Dust suppressant treatment composition

Abstract

To provide a dust-emission suppressing composition that is effective in suppressing dust-emission, retains re-dispersibility of PTFE particles, as the solid content of the composition, even after left standing for a long time, and also demonstrates excellent environment performance.SOLUTION: The present invention discloses a dust-emission suppressing composition for suppressing the emission of dust from a dust-emitting substance, the composition containing at least one selected from water-soluble cellulose derivatives containing at least one selected from a methyl group (-CH3), a hydroxypropyl group (-CH2CHOHCH3), and a hydroxyethyl group (-CH2CH2OH), and an aqueous polytetrafluoroethylene dispersion.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a dust suppressant treatment composition that has excellent performance in suppressing dust from dust-generating substances and also has excellent redispersibility, and more specifically, to a dust suppressant treatment composition comprising at least one water-soluble cellulose derivative containing at least one group selected from the group consisting of a methyl group (-CH3), a hydroxypropyl group (-CH2CHOHCH3), and a hydroxyethyl group (-CH2CH2OH), and an aqueous PTFE dispersion. [Background technology]

[0002] The technology to suppress dust from dust-producing substances is an important technology for daily life and industry from the viewpoints of health, safety, the environment, and other requirements. As such a dust suppression technique, Patent Document 1 below proposes a method in which polytetrafluoroethylene (PTFE) is mixed with a powdered substance and the mixture is subjected to a compression-shear action at a temperature of approximately 20 to 200°C to fibrillate the PTFE and suppress the generation of dust from the powdered substance.

[0003] The PTFE described in Patent Document 1 is Teflon (registered trademark) 6 or Teflon (registered trademark) 30, which is a homopolymer of tetrafluoroethylene in the form of a fine powder or emulsion, or Teflon (registered trademark) 6C, which is a modified polymer of tetrafluoroethylene in the form of a fine powder.

[0004] Furthermore, Patent Document 2 listed below proposes a stable dust suppression method that uses an aqueous emulsion containing 1.0% by mass or more of a hydrocarbon-based anionic surfactant relative to PTFE, and shows that this method has a dust suppression effect for powdery substances. According to Patent Document 2, PTFE particles are produced in the form of an aqueous emulsion by the emulsion polymerization method disclosed in Patent Document 3 listed below, that is, by forcing tetrafluoroethylene into an aqueous medium containing a water-soluble polymerization initiator and an anionic surfactant having a fluoroalkyl group as a hydrophobic group (hereinafter referred to as a fluorine-containing emulsifier) ​​as an emulsifier, and polymerizing the mixture, but an emulsion stabilizer is further added to increase stability.

[0005] Furthermore, Patent Document 4 listed below describes a method for suppressing dust without concern for the impact on the environment, by using a dust-suppressing treatment composition comprising an aqueous fluorinated polymer dispersion having a fluorinated emulsifier content of 50 ppm or less, which has a dust-suppressing effect.

[0006] However, the PTFE used as the dust suppression treatment composition in these methods has a high molecular weight, and its aqueous dispersion is prone to settling when left standing for a long period of time. Once settling, the PTFE solidifies and is difficult to re-disperse. In addition, this causes a decrease in the PTFE concentration in the PTFE aqueous dispersion, and there is a risk that the dust suppression effect inherent to PTFE may not be fully exhibited depending on the conditions of use. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 52-32877 [Patent Document 2] Japanese Patent Application Publication No. 8-20767 [Patent Document 3] U.S. Patent No. 2,559,752 [Patent Document 4] International Publication No. WO2007 / 000812 Summary of the Invention [Problem to be solved by the invention]

[0008] That is, an object of the present invention is to provide a dust suppressant treatment composition that has an excellent dust suppression effect, is excellent in redispersibility of PTFE particles, which are the solid content in the dust suppressant treatment composition, after being left standing for a long period of time, and is also excellent in environmental performance. [Means for solving the problem]

[0009] The present invention provides At least hydroxypropyl methylcellulose having a melting point of 225 to 230°C Contains water-soluble cellulose derivatives body, and an aqueous dispersion of polytetrafluoroethylene.

