WO2006077737A1

WO2006077737A1 - Method for preparation of aqueous fluorinated polymer dispersion

Info

Publication number: WO2006077737A1
Application number: PCT/JP2005/024115
Authority: WO
Inventors: Nobuhiko Tsuda; Chie Sawauchi
Original assignee: Daikin Industries, Ltd.
Priority date: 2004-12-28
Filing date: 2005-12-28
Publication date: 2006-07-27
Also published as: JPWO2006077737A1

Abstract

Disclosed is a method for the preparation of an aqueous fluorinated polymer dispersion having a reduced amount of a fluorinated emulsifier or the like remaining in the dispersion. The method comprises preparing an aqueous fluorinated polymer dispersion via a concentration step, in which the concentration step comprises concentrating an aqueous fluorinated polymer dispersion A in the presence of a specific nonionic surfactant and/or a specific anionic surfactant. The specific nonionic surfactant has a hydrophilic group with a molecular weight of 400 or lower and a hydrophobic group with 10 to 20 carbon atoms. The specific anionic surfactant is a non-fluorinated anionic surfactant which has a hydrocarbon group as a hydrophobic group and has a total of 10 to 20 carbon atoms in the hydrocarbon group.

Description

Specification

Fluorine-containing polymer aqueous dispersion production method

Technical field

[0001] The present invention relates to a method for producing an aqueous fluoropolymer dispersion.

Background art

[0002] As a method for producing a fluorine-containing polymer aqueous dispersion, a method of carrying out polymerization in the presence of a fluorine-containing emulsifier is known.

However, although the fluorine-containing emulsifier is very useful for the production of a fluorine-containing polymer, it is expensive, and therefore, a method of emulsion-polymerizing the fluorine-containing polymer in the absence of the fluorine-containing emulsifier has been studied. (For example, see Patent Document 1.) o

In this production method, emulsion polymerization of the fluorine-containing polymer is carried out in the absence of the fluorine-containing emulsifier, so that an aqueous dispersion containing no fluorine-containing emulsifier can be obtained, but tetrafluoroethylene [TFE ] Some fluoropolymers such as homopolymers have a problem in that the aqueous dispersion is not sufficiently stable.

[0003] When a fluorine-containing polymer aqueous dispersion is applied as various coating materials and the like, if a fluorine-containing emulsifier is mixed, the properties of the fluorine-containing polymer such as heat resistance, chemical resistance and mechanical strength are exhibited. In some cases, however, a method for reducing the fluorine-containing polymer aqueous dispersion power and the fluorine-containing emulsifier is being studied.

Fluorine-containing polymer aqueous dispersion power A method for reducing the fluorine-containing emulsifier is, for example, adding a certain amount of water and a specific type of nonionic surfactant to polytetrafluoroethylene [PTFE] aqueous dispersion. Concentration operation was carried out, the fluorine-containing emulsifier adsorbed on the surface of PTFE particles was transferred to the aqueous phase, the aqueous phase was removed after concentration, and this concentration operation was repeated to repeat the concentration in the aqueous dispersion. fluorinated emulsifier further method of reducing is known (see Patent Document 2.) of _0, however, this concentration method, as they may time consuming to concentration operation, the fluorinated emulsifier adsorbed on the PTFE particle surface The efficiency of transferring water to the aqueous phase was extremely low.

Patent Document 1: US Application Publication No. 2002Z0198334 Patent Document 2: International Publication No. 2003Z078479 Pamphlet

Disclosure of the invention

Problems to be solved by the invention

[0004] In view of the above situation, an object of the present invention is to provide a method for producing a fluorine-containing polymer aqueous dispersion in which the remaining amount of a fluorine-containing emulsifier and the like is reduced.

Means for solving the problem

[0005] The present invention is a method for producing an aqueous fluoropolymer dispersion comprising producing an aqueous fluoropolymer dispersion through a concentration step, wherein the concentration step comprises a specific nonionic surfactant and Z Or an aqueous fluoropolymer dispersion in the presence of a specific surfactant

The specific nonionic surfactant is a nonionic surfactant having a hydrophilic group molecular weight of not more than 00 and a hydrophobic group having 10 to 20 carbon atoms. And the specific anion surfactant is a fluorine-free anionic surfactant having a hydrocarbon group as a hydrophobic group and having a total of 10 to 20 carbon atoms in the hydrocarbon group. This is a method for producing an aqueous fluoropolymer dispersion.

The present invention is described in detail below.

[0006] The fluorine-containing polymer aqueous dispersion production method of the present invention comprises producing a fluorine-containing polymer aqueous dispersion through a concentration step.

The concentration step is a step comprising concentrating the fluoropolymer aqueous dispersion A in the presence of a specific non-one surfactant and Z or a specific key-on surfactant.

The concentration in the concentration step is an operation of separating into a supernatant phase not containing a fluorine-containing polymer and a concentrated phase containing a fluorine-containing polymer (hereinafter, sometimes referred to as “separation operation”). .).

In this specification, te, “specific nonionic surfactant and Z or specific anionic surfactant

"Surfactants" may be collectively referred to.

[0007] In the present invention, the fluoropolymer aqueous dispersion A is obtained by dispersing fluoropolymer particles in an aqueous medium.

