JPS6152675A - Picture transfer device - Google Patents

Abstract

PURPOSE:To eliminate the color staggering of a multi-colored electrostatic picture by giving a charge of a polarity reverse to a toner on a transfer material, switching appropriately voltages of the same and reverse polarities so as to impress them on a transfer drum, attracting and fixing the transfer material. CONSTITUTION:An image of a negatively charged toner 9 is formed on, for instance, a selenium photosensititve drum 10. A transfer drum 30 is so constituted to provide a conductive elastic layer 4 and an insulating layer 5 on a conductive base body 3, and said drum 30 is brought into contact A with the photosensitive drum. A transfer material 10 is advanced so shown by an arrow D. The surface of said material is positively charged by a corona discharge device 7, and the toner 9 is transferred at the drum contact part A. First, a negative voltage 6 is impressed on the transfer drum 30, and the transfer material 10 is attracted to be would on the drum 30. After the transfer material 10 passes through the contact part A by several tenmm., a positive voltage 6' is impressed on the transfer drum 30, and the toner is further attracted. Moreover, after the transfer material 10 is wound on the drum 30, it is securely fixed and will not move. Therefore even if colors of the toner are sequentially changed, the dark multi-colored picture can be obtained without the color staggering.

Description

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

[Prior art]

Various methods and apparatuses have been proposed in the United States for the purpose of obtaining multicolor images using electrophotography. After developing with toner, transfer to a transfer material such as paper, and repeat the same process at f52. The most common method is to repeatedly transfer a plurality of color toner images onto the same transfer material in a superimposed manner in accordance with the number of required color separations to obtain a multicolor image. In the method of sequentially overlapping color images on a transfer material, alignment of the transfer material to the image carrier is extremely important, and if this is inaccurate, color misregistration may occur, making the image unusable. 6. As a means for accurately regulating the position of the transfer material relative to the image carrier, a transfer drum is provided in contact with the image carrier, the transfer material is fixed on the drum, and the transfer material is rotated synchronously with the image carrier. 2. Description of the Related Art Transfer devices in which a transfer material always maintains a constant relative position with an image carrier are often used. Generally, a mechanical 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, an electrostatic process such as applying an electric charge to the transfer material is required in order to move the toner onto the transfer material. The transfer material has a charge, etc., so complex power saving functions work on the transfer material, and combined with the mechanical force from the image carrier or transfer drum, the transfer material tends to shift, so mechanically locking is the most reliable method. The current situation is that it is adopted.

For example, US Pat. No. 3,729,311 discloses a color copying system 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 a transfer material support made of a mesh screen having an insulating surface in contact with an image bearing drum.

Here, since the transfer material is electrostatically attracted to the transfer material support, it is said that 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 portion is provided on the transfer drum, a complicated ring groove is required for automatic locking, unlocking, and separation of the transfer material, and the speed of copying operation is reduced due to waiting for the locking position, etc. The sequence is restricted, the locking part becomes dirty, the transfer material locked in the locking part creates a blank at the leading edge, the cleaning device for the transfer material holding drum needs to be terminated to avoid the gripper part, the gripper Many problems have arisen, such as the transfer material being stained by toner stains, and it has been desired to develop a simpler and more reliable means for fixing the transfer material.6 [Object of the Invention] The object of the present invention is to It is an object of the present invention to provide an image transfer device 6 for a multicolor electrostatic recording device, which has a simple structure and can reliably perform multiple transfers onto a transfer material without causing misalignment.

[Structure of the invention]

The above purpose is to provide a transfer drum which has an insulating surface and which is capable of applying a bias voltage of the opposite polarity and the same polarity as the charge of the toner to be transferred, and which is provided opposite to the transfer drum. This has been achieved by an image transfer apparatus characterized by comprising a transfer material charge applying means for applying a charge of opposite polarity to the charge of the toner to the surface of the transferred transfer material.

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 by switching 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.
There is no need for any locking means such as a gripper to fix the transfer material on the transfer drum, so multiple toner transfers can be performed without color misregistration without causing the various problems described above. At the same time, the toner transfer rate is improved.

In the present invention, the transfer material charge applying means provided opposite to the transfer drum is not particularly limited as long as it can apply a charge to the surface of the transfer material, but a corona discharger is particularly preferably used. The polarity of the applied charge is set to be opposite to the charge of the toner, depending on the charge of the toner to be transferred (determined according to the polarity of the electrostatic image on the image carrier).

