JP2015127111A - Conductive sheet, production method thereof, and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive sheet formed by dispersing a carbon nano-tube (CNT) in binder resin, and having a smooth surface, and an image forming device having the conductive sheet as a transfer belt.SOLUTION: When CNT as a conductive filler is blended in a varnish for binder resin (S104), before and after blending the CNT, defoaming of the varnish is performed respectively (S102, S105). By the defoaming, air bubbles are sufficiently removed from the varnish, and a conductive sheet having no salient defect due to the air bubbles, is acquired.

Description

  The present invention relates to a conductive sheet, a method for manufacturing the conductive sheet, and an image forming apparatus having the conductive sheet as a transfer belt.

  In an image forming apparatus having an intermediate transfer member, a toner image formed on a photosensitive member is transferred to an intermediate transfer member and then transferred to a recording medium such as plain paper. An endless transfer belt is known as an intermediate transfer member. As such a transfer belt, a belt is known in which carbon nanotubes (for example, carbon nanotubes formed by vapor deposition, hereinafter also referred to as “CNT”) are dispersed in a binder resin such as polyimide (for example, Patent Document 1). To 3).

Japanese Patent No. 4684840 JP 2003-246927 A JP 2007-023149 A

  The transfer belt is generally produced by dispersing CNTs in a binder resin or its precursor varnish, applying the obtained paint to a substrate, and drying and solidifying it. When CNT is added to the varnish, bubbles are generated. However, when the viscosity of the varnish is high, the bubbles may not be sufficiently removed even if a defoaming step is performed on the paint before application. As a result, fine convex portions (convex defects) due to the bubbles may occur on the surface of the transfer belt. The convex defect may cause a transfer defect in an electrophotographic image forming method, and as a result, may cause an image defect such as white spots.

A first object of the present invention is to provide a conductive sheet having a smooth surface in a conductive sheet in which CNTs are dispersed in a binder resin.
A second object of the present invention is to provide an image forming apparatus having the conductive sheet as a transfer belt.

  The method for producing a conductive sheet according to the present invention is a method for producing a conductive sheet in which CNTs are dispersed in a binder resin sheet. The manufacturing method includes a first defoaming step of defoaming the binder resin or its precursor varnish, a dispersion step of dispersing CNT in the varnish defoamed in the first defoaming step, A second defoaming step of defoaming the dispersed varnish, a step of applying the varnish defoamed in the second defoaming step to a substrate, drying and curing the conductive sheet, and including.

Further, the conductive sheet according to the present invention contains a binder resin and CNTs, and the CNTs are dispersed in the binder resin sheet, and the convexity per square centimeter of the surface of the conductive sheet. The number of defects is 5.20 × 10 ⁻⁴ or less.

  Further, the image forming apparatus according to the present invention includes at least an endless transfer belt that is the conductive sheet for transferring a toner image formed on the photosensitive member to a recording medium.

  The method for producing a conductive sheet according to the present invention can provide a conductive sheet having a smooth surface that is substantially free from the convex defects, although CNTs are dispersed in a binder resin. Therefore, according to the present invention, it is possible to provide an image forming apparatus having the conductive sheet as a transfer belt, and as a result, it is possible to form a high-quality image in which image defects due to transfer defects are prevented. It becomes.

It is a figure which shows an example of the preparation method of the coating material for sheets in one embodiment of this invention. 1 is a diagram schematically illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3A is an image (photograph) of a surface of a first example of a conductive sheet having a convex defect, taken with a micro high scope, and FIG. 3B is a second example of a conductive sheet having a convex defect. It is an image (photograph) of a surface taken with a micro high scope. FIG. 4A is a scanning electron microscope (SEM) photograph of a cross section of a third example of a conductive sheet having a convex defect, and FIG. 4B is an SEM photograph showing an enlarged bubble portion in the cross section. .

[Conductive sheet]
The conductive sheet according to the present embodiment contains a binder resin and CNTs, and the CNTs are dispersed in the binder resin sheet.

  One or more binder resins may be used. The binder resin can be appropriately determined according to the desired physical properties of the conductive sheet. For example, a binder resin having flexibility when formed into a sheet is selected as the binder resin of the conductive sheet that requires flexibility. Examples of the binder resin include polyimide, polyamideimide, fluorine-based resin, and polyetheretherketone. From the viewpoint of combining flexibility and mechanical strength, the binder resin is preferably polyimide or polyamideimide.

  The weight average molecular weight Mw of the binder resin is preferably 35,000 to 80,000 from the viewpoint of optimizing the viscosity of the coating material for sheet described later. Moreover, it is preferable from said viewpoint that the number average molecular weight Mn of the said binder resin is 15000-30000. The Mw and Mn of the binder resin can be measured by GPC, and can be adjusted by, for example, crosslinking of a precursor or binder resin described later at the time of solidifying the coating material for a sheet.

  The CNT is a tubular body composed of a honeycomb-like hexagonal lattice structure (graphene sheet) composed of carbon atoms and bonds thereof. One or more CNTs may be used, and a single layer or multiple layers may be used. The type of the CNT can be appropriately determined within the range in which the effect of the present embodiment can be obtained and according to the intended use of the conductive sheet.

  For example, in the case of a conductive sheet for a transfer belt of an image forming apparatus, the average fiber diameter of the CNT is 10 to 45 nm, from the viewpoint of suppressing an increase in cohesion between CNTs, and a large amount of CNT. It is preferable from the viewpoint of obtaining desired conductivity without being added. Moreover, it is preferable from said viewpoint that the fiber length of the said CNT is 1-10 micrometers. The average fiber system and the fiber length can be obtained from, for example, an SEM photograph of a cross section of the conductive sheet, and can be adjusted by cutting (pulverizing) CNT or mixing two or more CNTs. is there.

  The content of the CNT is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the binder resin from the viewpoint of realizing the desired conductivity in the conductive sheet.

