JP7558706B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming device that forms an image on a sheet.

Conventionally, when creating documents such as pay slips that require confidentiality and therefore need to be sealed, preprinted paper with adhesive applied to it was prepared in advance, variable data was printed on the preprinted paper, and then 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.

Patent Document 1 proposes an image forming device that uses an adhesive toner (powder adhesive) in addition to an image forming toner using an electrophotographic process to output a sealed document using a single device while using plain paper. The adhesive toner is designed to melt at a lower temperature than the image forming toner, and is applied to a sheet, which is a recording medium, by being transferred in the same electrophotographic process as the image forming toner. The sheet is then folded so that the surfaces on which the adhesive toner image is formed face each other, and finally the sheets are bonded together by heating while the adhesive surfaces of the sheets are in close contact with each other via the adhesive toner. This method is efficient even for applications requiring a small number of items, since the printing process and adhesive process are completed in a single image forming device. In addition, the method of bonding by heating and melting the adhesive does not require strong pressure, which is advantageous for making the device smaller and quieter.

JP 2006-171607 A

As in the above document, when the printing process and the bonding process are performed within a single image forming apparatus, a heating device for fixing the image and a heating device for bonding the sheet are used in combination. Heating resistors, halogen lamps, induction heating mechanisms, etc. are known as heating elements for heating devices, but all of these are elements that consume a large amount of power in image forming apparatuses, so power saving is required. In addition, if the temperature of a heating member such as a heating roller is too high in the bonding process, there is a concern that an image defect called hot offset will occur, in which the printed image that should have been fixed will remelt and adhere to the sheet.

Therefore, the present invention aims to obtain sufficient adhesive strength while reducing the amount of heat supplied to the sheet during the bonding process.

An image forming apparatus according to one embodiment of the present invention comprises an image forming means for forming a toner image on a sheet using printing toner and applying a powder adhesive to the sheet, a fixing means for heating the toner image formed on the sheet by the image forming means to fix it to the sheet, a folding means for folding the sheet that has passed through the fixing means, and an adhesive means for heating the sheet folded by the folding means and adhering the sheet with the powder adhesive, wherein the sheet conveying speed of the adhesive means is slower than the sheet conveying speed of the fixing means, and the folding means starts to convey the sheet toward the adhesive means at a sheet conveying speed faster than the sheet conveying speed of the adhesive means, and then decelerates the sheet conveying speed to the sheet conveying speed of the adhesive means before the leading edge of the sheet in the sheet conveying direction reaches the adhesive means.

According to the present invention, it is possible to obtain sufficient adhesive strength while reducing the amount of heat supplied to the sheet during the bonding process.

1 is a schematic diagram of an image forming apparatus according to a first embodiment. 3A and 3B are diagrams for explaining attachment of a post-processing unit to an apparatus body of the image forming apparatus according to the first embodiment. FIG. 2 is a diagram illustrating a sheet transport path in the image forming apparatus according to the first embodiment. 6 is a diagram illustrating another sheet transport path in the image forming apparatus according to the first embodiment. FIG. 4A to 4F are diagrams for explaining the contents of a folding process according to the first embodiment. FIG. 1 is a perspective view showing an external appearance of an image forming apparatus according to a first embodiment. 3A to 3C are diagrams illustrating examples of products output by the image forming apparatus according to the first embodiment. FIG. 2 is a schematic diagram of a process cartridge according to the first embodiment. FIG. 4 is a schematic diagram of a first fixing unit according to the first embodiment. FIG. 4A is a diagram for explaining an image defect occurring in a bonding process, and FIG. 4B is a schematic diagram of a second fixing unit according to the first embodiment. 1A is a graph showing the change in temperature of a powder adhesive over time, and FIG. 1B is a graph showing the relationship of the heater temperature during bonding required for strong bonding. FIG. 13 is a diagram showing the results of measuring a powder adhesive using a differential scanning calorimeter. Illustrates (a) to (c) changes in the powder adhesive during the fixing process. 4A and 4B are diagrams for explaining changes in powder adhesive during the folding process.

An exemplary embodiment of the present invention will now be described with reference to the drawings.

(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 a cross-sectional configuration of an image forming apparatus 1 including an image forming apparatus main body (hereinafter referred to as an apparatus main body 10) according to a first 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) including the apparatus main body 10 equipped with an electrophotographic printing mechanism and the post-processing unit 30 as a sheet processing device.

Figure 6 is a perspective view showing the exterior of the image forming device 1. The post-processing unit 30 is attached to the top of the device body 10. The image forming device 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.

First, the internal structure 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 a recording medium, an image forming unit 1e as an image forming means, a first fixing device 6 as a 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 creates a printed matter that has been subjected to a fixing process by the first fixing device 6. It should be noted that, for example, paper is used as the sheet P as a recording medium.

The sheet cassette 8 is inserted into the housing 19 at the bottom of the device main body 10 so that it can be pulled out, 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 transported by the transport roller 8a in a state where they are separated one by one by a separation roller pair. It is also possible to feed sheets set in the open tray 20 (Figure 6) one by one.

The image forming unit 1e is a tandem-type 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 parts that are responsible for the image forming process are integrated and replaceable. The device main body 10 is provided with a cartridge support section 9 supported by a housing 19, and each of the process cartridges 7n, 7y, 7m, and 7c is removably mounted in the mounting sections 9n, 9y, 9m, and 9c provided on the cartridge support section 9. The cartridge support section 9 may be a tray member that can be pulled out from the housing 19.

Each process cartridge 7n, 7y, 7m, 7c has a substantially common configuration, except for the type of powder contained in the four powder containers 104n, 104y, 104m, 104c. That is, each process cartridge 7n, 7y, 7m, 7c includes a photosensitive drum 101 which is an image carrier, a charging roller 102 which is a charger, a powder container 104n, 104y, 104m, 104c which contains the powder, and a developing roller 105 which performs development using the powder.

Of the four powder containers, the three powder containers 104y, 104m, and 104c on the right side of the figure 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 leftmost side of the figure 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. In addition, 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 an image of powder adhesive in a predetermined application pattern.

In this embodiment, when printing black images such as text, they are expressed using process black, which is a combination of yellow (Ty), magenta (Tm), and cyan (Tc) toners. However, for example, a fifth process cartridge using black printing toner may be added to image forming unit 1e, so that black images can be expressed using black printing toner. This is not a limitation, and the type and number of printing toners can be changed depending on the application of image forming device 1.

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 means in this embodiment that irradiates the photosensitive drum 101 of each process cartridge 7n, 7y, 7m, and 7c with laser light G to write an electrostatic latent image.

The transfer unit 3 is equipped with 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 process cartridge 7n, 7y, 7m, and 7c. On the inner circumferential side of the transfer belt 3a, a primary transfer roller 4 is disposed at a position corresponding to each photosensitive drum 101. In addition, a secondary transfer roller 5 as a transfer means is disposed at a position facing the secondary transfer inner roller 3b. The transfer nip 5N between the secondary transfer roller 5 and the transfer belt 3a is a transfer section (secondary transfer section) where a toner image is transferred from the transfer belt 3a to the sheet P.

The first fixing device 6 is disposed above the secondary transfer roller 5. FIG. 9 is a detailed view of the first fixing device 6. The first fixing device 6 has 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 with the heater 6a1 through the fixing film 6a. The fixing film 6a and the pressure roller 6b function as a pair of rotating bodies (first rotating body pair) that rotate while sandwiching the sheet P. The fixing film 6a has a base layer with a thickness of 30 to 70 μm made of heat-resistant resin such as polyimide, polyamide, PEEK, or metal such as stainless steel. The fixing film 6a has an elastic layer with a thickness of 0.1 to 1 mm made of silicone rubber or the like and a release layer with a thickness of 5 to 30 μm made of fluororesin such as PFA or PTFE on the base layer. The surface of the fixing film 6a becomes the surface that comes into contact with the molten toner and powder adhesive, and after the fixing process is completed, the toner surface is smoothed to match the shape of the surface of the fixing film 6a, as described below.

The pressure roller 6b has a core 6b1 made of iron or aluminum, an elastic layer 6b2 made of silicone rubber or the like and having a thickness of 2 to 4 mm, and a release layer made of a fluororesin such as PFA or PTFE provided on the outermost surface.

