JP3730645B2 - High voltage side electrode for electrostatic precipitator - Google Patents

Description

  The present invention relates to an electrostatic precipitator, and more particularly, to a high-voltage side electrode of a collector that collects charged fine particles floating in an air current.

  The electrostatic precipitator collects and removes charged particles by electrostatic force while the charged particles pass through the electric field to the fine particles in the airflow by corona discharge. Various types are used from large-sized devices to small-sized devices for home use.

  A conventional collector uses an aluminum parallel plate type electrode, and generally includes a high voltage side electrode connected to the positive electrode (high voltage) side of a high voltage power source and a dust collecting electrode connected to the negative electrode (ground) side thereof. The structure is arranged in parallel alternately, and both the high-voltage side electrode and the dust collection electrode are made of aluminum flat plates.

  However, in the collector of the electrostatic precipitator using the conductive metal as an electrode in this way, if the conductive particles are mixed in the charged particles guided to the collector, the electrodes on the high voltage side and the dust collection side Spark discharge between the electrodes was unavoidable, for example, spark discharge occurred between them, or the collected dust accumulated on the electrodes, resulting in a decrease in resistance and spark discharge. In addition, the insulating part holding these electrodes, the spacers, etc. become dirty, or the resistance decreases due to moisture, so that the collector leakage current flows from the part in contact with the electrodes, which reduces the voltage. There was the fault that it raises and the collection performance falls. Further, there is a problem that the pressure loss of the air flowing between the electrodes is large due to a spacer between the electrodes.

  Accordingly, an object of the present invention is to provide an electrostatic precipitator capable of preventing the occurrence of spark discharge between electrodes and stably suppressing a decrease in collection performance over time.

The present invention relates to an electrostatic precipitator including an ionizer that applies electric charges to fine particles in an air stream, and a collector that includes a dust collecting electrode that collects charged particles by electrostatic force and a high voltage electrode. The high-voltage side electrode is an electrostatic precipitator made of a hygroscopic resin of a semi-insulating resin whose volume resistivity value is on the order of 10 ¹⁰ to 10 ¹³ Ωcm in the temperature and humidity of the use environment. .

  Further, the hygroscopic resin used for the high-voltage side electrode is a resin whose volume resistivity value satisfies the following formula 2.

(Equation 1)
Δlog R / Δlog V ≧ −1 Equation 2

However, in Formula 2, R is a volume specific resistance value and V is an applied voltage.

  Furthermore, the hygroscopic resin used for the high voltage side electrode of the electrostatic precipitator of the present invention is a resin obtained by blending a water absorbent resin with an ABS resin as a base material or a resin with a phenol resin base material. To do.

  Further, the present invention has a structure in which a high voltage is supplied to a portion that holds the high-voltage side electrode in the collector portion, and a collector portion having a high-voltage side electrode to which a voltage is applied by the holding portion is provided. The high-voltage side electrode of the electrostatic precipitator of the present invention is an integrally formed high-voltage ladder type electrode.

In order to prevent spark discharge between the electrodes and to obtain high collection performance, while applying a high voltage to the electrodes, the electric field is prevented from being localized on the electrodes and an excessive current flows through the electrodes. It is thought that it must be prevented. Therefore, by making the electrode semi-insulating, the instantaneous charge movement on the electrode is limited, and the occurrence of spark discharge can be suppressed. When the volume resistivity of the electrode and the presence or absence of sparks were examined, when the volume resistivity of the electrode was less than 10 ⁸ Ωcm, there was a tendency for spark discharge to occur between the high voltage side and the dust collecting side electrode. In addition, when the volume resistivity exceeds 10 ¹³ Ωcm, there is a tendency for dust collection efficiency to decrease. Accordingly, spark discharge does not occur when an electrode having a volume resistivity in the order of 10 ⁸ to 10 ¹³ Ωcm, particularly in the order of 10 ¹⁰ to 10 ¹³ Ωcm, and has excellent dust collection performance. Is obtained. Furthermore, in consideration of the man-hours at the time of electrode assembly processing and the reliability of the electrodes, it is preferable to form the electrodes by integrally molding using the above-described semi-insulating resin having a volume resistivity.

