JP5109760B2 - 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.

  Electrophotographic image formation is generally performed by developing and visualizing an electrostatic charge image with toner and transferring the toner image obtained by development 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.

  A general method for producing toner by the pulverization method is as follows. First, 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, etc., cooled and solidified, and then coarsely pulverized to obtain a kneaded crushed product . Thereafter, 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 this manufacturing process, the kneading step is an important step in which the toner material is uniformly dispersed, and high dispersion is required. In particular, in the case of a color toner, the dispersion of the pigment used as the colorant is important. If the dispersion is poor, the color developability at the time of imaging is inferior or the transparency is deteriorated.

  The stronger the kneading strength, the better the dispersion of the pigment. However, in the kneading process, the main resin molecules are broken together with the toner material, so the kneading conditions affect the softening point of the toner. If the kneading is too strong, the melt viscosity of the toner is lowered and a hot offset phenomenon occurs in fixing as a problem. Therefore, it is necessary to set appropriate conditions.

  As a method for evaluating the pigment dispersibility of the toner, there is a method of observing the pigment dispersion with a transmission electron microscope (TEM). However, the evaluation takes time and is expensive. Practically, toner is printed and imaged for evaluation.

  Evaluation at the time of imaging is performed as follows. The color developability is evaluated by measuring the chromaticity (CIEL * a * b *) with a spectrophotometer or the like and judging the difference from the reference chromaticity. Transparency is evaluated by printing a solid image on an OHP sheet and measuring the transmittance. In particular, it is difficult to disperse pigments in color toners, and the color difference changes greatly with changes in kneading conditions. For example, when the dispersion of yellow toner deteriorates, the value of b * measured with a spectrophotometer decreases. In the L * a * b * color system, when b * is low, the color is dull yellow.

  Among the kneading conditions, as the parameters of the kneading machine, 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. The screw configuration greatly affects the kneading strength. The parameters of the production conditions include the set temperature of the barrel for each cylinder of the kneader, the number of rotations of the screw, and the supply amount of the raw material. Of these, the screw rotation speed is a condition that can be easily fine-tuned during operation.

  However, even if the above-mentioned mixed line conditions are optimized, the toner softening point and pigment dispersion may fluctuate in actual mass production operation. One of the causes is fluctuation of the softening point of the binder resin. When the softening point of the binder resin used is high, the softening point of the toner is high and the dispersibility of the pigment is deteriorated.

  When the softening point of the binder resin is low, the softening point of the toner is low and the dispersion of the pigment is good. Usually, the softening point and chromaticity are standardized within a range in which the quality of the product can be ensured. However, depending on the toner brand and kneading conditions, there may be cases where the standard is not satisfied. When the softening point of the binder resin is too high, the glossiness is lowered and the transparency when printed on the OHP sheet is deteriorated, and a good image is not displayed on the overhead projector. Further, when the softening point of the binder resin is too low, a hot offset phenomenon occurs. Usually, these are balanced, and kneading conditions and toner softening point specifications are set.

  Possible causes of fluctuations in the softening point of the binder resin include fluctuations in raw material lots and manufacturing processes. In general, the standard range of 4 ° C or 5 ° C is allowed for softening points. It is.

  In order to solve the problem of quality instability due to the lot variation of the binder resin in the kneading process, at least the temperature setting of the kneading machine or the number of rotations of the screw is required to maintain the power consumption for rotating the screw within a certain range. A method of adjusting one has been proposed (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. In the case of a resin having low viscoelasticity, the power consumption for rotating the screw is small, and therefore, the barrel temperature is lowered or the screw rotational speed is lowered.

Thereby, for example, attempts have been 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 to be effective in stabilizing the shearing force and dispersibility of the kneaded material, but the softening point of the toner varies. As a countermeasure to change the dispersion of the pigment and the pigment, a sufficient effect cannot be obtained.
JP 2003-107800 A

  The present invention has been made under the circumstances as described above, and an object of the present invention is to provide a method and an apparatus for producing an electrophotographic toner having a stable softening point.

