JP2007065546A - Intermediate transfer belt - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an intermediate transfer belt free from the occurrence of memory resulting from the intermediate transfer belt, capable of transferring a toner image formed on the intermediate transfer belt to a transfer medium at a high transfer rate, and having such an excellent effect that a high-quality toner image such as a solid image free from void, a character image free from central blanking and a character portion free from toner scattering is formed. <P>SOLUTION: In the intermediate transfer belt 2 having multilayer structure containing conductive substances 101 and 102, the maximum surface potential (V<SB>max</SB>) is ≥100 V when the intermediate transfer belt is electrified, and a ratio (V<SB>max</SB>)/(V<SB>2.0</SB>) of the maximum surface potential (V<SB>max</SB>) to surface potential (V<SB>2.0</SB>) obtained two seconds after attaining the maximum surface potential satisfies an expression (1): (V<SB>max</SB>)/(V<SB>2.0</SB>)≥2.0. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an intermediate transfer belt.

  In recent years, the importance of image forming methods using an intermediate transfer belt has increased in the trend of colorization, high speed, and compactness.

  As shown in FIG. 1, there are two processes for transferring the toner image formed on the photosensitive member once onto the intermediate transfer belt and then transferring it onto the recording medium. Specifically, the toner image is formed on the photosensitive member. The process of transferring the four color toner images collectively to the intermediate transfer belt (for example, a four-cycle process), and the process of sequentially transferring the toner image formed on the photosensitive member to the intermediate transfer belt (for example, a tandem process) Is mainly used. In the future, it is estimated that the process of sequentially transferring the toner image formed on the photosensitive member to the intermediate transfer belt will be the main process because it is suitable for high speed and compactness.

  FIG. 1 is a diagram illustrating a transfer process.

  In FIG. 1, 1 is a photosensitive member, 2 is a developing unit, 3 is an intermediate transfer belt, 4 is a transfer medium, 11 is a primary transfer unit, and 12 is a secondary transfer unit.

  FIG. 1-a shows a 4-cycle process, and FIG. 1-b shows a tandem process.

  An important physical property point of the intermediate transfer belt required for this tandem type process is that an appropriate electric field is applied to the toner when the toner image on the first (first) photoreceptor is transferred (primary transfer) to the intermediate transfer belt. On the other hand, the charge on the surface of the intermediate transfer belt needs to be neutralized so that it does not receive the memory (history) of the first toner image when it reaches the next (second) photoconductor. .

  However, in the recent trend of speeding up and downsizing of the image forming apparatus, an increase in the linear speed of the intermediate transfer belt and the distance between the first (first) photoreceptor and the second (second) photoreceptor are increased. Due to the shortening, the tendency for the passing time of the intermediate transfer belt between the first photosensitive member and the second photosensitive member to be short is remarkable.

  In the conventional intermediate transfer belt, in order to cope with this, the volume resistance of the intermediate transfer belt has been lowered to reduce the surface potential of the intermediate transfer belt from the first transfer to the next transfer. This is because the volume resistance of the intermediate transfer belt is high, and if the surface potential does not drop sufficiently from the first transfer to the next transfer, the previous toner image remains on the intermediate transfer belt as a memory.

  However, when the volume resistance of the intermediate transfer belt is lowered, charge leakage occurs when a high voltage is applied during transfer, or charge is injected into the toner, and the transfer electric field is not applied to the toner, and transfer defects are likely to occur. .

  As described above, in the intermediate transfer belt used in the tandem process suitable for high speed and compactness, it is an important issue to achieve both the memory and the transferability.

For the purpose of improving memory and transferability,
Examination of volume resistance value of intermediate transfer belt (for example, refer to Patent Document 1),
Study using carbon black, ion conductive material, and metal oxide as the conductive material of the intermediate transfer belt (for example, see Patent Documents 2, 3, and 4),
Study to improve the leak resistance by adjusting the resistance value by making the layer structure of the intermediate transfer belt into a plurality of layers (for example, see Patent Document 5).
Studies have been made to include both an electronic conductive material and an ionic conductive material as conductive materials for the intermediate transfer belt (see, for example, Patent Document 6).
JP 2002-148895 A JP 2001-133999 A JP-A-8-110711 JP 2004-302094 A JP 2002-137317 A JP 2001-166605 A

  However, in the examination of the intermediate transfer belt described above, when used in an image forming method employing a high-speed and compact tandem type process, it was not possible to satisfy both memory and transferability.

