JPS6151178A - Image transfer device - Google Patents

Abstract

PURPOSE:To make multiple transfer possible by providing a means, which gives the electric charge having a polarity opposite to that of a toner to a transfer material, and a transfer drum, which has an insulating surface and to which a bias voltage having a polarity opposite to the electric charge of the toner or a bias voltage having the same polarity are applied by switching, so that these means face an image carrier. CONSTITUTION:A negative or positive bias voltage is applied to a transfer drum 3 by bias power sources 6 and 6' which are switched by a switch circuit SW. An image carrier 1 and the transfer drum 3 are pressed to each other in a transfer part A, and they are rotated in directions of arrows B and C respectively at the operation time. A negative bias electric charge is applied to the drum 3 at the operation start time, and an electrostatic image formed on the image carrier 1 is developed by a developing device omitted in the figure and has a negatively electrified toner 9. A positive electric charge opposite to the polarity of the toner 9 is given to a transfer material 10, which is fed in the direction of an arrow D, from the rear face by a corona discharger 7, and the transfer material 10 enters into the transfer part A. The toner 9 is transferred to the transfer material 10, and the bias voltage of the drum 3 is switched to the positive bias voltage after transfer. Thus, sure multiple transfer is performed easily.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image transfer device for transferring a toner image formed by electrophotography or the like to a transfer material such as paper, and more specifically, The present invention relates to an image transfer device suitable for overlapping toner images by performing multiple transfers onto a material to obtain a multicolor image.

[Conventional Jj2VPI] Various methods and apparatuses have been proposed in the past for the purpose of obtaining multicolor images using electrophotography. After developing with the first color toner, it is transferred to a transfer material such as paper, and the same process is applied to the second color toner. Third, multiple color toner images are sequentially superimposed on the same transfer material according to the number of color separations required.
The most common method is to copy or print a polychrome image. In this method, in which color images are sequentially superimposed on a transfer material, the alignment of the transfer material with respect to the image carrier is extremely important; if this is inaccurate, color misregistration may occur, and the resulting image may be unusable. It becomes something that doesn't exist.

As a means for accurately regulating the position of the transfer material on the image carrier, a transfer drum is provided in contact with the image carrier, and
There are many transfer apparatuses in use in which 11 types of transfer material are fixed on a drum and rotated in synchronization with the image carrier so that the transfer material always maintains a constant position relative to the image carrier. Generally, a regional locking means (gripper) is provided on the transfer drum to automatically lock the leading edge of the transfer material fed by a feed roller or the like and fix it on the drum.

When transferring the toner image on the image carrier to a transfer material, a D-type process is required, such as applying a charge to the transfer material in order to move the toner onto the transfer material, and the image carrier is also charged. A complicated static power acts on the transfer material, and combined with the mechanical force of the image carrier or the transfer drum, the transfer material tends to shift, so the most reliable method is to lock it in the same manner as the Ten Commandments. The current situation is that it is adopted.

For example, US Pat. No. 3,729,311 discloses a color copying machine having a transfer material holding drum in contact with an image bearing drum, and the transfer material holding drum is provided with a gripper for fixing the transfer material. Also, JP-A-55-18653
The publication discloses a color copying machine having an Ig photographic material support consisting of a mesh screen having an insulating surface in contact with an image bearing drum.

Here, the transfer material is attracted to the transfer material support in a streetcar manner, so mechanical means for locking the transfer material is not necessarily necessary, but the screen-shaped transfer material support is In order to securely hold and fix the transfer material since the contact area is small, it is necessary to lock it to the support body.

However, when a locking part is provided on the transfer drum, the speed and sequence of the copying operation are affected due to the need for a complicated mechanism for automatically locking, releasing, and separating the transfer material, and waiting for the locking position. Due to contamination of the locking part, blanks are created at the leading edge of the transfer material that is locked to the locking part, a mechanism to avoid the gripper part is required in the cleaning device for the transfer material holding drum, and due to toner stains on the gripper. Many problems such as staining of the transfer material have occurred, and it has been desired to develop a simpler and more reliable means for fixing the transfer material.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image transfer device for a multicolor power-saving recording device with a simple structure that can reliably transfer a plurality of toner images onto a transfer material without causing color misregistration. .

[Structure of the invention]

The object of the present invention is to provide a charge applying means that is provided opposite to the image carrier and applies a charge having a polarity opposite to that of the toner from the back side of the transfer material, and has an insulating surface and a This was achieved by an image transfer device characterized by having a transfer drum to which bias voltages of opposite polarity and the same polarity are applied in a switchable manner.

