JPH02262160A - Developing method - Google Patents

Abstract

PURPOSE:To obtain an image having image quality high in image density and precision by combining a developer-carrying elastic member with a developer specified in particle diameter. CONSTITUTION:An image is developed by forming a one-component developer layer having a 50% particle diameter of <=8mum into one layer on the surface of the developer-carrying elastic member 6, using such a small-sized toner, and preventing deterioration of image density due to it by contact development using the elastic member 6, thus permitting this developing method to give sufficient developing time by the contact development and to maintain sufficient image density, and consequently, the image having image quality high in image density and precision to be obtained.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a developing method used in an electrophotographic device or an electrostatic recording device, and in particular, to a method for forming an image with high definition and high image density. This invention relates to a developing method suitable for.

(Prior Art) As a method for developing an electrostatic latent image, many methods such as a cascade method, a magnetic brush method, and a -component touchdown method are known, and each method is in practical use. Improvements have been made to these developing methods to achieve higher image quality as technology advances, but in recent years, even higher resolution has been developed in fields such as plate preparation in the printing field, phototypesetting, and electronic publishing. There is a growing demand for images.

As is well known, in order to obtain a higher definition image, it is necessary to use a fine toner with a smaller particle size as a developer. However, there are two technical problems in producing fine toner by conventional methods.

One is that toner materials (resin,
When kneading, cooling, pulverizing, and further classifying (coloring agent, charge control agent), in order to obtain a toner with a smaller particle size, the time required for pulverizing and classifying is too long. Difficult to adjust particle size and yield
It also gets extremely worse. As a result, the toner becomes expensive, and it becomes difficult to produce toner with an average particle diameter of 8 to 5 μm or less at a low cost. In addition, a certain improvement can be achieved by using a soft resin that is easy to crush as the resin used in the toner, but in this case, the toner often tends to be crushed during use and stick to the carrier.
This results in a side effect that printing durability also decreases. As described above, obtaining toner with a small particle size simply by the conventional method has disadvantages in terms of cost and performance.

Second, when toners with a constant carbon concentration of 5% by weight were prepared with various particle sizes and images were formed using them under exactly the same conditions, including the potential of the photoreceptor, the particle size of the toner became smaller. Accordingly, it was found that the image density decreased as shown by curve A in FIG. 4. This is considered to be because as the particle size of the toner becomes smaller, the image layer thickness also becomes thinner, and the light hiding power also decreases.

That is, for toner particles of about 8 μm or less, the density is lower than the normally required density of 1.25. To prevent this,
It is conceivable to adjust the development conditions so that the toner thickly adheres to the image, but doing so would have side effects that are completely contradictory to the objective of achieving high resolution and high definition by reducing the toner particle size. This will not provide a fundamental solution.

Therefore, in order to increase the hiding power of the toner, it is conceivable to increase the amount of colorant (for example, carbon) higher than the conventional general concentration (2 to 6%). Curves B and C in Figure 4 are
These results show that carbon concentrations are 8% and 12%, respectively, and it can be seen from these results that sufficient image density can be obtained even with toner having a small particle diameter of 7 to 3 μm. However, detailed tests have revealed that these toners of curve B1C are defective toners that cause fogging and poor transfer when left for more than one day under high environmental conditions with humidity of about 75%. The cause of this is that when carbon (Ketchen Black EC, manufactured by Lion Corporation) is used as a colorant and its proportion (weight %) to the total amount of toner is changed,
As shown in the figure, the electrical resistance changes significantly even at room temperature (relative humidity 60%), and if the additive ff is 18% or more, the resistance will be less than 1014 Ω・am, which is required for electrostatic toner. Understood. This electrical resistance value is determined by pressure-molding powder toner at a pressure of 1000 kg/c-, forming it into a plate shape with a thickness of 300 mm, and depositing gold on both sides of the plate to form electrodes. This is a value obtained by measurement using a measuring method.

(Problems to be Solved by the Invention) As described above, it is difficult to obtain highly reliable high-definition toner using the conventional cross-line pulverization type toner manufacturing method. It is difficult to obtain accurate images.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a developing method that makes it possible to obtain an image with high image density and high definition quality.

