JPH04358161A - Positively chargeable toner - Google Patents

Abstract

PURPOSE:To provide a positively chargeable toner having excellent flowability and shelf stability, satisfactory positive chargeability and retentivity of the charged state and giving a copied image hardly causing the lowering of image density and fogging due to continuous copying. CONSTITUTION:This toner contains toner particles with positively chargeable silica particles tightly stuck to the surfaces and negatively chargeable silica particles mixed with the toner particles.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to positively charged toner used in electrophotographic processes such as electronic copying machines and laser printers.

0002

[Prior Art] As is generally known, in the electrophotographic process, an electrostatic latent image is formed on a photoconductor, and then charged toner is attached to the photoconductor by contacting or bringing it close to the photoconductor. The electrostatic latent image is visualized, further transferred to paper, and fixed to form a copy image. In this process, many physical, chemical, and thermal properties are required of the toner, and various inventions and
Improvements have been made. Particular attention is paid to the charging properties of toner and its persistence, since they have the most important effect on copied images.

[0003] As a method for improving the characteristics of such toner, for example, there is a method of adding hydrophobized silica to toner or developer as described in Japanese Patent Laid-Open No. 46-5782. widely known. Adding this hydrophobic silica to a toner or developer not only improves the charging characteristics of the toner, but also improves the storage stability and fluidity of the toner. When this fluidity improves, the cleaning properties of the photoreceptor become better in the electrophotographic process. Because of these advantages, hydrophobic silica is now added to most toners.

[0004] The hydrophobic silica used here is obtained by treating fine silica powder with a silane coupling agent having an organic group to form silanol groups (Si-OH) on the silica surface.
), but generally has a strong negative charge. Therefore, it is mainly added to negatively charged toner.

On the other hand, as a positively charged toner, a toner containing positively charged silica treated with a nitrogen-containing coupling agent has been developed, for example, as shown in Japanese Patent Publication No. 53-22447. .

[0006]

[Problems to be Solved by the Invention] Conventionally, this positively charged silica has poor moisture resistance, storage stability, and flowability compared to negatively charged silica, so when added to toner, it has been found that the image quality has deteriorated. There was a problem of poor sustainability. On the other hand,
Negatively charged silica has good moisture resistance, storage stability, and fluidity. However, when negatively charged silica is added to positively charged toner, the amount of charge on the toner and the speed at which the charge rises after being supplied to the developer decreases due to the negative chargeability of this silica, resulting in a reduction in the quality of the copied image. There was a problem that fogging and toner scattering inside the machine increased.

The present invention has been made in view of the above circumstances, and has excellent moisture resistance, fluidity, and storage stability, as well as good charging properties and durability of charging, as well as reducing image density due to continuous copying. Another object of the present invention is to provide a positively charged toner that can produce copied images with less fog.

[0008]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a positively charged toner using a combination of negatively chargeable silica and positively chargeable silica.

That is, the positively chargeable toner of the present invention is characterized in that it contains negatively chargeable silica particles. It is characterized in that it includes toner particles having positively charged silica particles firmly attached to their surfaces, and negatively charged silica particles mixed with the toner particles.

It is preferable to add positively chargeable silica in an amount of 0.05 to 2.0 parts by weight per 100 parts by weight of toner particles, and if the amount is less than 0.05 parts by weight, toner scattering into the machine will occur. If it exceeds 2.0 parts by weight, fluidity, toner storage stability, and image persistence tend to decrease. Further, it is preferable that the negatively chargeable silica be added in an amount of 0.01 to 1.0 parts by weight per 100 parts by weight of toner particles. There is a tendency for the sustainability of 1.
If it exceeds 0 parts by weight, toner tends to scatter into the machine.

Positively charged hydrophobic silica particles are firmly attached to the particle surface of the toner used in the present invention. Surface treatment methods for firmly adhering positively charged hydrophobic silica include, for example, mixing toner particles and silica particles in an air vortex using a Henschel mixer, colliding them using a jet mill, and using a hybridizer. Conventional methods can be used, such as granulation using a method of granulation.

[0012] In such surface treatment, it is preferable to make the surface treatment conditions stricter than usual, for example, making the mixing time longer than usual and increasing the mixing rotation speed. On the other hand, if surface treatment is performed under conditions that are more relaxed than usual,
Floating silica that is free from the toner remains and tends to have an adverse effect on the fluidity of the toner.Furthermore, when mixed with negatively charged silica, the silica tends to aggregate and a homogeneous mixture cannot be obtained. This tends to cause an increase in fog.

Considering the above, an effective and easy method for surface treatment of toner with positively charged hydrophobic silica is to pulverize the toner with a jet mill and then add silica to the air stream. It is preferable to do so. To this end, it is possible to install a quantitative supply port for silica in the raw material supply port of the jet mill, but it is also possible to supply a mixture of toner coarse particles and silica as a raw material to the jet mill and pulverize it. is simple. By such a method, it is possible to uniformly and firmly adhere positively charged silica to the surface of the toner.

