Image forming apparatus

Abstract

To print both an image with high glossiness and an image with low glossiness without causing hot offset, in printing a black image in an image forming apparatus capable of color printing.SOLUTION: An image forming apparatus is used, which prints a plurality of toner images formed by using toners in a plurality of colors in a superimposed manner on a recording material, and the plurality of toners include first to third toners different in color from each other. The image forming apparatus has: image forming units that are used respectively for formation of a first toner image to a third toner image; transfer means that transfers the first toner image, second toner image, and third toner image in a superimposed manner to the recording material in order from one closer to the recording material; and fixing means that has heating means heating the recording material from a side to which the toner images are transferred, and causes the heating means to heat and fuse the toner images to fix the toner images to the recording material. Of the first to third toners, the first toner has the highest modulus of elasticity, and the second toner has the lowest modulus of elasticity.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] In conventional image forming apparatuses using electrophotography or electrostatic recording, such as laser beam printers, copiers, and facsimile machines, a toner image is formed on an image carrier such as a photoconductor or intermediate transfer body by an appropriate image forming process. This toner image is transferred to a recording material by a transfer means, and then fixed on the recording material by a fixing device having a heating means as a fixing means. The recording material on which the toner image is fixed is then output from the image forming apparatus as an image formed product.

[0003] In recent years, electrophotographic image forming devices are becoming full-color. Some of these color image forming devices transfer toner images of four colors, yellow, magenta, cyan, and black, one by one onto a recording material in a superimposed manner, and then fix the transferred toner images of multiple colors to the recording material using a fixing device. In these color image forming devices, in order to achieve a wide range of color reproducibility and saturation in a full-color image, toners with low viscoelasticity when melted in the fixing device are used to improve the mixing properties of the toners of each color.

[0004] Here, when forming a color photographic image, high gloss is required. On the other hand, when forming a black character image during black-and-white printing, low gloss is also required. Therefore, there is a technology for lowering the glossiness of black by making the viscoelastic properties of black toner higher than those of other toners. In order to achieve both of these requirements, in Patent Document 1, when printing black-and-white, only black toner is used to create an image with low glossiness (monochrome black). On the other hand, when printing a color image, four toner images of yellow, magenta, cyan, and black are superimposed to create a so-called process black, thereby increasing the glossiness. Then, a technology is proposed for forming a black image by superimposing toners so that the toner with lower glossiness is on the recording material side and the toner with higher glossiness is on the heating means side, and then heating, fusing, and fixing the toners together to prevent uneven glossiness of the image. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-197256 Summary of the Invention [Problem to be solved by the invention]

[0006] When using a toner with low viscoelasticity when melted in a fixing device, if the toner with high glossiness is subjected to excessive heat by the heating means, the toner may adhere to the fixing member. This is called hot offset. When hot offset occurs, the surface of the image after fixing becomes rough, and the reflected light is scattered, resulting in a problem of reduced glossiness.

[0007] The present invention has been made to solve the above-mentioned problems, and aims to print both high and low gloss images without causing hot offset when printing black images in an image forming device capable of color printing. [Means for solving the problem]

[0008] The present invention employs the following configuration. 1. An image forming apparatus that forms a plurality of toner images using a plurality of color toners and prints the plurality of toner images on a recording material by superimposing the plurality of toner images, The plurality of toners include a first toner, a second toner, and a third toner, each having a different color. Including, an image forming unit that forms a first toner image using the first toner, a second toner image using the second toner, and a third toner image using the third toner; a transfer unit that transfers the first toner image, the second toner image, and the third toner image onto the recording material in a superimposed manner in order from the closest position to the recording material; a fixing unit having a heating unit for heating the recording material from the side to which the toner image has been transferred, and for heating and melting the toner image by the heating unit to fix it on the recording material; Equipped with Among the first toner, the second toner, and the third toner, the first toner has the highest elastic modulus and the second toner has the lowest elastic modulus. The image forming apparatus is characterized in that: Effect of the Invention

[0009] As described above, according to the present invention, when printing black images in an image forming apparatus capable of color printing, it is possible to print both high and low gloss images without causing hot offset. [Brief description of the drawings]

[0010] [Figure 1] Cross-sectional view of a color image forming apparatus [Diagram 2] FIG. 13 is a diagram showing the state of toner lamination when transferred onto a recording material P. [Diagram 3] Cross-sectional view of the fixing unit [Figure 4] Control block diagram of an image forming apparatus [Diagram 5] FIG. 1 is a diagram showing an example of a measurement result of the storage elastic modulus of a toner. [Figure 6] Pressure profile in the recording material transport direction [Figure 7] Flowchart showing the execution procedure of the second embodiment DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. Note that the following embodiments do not limit the scope of the invention, and all combinations of features described in the embodiments are not necessarily essential to the solution of the invention.

