JP2008238597A - Polyimide resin seamless belt, its manufacturing method and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a polyimide resin seamless belt, capable of preventing the warpage of the belt generated on the imidized film forming process. <P>SOLUTION: In forming the imidized film by heating a dry film of a polyimide precursor formed on a cylindrical mold with an atmosphere heating means, a heating restricting means which restricts the heating from the air side surface of the dry film is employed. The heating restricting means is, for example, formed of the cylindrical, heating restricting cover 4 that covers the dry film 2b of the polyimide precursor on the cylindrical mold 1 and the holding means 3 that holds the cover 4 concentrically with the cylindrical mold 1. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a polyimide resin seamless belt used in an electrophotographic image forming apparatus such as a copying machine, a printer, and a facsimile machine, a seamless belt produced by the production method, and the seamless belt as an intermediate transfer belt. The present invention relates to an image forming apparatus.

  Conventionally, as an electrophotographic image forming apparatus, a toner image formed on an image carrier is transferred to an intermediate transfer belt, and the toner image on the intermediate transfer belt is transferred to a transfer material to form an image. Widely used. A seamless polyimide resin seamless belt is used as the intermediate transfer belt. Many polyimide resin seamless belts flow a polyimide precursor coating solution into the inner surface of a rotating cylindrical mold, and spread the coating solution by centrifugal force while rotating this mold at a high speed to form a uniform film. It has been manufactured by centrifugal molding (inner surface coating) to solidify.

  However, in centrifugal molding, since the required accuracy of the roughness of the outer surface of the seamless belt is high, a glossy and high-quality seamless belt cannot be obtained unless the roughness of the inner surface of the mold contacting the outer surface of the belt is reduced. Therefore, the manufacturing cost of the mold becomes very high. In addition, the coating solution must be spread uniformly by the rotation of the mold and centrifugal force in a closed space surrounded by the mold, and it is very difficult to form a uniform film when the belt is thin.

  Therefore, a method is adopted in which a coating device capable of coating a thin film is inserted into the mold to form a film that is uniform to some extent, and then the film thickness is further uniformed by centrifugal force. However, not only has the disadvantage that the manufacturing equipment becomes large due to the application to the inner surface of the mold, but also the drying of the coating film involves heating the polyimide precursor solvent in a closed space surrounded by the mold. Since it has to be evaporated, there is a problem that the drying efficiency is poor and the molding takes time.

  In order to solve these problems of centrifugal molding, a method for producing a seamless belt by applying a polyimide precursor coating solution to the outer surface of a cylindrical mold and heating and drying it has been studied.

  In this way, by applying the coating liquid to the outer surface of the mold, the seamless belt outer surface having a high required accuracy of roughness is formed by the air surface of the coating film (one that hits the air instead of the mold side) By adjusting the leveling properties of the liquid, a belt surface that satisfies the required specifications can be easily obtained. Further, since the required accuracy of the roughness of the inner surface of the seamless belt in contact with the mold is low, the roughness of the mold surface can be increased to some extent, and the manufacturing cost of the mold can be reduced. Further, since the coating liquid is applied to the outer surface of the mold, it is easy to install a coating apparatus, and sheet and film coating apparatuses (die coating, roll coating, blade coating, etc.) can be used almost as they are. Also, with regard to drying, a heating means for the coating film and a supply / exhaust means for removing the generated solvent vapor can be easily installed, so that the drying efficiency can be increased and the molding time can be shortened.

  By the way, the manufacturing process of a polyimide seamless belt generally involves applying a polyimide precursor coating solution to the inner or outer surface of a mold to form a uniform film thickness, and the polyimide precursor solvent at a relatively low temperature (60- 130 ° C) is a polyimide precursor dry film forming step that evaporates by heating, a polyimide resin imidized film forming step that raises the heating temperature (about 300 to 350 ° C) to cause an imidization reaction, and the end of imidization There is a mold release step of peeling the polyimide resin film from the mold.