  Examples of the CNT include single-walled CNT, multilayered CNT, carbon nanohorn, and cup-shaped CNT.

The number of convex defects per square centimeter on the surface of the conductive sheet can be appropriately determined according to the use of the conductive sheet, and is, for example, 5.20 × 10 ⁻⁴ or less. If the number of defects exceeds 5.20 × 10 ⁻⁴ / cm ² , the convex defects may adversely affect the surface characteristics of the conductive sheet. For example, when the conductive sheet is used for an intermediate transfer belt in an image forming apparatus, an image defect due to a transfer defect may be caused.

  The said convex defect is a convex part mainly by the bubble which generate | occur | produces with dispersion | distribution in the said binder resin of the said CNT, and remains in an electroconductive sheet. For example, the maximum length of the convex defect is 0.3 mm or less, and the height of the convex defect is 0.03 mm or less (see FIGS. 3A and 3B). The convex defect is found in the conductive sheet containing CNT, and can be confirmed by the presence of bubbles in the inside in addition to the above size. The number of the convex defects can be reduced or eliminated by manufacturing a conductive sheet by a manufacturing method described later.

The volume resistivity of the conductive sheet can be appropriately determined according to the use of the conductive sheet. For example, it is 1 × 10 ⁸ to 1 × 10 ¹² Ω · cm. This is preferable from the viewpoint of realizing conductivity. The volume resistivity of the conductive sheet can be measured by a known resistance measuring device, and can be adjusted by the content of the CNT in the conductive sheet.

  The conductive sheet may further contain a material other than the binder resin and CNT. Examples of such other materials include antioxidants, mold release agents, plasticizers and flame retardants. The type of the other material and the content in the conductive sheet can be appropriately determined within a range where the effect of the present embodiment can be obtained.

  By satisfying the range of the number of convex defects, a conductive sheet having a smooth surface with a ten-point average roughness Rzjis of 1 μm or less can be formed. The conductive sheet having such a smooth surface is suitable for an intermediate transfer belt in an electrophotographic image forming apparatus.

  The conductive sheet may further include a layer disposed on the outer peripheral surface or the inner peripheral surface. For example, the conductive sheet is also suitable for a base layer in a laminated transfer belt having a conductive base layer, an elastic layer disposed on the base layer, and a surface layer disposed on the elastic layer. For example, a rubber material such as chloroprene rubber is preferably used as the material of the elastic layer. The material of the surface layer includes, for example, a layer having moderate flexibility including polyurethane (meth) acrylate and (meth) acrylate having a fluorinated alkyl group or polysiloxane compound having a (meth) acryloyl group. A configurable curable composition is used. The surface layer may further preferably contain metal oxide particles surface-treated with a surface treatment agent such as a silane coupling agent.

As is clear from the above description, the conductive sheet is a conductive sheet containing a binder resin and CNTs, the CNTs being dispersed in the binder resin sheet, Since the number of convex defects per square centimeter on the surface of the conductive sheet is 5.20 × 10 ⁻⁴ or less, the above-mentioned convex defects are substantially eliminated while being a conductive sheet in which CNTs are dispersed in a binder resin. I don't have it. Therefore, the conductive sheet can be suitably used in applications that require a smooth surface, such as a transfer belt.

The volume resistivity of the conductive sheet is 1 × 10 ⁸ to 1 × 10 ¹² Ω · cm, which is more effective from the viewpoint of configuring the transfer belt having more preferable electrical characteristics.

  Moreover, the said electroconductive sheet contains the said CNT as an electroconductive filler. For this reason, the fine conductive path in the direction along the surface of the conductive sheet can be configured with a small amount of conductive filler (CNT) in the conductive sheet as compared with other conductive fillers. Therefore, compared to other conductive fillers, it is possible to constitute a conductive sheet that has a smaller variation in electrical resistance in the surface direction, especially compared to other carbon-based conductive materials such as carbon black. Thus, the said electroconductive sheet is much more effective from a viewpoint of making the electrical resistance in the surface direction uniform.

Furthermore, since the conductive sheet can form a sufficient conductive path with a smaller amount of conductive filler, the strength of the sheet made of the binder resin can be further suppressed from being reduced by the addition of the conductive filler. . Therefore, the said electroconductive sheet is much more effective from a viewpoint of implement | achieving an electrical property and higher mechanical strength which are intended.
High strength

[Method for producing conductive sheet]
The conductive sheet according to the above-described embodiment can be manufactured by the following manufacturing method. The method for producing a conductive sheet according to the present embodiment includes a first defoaming step, a dispersion step, a second defoaming step, and a film forming step.

  The first defoaming step is a step of defoaming the binder resin or its precursor varnish. The varnish is a liquid of the binder resin or a precursor thereof. The varnish usually further contains a solvent, but it may contain only the binder resin or only the precursor. The varnish may contain both the binder resin and the precursor.

  The precursor is a compound that becomes a binder resin by an operation in the film forming process such as heating and ultraviolet irradiation. Examples of the precursor include polyamic acid. Polyamic acid is a polymer compound having a structure of a reaction product of diamine and tetracarboxylic dianhydride, and is a precursor of polyimide.

  As the solvent, an organic solvent capable of dissolving the binder resin or the precursor can be used. The organic solvent may be one kind or more. The content of the organic solvent in the varnish can be appropriately determined as long as the binder resin or the precursor is not dissolved and precipitated. Examples of the organic solvent include N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide and dimethyl sulfoxide.

  The viscosity of the varnish is preferably 10 Pa seconds or more, more preferably 15 Pa seconds or more, and further preferably 20 Pa seconds or more, from the viewpoint of applicability of the sheet coating described later. In addition, the viscosity of the varnish is preferably 200 Pa seconds or less, more preferably 150 Pa seconds or less, and even more preferably 100 Pa seconds or less, from the viewpoint of applicability of the sheet paint described later. The viscosity of the varnish can be measured by a known viscometer such as a rotational viscometer, and can be adjusted by, for example, the content of the solvent.

