Image forming device

Abstract

To acquire sufficient bond strength even without setting a heating temperature at the bonding time to an extremely high temperature.SOLUTION: An image forming device includes: image forming means for forming a toner image on a sheet by using printing toner, and for coating a powder adhesive agent to a sheet; fixing means having a first rotary body pair for forming a first nip part, and for fixing the toner image to the sheet by heating and pressurizing the sheet conveyed from the image forming means while holding and conveying it by the first nip part; folding means for folding the sheet conveyed from the fixing means with the surface where the powder adhesive agent is coated being inside; and bonding means having a second rotary body pair for forming a second nip part, and for bonding the sheet by the powder adhesive agent by heating and pressurizing the sheet folded by the folding means while holding and conveying it by the second nip part. A peak value of the pressure which the second rotary body pair applies to the sheet at the second nip part is larger than a peak value of the pressure which the first rotary body pair applies to the sheet at the first nip part.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus that forms an image on a sheet. [Background technology]

[0002] In the past, when creating documents that needed to be sealed due to confidentiality, such as pay slips, preprinted paper with adhesive applied was prepared in advance, and after variable data was printed on the preprinted paper, the paper was sealed as a post-processing step. This method took time to create the preprinted paper, which required the application of adhesive, and was inefficient when only a small number of documents were required.

[0003] Patent Document 1 proposes an image forming apparatus that uses an electrophotographic process to output sealed documents using plain paper by using a powder adhesive (adhesive toner) in addition to image-forming toner (printing toner). In this method, the adhesive toner is applied to a sheet, which is a recording medium, by being transferred using the electrophotographic process, just like the image-forming toner. The sheet is then folded with the side containing the powder adhesive facing inward, and the folded sheet is heated and pressurized to adhere the sheets together with the powder adhesive. Patent Document 2 describes a powder adhesive containing a cyclic polyolefin resin and a thermoplastic elastomer as a powder adhesive to be applied to base paper such as a pressure-bonded postcard using an electrophotographic process. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-171607 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-170659 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when performing both the printing process and the bonding process using a single image forming apparatus, as in Patent Document 1, the following problems can occur. In the bonding process, the outer surface of the folded sheet comes into contact with a heating element, such as a heating roller or a heating film, and is heated. The heat then travels through the sheet, heating the powder adhesive applied to the inner surface of the folded sheet. Because the sheet is heated while being transported at a preset transport speed, if the temperature of the heating element is low, the powder adhesive may not be sufficiently heated while the heating element is in contact with the sheet, resulting in poor bonding. On the other hand, if the heating temperature during bonding is set too high, problems such as poor image quality (so-called hot offset) may occur, in which printing toner fixed on the outer surface of the sheet remelts and adheres to the heating element, then re-adheses to the sheet, smearing the sheet surface.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image forming apparatus that can obtain sufficient adhesive strength without setting the heating temperature during adhesion to an excessively high level. [Means for solving the problem]

[0007] One aspect of the present invention is an image forming apparatus comprising: image forming means for forming a toner image on a sheet using printing toner and applying a powder adhesive to the sheet; fixing means having a first pair of rotating bodies forming a first nip portion, and fixing the toner image to the sheet by applying heat and pressure to the sheet conveyed from the image forming means while sandwiching and conveying the sheet at the first nip portion; folding means for folding the sheet conveyed from the fixing means with the surface on which the powder adhesive is applied facing inward; and bonding means having a second pair of rotating bodies forming a second nip portion, and bonding the sheet with the powder adhesive by applying heat and pressure to the sheet folded by the folding means while sandwiching and conveying the sheet at the second nip portion, wherein the peak value of the pressure applied to the sheet by the second pair of rotating bodies at the second nip portion is The second peak value is is the peak value of the pressure applied to the sheet by the first rotating body pair in the first nip portion. The first peak value is Bigger The width of the second nip portion in the sheet transport direction is shorter than the width of the first nip portion in the sheet transport direction, and the value of the product of the second peak value and the width of the second nip portion is greater than the value of the product of the first peak value and the width of the first nip portion. The image forming apparatus is characterized by the above. [Effects of the Invention]

[0008] According to the present invention, it is possible to obtain sufficient adhesive strength without setting the heating temperature during bonding to an excessively high temperature. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment. [Figure 2] 3A and 3B are diagrams illustrating attachment of a post-processing unit to the main body of the image forming apparatus according to the embodiment. [Figure 3] FIG. 2 is a diagram illustrating a sheet transport path in the image forming apparatus according to the embodiment. [Figure 4] FIG. 10 is a diagram illustrating another sheet transport path in the image forming apparatus according to the embodiment. [Figure 5] 10A to 10F are diagrams for explaining the details of a folding process according to an embodiment. [Figure 6] FIG. 1 is a perspective view showing the appearance of an image forming apparatus according to an embodiment. [Figure 7] 1A and 1B are diagrams illustrating examples of products output by an image forming apparatus according to an embodiment. [Figure 8] FIG. 2 is a schematic view of a process cartridge according to an embodiment. [Figure 9] FIG. 2 is a schematic diagram of a fixing device according to the embodiment. [Figure 10] FIG. 2 is a schematic view of the inside of a post-processing unit according to the embodiment. [Figure 11] Graphs (a) to (c) show pressure distribution in the fixing nip and the bonding nip. [Figure 12] FIG. 10 is a schematic diagram for explaining setting conditions for adhesive treatment. [Figure 13] Schematic diagram (a) showing the contact state between the fixing film and the sheet surface in the fixing nip and table (b) showing parameters related to that adhesion, and schematic diagram (c) showing the contact state between the surfaces of the sheets in the adhesive nip and table (d) showing parameters related to that adhesion. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0011] (Overall device configuration) First, the overall configuration of the image forming apparatus will be described with reference to Figures 1, 2, and 6. Figure 1 is a schematic diagram showing the cross-sectional configuration of an image forming apparatus 1 that includes an image forming apparatus main body (hereinafter referred to as apparatus main body 10) according to this embodiment and a post-processing unit 30 connected to the apparatus main body 10. The image forming apparatus 1 is an electrophotographic image forming apparatus (electrophotographic system) that includes the apparatus main body 10 that includes an electrophotographic printing mechanism and the post-processing unit 30 that serves as a sheet processing device.

[0012] 6 is a perspective view showing the appearance of the image forming apparatus 1. The post-processing unit 30 is attached to the top of the apparatus main body 10. The image forming apparatus 1 has a sheet cassette 8 at the bottom, an openable tray 20 on the right side, and a first discharge tray 13 on the top.

[0013] First, the internal configuration of the device main body 10 will be described. As shown in Fig. 1, the device main body 10 includes a sheet cassette 8 as a sheet storage section that stores sheets P as recording media, an image forming unit 1e as image forming means, a fixing device 6 as fixing means, and a housing 19 that houses these. The device main body 10 has a printing function that forms a toner image on a sheet P fed from the sheet cassette 8 by the image forming unit 1e, and then performs a fixing process by the fixing device 6 to create a printed matter. Note that, for example, paper is used as the sheet P as a recording medium.

[0014] The sheet cassette 8 is inserted into the housing 19 at the bottom of the device main body 10 so as to be removable, and stores a large number of sheets P. The sheets P stored in the sheet cassette 8 are fed from the sheet cassette 8 by a feeding member such as a feeding roller, and are separated one by one by a pair of separation rollers and then transported by a transport roller 8a. It is also possible to feed sheets set in an open tray 20 (FIG. 6) one by one.

[0015] The image forming unit 1e is a tandem electrophotographic unit equipped with four process cartridges 7n, 7y, 7m, and 7c, a scanner unit 2, and a transfer unit 3. A process cartridge is a unit in which multiple components responsible for the image forming process are integrated into one replaceable unit. The apparatus main body 10 is provided with a cartridge support portion 9 supported by a housing 19, and the process cartridges 7n, 7y, 7m, and 7c are detachably mounted in mounting portions 9n, 9y, 9m, and 9c provided on the cartridge support portion 9. The cartridge support portion 9 may be a tray member that can be pulled out from the housing 19.

