JP2012247600A - Intermediate transfer belt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an intermediate transfer belt which has a small water absorption, causes no image unevenness depending on an environment, causes no toner scattering and has excellent durability for long-term use.SOLUTION: There is provided an intermediate transfer belt made of a polyimide resin containing a conductive filler, in which 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA) is used as an anhydrous carboxylic acid monomer constituting the polyimide resin and p-phenylenediamine (PDA) and 4,4'-diaminophenyl ether (ODA) are used as the diamine. A molar ratio of the diamine component, PDA/(PDA+ODA), is 10 to 38% and the content of carbon black as the conductive filler is 10 to 25 mass%.

Description

  The present invention relates to an intermediate transfer belt that has been widely used in recent years for electrophotographic image forming apparatuses.

  Conventionally, as an image forming apparatus for forming and recording an image by an electrophotographic method, a copying machine, a laser printer, a video printer, a facsimile, a complex machine thereof, and the like are known. In order to improve the life of the apparatus of this type, an intermediate transfer system has been recently developed in which a toner image on an image carrier such as a photosensitive drum is once transferred to an intermediate transfer belt and then transferred and fixed on a printing sheet. Widely adopted.

  As a semiconductive belt that can be used for an intermediate transfer belt, an intermediate transfer belt is proposed in which a conductive filler is dispersed in a polyimide resin having excellent mechanical properties and heat resistance.

  However, the semiconductive intermediate transfer belt made of polyimide resin proposed so far has a poor balance between flexibility and rigidity, and it cannot be said that the durability as an intermediate transfer belt or a transfer conveyance belt is sufficient. In addition, the intermediate transfer belt made of polyimide resin has a problem that even if the flexibility is sufficient, the tear strength is reduced, and cracking is likely to occur from the end of the belt in long-term use (see Patent Document 1).

  In addition, BPDA / ODA type polyimides using 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) and 4,4′-diaminodiphenyl ether (ODA), which are conventionally used, High flexibility and excellent durability as an intermediate transfer belt, but because the rigidity is low, the belt itself is easy to stretch, and the image transferred from the photoconductor to the intermediate transfer belt also stretches, so that it can be Image misalignment is likely to occur, and as an intermediate transfer belt, the moisture content is slightly high, so the resistivity is highly dependent on the environment, and image unevenness occurs due to environmental changes. In order to improve this property, a diamine may be added with a highly rigid BPDA / PDA-based polyimide using p-phenylenediamine (PDA) instead of ODA. However, if the ratio of BPDA / PDA is increased, flexibility is improved. Insufficient and long-term belt cracking occurs (Patent Document 2).

  That is, with BPDA / ODA, the rigidity is insufficient and image misalignment is likely to occur, and with color images, the problem of color misalignment becomes significant. In order to balance flexibility and rigidity, Patent Document 2 defines the ratio of BPDA / PDA polyimide added to BPDA / ODA polyimide. However, it is difficult to say that sufficient characteristics are obtained.

Japanese Patent Laying-Open No. 2005-247988 Japanese Patent No. 4263825

  The present invention has been made to solve the above problems. Furthermore, as a result of studies based on the recent trend toward high image quality, it has become clear that toner scattering occurs on an image when the above-described conventional technology is used.

  In order to analyze the cause of the scattering of the toner, when the occurrence location was confirmed, the scattering was confirmed on the image already transferred onto the intermediate transfer belt. When the factor analysis is further advanced, one of the factors is that the belt itself vibrates due to the driving of the intermediate transfer belt by the image forming operation, and the toner is electrostatically moved from the photosensitive member to the intermediate transfer belt. It was found that it was not transcribed correctly.

  That is, an object of the present invention is to provide an intermediate transfer belt that is free from toner scattering due to the environment and also has excellent durability that can withstand long-term use.

  Conventionally used BPDA / ODA-based polyimide has high flexibility and excellent durability as an intermediate transfer belt, but because of low rigidity, image misalignment is likely to occur as an intermediate transfer belt, or water absorption Therefore, the resistivity of the intermediate transfer belt is highly dependent on the environment, and image unevenness occurs due to environmental changes.

