JPH0627734A - Toner for electrophotography and image forming method - Google Patents

Abstract

PURPOSE:To establish an image forming method presenting good reproducibility for thin line, durability, and cleaning performance and provide a simplified and small-sized device for forming a multi-color image. CONSTITUTION:A toner is prepared from a stylene-acrylic acid copolymer at least not having a common bond type bridge structure and a pigment, wherein the volume-averaged particle size of the toner particles ranges from 5 to 9mum, and the value of relation (Dp50)<2>/(Dp25) is between 3.90-4.9g, where Dp25 represents the 25% cumulative value from the greater side in the particle side distribution and Dp50 represents the corresponding 50% cumulative value. In this transfer image forming method where the described electrophotographic toner is used, the toner remaining upon an organic sensitive substance is cleaned by the use of blade.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic multicolor image forming method and an electrophotographic toner used in the method.

[0002]

2. Description of the Related Art It is already known that the diameter of a toner is reduced in order to improve the image quality, and in particular, a toner having a particle diameter of around 5 μm improves the fidelity of fine line reproduction.
~ 60% by number, and the number of regions / volume ratio; N /
It is said that when V is -0.04 + K (K is 4.5 to 6.5), both image quality and durability can be achieved at the same time (JP-A-2-877, etc.).

Further, as a method for forming a multicolor image, a transfer drum system in which toner images of 3 to 4 colors are repeatedly developed and transferred onto an intermediate transfer drum, and a toner of 3 to 4 colors are developed in a multiple manner on a photoconductor. A batch transfer method is known in which the formed multiple toner image layers are batch-transferred and then transferred to batch fixing. However, the batch transfer method has a great advantage because the apparatus can be downsized.

However, in the batch transfer method, the residence time of the toner developed on the photoconductor is long, which promotes adhesion between the photoconductor and the toner, and when an organic photoconductor (OPC) having a low surface hardness is used, The adhesion phenomenon becomes remarkable. Further, a toner binder having a large number of functional groups in its structure, such as polyester, has a chemical affinity with the surface of the photoconductor and the adhesion phenomenon becomes more serious.

Further, it is difficult for the toner having a small diameter to effectively receive the force of the cleaning blade, the permissible width for cleaning is narrow, and a large force is required for cleaning. Further, a small-diameter toner using a binder having a covalently-bonded cross-linking structure has a high hardness, so that the blade is easily damaged and the allowable cleaning width is further narrowed.

[0006] In particular, when a small-diameter toner is used in the batch transfer method, there is almost no possibility of cleaning due to the above circumstances. Regarding cleaning, especially 4-6
It was found that the toner on the order of μm is difficult to be removed, particles of 6 μm or more can be easily removed without any special treatment, and particles of 4 μm or less act as a cleaning aid for other particles. From this knowledge, it is considered that cleaning is more severe because the structure of JP-A-2-877 has a large area around 5 μm and conversely a small area below 4 μm.

[0007]

SUMMARY OF THE INVENTION In view of the above situation, the object of the present invention is to achieve excellent reproducibility of fine lines and satisfactory durability, and is good even in processes such as batch transfer method in which the residence time of the toner on the photoreceptor is long. To maintain excellent cleaning performance, and to provide a simple and compact device in a multicolor image forming method.

[0008]

The above-mentioned object of the present invention is to provide a toner containing a styrene-acrylic acid and / or methacrylic acid-based copolymer having no at least a covalent cross-linking structure and a colorant, and the volume of the toner particles. 25% cumulative value Dp with the average particle size of 5 to 9 μm and the larger number particle size distribution
25, Relationship between 50% cumulative value Dp50; (Dp50) ² / Dp25
Of the electrophotographic toner having a value of 3.90 to 4.90, and the electrophotographic toner described above are used to perform multi-development of a multicolor image on an organic photoconductor, to directly transfer the images directly onto a transfer material, and then to batch fixing. This is achieved by an image forming method including the steps of cleaning the electrophotographic toner remaining on the organic photoconductor after batch transfer with a blade.

In the present invention, the volume average diameter is 5 to 9 μm,
The toner in the range of (Dp50) ^{2 /} Dp25 = 3.90 to 4.90 has a relatively high toner content in the vicinity of 5 .mu.m, which plays an important role in reproducing fine lines, and a good image quality can be obtained. Ie 5
The toner in the vicinity of μm effectively fills the peripheral portion when a fine line is formed and can reproduce a sharp line with no zigzag edge.

