JP7386610B2 - PTFE aqueous dispersion and dust suppression treatment agent composition comprising the aqueous dispersion - Google Patents

Description

The present invention relates to an aqueous dispersion of polytetrafluoroethylene (hereinafter referred to as PTFE), which has a high dustproofing effect and excellent dispersion stability and redispersibility. ) is from 1 to 6.

BACKGROUND ART Technology for suppressing dust from substances that produce dust is an important technology for life and industry due to health, safety, environmental, and other requirements.
As such dust suppression technology, Patent Document 1 below discloses that PTFE is mixed with a powdery substance, and the mixture is subjected to a compression-shearing action at a temperature of about 20 to 200°C to fibrillate the PTFE and form it into a powdery substance. Methods have been proposed to suppress the generation of dust from materials.

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

Further, Patent Document 2 below proposes a highly stable dust suppression method using an aqueous emulsion containing 1.0% by mass or more of a hydrocarbon-based anionic surfactant based on PTFE. It has been shown that the substance has a dust suppressing effect. According to the publication, PTFE particles can be produced using the emulsion polymerization method disclosed in Patent Document 3 below, in which an anionic surfactant (hereinafter referred to as It is produced in the form of an aqueous emulsion by pressurizing it into an aqueous medium containing a fluorine-containing emulsifier) as an emulsifier and polymerizing it, but an emulsion stabilizer is further added to increase stability.

Further, in Patent Document 4 listed below, by using a dust suppression treatment composition made of an aqueous fluoropolymer dispersion in which the content of a fluorine-containing emulsifier is 50 ppm or less, there is a dust suppression effect and environmental protection. It describes a method that can suppress dust without worrying about its effects.

However, the PTFE used as the dust suppression treatment agent composition in these methods has a high molecular weight, and its aqueous dispersion tends to settle when left standing for a long period of time, and once the PTFE settles, it solidifies and becomes difficult to redisperse. Depending on the conditions of use, there is a risk that the dust suppressing effect that PTFE originally has may not be fully exhibited, such as causing a decrease in the PTFE concentration in the PTFE aqueous dispersion.
Therefore, the present inventors have devoted themselves to developing a method that has excellent dispersion stability and redispersibility, has a dust suppression effect, and can suppress dust without worrying about the impact on the environment, and as a result, has arrived at the present invention. It is something.

Special Publication No. 52-32877 Japanese Patent Application Publication No. 8-20767 U.S. Patent No. 2,559,752 International Publication No. WO2007/000812

The present inventors focused on the problem that high molecular weight PTFE in an aqueous PTFE dispersion tends to settle when left standing for a long period of time, and once the PTFE settles, it hardens solidly and is difficult to redisperse. We have developed an aqueous PTFE dispersion with excellent stability and redispersibility.
That is, an object of the present invention is to provide a PTFE aqueous dispersion that has excellent dispersion stability and redispersibility and is less likely to cause environmental problems, and a dust suppression treatment agent composition using the PTFE aqueous dispersion. do.

The present invention provides a dust-suppressing treatment agent composition for dust-producing substances comprising an aqueous dispersion of polytetrafluoroethylene, wherein the aqueous dispersion is selected from acids having an acid dissociation constant (pKa) of 1 to 6. An aqueous dispersion of polytetrafluoroethylene containing at least one of Provided is a dust-inhibiting treatment agent composition for a dust-producing substance, characterized in that the amount of the dust-producing substance is % by mass.

In the dust suppression treatment composition of the present invention,
1. The pH of the polytetrafluoroethylene aqueous dispersion is 5 to 8;
2. Containing a fluorine-containing emulsifier in an amount of 50 ppm or less,
is a preferred embodiment.

The dust suppressing agent composition of the present invention can be suitably used for dust-producing powdery substances as the dust-producing substance.

The present invention provides a PTFE aqueous dispersion that has excellent dispersion stability and redispersibility and is less likely to cause environmental problems, and a dust suppression treatment agent for dust-producing substances that suppresses dust generation and is less likely to cause environmental problems. A composition is provided.