  However, the warp of the belt occurs in the imidized film forming process in the manufacturing process. Heating in the imidized film forming step is generally performed by placing a mold in which a dried film of a polyimide precursor is formed in an oven for heating the atmosphere by circulating air heated by a heater or a drying furnace. However, because of the heat capacity of the mold, the mold surface of the coating film is delayed in temperature rise compared to the air surface, and a temperature difference is generated. Due to this temperature difference, the imidization reaction of the air surface proceeds first and shrinkage occurs. Since the imidization reaction of the mold surface proceeds with a delay, residual stress finally remains on the mold surface. As a result, an imidized film of polyimide resin that warps toward the mold surface is formed. In the case of the manufacturing method applied to the inner surface of the mold, there is a tendency to warp, and in the case of the manufacturing method applied to the outer surface of the mold, there is a tendency to warp. This tendency of warping tends to become stronger when the temperature increase rate is increased in order to shorten the time of the imidized film forming step.

  When a seamless belt with such warpage is used in an image forming device, the belt may be damaged due to interference between the warped belt end and other parts, or transfer defects may occur, resulting in image quality such as linear whiteout images. Cause a drop in

In Patent Document 1, when a belt that originally warped or a belt that has warped over time in an image forming apparatus and a unit that is disposed close to the outer peripheral surface of the belt relatively move, It is described that a belt pressing member that abuts against the end portion and pushes down the end portion on the belt side is provided, thereby correcting the warp of the belt and preventing the belt side end portion from being damaged due to the interference described above.
Japanese Patent Application Laid-Open No. 2004-228561 describes that image quality is stabilized by providing a transfer condition changing unit that detects a warp amount of an intermediate transfer belt of an image forming apparatus and changes a transfer condition.

  In this way, various countermeasures against the warp of the belt have been proposed, but none of these measures basically solves the warp of the belt, so there is still a limit, and an initial belt without a warp is required. .

In Patent Document 3, in order to provide a polyimide resin seamless belt with less warping, the inner warp of the polyimide precursor coating film is reduced by heating from the cylindrical core body side during the heat drying and / or heating reaction. It has been proposed. However, the air surface of the polyimide precursor coating film is at room temperature when the cylindrical core is heated by induction heating or heating means using hot air that uniformly heats the cylindrical core to the imidization temperature (about 300 to 350 ° C.). There is a concern that drying and imidization on the mold side will be faster than the air surface, and on the contrary, will be warped.
Japanese Patent Application Laid-Open No. 2002-148954 Japanese Patent No. 3744670 JP 2004-268367 A

  The present invention provides a method for producing a polyimide resin seamless belt capable of preventing belt warpage occurring in the imidized film forming step in the above-described production process even under conditions where the imidization time is shortened, that is, under conditions where the temperature rise rate is large. It is another object of the present invention to provide a polyimide resin seamless belt manufactured by the manufacturing method and an image forming apparatus using the seamless belt.

  In order to solve the above-mentioned problem, the invention described in claim 1 is a polyimide precursor coating film forming step of applying a polyimide precursor coating solution to a cylindrical inner surface or outer surface to form a coating film, A polyimide precursor dry film formation process that heats the polyimide precursor coating film to evaporate the solvent in the coating film, and an imidization reaction is performed by raising the heating temperature of the dry film to form a polyimide resin imidized film. A polyimide resin seamless belt manufacturing method comprising: an imidized film forming step to perform; and a mold releasing step of peeling the imidized film of the polyimide resin from the mold, wherein the dried film of the polyimide precursor is heated in an atmosphere When the imidized film is formed by heating by the means, a heating limiting means for limiting heating from the air surface of the polyimide precursor dry film is used.

  According to a second aspect of the present invention, in the method for producing a polyimide resin seamless belt according to the first aspect, the heating limiting means includes a cylindrical heating limiting cover that covers the polyimide precursor dry film on the cylindrical shape, and It is characterized by comprising a holding means for holding the cover concentrically with the cylindrical shape.

  According to a third aspect of the present invention, in the method for producing a polyimide resin seamless belt according to the second aspect, a gas vent hole is provided in the cylindrical heating restriction cover.

