JP2017134229A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide means that suppresses unevenness in the amount of toner to be reversely transferred to improve print quality.SOLUTION: An image forming apparatus comprises: image forming parts that form developer images; a transfer body that carries the developer images formed by the image forming parts; and transfer members that are arranged opposite to the image forming parts and transfer the developer images from the image forming parts to the transfer body. The difference between the maximum value and minimum value of a stress per unit length of a surface of the transfer member is set to 0.105 or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus using an electrophotographic process.

  Conventional image forming apparatuses using an electrophotographic process include those using an intermediate transfer method. For example, a toner image formed on a photosensitive drum corresponding to each color of black K, yellow Y, magenta M, and cyan C is obtained. Then, the images are formed by sequentially transferring (primary transfer) to the intermediate transfer belt and superimposing them, and then transferring the toner image carried on the intermediate transfer belt onto the recording medium again (secondary transfer). (For example, refer to Patent Document 1).

JP 2014-106413 A

However, in the conventional technology, when the toner primarily transferred onto the intermediate transfer belt at the primary transfer portion on the upstream side of the primary transfer passes through the primary transfer portion on the downstream side, a part of the toner is transferred to the photosensitive drum side. There is a case where reverse transfer to which the toner adheres may occur, and the amount of toner to be reversely transferred is not uniform, thereby causing unevenness in the printed image and lowering the print quality.
An object of the present invention is to solve such a problem, and an object of the present invention is to suppress unevenness in the amount of toner to be reversely transferred and improve print quality.

  Therefore, the present invention is an image forming unit that forms a developer image, a transfer member that carries the developer image formed by the image forming unit, and the transfer member that is sandwiched between the image forming unit, A transfer member that transfers the developer image from the image forming unit to the transfer body, and a maximum value of a difference between a maximum value and a minimum value of a unit length of the surface of the transfer member is set to 0. It is characterized by being 105 or less.

  According to the present invention as described above, the effect of suppressing unevenness in the amount of toner to be reversely transferred and improving the printing quality can be obtained.

Schematic side sectional view showing the structure of the image forming apparatus in the embodiment Explanatory drawing of hardness measurement of the primary transfer roller in the embodiment Explanatory drawing of the resistance measurement of the primary transfer roller in an Example Sample No. 1 is a graph showing the stress of the primary transfer roller 1 Sample No. 4 is a graph showing the stress of the primary transfer roller 4 Sample No. 9 is a graph showing the stress of the primary transfer roller 9 Sample No. The graph which shows the stress of 13 primary transfer rollers of 13 Sample No. Graph showing the stress of 15 primary transfer rollers Graph showing transfer efficiency in Examples Graph showing reverse transcription rate in Examples

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic cross-sectional side view showing the configuration of the image forming apparatus in the embodiment.
In FIG. 1, an image forming apparatus 100 is, for example, a printer that uses an electrophotographic process, and corresponds to colored toners as developers of a total of four colors of yellow: Y, magenta: M, cyan: C, and black: K. Image forming units 8Y, 8M, 8C, and 8K having the same configuration are arranged.

The image forming units 8Y, 8M, 8C, and 8K as image forming units form toner images as developer images.
Each of the image forming units 8Y, 8M, 8C, and 8K has photosensitive drums 3Y, 3M, 3C, and 3K as image carriers, and a charging roller is provided around each of the photosensitive drums 3Y, 3M, 3C, and 3K. 4Y, 4M, 4C, 4K, exposure devices 5Y, 5M, 5C, 5K, developing devices 6Y, 6M, 6C, 6K, primary transfer rollers 1Y, 1M, 1C, 1K, and cleaning blades 7Y, 7M, 7C, 7K Is arranged.

The photosensitive drums 3Y, 3M, 3C, and 3K are organic photosensitive drums that have an OPC (Organic PhotoConductor) photosensitive layer.
The charging rollers 4Y, 4M, 4C, and 4K are configured to uniformly charge the surfaces of the photosensitive drums 3Y, 3M, 3C, and 3K when a charging bias (voltage) is applied from a charging power source.
The exposure devices 5Y, 5M, 5C, and 5K have LED (Light Emitting Diode) heads and support image information on the surfaces of the photosensitive drums 3Y, 3M, 3C, and 3K charged by the charging rollers 4Y, 4M, 4C, and 4K. The electrostatic latent image is formed by irradiating the exposed light and exposing.

The developing devices 6Y, 6M, 6C, and 6K attach toner as a developer to the electrostatic latent images formed on the surfaces of the photosensitive drums 3Y, 3M, 3C, and 3K by using the one-component nonmagnetic contact developing method. Thus, a toner image is formed. The developing devices 6Y, 6M, 6C, and 6K contain Y toner, M toner, C toner, and K toner, respectively.
The primary transfer rollers 1Y, 1M, 1C, and 1K as transfer members transfer the toner images formed by the image forming units 8Y, 8M, 8C, and 8K to the photosensitive drums 3Y, 3M of the image forming units 8Y, 8M, 8C, and 8K. 3C and 3K are transferred to the intermediate transfer belt 2.