[0016] The process cartridges 7n, 7y, 7m, and 7c have a substantially common configuration except for the type of powder contained in the four powder containers 104n, 104y, 104m, and 104c. That is, each of the process cartridges 7n, 7y, 7m, and 7c includes a photosensitive drum 101 as an image carrier, a charging roller 102 as a charger, powder containers 104n, 104y, 104m, and 104c that contain powder, and a developing roller 105 that performs development using the powder.

[0017] Of the four powder containers, the three powder containers 104y, 104m, and 104c on the right side of the drawing contain yellow, magenta, and cyan printing toners Ty, Tm, and Tc, respectively, as toners (first powder, powder developer) for forming a visible image on the sheet P. In contrast, the powder container 104n on the far left side of the drawing contains powder adhesive Tn, which is a toner (second powder) for performing an adhesive process after printing. The powder containers 104y, 104m, and 104c are all examples of first containers that contain printing toner, and the powder container 104n is an example of a second container that contains powder adhesive. Furthermore, the process cartridges 7y, 7m, and 7c are all examples of first process units that form a toner image using printing toner, and the process cartridge 7n is an example of a second process unit that forms a powder adhesive image in a predetermined application pattern.

[0018] In this embodiment, when printing black images such as text, the process black is produced by superimposing yellow (Ty), magenta (Tm), and cyan (Tc) toners. However, for example, a fifth process cartridge using black printing toner may be added to the image forming unit 1e so that black images can be produced using black printing toner. However, the present invention is not limited to this, and the type and number of printing toners can be changed depending on the application of the image forming apparatus 1.

[0019] The scanner unit 2 is disposed below the process cartridges 7n, 7y, 7m, and 7c and above the sheet cassette 8. The scanner unit 2 is an exposure unit in this embodiment that writes an electrostatic latent image by irradiating the photosensitive drum 101 of each of the process cartridges 7n, 7y, 7m, and 7c with laser light G.

[0020] The transfer unit 3 includes a transfer belt 3a as an intermediate transfer body (secondary image carrier). The transfer belt 3a is a belt member wound around a secondary transfer inner roller 3b and a tension roller 3c, and its outer circumferential surface faces the photosensitive drums 101 of each of the process cartridges 7n, 7y, 7m, and 7c. Primary transfer rollers 4 are disposed on the inner circumferential side of the transfer belt 3a at positions corresponding to the photosensitive drums 101. Furthermore, a secondary transfer roller 5 as a transfer means is disposed at a position facing the secondary transfer inner roller 3b. A transfer nip 5N between the secondary transfer roller 5 and the transfer belt 3a is a transfer portion (secondary transfer portion) where a toner image is transferred from the transfer belt 3a to a sheet P.

[0021] The fixing device 6 is disposed above the secondary transfer roller 5. FIG. 9 is a detailed view of the fixing device 6. The fixing device 6 includes a cylindrical fixing film (endless belt) 6a, a heater 6a1 that contacts the inner surface of the fixing film 6a, and a pressure roller 6b that forms a fixing nip 6N together with the heater 6a1 via the fixing film 6a. The fixing film 6a is a heating member (first heating member) in this embodiment, and the heater 6a1 is a first heating means in this embodiment. The fixing film 6a and the pressure roller 6b function as a pair of rotating bodies (first pair of rotating bodies) that rotate to sandwich and transport the sheet P at the fixing nip 6N as the first nip portion.

[0022] The fixing film 6a is a heat-resistant and flexible film member. For example, the fixing film 6a may be a 60 μm-thick polyimide base layer, on which a 0.3 mm-thick elastic layer made of silicone rubber and a 20 μm-thick release layer made of fluororesin (PFA) are provided. The surface roughness (Ra value) of the fixing film surface is set to 0.4 μm or less to ensure sufficient smoothness. The surface roughness (Ra value) shown here is a value measured using a surface roughness measuring instrument SE-3400 (manufactured by Kosaka Laboratory Co., Ltd.). The cutoff wavelength is set to 0.80 mm or more. The inner diameter of the fixing film 6a is 24 mm, and the width of the fixing film 6a in the longitudinal direction of the fixing nip 6N is 240 mm. The surface of the fixing film 6a is the surface that comes into contact with the toner on the sheet that has been melted (softened) by heating. After the fixing process, the toner surface is smoothed along the surface shape of the fixing film 6a, as described below. The longitudinal direction of the fixing nip 6N is a direction perpendicular to the sheet conveying direction in the fixing nip 6N, and is substantially parallel to the rotation axis direction of the pressure roller 6b and the main scanning direction during image formation.

[0023] The pressure roller 6b includes a core 6b1, an elastic layer 6b2 formed on the outer periphery of the core 6b1, and a release layer formed on the outermost surface. The core 6b1 is made of, for example, iron. The elastic layer 6b2 is a 4.0 mm thick layer made of, for example, soft silicone rubber. The release layer is made of a fluororesin such as PFA or PTFE. The hardness of the silicone rubber used for the pressure roller 6b is approximately 20° as measured by an Asker C hardness tester manufactured by Kobunshi Keiki. The pressure roller 6b is rotated by receiving power from a motor mounted in the device main body 10 via a drive gear (not shown) connected to a shaft provided at the axial end of the iron core 6b1. The length of the outer periphery of the pressure roller 6b in the longitudinal direction of the fixing nip 6N (the axial direction of the pressure roller 6b) (the length of the area where the elastic layer 6b2 and the release layer are formed) is 230 mm, and the diameter of the outer periphery of the pressure roller 6b is 25 mm.

[0024] The heater 6a1, which serves as a heating means (first heating means), includes a thin substrate 6a11, a heating resistor 6a12, and an insulating protective layer 6a13 formed on the substrate 6a11. The substrate 6a11 may be a 0.7 mm-thick thin plate primarily composed of ceramics such as alumina. The heating resistor 6a12 is made of a material that generates heat when energized, such as Ag / Pd (silver-palladium). The insulating protective layer 6a13 is made of an insulating material (glass in this embodiment). The heater 6a1 has a width of 8.7 mm in the sheet conveyance direction and a width of 240 mm in the longitudinal direction of the fixing nip 6N.

[0025] A temperature detection element 6a2, such as a thermistor, is in contact with the substrate 6a11 and is electrically connected to a CPU 6a3, which serves as a control unit mounted on the image forming apparatus 1. The heater 6a1 heats up when current is applied to the heating resistor 6a12. This temperature rise is detected by the temperature detection element 6a2, and the CPU 6a3 controls the power supply to the heating resistor 6a12 via a triac 6a4. For example, if the temperature detected by the temperature detection element 6a2 is lower than a preset temperature, the amount of power supplied to the heating resistor 6a12 is increased so that the heater 6a1 heats up; if the temperature detected by the temperature detection element 6a2 is higher than the preset temperature, the amount of power is decreased so that the heater 6a1 cools down. This maintains the heater 6a1 at a substantially constant temperature. In this embodiment, the CPU 6a3 controls the power supply to the heater 6a1 so that the surface temperature of the fixing film 6a reaches the target temperature of 175°C.

[0026] The heater 6a1 is held by a holding member 6a5 made of heat-resistant resin such as LCP (liquid crystal polymer). The holding member 6a5 also functions as a guide for guiding the rotation of the fixing film 6a. A spring (not shown) attached to a metal stay 6a6 applies a force to the holding member 6a5 in the direction toward the pressure roller 6b. The pressure roller 6b is pressed toward the heater 6a1 via the fixing film 6a with a total pressure of 25 kgf by a pressure means (not shown), such as a spring member. This forms a fixing nip 6N between the pressure roller 6b and the heater 6a1 and holding member 6a5, which constitute the nip forming unit. The width of the fixing nip 6N in the longitudinal direction and the sheet conveying direction is the length and width of the approximately rectangular area where the heater 6a1 and pressure roller 6b are in pressure contact with each other across the fixing film 6a. In the configuration example described above, the width of the fixing nip 6N in the longitudinal direction is 230 mm (the length of the pressure roller 6b). The width of the fixing nip 6N in the sheet conveying direction can be measured by a measuring method using a pressure-sensitive sensor sheet, which will be described later.

