Swelling-delayed granules and swelling-delayed composite granules

Abstract

The present invention provides swelling-delaying granules and swelling-delaying composite granules that exhibit excellent delay in the onset of swelling of swelling-type granules. [Solution] The swelling-delaying granules comprise swelling granules having swelling properties in water and an external dimension of 10.0 mm or more, and a laminated structure layer formed by repeating at least once in this order a swelling-delaying layer that covers the surface of the swelling granules and delays the start of swelling of the swelling granules, and a non-swelling powder layer consisting of a plurality of non-swelling powders.

Description

Technical Field

[0001] The present invention relates to swelling-delay granules and swelling-delay composite granules.

Background Art

[0002] As a material for closing an excavation hole filled with groundwater, it has been considered to use bentonite pellets (hereinafter also simply referred to as pellets) obtained by granulating bentonite having the property of swelling when it comes into contact with water. Such pellets are also used as a countermeasure against muddy water leakage in boring work, like the water-blocking granulated material of Patent Document 1.

[0003] The excavation hole to be closed is assumed to reach several hundred to one thousand meters or deeper underground. Therefore, at the time of closing construction, instead of freely dropping the pellets from the hole opening on the ground, it has been considered to transport the pellets to the deep underground using a device called a dump bailer and emit the pellets at a predetermined construction location.

[0004] However, in the water-blocking granulated material of Patent Document 1, it is not possible to sufficiently delay the start of swelling of swelling granules such as bentonite in water.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide swelling-delay granules and swelling-delay composite granules having excellent delay properties in the start of swelling of swelling granules.

Means for Solving the Problems

[0007] [1] Swelling-delaying granules comprising swelling granules having the property of swelling in water and having an external dimension of 10.0 mm or more, and a laminated structure layer having a swelling-delaying layer covering the surface of the swelling granules and delaying the start of swelling of the swelling granules, and a non-swelling powder layer consisting of a plurality of non-swelling powders, repeated in this order at least once. [2] The swelling-delaying granules described in [1] above, wherein the swelling-delaying granules are composed of a bentonite-based material. [3] The swelling retarding granules according to [1] or [2] above, wherein the swelling retarding layer is composed of shellac or polyvinyl alcohol. [4] The non-swelling powder is a swelling-delaying granular material according to any one of [1] to [3] above, composed of kaolin clay. [5] A swelling-delay composite granule comprising a plurality of first swelling-delay granules and a plurality of second swelling-delay granules, wherein the first swelling-delay granules comprises a first swelling granule having swelling properties in water and an external dimension of 10.0 mm or more, and a laminated structure layer comprising a first swelling-delay layer covering the surface of the first swelling granules and delaying the start of swelling of the first swelling granules, and a non-swelling powder layer consisting of a plurality of non-swelling powders, repeated in this order at least once, and the second swelling-delay granules comprises a second swelling granule having swelling properties in water and an external dimension of 1.0 mm or more and 5.0 mm or less, and a second swelling-delay layer covering the surface of the second swelling granules and delaying the start of swelling of the second swelling granules. [6] The swelling-delayed composite granules described in [5], wherein each of the first swelling-delayed granules and the second swelling-delayed granules is composed of a bentonite-based material. [7] The swelling-delayed composite granules according to [5] or [6], wherein each of the first swelling-delayed layer and the second swelling-delayed layer is composed of shellac or polyvinyl alcohol. [8] The non-swelling powder is a swelling-delayed composite granule according to any one of [5] to [7] above, comprising kaolin clay. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide swelling-delaying granules and swelling-delaying composite granules that exhibit excellent delay in the initiation of swelling of swelling granules. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a digital camera photograph of the bentonite granules after drying the shellac solution in Comparative Example 1. [Modes for carrying out the invention]

[0010] The following will provide a detailed explanation based on the embodiments.

[0011] The inventors of this invention have diligently conducted research on the following matters.