  However, as a result of intensive studies by the inventor, although this is a limited region, these balances are balanced, the water absorption is small, image unevenness does not occur due to the environment, toner scattering does not occur, and long-term It has been found that there is a configuration in which an intermediate transfer belt excellent in durability can be obtained without causing cracks at the end of the belt in use.

  That is, it has been found that the object of the present invention is achieved by adopting the following configuration.

(1)
In an intermediate transfer belt containing a conductive filler in polyimide resin,
As the monomeric carboxylic anhydride constituting the polyimide resin, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) is used,
As the diamine, p-phenylenediamine (PDA) and 4,4′-diaminodiphenyl ether (ODA) are used.
The molar ratio of PDA / (PDA + ODA) of the diamine component is 10 to 38%,
An intermediate transfer belt comprising 10 to 25% by mass of carbon black as a conductive filler.

(2)
The intermediate transfer belt according to (1), wherein 95% by mass or more of the mass obtained by subtracting the mass of the conductive filler from the total mass of the intermediate transfer belt is the total mass of BPDA, PDA, and ODA.

(3)
The intermediate transfer belt according to (1), wherein the polyimide resin has a weight average molecular weight of 70,000 or more and 200,000 or less.

  According to the present invention, it is possible to provide an intermediate transfer belt that does not cause image unevenness depending on the environment, does not scatter toner, and has excellent durability for long-term use.

  The present invention will be further described.

  In the present invention, the BPDA / ODA-based polyimide belt has an image shift, and it has been found that the addition of BPDA / PDA-based polyimide to the BPDA / ODA-based polyimide or the use of these copolymers improves the BPDA / ODA-based polyimide belt. However, it was found that even when the image was viewed in detail, toner scattering occurred.

  Inferring this point, it is considered that the loss tangent (tan δ) reflecting the vibration absorption is related.

  That is, there is a dynamic viscoelasticity measurement method as one of the methods for analyzing the mechanical properties of a polymer having both elasticity and viscosity, and a storage elastic modulus (E ′) corresponding to elasticity and a loss elastic modulus (E) corresponding to viscosity. "), And the ratio of E" and E ', and the loss tangent (tan δ) reflecting the vibration absorption can be measured.

  When dynamic viscoelasticity is measured for belts with different ratios of BPDA / PDA to BPDA / ODA, when BPDA / PDA is added to BPDA / ODA-based polyimide, tan δ increases until BPDA / PDA ratio is up to 25%. When the mixing ratio was increased as described above, a tendency to decrease was observed. As the ratio of BPDA / PDA is increased, the belt property changes from flexible to rigid, and the belt itself becomes hard. Therefore, it is considered that the vibration absorbability of the material itself is lost.

  As tan δ increases, vibration absorbability increases and vibration during belt driving is suppressed. As a result, toner scattering was reduced and image quality was improved. An effect was obtained when tan δ was 0.025 or more, and the ratio of BPDA / ODA and BPDA / PDA at that time was in the range of 10 mol% to 38 mol%.

  In the present invention, the tan δ value was measured with a Seiko Instruments Viscoelastic Spectrometer EXSTAR DMS6100 at a frequency of 50 Hz and a temperature of 30 degrees.

  Further, the rigidity decreases in a region where the ratio of BPDA / PDA is small, but in order to increase the rigidity, it is necessary to increase the molecular weight, and the weight average molecular weight is preferably 70,000 or more. The upper limit is not particularly limited, but a weight average molecular weight of 200,000 or less is convenient from the viscosity at the time of coating.

  In order to increase the rigidity, it is desirable to sufficiently perform the imidization reaction. In particular, when two kinds of polyimides having different optimum imide conversion temperatures are used, heating at 300 ° C. for 1 hour or more is necessary.

