JP2002050336A - Separator for zinc halogen battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a zinc halogen battery with excellent heat resistance and electric characteristics. SOLUTION: The separator consists of polyethylene of viscosity-average molecular weight of 50 thousand or more and less than 350 thousand and fine powder silica, of which, molecular weight distribution (Mw/Mn) of polyethylene is 8 or less and partial rate of polyethylene at a film surface not including the cut surface of the separator is 30% or more and 75% or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a zinc halide battery, and more particularly to a separator used for a zinc bromine battery.

[0002]

2. Description of the Related Art The characteristics required of a separator generally used in a zinc halide battery are as follows. 1) It has ion conductivity, low resistance of the separator, and a function of reducing self-discharge of zinc and halogen generated in the bipolar chamber. 2) A stable film that prevents the diffusion of halogen particularly generated at the anode and does not deteriorate the separator due to the strongly oxidizing halogen. 3) The film must have a long life with little swelling and bending of the film. 4) The manufacturing cost of the separator is low and it is easy to obtain. At present, ion separators, fluorinated resinous porous membranes, and polyolefin porous membranes are used as separators that can be considered in terms of the above characteristics. Among them, a separator made of polyethylene and finely divided silica as disclosed in JP-B 5-27233 is one which is inexpensive and has excellent oxidation resistance.

However, the separator described in Japanese Patent Publication No. 5-27233 is disclosed in Japanese Patent Application Laid-Open No. Sho 62-1794.
As described in Japanese Patent Publication No. 5, there is a problem that an electrode frame is attached to a separator by injection molding or the separator is cracked by heating in a sealing process using a hot plate or an ultrasonic wave. In order to solve this drawback, a technique of blending ultra-high molecular weight polyethylene as disclosed in JP-A-9-231957 is disclosed. However, although heat resistance and stress crack resistance are increased, a polyethylene film is formed on the film surface, and the electric property is poor due to the deterioration of the surface wettability of the electrolytic solution or the fusion time to the frame is long. Therefore, there was a problem that the separator was deformed.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a zinc halide battery separator having excellent heat resistance and electrical properties.

[0005]

Means for Solving the Problems The present inventor has solved the above problems. That is, the present invention is a separator comprising polyethylene having a viscosity average molecular weight of 50,000 or more and less than 350,000 and finely divided silica, wherein the polyethylene has a molecular weight distribution (Mw / Mn) of 8 or less and does not include a cut surface of the separator. The percentage of polyethylene on the surface is 30% or more 7
The present invention relates to a zinc-halogen battery separator characterized in that the content is 5% or less.

Hereinafter, the present invention will be described in detail. The polyethylene constituting the separator for a zinc halide battery of the present invention has a viscosity average molecular weight of 50,000 or more and less than 350,000, and preferably 100,000 to less than 350,000. When the viscosity average molecular weight is less than 50,000, the mechanical strength becomes poor, and the separator becomes poor in stress crack resistance. If the viscosity average molecular weight exceeds 350,000, the adhesiveness becomes poor.

The molecular weight distribution Mw / Mn of the polyethylene constituting the separator for a zinc-halogen battery of the present invention must be 8 or less, preferably 7 or less, more preferably 6 or less. If the molecular weight distribution exceeds 8, the heat resistance will be poor. Examples of such polyethylene include polyolefin polymerized using a metallocene catalyst. In recent years, a technique for polymerizing a polyolefin having a narrow molecular weight distribution using a metallocene catalyst technique or the like has been developed (for example, “Metallocene Polymer Technology and Product Development”, Osaka Chemical Marketing Center version). Recently, a technique for polymerizing high-density polyethylene using a metallocene catalyst has been developed (for example, Kishimoto et al.,
Molding '99, B308, Abstracts of Lectures, edited by Japan Society of Plastics Processing, pages 305-306). Such a resin or the like can be used as polyethylene constituting the present invention.

