JP5002901B2 - Immersion coating method and fixing belt manufacturing method - Google Patents

Description

  The present invention relates to a dip coating method for forming a coating film on a surface of a cylindrical substrate by dip coating, and a method for manufacturing a fixing belt having a fluororesin layer formed by using the dip coating method. The fixing belt is used in a heat fixing device of an electrophotographic apparatus such as a copying machine or a laser printer.

  In an electrophotographic apparatus, a rotating body made of metal, plastic, or rubber is used as a fixing body for heat-fixing a toner image on a recording sheet, but in order to reduce the size and power consumption of the apparatus, As described in Patent Document 1 and Patent Document 2, a deformable thin resin belt is used for the rotating body. In this case, if there is a seam in the belt, a defect due to the seam occurs in the output image. Therefore, an endless belt without a seam is preferable. As the material, polyimide resin is particularly preferable in terms of strength, dimensional stability, heat resistance, and the like.

  The polyimide resin belt is produced by applying the precursor to a substrate, drying, and heating and baking. The precursor is synthesized by dissolving an acid anhydride and a diamine in an aprotic polar solvent. Examples of the aprotic polar solvent include N-methylpyrrolidone, N, N-dimethylacetamide, acetamide, N, N-dimethylformamide and the like. The concentration, viscosity, etc. of the solution are appropriately selected.

  In order to use a polyimide resin belt as a fixing member, it is preferable to provide a non-adhesive layer on the surface of the belt for the releasability of the toner adhering to the surface. As the material of the layer, fluororesins such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and the like are preferable. For non-adhesive layers, carbon powder, inorganic compound powders such as titanium oxide and barium sulfate, etc. are used to improve wear resistance, electrostatic offset, and compatibility with toner adhesion prevention oil. Materials other than resin may be included. As the fixing belt, the thickness of the polyimide resin layer is preferably in the range of 25 to 200 μm, and the thickness of the non-adhesive layer is preferably in the range of 5 to 50 μm.

  In order to produce an endless belt with a polyimide resin, a centrifugal molding method described in Patent Document 3 is that a polyimide precursor solution is applied to the inner surface of a cylindrical substrate and dried while rotating, or a cylindrical substrate described in Patent Document 4. There is an inner surface coating method in which a polyimide precursor solution is spread on the inner surface. However, in the method of forming a film on the inner surface, it is necessary to heat-treat the polyimide precursor film until it can maintain strength as a tubular body, and then remove it from the cylindrical substrate and mount it on the outer mold, which increases the number of steps. There was a problem. In addition, when a fluororesin is applied to the surface, it is necessary to apply the fluororesin after it is mounted on the outer mold.

  As another method for producing a polyimide resin endless belt, there is a method of forming a polyimide resin film on the outer surface of the substrate by applying a polyimide precursor solution to the surface of the substrate by a dip coating method, drying, and heating. If the film thickness becomes too thick due to the high viscosity of the polyimide precursor solution, as disclosed in Patent Document 5, an annular body having holes larger than the outer diameter of the substrate is floated on the polyimide precursor solution, There is a method of controlling the film thickness of the polyimide precursor solution, and this method does not require the man-hours for mounting on the outer mold.

  Furthermore, as another method for forming a polyimide resin film on the surface of the substrate, as described in Patent Document 6, a highly viscous resin solution is supplied by a dispenser while rotating the substrate, and the dispenser is moved in the axial direction of the substrate. There is also a method in which the coating is wound and spirally wound. Although this method can be applied to a desired film thickness even with a high-viscosity polyimide precursor solution, depending on the conditions, a spiral striped pattern may occur, especially when the film thickness is as thick as 50 μm or more. It was easy to occur when the movement speed of the dispenser was increased.

  On the other hand, in order to form a fluororesin layer, since the fluororesin is insoluble in a solvent, after applying a paint in which a fluororesin powder is dispersed in a solvent such as water, the solvent is dried, baked and heated to melt The way to do is taken.

  However, since the fluororesin layer is in contact with the front surface and / or back surface of the recording paper, if the surface is rough, the rough surface is transferred to the toner layer on the recording paper and the image is disturbed. The surface of the resin layer is preferably smooth.

  As a coating method of the fluororesin dispersion, the spray coating method is not preferable because of poor surface smoothness and poor coating efficiency of the expensive fluororesin dispersion.

Further, as described in Patent Document 7, while rotating the substrate, the fluororesin dispersion is also supplied by the dispenser, and the dispenser is moved in the direction of the rotation axis of the substrate to be spirally wound and applied. There is also a method, but because the fluororesin dispersion is poor in castability, the spiral streaks are difficult to disappear, especially when the film thickness is as thick as 25 μm or when the movement speed of the dispenser is increased. There was a problem that occurred easily.
JP-A-8-262903 Japanese Patent Application Laid-Open No. 11-133776 JP-A-57-74131 Japanese Patent Laid-Open No. 62-19437 JP 2002-91027 A JP-A-9-85756 JP-A-9-297482

  As another method of applying the fluororesin dispersion, there is also a dip coating method in which the cylindrical substrate is immersed in the fluororesin dispersion with its axial direction vertical, and then pulled up to form a smooth coating. Preferred in some cases.

  It is conventionally known to form a coating film on the surface of a cylindrical substrate by a dip coating method. In this case, if the paint enters the inside of the cylindrical substrate, the paint adheres to the inner surface of the cylindrical substrate, which is not preferable because the paint is wasted and the inner surface is soiled.

  It has been conventionally known that the opening surface of the bottom of the cylindrical base is sealed with a lid, fixed with an adhesive tape, and covered with a joint. In that case, it is necessary to peel off the adhesive tape and remove the lid after coating or drying, but it took time to remove the adhesive tape.

