Coating film forming method, charging roller manufacturing method, and coating film forming apparatus

Abstract

To provide a coating film forming method capable of forming a coating film free from a mottled pattern.SOLUTION: A coating film forming method for forming a coating film by discharging droplets of a coating liquid to a cylindrical member to be coated by a liquid discharger in which a plurality of nozzles are arranged, the method comprising: discharging droplets from the liquid discharger while moving the liquid discharger in an axial direction of the member to be coated so that an arrangement direction of the nozzles becomes an axial direction of the member to be coated; The liquid discharge means is moved a plurality of times between one end side and the other end side of the member to be coated, and in one movement of the liquid discharge means from the one end side to the other end side or from the other end side to the one end side of the member to be coated, a gradient in which a thickness of a coating film decreases from a coating start position toward a coating end position on the member to be coated is formed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a coating film forming method, a method for manufacturing a charging roller, and a coating film forming apparatus. [Background technology]

[0002] Known coating film forming devices for forming coating films include those equipped with a liquid ejection means (droplet ejection means) such as a liquid ejection head (droplet ejection head). Such coating film forming devices can apply liquid to a target area by controlling the ejected droplets.

[0003] For example, a coating device that forms a coating film by ejecting droplets onto a cylindrical substrate is known (Patent Document 1). In Patent Document 1, the ejection of droplets is controlled in order to eliminate unevenness in film thickness near the boundary between the coated and non-coated areas. Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, to improve productivity, a coating film has been formed by ejecting droplets on the forward and backward movements of a liquid ejection head. However, with this conventional technology, the second coating is performed before the coating film has sufficiently dried, causing the applied droplets to be repelled, resulting in mottled patterns and preventing the formation of a good coating film.

[0005] An object of the present invention is to provide a method for forming a coating film that is capable of forming a coating film without mottling. [Means for solving the problem]

[0006] In order to solve the above problems, the coating film forming method of the present invention is a coating film forming method in which droplets of a coating liquid are ejected onto a cylindrical coated member using a liquid ejection means having a plurality of nozzles arranged thereon, and droplets are ejected from the liquid ejection means while the liquid ejection means is moved in the axial direction of the coated member so that the arrangement direction of the nozzles is the axial direction of the coated member, and the liquid ejection means is moved multiple times between one end side and the other end side of the coated member, and in each movement of the liquid ejection means from one end side to the other end side or from the other end side to one end side of the coated member, a gradient is formed in which the thickness of the coating film decreases from the coating start position to the coating end position on the coated member. [Effects of the Invention]

[0007] According to the present invention, a coating film forming method capable of forming a coating film without mottled patterns can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram for explaining one embodiment of the present invention, illustrating an example of a first application. [Figure 2] FIG. 2 is a schematic plan view illustrating an example of a nozzle arrangement. [Figure 3] FIG. 1 is a schematic diagram for explaining one embodiment of the present invention, and is a diagram for explaining an example of a second application. [Figure 4] FIG. 2 is a block diagram illustrating an example of a control unit. [Figure 5] FIG. 1 is a schematic diagram for explaining Comparative Example 1. [Figure 6] 1A is a schematic side view and FIG. 1B is a schematic cross-sectional view illustrating an example of a charging roller. DETAILED DESCRIPTION OF THE INVENTION

[0009] The coating film forming method, charging roller manufacturing method, and coating film forming apparatus according to the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the following embodiments, and other modifications, additions, corrections, deletions, and other changes can be made within the scope of what a person skilled in the art can conceive. Any embodiment is within the scope of the present invention as long as it achieves the functions and effects of the present invention.

[0010] (Coating film forming method and coating film forming device) The coating film forming method of the present invention is a coating film forming method in which droplets of a coating liquid are ejected onto a cylindrical coated member using a liquid ejection means having a plurality of nozzles arranged thereon, and droplets are ejected from the liquid ejection means while moving the liquid ejection means in the axial direction of the coated member so that the arrangement direction of the nozzles is the axial direction of the coated member, and the liquid ejection means is moved multiple times between one end side and the other end side of the coated member, and in each movement of the liquid ejection means from one end side to the other end side or from the other end side to one end side of the coated member, a gradient is formed in which the thickness of the coating film decreases from the coating start position to the coating end position on the coated member.

