Nonwoven sheet and method for producing the same

Abstract

An object of the disclosure is to provide a nonwoven sheet made mainly of fine glass fibers with smooth surface properties of a top surface and a bottom surface and a method for producing the same. The nonwoven sheet formed by a wet papermaking process using glass fibers with a weighted average fiber diameter of 3.0 μm or less as a main component, wherein a thickness under a load of 20 kPa is 100 μm or more, an apparent bulk density is 0.30 g / cm3 or less, a ratio of a three-dimensional surface roughness (Sq) to a thickness of the nonwoven sheet is 7% or less on a TOP surface side and 7% or less on a bottom forming wire surface side.

Description

NONWOVEN SHEET AND METHOD FOR PRODUCING THE SAMERelated Applications

[0001] This application claims priority to U.S. Provisional Application No 63 / 696,141, filed on September 18, 2024, and titled NONWOVEN SHEET AND METHOD FOR PRODUCING THE SAME, which is incorporated herein by reference in its entirety.Technical Field

[0002] The present disclosure relates to separators for reducing acid stratification in lead batteries, more specifically in enhanced flooded lead acid batteriesBackground

[0003] Enhanced flooded batteries (EFB) have been developed to meet the high cycling requirements in “start-stop” or “micro-hybrid” vehicle applications. In such applications, the engine is shut off while the vehicle is stopped (e.g., at a traffic light) and then re-started afterwards. The advantage of a “start-stop” vehicle design is that it results in reduced CO2 emissions and better overall fuel efficiency. A major challenge in “start-stop” vehicles is that the battery must continue to supply all electrical functions during the stopped phase while being able to supply sufficient current to re-start the engine at the required moment. In such cases, the battery must exhibit higher performance with respect to cycling and recharge capability as compared to a traditional flooded lead-acid battery design. In such cases, the battery operates in a partial-state-of-charge (PSOC). PSOC operation results in acid stratification and contributes to shorter cycle and calendar life in flooded batteries.

[0004] Acid stratification occurs as a result of the participation of the sulfuric acid electrolyte in the charge and discharge reactions of the battery. These reactions are shown below. During discharge, the reactions proceed from left to right; and, during charge, they proceed from right to left.Positive electrode: PbC>2 + H2SO4 + 2H++ 2e- PbSCM + 2H2ONegative electrode: Pb + H2SO4 «-> PbSO4 + 2H++ 2e-

[0005] During discharge, sulfuric acid is consumed at both electrodes and water is produced at the positive electrode. This results in a dilution of the acid next to the electrode. The dilute acid has a lower density, and this creates a driving force for natural convection; the lower density acid next to the electrodes rises and the higher density acid, in the middle of the space between the two electrodes, sinks.

[0006] At higher discharge rates, the gradient in density from the electrode to the bulk will be greater than that at low discharge rates, where diffusion from the bulk is fast enough to replace the acid that is consumed at the electrodes and for water produced at the positive electrode to move to the bulk. The density gradient is also increased at lower temperatures, when diffusion is slowed down, as described generically by the Nernst-Einstein equation.

[0007] During charge, the process is reversed and acid is generated at both electrodes. This will have the effect of reversing the density gradient between the electrodes so that the acid is denser at the electrode surface and less dense in the bulk between the electrodes. This will be true particularly if there has been a rest period between discharge and charge. The convective flow will also bereversed: the denser acid next to the electrodes will sink, and the lower density acid in the bulk will rise.

[0008] Another contributor to acid stratification is non-uniform current distribution on the electrode. The higher current density at the top will result in a higher rate of acid depletion at the top of the electrode than that at the bottom of the electrode This effect will be exacerbated by high rate discharge, such as that which occurs during the starting of the engine.

[0009] The net effect of the convective flows and non-uniform current distribution is that the acid becomes gradually less dense at the top of the cell and denser at the bottom of the cell. This is the phenomenon referred to as acid stratification

[0010] The separator can affect acid stratification. In general, lead-acid batteries manufactured with Absorptive Glass Mat (AGM) separators can better mitigate acid stratification than polyethylene / si I ica separators. Even in the case of AGM separators there continues to be a need for further improvements to reduce acid stratification.

[0011] Heretofore, AGM manufacturers have not considered the importance of surface roughness and the need for intimate contact and conformity with both the positive and negative electrode surfaces. In most cases, AGM separators have a significantly smoother surface on the side that was in contact with the forming wire during the papermaking process.

[0012] In this disclosure, we have developed fiber formulations and processes to ensure that each surface of the AGM has a three-dimensional surface roughness (Sq) relative to total thickness that is less than 7% and the ratio of the absolute surface roughness for each surface is less than 4: 1. As a result, these separators are more effective at mitigating acid stratification through intimate contact at the electrode surface.Summary

[0013] An object of the disclosure is to provide a nonwoven sheet made mainly of fine glass fibers with smooth surface properties of a top surface and a bottom surface and a method for producing the same.

[0014] Further, an object of the disclosure is to provide a nonwoven sheet made mainly of fine glass fibers and suitable for use such as a separator with excellent top surface (TOP surface) and bottom surface (bottom forming wire surface) smoothness and a method for producing the same, in which roughness of a top surface (a TOP surface) and a bottom surface (bottom forming wire surface) of the nonwoven sheet is smoothed and flattened to suppress a decrease in battery capacity and other battery characteristics caused by spaces between the nonwoven sheet and an electrode plate surface resulting from the surface roughness of a bottom forming wire surface and a TOP surface, thereby allowing the electrode plate surface to adhere closely to the nonwoven sheet and allowing a smooth battery reaction between an electrode plate active material and an electrolyte.

[0015] As a result of intensive research aimed at solving the above problems, a nonwoven sheet of the disclosure is a nonwoven sheet having the following characteristics

[0016] (1 ) A nonwoven sheet formed by a wet papermaking process using glass fibers with a weighted average fiber diameter of 3.0 pm or less as a main component, wherein a thickness under a load of 20 kPa is 100 pm or more, an apparent bulk density is 0.30 g / cm3or less, a ratio of a three-dimensional surface roughness (Sq) to a thickness of the nonwoven sheet is 7% or less on a TOP surface side and 7% or less on a bottom forming wire surface side. A three-dimensional surface roughness (Sq) is as specified in International Standard 25178 (2024).

[0017] (2) The nonwoven sheet according to (1 ), wherein the ratio of the three-dimensional surface roughness (Sq) to the thickness of the nonwoven sheet is 5% or less on the TOP surface side and 5% or less on the bottom forming wire surface side.

[0018] (3) The nonwoven sheet according to (1) or (2), wherein the ratio of the three-dimensional surface roughness (Sq) to the thickness of the nonwoven sheet is 3% or less on the TOP surface side and 3% or less on the bottom forming wire surface side

[0019] (4) The nonwoven sheet according to any one of (1 ) to (3), wherein the ratio of the three- dimensional surface roughness (Sq) on the TOP surface side to the three-dimensional surface roughness (Sq) on the bottom forming wire surface side is 4 or less.

[0020] (5) The nonwoven sheet according to any one of (1) to (4), wherein a blending amount of the glass fibers is 60 wt% or more of a fibrous material constituting the nonwoven sheet

[0021] (6) The nonwoven sheet according to any one of (1) to (5), wherein a blending amount of the glass fibers is 80 wt% or more of a fibrous material constituting the nonwoven sheet

[0022] (7) The nonwoven sheet according to any one of (1 ) to (6), wherein the glass fibers constituting the nonwoven sheet have a weighted average fiber diameter of 2.0 pm or less.

[0023] (8) The nonwoven sheet according to any one of (1) to (7), where the nonwoven sheet includes heat-fusible organic fibers.

[0024] (9) The nonwoven sheet according to any one of (1) to (8), wherein the nonwoven sheet has excellent anti-cracking properties

[0025] (10) The nonwoven sheet according to (9), where the fracture properties are characterized by placing a 1 mm thick iron plate on the nonwoven sheet and visually evaluating the presence or absence of fractures on the nonwoven sheet surface due to folding along the side of the iron plate.

