JPH08212997A - Batterry separator, manufacture thereof, and sealed secondary battery - Google Patents

Abstract

PURPOSE: To provide a battery separator made of a nonwoven fabric with high short circuit preventing performance, high electrolyte holding capability for an electrode in charge/discharge cycles, high gas permeation capability, and sufficient mechanical strength. CONSTITUTION: A battery separator is made of a nonwoven fabric comprising thermoplastic fibers and heat-fusible fibers which are heat-fused to bond fibers, and having raising on the surface on at least one side of the nonwoven fabric. The thermoplastic fibers and the heat-fusible fibers are three-dimensionally entangled by water stream, and the heat-fusible fibers are heat-fused to bond fibers to obtain a wet type nonwoven fabric. A raising treatment is conducted on the surface of at least one side o the nonwoven fabric prepared by an entangling treatment in which water steam is struck to a fiber web comprising the thermoplastic fibers and the heat-fusible fibers, or by a heat treatment in which the heat-fusible fibers are melted to bond fibers without conducting the entangling treatment. A sealed secondary battery in which the battery separator is arranged is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery separator, a method for manufacturing the same, and a sealed secondary battery.

[0002]

2. Description of the Related Art Generally, the performance required for a battery separator is excellent in separating a positive electrode and a negative electrode, preventing a short circuit, and retaining an electrolytic solution. Further, in a sealed secondary electrode in which a gas such as oxygen generated in the positive electrode is consumed in the negative electrode, it is possible not to prevent passage of gas generated by the electrode reaction.
As described above, the non-woven fabric used for the battery separator is required to have the above-described performance sufficiently, and tension is applied in the battery manufacturing process, so that the tensile strength is not less than a certain value and the width is not widened when inserting the electrode. Performance is also required.

In particular, recent sealed secondary batteries are required to have high capacity, high current charging / discharging performance, and high cycle performance, and battery separators used therein are required to have even higher performance. ing. That is, while lowering the weight of the separator and reducing the thickness are required to increase the capacity of the battery, in order to satisfy the high cycle performance, depletion of the electrolyte solution inside the separator by repeating charging and discharging of the secondary battery ( Dry out) must be suppressed. For example, in the case of a nickel-cadmium secondary battery, a change in the volume of the polar material occurs during the charge / discharge cycle, which causes a change in the electrode thickness. The thickness of the positive electrode gradually increases and the separator is compressed. As a result, the electrolytic solution in the separator is absorbed by the electrode, causing dryout. When the separator is dried out, the internal resistance increases, the charge / discharge reaction is obstructed, and the cycle life of the battery is shortened. Therefore, a battery separator having a sufficient electrolyte retaining capacity even if the weight is reduced is required.

Further, a high-performance separator is particularly required to have a property of allowing a gas generated from an electrode plate to pass therethrough during charging of a secondary battery and a property of not inhibiting a gas consumption reaction at an opposite electrode. For example, in the case of a nickel-cadmium secondary battery, a large amount of oxygen gas is generated from the positive electrode when it is charged for a long time or when it is charged at a high current in a short time. Therefore, it is required that the oxygen consuming reaction does not interfere with the oxygen consumption reaction that occurs in the negative electrode. However, these have not been sufficiently realized in the conventional melt blown nonwoven fabric, flash spinning nonwoven fabric, spunbonded nonwoven fabric, dry nonwoven fabric, wet nonwoven fabric and the like.

In Japanese Patent Laid-Open No. 1-157055, it is attempted to increase strength, improve short-circuit prevention performance, and ensure high liquid retention by forming a dense structure only in the surface layer of a meltblown nonwoven fabric made of ultrafine fibers. It cannot be said that the liquid retaining capacity is sufficient for the compression by the electrode due to the charge / discharge cycle. Further, in Japanese Unexamined Patent Publication (Kokai) No. 5-89869, a net material is provided on the surface in contact with the negative electrode, and the separator is provided with sufficient compression characteristics to prevent depletion of the electrolytic solution due to charge / discharge cycles, and the cycle life of the battery. Attempts have been made to improve the characteristics and to improve the oxygen gas absorption reaction by providing a fine space between the negative electrode and the separator by disposing the mesh material. Certainly, the arrangement of the net material improves the compression resistance of the separator, and as a result of the separator becoming less likely to be crushed due to volume swelling of the electrode, etc., the electrolytic solution is difficult to dry out, and it can be expected to extend the cycle life,
It cannot be said to be sufficient considering the recent trend toward higher capacity.

For example, in a nickel-cadmium secondary battery, the absorption of the electrolytic solution from the separator has a higher hydrophilicity than the negative electrode and is likely to occur in the positive electrode where water participates in the charge / discharge reaction. If it is not provided in the above, there is a problem that the electrolytic solution is easily absorbed by the positive electrode. In addition, it is expected that dryout will be difficult if the mesh material is placed on both sides to further increase the compression resistance, but the thickness of the separator increases and it becomes difficult to adapt to the higher capacity of the battery, As a result, the adhesion between the electrode and the separator is hindered, the movement of ions is hindered, and the internal resistance increases, which causes new problems.