  The primary transfer rollers 1Y, 1M, 1C, and 1K are arranged to face the respective photosensitive drums 3Y, 3M, 3C, and 3K with the intermediate transfer belt 2 interposed therebetween, and at the time of printing operation, the photosensitive drums 3Y, The toner images on the photosensitive drums 3Y, 3M, 3C, and 3K are moved onto the intermediate transfer belt 2 by being pressed by 3M, 3C, and 3K, and a transfer bias is applied by a transfer power source, thereby performing primary transfer. The primary transfer rollers 1Y, 1M, 1C, and 1K may include a mechanism and a control unit that separate the primary transfer rollers 1Y, 1M, and 1C from the intermediate transfer belt 2 during monochrome printing, for example.

  The cleaning blades 7Y, 7M, 7C, and 7K are disposed so that the edges thereof are in contact with the photosensitive drums 3Y, 3M, 3C, and 3K, and are transferred to the intermediate transfer belt 2 by the primary transfer rollers 1Y, 1M, 1C, and 1K. The transfer residual toner remaining on the surfaces of the photosensitive drums 3Y, 3M, 3C, and 3K without being able to be removed is removed.

  The intermediate transfer belt 2 as a transfer member carries a toner image formed by the image forming units 8Y, 8M, 8C, and 8K. The intermediate transfer belt 2 is stretched around a drive roller 12, a support roller 13, and a secondary transfer counter roller 11, and is endless in the direction indicated by the arrow A in FIG. It is.

The secondary transfer roller 10 is disposed so as to face the secondary transfer counter roller 11 with the intermediate transfer belt 2 interposed therebetween, and forms a secondary transfer portion. The secondary transfer roller 10 performs a secondary transfer by moving a toner image on the intermediate transfer belt 2 onto a printing sheet as a printing medium by applying a transfer bias from a transfer power source during a printing operation.
The cleaning blade 14 is disposed so as to contact the intermediate transfer belt 2 on the downstream side of the secondary transfer roller 10 in the rotation direction of the intermediate transfer belt 2, and is a transfer residual toner that has not been transferred onto the printing paper at the secondary transfer unit. Is to be removed.

A paper feed tray 17, paper feed rollers 41 to 47, a secondary transfer roller 10, a secondary transfer counter roller 11, and a fixing device 15 are arranged in order from the upstream side of the printing paper conveyance path.
The paper feed tray 17 accommodates the printing paper P before printing. The paper feed rollers 41 to 47 sandwich the printing paper P and convey it to the secondary transfer unit. The fixing device 15 fixes the toner image transferred onto the printing paper P by the secondary transfer unit to the printing paper P with heat and pressure.

Next, the photosensitive drums 3Y, 3M, 3C, and 3K (photosensitive drum 3) used in this embodiment will be described.
The photosensitive drum 3 includes a charge generation layer mainly composed of a charge generation material and a binder resin on a conductive support such as aluminum and stainless steel, and a charge transport layer mainly composed of a charge transport material and a binder resin. It is constituted by laminating.

  Various organic pigments and dyes can be used as the charge generation material. Among them, metals such as metal-free phthalocyanine, copper indium chloride, gallium chloride, tin, oxytitanium, zinc and vanadium, or oxides and chlorides thereof are arranged. Azo pigments such as phthalocyanines, monoazo, bisazo, trisazo, polyazo, etc. can be used, and fine particles of these substances can be used, for example, polyester resin, polyvinyl acetate, polyacrylate ester, polymethacrylate ester, polyester, polycarbonate, It can be used in a dispersion layer in a form bound with various binder resins such as polyvinyl acetoacetal, polyvinyl propional, phenoxy resin, epoxy resin, urethane resin, cellulose ester, and cellulose ether.

  The charge transport layer is composed of, for example, a heterocyclic compound such as carbazole, indole, imidazole, oxazole, biazole, oxadiazole, pyrazoline, thiadiazole, aniline derivative, hydrazone compound, aromatic amine derivative, stilbene derivative, or these compounds. An electron donating substance such as a polymer having a group in the main chain or side chain can be used, and a binder resin for the charge transport layer is a vinyl polymer such as polycarbonate, polymethyl methacrylate, polystyrene, polyvinyl chloride, polyester, polyester carbonate. , Polysulfone, polyimide, phenoxy, epoxy, silicone resin, and copolymers thereof, or partially crosslinked cured products, etc. may be used alone or as a mixture, and polycarbonate is particularly suitable. There. Moreover, you may contain various additives, such as antioxidant and a sensitizer, as needed.

  In this example, an alumite treatment was used on the surface of the aluminum tube as the conductive support, phthalocyanine was used as the charge generation material for the charge generation layer, and polyvinyl acetal resin was used as the binder resin. For the charge transport layer, a hydrazone compound was used as the charge transport material, a polycarbonate resin was used as the binder resin, and an antioxidant was further added. The thickness of the charge transport layer of the photosensitive drum was 18 μm, and the outer diameter of the photosensitive drum was 30.0 mm.

Next, the intermediate transfer belt 2 used in this embodiment will be described.
The intermediate transfer belt 2 is formed from a single layer or a plurality of resin layers.
As a molding method, extrusion molding, inflation molding, injection molding, centrifugal molding, dip molding, or the like may be used. Furthermore, the surface layer may be formed by spray coating, roller coating, or dip coating on the surface of the base layer thus formed. The film thickness of the surface layer is adjusted by the concentration of the material to be applied and the coating amount.