Toner satisfying the above relational expression is 5 μm
The ratio of the toner in the vicinity to the toner of 4 μm or less is appropriate, and the effect of the toner of 4 μm or less as a cleaning aid can be sufficiently extracted.

If (Dp50) ² / Dp25 is less than 3.90, 4 μm
If the amount of the following toner is too large, the durability deteriorates. On the other hand, if it exceeds 4.90, the amount of toner of 4 μm or less is small and the cleaning property deteriorates.

Further, since the binder has the above-mentioned molecular constitution, the chemical affinity is small, the adhesion is small, and the hardness is not so high, so that the cleaning property is good and the damage to the cleaning blade is small.

In the batch transfer method, for example, as shown in FIG. 1, a unit having four developing devices develops one color at a time during four rotations of the photosensitive member, and transfers at the end of four rotations.

The binder resin used in the toner is a styrene-acrylic copolymer having no covalent cross-linking structure, and has a molecular weight of Mw: 2 × 10 ⁴ to 30 × 10 ⁴ ,
It is preferable that Mn; 5 × 10 ³ to 15 × 10 ³ , and Tg is 50 to 65 ° C.

Carbon black (CB), azo-based, diazo-based, quinacridone-based, perylene-based, phthalocyanine-based, triallylamine-based pigments, rhodamine-based dyes, etc. are used as colorants that are mixed in the toner, and charge control is performed. The agent (CCA) may be added if necessary, but in the case of color, colorless is preferable, and zinc salt of salicylic acid or its derivative, naphthoic acid or its derivative is preferable in that respect.

As the release agent, a low molecular weight polyolefin,
Fatty acid amides, fatty acid esters, etc. may be mentioned and added.

Inorganic fine particles of silica, alumina, titania or the like can be used as the fluidizing agent, and those having a hydrophobic surface are particularly preferable from the viewpoint of environment resistance. Organic fine particles can also be used.

As the cleaning aid, a fatty acid or a metal salt thereof can be used. Particle size is 5 volume average diameter
As a method for producing (Dp50) ^{2 /} Dp25; 3.90-4.90 toner particles at 9 μm, external addition treatment may be performed after the kneading → pulverization → classification step.

Although a general carrier is used as the carrier according to the present invention, the particle size is 30 to 55 μm in the batch transfer process.
m, magnetization 15 to 35 emu / g is preferable.

Further, in order to improve the durability, which is one of the problems in using a toner having a smaller diameter, it is preferable that the toner is coated with a silicone resin having a high hardness and a small critical surface energy.

In the coated carrier according to the present invention, a magnetic material such as iron, nickel, ferrite or magnetite is used for the core.

In particular, ferrite is preferable from the viewpoint of easy control of magnetic characteristics. Ferrite is a general term for magnetic oxides containing iron, and is not limited to spinel type ferrite represented by the chemical formula of MO.Fe ₂ O ₃ (M is a divalent metal). Since various magnetic properties can be obtained by changing the composition of the contained metal component, ferrite may have any composition as long as it falls within the range of the magnetic properties of the present invention.
For example, Cu ferrite, Cu-Zn ferrite, Cu
-Mg ferrite.

The silicone resin used as the coating agent is not particularly limited, but for example, a condensation reaction type silicone resin which is cured by the following can be used.

[0024]

[Chemical 1]

In the formula, OX represents an alkoxy group, a ketoxime group, an acetoxy group, an aminoxy group and the like.

Particularly preferred in such condensation reaction type silicone resin is one in which the substituent is a methyl group. In the coating layer obtained by the condensation reaction type silicone resin having a methyl group as a substituent, the structure becomes dense, the water repellency is good, and the carrier having good moisture resistance can be obtained.

As the silicone resin used for forming the coating layer of the carrier, either a heat-curing type silicone resin or a room temperature curing type silicone resin can be used. In particular, since it is not necessary to heat the carrier to a high temperature, the carrier can be easily manufactured.

The room temperature curing type silicone resin is a silicone resin which cures at a temperature of about 20 to 25 ° C. or a temperature slightly higher than it in a normal atmosphere, and does not require a temperature exceeding 100 ° C. for curing. It is a thing.

As the silicone resin used for forming the coating layer of the carrier, the above-mentioned silicone resins may be used alone or in combination, or the above-mentioned silicone resin mixed with other resin may be used. Good.
As the other resin, those having high compatibility with the silicone resin are preferable. As such other resin,
For example, acrylic resin, styrene resin, epoxy resin, urethane resin, polyamide resin, polyester resin, acetal resin, polycarbonate resin, phenol resin,
Examples thereof include vinyl chloride resin, vinyl acetate resin, cellulose resin, polyolefin resin, copolymer resins thereof, and compounding resins.

