JP2006126719A - Developing roll - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing roll which can uniformize contact pressure against a photoreceptor drum, with respect to the shaft direction. <P>SOLUTION: The outer diameter of a shaft 1 corresponding to the central part in an axial direction of an elastic layer 2 is uniformly formed. The diameters of the shaft 1 at the outer parts outside the central part in the shaft direction are gradually reduced toward the right and left both end of the elastic layer 2, respectively, with reference to the outer diameter of the shaft 1 at the central part in the shaft direction. The outer diameter of the elastic layer 2 at the central part in the shaft direction is uniformly formed, and the outer diameter at the parts corresponding to the parts of the shaft 1 whose diameter is reduced is formed so as to be not larger than a diameter which is 15 μm larger than the outer diameter of the central part in the shaft direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a developing roll used in electrophotographic equipment such as a copying machine and a printer.

  In an electrophotographic apparatus such as a copying machine or a printer, a developing roll is provided against the photosensitive drum. In this developing roll, an elastic layer made of rubber or the like is formed on the outer peripheral surface of the shaft body. If necessary, one or two thin coating layers such as a resistance adjusting layer and a protective layer are formed on the surface of the elastic layer. More than one layer is formed.

  The developing roll is usually formed by using a cylindrical mold having a shaft body having a uniform outer diameter and a mold surface having a uniform inner diameter. That is, first, an adhesive is applied to the outer peripheral surface of the shaft body, this is coaxially installed in the hollow portion of the cylindrical mold, and the left and right ends are sealed with a lid, and then the elastic layer forming material is injected. Then, the elastic layer is formed by vulcanization by oven vulcanization or the like. Thereafter, the mold is removed, and both end edges of the elastic layer are cut to adjust the dimensions. Then, if necessary, after applying a forming material such as a resistance adjusting layer or a protective layer by a roll coating method, a spray coating method, a dipping method, etc., drying, heat treatment, etc. are performed, and the resistance adjusting layer or the protective layer is then applied. Etc.

  However, in the formation of the elastic layer, after demolding, the elastic layer contracts due to the action of residual stress (contraction stress). This shrinkage does not shrink in the axial direction because the inner peripheral surface portion of the elastic layer is bonded with an adhesive, but shrinks in the axial direction because the outer peripheral surface portion of the elastic layer is not constrained. Due to such contraction, as shown in FIG. 7, the elastic layer 52 jumps in the vicinity of both left and right ends, and the outer diameter of the elastic layer 52 gradually increases toward the left and right end edges. The elastic layer 52 is cut and removed at both left and right edge portions for adjusting the shape and dimension after the elastic layer 52 is shrunk, and most of the jumped up part is cut and removed. ), The left and right ends of the elastic layer 52 are slightly jumped up after cutting and removal. However, in FIG. 7, the deformation amount is exaggerated. In FIG. 7, reference numeral 51 denotes a shaft body.

  When such a developing roll is used for a contact developing method (the photosensitive drum and the developing roll are in contact with each other), the contact pressure with the photosensitive drum is increased near the left and right ends, and the frictional force is increased. Become. For this reason, the outermost layer (the resistance adjusting layer, the protective layer, etc.) is worn in the vicinity of both the left and right ends of the developing roll, leaks occur, and the image deteriorates. Also, the vicinity of the left and right ends of the developing roll is damaged, toner leakage occurs from the damaged portion, and the image is soiled by the leaked toner. Further, due to the frictional force in the vicinity of the left and right ends, the photosensitive drum and the developing roll cannot be smoothly slid, the rotation speed is not stable, and image unevenness (light unevenness) occurs when the rotation speed changes. .

Therefore, chamfering is usually performed on the spring-up portions near the left and right ends of the elastic layer 52. Further, as a method for making the chamfering process unnecessary, there has been proposed a method in which uneven charging with respect to the photosensitive drum is prevented with respect to the charging roll instead of the developing roll (see Patent Document 1). In this structure, a rubber roller is bonded to the outer peripheral portion of the core metal, and the core metal is gradually formed to have a smaller diameter from the central portion toward both ends. When contacted with the photosensitive drum, the central portion of the core bar bends away from the photosensitive drum, and uneven contact between the central portion and both end portions due to the bending is absorbed by deformation of the rubber roller. Thus, the thickness of the rubber roller portion on the side in contact with the photosensitive drum is made substantially constant, resistance unevenness due to the difference in thickness is prevented, the substantial resistance value in the axial direction of the charging roll is made uniform, and supplied to the photosensitive drum. The charge is also made uniform.
Japanese Patent Laid-Open No. 10-48915

  However, when the charging roll disclosed in Patent Document 1 is applied to a developing roll, the contact pressure with the photosensitive drum is increased and the frictional force is increased at the central portion where the outer diameter of the cored bar is large. For this reason, a bias pressure is generated in the axial direction as usual, and smooth sliding cannot be performed, and image unevenness occurs. Moreover, in the central portion, which is the image area, toner stress increases due to the high contact pressure, thereby causing filming and deterioration of the image.

