Paper feeding roll

Abstract

Provided is a paper feeding roll that is capable of ensuring durability by suppressing wear of the roll surface, and of suppressing paper jamming by removing paper powder adhered to the roll surface.　A paper feeding roll 12 comprises: a shaft body 12a; and an elastic body layer 12b formed on the outer peripheral surface of the shaft body 12a. A projecting section 13 that has an inclined surface 13a extending with the grain and having an inclination that becomes larger in the paper feed direction is provided on the outer peripheral surface of the elastic body layer 12b. The angle θ1 of the inclined surface 13a extending with the grain is 25° to 55°, inclusive. When a load of 500 g is applied, the ratio of the nip area to the product of the nip width and the roll surface length is 0.2 to 0.6, inclusive.

Description

Paper feed roll

[0001] The present invention relates to a paper feed roll that is suitably used in electrophotographic devices such as copying machines, printers, and facsimiles that employ an electrophotographic system.

[0002] Electrophotographic devices such as copiers, printers, and facsimiles that use electrophotography are equipped with a paper feeder, which includes a pickup roll that feeds paper from a paper cassette, a feed roll that transports the paper, and a retard roll.

[0003] JP-A No. 2000-281223 JP-A No. 2022-164161

[0004] These paper feed rolls maintain friction with the paper due to the tackiness inherent in the rubber, and transport the paper. Paper feed rolls must continue to maintain their paper transport function throughout their required service life. However, paper dust, typically calcium carbonate, falls off from the paper as it is transported and adheres to the roll surface. The adhesion of paper dust to the roll surface inhibits contact between the rubber and the paper, reducing the transport function. This can lead to paper jams.

[0005] In Patent Document 1, protrusions are provided on the outer peripheral surface of a cylindrical rotating body in a direction parallel to the rotation axis, and the shape of the protrusions is made more acute than before, which improves the bite into the paper and ensures stable paper feeding. Also, in Patent Document 2, the protrusions of the feed roller extend in the axial direction and the protrusions of the retard roller extend in the circumferential direction, allowing fine particles such as paper dust to escape into the grooves between the protrusions of the feed roller and the grooves between the protrusions of the retard roller, preventing paper dust from accumulating in the nip between the protrusions of the feed roller and the protrusions of the retard roller.

[0006] However, until now, little attention has been paid to how smoothly the paper dust adhering to the roll surface can be removed, and there has been room for improvement in preventing paper jams caused by paper dust.

[0007] The problem that the present invention aims to solve is to provide a paper feed roll that can reduce wear on the roll surface to ensure durability, and can remove paper dust adhering to the roll surface to reduce paper jams.

[0008] The paper feed roll of the present invention comprises a shaft body and an elastic layer formed on the outer peripheral surface of the shaft body, and a convex portion on the outer peripheral surface of the elastic layer having a slope with a grain that increases in slope along the paper feed direction, the angle of the slope with the grain being 25° or more and 55° or less, and the ratio of the nip area to the product of the nip width and the roll surface length at a load of 500 g is 0.2 or more and 0.6 or less.

[0009] The top of each convex portion may have a top surface with a smaller angle than the slope of the convex portion along the grain. In this case, the ratio of the circumferential length of the top surface to the circumferential length of the base of each convex portion may be 0.05 or more and 0.3 or less. The convex portion may have a cross-grain slope that increases in slope in the direction opposite to the paper feed direction. The angle of the cross-grain slope may be greater than the angle of the cross-grain slope. The angle of the cross-grain slope may be 60° or more and 90° or less. The height of each convex portion may be 40 μm or more and 200 μm or less. The JIS-A hardness of the surface of the elastic layer may be 35° or more and 75° or less.

[0010] (1) The paper feed roll according to the present invention comprises a shaft body and an elastic layer formed on the outer peripheral surface of the shaft body, and a convex portion on the outer peripheral surface of the elastic layer having a slope with a convex grain that increases in slope along the paper feed direction, the angle of the slope with a convex grain being 25° or more and 55° or less, and the ratio of the nip area to the product of the nip width and the roll surface length at a load of 500 g being 0.2 or more and 0.6 or less.