  According to a fourth aspect of the present invention, in the method for manufacturing a polyimide resin seamless belt according to the second or third aspect, the holding means is a ring-shaped jig for holding the cylindrical heating restriction cover. And

  A fifth aspect of the invention is characterized by a polyimide resin seamless belt manufactured by the method for manufacturing a polyimide resin seamless belt according to any one of the first to fourth aspects.

  The invention described in claim 6 is characterized in that the polyimide resin seamless belt described in claim 5 is an intermediate transfer belt used in an image forming apparatus.

  The invention according to claim 7 is an image forming apparatus for transferring a toner image formed on an image carrier to an intermediate transfer belt, and transferring the toner image on the intermediate transfer belt to a transfer material to form an image. The intermediate transfer belt is a polyimide resin seamless belt according to claim 5.

  According to the present invention, in order to imidize the dried film of the polyimide precursor, when heating in an oven that heats the atmosphere by circulating air heated by a heater or a drying furnace, the dried film of the polyimide precursor is heated. Since the heating limiting means for limiting the heating from the air surface is used, the air surface of the dry film can be heated with a temperature gradient closer to the mold surface. As a result, the imidization reaction is almost complete on the mold surface and the air surface. It is possible to provide a polyimide resin seamless belt that progresses simultaneously, can reduce the deviation in the belt thickness direction of residual stress generated by shrinkage due to imidization, and has less warpage.

  In addition, conventionally used atmosphere heating equipment such as ovens and drying furnaces can be used as they are, and since the temperature increase rate can be increased, the imidization time can be shortened.

  Furthermore, by using the seamless belt as an intermediate transfer member, there is no deterioration in image quality, such as damage to the belt due to interference at the belt side end, or generation of a linear blank image due to transfer failure. An image forming apparatus can be provided.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an explanatory view showing a production process of the polyimide resin seamless belt of the present invention. In the manufacturing process in the present invention, first, as shown in FIG. 1 (1), a polyimide precursor coating solution is applied to the outer surface (FIG. (A)) or inner surface (FIG. (B)) of the cylindrical mold 1. 10 and a dry film forming process in which the solvent in the coated polyimide precursor coating 2a is dried by heating to form a dry film of the polyimide precursor, and then shown in (2) of FIG. The imidized film forming step in which the dried film obtained in the previous step is heated at a higher temperature to cause an imidization reaction to form an imidized film of polyimide resin, and then formed in the previous step shown in FIG. The imidized film, that is, the polyimide resin film is peeled off from the cylindrical shape to form a seamless belt.

  In the dry film forming step, the solvent of the polyimide precursor is evaporated while heating at a relatively low temperature (60 to 130 ° C.) and rotating the cylindrical mold. By this heat drying, most of the solvent of the polyimide precursor is evaporated, and a dried film of the polyimide precursor can be obtained without worrying about dripping. In the processes so far, the residual stress that affects the warp of the belt has not accumulated in the dry film. For the heat drying in this step, heating with a far infrared heater or hot air drying for blowing air heated by the heater is used.

  The residual stress which is the cause of the warp of the belt which is a problem of the present invention is generated in the next imidized film forming step. In the imidized film forming step, the dried film dried in the previous step is heated to a heating temperature of about 300 to 350 ° C. to cause an imidization reaction. In this step, it is generally desirable to use an atmospheric drying means that can uniformly heat the entire dried film of the cylindrical mold 1 and the polyimide precursor.