[0014] According to the present invention, toner particles whose surfaces have been treated so that positively charged silica is firmly attached to them are
It is mixed with negatively charged silica using conventional methods. This mixing can be carried out using a normal mixing device under normal mixing conditions. Preferably, mixing conditions such as mixing time and mixing rotation speed may be made somewhat looser. Mixing under these mild conditions tends to improve the fluidity of the toner.

Specific examples of positively charged silica particles used in the present invention include RP-130, RA-130H (
(manufactured by Nippon Aerosil Co., Ltd.), HVK-2115, H
VK-2150 (manufactured by Wacker), etc. can be mentioned.

Further, specific examples of the negatively charged silica particles used in the present invention include R-811, R-812,
R-972, R-974, R-976 (manufactured by Degussa), RX-200 (manufactured by Nippon Aerosil), H
-2000 (manufactured by Hooker), etc. The toner particles are a composition consisting of common components such as a colorant, a resin binder, and a charging agent, and any common toner particles can be used.

As the coloring agent, dyes such as carbon black, iron oxide, ferrite, nigrosine, etc. can be used. It is also possible to prepare color toners by using organic or inorganic pigments of each color.

As the resin binder, polystyrene, styrene or styrene derivatives, methyl methacrylate,
Copolymers with unsaturated carboxylic acids (esters) such as acrylic acid, methacrylic acid, and maleic acid, styrene-butadiene copolymers, polyethylene, polypropylene, polyesters, epoxy resins, and polyvinyl butyral can be used. As the charge control agent, nigrosine, quaternary ammonium salts, phthalocyanine derivatives, etc. can be used as necessary.

[0019]

[Operation] The present invention improves a positively charged toner by adding positively chargeable silica and negatively chargeable silica. The inventors of the present invention have conducted various studies on the factors that improve the performance of positively charged toners due to these silicas, and as a result, have found an appropriate method for adding silica, and have accomplished the present invention.

That is, the present inventors have discovered that the characteristics of the toner vary depending on the state of the silica particles on the toner. Silica, which is free or weakly attached to the toner, improves the fluidity of the toner or developer, and is effective in improving the storage stability of the toner and the persistence of images. On the other hand, silica, which is strongly adhered to the toner, has little effect on fluidity, toner storage stability, and image persistence, but has an effect on charging properties. Therefore, positively chargeable silica, which has excellent chargeability although it has disadvantages in fluidity, toner storage stability, and image persistence, is firmly attached to the surface of toner particles. By mixing negatively charged silica, which is effective in improving storage stability and image persistence, with toner particles, a positively charged toner that takes advantage of the advantages of both negatively charged silica and positively charged silica can be obtained.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, FIG. 1 shows the basic structure of a copying apparatus as an example of an image forming apparatus using the developer of the present invention.

As shown in FIG. 1, a photoreceptor 2 serving as an image bearing member is provided approximately at the center of the main body 1 of the copying machine so as to be rotatable in the direction of the arrow. A charger 3, a slit glass 4, a developing device 5, a transfer charger 6, a cleaner 7, and a static eliminator 8 are sequentially arranged around the photoreceptor 2 along the direction of rotation thereof. Further, an optical system 9 for exposing a document to light is provided at the top of the main body 1, and a paper feed cassette 10 is installed at the bottom of the main body 1. Paper is supplied from this paper feed cassette 10, and the paper is conveyed along a conveyance path 11. Conveyance path 1
1 includes a registration roller 12 along the paper conveyance direction.
, a fixing device 13, and a paper discharge roller 14 are provided. Note that 15 is a paper discharge tray, and 16 is a document table.

The copying process in the above-mentioned copying apparatus is as follows. First, the optical system 9 scans the original platen 16.
The upper document is irradiated with light, and the reflected light is imaged on the photoreceptor 2 via the imaging lens array 4, so that an electrostatic latent image is formed on the photoreceptor 2. Toner supplied from the developing device 5 adheres to this electrostatic latent image, and the electrostatic latent image is visualized. On the other hand, the paper supplied from the paper feed cassette 10 is sent between the photoreceptor 2 and the transfer charger 6, and the developed image on the photoreceptor 2 is transferred to the paper. Thereafter, the paper is conveyed along the conveyance path 11 to the fixing device 13 consisting of a heat roller 54 and a press roller 55, and after being fixed there, the paper is
4 and is discharged onto the paper discharge tray 15. A paper ejection/reversal switching gate 67 is provided between the paper ejection roller 14 and the paper ejection tray 15, and when this switching gate 6 is on the paper ejection side, the paper after fixing is When the switching gate 67 is on the reverse side, the paper with an image formed on one side is ejected to the paper ejection tray 15.
is introduced into the reversing device. In the reversing device, the paper with an image formed on one side is reversed and introduced into the conveyance path 11 again, and an image is also formed on the other side. Using a copying apparatus having such a configuration, an image was formed using a developer having the following composition. Example 1

TB-1000 (St-Ac resin; Sanyo Chemical) 88 parts by weight, Viscoel 660P (PP wax; Sanyo Chemical) 4 parts by weight, MA-600 (carbon black; Mitsubishi Chemical) 6 parts by weight, N- 01 (nigrosine dye; Orient Chemical Co., Ltd.) 2 parts by weight were uniformly mixed and then kneaded for 30 minutes at 125° C. using a pressure kneader. After cooling, coarsely crush with a hammer mill to obtain an average particle size of 2.
A toner chip of less than mm in size was obtained.