[0026] Further, a method for producing a nonwoven sheet of the disclosure is a method for producing a nonwoven sheet having the following characteristics.

[0027] (11 ) A method for producing a nonwoven sheet, the nonwoven sheet formed by a wet papermaking process using glass fibers with a weighted average fiber diameter of 3.0 pm or less as a main component, having a thickness under a load of 20 kPa of 100 pm or more, and having an apparent bulk density of 0.30 g / cm3or less, wherein the nonwoven sheet is produced by sandwiching the sheet between two forming wires or between a forming wire and a water-absorbing felt so as to press the nonwoven sheet between two planes while maintaining water from the wet papermaking process to promote flat and smooth surface properties on top and bottom surfaces of the nonwoven sheet.

[0028] (12) The method for producing a nonwoven sheet according to (11 ), wherein the nonwoven sheet maintains water after the wet papermaking process and is sandwiched between a lower forming wire and an upper forming wire or felt so as to press the nonwoven sheet between two planes

[0029] (13) The method for producing a nonwoven sheet according to (11 ) or (12), wherein after the nonwoven sheet is sandwiched between two forming wires or between a forming wire and a felt so as to press the nonwoven sheet between two planes, the two forming wires or the forming wire and thefelt are pressed by an unpaired roll or press roll to create flat and smooth surface properties on the top and bottom surfaces of the nonwoven sheet.

[0030] (14) The method for producing a nonwoven sheet according to any one of (11) to (13), wherein after the nonwoven sheet is sandwiched between two forming wires or between a forming wire and a felt so as to press the nonwoven sheet between two planes, excess water is removed from a top side of the sheet using a vacuum or suction device on an upper side of the forming wire or an upper water removing felt.

[0031] (15) The method for producing a nonwoven sheet according to any one of (11) to (14), wherein a water content of the nonwoven sheet after the wet papermaking process is maintained or held to at least 50 wt% or more.

[0032] (16) The method for producing a nonwoven sheet according to any one of (11 ) to (15), wherein a water content of the nonwoven sheet after the wet papermaking process is maintained or held to at least 80 wt% or more.

[0033] (17) The method for producing a nonwoven sheet according to any one of (11) to (16), wherein an apparatus for sandwiching the nonwoven sheet while maintaining higher water content after the wet paper making process using two forming wires or with a forming wire and a felt is integrated into a papermaking machine.

[0034] (18) The method for producing a nonwoven sheet according to any one of (11 ) to (17), wherein the upper forming wire has a mesh size of 10 or more.

[0035] Further, a separator made of the nonwoven sheet of the disclosure, or a nonwoven sheet produced by the method for producing the same, is a separator having the following characteristics, and a lead-acid battery using the separator is a lead-acid battery having the following characteristics.

[0036] (19) A separator, comprising the nonwoven sheet according to any one of (1) to (10)

[0037] (20) A lead-acid battery, comprising a separator formed of the nonwoven sheet according to any one of (1) to (10).

[0038] (21) A separator, comprising a nonwoven sheet produced by the method for producing a nonwoven sheet according to any one of (11) to (18).

[0039] (22) A lead-acid battery, comprising a separator formed of a nonwoven sheet produced by the method for producing a nonwoven sheet according to any one of (11 ) to (18).

[0040] As described above, the present disclosure provides a nonwoven sheet made mainly of fine glass fibers with smooth surface properties of a top surface and a bottom surface and a method for producing the same.

[0041] Further, the present disclosure provides a nonwoven sheet made mainly of fine glass fibers and suitable for use such as a separator with excellent top surface (TOP surface) and bottom surface (bottom forming wire surface) smoothness and a method for producing the same, in which roughness of a top surface (a TOP surface) and a bottom surface (bottom forming wire surface) of the nonwoven sheet is smoothed and flattened to allow the electrode plate surface to adhere closely to the nonwoven sheet, thereby reducing acid stratification.

[0042] When a nonwoven sheet with excellent smoothness is used as a separator, the nonwoven sheet can have intimate contact with the electrode plates, and it makes easy with which ions can betransferred between the electrode plates and the electrolyte, that is, it allows a smooth battery reaction between the electrode plate active material and the electrolyte. Therefore, in addition to reducing acid stratification, other effects such as lowering internal resistance of a battery can also be expectedBrief Description of the Drawings

[0043] FIG. 1 is a schematic diagram illustrating an apparatus (a type in which a surface improvement device is included in a papermaking machine) for producing a nonwoven sheet of the disclosure.

[0044] FIG. 2 is a schematic diagram illustrating an apparatus (a type in which a surface improvement device is included in a papermaking machine) for producing a nonwoven sheet of the disclosure.

[0045] FIG. 3 is a schematic diagram illustrating an apparatus (a type in which a surface improvement device and a papermaking machine are separate) for producing a nonwoven sheet of the disclosure.

[0046] FIG. 4 is a schematic diagram illustrating an apparatus (a type in which a surface improvement device and a papermaking machine are separate) for producing a nonwoven sheet of the disclosure

[0047] FIG. 5 is an example of data where F calculation and L filter have been applied to three- dimensional coordinate data obtained by measuring a surface with a three-dimensional shape measuring instrument.

[0048] FIG. 6 is an example of data where F calculation and L filter have been applied to three- dimensional coordinate data obtained by measuring a surface with a three-dimensional shape measuring instrument.Detailed Description

[0049] A nonwoven sheet of the disclosure is a nonwoven sheet formed by a wet papermaking process using glass fibers with a weighted average fiber diameter of 3.0 pm or less as a main component, where a thickness under a load of 20 kPa is 100 pm or more, an apparent bulk density is 0.30 g / cm3or less, a ratio of a three-dimensional surface roughness (Sq) to a thickness of the nonwoven sheet is 7% or less on a TOP surface side and 7% or less on a bottom forming wire surface side. The nonwoven sheet of the disclosure may also contain long glass fibers, non-thermally fusible organic fibers, heat-fusible organic fibers, inorganic powders such as silica, and the like

[0050] By blending a non-thermally fusible monofilament organic fiber, compressive breaking strength (shear strength) of the nonwoven sheet can be increased (see, for example, JP4261821 B), and a better separator can be obtained.

[0051] In addition, it is expected that a composite effect can be obtained by various combinations with materials that do not have thermal fusion properties

[0052] As the glass fibers used in the nonwoven sheet of the disclosure, since the nonwoven sheet of the disclosure is used in an electrolyte (sulfuric acid aqueous solution having a specific gravity of 1 3), for suitable use such as a separator, acid-resistant C glass fibers are preferred, but there is no limitation thereto as long as the glass fibers are acid-resistant.

[0053] The glass fibers preferably have a weighted average fiber diameter of 0.5 pm or more and 3.0 pm or less, and more preferably 2.5 pm or less, from viewpoints of stratification suppression, suppression of an increase in internal resistance of the battery and suppression of a decrease in charge acceptance of the battery, although this varies depending on the other materials to be combined. Further, when it is necessary to further improve stratification suppression, such as when used in a lead- acid battery for an idling stop and start system (ISS), it is even more preferable that the weighted average fiber diameter is 2 0 pm or less.

[0054] For suitable for use such as a separator, the glass fiber is preferably a micro glass fiber from a viewpoint of physical strength of the separator

[0055] For suitable for use such as a separator, in the nonwoven sheet of the disclosure, a blending amount of the glass fibers is preferably 60 wt% or more, and more preferably 80 wt% or more, of the fibrous material constituting the nonwoven sheet from a viewpoint of maintaining absolute strength and an electrolyte retention function of the separator

[0056] In the nonwoven sheet of the disclosure, it is preferable to blend the heat-fusible organic fibers in order to maintain tensile strength (sheet strength). In addition, for suitably use the nonwoven sheet such as a separator, it is also preferable to blend the heat-fusible organic fiber in order to maintain tensile strength (sheet strength), puncture strength, and adhesion (peel strength) between nonwoven sheets of the nonwoven sheet of the disclosure.

