JP7519009B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming device.

Electrophotographic image forming devices that form images using toner are known as image forming devices such as copiers and printers.

Electrophotographic image forming devices are generally equipped with a fixing device that fixes the toner image transferred onto paper to the paper. The fixing device has a heating member such as a heater that heats the paper. When the paper passes through the fixing device, the paper is heated by the heating member, causing the toner on the paper to melt and be fixed to the paper.

For example, Patent Document 1 (JP 2016-62024 A) discloses a fixing device of this type that includes a plate-shaped heating member (heater) on a longitudinal substrate, the plate-shaped heating member having a heating element, electrical contacts, and a conductor pattern that electrically connects these.

In a heating member having such a conductor pattern provided on a substrate, when the heating element is heated, the conductor pattern also generates heat due to the passage of electricity through the conductor pattern. As a result, the heat distribution of the entire heating member is affected by the heat generated by the conductor pattern.

Therefore, if there is variation in the heat distribution of the conductor pattern, this will cause variation in the temperature distribution of the heating element. Furthermore, such variation in the temperature distribution of the heating element will also affect the protective agent supplying means that supplies the image carrier protective agent to the surface of the image carrier, which may cause variation in the amount of image carrier protective agent supplied.

In order to solve the above problems, the present invention provides an image forming apparatus including a heating device having a heating member, an image carrier that carries an image on its surface, and an image carrier protective agent that is supplied to the surface of the image carrier, the heating member having a substrate, a heating element, an electrode portion, and a conductive portion that connects the heating element and the electrode portion , the electrode portion having a first electrode portion and a second electrode portion, the conductive portion having a first conductive portion that connects the heating element and the first electrode portion, a second conductive portion that extends from the heating element toward a first direction side in the longitudinal direction of the substrate and is connected to the second electrode portion, and a third conductive portion that branches off from the second conductive portion, extends toward a second direction side opposite to the first direction, and constitutes at least a part of a branch path that is connected to the second conductive portion or the second electrode portion without passing through the first conductive portion, and the density of a portion of the image carrier protective agent corresponding to an arbitrary position on the longitudinal center side of the heat generating region of the heating member is defined as ρ _X where _Ix2 is the sum of the squares of the currents flowing through the conductive portions arranged at each position of the heating member at any position on the center side of the longitudinal direction, _ρY is the density of the image carrier protector agent corresponding to any position on both ends of the longitudinal direction of the heat generation area, and ^Iy2 is the sum of the squares _of the currents flowing through the conductive portions arranged at each position of the heating member at any position ^on both ends of the longitudinal direction, the relationship ¹ ≦ ⁽ _Iy2 × _ρy )/( _Ix2 × _ρx )<7 is satisfied.

According to the present invention, it is possible to suppress variation in the amount of image carrier protecting agent supplied.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic configuration diagram of a protective agent supplying device according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of a fixing device according to the present embodiment. FIG. 2 is a perspective view of the fixing device. FIG. 2 is an exploded perspective view of the fixing device. FIG. 2 is a perspective view of a heating unit included in the fixing device. FIG. 2 is an exploded perspective view of the heating unit. FIG. 2 is a plan view of the heater according to the embodiment. FIG. FIG. 4 is a perspective view showing a state in which a connector is connected to the heater. FIG. 13 is a diagram showing the amount of heat generated by the power supply lines for each block when all the resistance heating elements are caused to generate heat. FIG. 13 is a diagram showing the amount of heat generated by the power supply lines for each block when only some of the heat generating parts are caused to generate heat. FIG. FIG. 4 is a diagram showing the relationship between the temperature distribution of a heater and the temperature distribution of a brush roller. 1A to 1C are diagrams for explaining the center, both ends, and intermediate position in the longitudinal direction of a heat generating region of a heater. 1 is a graph showing the lubricant consumption coefficient (1/I ² ×ρ) of portions corresponding to blocks partitioned for each resistance heating element. 4 is a diagram for explaining the relationship between the density of the lubricant and the sum of the squares of the currents or the temperature according to the embodiment. FIG. FIG. 2 is a plan view of a miniaturized heater. FIG. 13 is a plan view of another heater. FIG. 13 is a plan view of yet another heater. FIG. 13 is a diagram showing the configuration of another fixing device. FIG. 13 is a diagram showing the configuration of another fixing device. FIG. 13 is a diagram showing the configuration of still another fixing device.

The present invention will be described below with reference to the attached drawings. In each drawing for explaining the present invention, components such as parts or components having the same function or shape are given the same reference numerals as far as possible to distinguish them, and the description will be omitted after the first description.

Figure 1 is a schematic diagram of an image forming apparatus according to one embodiment of the present invention.

The image forming device 100 shown in FIG. 1 includes an image forming unit 200, a transfer unit 300, a fixing unit 400, a recording medium supply unit 500, and a recording medium discharge unit 600.

The image forming section 200 is provided with four imaging units 1Y, 1M, 1C, and 1Bk, and an exposure device 6. Each imaging unit 1Y, 1M, 1C, and 1Bk is configured to be detachable from the image forming apparatus main body. In addition, each imaging unit 1Y, 1M, 1C, and 1Bk has a basically similar configuration except that it contains developers of different colors, yellow, magenta, cyan, and black, which correspond to the color separation components of the color image. Specifically, each imaging unit 1Y, 1M, 1C, and 1Bk is provided with a photoconductor 2, which is an image carrier that carries an image on its surface, a charging roller 3, which is a charging means for charging the surface of the photoconductor 2, a developing device 4, which is a developing means for forming a toner image on the photoconductor 2, a cleaning blade 5, which is a cleaning means for cleaning the surface of the photoconductor 2, and a protective agent supplying device 7, which supplies an image carrier protective agent to the surface of the photoconductor 2. The exposure device 6 is a latent image forming means that exposes the charged surface of the photoreceptor 2 based on image information to form an electrostatic latent image.

The transfer unit 300 is provided with a transfer device 8 that transfers an image onto a recording medium, which is paper. The recording medium on which an image is formed (transferred) may be paper (including plain paper, thick paper, thin paper, coated paper, label paper, envelopes, etc.), or a resin sheet such as an OHP sheet. The transfer device 8 has an intermediate transfer belt 11, four primary transfer rollers 12, and a secondary transfer roller 13. The intermediate transfer belt 11 is a transfer member that carries an image on its surface and transfers the image onto paper, and is composed of an endless belt member. Each primary transfer roller 12 contacts a different photoconductor 2 via the intermediate transfer belt 11. As a result, a primary transfer nip is formed between the intermediate transfer belt 11 and each photoconductor 2, where the intermediate transfer belt 11 and each photoconductor 2 contact each other. On the other hand, the secondary transfer roller 13 contacts one of the multiple rollers that stretch the intermediate transfer belt 11 via the intermediate transfer belt 11, and forms a secondary transfer nip between the intermediate transfer belt 11 and the secondary transfer roller 13.

The fixing section 400 is provided with a fixing device 9, which is a heating device that heats the paper and fixes the image on the paper by heating the paper.

The recording medium supply unit 500 is provided with a paper feed cassette 14 that stores paper P, and a paper feed roller 15 that feeds paper P from the paper feed cassette 14.

The recording medium ejection section 600 is provided with a pair of ejection rollers 17 that eject paper outside the image forming device, and an ejection tray 18 on which the paper ejected by the ejection rollers 17 is placed.

Next, the printing operation of the image forming device 100 according to this embodiment will be described with reference to FIG.

When an instruction to start the printing operation is given, the photoconductors 2 of each of the imaging units 1Y, 1M, 1C, and 1Bk and the intermediate transfer belt 11 start to rotate. In addition, the paper feed roller 15 rotates, causing paper P to be fed out of the paper feed cassette 14. The fed paper P comes into contact with a pair of timing rollers 16 and is temporarily stopped.

In each imaging unit 1Y, 1M, 1C, 1Bk, the surface of the photoconductor 2 is first charged to a uniform high potential by the charging roller 3. Next, the exposure device 6 exposes the surface (charged surface) of each photoconductor 2 based on the image information of the document read by the document reading device or the print image information instructed to be printed from the terminal. As a result, the potential of the exposed part is reduced and an electrostatic latent image is formed on the surface of each photoconductor 2. Then, toner is supplied from the developing device 4 to this electrostatic latent image, and a toner image is formed on each photoconductor 2. When the toner image formed on each photoconductor 2 reaches the primary transfer nip (the position of the primary transfer roller 12) as each photoconductor 2 rotates, it is transferred to the rotating intermediate transfer belt 11 so that they are overlapped one after another. Thus, a full-color toner image is formed on the intermediate transfer belt 11. After the toner image is transferred from the photoconductor 2 to the intermediate transfer belt 11, the toner and other foreign matter remaining on each photoconductor 2 are removed by the cleaning blade 5. Furthermore, a lubricant, which is an image carrier protective agent, is supplied from the protective agent supply device 7 to the cleaned surface of each photoreceptor 2, and the photoreceptor 2 is prepared for the formation of the next electrostatic latent image.

