JPH0468363A - Electrophotographic developer - Google Patents

Abstract

PURPOSE:To obtain an image with high fineness and also to obtain many pieces of high-definition images by combining a specified carrier with a positively electrostatical charged toner, and further combining it with a development system having a specified electric field strength region. CONSTITUTION:The development system having 5X10<3>-2X10<4>V/cm in the electric field strength between a photosensitive body and a developing sleeve is used. The developer consists of a positively electrostatical charged toner and a silicone applied ferrite carrier. The volume resistivity of the silicone applied ferrite carrier is >=10<12>OMEGA.cm at 10<4>V/cm of the electric field strength and the mean particle size is 20-60mum. In such a manner, the particle size of the carrier is made smaller and the napping of the carrier formed on the developing sleeve is made dense, then the high-definition image is attained and the electric field strength in the developing system is strengthened and the quantity of the toner transferred on the photosensitive body from the developer is increased, then the high-density image is available. Thus many pieces of images with high fineness are obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a toner and a carrier used for developing an electrostatic latent image formed by electrophotography, electrostatic recording, electrostatic printing, etc. This invention relates to an electrophotographic developer.

[Conventional technology]

Conventionally, an electrostatic latent image formed on a photoreceptor in electrophotography is developed with a developer, and then transferred and fixed onto a transfer sheet as required. As the developer used here, a two-component developer consisting of toner and carrier is conventionally known.

This developer is made up of toner that has been frictionally charged to the opposite polarity to that of the carrier and is held on the surface of a carrier with relatively coarse particles. Due to this action, toner adheres to the latent image to form a visible toner image. The developer is repeatedly used for long-term copying while replenishing the toner consumed by development.

In recent years, with the advancement of technology, copiers and laser printers that can output high-definition images have been developed. They are required to be durable enough to withstand copying and printing, and to have development characteristics that allow them to obtain detailed images.

Conventionally, developer durability has been improved by coating the surface of the ferrite carrier with silicone resin, styrene acrylic resin, acrylic resin, fluororesin, etc. to prevent toner from spilling onto the gear/rear surface during copying. Proposed. Furthermore, it has been proposed to reduce the toner particle size to 10 μm or less in order to obtain a dense image.

However, regarding durability, when using positively chargeable toner, coated ferrite carriers in which the surface of the ferrite carrier is coated with silicone resin, acrylic resin, etc. do not retain the necessary and sufficient amount of triboelectric charge for the toner, resulting in background noise when printing images. will occur. Further, when the toner has a small particle size with an average particle size of 10 .mu.m or less, there are problems in that the yield during classification deteriorates, the fluidity of the toner deteriorates, resulting in poor cleaning and toner replenishment.

[Problem to be solved by the invention]

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an electrophotographic developer capable of obtaining high-definition images and a large number of such images.

[Means to solve the problem]

As a result of intensive research, the present inventors discovered that there is a close relationship between the resistance value of the carrier and the electric field strength of the developing system, and thus arrived at the present invention.

That is, the present invention provides an electrophotographic developer (composed of a positively chargeable toner and a silicone coated ferrite carrier) used in a developing system in which the electric field strength between the photoreceptor and the developing sleeve is 5 x 104 to 2 x 104 V/cm.
(hereinafter referred to as developer), and the volume resistivity of the silicone-coated ferrite carrier is 104 V/c in electric field strength.
The electrophotographic developer is characterized in that m is 1012 Ω·011 or more and the average particle diameter is 20 to 6011 m.

The present invention will be explained in detail below.

In the present invention, by reducing the particle size of the carrier, the spikes of carrier formed on the developing sleeve are made denser, thereby achieving high image quality. By increasing the electric field strength in the developing system, the amount of toner transferred onto the photoreceptor is larger than that of the developer, making it possible to achieve high density.

The electric field strength to which the developer of the present invention is applied is determined by installing a voltmeter probe in the developer tank of the development system, measuring the surface potential of the photoreceptor surface, and using the surface potential using the following formula.

■ E= (V/cm) E: Electric field strength (V/cm) ■ Two-surface potential (V) D: Development gap between the developer tank and the photoreceptor (cm) The developer of the present invention is determined by the above formula. The electric field strength between the photoreceptor and the developing sleeve is 5 x 104 to 2 x 104 V/cm.
By applying it to the developing system, it exhibits suitable effects. That is, the developer of the present invention was
When applied to a development system with an electric field strength lower than V/cm, the image density will be insufficient, while 2 x 104
When applied to a developing system with an electric field strength stronger than V/cm, leakage occurs between the photoreceptor and the developing sleeve, making it impossible to form an image.

Next, the carrier constituting the present invention will be explained.