  The present invention has been made in view of such circumstances, and the contact pressure with the photosensitive drum is made substantially uniform in the axial direction, thereby adversely affecting the image (deterioration of the image due to leakage or filming, contamination of the image due to leaked toner). , Image unevenness, and the like).

  In order to achieve the above object, the developing roll of the present invention comprises a shaft body and an elastic layer formed by molding on the outer peripheral surface of the shaft body, and the outer peripheral surface of the elastic layer is a mold of the mold. A developing roll serving as a transfer surface of the surface, wherein a shaft body corresponding to a central portion in the axial direction of the elastic layer is formed to have a uniform outer diameter, and a shaft body in an outer portion in the axial direction from the central portion in the axial direction. The outer diameter of the elastic layer is gradually reduced toward the left and right edges of the elastic layer with reference to the outer diameter of the shaft body at the axial central portion, and the outer diameter of the elastic layer is uniform at the axial central portion. The portion corresponding to the reduced diameter portion of the shaft body is formed to have a diameter not more than 15 μm larger than the outer diameter at the central portion in the axial direction.

  That is, in the development roll of the present invention, in the formation of the elastic layer, after demolding and after cutting and removing the left and right edge portions, the vicinity of both ends in the axial direction of the elastic layer tries to jump up. The shape and size of the shaft body corresponding to the portion that is about to jump up are gradually reduced in diameter toward the left and right edges of the elastic layer. That is, in the reduced diameter portion, since the elastic layer is thicker than the axial central portion, the amount of radial contraction after demolding is larger than the axial central portion. As a result, even if the elastic layer of the portion that is going to jump is expanded in diameter, the maximum diameter is suppressed to a value that is 15 μm larger than the outer diameter of the elastic layer in the central portion in the axial direction. Even when a coating layer such as a resistance adjusting layer or a protective layer is formed on the outer peripheral surface of the elastic layer, by forming the coating layer with a uniform thickness, the maximum diameter of the portion of the developing roll that is about to jump up is formed. Is less than 15 μm larger than the outer diameter of the central portion in the axial direction. For this reason, in the contact development method, the contact pressure with the photosensitive drum can be made substantially uniform in the axial direction, and wear and damage in the vicinity of both ends can be prevented and smooth sliding can be achieved.

  In the present invention, the “axially central portion” is a portion corresponding to the electrostatic latent image forming region on the surface of the photosensitive drum, and the “axially outer portion than the axially central portion” means the photosensitive drum. This is a portion corresponding to an electrostatic latent image non-formation region located on the outer side in the axial direction from the surface electrostatic latent image formation region.

  In the developing roll of the present invention, since the diameter of the shaft corresponding to the vicinity of both ends of the elastic layer is gradually reduced toward the both ends of the elastic layer, the diameter expansion due to the jumping up near both ends of the elastic layer is reduced ( 15 μm or less). For this reason, when used in the contact development method, wear and damage in the vicinity of both ends do not occur, and leakage due to wear and toner leakage due to damage are prevented. Also, no axial bias is generated between the photosensitive drum and the photosensitive drum, thereby enabling smooth sliding and preventing image unevenness. Further, the smooth sliding reduces the torque required for rotational driving of the developing roll and the photosensitive drum, reducing the load on the driving motor that rotationally drives the developing roll and the driving motor that rotationally drives the photosensitive drum. As a result, it is possible to reduce the size of the electrophotographic equipment by suppressing heat generation of the electrophotographic equipment such as a printer or by downsizing the drive motor.

  In particular, the axial length of each reduced-diameter portion of the shaft body is in the range of 2 to 15% of the axial length of the elastic layer, and the shaft body corresponding to the left and right end edges of the elastic layer. When the outer diameter of the reduced diameter portion is in the range of 50 to 97% of the reference outer diameter of the axially central portion of the shaft body, the diameter expansion due to the jumping of the vicinity of both ends in the axial direction of the elastic layer is suitably reduced. be able to.

