JP2007121445A - Charging roller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging roller capable of preventing an image of a set mark. <P>SOLUTION: An amount of permanent compression strain of the charging roller left for one month in an environment having a temperature of 40°C and a humidity of 90% is set to 20 μm or less. The thickness of the elastic layer of the charging roller is also set to 1.5 mm or less. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a charging roller that is pressed and rotated by a photoconductor of an electrophotographic apparatus to supply charges to the photoconductor, and in particular, can prevent image deterioration after the charging roller is pressed against the photoconductor for a long time. About.

  Conventionally, in an electrophotographic apparatus such as a copying machine or a printer, first, the surface of the photosensitive member is uniformly charged, and an image is projected onto the photosensitive member from the optical system, and the charged portion is erased. An electrostatic latent image is obtained by an electrostatic latent image process for forming a latent image, and then the electrostatic latent image is visualized as a toner image by adhesion of toner, and by transferring the toner image to a recording medium such as paper, The method of printing is taken.

In order to charge the surface of the photoconductor, a contact charging method in which the surface of the photoconductor is charged by bringing an elastic roller into contact with the photoconductor and applying a voltage to the elastic roller while rotating them is widely implemented. Has been. The elastic roller used in this contact charging method is called a charging roller. For example, a material such as rubber or urethane foam is injected into a mold or extruded from an extruder to form an elastic layer around the shaft. A resistance adjustment layer is formed on the outer side of the elastic layer in the radial direction by adding a conductive agent to a resin such as urethane, acrylic urethane, acrylic ester, nylon, or a synthetic rubber such as NBR, and further adjusting the resistance. In addition, a resin layer in which a resin such as acrylic, urethane, or nylon is dissolved in an organic solvent or water is applied by a dipping method or the like to form a skin layer (for example, see Patent Document 1).
JP 2003-131474 A

  However, these charging rollers are left in a state of being pressed against the photoconductor without rotating when no charge is injected into the photoconductor, and during this time, they are pressed in the same posture for a long time. When the electrophotographic apparatus is operated after it has been left unattended, there is a possibility that a so-called set trace image appears, in which the shade of the pitch equal to the circumference of the charging roller appears in the print image, which is a problem. It was.

  The present invention has been made in view of such problems, and an object thereof is to provide a charging roller that does not generate a set trace image.

<1> is a charging roller in which an elastic layer is arranged around a core metal having a diameter of 5 to 6 mm.
The charging roller has a compression set of 20 μm or less after being left for 1 month in an environment of a temperature of 40 ° C. and a humidity of 90%, and the elastic layer has a thickness of 1.5 mm or less.

  <2> is that in <1>, the microhardness of the elastic layer is 35-50, and the runout is 70 μm or less in the entire region of the roller length direction, and the center in the length direction is the end in the cross section of the roller length direction. It is a charging roller that protrudes from the portion and has a crown amount of 45 to 120 μm representing the degree of protrusion.

  <3> is a charging roller in which the elastic layer is formed of a foam body in which closed cells are dispersed in <1> or <2>.

  <4> is a charging roller according to any one of <1> to <3>, wherein a skin layer constituting the roller surface is disposed outside the elastic layer, and the microhardness of the skin layer is higher than that of the elastic layer. is there.

  According to the invention <1>, by setting the elastic layer thickness to 1.5 mm or less, the amount of compression set is set to 20 μm or less, so that residual strain after removing the pressing force on the charging roller can be eliminated. And generation of set trace images can be suppressed.

  According to the invention <2>, the microhardness of the elastic layer is set to 35 to 50, the runout is set to 70 μm or less in the entire region in the roller length direction, and the center in the length direction is the end portion in the cross section of the roller length direction. Since the amount of crown that is more protruded and represents the degree of protrusion is set to 45 to 120 μm, an improvement effect can be obtained for a normal image as will be described in detail later.

  According to the invention <3>, since the elastic layer is composed of a foam body in which closed cells are dispersed, the above micro hardness can be easily realized.

  According to the invention <4>, the outer layer of the elastic layer is provided with a skin layer having a micro hardness higher than that of the elastic layer and has a multilayer structure composed of a plurality of layers having different functions. While suppressing, desired characteristics can be imparted to the roller surface.

