JP2018194611A - Fixing belt, fixing device, and image forming apparatus - Google Patents

Abstract

To provide a technology, in fixing of a toner image during image formation of an electrophotographic system, to enable excellent fixing of the toner image and separation of a recording medium even in high-speed image formation.SOLUTION: A fixing belt has a base layer 611 made of heat-resistant resin, an elastic layer 612 made of elastic material, and a release layer 613 made of fluorine resin in this order in a lamination direction, where the loss tangent tanδat 180°C, 1 Hz of the base layer is 0.05 or more.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fixing belt, a fixing device, and an image forming apparatus.

  A fixing device employed in an image forming apparatus such as a copying machine or a laser beam printer usually records a toner image by bringing a heated fixing belt into contact with a recording medium carrying an unfixed toner image. Fix to media. In the fixing device, for example, one of the two or more rollers that support the endless fixing belt is a heating roller for heating the fixing belt. Since the heat capacity of the fixing belt is relatively small, the fixing device is excellent in fixability, and is advantageous, for example, in speeding up image formation.

  A fixing belt having three layers of a base layer, an elastic layer, and a surface layer (release layer) is known for the purpose of having a relatively small heat capacity and achieving both strength and appropriate elasticity. An endless fixing belt (for example, see Patent Document 1) of 20 to 80 GPa and a loss tangent tan δ that is a ratio of a loss elastic modulus to a storage elastic modulus at 180 ° C., an amplitude of 10 μm, and a frequency of 1 Hz in an elastic layer An endless fixing belt of 0.06 to 0.2 (for example, see Patent Document 2) is known.

JP 2008-158053 A JP-A-2005-300591

  Conventionally, in order to improve the separation property of the recording medium in the fixing process, a measure has been taken to increase the curvature of the fixing belt nip portion on the exit side of the fixing belt where the recording medium is sandwiched. On the other hand, the image forming apparatus is required to further speed up image formation. When the printing speed of the image forming apparatus is increased, the roller diameter of the roller is generally increased from the viewpoint of the amount of heat that the roller should have in order to ensure the fixing property, and the curvature is decreased. The tension is also lower. As described above, in electrophotographic image formation using a fixing device having a fixing belt, it is difficult to achieve both high speed and maintaining and improving separation and fixing properties. Is left.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a technique that enables fixing excellent in both fixing of a toner image and separation of a recording medium even in high-speed image formation in fixing of a toner image in electrophotographic image formation. To do.

  The present invention has a base layer made of a heat-resistant resin, an elastic layer made of an elastic material disposed on the base layer, and a release layer disposed on the elastic layer. And a fixing belt having a loss tangent tan δ of 0.05 or more.

  The present invention also provides the endless fixing belt, two or more rollers for supporting the fixing belt endlessly, and a heating device for heating the fixing belt supported by the rollers. A pressure roller disposed so as to be relatively biased toward one of the two or more rollers, and biased by the pressure roller via the fixing belt. A fixing device having a roller diameter of 50 mm or more is provided.

  Furthermore, the present invention provides an electrophotographic image forming apparatus having the fixing device for fixing an unfixed toner image carried on a recording medium to the recording medium by heating and pressing.

  According to the present invention, it is possible to provide a fixing belt excellent in both toner image fixing property and recording medium separation property even in high-speed image formation. By using this fixing belt, an electrophotographic image can be provided. In the formation, both the fixing of the toner image and the separation of the recording medium realize a good fixing even in the high-speed image formation.

1 is a diagram schematically illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2A is a diagram schematically showing a configuration of a fixing belt according to an embodiment of the present invention, and FIG. 2B is an enlarged view showing a portion B in FIG. 2A. It is a figure which shows the correlation with the temperature of the loss tangent in 1 Hz in the fixing belt which concerns on embodiment of this invention, and the other fixing belt for comparison.

  Embodiments of the present invention will be described below. The fixing belt according to the present embodiment includes a base layer made of a heat resistant resin, an elastic layer made of an elastic material arranged on the base layer, and a release layer made of a fluororesin arranged on the elastic layer. Have. The fixing belt can be configured in the same manner as a known fixing belt in which the base layer, the elastic layer, and the release layer are arranged so as to overlap in this order, except that the base layer has specific elastic characteristics described later. .

  The base layer is made of a heat resistant resin. “Made of heat-resistant resin” means that the main material constituting the base layer is a heat-resistant resin, and “heat-resistant” means fixing toner images on recording media in electrophotographic image formation. It means that the fixing belt is sufficiently stable at a temperature (for example, 150 to 220 ° C.) and expresses desired physical properties.

The base layer has specific elastic properties. That is, the loss tangent of the base layer at 180 ° C. and 1 Hz (hereinafter, this loss tangent is also referred to as “tan δ ₁₈₀ ”) is 0.05 or more. The loss tangent is the ratio (G ″ / G ′) of the loss elastic modulus (G ″) to the storage elastic modulus (G ′), and is generally expressed as tan δ. The loss elastic modulus (G ″) represents the contribution of viscosity in the material mechanical properties, and the storage elastic modulus (G ′) represents the contribution of elasticity.

