Sponge, fixing roller, fixing device, and image formation device

Abstract

To provide sponge that has small compressive set when being compressed under high temperature and can sufficiently improve fixation property of a toner image when being used for a fixing roller, and to provide a fixing roller including the sponge, a fixing device, and an image formation device.SOLUTION: Sponge with a void ratio of 45% or more and 60% or less has a Young's modulus of 35kPa or more and 80kPa or less that is measured when being compressed so that a compression rate becomes 30% at 180°C according to JIS K 7181.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a sponge, a fixing roller, a fixing device, and an image forming apparatus.

Background Art

[0002] It is known that a sponge manufactured by foaming an elastomer such as rubber to form a large number of voids can be used for various applications.

[0003] For example, Patent Document 1 discloses a vibration isolator obtained by foaming a rubber composition containing ethylene-propylene-diene rubber, which contains a specific amount of sulfur atoms and has a Young's modulus at 23°C of 6.0×10 5 Pa or less.

[0004] Also, for example, Patent Document 2 discloses a conductive roll including a cylindrical elastic foam and an elastic layer having a Young's modulus of 150 kPa or less. In Patent Document 2, it is stated that the conductive roll can be used for a transfer device in an image forming apparatus.

[0005] Also, for example, Patent Document 3 discloses a heat insulating roll including a mandrel and a roller portion that is integrated around the mandrel and is a molded body made of a water-curable composition. In Patent Document 3, it is stated that the cured product of the water-curable composition can be porous, and the heat insulating roll can be used for a fixing roller or the like in an image forming apparatus.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

[0007] By the way, since stress relaxation is required for packings using sponges, etc., it is desirable that the sponge has a property of easily returning to its original shape after being compressed at high temperature (low compression set).

[0008] In addition, since the sponge has a low heat capacity, from the viewpoint of energy saving, as described in Patent Document 3, the sponge may be used for a fixing roller for a toner fixing device. At this time, it is desirable to form an image with sufficiently enhanced fixability using a fixing roller including the sponge.

[0009] An object of the present invention is to provide a sponge having a small compression set when compressed at high temperature and capable of sufficiently enhancing the fixability of a toner image when used for a fixing roller, a fixing roller including the sponge, a fixing device, and an image forming apparatus. [Means for Solving the Problems]

[0010] One aspect of the present invention for achieving the above object relates to the sponges of the following [1] to [7]. [1] A sponge having a porosity of 45% or more and 60% or less, The Young's modulus measured under the condition of being compressed so that the compression ratio becomes 30% at 180° C. in accordance with the measurement method of JIS K 7181 (2011) is 35 kPa or more and 80 kPa or less, Sponge. [2] The sponge according to [1], wherein the Young's modulus is 40 kPa or more and 70 kPa or less. [3] The content of voids having a diameter of 4 μm or less is 5% by volume or more and 20% by volume or less with respect to the total volume of the voids contained in the sponge, The content of voids having a diameter exceeding 4 μm and less than 60 μm is 80% by volume or more and 95% by volume or less with respect to the total volume, [1] or [2] The sponge according to [1] or [2]. [4] The content of voids with a diameter of 4 μm or less is 10% by volume or more and 15% by volume or less with respect to the total volume of voids contained in the sponge. The content of voids with a diameter exceeding 4 μm and less than 60 μm is 85% by volume or more and 90% by volume or less with respect to the total volume. [1] The sponge according to any one of [1] to [3]. [5] The material of the sponge is fluororubber or silicone rubber. The sponge according to any one of [1] to [4]. [6] The fluororubber or the silicone rubber has a tensile strength of 5.0 MPa or more. The sponge according to [5]. [7] The sponge according to any one of [1] to [6], having a thickness of 2.0 mm or more.

[0011] Another aspect of the present invention for achieving the above object relates to the fixing roller of the following [8] to [9]. [8] A fixing roller including the sponge according to any one of [1] to [7]. [9] The fixing roller according to [8], having a diameter of 50 mm or more.

[0012] Another aspect of the present invention for achieving the above object relates to the fixing device of the following

[10] to

[11] .

[10] A fixing device including the fixing roller according to [8] or [9].

[11] The fixing device according to

[10] , having a drive unit for adjusting the linear velocity of the fixing roller to 340 mm / s or more.

[0013] Another aspect of the present invention for achieving the above object relates to the image forming apparatus of the following

[12] .

[12] An image forming apparatus including the fixing device according to

[10] or

[11] . [Advantages of the Invention]

[0014] According to the present invention, there are provided a sponge having a small compression set when compressed at a high temperature and capable of sufficiently enhancing the fixing property of a toner image when used for a fixing roller, a fixing roller including the sponge, a fixing device, and an image forming apparatus.

