JP4992186B2 - Battery separator - Google Patents

Description

  The present invention prevents a short circuit between a positive electrode and a negative electrode of a battery, and is a battery separator that retains an electrolytic solution, in particular, a battery that is excellent in liquid retention of an electrolytic solution and excellent in permeability of gas generated during charging in a secondary battery. It relates to a separator.

  The battery separator separates the positive electrode and the negative electrode of the battery, holds the electrolytic solution, and allows ions to pass through while preventing contact between the two electrodes and a short circuit due to precipitates such as dendrites. In response to the recent trend toward smaller and lighter batteries, battery separators are becoming thinner and the amount of electrolyte to be impregnated tends to be reduced. For this reason, the battery separator is required to securely hold the electrolytic solution between the electrodes and keep the internal resistance of the battery low. However, since the positive electrode and the negative electrode of the secondary battery are usually formed of a porous material such as a sintered metal, a phenomenon occurs in which the electrolyte is sucked from the separator into the micropores of the polar material during long-term use. The battery performance was reduced.

  Moreover, the separator of the secondary battery is required to have excellent gas permeability. This is because the secondary battery is designed to guide the gas generated from the positive electrode during charging to the negative electrode, and reduce it on the negative electrode surface to return it to the electrolyte. This is because the gas is filled, the internal pressure increases, the amount of the electrolyte decreases, and the battery performance deteriorates.

  As a method of improving the liquid retention of the battery separator, the fineness of the fibers constituting the battery separator is reduced and the nonwoven fabric is densified, thereby reducing the pores between the fibers constituting the nonwoven fabric and utilizing the capillary effect. Attempts have been made to improve liquid retention. For example, an ultrafine fiber nonwoven fabric using fibers having an average diameter of 5 μm or less using a melt blow method has been proposed (see Patent Document 1). In addition, a technique for improving the liquid retention of the nonwoven fabric by dividing the composite fiber to generate ultrafine fibers has been proposed (see Patent Document 2), and the ultrafine fibers are highly dispersed to reduce the pore diameter of the nonwoven fabric. It has also been proposed to reduce (see Patent Document 3). However, if the pores between the fibers constituting the nonwoven fabric are reduced and the space is filled with an electrolyte solution, the liquid retention is improved, but the electrolyte solution fills the pores of the nonwoven fabric. There was a problem that the permeability of the generated gas was remarkably lowered.

  In addition, as a method for improving the gas permeability of the battery separator, attempts have been made to use a non-woven fabric composed of thick fibers, or to form a large hole partially by applying a water flow or the like to the non-woven fabric. (See Patent Document 4). However, in order to supplement gas permeability with some of the holes, it is necessary to form large holes, and there is a problem in that micro-shorts are likely to occur due to precipitation of dendrites and movement of the electrode active material. It was.

As described above, in the secondary battery separator, the liquid retention and gas permeability are contradictory properties, and there is no separator that satisfies both at the same time.
Japanese Unexamined Patent Publication No. 1-157055 (first page, claim 1) JP-A-3-257755 (first page, claim 2) JP-A-9-302563 (first page) Japanese Patent Laying-Open No. 2001-84983 (second page, claim 3)

  An object of the present invention is to provide a battery separator that has both liquid retention and gas permeability of an electrolyte solution and excellent battery performance.

In order to solve the above problems, the present invention employs the following configuration. That is, in the present invention, polymers having different solubility in two or more kinds of solvents are alloyed using a twin-screw extrusion kneader, and this is spun to obtain a polymer alloy fiber, which is then treated with the solvent. A battery separator comprising a fibrous material having a diameter of 1 μm or more formed by gathering ultrafine fibers having an average diameter of 500 nm or less made of polyamide or polyarylene .

  In addition, the battery separator includes fibers having a diameter of 1 μm or more in addition to a fibrous material having a diameter of 1 μm or more formed by collecting ultrafine fibers having an average diameter of 500 nm or less.

  Moreover, it is preferable that said super extra fine fiber consists of a thermoplastic resin.

  Moreover, it is preferable that said thermoplastic resin consists of polyamide, polyolefin, or polyarylene.

  According to the present invention, by collecting ultrafine fibers having an average diameter of 500 nm or less, the electrolyte solution can be held in the gaps between the ultrafine fibers, and the ultrafine fiber aggregate is made into a fiber having a diameter of 1 μm or more. By doing so, the pore diameter of a nonwoven fabric can be maintained and air permeability can be ensured, and the battery separator excellent in battery performance can be provided.

  It is important that the battery separator of the present invention comprises a fibrous material in which ultrafine fibers having an average diameter of 500 nm or less are gathered in a bundle. By adopting such a configuration, a large number of ultrafine fibers are present inside one fibrous material, and a lot of minute spaces are held between the ultrafine fibers. For this reason, when this fibrous material is brought into contact with the liquid, the liquid can be absorbed into the fibrous material and retained by the capillary effect of the minute space inside. In this way, by holding the electrolytic solution in the space inside the fibrous material, the electrolytic solution does not block the pores of the nonwoven fabric itself, and the separator has excellent air permeability. Since such an effect increases as the surface area present inside the fibrous material increases, it is important that the average diameter of the ultrafine fibers constituting the fibrous material is 500 nm or less and a nano-level fineness, The thickness is preferably 200 nm or less, and more preferably 100 nm or less. However, if the ultrafine fibers are too thin, the production efficiency is lowered and the cost is increased. Therefore, the average diameter of the ultrafine fibers is preferably 1 nm or more, and more preferably 10 nm or more.

