JPH07244015A - Measuring method for contact potential difference of polymer powder - Google Patents

Abstract

PURPOSE:To efficiently measure contact potential difference of a polymer powder within a short time by heat treating the powder at a temperature near the glass transition temperature of the polymer to remove the static charge, disposing the powder between vibration electrodes by cooling or without cooling after the removing the charge, and measuring the potential difference of the powder. CONSTITUTION:Before the measurement of contact potential difference of a polymer powder, the power is heat-treated at a temperature near its glass transition temperature of the powder (a heat treating time of 10-30min), thereby lowering the potential of the powder to zero or the vicinity of the zero within a short time, and hence a true contact potential difference of the powder can be obtained within a short time. A time required for measuring the difference is several minutes, and a time for a preparatory operation necessary for removing the static charge may also be about 30-40min. Further, since an operation for the removing static charge may be a simple sheet treatment, the measurement of a true contact potential difference of the powder can be efficiently executed within a short time.

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 a contact potential difference of a polymer powder, and more specifically, it can reduce a contact potential difference of a polymer powder which has been conventionally required to be measured for a short time. It relates to a method for measuring efficiently.

[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 Vc represents the work function of the metal surface by φ.
Let _{A be} the work function of the powder surface and φ _B be the formula

## EQU1 ## V _C = − (φ _A −φ _B ) / e In the equation, e is the 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. , 46 82 (1898) is used,
In JP-A-2-270885, an upper electrode facing a lower electrode supporting a powder sample is vibrated so that the distance between the electrodes changes, and a voltage is applied between both electrodes to measure a current,
A method for obtaining the voltage when the detected current value is zero as the contact potential difference of the powder is described.

[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 metal-powder contact potential difference to be measured with considerable accuracy. However, as will be described in detail later, the contact potential difference actually measured is as follows. Since the (apparent contact potential difference) is the true contact potential difference plus the potential of the powder layer, there is a problem that it is not always easy to obtain the true contact potential difference. That is, among various powders, with inorganic powders such as spherical silica, the charge of the powder layer is removed (saturation of the powder layer potential to zero) within a relatively short time. In the case of polymer powder such as a system resin, it takes about 5 days for the powder layer potential to reach zero. Therefore, even if the contact potential difference itself can be measured within a relatively short period of time, the preparation step requires a remarkably long period of time, which is not yet satisfactory in terms of practicality.

Therefore, it is an object of the present invention to provide a method capable of efficiently measuring the contact potential difference of polymer powder in a short time. Another object of the present invention is to quickly saturate the potential of the polymer powder layer to zero without disturbing the measurement of the contact potential difference of the polymer powder. An object of the present invention is to provide a measurement method that enables measurement in a short time.

[0008]

According to the present invention, a polymer powder is heat-treated at a temperature in the vicinity of the glass transition point of the polymer to remove the charge, and after the charge removal, the powder is cooled or cooled. There is also provided a method for measuring the contact potential difference of polymer powder, which is characterized in that it is positioned between the vibrating electrodes and the contact potential difference of polymer powder is measured.

In measuring the contact potential difference, the lower electrode supporting the polymer powder sample from which the charge has been removed is vibrated so that the distance between the electrodes changes so as to change the distance between the electrodes. A voltage is applied and the current is measured, and the voltage when the detected current value is zero is determined as the contact potential difference of the polymer powder.

[0010]

[Operation] FIG. 1 for explaining the principle of measuring the contact potential difference.
In the (electrical circuit diagram), this device has 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 _C generated in this way is represented by the previous equation "Equation 1". In the measurement circuit of FIG. 1, the current generated by the vibration of the upper electrode 3 is expressed by the following formula.

[0012]

[Equation 2]

Is given by Here, a: powder layer thickness ε _a : apparent dielectric constant of powder layer b: interelectrode distance ρ _b : volume charge density V ₀ : applied voltage α: upper electrode amplitude z ₀ : contact gap σ: surface Charge density ε ₀ : It is the dielectric constant of air. Σ is the surface charge density of the electric double layer generated by the contact between the powder layer and the lower electrode.