Brief Description of Drawings

[0015]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0016] 1. Sponge <Configuration of Sponge> The sponge according to the present embodiment has a porosity of 45% or more and 60% or less, and a Young's modulus measured when compressed to a compression ratio of 30% at 180° C. in accordance with JIS K 7181 is 35 kPa or more and 80 kPa or less. In this specification, the “porosity” refers to the ratio of the total volume of voids contained in the sponge to the total volume of the sponge. In the above sponge, the compression set of the sponge when compressed at a high temperature can be reduced.

[0017] Specifically, when the porosity is 45% or more, the amount of air contained in the sponge increases, so that the sponge is likely to return to its original shape after being compressed. Further, when the porosity is 60% or less, it is possible to suppress a decrease in the amount of resin contained in the sponge. Thereby, since a decrease in the elastic force of the sponge can be suppressed, the sponge is likely to return to its original shape after being compressed.

[0018] Furthermore, in the measurement method of JIS K 7181 (2011) for the sponge, the Young's modulus (hereinafter simply referred to as "Young's modulus") measured under the condition of compression at 180°C such that the compression ratio becomes 30% is 35 kPa or more and 80 kPa or less, so that the compression set (hereinafter simply referred to as "compression set") when the sponge is compressed at high temperature can be reduced. Specifically, since the Young's modulus is 35 kPa or more, the sponge is less likely to deform at high temperature, and the wall portions of the voids inside the sponge are less likely to be destroyed, so that the above compression set can be reduced. Also, since the Young's modulus is 80 kPa or less, the sponge can be moderately deformed without destroying the resin constituting the sponge, so that the compression set can be reduced.

[0019] In addition, by using the sponge disposed on the surface of a fixing roller, the fixability of the formed toner image can be improved. In the fixing step of the toner image, the toner is heated and melted and pressed onto the recording medium by the fixing roller. That is, the sponge contained in the fixing roller presses the toner and the recording medium at high temperature. At this time, since the Young's modulus of the sponge disposed on the surface of the fixing roller is 80 kPa or less, the sponge moderately deforms and easily follows the recording medium when the toner is pressed. Also, since the Young's modulus of the sponge is 35 kPa or more, excessive deformation of the sponge during fixing is suppressed, and the pressing force of the fixing roller can be increased. Therefore, the sponge can sufficiently press the toner against the recording medium. For these reasons, the fixability of the toner image can be improved.

[0020] Hereinafter, based on the above findings, the sponge of the present invention will be described.

[0021] The porosity is preferably 55% or more and 60% or less. When the porosity is within the above range, the compression set of the sponge can be made smaller. The porosity can be obtained as the ratio of the volume of the void portion to the total volume of the sponge portion from the CT image of the sponge taken using a computed tomography (CT) apparatus.

[0022] The above Young's modulus is preferably 40 kPa or more and 70 kPa or less. When the Young's modulus is within the above range, the compression set of the sponge can be made smaller. Also, when the Young's modulus is 40 kPa or more, when the sponge is used for a fixing roller, the pressing force of the fixing roller can be increased more, and the fixability of the toner image can be increased more. Further, when the Young's modulus is 70 kPa or less, when the sponge is used for a fixing roller, at the time of pressure bonding of the toner, it is easier to make the sponge follow the recording medium, and the fixability of the toner image can be increased more.

[0023] Examples of the sponge material include resin materials such as silicone rubber, fluororubber, isoprene rubber, chloroprene rubber, polyurethane, butadiene rubber, and nitrile rubber. Among these, the sponge material is preferably silicone rubber and fluororubber. The silicone rubber and fluororubber may be of a two-component type in which the main agent and the vulcanizing agent are mixed at the time of curing, or may be of a one-component type.

[0024] The above silicone rubber and the above fluororubber (the main agent when it is of a two-component type) preferably have a tensile strength after curing of 5.0 MPa or more, and more preferably 6.0 MPa or more. When the above tensile strength is 5.0 MPa or more, the above Young's modulus of the sponge can be increased more. The above tensile strength can be measured by a method conforming to JIS K 6251 (2017).

[0025] The content of the resin portion (the portion composed of the above resin material) contained in the sponge is preferably 40% by volume or more and 55% by volume or less, and more preferably 40% by volume or more and 45% by volume or less, based on the total volume of the sponge.

[0026] The sponge preferably has voids with a non-monodisperse diameter. More preferably, the content of voids with a smaller diameter is less than the content of voids with a larger diameter. More specifically, the sponge preferably has a content of voids with a diameter of 4 μm or less of 5% by volume or more and 20% by volume or less with respect to the total volume of voids contained in the sponge, and a content of voids with a diameter exceeding 4 μm and less than 60 μm of 80% by volume or more and 95% by volume or less with respect to the total volume. Thereby, it is possible to more easily adjust the Young's modulus of the sponge within the range of 35 kPa or more and 80 kPa or less.