The toner image transferred onto the intermediate transfer belt 11 is transported to the secondary transfer nip (the position of the secondary transfer roller 13) as the intermediate transfer belt 11 rotates, and is transferred onto the paper P that has been transported by the timing roller 16. The paper P onto which the toner image has been transferred is then transported to the fixing device 9, which fixes the toner image onto the paper P. The paper P is then discharged onto the paper discharge tray 18 by the paper discharge rollers 17, completing the printing process.

The above description of the printing operation is for forming a full-color image, but it is also possible to use any one of the four imaging units to form a monochrome image, or to use two or three imaging units to form a two- or three-color image.

Figure 2 is a schematic diagram of the protective agent supply device 7 according to this embodiment.

As shown in FIG. 2, the protective agent supplying device 7 according to this embodiment includes a lubricant 80 as an image carrier protective agent, a brush roller 81 as a lubricant supplying means (protective agent supplying means) that supplies the lubricant 80 to the photoreceptor 2, a spring 82 as a lubricant biasing means (protective agent biasing means) that biases the lubricant 80 to the brush roller 81, an application blade 83 as a layering member that turns the lubricant supplied to the photoreceptor 2 into a uniform thin layer, and a spring 84 as a layering member biasing means that biases the application blade 83 so that it comes into contact with the surface of the photoreceptor 2.

The brush roller 81 is in contact with the surface of the photoreceptor 2 and rotates in the opposite direction to the rotation direction of the photoreceptor 2. When the brush roller 81 rotates, the lubricant 80 is scraped off by the brush roller 81 and the scraped off lubricant 80 is supplied to the surface of the photoreceptor 2. The lubricant 80 supplied to the surface of the photoreceptor 2 is then thinned to a uniform thickness by the application blade 83. The lubricant 80, brush roller 81, and application blade 83 are arranged longitudinally over an area equal to or greater than the maximum image forming area on the photoreceptor 2.

In this way, by supplying a thin layer of lubricant 80 to the surface of the photoreceptor 2, the cleaning properties of the photoreceptor 2 are improved, and it is possible to prevent the occurrence of abnormal images due to poor cleaning. The lubricant supplying member may be a brush roller 81 or a urethane roller made of polyurethane foam or the like.

The lubricant 80 is formed by compressing a powder containing at least a fatty acid metal salt and an inorganic lubricant, for example.

Examples of fatty acid metal salts constituting the lubricant 80 include, but are not limited to, barium stearate, lead stearate, iron stearate, nickel stearate, cobalt stearate, copper stearate, strontium stearate, calcium stearate, cadmium stearate, magnesium stearate, zinc stearate, zinc oleate, magnesium oleate, iron oleate, cobalt oleate, copper oleate, lead oleate, manganese oleate, zinc palmitate, cobalt palmitate, lead palmitate, magnesium palmitate, aluminum palmitate, calcium palmitate, lead caprylate, lead caprate, zinc linoleate, cobalt linoleate, calcium linoleate, zinc ricinoleate, cadmium ricinoleate, and mixtures thereof. Mixtures of these may also be used.

The inorganic lubricant constituting the lubricant 80 refers to a material that cleaves and lubricates itself or causes internal sliding. Examples include, but are not limited to, mica, boron nitride, molybdenum disulfide, tungsten disulfide, talc, kaolin, montmorillonite, calcium fluoride, and graphite. For example, boron nitride has hexagonal mesh faces in which atoms are tightly interlocked, overlapping at wide intervals, and the layers are connected only by weak van der Waals forces, so the layers easily cleave and lubricate.

Next, we will explain the configuration of the fixing device 9 according to this embodiment.

As shown in FIG. 3, the fixing device 9 according to this embodiment includes a fixing belt 20, a pressure roller 21, a heater 22, a heater holder 23, a stay 24, and a temperature sensor 19.

The fixing belt 20 is a first rotating member that is rotatably arranged on the unfixed toner carrying surface side (image forming surface side) of the paper P, and is a fixing member that fixes the unfixed toner to the paper P. The fixing belt 20 is composed of an endless belt member having a cylindrical substrate with an outer diameter of 25 mm and a thickness of 40 to 120 μm. The substrate material may be a heat-resistant resin such as PEEK, or a metal material such as nickel or SUS, in addition to polyimide. In addition, in order to increase durability and ensure releasability, a release layer made of a fluororesin such as PFA or PTFE may be provided on the outer peripheral surface of the substrate. In addition, an elastic layer made of rubber or the like may be provided between the substrate and the release layer. Furthermore, a sliding layer made of polyimide, PTFE, or the like may be provided on the inner peripheral surface of the substrate.

The pressure roller 21 is a second rotating member that is separate from the fixing belt 20 and is an opposing member that is arranged to face the outer circumferential surface of the fixing belt 20. The pressure roller 21 is also a pressure member that is pressed against the outer circumferential surface of the fixing belt 20 to form a nip portion N between the fixing belt 20 and the pressure roller 21. The pressure roller 21 is, for example, a roller having an outer diameter of 25 mm and including an iron core, an elastic layer made of silicone rubber provided on the outer circumferential surface of the core, and a release layer made of fluororesin provided on the outer circumferential surface of the elastic layer.

The heater 22 is a heating member disposed inside the fixing belt 20 and heats the fixing belt 20 and the paper through the fixing belt 20. In this embodiment, the heater 22 is composed of a plate-shaped base material 50, a first insulating layer 51 provided on the base material 50, a conductor layer 52 provided on the first insulating layer 51, and a second insulating layer 53 that covers the conductor layer 52. The conductor layer 52 has a heat generating portion 60.

The substrate 50 is made of a metal material such as stainless steel (SUS), iron, or aluminum. In addition to metal materials, ceramics, glass, etc. can also be used as the material of the substrate 50. When an insulating material such as ceramics is used for the substrate 50, the first insulating layer 51 between the substrate 50 and the conductor layer 52 can be omitted. On the other hand, metal materials are excellent in durability against rapid heating and are easy to process, so they are suitable for reducing costs. Among metal materials, aluminum and copper are particularly preferable because they have high thermal conductivity and are less likely to cause temperature unevenness. Stainless steel also has the advantage of being cheaper to manufacture than these.

Each insulating layer 51, 53 is made of an insulating material such as heat-resistant glass. These materials may also be ceramic or polyimide. A separate insulating layer may be provided on the surface of the substrate 50 opposite to the surface on which the first insulating layer 51 and the second insulating layer 53 are provided.

In this embodiment, the heat generating section 60 is disposed closer to the nip portion N than the substrate 50, but the substrate 50 may be disposed closer to the nip portion N than the heat generating section 60. In that case, however, the heat from the heat generating section 60 is transferred to the fixing belt 20 via the substrate 50, so it is desirable that the substrate 50 be made of a material with high thermal conductivity, such as aluminum nitride.

In addition, in this embodiment, in order to increase the efficiency of heat transfer from the heater 22 to the fixing belt 20, the heater 22 is arranged so as to be in direct contact with the inner peripheral surface of the fixing belt 20. In addition, without being limited to this, the heater 22 may be arranged so as to be in indirect contact with the fixing belt 20 via a non-contact or low-friction sheet or the like. In addition, the contact point of the heater 22 with the fixing belt 20 may be the outer peripheral surface of the fixing belt 20. However, in order to avoid deterioration of fixing quality due to scratches on the outer peripheral surface of the fixing belt 20, it is desirable that the surface with which the heater 22 comes into contact is the inner peripheral surface of the fixing belt 20.

The heater holder 23 is a holding member that holds the heater 22 inside the fixing belt 20. The heater holder 23 is desirably made of a heat-resistant material because it is prone to becoming hot due to the heat of the heater 22. In particular, when the heater holder 23 is made of a heat-resistant resin with low thermal conductivity such as LCP or PEEK, the heat resistance of the heater holder 23 is ensured while heat transfer from the heater 22 to the heater holder 23 is suppressed, making it possible to efficiently heat the fixing belt 20.

The stay 24 is a reinforcing member disposed on the inside of the fixing belt 20. The stay 24 supports the surface of the heater holder 23 opposite the surface on the nip portion N side, thereby preventing the heater holder 23 from bending due to the pressure of the pressure roller 21. This forms a nip portion N of uniform width between the fixing belt 20 and the pressure roller 21. The stay 24 is preferably formed from an iron-based metal material such as SUS or SECC to ensure its rigidity.

The temperature sensor 19 is a temperature detection means for detecting the temperature of the heater 22. The output of the heater 22 is controlled based on the detection result of the temperature sensor 19, thereby maintaining the temperature of the fixing belt 20 at a desired temperature (fixing temperature). The temperature sensor 19 may be either a contact type or a non-contact type. For example, a known temperature sensor such as a thermopile, a thermostat, a thermistor, or an NC sensor can be used as the temperature sensor 19.