[0012] In addition, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described in this embodiment are not intended to limit the scope of this invention to those alone. In addition, the materials, shapes, etc. of the members once described in the following description are the same as those described initially in the following description unless otherwise specified. Well-known or publicly known technologies in the relevant technical field can be applied to configurations and processes that are not particularly illustrated or described. Also, duplicated descriptions may be omitted.

[0013] [Example 1] <Image forming device> First, the overall configuration of the image forming apparatus of this embodiment will be outlined.

[0014] FIG. 1 is a schematic cross-sectional view of a multi-color laser printer utilizing an electrophotographic image forming process, which is the image forming apparatus of this embodiment. The image forming apparatus 100 is equipped with process stations (process cartridges) 5Y, 5M, 5C, and 5K that are detachable from the apparatus main body 100a. The four cartridges 5Y, 5M, 5C, and 5K have the same structure, but differ in that they form images using toners (developers) of different colors, namely, yellow (Y), magenta (M), cyan (C), and black (K). Note that, hereinafter, the reference characters YMCK will be omitted except when describing a specific cartridge. Each cartridge 5 includes a toner container 23, a photosensitive drum 1 as a photosensitive member, a charging roller 2, a developing roller 3, a cleaning blade 4, It also has a waste toner container 24. An exposure device 7 disposed below the cartridge 5 exposes the photoconductor drum 1 to light based on an image signal corresponding to image data for each of yellow, magenta, cyan, and black.

[0015] During the rotation process, the photoconductor drum 1 is uniformly charged to a predetermined polarity and a predetermined potential by the charging roller 2. Thereafter, the photoconductor drums 1Y-1K are exposed by the exposure devices 7Y-7K, respectively, and electrostatic latent images corresponding to the first to fourth color component images are formed. The first to fourth color component images are color component images for forming a target color image, and correspond to yellow, magenta, cyan, and black, respectively. The charging roller 2 rotates in accordance with the rotation of the photoconductor drum 1.

[0016] The developing roller 3 causes toner T to adhere to the electrostatic latent image formed on the photosensitive drum 1, developing it into a toner image. The toner T in the toner container 23 is a negatively charged non-magnetic one-component toner, and the electrostatic latent image is developed by a non-magnetic one-component contact development method. A voltage is applied to the developing roller 3 from a power source (not shown), thereby performing development.

[0017] The intermediate transfer belt unit is composed of an intermediate transfer belt 8, a driving roller 9, a secondary transfer opposing roller 10, a belt cleaning blade 21, and a belt toner box 22. In the intermediate transfer belt unit, primary transfer rollers 6Y to 6K are disposed at positions facing the photoconductor drums 1Y to 1K on the inside of the intermediate transfer belt 8. When the driving roller 9 is rotated by a motor (not shown), the intermediate transfer belt 8 is rotated in the direction of the arrow A, and the secondary transfer opposing roller 10 is rotated accordingly. In addition, each photoconductor drum 1 rotates in the direction of the arrow. Here, a positive primary transfer voltage is applied from a power source to the primary transfer roller 6, so that the toner image on the photoconductor drum 1 is primarily transferred onto the intermediate transfer belt 8 in order from the toner image on the photoconductor drum 1Y. In the image forming apparatus of this embodiment, when four color toners are primarily transferred, the toner images are layered in the order of yellow, magenta, cyan, and black from the side closer to the intermediate transfer belt 8.

[0018] Thereafter, the four color toner images are transported to the secondary transfer roller 11 in a state where they are stacked on the intermediate transfer belt 8. The cleaning blade 4 of the photosensitive drum 1 is pressed against the photosensitive drum 1 to remove residual toner remaining on the surface of the photosensitive drum 1 without being primarily transferred to the intermediate transfer belt 8 and other residues on the photosensitive drum. In addition, the belt cleaning blade 21 is pressed against the intermediate transfer belt 8 stretched around a drive roller 9 to remove residual toner remaining on the surface of the intermediate transfer belt 8 without being secondary transferred to the recording material P in the secondary transfer described below and other residues on the intermediate transfer belt 8.

