JP2025115061A - Fixing device and image forming apparatus - Google Patents

Abstract

[Problem] To provide a fixing device that improves the temperature uniformity of a heat equalizer in the paper width direction, ensures productivity (throughput) when continuously fixing small-size paper, and maintains low sliding resistance between the heat equalizer and the fixing member. [Solution] The fixing device of the present invention includes a rotating fixing member, a heat equalizer that abuts the inner surface of the fixing member and equalizes the temperature of the fixing member in the rotational axis direction, a pressure member that abuts the heat equalizer via the fixing member to form a nip and pressurizes the recording material passing through the nip, and a heat source disposed inside the fixing member. The heat equalizer has a concave step portion in an area that at least partially overlaps the nip portion, and a sliding plate in the step portion. The sliding plate is made of a material that has lower sliding resistance and higher durability than the heat equalizer. Therefore, the heat equalizer's temperature uniformity in the paper width direction is improved, and sliding resistance between the heat equalizer and the fixing member can be maintained low. [Selected Figure] Figure 2

Description

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

Electrophotographic image forming devices such as copiers and printers widely use fixing film-based fixing devices, which have a fast heating temperature. The fixing film system directly heats a thin fixing film using a halogen heater or similar, and a pressure roller is brought into contact with a nip-forming member via the fixing film to form a fixing nip.

For example, Patent Document 1 discloses a fixing device that uses a copper heat equalizing member in the area that rubs against the fixing film to dissipate heat from the fixing film in the width direction of the paper when fixing small-sized paper continuously, in order to prevent both ends of the fixing film from becoming too hot.

Patent document 2 also discloses a fixing device that uses an aluminum heat equalizing member with an anodized aluminum coating on the part that rubs against the fixing film, thereby maintaining low sliding resistance with the fixing member without compromising reliability or heat equalization.

However, aluminum heat spreaders have a lower thermal conductivity than copper heat spreaders, making them unsuitable for use in high-speed machines with speeds of, for example, 70 ppm or higher, which inevitably reduces throughput. On the other hand, applying a sliding coating to copper heat spreaders to improve their sliding properties increases costs.

The present invention aims to provide a fixing device that improves the heat uniformity of the heat equalizing member in the paper width direction, ensures productivity (throughput) when continuously fixing small-size paper, and maintains low sliding resistance between the heat equalizing member and the fixing member.

The above problem is solved by a fixing device comprising: a rotating fixing member; a heat equalizer that contacts the inner surface of the fixing member and equalizes the temperature of the fixing member in the axial direction of rotation; a pressure member that contacts the heat equalizer via the fixing member to form a nip and applies pressure to recording material passing through the nip; and a heat source disposed inside the fixing member; wherein the heat equalizer has a concave stepped portion provided in an area that at least partially overlaps with the nip, the stepped portion has a sliding plate, and the sliding plate is made of a material that has lower sliding resistance and higher durability than the heat equalizer.

The fixing device of the present invention ensures high productivity (throughput) when continuously fixing small-size paper, while also maintaining low sliding resistance between the heat equalizing member and the fixing member.

1 is a schematic diagram illustrating the configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic diagram illustrating the configuration of a fixing device according to an embodiment of the present invention. FIG. 2 is a perspective view showing a heat spreader and a sliding plate according to an embodiment of the present invention. FIG. 4 is an enlarged cross-sectional view of the sliding plate shown in FIG. 3 . FIG. 3 is a detailed view (part 1) showing an enlarged view of a heat spreader and a sliding plate according to an embodiment of the present invention. FIG. 10 is a second enlarged detailed view of the heat spreader and the sliding plate according to the embodiment of the present invention.

Figure 1 is a schematic diagram of an image forming apparatus according to one embodiment of the present invention. Below, we will explain an embodiment in which the present invention is applied to a laser printer (hereinafter referred to as "printer"), which is an electrophotographic image forming apparatus.

