JP3243862B2 - Oxide-based conductive ceramic flake, method for producing the same, and lead storage battery using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide-based conductive ceramic flake used as an active material additive for a battery, an additive for a housing material of an antistatic and electromagnetic wave shielding type and a filler for a conductive paste, and a method for producing the same. It is about application.

[0002]

2. Description of the Related Art Conventionally, conductive ceramics have been used as transparent electrodes in liquid crystal displays, transparent touch panels and the like as ITO.
Thin films such as (indium oxide doped with tin) films are widely used. The manufacturing method is a physical vapor deposition method (PVD method) such as a sputtering method or an electron beam (EB) method.
And the film thickness is 0. Only a uniform film of about several μm was found. Also,
As flake-like ceramics, mica, talc, and flaky graphite have been known for a long time as natural products.

[0003] On the other hand, for housing materials and the like that require conductivity, resin materials in which metal, flaky graphite or carbon fibers are mixed as fillers, or materials whose surfaces are metal-plated, have been mainly used. However, in recent years, glass flakes or glass fibers coated with ITO have been produced as conductive fillers having excellent mechanical strength, corrosion resistance and heat resistance.

[0004] As an application field of these conductive fillers, for example, in the field of batteries, by adding a conductive material to an active material, the current collecting effect is improved and the passivation is prevented, thereby increasing the utilization rate of the active material and increasing the energy consumption. In order to increase the density and extend the service life, in the case of an electromagnetic shielding type housing material, metal fibers are mixed in a resin, or the surface is metal-plated. As the conductive paste, a mixture of silver powder, carbon, or the like using an epoxy resin as a binder has been mainly used (Hiroshi Kondo; Functional Materials August 1991, v.
ol. 11, No. 8, p19, JP-A-61-195
178).

[0005]

The only reason that fillers made of conductive ceramics have not been used as such conductive fillers, not of the type in which conductive ceramics are coated on glass, has been used. This is because fibrous or flake conductive ceramics could not be easily obtained at low cost. Some of the limited ones, such as zinc oxide and copper oxide, are obtained from whiskers,
It has low conductivity and cannot be used for the above purpose. Other than the oxide type, there are carbon fibers and the above-mentioned flaky graphite, etc., but their use is limited because they are black, and when mixed with resin due to poor surface wettability, the strength and conductivity are improved as calculated values. Had disadvantages which were not.

Considering the application field of the conductive filler, it is said that in the field of batteries, it is effective to add a conductive material as an active material additive for batteries to improve battery characteristics such as high energy density and long life. In addition, since the electrolytic solution is a strong acid or strong alkali, there is a disadvantage that the metal filler corrodes. Therefore, in the case of a conventional lead storage battery, a conductive material such as a material obtained by adding a filler obtained by depositing tin oxide on glass flakes to an active material or a carbon fiber to a negative electrode active material has been added.

However, when a filler obtained by depositing tin oxide on glass flakes is added to the active material, an increase in the weight of the glass decreases the utilization rate of the active material and the energy density per weight (Wh / kg). (JP-A-60-1758).

On the other hand, those having a carbon skeleton such as carbon fiber are effective for the negative electrode, but have the drawback of being anodized and disappearing when added to the positive electrode, so that a significant improvement in battery characteristics cannot be expected (Hojo). Eiji et al .; Yuasa Hourly Report No.72 APRIL P2
3-28 (1992), JP-A-48-101523).

On the other hand, in the case of a housing material for a computer or the like, a conductive metal filler is added to a resin or a metal plating is applied to the inside of the resin for antistatic and electromagnetic wave shielding. Restrictions,
There is a disadvantage that the cost is high.

As for the conductive paste, the mainstream is one in which particles such as silver or gold or filler such as graphite are dispersed in an epoxy resin. However, in the case of a metal filler, migration or corrosion is liable to occur. Has low conductivity, poor wettability with a binder, and has a weakened adhesive strength (Hiroshi Kondo; Functional Materials, August 1991, Vol. 11, No. 8, p19, JP-A-61-1).
95178).