In the present specification, the “fluorinated polymer aqueous dispersion A” refers to an aqueous component before separation into a supernatant phase and a concentrated phase in the concentration step in the present invention. Means spray.

In the present specification, the “fluorinated polymer aqueous dispersion A” is the subject of the above-mentioned separation. On the other hand, the “fluorinated polymer aqueous dispersion” described later obtained by the method for producing a fluoropolymer aqueous dispersion of the present invention is described below. Is a concept that distinguishes the two in that they have undergone the above separation.

The aqueous fluoropolymer dispersion A is a post-polymerization aqueous dispersion (including primary particles made of a fluoropolymer) after post-treatment such as concentration and dilution after polymerization of the fluoropolymer. Alternatively, it may be a fluoropolymer aqueous dispersion obtained by the above-mentioned post-treatment after the polymerization, and after the separation operation described later is performed once, the separation operation described later is performed once. In the case where two or more operation cycles are performed, a separation operation may be performed.

[0008] In the present invention, the fluorine-containing polymer constituting the fluorine-containing polymer particle is a polymer having a fluorine atom bonded to a carbon atom.

Examples of the fluorine-containing polymer include an elastomeric fluorine-containing polymer and a fluorine-containing polymer constituting a resin.

[0009] The elastomeric fluorine-containing polymer is an amorphous fluorine-containing polymer having rubber elasticity, and usually has a monomer unit of 30 to 80 mol% of the first monomer. is there. In the present specification, the “first monomer” means that a monomer unit occupying the most molar ratio among all monomer units in the molecular structure of the elastomeric fluoropolymer. Means a monomer. Examples of the first monomer include vinylidene fluoride [VDF] and tetrafluoroethylene [TFE].

In the present specification, the “monomer unit” such as the monomer unit of the first monomer means a part derived from the corresponding monomer, which is a part of the molecular structure of the fluorine-containing polymer. To do. For example, the TFE unit is a part of the molecular structure of the fluorine-containing polymer, is a part derived from TFE, and is represented by one (CF—CF 3) —. The above "total monomer units"

twenty two

It is all the part derived from a monomer on the molecular structure of a fluorine-containing polymer.

[0010] Regarding the elastomeric fluorine-containing polymer, for example, TFE-based polymers include TFE Z propylene copolymer, TFEZ perfluorobule ether [PAVE] copolymer, V DF polymers include VDFZHFP copolymer, VDFZ black trifluoroethylene [C

TFE] copolymer, VDFZTFE copolymer, VDFZPAVE copolymer, VDFZTFEZ HFP copolymer, VDFZTFEZCTFE copolymer, VDFZTFEZPAVE copolymer and the like.

[0011] Examples of the fluorine-containing polymer constituting the resin include non-melt processable fluorine-containing polymers and melt strength fluorine-containing polymers.

Examples of the non-melting power fluorine-containing polymer include polytetrafluoroethylene [PTFE].

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

In the present specification, the above “modified PTFE” means a copolymer of TFE and a trace monomer other than TFE, which is non-melt processable.

Examples of the trace monomer include fluoroolefins such as HFP and CTFE, fluoro having an alkyl group having 1 to 5 carbon atoms, particularly 1 to 3 carbon atoms (alkyl butyl etherol); Rosioxol; perfluoroalkylethylene; ω-hydroperfluoroolefin.

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

In this specification, “the content (mol%) of the trace monomer unit in the total monomer units” means the monomer from which the above “all monomer units” is derived, that is, the content. This means the mole fraction (mol%) of the trace monomer derived from the trace monomer unit in the total amount of the monomer that constitutes the fluoropolymer.

[0012] Examples of the melt-resistant fluorine-containing polymer include, for example, ethylene ZTFE copolymer [ETF E], TFEZHFP copolymer [FEP], TFEZ perfluoro (alkyl butyl ether) copolymer [TFEZPAVE copolymer] ], PVDF, PVD copolymer, polyfluoride bur [p _VF ] and the like.

The above TFEZPAVE copolymers include TFEZ perfluoro (methyl vinyl ether) [PMVE] copolymer [MFA], TFEZ perfluoro (ethyl vinyl ether) [PEVE ], TFEZ perfluoro (propyl butyl ether) [PPVE] copolymer, and the like. Among them, MFA and TFEZPPVE copolymer are preferred. TFEZPPVE copolymer is more preferred.

[0013] The fluoropolymer is more preferably PTFE, which is preferably a perfluoropolymer or a fluoropolymer that is substantially perfluoro.

The fluoropolymer particles constituting the fluoropolymer aqueous dispersion A preferably have an average primary particle diameter of 50 to 500 nm from the viewpoint of dispersion stability.

The average primary particle size is more preferably lower limit of lOOnm and more preferable upper limit force of 00 nm.

The above average primary particle size is measured by measuring the transmittance of 550 nm projection light per unit length of an aqueous dispersion with the fluorine-containing polymer concentration adjusted to 0.22 mass%, and the unidirectional diameter in a transmission electron micrograph. The transmittance force is determined based on a calibration curve with the average particle diameter determined in the above.

[0014] The fluoropolymer aqueous dispersion A preferably contains 1 to 50% by mass of a fluoropolymer.