The generated current i (t) fluctuates according to the vibration of the upper electrode, but when the applied voltage V ₀ is changed to make the amplitude of the generated current zero, there is an applied voltage for which A = 0 holds. That is, assuming that the applied voltage V ₀ at this time is the apparent contact potential difference V ₀ ^S , the following formula (4) is obtained from the formula (2) of “Equation 2”.

[0015]

[Equation 3]

Is obtained. Ignore the second term on the right side of equation (4)
The contact potential difference V is the third term on the right side. _CAnd
Therefore, the following formula (5)

[0017]

[Equation 4]

Is obtained. Since the first term on the right side of the equation (5) represents the potential of the powder layer, if the volume charge density ρ _b = 0, the contact potential difference can be directly obtained by setting V ₀ ^S = V _C.

[0019] "Figure 2" is a styrene - the acrylic resin powder (see details in Example), a graph plotting the relationship between the apparent contact potential difference V ₀ ^s and time, the apparent contact potential difference V ₀ The potential difference when ^s decreases and becomes saturated becomes the true contact potential difference V _C. From this FIG. 2, it will be understood that it takes a very long time to reduce and saturate the apparent contact potential difference V ₀ ^s of the polymer powder.

According to the present invention, the polymer powder is heat-treated at a temperature near the glass transition point of the polymer to reduce the potential of the polymer powder to zero or close to zero within an extremely short time. Therefore, the true contact potential difference V _C of the polymer powder can be obtained within a short time.

FIG. 3 is a plot of the relationship between the apparent contact potential difference V ₀ ^s and the treatment time for the styrene-acrylic resin powder while changing the heat treatment temperature. From this “FIG. 3”, when the heat treatment was performed at a temperature near the glass transition point (Tg) of the styrene-acrylic resin, the apparent contact potential difference V ₀ ^s was within a short time (20 minutes). It can be seen that it saturates at V _C. In the present specification, the vicinity of the glass transition point (Tg) generally means Tg.
Centered around −5 ° C., especially −3 ° C., where if it is much lower than the glass transition point, it takes a long time for the saturation, while if it is higher than the glass transition point,
It is not so preferable because the powder characteristics change due to aggregation or coagulation (fusion) of the powder particles.

The glass transition point (Tg) of a polymer can be determined by various methods known per se, but can be simply determined as a shoulder peak of endotherm in a differential thermal analysis curve. The glass transition point is the type of repeating unit of the polymer, the repeating structure,
Although it depends on the molecular weight and the presence or absence of a crosslinked structure,
As an example, the temperature is 60 to 70 ° C. in the case of styrene-acrylic resin used for toners for electrophotography, and 50 to 70 ° C. in the case of polyester resin.

According to the present invention, the time required for the measurement of the contact potential difference itself is several minutes, and the time required for the preparatory operation required for neutralization is about 30 to 40 minutes.
Moreover, since the operation for static elimination may be a simple heat treatment, the true contact potential difference of the polymer powder can be efficiently measured within a short time.

[0024]

EXAMPLE FIG. 4 is a schematic layout of the measuring apparatus used for measurement in this example. The measuring circuit shown in FIG. 1 includes a measuring control computer 7, a computer and a variable pressure digital device. An interface (GP-IB interface) 8 for connecting a power supply and a digital ammeter 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 stored, (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 powdered. It is calculated as the contact potential difference. In this device, by setting a measurement applied voltage and its step and the number of measurement points in the computer 7, the electrodes 2, 3 by the variable voltage power supply 5 are set through the interface 8.
The voltage applied to the computer 7 is automatically switched, and the current that changes due to the vibration of the upper electrode 3 is taken into the computer 7 from the ammeter 6 through the interface 8 by 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 a current generated when the applied voltage V ₀ is changed, and is expressed by GP-IB (gen
A fixed minute time, eg, 8 mse, via an interface port interface bus)
For each c, a large number of points for a constant applied voltage, for example, 400
By applying the points to the computer, the applied voltage at which the amplitude becomes zero is analytically obtained.

