JP4396167B2 - Semiconductive belt and image forming apparatus using the same - Google Patents

Description

  The present invention relates to a semiconductive belt used in an image forming apparatus using an electrophotographic system such as a copying machine or a printer, and an image forming apparatus using the semiconductive belt.

In an image forming apparatus using an electrophotographic system, first, a uniform charge is formed on the surface of an image carrier made of a photoconductive photoreceptor made of an inorganic or organic material, and the image signal is modulated with laser light or the like. After the electric image is formed, the electrostatic image is developed with a charged toner, and a visualized toner image is formed. Then, the toner image is electrostatically transferred to a transfer material such as recording paper via an intermediate transfer member, and fixed on the recording material, whereby a required reproduced image is obtained.
In particular, there is known an image forming apparatus that employs a system in which a toner image formed on the image carrier is primarily transferred to an intermediate transfer member, and a toner image on the intermediate transfer member is secondarily transferred to a recording sheet (for example, , See Patent Document 1).

  In the image forming apparatus adopting the intermediate transfer body system, polycarbonate resin, PVDF (polyvinylidene fluoride), polyalkylene phthalate, PC (polycarbonate) / PAT (polyalkylene terephthalate) blends are used as materials for the intermediate transfer body. Proposals have been made to use conductive endless belts of thermoplastic resins such as materials, ETFE (ethylene tetrafluoroethylene copolymer) / PC, ETFE / PAT, PC / PAT blend materials, etc. 7).

  However, the conductive materials of thermoplastic resins such as polycarbonate resin and PVDF (polyvinylidene fluoride) are inferior in mechanical properties, so the belt deformation is large with respect to stress during driving, and high-quality transfer image quality can be stably obtained. Absent. In addition, there is a problem that the belt life is short because a crack is generated from the belt end during driving.

  As a belt material used in an image forming apparatus employing an intermediate transfer body method, an elastic belt with a reinforcing material formed by laminating a woven fabric such as polyester and an elastic member has been proposed. However, the elastic belt with a reinforcing material may cause a problem of color misregistration due to creep deformation of the belt material over time (see, for example, Patent Documents 8 and 9).

  Furthermore, as a material used for the paper conveying belt, a conductive material is dispersed in an elastic member such as ETFE (ethylene tetrafluoroethylene copolymer) resin material, CR (chloropyrene), EPDM (ethylene propylene diene polymer), or the like. A proposal has been made to use a semiconductive endless belt.

  On the other hand, as a semiconductive belt that can be used for an intermediate transfer belt, a transfer conveyance belt, and the like, an intermediate transfer belt in which a conductive filler is dispersed in a polyimide resin having excellent mechanical properties and heat resistance has been proposed (for example, (See Patent Documents 10 and 11.)

  However, the semiconducting belts made of polyimide resin proposed so far have a poor balance between flexibility and rigidity, so it cannot be said that the intermediate transfer belt and transfer conveying belt satisfy the characteristics. It was. Furthermore, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, p-phenylenediamine, and polyamic acid (U varnish-S), which is a polymer, are used as raw materials for the polyimide resin, and the conductive filler A belt with dispersed therein is disclosed. This type of intermediate transfer belt has excellent mechanical characteristics, does not undergo belt deformation due to stress during driving, and can stably obtain high-quality transfer image quality without color misregistration. On the other hand, in the transfer portion, since the mechanical properties of the polyimide resin material are excellent, a primary image in which a recording sheet is pressed against a recording medium using a bias roller and an electric field is applied to electrostatically transfer a toner image. Since there is little deformation due to the pressing force by the bias roller at the transfer portion, the pressing force by the bias roller is concentrated. For this reason, the toner aggregates and the charge density increases, so that discharge occurs inside the toner layer, and image quality defects such as missing line images (holocharacter) occur due to changes in toner polarity, etc. (For example, refer to Patent Document 12).

There has been proposed a method of improving electrical characteristics and mechanical characteristics by forming a semiconductive belt made of polyimide with a plurality of layers and individually adjusting the electrical characteristics of each layer. For example, the resin component of the inner layer and the outer layer is made of the same polyimide resin, and the surface electrical resistance value shows different values, and the conductivity of the outer layer is increased by increasing the amount of conductive material added to the outer layer. Is disclosed (for example, see Patent Document 13).
Moreover, a semiconductive belt made of polyimide having a two-layer structure in which the thermal expansion coefficient of the inner layer is larger than that of the outer layer at a temperature of 50 to 400 ° C. has been proposed (see, for example, Patent Document 14).
However, since the linear expansion coefficient of the polyimide resin component of the outer layer is smaller than that of the polyimide resin component of the inner layer, there is a problem that the belt is warped outward and the flatness of the belt is deteriorated. .

  On the other hand, as a method for transferring a visible image onto a transfer paper such as paper, a so-called transfer is performed in which a transfer paper such as paper is wound around a transfer drum, and the visible image on the photoreceptor is transferred to the transfer paper for each color. A drum system or the like is known. The transfer drum method requires that the intermediate transfer member be rotated a plurality of times when transferring the visible image from the photosensitive member to the intermediate transfer member, as compared with the intermediate transfer method described above. On the other hand, the intermediate transfer system can transfer from multiple photoconductors by rotating the intermediate transfer body once, and can improve the transfer speed. It is being considered as a promising transfer method.

  However, the intermediate transfer member in this transfer system has a diameter larger than that of the conventional intermediate transfer belt and is provided with independent four-color developing devices and photoconductors, so that a high-precision device such as the accuracy of color misregistration for each color is provided. Design is required. That is, high accuracy flatness is required as an intermediate transfer member mounted on such an image forming apparatus.

If the belt is warped outward or the flatness of the belt is poor, the adhesion between the driving roll for driving the belt and the semiconductive belt changes, and as a result, the moving speed of the belt fluctuates, and each color developing device is provided. The moving speed of the intermediate transfer member is different for each color with respect to the photoconductor, so that high-precision image alignment is impossible, and image defects such as color misregistration occur.
Also, along with the downsizing of the image forming apparatus, the parts inside the image forming apparatus in recent years are close to each other, the flatness of the intermediate transfer member is poor, the belt is warped to the outside, and other parts may be lifted. Such as a defect that causes an image to be discharged due to approach to the discharge, damage to the end of the semiconductive belt due to contact with other members in the vicinity, or the intermediate transfer member may be broken due to being caught in the worst case. It will occur.
Further, when a multilayer belt having such a warp is used for an intermediate transfer belt or a transfer conveyance belt, the print sheet follows the warp due to the warp to the outside, causing a transfer unevenness and an image defect. There was a problem that the belt position detection marks and flags at the end of the belt could not be read well and the device itself stopped. Therefore, in the intermediate transfer belt and the transfer conveyance belt, it is necessary to maintain a state in which the belt is less warped not only in the initial stage but also in a long-term use.
JP-A-62-206567 JP-A-6-095521 Japanese Patent Laid-Open No. 5-200904 JP-A-6-228335 Japanese Patent Laid-Open No. 6-149081 Japanese Patent Laid-Open No. 6-149083 Japanese Patent Laid-Open No. 6-149079 Japanese Patent Laid-Open No. 9-305038 Japanese Patent Laid-Open No. 10-240020 JP-A-5-77252 Japanese Patent Laid-Open No. 10-63115 Japanese Patent Laid-Open No. 10-63115 JP 7-156287 A JP 2002-156835 A

  An object of the present invention is to solve the conventional problems and achieve the following objects. That is, the present invention has a high degree of flatness, has no problems such as shape deformation over time, is excellent in forming a nip shape in a transfer portion, and has a semiconductive property with little change in electrical resistance due to the environment. The object is to provide a belt. It is another object of the present invention to provide an image forming apparatus that includes the semiconductive belt and can stably obtain high-quality transfer image quality.

