RU2803928C2 - Method for producing modified polytetrafluoroethylene, method for producing modified polytetrafluoroethylene powder and method for producing stretched porous material - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to methods for producing modified polytetrafluoroethylene. A method for producing modified polytetrafluoroethylene is proposed, which includes copolymerization of tetrafluoroethylene and a monomer having a polar group in dispersion 1 containing a polymer containing links based on a non-fluorinated monomer and an aqueous medium, under such conditions that the amount of used monomer having a polar group is at most 0.150 wt.% with respect to the total amount of tetrafluoroethylene supplied to the polymerization system, wherein the monomer having a polar group is the monomer represented by the formula (3), where the substituents R³¹ and R³² each independently represent a hydrogen atom or a fluorine atom, the substituent R³³ means a hydrogen atom, a fluorine atom, or an alkyl group which may be substituted by a fluorine atom, L³ is a single bond or a divalent linking group, and R³⁴ is a polar -SO₃ M or -COOM group, where M is a hydrogen atom, NH₄ or an alkali metal atom; and where the non-fluorinated monomer is a monomer represented by formula (1) in which R¹¹ is a hydrogen atom or an alkyl group, L¹ is a single bond, -CO-O-*, -O-CO-* or -O -, "*" denotes a bonding position with R¹², and the R¹² substituent denotes a hydrogen atom, an alkyl group, an alkenyl group or a nitrile group, with the proviso that when L¹ is a single bond, the R¹² substituent is a nitrile group. An embodiment of the method for producing modified polytetrafluoroethylene, a method for producing modified polytetrafluoroethylene powder, the corresponding modified polytetrafluoroethylene powder and a method for producing a stretched porous material based on modified polytetrafluoroethylene powder are also proposed.

EFFECT: making modified polytetrafluoroethylene, in which the formation of a fluorinated oligomer containing hydrophilic functional groups as a by-product is negligible, which increases the environmental friendliness of the claimed method and improves the performance of the resulting product.

11 cl, 1 tbl, 10 ex

Description

Field of technology

[0001]

The present invention relates to a method for producing modified polytetrafluoroethylene, a method for producing modified polytetrafluoroethylene powder and a method for producing stretched porous material.

State of the art

[0002]

Polytetrafluoroethylene is used in various fields due to its excellent properties.

Until now, the production of polytetrafluoroethylene has used a fluorinated surfactant such as perfluorooctyl sulfonic acid. However, from an environmental point of view, it is advisable to refrain from using a fluorinated surfactant.

Therefore, as a new method for producing polytetrafluoroethylene, a method using a hydrocarbon-containing surfactant such as sodium dodecyl sulfate in polymerizing polytetrafluoroethylene has been proposed (Patent Document 1).

Prior Art Document

Patent document

[0003]

Patent Document 1: JP-A-2016-537499.

Description of the invention

Technical challenge

[0004]

On the other hand, when a hydrocarbon-containing surfactant such as sodium dodecyl sulfate is used, a chain transfer reaction occurs with respect to the hydrocarbon-containing surfactant during the polymerization of tetrafluoroethylene. As a result, the hydrocarbon surfactant method confirmed the presence of a fluorinated oligomer in the product containing hydrophilic functional groups having different chain length distributions, which was never confirmed by the conventional fluorinated surfactant method. Such a fluorinated oligomer is a by-product formed by a hydrocarbon-containing surfactant serving as the starting point for the chain transfer described above. The presence of such a by-product appears to degrade the performance of the polytetrafluoroethylene and is also undesirable from an environmental point of view.

[0005]

The object of the present invention is to develop a process for producing modified polytetrafluoroethylene in which the formation of a fluorinated oligomer containing hydrophilic functional groups as a by-product is negligible.

Another object of the present invention is to provide a method for producing modified polytetrafluoroethylene powder and a method for producing stretched porous material.

The solution of the problem

[0006]

As a result of intensive research, the applicants of the present invention have found that the achievement of the above-described objects is possible with the following designs.

[0007]

(1) A method for producing modified polytetrafluoroethylene, which includes copolymerizing tetrafluoroethylene and a monomer having a polar group,

in dispersion 1 containing a polymer containing units based on a non-fluorinated monomer and an aqueous medium,

under such conditions that the amount of monomer having a polar group used is at most 0.150% by weight. relative to the total amount of tetrafluoroethylene supplied to the polymerization system.

(2) The method for producing modified polytetrafluoroethylene according to paragraph (1), in which the polar group is a group represented by formula (A) described below or a group represented by formula (B) described below.

(3) The method for producing modified polytetrafluoroethylene according to item (2), in which the monomer having a polar group is the monomer represented by formula (3) described below.

(4) The method for producing modified polytetrafluoroethylene according to any of items (1) to (3), in which a non-fluorinated monomer is polymerized in an aqueous medium and then in a dispersion 1 containing a polymer containing units based on a non-fluorinated monomer and an aqueous medium, copolymerization of tetrafluoroethylene and a monomer having a polar group is carried out.

(5) A method for producing modified polytetrafluoroethylene according to any of items (1) to (4), wherein the non-fluorinated monomer is a monomer represented by formula (1) described below.

(6) The method for producing modified polytetrafluoroethylene according to any of items (1) to (5), wherein a polymerization initiator is used during the copolymerization of tetrafluoroethylene and a monomer having a polar group, and the amount of the polymerization initiator used is at least at least 0.10% wt. relative to the total amount of tetrafluoroethylene supplied to the polymerization system.

(7) The method for producing modified polytetrafluoroethylene according to any of items (1) to (6), in which the amount of monomer having a polar group used is at most 0.150 mol%. relative to the total amount of tetrafluoroethylene supplied to the polymerization system.

(8) A method for producing modified polytetrafluoroethylene, which includes copolymerizing tetrafluoroethylene and a monomer having a polar group,

in dispersion 2 obtained by mixing at least one component selected from the group consisting of a polyalkylene oxide compound and a hydrocarbon-containing surfactant with an oxidizing agent in an aqueous medium,

under such conditions that the amount of monomer having a polar group used is at most 0.150% by weight. relative to the total amount of tetrafluoroethylene supplied to the polymerization system to obtain modified polytetrafluoroethylene.

(9) The method for producing modified polytetrafluoroethylene according to item (8), in which copolymerization of tetrafluoroethylene and a monomer having a polar group is carried out in dispersion 2, and

the polyalkylene oxide compound is the compound represented by formula (2) described below.

(10) A method for producing modified polytetrafluoroethylene according to item (8) or (9), in which a polymerization initiator is used during copolymerization of tetrafluoroethylene and a monomer having a polar group, and

the amount of polymerization initiator used is at least 0.10% by weight. relative to the total amount of tetrafluoroethylene supplied to the polymerization system.

(11) The method for producing modified polytetrafluoroethylene according to any of items (8) to (10), in which the amount of monomer having a polar group used is at most 0.150 mol%. relative to the total amount of tetrafluoroethylene supplied to the polymerization system.

(12) A method for producing modified polytetrafluoroethylene powder, which includes producing an aqueous dispersion in which the modified polytetrafluoroethylene obtained by the method of any one of items (1) to (11) is dispersed in the form of particles, and coagulating the modified polytetrafluoroethylene particles to obtain modified polytetrafluoroethylene powder.

(13) Modified polytetrafluoroethylene powder in which the monomer-based units having a polar group are from 0.005 to 0.150 mol%. relative to tetrafluoroethylene-based units,

whose standard specific gravity is at most 2.230, and

which is substantially free of a C _6-34 fluorinated oligomer containing hydrophilic functionality and a fluorinated surfactant.

(14) A method for producing a stretched porous material, which includes producing modified polytetrafluoroethylene powder by the method of item (12), extruding a paste of the modified polytetrafluoroethylene powder to obtain an extruded rod, and stretching the extruded rod to obtain a stretched porous material.

Positive effects of the invention

[0008]

In accordance with the present invention, it is possible to develop a process for producing modified polytetrafluoroethylene in which the formation of a fluorinated oligomer containing hydrophilic functional groups as a by-product is negligible.

In addition, in accordance with the present invention, it is possible to develop a method for producing modified polytetrafluoroethylene powder and a method for producing stretched porous material.

Description of Embodiments of the Invention

[0009]

The terms in the present invention have the following meanings.

The term "unit" is a general term for a group of atoms originating from a single monomer molecule, which is directly formed by polymerization of the monomer.

[0010]

A characteristic feature of the method for producing modified polytetrafluoroethylene (hereinafter also called "modified PTFE (PTFE)") of the present invention may be that the polymerization of tetrafluoroethylene (hereinafter also called "TFE") is carried out together with a monomer having a polar group (hereinafter also also called "TFE"). called "specific monomer"), in a dispersion 1 containing a polymer containing units based on a non-fluorinated monomer (hereinafter also called "specific polymer"), and an aqueous medium, or in a dispersion 2 obtained by mixing at least one component, selected from the group consisting of a polyalkylene oxide compound and a hydrocarbon-containing surfactant, and an oxidizing agent in an aqueous medium.