As the atmosphere drying means, for example, as shown in (2) imidized film forming step of FIG. 1, there is an oven 14 that circulates and heats air heated by a heater 12 using a blower 13, or a drying furnace. When the polyimide precursor dry film 2b attached to the cylindrical mold 1 is heated by the atmospheric drying means 14, the air surface of the dry film 2b exposed to the heated air and the surface 1b of the mold are heated. 1 has a large heat capacity, so the temperature rise is slower than the surrounding area. For this reason, the temperature of the mold surface of the dry film 2b becomes lower than the temperature of the air surface of the dry film 2b.
Here, the air surface means a surface that is not in contact with a mold of a film formed on the mold. On the mold side (mold surface), a film surface almost conforming to the surface roughness of the mold can be formed. On the air surface, a film surface conforming to the leveling characteristics of the coating liquid and the drying conditions can be formed. At the time of drying, the mold surface is heated according to the mold temperature by the heat capacity of the mold, while the air surface is heated according to the air temperature of the atmosphere.

  If it does so, the reaction of imidation will also generate | occur | produce from the air surface where temperature rises easily, and the shrinkage accompanying imidation will occur to the air surface side first. On the mold surface side, the imidization reaction occurs behind the air surface, and the shrinkage accompanying imidization also occurs. However, since the imidization of the air surface has already progressed and the film has become rigid, it cannot shrink completely. The imidization reaction is finished as it is. Since the imidized film on the mold surface stores a residual stress that tends to shrink, the mold surface when the imidized film 2c is peeled from the cylindrical mold 1 in the mold release step shown in FIG. Warp to the side.

  Accordingly, the finished seamless belt tends to warp inward in the case of outer surface coating, and warps outward in the case of inner surface coating. This warping tendency is small when the temperature rising rate is small, but becomes prominent when the temperature rising rate is increased in order to shorten the imidization time.

  In the present invention, a heating limiting means for limiting heating of the polyimide precursor dry film 2b from the air surface is provided. As a result, the difference in temperature rise between the mold surface and the air surface of the dry film at the time of temperature rise is made as small as possible, and the progress of the imidization reaction proceeds almost simultaneously with the mold surface and the air surface. The deviation of the residual stress in the belt thickness direction can be reduced, and the occurrence of warpage can be reduced.

  As specifically shown in FIG. 2, the heating limiting means includes a cylindrical heating limiting cover 4 that covers the polyimide precursor dry film 2 b on the cylindrical mold 1 and a holding means that can hold it concentrically with the cylindrical mold 1. 3. If the holding means 3 is formed in a ring shape as shown in the figure, it is concentric with the cylindrical mold 1 and can easily hold the heating limiting cover 4.

  That is, as the holding means 3, the heating restriction cover 4 is a certain distance from the surface of the mold (cylindrical mold 1) (about 5 to 10 mm → the inner diameter of the heating restriction cover 4 is about the outer diameter of the mold +10 to 20 mm when applied to the outer surface. The ring-shaped jig 3 is used in order to hold it. The outer periphery of the ring-shaped jig 3 has a tapered shape (wedge), and the heat limiting cover 4 comes into contact with the tapered portion and is held.

The holding method is
(1) Place the ring-shaped jig 3 so that the tapered surface is on the top as shown in FIG.
(2) Set up the mold (cylindrical mold 1) so that it fits into the inner diameter of the ring-shaped jig 3.
(3) Set so that the lower end of the inner diameter of the heat limiting cover 4 hits the tapered surface of the ring-shaped jig 3.
(4) The upper ring-shaped jig 3 is set between the mold (cylindrical mold 1) and the heating restriction cover 4 so that the taper surface faces downward.
Do in the order.

  As can be seen from the above-described state, the air surface of the dry film 2b is covered with the heating restriction cover 4 and the holding means 3 in a state where the air layer is sealed, so that the heated air of the atmosphere drying means 14 is not directly touched. The temperature rise of the air surface of the dry film 2b is limited.

  By balancing the heat capacity and heat conduction of the heating restriction cover 4 and the mold 1, the temperature rise of the air surface can be limited to the same or somewhat slower than the temperature rise of the mold surface.

  In the description of the heating limiting means in FIG. 2, the outer surface coating (see FIG. 1A) is described as the cylindrical mold 1, so that the heating limiting cover 4 having an inner diameter larger than the outer diameter of the cylindrical mold 1 is covered. However, even in the case of inner surface coating (see FIG. 1B), the same effect can be obtained by covering the heating limiting cover having an outer diameter smaller than the inner diameter of the cylindrical mold 1.

