JP2016138917A - Intermediate transfer belt and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an intermediate transfer belt that has excellent transferability onto rugged paper and has high sensitivity to an optical sensor, and an image forming apparatus including the same.SOLUTION: An intermediate transfer belt of the present invention is an intermediate transfer belt in an electrophotographic image forming apparatus including means that detects the amount of toner adhered onto the intermediate transfer belt, and has an elastic layer and a surface layer containing polyimide resin formed on a substrate in this order; the polyimide resin constituting the surface layer can dissolve in a low-boiling point solvent having a boiling point of less than 120°C.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrophotographic image forming apparatus and an intermediate transfer belt provided therein.

  In an electrophotographic image forming apparatus, for example, a latent image formed on an image carrier (photosensitive member) is developed with toner, and the resulting toner image is transferred to an endless belt-shaped transfer member (hereinafter referred to as “intermediate transfer”). The toner image on the intermediate transfer belt is transferred onto an image support such as paper by temporarily holding it on a belt.

As a means of further improving image quality in an image forming apparatus using such an intermediate transfer belt, a transfer layer is formed by forming an elastic layer with an elastic body such as rubber on a base material and improving adhesion to uneven paper. It has been proposed to use an intermediate transfer belt with improved toner.
However, the intermediate transfer belt from which the elastic layer is exposed has a problem that since the surface is made of rubber or the like, the wear resistance is low and the surface is scraped during use. Therefore, an additional surface layer is formed on the elastic layer. (See Patent Document 1).

As the surface layer, for example, a cured film obtained by curing an acrylic monomer or the like by a polymerization reaction is used.
However, since the followability of the surface layer to the elastic layer is low, there is a problem that the effect of improving the transferability to the uneven paper by the elastic layer cannot be obtained sufficiently. Or, even if the surface layer follows the elastic layer, there is a problem that damage such as cracking of the surface layer occurs.

  As means for solving such a problem, an additive such as a filler is added to the surface layer. According to the surface layer to which the filler is added, the followability to the elastic layer can be obtained while the wear resistance is obtained.

  However, in an image forming apparatus including an optical sensor such as an IDC sensor (Image Density Control Sensor) that detects the amount of toner attached to the intermediate transfer belt, the surface layer to which the filler is added causes the light from the optical sensor to be absorbed by the filler. As a result, it is scattered, resulting in a low sensitivity to the optical sensor.

JP 2010-217777 A

  The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an intermediate transfer belt having high sensitivity to an optical sensor while having excellent transferability to uneven paper, and an intermediate transfer belt thereof. An image forming apparatus is provided.

The intermediate transfer belt of the present invention is an intermediate transfer belt in an electrophotographic image forming apparatus having means for detecting the amount of toner adhesion on the intermediate transfer belt by an optical sensor,
A surface layer containing an elastic layer and a polyimide resin is formed on the substrate in this order,
The polyimide resin constituting the surface layer can be dissolved in a low boiling point solvent having a boiling point of less than 120 ° C.

  In the intermediate transfer belt of the present invention, the polyimide resin constituting the surface layer preferably contains a structural unit having a fluorine atom and / or a structural unit having an alicyclic structure.

  In the intermediate transfer belt of the present invention, the surface layer preferably has a total light transmittance of 80% or more when the thickness is 10 μm.

An image forming apparatus of the present invention is an electrophotographic image forming apparatus having means for detecting the amount of toner adhesion on an intermediate transfer belt by an optical sensor,
As the intermediate transfer belt, the above-described intermediate transfer belt is provided.

  In the intermediate transfer belt of the present invention, the polyimide resin constituting the surface layer can be dissolved in a low boiling point solvent. As a result, high sensitivity to the optical sensor can be obtained while the intermediate transfer belt has excellent transferability to uneven paper.

  Since the image forming apparatus of the present invention includes the above-described intermediate transfer belt, high sensitivity can be obtained with respect to the optical sensor while having excellent transferability to uneven paper.

FIG. 3 is an explanatory cross-sectional view illustrating an example of a configuration of an intermediate transfer belt of the present invention. FIG. 3 is an explanatory cross-sectional view illustrating an example of a configuration of an image forming apparatus including the intermediate transfer belt of the present invention.

