Lead-acid battery separator

Abstract

To provide a separator for a lead-acid battery capable of suppressing stratification of an electrolyte and improving battery reliability (a long life in idling stop operation and stability of capacity detection) of the lead-acid battery.SOLUTION: A lead-acid battery separator is composed of a porous back web and a plurality of ribs extending on a surface side of the back web in contact with a positive electrode plate. The rib on a surface side in contact with the positive electrode plate is a fracture rib, and its shape has two or more bending points. The fracture rib is a linear rib that bends in opposite directions at each of two consecutive bending points or a curved rib having one or more inflection points.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a separator for a lead-acid battery, which is made of a ribbed microporous film having a plurality of ribs provided at predetermined intervals, and a lead-acid battery using the separator. [Background technology]

[0002] Today, automakers are working to reduce fuel consumption and greenhouse gas emissions in order to make effective use of limited resources and prevent global warming.One form of this is the micro-hybrid system, which uses gasoline to drive the vehicle and an electric motor to regenerate energy during braking and restart the vehicle after idling.

[0003] The micro-hybrid system can reduce excess energy consumption by recovering energy through regenerative braking and by stopping the engine when idling, thereby improving fuel efficiency.

[0004] The micro-hybrid system does not require large-capacity rechargeable batteries like those used in fully electric vehicles (full EVs) and plug-in hybrid vehicles (PHEVs), and is therefore able to improve fuel efficiency at low cost, so it is currently installed in many vehicles, especially light cars.

[0005] However, with the micro-hybrid system, all of the power used for air conditioning, audio, and various indicator lights when the vehicle is stopped due to the idle stop function must be supplied by electricity from the storage battery, which places a greater burden on the storage battery than conventional gasoline vehicles.

[0006] In lead-acid batteries used in automobiles, sulfuric acid produced during charging settles to the bottom of the battery, while water produced during discharge separates at the top of the battery due to the difference in their specific gravities, forming a layer; this phenomenon is known as stratification. In conventional gasoline-powered vehicles that are not hybrids with motors, lead-acid batteries can become overcharged during charging, causing the excess power to electrolyze water, producing gas, which rises to the surface, eliminating the stratification.

[0007] However, in charge-controlled vehicles such as micro-hybrid vehicles, excessive charging is suppressed by the idling stop operation, and the amount of gas generated by water electrolysis is minimized. Therefore, stratified batteries are not subjected to the agitation action of gas, making it difficult to eliminate stratification caused by partial charging.

[0008] It is known that the output voltage and charge quantity of a lead-acid battery depend on the concentration of the electrolyte, and the charge amount and degree of battery deterioration are monitored based on the electrolyte concentration. However, stratification causes differences in the electrolyte concentration at the top and bottom of the lead-acid battery, making it impossible to correctly determine the charge amount and degree of battery deterioration, resulting in reduced reliability of battery control and a shortened battery life.

[0009] In flooded lead-acid batteries, attempts have been made to suppress or eliminate stratification by using the shape of polyethylene separators, which are currently widely used (see, for example, Patent Documents 1 and 2), and expectations for separators are growing.

[0010] There is a demand for lead-acid batteries with high reliability (longer battery life during idling stop operation, stable charge level detection). To this end, separators with various rib shapes are required to control the movement of electrolyte inside the battery case and prevent stratification of the electrolyte. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Special Publication No. 2018-530126 [Patent Document 2] Japanese Patent Application Publication No. 2-94253 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a separator for a lead-acid battery that can suppress stratification of the electrolyte and improve the battery reliability (longer life during idling stop operation and more stable charge amount detection) of the lead-acid battery. [Means for solving the problem]

[0013] As a result of extensive research to solve the above problems, the separator for a lead acid battery of the present invention is a separator for a lead acid battery having the following characteristics. (1) A separator for a lead-acid battery used in a flooded lead-acid battery, comprising a porous back web and a plurality of ribs extending on the surface of the back web that contacts the positive electrode plate, wherein the ribs on the surface that contacts the positive electrode plate are breaking ribs, and the breaking ribs have two or more bending points and are either linear breaking ribs that bend in opposite directions at each of two consecutive bending points, or curved breaking ribs that have one or more inflection points. (2) The separator for a lead-acid battery according to (1) above, wherein the breaking ribs include those having different bending angles or line segments having different lengths. (3) The separator for a lead-acid battery according to (1) above, wherein the breaking rib has two-fold rotational symmetry. (4) The separator for a lead-acid battery according to (1) above, wherein the breaking rib is a straight breaking rib with line segments located at both ends being approximately parallel to each other. (5) The separator for a lead-acid battery according to any one of (1) to (4) above, wherein the breaking ribs are linear breaking ribs having a bending angle of 90 degrees or more and less than 180 degrees at all bending points. (6) The lead-acid battery separator according to any one of (1) to (5) above, wherein the breaking rib is a linear breaking rib having two bending points. (7) The lead-acid battery separator according to any one of (1) to (3), wherein the breaking rib is a curved breaking rib in which the angle of the interior formed by the tangent at an inflection point and the tangent at an adjacent inflection point, or the angle of the interior formed by the tangent at the inflection point and the tangent at the tip of the rib, is 90 degrees or more and less than 180 degrees. (8) The separator for a lead-acid battery according to (7), characterized in that the breaking rib is a curved breaking rib having one inflection point, and the interior angle formed by a tangent at the inflection point and a tangent at the tip of the rib is 90 degrees or more and less than 180 degrees. (9) A separator for a lead-acid battery according to any one of (1) to (8) above, characterized in that the plurality of breaking ribs are arranged approximately horizontally to one another with respect to the horizontal direction (CD direction) of the separator. (10) A separator for a lead-acid battery according to any one of (1) to (8) above, characterized in that the plurality of breaking ribs are arranged so that the breaking rib and another breaking rib adjacent to the breaking rib in the vertical direction (MD direction) of the separator do not completely overlap each other in the vertical direction (MD direction) of the separator. (11) A separator for a lead-acid battery according to any one of (1) to (8) above, characterized in that the plurality of breaking ribs are arranged so that a gap formed between a pair of breaking ribs adjacent to each other in the horizontal direction (CD direction) of the separator does not completely overlap in the vertical direction (MD direction) of the separator with a gap formed between another pair of breaking ribs adjacent to each other in the horizontal direction (CD direction) of the separator, the gap being adjacent in the vertical direction (MD direction) of the separator. (12) The lead-acid battery separator according to any one of (1) to (8), characterized in that the plurality of fracturing ribs are located on the right side of the fracturing rib in the horizontal direction (CD) of the separator, and the gap formed between the fracturing rib and the nearest adjacent fracturing rib is located on the right side of the fracturing rib in the horizontal direction (CD) of the separator, so as not to overlap with the gap formed between the fracturing rib and the second nearest adjacent fracturing rib in the up-down direction (MD) of the separator; or the fracturing ribs are located on the left side of the horizontal direction (CD) of the separator, and the gap formed between the fracturing rib and the nearest adjacent fracturing rib is located on the left side of the horizontal direction (CD) of the separator, so as not to overlap with the gap formed between the fracturing rib and the second nearest adjacent fracturing rib in the up-down direction (MD) of the separator. (13) A lead-acid battery using the separator according to any one of (1) to (12) above. [Effects of the Invention]