The present invention provides an aqueous dispersion of PTFE containing at least one acid selected from acids having an acid dissociation constant (pKa) of 1 to 6, and a dust suppression treatment agent composition comprising the aqueous dispersion of PTF. By mixing this dust suppression treatment composition with a dust-generating substance and subjecting the mixture to a compression-shearing action at a temperature of about 20 to 200°C, the PTFE is fibrillated and the dust-generating substance is removed. It is possible to suppress dust.

The PTFE in the PTFE aqueous dispersion of the present invention includes a homopolymer of tetrafluoroethylene (PTFE) called a homopolymer, and a copolymer of tetrafluoroethylene containing 1% or less of a comonomer called a modified polymer (modified PTFE). can be mentioned. Preferably, the PTFE is a homopolymer of TFE.
Dust control treatment compositions made of modified PTFE aqueous dispersions have lower dust control effects than dust control treatment compositions made of PTFE aqueous dispersions, and often require a 50% or more amount to achieve the same dust control effect. Treatment agents may have to be used.

The PTFE in the aqueous PTFE dispersion of the present invention is desirably colloidal particles with an average particle size of about 0.1 to 0.5 μm, preferably about 0.1 to 0.3 μm. Colloidal particles with an average particle size of less than 0.1 μm have a low dustproofing effect, while aqueous dispersions of colloidal particles with an average particle size of more than 0.5 μm have a drawback of low stability.
Further, it is desirable that the specific gravity is 2.27 or less, preferably 2.22 or less, and more preferably 2.20 or less. PTFE with a specific gravity exceeding 2.27 also has the disadvantage of low dustproofing effect.

The PTFE concentration in the PTFE aqueous dispersion of the present invention is not particularly limited, but in order to enhance the dispersion effect of PTFE into dust-generating substances, it is preferable that the concentration is as low as possible. On the other hand, when transporting the PTFE aqueous dispersion, the higher the concentration, the more the transportation cost can be saved, so it is usually 10% by mass or more, preferably in the range of 20 to 70% by mass. Higher concentrations are not preferred because they impair the stability of the aqueous PTFE dispersion. Therefore, the PTFE concentration in the dust suppression treatment composition sold as a product is 20 to 70% by mass, and when mixed with dust-generating substances, it is diluted with water to achieve a PTFE concentration of 5% by mass or less. It is also possible to use

The acid of the present invention is preferably at least one acid selected from acids having an acid dissociation constant (pKa) of 1 to 6, preferably 2 to 6, more preferably 4 to 6.
The acid dissociation constant (pKa) indicates the ease of dissociation in an aqueous solution (ease of releasing hydrogen ions), and the larger the acid dissociation constant, the weaker the acidity.
Such an acid can improve the dispersibility and redispersibility of PTFE in the aqueous PTFE dispersion. Therefore, an acid dissociation constant of less than 1 is undesirable because it tends to cause aggregation of PTFE, and an acid dissociation constant of more than 6 is undesirable because the dispersion stabilizing effect becomes low.

Examples of such acids include dicarboxylic acids represented by HO ₂ C-(CH ₂ )n-CO ₂ H (n=0 to 4), such as oxalic acid, malonic acid, succinic acid, glutaric acid, and adipic acid. At least one selected one or a mixture thereof can be suitably used. More preferred is alkyl dicarboxylic acid, and more preferred is ethylene dicarboxylic acid (succinic acid). In the case of dicarboxylic acids, two values are obtained as the acid dissociation constant (pKa), and in the present invention, both of these two values are in the range of 1 to 6, preferably 2 to 6, more preferably 4 to 6. It is desirable that there be.
The amount of such acid added is 0.5% by mass or more based on the mass of PTFE, preferably 0.5 to 2.0% by mass, more preferably 1.0 to 2.0% by mass. . If the amount added is less than 0.5% by mass, the effect of stabilizing the dispersion of the aqueous PTFE dispersion will be low, and if it exceeds 2% by mass, it will cause aggregation of PTFE, which is not preferred.

It is desirable that the pH of the dust suppression treatment composition of the present invention is 5 to 8, preferably 5 to 7. The pH of conventional dust suppressing treatment agent compositions is alkaline with a pH of 9 to 10, but a pH of 9 to 10 is not preferred because the dispersion stability is low. Furthermore, if the pH is acidic from 1 to 4, PTFE tends to aggregate, which is not preferable.

