JPH0529910B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an image forming apparatus, and for example, relates to an image forming apparatus that performs corona transfer of a developed image on an image carrier onto a transfer material guided by a transfer material guide, and fixes the transferred image on the transfer material with a fixing means. . Conventionally, in PPC type image forming apparatuses, corona transfer is commonly used, in which corona discharge is applied from the back side of a transfer material to transfer the image. By the way, in the case of the corona transfer method, it is necessary to maintain a predetermined transfer voltage and apply sufficient transfer corona discharge.
Necessary for good transfer. However, since the resistance of the transfer material decreases when the humidity is high, the transfer current is very likely to leak. For this reason, when the transfer material is in the transfer section, all the members that the transfer material comes into contact with are insulated or electrically suspended. Due to the flow of transfer current from the transfer material below, a transfer member such as a transfer material guide that comes into contact with the transfer material in the vicinity of the transfer portion becomes high in potential, resulting in the problem of staining due to toner scattering. In order to prevent leakage of transfer current that causes such transfer defects, it has been proposed to ground a transfer material guide or the like that comes into contact with the transfer material through an impedance element. However, simply grounding the transfer material guide via an impedance element was insufficient. The present invention has been made in view of the above points, and relates to an image forming apparatus that enables efficient transfer. The present invention provides a transfer charging means for electrostatically transferring a developed image on an image carrier to a transfer material at a transfer position, a guide means for guiding the transfer material to the transfer position, and a direction in which the transfer material moves from the transfer position. a pair of fixing rotors that fix the developed image onto a transfer material provided on the downstream side; a larger transfer material can be used, between the guide means and the ground, and between the fixing rotor and the ground on the same side of the fixing rotor as the transfer charging means with respect to the transfer material movement path; Each of the devices is characterized by having an impedance element. Hereinafter, details of the present invention will be explained using specific examples with reference to the drawings. FIG. 1 is an explanatory diagram of main parts of a specific example image forming apparatus according to the present invention. S denotes an image carrier that supports a photoreceptor or the like in the form of a drum, and rotates in the direction of the arrow. A latent image forming means and a developing means (not shown) are arranged around the image carrier S, and a transfer corona discharger 1 is arranged at the transfer position. A cleaning means (not shown) is arranged to act on the image carrier after the transfer is completed. 2 and 3 are transfer material guides that guide the transfer material to a transfer position, and 4 is a timing roller. 5 is a shield case of the transfer corona discharger 1. 6 and 7 are fixing rollers of the fixing means. 8 and 9 are resistors provided as impedance elements interposed between the transfer material guide, the fixing means, and the ground, respectively. 10 is a high-voltage power source for the transfer corona discharger, and 11 is a separation roller for the transfer material. 12 is a conveyance guide. In the illustrated example apparatus, the transfer material guides 2 and 3 and the fixing roller 7 of the fixing means are shown as members where leakage of transfer current occurs substantially. In the above-described apparatus, a latent image is formed on the image carrier S by a latent image forming means (not shown), and the latent image is developed by a developing means. In synchronization with the development images on the image carrier reaching the transfer position, the transfer material P fed by the timing roller 4 passes between the transfer material guides 2 and 3 and is guided to the transfer position. At the transfer position, a transfer corona is first applied from the back side near the leading edge of the transfer material by the transfer corona discharger 1, and the leading edge of the transfer material passes through the separation roller 11 and the conveyance guide 12 and reaches between the rollers 6 and 7 of the fixing means. do. At this time as well, the transfer corona is applied to the central portion of the transfer material from the back surface, while the rear end of the transfer material remains in contact with the transfer material guides 2 and 3. (First illustrated state) That is,
This apparatus can use a transfer material larger than the distance from the transfer material guide to the fixing roller in the transfer material movement path. Next, the rear end of the transfer material also passes through the transfer position, and successively passes through the fixing means position. In this way, the transfer and fixing onto the transfer material is completed. As will be described later, since the impedance elements connected to the transfer material guide and the fixing means are set in a correlated manner, good transfer conditions can be maintained even when the leading edge of the transfer material is at the transfer material guide position. . That is, in the device of the present invention, there are two cases in which the transfer material contacts a member on the intrusion side with respect to the transfer position and transfer current leakage occurs only from the intrusion side, and two cases in which the transfer material contacts a member on the ejection side with respect to the transfer position and is ejected. In addition to cases in which transfer current leakage may occur only from the side, good countermeasures are also taken against cases in which transfer current leakage may occur from both the entry side and the discharge side. Hereinafter, the principle of the device of the present invention will be schematically explained using an equivalent circuit. FIG. 2 is an equivalent circuit of the first illustrated device. A and B are the resistance values of resistors 8 and 9, respectively, C and D
are the distances between the transfer device, the transfer material guides 2, 3, and the fixing rollers 6, 7, respectively, and 10 is the resistance value per unit length of the transfer material T at high humidity. Due to the discharge of the transfer corona discharger 5, a current iT flows through the paper, a current i ₁ flows through the transfer material guide to the ground portion, and a current i ₂ flows through the fixing roller to the ground portion. In this circuit, i _T = i ₁ + i ₂ ... (1) V _T = R ₁ R ₂ /R ₁ + R ₂ i _T ... (2). Here, V _T is the potential of the transfer portion of the transfer material, and R ₁ =Cρ+A, R ₂ =Dρ+B. Incidentally, in order to obtain a good transferred image without transfer defects, it is necessary to apply a sufficient transfer electric field to the transfer material at the transfer section. For this purpose, the transfer portion potential V _T of the transfer material must be set higher than the minimum potential required for transfer. R ₁ R ₂ i _T /R ₁ +R ₂ ≧V _T min ...(3) That is, (Cρ+A)・(Dρ+B)/A+B+(C+D)ρiT
By satisfying ≧V _T min (3)', a good image without transfer defects can be obtained. For this reason, the values of the aforementioned impedance elements 8 and 9 are determined accordingly. For example, process speed 66mm/sec, drum diameter 60φmm, transfer high pressure 5.5KV, C=2cm, D=15cm
In an image forming apparatus, the current i ₁ flowing from the transfer material guide is measured, and the transfer material potential required for an image without transfer defects is calculated from the following formula V _T = (Cρ + A) i ₁ ...(4). 1.

