Elastic Roller

Abstract

To provide an elastic roller that has a curl prevention function in the roller itself independent of the configuration of an image forming apparatus.SOLUTION: As a substrate to form an elastic roller, one with recesses in its outer peripheral surface is used, and the recesses are filled with a material forming an elastic layer to form an elastic layer with thick wall parts and thin wall parts. The recesses are formed along a circumferential direction of a tubular substrate, and protrusions may be formed on an inner peripheral surface of the tubular substrate corresponding to the back side of the area where the recesses are present.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an elastic roller used in a fixing device for fixing a toner image in an image forming apparatus such as an electrophotographic copying machine, a facsimile machine, or a printer. [Background technology]

[0002] 2. Description of the Related Art A fixing device that fixes a toner image onto a recording medium such as printing paper includes a fixing roller (heating roller) having a built-in heater and a pressure roller that is in pressure contact with the fixing roller.

[0003] It is known that the printing paper may curl when heated and pressed during the fixing operation.

[0004] One of the causes of curling is the phenomenon in which moisture absorbed in the printing paper evaporates when the printing paper is heated, and the fibers that make up the printing paper shrink as the moisture evaporates.

[0005] Since curling of printing paper can cause paper jams in image forming apparatuses, various countermeasures have been proposed.

[0006] Patent Document 1 discloses an image forming device that detects the curl direction of paper and performs curl correction in the opposite direction to the curl direction. Patent Document 2 discloses an image forming device that corrects curls by applying heat and pressure to deform the paper in the opposite direction to the curl direction.

[0007] However, the image forming apparatuses disclosed in Patent Documents 1 and 2 are intended to correct curl that has occurred, and are not intended to suppress the occurrence of curl itself.

[0008] An example of an image forming apparatus intended to suppress the occurrence of curl itself is disclosed in Patent Document 3. The image forming apparatus disclosed in Patent Document 3 prevents the occurrence of curl by controlling the rotation speeds of the fixing roller and the pressure roller.

[0009] However, since the image forming apparatus disclosed in Patent Document 3 suppresses curl by controlling the image forming apparatus, many aspects depend on the overall configuration of the image forming apparatus, and the fixing roller and pressure roller that constitute the image forming apparatus do not themselves have the function of suppressing curl. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] JP 2010-1099 A [Patent Document 2] JP 2005-250275 A [Patent Document 3] JP 2003-316199 A Summary of the Invention [Problem to be solved by the invention]

[0011] An object of the present invention is to provide an elastic roller that has a curl suppressing function in the roller itself, independent of the configuration of an image forming apparatus.

[0012] As a result of thorough investigation into the structure of the elastic roller, the inventors have resolved the above-mentioned problem by using a base material that has a recess on its outer peripheral surface as the base material that constitutes the elastic roller, and by forming an elastic layer that has thick and thin portions.

[0013] The present invention is an elastic roller having a tubular substrate and an elastic layer covering the outer peripheral surface of the tubular substrate, wherein the tubular substrate has a recess on its outer peripheral surface, the elastic layer has a thick portion and a thin portion, and the thick portion is formed by filling the recess with a material that constitutes the elastic layer. Effect of the Invention

[0014] According to the present invention having the above configuration, the following actions and effects are achieved. (a) In the thick portion of the elastic layer, the amount of heat applied to the printing paper is relatively small. (b) The pressure applied to the printing paper becomes relatively large in the thick portion of the elastic layer. (c) As a result of the above, local differences occur in the amount of heat and pressure applied to the printing paper, which helps to suppress curling of the printing paper. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a cross-sectional view of the elastic roller of the present invention taken along an axial direction. [Diagram 2] FIG. 2 is a schematic diagram showing a nip formed by using the elastic roller of the present invention. [Diagram 3] 3 is a schematic diagram of deformation that occurs when printing paper is passed through the nip shown in FIG. 2. [Figure 4] This is a preferred method for providing the recesses. [Diagram 5] The elastic roller of the present invention has a convex portion provided on the inner peripheral surface of the tubular substrate. [Figure 6] 13 is an example of the shape of a protrusion. [Figure 7] This is a preferred shape of the protrusion. [Figure 8] 1 is a schematic diagram of a method for forming a protrusion DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention will now be described with reference to Fig. 1. Fig. 1 shows an example of an elastic roller 1 of the present invention, which is composed of a tubular substrate 10 and an elastic layer 20 coated on the outer peripheral surface of the tubular substrate 10.