[0057] The heat-fusible organic fiber is not particularly limited as long as it is one that is generally used in nonwoven sheets, but one having a core-sheath structure is preferably used. In this case, a core may be a commonly used resin such as a polyolefin resin such as a polyethylene resin or a polypropylene resin, or a polyester resin, but one that is acid-resistant is preferable, and a polyester resin is preferable A sheath is preferably a polyolefin resin such as a polyethylene resin or a polypropylene resin, or a polyester resin, and more preferably a crystalline polyolefin resin, or a crystalline or amorphous polyester resin.

[0058] Fineness of the heat-fusible organic fiber is preferably 2.5 dtex or less, more preferably 1.6 dtex or less, and even more preferably 1.5 dtex or less in order to increase the number of heat-fusible organic fibers contained in the nonwoven sheet, which is a measure to increase the tensile strength (sheet strength). Further, when the fineness of the heat-fusible organic fiber is less than 0.4 dtex, the heat-fusible organic fiber and the glass fiber are affected by a specific gravity difference when the nonwoven sheet is made, and the two are not mixed uniformly. In addition, from a viewpoint of suitable use as a separator, characteristics of the separator made of the nonwoven sheet vary greatly, and thus a nonwoven sheet of stable quality cannot be obtained. Thus, the fineness of the heat-fusible organic fiber is preferably 0.4 dtex or more, more preferably 0.5 dtex or more, and even more preferably 0.6 dtex or more.

[0059] A number average fiber length of the heat-fusible organic fibers used is preferably 1 mm to 25 mm

[0060] In the nonwoven sheet of the disclosure, it is also preferable to blend 5 wt% or more of the heat-fusible organic fiber in order to improve the mechanical strength.

[0061] In the nonwoven sheet of the disclosure, a thickness of the nonwoven sheet under a load of 20 kPa is preferably 100 m or more, and more preferably 130 pm or more.

[0062] When the thickness of the nonwoven sheet under a load of 20 kPa is less than 100 pm, the absolute strength of the nonwoven sheet decreases.

[0063] In order for the nonwoven sheet of the disclosure to be suitable for use as a separator, when the thickness of the nonwoven sheet under a load of 20 kPa is less than 100 pm, a total amount of electrolyte that the separator can hold decreases, and thus a function of preventing stratification of the electrolyte decreases.

[0064] In the nonwoven sheet of the disclosure, a density (apparent bulk density) of the nonwoven sheet is preferably 0.30 g / cm3or less, when the density (apparent bulk density) of the nonwoven sheet exceeds 0.30 g / cm3, a void ratio of the nonwoven sheet becomes extremely small. In order for the nonwoven sheet of the disclosure to be suitable for use as a separator, when the density (apparent bulk density) of the nonwoven sheet exceeds 0.30 g / cm3, a void ratio of the separator becomes extremely small, reducing a total amount of electrolyte that can be held, and thus reducing the function of preventing stratification of the electrolyte.

[0065] In addition, the density (apparent bulk density) of the nonwoven sheet of the disclosure is preferably 0.10 g / cm3or more. When the density (apparent bulk density) of the nonwoven sheet is less than 0.10 g / cm3, the void ratio of the nonwoven sheet will be high, resulting in a decrease in absolute strength. When the density (apparent bulk density) of the nonwoven sheet is less than 0.10 g / cm3, the void ratio of the separator will be extremely high, resulting in a decrease in absolute strength.

[0066] In the nonwoven sheet of the disclosure, a three-dimensional surface roughness (Sq) of the TOP surface side is preferably 7% or less, more preferably 5% or less, and even more preferably 3% or less, in terms of a ratio to the thickness of the nonwoven sheet When the ratio of the three- dimensional surface roughness (Sq) to the thickness of the nonwoven sheet exceeds 7%, and the nonwoven sheet is used as a separator, the interfacial contact between the separator and the electrode plate becomes less favorable such that acid transport and stratification can occur at the plate surface. In other words, acid stratification cannot be adequately reduced or mitigated.

[0067] In addition, the three-dimensional surface roughness (Sq) of the bottom forming wire surface side is preferably 7% or less, more preferably 5% or less, and even more preferably 3% or less, in terms of the ratio to the thickness of the nonwoven sheet When the ratio of the three-dimensional surface roughness (Sq) to the thickness of the nonwoven sheet exceeds 7%, and the nonwoven sheet is used as a separator, the interfacial contact between the separator and the electrode plate becomes less favorable such that acid transport and stratification can occur at the plate surface. In other words, acid stratification cannot be adequately reduced or mitigated.

[0068] The three-dimensional surface roughness (Sq) can be measured, for example, by a three- dimensional shape measuring instrument (VR3100, manufactured by KEYENCE CORPORATION).

[0069] In addition, a measured value (numerical value) of the three-dimensional surface roughness (Sq) of the TOP surface side itself tends to vary in relation to the thickness of the papermaking-made nonwoven sheet under a load of 20 kPa. Therefore, in accordance with the disclosure, when evaluating smoothness and flatness of a top surface and a bottom surface of a nonwoven sheet, inorder to eliminate errors due to variations in the thickness of the nonwoven sheet under a load of 20 kPa, the evaluation was made as a ratio (%) of the three-dimensional surface roughness (Sq) on the top surface side (the TOP surface) and the bottom surface side (the forming wire surface) of the nonwoven sheet to the thickness of the nonwoven sheet under a load of 20 kPa.

[0070] The ratio (%) of the three-dimensional surface roughness (Sq) on the top surface side (the TOP surface) and the bottom surface side (the forming wire surface) of the nonwoven sheet to the thickness of the nonwoven sheet under a load of 20 kPa was calculated by the following formula.

[0071] Ratio (%) = Three-dimensional surface roughness (Sq, pm) on top surface and bottom surface of nonwoven sheet - Thickness (mm) of nonwoven sheet under load of 20 kPa - 10

[0072] When a nonwoven sheet is used as a separator, a nonwoven sheet usually uses fine glass fibers with a weighted average fiber diameter of 3.0 pm or less as a main raw material. These fine glass fibers are mixed and uniformly dispersed in water or acidic water to form a slurry-like raw material (slurry raw material), which is dehydrated in a dehydration box of a papermaking machine to form a paper layer and become a wet paper (Wet mat). At this paper layer formation stage, the slurry raw material is dehydrated and the glass fibers are deposited on a forming wire of a papermaking machine (papermaking net) As the glass fibers deposited on the forming wire of the papermaking machine (papermaking net) gradually increase in thickness, unevenness occurs on a surface, and roughness (unevenness) of the surface increases as the thickness of the paper layer increases.

[0073] A pair of upper and lower press rolls and a calender roll used in a general papermaking machine are used to pass a target object between a pair of rolls and forcibly squeeze out water contained in a wet mat using nip pressure generated between the rolls, to reduce the thickness of the wet mat, to improve surface properties of the wet mat, and the like.

[0074] However, in this method, a raw material used as the target object must have strength to withstand high nip pressure. For example, a nonwoven sheet, which is mainly made of fine glass fibers with a weighted average fiber diameter of 3.0 m or less, has a high void ratio, low density (0.10 g / cm3to 0.30 g / cm3), and is thick (100 pm or more), and is in a very soft mat shape. Therefore, when passing through devices that apply strong nip pressure, such as a pair of upper and lower press rolls and a calender roll, a problem occurs such as destruction of the glass fibers and the thickness of the mat becoming extremely thin

[0075] The water in the wet paper (Wet mat) can also be made to flow by using a surfaceconditioning device such as a dandy roll. However, pressing the mat in a line with the dandy roll causes the water to move in front of and behind the dandy roll, and at the same time the glass fibers also flow, which can end up worsening the surface condition of the wet mat rather than improving it.

