JPH0961400A - Method for measuring contact potential difference of powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the true contact potential difference of a powder in a short time by emitting a soft X-ray to the powder having a particle surface formed out of a polymer or the circumference of the powder to eliminate static electricity, and inserting a material to be treated between vibrating electrodes to determine the contact potential difference of the powder. SOLUTION: A powder layer sample 1 is formed on a lower electrode 2, and an upper electrode 3 is provided opposite to the lower electrode 2. In measurement of contact potential difference, the upper electrode 3 is vibrated by a vibrating mechanism to the lower electrode 2 supporting the statically eliminated sample 1 so as to change the distance between the electrodes, a voltage is applied between both the electrodes 2, 3 by a variable voltage power source 5, and the current is measured by a digital ammeter 6. The voltage when the detected current value is zero is determined as the contact potential difference of the sample 1. The sample 1 is filled in such a manner that the powder has a layer thickness of 1-3mm. A soft X-ray is used as the static eliminating energy source, one having a dose rate of 10-50 roentgen-hour is used as the soft X-ray source, and preferably emitted for 1-100 seconds.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring powder having at least a particle surface made of a polymer. More specifically, the present invention relates to a method for measuring a contact potential difference of a powder, which has conventionally required a long time. The present invention relates to a method for efficiently measuring in a short time.

[0002]

2. Description of the Related Art When a powder and a metal come into contact with each other, a potential difference is generated at the interface between the powder and the metal. This potential difference varies depending on the type of powder and the state of the metal surface, and is called the contact potential difference of the powder. This contact potential difference V ₀ represents the work function of the metal surface by φ.
Assuming that _A and the work function of the powder surface are φ _B , the equation (0) V ₀ = − (φ _A −φ _B ) / e (0) In the equation, e is an elementary charge (1.6 × 10 ⁻¹⁹ C).

In the production of powder and various processing steps,
In many cases, powder electrification causes various troubles, and in the field of using electrification of powder such as electrophotographic toner and various powder paints and powder coating, charging characteristics Quantitative evaluation and characteristic control are becoming important issues. The contact potential difference between powder and metal is one of the basic characteristics in evaluating the charge code of powder particles and the degree thereof, and a measurement method excellent in accuracy and reproducibility is desired.

The metal-powder contact potential difference is measured by the Kelvin method (Kelvin, L .: Phil. Ma).
g. , 4682 (1898)), Japanese Patent Laid-Open No. 2-270885 discloses that an upper electrode facing a lower electrode supporting a powder sample is vibrated so that the distance between the electrodes changes, and A method is described in which a voltage is applied to measure a current and a voltage when a detected current value is zero is obtained as a contact potential difference of powder.

[0005] Further, Japanese Patent Application No.
No. 267645 discloses a lower electrode that supports a powder sample, an upper electrode that faces the lower electrode, a vibration mechanism that vibrates the upper electrode so that the distance between the electrodes changes, and a voltage is applied between both electrodes. The variable voltage digital power supply to do so, the digital ammeter to detect the current flowing between both poles, the applied voltage and the step and the number of measurement points are set, and the applied voltage and the detected current value are saved. A computer that calculates electric power as an absolute value by integration, calculates linear regression with respect to applied voltage and electric power, and calculates an applied voltage of zero electric power as a contact potential difference of powder, a computer, a digital power supply, and a digital ammeter. An apparatus for measuring the contact potential difference of powder is described, which comprises a connecting interface.

[0006] The above-mentioned proposal is of great significance as it enables the contact potential difference between metal and powder to be measured with considerable accuracy, but as will be described later in detail, the actually measured contact potential difference (apparent contact potential difference). Has a problem that it is not always easy to obtain the true contact potential difference because the potential of the powder layer is added to the true contact potential difference.
That is, among various powders, with inorganic powders such as spherical silica, the charge of the powder layer is eliminated (releasing the potential of the powder layer to zero) within a relatively short time. With polymer powders such as resin, it takes about 5 days for the powder layer potential to relax to zero. Therefore, even if the measurement of the contact potential difference itself can be performed within a relatively short time, the preparation step requires a significantly long time.
It was not yet fully satisfactory in terms of practicality.

Conventionally, in order to reduce the potential of powder to zero or a potential close to zero before measuring the contact potential difference of powder, particularly polymer powder, A It is already invented by the present inventor that B is subjected to AC corona discharge in a state where the polymer powder is filled in the measuring electrode cell, and C is exposed to the vapor of the organic solvent. Have been proposed (patent pending for these).