  In addition, all of the conventional single-layer belts have a residual potential value approximately defined by the relationship between the belt volume resistance and the electrostatic capacity in the belt film thickness direction, and the distance between the primary transfer processes. In the case of a process with a short and high linear velocity, the memory and transferability could not be satisfied.

  The present invention has been made in view of the above problems, and even in an image forming method employing a high-speed and compact tandem type process, there is no generation of memory due to the intermediate transfer belt, and a toner image formed on the intermediate transfer belt can be obtained. An object of the present invention is to provide an intermediate transfer belt that can be transferred to a transfer medium at a high transfer rate and can form a high-quality toner image without white spots on a solid image, voids in a character image, or toner scattering on a character part. To do.

  The present invention is achieved by adopting the following configuration.

(1)
In an intermediate transfer belt having a multilayer structure containing a conductive material, when the intermediate transfer belt is charged,
The maximum surface potential (V _max ) is 100V or more,
Intermediate transfer characterized in that the ratio (V _max ) / (V _2.0 ) between the maximum surface potential (V _max ) and the surface potential (V _2.0 ) 2 seconds after the maximum surface potential satisfies the following formula (1) belt.

Formula (1)
(V _max ) / (V _2.0 ) ≧ 2.0
(2)
The intermediate transfer belt according to (1), wherein the conductive material is different for each layer of the multilayer structure.

(3)
The intermediate transfer belt according to (1) or (2), wherein the conductive material includes at least an ionic conductive material and an electronic conductive material.

(4)
The multilayer structure has at least a layer containing an ion conductive material and a layer containing an electron conductive material, wherein any one of the above (1) to (3) is characterized. Intermediate transfer belt.

  The intermediate transfer belt of the present invention does not generate memory due to the intermediate transfer belt, and can transfer the toner image formed on the intermediate transfer belt to the transfer medium at a high transfer rate. It has an excellent effect of being able to form a high-quality toner image with no voids and no toner scattering in the character portion.

  The present inventor has no occurrence of memory due to the intermediate transfer belt, and can transfer the toner image formed on the intermediate transfer belt to the transfer medium at a high transfer rate. An intermediate transfer belt capable of forming a high-quality toner image free from toner scattering in the character portion was studied.

As a result of various investigations, the present inventor has an intermediate transfer belt of a multilayer structure containing an electrically conductive material, at its highest surface potential when charged intermediate transfer belt (V _max) is more than 100 V, the maximum surface potential (V _max ) And the surface potential (V _2.0 ) after 2 seconds from the maximum surface potential (V _max ) / (V _2.0 ) is 2.0 or more, using an intermediate transfer belt satisfies both memory and transferability. And found that the above problems can be solved.

  Furthermore, it has been found that the use of a different conductive material for each layer of the multilayer structure can prevent the occurrence of memory due to the intermediate transfer belt.

  Furthermore, it has been found that the occurrence of memory can be further prevented when the multilayer structure is composed of at least an ion conductive material layer and an electron conductive agent layer.

  The reason why the memory does not occur is not clear, but since the belt is electrically neutralized at the time of transfer, it is presumed that there is no history of uneven belt potential and a toner image without memory is obtained.

  Hereinafter, the present invention will be described in detail.

[Surface potential of intermediate transfer belt]
The surface potential of the intermediate transfer belt is a value measured under the following conditions.

Measuring device: Photoconductor tester “EPA8300” (manufactured by Kawaguchi Electric Co., Ltd.)
Measurement conditions: Static mode 6 (30 m / sec)
Charging current: -25.0 μA (constant current measurement)
Measurement environment: 20 ° C, 60% RH
Measurement: Obtain the maximum surface potential (V _max ) from the surface potential measurement curve and the surface potential (V ₂ ) after 2 seconds from the maximum surface potential.

  FIG. 2 is a diagram illustrating an example of a surface potential measurement curve.

In FIG. 2, the vertical axis represents the surface potential, the horizontal axis represents time, V _max represents the maximum surface potential, and V ₂ represents the surface potential after 2 seconds from the maximum surface potential.

  The intermediate transfer belt of the present invention requires a surface potential (chargeability) of 100 V or higher, preferably 150 V or higher, more preferably 200 V or higher, under the measurement conditions in the static mode 6 of the photoreceptor tester “EPA8300”.