[0011] (2) In the above (1), the top of the convex portion may have a top surface with an angle smaller than the slope of the grain of the convex portion.

[0012] (3) In the above (2), the ratio of the circumferential length of the top surface to the circumferential length of the bottom surface of the convex portion may be 0.05 or more and 0.3 or less.

[0013] (4) In any one of (1) to (3) above, the convex portion may have a slope of the reverse grain that increases in slope in the opposite direction to the paper feed direction, and the angle of the slope of the reverse grain may be configured to be greater than the angle of the slope of the normal grain.

[0014] (5) In the above (4), the angle of the inclined surface of the reverse grain may be 60° or more and 90° or less.

[0015] (6) In any one of the above (1) to (5), the height of the convex portion may be 40 μm or more and 200 μm or less.

[0016] (7) In any one of the above (1) to (6), the JIS-A hardness of the surface of the elastic layer may be 35° or more and 75° or less.

[0017] According to the paper feed roll of the present invention, the surface of the elastic layer is provided with convex portions having slopes with a forward grain that increase in slope along the paper feed direction, thereby forming spots for releasing paper dust. By setting the angle of the slopes with a forward grain of 25° or more, a strong shear force is applied to the convex portions and the paper dust, allowing the paper dust to be discharged to the spots. Furthermore, by setting the ratio of the nip area to the product of the nip width and the roll surface length at a load of 500 g to 0.6 or less, a strong shear force is applied to the convex portions and the paper dust, allowing the paper dust to be discharged to the spots. This allows the paper dust adhering to the roll surface to be removed and paper jams due to reduced friction are prevented. Furthermore, by setting the angle of the slopes with a forward grain of 55° or less, excessive shear force is not applied to the convex portions, thereby preventing a decrease in the coefficient of friction due to wear. Furthermore, by setting the ratio of the nip area to 0.2 or more, excessive shear force is not applied to the convex portions, preventing a decrease in the coefficient of friction due to wear. This prevents paper jams.

[0018] Furthermore, by providing the top of the convex portion with a top surface that has a smaller angle than the slope of the convex grain, wear on the top of the convex portion is suppressed, and a decrease in durability is suppressed. In this case, if the ratio of the circumferential length of the top surface to the circumferential length of the base surface of the convex portion is 0.05 or more, wear on the top of the convex portion is easily suppressed. Furthermore, if this ratio is 0.3 or less, paper dust is less likely to accumulate on the top of the convex portion, and paper dust can be easily discharged to the spot.

[0019] The convex portion preferably has a cross-grain slope that increases in slope in the direction opposite to the paper feed direction. In this case, if the angle of the cross-grain slope is configured to be larger than the angle of the forward-grain slope, paper dust is less likely to accumulate on the top of the convex portion, and paper dust is more likely to be discharged to the spot. If the angle of the cross-grain slope is 60° or more, the angle of the cross-grain slope is not too gentle, making it easier to discharge paper dust to the spot. If the angle of the cross-grain slope is 90° or less, the strength of the convex portion is ensured, making it easier for shear force to be applied to the convex portion, making it easier for shear force to be applied to the paper dust, making it easier for paper dust to be discharged to the spot.

[0020] When the height of the convex portions is 40 μm or more, deterioration of durability due to wear is easily suppressed. Also, shear force is easily applied to the paper powder, making it easier to discharge the paper powder into the spot. When the height of the convex portions is 200 μm or less, the strength of the convex portions is ensured, making it easier to apply shear force to the convex portions, making it easier to apply shear force to the paper powder, making it easier to discharge the paper powder into the spot. Also, excessive shear force is not applied to the convex portions, making it easier to suppress deterioration of durability due to wear.

[0021] When the JIS-A hardness of the surface of the elastic layer is 35° or more, deterioration in durability due to wear is easily suppressed.When the JIS-A hardness of the surface of the elastic layer is 75° or less, excessive shear force is not applied to the protrusions, and deterioration in durability due to wear is suppressed.