The voltage applied to the corona discharger for imparting charge to the transfer material varies depending on the properties of the image bearing member, toner, etc., but is usually in the range of 5 to 8 KV, which is opposite in polarity to the charge of the toner.

The transfer drum can be used by providing an insulating layer on the surface of a conductive substrate and applying a bias voltage to the conductive part to make a drawing of 1υ. Since it is necessary to perform toner transfer, it is preferable that the surface has a suitable degree of elasticity. Therefore, it is preferable to have a structure in which a conductive elastic layer is provided on a conductive substrate and an insulating layer is further provided on the surface. .

As the conductive substrate, it is preferable to use metal such as aluminum, for example. Preferred examples of the conductive elastic body include conductive rubber such as silicone-based or chloroprene-based conductive rubber. These conductive elastomers have a rubber hardness of 40” to 70° and a resistance of 108Ω.
- It is preferable to have a volume resistivity of cm or less, and the layer thickness on the conductive substrate is preferably about 1 to 10III11.

The insulating layer is made of various insulators such as polyester, polycarbonate, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, methacrylic resin, acrylic resin, polystyrene, silicone resin, fluororesin, styrene-butanoene copolymer, It can be constructed using various other polymers or copolymers, etc. These insulators can be applied to the surface of the conductive elastic body or directly to the surface of the conductive substrate, or they can be coated with heat-shrinkable tubes. The insulating layer may be formed by a method such as heat shrinking the insulating layer.The thickness of the insulating layer is preferably 10 to 100 us.If the thickness of the insulating layer is smaller than this, it will be difficult to manufacture and the mechanical strength will deteriorate. If the thickness becomes too low, it will cause major difficulties in production, and if it becomes too thick, it will be unfavorable in terms of retention of the transfer material and toner transfer efficiency.As mentioned above, the transfer drum should be supplied with a bias voltage of the same polarity and opposite polarity as the charge of the toner. Switch and apply at appropriate times.

Although the applied voltage and its polarity vary depending on the properties of the image carrier or toner, a bias with the same polarity as the toner charge is 100 to 800 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 layer 2, 3 is a conductive substrate 3, and a conductive elastic layer 4. , a transfer drum consisting of an insulating layer 5. The figure shows a case in which a photosensitive layer, such as selenium-based or amorphous silicon, which is formed by a single positive charge and forms an electric image is used.

A negative or positive bias voltage is applied to the transfer drum L from bias power supplies 6 and 6', respectively, which are switched by a switch circuit SH. rotate at the same circumferential speed in the directions of arrows B and C, respectively (in FIG. 1, the space between the two drums is shown as being open to schematically represent the state during transfer).

When the device starts operating, a negative bias charge is applied to the transfer drum.6 The electrostatic image formed on the image carrier drum L is developed by a developing device (not shown in the figure) 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) is moved in the direction of the arrow by a feeding means not shown in the figure. The surface of the toner is charged with a positive charge having a polarity opposite to that of the toner, and the toner enters the transfer section where the image bearing drum L and the transfer material holding drum support are in contact with each other. The negatively charged toner particles 9 are attracted by the positive charge on the surface of the eave material and move toward the transfer material 10, completing the transfer of the fjSi toner image. When the transfer material 10 comes out from the pressure contact portion of both drums, the leading edge of the transfer material 10 is subjected to electrostatic and attractive forces from both drums, but the positively charged transfer material 10 is moved by the transfer drum L to which a negative bias voltage is applied. Strong (attracted and fixed to the surface (Fig. 2-(1)).