[0027] The pressure roller 6b receives power from a motor (not shown) and rotates in the direction of arrow r1 in Figure 9, and the frictional force from the pressure roller 6b causes the fixing film 6a to rotate following the pressure roller 6b. The sheet P carrying an unfixed toner image is transported through the fixing nip 6N together with the fixing film 6a in the sheet transport direction, with the surface of the sheet P carrying the toner image and powder adhesive Tn (image surface) in close contact with the outer surface of the fixing film 6a in the fixing nip 6N. A feature of this configuration is that the heat capacity of the fixing film 6a and heater 6a1 is particularly small, and the holding member 6a5 is also made of a highly insulating material, making it possible to quickly heat the surface of the fixing film 6a to a high temperature with a small amount of heat supply.

[0028] The nip forming unit is not limited to one in which the heater 6a1 is in direct contact with the inner surface of the fixing film 6a, but may be one in which the heater 6a1 is in contact with the fixing film 6a via a sheet or plate material with high thermal conductivity such as an iron alloy or aluminum. Also, the fixing device 6 may be a fixing device equipped with a roller pair and a halogen heater, such as a bonding device 32 (FIG. 10) described later.

[0029] FIG. 11(a) shows the pressure distribution in the fixing nip 6N in the sheet conveyance direction. The pressure in the fixing nip 6N refers to the force (surface pressure) acting per unit area on the surface of the sheet P when it is sandwiched between the fixing film 6a and the pressure roller 6b in the fixing nip 6N. Here, the pressure distribution is shown as measured at the center of the fixing nip 6N in the longitudinal direction of the fixing nip 6N. The pressure was measured 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 6N. The resolution of the pressure-sensitive sensor sheet is 0.5 mm in the sheet conveyance direction. The pressure distribution measurement results shown in FIG. 11(a) represent the average value of the results obtained by repeatedly measuring five times using the pressure-sensitive sensor sheet.

[0030] As shown in FIG. 11(a), the length (pressure width, nip width) of the fixing nip 6N in the sheet conveyance direction was 9.0 mm, and the peak value (maximum value) of the pressure within the fixing nip 6N was approximately 0.12 MPa. To derive the peak value of the pressure within the fixing nip 6N, it is desirable that the resolution be 10% or less of the pressure width of the fixing nip 6N in the sheet conveyance direction. As shown in FIG. 11(b), since electronic noise (x) may be superimposed on the results of a single pressure distribution measurement, it is desirable to reduce the influence of electronic noise by, for example, averaging the results of multiple measurements. Furthermore, in this embodiment, the pressure distribution in the sheet conveyance direction is substantially uniform throughout the entire area of ​​the fixing nip 6N in the longitudinal direction, including both ends and the center.

[0031] The housing 19 is provided with a discharge port 12 (first discharge port), which is an opening for discharging the sheet P from the apparatus main body 10, and a discharge unit 34 is disposed in the discharge port 12. The discharge unit 34, which is a discharge means in this embodiment, uses a so-called triple roller configuration having a first discharge roller 34a, an intermediate roller 34b, and a second discharge roller 34c. In addition, a switching guide 33, which is a flap-shaped guide that switches the conveyance path of the sheet P, is provided between the fixing device 6 and the discharge unit 34. The switching guide 33 is rotatable around a shaft 33a so that a tip 33b reciprocates in the direction of the arrow c in the figure.

[0032] The device main body 10 is equipped with a mechanism for performing double-sided printing. A motor (not shown) is connected to the discharge unit 34, and the motor is configured to rotate the intermediate roller 34b forward and backward. A double-sided conveyance path 1r is also provided as a conveyance path connected in a loop to the main conveyance path 1m. The sheet P, on which an image has been formed on its first side while passing through the main conveyance path 1m, is sandwiched and conveyed between the first discharge roller 34a and the intermediate roller 34b by the switching guide 33 rotated clockwise (broken line position). After the trailing end of the sheet P in the traveling direction passes the switching guide 33, the switching guide 33 rotates counterclockwise (solid line position) and the intermediate roller 34b rotates in the reverse direction, so that the sheet P is reversed and conveyed to the double-sided conveyance path 1r. Then, an image is formed on the second side of the sheet P while the sheet P passes through the main conveyance path 1m again in an inverted state. After double-sided printing, the sheet P is guided to the switching guide 33 (solid line position) rotated counterclockwise, nipped and conveyed by the intermediate roller 34b and the second discharge roller 34c, and discharged from the apparatus main body 10.

[0033] Furthermore, the transport path passing through the transport roller 8a, the transfer nip 5N, and the fixing nip 6N in the apparatus main body 10 constitutes a main transport path 1m along which an image is formed on the sheet P. When viewed from the main scanning direction during image formation (the width direction of the sheet perpendicular to the transport direction of the sheet transported along the main transport path 1m), the main transport path 1m extends from below to above, passing along one side of the horizontal direction relative to the image forming unit 1e. In other words, the apparatus main body 10 of this embodiment is a so-called vertical transport type (vertical path type) printer in which the main transport path 1m extends in a substantially vertical direction. Note that, when viewed vertically, the first discharge tray 13, the intermediate path 15, and the sheet cassette 8 overlap one another. Therefore, the horizontal direction in which the sheet moves when the discharge unit 34 discharges the sheet P is opposite to the horizontal direction in which the sheet moves when the sheet P is fed from the sheet cassette 8.

[0034] 1 (when viewed in the main scanning direction during image formation), it is preferable that the horizontal area occupied by the main body portion of post-processing unit 30, excluding second discharge tray 35, is within the area occupied by device main body 10. By accommodating post-processing unit 30 in the space above device main body 10 in this way, it becomes possible to install image forming device 1 with adhesive printing function in an installation space approximately the same as that of a normal vertical pass printer.

[0035] (After-treatment unit) As shown in Fig. 2, post-processing unit 30 is attached to the upper part of device main body 10. Post-processing unit 30 is a post-processing unit in which folder 31 as folding means and bonding device 32 as bonding means are housed and integrated in housing (second housing) 39.

[0036] As shown in FIG. 10, the bonding device 32 includes a hollow heating roller 32b as a heating member (second heating member) and a pressure roller 32a as a pressure member pressed against the heating roller 32b. The bonding device 32 also includes a halogen heater 63 as a heating means (second heating means) disposed inside the heating roller 32b. The heating roller 32b and the pressure roller 32a function as a second pair of rotating bodies that rotate to sandwich and convey the sheet P at a bonding nip 32N as a second nip portion. The bonding device 32 heats and presses the sheet P conveyed in a folded state from the folder 31 while sandwiching it in the bonding nip 32N (second fixing nip) between the heating roller 32b and the pressure roller 32a. In this way, the bonding device 32 softens the powder adhesive Tn applied to the inner surface of the folded sheet P and bonds the sheet P.

[0037] Heating roller 32b has a core 32b1, an elastic layer 32b2 formed on the outer periphery of core 32b1, and a release layer 32b3 formed on the outermost surface. Core 32b1 is made of, for example, iron. Elastic layer 32b2 is a 0.3 mm thick layer made of, for example, hard silicone rubber. Release layer 32b3 is made of a fluororesin such as PFA. Heating roller 32b has a diameter of 50 mm. Heating roller 32b rotates in the direction of arrow r2 by receiving power from a motor (not shown) mounted in post-processing unit 30. Pressure roller 32a rotates following heating roller 32b due to frictional force received from the rotating heating roller 32b.