[0012] In a preferred embodiment of the present invention, the water-soluble cellulose derivative is contained in the dust suppressant treatment composition in an amount of 0.01 to 1.00% by mass.

[0013] In a preferred embodiment of the present invention, the PTFE aqueous dispersion contains PTFE in an amount of 1 to 80% by mass.

[0014] In a preferred embodiment of the present invention, the dust-generating substance is a powdery dust-generating substance.

[0015] In a preferred embodiment of the present invention, the settling rate of the dust-preventive treatment composition, as represented by the following formula (1), is less than 1.0. Sedimentation rate = X1 / X0<1.0 (1) In the formula, X0 is the solid sedimentation rate (%) shown by the following formula (2) when 10 g of the PTFE aqueous dispersion not containing the water-soluble cellulose derivative is centrifuged in a centrifuge at a temperature of 20°C and a rotation speed of 3000 rpm for 30 minutes. X1: The solid sedimentation rate (%) represented by the following formula (2) when 10 g of the dust-suppressing treatment composition is centrifuged at a temperature of 20° C. and a rotation speed of 3000 rpm for 30 minutes in a centrifuge. Solids settling rate (%) = (amount of solids settling after centrifugation) / (amount of solids before centrifugation) × 100 (2) [Effects of the Invention]

[0016] The present invention provides a dust suppression treatment composition for dust-generating substances that not only has excellent dust-suppressing properties for dust-generating substances, but also has excellent redispersibility of PTFE particles, which are the solid content in the dust suppression treatment composition, even after being left to stand for a long period of time, and is also excellent in environmental performance. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 shows the results of a static sedimentation test and a static sedimentation redispersion test for Examples 1 and 2 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0018] An important feature of the dust suppressant treatment composition for dust-generating substances of the present invention is that it comprises an aqueous dispersion of PTFE and a water-soluble cellulose derivative containing at least one group selected from a methyl group (-CH3), a hydroxypropyl group (-CH2CHOHCH3), and a hydroxyethyl group (-CH2CH2OH). By mixing the dust suppressant treatment composition of the present invention with a dust-generating substance and subjecting the mixture to a compression-shear action at a temperature of about 20 to 200°C, it is possible to fibrillate the PTFE and suppress the generation of dust from the dust-generating substance. As mentioned above, the PTFE particles, which are the solid content in the dust-suppressing treatment composition, tend to settle, and when the PTFE aqueous dispersion is left standing for a long period of time, the PTFE particles settle, and the settled PTFE particles solidify, making it difficult to redisperse them by stirring, etc. However, in the dust-suppressing treatment composition of the present invention, by containing the water-soluble cellulose derivative, it is possible to prevent the settled PTFE particles from solidifying, and to significantly improve the redispersibility of the PTFE particles. As a result, a small amount of the dust-suppressing treatment composition can be uniformly mixed with a dust-generating substance, making it possible to efficiently suppress the generation of dust from the dust-generating substance.

[0019] The excellent dust-suppressing performance and re-dispersibility of the dust-suppressing treatment composition used in the present invention are evident from the results of the static sedimentation test, static sedimentation re-dispersion test, centrifugation sedimentation test, centrifugation re-dispersion test and falling dust amount test in the examples described below. That is, as is clear from Figure 1 showing the results of the static sedimentation test and the static sedimentation redispersion test, the dust-suppressing treatment composition containing a water-soluble cellulose derivative exhibits a reduced sedimentation amount compared to an aqueous PTFE dispersion not containing a water-soluble cellulose derivative. Furthermore, as shown in Examples 3 to 6 below, it is clear that the dust-suppressing treatment composition of the present invention can be well redispersed when the sedimentation rate, which indicates the redispersibility of PTFE particles in the dust-suppressing treatment composition and is represented by the above formula (1), is less than 1.0, preferably 0.9 or less, and preferably 0.8 or less. Furthermore, it is clear that the dust-suppressing treatment composition can be well redispersed even after centrifugation when the sedimentation rate after redispersion, which is represented by the following formula (3), is less than 1.0, preferably 0.9 or less, and preferably 0.8 or less. That is, when the sedimentation rate represented by the above formula (1) is 1.0 or more, the settled PTFE particles become strongly agglomerated, making re-dispersion difficult. Furthermore, as a result of the sedimentation of the solid PTFE particles, the number of PTFE particles dispersed in the dust-suppressing treatment composition decreases, and in order to maintain the same dust-suppressing performance of dust-generating substances as before the sedimentation, a larger amount of PTFE aqueous dispersion is required. Furthermore, the firmly agglomerated PTFE cannot be used as a dust-suppressing treatment and must be discarded, which wastes much of the useful resource PTFE and incurs disposal costs, which is undesirable from an economic standpoint.