[0011] The coating film forming apparatus of the present invention comprises a liquid ejection means having a plurality of nozzles arranged therein, a holding unit for holding a cylindrical coated member, and a control unit, wherein the liquid ejection means ejects droplets of coating liquid onto the coated member to form a coating film, and the control unit ejects droplets from the liquid ejection means while moving the liquid ejection means in the axial direction of the coated member so that the arrangement direction of the nozzles is the axial direction of the coated member, and moves the liquid ejection means between one end side and the other end side of the coated member multiple times, and controls the liquid ejection means to form a gradient in the thickness of the coating film decreasing from the coating start position to the coating end position on the coated member in each movement of the liquid ejection means from one end side to the other end side or from the other end side to the one end side of the coated member.

[0012] The coating film forming method may be referred to as a coating method, a liquid ejection method, a coating film production method, etc. The coating film forming apparatus may be referred to as a coating apparatus, a liquid ejection apparatus, a coating film production apparatus, etc. Furthermore, the coated member may be referred to as a coated object, an ejection target, etc. The liquid ejection means may be referred to as a droplet ejection means, an ejection means, etc. As the liquid ejection means, for example, a liquid ejection head is used. The cylindrical shape may be referred to as a columnar shape, etc. One movement of the liquid ejection means from the coating start position to the coating end position may be referred to as one scan. The ejection of droplets of the coating liquid from the coating start position to the coating end position by one scan may be referred to as coating. The coating liquid may be referred to as a liquid, a liquid composition, an ejection liquid, a coating liquid, a coating liquid, etc.

[0013] In the present invention, a gradient is formed in which the thickness of the coating film decreases from the coating start position to the coating end position during one movement of the liquid discharge means. In one coating, the thickness of the coating film at the coating end position is smaller than the thickness of the coating film at the coating start position, so the coating film surface at the coating end position is dry immediately after the first coating is completed. Therefore, when a coating film is formed by discharging droplets on the outward and return paths of the liquid discharge means, even if a second coating is performed immediately after the first coating, the discharged droplets are properly leveled, and mottled patterns on the coating film surface are improved.

[0014] FIG. 1 is a schematic diagram illustrating an example of the present invention. The direction of movement of the liquid ejection head 1 is the main scanning direction. The white arrow in the figure indicates the direction of movement of the liquid ejection head 1. The figure illustrates one application of the liquid ejection head 1, and the time series is indicated by (a), (b), and (c). FIG. 1 also shows the first application of the liquid ejection head 1.

[0015] The movement direction of the liquid ejection head 1 is the nozzle arrangement direction, which is the axial direction of the coated member 3. In other words, in this embodiment, the liquid ejection head 1 is moved in the axial direction of the coated member 3 so that the nozzle arrangement direction coincides with the axial direction of the coated member 3. The axial direction may also be referred to as the rotation axis direction, etc. As shown in the figure, one position on the coated member 3 in the movement direction of the liquid ejection head 1 is the application start position, and another position is the application end position.

[0016] In this embodiment, the movement of the liquid ejection head 1 is described as movement from the application start position side to the application end position side. The liquid ejection head 1 is not limited to a form in which it moves only between the application start position and the application end position, but may also move in an area outside the application start position and the application end position. In other words, in one movement, the liquid ejection head 1 may start moving before the application start position, or may move past the application end position. To express this, the descriptions "application start position side" and "application end position side" are used.

[0017] Fig. 2 is a schematic plan view showing an example of the nozzle surface of the liquid ejection head 1. A plurality of nozzles 12 are arranged on the nozzle surface, and the direction in which the nozzles 12 are arranged is the nozzle arrangement direction. The nozzle arrangement direction is the same as the main scanning direction shown in Fig. 1. The figure shows two nozzle rows in which the nozzles 12 are arranged, but the present invention is not limited to this, and the number of nozzle rows may be changed as appropriate.