  Hereinafter, the present invention will be described in detail.

[Intermediate transfer belt]
The intermediate transfer belt of the present invention is, for example, an endless belt-like one provided in an electrophotographic image forming apparatus. Specifically, as shown in FIG. 1, an elastic layer 3 is provided on a substrate 2. The surface layer 4 is formed on the elastic layer 3.

[Substrate 2]
The substrate 2 constituting the intermediate transfer belt of the present invention has, for example, an endless belt shape, and may have a single layer configuration or a multi-layer configuration of two or more layers.
Although it does not specifically limit as a constituent material of the base material 2, For example, high intensity | strength and high, such as a polyimide resin (PI), a polyamide-imide resin (PAI), a polyphenylene sulfide resin (PPS), a polyether ether ketone resin (PEEK), etc. It is preferable to use one having durability. Moreover, it is preferable that the base material 2 has conductivity by dispersing a conductive agent in the resin as described above.
As the conductive agent, carbon black, carbon nanotube, or the like can be used.

  The layer thickness of the substrate 2 is preferably 50 to 250 μm in consideration of mechanical strength, image quality, and the like.

[Elastic layer 3]
The elastic layer 3 constituting the intermediate transfer belt of the present invention is made of an elastic body, and as its constituent material, for example, rubber, elastomer, resin or the like can be used, and in particular, an elastomer having a crosslinked structure is used. preferable. Moreover, it is preferable that what has thermoplasticity is not used.
Preferred examples of the rubber include chloroprene rubber and nitrile butadiene rubber from the viewpoints of hardness and durability.
As the elastic body forming the elastic layer 3, one having a heat resistant temperature of about 100 to 150 ° C. can be used.
You may use these individually by 1 type or in combination of 2 or more types.

  The layer thickness of the elastic layer 3 is preferably 200 to 500 μm in consideration of mechanical strength, image quality, and the like.

[Surface layer 4]
The surface layer 4 constituting the intermediate transfer belt of the present invention contains a polyimide resin, and the polyimide resin constituting the surface layer 4 may be dissolved in a low boiling point solvent having a boiling point of less than 120 ° C. It is possible to do it. The polyimide resin constituting the surface layer 4 is preferably one that can be dissolved in a low boiling point solvent having a boiling point of less than 80 ° C.
Since the surface layer 4 is made of a polyimide resin, basically, high wear resistance is obtained for the intermediate transfer belt, and followability with respect to the elastic layer 3 is obtained, so that transfer onto uneven paper is obtained. .
Moreover, when the polyimide resin which comprises the surface layer 4 can be melt | dissolved in a low boiling-point solvent, the surface layer 4 can be formed, without passing through the process heated at high temperature.
A general polyimide resin can only be dissolved in a high-boiling aprotic polar solvent. When the surface layer is formed using such a polyimide resin solution, a process of heating to 200 ° C. or higher is required to evaporate the aprotic polar solvent in the coating film applied on the elastic layer. When heated to 200 ° C. or higher, the elastic body constituting the elastic layer deteriorates and hardens.

A polyimide resin consists of a diamine compound and a carboxylic acid anhydride. The polyimide resin constituting the surface layer 4 according to the present invention is a polyimide resin containing a structural unit having a fluorine atom and / or a structural unit having an alicyclic structure (hereinafter referred to as “polyimide resin having a specific structural unit”). It is preferable that
In the present invention, “containing a structural unit having a fluorine atom and / or a structural unit having an alicyclic structure” means only a structural unit having an alicyclic structure containing only a structural unit having a fluorine atom. One of containing a structural unit having both a fluorine atom and an alicyclic structure, containing both a structural unit having a fluorine atom and a structural unit having an alicyclic structure.

  The structural unit having a fluorine atom is a structural unit derived from a diamine compound or a structural unit derived from a carboxylic acid anhydride, and specifically obtained from a diamine compound. Examples of the structural unit include those represented by the following formula (DaF-1), and examples of the structural unit obtained from the carboxylic acid anhydride include those represented by the following formula (CF-1). Can be mentioned.

