JP2021178912A - Method for producing low molecular weight polytetrafluoroethylene - Google Patents

Abstract

To provide a method for producing low molecular weight PTFE in which a low molecular weight PTFE having a low PFOA content can easily be produced.SOLUTION: The method for producing low molecular weight polytetrafluoroethylene of the present invention has a step 1 in which polytetrafluoroethylene is irradiated with radiation ray to yield a low molecular weight polytetrafluoroethylene, and, after the step 1, a step 2 in which the low molecular weight polytetrafluoroethylene is subjected to a cleaning treatment using a cleaning solvent, and in which the solvent contains a fluorine-based solvent.SELECTED DRAWING: None

Description

The present invention relates to a method for producing low molecular weight polytetrafluoroethylene.

Low molecular weight polytetrafluoroethylene (also referred to as "polytetrafluoroethylene wax" or "polytetrafluoroethylene micropowder"; hereinafter, simply referred to as "low molecular weight PTFE") having a molecular weight of several thousand to several hundred thousand is chemical. In addition to excellent thermal stability and extremely low surface energy, fibrillation is unlikely to occur. Therefore, it is used in the production of plastics, inks, cosmetics, paints, greases and the like as an additive for improving the slipperiness and the texture of the coating film surface.
As a method for producing low molecular weight PTFE, Patent Document 1 discloses a method of irradiating radiation. In Patent Document 1, in order to remove perfluorooctanoic acid or a salt thereof (hereinafter, also simply referred to as “PFOA”) produced as a by-product by irradiation with radiation, a cleaning treatment using an organic solvent is performed on low molecular weight PTFE. It is disclosed that it will be applied.

International Publication No. 2019/156065

On the other hand, in recent years, from the viewpoint of environmental protection, further reduction of PFOA in materials has been required.
When the low molecular weight PTFE was washed with ethanol shown in Patent Document 1, the present inventors further found that the content of PFOA produced as a by-product did not meet the recent required level. It was found that improvement was necessary.

An object of the present invention is to provide a method for producing low molecular weight PTFE, which can easily produce low molecular weight PTFE having a low PFOA content.

As a result of diligent studies on the above problems, the present inventors have found that a desired effect can be obtained by using a cleaning solvent containing a fluorine-based solvent for cleaning a low molecular weight PTFE, and have reached the present invention.

That is, the inventors have found that the above problem can be solved by the following configuration.
[1] After the step 1 of irradiating polytetrafluoroethylene with radiation to obtain low molecular weight polytetrafluoroethylene and the above step 1, the low molecular weight polytetrafluoroethylene is washed with a washing solvent. 2. A method for producing low molecular weight polytetrafluoroethylene, wherein the cleaning solvent contains a fluorinated solvent.
[2] The method for producing low molecular weight polytetrafluoroethylene according to [1], wherein the cleaning solvent is only a fluorinated solvent.
[3] The method for producing low molecular weight polytetrafluoroethylene according to [1], wherein the washing solvent further contains water.
[4] [1] to [3] further comprising a step 3 of pulverizing the low molecular weight polytetrafluoroethylene between the step 1 and the step 2 and at least one of the steps after the step 2. ] A method for producing any of the low molecular weight polytetrafluoroethylenes.
[5] The method for producing low molecular weight polytetrafluoroethylene according to any one of [1] to [4], further comprising a step 4 of subjecting the low molecular weight polytetrafluoroethylene to a heat treatment after the step 2.
[6] The content of perfluorooctanoic acid and a salt thereof in the low molecular weight polytetrafluoroethylene obtained by the production method having the above step 2 is 25 mass ppb or less, whichever is lower than [1] to [5]. Method for producing molecular weight polytetrafluoroethylene.

According to the present invention, it is possible to provide a method for producing low molecular weight PTFE, which can easily produce low molecular weight PTFE having a low PFOA content.

The meanings of the terms in the present invention are as follows.
The "unit" is a general term for atomic groups derived from one molecule of a monomer, which is directly formed by polymerizing a monomer.
The numerical range represented by "~" means a range including the numerical values before and after "~" as the lower limit value and the upper limit value.

A feature of the method for producing low molecular weight PTFE of the present invention is that the low molecular weight PTFE is washed with a washing solvent containing a fluorinated solvent.
Since the fluorinated solvent is superior in compatibility with PFOA as compared with an organic solvent such as ethanol, it is considered that low molecular weight PTFE having a low PFOA content was obtained. For the same reason, it is presumed that the removability of perfluorononanoic acid or a salt thereof (hereinafter, simply referred to as “PFNA”) produced as a by-product by irradiation of PTFE with radiation is also improved.

The method for producing low molecular weight PTFE of the present invention has at least the following two steps.
Step 1: Irradiate the PTFE with radiation to obtain low molecular weight PTFE Step 2: After step 1, the low molecular weight PTFE is subjected to a cleaning treatment using a cleaning solvent containing a fluorine-based solvent. The process will be described in detail.

