Patent Grant
8989631
This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2013-105295 filed May 17, 2013.
The present invention relates to image-forming apparatuses and methods.
According to an aspect of the invention, there is provided an image-forming apparatus including an image unit that forms an image using a white toner and a color toner and a fixing unit that fixes the image to a medium with heat. The toner mass per unit area of the white toner θ (g/m2) in an image of the color toner superimposed on the white toner formed on paper used as the medium satisfies:
0.03+1.31×Rw−0.47×Rc+0.02×Gw−0.07×Gc≦θ≦0.05+1.06×Rw+0.42×Rc−0.02×Gw+0.05×Gc
(where Rw is the average particle diameter (μm) of the white toner, Rc is the average particle diameter (μm) of the color toner, Gw is the storage modulus (kPa) of the white toner at 120° C., and Gc is the storage modulus (kPa) of the color toner at 120° C.).
Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein:
Exemplary embodiments of the present invention will now be described with reference to the drawings. The structure of an image-forming apparatus will be described first, and then the normal and special operations of the image-forming apparatus will be described. In the following description, the direction indicated by arrow Y in
Image-Forming Section
As shown in
The toner-image forming units 60Y, 60M, 60C, 60K, 60S, and 60W are examples of image units. The intermediate transfer device 80 is an example of a transfer unit. The fixing device 90 is an example of a fixing unit.
Yellow (Y), magenta (M), cyan (C), black (K), special color (S), and white (W) are examples of toner colors. The white (W) toner is an example of a white toner. The yellow (Y), magenta (M), cyan (C), and black (K) toners are examples of color toners.
The special color (S) is a color other than yellow (Y), magenta (M), cyan (C), black (K), and white (W). Examples of special colors (S) include gold (G), silver (S), transparent color (CL), and corporate colors (C/C). Corporate colors (C/C) are colors that are unique to individual users and are more frequently used than other colors.
Toner-Image Forming Unit
The toner-image forming units 60Y, 60M, 60C, 60K, 60S, and 60W have substantially the same structure except for the toner used. Therefore, in
The photoreceptor drum 62 is an example of an image carrier. The charging device 64 is an example of a charging unit. The exposure device 66 is an example of a latent-image forming unit. The developing device 68 is an example of a developing unit.
The toner-image forming units 60Y, 60M, 60C, 60K, 60S, and 60W form yellow (Y), magenta (M), cyan (C), black (K), special color (S), and white (W) toner images, respectively, on the outer surfaces of the photoreceptors drum 62Y, 62M, 62C, 62K, 62S, and 62W. As shown in
Photoreceptor Drum
As shown in
Charging Device
As shown in
Exposure Device
As shown in
Developing Device
As shown in
Removing Device
As shown in
Erasing Device
As shown in
Intermediate Transfer Device
As shown in
The intermediate transfer belt 82 is an endless belt entrained about the six first transfer rollers 84 and the rollers 88 and thereby set in a predetermined shape. In this exemplary embodiment, as shown in
Of the rollers 88 shown in
As shown in
As shown in
Fixing Device
The fixing device 90 includes a fixing belt 90A and a pressing roller 90B. As shown in
Medium Transport Section
The medium transport section 40 includes a medium feed unit 42 that feeds the media P to the image-forming section 20 and a medium output unit 44 that outputs a medium P on which an image is formed.
The medium feed unit 42 feeds the media P one by one to the transfer nip T2 in the image-forming section 20 in accordance with the timing of transfer. The medium output unit 44 outputs a medium P to which a toner image is fixed by the fixing device 90 outside the image-forming apparatus 10.
The medium transport section 40 also includes a retransport unit 48 that feeds a medium P to which a toner image is fixed on the front side thereof to the image-forming section 20 again. The medium transport section 40, including the retransport unit 48 as well as a transport roller 44A and a transport-direction switching unit 46, described later, allows a toner image to be formed on the front or back side of a medium P to which a toner image is fixed on the front side thereof.
To form images on both sides of the medium P, the medium transport section 40 outputs the leading portion of the medium P outside the image-forming apparatus 10. The medium transport section 40 then rotates the transport roller 44A in the reverse direction to draw the medium P back into the image-forming apparatus 10. At the same time, the medium transport section 40 switches the transport-direction switching unit 46, which is disposed between the fixing device 90 and the transport roller 44A, to transport the medium P to the retransport unit 48. Thus, the retransport unit 48 feeds the medium P to the image-forming section 20, with the back side of the medium P facing the outer surface of the intermediate transfer belt 82.
