JP2003098846A - Image forming device - Google Patents

Abstract

(57) [Problem] To prevent reverse transfer caused by discharge in a transfer portion and prevent white spots and serious image defects from occurring. SOLUTION: In an image forming apparatus having an intermediate transfer member using a toner in which a resin base particle surface is coated with an external additive, the adhesive force between the image carrier or the intermediate transfer member and the toner is reduced.
This is larger than the adhesion between toners.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using a toner having resin mother particle surfaces coated with an external additive.

[0002]

2. Description of the Related Art In color electrophotography, an intermediate transfer member is used to prevent abrasion of a photoconductor and facilitate superposition of color images. Further, resolution is improved by using a toner having a small particle diameter of 20 μm or less, or 10 μm or less. However, the toner having a small particle size has poor transferability as compared with the toner having a large particle size, and if the transfer electric field is strengthened to improve the transfer property, dielectric breakdown occurs and an image defect occurs. This transfer property largely depends on the adhesive force (van der Worth force, mirror image force) between the toner and the photoconductor and between the toner and the intermediate transfer body.

Therefore, in order to improve transferability, the adhesive force between the intermediate transfer member and the toner is made larger than the adhesive force between the photosensitive member and the toner, and further, the toner and the transfer sheet are separated from each other than the adhesive force between the intermediate transfer member and the toner. It has been proposed to increase the adhesive force to paper (Japanese Patent Publication No. 5-50337).

[0004]

By the way, in the primary transfer for transferring the toner from the photosensitive member to the intermediate transfer member, when a transfer bias is applied so as not to cause transfer residual,
After the transfer, when the photoconductor and the intermediate transfer body are about to be separated from each other, discharge is likely to occur between the photoconductor and the intermediate transfer body, especially in the non-image area, and the toner on the transferred intermediate transfer body is reversed by the discharge. It is charged to polarity and is reversely transferred to the photoconductor by the transfer electric field to cause color mixing and transfer residue on the photoconductor, while toner is missing on the intermediate transfer body and white spots occur, causing serious image defects. There are cases. Further, such a phenomenon also occurs in secondary transfer.

[0005]

SUMMARY OF THE INVENTION The present invention is intended to solve the above problems, and prevents white spots caused by discharge in a transfer portion and prevents serious image defects. Therefore, in the invention of claim 1, in an image forming apparatus having an intermediate transfer member using a toner in which the surface of a resin mother particle is coated with an external additive, the adhesive force between the toner and the intermediate transfer member or the transfer material is It is characterized in that it is made larger than the adhesive force between the toners. The invention according to claim 2 is characterized in that the toner is free mother particles having a small amount of coating of an external additive or a toner having deteriorated durability. According to a third aspect of the present invention, the image forming apparatus has a tandem configuration including a plurality of image forming units each having an image carrier. The invention of claim 4 is characterized in that the sphericity of the toner is 0.95 or more. The invention of claim 5 is characterized in that the toner is a polymerized toner. The invention of claim 6 is characterized in that the amount of the external additive is 1.6% or more. The invention of claim 7 is characterized in that the external additive of particle diameter is 0.5% or more.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration example of an image forming apparatus to which the present invention is applied. A charger 2, an exposure unit 3, and a rotary developing device 4 are arranged around the photoconductor 1, and the toner image developed by the rotary developing device 4 faces the photoconductor 1 with the intermediate transfer member 5 interposed therebetween. It is transferred to the intermediate transfer body 5 by the transfer electric field by the transfer charger 6 arranged,
The residual potential after the transfer is removed by the charge removing unit 7, an electrostatic latent image is formed again, and toner development is performed. The rotary developing device 4 includes a yellow developing device 4Y and a magenta developing device 4.
M, a cyan developing unit 4C, and a black developing unit 4K. The developing units for each color are rotary-typed intermittently brought to the developing position for development, and the toner image is color-superposed on the intermediate transfer member 5. It The color image on the intermediate transfer member is a secondary transfer roller 9 facing the backup roller 8 with the intermediate transfer member interposed therebetween.
Is transferred to the transfer material 10 by the transfer electric field, and the residual toner on the intermediate transfer material is cleaned by the cleaner 11.

FIG. 2 is a diagram schematically showing the occurrence of white spots due to discharge. Assuming that, for example, three layers of negatively charged toner 20 are attached on the image carrier 1 or the intermediate transfer member 5 and are transferred to the intermediate transfer member 5 or the transfer material 10 at the nip portion, the toner passes through the nip portion. At the moment when a predetermined gap is generated, the transfer electric field may cause discharge, particularly in a non-image portion, and as a result, the negatively charged toner may be positively charged by the ions and the polarity may change to the positively charged toner.
For example, as shown in the figure, assuming that the outermost toner 21 is positively charged, the toner 21 is attracted toward the image carrier 1 or the intermediate transfer member 5 by the transfer electric field, and is negatively charged by the adhesive force between the toners. The toner is also attracted together, and the three layers of toner 22 are reversely transferred to cause a transfer residue, and a blank portion 23 is generated, which causes a serious image defect.