The present invention has been made to solve the above problems, and
It is an object of the present invention to provide an oxide-based conductive ceramic flake having low specific resistance, excellent chemical resistance, not causing corrosion or migration, high mechanical strength, and excellent wettability, and a method for producing the same.

[0012]

In order to achieve the above object, the present invention provides a water-soluble resin layer on a hard substrate, and forms an oxide-based conductive ceramic layer thereon by physical vapor deposition. This substrate is immersed in water to separate the oxide-based conductive ceramic flakes from the hard substrate, filtered, and then fired at a temperature of 500 ° C. or more for one hour or more in oxygen or air. In addition, after providing a thermally decomposable resin layer on a hard substrate and forming an oxide-based conductive ceramics layer thereon by physical vapor deposition, the substrate is thermally decomposed in air or oxygen. Heating at a temperature not lower than the temperature and not higher than the heat deformation temperature of the hard substrate for not less than 1 hour to remove the thermally decomposable resin layer.

A battery, particularly a lead-acid battery, in which an oxide-based conductive ceramic flake is mixed with an active material in an amount of 1 to 8 wt% as an additive.

[0014] The present invention is a housing material in which oxide-based conductive ceramic flakes are mixed in an amount of 10 wt% or more. In particular, the material is preferably transparent and has a specific resistance of 9 × 10 ⁻⁴ Ω · cm or less.

[0015] Further, an oxide-based conductive ceramic flake having a specific resistance of 9 × 10 ⁻⁴ Ω · cm or less is added.

[0016]

According to the present invention, as described above, glass like
A resin layer is provided on a hard substrate, and a sputtering method
SnO by PVD method_Two Oxide conductive ceramics such as
Is formed once on the entire surface, and then the resin layer is removed.
After that, firing at high temperature in oxygen (air)
This is for producing a system conductive ceramic flake.
Conventionally, thin film type by PVD method such as sputtering or EB evaporation method
If the adhesion to the substrate is poor,
Peeling occurred. In this case, the part should be
It peels off partly and falls, and its size is also different
Was. In the method of the present invention, the film forming stress is moderated by the resin layer during the vapor deposition.
The adhesive strength of the thin film is strong, so it can be immersed in water,
By burning the resin layer, the film thickness is 0.1 μm to several μm,
The average radius of the peak is about 50 μm or more
Diameter is different) and the specific resistance is 10 ^-2Ω · cm or less
Flakes of oxide-based conductive ceramics only
Can be completely recovered. Also, it is deposited by PVD method
If it is used alone, the film will be insufficient in oxygen or insufficient in crystallization.
Since it does not become an oxide film with low resistance, oxygen
Alternatively, firing in air is important.

The film thickness is optimally 0.1 μm to several μm in view of the mechanical strength and productivity of the flake, and the average radius of the flake is 50 μm in view of the reinforcing effect and conductivity.
m or more is required. In the manufacturing process, the substrate is finally recovered in an initial state, so that the substrate can be repeatedly used by applying a resin layer again. In addition, the film forming process is performed by a general PVD method and evaporation conditions (for example, substrate temperature). Can be formed at room temperature), which has the advantage that the film-forming time can be shortened (it takes time if substrate heating is required), and the oxide-based conductive ceramic flake can be formed at low cost.