To form an image on one surface (front surface) of the medium P again, after the medium P is output from the fixing device 90, the medium transport section 40 switches the transport-direction switching unit 46 to transport the medium P to the retransport unit 48. The retransport unit 48 then feeds the medium P to the image-forming section 20 again, with the front side of the medium P facing the outer surface of the intermediate transfer belt 82.
Document Reader
The document reader 50 reads image information from a document and transmits the image information to the controller 100.
Controller
The controller 100 controls the various sections of the image-forming apparatus 10 based on image information received from the document reader 50 or an external device (not shown) such as a computer.
The controller 100 converts the image information into image signals for four colors (Y, M, C, and K) and transmit the image signals to the exposure devices 66Y, 66M, 66C, and 66K. The controller 100 also generates image signals for the special color (S) and white (W) and transmit the image signals to the exposure devices 66S and 66W.
Normal Operation of Image-Forming Apparatus
Next, the normal operation of the image-forming apparatus 10 according to the first exemplary embodiment will be described with reference to
Upon receiving image information, the controller 100 operates the image-forming apparatus 10. The controller 100 converts the image information into image data for yellow (Y), magenta (M), cyan (C), and black (K). The controller 100 then outputs the image data to the exposure devices 66Y, 66M, 66C, and 66K.
The exposure devices 66 emit exposure light L based on the image data. The exposure light L is incident on the outer surfaces of the photoreceptor drums 62 charged by the charging devices 64 to form electrostatic latent images corresponding to the image data on the outer surfaces of the photoreceptor drums 62.
The electrostatic latent images formed on the outer surfaces of the photoreceptor drums 62 are developed by the developing devices 68 to form toner images.
The toner images are transferred from the outer surfaces of the photoreceptor drums 62 to the outer surfaces of the intermediate transfer belt 82 by the first transfer rollers 84 disposed opposite the outer surfaces of the photoreceptor drums 62.
A medium P is fed from any medium container 30 to the medium feed unit 42 and is transported to the transfer nip T2 in accordance with the timing when the portion of the intermediate transfer belt 82 on which the toner image is located reaches the transfer nip T2. The toner image is transferred from the outer surface of the intermediate transfer belt 82 to the medium P transported to and passing through the transfer nip T2.
The medium P to which the toner image is transferred is transported to the fixing device 90. In the fixing device 90, the fixing belt 90A and the pressing roller 90B heat and press the toner image to fix the toner image to the medium P.
The medium P to which the toner image is fixed is output from the medium output unit 44 outside the image-forming apparatus 10. Thus, the image-forming operation is completed.
To form images on both sides of the medium P, the image-forming apparatus 10 operates as follows. Specifically, as shown in
The transport roller 44A is then rotated in the reverse direction to draw the medium P back into the image-forming apparatus 10. At the same time, the transport-direction switching unit 46 is switched to transport the medium P to the retransport unit 48. The medium P is fed to the image-forming section 20 again, with the back side of the medium P facing the outer surface of the intermediate transfer belt 82.
Thereafter, a toner image is transferred to the back surface of the medium P in the transfer nip T2 and is fixed by the fixing device 90. Finally, the medium P to which the toner images are fixed on both sides thereof is output from the medium output unit 44 outside the image-forming apparatus 10. Thus, the image-forming operation is completed.
Operation of Image-Forming Apparatus for Use of White (W) Toner
Next, the operation of the image-forming apparatus 10 according to the first exemplary embodiment for the use of the white (W) toner will be described with reference to FIGS. 1 and 2. In this operation, the image-forming apparatus 10 forms an image on a medium P using at least one of the yellow (Y), magenta (M), cyan (C), and black (K) toners (hereinafter also referred to as “color toner”) in combination with the white (W) toner (hereinafter also referred to as “white toner”). In this case, an image formed by the color toners is superimposed on a layer of the white toner on the medium P. That is, the white toner layer is used as an underlayer for the image formed by the color toners.
The medium P used in this operation is color paper such as black, blue, or red paper, i.e., paper other than white paper, rather than normal paper (PPC paper). Color paper is an example of a medium P.
Upon receiving image information, the controller 100 operates the image-forming apparatus 10. This image information contains information about the formation of an image on color paper.
