JPH09328566A - Porous thermoplastic fluoroplastic body, its production and production of battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a porous thermoplastic fluoroplastic body being lightweight and having improved chemical resistance, mechanical strength and mass transfer by melt-extruding a thermoplastic fluoroplastic containing vinylidene fluoride and cold-stretching the extrudate to form flat pores therein. SOLUTION: A thermoplastic fluoroplastic containing at least 90wt.% vinylidene fluoride and having and MFR of 0.1-500g/10min is mole-extruded into a sheet or a hollow body, and this sheet or body is heat-treated at 70-155 deg.C to increase its degree of crystallinity to 40% or above. It is then cold-stretched at a draw ratio of 1.1-6 to obtain a porous thermoplastic fluoroplastic body having a large number of flat pores having a width of 0.1-3μm and a length of 0.5-20μm and an apparent specific gravity of 1.7 or below.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoplastic fluororesin porous material, a method for producing the same, and a method for producing a battery.
Its purpose is to provide a thermoplastic fluororesin porous body excellent in chemical resistance, lightweight and excellent in mechanical strength and mass transfer, a method for producing the same, and a method for producing a battery using the porous body. To provide.

[0002]

2. Description of the Related Art Thermoplastic fluorinated resins are used in paints, electric / electronic parts, steel pipe linings, chemical plant parts, weather / fouling resistant films, etc. as resins having excellent weather resistance and chemical resistance. However, since a fluororesin generally has a high specific gravity, it has a drawback that it is heavy when formed into a molded product.
On the other hand, it has been attempted to make porous as a separation membrane by utilizing chemical resistance. For example, polyvinylidene fluoride (hereinafter PV
(Hereinafter abbreviated as DF) is dissolved in a solvent to form a wet film, and then the solvent is removed to form a porous body (Japanese Patent Publication No. 59-1269).
No. 1), a method of mixing inorganic particles to form a film, and then removing the inorganic particles (Japanese Patent Publication No. 62-17614, Japanese Patent Publication No. 61-242602, Japanese Patent Laid-Open No. 3-215535).
(Japanese Patent Publication No. JP-A-2003-101, etc.), a method of blending an extractable resin and extracting the resin after film formation (Japanese Patent Publication No. 57-10888, etc.), and mixing a leasable filler and sinter-molding, followed by filling the filler. (For example, JP-A-51-134761), a poorly compatible resin is blended to form a film, which is then stretched to form a crack at the interface between the poorly compatible resin and the matrix resin, thereby providing porosity. Method (Japanese Patent Publication No. 52-26788), PVD
A method in which F is mixed with a foaming agent to be molded and foamed (Japanese Patent Application Laid-open No. Sho 6-96).
1-533336, JP-A-1-268730, etc.), a method of rolling PVDF to a thickness of ½ or less and then stretching (JP-A-58-157831, etc.), PVD
A large number of methods and porous bodies made from them, such as a method of irradiating the F film with charged particles in an active gas atmosphere and then chemically etching it (Japanese Patent Publication No. 60-29742, Japanese Patent Laid-Open No. 3-38228, etc.) Proposed.

However, these use a large amount of solvent for wet film formation, remove other components after adding them, or etch them by special means.
There is a problem that equipment and a special device for collecting the solvent and the additive are required, and that the performance and the physical properties are deteriorated by the solvent and the additive remaining in the matrix polymer.

On the other hand, separators used in non-aqueous batteries such as lithium batteries prevent short circuit between positive and negative electrodes,
By holding the electrolytic solution in the innumerable holes formed in the separator, it plays a role of ensuring conductivity. Typical examples thereof include a porous film made of polyethylene (PE) or polypropylene (PP), a two-layer film in which PE and PP are bonded together, and a three-layer film in which PE is sandwiched between PP. However, PE and PP are flammable materials, and particularly in lithium batteries, materials with higher safety are required.