[0007]

SUMMARY OF THE INVENTION The present invention is intended to solve the above problems, has good short-circuit prevention performance, and retains an electrolytic solution against electrodes during charge / discharge cycles of a secondary battery. An object is to provide a non-woven fabric suitable for a battery separator, which has particularly excellent ability, good gas permeability, facilitates gas absorption reaction at electrodes, and has sufficient mechanical strength in the battery manufacturing process. It is what

[0008]

As a result of various studies on the above-mentioned problems, the present inventor comprises one or more kinds of thermoplastic fibers and heat-bonding fibers, and a part or all of the heat-bonding fibers are heat-melted. The inventors have found that the above problems can be solved by using a nonwoven fabric having naps on at least one surface of the nonwoven fabric that has been adhered and bonded between fibers as a battery separator, and has completed the present invention. That is, the present invention comprises: at least one surface of a nonwoven fabric comprising one or more types of thermoplastic fibers and heat-sealing fibers, part or all of which is heat-sealed and interfiber-bonded There is provided a battery separator having: Further, the non-woven fabric has one or more types of thermoplastic fibers and heat-sealing fibers hydroentangled three-dimensionally with each other, and a part or all of the heat-sealing fibers are heat-melted and bonded between fibers. It is also characterized by being a non-woven fabric. Also,

Another feature is that at least one surface has a raised stress F of 0.5 to 5.0 g / cm ² . In addition, a part or all of the above-mentioned heat-sealing fibers are melted by a entanglement treatment in which a water stream is collided with a fiber web composed of one or more kinds of thermoplastic fibers and heat-sealing fibers, or by a heat treatment without the heat treatment. Provided is a method for producing a battery separator in which at least one surface of the obtained nonwoven fabric is raised. Further, there is provided a sealed secondary battery in which the battery separator according to any one of (1) to (4) is arranged.

Hereinafter, the present invention will be described specifically. As the material of the thermoplastic fiber and the heat-sealing fiber used in the present invention, it is preferable to use a material having durability against the alkali of the electrolytic solution and the acid liquid. For example, as a typical sealed alkaline secondary battery, nickel-cadmium type, nickel-hydrogen type, nickel-zinc type, nickel-type
The present invention is not limited to the iron type, the silver oxide-zinc type and the button type or the cylindrical type.

When an alkali is used as the electrolytic solution of such a sealed type secondary battery, the material is a polyolefin type such as alkali resistant polyethylene or polypropylene; COOH, SO ₃ H, OH, COOM, SO ₃ M ,
Polyolefins with hydrophilic groups such as OM (M is light or heavy metal); nylon 6, nylon 66, nylon 610,
A polyamide-based material such as nylon 612, nylon 10 or nylon 12; an aramid-based material such as polyparaphenylene terephthalamide or the like is preferably used alone or in combination.

Lead-acid batteries are typically used as the acid sealed secondary batteries. In such a case, acid resistant polyester terephthalate such as polyethylene terephthalate or polybutylene terephthalate; Polyolefin type; COOH, SO ₃ H,
Preferable examples include polyolefins having hydrophilic groups such as OH, COOM, SO ₃ M, and OM (M is a light or heavy metal); acrylics; aramids such as polyparaphenylene terephthalamide; or a combination thereof.

The heat-fusible fiber constituting the battery separator of the present invention has a heat-melting temperature lower than the melting point of the thermoplastic fiber by 10 ° C. or more, and the fiber having the lowest melting point in the case of two or more thermoplastic fibers. It is preferably lower by 10 ° C. or more.
If the temperature is lower than 10 ° C, a part of the thermoplastic fiber may be melted when the heat-sealing fiber is heat-melted, the desired sufficient strength of the nonwoven fabric cannot be obtained, and the retention rate of the electrolytic solution is lowered. There is a problem. More preferably, it is 20 ° C. or higher.

The heat-fusible fiber in the present invention may be a sheath-core type, a side-by-side type composite fiber, a single component type or the like, which is used in the conventional heat-fusible dry type nonwoven fabric or heat-fusion type wet-laid nonwoven fabric. From the viewpoint of obtaining high tensile strength, it is particularly preferable to use a sheath-core type heat-sealing fiber. For example, as a specific sheath-core type heat-sealing fiber, in the case of alkali resistance, the core portion is nylon 66 and the sheath component is nylon 6, or the core component is nylon 6 or 66 and the sheath component is nylon 612 or 610. Copolymerized nylon and polyolefins such as polyethylene and polypropylene, and combinations such as polypropylene as the core component and polyethylene as the sheath component are preferably used.