  Here, the average diameter of the ultrafine fibers can be determined as follows. That is, the diameter obtained after measuring the diameter of each ultra-fine fiber by observing with a transmission electron microscope (TEM), cutting out the fibrous material which consists of a super-fine fiber in a surface perpendicular | vertical to a fiber axial direction. Is obtained by averaging. At this time, when the fiber shape is not circular, the diameter of a circle having the same area as the cross-sectional area of the fiber is used as the fiber diameter (hereinafter, the apparent fiber diameter converted in this way is abbreviated as the circle-converted diameter). Here, as the number of fibers to be measured is larger, the measured average diameter is closer to the average diameter of the entire ultra-fine fibers constituting the separator. Therefore, it is preferable to measure a larger number, which is selected at random. By measuring the diameter of 200 or more fibers, the total average diameter can be obtained.

  In addition, it is important that the diameter of the fibrous material that is an aggregate of the ultrafine fibers is 1 μm or more. The ultra-fine fibers are extremely low in rigidity, and it is difficult to produce a non-woven fabric with a large opening by itself, but normal fibers were used by gathering in the same thickness as ordinary ultra-fine fibers. It becomes possible to produce a non-woven fabric having the same opening as the case. In addition, as described above, by holding the electrolytic solution inside the fibrous material, a battery separator having excellent gas permeability is obtained. Thus, in order to ensure gas permeability, it is important that the diameter of the fibrous material is 1 μm or more, preferably 2 μm or more, and more preferably 5 μm or more. However, if the thickness of the fibrous material is too large, the opening of the nonwoven fabric becomes too large, and the positive electrode and the negative electrode are easily short-circuited especially when the separator is thin, so the thickness of the fibrous material is 100 μm or less. It is preferable that it is 50 μm or less.

  Here, the diameter of the fibrous material can be determined as follows. That is, the cross section of the battery separator is observed with an SEM, and the diameter is calculated by calculating the circle conversion diameter from the area of the cross section of the fibrous material. At this time, the battery separator was cut in three directions in different directions, and the circular equivalent diameters of the five fibrous materials that were considered to be cut in a plane near the fiber axis of the fibrous material in each cross section were calculated. The average of the diameters of a total of 15 fibrous materials is calculated to obtain the diameter of the fibrous material.

Polymer over constituting the fibrous material is made of a thermoplastic resin that having a resistance to electrolytes, nylon 6 (N6), nylon 66, polyamides such as nylon 12, polyphenylene ether, polyphenylene ether ketone, Polyarylene such as polyphenylene sulfide (PPS) can be used.

  In addition, the battery separator of the present invention is preferably composed of a polymer having a high affinity for the electrolytic solution. For example, when used in an alkaline secondary battery, it is preferably composed of a hydrophilic polymer having a high affinity for water, and nylon 6 or nylon 66 is preferably used. The battery separator of the present invention retains the liquid mainly due to the morphological effect of the capillary effect, so that it is possible to improve the liquid retention even if the hydrophilicity of the polymer itself is low. Since it is difficult to infiltrate the electrolyte inside the material, a surfactant is added when using a hydrophobic polymer, or hydrophilic treatment such as sulfonation, fluorination, corona discharge, plasma discharge, etc. It is preferable to improve wettability.

Method for producing a battery separator of the present invention can employ the following ways.

First, a polymer alloy melt obtained by alloying polymers having different solubilities in two or more kinds of solvents is formed, which is spun and then cooled and solidified to form a fiber. Then, if necessary, stretching and heat treatment are performed to obtain a polymer alloy fiber. When this polymer alloy fiber is treated with a solvent, the easily soluble polymer in the polymer alloy fiber is eluted, and at the same time the polyamide or polyarylene, which is a hardly soluble polymer in the polymer alloy fiber, forms a superfine fiber. The ultra-fine fibers made of polyamide or polyarylene present in one polymer alloy fiber are aggregated to form a fibrous material.

  Here, it is important to control the island size by making the easily soluble polymer into the sea (matrix) and the hardly soluble polymer into the island (domain) in the polymer alloy fiber that is the precursor of the ultrafine fiber assembly. is there. Here, the island size is obtained by observing the cross section of the polymer alloy fiber with a TEM and evaluating in terms of diameter. Since the diameter of the ultrafine fiber is substantially determined by the island size in the precursor, the island size distribution is designed according to the diameter distribution of the ultrafine fiber of the present invention. For this reason, kneading of the polymer to be alloyed is extremely important, and in the present invention, it is preferable to highly knead by a kneading extruder, a stationary kneader or the like. Note that, for example, as disclosed in JP-A-6-272114, simple chip blending is insufficient for kneading, so that it is difficult to disperse islands with an average size of 500 nm or less as in the present invention.