Furthermore, recently, a lithium battery has been proposed in which a vinylidene fluoride-based copolymer film is swollen with a solution prepared by dissolving a Li salt such as LiPF ₆ in a carbonate-based solvent to be used as a separator (Japanese Patent Laid-Open Publication No. 8-
507407 and flats 8-509100). However, a vinylidene fluoride-based copolymer film swollen with a solvent has insufficient temperature resistance at high temperature (50 ° C. or higher), or has poor battery characteristics such as capacity at low temperature (0 ° C. or lower). easy.

[0006]

The present invention is based on the conventional PV.
In order to eliminate the defects in the DF-based porous body and the battery separator, a study has been made to obtain a PVDF porous body which is light in weight and excellent in mechanical strength and a battery separator / separator and a battery made of the same by a physical means without using a solvent or an additive. As a result, the present invention has been reached.

[0007]

The present invention comprises a thermoplastic fluororesin containing at least 90% by weight of vinylidene fluoride as a constitutional unit of resin, and has a width (minor axis) of 0.1.
~ 3 μm, length (major axis) 0.5 to 20 μm of flat fluororesin, characterized by having a porous fluororesin porous body, and polyvinylidene fluoride melt extruded into a sheet or hollow, A thermoplastic fluorine-based resin characterized by having an apparent specific gravity of 1.7 or less by heat-treating to obtain a crystallinity of 40% or more and then cold drawing to generate a large number of flat pores. A method for producing a porous body, a battery separator comprising the porous body, and a method for producing a battery using the same.

In the present invention, "thermoplastic fluorocarbon resin"
Is a thermoplastic fluorine-based resin containing at least 90% by weight, preferably 95% by weight or more, of vinylidene fluoride as a structural unit of the resin. Therefore, the copolymer is not limited to a homopolymer composed of one kind of monomer, and may be a copolymer containing other components in an amount of 10% by weight or less as long as the characteristics of the thermoplastic fluororesin are not impaired. When the copolymerization rate exceeds 10% by weight, it is difficult to obtain the porous body of the present invention. Examples of the copolymerizable component include ethylene tetrafluoride, ethylene trifluoride, ethylene trifluoride chloride, vinyl fluoride, propylene hexafluoride, ethylene, and perfluoroalkyl vinyl ether. The thermoplastic fluororesin is obtained by a commonly used polymerization method such as emulsion polymerization or suspension polymerization.
A value of 0.1 to 500 g / 10 minutes is preferable.

The thermoplastic fluororesin of the present invention can be blended with a small amount of another type of polymer for modification, and also has conventionally known antioxidants, thermal decomposition inhibitors, ultraviolet absorbers and hydrolysis resistance improvement. Agent, colorant (dye, pigment), antistatic agent, conductive agent, crystal nucleating agent, crystallization accelerator, plasticizer, lubricant, lubricant, mold release agent, flame retardant, flame retardant aid, reinforcing agent, filling An agent, an adhesion aid, a pressure sensitive adhesive, etc. can be optionally contained.

The porous body of the present invention has a width (minor diameter) of 0.1 to 3.
It has flat pores with a diameter of 0.5 μm and a length (major axis) of 0.5 to 20 μm. If the pore size is too small, it is difficult to exert the effect of lowering the specific gravity, and conversely, if it is too large, the filtering effect and the mechanical strength decrease. A width of 0.2 to 2 μm and a length of 0.5 to 15 μm are preferable.

The apparent specific gravity of the porous material of the present invention is preferably 1.7 or less. More preferably, it is 1.6 or less and 1.2 or more. Although the apparent specific gravity can be further reduced by increasing the pore size or increasing the number of pores, it is not only technically difficult, but it is not preferable from the viewpoint of membrane performance and strength.

The porous body of the present invention is mainly in the form of a sheet or hollow. "Sheet" means thick (m
m-order) plates to thin (μm-order) films are included, and "hollow" means thick pipes to thin tubes, hollow fibers, blown films, and the like. Needless to say, it includes a sheet-shaped product obtained by cutting an inflation film.