More preferably, the fluoropolymer aqueous dispersion A contains 10 to 30% by mass of the fluoropolymer.

In the present specification, the content of the fluoropolymer may be within the above range at the start of the separation operation in the concentration step.

The content of the above-mentioned fluoropolymer is as follows: a calorie heat residue (Yg) obtained by heating about lg (X) of a sample at 100 ° C. for 1 hour, and further this heat residue (Yg) 1 at 300 ° C. It is a value calculated based on the relationship of fluoropolymer content P = (Z / X) X 100 (%) from the heating residue (Zg) heated for a period of time.

[0015] The aqueous medium constituting the fluoropolymer aqueous dispersion A is not particularly limited as long as it is a liquid containing water, and can be stored in water, for example, non-fluorine such as alcohol, ether, ketone, and paraffin wax. It also contains the organic solvent containing Z and fluorine-containing organic solvent.

[0016] The fluoropolymer aqueous dispersion A includes the fluoropolymer particles and the aqueous medium described above. In addition, a surfactant may also be included.

The surfactant contained in the fluoropolymer aqueous dispersion A is not particularly limited, and for example, a fluorine-containing emulsifier, a fluorine-free emulsifier, and the like can be used.

The aqueous fluoropolymer dispersion A may contain one or more of the surfactants.

[0017] The fluorinated emulsifier is not particularly limited as long as it has an emulsifying effect due to the strength of the fluorinated compound, but those having an average molecular weight of 1000 or less are preferably easy to remove and have an average molecular weight. More preferred are those that are 500 or less.

As the fluorine-containing emulsifier, those having a fluorine-containing compound having 5 to 12 carbon atoms are also preferable. When the number of carbon atoms is less than 5, generally, an emulsifying action cannot be exhibited.

Examples of the fluorine-containing emulsifier include fluorine-containing carboxylic acid compounds such as fluorine-containing carboxylic acid compounds and fluorine-containing sulfonic acid compounds. A compound made of a compound is more preferred, and a compound having a compound strength of a fluorine-containing carboxylic acid having 5 to 12 carbon atoms is more preferred.

As the fluorine-containing emulsifier, for example, perfluorooctanoic acid or a salt thereof is preferable. In the present specification, the “perfluorooctanoic acid or a salt thereof” may be abbreviated as “PFOA” hereinafter.

When the fluorine-containing emulsifier is a salt, examples of the counter ion forming the salt include an alkali metal ion or NH +. Examples of the alkali metal ion include Na +, Ka +.

Four

Etc. As the counter ion, NH + is preferable.

Four

[0018] In the fluoropolymer aqueous dispersion A, the concentration of the fluoroemulsifier is preferably 5 parts by mass or less with respect to 100 parts by mass of the aqueous medium. More preferably, the amount is 0.3 parts by mass or less. If it is in the said range, it may be 0.005 mass part or more with respect to 100 mass parts of aqueous media, and may be 0.01 mass part or more.

In the present invention, the concentration of the fluorinated emulsifier is determined by HPLC measurement after Soxhlet extraction is performed by adding an equal amount of methanol to the fluoropolymer aqueous dispersion to be measured. Is obtained under certain conditions.

[0019] Examples of the non-fluorine-containing emulsifier include “non-ionic surfactants having HLB of 10 to 15” described later.

The content of the “non-ionic surfactant having HLB of 10 to 15” will be described later.

[0020] The fluoropolymer aqueous dispersion A may contain an emulsifier used in the polymerization of the fluoropolymer (hereinafter, also referred to as "polymerization emulsifier" in the present specification). In the concentration step in the present invention, when the fluoropolymer aqueous dispersion A contains the above-described polymerization emulsifier, not only the specific surfactant but also the polymerization emulsifier is used as the surfactant. It may be.

Examples of the polymerization emulsifier include the above-described fluorine-containing emulsifiers such as PFOA.

[0021] The fluoropolymer aqueous dispersion A can be prepared by polymerizing the fluoropolymer by a known method such as suspension polymerization or emulsion polymerization.

As the fluorine-containing monomer, non-fluorine-containing monomer, and additive such as a polymerization initiator and a chain transfer agent in each of the above polymerizations, known ones can be used as appropriate. The above-described polymerization emulsifier can be used.

Each of the above polymerizations is preferably carried out in the presence of a fluorine-containing emulsifier in an amount of 0.0001 to 10% by mass of the aqueous medium from the viewpoint of polymerization efficiency. The amount of the fluorinated emulsifier is preferably 0.001% by mass or more of the aqueous medium, more preferably 1% by mass or more.

[0022] The polymerization is preferably carried out at a temperature of 10 to 120 ° C, for example, when preparing a fluorine-containing polymer having an average particle diameter in the above-mentioned range. ~: LOMPa, preferably 1. OMPa or higher, more preferably 6.2 MPa or lower.

The polymerized aqueous dispersion obtained after polymerization preferably has a fluorine-containing polymer concentration of 5 to 40% by mass, more preferably 15 to 35% by mass.

[0023] The concentration step in the present invention is performed in the presence of a specific non-one surfactant and Z or a specific key-on surfactant. [0024] The specific nonionic surfactant has a molecular weight of a hydrophilic group of 00 or less and a nonionic compound having a hydrophobic group having 10 to 20 carbon atoms.

