JP2005156955A - Endless belt - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost endless belt 1 which solves the problem that conventionally, the cost of polyimide used as the main constituent of the endless belt is high since the high temperature processing is required, without sacrificing performance which should be provided. <P>SOLUTION: In the endless belt 1, a base layer 4 is formed of a thermoplastic resin, and a surface layer 2 is formed of a thermoplastic resin or a thermoset resin that hardens at 300°C or below. The relative reflectivity of a toner image holding face 2a when measured at an incident angle of 5° in JIS K0134 is 3% or more. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an endless belt used in an electrostatic recording process, and more particularly to a belt that does not use an expensive thermosetting polyimide resin.

  Conventionally, in an electrostatic recording process in a copying machine, a printer, etc., first, the surface of a photosensitive member (latent image holding member) is uniformly charged, and an image is projected onto the photosensitive member from an optical system and exposed to light. An electrostatic latent image is formed by erasing the charged portion, and then toner is supplied to the electrostatic latent image to form a toner image by electrostatic adhesion of the toner, which is formed on paper, OHP, photographic paper For example, a method of printing by transferring to a recording medium such as the above is employed.

  In this case, color printers and color copiers basically print according to the above process, but in the case of color printing, the color tone is reproduced using toners of four colors, magenta, yellow, cyan, and black. Therefore, a process for obtaining a necessary color tone by superimposing these toners at a predetermined ratio is required, and several methods have been proposed for performing this process.

  These methods can be roughly classified according to the stage at which the toner is overlapped. First, the first method is to superimpose different color toners on the photosensitive drum. In the same manner as in the case where the toner is supplied, when the electrostatic latent image is visualized by supplying the toner onto the photosensitive member, development is performed by sequentially superposing the toners of the four colors of magenta, yellow, cyan, and black. This is called a multiple development method. According to this method, it is possible to configure the apparatus relatively compactly, but there is a problem in that it is very difficult to control gradation and high image quality cannot be obtained.

  In the second method, different color toners are superimposed on a recording medium. As one of these methods, four photosensitive drums are provided, and the latent image on each drum is developed with magenta, yellow, cyan, and black toners, so that a magenta toner image, a yellow toner image, and a cyan toner are developed. By forming four toner images, that is, an image and a black toner image, arranging the photosensitive drums on which the toner images are formed in a line, sequentially transferring the toner images onto a recording medium such as paper, and superimposing the toner images on the recording medium. There is a direct tandem method for reproducing color images. Although this method can obtain a good image, the four photosensitive drums, the charging mechanism and the developing mechanism provided for each photosensitive drum are arranged in a line, and the apparatus becomes large and expensive. It becomes.

  FIG. 1 shows a configuration example of a printing unit of a direct tandem image forming apparatus. Four printing units each composed of a photosensitive drum 11, a charging roll 12, a developing roll 13, a developing blade 14, a toner supply roll 15 and a cleaning blade 16 corresponding to yellow Y, magenta M, cyan C and black B toners. The toner images are sequentially transferred onto the paper that is circulated by the driving roller 18 and conveyed by the transfer conveyance belt 10 to form a color image. Charging and discharging of the transfer / conveying belt are performed by a charging roll 17a and a discharging roll 17b, respectively. Further, a suction roller (not shown) is used for charging the paper for sucking the paper onto the belt. Owing to these measures, generation of ozone can be suppressed. The suction roller places the paper on the transfer conveyance belt from the conveyance path and performs electrostatic adsorption on the transfer conveyance belt. Further, the sheet separation after the transfer can be performed only by the curvature separation by lowering the transfer voltage to weaken the adsorption force between the sheet and the transfer conveyance belt.

  As materials for the transfer / conveyance belt 10, there are a resistor and a dielectric, each having advantages and disadvantages. Since the resistance belt has a short charge holding time, when it is used for direct tandem transfer, there is little charge injection during transfer, and the voltage rise is relatively small even during continuous transfer of four colors. In addition, when it is repeatedly used for the transfer of the next sheet, the electric charge is released, and no electrical reset is required. However, since the resistance value changes due to environmental fluctuations, there are disadvantages such as affecting transfer efficiency and being easily influenced by the thickness and width of the paper.