[0019] The feeding and conveying device 12 has a paper feed roller 14 that feeds the recording material P from a paper feed cassette 13 that stores the recording material P, and a conveying roller pair 15 that conveys the fed recording material P. The recording material P conveyed from the feeding and conveying device 12 is conveyed to the secondary transfer roller 11 by a registration roller pair 16. In the secondary transfer from the intermediate transfer belt 8 to the recording material P, a positive voltage is applied to the secondary transfer roller 11 to transfer a toner image in which the four color toners T on the intermediate transfer belt 8 are superimposed on the conveyed recording material P. FIG. 2 shows the state of toner stacking when the four color toner images are transferred to the recording material P. The toner images are stacked in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the side closer to the recording material P, in the opposite order to when they were on the intermediate transfer belt 8. The arrangement of the image forming units in the conveying direction of the intermediate transfer belt 8 is such that when the toner images are superimposed and transferred onto the recording material, they are stacked in the order shown in this embodiment.

[0020] The recording material P after the toner image transfer is conveyed to a fixing device 30 as a fixing means. The fixing device 30 is a flatbed unit including a fixing film 31 and a pressure roller 32 for pressing the fixing film 31. The fixing unit 30 is a film heating type fixing unit. The fixing film 31 has a fixing heater 33 and a thermistor 331 built therein for measuring the temperature of the fixing heater 33. The fixing unit 30 heats and presses the recording material P, thereby fixing the toner image onto the recording material P. Thereafter, the recording material P passes through the paper discharge rollers 20 and is discharged outside the image forming apparatus 100.

[0021] <Fixing method> Next, an outline of the overall configuration of the fixing device 30 as a fixing means mounted on the image forming apparatus 100 will be described. Fig. 3 is a schematic cross-sectional view of the fixing device 30 of the first embodiment. For convenience of explanation, the fixing device 30 in Fig. 3 is rotated about 90 degrees to the right with respect to the arrangement state shown in Fig. 1 (XZ coordinate axes are shown in Figs. 1 and 3). Note that the toner T on the recording material P shows a state in which any one of yellow, magenta, cyan, and black toners, or any toner selected from each toner, is superimposed.

[0022] The fixing unit 30 of this embodiment has a fixing film 31, a pressure roller 32, and an entrance guide 36. The fixing film 31 has a fixing heater 33, a heater holder 34, a pressure stay 35, and a thermistor 331 built therein.

[0023] The fixing film 31 is an endless film-like member having an elastic layer 312 and a surface layer 313 provided on the outer peripheral surface of a base layer 311. The elastic layer 312 is made of a heat-resistant elastic material such as silicone rubber for the purpose of improving fixing properties and uniforming gloss. The surface layer 313 is made of a heat-resistant material with good releasability such as fluororesin for the purpose of improving separation from the recording material P and suppressing offset in which the toner T adheres to the surface layer 313.

[0024] The pressure roller 32 has a core shaft portion 321, at least one elastic layer 322, and a surface layer 323. The elastic layer 322 is made of a heat-resistant elastic material such as silicone rubber or fluororubber to ensure the width of the fixing nip portion N described below. The surface layer 323 is made of a heat-resistant material with good releasability such as fluororesin to prevent contamination by toner or paper powder. In this embodiment, the pressure roller 32 has an outer diameter of 25 mm.

[0025] The fixing heater 33 is a plate-shaped heating element that rapidly heats the fixing film 31 while contacting the inner circumferential surface of the fixing film 31. The fixing heater 33 is disposed over an area facing the fixing nip portion N. The plate-shaped heating element is configured by screen-printing an electric heat-generating resistive layer on a ceramic substrate. The temperature of the fixing heater 33 is detected by a thermistor 331 as a temperature detection means that is in contact with the surface of the substrate opposite to the surface that contacts the fixing film 31. Then, a temperature control means (not shown) controls the electric current to the electric heat-generating resistive layer based on a detection signal from the thermistor 331 so that the fixing heater 33 reaches a predetermined target temperature.

[0026] The heater holder 34 holds the fixing heater 33. The pressure stay 35 is made of a member having rigidity, and applies pressure force received from a pressure means (not shown) to the pressure roller 32 via the heater holder 34. This pressure force forms a fixing nip portion N having a predetermined width from the front end to the rear end between the fixing film 31 and the pressure roller 32.