The fluorine-containing emulsifier contained in the PTFE aqueous dispersion of the present invention is difficult to decompose and there is a concern that it may accumulate in the environment, so it is desirable that the content be low. It is preferable that the content is 50 ppm or less, which allows production at a specific content.

There are no particular limitations on the method for obtaining an aqueous PTFE dispersion in which the content of a fluorine-containing emulsifier is 50 ppm or less, but for example, the emulsion polymerization method as disclosed in the above-mentioned Patent Document 3, that is, water-soluble polymerization of tetrafluoroethylene. A fluorine-containing emulsifier (in the form of an ammonium salt and/or alkali salt) obtained by pressure injection into an aqueous medium containing an anionic surfactant (fluorine-containing emulsifier) having a fluoroalkyl group as a hydrophobic group as an initiator and an emulsifier and polymerization. The fluorine-containing emulsifier is removed from an aqueous dispersion containing about 0.02 to 1% by mass of perfluorooctanoic acid) based on the weight of the fluoropolymer, for example, by known methods such as Japanese Patent Publication No. 2005-501956 (WO2003/020836). and the method of separating and removing by contacting with an effective amount of anion exchanger described in Japanese Patent Publication No. 2002-532583 (WO00/35971), or the method of separating and removing fluorine-containing heavy metals described in U.S. Patent No. 4,369,226. It can be obtained by removing the combined aqueous dispersion by ultrafiltration. The method for removing the fluorine-containing emulsifier is not limited to these methods.

The surfactant (fluorine-containing emulsifier) contained in the PTFE aqueous dispersion as an emulsifier is indispensable because it is inactive during polymerization, but it is difficult to decompose and there are concerns about its impact on the environment, so it is used as a dust suppression treatment agent. It is desirable that they be removed from the composition as much as possible. Furthermore, since fluorine-containing emulsifiers are expensive, it is desirable that they be recovered and reused.

In the emulsion polymerization method for obtaining the aqueous PTFE dispersion of the present invention described above, the emulsifier disclosed in the aforementioned Patent Document 3 can be selected and used as the emulsifier, but for the purpose of the present invention, Particularly preferred are emulsifiers sometimes called non-telogenic emulsifiers, such as F(CF ₂ ) n(CH ₂ ) mCOOH (m: 0 or 1, n :6 to 20), fluorine-containing alkanoic acids or salts thereof, fluorine-containing alkylsulfonic acids or salts thereof, and the like. Examples of the salt include alkali metal salts, ammonium salts, and amine salts. Specific examples include perfluoroheptanoic acid, perfluorooctanoic acid, salts thereof, 2-perfluorohexylethanesulfonic acid and salts thereof, but are not limited thereto.

Furthermore, the aqueous PTFE dispersion of the present invention may contain an emulsion stabilizer to increase the stability of the aqueous PTFE dispersion. As the emulsion stabilizer, hydrocarbon anionic surfactants are preferred. This surfactant essentially forms water-insoluble or poorly soluble salts with soil components such as calcium, aluminum, and iron, making it possible to avoid river, lake, and groundwater contamination caused by surfactants. .

Examples of such hydrocarbon-based anionic surfactants include higher fatty acid salts, higher alcohol sulfate ester salts, liquid fatty oil sulfate ester salts, fatty alcohol phosphate ester salts, dibasic fatty acid ester sulfonates, and alkylaryl salts. There are sulfonic acid salts, but in particular polyoxyethylene alkylphenyl ether ethylene sulfonic acid (n of polyoxyethylene is 1 to 6, alkyl carbon number is 8 to 11), alkylbenzene sulfonic acid (alkyl carbon number is 10 to 12) and Na, K, Li, and NH ₄ salts such as dialkyl sulfosuccinic acid esters (alkyl has 8 to 10 carbon atoms) are exemplified as preferred because they provide high mechanical stability to the PTFE aqueous dispersion. be able to.

The amount of emulsion stabilizer added is 1.0% by mass or more, preferably in the range of 1.5 to 5% by mass, based on the weight of PTFE. If the amount added is less than 1.0% by mass, the effect of stabilizing the aqueous PTFE dispersion is low, and if the amount added is 10% by mass or more, it is economically disadvantageous.