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a first embodiment of the developing roll of the present invention. In this developing roll, an elastic layer 2 is formed on the outer peripheral surface of the shaft body 1 by molding. The outer diameter of the shaft body 1 is such that the portion corresponding to the central portion in the axial direction of the elastic layer 2 is formed to have a uniform outer diameter D _0, and the outer portion in the axial direction from the central portion in the axial direction is the center in the axial direction. With reference to the outer diameter D ₀ of the shaft body 1 of the portion, the diameter is gradually reduced toward the left and right end edges of the elastic layer 2 respectively, and the outer portions in the axial direction from the left and right end edges of the elastic layer 2 are respectively in the axial direction. It is formed to have the same uniform outer diameter D ₀ as the central portion. Corresponding to the shape and size of the shaft 1, the outer diameter of the elastic layer 2 is also formed so that the central portion in the axial direction has a uniform outer diameter, and the portion corresponding to the reduced diameter portion of the shaft 1 is the center in the axial direction. The diameter is gradually reduced toward the left and right ends of the elastic layer 2 with reference to the outer diameter of the portion. Here, the diameter-reduced portions on the left and right ends of the shaft body 1 and the elastic layer 2 are portions corresponding to the electrostatic latent image non-formation regions on both ends in the axial direction of the photosensitive drum surface. The central portion in the axial direction is a portion corresponding to the electrostatic latent image forming region on the surface of the photosensitive drum. The outer peripheral surface of the elastic layer 2 is a transfer surface of the mold surface of the mold, and after the demolding, the outer peripheral surface of the elastic layer 2 is not subjected to chamfering or the like, and the shape dimension Formed. Furthermore, in this embodiment, an intermediate layer (first coating layer) 3 is formed on the outer peripheral surface of the elastic layer 2 with a uniform thickness, and a surface layer (second coating layer) 4 is formed on the outer peripheral surface of the intermediate layer with a uniform thickness. Is formed. As a result, the outer diameter of the surface layer 4 is also formed so that the central portion in the axial direction has a uniform outer diameter, and the portion corresponding to the reduced diameter portion of the elastic layer 2 is elastic with respect to the outer diameter of the central portion in the axial direction. The diameter is gradually reduced toward the left and right edges of the layer 2.

  Such a developing roll can be produced by the same method as the conventional method described at the beginning except that the shaft body 1 having the reduced diameter portion is used. In this case, as shown in FIG. 2, the elastic layer 2 is first formed to the outside in the axial direction from the diameter-reduced portion of the shaft body 1, and the shaft body is adjusted when the shape dimension is adjusted after demolding. Cut along the surface (dashed line A) corresponding to the outer edge of the reduced diameter portion 1 and remove the left and right edge portions on the outer side in the axial direction. As a result, it is also possible to remove the jumping portions formed at the left and right edge portions that have been cut and removed.

Here, the shape dimension of the reduced diameter portion of the shaft body 1 will be described in more detail. The shape size of the reduced diameter portion is set in consideration of the shrinkage rate of the elastic layer 2. That is, as described in the background art at the beginning (see FIG. 7), the outer peripheral surface of the shaft body 51 is normally used by using a cylindrical mold having a shaft body 51 having a uniform outer diameter and a mold surface having a uniform inner diameter. When the elastic layer 52 is formed by mold forming, the elastic layer 52 is bent up near the both ends in the axial direction by the action of residual stress (shrinkage stress) after demolding or cutting and removing the left and right edges. The shape gradually increases in diameter toward both end edges. Therefore, in the present invention, the shape dimension of the enlarged diameter portion is obtained in advance as data, and in anticipation of the shape dimension of the enlarged diameter portion, as shown in FIG. The portion has a shape that is gradually reduced in diameter toward both end edges of the elastic layer 2. That is, in the reduced diameter portion, the elastic layer 2 immediately after demolding is thicker than the axial central portion, so that the radial shrinkage after demolding is greater than the axial central portion. By utilizing this fact, even if the vicinity of both ends in the axial direction of the elastic layer 2 tries to jump up, the maximum diameter of the elastic layer 2 in the portion where the elastic layer 2 tries to jump up is outside the central portion in the axial direction of the elastic layer 2. It is suppressed to be smaller than the diameter. As described above, the shape dimension of the reduced diameter portion of the shaft body 1 varies depending on the shrinkage rate of the elastic layer 2, that is, the type of forming material of the elastic layer 2, the molding temperature, etc., but the shrinkage rate of the elastic layer 2 is the same value. Even in this case, as a range that does not adversely affect the image, the axial length L ₁ of each reduced diameter portion of the shaft body ₁ is usually 2 to 15% of the axial length L ₀ of the elastic layer 2. The value can be taken within the range of 6 to 12%, preferably 6 to 12%. Similarly, the outer diameter D ₁ of the reduced diameter portion of the shaft body 1 corresponding to the left and right edges of the elastic layer 2 is usually in the range of 50 to 97% of the reference outer diameter D ₀ of the axial central portion of the shaft body 1. Value can be taken, Preferably the value within the range of 80 to 90% can be taken.

