Intermediate transfer member and image forming apparatus

Abstract

To solve the problem in which: an intermediate transfer body containing resin material and conductive filler has difficulty in stabilizing electrical characteristics over a long-term use.SOLUTION: An intermediate transfer body contains thermoplastic resin and carbon black. The value of the structure volume of the carbon black is 50 or more and 250 or less. The content of the carbon black is 15.0-30.0 mass% relative to the intermediate transfer body. When a range of 10 μm in a thickness direction from an inner peripheral surface being the back side of an outer peripheral surface on which a toner image carried is an inner peripheral surface area, the value of an L function indicating the dispersibility of the carbon black in the thermoplastic resin in the inner peripheral surface area is 150 nm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One aspect of the present disclosure relates to an intermediate transfer member used in an image forming apparatus such as a copying machine, a printer, a facsimile machine, etc., which uses an electrophotographic system or an electrostatic recording system. Another aspect of the present disclosure relates to an image forming apparatus. [Background technology]

[0002] Some electrophotographic image forming devices use an intermediate transfer method to transfer a toner image onto a transfer material, in which a toner image formed on a photosensitive member is first transferred onto a belt-like intermediate transfer member, and then the toner image is secondarily transferred onto the transfer material. The member used for the intermediate transfer member should preferably have a volume resistivity in the semiconductive region and also have small variations in volume resistivity depending on the location of the member, in order to electrostatically transfer the toner image on the surface of the photoreceptor accurately onto the transfer material. Therefore, it is required that the volume resistivity be substantially uniform within the surface involved in image formation. The electrical resistance value of the intermediate transfer member should be such that the volume resistivity is 1×10 8 ~1×10 13 Ω cm, surface resistivity 1×10 9 ~1×10 15 The target range of electrical resistance is selected to be optimal for the transfer section configuration of the image forming device in which the intermediate transfer belt is used and the charging characteristics of the toner particles.

[0003] Patent Document 1 discloses a belt obtained by extruding PEEK containing a conductive filler into a tubular film and then cutting it in a direction perpendicular to the axial direction. 8 ~10 17 It is disclosed to be Ω·cm. Patent Document 2 discloses a belt obtained by molding a thermoplastic resin containing carbon black having a pH value of 8 or more and potassium stearate or sodium stearate as a conductive filler into a tubular film. It also discloses that the content of carbon black is 18 to 30 parts by mass per 100 parts by mass of the thermoplastic resin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-254941 [Patent Document 2] JP 2015-87545 A [Non-patent literature]

[0005] [Non-Patent Document 1] Ripley BD, J.Appl.Prob, Vol.13,pp.255 (1976) Summary of the Invention [Problem to be solved by the invention]

[0006] However, intermediate transfer belts that use carbon black to impart conductivity can experience a decrease in electrical resistance over a long period of time when used to form electrophotographic images. Particularly in the primary transfer section, if a gap develops between the inner circumferential surface of the intermediate transfer body and the primary transfer roller, discharge can occur between the conductive filler aggregates in the intermediate transfer body and the primary transfer roller, resulting in a local decrease in the electrical resistance of the intermediate transfer body. Toner cannot be transferred to the areas with reduced electrical resistance, resulting in white spots (blank areas). Furthermore, in the secondary transfer section, if a gap develops between the outer circumferential surface of the intermediate transfer body and the paper, discharge can occur between the conductive filler aggregates in the intermediate transfer body and the paper, reversing the charge polarity of the toner on the intermediate transfer body, preventing transfer to the paper and resulting in white spots. These phenomena are particularly pronounced when the conductive filler is poorly dispersed or in low-humidity environments.

[0007] When the molding temperature and degree of mixing are increased in a cylinder equipped with a screw, such as a kneading extruder, extrusion molding machine, or injection molding machine, which involves melt-kneading to improve the dispersion of the conductive filler, the resin temperature rises due to shear heating. As a result, thermal degradation of the resin material (crosslinking due to thermal decomposition or oxidation) progresses, and the resulting thermal degradation products or aggregates of the thermal degradation products with the conductive filler or impurities make it difficult to achieve excellent mechanical, optical, and electrical properties. As described above, it has been difficult to stabilize the electrical properties of an intermediate transfer member containing a resin material and a conductive filler over a long period of use.

[0008] One aspect of the present disclosure is to provide an intermediate transfer member that can maintain stable electrical properties over a long period of time, and another aspect of the present disclosure is to provide an image forming apparatus that can stably form high-quality electrophotographic images. [Means for solving the problem]

[0009] According to one aspect of the present disclosure, there is provided an endless intermediate transfer member having a base layer, the base layer containing a thermoplastic resin and carbon black dispersed in the thermoplastic resin, the carbon black having a structure volume value of 50 or more and 250 or less, the carbon black content of the base layer being 15.0 to 30.0 mass % relative to the base layer, and in a cross section of the base layer in the thickness direction, when the range from the inner peripheral surface of the base layer to 10 μm in the thickness direction toward the outer peripheral surface is defined as an inner peripheral surface region, the value of the L function indicating the dispersibility of the carbon black in the thermoplastic resin in the inner peripheral surface region is 150 nm or less.