The heater 6a1 as the heating means (first heating means) has a heating resistor 6a12 such as Ag/Pd (silver palladium) that generates heat when electricity is applied, and an insulating protective layer (glass layer in this embodiment) 6a13 on a thin plate-shaped substrate 6a11 mainly composed of ceramics such as alumina. A temperature detection element 6a2 such as a thermistor is in contact with the substrate 6a11 and is connected to a CPU 6a3 as a control unit mounted on the image forming apparatus 1. The heater 6a1 heats up by supplying electricity to the heating resistor 6a12. The temperature rise is detected by the temperature detection element 6a2, and the CPU 6a3 controls the current to the heating resistor 6a12 via the triac 6a4. For example, if the temperature detected by the temperature detection element 6a2 is lower than a predetermined set temperature, the amount of power supplied to the heating resistor 6a12 is increased so that the heater 6a1 heats up, and if the temperature detected by the temperature detection element 6a2 is higher than the set temperature, the amount of power is decreased so that the heater 6a1 cools down, thereby keeping the heater 6a1 at a constant temperature.

The heater 6a1 is held by a holding member 6a5 made of a heat-resistant resin such as LCP (liquid crystal polymer). The holding member 6a5 also has a guide function for guiding the rotation of the fixing film 6a. A force is applied to the holding member 6a5 in a direction approaching the pressure roller 6b from a spring (not shown) attached to a metal stay 6a6. The pressure roller 6b is pressed toward the heater 6a1 via the fixing film 6a with a total pressure of 10 to 30 kgf by a pressure means such as a spring member (not shown). As a result, a fixing nip 6N with a width of 5 to 11 mm in the sheet conveying direction is formed between the pressure roller 6b and the heater 6a1 and holding member 6a5 that constitute the nip portion forming unit.

The pressure roller 6b receives power from a motor (not shown) and rotates in the direction of the arrow r1 in FIG. 9. The rotation of the pressure roller 6b causes the fixing film 6a to rotate accordingly. The sheet P carrying an unfixed toner image is transported in the sheet transport direction through the fixing nip 6N together with the fixing film 6a while the surface (image surface) of the sheet P carrying the toner image and powder adhesive Tn is in close contact with the outer surface of the fixing film 6a. This configuration is characterized by the fact that the thermal capacity of the fixing film and heater is particularly small, and the holding member 6a5 is also made of a material with high thermal insulation properties, so that it is possible to heat the surface of the fixing film 6a to a high temperature more quickly with a small amount of heat supply.

The housing 19 is provided with a discharge port 12 (first discharge port) which is an opening for discharging the sheet P from the device body 10, and a discharge unit 34 is disposed in the discharge port 12. The discharge unit 34, which is the discharge means in this embodiment, uses a so-called triple roller system 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 transport path of the sheet P, is provided between the first fixing device 6 and the discharge unit 34. The switching guide 33 can rotate around the shaft portion 33a so that the tip 33b reciprocates in the direction of the arrow c in the figure.

The device main body 10 is equipped with a mechanism for double-sided printing. A motor (not shown) is connected to the discharge unit 34, and the direction of rotation of the intermediate roller 34b can be rotated forward and backward. In addition, a double-sided conveying path 1r is provided as a conveying path connected in a loop to the main conveying path 1m. The sheet P, on which an image is formed on the first side while passing through the main conveying path 1m, is sandwiched and conveyed by 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 through the switching guide 33, the switching guide 33 rotates counterclockwise (solid line position) and the intermediate roller 34b rotates in reverse, and the sheet P is reversed and conveyed to the double-sided conveying path 1r. Then, while the sheet P passes through the main conveying path 1m again in an inverted state, an image is formed on the second side of the sheet P. After double-sided printing, the sheet P is guided to the switching guide 33 (solid line position) rotated counterclockwise, is sandwiched and transported between the intermediate roller 34b and the second discharge roller 34c, and is discharged from the device body 10.

In addition, the conveying path passing through the conveying roller 8a, the transfer nip 5N, and the fixing nip 6N in the device main body 10 constitutes the main conveying path 1m where image formation is performed on the sheet P. When viewed from the main scanning direction during image formation (the width direction of the sheet perpendicular to the conveying direction of the sheet conveyed through the main conveying path 1m), the main conveying path 1m extends from below to above passing one side of the horizontal direction relative to the image forming unit 1e. In other words, the device main body 10 of this embodiment is a so-called vertical conveying type (vertical path type) printer in which the main conveying 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 each other. Therefore, the movement direction of the sheet when the discharge unit 34 discharges the sheet P in the horizontal direction is opposite to the movement direction of the sheet when the sheet P is fed from the sheet cassette 8 in the horizontal direction.

1 (when viewed in the main scanning direction during image formation), it is preferable that the horizontal occupation area of the main body part of the post-processing unit 30 excluding the second discharge tray 35 is within the occupation area of the device main body 10. By accommodating the post-processing unit 30 in the space above the device main body 10 in this way, the sheet transport path (second path described later) when performing adhesive printing can be designed to be shorter than when the device main body 10 and the post-processing unit 30 are arranged side by side. As a result, the sheet P that passes through the first fixing device 6 and is discharged from the device main body 10 is immediately introduced into the post-processing unit 30, and the sheet P heated in the fixing process can enter the folding process and adhesive process without losing heat as much as possible. As described later, by allowing the sheet P to retain as much of the heat supplied in the fixing process as possible, it is possible to reduce the energy consumption in the adhesive process.

(Post-processing unit)
2, the post-processing unit 30 is attached to the upper part of the apparatus main body 10. The post-processing unit 30 is a post-processing unit in which a folder 31 as a folding means and a second fixing device 32 as an adhesive means (second fixing means) are housed in a housing (second housing) 39 and integrated with each other.

The second fixing device 32 in this embodiment has the same configuration as the first fixing device 6 as shown in FIG. 10B. It has a cylindrical heating film (endless belt) 32b and a pressure roller 32a, and the sheet P folded by the folder 31 is sandwiched and conveyed by the adhesive nip 32N (second fixing nip), which is a nip portion between the heating film 32b and the pressure roller 32a. The heating film 32b and the pressure roller 32a function as a pair of rotating bodies (second rotating body pair) that sandwich and rotate the sheet P. The inner surface side of the heating film 32b is provided with a heater 32b1 and a temperature detection element 32b2 as heating means, as in the first fixing device 6. The heating film 32b rotates following the pressure roller 32a that rotates in the direction of the arrow r2, so that the sheet P is sandwiched and conveyed by the adhesive nip 32N. During this process, the sheet P is heated and pressurized, causing the powder adhesive Tn applied to the sheet P to soften again, and the sheet P is adhered in a folded state.

The post-processing unit 30 is provided with a first discharge tray 13 that rotatably holds the 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 located on the upper surface of the entire image forming apparatus 1 (FIG. 1). The functions of each part of the post-processing unit 30 will be described later.

As shown in FIG. 6, three slits measuring 4 mm×150 mm are formed as openings 38 that connect the internal space of the image forming device 1 to the space above the image forming device 1 on the top surface (area 39a shown by dotted lines) of the cover member that covers the upper part of the second fixing device 32, which is a heat source. The area of area 39a as viewed in the direction of gravity is 460 mm×160 mm. The opening ratio of openings 38 to the top surface of the cover member (the ratio of the total opening area of the slits to the area of area 39a) is about 2.4%. The opening ratio of openings 38 is preferably about 0.1% to 5%. Openings 38 are designed to reduce the amount of air discharged near the fixing device compared to a fixing device used for normal image thermal fixing in an image forming device, and to make it easier for warm air to remain in the area below area 39a. The reason for this is explained below.

It is known that moisture evaporates from the sheet and generates water vapor around a normal fixing device, and as a countermeasure against condensation, the fixing device is designed to make it easy to exhaust air around the fixing device. However, in the case of the second fixing device 32 of this embodiment, moisture is released from the sheet when the fixing process (first heating process) by the first fixing device 6 is completed, so a large amount of water vapor does not usually occur after the adhesion process (second heating process) by the second fixing device 32. Therefore, compared to the first fixing device 6, the risk of condensation occurring in the second fixing device 32 is lower, and problems are less likely to occur even if the opening rate of the top surface (area 39a) of the cover member is reduced.

By reducing the opening ratio of the top surface of the cover member, the air warmed by the second fixing device 32 can be retained inside the post-processing unit 30 and reused to warm the folder 31. As described below, if the temperature of the roller member that contacts the sheet in the folder 31 is high, this is advantageous in reducing the energy consumption in the adhesion process.

The post-processing unit 30 is provided with a positioning portion (e.g., 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 connecting the connector 36 of the post-processing unit 30 with the 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.

(Process cartridge)
As described 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. FIG. 8 is a cross-sectional view showing a schematic configuration of the process cartridge 7n. The process cartridge 7n is composed of a photoconductor unit CC including a photoconductor drum 101 and the like, and a development unit DT including a development roller 105 and the like.

The photosensitive drum 101, which is a drum-shaped electrophotographic photosensitive member (image carrier), is rotatably attached to the photosensitive unit CC via a bearing (not shown). The photosensitive drum 101 receives a driving force from a motor serving as a driving means (driving source) (not shown) and is driven to rotate in a clockwise direction (arrow w) in the figure during image formation operation. In addition, the photosensitive unit CC has a charging roller 102 for charging the photosensitive drum 101 and a cleaning member 103 arranged around the photosensitive drum 101.

