JP2007093882A - Method for manufacturing electrophotographic toner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing electrophotographic toner that can prevent white stripes or fog in an image by effectively decreasing ultrafine powder. <P>SOLUTION: The method includes steps of mixing and kneading a binder resin, a colorant and a charge control agent, pulverizing the kneaded material from the kneading step, classifying a fine powder material from the pulverizing step, intensively stirring a fine powder material from the classifying step to embed an ultrafine powder material included in the fine powder material into mother particles of the fine powder material, and adding an external additive to the fine particles from the intensive stirring step, wherein an ultrafine powder material in a size of 2 μm or less is decreased by 5% or more in the intensive stirring step. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing an electrophotographic toner, and more particularly, to a method for producing an electrophotographic toner in which the amount of ultrafine powder is reduced.

  In general, an electrophotographic toner is produced by melt-kneading, pulverizing, and classifying a raw material mixture containing a colorant, a binder resin, a charge control agent, and a release agent. The so-called pulverized toner obtained by such a manufacturing method contains an ultrafine powder having a very small particle diameter.

  On the other hand, in response to customer demands such as high image quality and low consumption in recent years, it is an important factor in toner development to reduce the toner particle size. In the pulverized toner obtained by using a jet stream for pulverization as the particle size of the toner advances, the control of the ultra fine powder having a particle diameter of 2 μm or less, which is not expected by the designer, is mixed in the toner base particles. Become important. When the ratio of the ultrafine powder is large, in the non-magnetic one-component toner, a thin layer formation failure or the like due to toner aggregation occurs, and the image is likely to appear as white streaks and fogging.

  In order to solve such a problem, a method of removing ultrafine powder by classifying with an air stream has been proposed (see, for example, Patent Document 1), but this method requires a dedicated device, and There is a problem that the apparatus is complicated.

In addition, there is a method of premixing using a mixer for adding external additives (see, for example, Patent Document 2), but this method is not intended to remove ultrafine powder, and toner aggregates. In addition, since the rotational speed of the mixer is low, there is no effect in removing ultrafine powder.
JP 2000-267353 A Japanese Patent Laid-Open No. 10-319629

  The present invention has been made under the above circumstances, and provides an electrophotographic toner manufacturing method capable of preventing white streaks and fogging in an image by effectively reducing ultrafine powder. The purpose is to do.

  In order to solve the above problems, the present invention classifies a binder resin, a colorant and a charge control agent by mixing and kneading, a step of pulverizing a kneaded product from the kneading step, and a fine powder from the pulverizing step. Step, strongly stirring the fine powder from the classification step, burying the ultrafine powder contained in the fine powder in the fine powder mother particles, and adding the external additive to the fine particles from the strong stirring step And a method of producing an electrophotographic toner, wherein ultrafine powder of 2 μm or less is reduced by 5% or more in the strong stirring step.

  In such a method for producing an electrophotographic toner, the strong stirring step exceeds the driving time and / or the rotational speed of the mixer in the external additive addition step using the mixer used in the external additive addition step. This can be done by driving the mixer with drive time and / or speed. In this case, 0.1 to 0.5% by mass of silica having a particle size of 5 to 15 nm can be added in the strong stirring step.

By the method as described above, a toner having a particle size of 5.0 to 0 to 9.0 μm can be produced.
As an external additive, silica having a particle size of 5 to 15 nm can be used.

  According to the present invention, in the strong stirring step, the fine powder including the ultra fine powder from the classification step is mixed with a high shearing force so that the ultra fine powder particles are embedded in the fine base material particles. Thus, it is possible to obtain a toner in which the number of ultrafine powder particles is reduced at a reduction rate of 5% or more. By using such a toner, it is possible to form a good image quality without white stripes and fog.

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

  A method for producing a toner according to an embodiment of the present invention includes melt-kneading a raw material mixture containing a binder resin, a colorant, and a charge control agent, pulverizing the kneaded material, classifying, vigorously stirring, and external additives. Is added.