  Examples of the first defoaming step include centrifugal defoaming, vacuum defoaming, ultrasonic defoaming, and a method using these in combination. The centrifugal defoaming is defoaming by centrifugal force, and the vacuum degassing is defoaming by depressurization. A method of using the centrifugal defoaming and the vacuum degassing in combination is centrifugal vacuum defoaming. The centrifugal defoaming and the vacuum degassing are preferable from the viewpoint of being excellent in both mass productivity and defoaming property, and the centrifugal defoaming is more preferable from the viewpoint described above.

The centrifugal acceleration of the centrifugal defoaming is preferably 200 G (1.96 × 10 ³ m / s ² ) or more, more preferably 300 G or more, from the viewpoint of sufficiently removing bubbles from the varnish. More preferably, it is 400G or more. The upper limit value of the centrifugal acceleration of the centrifugal defoaming can be appropriately determined according to the viscosity of the varnish.

  The degree of vacuum of the vacuum degassing is preferably 0.3 kPa or more, more preferably 0.6 kPa or more, and 0.8 kPa or more from the viewpoint of sufficiently removing bubbles from the varnish. Further preferred. The upper limit value of the pressure reduction degree of the vacuum degassing can be appropriately determined according to the viscosity of the varnish.

  The “decompression degree” is a differential pressure from the normal pressure, and is a value obtained by subtracting the pressure after depressurization in the atmosphere of vacuum degassing from the normal pressure (1 atm).

  In the dispersing step, the CNTs are dispersed in the varnish defoamed in the first defoaming step. The dispersion step is preferably a step of adding a dispersion liquid in which the CNTs are dispersed in a dispersion medium to the varnish from the viewpoint of preventing aggregation of the CNTs in the varnish.

  The dispersion medium may be one kind or more. As the dispersion medium, a liquid having insolubility with respect to the CNT and having solubility in the binder resin or the precursor in the varnish in the dispersion step is preferably used. Examples of such a dispersion medium include the above-described organic solvent blended in the varnish. The dispersion medium is preferably the same as the organic solvent in the varnish from the viewpoint of preventing precipitation of the binder resin and the precursor from the varnish.

  The content of the CNT in the dispersion can be appropriately determined within a range in which the effect of the present embodiment can be obtained. If the content is too large, the viscosity of the varnish may be reduced, resulting in uneven distribution of CNTs in the varnish (for example, sedimentation). If too small, the dispersion of CNTs in the varnish is insufficient. It may become. From these viewpoints, the content of the CNT in the dispersion is preferably 3 to 20% by mass, more preferably 5 to 18% by mass, and still more preferably 8 to 15% by mass. .

  The second defoaming step is a step of defoaming the varnish in which the CNTs are dispersed. The second defoaming step can be performed by the same method as the first defoaming step described above.

  The second defoaming step is preferably a step having a strength less than that of the first defoaming step from the viewpoint of suppressing the occurrence of the convex defect. Hereinafter, the ratio of the strength of the first defoaming step to the second defoaming step is also referred to as “defoaming strength ratio”. The strengths of the first defoaming step and the second defoaming step can be compared by, for example, defoaming time, centrifugal acceleration, or degree of vacuum.

That is, it is preferable that both the first defoaming step and the second defoaming step are the centrifugal defoaming and satisfy the following formula (1). In the following formula (1), t ₁ represents the defoaming time in the first defoaming step, and t ₂ represents the defoaming time in the second defoaming step.
t ₁ / t ₂ ≧ 1.0 (1)

The t ₁ / t ₂ is more preferably 2 or more, and further preferably 3 or more, from the viewpoint of suppressing the occurrence of the convex defect. The t ₁ / t ₂ can be appropriately determined within a range in which entanglement between fine bubbles present in the varnish and CNTs is prevented.

Alternatively, it is preferable that both the first defoaming step and the second defoaming step are the centrifugal defoaming and satisfy the following formula (2). In the following formula (2), G ₁ represents the centrifugal acceleration in the first defoaming step, and G ₂ represents the centrifugal acceleration in the second defoaming step.
_{G 1 / G 2 ≧ 1.0 (} 2)

The G ₁ / G ₂ is more preferably 2 or more, and further preferably 3 or more, from the viewpoint of suppressing the occurrence of the convex defect. G ₁ / G ₂ can be appropriately determined within a range in which entanglement between fine bubbles and CNTs present in the varnish is prevented.

Alternatively, it is preferable that both the first defoaming step and the second defoaming step are the above-mentioned vacuum defoaming and satisfy the following formula (3). In the following formula (3), P ₁ represents the degree of decompression in the first defoaming step, and P ₂ represents the degree of decompression in the second defoaming step.
P ₁ / P ₂ ≧ 1.0 (3)

The P ₁ / P ₂ is more preferably 2 or more, and further preferably 3 or more, from the viewpoint of suppressing the occurrence of the convex defect. The P ₁ / P ₂ can be appropriately determined within a range in which the fine bubbles present in the varnish and the CNTs are prevented from being entangled.

  Any one formula related to the above defoaming strength ratio may be satisfied, or a plurality of formulas may be satisfied simultaneously.

  The varnish (hereinafter referred to as “sheet coating material”) defoamed in the second defoaming step, which is subjected to the film forming step by a method including the first defoaming step, the dispersing step and the second defoaming step. Is also obtained).

An example of the process for preparing the sheet coating material is shown in FIG.
First, the varnish is prepared (step 101). The varnish may be prepared by measuring and mixing the binder resin and the organic solvent, or may be prepared by measuring a commercial product.

  Next, the prepared varnish is degassed by, for example, vacuum degassing (step 102). The varnish is defoamed under the conditions of the first defoaming step described above.