[0027] Also, from the viewpoint of further reducing the compression set of the sponge, the sponge preferably has a content of voids with a diameter of 4 μm or less of 10% by volume or more and 15% by volume or less with respect to the total volume of voids contained in the sponge, and a content of voids with a diameter exceeding 4 μm and less than 60 μm of 85% by volume or more and 90% by volume or less with respect to the total volume. According to the findings of the present inventors, by increasing the content of voids with a smaller diameter, the sponge is more likely to return to its original shape after being compressed. On the other hand, by not excessively increasing the content of voids with a smaller diameter, it is easy to moderately reduce the porosity of the sponge. The content of voids for each void diameter can be adjusted, for example, by adjusting the particle size of the powdery sugar when adding the powdery sugar in the step of adding sugar, which will be described later, to adjust the content of voids with a desired void diameter.

[0028] As described above, the inclusion of voids having two types of void diameters in the sponge can be confirmed by the following procedure. 1) Take an image of the sponge surface using a laser microscope and measure the height difference from the average surface as the void diameter. 2) Create a plot (void distribution) with the void diameter on the horizontal axis and the number of voids on the vertical axis. When two peaks appear, treat the void diameters corresponding to each peak as two types of average void diameters.

[0029] When determining the content of voids with a diameter of 4 μm or less and the content of voids with a diameter greater than 4 μm and less than 60 μm, first, confirm that the average void diameters of the above two types are 4 μm or less and greater than 4 μm and less than 60 μm, respectively. Then, the content of voids corresponding to each diameter can be determined by the following procedure. 1) In the void distribution described above, determine the total number of voids belonging to voids with a diameter of 4 μm or less and the total number of voids belonging to voids with a diameter greater than 4 μm and less than 60 μm, respectively. 3) Take the ratio of the total number of voids belonging to voids with a diameter of 4 μm or less and the ratio of the total number of voids belonging to voids with a diameter greater than 4 μm and less than 60 μm to the total number of voids on the sponge surface as the content of each void.

[0030] The shape of the sponge is not particularly limited. For example, it can be a rectangular parallelepiped, a donut shape, etc. Also, the thickness of the sponge is not particularly limited, but it is preferably 2 mm or more, more preferably 2 mm or more and 20 mm or less, and even more preferably 2 mm or more and 15 mm or less. When the shape of the sponge is a rectangular parallelepiped or a donut shape, the "thickness" of the sponge refers to the shortest length among the lengths from one surface of the sponge to the other surface facing the above surface.

[0031] The sponge may contain other known components. Examples of the above other components include softeners, plasticizers, curing agents, antioxidants, surfactants, etc.

[0032] The use of the sponge in this embodiment is not particularly limited. The sponge can be used, for example, in fixing rollers, cushioning materials, packings, fixing materials, etc. Among these, the sponge can be suitably used in fixing rollers. This is because, as described above, the fixability of the formed toner image can be improved.

[0033] <Method for manufacturing a sponge> The manufacturing method of the above sponge is not particularly limited, and for example, the manufacturing method described below can be mentioned. The manufacturing method includes a step of kneading a resin material, a step of adding sugar to the kneaded resin material and further kneading, a step of adding a vulcanizing agent to the resin material to which sugar has been added, a step of subjecting the obtained kneaded product to vacuum defoaming, a step of curing the kneaded product, and a step of immersing the obtained cured product in warm water.

[0034] (Step of kneading the resin material) In this step, the resin material is kneaded. In this step, it is preferable to add the resin material to an organic solvent and then knead.

[0035] As the type of the above resin material, the same materials as those of the above-mentioned sponge can be used. The type of the above organic solvent is not particularly limited, and for example, triethylene glycol, diethylene glycol, tetraethylene glycol, etc. Among these, the above organic solvent is preferably triethylene glycol or tetraethylene glycol, and more preferably triethylene glycol.

[0036] When using an organic solvent in this step, the mass of the organic solvent used is preferably 5% by mass or more and 15% by mass or less, and more preferably 8% by mass or more and 10% by mass or less with respect to the mass of the resin material.

[0037] The method of kneading the resin material is not particularly limited, but from the viewpoint of easily dispersing the voids formed in the sponge uniformly, a method of kneading using a planetary mixer is preferable. The stirring speed when kneading the resin material is preferably 500 rpm or more and 1500 rpm or less, and more preferably 800 rpm or more and 1400 rpm or less. Also, the kneading temperature is preferably 10°C or more and 50°C or less, and more preferably 10°C or more and 40°C or less.

[0038] (Step of adding sugar) In this process, sugar is added to the kneaded resin material, and then the resin material is kneaded again. By adding sugar, when the step of immersing in warm water, which will be described later, is performed, the sugar dissolves and the portion where the sugar was contained in the resin material becomes voids. By using this method, foaming during kneading can be suppressed, and it is possible to make it difficult for the viscosity of the kneaded material to increase during kneading after addition. Therefore, the added sugar is more likely to be dispersed in the kneaded material, and the voids formed by the dissolution of the sugar are also more likely to be dispersed in the sponge. As a result, the Young's modulus of the produced sponge is likely to be in the range of 35 kPa or more and 80 kPa or less. Also, by using this method, voids with a polydisperse diameter can be formed.