When the tan δ ₁₈₀ is 0.05 or more, sufficient separability is expressed. This is because the fixing belt sufficiently follows the outer peripheral surface of the roller supporting the fixing belt on the exit side of the fixing nip portion, and the difference in the angle of the surface of the fixing belt with respect to the recording medium discharged from the fixing nip portion is This is considered to be because it becomes larger than the conventional fixing belt.

The upper limit of the tan δ ₁₈₀ is not limited from the viewpoint of the effect of improving separability. From the viewpoint that the effect of improving the separability reaches a peak, and from the viewpoint of supporting other layers so that the functions of the other layers on the base layer are sufficiently expressed, the tan δ ₁₈₀ may be 0.15 or less. . The tan δ ₁₈₀ is preferably 0.05 to 0.12 from the viewpoint of further improving the fixability.

The loss tangent of the base layer at 30 ° C. and 1 Hz (hereinafter, this loss tangent is also referred to as “tan δ ₃₀ ”) is preferably 0.015 or more from the viewpoint of matching with the elastic layer at room temperature. If tan δ ₃₀ is less than 0.015, the viscoelastic properties at 180 ° C. may be insufficient. Since the loss tangent generally increases with an increase in temperature, the tan δ ₃₀ may be 0.04 or less from the viewpoint of sufficiently realizing the loss tangent (tan δ ₁₈₀ ) at 180 ° C. and 1 Hz.

The tan δ ₁₈₀ and the tan δ ₃₀ are a known measuring device capable of measuring the loss tangent, for example, a dynamic viscoelasticity measuring device “RSA-G2” manufactured by TA Instruments Co., Ltd. It can be obtained by setting the temperature to 0.01% and changing the measurement temperature from 30 ° C. to 180 ° C. for measurement. The loss tangent may be obtained using a sample obtained by separating the base layer from the fixing belt, or may be obtained from the base layer in the manufacturing process of the fixing belt or the sample thereof.

The tan δ ₁₈₀ and the tan δ ₃₀ can be adjusted depending on the material or composition of the base layer. For example, the degree of crosslinking or material mechanical properties of the heat-resistant resin constituting the base layer, and the type or content of filler in the base layer It is possible to adjust by such as.

  The heat-resistant resin is appropriately selected from resins that do not undergo substantial modification and deformation at the use temperature of the fixing belt, and may be one or more. Examples of the heat resistant resin include polyphenylene sulfide, polyarylate, polysulfone, polyethersulfone, polyetherimide, polyimide, polyamideimide, and polyetheretherketone. Among these, polyimide is preferable from the viewpoint of heat resistance.

  A polyimide can be obtained by advancing dehydration and cyclization (imidization) reaction of a polyamic acid as a precursor thereof by heating at 200 ° C. or more or by using a catalyst. The polyamic acid may be produced by dissolving a tetracarboxylic dianhydride and a diamine compound in a solvent and mixing and heating the polycondensation reaction, or a commercially available product may be used. Examples of the diamine compound and tetracarboxylic dianhydride include the compounds described in paragraphs 0123 to 0130 of JP2013-25120A.

  The content of the heat resistant resin in the base layer may be an amount sufficient to form the base layer, and is preferably 50% by mass or more, and more preferably 60 to 75% by mass, for example. More preferably, it is 76 to 90% by mass.

  The base layer may further contain a component other than the heat resistant resin as long as the effect of the present embodiment is obtained. For example, the base layer may further contain the filler described above. The filler is, for example, a component that contributes to improving at least one of the hardness, heat conductivity, and conductivity of the base layer. The filler may be one kind or more, and examples of the material include carbon black, ketjen black, nanocarbon, and graphite.

  If the content of the filler in the base layer is too large, the toughness of the base layer may be lowered, and the fixing property and separation property of the fixing belt may be lowered. If the content is too small, for example, imparting appropriate conductivity, etc. The desired effect of the filler may be insufficient. From such a viewpoint, the content of the filler in the base layer is preferably 5% by mass or more, preferably 10% by mass or more, or preferably 15% by mass or more. From the above viewpoint, the content of the filler in the base layer is preferably 40% by mass or less, preferably 30% by mass or less, or preferably 20% by mass or less.

  The elastic layer is a layer having elasticity that contributes to improving the contact between the surface of the fixing belt in the fixing nip portion and the recording medium carrying the unfixed toner image, and is made of an elastic material. “Made of elastic material” means that the main material constituting the elastic layer is an elastic material, and “elasticity” means fixing in fixing a toner image onto a recording medium in electrophotographic image formation. This means that the fixing belt is deformed so that the belt sufficiently contacts the surface of the recording medium having an unfixed toner image.

  The elastic material may be one kind or more, for example, a material whose loss tangent tan δ (ratio of loss elastic modulus to storage elastic modulus) at 20 Hz is 0.1 or less. Examples of the elastic material include elastic resin materials, and examples thereof include silicone rubber, thermoplastic elastomer, and rubber material. Among these, the elastic material is preferably silicone rubber from the viewpoint of heat resistance in addition to the desired elasticity.

