CN101155857A - Process for producing aqueous fluoropolymer dispersion - Google Patents

Abstract

The present invention provides a method for producing an aqueous fluoropolymer dispersion capable of producing an aqueous fluoropolymer dispersion with a high concentration of fluoropolymer in a short period of time. The manufacturing method of the fluoropolymer aqueous dispersion liquid of the present invention comprises step (1), step (2) and step (3), in step (1), in the treated fluoropolymer aqueous dispersion liquid, add nonionic Type surfactant, in step (2), carry out phase separation after above-mentioned step (1), separate into supernatant phase and fluorine-containing polymer aqueous dispersion liquid phase, in step (3), remove above-mentioned supernatant phase , to obtain the above-mentioned fluoropolymer aqueous dispersion phase; the production method is characterized in that stirring is carried out in the above-mentioned step (2).

Description

Process for producing aqueous fluoropolymer dispersion

technical field

The present invention relates to a method for producing an aqueous fluoropolymer dispersion.

Background technique

Aqueous fluoropolymer dispersions can form films exhibiting excellent properties in terms of chemical stability, non-stickiness, and weather resistance by coating, dipping, etc., so they are widely used in cooking utensils, piping linings, and glass cloth impregnation film etc. In these applications, it is preferable that the fluoropolymer aqueous dispersion liquid has a high fluoropolymer concentration, so the fluoromonomer is usually polymerized in an aqueous medium in the presence of a fluorosurfactant and then concentrated, and the concentrated fluoropolymer is used. Aqueous polymer dispersions.

As a method for concentrating an aqueous fluoropolymer dispersion liquid, it is known to heat in the presence of a specific nonionic surfactant, separate it into a fluoropolymer-containing phase and a fluoropolymer-free phase, and then This is a method of removing the fluorine-containing polymer-free phase. However, this phase separation requires standing still under predetermined temperature conditions for a long time, and the production efficiency is not good.

Contents of the invention

In view of the above situation, an object of the present invention is to provide a method for producing an aqueous fluoropolymer dispersion capable of producing an aqueous fluoropolymer dispersion having a high concentration of fluoropolymer in a short period of time.

The present invention relates to a kind of manufacture method of fluorine-containing polymer aqueous dispersion liquid, it comprises step (1), step (2) and step (3), in step (1), in processed fluorine-containing polymer aqueous dispersion liquid Add non-ionic surfactant in step (2), carry out phase separation after above-mentioned step (1), separate into supernatant phase and fluoropolymer aqueous dispersion liquid phase, in step (3), remove The above-mentioned supernatant phase is obtained to obtain the above-mentioned fluoropolymer aqueous dispersion liquid phase; wherein, stirring is carried out in the above-mentioned step (2).

The present invention will be described in detail below.

The method for producing an aqueous fluoropolymer dispersion of the present invention includes the step (1) of adding a nonionic surfactant to the aqueous fluoropolymer dispersion to be treated.

The aqueous dispersion of the fluoropolymer to be treated is formed by dispersing the fluoropolymer in an aqueous medium.

The above-mentioned aqueous fluoropolymer dispersion to be treated is not particularly limited as long as it is formed by dispersing the fluoropolymer in an aqueous medium, and may be a polymerized aqueous dispersion obtained by polymerizing the above-mentioned fluoropolymer, It may also be an aqueous dispersion obtained by subjecting the polymerized aqueous dispersion to a treatment for reducing the fluorine-containing anionic surfactant and/or post-treatment such as concentration.

The fluoropolymer in the aqueous fluoropolymer dispersion to be treated is a polymer having fluorine atoms bonded to carbon atoms.

Examples of the fluoropolymer include elastomeric fluoropolymers, non-melt processable fluoropolymers, and melt processable fluoropolymers.

The aforementioned elastomeric fluoropolymer is an amorphous fluoropolymer having rubber elasticity, and generally has 30% by mass to 80% by mass of monomer units of the first monomer.