  At the time of dip coating of the fluororesin dispersion, it is preferable that a covering is attached to the bottom of the cylindrical substrate so that the fluororesin dispersion does not enter. However, the fluororesin dispersion has a problem that the liquid tends to foam due to the mixed surfactant. Therefore, it is necessary to pay sufficient attention to the generation of bubbles during immersion coating of the fluororesin dispersion, and it is unavoidable that air leaks from the gap between the cylindrical substrate and the cover, or that bubbles are generated from the impact of the step between the two. It must be done.

  However, when a covering is attached to the lower end of the substrate and its axial direction is vertical and dip-coated in the fluororesin dispersion, bubbles are generated when the covering is immersed in the fluororesin dispersion, and the coating film surface There was a problem that a smooth film could not be formed by being pulled up with bubbles adhering to it.

  In addition, by attaching a covering to the lower end of the base, the air in the base is compressed, and when it is dip coated in this state, air accumulated in the base in the liquid leaks, causing bubbles from the ridges of the covering. Occurred and a uniform film could not be formed.

  The object of the present invention is to solve the above-mentioned problems of the prior art. That is, the present invention is a dip coating method using a cylindrical substrate provided with a coating for preventing the coating liquid from entering the lower end portion, which suppresses the generation of bubbles in the paint and smoothes the surface of the cylindrical substrate. It is an object of the present invention to provide a dip coating method capable of forming a film. It is another object of the present invention to provide a method for manufacturing a fixing belt using the dip coating method.

The above problem is solved by the following means. That is,
The dip coating method of the present invention is a dip coating method in which a cylindrical substrate is immersed in a paint while maintaining its axial direction perpendicular, and then pulled up to apply the paint to the surface of the cylindrical substrate. Is the way
The cylindrical substrate is formed by sealing a lower end opening and covering a lower end outer peripheral surface, and a covering is held.
And a step formed by the difference between the maximum outer diameter of the covering body and the maximum outer diameter of the cylindrical base body, which is a boundary portion between the covering body and the cylindrical base body and is 0.5 mm or less. It is characterized in that the immersion speed T during the passage of the boundary portion formed by the portion passes the liquid surface of the coating liquid satisfies the following formula (1) and the following formula (2).
Formula (1): T ≦ −ρ + 1000
Formula (2): T ≦ −0.4ρ + 460
(Here, in formulas (1) and (2), T represents the dipping rate (mm / min), and ρ represents the viscosity of the coating liquid (mPa · s).)

  In the dip coating method of the present invention, the difference between the maximum outer diameter of the covering and the maximum outer diameter of the cylindrical substrate is preferably 0.5 mm or less.

  In the dip coating method of the present invention, it is preferable that the covering is held on the cylindrical substrate only by frictional force.

On the other hand, the manufacturing method of the fixing belt of the present invention is a method using the dip coating method of the present invention,
Forming a polyimide resin film or a polyimide precursor film on the surface of the cylindrical substrate;
The cylindrical substrate with the coating formed on the surface is immersed in a fluororesin paint while being held so that its axial direction is vertical, and then pulled up, so that the fluororesin is applied to the surface of the coating on the cylindrical substrate. Applying a paint; and
Heating and firing the applied fluororesin paint to form a fluororesin layer;
Extracting the film on which the fluororesin layer is formed from a cylindrical substrate;
Have
In the step of forming the fluororesin layer,
The cylindrical substrate is formed by sealing a lower end opening and covering a lower end outer peripheral surface, and a covering is held.
And a step formed by the difference between the maximum outer diameter of the covering body and the maximum outer diameter of the cylindrical base body, which is a boundary portion between the covering body and the cylindrical base body and is 0.5 mm or less. It is characterized in that the immersion speed T during the passage of the boundary portion formed by the portion passes the liquid surface of the coating liquid satisfies the following formula (1) and the following formula (2).
Formula (1): T ≦ −ρ + 1000
Formula (2): T ≦ −0.4ρ + 460
(Here, in formulas (1) and (2), T represents the dipping rate (mm / min), and ρ represents the viscosity of the coating liquid (mPa · s).)

  Also in the fixing belt manufacturing method of the present invention, it is preferable that the difference between the maximum outer diameter of the covering and the maximum outer diameter of the cylindrical substrate is 0.5 mm or less.

  Also in the fixing belt manufacturing method of the present invention, it is preferable that the covering is held on the cylindrical base body only by frictional force.

  According to the present invention, there is provided a dip coating method using a cylindrical base body provided with a coating for preventing the ingress of coating liquid at the lower end, which suppresses the generation of bubbles in the paint and smoothes the surface of the cylindrical base body. It is possible to provide a dip coating method capable of forming a thick film. In addition, a fixing belt manufacturing method using the dip coating method can be provided.

  Hereinafter, the manufacturing method of the fixing belt of the present invention will be described together with the dip coating method of the present invention.

  The method for producing a fixing belt of the present invention comprises a step of forming a polyimide resin film or a polyimide precursor film on the surface of a cylindrical substrate (film forming step), and a cylindrical substrate on which the film is formed on its surface. A process of applying a fluororesin paint to the surface of the coating on the cylindrical substrate (fluorine resin coating film forming process) by immersing and pulling up in the fluororesin paint while holding the direction to be vertical, A step of heating and baking the applied fluororesin coating material to form a fluororesin layer (heating and baking step), and a step of extracting the film on which the fluororesin layer has been formed from a cylindrical substrate (extraction step). Have. Hereinafter, each step will be described.

-Film formation process-

  In the film forming step, first, a polyimide precursor film is formed on the surface of the cylindrical substrate. This polyimide precursor film is formed from a polyimide precursor coating process in which a polyimide precursor is applied to a cylindrical substrate, and then a polyimide precursor drying process in which the polyimide precursor film is dried to form a polyimide precursor film.

