JPH11240918A - Tetrafluoroethylene-based copolymer, its production and its use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject copolymer excellent in extrusion processability, capable of allowing a uniform orientation processing and excellent in heat stability and strength by copolymerizing tetrafluoroethylene with a specific fluorinated comonomer. SOLUTION: The objective copolymer is obtained by copolymerizing tetrafluoroethylene with a fluorinated comonomer of the formula [(m) is 0-2; (n) is 1-3], [e.g. perfluoro(1,4-butanediol divinyl ether)]. The containing proportion of the polymerization unit based on the fluorinated comonomer is 0-0.5 mol.%. The standard specific gravity of the copolymer is preferably <2.155. The copolymer is obtained by an emulsion polymerization, by loading water, a free radical polymerization initiator, a disperse-stabilizer (e.g. a paraffin wax and a solvent) and an emulsifier, preferably successively adding or halfway- separately adding the tetrafluoroethylene, adding the fluorinated comonomer at once at the initial time, and polymerizing the loaded and added materials at 50-120 deg.C under 6-40 kg/cm<2> pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine powder of a tetrafluoroethylene copolymer (hereinafter referred to as PTFE), a method for producing the same, and a porous molded article thereof.

[0002]

2. Description of the Related Art Fine powder of PTFE is produced by coagulating polymer fine particles obtained by a so-called emulsion polymerization method in which polymerization is carried out using an emulsifier in an aqueous medium.
It is known in the art to modify PTFE by copolymerizing tetrafluoroethylene (hereinafter referred to as TFE) and a relatively small amount of a copolymerizable copolymer. Also,
It is known that the modification of PTFE is effective for improving the processability in extruding paste by adding an appropriate auxiliary to fine powder.

[0003] Japanese Patent Publication No. 56-262242, Japanese Patent Publication No. 56-2
6243 includes chlorotrifluoroethylene (hereinafter referred to as C).
In the production of modified PTFE using a comonomer such as TFE) and TFE, a method has been proposed in which the proportion of polymerized units based on a comonomer such as CTFE in the polymer formed substantially at the end of polymerization is increased.

Japanese Patent Publication No. 59-34724 discloses a modified PTF.
A method has been proposed in which the proportion of polymerized units based on various comonomers of E is increased in the early stage of polymerization.
E has a standard specific gravity of 2.2 or more, and has a low molecular weight, which is not sufficient for stretching.

[0005] Japanese Patent Publication No. 56-262242 proposes a method in which comonomer is added all the time during polymerization and the amount added in the initial stage is increased. In this case, it is assumed that the proportion of the polymerized unit based on the comonomer in the PTFE is large and insufficient for stretching.

In Japanese Patent Publication No. 3-66926, R ^f −
A method of modifying PTFE using CH = CH ₂ (R ^f is a perfluoroalkyl group) as a comonomer has been proposed.
Here, a method is described in which the comonomer is continuously added to the middle of the polymerization so that the degree of modification becomes large at the beginning.

[0007] The above-mentioned modification is mainly performed for the purpose of improving the paste extrusion processability of fine powder, for example, for reducing the extrusion pressure. With a decrease in sex.
Further, the modified PTFE has a problem that heat resistance is lowered due to the introduced comonomer structure.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide PTFE having excellent extrudability, capable of uniform stretching, and having excellent heat resistance and strength.

[0009]

Means for Solving the Problems The inventor has proposed that the amount of polymerized units based on a comonomer having two polymerizable groups to be copolymerized with TFE is limited to such an extent that the processability is not affected. It has been found that a modified PTFE having an improved heat resistance suitable for the production of a porous body by the method described above can be obtained.

That is, the present invention relates to TFE and a fluorinated comonomer represented by the formula 1 (where m is 0, 1 or 2,
n is 1, 2 or 3. And PTFE, wherein the content of the polymerized unit based on the fluorinated comonomer is more than 0 and 0.5 mol% or less. In addition, the standard specific gravity of PTFE is smaller than 2.155.
Provide TFE.

[0011]

Embedded image CF ₂ = CFO (CF ₂ CF ₂ ) _n (OCF (CF ₃ ) CF ₂ ) _m OCF = CF ₂ Formula 1

Further, in the above-mentioned method for producing PTFE,
Provided is a method for producing PTFE, characterized in that fluorinated comonomer is added all at once in the early stage of polymerization. After extruding the PTFE powder with a paste,
Provided is a polymer porous body which is stretched at a temperature of not less than ° C.