That is, in the process of image transfer, bias voltages of the opposite polarity and the same polarity as the toner (opposite polarity to the polarity with which the transfer material was initially charged) are applied to the transfer drum at appropriate times to promote the transfer of toner to the transfer material. At the same time, the transfer material is attracted to and fixed on the transfer drum surface by electrostatic attraction, and there is no need for any locking means such as a gripper on the transfer drum to fix the transfer material. %ffl transfer of toner without color misregistration can be performed without causing various problems, and at the same time, the toner transfer rate is improved.

The charge applying means used in the present invention is not limited to any type as long as it can apply a charge to the 1+7 photographic material from the back side of the transfer material, but a corona discharger is particularly preferably used. The polarity of the applied charge is determined by the charge of the toner to be transferred (
(determined according to the polarity of the static image on the image carrier), the polarity is set to be opposite to that of the toner charge. The voltage applied to the corona discharger varies depending on the properties of the image carrier, toner, etc., but is normally (+ or -) 5 to 8 KV appropriate.

The transfer drum may have a structure in which an insulating layer is provided on the surface of the conductive substrate and a bias voltage can be applied to the conductive portion, but the transfer drum applies a pressure of 7f to the surface of the image carrier to transfer the toner. Since it is necessary to carry out this process, it is preferable that the surface has appropriate elasticity, and for this reason, it is preferable to have a structure in which a conductive elastic layer is provided on the conductive substrate, and an insulating layer is further provided on the surface of the conductive substrate.

As the conductive substrate, it is preferable to use metal such as aluminum, for example. Preferred examples of the conductive elastic body include conductive rubbers such as silicone-based or chloroprene-based conductive rubbers. These conductive elastic bodies have a rubber hardness of 40° to 70' and a resistance of 10'Ω.
- It is preferable to have a volume resistivity of less than or equal to 100 mm, and the R1I thickness on the conductive substrate is preferably about 1 to 10 mm.

The above-mentioned absolute kWJ is made of various insulators such as polyester, polycarbonate, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, methacrylic resin, acrylic resin, polystyrene, silicone resin, fluorine 4'j (fat), styrene-butadiene copolymer, etc. It can be constructed using various polymers or copolymers, rubber, etc. These insulators can be applied to the surface of a conductive elastic material, directly applied to the surface of a conductive substrate, or covered as a heat-shrinkable tube. (The insulating layer may be formed by a method such as heat shrinking. The thickness of the insulating layer is 10 to too A11.
If the thickness of the insulating layer is smaller than this, it will be difficult to manufacture. The mechanical strength also becomes low, which causes practical difficulties, and the excessive thickness is unfavorable in terms of retention of the transfer material, toner transfer efficiency, and the like. As described above, bias voltages having the same polarity and the opposite polarity as the charge on the toner are applied to the transfer drum while being switched at appropriate times.

The applied voltage and its polarity vary depending on the image carrier, the power-saving properties of the toner, etc., but a bias with the same polarity as the toner charge is 100 to 300 V, and a bias with the opposite polarity is 200 to 8 V.
00v (all voltages are relative to ground potential).

The functions of the image transfer device of the present invention will be explained below. FIG. 1 is a schematic diagram of an image transfer apparatus of the present invention, in which L is an image bearing drum consisting of a conductive substrate 1 and a photoconductive photosensitive WI2, L is a conductive substrate 3, a conductive elastic layer 4, This is a transfer drum made of an insulating layer 5. The figure shows a case in which a photosensitive layer that forms a positively charged +'rP image, such as selenium-based or positively charged amorphous silicon, is used.

Negative or positive bias voltages are applied to the transfer drum L from bias power supplies 6 and 6', respectively, which are switched by switch circuit needles.

The image carrier drum L and the transfer drum L are pressed against each other in the transfer section A, and during operation, they rotate at the same circumferential speed in the directions of arrows B and C, respectively. At the start of operation of the device, a negative bias charge is applied to the transfer drum (the drums are shown open).

The electrostatic image formed on the image bearing drum L is developed by a developing device (not shown) loaded with negatively charged toner to form a toner image. 9 is a toner forming a toner image.

The transfer material 10 (its length is shorter than the circumference of the transfer material holding drum L), which advances in the direction of the arrow by a feeding means not shown in the figure, is polarized opposite to the toner by a corona discharger 7 from its back side. The image bearing drum L is given a positive charge of
and enters the transfer section where the transfer material holding drum L is in contact.

The negatively charged toner particles 9 are attracted by the positive charge on the surface of the transfer material and move toward the transfer material 10, completing the transfer of the toner image 11.