The leading edge of the transfer material 10 is attached to the transfer drum L by several mff1
The point at which the progress has been made by more than 10 l (!@Figure 2 - [2] state)
Switch the bias of the transfer driver l to positive. When the bias voltage applied to the transfer drum support is negative, it is extremely effective in attracting the transfer material 10 to the transfer drum, but since the toner 9 is negatively charged, the toner transfer material 10 migration, the adhesion is weakened. Therefore, 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. Transfer material 1 at the pressure contact area by switching the bias polarity
On the contrary, the suction force on the transfer drum L of 0 is weakened, but in order to hold the photo material 10 on the transfer drum L, the leading edge of the transfer material 10 is pressed against the image carrier drum L and the transfer drum L. Adsorption to the transfer drum 3 when entering and leaving section A is the most important, and if the top 10 mm of the transfer material 10 is securely held and passes through section A, the subsequent pressure contact portions will not be transferred. Even if the suction force to the drum weakens, it can be continuously attracted to the transfer drum, and the transfer material 10 will not slip or come off on the transfer material drum, and will be wrapped around the transfer drum L and held stably. (Figure 2 [3]). 1st
When the transfer shown in the figure is completed and the transfer drum rotates once and the leading edge of the transfer material 10 enters the transfer section to transfer the second toner image, the bias voltage is switched to negative again and the 11g photo material at the pressure bonding section is transferred. In order to strengthen the adsorption of the transfer material 10 to the transfer drum and prevent the transfer material from shifting (Fig. 2 [4]), when the leading edge of the transfer material 10 passes through the transfer section A, the polarity of the bias is returned to positive again and transfer is performed (Fig. 2 [4]). Figure 2 [5]). If necessary, repeat the processes in Fig. 52 [4] to [5], and after completion, activate the transfer material separation means such as the separation claw 11 to separate the transfer material 10 from the transfer drum 3 (Fig. 2 [6]), A multicolor image is obtained by feeding the device to a fixing section not shown in the figure.
If you set it to mode 6], it will enter the route shown by the dotted line in the figure,
The transfer material 10 that has been transferred can be immediately peeled off and sent to the fixing section, making it possible to perform high-speed and continuous copying. This is an advantage that can only be obtained with the image transfer apparatus of the present invention, which does not have a transfer material locking part on the transfer drum and can be used in any position, and is not available in devices with a locking part. In the case of a single color, operations such as positioning, locking, and unlocking of the transfer drum are required, making it difficult to increase the speed.

Furthermore, as will be described later, the image transfer apparatus of the present invention has the advantage that, due to its structure, it is suitable for so-called double-sided copying in which images are formed on both sides of the same transfer material.

All of the above explanations were made using a photosensitive layer that forms a positively charged static image, such as selenium-based or amorphous silicon for positive charging. When using cadmium, various organic photoreceptors, and a negatively charged photosensitive layer such as amorphous silicon for negative charges, the polarity of the electrostatic charges described above are all reversed, and the upper side functions, The effect is the same.Furthermore, photoreceptors (not only those in the form of a drum but also those in various forms such as a belt can also be used).

The switching of the bias voltage during the process is performed by electrically or mechanically switching the switch circuit 5II4 by a control sequence of the main body of the zero-voltage recording apparatus, or by a signal from a readout for rotation of the image bearing drum or transfer drum. All you have to do is activate it at the appropriate time.

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
70 and Japanese Patent Application Laid-open No. 56-5561, 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 Laid-Open No. 56-5561. 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, conditions under which the transfer can be performed well and the transfer paper is sufficiently held on the transfer drum will be explained with reference to FIG.

FIG. 3 is a schematic cross-sectional view of a main part of the pressure bonding part (part A in FIG. 1) of the transfer part in FIG. The width of the gap 23 is da, the thickness of the transfer paper is dp, the relative permittivity is εp, the electric charge is σp, the width of the gap 33 is clb%, the relative permittivity of the transfer drum 1p and the insulating layer 5 is εd
, the thickness is da, and the bias voltage is VB+ (only at the leading edge of the transfer paper) and +VB2, the transfer electric field ET (vector direction is shown) is expressed as, and when the value of ET is negative, it is negatively charged. Toner transfer is possible.

Further, the transfer paper is pulled toward the photoreceptor (the electric field E1 is expressed as .

When this value is negative, the transfer paper is pulled toward the photoreceptor, and the force F
1 becomes.

On the other hand, the electric field E2 that pulls the transfer paper toward the transfer drum is expressed by . When this value is positive, the transfer paper is pulled toward the photoreceptor, and the force F2 becomes.

IET+ is 100 for good transfer.
KV/C11 or higher (necessary tear'), 350
It is preferable that KV/ciI1 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 VB + Throat + F t + < + F
2 + ... ... ... It is necessary that the relationship (1) holds true.

By substituting Fl and F2 into the above equation (1), the conditions for each parameter can be determined, and by determining some of the parameters, other desirable parameters can be obtained.