  Meanwhile, the dispersion is prepared (step 103). The dispersion may be prepared by measuring and mixing the CNT and the dispersion medium, or may be prepared by measuring a commercial product.

  Next, the dispersion prepared in step 103 is mixed with the varnish degassed in step 102 (step 104). The said mixing is performed using the stirrer which can stir the said varnish.

  Next, the mixed solution of the varnish and the dispersion is degassed by, for example, vacuum degassing (step 105). Defoaming of the mixed solution is performed under the conditions of the second defoaming step described above.

  The atmosphere of the mixed solution is returned to normal pressure, and the mixed solution is taken out (step 106). Thus, the sheet coating material is obtained.

  The film forming step is a step of preparing the conductive sheet by applying, drying and curing the sheet coating material onto a substrate. The said base material is a member holding the coating film of the said coating material for sheets, for example, is a metal mold | die. The shape of the base material can be appropriately determined according to the desired shape of the conductive sheet to be produced. In the case where the desired shape of the conductive sheet is a sheet, the substrate is, for example, a mold having a flat surface, and in the case where the desired shape of the conductive sheet is an endless shape, The substrate is, for example, a columnar or cylindrical mold.

  The sheet coating material can be applied to the substrate by an appropriate method according to the properties of the sheet coating material. Examples of the coating method include a spiral coating method, a dip coating method, a centrifugal coating method, a blade coating method, and a ring coating method. For example, when applying the viscosity of a sheet paint having a relatively high viscosity to the outer peripheral surface of a cylindrical mold, a spiral coating method is preferable.

  The film forming step can be performed by an appropriate operation according to the type of the binder resin or the precursor in the sheet coating material. For example, when the sheet paint contains polyamic acid as the precursor, the film forming step can be performed by heating to imidize the polyamic acid. In addition, when the precursor has a polymerizable unsaturated carbon bond such as a (meth) acrylic acid compound, the film formation step includes heating that causes radical addition polymerization, or irradiation with an electron beam, or those It is possible to do both.

  The manufacturing method according to the present embodiment may further include a process other than the processes described above as long as the effect of the present embodiment is obtained.

  According to the manufacturing method according to the present embodiment, as described above, by performing the defoaming step before and after adding CNTs to the varnish, a conductive sheet substantially free from convex defects due to bubbles is obtained. It is done. The reason is considered as follows.

  Since the CNT has a network structure, it is considered that bubbles are easily collected. For this reason, when air bubbles are present in the varnish, the CNTs dispersed in the varnish in the dispersion step collect the air bubbles in the varnish. If the varnish is so viscous that it exhibits only a small fluidity (for example, the varnish has a viscosity in the above-mentioned range), the bubbles trapped in the CNTs are not easily degassed from the varnish. .

  However, in the present embodiment, bubbles are already removed from the varnish before CNTs are dispersed. For this reason, CNT does not collect bubbles when added to the varnish.

  In addition, bubbles may be mixed into the varnish when the varnish and the CNT are mixed. However, the bubbles are removed from the varnish in the second defoaming step before being collected by the CNTs in the varnish.

  In the above case, if the defoaming step is performed only before the CNTs are dispersed, the air bubbles mixed during the dispersion of the CNTs are not removed from the varnish, and the convex defects are generated. Further, when the defoaming step is performed only after the CNTs are dispersed, the bubbles collected by the CNTs in the varnish are not sufficiently removed, and the convex defect is generated.

  Thus, according to the manufacturing method according to the present embodiment, since the defoaming step is performed before and after the dispersion of CNTs in the varnish, the above-described sheet coating material from which bubbles are substantially removed is obtained. . Therefore, the said electroconductive sheet which does not have a convex defect substantially is obtained by manufacturing the said electroconductive sheet by solidification of the coating film of the said coating material for sheets.

  As is clear from the above description, the method for producing a conductive sheet according to the present embodiment is a method for producing the conductive sheet in which the CNTs are dispersed in the binder resin sheet, A first defoaming step for defoaming a binder resin or its precursor varnish; a dispersion step for dispersing CNT in the varnish defoamed in the first defoaming step; and the varnish in which the CNT is dispersed. A second defoaming step for defoaming, and a step of applying, drying and curing the varnish defoamed in the second defoaming step to produce the conductive sheet. Therefore, although the CNT is dispersed in the binder resin, the conductive sheet having a smooth surface without the convex defect can be provided.

  The first defoaming step and the second defoaming step both include a defoaming step by centrifugal force, and satisfying one or both of the above formulas (1) and (2) Is more effective from the viewpoint of increasing the amount of bubbles and from the viewpoint of sufficiently removing bubbles from the sheet coating material.

  Moreover, it is much more effective from said viewpoint that both said 1st defoaming process and said 2nd defoaming process include the defoaming process by pressure reduction, and satisfy | fill said Formula (3).

  Moreover, it is still more effective from said viewpoint that both the said 1st defoaming process and the said 2nd defoaming process are combined use of the defoaming process by centrifugal force, and the defoaming process by pressure reduction.

  Further, the dispersion step is a step of adding a dispersion liquid in which the CNTs are dispersed in a dispersion medium to the varnish, which is more effective from the viewpoint of increasing the dispersibility of the CNTs in the sheet coating material. .

[Image forming apparatus]
The image forming apparatus according to the present embodiment includes an endless transfer belt, which is the conductive sheet, for transferring a toner image formed on a photoreceptor to a recording medium. The image forming apparatus includes, for example, a photosensitive member, a charging device that charges the photosensitive member, an exposure device that irradiates light to the charged photosensitive member to form an electrostatic latent image, and a photosensitive member on which the electrostatic latent image is formed. A developing device that supplies toner and forms a toner image corresponding to the electrostatic latent image, a transfer device including an intermediate transfer belt for transferring the toner image formed on the electrostatic latent image to a recording medium, and the toner image A fixing device for fixing the image to the recording medium. The transfer belt can be suitably used as the intermediate transfer belt in an electrophotographic image forming apparatus. The “toner image” refers to a state where toner is gathered in an image form.