The carrier in the present invention has a volume resistivity of electric field strength 1
A silicone-coated ferrite carrier having a resistance of 1012 Ω-c or more at 0.4 V/cm and an average particle diameter of 20 to 60 uta is used. Volume resistivity is 10+2Ω・
If it is smaller than cm, a large current will flow through the silicone-coated ferrite carrier due to the strong electric field strength existing between the photoreceptor and the developing sleeve, resulting in a non-uniform image. In addition, if the average particle diameter is smaller than 20 μm, the particle diameter and volume are too close to the positively charged toner, and the positively charged toner's ability to act as a carrier is impaired electrostatically and physically; In some cases, high-definition images cannot be obtained.

In the present invention, the volume resistivity of the silicone-coated ferrite carrier can be determined as follows.

That is, 10 silicone-coated ferrite carriers
The silicone-coated ferrite carrier is weighed in g and put into the inner cylinder 2 of a measuring device as shown in FIG. Then, the thickness of the layer of silicone-coated ferrite carrier in the inner cylinder was measured, and the applied voltage was determined to be 10
A DC power supply is applied between the upper electrode 1 and the lower electrode 4 so that the voltage is 4 V/cm, the current value at that time is measured, and the volume resistivity is determined using the following formula.

ρ=RXS/l ρ: Volume resistivity (Ω・cm) R: Resistance value measured by microammeter (Ω) (Applied voltage/current value) S: Cross-sectional area of main electrode (cm”) t: Thickness (cm) The silicone-coated ferrite carrier in the present invention is generally used between Pe, O, (M is a divalent metal ion, for example, Mn", Fe"◆, Co"., Ni", Cu"÷
This is a resin-coated carrier with a core material of ferrite, a group of iron oxides with a composition of It is possible to obtain a developer with a long life.In addition, by increasing the volume resistivity of the coated ferrite carrier to 1012 Ω・cm and reducing the particle size to 20 to 60 μm, problems with conventional positively chargeable toners can be solved. It was also possible to improve the ground force blur during copying caused by the insufficient amount of triboelectric charge.

The silicone resin that coats the surface of ferrite is
Any conventionally known silicone resin may be used, such as room temperature curable silicone resins represented by the following structural formulas (I) to (Vl), but other silicone resins may also be used.

Structural formula [I] CH3C1h 0-Si-O Hi CH.

1+-3i- OH OCH.

Structural formula [Ir] C) 13 0 - Si -0 OH OH3 -Si　-0→- M-wheel 20,000 0-Si-0 CH.

Structural formula [111] % formula % Structural formula [■] 0-5i ~O OH3 Structural formula [vl 0CH30CH3 OH0 0-Si -0 CR3 Structural formula [VI] CH, Mw ', 50.0OO (Si-0) OH The volume resistivity of the silicone-coated ferrite carrier can be adjusted by changing the type of core material and the manufacturing method, and it is particularly effective to adjust it by increasing or decreasing the amount of silicone resin coated.

As a method for coating the core material with the silicone resin, the silicone resin may be dissolved in a solvent and applied to the surface of the core material using a known means such as a fluidized bed coating device.

Next, the positively chargeable toner constituting the present invention will be explained.

The positively chargeable toner in the present invention is obtained by mixing a binder resin, a colorant, a charge control agent, and other additives added as necessary into a desired composition, melting and kneading the mixture, and then crushing and classifying the mixture.

Examples of the above-mentioned binder resin include styrene resin, polyacrylic acid ester resin, styrene-acrylic copolymer resin, polyvinyl chloride, polyvinyl acetate, polyvinyldene chloride,
Examples include phenol resin, epoxy resin, polyester resin, and the like.

Examples of the coloring agent include carbon black, monoazo red pigments, disazo yellow pigments, quinacridone magenta pigments, and anthraquinone dyes.

Furthermore, as the charge control agent, those that can provide positive chargeability such as nigrosine dyes, alkoxylated amines, quaternary ammonium salts, alkylamides, molybic acid chelate pigments, etc. can be used, and in particular silicon coated ferrite. Nigrosine dyes are preferred because they have good triboelectric charging properties with carriers.

Other additives that may be added as necessary include polystyrene or polyacrylic resin powder, powders such as titanium dioxide, conductive titanium, and zinc, lubricating materials such as metal salts of higher fatty acids, hydrophobic silica, and colloidal powders. Examples include fluidizing agents such as silica.

〔Example〕

The present invention will be explained below based on Examples. In the examples, parts refer to parts by weight.

Example 1 Ferrite core material manufactured by Dowa Iron Powder Co., Ltd. (average particle size 50μ
m) is coated with a room temperature curing silicone resin (a toluene solution of Silicone 5H840 manufactured by Tou Silicone Co., Ltd.) and dried with a spray dryer to form a silicone-coated ferrite carrier with a volume resistivity of 10"Ω/Cl11. Obtained.