In the fixing device 9 according to this embodiment, when the printing operation is started, power is supplied to the heater 22, causing the heat generating section 60 to generate heat and the fixing belt 20 to heat up. The pressure roller 21 is also driven to rotate, and the fixing belt 20 starts to rotate. Then, when the temperature of the fixing belt 20 reaches a predetermined target temperature (fixing temperature), as shown in FIG. 3, a sheet P carrying an unfixed toner image is transported between the fixing belt 20 and the pressure roller 21 (nip portion N), whereby the unfixed toner is heated and pressurized, and the toner image is fixed to the sheet P.

Figure 4 is a perspective view of the fixing device 9 according to this embodiment, and Figure 5 is an exploded perspective view of the same.

As shown in Figures 4 and 5, the fixing device 9 according to this embodiment includes a device frame 40 formed in a rectangular frame shape. The device frame 40 is composed of a first device frame 25 having a pair of side walls 28 and a front wall 27 integrally therewith, and a second device frame 26 having a rear wall 29. The first device frame 25 and the second device frame 26 are assembled by engaging a plurality of engagement protrusions 28a provided on the pair of side walls 28 with a plurality of engagement holes 29a provided on the rear wall 29.

The fixing belt 20 and the pressure roller 21 are supported by a pair of side walls 28. For this reason, each side wall 28 is provided with an insertion groove 28b for inserting the rotating shaft of the pressure roller 21. The insertion groove 28b is open at one end (the rear wall 29 side) and has a butt section that is not open at the opposite end. This butt section is provided with a bearing 30 that rotatably supports the rotating shaft of the pressure roller 21. When the pressure roller 21 is supported by each side wall 28, the drive transmission gear 31 as a drive transmission member provided at one end of the axial direction of the pressure roller 21 is arranged in a state exposed outside the side wall 28. As a result, when the fixing device 9 is mounted on the image forming apparatus main body, the drive transmission gear 31 is connected to a gear provided on the image forming apparatus main body, and is in a state where it can transmit the driving force from the drive source. In addition, a drive transmission member such as a pulley or a coupling mechanism that stretches the drive transmission belt may be used instead of the drive transmission gear 31.

A pair of support members 32 that support the fixing belt 20 and the stay 24 are provided at both ends of the fixing belt 20 in the longitudinal direction. Each support member 32 has a guide groove 32a. As shown in FIG. 5, in a state where the pair of support members 32, the fixing belt 20, the stay 24, the heater holder 23, and the heater 22 are assembled, the support members 32 are assembled to the side wall portions 28 while aligning the guide grooves 32a of the support members 32 with the edges of the insertion grooves 28b of the side wall portions 28, so that the fixing belt 20, the stay 24, the heater holder 23, and the heater 22 are supported by the side wall portions 28. In addition, the fixing belt 20 is pressed against the pressure roller 21 by the support members 32 being biased by a pair of springs 33 as biasing members provided between the support members 32 and the rear wall portion 29, and a nip portion is formed.

The rear wall 29 is provided with a hole 29b as a positioning portion for positioning the fixing device body relative to the image forming device body. On the other hand, the image forming device body is provided with a protrusion 101 (see FIG. 5) as a positioning portion. When the protrusion 101 is inserted into the hole 29b of the fixing device 9, the protrusion 101 and the hole 29b fit together, and the fixing device body is positioned relative to the image forming device body. The position at which the hole 29b is provided is preferably closer to one of the ends than the longitudinal center of the rear wall 29. By providing the hole 29b at such a position, longitudinal expansion and contraction due to temperature changes is permitted at the end where the hole 29b is not provided, making it possible to suppress distortion of the device frame 40.

Figure 6 is a perspective view of a heating unit in which a heater 22 and other components are supported by a pair of support members 32, and Figure 7 is an exploded perspective view of the heating unit.

As shown in FIG. 6, the heater 22 and the heater holder 23 are longitudinal members that extend in the left-right direction of the figure. When the heater 22 and the heater holder 23 are incorporated in the fixing device, they are arranged longitudinally in the longitudinal direction of the fixing belt 20 or the axial direction of the pressure roller 21. Similarly, the stay 24 is also arranged longitudinally in the longitudinal direction of the fixing belt 20 or the axial direction of the pressure roller 21.

As shown in Figures 6 and 7, the heater holder 23 is provided with a rectangular storage recess 23a for storing the heater 22. The storage recess 23a is formed to have approximately the same shape and size as the heater 22. However, the longitudinal dimension L2 of the storage recess 23a is set to be slightly longer than the longitudinal dimension L1 of the heater 22. Therefore, even if the heater 22 expands in its longitudinal direction due to thermal expansion, interference between the heater 22 and the storage recess 23a can be avoided.

The pair of support members 32 has a C-shaped belt support portion 32b that is inserted inside the fixing belt 20 to support the fixing belt 20, a flange-shaped belt regulation portion 32c that contacts the end face of the fixing belt 20 to regulate the longitudinal movement (deviation) of the fixing belt 20, and a support recess 32d into which the heater holder 23 and the stay 24 are inserted near both ends in the longitudinal direction to support them. By inserting the belt support portions 32b into both ends in the longitudinal direction, the fixing belt 20 is supported in a so-called free belt manner in which no tension is applied in the circumferential direction (belt rotation direction) when the belt is not rotating.

As shown in Figures 6 and 7, a positioning recess 23e is provided as a positioning portion at one end of the heater holder 23 from the center in the longitudinal direction. The fitting portion 32e of the support member 32 on the left side in Figures 6 and 7 fits into this positioning recess 23e, thereby positioning the heater holder 23 and the support member 32. On the other hand, the support member 32 on the right side in Figures 6 and 7 does not have the fitting portion 32e, and is not positioned in the longitudinal direction relative to the heater holder 23. In this way, by positioning the heater holder 23 relative to the support member 32 only on one side in the longitudinal direction of the heater holder 23, longitudinal expansion and contraction of the heater holder 23 due to temperature changes is permitted.

As shown in FIG. 7, steps 24a are provided near both ends of the stay 24 in the longitudinal direction to restrict movement of the stay 24 relative to each support member 32. Each step 24a abuts against the support member 32 to restrict longitudinal movement of the stay 24 relative to the support member 32. However, at least one of these step portions 24a is disposed with a gap (backlash) relative to the support member 32. In this way, by disposing at least one step portion 24a with a gap relative to the support member 32, expansion and contraction of the stay 24 due to temperature changes is permitted.

Figure 8 is a plan view of the heater 22 according to this embodiment, and Figure 9 is an exploded perspective view of the heater 22.

9, a plurality of resistive heating elements 59 constituting a heating portion 60 are arranged on the substrate 50 of the heater 22 via a first insulating layer 51. The resistive heating elements 59 are arranged in a row in the longitudinal direction Z of the substrate 50. The conductor layer 52 is provided with a plurality of resistive heating elements 59, a plurality of electrode portions 61, and a plurality of power supply lines (conductive portions) 62. Each resistive heating element 59 is electrically connected to any two of the plurality of electrode portions 61 via a plurality of power supply lines 62. As shown in FIG. 8, the entire resistive heating element 59 and most of each power supply line 62 are covered by the second insulating layer 53 to ensure insulation. In addition, since the resistive heating elements 59 are arranged at intervals from each other, an insulating region (second insulating layer 53) is interposed between adjacent resistive heating elements 59. On the other hand, each electrode portion 61 is hardly covered by the second insulating layer 53 and is exposed so that a connector described later can be connected.

The resistive heating element 59 can be formed, for example, by applying a paste made of a mixture of silver palladium (AgPd) and glass powder to the substrate 50 by screen printing or the like, and then firing the substrate 50. Alternatively, the resistive heating element 59 may be made of a resistive material containing at least one of a silver alloy (AgPt) and ruthenium oxide (RuO ₂ ).

The electrode portion 61 and the power supply line 62 are made of a conductor having a resistance value smaller than that of the resistive heating element 59. For example, the electrode portion 61 and the power supply line 62 are formed by screen printing a material such as silver (Ag) or silver palladium (AgPd) on the substrate 50.

Figure 10 is a perspective view showing the heater 22 connected to a connector 70 as a power supply member.

As shown in FIG. 10, the connector 70 has a resin housing 71 and a number of contact terminals 72 provided on the housing 71. Each contact terminal 72 is made of a leaf spring. A power supply harness 73 is connected to each contact terminal 72.