[0022] 2(a) shows a state before one sheet of paper arrives between the rolls, and FIG. 2(b) shows the operation when one sheet of paper arrives between the rolls. FIG. 2(a) shows a state before two sheets of paper arrive between the rolls, and FIG. 3(b) shows the operation when two sheets of paper arrive between the rolls. FIG. 3(a) shows a state before two sheets of paper arrive between the rolls, and FIG. 3(b) shows the operation when two sheets of paper arrive between the rolls. FIG. 3(b) shows a schematic external view of a paper feed roll according to one embodiment of the present invention. FIG. 3(b) is a schematic diagram illustrating the shape of a convex portion. FIG. 3(b) is a schematic diagram showing another embodiment of a convex portion.

[0023] The paper feed roll according to the present invention will be described in detail. Fig. 1 is a schematic diagram of a paper feed device. Figs. 2 and 3 are diagrams showing the paper feeding operation of the paper feed device shown in Fig. 1. Fig. 4 is a schematic diagram of the appearance of a paper feed roll according to one embodiment of the present invention. Fig. 5 is a schematic diagram illustrating the shape of the convex portions.

[0024] As shown in FIG. 1 , the paper feed device 10 includes a paper feed roll 12 (feed roll) and a separation roll 14 (retard roll). The paper feed roll 12 includes a shaft 12a and an elastic layer 12b formed on the outer periphery of the shaft 12a. The separation roll 14 includes a shaft 14a and an elastic layer 12bb formed on the outer periphery of the shaft 14a. The paper feed roll 12 is driven to rotate by power from a drive source (motor) (not shown) and functions to transport paper P. The separation roll 14 is pressed against the paper feed roll 12 with a predetermined pressure by a biasing member (e.g., a spring) (not shown). The separation roll 14 also includes a built-in torque limiter (not shown) that applies a brake torque in the direction opposite to the rotational direction (indicated by the arrow) in which paper P is transported.

[0025] The paper P to be transported is stacked in a paper feed cassette 16. The surface of a pull-in roll 18 (pickup roll) is in frictional contact with the upper surface of the stacked paper P, and the pull-in roll 18 is configured to sequentially pay out the paper P from the paper feed cassette 16 toward the paper feed roll 12. The pull-in roll 18 has a shaft 18a and an elastic layer 18b formed on the outer periphery of the shaft 18a. The pull-in roll 18 is configured to rotate in conjunction with the drive of the paper feed roll 12 via a connecting member (such as a gear or timing belt) not shown.

[0026] As the paper feed roll 12 rotates, the pull-in roll 18 rotates, and paper P is fed one sheet at a time from the paper feed cassette 16 toward the paper feed roll 12. As shown in FIG. 2A, the paper feed roll 12 has been rotating since before the paper P arrived. As the paper feed roll 12 rotates, the separation roll 14, which is pressed against the paper feed roll 12, is driven to rotate against the brake torque due to the frictional force between the paper feed roll 12 and the separation roll 14 (between the rolls). When a sheet of paper P that has been fed arrives between the rolls, as shown in FIG. 2B, the paper P passes between the rolls and is conveyed in the paper feed direction Y.

[0027] When two sheets of paper P are fed from the paper feed cassette 16 toward the paper feed roll 12, as shown in FIG. 3A, before the arrival of the sheets P1 and P2, the paper feed roll 12 is driven to rotate, and the separation roll 14 is driven to rotate against the brake torque as the paper feed roll 12 rotates. When the two fed sheets P1 and P2 arrive between the rolls, as shown in FIG. 3B, the separation roll 14 comes into contact with the paper feed roll 12 via the two sheets P1 and P2. Because the frictional force acting between the two sheets P1 and P2 is small, the separation roll 14 is stopped by the brake torque and does not follow the rotation of the paper feed roll 12. As a result, the sheet P1 in contact with the paper feed roll 12 passes between the rolls as the paper feed roll 12 rotates, and is conveyed in the paper passage direction Y, while the sheet P2 in contact with the separation roll 14 is not conveyed. This prevents double feeding of sheets P.

[0028] The paper feed roll according to the present invention can be suitably used as a paper feed roll 12 (feed roll), a separation roll 14 (retard roll), a pull-in roll 18 (pickup roll), etc. in a paper feed device 10.