The porous body of the present invention can be produced by melt-extruding the thermoplastic fluororesin above the melting point and below the decomposition temperature, cooling and solidifying, and then carefully cold-drawing. Of course, other than extrusion molding, other methods such as injection molding and rotational molding can be used. The draw ratio depends on the type of resin (copolymerization rate) and extrusion / cooling conditions, but is 1.1
˜6 times and less than the breaking stretch ratio, preferably 1.2 to 4 times. Stretching may be uniaxial or biaxial (simultaneous or sequential), but in the case of multi-stage stretching, the shape of the pores tends to be largely determined by the conditions of the first stage, so caution is required.
It is difficult to obtain the porous body of the present invention by hot stretching.

The porous body of the present invention is heat treated before cold drawing,
When the crystallinity is 40% or more, it can be more easily produced, and it is more preferable to fix the structure by re-heat treatment after cold drawing. Recommended heat treatment temperature is 70-155 ° C, preferably 100-1
50 ° C. The heat treatment may be in a free state, limited contraction, constant length, or a tensioned state, but in the case of a tensioned state, 10
% Or less, preferably 5% or less. The point is that the spherulites generated when melted and solidified are not destroyed, and it is preferable to grow them in a state before they are destroyed and transferred to fine crystals.

The porous material of the present invention has a high energy (usually 2
It is possible to introduce crosslinks by irradiation with electron beams or γ-rays from 1 to 40 megarads or by chemical de-HF reaction. This makes it possible to improve the heat resistance and mechanical strength of the porous body.

[0016]

The porous material of the present invention is useful not only for various molded products, but also for filtration materials such as filters and separation membranes such as battery separators, and also has functionality by supporting ion-exchange groups and adsorptive substances. It is also expected as a raw material for the added film.

In particular, when applied to a lithium battery, the porous body (usually in the form of a film) of the present invention can be used as a separator or an electrode complexed with an electrode active substance. In the separator, LiPF ₆ , LiBF ₄ , LiCl
At least one lithium salt selected from O ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiCF ₃ SO ₃ , LiSbF _{6 and the} like is mixed with a suitable solvent (mainly ethylene carbonate, propylene carbonate, dimethyl carbonate, etc.). It is used in a state where the porous film is impregnated with an electrolyte solution prepared by dissolving it in a carbonate system) and the pores are filled with the electrolyte solution.
The present porous body can also be used as a support for a gel electrolyte (polymer gel swollen with a solution containing an electrolyte).

Further, the porous body of the present invention is a nickel-hydrogen battery, a silver-zinc battery, a lead-acid battery, a zinc-air battery,
It can be used as a separator or an electrode support in nickel-cadmonium batteries, alkaline batteries, zinc bromide batteries and the like.

[0019]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but it goes without saying that the present invention is not limited to these examples. The various characteristics in the examples are measured and evaluated by the following methods. (1) Melt index (M
FR) According to ASTM D1238, 230 ℃, 12.5kg
The load was measured. Unit g / 10 minutes. (2) Apparent specific gravity The value obtained by dividing the weight of the sample by the width * length * thickness of the sample was taken as the apparent specific gravity. (3) Crystallinity Using a differential calorimeter (DSC), the enthalpy of crystal fusion when heated at 10 ° C./min was divided by 104.5 J / g (reference value for 100% polyvinylidene fluoride crystals). It is shown as a percentage of the value. (4) Tensile strength and elongation The sample was cut into a strip with a width of 15 mm, and the gap between chucks was 5
The value obtained by dividing the breaking strength when pulled at 0 mm and a pulling speed of 50 mm / min by the cross-sectional area before pulling was taken as the tensile strength. Tensile elongation means elongation at break.