FIG. 3 is a diagram schematically showing the occurrence of white spots due to discharge between the image carrier and the intermediate transfer member. In a certain cycle of transfer, when the negatively charged toner 30 transferred onto the intermediate transfer body 5 passes through the nip portion with the image carrier and a gap is generated between the image carrier and the intermediate transfer body. As in the case of FIG. 2, the transfer electric field causes discharge, particularly in the non-image area, so that the toner 31 on the outermost layer is positively charged, and the positively charged toner and the negatively charged toner are combined together. The toner 32 in the layer is reversely transferred to the image carrier 1 to cause color mixing, and a white spot 33 is generated on the intermediate transfer member to cause a serious image defect.

The prevention of white spots due to such discharge will be described with reference to FIG. FIG. 4 is a schematic diagram for explaining white spot prevention due to discharge. In FIG. 4, the image carrier 1
Alternatively, the intermediate transfer member 5 and the intermediate transfer member 5 or the transfer material 10
To prevent the toner 40 in the outermost layer among the toners transferred by the transfer electric field between and from being positively charged by the discharge and from being reversely transferred together with the negatively charged toner 41 due to the adhesive force. F1 is the adhesive force between the toner and the image carrier or the intermediate transfer member, and F is the adhesive force between the toners.
2, the adhesion force between the toner and the intermediate transfer member or transfer material 10 is F
When it is set to 3, the relationship of F2 <F3 (1) is established. When the relationship of the equation (1) is established, and when the adhesive force F1 acts on the positively charged toner 40, the adhesive force between the toner and the intermediate transfer member or the transfer material toner is larger than the adhesive force between the toners. Interlayer separation of toner does not occur and the entire three-layer toner is not reversely transferred, and occurrence of white spots is prevented.

In the one-component non-magnetic toner, the surface of the resin mother particle is coated with an external additive. However, as a result of durability in use, the external additive on the toner surface is embedded in the mother particle or peels off. The amount of external additives on the toner surface is reduced. In addition, even in a new toner, there is a few percent of free mother particles which are not sufficiently covered with the external additive. In the case of toner or free mother particles whose surface has a reduced amount of external additive due to such use durability, mutual adhesive force F
2 increases. Therefore, the adhesive force F between the mother particles of the toner
Also for 2, the relationship of the adhesive force F3 between the mother particles and the intermediate transfer member or the transfer material satisfies the expression (1). By doing so, it is possible to more completely prevent the occurrence of blank areas.

The manner of preventing the occurrence of white spots in FIGS. 2 and 3 in this manner will be described with reference to FIGS. 5 and 6. Figure 5
FIG. 3 is a diagram schematically showing how white spots are prevented from occurring due to discharge between an image carrier or an intermediate transfer member and an intermediate transfer member or a transfer material. As in the case of FIG. 2, three layers of negatively charged toner 20 are attached on the image carrier 1 or the intermediate transfer member 5, and the toner at the outermost layer is positively charged by ions due to the discharge immediately after passing through the nip portion. Assuming that the positive toner becomes positive toner 21, the positive toner is transferred by the transfer electric field.
The toner 24 is attracted toward the image carrier 1 or the intermediate transfer member 5, but if the relationship of the expression (1) is established, the toner 24 of one layer or two layers is reversely transferred, but the toner is separated between layers and becomes one. The portion remains without being reverse-transferred, and the white spot portion 25 is not completely depleted of toner as in the case of FIG. 2, and as a result, the occurrence of a serious image defect is prevented without the white spot.

FIG. 6 is a diagram schematically showing how white spots are prevented from occurring due to discharge between the image carrier and the intermediate transfer member. Figure 3
In the same manner as in the above case, the three layers of negatively charged toner 30 transferred onto the intermediate transfer member are positively charged by the discharge immediately after passing through the nip portion, and the positively charged toner 31 is positively charged by the transfer electric field. , The toner is attracted toward the image carrier, but if the relationship of the expression (1) is established, the toner 34 of one layer or two layers is reversely transferred, but the toner is separated into layers and a part of the toner is reversely transferred. Without remaining, the blank area 35
In the case of FIG. 3, the toner does not completely disappear and white spots do not occur, and the occurrence of a serious image defect is prevented.