This image forming device 1 has an image forming unit 100 that forms an image on paper P, which is a recording material. The image forming unit 100 is a tandem image forming device in which imaging units 10Y, 10M, 10C, and 10K for the colors yellow (Y), magenta (M), cyan (C), and black (K) are arranged along the rotation direction of an intermediate transfer belt 20, which serves as an intermediate transfer body. Each imaging unit 10Y, 10M, 10C, and 10K has a photosensitive element 11Y, 11M, 11C, and 11K, respectively, which serves as a latent image carrier.

Each imaging unit 10Y, 10M, 10C, and 10K is equipped with a charging device as charging means, an optical writing device 9 as electrostatic latent image forming means, and a developing device as developing means around the photoreceptor 11Y, 11M, 11C, and 11K. Furthermore, a primary transfer device as primary transfer means and a cleaning device as cleaning means are also equipped around the photoreceptor 11Y, 11M, 11C, and 11K.

The charging device uniformly charges the photosensitive drum surface to a predetermined potential, and the optical writing device 9 writes an electrostatic latent image onto the photosensitive drum surface, which has been uniformly charged by the charging device, by exposing it to light according to image information. The developing device creates a toner image by developing the electrostatic latent image on the photosensitive drum with toner of each color (Y, M, C, K). The primary transfer device transfers the toner image on the photosensitive drum onto the intermediate transfer belt 20, and the cleaning device cleans the photosensitive drum by removing residual toner from the drum.

The color toner images formed on each photoreceptor 11Y, 11M, 11C, and 11K are primarily transferred onto the intermediate transfer belt 20 by the primary transfer device so that they overlap each other, forming a color toner image on the intermediate transfer belt 20. As the intermediate transfer belt 20 rotates, the color toner image on the intermediate transfer belt 20 is transported to the area facing the secondary transfer device 30 (secondary transfer area).

Meanwhile, below the image forming unit 100, a paper feed cassette 60 is located as a feed unit that feeds the held paper P. Paper P is fed one sheet at a time from the paper feed cassette 60 by a pickup roller 61. The paper P is then transported along the transport path to the secondary transfer area by a pair of registration rollers 62.

The color toner image on the intermediate transfer belt 20 is secondarily transferred by the secondary transfer device 30 onto paper P, which is transported by a pair of registration rollers 62 at a predetermined timing in the secondary transfer area. The paper P with the color toner image formed is then transported to the fixing device 40, which serves as a fixing means, where the color toner image is fixed onto the paper P by the action of heat and pressure. After fixing, the paper P is transported along the transport path and discharged onto the paper output tray 50 by the paper output rollers 63.

Figure 2 is a schematic diagram of a fixing device according to one embodiment of the present invention. The fixing device 40 includes a fixing belt 42, which is a rotating fixing member, a pressure roller 41, which is a pressure member, and a heat source 43 (a halogen heater in the illustrated example) located inside the fixing belt 42, and performs fixing by applying heat and pressure.

In addition, a nip forming member 45 is disposed within the fixing belt 42 and is held by a fixing stay 44, which is a stay member. The nip forming member 45 forms a nip with the pressure roller 41, sandwiching the fixing belt 42 between them.

(Pressure roller)
The pressure roller 41 contacts the outer peripheral surface of the fixing belt 42 to form a nip, and applies pressure to the recording material passing through the nip. The pressure roller 41 is a metal roller having a silicone rubber layer on the outer periphery thereof, and a release layer (PFA or PTFE layer) is provided on the surface of the silicone rubber layer to provide releasability.

The pressure roller 41 is pressed against the fixing belt by a spring or the like, and the rubber layer is crushed and deformed to create a predetermined nip width. In Figure 2, the unpressured state of the pressure roller 41 is shown by a solid line, and the pressed state is shown by a dashed line.