  The image forming apparatus includes, for example, a plurality of sets of image forming units 20Y, 20M, 20C, and 20Bk, an intermediate transfer unit 10, and a fixing device 30, as shown in FIG.

  The image forming units 20Y, 20M, 20C, and 20Bk are charged to give a uniform potential to the surfaces of the photoreceptors 11Y, 11M, 11C, and 11Bk that are electrostatic latent image carriers and the photoreceptors 11Y, 11M, 11C, and 11Bk. Exposure devices 22Y, 22M, 22C, and 22Bk that form electrostatic latent images of a desired shape on the uniformly charged photoreceptors 11Y, 11M, 11C, and 11Bk, and the devices 23Y, 23M, 23C, and 23Bk, and yellow (Y), magenta (M), cyan (C), and black (Bk) toners are conveyed onto the photoreceptors 11Y, 11M, 11C, and 11Bk to develop the electrostatic latent image, thereby developing devices 21Y, 21M, 21C, 21Bk, a portion of the surface of each of the photoreceptors 11Y, 11M, 11C, and 11Bk that faces a primary transfer roller, which will be described later, and a portion that faces the charging device In between, having photosensitive elements 11Y, 11M, 11C, a cleaning device 25Y for recovering the toner remaining on 11Bk, 25M, 25C, and 25Bk, the.

  The intermediate transfer unit 10 includes an intermediate transfer belt 16 disposed so as to be in contact with the photoreceptors 11Y, 11M, 11C, and 11Bk, and a primary transfer roller 13Y disposed so as to face the photoreceptors 11Y, 11M, 11C, and 11Bk. , 13M, 13C, 13Bk, and a cleaning blade 12 for collecting toner remaining on the surface of the intermediate transfer belt 16 on the upstream side of the photosensitive member in the driving direction of the intermediate transfer belt 16.

  The cleaning blade 12 is an elastic blade made of rubber, for example. The cleaning blade 12 is disposed so as to protrude in a direction opposite to the rotation direction of the intermediate transfer belt 16, and contacts the intermediate transfer belt 16 at the protruding edge of the cleaning blade 12 along the width direction of the intermediate transfer belt 16. It touches.

  The shape of the intermediate transfer belt 16 is an endless belt shape. The intermediate transfer belt 16 is stretched by a plurality of rollers and is rotatably supported. The intermediate transfer belt 16 is a transfer belt according to the present embodiment, for example, the transfer belt 1.

  The primary transfer rollers 13Y, 13M, 13C, and 13Bk contact the intermediate transfer belt 16 with the photoconductor to form a primary transfer nip portion.

  The fixing device 30 includes, for example, a heating roller and a pressure roller that forms a fixing nip portion in contact with the heating roller.

  The image forming apparatus includes a secondary transfer roller 17, a registration roller 46, and a conveyance belt 47. The secondary transfer roller 17 contacts the intermediate transfer belt 16 to form a secondary transfer nip portion.

  The registration roller 46 conveys the image support P to the secondary transfer nip portion. The conveyance belt 47 conveys the image support P from the secondary transfer nip portion to the fixing nip portion. The image support P is a so-called recording medium that finally carries a desired toner image. Examples of the image support P include plain paper from thin paper to thick paper, high-quality paper, coated printing paper such as art paper and coated paper, commercially available Japanese paper, postcard paper, plastic film and cloth for OHP Is included.

  The developer accommodated in the developing device may be a one-component developer using magnetic or non-magnetic toner, or may be a two-component developer in which a toner and a carrier are mixed. The toner is not particularly limited, but for example, a so-called polymerized toner having a volume-based median diameter of 3 to 9 μm and obtained by a polymerization method is preferable. By using the polymerized toner, an image having a high resolution and a stable image density can be obtained, and the occurrence of image fog is suppressed as much as possible.

  The carrier is not particularly limited. For example, a ferrite carrier having a volume-based median diameter of 30 to 65 μm and a magnetization amount of 20 to 70 emu / g is preferable. If the median diameter is less than 30 μm, white spots may occur due to carrier adhesion. If the median diameter is larger than 65 μm, the image density may be uneven.

Image formation by the image forming apparatus will be described.
The photoreceptors 11Y, 11M, 11C, and 11Bk are uniformly charged by the charging devices 23Y, 23M, 23C, and 23Bk, respectively. The charged photoconductors 11Y, 11M, 11C, and 11Bk are irradiated with, for example, laser light from the exposure devices 22Y, 22M, 22C, and 22Bk, and electrostatic latent images of desired images corresponding to the respective colors are formed on the photoconductors 11Y, 11Y, and 11B. 11M, 11C and 11Bk. To the photoconductors 11Y, 11M, 11C, and 11Bk on which the electrostatic latent images are formed, toner is supplied from the developing devices 21Y, 21M, 21C, and 21Bk, and toner images of each color are applied to the photoconductors 11Y, 11M, 11C, and 11Bk. Supported. The primary transfer rollers 13Y, 13M, 13C, and 13Bk approach the photoconductors 11Y, 11M, 11C, and 11Bk carrying the toner images and contact the intermediate transfer belt 16 to form a primary transfer nip portion.

  The primary transfer rollers 13Y, 13M, 13C, and 13Bk generate an electric field for transferring the toner image on the surface of the photosensitive member to the intermediate transfer belt 16 in the primary transfer nip portion. The toner images of the respective colors formed by the image forming units 20Y, 20M, 20C, and 20Bk are sequentially transferred onto the rotating intermediate transfer belt 16 by the primary transfer rollers 13Y, 13M, 13C, and 13Bk in the primary transfer nip. . By this primary transfer, a full-color toner image in which the respective color toner images are superimposed is formed on the intermediate transfer belt 16. The toner remaining on the surfaces of the photoreceptors 11Y, 11M, 11C, and 11Bk after the primary transfer is removed from the photoreceptors 11Y, 11M, 11C, and 11Bk by the cleaning devices 25Y, 25M, 25C, and 25Bk.