The developing unit DT is provided with a developing roller 105 as a developer carrier that contacts the photosensitive drum 101 and rotates in a counterclockwise direction (arrow d) in the figure. 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).

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 the opposing portion (contact portion). The supply roller 106 supplies powder adhesive (printing toner in the case of process cartridges 7y, 7m, and 7c) onto the developing roller 105. At the same time, the supply roller 106 acts to strip off the powder adhesive (printing toner in the case of 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 process cartridges 7y, 7m, and 7c) supplied onto the developing roller 105 by the supply roller 106.

The powder storage section 104n stores a powder adhesive (printing toner in the case of the process cartridges 7y, 7m, and 7c). A rotatably supported transport member 108 is provided within the powder storage section 104n. The transport member 108 rotates in a clockwise direction (arrow f) in the figure to agitate the powder stored in the powder storage section 104n and transport the powder to the development chamber 109 in which the development roller 105 and supply roller 106 are provided.

Here, the photoconductor unit CC and the development unit DT can be separately configured as a photoconductor unit cartridge and a development unit cartridge, respectively, and can be configured to be detachable from the main body of the image forming apparatus. Also, it is possible to configure a powder cartridge that has only the powder storage section 104 and the transport member 108, separate from the process cartridge having the photoconductor and developer carrier, and is detachable from the main body of the apparatus.

(Printing toner)
As the printing toners Tm, Tc, and Ty of this embodiment, conventionally known printing toners can be used. 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. In addition, the printing toner (printing developer) may contain a colorant, a magnetic material, a charge control agent, a wax, and an external additive.

(powder adhesive)
In addition, as the powder adhesive Tn of this embodiment, a powder adhesive containing a thermoplastic resin as a binder resin can be used. The thermoplastic resin is not particularly limited, and examples thereof include known thermoplastic resins such as polyester resin, vinyl resin, acrylic resin, styrene-acrylic resin, polyethylene, polypropylene, polyolefin, ethylene-vinyl acetate copolymer resin, and ethylene-acrylic acid copolymer resin. A plurality of these resins may be contained.

In addition, it is preferable that the powder adhesive Tn further contains a crystalline material that is compatible with the binder resin. As this crystalline material, known crystalline resins such as crystalline polyester resins and crystalline vinyl resins, and known waxes such as ester waxes, which are esters of alcohol and acid, and hydrocarbon waxes such as paraffin wax can be used. Crystalline resins and waxes may be used in combination. These crystalline materials act as plasticizers that impart plasticity to the powder adhesive Tn when heated. In other words, the crystalline material that is dispersed in a crystalline state in the binder resin at room temperature melts instantly when the powder adhesive Tn is heated and becomes compatible with the binder resin, which acts to facilitate deformation of the powder adhesive Tn.

The powder adhesive Tn may also contain a colorant. Known colorants such as black colorants, yellow colorants, magenta colorants, and cyan colorants can be used as the colorant. The content of the colorant in the powder adhesive is preferably 1.0% by mass or less, and more preferably 0.1% by mass or less. Furthermore, the powder adhesive Tn may contain a magnetic material, a charge control agent, a wax, and an external additive.

In order to form an adhesive portion on a sheet P using a powder adhesive by electrophotography, the weight average particle diameter of the powder adhesive Tn is preferably 5.0 μm or more and 30 μm or less, and more preferably 6.0 μm or more and 20 μm or less. Note that printing toner may be used as the powder adhesive Tn as long as it satisfies the adhesive properties.

(Example of powder adhesive manufacturing)
A method for producing the powder adhesive Tn is exemplified below. The powder adhesive Tn according to this production example contains an ester wax and a hydrocarbon wax as crystalline materials compatible with the binder resin (styrene-butyl acrylate copolymer and polyester resin).

First, the following materials were prepared.
Styrene 75.0 parts n-Butyl acrylate 25.0 parts Polyester resin 4.0 parts (non-crystalline polyester resin having a weight average molecular weight (Mw) of 20,000, a glass transition temperature (Tg) of 75° C., and an acid value of 8.2 mgKOH/g)
Ethylene glycol distearate 14.0 parts (ester wax obtained by esterifying ethylene glycol and stearic acid)
Hydrocarbon wax (HNP-9, manufactured by Nippon Seiro) 2.0 parts Divinylbenzene 0.5 parts

The mixture of the above materials was kept at 60°C and stirred at 500 rpm using a T.K. Homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) to dissolve uniformly, preparing a polymerizable monomer composition.

Meanwhile, 850.0 parts of 0.10 mol/L-Na ₃ PO ₄ aqueous solution and 8.0 parts of 10% hydrochloric acid were added to a vessel equipped with a high-speed stirring device Clearmix (manufactured by M Technique Co., Ltd.), the rotation speed was adjusted to 15,000 rpm, and the mixture was heated to 70° C. 127.5 parts of 1.0 mol/L-CaCl ₂ aqueous solution was added thereto to prepare an aqueous medium containing a calcium phosphate compound.

After adding the above polymerizable monomer composition to the aqueous medium, 7.0 parts of the polymerization initiator t-butyl peroxypivalate was added, and the mixture was granulated for 10 minutes while maintaining a rotation speed of 15,000 rpm. The high-speed agitator was then replaced with a propeller agitator, and the mixture was reacted at 70°C for 5 hours while refluxing, after which the liquid temperature was increased to 85°C and the mixture was reacted for an additional 2 hours.

After the polymerization reaction was completed, the resulting slurry was cooled, and hydrochloric acid was added to the slurry to adjust the pH to 1.4 and the slurry was stirred for 1 hour to dissolve the calcium phosphate salt. The slurry was then washed with three times the amount of water, filtered, dried, and classified to obtain powder adhesive particles.

Then, 2.0 parts of silica fine particles (number average particle size of primary particles: 10 nm, BET specific surface area: 170 ^m2 /g) that had been hydrophobized using dimethyl silicone oil (20% by mass) were added as an external additive to 100.0 parts of the powder adhesive particles. The powder adhesive particles to which the silica fine particles had been added were mixed at 3000 rpm for 15 minutes using a Mitsui Henschel mixer (manufactured by Mitsui Miike Chemical Engineering Co., Ltd.) to obtain a powder adhesive. The weight average particle size of the obtained powder adhesive was 6.8 μm.

(Method of measuring glass transition temperature (Tg))
The glass transition temperature (Tg) of the powder adhesive Tn 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 of the device, and the heat of fusion of indium is used for heat correction.

Specifically, 1 mg of sample is weighed out and placed in an aluminum pan, with an empty aluminum pan used as a reference. Using the modulation measurement mode, measurements are taken in the range of 0°C to 100°C with a heating rate of 1°C/min and temperature modulation conditions of ±0.6°C/60 seconds. Since the specific heat change is obtained during the heating process, the glass transition temperature (Tg) is determined as the intersection of the line midway between the baselines before and after the specific heat change and the differential thermal curve. The glass transition temperature (Tg) of the obtained powder adhesive Tn was 52°C.

(Example of the production of printing toner)
Next, a method for producing the printing toners Ty, Tm, and Tc will be exemplified. First, the following materials were prepared.
Styrene 60.0 parts Colorant 6.5 parts (C.I. Pigment T Blue 15:3, Dainichi Seika Chemicals Co., Ltd.)

The above materials were placed in an attritor (manufactured by Mitsui Miike Chemical Engineering Co., Ltd.) and further dispersed using zirconia particles with a diameter of 1.7 mm at 220 rpm for 5 hours to obtain a pigment dispersion.

In addition, the following materials were prepared:
Styrene 15.0 parts n-Butyl acrylate 25.0 parts Polyester resin 4.0 parts (Polyester resin having a weight average molecular weight (Mw) of 20,000, a glass transition temperature (Tg) of 75° C., and an acid value of 8.2 mgKOH/g)
Behenyl behenate 12.0 parts (ester wax obtained by esterifying behenic acid and behenyl alcohol)
Divinylbenzene 0.5 parts

The above materials were mixed and added to the pigment dispersion. The resulting mixture was kept at 60°C and stirred at 500 rpm using a T.K. Homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) to dissolve and disperse uniformly, preparing a polymerizable monomer composition.

Meanwhile, 850.0 parts of 0.10 mol/L-Na ₃ PO ₄ aqueous solution and 8.0 parts of 10% hydrochloric acid were added to a vessel equipped with a high-speed stirring device Clearmix (manufactured by M Technique Co., Ltd.), the rotation speed was adjusted to 15,000 rpm, and the mixture was heated to 70° C. 127.5 parts of 1.0 mol/L-CaCl ₂ aqueous solution was added thereto to prepare an aqueous medium containing a calcium phosphate compound.

