JP2004286851A - Image forming method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively eliminate or reduce the problem of toner scatter when a plurality of toner images are sequentially subjected to primary transfer to an intermediate transfer medium, and the problem of reverse transfer. <P>SOLUTION: An image forming method includes forming N(≥2) negative latent images on one or more electrostatic latent image carriers; reversely developing the negative latent images, thereby obtaining N positive toner images; subjecting the toner images to primary transfer onto the intermediate transfer medium one on another; and then subjecting the toner images from the surface of the intermediate transfer medium to secondarily transfer to the surface of a sheetlike recording medium. In the image forming method, at the time of primary transfer, a counterbias Vt is applied to the intermediate transfer body BL in the vicinity of the upstream of a transfer part. In addition, the potential of the counterbias Vt at the time of the M(=2 to N)th primary transfer is set almost equal to the reference potential of the previous image formed on the intermediate transfer body the (M-1)th by primary transfer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０１１８】
カウンタバイアスを印加しない場合と比較し、転写チリの少ない良好な画像が得られた。画像部電位の検出に際しては、前述の如く「専用のパターン」による作像を行った。
【０１１９】
図５に示す電位検出手段９０４２を用い、前述のようにして請求項３記載の方法により「カウンタバイアス：Ｖｔの決定」を行った。
図７に示すフロー図に従い、中間転写体ベルト上の画像部の電位を推定し、上記テーブルを参照してカウンタバイアスを決定した。
【０１２０】
感光体上画像部への逆転写による他色の混入、プレ転写による中間転写体ベルト上のトナー散りもなく、良好な画像が得られた。
【０１２１】
なお、各静電潜像担持体上のトナー画像の画像部電位と、中間転写媒体の各転写部の上流側での画像部電位とを各々電位検出して、これら電位を合致させるように各転写部におけるカウンタバイアスを定め得ることは勿論である。
【０１２２】
【発明の効果】
以上に説明したように、この発明によれば新規な画像形成方法および装置を実現できる。この発明の画像形成方法によれば上記の如く、複数のトナー画像を中間転写媒体上に１次転写する際のプレ転写・逆転写を有効に防止もしくは低減できる。従って、この発明の画像形成方法を実施する画像形成装置は、プレ転写や逆転写に起因する像質劣化を良好に防止もしくは低減して高品質の画像形成を行うことができる。
【図面の簡単な説明】
【図１】カウンタバイアスを説明するための図である。
【図２】カウンタバイアスを説明するための図である。
【図３】１次転写後の中間転写媒体上の画像部電位を説明するための図である。
【図４】画像形成装置の実施の１形態を説明するための図である。
【図５】図５の画像形成装置における転写部を説明するための図である。
【図６】実施例の画像部電位推定のフロー図である。
【図７】実施例の画像部電位推定の別のフロー図である。
【符号の説明】
ＰＣ 静電潜像担持体（光導電性の感光体）
ＢＬ 中間転写ベルト
Ｒ１ 転写ローラ
Ｒ２ カウンタバイアスローラ
ＴＹ イエロートナー[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming method and an image forming apparatus.
[0002]
[Prior art]
An image forming method of reversing development of a negative latent image formed on an electrostatic latent image carrier to obtain a positive toner image, and transferring and fixing the toner image on a sheet-like recording medium such as transfer paper is an electronic copying method. It is widely implemented in various image forming apparatuses such as apparatuses and optical printers.
[0003]
2. Description of the Related Art Recently, color image formation and the like have been widely used, and a plurality of negative latent images formed on one or more electrostatic latent image carriers are separately reverse-developed, and each toner image is transferred onto an intermediate transfer medium such as an intermediate transfer belt. An image forming method has been performed in which a toner image is synthesized by superimposing the images on a sheet and superimposing the toner images on each other, and then secondary-transferring and fixing the synthesized toner image onto a sheet-shaped recording medium.
[0004]
A problem of "toner scattering" has been conventionally known in connection with transfer of a toner image. Toner scattering is a phenomenon in which toner adheres to a “part that is not an original image” in an image finally carried on a sheet-shaped recording medium as if “scattered”, and impairs the image quality of the formed image. This phenomenon is caused by the fact that when the toner image enters the transfer area, when the distance between the toner image and the transfer material (in the case of the intermediate transfer method, the intermediate transfer medium) is reduced, some of the toner particles constituting the toner image It is thought to be based on so-called "pre-transfer", which flies toward and adheres to the transfer material surface.
[0005]
When a plurality of toner images are combined on the intermediate transfer medium as described above, the transfer (primary transfer) of the toner image to the intermediate transfer medium is repeated. When the transfer is performed, the toner particles of the toner image previously transferred onto the intermediate transfer medium fly and transfer to the latent image carrier, and are further transferred to the intermediate transfer medium (referred to as “reverse transfer”). ) Occurs. Even when reverse transfer occurs, an image formed has the same image deterioration as the above-mentioned "toner scattering".
[0006]
Regarding the toner scattering, various methods for preventing or reducing the toner scattering have been proposed (for example, Patent Documents 1 and 2), but a countermeasure for the "reverse transfer" is currently being sought. It is.
[0007]
[Patent Document 1]
JP-A-8-166728
[Patent Document 2]
JP-A-10-186878
[0008]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming method and apparatus capable of effectively eliminating or reducing the problem of reverse transfer as well as the problem of toner scattering.
[0009]
[Means for Solving the Problems]
The image forming method according to the present invention includes the steps of "forming N (≧ 2) negative latent images on one or more electrostatic latent image carriers, and reversal developing these negative latent images to form N positive toner images. Then, these toner images are sequentially primary-transferred onto an intermediate transfer medium, superimposed on each other, and then secondary-transferred from the intermediate transfer medium onto a sheet-shaped recording medium. "
[0010]
The “electrostatic latent image carrier” is a medium on which a desired electrostatic latent image is formed. The most common electrostatic latent image carrier is a "photoconductive photoconductor". In this case, the electrostatic latent image is formed by uniformly charging and exposing the photoconductor.
[0011]
The electrostatic latent image carrier may also be one having a dielectric surface and capable of holding the electrostatic latent image as a charge distribution on the surface. In this case, the electrostatic latent image is transferred to the electrostatic latent image formed on another electrostatic latent image carrier, or after the electrostatic latent image carrier is uniformly charged, and then moved to a position with a needle electrode or the like. It can be formed by selectively removing static electricity.