  Embodiments according to the present invention will be described. FIG. 1 is a longitudinal sectional view illustrating a charging roller of this embodiment. A charging roller 10 has an elastic layer 2 formed on the outer periphery of a core body 1 and a specific resin composition on the elastic layer 2. The resistance adjustment layer 3 can be formed, and the skin layer 4 can be formed on the resistance adjustment layer 3. Note that the resistance adjustment layer 3 is not an essential configuration, and the skin layer 4 may be formed directly outside the elastic layer 2. In this case, the description of the resistance adjustment layer 3 is described from the following description of the embodiment. Except it should be understood.

As the core 1, a metal or plastic shaft can be used. The elastic body forming the elastic layer 2 is not particularly limited as long as it is an elastic body capable of obtaining a good contact state with a charged body such as a photoreceptor, and may be a known rubber or resin, or It can be formed of a foam body in which closed cells are dispersed. Specifically, rubbers using a base rubber such as polyurethane, silicone rubber, butadiene rubber, isoprene rubber, chloroprene rubber, styrene-butadiene rubber, ethylene-propylene rubber, polynorbornene rubber, styrene-butadiene-styrene rubber, epichlorohydrin rubber, etc. The composition is exemplified, but polyurethane is particularly preferable, and polyurethane foam is more preferably used. In this case, the foaming ratio of the polyurethane foam is not particularly limited, but is preferably 1.2 to 50 times, particularly preferably about 1.5 to 10 times, and the foam density is suitably about 0.1 to 0.7 g / cm ³ .

By adding a conductive agent to the elastic layer 2, conductivity can be imparted or adjusted to a predetermined resistance value. The conductive agent is not particularly limited, but lauryltrimethylammonium, stearylmethylammonium, octadodecyltrimethylammonium, hexadecyltrimethylammonium, modified fatty acid / dimethylethylammonium perchlorate, chlorate, borofluoride , Cationic surfactants such as quaternary ammonium salts such as halogenated benzyl salts such as sulfates, etosulphate salts, benzyl bromide salts, benzyl chloride salts, aliphatic sulfonates, higher alcohol sulfates, Anionic surfactants such as higher alcohol ethylene oxide addition sulfate, higher alcohol phosphate, higher alcohol ethylene oxide addition phosphate, higher alcohol ethylene oxide, polyethylene glycol fatty acid ester Antistatic agents such as polyhydric nonionic antistatic agents such as alcohol fatty acid _{ester, NaClO 4, LiAsF 6, LiBF} 4, NaSCN, KSCN, such as NaCl Li ^+, Na ^+, periodic table first K ^+, etc. Electrolytes such as group metal salts or NH ₄ ⁺ salts, conductive carbons such as ketjen black, acetylene black, rubber carbons such as SAF, ISAF, HAF, FEF, GPF, SRF, FT, MT, Oxidized carbon for color (ink), pyrolytic carbon, natural graphite, artificial graphite, antimony-doped tin oxide, titanium oxide, zinc oxide, nickel, copper, silver, germanium and other metals and metal oxides, polyaniline , Conductive polymers such as polypyrrole and polyacetylene. In this case, the blending amount of these conductive agents is appropriately selected according to the type of the composition, and the volume resistivity of the elastic layer is usually 10 ⁰ to 10 ⁸ Ω · cm, preferably 10 ² to 10 ⁶ Ω · cm. It is adjusted to become.

  In addition to the conductive agent, the elastic layer 2 may include a thickener, an antifoaming agent, a leveling agent, a dispersing agent, a thixotropic agent, a wetting agent, an antiblocking agent, and a crosslinking agent as necessary. An appropriate amount of a known additive such as a film forming aid can be blended.

  The resistance adjusting layer 3 formed on the elastic layer 2 is formed of a resin composition in which a conductive agent is added to a resin base material. The resin base material constituting the resin composition may be any one as long as it has the above volume resistivity, and is not particularly limited, but specifically, urethane resin, acrylic urethane resin, acrylic resin Resins, ester resins, nylon resins, phenol resins, epoxy resins, fluororesins, silicone resins, etc. can be mentioned, and one or more of these can be mixed and used, especially urethane resins, acrylic urethane resins, acrylic resins An aqueous resin such as a resin is preferably used.

  As the conductive agent added to the resin base material, the same conductive agent as that used for the elastic layer 2 can be used.