  On the other hand, in the case of a dielectric belt, there is no spontaneous release of injected charge, and both charge injection and discharge must be electrically controlled. However, since the charge is stably held, the sheet can be adsorbed reliably and can be conveyed with high accuracy. Since the dielectric constant is less dependent on temperature and humidity, the transfer process is relatively stable to the environment. The drawback is that the transfer voltage increases because charges are accumulated on the belt each time the transfer is repeated.

  Of the second method, as a method different from the direct tandem method, a recording medium such as paper is wound around a transfer drum and rotated four times, and magenta, yellow, cyan, and black are sequentially recorded on each photosensitive drum. There is also a transfer drum system in which a color image is reproduced by transferring to a medium. According to this method, a relatively high image quality can be obtained. However, when the recording medium is a cardboard such as a postcard, it is difficult to wind the recording medium around the transfer drum, and the type of the recording medium is limited. There is.

  As a third method, there has been proposed an intermediate transfer method in which toner of each color on a photosensitive drum is superimposed on an intermediate transfer member, and the superimposed toner image is transferred to a recording medium as it is. With respect to the system, the direct tandem system, and the transfer drum system, a good image quality can be obtained, and the type of recording medium is not particularly limited.

  In other words, this intermediate transfer system is provided with an intermediate transfer member consisting of a drum and a belt that temporarily transfers and holds the toner image on the photosensitive member, and a magenta toner image, a yellow toner image, a cyan toner image, and a black toner on the photosensitive drum. By sequentially transferring the toner images on the intermediate transfer member, a color image is formed on the intermediate transfer member, and the color image is transferred onto a recording medium such as paper. Therefore, since the gradation is adjusted by superimposing the four color toner images, it is possible to obtain high image quality, and there is no need to wrap the recording medium around the drum, so the type of recording medium is limited. It is nothing.

  As a representative example of the third method, the intermediate transfer method, an intermediate transfer belt method in which one photosensitive drum and one intermediate transfer belt are combined, a plurality of photosensitive drums arranged in tandem, and one intermediate transfer belt There is a tandem intermediate transfer belt system in which these are combined, and these will be described below.

  FIG. 2 is a diagram showing the configuration of the intermediate transfer belt system, in which 21 is a photosensitive drum photosensitive member, which rotates in the direction of the arrow in the figure. The photosensitive drum 21 is charged by the primary charger 22, and then the charged portion of the exposed portion is erased by the image exposure 23, and an electrostatic latent image corresponding to the first color component is formed on the photosensitive drum 11. The electrostatic latent image is developed with the first color magenta toner M by the developing device 25 a, and the first color magenta toner image is formed on the photosensitive drum 21. Next, this toner image is circulated and driven by the drive roller 26 and transferred to the intermediate transfer belt 20 that circulates and rotates while contacting the photosensitive drum 21. In this case, the transfer from the photosensitive member 11 to the intermediate transfer belt 20 is performed at the nip portion between the photosensitive drum 21 and the intermediate transfer belt 20 by a primary transfer bias applied to the intermediate transfer belt 20 from the power source 27. After the first color magenta toner image is transferred to the intermediate transfer belt 20, the surface of the photosensitive drum 21 is cleaned by the cleaning device 24, and the developing and transferring operation for the first rotation of the photosensitive drum 21 is completed. Thereafter, the photosensitive drum 21 is rotated three times, and the cyan toner image of the second color, the yellow toner image of the third color, and the black toner image of the fourth color are sequentially used by the developing devices 25a to 25d for each rotation. The toner image is formed on the intermediate transfer belt 20 and is superimposed and transferred to the intermediate transfer belt 20 every round, and a composite color toner image corresponding to the target color image is formed on the intermediate transfer belt 20. In the apparatus of FIG. 2, the developing devices 25 a to 25 d are sequentially replaced with each rotation of the photosensitive drum 21 so that development with magenta toner M, cyan toner C, yellow toner Y, and black toner B is sequentially performed. It has become.