[0029] The configuration of the paper feed roll according to the present invention will be described below using the paper feed roll 12 as an example. Other paper feed rolls (separation rolls, pull-in rolls) have a similar configuration. In the paper feed rolls in Figures 4 and 5, the X direction is the axial direction and the Y direction is the paper feed direction.

[0030] The paper feed roll 12 according to one embodiment of the present invention includes a shaft 12a and an elastic layer 12b formed on the outer peripheral surface of the shaft 12a. The elastic layer 12b is a layer (base layer) that serves as the base of the paper feed roll 10. The elastic layer 12b is a layer that appears on the surface of the paper feed roll 12.

[0031] The shaft 12a may be a solid or hollow (cylindrical) body made of metal or resin. Examples of metal materials include iron, stainless steel, and aluminum. The elastic layer 12b may be bonded to the shaft 12a via an adhesive layer (primer layer). The adhesive, primer, etc. may be made conductive as necessary.

[0032] The elastic layer 12b is made of an elastic material and formed in a roll shape on the outer peripheral surface of the shaft 12a. The elastic layer 12b has a plurality of convex portions 13 on its outer peripheral surface. The convex portions 13 have forward-grain slopes 13a that increase in slope along the paper feed direction Y. The convex portions 13 also have counter-grain slopes 13b that increase in slope along the opposite direction to the paper feed direction Y. Furthermore, the tops of the convex portions 13 have top surfaces 13c that are parallel to the bottom surfaces 13d of the convex portions 13. The top surfaces 13c have a smaller angle than the forward-grain slopes 13a of the convex portions 13. The convex portions 13 are trapezoidal in shape when viewed in a circumferential cross section.

[0033] The multiple protrusions 13 are each formed as independent islands in both the circumferential direction and the axial direction X of the elastic layer 12b. The multiple protrusions 13 are regularly arranged in a staggered pattern on the outer peripheral surface of the elastic layer 12b. The first row of protrusions 13 are aligned along the axial direction X of the elastic layer 12b. Similarly, the second row of protrusions 13 and the third row of protrusions 13 are aligned along the axial direction X of the elastic layer 12b. When viewed in the circumferential direction of the elastic layer 12b, the second row of protrusions 13 are positioned at a position offset in the axial direction from the first row of protrusions 13 and the third row of protrusions 13. The first row of protrusions 13 and the third row of protrusions 13 are positioned at the same position in the axial direction. Therefore, in the circumferential direction, for example, a spot S is formed between the first row of protrusions 13 and the third row of protrusions 13, and this spot S serves as a portion for collecting paper dust discharged from the protrusions 13.

[0034] Here, the angle θ1 of the forward-grain slope 13a is set to be 25° or greater and 55° or less. If the angle θ1 of the forward-grain slope 13a is less than 25°, shear force is not applied to the convex portions 13 and paper dust, which results in poor paper dust discharge to the spot S, a decrease in the coefficient of friction of the roll surface after endurance testing, and increased paper jamming. On the other hand, if the angle θ1 of the forward-grain slope 13a is greater than 55°, excessive shear force is applied to the convex portions 13, resulting in increased wear of the convex portions 13. The disappearance of the slope reduces the coefficient of friction of the roll surface after endurance testing, making paper jamming more likely. Furthermore, because the forward-grain slope 13a of the convex portions 13 is too steep, it becomes difficult to discharge the paper dust to the spot S even when shear force is applied to the convex portions 13 and paper dust. The angle θ1 of the forward-grain slope 13a is preferably 30° or greater, more preferably 35° or greater, from the perspective of facilitating paper dust discharge to the spot S. On the other hand, the angle θ1 of the inclined surface 13a of the normal grain is preferably 50° or less, and more preferably 45° or less, from the viewpoint that the amount of wear of the convex portion 13 can be easily suppressed.