  The resin constituting the base layer is not particularly limited, and is preferably a material in which the tensile deformation at the time of belt driving is within a certain range from the viewpoint of durability and mechanical characteristics, and repeated sliding with meandering prevention means. It is desirable that the material be resistant to damage such as side wear, breakage, and cracking. For example, polyamide (PA), polyvinylidene fluoride (PVDF), polybutylene terephthalate (PBT), polycarbonate (PC), acrylonitrile-butadiene-styrene (ABS), acrylonitrile-ethylenepropylene-styrene, polyacetal, polyacrylonitrile, It is composed of polyvinyl fluoride, polyhexafluoroethylene propylene, polytrifluoride ethylene, polyamideimide, polyimide and the like. In this example, polyamide was used.

  When providing the surface layer, the constituent materials include polyacryl, polyacryl urethane, polyester urethane, polyether urethane, polyamide, acrylonitrile-butadiene-styrene (ABS), polycarbonate, polybutylene terephthalate, polyethylene terephthalate, styrene compound, A naphthalene compound or the like is preferable, and no surface layer is provided in this embodiment.

  Moreover, in order to ensure desired electroconductivity, a electrically conductive agent can be added to a base layer, a surface layer, and both a base layer and a surface layer. As the conductive material, an appropriate amount of an ionic conductive agent, an electronic conductive agent, or both can be provided. As an ionic conductive agent, alkali metal salts, alkaline earth metal salts, quaternary ammonium salts such as lithium perchlorate, sodium perchlorate, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, potassium thiocyanate, lithium thiocyanate, etc. , Organic phosphorus salts, borate salts and the like. Examples of the electronic conductive material include furnace black, channel black, ketjen black, and acetylene black. These can be used alone or in combination with a plurality of carbon blacks. In particular, channel black and furnace black are preferably used for the intermediate transfer belt used in the printer in this embodiment, and depending on the application, those that prevent oxidation deterioration such as oxidation treatment and graft treatment, and dispersibility in solvents. It is preferable to use one having improved

The volume resistivity ρv of the belt thus molded is preferably 10 ⁶ to 10 ¹⁴ Ω · cm, and more preferably 10 ⁹ to 10 ¹² Ω · cm. Further, the surface resistivity ρs is preferably 10 ⁷ to 10 ¹⁴ Ω / □, and particularly preferably 10 ⁹ to 10 ¹² Ω / □. As the resistance value of the intermediate transfer belt 2 used in the image forming apparatus of this embodiment, a volume resistivity ρv of 10 ¹⁰ Ω · cm and a surface resistivity ρs of 10 ^10.5 Ω / □ were used.
The film thickness of the base layer is determined by the magnitude of the elastic modulus of the material constituting the base layer from the viewpoint of mechanical durability described above, but generally the film thickness is 60 to 200 μm. The intermediate transfer belt used in the printer in this example was 100 μm.

Next, the toner used in this embodiment will be described.
As the toner as the developer, a toner obtained by mixing an external additive with toner particles serving as a base can be used. In this embodiment, a non-magnetic one-component negatively charged polymerized toner is used, and an external additive is added to toner particles formed by mixing and aggregating a styrene acrylic copolymer resin, a colorant and a wax produced by an emulsion polymerization method. As a mixture, fine powder of silica and titanium oxide was added and mixed. Toner particles having a circularity of 0.94 to 0.98 and an average particle size of about 7 μm were used, and external additives having a particle size of 50 to 200 nm were used. This was selected as one capable of obtaining image sharpness and high image quality by carrying out development with excellent transfer efficiency, fixing no discrete agent, and dot reproducibility and resolution.

Next, the primary transfer rollers 1Y, 1M, 1C, and 1K (primary transfer roller 1) used in this embodiment will be described.
As shown in FIG. 2B, the primary transfer roller 1 is provided on a conductive support 1b and the conductive support 1b, and at least an outer peripheral surface is formed by a conductive elastic layer 1a. . A charging power source is connected to the conductive support 1 b of the primary transfer roller 1.

  The primary transfer roller preferably contacts (nips) the photosensitive drum uniformly in the sub-scanning line direction with the intermediate transfer belt interposed therebetween, and the elastic layer has a rubber hardness of 70 degrees Asker C (hereinafter referred to as rubber hardness). Or less), preferably 50 degrees or less. For this reason, foam is often used for the elastic layer as a constituent material, and polyurethane foam, epichlorohydrin rubber (CO, ECO, GCO, GECO), acrylonitrile butadiene rubber (NBR), ethylene propylene rubber (EPM, EPDM). ), Chloroprene rubber (CR), butadiene rubber (BR), styrene butadiene rubber (SBR), isoprene rubber (IR), natural rubber, or a mixture of two or more thereof.

  Moreover, a surface layer can be further provided on the surface of the conductive elastic layer. When providing the surface layer, the constituent materials include polyacryl, polyacryl urethane, polyester urethane, polyether urethane, polyamide, acrylonitrile butadiene styrene (ABS), polycarbonate, polybutylene terephthalate, polyethylene terephthalate, styrene compound, naphthalene compound, etc. Is preferred.