  The heating restriction cover 4 should be sealed as much as possible so that the heated air of the atmosphere drying means 14 does not enter. However, in order to release residual solvent vapor generated during imidization and water vapor due to dehydration reaction, a small gas is partially used. It is preferable to provide a punched hole.

  FIG. 3 shows that a cylindrical mold 1 having a polyimide precursor dry film 2b formed on the outer surface thereof is placed in an oven (atmosphere heating means) 14 in which air heated by an atmosphere heating source 12 such as a heater is circulated and heated by a blower 13. The heating restriction cover 4 is held by the holding means 3 so as to cover the dry film 2b and the atmosphere is heated. Reference numeral 5 denotes a vent hole provided in the heating restriction cover. It can be seen from FIG. 3 that the outer periphery of the ring-shaped jig 3 is tapered, and that the heating limiting cover 4 hits the tapered portion and is held.

In order to confirm the effectiveness of the production method of the present invention described above, the following tests were conducted.
In order to produce a polyimide resin seamless belt by coating the outer surface using a SUS cylindrical mold 1 having an outer diameter of 130 mm, a length of 300 mm, and a thickness of 5 mm, a SUS heat limiting cover 4 having an inner diameter of 140 mm, a length of 300 mm, and a thickness of 5 mm A ring-shaped holding means 3 made of SUS having an inner diameter of 130 mm, an average outer diameter of 140 mm, and a width of 15 mm was produced.

  Next, an equimolar amount of biphenyl-3,4,3 ′, 4′-tetracarboxylic anhydride and 4,4′-diaminodiphenyl ether is polymerized at room temperature in an N-methylpyrrolidone solvent to obtain a polyamic acid. It was. A carbon black (BP-L manufactured by Cabot) dispersion liquid finely pulverized and dispersed in N-methylpyrrolidone with a bead mill was mixed with this solution. Further, polydimethylsiloxane (Toray Dow Corning Silicone SH200) having a kinematic viscosity at 25 ° C. of 1 cSt is added to 0.01 wt% of the carbon black-dispersed polyamic acid solution, and well stirred and mixed to prepare a coating solution. did.

  While the cylindrical mold was rotated at 1 rpm, the coating liquid was applied uniformly onto the outer surface of the cylindrical mold by extrusion from a die slit by a die coating method. Next, the number of revolutions was increased to 500 rpm, the temperature was raised to 120 ° C. and heated for 30 minutes to form a dry film. Next, the cylindrical mold with the dried film formed therein is put in an atmosphere heating oven similar to that shown in FIG. 3 and a heating restriction cover is held on the dried film, and then the temperature is gradually raised to 300 to 320 ° C. and baked for 30 minutes. Thus, an imidized film was formed. After the heating, the film was gradually cooled to room temperature and then taken out. The formed coating film was peeled off from the cylindrical mold 1 to obtain a polyimide resin seamless belt having a film thickness of 60 to 80 μm.

As shown in Table 1, the obtained seamless belt was found to have a significantly reduced warpage as compared to the seamless belt produced in the same manner except that the above-mentioned heating restriction cover was not used. When comparing the heating limit covers “No (*)” and “Yes (*)” in Table 1 with a higher temperature rise rate, the heating limit cover “Yes (*)” is clearly “diameter of the cutting belt”. It can be seen that is increasing.
(Note) “Diameter of cutting belt” in Table 1 is a value obtained by measuring the diameter when a belt made into a sheet is naturally curled by cutting an endless belt of φ130 mm in one width direction. The diameter becomes smaller.

  Next, an example of an electrophotographic apparatus in which the polyimide resin seamless belt of the present invention is used as an intermediate transfer member will be described. An image forming apparatus 200 illustrated in FIG. 4 includes a photosensitive drum 100 as an electrostatic latent image carrier, a charging roller 20 as a charging unit, an exposure device 30 as an exposure unit, and a developing device 40 as a developing unit. An intermediate transfer member 50, a cleaning device 60 having a cleaning blade as a cleaning means, and a static elimination lamp as a static elimination means are provided.