In this specification, the above-mentioned "first monomer" refers to vinylidene fluoride [VDF] or tetrafluoroethylene [ TFE].

In the present specification, a "monomer unit" such as a monomer unit of the above-mentioned first monomer is a part of the molecular structure of the fluorine-containing polymer, and refers to a part derived from the corresponding monomer. For example, a TFE unit is a part of the molecular structure of a fluoropolymer, a part derived from TFE, and represented by -(CF ₂ -CF ₂ )-. The above-mentioned "all monomer units" is the sum of the moieties derived from monomers in the molecular structure of the fluorine-containing polymer.

Examples of the aforementioned elastomeric fluoropolymers include TFE/propylene copolymers and TFE/perfluorovinyl ether copolymers for TFE-based polymers; HFP/ethylene copolymers for hexafluoropropylene [HFP]-based polymers. VDF-based polymers include VDF/HFP copolymer, VDF/chlorotrifluoroethylene [CTFE] copolymer, VDF/TFE copolymer, VDF/perfluoro(alkyl vinyl ether) [PAVE] copolymer, VDF/TFE/HFP copolymer, VDF/TFE/CTFE copolymer, VDF/TFE/PAVE copolymer, etc.

Polytetrafluoroethylene [PTFE] is mentioned as said non-melt processability fluoropolymer.

In this specification, the above-mentioned PTFE is a concept including not only TFE homopolymer but also modified polytetrafluoroethylene [modified PTFE].

As the above-mentioned trace monomers, for example, fluoroolefins such as HFP and CTFE; fluoro(alkyl vinyl ethers) having an alkyl group with 1 to 5 carbon atoms, especially 1 to 3 carbon atoms; Fluorinated dioxole; perfluoroalkylethylene; ω-hydrogen perfluoroalkene, etc.

In the modified PTFE, the content of the trace monomer units derived from the above trace monomers in the total monomer units is usually in the range of 0.001 mol % to 2 mol %.

In this specification, "the content (mol %) that the trace monomer unit occupies in all monomer units" means that the trace monomer forming the above trace monomer unit accounts for all the monomers forming the above "all monomer units" (i.e. The mole fraction (mol %) occupied in the total of the monomers constituting the fluoropolymer).

Examples of the melt processable fluoropolymer include ethylene/TFE copolymer [ETFE], TFE/HFP copolymer [FEP], TFE/perfluoro(alkyl vinyl ether) copolymer [TFE/PAVE copolymer Material], PVDF, VDF-based copolymers, polyvinyl fluoride [PVF], etc.

Examples of the TFE/PAVE copolymer include TFE/perfluoro(methyl vinyl ether) [PMVE] copolymer [MFA], TFE/perfluoro(ethyl vinyl ether) [PEVE] copolymer, TFE/ Perfluoro(propyl vinyl ether) [PPVE] copolymer, etc.

Examples of VDF-based copolymers that are melt-processable fluoropolymers include VDF/TFE copolymers, VDF/HFP copolymers, VDF/CTFE copolymers, VDF/TFE/HFP copolymers, and VDF/TFE/CTFE copolymers. Copolymer etc.

As the fluoropolymer in the aqueous fluoropolymer dispersion to be treated, perfluoropolymers are preferred, and PTFE is particularly preferred.

The above-mentioned fluoropolymer has an average particle diameter of 50 nm to 500 nm, preferably 100 nm to 350 nm.

The above-mentioned average particle size is determined as follows: the concentration of the fluoropolymer in the aqueous dispersion is adjusted to 0.22% by mass, based on the light transmittance (the light transmittance of the incident light of 550 nm to the light transmittance of the aqueous dispersion per unit length rate) and the average particle diameter (the average particle diameter is determined by measuring the directional diameter in the transmission electron micrograph), the average particle diameter is determined from the above-mentioned light transmittance.