[Polyimide resin]
The polyimide resin in the present invention comprises a component A formed by imide bonding of a wholly aromatic skeleton that is a tetracarboxylic acid residue and a p-phenylene skeleton that is a diamine residue, and a wholly aromatic skeleton that is a tetracarboxylic acid residue. And a copolymer obtained by repeating a B component formed by imide bonding of a diamine residue and a diphenyl ether skeleton, and / or a polymer having the A component as a repeating unit and a polymer having the B component as a repeating unit, Is a blended body. However, for the reasons described above, it is preferable to use a copolymer.

  Further, such a copolymer forms, for example, an acid component such as a tetracarboxylic dianhydride having a wholly aromatic skeleton for forming the A component, a diamine component having a p-phenylene skeleton, and a B component. It can be obtained by copolymerizing an acid component such as tetracarboxylic dianhydride having a wholly aromatic skeleton (unnecessary if it is the same as component A) and a diamine component having a diphenyl ether skeleton. In addition, the blend is prepared by previously polymerizing an acid component such as a tetracarboxylic dianhydride having a wholly aromatic skeleton for forming the component A and a diamine component having a p-phenylene skeleton to form a polyamic acid (polymerization varnish). ) And an acid component such as tetracarboxylic dianhydride having a wholly aromatic skeleton for forming the B component and a diamine component having a diphenyl ether skeleton were previously polymerized to obtain a polyamic acid (polymerized varnish). Then, after mixing both polyamic acids, it can obtain by carrying out imide conversion.

  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- Naphthalenetetracarboxylic dianhydride, or compounds obtained by substituting these aromatic rings with lower alkyl groups, etc. are mentioned. Among them, 3,3 ′, 4,4′-biphenyltetracarboxylic acid is used in the present invention. Use dianhydride.

  Examples of the diamine component having a p-phenylene skeleton include p-phenylenediamine or a compound obtained by substituting the aromatic ring with a lower alkyl group, etc. In the present invention, p-phenylenediamine is used. Furthermore, examples of the diamine component having a diphenyl ether skeleton include 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether, and compounds obtained by substituting these aromatic rings with lower alkyl groups. 4,4'-diaminodiphenyl ether is used.

[Conductive filler]
As the conductive filler in the present invention, conductive or semiconductive fine powder can be used, and there is no particular limitation, but carbon black such as Ketchen black and acetylene black, metals such as aluminum and nickel, tin oxide and the like Examples of the metal oxide compound and potassium titanate are carbon black in the present invention. In particular, the average primary particle diameter is preferably 5 to 100 nm, and particularly preferably 10 to 50 nm.

The amount of the conductive filler is preferably in the range of 1 to 50 parts by mass, more preferably 2 to 30 parts by mass with respect to the type of filler, particle size, and 100 parts by mass of the polyimide resin (solid content). In the present invention, the surface resistivity (10 ⁸ to 10 ¹⁶ Ω / □) and the volume resistivity (10 ⁸ to 10 ¹⁶ ) suitable for the intermediate transfer belt and the like are selected by combining the conductive filler and an appropriate blending amount. (Ω · cm) is preferably adjusted.

If the volume resistivity or the like is too high, the transfer belt is remarkably charged when the toner image is transferred, so that when the toner image is separated from the image carrier, peeling discharge occurs and the transferred toner image is scattered. If the volume resistivity or the like is too low, an excessive current flows between the transfer belt and the image carrier, so that the toner image transferred to the belt returns to the image carrier. From this viewpoint, it is preferable that the surface resistivity is 10 ⁹ to 10 ¹³ Ω / □ and the volume resistivity is 10 ⁸ to 10 ¹² Ω · cm.

  In this invention, the composition range of a suitable polyimide resin exists according to the compounding quantity of an electroconductive filler. The semiconductive belt of the present invention is obtained by, for example, uniformly dispersing a conductive filler in a solvent used for synthesizing a polyamic acid which is a polyimide precursor, and then, after the diamine component (p-phenylenediamine and 4,4 ′ -Diaminodiphenyl ether) and acid dianhydride component (3,3 ', 4,4'-biphenyltetracarboxylic dianhydride) were added in a specific amount and copolymerized to obtain a polyamic acid solution. Can be formed into a belt shape, dried by heating and imide conversion. At that time, by using the mixture as described above as the polyamic acid, a semiconductive belt comprising a polyimide resin blend containing a conductive filler can be produced.

