Transfer unit and image forming apparatus

Abstract

To prevent, during use of an image forming apparatus, the occurrence of a printing failure which occurs when a developer attached to a surface of a driving roller reduces the frictional force between the driving roller and a transfer belt and deteriorates conveyability.SOLUTION: A transfer unit (30, 30a) transfers a developer image formed with a developer (T), and comprises a belt (33) and a rotating body (31) that stretches the belt (33). The rotating body (31) has a shaft body (311), and a surface layer (312) provided on the outside in a radial direction of the shaft body (311). The surface roughness (Rz) of an outer peripheral surface of the surface layer (312) is larger than the volume average particle diameter (MV) of the developer (T).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This disclosure relates to a transfer unit and an image forming apparatus. [Background technology]

[0002] There is a proposed image forming apparatus that includes a transfer belt for transferring a developer image formed on an image carrier and a roller for tensioning the transfer belt, and reduces damage to the back surface (i.e., the inner surface) of the transfer belt by making the surface roughness of the outer surface of the roller 2 μm or less (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2005-43593 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, if developer adheres to the outer surface of the drive roller that tensions and drives the transfer belt, slippage is more likely to occur between the outer surface of the drive roller and the inner surface of the transfer belt, and if slippage occurs, printing defects will occur.

[0005] This disclosure aims to reduce the occurrence of printing defects caused by slippage of the transfer belt against the drive roller. [Means for solving the problem]

[0006] The transfer unit of this disclosure is a unit for transferring a developer image formed by a developer, and comprises a belt and a rotating body that tensions the belt, wherein the rotating body comprises a shaft and is provided radially outward from the shaft. , formed from resin material It has a surface layer, before Volume-average particle size of the developer The ratio of the surface roughness Rz of the outer surface of the surface layer to the storage modulus E' of the resin material at a temperature of 10°C is 2.2 times or more and 3.2 times or less. 10 The storage modulus of the resin material at a temperature of 70°C is expressed as E'.70 When expressed as, 44.7≦(E´ 70 / E´ 10 It is characterized by satisfying the condition ) × 100[%] ≤ 77.9 . [Effects of the Invention]

[0007] According to the transfer unit and image forming apparatus of this disclosure, it is possible to reduce the occurrence of printing defects caused by slippage of the transfer belt against the drive roller. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view showing the configuration of the transfer unit and image forming apparatus according to the embodiment. [Figure 2] This is a schematic cross-sectional view showing the configuration of a transfer unit and an image forming apparatus according to a modified embodiment. [Figure 3] (A), (B), and (C) are schematic perspective views, schematic cross-sectional views, and enlarged cross-sectional views of the main part of the drive roller of the transfer unit according to the embodiment. [Figure 4] (A) and (B) are schematic diagrams showing the state of the drive roller and transfer belt of the transfer unit of the comparative example. [Figure 5] (A) and (B) are schematic diagrams showing the state of the drive roller and transfer belt of the transfer unit according to the embodiment. [Figure 6] (A) shows the surface roughness of the surface layer of the drive rollers of Comparative Example C1, Comparative Example C2, Example 1 of the Embodiment, and Example 2 of the Embodiment, and (B) shows the evaluation results thereof. [Figure 7] This is a schematic diagram showing a dynamic viscoelasticity measuring device. [Figure 8] This figure shows the measurement results of the temperature characteristics of the loss tangent tangent tanδ of the resin material (paint) of the surface layers of Comparative Example C1, Example 1, and Example 2. [Figure 9] This figure shows the measurement results of the temperature characteristics of the storage modulus E' of the resin material (paint) of the surface layers of Comparative Example C1, Example 1, and Example 2. [Figure 10](A) is a schematic cross-sectional view of the surface layer of a driving roller, and (B) shows the state of the outer peripheral surface of the surface layer. [Figure 11] (A) is a schematic cross-sectional view of the surface layer of the driving roller after heat and excessive pressure are applied, and (B) shows the state of the outer peripheral surface of the surface layer at that time. [Figure 12] It is a diagram showing measurement results of temperature characteristics obtained by differential scanning calorimetry (DSC) of each surface layer of Comparative Example C1, Example 1, and Example 2. MODE FOR CARRYING OUT THE INVENTION

[0009] Hereinafter, a transfer unit and an image forming apparatus according to embodiments will be described with reference to the drawings. The following embodiments are merely illustrative, and combinations of embodiments and modifications to respective embodiments may be made as appropriate.

[0010] <1> Image forming apparatus 1 FIG. 1 is a schematic cross-sectional view showing the configurations of a transfer unit 30 and an image forming apparatus 1 according to an embodiment. The image forming apparatus 1 is a color printer capable of printing a color image through an electrophotographic process using developers of four colors, that is, toner, of black (K), cyan (C), magenta (M), and yellow (Y).