The dust suppression treatment method using the dust suppression treatment agent composition of the present invention involves mixing PTFE with a dust-generating substance and subjecting the mixture to a compression-shearing action at a temperature of 20 to 200°C to fibrillate the PTFE. In the method of suppressing dust of dust-generating substances, for example, the method of Japanese Patent No. 2827152 and Japanese Patent No. 2538783, a PTFE aqueous dispersion containing a stabilizer having an acid dissociation constant in the range of 1 to 6 is used. It is preferable to use a dust suppression treatment agent composition.

Certain PTFE becomes ultra-fine fibers in the form of fibrillated spider webs when subjected to compression-shearing under moderate conditions as described above, but when treated with the dust suppression treatment composition of the present invention, It is thought that in the dust-suppressing treated product, dust-generating substances are trapped and aggregated in spider web-like fine fibers, thereby suppressing dust.

The dust-generating substance subjected to dust-suppressing treatment using the dust-suppressing treatment agent composition of the present invention is an inorganic and/or organic dust-generating substance, and there are no particular limitations on the substance, shape, etc. The present invention can be effectively applied to dust-producing powdery substances as dust-producing substances. Particularly suitable dust-generating substances that can be treated include cements such as Portland cement and alumina cement, mineral powders such as slaked lime, quicklime powder, calcium carbonate, dolomite, magnesite, talc, silica, and fluorite; Clay mineral powder such as kaolin and bentonite, metals such as steel, slag powder by-produced in the manufacturing process of non-ferrous metals, combustion ash powder such as coal and garbage, gypsum powder, powdered metals, carbon black, activated carbon powder, metals Examples include ceramic powders such as oxides, pigments, etc., that is, all dust-producing substances whose solid particulate substances are scattered and suspended in the air and generate dust.

The dust suppression treatment method using the dust suppression treatment agent composition of the present invention is applicable to various fields such as building materials field, soil stabilizing material field, solidification material field, fertilizer field, incineration ash and hazardous substance landfill disposal field, explosion prevention field, cosmetics field, etc. It is suitably used for dust-suppressing treatment in the field of fillers for plastics, etc., to obtain dust-suppressing treated products of dust-producing substances.

The present invention will be explained in more detail below by giving Examples and Comparative Examples, but this explanation does not limit the present invention.
In the present invention, each physical property was measured by the following method.

(1) Average particle size of PTFE particles The average particle size of PTFE particles is as follows: Microtrac UPA150 Model No. 9340 (manufactured by Nikkiso Co., Ltd.).
(2) Particle size of dust-generating powder Measured using a laser diffraction/scattering particle size distribution analyzer manufactured by Horiba, Ltd. using ethanol as a dispersion medium.

(3) Standard specific gravity of PTFE Measured according to ASTM D-4894.
A PTFE aqueous dispersion obtained by emulsion polymerization is adjusted to a concentration of 15% by mass using pure water. Approximately 750 ml of the mixture was then placed in a polyethylene container (1000 ml capacity) and shaken vigorously by hand to coagulate the polymer. The polymer powder separated from the water is dried at 150° C. for 16 hours. 12.0 g of dried resin powder was placed in a cylindrical mold with a diameter ^{of 2.85 cm, and the pressure was gradually increased so that the final pressure was 350 kg/cm 2 after} 30 seconds. Hold for 2 minutes. The preform thus obtained was fired in an air oven 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, and then removed from the air oven. Take out the sample, cool it to room temperature (23±1°C), and use it as 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 serves as a guideline for the average molecular weight; generally, the lower the standard specific gravity, the greater the molecular weight.

(4) Concentration of fluorine-containing emulsifier in aqueous PTFE dispersion The aqueous PTFE dispersion was placed in a -20°C freezer and frozen to coagulate PTFE and separate it from water. All contents of the plastic container were transferred to a Soxhlet extractor and extracted with about 80 ml of methanol for 7 hours. The diluted sample liquid is measured using a liquid chromatograph, and the concentration of the fluorine-containing emulsifier in the PTFE aqueous dispersion is calculated.