On the other hand, in the case of acid resistance, a polyester such as polyethylene terephthalate or polybutylene terephthalate as a core component and a copolymerized polyester as a sheath component or a polyolefin such as polyethylene or polypropylene can be preferably used in the present invention. In the battery separator of the present invention, the mixing ratio of the heat-sealing fibers is preferably 5 to 80% of the whole nonwoven fabric,
More preferably, it is 10 to 70%. 80% mixing ratio
If it exceeds, the fiber surface area will decrease due to the increase of the fiber surface adhesion part,
It is not preferable because it causes a decrease in liquid retention rate. On the other hand, if the mixing ratio is less than 5%, the tensile strength becomes low, which is not preferable.

The thermoplastic fiber used in the present invention may be a fiber directly obtained by spinning, or may be a splittable or sea-island fiber called a composite fiber.
Further, the single yarn diameter of the thermoplastic fiber can be appropriately selected from the viewpoints of gas permeability, short circuit prevention property, compression resistance property, and liquid retention property, but is preferably 1 to 25 μm, more preferably 3 to 20 μm. It is preferable to use one kind or a mixture of several kinds from the inside. For example, if a single yarn diameter of less than 1 μm is used alone, gas permeability and compression resistance are insufficient, and if it exceeds 25 μm, the distance between single yarns becomes large and the short-circuit prevention performance is poor, which is not preferable. 1-8 μm ultrafine fibers and compression resistance because of short circuit prevention and liquid retention performance
It is one of the preferred embodiments to appropriately mix 8 to 25 μm ordinary fibers to form the nonwoven fabric of the present invention because it imparts gas permeability, but is not particularly limited as long as the performance as a battery separator is achieved. Not something.

The diameter of the single fiber of the heat-fusible fiber is preferably 1 to 25 μm, more preferably 3 to 20 μm in terms of gas permeability, short circuit prevention and liquid retention, but as a battery separator. There is no particular limitation as long as the performance of 1 is achieved. The cross section of the single yarn may be circular or various non-circular cross sections. When the cross section of a single yarn is circular, the diameter of the single yarn is used as the value obtained by directly measuring the diameter, and in the case of a modified cross section, the fineness (denier) is measured by the gravimetric method. It is expressed by the average diameter obtained by the following equation.

[0018]

## EQU1 ## R = √ (4d / (π × 9 × 10 ⁵ × ρ)) × 10 ⁴ [where R is the diameter of the single fiber (μm), ρ is the density of the high molecular weight polymer constituting the single fiber ( g / cm ² ), d is the single fiber fineness (denier), and π is the circular constant. ]

As the non-woven fabric of the present invention, a product obtained by a conventional method from one or more types of the above-mentioned thermoplastic fibers and heat-bonding fibers can be used. For example, a dry method such as a card-cross layer method or a card / air ray method from a thermoplastic fiber and a heat-sealing fiber, a wet non-woven fabric obtained from the same fiber by a paper-making method, or a spun-bond method for forming a non-woven fabric at the same time as spinning, Although a melt-blowing method, a flash spinning method, or the like can be appropriately selected, a wet nonwoven fabric produced by a papermaking method is preferable as a separator for a high-performance battery because of its uniformity, it is excellent in short-circuit prevention performance, and it is superior in weight reduction.

It is preferable that the constituent fibers of the non-woven fabric are three-dimensionally entangled with each other, but the effect of the present invention is not impaired even if the three-dimensional entanglement is not performed. In particular, when the nonwoven fabric of the present invention is the above-mentioned wet type nonwoven fabric, high strength is obtained by three-dimensional entanglement of the constituent fibers, and therefore, a fiber entanglement treatment that causes a water stream or the like to collide is particularly preferable. The battery separator of the present invention has a part or all of the heat-sealing fibers constituting the heat-sealing fibers and has a nap on at least one surface of the non-woven fabric interfiber-bonded, so that the electrolytic solution in the separator is absorbed by the electrodes. It has the characteristic that it is difficult to get rid of. That is, since the electrode and the separator of the present invention are adhered to each other via the raised hair on the surface, a discontinuous and extremely fine discontinuous void is formed between the electrode and the conventional separator having no raised hair. As a result, it was found that the electrolytic solution of the separator becomes difficult to be absorbed by the electrode, and the extremely fine voids also have an effect of promoting the gas absorption reaction.

When a mesh made of fibers having a diameter of 0.12 mm and a mesh size of 3 mm, which is described in the embodiment of JP-A-5-89869, is arranged between the negative electrode and the negative electrode, voids formed therein are They differ in size, in other words, they differ drastically in terms of the contact density between the fiber and the electrode. That is, the napped separator of the present invention contacts the electrode at a single yarn level of constituent fibers, at a level of micrometer fineness and at a high density, and voids generated in the nap-free portion are also extremely fine and discontinuous. . As a result, the contact point between the napped fibers of the separator constituent fibers and the electrode is high density, but discontinuous, and contains a large number of fine voids, which is suppressed by the migration of the electrolytic solution from the separator to the electrode.

