JPH03125157A - Negatively charged toner - Google Patents

Abstract

PURPOSE:To eliminate a decrease in image density, fogging, in-machine scattering, etc., while maintaining good storage performance and flowability by incorporating surface-processed toner particles which are positively charged silica particles and negatively charged silica particles which are mixed with the toner particles. CONSTITUTION:The toner contains the surface-processed toner particles which are the positively charged silica particles and the negatively charged silica particles which are mixed with the toner particles. Then 0.05 - 3 pts.wt. positively charged silica is obtained preferably to 100 pts.wt. toner particles; when <=0.05 pts.wt. silica particles are added, variation in electrostatic charging quantity and the resulting increase in toner specific density tend to be caused in continuous copying operation, but when >=3 pts.wt. silica particles are added, the quantity of toner electrostatic charging tends to increase. Further, 0.05 - 2 pts.wt. negatively charged silica is added preferably to 100 pts.wt. toner particles; and the flowability and storage performance tend to deteriorate below 0.05 pts.wt. and the electrostatic charging performance and its persist ence tend to decrease as the toner specific density increases exceeding 2 pts.wt. Conse quently, no decrease in image density, fogging, toner scattering into the machine, etc., is caused and the flowability and storage performance are excellent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a negatively charged toner used in electrophotographic processes such as electronic copying machines and laser printers.

(Prior Art) As is generally known, in the electrophotographic process, an electrostatic latent image is formed on a photoreceptor, and then charged toner is brought into contact with or in close proximity to the electrostatic latent image. A copy image is formed by visualizing the image, transferring it to paper, and fixing it. In this process, the toner is required to have many physical, chemical, and thermal properties, and various inventions and improvements have been made in the past. In particular, the toner's chargeability and its durability are the most effective for copying images.
The greatest attention is being paid to this because of its significant impact.

As a method for improving the characteristics of such toner, a method of adding hydrophobized silica to toner or developer is widely known, for example, as described in JP-A-46-5782. There is. 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 performance of the photoreceptor becomes better in the electrophotographic process. Because of these advantages, the addition of hydrophobic silica is now practiced in most toners. However, liquidity
Since the storage stability is improved, the toner supply becomes excessive, and the toner specific concentration increases too much, resulting in a decrease in charging performance and charging sustainability, and problems such as in-machine scattering and fogging are likely to occur. Note that the hydrophobic silica used here is one obtained by treating fine silica powder with a silane coupling agent having an organic group and condensing it with a silanol group (-8i-OH) on the surface of the silica.

- Has a strong negative charge for boat fishing. Therefore, it is mainly added to negatively charged toner.

(Problems to be Solved by the Invention) The present invention has been made in view of the above circumstances.
It is an object of the present invention to provide a negatively charged toner that has good fluidity and does not cause a decrease in image density, fogging, or scattering inside a machine.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention improves the toner properties by adjusting the addition form and polarity of silica added to the toner. That is, the toner of the present invention is characterized in that it contains toner particles whose surface has been treated with positively chargeable silica particles, and negatively chargeable silica particles mixed with the toner particles.

Positively chargeable silica is used in an amount of 0 to 100 parts by weight of toner particles.
．． It is desirable to add 0.05 to 3 parts by weight, and if it is less than 0.05 parts by weight, there is a tendency for a change in the amount of charge during continuous copying and an accompanying increase in the specific toner concentration. If it exceeds 3 parts by weight, the toner charge amount tends to decrease. Further, the negatively chargeable silica is 0.05 parts by weight per 100 parts by weight of toner particles.
It is preferable to add ~2 parts by weight; if it is less than 0.05 parts by weight, fluidity and storage stability tend to deteriorate;
If the amount exceeds 1 part by weight, the charging property and the sustainability of the charging property tend to decrease as the specific toner concentration increases.

In the present invention, the surface treatment of toner particles with positively charged silica can be carried out by, for example, a method in which toner particles and positively charged silica are mixed in an air vortex using a Henschel mixer, a method in which they are collided using a jet mill, or a hybrid method. This can be carried out by a method such as granulation using a tizer.

In this surface treatment, the mixing time is longer than normal conditions.
It is preferable to make conditions such as the mixing rotation speed stricter. This is because negatively charged silica is firmly attached to the surfaces of the obtained toner particles.

If surface treatment is performed under milder conditions than usual, floating silica released from the toner tends to remain, which has a negative effect on the toner's chargeability and its sustainability, and when mixed with negatively chargeable silica afterwards. As a result, silica tends to aggregate together, making it impossible to obtain a homogeneous mixture, which tends to increase fog.

Considering the above, as an effective and cost-effective method of surface treatment of toner with positively charged silica, it is preferable to pulverize the toner with a jet mill and add this silica to the air stream at that time. . To this end, it is possible to add a fixed quantity supply port for positively charged silica to the raw material supply port of the jet mill, but it is also possible to supply a mixture of toner coarse particles and silica to the jet mill as a raw material. However, it is easier to finely pulverize. By such a method, it is possible to uniformly and firmly adhere the positively charged silica to the surface of the toner, and since the toner is less likely to aggregate in the pulverizer, the fluidity of the toner is also improved.

