JP4957112B2 - Toner supply roller - Google Patents

Description

  The present invention relates to a toner supply roller that is incorporated in a developing device of an electrophotographic image forming apparatus and supplies toner to a developing roller.

  In image forming apparatuses such as copying machines, printers, facsimiles, etc., developing devices that develop and visualize electrostatic latent images formed on image carriers such as electrophotographic photosensitive members and electrostatic recording dielectrics are used. Has been. Development devices are roughly classified into a two-component development method in which development is performed using a two-component developer mainly composed of toner and a carrier, and a one-component development method in which development is performed mainly using a one-component developer.

  The developing device of the one-component developing system includes a developing roller that conveys toner to an image carrier (for example, a photosensitive drum), a regulating member that regulates the layer thickness of the toner layer on the developing roller and frictionally charges the toner, A toner supply roller that contacts the developing roller to supply toner onto the developing roller and peels off toner remaining on the developing roller after development; The developing roller is rotatably supported by spacer members provided at both end portions thereof, and is disposed so as to face the photosensitive drum in the axial direction. Further, the toner supply roller is disposed so as to strongly contact the developing roller by a biasing member such as a spring.

  As a function of the toner supply roller, it is of course necessary to convey the toner to the developing roller, but at the same time, it is also necessary to scrape off the toner remaining on the developing roller without being developed on the photosensitive drum. That is, the toner supply roller must have both a toner supply function and a toner peeling function. As a toner supply roller, many proposals such as a solid rubber material, a brush material, and a foam rubber material have been made.

  Paying attention to the toner supply function, the solid rubber material has a smooth surface, so that sufficient toner transportability cannot be obtained. Although the brush material is excellent in toner transportability, problems such as brush fiber disconnection, cutting, and falling occur. On the other hand, the foamed rubber material is suitable as a material for the toner supply roller because the foaming hole formed on the surface greatly improves the toner transportability compared to the solid rubber material.

  As a toner supply roller that uses a foamed rubber material to improve toner transportability, for example, there is a toner supply member disclosed in Patent Document 1. Concavities and convexities that are continuous in the circumferential direction are formed on the surface of the foamed elastic body of the toner supply member. Specifically, the foam body is processed by a hot wire cutting method to form irregularities on the roll surface. In the toner supply member, by forming the concave portion, more toner can be taken in, and toner transportability is improved.

  In recent years, toners used in image forming apparatuses tend to have smaller particle diameters and lower temperatures due to the need for improved image quality and improved printing speed. Along with this, the toner tends to aggregate due to charging or long-term standing. For this reason, the toner aggregated and adhered on the developing roller is not scraped off by the toner supply roller and remains on the developing roller. As a result, image unevenness occurs.

  Therefore, it is necessary to improve the scraping performance of the toner in preparation for further reducing the particle size of the toner and fixing at a low temperature. Possible solutions include increasing the mechanical force such as increasing the amount of penetration into the developing roller, increasing the nip width, and increasing the rotational speed of the foamed elastic roller. However, in any case, although the scraping property of the toner is improved, the frictional force with the developing roller is increased. As a result, the roller is worn or damaged, or toner deterioration is promoted to cause abnormal charging. Accordingly, in the long-term use, image defects such as density reduction and background stains occur.

  It is also conceivable to improve the toner scraping performance using electrostatic force. However, when using electrostatic force, the foamed elastic roller must be made conductive. For this reason, the necessary physical properties of the foamed elastic body are easily inhibited by the addition of the conductive material. In addition, a bias power source or the like is required, and the configuration is complicated and the cost is increased.

  Therefore, attention is paid to a toner supply roller having a surface of a foamed elastic body having an uneven shape, such as the toner supply roller disclosed in Patent Document 1. If the surface of the toner supply roller has a concavo-convex shape, the toner is scraped off by the convex portion, so that the toner scraping property is improved in addition to the toner transportability. However, because of the concavo-convex shape, there is a difference in scraping force between the concave portion and the convex portion. In addition, if the uneven shape varies, stable scraping performance cannot be expected. Therefore, unevenness due to poor toner scraping occurs unless the developing roller is contacted and rotated under appropriate conditions.