[0027] Next, the fixing process in the fixing device 30 will be described. The pressure roller 32 is driven to rotate in the direction of the arrow R1 by a driving means (not shown). The fixing film 31 is rotated in the direction of the arrow R2 in accordance with the rotation of the pressure roller 32. The fixing heater 33 rapidly heats up to heat the fixing film 31. In a state in which the fixing heater 33 is controlled to a predetermined target temperature, the recording material P is guided to the fixing nip portion N along the entrance guide 36, and is sandwiched and conveyed by the fixing film 31 and the pressure roller 32 in the conveying direction, that is, the arrow D direction. During the conveying process, heat and pressure are applied to the recording material P, and the unfixed toner image T is fixed.

[0028] <Control block diagram> Next, a control block related to the embodiment of the present invention in the image forming apparatus 100 will be described. FIG. 4 is a control block diagram of the image forming apparatus 100 of this embodiment. The control unit 60 as a control means is a CPU that controls the entire image forming apparatus 100. The RAM 63 is a work memory, and the ROM 64 stores a program that controls the image forming apparatus. The control unit 60 operates according to the program and a user instruction, thereby functioning as an image formation control unit 61 and a fixing temperature control unit 62. The image formation control unit 61 operates the image forming unit 50 as an image forming means, and performs control for printing an image on a recording material P based on image information transmitted from a terminal. The fixing temperature control unit 62 controls the temperature of the fixing heater 33 of the fixing unit 30 to a predetermined temperature based on the detection result of the thermistor 331, which is a temperature detection element.

[0029] The network interface 70 is connected to an external terminal 220 used by a user via a LAN or the like, and performs input / output (communication processing) of image information and device information between the external terminal 220 and the image forming apparatus 100. The HDD 73 as a storage means is a hard disk drive. The HDD 73 stores system software and the like. As a storage means, a writable non-volatile memory such as a semiconductor memory may be used in addition to a hard disk. The calculation unit 74 as a calculation means converts image information such as an RGB display system transmitted from a terminal into image data of yellow, magenta, cyan, and black using information stored in the HDD 73, and outputs the converted image data. When the calculation unit 74 converts a black image into image data, if the calculation unit 74 recognizes the image as a black character image, it converts the image into monochrome black image data. On the other hand, if the calculation unit 74 recognizes the image as a picture such as a photograph, it converts the black part in the image into process black image data formed by laminating yellow, magenta, cyan, and black. The hardware configuration of the image forming apparatus of this embodiment has been described above. Note that the hardware configuration is an example, and is not limited to this configuration.

[0030] <Explanation of verification study> As an index of toner softness, the storage modulus, which is a viscoelastic property of the toner, was used to carry out verification and examination. Toners with different storage moduli were produced as prototypes, and Example 1 was compared with Comparative Example 1. However, the index used is not limited to the storage modulus, and any index that can express the softness of the toner may be used.

[0031] FIG. 5 shows an example of the results of measuring the storage modulus of a toner. The horizontal axis indicates temperature [°C], and the vertical axis indicates the storage modulus G' [Pa]. As a representative value, the storage modulus G' at 100°C (100 Here, the storage modulus G'(100°C) = 2.2 × 10 4 Pa. Here During fixing, the toner T on the recording material P is heated to about 100° C. while passing through the fixing nip N of the fixing device 30. Therefore, the storage modulus G'(100° C.) at 100° C. is used as an index. .

[0032] It is possible to change the glossiness by changing the viscoelastic properties such as the storage modulus of the toner when it is melted in the fixing device 30. A toner having a high storage modulus G' (100°C) has a low glossiness. In addition, toner with a high storage modulus G' (100°C) is hard, so the toner melts and spreads. Since it is difficult to remove the toner, unevenness on the toner surface tends to remain. If there are uneven surfaces, the reflected light will be scattered, resulting in low gloss. In order to achieve low gloss on characters, the storage modulus G'(100°C) of the black toner is designed to be high. On the other hand, a toner with a low storage modulus G'(100°C) will have a high gloss. A toner with a low storage modulus G'(100°C) is soft, so it is difficult to remove the toner. The toner dissolves and spreads easily, making the toner surface smooth. When the toner surface is smooth, the reflected light is less likely to scatter, resulting in a higher gloss level.

[0033] <Explanation of toner viscoelastic properties> First, a method for measuring the storage elastic modulus will be described. The storage elastic modulus of toner T is measured by dynamic viscoelasticity measurement. The measurement is performed using a rheometer ARES (manufactured by Rheometrics Scientific). Measurement tool: A serrated parallel plate with a diameter of 7.9 mm is used. However, the measurement method is not limited to this, and any device or method can be used.

