JP2011236436A - Method for suppression-treating dust - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for suppression-treating dusts of dusting substances, which uses a composition of a dust suppression-treating agent comprising a PTFE aqueous dispersion liquid having little possibility of imparting the environmental problem, has a high dust suppressing effect, and has little possibility of imparting the environmental problem; and to provide dust-suppressed materials of dusting substances.SOLUTION: The method for suppression-treating dusts of dusting substances includes: mixing the dust suppression-treating agent composition comprising an aqueous dispersion liquid of a polytetrafluoroethylene having a fluorine-containing emulsifier content of ≤50 ppm wherein the specific gravity of the polytetrafluoroethylene is ≤2.27 and the average particle diameter thereof is 0.1 to 0.5 μm, and containing a hydrocarbon-based anionic surfactant as an emulsion stabilizer, with the dusting substances; and subjecting the mixture to a compression-shearing action at about 20 to 200°C, to thereby fibrillate the polytetrafluoroethylene.

Description

  The present invention relates to a dust suppression treatment method using a dust suppression treatment agent composition comprising an aqueous dispersion of polytetrafluoroethylene (hereinafter referred to as PTFE) having a high dustproof effect and less concern for the environment. More specifically, the present invention relates to a dust suppression treatment method using a dust suppression treatment composition comprising an aqueous dispersion of polytetrafluoroethylene (hereinafter referred to as PTFE) in which the content of a fluorine-containing emulsifier is in a specific range, and The present invention relates to a dust suppression treatment product using a dust suppression treatment agent composition comprising an aqueous dispersion of polytetrafluoroethylene (hereinafter referred to as PTFE) with little environmental concern.

The technology for controlling dust, which is a substance that generates dust, is an important technology for daily life and industry for health, safety, environmental and other demands.
As such dust control technology, in Japanese Patent Publication No. 52-32877, PTFE is fibrillated by mixing PTFE with a powdery substance and subjecting the mixture to a compression-shearing action at a temperature of about 20 to 200 ° C. Thus, a method for suppressing dust generation of a powdery substance has been proposed.

  The PTFE described in the proposal is a tetrafluoroethylene homopolymer as a composition, Teflon (registered trademark) 6 or Teflon (registered trademark) 30 as a fine powder or emulsion as a form, and tetrafluoro as a composition. The modified polymer of ethylene is Teflon (registered trademark) 6C, which is also a fine powder.

  JP-A-8-20767 proposes a stable dust control method using an aqueous emulsion containing 1.0% by weight or more of a hydrocarbon-based anionic surfactant with respect to PTFE. Cement has been shown to have a dust control effect. According to the publication, PTFE particles are prepared by emulsion polymerization disclosed in US Pat. No. 2,559,752, that is, an anionic system using tetrafluoroethylene as a water-soluble polymerization initiator and a fluoroalkyl group as a hydrophobic group. A surfactant (hereinafter referred to as a fluorine-containing emulsifier) is injected into an aqueous medium containing an emulsifier and polymerized to produce it in the form of an aqueous emulsion, but an emulsion stabilizer is added to increase the stability. Yes.

However, these dust control agents are used in large quantities in fertilizers, soil stabilizers, soil conditioners, and landfill materials such as coal ash. Has become a concern.
A surfactant (fluorine-containing emulsifier) contained as an emulsifier in an aqueous PTFE dispersion is used for polymerization, but it is hardly decomposable and there is a concern about influence on the environment. Moreover, since it is not biodegradable but classified as an environmental pollutant, it has been possible to pollute groundwater, lakes and rivers.
Therefore, the present inventors have reached the present invention as a result of intensive efforts to develop a method that has a dust suppressing effect and can suppress dust without concern about the influence on the environment.

Japanese Patent Publication No. 52-32877 JP-A-8-20767 US Pat. No. 2,559,752

The present inventors have disclosed that surfactants (fluorine-containing emulsifiers) contained as an emulsifier in PTFE aqueous dispersions are indispensable in polymerization to obtain PTFE aqueous dispersions, but are hardly decomposable and have an impact on the environment. Focusing on the concerns, we developed a dust control method that is less likely to cause environmental problems.
That is, the present invention uses a dust suppression treatment composition composed of an aqueous PTFE dispersion having a low possibility of environmental problems, and has a high dust suppression effect as in the conventional method and a low possibility of environmental problems. It is an object of the present invention to provide a dust suppressing treatment method for dust generating substances and a dust suppressing treatment product for dust generating substances.