FIG. 5 shows the output results of the applied voltage-current value by the computer when the fine acrylic resin powder was used as a sample at the measurement start applied voltage of -10 V, the measurement end applied voltage of +10 V, and step 1 V. One dot of corresponds to one measurement point.

FIG. 6 shows the output by the computer regarding the result of the first-order regression of the applied voltage and the power calculated by integrating the power as an absolute value from the measured values of FIG. 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. If you fold back with respect to the line of zero power,
Both of these straight line portions become a complete straight line, in other words, the turning point between the straight line portion of the negative slope and the straight line portion of the positive slope is always located on the coordinate axis where the power is zero. The correlation coefficient of this linear regression is as high as 1.00, for example.

Thus, as the applied voltage of zero power,
Tactile potential difference V_C, In the figure 1.124V is automatically calculated
Will be done. Contact potential difference V_CIs the negative in FIG.
From the straight part of the slope and from the straight part of the positive slope
Can be found, but from both straight lines, especially one
Bend the gradient part of symmetrically about the axis of zero power,
It is extremely accurate to obtain the applied voltage with zero power.
High contact potential difference V_CCan be asked. For this measurement
In addition, the measurement time (setting time and
(Excluding the time required for data analysis)
Depending on the number of points and the number of measurement points, it is generally 180
It is about 300 seconds, and the contact potential difference is within a very short time.
V₀ ^sCan be measured.

In the measuring device of FIG. 4, 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 chamber 12 for performing measurement under constant conditions, that is, constant temperature and constant chamber conditions.

The lower electrode 2 is provided on the electrode supporting member 13 so as to be detachably and positioned so as to be electrically connected, and the electrode supporting member 13 is connected to the measuring cell 10.
It is being fixed to via the insulating member 14. Lower electrode 2
Is a powder layer filling cell 15 which is recessed from the upper surface by a certain depth.
The sample powder layer 1 having a constant filling rate is filled therein. The diameter of the measurement surface of the electrode is generally 25 to 30 mm
It should be in the range of. In this embodiment, the diameter is 30 mm
Then, use a nickel-plated one with a filled cell with a depth of 3 mm, and adjust the depth by preparing several disks of the same quality with a thickness of 0.5 mm and installing this disk in the cell. By doing so, 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. Connection cable 16 is normal 2
A shaft cable may be used, 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 as appropriate, but the number of fluctuations 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. In this example, 50 points were set in the preliminary test for determining the range of the applied voltage, and 400 points were set in the main test. 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 number of points is loaded into the computer.
This operation is performed for each step voltage up to the measurement end voltage. These measurement data are stored in an opened file, and the measurement results are shown in FIG. 4 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 polymer powder is made of a thermoplastic resin, a thermosetting resin, or a composite material thereof, and generally has a particle size of 0.001 to 100 μm, particularly 1 to 100 μm. To be done. This powder may be in any shape such as spherical, pellet, granular or amorphous. The present invention is of course applicable to those having Tg higher than room temperature.

As the thermoplastic resin, polyethylene (T
g: 100 ° C.) and other hydrocarbon resins; polymethyl methacrylate (Tg: 72-105 ° C.), polyethyl methacrylate (Tg: 47 ° C.) and other acrylic resins; nylon 6, nylon 6,6, nylon 6, 10 (Tg: 45
Polyamide resin such as polyethylene terephthalate (PET) (Tg: 67 to 81 ° C.) and polybutylene terephthalate (PBT); polyacetal resin, polyarylate; halogen-containing resin such as polytetrafluoroethylene; polycarbonate; Phenoxy resin; and the like.

As the thermosetting resin, phenol resin,
An epoxy resin, a urea resin, a melamine resin, etc. are mentioned. These polymer powders may be spherical ones obtained by emulsion polymerization, suspension polymerization, fine suspension polymerization, seed polymerization, dispersion polymerization, etc., or amorphous ones obtained by a pulverization method, or sprayed. It may be a regular particle produced by a granulation method or a hot air granulation method.

