JPH03238474A - Image forming device - Google Patents

Abstract

PURPOSE:To reproduce a first toner image without deteriorating the color toner thereof by adjusting relation between first toner and second toner to the specified relation. CONSTITUTION:The first toner and the second toner are adjusted to the relation shown by a formula I. In the formula I, K shows color mixture evaluation coefficient, Xi shows ratio that the toner exists in the width of a particle diameter [r(i-1) to r(i)] as for the first toner, Yi shows the ratio that the toner exists in the width of the particle diameter [r(i-1) to R(i)] as for the second toner and (alpha) shows a color mixture limit. Thus, the second toner mixed in an image produced with the first toner is reduced and color mixture is restrained to a level which is insignificant in practical use. As the result, the first toner image is reproduced without deteriorating the color toner thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a multicolor image forming apparatus using an electrophotographic copying process.

(Prior Art) Conventionally, as one aspect of the image forming apparatus, two sets of processes including a charging device, an exposure device, and a magnetic brush type developing device are provided around the photoconductor, and the first process applies a second process to the photoconductor. A second toner is used to form a first toner image, and in a second process, a second toner image is formed using a second toner having a different color from the first toner and having the same charging tendency to the carrier as the first toner. A two-color image forming apparatus has been proposed in which two toner images are formed and the first toner image and second toner image on a photoreceptor are collectively transferred to a recording medium.

By the way, in the image forming apparatus, the first toner image formed in the first process passes through the opposing part of the developing device having a different color toner in the second process, so that the second toner is mixed into the first toner image. This causes color mixture.

Therefore, in the image forming apparatus, in the second process, the band of the photoreceptor! potential and the surface potential of the first toner to the second toner.
The bias was set higher than the developing bias to prevent the second toner from adhering to the first toner image.

(Problem to be solved by the invention) However, even if the above-mentioned measures are taken, the mixing of the second toner into the first toner image cannot be eliminated, and when the amount of mixing exceeds a certain level, The presence of the second toner is noticeable in the toner image, resulting in poor image quality.

(Means for Solving the Problems) The present invention has been made to solve the above-mentioned problems, and includes developing a first electrostatic latent image on a photoreceptor with a first toner, and then developing a first electrostatic latent image on the photoreceptor. The second electrostatic latent image formed on the first
In an image forming apparatus that develops with a second toner having a color different from that of the toner and having the same charging tendency as the carrier, and transfers a toner image created with the first toner and the second toner to a recording medium, The first toner and the VGL toner, K: color mixture evaluation coefficient
(i)) Ratio of toner present Yi: Mini 2nd
The ratio α of toner present within the particle size width [r(i −1)−“0)] is adjusted to the relationship of color mixing limit.

(Example) Examples of the present invention will be described below.

01 Configuration of Image Forming Apparatus (i) Schematic Configuration (Refer to Figure 1) In the image forming apparatus, around the photoreceptor l, there are a first charging charger 2, a first developing device 3, a second charging charger 7-layer 4, second developing device 5, transfer charger 6, separation charger 7, cleaning device 8, and eraser lamp 9 are arranged.

The optical system 10 includes a rotating polygon mirror 11. second laser head 13;
It is equipped with a second laser head 13 and the like.

The paper feeding device 16 is arranged on the left side in FIG. 1, and the fixing device 20
is placed on the right.

(ii) Structure of developing device (see Figure 2.3) The developing device 3
1 is a magnetic plan type developing device, which includes a developing roller 31 consisting of a magnet body 32 and a cylindrical sleeve 33 wrapped around the magnetic body 32;
A developer supply member 35 is provided.

A plurality of magnetic poles extending in the axial direction are provided around the magnet body 32, and the magnetic poles of the same polarity are adjacent to the portion l facing the developer supplying member 35.

The sleeve 33 is configured to rotate in the direction indicated by the arrow, so that a developing bias VB is applied thereto.

The second developing device 5 has the same basic structure as the first developing device. Therefore, the same members are given the same reference numerals and their explanations will be omitted. Regarding the developing bias V8, the one related to the first developing device 3 is distinguished as Vo, and the developing bias related to the second developing device 5 is distinguished as V112.

Further, the first developing device 3 accommodates a two-component developer containing a non-magnetic color toner other than black and a carrier, and the second developing device 5
A two-component developer containing magnetic black toner and carrier is contained therein. Furthermore, color toner and black toner are both used which tend to be charged to the same polarity when they come into contact with a carrier.

(2) Two-color image forming operation of an image forming apparatus equipped with a two-color image forming operation configuration,
This will be explained with reference to FIG.