Dispersion 1 and dispersion 2 are able to create a hydrophobic environment where the polymerization of TFE can proceed satisfactorily, and in addition, the specific monomer plays the role of stably promoting the polymerization of TFE while suppressing the occurrence of chain transfer. As a result, it is possible to produce modified PTFE exhibiting good molecular weight while suppressing the formation of fluorinated oligomer containing hydrophilic functional groups as a by-product. Moreover, according to the method of the present invention, modified PTFE can be produced without using a hydrocarbon-containing surfactant during the polymerization of TFE.

In addition, the fluorinated oligomer containing hydrophilic functional groups preferably includes an oligomer having a CF ₂ group linked to have from about 6 to 34 carbon atoms.

Such a fluorinated oligomer having hydrophilic functional groups and a fluorinated surfactant are not substantially included in the modified polytetrafluoroethylene of the present invention. The expression “substantially not included” means a value less than 3 ppb, which is the analytical detection limit.

[0011]

It is believed that the specific polymer replaces at least part of the action and effect in the case of using a fluorinated surfactant, for example, for the dispersibility of the resulting PTFE.

[0012]

The amount of the specific polymer in the modified PTFE in the present invention is very small, as described later, and therefore, the amount of the specific polymer in the specific polymer-containing aqueous medium in which the TFE is polymerized is also very small. Thus, the specific polymer-containing aqueous medium in which the TFE is polymerized is preferably an aqueous medium obtained by polymerizing a non-fluorinated monomer in an aqueous medium. In such a case, the specific polymer in the aqueous medium is said to be dispersed in the aqueous medium in the form of solid particles, as described later.

The aqueous medium containing the specific polymer used for the polymerization of TFE may be an aqueous medium obtained by polymerizing a non-fluorinated monomer in an aqueous medium, or may be an aqueous medium obtained by further diluting an aqueous medium obtained by polymerizing a non-fluorinated monomer in an aqueous medium, aquatic environment.

In the case where an aqueous medium obtained by polymerizing a non-fluorinated monomer in an aqueous medium is used as it is, it is preferable that the non-fluorinated monomer is polymerized in a polymerization system (in a polymerization vessel, etc.) for polymerizing TFE, and then polymerizing TFE is carried out in the same polymerization vessel. In the case where an aqueous medium obtained by polymerizing a non-fluorinated monomer in an aqueous medium is to be used in its dilution, the TFE polymerization can be carried out in the same polymerization system or the TFE polymerization can be carried out in a different polymerization system.

[0013]

First embodiment

As a first embodiment of the method for producing modified PTFE, an embodiment having the following two steps may be mentioned.

Step A1: The step of polymerizing the non-fluorinated monomer in an aqueous medium to obtain a dispersion 1 containing a specific polymer and an aqueous medium.

Step A2: the step of carrying out copolymerization of TFE and a specific monomer in dispersion 1 under such conditions that the amount of specific monomer used is at most 0.150% by weight. relative to the total amount of TFE supplied to the polymerization system to obtain modified PTFE.

The aqueous medium containing the specific polymer obtained in step A1 described above can be diluted with the aqueous medium and used in step A2 as the aqueous medium containing the specific polymer. In addition, in step A2, before the copolymerization of TFE and the specific monomer begins, additives that are described later can be added to dispersion 1 to effect copolymerization. In some cases, additives used in the copolymerization may be added to the aqueous medium used in step A1 to form an aqueous medium containing the additives and the specific polymer in step A1, and the resulting aqueous medium can be used as the aqueous medium for step A2.

Hereinafter, the present invention will be described in detail, taking the above-mentioned preferred embodiment as an example.

[0014]

Stage A1

Below, the materials used in Step A1 are first described in detail, and then the procedure for carrying out Step A1 is described in detail.

[0015]

Non-fluorinated monomer

A non-fluorinated monomer is a monomer that does not contain fluorine atoms.

The non-fluorinated monomer generally has a polymerizable group, and the number of polymerizable groups is preferably 1 to 3, more preferably 1.

The polymerizable group is preferably an ethylenically unsaturated group. More specifically, an acryloyl group, a methacryloyl group, a vinyl ester group, a vinyl ester group, a vinyl group or an allylic group may be mentioned, and the acryloyl group, methacryloyl group, vinyl ester group or vinyl ester group is preferred.

[0016]

The non-fluorinated monomer is preferably a monomer represented by formula (1).

Formula (1): CH ₂ =CR ¹¹ -L ¹ -R ¹²

Substituent R ¹¹ means a hydrogen atom or an alkyl group. The number of carbon atoms in the alkyl group is preferably 1 to 3, more preferably 1.

Group L ¹ means a single bond, -CO-O-*, -O-CO-* or -O-. "*" denotes the binding position with R ¹² . For example, when L ¹ is -CO-O-*, formula (1) is CH ₂ =CR ¹¹ -CO-OR ¹² .

Substituent R ¹² means a hydrogen atom, an alkyl group, an alkenyl group or a nitrile group. However, when L ¹ represents a single bond, R ¹² represents a nitrile group.

The number of carbon atoms in the alkyl group or alkenyl group is preferably 1 to 10, more preferably 1 to 6, also preferably 1 to 4.

The alkyl group may be linear or cyclic. When an alkyl group is cyclic, it corresponds to a cycloalkyl group.

The alkenyl group may be linear or cyclic.

[0017]

The monomer represented by formula (1) is preferably a monomer selected from the group consisting of a monomer represented by formula (1-1), a monomer represented by formula (1-2), a monomer represented by formula (1-3), and a monomer , represented by formula (1-4).

Formula (1-1): CH ₂ =CR ¹¹ -CO-OR ¹³

Formula (1-2): CH ₂ =CR ¹¹ -O-CO-R ¹⁴

Formula (1-3): CH ₂ =CR ¹¹ -OR ¹⁵

Formula (1-4): CH ₂ =CR ¹¹ -R ¹⁶

Substituent R ¹¹ has the meanings described above.

Substituent R ¹³ represents a hydrogen atom, an alkyl group or an alkenyl group, and is preferably a C _1-6 alkyl group or a C _1-6 alkenyl group.

Substituent R ¹⁴ represents an alkyl group, and preferably represents a C _1-3 alkyl group, more preferably a methyl group.

Substituent R ¹⁵ represents an alkyl group, and is preferably a linear alkyl group or a cyclic alkyl group.

Substituent R ¹⁶ represents a nitrile group.

[0018]

The non-fluorinated monomer, for example, may be methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, vinyl methacrylate, vinyl acetate, acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, ethyl vinyl ether or cyclohexyl vinyl ether.

As the non-fluorinated monomer, one type may be used alone, or two or more types may be used in combination.

As the non-fluorinated monomer, the monomer represented by formula (1-1) above and the monomer represented by formula (1-2) above are more preferable, and the monomer represented by formula (1-1) above is especially preferred, wherein R ¹³ represents an alkyl group . The monomer represented by formula (1-1) and the monomer represented by formula (1-2) have an ester group or a carboxyl group that is a water affinity group, whereby such a monomer or a polymer thereof has an affinity for water. Therefore, such a monomer or a polymer thereof is believed to be stably dispersed in an aqueous medium without requiring a surfactant, especially at a low concentration.

[0019]

Specific polymer

A specific polymer is a polymer consisting of units based on a non-fluorinated monomer.

The polymer typically contains only non-fluorinated monomer units, but may contain fluorinated monomer units within a range that does not interfere with the effects of the present invention. A fluorinated monomer is a monomer having a fluorine atom, and, for example, TFE may be mentioned.

In the case where a dispersion 1 containing a specific polymer and an aqueous medium is obtained in step A1, and then the TFE polymerization in step A2 is carried out continuously in the dispersion 1 containing a specific polymer and an aqueous medium in the polymerization system used in step A1, a case may exist wherein the specific polymer in polymerization or the specific polymer-containing aqueous medium containing unreacted non-fluorinated monomer may be used in step A2. Moreover, there may be a case where the atmosphere in the polymerization system of step A1 can be configured such that, taking into account step A2, it is a TFE-containing atmosphere. In such a case, it is believed that part of the specific polymer in step A2 may be a polymer containing TFE units.

From another point of view, the modified PTFE particles obtained in step A2 are not limited to particles consisting of a physical mixture of a specific polymer and PTFE, but are considered to be particles containing a TFE copolymer including non-fluorinated monomer-based units.

The content of non-fluorinated monomer units in the polymer is preferably at least 90% by weight, more preferably at least 95% by weight. relative to all units in the polymer. The upper limit corresponds to 100% of the mass.

[0020]

Water environment

The aqueous medium, for example, may be water or a mixture of water and a water-soluble organic solvent.

The water-soluble organic solvent, for example, may be tert-butanol, propylene glycol or dipropylene glycol. In the case of using a mixture of water and a water-soluble organic solvent, the concentration of the water-soluble organic solvent is preferably at most 10% by weight.

Preferably, the aqueous medium is only water.

[0021]

Polymerization initiator

In step A1, a polymerization initiator may be used. That is, a polymerization initiator can be used during the polymerization of the non-fluorinated monomer.

As the polymerization initiator, a water-soluble radical initiator or a water-soluble redox catalyst is preferred.

As the water-soluble radical initiator, a persulfate such as ammonium persulfate or potassium persulfate, a water-soluble organic peroxide such as disuccinic acid peroxide, diglutaric acid peroxide or tert-butyl hydroperoxide is preferred.

