Low-dusting powder, method for producing the same, and dust-proof treatment liquid

Abstract

This invention provides a novel low-dusting powder and a method for producing the same, which can suppress dust generation during operation without using PTFE. [Solution] A low-dusting powder containing a dust-generating powder, polyvinyl alcohol, a polyhydric alcohol, and water. A method for producing a low-dusting powder, comprising the steps of: mixing polyvinyl alcohol, a polyhydric alcohol, and water to dissolve the polyvinyl alcohol and obtain a dust-proof treatment liquid; and mixing the dust-proof treatment liquid with the dust-generating powder to obtain a low-dusting powder.

Description

Technical Field

[0001] The present invention relates to a low-dusting powder and a method for producing the same. The present invention also relates to a dust-proof treatment liquid that can be used for producing the low-dusting powder.

Background Art

[0002] Conventionally, a ground improvement material mainly made of quicklime, slaked lime or cement has been constructed on soft soil, and after mixing the soil and curing, soil improvement such as modifying the soil to the target strength has been carried out. The ground improvement materials used for soil improvement and the like are usually in powder form from the viewpoints of uniform mixing into the soil and hydration reactivity.

[0003] However, when a large amount of dust is generated during the discharge of the ground improvement material by a freight container or the like at the construction site and mixing with a heavy machine or the like, it has an adverse effect on the working environment and the surrounding environment. Therefore, materials subjected to dust-proof treatment are increasingly being selected.

[0004] Currently, polytetrafluoroethylene (PTFE) is used as the mainstream of dust-proof treatment (for example, Patent Document 1). However, PTFE is one of PFAS that has become an environmental problem in recent years, and alternative technologies are required. As a dust-proof treatment using other than PTFE, those using polyhydric alcohols, saccharides, etc. for dust-proof treatment are known (for example, Patent Documents 2 and 3).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] New dust control technologies expand the options available for dust control, and various technologies are being considered in response to the needs of construction sites.

[0007] Under these circumstances, the present invention aims to provide a novel low-dusting powder and a method for producing the same that can suppress dust generation during operation without using PTFE. Furthermore, the objective is to provide a dust-proofing liquid that can be used in the production of the low-dusting powder. [Means for solving the problem]

[0008] The inventors of this invention have conducted extensive research to solve the above problems and have found that the following invention is suitable for the above purpose, leading to the present invention. That is, the present invention relates to the following invention.

[0009] <1> A low-dusting powder containing dust-generating powder, polyvinyl alcohol, polyhydric alcohol, and water. <2> The ground improvement material, <1> Low-dusting powder as described above. <3> The polyvinyl alcohol is present in an amount of 0.05 to 1.5 parts by mass per 100 parts by mass of the dust-generating powder, and the polyhydric alcohol is present in an amount of 0.5 to 20 parts by mass per 100 parts by mass of the dust-generating powder, <1> or <2> Low-dusting powder as described above. <4> A method for producing a low-dusting powder, comprising the steps of: mixing polyvinyl alcohol, a polyhydric alcohol, and water to dissolve the polyvinyl alcohol and obtain a dust-proof treatment liquid; and mixing the dust-proof treatment liquid with a dust-generating powder to obtain a low-dusting powder containing the dust-generating powder, the polyvinyl alcohol, the polyhydric alcohol, and the water. <5> The step of obtaining the dustproof treatment liquid is to mix the mixed solution of the polyhydric alcohol and the water with the polyvinyl alcohol at 80 to 100°C to dissolve the polyvinyl alcohol. <4> A method for producing low-dusting powder as described above. <6> When the total of the polyvinyl alcohol, polyhydric alcohol, and water in the dustproofing solution is 100% by mass, the proportion of the polyvinyl alcohol is 1 to 5% by mass. <4> or <5> A method for producing low-dusting powder as described above. <7> When the total amount of polyvinyl alcohol, polyhydric alcohol, and water in the dustproofing solution is set to 100% by mass, the proportion of the polyhydric alcohol is 10 to 80% by mass. <4> from <6> A method for producing a low-dusting powder as described in any of the above. <8> The dust-generating powder and the dust-proofing liquid are mixed in a mass ratio of dust-generating powder:dust-proofing liquid = 80:20 to 95:5. <4> from <7> A method for producing a low-dusting powder as described in any of the above. <9> The D90 of the low-dusting powder is 1.5 to 2.5 times that of the D90 of the dust-generating powder. <4> from <8> A method for producing a low-dusting powder as described in any of the above. <10> A dustproofing solution containing polyvinyl alcohol, a polyhydric alcohol, and water, wherein when the total amount of the polyvinyl alcohol, the polyhydric alcohol, and the water is 100% by mass, the proportion of the polyvinyl alcohol is 1 to 5% by mass, and the proportion of the polyhydric alcohol is 10 to 80% by mass. [Effects of the Invention]