The pressure roller 41 rotates by receiving a driving force from a drive source such as a motor provided in the image forming apparatus 1 via gears. The fixing belt 42 rotates together with the pressure roller 41 by receiving a driving force from the pressure roller 41 at the nip portion.

The pressure roller 41 may be a solid roller, but a hollow one is preferable because it has less heat capacity. The pressure roller 41 may also have a heat source such as a halogen heater. The silicone rubber layer may be solid rubber, but if there is no heater inside the pressure roller, sponge rubber may be used. Sponge rubber is more preferable because it has better heat insulation properties and is less likely to lose heat to the fixing belt 42.

(fixing belt)
The fixing belt 42 is an endless belt (or film) made of a metal belt such as nickel or SUS, or a resin material such as polyimide. The surface layer of the fixing belt 42 has a release layer such as a PFA or PTFE layer, which provides release properties to prevent toner from adhering to the belt.

An elastic layer formed of a silicone rubber layer or the like may be present between the base material and the release layer of the fixing belt 42. Without a silicone rubber layer, the heat capacity is reduced and fixing performance is improved, but when the unfixed image is crushed and fixed, subtle irregularities on the belt surface are transferred to the image, leaving citrus peel marks in solid areas of the image. To improve this, a silicone rubber layer of 100 μm or more is required. The deformation of the silicone rubber layer absorbs the subtle irregularities, improving the citrus peel image.

(Nip forming member)
Nip forming member 45 is composed of heat equalizing member 45a, which is a sliding member and heat transfer member disposed on the nip surface, and resin pad 45b that supports it. One of the roles of resin pad 45b is heat insulation, which suppresses heat absorption of fixing belt 42 by fixing stay 44 via nip forming member 45, thereby suppressing an increase in warm-up time and TEC value.

The heat equalizing member 45a extends in the width direction of the fixing belt 42 and has, for example, a pad shape. This heat equalizing member 45a is arranged to equalize the temperature in the axial direction of the fixing belt 42. In other words, it absorbs heat from high-temperature areas of the fixing belt 42 and transfers the absorbed heat to low-temperature areas of the fixing belt 42, thereby equalizing the temperature in the axial direction of the fixing belt 42.

The heat-equalizing member 45a is made of a metal material with high thermal conductivity, such as copper (thermal conductivity: 398 W/mK), which allows for rapid heat transfer. The surface of the heat-equalizing member 45a is coated with a coating that provides excellent sliding properties. Examples of coating materials include resin-based materials such as polyimide resin, fluororesin, polyphenylene sulfide resin, and saturated polyester resin. Alternatively, such resin-based coating materials may be mixed with glass fiber, carbon, graphite, graphite fluoride, carbon fiber, molybdenum disulfide, or fluororesin.

Metal-based coating materials can also be used. Examples of metal-based coating materials include molybdenum disulfide, nickel, and composite plating of nickel and fluororesin. Examples of metal-based coating materials include anodized aluminum and anodized aluminum impregnated with resin or metal. Ceramics can also be used as coating materials. Examples of ceramics used as coating materials include silicon carbide ceramic, silicon carbide ceramic, alumina ceramic, and mixtures of these with molybdenum disulfide, fluororesin, etc.

In this embodiment, the high thermal conductivity heat-equalizing member 45a is made from a material with high thermal conductivity that allows heat to transfer in a short time, and is processed as described above. In this way, the high thermal conductivity heat-equalizing member 45a is produced.

(Fixed stay)
The fixing stay 44 is a hollow metal pipe made of aluminum, iron, stainless steel, or another metal. In this embodiment, the fixing stay 44 is rectangular, but may have any other cross-sectional shape. The fixing stay 44 prevents the nip forming member 45, which receives pressure from the pressure roller 41, from bending, thereby ensuring a uniform nip width in the axial direction.