As shown in FIG. 10, the connector 70 is attached so as to sandwich the heater 22 and the heater holder 23 together. As a result, the heater 22 and the heater holder 23 are held together by the connector 70. In this state, the tips (contact portions 72a) of the contact terminals 72 of the connector 70 elastically contact (pressure weld) with the corresponding electrode portions 61, electrically connecting the contact terminals 72 and the electrode portions 61. Similarly, the connector 70 is also connected to the electrode portion 61 at the end opposite the longitudinal end of the heater 22 shown in FIG. 10. This allows power to be supplied to the heat generating portion 60 from a power source provided in the image forming apparatus via the connector 70.

The configuration of the heater 22 according to this embodiment is described in more detail below with reference to FIG. 11.

As shown in FIG. 11, the heater 22 according to this embodiment is provided with seven resistive heating elements 59A-59G, three electrode portions 61A-61C, and four power supply lines 62A-62D connecting them. Of the three electrode portions 61A-61C, two electrode portions 61A, 61C are arranged closer to one end of the substrate 50 in the longitudinal direction Z than the resistive heating elements 59A-59G (left side in FIG. 11), and the remaining electrode portion 61B is arranged closer to the other end of the substrate 50 in the longitudinal direction Z than the resistive heating elements 59A-59G (right side in FIG. 11). Each resistive heating element 59A-59G is electrically connected to one of the two electrode portions 61A, 61C arranged at one end and to one electrode portion 61B arranged at the other end.

More specifically, of the seven resistive heating elements 59A-59G, the resistive heating elements 59B-59F other than those at both ends are connected in parallel to the first electrode 61A via the first power supply line 62A, and are connected in parallel to the second electrode 61B via the second power supply line 62B. On the other hand, the resistive heating elements 59A, 59G at both ends are connected in parallel to the third electrode 61C via the third power supply line 62C or the fourth power supply line 62D, and are connected in parallel to the second electrode 61B via the second power supply line 62B.

By adopting such a connection structure, in this embodiment, it is possible to independently control the heat generation of the first heating portion 60A composed of the resistive heating elements 59B to 59F other than those at both ends, and the second heating portion 60B composed of the resistive heating elements 59A, 59G at both ends. Specifically, when a voltage is applied to the first electrode portion 61A and the second electrode portion 61B to generate a potential difference between the two electrodes 61A, 61B, the resistive heating elements 59B to 59F other than those at both ends are energized, and only the first heating portion 60A generates heat. On the other hand, when a voltage is applied to the third electrode portion 61C and the second electrode portion 61B to generate a potential difference between the two electrodes 61C, 61B, the resistive heating elements 59A, 59G at both ends are energized, and only the second heating portion 60B generates heat. In addition, when a voltage is applied to all the electrodes 61A-61C to generate a potential difference between the first electrode 61A and the second electrode 61 and between the third electrode 61C and the second electrode 61B, all the resistive heating elements 59A-59G are energized, and both the first heating element 60A and the second heating element 60B generate heat. For example, when passing a relatively small width paper of A4 size (paper passing width: 210 mm) or less, only the first heating element 60A generates heat, and when passing a relatively large width paper of A3 size (paper passing width: 297 mm) or more, the second heating element 60B is also heated in addition to the first heating element 60A, making it possible to create a heating area according to the paper width.

Here, we will explain the temperature variation (temperature distribution deviation) that occurs in the heater 22 according to this embodiment.

In general, in a heater in which a resistive heating element as described above is connected to an electrode portion via a power supply line, when the resistive heating element is heated, the power supply line also generates a small amount of heat due to current passing through the power supply line. Therefore, depending on the heat distribution in the power supply line, there is a risk that the temperature distribution of the heater will vary. In particular, as the speed of image forming devices increases, if the current flowing through the heating element is increased to increase the amount of heat generated, the amount of heat generated in the power supply line also increases, and the effect of this cannot be ignored.

Figure 12 shows the amount of heat generated by each of the power supply lines 62A, 62B, and 62D in each block divided for each of the resistance heating elements 59A to 59G and the total amount of heat generated in each block when 20% of the current flows through each of the resistance heating elements 59A to 59G. Here, if the direction Y (see Figure 11) that intersects with the longitudinal direction Z along the surface of the substrate 50 on which the resistance heating elements 59 are provided is called the "short direction" of the substrate 50, in this embodiment, the portion of each of the power supply lines 62A, 62B, and 62D that extends in the short direction Y is short and the amount of heat generated in this portion is small, so it is ignored and only the amount of heat generated in the portion that extends in the longitudinal direction Z is calculated. In addition, since the amount of heat generated (W) is expressed by the following formula (1), the amount of heat generated in the table in Figure 12 is calculated as the square of the current (I) flowing through each power supply line for convenience. Therefore, the calculated value of the amount of heat generated is merely a simplified calculation value and differs from the actual amount of heat generated.

Regarding the method of calculating the amount of heat generated, the first block and the second block in FIG. 12 are used as examples. In the first block, the current flowing through the first power supply line 62A is 100%, and the current flowing through the fourth power supply line 62D is 20%, so the sum of the squares of these is 10,400 (10,000 + 400), which is the total heat generated by the power supply lines in the first block. In the second block, the current flowing through the first power supply line 62A is 80%, the current flowing through the second power supply line 62B is 20%, and the current flowing through the fourth power supply line 62D is 20%, so the sum of the squares of these is 7,200 (6,400 + 400 + 400), which is the total heat generated by the power supply lines in the second block. The heat generated by the other blocks is calculated in a similar manner.

The graph in Figure 12 shows the total heat generation of each block on the vertical axis. As can be seen from this graph, the total heat generation of each power supply line is large in the blocks at both ends and low in the blocks in the center. Furthermore, the total heat generation of each power supply line in blocks symmetrical to the center (for example, the first block and the seventh block) also differs. In this way, the heat generation distribution of the power supply lines varies across the longitudinal direction Z of the substrate, and this variation also causes variation in the heat generation distribution of the heater.

In addition, such temperature variation caused by heat generation from the power supply line is not limited to the case where all the resistance heating elements are heated (example shown in FIG. 12), but may occur even when only some of the resistance heating elements are heated. In particular, when unintended current shunting occurs in the power supply line due to miniaturization of the heater or speed-up of the image forming device, there is a risk that the temperature variation will become significant. In addition, unintended current shunting is likely to occur when the resistance value of the power supply line increases as a result of reducing the width of the power supply line in the short side direction of the heater in order to miniaturize the heater in the short side direction, or when the resistance value of the resistance heating element is reduced in order to increase the heat generation amount of the resistance heating element in order to speed up the image forming device. In other words, when the resistance value of the power supply line and the resistance value of the resistance heating element become relatively close due to miniaturization or speed-up, it becomes possible for current to flow through paths that have not previously flowed (unintended current shunting may occur).

For example, as shown in FIG. 13, when electricity is applied to only the resistive heating elements 59B-59F (first heating portion 60A) other than those at both ends, part of the current that passes through the second resistive heating element 59B from the left in the figure may unintentionally split into two parts at the branch point X of the second power supply line 62B, flowing to the opposite side of the second electrode portion 61B (the left side of the figure). The split current passes through the resistive heating element 59A on the left side in FIG. 13, and then passes through the resistive heating element 59G on the right side via the third power supply line 62C, the third electrode portion 61C, and the fourth power supply line 62D, before joining the second power supply line 62B.

In this way, the unintended diversion flows from the branch point X through the branch path shown by the dotted line K3 in Figure 13 to the second power supply line 62B. Furthermore, such unintended branching can occur if the conductive path of the heater 22, such as the heater 22 according to this embodiment, has at least a first conductive path (first conductive portion) K1 connecting each of the resistive heating elements 59B to 59F (first heating portion 60A) other than at both ends to the first electrode portion 61A, a second conductive path (second conductive portion) K2 extending from each of the resistive heating elements 59B to 59F other than at both ends toward the first direction S1 side (rightward in FIG. 13) of the longitudinal direction of the heater 22 and connected to the second electrode portion 61B, and a third conductive path (branch path) K3 branching off from the second conductive path K2, extending toward the second direction S2 side (leftward in FIG. 13) opposite to the first direction S1, and connected to the second conductive path K2 or the second electrode portion 61B without passing through the first conductive path K1. In this embodiment, the third conductive path (branch path) K3 is composed of a conductive path including a third conductive section consisting of a part of the second power supply line 62B (the part from the branch point X to the left in FIG. 13), the third power supply line 62C, and the fourth power supply line 62D, as well as the resistive heating elements 59A and 59G (second heating element 60B) at both ends and the third electrode portion 61C. The third conductive path K3 may also be a conductive path consisting of only the power supply line, without the resistive heating elements and the electrode portions. Even in such a case, unintended shunting may occur.

The table and graph in Figure 13 show the amount of heat generated in each power supply line 62A, 62B, 62D for each block and the total amount of heat generated when unintended current shunting occurs. In this example, when 20% of the current flows evenly to each of the resistive heating elements 59B to 59F other than at both ends, a portion of that current is assumed to be diverted by 5% at branch point X, and the amount of heat generated in each power supply line 62A, 62B, 62D for each block (block 2 to block 6) is calculated. The method for calculating the amount of heat generated is the same as that described in the example shown in Figure 12.