[0038] The pressure roller 32a includes a core 32a1, an elastic layer 32a2 formed on the outer periphery of the core 32a1, and a release layer 32a3 formed on the outermost surface. The core 32a1 is made of, for example, iron. The elastic layer 32a2 is, for example, a 4.5 mm thick layer made of silicone rubber with a Shore A hardness of 20°. The release layer 32a3 is, for example, a 50 μm thick layer made of fluororesin. The diameter of the pressure roller 32a is 40 mm. The pressure roller 32a is pressed against the heating roller 32b with a total pressure of, for example, 45 kgf by a pressure means such as a spring, which biases the bearing member holding the core 32a1. This forms an adhesive nip 32N between the heating roller 32b and the pressure roller 32a. The width of the adhesive nip 32N in the longitudinal direction and the sheet conveying direction is the length and width of the approximately rectangular area where the heating roller 32b and the pressure roller 32a are in pressure contact. In the configuration example described above, the longitudinal width of the adhesive nip 32N is approximately the same as that of the fixing nip 6N (approximately 230 mm). The width of the adhesive nip 32N in the sheet conveying direction can be measured by a measurement method using a pressure-sensitive sensor sheet, which will be described later.

[0039] The surface temperature of heating roller 32b is detected by a non-contact temperature detection element 63a2 disposed opposite the outer circumferential surface of heating roller 32b. Temperature detection element 63a2 is electrically connected to CPU 6a3 of image forming apparatus 1. Based on the detection signal of temperature detection element 63a2, CPU 6a3 controls triac 63a4 provided in the power supply path from AC power source AC to halogen heater 63, thereby controlling the power supply to halogen heater 63. In this embodiment, CPU 6a3 controls the power supply to halogen heater 63 so that the surface temperature of heating roller 32b reaches the target temperature of 160°C.

[0040] Note that bonding device 32 may be configured as in the above-described fixing device 6 (FIG. 9), in which a heater such as a ceramic heater is disposed inside a cylindrical film, and the film heated by thermal conduction (non-radiant heat) from the heater heats sheet P. Whether fixing device 6 and bonding device 32, which are image heating devices, are to be of the film type or the heat roller type can be selected appropriately by comprehensively judging the characteristics of each type, such as quick start, heat capacity (stability of heating temperature), and energy-saving performance.

[0041] 11(c) shows the pressure distribution in the sheet conveyance direction in the adhesive nip 32N measured using the roller pressure distribution measurement system (PINCH) described above. The pressure in the adhesive nip 32N refers to the force (surface pressure) acting per unit area on the surface of the sheet P when the sheet P is sandwiched between the heating roller 32b and the pressure roller 32a in the adhesive nip 32N. Here, the pressure distribution measured at the center of the adhesive nip 32N in the longitudinal direction of the adhesive nip 32N is shown. The details of the pressure measurement method are the same as those for the fixing nip 6N.

[0042] As shown in FIG. 11(c), in the exemplary configuration of this embodiment, the length (pressure width, nip width) of the adhesive nip 32N in the sheet conveyance direction is 6.5 mm, and the peak value (maximum value) of the pressure within the adhesive nip 32N is approximately 0.24 MPa. The nip width of the adhesive nip 32N is shorter than the nip width of the fixing nip 6N. In this case, even if the peak value of the nip pressure in the adhesive nip 32N is set larger than the peak value of the nip pressure in the fixing nip 6N, the ratio of the total pressure in the adhesive nip 32N to the total pressure in the fixing nip 6N does not become as large as the ratio of the peak values. Note that in this embodiment, the pressure distribution in the sheet conveyance direction is substantially uniform throughout the entire area of ​​the adhesive nip 32N in the longitudinal direction, including both end portions and the center of the adhesive nip 32N.

[0043] The post-processing unit 30 is provided with a first discharge tray 13 that rotatably holds a tray switching guide 13a, an intermediate path 15, and a second discharge tray 35. The first discharge tray 13 is provided on the upper surface of the post-processing unit 30 and is also located on the upper surface (FIG. 1) of the entire image forming apparatus 1. The functions of each part of the post-processing unit 30 will be described later.

[0044] The post-processing unit 30 is provided with a positioning portion (for example, a convex shape that engages with a concave portion of the housing 19) for positioning the housing 39 relative to the housing 19 (first housing) of the device body 10. The post-processing unit 30 is also provided with a drive source and control unit separate from the device body 10, and is electrically connected to the device body 10 by coupling a connector 36 of the post-processing unit 30 with a connector 37 of the device body 10. This allows the post-processing unit 30 to operate based on commands from the control unit provided in the device body 10, using power supplied via the device body 10.

[0045] (Process cartridge) As mentioned above, each of the process cartridges 7n, 7y, 7m, and 7c has a substantially common configuration except for the type of powder contained in the four powder containers 104n, 104y, 104m, and 104c. Here, the process cartridge 7n will be described as a representative. Figure 8 is a cross-sectional view showing the schematic configuration of the process cartridge 7n. The process cartridge 7n is made up of a photosensitive unit CC including a photosensitive drum 101 and the like, and a developing unit DT including a developing roller 105 and the like.

[0046] A photosensitive drum 101, which is a drum-shaped electrophotographic photosensitive member (image carrier), is rotatably mounted on the photosensitive unit CC via a bearing (not shown). The photosensitive drum 101 receives a driving force from a motor (not shown) serving as a driving means (drive source) and is driven to rotate in a clockwise direction (arrow w) in the drawing during image formation. The photosensitive unit CC also has a charging roller 102 for charging the photosensitive drum 101 and a cleaning member 103 arranged around the photosensitive drum 101.

[0047] The developing unit DT is provided with a developing roller 105 as a developer carrier that rotates counterclockwise (arrow d) in the figure in contact with the photosensitive drum 101. The developing roller 105 and the photosensitive drum 101 each rotate so that their surfaces move in the same direction at the opposing portion (contact portion).

[0048] The developing unit DT is also provided with a developer supply roller (hereinafter simply referred to as "supply roller 106") as a developer supply member that rotates in a clockwise direction (arrow e) in the figure. The supply roller 106 and the developing roller 105 rotate so that their surfaces move in the same direction at their opposing (contacting) portions. The supply roller 106 supplies powder adhesive (printing toner in the case of the process cartridges 7y, 7m, and 7c) onto the developing roller 105. At the same time, the supply roller 106 acts to strip off any powder adhesive (printing toner in the case of the process cartridges 7y, 7m, and 7c) remaining on the developing roller 105 from the developing roller 105. The developing unit DT is also provided with a developing blade 107 as a developer regulating member that regulates the layer thickness of the powder adhesive (printing toner in the case of the process cartridges 7y, 7m, and 7c) supplied onto the developing roller 105 by the supply roller 106.

[0049] The powder storage unit 104n stores a powder adhesive (printing toner in the case of the process cartridges 7y, 7m, and 7c) as the powder. A rotatably supported transport member 108 is provided within the powder storage unit 104n. The transport member 108 rotates in a clockwise direction (indicated by an arrow f) in the drawing to agitate the powder stored in the powder storage unit 104n and transport the powder to a developing chamber 109 in which the developing roller 105 and the supply roller 106 are provided.

[0050] Here, the photosensitive unit CC and the developing unit DT may be separated into a photosensitive unit cartridge and a developing unit cartridge, respectively, and configured to be detachable from the main body of the image forming apparatus. Also, it is possible to configure a powder cartridge that is detachable from the main body of the apparatus by having only the powder containing portion 104 and the conveying member 108, separate from the process cartridge having the photosensitive member and the developer carrier.

[0051] (printing toner) Conventionally known printing toners can be used as the printing toners Tm, Tc, and Ty of this embodiment. Among them, printing toners using a thermoplastic resin as a binder resin are preferred. The thermoplastic resin is not particularly limited, and those used in conventional printing toners, such as polyester resin, vinyl resin, acrylic resin, and styrene-acrylic resin, can be used. A plurality of these resins may be contained. Among them, printing toners using styrene-acrylic resin are more preferred. Furthermore, the printing toner (printing developer) may contain a colorant, a magnetic material, a charge control agent, wax, and external additives.

