JPH05283053A - Separator for sealed lead-acid battery - Google Patents

Abstract

PURPOSE:To ensure the low cost, high water retentivity and acid resistance, and low density of a separator without use of glass fiber, and provide a sealed lead-acid battery having large discharge capacity at low temperature, using the separator. CONSTITUTION:A material mainly comprising a polyolefine synthetic pulp and a binder having a fusion point lower than the synthetic pulp are mixed and formed into a sheet at a dry process. Also, the sheet is subjected to heat treatment at a temperature lower than the fusion point of the pulp, or at a temperature equal to or above the fusion point of the binder, thereby providing a porous mat for a lead-acid battery separator. The polyolefine synthetic pulp preferably has a specific surface area equal to or above 1m<2>/g on the basis of the BET adsorption method. Also, the separator is subjected to hydropholic treatment, using the water solution of a surface active agent, thereby enabling the water retentivity of the mat to be all the more improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealed lead-acid battery separator composed of a porous mat, and more specifically, a porous material obtained by dry-making a raw material mainly composed of a polyolefin-based synthetic pulp. The present invention relates to a sealed lead-acid battery separator made of a mat.

[0002]

2. Description of the Related Art There are two types of sealed lead-acid batteries, a retainer type and a gel type, in which a negative electrode absorbs oxygen gas generated from a positive electrode during charging of the battery. The retainer type inserts a mat-shaped separator having a liquid retaining property between the positive electrode plate and the negative electrode plate, thereby maintaining the electrolytic property necessary for discharging the battery and isolating the electrode, and maintenance-free, In recent years, it has come to be used as a backup power source for portable devices, computers in an emergency (power failure), or a power source for automobiles, etc., by taking advantage of its characteristics such as no leakage and position-free. For retainer type sealed lead-acid batteries, mats made of ultrafine glass fibers (hereinafter referred to as glass separators) and the like are generally used (for example, JP-A-60-1011861 and JP-A-59-). 7384
No. 2), and a separator made of a polyolefin-based wet non-woven fabric has also been proposed (JP-A-62-268).
See Japanese Patent Publication No. 900).

[0003]

However, in a separator using ultrafine glass fiber, it is difficult to say that it is an industrially suitable material because the glass fiber is very expensive. In order to have sufficient liquid retaining property, the separator must be made bulky, and as a means for that, it is necessary to mix glass fibers and the like, and the cost disadvantage is unavoidable.

On the other hand, in general, batteries used for many purposes are demanded to be lightweight and high in capacity.
In particular, even for retainer type sealed lead-acid batteries, there is a strong demand for rapid market expansion and further weight reduction and higher capacity of batteries for portable devices, backup power supplies, automotive power supplies and the like.

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a separator for a sealed lead-acid battery, which has a reduced cost, an improved low-temperature high-rate discharge capacity, an excellent discharge characteristic of the battery, and a light weight. Especially.

[0006]

The present invention has been proposed in order to achieve the above-mentioned object, and as a separator, a mat made of a material mainly composed of a polyolefin-based synthetic pulp made porous by a special method. It is characterized by using. That is, according to the present invention, it comprises a porous mat obtained by dry-making 100 to 50% by weight of a polyolefin synthetic pulp and 0 to 50% by weight of a binder having a melting point lower than that of the synthetic pulp. A characteristic sealed lead acid battery separator is provided.
Further, according to the present invention, a polyolefin-based synthetic pulp 9
A sealed lead-acid battery separator, comprising a porous mat obtained by dry-making 8 to 50% by weight and 2 to 50% by weight of a binder having a melting point lower than that of the synthetic pulp. It Further, according to the present invention, the polyolefin synthetic pulp having a specific surface area of 1 m ² / g or more as measured by a BET adsorption method is used, and thus the separator for a sealed lead-acid battery having further excellent characteristics is used. Will be provided.

By using the polyolefin synthetic pulp which has been subjected to a hydrophilic treatment, particularly a hydrophilic treatment using an aqueous solution of a surfactant, a sealed lead-acid battery separator having further excellent physical properties is provided. Furthermore, the strength of the mat can be increased by heat-treating the porous mat to such an extent that the bulkiness is not impaired.
In the range of 5% by weight or less, it is possible to provide a suitable sealed lead-acid battery separator by blending various synthetic fibers, natural pulp, and acid-resistant inorganic powder. Since the separator obtained by the present invention is manufactured by dry-type papermaking in particular, it is characterized in that it does not shrink due to the surface tension of water during drying and can easily be bulky.