[0017] The elastic roller 1 of the present invention is intended to be used as a pressure roller or a fixing roller member in a fixing device in an image forming apparatus, and has preferable characteristics when used as a fixing roller. In the following description, the elastic roller 1 will be described assuming that it is used as a fixing roller.

[0018] A feature of the present invention is that recesses 11 are present on the outer peripheral surface of the tubular substrate 10, and the recesses 11 are filled with a material constituting the elastic layer 20, thereby forming a thick portion 21 and a thin portion 22 in the elastic layer 20. That is, the elastic layer 20 provided in the portion where the recesses 11 exist becomes the thick portion 21, and the elastic layer 20 provided in the portion where the recesses 11 do not exist becomes the thin portion 22.

[0019] The outer peripheral surface of the elastic layer 20 in the elastic roller 1 of the present invention is formed to have a constant outer diameter, or to have an outer diameter that changes continuously, such as a crown shape or an inverted crown shape, which will be described later.

[0020] When the elastic roller 1 is used as a fixing roller, a heat source such as a halogen lamp heater is provided inside the elastic roller 1 to heat the elastic roller 1, and at this time, heat conduction occurs in the radial direction of the elastic roller 1 (the direction from the inner surface of the tubular substrate 10 toward the outer surface of the elastic layer 20).

[0021] At this time, a difference occurs in the radial heat conduction between the region where the thick portion 21 exists and the region where the thin portion 22 exists.

[0022] Typically, the tubular substrate 10 of the elastic roller 1 used in an image forming apparatus is made of a metal material having excellent thermal conductivity, and the elastic layer 20 is made of an elastic material such as silicone rubber having relatively low thermal conductivity compared to the metal material.

[0023] The thick portion 21, where the radial dimension of the elastic layer 20 is larger, has a longer heat transfer distance than the thin portion 22. Combined with the fact that the elastic layer 20 is formed from a material with relatively low thermal conductivity, heat from the heat source is less likely to be transferred to its surface than to the thin portion 22.

[0024] As a result, a difference in the heat supply state occurs on the surface of the elastic layer 20 due to the distribution of the thick portions 21 and the thin portions 22, and the heat supply to the surface of the thick portions 21 is relatively less than that to the thin portions 22.

[0025] When fixing to printing paper using the elastic roller 1 in this state, the amount of heat applied to the area of ​​the printing paper that contacts the thick portion 21 is relatively small compared to the amount of heat applied to the thin portion 22.

[0026] As a result, in the area of ​​the printing paper in contact with the thick section 21, the shrinkage of the fibers that make up the printing paper is suppressed compared to the area of ​​the printing paper in contact with the thin section 22, and the shrinkage of the fibers is also suppressed when looking at the printing paper as a whole, which ultimately contributes to suppressing curling of the printing paper.

[0027] As described above, the presence of the thick portions 21 and thin portions 22 in the elastic layer 20 creates a change in the state of heat supply to the surface of the elastic layer 20, and this change contributes to suppressing curling of the printing paper.

[0028] Furthermore, the elastic roller 1 of the present invention, in which the thick portion 21 and the thin portion 22 exist in the elastic layer 20, also contributes to suppressing curling of the printing paper from the viewpoint of other than the supply of heat.

[0029] When the elastic roller 1 is used in an image forming apparatus, as shown in FIG. 2, it is used in a state where another roller 100 is brought into contact with the elastic roller 1 with a predetermined pressure to form a nip N.

[0030] When the surface of the elastic layer 20 is pressed with a predetermined pressure, the elastic layer 20 shrinks and deforms due to the pressure.

[0031] Therefore, when a nip N is formed using the elastic roller 1 of the present invention, the nip N is formed in a wavy state in the region where the thick portion 21 exists as shown in FIG.

[0032] When a printing paper is passed through such a nip N, as shown in Figure 3, area P1 of the printing paper P abutting against the thick portion 21 will be deformed more than area P2 abutting against the thin portion 22.

[0033] The deformation of the printing paper caused by contact with the thick portion 21 offsets the deformation of the printing paper caused by curling, so that deformation of the printing paper as a whole is suppressed, which contributes to suppressing curling of the printing paper.

