JP2007011117A - Intermediate transfer belt - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an intermediate transfer belt capable of stably forming a toner image that is free of image defects by preventing the generation of peeling-discharge between an intermediate transfer belt and a recording medium, at secondary transfer. <P>SOLUTION: The intermediate transfer belt has at least a surface layer on a base material. The surface layer contains an aggregate of conductive particles, having an average particle diameter of 0.5 to 25μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an intermediate transfer belt used in an electrophotographic image forming apparatus, and more particularly to an intermediate transfer belt capable of forming a good toner image without image defects on a recording medium.

  In addition to copiers and printers for office use, electrophotographic image forming apparatuses have recently become widespread in the printing field called light printing, and can print thousands of pages in a short time without printing. It has come to attract attention from the merit.

  In one of the electrophotographic image forming methods, a toner image formed on a photosensitive member is copied onto a transfer intermediate, and then transferred to a recording medium from the transfer intermediate to form an image through a process called secondary transfer. There is something to do. One embodiment of the intermediate transfer member is an intermediate transfer belt using an endless belt made of resin, and the improvement of the intermediate transfer belt has been promoted so far in order to develop good transfer performance. .

  For example, by using a material that imparts high water repellency and that exhibits a triboelectric charge property opposite to that of the toner on the surface of the intermediate transfer belt, stable transfer without the occurrence of local transfer defects called worm-engraving prints. There is a technique capable of performing (see, for example, Patent Document 1).

  In addition, there is a technique that maintains toner releasability for a long period of time and improves tensile strength by providing a layer containing a conductive filler and an outermost layer containing a silicone resin (see, for example, Patent Document 2). ).

  Recently, a technique for improving the performance of the surface area of the intermediate transfer belt has been studied so that a high-definition toner image can be accurately transferred in accordance with the progress of digitization. Specific examples include an intermediate transfer belt having a surface layer containing a conductive agent and an intermediate transfer belt containing a coupling agent having an electron accepting or electron donating atomic group in the surface layer (for example, patents). References 3, 4).

  By the way, when the toner image on the intermediate transfer belt is transferred to the recording medium and then the recording medium is peeled off from the intermediate transfer belt, a phenomenon called peeling discharge occurs. This is because a potential difference occurs between the gap on the intermediate transfer belt side and the paper side, and an electric field is formed between the two, causing a discharge. On the toner image, an image defect of several millimeters in size called white spots is generated. Let

  That is, when the recording medium is peeled from the intermediate transfer belt, the residual charge and the toner charge coexist, whereby an electric field is formed in the gap between the intermediate transfer belt and the recording medium. On the other hand, the withstand voltage value in the air gap is defined by Paschen's law, but when an electric field higher than the withstand voltage value is formed in the air gap, the electric charge leaks and tends to be below the withstand voltage value. As a result of this electric charge leak appearing as a discharge, the toner image is disturbed. Proper toner transfer cannot be performed at the location where the discharge has occurred, and a white-out image defect occurs.

As one of the methods for preventing image defects due to white spots, as described in Patent Document 3, conductive fine particles such as carbon black are added to the surface layer of the intermediate transfer belt to eliminate the resistance decrease due to the transfer voltage, thereby eliminating the image defects. A method of suppressing the occurrence was examined. However, as in the case of image formation in light printing described above, in the case where prints of several thousand levels are continuously made in a short time, secondary transfer is continuously carried out, so that charge accumulation occurs on the surface of the intermediate transfer belt. However, there is a concern that the generation of peeling discharge cannot be prevented. Thus, there has been a demand for an intermediate transfer belt that does not cause image defects due to peeling discharge even under severe image forming conditions in which a large amount of printing is continuously performed.
JP-A-9-230714 (see paragraph 0007, etc.) Japanese Patent Laid-Open No. 9-269676 (see paragraph 0007 and the like) JP 2001-242725 A (see paragraph 0017 etc.) JP 2002-328535 A (see paragraph 0028 and the like)

  According to the present invention, when secondary transfer from an intermediate transfer belt to a recording medium is performed, a recording medium on which a toner image is transferred without causing peeling discharge can be peeled off from the intermediate transfer belt. An object of the present invention is to provide an intermediate transfer belt capable of obtaining a high-quality toner image free from image defects such as voids and toner scattering in character portions.

  In particular, an object of the present invention is to provide an intermediate transfer belt that does not cause peeling discharge when a large amount of image formation is performed and can obtain a toner image free from image defects, such as when continuously creating 5000 or more sheets. .

  The object of the present invention is achieved by the configurations described below.

(Claim 1)
An intermediate transfer belt having at least a surface layer on a substrate,
The intermediate transfer belt, wherein the surface layer contains an aggregate of conductive particles having an average particle diameter of 0.5 to 25 µm.

(Claim 2)
The intermediate transfer belt according to claim 1, wherein the surface layer has a surface energy of 30 mN / m or less.