[0018] As shown in Figure 1, the liquid ejection head 1 ejects droplets 4 onto the workpiece 3 from the application start position while moving in the main scanning direction, and finishes ejecting at the application end position. More specifically, the nozzle that reaches the application start position starts ejecting droplets, and the nozzle that reaches the application end position finishes ejecting droplets. After one application by the liquid ejection head 1 is completed, a coating film 5 is formed.

[0019] As shown in the figure, the coating film 5 formed by one coating has a gradient such that the thickness of the coating film decreases from the coating start position to the coating end position. Forming such a gradient may also be referred to as giving the coating film a gradient. Forming such a gradient may also be referred to as the coating film having a gradient.

[0020] Because the thickness of the coating film at the end of coating is thinner than the thickness at the start of coating, the surface of the coating is dry immediately after the first coating is completed, and the discharged liquid is properly leveled (smoothed) even if the second coating (next coating) is performed immediately. This prevents the formation of mottled patterns on the coating surface, resulting in a coating film with a good surface shape. Furthermore, productivity can be improved because the next coating can be performed immediately.

[0021] On the other hand, when the coating thickness is the same at the coating start position and the coating end position, as in Comparative Example 1 described below, the coating surface near the coating end position is not dry at the end of the first coating, and when the second coating is performed, the ejected droplets are repelled, resulting in incorrect leveling and the formation of mottled patterns on the coating surface.

[0022] The thickness of the coating film can be selected as appropriate. For example, in the example shown in Figure 1, after one coating is completed, the thickness of the coating film at the coating start position is 3.5 μm and the thickness at the coating end position is 1.5 μm.

[0023] In the coating film formed in a single movement of the liquid ejection means (e.g., liquid ejection head 1) from the coating start position to the coating end position, it is preferable that the thickness of the coating film at the coating start position is 3 μm or more and 4 μm or less, and the thickness of the coating film at the coating end position is 1 μm or more and 2 μm or less. In this case, a sufficient gradient of decreasing film thickness can be formed, and by forming a gradient of decreasing film thickness, the return pass can be started immediately after the end of the forward pass. This shortens the time from the end to the start of painting, preventing the nozzles of the droplet ejection head from drying out and suppressing ejection problems.

[0024] Whether or not the formed coating film has a gradient can be confirmed using a known measuring device. For a coating film formed by the first coating, the gradient can be confirmed by measuring after the first coating is completed. For a coating film formed by the second coating, the thickness of the coating film formed by the first coating can be measured and confirmed by subtracting the first thickness from the total thickness of the coating film after the second coating is completed. This is not limited to this, and even if the thickness formed by the first coating has not been measured, it is also possible to measure the thickness of the coating film formed by the second coating by measuring the coating film after the second coating is completed. The same applies to the third coating and beyond. In other words, the thickness of the coating film formed by the Nth coating can be measured.

[0025] In this embodiment, the thickness of the coating film formed by one application has a gradient, so that not only the coating film formed by the first application, but also the coating films formed by the second application etc. have a gradient. The gradient of the thickness of the coating film may be continuous or discontinuous.

[0026] In this embodiment, the liquid ejection means (e.g., liquid ejection head 1) is moved multiple times between the application start position and the application end position, and application is performed during each movement, forming a coating film at one scanning location. In other words, the liquid ejection head 1 moves (scans) the same scanning location on the coated member multiple times, performing multiple coatings. As a result, a coating film is formed at one scanning location on the coated member. After a coating film is formed at one scanning location, the coated member is, for example, rotated, and the liquid ejection head 1 applies coating to another scanning location on the coated member. Both a coating film formed in one coating run and a coating film formed as a whole through multiple coating runs are referred to as a coating film. A coating film formed in one coating run is referred to, for example, as a coating film formed in the first coating run. The number of times the liquid ejection head is moved (scanned) is not particularly limited and can be selected appropriately.