As shown in the table and graph in FIG. 13, in this case too, the total heat generation of the power supply line is large in the blocks at both ends and low in the blocks in the center, resulting in variation. However, in the case of FIG. 13, contrary to FIG. 12, the temperature of the blocks on the left side of the graph is higher than that of the blocks on the right side. Note that although FIGS. 12 and 13 show the current flowing in one direction, the current flowing through the heater 22 may be either DC or AC.

As described above, in the fixing device according to this embodiment, the temperature distribution of the heater also varies along the longitudinal direction due to the variation in the amount of heat generated by the power supply lines for each block. Furthermore, the effect of such variation in the temperature distribution of the heater does not only affect the fixing device, but also affects other devices installed in the image forming apparatus. Therefore, the temperature distribution of the heater also affects the protective agent supply device 7 that supplies the above-mentioned lubricant, which may cause variation in the amount of lubricant supplied.

Generally, the amount of lubricant supplied varies depending on the frictional force of the lubricant supplying member (e.g., brush roller 81 shown in FIG. 2) against the lubricant, so the rotation speed or material of the lubricant supplying member are design parameters that specify the amount of lubricant supplied. However, the hardness of the lubricant supplying member varies depending on its temperature, so when the temperature of the lubricant supplying member changes, the amount of lubricant supplied also fluctuates. In other words, the higher the temperature of the lubricant supplying member, the softer the lubricant supplying member becomes, so the amount of lubricant supplied tends to decrease.

Therefore, when the lubricant supplying member is affected by the variation in the heater temperature distribution as described above, and high and low temperature areas are generated, the amount of lubricant supplied also varies accordingly. Specifically, as in the heater 22 described above, when the temperature is higher at both ends e of the heat generating area H in which the multiple resistance heating elements 59A to 59G shown in FIG. 14 are arranged than at the center c in the longitudinal direction, the temperature of the brush roller 81 also becomes higher in the parts corresponding to both ends e of the heat generating area H in the longitudinal direction, and the amount of lubricant supplied is particularly low in the parts corresponding to both ends e. Note that FIG. 14 shows an example of the temperature distribution of the heater 22 when all the resistance heating elements 59 shown in FIG. 12 are heated. In this way, if the amount of lubricant supplied at both ends is reduced due to the temperature deviation of the brush roller 81, the cleaning performance of the photosensitive member may be reduced.

Incidentally, the amount of lubricant consumed (amount of lubricant supplied) is correlated not only with the temperature inside the image forming device (particularly the temperature of the brush roller 81) as described above, but also with the density of the lubricant. In other words, the higher the density of the lubricant, the less the lubricant is consumed. In this way, since the amount of lubricant consumed is correlated with the temperature inside the image forming device or the density of the lubricant, it is possible to adjust the amount of lubricant consumed by setting the density of the lubricant based on the temperature inside the image forming device.

Therefore, in the image forming apparatus according to the present embodiment, in order to suppress the variation in the amount of lubricant supplied as described above, the density of the lubricant in the longitudinal direction is set as follows. In this specification, the "longitudinal direction of the lubricant" means the same direction as the "longitudinal direction of the heater" or the "longitudinal direction of the heater base material". In addition, the absolute value of the density of the lubricant in the present invention is not particularly limited and can be appropriately selected according to the purpose, but it is generally known that if it is 1.190 g/cm ³ or less, the lubricant can be easily applied to the image carrier using a lubricant supply member, particularly a roller made of urethane sponge (see JP 2017-68225 A). The density of the lubricant, which is the image carrier protective agent, can be calculated by dividing the mass (W) of the image carrier protective agent by the volume (V) of the image carrier protective agent. The mass (W) can be calculated using an analytical balance (device name: AB204-S, manufactured by Mettler Toledo K.K.), and the volume (V) can be calculated using a micrometer or vernier calipers.

First, when considering the setting of the lubricant density, we conducted a test to examine the relationship between density and lubricant consumption.

Here, if the temperature at a specific position of the heater is "T" and the density of the portion of the lubricant corresponding to the specific position is "ρ", the consumption of the lubricant decreases as the temperature (T) or density (ρ) increases, so the inverse of the value obtained by multiplying "T" and "ρ" is "1/T×ρ", which is an index (lubricant consumption coefficient) that indicates the ease of consumption of the lubricant. Note that the "portion of the lubricant corresponding to the specific position of the heater" here means a portion of the lubricant in the longitudinal direction that is at the same position as the specific position of the heater in the paper feed direction (recording medium conveying direction), and the same applies to the "corresponding portion" described below. In addition, since the temperature (T) of the heater is correlated with the sum of the squares of the currents (I ² ) flowing through each portion of the heater {see formula (1) above}, it is possible to use the sum of the squares of the currents (I ² ) instead of the temperature (T) as one of the parameters that determine the ease of consumption of the lubricant. Therefore, here, "1/I ² ×ρ" is used as the lubricant consumption coefficient, using the sum of squares of currents (I ² ) instead of temperature (T).

In this test, a number of lubricants were prepared, each of which had different lubricant consumption coefficients (1/I ² ×ρ) for a portion of lubricant 80 shown in Fig. 15 that corresponded to the longitudinal center c of heat generation region H of heater 22, a portion that corresponded to both longitudinal ends e of heat generation region H, and a portion that corresponded to an intermediate position m between the center c and both ends e. Some of these lubricants (Examples 1 to 3) are shown in Table 1 below. The graph in Fig. 16 shows the lubricant consumption coefficients (1/I ² ×ρ) for portions J1 to J7 corresponding to each of resistance heating elements 59A to 59G in Examples 1 to 3 shown in Table 1.

Each lubricant used in this test is a lubricant containing zinc stearate and boron nitride as ingredients, and is formed by compression molding. However, the lubricant consumption coefficient (1/I ² ×ρ) of each lubricant is different. Specifically, in Example 1, the lubricant consumption coefficient (1/I ^{2 ×ρ) of each part of the center c, both ends e1, e2, and the middle position m is set to a substantially equal value, in Example 2, the lubricant consumption coefficient (1/I 2 ×} ρ) of the center c is higher than that of the other parts, and further, in Example 3, the difference between the lubricant consumption coefficient (1/I ² ×ρ) of the center c and the other parts is larger than that of Example 2. That is, in Example 1, the lubricant consumption ease is set to be equal in all parts, in Example 2, the center c is more easily consumed than the other parts, and further, in Example 3, the center c is more easily consumed than the other parts. In this test, each of these lubricants was installed in an image forming apparatus of the same configuration, and image formation was performed under the same conditions, after which the cleaning ability of the photoreceptor and the degree of variation in the amount of lubricant consumed (uneven wear) were examined.

As a result, it was found that the cleaning performance in the axial center region of the photoconductor decreased when the ratio of the lubricant consumption coefficient of the center c to both ends e ( ^Ie2 x ρe/ ^Ic2 x ρc) became smaller than that in Example 1. That is, when the ratio of the lubricant consumption coefficient of the center c to both ends e ( ^Ie2 x ρe/ ^Ic2 x ρc) became smaller than "1" in Example 1, the lubricant was more likely to be consumed at both ends e than at the center c, and the cleaning performance in the axial center region of the photoconductor decreased. In addition, according to the test results, when the lubricant consumption coefficient ratio ( ^Ie2 x ρe/ ^Ic2 x ρc) became equal to or greater than "7", which is the lubricant consumption coefficient ratio in Example 3, the amount of lubricant supplied at both ends of the axial direction of the photoconductor fell below the required amount, and a phenomenon called filming, which causes abnormal images, became more likely to occur. In other words, when the difference in the ease of consumption of the lubricant between both ends e and the center c is the same as or greater than that in Example 3, the lubricant becomes extremely difficult to consume at both ends e, and it becomes impossible to supply a sufficient amount of lubricant to both axial ends of the photosensitive member.

Based on the above test results, firstly, in order to ensure good cleaning performance in the central axial region of the photoreceptor, it is necessary to set the density of the lubricant so that the ratio of the lubricant consumption coefficient at the center c to both ends e is equal to or greater than "1" as in Example 1 above.

Therefore, in lubricant 80 shown in FIG. 17 , if the density of a portion corresponding to any position on the longitudinal center c side of heat generation region H of heater 22 is _ρX , the sum of the squares of the currents flowing through heater ²² at any position on the longitudinal center c side is _IX2 , and further, the density of a portion corresponding to any position α1, α2 on both longitudinal ends e of heat generation region H _{is ρY} , and the sums of the squares of the currents flowing through heater 22 at the any positions α1, ^α2 are _IY2 , respectively, then the density of lubricant 80 needs to be set so as to satisfy the following formula (2).

