JP2003040936A - Fluorine-containing copolymer for film-forming - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fluorine-containing copolymer for film-forming, in which coating and film-forming properties are compatible with high heat resistant characteristics, enabling it to use effectively for a polymer matrix of a gel polymer electrolyte and the like. SOLUTION: In the fluorine-containing copolymer for film-forming, relation between solution viscosity y and a number of revolutions of a rotator x at the measured time is specified by the relative formula: y=ax<2> -bx+c (unit is Pa.s; a is a number in the range of 0-0.001; b is that of 0-0.2000; c is that of 0.1-10) and its logarithmic viscosity is 1.0-1.5 dl/g. This copolymer is improved in coating properties enabling it to form continuously a film having a uniformed thickness and also is improved in composite film-formability with heat resistant materials, by controlling the thixotropic behavior of the copolymer solution to give a constant solution behavior, enabling it to effectively produce a gel electrolyte film in the production process of a gel polymer electrolyte-based lithium ion secondary battery.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a fluorine-containing copolymer for film formation. More specifically, it relates to a film-forming fluorinated copolymer effectively used as a polymer matrix of a gel polymer electrolyte.

[0002]

2. Description of the Related Art In recent years, in order to reduce the size and weight of mobile phones and personal computers, batteries having high energy density and excellent charge / discharge cycles have been required. Lithium-ion secondary batteries that use a lithium ion battery have attracted attention. Among them, in response to the demand for improved safety such as measures against leakage of organic electrolyte and measures to reduce ignitability, the reliability and safety of batteries due to elimination of liquid leakage are improved, and thin film, laminated body, package A gel polymer electrolyte lithium ion secondary battery has been proposed from the viewpoint of simplification and weight reduction. As the polymer matrix for forming such a gel polymer electrolyte, a fluorine-containing copolymer having a characteristic of flame retardance is often used, and particularly vinylidene fluoride (VdF) and hexa with a good balance of crystallinity and amorphousness. A copolymer with fluoropropylene (HFP) is mentioned as a particularly preferred example (US Pat. No. 5,296,318, JP-A-8-507407).

In the above VdF-HFP copolymer, VdF contributes to the improvement of mechanical strength in the skeleton of the copolymer, and further functions to retain the organic electrolytic solution. In addition, HFP
By imparting an amorphous property to the copolymer, it functions as a lithium ion permeation part and further contributes to retention of the organic electrolyte. Therefore, in order to increase the organic electrolyte holding capacity of this copolymer, it is sufficient to increase the copolymerization ratio of HFP. However, the maximum HFP copolymerization ratio is
Usually, it is about 40 mol% and not only the limit is seen, but increasing the copolymerization ratio of HFP increases the retention capacity of the organic electrolyte, but the mechanical strength of the gel polymer electrolyte decreases, and this is formed into a film. When handled, problems such as breakage and bleeding of the organic electrolyte occur. In addition, a large amount of HFP copolymerized causes a problem of not forming a gel. Therefore,
In conventional gel polymer electrolytes, increasing the retention capacity of the organic electrolytic solution, preventing the organic electrolytic solution from seeping out, and improving the mechanical strength are issues to be solved. Moreover,
High heat resistance is regarded as a very important property for use at higher temperatures, and higher heat resistance polymers are being developed.

In recent years, in order to impart even higher mechanical properties and higher heat resistance, not only the polymer itself itself is used, but also a composite type polymer electrolyte in which a polymer and a heat resistant material are combined and integrated. The so-called gel electrolyte has been studied, and it has been desired to develop a polymer having improved compatibility with a heat-resistant material and film-forming property on the heat-resistant material for composite integration.

The high melting point of the polymer for improving the high heat resistance property can be achieved by bringing the composition ratio close to that of the VdF homopolymer. However, the higher the melting point of the VdF homopolymer, the higher the melting point. , Not only the swelling property in the electrolytic solution is deteriorated, it becomes difficult to use as a gel polymer electrolyte,
In the film forming step, which is an important step in manufacturing a gel polymer battery, the film is curled or shrunk, so that a film having a uniform film thickness cannot be obtained. Further, in the low-melting-point polymer that attaches importance to the film-forming property, not only the high heat resistance, which is currently regarded as an important property, is not satisfied, but also the drying temperature has to be lowered in the drying process of the gel polymer battery manufacturing process. Since the drying efficiency for removing the solvent is deteriorated, and further the drying cannot be sufficiently performed, the solvent remaining in the gel polymer electrolyte has a problem that the performance of the battery is adversely affected.