  The intermediate transfer member 50 is an endless polyimide resin seamless belt, and is designed to be movable in the direction of an arrow by three rollers 51 that are arranged on the inner side and stretch the belt. Part of the three rollers 51 also functions as a transfer bias roller that can apply a predetermined transfer bias (primary transfer bias) to the intermediate transfer member 50. The intermediate transfer body 50 is provided with a cleaning device 90 having a cleaning blade in the vicinity thereof, and a transfer capable of applying a transfer bias for secondary transfer of a toner image onto a transfer sheet 95 as a final transfer material. A transfer roller 80 serving as a means is arranged to face. Around the intermediate transfer member 50, a corona charger 58 for applying a charge to the toner image on the intermediate transfer member 50 is in contact with the photosensitive member 10 and the intermediate transfer member 50 in the rotation direction of the intermediate transfer member 50. And the contact portion between the intermediate transfer member 50 and the transfer paper 95.

  In the above description, the one-drum type image forming apparatus in which the polyimide resin seamless belt of the present invention is used as an intermediate transfer member is shown, but of course, it may be used in a four-drum type image forming apparatus.

It is explanatory drawing which shows the manufacturing process of the polyimide resin seamless belt of this invention. (1) is a coating / drying film forming step, (2) is an imidized film forming step, and (3) is a mold releasing step. It is explanatory drawing of the heating limiting means of this invention used at an imidation film formation process. It is explanatory drawing which shows the state which carries out atmosphere heating of the dry film | membrane of a polyimide precursor using the heating restriction | limiting means of this invention. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus using an intermediate transfer belt.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cylindrical type 2a Polyimide precursor coating film 2b Drying film of polyimide precursor 2c Imidized film or polyimide resin seamless belt 3 Holding means or ring-shaped jig 4 Cylindrical heating restriction cover or heating restriction cover 5 For degassing Hole 10 Application means 11 Heating means 12 Heat source for atmosphere heating 13 Air blower for atmosphere heating 14 Atmosphere heating means or oven for atmosphere heating 50 Intermediate transfer body 100 Photosensitive drum or photoreceptor

Claims (7)

Applying a polyimide precursor coating solution to the cylindrical inner or outer surface, and forming a coating film of the polyimide precursor to form a coating film,
The polyimide precursor dry film forming step of heating the polyimide precursor coating film to evaporate the solvent in the coating film;
An imidized film forming step of forming an imidized film of a polyimide resin by increasing the heating temperature to imidize the dry film;
A polyimide resin seamless belt manufacturing method comprising a mold release step of peeling the polyimide resin imidized film from the mold,
A polyimide resin characterized by using a heating restriction means for restricting heating of the polyimide precursor dry film from the air surface when the polyimide precursor dry film is heated by an atmosphere heating means to form an imidized film. Seamless belt manufacturing method.   The heating limiting means comprises a cylindrical heating limiting cover for covering the polyimide precursor dry film on the cylindrical mold and a holding means for holding the cover concentrically with the cylindrical mold. Item 2. A method for producing a polyimide resin seamless belt according to Item 1.   The method for producing a polyimide resin seamless belt according to claim 2, wherein a gas vent hole is provided in the cylindrical heating restriction cover.   The method for producing a polyimide resin seamless belt according to claim 2 or 3, wherein the holding means is a ring-shaped jig for holding the cylindrical heating restriction cover.   A polyimide resin seamless belt produced by the method for producing a polyimide resin seamless belt according to claim 1.   The polyimide resin seamless belt according to claim 5, which is an intermediate transfer belt used in an image forming apparatus.   An image forming apparatus for transferring a toner image formed on an image carrier to an intermediate transfer belt, and transferring the toner image on the intermediate transfer belt to a transfer material to form an image, wherein the intermediate transfer belt is claimed. An image forming apparatus comprising the polyimide resin seamless belt according to claim 5.

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