Image forming apparatus, non-transitory computer readable medium, and image forming method

An image forming apparatus includes a first image forming unit that forms a metallic-color toner image having a metallic color, a second image forming unit that forms a non-metallic-color toner image having a color different from the metallic color, and a transfer unit that transfers the toner images onto a recording material so that the non-metallic-color toner image is superimposed on an upper side of the metallic-color toner image on the recording material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2015-129066 filed Jun. 26, 2015.

BACKGROUND

Technical Field

The present invention relates to an image forming apparatus, a non-transitory computer readable medium, and an image forming method.

SUMMARY

According to an aspect of the present invention, there is provided an image forming apparatus including a first image forming unit that forms a metallic-color toner image having a metallic color, a second image forming unit that forms a non-metallic-color toner image having a color different from the metallic color, and a transfer unit that transfers the toner images onto a recording material so that the non-metallic-color toner image is superimposed on an upper side of the metallic-color toner image on the recording material.

DETAILED DESCRIPTION

Description of Image Forming Apparatus

FIG. 1illustrates a configuration example of an image forming apparatus1according to the exemplary embodiment.

The image forming apparatus1illustrated inFIG. 1is a color printer of a so-called tandem type, and includes an image forming section10that performs image formation according to image data, a controller50that controls the operation of the entire image forming apparatus1, performs communication with, for example, a personal computer, and executes image processing of the image data, and a user interface section30that receives operation input from the user and displays various information to the user.

Description of Image Forming Section

The image forming section10is a functional section that forms an image by, for example, an electrophotographic system. The image forming section10includes six image forming units, that is, an image forming unit11Y for yellow (Y), an image forming unit11M for magenta (M), an image forming unit11C for cyan (C), an image forming unit11K for black (K), an image forming unit11T for a transparent color (T), and an image forming unit11G for a metallic color (G).

In the following description, when the image forming units are not discriminated, they are generically referred to as “image forming units11.”

Each of the image forming units11includes, for example, a photoconductor drum12on which an electrostatic latent image is formed and color toner images are then formed, a charging device13that charges a surface of the photoconductor drum12with a predetermined potential, an exposure device14that exposes the photoconductor drum12charged by the charging device13according to image data, a developing device15that develops the electrostatic latent image formed on the photoconductor drum12with color toners, and a cleaner16that cleans the surface of the photoconductor drum12after transfer. The image forming units11have substantially similar structures except for toner contained in the developing device15.

The image forming section10further includes an intermediate transfer belt20on which a color toner image formed on the photoconductor drum12in each image forming unit11is to be transferred, and first transfer rollers21each of which transfers (first-transfers) the color toner image formed in the image forming unit11onto the intermediate transfer belt20. The image forming section10further includes a second transfer roller22that collectively transfers (second-transfers) color toner images superposed and transferred on the intermediate transfer belt20onto a sheet P, and a fixing unit60that fixes the second-transferred color toner images on the sheet P.

In the exemplary embodiment, a region where the second transfer roller22is disposed and the color toner images on the intermediate transfer belt20are second-transferred on the sheet P is referred to as a second transfer region23hereinafter.

In the exemplary embodiment, the intermediate transfer belt20, the first transfer rollers21, and the second transfer roller22function as an example of a transfer unit.

In the exemplary embodiment, the image forming unit11G for a metallic color, the image forming unit11K for black, the image forming unit11C for cyan, the image forming unit11M for magenta, the image forming unit11Y for yellow, and the image forming unit11T for a transparent color are arranged in this order from the downstream side to the upstream side with reference to the second transfer region23in the rotating direction of the intermediate transfer belt20. In particular, the image forming unit11G for the metallic color is disposed on the most downstream side with reference to the second transfer region23in the rotating direction of the intermediate transfer belt20.

Description of Structure of Fixing Unit

Next, the fixing unit60used in the image forming apparatus1of the exemplary embodiment will be described.