  One or more silicone rubbers may be used. Examples of the silicone rubber include polyorganosiloxane or a heat-cured product thereof, and addition reaction type silicone rubber described in JP-A-2009-122317. Examples of the polyorganosiloxane include dimethylpolysiloxane described in JP-A-2008-255283, in which both ends are blocked with a trimethylsiloxane group and a side chain has a vinyl group.

  The thickness of the elastic layer is, for example, preferably 5 to 300 μm, more preferably 50 to 250 μm, and still more preferably 100 to 200 μm, from the viewpoint of sufficiently exhibiting heat transfer and elasticity.

  The elastic layer may further contain components other than the elastic resin material as long as the effects of the present embodiment can be obtained. For example, the elastic material may further include a heat conductive filler for increasing the heat transfer property of the elastic layer. Examples of the filler material include silica, metal silica, alumina, zinc, aluminum nitride, boron nitride, silicon nitride, silicon carbide, carbon, and graphite. The form of the filler is not limited and is, for example, a spherical powder, an amorphous powder, a flat powder, or a fiber.

  The content of the elastic resin material in the elastic material is preferably, for example, 60 to 100% by volume, more preferably 75 to 100% by volume, from the viewpoint of achieving both heat transfer and elasticity. More preferably, it is 100 volume%.

  Further, for example, the release layer is a layer having a release property that contributes to an improvement in the separation property of the molten toner layer on the recording medium from the surface of the fixing belt in the fixing nip portion. Have sex. The release layer constitutes the outer surface of the fixing belt that contacts the recording medium during fixing. The release layer is made of a fluororesin. “Made of fluororesin” means that the main material constituting the release layer is fluororesin.

  Examples of the fluororesin include perfluoroalkoxy fluororesin (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-ethylene copolymer (ETFE). Among these, PFA is more preferable.

  The thickness of the release layer is preferably 5 to 40 μm, more preferably 10 to 35 μm, for example, from the viewpoint of heat transfer, follow-up of deformation of the elastic layer, and expression of release properties. More preferably, it is 20-30 micrometers.

  The release layer may further include other components than the fluororesin as long as the effect of the present embodiment is obtained. For example, the release layer may further contain lubricant particles. Examples of the lubricant particles include fluororesin particles, silicone resin particles, and silica particles.

  The content of the fluororesin in the release layer material is preferably 70 to 100% by volume from the viewpoints of heat conductivity and flexibility to sufficiently follow deformation of the elastic layer.

  The fixing belt can be formed by a known method capable of producing a fixing belt having a base layer, an elastic layer, and a release layer in this order.

The loss tangent of the fixing belt at 180 ° C. and 1 Hz can be determined as appropriate within the range in which the effects of the present embodiment can be obtained. For example, the viewpoint of maintaining the shape of the endless track of the traveling fixing belt and From the viewpoint of ensuring sufficient followability to a recording medium carrying an unfixed toner image, it is preferably 0.04 to 0.07. The loss tangent can be obtained by the same method as tan δ ₁₈₀ described above except that the fixing belt is used as a measurement target, and can be adjusted by the viscoelastic characteristics of other layers (for example, an elastic layer) other than the base layer. It is.

  The fixing belt is applied to a fixing device in an electrophotographic image forming apparatus. An image forming apparatus having the fixing belt includes a fixing device for fixing an unfixed toner image on a recording medium to the recording medium by heating and pressurization using the fixing belt, except for the fixing belt. The image forming apparatus can be configured similarly to a known image forming apparatus. The fixing belt can be used for image formation at high speed in an electrophotographic system, and can also be used for image formation at a lower speed. “High speed” in high-speed image formation means, for example, a printing speed of 60 sheets / minute or more with an A4 size recording medium, and more specifically, printing with 60 to 80 sheets / minute with an A4 size recording medium. It can also be said to be speed.

  The fixing device includes an endless fixing belt, two or more rollers for supporting the fixing belt endlessly, a heating device for heating the fixing belt supported by the roller, and the two A pressure roller arranged to be relatively biased toward one of the above rollers. The fixing device can be configured in the same manner as a known so-called biaxial belt type fixing device except that the fixing belt of the present embodiment is used as the endless fixing belt.

  The two or more rollers may incorporate the heating device in at least one of them, and may include, for example, a heating roller for heating the fixing belt. The heating roller includes, for example, a heat conductive sleeve made of aluminum, and a heating source such as a halogen heater disposed inside the sleeve. The outer peripheral surface of the sleeve may be covered with a layer made of a fluororesin such as polytetrafluoroethylene (PTFE).

  The heating device is a heating device arranged outside the roller, that is, a heating device arranged toward the endless track on the inner peripheral side or outer peripheral side of the endless track formed by the supported fixing belt, It is also possible to include both a heating device built in the roller and a heating device arranged outside the roller.

  Of the two or more rollers, the number of rollers other than the heating roller may be one or more, and can be appropriately configured according to other desired functions.

  The roller diameter of the roller urged by the pressure roller via the fixing belt is preferably large from the viewpoint of adapting to high-speed image formation, for example, 50 mm or more. When the roller diameter is large, it is difficult to separate the recording medium from the fixing belt at the fixing nip portion at the time of fixing, and the separation in the image formation at high speed tends to be difficult. In the fixing device, the fixing belt The roller diameter can be appropriately set according to the excellent separation and fixing properties and the desired image forming speed. For example, the roller diameter is more preferably 60 mm or more from the viewpoint of speeding up image formation and improving the fixability of the fixing belt to the recording medium at the time of fixing, and sufficient separation and fixability. 100 mm or less is preferable from a viewpoint of ensuring.