In order to prepare such a resin for a semi-insulating electrode, (1) carbon black, (2) carbon fiber, (3) conductive or semiconductive whisker, (4) stainless steel as a base resin It is thought that it can be obtained by blending an appropriate amount of a conductive material such as fiber. However, when actually conducted, a resin having a relatively low resistance value of 10 ⁶ Ωcm or less can be easily obtained, but has a target resistance value in the order of 10 ¹⁰ to 10 ¹³ Ωcm. Preparation of the resin was extremely difficult. This is probably due to the following reasons. That is, (1) In order to prepare a resin having a high resistance value, it is not always possible to add a large amount of conductive material to the resin as usual, and the resistance value of the resin is controlled with a small amount of conductive material. Must. However, when the amount of the conductive material added to the resin is small, the resistance value changes greatly with respect to the added amount, and even if the amount of the conductive material changes slightly, the resistance value of the resin changes greatly. It becomes. Furthermore, since the resistance value changes greatly due to slight differences in the dispersion state of the conductive material in the resin, a stable resistance value cannot be obtained. Further, (2) when the electrode is molded, a resin layer containing no conductive material is formed on the electrode surface, and this thickness largely changes depending on the molding conditions, causing the resistance value to change. .

  Furthermore, it is possible to keep the resistance value within a certain range with a resin in which a certain amount of conductive material is blended and the resin layer on the surface of the resin generated by molding is scraped to expose the portion containing the conductive material. However, the resistance value of the resin shows voltage dependency that varies depending on the voltage applied to the resin. That is, when the potential gradient applied to the resin is small, a high resistance value is exhibited, and when the potential gradient is large, a low resistance value is exhibited. When a voltage higher than a certain voltage is applied, a short circuit occurs suddenly. Therefore, when an electrode having a resistance value within the above range is made of such a resin, a spark discharge is generated when the high voltage side and the ground side electrode are bridged by the conductive material. Further, it has been found that when a short circuit occurs at a voltage higher than a certain voltage, the resin changes in quality and does not return to the original resistance value even if the voltage is removed.

Therefore, in order to obtain a high-resistance resin, it is not achieved by adding a very small amount of conductive material having a conductivity different by 10 orders of magnitude or more to the originally insulating resin, but by the moisture adsorbed on the resin. Focusing on the fact that the resistance value changes, it was found that the resistance value of the resin can be in the order of 10 ¹⁰ to 10 ¹³ Ωcm even for a high voltage by controlling the hygroscopicity of the resin. Therefore, it is possible to use an electrode using a hygroscopic resin as the high-voltage side electrode of the electrostatic precipitator, and the present invention has been made.

  According to the present invention, it is possible to provide an electrostatic precipitator that does not generate a spark discharge between collector electrodes, has very little collector leakage current, and has stable and excellent collection performance over time.

  The present invention will be described in detail below.

As a hygroscopic resin that can be used in the present invention have a hygroscopicity, 10 ⁸ to 10 ¹³ [Omega] cm for the high voltage at the temperature and humidity of the use environment, preferably in the range of the order of 10 ¹⁰ to 10 ¹³ [Omega] cm A resin having a certain volume resistivity can be used. Such a hygroscopic resin has hygroscopicity in the resin itself and can have a volume specific resistance value as described above.For example, a water absorbent resin is added to a resin base material such as a thermoplastic resin, A resin imparted with hygroscopicity by blending can be used. Such a resin exhibits semi-insulating properties due to moisture absorbed by the water-absorbing resin blended in the resin. By adjusting the blending amount of the water-absorbing resin, the volume specific resistance value of the resin is 10 It is a preferred resin because it can be freely prepared to be in the order of ⁸ to 10 ¹³ Ωcm. In general, the blending amount varies depending on the type of resin, but is 5 to 50% by weight. Examples of the resin base material include thermoplastic resins such as ABS resin, polyester resin, and acrylic resin. In particular, when ABS resin is used as the base material, the moldability, flame retardancy, heat resistance, and impact resistance are excellent. Can be obtained, and the manufacturing cost is low. In addition, examples of the resin base material in which the resin itself has hygroscopicity include a phenol resin, a melamine resin, and a urea resin. Further, as an example of such a thermosetting resin, in particular, when a phenol resin is used as a base material, a desired resistance value is easily obtained and a preferable result is obtained. On the other hand, the water-absorbing resin to be mixed includes acrylate-based, poval-based, polyamide-based, etc., and is selected in consideration of water absorption ability, durability of resistance value, compatibility with base resin, and the like. As such a hygroscopic resin, for example, commercially available products such as Maxroy (trade name, manufactured by JSR) and Sumilite (trade name, manufactured by Sumitomo Bakelite) can be used.