  In the present invention, by including an aggregate of conductive particles having a specific particle size in the surface layer of the intermediate transfer belt, white spots on the solid image portion or character images on the toner image transferred from the intermediate transfer belt onto the recording medium. It has become possible to stably form a high-quality toner image free from image defects such as voids and toner scattering in character images.

  In particular, in the present invention, even in the case where 5000 or more prints are continuously produced, local peeling discharge due to secondary transfer does not occur, so that good image formation without image defects can be stably performed over a long period of time. It became so. As a result, it has become possible to stably provide prints of good quality in the light printing field in which prints on the order of several thousand sheets are made in a short time.

  The present invention relates to an intermediate transfer belt containing an aggregate of conductive particles having a specific particle diameter in a surface layer.

  In the present invention, the surface layer of the intermediate transfer belt contains an aggregate of conductive particles having an average particle diameter of 0.5 to 25 μm, thereby eliminating image defects due to peeling discharge. This is probably because dispersion of conductive particles agglomerates to form a lot of dischargeable areas on the intermediate transfer belt, thus avoiding charge accumulation on the surface of the intermediate transfer belt, and the intermediate transfer belt and the recording medium. This is presumably because an electric field is hardly formed between the two. In addition, since the movement of charges is performed only in the aggregate region of the conductive particles, it is assumed that the charges can be quickly lost even if an electric field is formed on the surface of the intermediate transfer belt.

  Even in the conventional technology, there is a technology in which conductive particles such as carbon black are added to the surface layer of the intermediate transfer belt. However, since the generated charges move through the inside of the particles, the movement of the charges becomes slow, and the surface of the intermediate transfer belt It is presumed that the electric field formed on the surface cannot be quickly lost.

  The present invention will be described below.

  First, the intermediate transfer belt of the present invention will be described.

  The intermediate transfer belt of the present invention has a so-called multilayer structure having a surface layer on a substrate, and contains the above-mentioned aggregate of conductive particles in the surface layer. In the present invention, the intermediate transfer belt has a multilayer structure, so that flexibility and rigidity that cannot be obtained with a single material structure can be expressed in a balanced manner. In the present invention, the aforementioned base material is also referred to as a base material layer.

  FIG. 1 is a schematic view showing an example of the intermediate transfer belt of the present invention.

  In FIG. 1, 2 is an intermediate transfer belt, 21 is a surface layer, 22 is an aggregate of conductive particles, 23 is a base material layer, and 24 and 25 are intermediate layers.

  The intermediate transfer belt 2 shown in FIG. 1 is preferably endless. The intermediate transfer belt 2 shown in FIG. 1A has a two-layer structure composed of a surface layer 21 and a base material layer 23. The intermediate transfer belt 2 shown in FIG. 1B has a three-layer structure having an intermediate layer 24 on a base material layer 23 and a surface layer 21 on the intermediate layer 24. In addition, the intermediate transfer belt shown in FIG. 1C has a four-layer structure having two intermediate layers 24 and 25 outside the base material layer 23 and a surface layer 21 outside the intermediate layer 25. .

  The aggregate of conductive particles contained in the surface layer 21 will be described.

  The average particle size of the aggregate of conductive particles is 0.5 to 25 μm, preferably 1 to 10 μm.

  The particle diameter of the aggregate of conductive particles contained in the surface layer of the intermediate transfer belt of the present invention is measured as follows. That is, a photograph is taken using a scanning electron microscope (SEM), and the photographed image information is arithmetically processed by an image processing apparatus “Luzex F” (manufactured by Nireco) to calculate an average particle diameter.

  The equivalent circle diameter (the diameter of a circle having the same projected area as the photographed particle) of the photographed aggregate particles is calculated by the arithmetic processing using “Luzex F”, and measurement of 10 or more aggregate particles is performed. The average particle diameter is calculated from the result.

In addition, the measurement with a scanning electron microscope (SEM) is performed by fixing the intermediate transfer belt on a conductive sample stand (grounded) with a conductive double-sided tape and irradiating an electron beam from the surface of the fixed intermediate transfer belt. Is done. For example, measurement conditions when a scanning electron microscope “S-3500N” (manufactured by Hitachi, Ltd.) is used are as follows. That is,
Vacuum mode: Low vacuum mode Acceleration voltage: 5 kV
Magnification: 250 times Time from the start of electron irradiation to the start of imaging: 3 minutes Sample: No sputter processing Sample stage: Made of aluminum, grounded Others: Photographed using a scale bar Also, on the surface layer of the intermediate transfer belt of the present invention The amount of the aggregate of conductive particles contained is 20 to 80 particles / cm ² per unit area, and preferably 30 to 70 particles / cm ² . The amount per unit area is also confirmed by observation with the scanning electron microscope.

