JP5034549B2 - Method and apparatus for producing toner for electrophotography - Google Patents

Description

  The present invention relates to a method and an apparatus for producing an electrophotographic toner, and more particularly, to a method and an apparatus for producing an electrophotographic toner having a stable softening point.

  In general, an electrophotographic image is formed by developing and visualizing an electrostatic image with toner and transferring the obtained toner image onto a sheet. The toner used for such image formation includes a dry toner and a wet toner, and the dry toner is the mainstream. As a dry toner manufacturing method, there are a pulverization method, a polymerization method, and the like, but in general, the pulverization method dominates.

  The general manufacturing process of toner by the pulverization method is as follows. Raw materials such as a binder resin, a colorant, a release agent, and a charge control agent are mixed in a dry manner, then melt-kneaded with a twin screw extruder or the like, cooled and solidified, and then coarsely pulverized to obtain a kneaded crushed product. After that, fine pulverization is performed with a jet mill or the like, and the particle size is adjusted with a classifier so as to obtain an appropriate particle size distribution. Furthermore, it is surface-treated by mixing with silica etc. with a mixer to obtain a toner.

  In such a toner manufacturing process, the kneading step is an important step in which the toner material is dispersed, and the toner material is required to be highly dispersed. In the kneading step, the binder resin molecules are also cut along with the dispersion of the toner material. Therefore, the kneading conditions greatly affect the softening point of the toner. That is, if the kneading is too strong, the melt viscosity of the toner decreases, and a problem such as a hot offset phenomenon occurs in the fixing process, so it is necessary to set appropriate conditions. Examples of evaluation of the material dispersibility of the toner include observation of pigment dispersion by a TEM (Transmission Electron Microscope), and evaluation of fogging.

  Among the kneading conditions, as the parameters of the kneader, in the case of a twin screw extruder, the kneading zone length (L), cross section (D) and ratio (L / D), and the screw are segmented In such a case, the screw configuration greatly affects the kneading strength. The parameters of the production conditions include the barrel temperature setting for each cylinder of the kneader, the screw rotation speed, and the raw material supply amount.

  However, even if the kneading conditions are optimized, the softening point of the toner may fluctuate in actual mass production operation. One of the causes is a variation in the softening point of the binder resin used. That is, when the softening point of the binder resin is high, the softening point of the toner is high, and when the softening point of the binder resin is low, the softening point of the toner is also low. Usually, the softening point is standardized within a range where the quality of the product can be ensured, but depending on the brand of the toner and the kneading conditions, a toner that does not satisfy the standard may be generated.

  When the softening point of the toner is too high, the glossiness is lowered and the transparency when printed on the OHP sheet is deteriorated, and it becomes difficult to display a good image with an overhead projector. Further, when the softening point of the toner is too low, a hot offset phenomenon occurs. Usually, these are balanced and kneading conditions and toner softening point standards are set. Possible causes of fluctuations in the softening point of the binder resin include raw material lots and fluctuations in manufacturing. In general, the standard range of about 4 to 5 ° C. is allowed at the softening point. .

  As a method of solving the quality instability problem due to lot fluctuation of the binder resin in the kneading process, in order to maintain the power consumption for screw rotation within a certain range, the set temperature of the kneader or the rotation speed of the screw It has been proposed to adjust at least one of the above (see, for example, Patent Document 1).

  Specifically, in the case of a resin having a large viscoelasticity, power consumption for rotating the screw increases, so the barrel temperature is increased or the screw rotation speed is increased. Further, in the case of a resin having low viscoelasticity, power consumption for rotating the screw is reduced, and therefore, adjustment is made to lower the barrel temperature or lower the screw rotation speed. Thereby, for example, an attempt is made to stabilize the dispersion state of carbon black in the toner.

However, the index of the kneading state in the above proposal is the power consumption of the screw rotation speed, which is considered preferable for stabilizing the shearing force and dispersibility of the kneaded product, but for stabilizing the softening point of the toner. A sufficient effect cannot be obtained.
JP 2003-107800 A

  An object of the present invention is to provide a method and an apparatus for producing an electrophotographic toner having a stabilized softening point, which has been made under such circumstances.