[0027] In this embodiment, in the next application, the application start position and application end position are reversed from those of the previous application. In other words, the liquid ejection head 1 moves back and forth in the scanning direction, ejecting droplets onto the coated member 3 in both the forward and backward movements. Therefore, the application start position in the next application is the application end position in the previous application, and the application end position in the next application is the application start position in the previous application. By doing this, the total coating film obtained after multiple scans has no or only a small thickness deviation between one end and the other end. Also, in this embodiment, the thickness of the coating film at the coating end position during one movement of the liquid ejection head 1 is smaller than the thickness of the coating film at the coating end position, so the coating film at the coating end position is dry after the movement, and even if the next coating is performed immediately on the return pass, it is possible to prevent the droplets from being repelled.

[0028] In this embodiment, when one movement of the liquid discharge means from one end side to the other end side or from the other end side to one end side of the member to be coated is considered to be one scan, the coating end position in the previous scan becomes the coating start position in the next scan, and the coating start position in the previous scan becomes the coating end position in the next scan. This prevents the occurrence of mottled patterns on the coating surface and improves productivity. Furthermore, the total coating film obtained after multiple movements (scans) can be prevented from being unevenly thick at one end of the coated member and thin at the other end.

[0029] In this embodiment, it is preferable to rotate the coating target member while scanning the liquid ejection means to eject droplets. By doing so, productivity can be improved. There are no particular restrictions on the method for rotating the coating target member, and any driving means can be used, for example.

[0030] Fig. 3 is a schematic diagram for explaining an example of the second coating in this embodiment. Fig. 3 is a diagram similar to Fig. 1, and the explanation within the figure will be omitted here. As can be seen by comparing Fig. 1 and Fig. 3, in the second coating shown in Fig. 3, the liquid ejection head 1 moves in the opposite direction to the first coating to eject droplets of the coating liquid. The coating film formed in the second coating is indicated by the reference numeral 6.

[0031] If the first coating is the outgoing path, the second coating is the returning path. In this embodiment, coating (discharging droplets) is performed on the outgoing path and the returning path of the movement of the liquid ejection head 1. As described above, in one movement of the liquid ejection head 1, the thickness of the coating film at the coating end position is smaller than the thickness of the coating film at the coating start position, so the surface of the coating film at the coating end position is more likely to dry. Therefore, even if coating on the returning path is started immediately after coating on the outgoing path is completed, it is possible to prevent droplets from being repelled by the coating film surface at the coating end position on the outgoing path, and prevent the occurrence of mottled patterns.

[0032] Furthermore, the coating film formed by the first and second coatings is thicker at the coating end position and thinner at the coating end position, and the coating start position and coating end position are reversed between the first and second coatings. As shown in the figure, the total coating film obtained in this way can be a coating film with no or only small thickness deviation between one end and the other end.

[0033] The method for providing the gradient can be selected as appropriate. For example, a method of thinning out the amount of droplets to be ejected can be used. Thinning out the amount of droplets to be ejected also corresponds to reducing the amount of droplets to be ejected. In one example of this embodiment, the number of droplets ejected from one nozzle in the liquid ejection means is reduced from the application start position toward the application end position. This allows the coating film to have a gradient in thickness that decreases from the coating start position to the coating end position. Also, by controlling the number of droplets to be reduced, the control can be prevented from becoming complicated.

[0034] When the number of droplets ejected from one nozzle of the liquid ejection means is reduced from the application start position toward the application end position, the number of droplets to be reduced should be increased. In other words, it is preferable to gradually reduce the number of droplets ejected from one nozzle from the application start position toward the application end position. This makes it possible to make the gradient gentler and to make the coating surface flatter.

[0035] An example of a method for thinning out droplets will now be described. In the example shown in Figure 1, the number of droplets ejected from one nozzle is reduced; for example, control is performed to thin out the number of droplets that had been ejected from two to one droplet. Figure 1 shows that the ejection of two droplets has been thinned out to one droplet. The dashed circle in the figure schematically shows the thinned droplets.

[0036] As shown in (a), droplets are not thinned out from nozzles that have reached the coating start position in the coating area. As shown in (b), droplets are thinned out from nozzles that have passed the coating start position. As shown in (c), droplet ejection is stopped from nozzles that have reached the coating end position. By controlling in this way, a gradient can be created in the thickness of the coating film that is formed, and the thickness of the coating film decreases from the coating start position to the coating end position.

