JP2010037569A - Metal porous electrode base material and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal porous electrode base material which has a pore structure capable of sufficiently being filled with an electrode material and active material, and also hardly dropping out them therefrom, and can make a battery high in performance. <P>SOLUTION: In the planar metal porous electrode base material 10, a plurality of polyhedrons whose sides are composed of skeletons 11 of a metal sintered compact are formed in a mutually continuous. In the skeletons 11, the thickness of the skeletons 11A arranged at the outermost surface 10A is ≥5 to ≤65 μm, the thickness of the skeletons 11B arranged at the inside is ≥3 to ≤35 μm, also, the thickness of the skeletons 11A in the outermost surface 10A is ≥1.2 to ≤2.5 times that of the skeletons 11B at the inside, and the voidage of voids 12 formed between the skeletons 11 i≥s 97 to ≤99%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a metal porous electrode substrate used in secondary batteries such as electric double layer capacitors, lithium ion batteries and nickel metal hydride batteries, and primary batteries such as manganese dry batteries, alkaline manganese dry batteries, silver oxide batteries and manganese dioxide lithium batteries. The present invention relates to a material and a manufacturing method thereof.

  As a base that is filled with an active material and used as an electrode of an alkaline secondary battery, a porous metal plate that is composed of a skeleton and a void of a sintered metal body and is filled with the electrode material and the active material is used. Yes. Such a porous metal plate has been required to have a void structure with a large surface area in order to reliably hold many active materials and realize an electrode with a large capacity.

For example, in Patent Document 1, the capacity of a capacitor is increased by increasing the porosity of porous nickel constituting the current collector of the negative electrode to 80 to 99%.
Patent Document 2 describes that it is preferable to increase the porosity and the average pore diameter. Specifically, the average pore diameter of the porous metal plate is larger than twice the thickness of the negative electrode active material layer so that the pores of the porous metal plate constituting the negative electrode material for secondary batteries are not blocked by the active material or the like. It has been proposed to do. Further, in order to ensure a large surface area for holding the negative electrode active material, the porosity of the porous metal plate is set to 10% to 99% by volume, and the average pore diameter is set to 2 μm to 150 μm.
In Patent Document 3, in a porous metal plate formed by subjecting a porous resin to metal plating, uniform thickness plating is formed, the porous metal plate is prevented from being damaged, and the active material utilization rate is improved. Therefore, an appropriate average number of cells per inch in the porous metal plate is set.
Patent Document 4 proposes a porous molded body capable of obtaining a porous metal plate having a porosity of 80 to 98% by volume and an average pore diameter of 5 μm to 100 μm. As the material, it has been proposed to use a metal powder having an average particle size of 0.5 μm to 500 μm.
Japanese Patent No. 3689948 JP 2008-16329 A Japanese Patent No. 4085434 Japanese Patent No. 3246190

  Thus, in order to improve the performance of various batteries, it is required to form an appropriate pore structure in the porous metal plate. However, with the various porous metal plates described in the above patent documents, sufficient performance can be obtained as an electrode base material used in electric double layer capacitors for automobiles and lithium ion batteries, which have recently been required to have high performance. Absent.

  The present invention has been made in view of such circumstances, and has a porous structure that can be sufficiently filled with an electrode material and an active material and has a pore structure in which they are not easily dropped, and can improve the performance of a battery. An object of the present invention is to provide a porous electrode substrate.

The present invention is a plate-like metal porous electrode base material in which a plurality of polyhedrons whose sides are constituted by a skeleton of a metal sintered body is formed in a continuous state, and the skeleton is disposed on the outermost surface. The thickness of the skeleton is 5 μm or more and 65 μm or less, the thickness of the skeleton disposed inside is 3 μm or more and 35 μm or less, and the thickness of the skeleton on the outermost surface is 1 of the thickness of the skeleton in the inside .2 to 2.5 times, and voids formed between the skeletons have a porosity of 97% to 99%.
According to the present invention, since the skeleton forming the gap is thin, the gap is easily filled with the electrode material or the active material. Moreover, since this skeleton is thicker than the inside at the outermost surface of the base material, it is possible to suppress the dropping of the electrode material and the active material filled in the base material. The reason why the porosity is 97% or more is to increase the filling amount of the electrode material or the active material, and the reason why the porosity is 99% or less is to ensure the strength of the base material.