The resistance adjustment layer 3 adjusts the electrical resistance value of the charging member, and the resistance value of the resistance adjustment layer 3 is appropriately set according to the resistance value of the elastic layer 2 and the resistance value required for the member. However, it is usually set to 1 × 10 ^{3 to} 1 × 10 ⁸ Ω · cm, particularly 1 × 10 ^{5 to} 1 × 10 ⁷ Ω · cm. In this case, the blending amount of the conductive agent is an appropriate amount to achieve this resistance value, but usually 0.1 to 20 parts by weight, particularly 1 to 10 parts by weight with respect to 100 parts by weight of the resin base material. It is preferable to do.

  In addition to the conductive agent, an appropriate additive can be blended in the resistance adjusting layer 3 without departing from the object of the present invention. For example, an oxazoline-based, epoxy-based, melamine-based, guanamine-based, isocyanate-based layer can be used. An appropriate amount can be blended depending on the low-resistance resin substrate using a phenol-based cross-linking agent, and the film-forming aid, dispersant, thickener, and leveling are within the range not departing from the purpose of the resistance adjusting layer 3. An appropriate amount of known additives such as an agent, a thixotropy imparting agent, and a structural viscosity imparting agent can be blended.

  The thickness of the resistance adjusting layer 3 is appropriately selected according to the thickness of the elastic layer 2 and the form of the charging member, and is not particularly limited, but is usually 10 to 500 μm, particularly 50 to 300 μm. When the thickness is less than 50 μm, it may be difficult to adjust the resistance sufficiently. On the other hand, when the thickness exceeds 300 μm, the elastic layer becomes relatively thin and the roller hardness (member hardness) is relatively small. It may be expensive or it may be more expensive than necessary.

  The method for forming the resistance adjusting layer 3 is not particularly limited, and can be formed by a known method such as a known dipping method, spray method, extrusion molding method, etc. A method of coating on the elastic layer 2 by a dipping method, a spray method or the like using a coating solution in which an active substance or other additives are dispersed or dissolved is preferably used, and a dipping method is particularly preferably used.

  Next, as the material for forming the skin layer 4, known rubbers and resins used for forming the skin layer of the charging member can be used, and the urethane-modified acrylic resin is not particularly limited. , Polyurethane resin, acrylic resin, polyamide resin, fluororesin and the like are exemplified, and one or more of these may be used in combination. Among these, a fluororesin is particularly preferably used. By using the fluororesin, good low friction property and toner adhesion (non-adhesion) can be achieved.

  Specific examples of the fluororesin include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-ethylene copolymer, polychlorotrifluoroethylene, chlorotrifluoroethylene-ethylene copolymer. And tetrafluoroethylene-vinylidene fluoride copolymer, polyvinylidene fluoride, and polyvinyl fluoride.

  Further, the resin forming the skin layer 4 is not particularly limited, but the conductivity (electric resistance) of the skin layer can be imparted or adjusted by adding a conductive agent. In this case, the conductive agent is not particularly limited, and various electronic conductive agents and various ionic conductive agents can be used. In the present invention, it is particularly preferable to use carbon.

The addition amount of the conductive agent can be appropriately adjusted so that a desired resistance is obtained. In this case, the resistance of the skin layer 4 is preferably a volume resistivity of 1 × 10 ^{4 to} 1 × 10 ¹² Ω · cm, particularly 1 × 10 ^{6 to} 1 × 10 ⁸ Ω · cm, and a conductive agent is used to achieve such a volume resistivity. The amount of addition when carbon is used as the conductive agent is usually about 1 to 100 phr, particularly about 10 to 70 phr with respect to the base resin.

  In addition, additives, such as a crosslinking agent, a thickener, a thixotropy imparting agent, and a structural viscosity imparting agent, can be added to the resin composition forming the skin layer as necessary.

  The method for forming the skin layer 4 is not particularly limited. Usually, a coating solution in which the resin component and the conductive agent are dispersed or dissolved is prepared, and the coating solution is dipped, sprayed, or rolled. A method of applying on the resistance adjusting layer by a coater method and drying and solidifying is employed, and a dipping method is particularly preferably used. In addition, what is necessary is just to select suitably as a solvent for preparing the said coating solution according to the kind etc. of base resin which comprises a resin composition, for example, when using a fluororesin as base resin, methyl ethyl ketone ( MEK), methyl isobutyl ketone (MIBK), toluene, xylene and the like are preferably used.