The present invention comprises an aqueous dispersion of polytetrafluoroethylene having a fluorine-containing emulsifier content of 50 ppm or less, the polytetrafluoroethylene having a specific gravity of 2.27 or less, and an average particle size of 0.1 to 0.1. 0.5μm der is, an emulsion stabilizer dust suppression treatment composition containing a hydrocarbon-based anionic surfactant is mixed with dusting material as compression at a temperature of about 20 to 200 ° C. to the mixture - Provided is a dust control method for a dusting substance that suppresses dust of a dusting substance by fibrillating polytetrafluoroethylene by applying a shearing action.

  The present invention also provides a dust suppression treatment product of a dust generating material in which dust is suppressed, which is obtained by the dust suppression processing method described above.

According to the present invention, dust generation effect using a dust suppression treatment composition composed of an aqueous PTFE dispersion having a low possibility of environmental problems is high as in the conventional method, and the possibility of environmental problems is low. Provided is a method for controlling dust of a sexual substance.
According to the present invention, there is provided a dust suppressing treatment product of a dust generating substance that is processed by an excellent dust suppressing method of a dust generating substance and that is less likely to cause environmental problems.

  In the present invention, a dust suppressing treatment composition comprising an aqueous dispersion of polytetrafluoroethylene having a fluorine-containing emulsifier content of 50 ppm or less is mixed with a dusting substance, and the mixture is heated to a temperature of about 20 to 200 ° C. A dust-reducing treatment method for a dust-generating substance that suppresses dust of a dust-generating substance by fibrillating polytetrafluoroethylene by applying a compression-shearing action, and a dust-suppressing treatment product for the dust-generating substance are provided. .

The PTFE of the present invention includes a tetrafluoroethylene (TFE) homopolymer (PTFE) called a homopolymer and a tetrafluoroethylene copolymer (modified PTFE) containing 1% or less of a comonomer called a modified polymer. It is done. PTFE is preferably a homopolymer of TFE.
The dust suppression treatment agent composed of the modified PTFE aqueous dispersion has a lower dust suppression effect than the dust suppression treatment agent composed of the PTFE aqueous dispersion, and the amount of the treatment agent used is often 50% or more in order to produce the same dust suppression effect. There are things you have to do.

The fluoropolymer in the fluoropolymer aqueous dispersion of the present invention is desirably a colloidal particle having an average particle size of about 0.1 to 0.5 μm, preferably about 0.1 to 0.3 μm. Colloidal particles having an average particle size of less than 0.1 μm have a low dustproof effect, while an aqueous dispersion of colloidal particles having an average particle size of more than 0.5 μm has a disadvantage of low stability.
The specific gravity is 2.27 or less, preferably 2.22 or less, more preferably 2.20 or less. Polytetrafluoroethylene having a specific gravity exceeding 2.27 also has a drawback that the dustproof effect is low.

  The concentration of the fluoropolymer in the aqueous fluoropolymer dispersion of the present invention is not particularly limited, but in order to enhance the effect of dispersing the fluoropolymer in the dust generating substance, the lower the concentration, the better. On the other hand, when the fluoropolymer aqueous dispersion is transported, the higher the concentration, the more the transportation cost can be saved. Therefore, it is usually 10% by weight or more, preferably 20 to 70% by weight. A higher concentration is not preferable because it impairs the stability of the aqueous fluoropolymer dispersion. Accordingly, the concentration of the fluoropolymer in the dust control agent composition sold as a product is 20 to 70% by weight, and when mixed into a dust generating substance, it is diluted with water to 5% by weight or less. It can also be used as the fluoropolymer concentration.

  The fluorine-containing emulsifier of the fluoropolymer aqueous dispersion of the present invention is hardly decomposable and is likely to accumulate in the environment, so it is desired that the content is low, and the fluorine-containing emulsifier is stabilized by a practical removal method. It is preferable that it is 50 ppm or less which can be manufactured at a content rate.