  As a specific guideline for kneading, although it depends on the polymer to be combined, it is preferable to use a biaxial extrusion kneader when using a kneading extruder, and when using a static kneader, the number of divisions is 100. It is preferable to set it to 10,000 or more. Moreover, in order to avoid blend spots and fluctuations in the blend ratio over time, it is preferable to measure each polymer independently and supply the polymers to the kneading apparatus independently. At this time, the polymer may be supplied separately as pellets, or may be supplied separately in a molten state. Two or more kinds of polymers may be supplied to the root of the extrusion kneader, or may be a side feed that supplies one component from the middle of the extrusion kneader.

  When a twin screw extrusion kneader is used as the kneading apparatus, it is preferable to achieve both high kneading and suppression of the polymer residence time. The screw is composed of a feeding part and a kneading part, but it is preferable that the kneading part has a length of 20% or more of the effective length of the screw so that high kneading can be achieved. In addition, by setting the length of the kneading part to 40% or less of the effective screw length, excessive shear stress can be avoided and the residence time can be shortened. Can be suppressed. Further, the kneading part is positioned as close as possible to the discharge side of the twin-screw extruder, so that the residence time after kneading can be shortened and re-aggregation of the island polymer can be suppressed. In addition, when strengthening kneading, it is possible to provide a screw having a backflow function for sending the polymer in the reverse direction in an extrusion kneader.

  In addition, a combination of polymers is also important for the ultra-fine dispersion of islands with a size of 500 nm or less.

  In order to obtain a clear sea-island structure, the polymers to be mixed must be incompatible with each other. However, if the compatibility between the two polymers is too poor, the island domains are non-uniform in size even when highly kneaded and large islands are mixed. For this reason, it is necessary to make compatibility of both polymers into an appropriate range. Here, in order to control the compatibility, a small amount of a third component (such as a compatibilizing agent) can be used.

  Further, it is preferable that the difference in melting point between polymers is 20 ° C. or less because kneading with an extrusion kneader is unlikely to cause a difference in the melting state in the extrusion kneader, so that kneading with high efficiency is easy. In particular, when a polymer that easily undergoes thermal decomposition or thermal degradation is used as one component, it is necessary to keep the kneading and spinning temperatures low, which is also advantageous. Here, in the case of an amorphous polymer, since there is no melting point, it is replaced by the glass transition temperature, Vicat softening temperature or heat distortion temperature.

Furthermore, the melt viscosity is also important, and if the polymer forming the island is set lower, the island polymer is likely to be deformed by a shearing force. However, if the island polymer is excessively low in viscosity, it tends to be seamed and the blend ratio with respect to the whole fiber cannot be increased. Therefore, the island polymer viscosity is preferably 1/10 or more of the sea polymer viscosity. Further, the melt viscosity of the sea polymer may greatly affect the spinnability, and it is preferable to use a low viscosity polymer of 100 Pa · s or less as the sea polymer because the spinnability can be improved. At this time, the melt viscosity is a value at a shear rate of 1216 sec ⁻¹ at the die surface temperature during spinning.

  In addition, the amount of the island polymer in the fiber is important in order to form the fibrous material by gathering the ultrafine fibers made of the island polymer after removing the sea polymer. If the blend ratio of the island polymer is low, the ultrafine fibers left after the sea polymer is removed will not assemble sufficiently and will not form a clear fibrous material, or the strength will be very low even if a fibrous material is formed. It becomes a thing. In order to form a strong fibrous material after removing the sea polymer, the weight fraction of the island polymer in the entire fiber is preferably 20% or more, and more preferably 35% or more. However, if the island polymer fraction is too large, the sea-island structure will be destroyed and superfine fibers will not be obtained.

  When spinning the ultrafinely dispersed polymer alloy used in the present invention, the spinneret design is important, but the cooling condition of the yarn is also important. As described above, since the polymer alloy is a very unstable molten fluid, it is preferable to quickly cool and solidify after discharging from the die. For this reason, it is preferable that the distance from a nozzle | cap | die to the cooling start shall be 1-15 cm. Here, the start of cooling means a position where positive cooling of the yarn is started, but in the actual melt spinning apparatus, it is replaced with this at the upper end of the chimney.

  The spun polymer alloy fibers are preferably subjected to stretching and heat treatment, but the preheating temperature during stretching is preferably higher than the glass transition temperature (Tg) of the island polymer because the yarn spots can be reduced. .

  As described above, by treating the polymer alloy fiber thus obtained with a solvent, a fibrous material in which ultrafine fibers are aggregated can be obtained. In this case, it is preferable to use an aqueous solution as the solvent from the viewpoint of reducing the environmental load. Specifically, it is preferable to use an alkaline aqueous solution or hot water. For this reason, as the easily soluble polymer, a polymer hydrolyzed by alkali such as polyester or a derivative thereof, or a hot water-soluble polymer such as polyalkylene glycol, polyvinyl alcohol or a derivative thereof is preferable.