[0020]

Example 1 A vinylidene fluoride homopolymer of MFR11 was melted at 240 ° C. using a uniaxial extruder with a T-die having a width of 15 cm, and the thickness was about 200 μm on a cooling drum having a surface temperature of 20 ° C. Extruded as a sheet of. The crystallinity of this sheet was 38%. The sheet was uniaxially stretched 2.5 times between the two rolls at room temperature (23 ° C.). Both ends were slightly necked in, but a slightly whitened film having a thickness of 105 μm was obtained. When the film was observed under a microscope, it was confirmed that a large number of flat pores having a width of about 0.5 to 1 μm and a length of about 1 to 10 μm were present. The apparent specific gravity is 1.
6. Tensile strength and elongation are 130 MPa and 150%, and the physical properties of the raw sheet before stretching are 1.78 and 60 MPa, respectively.
It was found that the specific gravity was 10% or more lower than that of 250%, the strength was more than doubled, and sufficient elongation was maintained.

[0021]

Example 2 The raw sheet obtained in Example 1 was heated at 130 ° C. for 3 days.
After performing a constant length heat treatment for 0 minutes, the crystallinity was 45%. A film having a thickness of about 120 μm obtained by stretching this sheet 2.1 times at room temperature has an apparent specific gravity of 1.58, a tensile strength and elongation of 140 MPa, 110%, and a width of about 1 when viewed with a microscope.
A large number of relatively uniform flat pores having a size of μm and a length of 5 to 10 μm were observed.

[0022]

[Comparative Example 1] The raw sheet obtained in Example 1 was heated at 120 ° C for 3 days.
When stretched twice, the tensile strength was dramatically improved to 190 MPa, but the apparent specific gravity was 1.79, and no pores were observed. No pores were observed when the hot-stretched film was cold-stretched 1.3 times.

[0023]

Example 3, Comparative Example 2 Hexafluoropropylene 4
% Polyvinylidene fluoride of MFR5 copolymerized (Example 3) and polyvinylidene fluoride of MFR7 copolymerized with 14% of hexafluoropropylene (Comparative Example 2) at 230 ° C. in the same equipment used in Example 1, respectively. 220 ° C
Then, it was extruded to obtain a raw sheet. Both were cold-stretched 3.5 times, but in the film of Example 3, pores having a width of 0.3 to 3 μm and a length of 0.8 to 8 μm were observed, whereas the film of Comparative Example 2 was thin. No holes were observed.

[0024]

Example 4 100 parts by weight of coal pitch coke crushed by a ball mill as a negative electrode active material-supporting material was used as a binder, polyvinylidene fluoride (manufactured by Elf Atchem, Kainer 500, 230 ° C., under 2.16 kg load). 10 parts by weight (having an MFR of 0.03 g / 10 min.) Was added to a solution of N-methylpyrrolidone to form a slurry (paste). This slurry has a thickness of 20 μm
After applying on both sides of the copper foil of, and left for 1 hour at 120 ℃,
It was dried under reduced pressure and pressed to obtain a negative electrode having a thickness of 140 μm and a width of 20 mm.

Next, a positive electrode was obtained as follows. 100 parts by weight of LiCoO ₂ as a positive electrode active material and 6 parts by weight of graphite as a conductive agent were dispersed in 10 parts by weight of polyvinylidene fluoride as a binder in N-methylpyrrolidone to form a slurry (paste). . This slurry is applied to both sides of an aluminum foil having a thickness of 20 μm,
After leaving at 120 ° C. for 1 hour, vacuum drying and pressing were performed to obtain a positive electrode having a thickness of 175 μm and a width of 20 mm.

Further, the obtained negative electrode, positive electrode, and separator were manufactured in the same manner as in Example 1 and had a thickness of 30 μm.
Using a porous film of m, a separator, a negative electrode, a separator, a positive electrode, and a separator were laminated in this order, and then the spirally wound electrode body was produced by spirally winding the laminated body. Then, after attaching a lead wire to each electrode of the electrode body, the electrode body was housed in a stainless steel can, and 1 M of LiPF ₆ was dissolved in an equal volume mixed solvent of propylene carbonate and 1,2-dimethoxyethane as an electrolytic solution. The injected solution was injected.