The aqueous medium in the above-mentioned aqueous fluoropolymer dispersion to be treated is not particularly limited as long as it is a liquid containing water. In addition to water, it may also contain, for example, fluorine-free organic solvents such as alcohols, ethers, ketones, and paraffins, and /or fluorinated organic solvents.

In the aqueous fluoropolymer dispersion to be treated, the concentration of the fluoropolymer is usually 20 to 50 parts by mass, preferably 25 to 45 parts by mass, per 100 parts by mass of the aqueous medium.

When the concentration of the above-mentioned fluoropolymer is less than 20 parts by mass relative to 100 parts by mass of the aqueous medium, it is sometimes difficult to separate the supernatant phase and the aqueous dispersion phase of the fluoropolymer, and the concentration of the above-mentioned fluoropolymer is greater than 50 parts by mass In some cases, it is sometimes difficult to remove the fluorine-containing anionic surfactant that may exist in the above-mentioned aqueous fluoropolymer dispersion to be treated.

In this specification, the fluoropolymer concentration (P) is determined as follows: about 1 g (X) of a sample is placed in an aluminum crucible with a diameter of 5 cm, dried at 100°C for 1 hour and further dried at 300°C for 1 hour, based on Heating the residue (Z), using the calculation formula: P=Z/X×100(%) to determine the fluoropolymer concentration (P).

The above-mentioned aqueous fluoropolymer dispersion to be treated may further contain a surfactant.

The above-mentioned surfactant is not particularly limited, and examples thereof include conventionally known nonionic surfactants, anionic surfactants, and the like, and fluorine-containing surfactants may also be used.

Known ones can be used as the above-mentioned nonionic surfactant, and examples thereof include ether-type nonionic surfactants such as polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, and polyoxyethylene alkylene alkyl ether. Surfactant; polyoxyethylene derivatives such as ethylene oxide/propylene oxide block copolymer; sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, glycerin Ester-type nonionic surfactants such as fatty acid esters and polyoxyethylene fatty acid esters; amine-based nonionic surfactants such as polyoxyethylene alkylamines and alkyl alkanolamides; etc.

The above-mentioned nonionic surfactant can be any form of an aromatic compound, a straight-chain compound and a compound with a branch, but preferably does not have a straight-chain compound of an alkylphenol in the structure or a compound with a branch, more preferably in Compounds mentioned as the nonionic surfactant to be added in the step (1) described later.

As the above-mentioned anionic surfactant, an anionic surfactant formed of a fluorine-containing anionic compound such as a fluorine-containing carboxylic acid compound or a fluorine-containing sulfonic acid compound is preferred, and an anionic surfactant formed of a fluorine-containing carboxylic acid compound is more preferred, An anionic surfactant composed of a fluorine-containing carboxylic acid compound having 5 to 12 carbon atoms is more preferable.

As the above-mentioned anionic surfactant, anionic fluorine-containing surfactant (hereinafter sometimes referred to as "fluorine-containing anionic surfactant") can be used, and as the fluorine-containing anionic surfactant, for example, perfluorooctanoic acid and its salts can be used ("perfluorooctane sulfonic acid and its salts" are sometimes abbreviated as "PFOA" below), perfluorooctane sulfonic acid and its salts (hereinafter "perfluorooctane sulfonic acid and its salts" are sometimes abbreviated as "PFOS" ) and other known fluorinated anionic surfactants.

When the above-mentioned PFOA and PFOS are salts, there are no particular limitations, and examples thereof include ammonium salts and the like.

The above-mentioned fluorine-containing surfactant may be a substance added as an emulsifier when the fluorine-containing polymer constituting the above-mentioned aqueous fluoropolymer dispersion to be treated is polymerized in an aqueous medium.

The above-mentioned aqueous fluoropolymer dispersion to be treated can be prepared by polymerizing the fluoropolymer by known methods such as suspension polymerization and emulsion polymerization.

For the fluorine-containing monomers, fluorine-free monomers, polymerization initiators, chain transfer agents and other additives used in each of the above polymerizations, known ones can be appropriately used, and the above-mentioned surfactants can be used in each of the above polymerizations.