[0039] Examples of the types of the above sugar include sucrose, lactose, maltose, etc. Among these, the above sugar is preferably sucrose or maltose, and more preferably sucrose.

[0040] In this process, it is preferable to add powdery sugar. The volume average particle diameter of the powder is preferably 0.1 μm or more and 30 μm or less, and more preferably 0.5 μm or more and 20 μm or less. When the particle diameter is within the above range, voids with a void diameter of 4 μm or less are more likely to be formed. The above particle diameter can be measured using a dry particle size distribution measuring device (Mastersizer 3000, manufactured by Malvern).

[0041] The content of the powder having a volume average particle diameter of 4 μm or less in the above powder is preferably 10% by volume or more and 15% by volume or less with respect to the total volume of the powder, and the content of the powder having a volume average particle diameter of more than 4 μm and less than 60 μm is preferably 85% by volume or more and 90% by volume or less with respect to the above total volume. Thereby, the content of the voids having a void diameter of 4 μm or less and the content of the voids having a void diameter of more than 4 μm and less than 60 μm are more easily adjusted to the more preferable range described above.

[0042] As described above, the fact that the powder contains two types of diameters can be confirmed by the following procedure. The particle size of the powder was measured using a dry particle size distribution measuring device (Mastersizer 3000, manufactured by Malvern), and a plot (powder distribution) with the horizontal axis representing the powder diameter and the vertical axis representing the powder amount was created. When two peaks appeared, the powder diameters corresponding to each peak were treated as two types of volume average diameters.

[0043] When determining the content of powder with a diameter of 4 μm or less and the content of powder with a diameter greater than 4 μm and less than 60 μm, first, it is confirmed that the above two types of average diameters are 4 μm or less and greater than 4 μm and less than 60 μm, respectively. Then, the content of the powder corresponding to each diameter can be determined by the following procedure. 1) In the above powder distribution, determine the total number of powders belonging to powders with a diameter of 4 μm or less and the total amount of powders belonging to powders with a diameter greater than 4 μm and less than 60 μm, respectively. 2) The ratio of the total amount of powders belonging to powders with a diameter of 4 μm or less and the ratio of the total amount of powders belonging to powders with a diameter greater than 4 μm and less than 60 μm to the total amount of powders are taken as the content of each powder.

[0044] The addition amount of the above sugar is preferably 50% by mass or more and 150% by mass or less, and more preferably 80% by mass or more and 130% by mass or less, based on the addition amount of the resin material added in the step of kneading the resin material.

[0045] In this step, after adding the sugar, the resin material is further kneaded. The kneading method, stirring speed, and kneading temperature during kneading are the same as those described above.

[0046] (Step of adding a vulcanizing agent) In this step, a vulcanizing agent is added to the above resin material to which sugar has been added.

[0047] Examples of the types of the above vulcanizing agents include sulfur, dicumyl peroxide, benzoyl peroxide, t-butyl hydroperoxide, and the like.

[0048] The addition amount of the vulcanizing agent is preferably 80% by mass or more and 100% by mass or less with respect to the addition amount of the resin material added in the step of kneading the resin material.

[0049] In this step, a vulcanization accelerator may be added together with the vulcanizing agent. Examples of the vulcanization accelerator include sulfenamide-based vulcanization accelerators, thiazole-based vulcanization accelerators, guanidine-based vulcanization accelerators, and the like.

[0050] Examples of the sulfenamide-based vulcanization accelerator include N-tert-butyl-2-benzothiazolylsulfenamide (TBBS), N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), and the like.

[0051] Examples of the thiazole-based vulcanization accelerator include 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, and the like.

[0052] Examples of the guanidine-based vulcanization accelerator include 1,3-diphenylguanidine (DPG), 1,3-di-o-tolylguanidine, 1-o-tolylbiguanide, and the like.

[0053] (Step of degassing the kneaded product under reduced pressure) In this step, a degassing treatment under reduced pressure is performed on the kneaded product obtained by adding the vulcanizing agent. By performing the degassing treatment under reduced pressure, it is possible to easily manufacture a sponge in which voids are dispersed. The pressure when performing the degassing treatment under reduced pressure is preferably 0.1 kPa or less.

[0054] (Step of curing the kneaded product) In this step, the kneaded product (resin composition) after the degassing treatment under reduced pressure is heated and cured.

[0055] The temperature for heating the resin composition is preferably 100°C or higher and 150°C or lower, and more preferably 110°C or higher and 120°C or lower.

[0056] (Step of immersing the cured product in warm water) In this process, the cured product of the resin composition obtained in the above-mentioned curing process is immersed in warm water. As a result, the sugar contained in the resin composition dissolves in the warm water, and the site where the sugar was contained becomes the voids of the sponge.