[0020] (Water-soluble cellulose derivative) The water-soluble cellulose derivative contained in the dust suppression treatment composition of the present invention is preferably a water-soluble cellulose derivative containing at least one group selected from a methyl group (-CH), a hydroxypropyl group (-CHCHOHCH), and a hydroxyethyl group (-CHCHOH). More preferably, it is at least one group selected from methyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, and ethyl cellulose, and even more preferably, it is hydroxypropyl methyl cellulose having a melting point of 225 to 230°C.

[0021] The water-soluble cellulose derivative is preferably contained in the dust suppressant treatment composition in an amount of 0.01 to 1.00% by mass, preferably 0.01 to 0.05% by mass, and more preferably 0.01 to 0.03% by mass. If the content of the water-soluble cellulose derivative is less than 0.01% by mass, the redispersibility of settled PTFE particles is inferior compared to when the content is within the above range. On the other hand, if the content exceeds 1.00% by mass, fibrillation of PTFE is inhibited compared to when the content is within the above range. As a result, not only is the dust suppressant performance reduced, but the viscosity of the dust suppressant treatment composition increases, which may significantly reduce handleability. An increase in the viscosity of the dust suppressant treatment composition is undesirable because it makes it difficult to dilute the dust suppressant treatment composition with water before use. In the present invention, even if the PTFE particles, which are the solid content in the dust suppression treatment composition, settle due to standing during transportation or storage, the inclusion of a water-soluble cellulose derivative makes it easy to redisperse the PTFE particles by stirring, rolling, etc. (improved redispersibility), and therefore the dust suppression treatment composition can be used efficiently.

[0022] (PTFE aqueous dispersion) In the PTFE aqueous dispersion used in the present invention, the PTFE may be either a homopolymer of tetrafluoroethylene (TFE) (PTFE), called a homopolymer, or a copolymer of tetrafluoroethylene containing 1% or less of a comonomer (modified PTFE), called a modified polymer, but PTFE, which is a homopolymer of TFE, is particularly preferred. A dust suppressant treatment composition comprising a modified PTFE aqueous dispersion has a lower dust suppression effect than a dust suppressant treatment composition comprising a PTFE aqueous dispersion, and it is often necessary to use a treatment agent in an amount 50% or more greater to achieve the same dust suppression effect.

[0023] The PTFE in the aqueous PTFE dispersion is desirably colloidal particles having an average particle size of 0.1 to 0.5 μm, preferably 0.1 to 0.3 μm. If the average particle size is smaller than the above range, the effect of suppressing dust from dust-generating substances may be lower than when the average particle size is within the above range, while if the average particle size is larger than the above range, the dispersion stability of the colloidal particles may be lower than when the average particle size is within the above range. Furthermore, it is desirable that the specific gravity (SSG) of PTFE is 2.27 or less, preferably 2.22 or less, and more preferably 2.20 or less. If the specific gravity (SSG) of PTFE is higher than the above range, the effect of suppressing dust from dust-generating substances may be inferior compared to when the specific gravity is within the above range.

[0024] In the present invention, the PTFE concentration in the aqueous PTFE dispersion is not particularly limited, but is in the range of 10 to 80 mass %, preferably 15 to 80 mass %, and more preferably 20 to 80 mass %. In order to enhance the dispersibility of PTFE in dust-generating substances, a lower PTFE concentration is preferable; however, a high PTFE concentration may impair the dispersion stability of the PTFE aqueous dispersion. On the other hand, when transporting the PTFE aqueous dispersion, a higher concentration can reduce transportation costs. Therefore, the PTFE concentration in the dust-suppressing treatment composition of the present invention is preferably 10% by mass or more, particularly in the range of 20 to 80% by mass. When mixing with dust-generating substances, the dust-suppressing treatment composition can be diluted with water to a PTFE concentration of 5% by mass or less in order to enhance the dispersibility of PTFE.