  Next, the transfer roller 31 comes into contact with the intermediate transfer belt 20 on which the composite color toner image is formed, and a recording medium 33 such as paper is fed from the paper feed cassette 32 to the nip portion. At the same time, a secondary transfer bias is applied from the power source 34 to the transfer roller 31, and the composite color toner image is transferred from the intermediate transfer belt 20 onto the recording medium 33 and is heat-fixed to form a final image. After the composite color toner image is transferred to the recording medium 33, the transfer residual toner on the surface of the intermediate transfer belt 20 is removed by the cleaning device 28 to return to the initial state and prepare for the next image formation.

  FIG. 3 is a diagram showing a configuration example of the tandem intermediate transfer belt system. The first developing device 44a develops the electrostatic latent image on the photosensitive drum 42a with yellow, and the electrostatic latent image on the photosensitive drum 42b is magenta. A second developing device 44b for developing the electrostatic latent image on the photosensitive drum 42c, a third developing device 44c for developing the electrostatic latent image on the photosensitive drum 42c with cyan, and a fourth developing device 44d for developing the electrostatic latent image on the photosensitive drum 42d with black. Are arranged along the intermediate transfer belt 40, and the intermediate transfer belt 40 is driven to circulate in the direction of the arrow in the figure to form toner images of four colors formed on the photosensitive drums 42a to 42d of the developing devices 44a to 44d. Are sequentially transferred onto the intermediate transfer belt 40 to form a color toner image on the intermediate transfer belt 40, and the toner image is transferred onto a recording medium 43 such as paper to be preliminarily transferred. It is intended to theft.

  In the figure, 45 is a driving roller or tension roller for circulatingly driving the intermediate transfer belt 40, 46 is a recording medium feeding roller, 47 is a recording medium feeding device, 48 is an image on a storage medium, etc. It is a fixing device that fixes by means of In the figure, reference numeral 49 denotes a power supply device (voltage application means) for applying a voltage to the intermediate transfer belt 40. The power supply device 49 transfers toner images from the photosensitive drums 42a to 42d to the intermediate transfer belt 40. The polarity of the applied voltage can be reversed when the toner image is transferred from the intermediate transfer belt 40 to the recording medium 43.

  Among the above descriptions, in the direct tandem system, the intermediate transfer belt system, and the tandem intermediate transfer belt system, the transfer conveyance belt used for each system in order to control or monitor the photosensitive drum, the recording medium supply unit, and the like. 10. The leading position (or the trailing end position) of the toner images on the intermediate transfer belt 20 and the intermediate transfer belt 40 is detected. This detection is performed on the belt surface running from a fixed position. The infrared reflected light detection device is configured to irradiate infrared light of a predetermined intensity and detect the reflected light at that time by the infrared reflected light detection device. , 52 and 53 are shown.

  As the endless belt functioning as the transfer conveyance belt 10 and the intermediate transfer belts 20 and 40 described above, a single-layer or double-layer structure is formed, and these layers are formed of a thermosetting polyimide resin. It is known (for example, refer to Patent Document 1). Thermosetting polyimide resin is excellent in mechanical properties such as high tensile strength, high rigidity, and low elongation even under high tension. Can be easily controlled, and has a sufficiently high surface reflectance to specify the toner image head position by the infrared reflected light detection device, and has characteristics suitable as an endless belt material.

However, the biggest problem of thermosetting polyimide resin is that this resin is expensive, and in order to obtain the excellent mechanical properties of thermosetting polyimide resin, the polyimide system formed in an endless belt shape It is necessary to cause the precursor to undergo a condensation reaction to form a ring-closing imidization. For this ring-closing treatment, it is necessary to hold the polyimide precursor at a high temperature of 200 to 400 ° C. for a long time, for example, in a high-temperature holding tank. Because of this, the cost of equipment, energy, etc. was large, which was a problem.
JP 7-156287 A

  The present invention has been made in view of such problems, and provides an inexpensive endless belt that does not use a conventional expensive thermosetting polyimide resin without sacrificing characteristics to be provided. For the purpose.