  In the metal porous electrode substrate of the present invention, it is preferable that the aperture ratio on the outermost surface is 70% or more and 90% or less. In this case, by setting the aperture ratio to 70% or more, it is possible to secure an entrance area when filling the gap with the electrode material or the active material, so that the electrode material or the active material is easily filled. Moreover, the intensity | strength of a base material is securable by making an aperture ratio into 90% or less.

  In this metal porous electrode substrate, it is preferable that an average opening diameter on the outermost surface is 100 μm or more and 500 μm or less. In this case, it is possible to ensure the entrance area and the strength of the base material when the electrode material or the active material is filled in the gap.

The method for producing a metal porous electrode substrate according to the present invention comprises a plate-like metal porous electrode substrate in which a plurality of polyhedrons whose sides are constituted by a skeleton of a metal sintered body are formed in a continuous state. A manufacturing method comprising a foamable slurry creating step of creating a foamable slurry containing a metal powder and a foaming agent, a homogenizing step of passing the foamable slurry through a strainer, and forming the foamable slurry into a thin plate shape A green sheet forming step of forming and foaming to form a green sheet; and a sintering step of sintering the green sheet.
According to this invention, by filtering with a strainer, coarse materials such as agglomerated metal powder and excessive bubbles can be removed from the foaming slurry, and a green sheet can be formed uniformly.

  In this manufacturing method, the metal powder preferably has an average particle size of 0.5 μm to 5 μm and a maximum particle size of 50 μm, and the strainer preferably has openings corresponding to a particle size of 35 μm to 125 μm. If the opening of the strainer exceeds a particle size equivalent to 125 μm, aggregates of metal powder remain in the foamable slurry, and when the foamable slurry is molded, streaks may be formed, or there may be a place where sintering is insufficient. is there. On the other hand, if the opening of the strainer is smaller than the particle size equivalent to 35 μm, the pressure for allowing the foaming slurry to pass through may increase, or filtration may take a long time, and productivity may be reduced.

  Moreover, in this manufacturing method, it is preferable that the content rate with respect to the said foamable slurry of the said foaming agent is 2.3 to 5 weight%. In this case, appropriate bubbles can be formed when the foamable slurry is foamed.

  According to the metal porous electrode base material of the present invention, a sufficient amount of electrode material or active material is easily filled in the gap, and the filled electrode material or active material is difficult to fall off. It is possible to improve. Further, according to the method for producing a metal porous electrode substrate of the present invention, a high porosity substrate having fine and uniform voids can be obtained, so that various types of batteries can be improved in performance.

Hereinafter, an embodiment of a metal porous electrode substrate and a method for producing the same according to the present invention will be described.
A metal porous electrode substrate (hereinafter referred to as a substrate) 10 of the present invention is a plate-like porous body made of a skeleton 11 of a sintered metal body.

  FIG. 1 is a plan view showing the substrate 10. Among the skeletons 11, the thickness of the skeleton 11 </ b> A disposed on the outermost surface 10 </ b> A is 5 μm or more and 65 μm or less, and the thickness of the skeleton 11 </ b> B disposed therein is 3 μm or more and 35 μm or less. The thickness of the skeleton 11A is not less than 1.2 times and not more than 2.5 times the thickness of the skeleton 11B. That is, the skeleton 11 of the substrate 10 is thick on the outermost surface 11A and thin on the inside. Such a thickness of the skeleton 11 can be actually measured from a photograph of an SEM (scanning electron microscope) obtained by photographing the base material 10.

  In this base material 10, voids 12 are formed between the skeletons 11. The void 12 is formed such that a plurality of polyhedral pores whose sides are constituted by the skeleton 11 are continuous with each other, and occupies 97% or more and 99% or less in the volume of the base material 10. Hereinafter, the volume ratio of the void 12 is referred to as a void ratio. The porosity can be calculated from the actual weight of the base material 10 with respect to the weight of the solid body having the same shape as the base material 10.