In order to solve the above-mentioned problems, the first aspect of the present invention includes a step of mixing and melting and kneading a raw material containing a binder resin and a colorant using a biaxial extrusion kneader , and cooling and solidifying the kneaded product. In the method for producing an electrophotographic toner comprising the steps of pulverizing and classifying, the temperature of the kneaded material at the kneader outlet of the biaxial extrusion kneader is monitored, and the biaxial extrusion kneader according to the temperature of the kneaded material An electrophotographic toner manufacturing method is provided, wherein the temperature of the kneaded product is maintained within a predetermined range by controlling the number of rotations of the screw.

In such a method for producing an electrophotographic toner, polyester can be used as a binder resin .

The second aspect of the present invention includes means for mixing raw materials including a binder resin and a colorant, a twin-screw extrusion kneader for melt-kneading the raw material mixture, and means for pulverizing and classifying the kneaded material after cooling and solidifying. In the electrophotographic toner manufacturing apparatus, the biaxial extrusion kneader is a means for monitoring the temperature of the kneaded material at the outlet, and controls the screw rotation speed of the biaxial extrusion kneader according to the temperature of the kneaded material. There is provided an apparatus for producing an electrophotographic toner, characterized in that the temperature of the kneaded product is maintained within a predetermined range by controlling the screw rotation speed of the biaxial extrusion kneader.

  According to the present invention, an electrophotographic toner having a stabilized softening point can be obtained.

  Embodiments of the present invention will be described below.

  As a result of various studies on the problem that the softening point of the toner fluctuates due to the fluctuation of the softening point of the resin, the inventors have found that the softening point of the binder resin used as a raw material and the temperature of the kneaded material at the kneader outlet are determined. We found that there is a correlation. In addition, from the relationship between the screw rotation speed, the kneaded material temperature at the kneader outlet, and the toner softening point, the temperature of the kneaded material at the kneader outlet is monitored in the kneading step so that it is within a predetermined temperature range. It was found that a toner having a stable toner softening point can be obtained even if the softening point of the resin fluctuates by appropriately adjusting the screw rotation speed. The present invention has been made under such knowledge.

  That is, the temperature of the kneaded material at the kneader outlet is constantly measured by a thermometer installed at the kneader outlet, and if it is below the lower limit of the predetermined range, the screw rotation speed of the kneader is increased to increase the upper limit of the predetermined range. In the case of exceeding, the screw rotation speed of the kneader is decreased, and the temperature of the kneaded product at the kneader outlet is kept within a predetermined range. Thereby, the softening point of the toner can be stabilized.

  Next, a toner manufacturing method according to an embodiment of the present invention based on the above kneading action will be described.

First, materials such as a binder resin, a colorant, a release agent, and a charge control agent are measured, and the measured materials are mixed by a mixer. As a mixing machine, arbitrary things, such as a Henschel mixer, a super mixer, a V-type blender, and a Nauta mixer, can be used.
The mixture is then melt kneaded. For melt kneading, a twin screw extrusion kneader, a single screw extrusion kneader, or the like can be used.

  FIG. 1 is a side view showing a twin-screw extrusion kneader as an example. This twin-screw extrusion kneader includes a feeder 1 to which a raw material mixture is supplied, a cylinder 2 divided into a plurality of zones, and a die 3 from which a melt-kneaded product is discharged. Each zone of the cylinder 2 is heated to a predetermined temperature by a heater (not shown), and in the cylinder 2, two cylindrical shapes are arranged so that their axes are parallel or at a predetermined angle. Screw 4 is arranged. The screw 4 rotates in the same direction or in the opposite direction. The die 3 is provided with a thermometer 5 for measuring the temperature of the kneaded product.

  There are various methods for measuring the temperature of the kneaded material in the die 3, but in order to measure the temperature of the kneaded material more stably, a thermometer 5 as shown in FIG. It is desirable to monitor.

  The toner raw material mixture including the binder resin, the colorant, and the release material supplied from the feeder 1 is introduced into the cylinder 2 and melted by the heat from the heated cylinder 2 in the gap between the screws 4. At the same time, they are mixed by the compression force and shearing force due to the rotation of the screw, moved along the spiral blades of the screw 4 to the side of the die 3, and discharged from the die 3.