Raw Material As the synthetic pulp used as the main material in the present invention, a polyolefin-based synthetic pulp is used, and particularly a solution or emulsion produced by flash spinning is preferably used. Polyolefin synthetic pulp is
It is known per se, and those manufactured by various methods as described below can be used. For details on the production method of polyolefin-based synthetic pulp, see Encyclopedia o
f ChemicalTechnology 3rd ed. Vol. 19 P420 to 425
Examples of the method include a method in which melt-spun fibers are cut into short pieces and then beaten, a method in which solution flash or emulsion flash is performed, and then beaten. Among them, those produced by the emulsion flash method using polyvinyl alcohol (PVA) as a hydrophilic agent are preferably used. In this case, the PVA content is preferably 0.01 to 10% by weight. Moreover, it is preferable that these polyolefin-based synthetic pulps have a specific surface area of 1 m ² / g or more as measured by the BET adsorption method.

Examples of the polyolefin to be used include homopolymers of olefins such as polyethylene and polypropylene, ethylene-propylene copolymers and ethylene-1.
-Butene copolymer, ethylene-4-methylpentene-1
Copolymers of ethylene and other α-olefins such as copolymers are preferable, and crystalline polyolefins are preferably used from the viewpoint of mechanical strength. The polyolefin-based synthetic pulp thus obtained has a fiber length of 0.1 to 10 mm and can be easily subjected to dry papermaking thereafter, and the obtained porous mat has good discharge characteristics of the battery. It also has the features of being excellent, lightweight and inexpensive.

The polyolefin synthetic pulp is
Since the separator itself is hydrophobic, it is possible to use a separator that has been hydrophilized in order to improve the water retention of the obtained separator. Further, in the present invention, as long as the object of the invention is not impaired, for example, in the range of 45% by weight or less, polyester, acrylic, polypropylene,
Various synthetic fibers such as polyethylene, polystyrene, methylmethacrylate, acrylonitrile, vinylidene chloride resin, inorganic pulp such as natural pulp, glass fiber, silica fiber, alumina silicate fiber, slag fiber, silica powder, diatomaceous earth, etc. Acid resistant inorganic powder and the like can be blended as necessary.

Matting In the present invention, it is an important requirement that after the above-mentioned raw materials are mixed, they are dry-processed to be matted. Dry papermaking is mainly a method of using a card or the like to form a sheet of the synthetic pulp in a dried state, for example, the polyolefin synthetic pulp is mixed with a binder having a lower melting point than that, The method called the fiber bond method, in which both are heat-sealed at the melting temperature of the binder, has the shortest process and is simple and economical. As a specific method of the fiber bond method, a hot air penetration type method of heating the above raw material sprinkled on a running mesh-like support from above while vacuuming from below, a formed web is a heat roll By melting the low melting point binder mixed in, fixing the polyolefin-based synthetic pulp, by melting and bonding the formed web with the binder in a heat oven, using an infrared heater or ultrasonic energy. Examples of the method include a method of melting a binder to bond a web, and the like, and a hot air penetration type method is preferably used from the viewpoint of heat treatment temperature and imparting the bulkiness of the product.

In this case, what is used as the binder has a melting point higher than that of the synthetic pulp in the polyolefin synthetic pulp, the polyolefin fiber and the core, and lower than that of the synthetic pulp in the sheath. Selected from the group consisting of so-called sheath-core type composite fibers having a melting point, polyolefin resin powder, low melting point polyester powder, vinyl chloride resin powder, epoxy resin powder, or emulsion thereof, natural or synthetic rubber latex and acrylic emulsion. At least one of the above is exemplified, and among them, it is preferable to use a polyolefin-based synthetic pulp. It is necessary that this binder has a melting point lower than that of the polyolefin-based synthetic pulp as the main raw material, preferably 5 ° C. or more. The mixing ratio of the polyolefin synthetic pulp and the binder is 100 to 50% by weight of the polyolefin synthetic pulp, preferably 98 to 50% by weight, and the binder is 0 to 50% by weight, preferably 2 to 50%.
It is desirable that the content is wt%.

In addition to the above-mentioned method, for example, the air-laid method described in "Paper and Pulp Technology Co., Ltd." Vol. 41, No. 2, or a polyolefin synthetic pulp opened in parallel and a low melting point is used. Examples include a method of randomly arranging the binder with an air flow and thermally adhering the binder. The product obtained by dry papermaking is a bulky (low density) product as compared with wet papermaking, that is, it is possible to obtain a porous mat excellent in water retention with a large porosity, which is an object of the present invention. It can be used very suitably as a lead-acid battery separator.

Hydrophilic treatment In the present invention, the water retention of the mat can be further improved by subjecting the mat obtained as described above to the hydrophilic treatment. This hydrophilic treatment is carried out by, for example, immersing the mat in an aqueous solution of a surfactant,
Alternatively, the mat is sprayed and then dried. As the surfactant used,
Anionic surfactants are preferred. The degree of hydrophilic treatment depends on the amount of the surface active agent deposited, which is 0.05 to 5.0% by weight.
More preferably, it is in the range of 0.2 to 2.0% by weight.