  By setting the content of the aggregates of the conductive particles contained in the surface layer of the intermediate transfer belt of the present invention within the above range, the intermediate transfer belt can appropriately maintain the conductivity, and the environment during printing can be maintained. Stable image formation can be performed with less influence. According to the intermediate transfer belt of the present invention, when image formation is performed in a high temperature and high humidity environment (for example, 30 ° C. and 80% RH), white portions of the solid image portion and void portions of the character portion are generated on the toner image. In addition, it has been confirmed that stable image formation can be performed in a low-temperature and low-humidity environment (for example, 10 ° C., 20% RH) without the toner scattering and the transfer rate of the character portion being reduced.

The conductive particles used in the present invention are not particularly limited, and specifically, conductive powder such as carbon black, metal powder such as aluminum powder, nickel powder, stainless steel powder, c-ZnO, c-TiO _2. , C-ZnO ₄ , c-SnO _{2 and} other conductive metal oxides. These conductive particles may be a mixture of two or more.

  The number average primary particle diameter of the conductive particles is preferably 0.05 to 1.5 nm, more preferably 0.2 to 0.8 nm.

  Here, the number average primary particle diameter was measured by using a transmission electron microscope “LEM-2000” (manufactured by TOPCON), taking a 60,000 times projection photograph of the conductive particles dispersed on the sample support mesh, and obtaining a high-speed image. This is a value obtained by measuring the equivalent-circle particle diameter of about 100 primary particles with an analyzer “SPICCA” (manufactured by Nippon Avionics Co., Ltd.).

The volume resistivity of the conductive particles is preferably 10 ⁴ Ωcm or more. By making the volume resistivity 10 ⁴ Ωcm or more, the characteristics become stable.

  The average particle diameter of the aggregates of the conductive particles can be controlled by conditions for dispersing the conductive particles in the resin solution. For example, if the conductive particles are dispersed in the resin solution by high-speed stirring, the average particle size becomes small, and if dispersed at low speed, the average particle size becomes large.

  The surface layer constituting the intermediate transfer belt will be described.

  The surface layer is a layer formed by containing an aggregate of conductive particles having at least the specific particle diameter described above in the binder resin.

  In addition to the aggregate of conductive particles, a material having a low surface energy is mixed in the surface layer to reduce the surface energy on the intermediate transfer belt and promote separation of the toner image from the intermediate transfer belt. It is preferable. As a result, the transferability of the toner image from the intermediate transfer belt to the recording medium during the secondary transfer is promoted, and a high-quality toner image can be obtained on the recording medium.

  Examples of the material having low surface energy include a fluorine-based material, a silicon-based material, or a material containing these as a main component, a fluorine resin powder, a silicone resin, a material obtained by dispersing a silicone oil component, and the like.

  Among these, a surface layer formed using a silicone resin is preferable. The silicone resin used for the formation of the surface layer is not particularly limited, but usually a liquid silicone resin is preferable from the viewpoint of work efficiency, and an organic solvent containing an organic solvent such as n-hexane or an organic solvent is not used. A reactive type is mentioned. In particular, a hard type one-component or two-component curable silicone resin is preferable. Of these, thermosetting silicone resins (methyl) and room temperature curable silicone resins are suitable.

  In addition, it can be confirmed by the above-described scanning electron microscope (SEM) measurement that the surface layer contains aggregates of conductive particles.

  The base material layer constituting the intermediate transfer belt will be described.

  The base material layer has rigidity that avoids deformation of the belt due to a load applied to the intermediate transfer belt including around the cleaning blade, and reduces the influence on the transfer portion. The base material layer is preferably formed using a material having a Young's modulus of 200 MPa or more, and more preferably a material of 300 MPa or more.

  Examples of materials that exhibit such performance include resin materials such as polycarbonate, polyvinylidene fluoride (PVDF), polyimide, and (PEEK) polyether ether ketone (PEEK). These resin materials have a Young's modulus exceeding 200 MPa, have a thickness of 100 to 150 μm, and satisfy the mechanical properties as a belt base material.

  The material used for the base layer is, for example, a resin material such as polyimide, polyester, polyetheretherketone, polyamide, polycarbonate, polyvinylidene fluoride (PVDF), polyfluoroethylene-ethylene copolymer (ETFE), and the like. Resin materials mainly composed of these materials are listed. Furthermore, it is also possible to use a material obtained by blending the aforementioned fat material and elastic material. Examples of the elastic material include polyurethane, chlorinated polyisoprene, NBR, chloropyrene rubber, EPDM, hydrogenated polybutadiene, butyl rubber, and silicone rubber. These may be used alone or in combination of two or more.

  Among these, it is preferable to contain a polyimide resin. The polyimide resin is formed by heating polyamic acid that is a precursor of the polyimide resin. The polyamic acid can be obtained by dissolving tetracarboxylic dianhydride or an approximately equimolar mixture of its derivative and diamine in an organic polar solvent and reacting in a solution state.

  Further, when a material in which carbon black is dispersed in a polybiphenyltetracarboxylic imide-based resin material such as Upilex S manufactured by Ube Industries, Ltd. is used as the base material of the intermediate transfer belt of the present invention, the Young's modulus of the material is used. Is 200 MPa or more, and a belt thickness of 70 to 100 μm can satisfy the mechanical properties as a belt substrate.