[0011] As shown in Figure 1, the image forming apparatus 1 includes image forming units 10K, 10C, 10M, and 10Y (also referred to as "image forming unit 10") which form a developer image (i.e., a toner image) on a photoreceptor drum 13K, 13C, 13M, and 13Y (also referred to as "photoreceptor drum 13") which serve as an image carrier, and a transfer unit (also referred to as "primary transfer unit") 30 which transfers the developer image formed on the photoreceptor drum 13K, 13C, 13M, and 13Y onto a transfer belt (also referred to as "intermediate transfer belt") 33 (also referred to as "primary transfer"). Furthermore, the image forming apparatus 1 includes a secondary transfer roller 37 that transfers the developer image supported on the transfer belt 33 onto a recording medium P such as paper at a secondary transfer position (also called "secondary transfer"), a media supply unit (also called "media transport unit") 20 that supplies and transports the recording medium P, a fuser 40, and a discharge roller 25 that serves as a media discharge unit for discharging the recording medium P that has passed through the fuser 40 to the outside. The image forming unit is also called an "image drum (ID) unit" or a "drum unit". The number of image forming units in the image forming apparatus 1 may be 3 or less, or 5 or more. Also, the image forming apparatus 1 may be a monochrome printer using an electrophotographic process.

[0012] As shown in Figure 1, the media supply unit 20 includes a media cassette 21, a hopping roller 22 that feeds out recording media P one by one from the media cassette 21, a register roller 23 that transports the recording media P fed out from the media cassette 21, and a pair of rollers 24 that transport the recording media P.

[0013] The image forming units 10K, 10C, 10M, and 10Y are arranged in a single row in the direction of travel (i.e., the direction of movement) on the upper part of the transfer belt 33. The image forming units 10K, 10C, 10M, and 10Y are detachably attached to the main body structure of the image forming apparatus 1. The image forming units 10K, 10C, 10M, and 10Y have the same structure as each other, except that they have different toner colors. However, the image forming units 10K, 10C, 10M, and 10Y may include image forming units with different structures.

[0014] Above the image forming units 10K, 10C, 10M, and 10Y, there are optical print heads 11K, 11C, 11M, and 11Y (also referred to as "optical print head 11"), which serve as exposure units for each color. Each of the optical print heads 11K, 11C, 11M, and 11Y includes an array of light-emitting elements arranged in the axial direction of the photoreceptor drums 13K, 13C, 13M, and 13Y. The light-emitting elements are, for example, LEDs (Light Emitting Diodes) or light-emitting thyristors. Exposure by each of the optical print heads 11K, 11C, 11M, and 11Y is performed on the uniformly charged surface of the photoreceptor drums 13K, 13C, 13M, and 13Y based on image data for printing. The exposure unit may also be composed of a laser optical system.

[0015] Each of the image forming units 10K, 10C, 10M, and 10Y includes a rotatably supported photoreceptor drum 13K, 13C, 13M, and 13Y, charging rollers 14K, 14C, 14M, and 14Y (also referred to as "charging roller 14") which serve as charging members to uniformly charge the surface of the photoreceptor drums 13K, 13C, 13M, and 13Y, and a developing device 15K, 15C, 15M, and 15Y (also referred to as "developing device 15") which, after forming an electrostatic latent image on the surface of the photoreceptor drums 13K, 13C, 13M, and 13Y by exposure with an optical print head 11K, 11C, 11M, and 11Y, supplies toner to the surface of the photoreceptor drums 13K, 13C, 13M, and 13Y to form a developer image corresponding to the electrostatic latent image. The photosensitive drums 13K, 13C, 13M, and 13Y are composed of, for example, a conductive support processed into a cylindrical shape and a photosensitive layer coated on its surface. The photosensitive layer has a structure in which a blocking layer, a charge generation layer, and a charge transport layer are stacked in that order from the surface of the conductive support.

[0016] The developing devices 15K, 15C, 15M, and 15Y each include a developer storage section which is a container for storing developer, developing rollers 16K, 16C, 16M, and 16Y (also referred to as "developing roller 16") which serve as developer carriers for supplying developer to the surface of the photosensitive drums 13K, 13C, 13M, and 13Y, supply rollers 17K, 17C, 17M, and 17Y (also referred to as "supply roller 17") which serve as developer suppliers for supplying developer stored in the developer storage section to the developing rollers 16K, 16C, 16M, and 16Y, and layer-forming blades 18K, 18C, 18M, and 18Y (also referred to as "layer-forming blade 18") which serve as developer regulating members for regulating the thickness of the developer layer on the surface of the developing rollers 16K, 16C, 16M, and 16Y. The developing rollers 16K, 16C, 16M, and 16Y are composed of, for example, a metal shaft and an elastic body provided on its outer circumference. For this elastic body, for example, a semiconductive urethane rubber with a rubber hardness of 70° (Asker C) can be used. The supply rollers 17K, 17C, 17M, and 17Y are composed of a metal shaft and a foam provided on its outer circumference. For this foam, a silicone foam with a hardness of 50° (Asker F) can be used.