  The gap 12 has a plurality of openings 12a that open to the outermost surface 10A, and the opening area occupies 70% or more and 90% or less of the area of the outermost surface 10A. Hereinafter, the ratio of the opening area of the outermost surface 10A of the gap 12 is referred to as the opening ratio. The average area of the opening 12a is 100 μm or more and 500 μm or less when the opening 12a is regarded as a circle, and this is hereinafter referred to as an average opening diameter.

More specifically, the aperture ratio and the average aperture diameter can be calculated as follows.
First, the SEM photograph which image | photographed 10 A of outermost surfaces is image-processed, and it binarizes into the frame | skeleton 11 and the opening part 12a, and measures the visual field area and the area of the opening part 12a in a visual field. The aperture ratio is expressed as a percentage of the area of the opening 12a with respect to the visual field area. The average aperture diameter is obtained by calculating the equivalent circle diameter from the area and the number of the apertures 12a in the field of view.

This metal porous electrode substrate 10 can be manufactured as follows.
<Foaming slurry preparation process>
First, a foamable slurry containing a metal powder and a foaming agent is prepared. The foamable slurry is prepared by mixing the metal powder forming the skeleton 11, the binder (water-soluble resin binder), the foaming agent and water, and if necessary, the surfactant and / or the plasticizer. More specifically, a slurry containing a metal powder, a binder, and water is first prepared, and then a foaming agent is added to the slurry, followed by stirring with a stirring device such as a mixer.

  Although it does not specifically limit as metal powder, Ni, Cu, Ti, Al etc. are preferable from points, such as corrosion resistance. The metal powder preferably has an average particle size of 0.5 μm or more and 5 μm or less. Such a powder can be produced by an atomizing method such as a water atomizing method or a plasma atomizing method, a chemical process method such as an oxide reduction method, a wet reduction method, or a carbonyl reaction method.

  As the binder (water-soluble resin binder), methylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, carboxymethylcellulose ammonium, ethylcellulose, polyvinyl alcohol, and the like can be used.

  The foaming agent is not particularly limited as long as it can generate gas and form bubbles in the slurry, and is a volatile organic solvent such as pentane, neopentane, hexane, isohexane, isopeptane, benzene, octane, toluene, etc. The water-insoluble hydrocarbon-based organic solvent can be used. The content of the foaming agent is preferably 2.3 to 5% by weight based on the foamable slurry.

  Surfactants include anionic surfactants such as alkylbenzene sulfonate, α-olefin sulfonate, alkyl sulfonate, alkyl ether sulfate, alkane sulfonate, polyethylene glycol derivatives, polyhydric alcohol derivatives, etc. Nonionic surfactants and amphoteric surfactants can be used.

  The plasticizer is added to impart plasticity to a molded product obtained by molding a slurry. For example, polyhydric alcohols such as ethylene glycol, polyethylene glycol, and glycerin, fats and oils such as coconut oil, rapeseed oil, and olive oil, petroleum ether, etc. Ethers such as diethyl phthalate, di-N-butyl phthalate, diethyl hexyl phthalate, dioctyl phthalate, sorbitan monooleate, sorbitan trioleate, sorbitan palmitate, sorbitan stearate, and the like can be used.

  Furthermore, an optional additive component may be added to improve the properties and moldability of the slurry. For example, a preservative can be added to improve the storage stability of the slurry, or a polymer compound can be added as a binding aid to improve the strength of the molded body.

<Uniformization process>
Next, the foamable slurry thus prepared is passed through a strainer to make it uniform. As the strainer, for example, a mesh made of SUS having an opening having a particle size of 35 μm or more and 125 μm or less can be used. By allowing the foamable slurry to pass through the mesh, coarse substances such as metal powder aggregates are removed from the foamable slurry, and the size of the bubbles formed in the foamable slurry is uniformly adjusted.

<Green sheet forming process>
A green sheet is formed from the foamed slurry thus homogenized using the molding apparatus 20 shown in FIG.
The molding apparatus 20 has a hopper 21 in which the foamable slurry is stored, a carrier sheet 22 for transferring the foamable slurry supplied from the hopper 21, a roll 23 for supporting the carrier sheet 22, and a foamable slurry on the carrier sheet 22. A doctor blade 24 to be molded to a thickness, a constant temperature / high humidity tank 25 for foaming foamable slurry, and a drying tank 26 for drying the foamed slurry are provided.