  The structural unit having an alicyclic structure is a structural unit obtained from a carboxylic acid anhydride or a structural unit obtained from a diamine compound, and specifically, derived from a carboxylic acid anhydride. Examples of the structural unit obtained in this way include those represented by the following formulas (CA-1) to (CA-2).

〔式（ＣＡ−１）において、Ｒはアルキル基を示す。〕

[In the formula (CA-1), R represents an alkyl group. ]

  The structural unit having both a fluorine atom and an alicyclic structure is a structural unit derived from a diamine compound, or a structural unit derived from a carboxylic acid anhydride. Examples of the structural unit obtained from the above can include those represented by the following formulas (DaFA-1) to (DaFA-2).

The solubility of the polyimide resin having a specific structural unit is improved by its molecular structure, and as a result, it can be dissolved in a low boiling point solvent having a boiling point of less than 120 ° C.
In addition, a polyimide resin having a specific structural unit has a molecular structure having a higher electronegativity due to fluorine atoms or a reduced conjugated structure in the molecule as compared with a general polyimide resin. Colors such as brown color resulting from conjugation between the structure and the benzene ring are suppressed, and the transparency is high. Therefore, according to the intermediate transfer belt having the surface layer 4, absorption of light in the surface layer 4 is suppressed, and stable reflected light can be obtained with respect to the light from the optical sensor. Sensitivity can be increased. As a result, the amount of light used for detecting the toner adhesion amount on the intermediate transfer belt by the optical sensor can be reduced, and as a result, the image forming apparatus can be downsized.

The surface layer 4 preferably has a transparency with a total light transmittance of 80% or more, for example, when the thickness is 10 μm, and more preferably 90% or more. However, it is practically difficult to form a surface layer having a total light transmittance of 100% when the thickness is 10 μm.
The total light transmittance is measured in accordance with JIS K 7375: 2008.

The surface roughness Rz of the surface layer 4 is preferably 0.5 μm or less.
Further, the waviness Wt of the surface layer 4 is preferably 0.7 μm or less.

  The layer thickness of the surface layer 4 is preferably 0.5 to 10 μm, more preferably 0.5 to 5 μm in consideration of mechanical strength, image quality, and the like.

[Method of manufacturing intermediate transfer belt]
The intermediate transfer belt of the present invention is formed, for example, by applying an elastic layer forming coating solution for forming the elastic layer 3 on the base material 2 to form a coating film, and then drying the coating film. The surface layer 4 is formed by applying a surface layer forming coating solution for forming the surface layer 4 on the elastic layer 3 to form a coating film and drying the coating film. Thus, it can be manufactured.

  In the case of using a polyimide resin as a constituent material, for example, a method of immersing the polyamic acid solution in the outer peripheral surface of the cylindrical mold, a method of applying the inner peripheral surface, or further centrifuging the base material 2 Developed in a ring shape by an appropriate method such as a method or a method of filling a casting mold, the formed layer is dried and formed into a bell-shaped shape, and the molded product is heat treated to immobilize the polyamic acid. Can be carried out by an appropriate method according to the prior art, such as a method of converting to a mold and recovering from a mold (Japanese Patent Laid-Open Nos. 61-95361, 64-22514, 3-180309, etc.) ). In manufacturing the endless belt-like substrate, an appropriate treatment such as mold release treatment or defoaming treatment can be performed.

Examples of the method for preparing the elastic layer forming coating solution include a method of adding a constituent material for forming the elastic layer to the solvent at a solid content concentration of 20 to 30% by mass.
Examples of the coating method of the elastic layer forming coating liquid include dipping coating.

  Examples of the method for preparing the coating solution for forming the surface layer include a method in which a polyimide resin having a specific structural unit for forming the surface layer 4 is added to the low boiling point solvent at a ratio of 3 to 30% by mass.

  Examples of the diamine compound for synthesizing a polyimide resin having a specific structural unit include those represented by the following formulas (Da1) to (Da3). Moreover, when using the carboxylic acid anhydride for synthesize | combining the polyimide resin which has the below-mentioned specific structural unit as carboxylic acid anhydride, a general diamine compound can also be used.

