JP7501052B2 - NIP FORMING MEMBER, FIXING DEVICE AND IMAGE FORMING APPARATUS - Google Patents

Description

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

Conventionally, a fixing device is known that includes an endless fixing belt, a heating element disposed inside the fixing belt, a flat nip member disposed inside the fixing belt, and a pressure roller that sandwiches the fixing belt between the nip member and the fixing belt (see, for example, Patent Documents 1 and 2).

In configurations where these nip members are directly heated by a heating element, a portion of the nip member is extended to contact a thermostat or thermistor to detect the temperature of the nip member.

Figure 1 is a perspective view showing the configuration of a conventional nip member. As shown in Figure 1, the nip member 10 has detectable parts 14 that protrude upward from the upper end of the nip portion 12. These detectable parts 14 are provided with contact sensors (thermistors, thermostats, etc.) that detect the temperature of the nip member 10.

However, the portion of the nip portion 12 where the detected portion 14 (and the contact sensor) is provided has a higher heat capacity per width than other portions, causing temperature unevenness in the longitudinal direction of the nip portion 12. As a result, there is a risk of unevenness in the fixability and glossiness of the image.

In response to this, Patent Document 3 discloses a configuration in which a notch is formed at the end of the nip member in the belt rotation direction and the temperature detection means is disposed in that portion in order to stabilize the contact pressure of the temperature detection means and prevent thermal deterioration.

Patent Document 4 also discloses a configuration that suppresses an increase in heat capacity by thinning the area of the nip member that comes into contact with the temperature detection means in order to prevent a deterioration in the heating efficiency of the nip member.

However, in either configuration, the heat capacity per widthwise cross section of the nip member is not uniform, so the temperature unevenness in the longitudinal direction of the nip member is not sufficiently improved.

The present invention aims to provide a nip forming member in which a contact-type temperature detection means is provided in an extension portion provided in the nip portion, and which can suppress temperature unevenness in the longitudinal direction.

The above problem is solved by a nip forming member that forms a fixing nip portion of a fixing device, the nip forming member having at least one contact-type temperature detection means for detecting the temperature of the nip forming member, the nip forming member having a nip portion that forms the fixing nip portion and an extension portion provided at a short end portion of the nip portion along the longitudinal direction of the nip portion, the extension portion having at least one contact portion with which the temperature detection means comes into contact, and the extension portion being divided by a slit formed in the transport direction of the recording medium into a contact area including the contact portion and a non-contact area that does not come into contact with the temperature detection means.

The nip forming member of the present invention has an extension portion provided in the nip portion that is divided into a contact region including a contact portion where the temperature detection means is provided and a non-contact region, so that the transfer of heat from the contact region to the non-contact region can be blocked. Therefore, the difference in the amount of heat transferred from the nip portion between the contact region including the temperature detection means and the non-contact region is small, and temperature unevenness in the direction perpendicular to the conveying direction (longitudinal direction) can be suppressed.

FIG. 11 is a perspective view showing a configuration of a conventional nip member. 1 is a cross-sectional view of a fixing device according to an embodiment of the present invention; FIG. 3 is a perspective view of the fixing device shown in FIG. 2 . FIG. 3 is a side view of the fixing device shown in FIG. 2 . FIG. 2 is a perspective view (part 2) illustrating a configuration of a fixing device according to an embodiment of the present invention. FIG. 2 is a perspective view illustrating a configuration of a nip forming member according to an embodiment of the present invention. FIG. 13 is a plan view showing the depth of a slit formed in an extension portion. FIG. 13 is a perspective view showing a modified example in which the extension portion is bent. FIG. 11 is a plan view (part 1) illustrating the shape of the contact area of the extension portion. FIG. 11 is a plan view (part 2) illustrating the shape of the contact area of the extension portion. FIG. 2 is a plan view showing contact and non-contact areas. FIG. 13 is a diagram showing the heat capacities of a contact region and a non-contact region. 11A and 11B are diagrams illustrating a method for adjusting the area of a contact region. FIG. 2 is a diagram (part 2) showing a method for adjusting the area of the contact region. 1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention.

The fixing device according to one embodiment of the present invention will be described with reference to Figs. 2 to 4. Fig. 2 is a cross-sectional view of the fixing device according to one embodiment of the present invention, and Fig. 3 is a perspective view of the fixing device shown in Fig. 2. Fig. 4 is a side view of the fixing device shown in Fig. 2.

The fixing device 100 includes an endless fixing belt 110, which is a thin, flexible, cylindrical fixing member, and a pressure roller 150, which is a pressure member that contacts the outer periphery of the fixing belt 110.

Inside the fixing belt 110, there are arranged a halogen heater 120 as a fixing heat source, a nip forming member 130 that essentially forms a fixing nip portion N with the pressure roller 150 via the fixing belt 110, and a stay member 160 that supports the nip forming member 130. In addition, there is arranged a reflecting member 140 that collects radiant heat from the halogen heater 120 to the nip forming member 130.