[0014] The lead-acid battery separator of the present invention has breaking ribs with a shape effective for controlling the movement of the electrolyte inside the battery case, and the breaking ribs are arranged so as to effectively control the movement of the electrolyte inside the battery case, so that stratification of the electrolyte can be suppressed, and deterioration in the reliability of battery control and shortened battery life due to stratification of the electrolyte can be suppressed. [Brief explanation of the drawings]

[0015] [Figure 1] This is an example of a linear breaking rib that bends in opposite directions at two consecutive bending points. [Figure 2] 10 shows an example of the arrangement of breaking ribs arranged on the surface of the separator that comes into contact with the positive electrode plate. [Figure 3] 10 shows an example of the arrangement of breaking ribs arranged on the surface of the separator that comes into contact with the positive electrode plate. [Figure 4]10 shows an example of the arrangement of breaking ribs arranged on the surface of the separator that comes into contact with the positive electrode plate. [Figure 5] 10 shows an example of the arrangement of breaking ribs arranged on the surface of the separator that comes into contact with the positive electrode plate. [Figure 6] 10 shows an example of the arrangement of breaking ribs arranged on the surface of the separator that comes into contact with the positive electrode plate. [Figure 7] 10 shows an example of the arrangement of breaking ribs arranged on the surface of the separator that comes into contact with the positive electrode plate. DETAILED DESCRIPTION OF THE INVENTION

[0016] The lead-acid battery separator of the present invention comprises a porous back web and a plurality of ribs extending on the surface of the back web that contacts the positive electrode plate, and the ribs on the surface that contacts the positive electrode plate are either linear ribs having two or more bending points and bending in opposite directions at each of two consecutive bending points, or curved ribs having one or more inflection points. This prevents the high-specific-gravity electrolyte (sulfuric acid) from migrating downward toward the bottom of the battery during charging, thereby suppressing stratification of the electrolyte.

[0017] FIG. 1 shows an example of the linear fracture rib used in the lead-acid battery separator of the present invention, which has two or more bending points and is bent in opposite directions at each of two consecutive bending points. The straight breaking rib shown in FIG. 1 has two bending points, and in this case, (a), (b), and (c) respectively represent line segments of the straight breaking rib. As the linear breaking rib having two or more bending points and bending in opposite directions at each of two consecutive bending points, those having two-fold rotational symmetry are preferably used, for example, those in which the interior angle (bending angle) formed by line segment (a) and line segment (b) is the same as the interior angle (bending angle) formed by line segment (b) and line segment (c), and the lengths of line segment (a) and line segment (c) are the same. However, those in which the interior angle (bending angle) formed by line segment (a) and line segment (b) is different from the interior angle (bending angle) formed by line segment (b) and line segment (c), or those in which the lengths of line segment (a) and line segment (c) are different are also acceptable.

[0018] In the present invention, the linear breaking rib has two or more bending points and bends in opposite directions at two consecutive bending points, and the line segments located at both ends, for example, line segment (a) and line segment (c), are preferably approximately parallel to each other, i.e., the difference between the interior angle (bending angle) formed by line segment (a) and line segment (b) and the interior angle (bending angle) formed by line segment (b) and line segment (c) is preferably within 10 degrees, and more preferably within 5 degrees.

[0019] In the present invention, as for the linear breaking rib having two or more bending points and bending in opposite directions at each of two consecutive bending points, it is preferable that the bending angle (inner angle) at all bending points is 90 degrees or more and less than 180 degrees, and more preferably 120 degrees or more and 150 degrees or less. Also, those having an even number of bending points are preferred, and those having two bending points are more preferred.

[0020] The line segments in the curved fracture rib having one or more inflection points used in the lead-acid battery separator of the present invention refer to the segments between adjacent extreme points in the curved fracture rib, and between an end of the fracture rib and an adjacent extreme point. The curved breaking rib having one or more inflection points is preferably one having two-fold rotational symmetry. For example, in the case of a curved breaking rib having one inflection point, the radii of curvature at two adjacent extreme points are the same, and the lengths of the two line segments located between the two breaking rib ends and the adjacent extreme point are the same. However, the radii of curvature at two adjacent extreme points may be different, or the lengths of the two line segments located between the two breaking rib ends and the adjacent extreme point may be different.

[0021] In the present invention, the curved breaking rib having one or more inflection points is preferably one in which the interior angle formed by the tangent at an inflection point and the tangent at an adjacent inflection point, or the interior angle formed by the tangent at the inflection point and the tangent at the tip of the rib, is 90 degrees or more and less than 180 degrees, and more preferably 120 degrees or more and 150 degrees or less. It is also preferable to have an odd number of inflection points, and more preferably to have one inflection point, and the interior angle formed by the tangent at the inflection point and the tangent at the tip of the rib is preferably greater than or equal to 90 degrees and less than 180 degrees, and more preferably greater than or equal to 120 degrees and less than 150 degrees.