Further, in the process for producing a gel polymer battery, a film having a constant film thickness is continuously formed, so that a solution having a good solution property and a constant solution behavior is required. The behavior when the polymer is made into a solution is also an important factor.

[0007]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a fluorine-containing copolymer for film formation, which has both coatability and film-forming property and high heat resistance and is effectively used as a polymer matrix of a gel polymer electrolyte. To provide a coalesce.

[0008]

The object of the present invention is as follows.
The solution viscosity y is the rotor speed x at the time of measurement, and y = ax ² -bx + c (unit: Pa ・ s) (where a is 0 to 0.001, b is 0 to 0.2000, and c is 0.1 to 10). It is achieved by a fluorine-containing copolymer for forming a film having a logarithmic viscosity of 1.0 to 1.5 dl / g.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The solution viscosity of a fluorinated copolymer is
For a 10 wt% N, N-dimethylacetamide solution of the copolymer, according to JIS K-7117, using a B8H type rotational viscometer, 2
Rotor speeds of 10 rpm, 20 rpm, 50 rpm and 100 r at 5 ° C
It is measured as pm, and the approximate quadratic curve shown by the above relational expression is obtained between each rotation speed x and the solution viscosity y.

It is desirable that the dependency of the solution viscosity on the rotation speed at a rotor rotation speed of 10 to 100 rpm, that is, the slope of the relationship between the rotation speed x and the solution viscosity y be linear. More specifically,
In the above quadratic equation, a is 0 to 0.001 and b is 0 to 0.2.
It is specified from experimental examples that 000 and c are preferably numerical values within the range of 0.1 to 10. When the values of a, b, and c are out of the range of these values, the solution viscosity has a rotation speed dependency.

The difference in solution viscosity between when the solution is in a state of being almost stationary and when the solution is flowing can be recognized as thixotropic behavior. When this thixotropy behavior is exhibited, the solution viscosity easily changes depending on the state of the solution, so that the handleability is deteriorated, and further it becomes difficult to form a uniform film.

In particular, the fluorine-containing copolymer that achieves the solution behavior with improved coatability has a value of the intercept of the above quadratic curve.
(c) must be 10 Pa · s or less. A solution having a value higher than this not only makes it difficult to prepare a film having a constant film thickness because of its high viscosity, but also polyethersulfone, polysulfone, polyphenylene sulfide, polyimide, polyamideimide, wholly aromatic polyamide, polyacrylate. , Deteriorates the composite film forming property for heat resistant materials such as wholly aromatic polyester, polycarbonate, and polytetrafluoroethylene.

Also, the logarithmic viscosity of the fluorine-containing copolymer used in the present invention is measured at 30 ° C. by a Ubbelohde viscometer of a solution of this copolymer dissolved in N, N-dimethylformamide at a concentration of 4 g / L. From the drop time, logarithmic viscosity [η] = ln (η _red ) / c η _red = (Solution drop seconds) / (Solvent drop seconds) c = Solution concentration (0.4g / dl) , This value is 1.0-1.5dl / g, preferably 1.2
It is desirable to be ~ 1.4 dl / g. When the logarithmic viscosity is higher than this, the solution viscosity when mixed with the organic electrolyte becomes extremely high, and not only uniform mixing with the lithium salt becomes difficult, but also the coatability deteriorates and good film-forming property is obtained. I can't get it. On the other hand, when the logarithmic viscosity is less than this, although the coatability of the solution is good, non-uniform portions such as pinholes are likely to occur in the film-forming film, and the film-forming property deteriorates.

The fluorine-containing copolymer is preferably produced by an emulsion polymerization method. The emulsion polymerization reaction is carried out by using a redox system of a water-soluble inorganic peroxide such as ammonium persulfate or the like and a reducing agent as a catalyst to proceed the polymerization, and the polymerization pressure is about 0 to 10 MPa · G, preferably about 1 to 5 MPa · G. Polymerization is performed within the range.