As a water-soluble redox catalyst, a combination of an oxidizing agent such as bromic acid or a salt thereof, perchloric acid or a salt thereof, persulfuric acid or a salt thereof, permanganic acid or a salt thereof, or hydrogen peroxide, and a reducing agent such as sulfur dioxide is preferred. acid or its salt, hydrosulfite or its salt, thiosulfuric acid or its salt, or organic acid. Of these, more preferable are a combination of bromic acid or a salt thereof and sulfurous acid or a salt thereof (eg ammonium sulfite), and a combination of manganese acid or a salt thereof (eg potassium permanganate) and oxalic acid.

As the polymerization initiator, ammonium persulfate alone or a mixed system of persulfate and disuccinic acid peroxide is preferred, and ammonium persulfate alone or a mixed system of ammonium persulfate and disuccinic acid peroxide is more preferable.

As the polymerization initiator, one type may be used alone, or two or more types may be used in combination.

As a method of loading the polymerization initiator, the entire amount may be loaded into the reaction system before starting the polymerization reaction, or it may be added to the reaction system continuously or batchwise.

[0022]

Methodology for stage A1

In step A1, the polymerization of the non-fluorinated monomer is carried out in an aqueous medium. More specifically, it is preferable that the non-fluorinated monomer and an aqueous medium are mixed, and the polymerization of the non-fluorinated monomer is carried out in the resulting mixed liquid.

[0023]

The amount of non-fluorinated monomer used is preferably 0.001 to 0.050 wt%, more preferably 0.001 to 0.020 wt%, also preferably 0.002 to 0.020 wt%, particularly preferably 0.003 to 0.016 wt%. relative to the total amount of TFE used in step A2 described below.

Here, as a method of loading the non-fluorinated monomer, it is preferable to add an initial charge so that the entire amount is loaded into the reaction system before initiating the polymerization reaction.

[0024]

The amount of non-fluorinated monomer used is preferably 0.0005 to 0.050 mol%, more preferably 0.0005 to 0.020 mol%, also preferably 0.001 to 0.020 mol%, particularly preferably 0.002 to 0.015 mol%. relative to the total amount of TFE used in step A2, which is described below.

Here, as a method of loading the non-fluorinated monomer, it is preferable to add an initial charge so that the entire amount is loaded into the reaction system before initiating the polymerization reaction.

[0025]

The content of the non-fluorinated monomer in the dispersion obtained by mixing the non-fluorinated monomer and the aqueous medium is preferably 0.0005 to 0.0080 wt%, more preferably 0.0005 to 0.0030 wt%. relative to the total mass of the dispersion.

Since the non-fluorinated monomer is typically polymerized in its entirety to form the specific polymer, the concentration of the specific polymer in the resulting aqueous medium containing the specific polymer falls within the numerical range mentioned above.

The concentration of the above-described non-fluorinated monomer and the concentration of the specific polymer are concentrations when the resulting specific polymer-containing aqueous medium is used in step A2 without dilution with the aqueous medium. In the case where the obtained specific polymer-containing aqueous medium is diluted with the aqueous medium to obtain the above-mentioned concentration of the specific polymer, and the diluted solution is used in step 2, in step A1, a specific polymer with a high concentration corresponding to the dilution degree is obtained. The dilution rate is not particularly limited, but is preferably 10-fold at most.

[0026]

The amount of polymerization initiator used is preferably from 0.2 to 1000% by weight, more preferably from 0.2 to 500% by weight. relative to the total amount of non-fluorinated monomer.

[0027]

The amount of polymerization initiator used is preferably from 0.1 to 1000 mol%, more preferably from 0.1 to 300 mol%. relative to the total amount of non-fluorinated monomer.

[0028]

The polymerization temperature of the non-fluorinated monomer is preferably in the range from 10 to 95°C, more preferably from 50 to 90°C. The polymerization time is preferably from 5 to 400 minutes, more preferably from 5 to 300 minutes, also preferably from 5 to 200 minutes.

The pressure conditions during polymerization are preferably reduced pressure conditions or normal pressure conditions. In particular, a pressure of 0 to 2.0 MPa is preferable, more preferably 0 to 1.0 MPa, and also preferably 0 to 0.5 MPa.

In addition, polymerization can be carried out by creating an atmosphere such as a TFE atmosphere during polymerization. In such a case, usually the polymerization of the non-fluorinated monomer in an aqueous medium predominantly proceeds in the direction of TFE polymerization.

[0029]

The specific polymer can be obtained through the above-described step A1.

The specific polymer is said to be dispersed in the aqueous medium in particulate form. It is believed that when copolymerizing TFE and a specific monomer in step A2, described below, although the specific polymer is not an emulsifier, due to the balance of surface tension at the interface relative to both the aqueous medium and the modified PTFE particles, the specific polymer is present at the interface of both phases, and therefore contributes to the stabilization of the dispersion of modified PTFE particles in an aqueous environment.

The particle size for the specific polymer particles is preferably from 0.1 to 100 nm, more preferably from 0.1 to 50 nm.

[0030]

Stage A2

Step A2 is a step of carrying out copolymerization of TFE and a specific monomer in dispersion 1 under such conditions that the amount of specific monomer used relative to the total amount of TFE is at most 0.150 wt%, to obtain modified PTFE. It is believed that by performing this step, a dispersion of modified PTFE particles stabilized in an aqueous environment by a specific polymer will have surface activity enhanced by copolymerization with the specific monomer. As a result, it is believed that the growth of the molecular weight of the modified PTFE is stimulated, and this will contribute to the improvement of physical tensile properties, etc.

Below, the materials used in Step A2 are first described in detail, and then the procedure for carrying out Step A2 is described in detail.

[0031]

An aqueous medium containing a specific polymer

In step A2, the aqueous medium containing the specific polymer obtained in step A1 or the aqueous medium containing the specific polymer obtained by diluting the aqueous medium containing the specific polymer obtained in step A1 as the aqueous medium containing the specific polymer is used as the aqueous medium containing the specific polymer.

The amount of the specific polymer in the specific polymer-containing aqueous medium used for the polymerization of TFE is preferably from 0.001 to 0.050 wt%, more preferably from 0.001 to 0.020 wt%, also preferably from 0.002 to 0.020 wt%, further preferably from 0.003 up to 0.016% wt., especially preferably from 0.003 to 0.010% wt. relative to the total amount of TFE supplied to the polymerization system.

The aqueous medium, for example, may be water or a mixture of water and a water-soluble organic solvent. As the water-soluble organic solvent, the solvents exemplified in Step A1 may be mentioned.

In the case where the specific polymer-containing aqueous medium obtained in step A1 is used as it is without dilution, the aqueous medium in step A2 is the same as the aqueous medium in step A1. In the case where the specific polymer-containing aqueous medium obtained in step A1 is diluted and used, the same applies in the case where the diluted aqueous medium is the same aqueous medium as in step A1.

[0032]

Specific monomer

A specific monomer is used when carrying out copolymerization with TFE. Since the polar group in a specific monomer interacts with the aqueous medium, it is believed that it is interposed between the TFE and the aqueous medium at the time of polymerization of the TFE and exhibits a function similar to that of a surfactant. As a result, the polymerization of TFE proceeds well, and the occurrence of chain transfer will be suppressed.

[0033]

The polar group present in a specific monomer may be, for example, a sulfonic acid group, a sulfonate group, a carboxylic acid group, a carboxylate group, a phosphonic acid group, or a phosphonate group. Of these, the group represented by formula (A) or the group represented by formula (B) is preferable, and the group represented by formula (A) is more preferable so that the formation of fluorinated oligomer will be further suppressed.

Formula (A): -SO ₃ M

Formula (B): -COOM

In formula (A) and formula (B), M represents a hydrogen atom, NH ₄ or an alkali metal atom. The alkali metal atom, for example, may be a lithium atom, a sodium atom or a potassium atom.

[0034]

The specific monomer generally has a polymerizable group, and the number of polymerizable groups is preferably 1 to 3, more preferably 1.

The polymerizable group is preferably an ethylenically unsaturated group. More specifically, an acryloyl group, a methacryloyl group, a vinyl ester group, a vinyl ester group, a vinyl group or an allylic group may be mentioned, and the acryloyl group, methacryloyl group, vinyl ester group or vinyl ester group is preferred.

[0035]

As the specific monomer, the monomer represented by formula (3) is preferred since the formation of fluorinated oligomer will be further suppressed.

Formula (3): CR ³¹ R ³² =CR ³³ -L ³ -R ³⁴

In formula (3), the substituents R ³¹ and R ³² each independently represent a hydrogen atom or a fluorine atom.

[0036]

Substituent R ³³ represents a hydrogen atom, a fluorine atom or an alkyl group, which may be substituted by a fluorine atom. Among them, hydrogen atom or fluorine atom is preferred, as a result of which the copolymerization ability with TFE will be better.

Here, the expression “an alkyl group that may be substituted by a fluorine atom” means an alkyl group that may have at least one hydrogen atom in the alkyl group substituted by a fluorine atom.

The number of hydrogen atoms in the alkyl group that can be replaced by a fluorine atom is preferably from 1 to 3, more preferably 1.