The hydrophilizing treatment is carried out as a synthetic pulp.
It is particularly effective when using those which have not been subjected to hydrophilic treatment. The lead-acid battery separator made of the mat thus obtained has a low density of 0.05 to 0.30 g / cc and is excellent in water retention, and the sealed lead-acid battery using this also has a low temperature and high rate discharge capacity. Are better.

In the separator of the present invention, water retention and maximum pore size are related to the following characteristics of the lead storage battery. Water retention: Generally, the capacity of a lead-acid battery is determined by the amount of active material on the electrode plate and the amount of electrolyte. In the current retainer-type sealed lead-acid battery, the electrolytic solution is limited to that contained in the retainer mat and that contained in the electrode plate. Therefore,
When the plates are the same, the capacity of the battery, especially the capacity under low temperature and high rate discharge depends on the amount of electrolyte contained in the retainer mat, so the retainer mat contains more electrolyte, that is, water retention. It is preferable that the property is excellent.

Maximum pore size: The separator (retainer mat in the case of a retainer-type sealed lead-acid battery) is + electrode plate and-
It is inserted between the electrode plates and plays a role of preventing a contact short circuit between both electrode plates. The lead diameter deposited by repeated charging and discharging and the lead powder that separates from the electrode plate pass through the pores of the separator to short-circuit both electrode plates and shorten the battery life, so the separator pore size should be as small as possible. .. That is, since the life performance of the battery depends on the size of the maximum pore size of the separator, it is preferable that the maximum pore size of the separator is small.

[0018]

EFFECTS OF THE INVENTION According to the present invention, since synthetic pulp mainly composed of polyolefin is used as a raw material, it is superior in water retention and has a maximum maximum hole diameter as compared with the one using synthetic fiber. .. This is because while synthetic fibers made by melt-spinning etc. have a columnar structure, polyolefin-based synthetic pulp is highly branched and has many folds on the surface, so it exhibits such excellent performance. It is thought to be done. Further, according to the present invention, by dry-making synthetic pulp, it is possible to provide a separator having excellent acid resistance and low density and low cost, in particular, a sealed lead-acid battery using this separator is a low temperature high rate discharge. It has the feature of being excellent in capacity.

[0019]

EXAMPLES Example 1 The following materials were used as raw materials. A. High-density polyethylene synthetic pulp Average fiber length 1.0 mm Average fiber diameter 10 μm Melting point 135 ° C. PVA adhesion amount 1.5% Specific surface area 8.2 m ² / g B. Linear low density polyethylene synthetic pulp (low melting point polyethylene synthetic pulp) Average fiber length 1.0 mm Average fiber diameter 30 μm Melting point 125 ° C. PVA adhesion amount 1.2% Specific surface area 2.7 m ² / g C.I. Linter pulp (cellulosic pulp) The raw materials A, B, and C are crushed by a hammer mill crusher, respectively, and then A = 75% by weight, B = 15% by weight, and C = 10% by weight. The mixture was mixed and dry papermaking was carried out by an air raid method to obtain a mat having a thickness of 2.0 mm. On this mat, 132 ℃
Was passed through the hot air for 60 seconds to perform heat treatment. Then, a hydrophilic treatment was carried out with an anionic surfactant (aqueous solution of sodium dialkylsulfosuccinate) to obtain 0.8% by weight of mat. Table 1 shows the physical properties of the obtained mat.

Example 2 As a raw material, D. Silica powder (Nipseal VN3 manufactured by Nippon Silica Industry Co., Ltd.) was used, and the use ratio of each raw material was A = 68% by weight, B = 14% by weight, C = 9% by weight, D =
A mat was obtained in the same manner as in Example 1 except that the content was 9% by weight. Table 1 shows the separator characteristics of the obtained mat.

Example 3 A mat was obtained in the same manner as in Example 1 except that the use ratios of the respective raw materials were A = 85% by weight and B = 15% by weight. Table 1 shows the physical properties of the obtained mat.

Comparative Example 1 Wet-papermaking was carried out using the same raw materials and the same proportions as in Example 1 to obtain a mat having a thickness of 2.0 mm. 1 on this mat
Heat treatment was performed by passing hot air at 32 ° C. for 120 seconds.
Then, a hydrophilic treatment was performed with an anionic surfactant (aqueous solution of sodium dialkylsulfosuccinate) to obtain a mat having a surfactant adhesion amount of 0.8% by weight. Table 1 shows the physical properties of the obtained mat.