  At this time, the rotational speed of the screw 4 is adjusted according to the temperature of the kneaded material detected by the thermometer 5. The adjustment of the rotational speed of the screw 4 can be performed manually, but can also be automatically performed by a controller 6 connected to the thermometer 5 and the motor 7 as shown in FIG. That is, a temperature signal from the thermometer 5 is input to the controller 6, and a signal for controlling the rotational speed is sent from the controller 6 to the motor 7 that drives the screw 4. For example, the temperature of the kneaded material at the kneader outlet is set to 180 ° C. ± 10 ° C., the temperature of the kneaded material in the die 3 is monitored by the thermometer 5, and the number of revolutions of the motor 7 is increased when the temperature of the kneaded material decreases. A signal is sent from the controller 6 to the motor 7, and when the temperature of the kneaded material becomes high, a signal for reducing the rotation speed of the motor 7 is sent from the controller 6 to the motor 7. As a result, the rotation speed of the motor 7, that is, the rotation speed of the screw 4 is controlled so that the temperature of the kneaded material is maintained within the range of 180 ° C. ± 10 ° C.

  The melt-kneaded product discharged from the die 3 is usually cooled, pulverized, and classified to a predetermined particle size according to a method used for toner production to obtain a toner particle matrix. The cooling means, the pulverizing means, and the classification means are not particularly limited, and those usually used for toner production can be employed. For example, a cooling means by rolling or blowing an air flow can be used for cooling, and an airflow pulverizer such as a collision plate pulverizer can be used for pulverization, and various airflow classifiers can be used for classification. Can be used.

  An electrophotographic toner can be obtained by adding an external additive such as silica to the toner particle matrix thus obtained, followed by mixing and stirring.

  According to the toner manufacturing method described above, since the temperature of the kneaded material at the kneader outlet is controlled within a predetermined range, a toner having a stable softening point can be obtained.

  Examples of the present invention and comparative examples are shown below to describe the present invention more specifically.

  In Examples and Comparative Examples, the following resins having different softening points depending on lots were used as binder resins.

Polyester resin A: Lot with softening point 134 ° C., low softening point Polyester resin B: Lot with softening point 140 ° C., high softening point Polyester resin C: Lot with softening point 137 ° C., average softening point Example 1
92 parts by mass of polyester resin A (softening point 134 ° C.) as a binder resin and C.I. 4 parts by weight of I Pigment Red 57: 1, 1 part by weight of “LR-147” (manufactured by Nippon Carlit Co., Ltd .: organoboron compound) as a charge control agent, and “NP056” (Mitsui Chemicals, Inc.) as a release agent 3 parts by mass of polypropylene wax) were mixed using a Henschel mixer (Mitsui Mining Co., Ltd.).

  The mixed powder is melt-kneaded with a twin-screw kneader (screw diameter: 43 mm, L / D = 34), stretched, cooled, and coarsely crushed with a Rotoplex (manufactured by Hosokawa Micron Corporation, 2 mm screen). Using a pulverizer / air classifier, pulverization classification was performed so that the average particle diameter of the toner was 9.0 μm, and fine particles were obtained.

  To 100 parts by mass of the obtained fine particles, 2 parts by mass of “R972” (manufactured by Nippon Aerosil Co., Ltd .: hydrophobic silica) was added as an external additive and mixed with a Henschel mixer to obtain a toner.

  At this time, the kneading conditions were performed at a supply rate of 30 kg / h, and the kneader was operated for about 1 hour. The temperature of the kneaded product at the kneader outlet was monitored, and the screw rotation speed of the kneader was varied as appropriate so that the temperature was in the range of 180 ± 10 ° C. The variable range of the screw rotation speed at that time was 250 to 300 rpm. The obtained toner had a softening point of 125 ° C.

Example 2
A toner was produced in the same manner as in Example 1 except that polyester resin B (softening point 140 ° C.) was used instead of polyester resin A as the binder resin.

  In the kneading process, the temperature of the kneaded product at the kneader exit was monitored, and the screw rotation speed of the kneader was varied as appropriate so that it was in the range of 180 ± 10 ° C. The screw rotation speed at that time was 350-400 rpm. The obtained toner had a softening point of 125 ° C.