[0012] Regarding the construction of sealing boreholes filled with groundwater, the inventors investigated the use of a dump bailinger to transport swelling-delaying granular material and swelling-delaying composite granular material (hereinafter, these granular materials are collectively referred to as swelling-delaying granular material, etc.) to deep underground, and then discharged the swelling-delaying granular material, etc. at a predetermined construction site in the borehole. The inventors found that transporting the swelling-delaying granular material, etc. while submerged in water is effective.

[0013] Based on these findings, we investigated a sealing technology for swelling-delay granules that delays the start of swelling of swelling-delay granules during transport by dump baler, and allows the swelling of the swelling-delay granules to begin after they are released into the borehole. We then investigated two methods for applying a coating to swelling granules that temporarily delays the start of swelling.

[0014] First, we considered a method using a coating machine. Multiple swellable granules were placed in the drum of the coating machine, and while the drum rotated, a coating liquid containing a substance that delays the onset of swelling of the swellable granules was sprayed into the drum from a nozzle. By drying the coating liquid while the multiple swellable granules flowed, multiple swelling-delayed granules were produced in which the surface of the swellable granules was coated with a swelling-delaying layer.

[0015] As a result, it was found that when swellable granules with external dimensions smaller than the specified size were used, a swelling retardation layer was formed over the entire surface of the swellable granules, and therefore the resulting swellable granules had an excellent swelling retardation effect. On the other hand, when swellable granules with external dimensions larger than the specified size were used, a swelling retardation layer was not formed over the entire surface of the swellable granules, and there were exposed parts of the swellable granules, so the resulting swellable granules did not have an excellent swelling retardation effect.

[0016] Secondly, a manual method was considered. Multiple swelling-delayed granules were produced by immersing multiple swelling granules in a coating solution, removing them, and then drying the coated swelling granules while keeping them separated and without contact with each other.

[0017] As a result, it was found that the obtained swelling-delaying granules, regardless of their external dimensions, possessed an excellent swelling-delaying effect. However, manual coating is extremely inefficient due to its low labor cost. In particular, the process of separating multiple swellable granules coated with the coating liquid without allowing them to come into contact with each other is a bottleneck in improving work efficiency. Furthermore, if multiple swellable granules coated with the coating liquid are dried in a state of so-called aggregation, the swelling-delaying layer may peel off from the surface of the swellable granules when the resulting swelling-delaying granules are separated after drying.

[0018] Therefore, the problems of manual coating were further studied. As a result, after removing the swellable granules from the coating solution, by dusting the surface with non-swellable powder before the separation operation, the viscosity caused by the coating solution on the surface of the swellable granules after removal is reduced. Therefore, the agglomeration of the swellable granules after dusting the non-swellable powder on the surface can be significantly suppressed. Even if the swellable granules are agglomerated, the separation operation of the agglomerated swellable granules is labor-saving, and it has been found that the efficiency of the coating operation is improved. Furthermore, it has been found that the swellable delayed granules obtained by drying the coating solution thereafter have an excellent swellable delay effect. The present invention has been completed based on the above findings.

[0019] The swellable delayed granules of the present invention include a swellable granule having a swelling property with respect to water and an outer dimension of 10.0 mm or more, a swellable delay layer covering the surface of the swellable granule and delaying the start of swelling of the swellable granule, and a laminated structure layer formed by repeating at least once in this order a non-swellable powder layer composed of a plurality of non-swellable powders.

[0020] The swellable delayed composite granules of the present invention include a plurality of first swellable delayed granules and a plurality of second swellable delayed granules. The first swellable delayed granule includes a first swellable granule having a swelling property with respect to water and an outer dimension of 10.0 mm or more, a first swellable delay layer covering the surface of the first swellable granule and delaying the start of swelling of the first swellable granule, and a laminated structure layer formed by repeating at least once in this order a non-swellable powder layer composed of a plurality of non-swellable powders. The second swellable delayed granule includes a second swellable granule having a swelling property with respect to water and an outer dimension of 1.0 mm or more and 5.0 mm or less, and a second swellable delay layer covering the surface of the second swellable granule and delaying the start of swelling of the second swellable granule.

[0021] First, the swellable delayed granules of the present invention will be described.

[0022] The swellable delayed granules of the present invention include a swellable granule and a laminated structure layer.