[0010] According to the present invention, a novel low-dusting powder and a method for producing the same are provided, which can suppress dust generation during operation without using PTFE. Furthermore, a dust-proofing liquid that can be used in the production of the low-dusting powder is provided. [Brief explanation of the drawing]

[0011] [Figure 1] The particle size distribution of quicklime before and after dust suppression treatment is shown. (A) is a frequency graph, and (B) is a cumulative graph. [Figure 2] This is an image of quicklime before dustproofing treatment, observed with a scanning microscope. [Figure 3]This is an image obtained by observing quicklime (powder P7) after dust-proof treatment with a scanning electron microscope.

Mode for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to the following contents unless the gist thereof is changed. In the present specification, when the expression "~" is used, it shall be used as an expression including the numerical values or physical property values before and after it.

[0013] <Low-dust-generating powder> The present invention relates to a low-dust-generating powder (hereinafter, may be referred to as "the low-dust-generating powder of the present invention") containing a dust-generating powder, polyvinyl alcohol, a polyhydric alcohol, and water. The low-dust-generating powder of the present invention is such that the dust-generating powder is treated with a dust-proof treatment liquid containing polyvinyl alcohol, a polyhydric alcohol, and water. At least a part of the dust-generating powder is aggregated and the particle size is increased, so that the generation of dust can be suppressed. Further, by containing polyvinyl alcohol and a polyhydric alcohol, even when the dust-generating powder has reactivity with water like quicklime, the reaction between the dust-generating powder and water can be suppressed during production and storage, and a dust-proof effect can be obtained during work. Polyvinyl alcohol is a biodegradable material, and the low-dust-generating powder of the present invention that is dust-proof-treated using such a material is excellent from the viewpoints of environmental pollution and safety.

[0014] (Dust-generating powder) The low-dust-generating powder of the present invention contains a dust-proof-treated dust-generating powder. The low-dust-generating powder of the present invention may contain one type of dust-generating powder or two or more types of dust-generating powders.

[0015] Examples of the dust-generating powder include powders used as soil improvers such as quicklime, slaked lime, Portland cement, cement-based ground improvement materials, gypsum, and neutral ground improvement materials (e.g., magnesium hydroxide, etc.); sedimentary soil; powder deposits such as calcium carbonate; and the like. Among these, the dust-generating powder preferably has reactivity with water, and more preferably contains quicklime.

[0016] The D90 of the dust-generating powder is preferably 3 mm or less, and more preferably 1 mm or less. Also, the lower limit of the D90 of the dust-generating powder is 250 μm or more, 300 μm or more, 400 μm or more, etc. With such particle sizes, a more excellent dust-proof effect can be obtained. Note that D90 is the particle size at which the cumulative frequency from the small particle size side is 90% in the volume-based particle size distribution by the laser diffraction scattering method.

[0017] (Polyvinyl alcohol (PVA)) The low-dust-generating powder of the present invention contains polyvinyl alcohol. The low-dust-generating powder of the present invention may contain one type of polyvinyl alcohol or two or more types. Also, polyvinyl alcohol is not limited to unmodified polyvinyl alcohol, and a part thereof may be modified polyvinyl alcohol modified with other monomers.

[0018] Polyvinyl alcohol may be a completely saponified type or a partially saponified type. However, since it is easily soluble in a mixed solution of water and polyhydric alcohol and it is easy to adjust the dust-proof treatment liquid described later, it is preferably a completely saponified type, more preferably the saponification degree is 97% or more, and even more preferably the saponification degree is 97 - 99%.

[0019] The average polymerization degree of polyvinyl alcohol is not particularly limited, but generally it is 300 - 4000. From the viewpoints of solubility in a mixed solution of water and polyhydric alcohol and the dust generation suppression effect, preferably the average polymerization degree is 500 - 3000, more preferably the average polymerization degree is 800 - 2500, and even more preferably the average polymerization degree is 1200 - 2000.