[0013] The fluorinated comonomer is produced by the following method. That is, the reaction of iodine and TFE yields diiodide (ICF ₂ CF ₂ CF ₂ CF ₂ I), which is further reacted with TFE.
To obtain a diiodide of I (CF ₂ CF ₂ ) _n I (n is 2 or 3). These diiodides are oxidized with fuming sulfuric acid to synthesize the corresponding perfluoro (γ-lactone) (perfluoro (γ-butyrolactone having n = 2))
The synthesis of is described in JP-B-55-12907). Hexafluoropropylene (hereinafter referred to as HFPO) is added thereto to produce a 2-mol adduct, 3-mol adduct or 4-mol adduct of HFPO (2 mol adduct of HFPO or HFPO)
For the preparation of a 3 mol adduct of PO, see JP-B-54-4931).

Next, the above HFPO adduct is neutralized with a methanol dispersion of KOH to remove methanol and water, and then subjected to a decarboxylation reaction at 250 to 300 ° C. under reduced pressure to obtain a 2 mol HFPO adduct. Is m = 0 in equation 1.
A fluorinated comonomer of m = 1 in Formula 1 can be obtained from a 3 mol adduct of HFPO, and a fluorinated comonomer of m = 2 in Formula 1 can be obtained from a 4 mol adduct of HFPO.

As the fluorinated comonomer, perfluoro (1,4-butanediol divinyl ether) (hereinafter referred to as perfluoro
PFBDVE) (a compound of formula 1 where m = 0 and n = 2) and a compound of formula 1 where m = 1 and n = 2 are obtained as PT
Stretchability of FE, heat resistance of stretched workpiece,
Particularly preferred from the viewpoint of uniformity. The fluorinated comonomer is
It has two polymerizable groups, and a very small amount of a crosslinked structure can be introduced into the resulting polymer.

The content of the polymerized unit based on the fluorinated comonomer in the present invention needs to be strictly controlled from the viewpoint of stretchability. The content is 0.5 mol% or less in the modified PTFE. If the content is more than 0.5 mol%, the crystallinity of the polymer is slightly lowered, and the extrusion pressure of the paste is reduced, but the stretchability is significantly reduced. In addition, the stability of the emulsified dispersion during the polymerization reaction is substantially reduced, the fine particles aggregate during the polymerization, and the dispersion is easily broken. In particular, 0.1
A range of at most mol% is preferred. 0.005 mol%
If it is less than 3, it is difficult to substantially obtain the effect of modification such as improvement in physical properties of the stretched product. Therefore, it is preferably 0.005 to 0.1 mol%, particularly preferably 0.01 to 0.07 mol%.

Furthermore, it is preferable that the molecular weight of PTFE is sufficiently high from the viewpoint of stretchability. Generally, the standard specific gravity of a polymer having a correlation with the molecular weight is used as a measure of the molecular weight. That is, the higher the molecular weight, the smaller the standard specific gravity. In the case of a copolymer, in principle, the molecular weight based on standard specific gravity is strictly different from a homopolymer, but in the present invention,
Since the amount of the fluorinated comonomer to be added is small, the standard specific gravity is adopted as a measure of the molecular weight for convenience.

The standard specific gravity of the PTFE of the present invention is 2.155.
Preferably, it is smaller, ie of high molecular weight.
If the molecular weight is too high, the crystallinity will be extremely reduced and the heat resistance will be reduced. Therefore, the standard specific gravity of PTFE is preferably 2.130 or more.

The PTFE of the present invention is produced by emulsion polymerization commonly used for producing PTFE. This polymerization method is disclosed in U.S. Pat. No. 3,142,665 and U.S. Pat.
9 and the like.

After water, an ordinary free radical polymerization initiator, a dispersion stabilizer (for example, paraffin wax or a solvent) for suppressing the formation of aggregates and an emulsifier are charged into the autoclave, TFE is injected while stirring. After this, the autoclave is gently stirred and the polymerization is carried out at a suitable temperature and pressure. The emulsified dispersion obtained upon completion of the polymerization can be used as it is, but for molding use, generally, fine powder obtained by aggregating polymer fine particles by a known method is generally used.

