JPH0862885A - Method and device for measuring electrification characteristics of electrophotographic toner - Google Patents

Abstract

PURPOSE: To easily and accurately obtain quantitative data relating to the thermal stability of charge traps in charged toner particles by raising temp. of a charged sample disposed between electrodes facing each other and measuring a thermally stimulated current. CONSTITUTION: A powder sample 3 of a charged electrophotographic toner is held on a supporting electrode 1 for a sample. The counter electrode 2 is disposed at a specified distance from the supporting electrode 1 to vertically coincide with each other. The supporting electrode 1 is provided with a thermocouple 4 to detect the temp. (temp. of the sample to be measured). Further, the set of the supporting electrode 1, counter electrode 2 and thermocouple 4 is housed in a heating and temp. raising mechanism 5. A controlling mechanism 6 is attached to this heating and temp. raising mechanism (heater) 5 so as to heat the set in such a manner that the temp. of the sample is increased by a specified rate. By placing the charged electrophotographic toner sample 3 between the electrodes 1, 2 facing each other and by increasing the temp. of the charged sample 3 as above described, the thermally stimulated current is measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for measuring the charging characteristics of electrophotographic toners, and more particularly to a method and apparatus for measuring various charging characteristics of electrophotographic toners by thermal stimulation current measurement. Regarding the device.

[0002]

2. Description of the Related Art In electrophotography, the surface of a photosensitive layer is uniformly charged by corona discharge or the like and then imagewise exposed through an optical system to form a charge image corresponding to the image. A toner image is formed by developing with a toner having a charge of the opposite polarity.

Two-component developers consisting of a mixture of magnetic carriers and electrographic toner particles are most commonly used for developing this charge image. At the time of development, the carrier and the sensible toner are mixed, and are triboelectrically charged to have opposite polarities, and are rubbed against the photosensitive layer in the form of a magnetic brush.
The electrostatic toner is attracted to the charge image by Coulomb force to form a toner image. Thus, it will be appreciated that the evaluation of the charging characteristics of the electrographic toner is the most important factor in evaluating the suitability of the developer for electrophotography.

Conventionally, a method of using a blow-off charge amount measuring device has been known as a method of evaluating the charging characteristics of toner. According to this method, toner and carrier are mixed to perform triboelectric charging, Only toner from this mixture
Blow off with ₂ gases and measure the amount of charge per unit weight.

A large number of methods for measuring the distribution of toner charge are also used. For example, a method using an Yerspart analyzer and, as described in JP-B-5-52901, between parallel counter electrode plates are used. A downward airflow is formed in the vertical passage of the toner, a voltage is applied to the counter electrode plate, and a developer composed of a mixture of carriers and electroscopic toner is supplied into the vertical passage to change the flow velocity of the airflow to the toner. The particles are attached to the electrode plate, but the carrier particles are within the range where they are not attached to the electrode plate, and the toner pattern attached to the electrode plate is directly or transferred, and then, depending on the relation between the attachment position and the reflection density or the transmission density. There is also known a method for evaluating toner charging characteristics, which is characterized by evaluation.

[0006]

The above-mentioned toner charge amount measuring method can measure the average charge amount of toner and the distribution of the charge amount of individual toner particles, even if the distribution of charge amount of individual toner particles can be measured. No internal information such as charge traps associated with powder manufacturing conditions can be known.

We have measured quantitatively the thermal stability of charge traps in charged toner particles by measuring the thermal stimulating currents on charged electrophotographic toners, ie, the charge at each temperature. It was found that quantitative data on the amount of loss and the amount retained can be obtained accurately and with good reproducibility.

That is, the object of the present invention is to provide quantitative data on the thermal stability of charge traps in charged toner particles, that is, the amount of charge lost at each temperature, by a simple operation of changing the temperature by raising the temperature. Another object of the present invention is to provide a novel method and apparatus for measuring the charging characteristics of a toner for electrophotography, which is capable of accurately and reproducibly obtaining quantitative data on the amount of toner and the amount retained.

Another object of the present invention is to provide quantitative data on the thermal stability of charge traps in charged toner particles, ie quantitative data on the amount of charge lost or retained at each temperature of the toner resin. It is an object of the present invention to provide a method and an apparatus which can be measured in relation to thermal characteristics such as glass transition point and melting point.

[0010]

According to the present invention, a charged electrophotographic toner sample is placed between opposing electrodes,
A method for measuring the charging characteristic of an electrophotographic toner is provided, in which the temperature of the charged sample is changed by heating to measure a thermal stimulation current.