  In order to solve the above-mentioned problems, the first aspect of the present invention includes a step of mixing a toner raw material containing a binder resin and a colorant, and a raw material mixture obtained in the mixing step is melted by a kneader capable of continuous kneading. A kneading step, a step of cooling and solidifying the melt-kneaded product, and a step of pulverizing and classifying the cooled and solidified kneaded product, and monitoring the chromaticity of the cooled and solidified kneaded product. There is provided a method for producing an electrophotographic toner, characterized in that the chromaticity of the kneaded product is maintained within a predetermined range by controlling the screw rotation speed of the kneader according to chromaticity.

  In such a method for producing an electrophotographic toner, polyester can be used as a binder resin. A twin screw extruder can be used as a kneader for melt kneading the raw material mixture.

According to a second aspect of the present invention, there is provided means for mixing a toner raw material containing a binder resin and a colorant, a kneader for continuously melting and kneading the raw material mixture, a means for cooling and solidifying the molten kneaded product, the cooling In the electrophotographic toner manufacturing apparatus having means for pulverizing and classifying the solidified kneaded material, the kneader is adapted to monitor the chromaticity of the cooled and solidified kneaded material, and to the chromaticity of the kneaded material. And a means for controlling the rotational speed of the screw of the kneading machine, and a toner manufacturing apparatus characterized by maintaining the chromaticity of the kneaded material within a predetermined range by controlling the rotational speed of the screw of the kneading machine. To do.

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

  Hereinafter, embodiments of the present invention will be described.

  The inventors of the present invention have studied the phenomenon in which the softening point of the toner and the pigment dispersion fluctuate due to the fluctuation of the softening point of the binder resin. As a result, the softening point of the binder resin used as the raw material and the kneading outlet of the kneader It was found that there is a correlation between the chromaticity of the cooled and solidified kneaded product.

  Furthermore, the present inventors have found that the kneaded material cooled and solidified at the kneader outlet from the relationship between the screw rotation speed of the kneader, the chromaticity of the cooled and solidified kneaded material at the kneader outlet, and the chromaticity when imaged. It is found that a toner with stable pigment dispersion can be obtained even when the softening point of the binder resin is changed by continuously changing the screw rotation speed so that the chromaticity is constant. It was.

  The present invention has been made based on such findings.

  An electrophotographic toner manufacturing method according to an embodiment of the present invention is a method of measuring the chromaticity of a cooled and solidified kneaded product in a kneading of a raw material mixture by an extruder capable of continuous kneading, and kneading machine according to the measured value The chromaticity of the kneaded material is controlled to be constant by changing the number of rotations of the screw.

  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. Usable binder resins can be selected from a wide range including known ones. Specifically, a polyester resin is preferable.

  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 diagram showing an example of a kneader used in a method for producing an electrophotographic toner according to an embodiment of the present invention. The kneading machine shown in FIG. 1 is a twin-screw extrusion kneading machine, in which a screw 1 is disposed in a barrel 2 and is driven by a motor 3. The toner raw material supplied from the feeder 4 is melt-kneaded by the screw 1 driven by the motor 3 and discharged through the die 5.

  The kneaded material 6 discharged through the die 5 is cooled and rolled by the cooling roll 7, sent to the conveyor 8, and transported to the next process. At that time, the chromaticity of the kneaded product 6 is measured by the chromaticity sensor 9 installed above the conveyor 8.

  As the chromaticity sensor 9 for measuring chromaticity, various color meters commercially available from various companies can be used, and for example, X-Rite 938 (manufactured by X-Rite Co., Ltd.) can be used.

  The melt-kneaded product whose chromaticity is measured is usually pulverized and classified according to a method used for producing a toner to obtain a toner particle matrix having a predetermined average particle diameter. The pulverizing means and the classifying 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 is obtained by adding silica as an external additive to the toner particle matrix thus obtained, and mixing and stirring.