[0037] In the example shown in FIG. 1, the range for thinning out droplets at location (b) can be selected as appropriate. For example, a thinning range of 100% is preferable. Specifically, the thinning range refers to the thinning range within the coating area, and a thinning range of 100% refers to the entire area from the coating start position to the coating end position in the coating area. Note that a thinning range of 50% means that, assuming the coating area is 100 mm, thinning out droplets begins 50 mm from the coating start position in the coating area.

[0038] In this embodiment, it is preferable that the coating area in the first scan is the same as the coating area in the second and subsequent scans. It is also preferable that the thinning range in the first scan is the same as the thinning range in the second and subsequent scans. In this case, quality can be improved.

[0039] In Figure 1, for ease of explanation, the droplets are thinned from two to one, but the method of thinning can be selected as appropriate. To create a gradient in the coating film, it is preferable to increase the amount of droplets thinned from the coating start position to the coating end position. In other words, the droplets discharged are gradually reduced as described above. For example, for droplets discharged from a certain nozzle, no thinning is performed at point (a), and at point (b), the amount of thinning is increased, such as thinning from two to one drop, thinning from three to one drop, thinning from four to one drop, and so on. Then, droplet discharge stops at point (c).

[0040] In addition to the above, another method for forming a gradient is to reduce the amount of each droplet (volume of the droplet) ejected. The volume of the droplet is gradually reduced from the application start position to the application end position. This method also allows a gradient to be formed in the film thickness of the coating film.

[0041] The coating film formed may be a single layer or multiple layers. When multiple layers are formed, for example, after the first coating film is formed, a coating liquid different from the coating liquid used to form the first coating film is ejected onto the coated member. When multiple layers are formed, one liquid ejection head may eject multiple types of coating liquid, or multiple liquid ejection heads may each eject a different coating liquid.

[0042] Next, the control unit of the coating / forming apparatus will be described with reference to the block diagram of Fig. 4. The coating / forming apparatus of this embodiment includes a liquid discharge means having a plurality of nozzles arranged therein, and a control unit. The control unit controls the liquid discharge means and the like to form the coating film gradient as described above.

[0043] The control unit 40 includes a microcomputer or the like consisting of a CPU, ROM, RAM, I / O, etc., and controls the entire coating and forming apparatus. The control unit 40 outputs a discharge signal to the liquid discharge head 1 to cause droplets to be discharged from the nozzles 12 of the liquid discharge head 1, and also controls the movement of the liquid discharge head 1 by issuing a move / stop command to the single-axis actuator 15.

[0044] The control unit 40 has a coating area storage unit 42 that stores information regarding the coating start position and coating end position, which are the coating boundaries for each coating target member 3. The coating start position and coating end position are determined by the movement amount of the liquid ejection head (count value of counter 41) based on a predetermined coating start standby position.

[0045] The liquid ejection head 1 is moved by a single-axis actuator 15 in a direction along the nozzle arrangement direction (main scanning direction) parallel to the axis of the coating target member 3. A pulse signal is output from an encoder 16 in accordance with the movement of the liquid ejection head 1. The control unit 40 has a counter 41 that counts the pulse signals from the encoder 16.

[0046] The control unit 40 has a discharge table 43 that tabulates information about the amount of droplets to be discharged according to the head position (head movement amount) for each nozzle 12 of the liquid discharge head 1, and outputs a discharge signal to the liquid discharge head 1 in accordance with the discharge table 43. By performing control in this manner, it is possible to thin out the droplets.

[0047] Although not shown in FIG. 1 , the coating film forming apparatus of the present invention has a holding part for holding a cylindrical substrate 3. The holding part is not particularly limited and can be selected as appropriate. If the substrate 3 has a protruding axis, the holding part holds the axis. The substrate 3 is not limited to this and may be hollow. For example, the holding part may be inserted into the hollow interior to hold the substrate 3. The coating film forming apparatus of the present invention may also have other components as needed, such as a drive means for rotating the substrate. An example of the drive means is a drive motor. The coating film forming apparatus includes a holding part and a drive means, and a control unit controls the drive means to rotate the substrate, thereby efficiently forming a coating film on the coating area of ​​the substrate.