[Step 1]
Step 1 is a step of irradiating the PTFE with radiation to obtain a low molecular weight PTFE. By carrying out this step, PTFE as a raw material is further reduced in molecular weight, and low molecular weight PTFE is obtained.
In the following, first, PTFE as a raw material will be described in detail, and then the procedure of the process will be described in detail.

The PTFE may be a homo-PTFE consisting only of tetrafluoroethylene (hereinafter, also simply referred to as "TFE") units, or a modified PTFE containing a TFE unit and a modified monomer unit based on a modified monomer copolymerizable with TFE. It may be.
In the modified PTFE, the content of the modified monomer unit is preferably 0.001 to 1% by mass, more preferably 0.01 to 0.5% by mass, and 0.01 to 0.% With respect to all the units of the modified PTFE. 1% by mass is more preferable.
The modified monomer unit means a part derived from the modified monomer which is a part of the molecular structure of the modified PTFE, and the whole unit of the modified PTFE means a portion derived from all the monomers in the molecular structure of the modified PTFE. means.
The content of the modified monomer unit can be determined by a known method such as Fourier transform infrared spectroscopy (FT-IR).

The modified monomer may be a monomer capable of copolymerizing with TFE, and may be, for example, a perfluoroolefin such as hexafluoropropylene; a chlorofluoroolefin such as chlorotrifluoroethylene; a hydrogen-containing such as trifluoroethylene or vinylidene fluoride. Fluoroolefin; perfluorovinyl ether; perfluoroalkylethylene; ethylene.
The modified monomer used may be one kind or a plurality of kinds.

Examples of the perfluorovinyl ether include perfluorounsaturated compounds represented by the formula (1).
Equation (1) CF ₂ = CF-ORf
In the formula, Rf represents a perfluoroorganic group.
The above-mentioned "perfluoroorganic group" means an organic group in which all hydrogen atoms bonded to carbon atoms are replaced with fluorine atoms. The perfluoroorganic group may have ether oxygen.

Examples of the perfluorovinyl ether include perfluoro (alkyl vinyl ether) in which Rf represents a perfluoroalkyl group having 1 to 10 carbon atoms (preferably 1 to 5) in the formula (1).
Examples of the perfluoroalkyl group include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, and a perfluorohexyl group.
Of these, purple olo (propyl vinyl ether) in which the perfluoroalkyl group is a perfluoropropyl group is preferable.

Further, as the perfluorovinyl ether, in the formula (1), a compound in which Rf is a perfluoro (alkoxyalkyl) group having 4 to 9 carbon atoms, and a compound in which Rf is a group represented by the formula (2), Examples thereof include compounds in which Rf is a group represented by the formula (3).

In the formula, m represents an integer from 0 to 4.

In the formula, n represents an integer of 1 to 4.

Examples of the perfluoroalkyl ethylene include (perfluorobutyl) ethylene (PFBE), (perfluorohexyl) ethylene, and (perfluorooctyl) ethylene.

The PTFE used may be a powder of PTFE, a molded product of PTFE, or cutting chips generated when the molded product of PTFE is cut.

The PTFE used may be PTFE obtained through a firing step of heating to a primary melting point or higher.
The primary melting point can be measured using a differential scanning calorimeter (DSC) and is the maximum peak temperature of the endothermic curve that appears on the crystal melting curve. The endothermic curve is obtained by raising the temperature of PTFE, which has not undergone the firing step, at a heating rate of 10 ° C./min.
The primary melting point is usually 320 ° C. or higher.

The standard specific gravity (SSG) of PTFE is preferably 2.130 to 2.230. The standard specific density (SSG) is a measured value in accordance with ASTM D 4895.

Next, the procedure of step 1 will be described in detail.
The radiation may be ionizing radiation, and examples thereof include electron beams, ultraviolet rays, gamma rays, X-rays, neutron rays, and high-energy ions, and electron beams or gamma rays are preferable.
The irradiation dose of radiation is 20 to 100 kGy, preferably 30 to 100 kGy, and more preferably 50 to 75 kGy.

The irradiation temperature of radiation is preferably 5 ° C. or higher and lower than the melting point of PTFE. Among them, the upper limit is more preferably 320 ° C. or lower, further preferably 300 ° C. or lower, and particularly preferably 260 ° C. or lower. Economically, it is preferable to irradiate at room temperature.

The irradiation of the above radiation may be carried out in any atmosphere, and examples thereof include air, an inert gas, and a vacuum. Irradiation in air is preferable from the viewpoint of low cost, and irradiation in the absence of oxygen is preferable from the viewpoint of difficulty in generating PFOA.