  Then, when the developing roll of this embodiment is assembled in a contact developing type actual machine, as shown in FIG. 3, the central portion in the axial direction of the surface layer 4 of the developing roll is an electrostatic latent image forming region on the surface of the photosensitive drum 10. With a uniform contact pressure, and on the outer side in the axial direction, a gap is formed between the electrostatic latent image non-formation region on the surface of the photosensitive drum 10 due to the reduced diameter portions on the left and right ends of the surface layer 4 of the developing roll. Is done.

  Therefore, when the developing roll is used in a contact developing type actual machine, wear and damage in the vicinity of both ends are prevented, and leakage due to the wear and toner leakage due to damage are prevented. Further, no axial pressure is generated between the photosensitive drum 10 and the photosensitive drum 10, thereby enabling smooth sliding and preventing image unevenness. Further, the smooth sliding reduces the torque required for rotational driving of the developing roll and the photosensitive drum 10, and reduces the load on each driving motor that rotationally drives the developing roll and the photosensitive drum 10, respectively. As a result, it is possible to reduce the size of the electrophotographic equipment by suppressing heat generation of the electrophotographic equipment such as a printer or by downsizing the drive motor.

  Next, materials for forming the shaft body 1, the elastic layer 2, the intermediate layer (first coating layer) 3, and the surface layer (second coating layer) 4 constituting the developing roll of the present invention will be described.

  The shaft body 1 is not particularly limited, and may be solid or hollow. The material of the shaft body 1 is not particularly limited, and examples thereof include iron, iron plated, stainless steel, and aluminum. Then, an adhesive, a primer or the like is usually applied to the surface of the shaft body 1. Further, the adhesive, primer, etc. may be made conductive as necessary.

  As the material for forming the elastic layer 2, the following main material containing a conductive agent is used. That is, the main material is not particularly limited. For example, polyurethane elastomer, ethylene-propylene-diene rubber (EPDM), styrene-butadiene rubber (SBR), silicone rubber, acrylonitrile-butadiene rubber (NBR). , Hydrogenated acrylonitrile-butadiene rubber (H-NBR), chloroprene rubber (CR), and the like. Among these, it is preferable to use conductive silicone rubber from the viewpoint of low hardness and less sag. If necessary, a conductive agent, silicone oil, vulcanizing agent, vulcanization accelerator, lubricant, auxiliary agent, and the like may be added as appropriate. And the thickness of the said elastic layer 2 is although it does not specifically limit, Usually, it is set to about 0.5-5 mm.

  As a material for forming the intermediate layer (first covering layer) 3, the following main material containing a conductive agent is used. That is, the main material is not particularly limited. For example, hydrogenated acrylonitrile-butadiene rubber (hydrogenated nitrile rubber: H-NBR), acrylonitrile-butadiene rubber (nitrile rubber: NBR), polyurethane-based elastomer, Chloroprene rubber (CR), natural rubber, butadiene rubber (BR), acrylic rubber (ACM), isoprene rubber (IR), styrene-butadiene rubber (SBR), hydrin rubber (ECO, CO), urethane rubber, fluorine rubber, etc. It is done. These may be used alone or in combination of two or more. Among these, H-NBR is particularly preferable from the viewpoint of adhesiveness and coating solution stability. And the thickness of the said intermediate | middle layer (1st coating layer) 3 is although it does not specifically limit, Usually, it sets to about 3-50 micrometers.

  As a material for forming the surface layer (second coating layer) 4, the following main material containing a conductive agent is used. That is, the main material is not particularly limited. For example, urethane resin, polyamide resin, acrylic resin, acrylic silicone resin, butyral resin (PVB), alkyd resin, polyester resin, fluorine rubber, fluorine resin, fluorine Examples thereof include a mixture of rubber and fluororesin, silicone resin, silicone graft acrylic polymer, acrylic graft silicone polymer, nitrile rubber, urethane rubber and the like. These may be used alone or in combination of two or more. Among these, urethane resin is preferable in terms of wear resistance. And although the thickness of the said surface layer (2nd coating layer) 4 is not specifically limited, Usually, it sets to about 3-50 micrometers.