[0034] Measurement sample: Using a pressure molding machine, mold a 0.1g sample into a cylindrical sample with a diameter of 8mm and a height of 2mm (maintain 15kN for 1 minute at room temperature). The pressure molding machine used is a 100kN press NT-100H manufactured by NPa Systems.

[0035] The temperature of the serrated parallel plate is adjusted to 120°C, the cylindrical sample is heated and melted, the sawtooth is inserted, and a load is applied vertically so that the axial force does not exceed 30 (gf) (0.294N) to fix it to the serrated parallel plate. A steel belt may be used at this time so that the diameter of the sample is the same as that of the parallel plate. The serrated parallel plate and the cylindrical sample are slowly cooled down to the measurement start temperature of 30.00°C over one hour.

[0036] Measurement frequency: 6.28 rad / sec Measurement distortion setting: Set the initial value to 0.1%, and perform the measurement in automatic measurement mode. Sample elongation correction: Adjusted in automatic measurement mode. Measurement temperature: 30°C to 140°C at a rate of 2°C per minute. Measurement interval: Measure viscoelastic data every 30 seconds, i.e., every 1°C.

[0037] Table 1 shows the storage elastic modulus G' (100° C.) of each of the yellow, magenta, cyan and black toners of Example 1 and Comparative Example 1. [Table 1]

[0038] The toner layer disposed closest to the recording material P is called the lower layer toner, the toner layer disposed farthest from the recording material P is called the upper layer toner, and the toner layer disposed between the lower layer toner and the upper layer toner is called the middle layer toner. In the example of FIG. 2, black is the lower layer toner, yellow is the upper layer toner, and cyan and magenta are the middle layer toners. The cyan closest to the lower layer toner is also called the first middle layer toner, and the magenta closest to the upper layer toner is also called the second middle layer toner. Note that whether yellow, cyan, and magenta are disposed in the upper layer or middle layer can be determined according to the elastic modulus, and is not limited to this embodiment.

[0039] From the table, the storage modulus G' (100°C) of Example 1 is the highest for the black toner in the lower layer. It has a structure where cyan, which is the upper-middle layer toner, is the lowest, yellow, which is the upper layer toner, is lower than the lower layer toner and higher than the upper-middle layer toner. That is, the storage elastic modulus G’(10 0 °C) is in the order of upper-middle layer toner < upper layer toner < lower layer toner. More specifically, it is in the order of C (the first upper-middle layer toner) < M (the second upper-middle layer toner) < Y (upper layer toner) < K (lower layer toner).

[0040] On the other hand, for the storage elastic modulus G’(100 °C) of Comparative Example 1, black, which is the lower layer toner, is the highest and yellow, which is the upper layer toner, is the lowest. Magenta and cyan, which are the upper-middle layer toners, are lower than the lower layer toner and higher than the upper layer toner. That is, the storage elastic modulus G’ (100 °C) is in the order of upper layer toner < upper-middle layer toner < lower layer toner. More specifically it is in the order of Y (upper layer toner) < M (the second upper-middle layer toner) < C (the first upper-middle layer toner) < K (lower layer toner).

[0041] Table 2 shows the results of a comparative experiment using Example 1 and Comparative Example 1. It shows the glossiness after fixing in the process black state with each toner of yellow, magenta , cyan, and black placed on the recording material P. Also, as a reference value, it shows the glossiness of single-color black. The recording material P used in this measurement is "Futura 80lb (manufactured by VERSO), basis weight 216 g / m 2 ". Also, the glossiness is measured using PG-1 (manufactured by Nippon Denshoku Industries Co., Ltd.) at an incident angle of 75°.

Table 2

[0042] Example 1 realizes high gloss with process black as compared with Comparative Example 1. This is because in Example 1, among the color toners, the storage elastic modulus G’(100 °C) of the upper layer yellow This is because the storage modulus G'( of the upper layer yellow of the color toner is relatively high and resistant to heat, so that hot offset is unlikely to occur. As a result, the toner surface after fixing is smooth, so that reflected light is unlikely to be scattered, and the glossiness is high. On the other hand, in Comparative Example 1, the storage modulus G'( 100℃) is relatively low and vulnerable to heat, so hot offset is likely to occur. As a result, the toner surface becomes rough after fixing, the reflected light is scattered, and the gloss level is low.