[0010] According to another aspect of the present disclosure, An image forming apparatus comprising: a first image carrier; an intermediate transfer member onto which an unfixed toner image formed on the first image carrier is primarily transferred; and a secondary transfer means for secondarily transferring the toner image primarily transferred onto the intermediate transfer member onto a second image carrier, There is provided an image forming apparatus in which the intermediate transfer member is the intermediate transfer member described above. [Effects of the Invention]

[0011] According to one aspect of the present disclosure, it is possible to obtain an intermediate transfer member capable of stably maintaining excellent electrical properties for a long period of time, and according to another aspect of the present disclosure, it is possible to provide an image forming apparatus capable of stably forming high-quality electrophotographic images for a long period of time. [Brief explanation of the drawings]

[0012] [Figure 1] Schematic diagram of a cross section of an intermediate transfer member according to the present disclosure [Figure 2] Schematic cross-sectional view of an image forming apparatus using an intermediate transfer member according to the present disclosure. [Figure 3] Schematic diagram showing the area of ​​the intermediate transfer body where measurements are taken to evaluate dispersibility DETAILED DESCRIPTION OF THE INVENTION

[0013] The intermediate transfer member and the method for manufacturing the intermediate transfer member according to the present disclosure will be described in more detail below with reference to the drawings. 1. Image forming device First, an embodiment of an image forming apparatus using an intermediate transfer member (intermediate transfer belt) according to the present disclosure will be described. Fig. 2 is a schematic cross-sectional view of image forming apparatus 100 according to this embodiment. Image forming apparatus 100 according to this embodiment is a tandem color laser printer employing an intermediate transfer system, capable of forming full-color images using an electrophotographic system.

[0014] The image forming apparatus 100 has a plurality of image forming sections, namely, first, second, third, and fourth image forming sections Py, Pm, Pc, and Pk. These first, second, third, and fourth image forming sections Py, Pm, Pc, and Pk are arranged in this order along the moving direction of a flat section (image transfer surface) of an intermediate transfer belt 7, which will be described later. Elements having the same or corresponding functions or configurations in the first, second, third, and fourth image forming sections Py, Pm, Pc, and Pk may be generally described by omitting the suffix Y or y, M or m, C or c, or K or k, which indicates that the element is for one of the colors. In this embodiment, the image forming section P is configured to have a photosensitive drum 1, a charging roller 2, an exposure device 3, a developing device 4, and a primary transfer roller 5, which will be described later. do.

[0015] The image forming unit P has a photosensitive drum 1, which is a drum-shaped (cylindrical) photosensitive member (electrophotographic photosensitive member) that serves as an image carrier. The photosensitive drum 1 is formed by sequentially laminating a charge generation layer, a charge transport layer, and a surface protection layer on an aluminum cylinder that serves as a base. The photosensitive drum 1 is driven to rotate in the direction of arrow R1 (counterclockwise) in the figure. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative in this embodiment) by a charging roller 2, a roller-shaped charging member that serves as a charging means. During the charging process, a predetermined charging bias (charging voltage) containing a negative DC component is applied to the charging roller 2. The charged surface of the photosensitive drum 1 is scanned and exposed by an exposure device (laser scanner) 3, which serves as an exposure means, in accordance with image information, forming an electrostatic image (electrostatic latent image) on the photosensitive drum 1.

[0016] The electrostatic image formed on the photosensitive drum 1 is developed (visualized) by the developing device 4 as a developing means, which supplies toner as a developer, and a toner image (developer image) is formed on the photosensitive drum 1. During the development process, a predetermined development bias (developing voltage) including a negative DC component is applied to the developing roller 4a as a developer carrier provided in the developing device 4. In this embodiment, toner charged with the same polarity as the charging polarity of the photosensitive drum 1 (negative polarity in this embodiment) adheres to the exposed portion (image portion) on the photosensitive drum 1, which has been uniformly charged and then exposed to light, thereby reducing the absolute value of the potential.

[0017] An intermediate transfer belt 7, which is an endless belt serving as an intermediate transfer body, is disposed facing the four photosensitive drums 1. The intermediate transfer belt 7 is stretched around a plurality of tension rollers, including a drive roller 71, a tension roller 72, and a secondary transfer opposing roller 73, and is tensioned under a predetermined tension. When the drive roller 71 is driven to rotate, the intermediate transfer belt 7 contacts the photosensitive drums 1 and rotates (circulates) in the direction of arrow R2 (clockwise) in the figure. Primary transfer rollers 5, which are roller-shaped primary transfer members serving as primary transfer means, are disposed on the inner circumferential surface of the intermediate transfer belt 7 and correspond to each photosensitive drum 1. The primary transfer rollers 5 are pressed against the photosensitive drums 1 via the intermediate transfer belt 7, forming a primary transfer region (primary transfer nip) T1 where the photosensitive drums 1 and the intermediate transfer belt 7 come into contact. The unfixed toner image formed on the photosensitive drum 1 as described above is primarily transferred onto the rotating intermediate transfer belt 7 at the primary transfer region T1 by the action of the primary transfer rollers 5. During the primary transfer process, a primary transfer bias (primary transfer voltage), which is a DC voltage of opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner (charging polarity during the development process), is applied to the primary transfer roller 5. The primary transfer roller 5 is often configured with a metal rotating shaft and an elastic layer formed on the outer surface of the rotating shaft, and is adjusted to the desired resistance value. However, it may also be configured as a metal roller made of material such as SUM (sulfur and sulfur composite free-cutting steel) or SUS (stainless steel) and having a straight shape in the thrust direction.