[0020] The degree of saponification and the average degree of polymerization can be measured using methods compliant with JIS K 6726 (1994).

[0021] (Polyhydric alcohol) The low-dusting powder of the present invention contains a polyhydric alcohol. The low-dusting powder of the present invention may contain one type of polyhydric alcohol or two or more types. Preferably, the polyhydric alcohol has low reactivity with the dust-generating powder when mixed with water and has high solubility of polyvinyl alcohol.

[0022] A polyhydric alcohol is an alcohol that contains two or more hydroxyl groups (OH groups) in one molecule. Dihydric alcohols and / or trihydric alcohols are preferred, with dihydric alcohols being more preferred from the viewpoint of reactivity with dusty powders and solubility of polyvinyl alcohol. Examples of dihydric alcohols include ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, and polyalkylene glycol.

[0023] Polyalkylene glycols have two or more oxyalkylene structures and include oligoalkylene glycols such as diethylene glycol and dipropylene glycol. Liquid polyalkylene glycols are preferred.

[0024] In particular, polyalkylene glycol is given by the following formula (1); HO-(RO) n -H ···(1) A representation of this is preferable.

[0025] In formula (1), R is an ethylene group or a propylene group, and n is 2 to 20. R is preferably an ethylene group. Also, n is preferably 2 to 15, and more preferably 2 to 10.

[0026] In particular, the dihydric alcohol preferably contains diethylene glycol and / or ethylene glycol, and more preferably contains diethylene glycol.

[0027] Examples of trihydric alcohols include glycerin, trimethylolethane, and trimethylolpropane.

[0028] (water) The low-dusting powder of the present invention contains water. The water is not particularly limited and includes tap water, distilled water, deionized water, industrial water, and the like.

[0029] (Other ingredients) In the low-dusting powder of the present invention, the proportion of dust-generating powder, polyvinyl alcohol, polyhydric alcohol, and water is usually 95% by mass or more, preferably 99% by mass or more. The low-dusting powder of the present invention may contain other components besides dust-generating powder, polyvinyl alcohol, polyhydric alcohol, and water, as long as they do not hinder the effects of the present invention. Examples of other components include ligninsulfonic acid, stearic acid, boric acid, borax, and baking soda. Including one or more of these components can extend the dust-proof effect.

[0030] (Composition) To obtain a better dust-proof effect, the low-dusting powder of the present invention preferably contains 0.05 to 1.5 parts by mass of polyvinyl alcohol per 100 parts by mass of dust-generating powder, more preferably 0.08 to 1.0 parts by mass, and even more preferably 0.1 to 0.5 parts by mass.

[0031] Furthermore, in order to obtain a better dust-proof effect, the low-dusting powder of the present invention preferably contains 0.5 to 20 parts by mass of polyhydric alcohol per 100 parts by mass of dust-generating powder, more preferably 1.0 to 15 parts by mass, even more preferably 2.0 to 10 parts by mass, and even more preferably 3.0 to 8.0 parts by mass.

[0032] When using low-dusting powder as a ground modifier, in order to obtain the same effect as low-dusting powder that has not been treated for dust prevention, the proportion of dust-generating powder in the low-dusting powder of the present invention is preferably 85 to 96% by mass, and more preferably 90 to 95% by mass.

[0033] <Method for producing low-dusting powder> The method for producing the low-dusting powder of the present invention is not particularly limited, but for example, the low-dusting powder of the present invention can be produced by a method comprising: step S1 of mixing polyvinyl alcohol, a polyhydric alcohol, and water to dissolve the polyvinyl alcohol and obtain a dust-proof treatment liquid; and step S2 of mixing the dust-proof treatment liquid with a dust-generating powder to obtain a low-dusting powder (hereinafter sometimes referred to as "the method for producing the present invention").

[0034] (Process S1) Step S1 is a step of mixing polyvinyl alcohol, a polyhydric alcohol, and water to dissolve the polyvinyl alcohol and obtain a dustproof treatment solution. Step S1 provides a dustproof treatment solution containing polyvinyl alcohol, a polyhydric alcohol, and water.

[0035] The preferred degree of saponification and average degree of polymerization of the polyvinyl alcohol used are as described above. The polyhydric alcohol and water used are also as described above, and the preferred embodiments are similar.