[0052] The glass transition temperatures (Tg) of printing toners Tm, Tc, and Ty can be measured using a differential scanning calorimeter (Q1000, manufactured by TA Instruments). The melting points of indium and zinc are used for temperature correction of the detector, and the heat of fusion of indium is used for heat correction. Specifically, 1 mg of sample is precisely weighed and placed in an aluminum pan, with an empty aluminum pan used as a reference. Measurements are performed in modulation measurement mode, with a temperature ramp rate of 1°C / min and temperature modulation conditions of ±0.6°C / 60 seconds, over a range from 0°C to 100°C. The specific heat change is measured during the temperature ramp, and the intersection of the line midway between the baselines before and after the specific heat change and the differential heat curve is taken as the glass transition temperature (Tg). The glass transition temperatures (Tg) of the resulting printing toners Ty, Tm, and Tc were all 77°C.

[0053] (powder adhesive) The powder adhesive Tn used in this embodiment is refined using the following materials and manufacturing method. Specifically, 36.3 to 39.8% by weight of a cyclic polyolefin resin, 18.5% by weight of a cyclic polyolefin resin, 30% by weight of an alicyclic saturated hydrocarbon resin, 10% by weight or less of a thermoplastic elastomer or polyolefin, 1.2% by weight of a charge control agent, and 4.0% by weight of a release agent are mixed in a Henschel mixer. The resulting mixture is kneaded in a twin-screw continuous mixer at a maximum temperature of 180°C, cooled, pulverized in a supersonic jet mill, and finely divided into powders with a mass average particle size of approximately 9 μm using a high-precision classifier. This powder is then externally mixed with 0.3% by weight of fine silica particles and 0.3% by weight of fine alumina particles to obtain the powder adhesive Tn.

[0054] The glass transition temperature (Tg) of the powder adhesive Tn can be measured using the above-mentioned differential scanning calorimeter "Q1000" (manufactured by TA Instruments) in the same manner as for the printing toners Ty, Tm, and Tc. The glass transition temperature (Tg) of the obtained powder adhesive Tn was 50°C.

[0055] (Image formation operation) Next, the image forming operation performed by the image forming apparatus 1 of this embodiment will be described with reference to Figs. 3 and 4 are diagrams showing the sheet transport path in the image forming apparatus 1. Figs. 5(a) to 5(f) are diagrams for explaining the contents of the folding process.

[0056] When data of an image to be printed and a command to execute printing are input to the image forming apparatus 1, the control unit of the image forming apparatus 1 starts a series of operations (image forming operation) in which the sheet P is conveyed to form an image thereon and, if necessary, post-processing is performed by the post-processing unit 30. In the image forming operation, first, as shown in FIG. 1, the sheets P are fed one by one from the sheet cassette 8 and conveyed toward the transfer nip 5N via the conveying roller 8a.

[0057] In parallel with the feeding of the sheet P, the process cartridges 7n, 7y, 7m, and 7c are driven sequentially, and the photosensitive drums 101 are driven to rotate in the clockwise direction (arrow w) in the figure. At this time, a uniform charge is applied to the surface of the photosensitive drum 101 by the charging roller 102. In addition, the scanner unit 2 irradiates the photosensitive drums 101 of each of the process cartridges 7n, 7y, 7m, and 7c with laser light G modulated based on image data, thereby forming an electrostatic latent image on the surface of the photosensitive drum 101. Next, the electrostatic latent image on the photosensitive drum 101 is developed into a powder image by powder carried by the developing rollers 105 of each of the process cartridges 7n, 7y, 7m, and 7c.

[0058] The powder adhesive layer formed on the photosensitive drum 101 by development with the powder adhesive Tn differs from a toner image (normal toner image) of printing toner used to record images such as figures and text on a recording medium in that it is not intended to transmit visual information. However, in order to apply the powder adhesive Tn to the sheet P in a predetermined application pattern, the layer of powder adhesive Tn developed in a shape corresponding to the application pattern by an electrophotographic process may also be considered a "toner image."

[0059] The transfer belt 3a rotates counterclockwise (indicated by arrow v) in the figure. The toner images formed in the process cartridges 7n, 7y, 7m, and 7c are primarily transferred from the photosensitive drum 101 to the transfer belt 3a by an electric field formed between the photosensitive drum 101 and the primary transfer roller 4.

[0060] As shown in Figure 1, process cartridge 7n, which uses powder adhesive Tn, is located most upstream of the four process cartridges in the direction of rotation of transfer belt 3a. Yellow, magenta, and cyan process cartridges 7y, 7m, and 7c are arranged in this order downstream from process cartridge 7n in the direction of rotation of transfer belt 3a. Therefore, when the four toner images are superimposed on the transfer belt 3a, powder adhesive Tn becomes the bottom layer (the layer in contact with transfer belt 3a), and yellow (Ty), magenta (Tm), and cyan (Tc) printing toners are superimposed on top of it in this order.

[0061] The toner image carried by the transfer belt 3a and reaching the transfer nip 5N is secondarily transferred onto the sheet P conveyed along the main conveying path 1m by the electric field formed between the secondary transfer roller 5 and the inner secondary transfer roller 3b. At this time, the toner layer is turned upside down. That is, the transfer nip 5 N On the sheet P that has passed through, printing toners of cyan (Tc), magenta (Tm), and yellow (Ty) are layered from the bottom layer (the layer that comes into contact with the sheet P), and a layer of powder adhesive Tn is formed on top of that. Therefore, in the toner image transferred to the sheet P, the layer of powder adhesive Tn becomes the outermost surface.

[0062] Thereafter, the sheet P bearing the unfixed toner image is nipped and conveyed through the fixing nip 6N together with the fixing film 6a, with the image side of the sheet P in close contact with the outer surface of the fixing film 6a. During this nipping and conveying process, heat from the heater 6a1 is applied to the image side of the sheet P through the fixing film 6a, melting the printing toners Ty, Tm, Tc and the powder adhesive Tn and fixing them onto the sheet P. After passing through the fixing nip 6N, the sheet P is separated from the fixing film 6a by curvature while retaining the fixed toner image, and the fixed image is obtained on the sheet P.

[0063] Regardless of whether single-sided or double-sided printing is performed, the sheet P discharged from the device main body 10 is sandwiched between the intermediate roller 34b and the second discharge roller 34c, as shown in Figures 3 and 4, and is transported to the first path R1 or the second path R2 by the tray switching guide 13a.

[0064] 3 is a path along which, in a normal printing mode that does not use the post-processing unit 30, the sheet P that has passed through the fixing device 6 is discharged to the first discharge tray 13 by the discharge unit 34. The second path R2 shown in FIG. 4 is a path along which, in an adhesive printing mode, the sheet P that has passed through the fixing device 6 is discharged to the second discharge tray 35 via the discharge unit 34, the folder 31, and the adhesive device 32.

[0065] An intermediate path 15 is provided between the fixing device 6 and the folder 31 on the second route R2. The intermediate path 15 is a sheet transport path that passes through the upper surface (top surface) of the image forming apparatus 1, and extends below the first discharge tray 13 and substantially parallel to the first discharge tray 13. The intermediate path 15 and the first discharge tray 13 are inclined vertically upward toward the folder 31 with respect to the horizontal direction. Therefore, the entrance of the folder 31 (the pair of guide rollers (31c, 31d) described below) is inclined upward. ) is located vertically above the outlet of the apparatus main body 10 (the nip between the intermediate roller 34b and the second discharge roller 34c).

[0066] The folder 31 has four rollers, namely, a first guide roller 31c, a second guide roller 31d, a first folding roller 31a, and a second folding roller 31b, and a lead-in portion 31e. The first guide roller 31c and the second guide roller 31d are a pair of guide rollers that sandwich and transport the sheet P received from a transport path (intermediate path 15 in this embodiment) on the upstream side of the folder 31. The first folding roller 31a and the second folding roller 31b are a pair of folding rollers that feed the sheet P while folding it.

[0067] The distance M (FIG. 1) between the second discharge roller 34c and the first guide roller 31c in the sheet transport direction along the second path R2 is configured to be shorter than the overall length L (FIG. 5(a)) of the sheet P in the transport direction before folding. In other words, the distance M between the second discharge roller 34c and the first guide roller 31c determines the lower limit of the length of the sheet in the transport direction that can be processed by the post-processing unit 30. With this configuration, the sheet P is smoothly delivered from the discharge unit 34 to the pair of guide rollers.