[0034] The curl suppression effect due to the difference in the amount of shrinkage between the thick portion 21 and the thin portion 22 described above can be obtained not only in situations where the elastic roller 1 is used as a heated fixing roller, but also in situations where the elastic roller 1 is used without being heated, such as a pressure roller or a conveying roller.

[0035] There is no particular limitation on the method of providing the recesses 11, and any method can be selected, such as providing them regularly, randomly, entirely, or partially on the surface of the tubular substrate 10. However, considering that the elastic roller 1 will be used in an image forming device, it is preferable to form the recesses 11 along the circumferential direction of the tubular substrate 10.

[0036] When the recesses 11 are formed along the circumferential direction of the tubular substrate 10, the length can be selected from a quarter, half, or full circumference, with the most preferred length being full circumference.

[0037] Since the recess 11 is formed along the circumferential direction of the tubular substrate 10, the thick portion 21 is also formed along the circumferential direction of the elastic layer 20, and the direction in which the printing paper deforms upon contact with the thick portion 21 is approximately perpendicular to the paper feed direction of the printing paper.

[0038] Normally, curling occurs along the direction in which the print paper passes, but by promoting deformation in a direction approximately perpendicular to the print paper's direction, the bias in the direction of the force promoting deformation of the print paper is mitigated, and the print paper as a whole is placed in a state in which deformation in a specific direction is suppressed, which contributes to suppressing curling of the print paper.

[0039] Furthermore, when the recess 11 is formed around the circumference of the tubular substrate 10, the thick portion 21 is always in contact with the printing paper, and the heat supply control effect and deformation effect of the thick portion 21 are always acting on the printing paper, improving the curl suppression effect.

[0040] When the recesses 11 are formed along the circumferential direction of the tubular substrate 10, the number and positions of the recesses 11 are not particularly limited, and in addition to the state shown in Figure 1, they can be appropriately selected depending on the desired curl suppression effect and the specifications of the image forming device in which the elastic roller 1 is used, such as only one recess at the center in the axial direction of the tubular substrate 10, only one at an end, one at each end, or a total of three recesses at the center and both ends.

[0041] When taking into consideration the curl suppression effect, as shown in Figure 4, it is preferable to form multiple recesses 11 in the tubular substrate 10, and to make the number of recesses 11 per unit length in the axial center of the paper passage area of ​​the tubular substrate 10 less than the number of recesses 11 per unit length in areas other than the axial center of the paper passage area.

[0042] In other words, it is preferable to form relatively more recesses 11 toward the ends of the tubular substrate 10 than near the center in the axial direction.

[0043] By forming a relatively large number of recesses 11 at the end of the tubular substrate 10, deformation of the printing paper due to contact with the thick portions 21 is concentrated at the end of the printing paper, and deformation of the printing paper as a whole in a specific direction is suppressed, which contributes to suppressing curling.

[0044] More specifically, a first recess 111 is formed in the axial center of the paper-passing area, and a second recess 112 adjacent to the first recess 111 is formed in an area other than the axial center of the paper-passing area, and the distance between the first recess 111 and the adjacent second recess 112 is at least twice the distance between the recesses formed in the area other than the axial center of the paper-passing area. In Fig. 4, the second recess 112, the third recess 113, and the fourth recess 114 correspond to the recesses formed in the area other than the axial center of the paper-passing area.

[0045] Since the distance between the first recess 111 formed in the axial center and the second recess 112 adjacent to the first recess 111, and the distance between recesses formed in other areas are sufficiently long, deformation of the printing paper caused by contact with the thick portion 21 can be concentrated more at the edge of the printing paper, contributing to suppression of curling.

[0046] In addition, from the viewpoint of suppressing curl by controlling the state of heat supply to the printing paper, it is preferable to set the heat flux per unit area in the thickness direction of the elastic layer 20 in the thick portion 21 to a range of 30% to 70% of the heat flux per unit area in the thickness direction of the elastic layer 20 in the thin portion 22.

[0047] By making the heat flux in the thick portion 21 70% or less of that in the thin portion 22, a clear difference in the amount of heat supplied to the surface of the elastic layer 20 in the thick portion 21 and the thin portion 22 occurs, which contributes to suppressing curling.

[0048] By making the heat flux in the thick portion 21 30% or more of that in the thin portion 22, a constant level of heat supply is maintained in the thick portion 21, which contributes to maintaining print quality.