[0017] Black, yellow, magenta, and cyan developers primarily consist of polyester resin, colorants, antistatic agents, and release agents, with the addition of an external additive (hydrophobic silica). The developer is a powder obtained, for example, by a grinding method. However, the developer may also be a powder produced by other methods such as polymerization. The volume-average particle size of the developer is 7 μm (i.e., approximately 7 μm).

[0018] As shown in Figure 1, the transfer unit 30 includes an endless transfer belt 33 for transferring a developer image to a recording medium P, a drive roller 31 and a driven roller 32 which are rotating bodies that tension the transfer belt 33, a backup roller 36 for secondary transfer, and transfer rollers 35K, 35C, 35M, and 35Y. The drive roller 31 rotates by a driving force from a drive mechanism such as a motor, causing the transfer belt 33 to move. The driven roller 32 rotates in conjunction with the movement of the transfer belt 33. The drive roller 31 has a shaft (shown in Figure 3 below) and a surface layer formed on the surface of the shaft (shown in Figure 3 below). The surface layer is also called the coating layer.

[0019] The transfer rollers 35K, 35C, 35M, and 35Y are positioned opposite the photoreceptor drums 13K, 13C, 13M, and 13Y, with the transfer belt 33 in between. The developer images formed on the surfaces of the photoreceptor drums 13K, 13C, 13M, and 13Y are sequentially transferred onto the transfer belt 33 by the transfer rollers 35K, 35C, 35M, and 35Y, forming a color image in which multiple developer images are superimposed. After transfer, any developer remaining on the photoreceptor drums 13K, 13C, 13M, and 13Y is removed by a cleaning member.

[0020] Examples of resin materials constituting the transfer belt 33 include polyimide (PI), polyvinylidene fluoride (PVDF), and polyamideimide (PAI). The transfer belt 33 is manufactured using a rotational molding method or an inflation method, and the inner surface roughness of the transfer belt 33 is, for example, 0.05 μm or less. The transfer belt 33 is suspended between the drive roller 31 and the driven roller 32. The transfer belt 33 is also provided with a spring mechanism 34 that applies force in the direction of arrow F (i.e., the direction that presses the drive roller 31 toward the transfer belt 33) to both ends (e.g., bearing portions) that rotatably support the drive roller 31. The spring mechanism 34 allows the transfer belt 33 to maintain a state of tension under a constant load.

[0021] The transfer belt 33 is further configured to pass through a secondary transfer section located below the transfer unit 30. The secondary transfer section consists of a secondary transfer roller 37 and a backup roller 36, with the backup roller 36 suspending the transfer belt 33. The secondary transfer roller 37 forms a transfer electric field for transferring the developer image on the transfer belt 33 to the recording medium P. A pre-contact roller may also be provided in front of the secondary transfer roller 37 to pre-contact the medium. The driven roller 32 and the backup roller 36 rotate together with the transfer belt 33, which is driven by the drive roller 31.

[0022] Downstream of the secondary transfer roller 37, a fuser 40 is positioned to fix the developer image on the recording medium P to the recording medium P by heating and pressurizing. The fuser 40 has a pair of rollers 41 and 42 that press against each other. Roller 41 is a heat roller with a built-in heating element, and roller 42 is a pressure roller that is pressed against roller 41. The recording medium P, which has an unfixed developer image, passes between the pair of rollers 41 and 42 of the fuser 40. At this time, the unfixed developer image is heated and pressurized to fix it onto the recording medium P.

[0023] Downstream of the fuser 40, there is an discharge passage and a discharge roller 25 for discharging the recording medium P to the outside, and the discharged recording medium P is discharged to the stacker on the housing.

[0024] 《2》Image forming device 1a Figure 2 is a schematic cross-sectional view showing the configuration of a transfer unit 30a and an image forming apparatus 1a according to a modified embodiment. In Figure 2, components that are the same as or corresponding to the components shown in Figure 1 are denoted by the same reference numerals as those shown in Figure 1. The image forming apparatus 1a in Figure 2 differs from the image forming apparatus 1 in Figure 1, which has a transfer unit 30 that transfers the developer image, which has been primary transferred onto a transfer belt (transport belt) 33, onto the recording medium P, in that the transfer unit 30a transports the recording medium P and transfers the developer image onto the recording medium P (it does not have a secondary transfer unit). Except for this point, the image forming apparatus 1a shown in Figure 2 is the same as the image forming apparatus in Figure 1.

[0025] (3) Drive roller 31 Figures 3(A), (B), and (C) are schematic perspective views, schematic cross-sectional views, and enlarged cross-sectional views of the main part of the drive roller 31 of the transfer unit 30 (or 30a) according to the embodiment. Figure 3(C) is an enlarged view of part 313 of Figure 3(B). As shown in Figures 3(A), (B), and (C), the drive roller 31 has a shaft body 311 and a surface layer 312 provided radially outward of the shaft body 311 (for example, formed on the surface of the shaft body 311). In this embodiment, the surface layer 312 is formed such that the surface roughness Rz of the outer circumferential surface of the surface layer 312 is greater than the volume average particle size of the developer used in the image forming apparatus 1 (or 1a).