The hydrophilic group preferably has a molecular weight of 150 to 350.

If the number of carbon atoms in the hydrophobic group is within the above range, it is preferably 16 or less.

[0025] In the specific non-one surfactant, the hydrophilic group is a repeating unit to which alkylene oxide is added (one O—R—, where R represents an alkylene group having 2 to 4 carbon atoms). Powerful groups are preferred. The repeating unit of alkylene oxide may be an oxypropylene group! /, But an oxyethylene group is preferred.

[0026] In the specific nonionic surfactant, the hydrophilic group is preferably one having an alkylene oxide repeating unit of 7 or less, and preferably having an oxyethylene group strength of 5 or less. More preferred.

The hydrophilic group may be one in which a hydrocarbon group (including a polyoxyalkylene group) has a hydroxyalkyl group as a side chain! /.

[0027] As the specific non-ionic surfactant, those having HLB of 5 or more and less than 10 are particularly preferable. Conventionally, cloud point concentration (sometimes referred to as phase separation method or heat concentration method) that uses a nonionic surfactant with an HLB of 10 to 15 and heats the cloud point to heat it has been frequently used. However, a non-ionic surfactant having an HLB power of less than 10 was not used for concentration because of its low cloud point. On the other hand, the present invention can include concentration using a nonionic surfactant having an HLB of 5 or more and less than 10.

As the specific non-one surfactant, for example, TDS-50 (Daiichi Kogyo Seiyaku Co., Ltd.) is preferably used.

[0028] The specific anion surfactant is a fluorine-free anionic surfactant having a hydrocarbon group as a hydrophobic group and a total carbon number of 10 to 20 carbon atoms.

In the present specification, “the total number of carbon atoms of the hydrocarbon group” means that when the fluorine-free ionic surfactant has only one hydrocarbon group as a hydrophobic group in one molecule, Means the number of carbon atoms of the hydrocarbon group, and when the fluorine-free cation surfactant has two or more hydrocarbon groups as hydrophobic groups in one molecule, It means the total number of carbon atoms obtained by summing up the carbon number of each hydrogen group.

[0029] The hydrocarbon group that the non-fluorine-containing surfactant, which is the specific surfactant, has as a hydrophobic group is preferably an alkyl group. For example, the following general formula (I ) And (Π) and those corresponding to R ² and R ⁴ in the following general formula (Π).

As the specific key-on surfactant, the following general formula (I)

R ¹ — SO M ¹ (I)

Three

(Wherein R ¹ represents an alkyl group having 8 to 20 carbon atoms, preferably 10 to 20 carbon atoms, and M ¹ represents H, NH, Na or K), or a salt thereof,

Four

The following general formula (π)

R'-OSO M ¹ (II)

Three

(Wherein R ¹ represents an alkyl group having 8 to 20 carbon atoms, preferably 10 to 20 carbon atoms, and M ¹ represents H, NH, Na or K) or a salt thereof Or

Four

The following general formula (III)

R ² -OCO-CH (-SO M ² ) -R ³ -COO-R ⁴ (III)

Three

(Wherein R ² and R ⁴ are the same or different and each represents an alkyl group having 4 to 12 carbon atoms, R ³ represents an alkylene group having 1 to 3 carbon atoms, M ² represents H, NH, Represents Na or K, provided above

Four

The carbon number of each alkyl group represented by R ² and R ⁴ is 10 to 20 in total. The sulfodicarboxylic acid ester or its salt represented by) is preferred! /.

[0030] In the above general formula (I) and the above general formula (上記), the preferred lower limit of the carbon number of the alkyl group represented by R ¹ is 10, the preferred upper limit is 16, and the more preferred upper limit is 14. It is.

As the M ^1, Na is preferred.

Examples of the alkyl sulfuric acid represented by the general formula (I) or the general formula (II) or a salt thereof include sodium dodecyl sulfate [SDS].

[0031] In the general formula (ΠΙ), the alkyl group represented by R ² and R ⁴ each has a preferred lower limit of 5 carbon atoms, a more preferred lower limit of 6, and a preferred upper limit of 10, A more preferred upper limit is 8.

The alkyl groups represented by R ² and R ⁴ may be the same or different from each other. Yes.

In the general formula (m), the number of carbon atoms of the alkylene group represented by R ³ is not particularly limited as long as it is within the above range, but the preferable upper limit is 2, more preferably 1.

As the M ^2, Na is preferred.

Examples of the sulfodicarboxylic acid ester represented by the general formula (ΠΙ) or a salt thereof include sodium dioctylsulfosuccinate.

[0032] In the concentration step in the present invention, it is preferable that the specific non-ionic surfactant and Z or the specific cationic surfactant are present in a total of 1 to 50 parts by mass with respect to 100 parts by mass of the fluoropolymer. .

The preferred upper limit of the amount of the specific surfactant present relative to 100 parts by mass of the fluoropolymer is the sum of suppressing the increase in viscosity and suppressing the increase in the amount of specific surfactant transferred into the supernatant phase. It is 20 parts by mass.