As will be described later, it has been confirmed that the above-mentioned requirements are satisfied in an apparatus that actually performs good transfer.

〔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. In this figure as well, members having the same functions as those in FIG. 1 are indicated by the same numbers. The arrow mark in the figure indicates the optical path of image exposure that scans the original image sent from an optical system not shown in the figure. The scanning is repeated three times, and each time filters FR (red), FG (green), and FB (blue) are alternately inserted into the optical path to perform color separation exposure. The figure shows a state in which a blue filter FB is placed in the optical path. Development was performed using a two-component developer.

L is a photosensitive drum configured similarly to the image bearing drum in figure f51, and has a relative dielectric constant εm=6 and a film thickness dm=60.
A J4'l 5e-Te photoreceptor is used. The drum rotates in the direction of the arrow, and after its entire surface is positively charged by the corona discharger 20, it is exposed to image by light from the optical path. First, a blue filter is placed in the optical path for exposure, and a power-saving image is formed on the photosensitive drum L. After that, the image is developed by a developing device 21Y loaded with a negatively charged yellow developer to form a yellow toner image. The photosensitive drum carrying the yellow toner image is neutralized by the pre-transfer static eliminating lamp 22 and advances to the transfer position A.

On the other hand, the transfer paper 10 fed through the paper feed row 223 is coated with i x to-' C/ on its surface by the corona discharger 7.
It is given a positive charge of m2 and sent to the transfer position A, and is pinched between the photosensitive drum L and the transfer drum 1 to start transferring the yellow toner image. During this time, the transfer drum is powered by bias power 6.
A negative bias VB+ of -500V is applied to the transfer material 10 (attracting it strongly), but the leading edge 110 of the transfer paper
After about 0II1 passes through point A, the bias is changed to +500V positive bias +VB from power supply 6' by the operation of S-.
2, and the transfer of the yellow toner image continues.

The transfer drum L has the same structure as that shown in FIG. 1, but the details are omitted in the figure. The diameter of the transfer drum L is 150
III11, and the conductive elastic layer has a thickness of 2IIIf.
It was made of conductive rubber with a fl hardness of 50° and a volume resistance of 105 Ωc'm, and the insulating layer was made of polyester with a thickness dd=25 JjI and a dielectric constant εd=3.

Also, the dielectric constant εp of the transfer paper used was 2, and the thickness dp was
The distance da between the photoreceptor and the transfer paper and the distance db between the transfer drum and the transfer paper were both 1 p.

After the photosensitive drum has been transferred, the toner remaining on the surface of the drum is removed by a cleaning device 24, and the residual charge is removed by a static eliminator 25 before being reused.

The transfer paper 10 held by the transfer drum L advances as the drum L rotates, and its position is read by the sensor 26, and the second exposure operation is started in synchronization with this position. The second exposure uses a green filter FG, and development is performed by a developing device 21M loaded with a negatively charged magenta developer. The obtained magenta toner image is transferred overlappingly onto the yellow image on the transfer paper 10 held on the transfer drum and entering point A. The bias voltage applied to the transfer drum L is switched to negative before the transfer paper 10 reaches point A, and the transfer paper 10 is strongly attracted to the transfer drum L. The pressure g I/'fJ1 (immediately transfers the magenta toner image to the correct position.

After about 10 mm of the leading edge of the transfer paper passes point A, the polarity of the bias is returned to positive again.The yellow toner that was transferred earlier is
In addition to the positive charge on the transfer material, the positive bias applied to the transfer drum L also causes strong attraction to the transfer material, so even when magenta toner images are transferred overlappingly, the yellow image may become distorted or the photosensitive drum L It will not be retransferred to the side.

Furthermore, through a similar process, a cyan toner image obtained by exposure through the red filter FR and development by the developing device 21C loaded with cyan developer is transferred overlappingly. The transfer paper 10 on which the cyan toner image has been transferred is neutralized by applying AC corona discharge from the transfer material static eliminator 27, and the separation claw 1
1 is lowered to the transfer drum L side and separated from the surface of the drum 1, and sent to a heat roller fixing device (not shown), where the toner image is fixed.

The three color toners transferred onto the transfer paper 10 are fixed and melted and mixed to reproduce a color image using a subtractive color method.