<1> The present invention provides an endless belt comprising an insulating surface layer that holds a toner image transferred from an image forming body, and a conductive base layer disposed inside the surface layer.
The base layer is made of a thermoplastic resin, the surface layer is made of a thermoplastic resin or a thermosetting resin that is cured at 300 ° C. or lower, and the relative reflection of the toner image holding surface on the surface layer when measured at an incident angle of 5 degrees in JIS K0134 An endless belt having a rate of 3% or more.

  <2> The present invention is the endless belt according to <1>, wherein the surface roughness Ra of the toner image holding surface is 1 μm or less.

  <3> In the present invention, in <1> or <2>, the thermoplastic resin forming the surface layer or the thermosetting resin cured at 300 ° C. or lower is an endless belt comprising an aromatic compound.

  <4> The present invention is the endless belt according to any one of <1> to <3>, wherein the surface layer has a thickness of 1 to 200 μm.

  <5> The present invention is the endless belt according to <4>, wherein the surface layer has a thickness of 1 to 50 μm.

  <6> The present invention is the endless belt according to any one of <1> to <5>, wherein the elastic modulus of the base layer is 300 to 5000 MPa.

  <7> The present invention is an endless belt using any one of <1> to <6> using a resin whose main component is polyurethane as an intermediate layer.

  According to the invention of <1>, since the base layer is formed of a thermoplastic resin and the surface layer is formed of a thermoplastic resin or a thermosetting resin that is cured at 300 ° C. or less, it can be made inexpensive. Since the relative reflectance of the toner image holding surface is set to 3% or more, the portion without the toner image on the toner image holding surface can be distinguished from the low reflection portion with the toner image, and the head position of the toner image can be specified. Can be made possible.

  Furthermore, since each material of the surface layer and the base layer does not need to be composed of the same resin material, a material capable of forming a surface with the relative reflectance of 3% or more is used for the surface layer, By selecting a material with mechanical performance equal to or higher than that of polyimide resin, the optical and mechanical characteristics equivalent to those of polyimide resin belts can be obtained without using expensive thermosetting polyimide resin. Can be prepared.

  According to the invention <2>, since the surface roughness Ra is 1 μm or less, the transfer efficiency when transferring the toner to the recording medium can be improved. When Ra exceeds 1 μm, the reflectivity of the toner image holding surface is lowered, and the belt is rough, so that the toner sticks to the toner image holding surface of the endless belt and is difficult to transfer to the recording medium, and then adheres to the cleaning member. Even if you try to scrape off the toner, it will not come off.

  The relative reflectance is higher as the refractive index of the material forming the surface is higher, and the material containing the aromatic compound has a higher refractive index. According to the invention <3>, since an aromatic compound is included, a high relative reflectance can be achieved.

  According to the invention <4>, since the thickness of the surface layer is 1 to 200 μm, transfer performance when forming a toner image between the image forming body and the recording medium, that is, transferring as much toner as possible. Performance can be ensured, and this makes it possible to obtain an image of a predetermined quality.

  According to the invention <5>, since the thickness of the surface layer is 1 to 50 μm, the transfer performance can be further ensured, and the ability to form a higher quality image can be imparted to the image forming apparatus. .

  According to the invention <6>, since the elastic modulus of the base layer is set to 300 to 5000 MPa, mechanical characteristics such as dimensional accuracy and creep of the belt can be ensured.