Here, the emulsifier, the polymerization temperature, and the polymerization temperature in the emulsion polymerization method for obtaining the fluorine-containing copolymer having improved coatability.
The selection of polymerization monomer charging method is the most important. That is, since the thixotropic behavior can be controlled by selecting these polymerization conditions, the fluorine-containing copolymer will have a large difference in coatability.

As an emulsifier necessary for obtaining a fluorine-containing copolymer having improved coatability, a general formula C _n F _{2n + 1} COONH ₄ (n =
A perfluorocarboxylic acid ammonium salt represented by the formulas 6 to 11) or a mixture thereof can be used. Especially when ammonium perfluorooctanoate, ammonium perfluorononanoate, etc. are used alone or SURFLO
It is preferable to use a mixture of n = 6 to 11 such as N S-111 SWB (Seimi Chemical product). As a particularly preferred emulsifier, ammonium perfluorononanoate, which is more difficult to develop thixotropic behavior, is selected.

Further, as a method of charging the raw material monomer necessary for obtaining the fluorine-containing copolymer having improved coatability, the polymerization monomer should be added by charge, that is, the polymerization monomer should be obtained as the polymerization reaction proceeds. It is important to introduce into the sequential reaction system in a ratio equivalent to the composition of the polymer. As a result, the compositional distribution of the polymer becomes small, and high heat resistance and high swelling properties can both be achieved, and since thixotropic behavior is not exhibited, film formability on a heat resistant material and the like becomes good.

The polymerization temperature range required for obtaining a fluorine-containing copolymer having improved coatability is more important. The polymerization reaction is carried out under conditions of a temperature of about 30 to 70 ° C, preferably about 45 to 65 ° C. When the polymerization is carried out in this temperature range or higher, the thixotropic behavior becomes prominent. Further, when the polymerization is carried out at a polymerization temperature of less than this, although the thixotropic behavior is not expressed, it becomes difficult to obtain a stable emulsion in emulsion polymerization, and further, the polymerization time becomes long, which is also disadvantageous in terms of cost. .

The melting point of the fluorine-containing copolymer obtained in such a polymerization temperature range varies depending on the copolymerization composition ratio thereof, but is preferably about 130 ° C to 160 ° C. If the melting point is higher than this, the strength is high but the degree of swelling is low. On the other hand, if the melting point is lower than this, the degree of swelling is high but the strength is low, making it difficult to achieve both strength and swelling degree. .

As the fluorine-containing copolymer composition, a polymerization unit based on vinylidene fluoride [VdF] is 80 to 98 mol%, preferably 90 to 96 mol%, a polymerization based on a fluorine-containing monomer other than vinylidene fluoride. Unit is 2 to 20 mol%, preferably 4 to 10
Must contain mol%.

When the VdF copolymerization ratio in the copolymer is below this range, flexibility and high swelling degree are satisfied, but melting point is lowered and resin deterioration degree is increased or its swelling is caused. Reduces the mechanical strength of the body. On the other hand, if the VdF copolymerization ratio is more than this range, it has a high melting point and a high mechanical strength, but only a low swelling degree can be obtained, and further, when a film is formed by casting, the film has a curl or Shrinkage occurs and good film formation cannot be achieved.

Examples of the fluorine-containing monomer other than VdF include tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene and perfluoro.
(Methyl vinyl) ether, perfluoro (ethyl vinyl)
Ether, perfluoro (propyl vinyl) ether, 2,
At least two kinds of 2,3,3,3-pentafluoropropyl trifluorovinyl ether, α-trifluoromethylacrylic acid, α-fluoroacrylic acid, perfluoroacrylic acid, perfluoromethacrylic acid and the like are used. Particularly when hexafluoropropylene-chlorotrifluoroethylene and perfluoro (methylvinyl) ether-chlorotrifluoroethylene are used in combination,
The content of hexafluoropropylene and perfluoro (methyl vinyl) ether mainly contributes to the swelling degree, film-forming property, and flexibility, while the content of chlorotrifluoroethylene mainly contributes to mechanical strength, melting point, and adhesiveness. Contributes to swelling, heat resistance,
It becomes a terpolymer with good adhesiveness. Further, by copolymerizing a fluorine-containing unsaturated carboxylic acid, high adhesiveness to a heat resistant material or a current collector can be achieved.