[0037]

The L ³ group means a single bond or a divalent linking group. Of these, a simple bond is preferred, resulting in better copolymerization ability with TFE.

The divalent linking group may, for example, be a divalent hydrocarbon group (which may be a divalent saturated hydrocarbon group, a divalent aromatic hydrocarbon group, an alkenyl group or an alkynyl group; the divalent saturated hydrocarbon group may be linear, branched or cyclic, and for example, an alkylene group may be mentioned group; the number of carbon atoms is preferably from 1 to 20; and the divalent aromatic hydrocarbon group preferably has from 5 to 20 carbon atoms, for example, a phenylene group may be mentioned; in addition, it may be a C _2-20 alkenylene group or a C _{2 -20} -alkynylene group), divalent heterocyclic group, -O-, -S-, -SO ₂ -, -C(O)-, -Si(R ^a ) ₂ -, -N(R ^b )- groups and the , in which two or more of them are combined. In this case, the substituent R ^a means an alkyl group (preferably having from 1 to 10 carbon atoms) or a phenyl group. The substituent R ^b represents a hydrogen atom or an alkyl group (preferably having from 1 to 10 carbon atoms).

The above group in which two or more of these groups are combined, for example, may be -OC(O)-, -C(O)N(R ^b )-, (alkylene group)-O-alkylene group, (alkylene group) group. -OC(O)-alkylene group or (alkylene group)-Si(R ^a ) ₂ -phenylene group-Si(R ^a ) ₂ .

In addition, the divalent hydrocarbon group described above may have a substituent. The substituent may be, for example, a halogen atom (for example, a fluorine atom or a chlorine atom). That is, the hydrogen atom in the above-described divalent hydrocarbon group may be replaced by a halogen atom.

[0038]

Substituent R ³⁴ means a group represented by formula (A) above or a group represented by formula (B) above.

[0039]

As the monomer represented by formula (3), preferable is at least one monomer selected from the group consisting of a monomer represented by formula (3-1), a monomer represented by formula (3-2), a monomer represented by formula ( 3-3), a monomer represented by formula (3-4), a monomer represented by formula (3-5), and a monomer represented by formula (3-6), and the monomer represented by formula (3-1) is more preferable.

Formula (3-1): CR ³¹ R ³² =CR ³³ -R ³⁴

Formula (3-2): CR ³¹ R ³² =CR ³³ -(CF ₂ ) _m1 -R ³⁴

Formula (3-3): CR ³¹ R ³² =CR ³³ -(CF ₂ C(CF ₃ )F) _m2 -R ³⁴

Formula (3-4): CR ³¹ R ³² =CR ³³ -O-(CFR ³⁵ ) _m3 -R ³⁴

Formula (3-5): CR ³¹ R ³² =CR ³³ -O-(CF ₂ CFR ³⁵ O) _m4 -CF ₂ CF ₂ -R ³⁴

Formula (3-6): CR ³¹ R ³² =CR ³³ -CF ₂ -O-(CF(CF ₃ )CF ₂ O) _m5 -CF(CF ₃ )-R ³⁴

[0040]

In formulas (3-1)-(3-6), the definitions of substituents R ³¹ -R ³⁴ have the meanings described above.

In formula (3-2), m1 means an integer from 1 to 10.

In formula (3-3), m2 means an integer from 1 to 5.

In formula (3-4), m3 is an integer from 1 to 10. Substituent R ³⁵ represents a fluorine atom or CF ₃ .

In formula (3-5), m4 means an integer from 1 to 10. The definition of the substituent R ³⁵ is as described above.

In formula (3-6), m5 means 0 or an integer from 1 to 10.

[0041]

A specific example of a specific monomer may be ammonium vinyl sulfonate.

As the specific monomer, one type alone may be used, or two or more types may be used in combination.

[0042]

Polymerization initiator

In step A2, a polymerization initiator may be used. That is, a polymerization initiator can be used when carrying out the polymerization of TFE.

As the polymerization initiator used, the polymerization initiator described in Step A1 may be mentioned.

As the polymerization initiator, a mixed system of persulfate and disuccinic acid peroxide is preferred, and a mixed system of ammonium persulfate and disuccinic acid peroxide is more preferable.

The amount of polymerization initiator used is preferably at least 0.10 wt%, more preferably 0.10 to 1.5 wt%, also preferably 0.20 to 1.0 wt%. relative to the total amount of TFE supplied to the polymerization system.

[0043]

Stabilizing additive

At stage A2 a stabilizing additive can be used.

As the stabilizing additive, paraffin wax, fluorinated solvent or silicone oil is preferred, and paraffin wax is more preferred. Paraffin wax can be liquid, semi-solid, or solid at room temperature. Of these, a saturated hydrocarbon having 12 or more carbon atoms is preferred. The melting point of paraffin wax is preferably 40 to 65°C, more preferably 50 to 65°C.

One type alone can be used as a stabilizing agent, or two or more types can be used in combination.

[0044]

Other

In addition, monomers other than TFE and a specific monomer may be used in step A2 within a range not to interfere with the effects of the present invention, but the total amount of TFE used is preferably at least 99.5% by weight, more preferably at least 99.8% of the mass. relative to the total amount of monomers used in step A2, from the viewpoint that various properties of the modified PTFE will be more superior.

[0045]

Methodology for stage A2

TFE and the specific monomer are loaded into the reaction system (ie, the polymerization reaction vessel) in the usual manner. For example, TFE is continuously or periodically charged into the reaction system (polymer 1) so that the polymerization pressure becomes a predetermined pressure. In addition, for example, a specific monomer is dissolved in an aqueous medium, and the resulting solution is continuously or periodically charged into the reaction system (polymer 1).

In the case where a polymerization initiator is to be used, the polymerization initiator may be added to the reaction system all at once or may be added in portions.

[0046]

The amount of specific monomer used relative to the total amount of TFE is at most 0.150% by weight. That is, the loaded amount of the specific monomer relative to the total loaded amount of TFE is at most 0.150% by weight.

From the point of view of the stability of the emulsion during polymerization, the amount of specific monomer used relative to the total amount of TFE is preferably at most 0.100% by weight, more preferably at most 0.090% by weight. From the point of view of improving the molecular weight, the amount of specific monomer used relative to the total amount of TFE is preferably at least 0.020% by weight, more preferably at least 0.030% by weight.

Moreover, in the case where two or more specific monomers are to be used, the total number of specific monomers used may be within the ranges given above.

[0047]

The amount of specific monomer used relative to the total amount of TFE is preferably at most 0.150 mol%. That is, the loaded amount of the specific monomer relative to the total loaded amount of TFE is preferably at most 0.150 mol%.

From the point of view of the stability of the emulsion during polymerization, the amount of specific monomer used relative to the total amount of TFE is preferably at most 0.100 mol%, more preferably at most 0.090 mol%. From the point of view of improving the molecular weight, the amount of specific monomer used relative to the total amount of TFE is preferably at least 0.001 mol%, more preferably at least 0.005 mol%, also preferably at least 0.010 mol%.

In the case where two or more specific monomers are to be used, the total number of specific monomers used may be within the ranges given above.

[0048]

The polymerization temperature is preferably 10 to 95°C, more preferably 15 to 90°C. The polymerization pressure is preferably 0.5 to 4.0 MPa, more preferably 0.6 to 3.5 MPa. The polymerization time is preferably from 50 to 520 minutes, more preferably from 50 to 450 minutes, also preferably from 50 to 300 minutes.

[0049]

In addition, steps A1 and A2 can be carried out continuously in the same polymerization reaction vessel.

Moreover, in the production method of the present invention, specific particles can be formed in step A1, and step A2 can be carried out before the non-fluorinated monomer is completely consumed in step A1.

[0050]

By the above-described technique, an aqueous dispersion (modified PTFE particle-containing aqueous dispersion) in which the modified PTFE is dispersed in the form of particles can be obtained. The concentration of the modified PTFE particles in the aqueous dispersion is preferably 10 to 45 wt%, more preferably 10 to 30 wt%, also preferably 10 to 25 wt%. Within the range described above, the modified PTFE particles in the aqueous dispersion can be more easily coagulated, and the turbidity of the coagulated liquid can be suppressed.

The average size of the primary particles in the case of modified PTFE particles is preferably 100 to 500 nm, more preferably 150 to 300 nm. When the average size of the primary particles is at least 100 nm, paste extrusion molding can be carried out at low extrusion pressure, and a molded article having no surface waviness and excellent surface smoothness can be easily obtained. When the average size of the primary particles is at most 500 nm, the voids between the particles are reduced, and therefore the extrusion stability will be excellent, and a molded article having excellent surface smoothness will be easily obtained.

The average primary particle size for modified PTFE particles corresponds to the D50 value measured using a laser scattering particle size distribution analyzer.

[0051]

The modified PTFE produced by the above procedure contains TFE-based units (hereinafter referred to as TFE units), specific monomer-based units and non-fluorinated monomer-based units.

Modified PTFE usually contains TFE units as the main component. The main component means that the content of TFE units is at least 99.700% by weight, preferably at least 99.900% by weight. relative to all units of modified PTFE. The content of TFE units is usually at most 99.999% by weight. relative to all units of modified PTFE.