[0008]

SUMMARY OF THE INVENTION The object of the present invention is to provide another method which makes it possible to measure the true contact potential difference of a powder in which at least the particle surface is formed of a polymer in a short time. It is in.

Another object of the present invention is to rapidly relax the potential of the powder layer to zero without disturbing the measurement of the contact potential difference of the powder, thereby measuring the true contact potential difference. The purpose of the present invention is to provide a measuring method that can be performed in a short time.

[0010]

According to the present invention, a powder having at least a particle surface formed of a polymer or its periphery is irradiated with soft X-rays to remove electric charge, and the processed product is removed between the vibrating electrodes. A method for measuring a contact potential difference of a powder is provided by inserting into a substrate to determine a contact potential difference of the powder.

In measuring the contact potential difference, an upper electrode facing the lower electrode supporting the powder sample from which electricity was removed was vibrated so that the distance between the electrodes was changed, and a voltage was applied between both electrodes. The electric current is measured by measuring the current, and the voltage when the detected current value is zero is obtained as the contact potential difference of the powder.

[0012]

FIG. 1 shows the principle of measuring the contact potential difference.
In the (electrical circuit diagram), this device shows a lower electrode 2 supporting a powder layer sample 1, an upper electrode 3 facing the lower electrode,
A vibrating mechanism 4 for vibrating the upper electrode so that the distance between the electrodes changes, a variable voltage power source 5 for applying a voltage between both electrodes,
It is composed of a digital ammeter (electrometer) 6 for detecting a current flowing between both electrodes.

In FIG. 1, when the powder layer 1 is formed on the surface of the lower electrode 2, charging occurs at the interface between the two. That is, electrons move from the one having a small work function to the one having a large work function, and a substance having a small work function is positively charged and a substance having a large work function is negatively charged. The potential difference V ₀ thus generated is represented by the previous equation (0).

In the measuring circuit of FIG. 1, the current generated by the vibration of the upper electrode 3 is expressed by the following equation.

[0015]

[Equation 1] Given in. Here, a ₁ : thickness of powder layer ε _a : apparent dielectric constant of powder layer S: area of upper electrode a ₂ : average inter-electrode distance ρ _a : volume charge density V _{sample / Au} : sample of Au Contact potential difference V: Applied voltage α: Amplitude of upper electrode ε ₀ : Dielectric constant of air ω: Frequency of upper electrode

The generated current i varies according to the vibration of the upper electrode, but when the applied voltage V is changed to make the amplitude of the generated current zero, there is an applied voltage at which i = 0 holds. That is,
Assuming that the applied voltage V at this time is an apparent contact potential difference V ₀ ′, from the equation (1), the following equation (2) is obtained.

[0017]

[Equation 2]

When the volume charge of the powder layer is relaxed, the applied voltage is directly measured as the potential difference of the sample with respect to Au, as in the following equation (3).

V ₀ = V _{sample / Au} (3) is obtained. The white circle plot in FIG. 2 shows the apparent contact potential difference V ₀ ′ and time for the coated carrier powder A (refer to Examples described later in detail) in which ferrite core particles are coated with a fluorine-containing acrylic silicone resin. The relationship is plotted, and the apparent contact potential difference V
The potential difference when ₀ ′ decreases and becomes saturated becomes the true contact potential difference V ₀ (about 0.917 volt).

From this FIG. 2, the apparent appearance of the coated carrier is shown.
Contact potential difference V₀′ Is decreased and V ₀To saturate
It will be appreciated that it will take a significant amount of time.

Attenuation of the apparent contact potential difference V _O ′ means relaxation of the initial potential of the powder layer because the electrostatic capacity of the powder layer is constant, which follows the exponential rule from FIG. I understand. When the charge relaxation process conforms to the exponential law, its decay characteristic is represented by a time constant τ. In the case of powder, the apparent dielectric constant ε _a and the apparent specific resistance ρ _a are expressed by the following equation (4 ) Where Q is the charge after t (hr) and Q ₀ is the initial potential. In the case of the white circle plot in FIG. 2, the time constant τ = 1800 (hr) is obtained from the measured value.

According to the present invention, by irradiating the powder sample to be measured or the periphery of the powder sample with the soft X-ray, the charging potential of the powder is reduced to zero or close to zero within an extremely short time. Therefore, the true contact potential difference V ₀ of the powder can be obtained within a short time.