FIG. 2is a cross-sectional structural view illustrating the structure of the fixing unit60in the exemplary embodiment.

As illustrated inFIG. 2, the fixing unit60includes a fixing belt module61that heats a sheet P, a pressing roller62configured to move into contact with and away from the fixing belt module61, and an external heating roller63that heats a fixing belt610(to be described later) while stretching the fixing belt610from the outer side.

The fixing belt module61includes a fixing belt610, and a fixing roller611that rotates while stretching the fixing belt610to heat the fixing belt610from the inner side at a nip N serving as a region where the fixing belt module61and the pressing roller62are in pressure contact with each other (are in contact while being pressed against each other).

The fixing belt module61further includes an internal heating roller612that heats the fixing belt610. The fixing belt module61further includes a stretching roller614that stretches the fixing belt610between the fixing roller611and the internal heating roller612(on the upstream side of the nip N), a peeling pad64disposed within a downstream area of the nip N and near the fixing roller611, and a stretching roller615that stretches the fixing belt610on the downstream side of the nip N.

For example, the fixing belt610is composed of a base layer, an elastic layer stacked on a front side (outer peripheral side) of the base layer, and a release layer with which the elastic layer is coated. In the exemplary embodiment, the fixing belt610is provided opposed to a toner image transferred on a sheet P. In the exemplary embodiment, the fixing belt610is an endless belt.

The fixing roller611is a cylindrical roller. The fixing roller611is rotated in a direction of arrow inFIG. 2by rotating driving force from an unillustrated driving motor. The fixing roller611is preheated to a predetermined temperature by halogen heaters71disposed therein.

The internal heating roller612is a cylindrical roller. The internal heating roller612is preheated to a predetermined temperature by halogen heaters72disposed therein.

The external heating roller63is a cylindrical roller. The external heating roller63is preheated to a predetermined temperature by, for example, three halogen heaters73disposed therein. In this way, the fixing unit60in the exemplary embodiment adopts a structure in which the fixing belt610is heated by the fixing roller611, the internal heating roller612, and the external heating roller63.

The peeling pad64is a block member having a substantially arc-shaped cross section. The peeling pad64is fixed and disposed all over the entire axial area of the fixing roller611at a position near and downstream of a region where the pressing roller62is in pressure contact with the fixing roller611with the fixing belt610being disposed therebetween (hereinafter, referred to as a “roll nip N1”). Further, the peeling pad64is disposed to uniformly press the pressing roller62with the fixing belt610being disposed therebetween with a predetermined load along a predetermined widthwise region, and forms a “peeling-pad nip N2” continuing from the roll nip N1.

Next, the pressing roller62is formed by stacking a columnar roller serving as a base body, an elastic layer, and a release layer in this order from the base body side. The pressing roller62is disposed to move into contact with and away from the fixing belt module61. When the pressing roller62is set to be in contact (pressure contact) with the fixing belt module61while pressing the fixing belt module61, it is rotated in a direction of arrow inFIG. 2along with the rotation of the fixing roller611of the fixing belt module61in a direction of arrow inFIG. 2.

Next, a description will be given of toner contained in each developing device15in the exemplary embodiment.

In the exemplary embodiment, yellow toner, magenta toner, cyan toner, and black toner are generically referred to as colored toner Tymck.

Clear toner (clear toner) Tt shows a transparent color when fixed on a sheet P. In the exemplary embodiment, the term “transparent” means “transparent to at least visible light.” The clear toner Tt transmits light reflected by a back sheet P or other toners. In the exemplary embodiment, the clear toner Tt also serves to give gloss.

In the exemplary embodiment, the clear toner Tt needs to contain a binder resin and a parting agent, and substantially does not contain a colorant. Here, “substantially does not contain” means the degree such that the coloring degree is not conspicuous to the naked eyes.

Metallic-color toner Tg shows a metallic color when fixed on a sheet P. Here, the metallic color is, for example, gold or silver.