The negatively charged toner of the present invention is prepared by mixing a toner surface-treated with positively chargeable hydrophobic silica and negatively chargeable silica using a conventional method. This mixing can be performed 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 improves toner fluidity,
and good charging properties.

The toner particles used in the present invention are a composition consisting of components such as a coloring agent, a binder, and a charge control agent, and ordinary toner particles can be used.

As the colorant, carbon black, iron oxide, and ferrite can be used. It is also possible to prepare color toners by using organic or inorganic pigments of each color.

The binder may be a combination of polystyrene, styrene or a styrene derivative and an unsaturated carboxylic acid (ester) such as methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, acrylic acid, methacrylic acid, or maleic acid. Copolymers, styrene-butadiene copolymers, polyethylene, polypropylene, polyesters, epoxy resins, polyvinyl butyral, etc. can be used. As the charge control agent, metal dye nigrosine, quaternary ammonium salt, phthalocyanine derivative, etc. can be used as required.

(Function) The present inventor has found that the effect of adding silica particles is different depending on whether the silica particles are strongly attached to the negatively charged toner or when they are weakly attached. That is,
Weakly attached or liberated silica affects the fluidity and chargeability of toners and developers, while strongly attached silica affects image persistence without substantially affecting the fluidity and chargeability.

Considering the above-mentioned method of existence of silica particles and the advantages of both negatively chargeable silica and positively chargeable voltage silica, by mixing toner particles surface-treated with positively chargeable silica and negatively chargeable silica. A negatively charged toner having excellent chargeability, fluidity, and image persistence can be obtained.

[Example] Hereinafter, the present invention will be specifically explained by showing examples and comparative examples of the present invention.

Example I 88 parts by weight of TB-1000 (St-Ac resin; Kochu Kasei), Viscol 660P (PP wax; Kochu Kasei)
After uniformly mixing 4 parts by weight, MA-600 (carbon black; Mitsubishi Kasei), 6 parts by weight, and 2 parts by weight of 5-34 (chromium dye; Orient Chemical), the mixture was heated at 125°C for 30 minutes using a pressure kneader. Kneaded. After cooling, it was crushed using a hammer mill to obtain toner chips having an average particle size of 2 m11 or less.

100 parts by weight of this chip and positively charged hydrophobic silica RP
-130 (Japan Aerosil) After mixing 1 part by weight, the average particle size was 11.0 using a summer jet mill-DS classifier.
It was finely pulverized and classified to a size of μm. Furthermore, 100 parts by weight of this finely pulverized material and 3 parts by weight of negatively chargeable silica R-9720 were mixed in a Henschel mixer to obtain a negatively charged toner.

The toner thus obtained had good fluidity and also showed 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 were mixed with 100 parts by weight of the toner to prepare a developer. Using this developer, electrophotographic copying machine RheoDry BD-
5610 (manufactured by Toshiba) was used to conduct an evaluation test of continuous copying of 100,000 sheets.

As a result, no decrease in image density or fogging was observed, and there was little developer scattering into the machine. Further, when the same test as described above was conducted using the toner that was left in an environment of 30° C. and 85% humidity 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 positively chargeable silica RP-1300,
Mix 5 parts by weight and add hybridizer (manufactured by Nara Kikai).
Surface treatment was carried out for 5 minutes in a vacuum chamber. Further, 3M parts of negatively charged hydrophobic silica R-9720 was mixed with 100 parts by weight of this surface-treated toner using a Henschel mixer to obtain a negatively charged toner. The obtained toner has fluidity,
Both storage properties were good.

When this toner was subjected to a copy image evaluation test in the same manner as in Example 1, similar good results were obtained.

Further, when a test was conducted using the toner after being left in the same manner as in Example 1, similar good results were obtained.

Comparative Example 1 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 3 parts by weight of R-9720 were mixed in a Henschel mixer to obtain a toner. The obtained toner had insufficient fluidity and storage stability. Further, when this toner was subjected to an evaluation test for copied images in the same manner as in Example 1, a decrease in image density and an increase in fog were observed.

A negatively charged toner was obtained in the same manner as in Example 1 except that positively chargeable silica was not added to the toner. The obtained toner had good fluidity and storage stability, but the transfer efficiency was 8.
It was low, ranging from 0 to 82%.

Comparative Example 2 100 parts by weight of toner finely pulverized and classified in the same manner as in Example 1, 2 parts by weight of positively chargeable silica RP-1300, and 2 parts by weight of negatively chargeable silica R-9720 were mixed in a Henschel mixer. And got toner. The obtained toner had good fluidity and storage stability. Further, when this toner was subjected to an evaluation test for copied images in the same manner as in Example 1, the image density decreased and fog increased as the number of test copies increased.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain a negatively charged toner that does not cause a decrease in image density, fog, or toner scattering into the machine during continuous copying, and has good fluidity and storage stability.

Claims (1)

[Claims] A negatively charged toner comprising toner particles surface-treated with positively charged silica particles and negatively charged silica particles mixed with the toner particles.