Example 3
A toner was produced in the same manner as in Example 1 except that polyester resin C (softening point 137 ° C.) was used instead of polyester resin A as the binder resin.

  In the kneading process, the temperature of the kneaded product at the kneader exit was monitored, and the screw rotation speed of the kneader was varied as appropriate so that it was in the range of 180 ± 10 ° C. The screw rotation speed at that time was 325 rpm. The obtained toner had a softening point of 125 ° C.

Comparative Example 1
A toner was obtained in the same manner as in Example 1 except that the screw rotation speed of the kneader was fixed at 325 rpm in the kneading step. The temperature of the kneaded material at the kneader outlet at this time was 195 ° C. The softening point of the obtained toner was 122 ° C.

Comparative Example 2
A toner was obtained in the same manner as in Example 2 except that the screw rotation speed of the kneader was fixed at 325 rpm in the kneading step. The temperature of the kneaded material at the kneader outlet at this time was 160 ° C. The softening point of the obtained toner was 128 ° C.

Comparative Example 3
A toner was obtained in the same manner as in Example 3 except that the screw rotation speed was fixed at 250 rpm in the kneading step. The temperature of the kneaded material at the kneader outlet at this time was 150 ° C. The resulting toner had a softening point of 129 ° C.

Comparative Example 4
A toner was obtained in the same manner as in Example 3 except that the screw rotation speed was fixed at 400 rpm in the kneading step. The temperature of the kneaded material at the kneader outlet at this time was 195 ° C. The resulting toner had a softening point of 120 ° C.

Kneading conditions A twin-screw extruder (screw diameter 43 mm, L / D = 34) was used, and the kneading temperature was 7 zones C1 to C7 in the screw length direction, adapter and die, C1 was 50 ° C, C2 To C4 were set to 100 ° C, C5 to C7 were set to 130 ° C, and the adapter and the die were set to 150 ° C.

  The following characteristics are evaluated.

Test 1-OHP Permeability Non-magnetic one-component developing device “Casio Page Presto N-5” (manufactured by Casio Computer Co., Ltd .: color printer, 29 sheets per minute (A4 side)) in normal environment (25 After printing a solid print image on OHP paper (dedicated OHP sheet N-OHPS) at 50 ° C. and 50% RH), the obtained image was projected onto a screen with an overhead projector to evaluate color development and transparency. .

Test 2-Fixing characteristics The fixing device is modified so that the temperature of the fixing portion of the developing device similar to that used in Test 1 can be varied. With the fixing tester, the temperature was varied every 10 ° C. within the fixing temperature range of 130 to 200 ° C., printing was performed, and the fixing property was evaluated. The fixing temperature here is the upper set temperature of the two fixing rolls, and the lower fixing roll is set to the upper roll of −20 ° C. The image pattern was solid printing, and the paper was XEROX P paper A4 size (64 g / m ² ).

Measurement of softening point of toner Device: Flow tester (manufactured by Shimadzu Corporation, CFT-500D)
Sample: 1g
Temperature increase rate: 6 ° C./min Load: 30 kg when measuring the softening point of the resin, 20 kg when measuring the softening point of the toner.

Nozzle: 1mm diameter, 1mm length
1/2 method: The temperature at which half of the sample flowed out was taken as the softening point.

  The sample and measurement environment were carefully considered to avoid extreme temperature and humidity.

Toner particle size measurement device: Multisizer II (Coulter Co., Ltd.)
Sample: A small amount of sample, purified water, and a surfactant were placed in a beaker and dispersed with an ultrasonic cleaner.

  Measurement: The aperture was 100 μm, the count was 50,000, and the volume average particle size was obtained.

The above tests and measurements were performed on the toners of Examples 1 to 3 and Comparative Examples 1 to 4. The results are shown in Table 1 below.

  From Table 1 above, the following can be understood. That is, the toners obtained in Examples 1 to 3 in which the screw rotation speed was adjusted so that the temperature of the kneaded product was 180 ± 10 ° C., even if the softening point of the binder resin used changed, All of the characteristics were good.