The polyethylene constituting the present invention includes well-known homopolymers and copolymers such as high-density polyethylene, low-density polyethylene, and linear low-density polyethylene. In particular, a density of 0.9 g / cm ³ or more
0.99 g / cm ³ , more preferably 0.93 g / cm ³
A separator made of a polyethylene resin made of a high-density polyethylene resin having a density of cm ^{3 to} 0.98 g / cm ³ is preferable because of good heat resistance. Further, such a polyethylene resin may be a mixture of the above-mentioned polyethylenes, or may be mixed with another polyolefin resin such as polypropylene. Also,
If necessary, additives such as an antioxidant, an ultraviolet absorber, a lubricant, an antiblocking agent, a coloring agent, and a flame retardant may be added as long as the object of the present invention is not impaired.

In the present invention, the polyethylene portion of the surface of the separator not including the cut surface is not less than 30% and not more than 75%.
% Or less. If it exceeds 75%, the electrical properties will be poor, and if it is less than 30%, the mechanical strength will be poor. The separator of the present invention has a porosity of 30.
It is preferably in the range of 80%. 30% porosity
If it is less than 80%, the electrical properties will be poor, and if it is more than 80%, the mechanical strength will be poor.

The thickness of the separator of the present invention is 0.2 mm to
It is preferably 1.4 mm, more preferably 0.4 mm to 0.8 mm. When the film thickness is larger than 1.4 mm, the electrical properties tend to be poor, and when the film thickness is smaller than 0.2 mm, the mechanical strength tends to be poor. The zinc-halogen battery separator of the present invention uses, for example, a polyethylene resin having a viscosity average molecular weight of 50,000 to 350,000, a polyethylene molecular weight distribution (Mw / Mn) of 8 or less, and a polyethylene / fine silica powder weight ratio of 0.5. Above 2
Hereinafter, it can be obtained by extrusion-molding an organic liquid material / fine-powder silica at a weight ratio of 1.5 to 3.5, and then extracting and drying the organic liquid material. By adopting such a composition and the processing conditions described later, the polyethylene ratio of the film surface not including the cut surface of the separator is 30% or more and 7% or more.
It can be 5% or less.

First, a polyethylene resin having a viscosity average molecular weight of 50,000 to 350,000 and a polyethylene molecular weight distribution (Mw / Mn) of 8 or less, and a weight ratio of polyethylene / fine silica powder of 0.5 to 2 and an organic liquid Polyethylene, an organic liquid and fine silica are mixed so that the weight ratio of the fine silica is 1.5 or more and 3 or less. If the weight ratio of polyethylene / fine silica exceeds 2, the electrical properties will be poor, and if it is less than 0.5, the mechanical strength will be poor,
It is inferior in stress crack resistance. If the weight ratio of the organic liquid / micronized silica is less than 1.5, the moldability tends to be poor, and if it exceeds 3.5, the extrudability tends to be poor.

The mixture used as the organic liquid must be liquid at the time of melt molding and inert. Examples include phthalic acid esters and phosphates such as diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DnOP), bis (2-ethylhexyl) phthalate (DOP), and liquid paraffin. And the like. Of these, DBP, DnOP, DOP and mixtures thereof are particularly preferred. Examples of the finely divided silica include hydrophilic wet silica, dry silica, and hydrophobic silica obtained by surface-treating these finely divided silicas. It is preferable to use hydrophilic finely divided silica because of its excellent electrical characteristics. .

For mixing these three components, polyethylene, finely divided silica, and an organic liquid, an ordinary mixing method using a blending machine such as a Henschel mixer, a V-blender, a pro-share mixer, a ribbon blender is sufficient. As for the mixing order of the three components, rather than mixing the three components at the same time, first, the fine silica and the organic liquid are mixed, the organic liquid is sufficiently adsorbed on the fine silica, and then the polyethylene resin is blended and mixed. This is effective in improving the melt moldability and the porosity and uniformity of the obtained porous material. This mixture is kneaded by a melt kneading device such as an extruder or a kneader. The resulting kneaded material is formed into a sheet by melt molding using a T die. In this case, molding via a gear pump is preferable from the viewpoint of dimensional stability, and it is particularly preferable to perform molding by controlling the pressure before the gear pump at a constant level from the viewpoint of dimensional stability.