FIGS. 3, 4 and 5 show the above-mentioned coated carrier powder having a layer thickness A of 1 mm, 2 mm and 3 mm, respectively.
The results obtained by irradiating soft X-rays with various initial apparent contact potential differences and plotting the relationship between the irradiation time and the apparent contact potential difference. FIG.
FIG. 3 is an excerpt of the typical examples of FIGS. 3, 4 and 5 together.

According to the results of these figures, the irradiation of the soft X-ray is effective in reducing the potential of the powder regardless of the level of the initial apparent contact potential difference of the powder,
Moreover, the surprising fact that the irradiation time is several seconds to several tens seconds is sufficient.

The white square plot in FIG. 2 shows the result of actual contact potential difference measurement of the above coated carrier powder A irradiated with soft X-rays for 180 seconds. From the measured value to the time constant τ = 5.0
(Hr) is calculated and compared with the untreated case, the time constant τ
It is understood that is significantly shortened.

The present invention is characterized in that soft X-rays are used as an energy source for static elimination. Although soft X-rays are a type of X-rays belonging to ionizing radiation, they are weak X-rays having a wavelength of several angstroms or more and several hundred angstroms or less. Although this soft X-ray has a weak penetrating power, it has the ability to ionize molecules such as atmospheric gas.

In FIG. 7 (explanatory diagram) for explaining the ionization by the soft X-rays, when the soft X-rays hν from the soft X-ray generator 30 collide with the molecule 31, primary electrons 32 are emitted from the molecule. , Cations 33 are generated. The primary electron 32 is absorbed by the molecule 31 to generate an anion 34. Thus, it is recognized that the electrons, anions or cations in the atmosphere formed around the powder sample effectively act on the charge removal of the powder.

In the ionization by the soft X-ray used in the present invention, the ions to be formed are always generated in the positive and negative equal amounts, so that there is an advantage that the powder is not reversely charged.

Further, the static elimination of the present invention has the advantage that it can be easily carried out in the atmosphere. For example, in the static elimination method using ultraviolet rays, it was necessary to place the powder in a high vacuum and irradiate it with ultraviolet rays, but in the present invention, since it is possible to eliminate static electricity in the atmosphere, a vacuum device is not required and degassing No preparation operation is required and the operation is easy.

Further, since the soft X-ray has a weak penetrating power, it is easy to shield it for safety. For example, a plastic shield plate such as a vinyl chloride resin plate is used according to the ICRP60 limited exposure regulations (recommended value). Adults who are exposed to the atomic bomb ... 50mSv / year Members of the public ............ 1mSv / year 50mSv / year There is also an advantage that the safety regulation value can be maintained.

The charge removal of the powder is carried out in a state where the powder is filled in the electrode cell, which is advantageous for the subsequent measurement of the contact potential difference, and the thickness of the powder packed layer is not particularly limited. Thicknesses commonly used for measuring contact potential differences, especially 1 to 3
A thickness of mm is sufficient.

The soft X-ray source has a dose rate of 1 to 100.
X-ray / hour, particularly about 10 to 50 X-ray / hour is preferable, and irradiation time is 1 to 500 seconds,
Particularly, about 2 to 100 seconds is preferable.

[0033]

FIG. 8 shows the arrangement of the measuring device of this embodiment. This device is an interface for connecting the measuring circuit of FIG. 1 to the measuring control computer 7, and a computer and a variable pressure digital power supply and a digital ammeter. (GP-I
B interface) 8 is added.

The measurement control computer 7 sets (i) the measurement applied voltage, its step and the number of measurement points, and
i) The applied voltage and the detected current value are saved, (iii) the electric power as an absolute value is calculated from these, and (iv) the linear regression is obtained with respect to the applied voltage and the electric power, and the applied voltage of zero electric power is measured by the powder. It is calculated as the contact potential difference. In this device, the applied voltage to the electrodes 2 and 3 by the variable voltage power supply 5 is automatically switched through the interface 8 by setting the measured applied voltage and its step and the number of measurement points in the computer 7. The current that changes due to the vibration of the electrode 3 is taken into the computer 7 from the ammeter 6 through the interface 8 for the set number of measurement points. Therefore, a large number of measurement values can be accurately captured in the computer without loss time.
Further, since the applied voltage and the detected current value taken in through the interface 8 are stored in the computer in the form of a file, this is not only used for the data analysis described later, but also when necessary. It can be taken out and used at any time for checking and comparative reference purposes.