[0033] It is preferable that the specific non-one surfactant and the Z or specific key-on surfactant are added after the above-mentioned fluoropolymer polymerization.

In the present specification, “added after polymerization of the fluorine-containing polymer” means adding after the completion of the polymerization reaction rather than being added as an emulsifier in the polymerization reaction for obtaining the fluorine-containing polymer. In the present invention, the timing of “adding after the fluoropolymer polymerization” may be added at any time as long as it is after the completion of the fluoropolymer polymerization reaction and before the separation operation described later. For example, adding after performing a post-treatment such as dilution after completion of the fluoropolymer reaction can be said to be “added after polymerization of fluoropolymer”.

[0034] In the concentration step of the present invention, the separation operation is not particularly limited. For example, known separation methods such as cloud point concentration, phase separation concentration using centrifugation, electric concentration, ultrafiltration concentration, ion exchange concentration, etc. The operation by a method is mentioned.

In the present invention, the separation operation is carried out in the presence of a specific non-ionic surfactant. In the presence of a specific anionic surfactant, phase separation concentration using cloud point concentration, centrifugation, etc. is preferred. However, phase separation and concentration using centrifugation is preferable, but other separation operations may be possible by using other surfactants in combination. other When using a surfactant in combination, for example, it is possible to concentrate cloud points by using a specific anionic surfactant and a nonionic surfactant having an HLB of 10 to 15 in combination. Can be mentioned.

[0035] As a separation operation in the present invention, when performing cloud point concentration, a non-surfactant having an HLB of 10 to 15 is used in combination.

In the cloud point concentration, the fluorine-containing polymer is precipitated with a nonionic surfactant having an HLB of 10 to 15, and the above-mentioned specific surfactant is a fluorine-containing polymer aqueous dispersion A containing a fluorine-containing emulsifier. When it is contained, it is considered that the fluorine-containing emulsifier is replaced.

[0036] The non-ionic surfactant that can be used for the cloud point concentration generally has an HLB of 10 to 15.

Examples of the nonionic surfactant having an HLB of 10 to 15 include, for example, the following general formula (IV):

R ^ O-A '-H (IV)

(Wherein R ⁵ is a linear or branched alkyl group having 8 to 19, and preferably 10 to 16 carbon atoms; A ¹ is a polyoxyalkylene chain having 8 to 58 carbon atoms)

A polyoxyalkylene alkyl ether represented by the following general formula (V): R ⁶ — CHO— A ² — H (V)

6 4

(Wherein R ⁶ is a linear or branched alkyl group having 4 to 12 carbon atoms, and A ² is a polyoxyalkylene chain having 8 to 58 carbon atoms.) Examples thereof include those composed of oxyethylene alkyl kiln ether.

The nonionic surfactant having an HLB of 10 to 15 is preferably added in an amount of 3 to 50% by mass of the fluoropolymer.

[0037] In the concentration step in the present invention, the separation operation comprises an operation of separating the fluoropolymer aqueous dispersion A into a supernatant phase and a concentrated phase under the condition that the field coefficient exceeds 1. It may be.

The above “field coefficient” is the ratio [GZG] of the gravitational acceleration [G] under a certain gravitational acceleration condition to the standard heavy acceleration [G] on the ground.

0 0

[0038] With respect to the above field factor, the product of the field factor and the processing time T (seconds) is 1 X 10 ⁵ to 1 X 10 in that separation of the supernatant phase and the concentrated phase can be performed quickly and efficiently. ^The condition that is ⁷ (in this specification In some cases, it is called “specific gravity acceleration conditions”. ) Is preferred.

When the separation operation is performed under the specific gravity acceleration condition, aggregation of the fluorine-containing polymer transferred to the concentrated phase can be suppressed, and the fluorine-containing polymer that is not substantially aggregated in the concentrated phase. Can be dispersed again in a dispersion medium such as an aqueous medium. An example of the separation operation performed under the specific gravity acceleration condition includes centrifugation.

[0039] In the present invention, prior to the separation operation, the concentration step includes increasing the amount of water in the fluoropolymer aqueous dispersion A by dilution or the like, if necessary, in order to improve selectivity in two-phase separation. It may be preferable to adjust the fluoropolymer concentration within the above-mentioned range. When the amount of water in the fluoropolymer aqueous dispersion A is relatively large, for example, even if the fluoropolymer aqueous dispersion A contains a fluorinated emulsifier, the fluorinated polymer aqueous dispersion A will contain a fluorinated polymer throughout the separation operation. Basic polymer strength Easily to separate the fluorine-containing emulsifier.

[0040] The fluoropolymer aqueous dispersion production method of the present invention may further include a fractionation step comprising removing the supernatant phase in addition to the concentration step.

The fractionation step is not particularly limited as long as the supernatant phase can be removed. For example, the fractionation step can be performed by a known fractionation operation such as filtration or decantation.

By performing the fractionation step, the fluorinated emulsifier contained in the supernatant phase can be discharged out of the system as the supernatant phase obtained by the separation operation is removed.

[0041] The method for producing an aqueous fluoropolymer dispersion of the present invention may comprise a concentration step performed in the presence of the above-mentioned specific surfactant and another concentration step other than the concentration step.