[Structure of the Invention] (Means for Solving the Problems) The developing method of the present invention includes forming a layer of a monocomponent developer having a 50% volume particle diameter of 8 μm or less on the surface of an elastic developer holding member, The method is characterized in that an electrostatic latent image is developed using this one-component developer.

The 50% volume particle diameter of the developer used in the developing method of the present invention is preferably 6 to 8 μm. The developer is preferably a polymerized toner produced by dispersing or suspending at least a polymerizable monomer and a colorant in an aqueous solution and then polymerizing the resulting mixture.

(Function) In the developing method of the present invention, in order to obtain a high-definition image,
A toner with a small particle size is used. The resulting decrease in image density is prevented by employing a developing method called contact development using an elastic developer holding member.

That is, contact development allows sufficient development time, thereby making it possible to maintain sufficient image density.

(Example) Hereinafter, the developing method of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of a developing device used in the developing method of the present invention. Reference numeral 1 in the figure indicates a typical laminated photoreceptor drum obtained by coating the surface of an aluminum tube with an organic photoreceptor. The photoreceptor of this photoreceptor drum is charged at about -650 by a scorotron charger (not shown).
(2) It is electrically charged and exposed by a laser scanner to form an electrostatic latent image. This electrostatic latent image is reversely developed by the developing device 2. A toner 3 is stored in the developing device 2, and the toner 3 is stirred by a stirring blade Iff 4.
The toner is supplied to the surface of the developing roller 6 by the toner supply roller 5 . Toner 3 supplied to the surface of the developing roller 6
is attached to the developing roller 6 by electrostatic force such as mirror image force or physical adhesion force.

The attached toner reaches near the coating blade 7 as the developing roller 6 rotates, and during this time, the toner in contact with the developing roller 6 is charged by friction with the developing roller 6. And coating blade 7
The thickness of the toner layer 8 is regulated when passing through the toner layer 8 , and the toner on the surface of the toner layer 8 is charged by friction with the coating blade 7 . The thickness of the toner layer 8 regulated by the coating blade 7 is, for example, about 30 μm.

As shown in FIG. 2, the portion 8a of the toner layer 8 that is in contact with the developing roller 6 always rolls on the developing roller 6'' and is sufficiently charged with negative polarity, but the toner 8b on the surface is The toner 8a is insufficiently charged, and therefore, the toner 8b includes uncharged toner or toner charged to the opposite polarity due to friction between the toners. The toner layer 8 comes into contact with the surface of the photoreceptor drum 1 as the developing roller 6 rotates, and develops the electrostatic latent image on the surface of the photoreceptor drum 1 .

The developing roller 6 used in this embodiment has elasticity, and is pressed against the photosensitive drum 1 and deforms to form a developing nip 9, as shown in FIG.

In this developing nip 9, the toner layer is in frictional contact with the photoreceptor drum, and the surface toner 8b containing uncharged or oppositely charged toner is frictionally charged with the photoreceptor drum 1 and the developing roller 6, and as a result, it becomes negatively polarized. Acquires a larger charge, resulting in clear development without fogging.

The undeveloped toner is collected into the developing device by the recovery blade 10, and the toner adhering to the developing roller 6 is scraped off by the toner supply roller 5.
The developing roller 6 is thereby refreshed.

In this example, a photosensitive drum having the following structure was used.

Structure Bifunctionally separated laminated photoreceptor CT (charge transport) layer: A layer made of a hydrazine derivative using polyether carbonate as a binder CG (charge generation) layer: A layer made of a hydrazine derivative using a phenoxy resin as a binder As explained above According to a developing device using an elastic developing roller, as shown in the curve of FIG. As shown in E, it was found that the burr on the drum upper edge could also be kept low. The reason for this is that since the developing electrode is placed in contact with or close to the latent image surface, sufficient electric field strength can be obtained in the developing area, sufficient charging of the toner can be achieved, and sufficient contact time can be secured. Conceivable.

As a result, it has the following excellent features:

(1) An image faithful to the latent image charge distribution can be obtained.

(2) Sharp line images and uniform, high-density solid images with suppressed edge effects can be obtained.

(3) Low potential development is possible.

(4) High mechanical precision is not required.

The developing method of the present invention is characterized by not only using an elastic developing roller but also using a toner having a 50% volume particle diameter of 8 μm or less. Below, the results of actually manufacturing toner and studying the requirements for such toner will be shown.