[0022] The fracture ribs used in the lead-acid battery separator of the present invention preferably have a total length (for example, in the linear fracture rib shown in FIG. 1, the sum of the lengths of line segments (a), (b), and (c)) of 5 to 40 mm, a height of 0.05 to 1.20 mm, and a width of 0.5 to 2.0 mm (preferably 0.5 mm to 1.0 mm). The vertical cross-sectional shape of the fracture rib is preferably a square, a trapezoid, a semicircular, a rectangle with a dome-shaped top, a trapezoid with a dome-shaped top, a trapezoid with curved sides in the height direction, a square with chamfered corners of the top, or an isosceles triangle.

[0023] In lead-acid batteries used in automobiles, the high specific gravity of sulfuric acid generated on the positive electrode plate during charging sinks to the bottom (bottom) of the battery due to the difference in specific gravity, causing stratification of the electrolyte. The separator for a lead-acid battery of the present invention has a breaking rib having a specific shape arranged on the surface that comes into contact with the positive electrode plate, thereby inhibiting the migration of high-density sulfuric acid, which is generated during charging, to the bottom (downward) of the battery and suppressing stratification of the electrolyte.

[0024] The high-specific-gravity sulfuric acid generated at the positive electrode plate flows down the surface of the separator that contacts the positive electrode plate and settles to the bottom (downward) of the battery. At this time, the movement of the sulfuric acid to the bottom (downward) of the battery is inhibited by the breaking rib having the specific shape that is arranged on the surface that contacts the positive electrode plate.

[0025] Furthermore, in the lead-acid battery separator of the present invention, the breaking ribs having the specific shape are arranged so that when the sulfuric acid moves to the bottom (downward) of the battery, the sulfuric acid is prevented from moving downward in a straight line from the top of the battery to the bottom, and moves downward in a zigzag pattern. That is, in the lead-acid battery separator of the present invention, as in the examples of arrangement of the breaking ribs shown in Figures 2 to 5, the breaking ribs are arranged approximately horizontally to each other with respect to the horizontal direction (CD direction) of the separator, thereby inhibiting the movement of sulfuric acid toward the bottom (downward) of the battery. For example, in the case of the linear breaking rib shown in FIG. 1, it is preferable that the line segment (b), or the line segment (a) and / or the line segment (c) be arranged at an inclination of 90 degrees or less relative to the horizontal direction (CD direction) of the separator, and it is more preferable that they be arranged at an inclination of 60 degrees or less. Furthermore, for example, in the case of a curved breaking rib having one inflection point, it is preferable that the tangent at the inflection point is inclined at an angle of 45 degrees or less relative to the horizontal direction (CD direction) of the separator, more preferably at an angle of 30 degrees or less, and even more preferably at an angle of 10 degrees or less.

[0026] In the lead-acid battery separator of the present invention, it is preferable that adjacent breaking ribs in the vertical direction (MD direction) of the separator are arranged so that they do not completely overlap each other when viewed from the vertical direction (MD direction) of the separator, so that sulfuric acid generated during charging is prevented from moving downward linearly by the arranged breaking ribs and moves downward in a zigzag pattern.

[0027] In the lead-acid battery separator of the present invention, to prevent sulfuric acid generated during charging from passing through the gap between a breaking rib and another breaking rib adjacent to the breaking rib in the horizontal direction (CD direction) of the separator and moving linearly downward (parallel to the up-down direction of the separator) from the top of the battery to the bottom of the battery, the overlap between the gap formed between a pair of adjacent breaking ribs in the horizontal direction (CD direction) of the separator and the gap formed between another pair of adjacent breaking ribs in the horizontal direction (CD direction) of the separator, which are arranged adjacent to each other in the up-down direction (MD direction) of the separator, is preferably less than 50%, more preferably less than 20%, and even more preferably 0%. In this case, the gap formed between a pair of adjacent fracture ribs in the horizontal direction (CD direction) of the separator refers to the gap formed between a pair of adjacent fracture ribs arranged approximately parallel to the horizontal direction (CD direction) of the separator, as shown in the fracture rib arrangement examples in Figures 3 to 5. For example, in the example of the arrangement of the fracture ribs in Figure 4, there is no overlap (0% overlap) between the gap formed between a pair of adjacent fracture ribs located on the top left side and the gap formed between a pair of adjacent fracture ribs located on the left side in the second row from the top, which are arranged adjacently below in the vertical direction (MD direction) of the separator. The same applies to the examples of arrangement of the breaking ribs shown in FIGS. Furthermore, in the example of the arrangement of the fracture ribs shown in Figure 2, for example, there is no overlap (0% overlap) between the gap formed between the fracture rib arranged first from the top in the third row from the left and the fracture rib arranged first from the top in the second row from the left, and the gap formed between the fracture rib arranged first from the top in the second row from the left and the fracture rib arranged second from the top in the third row from the left, which are adjacent gaps arranged below in the vertical direction (MD direction) of the separator. In the lead-acid battery separator of the present invention, it is preferable that the breaking ribs arranged while maintaining the above-mentioned relationship (the degree of overlap, as viewed from the vertical direction (MD) of the separator, between the gap formed between one pair of adjacent breaking ribs and the gap formed between another pair of adjacent breaking ribs arranged adjacently below in the vertical direction (MD) of the separator) account for 50% or more of the total breaking ribs arranged on the surface of the separator that comes into contact with the positive electrode plate.