[0012]
The “negative latent image” is an electrostatic latent image in which the potential of an image portion (the portion where toner adheres) is attenuated, and a positive toner is formed by reversal development using toner having the same polarity as the electrostatic latent image charge. Visualized as an image. If the electrostatic latent image carrier is, for example, a photoconductive photoconductor, after uniformly charging the photoconductor, the potential of the image portion is optically attenuated by optical writing such as optical scanning, or It can be formed by irradiating a negative image of a document as a light image.
[0013]
The N electrostatic latent images may be formed differently from each other. For example, when forming two negative latent images, one may be formed by optical scanning, and the other may be formed by irradiating a negative image of a document as a light image.
[0014]
Two or more negative latent images may be visualized with “the same color toner” or may be visualized with different color toners. In the case of performing visualization using different color toners, a two-color image, a multicolor image, or a color image can be formed by combining the toner images.
[0015]
The electrostatic latent image carrier is in the form of a drum or a belt.
The intermediate transfer medium is also in the form of a drum or a belt. As a combination in form of the intermediate transfer medium and the electrostatic latent image carrier, a combination of a drum shape and a belt shape, or a combination of a belt shape and a belt shape is possible.
[0016]
In such a morphological combination, a drum-shaped or belt-shaped electrostatic latent image carrier and a belt-shaped or drum-shaped intermediate transfer medium come into contact with each other at a primary transfer portion to form a “nip portion”.
[0017]
The image forming apparatus according to the first aspect has the following features.
That is, at the time of the primary transfer, a counter bias: Vt is applied to the intermediate transfer medium near the upstream side of the transfer portion, and the counter bias: Vt at the time of the M (= 2 to N) -th primary transfer is set to M The “potential of the image portion previously formed on the intermediate transfer medium” by the first primary transfer is substantially equal to the potential of the image portion of the electrostatic latent image carrier having the M-th toner image. Set to be.
[0018]
The “potential of the image portion previously formed on the intermediate transfer medium by the M-1 primary transfer” is obtained by primary-transferring the toner image formed by exposure and development of the reference pattern onto the intermediate transfer medium. By measuring the potential of the image portion after the transfer with a surface voltmeter, the potential can be known in advance. The image portion potential is "shifted by the counter bias: Vt, and the shift amount by the counter bias is set so as to be substantially the same as the potential of the toner image portion on the electrostatic latent image carrier".
[0019]
The potential of the "image portion of the M-th toner image" can be known in advance from the electrostatic latent image forming condition and the developing condition.
The “upstream side of the transfer section” is a side on which the toner image primarily transferred to the intermediate transfer medium enters the transfer section.
[0020]
When the counter bias: Vt is applied as described above, when the M-th toner image primarily transferred to the intermediate transfer medium enters the transfer portion, the surface of the electrostatic latent image carrier and the surface of the intermediate transfer medium are moved. Even when the toner image is close to the toner, a large electric force is applied to the toner constituting the toner image on the electrostatic latent image carrier (the toner image to be primary transferred first) toward the intermediate transfer medium. In addition, the toner constituting the image formed on the intermediate transfer medium (formed by the first-transferred first-toned toner image) is also reversed to the electrostatic latent image carrier side. The big electric force to make a picture does not work.
Therefore, pre-transfer and reverse transfer can be favorably prevented or reduced.
[0021]
2. The image forming method according to claim 1, wherein the counter bias: Vt at the time of the M (= 2 to N) -th primary transfer is "based on an image portion formed on the intermediate transfer medium by the first primary transfer. And can be estimated and set based on the potential of the image portion formed on the intermediate transfer medium by the N-th primary transfer (claim 3). .
[0022]
For example, when N = 4, four electrostatic latent images are visualized with four colors of yellow, magenta, cyan, and black toners, and are primarily transferred onto the intermediate transfer belt in the above order. After the yellow toner image obtained according to the reference pattern is primarily transferred onto the intermediate transfer medium, the potential is shifted by applying a counter bias to the potential obtained by measuring the surface potential of the image portion, In the vicinity of the upstream side of the transfer portion, the potential of the image portion is set to be substantially equal to “the potential of the magenta toner image portion of the latent image carrier having the magenta toner image”.
[0023]
Since the conditions for transferring each color toner image to the intermediate transfer medium are known in advance, if the potential of the yellow toner image (the first primary transferred image) on the intermediate transfer medium is known as described above, Since the image portion potential on the intermediate transfer medium by the primary transfer of each color toner image can be empirically estimated (by a preliminary experiment), the counter bias: Vt can be set based on such an estimated value.
[0024]
As in the case of the third aspect, the image portion potential on the intermediate transfer medium is measured in a state where the four color toner images (all formed by the reference pattern) from the yellow toner image to the black toner image are primarily transferred. Conversely, a counter bias: Vt at the time of primary transfer of each toner image may be estimated and determined from this value. In the case of claim 3, magenta, cyan, and black toner images based on the potential of the image portion after the primary transfer of all four color toner images and the potential of the image portion after the transfer of the yellow toner image. Of the counter bias at the time of the primary transfer of the image may be estimated.
[0025]
In the image forming method according to any one of claims 1 to 3, a maximum potential value can be used as the potential of the image portion formed on the intermediate transfer medium (claim 4). That is, in this case, the maximum value of the potential of the toner image formed on the intermediate transfer medium is shifted to be substantially equal to the potential of the toner image portion on the electrostatic latent image carrier.
[0026]
In the image forming method according to any one of the first to fourth aspects, the potential of the image portion can be determined based on an output voltage detected by a surface potential detecting unit that detects a potential of the surface of the intermediate transfer medium. As described above, the counter bias: Vt is determined at the same time when the potential of the image portion is determined.
[0027]
An image forming method according to any one of claims 1 to 5, wherein N = 3 or 4, and different electrostatic latent images are formed of three colors of yellow, magenta, cyan or red, green, and blue, or black on these. It can be developed with the added four color toners. In this case, different electrostatic latent images can be “sequentially formed on the same electrostatic latent image carrier”, but can be “separately formed on two or more electrostatic latent image carriers” (claims). Item 7).