[Step 2]
Step 2 is a step of performing a cleaning treatment using a cleaning solvent containing a fluorine-based solvent on the low molecular weight PTFE after the step 1. By carrying out this step, PFOA and PFNA by-produced in step 1 can be removed.
The cleaning solvent may be a solvent consisting only of a fluorine-based solvent, or may contain a fluorine-based solvent and a solvent other than the fluorine-based solvent (hereinafter, also referred to as “other solvent”).

The fluorine-based solvent means a solvent having a fluorine atom.
Specific examples of the fluorinated solvent include fluorinated alkanes, fluorinated aromatic compounds, fluoroalkyl ethers, fluorinated alkylamines, and fluoroalcohols. Of these, fluorinated alkanes and fluorinated alkyl ethers are preferable because the effects of the present invention are more excellent.
The fluorinated alkane is preferably a compound having 3 to 10 carbon atoms because the effect of the present invention is more excellent. For example, C ₆ F ₁₃ H (AC-2000: product name, manufactured by AGC), C ₆ F ₁₃ C. ₂ H ₅ (AC-6000: product name, manufactured by AGC), C ₂ F ₅ CHFCHFCF ₃ (Bertrel: product name, manufactured by DuPont), 1,1,2,2,3,3,4-heptafluorocyclo Pentan, (Zeorolla H: product name, manufactured by Zeon Corporation), dichloropentafluoropropane (AK-225: product name, manufactured by AGC Inc., a mixture of _{CF 3} CF ₂ CHCl ₂ and CClF ₂ CF _{2 CHClF).} Be done.
Specific examples of the fluorinated aromatic compound include hexafluorobenzene, trifluoromethylbenzene, perfluorotoluene, 1,3-bis (trifluoromethyl) benzene, and 1,4-bis (trifluoromethyl) benzene.
The fluoroalkyl ether is preferably a compound having 4 to 12 carbon atoms, for example, CF ₃ CH ₂ OCF ₂ CF ₂ H (AE-3000: product name, manufactured by AGC), C ₄ F ₉ OCH ₃ (Novec-7100:). Product name, 3M company), C ₄ F ₉ OC ₂ H ₅ (Novec-7200: Product name, 3M company), C ₂ F ₅ CF (OCH ₃ ) C ₃ F ₇ (Novec-7300: Product name, 3M).
Specific examples of the fluorinated alkylamine include perfluorotripropylamine and perfluorotributylamine.
Specific examples of the fluoroalcohol include 2,2,3,3-tetrafluoropropanol, 2,2,2-trifluoroethanol and hexafluoroisopropanol.
The fluorine-based solvent may be used alone or in combination of two or more.

Examples of the other solvent include water and organic solvents other than the above-mentioned fluorine-based solvent, and water is preferable from the viewpoint of excellent effect of the present invention and cost.
The organic solvent other than the fluorine-based solvent is not particularly limited, and examples thereof include a hydrocarbon-based organic solvent, a ketone-based organic solvent, an ether-based organic solvent, an ester-based organic solvent, and an alcohol-based organic solvent.
Other solvents may be used alone or in combination of two or more.

When the cleaning solvent contains a fluorine-based solvent and another solvent, the content of the fluorine-based solvent is preferably 1% by mass or more and less than 100% by mass, and 3% by mass or more and 100% by mass, based on the total mass of the cleaning solvent. Less than 5% by mass is more preferable, and 5% by mass or more and less than 100% by mass is particularly preferable. When the content of the fluorinated solvent is within the above range, the function of removing PFOA and PFNA by the fluorinated solvent is fully exhibited.
When the cleaning solvent contains a fluorine-based solvent and another solvent, the content of the other solvent (preferably water) is preferably more than 0% by mass and 99% by mass or less, preferably 0% by mass, based on the total mass of the cleaning solvent. More than 97% by mass is more preferable, and more than 0% by mass and 95% by mass is particularly preferable.

The cleaning treatment may be carried out only once or may be carried out a plurality of times. When performing a plurality of times, the same type of cleaning solvent may be used for each implementation, or different types of cleaning solvent may be used for each implementation. As the cleaning solvent, a cleaning solvent having the same concentration may be used, or a cleaning solvent having a different concentration may be used.

Examples of the cleaning treatment method include a method of immersing the low molecular weight PTFE in the cleaning solvent and a method of spraying the cleaning solvent on the low molecular weight PTFE by a spray or the like. Is preferable.
The dipping method is preferably carried out together with at least one treatment selected from the group consisting of stirring treatment, heat treatment and ultrasonic treatment, because the effect of the present invention is more excellent.

The temperature of the cleaning solvent in the cleaning treatment is preferably 0 to 100 ° C, more preferably 5 to 95 ° C, and particularly preferably 10 to 90 ° C.
The washing treatment time (for example, the immersion time of the low molecular weight PTFE in the washing solvent) is preferably 3 to 360 minutes, more preferably 3 to 300 minutes, and particularly preferably 5 to 240 minutes.