In order to obtain such a fluorine-containing copolymer, particularly a fluorine-containing copolymer having a desired logarithmic viscosity, it is preferable to add a chain transfer agent in the copolymerization reaction system, and particularly preferable chain. Examples of the transfer agent include acetone, methanol, isopropanol, ethyl malonate, ethyl acetate and the like. These chain transfer agents are used in a proportion of about 0.01-10% by weight, preferably about 0.5-5% by weight, based on the monomers. When carrying out the copolymerization reaction,
In order to adjust the pH, an electrolyte substance having a buffering capacity such as Na ₂ HPO ₄ , NaH ₂ PO ₄ , KH ₂ PO ₄ or sodium hydroxide may be added and used. Coagulation of the fluorinated copolymer from the aqueous latex formed by the emulsion polymerization reaction is carried out by dropping the aqueous latex into an aqueous salt solution of calcium chloride, sodium chloride, potassium alum or the like.

After coagulation, a film is formed from the dried fluorine-containing copolymer by melting the copolymer at a temperature higher than its melting point and then extruding or compressing the copolymer, or by using the copolymer as acetone, methyl ethyl ketone, A glass plate, metal plate, resin sheet (polyether sulfone, polysulfone) prepared by dissolving a solution in a soluble solvent such as methyl isobutyl ketone, N, N-dimethylformamide, N, N-dimethylacetamide, or N-methyl-2-pyrrolidone. , Polyphenylene sulfide, polyimide, polyamideimide, wholly aromatic polyamide, polyacrylate, wholly aromatic polyester, polycarbonate, polytetrafluoroethylene, etc.) on a substrate using a bar coater, a doctor blade, or a cast spin coating method. Apply and dry the solvent at room temperature to about 150 ° C It is carried out by letting removed by.

The film-like fluorine-containing copolymer thus obtained and the compounded fluorine-containing copolymer with the heat-resistant material are
A gel composition is formed by holding a lithium salt-soluble organic solvent therein. Further, a gel electrolyte for a lithium ion battery is formed by holding an organic electrolytic solution in which a lithium salt is dissolved in this film-shaped fluorine-containing copolymer.

Examples of lithium salts include LiPF ₆ and LiASF.
₆ , LiCIO ₄ , (CF ₃ SO ₂ ) ₂ NLi, LiBF ₄ , LiSbF ₆ , CF ₃ SO ₃ Li,
At least one kind of lithium salt such as C ₄ F ₉ SO ₃ Li is used. These lithium salts are dissolved in the soluble organic medium at a concentration of about 0.1 to 2.0 mol%, preferably about 0.25 to 1.75 mol% and used as an organic electrolyte.

Approximately 10 to 400% by weight of the fluorocopolymer,
As the lithium salt-soluble organic solvent preferably used in the proportion of 30 to 200%, any chemically stable one can be used, but carbonic acid ester is preferably used. Further, since this lithium salt-soluble organic solvent is used as an electrolytic solution, a solvent having a higher dielectric constant is more effective in promoting dissociation of the lithium salt.

The carbonic acid ester may be cyclic or chain-like, and examples of the high dielectric constant organic solvent include ethylene carbonate, propylene carbonate, γ-ptyrolactone and the like. Further, a solvent having a high relative permittivity and a strong polarity generally has a high viscosity, so that there is a drawback that the resistance to migration of ions increases. Therefore, the carbonate ester used as the electrolytic solution may be used after adjusting the viscosity of the electrolytic solution by adding a low viscosity solvent to the high dielectric electrolyte. Dimethyl carbonate as a low viscosity organic solvent,
Examples include diethyl carbonate and ethyl methyl carbonate. Further, in the present invention, the carbonate ester may be used alone or in combination of two or more kinds. Moreover, you may use it, mixing with another solvent.