[0026] The shaft body 311 is composed of, for example, a three-pronged extruded tube 311a and a shaft 311b. The surface layer 312 formed on the outer circumferential surface of the shaft body 311 is a paint layer formed by applying a resin material (paint). The surface layer 312 provided on the outer circumferential surface of the shaft body 311 is provided to increase the frictional force between the inner surface of the transfer belt 33 and the outer circumferential surface of the drive roller 31. The three-pronged extruded tube 311a is made of aluminum. The shaft 311b is made of free-cutting steel, and its surface is electroless nickel-treated. The resin material (paint) constituting the surface layer 312 is composed of a resin solution, a coloring pigment, an extender pigment, an additive (curing catalyst), and a diluent. The thickness of the surface layer 312 is approximately 100 μm. In this embodiment, a urethane-based resin material is used as the resin material constituting the surface layer 312. The resin material constituting the surface layer 312 contains, for example, urethane resin as its main component. The main component refers to the component that accounts for 50% or more by weight of the entire surface layer 312. Furthermore, known measurement methods for identifying the urethane resin in the surface layer 312 include, for example, gas chromatography-mass spectrometry and Fourier transform infrared spectroscopy (FTIR). Examples of curing catalysts for urethane-based resin materials (paints) include toluene isocyanate (TDI)-based curing agents or hexamethylene diisocyanate (HDI)-based curing agents. It is also possible to use acrylic resin, silicone resin, or epoxy resin as the resin material constituting the surface layer 312.

[0027] In the manufacturing of the shaft body 311 of the drive roller 31, both ends of the three-pronged extruded tube 311a are processed so that the shaft 311b can be press-fitted, and the surface of the shaft body 311 is surface-machined to fit the dimensions in the drawing. Then, the shaft 311b is press-fitted into both ends of the three-pronged extruded tube 311a. The resin material constituting the surface layer 312 is uniformly applied to the surface of the three-pronged extruded tube 311a at a constant speed using a spray or the like. Then, firing is performed in an electric furnace to complete the drive roller 31. In this embodiment, comparative examples (Comparative Examples C1 and C2) and examples (Examples 1 and 2) were used. The surface roughness of the surface layer 312 of Comparative Example C1 was the smallest (Rz = approximately 6 μm), and the surface roughness of the surface layer 312 of Comparative Example C2 was the largest (Rz = 55.4 μm). Examples 1 and 2 differ in the content of the curing catalyst; Example 1 has 0% curing catalyst, and Example 2 has approximately 2% curing catalyst. The surface roughness Rz of the surface layer 312 in Example 1 is 22.2 μm, and the surface roughness Rz of the surface layer 312 in Example 2 is 15.6 μm. The surface roughness Rz was calculated from an area of ​​approximately 1 mm × 1 mm on the surface of the drive roller 31 using a laser microscope.

[0028] The function required of the drive roller 31 is to drive the transfer belt 33. In addition to the drive roller 31, the other rollers in contact with the transfer belt 33 within the transfer unit 30 are the transfer roller 35, the driven roller 32, and the backup roller 36. The transfer belt 33 is rotated by the roller with the highest frictional force against the transfer belt 33 among the rollers in contact with it. Therefore, the drive roller 31 is configured to have the greatest frictional force among the rollers in contact with the transfer belt 33. In this embodiment, the driving force required for the drive roller 31 to drive the transfer belt 33 is 6.66 N or more, so the frictional force between the outer surface of the drive roller 31 and the inner surface of the transfer belt 33 must be 6.66 N or more. Furthermore, it is necessary to have a stable driving force even when the image forming apparatus 1 is stored or during use (when developer is interposed between the outer surface of the drive roller 31 and the inner surface of the transfer belt 33 due to use). For this reason, in this embodiment, the frictional characteristics and surface roughness Rz of the material of the surface layer 312 of the drive roller 31 are defined. Furthermore, to prevent the drive roller 31 from sticking to the transfer belt 33, the surface roughness Rz of the outer surface of the drive roller 31 is limited. Also, to suppress deformation of the transfer belt 33 due to irregularities on the outer surface of the drive roller 31, the surface roughness Rz of the outer surface of the drive roller 31 is limited. In addition, to prevent changes in the state of the resin material (paint) of the surface layer 312 within the operating and transport temperature range (e.g., 10°C to 70°C), the thermal properties of the resin material are specified.

[0029] For measuring the volume-average particle size, a Multisizer3 precision particle size distribution analyzer (manufactured by Beckman Coulter, Inc.) was used to measure the median diameter of the developer by volume. The measurement conditions were as follows: • Aperture diameter: 100 μm • Electrolyte: Isoton II (manufactured by Beckman Coulter, Inc.) • Dispersion: Neogen S-20F (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) dissolved in the aforementioned electrolyte solution and adjusted to a concentration of 5%.

[0030] For this measurement, 10 mg to 20 mg of the sample to be measured was added to 5 mL of the aforementioned dispersion and dispersed in an ultrasonic disperser for 1 minute. Then, 25 mL of electrolyte was added and dispersed in an ultrasonic disperser for 5 minutes, and aggregates were removed by passing the mixture through a 75 μm mesh to prepare the sample dispersion.