As a toner supply roller focusing on these problems, for example, there are toner supply rollers disclosed in Patent Document 2 and Patent Document 3. Patent Document 2 and Patent Document 3 disclose a toner supply roller that defines the surface of a foamed elastic body with an uneven shape and defines the cell diameter and the uneven shape. By defining the relationship between the size of the cell diameter and the shape of the irregularities, the electrostatic force is not used, the toner is not deteriorated, and the developing roller is not deteriorated. The scraping performance can be improved.
JP-A-5-61350 JP 2004-94101 A JP-A-11-230157

  However, the conventional toner supply roller described above has the following problems. As shown in FIG. 11, the surface of the toner supply roller disclosed in Patent Document 2 or Patent Document 3 has a trapezoidal cross section of a convex portion 39 that forms a concave-convex shape. In FIG. 11, the arrow A indicates the rotation direction of the toner supply roller, and the arrow B indicates the rotation direction of the developing roller in contact with the toner supply roller. In Patent Document 2 and Patent Document 3, the shape of the convex portion 39 is defined. However, this alone causes the following problems caused by recent high-speed printing, toner particle size reduction, and low-temperature fixing. I can't deal with it enough.

  First, a toner pool is generated in the ridge downstream of the convex portion 39 in the rotation direction A (P1 in FIG. 11). In other words, the toner flow is poor around the ridge of the convex portion 39 (around the edge of the concave portion). Therefore, the toner tends to stay and the toner aggregates. As the inclination angle of the convex portion 39 (α in FIG. 11) increases, the toner tends to stay. Of course, if the inclination angle of the convex portion 39 is reduced, the toner flow is improved, but the toner scraping property is deteriorated. The retention of toner is more likely to occur as the toner has a smaller particle size. Further, toner aggregation is more likely to occur as the softening point temperature of the toner is lower.

  Secondly, a crack is also generated in the ridge on the downstream side in the rotation direction A of the convex portion 39 (P2 in FIG. 11). That is, the vicinity of the ridge of the convex portion 39 receives a shear stress due to contact with the developing roller. And the influence by a shear stress becomes strong, so that the inclination | tilt angle ((alpha) in FIG. 11) of the convex part 39 is large. Of course, if the inclination angle of the convex portion 39 is reduced, the stress concentration can be relaxed, but the scraping property of the toner is deteriorated. In addition, when a toner having a small particle diameter and low-temperature fixing is used, the toner easily enters the foamed cell, and further easily aggregates in the cell. When the toner aggregates in the cell, the portion is cured and the flexibility of the portion is lost. Therefore, cracks are more likely to occur. In addition, the shear stress increases as the rotational speed of each roller increases. For this reason, this problem has become prominent due to the recent trend toward high-speed printing.

  The present invention has been made to solve the problems of the conventional toner supply roller. That is, an object of the present invention is to provide a toner supply roller that suppresses toner accumulation and cracks while maintaining high image quality, and a developing device including the toner supply roller.

The toner supply roller made for the purpose of solving this problem includes a core material and a foamed elastic layer located on the outer peripheral surface of the core material, and the surface of the foamed elastic layer is continuously provided in the circumferential direction of the roller. The toner supply roller is provided with a convex portion that extends in the axial direction of the roller and is used for conveying toner, and the shape of the cross section perpendicular to the axial direction of the roller at the convex portion is the outer periphery of the roller A shape in which at least one side of the trapezoid whose width becomes narrower toward the side is changed so as to be gradually inclined from a predetermined position P of the side toward the root of the convex portion. And the recessed part formed between adjacent convex parts is characterized by satisfy | filling following Formula (A).
p1> p 2, however, p1 <100, p2 ≧ 0 (A)
p1: total open area of cells existing on the surface of the convex part / total surface area of convex part p2: total open area of the cell existing on the bottom surface of the concave part / total surface area of the bottom surface of the concave part

  In the toner supply roller of the present invention, a convex portion that forms continuous irregularities in the circumferential direction of the roller is provided on the surface of the foamed elastic layer contacting the developing roller. The convex portion has a mountain shape whose width in the circumferential direction becomes narrower toward the outer peripheral side of the roller. Furthermore, at least one root portion (around the heel) of the convex portion has a continuously curved shape so that the skirt extends outward. For this reason, compared with the trapezoid-shaped convex part which is the conventional form, it becomes a shape which the base part of a convex part inclines gently as it goes to a root. Therefore, toner retention is alleviated and toner aggregation can be suppressed. Moreover, by expanding the base of the convex part, the stress concentration around the root is alleviated and the base part of the convex part is reinforced. Therefore, the crack of the base part of a convex part can be suppressed.