In the method for producing PTFE of the present invention,
It is preferred that the required amount of the fluorinated comonomer be added all at once in the initial stage without continuous or intermediate addition. By the initial batch addition, the ratio of the polymerized units based on the fluorinated comonomer in the core portion of the polymer fine particles generated in the initial stage of polymerization is high, and the ratio gradually decreases with the progress of the polymerization. In the shell, a homopolymer substantially free of fluorinated comonomers is formed. Such a structure is preferable from the viewpoint of stretchability and physical properties of a stretched product.

In the method of continuously adding the fluorinated comonomer or the method of adding the fluorinated comonomer until a certain period of polymerization, a relatively high proportion of the polymerized unit based on the fluorinated comonomer occupies the whole particles, which is advantageous for paste extrusion. Even so, it is difficult to obtain fine powder that is advantageous for stretching.

The TFE can be produced by adding TFE all at once in the initial stage and polymerizing it. However, in order to increase the ratio of polymerized units based on fluorinated comonomer in the core of the polymer fine particles formed in the initial stage of polymerization, TFE can be added continuously. It is preferable to produce it by dividing and adding it during the polymerization.

In the present invention, one or more fluorinated comonomers copolymerizable with TFE can be used, and can be used in combination with other copolymerizable monomers.
The structure of the monomer used in this case is not particularly limited as long as it is a polymerizable compound copolymerizable with TFE, but from the viewpoint of heat resistance of the obtained modified PTFE, a structure containing fluorine, for example, a polymerizable compound of perfluoropolymer Is preferred.

The size of the polymer particles in the emulsified dispersion is
It can be controlled by a known method. For example, US Pat.
As described in 99, a desired particle size can be obtained by controlling the addition of an emulsifier. Further, as shown in JP-A-60-76516, it can be controlled by changing the TFE pressure during polymerization.

As the emulsifier, a salt of perfluoroalkanecarboxylic acid or a salt of perfluoroalkanesulfonic acid which does not participate in chain transfer can be used. Particularly, ammonium perfluoroalkanecarboxylate having 7 to 9 carbon atoms is preferably used.

As the initiator, peroxides such as disuccinic peroxide and diglutaric peroxide or persulfates such as ammonium persulfate and potassium persulfate are used alone or in combination. In addition, it is used as a redox system in common with a reducing agent such as sodium sulfite. Further, during the polymerization, the radical concentration during the polymerization can be adjusted by adding a radical scavenger such as hydroquinone or catechol, or by adding a peroxide decomposer such as ammonium sulfite.

The polymerization is usually carried out at a temperature of 50 to 120 ° C. and a pressure of 6 to 40 kg / cm ² . Usually, when the concentration of the polymer fine particles reaches 20 to 40% by weight, unreacted monomers are released to the outside of the system, stirring is stopped, and after the polymerization is completed, the polymer fine particles are aggregated. Aggregation can be performed by a known method. That is, the concentration of the polymer fine particles is 10 to 20% by weight.
After diluting with water, the mixture is vigorously stirred to cause aggregation. Depending on the case, the pH may be adjusted, or a coagulation aid such as an electrolyte or a water-soluble organic solvent may be added.
Thereafter, by performing appropriate stirring, the aggregated polymer fine particles are separated from water, granulated and sized, and then dried.

Drying is usually carried out in a state where the wet powder obtained by agglomeration does not flow much, preferably still, and is subjected to vacuum, high frequency, hot air or the like. Fine powder has the property of easily fibrillating even with a small shearing force and losing the state of the crystal structure after the completion of the original polymerization. Particularly in stretching applications, contact or friction between the powders at particularly high temperatures is not preferred in order to prevent a reduction in workability. Drying is
It is preferably carried out at 10 to 250 ° C, particularly preferably at 100 to 250 ° C.

The expanded porous PTFE material of the present invention can be produced by the following general method. That is, after 5 to 20% by weight of a lubricant is added to and mixed with the fine powder, the lubricant is sufficiently aged in a closed container.

The lubricants used are, for example, petroleum solvents such as solvent naphtha and white oil, hydrocarbon oils such as toluenes, ketones and esters, silicone oils, fluorine oils and fluorine-containing compounds.
Any material can be used as long as it can wet the fine powder and can be easily evaporated and removed from the extruded product after the extrusion.

Fine powder to which a lubricant is added is
After preforming at a pressure of about 50 kg / cm ² , the paste is extruded. In some cases, the extruded material is formed into a sheet by calendaring or the like.