  Here, as a method of creating a nonwoven fabric made of a fibrous material that can be used in the battery separator of the present invention, a method of forming a nonwoven fabric after treating a polymer alloy fiber with a solvent, and a method of producing a nonwoven fabric of a polymer alloy fiber after producing a nonwoven fabric The method of processing is mentioned. When a nonwoven fabric is prepared after treatment with a solvent, the fibrous material is loosened by the external force during the preparation of the nonwoven fabric and superfine fibers are generated, which may reduce the gas permeability when used as a battery separator. It is preferable to produce a fibrous material by preparing a nonwoven fabric of alloy fibers and then treating with a solvent. In addition, as a method for producing the nonwoven fabric, it is possible to use a known production method such as a wet method, a dry method, etc., and when priority is given to air permeability, a dry method with a large opening is desired, and thinness is preferred. In this case, it is preferable to select a wet method that increases the coverage.

  The nonwoven fabric used for the battery separator of the present invention may be composed only of a fibrous material generated from the polymer alloy fiber, but may be used in combination with other fibers. In particular, fibrous materials produced from polymer alloy fibers have poor shape stability when wet, so they can be used by mixing with fibers that do not change shape due to solvent treatment in order to maintain the shape and ensure porosity. preferable. At this time, a nonwoven fabric may be prepared by mixing the fibrous material and other fibers, or a nonwoven fabric composed of the fibrous material and a nonwoven fabric composed of other fibers may be laminated and integrated. At this time, there is no particular restriction on the ratio of the fibrous material to the other fibers, but in order to maintain sufficient liquid retention as the battery separator, the fibrous material occupies the total mass of the battery separator. The ratio is preferably 40% or more, and more preferably 60% or more.

  Here, the fineness of the fiber to be mixed is not particularly limited, but it is preferably mixed with a fiber having a diameter of 1 μm (fineness of about 0.01 dtex) or more in order to improve the shape stability when wet, and the diameter is 5 μm (fineness). More preferably about 0.25 dtex) or more. However, if the diameter of the fiber to be mixed becomes too large, the pores of the nonwoven fabric become large and the positive electrode and the negative electrode are easily short-circuited. Therefore, the diameter of the mixed fiber is preferably 50 μm (fineness of about 25 dtex) or less. 30 μm (fineness of about 10 dtex) or less is more preferable.

  Here, the diameter of the mixed fiber can be determined as follows. That is, the cross section of the battery separator is observed with an SEM, and the diameter is calculated by calculating the diameter in terms of a circle from the area of the cross section of the fiber. At this time, the battery separator was cut at three locations in different directions, and the circle-converted diameters of five fibers that were considered to be cut in a plane near the fiber axis of the mixed fibers in each cross section were calculated. The average diameter of the fibers of the book is calculated to obtain the fiber diameter.

  In addition, the fiber material to be mixed may be the same as or different from the fibrous material, but it is important that the fiber material has sufficient durability against the electrolyte solution for use as a battery. When used for secondary batteries, polyolefins such as polyethylene and polypropylene (PP), polyamides such as nylon 6 (N6), nylon 66, and nylon 12, polyphenylene ether, polyphenylene ether ether ketone, polyphenylene sulfide (PPS) Polyarylenes such as can be used. Here, it is preferable to combine fibers having a melting point lower than that of the fibrous material because the strength of the nonwoven fabric can be improved by subsequent fusion by heat treatment.

  The obtained nonwoven fabric can be improved in hydrophilicity by performing a hydrophilization treatment as necessary, and water retention can be further increased. As a hydrophilic treatment method, a known method can be used. For example, when the nonwoven fabric is formed of polyolefin, sulfonation treatment, fluorination treatment, corona discharge treatment, plasma treatment, etc. can be used.

  Hereinafter, the present invention will be specifically described with reference to examples. In addition, the measuring method in an Example used the following method.

A. Polymer melt viscosity The polymer melt viscosity was measured by Toyo Seiki Capillograph 1B. The polymer storage time from sample introduction to measurement start was 10 minutes.

B. Melting | fusing point The peak top temperature which shows melting | fusing of a polymer by 2nd run using Perkin Elmaer DSC-7 was made into melting | fusing point of a polymer. The temperature rising rate at this time was 16 ° C./min, and the sample amount was 10 mg.

C. Worcester spots on fibers (U%)
Measurement was performed in the normal mode at a yarn feeding speed of 200 m / min using a USTER TESTER 4 manufactured by Zerbegger Worcester.

D. Fiber cross-sectional observation by TEM Ultra-thin sections were cut in the cross-sectional direction of the fiber, and the fiber cross-section was observed with a transmission electron microscope (TEM). Nylon was metal dyed with phosphotungstic acid.

TEM apparatus: H-7100FA type manufactured by Hitachi, Ltd. Average diameter of ultrafine fibers The fiber equivalent cross-sectional photograph by TEM was used to calculate the circle-converted diameter using image processing software (Mitani Corporation, WinROOF). At this time, 300 fibers were randomly extracted within the same cross section to obtain an average value.

F. SEM observation A part of the battery separator is sampled, arbitrarily cut at three points, a cross section is created, and a platinum-palladium alloy is vapor-deposited on the exceptional surface, followed by observation with a scanning electron microscope (SEM). The circle-converted diameter was calculated using image processing software (Mitani Corporation, WinROOF) for the five fibrous materials, and the average value of a total of 15 fibers was obtained.