Means for solving the above-described problems can be achieved by the present invention described below.
That is, the present invention
<1> An endless semiconductive belt that is used in an electrophotographic image forming apparatus and includes an outer layer and an inner layer mainly composed of a polyimide-based resin containing any oxidized carbon black having a pH of 5 or less, the ratio of the difference in linear expansion coefficient at 10 to 80 ° C. with the inner layer, 35 × 10 ^-6 / ℃ or less and the coefficient of linear expansion of the outer layer is rather larger than the linear expansion coefficient of the inner layer, the thickness of the outer layer Is 10 to 25% of the total thickness, and imide bond between 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and 4,4′-diaminophenyl ether is used as the polyimide resin of the outer layer. And a polymer formed by imide bonding of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and p-phenylenediamine is used as the polyimide resin for the inner layer. This is a semiconductive belt.

<2> The semiconductive belt according to <1>, wherein the content of the oxidized carbon black having a pH of 5 or less in the outer layer is 20 to 23 parts by mass with respect to 100 parts by mass of the polyimide resin. There is .

< 3 > An image forming apparatus using the semiconductive belt according to <1> or <2> as an intermediate transfer belt.
< 4 > An image forming apparatus using the semiconductive belt according to <1> or <2> as a paper transport belt.

<5> The image forming apparatus according to < 3 > or < 4 >, wherein a spherical toner having a shape factor (ML2 / A) defined by the following formula (1) of 140 or less is used.
Formula (1)
(ML2 / A) = [(absolute maximum length of toner particles) × 2] / [(projected area of toner particles) × π × 1/4 × 100]

  The present invention provides a semiconductive belt that has high precision flatness, is free from problems such as shape deformation over time, is excellent in forming a nip shape at a transfer portion, and has little change in electrical resistance due to the environment. Can be provided. Furthermore, it is possible to provide an image forming apparatus that includes the semiconductive belt and can stably obtain high-quality transfer image quality.

<Semiconductive belt>
The semiconductive belt of the present invention will be described with reference to FIG. The semiconductive belt 1 of the present invention is an endless belt comprising an outer layer 2 and an inner layer 3 that is used in an electrophotographic image forming apparatus. The outer layer 2 and the inner layer 3 are made of oxidized carbon black having a pH of 5 or less. The main component is a polyimide-based resin, and the difference in linear expansion coefficient between the outer layer 2 and the inner layer 3 at 10 to 80 ° C. is 35 × 10 ⁻⁶ / ° C. or less, and the linear expansion coefficient of the outer layer 2 is the inner layer. The linear expansion coefficient is larger than 3. Here, FIG. 1 is a cross-sectional view showing the configuration of the semiconductive belt of the present invention.
In the present invention, the phrase “mainly composed of a polyimide resin containing a conductive substance” means that the content of the polyimide resin containing a conductive substance in the outer layer or the inner layer is 51% or more.

  As described above, the semiconductive belt of the present invention has a two-layer structure composed of the outer layer 2 and the inner layer 3 to satisfy the balance between flexibility and rigidity that cannot be obtained with a single material structure. be able to.

(Polyimide resin)
Each of the semiconductive belts of the present invention comprises an outer layer and an inner layer mainly composed of a polyimide resin containing a conductive substance. Hereinafter, the polyimide resin in the present invention will be described by dividing it into an outer layer and an inner layer.

[Outer layer polyimide resin]
As the polyimide resin of the outer layer in the present invention, a tetracarboxylic dianhydride having a wholly aromatic skeleton that is a tetracarboxylic acid residue and a diamine component having a diphenyl ether skeleton that is a diamine residue, that is, a diamine residue with an ether It is preferable to use a polymer formed by imide bonding with a diamine component having a skeleton.
Examples of the diamine component having a diphenyl ether skeleton include 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether, or diamine components mainly composed of compounds obtained by substituting these aromatic rings with lower alkyl groups. Among them, a diamine component mainly composed of 4,4′-diaminodiphenyl ether is preferable, and a diamine component composed of 4,4′-diaminodiphenyl ether is more preferable.
The main component in the polyimide resin according to the present invention is 51% or more.

  Examples of the tetracarboxylic dianhydride having a wholly aromatic skeleton include pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,3,3 ′, 4 ′. -Biphenyltetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalene Examples thereof include tetracarboxylic dianhydrides or compounds obtained by substituting these aromatic rings with lower alkyl groups. Among these, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride is particularly preferable.

In addition, the polyimide resin of the outer layer in the present invention includes a polymer formed by imide bonding of a tetracarboxylic dianhydride having a wholly aromatic skeleton and a diamine component having a diphenyl ether skeleton. It is also preferable that a polymer formed by imide bonding of a tetracarboxylic dianhydride having a wholly aromatic skeleton preferable as a polyimide resin and a diamine component having a p-phenylene skeleton is also included.
Specific examples of polyimide resins formed by imide bonding of the tetracarboxylic dianhydride having a wholly aromatic skeleton and a diamine component having a diphenyl ether skeleton include 3,3 ′, 4,4′-biphenyltetracarboxylic Examples include polyimide resins formed by imide bonding of acid dianhydride (BPDA) and 4,4′-diaminodiphenyl ether (DDE). The linear expansion coefficient of the polyimide resins at 10 to 80 ° C. is 43 × 10 ⁻⁶ / ° C.

[Inner layer polyimide resin]
As the polyimide resin of the inner layer in the present invention, a tetracarboxylic dianhydride having a wholly aromatic skeleton that is a tetracarboxylic acid residue and a diamine component having a p-phenylene skeleton that is a diamine residue are imide-bonded. It is preferable to use a polymer obtained by By using as a main component a polymer formed by imide bonding of a tetracarboxylic dianhydride having a wholly aromatic skeleton and a diamine component having a p-phenylene skeleton, it becomes rigid and can satisfy mechanical properties. .

Examples of the diamine component having a p-phenylene skeleton include a diamine component mainly composed of p-phenylenediamine or a compound obtained by substituting an aromatic ring thereof with a lower alkyl group, and the like. A diamine component is preferable, and a diamine component composed of p-phenylenediamine is more preferable.
Further, the tetracarboxylic dianhydride having a wholly aromatic skeleton in the inner layer is synonymous with the tetracarboxylic dianhydride having a wholly aromatic skeleton in the outer layer, and the preferred embodiment is also the same.
The polyimide resin of the inner layer in the semiconductive belt of the present invention has a tetracarboxylic dianhydride having the wholly aromatic skeleton within a range where the Young's modulus can be maintained at a preferable range of 4000 MPa or more as described later. In addition to the polymer formed by imide bond between the product and a diamine component having a p-phenylene skeleton, the above-described tetracarboxylic dianhydride having a wholly aromatic skeleton and a diamine component having a diphenyl ether skeleton are included. It is also preferable that a polymer formed by imide bonding is contained.
Specific examples of polyimide resins formed by imide bonding of the tetracarboxylic dianhydride having a wholly aromatic skeleton and a diamine component having a p-phenylene skeleton include 3,3 ′, 4,4′-biphenyl. Examples thereof include polyimide resins formed by imide bonding of tetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA). The linear expansion coefficient of the polyimide resin at 10 to 80 ° C. is 23 × 10 ⁻⁶ / ° C.

Semiconductive belt of the present invention, a polyimide resin before Kigaiso 3,3 ', and 4,4'-biphenyltetracarboxylic dianhydride and 4,4'-diaminodiphenyl ether and imide bond a made polymer, and the inner layer of polyimide resin, 3,3 ', Ru polymer der that the 4,4'-biphenyl tetracarboxylic acid dianhydride and p- phenylenediamine formed by imide bond.

(Conductive substance)
The outer layer and inner layer mainly composed of polyimide resin in the semiconductive belt of the present invention contain a conductive substance. As the conductive material, conductive or semiconductive fine powder can be used, and there is no particular limitation as long as a desired electrical resistance can be stably obtained, carbon black such as Ketchen Black, acetylene black, Examples thereof include metals such as aluminum and nickel; metal oxide compounds such as tin oxide; potassium titanate and the like. The said conductive substance may be used individually by 1 type, and may be used in combination of 2 or more type.
As the conductive material in the present invention, good dispersion stability is obtained because of its good dispersibility in the polyimide resin, the resistance variation of the semiconductive belt can be reduced, and the electric field dependency is also small. Further, since the electric field concentration due to the transfer voltage becomes less likely to improve the stability of the electrical resistance over time, oxidized carbon black having a pH of 5 or less is used .