In the case of the hygroscopic resin thus prepared, for example, in the case of a resin to which ABS is used as a resin base material and a water absorbent resin is added, a sufficiently dried resin plate (thickness 2 mm) is obtained at a temperature of 70 ° C. and humidity. The moisture absorption after standing in a 65% constant temperature and humidity chamber for 48 hours is 0.7 to 1.5% by weight with respect to the dry resin. At this time, it is returned to the normal atmosphere and left for a certain time (48 hours or more). The volume resistivity value of the resin after the treatment was on the order of 10 ¹⁰ to 10 ¹³ Ωcm.

Similarly, in the case of phenol resin, the volume resistivity value was on the order of 10 ¹² to 10 ¹³ Ωcm.

  Next, the properties required of the electrode from the relationship between the resistance value and the applied voltage for the hygroscopic resin will be described with reference to FIG.

  FIG. 1 is a graph showing changes in the volume resistivity of the resin when the voltage applied to the resin electrode is changed. From this graph, a common logarithm is taken for the applied voltage V and the volume resistivity R, and the slope K defined by Equation 3 is obtained. The obtained slope K is shown in Table 1.

(Equation 2)
K = ΔlogR / ΔlogV Equation 3

The fact that the slope K is smaller than −1 means that when the applied voltage is increased, the resistance value is greatly reduced, the charge transfer is facilitated, and spark discharge is likely to occur. In fact, in the resin blended with the conductive material shown in Experimental Examples 3 and 4, the slope K has a large voltage dependency with a value of −2 to −3, and spark discharge occurs at a voltage of 7 to 8 kV. Therefore, any resin can be used as the electrode of the present invention as long as the volume specific resistance value of the resin does not greatly decrease due to an increase in applied voltage. For this purpose, the value of the slope K needs to be a value of −1 or more. That is, when the slope K is a value of −1 to 0, the voltage dependency of the volume resistivity is small, and the volume resistivity does not decrease until a spark discharge occurs due to an increase in applied voltage and current flows. In the case of 0 or more, if the applied voltage is increased, the volume specific resistance value will increase conversely, and a higher voltage can be applied between the electrodes, and the collection efficiency can be improved.

Therefore, if the value of the slope K of the resin is -1 or more, an electrode in which no spark discharge occurs between the electrodes can be obtained, and a stable collection performance can be ensured. Good results can be obtained by using a resin having a slope K of 6 or more.

  Using these resins, the electrode can be integrally formed by casting, compression molding, injection molding or the like in the case of a thermosetting resin, or by injection molding or the like in the case of a thermoplastic resin. The shape of the electrode may be various shapes such as a flat plate shape and a ladder type. Particularly, when a ladder type electrode is used, preferable results are obtained in terms of dust collection performance and assembly man-hours.

  An electrode made of the hygroscopic resin of the present invention is used as a high-pressure electrode, and a metal such as highly conductive aluminum or a conductive resin is used as the dust collecting electrode. The reason for this is that if the electric resistance of the dust collection side electrode is high, the charge from the collected charged particles accumulates on the dust collection side electrode. This is because the trapping efficiency at the dust collecting side electrode tends to decrease as a result of acting to cancel the electric field.

  When using flat electrodes, for example, the resin electrode on the high-voltage side and the dust-collecting-side aluminum electrode on the ground side are alternately arranged in parallel, and each electrode is fixed with an insulating spacer, etc. Arrange to maintain. Moreover, when using a ladder-type electrode, for example, as shown in FIG. 2, a dust collecting side electrode and a high voltage side ladder electrode are combined.

FIG. 2 is an exploded perspective view showing the configuration of the collector portion when ladder type electrodes are used. In the figure, reference numeral 1 is a high-pressure side ladder, and reference numeral 2 is a dust collecting electrode plate. A plurality of high voltage side electrodes 3 _{1 to} 3 _n are formed on the high voltage side ladder 1, and a plurality of dust collection side electrodes 4 ₁ to 4 _n−1 are also formed on the dust collection electrode plate 2. The high pressure side ladder 1 and the dust collecting electrode plate 2 are combined, and the dust collecting side electrodes 4 ₁ to 4 _n-1 are inserted between the high pressure side electrodes 3 _{1 to} 3 _n to constitute a collector part.