As a method for coating the carrier, a coating solution in which a silicone resin is dissolved in an organic solvent is applied to the surface of carrier core material particles, followed by heating and drying to remove the solvent and curing. Examples of the coating method include dip coating, spray coating, and fluidized bed method, but any method may be used.

As another means, it is also possible to manufacture by means of electrostatically adhering fine particles of a silicone resin to the surface of a carrier core material and fixing them thermally and mechanically.

[0032]

EXAMPLES The present invention will be described in detail with reference to examples.

First, with the compositional constitution shown in Table 1, toner materials; t-1 to t-6 were prepared by mixing and kneading.

[0034]

[Table 1]

Next, a base toner of T-1 to 8 and H-1 to 7 was prepared using a particle collision type fine pulverizer and an airflow classifier.

To 100 parts of these base toners, 0.6 part of hydrophobic silica R-972 and 0.8 part of hydrophobic titania T-805 were added and mixed using a Henschel mixer.

The specifications of the obtained toner are shown in Table 2 and FIG.

Next, a carrier prepared by coating ferrite particles having a saturation magnetization of 22 emu / g and an average particle size of 40 μm with 2 wt% of dimethyl silicone resin and a toner / carrier ratio of 7% were mixed, and each mother toner was used as a developer. It was created.

[0039]

[Table 2]

Evaluator “9028” manufactured by Konica was used.

The 9028 is equipped with an OPC photoconductor and a blade cleaning device. In the monochromatic mode, development and transfer are repeated every cycle, and in the multicolor mode, development is repeated a plurality of times to form a multicolor image on the photoconductor. , And then transferred all at once.

The evaluation was carried out by using fine line reproducibility, durability and cleaning property as criteria.

Reproducibility of fine lines: An original document in which five lines each having a width of 100 μm and a length of 5 mm are arranged at intervals of 200 μm is arranged so that development progresses in the length direction of the line, and is copied. The line width was measured using an image analyzer RT-2000C (Yaman Co., Ltd.) at 9 points at 0.5 mm intervals.
It was judged by the difference of the minimum value.

Durability: Fogging density and the above fine line when 20,000 copies of an original document with a blackened area ratio of 5% were copied, and a patch of size 5 cm x 5 cm with original density 0.0 was copied at the initial and after 20,000 copies. 9 when measuring the line width
It was judged by the average value of the points.

Cleanability: Judgment was made based on the timing of occurrence of defective cleaning after copying 20,000 sheets. Examples 1 to 8 and Comparative Examples (1) to (7) Table 3 shows the evaluation results in the single color mode.

[0046]

[Table 3]

Examples 9 to 16 and Comparative Examples (8) to (14) Using the developers of the above Examples and Comparative Examples, the same test as above was conducted in the multicolor mode, and the results are shown in Table 4. .

[0048]

[Table 4]

[0049]

According to the structure of the present invention, the reproducibility of fine lines, the cleaning property and the durability are improved, and the size and simplification of the apparatus can be achieved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of development by an electrophotographic copying apparatus used for forming a multicolor image of the present invention.

FIG. 2 shows (Dp50) ^{2 of} toner used in Examples and Comparative Examples.
FIG. 4 is a particle characteristic diagram relating to a volume average diameter of (/ Dp25).

[Explanation of symbols]

 1 1st developing device 2 2nd developing device 3 3rd developing device 4 4th developing device 5 Photosensitive drum 6 Transfer unit 7 Cleaning unit 8 Charging unit 9 Paper feeding unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Keiko Ogawa 2970 Ishikawacho, Hachioji City, Tokyo Konica Stock Company

Claims (2)

[Claims] 1. A toner containing a styrene-acrylic acid-based and / or methacrylic acid copolymer having no at least a covalent cross-linking structure and a colorant, wherein the volume average particle diameter of the toner particles is 5 to 9 μm. And the 25% cumulative value Dp25 and the 50% cumulative value Dp from the larger number particle size distribution.
Relationship between 50: Electrophotographic toner having a value of (Dp50) ² / Dp25 of 3.90 to 4.90. 2. A multicolor image is multi-developed on an organic photoconductor using the toner for electrophotography, directly transferred onto a transfer material in a batch and then transferred to a batch fixing, and after the batch transfer, onto the organic photoconductor. An image forming method, comprising the steps of cleaning the remaining electrophotographic toner with a blade.