-Polyimide precursor coating process In a polyimide precursor coating process, first, a polyimide precursor solution in which a polyimide precursor is dissolved in an aprotic polar solvent is prepared. As a polyimide precursor, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (hereinafter abbreviated as “BPDA” where appropriate) and p-phenylenediamine (hereinafter abbreviated as “PDA” where appropriate). Using polyimide precursor, using polyimide precursor consisting of BPDA and 4,4'-diaminodiphenyl ether, polyimide consisting of pyromellitic dianhydride (PMDA) and 4,4'-diaminodiphenyl ether Those using a precursor, those using a polyimide precursor composed of 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride and 4,4′-diaminodiphenylmethane, 3,3 ′, 4, Various using a polyimide precursor composed of 4′-benzophenone tetracarboxylic dianhydride and 4,4′-diaminobenzophenone It can be used consisting of a combination. Further, the polyimide precursor may be used by mixing two or more kinds, or may be a copolymer obtained by mixing acid or amine monomers.

  A polyimide precursor is prepared as a polyimide precursor solution by dissolving in an aprotic polar solvent such as N-methylpyrrolidone, N, N-dimethylacetamide, acetamide, N, N-dimethylformamide. In addition, selection of the mixing ratio, concentration, viscosity, and the like of the polyimide precursor in the preparation is performed by appropriately adjusting.

  In the polyimide precursor coating process, as one of the coating methods, the polyimide precursor solution is flattened with a spatula while the polyimide precursor solution is allowed to flow from the nozzle to the surface of the cylindrical substrate, and the nozzle and spatula are removed from one end of the cylindrical substrate. There is a method of applying a polyimide precursor solution to the surface of a substrate by moving it horizontally to the other end (spiral application method).

  Specifically, it can apply | coat using the coating device shown in FIG. In the coating apparatus shown in FIG. 1, although not shown, the cylindrical substrate 10 is disposed on a pedestal having an arm that is supported by holding members at both ends and is horizontally rotatable (arrow A) via a holding body. It is installed. Although not shown, the cylindrical base 10 is connected to a driving means (rotating means) for rotating the cylindrical base 10 through a holding member.

  In the vicinity of the cylindrical substrate 10, a flow-down device 14 (flowing means) for flowing the polyimide precursor solution 12 and attaching the polyimide precursor solution 12 to the cylindrical substrate 10 is disposed. The flow down device 14 includes, for example, a nozzle 16 for flowing down the polyimide precursor solution 12 and a container 18 for supplying the polyimide precursor solution 12 to the nozzle 16. As the container 18, for example, an apparatus using a meniscus cylinder, a screw, or the like is applied. The flow-down device 14 may be configured such that the nozzle 16 and the container 18 are connected by a connecting pipe, and the nozzle 16 and the container 18 are separated and arranged separately, or the nozzle 16 and the container 18 are integrally configured. The form may be sufficient.

  Since the polyimide precursor solution 12 having a high viscosity from the nozzle 16 is unlikely to flow down naturally by gravity alone, it is also effective to push out from the container 18 with air pressure or a pump. The distance between the nozzle 16 and the cylindrical substrate 10 may be arbitrary, but is preferably about 10 to 100 mm so that the falling liquid is not interrupted. If the liquid breaks off, bubbles may be involved.

  A spatula 20 for smoothing the polyimide precursor solution 12 adhering to the cylindrical substrate 10 is provided around the cylindrical substrate 10.

  The spatula 20 can be comprised from the material which is not attacked by the polyimide precursor solution 12, for example, plastics, such as polyethylene and a fluororesin, or a thin board of metals, such as a brass and stainless steel.

  The flow-down device 14 (nozzle 16) and spatula 20 have relative attachment and smoothing portions for each rotation of the cylindrical substrate 10 as the polyimide precursor solution 12 adheres to and smoothes the cylindrical substrate 10. The cylindrical substrate 10 is moved in the horizontal direction (arrow B) from one end of the cylindrical substrate 10 to the other end. Although not shown, this configuration may be configured to move the flow-down device 14 (nozzle 16) and spatula 20, or may be configured to move the cylindrical substrate 10, and may be configured by a known technique.

  By applying the flow-down device 14 (nozzle 16) and the spatula 20 in conjunction with each other and moving in a horizontal direction from one end of the cylindrical substrate 10 to the other end, it can be applied to the surface of the cylindrical substrate 10. The moving speed can be said to be the coating speed.

  The coating condition is that the rotational speed of the cylindrical substrate 10 is 20 to 200 rpm, and the coating speed V is related to the outer diameter k of the substrate, the flow amount f of the polyimide precursor solution, and the desired wet film thickness t. , V = f / (t · k · π). π represents the circumference.

  In the coating apparatus having the above configuration, first, while rotating the cylindrical substrate 10 in the direction of arrow A, the polyimide precursor solution 12 is caused to flow down from the nozzle 16 of the flow-down device 14, and the polyimide precursor solution 12 is transferred to the cylindrical substrate 10. Adhere. At the same time, the spatula 20 smoothes the polyimide precursor solution 12 attached to the cylindrical substrate 10. Then, the attachment point and the smoothing point are moved in the horizontal direction (arrow B) from one end of the cylindrical substrate 10 to the other end each time the cylindrical substrate 10 rotates. In this way, the polyimide precursor solution 12 is applied to the outer peripheral surface of the cylindrical substrate 10 to form a coating film.

  In addition, the application method of the polyimide precursor solution is not limited to this, and other application methods can also be applied. As another coating method, although not shown, there is a dip coating method in which a cylindrical substrate is dipped in a polyimide precursor solution and raised (pulled up). However, when the film thickness becomes too thick due to the high viscosity of the polyimide precursor solution, the film thickness of the polyimide precursor solution is controlled by an annular body having holes larger than the outer diameter of the cylindrical substrate. A dip coating method can be applied.