[0023] The swellable granules constituting the swelling-delayed granules have the property of swelling in water. Therefore, swelling begins rapidly when the swellable granules come into contact with water. From the viewpoint of good swelling in water, it is preferable that the swellable granules are composed of a bentonite-based material.

[0024] Bentonite-based materials consist solely of bentonite, or of bentonite and other materials.

[0025] When a bentonite-based material is said to consist solely of bentonite, it means that the swellable granules are composed solely of bentonite. Furthermore, when a bentonite-based material is said to consist of bentonite and other substances, it means that the swellable granules are composed of bentonite and other substances. As long as the granules swell well in water, the types of substances other than bentonite included in the swellable granules are not particularly limited.

[0026] Furthermore, the external dimensions of the swellable granules are 10.0 mm or larger. When the external dimensions are within the above range, the swellable granules are easy to handle, and the swelling-delayed granules can be efficiently manufactured by hand, resulting in excellent delay in the onset of swelling of the swellable granules. In addition, the external dimensions of the swellable granules are preferably 30.0 mm or less, more preferably 25.0 mm or less. When the external dimensions are within the above range, the delay in the onset of swelling of the swellable granules can be further improved.

[0027] The external dimensions of a swellable granular material refer to its maximum external dimensions.

[0028] The laminated structural layer constituting the swelling-delayed granules covers the entire surface of the swelling granules. The laminated structural layer consists of a swelling-delayed layer and a non-swelling powder layer, repeated at least once in this order from the swelling granule side. The layer located closest to the swelling granules in the laminated structural layer, that is, the layer covering the entire surface of the swelling granules, is the swelling-delayed layer, not the non-swelling powder layer. Thus, the laminated structural layer comprises a swelling-delayed layer and a non-swelling powder layer, with the swelling-delayed layer and the non-swelling powder layer laminated in this order from the swelling granule side.

[0029] The swelling-delaying layer constituting the laminated structure delays the onset of swelling of the swellable granules. Since the swelling-delaying layer covers at least the surface of the swellable granules, it inhibits contact between the swellable granules and water, thereby delaying the onset of swelling of the swellable granules. However, the swelling-delaying layer does not completely prevent the swelling of the swellable granules, but rather delays the onset of swelling of the swellable granules by a predetermined time.

[0030] From the viewpoint of delaying the onset of swelling of swellable granular material, the swelling delay layer is preferably composed of shellac or polyvinyl alcohol.

[0031] The non-swelling powder layer constituting the laminated structure consists of multiple non-swelling powders. During the production of swelling-delayed granules, the non-swelling powder layer suppresses the aggregation of multiple swelling granules to which the swelling-delaying layer coating liquid has been applied, and further improves the effect of delaying the start of swelling in the swelling granules. The external dimensions of the non-swelling powders are significantly smaller than those of the swelling granules.

[0032] From the viewpoint of suppressing the aggregation of multiple swellable granular materials to which a swelling delay layer coating liquid has been applied, and improving the effect of delaying the onset of swelling in the swellable granular materials, it is preferable that the non-swellable powder be composed of kaolin clay.

[0033] If the swelling-delayed granules remain in water for a predetermined time or longer without swelling of the swelling-delayed granules, the swelling-delayed layer and the non-swelling powder layer will be damaged or detached from the swelling-delayed granules due to water pressure or deterioration over time, resulting in defects in the swelling-delayed layer and the non-swelling powder layer. When water penetrates the swelling-delayed granules through the defects in the swelling-delayed layer and the non-swelling powder layer, the swelling-delayed granules come into contact with the water and begin to swell.

[0034] Thus, the time from when the swelling-delayed granules come into contact with water until the swelling granules come into contact with water can be delayed by the swelling-delayed layer and the non-swelling powder layer. Therefore, the swelling-delayed layer and the non-swelling powder layer can delay the swelling initiation time of the swelling granules. In this way, the swelling initiation time of the swelling-delayed granules in water can be delayed.

[0035] The number of layers (number of stacks) of the swelling-delaying layer and the non-swelling powder layer that constitute the laminated structure is set appropriately according to the application of the swelling-delaying granules.