After adding the above polymerizable monomer composition to the aqueous medium, 7.0 parts of the polymerization initiator t-butyl peroxypivalate was added, and the mixture was granulated for 10 minutes while maintaining a rotation speed of 15,000 rpm. The high-speed agitator was then replaced with a propeller agitator, and the mixture was reacted at 70°C for 5 hours while refluxing, after which the liquid temperature was increased to 85°C and the mixture was reacted for an additional 2 hours.

After the polymerization reaction was completed, the resulting slurry was cooled, and hydrochloric acid was added to the slurry to adjust the pH to 1.4. The slurry was then stirred for one hour to dissolve the calcium phosphate salt. The slurry was then washed with three times the amount of water, filtered, dried, and classified to obtain toner particles.

Then, 2.0 parts of silica fine particles (number average particle diameter of primary particles: 10 nm, BET specific surface area: 170 ^m2 /g) that had been hydrophobized using dimethyl silicone oil (20% by mass) were added as an external additive to 100.0 parts of the toner particles. The toner particles to which the silica fine particles had been added were mixed at 3000 rpm for 15 minutes using a Mitsui Henschel mixer (manufactured by Mitsui Miike Chemical Engineering Co., Ltd.) to obtain a toner. The weight average particle diameter of the obtained printing toner was 6.5 μm.

(Method of measuring weight average particle size)
The weight average particle diameter of the printing toners Ty, Tm, Tc and the powder adhesive Tn is calculated as follows. The measurement device is a precision particle size distribution measurement device using the pore electrical resistance method with a 100 μm aperture tube, "Coulter Counter MulTisizer 3" (registered trademark, manufactured by Beckman Coulter, Inc.). The measurement conditions are set and the measurement data is analyzed using the accompanying dedicated software, "Beckman Coulter MulTisizer 3 Version 3.51" (manufactured by Beckman Coulter, Inc.). The measurement is performed with an effective measurement channel count of 25,000 channels.

The electrolyte solution used for the measurements is one in which special grade sodium chloride is dissolved in ion-exchanged water to give a concentration of 1% by mass, for example "ISOTON II" (manufactured by Beckman Coulter).

Before performing measurements and analysis, the dedicated software is set as follows. On the "Change Standard Measurement Method (SOM)" screen of the dedicated software, the total count number in the control mode is set to 50,000 particles, the number of measurements is set to 1, and the Kd value is set to the value obtained using "Standard particle 10.0 μm" (manufactured by Beckman Coulter). The threshold and noise level are automatically set by pressing the "Threshold/Noise Level Measurement Button." In addition, the current is set to 1600 μA, the gain to 2, the electrolyte to ISOTON II, and "Flush aperture tube after measurement" is checked. On the "Pulse to particle size conversion setting" screen of the dedicated software, the bin interval is set to logarithmic particle size, the particle size bin to 256 particle size bin, and the particle size range to 2 μm to 60 μm.

The specific measurement method is as follows.
(1) Pour 200 mL of the electrolyte solution into a 250 mL round-bottom glass beaker made exclusively for the MulTisizer 3, set it on the sample stand, and stir the stirrer rod counterclockwise at 24 revolutions per second. Then, remove dirt and air bubbles from inside the aperture tube using the "Aperture Tube Flush" function of the dedicated software.
(2) 30 mL of the aqueous electrolyte solution is placed in a 100 mL flat-bottom glass beaker, and 0.3 mL of a dilution of "Contaminon N" (a 10% aqueous solution of a neutral detergent for cleaning precision measuring instruments with a pH of 7, consisting of a nonionic surfactant, an anionic surfactant, and an organic builder, manufactured by Wako Pure Chemical Industries, Ltd.) diluted 3 times by mass with ion-exchanged water is added thereto as a dispersant.
(3) Prepare an ultrasonic disperser "UlTransonic Dispersion SysTem TeTora150" (manufactured by Nikkaki Bios Co., Ltd.) that has two built-in oscillators with an oscillation frequency of 50 kHz and a phase shift of 180 degrees and an electrical output of 120 W. Place 3.3 L of ion-exchanged water in the water tank of the ultrasonic disperser, and add 2 mL of Contaminon N to this water tank.
(4) The beaker (2) is set in the beaker fixing hole of the ultrasonic disperser described above, and the ultrasonic disperser is operated. Then, the height position of the beaker is adjusted so that the resonance state of the liquid surface of the electrolyte solution in the beaker is maximized.
(5) While the electrolyte solution in the beaker in (4) is being irradiated with ultrasonic waves, the toner or powder adhesive is added to the electrolyte solution in small amounts of 10 mg at a time and dispersed. The ultrasonic dispersion process is then continued for another 60 seconds. During the ultrasonic dispersion process, the water temperature in the water tank is appropriately adjusted to be 10°C or higher and 40°C or lower.
(6) Using a pipette, the electrolyte solution (5) in which the toner or powder adhesive is dispersed is dropped into the round-bottom beaker (1) placed in the sample stand to adjust the measurement concentration to 5%. Measurements are then continued until the number of particles measured reaches 50,000.
(7) The measurement data is analyzed using dedicated software provided with the device to calculate the weight average particle diameter.

(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. 1 to 8. Figs. 3 and 4 are diagrams showing the sheet transport path in the image forming apparatus 1. Figs. 5(a to f) are diagrams for explaining the contents of the folding process. Figs. 7(a to c) are diagrams showing the process in which the image forming apparatus 1 creates a paper bag, which is a bag-shaped adhesive printed product, from one sheet P. Fig. 7(a) shows an image formed on the first side of the sheet P with printing toner, Fig. 7(b) shows the application pattern of powder adhesive on the second side of the sheet P, and Fig. 7(c) shows the paper bag output as a product after the adhesive process.

When data of an image to be printed and a command to execute printing are input to the image forming device 1, the control unit of the image forming device 1 starts a series of operations (image forming operation) in which the sheet P is transported to form an image 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 transported toward the transfer nip 5N via the transport roller 8a.

The image forming device 1 of this embodiment can form images or apply powder adhesive to sheets at a print speed of 40 sheets per minute with single-sided printing while transporting the sheets at a speed (process speed) of 210 mm/sec. When producing the paper bag shown in FIG. 7(c), images are formed or powder adhesive is applied to the first and second sides of the sheet P, making it possible to continuously produce paper bags at a rate of approximately 20 bags per minute.

In parallel with the feeding of the sheet P, the process cartridges 7n, 7y, 7m, and 7c are driven in sequence, and the photosensitive drum 101 is rotated in the clockwise direction (arrow w) in the figure at a surface speed of 210 mm/sec. At this time, the photosensitive drum 101 is uniformly charged on the surface by the charging roller 102. In addition, the scanner unit 2 irradiates the photosensitive drum 101 of each process cartridge 7n, 7y, 7m, and 7c with laser light G modulated based on image data to form an electrostatic latent image on the surface of the photosensitive drum 101. Specifically, the scanner unit 2 irradiates the photosensitive drum 101 of the process cartridges 7y, 7m, and 7c with laser light G to form an electrostatic latent image at a position corresponding to the image 53c shown in FIG. 7(a). Next, the electrostatic latent image on the photosensitive drum 101 is developed into a toner image by the printing toner carried by the developing roller 105 of the process cartridges 7y, 7m, and 7c.

The transfer belt 3a rotates in the counterclockwise direction (arrow v) in the figure at a speed of 210 mm/sec. The toner images formed in each process cartridge 7y, 7m, and 7c are primarily transferred from the photosensitive drum 101 to the transfer belt 3a by the electric field formed between the photosensitive drum 101 and the primary transfer roller 4.

As shown in FIG. 1, process cartridge 7n, which uses powder adhesive Tn, is located most upstream of the four process cartridges in the rotation direction of transfer belt 3a. Yellow, magenta, and cyan process cartridges 7y, 7m, and 7c are lined up in this order from process cartridge 7n toward the downstream side in the rotation direction of transfer belt 3a. Therefore, when the four types of toner images are superimposed on 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.

The toner image carried by the transfer belt 3a and reaching the transfer nip 5N is secondarily transferred to the sheet P transported along the main transport path 1m by the electric field formed between the secondary transfer roller 5 and the secondary transfer inner roller 3b. At that time, the toner layer is turned upside down. That is, on the sheet P that has passed through the transfer nip 5n, the printing toners of cyan (Tc), magenta (Tm), and yellow (Ty) are layered from the bottom layer (the layer that contacts 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.