Therefore, since the electrolyte has a sufficient ability to retain the electrolytic solution against the compression due to the increase in the thickness of the electrode due to the charging / discharging cycle of the secondary battery, the internal resistance caused by the transfer of the electrolytic solution to the electrode is reduced. The rise is low and it is possible to achieve extremely high cycle life. Furthermore, in the battery separator having a raised hair of the present invention, the dense discontinuous voids formed between the electrode and the electrode are gas phase-liquid phase-in the case of the nickel-gadium secondary battery described in JP-A-5-89869. It realizes an environment that promotes the oxygen gas absorption reaction at the three-phase interface of the solid phase. Moreover, since the battery separator of the present invention is in contact with the electrode at a high density due to the raised fibers of the constituent fibers, it has been found that an excellent effect that the migration of ions easily proceeds and the internal resistance is not increased is found. Is completed.

The preferable range of the degree of raising of the surface of the battery separator of the present invention will be described. As a result of investigating a method for quantitatively evaluating the length and density of the raised hair, it was found that it can be expressed by measuring the compressive stress in the thickness direction. That is, when the repulsive stress (hereinafter referred to as raised stress F) at a position 0.1 mm away from the thickness of the nonwoven fabric in which the surface raised is completely laid down, the raised hair is long and the density is high. On the contrary, when the raised stress F is small, it can be said that the raised hair is short and the raised density is small.

The raised stress F of the battery separator of the present invention is preferably in the range of 0.5 to 5.0, more preferably 1.0.
˜4.0, and even more preferably 1.5 to 4.0.
When the raised stress F is 0.5 or less, the raised amount is small and the length is short. Therefore, the discontinuous contact with the electrode through the raised densities, which is the object of the present invention, is not sufficiently achieved and the electrolytic solution The effect of suppressing the transfer of the metal to the electrode is insufficient. On the other hand, if the raised stress exceeds 5.0, it may cause other adverse effects such as falling of the raised hair, which is not preferable.

The basis weight of the raised nonwoven fabric of the battery separator of the present invention is not particularly limited, but preferably 10
To 350 g / m ² , more preferably 35 to 100
g / m ² . The preferred range of the thickness is 0.0
8 to 1.0 mm, more preferably 0.08 to 0.
It is 25 mm. A basis weight of 10 g / m ² or less and a thickness of 0.
If it is less than 08 mm, it will not be able to secure practical strength when attached to the battery because it will be too light weight, and it will not be possible to completely prevent the passage of the active material, and will also reduce the amount of electrolytic solution used. Will be difficult. If the basis weight exceeds 350 g / m ² and the thickness exceeds 1.0 mm, the separator has a large volume and is not suitable for increasing the battery capacity, and the internal resistance also increases, which is not preferable.

Next, a method for manufacturing the battery separator of the present invention will be described. Obtained by melting a part or all of the above-mentioned heat-bonded fibers by heat treatment with or without a entanglement treatment in which a fiber web composed of one or more thermoplastic fibers and heat-bonded fibers is subjected to a water stream collision The battery separator of the present invention can be obtained by performing a raising treatment on at least one surface of the nonwoven fabric.

The fibrous web in the present invention is obtained by a dry method such as a card-cross layer method or a card-airlay method from thermoplastic fibers and heat-sealing fibers, a wet method obtained from the fibers by a paper-making method, or A fiber web obtained by a spunbond method, a melt blow method, a flash spinning method, etc., which forms a nonwoven fabric at the same time as spinning, can be appropriately selected, but a wet method by a papermaking method has excellent uniformity and excellent short-circuit prevention performance, and has a low It is preferable in terms of superiority in unit weight.

Such a fibrous web is immediately heat-treated with a hot air drier, felt calender, hot roll, etc. to heat-melt a part or all of the heat-bonded fibers to obtain a nonwoven fabric strength and compression resistance sufficient for use in a battery separator. Can be given. Further, a high-strength non-woven fabric can be obtained by causing a high-pressure water stream to collide with the fiber web to three-dimensionally entangle the fibers and then subjecting the fiber to the heat treatment.
In particular, when the fibrous web is a wet web formed by a papermaking machine from a slurry in which short fibers are dispersed in water, it is preferable to three-dimensionally entangle the constituent short fibers by colliding a water stream with the fibrous web. Particularly preferred. In that case, the water pressure varies depending on the type of raw yarn used and the basis weight of the fiber web, but in order to obtain sufficient entanglement between the fibers, 3 to 100 kg /
cm _2, preferably to collide in the range of 3~50kg / cm ^2. In the case of the same fiber, the lower the basis weight, the lower the water pressure, and the higher the basis weight, the higher the water pressure. Further, in the case of the same basis weight, when the raw yarn having a high Young's modulus is treated with high water pressure, the high strength which is the object of the present invention can be obtained.