  Toner raw materials including a binder resin, a colorant, and a charge control agent are first 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 binder resin can be selected from a wide range including known ones. Specific examples include styrene resins such as polystyrene, styrene-acrylic acid ester copolymers, styrene-methacrylic acid copolymers, and styrene-butadiene copolymers, saturated polyester resins, unsaturated polyester resins, and epoxy resins. Phenolic resin, coumarone resin, xylene resin, vinyl chloride resin, polyolefin resin and the like can be exemplified, and two or more of these resins may be used in combination. Of these resins, polyester resins, particularly crosslinked polyester resins are preferred.

  As the colorant and charge control agent, any of those usually used for electrophotographic toners can be used.

  The raw material mixture is then fed to a kneader where it is melt kneaded. As the kneading machine, any type of extrusion kneading machine such as a twin-screw extrusion kneading machine and a single-screw extrusion kneading machine, an open roll type kneading machine such as a continuous two-roll mill, a continuous three-roll mill, and a batch roll mill can be used. Things can be used.

  The kneaded product from the kneader is then cooled and then pulverized. In this pulverization step, for example, coarse pulverization to a particle size of several mm using a hammer mill or the like may be performed, and then pulverized to a particle size of about 5 to 15 μm using a jet mill or the like.

  Next, the fine powder obtained by pulverization is classified so as to obtain a predetermined average particle diameter by removing fine particles and coarse particles. An air classifier can be used for classification.

  In addition, since ultrafine powder of 2 μm or less cannot be removed depending on classification, ultrafine powder of 2 μm or less is still included in the fine powder from the classification step. The presence of such ultra fine powders needs to be reduced because it reduces toner fluidity, causes toner scattering in the image forming apparatus, and causes white streaks and fog in the image.

  In the present invention, such an ultra fine powder is not removed from the toner, but is embedded in the base particles to reduce the amount thereof. A strong stirring step is performed for embedding the ultrafine powder in the base particles. The strong stirring step is performed by mixing the fine powder including the ultra fine powder from the classification step with a high shearing force. Mixing with a high shear force can be performed by driving the mixer at high speed, driving the mixer for a long time, or both. By such strong stirring, the ultrafine powder particles are embedded in the base particles of the fine powder, and as a result, the number of ultrafine powder particles is greatly reduced.

  The strong stirring step is performed so that the reduction rate of the number of ultrafine powder particles is 5% or more. If the reduction rate is less than 5%, there is no effect of the strong stirring step, and white streaks resulting from the presence of ultrafine powder particles cannot prevent the occurrence of fog.

  The strong stirring step can be performed using the same mixer as that used in the subsequent external additive addition step. In this case, it can be carried out by driving the mixer at a driving time and / or rotational speed exceeding the driving time and / or rotational speed of the mixer in the external additive addition step.

  In this strong stirring step, it is desirable to add silica particles in order to improve the fluidity and uniformity of the toner. The particle diameter of the added silica particles is preferably 5 to 15 nm. When the particle size of the silica particles is too small, it is difficult to obtain the effect of adding silica particles, and when it is too large, it is difficult to obtain the effect of reducing the ultrafine powder particles by vigorous stirring, and white streaks are likely to occur in the image. Moreover, it is preferable that the addition amount of a silica particle is 0.1-0.5 mass%. When the addition amount of the silica particles is too small, it is difficult to obtain the effect of adding the silica particles, and when it is too large, the image is likely to be fogged.

  The fine powder in which the ultrafine powder particles are reduced by the strong stirring process is subjected to the external additive adding process. The external additive is added for the purpose of improving the fluidity of the toner, adjusting the triboelectric charge amount, improving the cleaning property, etc., and as the external additive, silica, titanium oxide, fatty acid metal salt, etc. are used. In particular, hydrophobic silica is preferably used.

  The particle size of the toner produced by the above method is desirably 5.0 to 0 to 9.0 μm. When the particle size of the toner is too small, white streaks and fog are likely to occur in the image, and when it is too large, fog is likely to occur in the image.

  Examples of the present invention and comparative examples will be described below.

Example 1
2. 93.0 parts by mass of a crosslinked polyester resin (Tg: 62 ° C., Tm: 141 ° C.), 5 parts by mass of a colorant (CI Pigment Red 57.1), a release agent (Biscol 660P: manufactured by Sanyo Chemical Co., Ltd.) 0% by mass and 1.0 part by mass of a charge control agent (E-84: manufactured by Orient Chemical Co., Ltd.) were premixed with a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.).