  FIG. 4 shows a second embodiment of the developing roll of the present invention. In this embodiment, the outer diameter of the portion of the elastic layer 2 corresponding to the reduced diameter portion of the shaft body 1 is the same uniform outer diameter as the reference outer diameter of the central portion in the axial direction of the elastic layer 2. This can be achieved by appropriately adjusting the shape of the reduced diameter portion of the shaft body 1 in accordance with the shrinkage rate of the elastic layer 2. Similarly, the outer diameter of the surface layer 4 is a uniform outer diameter. Other parts are the same as those in the first embodiment, and the same operations and effects as in the first embodiment are achieved. In the case of the second embodiment, a gap is formed between the surface layer 4 of the developing roll and the electrostatic latent image non-formation regions (left and right end sides) on the surface of the photosensitive drum 10 (see FIG. 3). Not.

FIG. 5 shows a third embodiment of the developing roll of the present invention. In this embodiment, the portion corresponding to the reduced diameter portion of the shaft body 1 is gradually expanded toward the left and right end edges of the elastic layer 2 on the basis of the outer diameter of the axial central portion, The outer diameter d ₁ of the left and right end edges of the elastic layer 2 corresponding to the outer edge of the reduced diameter portion of the shaft body 1 is 15 μm larger than the reference outer diameter d _{0 of the} central portion in the axial direction of the elastic layer 2. This can be achieved by appropriately adjusting the shape of the reduced diameter portion of the shaft body 1 in accordance with the shrinkage rate of the elastic layer 2. Similarly, the outer diameter of the surface layer 4 is 15 μm larger than the reference outer diameter of the central portion in the axial direction at the left and right end edges. Other parts are the same as those in the first embodiment. In the case of the third embodiment, the contact pressure with the photosensitive drum 10 (see FIG. 3) increases at the diameter-enlarged portions on both the left and right ends, but the contact diameter increases because the diameter expansion amount is as small as 15 μm at the maximum. The amount is small, almost no wear or damage occurs, and smooth sliding is hardly hindered. For this reason, there exists an effect | action and effect similar to the said 1st Embodiment.

  FIG. 6 shows a fourth embodiment of the developing roll of the present invention. In this embodiment, in the first embodiment (see FIG. 1), the portion of the shaft body 1 outside the both ends of the elastic layer 2 in the axial direction has a reduced diameter of the shaft body 1. It is formed in a reduced diameter shape so as to extend to both end edges. Other parts are the same as those in the first embodiment, and the same operations and effects as in the first embodiment are achieved. However, since a bearing is externally fitted to a portion of the shaft body 1 that is axially outer than both end edges of the elastic layer 2, a bearing corresponding to the above-mentioned reduced-diameter shape dimension is required as the bearing.

  In each of the above embodiments, two coating layers of the intermediate layer (first coating layer) 3 and the surface layer (second coating layer) 4 are formed on the outer peripheral portion of the elastic layer 2. One layer may be sufficient, three or more layers may be sufficient, and it does not need to be formed.

  Next, examples will be described together with comparative examples.

[Example 1]
[Shaft]
An iron solid cylindrical rod having an outer diameter (D _{0 in} FIG. 1) of 8 mm and a length of 260 mm is prepared, and 15.0 mm from the position inside 25.0 mm from the both ends of the rod to the outside in the axial direction. A portion of [corresponding to L ₁ in FIG. 1: 6% of L ₀ (250 mm) below] was cut so as to reduce the diameter at a constant rate. The minimum outer diameter (D _{1 in} FIG. ₁ ) of the outer edge of the reduced diameter portion was 5.00 mm [62.5% of D ₀ (8 mm)]. What was obtained in this way was used as a shaft.

[Material for forming elastic layer]
An elastic layer forming material was prepared by kneading conductive silicone rubber (KE1357 A / B, manufactured by Shin-Etsu Chemical Co., Ltd.) using a kneader.

