Embodiments described herein relate to an image forming apparatus that forms an image with a decolorizable color material.
To preserve the environment, one type of an image forming apparatus prints an image on a sheet with a decolorizable color material. Such a decolorizable color material can be decolorized when heated to a certain temperature. Therefore, a sheet from which the image formed of the decolorizable color material has been erased can be reused. In some cases, for example, when forming a full-color image on a sheet, an image forming apparatus forms the image with plural layers of color materials, and some or all of the color materials may be decolorizable.
However, depending on the environmental conditions for the printing, a density of the printed image, the number of times the sheet has been reused, and the type of the sheet, a part of the printed image may be left after an erasing process. Especially, when the image is formed on a sheet with plural layers of color materials, as described above, and a layer of the decolorizable color material is formed underneath the other layers, the color of the decolorizable material may not be sufficiently decolorized. This is because the decolorizable color material does not reach the decolorizable temperature when the sheet is heated.
The image forming apparatus according to embodiments described herein forms a color image with layers of color materials, each having a unique color.
According to embodiments, an image forming apparatus includes a first image forming unit configured to form a first image to be transferred to a sheet with a first toner that is decolorizable and has a first brightness, and a second image forming unit configured to form a second image to be transferred to the sheet with a second toner that has a second brightness that is greater than the first brightness. At least a part of the first image transferred to the sheet is formed above the second image transferred to the sheet.
The image forming apparatus according to the embodiment is described below in detail with reference to accompanying drawings.
As shown in
In this embodiment, the first image forming station 11 to the fourth image forming station 14, each have the same structure. Each of the image forming stations includes a developer 15 for housing a decolorizable toner serving as a decolorizable color material, a photoconductive drum 17 for forming a latent image with the image exposure light emitted from an image exposure section 16, and a charger 18 for charging the photoconductive drum 17 uniformly.
Moreover, a primary transfer roller 19 is disposed opposite to each of the photoconductive drums 17 across a secondary transfer belt 10. For example, when copying an image scanned by a scanner 20, RGB image signals generated by the scanner 20 are converted to color signals, each corresponding to the first to the fourth image forming stations 11-14 in an image processing section 21. Then, an exposure light source of the image exposure section 16 is controlled to irradiate corresponding photoconductive drums 17 based on the generated color signal in order to form a latent image on each of the photoconductive drums 17.
The latent image formed on each of the photoconductive drums 17 is developed into a toner image with a decolorizable toner of a corresponding color by the developer 15.
Here, a first toner image 31 of a first color is primarily transferred on the secondary transfer belt 10 from the photoconductive drum 17 of the first image forming station 11. Next, a second toner image 32 of a second color formed on the photoconductive drum 17 of the second image forming station 12 is transferred on the first toner image 31 formed on the secondary transfer belt 10. Similarly, a third toner image 33 of a third color is disposed on the second toner image 32 at the third image forming station 13, and a fourth toner image 34 of a fourth color is disposed on the third toner image 33 at the fourth image forming station 14.
In this embodiment, image density of the first toner image 31, the second toner image 32, the third toner image 33, and the fourth toner image 34 can be set to be the same or be adjusted individually. An image density adjustment section 22 for adjusting an image density may be provided, for example, in the image processing section 21, to adjust an image density by, for example, adjusting the exposure intensity (luminance) of the image exposure light emitted from the image exposure section 16 onto the photoconductive drum 17. Additionally, the image density may also be adjusted by adjusting the charge quantity of the photoconductive drum 17, and therefore a method to adjust the image density is not limited to be adjusted by adjusting the exposure intensity.
Unfixed toner images 35 formed of four layered toner images are secondarily transferred onto a sheet by a secondary transfer roller 36. The unfixed toner images 35 secondarily transferred onto the sheet P has a structure that the third toner image 33, the second toner image 32, and the first toner image 31 are orderly laminated on the fourth toner image 34 on the sheet P.