[0048] Next, a description will be given of Comparative Example 1. Fig. 5 is a schematic diagram for explaining Comparative Example 1, and is a diagram similar to Fig. 1.

[0049] As shown in (a), droplets are ejected in order from the nozzle that has reached the coating start position in the coating area. As shown in (b) and (c), in Comparative Example 1, droplets are not thinned out, and the same amount of droplets is ejected uniformly from the coating start position to the coating end position. In Comparative Example 1, the ejection of droplets from the coating start position to the coating end position is repeated four times. In Comparative Example 1, for example, a coating film with a thickness of 2.5 μm is formed in one coating, and by repeating this four times, a coating film with a thickness of 10±3 μm is formed.

[0050] In Comparative Example 1, the thickness of the coating film does not have a gradient, and is the same from the coating start position to the coating end position. In Comparative Example 1, the liquid ejection head ejects only droplets and does not dry, so the coating film does not dry quickly. Therefore, when the second ejection begins after the first ejection by the liquid ejection head is completed, the surface of the coating film near the end of the first application is not dry, and the droplets ejected in the second application are repelled, resulting in improper leveling. This results in the occurrence of mottled patterns on the surface of the coating film. When mottled patterns occur on the surface of the coating film, the thickness of the coating film is not uniform, resulting in a mixture of thick and thin areas. When thick film areas occur due to mottled patterns, the charging roller becomes more susceptible to contamination, which may result in abnormal images.

[0051] To address this issue, one possible solution is to set a waiting time until the surface of the coating near the end of coating dries, in order to prevent mottling on the surface of the coating. However, setting a waiting time in this manner increases the time required for manufacturing. Furthermore, the waiting time can cause the nozzles of the liquid ejection head to dry, resulting in ejection problems, such as missing droplets. However, the present invention can solve these problems.

[0052] (Method of manufacturing the charging roller) Next, a method for producing the charging roller of the present invention will be described. The method for producing a charging roller of the present invention is characterized in that a charging roller for use in an electrophotographic image forming apparatus is produced using the coating film forming method of the present invention. According to the method for producing a charging roller of the present invention, it is possible to prevent the occurrence of mottled patterns in the coating film and produce a charging roller of good quality. The charging roller obtained by the present invention has good quality, and is therefore capable of charging a photoreceptor (which may also be called an image carrier, etc.) well.

[0053] In the method for manufacturing a charging roller of the present invention, the layer of the charging roller is formed by the coating film forming method of the present invention. The layer of the charging roller is a coating film, but for the sake of explanation, the layer and the coating film may be described separately here.

[0054] The coating film forming apparatus of the present invention described above may be used as a charging roller manufacturing apparatus.

[0055] As explained above, the coating film forming method of the present invention forms a gradient in which the coating film thickness decreases from the coating start position to the coating end position during one movement of the liquid discharge means. This allows the coating film at the coating end position to be dried before the next coating film is formed, preventing mottled patterns from occurring in the coating film. Therefore, by manufacturing a charging roller using the coating film forming method of the present invention, mottled patterns in the layer of the charging roller are suppressed, resulting in good quality.

[0056] When the charging roller obtained by the present invention is used in an image forming apparatus, the charging roller may be of a contact type or a non-contact type, but it is assumed that the charging roller rotates in contact with the photosensitive member to charge the photosensitive member. The layer of the charging roller obtained by the present invention does not produce a spotted pattern, so that the charging roller can exhibit good charging performance even when used in contact with the photosensitive member.

[0057] The charging roller obtained by the present invention may be directly provided in an image forming apparatus or may be provided in a process cartridge. The process cartridge is detachably provided in the image forming apparatus. Even when the charging roller is provided in a process cartridge, it is included in the use in an electrophotographic image forming apparatus.

[0058] The layer structure of the charging roller is not particularly limited and can be selected appropriately. The layer (coating film) of the charging roller may be a single layer or multiple layers. In the case of multiple layers, the layers can be selected appropriately, and examples thereof include a resistance adjustment layer and a protective layer.