[0028] Furthermore, except when the breaking rib is positioned at the top or bottom of the separator, the overlap between the gap formed between the breaking rib and another breaking rib located to the right of the breaking rib in the horizontal direction (CD direction) of the separator and positioned closest to the breaking rib, and the gap formed between the breaking rib and another breaking rib located to the right of the breaking rib in the horizontal direction (CD direction) of the separator and positioned second closest to the breaking rib, when viewed from the top to bottom (MD direction) of the separator, is preferably less than 50%, more preferably less than 20%, and even more preferably 0%. In this case, the gap formed between a breaking rib and another breaking rib located to the right of the breaking rib in the horizontal direction (CD direction) of the separator and arranged closest to the breaking rib means, for example, in the example of breaking rib arrangement in Figure 2, the gap formed between the breaking rib arranged second from the top in the second row from the left and another breaking rib located to the right of the breaking rib in the horizontal direction (CD direction) of the separator and arranged closest to the breaking rib, i.e., the breaking rib arranged third from the top in the third row from the left (the shortest distance between the end of the breaking rib and the adjacent breaking rib). Furthermore, the gap formed between the break rib and another break rib located to the right of the break rib in the horizontal direction (CD direction) of the separator and arranged adjacent to the break rib in the second closest position means, for example, in the example of break rib arrangement in Figure 2, the gap formed between the break rib arranged second from the top in the second row from the left and another break rib located to the right of the break rib in the horizontal direction (CD direction) of the separator and arranged adjacent to the break rib in the second closest position (the shortest distance between the break rib and the end of the adjacent break rib). In the example of the arrangement of the rupture ribs in FIG. 2, these two gaps do not overlap (0% overlap) when viewed from the top-bottom direction (MD direction) of the separator. Similarly, except when the rib is positioned at the top or bottom of the separator, the overlap between the gap formed between the rib and another rib located to the left of the rib in the horizontal direction (CD) of the separator and positioned closest to the rib, and the gap formed between the rib and another rib located to the left of the rib in the horizontal direction (CD) of the separator and positioned second closest to the rib, when viewed from the top to bottom (MD) of the separator, is preferably less than 50%, more preferably less than 20%, and even more preferably 0%. In this case, the gap formed between a breaking rib and another breaking rib located to the left of the breaking rib in the horizontal direction (CD direction) of the separator and arranged closest to the breaking rib means, for example, in the example of breaking rib arrangement in Figure 2, the gap formed between the breaking rib arranged third from the top in the second row from the right and another breaking rib located to the left of the breaking rib in the horizontal direction (CD direction) of the separator and arranged closest to the breaking rib, i.e., the breaking rib arranged second from the top in the third row from the right (shortest distance between the breaking rib and the end of the adjacent breaking rib). Furthermore, the gap formed between the break rib and another break rib located to the left of the break rib in the horizontal direction (CD direction) of the separator and arranged adjacent to the break rib in the second closest position means, for example, in the example of break rib arrangement in Figure 2, the gap formed between the break rib arranged third from the top in the second row from the right and another break rib located to the left of the break rib in the horizontal direction (CD direction) of the separator and arranged adjacent to the break rib in the second closest position (i.e., the break rib arranged third from the top in the third row from the right) (the shortest distance between the end of the break rib and the adjacent another break rib). In the example of the arrangement of the rupture ribs in FIG. 2, these two gaps do not overlap (0% overlap) when viewed from the top-bottom direction (MD direction) of the separator.

[0029] The fracture rib shown in the fracture rib arrangement example in Figure 2 is a linear fracture rib with two bending points, with the line segments at both ends being approximately parallel to each other, and the bending angles at all bending points being greater than or equal to 90 degrees and less than 180 degrees. The line segments (b) (see FIG. 1) of the breaking ribs are arranged so as to be substantially parallel to each other in the horizontal direction (CD direction) of the separator. Furthermore, except when the breaking rib is arranged at the top or bottom of the separator, the breaking rib is arranged so that there is no overlap (0% overlap) between the gap formed between the breaking rib and another breaking rib located to the right of the breaking rib in the horizontal direction (CD direction) of the separator and arranged closest to the breaking rib, and the gap formed between the breaking rib and another breaking rib located to the right of the breaking rib in the horizontal direction (CD direction) of the separator and arranged second closest to the breaking rib. With this arrangement, when sulfuric acid generated in the positive electrode plate sinks down the surface of the separator that contacts the positive electrode plate to the bottom (bottom) of the battery, its linear downward movement is hindered by the arranged fracture ribs, and it moves along the shape of the fracture ribs. Then, sulfuric acid that has moved along the shape of the fracture ribs will sink to the bottom (bottom) of the battery from the lower end of the fracture rib in the vertical direction (MD) of the separator (the gap formed between a pair of adjacent fracture ribs). However, its linear downward movement is hindered by another fracture rib arranged adjacently below in the vertical direction (MD) of the separator, and it moves along the shape of the fracture rib. In this way, sulfuric acid generated in the positive electrode plate is prevented from moving linearly downward from the top to the bottom of the battery, and moves downward in a zigzag pattern due to the arranged fracture ribs and their shape, which is thought to make it less likely for the electrolyte to stratify.

[0030] The fracture rib shown in the fracture rib arrangement example in Figure 3 is a linear fracture rib with two bending points, with the line segments at both ends parallel to each other and the bending angles at all bending points being greater than 90 degrees and less than 180 degrees. The line segments (a) and (c) (see FIG. 1) of the breaking ribs are arranged so that they are parallel to each other in the horizontal direction (CD direction) of the separator. Furthermore, the breaking ribs are arranged so that there is no overlap (0% overlap) between a gap formed between a pair of breaking ribs adjacent to each other in the horizontal direction (CD direction) of the separator and a gap formed between another pair of breaking ribs adjacent to each other in the horizontal direction (CD direction) of the separator, as viewed from the vertical direction (MD direction) of the separator. By adopting such an arrangement, similar to the arrangement example shown in FIG. 2, sulfuric acid generated in the positive electrode plate is prevented from moving downward in a straight line from the top of the battery to the bottom of the battery, but moves downward in a zigzag pattern due to the arranged breaking ribs and their shape, which is thought to make it difficult for stratification of the electrolyte to occur.

[0031] The fracture rib shown in the fracture rib arrangement example in Figure 4 is a linear fracture rib with two bending points, with the line segments at both ends parallel to each other and the bending angle at all bending points being 90 degrees. The line segments (b) (see FIG. 1) of the breaking ribs are arranged so that they are parallel to each other in the horizontal direction (CD) of the separator. Furthermore, the breaking ribs are arranged so that there is no overlap (0% overlap) between a gap formed between a pair of breaking ribs adjacent to each other in the horizontal direction (CD) of the separator and a gap formed between another pair of breaking ribs adjacent to each other in the horizontal direction (CD) of the separator, as viewed from the vertical direction (MD) of the separator. By adopting such an arrangement, similar to the arrangement example shown in FIG. 2, sulfuric acid generated in the positive electrode plate is prevented from moving downward in a straight line from the top of the battery to the bottom of the battery, but moves downward in a zigzag pattern due to the arranged breaking ribs and their shape, which is thought to make it difficult for stratification of the electrolyte to occur.