  Moreover, the convex part and the recessed part formed between adjacent convex parts satisfy | fill the said Formula (A). That is, the opening area ratio p2 of the bottom surface of the recess is made smaller than the opening area ratio p1 of the entire protrusion. As a result, the inflow of toner to the bottom surface of the recess is suppressed, and a partial increase in hardness on the roller surface is suppressed. Therefore, the deterioration of the toner and the image quality due to the increase in the hardness of the roller surface are suppressed.

  Furthermore, the toner supply roller of the present invention is suitable for the use of toner having a small particle size (average particle size: 5.5 μm to 7.0 μm) and low-temperature fixing (softening point temperature: 80 ° C. to 85 ° C.). That is, when such toner is used, toner accumulation and cracks at the root are particularly problematic. Since the toner supply roller of the present invention improves the toner flow and reinforces the vicinity of the root of the convex portion, these problems can be avoided.

In addition, the shape of the convex portion of the toner supply roller of the present invention is better when the following formula (B) is satisfied.
0.7 ≦ (b / a) <2.0 (B)
a: Average cell diameter of the foamed elastic layer.
b: Width of the top of the convex part.
By satisfy | filling said Formula (B), the surface cell located in a convex part is regularly arrange | positioned in the axial direction of a roller about the foaming elastic body roller manufactured by an integral molding method. Therefore, variations in surface cells are suppressed and high image quality is obtained. Note that “height” defined by the formula (B) and formulas (C) and (D) described later means the radial distance of the toner supply roller, and “width” means the toner supply roller. It means the distance in the circumferential direction.

In addition, the shape of the convex portion of the toner supply roller of the present invention is better when the following formula (C) is satisfied.
c / 4 ≦ h ≦ c (C)
h: Height of the position P in the side surface of the convex part.

In addition, the shape of the convex portion of the toner supply roller of the present invention is better when the following formula (D) is satisfied.
b / 3 ≦ w ≦ b (D)
w: Distance in the circumferential direction from the position P in the side surface of the convex portion to the root of the convex portion.

  That is, by satisfying at least one of the above formula (C) and formula (D), the edge of the concave portion is surely eliminated and the wrinkles of the convex portion are sufficiently reinforced. Therefore, toner aggregation and a crack at the root can be reliably avoided.

  According to the present invention, a toner supply roller that suppresses toner accumulation and cracks while maintaining high image quality and a developing device including the toner supply roller are realized.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the accompanying drawings. In the present embodiment, the present invention is applied to an electrophotographic image forming apparatus provided with a developing device for storing and supplying non-magnetic one-component toner.

  As shown in FIG. 1, the image forming apparatus 100 according to the embodiment includes a photosensitive drum 11 that is an image carrier, and the surface of the photosensitive drum 11 is uniformly charged around the photosensitive drum 11. A charging device 12, an exposure device 13 for forming an electrostatic latent image on the surface of the photosensitive drum 11, and an electrostatic latent image on the photosensitive drum 11 to be a visible image (toner image). The developing device 14, the transfer device 15 for transferring the toner image on the photosensitive drum 11 to the sheet, and the cleaning device 16 for removing the transfer residual toner from the photosensitive drum 11. In line with. Further, a timing roller 17 for adjusting the timing of conveying the sheet to the transfer position and a fixing device 18 for fixing the transferred toner image on the sheet are provided in the sheet conveying path. In this embodiment, the charging device 12, the transfer device 15, and the fixing device 18 are all roller-shaped. The cleaning device 16 uses a cleaning blade.

  Next, an image forming operation by the image forming apparatus 100 will be briefly described. The image forming apparatus 100 starts operation by receiving a start signal, image data, and the like. The photosensitive drum 11 is rotationally driven in the direction of the arrow in FIG. Then, it is uniformly charged by the charging roller at a position facing the charging device 12. Next, exposure is performed by the exposure device 13, and an electrostatic latent image based on the image data is formed on the surface.

  Next, when the electrostatic latent image reaches the position of the developing device 14, the toner charged by the electric field formed between the developing bias voltage applied to the developing roller and the electrostatic latent image on the photosensitive drum 11 moves. Then, the electrostatic latent image is developed with toner.