Further, in the present invention, as a cooling method at the time of melt-extruding the kneaded material, a method of cooling with air, a method of contacting with a roll whose temperature is lower by 20 to 120 ° C. than the temperature of the resin discharged from the T-die, is employed. A method of cooling can be adopted, in which a roll is formed by calendering with a calender roll that is 20 to 120 ° C. lower than the temperature of the T-die discharge resin and is cooled while being formed into a sheet.
It is preferable to adopt a method of cooling while rolling into a sheet by calendering with a calender roll lower by ~ 120 ° C in terms of film thickness uniformity. When a roll is used, the contact between the T die and the roll sheet is preferably used. The molding is preferably performed at a distance in the range of 100 to 500 mm. By molding under such conditions, the percentage of polyethylene on the surface not including the cut surface of the separator can be 30% or more and 75% or less. The die discharge temperature can be measured by using a usual thermocouple thermometer so that the terminal does not touch the die and is brought into contact with the discharged resin.

Next, the organic liquid in the film obtained by these methods is extracted with a solvent. As a solvent used for extracting the organic liquid, an organic solvent such as methanol, ethanol, methyl ethyl ketone and acetone, and a halogenated hydrocarbon solvent such as methylene chloride can be used. As described above, the separator for a zinc-halogen secondary battery of the present invention can be manufactured.

[0016]

Embodiments of the present invention will be described below. Various physical properties shown in this example were measured by the following measurement methods. (1) Polyethylene viscosity average molecular weight (Mv) Dissolve a separator from which silica is extracted by a method for producing a polyethylene single film described below in a solvent (decalin), measure the intrinsic viscosity [η] at a measurement temperature of 135 ° C., and calculate from the following equation. did. [Η] = (6.2 × 10 ⁻⁴ ) × Mv ^0.7 (Chiang
(2) Polyethylene melt index (MI) A separator from which silica was extracted by a method for producing a single polyethylene film was pulverized. Unless otherwise specified, ASTM-D was used.
It measured according to -1238.

(3) Polyethylene Molecular Weight Distribution (Mw / Mn) A separator from which silica was extracted by a method for producing a single polyethylene film was dissolved and measured by GPC. GPC measuring device: WATERS 150-GPC Temperature: 140 ° C Solvent: 1,2,4-trichlorobenzene Concentration: 0.05% (injection amount: 500 microliter) Column: Shodex GPC AT-807 / S1
Book, Tosoh TSK-GEL GMH6-HT 2
This dissolution condition: 160 ° C., 2.5 hours Calibration curve: Measure a standard sample of polystyrene, and use a polyethylene conversion constant (0.43).
A calibration curve was calculated using a cubic curve. (4) Polyethylene density (g / cm ³ ) The membrane obtained by the polyethylene simple membrane fabrication method was made transparent by cold pressing, air was not included in the membrane, and the density was measured using a density gradient tube. did.

(5) Film thickness (mm) Measured with a micrometer. (6) Porosity (%): Porosity calculated from the following equation = (1- (0.1 × X / (Y × Z))) × 100 X: Weight of film (g / dm ² ) Y: The specific gravity (g / cm ³ ) of the membrane was calculated using the density of polyethylene and the specific gravity of fine silica of 1.9 and the composition ratio obtained from the polyethylene / silica composition analysis method described later. Z: film thickness (mm) (7) Surface polyethylene partial ratio It was measured from an SEM photograph by an image analyzer. SEM: S-4100 (FE-SEM) Hitachi, Ltd. Acceleration voltage: 3 kV Pretreatment: Pt-Pd deposition 0.1 Torr, 0.5 m
A, 15 seconds × 4 times D: 15mm

The film surface is photographed at a magnification of 5000 under the above conditions. The aperture knob of this photo is 0.96-0.98
After adjusting the illuminance, the image was taken into a computer using a CCD camera, and the area of the white portion in the photograph was calculated “automatically” using the image analysis software Quantimet 500 (trade name) manufactured by Leica. . The analysis range was 5 cm long × 8 cm wide. This is performed three times for one sample, and the average is defined as the surface silica ratio (%).
Subtracting the surface silica ratio from 100% gave the surface polyethylene partial ratio. (8) Electric properties Evaluation was made based on electric resistance according to JIS C-2313. (9) Polyethylene single membrane production method The separator was immersed in alcohol, air was roughly extracted, and then immersed in a 20% aqueous solution of caustic soda at 80 ° C for one day.
After washing with warm water of 60 ° C., washing was carried out with running water all day and night. The film was dried all day and night with a dryer set at 40 ° C.
A part of the prepared film is measured by a residual silica measuring method described later, and it is confirmed that the residual silica amount is 1 wt% or less.