The unfixed toner images 35 secondarily transferred on the sheet P are heated and pressed by a fixer 38 to be fixed on the sheet P. Then, the sheet is discharged to a sheet discharging section (not shown) by a sheet discharging roller 39. Here, the fixed toner image 41, as shown in
In this embodiment, a black toner is held in the developer 15 of the first image forming station 11, and the black toner image 31 formed of the black toner is primarily transferred onto the secondary transfer belt 10. A cyan toner is held in the developer 15 of the second image forming station 12, and the cyan toner image 32 of the cyan toner is laminated on the black toner image 31. Further, a magenta toner is held in the developer 15 of the third image forming station 13, and the magenta toner image 33 of the magenta toner is laminated on the cyan toner image 32. A yellow toner is held in the developer 15 of the fourth image forming station 14, and the yellow toner image 34 of the yellow toner is laminated on the magenta toner image 33.
The sheet P is conveyed along a sheet conveyance path 44 extending from a paper feed cassette 42 to the sheet discharging roller 39 through a register roller 43, a secondary transfer position 37 and a fixer 38.
The yellow toner image 34, which has the highest brightness, the magenta toner image 33, the cyan toner image 32, and the black toner image 31, which has the lowest brightness, are transferred on the sheet P at the secondary transfer position, as shown in
The decolorizable color material is described below.
The decolorizable toner used in the embodiment contains a binder resin, an electron donating coloring agent, and an electron accepting color developing agent. A decolorizing agent may also be added in the decolorizable toner. Further, particles of the electron donating coloring agent, the electron accepting color developing agent, and the decolorizing agent may be encapsulated in capsules and formed as encapsulated color material particles, which are contained in the decolorizable toner.
(Electron Donating Coloring Agent)
The electron donating coloring agent mainly refers to leuco dye, which is an electron donating compound that can develop a color when combined with a color developing agent. The electron donating compound is, for example, diphenylmethanephthalides, phenylindolylphthalides, indolylphthalides, diphenylmethaneazaphthalides, phenylindolylazaphthalides, fluorans, styryl quinolines, diazarhodaminelactones, and the like.
(Electron Accepting Color Developing Agent)
The color developing agent is an electron-accepting compound which provides the electron donating coloring agent with protons. The electron-accepting compound is, for example, phenols, metal salts of phenol, metal salts of carvone acid, aromatic carboxylic acid and aliphatic acids having 2-5 carbons, benzophenones, sulfone acid, sulphonate, phosphoric acids, metal salts of phosphoric acid, alkyl acid phosphate, metal salts of acid phosphate, phosphorous acids, metal salts of phosphorous acid, monophenols, polyphenols, 1,2,3-triazole, and derivatives thereof.
(Decolorizing Mechanism)
The coloring agent of leuco dyes such as CVL (crystal violet lactone) has a characteristic that it develops a color when combined with a color developing agent and is decolorized when dissociated from the color developing agent. In addition to the coloring agent and the color developing agent, a temperature controlling agent that has a large difference between its melting point and a solidifying point may be used. When the temperature controlling agent that has a solidifying point lower than a normal temperature is used, the color of toner is decolorized when heated above the melting point and the decolorized state can be maintained at the normal temperature. In embodiments described herein, for example, a color material that can develop a color and decolorized may be formed byencapsulating a leuco coloring agent, a color developing agent, and a temperature controlling agent.
Methods for producing particles of each color material particles and the toner are described below.
(Production of Yellow Color Developing Particles)
Hereinafter, “parts” refer to “parts by weight” and “%” refers to “% by weight.”
A solution obtained by uniformly heat-dissolving a composition containing 3.0 parts of 4-[2,6-bis(2-ethoxyphenyl)-4-pyridinyl]-N,N-dimethylbenzenamine, 10.0 parts of 2,2-bis(4′-hydroxyphenyl)hexafluoropropane, and 50 parts of a diester compound of pimelic acid with 2-(4-benzyloxyphenyl)ethanol as a decolorizing agent, and adding 20 parts of an aromatic polyvalent isocyanate prepolymer and 40 parts of ethyl acetate thereto as encapsulating agents was added to 300 parts of an aqueous solution of 8% polyvinyl alcohol and emulsified and dispersed therein.