[0028]
The image forming apparatus according to the present invention is configured such that “N (≧ 2) negative latent images are formed on one or more electrostatic latent image carriers, and these negative latent images are reversal-developed to form N positive toner images. Then, these toner images are sequentially primary-transferred onto an intermediate transfer medium, superimposed on each other, and then secondary-transferred from the intermediate transfer medium onto a sheet-shaped recording medium. "
[0029]
The image forming apparatus according to claim 8 has the following features.
[0030]
That is, a primary transfer unit for performing primary transfer applies a transfer bias applying unit that applies a transfer bias to the primary transfer unit, and applies a counter bias: Vt to the intermediate transfer medium near the upstream side of the primary transfer unit. It has "counter bias means".
[0031]
Then, the counter bias: Vt at the time of the M (= 2 to N) primary transfer is set to substantially the same potential as the potential of the image portion previously formed on the intermediate transfer medium by the M-1 primary transfer. And a “counter bias setting unit”.
[0032]
The counter bias setting unit estimates the counter bias: Vt at the time of the M (= 2 to N) th primary transfer based on the potential of the image portion formed on the intermediate transfer medium by the first primary transfer. It is also possible to set the counter bias: Vt at the time of (M (= 2 to N) th primary transfer) the image formed on the intermediate transfer medium by the Nth primary transfer. It can be set by estimating based on the potential of the unit (claim 10).
[0033]
The image forming apparatus according to any one of claims 8 to 10, wherein the counter bias setting unit uses the maximum value of the potential of the image portion formed on the intermediate transfer medium as the potential of the image portion used for setting the counter bias. (Claim 11).
[0034]
The image forming apparatus according to any one of claims 8 to 11, wherein the image forming apparatus includes: a surface potential detecting unit configured to detect a potential of an image portion on the intermediate transfer medium after the primary transfer; The potential of the image portion is determined based on the potential detected by the surface potential detecting means, and the counter bias in the second and subsequent transfer in the primary transfer is set based on this potential. "
[0035]
The image forming apparatus according to any one of claims 8 to 12, wherein N = 3 or 4, wherein different electrostatic latent images are three colors of yellow, magenta, cyan or red, green, and blue or black is added to these. The toner can be developed with four different colors.
In this case, different electrostatic latent images may be sequentially formed on the same electrostatic latent image carrier, but different electrostatic latent images are formed separately on two or more electrostatic latent image carriers. It is also possible to adopt a configuration in which primary transfer is performed from each electrostatic latent image carrier to an intermediate transfer medium (claim 14).
[0036]
The image forming apparatus according to the fourteenth aspect may be configured as a “tandem type image forming apparatus in which three or four electrostatic latent image carriers are arranged in the running direction of the surface of the intermediate transfer medium”. 15).
[0037]
To add a little, in the present invention, the number of toner images to be provided for forming one image: N can be N = 2, 3 or 4 as described above, but is not limited to this. The present invention is also applicable to the case of N of 5 or more. For example, when a color image is formed, normally, N = 4, and four electrostatic latent images are visualized with four colors of yellow, magenta, cyan, and black toners. More precise color expression is possible in the formed image.
[0038]
Here, the operation of the present invention will be described.
FIG. 1 schematically shows the state of primary transfer of a toner image from an electrostatic latent image carrier to an intermediate transfer medium. The electrostatic latent image carrier is rotated in the direction of the arrow by a photoconductive photoconductor PC formed in a drum shape. The intermediate transfer medium travels rightward in the figure on an intermediate transfer belt BL formed in an endless belt shape.
[0039]
A transfer voltage is applied to a “transfer roller” indicated by a symbol R1 from a power supply D1. Symbol R2 indicates a counter bias roller. A counter bias: Vt is applied to the counter bias roller R2 from the power supply D2. The counter bias roller R2 and the power supply D2 constitute "counter bias means".
[0040]
Since the rotation direction of the photoconductor PC and the traveling direction of the intermediate transfer belt BL are as described above, the counter bias: Vt by the counter bias roller R2 is intermediate on the upstream side of the position of the transfer roller R1 which is the “transfer section”. The voltage is applied from the back side of the transfer belt BL.
[0041]
FIG. 1 shows a state in which a yellow toner image formed by the yellow toner TY is transferred. Here, it is assumed that the yellow toner image is firstly transferred first.
[0042]
The yellow toner image enters the transfer section from the left side of the drawing as the photoconductor PC rotates in the direction of the arrow, and is transferred onto the intermediate transfer belt BL by the transfer voltage applied by the transfer roller R1.
[0043]
For the sake of specificity, in the following description, in the following description, an electrostatic latent image is a negative latent image formed by a negative potential distribution (a non-image portion has a uniform negative potential; The surface potential is attenuated due to light). The yellow toner TY is negatively charged to the same polarity as the electrostatic latent image, and is captured by the image portion of the negative latent image whose potential has been attenuated by reversal development to form a yellow toner image. Therefore, in order to transfer this yellow toner image to the intermediate transfer belt BL, the transfer roller R1 applies a positive potential to the transfer portion.
[0044]
FIG. 2A schematically shows a potential relationship between a yellow toner image portion and a non-image portion on the photoconductor PC. The potential changes in the vertical direction, and the upper part of the figure indicates the direction in which the positive potential increases, and GND indicates the ground level. The surface of the photoconductor PC has a uniform negative potential: V ₀ In the negative latent image portion, the latent image potential: V _L In this portion, the yellow toner TY of negative polarity is captured.
[0045]
Latent image potential: V _L Is 0 V if optical attenuation is ideally performed, but in reality, a potential of about -100 to -150 V remains. The transfer voltage by the transfer roller R1 forms an "electric field from the intermediate transfer belt BL to the photoconductor PC" at the transfer portion, and the yellow toner TY is transferred onto the intermediate transfer belt BL by the action of the electric field.
That is, since the yellow toner TY has a negative polarity, the yellow toner TY moves to the higher potential side (the side where the potential increases in the positive direction, that is, upward in FIG. 2A).
[0046]
Considering the "pre-transfer" described above, if the counter bias by the counter bias roller R2: Vt is set to 0, the potential of the image portion of the electrostatic latent image shown in FIG. _L If the ideal value is 0 V, even if the surface of the photoconductor PC and the surface of the intermediate transfer belt BL are close to each other in the vicinity of the upstream side of the transfer unit, the “yellow toner TY is applied to the intermediate transfer belt BL” in the gap therebetween. The "electric field to fly to the side" does not substantially occur, and pre-transfer does not occur.