(a) First charging [see Figure 4 (a)] When a printing command is issued, the photoconductor l rotates in the direction of arrow a, and the first charger 2 discharges, thereby causing the outer periphery of the photoconductor l to be The surface is charged to a predetermined surface potential VO1=-600CV).

In the developing units 3.5, the developing sleeves 33 rotate in the directions indicated by the arrows, and the developing biases V B l and V B □
are respectively Vitl--450 (V) and V12""
It is set to 550 [V].

(b) First g light [see FIG. 4(b)] Next, the first laser head 12 projects the laser beam 14 onto the rotating polygon mirror +1 in accordance with the color image, and the reflected light passes through the mirror to the 1 charging chaffeer 2 and first developing device 3
The surface potential V1 of the exposed area is -50 [
V] first electrostatic latent image I4. or formed.

(c) First development [See FIG. 4(c)] The first development is a latent image I. 1 is the first as the photoreceptor l moves.
A portion facing the developing device 3 (hereinafter referred to as a “first developing region”).

) Xl and visualized.

Here, in the first developing device 3, the first developer is supplied to the developing sleeve 33 without being mixed by the developer supplying member 35. The developer supplied to the developing sleeve 33 is transferred to the magnetic body 32
A magnetic bra/ is formed along the magnetic field lines of the sleeve 330.
As it rotates, it is conveyed in the direction indicated by the arrow, passes through the tip of the regulating plate 34, and is conveyed to the development area X. In the development area The charged color toner Tc adheres to the electrostatic latent image area and is visualized as a color toner image.

(d) Second charging [see FIG. 4(d)] Next, when the photoreceptor 1 reaches a portion facing the second charging charger 4, V is applied thereto. , --700CV].

(e) Second exposure [see FIG. 4(e)] Also, the second laser head 13 corresponds to a black image! :
The laser beam 15 is projected onto the rotating polygon mirror 11, and the reflected light is transmitted to the second charging charger 4 and the second developing device 5 via the mirror.
The surface potential V12 of the exposed part is -60
A second electrostatic latent image 12 of (V') is formed.

This second static latent image 1.2 is generated in the development region contrast 49
Based on Q[:V), the negatively charged black toner Tb is supplied from the second developing device 5 to the electrostatic latent image area, and is visualized as a black toner image.

The electrostatic contrast here is 490 (V) or the development area
The electrostatic contrast 400 (which is larger than VE) is that a non-magnetic toner is used as the black toner Tb, and in the second developing unit 5, the toner itself is subjected to the binding force of the toner itself or the magnetic body 32. Therefore, by increasing the electrostatic contrast, the electrostatic attractive force for the black toner Tb is increased, and the adhesion force of the black toner Tb to the photoreceptor l is strengthened, thereby ensuring image density.

(g) Transfer, etc. [See Fig. 4 (g) 3 The color toner Tc and black toner Tb that have adhered to the outer circumferential surface of the photoreceptor l as described above are transferred to the transfer material P at the portion facing the transfer chart 7 transcribed into.

The transfer material P is supplied into the main body of the image forming apparatus from a paper feed section 16 by a paper feed roller 17, and is conveyed by a timing roller 18 to a portion facing the transfer charger 6 in time with the toner image.

The transfer material P on which the toners Tc and Tb have been transferred is separated from the surface of the photoreceptor l by the separation charger 7, and is conveyed to the fixing device 1120 by the conveyance bell H9, where the toners Tc and Tb are transferred.
The image is then heated and fixed onto the transfer material P.

The transfer material P on which the toners Tc and Tb have been fixed is discharged onto a paper discharge tray 22 by a paper discharge roller 21 .

On the other hand, toner Tc is generated at a portion facing the transfer charger 6.

After the remaining toner is removed from the photoreceptor 1 which has lost Tb by the subsequent cleaning device 8, the remaining charge is erased by the illumination of the eraser lamp 9, and the photoreceptor 1 is prepared for the subsequent first charging.

(2) Mechanism of color mixing As described above, in this image forming apparatus, when forming a two-color image, the color toner image formed by the first developer 3 is transferred to the second color toner image.
Since the black toner passes through the developing area X2 of the developing device 5, the black toner comes into contact with and adheres to the color toner image, causing color mixing.

(i) The mechanism of color mixing will be explained.

In the second developing area X2, the developing sleeve 3 of the second developing device 5
A magnetic brush developer held at 3 is in contact with the surface of photoreceptor 1.

In this state, when the first toner image made of color toner is conveyed to the development area void (hereinafter referred to as "concavity").

) can be done. In most cases, black toner having a smaller diameter than the scraped off color toner enters into this recess.