  There is no particular limitation on the method for obtaining an aqueous dispersion of a fluoropolymer having a content of the fluoroemulsifier of the present invention of 50 ppm or less. For example, emulsification weight as disclosed in US Pat. No. 2,559,752 Fluorine-containing emulsifiers obtained by injection and polymerization in an aqueous solution containing an anionic surfactant (fluorine-containing emulsifier) having a fluoroalkyl group as a hydrophobic group using tetrafluoroethylene as a water-soluble polymerization initiator and emulsifier A known method for removing the fluorine-containing emulsifier from an aqueous dispersion containing about 0.02 to 1% by weight (perfluorooctanoic acid in the form of ammonium salt and / or alkali salt) with respect to the weight of the fluorine-containing polymer, for example, Effectiveness described in Table 2005-501956 (WO 2003/020836) and Special Table 2002-32583 (WO 00/35971) Removing by contacting with an amount of anion exchanger and separating, or removing by fluorofiltration of an aqueous fluoropolymer dispersion described in US Pat. No. 4,369,226 Can be obtained. The method for removing the fluorine-containing emulsifier is not limited to these.

  A surfactant (fluorinated emulsifier) contained as an emulsifier in an aqueous PTFE dispersion is indispensable because of reaction inactivity in polymerization, but it is difficult to decompose and there is a concern about the influence on the environment. It is desirable to remove as much as possible. Moreover, since the fluorine-containing emulsifier is expensive, it is desirable to collect and reuse it.

In the emulsion polymerization method for obtaining the fluoropolymer aqueous dispersion of the present invention described above, the emulsifier disclosed in US Pat. No. 2,559,752 can be selected and used as the emulsifier. For this purpose, an emulsifier that may be called a non-telogenic emulsifier is particularly preferable. For example, F (CF ₂ ) n (CH ₂ ) mCOOH having about 6 to 20 carbon atoms, preferably about 6 to 12 carbon atoms m: 0 or 1, n: 6 to 20), a fluorine-containing alkanoic acid or a salt thereof, a fluorine-containing alkylsulfonic acid or a salt thereof, and the like. Examples of the salt include alkali metal salts, ammonium salts, and amine salts. Specific examples include perfluoroheptanoic acid, perfluorooctanoic acid, and salts thereof, 2-perfluorohexylethanesulfonic acid, and salts thereof, but are not limited thereto.

  Furthermore, the fluoropolymer aqueous dispersion of the present invention may contain an emulsion stabilizer in order to improve the stability of the fluoropolymer aqueous dispersion. As the emulsion stabilizer, a hydrocarbon-based anionic surfactant is preferable. This surfactant forms salt, which is essentially insoluble in water and calcium, aluminum, and iron, which are components in the soil, and can avoid river, lake and groundwater contamination caused by the surfactant. .

Examples of such hydrocarbon anionic surfactants include higher fatty acid salts, higher alcohol sulfate esters, liquid fatty oil sulfate esters, aliphatic alcohol phosphate esters, dibasic fatty acid ester sulfonates, alkyl allyls. Although there are sulfonates, etc., in particular, polyoxyethylene alkylphenyl ether ethylene sulfonic acid (wherein polyoxyethylene n is 1 to 6, alkyl has 8 to 11 carbon atoms), alkylbenzene sulfonic acid (alkyl has 10 to 10 carbon atoms). 12) and Na, K, Li, and NH ⁴ salts such as dialkylsulfosuccinic acid esters (wherein the alkyl has 8 to 10 carbon atoms) give high mechanical stability to the aqueous PTFE emulsion, and should be exemplified as preferred. Can do.

  The addition amount of the emulsion stabilizer is 1.0% by weight or more per weight of PTFE, preferably in the range of 1.5 to 5% by weight. When the addition amount is less than 1.0% by weight, the effect of stabilizing the fluoropolymer aqueous dispersion is low, and when the addition amount is 10% by weight or more, it is economically disadvantageous.