[0035] The angle θ2 of the counter-grain slope 13b is not particularly limited, but it is preferable that it be larger than the angle θ1 of the normal-grain slope 13a. This makes it difficult for paper dust to accumulate on the top surface 13c of the convex portion 13, making it easier to discharge the paper dust into the spot S. The angle θ2 of the counter-grain slope 13b is preferably 60° or greater and 90° or less. When the angle θ2 of the counter-grain slope 13b is 60° or greater, the angle θ2 of the counter-grain slope 13b is not too gentle, making it easier to discharge the paper dust into the spot S. When the angle θ2 of the counter-grain slope 13b is 90° or less, the strength of the convex portion 13 is ensured, making it easier for shear force to be applied to the convex portion 13 and the paper dust, making it easier to discharge the paper dust into the spot S. From the above perspective, the angle θ2 of the counter-grain slope 13b is more preferably 65° or greater and 90° or less, and even more preferably 70° or greater and 90° or less.

[0036] The angle of the top surface 13c is preferably 0° or more and 20° or less with respect to a plane parallel to the bottom surface 13d of the convex portion 13. It is more preferably 0° or more and 15° or less, and even more preferably 0° or more and 10° or less. When the angle of the top surface 13c is smaller than the inclined surface 13a of the convex portion 13, wear on the top of the convex portion 13 is suppressed, and a decrease in durability is suppressed. Furthermore, a smaller angle of the top surface 13c makes it easier to increase the nip area. Furthermore, a larger angle of the top surface 13c makes it easier for a shear force to be applied to the paper powder, making it less likely for paper powder to accumulate on the top surface 13c and making it easier for paper powder to be discharged into the spot S.

[0037] The ratio (A / B) of the circumferential length A of the top surface 13c of the convex portion 13 to the circumferential length B of the bottom surface 13d of the convex portion 13 is preferably 0.05 or more and 0.3 or less. When the ratio is 0.05 or more, wear at the top of the convex portion 13 is easily suppressed. Furthermore, when the ratio is 0.3 or less, paper dust is less likely to accumulate at the top of the convex portion 13, and paper dust is easily discharged to the spot S. The ratio is more preferably 0.10 or more and 0.3 or less, and even more preferably 0.10 or more and 0.25 or less.

[0038] The height C of the convex portions 13 is preferably 40 μm or more and 200 μm or less. When the height C of the convex portions 13 is 40 μm or more, a decrease in durability due to wear can be easily suppressed. Furthermore, shear force is easily applied to the paper powder, making it easy to discharge the paper powder into the spot S. When the height C of the convex portions 13 is 200 μm or less, the strength of the convex portions 13 is ensured, making it easy to apply shear force to the convex portions 13, making it easy to apply shear force to the paper powder, making it easy to discharge the paper powder into the spot S. Furthermore, excessive shear force is not applied to the convex portions 13, making it easy to suppress a decrease in durability due to wear. The height C of the convex portions 13 is more preferably 50 μm or more and 150 μm or less, and even more preferably 60 μm or more and 100 μm or less.

[0039] The JIS-A hardness of the surface of the elastic layer 12b is preferably 35° or more and 75° or less. When the hardness is 35° or more, deterioration in durability due to wear is easily suppressed. Furthermore, when the hardness is 75° or less, excessive shear force is not applied to the protrusions 13, and deterioration in durability due to wear is suppressed. The hardness is more preferably 35° or more and 70° or less, and even more preferably 40° or more and 65° or less.

[0040] In the paper feed roll according to the present invention, the nip area is important. The ratio of the nip area to the product of the nip width and the roll surface length under a load of 500 g is set to 0.2 or more and 0.6 or less. The nip width is the length of the nip in the circumferential direction, and the roll surface length is the roll length (the length of the elastic layer 12b) in the axial direction of the roll. Setting the nip area ratio to 0.2 or more prevents excessive shear force from being applied to the protrusions 13, thereby suppressing a decrease in the coefficient of friction due to wear. This reduces paper jams. Setting the nip area ratio to 0.6 or less applies a strong shear force to the paper dust, allowing the paper dust to be discharged into the spot S. This removes paper dust adhering to the roll surface and prevents paper jams due to a decrease in friction. The nip area ratio is preferably 0.25 or more and 0.55 or less, more preferably 0.3 or more and 0.5 or less. The nip area can be determined from the contact area when a glass plate is pressed against the outer peripheral surface of the elastic layer 12a of the paper feed roll 10 with a load of 500 gf.

