JP4779763B2 - Method for producing toner for electrophotography - Google Patents

Description

  The present invention relates to a method for producing an electrophotographic toner, and more particularly, to a method for producing an electrophotographic toner having good fog characteristics, image quality, and durability, and a toner produced thereby.

  In general, image formation by electrophotography is performed by developing and visualizing an electrostatic image with charged toner, and transferring and fixing the toner image obtained by development onto a sheet. As a method for producing such a toner used for image formation, there are a pulverization method, a polymerization method, and the like. In general, the pulverization method dominates.

  A general production method of the pulverization method is to mix raw materials such as a binder resin, a colorant, a release agent, and a charge control agent in a dry manner, then melt and knead with a twin-screw extruder or the like, and after cooling and solidifying, Crushing is performed to obtain a kneaded crushed material. 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. Further, the toner is obtained by performing surface treatment by mixing with silica etc. in a mixer.

  In such a pulverized toner manufacturing process, fine powder having a prescribed particle size or less is generated during pulverization classification, but such fine powder has been discarded. Thus, in order to improve the yield of materials and reduce waste, it has been conventionally practiced to reuse fine powder. In this case, the ratio of fine powder having a specified particle size or less is about 10 to 40% by mass of the whole, and it is preferable to return all generated fine powder to the manufacturing process even for the purpose of reuse. However, since the fine powder is an additive-free toner with a small particle size, its powder characteristics are low in bulk density, poor fluidity, and large in specific surface area, so that it has high chargeability and adhesion.

  In addition, during pulverization, the release agent and charge control agent often become the pulverization interface, and the composition of the fine powder contains a lot of the release agent and charge control agent. It is preferable to disperse uniformly during mixing.

  However, as in the past, if the fine powder is returned to the raw material mixture as it is, the flowability of the fine powder is poor, so the mixing strength of the raw material cannot be obtained, or the charge control with high chargeability and adhesion It was difficult to mix the raw materials uniformly, such as causing selective aggregation with the agent and mold release agent.

  Further, as a recent demand for toner, there is a reduction in the particle size of the toner, and the particle size of the generated fine powder tends to be small and the amount of generation tends to increase. By reducing the particle size of the fine powder, the bulk density becomes lower, the chargeability and the adhesive force become higher, and the problem becomes remarkable. Furthermore, an increase in the amount of fine powder returned also hinders uniform raw material mixing.

  In order to eliminate such problems, a method has been proposed in which the fine powder is first mixed in a state where the fine powder is not returned, and then the fine powder is returned and mixed again (for example, see Patent Document 1). However, in this method, since the fine powder is added as it is, when the particle diameter of the fine powder is small and the return amount is large, a sufficient effect cannot be exhibited.

  If the mixing of the raw materials is not uniform, the charging property of the toner particles varies, and the toner moves onto the photosensitive drum of the blank paper printing portion, resulting in a worse white paper fog. In addition, when blank paper printing continues, there is a problem that the toner remaining amount is reduced by fog toner even though toner is not printed. Furthermore, when the release agent is dispersed non-uniformly, particularly in the case of a non-magnetic one component that imparts charge to the toner by friction between the doctor blade and the developing roll, the toner is fused to the blade, and a thin toner layer is formed on the developing roll As a result, a white streak image is generated.

  Another problem when reusing fine powder is that the bulk density of the mixed powder after mixing the raw materials becomes low, causing a feed neck phenomenon in the kneading and supplying step. The feed neck phenomenon is a raw material powder that contains a lot of air with a low bulk density.In the resin melting process, the air is squeezed out and returns to the supply side. It acts to push back. Therefore, the biting of the raw material into the screw is deteriorated, and the amount that can be kneaded by the kneader is reduced.

  Even if the screw rotation speed is increased in order to increase the production amount, a sufficient effect cannot be obtained, and the molecular cutting of the resin becomes remarkable, causing problems such as occurrence of hot offset. By taking measures such as increasing the kneading temperature, the viscosity of the resin decreases and the dispersibility of the material deteriorates.

  In order to solve such problems, methods have been proposed in which fine powder is granulated and then returned to the raw material mixing step (for example, Patent Documents 2 and 3). According to this method, the fine powder is compressed and granulated, so that the bulk density is increased, the supply amount in the kneading process is not reduced, and the fine powder can be reused without causing image deterioration.

  However, the method as described above requires the introduction of a granulator facility, which increases the number of manufacturing steps.