[0047]
However, as described above, actually, the image portion potential: V _L Is a finite negative potential, not 0, and if the counter bias: Vt is set to 0, an electric field is generated in the gap from the photoconductor PC toward the intermediate transfer belt BL, and the yellow toner TY is generated by the action of the electric field. It flies toward the intermediate transfer belt BL and generates "toner scattering" due to pre-transfer.
[0048]
In order to prevent such pre-transfer, it is necessary to set the counter bias: Vt as “absolute value is at least latent image potential: V _L In this case, the yellow toner TY is repelled from the intermediate transfer belt BL to the gap between the photoconductor PC and the intermediate transfer belt BL near the upstream side of the transfer unit. An electric field is generated, and pre-transfer is effectively prevented.
[0049]
FIG. 2B schematically shows the state of the potential on the intermediate transfer belt BL on which the yellow toner image is transferred by the yellow toner TY. When the yellow toner image is transferred onto the intermediate transfer belt, the surface potential of the intermediate transfer belt BL becomes more positive than the ground level GND as shown in the figure. This is because a positive charge is applied to the intermediate transfer belt from the transfer roller R1 at the time of transfer.
[0050]
The potential of the surface of the intermediate transfer belt is not uniform, and the potential of the “image portion” to which the yellow toner TY adheres is higher than the surface potential of the non-image portion. This is because, when the transfer is performed, “the negative charges constituting the non-image portion on the photoconductor PC are transferred by peeling discharge” to the non-image portion, and the potential is biased to the minus side from the image portion. is there.
[0051]
FIGS. 2C to 2E are explanatory diagrams showing potential relationships when a magenta toner image is transferred by the magenta toner TM onto an intermediate transfer belt on which a yellow toner image is transferred by the yellow toner TY. .
[0052]
In the state shown in FIG. 2C, “counter bias: the negative polarity of Vt is not sufficient” near the upstream side of the transfer portion of the magenta toner image, and the surface potential on the intermediate transfer belt BL is the image portion of the electrostatic latent image. Potential: higher than VL. In this case, since the electric force F1 toward the photoconductor PC acts on the negative magenta toner TM constituting the magenta toner image on the photoconductor, toner scattering due to the pre-transfer of the magenta toner YM occurs. appear.
[0053]
Conversely, the state of FIG. 2C shows a state in which the negative polarity of the counter bias: Vt is too large, and the surface potential of the intermediate transfer belt is lower than the surface potential of the photoconductor near the upstream side of the transfer unit. In this case, an electric field from the photoconductor to the intermediate transfer belt is generated between the surface of the adjacent photoconductor and the surface of the intermediate transfer belt, and the yellow toner TY transferred on the intermediate transfer belt is directed to the photoconductor. The electric force F2 is generated, and the “reverse transfer” of the yellow toner TY is generated by the action of the electric force F2.
[0054]
FIG. 2E shows that the "potential of the image portion" of the yellow toner image formed on the intermediate transfer belt becomes equal to the image portion potential of the magenta toner image on the photoconductor by an appropriate counter balance: Vt. If it is. In this case, neither the force for reversely transferring the yellow toner on the intermediate transfer belt nor the force for pre-transferring the magenta toner on the photoreceptor acts, and the magenta toner image is transferred to the intermediate transfer medium without pre-transfer and reverse transfer. Can be transferred on top.
[0055]
Hereinafter, even when the cyan toner image and the black toner image are primarily transferred onto the intermediate transfer belt, the counter bias: Vt is appropriately set so that the image portion potential of the toner image on the intermediate transfer belt becomes By making the potential substantially equal to the image portion potential of the toner image, the primary transfer of each toner image can be appropriately performed.
[0056]
That is, in general, when there are N toner images to be subjected to the primary transfer, the counter bias: Vt at the time of the M (= 2 to N) -th primary transfer is first increased by M-1 times of the primary transfer. By setting the potential of the image portion formed on the intermediate transfer medium to be substantially the same as the potential of the image portion on the electrostatic latent image carrier having the M-th toner image (claim 1) Appropriate primary transfer can be performed.
[0057]
The description with reference to FIG. 2E illustrates that the potential of the image portion during the primary transfer of the magenta toner image is “equal to the reference potential of the image portion of the yellow toner image on the intermediate transfer belt”. In this case, it is difficult to make the two potentials “equal”.
[0058]
However, even if these potentials do not completely match, if "the difference between the two potentials is small to some extent", pre-transfer and reverse transfer due to toner flying do not occur. That is, if the potential difference between the potential of the image portion on the intermediate transfer belt and the potential of the image portion of the toner image on the photoreceptor is "about 200 V", the experimental result indicates that the problem of "pre-transfer / reverse transfer" does not occur. Was obtained.
[0059]
Therefore, "the potential of the image portion formed on the intermediate transfer medium is substantially the same as the potential of the image portion on the electrostatic latent image carrier having the toner image to be newly primary-transferred" It means that the difference between these potentials is smaller than about 200V.
[0060]
When the potential difference between the “potential of the image portion of the toner image” on the intermediate transfer medium and the potential of the image portion of the toner image on the photosensitive member is compared as “the same potential difference”, the flying from the intermediate transfer medium to the photosensitive member It was confirmed that (reverse transfer) is less likely to occur than flying from the photoconductor to the intermediate transfer medium (pre-transfer).
[0061]
This means that the image on the photoreceptor is a negative / positive image, whereas the image on the intermediate transfer medium is a positive / positive image. It is thought that.
[0062]
Surface potential of the image portion on the electrostatic latent image carrier near the upstream portion of the transfer portion: V _L And the surface potential of the image area on the intermediate transfer medium: V _tL Therefore, to obtain the counter bias: Vt, the relation: V _L = V _tL + Vt may be used, and the surface potential on the intermediate transfer medium: V _tL Is known, that is, when it is previously obtained as data by experiment, the operation: Vt = V _L -V _tL Can be obtained by
[0063]
In practice, it is preferable to form a table based on experimentally obtained data in advance and set the counter bias: Vt by referring to the table.
[0064]
Thus, V _L The value can be set as a "value stored in the table in advance", but it is possible to add the "deterioration degradation change" predicted from the number of image formation or to measure the residual potential in the image portion of the electrostatic latent image It is preferable to provide an appropriate means and determine the value based on the output.