The diameter of the nozzle for jetting the water flow is 0.01 to 1
mm is preferred. The trajectory shape of the water flow may be a straight line parallel to the advancing direction of the mixed sheet, or a curved shape obtained by the rotational movement of the header with the nozzle attached or the vibration movement reciprocating at right angles to the advancing direction of the sheet. May be. The confounding of circular water flow loci obtained by the rotary motion is efficient because the jet area of the water flow to the sheet per nozzle weight is large, and at the same time,
It becomes difficult to see spots on the water flow that reduce the product value.

As a method of treating the fibrous web with a water stream, a method of alternately injecting a water stream on the front and back sides or a method of treating only one side may be used. Also, regarding the number of times of processing, an optimum condition may be selected according to the purpose. The hydraulic conditions for the water flow treatment of these fibrous webs are selected under the conditions such that the desired sufficient fiber entanglement is obtained and uniformity is obtained, but for example, 10 to 100.
3 to 3 in the case of a mixed sheet having a relatively small weight per unit area of g / m ^2.
It is preferable to perform one side or both sides treatment with a water pressure of 40 kg / cm ² .

By this entanglement treatment, the constituent fibers of the fibrous web are moved by the water flow and entangled with each other to obtain a strong bond. That is, the constituent thermoplastic staple fibers and the heat-sealing fibers are three-dimensionally entangled with each other, and the entanglement bond thus obtained is extremely strong. Then, the obtained entangled nonwoven fabric is heat-treated to melt a part or all of the heat-sealing fibers. The heat treatment condition is preferably a short time treatment of 5 seconds to 10 minutes using a non-contact hot air dryer in order not to impair the gas permeability and the electrolyte retention rate. The heat treatment temperature is set to a temperature not lower than the melting point of the heat-sealing fibers and not higher than the melting point of the thermoplastic short fibers.

At least one surface of the non-woven fabric thus obtained is subjected to nap treatment. As the method of raising hair, puffing treatment with emery paper, brushing treatment with various brushes such as metal, plasticity such as vinyl chloride, pig hair, etc., brushing treatment with MC brush, and conventional methods such as MC roll can be appropriately selected. This brushing treatment can achieve the effect depending on the purpose even on only one side, but it is not necessary to consider the front and back when incorporating it into the battery by raising both sides, and it is the effect of improving the electrolyte retention capacity and gas absorption reaction. Is also preferable because it is large.

For example, in the case where the battery separator of the present invention having a raised surface only on one side is applied to a nickel-cadmium secondary battery, if the raised surface is arranged so as to contact the positive electrode, absorption of the electrolytic solution by the positive electrode will occur. Suppressed and expected to improve charge / discharge cycle performance. On the other hand, when the negative electrode is brought into contact with the raised surface, the oxygen gas absorption reaction easily proceeds, and the overcharge characteristic and the high current charge / discharge characteristic are improved. Therefore, when the battery separator of the present invention having naps on both sides of the non-woven fabric is attached to the sealed type secondary battery, the napped surfaces are provided on both the positive electrode and the negative electrode, and thus the charge / discharge cycle performance is improved at the same time. Since it can be expected that the overcharge characteristic and the high-current charge / discharge characteristic are improved, it can be said to be a preferable mode.

The raising treatment may be carried out on one side at a time, but it may be done on both sides at the same time. When the thickness of the battery separator thus obtained is adjusted, the battery separator may be pressure-bonded by a calendar dryer, an embossing machine or the like. However, since the raising effect is weakened when the above-mentioned surface raising is pressure-bonded by a calender drier or an embossing machine, it is preferable to perform a raising treatment after the pressure-bonding treatment and the like.

Further, this pressure-bonding treatment must be selected so as not to extremely reduce gas permeability and electrolyte retention. It is also preferable to perform hydrophilic treatment in order to increase the initial affinity with the electrolytic solution. In this case, the hydrophilic treatment is carried out by a method of attaching a generally used surfactant,
When it is desired to carry out permanent hydrophilization, introduction of a hydrophilic functional group into the fiber or a modification treatment method of the fiber surface such as a plasma treatment method or a dissolution treatment method may be used. The hydrophilic treatment is preferably performed before adjusting the thickness. If the hydrophilic treatment is performed after the thickness is adjusted, not only the adjusted thickness is changed, but also the hydrophilic treatment in a high density state is not uniform and is not preferable.

[0036]

The present invention will be described in more detail with reference to the following examples, which do not limit the scope of the present invention. In the examples, the measured values are those measured by the following method,
All percentages are weight percentages. 1) Tensile strength According to JIS L1096 strip method, the traveling direction of the nonwoven fabric is measured. 2) Gas permeability Measured according to JIS L1096 Frazier method.