  Moreover, in order to ensure desired electroconductivity, a electrically conductive agent can be added to an elastic layer, an elastic layer surface, and both an elastic layer and an elastic layer surface. As the conductive agent, an appropriate amount of an ionic conductive agent, an electronic conductive agent, or both can be provided. As an ionic conductive agent, alkali metal salts, alkaline earth metal salts, quaternary ammonium salts such as lithium perchlorate, sodium perchlorate, lithium trifluoromethanesulfonate, lithium tetrafluoroborate, potassium thiocyanate, lithium thiocyanate, etc. , Organic phosphorus salts, borate salts and the like. Examples of the electronic conductive material include furnace black, channel black, ketjen black, and acetylene black. These can be used alone or in combination with a plurality of carbon blacks.

The conductive property of the primary transfer roller is preferably 10 ⁹ Ω or less as a resistance. As the conductivity of the elastic layer, either electronic conductivity or ionic conductivity may be used. However, partial resistance unevenness may easily affect transfer unevenness. In many cases, ionic conductivity is used rather than conductivity.

  Here, as shown in FIG. 3, the resistance of the primary transfer roller 1 is measured by using a high resistance meter (4339B manufactured by Hewlett Packard) as a resistance measuring device 52 and applying a linear pressure to a metal drum 53 made of SUS of φ30. The primary transfer roller 1 is brought into contact (nip) at 50 gf / cm, and the resistance value is measured while rotating the primary transfer roller 1 and the metal drum 53 at a constant speed.

In this example, the primary transfer roller of Examples 1 to 4 below was used.
<Example 1>
A polyurethane foam was used for the conductive elastic layer of the primary transfer roller of Example 1. As raw materials, polyols, polyisocyanates, catalysts, foam stabilizers, and conductive agents are contained.

  As the polyols, polyether polyol or polyester polyol is used. Polyether polyols include polymers obtained by addition polymerization of propylene oxide to polyhydric alcohols, polymers obtained by addition polymerization of ethylene oxide, polymers obtained by addition polymerization of propylene oxide and ethylene oxide, or modified products thereof. Used. Examples of the modified body include those obtained by adding acrylonitrile or styrene to polyether polyol, or those obtained by adding both acrylonitrile and styrene. Here, the polyhydric alcohol is a compound having a plurality of hydroxyl groups in one molecule, and examples thereof include glycerin and dipropylene glycol.

  Polyisocyanates to be reacted with polyols are compounds having a plurality of isocyanate groups, specifically, tolylene diisocyanate (TDI), 4,4-diphenylmethane diisocyanate (MDI), 1,5-naphthalene diisocyanate (NDI). , Aromatic polyisocyanates such as triphenylmethane triisocyanate and xylylene diisocyanate (XDI), alicyclic polyisocyanates such as isophorone diisocyanate (IPDI) and dicyclohexylmethane diisocyanate, and aliphatic polyisocyanates such as hexamethylene diisocyanate (HDI) Isocyanates, or modified polyisocyanates such as free isocyanate prepolymers by reaction of these with polyols, carbodiimide-modified polyisocyanates, These mixtures polyisocyanate is used for al. Of these, tolylene diisocyanate and derivatives thereof, and 4,4-diphenylmethane diisocyanate and derivatives thereof are preferable, and these can be used in combination.

  The isocyanate index (isocyanate index) of the polyisocyanates may be 100 or less, or may exceed 100, but is in the range of 100 to 110 in order to make the polyurethane foam suitable for the foam roller. Is preferred. Here, the isocyanate index represents the equivalent ratio of isocyanate groups of polyisocyanates to active hydrogen groups such as hydroxyl groups of polyols in percentage.

Next, the catalyst is for accelerating each reaction such as urethanization reaction (resinification reaction) between polyols and polyisocyanates, and curing reaction (crosslinking reaction) between the product and polyisocyanates. . Specific examples of the catalyst include triethylenediamine (TEDA), dimethylethanolamine, tertiary amines such as N, N ′, N′-trimethylaminoethylpiperazine, organometallic compounds such as tin octylate (tin octoate), Acetates, alkali metal alcoholates and the like are used. As other catalysts, morpholine catalysts such as N-methylmorpholine and N-ethylmorpholine can also be used in order to improve the curability on the foam surface. The compounding amount of the catalyst is about 0.05 to 0.5 parts by mass per 100 parts by mass of polyols.
The conductive agent is adjusted to a predetermined resistance value using an ionic conductive agent.

  Subsequently, as the foam stabilizer, any of those usually blended in the raw material of polyurethane foam can be used. For example, nonionic systems such as organosiloxane-polyoxyalkylene copolymer, silicone-grease copolymer, etc. Surfactants, or a mixture thereof, anionic surfactants such as sodium dodecylbenzenesulfonate and sodium lauryl sulfate, and phenolic compounds are exemplified. The blending amount of the foam stabilizer is preferably about 0.1 to 2.0 parts by mass per 100 parts by mass of polyols.