In the exemplary embodiment, the metallic-color toner Tg is compounded of metallic pigment having a relatively large particle diameter, such as silver powder or metallic aluminum powder, in addition to a binder resin of synthetic resin, such as styrene or acrylic resin, a colorant, and a compounding agent. Metallic pigment, such as silver powder, has a flat shape, a scaly shape, a disc shape, or a spherical shape. Further, the average particle diameter of the metallic pigment, such as silver powder, is relatively larger than that of normal toner such as yellow, magenta, cyan, and black toners.

The metallic-color toner Tg is not limited to the metallic-color toner containing the metallic pigment (powder) such as silver powder or metallic aluminum powder, and may be a mixture of a colorant and scaly pigment in which a thin inorganic crystalline substrate is coated with a thin film of titanium dioxide, or may contain scaly thin films of metal. In the exemplary embodiment, as the metallic-color toner Tg, a flat metallic-color toner having an average particle diameter relatively larger than that of the colored toner Tymck can be used.

In the exemplary embodiment, clear toner Tt, yellow toner, magenta toner, cyan toner, and black toner, which show colors different from the metallic color, are generically referred to as non-metallic-color toner.

Here, the metallic-color toner Tg is sometimes used alone to express a metallic color (gold or silver), and is also sometimes used to show a colored and metallic color by superimposing the colored toner Tymck thereon. For example, to express a bluish metallic color, cyan toner is superimposed on silver metallic-color toner Tg.

Expression of a colored and metallic color does not exclude stacking colored toner Tymck on a lower side of metallic-color toner Tg. For example, colored toner Tymck, metallic-color toner Tg, and colored toner Tymck may be stacked in order.

In the exemplary embodiment, the image forming unit11G for the metallic color functions as an example of a first image forming unit. The image forming unit11Y for yellow, the image forming unit11M for magenta, the image forming unit11C for cyan, the image forming unit11K for black, and the image forming unit11T for the transparent color function as an example of a second image forming unit for forming a non-metallic-color toner image. Further, the image forming unit11Y for yellow, the image forming unit11M for magenta, the image forming unit11C for cyan, the image forming unit11K for black, and the image forming unit11T for the transparent color function as an example of a third image forming unit for forming a colored toner image.

Description of Image Forming Operation

Next, a description will be given of a basic image forming operation in the image forming apparatus1according to the exemplary embodiment.

The image forming units11in the image forming section10form color toner images of a transparent color, black, cyan, magenta, yellow, and a metallic color by an electrophotographic process using the above functional members. The color toner images formed in the image forming units11are first-transferred in order onto the intermediate transfer belt20by the first transfer rollers21and are superimposed to form a synthetic toner image. The synthetic toner image on the intermediate transfer belt20is transported along with movement of the intermediate transfer belt20(in the direction of the arrow) to the second transfer region23where the second transfer roller22is disposed.

In a sheet transport system, a sheet P fed out from a paper container40by a feed roller is transported along a transport path, and reaches the second transfer region23. In the second transfer region23, the synthetic toner image held on the intermediate transfer belt20is collectively second-transferred onto the sheet P by a transfer electric field generated by the second transfer roller22.

After that, the sheet P on which the synthetic toner image is transferred is separated from the intermediate transfer belt20, and is transported along the transport path to the fixing unit60. The synthetic toner image on the sheet P transported to the fixing unit60is fixed on the sheet P by a fixing process of the fixing unit60.

In duplex printing, the sheet P having the fixed image formed on its first surface by the above-described process is guided along the transport path, is inverted, and reaches the second transfer region23again. In the second transfer region23, similarly to the first surface, color toner images held on the intermediate transfer belt20are collectively second-transferred onto a second surface of the sheet P by a transfer electric field generated by the second transfer roller22. Similarly to the first surface, a fixed image is formed on the second surface by a fixing process of the fixing unit60.

FIGS. 3A and 3Billustrate an example of a toner stack state on the sheet P.