3) Liquid Retention Performance 3 pieces of test pieces cut into a square of 10 cm × 10 cm were sampled, and the weight (W ₁ ) in the state of reaching water equilibrium was 1 mg.
Measure up to. Then, the test piece weight (W ₂ ) was measured after spreading and soaking in a 31% aqueous potassium hydroxide solution for 1 hour or more and then lifting it from the solution and hanging it for 10 minutes with one corner of the square facing up. , Hoekiritsu of _{(%) (W 2 -W 1} ) / W
Liquid retention is evaluated by calculating ₁ × 100. 4) Liquid holding performance: Two test pieces cut into a shape of 3.4 cm × 5 cm are sampled, and the weight (a ₁ ) in a state where water equilibrium is reached is measured up to 1 mg. Next, the same amount (a ₁ ) of a 31% aqueous potassium hydroxide solution is held. The test piece is a filter paper (ADVANTE
C, No4A) and put a load of 100 g. The weight (a ₂ ) of the test piece after 30 seconds was measured, and the liquid retention rate (%) was a.
₂ / a ₁ × 100 is calculated to evaluate the liquid holding performance.

5) Liquid absorption rate A 5 mm edge of a 20 cm × 2.5 cm test piece was vertically immersed in a 31% aqueous potassium hydroxide solution, and the rising height (mm) of the aqueous potassium hydroxide solution after 30 minutes due to capillary action was measured. ) Is measured and the liquid absorption rate is evaluated. 6) Internal resistance test A 1.5 cm x 5 cm test piece is sandwiched between nickel and cadmium plates of the same size, and the outside is 5 cm x 5c.
It is sandwiched between m-sized acrylic plates. Insert the spacer between the acrylic plates and apply pressure so that the thickness of the test piece is 0.14 mm. To this test piece, 31% potassium hydroxide is injected in the same weight as the test piece, and the difference in electric resistance immediately after the injection and after standing for 72 hours is measured with a milliommeter.

7) Battery cycle characteristic test Using the battery separator of the present invention, S having a nominal capacity of 1.2 AH
A C size sealed nickel-cadmium secondary battery was prepared and a cycle characteristic test was conducted. The condition at this time is 1.8.
After charging for 1 hour at a current of A, it is discharged at a final voltage of 1.0 V at a current of 1.2A. 8) Battery overcharge characteristic test Using the battery separator of the present invention, S having a nominal capacity of 1.2 AH
C size sealed nickel-cadmium secondary battery 100
An individual piece was prepared and an overcharge characteristic test was conducted. The number of times the safety valve of the secondary battery is activated after being continuously charged for one week is expressed as a percentage.

9) Measurement test for raised stress F The surface compression load-displacement curve of a sample whose napped surface is straightened with a soft pig bristle brush is measured with a KES-3 compression tester. The result is shown in FIG. The thickness at a load of 7 g / cm ² is taken as the sample thickness in the state in which the raised hair is laid down, and the stress at the thickness of +0.1 mm added to this sample thickness is read as the raised hair stress F.

(Example 1) A fiber length of 7.5 mm was measured.
Nylon 66 with 5 denier (single yarn diameter D = 7.8 μm)
Unimelt UL, 2% denier (single yarn diameter D = 14.1 mm) with 80% short fibers and 10 mm fiber length
-61 [manufactured by Unitika Ltd., core: nylon 6, sheath:
20% of copolymerized nylon] was dispersed in water to prepare a slurry liquid having a concentration of 1%. A mixed paper sheet of 70 g / m ² was obtained from this slurry liquid by an inclined fourdrinier paper machine.

The obtained mixed paper sheet was placed on a wire mesh of 80 mesh, a nozzle header equipped with a nozzle having a nozzle diameter of 0.15 mm was circularly moved at 285 rpm, a wire mesh of 40 mesh was inserted between the sheet and the nozzle, and a pressure of 20 kg was applied. / C
Short fibers and heat-bonded fibers were entangled by spraying m ² of water and colliding with the mixed sheet. The same process 6
After repeating the process, the sheet was turned upside down and the same treatment was applied 7 times. Subsequently, the nozzle header was rotated at 420 rpm, a 60-mesh wire net was inserted between the sheet and the nozzle, and the front and back were treated twice each at a water pressure of 15 kg / cm ² to complete an entangled sheet.

The obtained entangled sheet was dried by a pin tenter dryer set at a temperature of 180 ° C., and at the same time, the sheath portion (melting point 140 ° C.) of Unimelt UL-61 between the entangled sheets was melted. Next, after immersing in an aqueous solution containing 0.2% of the nonionic surfactant Synthol KP (manufactured by Takamatsu Yushi Co., Ltd.), the temperature was set to 160 ° C. by squeezing so that the adhesion rate was 200% of the nonwoven fabric. It was dried with a pin tenter dryer. Further, it is guided to a pair of metal rolls heated to 100 ° C., calendered at a linear pressure of 35 kg / cm, and brushed on both sides with 500 mesh sandpaper to give a fabric weight of 68 g / m ² , a thickness of 0.15 mm, A battery separator having a raised stress of 2.5 g / m ² was obtained.