  An inert foam-forming gas is injected into a mixed foaming mold using a mechanical floss (mechanical stirring) method as a raw material for the polyurethane foam. Moreover, in the mechanical floss method, a normal foaming agent is not required, but when the mechanical floss method is not adopted, foaming can be performed using the foaming agent. Such foaming agents typically include water as a chemical foaming agent. Water mainly reacts with polyisocyanates (foaming reaction) to generate carbon dioxide gas. As the foaming agent, in addition to water, other chemical foaming agents or physical (mechanical) foaming agents can be used. Examples of the chemical foaming agent include inorganic acids such as organic acids and boric acid, alkali metal carbonates, cyclic carbonates, dialkyl carbonates, and the like. These chemical foaming agents generate gas by reaction with raw material components of polyurethane foam or decomposition by heating. On the other hand, examples of the physical blowing agent include hydrocarbons such as pentane and cyclopentane, and gases such as methylene chloride, air, nitrogen gas, and carbon dioxide (carbon dioxide). Other raw materials for polyurethane foams can be blended with cell openers such as polyalkylene oxide polyols, flame retardants such as condensed phosphate esters, antioxidants, plasticizers, ultraviolet absorbers, and colorants.

  And the polyurethane foam is manufactured by inject | pouring the raw material of the polyurethane foam mentioned above into a shaping | molding die, and making it react and harden | cure. The heating temperature at that time is usually about 100 to 150 ° C., and the heating time is usually about 20 to 40 minutes. When the heating temperature is less than 100 ° C. and the heating time is less than 20 minutes, the urethanization reaction does not proceed sufficiently, and when the heating temperature exceeds 150 ° C. and the heating time exceeds 40 minutes, scorch (early crosslinking) ) Are likely to occur and are colored, and the polyurethane foam is deteriorated.

  The reaction when the polyurethane foam is formed basically includes an addition polymerization reaction (urethanization reaction or resinification reaction) between a polyol and a polyisocyanate and crosslinking (curing) between the reaction product and the polyisocyanate. ) Reaction. The polyurethane foam thus obtained has a structure in which a skeleton extends three-dimensionally in a network and a large number of fine cells are uniformly formed therebetween. In addition, the polyurethane foam can exhibit a certain strength and required elasticity based on the properties of polyurethane composed of hard segments and soft segments.

Next, a primary transfer roller can be obtained by polishing the resulting polyurethane foam through a conductive core material into a roll shape.
In Example 1, the primary transfer roller was created with an outer diameter of 19.0 mm and an axial core diameter of φ10. The resistance is adjusted to about 7.1 logΩ, the rubber hardness is Asker C35 degrees, and the average cell diameter of the foamed cells is 150 μm. Sample No. 1 1 to 6 primary transfer rollers were prepared.

<Example 2>
A conductive rubber foam was used for the conductive elastic layer of the primary transfer roller of Example 2. As raw materials, a mixture of about 80 parts by weight of acrylonitrile butadiene rubber (NBR), about 20 parts by weight of epichlorohydrin rubber (ECO) is used as a base polymer, 10 to 20 parts by weight of carbon black, and 3 to 5 parts by weight of a blowing agent. 2 to 4 parts by weight of a foaming aid, 0 to 10 parts by weight of a softening agent, and 5 to 10 parts by weight of a crosslinking agent and a crosslinking aid were mixed. Furthermore, at least one additive such as a conductive agent, an acid acceptor, an antioxidant, an antioxidant, a processing aid, a filler, a pigment, a flame retardant, and a neutralizing agent can be contained.

The cross-linking agent component of the base polymer includes at least one cross-linking agent and sulfur-containing thiourea-based cross-linking agent for cross-linking ECO and an accelerator thereof, and sulfur and a sulfur-containing cross-linking agent for cross-linking NBR. It is desirable to use a system accelerator in combination.
Next, as a method for manufacturing a roller, a roll shape is created by kneading, extruding, vulcanizing, forming, and polishing the above composition.

In the kneading process, the additive is uniformly blended into the polymer using a kneader or an open roll.
In the extrusion process, the blended polymer is preformed into a cylindrical tube shape. At this time, the rubber hardness, resistance unevenness and foaming unevenness after molding can be kept more uniform by keeping the pressure, speed, extrusion outer diameter, and temperature constant.

  The preformed polymer is foamed and vulcanized by the vulcanization process. At this time, the vulcanization method includes a continuous vulcanization method and a vulcanization can method, and is often used as a conventional method. In the continuous vulcanization method, a continuous vulcanizer is installed immediately after the extrusion step in the previous step, and the extruded tube is vulcanized with microwaves and hot air by the continuous vulcanizer. The crosslinking density and foaming state are adjusted by the temperature, length, passing speed, microwave strength, etc. in the continuous vulcanizer. In the vulcanization can method, the crosslinking density and the foaming state are adjusted by adjusting the steam pressure, temperature and time using a steam kettle. The continuous vulcanization method is preferable for making the foamed cells more uniform, and the vulcanization can method is preferable for increasing the crosslinking density and reducing the compression set. Further, secondary vulcanization can be performed using an oven.

Next, a primary transfer roller can be obtained by polishing the foamed rubber tube into a roll shape through a conductive core material.
In Example 2, the primary transfer roller was created with an outer diameter of 19.0 mm and an axial core diameter of φ10. Using the continuous vulcanization method and the vulcanization can method, the vulcanization method was adjusted so that the average cell diameters of the foamed cells were 150 μm and 250 μm, respectively, the resistance was about 7.1 logΩ, and the rubber hardness was Asker C35 degrees. Sample No. in Table 2 7 to 10 primary transfer rollers were prepared.