[0031] Furthermore, for this measurement, the sample dispersion was added to 100 mL of the aforementioned electrolyte solution, and 30,000 particles were measured using the aforementioned precision particle size distribution analyzer to determine the distribution (i.e., volume particle size distribution). Subsequently, in this measurement, the volume median diameter was determined as the volume average particle size (MV) based on this volume particle size distribution. The volume average particle size refers to the particle size at which the mass of particles larger than a certain diameter accounts for 50% of the total mass of the powder in the particle size distribution. The aforementioned precision particle size distribution analyzer measures particle size distribution using the Coulter principle. This Coulter principle, also known as the pore electrical resistance method, is a method of measuring particle volume by passing a constant current through pores (apertures) in an electrolyte solution and measuring the change in the electrical resistance of the pores as particles pass through them.

[0032] Figures 4(A) and (B) are schematic diagrams showing the state of the surface layer 312 and transfer belt 33 of the drive roller of the transfer unit in Comparative Examples C1 and C2. As shown in Figure 4(A), in Comparative Example C1 (where the surface roughness Rz is smaller than the volume-average particle size MV), when developer T adheres between the outer surface of the surface layer 312 (the upward-facing surface in the figure) and the inner surface of the transfer belt 33 (the downward-facing surface in the figure), the frictional force decreases, causing slippage between the surface layer 312 and the transfer belt 33, which easily leads to printing defects (such as image shrinkage). Also, as shown in Figure 4(B), in Comparative Example C2 (where the surface roughness Rz is too large), the irregularities of the surface layer 312 are transferred to the transfer belt 33, causing an irregular shape to appear on the outer surface of the transfer belt 33 (the upward-facing surface in the figure), resulting in printing defects due to deformation of the transfer belt 33.

[0033] Figures 5(A) and (B) are schematic diagrams showing the state of the drive roller 31 and transfer belt 33 of the transfer unit 30 in Example 1 or Example 2 according to the embodiment. As shown in Figure 5(A), in Example 1 or Example 2 (when the surface roughness Rz is greater than the volume average particle size MV), when the developer T is attached between the outer circumferential surface of the surface layer 312 (the upward-facing surface in the figure) and the inner surface of the transfer belt 33 (the downward-facing surface in the figure), there is almost no change in the shape of the outer circumferential surface of the surface layer 312, and the frictional force does not decrease. In addition, in Example 1 or Example 2 (when the surface roughness Rz is within an appropriate range greater than the volume average particle size MV), the surface layer 312 deforms as shown in Figure 4(B) when the drive roller rotates, but the convexity of the surface layer 312 makes broad contact with the transfer belt 33, maintaining a high frictional force. For this reason, no printing defects occur in Example 1 or Example 2 (when the surface roughness Rz is greater than the volume average particle size MV).

[0034] Figure 6(A) shows the surface roughness Rz [μm] of the surface layers of the drive rollers for Comparative Example C1, Comparative Example C2, Example 1, and Example 2, and Figure 6(B) shows the evaluation results thereof. The surface roughness Rz varies depending on the resin material of the coating applied, and if the surface roughness Rz is too large, the irregularities on the surface of the drive roller 31 are transferred to the transfer belt 33, resulting in printing defects.

[0035] As shown in Comparative Example C1 in Figures 6(A) and (B), if the surface roughness Rz is too small, the frictional force between the transfer belt 33 and the surface layer 312 of the drive roller 31 decreases when developer adheres to the surface of the drive roller 31 (indicated by the symbol "×" in Figure 6(B)). In this case, printing defects occur in the image forming apparatus 1 of Figure 1. Also, printing defects occur in the image forming apparatus 1a of Figure 2 due to a decrease in the transportability of the recording medium P. Furthermore, as shown in Comparative Example C2 in Figures 6(A) and (B), if the surface roughness Rz is too large, the irregularities of the surface layer 312 of the drive roller 31 appear on the upper surface of the transfer belt 33, causing the transfer belt 33 to deform (indicated by the symbol "×" in Figure 6(B)). In this case, printing defects occur in the image forming apparatus 1 of Figure 1 due to deformation of the transfer belt 33. Also, printing defects occur in the image forming apparatus 1a of Figure 2 due to a decrease in the transportability of the recording medium P.

[0036] As shown in Figures 6(A) and (B) as Examples 1 and 2, if the surface roughness Rz is within the appropriate range, when developer adheres to the surface of the drive roller 31, the frictional force between the transfer belt 33 and the surface layer 312 of the drive roller 31 does not decrease (indicated by the symbol "〇" in Figure 6(B)), and no deformation of the transfer belt 33 occurs (indicated by the symbol "〇" in Figure 6(B)). In this case, no printing defects occur in the image forming apparatus 1 or 1a. As shown in Figures 6(A) and (B), the appropriate range for the surface roughness Rz is, for example, as follows. 15.6 ≤ Rz[μm] ≤ 22.2

[0037] The ratio of the surface roughness Rz of the outer surface of the surface layer 312 to the volume-average particle size MV of the developer is preferably 2.2 (≒15.6 μm / 7 μm) or higher. Furthermore, the ratio of the surface roughness Rz of the outer surface of the surface layer 312 to the volume-average particle size MV of the developer is preferably 3.2 (≒22.2 μm / 7 μm) or lower.