[0076] Examples of an apparatus for producing a nonwoven sheet of the disclosure are schematically shown in FIGS. 1 to 4. The apparatuses shown in FIGS. 1 and 2 are each a type (an integrated type) in which a device (a surface improvement device 1) for sandwiching a nonwoven sheet is included in a papermaking machine 2, while the apparatuses shown in FIGS 3 and 4 are each a type (a separated type) in which the device (the surface improvement device 1) for sandwiching a nonwoven sheet is separate from the papermaking machine 2. The apparatuses shown in FIGS. 1 and 3 are each a type in which the papermaking machine 2 is a cylindrical papermaking machine, while theapparatuses shown in FIGS. 2 and 4 are each a type in which the papermaking machine 2 is an inclined papermaking machine Each papermaking machine 2 has a dehydration box for water removal 2a, which is an apparatus for dehydrating water from a slurry-like raw material (slurry raw material) and forming a paper layer to form a wet paper (Wet mat) 3.

[0077] Either type of apparatus can improve smoothness and flatness of a top surface 13 and a bottom surface 14 of a nonwoven sheet, but the type (the integrated type) in which the device (surface improvement device 1) for sandwiching the nonwoven sheet (the wet paper 3) is included in the papermaking machine 2 is preferable because it is easy to press the nonwoven sheet (the wet paper 3) by two planes even when a water content of the wet paper 3 is high (for example, the water content of 80 wt% or more), which increases an amount of water that flows out of the wet paper (wet mat) 3 and makes it easier for glass fibers to flow, thereby improving an effect of improving the smoothness and flatness of the top surface 13 and the bottom surface 14 of the nonwoven sheet

[0078] With a dandy roll 4 and a pair of upper and lower press rolls used in a typical papermaking machine 2, when the water content of the wet paper (Wet mat) 3 is high, the flow of glass fibers that occurs as the water flows out becomes extremely large, and the smoothness and flatness of the top surface 13 and the bottom surface 14 deteriorate instead Therefore, such rollers cannot be used for the wet paper with high water contents. In addition, the fine glass fibers used in a nonwoven sheet have very high water retention properties, and even after the paper layer is formed, the water content is so high. Therefore, when the paper layer is pressed down with great force, the paper layer will easily be destroyed.

[0079] Even when the wet paper (Wet mat) 3 immediately after the paper layer is formed has a largely uneven surface, when the water content is very high (for example, the water content of 50 wt% or more), the glass fibers are not completely entangled (fine glass fibers, by its nature, unlike pulp, do not have a fibrillated surface and are straight fibers) Therefore, external stress can easily cause the fibers to move.

[0080] In the disclosure, in this state (when the water content is very high), instead of applying a strong linear force from above and below as with a pair of upper and lower press rolls, the wet paper (Wet mat) 3 is pressed down by two planes from below with a forming wire 6 and from above with a forming wire 5 or water-absorbing felt 5, so that the water held by the wet paper (Wet mat) 3 can be moved to the two forming wires 5 and 6 or the water-absorbing felt 5 And at the same time as this water moves, the fine glass fibers flow, but because the wet paper (Wet mat) 3 is sandwiched and pressed down from above and below by the two forming wires 5 and 6 or the forming wire 6 and waterabsorbing felt 5, the movement of the fine glass fibers is restricted and limited to movement from convex parts to concave parts on the surface of the wet paper (Wet mat) 3. This makes it possible to improve the smoothness and flatness of the top surface 13 and the bottom surface 14 of the nonwoven sheet of the disclosure.

[0081] In the disclosure, the water content of the wet paper (Wet mat) 3 can be further reduced by sucking up the water from above and below that has been moved to the two forming wires 5 and 6 or the water-absorbing felt 5 using vacuum or suction devices (suction) 8, 9 which have the function offurther removing water from the wet paper (Wet mat) 3 in which a paper layer has already been formed, and the entanglement of the glass fibers can also be strengthened.

[0082] In addition, by using the vacuum or suction device 8 to dehydrate the excess water that has floated upward from the upper forming wire 5 side or the upper water-absorbing felt 5 side, the smoothness and flatness of the TOP surface 13 of the wet paper (Wet mat) 3 can be further improved by the flow of the glass fibers, so it is more effective to perform vacuum or suction using the vacuum or suction device 8 on an upper side rather than the vacuum or suction device 9 on a lower side.

[0083] In the figures, 10a shows a drive roll, 10b shows an auxiliary drive roll, and 10c shows a support roll

[0084] In the disclosure, as schematically illustrated in FIGS. 1 to 4, the wet paper (Wet mat) 3 sandwiched between the two forming wires 5 and 6 or the forming wire 6 and the water-absorbing felt 5 is further pressed down from above and below by a top roll 11 and a bottom roll 12, and thus the wet paper (Wet mat) 3 can be pressed down with a stronger force than when the wet paper (Wet mat) 3 is simply sandwiched between the two forming wires 5 and 6 or the forming wire 6 and water-absorbing felt 5 from above and below. This is preferable because it allows for even more water to be moved and further improves the smoothness and flatness of the top surface 13 and the bottom surface 1

[0085] Here, the smaller a roll diameter of the top roll 11, the stronger the line pressure that presses the two forming wires 5 and 6 or the water-absorbing felt 5 sandwiching the wet paper (Wet met) 3 from above and below, which is more effective and preferable. Therefore, in an apparatus for producing the nonwoven sheet of the disclosure, it is desirable to design the roll to have a minimum diameter that does not cause bending of the roll due to a width of equipment

[0086] In addition, the top roll 11 and the bottom roll 12 must be installed so that they do not come into contact with each other (are positioned apart each other and unpaired) When the rolls 11 and 12 come into contact with each other (are not positioned apart and paired), nip pressure will be generated, and as with the pair of press rolls, the wet paper (Wet mat) 3 will be pressed down excessively, causing problems such as over-compressing the thickness of the nonwoven sheet or destroying the fine glass fibers.

[0087] In the disclosure, the upper forming wire 5 or the upper water-absorbing felt 5 is preferably as dense as possible. A mesh size of the upper forming wire 5 is preferably 10 or more, and more preferably 15 or more When the mesh size is less than 10, fine glass fibers will get between the meshes of the forming wire 5, and even when the smoothness and flatness of the surface of the wet paper (Wet mat) 3 are improved, a large forming wire mesh pattern will appear on the surface of the wet paper (Wet mat) 3, deteriorating the smoothness and flatness of the surface of the nonwoven sheet. Here, the mesh size is expressed as a value calculated by "[(Number of warp threads per 25.4 mm) + (Number of weft threads per 25.4 mm)] * 2"

[0088] As for the upper water-absorbing felt 5, the felt is obviously finer than a general forming wire, and is not particularly limited as long as it is a generally used felt, but the denser it is, the more preferable it is.

[0089] In the disclosure, as a method for improving the surface smoothness and flatness of a thick wet paper (Wet mat) 3 that contains a large amount of water, the wet paper (Wet mat) 3 is sandwichedbetween the two forming wires 5 and 6 from above and below, or between the forming wire 6 and the water-absorbing felt 5, and the water that moves when the wet paper (Wet mat) 3 is pressed down is absorbed by the two forming wires 5 and 6 or the water-absorbing felt 5, or even by the vacuum or suction device 8 above, thereby limiting the movement of glass fibers that move together with the water to from convex parts to concave parts on the surface of the wet paper (Wet mat) 3.

[0090] The nonwoven sheet of the disclosure has improved top surface 13 and bottom surface 14 smoothness and flatness, and therefore has excellent fracture properties.