In other words, it is thought that color mixing occurs when black toner having a smaller diameter than the color toner replaces the concave portion where the color toner has been scraped off by the black toner magnetic brush.

Therefore, by setting the particle size of color toner and the particle size of black toner to satisfy a certain relationship, the absolute amount of black toner that replaces color toner can be reduced to a level where black toner is not visually noticeable. It is considered that the degree of color mixing can be reduced.

(u) Here, using a first toner having a particle size distribution shown in FIG. 5 and a second toner having a particle size shown in FIG. 6, the second toner is mixed into the image formed with the first toner. Consider the degree to which

As described above, the first toner of the first toner image is scraped off in the second development area, and the size of the recess formed in the scraped trace corresponds to the particle size distribution of the first toner. Become something.

In other words, the probability of entering rl from the size of the concave r-1 is
l (%) (see Figure 5).

Next, the second toner that enters the recess has the same diameter or a smaller diameter than the first toner that was previously located in the recess.

Therefore, the first toner scraped off from the recessed portion rl-
If it belongs to the particle size range of 3 to rl, this second
Assuming that the probability of toner entering is Pl, as shown in FIG. 6, it is a correction coefficient for the fact that both toners belong to the same particle size band (r t-+ to r,).

From the above, the size of the recess is (r, -,) to (rl)
, and the probability that the second toner enters the recess is 1, K=
X-P table Therefore, find Ki for all the particle size ranges of the first toner, and calculate the sum of these K (=Σ) or the ease with which the second toner enters the recesses of the first toner. In other words, a value indicating the likelihood of color mixture occurring (hereinafter referred to as "color mixture evaluation coefficient").

).

(iii) How to obtain the color mixture evaluation coefficient (K) will be explained for a specific case.

First, the target first toner and second toner are sieved, and the ratio of toners belonging to a predetermined particle size range is determined as shown in FIG. 7.8.

Next, as shown in Table 1 below, Pl·K is determined for each particle size range based on the formula (2), and the coefficient K (-ΣPi-Ki) is determined by summing them. In this case, the value is -0.26.

(2) Color mixing experiment The developer 3.5 was set under the following conditions, and the degree of color mixing was observed.

(5) Image forming device setting conditions a, photoreceptor type: OPC photoreceptor, diameter: 100 mm / stem speed - 110 mm / 5ecb, first developer 3 - carrier average particle size: 60 μm Type: Spherical ferrite carrier Charging polarity: Positive, First toner number average particle size: 8,4 μm Type: Non-magnetic color toner Charging polarity: Negative, Toner composition Styrene acrylic copolymer. ...100 parts by weight Charge control agent for negative charging ... 4 Red pigment
... 5/! - Toner manufacturing method After melting and mixing the above-mentioned composition materials, it is obtained by cooling, crushing, and classifying.

- Toner concentration...5wt% *Toner concentration refers to the weight mixing ratio of toner to carrier.

C8 second developing device 5 ・Carrier average particle size...58 μm Type: Binder type carrier charging polarity: Positive, 2nd toner number average particle size...8.9 μm Type: Magnetic black toner charging Polarity: Negative Toner composition: Styrene-acrylic copolymer: 100 parts by weight Charge control agent for negative charging: 5 //Carbon black: 4 Magnetic powder:
40 〃・Toner manufacturing method Same as the color toner mentioned above.

・Toner concentration...15wt% d,) Toner particle size/Number average particle size Table-2 ・Production l: The second toner of 1009 μm used in Experiments 3 to 5 was classified to reduce the particle size of 10 μm or less. Toner *2: The second toner of 8 and 9 μm used in Experiment 1.2 was classified to reduce particles of 8 μm or less. Particle size distribution A, the first toner used in the first toner particle size distribution experiments I to 6. The particle size distribution of (color toner) is shown in Figure 89.

B. Second Toner Average Particle Size Distribution The particle size distribution of the second toner (black toner) used in Experiments 1 to 6 is shown in Figure 1O.

Note that the number average particle size is the center particle size (based on the number of toner particles).
- total toner particle size/number of toner).

(ii) Experimental method A first developing device using the first toner and a second developing device using the second toner are driven simultaneously, a solid image (color image) is formed in the first developing device, and this is transferred to the second developing device. After passing through the opposing parts of two developing devices, the image was transferred onto paper to create an image sample without being fixed.

Then, this image sample was magnified 200 times with an optical microscope, and within the field of view (this is approximately 0.57 mm2 in the actual image).
corresponds to ) The number of second toners present was counted. In addition, the solid image was visually observed to visually evaluate the color mixture.