[0025] The PTFE aqueous dispersion used in the present invention may contain a small amount of a fluorine-containing emulsifier (surfactant) as an emulsifier. Although the fluorine-containing emulsifier is essential due to its inertness in polymerization, its content is desired to be low, preferably 50 ppm or less, because it is persistent and has environmental concerns. The fluorine-containing emulsifier concentration in the PTFE aqueous dispersion can be calculated by freezing the PTFE aqueous dispersion in a -20°C freezer, flocculating the PTFE and separating it from the water, transferring the entire contents of the polyethylene container to a Soxhlet extractor, extracting with approximately 80 ml of methanol for 7 hours, and measuring the diluted sample solution by liquid chromatography to calculate the fluorine-containing emulsifier concentration in the PTFE aqueous dispersion.

[0026] There are no particular limitations on the method for preparing an aqueous PTFE dispersion having a fluorine-containing emulsifier content of 50 ppm or less, but the following method can be exemplified. For example, the PTFE aqueous dispersion obtained by emulsion polymerization as disclosed in the aforementioned Patent Document 3, i.e., the PTFE aqueous dispersion obtained by injecting TFE into an aqueous medium containing a water-soluble polymerization initiator and an anionic surfactant (fluorine-containing emulsifier) ​​having a fluoroalkyl group as a hydrophobic group, followed by polymerization, contains about 0.02 to 1 mass% of the fluorine-containing emulsifier (perfluorooctanoic acid in the form of an ammonium salt and / or alkali salt) relative to the weight of the fluorine-containing polymer. The fluorine-containing emulsifier can be removed from the PTFE aqueous dispersion by known methods for removing the fluorine-containing emulsifier, such as a method of contacting the PTFE with an effective amount of anion exchanger for separation and removal (JP-T-2005-501956 and JP-T-2002-532583), or a method of removing the fluorine-containing emulsifier by ultrafiltration of the fluorine-containing polymer aqueous dispersion (U.S. Pat. No. 4,369,226). The method for removing the fluorine-containing emulsifier is not limited to the above methods. Furthermore, since the fluorine-containing emulsifier is expensive, it is desirable that the fluorine-containing emulsifier removed by the above method be recovered and reused.

[0027] In the emulsion polymerization method for preparing the aqueous PTFE dispersion used in the present invention, the emulsifiers disclosed in the aforementioned Patent Document 3 can be used as the emulsifier. However, for the purposes of the present invention, emulsifiers sometimes referred to as non-telogenic emulsifiers are particularly suitable. Examples of non-telogenic emulsifiers include fluorine-containing alkanoic acids or salts thereof, represented by F(CF2)n(CH2)mCOOH (m: 0 or 1, n: 6 to 20), each having approximately 6 to 20 carbon atoms, preferably approximately 6 to 12 carbon atoms, and fluorine-containing alkylsulfonic acids or salts thereof. Examples of salts include alkali metal salts, ammonium salts, and amine salts. Specific examples include, but are not limited to, perfluoroheptanoic acid, perfluorooctanoic acid, and salts thereof, and 2-perfluorohexylethanesulfonic acid and salts thereof.

[0028] Furthermore, the aqueous PTFE dispersion used in the present invention may contain an emulsion stabilizer to enhance the stability of the aqueous PTFE dispersion. As the emulsion stabilizer, a hydrocarbon-based anionic surfactant is preferred. This surfactant essentially forms water-insoluble or poorly soluble salts with calcium, aluminum, and iron, which are soil components, thereby preventing contamination of rivers, lakes, and groundwater caused by the surfactant.