  The fixing belt is supported by the two or more rollers in a tensioned state, that is, in a state where a predetermined tension is applied. If the tension is too large, the physical properties that contribute to the adhesion of the fixing belt to the recording medium, such as the elasticity of the elastic layer, may be insufficiently expressed in the fixing nip portion. From the viewpoint of adhesion, the tension is preferably 45 N or less, and more preferably 50 N or less. The tension may be large enough to maintain the shape of the endless track formed by the fixing belt supported by the roller, and may be, for example, 20 N or more. The tension can be adjusted by, for example, the distance between the two or more rollers.

  An image forming apparatus having the fixing belt includes a fixing device for fixing an unfixed toner image on a recording medium to the recording medium by heating and pressurization using the fixing belt, except for the fixing belt. The image forming apparatus can be configured similarly to a known image forming apparatus.

Hereinafter, embodiments of the present invention will be further described with reference to the drawings.
As shown in FIG. 1, the image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper transport unit 50, a fixing unit 60, and a control unit 100.

  The control unit 100 is a device for centrally controlling the operation of each block of the image forming apparatus 1 in cooperation with the developed program. For example, the control unit 100 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (RAM). Random Access Memory).

  The image reading unit 10 includes an automatic document feeder 11 called an ADF (Auto Document Feeder), a document image scanning device 12 (scanner), and the like. The operation display unit 20 includes, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit and an operation unit. The image processing unit 30 includes a circuit that performs digital image processing on input image data according to initial settings or user settings.

  The image forming unit 40 includes, based on input image data, an image forming unit 41, an intermediate transfer unit 42, and a secondary transfer unit for forming an image using colored toners of Y component, M component, C component, and K component. 43 and the like.

  The image forming unit 41 includes four image forming units 41Y, 41M, 41C, and 41K for Y component, M component, C component, and K component. Since the image forming units 41Y, 41M, 41C, and 41K have the same configuration, for the sake of illustration and description, common components are denoted by the same reference numerals, and the Y, M, and C are denoted by the same reference numerals when distinguished from each other. Or K. In FIG. 1, only the components of the Y-component image forming unit 41Y are denoted by reference numerals, and the constituent elements of the other image forming units 41M, 41C, and 41K are omitted.

  The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, a drum cleaning device 415, and the like.

  The photosensitive drum 413 has, for example, an undercoat layer (UCL), a charge generation layer (CGL), a charge transport layer (CGL) on the peripheral surface of an aluminum conductive cylinder (aluminum tube). It is a negatively charged organic photoconductor (OPC) in which CTL (Charge Transport Layer) is sequentially laminated.

  The charging device 414 is a non-contact charging device that uses, for example, corona discharge. The charging device 414 may be a contact type charging device that contacts and charges the photosensitive drum 413. The exposure apparatus 411 is composed of, for example, a semiconductor laser. The developing device 412 is a developing device for a two-component developer, and contains a developer for each color component (for example, a two-component developer composed of a toner having a small particle diameter and a magnetic material). The drum cleaning device 415 includes a drum cleaning blade such as an elastic blade disposed so as to be slidable on the surface of the photosensitive drum 413.

  The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423 including a backup roller 423A, a belt cleaning device 426, and the like.

  The intermediate transfer belt 421 is an endless belt, and is stretched around a plurality of support rollers 423 in a loop shape. At least one of the plurality of support rollers 423 is configured by a driving roller, and the other is configured by a driven roller. The belt cleaning device 426 has a belt cleaning blade such as an elastic blade disposed so as to be slidable on the surface of the intermediate transfer belt 421.

  The secondary transfer unit 43 includes a secondary transfer roller 431, for example. The secondary transfer unit 43 may have a configuration in which a secondary transfer belt is looped around a plurality of support rollers including a secondary transfer roller.

  The fixing unit 60 is disposed in the fixing device F as a unit. The fixing unit 60 heats the endless fixing belt 61, two rollers 64 and 65 for supporting the fixing belt 61 in an endless manner, and the fixing belt 61 supported by the rollers 64 and 65. It has a heating device 63 and a pressure roller 62 arranged to be biased relative to the roller 64.

  The roller 64 is disposed to face the pressure roller 62 with the fixing belt 61 interposed therebetween, and the roller diameter is 50 mm or more. The rollers 64 and 65 support the fixing belt 61 on an endless track with a tension of 45N. For example, the roller 64 is a driving roller, and the roller 65 is a driven roller. The heating device 63 is composed of, for example, a halogen lamp or a resistance heating element, and is built in the roller 65. The pressure roller 62 is disposed so as to be able to approach and leave the roller 64. When the pressure roller 62 is brought into pressure contact with the fixing belt 61 supported by the roller 64, a fixing nip portion that holds the sheet S and conveys it is formed. The paper S corresponds to a recording medium, and is, for example, a standard paper or a special paper.