<Example 3>
For the primary transfer roller of Example 3, a urethane layer was further applied to the surface of the primary transfer roller prepared in Example 2 to form a resin layer. As the coating method, conventional methods such as spraying, roll coater, dipping and the like can be used. In Example 3, a primary transfer roller having a urethane coat applied by spray coating was prepared.

As raw materials, water was used as a solvent, polyurethane as a base polymer, polytetrafluoroethylene (PTFE) as a release agent, and carbon black as a conductive material were added.
After the raw material is spray-coated, it is dried using an oven. At this time, the applied coat thickness is adjusted to 5 to 10 μm.
As a result, the resistance is about 7.2 logΩ and the rubber hardness is Asker C40 degrees. 11 to 14 primary transfer rollers were prepared.

<Example 4>
In the primary transfer roller of Example 4, sample Nos. 1 and 2 prepared in Examples 1 and 2 were formed on a resin tube as a resin layer. 6 and sample no. Ten primary transfer rollers were press-fitted.
As the tube, a resin tube or a rubber tube can be used. Examples of the resin tube include polyamide (PA), polyvinylidene fluoride (PVDF), polybutylene terephthalate (PBT), polycarbonate (PC), acrylonitrile-butadiene-styrene (ABS), acrylonitrile-ethylenepropylene-styrene, polyacetal, polyacetal. Acrylonitrile, polyvinyl fluoride, polyhexafluoroethylene propylene, polytrifluoride ethylene, polyamideimide, polyimide and the like can be used. In Example 3, polyvinylidene fluoride (PVDF) was used.

Moreover, in order to ensure desired electroconductivity, a electrically conductive agent can be added to a tube. As the conductive agent, an appropriate amount of an ionic conductive agent, an electronic conductive agent, or both can be provided. An ionic conductive agent was added to the tube in Example 4.
The thickness of the tube depends on the hardness and elasticity of the primary transfer roller, the mechanical durability of the tube, etc. In Example 4, a 60 μm one was used.

As a result, the resistance is about 7.2 log Ω and the rubber hardness is Asker C 48 degrees. 15 and 16 primary transfer rollers were prepared.
The operation of the above configuration will be described.
The following evaluation was performed about the primary transfer roller (sample No. 1-16) produced in Example 1- Example 4. FIG.

<Rotational hardness measurement>
For the primary transfer rollers of Examples 1 to 4 and Comparative Example, the hardness of the surface of the primary transfer roller was measured by a hardness measuring machine (micro load cell LTS-500GA (manufactured by Kyowa Denki Co., Ltd.)) using the method shown in FIG. taking measurement. 2A is a perspective view of the primary transfer roller 1 and the tip terminal 51 of the hardness measuring machine, and FIG. 2A is a side view of the primary transfer roller 1 and the tip terminal 51 of the hardness measuring machine.

In FIG. 2, the tip terminal (SUS material) 51 of the hardness measuring machine is pressed against the elastic layer 1 a which is the surface of the primary transfer roller 1. The tip terminal 51 has a cylindrical shape of φ2 and a length of 10 mm. The tip terminal 51 is placed in the center of the primary transfer roller 1 with the cylindrical shaft of the tip terminal 51 parallel to the axis 1 b of the primary transfer roller 1. Press in the axial direction as a push amount Δd (0.4 mm).
In this state, while the primary transfer roller 1 is rotated in the direction indicated by the arrow C in the figure, the repulsive stress F applied to the tip terminal 51 is measured by rotating it one or more times, in this evaluation, 1.25 (450 degrees) rotation.

Based on the measurement result, the maximum value Fmax, the minimum value Fmin, and the difference Fp-p between the maximum value and the minimum value of the stress F are calculated. Further, the circumferential direction of the surface of the primary transfer roller 1 indicated by the arrow C in the figure is calculated. The difference between the maximum value and the minimum value of stress F per unit length (distance) 3 mm (hereinafter referred to as “unit stress difference”) ΔF was calculated, and the maximum value ΔFmax of unit stress difference ΔF was calculated.
The primary transfer roller (urethane foam roller) using the polyurethane foam of Example 1 is sample No. 1 shown in Table 1. The maximum value Fmax, the minimum value Fmin, the difference between the maximum value and the minimum value Fp-p, and the maximum value ΔFmax of the unit stress difference ΔF are as shown in Table 1.

  The primary transfer roller (urethane foam roller) using the polyurethane foam of Example 1 is, for example, Sample No. The repulsive stress F of the primary transfer roller 1 is a graph shown in FIG. 4A, and the unit stress difference ΔF is a graph shown in FIG. 4B. 4A, the maximum value Fmax is 1.901 (N), the minimum value Fmin is 1.489 (N), and the difference Fp-p between the maximum value and the minimum value is 0.412 (N). Further, from FIG. 4B, the maximum value ΔFmax of the unit stress difference is 0.073 (N).

Since the primary transfer roller (urethane foam roller) of Example 1 is a liquid raw material, fine unevenness hardly occurs and the stress F tends to be smooth. On the other hand, it is difficult to manage the flow rate and the liquid level at the time of pouring the liquid raw material into the mold, and the flow mark may be generated depending on the shape of the forming mold.
Also, for example, sample no. 4 is a graph shown in FIG. 5A, and the unit stress difference ΔF is a graph shown in FIG. 5B. 5A, the maximum value Fmax is 1.709 (N), the minimum value Fmin is 1.536 (N), and the difference Fp-p between the maximum value and the minimum value is 0.173 (N). Further, from FIG. 5B, the maximum value ΔFmax of the unit stress difference is 0.175 (N).