[0057] The temperature of the above-mentioned warm water is not particularly limited as long as the added sugar dissolves, but for example, it is 50°C or higher and 90°C or lower.

[0058] 2. Image Forming Apparatus, Fixing Apparatus, and Fixing Roller FIG. 1 is a schematic cross-sectional view showing an example of the configuration of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 has a fixing apparatus 120 including a fixing roller 120a. The fixing roller 120a includes the above-mentioned sponge 20.

[0059] As shown in FIG. 1, the image forming apparatus 100 has an image forming unit 110, a fixing apparatus 120, an image reading unit 130, and a paper conveyance unit 140.

[0060] The image forming unit 110 has image forming units 111Y, 111M, 111C, and 111K that form images using toners of each color of Y (yellow), M (magenta), C (cyan), and K (black). Since these all have the same configuration except for the toner to be accommodated, the symbols representing the colors may be omitted hereafter.

[0061] The image forming unit 110 has a scanning optical device 112, a developing device 113, an electrophotographic photoreceptor (image carrier) 114, a charging device 115, and a drum cleaning device 116. The image forming unit 110 further has an intermediate transfer unit 117 and a secondary transfer unit 118. These correspond to transfer devices.

[0062] The scanning optical device 112 is a device for forming an electrostatic latent image by emitting light and performing exposure scanning on the outer peripheral surface of the electrophotographic photoreceptor 114. The light emitted by the scanning optical devices 112Y, 112M, 112C, and 112K has its light amount adjusted according to the image data of each color of YMCK.

[0063] The developing device 113 is a developing device using the two-component developing method. The developing device 113 includes, for example, a developing container that houses a two-component developer, a developing roller (magnetic roller) rotatably disposed at the opening of the developing container, a partition wall that partitions the inside of the developing container so that the two-component developer can communicate, a conveying roller for conveying the two-component developer on the opening side of the developing container toward the developing roller, and a stirring roller for stirring the two-component developer in the developing container. The developing container houses, for example, a two-component developer.

[0064] The charging device 115 is, for example, a corona charger. The charging device 115 may be a contact charging device that brings a contact charging member such as a charging roller, a charging brush, or a charging blade into contact with the electrophotographic photoreceptor 114 to charge it. The electrophotographic photoreceptor 114 is a negatively charged organic photoreceptor having photoconductivity. The electrophotographic photoreceptor 114 is charged by the charging device 115.

[0065] The intermediate transfer unit 117 includes an intermediate transfer belt (intermediate transfer member) 1171, a primary transfer roller 1172 that presses the intermediate transfer belt 1171 against the electrophotographic photoreceptor 315, and a belt cleaning device 1173. The intermediate transfer belt 1171 is looped around a plurality of support rollers. The intermediate transfer belt 1171 travels at a constant speed in the direction of arrow A.

[0066] The belt cleaning device 1173 has an elastic member 1173a. The elastic member 1173a abuts against the intermediate transfer belt 1171 after secondary transfer to remove the deposits on the surface of the intermediate transfer belt 1171. The elastic member 1173a is made of an elastic body and includes a cleaning blade, a brush, and the like.

[0067] The secondary transfer unit 118 includes a secondary transfer roller 1181 that is pressed against the outer peripheral surface of the intermediate transfer belt 1171, and a secondary transfer belt 1182. A secondary transfer voltage is applied to the secondary transfer roller 1181. When the recording medium S is inserted between the intermediate transfer belt 1171 and the secondary transfer roller 1181, the toner image is electrostatically transferred (secondary transfer) from the outer peripheral surface of the intermediate transfer belt 1171 onto the image forming surface of the recording medium S.

[0068] The fixing device 120 is formed by pressing a pressure roller against a high-temperature fixing roller 120a to form a fixing nip. When the recording medium S is inserted into the fixing nip, the toner image is thermally fixed to the recording medium S.

[0069] FIG. 2 is a schematic cross-sectional view showing the configuration of the fixing roller 120a. As shown in FIG. 2, the fixing roller 120a includes a core metal 10 and the sponge 20 disposed on the surface of the core metal 10 described above.

[0070] The material of the core metal 10 is not particularly limited, and includes, for example, metals such as aluminum, iron, and copper, and alloys thereof.

[0071] Since the sponge 20 can have the same configuration as the above-described sponge, a detailed description thereof is omitted.

[0072] The diameter of the fixing roller 120a is not particularly limited, but is preferably 50 mm or more, and more preferably 50 mm or more and 70 mm or less.

[0073] The fixing device 120 may have a driving unit 120b for rotating the fixing roller 120a at a linear speed of 340 mm / s or more. By rotating the fixing roller 120a at the above linear speed, the production efficiency of the image can be increased.

