JPH10241676A - Manufacture of porous belt body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a powder filling factor in a powder layer without making reduction of carrier itself, so as to secure high productivity by setting reduction speed in a specified arrange in the case of successive press reduction in a lengthwise direction in the reduction of wide width face. SOLUTION: A powder layer in a predetermined thickness is applied to both top and bottom faces of a porous carrier, for instance, a punching metal 10 via a powder-applying process 12. The powder filling factor-enhanced porous belt body by a reduction device 20 is taken up by a take-up reel 22. At this time, the range of reduction speed is limited to 1 to 100mm/minute, preferably 10 to 50mm/minute. That is, in the case of press reduction, when pressurizing speed is increased, friction force between a tool contact face and the powder layer is enlarged, so that the elongation in a width direction and a lengthwise direction is suppressed such that filling density is enhanced. A reduction device is composed of a pair of flat dies, in which the direction can be conducted generally in a right angle direction against a wide width face, that is, in a thickness direction. In the case of reduction, preferably the width direction of the porous belt body is constrained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a porous band having a powder layer formed on both sides of a porous carrier, and more particularly to a method for manufacturing a porous band which can be used as an electrode material for a secondary battery. It relates to a manufacturing method.

[0002]

2. Description of the Related Art For example, as an electrode for a secondary battery using a hydrogen storage alloy, a porous band formed by providing a hydrogen storage alloy powder layer on both sides of a porous carrier is used.
In such a porous strip, it has been found that improving the filling rate of the powder layer is effective for improving the battery capacity, so how to improve the powder filling rate becomes a problem. ing.

Japanese Patent Application Laid-Open No. 3-77270 discloses a filling process by rolling, and it has been proposed to use a roll having a diameter of 3 cm or more in order to suppress elongation in the rolling direction. However, the above-mentioned publication does not disclose specific contents of the improvement of the filling rate, and the rolling causes mechanically large elongation in the longitudinal direction, and the filling rate does not increase due to this strain.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a porous strip having a powder layer, which involves the development of a technique for improving the powder filling rate in the powder layer and ensuring high productivity. is there.

[0005]

Means for Solving the Problems The inventors of the present invention have made it possible to reduce the width of the carrier in the longitudinal direction by sequentially reducing the pressing speed in the longitudinal direction at a rolling speed of 1 to 100 mm / min so that the carrier itself is not reduced. As a result, they found that the powder filling rate in the powder layer could be remarkably improved, and completed the present invention.

Further, according to the knowledge of the present inventor, when a reduction is applied without applying a constraint in the width direction, the band is stretched at most 5% in the width direction. Therefore, when the width of the groove is set to 5% or less of the width of the band before rolling, the packing density is improved as compared with the case where no binding is performed.

Thus, the present invention relates to a method for producing a porous strip having a powder layer formed on both sides of a porous carrier, wherein the strip is run in the longitudinal direction, and the wide surface of the strip is removed. A method for producing a porous band, characterized in that rolling is sequentially performed at a pressing speed of 1 to 100 mm / min in a direction perpendicular to the wide surface of the band by a tool placed therebetween.

[0008] In a preferred embodiment of the present invention, one of the tools to be used may be provided with a shape that ties up the width of the band. According to yet another aspect of the present invention,
One of the tools used may have a convex surface in contact with the powder layer. In the present invention, the processing rate during rolling, that is, the rolling rate is not particularly limited, but generally,
It is 10 to 40%, preferably 15 to 25%.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic explanatory view of a method for manufacturing a porous band according to the present invention. In the figure, a porous carrier, for example, a punching metal 10 is subjected to a powder coating step 12 through A powder layer having a predetermined thickness is applied to both upper and lower surfaces. In the subsequent drying step 14, the powder layer is dried and solidified. However, at this stage, since the applied paste is usually only dried, the packing density of the functional powder such as the hydrogen storage alloy powder is considerably reduced. As already mentioned, the characteristics as an electrode are maximally improved by increasing the density of the functional powder as described above as much as possible. Necessary for improving electrode characteristics. Therefore, even in the present invention, the filling ratio of the powder is improved by the rolling-down device 20. The porous strip having an improved filling factor is taken up by a take-up reel 22.

In the present invention, when the porous strip is reduced in pressure, if the rolling rate is increased with a constant reduction rate, the packing density of the powder in the powder layer provided on at least one surface of the strip increases. This is to take advantage of the fact that rolling of the carrier constituting the belt does not occur, and the range of the rolling speed for that purpose is limited to the range of 1 to 100 mm / min, preferably 10 to 50 mm / min.

That is, when the pressing speed is increased at the time of press reduction, the frictional force between the tool contact surface and the powder layer increases, and the stretching in the width direction and the longitudinal direction is suppressed, and the packing density increases. The press itself is not limited at all, but generally, for example, a hydraulic press of about 10 to 100 T may be used in the present invention.