From the viewpoint of polymerization efficiency, each of the above-mentioned polymerizations is preferably carried out under the condition that the amount of the fluorine-containing surfactant is 0.0001% by mass to 10% by mass of the above-mentioned aqueous medium. Specifically, the amount of the fluorine-containing surfactant is 100 ppm or more, more specifically 1000 ppm or more, more specifically 1500 ppm or 2000 ppm or more, or 1 mass % or more of the above-mentioned aqueous medium.

The above-mentioned treated fluorine-containing polymer aqueous dispersion can also be the above-mentioned fluorine-containing polymer after polymerization, such as ion exchange treatment, etc. to reduce the treatment of fluorine-containing anionic surfactants and/or after-treatment such as concentration. liquid. With regard to the aqueous fluoropolymer dispersion to be treated after the above-mentioned post-treatment of the aqueous fluoropolymer dispersion obtained by polymerization, the concentration of the fluorosurfactant may be, for example, the aqueous fluoropolymer dispersion to be treated. below 100ppm.

As said ion exchange treatment, the method etc. which use the ion exchanger described in Japanese Patent Application Publication No. 2002-532583 are mentioned, for example.

In this specification, the concentration of a fluorine-containing anionic surfactant is a value obtained by (1) performing high-performance liquid chromatography [HPLC] under the following conditions, or (2) dispersing in an aqueous fluorine-containing polymer to be measured. Methanol equivalent to the aqueous dispersion was added to the solution for Soxhlet extraction, and HPLC measurement was performed under the following conditions to obtain the value of the concentration of the fluorine-containing anionic surfactant. In addition, the above-mentioned method (1) is suitable for the supernatant phase mentioned later, and the above-mentioned method (2) is suitable for the aqueous fluorine-containing polymer dispersion liquid phase mentioned later.

HPLC determination conditions

Column: ODS-120T (4.6φ×250mm, manufactured by Tosoh Corporation)

Eluent: acetonitrile/0.6% by mass perchloric acid aqueous solution=60/40 (vol/vol%)

Sample volume: 20μL

Flow rate: 1.0ml/min

Detection wavelength: UV 210nm

Column temperature: 40°C

Lower detection limit: 10ppm

When calculating the concentration of fluorine-containing anionic surfactant, use the above-mentioned eluent and carry out HPLC measurement on the aqueous solution of fluorine-containing anionic surfactant under the above-mentioned conditions to obtain the standard curve, and use the obtained standard curve to calculate the concentration.

In the above step (1), as the nonionic surfactant to be added to the aqueous fluoropolymer dispersion to be treated, for example, those mentioned in the description of the aqueous fluoropolymer dispersion to be treated Examples, wherein preferred nonionic surfactants of polyoxyethylene alkyl ether structure, more preferably nonionic surfactants with alkyl carbon atoms of 10 to 20 polyoxyethylene alkyl ether structures, more preferably with A nonionic surfactant with a polyoxyethylene alkyl ether structure with an alkyl group of 10 to 15 carbon atoms. Examples of the nonionic surfactant having the polyoxyethylene alkyl ether structure include Noigen TDS-80 (manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.).

In the above step (1), the amount of the nonionic surfactant added is preferably 5 to 30 parts by mass relative to 100 parts by mass of the fluoropolymer in the aqueous fluoropolymer dispersion to be treated.

When the amount of the above-mentioned nonionic surfactant is less than 5 parts by mass relative to 100 parts by mass of the above-mentioned fluoropolymer, it may be difficult to separate the supernatant phase and the aqueous fluoropolymer dispersion phase. When the amount of the active agent exceeds 30 parts by mass relative to 100 parts by mass of the above-mentioned fluoropolymer, economical efficiency is impaired.

As for the amount of the nonionic surfactant added in the above step (1), a more preferable lower limit is 10 parts by mass, and a more preferable upper limit is 25 parts by mass relative to 100 parts by mass of the above-mentioned fluoropolymer.