[0018] A secondary transfer roller 8, a roller-shaped secondary transfer member serving as a secondary transfer means, is disposed on the outer peripheral surface of the intermediate transfer belt 7, facing the secondary transfer opposing roller 73. The secondary transfer roller 8 is pressed against the secondary transfer opposing roller 73 via the intermediate transfer belt 7, forming a secondary transfer region (secondary transfer nip) T2 where the intermediate transfer belt 7 and the secondary transfer roller 8 come into contact. The toner image formed on the intermediate transfer belt 7 as described above is secondarily transferred by the action of the secondary transfer roller 8 onto a recording material (sheet, transfer material) S, such as paper, being nipped and transported between the intermediate transfer belt 7 and the secondary transfer roller 8 at the secondary transfer region T2. ​​During the secondary transfer process, a secondary transfer bias (secondary transfer voltage), which is a DC voltage of opposite polarity to the normal charging polarity of the toner, is applied to the secondary transfer roller 8. A transfer voltage of several kV is typically applied during secondary transfer to ensure sufficient transfer efficiency. The recording material S is supplied to a transport path by a pickup roller 13 from a cassette 12 containing the recording material S. The recording material S supplied to the conveying path is conveyed to the secondary transfer portion T2 by a pair of conveying rollers 14 and a pair of registration rollers 15 in synchronization with the toner image on the intermediate transfer belt 7.

[0019] The recording material S onto which the toner image has been transferred is conveyed to a fixing device 9 serving as a fixing means. The fixing device 9 applies heat and pressure to the recording material S bearing the unfixed toner image, thereby fixing (melting and solidifying) the toner image onto the recording material S. The recording material S onto which the toner image has been fixed is discharged (output) to the outside of the main body of the image forming apparatus 100 by a pair of conveying rollers 16, a pair of discharging rollers 17, etc.

[0020] Toner that remains on the surface of the photosensitive drum 1 without being transferred to the intermediate transfer belt 7 in the primary transfer step (primary transfer residual toner) is developed and collected by the developing device 4, which also serves as a photosensitive body cleaning means. Furthermore, toner that remains on the surface of the intermediate transfer belt 7 without being transferred to the recording material S in the secondary transfer step (secondary transfer residual toner) is removed from the surface of the intermediate transfer belt 7 and collected by a belt cleaning device 11, which serves as an intermediate transfer body cleaning means. The belt cleaning device 11 is disposed downstream of the secondary transfer portion T2 and upstream of the most upstream primary transfer portion T1y in the rotation direction of the intermediate transfer belt 7 (in this embodiment, it faces the drive roller 71). The belt cleaning device 11 scrapes the secondary transfer residual toner from the surface of the rotating intermediate transfer belt 7 using a cleaning blade, which serves as a cleaning member disposed in contact with the surface of the intermediate transfer belt 7, and collects the scraped toner in a collection container 11b. In this way, in the image forming operation, the process of electrically transferring the toner image from the photosensitive drum 1 to the intermediate transfer belt 7 and from the intermediate transfer belt 7 to the recording material S is repeated. Furthermore, by repeating image formation on a large number of recording materials S, the electrical transfer process is further repeated.

[0021] 2. Intermediate transfer body The intermediate transfer belt 7 as an intermediate transfer member includes at least a base layer (substrate) and may be a laminate composed of multiple layers, including a surface layer (surface layer). FIG. 1 is a schematic cross-sectional view illustrating an example of the layer structure of the intermediate transfer belt 7. As shown in FIG. 1(a), the intermediate transfer belt 7 may be composed of a single layer 7a (here, a single layer may also be referred to as the "base layer") 7a. Alternatively, as shown in FIG. 1(b), the intermediate transfer belt 7 may be composed of at least two layers: the base layer 7a and a surface layer 7b provided on the base layer 7a. Note that, for example, another layer, such as an intermediate layer, may be provided between the base layer 7a and the surface layer 7b. As will be described in detail below, the base layer 7a is a semiconductive film made of resin containing a conductive filler.

[0022] 2-1. Structure and characteristics of intermediate transfer body <Resin materials> Examples of resin materials for the base layer of an intermediate transfer belt consisting of a single layer or an intermediate transfer belt consisting of at least two layers include crystalline thermoplastic resins such as polyphenylene sulfide resin (PPS), polyamide resin, polyetherimide resin (PEI), and polyether ether ketone resin (PEEK). Since intermediate transfer belts are required to not stretch even when subjected to a tensile load over a long period of time and not suffer surface wear from rubbing by a cleaning blade, polyether ether ketone resin (PEEK) is particularly suitable. Furthermore, two or more of these resins may be selected and mixed for use as needed.

[0023] <Conductive filler> To impart conductivity to the base layer, at least one type of conductive filler, such as carbon black particles (hereinafter simply referred to as "carbon black" or "CB") or metal fine particles, is blended into the resin material. In this disclosure, carbon black is used from the perspective of mechanical properties. Carbon black is known by various names depending on its manufacturing method and raw materials. Specific examples include ketjen black, furnace black, acetylene black, thermal black, and gas black.