[0068] The folding process by folder 31 will be described with reference to Figures 5(a) to 5(f). When performing the folding process, first guide roller 31c and first folding roller 31a rotate clockwise in the figure, and second guide roller 31d and second folding roller 31b rotate counterclockwise in the figure. First, a leading edge q of sheet P sent out from discharge unit 34 is pulled into the pair of guide rollers (31c, 31d) as shown in Figure 5(a). As shown in Figure 5(b), leading edge q of sheet P is guided downward by guide wall 31f and comes into contact with first folding roller 31a, and is then pulled into the opposing first folding roller 31a and second guide roller 31d and abuts against wall 31g of pull-in section 31e.

[0069] As the guide roller pair (31c, 31d) pulls in the sheet P, the leading edge q slides against the wall 31g and advances deeper into the pull-in section 31e. Eventually, the leading edge q hits the end 31h of the pull-in section 31e, as shown in FIG. 5(c). The pull-in section 31e forms a space below the intermediate path 15 that extends substantially parallel to the intermediate path 15, and at the stage shown in FIG. 5(c), the sheet P wraps around the second guide roller 31d and is bent into a U-shape.

[0070] When the guide roller pair (31c, 31d) further pulls the sheet P from the state shown in FIG. 5(c), bending begins to occur at the middle portion r as shown in FIG. 5(d). Eventually, as shown in FIG. 5(e), the middle portion r comes into contact with the second folding roller 31b, and the sheet is pulled into the nip portion of the folding roller pair (31a, 31b) by the frictional force received from the second folding roller 31b. Then, as shown in FIG. 5(f), the sheet P is folded with the middle portion r as the crease, and is discharged by the folding roller pair (31a, 31b) with the middle portion r leading.

[0071] Here, the depth N of the retraction portion 31e (FIG. 5(e)), i.e., the distance from the nip portion of the pair of folding rollers (31a, 31b) to the end portion 31h of the retraction portion 31e, is set to half the total length L of the sheet P. This allows the folder 31 to fold the sheet P in half (center folding). Note that by changing the depth N of the retraction portion 31e, the position of the fold can be changed as desired.

[0072] The folder 31 described above is one example of a folding means, and a folding mechanism may be used that forms a crease by pressing a blade against the sheet P and forcing it into the nip between a pair of rollers. The folding process is not limited to folding in half, and a folding mechanism that performs, for example, a Z-fold or a triple fold may be used. Since the folder 31 of this embodiment is composed of rotating rollers and a fixed retraction section 31e, the drive mechanism can be simplified compared to a folding mechanism that uses a reciprocating blade. Furthermore, since the folder 31 of this embodiment only requires the retraction section 31e, which has a depth N half the length of the sheet, in addition to the four rollers, the post-processing unit 30 can be made smaller.

[0073] The sheet P folded by the folder 31 is transported to the bonding device 32, where it is subjected to a bonding process in which it is heated and pressurized while being nipped and transported in the bonding nip 32N. The sheet P is subjected to the bonding process (a second thermal fixation on the image surface on which the powder adhesive has been applied), and is thereby bonded while remaining in a folded state, as shown in Fig. 10. That is, when the sheet P passes through the bonding nip 32N, the powder adhesive Tn on the sheet P is heated and pressurized again in a softened state, so that the inner surfaces of the sheet P are bonded (bonded) together via the powder adhesive Tn.

[0074] 4, the sheet P that has been subjected to the bonding process by the bonding device 32 is discharged to the left side in the drawing from a discharge outlet 32c (second discharge outlet) provided in the housing 39 of the post-processing unit 30. Then, the sheet P is stored in a second discharge tray 35 (see FIG. 1) provided on the left side surface of the apparatus main body 10. This completes the image formation operation when the sheet P is transported along the second path R2.

[0075] The bonding location of the folded sheet P can be changed by varying the pattern of the powder adhesive Tn applied to the sheet P. Figures 7(a) and 7(b) show examples of two deliverables with different patterns of powder adhesive Tn. Here, we show deliverables (semi-adhesive printed matter) intended for opening by the recipient. In the case of the pressure-bonded postcard 51 shown in Figure 7(a), the powder adhesive Tn is applied to the entire surface 51a of one side of the sheet P, and the sheet P is adhered while folded at the central fold 51b. In the case of the pay slip 52 shown in Figure 7(b), the powder adhesive Tn is applied to the entire periphery 52a of one side of the sheet P, and the sheet P is adhered while folded at the central fold 52b. Alternatively, for example, a bag (paper bag, envelope) can be created by applying the powder adhesive Tn to three sides of the periphery of the sheet P so that an opening is formed when the sheet P is folded. Fully adhered printed matter that is not intended to be opened later can also be created.

[0076] The image forming apparatus 1 of this embodiment can output any of the products illustrated in FIGS. 7(a) and 7(b) in one step from base paper without preparing preprinted paper. That is, in parallel with the operation of recording an image on one or both sides of a sheet P using printing toner, an adhesive layer using powder adhesive Tn can be formed in a predetermined pattern, and the product can be output in a state where folding and adhesive processing have been performed. For example, when outputting the product shown in FIGS. 7(a) and 7(b), one side of the sheet P used as base paper becomes the outer side of the product, and the other side becomes the inner side of the product. Therefore, in double-sided printing, an image for the outer surface can be formed using printing toner as the image forming operation for the first side, and an image for the inner surface can be formed using printing toner as the image forming operation for the second side, and an adhesive layer using powder adhesive Tn can be formed in a predetermined pattern.

[0077] The image recorded by the image forming apparatus 1 using printing toner can include a format (invariant portion) when using preprinted paper, and variable portions such as personal information. Therefore, as described above, in this embodiment, a product bonded by a gluing process can be output from base paper such as blank paper that is not preprinted paper. However, the image forming apparatus 1 of this embodiment can also be used in applications where preprinted paper is used as a recording medium and printing and gluing processes for variable portions are performed.

[0078] In this embodiment, the sheet conveying speeds of the fixing device 6 and the bonding device 32 are set to the same speed (210 mm / sec). When the sheet size when passing through the fixing device 6 is A4 (210 mm x 297 mm), the size of the folded product (such as a pressure-bonded postcard) produced by the post-processing unit 30 is A5 (149 mm x 210 mm). The sheet P used to examine the conditions for bonding processing by the bonding device 32 described below is Red Label Presentation (basis weight 80 g / m) manufactured by Canon Inc. 2 ,A4 size).

[0079] (Consideration of adhesive treatment conditions) Next, we will explain the results of our investigation into the conditions for the bonding process that enable both suppression of hot offset and adhesion strength. Fig. 12 is a schematic diagram illustrating the settings for bonding the sheet P using the bonding device 32. Table 1 is a list showing the evaluation results (f) of whether hot offset occurred on the sheet surface and the evaluation results (g) of the adhesiveness inside the sheet when the bonding settings (a to e) were changed to create a pressure-bonded postcard (Fig. 7(a)) as an adhesive printed matter. [Table 1]

[0080] The following describes each of the setting conditions (a) to (e). (a) is the target temperature Th of the surface temperature of the heating roller 32b of the bonding device 32, and any target temperature can be set to the CPU 63a3 (FIG. 10). (b) is the pressure Pt (total pressure) of the bonding device 32, which can be adjusted by adjusting the spring constant of the spring member used in the pressure means and the deformation amount in the attached state. The pressure Pt is the magnitude of the force pressing the heating roller 32b and pressure roller 32a, which constitute the second rotating body pair, in the sheet conveyance direction and the sheet thickness direction perpendicular to the longitudinal direction in the bonding nip 32N. (c) is the maximum surface pressure Pmax of the bonding nip 32N, which can be adjusted by the pressure Pt of (b). The maximum surface pressure Pmax also varies depending on the diameters of the heating roller 32b and pressure roller 32a, and the Young's modulus and thickness of the elastic layers 32a2, 32b2 and release layers 32b3, 32a3. The maximum surface pressure Pmax is the peak value (maximum value, see FIG. 11(c)) when the distribution of pressure acting per unit area on the sheet surface when the sheet S passes through the adhesive nip 32N is plotted in the sheet conveying direction.