SEM apparatus: Hitachi S-4000 model Mechanical properties At room temperature (25 ° C.), an initial sample length = 200 mm, a pulling speed = 200 mm / min, and a load-elongation curve was obtained under the conditions shown in JIS L1013. Next, the load value at break was divided by the initial fineness, which was used as the strength, and the elongation at break was divided by the initial sample length to obtain a strong elongation curve.

H. Liquid retention The liquid retention of the battery separator was evaluated based on the pressurized liquid retention. First, a 5 cm × 5 cm test piece was sampled and maintained in an environment of a temperature of 20 ° C. and a humidity of 65% for 24 hours to adjust the equilibrium moisture content, and then the weight (W0) was measured. Next, the test piece was submerged in ion-exchanged water, kept under reduced pressure of 93 kPa for 15 minutes, and then immersed for 1 hour to retain moisture. Next, the test piece was sandwiched between three upper and lower filter papers (Advantech Co., Ltd. No. 1), and a pressure of 5.7 MPa was applied for 30 seconds with a pressure pump, and then the weight (W1) of the separator was measured. did. And the pressurization liquid retention was computed from the following formula. This measurement was performed four times for each separator, and the average value was taken as the pressurized liquid retention.

Pressure retention ratio (%) = [(W1-W0) / W0] × 100
I. Air Permeability In order to evaluate the actual air permeability inside the battery, according to the method described in Japanese Patent Application Laid-Open No. 2001-84983, the wet flanged air permeability, which is the air permeability in the state of holding the electrolyte, was measured. First, a 20 cm × 20 cm test piece was prepared, and after sufficient water was exhausted, the water content was adjusted to hold 2.88 g (0.0072 g / cm ² ) of deionized water (water temperature 20 ° C.). I let you. The test piece was measured for air permeability according to JIS L 1096 (1999) using a Frazier type tester.

Example 1
Melt viscosity 212 Pa · s (262 ° C., shear rate 121.6 sec ⁻¹ ), melting point 220 ° C. nylon 6 (hereinafter abbreviated as N6), weight average molecular weight 120,000, melt viscosity 30 Pa · s (240 ° C., 2432 sec ⁻¹⁾ ), A poly-L lactic acid having a melting point of 170 ° C. (hereinafter abbreviated as PLA) (optical purity of 99.5% or more), N6 content of 40% by weight, and kneading at 220 ° C. with a twin-screw extrusion kneader. A polymer alloy chip was obtained. In addition, the weight average molecular weight of PLA was calculated | required as follows. The sample chloroform solution was mixed with THF (tetrahydrofuran) to obtain a measurement solution. This was measured at 25 ° C. using water permeation gel permeation chromatography (GPC) Waters 2690, and the weight average molecular weight was determined in terms of polystyrene.

Screw type Same direction complete meshing type Double thread screw Screw diameter 37mm, effective length 1670mm, L / D = 45.1
The kneading part length is 28% of the effective screw length
The kneading part was located on the discharge side from 1/3 of the effective screw length.

There are three backflow parts on the way. Polymer supply N6 and PLA were weighed separately and supplied separately to the kneader.

Temperature 220 ° C
Two vents This polymer alloy was melted at 230 ° C and led to a spin block with a spinning temperature of 230 ° C. The polymer alloy melt was filtered with a metal nonwoven fabric having a limit filtration diameter of 15 μm, and then melt-spun from a die having a die surface temperature of 215 ° C. At this time, a die having a discharge hole diameter of 0.3 mm and a discharge hole length of 0.75 mm was used. And the discharge amount per single hole at this time was 0.8 g / min. Furthermore, the distance from the base lower surface to the cooling start point was 9 cm. The discharged yarn is cooled and solidified with a cooling air of 20 ° C. over 1 m, and is supplied with an oil supply guide installed 1.8 m below the base, and then passed through an unheated first take-up roller and second take-up roller. It was wound up at 1350 m / min. The spinnability at this time was good, and there was no yarn breakage during continuous spinning for 24 hours. This was subjected to a stretching heat treatment with the temperature of the first hot roller being 90 ° C. and the temperature of the second hot roller being 130 ° C. At this time, the draw ratio between the first hot roller and the second hot roller was 2.05 times. The resulting polymer alloy fiber exhibited excellent properties of 105 dtex, 36 filament, strength 3.4 cN / dtex, elongation 36%, U% = 1.3%. Moreover, when the cross section of the obtained polymer alloy fiber was observed by TEM, PLA showed the sea (thin part), N6 (dense part) showed the sea-island structure of the island, and the number average diameter of the island N6 was 85 nm. , A polymer alloy fiber in which N6 is ultrafinely dispersed is obtained.

The polymer alloy fibers were combined with 150,000 dtex, and then crimped with a crimping machine, cut into 51 mm, and made into raw cotton. This raw cotton was carded with a roller card and entangled with a needle punch to obtain a nonwoven fabric having a basis weight of 150 g / m ² . The obtained non-woven fabric was immersed in a 3% aqueous sodium hydroxide solution (95 ° C., bath ratio 1: 100) for 2 hours to hydrolyze and remove 99% or more of the sea polymer in the polymer alloy fiber, and substantially N6 A battery separator having a basis weight of 60 g / m ² was prepared.