The “other concentration step” is a step different from the above-described concentration step in that the cloud point concentration method, the electric concentration method, and the like are performed in the absence of the above-mentioned specific surfactant.

[0042] In the fluoropolymer aqueous dispersion production method of the present invention, in the case where it further includes a fractionation step in addition to the concentration step, the separation operation is performed once and then the fractionation operation is performed once. Even if the operation cycle is performed more than once.

In the present invention, the removal rate of the fluorine-containing emulsifier and the like can usually be increased by performing the operation cycle twice or more. Choose the number of operation cycles from the balance with ease of operation.

[0043] The method for producing an aqueous fluoropolymer dispersion of the present invention comprises the above-described concentration step and fractionation step, and further, with respect to the concentrated phase obtained by the fractionation step, the target fluoropolymer aqueous dispersion It may include a post-process for performing fine adjustment for imparting characteristics.

The fine adjustment is not particularly limited. For example, (1) a stirring operation in which the concentrated phase obtained by the fractionation step is appropriately stirred to obtain a uniform aqueous dispersion, (2) the concentrated phase is a desired fluorine-containing polymer concentration (3) To improve the desired properties such as dispersion stability and film-forming property, and to add additive agents such as surfactants and film-forming aids. It can be carried out by blending operation, etc.

[0044] Since the present invention performs the cloud point concentration in the presence of the above-mentioned specific surfactant, not only the concentration of the fluorine-containing polymer but also the removal of the fluorine-containing emulsifier can be performed efficiently. It is.

Conventional cloud point concentration is a force capable of precipitating a fluorine-containing polymer using a nonionic surfactant having an HLB of 10 to 15 and having a HLB of 10 to 15. ON Surfactant cannot transfer fluorinated emulsifier to the supernatant phase during cloud point concentration when the substitution efficiency of the fluorinated emulsifier is extremely poor, and therefore the fluorinated emulsifier cannot be removed. It was.

[0045] The aqueous fluoropolymer dispersion obtained by the method of the present invention is the above-mentioned fluoropolymer monoaqueous dispersion A force, and is obtained by dispersing fluoropolymer particles in an aqueous medium. It is.

The fluoropolymer aqueous dispersion is added to the surfactant (preferably a surfactant other than the fluoroemulsifier) and the fluoropolymer aqueous dispersion A in addition to the fluoropolymer particles and the aqueous medium. It may contain various additives.

[0046] The aqueous fluoropolymer dispersion obtained by the method of the present invention preferably has a fluoropolymer concentration of S30 to 80% by mass.

The fluorine-containing polymer concentration has a more preferable lower limit of 50% by mass, and a more preferable lower limit of 5%. 5% by mass, a particularly preferred lower limit is 60% by mass, a more preferred upper limit is 75% by mass, and a further preferred upper limit is 70% by mass.

[0047] In the fluoropolymer aqueous dispersion, the specific surfactant is preferably 15 parts by mass or less with respect to 100 parts by mass of the fluoropolymer. If the amount exceeds 15 parts by mass with respect to 100 parts by mass of the fluoropolymer, a dispersion effect commensurate with the abundance may not be obtained, and if it is necessary to reduce the concentration to the desired specific surfactant, it is removed. Processing becomes complicated.

The above-mentioned specific surfactant concentration has a more preferable upper limit of 10 parts by mass with respect to 100 parts by mass of the fluorine-containing polymer, and a more preferable upper limit of 5 parts by mass, in that the effect of allowing the specific surfactant to exist is obtained. It is preferably 5 parts by mass or more.

[0048] The aqueous fluoropolymer dispersion obtained by the method of the present invention is preferably such that the concentration of the fluoroemulsifier is not more than lOOOppm of the fluoropolymer in terms of maintaining the properties of the fluoropolymer. 10 ppm or less is more preferred 10 ppm or less is more preferred 1 ppm or less is particularly preferred.

[0049] Since the fluoropolymer aqueous dispersion has a high fluoropolymer concentration as described above, it is excellent in handleability and can be easily processed into a fluoropolymer powder, a fluoropolymer molded body, and the like.

The aqueous fluoropolymer dispersion is a high-purity fluoropolymer with a low concentration of various surfactants, so that the heat-resistant properties of the fluoropolymer are not deteriorated due to the fluoroemulsion. It is possible to cover a fluoropolymer molded article having excellent physical properties such as property, chemical resistance, durability, weather resistance, surface characteristics, and mechanical characteristics.

The invention's effect

[0050] Since the fluorine-containing polymer aqueous dispersion production method of the present invention has the above-mentioned configuration, the fluorine-containing polymer mono-aqueous dispersion containing very little contaminants such as a fluorine-containing emulsifier easily and efficiently. Can be prepared.

BEST MODE FOR CARRYING OUT THE INVENTION

[0051] The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples and Comparative Examples. [0052] Measurements performed in each example and comparative example were performed by the following method.