It is good practice to raise the temperature of the charged sample at a constant temperature rising rate and obtain the distribution of temperature and current. For this purpose, electrophotographic toner powder is pressure-molded into a plate shape, charged, and then measured. It is preferable to attach.

According to the present invention, an electromagnetic shield, a heating / heating mechanism housed in the electromagnetic shield, and a supporting electrode housed inside the heating / heating mechanism and on which a charged sample of electrophotographic toner is placed. A support provided, a counter electrode housed inside the heating and heating mechanism and provided to face the support electrode and spaced apart therefrom, a thermocouple provided on the support, and a current from the counter electrode is detected. Toner for electrophotography, comprising: a current detecting mechanism for controlling the temperature and a display recording mechanism for displaying or recording the distribution of temperature and current based on the current signal from the current detecting mechanism and the temperature signal from the thermocouple. An apparatus for measuring the charging characteristic of the above is provided.

[0013]

In the present invention, the charge amount of the toner is changed by raising the temperature of the toner to change the thermal stimulation current (Thermal).
Measured as ly Stimulated Current). Thermally stimulated current (TSC) is a change in the charge (dipole space charge, hereinafter referred to as the amount of retained charge) accumulated in the insulator, which is released (released) at a certain temperature change (δT). The electric current (i) corresponding to the quantity (δQ), which is expressed by the following formula (1) i = δQ / δT (1). Thus, by plotting the relationship between the temperature T and the thermally stimulated current i, the distribution of the amount of charge disappearance corresponding to each temperature can be accurately obtained at a glance.

Further, when the equation (1) is modified and integrated, the following equation (2) becomes ∫iδT = Q ..... (2), and the T-i distribution curve is obtained over the entire temperature range (actually from room temperature to a little from the melting point). The total charge amount can be obtained by integrating in the temperature range above), and the lost charge amount in that temperature range can be obtained by performing the integration in a certain temperature range. The amount of lost charge and the amount of retained charge at a certain temperature have the relationship of the following formula (3). Lossed charge amount + retained charge amount = total charge amount (3) Since the total charge amount corresponds to the area of the T-i distribution curve, the charge amount distribution can be easily understood.

In general, a toner resin for electrophotography always contains a binder resin, and this resin plays an important role not only in the fixing property of the toner but also in holding the electrostatic charge of the toner. The important thermal characteristics of the resin for toner are a glass transition point (Tg) and a melting point (Tm), and the former glass transition point (Tg) depends on the heat resistance of the toner and the melting point (Tg) of the latter.
m) is closely related to the heat fixing property of the toner.

According to the present invention, by obtaining a distribution diagram (referred to as a spectrum) of temperature and thermally stimulated current, charging is performed in relation to the glass transition point (Tg) and melting point (Tm) of the toner resin. You can know the distribution of quantity.

For example, FIG. 1 of the accompanying drawings is a thermal stimulation current spectrum for toners A and B in Example 1 described later. In this spectrum, a low peak P0 on the low temperature side on the left side and a high peak P1 on the high temperature side on the right side are observed, and the ridge on the right side of the low temperature side peak P0 is at the glass transition point (Tg) and on the right side of the high temperature side peak P1. The bottom of the mountain has a melting point (T
It corresponds to m). From this, it is understood that the degree of discharge of electric charges is small in the process of transition of the resin polymer for toner from the glass state to the rubber state, and the discharge of electric charges is large due to melting of the crystal or microcrystal of the polymer. Of course, it is possible to accurately calculate how much charge is lost and how much charge is retained in each temperature range.

According to the present invention, the information obtained by measuring the thermal stimulation current is the glass transition point (T) of the above-mentioned toner resin.
The relationship between g) and the melting point (Tm) and the charge amount is not limited.
For example, as shown in FIG. 4, the toner morphology and the granulation history differ depending on whether the toner is manufactured by a pulverization method, the toner is manufactured by a melt granulation method, or the toner is manufactured by a solution granulation method. Differences in charging characteristics (temperature characteristics) can also be detected. Further, as shown in FIGS. 2 and 3, even in the case of the toner obtained by the pulverization method, the influence of the pulverization conditions on the toner charging characteristic (temperature characteristic) can be examined.

It is also important to position the charged sample between the opposing electrodes and raise the temperature at a constant rate of temperature to obtain the distribution of temperature and current, which results in a standardized thermal stimulation current curve. By integrating this, the amount of charge lost when the temperature is raised to a certain temperature can be easily calculated.