In this specification, the content (N) of the nonionic surfactant is determined as follows: about 1 g (X) of the sample is placed in an aluminum crucible with a diameter of 5 cm, and dried at 100° C. for 1 hour to obtain a heating residue (Y) , and then dried at 300°C for 1 hour to obtain a heating residue (Z), based on the heating residue (Y) and the heating residue (Z), using the calculation formula: N=(Y-Z)/X×100(%) to determine Content of nonionic surfactant (N).

The above step (1) preferably includes the operation of stirring the aqueous fluoropolymer dispersion to be treated. By stirring the treated fluoropolymer aqueous dispersion, the added nonionic surfactant is uniformly dispersed in the treated fluoropolymer aqueous dispersion, and is easily Rapid transfer to the supernatant phase, so the step time can be further shortened.

In the above step (1), for example (i) the aqueous fluoropolymer dispersion to be treated may be stirred in advance, and the above-mentioned nonionic surfactant may be added to the aqueous fluoropolymer dispersion to be treated under stirring , It is also possible to (ii) start stirring after adding the above-mentioned nonionic surfactant to the treated aqueous fluoropolymer dispersion which has been left standing.

The addition of the nonionic surfactant can be performed after adjusting the pH of the aqueous fluoropolymer dispersion to be treated to 3 to 12 using an ammonia solution or the like.

The addition of the nonionic surfactant in the above step (1) is preferably carried out under the condition that the temperature of the aqueous fluoropolymer dispersion to be treated is not higher than the temperature at which phase separation occurs in the step (2).

In the present invention, when the above-mentioned nonionic surfactant is added in the above-mentioned temperature range, the separation of the supernatant phase and the aqueous fluoropolymer dispersion phase described later becomes faster, and the fluorine-containing polymer obtained by phase separation The viscosity stability of the aqueous dispersion liquid becomes better, so it is preferable.

The liquid temperature of the treated aqueous fluoropolymer dispersion for adding the above-mentioned nonionic surfactant is related to the type of nonionic surfactant used, but usually it is the temperature that can make the nonionic surfactant The temperature at which the fluoropolymer is uniformly dispersed in the aqueous dispersion is usually below the cloud point. For example, when the nonionic surfactant is the above-mentioned NoigenTDS-80, the temperature is preferably 30°C to 50°C .

In the present invention, the above-mentioned "phase separation temperature in step (2)" is usually the temperature within the range of the phase separation temperature ± 5°C, and the phase separation temperature is: when implementing the present invention, the above step (1) ), when the supernatant phase produced by adding nonionic surfactant in ) is separated from the fluoropolymer aqueous dispersion phase, the temperature at which the speed reaches the maximum is called "phase separation temperature".

The above-mentioned phase separation temperature does not have to be consistent with the cloud point of the nonionic surfactant. When the type and amount of the coexisting electrolyte, anionic surfactant, etc. are different, the above-mentioned phase separation temperature is also different, but it is usually lower than that of the added The temperature of the cloud point of a nonionic surfactant is 20 degreeC - 20 degreeC higher than this cloud point, More specifically, it is the temperature in the temperature range of 40-90 degreeC.

The above-mentioned cloud point means that when the nonionic surfactant aqueous solution is continuously heated, the aqueous solution becomes cloudy to form a cloudy liquid, and when the cloudy liquid is slowly cooled, the entire solution becomes transparent, and the temperature at this time is the cloud point.

In this specification, the above-mentioned cloud point is a value measured as follows: According to ISO1065 (Method A), 15 mL of a measurement diluted sample is put into a test tube, heated until completely opaque, and the entire solution becomes transparent when slowly cooled under stirring. temperature, which is the cloud point.

When the above-mentioned nonionic surfactant is added at a temperature lower than the temperature at which phase separation occurs, the above-mentioned step (1) may further include an operation of raising the temperature after the addition.