Step 2 may include a water washing treatment for washing the low molecular weight PTFE after the washing treatment with water.

[Other processes]
The production method of the present invention may have steps other than steps 1 and 2, and has at least one of step 3 for pulverizing the low molecular weight PTFE and step 4 for heat-treating the low molecular weight PTFE. Is preferable.

(Step 3)
Step 3 is a step of pulverizing the low molecular weight PTFE, and is preferably carried out between step 1 and step 2 and at least one after step 2. That is, the manufacturing method of the present invention may have the process 3 only between the process 1 and the process 2, may have the process 3 only after the process 2, and may have the process 3 and the process 1. Step 3 may be provided both during and after step 2.

Examples of the crushing method include a method of crushing with a crusher.
Examples of the crusher include an impact type such as a hammer mill, a pin mill, and a jet mill, and a crushing type such as a cutter mill in which a rotary blade and an outer peripheral stator are crushed by a shearing force due to unevenness.

The crushing temperature is preferably −200 ° C. or higher and lower than 50 ° C.
In freezing pulverization, the temperature is usually −200 to −100 ° C., but pulverization may be performed at a temperature near room temperature (10 to 30 ° C.).
Among them, pulverization at 10 ° C. or higher and lower than 50 ° C. is more preferable, pulverization at 10 to 40 ° C. is further preferable, and pulverization at 10 to 30 ° C. is particularly preferable, in that the pulverization cost can be suppressed. ..

After crushing, airflow classification may be carried out if necessary.
In the air flow classification, the crushed material is sent to the columnar classification chamber by the decompressed air, dispersed by the swirling airflow in the room, and the crushed material is classified by the centrifugal force. A rotating body such as a conical cone or a rotor is installed in the classification chamber so that the crushed material and the air make a uniform swirling motion.
When a classification cone is used, the classification point is adjusted by adjusting the air volume of the secondary air and the gap between the classification cones. When using a rotor, adjust the air volume in the classification room according to the rotation speed of the rotor.

Further, after the air flow classification, coarse particles may be removed by the classification, if necessary.
Examples of the method for removing coarse particles include airflow classification, a vibration sieve using a mesh, and an ultrasonic sieve using a mesh, and airflow classification is preferable.

(Step 4)
Step 4 is a step of heat-treating the low molecular weight PTFE, and is preferably carried out after step 2. By having the step 4, the PFOA and PFNA that are by-produced in the step 1 can be further removed. In addition, the cleaning solvent in step 2 can be removed.

When the manufacturing method of the present invention has step 3 and step 4, step 4 may be carried out before step 3 or after step 3 as long as it is carried out after step 2. good. For example, when the process 3 is provided between the process 1 and the process 2, the process 1, the process 3, the process 2 and the process 4 are carried out in this order. Further, when the step 3 is provided after the step 2, the step 1, the step 2, the step 4 and the step 3 may be carried out in this order, or the step 1, the step 2, the step 3 and the step 4 are carried out in this order. May be good.

The temperature of the heat treatment is preferably 50 ° C. or higher, more preferably 70 ° C. or higher, further preferably 90 ° C. or higher, and particularly preferably 100 ° C. or higher. Further, 300 ° C. or lower is preferable, 250 ° C. or lower is more preferable, and 200 ° C. or lower is further preferable.
When the temperature of the heat treatment is within the above range, the removal of PFOA and PFNA is more likely to proceed, and the removal of the cleaning solvent is excellent.

The heat treatment time is preferably 10 seconds or longer, more preferably 5 minutes or longer, and even more preferably 10 minutes or longer. Further, 72 hours or less is preferable, 48 hours or less is more preferable, and 36 hours or less is further preferable.
When the heat treatment time is within the above range, the removal of PFOA and PFNA is more likely to proceed, and the removal of the cleaning solvent is excellent.

For heat treatment, box dryer, band dryer, tunnel dryer, spout dryer, mobile layer dryer, rotary dryer, fluid layer dryer, air flow dryer, box dryer, disk dryer , Cylindrical stirring dryer, inverted conical stirring dryer, microwave device, vacuum heat treatment device, box type electric furnace, hot air circulation device, flash dryer, vibration dryer, belt dryer, extrusion dryer, spray dryer, etc. You may use the heat treatment apparatus of.

The heat treatment may be carried out in any atmosphere, but it is preferably carried out in air from the viewpoint of safety and economy.

The heat treatment can be performed by installing low molecular weight PTFE in a heating furnace, raising the temperature in the heating furnace to a desired temperature, and then leaving it to stand for a desired time.

[Low molecular weight PTFE]
The low molecular weight PTFE obtained by the production method of the present invention preferably has a melt viscosity at 380 ° C. of 1 × 10 ^{2 to} 7 × 10 ⁵ Pa · s.
The melt viscosity is based on ASTM D 1238, and a 2 g sample that has been preheated at 380 ° C for 5 minutes using a flow tester (manufactured by Shimadzu Corporation) and a 2φ-8L die is loaded with 0.7 MPa. It is a value measured while keeping the above temperature.