Further, when the semi-insulating electrode made of the hygroscopic resin of the present invention is used, in order to prevent the voltage drop of the parallel plate type high voltage side electrode and the ladder type high voltage side electrodes 3 _{1 to} 3 _n , Of course, it should not be in contact with the ground-side electrode, but it must be avoided that even an ungrounded insulator is in contact with the high-voltage side electrode. In other words, these insulators are indirectly grounded through the surfaces of the insulators such as the collector part and the frame and case of the dust collector, resulting in a potential drop. This is a phenomenon that occurs because the resistance value of the high-voltage side electrode is high. If the high-voltage side electrode is a conductor, a potential drop does not occur even if an insulator comes into contact. Furthermore, the potential drop is further amplified when the surface of the insulator becomes dirty and wet. However, on the other hand, the high voltage side electrode must be held somewhere. For this purpose, the above problem can be solved by adopting a structure in which a high voltage is supplied to the portion holding the high-voltage side electrode. With this configuration, the entire high-voltage side electrode can have the same high potential, and no potential difference occurs between the portions of the electrode, and no collector leakage current flows, so that a stable state can be maintained. Therefore, it is possible to obtain an electrostatic precipitator that is not affected by dirt or moisture and that can exhibit not only initial collection performance but also sufficient collection performance over time.

  Depending on the electrostatic precipitator, heat resistance may be required. At this time, the heat distortion temperature can be increased by adding an inorganic filler such as glass fiber treated with a silane coupling agent to the resin. Can be improved. In the case of the ABS system, the temperature rises to 110 ° C. by adding glass fiber. Moreover, a flame retardant etc. can be added to resin as needed.

  The electrostatic precipitator is composed of a collector section using the high-voltage side electrode of the present invention and an ionizer section that usually gives electric charge to the fine particles in the airflow, but how to arrange such a structure, The shape, size and arrangement of the electrodes, the method of supplying power to the electrodes, etc. are determined in a timely manner according to the use and type of the electrostatic precipitator.

According to the configuration of the present invention, the volume specific resistance of the resin electrode can be maintained in the range of 10 ⁸ to 10 ¹³ by the moisture absorbed by the water absorbent resin blended in the resin in the high voltage side electrode of the collector. In the resin electrode, the movement of electric charges is limited, and the occurrence of spark discharge is suppressed. Furthermore, since the movement of charges is limited, the collector leakage current is also reduced, and a high voltage is maintained without causing a voltage drop.

  Hereinafter, the present invention will be described in more detail with reference to experimental examples and examples.

Experimental example 1
Hygroscopic resin in which water-absorbent resin is blended with ABS resin as electrode material (moisture absorption: 1.3 wt%, temperature 25 ° C., humidity 60%, volume specific resistance at 500 V applied voltage: 6 × 10 ¹¹ Ωcm, trade name: Maxroy S704HW A plate electrode having a length of 10 cm, a width of 10 cm, and a thickness of 2.5 mm was manufactured using JSR Corporation. As shown in FIG. 3a, when a voltage applied to the resin electrode is changed and brought close to contact with a grounded metal ball having a diameter of 6 mm, a spark discharge is generated between the resin electrode and the metal ball. The voltage was measured when this occurred. The results are shown in Table 1. Further, based on ASTM-D257, as shown in FIG. 3b, the voltage applied to the resin electrode sample was changed to obtain the volume resistivity of the resin electrode. The results are shown in Table 1 and FIG.

Experimental example 2
Hygroscopic resin made of phenol resin as electrode material (moisture absorption: 1% by weight, temperature 25 ° C., humidity 60%, volume specific resistance at 500 V applied voltage: 3 × 10 ¹² Ωcm, trade name: Sumilite PLC2147, manufactured by Sumitomo Bakelite Co., Ltd.) An electrode having the same size as in Experimental Example 1 was prepared and evaluated in the same manner as in Experimental Example 1. The results are shown in Table 1 and FIG.

Experimental example 3
Semiconductive resin in which conductive whisker is blended with PBT resin as an electrode material (blending amount: 15% by weight) (moisture absorption amount: 0.5% by weight or less, temperature 25 ° C., humidity 60%, applied volume resistivity at 500 V: 1. 3 × 10 ¹¹ Ωcm), an electrode having the same size as that of Experimental Example 1 was produced and evaluated in the same manner as Experimental Example 1. The results are shown in Table 1 and FIG.