The conditions for raising the temperature can be appropriately set according to the type and amount of the fluoropolymer, nonionic surfactant, and the like to be used.

The temperature rise in the above step (1) is generally performed until the added aqueous dispersion reaches a temperature at which phase separation occurs in the above step (2).

The step (2) in the present invention is a step of performing phase separation after the above-mentioned step (1), and separating into a supernatant phase and a fluoropolymer aqueous dispersion liquid phase.

Step (2) in the present invention is generally through the steps of following two moments: when implementing the present invention, add the supernatant phase that non-ionic surfactant produces in making above-mentioned step (1) and fluorine-containing polymerization When the aqueous dispersion liquid phase of the polymer is separated, its temperature reaches the moment when the separation speed reaches the maximum value that can be set; the time when the respective volumes of the supernatant phase and the aqueous dispersion liquid phase of the fluoropolymer resulting from the separation become constant. In this regard, step (2) above can be distinguished from step (1) above.

Step (2) above may, for example, be initiated as follows:

(i) In the above step (1), before, during or after the addition, stirring of the aqueous dispersion of the fluoropolymer to be treated is started, and the phase separation is carried out at a temperature lower than that of adding After the non-ionic surfactant, when the temperature is raised to the temperature for phase separation, the above step (2) is started by reducing the stirring speed;

(i-2) In the above-mentioned step (1), before, during or after the addition, agitation of the aqueous fluoropolymer dispersion to be treated is started, and at a temperature lower than the temperature at which phase separation occurs, After adding the non-ionic surfactant, when the temperature is raised to the temperature for phase separation, after continuing the above-mentioned stirring for a period of time, start the above-mentioned step (2) by reducing the stirring speed or stopping the stirring;

(ii) In the above-mentioned step (1), before, during or after the addition, agitation of the aqueous fluoropolymer dispersion to be treated is started, and the addition is performed at a temperature lower than the temperature at which phase separation occurs. Nonionic surfactant, after making it mix evenly, suspend stirring, when the temperature is raised to the temperature for phase separation, stir again, thus starting the above step (2);

(iii) In the above step (1), the aqueous fluoropolymer dispersion to be treated is preliminarily brought to a temperature at which phase separation occurs, and then a nonionic surfactant is added while stirring, thereby making the nonionic surface active The agent is mixed uniformly in the fluoropolymer aqueous dispersion, and then the stirring speed is reduced, thus starting the above step (2).

The phase separation in the above step (2) is carried out by appropriately setting the temperature at which the aqueous fluoropolymer dispersion to be treated to which the nonionic surfactant is added undergoes the phase separation.

In the production method of the aqueous fluoropolymer dispersion of the present invention, stirring is performed in the above-mentioned step (2).

In the past, in the case of producing an aqueous fluoropolymer dispersion by phase separation, in order not to interfere with the formation of the aqueous fluoropolymer dispersion phase and the supernatant phase, it was considered in the past that the mixture of the liquid to be treated and the surfactant was obtained. Resting is required after the temperature at which phase separation occurs.

However, the feature of the present invention is that even after reaching the temperature at which the mixed liquid of the aqueous fluoropolymer dispersion to be treated and the nonionic surfactant phase-separates, the mixed liquid is stirred. In comparison, the time for phase separation of the supernatant phase and the aqueous fluoropolymer dispersion phase to reach a constant volume ratio can thus be shortened.

The mechanism by which the present invention can shorten the time for phase separation is unclear, but it is considered that the phase separation is initiated by the precursor (droplet) formed by the nonionic surfactant molecule and water, and the stirring promotes the phase separation of the precursor. combination, resulting in a more rapid formation of the supernatant phase.

The stirring in the above step (2) may be performed on the entire aqueous fluoropolymer dispersion to be treated, but it is preferable to stir only the aqueous fluoropolymer dispersion phase from the viewpoint of maintaining a higher phase separation rate.