[0029] Examples of such hydrocarbon-based anionic surfactants include higher fatty acid salts, higher alcohol sulfate salts, liquid fatty oil sulfate salts, fatty alcohol phosphate salts, dibasic fatty acid ester sulfonates, and alkyl aryl sulfonates. In particular, Na, K, Li, and NH salts of polyoxyethylene alkyl phenyl ether ethylene sulfonates (polyoxyethylene n is 1 to 6, alkyl has 8 to 11 carbon atoms), alkyl benzene sulfonates (alkyl has 10 to 12 carbon atoms), dialkyl sulfosuccinates (alkyl has 8 to 10 carbon atoms), etc., can be given as examples of preferred surfactants because they can impart high mechanical stability to the aqueous PTFE dispersion and prevent the PTFE particles from agglomerating due to high-speed stirring, etc.

[0030] (Dust suppression treatment method) The dust suppression treatment method using the dust suppression treatment composition of the present invention comprises mixing the dust suppression treatment composition of the present invention with a dust-generating substance, and subjecting the mixture to a compression-shear action at a temperature of 20 to 200°C, preferably 50 to 150°C, to fibrillate the PTFE in the composition, thereby suppressing the generation of dust from the dust-generating substance. That is, when a specific PTFE is subjected to compression-shear action under the appropriate conditions as described above, it becomes fibrillated into ultra-fine spider web-like fibers, and therefore it is thought that in dust-suppressed treated products treated with the dust-suppressing treatment composition of the present invention, dust-generating substances are captured and agglomerated in the spider web-like fine fibers, thereby suppressing dust.

[0031] The dust-producing substances to be treated for dust suppression using the dust-suppressing treatment composition of the present invention are inorganic and / or organic dust-producing substances, and there are no particular limitations on the substance, shape, etc. The present invention can also be effectively applied to dust-producing powdery substances. Particularly suitable dust-producing substances that can be treated include cements such as Portland cement and alumina cement, slaked lime, quicklime powder, mineral powders such as calcium carbonate, dolomite, magnesite, talc, silica stone, and fluorite, clay mineral powders such as kaolin and bentonite, slag powders by-produced in the production processes of metals such as steel and non-ferrous metals, combustion ash powders such as coal and garbage, gypsum powder, powdered metals, carbon black, activated carbon powder, ceramic powders such as metal oxides, pigments, etc. In other words, all dust-producing substances that generate solid particulate matter that scatter and float in the air and generate dust are included.

[0032] The amount of the dust-suppressing treatment composition of the present invention to be added to a dust-generating substance can be appropriately determined depending on the type of dust-generating substance, particle size distribution, specific gravity (true specific gravity, apparent specific gravity), dust-suppressing treatment temperature, the degree of compression-shear action applied, the degree of dust suppression of the resulting dust-suppressing treated product, and the like. As a guideline for the amount to be added, for example, the dust-suppressing treatment composition can be added in an amount of 0.001 to 1.0 mass %, preferably 0.005 to 0.5 mass %, calculated as the PTFE resin solid content, to the dust-generating powdery substance to suppress dust generated from the dust-generating powdery substance. [Example]

[0033] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the present invention, the physical properties were measured by the following methods.

[0034] (1) Average particle size of PTFE particles The average particle size of the PTFE particles was measured using a Microtrac UPA150 Model No. 9340 (manufactured by Nikkiso Co., Ltd.). (2) Particle size of dust-generating powder Measurements were made using a laser diffraction / scattering particle size distribution analyzer manufactured by Horiba Ltd., using ethanol as a dispersion medium.

[0035] (3) Standard specific gravity of PTFE (SSG) Measured according to ASTM D-4894. The aqueous PTFE dispersion obtained by emulsion polymerization is adjusted to a concentration of 15% by mass using pure water. Approximately 750 ml of the dispersion is then placed in a polyethylene container (1000 ml capacity) and vigorously shaken by hand to agglomerate the polymer. The polymer powder separated from the water is dried at 150°C for 16 hours. 12.0 g of the dried resin powder is placed in a cylindrical mold with a diameter of 2.85 cm and flattened. After 30 seconds, a final pressure of 350 kg / cm is applied. 2 The pressure was gradually increased to 350 kg / cm 2 The preform thus obtained is fired in an air furnace at 380°C for 30 minutes, then cooled to 294°C at a rate of 1°C per minute, held at 294°C for 1 minute, removed from the air furnace, and cooled to room temperature (23±1°C) to form a standard sample. The ratio of the weight of the standard sample to the weight of the same volume of water at room temperature (23±1°C) is taken as the standard specific gravity. This standard specific gravity serves as a guide for the average molecular weight, and generally the lower the standard specific gravity, the higher the molecular weight.