[0065]
FIG. 2 illustrates a case where a magenta toner image is transferred onto an intermediate transfer medium on which a yellow toner image is primarily transferred. As described above, the surface potential of the intermediate transfer medium after the transfer of the yellow toner image is positive as a whole, and the potential of the image portion is higher than the potential of the non-image portion.
[0066]
In FIG. 3, the vertical axis represents the potential on the surface of the intermediate transfer medium. The reference numeral 3-1 indicates the surface potential on the intermediate transfer medium when the yellow toner image is first transferred first by the yellow toner TY as described above. Reference numeral 3-2 indicates the surface potential on the intermediate transfer medium after the magenta toner image is primarily transferred by the magenta toner TM onto the intermediate transfer medium on which the yellow toner image has been primarily transferred.
[0067]
Surface potential portion: A is a portion where the yellow toner image and the magenta toner image are both non-image portions; surface potential portion: B is a portion where the yellow toner image is an image portion and the magenta toner image is a non-image portion; : C indicates a portion where both the yellow toner image and the magenta toner image are image portions, and D indicates a portion where the yellow toner image is a non-image portion and the magenta toner image is an image portion.
[0068]
In each of the surface potential portions, the potential is shifted to the negative side (downward in the figure) from after the primary transfer of the yellow toner image. This is due to the effect of the increase of the negative charge of the magenta toner TM due to the transfer of the magenta toner image and the effect of “peeling discharge during transfer”.
[0069]
Hereinafter, the potential distribution on the intermediate transfer medium in the case where the cyan toner image and the black toner image are primarily transferred changes in the same manner as in FIG. 3, and generally, as the number of times of the primary transfer increases, the potential distribution becomes negative. Shift to the side.
[0070]
When the conditions such as the charge amount and the proper adhesion amount of each color toner are made substantially the same, it is possible to estimate “the potential change of the image portion on the intermediate transfer medium due to one-color transfer”.
[0071]
Assuming that the difference between the surface potential of the intermediate transfer medium before the start of the primary transfer and the surface potential after the transfer of the first color (the yellow toner image in the above-described example) is ΔV (this value is obtained experimentally in advance), With ΔV, it can be estimated as “the potential change of the image portion due to one-color transfer”, and a counter bias: Vt can be set based on this ΔV (claim 2).
[0072]
As described above, if the conditions such as the charge amount and the proper adhesion amount of each color toner are set to be substantially the same, the potential change of the image portion due to one color transfer (primary transfer of one color toner image) can be estimated. Although it is possible, as another method, the primary transfer is started by considering the potential of the image portion of the intermediate transfer medium “after all the primary transfer” of the yellow toner image to the black toner image on the intermediate transfer medium. If the difference in surface potential between before and after four-color transfer: V is experimentally determined, the potential change for each one-color transfer: ΔV can be estimated as V / 4, and based on this V / 4, the counter bias: Vt Can be set (claim 3)
Referring again to FIG. 3, the surface potential distribution 3-2 on the intermediate transfer medium after the primary transfer of the magenta toner image changes stepwise according to the degree of overlap between the yellow toner image and the image portion of the magenta toner image. In such a case, how to determine the shift amount of the surface potential due to the counter bias: Vt at the time of the next primary transfer of the cyan toner image becomes a problem.
[0073]
In this case, the maximum potential value V1 at the potential 3-2 after the primary transfer of the magenta toner image is used, and this is shifted by the counter bias: Vt, so that the cyan toner image on the photosensitive member is shifted. It is made substantially equal to the image portion potential. That is, the potential of the surface potential portion: C in FIG. 3 is shifted to the negative polarity side by the counter bias, and is made equal to “the potential of the cyan toner image portion on the electrostatic latent image carrier”.
[0074]
In this case, in the surface potential portions: A, B, C, and D in FIG. 3, the potential state in which the cyan toner does not move (pre-transfer) from the electrostatic latent image carrier onto the intermediate transfer medium (in the vicinity of the upstream side of the transfer portion) The electric field in the vicinity of the electrostatic latent image carrier and the intermediate transfer medium is directed from the electrostatic latent image carrier to the intermediate transfer medium.
[0075]
In this potential state, the yellow toner and the magenta toner can move from the intermediate transfer medium onto the electrostatic latent image carrier in terms of potential, but as described above, the yellow toner and the magenta toner move from the intermediate transfer medium to the electrostatic latent image carrier. Since the toner is unlikely to fly, the above-described procedure makes it possible to execute the primary transfer of the cyan toner image by effectively preventing or reducing the reverse transfer while preventing the pre-transfer.
[0076]
Similarly, when the last black toner image is primarily transferred, the reference potential obtained by shifting the maximum potential value of the image portion potential of the yellow, magenta, and cyan toner images on the intermediate transfer medium by the counter bias: Vt is What is necessary is just to make it substantially equal to the image portion potential of the black toner image on the electrostatic latent image carrier.
[0077]
When the polarity of the electrostatic latent image formed on the electrostatic latent image carrier is positive and the reversal development is performed using positively charged toner, the above “maximum potential value” is “negative polarity”. The maximum value of the absolute value of the potential of
[0078]
As described above, the method of setting the counter bias: Vt does not require the individual detection of “the potential of the image portion of the intermediate transfer medium after the primary transfer of the toner image of each color”. Since it becomes unnecessary, space saving and cost reduction can be realized.
[0079]
In an actual operation state of the image forming apparatus, when the intermediate transfer medium passes through the application part of the counter bias: Vt, the potential state of the surface of the intermediate transfer medium is influenced by the secondary transfer, the degree of the neutralization of the intermediate transfer medium, It may change depending on the presence or absence of toner on the transfer medium, and the effect of the counter bias differs depending on the potential state when passing through the counter bias applying unit.
[0080]
From this point of view, a surface potential detecting unit that detects the potential of the surface of the intermediate transfer medium is provided upstream of each transfer unit, and the “potential of the image portion of the intermediate transfer medium” detected by the surface potential detecting unit is detected. It can be said that it is preferable to set the counter bias: Vt based on this (claim 5).
[0081]
The occurrence of pre-transfer is considered that the gap between the electrostatic latent image carrier and the intermediate transfer medium is considered to be “a region of several hundred μm or less”. : It is preferable that the position to which Vt is applied is a "part as close as possible" to the transfer portion on the upstream side of the transfer portion.