[Formation material of intermediate layer (first coating layer)]
Stearic acid 0.5 parts by weight, zinc white (ZnO) 5 parts by weight, carbon black (Denka Black HS-100, Denki Kagaku Kogyo Co., Ltd.) with respect to 100 parts by weight of H-NBR (Zetpol 0020, manufactured by Nippon Zeon) 30 parts by weight, 1 part by weight of vulcanization accelerator (BZ), 2 parts by weight of vulcanization accelerator (CZ) and 1 part by weight of sulfur were kneaded using a kneader, and then 400 parts by weight of MEK was added and mixed and stirred. Thus, a material for forming the intermediate layer (first coating layer) was prepared.

[Material for forming surface layer (second coating layer)]
Kneading 10 parts by weight of carbon black (Denka Black HS-100, manufactured by Denki Kagaku Kogyo) with 100 parts by weight of urethane resin (Nipporan 5199, manufactured by Nippon Polyurethane Co., Ltd.) using a ball mill, then adding 400 parts by weight of MEK. Then, a material for forming the surface layer (second coating layer) was prepared by mixing and stirring.

[Cylindrical mold]
As the cylindrical mold for forming the elastic layer, a mold having an inner diameter of 18 mm (uniform in the axial direction) and an axial length of 260 mm was prepared.

[Production of roll body]
In the same manner as in the above embodiment, after forming an elastic layer on the outer peripheral surface of the shaft body by molding (190 ° C. × 30 minutes) using the shaft body and a cylindrical mold, the diameter of the shaft body is reduced. Cutting was performed at a surface corresponding to the outer edge of the portion, and both end edges on the outer side in the axial direction were removed. Thereby, a roll body in which the axial length of the elastic layer was adjusted to 250 mm (corresponding to L ₀ in FIG. 1) was obtained. In the elastic layer of the roll body, the portion corresponding to the reduced diameter portion of the shaft body was gradually reduced in diameter toward the left and right end edges of the elastic layer.

(Formation of coating layer)
After forming the intermediate layer (first coating layer) forming material on the outer peripheral surface of the elastic layer of the roll body by the roll coating method, it is dried to form a uniform intermediate layer (first coating layer) having a thickness of 10 μm. did. Thereafter, the surface layer (second coating layer) forming material is applied to the outer peripheral surface of the intermediate layer (first coating layer) by a roll coating method, and then dried, and a uniform surface layer (second coating layer) having a thickness of 10 μm. ) Was formed. Thereby, a developing roll was obtained. As for the outer diameter of the surface layer (second coating layer) of the developing roll, the portion corresponding to the reduced diameter portion of the shaft body was gradually reduced in diameter toward the left and right edges of the elastic layer (see FIG. 1).

[Example 2]
In Example 1, the minimum outer diameter (D _{1 in} FIG. ₁ ) of the outer edge of the reduced diameter portion of the shaft was 6.40 mm (80% of D ₀ ). Other than that, it was the same as in Example 1 above. And as for the outer diameter of the obtained roll body and developing roll, the part corresponding to the diameter-reduced part of the shaft body had the same uniform outer diameter as the reference outer diameter of the central part in the axial direction (see FIG. 4). .

Example 3
In Example 1 above, the axial length (L _{1 in} FIG. ₁ ) of each reduced diameter portion of the shaft body is 5.0 mm (2% of L ₀ above), and the minimum outer edge of the reduced diameter portion of the shaft body is The outer diameter (D _{1 in} FIG. 1) was 4.00 mm (50% of D ₀ above). Other than that, it was the same as in Example 1 above. And as for the outer diameter of the obtained roll body and image development roll, the part corresponding to the diameter-reduced part of a shaft body was gradually reduced in diameter toward the right-and-left both-ends edge of an elastic layer (refer FIG. 1).

Example 4
In Example 1 above, the axial length (L _{1 in} FIG. ₁ ) of each reduced diameter portion of the shaft body is 5.0 mm (2% of L ₀ above), and the minimum outer edge of the reduced diameter portion of the shaft body is The outer diameter (D _{1 in} FIG. 1) was 7.76 mm (97% of D ₀ above). Other than that, it was the same as in Example 1 above. And as for the outer diameter of the obtained roll body and image development roll, the part corresponding to the reduced diameter part of a shaft body was gradually diameter-expanded toward the right-and-left both-ends edge of an elastic layer (refer FIG. 5).

Example 5
In Example 1, the axial length (L _{1 in} FIG. ₁ ) of each reduced diameter portion of the shaft body is 37.5 mm (15% of L ₀ above), and the minimum outer edge of the reduced diameter portion of the shaft body is The outer diameter (D _{1 in} FIG. 1) was 4.00 mm (50% of D ₀ above). Other than that, it was the same as in Example 1 above. And as for the outer diameter of the obtained roll body and image development roll, the part corresponding to the diameter-reduced part of a shaft body was gradually reduced in diameter toward the right-and-left both-ends edge of an elastic layer (refer FIG. 1).