  When the surface potential is lower than 100 V, toner scattering during primary transfer and transferability degradation during secondary transfer are likely to occur.

The ratio (V _max ) / (V _2.0 ) between the maximum surface potential (V _max ) and the surface potential (V _2.0 ) after 2 seconds from the maximum surface potential is 2.0 or more, preferably 3.0 or more, Preferably it is 3.0-5.0.

  The larger this value is, the better the image transferability is, and it is less likely that white spots in solid images and voids in character images occur, and there is little scattering of toner in the character area.

  However, if this value is too high (for example, 5.0 or more), it is necessary to increase the required electric field strength during primary transfer, which is not preferable from the viewpoint of energy saving.

[Configuration of intermediate transfer belt]
The shape of the intermediate transfer belt of the present invention is generally a seamless (endless) belt structure, but is not limited to this, such as production of a belt from a sheet-like film.

  The intermediate transfer belt of the present invention is formed by a multilayer structure containing a conductive material.

  Each layer of the multilayer structure contains a different conductive material for each layer, and specifically, it is preferably composed of a layer having an ion conductive material and a layer having an electron conductive agent.

  At this time, it is preferable that the conductive materials are not evenly distributed in each layer but the conductive materials are unevenly distributed.

  Examples of specific technical means for achieving the conditions of the present invention include the following means.

1. The first layer (surface layer) is formed with a coating film forming liquid containing an ion conductive substance in polyamic acid,
2. Next, a second layer (base material layer) is formed with a coating film forming liquid containing an electroconductive substance in polyamic acid,
Obtain an intermediate transfer belt.

  At this time, the electric resistance value of the second layer is preferably lower than that in the case of using a single layer.

  The belt thus obtained has a high electric resistance during charging, and has a characteristic that the subsequent attenuation of the surface potential is faster than that of a conventional polyimide belt.

  This is because each conductive substance has different dielectric constants or follow-up characteristics of conductive carriers, and in order to design the belt so that the electric resistance value of the intermediate transfer belt varies greatly depending on the response time, the density of each is non-uniform. This is because it is preferable.

  As a preferable structure of the intermediate transfer belt, it is preferable to separately provide a layer containing an electron conductive substance and a layer containing an ion conductive substance. However, having an interface slightly mixed by mutual dissolution at the time of application at the interface where both layers are in contact does not adversely affect the configuration of the present invention, and smooth transfer between the layers of different conductive carriers is unnecessary. This is a rather preferable form in order to suppress the residual potential in the layer.

  Furthermore, it is preferable that the conductive substance is unevenly distributed in the film thickness direction of the second layer (base material layer). Specifically, centrifugal molding that makes it possible to unevenly distribute the conductive material within the film thickness by utilizing the specific gravity difference between the dispersant (solvent, binder resin) and the dispersion medium (conductive material) of the coating film forming liquid. It is preferable to produce the second layer (base material layer) of the intermediate transfer belt by the method.

  Since the ion conductive substance has a slower response speed than the electronic conductive agent, it is preferable to add the ion conductive substance to the thin first layer (surface layer) to cover the response. On the other hand, a layer to which an ion conductive material is added functions as an insulator against instantaneous voltage application, and thus has high leakage resistance and the like.

  Since the electronic conductive agent has a faster response speed than the ion conductive material, it can be added to the thick second layer (base material layer). On the other hand, since it acts as a conductive substance for instantaneous charging, the injection or leakage resistance is weak.

[Conductive substance]
Examples of the conductive substance used in the present invention include an ionic conductive substance and an electronic conductive substance.