  In the dust suppression treatment method of the present invention, PTFE is mixed with a dusting substance, and the mixture is subjected to a compression-shearing action at a temperature of 20 to 200 ° C. to thereby fibrillate PTFE and suppress dust of the dusting substance. For example, in a method such as Japanese Patent No. 2827152, Japanese Patent No. 2538783, etc., it is preferable to use a dust suppressing treatment agent comprising a PTFE aqueous dispersion having a fluorine-containing emulsifier content of 50 ppm or less.

  Moreover, the dust suppressing treatment agent composition used in the present invention can be used as the fibrillating PTFE described in JP-A No. 2000-185556, JP-A No. 2000-185959, and JP-A No. 2002-60738.

  When a specific polytetrafluoroethylene is subjected to compression-shearing under appropriate conditions as described above, it becomes ultrafine fibers in a fibrillated cobweb shape. It is considered that the dust-generating substance is captured and aggregated in the spider web-like fine fibers to suppress dust.

  In the present invention, the dust generating material to be subjected to dust suppression treatment is an inorganic and / or organic dust generating material, and there is no particular limitation on the material, shape, and the like. The present invention can also be effectively applied to a dusting powdery substance as a dusting substance. Particularly suitable dusting substances include, for example, cements such as Portland cement and alumina cement, slaked lime, quicklime powder, calcium carbonate, dolomite, magnesite, talc, silica, fluorite and other mineral powders, kaolin, bentonite, etc. Clay mineral powder such as steel, slag powder produced as a by-product in the manufacturing process of non-ferrous metals, combustion ash powder such as coal and garbage, gypsum powder, powdered metal, carbon black, activated carbon powder, metal oxide, etc. Ceramic powders, pigments, and the like, that is, all dust generating substances that generate dust by scattering and floating in the air.

  The dust suppression treatment method of the present invention includes the building material field, the soil stabilizing material field, the solidified material field, the fertilizer field, the landfill disposal field for incinerated ash and harmful substances, the explosion-proof field, the cosmetics field, the field of fillers for various plastics, etc. Is suitably used to obtain a dust-suppressed product of a dust generating substance.

The present invention will be described more specifically with reference to examples and comparative examples below, but this description does not limit the present invention.
In the present invention, each physical property was measured by the following method.

(1) Average particle diameter of fluoropolymer particles The average particle diameter of the fluoropolymer particles was measured by Microtrac UPA150 Model No. It measured using 9340 (made by Nikkiso Co., Ltd.).
(2) Particle Size of Dust-Generating Powder Using a laser diffraction / scattering particle size distribution measuring instrument manufactured by Horiba Ltd., ethanol was measured as a dispersion medium.

(3) Standard specific gravity of fluoropolymer Measured by ASTM D-4894.
The PTFE aqueous dispersion obtained by emulsion polymerization is adjusted to a concentration of 15% by weight using pure water. Thereafter, the polymer is aggregated by vigorously shaking about 750 ml in a polyethylene container (1000 ml capacity). The polymer powder separated from the water is dried at 150 ° C. for 16 hours. The dried resin powder 12.0g break were placed in cylindrical mold having a diameter of 2.85Cm, gradually increasing the pressure to a final pressure becomes 350 kg / cm ² after 30 seconds, at a final pressure of 350 kg / cm ² Hold for 2 minutes. The preform thus obtained was fired in an air furnace at 380 ° C. for 30 minutes, cooled to 294 ° C. at a rate of 1 ° C. for 1 minute, held at 294 ° C. for 1 minute, and then from the air furnace. Take out and cool at room temperature (23 ± 1 ° C.) to make a standard sample. The weight ratio of the standard sample to the weight of the same volume of water at room temperature (23 ° C. ± 1 ° C.) is defined as the standard specific gravity.
This standard specific gravity is a measure of the average molecular weight. In general, the lower the standard specific gravity, the higher the molecular weight.

(4) Concentration of fluorinated emulsifier in fluororesin aqueous dispersion The fluororesin aqueous dispersion was frozen in a −20 ° C. freezer, and the fluoropolymer was aggregated and separated from water. The entire contents of the plastic container are transferred to a Soxhlet extractor and extracted with about 80 ml of methanol for 7 hours. The sample solution that has been measured up is measured with a liquid chromatograph, and the concentration of the fluorinated emulsifier in the aqueous fluororesin dispersion is calculated.