The mixture obtained is continuously stirred for about 1 hour at 90 degrees centigrade and then 2.5 parts of water-soluble aliphatic modified amine serving as a reactant is added therein. Then, the mixture obtained is continuously stirred for 6 hours, and leuco capsule particles dispersed in the stirred solution are obtained. Further, the capsule particle dispersion is placed in a freezer to develop color, and thereby yellow color developing particle dispersion is obtained. When measured by the SALD7000 produced by SHIMADZU Corporation, the yellow color developing particle has a volume average particle diameter of 3 μm. Further, a fully-decolorizing temperature Th of the yellow color developing particle is 62 degrees centigrade and a fully-coloring temperature Tc of the yellow color developing particle is −14 degrees centigrade.
(Production of Magenta Color Developing Particles)
A solution obtained by uniformly heat-dissolving a composition containing 1.0 part of 1,2-benz-6-(N-ethyl-N-isoamylamino)fluoran, 2.0 parts of 1,3-dimethyl-6-diethylaminofluoran, 4.5 parts of 4,4′-(2-methylpropylidene)bisphenol, 7.5 parts of 2,2-bis(4′-hydroxyphenyl)hexafluoropropane, and 50 parts of a diester compound of pimelic acid with 2-(4-benzyloxyphenyl)ethanol as a decolorizing agent, and adding 30 parts of an aromatic polyvalent isocyanate prepolymer and 40 parts of ethyl acetate thereto as encapsulating agents was added to 300 parts of an aqueous solution of 8% polyvinyl alcohol and emulsified and dispersed therein.
Then, the mixture obtained is continuously stirred for about 1 hour at 90 degrees centigrade and then 2.5 parts of water-soluble aliphatic modified amine serving as a reactant is added therein. Then, the mixture obtained is continuously stirred for 6 hours, and leuco capsule particles dispersed in the stirred solution are obtained. Further, the capsule particle dispersion is placed in a freezer to develop color, and thereby magenta color developing particle dispersion is obtained. When measured by the SALD7000, the magenta color developing particle has a volume average particle diameter of 3 um. Further, the fully-decolorizing temperature Th of the magenta color developing particle is 62 degrees centigrade, and the fully-coloring temperature Tc of the magenta color developing particle is −14 degrees centigrade.
(Production of Cyan Color Developing Particles)
A solution obtained by uniformly heat-dissolving a composition containing 2.0 parts of 4,5,6,7-tetrachloro-3-[4-(dimethylamino)-2-methylphenyl]-3-(1-ethyl-2-methyl-1H-indol-3-yl)-1(3H)-isobenzofuranone, 3.0 parts of 4,4′-(2-ethylhexane-1,1-diyl)diphenol, 5.0 parts of 2,2-bis(4′-hydroxyphenyl)hexafluoropropane, and 50 parts of a diester compound of pimelic acid with 2-(4-benzyloxyphenyl)ethanol as a decolorizing agent, and adding 30 parts of an aromatic polyvalent isocyanate prepolymer and 40 parts of ethyl acetate thereto as encapsulating agents was added to 300 parts of an aqueous solution of 8% polyvinyl alcohol solution.
Then, the mixture obtained is continuously stirred for about 1 hour at 90 degrees centigrade and then 2.5 parts of water-soluble aliphatic modified amine serving as a reactant is added. Then the mixture obtained is continuously stirred for 6 hours, and leuco capsule particles disposed in the stirred solution are obtained. Further, the capsule particle dispersion is placed in a freezer to develop color, and thereby cyan color developing particle dispersion is obtained. When measured by the SALD7000, the magenta color developing particle has a volume average particle diameter of 3 um. Further, the fully-decolorizing temperature Th of the magenta color developing particle is 62 degrees centigrade, and the fully-coloring temperature Tc of the magenta color developing particle is −14 degrees centigrade.