In the exemplary embodiment, as illustrated inFIG. 3A, when a synthetic toner image is transferred on the sheet P, non-metallic-color toner having a color different from the color of metallic-color toner Tg is superimposed on the upper side of the metallic-color toner Tg relative to the sheet P. That is, a process for coating the metallic-color toner Tg with the non-metallic-color toner on the sheet P (hereinafter, referred to as a coating process) is performed.

For example, in the exemplary embodiment, clear toner Tt is superimposed on the upper side of the metallic-color toner Tg on the sheet P. Specifically, an image having a shape similar to that of an image formed as a metallic-color toner image is formed as a clear toner image. Then, the metallic-color toner image and the clear toner image are aligned and superimposed on the intermediate transfer belt20to form a synthetic toner image.

Description of Fixing Operation in Fixing Unit

Next, the fixing operation in the fixing unit60of the exemplary embodiment will be described.

After a synthetic toner image (unfixed toner image) is electrostatically transferred on the sheet P in the second transfer region23(seeFIG. 1) in the image forming apparatus1, the sheet P is transported along the transport path (seeFIG. 1) toward the nip N (seeFIG. 2) in the fixing unit60. Then, the unfixed toner image on the surface of the sheet P passing through the nip N is fixed on the sheet P by pressure and heat principally acting on the roll nip N1.

After passing through the roll nip N1, the sheet P is transported to the peeling-pad nip N2. The peeling-pad nip N2is configurated so that the peeling pad64is pressed against the pressing roller62and the fixing belt610is in pressure contact with the pressing roller62. Therefore, the roll nip N1is shaped like a downward convex curve by the curvature of the fixing roller611, whereas the peeling-pad nip N2is shaped like an upward convex curve by the curvature of the pressing roller62.

For this reason, after the sheet P is heated and pressed at the curvature of the fixing roller611in the roll nip N1, the traveling direction of the sheet P is changed to an opposite direction by the curvature of the pressing roller62in the peeling-pad nip N2. At this time, a minute micro-slip occurs between the toner image on the sheet P and the surface of the fixing belt610. This reduces the adhesion between the toner image and the fixing belt610, and the sheet P is brought into a state in which it is easily peeled off from the fixing belt610.

In the exemplary embodiment, the metallic-color toner Tg is used, as described above. When the fixing unit60of the exemplary embodiment is used, the above-described micro-slip (slippage) occurs between the toner image and the surface of the fixing belt610, so that shear force is applied to the flat metallic pigment. As a result, the metallic pigment steeply standing from the plane of the sheet P when transferred on the sheet P, as illustrated inFIG. 3A, tilts toward the sheet plane, as illustrated inFIG. 3B. That is, the metallic pigment points in the direction along the sheet plane. As a result, when the fixing unit60of the exemplary embodiment is used, the luminance of the metallic-color toner Tg is increased further.

On the other hand, when the metallic-color toner Tg is transferred on the sheet P, the metallic pigment in the metallic-color toner Tg steeply stands from the sheet P, as described above. Therefore, when the sheet P on which the metallic-color toner Tg is transferred is pressed while being nipped between the fixing belt610and the pressing roller62, a minute flaw may occur on the surface of the fixing belt610.

In contrast, in the exemplary embodiment, a toner image formed of non-metallic-color toner, such as clear toner Tt, other than the metallic-color toner is superimposed on the metallic-color toner Tg. That is, the metallic-color toner image is coated with the non-metallic-color toner image on the sheet P. This suppresses damage that may occur on the surface of the fixing belt610when the fixing belt610applies pressure to the metallic-color toner Tg.

Description of Coating Process

Next, the coating process will be described in detail.

FIG. 4is a flowchart of the coating process in the exemplary embodiment.

FIG. 5is a conceptual view illustrating the relationship among metallic-color toner Tg, colored toner Tymck, and clear toner Tt on a sheet P.

The coating process is carried out by the control of the controller50over the image forming units11and the intermediate transfer belt20.