Example 6
In Example 1, the axial length (L _{1 in} FIG. ₁ ) of each reduced diameter portion of the shaft body is 37.5 mm (15% of L ₀ above), and the minimum outer edge of the reduced diameter portion of the shaft body is The outer diameter (D _{1 in} FIG. 1) was 7.76 mm (97% of D ₀ above). Other than that, it was the same as in Example 1 above. And as for the outer diameter of the obtained roll body and image development roll, the part corresponding to the reduced diameter part of a shaft body was gradually diameter-expanded toward the right-and-left both-ends edge of an elastic layer (refer FIG. 5).

Example 7
In Example 1, the axial length (L _{1 in} FIG. ₁ ) of each reduced diameter portion of the shaft body is 30.0 mm (12% of L ₀ above), and the minimum outer edge of the reduced diameter portion of the shaft body is The outer diameter (D _{1 in} FIG. 1) was 7.20 mm (90% of D ₀ above). Other than that, it was the same as in Example 1 above. And as for the outer diameter of the obtained roll body and image development roll, the part corresponding to the reduced diameter part of a shaft body was gradually diameter-expanded toward the right-and-left both-ends edge of an elastic layer (refer FIG. 5).

Example 8
In Example 1, the axial length (L _{1 in} FIG. ₁ ) of each reduced diameter portion of the shaft body is 30.0 mm (12% of L ₀ above), and the minimum outer edge of the reduced diameter portion of the shaft body is The outer diameter (D _{1 in} FIG. 1) was 6.40 mm (80% of the above D ₀ ). Other than that, it was the same as in Example 1 above. And as for the outer diameter of the obtained roll body and developing roll, the part corresponding to the diameter-reduced part of the shaft body had the same uniform outer diameter as the reference outer diameter of the central part in the axial direction (see FIG. 4). .

Example 9
In Example 1, the axial length (L _{1 in} FIG. ₁ ) of each reduced diameter portion of the shaft body is 15.0 mm (6% of L ₀ above), and the minimum outer edge of the reduced diameter portion of the shaft body The outer diameter (D _{1 in} FIG. 1) was 7.20 mm (90% of D ₀ above). Other than that, it was the same as in Example 1 above. And as for the outer diameter of the obtained roll body and image development roll, the part corresponding to the reduced diameter part of a shaft body was gradually diameter-expanded toward the right-and-left both-ends edge of an elastic layer (refer FIG. 5).

[Comparative Example 1]
In Example 1 described above, a shaft body having an outer diameter of 8 mm and uniform in the entire axial direction was used. Other than that, it was the same as in Example 1 above. And the both-ends vicinity part of the obtained roll body and image development roll was gradually diameter-expanded toward the right-and-left both-ends edge of an elastic layer so that it might jump up.

[Comparative Example 2]
In Comparative Example 1, after cutting off both edge portions of the elastic layer, the outer peripheral edge portions at the left and right ends of the elastic layer were chamfered (C1) prior to forming the intermediate layer (first covering layer). Other than that, it was the same as in Comparative Example 1 above. And the both-ends vicinity part of the obtained roll body and image development rolls up, and the diameter was gradually expanded toward the right-and-left both-ends edge of an elastic layer.

[Comparative Example 3]
In Comparative Example 1, when the both edge portions of the elastic layer are cut and removed, the angle between the cut surface (see the chain line A in FIG. 2) and the shaft body axis (the angle on the side where the elastic layer remains) is 80 °. Cut to become. That is, the cut surface is like a side surface of a truncated cone (a truncated cone having the diameter of the shaft body as the diameter of the upper surface and the diameter of the elastic layer as the diameter of the lower surface). Other than that, it was the same as in Comparative Example 1 above. And the both-ends vicinity of the obtained roll body and image development rolls up, and the diameter was gradually expanded toward the right-and-left both-ends edge of an elastic layer.