In the present invention, the pressing device is not particularly limited as long as it can realize the filling of the powder in the powder layer of the porous band. It is composed of a pair of flat molds capable of rolling down in the direction. As the rolling-down mechanism, it is sufficient that a predetermined rolling-down speed is ensured, but it is preferable to use a hydraulic pressure, a hydraulic pressure, a motion perpendicular to a wide surface by a crank mechanism or an electromagnetic solenoid mechanism.

Further, as means for further improving the packing density in the present invention, at the time of the above-mentioned pressing reduction,
The press reduction may be performed while tying the porous band in the width direction. As described above, by suppressing the stretching in the width direction of the carrier constituting the porous band, the packing density can be further improved.

The constraint in the width direction at this time may be of any shape, such as cutting a groove, providing a wall, or the like, as long as the method stops the stretching in the width direction. However, it has been found to be feasible to create grooves of a predetermined width.

FIGS. 2A to 2C are schematic explanatory views of the tool shape in such an embodiment. In FIG. 2 (a), a flat press die 30 is used as a lower die, and the porous strip 34 is pressed down from above by a flat press die 32. In FIG. 2 (b), press reduction is performed by using a press die 40 having a groove as a lower die and an upper die 42 having a convex portion corresponding to the groove of the lower die. In any case, the porous band 34 moves in a direction perpendicular to the drawing.

In FIG. 2C, the circular mold 52 is pressed down from above the flat mold 50. in this way,
If the contact surface of the tool with one powder layer is a convex curved surface,
Surface pressure rises and can be manufactured with smaller load. That is,
There is an advantage that it can be used with equipment with a small pressurizing capacity. In this case, the shape of the curved surface may be, for example, a circular cross section or a parabolic cross section in the belt running direction.

In any case, the above-described press reduction is performed while the porous strip intermittently travels in the longitudinal direction.
According to the test results of the present inventor, when a reduction is applied without restricting the width, the porous strip is stretched at most 5% in the width direction.

That is, (width of band after rolling / width of original band) = 1.05 Therefore, as shown in FIGS. 2 (a) to 2 (c), a case where rolling is performed while restraining by various means. When the width of the groove is set to 5% or less of the width of the band before the rolling, the packing density is improved as compared with the case where no binding is performed. Further, if the width of the groove is the same as the width of the band, the effect is further enhanced.

According to a further preferred aspect of the present invention, when the above-mentioned tool used in the rolling device is cooled, the viscosity of the powder layer (slurry) rises, suppressing stretching at the time of rolling and increasing the packing density.

Since the viscosity of the slurry containing the organic binder increases as the temperature decreases, by cooling the mold, the flow of the powder layer during rolling can be reduced. It is also conceivable that the band is heated by applying the powder layer to the carrier after drying, and the viscosity of the slurry is lowered. Therefore, it is possible to press the mold at a low temperature even on a continuous line as shown in FIG. 1 by cooling the mold. It is possible. As the cooling temperature, the temperature of the mold is appropriate, and preferably 5 to 15 ° C.

The cooling method in that case is water, liquid gas
(N, Ar, air, etc.) as a cooling medium or a thermoelectric element such as a Peltier element as a cooling means. They may be used in combination.

Thus, for example, a spherical powder such as a gas atomized powder has a higher packing density of 10 to 25% in a powder state because it has a more spherical shape than a powder obtained by pulverizing an ingot material. However, when a powder layer is formed as a slurry, Due to the spherical shape, the fluidity was high, the powder flow during pressing or rolling was large, and the density after rolling was not as high as the powder state. Is also improved by 10-25% compared to ingot grinding.

Here, the method for producing a porous strip according to the present invention will be described in more detail as follows. For the production of the electrode, for example, a hydrogen storage alloy powder and an organic binder are converted into a slurry or paste using an appropriate solvent (e.g., water, alcohols, etc.), and a porous carrier functioning as an electrode substrate (e.g., After applying to a porous metal carrier, a porous carrier such as a punched plate having a large number of through-holes, drying and removing the solvent to an appropriate degree, the resulting porous strip is roll-pressed or pressed to form the sheet. Can be performed.

In the present invention, the above-mentioned hydrogen storage alloy powder,
The organic binder is not particularly limited as long as it can produce an electrode for a normal secondary battery.

Examples of the organic binder include polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), polyethylene (PE), polyethylene oxide (PEO), and carboxymethyl cellulose (CMC). The amount of the organic binder used is preferably a small amount within a range necessary for bonding of the hydrogen storage alloy powder.
About 5% by weight is preferable. As the porous carrier, a suitable material such as a punched metal and a sintered metal short fiber can be used.

Thus, according to the present invention, the same reduction amount
In (Sheet thickness reduction), <filling ratio> is improved and <longitudinal elongation> is small, so that the battery characteristics when used as an electrode are greatly improved, and there is no stretching in the width direction. This greatly contributes to efficiency improvement. Next, the present invention will be described more specifically with reference to examples.