Then, the sheet P carrying the unfixed toner image is sandwiched and transported through the fixing nip 6N together with the fixing film 6a while the image side of the sheet P is in close contact with the outer surface of the fixing film 6a. The first fixing device 6 is adjusted so that the surface speed of the pressure roller 6b is 210 mm/sec, and sandwiches and transports the sheet P in synchronization with the transfer process. During this sandwiching and transporting 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 on the sheet P. The sheet P that has passed through the fixing nip 6N is curvature-separated from the fixing film 6a while retaining the fixed toner image, and the image fixed on the sheet P is obtained.

The sheet P is sandwiched and conveyed between the first discharge roller 34a and the intermediate roller 34b by the switching guide 33 rotated clockwise. After the trailing end of the sheet P in the traveling direction passes the switching guide 33, the switching guide 33 rotates counterclockwise and the intermediate roller 34b rotates in the reverse direction, and the sheet P is conveyed in reverse to the double-sided conveying path 1r. Then, while the sheet P passes through the main conveying path 1m again in an inverted state, the powder adhesive Tn is applied to the second side of the sheet P in the application pattern shown in FIG. 7(b). The process of applying the powder adhesive Tn to the second side of the sheet P is the same as when forming the image 53c on the first side, except that the powder adhesive Tn is used as the developer instead of the printing toners Ty, Tm, and Tc.

It is preferable to apply the powder adhesive Tn to the second side rather than the first side in a double-sided printing operation. This is because if the powder adhesive Tn is applied to the first side, it will be heated in the fixing process for the first side and then come into contact with the pressure roller 6b on the opposite side to the fixing film 6a in the fixing process for the second side, causing the temperature to drop. In contrast, the powder adhesive Tn applied to the second side receives heat from the fixing film 6a in the fixing process for the second side, and can enter the folding process at a relatively high temperature.

Regardless of whether single-sided or double-sided printing is being performed, the sheet P discharged from the device 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.

The first path R1 shown in FIG. 3 is a path along which the sheet P that has passed through the first fixing device 6 is discharged to the first discharge tray 13 by the discharge unit 34 in a normal printing mode that does not use the post-processing unit 30. The second path R2 shown in FIG. 4 is a path along which the sheet P that has passed through the first fixing device 6 is discharged to the second discharge tray 35 via the discharge unit 34, the folder 31, and the second fixing device 32 in an adhesive printing mode.

Between the first fixing device 6 and the folder 31 in the second route R2, an intermediate path 15 is provided. 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 approximately parallel to the first discharge tray 13. No opening is provided in the area from the tray switching guide 13a to the folder 31 in the sheet transport direction, and the heat of the sheet P is not discharged into the air as much as possible. 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 guide roller pair (31c, 31d) described below) is located vertically above the exit of the device main body 10 (the nip between the intermediate roller 34b and the second discharge roller 34c).

The folder 31 has four rollers, a first guide roller 31c, a second guide roller 31d, a first folding roller 31a, and a second folding roller 31b, and a retraction section 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 the transport path (intermediate path 15 in this embodiment) upstream of the folder 31. The first folding roller 31a and the second folding roller 31b are a pair of folding rollers that send out the sheet P while folding it. With this configuration, the sheet P is smoothly delivered from the discharge unit 34 to the pair of guide rollers.

The second guide roller 31d, which is a rotating body that contacts the sheet, comes into contact with the powder adhesive Tn on the sheet P, so it is desirable to cover its surface with a material with low thermal conductivity so as not to take away heat from the powder adhesive Tn as much as possible, and to reduce the contact area by providing moderate unevenness on the surface. An EPDM rubber layer is formed on the surface of the second guide roller 31d, and the surface roughness (ten-point average roughness Rzjis) is set to 10 μm or more. A surface roughness of 10 μm or more is suitable to minimize contact with the paper while obtaining sufficient frictional force. The surface roughness (Rzjis) shown here is a value measured using a surface roughness measuring device SE-3400 (product name) manufactured by Kosaka Laboratory Co., Ltd.

The second guide roller 31d is desirably hollow (having a space on the radially inner side of the outer periphery that contacts the sheet) to reduce its heat capacity so that the temperature rises quickly with a small amount of heat. In this embodiment, the core of the second guide roller 31d is a hollow pipe roller with a thickness of 1 mm.

The three rollers, the first guide roller 31c, the first folding roller 31a, and the second folding roller 31b, which are other examples of rotating bodies that come into contact with the sheet, are also configured in the same way as the second guide roller 31d so as to minimize the loss of heat from the sheet.

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)) in the transport direction of the sheet P before folding. This eliminates the need to provide additional transport rollers between the second discharge roller 34c and the folder 31, preventing heat from being lost from the sheet by such transport rollers.

The folding process by the folder 31 will be described with reference to Figures 5(a-f). When performing the folding process, the first guide roller 31c and the first folding roller 31a rotate in a clockwise direction in the figure, and the second guide roller 31d and the second folding roller 31b rotate in a counterclockwise direction in the figure. The rotation speed is 210 mm/sec at the surface speed of each roller when the sheet P is introduced. First, the leading edge q of the sheet P sent out from the discharge unit 34 is drawn into the pair of guide rollers (31c, 31d) as shown in Figure 5(a). At this time, since the powder adhesive Tn is applied to the lower surface of the sheet P in the figure, the powder adhesive Tn only contacts the guide roller 31d. As shown in Figure 5(b), the leading edge q of the sheet P is guided downward by the guide wall 31f and contacts the first folding roller 31a, and is drawn into the first folding roller 31a and the second guide roller 31d, which are opposed to each other, and abuts against the wall 31g of the drawing section 31e.

As the guide roller pair (31c, 31d) pulls in the sheet P, the leading edge q slides against the wall 31g and advances further 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 approximately parallel to the intermediate path 15, and at the stage shown in FIG. 5(c), the sheet P is wrapped around the second guide roller 31d and bent into a U-shape.

When the sheet P is further pulled in by the guide roller pair (31c, 31d) from the state shown in FIG. 5(c), it starts to bend at the middle part r as shown in FIG. 5(d). Eventually, as shown in FIG. 5(e), the middle part r comes into contact with the second folding roller 31b, and is pulled into the nip of the folding roller pair (31a, 31b) by the frictional force it receives from the second folding roller 31b. Then, as shown in FIG. 5(f), the sheet P is folded with the middle part r as the crease, and is discharged by the folding roller pair (31a, 31b) with the middle part r at the front.

Here, the depth N of the retraction section 31e (FIG. 5(e)), i.e., the distance from the nip of the pair of folding rollers (31a, 31b) to the end 31h of the retraction section 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 section 31e, the position of the fold can be changed as desired.

When the sheet P is discharged, the conveying speed (surface speed) of the pair of folding rollers is decelerated to match the conveying speed of the second fixing device 32 immediately before the sheet P reaches the adhesive nip 32N of the second fixing device 32. That is, the folding device 31 decelerates the sheet conveying speed from the sheet conveying speed V1 of the first fixing device 6 to the sheet conveying speed V2 of the second fixing device 32 before the leading edge of the sheet P in the sheet conveying direction reaches the second fixing device 32. Specifically, since the sheet conveying speed V2 of the second fixing device 32 is set to 105 mm/sec, the sheet conveying speed of the pair of folding rollers is decelerated from 210 mm/sec to 105 mm/sec. It is desirable to slow down the timing as much as possible, so that the time difference between the end of the fixing process and the start of the bonding process can be shortened. The shorter this time difference, the less the heat stored in the sheet P during the fixing process is released, and the bonding process can be started while the temperature of the powder adhesive Tn is high.

The folder 31 described above is an example of a folding means, and a folding mechanism may be used that, for example, presses a blade against the sheet P and pushes it into the nip between a pair of rollers to form a crease. 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 with a depth N of half the sheet length in addition to the four rollers, the post-processing unit 30 can be made smaller.

The sheet P folded by the folder 31 is transported to the second fixing device 32, where it is subjected to a bonding process in which it is heated and pressurized while being sandwiched and transported through the adhesive nip 32N. The pressure roller 32a of the second fixing device 32 is rotated so that the surface speed is 105 mm/sec. The sheet P is subjected to a bonding process (a second heat fixing of the image surface to which the powder adhesive has been applied) while being sandwiched and transported through the adhesive nip 32N, and is bonded while still in the folded state as shown in FIG. 10. That is, when the sheet P passes through the adhesive 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 sheets P are bonded (bonded) together via the powder adhesive Tn.

As shown in FIG. 4, the sheet P that has been subjected to the adhesive process by the second fixing device 32 is discharged to the left side in the figure from the discharge outlet 32c (second discharge outlet) provided in the housing 39 of the post-processing unit 30. It is then stored in the second discharge tray 35 (see FIG. 1) provided on the left side surface of the device main body 10. This completes the image formation operation when the sheet P is transported along the second path R2, and a paper bag can be obtained as the final product shown in FIG. 7(c). This concludes the explanation of the series of operations during image formation.