  In addition, in this invention, when using polyimide-type resin for a base material layer, it is preferable that the content rate of the polyimide-type resin in a base material layer is 51% or more.

  In the intermediate transfer belt of the present invention, as shown in FIGS. 1B and 1C, an intermediate layer can be provided between the base material layer and the surface layer. Examples of materials that can be used for the intermediate layer include polyamide resins. Specific examples of polyamide resins include N-methoxymethylated nylon (hereinafter abbreviated as “nylon 8”), nylon 12, and copolymer nylon. Can be mentioned. In the present invention, it is preferable to provide the intermediate layer 24 in order to improve the adhesion strength between the base material layer 23 and the surface layer 21 and to prevent these layers from being compatible with each other.

  As the solvent for the polyamide resin, a single solvent such as methanol or ethanol, or a mixed solvent obtained by mixing water, toluene or the like with these single solvents, 1-propanol, 2-propanol or the like is used. Among these, a combination of nylon 8 and a methanol / water mixed solvent (methanol / water = 3/1) is preferable.

  It is also possible to provide two intermediate layers as in the belt of FIG. 1 (c). A second intermediate layer 25 is provided adjacent to the polyamide resin intermediate layer 24, and an intermediate transfer belt is formed by multilayering. The strength of is increased. Resin materials that can be used for the second intermediate layer 25 include, in addition to the aforementioned polyimide resin and polyamide resin, vinylidene fluoride-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychloro Examples of the fluororesin include trifluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer.

In the intermediate transfer belt of the present invention, each layer may contain a conductive or semiconductive fine powder called a conductive filler. Usable conductive fillers include, for example, conductive powder such as carbon black, metal powder such as aluminum powder, nickel powder, stainless steel powder, c-ZnO, c-TiO ₂ , c-ZnO ₄ , c-SnO _2. And conductive metal oxides such as graphite, quaternary ammonium salts, phosphate esters, sulfonates, aliphatic polyhydric alcohols, aliphatic alcohol sulfate salts, and the like. Among these conductive fillers, carbon black such as ketjen black and acetylene black, c-TiO ₂ , and c-SnO ₂ that can provide good dispersion stability are preferable. In addition, the above “c−” means having conductivity. These conductive fillers may be used alone or in combination of two or more.

  In the present invention, by containing a conductive filler in the intermediate transfer belt, adjustment of resistivity and resistance variation in the intermediate transfer belt are suppressed, and further, the conductive resin fine particles contained in the surface layer are assisted to transfer voltage. It is expected to be able to more effectively suppress the occurrence of electric field concentration due to.

  The method for producing the intermediate transfer belt of the present invention is not particularly limited. For example, each layer forming material and its solvent are appropriately blended, and kneaded and stirred with a ball mill or the like to prepare each coating solution. . The concentration of the coating solution thus prepared is appropriately set according to the layer thickness. Next, each coating solution is accommodated in a tank, and on the other hand, a shaft made of metal such as aluminum or stainless steel is prepared, and this shaft is vertically placed in a tank in which the coating liquid for the base material layer is accommodated. Put in a standing condition and immerse. At this time, the immersion is repeated several times to form a coating film having a predetermined thickness, and then the shaft is pulled up from the coating solution. Subsequently, the same operation is repeated using the coating liquid of each layer to form a multilayer structure. Next, after drying and removing the solvent, heat treatment (for example, 60 to 150 ° C. × 60 minutes) is performed, and the shaft body is extracted to produce the endless intermediate transfer belt shown in FIG.

  In addition to this dipping method, an intermediate transfer belt can be produced by methods such as extrusion molding, spray coating, inflation, and blow molding.

  In particular, when a polyimide resin is used for the base material layer, for example, a polyamic acid solution obtained by polymerizing a tetracarboxylic dianhydride having a wholly aromatic skeleton and a diamine component is developed in an appropriate manner. Then, the development layer is dried and formed into a film, and the base material layer is obtained by a method of heat-treating the molded product to convert the polyamic acid into an imide. Then, an intermediate transfer belt is produced by sequentially dipping or spray-coating a coating solution constituting another layer on the base material layer.

  When forming a seamless intermediate transfer belt, for example, a method in which a polyamic acid solution is immersed in the outer peripheral surface of a cylindrical mold, a method in which it is applied to the inner peripheral surface, a method in which centrifugation is further performed, or a method in which a casting mold is filled Such as a method of expanding into a ring shape by an appropriate method such as, drying the formed layer into a bell-shaped shape, heat-treating the molded product to convert the polyamic acid into an imide, and recovering from the mold Can be carried out by an appropriate method according to the conventional method (JP-A 61-95361, JP-A 64-22514, JP-A 3-180309, etc.). In forming the seamless belt, an appropriate treatment such as mold release treatment or defoaming treatment can be performed.