The controller 100 converts the image information into image data for yellow (Y), magenta (M), cyan (C), and black (K). The controller 100 also generates layer data for white (W) based on the image data for yellow (Y), magenta (M), and cyan (C). The controller 100 outputs the image data and the layer data for white (W) to the exposure devices 66Y, 66M, 66C, 66K, and 66W. The layer data for white (W) is used to form an underlayer for an image formed by the color toners.
The exposure devices 66Y, 66M, 66C, and 66K emit exposure light L based on the image data. The exposure light L is incident on the outer surfaces of the photoreceptor drums 62Y, 62M, 62C, and 62K charged by the charging devices 64Y, 64M, 64C, and 64K to form electrostatic latent images corresponding to the image data on the outer surfaces of the photoreceptor drums 62Y, 62M, 62C, and 62K.
In synchronization with this, the exposure device 66W emits exposure light L based on the layer data for white (W). The exposure light L is incident on the outer surface of the photoreceptor drum 62W charged by the charging device 64W to form an electrostatic latent image corresponding to the layer data for white (W) on the outer surface of the photoreceptor drum 62W.
The electrostatic latent images formed on the outer surfaces of the photoreceptor drums 62Y, 62M, 62C, and 62K are developed by the developing devices 68Y, 68M, 68C, and 68K to form yellow (Y), magenta (M), cyan (C), and black (K) toner images, respectively. The electrostatic latent image formed on the outer surface of the photoreceptor drum 62W is developed by the developing device 68W to form a white toner layer.
The yellow (Y), magenta (M), cyan (C), and black (K) toner images are transferred from the outer surfaces of the photoreceptor drums 62Y, 62M, 62C, and 62K to the outer surface of the intermediate transfer belt 82 by the first transfer rollers 84 disposed opposite the outer surfaces of the photoreceptor drums 62Y, 62M, 62C, and 62K. The white toner layer is transferred from the outer surface of the photoreceptor drum 62W to the outer surface of the intermediate transfer belt 82 by the first transfer roller 84 disposed opposite the outer surface of the photoreceptor drum 62W.
In this case, the white toner layer is transferred to the outer surface of the intermediate transfer belt 82 such that the white toner layer is superimposed on the color toner images previously transferred thereto.
Color paper is fed from any medium container 30 to the medium feed unit 42 and is transported to the transfer nip T2 in accordance with the timing when the color toner image and the white toner layer superimposed on the color toner image on the outer surface of the intermediate transfer belt 82 reach the transfer nip T2. The toner image and the white toner layer are transferred from the outer surface of the intermediate transfer belt 82 to the color paper transported to and passing through the transfer nip T2.
After passing through the transfer nip T2, the color paper is transported to the fixing device 90. In the fixing device 90, the fixing belt 90A and the pressing roller 90B heat and press the toner image and the white toner layer to fix the toner image and the white toner layer to the color paper. In this exemplary embodiment, the temperature of the outer surface of the fixing belt 90A is 160° C. In this case, the temperature at which the toner image and the white toner layer are fixed to the color paper (hereinafter referred to as “fixing temperature”) is 160° C.
The color paper is then output from the medium output unit 44 outside the image-forming apparatus 10. Thus, the image-forming operation is completed.
To form images on both sides of the color paper, after the toner image is fixed to the front side of the color paper, the color paper is drawn back into the image-forming apparatus 10 and is transported by the retransport unit 48, as in the normal operation of the image-forming apparatus 10. The color paper is then fed to the image-forming section 20, with the back side of the color paper facing the outer surface of the intermediate transfer belt 82, and a color toner image superimposed on a white toner layer is formed in the same manner as the toner image on the front side.
TMA of White Toner on Color Paper
In the image-forming apparatus 10 according to the first exemplary embodiment, the toner mass per unit area of a white toner θ (g/m2) transferred to color paper satisfies expression 1 below. Expression 1 below is defined by the average particle diameter Rw (μm) of a white toner, the average particle diameter Rc (μm) of a color toner, the storage modulus Gw (kPa) of the white toner, and the storage modulus Gc (kPa) of the color toner. The toner mass per unit area θ (g/m2) is hereinafter abbreviated as “TMA”.
Expression 1
Expression 1 is as follows:
0.03+1.31×Rw−0.47×Rc+0.02×Gw−0.07×Gc≦θ≦0.05+1.06×Rw+0.42×Rc−0.02×Gw+0.05×Gc
In the first exemplary embodiment, the average particle diameters of the white toner and the color toner are by volume.