As described above, the image forming apparatus 1 of this embodiment can output a product that is bonded by an adhesive process from a base paper such as blank paper that is not preprinted paper. The bonding points of the folded sheet P can be changed by applying the powder adhesive Tn to the sheet P in a different pattern. For example, it is possible to create semi-adhesive products that are intended to be peeled off later, such as envelopes for enclosing documents or pay slips. Furthermore, the image recorded by the image forming apparatus 1 using printing toner can include a format (unchanging part) when preprinted paper is used, and a variable part such as personal information. Furthermore, the image forming apparatus 1 of this embodiment can be used for applications in which preprinted paper is used as a recording medium and printing and adhesive processes are performed on the variable parts.

(hot offset)
Next, problems that may occur when the fixing process (primary fixing process, first heating process) and the bonding process (secondary fixing process, second heating process) are performed in one image forming apparatus 1 will be described. Depending on the temperature and power conditions of the bonding process, an image defect 53d called hot offset as shown in FIG. 10(a) may occur. When outputting a product 54, the powder adhesive Tn is applied to the inside of the folded sheet P as shown in FIG. 10(b). In order to obtain sufficient adhesive strength in the output product 54, it is necessary to set the power supplied to the heater 32b1 of the second fixing device 32 in the bonding process (hereinafter, simply referred to as "power supplied in the bonding process") so that the applied powder adhesive Tn is sufficiently softened.

Increasing the power supply in the adhesion process increases the temperature of the heating film 32b. However, if the temperature of the heating film 32b becomes excessively high, the printing toner image 53c formed on the surface of the sheet P (i.e., in direct contact with the heating film 32b) melts excessively and becomes liquid. As the toner melts into a liquid state, its viscosity decreases and some of the toner adheres to the heating film 32b from the surface of the sheet P as stains. The adhered stains re-adhere to the sheet P as the heating film 32b rotates, and become apparent as the image defect 53d in FIG. 10(a).

To prevent the occurrence of hot offset while ensuring the adhesive strength of the product 54, it is necessary to achieve adhesion via the powder adhesive Tn while avoiding an excessive rise in temperature of the heating film 32b. In other words, it is necessary to suppress the amount of heat supplied to the sheet P in the adhesion process while allowing the powder adhesive Tn applied to the adhesive surface of the sheet P to bond together.

Another reason for suppressing the amount of heat supplied to the sheet P in the adhesion process is to reduce power consumption. The first and second fixers 6 and 32 are thermal fixing type heating devices (image heating devices) and perform the process that consumes the most power in the electrophotographic process. The image forming apparatus 1 of this embodiment has two heating devices, one for the fixing process and one for the adhesion process, and therefore is required to save as much power as possible. When power is supplied to the apparatus main body 10 and the post-processing unit 30 from a single outlet (a plug socket for commercial power), there may be restrictions, such as the current flowing through the outlet having to be kept within 15 A.

(Temperature change on sheet surface after fixing process)
11A shows the change in temperature over time of the surface of the sheet P from when the paper used as the sheet P starts to pass through the first fixing device 6 until the folded surface of the sheet P comes into contact with it. The horizontal axis is time, and the vertical axis is the temperature measurement result. A thermocouple with a small heat capacity of the temperature detection part (e.g., K-type thermocouple wire diameter of 50 μm or less manufactured by Anritsu Meter Co., Ltd.) was attached to the surface of the sheet P, and the sheet P was passed through the fixing nip 6N of the first fixing device 6 to perform the measurement. At that time, the potential difference signal from the thermocouple was measured with a Memory HiCorder manufactured by Hioki E.E. Corporation to obtain the change in temperature over time.

As can be seen from the graph, the temperature continues to rise while the measurement area of the sheet surface (the portion of the surface facing the fixing film 6a where the thermocouple is attached) is passing through the fixing nip 6N, reaching a peak temperature of approximately 110°C (point X). The temperature starts to drop the moment the measurement area leaves the fixing nip 6N, and as shown in Figure 5(a), it has dropped to approximately 60°C by the time it enters the folder 31 (point Y). Thereafter, by the time the sheet P begins to be folded with the surface where the thermocouple is attached facing inward (point Z), as shown in Figure 5(e), it has dropped to 50°C.

In the image forming apparatus 1 of this embodiment, the temperature at the timing of this point Z, i.e., the temperature at the timing when the bonding surfaces coated with the powder adhesive Tn begin to come into contact with each other, is important. Specifically, by making the surface temperature of the surfaces coated with the powder adhesive Tn at this point higher than, for example, the crystallization temperature of the compatible wax added to the powder adhesive Tn (45°C in this embodiment), sufficient adhesive strength can be obtained even if the temperature of the bonding process is set low. The reason for this will be explained below.

The graph in FIG. 11(b) shows the relationship between the temperature Z [°C] (horizontal axis) of the powder adhesive at the start of folding and the heater temperature [°C] (vertical axis) required for strong adhesion. The "heater temperature required for strong adhesion" was determined by feeding a sample sheet P through the image forming apparatus 1 while gradually increasing the heater temperature setting of the second fixing device 32, repeatedly outputting the final product (adhesive print), and peeling the resulting product by hand to evaluate the adhesiveness. The evaluation criterion is the level of "when an external force is applied in the direction of peeling the adhesive surface, the adhesive surface does not peel off and the sheet strength reaches its limit first" to be judged as OK. The lowest heater temperature of the second fixing device 32 that achieved an adhesiveness evaluated as OK is defined as the "heater temperature required for strong adhesion".

The adhesive properties of the finished product output through the folding and gluing processes were repeatedly evaluated while changing the temperature Z of the powder adhesive at the start of folding. As a result, when the sample was completely cooled to room temperature (20°C) after the fixing process, sufficient adhesive properties could not be obtained unless the heater temperature of the second fixing device 32 was set to 200°C. In addition, a tendency was observed that the "heater temperature required for strong adhesion during gluing" tended to decrease when the time for cooling the sample after the fixing process was gradually shortened and the temperature Z was increased.

Here, if the conveying distance from the first fixing device 6 to the folding device 31 is made very short and the temperature Z of the powder adhesive at the start of folding is set to 75°C, the heater temperature required for strong adhesion is 160°C. And, when the heater temperature required for strong adhesion is plotted for temperatures Z between 75°C and 20°C, it was found that it can be approximated by two straight lines K and L that are discontinuous near Z = 45°C.

If the plot points change continuously without discontinuities, the negative correlation between the heater temperature required for strong adhesion and the temperature Z of the powder adhesive at the start of folding can be explained simply by the amount of accumulated heat. In other words, the less heat stored in the sheet P when it reaches the adhesion nip 32N of the second fixer 32, the higher the temperature of the heater 32b1 of the second fixer 32 must be in the adhesion process to heat the powder adhesive Tn to a temperature suitable for adhesion. However, since the above-mentioned discontinuities are seen in Figure 11(b), other phenomena occur between the fixing process and the adhesion process. The cause of the discontinuities in Figure 11(b) can be explained as follows.

(Effect of wax components)
FIG. 12 shows the results of measuring the heat flow of the powder adhesive Tn 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, and an empty aluminum pan is used as a reference. Using the modulation measurement mode, measurements are performed in the range of 10°C to 90°C with a temperature rise rate of 20°C/min and a temperature fall rate of 20°C/min. The curve Qu shows the temperature rise process, with the wax melting point peak Qu1 (peak due to endothermic heat during melting) appearing near 70°C. The curve Qd shows the temperature fall process, with the heat generation peak Qd1 due to wax crystallization appearing near 45°C.

In general, when a toner used in an electrophotographic image forming apparatus contains a crystalline material that is compatible with the binder resin, it is known that the hardness (plasticity) of the toner varies greatly depending on whether the crystalline material is melted and compatible with the binder resin. In the powder adhesive Tn according to this embodiment, the hardness (plasticity) of the powder adhesive Tn varies greatly depending on whether the wax contained as a crystalline material is melted. It is considered that the behavior of the powder adhesive Tn in the folding and bonding processes changes depending on whether the wax melted by the fixing process by the first fixing device 6 is crystallized by the time of the folding process. In other words, it is considered that the boundary of the discontinuous point that appears in FIG. 12 is determined by the crystallization temperature of the wax, which is a crystalline material contained in the powder adhesive Tn of this embodiment, when the temperature is decreased.

The "crystallization temperature during cooling" of the crystalline material contained in the powder adhesive Tn can be determined as the peak temperature (Qd1) of heat generation during the cooling process from the heat flow measurement results shown in FIG. 12, for example. When a polymer crystallizes, not only temperature but also time is an important variable, and generally, the crystallization rate tends to decrease with increasing molecular weight. Therefore, when a polymer such as crystalline polyester is used as the crystalline material, the faster the temperature drops, the lower the crystallization start temperature may be. Therefore, when determining the crystallization temperature during cooling, it is desirable to set the cooling rate close to the average cooling rate during the period from passing through the fixing nip 6N to reaching the folding roller pair in an actual image forming apparatus.