  EXAMPLES Hereinafter, the Example and comparative example of this invention are shown and this invention is demonstrated in detail.

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

Polyester resin A: Lot with softening point 134 ° C. and low softening point Polyester resin B: Lot with softening point 140 ° C. and high softening point Polyester resin C: Lot with softening point 137 ° C. and average softening point

Example 1
93 parts by mass of polyester resin A (softening point 134 ° C.) as a binder resin and C.I. 3 parts by weight of I Pigment Yellow 185, 1 part by weight of “LR-147” (manufactured by Nippon Carlit Co., Ltd .: organoboron compound) as a charge control agent, and “NPO56” (manufactured by Mitsui Chemicals, Inc.) as a release agent : Polypropylene wax) 3 parts by mass was mixed using a Henschel mixer (Mitsui Mine Co., Ltd.).

  Next, the mixed powder was melt-kneaded with a twin-screw kneader (screw diameter 43 mm, L / D = 34), stretched and cooled, and coarsely crushed with a Rotoplex (2 mm screen manufactured by Hosokawa Micron Corporation). Using a collision 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.

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

  In the above toner production process, the kneading was performed using a twin screw extruder (screw diameter: 43 mm, L / D = 34). The kneading temperature setting of the twin screw extruder has seven zones from C1 to C7 in the screw length direction, adapter and die, C1 is 50 ° C, C2 to C4 is 100 ° C, C5 to C7 is 130 ° C, adapter The die was set at 150 ° C.

  The kneading by such a twin-screw extruder was performed at a supply rate of 30 kg / h for about 1 hour.

  The chromaticity b * of the kneaded product cooled and solidified at the kneader outlet was monitored, and the screw rotation speed of the kneader was varied as appropriate so that b * was 96. The variable range of the screw rotation speed at that time was 250 to 300 rpm.

  As a result, the softening point of the obtained toner was 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 step, the chromaticity b * of the kneaded product cooled and solidified at the kneader outlet was monitored, and the screw rotation speed of the kneader was varied as appropriate so that b * was 96. 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 step, the chromaticity b * of the kneaded product cooled and solidified at the kneader outlet was monitored, and the screw rotation speed of the kneader was varied as appropriate so that b * was 96. 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 was fixed at 325 rpm in the kneading step. The chromaticity b * of the kneaded product cooled and solidified at the kneader outlet at this time was 105. 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 was fixed at 325 rpm in the kneading step. The chromaticity b * of the kneaded product cooled and solidified at the kneading outlet at this time was 90. The softening point of the obtained toner was 128 ° C.

  The toners according to Comparative Examples 1 and 2 described above are toners according to a conventional manufacturing method manufactured by fixing manufacturing conditions with respect to softening points of different resins.

Reference example 1
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 chromaticity b * of the kneaded product cooled and solidified at the kneading outlet at this time was 90. The resulting toner had a softening point of 129 ° C.

Reference example 2
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 chromaticity b * of the kneaded product cooled and solidified at the kneading outlet at this time was 105. The resulting toner had a softening point of 120 ° C.

Reference Example 3
A toner was obtained in the same manner as in Example 1 except that the screw rotation speed was fixed at 400 rpm in the kneading step. The chromaticity b * of the kneaded product cooled and solidified at the kneading outlet at this time was 114. The softening point of the obtained toner was 117 ° C.

Reference example 4
A toner was obtained in the same manner as in Example 1 except that the screw rotation speed was fixed at 250 rpm in the kneading step. The chromaticity b * of the kneaded product cooled and solidified at the kneading outlet at this time was 84. The softening point of the obtained toner was 131 ° C.

  The toners according to the above Reference Examples 1 to 4 are toners that were prototyped to find out the relationship between the kneading rotation speed, the kneaded material chromaticity, and the toner softening point.

  The toner obtained in each of the above examples was subjected to the following tests to evaluate the characteristics.

Test 1—Color difference A 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) machine) is mounted with toner, and the normal environment (25 ° C., 50% RH), a solid image is printed on XEROXP paper A4, and L *, a *, and b * are measured using a spectrocolorimetric densitometer (X-Rite 938) manufactured by X-Rite.