  Next, physical properties of the intermediate transfer belt will be described.

<Surface resistivity>
The intermediate transfer belt of the present invention preferably has a surface resistivity of 1 × 10 ¹⁰ to 1 × 10 ¹⁴ Ω / □ on the belt surface. By setting the surface resistivity within the above range, local peeling discharge at the post nip (where the recording medium and the intermediate transfer belt peel at the secondary transfer portion) due to the action of the above-described aggregate of conductive particles. It is presumed that it helps to suppress this. In addition, it is presumed that the pre-nip portion (where the recording medium in the secondary transfer portion and the intermediate transfer belt start to contact) also assists in uniformizing the electric field strength. The influence on the graininess of the image quality that has been a concern is also improved.

  The surface resistivity on the surface of the intermediate transfer belt of the present invention can be measured based on JIS K6991 using a circular electrode (for example, “HR probe” of Hiresta IP manufactured by Mitsubishi Yuka Co., Ltd.). For the method of measuring the surface resistivity of the intermediate transfer belt of the present invention, reference can be made to, for example, the description in paragraph 0047 and FIG. 7 of JP-A-2001-242725.

<Volume resistivity>
The volume resistivity of the intermediate transfer belt of the present invention is preferably 1 × 10 ⁸ to 1 × 10 ¹² Ω · cm. By setting the volume resistivity within the above range, the electrostatic force between the toners is increased by an electrostatic force that acts to appropriately hold the charge of the unfixed toner image transferred from the intermediate transfer belt to the recording medium. It is estimated that the influence of the repulsive force and the fringe electric field near the image edge is suppressed. As a result, the toner image transferred onto the recording medium does not scatter, and stable image formation is expected without being affected by noise due to electrostatic repulsion. In this way, the intermediate transfer belt of the present invention does not need to worry about the occurrence of toner scattering in addition to preventing the occurrence of image defects.

  The volume resistivity can be measured based on JIS K6991 using a circular electrode (for example, HR probe of Hirester IP manufactured by Mitsubishi Yuka Co., Ltd.) in the same manner as the surface resistivity described above. For a specific method of measuring the volume resistivity, reference can be made to, for example, paragraph 0048 of JP-A-2001-242725 and the description of FIG.

<Surface energy>
The surface layer of the intermediate transfer belt of the present invention preferably has a surface energy of 30 mN / m or less, more preferably 15 to 25 mN / m. That is, when the surface energy is 30 mN / m or less, moderate adhesion between the intermediate transfer belt and the toner can be obtained, and factors that cause transfer rate or image quality degradation can be eliminated and good image formation can be achieved. Guessed.

  In general, the surface energy of a solid material is determined by using a liquid having a known surface energy, and measuring the contact angle that this liquid forms on the solid for which the surface energy is desired to be measured. (For example, see Kyowa Interface Chemical Co., Ltd. Surface Free Energy Analysis Software EG-11 instruction manual).

  The adhesion work between the solid and the liquid is expressed by the following relational expression.

W _SL = γ _L (1 + cos θ _SL )
W _SL : Adhesion work of solid sample / liquid sample
γ _L : surface free energy of liquid sample
θ _SL : Solid sample / liquid sample contact angle This adhesion work is considered to be decomposed into three components: a dispersion force component, a dipole force component, and a hydrogen bond component.

W _SL = W _SL ^d + W _SL ^p + W _SL ^h
W _SL ^d : Adhesion work (dispersion force component)
W _SL ^p : Adhesion work (dipole force component)
W _SL ^h : Adhesion work (hydrogen bonding component)
Similarly, the surface free energy of the solid sample is considered to be decomposed into three components.

γ _S = γ _S ^d + γ _S ^p + γ _S ^h
γ _S : surface free energy of solid sample
γ _S ^d : surface free energy of solid sample (dispersion force component)
γ _S ^p : surface free energy of solid sample (dipole force component)
γ _S ^h : surface free energy of solid sample (hydrogen bond component)
The same applies to liquids.

γ _i = γ _i ^d + γ _i ^p + γ _i ^h (i = 1, 2, 3)
γ _i : surface free energy of liquid sample i
γ _i ^p : surface free energy of liquid sample i (dispersion force component)
γ _i ^h : surface free energy of liquid sample i (dipole force component)
For example, when i = 1 is α-bromonaphthalene, i = 2 is methylene iodide, and i = 3 is water, each component of the surface free energy of each liquid sample is known.

  Further, regarding the bonding work, it is considered that the following geometric average relational expression is established.

  From these equations, the following extended Fowkes equation holds.

Since W _S1 , W _S2 , and W _S3 are calculated based on the contact angle assumption and the numerical values in the matrix are known numerical values, if the inverse calculation is performed based on this relational expression, (γ _S ^d ) ^{1 / 2} , (γ _S ^p ) ^1/2 , (γ _S ^h ) ^1/2, that is, γ _S ^d , γ _S ^p , γ _S ^h can be obtained. If you know this number,
γ _S = γ _S ^d + γ _S ^p + γ _S ^h
Further, the surface energy γ _{S of the} solid sample can be calculated.