[0041] The elastic layer 12b is made of an elastic material such as rubber, elastomer, or resin. The material is not particularly limited as long as it is a rubber-like elastic material. For example, known materials such as urethane rubber, hydrin rubber, silicone rubber, and EPDM can be used.

[0042] Various additives may be added to the elastic layer 12b as needed, such as lubricants, vulcanization accelerators, antioxidants, light stabilizers, viscosity modifiers, processing aids, flame retardants, plasticizers, fillers, dispersants, antifoaming agents, pigments, and mold release agents.

[0043] The thickness of the elastic layer 12b is not particularly limited, and may be set appropriately within the range of 2 to 25 mm.

[0044] The elastic layer 12b can be formed by molding using a mold. For example, a core material is coaxially placed in the hollow portion of a roll molding mold, an uncrosslinked rubber composition is injected, and the composition is heated and cured (crosslinked), followed by demolding to form a tubular elastic layer 12b. A molding mold having recesses formed on its inner circumferential surface in shapes corresponding to the protrusions 13 can be used. The paper feed roll 10 can be formed by inserting the shaft 12a into the cylindrically formed elastic layer 12b. Note that the method for imparting a shape to the outer circumferential surface of the elastic layer 12b is not limited to transfer using a mold, and may also be polishing or the like.

[0045] According to the paper feed roll 10 configured as described above, the surface of the elastic layer 12b is provided with convex portions 13 having forward-grain slopes 13a that increase in slope along the paper feed direction Y, thereby forming spots S for releasing paper dust. By setting the angle θ1 of the forward-grain slopes 13a to 25° or more, a strong shear force is applied to the convex portions 13 and the paper dust, allowing the paper dust to be discharged to the spots S. Furthermore, by setting the ratio of the nip area to the product of the nip width and the roll surface length at a load of 500 g to 0.6 or less, a strong shear force is applied to the convex portions 13 and the paper dust, allowing the paper dust to be discharged to the spots S. This removes paper dust adhering to the roll surface and prevents paper jams due to reduced friction. By setting the angle θ1 of the forward-grain slopes 13a to 55° or less, excessive shear force is not applied to the convex portions 13, preventing a decrease in the coefficient of friction due to wear. Furthermore, by setting the ratio of the nip area to 0.2 or more, excessive shearing force is not applied to the protrusions 13, and a decrease in the coefficient of friction due to wear is suppressed, thereby making it possible to prevent paper jams.

[0046] Furthermore, by providing the tops of the convex portions 13 with top surfaces 13c that have a smaller angle than the slopes 13a of the convex portions 13 in the direction of the grain, wear at the tops of the convex portions 13 is suppressed, and a decrease in durability is suppressed. In this case, if the ratio (A / B) of the circumferential length A of the top surfaces 13c to the circumferential length B of the bottom surfaces 13d of the convex portions 13 is 0.05 or more, wear at the tops of the convex portions 13 is likely to be suppressed. If the ratio is 0.3 or less, paper dust is unlikely to accumulate at the tops of the convex portions 13, and paper dust can be easily discharged into the spot S.

[0047] The convex portion 13 has a cross-grain slope 13b that increases in slope in the direction opposite to the paper feed direction Y. In this case, the angle θ2 of the cross-grain slope 13b is configured to be larger than the angle θ1 of the normal-grain slope 13a, so that paper dust is less likely to accumulate on the top of the convex portion 13 and paper dust is easily discharged to the spot S. When the angle θ2 of the cross-grain slope 13b is 60° or more, the angle θ2 of the cross-grain slope 13b is not too gentle, making it easy to discharge paper dust to the spot S. When the angle θ2 of the cross-grain slope 13b is 90° or less, the strength of the convex portion 13 is ensured, making it easy for shear force to be applied to the convex portion 13 and for shear force to be applied to the paper dust, making it easy to discharge paper dust to the spot S.

[0048] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention.

[0049] For example, the convex portions 13 in Fig. 5 have top surfaces 13c at the top of the convex portions 13 that are smaller in angle than the slopes 13a of the grains of the convex portions 13, but in the paper feed roll of the present invention, the tops of the convex portions do not have to have top surfaces as shown in Fig. 5. Also, the top surfaces 13c of the convex portions 13 in Fig. 5 are parallel to the bottom surfaces 13d of the convex portions 13, but the top surfaces 13c of the convex portions 13 do not have to be parallel to the bottom surfaces 13d of the convex portions 13.