(Oxidized carbon black of pH 5 or less)
The oxidation-treated carbon black having a pH of 5 or less can be produced by oxidizing the carbon black to impart a carboxyl group, a quinone group, a lactone group, a hydroxyl group, or the like to the surface. This oxidation treatment is an air oxidation method in which contact is made with air in a high-temperature atmosphere to react, a method of reacting with nitrogen oxides or ozone at room temperature, and air oxidation at high temperature, followed by ozone oxidation at a low temperature. It can be performed by a method or the like. Specifically, oxidized carbon black having a pH of 5 or less can be produced by a contact method. Examples of the contact method include a channel method and a gas black method. Oxidized carbon black can also be produced by a furnace black method using gas or oil as a raw material. Further, if necessary, after performing these treatments, a liquid phase oxidation treatment with nitric acid or the like may be performed. Acidic carbon black can be produced by a contact method, but is usually produced by a closed furnace method. In the furnace method, only carbon black having a high pH and a low volatile content is usually produced, but the pH can be adjusted by subjecting it to the above-mentioned liquid phase acid treatment. For this reason, in the present invention, carbon black obtained by furnace method production and adjusted to have a pH of 5 or less by post-treatment is considered to be included in the oxidized carbon black having a pH of 5 or less.

  The pH value of the oxidized carbon black in the present invention is preferably pH 5.0 or less, more preferably pH 4.5 or less, and further preferably pH 4.0 or less. Oxidized carbon having a pH of 5.0 or lower has an oxygen-containing functional group such as a carboxyl group, a hydroxyl group, a quinone group, and a lactone group on the surface, so that it has good dispersibility in the resin and good dispersion stability is obtained. The resistance variation of the semiconductive belt can be reduced, and the electric field dependency is also reduced, making it difficult to concentrate the electric field due to the transfer voltage.

  The pH of the carbon black is determined by adjusting an aqueous suspension and measuring with a glass electrode. Further, the pH of the carbon black can be adjusted by conditions such as the treatment temperature and treatment time in the oxidation treatment step.

The oxidized carbon black having a pH of 5.0 or less preferably has a volatile component content of 1 to 25%, more preferably 3 to 20%, and further preferably 3.5 to 15%. preferable. When the content of the volatile component is less than 1%, the effect of the oxygen-containing functional group attached to the surface is lost, and the dispersibility in the binder resin may be reduced. On the other hand, when the content of the volatile component is higher than 25%, it may be decomposed when dispersed in the polyimide resin, or the amount of water adsorbed on the oxygen-containing functional group on the surface increases. The appearance of the outer layer or the inner layer in the present invention may deteriorate.
On the other hand, the dispersion | distribution in the said polyimide-type resin can be made more favorable because content of the said volatile component shall be 1-25%. The content of the volatile component can be determined from the ratio of organic volatile components (carboxyl group, hydroxyl group, quinone group, lactone group, etc.) that come out when carbon black is heated at 950 ° C. for 7 minutes.

  In the semiconductive belt of the present invention, two or more types of carbon black may be contained. At that time, these carbon blacks are preferably substantially different in conductivity from each other, for example, those having different physical properties such as the degree of oxidation treatment, DBP oil absorption, specific surface area by BET method utilizing nitrogen adsorption, etc. Use. When two or more types of carbon blacks having different conductivity are added in this way, for example, carbon black that expresses high conductivity is preferentially added, and then carbon black with low conductivity is added to adjust the surface resistivity. It is possible to do. Even when two or more types of carbon black are contained in this way, at least one of them can be mixed and dispersed by using an oxidation-treated carbon black having a pH of 5.0 or less.

  Specifically, as the oxidation-treated carbon black having a pH of 5.0 or less, “Printex 150T” (pH 4.5, volatile content 10.0%) manufactured by Degussa, “Special Black 350” (pH 3.5, volatile) 2.2%), "Special Black 100" (pH 3.3, volatile content 2.2%), "Special Black 250" (pH 3.1, volatile content 2.0%), "Special Black 5" (PH 3.0, volatile matter 15.0%), "Special Black 4" (pH 3.0, volatile matter 14.0%), "Special Black 4A" (pH 3.0, volatile matter 14.0%) ), "Special Black 550" (pH 2.8, volatile content 2.5%), "Special Black 6" (pH 2.5, volatile content 18.0%), "Color Black FW200" (pH 2.5) , "Color Black FW2" (pH 2.5, volatile content 16.5%), "Color Black FW2V" (pH 2.5, volatile content 16.5%), manufactured by Cabot Corporation MONARCH1000 "(pH 2.5, volatile content 9.5%)," MONARCH 1300 "(pH 2.5, volatile content 9.5%) manufactured by Cabot," MONARCH 1400 "(pH 2.5, volatile content 9.0) manufactured by Cabot %), “MOGUL-L” (pH 2.5, volatile matter 5.0%), “REGAL400R” (pH 4.0, volatile matter 3.5%), and the like.

  The oxidation-treated carbon black having a pH of 5.0 or lower is more conductive than the general carbon black because of its excellent dispersibility in the resin composition due to the effect of the oxygen-containing functional group present on the surface as described above. It is preferable to increase the addition amount as a fine powder. Thereby, since the amount of carbon black in the semiconductive belt increases, the effect of using the oxidized carbon black that can suppress the in-plane variation of the electrical resistance value can be maximized. .

  In the present invention, if the content of the oxidized carbon black having a pH of 5.0 or less in the inner layer and the outer layer is 10 to 30% by mass, oxidation within the surface of the surface resistivity of the semiconductive belt is suppressed. The effect of the treated carbon black can be exhibited, which is preferable. If the content of the oxidized carbon black having a pH of 5.0 or less is less than 10% by mass, the uniformity of the electrical resistance is lowered, and the in-plane unevenness of the surface resistivity and the electric field dependency may increase. On the other hand, if the content of the oxidized carbon black having a pH of 5.0 or less exceeds 30% by mass, it may be difficult to obtain a desired resistance value. Furthermore, it is more preferable to contain 18 to 30% by mass of the oxidized carbon black having a pH of 5.0 or less. By containing 18 to 30% by mass of the oxidized carbon black having a pH of 5.0 or less, the effect is maximized. It is possible to exert the limit, and the in-plane unevenness of the surface resistivity and the electric field dependency can be remarkably improved.

(Linear expansion coefficient)
In the semiconductive belt of the present invention, the difference in linear expansion coefficient at 10 to 80 ° C. between the outer layer and the inner layer is 35 × 10 ⁻⁶ / ° C. or less, and the linear expansion coefficient of the outer layer is the linear expansion of the inner layer. It is characterized by being larger than the coefficient.
By increasing the linear expansion coefficient of the outer layer to be larger than the linear expansion coefficient of the inner layer at 10 to 80 ° C., the problem of the belt being warped outward does not occur, and high-precision flatness can be obtained. Furthermore, at 10 to 80 ° C., the difference in the linear expansion coefficient between the outer layer and the inner layer is set to 35 × 10 ⁻⁶ / ° C. or less, so that the initial amount of warpage of the belt is small and the outer layer is not warped. The amount of warpage over a period can be kept small.

The difference in linear expansion coefficient at 10 to 80 ° C. between the outer layer and the inner layer is preferably 5 × 10 ⁻⁶ / ° C. to 30 × 10 ⁻⁶ / ° C., and 10 × 10 ⁻⁶ / ° C. to 25 × 10. ^-6 / ° C is more preferable.
More specifically, the difference in linear expansion coefficient at 10 to 80 ° C. between the outer layer and the inner layer is 20 × 10 ⁻⁶ / ° C. or more when the thickness ratio of the outer layer is 10 to 20% of the total thickness. 30 × 10 ⁻⁶ / ° C. is preferable, and when the thickness ratio of the outer layer is 20 to 30% of the total thickness, it is 10 × 10 ⁻⁶ / ° C. to 25 × 10 ⁻⁶ / ° C. When the ratio of the thickness of the outer layer is 30 to 50% of the total thickness, it is preferably 5 × 10 ⁻⁶ / ° C. to 15 × 10 ⁻⁶ / ° C.
In the present invention, the coefficient of linear expansion at 10 to 80 ° C. of the outer layer and the inner layer was obtained by cutting out a test piece having a width of 3 mm and a length of 10 mm of the outer layer and inner layer of the semiconductive belt to be evaluated. It measured in the temperature range of 10-80 degreeC on TMA-50 on conditions with a temperature increase rate of 10 degree-C / min, and a load of 2 g. From the result, the linear expansion coefficient (average value) at 10 to 80 ° C. was obtained.