Further, the following raw materials were mixed in a super mixer, melted and kneaded, and then pulverized and classified to obtain a positively chargeable toner having an average particle size of 12 μm.

An electrophotographic developer of the present invention was prepared by mixing 100 parts of the silicone-coated ferrite carrier and 8 parts of the positively chargeable toner.

Example 2 Ferrite core material manufactured by Dowa Iron Powder Co., Ltd. (average particle size 40μ
A silicone coated ferrite carrier having a volume resistivity of 1014 Ω·cm was obtained by coating the surface of the carrier with room temperature curable silicone resin (a toluene solution of silicone SH840 manufactured by Tomu Silicone Co., Ltd.) and drying it with a spray dryer.

Further, the following raw materials were mixed in a super mixer, melted and mixed, and then pulverized and classified to obtain a positively chargeable toner having an average particle diameter of 12 μm.

An electrophotographic developer of the present invention was prepared by mixing 100 parts of the silicone-coated ferrite carrier and 10 parts of the positively chargeable toner.

Example 3 The above raw materials were mixed in a super mixer, melted and kneaded, and then pulverized and classified to obtain a positively chargeable toner having an average particle size of 12 μm.

8 parts of the positively chargeable toner and 100 parts of the silicone coated ferrite carrier obtained in Example 1 were mixed to prepare an electrophotographic developer of the present invention.

Comparative Example 1 Ferrite core material manufactured by Dowa Iron Powder Co., Ltd. (average particle size 40μ
m) was coated with a toluene solution of acrylic resin and dried with a spray dryer to obtain an acrylic coated ferrite carrier having a volume resistivity of 1013Ω·Cl11.

A comparative developer was prepared by mixing 100 parts of the acrylic coated ferrite carrier and 8 parts of the positively chargeable toner obtained in Example 1.

Comparative Example 2 Ferrite core material manufactured by Dowa Iron Powder Co., Ltd. (average particle size 40μ
m) is coated with a toluene solution of fluororesin and dried with a spray dryer until the volume resistivity is 1.
A fluorine-coated ferrite carrier of 0'4 Ω·cm was obtained.

100 parts of the fluorine coated ferrite carrier and Example 2
A comparative developer was prepared by mixing 8 parts of the positively chargeable toner obtained in .

Next, the electrophotographic developers of the present invention based on Examples 1 to 3 and the developers based on Comparative Examples 1 to 2 for comparison were used at an electric field strength of 1.5 1
A continuous copy test of 50,000 copies was conducted by installing the printer in a copying machine with a voltage of 0.04 V/cm. The developing system in this case is EP-470 manufactured by Minolta with a developing gap of 0.5++u+.
+, a doctor gap adjusted to 0.5 mm was used. The results are shown in Table 1.

The amount of triboelectric charge in Table 1 was measured using a blow-off triboelectricity measuring device, the image density was measured using a Macbeth densitometer manufactured by Macbeth Co., Ltd., and the soil strength was measured using a Hunter brightness meter manufactured by Nippon Heavy Industries Co., Ltd.

Furthermore, the uniformity of the black solid color was visually evaluated using the following items in the black image area.

The fine line reproducibility of Kan 1 is as shown in Figure 2, with a line width of 100 μm and a line spacing of 100 mm.
Copies were made using a μm test pattern, and the images were evaluated according to the following criteria.

As is clear from Table 1, the electrophotographic developer of the present invention showed good performance in all characteristics including image density, ground force blur, black solid uniformity, and fine line reproducibility in the process of continuous copying of 50,000 sheets. It was confirmed that the results were obtained and that it had sufficient durability.
It was confirmed that excellent image quality was obtained, especially in terms of fine line reproducibility.

On the other hand, it was confirmed that the comparative developer had an unstable triboelectric charge amount, had a lot of ground force blur, and had poor fine line reproducibility.

[Effects of the Invention] The present invention combines a specific carrier with a positively chargeable toner,
Furthermore, by combining it with a development system that has a specific electric field strength range, it is possible to not only obtain high-definition images (resolution) that were impossible with conventional technology, but also to produce a large number of high-quality images, including high image density. It is possible to provide an electrophotographic developer that can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus for measuring the volume resistivity of a carrier. FIG. 2 is a diagram of a test pattern for evaluating thin line reproducibility. 1... Upper electrode (Cu-Zn A11ot) 2...
Inner cylinder (PTFE) 3...Carrier

Claims (1)

[Claims] The electric field strength between the photoreceptor and the developing sleeve is 5×10^3~2
An electrophotographic developer consisting of a positively chargeable toner and a silicone-coated ferrite carrier used in a developing system having a voltage of 10^4 V/cm, the silicone-coated ferrite carrier having a volume resistivity of
An electrophotographic developer characterized by having a resistance of 10^1^2 Ω·cm or more at 4 V/cm and an average particle diameter of 20 to 60 μm.