(Example 2) The same procedure as in Example 1 was carried out except that 180 mesh sandpaper was used to brush both sides, and the fabric weight was 68 g / m ² , the thickness was 0.15 mm, and the raised stress was 3.5.
A battery separator of g / m ² was obtained.

(Example 3) The same procedure as in Example 1 was carried out except that both sides were raised with a roll brush having nylon fibers planted, and the fabric weight was 68 g / m ² , the thickness was 0.15 mm, and the raising stress was 1.8 g / m. A battery separator ² was obtained. (Example 4) The same procedure as in Example 1 was carried out except that both sides were raised with a roll brush having pig hair planted, and the fabric weight was 68 g / m 2.
² , a battery separator having a thickness of 0.15 mm and a raised stress of 1.3 g / m ² was obtained.

Comparative Example 1 A fabric weight of 68 g / same as in Example 1 except that no raising treatment was applied in the last step.
A battery separator having m ² , thickness of 0.15 mm, and raised stress of 0.9 g / m ² was obtained. Table 1 shows the performance of the battery separators obtained in Examples 1 to 4 and Comparative Example 1. As is clear from Table 1, the battery separators of Examples 1 to 4 of the present invention have an excellent electrolyte retaining ability as compared to Comparative Example 1, good gas permeability, and excellent internal resistance. It has a low rise and has sufficient performance as a high performance battery separator.

Actually, a sealed nickel-cadmium secondary battery equipped with the battery separator obtained here was manufactured, and its overcharge characteristics were evaluated. As a result, the battery separator of the embodiment of the present invention was installed. In comparison with Comparative Example 1, no safety valve leakage due to an increase in internal gas pressure occurred. It is considered that this is because the oxygen gas generated from the positive electrode easily passed the consumption reaction in the negative electrode after passing through the battery separator. In addition, as shown in the cycle test results in FIG. 2, the battery of Example 1 of the present invention, which has an excellent ability to hold an electrolyte solution, has an extremely long life and excellent cycle performance, as compared with the battery of Comparative Example 1, which has a poor capability. Characterized.

Example 5 0.5% denier (single yarn diameter D = 7.8 μm) nylon 66 short fibers having a fiber length L = 38 mm and 80% of 2 denier (single yarn diameter D = L = 51 mm) = 14.1 mm) heat fusion fiber Unimelt UL-61 [manufactured by Unitika Ltd., core: nylon 6, sheath: copolymerized nylon] 20% are mixed, and a basis weight of 75 g / m ² mixed fiber is obtained by the card method. Got the web. Temperature 18
At the same time as drying with a felt calender dryer set to 0 ° C., the sheath portion of the heat-sealing fiber Unimelt UL-61 (melting point 1
40 ° C.) was melted to obtain a dry non-woven fabric. Next, nonionic surfactant synthol KP [manufactured by Takamatsu Yushi Co., Ltd.]
After being dipped in an aqueous solution containing 0.2%, it was squeezed so that the adhesion rate was 200% of the nonwoven fabric, and dried with a pin tenter dryer in which the temperature was set to 160 ° C.

Further, the sheet was guided to a pair of metal rolls heated to 100 ° C., calendered at a linear pressure of 35 kg / cm, and brushed on both sides with 360 mesh sandpaper to give a basis weight of 72 g / m ² and a thickness of 0. A battery separator of 0.18 mm and a raised stress of 2.0 g / cm ² was obtained. The performance of this product is shown in Table 1 and FIG. Although the tensile strength level is slightly low, it exhibits excellent performances other than gas permeability, internal resistance, electrolyte retention, overcharge characteristics, and cycle performance.

Example 6 A dry non-woven fabric obtained by subjecting the mixed fiber web obtained in the same manner as in Example 5 to entanglement treatment with a water stream, pin tenter drying, surface treatment and calendering in the same manner as in Example 1. By brushing both sides with sandpaper of 360 mesh, the fabric weight is 72g /
A battery separator with m ² , thickness of 0.18 mm and raised stress of 2.3 g / cm ² was obtained. The performance of this product is shown in Table 1 and FIG. It has excellent gas permeability, internal resistance, electrolyte retention, overcharge characteristics, and cycle performance.

(Comparative Examples 2 and 3) The physical properties of the battery separators obtained in Example 5 and Example 6 without any final raising treatment are shown in Table 1 as Comparative Example 2 and Comparative Example 3, respectively. As compared with Examples 5 and 6, the electrolyte holding power was small and the cycle life of the battery was short. This is because the electrolytic solution in the separator was attracted to the electrodes by continuing the charge / discharge cycle of the battery, and as a result, the charging resistance increased and the charging did not proceed completely, resulting in a decrease in the discharge capacity.