(Flatness)
As described above, the semiconductive belt of the present invention has a difference in linear expansion coefficient at 10 to 80 ° C. between the outer layer and the inner layer of 35 × 10 ⁻⁶ / ° C. or less, and the linear expansion coefficient of the outer layer is equal to that of the inner layer. By making it larger than the linear expansion coefficient, it becomes possible to reduce the flatness when stretched by applying a load of 4 kg with two parallel shafts.
The flatness of the semiconductive belt of the present invention is preferably 4 mm or less, and more preferably 2 mm or less. If the flatness exceeds 4 mm, the adhesion between the driving roll for driving the belt and the semiconductive belt may change when used in an image forming apparatus described later, and the moving speed of the belt fluctuates. In some cases, the moving speed of the intermediate transfer member differs for each color with respect to the photosensitive member provided with each color developing device, so that high-precision image alignment becomes impossible, and image defects such as color misregistration may occur.
As shown in FIG. 2, the flatness in the present invention is such that the semiconductive belt 1 is stretched by applying a load of 4 kg with two parallel shafts 12 (Φ28 mm), and the surface of the semiconductive belt at that time The laser displacement meter 11 (LK-030 manufactured by Keyence Co., Ltd.) and the center of the shaft paired with the shaft are parallel to the axis. The difference between the minimum values is read.

The total thickness of the semiconductive belt of the present invention is preferably 0.05 to 0.5 mm, more preferably 0.05 to 0.2 mm, and 0.06 to 0.15 mm. More preferably.
The thickness ratio of the outer layer is 10 to 25 % of the total thickness. When the ratio of the thickness of the outer layer is 10 to 25 % of the total thickness, when the Young's modulus described later of the polyimide resin of the inner layer is 4000 MPa or more and a high Young's modulus, the mechanical characteristics as a semiconductive belt are also obtained. Can be satisfied.

(Surface micro hardness)
In the semiconductive belt of the present invention, the surface microhardness of the outer layer is preferably 30 or less, and more preferably 25 or less. The present inventors have found that there is a very accurate correlation between the surface microhardness of the outer layer and the generation level of the holocharacter. That is, when the surface microhardness of the outer layer is 30 or less, more preferably 25 or less, the semiconductive belt of the present invention has a transfer surface (outer layer) by the pressing force of the bias roller when used in an image forming apparatus described later. ), And the pressing force concentrated on the semiconductive toner is dispersed. For this reason, the toner does not aggregate, and image quality defects such as a holocharacter in which the line image disappears are not generated.

The surface microhardness can be determined by a method of measuring how much the indenter has entered the sample. A method for measuring the surface microhardness will be described. FIG. 3 is a schematic cross-sectional view showing the measurement principle of the surface microhardness of the outer layer. In FIG. 3, 13 represents the outer layer surface, 14 represents a needle-like indenter, and arrow L represents the load applied to the needle-like indenter 14. means.
When measuring the surface microhardness, the tip of the needle-shaped indenter 14 having a predetermined shape is pressed to the outermost surface portion of the outer layer surface 13 until the load L (mN) is changed from the load 0 to the predetermined load P. When the depth of penetration of the needle-like indenter 14 into the surface layer 13 in the vertical direction is D (μm), the surface microhardness DH is expressed by the following formula (1).
Formula (1) DH≡αP / D ²
Here, α is a constant depending on the shape of the indenter, and α = 3.8854 (used indenter: in the case of a triangular pyramid indenter).

  This surface microhardness is the hardness obtained from the excessive weight and indentation depth in the process of indenting the indenter, and represents the strength characteristics of the material including not only plastic deformation of the sample but also elastic deformation. is there. In addition, the measurement area is very small, and more accurate hardness measurement is possible within a range close to the toner particle diameter.

The surface microhardness of the outer layer was determined by the following method. A sheet of material (surface layer) constituting the transfer surface is cut to about 5 mm square, and the small piece is fixed to the glass plate with an instantaneous adhesive. The surface microhardness of the surface of this sample is measured using an ultra micro hardness meter DUH-201S (manufactured by Shimadzu Corporation). The measurement conditions are as follows.
Measurement environment: 23 ° C, 55% RH
Working indenter: Triangular pyramid indenter test mode: 3 (soft material test)
Test load: 6.9 × 10 ⁻³ N (0.70 gf)
Load speed: 0.142 × 10 ⁻³ N (0.0145 gf / sec)
Holding time: 5 sec

<Surface resistivity>
In the semiconductive belt of the present invention, the surface resistivity in at least one of the inner layer and the outer layer is preferably 1 × 10 ¹⁰ to 1 × 10 ¹⁴ Ω / □, and 1 × 10 ¹¹ to 1 × 10 ¹³ Ω / □. More preferably, □. Moreover, it is more preferable that both the inner layer and the outer layer satisfy the above-mentioned preferable surface resistivity range. If the surface resistivity of 1 × 10 ¹⁴ Ω / □ higher, when used in an image forming apparatus described later, separation discharge in the post-nip portion and the image carrier and the semiconductive belt of the primary transfer portion is peeled off In the portion where the discharge easily occurs and the discharge is likely to occur, an image quality defect that causes white spots may occur. On the other hand, when the surface resistivity of the outer layer is less than 1 × 10 ¹⁰ Ω / □, the electric field strength at the pre-nip portion becomes strong, and gap discharge at the pre-nip portion is likely to occur. May get worse. Accordingly, when the surface resistivity of the outer layer is set to 1 × 10 ¹⁰ to 1 × 10 ¹⁴ Ω / □, white spots are generated due to discharge that occurs when the surface resistivity is high, and the surface resistivity is low. Deterioration of image quality can be prevented.

In the semiconductive belt of the present invention, the surface resistivity of the outer layer can be measured according to JIS K6991 using a circular electrode (for example, “HR probe” of High Lester IP manufactured by Mitsubishi Oil Chemical Co., Ltd.). A method for measuring the surface resistivity will be described with reference to FIG. FIG. 4 is a schematic plan view (a) and a schematic cross-sectional view (b) showing an example of a circular electrode. The circular electrode shown in FIG. 4 includes a first voltage application electrode A and a plate-like insulator B. The first voltage application electrode A has a cylindrical electrode portion C and a cylindrical ring electrode having an inner diameter larger than the outer diameter of the cylindrical electrode portion C and surrounding the cylindrical electrode portion C at a constant interval. Part D is provided. The semiconductive belt 1 is sandwiched between the cylindrical electrode part C and the ring-shaped electrode part D and the plate-like insulator B in the first voltage application electrode A, and the cylindrical electrode part C in the first voltage application electrode A and A current I (A) that flows when a voltage V (V) is applied to the ring-shaped electrode portion D is measured, and the surface resistivity ρs (of the transfer surface of the semiconductive belt 1 is calculated by the following equation (2). Ω / □) can be calculated. Here, in the following formula (2), d (mm) indicates the outer diameter of the cylindrical electrode portion C, and D (mm) indicates the inner diameter of the ring-shaped electrode portion D.
Formula (2) ρs = π × (D + d) / (D−d) × (V / I)

<Volume resistivity>
In the semiconductive belt of the present invention, the surface resistivity of at least one of the inner layer and the outer layer is preferably 1 × 10 ⁸ to 1 × 10 ¹³ Ωcm, and preferably 1 × 10 ⁹ to 1 × 10 ^12. More preferably, it is Ωcm. Moreover, it is more preferable that both the inner layer and the outer layer satisfy the above-mentioned preferable surface resistivity range. When the volume resistivity is less than 1 × 10 ⁸ ΩCm, the electrostatic force that holds the charge of the unfixed toner image transferred from the image carrier to the semiconductive belt becomes difficult to work. Due to the electrostatic repulsion force between them and the force of the fringe electric field near the image edge, the toner is scattered around the image (blur), and an image with a large noise may be formed. On the other hand, when the volume resistivity is higher than 1 × 10 ¹³ Ωcm, since the charge retention is large, the surface of the semiconductive belt is charged by the transfer electric field in the primary transfer, so a static elimination mechanism is necessary. It may become. Therefore, by setting the volume resistivity of the outer layer to 1 × 10 ⁸ to 1 × 10 ¹³ Ωcm, it is possible to solve the problem of toner scattering and the need for a static elimination mechanism.