By the way, the current flowing between both electrodes is an alternating current that fluctuates according to the vibration of the upper electrode, and therefore has a value that fluctuates from positive to negative. The applied voltage also has a value that fluctuates between positive and negative. Therefore, an absolute value is taken for the sampled voltage value and current value, and these are integrated to calculate a power value. This calculation is quickly performed by the calculation program.

Next, a linear regression is obtained with respect to the applied voltage and the electric power, and the applied voltage with zero electric power is calculated as the contact potential difference of the powder. The results of these calculations and data analysis can all be saved in a file. At the time of measurement, i (t) is the current generated when the applied voltage V is changed, and GP (IB) (gene)
Ral port interface bus) interface for a fixed minute time, eg 8 msec
For each constant applied voltage, a large number of points, for example 400 points,
By inputting to a computer, the applied voltage at which the amplitude becomes zero is analytically obtained.

FIG. 9 shows the output results of the applied voltage-current value by the computer when the fine acrylic resin powder was used as the sample at the measurement start applied voltage of -10 V, the measurement end applied voltage of +10 V, and the step 1 V. One dot of corresponds to one measurement point.

FIG. 10 shows the output by the computer regarding the result of linearly regressing the applied voltage and the power by calculating the power as an absolute value from the measured values of FIG. 9 by integration. According to this result, there is a linear portion with a negative slope in which the power decreases as the voltage rises and a linear portion with a positive slope in which the power increases as the voltage rises. When is folded back with respect to the line of zero power, these straight line parts become a complete straight line.In other words, the turning point between the straight line part of negative slope and the straight line part of positive slope is zero power. Be sure to be located on the coordinate axis. The correlation coefficient of this linear regression is as high as 1.00, for example. Thus, the contact potential difference V ₀ , 1.124 V in the figure, is automatically obtained as the applied voltage of zero power.

The contact potential difference V ₀ can be obtained from the straight line portion having the negative slope and the straight line portion having the positive slope in FIG. Bending symmetrically with respect to the axis to obtain an applied voltage of zero power makes it possible to obtain a highly accurate contact potential difference V ₀ . In this measurement, the measurement time required for one sample (excluding the setting time and the time required for data analysis) varies depending on the number of steps of the applied voltage and the number of measurement points, but is generally 180 to 3
It is about 00 seconds, and the contact potential difference V ₀ within an extremely short time.
'Can be measured.

In the measuring device of FIG. 8, the lower electrode 2 and the upper electrode 3 are housed in the measuring cell 10, and the measuring cell 10 is housed in the shield 11 for shielding the measuring cell 10 from external noise. ing. Further, the shield 11 is housed in a constant temperature and constant humidity tank 12 for performing measurement under a constant condition, that is, a constant temperature and constant humidity condition.

The lower electrode 2 is provided on the electrode supporting member 13 so as to be electrically connected in a detachable and positioned state, and the electrode supporting member 13 is connected to the measuring cell 10.
It is being fixed to via the insulating member 14. As shown in FIG. 11, the lower electrode 2 which also serves as a cell has a powder layer filling cell 15 which is recessed from the upper surface by a certain depth, and the sample powder layer 1 having a constant filling rate is filled therein. There is. Generally, the diameter of the measurement surface of the electrode should be in the range of 25 to 30 mm. In this example, a nickel-plated one with a filling cell having a diameter of 30 mm and a depth of 3 mm was used, and the depth was adjusted by preparing several discs of the same quality having a thickness of 0.5 mm. ,
By installing this disk in the cell, the depth can be adjusted.

The measuring cell 10 and the shield 11 are both grounded, and the electrode supporting member 13 is connected to a digital ammeter (electrometer) 6 via a cable 16. The connection cable 16 may be a normal biaxial cable, but if a three-wire coaxial cable provided with a double shield is used, accurate measurement can be performed without external noise.

The upper electrode 3 is covered with a guard electrode 17 which covers the upper surface of the upper electrode 3 so as to prevent the edge effect except for the working surface.
Are integrally provided, and the guard electrode 17 is grounded. The upper electrode 3 and the guard electrode 17 are supported by a hollow support shaft 18, and the support shaft 18 is driven by a drive mechanism 4 known per se such as a cam at a specific time. A connection cable 19 extends through the support shaft 18 and electrically connects the upper electrode 3 and the variable voltage power supply 5. The upper electrode 3 is preferably composed of a gold-plated plate or the like. The frequency and amplitude of the upper electrode 3 can be set appropriately, but the frequency is generally 6
The amplitude is preferably in the range of 0 to 120 rpm (times / minute) and the amplitude is in the range of 2.0 to 3.0 mm. In this embodiment, the frequency is 72 rpm and the amplitude is 2.5 mm. In this device, control of the variable voltage power supply 5 and acquisition of the current value from the digital ammeter 6 are performed by the measurement control computer via the GP-IB interface 8.