  Here, “applying to the surface of the cylindrical substrate” means applying to the surface of the side surface of the cylindrical substrate including the column and, if the surface has a layer, to the surface of the layer. Further, “rising the cylindrical substrate” is a relative relationship with the liquid level during coating, and includes the case of “stopping the cylindrical substrate and lowering the coating liquid level”.

-Polyimide precursor drying process When the polyimide precursor solution is applied to the surface of the cylindrical substrate and then dried, a film made of the polyimide precursor is formed. The drying temperature is preferably in the range of 50 to 200 ° C., and the drying time is preferably in the range of 30 to 200 minutes. Depending on the temperature at the time of drying, the coating film before drying has a reduced viscosity and is susceptible to sag due to the influence of gravity. In this case, the axial direction of the cylindrical substrate is horizontal and 10-60 rpm. It is better to rotate around the range.

  Of course, when the polyimide precursor is applied, the end portion of the cylindrical substrate is provided with an uncoated portion, but even when applied over the entire surface of the cylindrical substrate, the polyimide precursor coating shrinks due to drying. Therefore, an exposed portion is generated at the end of the cylindrical base.

  The cylindrical substrate on which the coating made of the polyimide precursor thus obtained is formed may be subjected to the next fluororesin coating film forming step, but at this stage, the coating made of the polyimide precursor is heated and reacted, A resin film may be formed and then subjected to a fluororesin coating film forming step.

  A polyimide resin film can be formed by heat-reacting a film made of a polyimide precursor preferably in the range of 300 to 450 ° C., more preferably around 350 ° C. for 20 to 60 minutes.

  Here, examples of the material of the cylindrical substrate include metals (for example, aluminum, stainless steel, etc.). The metal surface is coated with a fluororesin, a silicone resin, or a mixed resin thereof, or nickel or chromium is used. Those plated with or coated with a release agent are also effective from the viewpoint of facilitating peeling of the film after film formation.

  When a polyimide resin film or the like is formed and dried, the remaining solvent or water generated from the resin during the heating reaction may not be completely removed. In this case, the polyimide resin film may be swollen, particularly when the film thickness of the polyimide resin film exceeds 50 μm. In that case, roughening the surface of the cylindrical substrate is effective.

  The roughness of roughening is preferably about 0.2 to 2 μm in terms of arithmetic roughness Ra. Roughening methods include blasting, cutting, sandpaper peeling, etc. In order to make the polyimide resin belt inner surface into a spherical surface with good slidability and a convex shape, the surface of the cylindrical substrate is spherical. It is preferable to perform blasting using the particles.

  By the roughening, the residual solvent or water vapor generated from the polyimide resin film can be discharged to the outside through a slight gap formed between the cylindrical substrate and the polyimide resin film, and no swelling occurs.

  The surface of the cylindrical substrate is preferably given releasability so that the polyimide resin does not adhere. In order to provide releasability, the surface of the cylindrical substrate is releasable so that the surface of the cylindrical substrate is plated with chromium or nickel, or the surface is covered with fluorine resin or silicone resin, or polyimide resin is not adhered to the surface. It is effective to apply an agent.

  In this way, a polyimide resin film or a polyimide precursor film can be formed on the surface of the cylindrical substrate.

-Fluororesin coating film formation process-
In the fluororesin coating film forming step, when the cylindrical substrate on which either the polyimide resin film or the polyimide precursor film is formed is perpendicular to the axial direction, the covering is applied to the lower part (bottom part). The cylindrical substrate together with the covering is immersed and applied in a fluororesin dispersion (fluororesin paint).

  Specifically, it can apply | coat using the coating device shown in FIG. In the coating apparatus shown in FIG. 2, first, as shown in FIG. 3, a cylindrical substrate holding member 22 is attached to the upper end portion (upper side in FIG. 3: the side facing the lower end portion) of the cylindrical substrate 10, The covering 24 is attached to the lower end (lower side in FIG. 3). In FIG. 3, the polyimide resin film or the polyimide precursor film is omitted.

  The cylindrical substrate holding member 22 is connected to an elastic film 26 (sealing member), and is fitted into the upper opening (upper end surface) of the cylindrical substrate 10 so that the outer surface of the holding member is in contact with the inner surface of the cylindrical substrate 10. The elastic film 26 is expanded and held while being chucked (sealed).

  As shown in FIG. 4, the covering body 24 includes a bottom portion 28 for closing the lower end surface (lower opening) of the cylindrical base body 10, a cylindrical portion 30 for covering the outer peripheral surface of the lower end portion of the cylindrical base body 10, It is composed of The covering 24 seals the opening surface of the lower end of the cylindrical substrate 10 with the bottom portion 28, and covers the lower opening (lower surface) of the cylindrical substrate 10 with the cylindrical portion 30 covering the outer peripheral surface of the lower end portion of the cylindrical substrate 10. (End face) and is held. Thus, it is not necessary to fix the covering body 24 with the adhesive tape, and the working efficiency can be improved by holding the cylindrical base body 10 only with the frictional force.

  As the material of the covering 24, a resin or metal that is not affected by the paint is used.

  The upper end surface of the cylindrical portion 30 of the covering 24 has an inner edge portion (corner) taken, for example, in a mortar shape. In this way, by making the upper end surface tilt inward with respect to the central axis of the cylindrical body, the fitting between the cylindrical base body 10 and the covering body 24 becomes easy, and the workability becomes easy. . Further, the inner wall of the cylindrical portion 30 of the covering 24 is provided with a rib 34 at the abutting portion when the cylindrical base body 10 is fitted. Thereby, there is an advantage that the covering region of the cylindrical portion 30 of the covering 24 on the outer peripheral surface of the lower end portion of the cylindrical base body 10 becomes constant, and the range in which the paint is applied to the cylindrical base body 10 can be repeatedly reproduced.