In the semiconductive belt of the present invention, the volume resistivity can be measured according to JIS K6991 using a circular electrode (for example, HR probe of Hiresta IP manufactured by Mitsubishi Yuka Co., Ltd.). A method for measuring the volume resistivity will be described with reference to the drawings. FIG. 5 is a schematic plan view (a) and a schematic cross-sectional view (b) showing an example of a circular electrode. The circular electrode shown in FIG. 5 includes a first voltage application electrode A ′ and a second voltage application electrode B ′. The first voltage application electrode A ′ has a cylindrical electrode part C ′ and a cylindrical shape having an inner diameter larger than the outer diameter of the cylindrical electrode part C ′ and surrounding the cylindrical electrode part C ′ at a constant interval. Ring-shaped electrode portion D ′. The semiconductive belt 1 is sandwiched between the cylindrical electrode portion C ′ and ring-shaped electrode portion D ′ and the second voltage application electrode B ′ in the first voltage application electrode A ′, and the first voltage application electrode A ′. The current I (A) that flows when the voltage V (V) is applied between the cylindrical electrode portion C ′ and the second voltage application electrode B ′ is measured, and the semiconductive belt 1 is expressed by the following equation (3). The volume resistivity ρv (Ωcm) of can be calculated. Here, in the following formula (3), t represents the thickness of the semiconductive belt 1.
Formula (3) ρv = 19.6 × (V / I) × t

In the semiconductive belt of the present invention, the Young's modulus of the inner layer is preferably 4000 MPa or more, more preferably 4500 MPa or more, and further preferably 5000 MPa or more. The relationship between the Young's modulus of the inner layer and the amount of displacement of the belt due to disturbance (load fluctuation) during driving of the belt can be expressed by the following equation (4).
Formula (4) Δl = P · l · α / (t · w · E)
Where Δl: belt displacement (μm)
P: Load (N)
l: Belt length between two tension rolls (mm)
α: Coefficient t: Belt thickness (mm)
w: Belt width (mm)
E: represents the Young's modulus (N / mm ² ) of the belt material.

  As described above, the belt expansion / contraction (displacement amount) due to disturbance (load fluctuation) during belt driving is inversely proportional to the Young's modulus and thickness of the belt material. When an inner layer having a high Young's modulus (4000 MPa or more) is used, the amount of displacement of the belt due to disturbance (load fluctuation) during driving of the belt decreases, belt deformation due to stress during driving decreases, and good image quality is stably obtained. be able to. However, as the thickness of the belt increases, the amount of deformation of the outer surface of the belt at the belt bending portion such as the drive system roll increases, and a good image quality may not be obtained. Further, the deformation amount between the outer side and the inner side of the belt increases, and there may be a problem that the belt breaks due to local repeated stress.

  The semiconductive belt of the present invention having the above-described configuration is free from a decrease in resistance due to a transfer voltage, is free from problems such as shape deformation over time, has no electric field dependency, and has little change in electrical resistance due to the environment. It has excellent properties. As will be described later, the semiconductive belt of the present invention can be used as an intermediate transfer belt and a paper conveying belt in an image forming apparatus such as an electrophotographic copying machine or a laser printer.

  The semiconductive belt of the present invention comprises an outer layer and an inner layer mainly composed of the polyimide resin as described above, and both the outer layer and the inner layer contain a conductive material, but contain additives other than the conductive material. May be. Further, in addition to the outer layer and the inner layer, the number of layers can be further increased as long as the effects of the present invention are not impaired.

  Since the formation of the semiconductive belt is endless, it can be formed by an appropriate connection method such as an adhesive method using an adhesive at the film end or a seamless belt. The seamless belt has an advantage that an arbitrary portion can be set as the rotation start position without any change in the thickness of the joint, and a control mechanism for the rotation start position can be omitted.

  The inner layer and outer layer are formed by, for example, developing the polyamic acid solution obtained by polymerizing the above-described tetracarboxylic dianhydride having a wholly aromatic skeleton and a diamine component in an appropriate manner. The layer can be dried and formed into a film, and the molded product can be heat treated to convert the polyamic acid into an imide. Lamination of the outer layer and the inner layer is possible by repeating these operations, but a method of simultaneously converting both layers to imide after repeating the steps until conversion to imide is preferred from the viewpoint of adhesiveness of each layer.

  When forming a seamless belt, for example, a method of immersing a polyamic acid solution in the outer peripheral surface of a cylindrical mold, a method of applying to a peripheral surface, a method of further centrifuging, or a method of filling a casting mold Conventional methods such as a method of spreading the ring layer in an appropriate manner, forming the dried layer into a bell-shaped mold, heat-treating the molded product to convert the polyamic acid into an imide, and recovering it from the mold Can be carried out by an appropriate method according to the above (Japanese Patent Laid-Open No. 61-95361, Japanese Patent Laid-Open No. 64-22514, Japanese Patent Laid-Open No. 3-180309, etc.). In forming the seamless belt, an appropriate treatment such as mold release treatment or defoaming treatment can be performed.

  When forming the semiconductive belt of the present invention as a seamless belt, for example, using the raw material liquid of each layer having the above-described components, forming an outer layer and an inner layer sequentially to form a cylindrical body, and then performing imide conversion Good. The cylindrical body is formed, for example, by spreading the first layer of the raw material liquid into a cylindrical shape on the inner peripheral surface and outer peripheral surface of a cylindrical mold by the above-mentioned coating method, and forming the developed layer into a dry film. What is necessary is just to expand | deploy and dry similarly using the raw material liquid of a layer.

<Image forming apparatus>
The image forming apparatus of the present invention is not particularly limited as long as it is an intermediate transfer body type image forming apparatus. For example, a normal monocolor image forming apparatus that contains only a single color toner in a developing device, or a color image in which a toner image carried on an image carrier such as a photosensitive drum is subjected to primary transfer sequentially to an intermediate transfer member Any of a forming apparatus, a tandem color image forming apparatus in which a plurality of image carriers having developing units for respective colors are arranged in series on an intermediate transfer member may be used.

Further, spherical toner is preferable as the toner that can be used in the image forming apparatus of the present invention. Here, the spherical toner is a toner capable of obtaining a high transfer efficiency, and a spherical toner having a shape factor (ML2 / A) defined by the following formula (1) represented by the following formula (1) of 140 or less. Say.
Formula (1)
(ML2 / A) = [(absolute maximum length of toner particles) × 2] / [(projected area of toner particles) × π × 1/4 × 100]

As described above, the spherical toner refers to a toner having an average shape factor (ML 2 / A) of 140 or less. The average shape factor is preferably 100 to 140, more preferably 100 to 130, and 100 More preferably, it is -120. When the average shape factor (ML2 / A) is greater than 140, the transfer efficiency is lowered, and the deterioration of the image quality of the print sample can be visually confirmed.
The absolute maximum length of the toner particles and the projected area of the toner particles are measured using a video camera with an optical microscope image of the toner dispersed on the slide glass using a Luzex image analyzer (manufactured by Nireco Corporation, FT). It was carried out by taking in a Luzex image analyzer and processing the image.

  The spherical toner contains at least a binder resin and a colorant. The volume average particle size of the spherical toner is preferably 2 to 12 μm, and more preferably 3 to 9 μm.

  Examples of the binder resin include styrenes such as styrene and chlorostyrene, monoolefins such as ethylene, propylene, butylene, and isoprene, vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, and vinyl butyrate, and acrylic acid. Α-methylene aliphatic monocarboxylic acid esters such as methyl, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate, Homopolymers and copolymers of vinyl ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl butyl ether, vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and vinyl isopropenyl ketone can be exemplified. Particularly typical binder resins include polystyrene, styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer. A polymer, polyethylene, polypropylene, etc. are mentioned. Furthermore, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin wax, and the like can also be mentioned.