The present invention is particularly applicable to the measurement of the contact potential difference of electrophotographic toners in which charging characteristics are a problem, resin-magnetic powder type magnetic carriers used for developing the toners, powder coatings, resin powders 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, or a charge control agent, a release agent, etc. are 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

In the present invention, the polymer powder is heat-treated at a temperature near the glass transition point (Tg) prior to measuring the contact potential difference. The heat treatment time is generally 10 to 30 minutes,
In particular, a range of 15 to 25 minutes is sufficient.

For the heat treatment, an oven, a hot air circulating furnace, infrared heating or the like can be used. When the heat treatment is performed with the lower electrode (cell) filled with the polymer powder layer, care should be taken not to overheat the powder layer in contact with the electrode surface. Generally, it is preferable to perform the heat treatment in a state where the lower electrode (cell) is filled with the powder layer, but the heat treatment of the sample powder is performed separately from the lower electrode, and the heat treated powder is applied to the lower electrode (cell) after the heat treatment. It may be filled. It is preferable to ground the powder sample during the heat treatment.

The heat treatment in the present invention can be carried out not only in the measuring device but also in the measuring device. In the latter case, the constant temperature constant temperature chamber 12 described above is used.
For example, a hot air circulation system 20 is attached, and the hot air and the sample powder layer 1 are brought into contact with each other to remove electricity. Or sample powder layer 1
If the layer is thin, install an infrared lamp inside the device,
The sample powder layer may be heated to a predetermined temperature by infrared irradiation. Of course, the sample after the heat treatment may be directly measured, or may be cooled and then measured.

The thickness of the sample powder layer is generally 1 to 10 ¹⁰ times, especially 1 to 10 ⁵ times the average particle diameter of the powder (volume basis x dian diameter), and the thickness is small. In that case, the processing for static elimination can be completed in a short time.

[0046]

According to the present invention, prior to the measurement of the contact potential difference of the polymer powder, the polymer powder is heat-treated at a temperature in the vicinity of its glass transition point to reduce the potential of the polymer powder. It can be reduced to zero or close to zero within the time, whereby the true contact potential difference of the polymer 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 apparent contact potential and time in conventional measurement.

FIG. 3 is a graph plotting the relationship between apparent contact potential and time when the heat treatment temperature is changed.

FIG. 4 is a schematic layout of the measuring device of the present invention.

FIG. 5 is a graph showing an output regarding a relationship between an applied voltage and a current value.

FIG. 6 is a graph showing an output regarding a relationship between an applied voltage and electric power.

FIG. 7 is a flow chart of measurement in the present invention.

[Explanation of symbols]

1 is a powder layer sample, 2 is a lower electrode, 3 is an upper electrode, 4 is a vibration mechanism, 5 is a variable pressure power source, 6 is a digital ammeter (electrometer), 7 is a measurement control computer, 8 is an interface (GP). -IB interface), 10
Is a measuring cell, 11 is a shield, 12 is a constant temperature chamber, 13
Is an electrode supporting member, 14 is an insulating member, 15 is a powder layer filling cell, 16 is a cable, 17 is a guard electrode, 18 is a support shaft, 19 is a connecting cable, 20 is a vapor circulation system, and 21 is a heater.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location G03G 9/107 // C09D 5/03 PMZ (72) Inventor Hiroaki Masuda 6 Gojobashi Higashi, Higashiyama-ku, Kyoto Chome 538-14

Claims (4)

[Claims] 1. A polymer powder is heat-treated at a temperature in the vicinity of the glass transition point of the polymer to eliminate static electricity, and after the static elimination, the powder is placed between the vibrating electrodes with or without cooling. A method for measuring a contact potential difference of a polymer powder, which comprises measuring a contact potential difference of the polymer powder. 2. The polymer powder is 0.001 to 100 μm.
The measuring method according to claim 1, which has a particle size of. 3. The measuring method according to claim 1, wherein the polymer powder is an electrophotographic toner comprising a fixing resin and a colorant dispersed in the resin. 4. A lower electrode supporting a polymer powder sample from which electricity has been removed is vibrated so that the distance between the electrodes is changed so that the upper electrode facing the lower electrode is oscillated, and a voltage is applied between both electrodes to generate a current. The measuring method according to claim 1, wherein the voltage is measured and the voltage when the detected current value is zero is determined as the contact potential difference of the polymer powder.