(5) Amount of falling dust A 200 g sample was allowed to fall naturally from the top input port of a cylindrical container with an inner diameter of 39 cm and a height of 59 cm, and the amount of suspended dust (relative concentration (CPM)) in the container at a height of 45 cm from the bottom was calculated. ) is measured using a scattered light digital dust meter.The amount of suspended dust is measured five times in a row for 1 minute after adding the sample, and the geometric mean value of the value obtained by subtracting the measured value (dark count) before adding the sample is measured. is the "falling dust amount" of the sample.The geometric mean value x is determined by the following formula.
Log x=1/5・Σlog(xI-d)
Here, xI: individual amount of suspended dust, d: dark count.

(Example 1)
An aqueous dispersion of PTFE with a resin solid content concentration of 30% by mass obtained by an emulsion polymerization method (average particle size 0.2 μm, fluorine-containing emulsifier content 21 ppm, specific gravity 2.19, anionic surfactant added to the weight of PTFE) While rotating a stirrer (100 rpm) in a beaker with a capacity of 1000 ml, 500 ml of a 6.0 mass % succinic acid aqueous solution (acid dissociation constant in water with pKa1 of 4.2 and pKa2 of 5.6) was added with a succinic acid concentration of 1.6% by mass based on the weight of PTFE, and the mixture was gently stirred for 5 minutes to obtain an aqueous PTFE dispersion (I). The resulting PTFE aqueous dispersion (I) had a pH of 7.2.
18 g of this PTFE aqueous dispersion (I) was placed in a test tube, and the amount of sedimentation after standing for 30 days and 70 days at room temperature was measured to determine the dispersion stability.
Similarly, after standing still for 30 days and after standing still for 70 days, the amount of sedimentation after shaking the test tube up and down by hand 10 times was measured to measure the amount of redispersion sedimentation. The results are shown in Table 1.

(Example 2)
An aqueous dispersion of PTFE with a resin solid content concentration of 30% by mass obtained by an emulsion polymerization method (average particle size 0.2 μm, fluorine-containing emulsifier content 21 ppm, specific gravity 2.14, anionic surfactant added to the weight of PTFE) An aqueous dispersion (II) of PTFE was obtained in the same manner as in Example 1, except that PTFE (containing 3.0% by mass) was used. The resulting aqueous PTFE dispersion (II) had a pH of 6.9.
Using this PTFE aqueous dispersion (II), the dispersion stability and redispersion sedimentation amount were measured in the same manner as in Example 1. The results are shown in Table 1.

(Comparative example 1)
An aqueous dispersion of PTFE with a resin solid content concentration of 30% by mass obtained by an emulsion polymerization method (average particle size 0.2 μm, fluorine-containing emulsifier content 21 ppm, specific gravity 2.19, anionic surfactant added to the weight of PTFE) 3.0% by mass) was used as an aqueous dispersion of PTFE (III). The aqueous dispersion (III) of PTFE had a pH of 9.0.
Using this PTFE aqueous dispersion (III), the dispersion stability and redispersion sedimentation amount were measured in the same manner as in Example 1. The results are shown in Table 1.

(Example 3)
Powdered quicklime containing 93.7% CaO and 1.06% MgO (passed through a 2.0 mm standard mesh sieve, 7.86% remaining on a 600 μm standard mesh sieve, 25.19% remaining on a 300 μm standard mesh sieve, 150 μm 1,000 g of powdered quicklime (18.80% remaining through a standard mesh sieve and 48.15% passing through a 150 μm standard mesh sieve) was put into a small soil mixer with a capacity of 5 liters, and the rotation speed was 140 r. p. m. A dispersion in which 0.33 g of PTFE aqueous dispersion (I) (PTFE resin solid content 0.10 g, equivalent to 0.01% by mass of PTFE resin solid content based on quicklime) was dispersed in 99.77 g of clean water while stirring with was gradually introduced.
Approximately 1 minute after the start of addition, water vapor began to be generated due to the heat of the hydration reaction of quicklime, and in about 2 minutes thereafter, all of the water was used to generate slaked lime due to the hydration of quicklime, and no more water vapor was generated. The stirring of the mixer was stopped 3 minutes after the start of stirring. The temperature at this time was measured with a thermometer and was 103°C. This dust-suppressed quicklime was a mixture of quicklime and slaked lime containing about 30% of slaked lime newly produced by a hydration reaction. The amount of dust generated by falling of the obtained dust-suppressed material was measured. The results are shown in Table 2.