[0050] FIG. 6 shows another embodiment of the protrusion.

[0051] As shown in Fig. 6(a), the convex portion 131 has a forward-grain slope 131a that increases in slope along the paper feed direction Y and a reverse-grain slope 131b that increases in slope along the opposite direction to the paper feed direction Y. The convex portion 131 does not have a top surface at the top of the convex portion 131 as shown in Fig. 5. When viewed in a circumferential cross section, the convex portion 131 has a triangular shape.

[0052] 6B, the convex portion 132 has a forward-grain slope 132a that increases in slope along the paper feed direction Y, and a reverse-grain slope 132b that increases in slope along the opposite direction to the paper feed direction Y. The top of the convex portion 132 also has a top surface 132c whose angle (θ32) is smaller than the angle θ12 of the forward-grain slope 132a of the convex portion 132. The top surface 132c of the convex portion 132 is not parallel to the bottom surface of the convex portion 132.

[0053] 5 is a flat surface, it may be a curved surface. The shape of the convex portion is not limited to the shape shown in FIG.

[0054] The plurality of protrusions may be uniformly distributed or arranged on the peripheral surface of the elastic layer 12b, or may be arranged randomly or in an array.

[0055] The present invention will be described in detail below using examples and comparative examples.

[0056] Using a cylindrical molding die having multiple recesses on its inner peripheral surface, an elastic layer of a urethane rubber composition was formed on the outer periphery of a core material (φ6, made of SUS304). This resulted in a paper feed roll having multiple protrusions on the outer peripheral surface of the elastic layer, as shown in Figures 4 and 5. By observing the radial cross section of the elastic layer of the prepared paper feed roll, the following were measured: the grain slope angle θ1, the grain slope angle θ2, the circumferential length A of the top surface, the circumferential length B of the bottom surface, and the height C of the protrusions. The JIS-A hardness of the outer peripheral surface of the elastic layer of the prepared paper feed roll was also measured.

[0057] (Nip Area Ratio) The nip area was determined from the contact area when a glass plate was pressed into the outer peripheral surface of the elastic layer of the paper feed roll with a load of 500 gf. A Keyence laser microscope was used for the measurement. The ratio of the nip area to the product of the nip width and the roll surface length was then calculated.

[0058] (Friction Measurement) The paper feed roll was set in the friction coefficient measuring instrument with the rotation direction aligned, and a load of 2.94 N (300 gf) (W １ The tension speed was set to 180 mm / s. Next, a sheet of paper (Ricoh 6200 A4) was set between the paper feed roll and the lifting plate, and the edge of the paper was connected to a load measuring device (load cell). Next, the paper feed roll was rotated for 10 seconds or more, and the tension force (W ２ The tensile force was the average value in the stable region of the measurement chart. The coefficient of friction was calculated by W ２ / W １ The coefficient of friction was measured at the initial stage before the test and at the endurance stage after passing 20,000 sheets.

[0059] (Durability Test) Using the prepared paper feed roll, printing was repeatedly performed until a paper jam occurred, and the number of sheets passed before the jam was measured. After 20,000 sheets had been passed, the coefficient of friction of the outer surface of the elastic layer and the amount of wear of the convex portions (calculated from the difference in the height of the convex portions before and after the test) were also measured. The evaluation was performed using a Ricoh MP C2503 test machine under a 10°C x 10% RH environment, using Ricoh My Paper A4. A test in which the number of sheets passed before the jam occurred was rated as "◎" (Excellent), a test in which the number was between 50,000 and 100,000 was rated as "○", and a test in which the number was less than 50,000 was rated as "×".

[0060]

[0061] In Comparative Example 1, the slope angle θ1 of the convex portion's forward grain is too small. In Comparative Example 1, shear force is not easily applied to the convex portion and paper dust, which makes it difficult for the paper dust to be discharged to the spot, resulting in a decrease in the coefficient of friction of the roll surface after endurance testing and making paper jams more likely to occur. In Comparative Example 2, the slope angle θ1 of the convex portion's forward grain is too large. In Comparative Example 2, too much shear force is applied to the convex portion, increasing the amount of wear on the convex portion, and the disappearance of the slope reduces the coefficient of friction of the roll surface after endurance testing, making paper jams more likely to occur.