[0082]
For example, in the case shown in FIG. 1, when the diameter of the photoconductor PC is 40 mm and the contact width (nip width) between the photoconductor PC and the intermediate transfer belt BL is about 10 mm, the counter bias: Vt is set by the counter bias roller R2. Is preferably located at a position about 5 mm away from the nip portion where the photoconductor PC and the intermediate transfer medium BL are in contact with each other.
[0083]
The means for applying the transfer voltage or the counter bias does not necessarily have to be “roller-shaped”, and it is sufficient that the voltage can be applied by securely contacting the back side of the intermediate transfer medium. For example, instead of the transfer roller and the counter bias roller, a blade-shaped or plate-shaped application member may be used, and these may be brought into contact with the back side of the intermediate transfer medium to apply the transfer voltage and the counter bias. .
[0084]
BEST MODE FOR CARRYING OUT THE INVENTION
One embodiment of an image forming apparatus embodying the present invention will be described with reference to FIGS. FIG. 4 is an overall view of the apparatus, and FIG. 5 is a partial view for explaining the features of the present invention. An overview of the image forming process will be described first with reference to FIG.
[0085]
The image forming apparatus 900 shown in FIG. 4A is a “tandem type color image forming apparatus”. The color original is read by the reading unit 901 after being separated into red, green, and blue, and based on the read information, image data for each of black (B), yellow (Y), magenta (M), and cyan (C) is obtained. Generated. The configuration of such a reading unit has been widely known.
[0086]
These image data are provided for optical writing at the image forming stations 903B, 903Y, 903M, and 903C by the optical writing device 902. Since the image forming stations 903B to 903C are structurally the same, the image forming station 903B will be described as an example.
[0087]
As shown in FIG. 4B, the image forming station 903B is charged around a photoconductive photoconductor (electrostatic latent image carrier) 91B formed in a drum shape that is driven to rotate counterclockwise. The configuration is such that a charger 92, a developing device 93, a transfer means 94, and a cleaning device 95 are provided.
[0088]
The transfer unit 94 includes a transfer roller 94A, a counter bias roller 94B, and a unit (not shown) for applying a predetermined voltage to these.
[0089]
As shown in FIG. 4A, an intermediate transfer belt 9041 as an intermediate transfer medium runs between the photoreceptor 91B and the transfer roller 94A / counter bias roller 94B in the direction of the arrow. The photoreceptor 91B is uniformly charged by the charger 92 while rotating counterclockwise, and B image data corresponding to a black image is written by the laser beam LBB to form a B latent image (negative latent image).
[0090]
The B latent image is reversely developed by the developing device 93 to become a “black toner image” using black toner, and the black toner image is primarily transferred onto the intermediate transfer belt 9041 by the transfer roller 94A. At this time, a counter bias: Vt is applied by the counter bias roller 94B to prevent pre-transfer.
[0091]
The photoconductor 91B after the transfer of the toner image is cleaned by the cleaning device 95.
[0092]
Similarly, in the image forming stations 903Y, 903M, and 903C shown in FIG. 4A, yellow, magenta, and cyan color toner images are formed, and these color toner images are displayed on the intermediate transfer belt 9041 as "black toner image". It is transferred so as to "overlap". The color image formed by the black, yellow, magenta, and cyan toner images formed on the intermediate transfer belt 9041 in this manner is secondarily transferred onto a transfer sheet S as a “sheet recording medium”.
[0093]
The transfer paper S is fed from a cassette 906 at the bottom of the image forming apparatus main body, or is manually distributed from a manual feed unit 907, and is registered by a registration roller 909 in a “secondary transfer unit”, that is, an intermediate transfer belt 9041 and a secondary transfer belt. The color image is transferred to the contact portion with the timing 905 at a time when the color image is moved, and the color image is transferred by the action of the secondary transfer bias applied to the secondary transfer belt 905 from a bias applying unit (not shown). The secondary transfer belt 905 and a bias applying unit (not shown) constitute a “secondary transfer unit”.
[0094]
The transfer paper S on which the color image has been transferred is conveyed by a secondary transfer belt 905, is discharged by a charge eliminator (not shown), is separated from the secondary transfer belt 905, and the color image is fixed by a fixing device 910. The sheet is conveyed and discharged out of the apparatus by discharge rollers 912.
[0095]
The outer peripheral surface of each of the intermediate transfer belt 9041 and the secondary transfer belt 905 after the secondary transfer is cleaned by a belt cleaning device (not shown).
[0096]
In the case of the “double-sided image forming mode” in which images are formed on both sides of the transfer sheet S, the transfer path of the transfer sheet S on which the color image is fixed on one side is switched by the switching claw 915 to switch between the transfer roller 911 and a guide (not shown). To the reversing section 913, and turn over the sheet at the reversing section 913, stack the sheets on the stacker 914 with the “surface on which the color image is formed facing upward”, convey again to the position of the registration roller 909, and do the same as above. To transfer the color image to the back side. Thereafter, the color image on the back surface is fixed by the fixing device 910, conveyed by the conveyance roller 911, and discharged out of the device by the discharge roller 912.
[0097]
FIG. 5 is a diagram for explaining a transfer unit in the image forming apparatus shown in FIG. In FIG. 5A, reference numerals 91B to 91C denote photoconductive photoconductors, respectively, wherein a black toner image is on the photoconductor 91B, a yellow toner image is on the photoconductor 91Y, a magenta toner image is on the photoconductor 91M, The cyan toner images are respectively formed on the photoconductors 91C. Reference numerals 94BK to 94C denote "primary transfer means" for performing primary transfer on each photoconductor, and in the figure, a transfer roller and a counter bias roller provided near the upstream side thereof are shown.
[0098]
The primary transfer performed in each primary transfer unit is as described above with reference to FIGS. 1 to 3. The counter bias: Vt is applied to the counter bias roller in each primary transfer unit. The primary transfer is performed while effectively preventing or reducing pre-transfer and reverse transfer.
[0099]
If the electric resistance of the intermediate transfer belt is low, a large current flows between the counter bias roller and the transfer roller via the intermediate transfer belt at each transfer section, and thus the volume resistance of the intermediate transfer belt may be high to some extent. Necessary, specifically 10 ⁸ -10 ¹⁰ Ωm can be used, but preferably 1 × 10 ⁹ Ωm is good.