  Examples of the colorant include magnetic powders such as magnetite and ferrite, carbon black, aniline blue, calcoil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, and lamp. Black, Rose Bengal, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 57: 1, C.I. I. Pigment yellow 97, C.I. I. Pigment yellow 17, C.I. I. Pigment blue 15: 1, C.I. I. Pigment Blue 15: 3 is a typical example.

  The spherical toner may be subjected to internal addition treatment or external addition treatment with a known additive such as a charge control agent, a release agent, and other inorganic fine particles. Typical examples of the release agent include low molecular weight polyethylene, low molecular weight polypropylene, Fischer-Tropsch wax, montan wax, carnauba wax, rice wax, and candelilla wax.

  As the charge control agent, known ones can be used, but azo metal complex compounds, metal complex compounds of salicylic acid, and resin type charge control agents containing polar groups can be used. When the toner is manufactured by a wet manufacturing method, it is preferable to use a material that is difficult to dissolve in water in terms of controlling ionic strength and reducing wastewater contamination.

As the other inorganic fine particles, small-sized inorganic fine particles having an average primary particle size of 40 nm or less are used for the purpose of powder flowability, charge control, etc. Inorganic or organic fine particles having a diameter may be used in combination. As these other inorganic fine particles, known ones can be used. Examples thereof include silica, alumina, titania, metatitanic acid, zinc oxide, zirconia, magnesia, calcium carbonate, magnesium carbonate, calcium phosphate, cerium oxide, and strontium titanate.
In addition, the surface treatment of the small-diameter inorganic fine particles is effective because the dispersibility becomes high and the effect of increasing the powder fluidity increases.

  The spherical toner is not particularly limited by the production method, and can be obtained by a known method. Specifically, for example, a kneading and pulverizing method in which a binder resin and a colorant and, if necessary, a release agent and a charge control agent are kneaded, pulverized and classified, and particles obtained by the kneading and pulverizing method are mechanically impacted. Method of changing shape by force or heat energy, emulsion polymerization of binder resin polymerizable monomer, dispersion of formed dispersion, colorant, release agent and charge control agent as required The emulsion polymerization aggregation method to obtain a spherical toner by mixing and agglomerating and heat-fusing the solution, a polymerizable monomer for obtaining a binder resin, a colorant, and a release agent, if necessary, a charge control agent Suspension polymerization method in which a solution such as a suspension is polymerized, a binder resin and a colorant, and if necessary, a release agent and a charge control agent are suspended in an aqueous solvent and granulated. And the dissolution suspension method. In addition, a manufacturing method may be performed in which the spherical toner obtained by the above method is used as a core, and aggregated particles are further adhered and heat-fused to give a core-shell structure. When the external additive is added, it can be produced by mixing the spherical toner and the external additive with a Henschel mixer or a V blender. In addition, when the spherical toner is manufactured by a wet method, it can be externally added by a wet method.

  According to a first aspect of the image forming apparatus of the present invention, the above-described semiconductive belt of the present invention is used as an intermediate transfer belt. According to a second aspect of the image forming apparatus of the present invention, the above-described semiconductive belt of the present invention is used as a paper transport belt.

  As an example, FIG. 6 shows a schematic diagram of a color image forming apparatus using the semiconductive belt of the present invention as an intermediate transfer belt and sequentially repeating primary transfer. FIG. 6 is a schematic diagram for explaining a main part of an image forming apparatus to which the present invention is applied. The image forming apparatus includes a photosensitive drum 21 as an image carrier, an intermediate transfer belt 22 as an intermediate transfer member, a bias roller 23 (second transfer means) as a transfer electrode, and a sheet for supplying recording paper as a transfer medium. Tray 24, developing device 25 using Bk (black) toner, developing device 26 using Y (yellow) toner, developing device 27 using M (magenta) toner, developing device 28 using C (cyan) toner, intermediate transfer body cleaner 29, peeling Claw 33, belt rollers 41, 43 and 44, backup roller 42, conductive roller 45 (first transfer means), electrode roller 46, cleaning blade 51, recording paper 61, pickup roller 62, and feed roller 63. Become.

  In FIG. 6, the photosensitive drum 1 rotates in the direction of arrow A, and the surface thereof is uniformly charged by a charging device (not shown). An electrostatic latent image of the first color (for example, Bk) is formed on the charged photosensitive drum 21 by image writing means such as a laser writing device. The electrostatic latent image is developed with toner by the black developing device 25 to form a visualized toner image T. The toner image T reaches the primary transfer portion where the conductive roller 45 (first transfer means) is disposed by the rotation of the photosensitive drum 21, and an electric field having a reverse polarity is applied to the toner image T from the conductive roller 45. Thus, the toner image T is primarily transferred by the rotation of the intermediate transfer belt 22 in the arrow B direction while being electrostatically attracted to the intermediate transfer belt 22.

Thereafter, similarly, a second color toner image, a third color toner image, and a fourth color toner image are sequentially formed and superimposed on the intermediate transfer belt 22 to form a multiple toner image.
The multiple toner image transferred to the intermediate transfer belt 22 reaches the secondary transfer portion where the bias roller 23 (second transfer means) is installed by the rotation of the intermediate transfer belt 2. The secondary transfer unit includes a bias roller 23 installed on the surface side on which the toner image of the intermediate transfer belt 22 is carried, a backup roller 42 disposed so as to face the bias roller 23 from the back side of the intermediate transfer belt 22, and It is composed of an electrode roller 46 that rotates in pressure contact with the backup roller 42.

  The recording paper 61 is picked up one by one from the recording paper bundle stored in the paper tray 24 by the pickup roller 62, and is fed at a predetermined timing between the intermediate transfer belt 22 and the bias roller 23 of the secondary transfer portion by the feed roller 63. It is sent by. The toner image carried on the intermediate transfer belt 22 is transferred to the fed recording paper 61 by the pressure contact conveyance by the bias roller 23 and the backup roller 42 and the rotation of the intermediate transfer belt 22.

  The recording paper 61 onto which the toner image has been transferred is peeled from the intermediate transfer belt 22 by operating the peeling claw 33 in the retracted position until the primary transfer of the final toner image is completed, and is conveyed to a fixing device (not shown). The toner image is fixed by heat treatment to be a permanent image. The intermediate transfer belt 22 having completed the transfer of the multiple toner image to the recording paper 61 is prepared for the next transfer by removing residual toner by an intermediate transfer body cleaner 29 provided downstream of the secondary transfer portion. The bias roller 23 is attached so that a cleaning blade 51 made of polyurethane or the like is always in contact therewith, and foreign matters such as toner particles and paper dust adhered by transfer are removed.

In the case of transfer of a single color image, the primary transferred toner image T is immediately secondarily transferred and conveyed to the fixing device. In the case of transfer of a multicolor image by superimposing a plurality of colors, the toner image of each color is transferred to the primary transfer unit. Therefore, the rotation of the intermediate transfer belt 22 and the photosensitive drum 21 is synchronized so that the toner images of the respective colors do not shift so as to match exactly. In the secondary transfer portion, an output pressure (transfer voltage) having the same polarity as the polarity of the toner image is applied to the electrode roller 46 that is in pressure contact with the backup roller 42 that is disposed opposite to the bias roller 23 via the intermediate transfer belt 22. Then, the toner image is transferred to the recording paper 61 by electrostatic repulsion.
With the image forming apparatus having the above-described configuration, high-quality transfer image quality can be stably obtained.

  The image forming apparatus according to the first aspect of the present invention using the semiconductive belt according to the present invention as the intermediate transfer belt has been described above, but the second aspect using the semiconductive belt according to the present invention as the paper conveying belt. The same effect can be obtained in the image forming apparatus.