As an application example, in the field of batteries, a conductive material which is resistant to strong acids and strong alkalis as an additive to an active material, has a specific resistance of 10 ^-2 to 10 ^-3 Ω · cm, and has a reinforcing effect. Even if lead sulphate generated at the time of discharge by adding 1 to 8 wt% or less of conductive ceramic flakes covers lead (negative electrode) or lead dioxide (positive electrode) and passivates the active material, it remains conductive during charging. Since current flows on the ceramic flakes, lead sulfate can be almost completely regenerated into lead or lead dioxide, and the cycle life can be greatly extended. Also,
Since the active material is entangled with the conductive ceramic flakes, it is easy to take out a current at the time of discharge, and a high energy density is possible. Compared to conventional glass flakes formed of conductive ceramics, the additive has excellent weight efficiency and a large effect of increasing energy density. As a result of intensive studies on the specific resistance of conductive ceramic flakes, 1
It has been found that the utilization factor can be sufficiently improved at 0 ^-2 to 10 ^-3 Ω · cm (10 ^-4 Ω · cm for lead dioxide). Further, those doped with antimony (Sb) or the like to lower the specific resistance are effective for high-rate discharge characteristics and high capacity, but Sb precipitates on the negative electrode side during the cycle life, and the hydrogen overvoltage is reduced. It was disadvantageous to offer it.

Antistatic and electromagnetic waves can be obtained by mixing 10 wt% or more of conductive ceramic flakes having a specific resistance of 10 ⁻⁴ Ω · cm or less as a filler in antistatic or electromagnetic shielding type housing materials such as computer housings. Shielding is possible, and the advantage of using transparent oxide ceramics is that the color (including transparency) of the housing material can be freely selected, and the oxide conductive ceramic flakes have high elasticity in terms of mechanical strength. Significant improvement is possible.

In the conductive paste, a conductive ceramic flake such as ITO having a specific resistance of 10 ⁻⁴ Ω · cm or less is mixed with a binder as much as possible (about 30 vol%) to form a silver paste or a gold paste. Thus, a stable conductive paste that does not cause migration and a paste having lower resistance than a stable carbon-based paste can be obtained.

[0021]

An embodiment of the present invention will be described below with reference to the drawings.

(Example 1) FIG. 1 is a manufacturing process diagram of SnO ₂ flakes in a first example. In the figure, 11 is a glass substrate, 12 is polyvinyl alcohol, 13 is water, 14
Is SnO ₂ flake. Hereinafter, each step will be described. Polyvinyl alcohol PVA1 on glass substrate 11
2 (Denka Poval B-05) was applied and spin-coated to form a PVA resin layer (0.4 μm thick) on the glass.

Next, the glass substrate on which the PVA resin layer was formed was mounted on an EB apparatus, and SnO ₂ was deposited. The deposition conditions were as follows: ultimate vacuum degree was 3 × 10 ⁻⁴ Pa, substrate temperature was normal temperature, and deposition rate was 400 ° / min for 30 minutes.

Next, the substrate was immersed in warm water of about 50 ° C. The PVA resin immediately dissolved in the warm water and the flake-shaped conductive ceramic was completely separated from the entire surface of the glass substrate. Thereafter, the liquid containing SnO ₂ flakes was subjected to suction filtration to collect SnO ₂ flakes.

Next, the recovered flakes were fired in a muffle furnace at 550 ° C. for 90 minutes in an air atmosphere to obtain SnO ₂ flakes 14 having low specific resistance. Those that were not fired lacked oxygen in the molecule and dissolved in sulfuric acid in a state close to SnO, and had a high specific resistance. This SnO ₂ flake had a plate shape with a thickness of 1.2 μm and an average radius of 800 μm and a specific resistance of 4 × 10 ⁻² Ω · cm.

Next, a lead-acid battery was manufactured using the SnO ₂ flakes. The above SnO ₂ per 100 parts by weight of lead powder
After adding 2 parts by weight of flakes and kneading while dripping water and dilute sulfuric acid according to a conventional method, filling this into a grid made of a Pb-Ca-Sn alloy, passing through aging and drying steps, a positive electrode unformed plate Was prepared. A small amount of lignin and barium sulfate was added to lead powder for the negative electrode, and water and dilute sulfuric acid were added dropwise and kneaded to form Pb-
After filling in a Ca alloy lattice, an aged and dried standard negative electrode non-formed plate was obtained.