Examples of ionic conductive substances include lauryltrimethylammonium, stearyltrimethylammonium, octadodecyltrimethylammonium, dodecyltrimethylammonium, hexadecyltrimethylammonium, dechlorinated fatty acid / dimethylethylammonium salt perchlorate, chlorate, borofluoride Cationic surfactants such as acid salts, sulfates, ethosulphate salts, benzyl bromide salts, benzyl halide salts such as benzyl chloride salts, quaternary ammonium salts, aliphatic sulfonates, higher alcohol sulfates Salts, higher alcohol ethylene oxide addition sulfate ester salts, higher alcohol phosphate ester salts, anionic surfactants such as higher alcohol ethylene oxide addition phosphate ester salts, amphoteric surfactants such as various betaines, higher Le Call ethylene oxide, polyethylene glycol fatty acid esters, antistatic agents such as nonionic antistatic agents such as polyhydric alcohol fatty acid _{esters, LiCF 3 SO 3, NaClO 4} , LiClO 4, LiAsF 6, LiBF 4, NaSCN, KSCN, NaCl Such as Li ₊ , Na ₊ , K _+, etc., group 1 metal salts, NH ₄₊ salts, etc., electrolytes such as Ca (ClO ₄ ) ₂ , Ca ₂₊ , Ba _2+, etc. Examples of the metal salts of Group 2 of the Periodic Table and those antistatic agents having at least one group having an active hydrogen that reacts with an isocyanate such as a hydroxyl group, a carboxyl group, or a primary or secondary amine group. . Further, these and other complexes with polyhydric alcohols such as 1,4 butanediol, ethylene glycol, polyethylene glycol, propylene glycol and polyethylene glycol and derivatives thereof, or monools such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether. Complexes are mentioned, and one kind or two or more kinds selected from these can be used. However, other known ion conductive resistance control agents can be used and are not limited to the above compounds.

  Examples of the electronic conductive material include carbon black such as kettin black and acetylene black, metal such as aluminum and nickel, metal oxide compound such as tin oxide, and conductive or intermediate transfer powder such as potassium titanate, or polyaniline and polyacetylene. One kind or two or more kinds of suitable conductive polymers can be used, and the kind is not particularly limited.

[Production of intermediate transfer belt]
FIG. 3 is a schematic diagram showing an example of the structure of the intermediate transfer belt of the present invention.

  In FIG. 3, 21 is a surface layer, 22 is a base material layer, 101 is an ion conductive material, and 102 is an electronic conductive material.

  The intermediate transfer belt shown in FIG. 3 has a two-layer structure composed of a surface layer 21 and a base material layer 22, and the surface layer 21 has at least the above-described ion conductive substance and binder resin, and the base material layer 22 has at least It has the above-mentioned electronic conductive substance and binder resin.

  The binder resin is preferably a resin that has electrical stability and mechanical durability and can form a layer containing the conductive substance used in the present invention in a preferable state.

  Specific examples include resin materials such as polycarbonate, polyphenylene sulfide (PPS), polyvinylidene fluoride (PVDF), polyimide, and polyether ether ketone (PEEK), and a polyimide resin is preferable.

These binder resins preferably have a Young's modulus exceeding 200 MPa (200 kg / mm ² ), have a thickness of 70 to 150 μm, and satisfy the mechanical properties as a belt.

  In the intermediate transfer belt of the present invention, an intermediate layer can be provided between the base material layer 22 and the surface layer 21. Examples of materials that can be used for the intermediate layer include vinyl chloride / vinyl acetate / maleic acid copolymer resins and polyamide resins. Specific examples of the polyamide resin include N-methoxymethylated nylon (nylon 8), nylon 12, and copolymer nylon.

  The intermediate transfer belt of the present invention can be produced by a centrifugal molding method, a dipping method, an extrusion molding method, a spray coating method or the like. Among these, the centrifugal molding method is used to form a multilayered coating film. Is suitable.

  Hereinafter, production of an intermediate transfer belt using a centrifugal molding method will be described.

(Centrifugal molding)
Centrifugal molding method is a method of applying a coating film forming liquid to the inner surface of a cylindrical cylinder, and rotating the cylindrical cylinder to produce a cylindrical intermediate transfer belt, that is, a seamless belt by the centrifugal force. The number of rotations of the cylinder may be appropriate and is not particularly limited, but is preferably 500 to 1500 rpm, more preferably 800 to 1000 rpm.

  An intermediate transfer belt having a seamless structure is preferable because it does not change in thickness due to superposition, and an arbitrary portion can be used as a belt rotation start position, and a control mechanism for the rotation start position can be omitted.

  FIG. 4 is a front sectional view showing an example of a main part of the centrifugal molding apparatus.

  FIG. 5 is a cross-sectional view showing an example of the coating film forming liquid coating apparatus.

  FIG. 6 is a perspective view showing an example of a main part of the centrifugal molding apparatus.

  4, 5 and 6, 1 is a cylinder, 2 is a cylindrical cylinder, 8 is a heater, 11 is a coating device, and 15 is a slit.