On the other hand, when manufacturing a pigment masterbatch, adding water and kneading | mixing is proposed (for example, refer patent document 4). However, this proposal does not solve the problem that occurs when the fine powder generated in the classification process is returned to the mixing process.
Japanese Patent Laid-Open No. 5-34976 JP-A-6-266157 JP-A-6-266158 JP 2004-191787 A

  The present invention has been made under the circumstances as described above, and reuses fine powder in a simpler method and improves the dispersibility of the material, thereby improving electrophotographic characteristics of fog characteristics, image quality, and durability. It is an object of the present invention to provide a method for producing a toner and a toner produced thereby.

In order to solve the above problems, a first aspect of the present invention includes a step of mixing raw materials including a binder resin, a colorant, a release agent, and a charge control agent, a step of melt-kneading the raw material mixture, and a kneaded product. In a method for producing an electrophotographic toner comprising a step of pulverizing and solidifying after cooling and a step of classifying a pulverized product, 100 parts by mass of the raw material is used to reuse fine powder having a particle size of not more than a specified particle size generated in the classification step. to together be returned to the mixing step so as to be 5 to 35 parts by weight, in the mixing step, the electrophotographic toner, which comprises mixing with the addition of 10 to 50 mass% of water in the amount of fine powder A manufacturing method is provided.

  In such a method for producing an electrophotographic toner, carnauba wax can be used as a release agent.

  The electrophotographic toner produced by the above method desirably has a particle size of 5 to 7 μm.

The second aspect of the present invention provides an electrophotographic toner produced by the above method .

  According to the present invention, when the fine powder is returned to the raw material mixture and reused, by adding water, selective aggregation of the fine powder and the internal additive can be prevented and the dispersibility of the internal additive can be improved. As a result, an electrophotographic toner having good fog characteristics, image quality, and durability can be obtained.

  The best mode for carrying out the invention will be described below.

  The method for producing an electrophotographic toner according to an embodiment of the present invention is characterized in that fine powder having a particle size equal to or smaller than a specified particle size generated in the classification step is returned to the mixing step, and water is added when mixing the raw materials in the mixing step. To do.

  Thus, it is considered that when the fine powder having a particle size of not more than the specified particle size generated in the classification step is returned to the mixing step and the raw materials are mixed, the following effects are produced by adding water.

  That is, the static electricity of the whole raw material powder is neutralized, and the selective aggregation between the fine powder and the charge control agent is alleviated, so that more uniform mixing than in the past occurs. In addition, when the resin is melted in the kneading step, heat absorption occurs due to evaporation of water contained in the raw material, and the dispersibility of the internal additive such as the charge control agent is improved by the function of lowering the resin temperature. Furthermore, neutralization of static electricity obtained by adding water reduces electrostatic repulsion between materials, increases the viscosity of the powder, improves biting into the screw, and improves the raw material to the kneading process. Supply performance is improved.

  As a result of the above action, an electrophotographic toner having good fog characteristics, image quality, and durability can be obtained by adding water during mixing of the raw material containing the returned fine powder.

  In the method for producing an electrophotographic toner according to an embodiment of the present invention, the amount of fine powder having a specified particle size or less generated in the classification step and returned to the mixing step should be 5 to 35 parts by mass with respect to 100 parts by mass of the raw material. I must. When the amount of the fine powder is less than 5 parts by mass, the durability is lowered, and when it exceeds 35 parts by mass, the fog characteristic and the durability are lowered.

  Moreover, the quantity of the water added must be 10-50 mass% of the amount of fine powder. If the amount of water is less than 10% by mass, the fog characteristics and durability deteriorate, and if it exceeds 50% by mass, all of fog characteristics, image quality, and durability decrease.

  The specified particle size of the fine powder returned to the mixing step is usually 5 μm or less.

  The toner manufacturing method according to an embodiment of the present invention is performed as follows.

  First, materials such as a binder resin, a colorant, a release agent, and a charge control agent are measured. At this time, the fine powder amount returned from the classification step described later is determined within a range of 5 to 35 parts by mass with respect to 100 parts by mass of the raw material.