  The outer surface of the bottom portion 28 of the covering 24 is a non-square surface. Further, the boundary 32 between the bottom portion 28 and the cylindrical portion 30 is also formed of a non-square surface. In this way, by forming the outer surface of the covering 24 with non-each surface, it is possible to prevent the generation of bubbles as much as possible. Here, the non-corner surface refers to a shape surface having no corners, for example, an arc shape having a curvature.

The difference between the maximum outer diameter of the covering 24 and the maximum outer diameter of the cylindrical substrate 10 is 0.5 mm or less , more preferably 0.4 mm or less, and further preferably 0.3 mm or less. The smaller this difference is, the more the generation of bubbles in the coating liquid during dip coating is further suppressed. This difference corresponds to the cylindrical portion 30 thickness F of the covering 24.

  Next, as shown in FIG. 2, the cylindrical substrate 10 having the coating 36 formed on the surface thereof is directed by the holding member 22 so that the side to which the covering 24 is attached faces downward and the axial direction is vertical. Hold. And the coating 48 of the fluororesin dispersion 40 is formed by immersing the cylindrical base | substrate 10 in the fluororesin dispersion 40 (fluororesin coating material) in the coating tank 38, and pulling up.

When the fluororesin dispersion 40 is applied, the cylindrical substrate 10 is dipped at a rate of 50 to 1000 mm / min. The boundary between the covering 24 and the cylindrical substrate 10 (boundary 32: see FIG. 4). The immersion speed T while passing through the liquid surface of the fluororesin dispersion (coating liquid) needs to satisfy the following formula (1). However, in the present invention, the following formula (2) is also satisfied.
Formula (1): T ≦ −ρ + 1000
(Here, in formula (1), T represents the immersion rate (mm / min), and ρ represents the viscosity (mPa · s) of the coating liquid.)

Thereby, generation | occurrence | production of the bubble by the boundary part of the coating body 24 and the cylindrical base | substrate 10 is prevented. On the other hand, from the viewpoint of preventing generation of bubbles, the immersion speed T may satisfy the above formula, but from the viewpoint of work efficiency, the immersion speed T is preferably 200 mm / min or more. Moreover, it is preferable that the said immersion speed T satisfy | fills following formula (2) from a viewpoint of bubble generation | occurrence | production prevention more effectively.
Formula (2): T ≦ −0.4ρ + 460
(Here, in formula (2), T represents the immersion speed (mm / min), and ρ represents the viscosity (mPa · s) of the coating liquid.)

  On the other hand, the pulling speed of the cylindrical substrate 10 is preferably in the range of about 50 to 500 mm / min, although it depends on the desired film thickness.

  Although the fluororesin dispersion 40 can be stored in the coating tank 38, as shown in FIG. 2, an external tank 42 having a capacity equal to or larger than the volume of the cylindrical substrate 10 is provided outside the coating tank 38. It is preferable that the fluororesin dispersion liquid 40 is supplied from the lower part of the application tank 38 in FIG. The pump 44 is preferably of a type in which mechanical stress is not easily applied to the fluororesin dispersion, and specific examples include a roller tube pump, a sine pump, a mono pump, and a gear pump.

  Circulation in this way is preferable because sedimentation and aggregation of the fluororesin dispersion 40 can be prevented and the surface of the liquid can be always kept fresh. Circulation with the external tank 42 can reduce the total amount of the expensive fluororesin dispersion 40 to be used and spill over from the upper part of the coating tank 38, compared with the circulation with another paint tank provided outside. There is also an advantage that foaming due to the fluororesin dispersion 40 falling to the external paint tank hardly occurs. A filter 46 is provided in the circulation path. Although not shown, it is also preferable to add a viscometer, a diluting liquid adding device and the like.

  Further, the fluororesin dispersion 40 is relatively slow to dry because the main solvent is water, and when applied by a dip coating method, irregular sagging occurs in the coating film 48 while the cylindrical substrate 10 is being pulled up. In some cases, the film thickness may be uneven in the axial direction. These problems are particularly likely to occur when the film thickness is 25 μm or more. In order to quickly dry the solvent of the coated film after coating, there is a method of blowing air to the coated film 48, but the temperature of the cylindrical substrate 10 is changed, which may cause bubbles.

  Therefore, when dripping occurs in the coating film 48 of the fluororesin dispersion 40 during the pulling up, as shown in FIG. 2, an air blower 50 is provided on the upper part of the coating tank 38 in FIG. Better, drying of the solvent is promoted. The air flow applied to the coating film 48 is preferably applied in a circular or annular manner so as to be uniform in the circumferential direction rather than from one direction.

  The wind speed of this airflow is preferably in the range of about 1 to 10 m / min. If this is weak, the effect of promoting drying is small, and if it is too strong, defects such as streaks and unevenness may occur in the coating film 48. Further, when the airflow hitting the coating film 48 flows into the coating tank 38, the liquid surface is shaken or the solvent is dried on the liquid surface, so that the airflow is applied upward in FIG. Is preferred. An air flow can be used as the air flow.

  By applying an air flow to the coating film 48 of the fluororesin dispersion 40, drying of the solvent mainly composed of water is promoted, so that the coating film 48 is dried soon without causing dripping.

  Here, in the fluororesin dispersion 40, fluororesin powder having a particle size in the range of 0.1 to 20 μm is dispersed. Examples of the material include fluorine resins such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). In addition, materials other than fluororesins such as carbon powder, inorganic compound powder such as titanium oxide and barium sulfate are used to improve wear resistance, electrostatic offset, and compatibility with toner adhesion prevention oil. May be included.

  As the solvent of the fluororesin dispersion 40, water, alcohols such as ethanol and butanol, glycols such as ethylene glycol, and esters thereof may be used in combination. Moreover, you may add surfactant, a viscosity modifier, etc. When materials other than fluororesins such as carbon powder, titanium oxide, and barium sulfate are included, these may be mixed and dispersed in the fluororesin dispersion 40. Those added with a surfactant are very easy to foam, and once the foam is formed, the foam is difficult to disappear, so that it can be suitably used in the present invention.