  Next, an image forming apparatus that can use the intermediate transfer belt of the present invention will be described.

  Examples of the image forming apparatus capable of using the intermediate transfer belt of the present invention include a copying machine and a laser printer. In particular, an image forming apparatus capable of continuous printing of 5000 sheets or more is preferably used. In such an apparatus, an electric field is easily generated between the intermediate transfer belt and the recording medium because a large amount of printing is performed in a short time, but the generation of the electric field is suppressed and stable by the intermediate transfer belt of the present invention. Secondary transfer can be performed.

  An image forming apparatus used in the present invention includes an image carrier that forms an electrostatic latent image according to image information, a developing device that forms a toner image by developing the electrostatic latent image formed on the image carrier, and an image A primary transfer unit that transfers the toner image on the carrier onto the intermediate transfer belt; and a secondary transfer unit that transfers the toner image on the intermediate transfer belt onto a recording medium such as paper or an OHP sheet. By using the intermediate transfer belt of the present invention as the intermediate transfer belt, stable toner image formation can be performed without causing peeling discharge during secondary transfer.

  The image forming apparatus used in the present invention includes a monochrome image forming apparatus that forms an image with a single color toner, a color image forming apparatus that sequentially transfers a toner image on an image carrier onto an intermediate transfer belt, and a plurality of images for each color. Examples thereof include a tandem color image forming apparatus in which a carrier is arranged in series on an intermediate transfer belt.

  FIG. 2 is a cross-sectional configuration diagram showing an example of an image forming apparatus that can use the intermediate transfer belt of the present invention.

  This image forming apparatus is called a tandem color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, an endless belt-shaped intermediate transfer belt unit 7 as a transfer unit, and a recording member P. An endless belt-shaped sheet feeding and conveying means 21 and a belt type fixing device 24 as a fixing means. A document image reading device SC is disposed on the upper part of the main body A of the image forming apparatus.

  As one of the different color toner images formed on each photoconductor, an image forming unit 10Y that forms a yellow image includes a drum-shaped photoconductor 1Y as a first image carrier, and the photoconductor 1Y. A charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, a primary transfer roller 5Y as a primary transfer unit, and a cleaning unit 6Y are arranged around the periphery. In addition, an image forming unit 10M that forms a magenta image as another different color toner image is a drum-shaped photoconductor 1M as a first image carrier, and is arranged around the photoconductor 1M. The charging unit 2M, the exposure unit 3M, the developing unit 4M, the primary transfer roller 5M as the primary transfer unit, and the cleaning unit 6M are included. In addition, an image forming unit 10C that forms a cyan image as another different color toner image includes a drum-shaped photoconductor 1C as a first image carrier, and around the photoconductor 1C. A charging unit 2C, an exposure unit 3C, a developing unit 4C, a primary transfer roller 5C as a primary transfer unit, and a cleaning unit 6C are disposed. In addition, an image forming unit 10K that forms a black image as one of other different color toner images is disposed around a drum-shaped photoconductor 1K as a first image carrier and the photoconductor 1K. A charging unit 2K, an exposure unit 3K, a developing unit 4K, a primary transfer roller 5K as a primary transfer unit, and a cleaning unit 6K.

  The endless belt-shaped intermediate transfer belt unit 7 has an endless belt-shaped intermediate transfer belt 70 as a second image carrier having a semiconductive endless belt shape that is wound around a plurality of rollers and is rotatably supported.

  The images of the respective colors formed by the image forming units 10Y, 10M, 10C, and 10K are sequentially transferred and synthesized on the rotating endless belt-shaped intermediate transfer belt 70 by the primary transfer rollers 5Y, 5M, 5C, and 5K. A color image is formed. A recording member P such as paper as a recording medium accommodated in the paper feeding cassette 20 is fed by the paper feeding / conveying means 21, passes through a plurality of intermediate rollers 22 A, 22 B, 22 C, 22 D, and registration rollers 23, and is secondary. A color image is transferred onto the recording member P at a time by being conveyed to a secondary transfer roller 5A as a transfer means. The recording member P to which the color image has been transferred is fixed by the belt-type fixing device 24, is sandwiched between the discharge rollers 25, and is placed on the discharge tray 26 outside the apparatus.

  On the other hand, after the color image is transferred to the recording member P by the secondary transfer roller 5A, the residual toner is removed by the cleaning means 6A from the endless belt-shaped intermediate transfer belt 70 from which the recording member P is separated in curvature.

  During the image forming process, the primary transfer roller 5K is always in pressure contact with the photoreceptor 1K. The other primary transfer rollers 5Y, 5M, and 5C are in pressure contact with the corresponding photoreceptors 1Y, 1M, and 1C, respectively, only during color image formation.