  In the green sheet forming process using the molding apparatus 20, first, the homogenized foaming slurry is put into the hopper 21, and the foaming slurry is supplied onto the carrier sheet 22 from the hopper 21. The carrier sheet 22 is supported by a roll 23 that rotates in the right direction in the figure, and its upper surface moves in the right direction in the figure. The foamable slurry is formed into a thin plate shape by the doctor blade 24 while moving together with the carrier sheet 22.

  Next, the thin plate-like foaming slurry foams while moving in the constant temperature / high humidity tank 25 under predetermined conditions (for example, temperature 30 ° C. to 40 °, humidity 75% to 95%) over 10 minutes to 20 minutes, for example. To do. Subsequently, the slurry foamed in the constant temperature / high humidity tank 25 moves in the drying tank 26 under a predetermined condition (for example, a temperature of 50 ° C. to 70 ° C.) over 10 minutes to 20 minutes, for example, and is dried. Thereby, a sponge-like green sheet is obtained.

<Sintering process>
The green sheet thus obtained is degreased and sintered to form a thin plate-like metal porous body. Specifically, for example, after removing (degreasing) the binder (water-soluble resin binder) in the green sheet under vacuum at temperatures of 550 ° C. to 650 ° C. for 25 minutes to 35 minutes, the temperature is further increased in vacuum. A metal porous body is obtained by sintering under conditions of 1200 ° C to 1300 ° C and 60 minutes to 120 minutes.
This thin plate-like metal porous body is cut by electrical discharge machining, laser machining, etc., filled with a filling material such as electrode material in the gap, and then adjusted in thickness by rolling to provide a metal with an appropriate size. The porous electrode substrate 10 can be formed.

Next, Examples 1-2 of the present invention and Comparative Examples 1-6 according to the prior art will be described.
In Examples 1 and 2, from the foamable slurry obtained by mixing the materials shown in Table 1, using the above production method including the step of homogenizing the foamable slurry, a thickness of 1.5 mm and a planar dimension of 50 mm A metal porous electrode substrate with a size of 50 mm was formed, and after filling the metal porous electrode substrate with various fillers, the metal porous electrode substrate was rolled until the thickness became 1 mm.

  In Comparative Examples 1 to 6, the materials shown in Table 2 were mixed to produce a foamed slurry, but unlike each example, a thickness of 1.5 mm and a planar dimension were obtained without going through the step of homogenizing the foamable slurry. A metal porous electrode base material of 50 mm × 50 mm was formed, and after filling various fillers into this metal porous electrode base material, it was rolled to a thickness of 1 mm. In Comparative Examples 1, 4 and 5, metal powder having an average particle size larger than the range of the present invention was used. Moreover, the content rate of the foaming agent was less than the range of the present invention in Comparative Examples 1 to 5, and greater than the range of the present invention in Comparative Example 6. In the table, what is described in the upper and lower two columns in the column of surfactant indicates that the upper and lower active agents are mixed.

About these Examples 1-2 and Comparative Examples 1-5, the structure of the obtained base material, the filling property at the time of filling each base material with a filling material, and the falling-off property of the filling material by rolling after filling, Evaluation was made as shown in Table 3.
The filling property of the packing was evaluated by the packing density. The higher the filling amount, the higher the performance of the battery. Therefore, the higher the filling density, the higher the evaluation.
The dropout property of the packing was evaluated by the change in weight before and after rolling. The smaller the packing that falls off during rolling, the higher the performance of the battery, so the smaller the weight change, the higher the rating.

The filling material filled in each base material is as follows.
<Filling paste A>
Electrode material for capacitors (100 parts by mass of activated carbon (Maxsorb (registered trademark) MSP20N, manufactured by Kansai Thermochemical Co., Ltd.)), conductive material (12.0 parts by mass of carbon black (Denka Black HS (registered trademark) -100, electrochemistry) Manufactured by Kogyo Co., Ltd.), binder (6.0 parts by mass of PVdF (polyvinylidene fluoride) suspension (40.2 wt% BM-400S aqueous suspension, manufactured by Nippon Zeon Co., Ltd.)), thickener (hydroxy) A paste A for filling is prepared by mixing and kneading 1.0 mass% aqueous solution of propylmethylcellulose (Metroses (registered trademark) 90SH-1500, manufactured by Shin-Etsu Chemical Co., Ltd.) and water (32 parts by mass). It was adjusted.
<Filling paste B>
A filling paste B was prepared by mixing and kneading a lithium ion battery active material (olivine-type LiFePO ⁴ ), 20 parts by weight of a conductive material (acetylene black), 10 parts by weight of a binder (PVdF), and a solvent (NMP).