Examples of the present invention will be described below, but the present invention is not limited to these examples.
<Example 1>
(Preparation of polyamic acid solution (A))
N-methyl-2-pyrrolidone (NMP) solution of polyamic acid composed of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-diaminodiphenyl ether (DDE) (manufactured by Ube Industries) Euvanis A (solid content: 18% by mass) was dried with oxidized carbon black (SPECIAL BLACK4 (Degussa, pH 3.0, volatile content: 14.0%) with respect to 100 parts by mass of polyimide resin solids. Add to 23 parts by mass, and use a collision type disperser (GeanusPY manufactured by Seanas), collide after splitting into 2 parts with a pressure of 200 MPa and a minimum area of 1.4 mm ² , and pass through the path that splits again into 5 parts 5 times. To obtain a polyamic acid solution (A) containing carbon black for the outer layer.

(Preparation of polyamic acid solution (B))
N-methyl-2-pyrrolidone (NMP) solution of polyamic acid composed of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA) (Uwanisu S 23 parts by mass of dry oxidized carbon black (SPECIAL BLACK4 (manufactured by Degussa, pH 3.0, volatile content: 14.0%)) to 100 parts by mass of polyimide resin solids Using a collision-type disperser (GeanusPY made by Seanas), the mixture is collided after being divided into two parts with a pressure of 200 MPa and a minimum area of 1.4 mm ² , and then again divided into two parts and mixed five times. Thus, a polyamic acid solution (B) containing carbon black for the inner layer was obtained.

(Production of semiconductive belt)
The polyamic acid solution containing carbon black (A) is applied to the inner surface of the cylindrical mold to a thickness of 0.5 mm via a dispenser, rotated at 1500 rpm for 15 minutes to form a spread layer having a uniform thickness, and then rotated at 250 rpm. However, 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, and then cooled to room temperature to form an outer layer. Next, the carbon black-containing polyamic acid solution (B) was similarly applied to the inner surface of the carbon black-dispersed polyimide precursor obtained in this state to form an inner layer. 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 the mold was peeled from the mold to obtain the intended semiconductive belt. The total thickness of this semiconductive belt was 0.08 mm, and the thickness of the outer layer was 0.02 mm.

<Example 2>
In Example 1, 23 parts by mass of oxidation-treated carbon black (SPECIAL BLACK4) used for “Preparation of polyamic acid solution (A)” (based on 100 parts by mass of polyimide resin solids) was added to Printex 150T (Degussa). A semiconductive belt was obtained in the same manner as in Example 1 except that the pH was changed to 20 parts by mass (based on 100% by mass of polyimide resin solid content). It was. The total thickness of this semiconductive belt was 0.1 mm, and the thickness of the outer layer was 0.01 mm.

<Example 3>
In Example 1, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) used in “Preparation of polyamic acid solution (A)” was converted into 3,3 ′, 4,4′- Biphenyltetracarboxylic dianhydride (BPDA) and pyromellitic dianhydride (PMDA) were changed to a tetracarboxylic dianhydride combined at a ratio of 1: 1, and then oxidized carbon black (SPECIAL BLACK4). 23 parts by mass (based on 100 parts by mass of polyimide resin solids), 20 parts by mass of Printex 150T (Degussa, pH 4.5, volatile content: 10.0%) (100 parts by mass of polyimide resin solids) A semiconductive belt was obtained in the same manner as in Example 1 except that the above was changed. The total thickness of this semiconductive belt was 0.1 mm, and the thickness of the outer layer was 0.01 mm.

<Comparative Example 1>
Polyamide used in forming the inner layer by changing the polyamic acid solution (A) used for forming the outer layer to the polyamic acid solution (B) in “Preparation of semiconductive belt” in Example 1 A semiconductive belt was obtained in the same manner as in Example 1 except that the acid solution (B) was changed to the following polyamic acid solution (B1) to form an inner layer. The total thickness of this semiconductive belt was 0.1 mm, and the thickness of the outer layer was 0.02 mm.

(Preparation of polyamic acid solution (B1)) In “Preparation of polyamic acid solution (B)”, p-phenylenediamine (PDA), p-phenylenediamine (PDA), 4,4′-diaminodiphenyl ether (DDE) and Was changed to a diamine component having a PDA / DDE = 8: 2 molar ratio, and the addition amount of oxidized carbon black (SPECIAL BLACK4) was changed to 13 parts by mass (based on 100 parts by mass of polyimide resin solids). A polyamic acid solution (B1) was prepared in the same manner as in the preparation of the polyamic acid solution (B).

<Comparative example 2>
(Preparation of polyamic acid solution (A2))
N-methyl-2-pyrrolidone (NMP) solution of polyamic acid composed of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA) (Uwanisu S 18 mass% solid content)) and 13 parts by mass of dried carbon black (acetylene black (pH 5.7 manufactured by Denki Kagaku Kogyo Co., Ltd., volatile content 0.89%) with respect to 100 parts by mass of the polyimide resin solid content. Using a collision-type disperser (GeanusPY made by Seanas), the mixture is collided after being divided into two parts with a pressure of 200 MPa and a minimum area of 1.4 mm ² , and then again divided into two parts and mixed five times. Thus, a polyamic acid solution (A2) containing carbon black was obtained.

(Preparation of polyamic acid solution (B2))
N-methyl-2-pyrrolidone (NMP) solution of polyamic acid composed of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-diaminodiphenyl ether (DDE) (manufactured by Ube Industries) Euvanis A (solid content: 18% by mass) and dry carbon black (acetylene black (pH 5.7, manufactured by Denki Kagaku Kogyo Co., Ltd., volatile content: 0.89%) were added to 8 parts by mass of polyimide resin solid content of 8 parts Add to mass part, and use collision type disperser (GeanusPY made by Seanas), pressure is 200 MPa, minimum area is 1.4 mm ² , collides after two divisions, and again passes through the path divided into two parts five times. And mixed to obtain a polyamic acid solution (B2) containing carbon black.

(Production of semiconductive belt)
In the production of “production of semiconductive belt” in Example 1, the above-described polyamic acid solution (A2) and polyamic acid solution (B2) were used instead of the polyamic acid solution (A) and the polyamic acid solution (B). A semiconductive belt was obtained in the same manner as in “Preparation of semiconductive belt” in Example 1, except for the above. The total thickness of this semiconductive belt was 0.1 mm, and the thickness of the outer layer was 0.02 mm.

<Comparative Example 3>
In Example 1, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) used in “polyamic acid solution (A)” used for forming the outer layer was changed to 3,3 ′, 4. , 4′-biphenyltetracarboxylic dianhydride (BPDA) and pyromellitic dianhydride (PMDA) are combined into a tetracarboxylic dianhydride in a ratio of 1: 1, and oxidized carbon black ( SPECIAL BLACK4) 23 parts by mass (based on 100 parts by mass of polyimide resin solids) 8 parts by mass of dried acetylene black (manufactured by Denki Kagaku Kogyo, pH 5.7, volatile content 0.89%) The dry oxidized carbon black (SPECIAL) used for “(polyamic acid solution (B))” used for forming the inner layer The same method as in Example 1 except that LACK4 (Degussa, pH 3.0, volatile content: 14.0%) was changed to 28 parts by mass with respect to 100 parts by mass of the polyimide resin solids. A semiconductive belt was obtained with a total thickness of 0.1 mm and an outer layer thickness of 0.02 mm.

<Evaluation>
For the semiconductive belts obtained in Examples 1, 2, 3 and Comparative Examples 1, 2, 3, evaluation of linear expansion coefficient, surface resistivity, volume resistivity, flatness, and transfer image quality at 10 to 80 ° C. Then, after 3000 copies of postcards were copied continuously, the occurrence of white spots was evaluated when a halftone of 30% magenta was copied. These results are shown in Table 1.

(Linear expansion coefficient)
The linear expansion coefficient of the inner layer and the outer layer was determined by measuring the inner layer and the outer layer of the obtained semiconductive belt by cutting a test piece having a width of 3 mm and a length of 10 mm, using a thermal analyzer TMA-50 manufactured by Shimadzu Corporation, and raising the temperature. The measurement was performed at a rate of 10 ° C./min, a load of 2 g, and a temperature range of 10 to 80 ° C. From the result, the linear expansion coefficient (average value) at 10 to 80 ° C. was obtained.