  The secondary transfer roller 5A is in pressure contact with the endless belt-shaped intermediate transfer belt 70 only when the recording member P passes through the secondary transfer roller 5A and secondary transfer is performed.

  Further, the housing 8 can be pulled out from the apparatus main body A through the support rails 82L and 82R.

  The housing 8 includes image forming units 10Y, 10M, 10C, and 10K, and an endless belt-shaped intermediate transfer belt unit 7.

  The image forming units 10Y, 10M, 10C, and 10K are arranged in tandem in the vertical direction. An endless belt-shaped intermediate transfer belt unit 7 is disposed on the left side of the photoreceptors 1Y, 1M, 1C, and 1K in the figure. The endless belt-shaped intermediate transfer belt unit 7 includes an endless belt-shaped intermediate transfer belt 70 that can be rotated by winding rollers 71, 72, 73, 74, and 76, primary transfer rollers 5Y, 5M, 5C, and 5K, and a cleaning unit 6A. It consists of.

  The image forming units 10Y, 10M, 10C, and 10K and the endless belt-shaped intermediate transfer belt unit 7 are integrally pulled out from the main body A by the drawer operation of the housing 8.

  In this way, toner images are formed on the photoreceptors 1Y, 1M, 1C, and 1K by charging, exposure, and development, and the toner images of the respective colors are superimposed on the endless belt-like intermediate transfer belt 70, and are collectively applied to the recording member P The image is transferred and fixed by a belt-type fixing device 24 by pressing and heating. The photoreceptors 1Y, 1M, 1C, and 1K after transferring the toner image to the recording member P are cleaned with the cleaning device 6A to remove the toner remaining on the photoreceptor, and then the above-described charging, exposure, and development cycle. The next image formation is performed.

<recoding media>
The recording medium used in the present invention is a support for holding a toner image, and is usually called an image support, a transfer material or a transfer paper. Specific examples include various types of transfer materials such as plain paper from thin paper to thick paper, coated printing paper such as art paper and coated paper, commercially available Japanese paper and postcard paper, plastic films for OHP, and cloth. However, it is not limited to these.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

Production of Intermediate Transfer Belt Production of Intermediate Transfer Belt 1 (1) Production of Substrate Layer Consists of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA) Polyamide acid in an N-methyl-2-pyrrolidone (NMP) solution (Ube Industries, Ltd. Euvarnish S (solid content 18% by mass)), dried oxidized carbon black “SPECIAL BLACK4” (Degussa, pH 3.0, Volatile content: 14.0%) is added to 100 parts by mass of polyimide resin solids so as to be 23 parts by mass, and using a collision type disperser “GeanusPY” (manufactured by Seanas), at a pressure of 200 MPa, minimum area is allowed to collide after two split 1.4 mm ^2, by passing five times a path divided into two again, mixed, carbon black-containing poly base material layer To obtain a bromide acid solution.

  After applying the polyamic acid solution containing carbon black for the base material layer to the inner surface of the cylindrical mold to 0.5 mm via a dispenser and rotating it at 1500 rpm for 15 minutes to form a development layer having a uniform thickness, at 250 rpm While rotating, hot air at 60 ° C. was applied for 30 minutes from the outside of the mold, and then heated at 150 ° C. for 60 minutes. Thereafter, the temperature was raised to 360 ° C. at a rate of 2 ° C./min, and further heated at 360 ° C. for 30 minutes to remove the solvent, remove dehydrated ring-closing water, and complete the imide conversion reaction. Thereafter, the temperature was returned to room temperature, and it was peeled off from the mold to obtain a target endless belt-like base material layer. The thickness of this base material layer was 100 μm.

(2) Formation of intermediate layer 100 parts by mass of a copolymer resin having a composition ratio of 80% vinyl chloride, 15% vinyl acetate, and 5% maleic acid was dissolved in 400 parts by mass of cyclohexanone. Oxidized carbon black “SPECIAL BLACK4” (manufactured by Degussa, pH 3.0, volatile content: 14.0%) was added to this solution so as to be 10 parts by mass with respect to 100 parts by mass of the copolymer resin. After the addition, with a collision type disperser “GeanusPY” (manufactured by Sinaus), the pressure is 200 MPa, the minimum area is 1.4 mm ² , and then the collision is performed after two divisions. A copolymer resin solution containing carbon black for the base material layer was obtained.

  This solution was spray-coated on the base material layer so as to have a thickness of 10 μm to form an intermediate layer.

(3) Formation of surface layer (3-1) Preparation of coating liquid for surface layer formation Silicone resin “trade name X-40-2269” (manufactured by Shin-Etsu Chemical Co., Ltd.) 100 parts by mass Tetramethoxysilane 3 parts by mass n-hexane 400 parts by mass Carbon black “SPECIAL BLACK4” (Degussa)
23 parts by mass was blended and mixed and dispersed in a sand grinder for 20 minutes to prepare a coating solution having a viscosity of 1 × 10 ⁻² Pa · s.