  The solid content concentration of the fluororesin dispersion 40 is preferably in the range of 10 to 70% by mass, and the viscosity is preferably in the range of about 0.1 to 1 Pa · s, although it depends on the applied film thickness. . When the concentration of the fluororesin dispersion 40 changes due to evaporation of the solvent, adjustment may be made by adding alcohol or the like.

  Before putting the fluororesin dispersion 40 into the coating tank 38, it is preferable to remove bubbles from the liquid by defoaming treatment. As a method for defoaming, there are a method of standing by taking time, and a method of reducing pressure, centrifuging, filtration, applying ultrasonic waves, and the like.

  Note that water has a solubility of about 1.19% by volume of nitrogen and about 0.64% by volume of oxygen at 20 ° C., and these gases are dissolved in the fluororesin dispersion. It is preferable to remove by decompression.

  In this manner, a fluororesin coating film 48 is formed on the cylindrical substrate 10 on the surface of which the coating 36 made of polyimide resin or polyimide precursor is formed.

-Heating and baking process-
In the heating and baking step, first, after applying the fluororesin dispersion, the solvent is dried by placing it at room temperature to 150 ° C. for 5 to 20 minutes. In order to promote drying, it is also effective to blow hot air, but there are cases where streaks or roughness are uneven between the portion where the hot air hits and the portion where the hot air does not hit. In order to prevent this, it is preferable to adopt a method in which the hot air is lowered from above in a state where the axial direction of the cylindrical substrate is set up vertically so that the hot air does not directly hit the coating film.

  Or, with the axial direction of the cylindrical substrate standing vertically, rotate the cylindrical body and blow hot air from the lateral direction so that even if the hot air hits the coating directly, it should be uniform Is preferred. By adopting any one of the above methods, drying of the solvent is promoted without causing streaking or unevenness.

  Before and after drying, the previously formed coating treatment is removed. Thereafter, when heated in the temperature range of 350 to 450 ° C. for 20 to 60 minutes, the polyimide precursor undergoes a condensation reaction to become a polyimide resin film, and the fluororesin powder is melted and fired to become a fluororesin layer. At this time, if the solvent remains in the polyimide precursor film, the film may be swollen. Therefore, it is preferable to completely remove the residual solvent by the time the temperature is reached. It is preferable to raise or slowly raise.

  Then, when it cools to normal temperature, the polyimide resin film in which the fluororesin layer was formed is formed.

-Extraction process-
In the extraction step, the polyimide resin endless belt is obtained by removing the polyimide resin film on which the fluororesin layer is formed from the cylindrical substrate. Furthermore, if necessary, a cutting process for aligning the length of the end part, a polishing process for adjusting the roughness of the surface, and the like are performed to obtain a fixing belt.

  The polishing process may be performed by either a dry method or a wet method. As a dry method, there is a method of polishing using sand paper or a polishing film. As a wet method, there is a method of performing the same thing as the above through a liquid such as water.

  In this way, the fixing belt is manufactured. The thickness of the polyimide resin film as the fixing belt is preferably in the range of 25 to 200 μm, and the thickness of the non-adhesive layer is preferably in the range of 5 to 50 μm.

  In the manufacturing method of the fixing belt of the present invention described above, the dip coating method (the immersing method of the present invention) for forming the fluororesin coating film is not limited to the above-described form, and can be used for various applications. For example, it can be preferably used for the formation of a layer of an electrophotographic photoreceptor, the production of an endless belt as various rotating bodies such as a transfer belt and a conveyance belt used in an electrophotographic apparatus. In particular, the paint applied to the dip coating method of the present invention includes a fluororesin paint and a coating for forming a photosensitive layer, for example, contains a surfactant, or easily generates bubbles such as high viscosity. It is preferably used when a paint that does not easily disappear is used.

  For example, when an electrophotographic photosensitive member is produced, a conductive substrate can be used as the cylindrical substrate and a photosensitive layer-forming coating material can be used as the coating material in accordance with the dip coating method described above. It can be applied to any layer formation in an electrophotographic photoreceptor.

  Here, when manufacturing an electrophotographic photosensitive member, examples of the material of the conductive substrate as the cylindrical substrate include conventionally known materials such as metals (for example, aluminum, stainless steel, etc.), plastics imparted with conductivity, and the like. .

  On the other hand, as a coating for forming a photosensitive layer, for example, in the case of forming a charge transport layer, a charge transport agent (for example, a hydrazone compound, a stilbene compound, a benzidine compound, a butadiene compound, a triphenylamine compound, etc.) is used as a binder resin (polycarbonate, poly Arylate, polymethylmethacrylate, polyester, etc.) and a paint. In addition, a paint for forming the undercoat layer is also applicable.

  In the fixing belt manufacturing method of the present invention described above, the embodiment in which the polyimide precursor solution is used as the film-forming coating material has been described. This is because polyimide is particularly preferable in terms of strength and dimensional stability. . In addition, examples of the film-forming paint include those obtained by coating a film-forming resin (eg, polyamideimide, polybenzimidazole, phthalic polyester, polyurethane, etc.). The solid content concentration of the coating material for film formation is about 15 to 50% by mass, and the viscosity is preferably about 1 to 100 mPa · s. As a condition for coating, the pulling speed is preferably about 50 to 1000 mm / min.

  Here, in order to form a film, it is preferable that after drying, the film is heated together with the substrate at a predetermined temperature to cure the resin. When the resin material inevitably hangs down when the coating film is dried, there is a method in which the substrate is dried while being rotated sideways. Then, an endless belt can be obtained by peeling the formed film from the substrate. The endless belt is further subjected to slit processing at the end, punching drilling, tape winding, and the like as necessary.