(Example 7) Nylon 66 of 0.5 denier (single yarn diameter: 7.8 μm) having a fiber length of 7.5 mm
40% short fiber, 40 40% nylon 66 short fiber with a fiber length of 12.5 mm and 1.5 denier (single yarn diameter 13.5 μm)
%, Fiber length 10 mm, 2 denier (single yarn diameter 14.1 m
m) Heat-fusion fiber Unimelt UL-61 [manufactured by Unitika Ltd., core: nylon 6, sheath: copolymerized nylon]
20% was dispersed in water to prepare a slurry liquid having a concentration of 1%.
75 g / m from this slurry liquid using a slanted Fourdrinier paper machine
^After the mixed sheet of No. ² was obtained, a battery separator having a basis weight of 72 g / m ² , a thickness of 0.18 mm, and a raised stress of 2.2 g / m ² was raised on both sides in the same manner as in Example 1. Performance data are shown in Table 1 and FIG.

(Example 8) 0.2 with a fiber length of 6 mm
Nylon 6 short fiber of 5 denier (single yarn diameter 4 μm) 4
0%, 1.0 denier with 10 mm fiber length (single yarn diameter 1
1.0% Nylon 66 short fiber 40%, fiber length 1
20% of a heat fusion fiber Unimelt UL-61 [manufactured by Unitika Ltd., core: nylon 6, sheath: copolymerized nylon] of 2 denier (single yarn diameter D = 14.1 mm) at 0 mm is dispersed in water. A slurry liquid having a concentration of 1% was prepared. After obtaining a mixed paper sheet of 75 g / m ² from this slurry liquid by an inclined fourdrinier paper machine, the weight per unit area was raised to 72 g / m ² on both sides in the same manner as in Example 1, the thickness was 0.18 mm, and the raising stress was 1.
A battery separator of 6 g / m ² was obtained. Performance data are shown in Table 1 and FIG.

Example 9 Average fiber diameter 2 μm, basis weight 36
A fiber length of 7.5 m in a meltblown non-woven fabric made of nylon 6 manufactured to have a thickness of g / m ² and a thickness of 0.3 mm.
80% of nylon 66 short fiber of 0.5 denier (single yarn diameter D = 7.8 μm), which is m, and heat-bonded fiber Unimelt U
L-61 A mixed paper sheet having a basis weight of 40 g / m ^{2 made up} of 20% was laminated, subjected to entanglement treatment, surfactant addition and calendering in the same manner as in Example 1, and finally 500 mesh in the same manner as in Example 1. Both sides of the non-woven fabric are napped with the sand paper of 74g / m ² , and the thickness is 0.18m.
m, brushed stress terms of nylon 66 with meltblown surface 1.8 g / m ² was obtained battery separator 2.3 g / m ^2.
The performance data are shown in Table 1.

[0055]

[Table 1]

[0056]

EFFECTS OF THE INVENTION The battery separator of the present invention has sufficient mechanical strength to prevent breakage and width insertion when the battery is mounted, and also has good gas permeability, liquid retention rate, liquid absorption rate performance, and electrolysis. Since it is particularly excellent in liquid holding ability and gas consumption reactivity, it can be suitably used for a sealed secondary battery, and can sufficiently cope with the recent increase in capacity of secondary batteries. . In fact, the secondary battery equipped with the battery separator of the present invention has excellent overcharge characteristics and long charging / discharging cycle life, and thus has an extremely large industrial value.

[Brief description of drawings]

FIG. 1 is a graph showing surface compression load-displacement of a nonwoven fabric sample of the present invention.

FIG. 2 is a graph showing the relationship between the electrolyte holding capacity and the number of cycles of the battery separator of the present invention.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area H01M 10/34

Claims (5)

[Claims] 1. A raised fabric is formed on at least one surface of a non-woven fabric comprising one or more kinds of thermoplastic fibers and heat-sealed fibers, part or all of which is heat-sealed and interfiber-bonded. A battery separator characterized by having. 2. The non-woven fabric comprises one or more kinds of thermoplastic fibers and heat-sealing fibers hydro-entangled three-dimensionally with each other, and part or all of the heat-sealing fibers are heat-melted to bond the fibers. 2. The battery separator according to claim 1, wherein the separator is a wet non-woven fabric. 3. The battery separator according to claim 1, wherein at least one of the surfaces has a raised stress F of 0.5 to 5.0 g / cm ² . 4. A part or all of the above-mentioned heat-sealing fibers are melted by a entanglement treatment in which a water stream is made to collide with a fiber web composed of one or more kinds of thermoplastic fibers and heat-sealing fibers, or by a heat treatment without the heat treatment. A method for producing a battery separator, characterized in that at least one surface of the non-woven fabric thus obtained is subjected to a raising treatment. 5. A sealed secondary battery in which the battery separator according to claim 1 is arranged.