  First, if necessary, after applying a release agent such as fluorine-based or silicon-based to the inner surface of the cylindrical cylinder 2, for example, a coating film forming solution dissolved in a solvent is supplied from the coating device 11, and is applied to the inner surface of the cylinder 1 as needed. Apply. At this time, the cylinder 1 is rotated slowly so that a uniform application state is easily obtained.

  Next, the cylinder 1 is rotated at a high speed so that the hard particles are unevenly distributed on the outer peripheral surface portion, and then heated to a predetermined temperature by the heater 8 to remove the solvent and react in the case of a reactive resin. An intermediate transfer belt is formed. Subsequently, the intermediate transfer belt of the present invention is obtained by cooling and taking out the cylindrical molded product from the cylindrical cylinder 1. At this time, the coating apparatus 11 supplies the coating film forming liquid from 12, and the coating apparatus 11 can be inserted into the cylinder and can approach the inner surface in the cylinder in order to apply the coating film forming liquid to the cylinder inner surface from the slit 15. It has a structure like this. The above is an example of a centrifugal molding apparatus, and the above apparatus is not limited.

  The binder resin constituting the belt is preferably a resin that reacts by heat irradiation after forming a coating film from the viewpoint of mechanical strength and dimensional stability. Specifically, polyamic acid, photo-curing silicone resin, acrylic resin, and thermosetting silicone resin are preferable. Particularly preferred is polyamic acid.

  The heater may be an electromagnetic wave irradiator capable of reacting a reactive compound.

  When preparing an intermediate transfer belt having a multilayer structure, a coating film forming solution for a surface layer containing at least a conductive substance and a reactive compound is formed by a centrifugal method, and subjected to a centrifugal treatment and a heat irradiation treatment. After the layer is formed, a coating film-forming solution containing at least a different kind of conductive material and reactive compound from the surface layer is formed thereon by centrifugation, and subjected to centrifugal treatment and heat irradiation treatment. It is preferable.

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

  The intermediate transfer belt of the present invention can be used for, for example, a copying machine, a laser printer, and the like, but can be preferably used particularly for a small color image forming apparatus capable of continuous printing at high speed.

  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 capable of using the intermediate transfer belt of the present invention includes a photosensitive member that forms an electrostatic latent image according to image information, a developing device that develops the electrostatic latent image formed on the photosensitive member, and a photosensitive member on the photosensitive member. Primary transfer means for transferring the toner image onto the intermediate transfer belt, and secondary transfer means for transferring the toner image on the intermediate transfer belt onto a recording medium such as paper or an OHP sheet. By providing the intermediate transfer belt of the present invention as an intermediate transfer belt, stable toner image formation can be performed without causing peeling discharge during secondary transfer.

  The intermediate transfer belt of the present invention is 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 a photoconductor to the intermediate transfer belt, and an intermediate transfer of a plurality of photoconductors for each color. Although it can be used for a tandem type color image forming apparatus arranged in series on a belt, it is particularly effective when used for a tandem type high speed and small color image forming apparatus.

  FIG. 7 is a cross-sectional configuration diagram illustrating an example of an image forming apparatus in which the intermediate transfer belt of the present invention can be used.

  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 photoconductor, and a periphery of 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. An image forming unit 10M that forms a magenta image as another different color toner image is disposed around a drum-shaped photoconductor 1M as a first photoconductor, and the photoconductor 1M. A charging unit 2M, an exposure unit 3M, a developing unit 4M, a primary transfer roller 5M as a primary transfer unit, and a cleaning unit 6M. In addition, an image forming unit 10C that forms a cyan image as one of other different color toner images is disposed around the photoconductor 1C as a drum-type photoconductor 1C as a first photoconductor. The charging unit 2C, the exposure unit 3C, the developing unit 4C, the primary transfer roller 5C as the primary transfer unit, and the cleaning unit 6C are provided. Further, an image forming unit 10K that forms a black image as one of other different color toner images is disposed around a drum-shaped photosensitive member 1K as a first photosensitive member, and the photosensitive member 1K. It has 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 an intermediate transfer endless belt-shaped second photosensitive member 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.

Preparation of coating film forming liquid (Preparation of coating film forming liquid 1)
Equimolar amounts of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA) were duplicated at 20 ° C. in N-methylpyrrolidinone (NMP) solvent. By condensation reaction, 2 kg of “aromatic polyamic acid solution 1” (solution viscosity: 4.1 Pa · s) having a solid content of 16% by mass was synthesized.