[0074] The image reading unit 130 reads a document and generates image data. The image reading unit 130 has an operation panel 131. The operation panel 131 presents information to the user of the image forming apparatus 100 and accepts instruction inputs from the user.

[0075] The paper conveyance unit 140 has a paper feeding unit 141, a paper discharging unit 142, and a conveyance path unit 143. In the three paper feeding tray units 141a to 141c that constitute the paper feeding unit 141, sheets of paper S (standard paper, special paper) identified based on basis weight, size, etc. are stored for each preset type. The conveyance path unit 143 has a plurality of conveyance roller pairs such as a registration roller pair 143a.

[0076] The image forming apparatus 100 having the above configuration operates as follows.

[0077] The current is read by the image reading unit 130 to become input image data. The input image data is subjected to predetermined image processing in an image processing unit (not shown) and sent to the scanning optical device 200.

[0078] The electrophotographic photoreceptor 114 rotates at a constant peripheral speed. The charging device 115 uniformly charges the surface of the electrophotographic photoreceptor 114 to a negative polarity. In the scanning optical device 112, the polygon mirror of the polygon motor included in the device rotates at high speed, and the laser light corresponding to the input image data of each color component is expanded along the axial direction of the electrophotographic photoreceptor 114 and irradiated onto the outer peripheral surface of the electrophotographic photoreceptor 114 along the axial direction. Thus, an electrostatic latent image is formed on the surface of the electrophotographic photoreceptor 114.

[0079] In the developing device 113, the toner base particles are charged by stirring and transporting the two-component developer in the developing container, and the two-component developer is transported to the developing roller to form a magnetic brush on the surface of the developing roller. The charged toner base particles electrostatically adhere from the magnetic brush to the portion of the electrostatic latent image on the electrophotographic photoreceptor 114. Thus, the electrostatic latent image on the surface of the electrophotographic photoreceptor 114 is visualized, and a toner image corresponding to the electrostatic latent image is formed on the surface of the electrophotographic photoreceptor 114. Note that the "toner image" refers to a state in which toner is aggregated in an image shape.

[0080] The toner image on the surface of the electrophotographic photoreceptor 114 is transferred to the intermediate transfer belt 1171 by the intermediate transfer unit 117. The transfer residual toner remaining on the surface of the electrophotographic photoreceptor 114 after transfer is removed by the drum cleaning device 116 having a drum cleaning blade that is in sliding contact with the surface of the electrophotographic photoreceptor 114.

[0081] When the intermediate transfer belt 1171 is pressed against the electrophotographic photoreceptor 114 by the primary transfer roller 1172, a primary transfer nip is formed for each electrophotographic photoreceptor by the electrophotographic photoreceptor 114 and the intermediate transfer belt 1171. In the primary transfer nip, the toner images of each color are sequentially overlapped and transferred to the intermediate transfer belt 1171.

[0082] On the other hand, the secondary transfer roller 1181 is pressed against the intermediate transfer belt 1171 and the secondary transfer belt 1182. Thereby, a secondary transfer nip is formed by the intermediate transfer belt 1171 and the secondary transfer belt 1182. The sheet S passes through the secondary transfer nip. The sheet S is transported to the secondary transfer nip by the sheet transport unit 140. The correction of the inclination of the sheet S and the adjustment of the transport timing are performed by the registration roller unit provided with the registration roller pair 143a.

[0083] When the paper S is conveyed to the secondary transfer nip, a transfer bias is applied to the secondary transfer roller 1181. By applying this transfer bias, the toner image carried on the intermediate transfer belt 1171 is transferred to the paper S (the step of attaching the toner for electrostatic charge image development to the recording medium). The paper S onto which the toner image has been transferred is conveyed toward the fixing device 120 by the secondary transfer belt 1182.

[0084] Adhesions such as residual transfer toner remaining on the surface of the intermediate transfer belt 1171 after secondary transfer are removed by a belt cleaning device 1173 having a cleaning blade that is in sliding contact with the surface of the intermediate transfer belt 1171. At this time, since the aforementioned intermediate transfer body is used as the intermediate transfer belt, the dynamic frictional force can be reduced over time.

[0085] The fixing device 120 forms a fixing nip by sandwiching a fixing belt between a rotating fixing roller and a pressure roller, and heats and presses the conveyed paper S at the fixing nip portion. In this way, the toner image is fixed to the paper S (the step of fixing the toner for electrostatic charge image development to the recording medium). The paper S onto which the toner image has been fixed is discharged outside the machine by a paper discharge unit 142 equipped with a paper discharge roller.

Example

[0086] Hereinafter, the present invention will be described with reference to examples. The scope of the present invention is not construed as being limited by the examples.