The arbitrary position on the longitudinal center c side of the heat generating area H and the arbitrary position on both ends e side of the longitudinal direction may be a point on the heat generating area H, or may be a certain range specified by block unit for each resistance heating element. The arbitrary position on the longitudinal center c side may be the longitudinal center c, or may be a position slightly shifted from the longitudinal center c. For example, if an even number of resistance heating elements are arranged and there is no resistance heating element at the longitudinal center c of the heat generating area H, the sum of the squares of the current flowing through the heater may be calculated at a position shifted from the longitudinal center c (the position where the resistance heating element is arranged). The arbitrary position on both ends e side of the longitudinal direction of the heat generating area H may be a position on both ends e side from the longitudinal center c. However, if the position on the longitudinal center c side is a position shifted from the longitudinal center c, the position on both ends e side from the center c is the position farther from the center c to both ends e side than the distance between the shifted position and the center c. That is, the positions on both ends e in the longitudinal direction are not limited to positions corresponding to both ends e of the heat generating region H, but may be positions between the center c and both ends e, as long as they are farther from the center c toward both ends e than any position on the center c side. Furthermore, the positions on both ends e are not limited to positions that are symmetrically arranged with respect to the center c, but may be positions that are asymmetrically arranged with respect to each other.

In this way, by setting the density of each portion of the lubricant 80 to satisfy the above formula (2), the lubricant is less likely to be consumed at both ends in the longitudinal direction than at the center, and conversely, the lubricant is more likely to be consumed at the center. This ensures good cleaning performance in the axial central region of the photoconductor, and also allows the attitude of the lubricant to be maintained in a well-balanced manner at both ends in the longitudinal direction.

However, on the other hand, if the difference in lubricant consumption coefficient (1/ ^I2 ×ρ) between the longitudinal center and both ends of the lubricant becomes large and the ease of lubricant consumption at both ends e becomes extremely low compared to the longitudinal center c, the lubricant cannot be sufficiently supplied to both axial ends of the photoconductor, causing filming. Furthermore, in that case, as the lubricant comes into contact with the brush roller mainly at both longitudinal ends over time, it becomes difficult for the lubricant to come into contact with the brush roller at the central side, so there is a risk that the lubricant will not be sufficiently supplied to the axial center of the photoconductor.

Therefore, the lubricant consumption coefficient ratio at any position on the center c side relative to any position on both ends e side must be less than 7, which is the lubricant consumption coefficient ratio in the above Example 3. Therefore, the relationship shown in the following formula (3) must be satisfied.

In short, in order to satisfactorily supply the lubricant to the photoconductor while suppressing the variation in the consumption amount of the lubricant along the longitudinal direction, the density of the lubricant should be set so as to satisfy the relationship shown in the following formula (4), which is obtained by adding the condition of the above formula (3) to the condition of the above formula (2). This makes it possible to satisfactorily supply the lubricant to the surface of the photoconductor 2 while suppressing the difference in the lubricant consumption coefficient (1/ ^I2 ×ρ) between the center side and both ends in the longitudinal direction of the lubricant from becoming large, even in an image forming apparatus in which the temperature distribution of the heater is uneven.

In addition, in order to better maintain the orientation of the lubricant in the longitudinal direction, it is preferable that the difference between the lubricant consumption coefficients (1/ ^I2 x ρ) at one end side and the other end side in the longitudinal direction of the lubricant is small. In other words, the closer the ratio of the lubricant consumption coefficients at one end side and the other end side is to "1", the more preferable it is. However, in reality, it is difficult to completely eliminate the difference between the lubricant consumption coefficients at one end side and the other end side (to make the lubricant consumption coefficient ratio "1") due to the variation in density of the lubricant when molded. Therefore, it is preferable that the lubricant consumption coefficient ratio of the other end side to the one end side is ¹ or more and 1.4 or less. Therefore, it is sufficient that the lubricant consumption coefficient ratio of the other end side to the one end side {( _Iv2 x _ρv )/( _Iw2 ^x _ρw )} satisfies the relationship of the following formula (5).

In the above formula (5), _ρV is the density of a portion of the lubricant 80 corresponding to an arbitrary position on one longitudinal end e1 side of the heat generating region H shown in Fig. 17, ^and _IV2 is the sum of the squares of the currents flowing to the heater 22 at an arbitrary position on the longitudinal end e1 side. Also, in the above formula (5), _ρW is the density of a portion of the lubricant 80 corresponding to an arbitrary position on the longitudinal other end e2 side of the heat generating region H shown in Fig. 17, and _IW2 is the sum of the squares of the currents flowing to the heater ²² at an arbitrary position on the longitudinal other end e2.

In this way, by setting the lubricant consumption coefficient ratio of the other end side to the one end side {(I _V ² × ρ _V )/(I _W ² × ρ _W )} to be greater than or equal to 1 and less than 1.4, it is possible to highly suppress the variation in the amount of lubricant consumed between the one end side and the other end side, and it is possible to better maintain the posture of the lubricant.

In this case, too, each of the arbitrary positions on the longitudinal end e1 side and the longitudinal end e2 side of the heat generating region H may be a single point on the heat generating region H, or may be a certain range specified in block units for each resistive heating element. Furthermore, each of the positions on the longitudinal end e1 side and the longitudinal end e2 side is not limited to positions corresponding to both ends e of the heat generating region H, but may be positions between the center c and both ends e, as long as they are closer to both ends e than the center c. Furthermore, each of the positions on the one end e1 side and the other end e2 side is not limited to positions that are symmetrically arranged with respect to the center c, but may be positions that are asymmetrically arranged with respect to each other.

As already mentioned, it is easier to maintain a balanced posture of the lubricant in the longitudinal direction if the lubricant is less consumed at both ends than at the center of the longitudinal direction. However, the heating mode of the heater is not limited to the case where all the resistance heating elements 59A to 59G are heated as shown in FIG. 12, but may also be the case where the resistance heating elements 59B to 59F other than the two ends are heated as shown in FIG. 13. In particular, in the example shown in FIG. 13, the resistance heating elements 59A and 59G at both ends are not actively heated (however, there is heat generation due to unintended shunting), so the temperature in the first block and the seventh block is lower than in the other blocks. For this reason, the amount of lubricant consumed temporarily increases in the portions of the lubricant at both ends corresponding to the first block and the seventh block. If such a heating mode continues, the amount of lubricant consumed at both ends may increase, and the posture balance of the lubricant may not be maintained over time.

Therefore, in a configuration in which the heat generation mode changes between the mode shown in Fig. 12 and the mode shown in Fig. 13 depending on the paper size, like the image forming apparatus according to this embodiment, it is preferable to make the lubricant less likely to be consumed at any intermediate position m between the longitudinal center c and both longitudinal ends e of the heat generation area H shown in Fig. 17 than at any intermediate position m between them. In other words, it is preferable to make the lubricant consumption coefficient (1/ ^I2 × ρ) smaller at any intermediate position m between the longitudinal center c and both longitudinal ends e of the heat generation area H than at any intermediate position m between them. Here, ^assuming that the density of a portion of the lubricant 80 corresponding to an arbitrary intermediate position m is _ρZ , the sum of the squares of the currents flowing through the heater 22 at that arbitrary intermediate position m is _IZ2 , the density of a portion corresponding to the longitudinal center c side is _ρX , the sum of the squares of the currents flowing through the heater 22 at the longitudinal center c side ^is _IX2 , the density of a portion of the lubricant 80 corresponding to both longitudinal ends e side ^{is ρU, and the sum of the squares of the currents flowing through the heater 22 at both ends e side is IU2} _{, it} is preferable to satisfy the relationships in the following equations (6) and (7).

The arbitrary intermediate position m may be, for example, a position passing through the second block B2 and the sixth block B6 as shown in FIG. 17, or a position passing through the third block B3 and the fifth block B5. The arbitrary intermediate position m may be another point on the heat generating region H, or may be a certain range specified on a block basis for each resistive heating element. Furthermore, the arbitrary intermediate position m is not limited to positions that are symmetrically arranged with respect to the center c, and may be positions that are asymmetrically arranged with respect to each other.

In this way, by making the lubricant consumption coefficient (1/ ^I2 × ρ) smaller at an arbitrary intermediate position m between the longitudinal center c and both longitudinal ends e of the heat generation region H than at any arbitrary position between them, it becomes possible to maintain the orientation of the lubricant in a well-balanced manner in the longitudinal direction even in a configuration in which the heat generation mode changes between the mode shown in Fig. 12 and the mode shown in Fig. 13 depending on the paper size. This makes it possible to more effectively suppress variations in the amount of lubricant consumed.

In addition, when zinc stearate is used as the fatty acid metal salt contained in the lubricant, or when boron nitride is used as the inorganic lubricant contained in the lubricant, the amount of lubricant supplied to the photoreceptor can be stably ensured over time, which is effective in suppressing deterioration due to wear of the photoreceptor or filming. Furthermore, since the variation in the amount of lubricant consumed can be more effectively suppressed, the life of the lubricant can also be extended.