[0036] Such swelling-delaying granules are particularly suitable as a material for sealing boreholes because they exhibit excellent delay in the onset of swelling of swelling granules. The borehole diameter is, for example, about 160 mm.

[0037] Next, we will explain the method for producing swelling-delayed granules.

[0038] As an example, multiple swellable granules are immersed in a coating solution containing a dissolved or dispersed substance that constitutes the swelling-delaying layer, and then removed. At this time, excess coating solution is wiped off. Next, multiple non-swellable powders are sprinkled over the entire surface of the swellable granules coated with the coating solution. In this way, aggregation of the multiple swellable granules is suppressed, and the effect of delaying the start of swelling on the swellable granules is further improved. Subsequently, if the multiple swellable granules sprinkled with non-swellable powders have aggregated, the multiple swellable granules are separated, and then the coating solution is dried to produce swelling-delaying granules.

[0039] Preferred methods for coating with non-swelling powder include transferring the swelling granules removed from the coating solution to a container such as a tray, and then coating the swelling granules with non-swelling powder on top of the container, or placing the swelling granules and non-swelling powder removed from the coating solution into a plastic bag and shaking the bag.

[0040] Next, the swelling-delayed composite granules of the present invention will be described.

[0041] The swelling-delayed composite granules of the present invention comprises a plurality of first swelling-delayed granules and a plurality of second swelling-delayed granules.

[0042] The first swelling-delayed granules contained in the swelling-delayed composite granules comprise a first swelling-prone granule and a laminated structure layer.

[0043] The first swelling granules constituting the first swelling-delayed granules have swelling properties in water. Therefore, the first swelling granules begin to swell rapidly upon contact with water. From the viewpoint of good swelling in water, it is preferable that the first swelling granules are composed of a bentonite-based material.

[0044] Furthermore, the external dimensions of the first swelling granules are 10.0 mm or larger. When the external dimensions are within the above range, the handling of the first swelling granules is good, and the first swelling-delayed granules can be efficiently manufactured by hand, resulting in excellent delay in the start of swelling of the first swelling granules. In addition, the external dimensions of the first swelling granules are preferably 30.0 mm or less, more preferably 25.0 mm or less. When the external dimensions are within the above range, the delay in the start of swelling of the first swelling granules can be further improved.

[0045] The laminated structural layer constituting the first swelling-delayed granules covers the entire surface of the first swelling-delayed granules. The laminated structural layer consists of the first swelling-delayed layer and the non-swelling powder layer, repeated at least once in this order from the side of the first swelling-delayed granules. The layer located closest to the first swelling-delayed granules in the laminated structural layer, that is, the layer covering the entire surface of the first swelling-delayed granules, is the first swelling-delayed layer, not the non-swelling powder layer. Thus, the laminated structural layer comprises the first swelling-delayed layer and the non-swelling powder layer, and the first swelling-delayed layer and the non-swelling powder layer are laminated in this order from the side of the first swelling-delayed granules.

[0046] The first swelling-delaying layer, which constitutes the laminated structure layer, delays the start of swelling of the first swelling-delaying granules. Since the first swelling-delaying layer covers at least the surface of the first swelling-delaying granules, it inhibits contact between the first swelling-delaying granules and water, thereby delaying the start of swelling of the first swelling-delaying granules. However, the first swelling-delaying layer does not completely prevent the swelling of the first swelling-delaying granules, but rather delays the start of swelling of the first swelling-delaying granules by a predetermined time.

[0047] From the viewpoint of delaying the initiation of swelling of the first swelling granules, the first swelling delay layer is preferably composed of shellac or polyvinyl alcohol.

[0048] The non-swelling powder layer constituting the laminated structure consists of multiple non-swelling powders. During the production of the swelling-delayed composite granules, the non-swelling powder layer suppresses the aggregation of multiple first swelling granules to which the coating liquid of the first swelling-delaying layer has been applied, and further improves the effect of delaying the start of swelling in the first swelling granules. The external dimensions of the non-swelling powders are significantly smaller than the external dimensions of the first swelling granules.