The gel composition containing the lithium salt-soluble organic solvent is prepared by adding the film-shaped fluorine-containing copolymer to a lithium salt-soluble organic solvent kept at room temperature or lower than the boiling point of the used lithium salt-soluble organic solvent. It is carried out by dipping for about 10 minutes to 10 hours, and then physically removing the lithium salt-soluble organic solvent adhering to the surface of the film pulled up from the dipping solution by a method such as absorbing with a paper. Further, by using an organic electrolyte solution containing a lithium salt, the gel polymer electrolyte can be prepared by the same method.

The gel polymer electrolyte thus obtained is composed of a lithium composite oxide, which is a substance capable of occluding and releasing lithium ions, and a conductive substance, which is a substance capable of occluding and releasing lithium. A gel polymer electrolyte lithium ion secondary battery is formed with a negative electrode made of a carbonaceous material or the like.

[0031]

The fluorine-containing copolymer for film formation according to the present invention is a film having a constant film thickness continuously obtained by controlling the thixotropic behavior of the copolymer solution to obtain a solution exhibiting a constant solution behavior. Not only is the coating property that enables film formation of the gel polymer to be improved, but the composite film formation property for heat-resistant materials is also improved. Therefore, in the gel polymer electrolyte lithium ion secondary battery process, the gel electrolyte It enables efficient film production.

[0032]

EXAMPLES The present invention will now be described with reference to examples.

Example 1 Ammonium perfluorononanoate 1.0Kg Na ₂ HPO ₄ · 12H ₂ O 0.2Kg NaHSO ₃ 0.01Kg Ion-exchanged water 70Kg was charged into an autoclave made of SUS316 having an internal capacity of 100L, and deaerated sufficiently. Then, 0.4 kg of methanol as a chain transfer agent and as initial charge, vinylidene fluoride [VdF] 5.0 kg hexafluoropropylene [HFP] 0.3 kg chlorotrifluoroethylene [CTFE] 0.1 kg α-trifluoromethyl acrylic acid [TFMA ] When 0.1 kg was charged and heated to 50 ° C, the internal pressure in the autoclave became 2.5 MPa · G. Here, by the metering pump,
0.17 Kg of ammonium peroxodisulfate was introduced to initiate the polymerization reaction.

When the internal pressure of the autoclave decreased to 2.4 MPa · G as the polymerization reaction proceeded, VdF was increased to 2.5 MPa · G.
The operation of recovering to G was repeated until the amount of VdF added was 15.0 kg. Further, other copolymerized monomers were also uniformly added at a composition ratio of VdF / HFP / CTFE / TFMA = 96/2/1/1 mol% according to the amount of VdF added. After the addition was completed, aging was performed up to 0.5 MPa · G to complete the polymerization reaction.

The emulsion taken out from the autoclave was dropped into a 0.1 wt% calcium chloride aqueous solution while stirring, and the coagulated product was separated by filtration, thoroughly washed by stirring with ion-exchanged water, filtered and dried. 20 kg of a white powdery fluorocopolymer powder (copolymerization rate: 91%) having a copolymerization composition (by ¹⁹ F-NMR) of VdF / HFP / CTFE / TFMA = 96/2/1/1 mol% was obtained.

The following items were measured for the obtained fluorocopolymer. Solution viscosity: Approximate quadratic curve of rotation speed x and solution viscosity y by the above method y = ax ² -bx + c (unit: Pa · s) Thixotropic behavior: c value is 10 Pa · s or more, that is, solution When there is a large difference in the solution viscosity between when the solution is near the static state and when it is flowing, it is determined that the solution viscosity has a rotation speed dependency, and it is defined as ×, and when the value of c is 10 Pas or less. The logarithmic viscosity with ◯: melting point by the above method: using Seiko Instruments Inc. DSC220 type,
After heating the sample from 30 ℃ to 250 ℃ at 10 ℃ / minute, and then at 30 ℃ at 30 ℃
Measure the temperature at the apex of the endothermic peak when cooled to ℃, and again heated to 250 ℃ Film forming property: 10% by weight N, N during casting film production
-If the dimethylformamide solution is gelled and cannot be applied, x is given, and if curling or shrinkage occurs after casting and a film having a constant film thickness cannot be obtained, Δ is good and the coating and film forming properties are good. The degree of swelling is ◯: Thickness 0.1 mm that was compression molded at 230 ° C by hot pressing
A strip-shaped film was punched out from the film-shaped fluorinated copolymer of, and a Li salt-soluble organic solvent (ethylene carbonate-propylene carbonate etc. weight mixed solution) kept at 35 ° C
After immersing in the film for 1 hour, pull up the film, measure the weight after wiping off the solvent adhering to the film surface,
Calculated as the percentage of increased weight to the sample weight before swelling