(10) Method of analyzing composition of polyethylene / silica Thermogravimetric analyzer TG / D manufactured by Seiko Denshi Kogyo KK
Using TA220, the composition was calculated from the initial weight of about 10 mg of the sample in an air stream and the weight after being left at 550 ° C. for 60 minutes. (11) Residual silica analysis method A weighted separator was put into a crucible having a constant weight in advance, left at 900 ° C. for 3 hours, and the weight of the polyethylene in the crucible after being completely incinerated was measured. Residual silica wt% was evaluated by weight / separator weight. (12) Heat resistance The rate at which the film was deformed when the operation of welding the separator to the polyethylene frame by ultrasonic welding was performed 20 times.

[0021]

Example 1 Polyethylene having the following properties was polymerized using a metallocene catalyst. MI = 0.01 g / 10 min, Mw / Mn = 4.1 23 wt% of this polyethylene, 20 wt% of finely divided silica, and bis (2-ethylhexyl) phthalate (DOP) 57 w
t% was mixed with a super mixer. 30
A T-die having a width of 450 mm was attached to a mmφ twin-screw extruder, and the T-die was extruded at a resin temperature of 220 ° C.
At this time, in order to provide dimensional stability, melt extrusion was performed with a constant pressure before the gear pump via a gear pump. T
The resin extruded from the die was roll-formed with a calender roll controlled at 140 ° C. to form a sheet having a thickness of 0.65 mm.

The formed sheet is immersed in methylene chloride for 1 hour to prepare bis (2-ethylhexyl) phthalate (D
OP) was extracted and dried. Table 1 shows the characteristics of the separator thus obtained.

[0023]

Example 2 Polyethylene having the following properties was polymerized using a metallocene catalyst. MI = 0.09 g / 10 min, Mw / Mn = 5.4 A separator was obtained in the same manner as in Example 1 except that the above polyethylene was used. Table 1 shows the characteristics of the obtained separator.
Shown in

[0024]

Comparative Example 1 Polyethylene having the following characteristics was polymerized using a Ziglana catalyst. MI = 0.23 g / 10 min (5 kg), Mw / Mn
= 9 A separator was obtained in the same manner as in Example 1 except that the above polyethylene was used. Table 1 shows the characteristics of the obtained separator.
Shown in

[0025]

Comparative Example 2 28% by weight of polyethylene of Example 1 and 52% by weight of bis (2-ethylhexyl) phthalate (DOP)
% And 20 wt% of finely divided silica were mixed with a super mixer. This mixture was attached to a 30 mmφ twin screw extruder with a T die having a width of 450 mm, and the resin temperature of the T die discharged was 220 ° C.
And extruded. Thereafter, a separator was obtained in the same manner as in Example 1. Table 1 shows the properties of the obtained separator.

[0026]

[Comparative Example 3] 23 wt% of finely divided silica and bis (2
-Ethylhexyl) (DOP) 54 wt% was mixed with a super mixer, and the viscosity average molecular weight was 3,000,000.
9 wt% ultra high molecular weight polyethylene, viscosity average molecular weight 3
00000 high molecular weight polyethylene 14wt%,
The mixture was mixed again with a super mixer. A separator was obtained in the same manner as in Example 1 except that this mixture was used. Table 1 shows the properties of the obtained separator.

[0027]

[Table 1]

[0028]

According to the present invention, a zinc-halogen battery separator excellent in heat resistance and electrical properties can be obtained.

Claims (1)

[Claims] 1. A separator comprising polyethylene having a viscosity average molecular weight of 50,000 or more and less than 350,000 and finely divided silica, wherein the polyethylene has a molecular weight distribution (Mw / Mn) of 8 or less and does not include a cut surface of the separator. Wherein the percentage of polyethylene is 30% or more and 75% or less.