  Examples of the carboxylic acid anhydride for synthesizing the polyimide resin having the specific structural unit include those represented by the following formulas (C1) to (C3). Moreover, when using the diamine compound for synthesize | combining the polyimide resin which has a below-mentioned specific structural unit as a diamine compound, a general carboxylic acid anhydride can also be used.

〔式（Ｃ２）において、Ｒはアルキル基を示す。〕

[In the formula (C2), R represents an alkyl group. ]

  As the low boiling point solvent, any solvent may be used as long as the boiling point is less than 120 ° C. and the polyimide resin can be dissolved, and the boiling point is a temperature at which the elastic body forming the elastic layer 3 does not deteriorate. Specifically, for example, tetrahydrofuran (THF) (boiling point 66 ° C.), methyl ethyl ketone (MEK) (boiling point 79.64 ° C.), acetone (boiling point 56 ° C.), methyl isobutyl ketone (MIBK) (boiling point 116.2 ° C.), etc. Among these, it is preferable to use tetrahydrofuran because of its high solubility.

  Examples of the coating method of the surface layer forming coating liquid include dipping coating.

  The drying method of the coating film related to the surface layer 4 can be appropriately selected depending on the kind of the low boiling point solvent, the layer thickness of the surface layer to be formed, etc., but the drying temperature is equal to or higher than the boiling point of the low boiling point solvent, The temperature may be any temperature that does not cause deterioration of the elastic body forming the elastic layer 3. For example, the temperature is preferably 40 to 100 ° C., more preferably about 70 ° C. The drying time is preferably, for example, 1 to 5 minutes, and more preferably about 3 minutes.

[Image forming apparatus]
The intermediate transfer belt as described above is used in various known electrophotographic image forming apparatuses such as a monochrome image forming apparatus and a full color image forming apparatus.

  FIG. 2 is an explanatory sectional view showing an example of the configuration of an image forming apparatus provided with the intermediate transfer belt of the present invention.

  This image forming apparatus includes a plurality of sets of image forming units 20Y, 20M, 20C, and 20Bk and an intermediate transfer that transfers toner images formed in these image forming units 20Y, 20M, 20C, and 20Bk onto an image support P. And a fixing device 30 that performs a fixing process to obtain a toner layer by fixing the toner image by heating and pressing the image support P.

  The image forming unit 20Y forms a yellow toner image, the image forming unit 20M forms a magenta toner image, and the image forming unit 20C forms a cyan toner image. At 20 Bk, a black toner image is formed.

  The image forming units 20Y, 20M, 20C, and 20Bk give a uniform potential to the photoreceptors 11Y, 11M, 11C, and 11Bk that are electrostatic latent image carriers and the surfaces of the photoreceptors 11Y, 11M, 11C, and 11Bk. Charging means 23Y, 23M, 23C, 23Bk; exposure means 22Y, 22M, 22C, 22Bk for forming electrostatic latent images of a desired shape on the uniformly charged photoreceptors 11Y, 11M, 11C, 11Bk; Developing means 21Y, 21M, 21C, and 21Bk that convey the toners of the respective colors onto the photoreceptors 11Y, 11M, 11C, and 11Bk to visualize the electrostatic latent images, and the photoreceptors 11Y, 11M, 11C, and 11Bk after the primary transfer. Cleaning means 25Y, 25M, 25C, 25Bk for collecting the residual toner remaining on the upper side are provided.

The intermediate transfer unit 10 performs primary transfer as a primary transfer unit that transfers a toner image formed by the intermediate transfer belt 16 of the present invention that circulates and the image forming units 20Y, 20M, 20C, and 20Bk to the intermediate transfer belt 16. A secondary transfer unit that transfers the toner images transferred onto the intermediate transfer belt 16 by the rollers 13Y, 13M, 13C, and 13Bk and the primary transfer rollers 13Y, 13M, 13C, and 13Bk onto the image support P. The image forming apparatus includes a transfer roller 13 </ b> A and a cleaning unit 12 that collects residual toner remaining on the intermediate transfer belt 16.
The intermediate transfer belt 16 is an endless belt that is stretched by a plurality of support rollers 16a to 16d and is rotatably supported.

