16 is turned by the turning roller 18 in the direction of the conveyance line of the front cover base paper 11 .

Then, both the surface-covering base paper 11 and the back-covering base paper 16 arrive at the forming machine 19. Here, low-density gypsum slurry 14 is supplied from the mixer 12 through a pipe 126 between the thin layers formed on each base paper 11 and 16. This forms a continuous three-layered stack of the surface-covering base paper 11, the low-density gypsum slurry 14, and the back-covering base paper 16. This stack hardens and arrives at a rough cutter (not shown). The rough cutter cuts the continuous stack into plates of predetermined lengths, forming plates composed primarily of gypsum covered with base paper as a core material—the semi-finished gypsum board.

The roughly cut laminated body is further passed through a dryer (not shown) to be forcedly dried and then cut into products of a predetermined length. In this way, gypsum board products can be manufactured.

The gypsum board produced in the above-mentioned production steps was molded so as to have a thickness of 12.5 mm.

The base paper used for the board, both for the front and back covers, was 200 g/ ^m² . The gypsum slurry used as the raw material for the gypsum board was prepared by mixing 70% calcining water, 0.5% adhesion promoter, 1% hardening regulator, 0.3% water reducer, and urea phosphate-esterified starch or pregelatinized starch in predetermined amounts per 100 parts by mass of gypsum, as shown in Tables 5 and 6. Foam was further added to the low-density gypsum slurry to achieve a specific gravity of 0.5.

Next, test pieces were prepared using slices of gypsum board of predetermined dimensions cut from the center of the manufactured gypsum board, and the tests described in (1-3) to (1-5) were performed. Furthermore, the foam shape in the gypsum board (1-4) was confirmed using test pieces No. 3-3 and No. 3-9, which had 3% urea-phosphate starch or α-starch added. Furthermore, the heat generation test (1-5) was confirmed using test pieces No. 3-1 to 3-5, which had urea-phosphate starch added.

The results are shown in Tables 5 and 6. The compressive strengths of the test pieces of Samples No. 3-1 to 3-5, which were made from gypsum board sheets produced using urea phosphate-esterified starch, were higher than the compressive strengths of the test pieces of Samples No. 3-6 to 3-11, which were made from gypsum board sheets produced using the same amount of α-starch.

Furthermore, even in this example, at high mixing amounts (5% or more relative to plaster of Paris), the compressive strength improvement of the test specimens using α-starch approached its limit, while that of the test specimens using urea-phosphate starch did not reach this limit. In other words, this indicates that urea-phosphate starch can be added depending on the desired compressive strength.

In the heat generation test, in the gypsum boards of Samples No. 3-1 to 3-5 using urea phosphate starch, when the blending amount of urea phosphate starch was 5.0 parts by mass or less per 100 parts by mass of gypsum, the total calorific value was 8.0 MJ/m² and the maximum heat generation rate was 100 kW/ ^m² . Even when using board base paper with a relatively large mass per unit area, the conditions for heat generation class 1 as defined in JIS A 6901 were met.

SEM photographs of the cured gypsum in the low-density portion (low-density portion) of the gypsum boards of Samples No. 3-3 and No. 3-9 are shown in Figures 3 and 4. Figure 3 is an SEM photograph of Sample No. 3-3, and Figure 4 is an SEM photograph of Sample No. 3-9.

Therefore, compared to the foams of sample No. 3-3 mixed with urea phosphate starch, which remained roughly spherical and had a roughly uniform diameter, sample No. 3-9 mixed with alpha-starch had deformed foams and a mixture of foams with large diameters and foams with small diameters, which was a dangerous state with a high possibility of expansion on the gypsum board surface.

[Table 5]

[Table 6]

This international application claims the benefit of priority from Japanese Patent Application No. 2012-200953, filed on September 12, 2012, the entire contents of which are hereby incorporated by reference.

Claims (8)

1. A gypsum hardened body, which is a gypsum hardened body obtained by hardening a gypsum paste comprising calcined gypsum, urea-phosphated starch, and water. The gypsum slurry contains urea-phosphated starch in a ratio of 0.2 to 10 parts by weight relative to 100 parts by weight of the calcined gypsum. 2. The gypsum hardened body according to claim 1, wherein the gypsum slurry further contains foam. 3. The gypsum hardened body according to claim 1 or 2, wherein the specific gravity of the gypsum hardened body is 0.4 or more and 0.65 or less. 4. A gypsum-based building material, wherein the gypsum-based building material is a gypsum-based building material with the gypsum hardened body as the core material as described in any one of claims 1 to 3. 5. A gypsum hardened body, which is a gypsum hardened body obtained by hardening a gypsum slurry comprising calcined gypsum, urea-phosphated starch, foam and water. 6. The gypsum hardened body according to claim 5, wherein the specific gravity of the gypsum hardened body is 0.4 or more and 0.65 or less. 7. A gypsum-based building material, wherein the gypsum hardened body as described in claim 5 or 6 is used as the core material. 8. The gypsum-based building material according to claim 7, wherein the gypsum-based building material is gypsum board.