[0032] The fracture rib shown in the fracture rib arrangement example in Figure 5 is a curved fracture rib with one inflection point, and the interior angle formed by the tangent at the inflection point and the tangent at the tip of the rib is greater than 90 degrees and less than 180 degrees. The tangential lines at the inflection points of the breaking ribs are arranged so as to be approximately parallel to the horizontal direction (CD) of the separator. Furthermore, the breaking ribs are arranged so that there is no overlap (0% overlap) between a gap formed between a pair of breaking ribs adjacent to each other in the horizontal direction (CD) of the separator and a gap formed between another pair of breaking ribs adjacent to each other in the horizontal direction (CD) of the separator, as viewed from the vertical direction (MD) of the separator. By adopting such an arrangement, similar to the arrangement example shown in FIG. 2, sulfuric acid generated in the positive electrode plate is prevented from moving downward in a straight line from the top of the battery to the bottom of the battery, but moves downward in a zigzag pattern due to the arranged breaking ribs and their shape, which is thought to make it difficult for stratification of the electrolyte to occur.

[0033] In the separator for a lead-acid battery of the present invention, when the size of the separator is 115 mm × 120 mm, the number of breaking ribs is preferably 4 to 20 in the horizontal direction (CD direction) of the separator and 10 to 20 in the vertical direction (MD direction) of the separator, and more preferably 5 to 10 in the horizontal direction (CD direction) of the separator and 10 to 15 in the vertical direction (MD direction) of the separator.

[0034] In the separator for a lead-acid battery of the present invention, the thickness of the separator, excluding the height of the ribs, is preferably 0.1 to 0.3 mm, more preferably 0.15 mm or more and 0.25 mm or less. If the base thickness is too thick, the internal resistance of the lead-acid battery increases, making it undesirable for use in a lead-acid battery for an idle-stop vehicle. On the other hand, if the base thickness is less than 0.15 mm, the strength of the separator decreases, and the separator may break when vibrated, which is undesirable. It is also preferable that the total thickness of the separator including the ribs is 1.4 mm or less.

[0035] In the lead-acid battery separator of the present invention, the porosity of the separator (mercury porosimetry) is preferably 50 to 90% by volume. A porosity of 50% by volume or more can keep the internal resistance (electrical resistance) of the separator low, contributing to improved performance of the lead-acid battery. Therefore, the porosity of the separator (mercury porosimetry) is more preferably 60 to 90% by volume, and even more preferably 70 to 90% by volume.

[0036] In the lead-acid battery separator of the present invention, the breaking ribs are preferably made of the same material as the separator base, which is the flat plate portion of the separator, and are integrally molded with the base. In this case, the separator can be advantageous in terms of productivity and manufacturing costs.

[0037] The separator for a lead-acid battery of the present invention is not particularly limited in terms of constituent materials, manufacturing method, etc., but may be obtained, for example, by extruding a raw material composition containing appropriate amounts of a thermoplastic resin, inorganic powder, and plasticizer into a sheet while heating, melting, and kneading it using a twin-screw extruder or the like, passing the extruded material between a pair of forming rolls having predetermined grooves cut into them in advance so as to impart a predetermined rib shape to a sheet of predetermined thickness and shape, immersing the sheet in an appropriate solvent that is compatible with the plasticizer to extract and remove a predetermined amount of the plasticizer, and then drying the extruded material.

[0038] Examples of thermoplastic resins that can be used in the lead acid battery separator of the present invention include polyvinyl resins such as polyvinyl chloride (PVC); and polyolefin resins such as polyethylene, polypropylene, and ethylene-butene copolymers. In the lead-acid battery separator of the present invention, a polyolefin resin is preferably used, more preferably a polyethylene resin, and even more preferably a high-molecular-weight polyethylene resin. The high-molecular-weight polyethylene resin preferably has a molecular weight of at least 600,000, and more preferably an ultra-high-molecular-weight polyethylene resin (UHMWPE) with a molecular weight of 5,000,000.

[0039] Examples of inorganic powders that can be used in the lead-acid battery separator of the present invention include silica such as precipitated silica and fumed silica, mica, montmorillonite, kaolinite, talc, diatomaceous earth, vermiculite, natural and synthetic zeolites, calcium silicate, clay, aluminum silicate, sodium aluminum silicate, aluminum polysilicate, alumina silica gel, glass particles, carbon black, activated carbon, carbon fiber, graphite, titanium oxide, iron oxide, copper oxide, zinc oxide, lead oxide, tungsten, antimony oxide, zirconia, magnesia, alumina, molybdenum disulfide, zinc sulfide, barium sulfate, strontium sulfate, calcium carbonate, and magnesium carbonate. In the lead acid battery separator of the present invention, silica such as precipitated silica and fumed silica is preferably used.

[0040] The plasticizer used in the lead-acid battery separator of the present invention is preferably a material that can act as a plasticizer for polyolefin-based resins, and various organic liquids that are compatible with polyolefin-based resins and can be easily extracted with various solvents can be used. Specifically, the plasticizer can be mineral oil such as industrial lubricating oil made from saturated hydrocarbons (paraffins), higher alcohols such as stearyl alcohol, or ester-based plasticizers such as dioctyl phthalate. Among these, mineral oil is preferred because of its ease of reuse. The plasticizer is preferably blended in the raw material composition in an amount of 30 to 70% by weight.

[0041] As the solvent used to extract and remove the plasticizer, a saturated hydrocarbon organic solvent such as hexane, heptane, octane, nonane, or decane can be used.

[0042] If necessary, additives such as antioxidants, ultraviolet absorbers, weathering agents, lubricants, antibacterial agents, antifungal agents, pigments, dyes, colorants, antifogging agents, and matting agents may be added (blended) or contained in the raw material composition or the separator after film formation, within a range that does not impair the object and effect of the present invention.

[0043] Next, an embodiment of a lead-acid battery using the separator for a lead-acid battery of the present invention will be described, but the lead-acid battery of the present invention is not limited to the following embodiment.

[0044] [Electrolyte] The electrolyte contains sulfuric acid in an aqueous solution. The electrolyte may be gelled if desired. The electrolyte may optionally contain additives commonly used in lead-acid batteries. The specific gravity of the electrolyte at 20°C in a lead-acid battery in a fully charged state after formation is, for example, 1.10 g / cm 3 or more, and 1.35 g / cm 3 The following is the result.