[0049] From the viewpoint of suppressing the aggregation of multiple first swellable granules coated with the first swelling delay layer coating liquid, and improving the effect of delaying the start of swelling in the first swellable granules, it is preferable that the non-swellable powder be composed of kaolin clay.

[0050] If the first swelling-delayed granules remain in water for a predetermined time or longer without swelling of the first swelling-delayed granules, the first swelling-delayed layer and the non-swelling powder layer will be damaged or detached from the first swelling-delayed granules due to water pressure or deterioration over time, resulting in defects in the first swelling-delayed layer and the non-swelling powder layer. When water penetrates the first swelling-delayed layer and the non-swelling powder layer through these defects, the first swelling-delayed granules come into contact with the water, and swelling of the first swelling-delayed granules begins.

[0051] Thus, the time from when the first swelling-delayed granules come into contact with water until the first swelling-resistant granules come into contact with water can be delayed by the first swelling-delayed layer and the non-swelling powder layer. Therefore, the first swelling-delayed layer and the non-swelling powder layer can delay the swelling start time of the first swelling-resistant granules. In this way, the swelling start time of the first swelling-delayed granules in water can be delayed.

[0052] The number of layers of the first swelling-delaying layer and the non-swelling powder layer constituting the laminated structure is set appropriately according to the application of the swelling-delaying composite granules.

[0053] The second swelling-delayed granules contained in the swelling-delayed composite granules comprise a second swelling-resistant granule and a second swelling-delayed layer.

[0054] The second swelling granules constituting the second swelling-delayed granules have swelling properties in water. Therefore, the second swelling granules begin to swell rapidly upon contact with water. From the viewpoint of good swelling in water, it is preferable that the second swelling granules are composed of a bentonite-based material.

[0055] Furthermore, regarding the external dimensions of the second swelling granules, the lower limit is 1.0 mm or more, preferably 2.0 mm or more, and the upper limit is 5.0 mm or less, preferably 4.0 mm or less. When the external dimensions of the second swelling granules are 1.0 mm or more, the handling properties of the second swelling granules are good, and the delay in the start of swelling of the second swelling granules is excellent. Also, when the external dimensions of the second swelling granules are 5.0 mm or less, it is possible to manufacture second swelling-delayed granules with excellent delay in the start of swelling of the second swelling granules using a coating machine, resulting in a high production rate and efficiency. When the external dimensions of the second swelling granules exceed 5.0 mm, if the second swelling delay granules are manufactured mechanically using a coating machine, the external dimensions of the second swelling granules are too large, resulting in unevenness in the second swelling delay layer on the surface of the second swelling granules. As a result, there are exposed areas on the surface of the second swelling granules where the second swelling delay layer is not formed, and therefore the effect of delaying the start of swelling of the second swelling granules is insufficient.

[0056] The second swelling-delaying layer, which constitutes the second swelling-delaying granules, covers the entire surface of the second swelling-delaying granules and delays the start of swelling of the second swelling-delaying granules. Because the second swelling-delaying layer covers the surface of the second swelling-delaying granules, it inhibits contact between the second swelling-delaying granules and water, thereby delaying the start of swelling of the second swelling-delaying granules. However, the second swelling-delaying layer does not completely prevent swelling of the second swelling-delaying granules, but rather delays the start of swelling of the second swelling-delaying granules by a predetermined time.

[0057] From the viewpoint of delaying the initiation of swelling of the second swelling granules, the second swelling delay layer is preferably composed of shellac or polyvinyl alcohol.

[0058] If the second swelling-delayed granules remain in water for a predetermined time or longer without the second swelling-delayed granules swelling, the second swelling-delayed layer may be damaged or detached from the second swelling-delayed granules due to water pressure or deterioration over time, resulting in a defect in the second swelling-delayed layer. When water then penetrates the second swelling-delayed granules through the defect in the second swelling-delayed layer, the second swelling-delayed granules come into contact with the water, and swelling of the second swelling-delayed granules begins.