Next, the weighed material and a predetermined amount of fine powder 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.
At the time of mixing, 10-50 mass% of water of the amount of fine powder is added. The addition of water can be performed using, for example, a Henschel mixer 1 as shown in FIG. That is, a separating funnel 2 is attached to the material addition port of the upper lid of the Henschel mixer 1 via the rubber plug 3, and a predetermined amount of distilled water is accommodated in the separating funnel 2. When mixing the raw materials in the Henschel mixer 1, the cock of the separatory funnel 2 is opened and water is added. After mixing, the raw material mixture is discharged from the discharge port 4.

  Thereafter, the raw material mixture is melt-kneaded. Although it does not specifically limit as a kneader, For example, a biaxial kneader, an open roll type kneader, etc. can be used. As an open roll type kneader, an arbitrary type such as a continuous two-roll mill, a continuous three-roll mill, and a batch-type roll mill can be used. In such melt-kneading, since the raw material mixture supplied to the kneader has little segregation, each component is uniformly and finely dispersed.

  The melt-kneaded material kneaded and discharged by a kneader is usually cooled, pulverized, and classified into a predetermined particle size according to a method used for producing a toner 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.

  As described above, since the toner obtained by the method for producing an electrophotographic toner according to the embodiment of the present invention is mixed with the raw material when the fine powder returned from the classification step is mixed with water, mixing is performed. It is performed uniformly, and when kneading, the resin temperature is lowered by the endothermic action of water evaporation, and the dispersibility of the additive is improved, so that a toner having good fog characteristics, image quality, and durability can be obtained. it can.

  FIG. 2 shows an image forming apparatus for forming an image using the electrophotographic toner of the present invention described above.

  The image forming apparatus shown in FIG. 2 includes a developing device 11 and a photosensitive drum 12. The developing device 11 applies a toner hopper 13 that contains toner therein, a supply roll 14 that supplies toner, and toner supplied from the supply roll 14 to the photosensitive drum 12, and electrostatic latent on the surface of the photosensitive drum 12. A developing roll 15 made of an elastic body for developing an image, and a doctor blade 16 that is in sliding contact with the developing roll 15 and regulates the thickness of the toner layer on the surface of the developing roll 15 are provided. Around the photosensitive drum 12, there are a charging roll 17 for uniformly charging the surface of the photosensitive drum 12, and an LED 18 for exposing a document image to the charged surface of the photosensitive drum 12 to form an electrostatic latent image. Has been placed.

  A transfer belt 19 runs along with the rotation of the photoconductive drum 12 below the photoconductive drum 12. The developed toner image is transferred onto the paper 21 by contacting the photoconductive drum 12 by the transfer sheet 20. The The toner that has not been transferred and remains on the surface of the photosensitive drum 12 even after the transfer is removed by the cleaning blade 22.

  Even if the toner according to the present embodiment described above is mounted on the image forming apparatus configured as described above and the elastic developing roll is transported at a high speed of 100 mm / second or more, fog caused by aggregation of external additives occurs. Properties, image quality, and durability are good, and no fusion on the doctor blade occurs.

  Even if the fixing device of the image forming apparatus does not have an oil supply mechanism, fixing can be performed without any problem.

  Hereinafter, the present invention will be described in more detail with reference to reference examples, examples, and comparative examples.

  First, raw material mixing conditions, water addition conditions, external additive mixing conditions, kneading conditions, softening points, glass transition points, and particle diameter measuring methods in the following Examples and Comparative Examples will be described.

1. Raw material mixing conditions The raw materials are mixed using a Henschel mixer 1 as shown in FIG. 1, and the input amount is adjusted to be in the range of 70 to 80% with respect to the volume of the Henschel mixer 1. As a stirring blade, a standard blade is attached and rotated at a peripheral speed of 20 m / sec.

2. Water Addition Conditions Distilled water is weighed in advance into a separating funnel 2 attached via a rubber stopper 3 to the material addition port of the upper lid of the Henschel mixer 1 shown in FIG. 10 seconds after the start of stirring of the raw material stored in the Henschel mixer 1, the cock of the separatory funnel 2 is opened to start the addition of water, and the addition of the necessary amount is completed within 30 seconds.

3. External additive mixing conditions The external additive is mixed using a Henschel mixer. The input amount is adjusted to be in the range of 70 to 80% with respect to the volume of the Henschel mixer. The stirring blade is equipped with a strong stirring blade and is rotated at a peripheral speed of 40 m / sec.

4). Kneading conditions A twin screw extruder (screw diameter 43 mm, L / D = 34) is used. The kneading temperature is set to 70 ° C. for the 4 zones on the supply side and 100 ° C. for the 4 zones on the discharge side among the 8 zones divided in the screw length direction. The supply rate is 25 kg / h.