In FIGS. 5A and 5B, a weld line is seen near an angle of 320 degrees. If the mold diameter is small and the polishing scale is small, the flow rate is likely to fluctuate near the mold surface, and a weld line is likely to occur. Since the weld line is scraped off by increasing the mold diameter and polishing grind, the unit stress difference ΔF tends to decrease.
The primary transfer roller (foamed rubber roller) using the conductive rubber foam of Example 2 is a sample No. shown in Table 2. Table 2 shows the maximum value Fmax, the minimum value Fmin, the difference between the maximum value and the minimum value Fp-p, and the maximum value ΔFmax of the unit stress difference ΔF.

  The primary transfer roller (foam rubber roller) using the conductive rubber foam of Example 2 is, for example, Sample No. 9 is a graph shown in FIG. 6A, and the unit stress difference ΔF is a graph shown in FIG. 6B. 6A, the maximum value Fmax is 1.503 (N), the minimum value Fmin is 1.298 (N), and the difference Fp−p between the maximum value and the minimum value is 0.205 (N). Further, from FIG. 6B, the maximum value ΔFmax of the unit stress difference is 0.143 (N).

The primary transfer roller (foamed rubber roller) of Example 2 has small circumferential unevenness, local stress F unevenness is seen from the difference between the maximum value and the minimum value Fp-p, and the unit stress difference ΔF is large. There is a trend.
In the vulcanization can method, heat is applied from the surface at the start of heating, but since the continuous vulcanization method uses microwaves, heat is easily applied evenly inside the rubber, and the continuous vulcanization method is better. The cell spots tend to be small and uniformly foam. Regardless of the vulcanization method, the variation in the stress F is smaller when the cell diameter is smaller.

  The primary transfer roller of Example 3 is a sample No. shown in Table 3. The maximum value Fmax, the minimum value Fmin, the difference Fp-p between the maximum value and the minimum value, and the maximum value ΔFmax of the unit stress difference ΔF are as shown in Table 3.

The primary transfer roller of Example 3 has a unit stress difference ΔF larger than that of the primary transfer roller of Example 2 by coating the surface of the primary transfer roller (foamed rubber roller) of Example 2 and making it a little harder. It became smaller and the hardness unevenness of the surface became smaller.
The primary transfer roller of Example 3 is, for example, Sample No. 13 is a graph shown in FIG. 7A, and the unit stress difference ΔF is a graph shown in FIG. 7B. From FIG. 7A, the maximum value Fmax is 1.926 (N), the minimum value Fmin is 1.709 (N), and the difference Fp-p between the maximum value and the minimum value is 0.217 (N). Further, from FIG. 7B, the maximum value ΔFmax of the unit stress difference ΔF is 0.108 (N).

  The primary transfer roller of Example 4 is a sample No. shown in Table 4. Table 4 shows the maximum value Fmax, the minimum value Fmin, the difference between the maximum value and the minimum value Fp-p, and the maximum value ΔFmax of the unit stress difference ΔF.

When the primary transfer roller of Example 4 was wound around the tube, the hardness increased due to the elasticity of the tube. Further, the local hardness unevenness disappeared and only a smooth stress change was obtained, and the unit stress difference ΔF became very small.
The primary transfer roller of Example 4 is, for example, Sample No. The repulsive stress F of the primary transfer roller 15 is a graph shown in FIG. 8A, and the unit stress difference ΔF is a graph shown in FIG. 8B. From FIG. 8A, the maximum value Fmax is 2.458 (N), the minimum value Fmin is 2.296 (N), and the difference Fp-p between the maximum value and the minimum value is 0.162 (N). Further, from FIG. 8B, the maximum value ΔFmax of the unit stress difference ΔF is 0.047 (N).

  In this embodiment, the unit of the primary transfer roller is achieved by reducing the average cell diameter of the foamed cells, applying a urethane coat to the surface of the primary transfer roller, press-fitting the primary transfer roller into the resin tube, and the like. The maximum value ΔFmax of the stress difference ΔF was reduced.

<Printing test>
Next, a printing test was performed on the primary transfer rollers of Examples 1 to 4 and the comparative example using the printer 1 shown in FIG.
The conditions for the print test are:
(1) Temperature and humidity environment: NN environment (temperature 23 ° C, humidity 55%)
(2) Outer diameter of primary transfer roller 1: 19.0 mm, shaft core diameter: φ10
(3) Linear pressure of the primary transfer roller 1: 45 gf / cm
(4) The primary transfer roller 1 to be tested is installed at the position of the primary transfer roller 1K shown in FIG. 1. (5) The image pattern to be printed is a solid image of C color (entire printing)
(6) Adjust the printing density to an optical density in the range of 1.25 to 1.45 (the optical density is measured with an optical densitometer X-Rite 528 (manufactured by X-Rite))
(7) The primary transfer voltage of the primary transfer roller 1K is set to three types of 1000V, 1500V, and 2000V.