Example 2 In Example 1, the amount of chain transfer agent (methanol) was 0.5 kg.
To obtain 20 Kg (polymerization rate 91%) of a white powdery fluorocopolymer having a copolymer composition of VdF / HFP / CTFE / TFMA = 96/2/1/1 mol%.

Example 3 In Example 1, the initial charge was VdF 5.0 Kg and HFP 0.3 Kg.
And CTFE 0.1Kg, and uniform composition of VdF / HF
Change to P / CTFE = 96/2/2 mol% and change the copolymer composition to VdF / HFP /
CTFE = 96/2/2 mol% white powdery fluorocopolymer 21Kg
(Polymerization rate: 97%) was obtained.

Example 4 In Example 3, the polymerization temperature was changed to 70 ° C., and 21 Kg of a white powdery fluorocopolymer having a copolymer composition of VdF / HFP / CTFE = 96/2/2 mol% (polymerization Rate 97%).

Example 5 In Example 1, the amount of chain transfer agent (methanol) was 0.3 kg.
And the polymerization temperature was changed to 70 ° C, the white powdery fluorine-containing copolymer having a copolymerization composition of VdF / HFP / CTFE / TFMA = 96/2/1/1 mol% 21 Kg (polymerization rate 96%).

Example 6 In Example 3, the emulsifier was changed to the same amount of ammonium perfluorooctanoate and the copolymer composition was VdF / HFP / CTFE.
= 96/2/2 mol% white powdery fluorocopolymer 20 kg (polymerization rate 93%) was obtained.

Example 7 In Example 6, the amount of chain transfer agent (methanol) was 0.25 kg.
And the polymerization temperature was changed to 70 ° C., and 20 Kg (polymerization rate 93%) of a white powdery fluorocopolymer having a copolymerization composition of VdF / HFP / CTFE = 96/2/2 mol%. Obtained.

The measurement results in each of the above examples are shown in the following Table 1 together with the coefficient of the approximate quadratic curve. Table 1 Example 1 2 3 4 5 6 7 [approximate quadratic curve] a 0 0 0 0.0004 0.0006 0 0.0007 b 0 0 0 0.0695 0.1117 0 0.1339 c (Pa · s) 0.8 0.5 1.0 4.8 7.2 0.8 9.0 [measurement result] Thixotropic behavior 〇 〇 〇 〇 〇 〇 〇 〇 Logarithmic viscosity (dl / g) 1.5 1.0 1.4 1.0 1.5 1.4 1.3 Melting point (℃) 150 154 153 147 146 154 145 145 Film formation 〇 〇 〇 〇 〇 〇 〇 〇 Swelling degree (%) 53 51 50 55 56 54 56

Comparative Example 1 In Example 3, the amount of chain transfer agent (methanol) was 0.5 kg.
To obtain 20 Kg (polymerization rate 93%) of a fluorocopolymer having a copolymerization composition of VdF / HFP / CTFE = 96/2/2 mol%.

Comparative Example 2 In Example 3, the amount of chain transfer agent (methanol) was 0.2 kg.
To obtain 20 Kg (polymerization rate 93%) of a fluorocopolymer having a copolymerization composition of VdF / HFP / CTFE = 96/2/2 mol%.

Comparative Example 3 In Comparative Example 2, the polymerization temperature was changed to 80 ° C., and 20 Kg of a fluorine-containing copolymer having a copolymer composition of VdF / HFP / CTFE = 96/2/2 mol%.
(Polymerization rate 93%) was obtained.

Comparative Example 4 In Example 6, the amount of chain transfer agent (methanol) was 0.5 kg.
To obtain 20 Kg (polymerization rate 93%) of a fluorocopolymer having a copolymerization composition of VdF / HFP / CTFE = 96/2/2 mol%.