[0038] (4) Thermal characteristics of the surface layer 312 of the drive roller 31 《4-1》Measuring device for thermal properties Figure 7 is a schematic diagram showing a dynamic viscoelasticity measuring device 70 used to measure the thermal properties of the surface layer 312. The dynamic viscoelasticity measuring device 70 applies sinusoidal stress generated by a force generator 71 to the sample via a probe 73, and detects the strain of the sample caused by this stress using a strain detector 72. The vibration ratio of stress to strain at this time is proportional to the elastic modulus of the sample, and the complex elastic modulus E * This can be obtained. In the case of viscoelastic materials such as polymer materials, when stress is given in the form of a sinusoidal wave, strain is detected in the form of a sinusoidal wave with a phase difference, and the viscosity can be obtained from the phase lag between stress and strain. The heating furnace 75 is heated and controlled using the temperature signal of a thermocouple 74 that observes the temperature of the sample. The operation of the dynamic viscoelasticity measuring device 70 is controlled by the control device 76.

[0039] The measurement of the thermal characteristics of the surface layer 312 as a sample is performed for each of a plurality of temperatures and each of a plurality of frequencies. The measurement conditions in the present embodiment are shown below. ·Temperature condition: The temperature was changed at a rate of 1°C / min within the range of -70°C to 150°C. ·Frequency: Seven frequencies of force vibration, namely 0.05 Hz, 0.1 Hz, 0.5 Hz, 1 Hz, 5 Hz, 10 Hz, and 20 Hz, were used. ·Sample: A resin material having dimensions of approximately 20 mm length × 9 mm width × 0.6 mm thickness was used.

[0040] Here, the complex elastic modulus E * will be described with respect to its components, storage elastic modulus E' and loss elastic modulus E'', as well as loss tangent tanδ obtained from storage elastic modulus E' and loss elastic modulus E''. Storage elastic modulus E' reflects the characteristics of the elastic (spring) component of a sample, and is a measure of the energy that is stored from the force (energy) applied per one cycle and can be completely recovered. Loss elastic modulus E'' reflects the characteristics of the viscous (dashpot) component of a sample, and is a measure of the energy that is lost as heat among the force (energy) applied per one cycle. Complex elastic modulus E * and the relationship between storage elastic modulus E' and loss elastic modulus E'' is expressed by the following formulas (1) to (3). E * =E'+E'' (1) E'=E * cosθ (2) E''=E * sinθ (3)

[0041] Loss tangent tanδ is the ratio of loss elastic modulus E'' to storage elastic modulus E'. That is, tanδ indicates the ratio of energy lost as heat to the energy applied from the outside, and represents vibration absorption characteristics as one of the viscoelastic properties. Loss tangent tanδ is expressed by the following formula (4). tanδ=E'' / E' (4)

[0042] <<4-2>> Loss tangent tanδ and storage elastic modulus E' of surface layer 312 Figure 8 shows the measurement results of the temperature characteristics of the loss tangent tanδ of the resin material (paint) of the surface layer 312 for Comparative Example C1, Example 1, and Example 2. In Figure 8, the horizontal axis represents the sample temperature [°C], and the vertical axis represents the loss tangent tanδ. As the loss tangent tanδ approaches 1, the viscous properties of the resin material of the surface layer 312 become stronger, and as it approaches 0, the elastic properties of the resin material of the surface layer 312 become stronger.

[0043] As shown in Figure 8, the peak position of the loss tangent tanδ graph indicates the glass transition temperature Tg of the resin materials for Comparative Example C1, Example 1, and Example 2. When the temperature of the resin material exceeds the glass transition temperature Tg, the molecules become more mobile, resulting in a soft, rubbery state. When the temperature falls below the glass transition temperature Tg, the molecular motion is restricted, resulting in a hard, glassy state. The glassy state refers to a hard state, and the temperature at which the glassy state is reached is called the glass transition temperature (i.e., the glass transition point). In other words, this indicates that a structural change in the resin material occurs at the glass transition temperature Tg. When the usage and transport temperature range is set to a sample temperature of 10°C to 70°C, if the loss tangent tanδ is 0.2 or higher, a structural change in the resin material occurs within the usage and transport temperature range (actual usage temperature range), approaching a viscous state. Therefore, as a material for the surface layer 312, the resin material of Example 2 that satisfies the following equation (5) is desirable as a material that does not undergo a structural change due to glass transition, when the usage and transport temperature range is set to a sample temperature of 10°C to 70°C. tanδ<0.2 (5)

[0044] Figure 9 shows the measurement results of the temperature characteristics of the storage modulus E' of the resin material (paint) of the surface layers 312 of Comparative Example C1, Example 1, and Example 2. In Figure 9, the horizontal axis represents the sample temperature [°C], and the vertical axis represents the storage modulus E'.