  When the surface of the obtained battery separator was observed with an SEM, it was confirmed that it was composed of a fibrous substance as shown in FIG. Further, when TEM observation of the fibrous material was performed, it was confirmed that the fibrous material was formed by aggregation of ultrafine fibers having a diameter of 100 nm or less as shown in FIG. As a result of performing SEM observation of the cross section of this battery separator and TEM observation of the fibrous material, the diameter of the fibrous material was 13 μm, and the average diameter of the ultrafine fibers constituting the fibrous material was 95 nm.

Comparative Example 1
Using a base of the same type as that disclosed in Japanese Patent Publication No. 47-26723, the same N6 and PLA as used in Example 1 were used to produce a 24 island sea island type composite fiber where N6 is an island and PLA is the sea. did. The spinning conditions are: N6 melting temperature 250 ° C., PLA melting temperature 220 ° C., spinning temperature 250 ° C. (cap surface temperature 235 ° C.), N6 discharge amount: PLA discharge amount = 4: 6, winding speed 900 m / min. did. The obtained fiber was drawn at a drawing temperature of 90 ° C., a heat setting temperature of 120 ° C. and a draw ratio of 2.4 times to produce a fiber having a single yarn fineness of 8 dtex.

Using the obtained fiber, crimping, cutting, carding and needle punching were performed in the same manner as in Example 1 to prepare a dry nonwoven fabric, which was then treated with an aqueous sodium hydroxide solution to have a basis weight of 60 g substantially consisting of only N6. A battery separator of / m ² was produced. When the cross section of the obtained battery separator was observed with an SEM, it was confirmed that the battery separator was formed of N6 fibers having a diameter of 4 μm.

Reference example 1
A polypropylene having a melt viscosity of 350 Pa · s (220 ° C., shear rate of 121.6 sec ⁻¹ ) and a melting point of 162 ° C. (hereinafter abbreviated as PP) (30 wt%) and PLA used in Example 1 (70 wt%) are kneaded. The temperature was 220 ° C., and melt kneading was performed in the same manner as in Example 1 to obtain polymer alloy pellets. The PLA had a melt viscosity of 107 Pa · s at 220 ° C. and 121.6 sec ⁻¹ and a melt viscosity of 86 Pa · s at 215 ° C. and 1216 sec ⁻¹ .

  Using this polymer alloy pellet, a melting temperature of 230 ° C., a spinning temperature of 230 ° C. (die surface temperature of 215 ° C.), a die hole diameter of 0.7 mm (having a measuring part of 0.3 mm on the upper part), a single hole discharge amount of 1.50 g / The melt spinning was carried out in the same manner as in Example 1 at a spinning speed of 1300 m / min. The obtained undrawn yarn was drawn and heat-treated under the conditions of a drawing temperature of 80 ° C., a draw ratio of 2.7 times, and a heat setting temperature of 100 ° C. to obtain a polymer alloy fiber having a single yarn fineness of 4 dtex.

  Also, using the same PP, melt spinning was performed at a melting temperature of 220 ° C., a spinning temperature of 220 ° C. (die surface temperature of 210 ° C.), a die hole diameter of 0.3 mm, a single hole discharge rate of 1.5 g / min, and a spinning speed of 900 m / min. It was. The obtained undrawn yarn was drawn and heat-treated under the conditions of a drawing temperature of 80 ° C., a heat setting temperature of 100 ° C., and a draw ratio of 3.3 times to obtain a PP fiber having a single yarn fineness of 5 dtex.

The polymer alloy fiber was crimped with a crimping machine, cut into 51 mm, and made into raw cotton. PP fibers were similarly crimped and cut into 51 mm to make raw cotton. The obtained polymer alloy raw cotton and PP raw cotton were mixed at a weight ratio of 90/10, carded with a roller card, and then entangled with a needle punch to obtain a nonwoven fabric having a basis weight of 200 g / m ² . This nonwoven fabric was treated with an aqueous sodium hydroxide solution in the same manner as in Example 1 to remove PLA, and a battery separator having a basis weight of 75 g / m ² consisting essentially of PP was produced.

  When the cross section of the obtained battery separator was observed with an SEM, it was confirmed that the battery separator was composed of a fiber having a diameter of 25 μm and a fibrous substance having a diameter of 14 μm. Furthermore, when TEM observation of the fibrous material was performed, it was confirmed that this fibrous material was formed by agglomeration of ultrafine fibers having an average diameter of 240 nm.

Comparative Example 2
A nonwoven fabric was produced in the same manner as in Example 2 except that only PP raw cotton was used, and a battery separator having a basis weight of 75 g / m ² was produced.

Comparative Example 3
Ultrasonic waves were applied to the nonwoven fabric obtained in Example 2 according to the method described in Example 2 of JP-A-9-302563. When the cross section of the obtained battery separator was observed with an SEM, it was confirmed that the ultrafine fibers were dispersed and covered the surface.