[0059] Thus, the second swelling-delaying layer can delay the time from when the second swelling-delaying granules come into contact with water until when the second swelling-resistant granules come into contact with water. Therefore, the second swelling-delaying layer can delay the swelling initiation time of the second swelling-resistant granules. In this way, the swelling initiation time of the second swelling-delaying granules in water can be delayed.

[0060] Such swelling-delaying composite granules are particularly suitable as a material for sealing boreholes because they exhibit excellent delay in the initiation of swelling of the first and second swelling granules. The borehole diameter is, for example, about 160 mm.

[0061] Next, we will explain the method for producing a swelling-delayed composite granule.

[0062] As an example of a first swelling-delayed granule, multiple first swelling granules are immersed in a coating solution in which the substance constituting the first swelling-delayed layer is dissolved or dispersed, and then removed. At this time, excess coating solution is wiped off. Next, multiple non-swelling powders are sprinkled over the entire surface of the first swelling granules coated with the coating solution. In this way, aggregation of the multiple first swelling granules is suppressed, and the effect of delaying the start of swelling of the first swelling granules is further improved. Subsequently, if the multiple first swelling granules sprinkled with non-swelling powders have aggregated, the multiple first swelling granules are separated, and then the coating solution is dried to produce the first swelling-delayed granule.

[0063] Preferred methods for coating with non-swelling powder include transferring the first swelling granules removed from the coating solution to a container such as a tray, and then coating the first swelling granules with non-swelling powder on the container, or placing the first swelling granules and non-swelling powder, removed from the coating solution, into a plastic bag and shaking the bag.

[0064] As an example of a second swelling-delaying granule, multiple second swelling-delaying granules can be produced by placing them into the drum of a coating machine, and while the drum is rotating, spraying a coating liquid containing the dissolved or dispersed substances that make up the second swelling-delaying layer into the drum from a nozzle. This allows the coating liquid to dry while the multiple second swelling-delaying granules are flowing, thereby producing multiple second swelling-delaying granules in which the surface of the second swelling-delaying granules is coated with a second swelling-delaying layer.

[0065] Then, by mixing the first swelling-delayed granules and the second swelling-delayed granules, a swelling-delayed composite granule can be produced.

[0066] Although embodiments have been described above, the present invention is not limited to the embodiments described above, and includes all aspects included in the concepts and claims of this disclosure, and can be modified in various ways within the scope of this disclosure. [Examples]

[0067] Examples and comparative examples will be described next, but this disclosure is not limited to these examples.

[0068] (Example 1) Swelling-delay granules, in which the swelling-delay layer is composed of polyvinyl alcohol, were manufactured manually. Specifically, the process was as follows:

[0069] Granular, swellable granular material (ellipsoidal) consisting solely of bentonite, with an external dimension of 10.0 mm to 25.0 mm, was immersed in a polyvinyl alcohol solution and immediately removed from the solution. At this time, if any excess polyvinyl alcohol solution was present, it was wiped off. Next, kaolin clay powder was sprinkled over the entire surface of the swellable granular material coated with the polyvinyl alcohol solution. Subsequently, if multiple swellable granular materials coated with kaolin clay had aggregated, the multiple swellable granular materials were separated, and then the swellable granular material was placed in a drying oven with the temperature controlled at 80°C to dry the polyvinyl alcohol solution. In this way, a swelling-delayed granular material was obtained.

[0070] Observation of the obtained swelling-delayed granules revealed that the entire surface of the bentonite granules was coated with a polyvinyl alcohol layer, and the entire surface of the polyvinyl alcohol layer was coated with a kaolin clay powder layer. Furthermore, when the swelling-delayed granules were immersed in water, the swelling initiation of the bentonite granules was remarkably delayed.

[0071] (Example 2) A swelling-delayed granular material was produced in the same manner as in Example 1, except that the polyvinyl alcohol solution was replaced with a shellac solution, and the swelling-delayed layer was composed of shellac.

[0072] Observation of the obtained swelling-delayed granules revealed that the entire surface of the bentonite granules was covered with a shellac layer, and the entire surface of the shellac layer was covered with a kaolin clay powder layer. Furthermore, when the swelling-delayed granules were immersed in water, the swelling initiation of the bentonite granules was remarkably delayed.