[0036] (4) Static settling test As shown in Table 1, 18.0 g of the dust-inhibitory treatment composition or the PTFE aqueous dispersion was placed in a test tube, the mouth of the test tube was sealed with parafilm, and the contents were mixed by repeatedly inverting the tube upside down 20 times. The tubes were then left to stand at room temperature for 30 days or 60 days. After leaving the tubes to stand for 30 or 60 days, the parafilm was removed, and everything except the settled solids (liquid portion: supernatant and dust-inhibitory treatment composition) was removed. The weight of the removed liquid (the sum of the weight of the test tube and the amount of solids settled to the bottom of the test tube) was measured, and the amount of solids after leaving the tubes to stand was calculated.

[0037] (5) Static settling and redispersion test The weight of the test tube left standing in (4) above was measured, 10 g of pure water was added to the test tube, the mouth of the test tube was sealed with parafilm, and the mixture was mixed by turning it upside down 20 times. Thereafter, the liquid portion other than the solid content that had settled to the bottom of the test tube (the supernatant and the dust-suppressing treatment composition) was removed, and its weight (the sum of the weight of the test tube and the amount of solid content that had settled to the bottom of the test tube) was measured, and the amount of solid content after redispersion was calculated.

[0038] (6) Centrifugal sedimentation test 10 g of the dust-inhibiting treatment composition or PTFE aqueous dispersion having the composition shown in Table 2 was placed in a centrifuge tube (15 ml centrifuge tube manufactured by Corning Inc.) and centrifuged for 30 minutes at 20°C and 3000 rpm using a centrifuge (Tabletop Refrigerated Centrifuge 5500, Angle Rotor RA508 manufactured by Kubota Corporation). After centrifugation, everything except the solids that had settled to the bottom of the centrifuge tube (liquid portion: supernatant and dust-inhibiting treatment composition) was removed from the centrifuge tube, the centrifuge tube was left in an inverted position for 30 minutes, the liquid portion was further removed, and its weight (the sum of the weight of the centrifuge tube and the amount of solids that had settled to the bottom of the centrifuge tube) was measured. The solids sedimentation ratio was calculated using the above-mentioned formula (2), and the sedimentation rate was calculated using the above-mentioned formula (1).

[0039] (7) Centrifugal redispersion test The weight of the centrifuge tube from which the liquid portion was removed in (6) above was measured, 10 g of pure water was added to the centrifuge tube, and the solids that had settled to the bottom of the centrifuge tube were ultrasonically dispersed at 38 kHz for 1 minute. After that, all the solids (liquid portion) other than the solids that had settled to the bottom of the centrifuge tube were removed, and the centrifuge tube was left in an inverted position for 30 minutes to further remove the liquid portion. The weight (the sum of the weight of the centrifuge tube and the amount of solids that had settled to the bottom of the centrifuge tube) was measured, and the redispersed solid sedimentation ratio was calculated from the following formula (4), and the redispersion sedimentation rate was calculated from the following formula (3).

[0040] Redispersion sedimentation rate=X3 / X2...(3) During the ceremony, X2: The solid sedimentation rate (%), as shown by the following formula (4), when 10 g of the PTFE aqueous dispersion not containing the water-soluble cellulose derivative is centrifuged at a temperature of 20°C and a rotation speed of 3000 rpm for 30 minutes in a centrifuge and then redispersed. X3: The solid sedimentation rate (%) shown by the following formula (4) when 10 g of the dust suppressant treatment composition is centrifuged at a temperature of 20°C and a rotation speed of 3000 rpm for 30 minutes in a centrifuge and then redispersed. Solid sedimentation rate after redispersion (%) = (amount of settled solids after redispersion) / (amount of solids before centrifugation) × 100 (4)