Next, an example of the toner for establishing the condition of the formula (1) will be described below. Polymerized toner (having a sharper particle size distribution than pulverized toner) is used so that the wax is not exposed on the surface of the polymerized toner. The toner has a sphericity of 0.95 or more, a small surface energy, a small contact area, and a small adhesive force. The sphericity of the toner here is FPIA-2 manufactured by Sysmex Corporation.
It is the average sphericity measured by a 100 measuring device, and is calculated from the circularity of a two-dimensional projected image of toner (perimeter of a circle having the same area as the projected image / perimeter of the projected image). The weight ratio of the amount of the external additive coated on the toner to the weight of the toner is 1.6% or more. Since the external additive is effective in improving the fluidity of the toner, the adhesive force is reduced by coating at 1.6% or more. The weight ratio of the large particle diameter external additive (particle diameter 30 nm or more) to the toner weight is 0.5% or more. The external additive having a large particle diameter reduces the adhesive force and enters between the toner and the member to reduce the van der Waals force.

Further, as the intermediate transfer member, the belt material is urethane, polyester, polycarbonate, PE.
A resin layer such as T is provided on the outermost layer, and the surface roughness and Ra are set to 0.1 μm or more.

Using the toner and the intermediate transfer member as described above,
An example in which the coefficient of friction between the intermediate transfer member and the coefficient of friction between the toner tablets is obtained by converting the toner into tablets will be described below. [Embodiment] In a color electrophotographic printer, a toner X (a toner includes one or more of the above items)
And an intermediate transfer body A (an intermediate transfer body includes one or more of the above), toner X is compressed at 100 to 500 kgf / cm ² , and tableted to 20 gf / cm ^{2 to} 400 gf. / Cm ²
The friction coefficient when a toner tablet is slid on the sheet (fixed) by pressing against a sheet whose surface material is the same as that of the intermediate transfer body, the friction coefficient when one of the toner tablets is fixed and the same is slid. When an image was output using a larger toner, it was confirmed that no white spots occurred at the transfer portion.

[0016]

The image portion on the image carrier is reverse-transferred at the transfer portion (immediately after the toner once transferred passes through the nip portion, immediately after the transfer, or immediately after passing through the nip portion where the intermediate transfer member passes every revolution). By causing a phenomenon in which the polarity of the toner is reversed due to the electric discharge and the like, the toner of the image portion is transferred to the image carrier.
At that time, the toner on the intermediate transfer member is attracted to the toner on the outermost layer and is entirely transferred to the image carrier, resulting in a serious image defect called a blank image.

Therefore, by satisfying the magnitude relation of the adhesive force as in the present invention, even if the reverse transfer due to the discharge occurs, only the toner on the outermost layer is transferred to the image carrier side so that a blank image is not generated. You can Also in the secondary transfer (transfer from the intermediate transfer body to the transfer material), it is possible to prevent the occurrence of white spots due to the discharge immediately after the secondary transfer nip due to the same magnitude relationship of the adhesive force.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of an image forming apparatus to which the present invention is applied.

FIG. 2 is a diagram schematically showing an example of white spot occurrence due to discharge.

FIG. 3 is a diagram schematically showing an example of white spot occurrence due to discharge.

FIG. 4 is a schematic diagram for explaining how white spots are prevented from occurring due to discharge.

FIG. 5 is a diagram schematically showing how white spots are prevented from occurring due to discharge between an image carrier or an intermediate transfer member and an intermediate transfer member or a transfer material.

FIG. 6 is a diagram schematically illustrating how white spots are prevented from occurring due to discharge between an image carrier and an intermediate transfer member.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photosensitive member, 2 ... Charging device 2, 3 ... Exposure unit, 4 ... Rotary type developing device, 5 ... Intermediate transfer member, 6 ... Transfer charging device, 7
... Static elimination unit, 8 ... Backup roller, 9 ... Secondary transfer roller, 10 ... Transfer material 10, 11 ... Cleaner 11, 2
0 ... Negatively charged toner 20, 21, ... Positively charged toner, 22 ... Reversely transferred three-layer toner, 23 ... White spots.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/01 114 G03G 9/08 384 F term (reference) 2H005 AA08 AA15 AA21 AB06 EA05 EA07 2H030 AB02 AD01 BB24 BB42 2H200 FA05 GA12 GA23 GA46 GA47 GB02 HA02 HA12 HB12 HB22 JA02 JB06 JB16 JC03 JC07 JC12 JC13 JC15 JC17 MA04 MC05 MC06

Claims (7)

[Claims] 1. In an image forming apparatus having an intermediate transfer member using a toner having a surface of resin mother particles coated with an external additive, the adhesive force between the toner and the intermediate transfer member or the transfer material is determined by the adhesive force between the toners. An image forming apparatus characterized by being made larger than. 2. The image forming apparatus according to claim 1, wherein the toner is free mother particles coated with a small amount of an external additive or is a toner having deteriorated durability. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus has a tandem structure including a plurality of image forming units each having an image carrier. 4. The image forming apparatus according to claim 1, wherein the toner has a sphericity of 0.95 or more. 5. The image forming apparatus according to claim 1, wherein the toner is a polymerized toner. 6. The image forming apparatus according to claim 1, wherein the amount of the external additive is 1.6% or more. 7. The image forming apparatus according to claim 1 or 2, wherein the large particle size external additive is 0.5% or more.