  The thickness of the skin layer 4 is set according to the form of the charging roller 10 and the like, and is not particularly limited, but is usually 1 to 30 μm, particularly 1 to 20 μm, and less than 1 μm. The roller durability may be inferior. On the other hand, if it exceeds 20 μm, good surface properties may not be obtained such as adversely affecting the charging characteristics or wrinkling the surface.

  In the charging roller 10 of the present invention, the skin layer 4 is formed on the elastic layer 2 or the resistance adjusting layer 3 is disposed between the layers 2 and 4. Other layers can be interposed between the resistance adjusting layer 3 and the resistance adjusting layer 3 and the skin layer 4. For example, an adhesive layer having a thickness of about 1 to 50 μm can be provided between the elastic layer 2 and the resistance adjustment layer 3 in order to firmly bond both layers. In this case, the adhesive layer can be formed by applying a paint containing a resin material such as acrylic resin, urethane resin, acrylic urethane resin, polyester resin, polyamide resin or the like on the elastic layer 2 by a dipping method or the like. If necessary, a conductive agent and other additives can be added.

  Here, for the formation of the resistance adjusting layer 3, the skin layer 4, the adhesive layer, and the like, as described above, a method of forming a film by applying a paint by a dipping method and drying is preferably employed. The quality of the film forming operation by the dipping method greatly affects the uniformity of each layer and the like, which greatly affects the quality of the charging roller. For this reason, it is important to strictly manage the temperature conditions and the drying conditions at the time of film formation of these layers, and to reliably obtain a good film formation state.

  That is, when the resistance adjusting layer 3, the skin layer 4, the adhesive layer, etc. are formed by the dipping method, usually, industrially, a plurality of 30 or more rollers are suspended vertically on a hanger, and the plurality of rollers are At the same time, it can be soaked in the paint, pulled up, and dried by blowing. In this case, it is good to strictly control the temperature of the paint and the roller to be applied at the time of applying the paint and the blowing conditions for drying. It is important to obtain a proper film formation state.

  Specifically, for the management of the paint temperature, it is preferable to provide a heater and a temperature sensor in the dip tub, and keep the paint temperature almost constant in the range of 25 to 35 ° C., more specifically, It is preferable to apply the paint by dipping while keeping the paint in the temperature range of ± 1 ° C. As for the temperature control of the rollers, it is preferable to adjust all the rollers just before dipping in the paint to a substantially uniform temperature with a heater or warm air, more specifically, heating the rollers to a temperature of 3 ° C or higher. The temperature variation of each roller is preferably ± 1 ° C. of the average temperature of all the rollers. Furthermore, with respect to the air blowing conditions, it is preferable to dry the plurality of rollers suspended on the hanger by blowing air from below to above. It is preferable that the variation is within ± 0.1 m / s. By performing the paint temperature management, the roller temperature management, and the air blowing condition management, the resistance adjusting layer 3, the skin layer 4, and the adhesion can be satisfactorily produced without causing dripping of the paint, filming, or generation of bubbles. An agent layer or the like can be formed.

  The charging roller 10 configured as described above has a compression set of 20 μm or less after being left for 1 month in an environment where the temperature is 40 ° C. and the humidity is 90%, and the thickness of the elastic layer is It is characterized by being 1.5 mm or less. That is, conventionally, the amount of compression set is large due to the thick elastic layer, and as a result, there is a possibility that the set mark image is not good. By suppressing the thickness to 1.5 mm or less, the amount of compression set can be made 20 μm or less, and the problem of set trace images can be solved.

  Here, the amount of compression set can be defined by the difference in the outer diameter of the charging roller 10 before and after use (for example, before and after assembly of the anti-static roller 10 into the cartridge), and the measurement is performed using a general laser. It can be measured using a shape measuring machine (for example, a high precision laser measuring machine LSM-430V manufactured by Mitutoyo Corporation).

In the charging roller 10 of the present invention, the micro hardness of the elastic layer is set to 35 to 50, the runout is set to 70 μm or less in the entire region in the roller length direction, and the center in the length direction from the end in the cross section of the roller length direction. It is preferable that the amount of the crown that is projected and represents the degree of the projection is 45 to 120 μm. By doing so, a normal image can be further improved.