[0062] In Comparative Example 3, the nip area ratio is too large. In Comparative Example 3, shear force is not applied to the convex portions and paper dust, the paper dust is not easily discharged to the spot, the coefficient of friction of the roll surface after endurance testing is reduced, and paper jams are more likely to occur. In Comparative Example 4, the nip area ratio is too small. In Comparative Example 4, too much shear force is applied to the convex portions, increasing the amount of wear on the convex portions, and the disappearance of the slope reduces the coefficient of friction of the roll surface after endurance testing, making paper jams more likely to occur.

[0063] On the other hand, in the example, the slope angle θ1 of the convex portion is between 25° and 55°. The nip area ratio is between 0.2 and 0.6. In the example, an appropriate shear force is applied to the convex portion and paper dust, which improves the discharge of paper dust to the spot and reduces the reduction in friction and paper jams. Furthermore, because excessive shear force is not applied to the convex portion, the amount of wear on the convex portion is reduced, which reduces paper jams.

[0064] From the above, it can be seen that according to the examples and comparative examples, the outer peripheral surface of the elastic layer is provided with a convex portion having a slope with a grain that increases inclination along the paper feed direction, the angle of the slope with a grain that is between 25° and 55°, and the ratio of the nip area to the product of the nip width and the roll surface length at a load of 500 g is between 0.2 and 0.6, thereby reducing wear on the roll surface and ensuring durability, and removing paper dust adhering to the roll surface to reduce paper jams.

[0065] Although the embodiments and examples of the present invention have been described above, the present invention is not limited to the above embodiments and examples, and various modifications are possible within the scope of the invention.

[0066] 10 Paper feed device 12 Paper feed roll (paper feed roll) 12a Shaft 12b Elastic layer 14 Separation roll 14a Shaft 14b Elastic layer 16 Paper feed cassette 18 Pull-in roll 18a Shaft 18b Elastic layer P, P1, P2 Paper X Axial direction (of paper feed roll) Y Paper passing direction 13 Convex portion 13a Slope of the convex portion along the grain 13b Slope of the counter-grain (of the convex portion) 13c Top surface (of the convex portion) 13d Bottom surface (of the convex portion) θ1 Angle of the slope of the convex portion along the grain θ2 Angle of the slope of the counter-grain (of the convex portion) A Circumferential length of the top surface (of the convex portion) B Circumferential length of the bottom surface (of the convex portion) C Height of the convex portion S Spot

Claims

1. A paper feed roll comprising a shaft body and an elastic layer formed on the outer peripheral surface of the shaft body, a convex portion on the outer peripheral surface of the elastic layer having a slope with a gradient that increases in the paper feed direction, the angle of the slope of the gradient is 25° or more and 55° or less, and the ratio of the nip area to the product of the nip width and the roll face length at a load of 500g is 0.2 or more and 0.6 or less.

2. The paper feed roll according to claim 1, wherein the tops of the convex portions have top faces with an angle smaller than that of the inclined surfaces of the convex portions.

3. The paper feed roll according to claim 2, wherein the ratio of the circumferential length of the top surface of each of the protrusions to the circumferential length of the bottom surface of each of the protrusions is 0.05 or more and 0.3 or less.

4. A paper feed roll described in any one of claims 1 to 3, wherein the convex portion has a reverse-grain slope that increases in slope in the opposite direction to the paper feed direction, and the angle of the reverse-grain slope is larger than the angle of the normal-grain slope.

5. The paper feed roll according to claim 4, wherein the angle of the inclined surface of the reverse grain is between 60° and 90°.

6. A paper feed roll according to any one of claims 1 to 5, wherein the height of the convex portions is 40 μm or more and 200 μm or less.

7. The paper feed roll according to any one of claims 1 to 6, wherein the JIS-A hardness of the surface of the elastic layer is 35° or more and 75° or less.

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