(Measurement of flatness)
As shown in FIG. 2, the obtained semiconductive belt is stretched by applying a load of 4 kg with two parallel shafts 12 (Φ28 mm), and the surface of the semiconductive belt at that time is attached with a laser displacement meter 11 (keyence). The difference between the maximum value and the minimum value of the displacement amount of the belt surface was read by the laser displacement meter 11 with the center part of the shaft paired with the shaft stretched by LK-030) made in parallel with the shaft. . Judgment was evaluated according to the following criteria.
○: Flatness 4mm or less ×: When flatness exceeds 4mm

(Surface resistivity)
About the outer layer of the obtained semiconductive belt, the circular electrode shown in FIG. 5 (HR probe of Hiresta IP manufactured by Mitsubishi Yuka Co., Ltd .: outer diameter φ16 mm of the cylindrical electrode portion C, inner diameter φ30 mm of the ring-shaped electrode portion D) And an outer diameter of 40 mm), a voltage of 100 V was applied in a 22 ° C./55% RH environment, and a current value after 10 seconds was calculated. The semiconductive belt was divided into 8 parts in the circumferential direction and 3 parts in the width direction, and 24 points in the belt surface were measured, and the average value was used as the surface resistivity of the paper conveying belt. Further, the difference between logarithmic values of the maximum value and the minimum value was defined as the in-plane variation (ΔR) of the surface resistivity.

(Volume resistivity)
Similar to the surface resistivity, a circular electrode (HR probe of Hiresta IP manufactured by Mitsubishi Oil Chemical Co., Ltd.) is used, and the cylindrical electrode portion C ′ and the second voltage application electrode B ′ in the first voltage application electrode A ′. A voltage of 100 (V) was applied between and a current value after 30 seconds.

(Surface micro hardness)
About the outer layer of the obtained semiconductive belt, surface microhardness was measured on condition of the following using the apparatus (ultra-micro hardness meter DUH-201S (made by Shimadzu Corporation)) shown in FIG.
Measurement environment: 23 ° C, 55% RH
Working indenter: Triangular pyramid indenter test mode: 3 (soft material test)
Test load: 6.9 × 10 ⁻³ N (0.70 gf)
Load speed: 0.142 × 10 ⁻³ N (0.0145 gf / sec)
Holding time: 5 sec

(Evaluation of transfer image quality (color shift))
The obtained semiconductive belt was attached to Fuji Xerox Co., Ltd. Docu Color 1255CP as an intermediate transfer belt, and the transfer image quality (color shift) was evaluated according to the following criteria.
In the evaluation using the Docu Color 1255CP, a toner having a shape factor of 125 was used.
○: No color misregistration occurred.
Δ: Slight color misregistration is observed, but there is no problem in image quality.
X: The occurrence of color misregistration is recognized and there is a problem in image quality.

(Evaluation of white spots)
Furthermore, when the obtained semiconductive belt is attached to Fuji Xerox Co., Ltd. Docu Color 1255CP as an intermediate transfer belt, and 3000 copies of postcards are copied continuously, magenta 30% halftone is copied. Evaluation was made according to the following criteria.
○: No white spot occurs ×: White spot occurs and there is a problem in image quality

  FIG. 7 is an explanatory diagram showing a white-out occurrence state when copying a halftone of 30% magenta after continuously copying 3000 postcards. When the surface resistivity is 1.1 digits (logΩ / □) lower than the surrounding surface resistivity by continuously running paper (postcard) in a low temperature and low humidity environment of 10 ° C. and 15% RH, the above half In the tone (30% magenta), whitening occurs.

  FIG. 8 is a diagram for explaining a decrease in the surface resistivity of the secondary transfer portion of the intermediate transfer member. Immediately after the secondary transfer, the surface of the intermediate transfer belt 22 is charged to the plus side, and the belt side of the recording paper 61 is charged to the minus side. Therefore, peeling discharge occurs between the intermediate transfer belt 22 and the recording paper 61. Occurs, the surface of the intermediate transfer belt 22 is deteriorated, and the surface resistance is lowered.

  From the results shown in Table 1, the semiconductive belts of Examples 1 to 3 of the present invention had no variation in surface resistivity, and excellent image quality could be stably obtained over a long period of time. On the other hand, in Comparative Examples 1 and 2, since the linear expansion coefficient of the polyimide resin constituting the outer layer is smaller than the linear expansion coefficient of the polyimide resin constituting the inner layer, the flatness of the belt is bad, and the driving roll for driving the belt Adhesiveness with the semiconductive belt changes, and as a result, the belt moving speed fluctuates, and the moving speed of the intermediate transfer member differs for each color with respect to the photoconductor provided with each color developing device, so that a highly accurate image is obtained. Alignment became impossible and image defects such as color misregistration occurred. In Comparative Example 3, since the linear expansion coefficient of the polyimide resin constituting the outer layer is larger than the linear expansion coefficient of the polyimide resin constituting the inner layer, the flatness deteriorates and the nip shape at the transfer portion becomes unstable. Image alignment with high accuracy became impossible, and image defects such as color misregistration occurred. Further, in Comparative Examples 2 and 3, after continuously copying 3000 postcards, the surface resistance of the rear portion of the postcard layer decreased, and white spots occurred.

It is sectional drawing which shows the structure of the semiconductive belt of this invention. It is a schematic diagram which shows the method of measuring flatness. It is a schematic cross section which shows the measurement principle of the surface micro hardness of an outer layer. It is the schematic plan view (a) and schematic sectional drawing (b) which show an example of the circular electrode for measuring surface resistivity. It is the schematic plan view (a) and schematic sectional drawing (b) which show an example of the circular electrode for measuring volume resistivity. 1 is a schematic diagram for explaining a main part of an image forming apparatus to which the present invention is applied. FIG. 10 is an explanatory diagram illustrating a white spot occurrence state in a paper travel unit after 3000 sheets are continuously copied. It is explanatory drawing explaining the fall of the surface resistivity of the secondary transfer part of an intermediate transfer body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductive belt 2 Outer layer 3 Inner layer 11 Laser displacement meter 12 Two parallel shafts 13 Outer layer surface 14 Needle-shaped indenter 21 Photosensitive drum (image carrier)
22 Intermediate transfer belt (intermediate transfer member)
23 Bias roller (second transfer means)
24 Paper tray 25 Black developing device 26 Yellow developing device 27 Magenta developing device 28 Cyan developing device 29 Intermediate transfer member cleaner 33 Peeling claw 36 Photoconductor cleaner 41 Belt roller 42 Backup roller 43 Belt roller 44 Belt roller 45 Conductive roller (first roller Transfer means)
46 Electrode roller 61 Recording paper 62 Pickup roller 63 Feed roller T Toner image

Claims (5)

An endless semiconductive belt comprising an outer layer and an inner layer mainly composed of a polyimide-based resin which is used in an electrophotographic image forming apparatus and contains any oxidized carbon black having a pH of 5 or less ,
Difference in linear expansion coefficient at 10 to 80 ° C. between the outer layer and the inner layer, 35 × 10 ^-6 / ℃ or less and the coefficient of linear expansion of the outer layer rather greater than the linear expansion coefficient of the inner layer,
The thickness ratio of the outer layer is 10 to 25% of the total thickness,
As the polyimide resin of the outer layer, a polymer formed by imide bonding of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and 4,4′-diaminophenyl ether is used, and A semiconductive belt using a polymer formed by imide bonding of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and p-phenylenediamine as a polyimide resin . 2. The semiconductive belt according to claim 1, wherein the content of oxidized carbon black having a pH of 5 or less in the outer layer is 20 to 23 parts by mass with respect to 100 parts by mass of the polyimide resin . The semiconductive belt according to claim 1 or 2, the image forming apparatus characterized by using as an intermediate transfer belt. The semiconductive belt according to claim 1 or 2, the image forming apparatus characterized by using as the sheet conveying belt. Shape factor defined by the following formula (1) (ML2 / A) The image forming apparatus according to claim 3 or 4, characterized by using a spherical toner is 140 or less.
Formula (1)
(ML2 / A) = [(absolute maximum length of toner particles) × 2] / [(projected area of toner particles) × π × 1/4 × 100]

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