When the transfer material IO comes out of the pressure contact portion of both drums, the leading edge of the transfer material IO is subjected to the power-saving attractive force from both drums, but the positively charged transfer material IO is attracted by the transfer drum -3- to which a negative bias voltage is applied. It is strongly attracted and fixed to the surface (Fig. 2-[1]). The leading part of the transfer material 1o is the transfer drum-3
- At the point when it has progressed from several 1 to several lo several mm (Fig. 2-
[2] Condition! ! ! then switch the bias of the transfer drum to positive. When the bias voltage applied to the transfer drum L is negative, it is extremely effective in attracting the transfer material 10 to the transfer drum L, but since the toner 9 is negatively charged, the toner does not reach the transfer material 10. Migration and adhesion are weakened. At this time, by switching the bias to positive, the toner is strongly attracted to the transfer material side, and the toner transfer rate and transferred image quality can be improved. By switching the bias polarity, the suction force of the transfer material 10 against the transfer drum L at the pressure contact part is weakened, but in order to hold the IIt photographic material 10 on the transfer drum L, the leading edge of the transfer material 10 is held by the image carrier. Drum - Adsorption to the transfer drum L when it enters and leaves the transfer section A where the transfer drum L comes into pressure contact is most important, and the leading part 1 of the transfer material lO
If the front and rear parts of 0n++++ are held securely and pass through Ag, the transfer material drum L can be continuously attracted to the transfer drum even if the suction force to the transfer drum at the pressure contact part of the subsequent parts weakens.
At the top, the +lt photo material 10 does not slip or come off at all, and is wound around the transfer drum and held stably (FIG. 2 [3]). After the transfer shown in FIG. 1 is completed, the transfer drum rotates once and transfers the second toner image to the receiving material 10.
When the leading edge of the transfer material enters the transfer section, the bias voltage is changed to negative again to strengthen the adsorption of the transfer material to the transfer drum at the pressure contact section and prevent the transfer material from shifting. When the leading portion of the image passes through the transfer portion A, the polarity of the bias is returned to positive again and transfer is performed (Fig. f52 [5]). After repeating the process shown in FIG. 2 [4] to [5] as necessary, the transfer material separating means such as the separating claw 11 is activated to further separate the transfer material 10 from the transfer drum.ff12[J(6)] , to a fixing section not shown in the figure to obtain a multicolor image.

: In addition, single color. If you get an image, use the device first.

When placed in the mode shown in Fig. 2 [6], the transfer material 10 enters along the path indicated by the dotted line in the figure, and the transfer material 10 that has been transferred can be immediately peeled off and sent to the fixing section, so that high-speed and continuous fusing is possible.
I'm capable. This is an advantage that there is no photographic material locking part on the transfer drum, and the transfer drum can be placed at any position (this is an advantage that can be applied only in the image IM/copying apparatus of the present invention that can be used in history). Even in the case of 111 colors, operations such as positioning, locking, and unlocking of the transfer drum are required, making it difficult to increase the speed.

All of the above explanations have been made with reference to the case where a photosensitive layer that forms a positive charge streetcar image, such as selenium-based or amorphous silicon for positive i7 charge, is used. Even when a negatively charged photosensitive layer such as amorphous silicon for charging is used, the performance and effect are the same, except that the polarities of the electrostatic charges mentioned in item 1 are all reversed.

Further, the photoreceptor may be not only a drum-shaped photoreceptor but also a belt-shaped photoreceptor of various types.

The bias voltage during the process can be switched electrically or mechanically by the control sequence of the main body of the 0-volt recording apparatus, or by No. 48 from the readout for rotation of the image bearing drum, 1g copying drum, etc. This can be done by activating the circuit SW at appropriate times.

In addition to the transfer material separation means, the image transfer device of the present invention includes:
Transfer material static eliminator, transfer material holding drum static eliminator,
Additional devices such as a transfer material holding drum cleaner and positioning sensor can be added.

The image transfer device of the present invention can be applied to various known color image forming means using a three-color separation method, or for example, to the Japanese Patent Publication No. 48-347
It can be used in combination with various multicolor image forming means such as known two-color image forming means including a black image erasing process as disclosed in Japanese Patent No. 70, 1, R 1987-5561. I can do it. Further, various known paper feeding and fixing means can be used as a paper feeding means for supplying a transfer material such as paper to this apparatus, a fixing means for fixing an image transferred by this apparatus, and the like.

Next, referring to FIG. 3, the conditions under which the transfer can be performed well and the transfer paper can be held sufficiently 11 times on the photocopying drum will be explained.