Example 2
Melt viscosity 190 Pa · s (300 ° C., shear rate 121.6 sec ⁻¹ ), melting point 283 ° C. polyphenylene sulfide (hereinafter abbreviated as PPS) (40% by weight) and melt viscosity 520 Pa · s (300 ° C., shear rate 121. 6 sec ⁻¹ ), polyethylene terephthalate (hereinafter abbreviated as PET) (60 wt%) having a melting point of 255 ° C. was kneaded and spun using a melt spinning apparatus equipped with a twin-screw kneader extruder. The melt viscosity of this PET at 305 ° C. and 1216 sec ⁻¹ was 270 Pa · s.

  Here, the screw configuration is as follows, kneading temperature 300 ° C., spinning temperature 315 ° C. (die surface temperature 305 ° C.), die hole diameter 0.6 mm (having a measuring part of 0.3 mm in the upper part), single hole discharge Melt spinning was carried out at an amount of 1.5 g / min and a spinning speed of 1000 m / min. The obtained undrawn yarn was subjected to drawing heat treatment under the conditions of a drawing temperature of 100 ° C., a draw ratio of 3.1 times, and a heat setting temperature of 130 ° C. to obtain polymer alloy fibers.

Screw type Same direction complete meshing type Double thread Screw diameter 15mm, effective length 672mm, L / D = 44.8
The kneading part length is 33% of the effective screw length
There are two backflow parts on the way. Polymer supply PPS and PET were weighed separately and supplied separately to the kneader.

Temperature 300 ° C
No vent Also, PP having a melting point of 162 ° C., melting temperature 200 ° C., spinning temperature 200 ° C. (die surface temperature 180 ° C.), die hole diameter 0.3 mm, single hole discharge rate 0.5 g / min, spinning speed 900 m / min As a result, melt spinning was performed. The obtained undrawn yarn was drawn and heat-treated under the conditions of a drawing temperature of 80 ° C., a heat setting temperature of 100 ° C. and a draw ratio of 3.7 times to obtain a PP fiber having a single yarn of 1.5 dtex.

The polymer alloy fiber was cut into a length of 6 mm to obtain a cut fiber. Further, PP fibers were cut in the same manner to obtain cut fibers. This polymer alloy cut fiber and PP cut fiber were mixed at a weight ratio of 90:10 and impregnated with 1% nonionic surfactant, and then poured into water and stirred for 3 minutes with a mixer. To this dispersion, a 0.1% by weight aqueous solution (viscous agent) of polyacrylamide was appropriately added, and gently stirred to prepare a slurry. Using this slurry, a wet nonwoven fabric with a basis weight of 40 g / m ² was produced with a round net paper machine. This nonwoven fabric was treated with a 5% owf of a weight loss accelerator (Marserin PES, Meisei Chemical Co., Ltd.) in a 10% by weight aqueous sodium hydroxide solution, treated at a bath ratio of 1: 100, and a temperature of 98 ° C. for 2 hours, and polymer alloy. 99% or more of the PET components contained therein were hydrolyzed and removed to obtain a nonwoven fabric composed of PPS and PP. After passing the nonwoven fabric through a hot air dryer at 200 ° C. to fuse the PP component, the thickness was adjusted to 100 μm with a calender roll set at 80 ° C. to prepare a battery separator with a weight per unit area of 20 g / m ² .

  When the cross section of the obtained battery separator was observed with an SEM, it was confirmed that the battery separator was composed of a fiber having a diameter of 14 μm and a fibrous substance having a diameter of 14 μm. Furthermore, when TEM observation of the fibrous material was performed, it was confirmed that this fibrous material was formed by aggregating super extra fine fibers having an average diameter of 70 nm.

Comparative Example 4
Using the PPS polymer used in Example 3, a melting temperature of 310 ° C., a spinning temperature of 320 ° C. (a die surface temperature of 305 ° C.), a die hole diameter of 0.3 mm, a single hole discharge amount of 0.9 g / min, and a spinning speed of 900 m / min. The melt spinning was performed under the conditions, and a heat treatment was performed under the conditions of a stretching temperature of 90 ° C., a heat setting temperature of 230 ° C., and a draw ratio of 3.1 times to produce a single-ply 3 dtex PPS fiber. This PPS fiber was cut to 6 mm and mixed with the PP cut fiber used in Example 3 at a ratio of 10: 3, and then a wet nonwoven fabric was prepared in the same manner as in Example 3 and subjected to heat treatment to have a basis weight of 20 g / m. ² battery separators were prepared.

Example 3
Nylon 66 (hereinafter abbreviated as N66) (30% by weight) having a melt viscosity of 100 Pa · s (280 ° C., shear rate 121.6 sec ⁻¹ ) and a melting point of 250 ° C., and a melt viscosity of 180 Pa · s (280 ° C., shear rate 121. 6 sec ⁻¹ ) 8 mol% of isophthalic acid and 4 mol% of bisphenol A copolymerized PET (70 wt%) having a melting point of 225 ° C. was kneaded and spun using a melt spinning apparatus equipped with a twin-screw kneader extruder. went. The copolymerized PET had a melt viscosity of 125 Pa · s at 280 ° C. and 1216 sec ⁻¹ .