  According to the invention <7>, the intermediate layer is made of an elastic polyurethane-based resin. Therefore, when transferring a toner image to an image forming body such as a photosensitive drum or a recording medium, It is possible to make contact, and this can further improve the transfer performance.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG. FIG. 4 is a cross-sectional view showing an endless belt. The endless belt 1 has a three-layer structure including a surface layer 2 forming a toner image holding surface 2a, an intermediate layer 3 disposed adjacent to the inner side in the thickness direction of the surface layer, and a base layer 4 serving as an innermost layer in the thickness direction. Thus, the thickness of the surface layer 2 is preferably 1 to 200 μm, and more preferably 1 to 50 μm. In addition, the thickness of the intermediate layer 3 is preferably 1 to 500 μm, the thickness of the base layer 4 is preferably 10 to 300 μm, and the thickness of the base layer 4 is more preferably 30 to 200 μm.

  As the material for the surface layer 2, an inexpensive thermoplastic resin such as polyester urethane, polyamide, acrylonitrile-butadiene-styrene, or the like can be used. Further, by making the surface layer have a high refractive index, a high surface reflectance can be obtained. be able to. It is preferable to include an aromatic compound such as PET, a naphthalene compound, a styrene compound, a polycarbonate, phthalic acid, or an epoxy resin as a substance that increases the refractive index.

  As the material used for the intermediate layer 3, it is preferable to use various rubber materials having elasticity, thermoplastic elastomers, low-hardness urethane resins, and the like. In contact transfer with a storage medium such as paper or paper, contact can be made in a wide range, and high transfer efficiency can be obtained.

  The thermoplastic resin material used for the base layer is not particularly limited and may be a commercially available material. For example, polyamide 12, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-ethylenepropylene-styrene copolymer, polyamide 6/12, polyamide 6, polyamide 66, polyacetal, polymethyl methacrylate, poly vinylidene fluoride, polyvinyl fluoride, poly hexafluoroethylene propylene, poly trifluoride ethylene, ethylene-tetrafluoroethylene copolymer, polyacrylonitrile, poly Arylate, polybutylene terephthalate, polycarbonate, polyethersulfone, polyethylene, polyethylene terephthalate, polystyrene, polyphenylene oxide, polysulfone, polyarylate, polypropylene High mechanical performance can be supported using pyrene, thermoplastic polyester (PET, PBT, etc.) polyethylene naphthalate, polybutylene naphthalate, polyphenylene sulfide, polysulfone, polyether ketone, liquid crystal polyester, etc. Polyamide 12 and acrylonitrile-butadiene-styrene copolymer are preferred, and polyamide 12 is particularly preferred.

Here, the surface layer 2 has a relative reflectance at the toner image holding surface 2a of 3% or more when measured at an incident angle of 5 degrees according to JIS K0134. Thus, in general, the surface layer 2 has a wavelength of about 950 nm. The presence / absence of the toner image on the toner image holding surface 2a can be reliably detected by the infrared reflected light detection device using infrared rays. The surface roughness of the toner image holding surface 2a is preferably 1 μm or less.

  A method for forming the endless belt 1 will be described as follows. First, the base layer 4 is formed. For this reason, the resin is continuously extruded from a die having a cylindrical cross section having the same circumference as the final endless belt 1 to form a base layer 4 in which a plurality of portions are connected in the width direction. . Alternatively, as another method for forming the base layer 4, a cylindrical mold is dipped in a solution in which the material for forming the base layer 4 is dissolved, and this material is dip-coated on the outer surface of the mold, or the material is electrostatically charged. It is also possible to apply powder coating on the outer surface of a cylindrical mold using

  Next, the endless base layer 4 formed in this way is set on the outer peripheral surface of a mold having a predetermined size, and the intermediate layer 3 and the surface layer 2 are formed in this order by spray coating or dip coating. Each layer is dried for 20 to 120 minutes at a predetermined temperature, for example, 100 to 200 ° C. after the coating of each layer is completed. Thereafter, the endless belt 1 coated with the intermediate layer 3 and the surface layer 2 on the base layer 4 is removed from the mold, and finally is cut into a length corresponding to one product width. Exit.

Samples of five types of endless belts, which are Examples 1 to 4 and Comparative Example 1, were manufactured using the materials shown in Table 1 for each layer, and the image performance and machine detection performance for each layer. Was evaluated.