[0024] Various known carbon blacks can be used. Specific examples include ketjen black, furnace black, acetylene black, thermal black, and gas black. Among these, acetylene black and furnace black are preferred because they contain few impurities, have a low incidence of foreign matter defects when molded into a film shape with the above-mentioned thermoplastic resin, and are easy to obtain the desired conductivity. Specific examples of acetylene black include the following: the "Denka Black" series (manufactured by Denka Co., Ltd.), the "Mitsubishi Conductive Filler" series (manufactured by Mitsubishi Chemical Corporation), the "Vulcan" series (manufactured by Cabot Corporation), the "Brintex" series (manufactured by Degussa), and "SRF" (manufactured by Asahi Carbon Co., Ltd.). Specific examples of furnace black include the "Toka Black" series (manufactured by Tokai Carbon Co., Ltd.), the "Asahi Carbon Black" series (manufactured by Asahi Carbon Co., Ltd.), and the "Niteron" series (manufactured by Nippon Steel Carbon Co., Ltd.).

[0025] <Carbon black content> The content of carbon black is selected in consideration of whether the required electrical conductivity can be imparted to the belt member, the mechanical strength such as flex resistance and elastic modulus of the belt member, and the thermal conductivity. The carbon black content is 15.0 to 30.0 parts by mass relative to 100 parts by mass of the intermediate transfer member. That is, when the intermediate transfer member is composed of only a single base layer containing a thermoplastic resin and carbon black dispersed in the thermoplastic resin, the carbon black content is 15.0 to 30.0% by mass relative to the base layer. By keeping the carbon black content within the above range, it is possible to ensure conductivity suitable for the intermediate transfer belt and sufficient mechanical strength. The preferred carbon black content is 20.0 to 28.0% by mass relative to the intermediate transfer member.

[0026] 2-2. Manufacturing method of intermediate transfer member The base layer of the intermediate transfer member according to the present disclosure can be produced, for example, through the following steps (1) and (2). Step (1) mixing a thermoplastic resin and carbon black in a temperature environment equal to or higher than the glass transition point of the thermoplastic resin to obtain a resin mixture; Step (2) A step of melting the resin mixture at a temperature equal to or higher than the melting temperature of the thermoplastic resin and extruding the mixture into a tubular shape. Steps (1) and (2) will be described below.

[0027] <Process (1); Mixing process> In the mixing step, a thermoplastic resin and carbon black are mixed at a temperature equal to or higher than the glass transition point of the thermoplastic resin to obtain a resin mixture. A mixer that can be used in this step is, for example, a twin-screw kneader equipped with two screws in a barrel or cylinder. The mixture supplied from the supply hole of the supply section advances toward the die by the rotation of the screw, and is melted and mixed due to shear heat generated by friction between the barrel or cylinder, the screw, and the raw materials. If the temperature inside the barrel or cylinder becomes too high, the resin material will thermally decompose or thermally deteriorate. Therefore, it is preferable to control the temperature of the raw materials so that it does not become too high by externally cooling the barrel or cylinder, adjusting the temperature, adjusting the screw rotation speed, etc. Furthermore, if the temperature of the barrel or cylinder becomes too low, the resin material will not form a stable molten state, resulting in an uneven dispersion of the conductive filler, which may make it difficult to obtain a mixture with excellent mechanical, electrical, and optical properties. A strand die is usually installed at the tip of the twin-screw kneader, and the mixture is extruded into a rod shape, air-cooled, and then cut to produce a pellet-like mixture.

[0028] Before the mixing step, a pre-mixing step may be performed in which the thermoplastic resin and carbon black are mixed using a fluid mixer at a temperature below the glass transition point of the thermoplastic resin. As the fluid mixer, various known mixers having a mixing mechanism utilizing the fluid motion of solids can be used. Specifically, mixers such as a Henschel mixer, ribbon mixer, and planetary mixer can be used. Among these, it is preferable to use a Henschel mixer from the viewpoint of mixing efficiency. Furthermore, the rotation speed, processing time, processing amount, etc. of the fluid mixer must be appropriately selected depending on the materials.

[0029] <Process (2); Molding process> In the molding process, the resin mixture obtained in the mixing process is molded into a cylindrical tube in the shape of an endless belt (also referred to as an endless shape). For molding, methods such as extrusion molding and inflation molding can be selected depending on the resin used, but cylindrical extrusion molding is preferred from the standpoint of productivity. As an extruder for extrusion molding, either a single-screw extruder equipped with one screw in a barrel or cylinder or a multi-screw extruder equipped with a combination of two or more screws can be used. The pellet-like mixture supplied from the supply hole in the supply section advances toward the die by the rotation of the screw, receiving thermal energy from the barrel or cylinder and mechanical energy from the screw, and is substantially completely melted and supplied in a fixed quantity to the tip of the extruder. A cylindrical die is installed at the tip of the extruder, and the mixture is extruded downward from the cylindrical die and withdrawn from below to be molded into a cylindrical tube.

[0030] Although not limited thereto, the thickness of the base layer of an intermediate transfer member consisting of a single layer or an intermediate transfer member consisting of at least two or more layers is usually about 10 to 500 μm, typically about 50 to 200 μm.

[0031] 2-3. Decrease in resistance of intermediate transfer body When an appropriate amount of carbon black is added to a resin, the mixture is kneaded, and the kneaded material is formed into a sheet to exhibit electrical conductivity, multiple conductive paths formed by numerous CB molecules connected to each other are present in the resin from the front to the back of the sheet. In this case, the electrical resistance of the conductive path is the sum of the electrical resistance of the conductive part made of CB and the electrical resistance of the contact part when CB particles are connected to each other.