[0091] When the surface of a nonwoven sheet is not smooth and flat and has a large surface roughness (unevenness of the surface), the deposition state of glass fibers in the surface layer of the nonwoven sheet will be in a random fiber orientation that follows the unevenness of the nonwoven sheet surface, and the number of glass fibers per unit cross-sectional area will be small. As a result, strength of the entanglement of the glass fibers in the surface layer of the nonwoven sheet will also be weakened. When bending stress is applied to the nonwoven sheet, tensile stress is generated in the surface layer on a crest side (an outer side when folded). In this case, force is concentrated in the concave parts of the unevenness of the nonwoven sheet surface, and when the tensile stress becomes stronger than the force of the entanglement of the glass fibers, cracks will appear in the surface of the nonwoven sheet, resulting in fracture.

[0092] In the nonwoven sheet of the disclosure, the wet paper (Wet mat) 3 is sandwiched between the two forming wires 5 and 6 from above and below, or between the forming wire 6 and the waterabsorbing felt 5, and the water that moves when the wet paper (Wet mat) 3 is pressed down is absorbed by the two forming wires 5 and 6 or the water-absorbing felt 5, and further by the vacuum or suction device 8 from above, thereby improving the smoothness and flatness of the top surface 13 and bottom surface 14 of the nonwoven sheet Therefore, the deposition state of the glass fibers in the surface layer of the nonwoven sheet changes from a random fiber orientation to a horizontal orientation with respect to the nonwoven sheet surface, and the number of glass fibers per unit cross-sectional area increases. Accordingly, the strength of the entanglement between the glass fibers in the surface layer of the nonwoven sheet also increases. Therefore, even when bending stress is applied to the nonwoven sheet, the entanglement between the glass fibers is strong enough to withstand the tensile stress of the surface layer on the crest side (the outer side when folded), so no cracks (fractures) occur on the surface of the nonwoven sheet

[0093] The nonwoven sheet of the disclosure is preferably used as a separator.

[0094] Aseparator made of the nonwoven sheet of the disclosure preferably has a thickness of more than 0.50 mm under a load of 20 kPa, and more preferably 0.60 mm or more. When the thickness is 0.50 mm or less, a total amount of electrolyte that the separator can hold decreases, and a function of preventing stratification of the electrolyte decreases. In addition, absolute strength of the separator decreases.

[0095] The nonwoven sheet of the disclosure has been described for a separator of energy storage device applications, including a lead-acid battery, which is particularly preferred, but the nonwoven sheet of the disclosure is also preferably used for other applications such as a pasting paper for lead acid batteries, filter paper for air filters, heat insulating material, and liquid retention material.

[0096] A method for producing a nonwoven sheet of the disclosure can also be applied to improving top surface 13 and / or bottom surface 14 smoothness and flatness of nonwoven sheets other than those for a separator of energy storage device applications, for example, those mainly made of fine glass fibers with a weighted average fiber diameter of 3 0 pm or less. Specifically, the method can also be applied to, for example, a pasting paper for lead acid batteries, filter paper for air filters, heat insulating material, and liquid retention material.

[0097] Next, an embodiment of a lead battery using a separator made of the nonwoven sheet of the disclosure will be described, but the disclosure is not limited to the following embodiment.

[0098] The lead-acid battery may be either an open type or a sealed type (valve regulated type)

[0099] [Electrolyte]

[0100] The electrolyte contains sulfuric acid in an aqueous solution. The electrolyte may be gelled, as necessary. The electrolyte may contain additives utilized in lead-acid batteries, as necessary.

[0101] 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 / cm3or more and 1.35 g / cm3or less.

[0102] [Positive Electrode Plate]

[0103] There are two types of positive electrode plates: paste type and clad type

[0104] 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 the paste-type positive electrode plate, the positive electrode material is the positive electrode plate excluding the positive electrode current collector. The positive electrode current collector may be formed in the same manner as a negative electrode current collector, and may be formed by casting lead or a lead alloy or by processing a lead or lead alloy sheet.

[0105] A clad-type positive electrode plate includes a plurality of porous tubes, a core metal inserted into each tube, a positive electrode material filled into the tube with the core metal inserted therein, and a connecting seat connecting the plurality of tubes. In the clad-type positive electrode plate, the positive electrode material is the positive electrode plate excluding the tubes, the core metal, and the connecting seat.

[0106] As the lead alloy used forthe positive electrode current collector, lead-calcium (Pb-Ca) alloys and lead-calcium-tin (Pb-Ca-Sn) alloys are preferred in terms of corrosion resistance and mechanical strength Lead-antimony (Pb-Sb) alloys are also preferred because they are hard and easy to handle, and also facilitate the assembly of lead-acid batteries. The positive electrode current collector may have lead alloy layers with different compositions, or there may be a plurality of alloy layers. It is preferred to use a lead-calcium (Pb-Ca) alloy or a lead-antimony (Pb-Sb) alloy for the core metal.

[0107] The positive electrode material contains a positive electrode active material (lead dioxide or lead sulfate) that exhibits capacity through an oxidation-reduction reaction. The positive electrode material may contain other additives, as necessary.

[0108] In a lead-acid battery using a separator made of the nonwoven sheet of the disclosure, it is also preferable to include antimony in the positive electrode active material in order to increase the corrosion resistance of the electrode plate during actual battery use and extend the lifespan Antimony is included in the form of antimony oxide or the like, and the concentration in the positive electrodeactive material is preferably 0.01 wt% or more and 1 wt% or less, more preferably 0.02 wt% or more and 0.5 wt% or less, and even more preferably 0.05 wt% or more and 0.5 wt% or less, in terms of antimony metal. Instead of including antimony in the positive electrode active material, antimony may be introduced by laminating a foil of a lead-antimony alloy on a positive electrode grid, for example

[0109] An unformed paste-type positive electrode plate is obtained by filling a positive electrode current collector with positive electrode paste, maturing it, and drying it, similar to the case of a negative electrode plate. The unformed positive electrode plate is then formed. The positive electrode paste is prepared by kneading lead powder, additives, water, and sulfuric acid.

[0110] The clad-type positive electrode plate is formed by filling a tube having a core metal inserted therein with lead powder or lead powder slurry, and joining a plurality of tubes together with a connecting seat.

[0111] [Negative Electrode Plate]

[0112] A 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 excluding the negative electrode current collector. The negative electrode current collector may be formed by casting lead or a lead alloy, or may be formed 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 is easy to support the negative electrode material.

[0113] The lead alloy used for the negative electrode current collector may be any of lead-antimony (Pb-Sb) alloys, lead-calcium (Pb-Ca) alloys, and lead-calcium-tin (Pb-Ca-Sn) alloys. These lead or lead alloys may further contain at least one element selected from the group consisting of Ba, Ag, Al, Bi, As, Se, Cu, and the like, as an additive element

[0114] The negative electrode material contains a negative electrode active material (lead or lead sulfate) that exhibits capacity through an oxidation-reduction reaction, and may contain a shrinkage inhibitor, lignin, a carbonaceous material such as carbon black, barium sulfate, and the like, and may contain other additives, as necessary.

[0115] The negative active material in the charged state is sponge lead, but the unformed negative electrode plate is usually made from lead powder.

[0116] The negative electrode plate can be formed by filling a negative electrode current collector with a negative electrode paste, maturing and drying it to produce an unformed negative electrode plate, and then 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 necessary, and kneading them In a maturation process, it is preferable to maturate the unformed negative electrode plate at a temperature higher than room temperature and at high humidity.

[0117] The formation can be carried out by immersing an electrode plate group including unformed negative electrode plates in an electrolyte containing sulfuric acid in a lead-acid battery container and then charging the electrode plate group. However, the formation can also be carried out before assembling the lead-acid battery or the electrode plate group. The formation produces spongy lead.

[0118] [Examples]

[0119] The disclosure will be described in more detail below with reference to examples and comparative examples. However, the disclosure is not limited to the following examples as long as it does not depart from the gist of the disclosure.

[0120] The following raw materials were used to prepare nonwoven sheets (separators) in Examples 1 to 14 and Comparative Examples 1 to 4.