  On the other hand, the paper transported through the paper transport path is timed by the timing roller 17 to the front end position of the image and transported between the photosensitive drum 11 and the transfer device 15. Then, the toner image on the photosensitive drum 11 is transferred to a sheet by the transfer device 15. Further, the sheet holding the transferred toner image is further conveyed, and heat and pressure are applied by the fixing device 18 to fix the toner image on the sheet. Further, the transfer residual toner which is not transferred onto the sheet by the transfer device 15 and remains on the photosensitive drum 11 is scraped off by the cleaning device 16. Thereby, the image formation for one sheet is completed.

  Next, the developing device 14 will be described in detail. As shown in FIG. 2, the developing device 14 includes a developing container 1 that contains non-magnetic toner that is a one-component developer, a developing roller 2 that carries the toner and conveys the toner toward the photosensitive drum 11, A toner supply roller 3 that supplies toner to the developing roller 2 and scrapes off the toner on the developing roller 2, a toner amount regulating member 4 that regulates the thickness of the toner on the developing roller 2, and prevents toner leakage. And a toner neutralizing member 5 for neutralizing toner remaining on the developing roller 2 after development. Further, a power source is connected to the developing roller 2 and a bias for development is applied.

  In the developing device 14, the toner in the developing container 1 is transferred from the toner supply roller 3 to the development roller 2 by the potential difference between the toner supply roller 3 and the development roller 2 and the mechanical conveyance force of the toner supply roller 3 whose surface is foam. Transport. The toner supplied to the developing roller 2 is thinned while being frictionally charged by the toner amount regulating member 4 as the developing roller 2 rotates, and the electrostatic latent image is visualized at a portion facing the photosensitive drum 2. .

  After development, the toner remaining on the developing roller 2 is scraped off from the surface of the developing roller 2 at a nip portion with the counter-rotating toner supply roller 3. The toner scraped off is collected in the developing container 1. As the residual toner is scraped off, new toner is supplied onto the developing roller 2 by the rotation of the toner supply roller 3.

  As shown in FIG. 3, the toner supply roller 3 includes a cored bar 31 serving as a rotation shaft, and a foamed elastic layer 32 made of a foamed member and positioned around the cored bar 31. A material such as iron, stainless steel, or aluminum is used for the cored bar 31. In addition, as the metal core 31, any metal that has been subjected to rust prevention treatment is applicable. The foamed elastic layer 32 is formed of a foam of thermosetting resin such as polyurethane, epoxy resin, or acrylic resin. Further, it can be formed from a rubber foam of a thermoplastic resin such as polyethylene or polystyrene, but a polyurethane foam excellent in durability is preferred. In this embodiment, a polyurethane foam was used. In this embodiment, a non-conductive material is used. However, the foamed elastic layer 32 may contain a conductive substance as necessary.

  Further, as shown in FIG. 4, the surface of the foamed elastic layer 32 is provided with a convex portion 33 that forms continuous irregularities in the circumferential direction. Furthermore, the convex part 33 is formed so as to be substantially parallel to the axial direction of the roller so as to form a stripe shape at a predetermined pitch. In addition, the convex part 33 should just be the shape extended in the axial direction of a roller, and may be not only a linear form but the shape extended helically.

  FIG. 5 shows a state in which the surface of the foamed elastic layer 32 is enlarged and viewed microscopically. The foamed elastic layer 32 has a skin layer 321 that forms a continuous surface as a whole on its surface. The skin layer 321 is provided with an opening 323 for opening each cell 35 located immediately below the skin layer 321 to the outside. Further, the opening 323 is formed at a portion where the thickness of the skin layer 321 is the smallest, that is, a portion corresponding to the central portion of the cell 35. In this embodiment, the ratio of the area occupied by the opening 323 in the skin layer 321 is configured to be 20% or more. Note that the cells 35 may be independent bubble types independent of each other or may be open bubble types communicating with each other.

  Next, the outer shape of the convex portion 33 in the cross section orthogonal to the rotation axis direction will be described in detail with reference to FIGS. In FIG. 6, the arrow A indicates the rotation direction of the toner supply roller, and the arrow B indicates the rotation direction of the developing roller in contact with the toner supply roller. As shown in FIG. 6, the convex portion 33 has a mountain top surface 331 at the top, has a narrower width toward the mountain top surface 331, and has a mountain shape with the mountain top surface 331 as an upper base.