The behavior of the powder adhesive Tn during adhesive printing is described below. Figure 13 (a) shows the state in which the powder adhesive Tn has been transferred onto the paper as the sheet P. Figure 13 (b) shows how the state of the powder adhesive Tn changes during the fixing process by the first fixing device 6. In the fixing nip 6N of the first fixing device 6, heat from the heater 6a1 is applied to the powder adhesive Tn via the fixing film 6a, and the temperature of the powder adhesive Tn rises to, for example, 120°C, causing the powder adhesive Tn to become liquid. At this time, the wax as a crystalline material contained in the powder adhesive Tn melts and becomes compatible with the binding resin. As a result of the liquid-melted powder adhesive Tn being pressed against the fixing film 6a in the fixing nip 6N, a layer of adhesive Tn1 is formed that wets the surface of the paper so as to follow the concaves on the surface of the paper (smooth out the concaves and convexes).

After the sheet P passes through the first fixing device 6, the adhesive Tn1 solidifies, filling in the unevenness between the sheets of paper, as shown in FIG. 13(c), and the cellulose and adhesive Tn1 have a sufficient contact area, generating intermolecular attraction (van der Waals forces). In addition, the solidified adhesive Tn1 entangles three-dimensionally with the paper fibers, providing an overall mechanical bond (anchor effect) between the adhesive and the paper. Furthermore, the surface of the adhesive Tn1 is smoothed by the fixing film 6a while passing through the fixing nip 6N, so that the surface of the adhesive Tn1 after passing through the nip becomes smooth with a surface roughness similar to that of the surface of the fixing film 6a (the fluororesin release layer in this embodiment).

Figure 14 (a) shows the state in which sheet P has been folded by the folder 31 so that adhesive surfaces P1, P2 on which adhesive Tn2 has been applied face each other (see Figure 5 (e)). Paper as sheet P is sandwiched and pressed by a first folding roller 31a and a second folding roller 31b that make up a pair of folding rollers. The pressure of this pair of folding rollers causes the surfaces of adhesive Tn2 to deform, and it is believed that the discontinuity of lines K and L that appears in Figure 11 (b) is caused by whether or not they can be sufficiently adhered to each other. Below, we will explain the case where adhesive Tn1 has cooled and lost its plasticity by the start of the folding process, and the case where the plasticity of adhesive Tn1 has been maintained.

First, consider the case where the adhesive Tn1 has cooled and lost its plasticity by the start of the folding process. In this case, because the adhesive Tn2 has a high hardness, the adhesive Tn2 on the adhesive surfaces P1 and P2 is not easily deformed even when pressure is applied by the pair of folding rollers, and a gap remains between the surfaces of the adhesive Tn2 as shown in FIG. 14(a). When the sheet P is heated by the second fixing device 32, the sheet P is supplied with heat from the heater 32b1 via the heating film 32b from either the adhesive surface P1 or P2 side (FIG. 10(b)). At this time, the gap shown in FIG. 14(a) prevents smooth heat conduction from one adhesive surface side to the other adhesive surface side. Therefore, in order to replasticize the adhesive Tn2 on both adhesive surfaces P1 and P2 to obtain sufficient adhesion, it is necessary to supply a large amount of heat in a short time during the bonding process.

In contrast, if the hardness of adhesive Tn2 is low when folding by the pair of folding rollers begins, the adhesive Tn2 on the adhesive surfaces P1 and P2 is relatively easily deformed by pressure from the pair of folding rollers, and the surfaces of adhesive Tn3 come into close contact with each other as shown in FIG. 14(b). In this case, the heat supplied from heater 32b1 via heating film 32b is smoothly transferred from one adhesive surface side to the other adhesive surface side. As a result, sufficient adhesion can be obtained with at least the amount of heat supplied in the bonding process compared to the state shown in FIG. 14(b).

In the straight line K on the lower temperature side of the discontinuity in FIG. 11(b), the adhesive cooled and the wax crystallized before the sheet P reached the folder 31, which is thought to be why the adhesive had a high hardness when the folder 31 started to fold it. As a result, gaps remain between the adhesive even after the sheet is folded by the pair of folding rollers, and the heater temperature required for strong adhesion becomes high.

On the other hand, in line L on the higher temperature side of the discontinuity in FIG. 11(b), the temperature drop until the sheet P reaches the folder 31 is small, and it is believed that the wax is basically kept molten and compatible with the binder resin. In this state, the plasticity of the adhesive is maintained by the plasticizing action of the wax, so the adhesive adheres relatively easily when folded by the pair of folding rollers. As a result, it is believed that the heater temperature required for strong adhesion is lower than the temperature on the straight line extrapolated from line K. As described above, the mechanism by which the heater temperature required for strong adhesion (lines K and L in FIG. 11(b)) becomes discontinuous at the boundary near 45°C, the crystallization temperature of the wax, for the powder adhesive temperature Z at the timing of starting folding can be explained.

As explained above, by folding the sheets together and bonding the adhesive surfaces together before the wax crystallizes as a crystalline material, sufficient adhesive strength can be obtained while keeping the heater temperature in the bonding process as low as possible. By keeping the heater temperature low, the possibility of hot offset of images formed with printing toner can be reduced. In addition, power consumption in the bonding process can be reduced.

To achieve this, it is effective to shorten the time that elapses from the fixing step to the folding step. This makes it possible to perform the folding step while a larger portion of the heat stored in the sheet during the fixing step remains. It is also effective to reduce the amount of heat that is removed from the sheet by members that come into contact with the sheet between the fixing step and the folding step (particularly, the pair of folding rollers). Specifically, in this embodiment, the following configurations are combined.
(a) By appropriately roughening the surface roughness of the pair of folding rollers to reduce the contact area with the sheet, the amount of heat that the pair of folding rollers removes from the sheet is reduced.
(b) By making the pair of folding rollers hollow to reduce their heat capacity, the amount of heat that the pair of folding rollers removes from the sheet is reduced.
(c) By setting the opening ratio of the top surface (area 39a in Figure 6) of the cover member covering the upper surface of the post-processing unit 30 on which the folder 31 is mounted to 5% or less, warm air is trapped around the pair of folding rollers, thereby reducing the amount of heat that the pair of folding rollers removes from the sheet.
(d) The sheet conveying speed is maintained as fast as possible from when the sheet passes through the first fixing device 6 until immediately before the leading edge of the sheet reaches the adhesive nip 32N of the second fixing device 32, and the sheet conveying speed is decelerated immediately before the leading edge of the sheet reaches the adhesive nip 32N. This makes it possible to shorten the time elapsed from the fixing process to the folding process and to utilize the heat stored in the sheet during the fixing process.

In order to perform the folding process while maintaining the plasticity of the powder adhesive Tn, the above (a) to (d) may be used alone or in combination. In other words, the extent to which the cooling of the sheet should be suppressed in the section from the fixing process to the folding process should be considered depending on the properties of the crystalline material that imparts plasticity to the powder adhesive (particularly the crystallization temperature when cooled) and the temperature setting of the first fixing device 6, etc.

In Example 1, a method was described in which the folding process is performed while maintaining the plasticity of the powder adhesive by retaining as much heat as possible in the fixing process to maintain the molten state of the wax as a crystalline material. In this Example, a method for preparing a crystalline material is examined so that the plasticity of the crystalline material is maintained even at lower temperatures. Below, elements with common reference numbers to Example 1 have substantially the same configuration and function as Example 1, and differences from Example 1 will be explained.

A manufacturing example of the powder adhesive according to this embodiment will be described. This powder adhesive, like the powder adhesive Tn in Example 1, is stored in the powder storage unit 104n of the image forming device 1 and is applied to a sheet by an electrophotographic process when creating an adhesive print.

(Production Example of Crystalline Polyester Dispersion)
In a beaker equipped with a stirrer, 100.0 parts of ethyl acetate, 30.0 parts of crystalline polyester (condensate of 1,10-decanediol and sebacic acid, number average molecular weight (Mn) 7200, melting point 72 ° C.), 0.3 parts of 0.1 mol / L sodium hydroxide, and 0.2 parts of anionic surfactant (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Neogen RK) were charged, heated to 60.0 ° C., and stirring was continued until completely dissolved. With further stirring, 90.0 parts of ion-exchanged water was gradually added, phase inversion emulsification was performed, and a crystalline polyester dispersion (solid concentration: 20 mass %) was obtained by removing the solvent.