5. Measurement of softening point Apparatus: Flow tester (CFT-500D: manufactured by Shimadzu Corporation)
Sample: 1g
Temperature increase rate: 6 ° C / min Load: 20kg
Nozzle: 1mm diameter, 1mm length
1/2 method: The temperature at which half of the sample flows out is taken as the softening point.

6). Measurement of glass transition point (Tg) Device: differential scanning calorimeter (DSC-60: manufactured by Shimadzu Corporation)
Sample: 8mg
Temperature raising conditions: The temperature is raised to 160 ° C. at 10 ° C./min, cooled to 35 ° C. at a temperature lowering rate of 10 ° C./min, and then raised again to 160 ° C. at 10 ° C./min.

  At the time of the second temperature increase, the intersection of two tangents of the curve portion obtained by the transition is defined as the glass transition point.

7). Particle size measurement device: Multisizer II (Coulter)
Sample: Place a small amount of sample, purified water, and surfactant in a beaker and disperse with an ultrasonic cleaner.

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

Reference example (no fine powder reuse)
As a binder resin, 90 parts by mass of a polyester resin (softening point: 120 ° C., Tg: 67 ° C.) and a colorant: I. 5 parts by weight of Pigment Red 122, 4 parts by weight of Carnauba Wax No. 1 powder (Yoyuki Kato) as a release agent, 1 part by weight of E-84 (Orient Chemical Co., Ltd.) as a charge control agent, Henschel mixer (Mitsui (Mine Co., Ltd., equipped with standard wings) and mixed with stirring for 3 minutes.

 The obtained mixed powder is melt-kneaded with a twin screw extruder, stretched, cooled, coarsely pulverized with a Rotoplex (manufactured by Hosokawa Micron Co., Ltd., 2 mm screen), and then averaged with a collision pulverizer / air classifier. The fine particles were obtained by pulverization and classification so that the particle diameter was 6.0 μm. As an external additive, 2 parts by weight of “RY200” (hydrophobic silica: manufactured by Nippon Aerosil Co., Ltd.) is added to 100 parts by weight of the obtained fine particles, and the mixture is stirred for 3 minutes with a Henschel mixer (manufactured by Mitsui Mining Co., Ltd., equipped with stirring reinforcing blades). The toner was obtained by mixing. In addition, the fine powder below a regulation particle size was obtained at the classification process. The average particle size of the obtained fine powder was 3.5 μm.

Example 1
25 parts by weight of the fine powder obtained in the reference example was added to the binder resin, colorant, release agent, and charge control agent, and 5 parts by weight of water was added from the top of the mixer when mixing the raw materials. Thus, a toner was obtained in the same manner as in Reference Example 1.

Comparative Example 1
A toner was obtained in the same manner as in Example 1 except that water was not added when mixing the raw materials.

Comparative Example 2
The fine powder obtained in Reference Example 1 was granulated with a dry roll compactor (Freund Sangyo Co., Ltd., TF-208) to obtain granulated fine powder.

The screw feeder rotation speed was adjusted so that the roll diameter was 200 mm, the roll width was 80 mm, the roll pressure was 20 MPa, the roll rotation speed was 20 rpm, and the supply amount was 120 kg / h. In the granulator, a 2 mm opening was used for the screen. The bulk density of the fine powder before granulation was 0.25 g / cm ³ , and the bulk density of the fine powder after granulation was 0.53 g / cm ³ . A toner was obtained in the same manner as in Comparative Example 1 except that the fine powder was changed to the granulated fine powder.

Example 2
A toner was obtained in the same manner as in Example 1 except that the amount of fine powder was 5 parts by mass and water was 1 part by mass.

Example 3
A toner was obtained in the same manner as in Example 1 except that the amount of fine powder was 35 parts by mass and water was 7 parts by mass.

Comparative Example 3
A toner was obtained in the same manner as in Example 1 except that the amount of fine powder was 2 parts by mass.

Comparative Example 4
A toner was obtained in the same manner as in Example 1 except that the amount of fine powder was 40 parts by mass and water was 8 parts by mass.

Comparative Example 5
A toner was obtained in the same manner as in Example 1 except that the amount of fine powder was 25 parts by mass and water was 15 parts by mass.