[0121] [Blended Raw Materials](1) Glass fiberA: Entek Asia Co., Ltd. weighted average fiber diameter 0.8 m B: Entek Asia Co , Ltd weighted average fiber diameter 1 6 pm C: Entek Asia Co., Ltd. weighted average fiber diameter 2.5 pm(2) Heat-fusible organic fiberMelty 6080 manufactured by Unitika Co., Ltd., two-component core-sheath type (core: polyethylene terephthalate, sheath: polyethylene), fineness 1.5 dtex.

[0122] [Example 1]

[0123] 100% by mass of C glass fiber with a weighted average fiber diameter of 2.5 pm was dispersed in a sulfuric acid aqueous solution of pH3 to obtain a fiber slurry of 0 5 wt% This was made into paper using an inclined papermaking machine (forming wire: plastic net with mesh size of 100), and then passed through a surface improvement device (an integrated type) included in the papermaking machine while the wet paper had a water content of 85 wt%. The sheet (wet paper) was then dried to obtain a nonwoven sheet with a thickness of 3.0 mm under a load of 20 kPa and a density (apparent bulk density) of 0.15 g / cm3.

[0124] In this case, the surface improvement device is positioned so that the wet paper is sandwiched between a plastic net with a mesh size of 16 above the wet paper (a TOP surface side 13) and a plastic net with a mesh size of 100 below the wet paper (a forming wire surface side 14), and the vacuum or suction device (suction) is positioned above the wet paper (the TOP surface side 13). In addition, the top roll that supports the plastic net above (the TOP surface side 13) the wet paper and the bottom roll that supports the plastic net below (the forming wire surface side 14) the wet paper are positioned at a distance so that they do not form a pair.

[0125] [Example 2]

[0126] 100% by mass of C glass fiber with a weighted average fiber diameter of 2 5 pm was dispersed in a sulfuric acid aqueous solution of pH3 to obtain a fiber slurry of 0.2 wt%. After making paper in the same manner as in Example 1 , the wet paper was passed through a surface improvement device (an integrated type) in the same manner as in Example 1 , and then dried to obtain a nonwoven sheet having a thickness of 1.0 mm under a load of 20 kPa and a density (apparent bulk density) of 0.15 g / cm3.

[0127] [Example s]

[0128] A nonwoven sheet having a thickness of 3 0 mm under a load of 20 kPa and a density (apparent bulk density) of 0.15 g / cm3was obtained in the same manner as in Example 1, except that 100% by mass of C glass fiber having a weighted average fiber diameter of 1.6 pm was used.

[0129] [Example 4]

[0130] A nonwoven sheet having a thickness of 3.0 mm under a load of 20 kPa and a density (apparent bulk density) of 0.15 g / cm3was obtained in the same manner as in Example 1, except that 100% by mass of C glass fiber having a weighted average fiber diameter of 0.8 pm was used.

[0131] [Example s]

[0132] 100% by mass of C glass fiber with a weighted average fiber diameter of 0.8 pm was dispersed in a sulfuric acid aqueous solution of pH3 to obtain a fiber slurry of 0.1 wt%. This was made into paper using an inclined papermaking machine (forming wire: plastic net with mesh size of 150), and then passed through a surface improvement device (an integrated type) included in the papermaking machine while the wet paper had a water content of 85 wt% The sheet (wet paper) was then dried to obtain a nonwoven sheet having a thickness of 0.15 mm under a load of 20 kPa and a density (apparent bulk density) of 0 16 g / cm3.

[0133] In this case, the surface improvement device is positioned so that the wet paper is sandwiched between a plastic net with a mesh size of 16 above the wet paper (a TOP surface side 13) and a plastic net with a mesh size of 150 below the wet paper (a forming wire surface side 14), and the vacuum or suction device (suction) is positioned above the wet paper (the TOP surface side 13). In addition, the top roll that supports the plastic net above (the TOP surface side 13) the wet paper and the bottom roll that supports the plastic net below (the forming wire surface side 14) the wet paper are positioned at a distance so that they do not form a pair.

[0134] [Example 6]

[0135] 82% by mass of C glass fiber with a weighted average fiber diameter of 0.8 pm and 18% by mass of heat-fusible organic fiber was dispersed in a sulfuric acid aqueous solution of pH3 to obtain a fiber slurry of 0.3 wt% After making paper in the same manner as in Example 1, the wet paper was passed through a surface improvement device (an integrated type) in the same manner as in Example 1 , and then dried to obtain a nonwoven sheet having a thickness of 2.0 mm under a load of 20 kPa and a density (apparent bulk density) of 0.15 g / cm3.

[0136] [Example ?]

[0137] A nonwoven sheet having a thickness of 3.0 mm under a load of 20 kPa and a density (apparent bulk density) of 0.15 g / cm3was obtained in the same manner as in Example 1, except that the wet paper, with a water content of 60 wt%, was passed through a surface improvement device (an integrated type) included in an inclined papermaking machine

[0138] [Example s]

[0139] A nonwoven sheet having a thickness of 3.0 mm under a load of 20 kPa and a density (apparent bulk density) of 0.15 g / cm3was obtained in the same manner as in Example 1, except that the wet paper, with a water content of 35 wt%, was passed through a surface improvement device (an integrated type) included in an inclined papermaking machine.

[0140] [Example 9]

[0141] A nonwoven sheet having a thickness of 3 0 mm under a load of 20 kPa and a density (apparent bulk density) of 0.15 g / cm3was obtained in the same manner as in Example 7, except that a water-absorbing felt was placed on the upper side (the TOP surface side 13) of the wet paper in the surface improvement device through which the wet paper was passed.

[0142] [Example 10]

[0143] A nonwoven sheet having a thickness of 3.0 mm under a load of 20 kPa and a density (apparent bulk density) of 0.15 g / cm3was obtained in the same manner as in Example 7, except that a plastic net with a mesh size of 50 was placed below (the forming wire surface side) the wet paper in the surface improvement device through which the wet paper was passed.

[0144] [Example 11]

[0145] A nonwoven sheet having a thickness of 3.0 mm under a load of 20 kPa and a density (apparent bulk density) of 0.15 g / cm3was obtained in the same manner as in Example 7, except that in the surface improvement device through which the wet paper was passed, a plastic net having a mesh size of 10 was placed on the upper side (the TOP surface side 13) of the wet paper.

[0146] [Example 12]

[0147] A nonwoven sheet having a thickness of 3.0 mm under a load of 20 kPa and a density (apparent bulk density) of 0.15 g / cm3was obtained in the same manner as in Example 1, except that in the surface improvement device through which the wet paper was passed, a vacuum or suction device (suction) was positioned below (the forming wire surface side) the wet paper.

[0148] [Example 13]

[0149] A nonwoven sheet having a thickness of 3.0 mm under a load of 20 kPa and a density (apparent bulk density) of 0.15 g / cm3was obtained in the same manner as in Example 1, except that the surface improvement device through which the wet paper was passed was installed separately from the inclined papermaking machine (a separated type).

[0150] [Example 14]

[0151] A nonwoven sheet having a thickness of 3.0 mm under a load of 20 kPa and a density (apparent bulk density) of 0 15 g / cm3was obtained in the same manner as in Example 1, except that the paper was made using a cylindrical papermaking machine (an integrated type) including a surface improvement device through which a wet paper was passed.

[0152] [Comparative Example 1]

[0153] After making paper in the same manner as in Example 1 , the sheet (wet paper) was dried without passing through a surface improvement device while the water content of the wet paper was 85 wt%, thereby obtaining a nonwoven sheet having a thickness of 3.5 mm under a load of 20 kPa and a density (apparent bulk density) of 0 13 g / cm3

[0154] [Comparative Example 2]

[0155] After making paper in the same manner as in Example 1 , the wet paper was passed through a pair of upper and lower press rolls with a water content of 85 wt% without passing through a surface improvement device. However, the wet paper collapsed due to the water squeezed out by the pair of upper and lower press rolls, and it was not possible to obtain a nonwoven sheet.