[0087] 1. Production of a roller containing a sponge (Silicone rubber composition) 100 parts by mass of a liquid rubber (silicone rubber 1 (Agent A)) and 20 parts by mass of triethylene glycol were kneaded for 3 minutes under the conditions of a stirring speed of 800 rpm and a temperature of 40 °C using a rotation and revolution kneader (SK-350TV, manufactured by Shashin Kagaku Co., Ltd.). To the obtained kneaded product, 110 parts by mass of sucrose (powder form, manufactured by Fujifilm Wako Pure Chemical Corporation) was added and kneaded for 3 minutes using the above rotation and revolution kneader. Next, 100 parts by mass of a curing agent 1 (Agent B, containing a vulcanizing agent) was added and kneaded for another 3 minutes. Then, the obtained kneaded product was subjected to a vacuum degassing treatment at a pressure of 0.1 kPa using the above rotation and revolution kneader to obtain a rubber composition.

[0088] An aluminum mandrel (inner diameter 30 mm) with a primer treatment on its outer peripheral surface was placed in a cylindrical mold (inner diameter 60 mm). At this time, the mandrel was placed so that the center of the mandrel and the center of the mold overlapped. Next, the silicone rubber composition was injected between the mold and the mandrel, and the injected silicone rubber composition was heated at 130 °C for 1 hour to cure it. Then, the mandrel together with the cured silicone rubber composition was taken out of the mold, and the mandrel including the silicone rubber layer was immersed in warm water at 60 °C. After 10 hours, the mandrel was taken out of the warm water and heated at 200 °C for 4 hours to secondarily vulcanize the silicone rubber, thereby producing a roller 1 including a sponge (total thickness: 30 mm). The porosity of the sponge contained in roller 1 was 47%, and the Young's modulus when compressed by 30% at 180 °C was 76 kPa. Also, the voids with a diameter d of 4 μm or less were 5% of the total volume of the cells, and the voids with a diameter d of more than 4 μm and less than 60 μm were 95% of the total volume of the cells. The measuring methods for the above porosity, the above Young's modulus, and the content of the above cells will be described later.

[0089] In the production of the above roller 1, rollers 2 to 20 were produced in the same manner, except that the type of liquid rubber used, the particle size distribution of sucrose (content for each particle size), and the amount of sucrose added were changed as shown in Table 1. The porosity, Young's modulus, and cell content of the sponge contained in rollers 2 to 20 are also shown in Table 1. Note that for silicone rubbers 1 to 3 and fluororubber in Table 1, the following were used. Also, the catalog values of the tensile strength after curing of the following silicone rubbers 1 to 3 and fluororubber are shown. Silicone rubber 1: LSR7030 (main agent), manufactured by Momentive Performance Materials, tensile strength after curing: 6.0 MPa Silicone rubber 2: KE-1603 (main agent), manufactured by Shin-Etsu Chemical Co., Ltd., tensile strength after curing: 6.0 MPa Silicone rubber 3: X15-7354, manufactured by Momentive Performance Materials Fluororubber: SIFEL 3405 (main agent), manufactured by Shin-Etsu Chemical Co., Ltd., tensile strength after curing: 8.0 MPa

[0090] Also, for curing agents 1 to 4 in Table 1, the following were used. Vulcanizing agent 1: LSR7030 (curing agent), manufactured by Momentive Performance Materials Vulcanizing agent 2: KE-1603 (curing agent), manufactured by Shin-Etsu Chemical Co., Ltd., tensile strength after curing: 6.0 MPa Vulcanizing agent 3: X15-7354 (curing agent), manufactured by Momentive Performance Materials Vulcanizing agent 4: SIFEL 3405 (curing agent), manufactured by Shin-Etsu Chemical Co., Ltd., tensile strength after curing: 8.0 MPa

[0091] Note that the particle size distribution (content for each particle size) of powdery sucrose was measured and confirmed by the following procedure.

[0092] First, the fact that the powder contains two types of diameters was confirmed by the following procedure. The particle size of the powder was measured using a dry particle size distribution analyzer (Mastersizer 3000, manufactured by Malvern). A plot (powder distribution) with the horizontal axis representing the powder diameter and the vertical axis representing the powder amount was created. When two peaks appeared, the powder diameters corresponding to each peak were treated as two types of volume average diameters.

[0093] In the above powder distribution, the total number of powders belonging to powders with a diameter of 4 μm or less and the total amount of powders belonging to powders with a diameter greater than 4 μm and less than 60 μm were determined respectively. Then, the ratios of the total amount of powders belonging to powders with a diameter of 4 μm or less and the total amount of powders belonging to powders with a diameter greater than 4 μm and less than 60 μm to the total amount of powders were taken as the content of each powder.

[0094]

Table 1

[0095] 2. Measurement (Porosity) The sponge parts of rollers 1 to 20 were cut out into pieces of 8 mm × 8 mm × 8 mm, and one CT image (a region of 1 mm × 1 mm) was obtained using a computed tomography (CT) device. The ratio of the volume of the void part to the total volume of the sponge part derived from the obtained CT image was determined as the porosity.