In the extrusion, it is important to promote the orientation of the fine powder particles, and it is preferable that the reduction ratio R / R (the ratio of the barrel area to the extrusion die area) of the extruder is sufficient. R / R = 50-800, preferably 80-200. At this time, the pressure applied to the paste, that is, the extrusion pressure is usually 100 to 1000 kg / cm ² . The lower the extrusion pressure, the better the extrusion processability. However, if the extrusion pressure is too small, the orientation of the polymer particles is not sufficient, and the stretchability is reduced. From this point, it is preferable to set R / R.

Thereafter, the lubricant contained in the extruded product is removed by evaporation, and the extruded product is stretched 2 to 50 times at a temperature of 250 ° C. or more to obtain a preferable porous material. 25
When the temperature is lower than 0 ° C., only a porous body having a small stretching ratio is easily obtained. On the other hand, when the temperature is 350 ° C. or higher, the porous body is difficult to obtain because PTFE melts.

It is preferable that the porous body is stretched uniformly. The term “uniform” as used herein means that the entire molded body is uniformly stretched, and specifically, that the weight distribution and the pore size distribution in the stretching direction of the porous body are uniform.
The stretching ratio is not particularly limited, but it does not substantially have a porous structure at a stretching ratio of 2 or less, and does not have a stable porous structure at a stretching ratio of 50 or more, and in some cases easily breaks during stretching, and is about 2 to 50 times. It is preferable to carry out in. Also,
The stretching speed is not particularly limited, but is usually 50 to 1000%.
/ Sec.

The emulsified dispersion of PTFE of the present invention can be used as a coating material, and can be used for coating rolls, cooking utensils, impregnating glass cloth, and the like. In particular, it can be suitably used for a stretched product. The expanded porous body of PTFE of the present invention has a feature that heat resistance and durability are particularly excellent. This porous body is particularly useful for industrial products requiring durability, such as bag filters, packings, gaskets, and other coating applications.

[0037]

The present invention will now be described with reference to Examples (Examples 1, 2, 3,
6) and Comparative Examples (Examples 4 and 5), but the present invention is not limited thereto.

[Synthesis of fluorinated comonomer] Diiodide (ICF ₂ CF ₂ CF ₂ CF ₂ I) is oxidized with fuming sulfuric acid to synthesize perfluoro (γ-butyrolactone) (JP-B-55-129).
07), and HFPO was added thereto to produce a 2-mol adduct of HFPO or a 3-mol adduct of HFPO (see Japanese Patent Publication No. 54-4931). Next, the HFPO adduct was neutralized with a methanol dispersion of KOH to remove methanol and water, and then subjected to a decarboxylation reaction under reduced pressure at 250 to 300 ° C. to remove PFBDV from the 2-mol adduct of HFPO.
E (compound of Formula 1 where m = 0 and n = 2) was converted to HFP
In the formula 1, m = 1 and n =
A fluorinated comonomer represented by 2 was obtained. These fluorinated comonomers were purified by distillation, and those having a purity of 99% or more as measured by gas chromatography were used.

Example 1 100 baffles with baffles and stirrer
In a 1 liter stainless steel autoclave, 35 g of ammonium perfluorooctanoate, deionized water 63.
P dissolved in 4 liters and 1.5 kg of solvent perfluorotributylamine (FC-43, manufactured by Sumitomo 3M Limited)
5 g of FBDVE was charged. After the autoclave was replaced with nitrogen and further replaced with TFE, the temperature was raised to 72 ° C. while stirring. TFE is pressurized to 19 kg / cm ² and water 3
5.4 g of disuccinic peroxide dissolved in liter were injected. Internal pressure is 18.5kg / cm ^{2 in} about 3 minutes
Descended.

The polymerization was allowed to proceed while adding TFE so as to maintain the internal pressure of the autoclave at 19 kg / cm ² . T
When the amount of the FE added reached 720 g, 65 g of ammonium perfluorooctanoate dissolved in 3 liters of water was injected. The reaction was terminated when the amount of TFE added reached 25 kg, and TFE in the autoclave was released to the atmosphere.

The resulting emulsified dispersion was cooled to remove the precipitated FC-43. The concentration of polymer particles in the emulsified dispersion was about 26.8% by weight, and the average particle size of the polymer particles was 0.256 μm. This emulsified dispersion was diluted with ion-exchanged water to a polymer fine particle concentration of 10% by weight, and vigorously stirred until solidified. After coagulation, the mixture was further stirred for 5 minutes, and the coagulated polymer was dried at 200 ° C. The standard specific gravity of the obtained polymer was 2.151.