[0081] (d) is the sheet surface temperature Tp (maximum temperature reached) when passing through the bonding nip 32N. Specifically, a thermocouple was attached to the surface of the sheet facing the heating roller 32b, and the surface temperature detected by the thermocouple while passing through the bonding nip 32N was obtained with a data logger, and the maximum value was taken as the sheet surface temperature Tp. (e) is the sheet internal temperature (temperature of the powder adhesive Tn) Ttn (maximum temperature reached) when the sheet passes through the bonding nip 32N in a folded state. The measurement method was the same as for the sheet surface temperature Tp; a thermocouple was attached to the inner surface of the sheet in a folded state, and the temperature detected by the thermocouple while passing through the bonding nip 32N was obtained with a data logger, and the maximum value was taken as the sheet internal temperature Ttn.

[0082] For hot offset (f), the surface of the sheet that passed through the bonding device 32 facing the heating roller 32b (the upper surface of the sheet P in Figure 10) was observed with the naked eye. If no image defects due to hot offset were visible, the result was judged as OK; if no image defects were visible, the result was judged as NG. Hot offset occurs when printing toner on the sheet P adheres to the heating roller 32b, and the adhered toner re-adheres to the sheet P after one rotation of the heating roller 32b, contaminating the sheet P. Therefore, image defects due to hot offset are typically toner stains that appear at a position shifted in the sheet conveyance direction from the original image formed on the sheet P by a distance equivalent to the outer periphery of the heating roller 32b. For adhesiveness (g), the produced pressed postcards were left for 24 hours in an ambient environment at a temperature of 23°C and a humidity of 50%. The adhesiveness was judged by whether the adhesive surfaces separated spontaneously. If the adhesive surfaces did not separate, the adhesiveness was judged as OK; if the adhesive surfaces separated, the adhesiveness was judged as NG.

[0083] In Example 1, (a) the target temperature Th of the heating roller 32b was 160°C, the pressure Pt of the bonding device 32 was 45 kgf (approximately 440 N), and the maximum surface pressure Pmax of the bonding nip 32N was 0.24 MPa. The temperature conditions for (d) and (e) were (d) a sheet surface temperature Tp of 100°C, and (e) a sheet internal temperature Ttn of 65°C. In this case, (f) no image defects due to hot offset occurred on the sheet surface, and (g) the adhesion inside the sheet was good. In other words, the bonding conditions in Example 1 are particularly preferable.

[0084] In Example 2, (b) the pressure Pt of the bonding device 32 is the same as in Example 1, but the heating roller 32b is not heated ((a) the target temperature Th of the heating roller 32b is approximately the same as room temperature). In this case, (f) no image defects due to hot offset occurred on the sheet surface, but (g) the inside of the sheet did not bond at all.

[0085] In Example 3, (b) the pressure Pt of the bonding device 32 was set to twice that of Example 1, and the heating roller 32b was not heated. In this case, (f) no image defects due to hot offset occurred on the sheet surface, but (g) the inside of the sheet did not bond at all.

[0086] In Examples 2 and 3, the heating roller 32b of the bonding device 32 is not heated, so the temperature of the powder adhesive Tn inside the sheet (e) does not increase even when the sheet passes through the bonding device 32. The glass transition temperature of the powder adhesive Tn used in this embodiment is approximately 50°C, and the viscoelasticity of the powder adhesive Tn does not decrease significantly at temperatures below that temperature. Therefore, even in the configuration of Example 3 in which the heating roller 32b is not heated and the pressure Pt of the bonding device 32 is increased, the viscoelasticity of the layer of powder adhesive Tn does not decrease significantly even when the sheet passes through the bonding device 32. As a result, even when a relatively large maximum surface pressure Pmax is applied to the sheet, the surfaces of the layers of powder adhesive Tn facing each other inside the folded sheet do not sufficiently adhere to each other, which is thought to have caused poor adhesion.

[0087] In Example 4, (b) the pressure Pt of the bonding device 32 was set to twice that of Example 1, and (a) the target temperature Th of the heating roller surface was set to 140°C. However, even under these conditions, (f) no image defects due to hot offset occurred on the sheet surface, but (g) the adhesion inside the sheet was insufficient. This is thought to be because, although heating was performed by the heating roller 32b, the target temperature Th was low, and (e) the temperature Ttn inside the sheet did not reach the glass transition temperature.

[0088] In Example 5, (a) the target temperature Th of the heating roller surface was set to 160°C, the same as in Example 1, and (b) the maximum surface pressure Pmax of the bonding nip 32N was set to a lower value (0.10 MPa) than in Example 1. In Example 5, the temperature of the powder adhesive Tn was raised above the glass transition temperature by passing the sheet through the bonding device 32, which caused a decrease in the viscoelasticity of the powder adhesive Tn layer. However, because the maximum surface pressure Pmax was low, it is believed that the surfaces of the powder adhesive Tn layers facing each other inside the folded sheet did not adhere sufficiently to each other, resulting in poor adhesion.

[0089] In Example 6, (b) the maximum surface pressure Pmax of the bonding nip 32N was set to the same value as in Example 1, and (a) the target temperature Th of the heating roller surface was set to 200°C, higher than in Example 1. In this case, excessive heat was supplied to the sheet from the heating roller 32b, (d) the sheet surface temperature Tp became too high, and (f) hot offset occurred. On the other hand, the temperature of the powder adhesive Tn reached the glass transition temperature or higher, and a sufficiently large maximum surface pressure Pmax was applied, (g) so that the adhesive strength of the powder adhesive Tn inside the sheet was sufficient.

[0090] As can be seen from the above experimental results, by setting the peak value of the nip pressure in the bonding nip 32N higher than the peak value of the nip pressure in the fixing nip 6N, sufficient adhesive strength can be obtained even when the heating temperature (Th) during bonding is set to a lower temperature. Specifically, when the nip pressure in the bonding nip 32N is equal to or lower than that in the fixing nip 6N, poor adhesion occurs when the target temperature Th of the bonding device 32 is set to 160°C (Example 5). In contrast, by setting the peak value of the nip pressure (Pmax) in the bonding nip 32N higher than that of the fixing nip 6N, sufficient adhesive strength can be obtained even when the target temperature Th of the bonding device 32 is set to 160°C (Example 1). Furthermore, by setting the peak value of the nip pressure (Pmax) in the bonding nip 32N higher than that of the fixing nip 6N, good adhesiveness can be obtained in Example 1 without raising the target temperature Th of the bonding device 32 to the temperature range where hot offset occurs, as in Example 6.

[0091] Here, hot offset has been cited as a disadvantage of setting the target temperature Th of the bonding device 32 too high. However, if the target temperature Th can be lowered, it is expected that the amount of power consumed by the bonding device 32 will be reduced (improved energy efficiency). Furthermore, lowering the target temperature Th will prevent the housing of the post-processing unit 30 from becoming too hot. Therefore, it is preferable that the heating temperature during bonding is low, provided that sufficient adhesive strength can be obtained. Furthermore, the setting conditions for bonding shown in Table 1 are merely examples, and the preferred conditions may vary depending on the physical properties (particularly the glass transition temperature) of the printing toner and powder adhesive, and the material of the sheet P.

[0092] The reason why the adhesiveness of the sheet P by the bonding device 32 is improved by making the peak value (Pmax) of the nip pressure of the bonding nip 32N larger than the peak value of the nip pressure of the fixing nip 6N will be described with reference to FIGS. 13(a) to 13(d).