In the above embodiment, the sum of squares of the current ( ^I2 ) is used instead of the heater temperature (T) as one of the parameters that determine the ease of consumption of the lubricant, but the ease of consumption of the lubricant (lubricant consumption coefficient) may be determined using the temperature (T). That is, instead of " _Ix2 " and " ^Iy2 ", which are the sums of squares of the current in the above formula ₍ ⁴ ), the density of each portion of the lubricant may be set so as to satisfy the relationship of the following formula (8) using the temperature ( _Tx ) of the heater 22 at an arbitrary position on the longitudinal center c side of the heat generating region H and the temperature ( _Ty ) of the heater 22 at an arbitrary position on both longitudinal ends e side.

Similarly, in the above formulas (5), (6) and (7), the heater temperature (T) may be used instead of the sum of squares of the currents ( ^I2 ). Furthermore, instead of the heater temperature (T), it is also possible to use the temperature of the corresponding part, such as the brush roller 81, the lubricant 80 or the fixing belt 20, which is affected by the heater temperature distribution and causes temperature distribution variations.

As described above, according to the present invention, even in an image forming apparatus in which the temperature distribution of the heating member is nonuniform, it is possible to suppress the variation in the supply amount of image carrier protective agent, and to suppress the occurrence of abnormal images due to uneven or insufficient supply of image carrier protective agent to the image carrier. In addition, by improving the problem of uneven supply of image carrier protective agent caused by such variation in the temperature distribution of the heating member, it becomes possible to accommodate configurations using small heaters that are prone to temperature distribution variations, or heaters with increased heat generation for higher speeds.

By the way, there are three ways to make the heater smaller in its short direction:

The first method is to reduce the size of the heat generating portion (resistance heating element) in the short direction. However, with this method, the heat generating portion is reduced in the short direction, and as a result, the width of the heating area in which the fixing belt is heated is reduced. This causes a problem that the peak temperature rise value becomes higher when attempting to ensure the same amount of heat to be given to the fixing belt as before. If the peak temperature rise value becomes higher, there is a risk that the temperature of the overheating detection device, such as a thermostat or fuse provided on the back surface of the heater, will exceed its heat resistance temperature, or that the overheating detection device will malfunction. In addition, if the peak temperature rise value becomes higher, the efficiency of heat transfer from the heater to the fixing belt will also decrease, which is undesirable from the standpoint of energy efficiency. As such, there are circumstances that make it difficult to adopt the method of reducing the heat generating portion in the short direction.

The second method is to reduce the area in the short direction where the heating part, electrode part, and power supply line are not provided. However, this method reduces the gap between the heating part and the power supply line or between the electrode part and the power supply line, which may make it difficult to ensure insulation. In view of the current heater structure, it is difficult to further reduce the gap between the heating part and the power supply line or between the electrode part and the power supply line.

The third remaining method is to reduce the size of the power supply line in the short direction. This method is more feasible than the above two methods. However, when the power supply line is reduced in the short direction, the resistance value of the power supply line increases, which may cause unintended shunting on the conductive path of the heater and cause significant variations in temperature distribution. In particular, when the resistance value of the heating part is reduced in order to increase the heat generation amount of the heating part in response to the speed-up of the image forming device, the resistance value of the power supply line and the resistance value of the heating part become relatively close, making it easier for unintended shunting to occur. In addition, as a method of avoiding such unintended shunting, it is also possible to ensure the cross-sectional area and suppress the increase in the resistance value of the power supply line by increasing the thickness direction (the direction intersecting the long direction and short direction) by the amount that the power supply line is reduced in the short direction. However, in that case, it becomes difficult to screen print the power supply line, and the method of forming the power supply line must be changed, so it is difficult to adopt a solution of making the power supply line thicker. Therefore, to achieve miniaturization of the heater in the short direction, it is necessary to make the power supply line smaller in the short direction in anticipation of an increase in resistance, and to take separate measures against the unintended shunting and uneven heat distribution that may occur as a result. Therefore, in the present invention, as described above, by setting the density of each part of the lubricant, it is possible to suppress uneven supply of the lubricant caused by uneven temperature distribution, and to accommodate miniaturization or high speed.

Specifically, the present invention is expected to be particularly effective when applied to an image forming device equipped with a small heater such as the following:

Table 2 below shows the variation in heat distribution when the heater is made smaller in the short side direction. In the test to obtain the results shown in Table 2, the temperature difference between the center and end of the heat generation area in the longitudinal direction of each heater was measured when the ratio (R/Q) of the short side dimension R of each resistance heating element 59A-59G to the short side dimension Q of the substrate 50 shown in FIG. 18 was changed. In addition, the surface temperature of each heater was measured using an infrared thermography (FLIR T620) manufactured by FLIR Systems. Note that when the short side dimension ratio (R/Q) is 80% or more, the ratio of the short side dimension of each resistance heating element 59A-59G to the short side dimension of the substrate 50 becomes too large, making it practically difficult to secure the installation space for the power supply line, so the measurement was withheld.

As shown in Table 2, the larger the short-side dimension ratio (R/Q), the larger the temperature difference between the center and ends of the heat generation area in the longitudinal direction. Therefore, in a heater with a large short-side dimension ratio (R/Q), i.e., a heater that is compact in the short-side direction, there is a risk that the temperature variation at both ends in the longitudinal direction will also be significant. In particular, in a heater with a short-side dimension ratio (R/Q) of 25% or more or 40% or more, the temperature difference between the center and ends in the longitudinal direction in the heat generation area will be large (5°C or more), so there is a risk that the temperature variation at both ends in the longitudinal direction will also be significant. Therefore, the present invention can be expected to be particularly effective when applied to an image forming apparatus equipped with a heater with a short-side dimension ratio (R/Q) of 25% or more and less than 80%, or 40% or more and less than 80%.

The heater provided in the fixing device is not limited to the heater 22 having a block-shaped (square-shaped) resistance heating element 59 as shown in FIG. 18, but may be a heater 22 having a resistance heating element 59 shaped like a folded straight line as shown in FIG. 19. In the case of the heater 22 shown in FIG. 19, the short-side dimension R of the resistance heating element 59 does not mean the thickness of one linear part of the resistance heating element 59 formed to be folded back, but means the short-side dimension of the entire resistance heating element 59. In the example shown in FIG. 18 or FIG. 19, the base material 50 of the heater 22 is formed in a rectangular shape, so the short-side dimension Q of the base material 50 is the same at any position in the longitudinal direction Z, but the base material 50 may have a shape in which the short-side dimension Q changes depending on the position in the longitudinal direction Z. However, in that case, the short-side dimension Q of the base material 50 is the minimum short-side dimension within the longitudinal range (heating area) in which the resistance heating elements 59A to 59G are arranged.

Furthermore, the heater provided in the fixing device may be one in which one resistance heating element 59 is arranged to extend in the longitudinal direction Z of the substrate 50 as shown in FIG. 20. In this example, one side (upper side in FIG. 20) of the resistance heating element 59 extending in the longitudinal direction Z of the substrate 50 is connected to the first electrode portion 61A via the first power supply line 62A, and the other side (lower side in FIG. 20) of the resistance heating element 59 extending in the longitudinal direction Z of the substrate 50 is connected to the second electrode portion 61B via the second power supply line 62B. In addition, each of the electrode portions 61A, 61B is arranged on one end side (the same end side) from the center of the longitudinal direction Z of the substrate 50, and each of the power supply lines 62A, 62B is arranged without being folded back (without bending) across the longitudinal direction Z of the substrate 50.

In such a heater 22, when a potential difference is generated between the electrodes 61A, 61B to heat the resistance heating element 59, variation in temperature distribution occurs. For example, if the current flowing through each of the power feed lines 62A, 62B at the longitudinal center c of the heat generating region H shown in Fig. 20 and at arbitrary symmetrical positions α1 and α2 on both ends e thereof is 90%, 50%, and 10%, the amount of heat generated in each of the power feed lines 62A, 62B will be as shown in the table in Fig. 20. Note that in this case as well, the amount of heat generated is calculated as the square of the current ( ^I2 ) flowing through each power feed line for convenience.

As shown in the table in FIG. 20, the total heat generation amount of each power supply line 62A, 62B is higher at one end in the longitudinal direction (the left end in the figure) than at the other end (the right end in the figure), so there may be a problem of uneven supply of the image carrier protection agent due to the variation in the temperature distribution of the heater as described above. Therefore, by applying the configuration according to each of the above-mentioned embodiments to a fixing device equipped with such a heater, it is possible to suppress uneven supply of the lubricant.