The melting point of the low molecular weight PTFE is preferably 324 to 336 ° C.
The melting point is temperature-calibrated using indium and lead as standard samples in advance using a differential scanning calorimeter, and then about 3 mg of low molecular weight PTFE is placed in an aluminum pan (crimp container) and air is 200 ml / min. The temperature range of 250 to 380 ° C. is raised at 10 ° C./min under an air flow, and the minimum point of the heat of fusion in the above range is defined as the melting point.

The low molecular weight PTFE obtained by the production method of the present invention contains almost no PFOA.
In the low molecular weight PTFE obtained by the production method of the present invention, the PFOA content is preferably 25 mass ppb or less, more preferably 20 mass ppb or less, further preferably 10 mass ppb or less, and particularly preferably less than 5 mass ppb. The lower limit is not particularly limited and may be an amount less than the detection limit.
The content of PFOA can be measured by adding methanol to low molecular weight PTFE, ultrasonically treating at 60 ° C. for 120 minutes, extracting PFOA, and then measuring the extracted PFOA by liquid chromatography.
The content of PFOA in the low molecular weight PTFE means the content of perfluorooctanoic acid and its salt in the low molecular weight PTFE, and when both perfluorooctanoic acid and its salt are contained, the content of each compound is contained. It means the total amount, and when it contains only one compound, it means the content of one compound.

The low molecular weight PTFE obtained by the production method of the present invention contains almost no PFNA.
The content of PFNA in the low molecular weight PTFE obtained by the production method of the present invention is preferably 60 mass ppb or less, more preferably 20 mass ppb or less, further preferably 10 mass ppb or less, and particularly preferably less than 5 mass ppb. The lower limit is not particularly limited and may be an amount less than the detection limit.
The content of PFNA can be measured by the same method as the content of PFOA.
The content of PFNA in the low molecular weight PTFE means the total content of perfluorononanoic acid and its salt in the low molecular weight PTFE, and each compound when both perfluorononanoic acid and its salt are contained. It means the total content of one compound, and when it contains only one compound, it means the content of one compound.

The low molecular weight PTFE preferably has more than 5 carboxyl groups and less than 30 carboxyl groups per ^{10 6} carbon atoms in the main chain at the end of the molecular chain.

The shape of the low molecular weight PTFE obtained by the production method of the present invention is preferably powder. That is, it is preferable to obtain a powder containing low molecular weight PTFE (hereinafter, also simply referred to as “low molecular weight PTFE powder”).
When the low molecular weight PTFE is a powder, the average particle size is preferably 1.0 μm or more. The average particle size of the powder is preferably 600 μm or less, more preferably 550 μm or less, when the production method of the present invention does not have step 3. When the production method of the present invention has step 3, it is preferably 100 μm or less, more preferably 50 μm or less.
The average particle size was measured using a laser diffraction / scattering type particle size distribution measuring device (LA-920, manufactured by Horiba Seisakusho Co., Ltd.) using isopropyl alcohol as the dispersion solvent, and the medium diameter (particle size) of the particle size distribution integration was measured. The particle size corresponding to 50% of the distribution integration) is defined as the average particle size.

An unstable terminal group derived from the chemical structure of the polymerization initiator or chain transfer agent used in the polymerization reaction of PTFE may be generated at the end of the molecular chain of the low molecular weight PTFE.
Examples of the unstable terminal group include -CH ₂ OH, -COOH, and -COOCH ₃ .

For low molecular weight PTFE, unstable end groups may be stabilized. Examples of the method for stabilizing the unstable terminal group include a method of changing the terminal to a trifluoromethyl group by exposure to a fluorine-containing gas.

The low molecular weight PTFE may be terminally amidated. As the method of terminal amidation, for example, as disclosed in JP-A-4-020507, a method of contacting a fluorocarbonyl group obtained by exposure to a fluorine-containing gas with ammonia gas can be mentioned. Be done.

The low molecular weight PTFE obtained by stabilizing or terminal amidating the unstable terminal group described above is used as an additive to a mating material such as paints, greases, cosmetics, plating solutions, toners and plastics. It is easy to get used to and can improve the dispersibility.

[Powder]
The present invention is a powder containing low molecular weight PTFE, having a PFOA content of 25 mass ppb or less, a PFNA content of 60 mass ppb or less, and is also a powder.