Further, FC-43 from which polymer fine particles were removed was used.
And PFBDVE in water was not detected by gas chromatography. In addition, PF is contained in TFE released to the atmosphere.
BDVE could not be detected by gas chromatography. Therefore, all PFBDVEs were considered to have polymerized. As a result, the content of polymerized units based on PFBDVE in the polymer was 0.02 mol%. Tables 1 and 2 show the results of a stretchability test and a heat resistance test of the porous body using the obtained polymer.

The properties of the obtained polymer were measured by the following methods. (1) Standard specific gravity: The standard specific gravity of the powdery polymer is ASTM.
It was determined by the amount of water displaced by a standard molding test sample according to the D1457-69 method. This standard molding test sample was prepared as follows. First, a powdery polymer12.
0g into a 2.86cm diameter mold and 352kg / c
Hold for 2 minutes under a pressure of m ² and preform. Next, the preform is placed in an oven at 300C to 380C at 2C.
/ Minute, heated at 380 ° C. for 30 minutes, cooled at a rate of 1 ° C./minute to 294 ° C., taken out of the oven, kept at 23 ° C. for 3 hours or more, and used as test samples.

(2) Fine particle size: Laser diffraction type particle size measurement device (Otsuka Electronics, LPA-3000 / 3100)
The measurement was carried out three times at 25 ° C. at a concentration of about 0.1% by weight at 25 ° C., and the average value was defined as the particle diameter.

(3) Preparation of stretch processability evaluation sample: 50 g of polymer and 11.8 g of an extrusion lubricant (Supersol FP, manufactured by Idemitsu Petrochemical Co., Ltd.), which is a hydrocarbon oil, were mixed at 25 ° C.
And mature for 1 hour or more. Next, the cylinder (internal diameter 9.95m
m) with an extrusion die (diameter 1 mm at a drawing angle of 30 ° C)
Is filled with the above mixture, and the
Apply a load of g to the piston inserted in the cylinder and hold for 10 minutes. Thereafter, an extruded rod is obtained at a ram speed of 100 mm / min. In the second half of the extrusion, put the extrudate in the part where the pressure is in an equilibrium state
At 180 ° C., the lubricant is evaporated off. About 50mm
Into a sample for evaluation of stretching.

(4) Stretchability test: The above sample was stretched to 10 times the length at a distance between chucks of 10 mm, at a temperature of 250 ° C. and at a tensile speed of 1000% / sec using a tensile tester equipped with a high-temperature bath. The stretchability under these conditions was evaluated from the viewpoint of appearance and uniformity. The appearance was evaluated on the basis of A: smooth, B: slightly uneven, C: fairly uneven, D: cut during stretching. (5) Strength Evaluation of Stretched Rod: The strength of the five stretched rods obtained in (3) and (4) was measured, and the average value was defined as the strength (kg) per rod.

(6) Evaluation of uniformity of porous body: center of sample before stretching (10 mm between chucks) (5 mm from chuck)
After the stretching, the distance L (mm) from the position of the center (50 mm from the chuck) of the sample (100 mm) to the marking after the stretching is measured, and the value according to Equation 2 is used as an index of uniformity (%). did. The greater this value, the higher the uniformity.

[0048]

## EQU1 ## Uniformity (%) = ((100 / 2−L) / (100/2)) × 100 Equation 2

(7) Heat resistance test: Both ends of a porous rod obtained by stretching were fixed (distance between both ends: 50 mm)
A sample was placed in a 400 ° C. high-temperature bath and heat-treated every 3 minutes from 10 minutes to 10 minutes. The heat resistance was evaluated by visual observation of the porous rod after the heat treatment. It has been observed that longer treatment times generally lead to fracture through a stage where the rod diameter shrinks due to shrinkage. Even if the treatment time is long, the shape of the porous body rod does not change, and it can be determined that the porous body that does not break has high durability at high temperatures.

Example 2 A polymer was obtained in the same manner as in Example 1 except that 2 g of PFBDVE was used. The concentration of polymer particles in the emulsified dispersion was about 27.8% by weight, the average particle size of the polymer particles was 0.251 μm, and the standard specific gravity of the polymer was 2.150. Determined in the same manner as in Example 1,
The content of polymerized units based on PFBDVE in the polymer is 0.1%.
008 mol%. Tables 1 and 2 show the results of the stretching test and the heat resistance durability test performed in the same manner as in Example 1.