  Further, as shown in FIG. 7, the side surface 34 of the convex portion 33 is located on the mountain top side of the convex portion 33 with a predetermined position P as a boundary, and is a flat mountain top side surface 34 a and the mountain side of the convex portion 33. It is comprised by the mountain side surface 34b which is a continuous curved surface so that it may be located in and may spread outside. That is, the convex portion 33 has a shape in which a part of the side surface 34 is curved so as to spread outward and the skirt is widened. The slope of the mountain side surface 34b is gentler than the slope of the mountain top side surface 34a, and the slope gradually becomes gentler as it approaches the foot. In other words, the convex portion 33 has a shape that gently slopes from the boundary P between the top surface 34 a and the mountain side surface 34 b toward the base of the convex portion 33. Therefore, it is different from a perfect trapezoid. This is different from the conventional form (see FIG. 11) which is a complete trapezoid.

  The toner supply roller 3 according to the present embodiment has the following advantages because the wrinkles of the convex portion 33 are gently inclined.

  As a first advantage, the flow of toner is improved by gradually inclining the wrinkles of the convex portion 33 with a continuous curved surface. That is, as in the conventional embodiment, when the side surface of the convex portion 33 reaches the ridge while having a steep slope, the toner stays at the edge portion of the bottom surface of the concave portion 38 formed between the convex portions 33 and 33. In addition, it is difficult for the toner that has entered the cell 35 around the base portion of the convex portion 33 to flow out. On the other hand, as in the present embodiment, the side surface of the convex portion 33 is formed as a gentle slope whose inclination angle gradually changes, that is, the edge of the concave portion 38 is rounded, thereby suppressing toner retention and in the cell. Smooth outflow of toner. Therefore, toner accumulation is eliminated and toner aggregation can be avoided.

  As a second advantage, the root portion (periphery periphery) of the convex portion 33 is reinforced by widening the ridge of the convex portion 33. That is, the convex portion 33 of this embodiment is supplemented with a hatched portion 33a (hereinafter referred to as “reinforcing portion 33a”) in FIG. 7 as compared with the conventional embodiment. Therefore, the fall of the convex part 33 is suppressed. Further, in this embodiment, since the ridges of the convex portion 33 are formed of a curved surface, the stress concentration at the root portion of the convex portion 33 is alleviated. That is, since the convex portion 33 is reinforced and the stress concentration at the root portion is reduced, cracks at the root portion of the convex portion 33 can be suppressed.

  Further, the toner supply roller 3 according to this embodiment defines the shape of the convex portion 33 and the concave portion 38 formed between the adjacent convex portions 33 and 33 as the following formulas (1) to (4).

  In Expressions (1) to (4), b indicates the width of the peak surface 331 of the convex part 33, and c indicates the height of the convex part 33 (see FIG. 6). The “height” that defines the uneven shape means the distance in the radial direction of the toner supply roller 3, and the “width” means the distance in the circumferential direction of the toner supply roller 3. Further, a represents the cell diameter of the cell 35 of the foamed elastic layer 32. In this embodiment, ten cells existing in an arbitrary cross section of the foamed elastic layer 32 are extracted, the cell diameter of each cell is measured, and the average value is defined as the cell diameter a. Further, p1 represents the ratio of the opening area of the convex portion 33 expressed by the total surface area of the cells 35 existing on the surface of the convex portion 33 / the total surface area of the convex portions 33, and p2 represents the cell 35 existing on the bottom surface 381 of the concave portion 38. The ratio of the opening area of the concave portion 38 expressed by the total surface area of the concave portion 38 / the total surface area of the bottom surface 381 of the concave portion 38 is shown. In addition, h indicates the height from the ridge of the convex portion 33 to the boundary P between the side surface 34a and the ridge side surface 34b (hereinafter referred to as “the height of the ridge portion”), and w indicates the height from the ridge of the convex portion 33 to the top of the mountain. The width to the boundary P between the side surface 34a and the foothill side surface 34b (hereinafter referred to as “width of the foothill portion”) is shown (see FIG. 7).

First, the convex portion 33 and the concave portion 38 of the toner supply roller 3 of the present embodiment have a shape that satisfies the following expression (1).
p1> p 2, however, p1 <100, p2 ≧ 0 (1)

  That is, the opening area ratio p2 of the bottom surface of the recess is made smaller than the opening area ratio p1 of the entire protrusion (1). As a result, the inflow of toner to the bottom surface of the recess 38 is suppressed, and a partial increase in hardness on the surface of the roller is suppressed. Therefore, the deterioration of the toner and the image quality due to the increase in the hardness of the roller are suppressed. If the opening area ratio p1 is less than or equal to the opening area ratio p2, the toner holding force becomes weak and the toner transportability deteriorates. Alternatively, the amount of toner entering the bottom surface 381 of the recess 38 increases, and the surface of the roller is partially cured. Therefore, there is a concern about toner deterioration and image defects such as density unevenness occur.