Figure 3 shows the pressure contact part of the transfer part in Figure 1 (part A in Figure 1).
It is a schematic cross-sectional view of the main part of the photosensitive layer 2 of the photoreceptor, where the relative permittivity of the photosensitive layer 2 is εm, the thickness is dn+, the width of the gap 23 is da, the thickness of the transfer paper is dp, the relative permittivity is εp, Charge is σp, air gap 3
3 is db, and the dielectric constant of the insulating layer 5 of the transfer drum L is ε.
d, the thickness is da, and the bias voltage is -VB+ (only the leading edge of the transfer paper) and +VB2, the transfer electric field E・r(
When the value of l:T is negative, the transfer of negatively charged toner is possible.

Further, the electric field E1 that pulls the photographic paper 11 toward the photoreceptor is expressed as. When this value is negative, the transfer paper is pulled toward the photoreceptor, and the force F1 becomes.

On the other hand, the electricity that draws the 1g paper to the transfer drum? ILE2 is represented by . When this value is positive, the sheet of paper is pulled toward the photoreceptor, and the force F2 becomes.

For good l1g copying, IET+ must be 1
00KV/CTA or higher is required, and 350KV/CTA or higher is required.
It is preferable that KV/c is 11 or more.

In addition, in order for the transfer paper to wrap around the transfer drum, at least the leading part of the transfer paper, that is, the bias voltage must be low.
It is necessary that the relationship 1) holds true.

By substituting F, , F2 into the above equation (1), the necessary conditions for each parameter can be found, and by determining a part of the parameters, other desirable parameters can be selected.

As will be described later, it was confirmed that the above-mentioned requirements were met by an additional 7A in an apparatus in which good transfer was actually performed.

〔Example〕

An example in which the image transfer device according to the present invention is used in a color copying machine using a three-color separation method will be described below.

FIG. 4 is a schematic diagram of an image forming section and an image transfer section of a color copying machine using an image transfer device according to the present invention. Note that in this figure, members having the same functions as those in Figure 3:jSi are indicated by the same numbers. In the figure, arrow l indicates an optical path for image exposure by scanning an original image sent from an optical system not shown in the figure. The scan is repeated 3 times and the filter F is applied each time.
Color separation exposure is performed by alternately inserting R (red), Fo (0 color), and l''B (blue) into the optical path.The figure shows a blue filter F.
B is shown in the optical path. Development was performed using a two-component developer.

L is a photosensitive drum configured similarly to the image bearing drum shown in Fig.
= 60Jjl 5e-Te photoreceptor is used.

The drum rotates in the direction of the arrow, and the entire surface of the drum is given a positive charge by the corona discharger 20, after which the drum is exposed to image by the stray light. First, a blue filter is placed in the optical path and exposed, and an electrostatic image is formed on the photosensitive drum L (1?
A yellow toner image is formed by developing with a developing device 21Y loaded with an electroconductive yellow developer. The photosensitive drum carrying the yellow toner image is neutralized by the transfer 11η static elimination lamp 22 and advances to the transfer position.

On the other hand, the transfer paper 10 fed through the paper feed roller 23 is 3×10” C/m2 on its back side by the discharger 7.
The photosensitive drum L is given a positive charge and sent to the transfer position A.
Transfer of the yellow toner image is started by being pinched between the transfer drum L and the first transfer drum L. During this time, the transfer drum is given a negative bias of -VBI of -200V by the bias power supply 6 and strongly attracts the transfer material 10, but the leading edge of the transfer paper 10mm
After the level passes through the Δ point, the bias is switched to +Vuz, a positive bias of +500V from the power supply 6', by the operation of the SW, and the yellow toner image paste transfer continues.

Transfer drum? - has the same groove vicinity as that in Figure 1Ts1, but the details are omitted in the figure. The diameter of the transfer drum 3 is 50 mm, and the conductive elastic layer has a thickness of 2 m.
It was made of conductive rubber with a hardness of 50° m and a volume resistance of 105 Ωon, and the insulation layer was made of polyester with a thickness dd = 25 μm and a dielectric constant εd = 3.

Also, the dielectric constant εp of the transfer paper used was 2, and the thickness dp was
100jj11, the distance da between the photoreceptor and one transfer paper,
The distance db between the transfer drum and the transfer paper is 1jj11 in both cases.
Met.

After the photosensitive drum has been transferred, toner remaining on the surface thereof is removed by a cleaning device 24, and residual charges are removed by a charge removal lamp 25, and the photosensitive drum is used for the next time.