COMPARATIVE EXAMPLE 2 For comparison of battery characteristics, a battery using the most general glass separator as a sealed lead-acid battery separator was assembled, and 5 hour rate discharge capacity and low temperature high rate discharge capacity were measured. The results are shown in Table 2.

Comparative Example 3 A mat was prepared in the same manner as in Example 1 except that the following materials were used as the A material. A. Acrylic fiber Average fiber length 5.0 mm Average fiber diameter 13 μm Softening point 200 ° C

Comparative Example 4 The performance of polypropylene melt-blown spun fiber mats (meltblown nonwoven fabrics) was compared for comparison. Average fiber diameter 2 μm

Comparative Example 5 A mat was prepared in the same manner as in Example 1 except that the following materials were used as the materials for A. A. High-density polyethylene synthetic pulp Average fiber length 1.5 mm Average fiber diameter 80 μm Melting point 135 ° C. PVA adhesion amount 0.3% Specific surface area 0.7 m ² / g

[0027]

[0028] The separator characteristics were measured according to JIS C2313.

[0029]Water retention measurement method: Soak the sample in water and fully
After watering, leave it in the air vertically for 1 minute (hang)
Included in the separator against its own weight
% By weight of fresh water.Maximum pore size measurement method : Test piece 25mmφ in methanol solution
Fig. 1 shows the result of immersing in water and replacing the pores with methanol.
With the device, gradually apply pressure to the surface of the test piece.
Ribbon (N ₂ Read the differential pressure at the appearance of
Maximum pore size of the sample from the surface tension of methanol (σ≈23)
Find the diameter.

The calculation formula is σ = Surface tension of methanol dyn / cm g = Gravitational acceleration cm / sec ² H ₂ -H ₁ = Head difference in manometer cm ρ ₁ = Density of liquid in manometer g / cm ³ ρ ₂ = Density of methanol g / cm ³ d = depth of methanol cm

Comparative Example 2 using the same production lot electrode plate as Comparative Example 2 using the separators of each Example and Comparative Example
Assembling a retainer-type sealed lead-acid battery having a nominal capacity of 6 Ah at the same 2 V as above, and measuring the 5-hour rate discharge capacity and the low temperature high rate discharge capacity, the results are shown in Table 2.

[0032]

[0033]

For the 5-hour rate discharge capacity, the time from the start of discharge until the terminal voltage of the battery reached 1.70 V was measured and the time was taken as the discharge capacity. For the low temperature high rate discharge capacity, the time from the start of discharge until the terminal voltage of the battery reached 1.00 V was measured and the time was taken as the discharge capacity. The 5th second voltage is a measurement of the terminal voltage of the battery 5 seconds after the start of discharge when measuring the low temperature high rate discharge capacity.

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus for measuring the maximum pore size of a separator in an example of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Motofumi Nakamura 3-5 Kasumigaseki, Chiyoda-ku, Tokyo Within Mitsui Petrochemical Industries Ltd. (72) Inventor Motoyuki Ezaki 3-5-5 Kasumigaseki, Chiyoda-ku, Tokyo No. Mitsui Petrochemical Industry Co., Ltd. (72) Inventor Yoshitaka Tanaka, Takatsuki Town, Ika-gun, Shiga Prefecture Iguchi character Shimowasada 1400-1

Claims (8)

[Claims] 1. A porous mat obtained by dry-making 100 to 50% by weight of a polyolefin synthetic pulp and 0 to 50% by weight of a binder having a melting point lower than that of the synthetic pulp. Sealed lead acid battery separator. 2. The sealed lead acid battery separator according to claim 1, wherein the blending ratio of the polyolefin synthetic pulp / the binder is 98 to 50% by weight / 2 to 50% by weight. 3. The sealed lead-acid battery separator according to claim 1, wherein the melting point or curing temperature of the binder is lower than the melting point of the polyolefin synthetic pulp by 5 ° C. or more. 4. The sealed lead-acid battery separator according to claim 1, wherein the polyolefin synthetic pulp is hydrophilically treated. 5. The sealed lead-acid battery separator according to claim 1, wherein the porous mat has been subjected to hydrophilic treatment using an aqueous surfactant solution. 6. The sealed lead-acid battery separator according to claim 1, wherein the porous mat is heat-treated to such an extent that the bulkiness is not impaired to increase the strength of the mat. 7. The sealed lead-acid battery separator according to claim 1, wherein various synthetic fibers, natural pulp, inorganic fibers, or acid-resistant inorganic powders are mixed in a range of 45% by weight or less. 8. The sealed lead-acid battery separator according to claim 1, wherein the polyolefin synthetic pulp has a specific surface area of 1 m ² / g or more as measured by a BET adsorption method.