(Example 4)
Except for using a dispersion in which 0.67 g of PTFE aqueous dispersion (I) (PTFE resin solid content 0.20 g, PTFE resin solid content equivalent to 0.02% by mass relative to quicklime) was dispersed in 99.53 g of fresh water. A mixture of quicklime and slaked lime which had been subjected to dust suppression treatment was obtained in the same manner as in Example 1. The amount of dust generated by falling of the obtained dust-suppressed material was measured. The results are shown in Table 2.

(Example 5)
Except for using a dispersion in which 0.33 g of PTFE aqueous dispersion (II) (PTFE resin solid content 0.10 g, equivalent to 0.01% by mass of PTFE resin solid content based on quicklime) was dispersed in 99.77 g of clean water. A mixture of quicklime and slaked lime which had been subjected to dust suppression treatment was obtained in the same manner as in Example 1. The amount of dust generated by falling of the obtained dust-suppressed material was measured. The results are shown in Table 2.

(Example 6)
Except for using a dispersion in which 0.67 g of PTFE aqueous dispersion (II), 0.20 g of PTFE resin solid content, equivalent to 0.02% by mass of PTFE resin solid content based on quicklime, was dispersed in 99.53 g of clean water. A mixture of quicklime and slaked lime subjected to dust suppression treatment was obtained in the same manner as in Example 1. The amount of dust generated by falling of the obtained dust-suppressed material was measured. The results are shown in Table 2.

(Comparative example 2)
Example 1 except that a dispersion dispersed in 0.33 g of PTFE aqueous dispersion (III) (PTFE resin solid content 0.10 g, equivalent to 0.01% by mass of PTFE resin solid content based on quicklime) was used. A mixture of quicklime and slaked lime which had been subjected to dust suppression treatment was obtained in the same manner. The amount of dust generated by falling of the obtained dust-suppressed material was measured. The results are shown in Table 2.

(Comparative example 3)
Except for using a dispersion in which 0.67 g of PTFE aqueous dispersion (III) (PTFE resin solid content 0.20 g, PTFE resin solid content equivalent to 0.02% by mass relative to quicklime) was dispersed in 99.53 g of fresh water. A mixture of quicklime and slaked lime which had been subjected to dust suppression treatment was obtained in the same manner as in Example 1. The amount of dust generated by falling of the obtained dust-suppressed material was measured. The results are shown in Table 2.

(Comparative example 4)
The amount of falling dust generated from the resulting mixture of quicklime and slaked lime was measured in the same manner as in Example 1, except that 100 g of fresh water was used instead of the PTFE aqueous dispersion. The results are shown in Table 2.

The present invention provides an aqueous dispersion of PTFE that has excellent dispersion stability and redispersibility and is less likely to cause environmental problems, and a dust suppression treatment for dust-producing substances that suppresses dust generation and is less likely to cause environmental problems. A pharmaceutical composition is provided.

Claims (4)

A dust-suppressing treatment agent composition for dust-producing substances comprising an aqueous dispersion of polytetrafluoroethylene, wherein the aqueous dispersion contains at least one acid selected from acids having an acid dissociation constant (pKa) of 1 to 6. An aqueous dispersion of polytetrafluoroethylene containing seeds, wherein the acid is succinic acid, and the amount of the succinic acid added is 1.0 to 2.0% by weight based on the weight of the polytetrafluoroethylene. A dust-suppressing treatment composition for dust-producing substances, characterized in that: The dust control treatment composition according to claim 1, wherein the aqueous dispersion of polytetrafluoroethylene has a pH of 5 to 8. The dust suppression treatment composition according to claim 1 or 2, which contains a fluorine-containing emulsifier in an amount of 50 ppm or less. The dust suppression treatment composition according to any one of claims 1 to 3, wherein the dust-generating substance is a dust-generating powdery substance.