  The heating device 63 may be an electromagnetic induction heating (IH: Induction Heating) heating device. In the fixing device F, an air separation unit that separates the sheet S from the fixing belt 61 or the pressure roller 62 by blowing air may be further disposed. The fixing unit 60 corresponds to the fixing device described above.

2A, the fixing belt 61 is an endless belt. As shown in FIG. 2B, a base layer 611, an elastic layer 612, and a release layer 613 are stacked in this order. . The base layer 611 is a polyimide belt, and carbon black is dispersed in the base layer 611. The tan δ ₁₈₀ of the base layer 611 is 0.05 or more, and the base layer 611 corresponds to the base layer in the above-described embodiment.

  The elastic layer 612 is an elastic layer made of, for example, silicone rubber, and the release layer 613 is, for example, a perfluoroalkoxy fluororesin (PFA) layer.

  The paper transport unit 50 includes a paper feed unit 51, a paper discharge unit 52, a first transport unit 53, a second transport unit 57, and the like. In the three paper feed tray units 51 a to 51 c constituting the paper feed unit 51, the paper S identified based on the basis weight, size, or the like is stored for each preset type. The first transport unit 53 includes a plurality of transport roller units including an intermediate transport roller unit 54, a loop roller unit 55, and a registration roller unit 56. The second transport unit 57 includes a switchback path 58 and a back surface transport path 59 in which a plurality of transport roller units are arranged.

  In the image forming apparatus 1, the automatic document feeder 11 transports the document D placed on the document tray by the transport mechanism and sends it out to the document image scanning device 12. The automatic document feeder 11 can continuously read images (including both sides) of a large number of documents D placed on a document tray all at once. The document image scanning device 12 optically scans a document conveyed on the contact glass from the automatic document feeder 11 or a document placed on the contact glass, and reflects light from the document to a CCD (Charge Coupled Device). ) An image is formed on the light receiving surface of the sensor 12a, and an original image is read. The image reading unit 10 generates input image data based on the reading result by the document image scanning device 12. The input image data is subjected to predetermined image processing in the image processing unit 30 as necessary.

  The control unit 100 controls a drive current supplied to a drive motor (not shown) that rotates the photosensitive drum 413. Thereby, the photosensitive drum 413 rotates at a constant peripheral speed. The charging device 414 uniformly charges the surface of the photoconductive drum 413 to a negative polarity. The exposure device 411 irradiates the photosensitive drum 413 with laser light corresponding to the image of each color component, and an electrostatic latent image of each color component is formed on the surface of the photosensitive drum 413 due to a potential difference from the surroundings. . The developing device 412 visualizes the electrostatic latent image by attaching toner of each color component to the surface of the photosensitive drum 413 to form a toner image.

  On the other hand, the intermediate transfer belt 421 travels at a constant speed in the direction of arrow A as the support roller 423 serving as a driving roller rotates. When the intermediate transfer belt 421 is pressed against the photosensitive drum 413 by the primary transfer roller 422, a primary transfer nip portion is formed, and each color toner image on the photosensitive drum 413 is transferred to the intermediate transfer belt 421. Primary transfer is performed so as to overlap one another. Transfer residual toner remaining on the surface of the photosensitive drum 413 is removed from the surface after the primary transfer by the elastic blade in contact with the surface of the photosensitive drum 413 in the drum cleaning device 415.

  On the other hand, the secondary transfer roller 431 is pressed against the backup roller 423A via the intermediate transfer belt 421, thereby forming a secondary transfer nip portion. The paper S fed from the paper feed unit 51 or the second transport unit 57 is transported to the secondary nip transfer unit. The inclination of the sheet S and the position in the width direction (deviation) are corrected in the process of being conveyed by the first conveying unit 53.

  When the sheet S passes through the secondary transfer nip portion, the toner image carried on the intermediate transfer belt 421 is secondarily transferred to the sheet S. The sheet S to which the toner image is transferred is conveyed toward the fixing unit 60. Transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer is removed from the surface by the elastic blade in contact with the surface of the intermediate transfer belt 421 in the belt cleaning device 426.

  In the fixing unit 60, the rollers 64 and 65 and the pressure roller 62 all rotate at a speed of 60 sheets / min or more on an A4 size recording medium, and the fixing belt 61 moves on an endless track at the same speed. To do. The fixing unit 60 fixes the toner image on the sheet S by heating and pressurizing the conveyed sheet S at the fixing nip. Drive control of the fixing belt 61, the pressure roller 62, the heating device 63, and the like is performed by the control unit 100.

  The fixing belt 61 is heated by the heating device 63. As a result, the fixing belt 61 becomes uniform at a predetermined fixing temperature (for example, 180 ° C.) in the width direction. The fixing temperature is a temperature at which heat energy necessary to melt the toner on the paper S can be supplied, and varies depending on the paper type of the paper S on which an image is formed.

  In the case of double-sided printing, the second transport unit 57 once transports the paper S to the switchback path 58 and then reverses the paper S by switching it back and transporting it to the back surface transport path 59. Supplied to the transport unit 53 (upstream of the loop roller unit 55). Then, the sheet S is supplied again to the secondary transfer nip portion to transfer a desired toner image onto the sheet S, and then the toner image is fixed to the sheet S in the fixing unit 60.