  The image support P is conveyed from the paper feed cassette to the secondary transfer roller 17 via the registration roller 46 by the paper feed conveyance means. The secondary transfer roller 17 generates an electric field for transferring the toner image on the surface of the intermediate transfer belt 16 to the image support P at the secondary transfer nip portion. In the secondary transfer nip portion, the toner image is transferred from the intermediate transfer belt 16 to the image support P.

  Since the intermediate transfer belt 16 does not substantially have the convex defect on the surface thereof, transfer failure due to the convex defect does not occur in the primary transfer and the secondary transfer. As described above, the image forming apparatus also exhibits good transferability to the image support P.

  The image support P carrying the toner image is transported to the fixing device 30 by the transport belt 47, and the toner image is fixed to the image support P by the heat and pressure processing by the fixing device 30. Thereafter, the image support P is sandwiched between paper discharge rollers and placed on a paper discharge tray outside the apparatus.

  The toner remaining on the intermediate transfer belt 16 after the toner image is transferred to the image support P by the secondary transfer roller 17 is removed from the intermediate transfer belt 16 by the cleaning blade 12.

  Since the intermediate transfer belt 16 has a smooth surface that does not have the above-described convex defect, the transfer defect caused by the unevenness due to the convex defect does not occur. Therefore, the image forming apparatus can form a high-quality image that does not have an image defect due to a transfer defect.

[Example 1]
963.86 g of polyamidoimide (PAI) varnish (Toyobo Co., Ltd., Viromax HR-11NN) 963.86 g was defoamed with a revolving mixer (Sinky Co., Ltd., AR-250) (first defoaming step) ). Centrifugal acceleration in the first defoaming step is 400G (3.92 × 10 ³ m / s ² ), and the degree of vacuum of the defoaming atmosphere is 0 kPa (that is, the pressure of the defoaming atmosphere is normal pressure). The time was 5 minutes.

  “Vilomax” is a registered trademark of Toyobo Co., Ltd., the solvent of “Vilomax HR-11NN” is N-methyl-2-pyrrolidone (NMP), and the content of PAI in the varnish is The number average molecular weight of the PAI is 19 million. The degree of decompression is a value obtained by subtracting the pressure of the atmosphere after decompression from normal pressure (1 atm).

  Next, 36.145 g of CNT dispersion (manufactured by Ube Industries, AMC) was added to the PAI varnish after the first defoaming step and stirred. Next, the foam was further defoamed with the above-mentioned rotation and revolution mixer (second defoaming step). The centrifugal acceleration in the second defoaming step was 400 G, the degree of vacuum in the defoaming atmosphere was 0 kPa, and the defoaming time was 5 minutes. Thus, a paint 1 for belt was obtained. Content of CNT with respect to 100 mass parts PAI in the coating material 1 for belts is 1.25 mass parts.

  “AMC” is a registered trademark of Ube Industries, Ltd., the CNT content in AMC is 5.0 mass%, the dispersion medium is NMP, and the average fiber diameter of CNT in AMC is 11 nm. It is.

Further, the preparation of the belt paint 1, as defoaming intensity ratio that represents the intensity of the degassing of the first degassing step for the second degassing step, numerical R _G obtained from the following _formulas, the R _P and R _t each Asked.
R _G = G ₁ / G ₂
R _P = P ₁ / P ₂
R _t = t ₁ / t ₂

In the above formula, G ₁ is the centrifugal acceleration in the first defoaming step, and G ₂ is the centrifugal acceleration in the second defoaming step. P ₁ is the pressure reduction degree of the defoaming atmosphere in the first defoaming step, and P ₂ is the pressure reduction degree of the defoaming atmosphere in the second defoaming step. t ₁ is the defoaming time in the first degassing step, t ₂ is the defoaming time in the second degassing step.

  The obtained belt coating 1 is applied to the outer surface of a cylindrical mold having an outer diameter of 350 mm and a length of 400 mm by a spiral application method using a dispenser while rotating the mold, and the mold is further applied. The belt was rotated to obtain a uniform coating film of the belt coating 1. Next, from the outside of the rotating mold, the coating film is dried at 70 ° C. for 60 minutes by a far infrared heater, then the coating film is dried at 150 ° C. for 60 minutes in a hot air drying box, and then The coating film was baked at 250 ° C. for 60 minutes. Then, the temperature of the mold is lowered to room temperature (25 ° C.), the solidified coating film on the outer surface of the mold is peeled off from the outer surface, and both ends in the axial direction of the endless coating film are cut, An endless belt 1 having a belt diameter of 350 mm, an axial length of 362 mm, an outer peripheral length of 1066 mm, and a thickness of 60 μm was obtained.

[Example 2]
A belt coating 2 was prepared in the same manner as in Example 1 except that the defoaming time in the first defoaming step was changed to 15 minutes, and an endless belt 2 was obtained.

[Example 3]
A belt coating material 3 was prepared in the same manner as in Example 1 except that the defoaming time in the first defoaming step was changed to 2.5 minutes, and an endless belt 3 was obtained.

[Example 4]
Using varnish of polyamic acid (PAA), which is a precursor of polyimide (PI), instead of PAI varnish (Ube Industries Co., Ltd., U-Varnish-A), CNT content in 100 parts by mass of PAA in belt coating A belt paint 4 was prepared in the same manner as in Example 1 except that the amount was 5.0 parts by mass, and an endless belt 4 was obtained.

  U-Varnish-A is a registered trademark of Ube Industries, Ltd., the solvent of U-Varnish-A is NMP, the content of PAA in the varnish is 18% by mass, and the PAA The number average molecular weight is 22,000. PAA generates equimolar PI by heating by dehydration and ring closure.