[0100]
If the volume resistance value of the intermediate transfer belt is too high, the self-static elimination property of the intermediate transfer belt deteriorates, so that it is necessary to eliminate electricity by a dedicated static eliminator. Self-static elimination is performed by the charge flowing through the bulk of the intermediate transfer belt.Therefore, no current flows between the counter bias roller and the intermediate transfer roller, and the bulk of the intermediate transfer belt must have a structure that allows current to flow easily. preferable.
[0101]
For example, the intermediate transfer belt has a three-layer structure, and the volume resistivity of the first, second, and third layers: ρ1, ρ2, ρ3 from the side (back side) in contact with the counter bias roller, ρ1>ρ2> ρ3 or ρ1> ρ2 <ρ3, and the total resistance is 10 ⁸ -10 ¹⁰ Ωm.
[0102]
Referring to FIG. 5B, reference numerals 194B, 194Y, 194M, and 194C denote counter bias rollers in the transfer units 94BK to 94C, respectively, which are counter bias setting units CBS (configured by a microcomputer or the like). , A "counter bias: Vt set for each counter bias roller" is applied from the power supplies BDB, BDY, BDM, and BDC.
[0103]
In FIG. 5A, reference numeral 9042 denotes a potential detecting unit that detects the surface potential of the intermediate transfer belt 9041.
[0104]
In the case of realizing the method described in claim 2 in the image forming apparatus of FIGS. 4 and 5, a negative latent image of the reference pattern is formed on the photoconductor 91C on the most downstream side in the transfer unit, and this is inverted. The cyan toner image obtained by development is transferred onto the intermediate transfer belt 9041. At this time, the counter bias does not need to be applied.
[0105]
The potential of the image portion of the cyan toner image transferred onto the intermediate transfer belt 9041 is detected by the potential detecting means 9042, and the counter bias value of the primary transfer for the second color and thereafter is estimated and set as described above. The counter bias setting unit CBS in FIG. 5B performs the estimation and the setting according to the detected potential of the potential detecting means 9042.
[0106]
In the case of realizing the method according to claim 3, a negative latent image of a reference pattern is formed on each of the photoconductors 91BK to 91C in the transfer unit, and each color toner image obtained by reversing and developing the negative latent image is transferred to the intermediate transfer belt 9041. Transfer sequentially to the top. At this time, no counter bias is applied.
[0107]
The potential of the image portion of the color image thus obtained on the intermediate transfer belt is detected by the potential detecting means 9042, and the counter bias value for the primary transfer of each color toner image is determined by the counter bias setting unit CBS as described above. Estimate and set. In any of the above cases, the surface potential Vb of the intermediate transfer belt is detected before the primary transfer of the first toner image.
[0108]
【Example】
Image formation was performed using the image forming apparatus described with reference to FIGS. The order of primary transfer to the intermediate transfer medium is in the order of black, yellow, magenta, and cyan toner images in the case of color image formation. An image was formed with a color image and evaluated.
[0109]
First, a yellow toner image was formed on the photoreceptor 91Y. In the image portion of the yellow toner image, the image portion potential of the electrostatic latent image is approximately −100 V, and is approximately −200 V with the yellow toner attached.
[0110]
The surface potential on the intermediate transfer belt 9041 onto which the yellow toner image was transferred “without applying a counter bias” was measured by a potential detecting unit 9042. At this time, the image portion potential was +500 V. This potential changes depending on the bias condition at the time of the secondary transfer. Control is performed to change the bias condition of the secondary transfer in accordance with an environmental change or the like. The main purpose of this control is to correct a change in the efficiency of the secondary transfer caused by the “fluctuation in the resistance value of the transfer paper” due to the environment.
[0111]
At the time of primary transfer of the first color yellow toner image, there is no toner image previously transferred on the intermediate transfer belt, so a negative potential having a sufficiently large absolute value is applied as the counter bias: Vt.
[0112]
In the embodiment, vt = −700V. After the transfer of the yellow toner image, the transfer of the second color magenta toner image was performed. The latent image potential of the image portion of the magenta toner image on the photoconductor 91M is about -100V, and about -200V when the toner is attached. The potential of the image portion of the yellow toner image on the intermediate transfer belt before the transfer of the magenta toner image was measured to be +430 V.
[0113]
In this state, the value of the counter bias is changed variously, and after the primary transfer of the magenta toner image is performed, the apparatus is stopped, and the presence or absence of yellow toner due to the reverse transfer on the photoreceptor 91M is determined. Observation of the state of magenta toner scattering due to pre-transfer showed the following results.
[0114]
Counter bias (V) Yellow toner adhesion Magenta toner scattering
−200 ○ ×
−300 ○ ×
−400 ○ △
−500 ○ ○
-600 ○ ○
-700 × ○
-800 × ○
The mark “○” indicates that no adhesion or scattering was observed, the mark “X” indicates that much adhesion or scattering was observed, and the mark “△” indicates that only a small amount of scattering was observed.
[0115]
Using the potential detecting means 9042 shown in FIG. 5, "counter bias: determination of Vt" was performed by the method described in claim 2. FIG. 6 shows a flowchart. “Thr” in this flowchart is the upper limit of the amount of potential change due to one-color transfer, and when the amount of potential change of one color is equal to or more than this value, the image on the intermediate transfer belt before the primary transfer for the third color and thereafter Assuming that the partial potential is V1, the potential difference on the upstream side of the transfer portion at the time of the primary transfer of the fourth color becomes large, causing the toner to fly. If it is equal to or less than Thr, the image portion potential is set to V1 and no problem occurs.
[0116]
“Thr” is about 50 to 70 V, but was set to 70 V in the example. The counter bias value is determined by referring to the following table based on the roughly determined image portion potential on the intermediate transfer belt. This table stores the data fixed by the system in advance. In the image formation, a full-color image is formed, the apparatus is stopped at each timing after one-color transfer, two-color transfer, three-color transfer, and four-color transfer, and the toner on the photoreceptor and the intermediate transfer belt is stopped. Scattering (pre-transfer) and toner adhesion (reverse transfer) were observed.
[0117]

[0118]
As compared with the case where no counter bias was applied, a good image with less transfer dust was obtained. When detecting the image portion potential, an image was formed using the “dedicated pattern” as described above.
[0119]
Using the potential detecting means 9042 shown in FIG. 5, "counter bias: determination of Vt" was performed by the method of claim 3 as described above.