[0045] When the decrease rate of the storage modulus E' is 95.7%, a structural change occurs in the resin material during the use and transport temperature range (actual use temperature range), causing it to approach a viscous state. Since the transfer belt 33 is stretched within the transfer unit 30, the outer surface of the surface layer 312 of the drive roller 31 and the inner surface of the transfer belt 33 are in contact with a constant pressure. As the resin material of the surface layer 312 undergoes a structural change due to temperature and approaches a viscous state, the pressure from the tension of the transfer belt 33 can cause the resin material to partially deform, potentially causing the transfer belt 33 to stick to the drive roller 31. As a result, the frictional force of the part of the outer surface of the surface layer 312 of the drive roller 31 where the transfer belt 33 is attached differs from that of the part where the transfer belt 33 is not in contact, making it impossible to drive the transfer belt 33 at the desired transport speed. As can be seen from Figure 9, when the use and transport temperature range is set to a sample temperature range of 10°C to 70°C, it is desirable that the decrease rate of the storage modulus E' satisfies the following equation (6). 44.7≦E´reduction rate [%]≦77.9 (6)

[0046] Furthermore, as can be seen from Figure 9, when the usage and transport temperature range is set to a sample temperature of 10°C to 70°C, it is desirable that the storage modulus E' satisfies the following equation (7). 8.3E+06≦E´[Pa]≦1.95E+08 (7) Here, 8.3E+06 = 8.3 × 10 6 Therefore, 1.95E+08 = 1.95 × 10 8 That is the case.

[0047] In summary, as shown in Figures 4(A) and (B), both Example 1 and Example 2 have a surface roughness Rz that makes slippage less likely due to the developer on the outer surface of the surface layer 312. However, when the usage and transport temperature range is within the sample temperature range of 10°C to 70°C, the resin material of Example 2, which satisfies all of equations (5) to (7), is more desirable from the viewpoint of the thermal properties of the surface layer 312.

[0048] 《4-3》Condition of the outer surface of the surface layer 312 Figure 10(A) shows a schematic cross-section of the surface layer 312 of the drive roller 31, and Figure 10(B) shows the state of the outer surface of the surface layer 312. In Figure 10(B), the brighter the area, the higher the area (i.e., the convex portion). The average length Sm [μm] of the contour curve elements, which indicates the distance between convex portions of the surface layer 312, is 49.2 μm for the surface layer of Comparative Example C1, 54.7 μm for the surface layer of Comparative Example C2, 61.0 μm for the surface layer of Example 1, and 80.7 μm for the surface layer of Example 2. Here, the average length Sm [μm] of the contour curve elements is calculated using the following equation (8).

[0049]

number

[0050] Here, X si This is the length corresponding to one contour line element shown as the surface layer 312 in Figure 10(A). From this measurement result, it is desirable that the average length Sm [μm] of the contour curve elements of the surface layer 312 of the drive roller 31 satisfies the following equation (9). 61.0 ≤ Sm [μm] ≤ 80.7 (9)

[0051] Figure 11(A) shows a schematic cross-section of the surface layer 312 of the drive roller 31 after it has been stored at a constant high temperature and pressure using a resin material (paint) that is highly susceptible to temperature changes, and Figure 11(B) shows the state of the outer surface of the surface layer 312 at that time. Specifically, Figure 11(A) shows a schematic cross-section of the surface layer 312 of the drive roller 31 after it has been stored at a constant high temperature and pressure using a resin material (paint) that is highly susceptible to temperature changes. In Figure 11(B), the brighter the area, the higher the area (i.e., the convex part). As shown in Figure 11(A), if the viscosity of the resin material of the surface layer 312 is high, the top of the surface layer 312 of the drive roller 31 may deform after heat and excessive pressure are applied. Specifically, when a resin paint that is highly susceptible to temperature changes is used for the surface layer 312, and a test is conducted to reproduce the conditions in which the transfer belt is stretched at a constant pressure and stored at a high temperature during transport, the top of the surface layer 312 of the drive roller 31 that was in contact with the transfer belt becomes flat. In that case, the contact area between the transfer belt and the drive roller becomes larger than before the test, and the frictional force increases. As a result, the transport performance differs only in the part of the drive roller that was in contact with the transfer belt, so the proportion of the bright area in Figure 11(B) increases.