In addition, a resistive heating element with PTC characteristics may be used to suppress temperature variations in the heater. PTC characteristics are characteristics in which the resistance value increases as the temperature increases (when a constant voltage is applied, the heater output decreases). By using a heating element with PTC characteristics, it is possible to achieve high output at low temperatures and high speed rise in temperature, and low output at high temperatures to suppress overheating. For example, if the TCR coefficient of the PTC characteristics is set to about 300 to 4000 ppm/degree, it is possible to reduce costs while ensuring the resistance value required for the heater. It is more preferable to set the TCR coefficient to 500 to 2000 ppm/degree.

The temperature coefficient of resistance (TCR) can be calculated using the following formula (9). In formula (7), T0 is the reference temperature, T1 is the arbitrary temperature, R0 is the resistance value at reference temperature T0, and R1 is the resistance value at arbitrary temperature T1. For example, in the heater 22 described above and shown in FIG. 11, if the resistance value between the first electrode portion 61A and the second electrode portion 61B is 10Ω (resistance value R0) at 25°C (reference temperature T0) and 12Ω (resistance value R1) at 125°C (arbitrary temperature T1), the temperature coefficient of resistance is 2000 ppm/°C according to formula (9).

The fixing device provided in the image forming apparatus is not limited to the fixing device described above, but may be a fixing device as shown in Figures 21 to 23. The configuration of each fixing device shown in Figures 21 to 23 will be briefly described below.

The fixing device 9 shown in FIG. 21 differs from the fixing devices described above in that a pressure roller 90 is disposed on the side of the fixing belt 20 opposite the pressure roller 21 side. In this case, the fixing belt 20 is sandwiched and heated by the pressure roller 90 and heater 22. Meanwhile, on the pressure roller 21 side, a nip forming member 91 is disposed on the inner circumference of the fixing belt 20. The nip forming member 91 is supported by a stay 24, and the nip forming member 91 and the pressure roller 21 sandwich the fixing belt 20 to form a nip portion N.

Next, in the fixing device 9 shown in FIG. 22, the above-mentioned pressure roller 90 is omitted, and in order to ensure the circumferential contact length between the fixing belt 20 and the heater 22, the heater 22 is formed in an arc shape to match the curvature of the fixing belt 20. The rest of the configuration is the same as that of the fixing device 9 shown in FIG. 21.

Next, in the fixing device 9 shown in FIG. 23, in addition to the fixing belt 20, a pressure belt 92 is provided, and a heating nip (first nip portion) N1 and a fixing nip (second nip portion) N2 are separately configured. That is, a nip forming member 91 and a stay 93 are also arranged on the opposite side of the pressure roller 21 from the fixing belt 20 side, and the pressure belt 92 is arranged so as to enclose the nip forming member 91 and the stay 93. The rest of the configuration is the same as the fixing device 9 shown in FIG. 3.

By applying the present invention to image forming apparatuses equipped with fixing devices such as those shown in Figures 21 to 23, it becomes possible to suppress uneven supply of the image carrier protecting agent, improve image quality, and accommodate miniaturization or high speed.

7 Protective agent supplying device 9 Fixing device (heating device)
22 Heater (heating member)
59 Resistance heating element (heating element)
60 Heat generating portion 61 Electrode portion 62 Power supply line (conductive portion)
62 Power supply line (conductive part)
80 Lubricant (image carrier protective agent)
81 Brush roller (protective agent supplying means)
100 Image forming apparatus 200 Image forming section c Center in the longitudinal direction of the heat generating area e Both ends in the longitudinal direction of the heat generating area H Heat generating area K1 First conductive path K2 Second conductive path K3 Third conductive path (branch path)
m: Midpoint between the center of the heating area and both ends P: Paper (recording medium)
S1: First direction; S2: Second direction; Y: Short side direction of heater (substrate); Z: Long side direction of heater (substrate);

JP 2016-62024 A

Claims (8)

A heating device having a heating member;
an image carrier that carries an image on its surface;
an image carrier protecting agent applied to a surface of the image carrier;
An image forming apparatus comprising:
The heating member includes a base material, a heating element, an electrode portion, and a conductive portion that connects the heating element and the electrode portion,
The electrode portion includes a first electrode portion and a second electrode portion,
the conductive portion includes a first conductive portion that connects the heating element and the first electrode portion, a second conductive portion that extends from the heating element toward a first direction side in the longitudinal direction of the base material and is connected to the second electrode portion, and a third conductive portion that branches off from the second conductive portion, extends toward a second direction side opposite to the first direction, and constitutes at least a part of a branch path that is connected to the second conductive portion or the second electrode portion without passing through the first conductive portion,
The density of a portion of the image carrier protecting agent corresponding to an arbitrary position on the longitudinal center side of the heat generating region of the heating member is denoted by _ρX , and the sum of the squares of the currents flowing through the conductive parts arranged at each position of the heating member at the arbitrary position on the longitudinal center side is denoted ^{by IX2} _,
Let _ρY be the density of the portion of the image carrier protecting agent corresponding to any position on both ends of the heat generating region in the longitudinal direction, and _IY2 be the sum of the squares of the currents flowing through the conductive parts arranged at each position of the heating member at ^any position on both ends of the longitudinal direction,
An image forming apparatus that satisfies the relationship: 1≦( _IY ² × _ρY )/( _IX ² × _ρX )<7. The density of a portion of the image carrier protecting agent corresponding to an arbitrary position on one end side of the heat generating region in the longitudinal direction is denoted by ρ _V , and the sum of the squares of the currents flowing through the conductive parts arranged at each position of the heating member at the arbitrary position on one end side of the longitudinal direction is denoted by I _V ² ,
If the density of a portion of the image carrier protecting agent corresponding to an arbitrary position on the other end side of the heat generating region in the longitudinal direction is ρ _W , and the sum of the squares of the currents flowing through the conductive parts arranged at each position of the heating member at an arbitrary position on the other end side in the longitudinal direction is I _W ² , then:
^2. The image forming apparatus according to claim 1 ^, wherein the relationship 1≦( _IV2 × _ρV )/( _IW2 × _ρW )≦1.4 is satisfied. Let ρ be the density of the portion of the image carrier protecting agent corresponding to a specific position in the longitudinal direction of the heat generating region, and ^I2 be the sum of the squares of the currents flowing through the conductive parts arranged on the heating member at the specific position.
3. The image forming device according to claim 1, wherein a value 1/( ^I2 × ρ), which is the reciprocal of the product of ^I2 and ρ, is smaller at any intermediate position between the longitudinal center and both longitudinal end sides of the heat generating area than at any intermediate position between the longitudinal center and both longitudinal end sides of the heat generating area. A heating device having a heating member;
an image carrier that carries an image on its surface;
an image carrier protecting agent applied to a surface of the image carrier;
An image forming apparatus comprising:
The heating member includes a base material, a heating element, an electrode portion, and a conductive portion that connects the heating element and the electrode portion,
The electrode portion includes a first electrode portion and a second electrode portion,
the conductive portion includes a first conductive portion that connects the heating element and the first electrode portion, a second conductive portion that extends from the heating element toward a first direction side in the longitudinal direction of the base material and is connected to the second electrode portion, and a third conductive portion that branches off from the second conductive portion, extends toward a second direction side opposite to the first direction, and constitutes at least a part of a branch path that is connected to the second conductive portion or the second electrode portion without passing through the first conductive portion,
The density of the portion of the image carrier protecting agent corresponding to an arbitrary position on the longitudinal center side of the heat generating region of the heating member is denoted by ρ _X , and the temperature of the portion corresponding to the arbitrary position on the longitudinal center side is denoted by _TX ,
If the density of the image bearing member protecting agent in a portion corresponding to any position on both ends of the heat generating region in the longitudinal direction is ρ _Y and the temperature of the portion corresponding to any position on both ends in the longitudinal direction is _TY , then
An image forming apparatus that satisfies the relationship: 1≦( _TY × _ρY )/( _TX × _ρX )<7. 5. The image forming apparatus according to claim 1, wherein the third conductive portion, a third electrode portion different from the first electrode portion and the second electrode portion, and a heating element connected to the third electrode portion via the third conductive portion are arranged on the branch path. If a direction intersecting the longitudinal direction along the surface of the heating member on which the heat generating element is provided is defined as a short direction,
6. The image forming apparatus according to claim 1 , wherein a ratio of a widthwise dimension of the heat generating element to a widthwise dimension of the heating member is 25% or more and less than 80%. If a direction intersecting the longitudinal direction along the surface of the heating member on which the heat generating element is provided is defined as a short direction,
6. The image forming apparatus according to claim 1 , wherein a ratio of a widthwise dimension of the heat generating element to a widthwise dimension of the heating member is 40% or more and less than 80%. 8. The image forming apparatus according to claim 1 , further comprising a protective agent supplying unit that rotates in contact with the image bearing member protective agent to supply the image bearing member protective agent to the surface of the image bearing member .

Images