  The sheet S on which a desired image is formed in this manner is discharged out of the image forming apparatus 1 by a paper discharge unit 52 having a paper discharge roller 52a.

  The fixing belt 61 is excellent in the fixing property of the toner image to the paper S and the separation property of the paper S in the fixing nip even in high-speed image formation. The reason is considered as follows.

  The fixing belt 61 has the specific viscoelastic property of the base layer 611 as described above, and this viscoelastic property is higher than that of the base layer of a general fixing belt. FIG. 3 is a diagram showing a correlation between the loss tangent temperature at 1 Hz in the fixing belts A and B according to the present embodiment and other general fixing belts C. In FIG. 3, the solid line represents the fixing belt A, the alternate long and short dash line represents the fixing belt B, and the broken line represents the fixing belt C.

The tan δ ₃₀ is 0.019 for the fixing belt A, 0.018 for the fixing belt B, and 0.013 for the fixing belt C. The tan δ ₃₀ of the fixing belts A and B is compared with that of the fixing belt C. However, the difference in tan δ ₃₀ between the fixing belts A to C is about 0.01. The loss tangents of the fixing belts A and B increase as the temperature increases, and are 0.095 and 0.085 at 180 ° C. (tan δ ₁₈₀ ), respectively. On the other hand, tan δ _{180 of the} fixing belt C is 0.030, which is clearly lower than that of the fixing belts A and B, although it slightly increases as the temperature rises. Thus, the fixing belt of the present embodiment has a significantly high tan δ ₁₈₀ .

  Further, it is generally considered that the greater the loss tangent, the greater the viscosity. As described above, the fixing belt 61 is supported by the roller 64 and forms a fixing nip portion with the pressure roller 62. At this time, the base layer 611 is in contact with the roller 64.

  Since the base layer 611 has high viscosity, the followability to the outer peripheral surface of the roller 64 is high, and the base layer 611 contacts the outer peripheral surface of the roller 64 also at the exit of the fixing nip portion. The followability of the base layer 611 with respect to the roller 64 is not affected by the contact with the paper S because the base layer 611 does not contact the paper S. Accordingly, the fixing belt 61 moves in the direction away from the sheet S from the beginning along the outer peripheral surface of the roller 64 at the exit of the fixing nip portion. For this reason, an angle formed by the tangent to the surface of the fixing belt 61 and the surface of the paper S is formed at the outlet at an early stage, and as a result, good separation is exhibited.

  In addition, since the roller diameter of the roller 64 is as large as 50 mm and the fixing belt 61 is supported with a tension of 45 N or less, good fixability is exhibited and high speed (for example, 60 to 80 sheets / A4 plate) Min) image formation.

  In the image forming method having a lower image forming speed, the fixing belt 61 sufficiently exhibits the effect of improving the fixability by the above-described three-layer structure and the effect of improving the separability by the material of the release layer. Therefore, the image forming apparatus 1 can form a good image even in image formation at a speed lower than the above-described high speed.

As is clear from the above description, the fixing belt of the present embodiment includes a base layer made of a heat resistant resin, an elastic layer made of an elastic material arranged on the base layer, and a fluorine arranged on the elastic layer. It has a resin release layer, and the loss tangent tan δ ₁₈₀ at 180 ° C. and 1 Hz of the base layer is 0.05 or more. The fixing device of the present embodiment heats the endless fixing belt, two or more rollers for supporting the fixing belt endlessly, and the fixing belt supported by the rollers. And a pressure roller disposed so as to be relatively biased toward one of the two or more rollers, and the pressurizing belt via the fixing belt. The roller diameter of the roller urged by the pressure roller is 50 mm or more. Further, the image forming apparatus of the present embodiment is an electrophotographic system, and the fixing device for fixing an unfixed toner image carried on the recording medium to the recording medium by heating and pressing Have Therefore, in the fixing of the toner image in the electrophotographic image forming, it is possible to realize the fixing excellent in both the fixing of the toner image and the separation of the recording medium even in the high-speed image forming.

In addition, the loss tangent tan δ ₁₈₀ of 0.05 to 0.12 is more effective from the viewpoint of improving the fixability.

  In addition, the heat-resistant resin is polyimide, the elastic material is silicone rubber, and the release layer is made of a fluororesin. From the viewpoint of member durability, image fixing stability and image separation properties. It is more effective from the viewpoint, and it is more effective from the above viewpoint that the fluororesin is a perfluoroalkoxy fluororesin.

  The base layer further includes carbon black dispersed in the base layer, and the content of the carbon black in the base layer is 5 to 40% by mass, from the viewpoint of improving both separability and fixability. Is even more effective.

  Further, it is more effective that the fixing belt is supported by the two or more rollers with a tension of 45 N or less from the viewpoint of improving both the fixing property and the separation property.

  The present invention will be described more specifically with reference to the following examples and comparative examples. The present invention is not limited to the following examples.