[0036] The method of mixing polyvinyl alcohol, polyhydric alcohol, and water is not particularly limited as long as the polyvinyl alcohol can be dissolved. However, it is preferable to heat and dissolve the polyvinyl alcohol in the mixed solution of polyhydric alcohol and water, and it is preferable to mix them at 80 to 100°C to dissolve the polyvinyl alcohol. Dissolving polyvinyl alcohol in this temperature range is preferable because it suppresses the browning and change in physical properties of the polyvinyl alcohol, and it is easier to dissolve the polyvinyl alcohol.

[0037] When the total amount of polyvinyl alcohol, polyhydric alcohol, and water in the dustproofing solution is considered to be 100% by mass, the proportion of polyvinyl alcohol is preferably 1.0 to 5.0% by mass, more preferably 1.5 to 3.0% by mass, and even more preferably 2.0 to 2.5% by mass. A better dustproofing effect can be obtained when the proportion of polyvinyl alcohol is within the above numerical range.

[0038] When the total amount of polyvinyl alcohol, polyhydric alcohol, and water in the dustproofing solution is considered to be 100% by mass, the proportion of polyhydric alcohol is preferably 10 to 80% by mass, more preferably 30 to 70% by mass, and even more preferably 40 to 60% by mass. A better dustproofing effect can be obtained when the proportion of polyhydric alcohol is within the above numerical range.

[0039] Furthermore, as described above, the dustproofing solution may also contain other components such as lignin sulfonic acid, stearic acid, boric acid, borax, and baking soda, but the proportion of polyvinyl alcohol, polyhydric alcohol, and water in the dustproofing solution is usually 95% by mass or more, preferably 99% by mass or more.

[0040] (Process S2) Step S2 is a process of mixing a dust-proofing liquid with dust-generating powder to obtain a low-dusting powder. By mixing the dust-generating powder with the dust-proofing liquid, the dust-generating powder particles aggregate, increasing their particle size and resulting in a low-dusting powder that is less likely to generate dust.

[0041] The dust-generating powder used is as described above, and the preferred embodiment is the same.

[0042] The method of mixing the dust-proofing liquid and the dust-generating powder is not particularly limited; the dust-proofing liquid may be added to the dust-generating powder while stirring, or the dust-generating powder may be added to the dust-proofing liquid while stirring. The apparatus used for mixing is preferably one that can uniformly mix the dust-generating powder and the dust-proofing liquid, such as a Redigge mixer (Matsubo Co., Ltd.) or a Nauta mixer (registered trademark) (Hosokawa Micron Corporation).

[0043] The dust-generating powder and the dust-proofing liquid are preferably mixed in a mass ratio of dust-generating powder:dust-proofing liquid = 80:20 to 95:5, more preferably 85:15 to 92:8, and even more preferably 88:12 to 91:9. Such mixing ratios provide superior dust-proofing effects. Furthermore, such mixing ratios allow for ground improvement effects equivalent to those of untreated ground even when using low-dusting powder as a ground improvement material.

[0044] Furthermore, when the total amount of the dust-generating powder, polyvinyl alcohol, polyhydric alcohol, and water is set to 100% by mass, it is preferable to mix them so that the total proportion of polyvinyl alcohol, polyhydric alcohol, and water is 5 to 20% by mass, more preferably 8 to 15% by mass, and even more preferably 9 to 12% by mass. By using such mixing ratios, a better dust-proofing effect can be obtained.

[0045] The resulting low-dusting powder has a larger particle size than the dusty powder. For example, by treating a dusty powder with a D90 of 100-300 μm with a dust-suppressing solution, a low-dusting powder with a D90 1.5-2.5 times that of the dusty powder can be obtained.

[0046] Furthermore, when manufacturing low-dusting powders containing other components, the manufacturing method is not limited to treating the dust-generating powder with a dust-proofing solution containing the other components; the dust-generating powder and the other components may be mixed and then treated with a dust-proofing solution that does not contain the other components.

[0047] <Soil improvement material> The low-dusting powder of the present invention can be used, for example, as a ground improvement material. First, a container such as a flexible container bag containing the low-dusting powder of the present invention is suspended by heavy machinery and moved to the construction area. In the construction area, the low-dusting powder of the present invention is discharged from the container. Then, the low-dusting powder of the present invention is mixed with the soil of the construction area, compacted (rolled), and then cured to perform ground improvement.