  As shown in Table 3, in the substrates according to Examples 1 and 2, the thickness of the skeleton arranged on the outermost surface is 5 μm or more and 65 μm or less, the thickness of the skeleton arranged inside is 3 μm or more and 35 μm or less, and The thickness of the outer skeleton is 1.2 to 2.5 times the thickness of the inner skeleton, the porosity is 97% to 99%, the aperture ratio is 70% to 90%, and the average aperture diameter is 100 μm. It is 500 μm or less. The packing densities of the filling pastes A and B with respect to the base materials of Examples 1 and 2 are as high as 1.6 g / cm3 and 1.6 g / cm3, respectively, and the weight change after rolling is 0. It was found that the base materials of Examples 1 and 2 were filled with a sufficient amount of filler and were not easily dropped by rolling.

Comparative Example 1 is a metal porous electrode substrate produced by using a foamed slurry that has a larger average particle diameter of metal powder, less foaming agent, and is not homogenized compared to Example 1. For this reason, the base material of Comparative Example 1 has a larger skeleton thickness than that of Example 1.
In the base material according to Comparative Example 1, the porosity is equivalent to that in Example 1, but the skeleton thickness is large. Therefore, it is considered that pores larger than Example 1 are formed. Therefore, it is considered that the base material of Comparative Example 1 is not easily filled with the filling material because of its thick skeleton, and the filling material is likely to fall off due to the large pore as compared with each Example. That is, by using a uniform foamable slurry containing a metal powder having an appropriate average particle size, the metal porous electrode base is easily filled with a skeleton having an appropriate thickness and is difficult to fall off. It is thought that the material can be formed.

The comparative example 2 is a metal porous electrode base material manufactured using the foaming slurry which has few foaming agents compared with Example 1, and is not uniformized. For this reason, the base material of Comparative Example 2 has a slightly lower porosity than Example 1.
In the base material according to the comparative example 2, the porosity is small as compared with the example 1, so that the packing density is low, but the weight reduction after rolling does not occur. From these facts, it can be said that the base material of Comparative Example 2 cannot be filled with a large amount of filler because the volume of the voids is small. That is, it is considered that a metal porous electrode substrate filled with a sufficient amount of filler to have an appropriate porosity can be formed by using a uniform foamed slurry containing an appropriate amount of a foaming agent. It is done.

Comparative Example 3 is a metal porous electrode substrate produced by using a foamed slurry that has less foaming agent and surfactant than Example 1 and is not uniformized. For this reason, the base material of Comparative Example 3 has a smaller aperture ratio than that of Example 1.
In the base material according to Comparative Example 3, the opening ratio is smaller than that in Example 1, and thus the packing density is low, but the weight reduction after rolling does not occur. From these facts, it is considered that when the aperture ratio is small, the filling is difficult to be filled. That is, it is considered that a metal porous electrode substrate that has an appropriate opening ratio and is easily filled with a filler can be formed by using a uniform foamed slurry containing an appropriate amount of a foaming agent and a surfactant. It is done.

Comparative Examples 4 and 5 are metal porous electrode base materials produced by using a non-uniform foaming slurry having a larger average particle diameter of metal powder, less foaming agent and binder as compared with Example 2. It is. For this reason, compared with Example 2, the base material of Comparative Example 4 has a low porosity and a small average opening diameter, and the base material of Comparative Example 5 has a large average opening diameter.
In the base material according to Comparative Example 4, the porosity and the average opening diameter are small as compared with Example 2, and the weight density after rolling does not occur, but the packing density is low. From these facts, it is considered that a small pore is formed in the base material of Comparative Example 4 as compared with Example 2, and it is considered difficult to fill a large amount of filler for this reason.
In the base material according to Comparative Example 5, the average opening diameter is large and the packing density is high compared with Example 2, but the weight loss after rolling is large. From these facts, it is considered that the base material of Comparative Example 5 is easy to fall off while being filled with the filler.
Therefore, from these Comparative Examples 4 and 5, by using a uniform foamable slurry containing a metal powder having an appropriate average particle diameter and an appropriate amount of a foaming agent and a binder, an appropriate porosity and It is considered that a porous metal electrode substrate can be formed that has an average opening diameter, and that the filler is sufficiently emphasized and does not easily fall off.