First, it is determined whether or not to perform image formation using a metallic color on a sheet P serving as an object on which an image is to be formed (Step (hereinafter referred to as S)101). When image formation using the metallic color is not performed (No in S101), the process is finished.

Next, when image formation using the metallic color is performed (Yes in S101), it is determined, on the basis of the number of recording materials on which metallic-color toner Tg is to be transferred, whether or not to superimpose clear toner Tt on the metallic-color toner Tg. In the exemplary embodiment, it is determined whether or not the number of successive sheets P, on which the metallic-color toner Tg is to be transferred, is larger than or equal to a predetermined number (S102).

When the number of successive sheets P, on which the metallic-color toner Tg is to be transferred, is larger than or equal to the predetermined number in S102(Yes in S102), the process proceeds to S104.

Determining whether or not to perform coating with the clear toner Tt on the basis of the number of recording materials on which metallic-color toner Tg is transferred may be made according to not only the number of successive recording materials on which the metallic-color toner Tg is transferred, but also, for example, the number of sheets P on which the metallic-color toner Tg is transferred, of a fixed number of sheets P subjected to image formation. That is, the metallic-color toner Tg is coated with the clear toner Tt in a situation where the use frequency of the metallic-color toner Tg is high in a certain period.

As described above, when the metallic-color toner Tg is fixed, it may damage the fixing belt610. However, the surface of the fixing belt610is easily recovered from damage by fixing a toner image containing no metallic-color toner Tg. Accordingly, the metallic-color toner Tg is coated with clear toner Tt in the situation where the use frequency of the metallic-color toner Tg is high. In contrast, in a situation in which the use frequency of the metallic-color toner Tg is low, coating with the clear toner Tt is not performed to suppress consumption of the clear toner Tt.

On the other hand, when the number of successive sheets P on which the metallic-color toner Tg is transferred is smaller than the predetermined number (No in S102), it is determined, on the basis of the area on the sheets P where the metallic-color toner Tg is transferred, whether or not to superimpose the clear toner Tt on the metallic-color toner Tg. In the exemplary embodiment, it is determined whether or not the area of the metallic-color toner Tg on the sheet P is larger than or equal to a predetermined area (S103).

When the area of the metallic-color toner Tg on the sheet P is larger than or equal to the predetermined area (Yes in S103), the process proceeds to S104. In contrast, when the area of the metallic-color toner Tg on the sheet P is smaller than the predetermined area (No in S103), the process is finished.

First, when the area of the metallic-color toner Tg on the sheet P is large, the region of the fixing belt610in the fixing unit60to be damaged is also large. When the region of the fixing belt610to be damaged increases, the influence on other images to be fixed later increases. Accordingly, in the exemplary embodiment, when the area of the metallic-color toner Tg on the sheet P is large, the metallic-color toner Tg is coated with the clear toner Tt. In contrast, when the area of the metallic-color toner Tg is small, the metallic-color toner Tg is not coated with the clear toner Tt to suppress consumption of the clear toner Tt.

Determining whether or not to superpose the clear toner Tt on the basis of the region where the metallic-color toner image is formed may be made according to not only the area of the region, but also, for example, the length of the metallic-color toner image on the sheet P. Particularly when the length of the metallic-color toner image in the transport direction of the sheet P is longer than or equal to a predetermined length, the metallic-color toner Tg may be coated with the clear toner Tt.

A metallic-color toner image is continuously formed in one direction on a sheet P, for example, when a gold ornament frame for a commendation is formed using metallic-color toner Tg. In this case, since a portion of the fixing unit60opposed to the metallic-color toner image concentrates at a specific position, the load is high at the specific position. Accordingly, when the length of the metallic-color toner image is longer than or equal to the predetermined length in one direction, the metallic-color toner Tg is coated with the clear toner Tt.