  At this time, in order to obtain the effect of the present invention, the carbon black content needs to be 10% to 25% by weight of the belt, and the p-phenylenediamine component and 4,4′-diaminodiphenyl ether are required. The molar ratio of the components is 10/90 to 38/62. Further, 95% by mass or more of the mass obtained by subtracting the conductive filler from the total mass of the resin belt is p-phenylenediamine, 4,4′-diaminodiphenyl ether component, p-phenylenediamine component, and 4,4′-diaminodiphenyl ether component. It was found that the intermediate transfer belt must be the sum of the above.

[Intermediate transfer belt]
Embodiments of the present invention will be described below. The intermediate transfer belt of the present invention comprises a polyimide resin containing a conductive filler.

  The method of uniformly dispersing the conductive filler in the polyimide resin is not particularly limited, and the method of mixing and dispersing the conductive filler in the polyamic acid solution, which is a polyimide precursor, using a planetary mixer, a bead mill, a three-roll, etc. There is a method in which a conductive filler is dispersed in a solvent used for synthesizing a polyamic acid with a ball mill or ultrasonic waves, and then the polyamic acid is synthesized using this solvent.

  The film forming method is not particularly limited, and after applying polyamic acid containing a conductive filler on the inner peripheral surface or outer peripheral surface of the mold by dipping method, centrifugal molding method, coating method, etc., solvent removal, imide conversion And it can obtain by peeling from a metal mold | die after that. In that case, although the heating temperature of imide conversion is based also on the kind of polyimide resin, it is preferable to carry out at 300-450 degreeC, for example, and to carry out until imide conversion is fully completed. Further, if necessary, the mold may be released from the mold, or a defoaming step may be performed.

The intermediate transfer belt of the present invention obtained as described above, a tensile modulus of 1800 N / mm ² or more, in particular, tensile modulus 2200N / mm ² or more, and more preferably at least 10000 times MIT times.

  The thickness of the intermediate transfer belt of the present invention can be appropriately determined according to the purpose of use and the like, but in general, the thickness is preferably 5 to 500 μm and the thickness is 20 from the viewpoint of mechanical properties such as strength and flexibility. -200 micrometers is more preferable.

  Next, typical embodiments of the present invention and the effects thereof will be shown and further described, but the scope of the present invention is not limited thereto.

Example 1
1947.26 g of N-methyl-2-pyrrolidone (NMP) is heated to 70 ° C., and 294.20 g of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) is contained therein, Dissolve 10.81 g and 181.80 g of 4,4'-diaminodiphenyl ether (ODA) and p-phenylenediamine (PDA) at a molar ratio of PDA / ODA = 10/90, respectively, stir for 3 hours, and then cool. Take out the polyamic acid.

  The obtained polyamic acid and 48.68 g of carbon black (Degussa, Special black 4) (10 parts by mass with respect to 100 parts by mass of polyimide solid content) were dispersed for 3 hours with a bead mill disperser to obtain a polyamic acid solution. .

  A cylindrical metal core made of aluminum with a roundness of 25 μm, a diameter of 300 mm, a length of 500 mm, and holding members at both ends is prepared, the position of the metal core is fixed, and the nozzle is rotated while rotating the nozzle. Move in the direction. A polyamic acid solution was applied in a spiral shape to the entire peripheral surface of the cored bar prepared under the conditions shown below using a nozzle, and after forming a coating film, it was flattened and further cured to obtain a resin layer. . Thereafter, the cored bar was pulled out to produce a tubular product having an outer diameter of 300 mm to obtain a target intermediate transfer belt. The belt thickness was 70 μm.