Experimental Example 4
Semi-conductive resin (weight absorption: 0.5% by weight or less, temperature 25 ° C., humidity 60%, applied voltage 500 V, volume resistivity: PBT resin mixed with conductive whiskers as electrode material: 4. 3 × 10 ¹³ Ωcm), an electrode having the same size as that of Experimental Example 1 was produced and evaluated in the same manner as Experimental Example 1. The results are shown in Table 1 and FIG.

Example 1
As shown in FIG. 3c, a resin flat plate electrode having a length of 19 cm, a width of 10 cm and a thickness of 1 mm prepared in the same manner as in Experimental Example 1 is used as the high-voltage side electrode, and a 1 mm thick aluminum plate electrode is used as the dust collecting electrode. Were arranged in parallel to each other (electrode spacing: 7.5 mm) to produce a dust collector. Subsequently, the collection performance of this dust collector was measured according to the method of JIS B9908 format-1. The collector voltage Vc was 2.2 kV, the ionizer voltage Vi was 4.6 kV, the wind speed was 1 m / sec, DOP aerosol was used as the test aerosol, the evaluation particle size was 0.3 μm, and the collection rate was measured. . Further, as a comparison, a normal ABS resin in which a high-pressure side electrode is not mixed with a water-absorbing resin (generally, water absorption: 0.5% by weight or less, volume resistivity: 10 ¹⁴ Ωcm or more, for example, trade name: ABS15 , Manufactured by JSR) (Comparative Example 1) and an aluminum plate (Comparative Example 2) were evaluated. The results are shown in Table 2.

Example 2
Using the hygroscopic resin of Experimental Example 1, the ladder type electrode shown in FIG. 2 is injection-molded under the same conditions as in Experimental Example 1, and the conductive resin mixed with carbon fiber is collected on this electrode on the high pressure side. A dust collector was fabricated so that the collector depth d was 9 mm and the collector pitch was 2.9 mm as a side electrode. Next, the collection performance of the dust collector was set such that the collector voltage Vc was 2.3 kV, the ionizer voltage Vi was 4.6 kV, the wind speed was 1 m / sec, DOP aerosol was used as the test aerosol, and the evaluation particle size was 0.3 μm. And the collection rate was measured. Further, as a comparison, a ladder-type electrode was produced on the high-voltage side electrode using the normal ABS resin of Comparative Example 1 and evaluated in the same manner (Comparative Example 3). The results are shown in Table 3.

Example 3
Hygroscopic resin in which water-absorbent resin is blended with ABS resin as electrode material (moisture absorption: 0.9 wt%, temperature 25 ° C, humidity 60%, volume resistivity at applied voltage 500V: 3 × 10 ¹³ Ωcm, trade name: Maxroy HN -901 (manufactured by JSR) was used to produce a parallel plate electrode (length 46 cm, width 10 cm, thickness 1.5 mm) shown in FIG. Next, using this electrode as the high-pressure side and aluminum as the dust-collecting side electrode (thickness 0.5 mm), a dust collector was prepared so that the collector depth d was 100 mm and the collector pitch was 6 mm. Next, the collection performance of the dust collector is as follows. The collector voltage Vc is 8 kV, the ionizer voltage Vi is 6 kV, the wind speed is 1 m / sec, DOP aerosol is used as the test aerosol, and the evaluation particle size is 0.3 μm. When the rate was measured, a collection rate of 90% was obtained.

  Table 1 assumes that the high-voltage electrode and the grounding body should contact each other, and when a high voltage is applied to the resin and brought close to contact with a grounded metal ball having a diameter of 6 mm, spark discharge occurs between the electrodes. In the experimental examples 3 and 4, the insulation was broken at about 7 to 8 kV and spark discharge occurred, whereas in the experimental examples 1 and 2, spark discharge occurred even when 20 kV was applied. Absent. Usually, a voltage exceeding 20 kV is not often applied, so that an electrode which does not substantially cause a spark discharge can be produced.