[Diameter difference]
For each of the developing rolls of Examples 1 to 9 and Comparative Examples 1 to 3 thus obtained, the diameter of the surface layer was measured at different positions along the axial direction. That is, the diameter of the surface layer at a position 1 mm inward from both ends of the elastic layer was D0 and D6, respectively, and the larger one was _Dmax . In addition, the diameter of the surface layer at positions 10 mm inward from both ends of the elastic layer is D1 and D5, respectively, and the diameter of the surface layer at positions 67 mm inward from both ends of the elastic layer is D2 and D4, respectively. of the surface layer of the diameter at the axial center position and D3, the average value of D1~D5 was D _ave. Then, the value of D _max −D _ave was taken as the diameter difference, and is shown together in Table 1 below.

[Torque required for rotational drive]
The developing rolls of Examples 1 to 9 and Comparative Examples 1 to 3 were brought into contact with the photosensitive drum with a load of 9.8 N, and the torque required to drive the developing roll was measured. The torque was measured using a torque measuring machine (1.5BTG, manufactured by Tohnichi Seisakusho). The measured torque is also shown in Table 1 below.

[Image presence / absence]
The developing rolls of Examples 1 to 9 and Comparative Examples 1 to 3 were incorporated into a laser printer (LBP-2510, manufactured by Canon Inc.) employing a contact developing method, and were solid in an environment of 23 ° C. and 53% RH. The image was put out. Then, the image was visually checked for image unevenness (shading unevenness). As a result, it was evaluated as ○ when the image had no image unevenness, △ when the image had slight image unevenness, and × when the image could clearly check the image unevenness, and also listed in Table 1 below. did.

[Damage of the vicinity of both ends]
Further, after 2,000 images were printed, the developing roll was taken out from the laser printer, and the damage state in the vicinity of both ends was visually confirmed. As a result, it was evaluated as “◯” when there was no defect or peeling of the surface layer, “Δ” when there was a sign of defect or peeling of the surface layer, and “×” when defect or surface peeling could be confirmed.

[Toner leakage]
After the above-mentioned 2000 images were printed, the contamination inside the actual machine with toner was evaluated by visual observation. As a result, if there is no toner leakage in the actual machine due to the toner, it is assumed that there is no toner leakage. The case where the image is likely to be stained is evaluated as Δ, and the case where the toner is conspicuously stained in the actual machine is evaluated as X, and the result is also shown in Table 1 below.

  From the results of Table 1 above, the developing rolls of Examples 1 to 9 are smaller in diameter difference than the developing rolls of Comparative Examples 1 to 3, and the diameter expansion due to jumping in the vicinity of both ends is reduced. I understand. Due to the small diameter difference, the torque required for rotational driving is also reduced, and there is no unevenness of the image, no damage in the vicinity of both ends, and toner leakage is sufficiently prevented. In particular, Examples 2, 4, and 6-9, in which the diameter difference is 0 or more, are excellent in preventing toner leakage. In Comparative Examples 1 and 2, the diameter difference is too large, and thus the end portion is damaged and the toner is damaged. It is inferior in leak prevention.

It is sectional drawing which shows 1st Embodiment of the image development roll of this invention. It is sectional drawing which shows the manufacturing process of the elastic layer of the said image development roll. It is explanatory drawing which shows the contact state of the said developing roll and a photosensitive drum. It is sectional drawing which shows 2nd Embodiment of the developing roll of this invention. It is sectional drawing which shows 3rd Embodiment of the image development roll of this invention. It is sectional drawing which shows 4th Embodiment of the developing roll of this invention. It is sectional drawing which shows the state of the elastic layer of the conventional image development roll.

Explanation of symbols

1 shaft body 2 elastic layer

Claims (2)

  A developing roll comprising a shaft body and an elastic layer formed by molding on the outer peripheral surface of the shaft body, the outer peripheral surface of the elastic layer being a transfer surface of the mold surface of the mold, A shaft body corresponding to the axial center portion of the elastic layer is formed to have a uniform outer diameter, and the shaft body on the outer side in the axial direction with respect to the axial center portion is based on the outer diameter of the shaft body in the axial center portion. The outer diameter of the elastic layer is gradually reduced toward the left and right edges of the elastic layer, and the outer diameter of the elastic layer is a uniform diameter at the central portion in the axial direction, and corresponds to the reduced diameter portion of the shaft body. Then, the developing roll is formed to have a diameter not more than 15 μm larger than the outer diameter at the central portion in the axial direction.   The axial length of each reduced diameter portion of the shaft body is in the range of 2 to 15% of the axial length of the elastic layer, and the reduced diameter of the shaft body corresponding to the left and right edges of the elastic layer. The developing roll according to claim 1, wherein the outer diameter of the portion is in the range of 50 to 97% of the reference outer diameter of the axially central portion of the shaft body.

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