[0093] FIG. 13(a) is a schematic diagram showing the contact state between the fixing film 6a and the sheet P in the fixing nip 6N of the fixing device 6. FIG. 13(b) shows example values ​​of parameters related to the adhesion between the fixing film 6a and the sheet P. Adhesion between the surfaces of the fixing film 6a and the sheet P is important for fixing the powder adhesive Tn to the sheet P by applying heat and pressure in the fixing nip 6N (fixing process). It is known that the adhesion between the surface of the fixing film 6a (the heated surface) and the surface of the sheet P (the pressure-side surface) is related to the Young's modulus E, which indicates the rigidity of each elastic component, the thickness t of the elastic component, the surface roughness (Ra value) of the contacting surfaces (interface), and the pressure P1 at the fixing nip. For the heated surface and the pressure-side surface to adhere to each other, the unevenness on one surface must conform to the other surface due to the elastic deformation of the heated elastic component and the pressure-side elastic component. The greater the thickness t and the pressure P1, the better the adhesion. Meanwhile, the smaller the Young's modulus E and the surface roughness Ra, the better the adhesion.

[0094] Here, the elastic component of the fixing film 6a in this embodiment refers only to the elastic layer and the release layer, excluding the highly rigid base layer. The sheet P is assumed to have substantially uniform elasticity throughout. The Young's modulus E was determined by cutting each sample into a 15 mm × 120 mm strip, clamping the ends of the sample with a chuck member to fix it, and measuring the stress when the sample was stretched in the long side direction at a rate of 1.0 mm / sec using a load cell of a measuring instrument. The measuring instrument used was a benchtop testing machine, EZ-Test, manufactured by Shimadzu Corporation. The fixing film 6a was also prepared by tearing the elastic layer and release layer from the base layer with a cutter knife or the like to prepare a sample of only the elastic component.

[0095] FIG. 13(c) is a schematic diagram showing the contact state between the surfaces of the folded sheet P in the bonding nip 32N of the bonding device 32. FIG. 13(d) shows example values ​​of parameters related to the adhesion between the surfaces of the sheet P. Adhesion between the surfaces of the sheet P is important for bonding the surfaces of the sheet P by applying heat and pressure (adhesion process) in the bonding nip 32N. It is known that the adhesion between the surfaces of the sheet P is related to the Young's modulus E and thickness t of the sheet P, the surface roughness (Ra value) of the contacting surfaces (interfaces), and the applied pressure P2 in the bonding nip 32N. This is because, for the surfaces of the sheet P to adhere to each other, the unevenness on one surface must conform to the other surface due to elastic deformation of the sheet P. The greater the thickness t and applied pressure P2, the greater the adhesion, while the smaller the Young's modulus E and surface roughness Ra, the greater the adhesion.

[0096] 13(a, b) and 13(c, d), the Young's modulus E, thickness t, and surface roughness Ra of the sheet P generally have a detrimental effect on adhesion compared to the Young's modulus E, thickness t, and surface roughness Ra of the elastic components of the fixing film 6a. That is, the Young's modulus E and surface roughness Ra of the sheet P are generally greater than the Young's modulus E and surface roughness Ra of the fixing film 6a, and the thickness t of the sheet P is generally smaller than the thickness t of the fixing film 6a. Therefore, in order to make the adhesion between the surfaces of the sheet P in the adhesive nip 32N equal to or greater than the adhesion between the fixing film 6a and the sheet P in the fixing nip 6N, the pressure P2 in the adhesive nip 32N is set to be greater than P1 of the fixing device 6 (P2>P1).

[0097] Specifically, the experiment described using Table 1 has shown that it is preferable to set the maximum surface pressure Pmax of the bonding nip 32N to 0.2 MPa or more. On the other hand, sufficient fixation was obtained even with a maximum surface pressure of about 0.1 MPa (for example, 0.15 MPa or less) of the fixing nip 6N. In other words, it is preferable that the peak value of the pressure applied to the sheet by the bonding device 32 in the bonding nip 32N (0.24 MPa in the example of FIG. 11(c)) be at least twice the peak value of the pressure applied to the sheet by the fixing device 6 in the fixing nip 6N (0.12 MPa in the example of FIG. 11(a)).

[0098] In the above experiment, the sheet P was a Red Label Presentation (basis weight 80 g / m) manufactured by Canon Inc. 2 , A4 size) was used. However, a sheet with a basis weight of 60 g / m2 is generally used as a recording medium in an electrophotographic image forming apparatus. 2 ~230g / m 2 Examples of suitable sheets include plain paper, cardboard, glossy paper, and rough paper. The Young's modulus E of these sheets is 1000 to 8000 N / mm, the thickness t is 80 to 260 μm, and the surface roughness Ra is approximately 0.8 to 5.5 μm. Therefore, in most cases, the elastic component of the fixing film 6a is more advantageous for adhesion than the sheet P. Therefore, for most sheets used in electrophotography, good adhesion can be achieved by making the pressure P2 at the adhesive nip 32N greater than the pressure P1 at the fixing nip 6N (P2 > P1).

[0099] Furthermore, to prevent hot offset of the printing toner during the bonding process, it is desirable to set the target temperature (Th) of the bonding device 32 lower than the target temperature of the fixing device 6 and reduce the amount of heat applied to the sheet P in the bonding nip 32N. In particular, it is preferable to set the glass transition temperature of the powder adhesive lower than the glass transition temperature of the printing toner and reduce the amount of heat applied to the sheet P in the bonding nip 32N as much as possible within a range in which good adhesion can be achieved with the powder adhesive. A guideline for achieving good adhesion with the powder adhesive is for the maximum temperature of the powder adhesive to be equal to or higher than the glass transition temperature of the powder adhesive as it passes through the bonding nip 32N.

[0100] As described above, the configuration of this embodiment makes it possible to obtain sufficient adhesive strength without setting the heating temperature during bonding to an excessively high value. [Explanation of symbols]

[0101] 1...image forming apparatus / 1e...image forming means (image forming unit) / 6...fixing means (fixing device) / 6a, 6b...first pair of rotating bodies (fixing film, pressure roller) / 6N...first nip portion (fixing nip) / 31...folding means (folder) / 32...adhesion means (adhesion device) / 32a, 32b...second pair of rotating bodies (pressure roller, heating roller) / 32N...second nip portion (adhesion nip) / Tn...powder adhesive / Ty, Tm, Tc...printing toner

Claims

1. an image forming means for forming a toner image on a sheet using a printing toner and applying a powder adhesive to the sheet; a fixing unit having a first pair of rotating bodies that form a first nip portion, and that fixes the toner image on the sheet by applying heat and pressure to the sheet conveyed from the image forming unit while sandwiching and conveying the sheet at the first nip portion; a folding means for folding the sheet conveyed from the fixing means so that the surface on which the powder adhesive is applied is inward; an adhesive means having a second pair of rotating bodies that form a second nip portion, and that applies heat and pressure to the sheet folded by the folding means while sandwiching and conveying the sheet at the second nip portion, thereby adhesively bonding the sheet with the powder adhesive; An image forming apparatus comprising: a second peak value, which is a peak value of the pressure applied to the sheet by the second rotating body pair at the second nip portion, is greater than a first peak value, which is a peak value of the pressure applied to the sheet by the first rotating body pair at the first nip portion; a width of the second nip portion in the sheet conveying direction is shorter than a width of the first nip portion in the sheet conveying direction; an image forming apparatus, wherein a value of the product of the second peak value and the width of the second nip portion is greater than a value of the product of the first peak value and the width of the first nip portion;

2. 2. The image forming apparatus according to claim 1, The image forming apparatus is characterized in that the second peak value is 0.2 MPa or more.

3. 3. The image forming apparatus according to claim 1, The image forming apparatus is characterized in that the second peak value is at least twice as large as the first peak value.

4. 4. The image forming apparatus according to claim 1, the fixing unit has a first heating unit, the first rotating body pair has a first heating member heated by the first heating means, the bonding means has a second heating means, the second pair of rotating bodies has a second heating member heated by the second heating means, 10. An image forming apparatus according to claim 9, wherein the target temperature of the surface of the second heating member is lower than the target temperature of the surface of the first heating member.

5. 5. The image forming apparatus according to claim 4, the glass transition temperature of the powder adhesive is lower than the glass transition temperature of the printing toner; An image forming apparatus characterized in that the target temperature of the surface of the second heating member is set so that the maximum temperature reached by the powder adhesive when passing through the second nip portion is higher than the glass transition temperature of the powder adhesive.

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