Comparative Example 5 In Example 6, the amount of chain transfer agent (methanol) was 0.2 kg.
And the polymerization temperature was changed to 80 ℃, the copolymer composition VdF / HFP / CTFE = 96/2/2 mol% fluorine-containing copolymer 20Kg
(Polymerization rate 93%) was obtained.

Comparative Example 6 In Example 5, the amount of chain transfer agent (methanol) was 0.15 Kg.
And the emulsifier was changed to the same amount of C ₆ F ₁₁ C ₆ H ₄ SO ₃ Na (Neos product FS-1110) and the copolymer composition was VdF / HFP / CTFE / T.
FMA = 96/2/1/1 mol% fluorine-containing copolymer 19 Kg (polymerization rate 86%)
Got

Comparative Example 7 In Example 1, when the emulsifier was changed to the same amount of C ₆ F ₁₁ C ₆ H ₄ SO ₃ Na, the progress of the polymerization reaction was not confirmed. Also,
Even when the amount of the polymerization initiator (ammonium peroxodisulfate) was increased and the polymerization reaction was allowed to proceed, the reaction could not be completed because the resin was precipitated during the polymerization reaction.

The measurement results in each of the above comparative examples are shown in the following Table 2 together with the coefficient of the approximate quadratic curve. Table 2 Comparative example 1 2 3 4 5 6 [Approximate quadratic curve] a 0 0 0.0015 0 0.0037 0.0049 b 0 0 0.2813 0 0.6916 0.9353 c (Pa · s) 0.3 1.3 15.8 0.5 34.7 49.5 [Measurement result] Thixotropic behavior 〇 〇 × ○ × × Logarithmic viscosity (dl / g) 0.9 1.8 1.4 0.9 1.3 1.4 Melting point (℃) 153 155 138 155 137 137 Film forming property △ △ × △ × × Swelling degree (%) 52 52-52--

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the rotor rotation speed and solution viscosity when measuring solution viscosity in each example.

FIG. 2 is a graph showing the relationship between rotor rotation speed and solution viscosity when measuring solution viscosity in each comparative example.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) C08F 214: 18) C08F 220: 24 (C08F 214/22 216: 14) (C08F 214/22 220: 24) F term ( Reference) 4F071 AA26 AA26X AA84X AA88X AF05 AF45 AF53 AH12 AH15 BA02 BB02 BC02 4J100 AC24P AC27Q AC31Q AE09Q AL08Q BB10Q CA04 DA09 DA24 FA21 FA28

Claims (6)

[Claims] 1. The solution viscosity y is the rotor speed x at the time of measurement.
And y = ax ² -bx + c (unit: Pa ・ s) (where a is 0 to 0.001, b is 0 to 0.2000, and c is a number in the range of 0.1 to 10). The fluorine-containing copolymer for film formation, characterized by having an inherent viscosity of 1.0 to 1.5 dl / g. 2. Polymerized units 80-98 based on vinylidene fluoride
Fluorine-containing monomers other than mol% and vinylidene fluoride 20
The fluorine-containing copolymer for forming a film according to claim 1, which has a copolymer composition of ˜2 mol%. 3. A fluorine-containing monomer other than vinylidene fluoride is hexafluoropropylene, chlorotrifluoroethylene, perfluoro (methyl vinyl ether) and α-
Selected from the group consisting of trifluoromethylacrylic acid
The fluorine-containing copolymer for forming a film according to claim 2, which comprises two or more kinds of fluorine-containing monomers. 4. The method according to claim 1, which has a melting point of 130 to 160 ° C.
Alternatively, the fluorinated copolymer for forming a film according to 3 above. 5. The fluorine-containing copolymer for forming a film according to claim 1, which is used as a polymer matrix of a gel polymer electrolyte. 6. A copolymerization reaction of vinylidene fluoride and a fluorine-containing monomer other than vinylidene fluoride in an aqueous medium at a polymerization temperature of 70 ° C. or lower in the presence of an emulsifier of ammonium perfluorocarboxylic acid salt. The method for producing a fluorine-containing copolymer for forming a film according to claim 1.