According to the flowchart shown in FIG. 7, the potential of the image portion on the intermediate transfer belt was estimated, and the counter bias was determined with reference to the above table.
[0120]
A good image was obtained without mixing other colors due to reverse transfer to the image portion on the photoreceptor and toner scattering on the intermediate transfer belt due to pre-transfer.
[0121]
Note that the potential of the image portion of the toner image on each electrostatic latent image carrier and the potential of the image portion on the upstream side of each transfer portion of the intermediate transfer medium are respectively detected, and each potential is matched so that these potentials match. Of course, the counter bias in the transfer section can be determined.
[0122]
【The invention's effect】
As described above, according to the present invention, a novel image forming method and apparatus can be realized. According to the image forming method of the present invention, as described above, pre-transfer and reverse transfer during primary transfer of a plurality of toner images onto an intermediate transfer medium can be effectively prevented or reduced. Therefore, the image forming apparatus that performs the image forming method of the present invention can perform high quality image formation by favorably preventing or reducing image quality deterioration due to pre-transfer and reverse transfer.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a counter bias.
FIG. 2 is a diagram for explaining a counter bias.
FIG. 3 is a diagram for explaining an image portion potential on an intermediate transfer medium after primary transfer.
FIG. 4 is a diagram for explaining an embodiment of the image forming apparatus.
FIG. 5 is a diagram for explaining a transfer unit in the image forming apparatus of FIG. 5;
FIG. 6 is a flowchart of image portion potential estimation according to the embodiment.
FIG. 7 is another flowchart of the image portion potential estimation of the embodiment.
[Explanation of symbols]
PC electrostatic latent image carrier (photoconductive photoconductor)
BL Intermediate transfer belt
R1 transfer roller
R2 Counter bias roller
TY yellow toner

Claims (15)

N (≧ 2) negative latent images are formed on one or more electrostatic latent image carriers, and each of the negative latent images is reversely developed to obtain N positive toner images. An image forming method in which primary transfer is sequentially performed on a transfer medium and superimposed on each other, and then secondary transfer is performed on the sheet-shaped recording medium from the intermediate transfer medium,
At the time of the primary transfer, a counter bias: Vt is applied to the intermediate transfer medium near the upstream side of the transfer portion,
When the counter bias at the time of the M (= 2 to N) primary transfer: Vt, the potential of the image area previously formed on the intermediate transfer medium by the M-1 primary transfer is changed to the M-th toner. An image forming method, wherein the potential is set to be substantially the same as the potential of an image portion on an electrostatic latent image carrier having an image. The image forming method according to claim 1,
A counter bias: Vt at the time of the M (= 2 to N) primary transfer is estimated and set based on the potential of the image portion formed on the intermediate transfer medium by the first primary transfer. Image forming method. The image forming method according to claim 1, wherein
The counter bias: Vt at the time of the M (= 2 to N) primary transfer is estimated and set based on the potential of the image portion formed on the intermediate transfer medium by the N-th primary transfer. Image forming method. The image forming method according to any one of claims 1 to 3,
An image forming method, wherein a maximum potential value is used as a potential of an image portion formed on an intermediate transfer medium. The image forming method according to any one of claims 1 to 4,
An image forming method comprising: determining a potential of an image portion formed on an intermediate transfer medium on the basis of an output voltage detected by a surface potential detecting unit that detects a potential of the surface of the intermediate transfer medium. The image forming method according to any one of claims 1 to 5,
N = 3 or 4, wherein the different electrostatic latent images are developed with three colors of yellow, magenta, cyan or red, green, and blue, or four colors of black and black. Image forming method. The image forming method according to claim 6,
An image forming method, wherein different electrostatic latent images are formed separately on two or more electrostatic latent image carriers. N (≧ 2) negative latent images are formed on one or more electrostatic latent image carriers, and each of the negative latent images is reversely developed to obtain N positive toner images. In an image forming apparatus, a primary transfer is sequentially performed on a transfer medium, superimposed on each other, and then a secondary transfer is performed on the sheet-like recording medium from the intermediate transfer medium.
A primary transfer unit for performing primary transfer applies a transfer bias applying unit that applies a transfer bias to the primary transfer unit, and applies a counter bias: Vt to the intermediate transfer medium near the upstream side of the primary transfer unit. Having counter bias means,
When the counter bias at the time of the M (= 2 to N) primary transfer: Vt, the potential of the image area previously formed on the intermediate transfer medium by the M-1 primary transfer is changed to the M-th toner. An image forming apparatus comprising: a counter bias setting unit that sets a potential substantially equal to a potential of an image unit on an electrostatic latent image carrier having an image. The image forming apparatus according to claim 8,
A counter bias setting unit estimates and sets a counter bias: Vt at the time of the M (= 2 to N) th primary transfer based on the potential of the image portion formed on the intermediate transfer medium by the first primary transfer. An image forming apparatus, comprising: The image forming apparatus according to claim 8, wherein
The counter bias setting unit estimates a counter bias: Vt at the time of the M (= 2 to N) -th primary transfer based on the potential of the image portion formed on the intermediate transfer medium by the N-th primary transfer. An image forming apparatus characterized by setting. The image forming apparatus according to any one of claims 8 to 10,
An image forming apparatus, wherein a maximum value of the potential of an image portion formed on an intermediate transfer medium is used as a potential of an image portion used by a counter bias setting portion for setting a counter bias. The image forming apparatus according to any one of claims 8 to 11,
A surface potential detecting means for detecting a potential of an image portion on the intermediate transfer medium after the primary transfer; a counter bias setting portion determining a potential of the image portion based on a potential detected by the surface potential detecting portion; An image forming apparatus, wherein a counter bias is set in second and subsequent transfer in primary transfer based on a potential. The image forming apparatus according to any one of claims 8 to 12,
N = 3 or 4, wherein the different electrostatic latent images are developed with three colors of yellow, magenta, cyan or red, green, and blue, or four colors of black and black. Image forming method. The image forming apparatus according to claim 13,
Different electrostatic latent images are formed separately on two or more electrostatic latent image carriers, and are primarily transferred from each electrostatic latent image carrier to an intermediate transfer medium. Image forming device. The image forming apparatus according to claim 14,
An image forming apparatus comprising: a tandem image forming apparatus in which three or four electrostatic latent image carriers are arranged in a running direction of a surface of an intermediate transfer medium.

Images