[0043] In addition, the monochrome black shown as a reference value has a low gloss because the storage modulus of the black toner is high. In addition, the gloss level is also the same in both Example 1 and Comparative Example 1 because the storage modulus of the black toner is the same.

[0044] As described above, the image forming apparatus of this embodiment uses process black to realize a high gloss black image corresponding to a photographic image without causing hot offset. In addition, the image forming apparatus of this embodiment uses monochrome black to realize a low gloss image corresponding to black text.

[0045] (Modification) Next, as a modified example, a derivative of the embodiment 1 will be described. In the derivative of the embodiment 1, the pressure profile of the fixing nip portion N of the fixing device 30 is changed.

[0046] Fig. 6(a) shows the shape of the fixing heater 33 in Example 1. The lower surface in the figure is the contact surface 33a with the fixing film 31. The contact surface 33a has a flat shape. Fig. 6(b) shows the pressure profile in the recording material transport direction of the fixing nip portion N in Example 1. Since the fixing heater 33 has a flat shape, the pressure profile is symmetrical upstream and downstream in the recording material transport direction.

[0047] 6C shows the shape of the fixing heater 33 of this modified example. The lower surface in the figure is the contact surface 33b with the fixing film 31. The contact surface 33b has a convex shape 33 protruding toward the pressure roller 32. 6D shows the pressure profile in the recording material transport direction of the fixing nip N of this modified example. Since the downstream side of the fixing heater 33 has the convex shape 33c, the pressure profile has a higher pressure downstream in the recording material transport direction. In other words, when the recording material passes through the fixing nip N, the pressure is higher in the latter half than in the first half, and hereinafter this is also referred to as a "rear end pressurization" configuration.

[0048] The pressure profile was measured by using a roller pressure distribution measurement system (PINCH) manufactured by Nitta Corporation, by sandwiching a pressure-sensitive sensor sheet having a piezoelectric element (not shown) in the fixing nip portion N.

[0049] When a fixing device with the pressure profile of the fixing nip portion N of this modified example was used and other conditions were the same as in Example 1, the gloss level after fixing in the process black state in which the yellow, magenta, cyan, and black toners were placed on the recording material P was 65.

[0050] In this modification, the toner surface is smoothed by applying high pressure downstream in the recording material conveying direction where the toner temperature is high. Also, in this modification, compared to the first embodiment, the pressure applied to the recording material is rapidly reduced immediately before the recording material P leaves the fixing nip N downstream in the recording material conveying direction (from reference numeral 128 in FIG. 6(d) onward). As a result, the recording material P is rapidly separated from the fixing film 31. Since the separation speed when the toner T fixed on the recording material P is separated from the fixing film 31 is increased, the apparent viscoelasticity of the toner T is increased, so that the toner T is less likely to adhere to the fixing film 31, and hot offset is suppressed. Since the toner surface is made smoother by suppressing hot offset, it is possible to increase the glossiness compared to the first embodiment.

[0051] From the above, by setting the pressure profile in the fixing nip N to the trailing end pressure as in this modified example, it is possible to achieve even higher gloss. Here, the pressure profile in the fixing nip N is defined based on the shape of the fixing heater 33, but this is not limited as long as the trailing end pressure can be achieved. For example, the trailing end pressure can be achieved by making the force applied by the pressure means to the pressure stay 35 stronger at the trailing end of the fixing nip N than at the front end. Also, even if it is called trailing end pressure, the pressure at the rear end of the nip does not necessarily have to be the greatest, and it is sufficient that the pressure on the downstream side is generally stronger than the upstream side. Also, as long as the separation speed of the recording material P is faster than normal, the configuration is not limited to that shown in FIG. 6.

[0052] [Example 2] The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are given the same reference numerals as those of embodiment 1, and detailed explanations are omitted. The object of this embodiment is to provide an image forming apparatus in which the glossiness of a black image can be selected from a low gloss mode and a high gloss mode. In the low gloss mode, which is low gloss, a black image is printed in monochrome black, and in the high gloss mode, which is high gloss, a black image is printed using four colors of toner: yellow, magenta, cyan, and black.

[0053] 7 shows a flowchart for explaining the second embodiment. After printing starts, the user selects either the low gloss mode or the high gloss mode in step S101. The user may select the mode using a user input means such as an operation panel provided on the device main body 100a, or may select the mode in response to a print instruction from an external terminal. Alternatively, the control unit 60 may analyze image data and determine the mode. When the low gloss mode is selected, the process proceeds to step S102, and when the high gloss mode is selected, the process proceeds to step S105.