  The width e of the bottom surface of the recess is preferably 20 μm or more. When the width e is less than 20 μm, it becomes close to a structure in which the bottom surface 381 itself of the recess 38 does not exist. Therefore, excessive toner flows into the foamed elastic layer 32 and the surface of the roller is partially cured. On the other hand, if the width e is too large, the irregularities on the surface of the foamed elastic layer 32 are reduced and the toner transportability and scraping performance are reduced. Therefore, the width e of the bottom surface 381 of the recess 38 is preferably 20 μm or more and 1000 μm or less.

  Moreover, it is preferable that the opening area ratio p1 of the whole convex part is 20% or more. As a result, the portion where the thickness of the skin layer 321 of the foamed elastic layer 32 is small is reduced, and the tearing and fluffing of the skin layer 321 are eliminated. In addition, the toner flow is made uniform and toner clogging is suppressed.

  Further, the toner supply roller 3 of this embodiment is foam-molded integrally with the cored bar in a roller mold having irregularities formed on the inner surface. In such an integral molding method, the size of the cells 35 existing on the surface is not uniform, and the arrangement of the cells 35 tends to be irregular. For this reason, fine variations in surface cells appear as image unevenness. This problem becomes significant when toners with small particle size and low temperature fixing are used.

Therefore, it is better that the convex portion 33 of the toner supply roller 3 of the present embodiment has a shape that satisfies the following expression (2).
0.7 ≦ (b / a) <2.0 (2)

  That is, the ratio (b / a) between the width b of the convex crest surface and the cell diameter a is regulated. Specifically, the ratio is configured to be 0.7 or more and less than 2.0 (2). Thereby, the surface cell 35 located in the peak surface 331 of the convex part 33 is regularly arrange | positioned in the axial direction of a roller, as shown in FIG. Therefore, variations in the surface cell 35 are suppressed, and high image quality is obtained. If the ratio is smaller than 0.7, cell walls may not be formed on the top surface and the side surface, and the shape of the convex portion 33 becomes unstable. On the other hand, when the ratio is 2.0 or more, as shown in FIG. 8, at least two cells 35 enter the peak surface 331 of the convex portion 33, so that the regular arrangement of the cells 35 is insufficient. As a result, the sizes of the cells 35 are also non-uniform. In addition, the number of irregularities in the circumferential direction is reduced, and toner transportability and scraping are both insufficient.

Further, the periphery of the ridge of the convex portion 33 of the toner supply roller 3 of the present embodiment has a shape that satisfies the following expressions (3) and (4).
c / 4 ≦ h ≦ c (3)
b / 3 ≦ w ≦ b (4)

  That is, the height h of the ridge is set to be not less than the convex height c / 4 (3). Further, the width w of the ridge is set to be not less than the width b / 3 of the top surface of the convex portion (4). Thereby, the ridge of the convex part 33 becomes a shape which inclines gently, and the reinforcement part 33a of sufficient size is obtained. Therefore, toner aggregation and a crack at the root can be reliably avoided. If the height h of the ridge part is made smaller than the height c / 4 of the convex part, or if the width w of the ridge part is made smaller than the width b / 3 of the top part of the convex part, the ridge of the convex part 33 becomes a steep slope. As a result, the size of the reinforcing portion 33a is reduced. Therefore, the effect of making the mountain side surface 34b a curved surface cannot be obtained sufficiently.

  In this embodiment, among the ridges of the convex portion 33, both the upstream and downstream sides in the rotation direction A are gradually inclined with continuous curved surfaces, but only one of them may be used. That is, focusing on the first advantage described above, toner accumulation can be suppressed by providing a gentle slope only on the ridge on the downstream side in the rotation direction A (left side in FIG. 6).

  Further, if attention is focused on the second advantage, it is possible to suppress cracks at the root portion by forming the reinforcing portion 33a at least on one side of the ridge. That is, by forming the reinforcing portion 33a on the ridge on the downstream side in the rotation direction A, the root portion can be reinforced and stress concentration can be avoided. Therefore, cracks at the root can be suppressed. On the other hand, by forming the reinforcing portion 33a on the upstream side ridge in the rotation direction A, it is possible to suppress the collapse of the convex portion 33, and as a result, it is possible to suppress the crack on the downstream side.