[0045] [Positive electrode] There are two types of positive electrodes for lead-acid batteries: paste type and clad type. A paste-type positive electrode plate includes a positive electrode current collector and a positive electrode material. The positive electrode material is held by the positive electrode current collector. In a paste-type positive electrode plate, the positive electrode material is the positive electrode plate minus the positive electrode current collector. The positive electrode current collector may be formed in the same manner as the negative electrode current collector, and may be formed by casting lead or a lead alloy or by processing a lead or lead alloy sheet.

[0046] A clad positive electrode plate includes multiple porous tubes, a metal core inserted into each tube, a positive electrode material filled into the tube with the metal core inserted, and a connecting seat connecting the multiple tubes. In a clad positive electrode plate, the positive electrode material is the positive electrode plate excluding the tubes, the metal core, and the connecting seat.

[0047] The lead alloy used for the positive electrode current collector is preferably a Pb-Ca alloy or a Pb-Ca-Sn alloy in terms of corrosion resistance and mechanical strength. The positive electrode current collector may have lead alloy layers with different compositions, or may have multiple alloy layers. The core metal is preferably a Pb-Ca alloy or a Pb-Sb alloy. The positive electrode material contains a positive electrode active material (lead dioxide or lead sulfate) that generates capacity through an oxidation-reduction reaction. The positive electrode material may contain other additives as needed.

[0048] Unformed paste-type positive plates are obtained by filling a positive electrode current collector with positive electrode paste, aging it, and drying it, similar to the case of negative plates. The unformed positive plate is then formed. The positive electrode paste is prepared by kneading lead powder, additives, water, and sulfuric acid. The clad type positive electrode plate is formed by filling a tube with lead powder or lead powder slurry into a core metal inserted into the tube, and then joining a plurality of the tubes together with a connecting member.

[0049] [Negative electrode] The negative electrode plate of a lead-acid battery is composed of a negative electrode current collector and a negative electrode material. The negative electrode material is the negative electrode plate without the negative electrode current collector. The negative electrode current collector may be formed by casting lead (Pb) or a lead alloy, or by processing a lead or lead alloy sheet. Examples of processing methods include expanding and punching. It is preferable to use a negative electrode grid as the negative electrode current collector because it makes it easy to support the negative electrode material.

[0050] The lead alloy used for the negative electrode current collector may be any of a Pb-Sb alloy, a Pb-Ca alloy, and a Pb-Ca-Sn alloy. These lead or lead alloys may further contain at least one additive element selected from the group consisting of Ba, Ag, Al, Bi, As, Se, and Cu.

[0051] The negative electrode material contains a negative electrode active material (lead or lead sulfate) that exhibits capacity through an oxidation-reduction reaction, and may also contain a shrinkage inhibitor, a carbonaceous material such as carbon black, barium sulfate, etc., and may also contain other additives as necessary.

[0052] The negative electrode active material in the charged state is sponge lead, but the unformed negative electrode plate is usually made using lead powder.

[0053] The negative electrode plate can be formed by filling a negative electrode current collector with a negative electrode paste, aging and drying the paste to produce an unformed negative electrode plate, and then chemically forming the unformed negative electrode plate. The negative electrode paste can be produced by adding water and sulfuric acid to lead powder, an organic shrinkage inhibitor, and various additives as needed, and kneading the mixture. In the aging step, the unformed negative electrode plate is preferably aged at a temperature higher than room temperature and at a high humidity.

[0054] The formation can be carried out by immersing an electrode plate assembly including unformed negative plates in an electrolyte containing sulfuric acid in a battery jar of a lead-acid battery and then charging the electrode plate assembly. However, the formation can also be carried out before assembling the lead-acid battery or the electrode plate assembly. The formation produces spongy lead. [Example]

[0055] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention.

[0056] [Preparation of Microporous Film Separator] (Example 1) A mixer was used to mix 30 parts by weight of ultra-high molecular weight polyethylene (UHMWPE) resin powder with a weight-average molecular weight of 5 million as a thermoplastic resin, 70 parts by weight of fine silica powder with an average particle size of 15 μm as an inorganic powder, and paraffinic oil, a type of mineral oil, as a plasticizer. The resulting mixture was heated, melted, and kneaded in a twin-screw extruder, then extruded into a sheet through a T-die and pressure-molded between a pair of forming rolls with grooves on both sides corresponding to the rib pattern. This resulted in a non-porous film integrally molded with a main rib of a predetermined shape for contacting the positive electrode plate on one side and linear, continuous mini-ribs for contacting the negative electrode parallel to the extrusion flow direction (machine direction: MD) on the opposite side. The continuous nonporous film was then immersed in a bath of organic solvent to extract and remove the paraffinic oil, leaving only a portion of it. The film was then passed through a drying oven to produce a microporous film separator with a total thickness of 0.70 mm and a base thickness of 0.20 mm. The fracture rib for contacting the positive electrode has a linear fracture rib shape with two bending points as shown in Figure 1. The lengths and angles of each side of the fracture rib, line segment (a), line segment (b), and line segment (c), are 4.5 mm for line segment (a) and (c), and 10 mm for line segment (b). The angle between line segment (a) and line segment (c) and line segment (b) is 135 degrees, and line segment (b) is parallel to the horizontal direction (CD) of the separator. As shown in Figure 2, the fracture ribs are arranged approximately horizontally, and adjacent fracture ribs in the horizontal direction (CD) of the separator are mirror-symmetrical with respect to an axis parallel to the vertical direction (MD) of the separator. Furthermore, the gaps between adjacent break ribs in the horizontal direction (CD direction) of these separators and the gaps between adjacent break ribs in the horizontal direction (CD direction) of the separators that are positioned closest to each other in the up-down direction (MD direction) of the separators (for example, in Figure 2, the gap between the break rib positioned second from the top in the leftmost row and the break rib positioned second from the top in the second row from the left, and the gap between the break rib positioned second from the top in the leftmost row and the break rib positioned first from the top in the second row from the left) do not overlap with each other at all when viewed from the up-down direction (MD direction) of the separator, and all of these gaps are 3 mm. The breaking rib for contacting the positive electrode has a trapezoidal cross section perpendicular to the longitudinal direction of the rib, the height of the rib is 0.40 mm, the bottom width of the trapezoidal cross section of the rib is 0.80 mm, and the top width is 0.40 mm. On the other hand, the cross section of the negative electrode contacting mini-rib perpendicular to the longitudinal direction of the mini-rib is rectangular. The height of the mini-rib is 0.10 mm, the distance between the mini-ribs is 0.55 mm, and the width of the mini-rib is 0.10 mm.