[0032] When the sheet-shaped product is an intermediate transfer member mounted in a copying machine, for example, discharge may occur between the secondary transfer roller and the intermediate transfer member during printing. In such cases, the load caused by the current flowing to the intermediate transfer member is concentrated, causing the electrical resistance of the intermediate transfer member to decrease over time, resulting in a problem of reduced image quality. This is due to a decrease in the electrical resistance of the conductive path formed by the connection of many CB particles. Looking more closely, it can be inferred that this is due to a decrease in the electrical resistance of the contact points when CB particles are connected, rather than a decrease in the electrical resistance of the CB particles themselves (conductive parts) in the conductive path.

[0033] In other words, it is thought that the electric field concentrated at the contact points between the CB particles due to the voltage applied during printing, and the heat generated by the electric field concentration carbonized the resin around the contact points, causing insulation breakdown. Therefore, in order to prevent a decrease in the electrical resistance of the conductive path, it is important to suppress the heat generated by the electric field concentration and prevent the resin around the contact points from carbonizing.

[0034] The amount of heat Q generated at the contact point when CB particles in a conductive path are connected is expressed by equation (1). To reduce the amount of heat generated, it is necessary to reduce the voltage (V) or increase the resistance value (R). Q=V×V×t / R (1) Q: Heat generation V: Voltage flowing through the path R: Resistance value of the contact area t: time

[0035] The voltage (V) is determined by the printing conditions, so it cannot be reduced. On the other hand, the resistance value R of the contact area between CB particles is expressed by equation (2), and in order to increase the resistance value R of the contact area, it is necessary to reduce the structure volume a of the CB. R = ρ / (2 × a × n) (2) R: Resistance value of the contact area ρ: specific resistance value of carbon black a: carbon black structure volume n: number of contact points

[0036] 2-4. Primary particle size of carbon black The conductive filler to be added preferably has an average primary particle size of 10 nm to 30 nm. If a conductive filler with an average primary particle size of less than 10 nm is used, the filler is likely to re-aggregate and its heat resistance will be reduced, making it difficult to use in an intermediate transfer member. On the other hand, if a conductive filler with an average primary particle size of more than 30 nm is used, the dispersibility will be reduced if aggregates are formed, and the resistance of the intermediate transfer member will be likely to decrease due to discharge. Therefore, by using particles with an average primary particle size within the above range, good resistance retention without defects can be achieved.

[0037] 2-5. Method for evaluating the particle size of primary particles of carbon black contained in the base layer Observation of the carbon black contained in the base layer is performed using a transmission electron microscope (TEM), but thinned samples prior to observation are prepared using known methods. For example, samples can be thinned using an ion beam or a diamond knife. In the following examples, an "ULTRACUT-S" (trade name, manufactured by Leica) was used to obtain a cut specimen for observation, approximately 40 nm thick, which represents a cross section of the base layer in the full thickness direction. Then, a transmission electron microscope (TEM) (trade name: H-7100FA, manufactured by Hitachi, Ltd.) was used to acquire TEM images under measurement conditions of TE mode and an accelerating voltage of 100 kV. The obtained TEM images can be analyzed using known image analysis software such as "WinROOF" (trade name, manufactured by Mitani Shoji Co., Ltd.) or "ImagePro" (trade name, manufactured by Nippon Roper Co., Ltd.). In the following examples, "WinROOF" was used. The area-equivalent diameter of 50 primary particles of carbon black was measured, and the average value was used as the average particle size of the primary particles.

[0038] 2-6. Evaluation method for DBP oil absorption of carbon black contained in the base layer The DBP (dibutyl phthalate) oil absorption of the carbon black contained in the intermediate transfer member (conductive belt) to be measured can be confirmed as follows. Observation of the carbon black contained in the intermediate transfer belt can be performed using a transmission electron microscope (TEM). The exfoliated sample before observation can be prepared in the same manner as described above. In the following examples, TEM images of the obtained exfoliated sample were obtained using the above-mentioned TEM in TE mode, at an acceleration voltage of 100 kV, and at a magnification such that one side of the image was 3 μm or less. Since the smallest structural unit of carbon black is a primary aggregate formed by a series of primary particles, the distribution of the maximum Feret diameter in the carbon black primary aggregates was analyzed from the obtained TEM image. The maximum Feret diameter corresponds to the length of the longest side of a rectangle circumscribing the carbon black primary aggregate.

[0039] The above-mentioned known image analysis software can also be used to analyze the maximum Feret's diameter from the obtained TEM image, and in the present disclosure, "WinROOF" was used. The maximum Feret diameter distribution of the carbon black primary aggregates scattered throughout the TEM image can be analyzed by binarizing and extracting the carbon black primary aggregates using image analysis software. It is known that there is a correlation between the peak top position of the maximum Feret diameter and the DBP oil absorption, which is an index of the size of the carbon black primary aggregates. By checking the number and position of the maximum Feret diameter peak tops, it is possible to identify the types of carbon black with different DBP oil absorptions and the DBP oil absorption of each carbon black.