[0054] In step S102, which is the low gloss mode, the control unit 60 outputs black image data by using monochrome black for black images in the image information transmitted from the terminal. In step S103, the control unit 60 controls each component of the image forming apparatus 100 based on the image data to perform an image forming operation. Then, in step S104, the fixing unit 30 performs a fixing operation, and printing is completed.

[0055] On the other hand, in step S105, which corresponds to the selection of the high gloss mode, the control unit 60 outputs image data by using process black, which uses four color toners, yellow, magenta, cyan, and black, for black images among the image information transmitted from the terminal. After that, in step S103, the control unit 60 controls each component of the image forming apparatus 100 based on the image data to perform image forming operations. Then, in step S104, the fixing unit 30 performs a fixing operation, and printing is completed.

[0056] In this embodiment, the gloss level of black in low gloss mode was 18, and the gloss level of black in high gloss mode was 58. On the other hand, in the comparative example, the gloss level of black in low gloss mode was 18, and the gloss level of black in high gloss mode was 40. Therefore, in this embodiment, it was possible to increase the gloss of black in high gloss mode.

[0057] When controlling the low gloss mode and the high gloss mode, the fixing temperature and the process speed may be adjusted in combination. The gloss level increases by increasing the fixing temperature and decreasing the process speed.

[0058] As described above, according to this embodiment, it is possible to provide an image forming apparatus capable of selecting the gloss level of a black image between a low gloss mode and a high gloss mode.

[0059] As described above, in the past, when a process black image (typically a black image using four toners of YMCK) is fixed, a toner with low viscoelasticity may receive excessive heat and cause hot offset, resulting in a decrease in glossiness. Therefore, in each embodiment of the present invention, when a black image is formed using process black to increase the glossiness of a photographic image or the like, the toner located closest to the recording material is the lower layer toner, the toner located farthest from the recording material is the upper layer toner, and the toner located between the lower layer toner and the upper layer toner is the middle layer toner, and the storage elastic modulus of the lower layer toner is the highest, the storage elastic modulus of the upper layer toner is the next highest, and the storage elastic modulus of the middle layer toner is the lowest. This makes it possible to reduce the effect of hot offset and suppress the decrease in glossiness. In addition, in the present invention, when a low-gloss black image such as a character image is required, the glossiness can be reduced by using a single color black used as the lower layer toner located close to the recording material. Therefore, a high-gloss black image corresponding to a photographic image can be realized without the occurrence of hot offset, and a low-gloss black image corresponding to black characters can be realized.

[0060] [Configuration 1] 1. An image forming apparatus that forms a plurality of toner images using a plurality of color toners and prints the plurality of toner images on a recording material by superimposing the plurality of toner images, the plurality of toners include a first toner, a second toner, and a third toner that are different in color from one another; an image forming unit that forms a first toner image using the first toner, a second toner image using the second toner, and a third toner image using the third toner; a transfer unit that transfers the first toner image, the second toner image, and the third toner image onto the recording material in a superimposed manner in order from the closest position to the recording material; a fixing unit having a heating unit for heating the recording material from the side to which the toner image has been transferred, and for heating and melting the toner image by the heating unit to fix it on the recording material; Equipped with Among the first toner, the second toner, and the third toner, the first toner has the highest elastic modulus and the second toner has the lowest elastic modulus. 1. An image forming apparatus comprising: [Configuration 2] the first toner is black in color; When forming a black image, it is possible to select either monochrome black, which uses only the first toner, or process black, which uses all of the plurality of toners. 2. The image forming apparatus according to claim 1, [Configuration 3] The mode for forming an image can be selected between a high gloss mode and a low gloss mode, and in the high gloss mode, the black image is formed in the process black, and in the low gloss mode, the black image is formed in the monochrome black. 3. The image forming apparatus according to claim 2, [Configuration 4] When the black image is a photographic image, the black image is formed in the process black, and when the black image is a text image, the black image is formed in the monochromatic black. 3. The image forming apparatus according to claim 2, [Configuration 5] the image forming unit forms a fourth toner image by further using a fourth toner having a color different from both the second toner and the third toner; The second toner, the third toner and the fourth toner correspond to any one of the colors yellow, cyan and magenta. 5. The image forming apparatus according to any one of configurations 2 to 4. [Configuration 6] the fixing means includes a fixing film incorporating the heating means, and a pressure roller forming a fixing nip portion for applying pressure to the recording material between the fixing film and the pressure roller; The recording material is conveyed to the fixing nip portion so that the surface onto which the toner image has been transferred faces the fixing film. 6. The image forming apparatus according to any one of configurations 1 to 5. [Configuration 7] In the fixing nip portion, a pressure force on a downstream side in a conveying direction of the recording material is stronger than a pressure force on an upstream side in the conveying direction of the recording material. 7. The image forming apparatus according to configuration 6, [Configuration 8] The heating means is disposed in a region extending from the front end to the rear end of the fixing nip portion in the conveying direction of the recording material, and the heating means has a convex shape protruding toward the pressure roller on the rear end side, so that the pressure force on the downstream side in the conveying direction is increased. 8. The image forming apparatus according to claim 7, [Configuration 9] the image forming unit includes a first image forming unit that forms the first toner image, a second image forming unit that forms the second toner image, and a third image forming unit that forms the third toner image; the plurality of toner images are transferred in the order of the third toner image, the second toner image, and the first toner image in a superimposed manner onto an intermediate transfer body; The toner images are transferred from the intermediate transfer body to the recording material. 7. The image forming apparatus according to any one of configurations 1 to 6, [Explanation of symbols]