(heat source)
Two heat sources 43 for raising the temperature of the fixing belt 42 are provided inside the fixing belt 42. In this embodiment, the heat sources 43 are halogen heaters, and the fixing belt 42 is directly heated from the inner circumferential side by radiant heat from the heat sources 43. Here, the heat source 43 only needs to be able to heat the fixing belt 42, and may be an induction coil, a resistance heating element, a carbon heater, or the like.

(reflector)
Furthermore, a reflector 48 is disposed within the fixing belt 42 as a reflective member that reflects heat toward the fixing belt in order to minimize loss of radiant heat from the heat source 43. The reflector 48 is made of a high-purity aluminum metal material as a base, and is made of high-brightness aluminum with multiple reflection-enhancing films and protective films formed on the surface to achieve a high reflectivity, for example, a reflectivity of 95% or more. Depending on the configuration, an aluminum plate may be coated with silver to further improve reflectivity.

(Light blocking member)
The light-shielding member 49 has a stepped shape with a light-shielding area that matches the width of the recording medium (paper width). It is arranged to rotate without contact along the inside of the fixing belt 42, and rotates to a position corresponding to each paper width to shield areas that do not need to be heated. This makes it possible to prevent the non-paper-passing areas from becoming overheated, even when narrow recording media are continuously passed through.

Next, we will explain the characteristic features of the present invention.

Referring particularly to the central portion of Figure 2, the heat equalizing member 45a has a recessed step portion in its central region across the paper width direction (i.e., the region that at least partially overlaps with the nip portion), and has a sliding plate 46 that fits into this step portion.

The sliding plate 46 is preferably made of a highly durable material because it is rubbed against the fixing belt 42 at high pressure by the pressure roller 41. In this embodiment, an anodized aluminum plate (thermal conductivity: 236 W/mk) is used.

Anodized aluminum coatings (anodized aluminum layers) are extremely hard and highly wear-resistant, and are particularly resistant to abrasive wear. Therefore, the sliding plate 46 of this embodiment serves as a wear-resistant sliding member against the inner circumferential surface of the fixing belt 42.

The heat equalizing member 45a is made by forming a concave step in a copper plate using half-blanking, and fitting the sliding plate 46 into the step. "Half-blanking" is a type of plate processing method in which a specific part of the plate is made to protrude in a convex shape by approximately half the thickness of the plate. "Half-blanking" has the advantage of being quick and inexpensive to manufacture.

The heat equalizing member 45a and the sliding plate 46 are fixedly connected to each other with adhesive, double-sided tape, or fastening means (such as screws) provided outside the paper passage area to prevent misalignment.

The concave step of the heat equalizing member 45a is not limited to half-blanking, but can also be formed by drawing or cutting. The step can also be formed by bending across the entire width of the paper. This allows for a larger concave depth and greater freedom in selecting the sliding plate thickness.

The convex portion of the heat equalizing member 45a is in partial contact (over the minimum area that can be supported) with the resin pad 45b, which has a low thermal conductivity. This prevents the heat from the heat equalizing member 45a from escaping toward the fixing stay 44, allowing the heat of the fixing belt 42 to be used efficiently. Furthermore, the resin pad 45b fits into the convex portion of the heat equalizing member 45a, preventing misalignment between the two.

When continuously fixing small-sized paper sheets, the fixing device 40 of this embodiment can transfer heat from both ends of the sliding plate 46 to the center via the heat equalizing member 45a. This prevents the sliding plate 46 (and heat equalizing member 45a) at both ends of the paper from becoming too hot when continuously fixing small-sized paper sheets, ensuring productivity (throughput).

Next, we will explain the advantageous configuration.

Figure 3 is a perspective view showing a heat equalizing member and sliding plate according to one embodiment of the present invention, and Figure 4 is an enlarged cross-sectional view of the sliding plate shown in Figure 3. Using these figures, we will explain the advantageous configuration of the sliding plate 46.