(3-2) Surface layer formation The coating solution produced above was spray-coated on the intermediate layer produced above so as to have a thickness of 0.1 mm. Thereafter, it was dried in an oven at 120 ° C. for 1 hour.

  In this way, an “intermediate transfer belt 1” was produced.

Preparation of intermediate transfer belts 2 to 9 “Intermediate transfer belt” is similarly performed except that the mixing / dispersing time of the conductive particles, binder resin and sand grinder used in the preparation of “intermediate transfer belt 1” is changed as shown in Table 1. Belts 2-9 "were produced.

Production of Intermediate Transfer Belt 10 An “intermediate transfer belt 10” was produced in the same manner except that the conductive particles used in the production of the “intermediate transfer belt 1” were not added.

  Table 2 shows the average particle diameter and surface energy of the conductive particle aggregates of the “intermediate transfer belts 1 to 10” produced above.

<Evaluation>
The produced “intermediate transfer belts 1 to 10” were mounted on the image forming apparatus shown in FIG. 2, and 10,000 sheets were continuously printed. For image formation, a two-component developer made of toner having a median particle diameter (D ₅₀ ) of 6.0 μm based on the number basis was used.

  The printing environment was low temperature and low humidity (10 ° C., 20% RH) and high temperature and high humidity (33 ° C., 80% RH).

As the recording medium, high-quality paper (64 g / m ² ) of A4 size was used.

  A printed document is an original image in which a character image (3 points, 5 points) with a pixel rate of 7%, a color human face image (dot image including halftone), a solid white image, and a solid image are divided into quarters. (A4 version) was used.

  Five samples for evaluation were prepared for 1000 sheets, 5000 sheets, and 10,000 sheets during continuous printing.

  The evaluation was performed based on image defects (white spots in the solid image portion, occurrence of voids in the character image portion, toner scattering in the character portion, transfer rate) generated in the secondary transfer. In the evaluation, ◎ and ○ are acceptable and × is unacceptable.

<White area in solid image area>
The evaluation of white spots was determined by the number of white spots with a major axis of 0.4 mm or more per A4 plate in a solid image portion printed at high temperature and high humidity. Incidentally, the hollow major axis was measured with a microscope with a video printer.

Evaluation Criteria A: White spot frequency of 0.4 mm or more: Good when all print images are 3 or less ○: White spot frequency of 0.4 mm or more: 4 or more, 19 or less occur 1 or more ×: 0. White spot frequency of 4 mm or more: One or more of 20 or more is generated, and there is a problem in practical use.

<Cut out of text image>
The character image printed at high temperature and high humidity was magnified and observed with a magnifying glass, and it was visually evaluated whether or not the character image was hollowed out.

Evaluation Criteria A: No void occurred until the 10,000th print. ○: No void occurred until the 5000th print was completed. X: Remarkable void occurred in the 1000th print.

<Toner scattering in text>
The character image printed at low temperature and low humidity was magnified and observed with a magnifying glass, and the state of toner scattering around the character portion was visually evaluated.

Evaluation criteria A: Toner scattering is small until the end of printing 10,000 sheets ○: Toner scattering is small until the end of printing 50 million sheets ×: Toner scattering increases in printing less than 1,000 sheets, which is a practical problem.

<Transfer rate>
After 10,000 sheets were printed, a solid image (20 mm × 50 mm) having a pixel density of 1.30 was formed at low temperature and low humidity.

Transfer rate (%) = (mass of toner transferred onto transfer material / mass of toner remaining without being transferred onto intermediate transfer belt) × 100
Evaluation Criteria A: Good when the transfer rate is 90% or more B: A level at which the transfer rate is 80% or more and no practical problem ×: A level at which the transfer rate is less than 80% causes a practical problem.

  Table 3 shows the evaluation results.

  As is apparent from the results in Table 3, when the intermediate transfer belt of the present invention is used, white areas in the image area, character areas in the image area, character areas in the image area, even if 5000 or more prints are continuously produced. No image defects such as toner scattering were observed, and the transfer rate was good. On the other hand, in the comparative example, there was a problem in any of the evaluation items, and the result was clearly different from the intermediate transfer belt of the present invention.

FIG. 3 is a schematic diagram illustrating an example of an intermediate transfer belt according to the present invention. 1 is a cross-sectional configuration diagram illustrating an example of an image forming apparatus that can use an intermediate transfer belt of the present invention.

Explanation of symbols

2 Intermediate transfer belt 21 Surface layer 22 Aggregate of conductive particles 23 Base material layers 24 and 25 Intermediate layer

Claims (2)

An intermediate transfer belt having at least a surface layer on a substrate,
The intermediate transfer belt, wherein the surface layer contains an aggregate of conductive particles having an average particle diameter of 0.5 to 25 µm. The intermediate transfer belt according to claim 1, wherein the surface layer has a surface energy of 30 mN / m or less.

Images