  Here, the screw configuration is as follows, kneading temperature 270 ° C., spinning temperature 290 ° C. (die surface temperature 280 ° C.), die hole diameter 0.3 mm, single hole discharge rate 1.0 g / min, spinning speed 1000 m / min. As a result, melt spinning was performed. The obtained undrawn yarn was subjected to drawing heat treatment under the conditions of a drawing temperature of 100 ° C., a draw ratio of 2.6 times, and a heat setting temperature of 170 ° C. to obtain a polymer alloy fiber.

Screw type Same direction complete meshing type Double thread Screw diameter 15mm, effective length 672mm, L / D = 44.8
The kneading part length is 33% of the effective screw length
There are two backflow parts on the way. Polymer supply N66 and copolymerized PET were weighed separately and supplied separately to the kneader.

Temperature 270 ° C
2 vents Also, using a high-density polyethylene (hereinafter abbreviated as PE) having a melting point of 128 ° C., a melting temperature of 180 ° C., a spinning temperature of 180 ° C. (die surface temperature of 170 ° C.), a die hole diameter of 0.3 mm, and a single-hole discharge rate of 0 Melt spinning was carried out at a spinning speed of 900 g / min at 3 g / min. The obtained undrawn yarn was drawn and heat-treated under the conditions of a drawing temperature of 60 ° C., a heat setting temperature of 100 ° C., and a draw ratio of 3.3 times to obtain a PE fiber having a single yarn fineness of 1 dtex.

The polymer alloy fiber was cut into a length of 6 mm to obtain a cut fiber. The PE fiber was cut in the same manner to obtain a cut fiber. Polymer alloy cut fiber and PE cut fiber were mixed at a ratio of 80:20 and impregnated with 1% nonionic surfactant, then poured into water and stirred for 3 minutes with a mixer. To this dispersion, a 0.1% by weight aqueous solution (viscous agent) of polyacrylamide was appropriately added, and gently stirred to prepare a slurry. Using the slurry, a wet nonwoven fabric with a basis weight of 70 g / m ² was produced with a round net paper machine. This nonwoven fabric was treated with 5% by weight of a weight loss accelerator (Marserin PES, Meisei Chemical Co., Ltd.) in a 5% by weight aqueous sodium hydroxide solution, treated at a bath ratio of 1: 100 and a temperature of 98 ° C. for 2 hours, and polymer alloy. 99% or more of the copolymerized PET component was hydrolyzed and removed to obtain a nonwoven fabric composed of N66 and PE. Next, the PE component was fused by passing the nonwoven fabric through a hot air dryer at 130 ° C., and the thickness was adjusted to 150 μm with a calender roll set at 60 ° C. to prepare a battery separator having a basis weight of 30 g / m ² .

  When the cross section of the obtained battery separator was observed by SEM, it was confirmed that the battery separator was composed of a fiber having a diameter of 11 μm and a fibrous substance having a diameter of 14 μm. Furthermore, when TEM observation of the fibrous material was performed, it was confirmed that this fibrous material was formed by agglomeration of ultrafine fibers having an average diameter of 110 nm.

With respect to each of the battery separators of Examples 1 to 3 and Comparative Examples 1 to 4, tests for liquid retention and air permeability were performed. The results are shown in Table 1.

  As is apparent from Table 1, the battery separator containing the fibrous material of the present invention has excellent liquid retention and air permeability, and has good characteristics as a secondary battery separator. On the other hand, sufficient liquid retention was not obtained with a battery separator that does not contain ultrafine fibers. In addition, the battery separator in which the ultra-fine fibers are dispersed improves the liquid retention, but the air permeability is extremely low and the battery separator is weak against overcharge.

  Further, the battery separator of the present invention has improved liquid retention even when a hydrophobic polymer is used, and at the same time, the battery separator has excellent air permeability. This is because the hydrophobic polymer cannot absorb the electrolyte solution inside the polymer, and in the case of the normal nonwoven fabric, the electrolyte solution fills the voids of the nonwoven fabric, whereas in the battery separator of the present invention, the ultrafine particles inside the fibrous material are filled. This is probably because the electrolyte solution can be held between the fibers, so that the voids in the nonwoven fabric are not easily filled.

  As described above, the battery separator of the present invention has both liquid retention and gas permeability, and in particular, when the battery is repeatedly charged as a secondary battery separator and used over a long period of time, there is little phenomenon of electrolyte, resulting in a decrease in battery performance. Can be suppressed.

3 is a SEM photograph showing the shape of a fibrous material made of superfine fibers on the surface of the battery separator of Example 1. 3 is a cross-sectional TEM photograph showing the shape of the fibers constituting the fibrous material included in the battery separator of Example 1. FIG.

Claims (3)

Polyamide obtained by alloying polymers having different solubilities in two or more solvents using a twin-screw extrusion kneader, spinning them to obtain polymer alloy fibers, and treating the polymer alloy fibers with a solvent Or the battery separator characterized by including the fibrous material with a diameter of 1 micrometer or more formed by aggregating the super fine fibers of polyarylene having an average diameter of 500 nm or less. 2. The battery separator according to claim 1, further comprising fibers having a diameter of 1 [mu] m or more in addition to the fibrous material. Battery characterized by having a battery separators according to claim 1 or 2 wherein.