[0049] Moreover, the thickness of the elastic layer 20 in the thick portion 21 is preferably set to be 1.05 to 1.3 times the thickness of the elastic layer 20 in the thin portion 22 .

[0050] When the elastic roller 1 is used in a fixing device, the elastic roller 1 is heated to a fixing temperature (about 150 to 200° C.) during fixing operation, and at that time, the thickness of the elastic layer 20 increases due to thermal expansion.

[0051] In this case, if the thickness of the thick portion 21 is 1.05 times or more that of the thin portion 22, the amount of thermal expansion of the thick portion 21 will be about 5 to 10% higher than the amount of thermal expansion of the thin portion 22, although this value varies depending on the material of the elastic layer 20 and the fixing temperature.

[0052] By providing a difference in thickness so that the difference in the amount of thermal expansion between the thick portion 21 and the thin portion 22 at the fixing temperature is greater than a certain level, the difference in the amount of contraction between the thick portion 21 and the thin portion 22 when a nip N is formed on the elastic roller 1 at the fixing temperature can be increased, which contributes to improving the curl suppression effect due to the difference in the amount of contraction between the thick portion 21 and the thin portion 22.

[0053] Furthermore, by making the thickness of the thick portion 21 no greater than 1.3 times that of the thin portion 22, the difference in behavior exhibited by the thick portion 21 and the thin portion 22 remains within a certain range, which contributes to maintaining print quality.

[0054] 5, the tubular substrate 10 preferably has a protrusion 12 formed on the inner circumferential surface corresponding to the back side of the region where the recess 11 is present. The presence of the protrusion 12 on the back side of the recess 11 maintains the thickness of the tubular substrate 10 even when the recess 11 is provided, which contributes to maintaining the mechanical strength of the tubular substrate 10 and leads to maintaining the mechanical strength of the elastic roller 1.

[0055] The shape of the protrusions 12 can be appropriately selected from the shapes shown in FIG. 6, such as (A) a semicircular shape, (B) a rectangular shape, (C) a triangular shape, and (D) a triangular shape with R at the apex.

[0056] From the viewpoint of maintaining the mechanical strength of the tubular substrate 10, it is preferable to use a convex portion 12 having a rising portion rising in a substantially concave curve from the inner peripheral surface of the tubular substrate 10 and a tip portion that forms a substantially convex curve in the axial cross section of the elastic roller 1, as shown in FIG. 7.

[0057] The convex portion 12 shown in FIG. 7 has a shape in which the change in the cross-sectional area of ​​the tubular substrate 10 at the convex portion 12 is gradual, making it difficult for stress to concentrate at the rising portion and contributing to suppressing local deformation and cracks.

[0058] When forming the convex portion 12, as shown in Figure 8, the blank tube 10' which will become the tubular substrate 10 is fixed to an NC lathe (not shown), and while rotating the blank tube 10', a drawing tool T is pressed against its outer circumferential surface, thereby forming the concave portion 11 on the outer circumferential surface of the blank tube 10' and at the same time forming the convex portion 12 on the inner circumferential surface of the blank tube 10'.

[0059] The material for the tubular substrate 10 used in the present invention may be selected from metal materials widely used for elastic rollers 1 such as those of the present invention, such as aluminum and iron, and if necessary, a coating may be applied to the inner surface to improve thermal conductivity.

[0060] As the material for the elastic layer 20 used in the present invention, silicone rubber that is widely used for the elastic roller 1 of the present invention can be appropriately selected and used. The silicone rubber used for the elastic layer 20 may be either solid or liquid rubber, and various coating methods such as extrusion molding and casting can be used for the method of coating the tubular substrate 10, but from the viewpoint of filling the recesses 11 with the material that will become the elastic layer 20, the method of casting liquid rubber is most preferably used.

[0061] In the present invention, the elastic layer 20 may have a porous structure for the purpose of adjusting the hardness of the elastic layer 20. When the elastic layer 20 has a porous structure, a conventionally known method for making the elastic layer 20 porous may be appropriately selected and used, such as a method of mixing a heated foaming agent with millable silicone rubber and decomposing the foaming agent to gasify it during the step of crosslinking the rubber to generate bubbles to make the elastic layer porous, a method of using a hollow filler, or a method of mixing a water-absorbent polymer containing water with liquid silicone rubber and evaporating the water to form cavities.