The sliding plate 46 of this embodiment is made of aluminum or an aluminum alloy and has an alumite coating (alumite layer 54) on its surface (the surface facing the inner circumferential surface of the fixing belt 42) as shown in Fig. 3. In addition, as shown in Fig. 4, molybdenum disulfide ( _MoS2 ) 56, which is a solid lubricant, is filled in a plurality of regularly arranged micropores 54a in the alumite layer 54 (on the aluminum base material 52).

The anodized aluminum layer 54 is extremely hard and highly wear-resistant, and is particularly resistant to abrasive wear. On the other hand, molybdenum disulfide 56 is a solid lubricant with a lower coefficient of friction than the anodized aluminum layer 54. Therefore, the heat equalizing member 45a of this embodiment can be used as a sliding member that combines wear resistance and lubricity with the inner circumferential surface of the fixing belt 42.

(Modification)
In the above embodiment, molybdenum disulfide is used as the solid lubricant, but this is not limiting. Alternatively, polytetrafluoroethylene (PTFE) or fluorine grease may be impregnated and filled into the micropores 54a of the anodized aluminum layer 54.

Figure 5 is a detailed view (part 1) showing an enlarged view of the heat equalizing member and sliding plate according to one embodiment of the present invention. As shown in Figure 5, the length dimension (la) of the step portion of the heat equalizing member 45a is greater than the length dimension (lb) of the sliding plate 46 (la > lb), and a gap (g) of approximately 1 mm or less is formed between the step portion and the sliding plate 46 on the upstream side in the recording material transport direction.

A lubricant is applied between the fixing belt 42, which is rotated at high pressure, and the sliding plate 46 to reduce friction. The lubricant between the fixing belt 42 and the sliding plate 46 is temporarily held in the gap (g) while circulating, which refreshes the lubricant, slowing its deterioration rate and achieving a long lifespan. The gap (g) is not limited to being located upstream of the nip N (see Figure 5), but may also be located downstream of the nip N.

Figure 6 is a detailed view (part 2) showing an enlarged view of the heat equalizing member and sliding plate according to one embodiment of the present invention. As shown in Figure 6, the depth dimension (ta) of the step portion is greater than the thickness dimension (tb) of the sliding plate 46 (ta > tb), and the surface of the sliding plate 46 facing the fixing belt 42 has a step with respect to the surface of the heat equalizing member 45a facing the fixing belt 42. The pressure roller 41 is then pressed so that the nip portion N includes the step portion A on the downstream side in the conveyance direction of the recording material.

By forming a stepped nip, the leading edge of the paper is ejected closer to the pressure roller 41, improving the paper's ability to separate from the fixing belt 42. Furthermore, because the step creates a high load at the rear end of the nip N, the molten toner is pressed against the paper, improving fixing performance.

The present invention has been described in detail above using an embodiment. This embodiment is merely an example, and various modifications can be made without departing from the spirit of the invention. For example, the embodiment and modifications may be combined with each other.

Furthermore, the effects described in the embodiments of the present invention are merely a list of the most favorable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments of the present invention.