The content of specific monomer-based units is preferably 0.020 to 0.150 wt%, more preferably 0.030 to 0.100 wt%. relative to all units of modified PTFE.

Moreover, in the case where two or more specific monomers are to be used, the total unit content based on the respective specific monomers may be within the ranges described above.

The content of non-fluorinated monomer units is preferably 10 to 500 ppm, more preferably 10 to 200 ppm, also preferably 20 to 200 ppm, particularly preferably 30 to 150 wppm based on all modified PTFE units.

Moreover, in the case where two or more non-fluorinated monomers are to be used, the total content of units based on the corresponding non-fluorinated monomers may be within the ranges described above.

[0052]

The following will describe an embodiment in which Step A1 is carried out, but another method may be used as long as it is possible to obtain Solution 1. For example, a method in which a separately obtained specific monomer is added to an aqueous medium to obtain Solution 1, and then in solution 1 carry out polymerization of TFE.

[0053]

Second embodiment

As a second embodiment of the method for producing modified PTFE, an embodiment having the following two steps can be given.

Step B1: The step of mixing at least one component selected from the group consisting of a polyalkylene oxide compound and a hydrocarbon-containing surfactant with an oxidizing agent in an aqueous medium to obtain dispersion 2.

Step B2: the step of carrying out copolymerization of TFE and a specific monomer in dispersion 2 under such conditions that the amount of specific monomer used relative to the total amount of TFE is at most 0.150% by weight. to obtain modified PTFE.

The following describes in detail the methods for carrying out the corresponding stages.

[0054]

Stage B1

Step B1 is the step of mixing at least one component selected from the group consisting of a polyalkylene oxide compound and a hydrocarbon-containing surfactant (hereinafter also referred to as a “nucleating agent”) with an oxidizing agent in an aqueous medium to obtain dispersion 2.

In the following, the materials used in Step B1 are first described in detail, and then the procedure for carrying out Step B1 is described in detail.

[0055]

Polyalkylene oxide compound

The polyalkylene oxide compound is a compound for the formation of nuclei (active sites) during the polymerization of TFE and a specific monomer. In other words, it corresponds to a nucleation additive.

A polyalkylene oxide compound is a compound containing a polyalkylene oxide chain, and the polyalkylene oxide chain may be, for example, a polymethylene oxide chain, a polyethylene oxide chain, a polypropylene oxide chain, or a polytetramethylene oxide chain.

[0056]

The polyalkylene oxide compound preferably has a surface tension in water of greater than about 40 dynes/cm at a concentration of 1000 ppm. The surface tension is more preferably greater than about 42 dynes/cm, also preferably greater than about 45 dynes/cm. The above surface tension preferably has a value of at most about 73 dynes/cm.

[0057]

The number average molecular weight of the polyalkylene oxide compound is preferably 50 to 2000, more preferably 100 to 1500, also preferably 150 to 1300.

[0058]

From the point of view that the formation of fluorinated oligomer is suppressed to a greater extent, the compound represented by formula (2) is preferred as the polyalkylene oxide compound.

Formula (2): R ²¹ -(OL ² ) _n -OR ²²

In formula (2), the substituents R ²¹ and R ²² each independently represent a hydrogen atom, an alkyl group, an acryloyl group or a methacryloyl group.

The L ² group means a C _1-4 alkylene group and may be linear or branched.

n has a value from 1 to 50.

[0059]

Specific examples of the polyalkylene oxide compound include polyethylene glycol, polyethylene glycol acrylate, polyethylene glycol methacrylate, polyethylene glycol methyl ether, polyethylene glycol dimethyl ether, polyethylene glycol butyl ether, polypropylene glycol, polypropylene glycol acrylate, polypropylene glycol methacrylate, polypropylene glycol dimethacrylate, methyl Polypropylene glycol ether, polypropylene glycol dimethyl ether, polypropylene glycol butyl ether, polypropylene glycol dimethacrylate and polytetramethylene glycol.

[0060]

As the polyalkylene oxide compound, one type may be used alone, or two or more types may be used in combination.

[0061]

Hydrocarbon surfactant

A hydrocarbon surfactant is a surfactant containing a hydrocarbon. More specifically, at least some of the monovalent substituents on the carbon atoms are hydrogen, and substitution with halogen atoms such as fluorine and chlorine atoms is also possible. In the preferred hydrocarbon-containing surfactant, at least 75%, preferably at least 85%, more preferably at least 95%, of the monovalent substituents substituted on the carbon atoms are hydrogen atoms.

[0062]

As the hydrocarbon-containing surfactant, for example, a hydrocarbon surfactant and a siloxane surfactant can be mentioned.

Hydrocarbon surfactant means a surfactant that does not contain a silicon atom and does not contain a halogen atom, such as a chlorine atom or a fluorine atom, since 100% of the monovalent substituents on the carbon atoms are a hydrogen atom.

Siloxane surfactant means a hydrocarbon-containing surfactant having hydrophobic groups including a siloxane skeleton containing a large number of siloxane units.

[0063]

As the hydrocarbon surfactant, an anionic hydrocarbon surfactant is preferably used. Anionic hydrocarbon surfactant means a hydrocarbon surfactant having a negatively charged moiety such as carboxylic acid groups, sulfonic acid groups, sulfuric acid groups, phosphinic acid groups and phosphoric acid groups, and hydrocarbon moieties such as alkyl groups, in as hydrophobic fragments.

An example of an anionic hydrocarbon surfactant is the highly branched tertiary C ₁₀ carboxylic acid available as Versatic (registered mark) 10 from Resolution Performance Products.

Other examples of anionic hydrocarbon surfactants include the sodium linear alkyl polyether sulfonates available as the Avanel (registered mark) S series from BASF.

[0064]

As the anionic hydrocarbon surfactant, the anionic hydrocarbon surfactant represented by formula (4) is also preferable.

Formula (4): R ⁴¹ -L ⁴ -M

Substituent R ⁴¹ means an alkyl group. The alkyl group may be linear, branched or cyclic, and is preferably linear. The number of carbon atoms in an alkyl group is, for example, from 6 to 20.

Group L ⁴ means -ArSO ₃ ^- , -SO ₃ ^- , -SO ₄ ^- , -PO ₃ ^- , -PO ₄ ^- or ^-COO- . Here, Ar represents an arylene group.

M stands for monovalent cation. The monovalent cation, for example, can be H ⁺ , Na ⁺ , K ⁺ or NH ₄ ⁺ .

As a specific example of the anionic hydrocarbon surfactant represented by formula (4), sodium dodecyl sulfate may be mentioned.

[0065]

Another example of an anionic hydrocarbon surfactant is Lankropol (registered mark) K8300 sulfo-succinate surfactant, available from Akzo Nobel Surface Chemistry LLC.

[0066]

As the hydrocarbon surfactant, a nonionic hydrocarbon surfactant is also preferred. A nonionic hydrocarbon surfactant has no charged groups, but has a hydrophobic moiety, which is often a long-chain hydrocarbon. The hydrophilic portion of the nonionic hydrocarbon surfactant may be a water-soluble functional group, such as a polyethylene oxide chain produced by the polymerization of ethylene oxide.

As the nonionic hydrocarbon surfactant, block copolymers having various types of polyalkylene oxide blocks such as polyethylene oxide and polypropylene oxide may be mentioned.

[0067]

Suitable nonionic hydrocarbon surfactants may include those described in paragraphs 0043 to 0052 of JP-A-2016-537499.

[0068]

As suitable siloxane surfactants, mention may be made of the surfactants described in US Pat. Nos. 6,841,616 (Wille et al.) and 7,977,438 (Brothers et al.).

[0069]

Oxidizing agent

The oxidizing agent, for example, may be hydrogen peroxide and a polymerization initiator.

As the polymerization initiator, the compounds presented as the polymerization initiator described in the above-mentioned Step A1 may be mentioned. As the polymerization initiator, persulfate is preferred, and ammonium persulfate or potassium persulfate is more preferable.

[0070]

As the aqueous medium, the aqueous medium used in step A1 may be mentioned.

[0071]

Methodology for stage B1

In step B1, the nucleating agent and the oxidizing agent are mixed in an aqueous medium to obtain dispersion 2. In other words, in this step in an aqueous medium, the nucleating agent is exposed to the oxidizing agent.

When the nucleating agent and the oxidizing agent are mixed in an aqueous medium, a dispersion liquid 2 in which the lipophilic nucleating sites are dispersed in an aqueous medium can be obtained. More specifically, when a nucleating agent such as a polyalkylene oxide compound or a hydrocarbon-containing surfactant is mixed with an oxidizing agent, the hydrophilic portions of the nucleating agent are decomposed and the hydrophobic portions of the nucleating agent become lipophilic nucleating sites. The lipophilic nucleation sites will be dispersed in the aqueous environment, allowing fine distribution of the fluoropolymer at these sites.

Since the lipophilic nucleation sites have excellent affinity for TFE, the polymerization of TFE appears to proceed easily in dispersion 2 containing the lipophilic nucleation sites. That is, lipophilic nucleation sites may constitute a hydrophobic environment for TFE polymerization.

[0072]

The amount of nucleation additive used is preferably from 0.1 to 50 ppm by weight, more preferably from 0.5 to 25 ppm by weight, relative to the total weight of the aqueous medium.