The volume average particle diameters of the white toner and the color toner are measured, for example, using a Multisizer II (available from Beckman Coulter, Inc.) and, as an electrolyte, ISOTON-II (available from Beckman Coulter, Inc.). In this measurement, 0.5 to 50 mg of a measurement sample is added to 2 mL of a 5% aqueous solution of a surfactant, such as sodium alkylbenzenesulfonate, as a dispersant, and it is added to 100 to 150 mL of the electrolyte.
The sample suspended in the electrolyte is dispersed by an ultrasonic disperser for 1 minute. The particle diameter distribution of particles with particle diameters of 2.0 to 60 μm is then measured by a Multisizer II with an aperture diameter of 100 nm, where 50,000 particles are sampled.
In the first exemplary embodiment, the storage modulus of the white toner at the fixing temperature is higher than or equal to that of the color toner at the fixing temperature. If the storage modulus of the white toner is lower than that of the color toner, part of the white toner is absorbed into the color paper at the fixing temperature at which the color reproducibility after the fixing of the color toner is within the acceptable range. This decreases the hiding power of the white toner on the color paper.
The storage modulus G′ of a toner is the real part of the shear complex modulus G* at a measurement temperature of T° C. Specifically, the storage modulus G′ is measured by a viscoelastometer according to the method specified in JIS K7244-6, entitled “Plastics—Determination of Dynamic Mechanical Properties—Part 6: Shear Vibration—Non-Resonance Method”.
As shown in expression 1, the upper and lower limits of the TMA are specified using Rw, Rc, Gw, and Gc as parameters. The upper and lower limits of the TMA will now be described based on experimental results. The lower limit of the TMA will be described first, and then the upper limit of the TMA will be described.
Experiments for Determining Lower Limit of TMA of White Toner on Color Paper
Experiments for Determining Upper Limit of TMA of White Toner on Color Paper
Experiment Procedure
The upper and lower limits of the TMA in
Toner images formed on color paper are evaluated for color reproducibility as follows. An image is first formed on normal paper by the normal operation of the image-forming apparatus 10 described above to prepare an image sample used as a reference for color reproducibility. The photometric characteristics of a predetermined portion of the reference image sample are then measured by a photometer. Next, toner images are formed on color paper based on the same image data used in the above normal operation to prepare image samples with varying TMAs of the white toner layer. The photometric characteristics of a predetermined portion of each image sample are then measured by a photometer. The measurements of the image samples are compared with those of the reference image sample to determine whether they fall within predetermined reference limits (sensory evaluation).
Expression 1 is derived from a regression analysis of the lower limits of the TMA in
Method for Measuring TMA
As described above, an image formed by the color toners is superimposed on a layer of the white toner on a medium P. To measure the TMA of the white toner, only the white toner is transferred to the outer surface of the intermediate transfer belt 82 while preventing the color toners from being deposited on the outer surfaces of the photoreceptor drums 62Y, 62M, 62C, and 62K. The white toner is then transferred to color paper, and the image-forming apparatus 10 is stopped before the color paper passes through the fixing device 90. The color paper to which only the white toner is transferred but not fixed is removed from the image-forming apparatus 10. The TMA is determined by measuring the mass of the white toner transferred to the color paper and dividing it by the area in which the white toner is deposited.
To prevent the color toners from being deposited on the outer surfaces of the photoreceptor drums 62Y, 62M, 62C, and 62K, the controller 100 may shut off the exposure light L from the exposure devices 66Y, 66M, 66C, and 66K so that no electrostatic latent image is formed on the outer surfaces of the photoreceptor drums 62Y, 62M, 62C, and 62K. To measure the mass of the white toner transferred to the color paper, the white toner is collected by a suction device (not shown) equipped with a filter (filter that captures the white toner while allowing air to pass). The mass of the collected white toner is determined from the difference between the masses of the filter before and after suction and is divided by the area of the portion of the color paper from which the white toner is collected.
As shown in the conceptual diagram in
In contrast, if expression 1 is satisfied, the color reproducibility of the toner image may be improved compared to the case where expression 1 is not satisfied because the white toner underlayer may be substantially completely formed below the toner image. In addition, if expression 1 is satisfied, few white spots may appear in the image.
As shown in
In contrast, if expression 1 is satisfied, the color of the color toner may be maintained because little white toner may mix with the color toner.