[0096] (Young's modulus) The sponge parts of rollers 1 to 20 were cut out into pieces of 12 mm × 12 mm × 12 mm, and a compression test was conducted at 180 °C in accordance with JIS K 7181 (2011) such that the compression rate with respect to the test piece (sponge) was 30%. Thereby, the Young's modulus of the sponge was determined.

[0097] (Maximum diameter and content of voids) The surface of the sponge parts of rollers 1 to 20 was observed using a laser microscope (VKX-250, manufactured by Keyence Corporation). Based on the observed image, the arithmetic mean height Sa of the sponge surface was calculated and taken as the average diameter of the voids.

[0098] 3. Evaluation (Compression set of sponge) For the sponges of rollers 1 to 20 produced, a compression set test was conducted in accordance with JIS K 6262 (2013). This test was performed such that the compression rate for the test piece (sponge) was 25%, and it was carried out under the condition of maintaining compression for 22 hours in an environment at a temperature of 180°C. By this test, the compression rate of the sponge after compression retention was measured. The durability of the sponge was evaluated according to the following criteria using the measured compression rate values. a: The above compression rate was within 5%, and the compression deformability of the sponge was good. b: The above compression rate was more than 5% and within 8%, and the compression deformability of the sponge was not a problem in practical use. c: The above compression rate was more than 8% and within 10%, and the compression deformability of the sponge was not a problem in practical use. d: The above compression rate was more than 10%, and there was a problem with the compression deformability of the sponge.

[0099] (Fixing property) The fixing roller in the fixing device included in the image forming apparatus (full-color production printer C3070, manufactured by Konica Minolta, Inc.) was replaced with any one of rollers 1 to 20. Using this image forming apparatus, a solid image (cyan solid image) with cyan toner was formed on a recording medium (A4-sized coated paper, POD gloss coat 128, manufactured by Oji Paper Co., Ltd.). At this time, the linear speeds of rollers 1 to 20 were adjusted to 430 mm / s by the drive unit in the image forming apparatus. The formed cyan solid image was visually observed, and the fixing property was evaluated according to the following criteria. a: No defects due to poor fixing were observed in the cyan solid image. b: Fine pressure bonding defects were seen in the cyan solid image, but it was not a problem in practical use. c: Obvious defects due to poor pressure bonding were seen in the cyan solid image. d: The toner image could not be separated from the fixing roller, and the cyan solid image could not be fixed on the recording medium.

[0100]

Table 2

[0101] From the results of rollers 1 to 8, it was found that when the porosity is 45% or more and 60% or less, and the Young's modulus when compressed at 180°C so that the compression ratio becomes 30% is 35 kPa or more and 80 kPa or less, the compression set of the sponge can be suppressed. Further, it was found that by using the sponge (including rollers 1 to 8) as a fixing roller, the fixability of the formed toner image can be improved.

Industrial Applicability

[0102] The sponge according to the present invention is useful, for example, in the field of image formation.

Explanation of Signs

[0103] 10 Core metal 20 Sponge 100 Image forming apparatus 110 Image forming unit 120 Fixing device 120a Fixing roller 120b Driving unit 130 Image reading unit 140 Paper conveyance unit

Claims

1. A sponge having a porosity of 45% or more and 60% or less, wherein the Young's modulus measured under the condition of being compressed to a compression ratio of 30% at 180°C in accordance with the measurement method of JIS K 7181 (2011) is 35 kPa or more and 80 kPa or less. Sponge.

2. The sponge according to Claim 1, wherein the Young's modulus is 40 kPa or more and 70 kPa or less.

3. The content of voids having a diameter of 4 μm or less is 5% by volume or more and 20% by volume or less with respect to the total volume of the voids contained in the sponge, and the content of voids having a diameter of more than 4 μm and less than 60 μm is 80% by volume or more and 95% by volume or less with respect to the total volume. The sponge according to Claim 1.

4. The content of voids having a diameter of 4 μm or less is 10% by volume or more and 15% by volume or less with respect to the total volume of the voids contained in the sponge, and the content of voids having a diameter of more than 4 μm and less than 60 μm is 85% by volume or more and 90% by volume or less with respect to the total volume. The sponge according to Claim 1.

5. The sponge according to Claim 1, wherein the material of the sponge is fluororubber or silicone rubber.

6. The sponge according to Claim 5, wherein the fluororubber or the silicone rubber has a tensile strength of 5.0 MPa or more.

7. The sponge according to Claim 1, having a thickness of 2.0 mm or more.

8. A fixing roller including the sponge according to any one of Claims 1 to 7.

9. The fixing roller according to Claim 8, having a diameter of 50 mm or more.

10. A fixing device including the fixing roller according to Claim 8.

11. The fixing device according to Claim 10, having a drive unit for adjusting the linear velocity of the fixing roller to 340 mm / s or more.

12. An image forming apparatus including the fixing device according to Claim 10.

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