After mixing 100 parts by weight of this chip with 1 part by weight of positively charged hydrophobic silica RP-130, it was pulverized and classified using an I-type jet mill-DS classifier so that the average particle size was 11.0 μm. did. Furthermore, this finely pulverized material 10
0 parts by weight and negatively chargeable silica R-972 (Degussa)
0.3 parts by weight were mixed in a Henschel mixer to obtain a positively chargeable toner. It was found that the toner had good fluidity and good caking after being left at 50° C. for 8 hours, indicating that it had excellent storage stability.

Next, 4 parts by weight of ferrite carrier F-150 was mixed with 100 parts by weight of the toner to prepare a developer. Using this developer, an evaluation test of a copied image was conducted using an electrophotographic copying machine RheoDry BD-2810 (manufactured by Toshiba). As a result, no decrease in image density or fogging was observed even after continuous copying of 40,000 sheets. Further, when a test similar to the above was conducted using a toner that had been left in an environment at a temperature of 30° C. and a humidity of 85% for 24 hours, similarly good results were obtained. Example 2

Toner chips obtained in the same manner as in Example 1 were finely pulverized and classified to have an average particle size of 11.0 μm. 100 parts by weight of this finely pulverized toner and 0.5 parts by weight of positively charged hydrophobic silica RP-130 were mixed, and surface treatment was performed for 5 minutes in a hybridizer (manufactured by Nara Kikai). Further, 0.3 parts of negatively chargeable silica R-972 (Degussa) was added to 100 parts by weight of this surface-treated toner.
Parts by weight were mixed using a Henschel mixer to obtain a positively charged toner. The obtained toner had good fluidity and good storage stability. When this toner was subjected to a copy image evaluation test in the same manner as in Example 1, good results similar to those in Example 1 were obtained. In addition, similar evaluation tests were conducted using toner that had been left in an environment at a temperature of 30° C. and a humidity of 85% for 24 hours in the same manner as in Example 1, and similar good results were obtained. Comparative example 1

To 100 parts by weight of toner finely pulverized in the same manner as in Example 1, 0.3 parts by weight of negatively chargeable silica R-972 was mixed in a Henschel mixer without adding positively chargeable silica. Got toner. The obtained toner had good fluidity and storage stability, but when the copied images were evaluated in the same manner as in Example 1, a lot of fogging was observed from the beginning of continuous copying. Comparative example 2

100 parts by weight of toner finely pulverized in the same manner as in Example 1, and 0.0 parts by weight of positively chargeable silica RP-130.
3 parts by weight were mixed in a Henschel mixer to obtain a toner without adding negatively chargeable silica. The obtained toner had insufficient fluidity and storage stability. Further, when an evaluation test of the copied images was conducted in the same manner as in Example 1, the image density decreased after about 20,000 copies were continuously made. Example 1 was prepared using toner left in a high temperature and humidity environment in the same manner as in Example 1.
When a similar image evaluation test was conducted, fogging increased significantly. Comparative example 3

Negatively chargeable silica R-972 was added to 100 parts by weight of toner finely pulverized in the same manner as in Example 2.
2 parts by weight and 0.2 parts by weight of positively chargeable silica RP-130 were mixed in a Henschel mixer to obtain a toner. The obtained toner had good fluidity and storage stability. When the evaluation test of the copied image was conducted in the same manner as in Example 1,
More fog was observed from the beginning of continuous copying, and after 20,000 sheets of continuous copying, a decrease in image density and an increase in fog were observed.

As shown in Examples 1 and 2, when the toner of the present invention is used, there is hardly any decrease in image density or fog even when 40,000 sheets are continuously copied, and the nuclear toner is not used. Similar results can be obtained even if continuous copying is performed in the same manner after leaving the paper in a hot and humid environment. However, when only negatively charged silica is added as in Comparative Example 1, the resulting copied image has a lot of fog, and when only positively charged silica is used as in Comparative Example 2, the image density increases after continuous copying. Moreover, if toner is left in a hot and humid environment, image fogging will significantly increase. In addition, the toner obtained by simply mixing positively chargeable silica and negatively chargeable silica as in Comparative Example 3 had good fluidity and storage stability, but fogging of copied images occurred from the beginning of continuous copying. is seen, and the image density gradually decreases.

[0032]

As described above, according to the present invention, a positively charged toner having excellent moisture resistance, fluidity, and storage stability, as well as good chargeability and image sustainability can be obtained. Therefore, by using the positively charged toner of the present invention, it is possible to obtain a copied image with less reduction in image density and less fog due to continuous copying. Furthermore, toner scattering into the cabin is less likely to occur.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of an image forming apparatus that can use the developer of the present invention.

[Explanation of symbols]

Claims (1)

[Claims] 1. A positively charged toner comprising toner particles having positively charged silica particles firmly attached to the surface thereof and negatively charged silica particles mixed with the toner particles.