The powder of the present invention has a PFOA content of 25 mass ppb or less, preferably 20 mass ppb or less, more preferably 10 mass ppb or less, still more preferably less than 5 mass ppb. The lower limit is not particularly limited and may be an amount less than the detection limit.
The powder of the present invention has a PFNA content of 60 mass ppb or less, preferably 20 mass ppb or less, more preferably 10 mass ppb or less, still more preferably less than 5 mass ppb. The lower limit is not particularly limited and may be an amount less than the detection limit.
The content of PFOA can be measured by adding methanol to the powder of the present invention, performing ultrasonic treatment at 60 ° C. for 120 minutes, extracting PFOA, and then measuring the extracted PFOA by liquid chromatography.
The content of PFNA can be measured by the same method as the content of PFOA.

It is considered that the low molecular weight PTFE contained in the powder of the present invention has more than 5 and less than 30 carboxyl groups per ^{10 6 carbon atoms in the main chain at the end of the molecular chain.}

The specific surface area of the powder of the present invention ^{is preferably 0.1 to 20} m 2 / g. The specific surface area is ^{more preferably 0.2 to 15 m 2} / g or more.
For the specific surface area, a surface analyzer (trade name: BELSORP-miniII, manufactured by Microtrac Bell Co., Ltd.) was used, a mixed gas of 30% nitrogen and 70% helium was used as the carrier gas, and liquid nitrogen was used for cooling. Measure by the BET method.

The average particle size of the powder of the present invention is preferably 1.0 μm or more. The average particle size of the powder is preferably 600 μm or less, more preferably 550 μm or less.
The smaller average particle size is preferably 100 μm or less, more preferably 50 μm or less.
The average particle size was measured using a laser diffraction / scattering type particle size distribution measuring device (LA-920, manufactured by Horiba Seisakusho Co., Ltd.) using isopropyl alcohol as the dispersion solvent, and the medium diameter (particle size) of the particle size distribution integration was measured. The particle size corresponding to 50% of the distribution integration) is defined as the average particle size.

The composition and melt viscosity of the low molecular weight PTFE contained in the powder of the present invention are the same as those described for the low molecular weight PTFE obtained by the production method of the present invention.
Further, the low molecular weight PTFE contained in the powder of the present invention may have an unstable terminal group at the end of the molecular chain. Further, the low molecular weight PTFE contained in the powder of the present invention may be stabilized by stabilizing unstable terminal groups, may be terminal amidated, or may be terminally fluorinated. These aspects are also the same as those described for the low molecular weight PTFE obtained by the production method of the present invention.
The powder of the present invention can be obtained, for example, by producing low molecular weight PTFE in powder form by the production method of the present invention described above.

(Use)
The low molecular weight PTFE and the powder can be suitably used, for example, as a molding material, an ink, a cosmetic, a paint, a grease, a member for office automation equipment, an additive for modifying a toner, and an additive for a plating solution.
Examples of the molding material include engineering plastics such as polyoxybenzoyl polyester, polyimide, polyamide, polyamideimide, polyacetal, polycarbonate, and polyphenylene sulfide.
The low molecular weight PTFE is particularly suitable as a thickener for grease.

When used as an additive, for example, a dispersion liquid containing the low molecular weight PTFE and / or the powder may be mixed with a dispersion liquid such as various resins and rubbers.
Further, the low molecular weight PTFE and / or the powder may be added to the surface of pellets such as resin. The presence of the powder or the like on the surface of the pellet is preferable because the stickiness of the pellet is suppressed, the handleability is improved, and it is easy to put it into the extruder. Further, it is considered that the powder or the like present on the surface of the pellet is mixed with the pellet by melt-kneading to improve the dimensional stability during extrusion molding during melt-kneading and to be effective as a molding stabilizer. Further, it is considered that the melt fracture can be suppressed without lowering the extrusion speed.

The low molecular weight PTFE and the powder can be used as additives for molding materials, for example, for improving the non-adhesiveness / sliding characteristics of copy rolls, for molding engineering plastics for surface sheets of furniture, dashboards of automobiles, covers of home appliances, and the like. Used for improving the texture of products, and for improving the slipperiness and wear resistance of mechanical parts that cause mechanical friction such as light load bearings, gears, cams, pushphone buttons, projectors, camera parts, and sliding materials. be able to.

The low molecular weight PTFE and the powder can be used as additives for paints for the purpose of improving the slipperiness of varnishes and paints. The low molecular weight PTFE and the powder can be used as additives for cosmetics for the purpose of improving the slipperiness of cosmetics such as foundations.

The low molecular weight PTFE and the powder are also suitable for applications such as wax and the like for improving oil repellency or water repellency, and applications for improving the slipperiness of grease and toner.

The low molecular weight PTFE and the powder can also be used as an electrode binder for a secondary battery or a fuel cell, a hardness adjusting agent for the electrode binder, and a water repellent treatment agent for the surface of the electrode.

Greases can also be prepared using the low molecular weight PTFE or the powder and lubricating oil. Since the grease contains the low molecular weight PTFE or the powder and the lubricating oil, the low molecular weight PTFE or the powder is uniformly and stably dispersed in the lubricating oil, and has a load bearing capacity. It has excellent properties such as electrical insulation and low moisture absorption.