[0156] [Comparative Example 3]

[0157] After making paper in the same manner as in Example 1 , the wet paper was passed through a pair of upper and lower press rolls with a water content of 60 wt% without passing through a surface improvement device, and then dried to obtain a nonwoven sheet with a thickness of 3.0 mm under a load of 20 kPa and a density (apparent bulk density) of 0.15 g / cm3.

[0158] [Comparative Example 4]

[0159] After making paper in the same manner as in Example 1 , the sheet (wet paper) was dried without passing through a surface improvement device while the water content of the wet paper was 85 wt%, and then passed through a calender press to obtain a nonwoven sheet having a thickness of 3.0 mm under a load of 20 kPa and a density (apparent bulk density) of 0. 15 g / cm3.

[0160] [Testing and Evaluation Method]

[0161] The above examples and comparative examples were evaluated under the following conditions, and results are shown in Tables 1 and 2.

[0162] (1 ) Thickness (mm) under load of 20 kPa

[0163] The nonwoven sheet thus prepared was cut into a size of 250 mm x 200 mm to prepare a test piece The thickness (mm) of any five points of the test piece was measured using a dedicated thickness meter at 20 kPa, and an average value was rounded to two significant digits.

[0164] (2) Density (apparent bulk density) (g / cm3)

[0165] The nonwoven sheet thus prepared was cut into a size of 250 mm x 200 mm to prepare a test piece.

[0166] The weight (g) of the test piece was measured using a balance capable of measuring to two decimal places (0.01 g), and the measured value was multiplied by 20 to obtain a basis weight (g / m2).

[0167] The density (apparent bulk density) (g / cm3) was calculated by the following formula and rounded to two significant digits.

[0168] Density (g / cm3) = [Basis weight (g / m2)] + [Thickness (mm) under load of 20 kPa] * 1000.

[0169] (3) Three-dimensional surface roughness (root mean square height, Sq, pm) of TOP surface and bottom forming wire surface.

[0170] The nonwoven sheet thus prepared was cut into a size of 150 mm x 250 mm so that a short side direction was parallel to an MD direction (a flow direction when the nonwoven sheet is used as the separator) to prepare a test piece.

[0171] The test piece was placed on a stage of a three-dimensional shape measuring machine (VR3100, manufactured by KEYENCE CORPORATION), and an area of 100 mm x 200 mm was measured.

[0172] The obtained three-dimensional coordinate data was subjected to level correction of the data slope components by F calculation, and long wavelength components such as curling tendencies were removed by an L filter. A Gaussian filter (cutoff value: 25 mm, 1 / 2 cutoff at each end was removed) was used as the L filter.

[0173] From the obtained processing data, the three-dimensional surface roughness (root mean square height, Sq, pm) was calculated. FIGS. 5 and 6 are the example of the obtained processing data.

[0174] The measurement was repeated five times, and the average value was taken as the three- dimensional surface roughness (Sq, pm), and was expressed as an integer or rounded to two significant digits Note that FIG 5 shown above shows data for a surface with Sq of 81 pm and FIG 6 shows data for a surface with Sq of 215 pm.

[0175] In the disclosure, in order to eliminate errors due to variations in the thickness of the nonwoven sheet under a load of 20 kPa, the smoothness and flatness of the top surface and the bottomsurface of the nonwoven sheet are evaluated as the ratio (%) of the measured three-dimensional surface roughness (Sq) value to the thickness of the nonwoven sheet. The ratio (%) of the three- dimensional surface roughness (Sq) on the top surface side and the bottom surface side of the nonwoven sheet to the thickness of the nonwoven sheet under a load of 20 kPa was calculated using the following formula and rounded to two significant digits.

[0176] Ratio (%) = Three-dimensional surface roughness (Sq, pm) on top surface and bottom surface of nonwoven sheet - Thickness (mm) of the nonwoven sheet under load of 20 kPa - 10.

[0177] In addition, the ratio (%) of three-dimensional surface roughness (Sq) on the TOP surface and three-dimensional surface roughness (Sq) on the bottom forming wire surface was calculated using the following formula and rounded to two significant digits.

[0178] Ratio (%) = Three-dimensional surface roughness (Sq, pm) on the TOP surface - Three- dimensional surface roughness (Sq, pm) on the bottom forming wire surface.

[0179] (4) Fracture properties

[0180] The nonwoven sheet thus prepared was cut into a size of 100 mm x 300 mm so that a long side direction was parallel to the MD direction (the flow direction of the separator) to prepare a test piece

[0181] A 1 mm thick iron plate (120 mm x 100 mm) simulating an electrode was placed on top of the test piece so that the long side of the iron plate is perpendicular to the long side of the test piece, and the test piece was folded along the long side of the iron plate. Next, this state was maintained for 3 seconds, and then the nonwoven sheet surface was visually checked for the presence or absence of fractures due to folding. The position at which the iron plate was placed on the test piece was adjusted so that in terms of the folding position in this case, the folding length was at least 30 mm of the long side (300 mm) of the test piece

[0182] Next, the test piece was released (the folded state was returned to its original flat state), and then this folding operation was repeated four more times (a total of five times) at the same folding position In a state of the final (fifth) folding, the nonwoven sheet surface was visually checked forthe presence or absence of fractures due to folding.

[0183] When any fractures due to folding appeared on the nonwoven sheet surface after the first folding, the rating was "X". When no fractures appeared on the nonwoven sheet surface after the first folding but any fractures appeared on the nonwoven sheet surface after five foldings, the rating was "A" When no fractures appeared on the nonwoven sheet surface after five foldings, the rating was "O".

[0184] Measurements were taken both when the TOP surface was on the crest side (measurements were taken with an iron plate placed on the bottom forming wire surface) and when the bottom forming wire surface was on the crest side (measurements were taken with an iron plate placed on the TOP surface).

[0185] (5) Tensile strength reduction rate

[0186] Forthe nonwoven sheet thus produced, tensile strength in the MD direction (the flow direction when the nonwoven sheet is used as the separator) of the nonwoven sheet was measured in accordance with the method specified in SBA S0406-2005, and recorded as "tensile strength (S)".

[0187] Similarly, after papermaking, the sheets (wet paper) were dried without passing through a surface improvement device, and the tensile strengths in the MD direction (the flow direction when the nonwoven sheet is used as the separator) of the corresponding nonwoven sheets obtained were measured and recorded as "tensile strength (R)". The tensile strength in the MD direction (the flow direction when the nonwoven sheet is used as the separator) of the nonwoven sheet obtained by drying was measured for the sheet (wet paper) before passing through the pair of upper and lower press rolls for Comparative Example 3, and for the sheet (wet paper) before passing through the calender press for Comparative Example 4.

[0188] The tensile strength reduction rate (%) was calculated using the following formula Atensile strength reduction rate of 20% or less was marked as "O", and a tensile strength reduction rate of more than 20% was marked as "X". For Comparative Example 1, since [tensile strength (S)] = [tensile strength (R)], the tensile strength reduction rate was marked as 0% (no change).

[0189] Tensile strength reduction rate (%) = [tensile strength (R) - tensile strength (S)] [tensile strength (R)] x 100.

[0190] Evaluation results of Examples 1 to 14 and Comparative Examples 1 to 4 are summarized in Tables 1 and 2[Table 1][Table 2]

[0191] From the results in Tables 1 and 2, it was confirmed that the nonwoven sheets obtained in these Examples had favorable surface smoothness and flatness on both the TOP surface and the bottom forming wire surface, and had sufficient tensile strength.

[0192] The wet paper, with a water content of 50 wt% or more, was passed through a surface improvement device, in which the wet paper was sandwiched between two forming wires or between a forming wire and a water-absorbing felt from above and below, and the water that moves when the wet paper was pressed down was absorbed by the forming wire or the water-absorbing felt, or even by a vacuum or suction device above, thereby improving the smoothness and flatness of the top surface (the TOP surface) and the bottom surface (the forming wire surface) of the nonwoven sheet The nonwoven sheets in Examples 1 to 7 and 9 to 14 prepared in this way showed good fracture properties.