  Further, according to the result of FIG. 1 showing the change in the volume resistivity when the applied voltage is changed, in Examples 1 and 2 of FIG. 1, in particular, in FIG. 1, a substantially constant resistance value is obtained regardless of the applied voltage. On the other hand, in Experimental Examples 3 and 4, the resistance value changes by 2 to 3 digits or more depending on the applied voltage. From this fact and the experimental results in Table 1, spark discharge occurs in a resin that has a low resistance when the applied voltage is large and the applied voltage increases. Conversely, the resistance value is small and the resistance value is small. It can be seen that the resin staying in the range does not generate spark discharge.

  This is because the amount of the conductive material in the resin is small in the resin to which the conductive material is added, and the conductive material is not dispersed in a continuous state, but the conductive material is dispersed in the resin in a state of being isolated by the resin. Has been. Therefore, if the potential gradient inside the resin increases, the electric charge easily moves between the conductive materials isolated by the resin, so that current flows easily and the resistance value of the resin also decreases, resulting in a large voltage dependence. Showing sex. On the other hand, in the hygroscopic resin, the moisture absorbed by the resin contributes to the conductivity, and this moisture exists almost continuously in the resin and is easy to move. Is less than the conductive material-added resin. Furthermore, in the hygroscopic resin, when the voltage increases, a current flows. However, when the current flows, Joule heat is generated, and the moisture adsorbed on the resin is evaporated slightly by this Joule heat. Since the resistance increases, a high resistance value can be maintained.

  As described above, in the conductive material-added resin, the resistance decreases when the voltage applied to the electrode increases, the current flows more easily when the resistance decreases, and the resistance further decreases when the current easily flows, and spark discharge finally occurs. It will end up.

  On the other hand, in the case of a hygroscopic resin, a high resistance value is maintained even when a high voltage is applied to the electrode. Furthermore, the movement of electric charges is limited by a high resistance value, and the collector leakage current is very small and no voltage drop occurs. As described above, it is understood that a small change in the resistance value with respect to the voltage is important for ensuring stable collection performance.

  Furthermore, when the electrode is made of the hygroscopic resin of the present invention, the collector leakage current is extremely small, so that the collection performance does not deteriorate even in a high humidity environment.

  From the results shown in Table 2, it can be seen that the resin electrode made of the hygroscopic resin of the present invention has a collection efficiency substantially equal to that of the aluminum electrode and is an excellent electrostatic dust collector without causing spark discharge. Furthermore, since the electrode can be produced by integral molding using a hygroscopic resin, there is no exposure of the metal surface due to dielectric breakdown, etc., seen in an electrode etc. subjected to a semiconductive surface treatment on a metal plate. The stable electrode state is maintained, and the dust collection ability does not decrease with time.

  Further, it can be seen that when a ladder-type high-voltage side electrode as in Example 2 in Table 3 is used, an electrostatic dust collector having an extremely thin thickness of 9 mm and an excellent collecting ability can be obtained. In addition, a higher collection rate can be obtained by increasing the depth as in the third embodiment. Furthermore, since the ladder-type electrode can be manufactured by integrally molding a hygroscopic resin, the number of man-hours during assembly processing is reduced, and the manufacturing cost can be reduced. Further, when combined with a dust collecting electrode as shown in FIG. 2, a spacer or the like for maintaining the electrode interval becomes unnecessary, and the problem of pressure loss can be solved.

  Furthermore, since such a ladder-type electrode takes advantage of the parallel plate-type collector, contamination due to dirt or moisture does not progress and the collection performance does not deteriorate.

It is a graph which shows the change of the volume specific resistance of resin with respect to the applied voltage of resin. It is a disassembled perspective view which shows an example of a structure of the collector part using a ladder type electrode. It is a figure which shows an evaluation test method, Comprising: (a) is a circuit diagram for evaluating the relationship between an applied voltage and spark discharge, (b) is a circuit diagram for measuring volume specific resistance with respect to an applied voltage, (c) ) Is a diagram showing the arrangement of the electrodes of the parallel plate collector.

Explanation of symbols

1 high pressure ladder 2 collecting electrode plates 3 ₁ to 3 _n high voltage side electrode 4 ₁ to 4 _n-1 collection electrode d Depth

Claims (1)

A high-pressure electrode for an electrostatic precipitator made of a hygroscopic resin, wherein the relationship between the volume specific resistance value and the applied voltage satisfies the following formula 1.
(Equation 1)
Δlog R / Δlog V ≧ −1 Equation 1

(In Equation 1, R is a volume resistivity value, and V is an applied voltage.)

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