Thus, with the image-forming apparatus 10, the color reproducibility of a color toner image superimposed on a white toner layer fixed to color paper may be improved compared to the case where the TMA of the white toner does not satisfy expression 1 (see
In the image-forming apparatus 10, the intensity of the exposure light emitted from the exposure device 66W is set so that the TMA of the white toner satisfies expression 1. The intensity of the exposure light emitted from the exposure device 66W is adjusted based on temperature and humidity information transmitted from a temperature and humidity sensor (not shown) disposed in the image-forming apparatus 10 to the controller 100.
Next, a second exemplary embodiment will be described with reference to
TMA of White Toner on Film
In the second exemplary embodiment, the TMA of a white toner transferred to a film satisfies expression 2 below. Expression 2 below is defined by the average particle diameter Rw (μm) of a white toner, the average particle diameter Rc (μm) of a color toner, the storage modulus Gw (kPa) of the white toner at 120° C., and the storage modulus Gc (kPa) of the color toner at 120° C. In expression 2 below, the TMA is denoted by θ.
0.04+1.09×Rw−0.40×Rc+0.01×Gw−0.05×Gc≦θ≦0.05+0.96×Rw+0.38×Rc−0.02×Gw+0.04×Gc Expression 2
Experiments for Determining Lower Limit of TMA of White Toner on Film
Experiments for Determining Upper Limit of TMA of White Toner on Film
As shown in
In contrast, if expression 2 is satisfied, the white toner may hide the film, thus improving the color reproducibility of the color toner image superimposed on the white toner layer.
As shown in
In contrast, if expression 2 is satisfied, the color of the color toner may be maintained because little white toner may mix with the color toner.
Thus, according to the second exemplary embodiment, the color reproducibility of a color toner image superimposed on a white toner layer fixed to a film may be improved compared to the case where the TMA of the white toner does not satisfy expression 2 (see
Modification
Next, a modification of the second exemplary embodiment will be described, focusing on the differences from the first and second exemplary embodiments. This modification combines the functions of the first and second exemplary embodiments described above. Specifically, this modification has a mode in which an image is formed on normal paper by the normal operation, a mode in which an image is formed on color paper using a white toner as an underlayer, and a mode in which an image is formed on a film using a white toner as an underlayer. Any of the above modes is selected based on information about the medium received by the controller 100 to perform an image-forming operation.
Whereas color paper (paper) has surface irregularities of sizes equal to or larger than the particle diameter of the toner, a film has no such surface irregularities. Accordingly, the optimum TMA is smaller on a film than on color paper (see
Advantages of Modification
According to this modification, the color reproducibility of a color toner image superimposed on a white toner layer fixed to a selected medium P may be improved compared to the case where the functions of the first and second exemplary embodiments described above are not combined.
Although particular exemplary embodiments of the present invention have been described above in detail, the present invention is not limited to such exemplary embodiments; various other exemplary embodiments are possible within the scope of the present invention.
For example, the white toner may have any color that allows a color toner image superimposed on the white toner to have color reproducibility within the acceptable range if expression 1 or 2 is satisfied.
If the white toner is frequently used in image-forming operations, the toner-image forming unit 60S may be configured for use with the same white toner as the toner-image forming unit 60W. Alternatively, the toner-image forming units 60S and 60W may be configured for use with white toners having different color-forming properties.
Films are not limited to transparent films made of resins such as polyethylene terephthalate (PET) and polyvinyl chloride, but include color films containing dyes.
Although the white toner has been described as an underlayer for the color toner, the image-forming apparatus 10 may have a mode in which images such as characters and patterns are formed using the white toner.
Although the black (K) toner has been described as being deposited on a white toner layer (underlayer), the black (K) toner may be directly deposited on color paper or film without forming a white toner underlayer.
Although expression 1 (or expression 2) has been described as being satisfied by setting the intensity of the exposure light emitted from the exposure device 66W, it may be satisfied by setting, for example, the voltage applied to the toner supply members 68A of the developing device 68W, the distance between the limiting member and the toner supply members 68A, or the peripheral velocity of the toner supply members 68A. Alternatively, expression 1 (or expression 2) may be satisfied by setting, for example, the charge potential of the charging device 64W or the first transfer bias applied to the first transfer roller 84 opposite the photoreceptor drum 62W.
Although color toner images and a white toner layer have been described as being simultaneously transferred to a medium P by second transfer, monochrome toner images and layer may be formed on the respective image carriers and may then be sequentially transferred to a medium P.
The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.
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| 2013-105295 | May 2013 | JP | national |
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| 20140341615 A1 | Nov 2014 | US |