The amount of the oxidizing agent used is preferably from 0.5 to 100 ppmw, more preferably from 0.5 to 50 ppmw, based on the total weight of the aqueous medium.

The temperature at which the nucleating agent and the oxidizing agent are mixed is preferably in the range of 20 to 120°C, more preferably 40 to 120°C.

The stirring time when mixing the nucleating additive and the oxidizing agent is preferably from 0.05 to 1.00 hours.

[0073]

It is preferable to add the water-soluble inorganic salt to the aqueous medium before or during mixing of the nucleating agent and the oxidizing agent. The addition of a water-soluble inorganic salt is useful for increasing the number of fluoropolymer particles formed during nucleation.

The amount of water-soluble inorganic salt used is preferably from 0.01 to 80 ppmw, more preferably from 1 to 50 ppmw, based on the total weight of the aqueous medium.

As the water-soluble inorganic salt, for example, sodium sulfite, sodium hydrosulfite, sodium chloride, potassium sulfite, potassium hydrosulfite, potassium carbonate, ammonium oxalate, sodium tetraborate, sodium acetate, ammonium carbonate, ammonium dihydrogen phosphate or diammonium phosphate may be mentioned, preferably sulfite, and more preferred are sodium sulfite or ammonium sulfite.

[0074]

Stage B2

Step B2 is a step of carrying out copolymerization of TFE and a specific monomer in dispersion 2 under conditions such that the amount of specific monomer used relative to the total amount of TFE is at most 0.150 wt%, to obtain modified PTFE.

In this step, the same procedure is carried out as in step A2 described above, except that variance 2 is used instead of variance 1, and hence its description will be omitted.

The various properties of the modified PTFE obtained by step B2 are the properties described above for the various properties of the modified PTFE obtained by step A2. However, the modified PTFE obtained in step B2 does not contain non-fluorinated monomer units.

[0075]

Modified PTFE Powder

As a method for producing modified PTFE powder (fine modified PTFE powder) consisting of modified PTFE particles from an aqueous dispersion containing modified PTFE particles, for example, a method of coagulating modified PTFE particles may be mentioned.

More specifically, after bringing the temperature of the aqueous dispersion to a temperature of 5 to 35°C, for example, by diluting with water so that the concentration of the modified PTFE in the aqueous dispersion containing the modified PTFE particles becomes from 8 to 25% by weight, the aqueous dispersion is vigorously stirred for coagulation of modified PTFE particles. At this time the pH value can be adjusted if required. In addition, a coagulating agent such as an electrolyte or a water-soluble organic solvent may be added to the aqueous dispersion.

Thereafter, appropriate stirring is performed to separate the coagulated modified PTFE particles from water, and the resulting wet powder (wet fine powder) is coagulated and sized as required, and then dried as required. As a result, modified PTFE powder can be obtained.

[0076]

The above drying is carried out in a state where the wet powder does not flow too much, preferably in a stationary state. The drying method, for example, may be vacuum drying, high frequency drying or hot air drying.

The drying temperature is preferably 10 to 300°C, more preferably 100 to 300°C.

[0077]

In particular, it is preferable to dry the undried modified PTFE powder in an ammonia-containing atmosphere. Here, “ammonia-containing atmosphere” means an atmosphere in which ammonia gas can contact the undried modified PTFE powder. For example, it means an atmosphere containing ammonia gas, or an atmosphere in which ammonia or a compound that generates ammonia is dissolved in water contacted with undried modified PTFE powder, and ammonia gas is generated, for example, by heating.

The compound that releases ammonia, for example, can be ammonium salt or urea. Such a compound will decompose when heated and will release ammonia gas.

By drying the undried modified PTFE powder in an atmosphere containing ammonia, the extrusion pressure of the modified PTFE powder paste can be lowered without deteriorating the physical properties.

[0078]

The modified PTFE powder of the present invention has monomer-based units having a polar group in an amount of 0.005 to 0.150 mol%. relative to tetrafluoroethylene-based units. The monomer-based units having a polar group are more preferably 0.010 to 0.100 mol%.

[0079]

The standard specific gravity (SSG) of the modified PTFE powder is at most 2.230, preferably 2.130 to 2.230, more preferably 2.135 to 2.220, also preferably 2.135 to 2.210. The SSG value is used as a parameter for relative molecular weight, and the lower the value, the higher the molecular weight.

[0080]

The modified PTFE produced by Step A1 and Step A2 may be a polymer having all units of TFE units, specific monomer units and non-fluorinated monomer units, or it may be a mixture of a polymer having TFE units and units of based on a specific monomer, and a polymer having units based on a non-fluorinated monomer.

[0081]

Molded product

The above-described modified PTFE can be suitably used in paste extrusion molding.

By extrusion molding of modified PTFE paste (especially modified PTFE powder), the desired molded product can be obtained.

Paste extrusion molding is a method in which modified PTFE powder and a lubricant are mixed so that the modified PTFE powder becomes flowable, and the mixture is extruded to form a molded product such as a film or tube.

The mixing ratio of the lubricant can be suitably selected so that the modified PTFE powder has flowability. For example, when the total amount of modified PTFE powder and lubricant is 100 wt%, preferably 10 to 30 wt%, and more preferably 15 to 20 wt%.

As a lubricant, for example, naphtha or a petroleum hydrocarbon having a distillation end point of at least 100°C is preferred.

An additive such as pigment may be added to the mixture for the purpose of coloring, and various fillers may be added for the purpose of imparting strength and conductivity.

[0082]

The shape of the molded product, for example, may be a tube shape, a sheet shape, a film shape, or a fiber shape. Examples of applications include tubing, electrical wire coatings, sealing materials, porous membranes or filters.

In addition, the modified PTFE powder can be extruded into a paste to form an extruded rod, and the extruded rod can be stretched to form a stretched porous modified PTFE material. The stretching conditions, for example, may be a stretch rate of at least 500% at a speed of 5 to 1000%/sec.

The shape of the article formed by the stretched porous material, for example, may be a tube shape, a sheet shape, a film shape, or a fiber shape.

Examples

[0083]

Hereinafter, the present invention is described in more detail with reference to examples and comparative examples, but the present invention is not limited to them.

[0084]

The different measurement and evaluation methods are as follows.

(A) Average primary particle size (nm) (hereinafter also referred to as “PPS”) for modified PTFE particles

An aqueous dispersion of modified PTFE particles is used as a sample, and measurement is carried out using a laser scattering particle size distribution analyzer (manufactured by Horiba, Ltd., trade name: “LA-920”).

(B) Standard Specific Gravity (SSG)

Measured in accordance with ASTM D4895-04.

Weigh 12.0 g of sample (modified PTFE powder) and hold it in a cylindrical mold having an inner diameter of 28.6 mm at 34.5 MPa for 2 minutes. Place in an oven with a temperature of 290°C and heat at a speed of 120°C/hour. Then, after holding at 380°C for 30 minutes, the temperature is reduced at a rate of 60°C/hour and held at 294°C for 24 minutes. The sample is then kept in a desiccator at 23°C for 12 hours, the specific gravity of the sample at 23°C relative to water is measured and this value is taken as the standard specific gravity. The lower the SSG value, the higher the molecular weight.

(C) Extrusion pressure measurement

Modified PTFE powder (100 g), left at room temperature for at least 2 hours, is placed in a glass bottle having an internal capacity of 500 ml, and lubricating oil (Isopar H (registered mark), manufactured by Exxon) is added (21 .7 g) and stirred for 3 minutes to obtain a mixture. After incubating the mixture at 25°C for 2 hours with a compression ratio (the ratio of the cross-sectional area at the die inlet to the cross-sectional area at the die outlet) of 100 and an extrusion speed of 51 cm/min, the paste is extruded at 25°C through a hole having a diameter of 2.5 cm, a calibration zone length of 1.1 cm and an insertion angle of 30°, to obtain an extruded rod (rope-like material). The pressure required for extrusion at this point is measured and taken as the extrusion pressure (unit: MPa).

(D) Measurement of stress relaxation time

An extruded rod is obtained in the same way as in measuring the extrusion pressure, and the rod is dried at 230°C for 30 minutes to remove the lubricant. Next, the extruded rod is cut to the appropriate length and both ends are fixed so that the clamping interval becomes equal to 3.8 cm, after which the rod is heated to 300°C in an air circulation oven. The extruded rod is then stretched under the conditions of a stretch rate of 1000%/sec and a total stretch of 2400% to obtain a sample for measuring the stress relaxation time. Both ends of this sample are secured using a clamping device and pulled to a total length of 25 cm. The stress relaxation time is obtained as the time required for the sample to fail when left in an oven at 390°C.

(E) Measurement of fluorinated oligomer

The sample (modified PTFE powder) is subjected to ethanol extraction in a Soxhlet apparatus for 5 hours, and the extract obtained with ethanol is subjected to LC/MS analysis, resulting in the predominantly C _6-34 -CF ₂ chain group of the oligomer being quantified using as standard products perfluorooctylsulfonic acid and perfluorooctanoic acid. The option where the presence of the oligomer is confirmed is classified as “present”, and the option where the presence of the oligomer is not confirmed is classified as “absent”.