It is possible to directly charge the powder of the electrophotographic toner onto the electrode which also serves as a cell, and charge the powder-filled layer for measurement. However, in terms of handling, the powder of the electrophotographic toner is generally taken into consideration. It is desirable that the body is pressed into a plate shape, charged, and then subjected to measurement.

As described above, according to the present invention, the quantitative data regarding the thermal stability of the charge traps in the charged toner particles, that is, the quantitative data about the loss amount and the retention amount of the charge at each temperature are accurately obtained. And it can be obtained with good reproducibility,
It is useful for investigating the relationship between the composition and physical properties of the toner resin, the toner preparation method and its conditions, and the toner charging characteristics.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION In FIG. 5 showing an example of a measuring apparatus used in the present invention, this apparatus comprises a measurement sample supporting electrode (upper electrode) 1 and a counter electrode (lower electrode) 2. The measurement sample support electrode 1 supports the powder sample 3 of the electrophotographic toner charged on the upper portion thereof. Counter electrode 2
Are provided at a position which overlaps with the support electrode 1 at a constant interval in the vertical direction. It should be understood that the counter electrode 2 is provided such that its position is adjustable.

The support electrode 1 is provided with a thermocouple 4 for detecting its temperature (measurement sample temperature).

The set of the measurement sample supporting electrode 1, the counter electrode 2 and the thermocouple 4 is housed inside the heating / heating mechanism 5, and the heating / heating mechanism (heater) 5 has a thermal control mechanism ( Thermo-Controller) 6 is attached, so that the measurement sample is heated at a constant heating rate,
Heat the set.

The heating / heating mechanism 5 is housed in an electromagnetic shield (in this example, a triple electromagnetic shield) 7 in order to prevent noise.

The support electrode 1 is grounded, while the output from the counter electrode 2 is taken out via the wiring 8 and read by an ammeter (picoammeter pA) 9. The signal from the ammeter 9 and the signal from the thermocouple 4 are read by the XY recorder 10 to display and record temperature as one coordinate axis (X) and current as the other coordinate axis (Y). The signal from the thermocouple 4 is read by the Y-T recording device 11 to display and record the temperature as one coordinate axis (Y) and the time as the other coordinate axis (T). Further, the signal from the ammeter 9 and the signal from the thermocouple 4 are read by the data recording device 13 controlled by the host computer 12,
These data are recorded and saved in the form of electronic files (floppy desk). Incidentally, the Y-T recording device 11 is
This is for checking whether or not the temperature of the sample 3 is linearly increased.

In order to carry out the measurement of the present invention, first, a certain amount of the electrophotographic toner to be measured is weighed, the weighed toner is placed on a conductive support, and it is pressed with a plunger at room temperature. , Press-molding into a disk-shaped molded body having a constant thickness. The molded body is placed on a conductive support and charged by a corona charger to give a charged toner sample 3.

As the toner sample, it is sufficient that the amount of charge can be detected, generally 10 to 1000 mg, particularly 50 to 200 mg, and the thickness of the molded body is not particularly limited, but 10 to 1000 μm. A suitable thickness is appropriate. The reason is that if the thickness is thicker than the above range, temperature distribution may occur in the sample, and accurate measurement may not be possible. The pressing force on the powder is also
It is sufficient that the powder filling state is constant and the molded body does not collapse during handling. Generally, a load per unit area of about 1 to 35 kg / cm ² is suitable.

The polarity of the corona charging may be positive or negative, and the charging amount can be freely adjusted so as to correspond to the actual charging amount of the toner. For example, by using a needle-shaped electrode corona charger with a grid electrode and changing the voltage applied to the grid electrode, the surface charging potential can be adjusted freely.

The surface potential of the charged electrophotographic toner sample can be measured by a non-contact type surface electrometer, and it is generally suitable that the surface potential is in the range of 50 to 700 volts.

The sample 3 of the plate-shaped toner molded body can be transferred to the supporting electrode 1 to perform the thermal stimulation current measurement, or it can be placed on the supporting electrode 1 together with the conductive supporting member 15 for heat treatment. Stimulation current measurement may be performed. Further, the toner charge to be measured is not limited to the corona charge, and the Journal charge
of Applied Physics. Vol.
47, No. 10, Oct. Pp. 475, page 4475, p. W. Charging can be performed by contact with a liquid as described by Chudleigh, or triboelectric charging.
In order to apply the charged toner to the support electrode, the electrode may be charged and the charged toner may be applied to the support electrode in the same manner as in the development.