  The toner supply roller 3 of this embodiment can be easily manufactured by a known method. Hereinafter, an example of the integral foam molding of the urethane sponge material will be described. 9 to 10 show a roller mold 50 for manufacturing the toner supply roller 3.

  The roller mold 50 includes a pipe-shaped mold 51 having a length equal to the axial length of the foamed elastic layer 32, and caps 52, 52 attached to both ends of the pipe-shaped mold 51 and closing each end. have. On the inner surface of the pipe-shaped mold 51, a convex portion 53 having a shape corresponding to the concave portion 38 on the roller surface, that is, a round portion at the corner portion of the peak surface is formed. Therefore, the inner surface of the pipe-shaped mold 51 has an uneven shape together with the concave portion 54 located between the convex portions 53 and 53.

  First, the cored bar 31 is arranged at a position that becomes the center line in the pipe-shaped mold 51, and the cored bar 31 is supported by the caps 52 and 52. Next, the urethane sponge raw material is put into the pipe-shaped mold 51.

  Any known liquid material (a blend of a polyol component and a polyisocyanate component) can be used as the polyurethane material. In addition, a foaming agent, a foam stabilizer, a catalyst, and the like are further added to these polyurethane raw materials in accordance with the structure of the foamed elastic layer 32, thereby forming a reactive foaming raw material. However, it is necessary to consider the reactivity of the polyurethane raw material. That is, since the reaction of polyurethane foam is a competitive reaction between resinization and foaming, the resinization reaction needs to precede the foaming reaction in order to satisfy the above-mentioned formula (1). . Therefore, by prepolymerizing a part of the polyisocyanate component, leading the resin curing reaction, adding a catalyst having a strong resin curing ability, utilizing a foaming catalyst having a low reaction activity, etc. It selects suitably from various means.

  In filling the urethane sponge material, the top surfaces of all the convex portions 53 are connected so that the urethane sponge material does not enter the concave portion 54 (that is, the convex portion 33 of the foamed elastic layer 32) on the inner surface of the pipe-shaped mold 51. Foaming is performed in the axial direction while maintaining a circular cross-sectional shape. After the uncured urethane sponge spreads in the axial direction of the pipe-shaped mold 51, the inside of the concave portion 54 on the inner surface of the pipe-shaped mold 51 is filled with the urethane sponge.

  At this point, since the resin curing reaction has progressed to some extent, the cell film is stretched and broken when expanded by the amount of the concave portion 54 (the convex portion 33). At this time, the formulation is such that the resin curing reaction precedes the foaming reaction. Thereby, the opening area ratio p2 of the concave portion 38 can be made smaller than the opening area ratio p1 of the convex portion 33, and the toner supply roller 3 satisfying the above formula (1) is formed.

  As described above in detail, the toner supply roller 3 according to the present embodiment has a convex portion extending in the axial direction of the roller by forming continuous irregularities in the circumferential direction of the roller on the surface of the foamed elastic layer 32 located on the outermost surface. 33. Further, the root portion (mountain side surface 34 b) of at least one side surface 34 of the convex portion 33 has a continuously curved shape so as to spread outside the convex portion 33. For this reason, compared with the trapezoidal convex part 39 as shown in FIG. 11, the base of the convex part 33 is wide and the inclination is gentle. As a result, toner retention is alleviated and toner aggregation can be suppressed. Further, the stress concentration around the root is alleviated and the root of the convex portion 33 is reinforced. Therefore, it is possible to suppress cracks at the base portion of the convex portion 33.

  In addition, the opening area ratio p2 of the bottom surface 381 of the recess 38 is smaller than the opening area ratio p1 of the entire protrusion 33. As a result, the inflow of toner to the bottom surface 381 of the recess 38 is suppressed, and a partial increase in hardness of the roller surface is suppressed. Therefore, the deterioration of the toner and the image quality due to the increase in the hardness of the roller surface are suppressed.

  Further, the ratio (b / a) between the width b of the peak surface of the convex portion 33 and the cell diameter a may be configured to be 0.7 or more and less than 2.0. With this configuration, the cells 35 positioned on the convex portion 33 are regularly arranged in the axial direction of the roller. Therefore, the variation of the cells 35 is suppressed, and higher image quality can be obtained.