(1) Concentration of fluoropolymer and specific surfactant

About 1 lg (Xg) of the sample is placed in an aluminum cup with a diameter of 5 cm, and heated residue (Yg) heated at 100 ° C for 1 hour, and the obtained heated residue (Yg) is further heated at 300 ° C for 1 hour. Heated residue (from Z, specific surfactant concentration (S) and fluoropolymer concentration (P) were determined by the following formula. S = [(Y—Z) / X] X 100 (%)

P = (Z / X) X 100 (%)

(2) Average primary particle size

Average particle size determined by measuring the transmittance of 55 Onm projection light with respect to the unit length of the aqueous dispersion with the fluorine-containing polymer concentration adjusted to 0.22% by mass and the directional direction diameter in the transmission electron micrograph. Based on the calibration curve with the diameter, it was determined from the transmittance.

(3) Fluorine-containing emulsifier concentration

After soxhlet extraction was performed by adding an equal amount of methanol to the aqueous dispersion, HPLC measurement was performed under the following conditions.

(Measurement condition)

Column; ODS—120 mm (4.6 x 250 mm, manufactured by Toso Co., Ltd.)

Developing solution: acetonitrile ZO. 6 mass% perchloric acid aqueous solution = 1Z1 (vol / vol%) Sample amount: 20 / z L

Flow rate; 1. OmlZ min

Detection wavelength: UV210nm

Column temperature; 40 ° C

In calculating the fluorine-containing emulsifier concentration, a calibration curve obtained by HPLC measurement of the known concentration of the fluorine-containing emulsifier with the above eluate and conditions was used.

[0053] Comparative Example 1

Tetrafluoroethylene [TFE] homopolymer aqueous dispersion prepared by adding perfluorooctanoic acid ammonium [PFOA] (TFE homopolymer concentration 34 mass%, average particle size 280 nm, pH 3, PFOA concentration (2900 ppm with respect to fat solids) is placed in a 50 ml centrifuge tube and centrifuged for 30 minutes under a gravitational acceleration of 2500 rpm (field factor = 419) And separated into a supernatant phase (aqueous phase) and a concentrated phase (fluoropolymer aqueous dispersion phase). When the supernatant was subjected to HPLC under the above measurement conditions, the PFOA concentration was 20 ppm. Assuming that all PFOA in the system is in the aqueous phase, the concentration of PFOA in the aqueous phase is 1494ppm (if the aqueous dispersion is 100g, the PTFE contained is 34g, and the rest is water, so 66g , PFOAi 34 X 2900ppm = 0.0986g.If this is all S

The calculation is 86Z66 = 1494ppm. ), PFOA transferred to the water phase is only 1% (20ppmZ 1494ppm), and the rest is adsorbed on the particle surface.

Therefore, by measuring the PFOA concentration in the supernatant generated by centrifugation, the efficiency of transferring PFOA to the aqueous phase (efficiency of removing PFOA from the fluoropolymer aqueous dispersion A) can be compared.

[0054] Example 1

Tetrafluoroethylene [TFE] homopolymer aqueous dispersion prepared by adding perfluorooctanoic acid ammonium [PFOA] (TFE homopolymer concentration 34 mass%, average particle size 280 nm, pH 3, Polyoxyethylene tridecyl ether TDS-50 (ethylene oxide [EO] number 5, average molecular weight 420, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) is 0.16 mmol ZgTFE homopolymer ratio to PFOA concentration 2900ppm of fat solid content) Added, mixed and dispersed uniformly.

The obtained TFE homopolymer aqueous dispersion A-1 was placed in a 50 ml centrifuge tube, centrifuged at a gravitational acceleration of 25 00 111 (field factor = 419) for 30 minutes, and the supernatant phase ( The aqueous phase and the concentrated phase were separated.

When the supernatant was subjected to HPLC under the above measurement conditions, the PFOA concentration was 994 ppm of the fluorine-containing polymer (resin solid content). In other words, 67% of PFOA has been transferred to the water phase.

[0055] Example 2

Aqueous dispersion of TFE homopolymer (TFE homopolymer concentration 34% by weight, average particle size 280ηm, pH3, PFOA concentration 22.8ppm of rosin solids) and sodium dodecyl sulfonate (average molecular weight 272, reagent) 0.0556 mmol ZgTFE homopolymer was added and mixed and dispersed uniformly. 50 ml of the obtained TFE homopolymer aqueous dispersion A-2 The mixture was placed in a centrifuge tube having a capacity and centrifuged in the same manner as in Example 1 to separate into a supernatant phase (aqueous phase) and a concentrated phase.

When the supernatant was subjected to HPLC under the above measurement conditions, the PFOA concentration was 550 ppm of the fluorine-containing polymer (resin solid content). In other words, 37% of PFOA has shifted to the water phase.

[0056] Example 3

To a TFE homopolymer aqueous dispersion (TFE homopolymer concentration 34% by mass, average particle size 280ηm, pH 3, PFOA concentration 2900ppm with respect to the solid content of rosin), sodium dioctylsulfosuccinate (average molecular weight 443) 056mmol ZgTFE homopolymer was added and mixed, and dispersed uniformly. The obtained aqueous TFE homopolymer dispersion A-3 was placed in a 50 ml centrifuge tube and centrifuged in the same manner as in Example 1 to separate the supernatant phase (aqueous phase) and the concentrated phase.

When the supernatant was subjected to HPLC under the above measurement conditions, the PFOA concentration was 690 ppm of the fluorine-containing polymer (solid resin). In other words, 46% of PFOA has shifted to the water phase.