[0061] 5: process station, 6: transfer roller, 30: fixing unit, 50: image forming section, 100: image forming apparatus, P: recording material

Claims

1. 1. An image forming apparatus that forms a plurality of toner images using a plurality of color toners and prints the plurality of toner images on a recording material by superimposing the plurality of toner images, the plurality of toners include a first toner, a second toner, and a third toner that are different in color from one another; an image forming unit that forms a first toner image using the first toner, a second toner image using the second toner, and a third toner image using the third toner; a transfer unit that transfers the first toner image, the second toner image, and the third toner image onto the recording material in a superimposed manner in order from the position closest to the recording material; a fixing unit having a heating unit for heating the recording material from the side to which the toner image has been transferred, and for heating and melting the toner image by the heating unit to fix it on the recording material; Equipped with Among the first toner, the second toner, and the third toner, the first toner has the highest elastic modulus, and the second toner has the lowest elastic modulus.

1. An image forming apparatus comprising:

2. the first toner is black in color; When forming a black image, it is possible to select either monochrome black using only the first toner or process black using all of the plurality of toners.

2. The image forming apparatus according to claim 1,

3. The mode for forming an image can be selected between a high gloss mode and a low gloss mode, and in the high gloss mode, the black image is formed in the process black, and in the low gloss mode, the black image is formed in the monochrome black.

3. The image forming apparatus according to claim 2,

4. When the black image is a photographic image, the black image is formed in the process black, and when the black image is a text image, the black image is formed in the monochromatic black.

3. The image forming apparatus according to claim 2,

5. the image forming unit forms a fourth toner image by further using a fourth toner having a color different from both the second toner and the third toner; The second toner, the third toner and the fourth toner correspond to any one of the colors yellow, cyan and magenta.

5. The image forming apparatus according to claim 2, wherein the image forming apparatus is a multi-color image forming apparatus.

6. the fixing means includes a fixing film incorporating the heating means, and a pressure roller forming a fixing nip portion for applying pressure to the recording material between the fixing film and the pressure roller; The recording material is conveyed to the fixing nip portion so that the surface onto which the toner image has been transferred faces the fixing film.

5. The image forming apparatus according to claim 2, wherein the image forming apparatus is a multi-color image forming apparatus.

7. In the fixing nip portion, a pressure force on a downstream side in a conveying direction of the recording material is stronger than a pressure force on an upstream side in the conveying direction of the recording material.

7. The image forming apparatus according to claim 6,

8. The heating means is disposed in a region extending from the front end to the rear end of the fixing nip portion in the conveying direction of the recording material, and the heating means protrudes toward the pressure roller on the rear end side. By having a convex shape, the pressure on the downstream side in the conveying direction is increased.

8. The image forming apparatus according to claim 7,

9. the image forming unit includes a first image forming unit that forms the first toner image, a second image forming unit that forms the second toner image, and a third image forming unit that forms the third toner image; the plurality of toner images are transferred in the order of the third toner image, the second toner image, and the first toner image in a superimposed manner onto an intermediate transfer body; The toner images are transferred from the intermediate transfer body to the recording material.

5. The image forming apparatus according to claim 2, wherein the image forming apparatus is a multi-color image forming apparatus.

Images