[0062] In the present invention, if necessary, a release layer may be provided on the outer periphery of the elastic layer 20. As the material for the release layer, a material known as a material for a release layer, such as a fluororesin or a silicone resin, may be appropriately selected and used. As for the method for forming the release layer, a method known as a method for forming a release layer may be appropriately selected and used, such as covering the elastic layer 20 with a tubular molded material or coating the elastic layer 20 with a liquid material.

[0063] In the present invention, in order to increase the bonding strength between the layers including the tubular substrate 10, a primer, an RTV rubber adhesive, etc. may be used in combination as appropriate.

[0064] The present invention can be applied to various elastic rollers having an elastic layer, and can also be suitably used for crown-shaped rollers in which the outer diameter is thicker at the axial center of the roller, and conversely, inverted crown-shaped rollers in which the outer diameter is thinner at the axial center. EXAMPLES

[0065] An embodiment of the elastic roller 1 according to the present invention will be described below.

[0066] [Example 1] An aluminum pipe having a length of 270 mm, an outer diameter of φ24 mm, and a wall thickness of 1.5 mm is prepared, and recesses 11 are formed in predetermined positions on the outer circumferential surface to obtain a tubular substrate 10.

[0067] The recesses 11 form a first recess 111 in the axial center of the tubular substrate 10, and a plurality of recesses are formed symmetrically with respect to the axial center. The recesses 11 formed successively from the first recess 111 toward both axial ends of the tubular substrate 10 are referred to as a second recess 112, a third recess 113, a fourth recess 114, and a fifth recess 115.

[0068] The distance between the first recess 111 and the second recess 112 was 40 mm, the distance between the second recess 112 and the third recess 113 was 20 mm, and thereafter, the distance between the recesses 11 on the axial end side was 20 mm.

[0069] That is, the distance between a first recess 111 and an adjacent second recess 112 is twice the distance between recesses formed in an area other than the axial center of the paper passing area.

[0070] 8, the recesses 11 were formed by fixing an aluminum mother tube 10' to an NC lathe (not shown) and pressing a drawing tool T against the outer circumferential surface of the mother tube 10' while rotating the mother tube 10'. At this time, at the same time as forming the recesses 11, protrusions 12 were also formed on the inner circumferential surface of the mother tube 10', and a tubular base material 10 was obtained.

[0071] Each recess 11 was formed in a substantially semi-elliptical shape with a width of 4.5 mm and a maximum depth of 0.5 mm.

[0072] The tubular substrate 10 was inserted into a mold, and liquid silicone rubber that would become the elastic layer 20 was injected while the mold was held upright, and then the material was heated and vulcanized under predetermined conditions to form the elastic layer 20. The elastic layer 20 was a solid elastic layer with an outer diameter of φ31 mm, a thick portion 21 having a thickness of 5 mm, and a thin portion 22 having a thickness of 4.5 mm.

[0073] The heat flux of the thin-walled portion 22 is 7.2 kW / m 2 The heat flux of the thick portion 21 is set to 50% of that, 3.6 kW / m 2 It should be noted that this heat flux is a calculated value when the temperature of the inner circumferential surface of the tubular substrate 10 is room temperature (20° C.) and the surface temperature of the elastic layer 20 is the fixing temperature (200° C.).

[0074] Furthermore, an RTV rubber adhesive was applied onto the elastic layer 20, and a heat-shrinkable PFA tube having a thickness of 50 μm was coated as a release layer. The release layer was fixed by heating and shrinking under specified conditions, thereby obtaining an elastic roller 1 of the present invention.

[0075] [Comparative Example] A comparative elastic roller 1' was produced in the same manner as in Example 1, except that the tubular substrate 10 was not provided with the recesses 11 and protrusions 12, and the elastic layer 20 had a uniform thickness of 4.5 mm.

[0076] [Curl condition confirmation test] A curl state confirmation test was carried out on the elastic rollers of the above-described examples and comparative examples.

[0077] The test paper used was A4 size 60g / m 2 The paper was stored in a high-temperature and high-humidity environment of 27° C. and 80% humidity for 24 hours or more to allow it to fully absorb moisture.

[0078] The above test printing paper was passed through a test fixing device, and heat and pressure were applied to cause curling of the printing paper.