[0073] Furthermore, the difference in production rates between Example 2 and the conventional example was compared. Specifically, in the conventional example, granular swelling material (ellipsoid) consisting only of bentonite and having an external dimension of 10.0 mm to 25.0 mm was immersed in a shellac solution and immediately removed from the solution. At this time, if there was excess shellac solution, it was wiped off. Subsequently, multiple swelling material coated with shellac solution was placed in a drying oven, separated from each other without contact. At this time, if the multiple swelling material coated with shellac solution had aggregated, the multiple swelling material was separated. Subsequently, the temperature inside the drying oven was controlled to 80°C to dry the shellac solution. In this way, swelling-delayed granules were obtained.

[0074] Table 1 shows the unit costs when using swellable granular material (medium size) with external dimensions of 10.0 mm to 15.0 mm, and when using swellable granular material (large size) with external dimensions of 20.0 mm to 25.0 mm.

[0075] [Table 1]

[0076] In Example 2, the application of kaolin clay powder significantly suppressed the aggregation of the swellable granular material, thus reducing the labor required for separating the swellable granular material. In contrast, in the conventional example, kaolin clay powder was not applied. As a result, as shown in Table 1, in Example 2, all labor costs improved by approximately twice as much as in the conventional example, demonstrating an effect of increasing work efficiency.

[0077] (Example 3) A swelling-delayed composite granular material was produced in which the first swelling-delayed layer and the second swelling-delayed layer were each made of polyvinyl alcohol. Specifically, the details are as follows:

[0078] The first swelling-delayed granules were manufactured manually. Granular swelling-resistant granules (ellipsoidal) consisting solely of bentonite, with external dimensions between 10.0 mm and 25.0 mm, were immersed in a polyvinyl alcohol solution and immediately removed from the solution. At this time, if any excess polyvinyl alcohol solution was present, it was wiped off. Next, kaolin clay powder was sprinkled over the entire surface of the swelling-resistant granules coated with the polyvinyl alcohol solution. Subsequently, if multiple swelling-resistant granules coated with kaolin clay had aggregated, the granules were separated, and then the swelling-resistant granules were placed in a drying oven temperature-controlled to 80°C to dry the polyvinyl alcohol solution. In this way, the first swelling-delayed granules were obtained.

[0079] The second type of swelling-delayed granules was manufactured using a coating machine. Granular swelling-resistant granules (plate-shaped) consisting solely of bentonite and having an external dimension of 1.0 mm to 5.0 mm were placed into the drum of the coating machine. While the drum rotated, a polyvinyl alcohol solution was sprayed into the drum from a nozzle, causing multiple swelling-resistant granules to flow while the polyvinyl alcohol solution was dried. In this way, the second type of swelling-delayed granules was obtained.

[0080] Then, by mixing the first swelling-delayed granules and the second swelling-delayed granules, a swelling-delayed composite granule was obtained.

[0081] Observation of the obtained first swelling-delayed granules revealed that the entire surface of the bentonite granules was covered with a polyvinyl alcohol layer, and the entire surface of the polyvinyl alcohol layer was covered with a kaolin clay powder layer. Furthermore, when the first swelling-delayed granules were immersed in water, the swelling initiation of the bentonite granules was remarkably delayed.

[0082] Furthermore, observation of the second swelling-delayed granules revealed that the entire surface of the bentonite granules was coated with a polyvinyl alcohol layer. In addition, immersion of the second swelling-delayed granules in water showed excellent delay in the onset of swelling of the bentonite granules.

[0083] (Example 4) A swelling-delayed composite granular material was produced in the same manner as in Example 3, except that the polyvinyl alcohol solution was replaced with a shellac solution, and the first swelling-delayed layer and the second swelling-delayed layer were composed of shellac.

[0084] Observation of the obtained first swelling-delayed granules revealed that the entire surface of the bentonite granules was covered with a shellac layer, and the entire surface of the shellac layer was covered with a kaolin clay powder layer. Furthermore, when the first swelling-delayed granules were immersed in water, the swelling initiation of the bentonite granules was remarkably delayed.