  2 kg of “aromatic polyamic acid solution 1”, 72 g of carbon black (pH 7, number average primary particle diameter 21 nm) (18.4% by mass with respect to the solid content) as an electron conductive substance, and N-methylpyrrolidinone 462. as a diluting solvent. 4 g was added, and the mixture was stirred and mixed with a stirrer having blades attached to a three-one motor. Further, this was transferred to a sand grinder and sufficiently mixed and dispersed to prepare “film forming liquid 1”.

(Preparation of coating film forming liquid 2)
To 1 kg of “Aromatic Polyamic Acid Solution 1”, 22 g of compound (Chemical Formula 1) having the following structure as an ionic conductive substance (6.9% by mass with respect to the solid content) and 1 kg of N-methylpyrrolidinone as a diluent solvent were added. The mixture was stirred and mixed with a stirrer equipped with a blade on a motor, and further transferred to a sand grinder to sufficiently mix and disperse to prepare “Coating Film Formation Liquid 2”.

(Preparation of coating film forming liquid 3)
“Coating film forming liquid 3” was prepared in the same manner except that the ion conductive substance used for the preparation of “coating film forming liquid 2” was changed to a compound having the following structure (chemical formula 2).

(Preparation of coating film forming liquid 4)
1 kg of dimethylsilicone-modified PI varnish (solid content 20% by mass, cyclohexanone solvent) as a binder resin and 40 g of stearyltrimethylammonium as an ionic conductive substance were stirred and mixed to prepare “Coating Film Forming Liquid 4”.

(Preparation of coating film forming liquid 5)
“Coating film forming liquid 5” was prepared in the same manner except that 40 g of stearyltrimethylammonium used in the preparation of “coating film forming liquid 4” was changed to 40 g of carbon black (pH 7, number average primary particle diameter 21 nm).

(Preparation of coating film forming liquid 6)
“Coating film forming liquid 6” was prepared in the same manner except that the amount of carbon black used in the production of “coating film forming liquid 1” was changed from 72 g to 36 g.

(Preparation of coating film forming liquid 7)
"Coating film forming liquid 7" was prepared in the same manner except that the carbon black used in the preparation of "Coating film forming liquid 1" was not added.

(Preparation of coating film forming liquid 8)
“Coating film forming liquid 8” was prepared in the same manner except that the amount of carbon black used in the production of “coating film forming liquid 1” was changed from 72 g to 100 g.

  Table 1 shows the types and amounts of the binder resins used to prepare the coating film forming liquid, and the types and amounts of the conductive substances.

(Preparation of intermediate transfer belt 1)
"Coating film forming liquid 2" is applied to the inner surface of the cylindrical cylinder through a dispenser from the slit of the coating device on the inner surface of the cylindrical cylinder (die) of the centrifugal molding apparatus shown in FIG. 4 and rotated at 1000 rpm for 10 minutes. To obtain a uniform coating layer. Next, the cylindrical cylinder is heated to 150 ° C. with a heater, and the solvent is dried and cured for 30 minutes while rotating the cylindrical cylinder at 250 rpm. “Coating film of coating film forming liquid 2” having a film thickness of 15 μm (surface layer) Formed.

  Then, the temperature is returned to room temperature, and “Coating Film Forming Liquid 1” is applied onto “Coating Film of Coating Film Forming Liquid 2” from the slit of the coating film device via a dispenser, and rotated at 500 rpm for 10 minutes for uniform coating. A membrane layer was obtained. The cylindrical cylinder was again heated to 150 ° C. with a heater, and the solvent drying / curing reaction was performed for 30 minutes while rotating the cylindrical cylinder at 250 rpm. The temperature is once returned to room temperature, the belt is removed from the cylindrical cylinder, a mold is installed on the inner surface of the belt, and 10 ° C./min. After heating up to 200 ° C., the temperature was raised to 380 ° C. at a rate of 5 ° C./min and heated at 380 ° C. for 30 minutes to proceed with imide conversion, and “coated film of coating film forming liquid 1” (base material layer) Formed.

  After cooling to room temperature, the film was peeled off from the mold to obtain an “intermediate transfer belt 1” having a total film thickness of 85 μm. This is referred to as “Example 1”.