When an endless belt obtained by forming a film is used as a charged body such as a transfer belt or a contact charging film, a conductive substance is dispersed in the resin material as necessary. Examples of the conductive material include carbon black, carbon beads granulated from carbon black, carbon-based materials such as carbon fiber and graphite, metals or alloys such as copper, silver, and aluminum, tin oxide, indium oxide, antimony oxide, Examples thereof include conductive metal oxides such as SnO ₂ —In ₂ O ₃ composite oxide, and conductive whiskers such as potassium titanate.

  Hereinafter, the present invention will be specifically described by way of examples. However, each example does not limit the present invention.

Example 1
As the fluororesin coating material, a PFA aqueous coating material (solid content concentration: 60 mass%, viscosity: 500 mPa · s) containing ethanol and t-butanol was prepared in addition to water. Among them, as solids, PFA powder (large particles) having an average particle size of about 17 μm is 55% by mass, PFA powder (small particles) having an average particle size of about 1 μm is 40% by mass, and the average particle size is about 0.1%. 5% by mass of 1 μm carbon powder is dispersed. This liquid was allowed to stand for 12 hours under a reduced pressure of 20 hPa for defoaming treatment.

  This was put in a coating tank having an inner diameter of 90 mm and a height of 480 mm. At the top of the coating tank, an annular air blower was attached in which an air flow of 5 m / min in an annular shape was blown out upward 45 ° (see FIG. 2).

  As the cylindrical substrate, a cylindrical substrate was prepared in which the opening surfaces at both ends of the cylindrical substrate were sealed with a covering and a holding member (see FIG. 3). As the cylindrical substrate, an aluminum cylinder having an outer diameter of 30.1 mm and a length of 600 mm was used. The covering is made of polypropylene (PP), and is a cross-sectional view (cylindrical part height A: 48 mm, bottom part height B: 14 mm, rib height C: 2 mm, outer diameter E: 30.8 mm, inner diameter D : 30.0 mm, cylindrical part thickness F: 0.4 mm, see FIG. 4).

  The covering was pressed and fitted to the bottom of the cylindrical substrate until the lower end surface of the cylindrical substrate abutted against the rib. The cylindrical substrate holding member was configured to inflate and chuck the elastic membrane (see FIG. 3).

  Then, the elastic membrane was expanded, and the opening surface at the top of the cylindrical base was sealed. The elastic film was in close contact with the inner surface of the cylindrical substrate, and there was no air leakage at that portion.

  Next, the cylindrical substrate was immersed in the PFA aqueous paint at a speed of 1000 mm / min, and the immersion speed was reduced to 100 mm / min only while the boundary between the coating and the cylindrical substrate passed the liquid surface. Next, while applying an air flow with an annular blower, the film was pulled up at a speed of 200 mm / min to form a PFA coating film. After completion of the pulling, the covering was removed, and then dried for 10 minutes in a 60 ° C. airless drying furnace. Moreover, when the PFA water-based paint and the coating film were observed after the completion of the pulling up, no bubbles were generated and no bubbles were mixed into the film.

  Then, it heated at 150 degreeC for 20 minutes, 220 degreeC for 20 minutes, and 380 degreeC for 30 minutes as a heat-firing process. As a result, a uniform and defect-free PFA coating having a thickness of 40 μm could be formed on the surface of the aluminum cylinder.

(Example 2)
In Example 1, the cylindrical body thickness F (see FIG. 4) of the covering was changed to 1.0 mm as the cross-sectional shape of the covering, and the cylindrical base was formed in the same manner as in Example 1. When the covering 3 was attached and immersed in the PFA water-based paint, in the immersion process, it was observed that some bubbles were generated from the step portion at the boundary between the covering and the cylindrical substrate, and the bubbles adhered to the coating film surface. After pulling up in the state, the foam was adhered to the formed coating film, but it was at a level that does not cause any practical problems.

(Comparative Example 1)
In Example 1, the cylindrical substrate was coated on the cylindrical substrate in the same manner as in Example 1 except that the immersion speed only while the boundary between the coated body and the cylindrical substrate passed the liquid level was 600 mm / min. And was immersed in a PFA water-based paint, and during the immersion process, it was observed that bubbles were generated from the step at the boundary between the cover and the cylindrical substrate, and the bubbles were attached to the surface of the coating film. The foam was adhered to the formed coating film, resulting in a defect.

(Example 3)
In Example 1, the coated body was applied to the cylindrical substrate in the same manner as in Example 1 except that the immersion speed was set to a slow speed of 50 mm / min only while the boundary between the coated body and the cylindrical substrate passed through the liquid surface. When attached and immersed in PFA water-based paint, no bubbles are generated due to the step at the boundary between the cover and the cylindrical substrate in the immersion process, and formation after pulling up with bubbles attached to the coating film surface No bubbles were observed in the coated film, and a uniform and defect-free PFA film could be formed.

Example 4
A polyimide precursor solution was prepared (trade name: U varnish, manufactured by Ube Industries). This is a solution having a solid content concentration of 18% (mass%, the same shall apply hereinafter) and a viscosity of about 20 Pa · s.

  An element tube having an outer diameter of 29.8 mm and a length of 600 mm was heated at 350 ° C. for 10 minutes and naturally cooled, and then an aluminum cylinder having an outer diameter of 29.8 mm was prepared by cutting the surface. The surface was roughened to 0.8 μm with an arithmetic average roughness Ra by blasting with spherical alumina particles (Fuji Seisakusho, particle size: 105 to 125 μm), and then a silicone release agent (trade name) : KS700, manufactured by Shin-Etsu Chemical Co., Ltd.), and baked at 300 ° C. for 1 hour to obtain a cylindrical substrate.