In FIG. 6 showing another example of the measuring electrode, the sample charging electrode 15 having the supporting electrode 1 also serving as a sample filling cell is shown.
And the supporting member 16 and the material filling electrode 15 and the supporting electrode 16 are fitted or fastened with a screw or the like, so that the measurement work can be performed efficiently. In the embodiment shown in FIG. 6, it is possible to prepare a charged sample and attach it to the measuring device only by making the filling state constant without particularly molding the powder. In addition, by charging the charged toner blown off from the two-component developer into the sample filling cell, it becomes possible to measure the charging characteristics more practically. Around the upper electrode 2 is a guard electrode 1
7 is arranged and supported by the quartz support together with the upper electrode, and the signal line 19 is drawn out from the upper electrode.
In this specific example, the measurement unit is immersed in the temperature raising tank 20 to perform the measurement.

The measurement of the thermal stimulation current is performed as follows using the device shown in FIG. First, the temperature raising rate is set as a temperature range from room temperature to a temperature higher than the toner melting point, for example, about 180 ° C., and the temperature raising / heating mechanism 5 raises the temperature at a constant temperature raising rate determined as described above. Then, the current value is read by the ammeter 9, the current signal from the ammeter 9 and the temperature signal from the thermocouple 4 are read by the XY recording device 10, and these data are stored and displayed. Let

As a result, a curve of the thermally stimulated current with respect to the temperature change, that is, the amount of change in charge is obtained, and a wide range of charging characteristics such as the total amount of charge and the amount of charge held (or the amount of charge lost) at a constant temperature are obtained. be able to. Of course, based on the recorded temperature and current value, the total charge amount and the charge amount at each peak can be calculated by integration by the host computer, and can be recorded and displayed.

The toner used in the measuring method of the present invention may be a so-called two-component developer toner consisting of two components, a toner and a carrier, or a one-component toner using the toner alone. In this toner, a binder resin is mixed with a colorant and a compounding agent for toner, for example, a charge control agent, a release agent, and magnetic powder, and the toner particles are manufactured by a pulverization method. It may be any of amorphous particles, spherical particles produced by spray granulation of a solution or melt or granulation in a hot air stream, spherical particles formed by a direct polymerization method, and the like.

According to the measuring method of the present invention, for various toners having different morphologies as described above, quantitative data on the thermal stability of charge traps in the charged toner particles, that is, the amount of charge lost at each temperature, Quantitative data on the amount of storage can be obtained accurately and with good reproducibility.

[0037]

The present invention will be further described in the following examples.

Example 1 As samples of toner for electrophotography, commercially available toners A (toner for AC-6500) and B (D) manufactured by Mita Kogyo Co., Ltd.
C-2556 toner) was used. The weighed toner was placed on an aluminum plate having a diameter of 24 mm and a thickness of about 1 mm, and pressure-molded at room temperature into a disk shape having a thickness of about 1 mm. The aluminum plate was grounded, and the other sample surface was charged for about 2 minutes using a needle electrode corona charger. The surface potential of the charged sample was measured with a non-contact type surface potential meter and found to be -500 volts.

A charged sample was placed on the supporting electrode of the apparatus shown in FIG. 5, the distance between both electrodes was set to 7 mm, and the temperature was raised from room temperature to 170 ° C. at a constant heating rate of 3.5 ° C./min. The current was measured.

For toner A, the sample weight is 162 m
g and 137.3 mg, and for toner B, the sample weights were 81.5 mg and 97.3.
The measurement was performed on two kinds of mg. The results are shown in Fig. 1.

The peak appeared at the same temperature regardless of the filling rate and weight of the sampled toner, and the reproducibility was good. There are two small peaks on the low temperature side and a large peak on the high temperature side in the disappearance of the charge trap due to temperature rise.The small peak on the low temperature side is due to the transition to the rubber state, and the large peak on the high temperature side is high. It is considered to be accompanied by melting of the molecule.

Examples 2 and 3 In order to investigate the influence of pulverization conditions during toner production, as a model, a commercially available toner resin A (styrene-acrylic resin-Example 2) and a commercially available toner resin B (styrene-
The acrylic resin-Example 3) was crushed in a mortar, the crushing time was set to 5 minutes, 10 minutes, and 15 minutes, and the thermal stimulation current was measured in the same manner as in Example 1 except that this powder was used.