[0041] (8) Amount of falling dust A 200g sample (dust treatment material) is allowed to fall naturally from the top opening of a cylindrical container with an inner diameter of 39cm and a height of 59cm, and the amount of suspended dust (relative concentration (CPM: Counts per Minute)) inside the container at a position 45cm above the bottom is measured using a scattered light digital dust meter. The suspended dust amount is measured by measuring five times continuously for one minute after the sample is added, and the geometric mean value after subtracting the measured value before adding the sample (dark count) is taken as the "amount of fallen dust" for the sample. The geometric mean value x is calculated using the following formula (5):

[0042] Log x=1 / 5×Σlog(xi‐d) ···(5) In the formula, xi: amount of individual suspended dust particles, and d: dark count.

[0043] Examples 1 and 2 A PTFE aqueous dispersion (average particle size 0.2 μm, fluorine-containing emulsifier content 21 ppm, specific gravity (SSG) 2.19, containing 3.0% by mass of anionic surfactant relative to the weight of PTFE) having a resin solids concentration of 30% by mass obtained by emulsion polymerization, and hydroxypropyl methylcellulose (HPMC) (Metolose (registered trademark) 65SH manufactured by Shin-Etsu Chemical Co., Ltd.) were used in the amounts shown in Table 1 to prepare a dust suppressant treatment composition. The dust-suppressing treatment composition thus obtained was subjected to a static settling test and a static settling redispersion test, and the results are shown in Table 1 and FIG.

[0044] (Comparative Example 1) The aqueous PTFE dispersion having a resin solid content concentration of 30 mass % used in Example 1 was used to carry out a static settling test and a static settling re-dispersion test in the same manner as in Example 1. The results are shown in Table 1 and FIG.

[0045] Examples 3 to 5 Using the PTFE aqueous dispersion with a resin solids concentration of 30 mass% used in Example 1 and HPMC, a dust-inhibiting treatment composition was prepared with the composition shown in Table 2. The obtained dust-inhibiting treatment composition was subjected to a centrifugal sedimentation test and a centrifugal redispersion test. The results are shown in Table 2.

[0046] (Comparative Example 2) The PTFE aqueous dispersion having a resin solid content concentration of 30 mass % used in Example 1 was subjected to a centrifugal sedimentation test and a centrifugal redispersion test in the same manner as in Example 3. The results are shown in Table 2.

[0047] Example 6 200 g of the aqueous PTFE dispersion with a resin solids concentration of 30% by mass used in Example 1 was left to stand in a refrigerator (1 to 3°C) for 40 hours to separate into a resin phase and a supernatant phase. The supernatant phase was then recovered to obtain an aqueous PTFE dispersion with a resin solids concentration of 66.6% by mass and a surfactant concentration of 2.6% by mass. The recovered supernatant phase was added to the resulting aqueous PTFE dispersion to adjust the resin solids concentration to 60.0% by mass. This aqueous PTFE dispersion with a resin solids concentration of 60.0% by mass and the HPMC used in Example 1 were used to prepare a dust-inhibiting treatment composition with a total weight of 15.0 g and 0.18% by mass of HPMC, as shown in Table 2. The resulting dust-inhibiting treatment composition was subjected to a centrifugal sedimentation test and a centrifugal redispersion test. The results are shown in Table 2.

[0048] [Table 1]

[0049] [Table 2]

[0050] Example 7 1,000 g of powdered quicklime containing 92.3% CaO and 1.1% MgO (powdered quicklime that passed through a 2.0 mm standard mesh sieve, 6.69% on a 600 μm standard mesh sieve, 23.07% on a 300 μm standard mesh sieve, 20.00% on a 150 μm standard mesh sieve, and 50.24% passing through a 150 μm standard mesh sieve) was added to a small soil mixer with a volume of 5 liters, and while stirring at a rotation speed of 140 rpm, a mass of the dust suppressant treatment composition prepared in Example 5 equivalent to 0.1 g of PTFE in terms of resin solids (0.01% by mass of PTFE resin solids relative to the quicklime) was weighed out, and the dust suppressant treatment composition was diluted with fresh water so that the total amount of water contained in the dust suppressant treatment composition and the fresh water was 100 g, and the dispersion obtained by dispersing the composition was gradually added. Approximately one minute after the start of addition, steam began to be generated due to the heat generated by the hydration reaction of the quicklime, and approximately two minutes later, all of the water was used up to produce slaked lime through hydration of the quicklime, and steam generation ceased. Three minutes after the start of mixing, the mixer's stirring was stopped. At this point, the temperature was measured with a thermometer and was 116°C. This dust-suppressed quicklime was a mixture of quicklime and slaked lime, with approximately 30% slaked lime newly produced by the hydration reaction. The amount of falling dust from the resulting dust-suppressed product was measured. The results are shown in Table 3.