The above "stirring only the aqueous fluoropolymer dispersion phase" means stirring the aqueous fluoropolymer dispersion phase at such a speed range that the clear phase does not mix into the aqueous fluoropolymer dispersion phase. Usually, the formed supernatant phase is a transparent phase, and the aqueous fluoropolymer dispersion phase is a cloudy phase, so that the interface between the phases can be observed. Therefore, when the aqueous fluoropolymer dispersion is stirred at such a speed that the interface is not destroyed, only the aqueous fluoropolymer dispersion is stirred.

The stirring in the above-mentioned step (2) is preferably performed at the same or lower stirring speed than the stirring that can be implemented in the above-mentioned step (1).

The stirring in the above-mentioned step (2) can be performed, for example, at about half of the stirring speed in the above-mentioned step (1).

For the stirring in the above step (2), the stirring speed may be changed in the middle of this step. The aforementioned change in the stirring speed is preferably a reduction in the stirring speed.

As described above, the stirring in the above step (2) is preferably at a speed capable of stirring only the aqueous fluoropolymer dispersion phase.

The method for producing an aqueous fluoropolymer dispersion of the present invention includes the step (3) of removing the supernatant phase to obtain the aqueous fluoropolymer dispersion phase.

The method for removing the supernatant phase is not particularly limited, and conventionally known methods such as the pouring method can be used.

The aqueous fluoropolymer dispersion obtained by the present invention may be the aqueous dispersion itself obtained from the above-mentioned aqueous fluoropolymer dispersion phase, or may be an aqueous dispersion after a known post-treatment. For example, adding water and/or a nonionic surfactant to the obtained aqueous fluoropolymer dispersion phase to adjust the concentration, adding ammonia water, etc. to adjust the pH; and the like.

The aqueous fluoropolymer dispersion preferably has a fluoropolymer concentration of 35% by mass or more, more preferably 45% by mass or more, still more preferably 55% by mass or more, and usually 75% by mass or less when within the above range. Thus, the method for producing an aqueous fluoropolymer dispersion of the present invention can also be used as a method for concentrating a fluoropolymer.

The above-mentioned aqueous fluoropolymer dispersion can be easily processed into fluoropolymer powder, fluoropolymer molding, etc., and the heat resistance, It is excellent in physical properties such as chemical resistance, durability, weather resistance, surface properties, and mechanical properties, so it is useful as materials such as cooking utensils, piping linings, glass cloth impregnated films, and battery adhesives.

Since the method for producing an aqueous fluoropolymer dispersion of the present invention has the above-mentioned constitution, it is possible to produce an aqueous fluoropolymer dispersion having a high concentration of fluoropolymer in a short period of time.

Detailed ways

Hereinafter, the present invention will be described in more detail by way of examples and comparative examples, but the present invention is not limited by these examples and comparative examples.

In the present examples and comparative examples, unless otherwise specified, "parts" means "parts by mass".

The measurement performed in each Example or each comparative example was performed by the following method.

1. Nonionic Surfactant Concentration and Fluoropolymer Concentration

Put about 1 g of (X) sample into an aluminum crucible with a diameter of 5 cm, dry at 100°C for 1 hour to obtain a heating residue (Y), and then dry it at 300°C for 1 hour to obtain a heating residue (Z), based on heating Residue (Y) and heating residue (Z), the concentrations were determined using the following calculation formula.

N=(Y-Z)/X×100(%)

P=Z/X×100(%)

In each of the above calculation formulas, N is the concentration of the nonionic surfactant, and P is the concentration of the fluoropolymer.

2. Concentration of fluorinated anionic surfactant in PTFE aqueous dispersion

The measurement was performed based on the above-mentioned method (2). In Soxhlet extraction, an equivalent amount of methanol is added to about 10 g of polytetrafluoroethylene aqueous dispersion, and after coagulation, 100 g of methanol is used for extraction at 90° C. for 10 hours.