The obtained results are shown in FIGS. 2 and 3. Figure 2
In (Example 2), with the increase of the pulverization time, a shift of TSC to the minus side was observed at the lower right side of the low temperature side peak corresponding to the glass transition point (deorientation of dipole in the sample powder). Is recognized as based on). Further, in FIG. 2, it was confirmed that the peak on the high temperature side shifted to the low temperature side as the pulverization time became longer.

On the other hand, in FIG. 3 (Example 3), it is recognized that the TSC increases to the plus side in the right skirt portion of the low temperature side peak corresponding to the glass transition point as the crushing time increases. It is considered that this change in TSC spectrum is caused by the morphology of the sample powder changing with the progress of the pulverization process, resulting in a broader distribution of laps.

Example 4 The following sample was prepared as a model in order to see the influence of toner morphology. That is, toner A (powder), melt cast film of toner A (powder), cast film from a toluene solution of toner A (powder).

Thermal stimulation currents were measured under the same conditions according to Example 1 for these three types of samples. The obtained results are shown in FIG. From these results, even with the same composition, the TSC spectra are remarkably different depending on the morphology, and the thermal retention of the charge trap is also remarkably different.
In the solution method sample, charge traps are easily lost at low temperatures,
It was revealed that the melt sample had the most thermally stable charge trap, followed by the powder sample.

[0047]

According to the present invention, the quantitative data on the thermal stability of the charge traps in the charged toner particles, that is, the quantitative data on the loss and retention of the charge at each temperature can be accurately and accurately reproduced. It can be obtained with good properties, and is useful for investigating the relationship between the composition and physical properties of the toner resin, the toner preparation method and its conditions, and the toner charging characteristics.

In addition, quantitative data on the thermal stability of the charge traps in the charged toner particles, that is, quantitative data on the amount of charge lost and the amount of charge retained at each temperature, are given as the glass transition point and melting point of the toner resin. It also has the advantage that it can be measured in relation to the thermal properties of

[Brief description of drawings]

FIG. 1 is a thermally stimulated current spectrum of toners A and B in Example 1.

FIG. 2 is a thermally stimulated current spectrum of powder A in Example 2 with different pulverization times.

FIG. 3 is a thermally stimulated current spectrum of powder B in Example 3 with different grinding times.

4 is a thermally stimulated current spectrum for each sample in Example 4. FIG.

FIG. 5 is a layout view showing an example of a measuring apparatus used in the present invention.

FIG. 6 is a cross-sectional view showing an example of a measurement sample support electrode.

[Explanation of symbols]

 1 Measurement Sample Supporting Electrode 2 Counter Electrode 3 Electrophotographic Toner Powder Sample 4 Thermocouple 5 Heating and Temperature Raising Mechanism 6 Thermal Control Mechanism 7 Electromagnetic Shield 8 Wiring 9 Ammeter 10 XY Recording Device 11 Y-T Recording Device 12 Host computer 13 Data recording device 14 Electrophotographic toner 15 Sample filling electrode 16 Support member 17 Guard electrode 18 Quartz support 19 Signal line 20 Temperature raising tank

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masajun Matsuda 1-2-2 Tamatsukuri, Chuo-ku, Osaka Mita Industrial Co., Ltd.

Claims (4)

[Claims] 1. A charging of an electrophotographic toner, comprising: placing a charged sample of an electrophotographic toner between opposing electrodes and measuring a thermal stimulating current by changing the temperature of the charged sample while raising the temperature. How to measure characteristics. 2. The measuring method according to claim 1, wherein the electrophotographic toner powder is pressure-molded into a plate shape, charged, and then subjected to the measurement. 3. The method for measuring charging characteristics according to claim 1, wherein the temperature of the charged sample is raised at a constant temperature rising rate, and the distribution of temperature and thermally stimulated current is obtained. 4. A support provided with an electromagnetic shield, a heating and heating mechanism housed in the electromagnetic shield, and a support electrode housed in the heating and heating mechanism and on which a charged sample of electrophotographic toner is placed. A counter electrode housed inside the heating / heating mechanism and provided to face the support electrode and to be spaced apart therefrom;
A thermocouple provided on the support, a current detection mechanism for detecting a current from the counter electrode, and a distribution of temperature and current based on the current signal from the current detection mechanism and the temperature signal from the thermocouple, or An apparatus for measuring the charging characteristics of an electrophotographic toner, which comprises a display recording mechanism for recording.