[0057] Example 2 A microporous film separator similar to that of Example 1 was produced, except that the length of the line segment (b) of the positive electrode contact rib was set to 7 mm.

[0058] (Comparative Example 1) A microporous film separator similar to that of Example 1 was produced, except that the ribs for contacting the positive electrode were linear and continuous in the vertical direction (MD direction) of the separator, and the width between each rib was 10 mm.

[0059] (Comparative Example 2) As shown in Figure 6, the ribs for contacting the positive electrode consisted of straight ruptured ribs 12 mm long with no bending points, inclined at 75 degrees with respect to the horizontal direction (CD direction) of the separator, and arranged at equal intervals of 12 mm in the horizontal direction (CD direction) of the separator. Two sets of these ribs were aligned in the vertical direction (MD direction) of the separator (Arrangement 1), and two sets of these ribs were aligned in the vertical direction (MD direction) of the separator, inclined at 105 degrees with respect to the horizontal direction (CD direction) of the separator, and arranged at equal intervals of 12 mm in the horizontal direction (CD direction) of the separator (Arrangement 2). Except for this, Arrangements 1 and 2 were alternately arranged with no gaps in the vertical direction (MD direction) of the separator.

[0060] (Comparative Example 3) As shown in Figure 7, the rib for contacting the positive electrode consists of two types of linear fracture ribs (fracture rib A and fracture rib B) with a length of 25 mm and no bending points, the fracture rib A has an inclination of 45 degrees with respect to the horizontal direction (CD direction) of the separator and is arranged at equal intervals of 30 mm in the horizontal direction (CD direction) and the vertical direction (MD direction) of the separator, the fracture rib B has an inclination of 135 degrees with respect to the horizontal direction (CD direction) of the separator and is arranged at equal intervals of 30 mm in the horizontal direction (CD direction) and the vertical direction (MD direction) of the separator, and the midpoint of the fracture rib B is arranged so that it overlaps with the midpoint of the line connecting the end points of a pair of fracture ribs A arranged closest to the center point. A microporous film separator similar to that of Example 1 was produced.

[0061] Comparative Example 4 A microporous film separator similar to that of Example 1 was produced, except that the gap between adjacent fracture ribs in the horizontal direction (CD direction) of the separator and the gap between adjacent fracture ribs in the horizontal direction (CD direction) of the separator that are located closest to each other in the up-down direction (MD direction) of the separator completely overlap when viewed from the up-down direction (MD direction) of the separator (the narrower gap completely overlaps within the wider gap), and the narrowest gap was 3 mm and the widest was 6 mm.

[0062] [Testing and Evaluation Methods] Two acrylic plates, each 125 mm wide, 120 mm high, and 15 mm thick, were placed facing each other, and a microporous film separator prepared in Examples 1-2 and Comparative Examples 1-4, cut to a width of 115 mm and a length of 105 mm, was sandwiched between them, with the acrylic plates and the microporous film separator positioned so that their top ends were at the same height. Holes were drilled through the thickness direction on both the left and right ends of each of the two acrylic plates, and the two acrylic plates were fastened together using bolts and nuts. Hereinafter, the two acrylic plates sandwiching the microporous film separator will be referred to as a cell. The bolt tightening was adjusted so that the gap between the acrylic plates of the cell was 0.65 mm. The prepared cell was placed in a water tank filled with water to a height of 115 mm.

[0063] In order to evaluate the electrolyte's effect of suppressing sedimentation and ease of horizontal diffusion, a colored aqueous sodium chloride solution with a specific gravity of 1.20 was prepared and used using a black aqueous pigment instead of sulfuric acid with a specific gravity of 1.28 (36.9%) used as the electrolyte, from the viewpoint of ease of use. The space between the separator and the acrylic plate of the cell was filled with water. 2 ml of colored sodium chloride solution was dropped from the top of the cell onto the horizontal center of the space between the separator's positive electrode contact surface and the acrylic plate over a period of 10 seconds. The settling of the colored sodium chloride solution was visually observed, and the time required for the first drop of the colored sodium chloride solution to reach the bottom of the separator (settling time) and the extent to which the colored sodium chloride solution spread horizontally (CD) of the separator were measured. These measurements were used to evaluate the effectiveness of the positive electrode contact rib shape in suppressing electrolyte settling and the ease of diffusion horizontally (CD) of the separator (diffusion range).

[0064] [Evaluation results] The evaluation results are summarized in Table 1. [Table 1]

[0065] In Comparative Example 1, the ribs for contacting the positive electrode were arranged linearly in the vertical direction (MD) of the separator. The space between the positive electrode and the separator was divided into long sections in the vertical direction (MD) of the separator, making it difficult for the electrolyte to move between the sections corresponding to the horizontal direction (CD) of the separator. Therefore, the dropped colored sodium chloride solution settled in the vertical direction (MD) of the separator in the vertical region divided by the ribs and reached the bottom of the separator after 7 seconds. The diffusion of the colored sodium chloride solution in the horizontal direction (CD) of the separator was limited to the 10 mm wide area divided by the ribs for contacting the positive electrode. With the rib shape of Comparative Example 1, when an electrolyte with a high specific gravity is generated, the diffusion effect in the horizontal direction (CD direction) of the separator is low, and the downward movement along the positive electrode abutting ribs arranged in the vertical direction (MD direction) of the separator is fast, making it a shape that is prone to stratification of the electrolyte.