  The obtained raw material mixture was melt-kneaded with a twin-screw extrusion kneader to obtain a kneaded product. After cooling the kneaded product, it was pulverized to a mass average particle size of 5.8 μm with a counter jet pulverizer (AFG-2: manufactured by Hosokawa Micron), and further classified with a classifier (Elbow Jet: manufactured by Matsubo), Colored fine particles having an average particle diameter of 6.2 μm were obtained.

  The colored fine particles contained 4.3% (number) of ultrafine particles of 2 μm or less.

  Next, 0.1 part by mass of hydrophobic silica (R812: manufactured by Nippon Aerosil Co., Ltd.) was added to the colored fine particles, and the mixture was vigorously stirred with a Henschel mixer (FM-10) at a peripheral speed of wings of 40 m / s for 5 minutes. The particle size of this hydrophobic silica was 7 nm.

  By this strong stirring process, the ultrafine powder of 2 μm or less was reduced to 4.0% (number). The reduction rate of the ultrafine powder by the strong stirring process was 5.6%.

  Then, 0.5 parts by mass of hydrophobic silica (R812: manufactured by Nippon Aerosil Co., Ltd.) was added by the same mixer (Henschel mixer, FM-10) used in the strong stirring step, and the peripheral speed of the wings was 30 m / s. The mixture was stirred for 5 minutes to obtain a magenta toner having an average particle size of 6.1 μm.

  The number of ultrafine particles having a particle size of 2 μm or less and the toner particle size were measured under the following measurement conditions.

Measuring equipment: Multisizer III
Number of particles measured: 50000 Aperture diameter: 50 μm
Examples 2 to 4, Comparative Examples 1 and 2
Six types of magenta toners were obtained in the same procedure as in Example 1 except that the peripheral speed of the Henschel mixer blade in the strong stirring step, the particle size of the silica added in the strong stirring step, and the amount added were changed. .

  These toners were subjected to a printing test using a color printer “Speedia: N5” (manufactured by Casio Computer Co., Ltd.), and white stripes and fogging were visually evaluated. The results are shown in Tables 1 and 2 below.

  The evaluation criteria for white stripes and fog are as follows.

Color stripe
○: No white streak
Δ: Several white streaks can be confirmed
×: White streaks can be confirmed instantly
Fog
○: Fog is recognized.
Δ: Slightly fogged.
X: There is clearly fog.

  From the above Tables 1 and 2, the following is clear. That is, in the case of using the toner (Examples 1 to 4) in which the number of ultrafine particles was reduced by a reduction rate of 5% or more by a strong stirring process, neither white streaks nor fog occurred, and good image quality was obtained. showed that. On the other hand, in the strong agitation process, the Henshell mixer's peripheral speed of the wing is as low as 30 m / s. Therefore, the toner (Comparative Example 1) having a low reduction rate of the ultrafine powder of 4.7% causes fogging and strong. In the toner (Comparative Example 2) in which the reduction rate of the ultrafine powder was as low as 2.3% because the particle size of the silica added in the stirring step was too large at 40 nm, white streaks and fogging occurred.

Claims (5)

Mixing and kneading a binder resin, a colorant and a charge control agent;
Pulverizing the kneaded product from the kneading step,
A step of classifying the fine powder from the pulverization step,
A step of strongly stirring the fine powder from the classification step, burying the ultrafine powder contained in the fine powder in the fine powder mother particles, and a step of adding an external additive to the fine particles from the strong stirring step. And a method for producing an electrophotographic toner, wherein ultrafine powder of 2 μm or less is reduced by 5% or more in the strong stirring step.   Using the mixer used in the external additive addition step, the strong agitation step is performed at a drive time and / or rotation speed exceeding the drive time and / or rotation speed of the mixer in the external additive addition step. The method for producing an electrophotographic toner according to claim 1, wherein the toner is driven by driving the toner.   3. The method for producing an electrophotographic toner according to claim 1, wherein 0.1 to 0.5% by mass of silica having a particle diameter of 5 to 15 nm is added in the strong stirring step.   4. The method for producing an electrophotographic toner according to claim 1, wherein a toner having a particle size of 5.0 to 0 to 9.0 [mu] m is produced. The method for producing an electrophotographic toner according to claim 1, wherein the external additive is silica having a particle size of 5 to 15 nm.