Next, five positive electrode plates and six negative electrode plates manufactured in this manner were combined with a mat-shaped separator made of glass fiber interposed therebetween, and impregnated with dilute sulfuric acid as an electrolytic solution. The formation of a single cell of a sealed rate lead-acid storage battery with positive electrode rate control was performed by chemical formation.

For comparison, single-cell sealed lead-acid batteries of the same volume and weight using five and six conventional positive and negative plates, respectively, were also manufactured.

These batteries were charged at 0.1 C, ３
A cycle test was performed with constant current charge / discharge of C discharge, and the capacity and charge / discharge cycle life of each battery were measured. The discharge end voltage is 1.75 V, and the amount of charged electricity is 115% of the amount of discharged electricity.
And the charge / discharge cycle life is 80% of the initial capacity.
% Of the cycle.

As a result, the battery capacity of this embodiment was 4
The energy density is 0 Ah, 32 Ah for the conventional battery, and 45 Wh / kg for the present embodiment, and 36 Wh / kg for the conventional battery.
/ Kg. The cycle life of this embodiment was about 950 cycles, and that of the conventional battery was about 260 cycles. Thus, it was confirmed that by adding SnO ₂ flakes to the positive electrode active material, the energy density of the battery was increased by about 30% as compared with the conventional one, and the cycle life of the battery was significantly improved. FIG. 2 shows the amount of SnO ₂ flake mixed and the battery characteristics. It was found that the energy density and the cycle life were superior to those of the conventional positive electrode battery in the range of 1 to 8 wt%. FIG. 3 shows the relationship between the average radius of the SnO ₂ flake and the energy density. The average radius of the flake is required to be 50 μm or more. This is considered to be determined by the balance between the contact probability between flakes and the amount of active material around the flakes. The average radius of the flakes was adjusted by the flake thickness and pulverization.
The maximum average radius was effective up to about 2 mm. On the other hand, the thickness of the film is 0.1 mm in view of the mechanical strength of the flake.
1 μm or more is required, and several μm or less is desirable in terms of productivity and cost. The requirements for these flake shapes were similar in other applications.

The specific resistance of this SnO ₂ flake is PbO ₂
Although it was lower by one order of magnitude or more, it is considered to be sufficient to prevent the passivation due to the current collecting ability and PbSO ₄ . A similar effect was observed in addition to the negative electrode active material. It is also considered effective in addition to other battery systems such as nickel-cadmium batteries, nickel-metal hydride batteries, and lithium batteries.

As the water-soluble resin, pigments such as nitrocellulose, starch, glycogen, inulin and phthalocyanine were effective in addition to PVA.

The flake obtained by doping SnO ₂ with Sb at about 0.5 wt% has a low specific resistance of about 10 ⁻⁴ Ω · cm, and has a high energy density, but its cycle life is slightly shortened.

(Embodiment 2) A second embodiment of the present invention will be described below with reference to the drawings. FIG. 4 is a manufacturing process diagram of the ITO flake in the second embodiment. In the figure, 21 is a quartz substrate, 22 is polystyrene, 23 is acetone, and 24 is ITO flake.

Hereinafter, each step will be described. Quartz substrate 2
1 was coated with a 5 wt% acetone 23 solution of polystyrene PS22 and spin-coated to form a PS resin layer (film thickness 0.2 μm) on a quartz substrate.

Next, the substrate on which the PS layer was formed was mounted on a sputtering apparatus, and sputtering was performed on the PS layer using a target in which tin was mixed with indium oxide at 8%.
Sputtering conditions were as follows: ultimate vacuum was 2 × 10 ⁻⁴ Pa, argon gas pressure was 0.5 Pa, the substrate was water-cooled, and sputtering was performed at a sputtering rate of 70 ° / min for 20 minutes.

Next, the substrate was passed through a tunnel furnace (600 ° C., 60 minutes) in an oxygen atmosphere to eliminate the PS layer and simultaneously crystallize ITO.

The ITO flakes 24 thus formed were plate-like with a thickness of 0.14 μm and an average radius of about 200 μm, and had a specific resistance of 1.2 × 10 ⁻⁴ Ω · cm.