The transfer drum L from which the transfer paper has been separated is transferred to a transfer drum static eliminator 2.
8, the transfer drum cleaner 29 removes toner adhering to the surface of the drum, and prepares for the next copying operation cycle.

When making monochrome copies using this apparatus, only one developing device is operated, the separating claw 11 is placed in a lowered position, and the static eliminator 27 is operated continuously, so that copies can be obtained continuously and at high speed.

The parameters of this example are summarized as follows.

Photoreceptor: Se/Te εm=6, d+5=601jl
datdb: 177” Paper: εp=2, dp=1007j1σp:
IXlO"C/n+2 -VB+: -500V, +VB2: +5
00V.

Insulating layer: polyester t d=3, da=25m
ET-L+, F2 calculated using these parameters
, Fl, and F2 were as shown below, and it was confirmed that the above-mentioned requirements for holding the transfer material by the transfer drum were satisfied.

When VB+ and F Vrh, ET=-2,2
X 10@V/m 1.7X 10'V/mE
, = 2,2X 10'V/m -1,7X 1
0'V/mE2 = 4.5X IO'V/m
F toward the photoreceptor side = 2. IX 10 N/m21
．． 3X 1o2N/n2F 2= 1.8X 1G2N
/m2 To the photoreceptor side Figure 5 is a double-sided copy 8! on the color copying machine of Figure 4! This is an example with additional functions, and the developing device and other omitted parts are the same as in FIG.

The transfer material 10 is supplied in the same manner as in the case of Fig. 0's4, is given a positive charge by the corona discharger 7, and is held on a transfer drum to which a negative bias voltage is applied. Yellow, magenta, and cyan toner images are transferred by the same process. After the cyan image has been transferred, the transfer material 10 is moved along the path indicated by line a to remove static electricity from the transfer material 10:
The discharger 27 removes the static electricity, and the separation claw 11 separates the paper from the transfer drum L and sends it to the fixing device 31, where a color image is completed on the upper surface and is once discharged onto the paper discharge tray 32. The ejected transfer material is drawn into the copying machine from the rear by the feed roller 33 of tjS2, and is fed so that the r:tS1 surface on which an image has already been formed is in contact with the transfer drum L. The transfer material reaching the transfer drum L is near r:
A positive charge is applied to the fjS2 surface by the I-discharger 34, and the transfer drum is attracted and fixed to the transfer drum to which a negative bias voltage is applied, and advances as it rotates with the drum. Below f
After yellow, magenta, and cyan toner images are sequentially transferred in the same manner as on the PSi surface, the toner image is peeled off from the drum surface, passes through the fixing device 31, and is ejected onto the ejection tray 32 as a copy having color images on both sides. Ru.

In the above embodiment, the case of color copying using yellow, magenta, and cyan toners using a normal three-color separation filter was explained.
Of course, the number of developing devices 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 dedication material holding drum can be used at any position, and the transfer drum and image carrier are constantly pressed against each other. It has many advantages, such as eliminating the need for pressure releasing or positioning mechanisms to avoid the locking means hitting the image carrier, and the transfer drum being easy to clean. By switching the polarity of the bias voltage applied to the transfer drum in a timely manner, you can achieve a high toner transfer rate and a high quality multi-color image without color x-rays ($! /) 4*b+ 4 emotion 0 simple A multicolor electrostatic recording device can be obtained.

[Brief explanation of the drawing]

fjS1 and ft52 are schematic diagrams showing the operation of the image transfer device according to the present invention, FIG. 3 is a schematic diagram of the pressure contact portion of the transfer section, FIG. The figure is a schematic diagram of the color copying machine shown in FIG. 4 with a double-sided copying function added. L... Image bearing drum L... Transfer drum 3...
Conductive substrate 4... Conductive elastic layer 5... Insulating layer 7... Transfer material charge imparting corona discharge device Agent Patent attorney No 1) Parent-in-law Figure 4

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 device has an insulating surface and switches between bias voltages having opposite polarity and the same polarity as the toner. and a transfer material charge applying means provided opposite to the transfer drum to apply a charge of opposite polarity to the charge of the toner to the surface of the transfer material. Image transfer device. (2) The transfer drum having an insulating surface includes a conductive drum base, a conductive elastic layer provided on the base,
The image transfer device according to claim 1, further comprising an insulating layer provided on the surface of the conductive elastic layer.