In this case, the LC/MS analysis uses an Agilent 1260 series HPLC/6460MS instrument, and the column used is a CD-C18 2 mmφ×100 mm, 3 μm particle size column manufactured by Imtakt. In addition, the measurement uses a gradient of an aqueous solution of ammonium acetate and methanol.

[0085]

Example 1

Stage A1

A 100 L stainless steel autoclave is filled with paraffin wax (1500 g) and deionized water (60 L). After purging the autoclave with nitrogen, the pressure is reduced and n-butyl methacrylate (n-BMA) (1 g) and deionized water (0.5 L) are poured and loaded into the autoclave. Here, n-butyl methacrylate is loaded so that the amount of n-butyl methacrylate used becomes 0.011 wt%. relative to the total amount of TFE that is used further.

The interior of the autoclave is then maintained at atmospheric pressure and the solution in the autoclave is heated to 75°C with stirring. Then, a solution of ammonium persulfate (0.053 g) as a polymerization initiator dissolved in deionized water (1 L) was injected into the autoclave to polymerize n-butyl methacrylate.

Stage A2

After 10 min, the pressure is increased to 1.96 MPa using SPE and a solution containing ammonium persulfate (0.54 g) and disuccinic acid peroxide (concentration 80 wt%, the balance being water) (53 g) dissolved in warm water ( 1 l) approximately 70°C, inject into the autoclave. After 939 seconds, the internal pressure in the autoclave drops to 1.89 MPa. Here, the amount of polymerization initiators used above (ammonium persulfate and aqueous disuccinic acid peroxide) is 0.59 wt%. relative to the total amount of TFE.

Next, TFE is added so as to maintain the internal pressure in the autoclave at 1.96 MPa, and TFE is polymerized. After adding 1 kg of TFE, a solution containing ammonium vinyl sulfonate (13.3 g) dissolved in deionized water (1.5 L) is fed so that the amount of ammonium vinyl sulfonate becomes 0.60 g per 1 kg of TFE supplied, carrying out the supply of vinyl -ammonium sulfonate while simultaneously confirming the supplied amount of TFE using the flow meter.

The reaction is stopped when the amount of added TFE reaches 9 kg, and the TFE in the autoclave is released into the atmosphere. The polymerization time is 99 minutes.

The resulting aqueous dispersion of modified PTFE is cooled and the supernatant paraffin wax is removed. The wax recovery rate is 56%. The solids concentration (modified PTFE concentration) in the aqueous dispersion is approximately 12% by weight. The average size of the primary particles of modified PTFE in an aqueous dispersion is 177 nm.

The resulting aqueous dispersion is brought to 20°C and stirred to coagulate the modified PTFE particles to obtain modified PTFE powder. The resulting modified PTFE powder is then dried at 270°C along with an aqueous ammonium carbonate solution.

The resulting modified PTFE powder has an SSG of 2.182. The extrusion pressure is 22.3 MPa. The stress relaxation time is 92 seconds.

In addition, no fluorinated oligomer was detected in the resulting modified PTFE powder.

[0086]

Example 2

An aqueous dispersion of modified PTFE is prepared in accordance with the same procedure as described above (Example 1), except that the amount of ammonium vinyl sulfonate added is changed from 0.60 to 0.90 g per 1 kg of TFE supplied, and then obtained modified PTFE powder.

The results of the various assessments are summarized in Table 1.

[0087]

Example 3

An aqueous dispersion of modified PTFE is prepared in accordance with the same procedure as described above (Example 1), except that the amount of n-butyl methacrylate used is changed from 1 to 0.4 g, ammonium persulfate added after adjusting the temperature is changed from 0.053 to 0.11 g, and the amount of ammonium vinyl sulfonate added relative to 1 kg of TFE fed is changed from 0.60 to 0.79 g, and then modified PTFE powder is obtained.

The results of the various assessments are summarized in Table 1.

[0088]

Example 4

An aqueous dispersion of modified PTFE was prepared according to the same procedure as described above (Example 1), except that 1 g of iso-butyl methacrylate (i-BMA) was used instead of 1 g of n-butyl methacrylate, and then a modified PTFE powder was obtained.

The results of the various assessments are summarized in Table 1.

[0089]

Example 5

An aqueous dispersion of modified PTFE is prepared in accordance with the same procedure as described above (Example 1) except that 1 g of vinyl methacrylate (VMA) is used instead of 1 g of n-butyl methacrylate, and the added amount of ammonium vinyl sulfonate is changed from 0.60 to 0.62 g per 1 kg of TFE supplied, and then modified PTFE powder is obtained.

The results of the various assessments are summarized in Table 1.

[0090]

Example 6

Stage B1

A 100 L stainless steel autoclave is filled with paraffin wax (1500 g) and deionized water (60 L). After purging the autoclave with nitrogen, the pressure is reduced and PEG1000 (1000 number average molecular weight, polyethylene glycol) (0.39 g) and deionized water (0.5 L) are poured into the autoclave and loaded. Here, n-butyl methacrylate is loaded so that the amount of n-butyl methacrylate used becomes 0.011 wt%. relative to the total amount of TFE used further.

The interior of the autoclave is then maintained at atmospheric pressure and the solution in the autoclave is heated to 75°C with stirring. Then, a solution containing ammonium persulfate (0.053 g) as an oxidizing agent dissolved in deionized water (1 L) is injected into the autoclave to polymerize n-butyl methacrylate.

Stage B2

After 10 minutes, the pressure is increased to 1.96 MPa using SPE, and a solution containing ammonium persulfate (0.54 g) and disuccinic acid peroxide (concentration 80 wt%, the balance being water) (53 g) as polymerization initiators, dissolved in warm water (1 l) approximately 70°C, injected into the autoclave. After 939 seconds, the internal pressure in the autoclave drops to 1.89 MPa. Here, the amount of polymerization initiators used above (ammonium persulfate and aqueous disuccinic acid peroxide) is 0.59 wt%. relative to the total amount of TFE.

Next, TFE is added so as to maintain the internal pressure in the autoclave at 1.96 MPa, and TFE is polymerized. After adding 1 kg of TFE, a solution containing ammonium vinyl sulfonate (13.3 g) dissolved in deionized water (1.5 L) is fed so that the amount of ammonium vinyl sulfonate becomes 0.59 g per 1 kg of TFE fed, carrying out the supply of vinyl sulfonate ammonium while simultaneously confirming the supplied amount of TFE using the flow meter.

When the amount of added TFE reaches 9 kg, the reaction is stopped and the TFE in the autoclave is released into the atmosphere. The polymerization time is 99 minutes.

The resulting aqueous dispersion of modified PTFE is cooled and the supernatant paraffin wax is removed. The wax recovery rate is 57%. The solids concentration (modified PTFE concentration) in the aqueous dispersion is approximately 12% by weight. The average size of the primary particles of modified PTFE in an aqueous dispersion is 173 nm.

The resulting aqueous dispersion is brought to 20°C and stirred to coagulate the modified PTFE particles to obtain modified PTFE powder. This modified PTFE powder is then dried at 270°C along with an aqueous ammonium carbonate solution.

The resulting modified PTFE powder has an SSG of 2.182. The extrusion pressure is 23.5 MPa. The stress relaxation time is 88 seconds.

In addition, no fluorinated oligomer was detected in the resulting modified PTFE powder.

The results of the various assessments are summarized in Table 1.

[0091]

Example 7

An aqueous dispersion of modified PTFE is prepared according to the same procedure as described above (Example 1), except that 1 g of iso-butyl methacrylate (i-BMA) is used instead of 1 g of n-butyl methacrylate, the amount of ammonium persulfate added after temperature control is changed from 0.053 to 0.11 g, and the amount of ammonium vinyl sulfonate added relative to 1 kg of supplied TFE is changed from 0.60 to 1.1 g, and then modified PTFE powder is obtained.

The results of the various assessments are summarized in Table 1.

[0092]

Example 8

An aqueous dispersion of modified PTFE is prepared in accordance with the same procedure as described above (Example 4) except that the entry time to step A2 after step A1 is changed from the time of “after 10 minutes” to “after 30 minutes”, and then obtain modified PTFE powder.

The results of the various assessments are summarized in Table 1.

[0093]

Example 9

An aqueous dispersion of modified PTFE was prepared according to the same procedure as described above (Example 8), except that 0.053 g of ammonium persulfate as the polymerization initiator in step A1 was changed to 0.11 g, and then modified PTFE powder was obtained.

The results of the various assessments are summarized in Table 1.

[0094]

Example 10

An aqueous dispersion of modified PTFE is prepared in accordance with the same procedure as described above (Example 7) except that the supply of 0.60 g of ammonium vinyl sulfonate in step A2 is changed to 0.43 g of ammonium acrylate, and then a modified PTFE powder is obtained.

The results of the various assessments are summarized in Table 1.

[0095]

Comparative example 1

An aqueous dispersion of modified PTFE is prepared in accordance with the same procedure as described above (Example 6) except that sodium lauryl sulfate (SLS) is used instead of ammonium vinyl sulfonate, sodium lauryl sulfate is fed so that the amount of SLS supplied is 1.48 g per 1 kg of supplied TFE, and the supplied amount of TFE is confirmed by a flow meter, and the drying temperature is changed from 270 to 220°C, and then modified PTFE powder is obtained.