[Example 5]
The centrifugal acceleration in the first defoaming step was changed to 200G, and the same degassing time in the first defoaming step and the defoaming time in the second defoaming step were changed to 10 minutes. A belt coating 5 was prepared to obtain an endless belt 5.

[Example 6]
The decompression degree of the first defoaming step and the second defoaming step is changed to 0.3 kPa, the defoaming time of the first defoaming step is changed to 15 minutes, and the defoaming time of the second defoaming step is set to 7.5. A belt coating 6 was prepared in the same manner as in Example 4 except that the time was changed to minutes, and an endless belt 6 was obtained.

[Example 7]
A belt coating 7 was prepared in the same manner as in Example 6 except that the defoaming time in the first defoaming step was changed to 2.5 minutes and the defoaming time in the second defoaming step was changed to 5 minutes. An endless belt 7 was obtained.

[Example 8]
A belt coating 8 was prepared in the same manner as in Example 1 except that the reduced pressures in the first defoaming step and the second defoaming step were each 0.3 kPa, and an endless belt 8 was obtained.

[Example 9]
The paint for belts was the same as in Example 8, except that the centrifugal acceleration of the first defoaming step was changed to 200G and the defoaming times of the first defoaming step and the second defoaming step were both changed to 10 minutes. 9 was prepared to obtain an endless belt 9.

[Example 10]
In the first defoaming step and the second defoaming step, the belt coating material 10 was changed in the same manner as in Example 4 except that the centrifugal acceleration was changed to 200 G and the depressurization degree of the defoaming atmosphere was changed to 0.6 kPa. And an endless belt 10 was obtained.

[Example 11]
A belt coating material 11 was prepared in the same manner as in Example 10 except that the degree of decompression of the defoaming atmosphere in the first defoaming step was changed to 0.3 kPa, and an endless belt 11 was obtained.

[Comparative Example 1]
A belt paint C1 was prepared in the same manner as in Example 1 except that neither the first defoaming step nor the second defoaming step was performed, and an endless belt C1 was obtained.

[Comparative Example 2]
A belt paint C2 was prepared in the same manner as in Example 4 except that neither the first defoaming step nor the second defoaming step was performed, and an endless belt C2 was obtained.

[Comparative Example 3]
A belt paint C3 was prepared in the same manner as in Example 1 except that the first defoaming step was performed but the second defoaming step was not performed, and an endless belt C3 was obtained.

[Comparative Example 4]
A belt paint C4 was prepared in the same manner as in Example 1 except that the first defoaming step was not performed but the second defoaming step was performed, and an endless belt C4 was obtained.

[Evaluation]
(1) Volume resistivity The volume resistivity of each of the belts 1 to 11 and C1 to C4 is measured using a URS probe with a resistance measuring device (“HIRESTA UP MCP-HT450 type” manufactured by Mitsubishi Chemical Analytech Co., Ltd.). The voltage was 100 V, and the voltage application time was 10 seconds.

(2) Bubble defects The outer peripheral surfaces of the belts 1 to 11 and C1 to C4 are photographed with a micro high scope or a scanning electron microscope (SEM), and the maximum length in the outer peripheral surface is 0.3 mm or less and high. The number of fine projections (convex defects) having a thickness of 0.03 mm or less per belt was counted and evaluated according to the following criteria. If “◯” or “Δ”, there is no practical problem.
A: There is no convex defect (the number of convex defects is 0 / cm ² ).
Δ: The number of convex defects is 1 or 2 (the number of convex defects is 5.20 × 10 ⁻⁴ pieces / cm ² or less).
X: The number of convex defects is 3 or more (the number of convex defects is 7.77 × 10 ⁻⁴ pieces / cm ² or more).

  In addition, the image (photograph) image | photographed with the micro high scope of the outer peripheral surface of the belts C1 and C2 is shown in FIG. 3A, and the image (photograph) taken with the micro high scope of the outer peripheral surface of the belts C3 and C4 is shown in FIG. 3B. Each is shown. The convex portions projected in the image are all convex defects (bubble defects). It turns out that innumerable convex defects are formed on the outer peripheral surface of any belt.

  Moreover, the SEM photograph of the cross section of belt C1, C2 is shown in FIG. 4A, and the SEM photograph which expands and shows the part of the bubble in the said cross section is shown in FIG. 4B, respectively. All black dots in FIG. 4A are bubbles. It can be seen that a large number of bubbles are present inside the belt having convex defects.

(3) The white belts 1 to 11 and C1 to C4 are mounted as intermediate transfer belts on a remodeling machine of the image forming apparatus “bizhub PRO C 6000” (manufactured by Konica Minolta Business Technologies, Inc.), and are usually used as transfer materials. Using paper, a durability test was performed to output 100 black toner halftone images. The image forming apparatus is a tandem color complex machine including a laser exposure device, a reversal developing device, and an intermediate transfer belt. The modified machine is a device obtained by modifying the image forming apparatus for the evaluation of the intermediate transfer belt. is there.

After the endurance test, five halftone images were further formed, the number of white spots per sheet in the halftone image was determined, and evaluated according to the following criteria. If “◎” or “○”, there is no practical problem. The “white spot” is a portion having a size of φ0.5 mm or more where toner is not attached in the halftone image.
A: The number of white spots is 0.
A: The number of white spots is 1 or more and 4 or less (substantially no problem in terms of image quality).
XX: The number of white spots is 10 or more (substantially problematic in terms of image quality).

(4) Lines After the endurance test, five halftone images were further formed, the number of lines per sheet in the halftone image was determined, and evaluated according to the following criteria. If “◎” or “○”, there is no practical problem. “Streak” refers to a linear portion having a length of 0.5 mm or more to which no toner is attached in a halftone image.
A: The number of streaks is zero.
A: The number of streaks is 1 or more and 4 or less (substantially no problem in terms of image quality).
XX: The number of streaks is 10 or more (substantially problematic in image quality).