[0027]

EXAMPLE In this example, Mm _1.0 Ni _3.55 Co _0.75 Mn _0.4 Al
The AB ₅ type hydrogen storage alloy having a chemical composition of _0.3 was used. The raw material used to make this hydrogen storage alloy has a purity of 99.9
% Flake Ni, 99.8% pure electrolytic Co, 99.9% pure shot Al, 99.8% pure plate Mn, 99.8% or more misch metal (Mm: La = 28%, Ce = 48%, Nd = 18
%, Pr = 6%).

These raw materials were mixed at a predetermined ratio, and spherical powder (atomized powder) of a hydrogen storage alloy was cast by an Ar gas atomizing method (75 kg / ch), which is a rapid solidification method, and an ingot was cast by a high frequency induction heating vacuum melting method. (100 kg / ch) mechanical pulverization (in an Ar gas atmosphere, coarse pulverization with a disk grinder followed by fine pulverization with an attrition mill) to produce amorphous powders (pulverized powders) of the hydrogen storage alloy. In order to remove quenching strain of the atomized powder, a heat treatment at 900 ° C. for 4 hours was performed in an Ar atmosphere having a purity of 99.99%. Each of the obtained hydrogen-absorbing alloy powders having a size passing through a sieve having a diameter of 75 μm was selected and used in the test.

In preparing the electrode, 0.8% by weight of a PTFE (polytetrafluoroethylene) dispersion liquid (trade name: D-1) manufactured by Daikin Industries, and 12% by weight of water as a dispersion medium were mixed with the obtained powder. Then, a slurry to be applied to the electrode was prepared.

This slurry was prepared to have a thickness of 0.08 mm, a width of 50 mm, and a length of
It was evenly applied to both sides of a 10 m punching plate (made of iron and plated with Ni having a thickness of about 10 μm) to give a total thickness of the porous band of 0.65 mm. The size of the punching plate is determined by the size of the jig used in the present embodiment, and it is possible to process wider and longer shapes in actual mass production. It is also possible to work by uncoiling.

After the slurry is applied to the punching plate, a drying treatment is performed in an Ar atmosphere at 80 ° C. for 10 minutes, and the reduction processing method of the present invention is applied. If the density after processing is 5 g / cc or more, sufficient filling is performed. It was determined that the characteristics were improved.

Embodiment 1 In this embodiment, as shown in FIG. 2 (a), an example is shown in which both the upper and lower tools for processing the porous strip are flat.

The upper and lower molds are both fixed to a press, and can be continuously pressed by moving the band. In this example, the packing densities were compared by changing the pressing speed during the pressing. The results are summarized in Table 1.

In the table, since the flowability of the spherical powder is large,
In spite of the fact that the packing density in the powder state is high, the powder flows and the packing density in the conventional rolling becomes the same as in the case of the ingot pulverized powder.

[0035]

[Table 1]

The amount of pressurization is from 0.65 mm thickness to 0.45 mm thickness.
Example 2 In this example, as shown in FIG. 2 (b), the effect of improving the packing density by tying the porous band in the width direction was confirmed. In order to do so, a groove having a depth of 10 mm and a width changed as shown in Table 2 is formed in the lower mold in the longitudinal direction of the band body, and the upper mold is fitted with the groove so as to fit into the groove at the time of pressing down. A protrusion having a width corresponding to the groove width and having a height of 12 mm was used. In addition, the convex part of the upper die is not always necessary, and may be a flat type. In that case, it is necessary to make the depth of the groove shallow according to the thickness of the strip after the rolling.

Pressing speed at the time of pressing down: 10 mm / min, band width before processing: 50 mm, pressing amount: 0.65 mm thickness as in Example 1 →
The thickness was 0.45 mm. The results are summarized in Table 2.

[0038]

[Table 2]

[0039]

As described above, according to the present invention, the filling rate of powder is improved by about 10% or more as compared with the conventional powder, and as a result, the electrode capacity, for example, the electrode capacity is reduced by 10%. % Or more, which means a 10% increase in use time when considered as a characteristic of the secondary battery, and the contribution of the present invention in the art is great.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a method for producing a porous strip according to the present invention.

FIGS. 2 (a) to 2 (c) are schematic explanatory diagrams of tool shapes used in the present invention, respectively.

Claims (2)

[Claims] 1. A method for producing a porous strip having a powdery layer formed on both sides of a porous carrier, wherein the strip is run in a longitudinal direction, and is placed across a wide surface of the strip. A method for producing a porous strip, wherein the rolling is performed sequentially at a pressure of 1 to 100 mm / min in a direction perpendicular to the wide surface of the strip by a tool. 2. The method according to claim 1, wherein one of the tools to be used is provided with a tool having a shape for tying the width of the band.