[0193] On the other hand, in the nonwoven sheet of Example 8 in which the wet paper, with a water content of 35 wt%, was passed through a surface improvement device, the surface smoothness and flatness of the TOP surface were slightly inferior (the ratio of the three-dimensional surface roughness (Sq) to the thickness of the nonwoven sheet was 6.7%), so that a single folding with the TOP surface as the crest side did not cause any fractures on the surface of the nonwoven sheet, but repeated folding caused fractures on the surface of the nonwoven sheet This is thought to be because when the wet paper is sandwiched between two forming wires or between a forming wire and a water-absorbing felt from above and below and pressed down, if the water content of the nonwoven sheet is low, the degree to which the glass fibers on the surface layer of the TOP surface flow and move to change the deposition state of the glass fibers is small. For this reason, the fiber orientation of the glass fibers on the surface layer of the nonwoven sheet remains somewhat random. In particular, since the fiber orientation of the glass fibers in the concave parts of the unevenness of the surface layer of the nonwoven sheet hardly changes, the nonwoven sheet is more resistant to bending stress than a nonwoven sheet with a large surface roughness (surface unevenness), but it is thought that cracks (factures) will remain prone to occur in the concave parts of the unevenness of the nonwoven sheet surface.

[0194] The nonwoven sheet of Comparative Example 1 had large unevenness on the TOP surface. In Comparative Example 2, the wet paper collapsed and a nonwoven sheet could not be obtained, so no further testing or evaluation was performed. In Comparative Example 3, the nonwoven sheet had large unevenness on the TOP surface, and the tensile strength also decreased significantly. Therefore, cracks (fractures) occurred on the surface of the nonwoven sheet not only when the TOP surface was set as the crest side but also when the bottom forming wire surface was set as the crest side (measured while an iron plate is placed on the TOP surface). In the nonwoven sheet of Comparative Example 4, the surface of the nonwoven sheet stuck to the calender roll, and the unevenness of the TOP surface and the bottom forming wire surface became large The surface of the nonwoven sheet peeled off severely, making it not possible to visually check for the evaluation of fracture properties. The tensile strength also decreased significantly.

[0195] The nonwoven sheet of the disclosure has favorable smoothness and flatness on the TOP surface and the bottom forming wire surface of the nonwoven sheet. Thus, separator made of the nonwoven sheet can have intimate contact with the electrode plates, allowing the acid stratification to be reduced. In addition, fracture properties are excellent and there is no need to stack the separatorso that the bottom forming wire surface is on the outside, which improves the productivity of lead-acid batteries.

[0196] [Description of the Reference Numeral]

[0197] 1 surface improvement device

[0198] 2 papermaking machine

[0199] 3 wet paper (Wet mat)

[0200] 4 dandy roll

[0201] 5 water-absorbing felt or forming wire

[0202] 6 forming wire

[0203] 8 upper vacuum or suction device

[0204] 9 lower vacuum or suction device

[0205] 10a drive roll

[0206] 10b auxiliary drive roll

[0207] 10c support roll

[0208] 11 top roll

[0209] 12 bottom roll

[0210] 13 top surface of nonwoven sheet

[0211] 14 bottom surface of nonwoven sheet

Claims

What is claimed is:

1. A nonwoven sheet formed by a wet papermaking process using glass fibers with a weighted average fiber diameter of 3.0 pm or less as a main component, wherein a thickness under a load of 20 kPa is 100 pm or more, an apparent bulk density is 0.30 g / cm3or less, a ratio of a three-dimensional surface roughness (Sq) to a thickness of the nonwoven sheet is 7% or less on a TOP surface side and 7% or less on a bottom forming wire surface side.

2. The nonwoven sheet according to claim 1, wherein the ratio of the three-dimensional surface roughness (Sq) to the thickness of the nonwoven sheet is 5% or less on the TOP surface side and 5% or less on the bottom forming wire surface side.

3. The nonwoven sheet according to claim 1 , wherein the ratio of the three-dimensional surface roughness (Sq) to the thickness of the nonwoven sheet is 3% or less on the TOP surface side and 3% or less on the bottom forming wire surface side4. The nonwoven sheet according to claim 1, wherein the ratio of the three-dimensional surface roughness (Sq) on the TOP surface side to the three-dimensional surface roughness (Sq) on the bottom forming wire surface side is 4 or less.

5. The nonwoven sheet according to claim 1 , wherein a blending amount of the glass fibers is 60 wt% or more of a fibrous material constituting the nonwoven sheet.

6. The nonwoven sheet according to claim 1, wherein a blending amount of the glass fibers is 80 wt% or more of a fibrous material constituting the nonwoven sheet7. The nonwoven sheet according to claim 1 , wherein the glass fibers constituting the nonwoven sheet have a weighted average fiber diameter of 2.0 pm or less.

8. The nonwoven sheet according to claim 1 , where the nonwoven sheet includes heat-fusible organic fibers.

9. The nonwoven sheet according to claim 1 , wherein the nonwoven sheet has excellent anti-cracking properties.10 The nonwoven sheet according to claim 9, where the fracture properties are characterized by placing a 1 mm thick iron plate on the nonwoven sheet and visually evaluating the presence or absence of fractures on the nonwoven sheet surface due to folding along the side of the iron plate.

11. A method for producing a nonwoven sheet, the nonwoven sheet formed by a wet papermaking process using glass fibers with a weighted average fiber diameter of 3.0 pm or less as a main component, having a thickness under a load of 20 kPa of 100 pm or more, and having an apparent bulk density of 0.30 g / cm3or less, wherein the nonwoven sheet is produced by sandwiching the sheet between two forming wires or between a forming wire and a water-absorbing felt so as to press the nonwoven sheet between two planes while maintaining water from the wet papermaking process to promote flat and smooth surface properties on top and bottom surfaces of the nonwoven sheet.

12. The method for producing a nonwoven sheet according to claim 11, wherein the nonwoven sheet maintains water after the wet papermaking process and is sandwiched between a lower forming wire and an upper forming wire or felt so as to press the nonwoven sheet between two planes.

13. The method for producing a nonwoven sheet according to claim 11 , wherein after the nonwoven sheet is sandwiched between two forming wires or between a forming wire and a felt so as to press the nonwoven sheet between two planes, the two forming wires or the forming wire and the felt are pressed by an unpaired roll or press roll to create flat and smooth surface properties on the top and bottom surfaces of the nonwoven sheet.

14. The method for producing a nonwoven sheet according to claim 11 , wherein after the nonwoven sheet is sandwiched between two forming wires or between a forming wire and a felt so as to press the nonwoven sheet between two planes, excess water is removed from a top side of the sheet using a vacuum or suction device on an upper side of the forming wire or an upper water removing felt15. The method for producing a nonwoven sheet according to claim 11, wherein a water content of the nonwoven sheet after the wet papermaking process is maintained or held to at least 50 wt% or more.

16. The method for producing a nonwoven sheet according to claim 11, wherein a water content of the nonwoven sheet after the wet papermaking process is maintained or held to at least 80 wt% or more.17 The method for producing a nonwoven sheet according to claim 11 , wherein an apparatus for sandwiching the nonwoven sheet while maintaining higher water content after the wet paper making process using two forming wires or with a forming wire and a felt is integrated into a papermaking machine.

18. The method for producing a nonwoven sheet according to claim 12, wherein the upper forming wire has a mesh size of 10 or more19. A separator or a pasting paper, comprising the nonwoven sheet according to any one of claims 1 to 1020. A lead-acid battery, comprising a separator or a pasting paper formed of the nonwoven sheet according to any one of claims 1 to 10.

21. A separator or a pasting paper, comprising a nonwoven sheet produced by the method for producing a nonwoven sheet according to any one of claims 11 to 18.

22. A lead-acid battery, comprising a separator or a pasting paper formed of a nonwoven sheet produced by the method for producing a nonwoven sheet according to any one of claims 11 to 18.

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