For example, aspects of the present invention are as follows.
(Aspect 1)
a rotating fixing member;
a temperature equalizing member that contacts an inner circumferential surface of the fixing member and equalizes the temperature of the fixing member in the axial direction of the rotation;
a pressure member that contacts the heat equalizing member via the fixing member to form a nip portion and applies pressure to the recording material passing through the nip portion;
a heat source disposed inside the fixing member,
the temperature equalizing member has a recessed step portion provided in a region at least partially overlapping with the nip portion, the recessed step portion having a sliding plate thereon;
The fixing device is characterized in that the sliding plate is made of a material having lower sliding resistance and higher durability than the heat equalizing member.
(Aspect 2)
2. The fixing device according to claim 1, wherein the heat equalizing member has a thermal conductivity greater than that of the sliding plate.
(Aspect 3)
a length dimension of the step portion in the recording material conveyance direction is greater than a length dimension of the sliding plate in the recording material conveyance direction;
3. The fixing device according to claim 1, wherein the step portion and the sliding plate form a gap of about 1 mm or less on the upstream side or downstream side in the conveying direction of the recording material.
(Aspect 4)
The depth dimension of the step portion is greater than the thickness dimension of the sliding plate,
a surface of the sliding plate facing the fixing member has a step with respect to a surface of the heat equalizing member facing the fixing member; and
4. The fixing device according to claim 1, wherein the pressure member applies pressure so that the nip portion includes the step on the downstream side in the conveying direction of the recording material.
(Aspect 5)
5. The fixing device according to claim 1, wherein the step portion of the temperature equalizing member is formed by half-punching.
(Aspect 6)
The fixing device according to any one of Aspects 1 to 5, characterized in that the sliding plate is made of aluminum or an aluminum alloy, has an anodized aluminum layer on a surface facing the inner circumferential surface of the fixing member, and a plurality of micropores in the anodized aluminum layer are filled with a solid lubricant having a lower friction coefficient than the anodized aluminum layer.
(Aspect 7)
7. An image forming apparatus comprising the fixing device according to any one of aspects 1 to 6.

REFERENCE SIGNS LIST 1 Image forming device 9 Optical writing device 10C, 10K, 10M, 10Y Imaging unit 11C, 11K, 11M, 11Y Photosensitive member 20 Intermediate transfer belt 30 Secondary transfer device 40 Fixing device 41 Pressure roller 42 Fixing belt 43 Heat source 44 Fixing stay 45 Nip forming member 45a Heat equalizing member 45b Resin pad 46 Sliding plate 48 Reflector 49 Light blocking member 50 Paper output tray 52 Aluminum base material 54 Anodized aluminum layer 54a Micropores 56 Molybdenum disulfide 60 Paper feed cassette 61 Pickup roller 62 Pair of registration rollers 63 Paper output roller 100 Image forming unit A Stepped portion P Paper

Japanese Patent Application Laid-Open No. 2022-139858 Japanese Patent Application Laid-Open No. 2021-096348

Claims (7)

a rotating fixing member;
a temperature equalizing member that contacts an inner circumferential surface of the fixing member and equalizes the temperature of the fixing member in the axial direction of the rotation;
a pressure member that contacts the heat equalizing member via the fixing member to form a nip portion and applies pressure to the recording material passing through the nip portion;
a heat source disposed inside the fixing member,
the temperature equalizing member has a recessed step portion provided in a region at least partially overlapping with the nip portion, the recessed step portion having a sliding plate thereon;
The fixing device is characterized in that the sliding plate is made of a material having lower sliding resistance and higher durability than the heat equalizing member. The fixing device described in claim 1, characterized in that the thermal conductivity of the heat equalizing member is greater than the thermal conductivity of the sliding plate. a length dimension of the step portion in the recording material conveyance direction is greater than a length dimension of the sliding plate in the recording material conveyance direction;
2. The fixing device according to claim 1, wherein a gap of about 1 mm or less is formed between the step portion and the sliding plate on the upstream side or downstream side in the conveying direction of the recording material. The depth dimension of the step portion is greater than the thickness dimension of the sliding plate,
a surface of the sliding plate facing the fixing member has a step with respect to a surface of the heat equalizing member facing the fixing member; and
2. The fixing device according to claim 1, wherein the pressure member applies pressure so that the nip portion includes the step on the downstream side in the conveying direction of the recording material. The fixing device described in claim 1, wherein the step portion of the heat equalizing member is formed by half-punching. The fixing device described in claim 1, characterized in that the sliding plate is made of aluminum or an aluminum alloy, has an anodized aluminum layer on the surface facing the inner circumferential surface of the fixing member, and multiple micropores in the anodized aluminum layer are filled with a solid lubricant having a lower friction coefficient than the anodized aluminum layer. An image forming apparatus equipped with the fixing device described in any one of claims 1 to 6.