Comparative Example 6
A toner was obtained in the same manner as in Example 1 except that the amount of fine powder was 25 parts by mass and water was 2 parts by mass.

  The toner samples obtained in the above Reference Examples, Examples and Comparative Examples were subjected to the following tests and evaluated for characteristics.

Test 1-fogging Non-magnetic one-component developing device "Casio Page Presto N-5" (Casio Computer Co., Ltd .: color printer 29 sheets per minute (A4 horizontal) machine, process speed 129 mm / sec) mounted with toner in normal environment At 25 ° C and 50% RH, after printing 10,000 sheets of 5% print images continuously using plain paper (XEROX-P paper A4 size), white paper is printed and the front door is being printed. Then, the printing was forcibly terminated, the fog toner on the OPC drum at that time was copied onto a mending tape, visually compared, and evaluated according to the following criteria.

◎: Less fog than the reference example ○: Equivalent to the reference example ×: Test with more fog than the reference example 2-High image quality Normal in normal environment (25 ° C, 50% RH) using the equipment used in test 1 After continuous printing of 10,000 5% print images using paper (XEROX-P paper A4 size), halftone images and solid images were printed, and the uniformity of the images was evaluated according to the following criteria.

◎: Better than the reference example ○: Equivalent to the reference example ×: Test less uniform than the reference example 3—Durability 5% printed image in the normal environment (25 ° C., 50% RH) using the same equipment as test 1. 14,000 sheets were continuously printed. In the middle, solid images and halftone images were printed every 2,000 sheets, and the number of white lines generated by blade fusion was evaluated.

◎: Not generated up to 14,000 sheets ○: Generated after 12,000 sheets ×: Generated with less than 12,000 sheets Test 4-kneading supply performance In the kneading process, the raw material supply amount was changed from 25 kg / h to 45 kg / h. The feed rate was gradually increased to 5 kg / h until the feed neck phenomenon was observed.

  A: Good if there is a supply amount of 40 kg / h or more, and ○ 30 kg / h or more is acceptable. When it is 25 kg / h or less, the productivity is not sufficient.

The above test results are shown in the following table.

  From the above table, the following can be understood. That is, in Examples 1 to 3, by adding a predetermined amount of fine powder returned from the classification step and a predetermined amount of water during raw material mixing, kneading can be performed while maintaining sufficient kneading supply performance, A toner with good fog, high image quality, and durability could be obtained.

  On the other hand, in Comparative Example 1 in which water was not added, fogging, durability, and kneading supply performance were inferior, and in Comparative Example 2 in which fine powder was granulated instead of adding water, durability was inferior. Moreover, in Comparative Example 3 with a small amount of fine powder to be mixed, durability was inferior, and in Comparative Example 4 in which there was too much, fogging, durability, and kneading supply performance were inferior. Furthermore, in Comparative Example 5 in which the amount of water is too large, fog, image quality, and durability are inferior. In Comparative Example 6, in which the amount of water is small, fog and durability are inferior, and the kneading supply performance is inferior. .

The figure which shows the Henschel mixer provided with the separating funnel which adds water used for one Embodiment of this invention. 1 is a diagram schematically illustrating an image forming apparatus using toner according to an embodiment of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Henschel mixer, 2 ... Separation funnel, 3 ... Rubber stopper, 4 ... Discharge port, 11 ... Developing device, 12 ... Photoconductor drum, 13 ... Toner hopper, 14 ... Supply roll, 15 ... Developing roll, 16 ... Doctor Blade 17, charging roll 18 LED 19 transfer belt 20 transfer sheet 21 paper 22 cleaning blade

Claims (4)

Mixing raw materials including a binder resin, a colorant, a release agent, and a charge control agent;
A step of melt-kneading the raw material mixture,
In the method for producing an electrophotographic toner comprising the steps of cooling and solidifying the kneaded product and then pulverizing, and classifying the pulverized product,
In order to reuse the fines following provisions particle size generated in the classifying step, the to return to the mixing step so as to be 5 to 35 parts by mass with respect to the raw material 100 parts by weight, 10 in the mixing step, the amount of fine powder A method for producing an electrophotographic toner, comprising adding and mixing ˜50 mass% water.   The toner production method according to claim 1, wherein the release agent is carnauba wax.   The toner production method according to claim 1, wherein the toner has a particle size of 5 to 7 μm.   An electrophotographic toner produced by the toner production method according to claim 1.

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