 On the other hand, the toners obtained in Comparative Examples 1 and 2 in which the screw rotation number remained constant regardless of the temperature of the kneaded product, the softening point changed greatly depending on the softening point of the binder resin used, and the OHP permeability Both the fixing characteristics and the fixing characteristics were poor. Further, the toners obtained in Comparative Examples 3 and 4 are toners experimentally produced in order to find out the relationship between the kneading rotational speed, the kneaded product temperature, and the toner softening point. When the screw rotational speed is low, the temperature of the kneaded product is large. As a result, the softening point of the toner became very high, and when the screw rotation speed was high, the temperature of the kneaded material increased greatly, and the softening point of the toner became very low. Further, both the OHP transmittance and the fixing characteristics were poor.

  Next, the present inventors have investigated the relationship between the screw rotation speed, the kneaded product (kneader exit) temperature and the toner softening point, the binder resin softening point, the kneaded product (kneader exit) temperature, and the toner softening point. And the relationship between the softening point of the binder resin and the temperature of the kneaded product (kneader outlet) and the toner softening point were obtained, and the results shown in FIGS.

  When a binder resin having a softening point of 1.137 ° C. is used and the screw rotation speed is changed, as shown in FIG. 2, the temperature of the kneaded product (kneader outlet) increases as the screw rotation speed increases. The softening point decreases. This is presumably because when the screw rotation speed is increased, the molecular cutting of the resin becomes severe and the kneaded product generates heat.

  2. When the screw rotation speed is kept constant at 325 rpm and the softening point of the binder resin used is changed, as shown in FIG. 3, the temperature of the kneaded product (kneader outlet) decreases as the softening point of the binder resin increases. In addition, the softening point of the toner increases. This is considered that when the softening point of the binder resin is high, the temperature of the kneaded product is low, so that the resin has little molecular cutting, and as a result, the toner softening point is increased.

  3. When the screw rotation speed is changed so that the temperature of the kneaded product (kneader outlet) becomes constant at 180 ° C., as shown in FIG. 4, even if the softening point of the binder resin changes, the softening point of the toner Remains constant.

  As described above, from the results shown in FIGS. 2 to 4, the softening point of the binder resin is changed by changing the screw rotation speed so that the temperature of the kneaded product (kneader outlet) becomes constant at 180 ° C. However, it can be seen that the softening point of the toner can be stabilized.

It is a side view which shows the twin-screw extrusion kneader used for one Embodiment of this invention. FIG. 6 is a characteristic diagram showing the relationship between the screw rotation speed, the temperature of the kneaded product (kneader exit), and the toner softening point. FIG. 6 is a characteristic diagram showing the relationship between the softening point of a binder resin, the temperature of the kneaded product (kneader exit), and the toner softening point. FIG. 6 is a characteristic diagram showing the relationship between the softening point of a binder resin, the temperature of the kneaded product (kneader exit), and the toner softening point.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Feeder, 2 ... Cylinder, 3 ... Die, 4 ... Screw, 5 ... Thermometer, 6 ... Controller, 7 ... Motor.

Claims (3)

In a method for producing an electrophotographic toner comprising a step of mixing and kneading a raw material containing a binder resin and a colorant using a twin-screw extrusion kneader , and a step of cooling and solidifying the kneaded material followed by pulverization and classification by monitoring the temperature of the kneaded material in the kneading machine outlet of the two-axis extrusion kneader, and controls the screw rotation speed of the two-axis extrusion kneader according to the temperature of the kneaded product, the temperature of the kneaded product A method for producing an electrophotographic toner, wherein the toner is maintained within a predetermined range.   The method for producing an electrophotographic toner according to claim 1, wherein the binder resin is polyester. Electrophotographic toner production apparatus comprising means for mixing raw materials containing a binder resin and a colorant, a twin-screw extrusion kneader for melting and kneading the raw material mixture, and means for cooling and solidifying the kneaded material, followed by pulverization and classification in the biaxial extrusion kneader, the means for monitoring the temperature of the kneaded material at the outlet, and in accordance with the temperature of the kneaded product comprising means for controlling the screw rotation speed of the two-axis extrusion kneader, the two-axis extrusion An apparatus for producing an electrophotographic toner, characterized in that the temperature of the kneaded product is maintained within a predetermined range by controlling the number of screw revolutions of the kneader.

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