  In order to apply the polyimide precursor solution by the spin coating method (see FIG. 1), the axial direction of the cylindrical substrate was horizontal and rotated at 120 rpm. The spatula was made of a stainless plate having a width of 20 mm and a thickness of 0.1 mm, and had elasticity, and was pressed against the substrate. The polyimide precursor solution was extruded from the container through a nozzle with a diameter of 2 mm at an air pressure of 0.4 MPa and a flow rate of 22 g / min. When the polyimide precursor solution passed through the spatula, the spatula was pushed and bent, and a gap was formed between the spatula and the substrate. Subsequently, the nozzle and the spatula were applied by moving the substrate from one end to the other at a speed of 180 mm / min. Under this condition, the nozzle and the spatula move by 1.5 mm per rotation of the substrate. In addition, since the non-application part of 25 mm was provided in the both ends of the base | substrate at the time of application | coating, the applied length is 440 mm.

  After coating, the substrate was placed in a drying oven at 120 ° C. while rotating at 10 rpm. When taken out after 60 minutes, a polyimide precursor film having a thickness of about 150 μm was formed, and the outer diameter was 30.1 mm.

  Thereafter, as shown in Example 1, a fluororesin coating film was formed. Then, it heated at 150 degreeC for 20 minutes, 220 degreeC for 20 minutes, and 380 degreeC for 30 minutes, and while forming the polyimide resin film, the PFA coating film was baked. After cooling to room temperature, the coating was removed from the substrate, and an endless belt having a 30 μm thick PFA layer on a 150 μm thick polyimide resin could be produced. When the surface of the endless belt was observed, the polyimide resin layer and the PFA layer had a good finish with no bubbles or unevenness. Both ends were cut so that the length was 340 mm, and an electrophotographic fixing belt could be obtained.

(Example 5)
In Example 1, according to Table 1, the viscosity of the fluororesin coating material and the immersion speed only while the boundary between the coating and the cylindrical substrate passed through the liquid surface were changed. The generation of bubbles due to the level difference at the boundary with the substrate was examined. However, when the viscosity was 500 mPa · s or less, a viscous liquid prepared by adding a thickener to the aqueous solution was used instead of the fluororesin paint. The results are shown in Table 1 and FIG.

  The generation of bubbles was examined as follows. Put a fluororesin or viscous liquid in a transparent container with a depth of 500 mm, and press the cover into the bottom of the cylindrical substrate on which the film made of the polyimide precursor is formed. changed. At this time, the generation of bubbles was counted by counting the number of bubbles generated from the stepped portion at the boundary between the covering and the cylindrical substrate to a depth of 300 mm. ~ 2 occurrences were marked with Δ, and others were marked with x. In addition, Δ is a level that causes no problem in practical use although fine bubbles are generated.

  From the results of Table 1 and FIG. 5, by controlling the immersion speed only while the boundary between the covering and the cylindrical substrate passes through the liquid surface so as to satisfy the above formula (1), It can be seen that it is possible to obtain a coating film which prevents the generation of bubbles due to a step and does not cause defects due to this. It can also be seen that a fixing belt having a fluororesin layer formed on a polyimide resin film can be obtained by utilizing this.

It is a schematic block diagram which shows an example of a spiral coating device. It is a schematic block diagram which shows an example of a dip coating apparatus. It is a partial cross section block diagram which shows the cylindrical base | substrate at the time of applying to a dip coating apparatus. It is sectional drawing which shows the coating body attached to a cylindrical base | substrate. It is a figure which shows the result of Example 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Cylindrical base | substrate 12 Polyimide precursor solution 14 Flowing-down apparatus 16 Nozzle 18 Container 20 Spatula 22 Cylindrical base | substrate holding member 24 Covering body 26 Elastic film 28 Bottom part 30 Cylindrical part 32 Boundary 34 Rib 36 Film | membrane 38 Coating tank 40 Fluororesin dispersion liquid 42 External tank 44 Pump 46 Filter 48 Coating film 50 Blower

Claims (2)

A dip coating method in which a cylindrical substrate is dipped in a paint while holding its axial direction perpendicular, and then pulled up to apply the paint to the surface of the cylindrical substrate,
The cylindrical substrate is formed by sealing a lower end opening and covering a lower end outer peripheral surface, and a covering is held.
And a step formed by the difference between the maximum outer diameter of the covering body and the maximum outer diameter of the cylindrical base body, which is a boundary portion between the covering body and the cylindrical base body and is 0.5 mm or less. A dip coating method in which the dip speed T during the passage of the boundary portion formed by the portion passes the liquid surface of the coating liquid satisfies the following formula (1) and the following formula (2).
Formula (1): T ≦ −ρ + 1000
Formula (2): T ≦ −0.4ρ + 460
(Here, in formulas (1) and (2), T represents the dipping rate (mm / min), and ρ represents the viscosity of the coating liquid (mPa · s).) Forming a polyimide resin film or a polyimide precursor film on the surface of the cylindrical substrate;
The cylindrical substrate with the coating formed on the surface is immersed in a fluororesin paint while being held so that its axial direction is vertical, and then pulled up, so that the fluororesin is applied to the surface of the coating on the cylindrical substrate. Applying a paint; and
Heating and firing the applied fluororesin paint to form a fluororesin layer;
Extracting the film on which the fluororesin layer is formed from a cylindrical substrate;
Have
In the step of forming the fluororesin layer,
The cylindrical base body is configured to seal the opening at the lower end surface and cover the outer peripheral surface of the lower end portion to hold the covering.
And a step formed by the difference between the maximum outer diameter of the covering body and the maximum outer diameter of the cylindrical base body, which is a boundary portion between the covering body and the cylindrical base body and is 0.5 mm or less. A method for producing a fixing belt, characterized in that the immersion speed T during the passage of the boundary portion formed by the portion passes the liquid surface of the coating liquid satisfies the following formulas (1) and (2).
Formula (1): T ≦ −ρ + 1000
Formula (2): T ≦ −0.4ρ + 460
(Here, in formulas (1) and (2), T represents the dipping rate (mm / min), and ρ represents the viscosity of the coating liquid (mPa · s).)

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