The lubricating oil (base oil) may be a mineral oil or a synthetic oil. Examples of the lubricating oil (base oil) include paraffin-based and naphthen-based mineral oils, synthetic hydrocarbon oils, ester oils, fluorine oils, synthetic oils such as silicone oils, and the like. From the viewpoint of heat resistance, fluorine oil is preferable. Examples of the fluorine oil include perfluoropolyether oil and a low polymer of ethylene trifluoride chloride. The low polymer of ethylene trifluoride chloride may have a weight average molecular weight of 500 to 1200.

The grease may further contain a thickener. Examples of the thickening agent include metal soap, composite metal soap, bentonite, phthalocyanine, silica gel, urea compound, urea / urethane compound, urethane compound, and imide compound. Examples of the metal soap include sodium soap, calcium soap, aluminum soap, and lithium soap. Examples of the urea compound, urea-urethane compound and urethane compound include diurea compounds, triurea compounds, tetraurea compounds, other polyurea compounds, urea-urethane compounds, diurethane compounds and mixtures thereof.

The grease preferably contains the low molecular weight PTFE or the powder in an amount of 0.1 to 50% by mass, more preferably 0.5 to 30% by mass.

The grease may also contain, for example, a solid lubricant, an extreme pressure agent, an antioxidant, an oily agent, an anticorrosive agent, a viscosity index improver, and a cleaning dispersant.

Hereinafter, the present invention will be described in more detail by way of examples described later, but the present invention is not limited thereto. Examples 1 to 6 described later correspond to comparative examples, and examples 7 to 17 correspond to examples.

Various measurement methods and evaluation methods are as follows.

(Average particle size)
Using isopropyl alcohol as the dispersion solvent, measurement was performed using a laser diffraction / scattering type particle size distribution measuring device (LA-920 manufactured by Horiba Seisakusho Co., Ltd.), and the medium diameter of particle size distribution integration (50% of particle size distribution integration) was measured. The particle size corresponding to) was taken as the average particle size.

(Contents of PFOA and PFNA)
5 ml of methanol was added to 2 g of the measurement sample (low molecular weight PTFE), and sonication was performed at 60 ° C. for 120 minutes to extract PFOA. The obtained liquid phase was measured for the contents of PFOA and PFNA using a liquid chromatograph mass analyzer (Agilent, 1260HPLC / 6460MS) in accordance with British Standard (BSI) CEN / TS 15968 (2010). rice field. The detection limit in this measurement is 1 mass ppb.
The content of PFNA was measured only in Example 1, Example 2, and Example 7.

(Example 1)
PTFE molding powder (average particle size 25 μm) (manufactured by AGC) was calcined at 380 ° C. and used as a raw material PTFE.
The raw material PTFE was irradiated with cobalt-60γ rays at 200 kGy at room temperature in the air to obtain a low molecular weight PTFE powder A1. Then, the low molecular weight PTFE powder A1 was pulverized with a pulverizer (SK Jet O Mill 0202 type manufactured by Seishin Enterprise Co., Ltd.) (step 3) to obtain a low molecular weight PTFE powder A2 having an average particle diameter of 10 μm.

(Example 2)
50 g of the low molecular weight PTFE powder A2 was immersed in 200 g of ethanol (washing solvent) in a 500 mL stainless steel container (with a stirring blade), and the low molecular weight PTFE powder A2 was washed for 60 minutes at room temperature with stirring (step). 2).
The washed low molecular weight PTFE powder A2 was heat-treated at 100 ° C. for 24 hours using a high-temperature thermostat (Super Temp Oven STPH-200 manufactured by ESPEC) (step 4) to obtain a low molecular weight PTFE powder A3. ..

(Example 3)
Low molecular weight PTFE powder A4 was obtained in the same manner as in Example 2 except that the washing solvent shown in Table 1 was used instead of 200 g of ethanol.

(Example 4)
As the raw material PTFE, PTFE molding powder (average particle size 25 μm) (manufactured by AGC) was used.
The raw material PTFE was irradiated with cobalt-60γ rays at 50 kGy at room temperature in the air to obtain a low molecular weight PTFE powder B1. Then, the low molecular weight PTFE powder B1 was pulverized with a pulverizer (SK Jet O Mill 0202 type manufactured by Seishin Enterprise Co., Ltd.) (step 3) to obtain a low molecular weight PTFE powder B2 having an average particle diameter of 18 μm.

(Example 5)
As the raw material PTFE, PTFE fine powder (average particle size 550 μm) (manufactured by AGC) was used.
The raw material PTFE was irradiated with cobalt-60γ rays at 50 kGy at room temperature in the air to obtain a low molecular weight PTFE powder C1.