[0052] 《4-4》Measurement of Differential Scanning Calorimetry (DSC) Figure 12 shows the measurement results of the temperature characteristics of differential scanning calorimetry (DSC) [μW] for Comparative Example C1, Example 1, and Example 2. Another method for investigating the thermal properties of the resin material of the surface layer 312 of the drive roller 31 is to measure differential scanning calorimetry (DSC). In this embodiment, a differential scanning calorimeter (DSC6220, manufactured by Hitachi High-Technologies Corporation) was used to measure the DSC of the resin material (5 mg sample) of the surface layer 312 of Comparative Example C1, Example 1, and Example 2. DSC allows for the examination of reaction or thermal history, as well as the measurement of specific heat capacity, including transitions such as melting, glass transition, and crystallization. In this embodiment, the thermal flow difference of each resin material relative to a reference sample was detected using DSC. The measurement conditions for DSC in this embodiment are described in Table 1 below. Table 1 shows the measurement conditions specified in ISO. In Table 1, Cel represents Celsius temperature, min represents minutes, s represents seconds, On represents gas usage, ml represents milliliters, 1st Run represents the first data acquisition period, and 2nd Run represents the next data acquisition period.

[0053] [Table 1]

[0054] In Figure 12, the portion where the slope of the baseline behavior changes indicates the glass transition temperature Tg. If the glass transition temperature Tg exists within the sample temperature range of 10°C to 70°C, a structural change occurs in the resin material, causing partial deformation of the resin material, as shown in Figures 11(A) and (B), and the transfer belt 33 to stick to the surface layer 312 of the drive roller 31. Therefore, it is preferable that the resin material of the surface layer 312 is such that the slope of the baseline behavior of DSC 2nd Run does not change within the sample temperature range of 10°C to 70°C, and that there is no glass transition point within the 10°C to 70°C range, i.e., that no state change occurs in the resin material. In other words, it is desirable that the glass transition temperature [°C] exists outside the 10°C to 70°C range, or that it does not exist at all.

[0055] 《5》Effect As described above, by defining the surface roughness Rz of the outer surface of the surface layer 312 of the drive roller 31 and the thermal properties of the resin material of the surface layer 312, it is possible to suppress the decrease in frictional force between the transfer belt 33 and the drive roller 31 due to the developer that enters the transfer unit 30 (or 30a) during image formation, and the transportability between the transfer belt 33 and the recording medium P does not deteriorate. As a result, the effect of preventing printing defects such as image shrinkage is obtained.

[0056] Furthermore, by satisfying one or more (preferably two or more) of the thermal characteristics conditions of the surface layer 312 of the drive roller 31 described above, which are equations (5), (6), (7), (9), and "there is no glass transition temperature in the range of 10°C to 70°C", the occurrence of printing defects such as image shrinkage can be further suppressed.

[0057] (6) Modified form The transfer units 30, 30a and image forming apparatuses 1, 1a described above are also applicable to image forming apparatuses such as MFPs (multifunction printers), fax machines, and photocopiers. [Explanation of symbols]

[0058] 1, 1a Image forming apparatus, 30, 30a Transfer unit, 31 Drive roller (rotating body), 33 Transfer belt (belt), 34 Spring mechanism, 70 Dynamic elasticity measuring device, 311 Shaft body, 312 Surface layer (coated layer), DSC Differential scanning calorific value, E' Storage modulus, E″ Loss modulus, E * Complex modulus of elasticity, MV volume-average grain size, Rz surface roughness, T developer, tanδ loss tangent.

Claims

1. A transfer unit for transferring a developer image formed by a developer, belt and, A rotating body that tensions the aforementioned belt, Equipped with, The rotating body is The shaft and, A surface layer, which is provided on the radially outer side of the shaft body and is made of a resin material, It has, The ratio of the surface roughness Rz of the outer surface of the surface layer to the volume-average particle size of the developer is 2.2 times or more and 3.2 times or less. The storage modulus of the resin material at a temperature of 10°C is represented by E' 10. When the storage modulus of the aforementioned resin material at a temperature of 70°C is expressed as E' 70, The following conditions must be met: 44.7 ≤ (E' 70 / E' 10) × 100 [%] ≤ 77.9 A transfer unit characterized by the following features.

2. The aforementioned resin material consists of urethane resin accounting for 50% or more of the total weight. The transfer unit according to feature 1.

3. The aforementioned resin material does not have a glass transition temperature within a temperature range of 10°C to 70°C. The transfer unit according to feature 1.

4. The maximum loss tangent value of the aforementioned resin material is 0.2 or less within a temperature range of 10°C to 70°C. A transfer unit according to any one of claims 1 to 3.

5. The aforementioned resin material, when its storage modulus is expressed as E' within a temperature range of 10°C to 70°C, 8.3E+06 ≤ E'[Pa] ≤ 1.95E+08 A transfer unit according to any one of claims 1 to 3.

6. The aforementioned resin material, when its storage modulus is expressed as E' within a temperature range of 10°C to 70°C, 8.3E+06 ≤ E'[Pa] ≤ 1.95E+08 The transfer unit according to feature 4.

7. The average length Sm of the contour curve elements of the surface layer is The condition 61.0 ≤ Sm [μm] ≤ 80.7 is satisfied. A transfer unit according to any one of claims 1 to 3.

8. The surface roughness Rz is The condition 15.6 ≤ Rz [μm] ≤ 22.2 is satisfied. A transfer unit according to any one of claims 1 to 3.

9. An image forming apparatus comprising a transfer unit according to any one of claims 1 to 3.

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