  The measurement conditions were a D65 light source, a viewing angle of 2 degrees, and a measurement diameter of 4 mm.

  The color difference ΔE was determined from the following equation using L *, a *, and b * for the toner obtained in Example 3 as reference chromaticities.

Color difference ΔE = √ [{(reference L *) − (measurement L *)} ² + {(reference a *) one (measurement a *)} ² + {(reference b *) one (measurement b *)} ² ]
○: ΔE is less than 3 ×: ΔE is 3 or more Test 2-OHP permeability The toner is mounted on the same device as in Test 1, and OHP paper (dedicated OHP sheet N-) is used in a normal environment (25 ° C., 50% RH). After printing a solid print image using OHPS), the obtained image was projected onto a screen with an overhead projector, and the color development and transparency were evaluated.

Test 3-Fixing characteristic The fixing device is modified so that the temperature of the fixing part of the same apparatus as in Test 1 can be varied.

  With this fixing tester, the temperature was changed every 10 ° C. within a fixing temperature range of 130 to 200 ° C., printing was performed, and the fixing property was evaluated. Here, the fixing temperature is the set temperature of the fixing roll above the two fixing rolls, and the setting temperature of the lower fixing roll is the upper roll of −20 ° C.

The image pattern was solid printing, and the paper was XEROXP A4 size (mass 64 g / m ² ).

Test 4-Softening point The softening point was measured under the following conditions.

Apparatus: Flow tester (manufactured by Shimadzu Corporation, CFT-500D)
Sample: 1g
Temperature increase rate: 6 ° C./min Load: 30 kg for resin measurement and 20 kg for toner measurement.

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

  In the measurement, sufficient consideration was given to avoid extreme temperature and humidity in the sample and measurement environment.

Test 5-Measurement of particle size Apparatus: Multisizer II (manufactured by Coulter, Inc.) was used.

  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.

Test 6—Chromaticity Measurement of Kneaded Product Measuring instrument: X-Rite 938 (manufactured by X-Rite Co., Ltd.) was used.

  Measurement conditions: D65 light source, viewing angle 2 °, measurement diameter 4 mm.

The results of evaluation of the above characteristics are shown in Table 1 below.

  From Table 1 above, the toners obtained in Examples 1 to 3 were able to maintain the softening point of the toner at the same level even though the softening points of the resin were different. Further, the chromaticity b * of the kneaded product is also maintained at the same level, which indicates that the dispersibility is good. As a result, it was possible to obtain a toner with little variation in color difference and good OHP transmittance and fixing characteristics.

  On the other hand, in the toners obtained in Comparative Examples 1 and 2 and Reference Examples 1 to 4, the softening point of the toner fluctuated when the softening point of the resin was different. Further, the chromaticity b * of the kneaded product also fluctuates, indicating that the dispersibility is poor. As a result, the color difference was large, and the OHP transmission was cloudy due to insufficient toner melting and hot offset. Also, the fixing characteristics were hot offset or cold offset.

  Next, the inventors have determined the relationship between the screw rotation speed and the chromaticity b * of the kneaded product and the toner softening point, the relationship between the softening point of the binder resin and the chromaticity b * of the kneaded product and the toner softening point, Relationship between softening point of binder resin and chromaticity b * of kneaded material and toner softening point, relationship between screw rotation speed and chromaticity b * of kneaded material and resin softening point, screw rotation speed and toner softening point and resin Experiments for determining the relationship with the softening point were performed, and results as 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 chromaticity b * of the kneaded material increases with an increase in the screw rotation speed, and the toner softens. The point goes down. This is presumably because increasing the screw rotation speed improves the dispersibility of the pigment, but severely cuts the resin molecules.