Example 2
In Example 1, a polyamic acid solution was obtained in the same manner as in Example 1 except that the molar ratio of ODA to PDA was ODA / PDA = 8: 2 (161.60 g / 21.63 g respectively). A film was formed by the same method as in Example 1 to obtain an intermediate transfer belt having a thickness of 70 μm.

  Similarly, intermediate transfer belts of Examples 3 to 12 and Comparative Examples 1 to 19 were produced. Table 1 summarizes the configuration, amount of addition, and the like.

[Evaluation of properties]
The performance evaluation of the intermediate transfer belts of Examples 1 to 12 and Comparative Examples 1 to 19 was performed for the following items.

(Tensile strength, elongation at break)
The tensile strength at break of the film was measured based on JISK7127. As the test piece, a sheet-like molded product was cut into a 1B type test piece shape and measured at a speed of 5 mm / min. If the tensile strength is 50 MPa or more, there is no practical problem.

(MIT test)
The MIT value was measured using a MIT 揉 fatigue tester MIT-D manufactured by Toyo Seiki at a weight of 250 g, a swing angle of 90 °, and a frequency of 175 times / minute. The numerical value indicates the number of swings at the time of breakage, and the average value of 5 samples is obtained. The MIT value is 5000 times or more in a range where there is no practical problem.

(Viscoelasticity; tan δ)
The tan δ value was measured with a Seiko Instruments Viscoelastic Spectrometer EXSTAR DMS6100 at a frequency of 50 Hz and a temperature of 30 degrees.

  If tan δ is 0.025 or more, there is an effect.

(Surface resistivity)
The surface resistivity was measured using a Hiresta UP MCP-HT450 type (manufactured by Mitsubishi Chemical Analytech Co., Ltd.), a probe UR type, a measurement voltage of 500 V, and a value after 10 seconds. The surface resistivity is desirably in the range of 10 ⁹ to 10 ¹³ Ω / □.

(Volume resistivity)
The volume resistivity was measured using a Hiresta UP MCP-HT450 type (manufactured by Mitsubishi Chemical Analytech Co., Ltd.) and the value after 10 seconds of probe UR, measurement voltage 10V. The volume resistivity is desirably in the range of 10 ⁸ to 10 ¹² Ω · cm.

(Toner image scattering)
The intermediate transfer belt manufactured above is mounted on the bizhub 650 manufactured by Konica Minolta Business Technologies, Inc., and a character image (3 points, 5 points) with a pixel rate of 7% is printed on high-quality paper (64 g / m ² ) on A4 size. did. 100,000 charts were printed continuously. After continuous printing, the visual evaluation of the image forming surface of the intermediate transfer belt and the quality evaluation of the last printed image were performed based on the following.

○: Toner scattering is small until the end of printing on the 100,000th sheet. Δ; Toner scattering is small until the end of printing on the 50,000th sheet, but there was much toner scattering on the 100,000th print (practical problem).
X: Level of causing a problem in practical use due to increased toner scattering in a print of less than 10,000 sheets

  In Examples 1 to 12 in the present invention, all of the characteristics are at a level that causes no problem in practical use, and there is no scattering of the toner image. On the other hand, Comparative Examples 1 to 19 outside the present invention have a problem in at least one of the characteristics, and any of the toner images is inferior to that in the present invention with respect to scattering of the toner image.

Claims (3)

In an intermediate transfer belt containing a conductive filler in polyimide resin,
As the monomeric carboxylic anhydride constituting the polyimide resin, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) is used,
As the diamine, p-phenylenediamine (PDA) and 4,4′-diaminodiphenyl ether (ODA) are used.
The molar ratio of PDA / (PDA + ODA) of the diamine component is 10 to 38%,
An intermediate transfer belt comprising 10 to 25% by mass of carbon black as a conductive filler. 2. The intermediate transfer belt according to claim 1, wherein 95% by mass or more of the mass obtained by subtracting the mass of the conductive filler from the total mass of the intermediate transfer belt is a total mass of BPDA, PDA, and ODA. The intermediate transfer belt according to claim 1, wherein the polyimide resin has a weight average molecular weight of 70,000 or more and 200,000 or less.