Next, when the number of successive sheets P on which the metallic-color toner Tg is transferred is more than or equal to the predetermined number in S102(Yes in S102) or when the area of the metallic-color toner image on the sheets P is more than or equal to the predetermined area (Yes in S103), it is determined whether or not to superimpose a colored toner image on the metallic-color toner image (S104).

When the colored toner image is superimposed on the metallic-color toner image (Yes in S104), the process is finished. In contrast, when the colored toner image is not superimposed on the metallic-color toner image (No in S104), a clear toner image is superimposed on the metallic-color toner image (S105).

When the metallic-color toner image is coated with colored toner Tymck, since the colored toner Tymck is held between the fixing belt610and the metallic-color toner Tg, the fixing belt610is protected by the colored toner Tymck. Accordingly, in the exemplary embodiment, as illustrated inFIG. 5, when the metallic-color toner Tg is coated with the colored toner Tymck, it is not coated with the clear toner Tt to suppress consumption of the clear toner Tt. In contrast, when the metallic-color toner Tg is not coated with the colored toner Tymck, it is coated with the clear toner Tt.

As described above, in the exemplary embodiment, it is determined whether or not to coat the metallic-color toner Tg with the clear toner Tt, on the basis of the conditions such as the number of sheets P on which the metallic-color toner Tg is transferred, the area of the metallic-color toner image on the sheets P, and the presence or absence of the colored toner Tymck superimposed on the metallic-color toner image.

While all of the number of sheets P on which the metallic-color toner Tg is transferred, the area of the metallic-color toner image on the sheets P, and the presence or absence of the colored toner Tymck superimposed on the metallic-color toner image are adopted as the conditions in the above-described exemplary embodiment, it may be determined whether or not to coat the metallic-color toner Tg with the clear toner Tt, according to individual conditions.

As a condition for superimposing the clear toner Tt on the metallic-color toner Tg, the image ratio or density of the metallic-color toner image on the sheet P may be used. Specifically, when the image ratio serving as the number of pixels included per unit area of the metallic-color toner image formed on the sheet P is higher than or equal to a predetermined image ratio, the metallic-color toner Tg is coated with the clear toner Tt. Alternatively, when the density of the metallic-color toner image formed on the sheets P is higher than or equal to a predetermined density, the metallic-color toner Tg is coated with the clear toner Tt.

For example, when the amount of colored toner Tymck that coats the metallic-color toner Tg is smaller than a predetermined amount, clear toner Tt may be superimposed on the metallic-color toner Tg in addition to the colored toner Tymck in order to supplement the function of protecting the fixing belt610by coating with the colored toner Tymck.

While the shape of the clear toner image coincides with the shape of the metallic-color toner image when the metallic-color toner Tg is coated with the clear toner Tt in the exemplary embodiment, the present invention is not limited thereto. For example, a clear toner image may be formed over the entire sheet P, regardless of the shape of the metallic-color toner image. Alternatively, the metallic-color toner image may be partly coated with the clear toner Tt.

While toner images of plural colors are combined on the intermediate transfer belt20and are then collectively transferred onto a sheet P in the exemplary embodiment, the present invention is not limited to this manner. For example, the contents of the above-described exemplary embodiment are also applicable to an image forming apparatus in which toner images of plural colors are transferred in order onto a sheet P.

The image forming process and the coating process in the above-described exemplary embodiment are carried out by cooperation of software and hardware resources. That is, an unillustrated CPU in the controller50provided in the image forming apparatus1executes a program that fulfills the functions of the image forming process and the coating process, and fulfills these functions.

Hence, the program can be regarded as causing the computer to fulfill the function of forming a metallic-color toner image having a metallic color, the function of forming a non-metallic-color toner image having a color different from the metallic color, and the function of transferring a toner image onto a sheet P so that the non-metallic-color toner image is superimposed on the upper side of the metallic-color toner image on the sheet P.

The program that carries out the exemplary embodiment can be provided not only by a communication device but also by being stored in a recording medium such as a CD-ROM.