(5) Amount of falling dust 200 g of the sample is naturally dropped from the top inlet of a cylindrical container having an inner diameter of 39 cm and a height of 59 cm, and the amount of suspended dust (relative concentration (CPM: Count per minute) in the container at a height of 45 cm from the bottom. ) Is measured with a scattered-light digital dust meter, and the amount of airborne dust is measured five times for 1 minute after the sample is added, and the geometric average value obtained by subtracting the measured value (dark count) before the sample is added. Is the “falling dust amount.” The geometric mean value x is determined by the following equation.
Log x = 1/5 · Σlog (xi-d)
Here, xi: individual suspended dust amount, d: dark count.

(material)
The raw materials used in the examples and comparative examples of the present invention are as follows.
(1) PTFE aqueous dispersion (I)
(Average particle size 0.2 μm, resin solid content concentration 30 wt%, fluorine-containing emulsifier content 21 ppm, specific gravity 2.19, anionic surfactant is included 3.5 wt% with respect to the weight of PTFE)
(2) PTFE aqueous dispersion (II)
(Mitsui DuPont Fluorochemicals, 312-J, fluorine-containing emulsifier content 1040 ppm, specific gravity 2.19, containing 3.0% by weight of anionic surfactant based on the weight of PTFE)
(3) Powdered quicklime (CaO 93.5%, MgO 4.2%)
Powdered lime with a 300 μm standard mesh screen throughout, 150 μm standard screen screen residue 0.04%, 90 μm standard screen screen residue 0.17%, 90 μm standard screen screen through 99.83% Normal Portland cement (NPC) (Pacific cement)
(5) Type II anhydrous gypsum (average particle size 9.0 μm, maximum particle size 101 μm)
(6) Granulated blast furnace slag powder (average particle size 8.9 μm, maximum particle size 100 μm)

Example 1
1. 1,000 g of powdered quicklime was put into a small soil mixer having a volume of 5 liters and stirred at a rotational speed of 140 rpm, 1.67 g of the PTFE aqueous dispersion (I) (PTFE resin solid content 0. (Corresponding to 05% by mass) was gradually added to a dispersion of 98.8 g of fresh water.
About 1 minute after the start of charging, steam started to be generated due to the heat of hydration reaction of quick lime, and after about 2 minutes, all of the water was used up for the production of slaked lime due to the hydration of quick lime, and the generation of water vapor was eliminated. After 5 minutes from the start of stirring, stirring of the mixer was stopped. The temperature at this time was 95 ° C. when measured with a mercury thermometer. The quicklime subjected to the dust suppression treatment was a mixture of quicklime and slaked lime containing about 30% of slaked lime newly generated by a hydration reaction. The amount of falling dust of the quicklime that had been dust-suppressed was measured. The results are shown in Table 1.

(Example 2)
Dust in the same manner as in Example 1 except that a dispersion in which 1.00 g of PTFE aqueous dispersion (I) (corresponding to a solid content of PTFE resin of 0.03 mass% with respect to quicklime) was dispersed in 99.3 g of fresh water was used. Inhibited quick lime was obtained. The amount of falling dust of the obtained quick lime subjected to the dust suppression treatment was measured. The results are shown in Table 1.

(Example 3)
This is a method of heating dust from ordinary Portland cement (dust generating powder) using the heat of hydration reaction of quicklime and performing dust suppression treatment.
While putting 100 g of powdered quicklime into a small soil mixer having a volume of 5 liters and stirring at a rotational speed of 140 rpm, 1.67 g of PTFE aqueous dispersion (I) (PTFE resin solid content 0.50 mass relative to quicklime) %) Was gradually added to 35.0 g of fresh water.
About 1 minute after the start of charging, steam started to be generated due to the heat of hydration reaction of quick lime, and after about 2 minutes, all of the water was used up for the production of slaked lime due to the hydration of quick lime, and the generation of water vapor was eliminated. After 5 minutes from the start of stirring, stirring of the mixer was stopped. The temperature at this time was 95 ° C. when measured with a mercury thermometer. The quicklime subjected to the dust suppression treatment was a dumpling mixture of quicklime and slaked lime containing slaked lime newly generated by a hydration reaction.