[0048] The low-dusting powder of the present invention, when added to soil, quickly dissolves its aggregates and can react with water and other substances in the soil. Therefore, by using the low-dusting powder of the present invention as a ground improvement material, a ground improvement effect equivalent to or better than that of dust-removing powder that has not undergone dust-prevention treatment can be obtained. [Examples]

[0049] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless its essence is changed.

[0050] The following materials were used to produce the low-dusting powder. <Dust-generating powder> ·quicklime <Polyvinyl alcohol (PVA)> • PVA(1): Fully saponified type, degree of saponification 97-99 mol%, degree of polymerization 1400-1500, PVA material (powder) • PVA(2): Fully saponified type, degree of saponification 97-99 mol%, degree of polymerization 1400-1500, PVA material (sheet form) • PVA(3): Fully saponified type, degree of saponification 97-99 mol%, degree of polymerization 1400-1500, gelled PVA material. • PVA(4): Fully saponified type, degree of saponification 98-99 mol%, degree of polymerization 900-1000, reagent (powder) • PVA(5): Fully saponified type, degree of saponification 98-99 mol%, degree of polymerization 500-600, reagent (powder) <Polyhydric alcohols> • Diethylene glycol (DEG) • Ethylene glycol (EG)

[0051] <Example 1> (Examples 1-1 to 1-10) Using a small pan-type stirring device, a solution of water and diethylene glycol (DEG) was mixed and stirred with PVA(1) at 80-100°C to obtain dust-proof treatment solutions (L1-L10) in the proportions shown in Table 1, thereby dissolving the PVA(1). Next, using a small pan-type stirring device, the quicklime and dust-suppressing treatment liquid were mixed so that the ratio of quicklime to dust-suppressing treatment liquid was 90:10 (by mass) to obtain powders (P1 to P10, low-dusting powders).

[0052] (Comparative Examples 1-3) Except for using a solution (L11-L13) prepared by mixing water and diethylene glycol in the proportions shown in Table 1, instead of the dustproofing solution (L1-L10), dustproofing treatment was performed in the same manner as in Examples 1-1 to 1-10 to obtain powders (P11-P13).

[0053] (Evaluation of dustproof effect) The dust-proofing effect of the powders (P1-P13) was quantified using a method compliant with the dust generation test method described in Appendix-1 of the technical data of the PTFE-treated dust-proof solidification material association. 200g of powder (P1-P13) was allowed to fall naturally from the top of a cylindrical acrylic container (inner diameter 39cm x height 59cm). The amount of dust (CPM) was measured every minute for 5 minutes using a digital dust meter (LD-5R, Shibata Chemical Co., Ltd.) placed 45cm above the bottom surface. The geometric mean over 5 minutes was calculated and evaluated. Table 1 shows the measurement results (geometric mean over 5 minutes).

[0054] [Table 1]

[0055] <Example 2> (Examples 2-1 to 2-4) Powders (P14-P16) were obtained in the same manner as in Examples 1-7, except that the mixing ratio of quicklime and dust-proofing liquid was changed to the ratio shown in Table 2.

[0056] (Evaluation of dustproof effect) The dust-proofing capacity of the powders (P14-P16) was measured in the same manner as in Example 1. The measurement results are shown in Table 2.

[0057] (CaO amount) The CaO content of the powders (P14-P16) was measured according to the method of JIS R9011 (2006). The measurement results are shown in Table 2.

[0058] [Table 2]

[0059] <Example 3> (Examples 3-1 to 3-8) Powders (P17-P24) were obtained in the same manner as in Example 1, except that the type and proportion of polyvinyl alcohol and the type and proportion of polyhydric alcohol in the dustproofing solution were changed as shown in Table 3, instead of the dustproofing solution used in Example 1. The dust-proofing capacity of the powders (P17-P24) was measured in the same manner as in Example 1. The measurement results are shown in Table 3.

[0060] [Table 3]

[0061] <Example 4> The particle size of quicklime before dustproofing and powder P7 (quicklime after dustproofing) obtained in Examples 1-7 were measured using a laser diffraction apparatus (Partica LA-960V2, Horiba, Ltd.) to evaluate the change in particle size due to dustproofing. Table 4 and Figure 1 show graphs of the particle size distribution.