(Preparation of intermediate transfer belt 2)
The “intermediate transfer belt 1” was used in the same manner as the “intermediate transfer belt 1” except that the “film forming liquid 2” used in the production of the “intermediate transfer belt 1” was changed to the “film forming liquid 3”. A transfer belt 2 "was obtained. This is referred to as “Example 2”.

(Preparation of intermediate transfer belt 3)
Using the same cylindrical cylinder, first, “coating film forming liquid 4” was applied to the inner surface of the cylindrical cylinder through a dispenser and rotated at 1000 rpm for 10 minutes to obtain a uniform coating layer. Next, the temperature of the cylindrical cylinder was raised to 120 ° C., and the solvent was dried for 30 minutes while rotating the cylindrical cylinder at 250 rpm to form “coating film of coating film forming liquid 4” having a film thickness of 15 μm.

  Thereafter, the temperature was returned to room temperature, and “Coating film forming solution 5” was applied onto “Coating film of coating film forming solution 4” via a dispenser and rotated at 1000 rpm for 10 minutes to obtain a uniform coating film layer. Further, the temperature of the cylindrical cylinder was raised to 200 ° C. and dried for 30 minutes while rotating to form “coating film of coating film forming liquid 5”. After cooling to room temperature, it was peeled off from the cylindrical cylinder to obtain an “intermediate transfer belt 3” having a total film thickness of 85 μm. This is referred to as “Example 3”.

(Preparation of intermediate transfer belt 4)
In the production of the “intermediate transfer belt 1”, the “coating film of the coating film forming liquid 2” (surface layer) was not formed, and the “coating film forming liquid 1” was used to form the “coating film forming liquid 1”. An “intermediate transfer belt 4” having only a “film” (base material layer) was produced. The total film thickness was 70 μm. This is designated as “Comparative Example 1”.

(Preparation of intermediate transfer belt 5)
In the production of the “intermediate transfer belt 3”, the “coating film of the coating film forming liquid 4” (surface layer) is not formed, but the “coating film forming liquid 5” is used to form the “coating film forming liquid 5. An “intermediate transfer belt 5” having only a “film” (base material layer) was produced. The total film thickness was 70 μm. This is referred to as “Comparative Example 2”.

(Preparation of intermediate transfer belt 6)
“Intermediate transfer belt 6” was prepared in the same manner as “Intermediate transfer belt 1” except that “Coating film forming liquid 2” used in the preparation of “Intermediate transfer belt 1” was changed to “Coating film forming liquid 6”. did. The total film thickness was 80 μm. This is designated as “Comparative Example 3”.

(Preparation of intermediate transfer belt 7)
“Intermediate transfer belt 7” was prepared in the same manner as “Intermediate transfer belt 1” except that “Coating film forming liquid 2” used in the preparation of “Intermediate transfer belt 1” was changed to “Coating film forming liquid 7”. did. The total film thickness was 80 μm. This is designated as “Comparative Example 4”.

(Preparation of intermediate transfer belt 8)
“Coating film forming liquid 2” used in the production of “intermediate transfer belt 1” was changed to “coating film forming liquid 6”, and “coating film forming liquid 1” was changed to “coating film forming liquid 8”. An “intermediate transfer belt 8” was produced in the same manner as the “intermediate transfer belt 1”. The total film thickness was 80 μm. This is designated as “Comparative Example 5”.

  Table 2 shows coating film forming liquids (types of conductive substances) used for preparing the surface layer and the base material layer of “intermediate transfer belts 1 to 8”.

<< Potential characteristics >>
The surface potential of the “intermediate transfer belts 1 to 8” produced above was measured under the above-mentioned conditions, and the maximum surface potential (V _max ) and the surface potential (V ₂ ) after 2 seconds were obtained, and (V _max ) / The value of (V ₂ ) was calculated.

《Image evaluation》
The “intermediate transfer belts 1 to 8” produced above were mounted on “8050” (manufactured by Konica Minolta Business Technologies, Inc.), which was remodeled to 1.3 times the linear velocity, and evaluated.

For image formation, a two-component developer having a toner with a median particle diameter (D ₅₀ ) of 4.5 μm on a number basis and a carrier was used.

  The printing environment was low temperature and low humidity (10 ° C., 25% RH) and high temperature and high humidity (33 ° C., 85% 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.

  Image evaluation was performed on the following items by performing double-sided printing.