[0051] (Example 8, Comparative Example 3) Using the dust-suppressing treatment compositions prepared in Example 6 and Comparative Example 1, a dust-suppressed mixture of quicklime and slaked lime was obtained in the same manner as in Example 7. The amount of falling dust from the obtained dust-suppressing treated product was measured. The results are shown in Table 3.

[0052] Example 9 The dust-suppression treatment composition prepared in Example 5 was weighed out in an amount equivalent to 0.2 g of PTFE in terms of resin solids (0.02% by mass of PTFE resin solids relative to quicklime), and diluted with fresh water so that the total amount of water contained in the dust-suppression treatment composition and the fresh water was 100 g. A mixture of dust-suppressed quicklime and slaked lime was obtained in the same manner as in Example 7, except that a dispersion of the composition was used. The amount of fallen dust from the resulting dust-suppression treated product was measured. The results are shown in Table 3.

[0053] (Example 10, Comparative Example 4) Using the dust-suppressing treatment compositions used in Example 6 and Comparative Example 1, a mixture of dust-suppressed quicklime and slaked lime was obtained in the same manner as in Example 9. The amount of falling dust from the obtained dust-suppressing treated product was measured. The results are shown in Table 3.

[0054] (Comparative Example 5) The amount of falling dust from the mixture of quicklime and slaked lime obtained in the same manner as in Example 7 was measured, except that no dust-suppressing treatment composition was used and 100 g of fresh water was used. The results are shown in Table 3.

[0055] [Table 3] [Industrial Applicability]

[0056] The dust-suppressing treatment composition of the present invention is suitably used for dust-suppressing treatment of dust-generating substances to obtain dust-suppressed treated products of dust-generating substances in the fields of building materials, soil stabilizers, solidifying materials, fertilizers, landfill disposal of incineration ash or hazardous substances, explosion prevention, cosmetics, and fillers for various plastics.

Claims

1. A dust suppression treatment composition for dust-generating substances, characterized by comprising a water-soluble cellulose derivative containing at least hydroxypropyl methylcellulose having a melting point of 225 to 230°C, and an aqueous dispersion of polytetrafluoroethylene.

2. 2. The dust suppressant treatment composition according to claim 1, wherein the water-soluble cellulose derivative is contained in an amount of 0.01 to 1.00% by mass.

3. 3. The dust suppressant treatment composition according to claim 1, wherein the polytetrafluoroethylene aqueous dispersion contains polytetrafluoroethylene in an amount of 1 to 80% by mass.

4. 4. The dust-suppressing treatment composition according to claim 1, wherein the dust-generating substance is a dust-generating powdery substance.

5. 5. The dust suppressant treatment composition according to claim 1, wherein the sedimentation rate represented by the following formula is less than 1.0: Sedimentation rate = X1 / X0 < 1.0 During the ceremony, X0: The solid sedimentation rate (%), as expressed by the following formula, when 10 g of the aqueous polytetrafluoroethylene dispersion not containing the water-soluble cellulose derivative is centrifuged in a centrifuge at a temperature of 20°C and a rotation speed of 3,000 rpm for 30 minutes. X1: The solid sedimentation rate (%), as shown by the following formula, when 10 g of the dust-suppressing treatment composition is centrifuged in a centrifuge at a temperature of 20° C. and a rotation speed of 3,000 rpm for 30 minutes. Solid sedimentation rate (%) = (amount of solid sedimentation after centrifugation) / (amount of solids before centrifugation) × 100

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