The intermediate transfer unit 10 is provided with toner density detection means (not shown) including an IDC sensor that is an optical sensor using infrared light and detects the amount of toner attached on the intermediate transfer belt 16.
Specifically, the IDC sensors are provided on the near side and the far side in the direction perpendicular to the paper surface on the downstream side of the primary transfer roller 13Bk and the upstream side of the secondary transfer roller 13A, respectively. The amount of toner adhesion on the part and the back part is detected.

The respective color toner images formed by the image forming units 20Y, 20M, 20C, and 20Bk are sequentially transferred and superimposed on the rotating endless intermediate transfer belt 16 by the primary transfer rollers 13Y, 13M, 13C, and 13Bk. A color image is formed. The image support P accommodated in the paper feed cassette 41 is fed by the paper feed / conveyance means 42, passes through a plurality of intermediate rollers 44a to 44d, and a registration roller 46, and then a secondary transfer roller 13A as a secondary transfer means. The color images are transferred onto the image support P at once.
The image support P to which the color image has been transferred is subjected to fixing processing by a fixing device 30 equipped with a heat roller fixing device, and is sandwiched between paper discharge rollers and placed on a paper discharge tray outside the apparatus.
On the other hand, after the color image is transferred to the image support P by the secondary transfer roller 13A, the residual toner is removed by the cleaning means 12 from the intermediate transfer belt 16 from which the curvature of the image support P is separated.

(Developer)
The developer used in such an image forming apparatus may be a one-component developer using magnetic or non-magnetic toner, or may be a two-component developer in which a toner and a carrier are mixed.
The toner constituting the developer is not particularly limited, and various known toners can be used. For example, a so-called polymerized toner obtained by a polymerization method having a volume-based median diameter of 3 to 9 μm can be used. It is preferable to use it. By using the polymerized toner, a high resolution and a stable image density can be obtained in the formed image, and the occurrence of image fog is extremely suppressed.

  The carrier in the case of constituting the two-component developer is not particularly limited, and various known ones can be used. For example, the volume-based median diameter is 30 to 65 μm, and the magnetization is 20 to 70 emu. A ferrite carrier comprising / g of magnetic particles is preferred. When a carrier with a volume-based median diameter of less than 30 μm is used, carrier adhesion may occur and a white-out image may be generated. When a carrier with a volume-based median diameter of greater than 65 μm is used, There may occur a case where an image having a uniform image density is not formed.

(Image support)
Examples of the image support P used in such an image forming apparatus include plain paper from thin paper to thick paper, high-quality paper, coated printing paper such as art paper or coated paper, and commercially available Japanese paper or postcard paper. Various types of paper such as uneven paper such as resack paper, plastic films for OHP, and cloth can be used, but the invention is not limited to these.
In particular, since this image forming apparatus includes the intermediate transfer belt of the present invention, excellent transferability to uneven paper can be obtained even when uneven paper is used as the image support P.

  As mentioned above, although embodiment of this invention was described concretely, embodiment of this invention is not limited to said example, A various change can be added.

  Hereinafter, specific examples of the present invention will be described, but the present invention is not limited thereto.

[Example 1: Production Example 1 of Intermediate Transfer Belt]
(1) Production of base material An endless belt-like base material [1] having a thickness of 60 μm made of a polyimide resin containing a conductive agent was prepared.

(2) Formation of an elastic layer Carbon black is kneaded with chloroprene rubber, and the compound is dissolved and dispersed in a solvent: toluene so that the solid content concentration is 20% by mass, thereby forming an elastic layer forming coating solution. [1] is prepared, and the elastic layer forming coating solution [1] is applied onto the above endless belt-shaped substrate [1] by dipping coating to form an elastic layer [1] having a dry film thickness of 200 μm. Formed.