Example 1

Add 2500g polytetrafluoroethylene [PTFE] aqueous dispersion (25% fluorine-containing polymer content, perfluorooctanoic acid ammonium [ PFOA〕 content 625ppm), after adjusting the pH to 9 with 10% ammonia solution, under stirring at 120rpm, add 122g of Noigen TDS-80 (product name, polyoxyethylene alkyl ether type nonionic produced by Daiichi Pharmaceutical Co., Ltd. Type surfactant. Cloud point 58°C), mix well in a warm water bath at 40°C. Next, the temperature of the warm water bath was increased under stirring so that the internal temperature reached 70° C. after 1 hour. At this time, the stirring was set at 60 rpm, and the internal temperature was kept at 70°C. Immediately after changing the stirring speed, a supernatant phase was produced, and an increase in the volume fraction of the supernatant phase was observed over time. 50 minutes after changing the stirring speed, the volume ratio of the supernatant phase became almost constant, so the stirring was stopped, the obtained supernatant phase was removed, and the aqueous fluoropolymer dispersion phase was separated. The obtained aqueous fluoropolymer dispersion phase is the aqueous fluoropolymer dispersion in the present invention, and its fluoropolymer concentration is 64.9%.

Comparative example 1

Add 2500g of PTFE aqueous dispersion (25% fluorine-containing polymer content, 625ppm PFOA content) in a cylindrical glass container with a diameter of 6cm, an inner capacity of 5L, and a diameter of 16cm, with 10% ammonia After adjusting the pH of the aqueous solution to 9, add Noigen TDS-80 (122g) under stirring at 120rpm, and mix well in a warm water tank at 40°C. Next, the temperature of the warm water bath was increased under stirring so that the internal temperature reached 70° C. after 1 hour. At this time, the stirring was stopped, and the inner temperature was kept at 70°C. After the stirring was stopped, a supernatant phase was generated over time, and the volume ratio of the supernatant phase gradually increased. After stopping stirring for 120 minutes, the volume ratio of the supernatant phase became almost constant, so the supernatant phase was removed, and the fluoropolymer aqueous dispersion liquid phase was separated. The fluoropolymer concentration of the fluoropolymer aqueous dispersion liquid phase was 63.8%.

From the above, it can be seen that the method for producing an aqueous fluoropolymer dispersion (Example 1) of the present invention can obtain an aqueous fluoropolymer dispersion having a high concentration of fluoropolymer in a short period of time.

Industrial availability

Since the method for producing an aqueous fluoropolymer dispersion of the present invention has the above-mentioned configuration, it is possible to produce an aqueous fluoropolymer dispersion having a high concentration of fluoropolymer in a short period of time.

Claims (5)

1. the manufacture method of a fluoropolymer aqueous liquid dispersion, it comprises step (1), step (2) and step (3), in step (1), in processed fluoropolymer aqueous liquid dispersion, add nonionic surface active agent, in step (2), be separated afterwards in above-mentioned steps (1), be separated into supernatant mutually with the fluoropolymer aqueous liquid dispersion mutually, in step (3), remove above-mentioned supernatant phase, obtain above-mentioned fluoropolymer aqueous liquid dispersion phase; This manufacture method is characterised in that, stirs in above-mentioned steps (2).

2. the manufacture method of fluoropolymer aqueous liquid dispersion according to claim 1, wherein, the interpolation of nonionic surface active agent is that temperature at processed fluoropolymer aqueous liquid dispersion is less than or equal under the condition of the temperature that is separated in the step (2) and carries out in the step (1).

3. the manufacture method of fluoropolymer aqueous liquid dispersion according to claim 1 and 2, wherein, the median size of the fluoropolymer particles in the processed fluoropolymer aqueous liquid dispersion is 50nm～500nm.

4. according to the manufacture method of claim 1,2 or 3 described fluoropolymer aqueous liquid dispersions, wherein, described fluoropolymer is a (per) fluoropolymer.

5. according to the manufacture method of claim 1,2,3 or 4 described fluoropolymer aqueous liquid dispersions, wherein, described fluoropolymer is a tetrafluoroethylene.