(Production Example of Amorphous Polyester)
First, the following materials were prepared:
Terephthalic acid 30.0 parts Isophthalic acid 10.0 parts Sebacic acid 15.0 parts Dodecenylsuccinic acid 20.0 parts Trimellitic acid 6.9 parts Bisphenol A ethylene oxide (2 moles) adduct 70.0 parts Bisphenol A propylene oxide (2 moles) adduct 90.0 parts Dibutyltin oxide 0.1 parts

The above materials were placed in a heated and dried two-necked flask, and nitrogen gas was introduced into the container to maintain an inert atmosphere, while the temperature was raised while stirring. A condensation polymerization reaction was then carried out at 150-230°C for approximately 13 hours, after which the pressure was gradually reduced to 210-250°C, yielding an amorphous polyester. The number average molecular weight (Mn) of the resulting amorphous polyester was 19,400, the weight average molecular weight (Mw) was 85,000, and the glass transition temperature (Tg) was 58°C.

(Production Example of Amorphous Resin Dispersion)
An amorphous resin particle dispersion was obtained in the same manner as in the preparation example of a crystalline polyester dispersion, except that the crystalline polyester was replaced with an amorphous polyester.

(Example of Production of Wax Dispersion)
The following materials were prepared:
Behenyl behenate (melting point 72° C.) 50.0 parts Anionic surfactant 0.3 parts (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Neogen RK)
・Ion-exchanged water 150.0 parts

The above was mixed and heated to 95°C, and dispersed using a homogenizer (Ultra Turrax T50, manufactured by IKA). It was then dispersed using a Manton-Gaulin high-pressure homogenizer (manufactured by Gaulin) to prepare a wax dispersion (solids concentration: 20% by mass) in which the wax particles were dispersed.

(Example of powder adhesive manufacturing)
The following materials were prepared:
Amorphous resin dispersion (solid content 20% by mass) 150.0 parts Crystalline polyester dispersion (solid content 20% by mass) 65.0 parts Wax dispersion (solid content 20% by mass) 20.0 parts

The above materials were added to a beaker, and the total amount of water was adjusted to 250 parts, after which the temperature was adjusted to 30.0°C. The materials were then mixed by stirring at 5000 rpm for 1 minute using a homogenizer (IKA Ultra Turrax T50).

Furthermore, 10.0 parts of a 2.0% by mass aqueous solution of aluminum chloride, a polyvalent metal compound, was gradually added as a flocculant. The raw material dispersion was transferred to a polymerization kettle equipped with a stirrer and a thermometer, and the mixture was heated to 50.0°C with a mantle heater and stirred to promote the growth of the flocculant particles.

After 60 minutes had passed, 200.0 parts of a 5.0% by mass aqueous solution of ethylenediaminetetraacetic acid (EDTA) was added to prepare an aggregated particle dispersion. Next, the pH of the aggregated particle dispersion was adjusted to 8.0 using a 0.1 mol/L aqueous solution of sodium hydroxide, and the aggregated particle dispersion was then heated to 80.0°C and left for 180 minutes to allow the aggregated particles to coalesce.

After 180 minutes, a powder adhesive particle dispersion liquid in which the powder adhesive particles were dispersed was obtained. After cooling to 40°C or less at a temperature drop rate of 300°C/min, the powder adhesive particle dispersion liquid was filtered and washed with ion-exchanged water to remove the powder adhesive particles. The obtained powder adhesive particles were dried in an oven at 40°C for 24 hours to obtain powder adhesive particles.

0.5 parts of sol-gel silica with a particle diameter of 100 nm and 0.8 parts of hydrophobic silica fine particles with a primary particle number average diameter of 12 nm treated with silicone oil and a BET specific surface area value of 120 m2/g were added to 100 parts of powder adhesive particles. Then, they were mixed using an FM mixer (manufactured by Nippon Coke & Engineering Co., Ltd.) to obtain a powder adhesive. The glass transition temperature of the obtained powder adhesive was 49°C and the weight average particle diameter was 5.8 μm.

In the powder adhesive obtained by the above method, the crystalline polyester acts as a plasticizer that imparts plasticity to the powder adhesive when heated. In other words, the crystalline polyester functions as the crystalline material of this embodiment. That is, when the powder adhesive, which is an aggregate of crystalline polyester and amorphous resin, is heated, the crystalline polyester melts and becomes compatible with the amorphous resin, which acts to facilitate deformation of the powder adhesive.

In the case of the powder adhesive of this embodiment, crystallization of the crystalline polyester does not occur even if the temperature of the adhesive drops to a temperature lower than the crystallization temperature of the wax in Example 1 (about 45°C) after the fixing process. In other words, when drawing the graph of Figure 12, the temperature at which the lines K and L become discontinuous is a lower value (for example, 5°C or lower). In this case, when the powder adhesive of this embodiment is used, the plasticity of the adhesive is maintained even if the surface temperature of the adhesive drops to room temperature after the fixing process. Therefore, the surfaces of the adhesive can be relatively easily bonded together during the folding process, and sufficient adhesive strength can be obtained while reducing the amount of heat supplied to the sheet in the bonding process.

In addition, in this embodiment, there is no need to provide a structure (a) to (d) above for retaining the heat supplied to the sheet in the fixing process, and sufficient adhesive strength can be obtained while reducing the amount of heat supplied to the sheet in the bonding process, which has the advantage of increasing design freedom. However, it is also possible to use a method for lowering the crystallization temperature of the crystalline material contained in the powder adhesive when the temperature is reduced in combination with a method for retaining the heat supplied to the sheet in the fixing process.

Other Embodiments
In the first and second embodiments, a film-type image heating device having excellent quick start properties is used as the first and second fixing devices 6 and 32, but the configuration of the image heating device is not limited to this. For example, an image heating device that heats the toner and powder adhesive on the sheet P via a heating roller that is in pressure contact with the pressure rollers 6b and 32a may be used as the first and/or second fixing devices 6 and 32. The heating roller is, for example, a metal cylinder having an elastic layer such as silicone rubber and a release layer such as fluororesin formed on its outer periphery. In addition, the nip forming unit in the film type is not limited to one in which the heater directly contacts the inner surface of the film, but may be configured such that the heater contacts the film via a sheet material having high thermal conductivity such as iron alloy or aluminum. In addition, the heating means is not limited to one using a heat generating resistor, but may be, for example, a halogen lamp or an induction heating mechanism.

1...Image forming device / 1e...Image forming means (image forming unit) / 6...Fixing means (first fixing device) / 31...Folding means (folding device) / 31a, 31b...Rotating body, roller member (first folding roller, second folding roller) / 32...Adhesive means (second fixing device) / Tn...Powder adhesive / Ty, Tm, Tc...Printing toner

Claims (7)

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 for heating the toner image formed on the sheet by the image forming unit to fix the toner image on the sheet;
A folding means for folding the sheet that has passed through the fixing means;
a bonding means for heating the sheet folded by the folding means to bond the sheet with the powder adhesive;
An image forming apparatus comprising:
a sheet conveying speed of the adhesive means is slower than a sheet conveying speed of the fixing means;
the folding means starts conveying the sheet toward the bonding means at a sheet conveying speed faster than the sheet conveying speed of the bonding means, and then reduces the sheet conveying speed to the sheet conveying speed of the bonding means before the leading edge of the sheet in the sheet conveying direction reaches the bonding means;
1. An image forming apparatus comprising: The folding means has a rotating body that rotates in contact with the sheet,
The ten-point average roughness Rzjis of the surface of the rotating body is 10 μm or more.
2. The image forming apparatus according to claim 1 , The folding means has a rotating body that rotates in contact with the sheet,
The rotating body has a hollow structure.
2. The image forming apparatus according to claim 1 , The rotating body is a roller member that rotates while clamping a sheet and conveys the sheet while folding the sheet so that the surface on which the powder adhesive is applied faces inward.
4. The image forming apparatus according to claim 2, wherein the image forming apparatus is a multi-color image forming apparatus. a cover portion provided above the folding means and the bonding means and covering the folding means and the bonding means when viewed in a gravity direction;
the cover portion is provided with an opening portion that communicates a space above the image forming apparatus with an internal space of the image forming apparatus;
The ratio of the opening area of the opening to the area of the cover portion as viewed in the direction of gravity is 5% or less.
5. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction. If the sheet conveying speed of the fixing means is V1 and the sheet conveying speed of the adhesive means is V2,
The sheet is conveyed at a speed of V1 from when the sheet passes through the fixing means until the sheet conveying speed of the folding means is decelerated,
the folding means decelerates a sheet conveying speed from V1 to V2 before a leading edge of the sheet in the sheet conveying direction reaches the bonding means;
6. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction . the powder adhesive contains a binder resin and a crystalline material that is compatible with the binder resin and melts when heated by the fixing means;
the folding means folds the sheet in a state in which a surface temperature of the powder adhesive, which has been applied to the sheet and then heated by the fixing means, is higher than a crystallization temperature of the crystalline material during cooling;
7. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction.

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