[0040] 2-7. Structure volume CB particles have a structure in which multiple spherical primary particles are randomly fused together. This structure, the smallest structure of CB, is called the structure, and is one of the characteristics that indicates the interconnectedness of CB particles. DBP oil absorption (specified in JIS 6217-4) is used as an indicator to estimate the size of CB structure, but it is not perfect when considering the volume of the structure. Furthermore, the volume of the structure can be expressed as the product of the volume of the primary particle and the number of connections, but it is not easy to calculate the number of connections.

[0041] Therefore, the present inventors have clarified that the volume index value α corresponding to the structure volume of the CB is expressed by equation (3). α=(d 2 )×(D×c1+c2) (3) d: Primary particle size (nm) D:DBP oil absorption (mL / 100g) c1, c2: constants

[0042] The smaller the volume index value α, the smaller the structure volume of the CB, which increases the resistance value R at the contact points between CB particles, suppresses the heat generation amount Q at the contact points, and is thought to be able to suppress the decrease in electrical resistance over time due to the concentrated load caused by the current flowing to the intermediate transfer body. The structure volume of carbon black is evaluated by the method described below and is 50 to 250. If the structure volume exceeds 250, the resistance of the intermediate transfer member is likely to decrease due to electric field concentration at the contact points between CB particles. If the structure volume is below 50, the cohesive force between CB particles becomes too strong, making it difficult to maintain a good dispersion state of the conductive filler inside the intermediate transfer belt. In the present disclosure, the structure volume of carbon black is preferably 150 to 160.

[0043] Between the structure volume (structural volume) a and the volume index value α, there is a degree of freedom regarding the constants c1 and c2 as shown in formula (3), but the structure volume (structural volume) a according to the present disclosure is defined as being calculated by formula (4). a=(1 / 3)×π×(d 2 / 2)×(0.0046×D+0.1435)···(4 )

[0044] 2-8.Dispersibility The dispersibility of carbon black with a structure volume a in a resin is evaluated using the L function described below. When the intermediate transfer member according to the present disclosure is used in the primary transfer section, the value of the L function of the inner peripheral surface region of the intermediate transfer member described below should be 150 nm or less. This is because if the value of the L function is greater than 150 nm, the resistance of the intermediate transfer member is likely to decrease due to discharge in the primary transfer section. When the intermediate transfer member according to the present disclosure is used in a secondary transfer section, the intermediate transfer member should have an average value of the L function of the following central region, inner peripheral region, and outer peripheral region of 150 nm or less. If the average value of the L function is greater than 150 nm, the intermediate transfer member may be easily transferred by discharge in the secondary transfer section. This is because the body's resistance is likely to decrease.

[0045] 2-9. Evaluation method for dispersibility In the base layer 301 of the intermediate transfer member (conductive belt) to be measured, the dispersion state of the conductive filler in each of the following regions (1) to (3) shown in FIG. 3 was measured by the following procedure. (1) A region extending from the surface (outer peripheral surface) 301A on which the toner image is carried to 10 μm in the thickness direction (region 31 shown in FIG. 3, referred to as the outer peripheral surface region), (2) A region from the inner peripheral surface 301B on the back side of the outer peripheral surface to a thickness of 10 μm toward the outer peripheral surface 301A (region 32 shown in FIG. 3, referred to as the inner peripheral surface region), and (3) A range from the center in the thickness direction to 5 μm toward the outer circumferential surface and a range from the center in the thickness direction to 5 μm toward the inner circumferential surface (region 33 shown in FIG. 3, referred to as the central region)

[0046] First, the conductive belt is cut into strips of approximately 10 mm x 10 mm in the surface direction using a cutter knife or similar tool, and then embedded in epoxy resin. After curing, cross-sectional samples are prepared using abrasive paper to reveal the cross-section of the entire thickness. SEM images of the surface side (outer peripheral region), back side (inner peripheral region), and center (central region) of each obtained cross-sectional sample are obtained at 20,000x magnification using a scanning electron microscope (product name: XL-30 SFEG, manufactured by Philips). If the contrast is unclear, black-and-white enhancement processing or smoothing processing is performed as appropriate. Image processing software such as "Photoshop" (registered trademark) or "ImageJ" can be used.

[0047] Next, the coordinates of the center of gravity of the conductive filler in the field of view width are obtained, and the K function is calculated using the following formula.

[0048]

number

[0049] Here, i is an index indicating a particle in each image, λ is the particle number density in the image (number of particles per unit area), and n is the number of particles in the image. wi is the ratio (area B / area A) of "area A of circle i with radius d centered on the coordinates of the center of gravity of particle i" to "area B of the part of circle i with radius d centered on the coordinates of the center of gravity of particle i that is included in the image." wi is used to correct underestimation due to the absence of particles outside the image when particle i is present near the image boundary. Id(i,j) is a function that takes the value 1 when the coordinates of the center of gravity of particle j are within the circle with radius d centered on the coordinates of the center of gravity of particle i, and takes the value 0 otherwise. (See Non-Patent Document 1) Furthermore, the L function is calculated from the obtained K function using the following formula.