  2. When the screw rotation speed is kept constant at 325 rpm and the softening point of the binder resin to be used is changed, as shown in FIG. 3, the chromaticity b * of the kneaded material decreases as the softening point of the binder resin increases. The softening point of the toner increases. This is considered to be because when the softening point of the binder resin is high, the resin has few molecular breaks, and as a result, the toner softening point is increased.

  3. When the screw rotational speed is changed so that the chromaticity b * of the kneaded product becomes 96, as shown in FIG. 4, even if the softening point of the binder resin changes, the softening point of the toner is stable. .

  4). As shown in FIG. 5, when the softening point of the binder resin is shaken by 3 points (134 ° C., 137 ° C., 140 ° C.) and the screw rotation speed is varied, the kneaded product chromaticity b * increases as the screw rotation speed increases. Rises. This is presumably because increasing the screw rotation speed improves the dispersibility of the pigment, but severely cuts the resin molecules. Therefore, even with binder resins having different softening points, the optimum value of the chromaticity b * of the kneaded product can be found by making the screw rotation speed variable.

  5). When the softening point of the binder resin is swung by 3 points (134 ° C., 137 ° C., 140 ° C.) and the screw rotation speed is made variable, the toner softening point decreases as the screw rotation speed increases. This is considered to be because when the screw rotation speed is increased, the dispersibility of the pigment is improved, but the molecular cutting of the resin becomes severe. Therefore, the optimum value of the toner softening point can be found by making the screw rotational speed variable even at different resin softening points.

  As described above, from the results shown in FIGS. 2 to 6, even if the softening point of the binder resin is changed by changing the screw rotation speed so that the chromaticity b * of the kneaded material becomes constant, It can be seen that the softening point can be stabilized.

It is a side view which shows the twin-screw extrusion kneader used for one Embodiment of this invention. It is a characteristic view showing the relationship between the screw rotation speed, the chromaticity b * of the kneaded material, and the toner softening point. FIG. 6 is a characteristic diagram showing the relationship between the softening point of a binder resin, the chromaticity b * of the kneaded product, and the toner softening point. FIG. 6 is a characteristic diagram showing the relationship between the softening point of a binder resin, the chromaticity b * of the kneaded product, and the toner softening point. It is a characteristic view which shows the relationship between screw rotation speed, chromaticity b * of a kneaded material, and resin softening point. FIG. 5 is a characteristic diagram showing the relationship between screw rotation speed, toner softening point, and resin softening point.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Screw, 2 ... Barrel, 3 ... Motor, 4 ... Feeder, 5 ... Die, 6 ... Kneaded material, 7 ... Cooling roll, 8 ... Conveyor, 9 ... Chromaticity sensor.

Claims (5)

A step of mixing a toner raw material containing a binder resin and a colorant;
A step of melt kneading the raw material mixture obtained in the mixing step with a kneader capable of continuous kneading,
A step of cooling and solidifying the melt-kneaded product, and a step of pulverizing and classifying the cooled and solidified kneaded product,
Maintaining the chromaticity of the kneaded product within a predetermined range by monitoring the chromaticity of the cooled and solidified kneaded product and controlling the screw rotation speed of the kneader according to the chromaticity of the kneaded product. A method for producing an electrophotographic toner, comprising:   The method for producing an electrophotographic toner according to claim 1, wherein the binder resin is polyester.   2. The method for producing an electrophotographic toner according to claim 1, wherein the kneading machine is a twin screw extruder. Means for mixing a toner material containing a binder resin and a colorant;
A kneader for continuously melting and kneading the raw material mixture,
Means for cooling and solidifying the melt-kneaded product,
In the electrophotographic toner production apparatus comprising means for pulverizing and classifying the cooled and solidified kneaded product,
The kneader comprises a means for monitoring the chromaticity of the cooled and solidified kneaded material, and a means for controlling the screw rotation speed of the kneading machine according to the chromaticity of the kneaded material. A toner manufacturing apparatus that maintains the chromaticity of the kneaded material within a predetermined range by control. The electrophotographic toner manufacturing apparatus according to claim 4 , wherein the kneading machine is a twin screw extruder.

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