Next, a housing for a personal computer (PC) was manufactured using the ITO flake. First, 15 parts by weight of the ITO flake was added to 85 parts by weight of the polycarbonate pellets, mixed well, and then charged into a twin-screw kneading extruder from a hopper, and once a master pellet was prepared using a pelletizer. Next, a PC housing was produced using the master pellet by an injection molding machine.

The thus-produced PC housing was transparent, had high conductivity and high mechanical strength, and had an antistatic effect and an electromagnetic wave shielding effect that could be put to practical use.
It has been found that these effects can be provided by mixing conductive ceramic flakes having a specific resistance of 9 × 10 ⁻⁴ Ω · cm or less by 10 wt% or more. In a conventional PC housing, after molding a general resin (for example, ABS), the inside is plated or a metal fiber is mixed in the resin, so that a transparent material cannot be obtained and the cost is low. It was expensive. The use of the flakes of the present invention increased the width of the design, provided a much higher shielding effect in the high frequency range than the case where the same weight of metal fiber was mixed, and provided performance almost equivalent to that of single-sided plating. This is probably because the conductive ceramic flakes are oriented parallel to the surface (wall) of the housing. This has enabled a significant cost reduction.

FIG. 5 shows the relationship between the amount of ITO flake mixed and the shielding effect. It has been found that the effect equivalent to that of metal fibers can be obtained by mixing ITO flake in an amount of 10 wt% or more. However, when the mixing amount was 40 wt% or more, the melt viscosity was too high, and injection molding was not possible.

In the production process of the conductive ceramic flakes, as the thermally decomposable resin, a water-soluble resin such as polyvinyl alcohol or a resin soluble in an organic solvent such as α-methylstyrene was effective in addition to PS.

(Embodiment 3) A third embodiment will be described below with reference to the drawings. As in the first embodiment, a 1 μm PVA layer is formed on an alumina substrate, and EB is
Molybdenum oxide was deposited to a thickness of about 0.2 μm by a vapor deposition method (the substrate was at room temperature). Next, the substrate is heated at 800 ° C.
It was baked in a muffle furnace for 0 minutes. Through these steps, molybdenum oxide flakes having a thickness of 0.2 μm and an average radius of 50 μm were obtained. This was a composition containing Mo ₂ O ₅ as a main component, and the specific resistance was as low as about 8 × 10 ⁻⁵ Ω · cm.

Next, the obtained molybdenum oxide flakes were mixed in an epoxy resin at 30 vol% to prepare a conductive paste. The mixture was passed three times using a three-roll mill.

The specific resistance of the conductive paste after curing is 8 × 1.
The value was 0 ^-4 Ω · cm, which is one digit lower than that of the conventional carbon paste. Since the carbon-based (including graphite) conductive paste is a charge-transfer-type conductor in which electrons move from the π-electron conjugate onto the binder, the transfer of electrons does not proceed very well. It is considered that the paste has a low specific resistance because it is the same composite conductor as the metal filler mixed type. Furthermore, the conductive paste of this embodiment has an advantage that migration is less likely to occur as compared with a metal filler-based conductive paste such as a silver paste.

It is desirable that the oxide-based conductive ceramic flakes be added as much as possible with respect to the binder. However, considering the adhesion to the base, about 30 vol% with respect to the binder is considered appropriate. In addition, flakes to be added are required to have a low resistivity of 10 ⁻⁴ Ω · cm or less, such as ITO, in addition to molybdenum oxide.

As can be seen from the above three examples, at least 10%
^-2 Ω · cm or less specific resistance is required, and the film thickness is 0.1.
1 μm to several μm, average flake radius is 50 μm
The above is desired.

As for the firing conditions of the ceramics after the deposition by the PVD method, heating at a temperature of 500 ° C. or more and a heat deformation temperature of the hard substrate for at least 1 hour or more in oxygen or air in terms of specific resistance is required. did. The hard substrate of the present invention refers to a ceramic substrate such as glass or quartz or a metal substrate such as aluminum or stainless steel. In the case of the first embodiment, a resin-based material such as a polyimide film has no problem. 0.1 μm to several μm as the thickness of the resin layer
m was suitable.