  The image evaluation and the machine detection performance were evaluated by removing the belt mounted on a commercially available laser printer and replacing the belts of Examples 1 to 4 and Comparative Example 1 with each other, and OK / somewhat NG / The determination result was expressed as NG. At the time of the determination, for the image evaluation, the image printed on the paper is visually checked for the occurrence of color misregistration, and for the machine detection performance, when the end of the toner image on the belt cannot be detected, the laser printer It is determined whether or not the display of “Belt required replacement” appears on the screen.

Further, the relative reflectance was measured for each sample, and the relationship between the reflectance and the evaluation result was also investigated. The relative reflectance was obtained based on JIS K0134 (2002), specifically, The following conditions were followed.
1) Equipment used: U4000 type spectrophotometer manufactured by Hitachi High-Technology Corporation.
2) Measuring method: Measured by the specular reflection method (incident angle of 5 degrees).
3) Comparison standard: An aluminum vapor-deposited plate is used as Ref, and the relative reflectance is expressed with respect to this.
4) Wavelength used: 950 nm

  Table 2 shows the intermediate layer thickness, surface layer compounding type, surface layer thickness, relative reflectance, image performance evaluation result, and machine detection performance evaluation result of each sample.

  As described above, when the relative reflectance is 3% or more, the machine detection performance that the endless belt should have can be satisfied, and at the same time, no color shift occurs in the image evaluation. On the other hand, as shown in Comparative Example 1, when the relative reflectance is less than 3%, the machine detection performance cannot be satisfied, and the position of the toner image cannot be detected accurately, resulting in a slight color shift. The result was generated.

  The sample of Example 4 is obtained by improving the cleaning performance of the toner by making the blending type of the surface layer different from that of the other examples. Therefore, the result of lowering the relative reflectance than the samples of the other examples. However, it is still shown that good machine detection performance and image performance can be obtained by carrying a relative reflectance of 3%. In Comparative Example 1, since neither an intermediate layer nor a surface layer is provided, the surface of the base layer forms a toner image holding surface, and the relative reflectance is lowered.

  The present invention can be used for an endless belt such as a transfer conveyance belt or an intermediate transfer belt used in an electrostatic recording apparatus such as a copying machine or a printer.

1 is a schematic side view of an image forming apparatus that forms an image by a tandem method. 1 is a schematic side view of an image forming apparatus that forms an image by an intermediate transfer belt method. 1 is a schematic side view of an image forming apparatus that forms an image by a tandem intermediate transfer belt method. It is sectional drawing which shows the endless belt of embodiment which concerns on this invention.

Explanation of symbols

1 Endless Belt 2 Surface Layer 2a Toner Image Holding Surface 3 Intermediate Layer 4 Base Layer

Claims (7)

In an endless belt comprising an insulating surface layer for holding a toner image transferred from an image forming body, and a conductive base layer disposed inside the surface layer,
The base layer is made of a thermoplastic resin, the surface layer is made of a thermoplastic resin or a thermosetting resin that is cured at 300 ° C. or lower, and the relative reflection of the toner image holding surface on the surface layer when measured at an incident angle of 5 degrees in JIS K0134 Endless belt with a rate of 3% or more.   The endless belt according to claim 1, wherein the surface roughness Ra of the toner image holding surface is 1 μm or less.   The endless belt according to claim 1 or 2, wherein the thermoplastic resin forming the surface layer or the thermosetting resin curable at 300 ° C or lower contains an aromatic compound.   The endless belt according to any one of claims 1 to 3, wherein the surface layer has a thickness of 1 to 200 µm.   The endless belt according to claim 4, wherein the surface layer has a thickness of 1 to 50 μm.   The endless belt according to any one of claims 1 to 5, wherein the base layer has an elastic modulus of 300 to 5000 MPa.   The endless belt according to any one of claims 1 to 6, wherein a resin mainly composed of urethane is used for the intermediate layer.

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