[Table] That is, in the above example image forming apparatus, V _T min = 1000
(V). Based on this, determine A and B. Further, in the above image forming apparatus, guide stains occur depending on the transfer material potential, and the relationship is shown in Table 2.

[Table] Therefore, when considering dirt on the transfer material guide, it is effective to set V _T =1200−(V). Considering these points, 1000≦R ₁ R ₂ i _T /R ₁ +R ₂ ≦1200 ...Based on the condition (5), R ₁ and R ₂ , in other words, are determined as the values of A and B. By doing so, a good image without transfer defects can be obtained, and furthermore, the transfer material guide will not be soiled. Furthermore, in the specific example image forming apparatus described above, if the current i _T flowing through the paper is set to 20 (μA), and A = 90 (MΩ) and B = 30 (MΩ) to satisfy equation (4), then ,
Transfer defects such as transfer omissions do not occur. At this time, the resistance of the transfer material in a high humidity environment (30° C., 90% RH) is about 5 (MΩ/cm). The results shown in Table 3 are obtained by fixing the resistance 8 provided on the transfer material guide to 90 (MΩ) and varying the resistance 9 provided on the fixing device to evaluate the image.

[Table] As shown in Table 3, by satisfying the above-mentioned formula (5), good transfer is possible and guide staining can be prevented. Figure 3 shows an example in which constant voltage elements (varistors) 8' and 9' are used in place of the resistors as impedance elements in the device shown in Figure 1. Common parts are indicated by the same numbers as in Figure 1. . FIG. 4 shows an equivalent circuit of the device shown in FIG. The rated voltages of varistors 8' and 9' are F and G, respectively.
Then, V _T =CDρi _T +DF+CG/D+C...(6). For example, in an image forming apparatus with the same process conditions as mentioned above, it is desirable that 1000≦V _T ≦1200, so by satisfying 1000≦CDρi _T +DF+CG/D+C≦1200 (7), an image without transfer defects can be obtained. be able to. FIG. 5 shows a further modification of the device according to the present invention, in which a resistor is used as the impedance element on one side and a constant voltage element is used on the other side. In this case as well, it goes without saying that suitable conditions can be set in the same manner as described above. The above specific example was explained using a single contact member both before and after the transfer position, but it goes without saying that even if there is a plurality of contact members, it is possible to correlate and condition in the same way. . In addition, as shown in FIGS. 1, 3, and 5, an impedance element is provided between the fixing roller 7 and the ground on the same side as the transfer corona discharger 1 with respect to the transfer material movement path. As the transfer current flows into the roller 7, a bias having the same polarity as the charging polarity of the transfer corona discharger 1 is applied to the fixing roller 7. Therefore, by electrostatically attracting the toner on the transfer material to the fixing roller 7, offset in which the toner on the transfer material adheres to the fixing roller 6 can be prevented. The present invention enables stable and good transfer with the above-described configuration.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of main parts of a specific example image forming apparatus based on the present invention, FIG. 2 is an equivalent circuit of the transfer section of the first illustrated apparatus, FIG. 3 is an explanatory diagram of a modified example of the apparatus of the present invention, and FIG. The figure is an equivalent circuit diagram, and FIG. 5 is an explanatory diagram of a different modified example device of the present invention. In the figure, 1: transfer corona discharger, 2, 3: transfer material guide, 4: timing roller.

Claims (1)

[Scope of Claims] 1. Transfer charging means that electrostatically transfers the developed image on the image carrier to a transfer material at a transfer position, a guide means that guides the transfer material to the transfer position, and a pair of fixing rotors that fix the developed image onto a transfer material provided on the downstream side in a transfer material movement direction; It is possible to use a transfer material larger than the distance to the body, and between the guiding means and the ground, and between the fixing rotary body and the ground on the same side of the transfer material movement path as the transfer charging means among the fixing rotary body. An image forming apparatus comprising an impedance element between and.