(Example 6)
As the raw material PTFE, PTFE fine powder (average particle size 550 μm) (manufactured by AGC) was used.
The raw material PTFE was irradiated with cobalt-60γ rays at 100 kGy at room temperature in the air to obtain a low molecular weight PTFE powder D1. Then, the low molecular weight PTFE powder D1 was pulverized with a pulverizer (SK Jet O Mill 0202 type manufactured by Seishin Enterprise Co., Ltd.) (step 3) to obtain a low molecular weight PTFE powder D2 having an average particle diameter of 10 μm.

(Examples 7 to 10)
Low molecular weight PTFE powders A5 to A8 were obtained in the same manner as in Example 2 except that the washing solvent shown in Table 1 was used instead of 200 g of ethanol.
In the table, "AE-3000" represents CF ₃ CH ₂ OCF ₂ CF ₂ H (AE-3000: product name, manufactured by AGC Inc.). Further, "AK-225" represents dichloropentafluoropropane (AK-225: product name, manufactured by AGC Inc., a mixture of _{CF 3} CF ₂ CHCl ₂ and CClF ₂ CF _{2 CHClF).}

(Example 11)
A low molecular weight PTFE powder A9 was obtained in the same manner as in Example 2 except that the washing solvent shown in Table 1 was used instead of 200 g of ethanol and the washing time was set to 5 minutes.

(Example 12)
50 g of the low molecular weight PTFE powder B2 was immersed in 200 g of AE-3000 in a 500 mL stainless steel container (with a stirring blade), and the low molecular weight PTFE powder B2 was washed for 60 minutes at room temperature while stirring (step 2). ..
The washed low molecular weight PTFE powder B2 was heat-treated at 100 ° C. for 24 hours using a high-temperature thermostat (Super Temp Oven STPH-200 manufactured by ESPEC) (step 4) to obtain a low molecular weight PTFE powder B3. ..

(Example 13)
Low molecular weight PTFE powder B4 was obtained in the same manner as in Example 12 except that the washing time was set to 5 minutes.

(Example 14)
50 g of the low molecular weight PTFE powder C1 was immersed in 200 g of AE-3000 in a 500 mL stainless steel container (with a stirring blade), and the low molecular weight PTFE powder C1 was washed for 60 minutes at room temperature while stirring (step 2). ..
The washed low molecular weight PTFE powder C1 was heat-treated at 100 ° C. for 24 hours using a high-temperature thermostat (Super Temp Oven STPH-200 manufactured by ESPEC) (step 4) to obtain a low molecular weight PTFE powder C2. ..

(Example 15)
Low molecular weight PTFE powder C3 was obtained in the same manner as in Example 14 except that the washing time was set to 5 minutes.

(Example 16)
50 g of the low molecular weight PTFE powder D2 was immersed in 200 g of AE-3000 in a 500 mL stainless steel container (with a stirring blade), and the low molecular weight PTFE powder D2 was washed for 60 minutes at room temperature while stirring (step 2). ..
The washed low molecular weight PTFE powder D2 was heat-treated at 100 ° C. for 24 hours using a high-temperature thermostat (Super Temp Oven STPH-200 manufactured by ESPEC) (step 4) to obtain a low molecular weight PTFE powder D3. ..

(Example 17)
Low molecular weight PTFE powder D4 was obtained in the same manner as in Example 16 except that the washing time was set to 5 minutes.

In Table 1, the column "Step 3" indicates the presence or absence of pulverization treatment.
In Table 1, the "step 4" column represents the heating conditions (temperature x time) in the heat treatment.
In Table 1, "<1" means less than 1.

The low molecular weight PTFE and powder obtained by the production method of the present invention showed a desired effect.

Claims (6)

Step 1 to obtain low molecular weight polytetrafluoroethylene by irradiating polytetrafluoroethylene with radiation,
After the step 1, the step 2 of performing a cleaning treatment using a cleaning solvent on the low molecular weight polytetrafluoroethylene is provided.
A method for producing low molecular weight polytetrafluoroethylene, wherein the cleaning solvent contains a fluorinated solvent. The method for producing low molecular weight polytetrafluoroethylene according to claim 1, wherein the cleaning solvent consists only of a fluorinated solvent. The method for producing low molecular weight polytetrafluoroethylene according to claim 1, wherein the washing solvent further contains water. At least one between the step 1 and the step 2 and after the step 2.
The method for producing low molecular weight polytetrafluoroethylene according to any one of claims 1 to 3, further comprising the step 3 of pulverizing the low molecular weight polytetrafluoroethylene. The method for producing low molecular weight polytetrafluoroethylene according to any one of claims 1 to 4, further comprising a step 4 of subjecting the low molecular weight polytetrafluoroethylene to a heat treatment after the step 2. The low molecular weight according to any one of claims 1 to 5, wherein the content of perfluorooctanoic acid and a salt thereof in the low molecular weight polytetrafluoroethylene obtained by the production method having the step 2 is 25 mass ppb or less. Method for producing polytetrafluoroethylene.