<Transferability>
Transferability (T) was measured in a high temperature and high humidity environment as follows.

  First, the transfer residual toner of the solid image is peeled off from the intermediate transfer belt and attached to the mount, and the reflection density of the tape is measured to be A. Next, untransferred toner is recovered from the intermediate transfer belt with a tape, and the recovered amount of untransferred toner per unit area is defined as W. Transferability was determined from the following equation. Note that the smaller the value of transferability (T), the better.

formula
Transferability (T) = A / W ₀
W ₀ = W (sample) / W (intermediate transfer belt 1)
W (sample): Amount of untransferred toner collected from each sample
W (intermediate transfer belt 1): the amount of untransferred toner collected on the intermediate transfer belt 1 <whiteout of solid image>
Double-sided prints were created by changing the transfer current value when transferring a toner image from an intermediate transfer belt to a recording medium in a high-temperature and high-humidity environment to 25 μA, 50 μA, 75 μA, 100 μA, and 150 μA. It was evaluated by the presence or absence of white spots. The presence or absence of white spots was determined by observing the solid image with a 10 × magnifying glass and determining whether there was a small white spot of about 0.5 mm. The transfer current value is preferably as wide as possible because stable transfer is possible.

<Cut out of text image>
In a high-temperature and high-humidity environment, the character image printed on the back side (second side) of double-sided printing is magnified 10 times with a magnifying glass to visually evaluate whether the character image is voided. did.

Evaluation Criteria A: Good without occurrence of voids ○: Several voids have occurred, but there are no practical problems ×: Remarkable voids have remarkably occurred, and there are practical problems.

<Toner scattering in text>
In a low-temperature and low-humidity environment, a character image printed on the back surface (second surface) of double-sided printing was observed with a magnifier 10 times, and the state of toner scattering around the character portion was visually evaluated.

Evaluation Criteria A: Good with no toner scattering ○: Toner scattering is slightly occurring, but there is no practical problem ×: Toner scattering is remarkably generated, and there is a practical problem.

<Transfer memory>
In a low-temperature and low-humidity environment, a document having several black patches is printed continuously, and then a uniform halftone image is printed. The solid image and the history of the white background are printed in the halftone image. It was visually evaluated whether or not (memory generation) appeared (no memory generation).

Evaluation criteria ○: No memory generated ×: Memory generated

  Table 3 shows potential characteristics and image evaluation results.

As is apparent from the results of Table 3, in Examples 1 to 3 (intermediate transfer belts 1 to 3) of the present invention, the maximum surface potential (V _max ) is 100 V or more and (V _max ) / ( V ₂ ) was 2.0 or more, and in the image evaluation, good results were obtained for any of the evaluation items of transferability, solid image white void, character image void, character portion toner scattering, and transfer memory. However, “Comparative Examples 1 to 5” (intermediate transfer belts 4 to 8) of the comparative example have a problem in either the potential characteristics or the evaluation items, and “Examples 1 to 3” (intermediate transfer belt 1) of the present invention. The result was clearly different from that of ~ 3).

It is a figure explaining a transfer process. It is a figure which shows an example of the measurement curve of surface potential. FIG. 3 is a schematic diagram illustrating an example of an intermediate transfer belt according to the present invention. It is front sectional drawing which shows an example of the centrifugal molding apparatus principal part. It is sectional drawing which shows an example of the coating-film formation liquid coating device. It is a perspective view which shows an example of the principal part of a centrifugal molding apparatus. 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 Base material layer 101 Ion conductive material 102 Electronic conductive material

Claims (4)

In an intermediate transfer belt having a multilayer structure containing a conductive material, when the intermediate transfer belt is charged,
The maximum surface potential (V _max ) is 100V or more,
Intermediate transfer characterized in that the ratio (V _max ) / (V _2.0 ) between the maximum surface potential (V _max ) and the surface potential (V _2.0 ) 2 seconds after the maximum surface potential satisfies the following formula (1) belt.
Formula (1)
(V _max ) / (V _2.0 ) ≧ 2.0 The intermediate transfer belt according to claim 1, wherein the conductive material is different for each layer of the multilayer structure. The intermediate transfer belt according to claim 1, wherein the conductive material includes at least an ionic conductive material and an electronic conductive material. The intermediate transfer belt according to claim 1, wherein the multilayer structure includes at least a layer containing an ion conductive material and a layer containing an electron conductive material.

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