In this embodiment, the resulting modified PTFE powder contains a distribution of a group of fluorinated oligomers (H(CF ₂ CF ₂ ) _n SO ₃ H (n=3 to 16)) with a peak in the immediate vicinity of n=9 or 10, and a total of 230 was detected h/million

[0096]

In Table 1, the column “SLS (g/TFE kg)” indicates the amount of SLS added relative to 1 kg of TFE supplied.

The "APS (g)" column indicates the amount of ammonium persulfate used after temperature adjustment.

“Amount (% by weight) of non-fluorinated monomer” means the proportion (mass fraction used) that is the amount of non-fluorinated monomer used relative to the total amount of TFE.

“Amount (ppm) of PEG” means the proportion that the amount of PEG1000 used is relative to the total weight of the aqueous medium.

“Amount (wt.%) of a specific monomer” means the proportion (mass fraction used) which is the amount of the specific monomer used relative to the total amount of TFE.

“Amount (mol%) of non-fluorinated monomer” means the proportion (mole fraction) that is the amount of non-fluorinated monomer used relative to the total amount of TFE.

“Amount (mol%) of specific monomer” means the proportion (mole fraction) that the amount of specific monomer used is relative to the total amount of TFE.

[0097]

Table 1

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 Example 10 Compare example 1 n-BMA (g) (n-butyl methacrylate) 1 1 0.4 i-BMA (g) (iso-butyl methacrylate) 1 1 1 1 1 VMA (g) (vinyl methacrylate) 1 PEG1000 (g) (polyethylene glycol) 0.39 0.39 SLS (g/TFE kg) (sodium lauryl sulfate) 1.48 APS (g) (ammonium persulfate) 0.053 0.053 0.11 0.053 0.053 0.053 0.11 0.053 0.11 0.11 0.053 Amount (wt%) of non-fluorinated monomer 0.11 0.11 0.004 0.11 0.11 - 0.11 0.11 0.11 0.11 - Amount (ppm) of PEG - - - - - 6.5 - - - - 6.5 Amount (wt.%) of specific monomer 0.060 0.090 0.079 0.060 0.062 0.059 0.110 0.060 0.060 0.043 - Amount (% mol.) of non-fluorinated monomer 0.008 0.008 0.003 0.008 0.010 - 0.008 0.008 0.008 0.008 - Amount (% mol.) of specific monomer 0.048 0.072 0.063 0.048 0.050 0.047 0.088 0.048 0.048 0.048 - Curing time (minutes) 99 110 116 101 103 104 116 105 102 96 78 Wax recovery rate (%) 56 41 24 58 54 57 thirty 62 62 21 96 Average primary particle size (nm) 177 180 192 180 178 173 176 174 181 175 145 Standard Specific Gravity 2,182 2,179 2,181 2,183 2,184 2,182 2,182 2.177 2,179 2,183 2,197 Extrusion Pressure(MPa) 22.3 20.6 19.6 22.9 21.2 23.5 20.8 22.8 21.6 22.1 21.6 Stress relaxation time (s) 92 104 103 98 97 88 87 91 96 66 14 Presence (yes) or absence (no) of fluorinated oligomers No No No No No No No No No No Eat

[0098]

As shown in Table 1, according to the production method of the present invention, modified PTFE (an aqueous dispersion of modified PTFE particles) can be successfully produced without the formation of fluorinated oligomer.

The entire disclosure of Japanese Patent Publication No. 2018-087280, filed April 27, 2018, including the description, claims and abstract, is incorporated herein by reference in its entirety.

Claims (36)

1. A method for producing modified polytetrafluoroethylene, which includes copolymerization of tetrafluoroethylene and a monomer having a polar group, in dispersion 1 containing a polymer containing units based on a non-fluorinated monomer and an aqueous medium, under such conditions that the amount of monomer having a polar group used is at most 0.150% by weight. relative to the total amount of tetrafluoroethylene supplied to the polymerization system, wherein the monomer having a polar group is a monomer represented by formula (3): in formula (3), the substituents R ³¹ and R ³² each independently represent a hydrogen atom or a fluorine atom, the substituent R ³³ means a hydrogen atom, a fluorine atom or an alkyl group that can be replaced by a fluorine atom, L ³ means a single bond or a divalent a linking group, and the substituent R ³⁴ is a polar group represented by formula (A) or a group represented by formula (B): in formula (A) and formula (B), M represents a hydrogen atom, NH ₄ or an alkali metal atom; And where the non-fluorinated monomer is the monomer represented by formula (1): in formula (1), the substituent R ¹¹ represents a hydrogen atom or an alkyl group, the group L ¹ means a single bond, -CO-O-*, -O-CO-* or -O-, “*” means the bonding position with R ¹² and the substituent R ¹² represents a hydrogen atom, an alkyl group, an alkenyl group or a nitrile group, with the proviso that when L ¹ represents a single bond, the substituent R ¹² represents a nitrile group. 2. The method for producing modified polytetrafluoroethylene according to claim 1, in which a non-fluorinated monomer is polymerized in an aqueous medium, and then in a dispersion 1 containing a polymer containing units based on a non-fluorinated monomer and an aqueous medium, tetrafluoroethylene and a monomer having a polar group are copolymerized . 3. A method for producing modified polytetrafluoroethylene according to any one of paragraphs. 1, 2, in which during the copolymerization of tetrafluoroethylene and a monomer having a polar group, a polymerization initiator is used, and the amount of the polymerization initiator used is at least 0.10% by weight. relative to the total amount of tetrafluoroethylene supplied to the polymerization system. 4. A method for producing modified polytetrafluoroethylene according to any one of paragraphs. 1-3, in which the amount of monomer having a polar group used is at most 0.150 mol%. relative to the total amount of tetrafluoroethylene supplied to the polymerization system. 5. A method for producing modified polytetrafluoroethylene, which includes copolymerization of tetrafluoroethylene and a monomer having a polar group, in dispersion 2 obtained by mixing at least one component selected from the group consisting of a polyalkylene oxide compound and a hydrocarbon-containing surfactant with an oxidizing agent in an aqueous medium, under such conditions that the amount of monomer having a polar group used is at most 0.150% by weight. relative to the total amount of tetrafluoroethylene supplied to the polymerization system to obtain modified polytetrafluoroethylene. 6. The method for producing modified polytetrafluoroethylene according to claim 5, in which the copolymerization of tetrafluoroethylene and a monomer having a polar group is carried out in dispersion 2, and The polyalkylene oxide compound is the compound represented by formula (2): in formula (2), the substituents R ²¹ and R ²² each independently represent a hydrogen atom, an alkyl group, an acryloyl group or a methacryloyl group, the group L ² means a C _1-4 alkylene group, and n has a value from 1 to 50. 7. The method for producing modified polytetrafluoroethylene according to claim 5 or 6, in which a polymerization initiator is used during the copolymerization of tetrafluoroethylene and a monomer having a polar group, and the amount of polymerization initiator used is at least 0.10% by weight. relative to the total amount of tetrafluoroethylene supplied to the polymerization system. 8. A method for producing modified polytetrafluoroethylene according to any one of paragraphs. 5-7, in which the amount of monomer having a polar group used is at most 0.150 mol%. relative to the total amount of tetrafluoroethylene supplied to the polymerization system. 9. A method for producing modified polytetrafluoroethylene powder, which includes obtaining an aqueous dispersion in which the modified polytetrafluoroethylene obtained by the method according to any one of claims. 1-8, dispersed in the form of particles, and coagulating the solid particles of modified polytetrafluoroethylene to obtain modified polytetrafluoroethylene powder. 10. Modified polytetrafluoroethylene powder for producing molded products, containing a polymer containing units based on a non-fluorinated monomer, represented by formula (1): in formula (1), the substituent R ¹¹ represents a hydrogen atom or an alkyl group, the group L ¹ means a single bond, -CO-O-*, -O-CO-* or -O-, “*” means the bonding position with R ¹² , and the substituent R ¹² represents an alkyl group, an alkenyl group or a nitrile group, with the proviso that when L ¹ represents a single bond, the substituent R ¹² represents a nitrile group in which the units based on the monomer having a polar group are from 0.005 up to 0.150 mol%. relative to tetrafluoroethylene-based units, which has a standard specific gravity of at most 2.230, and which is substantially free of C _6-34 fluorinated oligomer containing hydrophilic functionality and free of fluorinated surfactant, wherein said monomer having a polar group is a monomer represented by formula (3): in formula (3), the substituents R ³¹ and R ³² each independently represent a hydrogen atom or a fluorine atom, the substituent R ³³ means a hydrogen atom, a fluorine atom or an alkyl group that can be replaced by a fluorine atom, L ³ means a single bond or a divalent a linking group, and the substituent R ³⁴ is a group represented by formula (A) or a group represented by formula (B): in formula (A) and formula (B), M represents a hydrogen atom, NH ₄ or an alkali metal atom. 11. A method for producing a stretched porous material, which includes producing a modified polytetrafluoroethylene powder by the method according to claim 9, extruding a paste of the modified polytetrafluoroethylene powder to obtain an extruded rod, and stretching the extruded rod to obtain a stretched porous material.