[0059] An embodiment of the method for producing a charging roller of the present invention will be described. In this embodiment, the charging roller has a conductive support, a resistance adjustment layer formed on the conductive support, and a protective layer formed on the resistance adjustment layer, and the coated member has the conductive support and the resistance adjustment layer, and the protective layer is formed by the coating film forming method of the present invention. According to this embodiment, a charging roller capable of performing good charging can be formed.

[0060] The conductive support may be, for example, a metal, and an example of the metal may be stainless steel.

[0061] The resistance adjustment layer includes, for example, a conductive material, a thermoplastic resin, and an elastomer. Examples of conductive materials include polymeric ion conductive materials. Examples of thermoplastic resins include general-purpose resins such as polyethylene, polypropylene, polymethyl methacrylate, polystyrene, and copolymers thereof. The resistance adjustment layer is manufactured by, for example, injection molding or extrusion molding.

[0062] The protective layer contains, for example, a thermosetting resin. Examples of thermosetting resins include acrylic silicone and fluororesin. Fluororesins, such as polyvinylidene fluoride, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene / hexafluoropropylene copolymer, polyamide, polyester, polypropylene, and the like, are preferred because of their excellent toner adhesion resistance. The protective layer may contain conductive particles, as needed, and examples of the conductive particles that can be used include carbon black, metal powder, metal oxide, and the like. The protective layer provides conductivity and contamination resistance.

[0063] The member to be coated when manufacturing a charging roller can be selected appropriately, and may be, for example, a conductive support on which no other layers are formed, or a conductive support on which other layers are formed. As in this embodiment, the member to be coated when manufacturing a charging roller preferably has a conductive support and a resistance adjustment layer. When the member to be coated has a conductive support and a resistance adjustment layer, it does not need to be strictly cylindrical, as long as it is approximately cylindrical.

[0064] The image forming apparatus in which the charging roller obtained by the present invention is used is not particularly limited, and known apparatuses can be used. The image forming apparatus may be of an electrophotographic type, and may have a photoreceptor (which may also be referred to as an image carrier, etc.) that is the target of charging by the charging roller. In an electrophotographic image forming apparatus, the photoreceptor is charged by a charging member (e.g., a charging roller), exposed by an exposure unit, and developed by a developing unit that supplies toner. The toner image formed by development is transferred to an intermediate transfer member or a recording medium by a transfer unit, and fixed by a fixing unit, if necessary.

[0065] 6A and 6B are diagrams illustrating an example of a charging roller obtained by the present invention, where (A) is a schematic side view and (B) is a schematic cross-sectional view. The charging roller 20 of this example has a conductive support 21, a gap retaining member 22, a protective layer 23, and a resistance adjusting layer 24. The gap retaining member 22 is, for example, insulating, and has the function of retaining the resistance adjusting layer 24 and the protective layer 23. The resistance adjusting layer 24 is formed on the conductive support 21, and the protective layer 23 is formed on the resistance adjusting layer 24. In this example, the resistance adjusting layer 24 is formed by, for example, injection molding or extrusion molding, and the protective layer 23 is formed by the coating film forming method of the present invention.