  Using this as a master of the master batch, 900 g of ordinary Portland cement was gradually added while stirring with a small soil mixer (rotation speed 140 rpm). Mixing of ordinary Portland cement was stopped after about 5 minutes. The temperature at this time was 57 ° C. when measured with a mercury thermometer. The amount of falling dust of the ordinary Portland cement subjected to the dust suppression treatment was measured. The results are shown in Table 1.

(Examples 4 to 6)
200 g of the dusting powder shown in Table 1 was preheated to 90 ° C. with an electric heating dryer. 20 g of heated dusting powder and a PTFE aqueous dispersion (I) having a solid content ratio (mass%) shown in Table 1 were heated in advance by an electrothermal drier at 90 ° C. to a volume of 1 liter of alumina. Mixing and stirring for about 5 minutes in a mortar gave a mixture. The obtained mixture was used as a master, and the remaining 180 g of the heated dust generating powder was added to the master and mixed and stirred for about 5 minutes to obtain a dust generating powder subjected to dust suppression treatment. The amount of falling dust of the resulting dusting powder was measured. The results are shown in Table 1.

(Comparative Example 1)
The amount of falling dust of quicklime was measured. The results are shown in Table 1.

(Comparative Example 2)
The amount of falling dust of normal Portland cement was measured. The results are shown in Table 1.

(Comparative Example 3)
The amount of falling dust of type II anhydrous gypsum was measured. The results are shown in Table 1.

(Comparative Example 4)
The amount of falling dust of granulated blast furnace slag powder was measured. The results are shown in Table 1.

(Reference Example 1)
Dust in the same manner as in Example 1 except that 1.67 g of PTFE aqueous dispersion (II) (corresponding to PTFE resin solid content of 0.05% by mass with respect to quicklime) was dispersed in 98.8 g of fresh water. Inhibited quick lime was obtained. The amount of falling dust of the obtained quick lime subjected to the dust suppression treatment was measured. The results are shown in Table 1.

(Reference Example 2)
Dust in the same manner as in Example 1 except that a dispersion obtained by dispersing 1.00 g of PTFE aqueous dispersion (II) (corresponding to 0.03% by mass of PTFE resin solid content with respect to quicklime) in 99.3 g of fresh water was used. Inhibited quick lime was obtained. The amount of falling dust of the obtained quick lime subjected to the dust suppression treatment was measured. The results are shown in Table 1.

(Reference Examples 3-5)
Except for using the PTFE aqueous dispersion liquid (II), dust-generating powders with reduced dust were obtained in the same manner as in Examples 4-6. The amount of falling dust of the resulting dusting powder was measured. The results are shown in Table 1.

  According to the present invention, a dust-generating substance using a dust-controlling agent composed of a PTFE aqueous dispersion having a low possibility of environmental problems has a high dust-control effect as in the conventional method and has a low possibility of environmental problems. There are provided a dust suppression treatment method and a dust suppression treatment product of a dusting substance.

Claims (5)

It consists of an aqueous dispersion of polytetrafluoroethylene having a content of fluorine-containing emulsifier of 50 ppm or less, the specific gravity of the polytetrafluoroethylene is 2.27 or less, and the average particle size is 0.1 to 0.5 μm. Yes, a dust control agent composition containing a hydrocarbon-based anionic surfactant as an emulsion stabilizer is mixed with a dusting substance, and the mixture is subjected to a compression-shearing action at a temperature of about 20 to 200 ° C. The dust-reducing treatment method for a dust-generating substance that suppresses dust of the dust-generating substance by fibrillating polytetrafluoroethylene. The dust control method for dusting substances according to claim 1, wherein the hydrocarbon-based anionic surfactant is 1.0 wt% or more and less than 10 wt% per weight of polytetrafluoroethylene. .   The dust control method for a dust generating material according to claim 1 or 2, wherein the dust generating material is a dust generating powdery material.   A dust suppression treatment product of a dust generating substance in which dust is suppressed by the dust suppression processing method according to claim 1.   The dust control treatment product of dust generating substances according to claim 4, wherein dusts are suppressed with respect to dust generating substances that can be used in building materials, soil stabilizing materials, solidifying materials, or fertilizers.