The measurement is performed according to the flow chart shown in FIG. First, as a measurement item, any one of contact potential, dielectric constant, and electric resistance is selected. For contact potential measurement,
Set the measurement conditions. First, the number of measurement points, that is, the number of measurement points for a constant voltage is set. Generally, 50 to 500 points are suitable for the number of measurement points, and in this example, 50 points in the preliminary test for determining the range of applied voltage and 400 points in the main test.
The point is set. Next, after setting the voltmeter measurement range and the ammeter measurement range according to the type of sample, set the measurement start applied voltage, measurement end applied voltage, and step voltage (voltage gap), and finally set the measurement data. Enter the file name to save.

This starts the measurement, and as described above, the vibration of the electrode, the application of the voltage, and the detection of the current are set for each minute time, and the points are loaded into the computer.
This operation is performed for each step voltage up to the measurement end voltage. These measurement data are saved in an opened file, and the measurement results are shown in FIG. 9 as a plot of the relationship between the applied voltage and the current value, which is displayed on the CRT of the computer.
Is displayed in.

The computer 7 analyzes the data according to the program, calculates the electric power as an absolute value for each applied voltage by integration, then obtains a linear regression with respect to the applied voltage and the electric power, and calculates the applied voltage with zero electric power. It is calculated as the contact potential difference of the body, and the measurement result is displayed as shown in FIG.

In the present invention, the powder sample used for measurement may be any powder as long as at least the particle surface is formed of a polymer, and the polymer here is a thermoplastic resin or a thermosetting resin. Resin, various rubbers, etc. are mentioned.

The particle shape of the powder may be any shape such as spherical shape, die shape, pellet shape, granular shape, and irregular shape,
The particle size is 0.001 to 100 μm, especially 1 to 10
It is preferably in the range of 0 μm.

As the thermoplastic resin, polyethylene, polypropylene, ionomer, polystyrene (Tg: 1
Hydrocarbon resins such as 00 ° C.); acrylic resins such as polymethyl methacrylate and polyethyl methacrylate; polyamide resins such as nylon 6, nylon 6,6, nylon 6,10; polyethylene terephthalate (PET),
Examples thereof include polyester resins such as polybutylene terephthalate (PBT); polyacetal resins; polyarylate; polytetrafluoroethylene; halogen-containing resins such as polyvinyl chloride; polycarbonates; phenoxy resins. Examples of the thermosetting resin include phenol resin, epoxy resin, urea resin, melamine resin, silicone resin, alkyd resin, unsaturated polyester, urethane resin, bismaleimide resin, cyanuric acid resin, and the like. Of course, these may be used alone or in combination of two or more.

As various rubbers, EPR, EPDM, S
Examples thereof include BR, NBR, CR, natural rubber and urethane rubber.

These polymer powders may be spherical particles obtained by emulsion polymerization, suspension polymerization, fine suspension polymerization, seed polymerization, dispersion polymerization, etc., or amorphous particles obtained by a pulverization method. Also, it may be a regular particle produced by a spray granulation method or a hot air granulation method.

The present invention is particularly applicable to the measurement of the contact potential difference of an electrophotographic toner in which the charging property is a problem, a resin-magnetic powder type magnetic carrier used for the development of the toner, a powder coating, a resin powder for fluid immersion and the like. It is useful. That is, these powders
Although the charging performance is high and the charge is little attenuated once it is charged, the potential of the powder can be rapidly reduced by the heat treatment in the present invention.

In the electrophotographic toner, a colorant, a charge control agent, a release agent, or the like is dispersed in a fixing resin medium and granulated to have a particle size of 5 to 15 μm, and hydrophobic silica is formed on the surface thereof. The amount of electric charge (absolute value) reaches 10 to 50 μC / g, and the true contact potential difference should be obtained from such toner within a short time. You can

Particles coated with a polymer may be used in place of the polymer powder. As a suitable example of such polymer-coated particles, the surface of the magnetic core is coated with the above-mentioned resin or the like. And a coated magnetic carrier for electrophotography.

Table 1 below shows the constitution and characteristics of the coated magnetic carrier used in this example.