(Production of Black Color Developing Particles)
A solution obtained by uniformly heat-dissolving a composition containing 4.5 parts of 2-(2-chloroamino)-6-dibutylaminofluoran, 3.0 parts of 4,4′-(2-ethylhexane-1,1-diyl)diphenol, 5.0 parts of 2,2-Bis(4′-hydroxyphenyl)-hexafluoropropane, and 50 parts of caprylic acid-4-benzyl oxy phenyl ethyl serving as a decolorizing agent and adding 30 parts of an aromatic polyvalent isocyanate prepolymer and 40 parts of ethyl acetate thereto as encapsulating agents was added to 300 parts of an aqueous solution of 8% polyvinyl alcohol solution.
Then, the mixture obtained is continuously stirred for about 1 hour at 90 degrees centigrade and then 2.5 parts of water-soluble aliphatic modified amine serving as a reactant is added therein. Then, the mixture obtained is continuously stirred for 6 hours, and leuco capsule particles dispersed in the stirred solution are obtained. Further, the capsule particle dispersion is placed in a freezer to develop color, and then a black color developing particle dispersion is obtained. When measured by the SALD7000, the black color developing particle has a volume average particle diameter of 3 um. Further, the fully-decolorizing temperature Th of the black color developing particle is 62 degrees centigrade, and the fully-coloring temperature Tc of the black color developing particle is −14 degrees centigrade.
(Manufacturing Method of the Toner)
1.7 parts of color developing particle dispersion, 15 parts of toner composition particle R1 dispersion, and 83 parts of ion exchange water are mixed. The mixture is stirred using a homogenizer (produced by IKA) at 6500 rpm while 5 parts of 5% aluminum sulfate solution is added, and the obtained mixture is stirred at 800 rpm in a 1 L agitation tank provided with paddle blades while being heated to 40 degrees centigrade. The heated mixture is held for one hour at 40 degrees centigrade, and then 10 parts of 10% sodium polycarboxylate solution is added and the mixture is heated to 68 degrees centigrade. The obtained mixture is held for one hour and cooled, and thereby leuco toner dispersion is obtained.
Then, the toner dispersion is repeatedly filtered and cleaned with ion exchange water until the conductivity of the filtrate becomes 50 us/cm. Then, the filtrate is froze in a freezer of −20 degrees centigrade to cause the toner to develop color, then the filtrate is dried with a vacuum dryer until the water content of the filtrate is below 1.0% by weight, and then dried particles are obtained.
After the drying procedure, two parts by weight of hydrophobic silica and 0.5 parts by weight of oxidized titanium serving as an additive are adhered to surfaces of the toner particles, and thereby a decolorizable toner is obtained. When measured by a multisizer 3 produced by Coulter Corporation, the volume average particle diameter Dv of 50% is 10.5 um.
The toner obtained is mixed with a ferrite carrier coated with silicon resin to serve as an image developing agent.
Next, when erasing a fixed color toner image 41 formed with the decolorizable toner using an erasing apparatus, for example, the sheet is fed to the nip section 51 of an erasing apparatus 50 shown in
The fixed toner image 41 passing through the nip section 51 is erased as shown in
On the other hand, as shown in
However, in this embodiment, the toner layer having a lowest brightness is formed at the top position furthest from the surface of the sheet P, but not at the position closest to the surface of the sheet P. As a result, the residual image portion formed of the toner having the lowest brightness left after the erasing process is less recognizable. Further, as the toner layer having a highest brightness is formed at the position closest to the surface of the sheet P, more image portion formed of the toner having the highest brightness tends to be left after the erasing process. However, as the color of the toner having the highest brightness can be observed in a state blended with the white color of the sheet P, that image portion is unrecognizable.
Further, measured by the Chroma Meter CR-200 produced by Minolta Corporation, when the solid images are formed on the sheet P by the image forming apparatus 1 on a condition that the amounts of the toners of each color adhered on the sheet P are equal, the following result is obtained: the brightness of the solid images are: Yellow (Y): 88.05, Cyan (C): 51.15, Magenta (M): 46.92, and Black (BK): 25.11, according to an exemplary brightness (L*) measurement result based on the CIE color system L*/a*/b*.