[0066] For example, aspects of the present invention are as follows. <1> A coating film forming method for forming a coating film by discharging droplets of a coating liquid onto a cylindrical coating target member using a liquid discharging means having a plurality of nozzles arranged thereon, Droplets are ejected from the liquid ejection means while moving the liquid ejection means in the axial direction of the member to be coated so that the arrangement direction of the nozzles coincides with the axial direction of the member to be coated, and the liquid ejection means is moved multiple times between one end side and the other end side of the member to be coated, and a gradient is formed in which the thickness of the coating film decreases from the coating start position to the coating end position on the member to be coated in one movement of the liquid ejection means from one end side to the other end side or from the other end side to the one end side of the member to be coated. A coating film forming method characterized by: <2> In the coating film formed by a single movement of the liquid discharge means from one end side to the other end side of the coated member or from the other end side to one end side, the thickness of the coating film at the coating start position is 3 μm or more and 4 μm or less, and the thickness of the coating film at the coating end position is 1 μm or more and 2 μm or less. Characterized by <1> The coating film forming method according to claim 1. <3> The number of droplets discharged from one nozzle of the liquid discharge means is reduced from the application start position toward the application end position. Characterized by <1> or <2> The coating film forming method according to claim 1. <4> <1> from <3> 2. A charging roller for use in an electrophotographic image forming apparatus is manufactured using the coating film forming method according to any one of claims 1 to 11. Charging roller manufacturing method. <5> the charging roller has a conductive support, a resistance adjusting layer formed on the conductive support, and a protective layer formed on the resistance adjusting layer; the member to be coated has the conductive support and the resistance adjusting layer, The protective layer is <1> from <3> The coating film is formed by the coating film forming method according to any one of Characterized by <4> 10. A method for manufacturing the charging roller according to claim 9. <6> The liquid ejection device includes a liquid ejection means having a plurality of nozzles arranged therein, a holding unit for holding a cylindrical member to be coated, and a control unit. the liquid ejection means ejects droplets of the coating liquid onto the member to be coated to form a coating film; The control unit causes the liquid discharge means to discharge droplets while moving the liquid discharge means in the axial direction of the member to be coated so that the arrangement direction of the nozzles coincides with the axial direction of the member to be coated, and moves the liquid discharge means between one end side and the other end side of the member to be coated a plurality of times, and performs control to form a gradient in which the thickness of the coating film decreases from the coating start position to the coating end position on the member to be coated in one movement of the liquid discharge means from one end side to the other end side or from the other end side to the one end side of the member to be coated. A coating film forming apparatus characterized by: [Explanation of symbols]

[0067] 1 Liquid ejection head 3 Part to be coated 5 Coating 40 Control Unit [Prior art documents] [Patent documents]

[0068] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-013283

Claims

1. A coating film forming method for forming a coating film by discharging droplets of a coating liquid onto a cylindrical coating target member using a liquid discharging means having a plurality of nozzles arranged thereon, Droplets are ejected from the liquid ejection means while moving the liquid ejection means in the axial direction of the member to be coated so that the arrangement direction of the nozzles coincides with the axial direction of the member to be coated, and the liquid ejection means is moved multiple times between one end side and the other end side of the member to be coated, and a gradient is formed in which the thickness of the coating film decreases from the coating start position to the coating end position on the member to be coated in one movement of the liquid ejection means from one end side to the other end side or from the other end side to the one end side of the member to be coated. A coating film forming method characterized by:

2. In the coating film formed by a single movement of the liquid discharge means from one end side to the other end side of the coated member or from the other end side to one end side, the thickness of the coating film at the coating start position is 3 μm or more and 4 μm or less, and the thickness of the coating film at the coating end position is 1 μm or more and 2 μm or less.

2. The method for forming a coating film according to claim 1.

3. The number of droplets discharged from one nozzle of the liquid discharge means is reduced from the application start position toward the application end position.

2. The method for forming a coating film according to claim 1.

4. 4. A method for producing a charging roller for use in an electrophotographic image forming apparatus, using the coating film forming method according to claim 1. Charging roller manufacturing method.

5. the charging roller has a conductive support, a resistance adjusting layer formed on the conductive support, and a protective layer formed on the resistance adjusting layer; the member to be coated has the conductive support and the resistance adjusting layer, The protective layer is formed by the coating film forming method according to any one of claims 1 to 3.

5. The method for manufacturing a charging roller according to claim 4.

6. The liquid ejection device includes a liquid ejection means having a plurality of nozzles arranged therein, a holding unit for holding a cylindrical member to be coated, and a control unit. the liquid ejection means ejects droplets of the coating liquid onto the member to be coated to form a coating film; The control unit causes the liquid discharge means to discharge droplets while moving the liquid discharge means in the axial direction of the member to be coated so that the arrangement direction of the nozzles coincides with the axial direction of the member to be coated, and moves the liquid discharge means between one end side and the other end side of the member to be coated a plurality of times, and performs control to form a gradient in which the thickness of the coating film decreases from the coating start position to the coating end position on the member to be coated in one movement of the liquid discharge means from one end side to the other end side or from the other end side to the one end side of the member to be coated. A coating film forming apparatus characterized by:

Images