[0056]

[Table 1]

In the present invention, the powder is subjected to soft X-ray irradiation prior to the measurement of the contact potential difference to lower the powder potential.

In FIG. 13 (arrangement) showing an apparatus used for soft X-ray irradiation, a soft X-ray generator 30 is connected to a power source 35, and a soft X-ray irradiation port 36 side is made of vinyl chloride resin or the like. A shield box 37 is provided, and the powder layer filling cell 15 shown in FIG. 11 is housed in the shield box 37. By supplying a predetermined electric power to the soft X-ray generator 30, The periphery of the body layer 15 is irradiated with soft X-rays to neutralize the powder.

In this embodiment, IRISSYS-SX manufactured by Takasago Industries Co., Ltd. is used as a soft X-ray generator, and a dose rate of 22
Irradiation with soft X-rays was performed at X-ray / hour, and the results shown in FIGS. 2, 3, 4, 5, and 6 were obtained.

[0060]

According to the present invention, the potential of powder is shortened by irradiating the powder or its surroundings with soft X-rays before measuring the contact potential difference of the powder having at least the surface made of a polymer. It can be reduced to zero or close to zero within the time, so that the true contact potential difference of the powder can be determined within a short time.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of an apparatus used for measurement of the present invention.

FIG. 2 is a graph plotting the relationship between the apparent contact potential difference and time for the coated carrier powder A of the example.

FIG. 3 shows a coated carrier powder A layer having a layer thickness of 1 mm,
It is the graph which plotted the relationship between apparent contact potential difference and soft X-ray irradiation time.

FIG. 4 is a graph similar to FIG. 3 for a layer thickness of 2 mm.

5 is a graph similar to FIG. 3 for a layer thickness of 3 mm.

FIG. 6 is a graph showing the typical results of FIGS. 3 to 5 together.

FIG. 7 is an explanatory diagram for explaining ionization by soft X-rays.

FIG. 8 is a layout view showing a measuring device of the present embodiment.

FIG. 9 is a graph showing an output regarding a relationship between an applied voltage and a current value.

FIG. 10 is a graph showing an output regarding a relationship between an applied voltage and electric power.

FIG. 11 is a top view and a cross-sectional view of a lower electrode.

FIG. 12 is a flow chart of measurement in the present invention.

FIG. 13 is a layout view showing an apparatus used for soft X-ray irradiation.

[Explanation of symbols]

 1 Powder Layer Sample 2 Lower Electrode (Ni) 3 Upper Electrode (Au) 4 Vibration Mechanism 5 Variable Pressure Power Supply 6 Digital Ammeter (Electrometer) 7 Computer for Measurement Control 8 Interface (GP-IB Interface) 10 Measurement Cell 11 Shield 12 constant temperature and humidity chamber 13 electrode supporting member 14 insulating member 15 powder layer filling cell 16 cable 17 guard electrode 18 supporting shaft 19 connection cable 30 soft X-ray generator 31 molecule 32 primary electron 33 cation 34 anion 35 power supply 36 soft X-ray Irradiation port 37 Shield box

Claims (8)

[Claims] 1. A powder having at least a particle surface formed of a polymer or its periphery is irradiated with a soft X-ray to remove electric charge,
A method for measuring the contact potential difference of powder, characterized in that the treated object is inserted between vibrating electrodes to obtain the contact potential difference of powder. 2. The measuring method according to claim 1, wherein the powder is filled in a cell which also serves as a lower electrode and is irradiated with soft X-rays. 3. The measuring method according to claim 2, wherein the powder is filled so as to have a layer thickness of 1 to 3 mm. 4. The measuring method according to claim 1, wherein a soft X-ray source having a dose rate of 10 to 50 roentgen hours is used and irradiation is performed for 1 to 100 seconds. 5. The measuring method according to claim 1, wherein the soft X-ray irradiation is performed in the air. 6. The measuring method according to claim 1, wherein the powder is an electrophotographic toner comprising a fixing resin and a colorant dispersed in the resin. 7. The measuring method according to claim 1, wherein the powder is a magnetic carrier for electrophotography, which comprises magnetic core particles and a resin coating layer coating the surfaces of the core particles. 8. An electric current is measured by oscillating an upper electrode facing the lower electrode supporting a powder sample from which electricity has been removed so that the distance between the electrodes changes and applying a voltage between both electrodes. The measuring method according to any one of claims 1 to 7, wherein the voltage when the detected current value is zero is obtained as the contact potential difference of the powder.