[0066] In contrast, the positive electrode contact ribs of Comparative Example 2 are linear fracture ribs arranged in the vertical direction (MD) of the separator, and are not separated by long sections in the vertical direction (MD) of the separator. The dropped colored sodium chloride solution spread 45 mm in the horizontal direction (CD) of the separator due to the inclined broken ribs, but reached the bottom of the separator after 5 seconds. Although the solution spread between the broken ribs and had a diffusing effect in the horizontal direction (CD) of the separator, the gaps formed between adjacent broken ribs in the horizontal direction (CD) of the separator overlap in the vertical direction (MD) of the separator, so the colored sodium chloride solution settled linearly in the vertical direction (MD) of the separator, making it relatively easy for stratification of the electrolyte to occur.

[0067] In Comparative Example 3, the time required for the colored sodium chloride aqueous solution to settle was shorter than in Examples 1 and 2. This is because the breaking ribs were linear and had no bending points, so the solution did not stagnate on the breaking ribs. Therefore, the effect of suppressing stratification of the electrolyte was smaller than in Examples 1 and 2.

[0068] In Comparative Example 4, the time required for the colored sodium chloride aqueous solution to settle is shorter than in Examples 1 and 2. The shape of the breaking ribs in Comparative Example 4 is linear with bending points, but the gaps formed between adjacent breaking ribs in the horizontal direction (CD direction) of the separator completely overlap in the vertical direction (MD direction) of the separator, so the effect of suppressing stratification of the electrolyte is smaller than in Examples 1 and 2.

[0069] In Examples 1 and 2, the dropped colored sodium chloride aqueous solution spread sufficiently in the horizontal direction (CD) of the separator while settling in the vertical direction (MD) of the separator, taking 16 seconds and 17 seconds, respectively, to reach the bottom of the separator. Compared to the comparative examples, the range (diffusion range) of the solution in the horizontal direction (CD) of the separator was wider, and the settling time in the vertical direction (MD) of the separator was also longer, which significantly suppressed electrolyte stratification. [Industrial Applicability]

[0070] The separator for a lead-acid battery of the present invention has a breaking rib shape that is effective for controlling the movement of the electrolyte inside the battery case, and the breaking ribs are arranged so as to effectively control the movement of the electrolyte inside the battery case, so that stratification of the electrolyte can be suppressed, and an optimal separator can be provided that can suppress the deterioration of battery control reliability and battery life that are associated with electrolyte stratification. [Explanation of symbols]

[0071] (a) Line segment between the end of the broken rib and the adjacent bending point (b) A line segment between an inflection point and an adjacent inflection point (c) The line segment between the bending point and the adjacent end of the broken rib. X: Horizontal direction of separator (CD direction) Y Separator vertical direction (MD direction)

Claims

1. A lead-acid battery separator for use in a flooded lead-acid battery, comprising a porous back web and a plurality of ribs extending on a surface of the back web that contacts a positive electrode plate, wherein the ribs on the surface that contacts the positive electrode plate are break ribs, and the break ribs have two or more bending points and are either linear break ribs that bend in opposite directions at two consecutive bending points, or curved break ribs that have one or more inflection points, and wherein gaps between adjacent break ribs in the horizontal direction (CD direction) of the separator and gaps between adjacent break ribs in the horizontal direction (CD direction) of the separator that are located closest in the vertical direction (MD direction) of the separator do not overlap when viewed from the vertical direction (MD direction) of the separator.

2. 2. The separator for a lead-acid battery according to claim 1, wherein the breaking ribs include those having different bending angles or different line lengths.

3. 2. The separator for a lead-acid battery according to claim 1, wherein the breaking ribs have two-fold rotational symmetry.

4. 2. The separator for a lead-acid battery according to claim 1, wherein the breaking ribs are linear breaking ribs with line segments at both ends substantially parallel to each other.

5. 5. The lead-acid battery separator according to claim 1, wherein the breaking ribs are linear breaking ribs having bending angles of 90 degrees or more and less than 180 degrees at all bending points.

6. 6. The lead-acid battery separator according to claim 1, wherein the breaking rib is a linear breaking rib having two bending points.

7. 4. The lead-acid battery separator according to claim 1, wherein the fracturing rib is a curved fracturing rib having an interior angle formed by a tangent at an inflection point and a tangent at an adjacent inflection point, or an interior angle formed by a tangent at an inflection point and a tangent at a tip of the rib, of 90 degrees or more and less than 180 degrees.

8. 8. The lead-acid battery separator according to claim 7, wherein the breaking rib is a curved breaking rib having one inflection point, and an interior angle formed by a tangent at the inflection point and a tangent at a tip of the rib is 90 degrees or more and less than 180 degrees.

9. 9. The separator for a lead-acid battery according to claim 1, wherein the plurality of breaking ribs are arranged substantially horizontally with respect to the horizontal direction (CD direction) of the separator.

10. The separator for a lead-acid battery according to any one of claims 1 to 8, characterized in that the plurality of breaking ribs are arranged so that the breaking rib and another breaking rib adjacent to the breaking rib in the vertical direction (MD direction) of the separator do not completely overlap each other in the vertical direction (MD direction) of the separator.

11. The lead-acid battery separator according to any one of claims 1 to 8, characterized in that the plurality of breaking ribs are arranged so that a gap formed between a pair of breaking ribs adjacent to each other in the horizontal direction (CD direction) of the separator does not overlap with a gap formed between another pair of breaking ribs adjacent to each other in the horizontal direction (CD direction) of the separator in the vertical direction (MD direction) of the separator, the gap being adjacent to each other in the vertical direction (MD direction) of the separator.

12. The lead-acid battery separator according to any one of claims 1 to 8, characterized in that the plurality of fracturing ribs are located on the right side of the fracturing rib in the horizontal direction (CD direction) of the separator, and the gap formed between the fracturing rib and the nearest adjacent fracturing rib is located on the right side of the fracturing rib in the horizontal direction (CD direction) of the separator, and are arranged so as not to overlap with the gap formed between the fracturing rib and the second nearest adjacent fracturing rib in the up-down direction (MD direction) of the separator, or the fracturing ribs are located on the left side of the horizontal direction (CD direction) of the separator, and the gap formed between the fracturing rib and the nearest adjacent fracturing rib is located on the left side of the horizontal direction (CD direction) of the separator, and are arranged so as not to overlap with the gap formed between the fracturing rib and the second nearest adjacent fracturing rib in the up-down direction (MD direction) of the separator.

13. A lead-acid battery using the separator according to any one of claims 1 to 12.

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