  Under this condition, the reverse transfer rate, which is the ratio of the reverse transfer toner from the intermediate transfer belt 2 to the K color photosensitive drum 3K, was measured at the position of the primary transfer roller 1K shown in FIG. This reverse transfer rate is determined by the weight A per unit area of the C color toner transferred from the C color photosensitive drum 3C to the intermediate transfer belt 2 and the unit area of the C color toner reversely transferred to the K color photosensitive drum 3K. The weight B was measured, and the weight B / weight A × 100 (%) was calculated as the reverse transcription rate.

  As shown in FIG. 9, the transfer efficiency of the toner transferred from the C-color photosensitive drum 3C to the intermediate transfer belt 2 is highest when the primary transfer voltage is 1000V and lowest when it is 3000V. The transfer efficiency is determined by measuring the weight C per unit area of the C color toner adhering to the C color photosensitive drum 3C and the weight D per unit area of the C color toner transferred to the intermediate transfer belt 2 by weight D / It calculated as weight Cx100 (%).

Also, the criteria for determining the print image are:
○: “Concentration unevenness, density step, and horizontal stripe cannot be confirmed”
×: “Image defect of density unevenness, density step, and horizontal stripe, or multiple image defects could be confirmed”
It was.

Here, the density unevenness is a phenomenon in which the density variation of the toner density spreads over the entire printed image, and the density step is a phenomenon in which a difference in toner density appears as a step in the printed image. The term “printing image” refers to a phenomenon in which streaks with different toner densities appear in the lateral direction, which is the axial direction of the primary transfer roller of a printed image.
The determination was made by visual observation by an inspector who can determine a density step with a density difference of 0.05 because density unevenness and horizontal stripes are difficult to measure with a measuring machine.

<Reverse transcription>
In reverse transfer, a part of the toner primarily transferred from the photosensitive drum onto the intermediate transfer belt 2 is transferred to the surface of the downstream photosensitive drum upstream in the rotation direction of the intermediate transfer belt 2. is there. The amount of toner to be reversely transferred increases as the primary transfer voltage increases. As shown in FIG. 10, the reverse transfer rate increases as the primary transfer voltage increases. Further, when the amount of toner to be reversely transferred increases, the color density of the toner arranged upstream decreases.
<Evaluation results>
The evaluation results are shown in Table 5.

  As shown in Table 5, when the primary transfer voltage is small and the reverse transfer rate is small, there is no problem in the quality of the printed image. However, when the primary transfer voltage increases and the reverse transfer rate increases by a certain amount, the quality of the printed image becomes defective. Even when the reverse transfer rate exceeds 10%, when the maximum value ΔFmax of the unit stress difference ΔF of the primary transfer roller is 0.105 or less, there is no defect in the quality of the printed image by the reverse transfer.

  The maximum value ΔFmax of the unit stress difference ΔF of the primary transfer roller is ideally 0, but it is extremely difficult to create a primary transfer roller in which the maximum value ΔFmax of the unit stress difference ΔF is 0. In this example, the sample No. Although the maximum value ΔFmax of the unit stress difference ΔF of 16 is the minimum 0.039, the maximum value ΔFmax of the unit stress difference ΔF may be smaller than 0.039, and the maximum value ΔFmax of the unit stress difference ΔF is As the value approaches 0, the quality of the printed image by reverse transfer is less likely to occur.

  A non-uniformity in the reverse transfer amount occurs due to a slight change in hardness on the surface of the primary transfer roller, resulting in density unevenness and a density step, but the hardness change on the surface of the primary transfer roller is controlled to a predetermined amount or less, that is, the primary transfer roller By setting the maximum value ΔFmax of the unit stress difference ΔF, which is the difference between the maximum value and the minimum value of the stress in the unit length of the surface, to 0.105 or less, it is possible to suppress poor print image quality due to reverse transfer. It was.

As described above, in this embodiment, by setting the maximum value ΔFmax of the unit stress difference ΔF of the primary transfer roller to 0.105 or less, unevenness in the amount of toner to be reversely transferred is suppressed, and print quality is improved. The effect that it can be obtained.
In this embodiment, the image forming apparatus is described as a printer. However, the image forming apparatus is not limited thereto, and may be a copier, a facsimile machine, or a multifunction peripheral (MFP).

DESCRIPTION OF SYMBOLS 1 Primary transfer roller 1a Elastic layer 1b Conductive support 2 Intermediate transfer belt 3 Photosensitive drum 4 Charging roller 5 Exposure device 6 Developing device 7, 14 Cleaning blade 8 Image forming unit 10 Secondary transfer roller 11 Secondary transfer counter roller

Claims (5)

An image forming unit for forming a developer image;
A transfer member carrying a developer image formed by the image forming unit;
A transfer member that is disposed opposite to the image forming unit with the transfer member interposed therebetween, and transfers the developer image from the image forming unit to the transfer member;
Have
An image forming apparatus, wherein a maximum value of a difference between a maximum value and a minimum value of a unit length of a surface of the transfer member is 0.105 or less. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the transfer member has an elastic layer having a foam on a surface thereof. The image forming apparatus according to claim 2,
The image forming apparatus, wherein the transfer member further includes a resin layer on a surface of the elastic layer. The image forming apparatus according to any one of claims 1 to 3,
The image forming apparatus, wherein the transfer member is a roller. The image forming apparatus according to claim 4,
The image forming apparatus, wherein the difference in stress is a difference between a maximum value and a minimum value of stress in a unit length in a circumferential direction of the surface of the roller.

Images