[0062] [Table 4]

[0063] <Example 5> Using a scanning electron microscope (S-4800, Hitachi, Ltd.), the quicklime before dustproofing treatment and the powder P7 obtained in Examples 1-7 were observed to evaluate the macroscopic changes due to dustproofing treatment. Figure 2 shows the observed image of quicklime before dustproofing treatment, and Figure 3 shows the observed image of powder P7 (quicklime after dustproofing treatment).

[0064] <Example 6> In the test plots, powder P7 obtained in Examples 1-7 was used, and in the control plots, untreated quicklime was used. A laboratory mix design test was conducted to evaluate the soil improvement effect. First, the soils listed in Table 5 were mixed with the test or comparative samples using a soil mixer. The mixture was then placed in a circular mold measuring 5.0 cm in diameter and 10 cm in height, and molded in three layers using a 1.5 kg rammer, 12 times each. The mixture was then cured for 28 days at 20°C and 80% humidity. The addition rates of the test or comparative samples to the soil were 30, 60, and 90 kg / m³. 3 Next, a uniaxial compression test of the soil was conducted in accordance with JIS A1216 (2020). Table 5 shows the measurement results of the unconfined compression test of soil, the relative values ​​calculated from the measurement results (= value in the test section / value in the control section × 100 (%)), and the average of the relative values.

[0065] [Table 5]

[0066] <Example 7> Field application tests were conducted using the powder P7 obtained in Examples 1-7. A flexible container bag filled with 500 kg of powder P7 was suspended by heavy machinery and discharged onto the soil in the construction area. The soil was then mixed and compacted using heavy machinery. The amount of dust during discharge and mixing, and the unconfined compressive strength after compaction were measured. For comparison, the same test was also conducted using untreated quicklime instead of powdered P7. Table 6 shows the test results.

[0067] [Table 6] [Industrial applicability]

[0068] The low-dusting powder of the present invention is industrially useful because it can be used for ground improvement and the like.

Claims

1. A low-dusting powder containing dust-generating powder, polyvinyl alcohol, polyhydric alcohol, and water.

2. A low-dusting powder as described in claim 1, which is a ground improvement material.

3. The amount of polyvinyl alcohol is 0.05 to 1.5 parts by mass per 100 parts by mass of the dust-generating powder. The low-dusting powder according to claim 1 or 2, wherein the polyhydric alcohol is 0.5 to 20 parts by mass per 100 parts by mass of the dust-generating powder.

4. A step of mixing polyvinyl alcohol, a polyhydric alcohol, and water to dissolve the polyvinyl alcohol and obtain a dustproof treatment solution, A method for producing a low-dusting powder, comprising the steps of: mixing the dust-proofing liquid with a dust-generating powder to obtain a low-dusting powder containing the dust-generating powder, the polyvinyl alcohol, the polyhydric alcohol, and the water.

5. The method for producing a low-dusting powder according to claim 4, wherein the step of obtaining the dustproof treatment liquid is to mix the mixed solution of the polyhydric alcohol and the water with the polyvinyl alcohol at 80 to 100°C to dissolve the polyvinyl alcohol.

6. The method for producing a low-dusting powder according to claim 4 or 5, wherein when the total amount of the polyvinyl alcohol, the polyhydric alcohol, and the water in the dustproofing liquid is 100% by mass, the proportion of the polyvinyl alcohol is 1 to 5% by mass.

7. A method for producing a low-dusting powder according to claim 4 or 5, wherein when the total amount of the polyvinyl alcohol, the polyhydric alcohol, and the water in the dustproofing liquid is 100% by mass, the proportion of the polyhydric alcohol is 10 to 80% by mass.

8. A method for producing a low-dusting powder according to claim 4 or 5, wherein the dust-generating powder and the dust-proofing liquid are mixed in a mass ratio of dust-generating powder:dust-proofing liquid = 80:20 to 95:

5.

9. The method for producing a low-dusting powder according to claim 4 or 5, wherein the D90 of the low-dusting powder is 1.5 to 2.5 times the D90 of the dust-generating powder.

10. This dustproofing solution contains polyvinyl alcohol, polyhydric alcohol, and water. A dustproofing solution in which, when the total of the polyvinyl alcohol, the polyhydric alcohol, and the water is 100% by mass, the proportion of the polyvinyl alcohol is 1 to 5% by mass, and the proportion of the polyhydric alcohol is 10 to 80% by mass.

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