[0050]

number

[0051] As shown below, the simple sum of L(d) calculated by changing d from 0 nm to 500 nm in increments of 10 nm is defined as the L function value in this case. L(0)=(K(0) / π)(1 / 2); L(10)=(K(10) / π)(1 / 2)-10; · · · L(490)=(K(490) / π)(1 / 2)-490; L(500)=(K(500) / π)(1 / 2)-500; L function value = L(0) + L(10) + + L(490) + L(500)

[0052] The range of d, 0 to 500 nm, used to calculate the L function indicates the radius of the circle centered on each particle in the image. Since the error increases if the SEM image area used for evaluation is too small relative to the maximum radius of the measurement circle, d = 500 nm, the SEM magnification during measurement is limited to 20,000x. The size of the actual observation area included in an image captured under these conditions depends on the measurement method and the size of the area where "information outside the image area that is included in the image" is displayed, but the short side is approximately 3 to 4 μm and the long side is approximately 5 to 6 μm. "Information outside the image area that is included in the image" refers to information such as magnification and scale, and the areas where this information is displayed are not included in the measurement target. Furthermore, in each of the following examples, the L function value is calculated in each of the following regions (1) to (3). (1) An area centered at a position 5 μm away from the toner image bearing surface (outer peripheral surface) in the thickness direction. (2) An area centered at a position 5 μm away from the back side (inner peripheral surface) of the outer peripheral surface of (1) in the thickness direction. (3) Region centered on the center of the thickness direction Table 1 shows the L function values ​​in each of the above regions (1) to (3) and their arithmetic mean values ​​(arithmetic mean values).

[0053] 2-10. pH of carbon black In this embodiment, carbon black having a pH value of at least 8 is used. By using a pH value of at least 8, the liquid bridging force due to the surface functional groups of the carbon black is reduced, and aggregation of CB particles is more effectively suppressed. The pH value of the carbon black is more preferably 9 or more, and even more preferably 10 or more, with no particular upper limit. The pH value of carbon black is measured by preparing a mixture of carbon black and pure water and using a glass electrode pH meter.

[0054] 2-11. Method for evaluating the amount of carbon black contained in the base layer The amount of carbon black contained in the intermediate transfer member can be evaluated by thermogravimetric analysis (TGA). In this example, a thermogravimetric analyzer (TGA851e / SDTA) manufactured by Mettler-Toledo was used. Heating the ITB at 600°C for 1 hour in a nitrogen gas atmosphere decomposes and removes the thermoplastic resin in the ITB, allowing the mass of the carbon alone to be evaluated.

[0055] According to one aspect of the present disclosure, an intermediate transfer member capable of stably maintaining excellent electrical properties for a long period of time can be obtained. Also, according to another aspect of the present disclosure, it is possible to provide an image forming apparatus using the same that can stably produce high-quality electrophotographic images. [Example]

[0056] The intermediate transfer member and electrophotographic image forming apparatus according to the present disclosure will be specifically described below using examples. Note that the present disclosure is not limited to the configurations embodied in the examples. Furthermore, the number of parts in the examples and comparative examples is based on weight unless otherwise specified.

[0057] <Preparation of carbon black> The carbon blacks shown in Table 1 below were prepared as the carbon blacks used in the production of the intermediate transfer belts according to the examples and comparative examples. The physical properties of each carbon black (DBP absorption amount, The primary particle size, pH value, and structure volume value are shown in Table 1.

[0058] [Table 1]

[0059] Example 1 The materials shown in Table 2 below were melted and mixed under the following conditions using a twin-screw kneading extruder (trade name: PCM43, manufactured by Ikegai Corporation) to prepare resin compositions. Output: 6kg / h Screw rotation speed: 225 rpm Barrel temperature control: 360℃

[0060] [Table 2]

[0061] The obtained resin composition was melt-extruded under the following conditions using a single-screw extruder (manufactured by Plastics Technology Research Institute Co., Ltd.) equipped with a spiral cylindrical die (inner diameter: 285 mm, slit width: 1.1 mm) at the tip to produce a resin tube of the following size. The resin tube thus obtained was used as the electrophotographic belt of this example. Output: 6kg / h Die temperature: 380℃ Size: Outer diameter 280mm, thickness 60μm

[0062] <Example 2> An electrophotographic belt for use as an intermediate transfer belt was produced in the same manner as in Example 1, except that the type and amount of carbon black and the amount of thermoplastic resin were as shown in Table 3.

[0063] <Comparative Examples 1 to 8> An electrophotographic belt for use as an intermediate transfer belt was produced in the same manner as in Example 1, except that the type and amount of carbon black and the amount of thermoplastic resin were as shown in Table 3.

[0064] [Table 3]

[0065] The electrophotographic belts according to Examples 1 and 2 and Comparative Examples 1 to 8 were subjected to the following Evaluations 1 to 3. The results are shown in Table 4. The electrophotographic belts according to Comparative Examples 2 and 3 were not subjected to Evaluations 2 and 3 because the amount of carbon black blended was large and the resulting electrophotographic belts were brittle.

[0066] [Rating 1] For the electrophotographic belts according to Examples 1 and 2 and Comparative Examples 1 to 8, the L functions of the outer region, inner region, and central region were determined using the method described above.