[Example 1]
A base layer containing a varnish of polyamic acid (manufactured by Ube Industries, “UPIA-ST”, “UPIA” is a registered trademark of the company) and 4% by mass of carbon black (average particle size: 10 μm) based on the polyamic acid. The coating material for coating is spin-coated on the outside of the cylindrical mold, and then the coating film of the base layer coating is dried at 400 to 450 ° C. and the polyamic acid in the coating film is imidized to have an inner diameter of 99 mm, a length of 360 mm, and a thickness. A base layer belt 1, which is a 70 μm cylindrical polyimide tube, was produced.

By using a dynamic viscoelasticity measuring device “RSA-G2” manufactured by TA Instruments Co., Ltd., the vibration is 1 Hz, the strain is 0.01%, and the measurement temperature is changed from 30 ° C. to 180 ° C. When the loss tangent tan δ ₁₈₀ at 180 ° C. and 1 Hz of the base layer belt 1 was determined, the tan δ _{30 of the} base layer belt 1 was 0.032, and the tan δ _{180 of the} base layer belt 1 was 0.14. The polyamic acid is a polymer obtained by dehydration condensation of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and p-phenylenediamine.

  Next, a cylindrical metal core made of stainless steel having an outer diameter of 99 mm is brought into close contact with the inner side of the base belt, and a cylindrical metal that holds a 30 μm thick PFA tube on the inner peripheral surface on the outer side of the base belt. The mold was covered, and thus the core metal and the cylindrical mold were held coaxially, and a cavity was formed between them. Next, a silicone rubber material was injected into the cavity and heat-cured to produce an elastic layer made of silicone rubber having a thickness of 200 μm. Thus, an endless fixing belt 1 having a polyimide base layer, a silicone rubber elastic layer, and a PFA release layer in this order was obtained.

The base layer belt 1 was peeled off from the fixing belt 1, and its tan δ ₁₈₀ was obtained using the above dynamic viscoelasticity measuring device, and it was confirmed that it was substantially the same as tan δ ₁₈₀ immediately after production of the base layer belt 1.

[Examples 2 to 5]
Except for changing the content of carbon black in the varnish to 10% by mass, 15% by mass, 20% by mass, and 30% by mass, respectively, in the same manner as in Example 1, to prepare each of the base belts 2 to 5, Then, each of fixing belts 2 to 5 was produced. The tan δ _{30 of the} base layer belt 2 was 0.025, and the tan δ ₁₈₀ was 0.12. The tan δ _{30 of the} base layer belt 3 was 0.016, and tan δ ₁₈₀ was 0.08. The tan δ _{30 of the} base layer belt 4 was 0.014, and tan δ ₁₈₀ was 0.07. The base layer belt 5 had a tan δ ₃₀ of 0.009 and a tan δ ₁₈₀ of 0.05.

[Example 6]
A base layer belt 6 was produced in the same manner as in Example 4 except that the imidization temperature was changed from 400 to 450 ° C. to 300 to 400 ° C., and a fixing belt 6 was produced. The tan δ _{30 of the} base layer belt 6 was 0.018, and tan δ ₁₈₀ was 0.09.

[Example 7]
Instead of the above-mentioned base layer paint, a polyamide imide varnish (manufactured by Hitachi Chemical Co., Ltd., “HPC-5012”) and a base layer paint containing 10% by mass of carbon black with respect to the polyamide imide were used. In the same manner as in Example 1, a base layer belt 7 was produced, and a fixing belt 7 was produced. The tan δ _{30 of the} base layer belt 7 was 0.023, and tan δ ₁₈₀ was 0.12.

[Example 8]
A base layer belt 8 was produced in the same manner as in Example 2 except that aluminum nitride (average particle diameter 10 μm) was used instead of carbon black, and a fixing belt 8 was produced. The tan δ _{30 of the} base layer belt 8 was 0.015, and tan δ ₁₈₀ was 0.08.

[Example 9]
In place of the base layer coating material, except that the base layer coating material containing the varnish of polyamideimide and 5% by mass of aluminum nitride with respect to polyamideimide is used, and the imidization temperature is changed to 300 to 400 ° C. In the same manner as in Example 1, a base layer belt 9 was produced, and a fixing belt 9 was produced. The tan δ _{30 of the} base layer belt 9 was 0.030, and tan δ ₁₈₀ was 0.14.

[Comparative Example 1]
A base layer belt C1 was produced in the same manner as in Example 1 except that the carbon black content was changed to 45% by mass, and a fixing belt C1 was produced. The tan δ _{30 of the} base layer belt C1 was 0.008, and the tan δ ₁₈₀ was 0.04.

[Evaluation]
Each of the fixing belts 1 to 9 and C1 is installed as a fixing belt of an electrophotographic image forming apparatus provided with a biaxial belt type fixing device as shown in FIG. The roller constituting the fixing nip portion, and the roller diameter (disposed facing the pressure roller) on the side that supports the fixing belt is 60 mm. For each fixing belt, the surface temperature of the fixing belt is 180 ° C., and a toner image (toner adhesion amount) of a magenta belt-like solid image having a width of 5 cm in a direction perpendicular to the plain paper transport direction on A4 size plain paper. : 8 g / m ² ) was transferred, and the plain paper was passed through the fixing nip portion in the vertical direction at a speed of 65 sheets / minute to form a fixed image of the belt-like image on the plain paper.