[0079] The test fixing device had an elastic roller of the embodiment or comparative example used as a fixing roller, and a pressure roller paired with the elastic roller, and was capable of applying heat and pressure to the printing paper at a predetermined temperature, pressure and speed.

[0080] The curl condition confirmation test was performed by pressing the pressure roller and the elastic roller to be evaluated with a load of 15 kg to form a nip, and passing a test printing paper vertically through the nip with the surface temperature of the elastic roller set to 200°C and the rotational speed of the elastic roller set to a peripheral speed of 120 mm / sec.

[0081] One end of the test printing paper that had been passed through the test fixing device was fixed on a flat plate, and the curl suppression effect was evaluated based on the amount by which the other end rose above the flat plate due to curling. Five sheets of test printing paper were passed through each of the examples and comparative examples for evaluation.

[0082] It was confirmed that the test printing paper passed through the elastic roller 1' of the comparative example all lifted by 25 mm or more, and obvious curling occurred.

[0083] On the other hand, the amount of lift of the test printing paper passed over the elastic roller 1 of the present invention was all 10 mm or less, confirming that the elastic roller 1 of the present invention has the effect of suppressing curling of the printing paper.

[0084] The above embodiment has been described with respect to an embodiment in which a solid elastic layer 20 is provided on the outer periphery of the tubular substrate 10, but the present invention is not limited to this embodiment. Depending on the desired characteristics of the fixing device member, an embodiment in which a sponge-like elastic layer is provided or an embodiment in which a solid elastic layer and a sponge-like elastic layer are combined can also be used. [Industrial Applicability]

[0085] The elastic roller of the present invention can be suitably used as a fixing roller, a pressure roller, a transport roller in a fixing device, and also as a transport roller in a printer and other rollers in various printing machines. [Explanation of symbols]

[0086] 1 Elastic roller 10 Tubular base material 11 Recess 12 Convex part 20 Elastic layer 21 Thick part 22 Thin section N Nip P printing paper

Claims

1. An elastic roller having a tubular substrate and an elastic layer covering the outer peripheral surface of the tubular substrate, wherein the tubular substrate has a recess formed on its outer peripheral surface along the circumferential direction of the tubular substrate, and the elastic layer has a thick portion and a thin portion, and the thick portion is formed by filling the recess with a material that constitutes the elastic layer, and wherein a plurality of recesses are formed in the tubular substrate, and the number of recesses per unit length in the axial center of the paper passing area is less than the number of recesses per unit length in areas other than the axial center of the paper passing area.

2. An elastic roller having a tubular substrate and an elastic layer covering the outer peripheral surface of the tubular substrate, wherein the tubular substrate has a recess on its outer peripheral surface and the elastic layer has a thick portion and a thin portion, the thick portion being formed by filling the recess with a material that constitutes the elastic layer, and wherein the heat flux in the thickness direction of the elastic layer at the thick portion is in the range of 30 to 70% of the heat flux in the thickness direction of the elastic layer at the thin portion.

3. 3. The elastic roller according to claim 2, wherein the recesses are formed along a circumferential direction of the tubular substrate.

4. The elastic roller described in claim 3, characterized in that the recesses are formed in multiple numbers in the tubular substrate, and the number of recesses per unit length in the axial center of the paper passing area is less than the number of recesses per unit length in areas other than the axial center of the paper passing area.

5. An elastic roller as described in any one of claims 1 or 4, characterized in that a first recess is formed in the axial center of the paper passing area, a second recess adjacent to the first recess is formed in an area other than the axial center of the paper passing area, and the distance between the first recess and the adjacent second recess is at least twice the distance between the recesses formed in the area other than the axial center of the paper passing area.

6. The elastic roller according to any one of claims 1 to 5, wherein the thickness of the elastic layer in the thick portion is in the range of 1.05 to 1.3 times the thickness of the elastic layer in the thin portion.

7. 7. The elastic roller according to claim 1, wherein a protrusion is formed on an inner peripheral surface of the tubular substrate corresponding to a back side of an area where the recess exists.

8. The elastic roller according to claim 7, characterized in that the convex portion has, in an axial cross section of the elastic roller, a rising portion that rises in a substantially concave curve from the inner peripheral surface of the tubular substrate, and a tip portion that draws a substantially convex curve.

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