  Further, the toner supply roller 3 is suitable for use of toner having a small particle size (average particle size: 5.5 μm to 7.0 μm) and low-temperature fixing (softening point temperature: 80 ° C. to 85 ° C.). That is, when such toner is used, toner accumulation and cracks at the root are particularly problematic. In the toner supply roller 3 of the present embodiment, the toner flow is improved and the base portion of the convex portion 33 is reinforced, so that these problems can be avoided.

  Further, the toner supply roller 3 of the present embodiment scrapes off the toner by a mechanical force and does not use an electrostatic force. Therefore, the configuration is simple and there is no cost increase.

  Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof. For example, the present invention can be applied to various image forming apparatuses such as a color printer, a monochrome printer, a copier, and a facsimile.

  Further, although a roller-shaped photosensitive drum is used as the image carrier, a belt-shaped photosensitive belt may be used. In addition to the roller charging method, the charging device may use a corona discharge charging charger, blade, brush, or the like. The exposure apparatus may be a laser or LED. The transfer device may use a transfer charger in addition to the transfer roller. Alternatively, in addition to a method of directly transferring a toner image from a photosensitive member to a sheet, a method of providing an intermediate transfer member and performing transfer in two or more stages may be used. In addition to the cleaning blade, the cleaning device may be a cleaning brush, a cleaning roller, or a combination thereof. Alternatively, the transfer residual toner may be collected by a developing device. In addition to the fixing roller, the fixing device may use a fixing belt or a non-contact type.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment. 1 is a diagram illustrating a schematic configuration of a developing device according to an embodiment. FIG. 2 is a diagram illustrating a schematic configuration of a toner supply roller according to an embodiment. FIG. 4 is a diagram illustrating an XX cross section and a perspective surface of a foamed elastic layer (b / a≈0.8) of the toner supply roller illustrated in FIG. 3. It is a figure which shows microscopically the surface of the foaming elastic-body layer of a toner supply roller. FIG. 4 is a diagram illustrating a surface cross section of a toner supply roller according to an embodiment. It is a figure which shows the side surface of the convex part of a foaming elastic-body layer. It is a figure which shows the surface cross section and perspective surface of the foaming elastic-body layer (b / a ≒ 2.2) of the toner supply roller which is a comparative example. It is a figure which shows the cross section of the shaping | molding die of a urethane sponge roll. It is a figure which shows the YY cross section of the shaping | molding die shown in FIG. It is a figure which shows the surface cross section of the toner supply roller concerning the conventional form.

Explanation of symbols

2 Developing roller 3 Toner supply roller 31 Core metal (core material)
32 Elastic foam layer 33 Convex part 34 Convex side surface 35 Cell 38 Concave part 11 Photoconductive drum 14 Developing device 100 Image forming apparatus

Claims (4)

A core material, and a foamed elastic layer positioned on the outer peripheral surface of the core material, the surface of the foamed elastic layer is formed with concavities and convexities extending in the circumferential direction of the roller, and extends in the axial direction of the roller In the toner supply roller provided with a convex portion and used for toner conveyance,
The shape of the cross section perpendicular to the axial direction of the roller in the convex portion, at least one of the sides of the trapezoid where the width toward the outer peripheral side of the roller is narrowed, the convex portion from a predetermined position P of the side edge The shape is changed so that the slope becomes gentler toward the root of
The toner supply roller, wherein the convex portion and the concave portion formed between adjacent convex portions satisfy the following formula (A).
p1> p 2, however, p1 <100, p2 ≧ 0 (A)
p1: total open area of cells existing on the surface of the convex part / total surface area of the convex part p2: total open area of cells existing on the bottom surface of the concave part / total surface area of the bottom surface of the concave part The toner supply roller according to claim 1,
The toner supply roller, wherein the shape of the convex portion satisfies the following formula (B).
0.7 ≦ (b / a) <2.0 (B)
a: Average cell diameter of the foamed elastic layer.
b: The width of the top surface of the convex portion. In the toner supply roller according to any one of claims 1 and 2,
The toner supply roller, wherein the shape of the convex portion satisfies the following expression (C).
c / 4 ≦ h ≦ c (C)
c: Height of the convex part.
h: The height of the position P in the side surface of the convex part. In the toner supply roller according to any one of claims 1 to 3,
The toner supply roller, wherein the shape of the convex portion satisfies the following expression (D).
b / 3 ≦ w ≦ b (D)
w: Distance in the circumferential direction from the position P in the side surface of the convex portion to the root of the convex portion.

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