(3) Formation of surface layer Polyimide resin [1] from carboxylic anhydride: 4,4 ′-(hexafluoroisopropylidene) diphthalic anhydride and diamine compound: 2,2′-bis (trifluoromethyl) benzidine Was synthesized.
Low boiling solvent: In tetrahydrofuran (THF), a polyimide resin [1] is added and dissolved so as to have a proportion of 5% by mass to prepare a surface layer forming coating solution [1]. [1] The surface layer-forming coating solution [1] is applied onto the surface layer by dipping coating to form a coating film, which is dried at 70 ° C., whereby the surface layer [1] having a dry film thickness of 2 μm Thus, an intermediate transfer belt [1] was produced.

[Examples 2 and 3, Comparative Example 1: Production Examples 2 to 4 of Intermediate Transfer Belt]
In the step of forming the surface layer in Production Example 1 of the intermediate transfer belt, polyimide resins [2] to [4] were synthesized according to the formulation in Table 1, and the intermediate transfer belt [ 2] to [4] were produced.

[Example 5 of production of intermediate transfer belt]
An intermediate transfer belt [5] was produced in the same manner as in the surface layer forming step of Production Example 4 of the intermediate transfer belt, except that spray coating was performed as the coating method for the surface layer forming coating solution [1]. .

(1) Evaluation of transferability to concavo-convex paper An evaluation machine in which the above intermediate transfer belts [1] to [5] were attached to an image forming apparatus “bizhub PRESS C1100” (manufactured by Konica Minolta) was prepared. And a toner image T1 of the toner image on the intermediate transfer belt before the blue solid image is output and transferred to the paper, and the residual toner amount T2 on the intermediate transfer belt after being transferred to the paper. And the transfer rate was calculated by (T2 / T1) × 100. The results are shown in Table 1. In Table 1, “A” indicates a transfer rate of 95% or more, “B” indicates a transfer rate of 93% or more and less than 95%, “C” indicates a transfer rate of 90% or more and less than 93%, and “D” indicates a transfer rate. Less than 90%. In the present invention, a case where the transfer rate is 93% or more, that is, a case where the transfer rate is “A” or “B” is regarded as acceptable.

(2) Total light transmittance The total light transmittance of the intermediate transfer belts [1] to [5] was measured. The results are shown in Table 1. In the present invention, the case where the total light transmittance is 80% or more is determined to be acceptable as the sensitivity to the IDC sensor is high.

2 Substrate 3 Elastic layer 4 Surface layer 10 Intermediate transfer portions 11Y, 11M, 11C, 11Bk Photoconductor 12 Cleaning means 13Y, 13M, 13C, 13Bk Primary transfer roller 13A Secondary transfer roller 16 Intermediate transfer belts 16a to 16d Support roller 20Y , 20M, 20C, 20Bk Image forming units 21Y, 21M, 21C, 21Bk Developing means 22Y, 22M, 22C, 22Bk Exposure means 23Y, 23M, 23C, 23Bk Charging means 25Y, 25M, 25C, 25Bk Cleaning means 30 Fixing device 41 Supply Paper cassette 42 Paper feed / conveying means 44a, 44b, 44c, 44d Paper feed roller 46 Registration roller N1 Fixing nip P Image support

Claims (4)

The intermediate transfer belt in an electrophotographic image forming apparatus having means for detecting the amount of toner attached on the intermediate transfer belt by an optical sensor,
A surface layer containing an elastic layer and a polyimide resin is formed on the substrate in this order,
An intermediate transfer belt characterized in that the polyimide resin constituting the surface layer can be dissolved in a low boiling point solvent having a boiling point of less than 120 ° C.   2. The intermediate transfer belt according to claim 1, wherein the polyimide resin constituting the surface layer contains a structural unit having a fluorine atom and / or a structural unit having an alicyclic structure.   The intermediate transfer belt according to claim 1, wherein the surface layer has a total light transmittance of 80% or more when the thickness is 10 μm. An electrophotographic image forming apparatus having means for detecting the toner adhesion amount on the intermediate transfer belt by an optical sensor,
An image forming apparatus comprising the intermediate transfer belt according to claim 1 as an intermediate transfer belt.

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