Depending on error factors such as environment and paper type are further considered, a color of the bottom toner layer may be left more significantly after the erasing process. In this case, if the color of the toner layer closest to the surface of the sheet P is black, which has a lowest brightness in a plurality of colors, then the residual image portion after the erasing process is likely to be more recognizable. With respect to this, as shown in
In order to form the toner layers according to the brightness with decolorizable toner, the developer 15 containing the toner having a highest brightness is arranged downstream with respect to the developer 15 containing the toner having a lowest brightness along the rotational direction of the secondary transfer belt 10 and located just upstream of the secondary transfer position to the sheet P serving as a recording medium. According to this arrangement of the developers 15, the order of the toner layers on the sheet can be determined, and the toner layer having a highest brightness can be formed at the bottom (in contact with the sheet). Consequently, even when a toner image portion is left after the erasing process, the residual image portion becomes unrecognizable, thus providing a good erasing quality for the next printing process.
The image forming apparatus according to a second embodiment has the same configuration as the image forming apparatus according to the first embodiment, and the developer of the first image forming station 11 contains a decolorizable black toner. However, developers 15 of the other image forming stations 12-14 contain non-decolorizable toners. The developer 15 of the second image forming station 12 contains cyan toner, the developer 15 of the third image forming station 13 contains magenta toner, and the developer 15 of the fourth image forming station 14 contains yellow toner.
If an erasing process is carried out for the fixed image 41 having such a toner layer structure, then only the color of the black toner image 31 formed on the top is decolorized and the other toner images remain. Thus, an image of the combined color of the other three colors is displayed.
Here, if the black toner image 31 is not fully erased through the erasing process, for example, a thin black residual image portion is left, then the quality of the image that should be displayed is degraded. In this embodiment, the toner layer on the top of the fixed image 41 is formed of the decolorizable toner. If the toner layer closest to the sheet P is a decolorizable toner layer, then the residual image portion left after the erasing process will be more recognizable.
If the density of toner images is set to be the same among the images fixed in the first image forming station, which forms a black toner image with a decolorizable black toner, and the images fixed in second image forming stations 12-14, which form cyan, magenta, and yellow toner images with non-decolorizable ordinary toners, then the amount of the decolorizable toner on the sheet should be much greater than those of the non-decolorizable ordinary toners. Thus more thermal conduction into the toner layers is needed for the erasing of the toner image.
In this embodiment, the density of the decolorizable toner image on the sheet is reduced to the extent that the quality of the image is not compromised. Thus, the residual image portion, if any, can be less recognizable.
A relationship between a toner adhesion amount and an image concentration is described below with reference to
In the chart shown in
Further, the data shown in
The bottom line of the chart shows image density formed with the non-decolorizable toners of yellow, magenta, and cyan, and the decolorizable black toner overlapped on the yellow, magenta, and cyan toners. The amount of decolorizable black toner is 0.28, 0.48, and 0.6, respectively.
In
In
That is, if the image density of the decolorizable black toner is higher than the minimum value of 0.44, the inking effect in a full-color image can be reliably obtained. In addition, even if a residual image of the decolorizable black toner is left after the erasing process, the residual image becomes unrecognizable with respect to the non-erased toner images of the other three colors, as the influence of the residual black image is slight. Further, as shown in
Thus, according to this embodiment, when forming a full-color image with overlapped toner layers, the image density of a decolorizable black toner is set to be lower than those of other ordinary toners. For example, the image density of the decolorizable black toner is set within a range from 0.44 (the minimum density) to 0.6 in which an inking effect can be obtained, and preferably within a range from 0.44 to 0.5. In this range, the amount of the decolorizable black toner used for the printing can be reduced without degrading the quality of a full-color image. In addition, the decolorizable black toner is sufficiently heated during the erasing process so that a residual image is less likely to remain on the sheet. Further, as the decolorizable black toner image is directly in contact with the heat roller 52 (refer to
Further, it is needless to say that the density of the black toner can be adjusted in the first embodiment in the same way as described in the second embodiment.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. Indeed, the novel embodiments described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.
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Number | Date | Country |
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2011107490 | Jun 2011 | JP |
Number | Date | Country | |
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20150277260 A1 | Oct 2015 | US |