Toner production example 1 Unsaturated polyester resin 93 as the resin component of colored particles
Weight%, carbon black (trade name MA-
100: manufactured by Mitsubishi Kasei) 4% by weight, wax (product name 66)
0P (manufactured by Sanyo Chemical Co., Ltd.) and an antistatic agent were kneaded in a pressure kneader for 1 hour, cooled, and then coarsely ground in a hammer mill, and further finely ground in a jet mill. The obtained powder was classified by an air classification method to obtain a toner.

The 50% volume average particle diameter of this toner was 11.8 μm.

The amount of triboelectric charge determined by the blow-off method was -44.0 μc/g.

When this L-toner was used for development using the above-mentioned developing device, the image density was sufficiently satisfactory, but there was a problem in high definition. That is, toner scattering occurred around the character image.

Toner Production Examples 2 to 4 Three types of toners were produced in the same manner as Production Example 1, except that the volume 50% average particle diameter was changed by changing the particle size range to be classified, and development was performed in the same manner. Where it was. The results shown in the table below were obtained.

From the table above, the image density is good for all toner production examples, but the toner of Production Example 4 with a 50% volume average particle diameter of 7.5 μm is good in terms of toner scattering around character images. Or, it turns out that other toners are not good. From this result, the 50% volume average particle diameter is 8μ
It can be seen that it must be less than or equal to m.

Note that as the 50% volume average particle diameter is made smaller, a problem arises in that the production yield decreases.

It has been found that this problem can be solved by producing a toner using the polymerization method shown in Toner Production Example 5 below.

Toner Production Example 5 80 parts by weight of styrene, 10 parts by weight of n-butyl acrylate, 12 parts by weight of carbon black (Ketchen Black EC Nilion Co., Ltd.) and 5 parts by weight of low molecular weight polypropylene (wax) were premixed in a ball mill. Next, 2 parts by weight of benzoyl peroxide and 33 parts by weight of a 1.2% aqueous solution of calcium phosphate were added to the T.
Approximately 600 Or
The mixture was stirred and dispersed at pm for 5 minutes. This suspension was stirred at 15 Orpm in a reaction vessel and stirred in a nitrogen gas atmosphere for 6 hours.
The polymerization reaction was carried out at 0°C for 6 hours. Then, 80℃
8 parts by weight of styrene, 0.3 parts by weight of dye, 0.2 parts by weight of lauryl mercaptan, and 2.
A mixed solution containing 0.7 parts by weight of 2'-azobisisobutyronitrile was further added, and stirring was continued for 3 hours to obtain granulated polymerized toner particles. The toner particles were washed with water and filtered, and then dried under reduced pressure at 50° C. to obtain a toner having a 50% volume average particle diameter of 7.2 μm.

When this toner was used for development in the same manner as described above, an image with an excellent image density of 1.3 to 1.5 and no toner scattering around the character image was obtained.

The raw material to be dispersed or suspended in the aqueous solution may contain a polymerizable 111 W substance and a colorant, and additives may be added during subsequent processing.

[Effects of the Invention] As explained above, according to the developing method of the present invention, which is characterized by a combination of an elastic developer holding member and a developer having a predetermined particle size, a high image density can be obtained, and the area around the character image can be improved. It is possible to obtain high-definition, high-quality images without developer scattering.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a developing device used in the method of the present invention, FIG. 2 is a diagram showing a toner layer near the coating blade, and FIG. 3 is a diagram showing the relationship between the circumferential speed ratio of the developing roller and image quality. FIG. 4 is a characteristic diagram showing the relationship between toner particle size and reflected image density, and FIG. 5 is a characteristic diagram showing the relationship between toner electrical resistance and carbon concentration. DESCRIPTION OF SYMBOLS 1... Photosensitive drum, 2... Developing device, 3... Toner 4... Stirring blade, 5... Toner supply roller, 6...
...Developing roller, 7...Coating blade, 8.
... Toner layer, 9... Development nip, 10... Recovery blade. Applicant's agent Patent attorney Takehiko Suzue (0mu)

Claims (1)

[Claims] A developing method comprising forming a layer of a monocomponent developer having a 50% volume particle diameter of 8 μm or less on the surface of an elastic developer holding member, and developing an electrostatic latent image with the monocomponent developer.