In the charge / discharge test, a current density of 30 mA / g of carbon was used to initially charge the battery to 4.1 V, and then the same current was discharged to 2.5 V. After the second time, charging and discharging were repeated under the same conditions, and the battery was evaluated by the discharge capacity. As a result, the discharge capacity at the 100th cycle was as good as 60% or more of that at the 10th cycle.

[0028]

As described above, the porous body of the present invention is lightweight and has excellent mechanical properties and is useful for various filtration materials, separation membranes and the like. Further, when applied to a separator such as a lithium battery, PVDF is flame-retardant, so that the battery has higher safety than the case where a polyethylene separator is used.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical display location C08L 27:12 (72) Inventor Yoshiyuki Miyaki 1 Awata-cho, Nakado-ji, Shimogyo-ku, Kyoto, Kyoto Elf Atchem Japan Co., Ltd. Kyoto Technical Center

Claims (12)

[Claims] 1. A thermoplastic fluororesin containing at least 90% by weight of vinylidene fluoride as a constitutional unit of a resin, having a width (minor axis) of 0.1 to 3 μm and a length (major axis).
A thermoplastic fluororesin porous body having a flat pore size of 0.5 to 20 μm. 2. The thermoplastic fluororesin porous material according to claim 1, wherein the porous material is a sheet-shaped material or a hollow material. 3. A thermoplastic resin characterized in that an apparent specific gravity is 1.7 or less by melt-extruding polyvinylidene fluoride into a sheet shape or a hollow shape and then cold-stretching to generate a large number of flat pores. Method for producing porous fluororesin. 4. Polyvinylidene fluoride is melt extruded into a sheet shape or a hollow shape and then heat-treated to obtain a crystallinity of 40%.
A method for producing a thermoplastic fluororesin porous material, which has an apparent specific gravity of 1.7 or less by forming a large number of flat pores by the above-mentioned cold stretching. 5. Polyvinylidene fluoride is melt extruded into a sheet shape or a hollow shape and then heat treated to have a crystallinity of 40%.
After the above, cold drawing is performed to generate a large number of flat pores,
The method for producing a thermoplastic fluororesin porous material according to claim 1, wherein the pores are fixed by subsequent heat treatment. 6. The method for producing a thermoplastic fluororesin porous material according to claim 1, wherein the polyvinylidene fluoride is melt-extruded into a sheet or hollow shape, cold-stretched, and crosslinked by radiation or chemical treatment. 7. A battery comprising an anode, a cathode, and a separator, wherein at least one of the separator and the electrode.
Is composed of a thermoplastic fluororesin porous material, and the thermoplastic fluororesin porous material is composed of a thermoplastic fluororesin containing at least 90% by weight of vinylidene fluoride as a constitutional unit of the resin, and has a width (minor diameter). 0.1-3 μm,
A method for producing a battery having flat pores having a length (major axis) of 0.5 to 20 μm. 8. A thermoplastic fluororesin porous material having a specific gravity of 1.7 or less is obtained by melting and extruding polyvinylidene fluoride into a sheet and then cold-drawing to produce a large number of flat pores. The method for manufacturing a battery according to claim 7, wherein the battery is a battery. 9. The method for producing a battery according to claim 7, wherein the thermoplastic fluororesin porous material is crosslinked by radiation or chemical treatment. 10. A thermoplastic fluororesin containing at least 90% by weight of vinylidene fluoride as a constitutional unit of the resin, having a width (minor axis) of 0.1 to 3 μm and a length (major axis).
A battery separator comprising a thermoplastic fluororesin sheet having flat pores of 0.5 to 20 μm. 11. The polyvinylidene fluoride is obtained by melting and extruding polyvinylidene fluoride into a sheet and then cold-drawing to produce a large number of flat pores with an apparent specific gravity of 1.7 or less. The battery separator according to claim 10. 12. The battery separator according to claim 10, which is crosslinked by radiation or chemical treatment.