Example 3 A polymer was obtained in the same manner as in Example 1 except that 40 g of PFBDVE was used. The concentration of polymer particles in the emulsified dispersion was about 25.6% by weight, the average particle size of the polymer particles was 0.239 μm, and the standard specific gravity of the polymer was 2.149. The content of polymerized units based on PFBDVE in the polymer, determined in the same manner as in Example 1, was 0.16 mol%. Tables 1 and 2 show the results of the stretching test and the heat resistance durability test performed in the same manner as in Example 1.

Example 4 A polymer was obtained in the same manner as in Example 1 except that PFBDVE was not used. The polymer particle concentration of the emulsified dispersion was about 28.0% by weight, the average particle diameter of the polymer particles was 0.258 μm, and the standard specific gravity of the polymer was 2.151. Tables 1 and 2 show the results of the stretching test and the heat resistance durability test performed in the same manner as in Example 1.

Example 5 150 g of PFBDVE was used (the content of polymerized units based on PFBDVE was 0.6 mol%
The polymerization was carried out in the same manner as in Example 1 except that
During the polymerization, the fine particles agglomerated and the dispersion was destroyed, so that the polymerization could not be continued.

In Examples 1, 2, 3, and 4, an expanded porous material was obtained. Examples 1 and 2 have the same extrudability as Example 4, and have improved uniformity, strength and heat resistance. Example 3 having a high PFBDVE content had a low paste extrusion pressure and was excellent in extrusion processability. However, the appearance after stretching was poor, and the uniformity and heat resistance were lower than those of the other examples. In Example 4 containing no PFBDVE, the rod diameter was reduced with a short heat treatment time, but in Examples 1 and 2, no change in shape was observed.

Example 6 Polymerization was carried out in the same manner as in Example 1 except that 5 g of the fluorinated comonomer represented by m = 1 and n = 2 in Formula 1 was used instead of PFBDVE. . The concentration of the polymer particles in the emulsified dispersion was about 27.1% by weight, the average particle diameter of the polymer particles was 0.240 μm, and the standard specific gravity of the polymer was 2.151.
Met. The content of the polymerized unit based on the fluorinated comonomer in the polymer, determined in the same manner as in Example 1, was 0.02 mol%. Tables 1 and 2 show the results of the stretching test and the heat resistance durability test performed in the same manner as in Example 1. Example 6 has the same extrusion workability as Examples 1, 2, and 4, and further has improved uniformity, strength, and heat resistance.

[0056]

[Table 1]

[0057]

[Table 2]

[0058]

According to the present invention, a polytetrafluoroethylene polymer particularly useful for stretching can be obtained by copolymerizing a trace amount of a comonomer having two polymerizable groups with tetrafluoroethylene. The stretched porous body made of this polymer has excellent heat resistance and durability.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C08F 216: 12)

Claims (7)

[Claims] 1. A copolymer of tetrafluoroethylene and a fluorinated comonomer represented by the formula (1), wherein m is 0, 1 or 2, and n is 1, 2 or 3. Content of polymerized units based on ≧ 0 and 0.5 mol%
A tetrafluoroethylene-based copolymer characterized by the following. Embedded image CF ₂ = CFO (CF ₂ CF ₂ ) _n (OCF (CF ₃ ) CF ₂ ) _m OCF = CF ₂ Formula 1 2. The tetrafluoroethylene copolymer according to claim 1, wherein m is 0 and n is 2. 3. A tetrafluoroethylene-based copolymer in which at least a core portion of the polymer fine particles obtained by emulsion polymerization of tetrafluoroethylene and a fluorinated comonomer is the copolymer according to claim 1 or 2. 4. The tetrafluoroethylene copolymer according to claim 1, wherein the standard specific gravity is less than 2.155. 5. A polymer fine particle having a structure in which the content of polymerized units based on fluorinated comonomer in the core portion is larger than the content ratio of polymerized units based on fluorinated comonomer in the shell portion. A powder comprising the tetrafluoroethylene-based copolymer according to 3 or 4. 6. The method for producing a tetrafluoroethylene-based copolymer according to claim 1, wherein the fluorinated comonomer is added at once in the initial stage of polymerization. A method for producing a fluoroethylene copolymer. 7. A powder comprising the tetrafluoroethylene-based copolymer according to claim 5 is extruded into a paste, and then extruded.
A polymer porous body, which is stretched at a temperature of not less than ° C.