[0067] [Rating 2] The surface resistivity of the inner peripheral surface of the electrophotographic belts according to Examples 1 and 2 and Comparative Examples 1 to 8 was measured using the following resistivity meter in accordance with Japanese Industrial Standards (JIS) K6911:2006 General Test Method for Thermosetting Plastics. Resistivity meter (product name: Hiresta UP MCP-HT450, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) The measurement was performed in an environment of a temperature of 23°C and a relative humidity of 50%, with a URSS probe in contact with the inner peripheral surface, an applied voltage of 10 V, and a measurement time of 10 seconds. The arithmetic mean value of the measurements taken at any four points was taken as the surface resistivity of the inner peripheral surface of each electrophotographic belt, and was evaluated based on the following criteria. Rank A: Surface resistivity is 1 x 10 9 Ω / □~1×10 15 It is within the range of Ω / □. Rank B: Surface resistivity is 1 x 10 9 Ω / □~1×10 15 It is outside the range of Ω / □.

[0068] [Rating 3] Each of the electrophotographic belts according to Examples 1 and 2 and Comparative Examples 1 to 8 was installed as an intermediate transfer belt in the electrophotographic image forming apparatus (product name: imageRUNNER-ADVANCE-C5540, manufactured by Canon Inc.) shown in FIG. 2. Using this electrophotographic image forming apparatus, 600,000 sheets of white solid images were printed on A3-size plain paper (product name: CS068, manufactured by Canon Inc.) in a low-humidity environment (temperature 23°C / relative humidity 5%). During this process, five full-surface black halftone images were printed consecutively every 10,000 white solid images. The resulting sixth set, i.e., the five full-surface halftone images printed after forming 600,000 white solid images, were visually observed and evaluated based on the following criteria.

[0069] Rank A: No white spots were observed in any of the five halftone images (the intermediate transfer body is resistant to a decrease in electrical resistance, i.e., has high resistance maintenance). Rank B: White spots were observed in one or two of the five halftone images. Rank C: White spots were observed in three of the five halftone images.

[0070] [Table 4]

[0071] Surface resistivity is 1×10 9 ~1×10 15 The electrophotographic belt according to Comparative Example 8, which could not be adjusted to the range of Ω / □, had a small structure volume of the carbon black used, which is thought to be the reason why the cohesive force between the carbon black particles was large and it was not possible to achieve a good dispersion state of the carbon black in the resin.

[0072] In addition, in Comparative Examples 1 and 8, the content of carbon black used was too small, making it impossible to achieve good dispersion of the carbon black in the resin, which is thought to be why the evaluation of white spots was C. In Comparative Examples 5 and 6, the low pH value of the carbon black promoted aggregation of the carbon black particles, making it impossible to achieve good dispersion of the carbon black in the resin, and it is thought that this is why the evaluation of blank areas was C. In these cases, it is thought that blank areas occurred due to discharge occurring in the gap between the inner surface of the intermediate transfer body and the primary transfer roller in the primary transfer unit, or in the gap between the outer surface of the intermediate transfer body and the paper in the secondary transfer unit. [Explanation of symbols]

[0073] 1 Photosensitive drum 2 Primary charging roller 3 Exposure equipment 4. Developing device 5 Primary transfer roller 7 Intermediate transfer belt 7a Base layer 7b Surface layer 8 Secondary transfer roller 9 Fixing device 12 cassettes 13 Pickup roller 15 Registration Roller Pair 71 Intermediate transfer belt tension roller (drive roller) 72 Intermediate transfer belt tension roller (tension roller) 73 Intermediate transfer belt tension roller (secondary transfer opposing roller) 301 Base layer 301A Outer surface 301B Inner surface

Claims

1. An endless intermediate transfer member having a base layer, the base layer contains a thermoplastic resin and carbon black dispersed in the thermoplastic resin; The carbon black has a structure volume value of 150 to 160, the content of the carbon black is 15.0 to 30.0% by mass relative to the base layer; an intermediate transfer member characterized in that, when an inner peripheral surface region is defined as a range of 10 μm in the thickness direction from the inner peripheral surface of the base layer toward the outer peripheral surface side in a cross section in the thickness direction of the base layer, the value of an L function indicating the dispersibility of the carbon black in the thermoplastic resin in the inner peripheral surface region is 150 nm or less.

2. 2. The intermediate transfer member according to claim 1, wherein the carbon black has a pH value of 8 or more.

3. 3. The intermediate transfer member according to claim 1, wherein the thermoplastic resin contains at least one resin selected from the group consisting of polyether ether ketone resin, polyphenylene sulfide resin, polyamide resin, and polyetherimide resin.

4. 4. The intermediate transfer member according to claim 1, wherein the average particle size of the primary particles of the carbon black is 10 nm to 30 nm.

5. An electrophotographic image forming apparatus comprising a first image carrier, an intermediate transfer member onto which an unfixed toner image formed on the first image carrier is primarily transferred, and a secondary transfer means for secondarily transferring the toner image primarily transferred onto the intermediate transfer member onto a second image carrier, The intermediate transfer member An endless intermediate transfer member having a base layer, the base layer contains a thermoplastic resin and carbon black dispersed in the thermoplastic resin; The carbon black has a structure volume value of 150 to 160, the content of the carbon black is 15.0 to 30.0% by mass relative to the base layer; an L function value indicating dispersibility of the carbon black in the thermoplastic resin in a cross section of the base layer in the thickness direction, the L function value indicating dispersibility of the carbon black in the thermoplastic resin in the inner circumferential surface region is 150 nm or less when the inner circumferential surface of the base layer extends from the inner circumferential surface to the outer circumferential surface of the base layer in a thickness direction of 10 μm.

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