(1) Separability Separation between each fixing belt and the plain paper at the time of fixing the belt-shaped solid image is determined according to the following criteria.
◎: Plain paper is separated without curling ○: Plain paper is slightly curled, but there is no problem △: Wrinkles appear on plain paper ×: Plain paper cannot be separated (paper jams)

(2) Fixability The above belt-like solid image is visually observed, and the fixability is determined according to the following criteria. The image defect due to fixing failure is an image defect due to cold offset (rough appearance) or an image defect due to hot offset (occurrence of paper jam).
○: Defect due to poor fixing is not found in solid image Δ: Fine fixing defect is seen but no problem level ×: Defect due to poor fixing is seen in solid image

  Table 1 shows the properties of the base layer belt and the evaluation results of the fixing belt for each of the fixing belts 1 to 9 and C1. In Table 1, “PI” represents polyimide, and “PAI” represents polyamideimide. “CB” represents carbon black, and “AlN” represents aluminum nitride.

  As is apparent from Table 1, the fixing belts 1 to 9 all exhibit sufficient performance for both fixing and separation in a high-speed image forming apparatus using a biaxial belt type fixing device. .

  On the other hand, the fixing belt C1 has insufficient separation. This is because the fixing belt C1 seems to have good viscoelastic characteristics as a whole, but the adhesion of the fixing belt C1 to the toner image on the recording medium is influenced at the exit of the fixing nip, This is considered to be because the fixing belt C1 cannot be moved in the direction away from the recording medium because it is pulled in the conveyance direction of the recording medium.

From the above examples and comparative examples, when the loss tangent tan δ ₁₈₀ at 180 ° C. and 1 Hz of the base layer of the fixing belt is 0.05 or more, sufficient separation and fixing properties can be obtained even in high-speed image formation. I understand.

The tan δ ₁₈₀ can be adjusted by the filler content according to, for example, the comparison between Examples 1 to 5 and Comparative Example 1, and according to the comparison between Example 4 and Example 6, the imidization of the resin. It can be adjusted by the temperature, and according to the comparison between Example 2 and Example 8, it can be seen that the adjustment can also be made by the type of filler. On the other hand, it can be seen that tan δ ₁₈₀ may not depend on the type of resin according to, for example, the comparison between Example 2 and Example.

  According to the present invention, both the fixing property of the fixing belt and the separation property of the fixing belt with respect to the recording medium can be improved in electrophotographic image formation by a high speed machine having a biaxial belt type fixing device. Therefore, according to the present invention, higher speed, higher performance, and labor saving are expected in the electrophotographic image forming apparatus, and further spread of the image forming apparatus is expected.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Image reading part 11 Automatic document feeder 12 Document image scanning device 12a CCD sensor 20 Operation display part 30 Image processing part 40 Image forming part 41 Image forming unit 42 Intermediate transfer unit 43 Secondary transfer unit 50 Paper conveyance Unit 51 paper feed unit 51a to 51c paper feed tray unit 52 paper discharge unit 52a paper discharge roller 53 first conveyance unit 54 intermediate conveyance roller unit 55 loop roller unit 56 registration roller unit 57 second conveyance unit 58 switchback path 59 Back surface transport path 60 Fixing unit 61 Fixing belt 62 Pressure roller 63 Heating device 64, 65 Roller 100 Control unit 411 Exposure device 412 Developing device 413 Photosensitive drum 414 Charging device 415 Drum cleaning device 421 Intermediate transfer belt 422 Primary transfer roller 423 Support b Roller 423A Backup roller 426 Belt cleaning device 431 Secondary transfer roller 611 Base layer 612 Elastic layer 613 Release layer D Document F Fixer S Paper

Claims (8)

In a fixing belt having a base layer made of a heat-resistant resin, an elastic layer made of an elastic material disposed on the base layer, and a release layer disposed on the elastic layer,
The loss tangent tan δ at 180 ° C. and 1 Hz of the base layer is 0.05 or more.
Fixing belt.   The fixing belt according to claim 1, wherein the loss tangent tan δ is 0.05 to 0.12.   The fixing belt according to claim 1, wherein the heat resistant resin is polyimide, the elastic material is silicone rubber, and the release layer is made of a fluororesin.   The fixing belt according to claim 3, wherein the fluororesin is a perfluoroalkoxy fluororesin.   The said base layer further has carbon black currently disperse | distributed in the said base layer, Content of the said carbon black in the said base layer is 5-40 mass%, It is any one of Claims 1-4. Fixing belt. An endless fixing belt, two or more rollers for supporting the fixing belt endlessly, a heating device for heating the fixing belt supported by the roller, and the two or more rollers A pressure roller arranged so as to be relatively biased toward one of the rollers, and a diameter of the roller biased by the pressure roller via the fixing belt is In a fixing device that is 50 mm or more,
The fixing device according to claim 1, wherein the fixing belt is the fixing belt according to claim 1.   The fixing device according to claim 6, wherein the fixing belt is supported by the two or more rollers with a tension of 45 N or less. In an electrophotographic image forming apparatus having a fixing device for fixing an unfixed toner image carried on a recording medium to the recording medium by heating and pressing,
The image forming apparatus, wherein the fixing device is the fixing device according to claim 6.

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