[0085] Furthermore, observation of the second swelling-delayed granules revealed that the entire surface of the bentonite granules was covered with a shellac layer. In addition, immersion of the second swelling-delayed granules in water showed excellent delay in the onset of swelling of the bentonite granules.

[0086] (Comparative Example 1) We manufactured granular material with a swelling delay layer composed of shellac. Specifically, the details are as follows:

[0087] Granular, swellable particles (ellipsoidal) consisting solely of bentonite, with external dimensions between 10.0 mm and 25.0 mm, were placed into the drum of a coating machine. While the drum rotated, shellac solution was sprayed into the drum from a nozzle, causing the multiple swellable particles to flow while the shellac solution was dried.

[0088] Figure 1 is a digital photograph of the bentonite granules after the shellac solution has dried. As shown in Figure 1, a shellac layer was formed on some parts of the surface of the bentonite granules, while there were also areas where the shellac layer was not formed and the bentonite granules were exposed. Therefore, the application of kaolin clay was not carried out.

[0089] Thus, in Comparative Example 1, the entire surface of the bentonite granules was not covered with a shellac layer, and there were exposed portions of the bentonite granules. Furthermore, when this sample was immersed in water, the delay in the onset of swelling of the bentonite granules was insufficient.

[0090] (Comparative Example 2) A swelling-delayed granular material in which the swelling-delayed layer is composed of polyvinyl alcohol was produced in the same manner as in Comparative Example 1, except that the shellac solution was replaced with a polyvinyl alcohol solution.

[0091] As a result, similar to Comparative Example 1, a polyvinyl alcohol layer was formed on some parts of the surface of the bentonite granules, while there were also exposed areas of the bentonite granules where no polyvinyl alcohol layer was formed. Therefore, the application of kaolin clay was not carried out.

[0092] Thus, in Comparative Example 2, the entire surface of the bentonite granules was not covered with the polyvinyl alcohol layer, and there were exposed portions of the bentonite granules. Furthermore, when this sample was immersed in water, the delay in the onset of swelling of the bentonite granules was insufficient.

Claims

1. A swellable granular material having swelling properties in water and an external dimension of 10.0 mm or more, A laminated structure layer is formed by repeating, at least once, a swelling delay layer that covers the surface of the swelling granules and delays the start of swelling of the swelling granules, and a non-swelling powder layer consisting of a plurality of non-swelling powders, in this order. A swelling-delaying granular material comprising the following characteristics.

2. The swelling-delaying granules according to claim 1, wherein the swelling-delaying granules are composed of a bentonite-based material.

3. The swelling-delaying granular material according to claim 1, wherein the swelling-delaying layer is composed of shellac or polyvinyl alcohol.

4. The non-swelling powder is composed of kaolin clay, as described in any one of claims 1 to 3.

5. It comprises a plurality of first swelling-delaying granules and a plurality of second swelling-delaying granules, The first swelling-delayed granular material is A first swellable granular material having swelling properties in water and an external dimension of 10.0 mm or more, A laminated structure layer comprising a first swelling delay layer that covers the surface of the first swelling granules and delays the start of swelling of the first swelling granules, and a non-swelling powder layer consisting of a plurality of non-swelling powders, repeated in this order at least once. Equipped with, The second swelling-delayed granular material is A second swellable granular material having swelling properties in water and an external dimension of 1.0 mm to 5.0 mm, A second swelling delay layer covers the surface of the second swelling granules and delays the start of swelling of the second swelling granules. A swelling-delayed composite granule comprising the following features.

6. The swelling-delayed composite granules according to claim 5, wherein each of the first swelling-delayed granules and the second swelling-delayed granules is composed of a bentonite-based material.

7. The swelling-delayed composite granules according to claim 5, wherein each of the first swelling-delayed layer and the second swelling-delayed layer is composed of shellac or polyvinyl alcohol.

8. The non-swelling powder is composed of kaolin clay, and is a swelling-delayed composite granule according to any one of claims 5 to 7.

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