  Although the charging roller 10 and the photosensitive member rotate while being in contact with each other, when the deflection of the charging roller 10 is large, a gap is generated between the charging roller 10 and the photosensitive member. Furthermore, the gap distance also varies. In this case, the toner particles and the external additive remaining on the photosensitive member are liable to enter the gap and adhere to the charging roller 10 as unevenness. As a result, the roller surface becomes mottled and causes image defects.

  Here, when the micro hardness is less than 35, when the elastic layer is formed, it is difficult to form closed cells by combining the air, and hardness unevenness is likely to occur. On the other hand, this exceeds 50. If it is used, the hardness is too high, and even if the charging roller is pressed against the photosensitive member, it is difficult to deform and an image defect occurs at the center of the roller. Further, when the shake exceeds 70 μm, the distance from the photoconductor changes at a portion where the shake is large and the charge amount becomes non-uniform. Problem arises. In order to achieve such micro hardness, the elastic layer 2 is preferably made of a foam body, and this configuration can be easily realized.

  In addition, when the crown amount is less than 45 μm, the contact pressure at the center portion in the roller length direction is low, whereas when it exceeds 120 μm, the center portion in the roller length direction is in strong contact. However, in any case, there is a possibility that the charge amount is non-uniform.

  The measurement of the deflection of the charging roller 10 in the present invention was performed using a high precision laser measuring machine LSM-430v manufactured by Mitutoyo Corporation. With this measuring machine, the outer diameter was measured for each of the five points in the roller length direction, and the average value of the difference between the maximum value and the minimum value of the outer diameter measured for each point was taken as the shake.

Further, the crown amount of the charging member in the present invention was also measured using the above-described high-precision laser measuring machine LSM-430v manufactured by Mitutoyo Corporation. With this measuring machine, the outer diameter is measured at the center of the roller and at a position of 90 mm from the center to the end, and the difference between the outer diameter of the center and the average value of the outer diameter at each 90 mm position in the direction of both ends is measured. The amount of roller crown. For example, in a charging member having a roller length of 250 mm, the outer diameter is measured at three points of 35 mm, 125 mm, and 215 mm from one end. At that time, if the outer diameter at the 35 mm position from one end is A (mm), the outer diameter at the 125 mm position is B (mm), and the outer diameter at the 215 mm position is C (mm), the crown amount (μm) is It is obtained in 1).

Crown amount (μm) = {B- (A + C) / 2} x1000 (1)

  A plurality of charging rollers with different diameters and mechanical properties were made as prototypes, and each roller was mounted on a printer cartridge for image evaluation. The results are summarized in Table 1.

  In the above, the length of the elastic layer was 220 mm. In addition, in the elastic layers of Comparative Example 1 and Example 1, 60 parts by mass of polyether polyol (Mitsui Takeda Chemical Co., Ltd., Actcol ED-26), TDI (Mitsui Takeda Chemical Co. Ltd., Cosmonate T-80) Solid urethane formed by adding 20 parts by mass of carbon (Asahi Carbon Co., Ltd./Asahi # 80) to 40 parts by mass is used. The elastic layers of Comparative Example 2 and Example 2 have the above materials and air. And foamed urethane molded so as to have a density of 0.5.

  The image was evaluated by visual observation after printing the image with each roller mounted on LBP2050 (Canon).

  The charging roller of the present invention can be used in various electrophotographic apparatuses.

1 is a longitudinal sectional view showing a charging roller according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Core body 2 Elastic layer 3 Resistance adjustment layer 4 Skin layer 10 Charging roller

Claims (4)

In the charging roller in which an elastic layer is arranged around a core metal having a diameter of 5 to 6 mm,
A charging roller having a compression set of 20 μm or less and a thickness of an elastic layer of 1.5 mm or less after being left for 1 month in an environment of a temperature of 40 ° C. and a humidity of 90%.   The micro hardness of the elastic layer is 35-50, and the runout is 70 μm or less in the entire region in the roller length direction, and the center in the length direction protrudes from the end in the cross section of the roller length direction, and the degree of the protrusion is The charging roller according to claim 1, wherein the crown amount is 45 to 120 μm.   The charging roller according to claim 1, wherein the elastic layer is formed of a foam body in which closed cells are dispersed.   The charging roller according to claim 1, wherein a skin layer constituting the roller surface is disposed outside the elastic layer, and the microhardness of the skin layer is made higher than that of the elastic layer.

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