[0057] Comparative Example 2

An aqueous dispersion of TFE homopolymer (TFE homopolymer concentration 34% by weight, average particle size 280ηm, pH 3, PFOA concentration 2900ppm with respect to the solid content of resin), polyoxyethylene octylphenol ether TritonX-100 (EO number 9) 5 and an average molecular weight of 624) were added so as to be a 0.056 mmol molZgTFE homopolymer, mixed and dispersed uniformly. The obtained TFE homopolymer aqueous dispersion was placed in a 50 ml centrifuge tube and subjected to centrifugal separation in the same manner as in Example 1 to separate into a supernatant phase (aqueous phase) and a concentrated phase.

When the supernatant was subjected to HPLC under the above measurement conditions, the PFOA concentration was 355 ppm of the fluorine-containing polymer (solid resin). In other words, 24% of PFOA has shifted to the water phase.

[0058] Comparative Example 3

TFE homopolymer aqueous dispersion (TFE homopolymer concentration 34% by weight, average particle size 280ηm, pH3, PFOA concentration 2900ppm with respect to solids of resin) Tilphenol ether TritonX-100 (EO number 9.5, average molecular weight 624) was added to be a 0.16 mm olZgTFE homopolymer, mixed and dispersed uniformly. The obtained TFE homopolymer aqueous dispersion was placed in a 50 ml centrifuge tube and centrifuged in the same manner as in Example 1 to separate the supernatant phase (aqueous phase) and the concentrated phase.

When the supernatant was subjected to HPLC under the above measurement conditions, the PFOA concentration was 680 ppm of the fluorine-containing polymer (solid resin). In other words, 46% of PFOA has shifted to the water phase.

[0059] Comparative Example 4

Aqueous dispersion of TFE homopolymer (TFE homopolymer concentration 34% by mass, average particle size 280ηm, pH 3, PFOA concentration 2900ppm with respect to the solid content of rosin), sodium octyl sulfonate (average molecular weight 216), 0.056mmolZgTFE The mixture was added to form a homopolymer, mixed and dispersed uniformly. The obtained TFE homopolymer aqueous dispersion was placed in a 50 ml centrifuge tube, centrifuged as in Example 1, and separated into a supernatant phase (aqueous phase) and a concentrated phase.

When the supernatant was subjected to HPLC under the above measurement conditions, the PFOA concentration was 26 ppm of the fluorine-containing polymer (solid resin). In other words, 1.7% of PFOA has shifted to the water phase.

Industrial applicability

[0060] The method for producing an aqueous fluoropolymer dispersion of the present invention makes it possible to prepare an aqueous fluoropolymer dispersion with very few contaminants such as a fluorine-containing emulsifier easily and efficiently.

The aqueous fluoropolymer dispersion is excellent as a material for a fluoropolymer molded article having excellent physical properties such as heat resistance, chemical resistance, durability, weather resistance, surface characteristics, and mechanical properties.

Claims

The scope of the claims

[1] A fluorine-containing polymer aqueous dispersion production method comprising producing a fluorine-containing polymer aqueous dispersion through a concentration step,

The concentration step is a step comprising concentrating the fluoropolymer aqueous dispersion A in the presence of a specific nonionic surfactant and Z or a specific anionic surfactant, and the specific nonionic surfactant is hydrophilic. A non-ionic surfactant having a molecular weight of 00 or less and a hydrophobic group having 10 to 20 carbon atoms,

The specific anion surfactant is a fluorine-free anion surfactant having a hydrocarbon group as a hydrophobic group and a total carbon number of 10 to 20 carbon atoms. Fluorine-containing polymer aqueous dispersion production method.

[2] The method for producing an aqueous fluoropolymer dispersion according to claim 1, wherein the hydrophilic group of the specific non-ionic surfactant has 7 or less repeating units of alkylene oxide.

[3] The method for producing an aqueous fluoropolymer dispersion according to claim 1 or 2, wherein the specific non-one surfactant and Z or specific key-on surfactant are added after polymerization of the fluoropolymer.

[4] The fluorine-containing polymer aqueous dispersion A contains a fluorine-containing emulsifier.

The method for producing a fluoropolymer aqueous dispersion according to 1, 2 or 3.

5. The method for producing an aqueous fluoropolymer dispersion according to claim 4, wherein the fluorine-containing emulsifier comprises a fluorine-containing compound having an average molecular weight of 1000 or less.

6. The method for producing an aqueous fluoropolymer dispersion according to claim 4 or 5, wherein the fluorine-containing emulsifier comprises a fluorine-containing compound having 5 to 12 carbon atoms.

[7] The fluorine-containing emulsifier is a perfluorocarboxylic acid or a salt thereof.

5. The method for producing a fluoropolymer aqueous dispersion according to 5 or 6.

[8] The fluoropolymer particles constituting the fluoropolymer aqueous dispersion A have an average particle size of 5

The method for producing an aqueous fluoropolymer dispersion according to claim 1, 2, 3, 4, 5, 6, or 7, wherein the dispersion is from 0 to 500 nm.

[9] The method for producing an aqueous fluoropolymer dispersion according to claim 1, 2, 3, 4, 5, 6, 7 or 8, wherein the fluoropolymer is polytetrafluoroethylene.