Comparative Example 6 is a metal porous electrode substrate produced using a foamed slurry that has a higher foaming agent content than Example 1 and is not uniformized. In addition, the foamable slurry has a large amount of surfactant and a small amount of plasticizer due to a large content of the foaming agent. For this reason, the base material of Comparative Example 6 has a thin skeleton, a high aperture ratio, and a large average aperture diameter compared to Example 1. Furthermore, there is no difference in the thickness of the skeleton between the outermost surface and the inside.
In the base material according to Comparative Example 6, the same packing density as in Example 1 was obtained, but the weight loss after rolling was large. From this, it is considered that when the aperture ratio is high and the average opening diameter is large, the filling is easy to be filled, but the filling is easy to drop off because there is no difference in the thickness of the skeleton between the outermost surface and the inside. In other words, by using a uniform foamable slurry containing an appropriate amount of foaming agent, it is considered that a metal porous electrode substrate can be formed in which a skeleton having an appropriate thickness is formed and the filling is less likely to fall off. It is done.

  As described above, according to the present invention, since the thickness of the skeleton, the porosity, the opening ratio, and the average opening diameter are appropriately set, the filling property of the metal porous electrode base material is excellent, The drop-off property is low, so that the performance of the battery can be improved. Further, according to the method for producing a metal porous electrode base material of the present invention, by using a foamable slurry prepared using an appropriate material in a uniform manner, a metal having excellent filling property and low dropout property. A porous electrode substrate can be produced.

  In addition, this invention is not limited to the thing of the structure of the said embodiment, In a detailed structure, a various change can be added in the range which does not deviate from the meaning of this invention.

It is a top view which shows the metal porous electrode base material of this invention. It is the schematic which shows the shaping | molding apparatus used for the manufacturing method of the metal porous electrode base material of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Metal porous electrode base material 10A Outermost surface 11,11A, 11B Frame | skeleton 12 Space | gap 12a Opening part 20 Molding apparatus 21 Hopper 22 Carrier sheet 23 Roller 24 Doctor blade 25 Constant temperature, high humidity tank 26 Drying tank

Claims (6)

A plate-like metal porous electrode substrate in which a plurality of polyhedrons whose sides are constituted by a skeleton of a metal sintered body is formed in a continuous state with each other,
The skeleton has a thickness of 5 μm or more and 65 μm or less in the thickness of the skeleton arranged on at least one outermost surface of the front and back surfaces, and a thickness of 3 μm or more and 35 μm or less in the skeleton arranged inside, The thickness of the inside is 1.2 to 2.5 times the thickness of the skeleton in the interior,
The void formed between the skeletons has a porosity of 97% or more and 99% or less.   The metal porous electrode substrate according to claim 1, wherein an opening ratio at the outermost surface is 70% or more and 90% or less.   3. The metal porous electrode substrate according to claim 1, wherein an average opening diameter on the outermost surface is 100 μm or more and 500 μm or less. A method for producing a plate-shaped metal porous electrode substrate in which a plurality of polyhedrons whose sides are constituted by a skeleton of a metal sintered body is formed in a continuous state,
A foamable slurry creating step for creating a foamable slurry containing a metal powder and a foaming agent;
A homogenization step of passing the foamable slurry through a strainer;
Forming a green sheet by forming the foamable slurry into a thin plate and foaming the green sheet; and
A method for producing a metal porous electrode base material, comprising a sintering step of sintering the green sheet. The metal powder has an average particle size of 0.5 μm to 5 μm and a maximum particle size of 50 μm,
The method for producing a metal porous electrode substrate according to claim 4, wherein the strainer has an opening corresponding to a particle size of 35 μm or more and 125 μm or less.   6. The method for producing a metal porous electrode substrate according to claim 4, wherein the content of the foaming agent in the foamable slurry is 2.3 wt% or more and 5 wt% or less.

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