  Table 1 shows the compositions of the belts 1 to 11 and C1 to C4, the conditions of the defoaming process, and the evaluation results.

  As is clear from Table 1, all of the belts 1 to 11 have sufficient volume resistivity, bubble defects (convex defects) are practically satisfactory, and the image quality of the obtained image is also good. . This is thought to be because bubbles in the sheet coating material were sufficiently removed by performing the varnish defoaming step before and after adding CNT to the varnish.

  In particular, in the belts 1, 2, 4, 6, 8, and 10 having a defoaming strength ratio of 1 or more, there were fewer bubble defects and the image quality obtained was even better. This is thought to be because the defoaming of the varnish by the first defoaming step contributes more strongly to the prevention of bubble defects than the defoaming of the varnish by the second defoaming step.

  From the above, PAI or PAA varnish was primarily defoamed, CNT was dispersed in the defoamed varnish, the varnish in which CNT was dispersed was further defoamed, and the obtained varnish-CNT dispersion was used as a basis. The belt obtained by applying, drying, and curing the material has a smooth surface although CNTs are dispersed in the binder resin, and an image forming apparatus having the belt as a transfer belt has a surface of the transfer belt. It can be seen that it is possible to form a high-quality image without image defects caused by transfer defects due to the unevenness.

  Further, by performing the primary defoaming more strongly than the secondary defoaming, bubble defects are further suppressed, and image defects due to transfer defects are further suppressed in the image forming apparatus. I understand.

  On the other hand, the belts C3 and C4 lacking one of the primary defoaming and the secondary defoaming, and the belts C1 and C2 lacking both the primary defoaming and the secondary defoaming both have sufficient volume resistance. However, it has a bubble defect that is a substantial problem, and in the image formation, the image defect due to the transfer defect occurred.

  From the above, the CNT has the ability to collect bubbles in the varnish, the bubbles inside the CNT structure filled with the varnish can be removed by the secondary defoaming, and the CNT that has collected the bubbles. When the varnish enters the structure, it is presumed that the bubbles cannot be removed by the above-described defoaming step.

  Since the conductive sheet according to the present invention does not have a convex defect peculiar to a conductive sheet containing CNT as a conductive filler, it is used as a transfer belt in an image forming apparatus, thereby preventing image defects due to transfer defects. This makes it possible to form an image with the desired image quality. In addition, according to the present invention, not only the transfer belt, but also a planar conductive member that requires a smooth surface and may have flexibility can be provided. It is expected to contribute to further development and popularization of the technical field using planar conductive members.

DESCRIPTION OF SYMBOLS 10 Intermediate transfer part 11Y, 11M, 11C, 11Bk Photoconductor 12 Cleaning blade 13Y, 13M, 13C, 13Bk Primary transfer roller 16 Intermediate transfer belt 17 Secondary transfer roller 20Y, 20M, 20C, 20Bk Image forming unit 21Y, 21M, 21C , 21Bk Developing device 22Y, 22M, 22C, 22Bk Exposure device 23Y, 23M, 23C, 23Bk Charging device 25Y, 25M, 25C, 25Bk Cleaning device 30 Fixing device 46 Registration roller 46 Registration roller 47 Conveyor belt P Image support

Claims (9)

A method for producing a conductive sheet in which carbon nanotubes are dispersed in a binder resin sheet,
A first defoaming step of defoaming the binder resin or its precursor varnish;
A dispersion step of dispersing carbon nanotubes in the varnish defoamed in the first defoaming step;
A second defoaming step of defoaming the varnish in which the carbon nanotubes are dispersed;
Applying the varnish defoamed in the second defoaming step to a substrate, drying and curing the conductive sheet,
including,
A method for producing a conductive sheet. 2. The method for producing a conductive sheet according to claim 1, wherein each of the first defoaming step and the second defoaming step includes a defoaming step by centrifugal force and satisfies the following formula (1).
t ₁ / t ₂ ≧ 1.0 (1)
(In the formula (1), t ₁ represents the defoaming time in the first defoaming step, and t ₂ represents the defoaming time in the second defoaming step.) The said 1st defoaming process and the said 2nd defoaming process are both the manufacturing methods of the electroconductive sheet of Claim 1 or 2 including the defoaming process by centrifugal force and satisfy | filling following formula (2).
_{G 1 / G 2 ≧ 1.0 (} 2)
(In Formula (2), G ₁ represents the centrifugal acceleration in the first defoaming step, and G ₂ represents the centrifugal acceleration in the second defoaming step.) The said 1st defoaming process and the said 2nd defoaming process both include the defoaming process by pressure reduction, and satisfy | fill following formula (3), The electroconductive sheet as described in any one of Claims 1-3 Manufacturing method.
P ₁ / P ₂ ≧ 1.0 (3)
(In Formula (3), P ₁ represents the degree of vacuum in the first defoaming step, and P ₂ represents the degree of vacuum in the second defoaming step.)   5. The method for producing a conductive sheet according to claim 4, wherein the first defoaming step and the second defoaming step are both a defoaming step using centrifugal force and a defoaming step using reduced pressure.   The said dispersion | distribution process is a manufacturing method of the electroconductive sheet as described in any one of Claims 1-5 which is a process of adding the dispersion liquid which disperse | distributed the said carbon nanotube to the dispersion medium to the said varnish. A conductive sheet containing a binder resin and carbon nanotubes, wherein the carbon nanotubes are dispersed in the binder resin sheet,
The number of convex defects per square centimeter on the surface of the conductive sheet is 5.20 × 10 ⁻⁴ or less. The conductive sheet according to claim 7, wherein the volume resistivity of the conductive sheet is 1 × 10 ⁸ to 1 × 10 ¹² Ω · cm. An image forming apparatus having at least an endless transfer belt which is a conductive sheet according to claim 7 or 8 for transferring a toner image formed on a photosensitive member to a recording medium.