(3) Experimental results - Number of mixed color toners The number of secondary toners confirmed in the image sample within the field of view of the microscope was as shown in Table 3.

Table-3 The results of Table 3 are shown in Figure 11.

・As a result of visual observation of the image samples of color mixture evaluation experiments 1 to 6, experiment 1
In the image sample (m=160), it was confirmed that colors were clearly mixed.

In the image sample (m-120) of Experiment 2, although the degree of color mixture was not clearly evident, the existence of color mixture could be confirmed.

In the image samples of Experiments 3 to 7 (m=23 to 96), the color mixture was not noticeable, and the presence of the color mixture could not be confirmed by looking at it.

・Conclusion From the above, visually checking the image and determining whether the mixed colors are noticeable or not can be determined by whether or not there are 100 different colored toners in the approximately 0.57 mm2 toner image. can.

Therefore, as shown in FIG. 9, the color mixture evaluation coefficient K is 0.
．． 50 or less, preferably 0.45 or less, about 0.
The number of different color toner mixed in 57mm2 is 10100l.
It is possible to suppress color mixture to a level that causes no practical problems. In other words, by satisfying the relationship σ: color mixture limit, it is possible to obtain an image visually free from color mixture.

(2) Others In the above experiment, the degree of color mixing was observed using red toner as the first toner and black toner as the second toner, and the color mixing limit σ (=0.5) was determined from the relationship between the red toner and black toner. However, the number of mixed toners that are recognized as mixed colors differs depending on the color of the contrasting toners. That is, whether mixed colors are noticeable or not depends on the brightness, saturation, and hue of the colors to be contrasted. For example, when black toner is mixed into an image formed with red toner and when black toner is mixed into an image formed with blue toner, the number of black toners that become conspicuous due to color mixing is It is more if one image is created with blue toner, and the number of second toner mixed into the first toner image is about 0.57.
When the number of particles is about 200 or less per mm 2 and the mixing limit a# is 0.7 or less, the image can be reproduced without impairing the tone of the first image.

Therefore, we conducted the above experiment with individual color combinations,
Count the number of mixed toners in the image that makes the color mixture less noticeable than the finished image sample, and set the corresponding color mixture limit α.
It is necessary to determine the toner and prepare the toner so that the color mixture evaluation coefficient K satisfies the relationship K <, a.

(Effects of the Invention) As is clear from the above description, according to the image forming apparatus according to the present invention, in the multicolor image forming apparatus, the first toner of the magnetic brush type first developing device and the movement of the photoconductor. The second toner of the magnetic plan type second developing device located downstream of the first developing device with respect to the direction is set so that the color mixing evaluation coefficient K is equal to or less than the color mixing limit α. The number of second toner mixed into an image created with one toner is small,
Color mixing can be suppressed to a level that poses no practical problems,
The first toner image can be reproduced without losing its tone.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the image forming apparatus, FIG. 2 is a partially cutaway side view of the first developing device, FIG. 3 is a partially cutaway side view of the second developing device, and FIG. 4 is an explanation of the image forming process. Figure 5 is a particle size distribution diagram of the first toner, Figure 6 is a particle size distribution diagram of the second toner,
7 and 8 show examples of particle size distributions; FIG. 7 is a particle size distribution diagram of the first toner, FIG. 8 is a particle size distribution diagram of the second toner, and FIG. 9 is a particle size distribution diagram of the second toner. Figure 10 is a particle size distribution diagram of the toner used in the experiment, Figure 9 is a particle size distribution diagram of the first toner, Figure 10 is a particle size distribution diagram of the second toner, and Figure 11 is the color mixture evaluation coefficient and microscope. FIG. 7 is a diagram showing the relationship with the number of mixed toners within the field of view. 1 ・Photoreceptor, 2 . . . 1st charging charger, 391.
First developing unit, 4...Second charging unit, 5...
Second developer, 10...optical system, V a r, V a
:...Development bias.

Claims (1)

[Claims] (1) Developing a first electrostatic latent image on the photoreceptor with a first toner,
Subsequently, the second electrostatic latent image formed on the photoreceptor is developed with a second toner having a color different from the first toner and having the same charging tendency with respect to the carrier, and the first toner is In an image forming apparatus that transfers a toner image created with a first toner and a second toner to a recording medium, the first toner and the second toner are expressed in mathematical formulas, chemical formulas, tables, etc. K: Color mixture evaluation coefficient Xi: First Regarding toner, particle size width [r(i-1) to r
(i)] The ratio Yi to which the toner belongs: For the second toner, the particle size width [r(i-1) to r
An image forming apparatus characterized in that the ratio α to which toner belongs in (i) is adjusted to a relationship of color mixing limit.