When the conductive ceramic is produced not by the PVD method but by the chemical vapor deposition (CVD) method or the dipping method, the conductive ceramic does not partially peel off from the underlying hard substrate at the time of firing, and the specific resistance is high. Tended to be.

[0050]

As is apparent from the above description, according to the present invention, a conductive ceramic is formed on a water-soluble resin,
Thereafter, the film is immersed in water, filtered, fired, or formed on a thermally decomposable resin, and then heated and fired to have a thickness of 0.1 μm to 5 μm.
μm, average radius of 50 μm or more and specific resistance of 10 ⁻² Ω · c
m or less can be obtained at low cost.

When this conductive ceramic flake is used, the energy density and cycle life can be improved by adding 1 to 8 wt% to the active material in the field of batteries.

The addition to the housing material makes it possible to prevent static electricity and shield electromagnetic waves at a low cost, and a transparent housing is obtained, thereby greatly increasing the degree of freedom in design.

In addition, when added to the conductive paste, a material having a lower specific resistance than carbon and having no corrosion and excellent corrosion resistance like a metal can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a manufacturing process of SnO ₂ flakes in a first embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the amount of mixed SnO ₂ flakes and the energy density in the first embodiment of the present invention.

FIG. 3 is a diagram showing the relationship between the average radius of SnO ₂ flakes and the energy density in the first embodiment of the present invention.

FIG. 4 is a diagram showing a process of manufacturing ITO flakes according to a second embodiment of the present invention.

FIG. 5 is a diagram showing the relationship between the amount of mixed ITO flakes and the electric field attenuation rate in the second embodiment of the present invention.

[Explanation of symbols]

11 Glass Substrate 12 Polyvinyl Alcohol 13 Water 14 SnO ₂ Flake 21 Quartz Substrate 22 Polystyrene 23 Acetone 24 ITO Flake

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-61-189450 (JP, A) JP-A-2-155112 (JP, A) JP-A-4-28113 (JP, A) JP-A-51-189 47233 (JP, A) JP-A-1-100023 (JP, A) JP-A-6-171908 (JP, A) JP-A-61-295208 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01B 13/00 501 C01G 19/02 H01B 1/08 H01B 5/00 H01M 4/57

Claims (6)

(57) [Claims] A hard substrate is provided with a water-soluble resin layer, an oxide conductive ceramic layer is formed thereon by physical vapor deposition, and then the substrate is immersed in water to form an oxide conductive ceramic flake. A method for producing an oxide-based conductive ceramic flake, comprising separating from the hard substrate, filtering, and then firing at a temperature of 500 ° C. or more in oxygen or air for 1 hour or more. 2. A heat-decomposable resin layer is provided on a hard substrate, and an oxide-based conductive ceramic layer is formed thereon by physical vapor deposition. A method for producing an oxide-based conductive ceramic flake, comprising heating at a temperature not lower than the thermal decomposition temperature of the hard substrate and not higher than the thermal deformation temperature of the hard substrate for at least one hour to remove the heat-decomposable resin layer. 3. The method for producing an oxide-based conductive ceramic flake according to claim 2 , wherein the thermally decomposable resin is a water-soluble resin or a resin soluble in an organic solvent. 4. The method according to claim 3 , wherein the resin soluble in the organic solvent is α-methylstyrene. 5. The method according to claim 1, 2, 3, or 4.
The film thickness is 0.1 μm to 5 μm,
The average radius of the metal is 50 μm or more and the specific resistance is 9 × 10 ^-2
Oxide-based conductive ceramic having a resistivity of Ωcm or less
Mix flakes. 6. The oxide-based conductive ceramic according to claim 5.
Lead storage characterized by containing flakes in the electrode
pond.