The 'IZ photo paper lO held on the transfer drum knee is on the drum L
) The position is read by the sensor 26, and the second exposure operation is started in synchronization with the position. A green filter FG is used for the second exposure of fjS, and development is performed by a developing device 21M loaded with a negatively charged magenta developer. The magenta toner image, which has been transferred by 1 yen, is transferred by 1 g overlappingly with the yellow image on the transfer paper 10 held on the transfer drum and entering the point A. The bias voltage applied to the transfer drum is nL.
Before the paper 10 reaches point A, it is switched to negative, 1 to 2;
In order to strongly attract the paper 10 to the transfer drum L, the transfer paper 1
The magenta toner image is transferred to an accurate position without being displaced by the pressure when the zero enters the pressure contact portion of the two drums. After about 10IIli+ of the leading edge of the transfer paper passes through point A, the polarity of the bias is returned to positive again. The yellow toner that was transferred first is strongly attracted to the transfer material not only by the positive charge on the transfer material but also by the positive bias applied to the transfer drum L, so that the magenta toner image is duplicated.
1, the yellow image is neither disturbed nor retransferred to the photosensitive drum L side.

Furthermore, through a similar process, the unused cyan toner image (41) is transferred overlappingly by exposure through the red filter FR and development by the developing device 21C loaded with cyan developer. After the transfer of the cyan toner image has been completed, the transfer paper 10 is charged with alternating current corona discharge from the transfer material static elimination corona discharger 27, and separated from the drum surface by lowering the separating claw 11 toward the transfer drum L side, as shown in the figure. It is not an image, but it is sent to a fixing device and fixed. 1 on the transfer paper 10; (The colored toners are melted and mixed as they are fixed, and a color image is reproduced by the subtractive color method.

The transfer drum L from which the transfer paper has been separated is transferred to a transfer drum static eliminator 2.
The charge is removed by step 8, and toner adhering to the surface of the transfer drum is removed by step 29, in preparation for the next copying operation cycle.

When making monochrome copies using this device, only one developing device is operated, and the separation claw 11 is placed in the lowered position, and the static eliminator 27 is operated continuously to make continuous and high-speed copies. I can do it.

The parameters of this example are summarized as follows.

Photoreceptor: Se/Te εm=6, dm=60nda
, db: 117m Paper: gp=2, dp=100Jnσp:3Xl
o″4(:/, 2 VB+: 200V +VB2: +500V
Definitely! & layer: polyester εd=3, dd=25j
jl ET, EF measured using these parameters
2, the values of Fl and F2 are as follows, which is iYj
It was confirmed that the necessary conditions for retaining the transfer material described above were met.

When Vn+ When -VB2 ET = 1,4X 10'V/+ 1,2X
10'V/mE, = -7X 10"V/+
6 x 10'V/mE 2 = 3.2 x 10
'V/m 2.2X 10'V/mF,
= 4.4N/m23.2X 102N/m2F,
= 4,6X 10N/m" 2.2X
10 N/m 2 In the above example, the case of a color cube using a normal three-color separation filter and yellow, magenta, and cyan toners was explained. Of course, the number of vessels is not limited to this.

〔Effect of the invention〕

In the image transfer apparatus of the present invention, which does not require a transfer material locking means on the transfer drum, since there is no locking means, the transfer material holding drum can be used at any position, and the transfer drum and image carrier can be used at any time. The transfer drum has many advantages, such as making it possible to keep it in pressure contact, eliminating the need for a mechanism for releasing the pressure or positioning it to avoid the engaging W means hitting the image carrier, and making it easy to clean the transfer drum. A simple multi-color electrostatic recording device that can obtain high-quality multi-color images with a high toner transfer rate and no color shift by timely switching the polarity of the bias voltage applied to the transfer drum. 1
:1・I can do it.

[Brief explanation of the drawing]

fjS1 and FIG. 2 are schematic diagrams showing the operation of the image+1 copying device according to the present invention, and FIG. 3 is a schematic diagram of the pressure contact portion of the transfer section.
FIG. 4 is a schematic diagram of a color copying machine using the image transfer device of the present invention. L...Image bearing drum L...-Transfer drum 3...
4 Conductive substrate 4... Conductive elastic layer 5... Insulation R agent Patent attorney field 1) Father-in-law Figure 4 Figure 2

Claims (2)

[Claims] (1) In an image transfer device that transfers a charged toner image formed on an image carrier onto a transfer material, the charge of the toner is transferred from the back side of the transfer material, which is provided opposite to the image carrier. and a transfer drum having an insulating surface and to which a bias voltage having a polarity opposite to that of the toner charge and a bias voltage having the same polarity as that of the toner charge can be applied to the transfer material in a switchable manner. Image transfer device. (2) The insulating transfer drum has a conductive base, a conductive elastic layer provided on the base, and an insulating layer provided on the surface of the conductive elastic layer. An image transfer device according to claim 1.