The nip forming member 130, which is disposed across the width of the fixing belt 110, is fixedly supported by the stay member 160, preventing the nip forming member 130 from being deflected by the pressure from the pressure roller 150. Therefore, a uniform nip width is obtained across the axial direction (longitudinal direction) of the pressure roller 150 (see FIG. 3).

The fixing belt 110 is heated by radiant heat from the halogen heater 120, which serves as a fixing heat source, via the nip forming member 130. The halogen heater 120 is a representative radiant heat source serving as the fixing heat source, which is the main heat source.

The stay member 160 and the halogen heater 120 are fixed at both ends in the longitudinal direction to the side plate 180 of the fixing device 100 or to a separately provided flange 170.

(Nip forming member)
The nip forming member 130 is made of a material with high thermal conductivity that allows heat transfer in a short time, such as a metal such as copper (398 W/mk) or aluminum (236 W/mk). The surface facing the inner circumferential surface of the fixing belt 110 is the nip forming surface that directly contacts the fixing belt 110.

The nip forming surface of the nip forming member 130 may be anodized or coated with a fluororesin material to improve wear resistance and sliding properties. In addition, to ensure long-term sliding properties, a lubricant such as fluorine grease may be applied, or the surface may be configured to maintain the lubricant.

In Figures 2 to 4, the nip forming surface is flat, but it may be concave or have other shapes. For example, if the nip forming surface is concave, the leading edge of the paper is discharged toward the pressure roller, improving separation and preventing jams.

Furthermore, a separating member that separates the paper P from the fixing belt 110 may be provided downstream of the fixing device 100 in the paper transport direction. Furthermore, a pressure means (shown as pressure force F in FIG. 4) that can pressurize/release the pressure roller 150 against the fixing belt 110 may also be provided.

The nip forming member 130 has an extension 134 that extends uniformly along the short edge on the downstream side in the paper feed direction, and a thermistor 190 or safety device 200, which is a contact type temperature detection means, is provided in contact with the extension 134 (see FIG. 2). Based on the detection result of this thermistor 190, the output of the halogen heater 120 can be appropriately controlled so that the nip forming member 130 reaches the desired temperature. The safety device 200 is a device that cuts off the circuit of the heating source when a predetermined temperature (abnormally high temperature) is detected. Examples include a contact type thermostat and a temperature fuse.

(Fixing member)
In order to reduce heat capacity, the endless fixing belt 110 is thin and small in diameter like a film, and is composed of an inner peripheral base material made of a metal material such as nickel or SUS or a resin material such as polyimide, and an outer peripheral release layer made of PFA (tetrafluoroethylene-perfluoroalkylvinylether copolymer), PTFE (polytetrafluoroethylene), etc. An elastic layer made of a rubber material such as silicone rubber, foamed silicone rubber, or fluororubber may be interposed between the base material and the release layer.

If the thickness of this elastic layer is set to about 100 μm, the elastic deformation of the elastic layer when crushing and fixing the unfixed toner can absorb minute irregularities on the belt surface, preventing uneven gloss. From the viewpoint of low heat capacity, the fixing belt 110 is set to an overall thickness of 1 mm or less and a diameter of 20 to 40 mm. The thicknesses of the base material, elastic layer, and release layer that make up the fixing belt 110 are set to the ranges of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, respectively.

To further reduce the heat capacity, it is preferable that the overall thickness of the fixing belt 110 is 0.2 mm or less, and more preferably, 0.16 mm or less, and the diameter is preferably 30 mm or less.

(Pressure Member)
The pressure roller 150 is composed of a core metal, an elastic layer made of foamed silicone rubber, fluororubber, etc. provided on the surface of the core metal, and a release layer made of PFA, PTFE, etc. provided on the surface of the elastic layer. The pressure roller 150 is pressed against the fixing belt 110 by a pressure means such as a spring, and the elastic layer of the pressure roller 150 is crushed at the point where it comes into pressure contact with the fixing belt 110, thereby forming a fixing nip portion N of a predetermined width.

The pressure roller 150 is driven to rotate by a driving source such as a motor provided in the printer body. When the pressure roller 150 is driven to rotate, the driving force is transmitted to the fixing belt 110 at the fixing nip portion N, and the fixing belt 110 is rotated. The fixing belt 110 rotates while being sandwiched in the fixing nip portion N, and runs guided by flanges 170 arranged at both ends outside the fixing nip portion N.

In this embodiment, the pressure roller 150 is a solid roller, but it may be a hollow roller. In that case, a heat source such as a halogen heater may be disposed inside the pressure roller 150. The elastic layer may be solid rubber, but if there is no heat source inside the pressure roller 150, sponge rubber may be used. Sponge rubber is more preferable because it has better insulating properties and is less likely to lose heat from the fixing belt 110.

(Stay member)
The stay member 160 is a member that ensures the rigidity of the nip forming member 130 by supporting both ends in the paper feed direction of the nip forming member 130. The stay member 160 has a cross section that is roughly U-shaped and is disposed so as to cover the nip forming member 130 in the direction of the nip forming member 130, and sufficient rigidity can be ensured by using an iron-based metal such as SUS or SECC.

(Reflective member)
A reflecting member 140 is disposed between the stay member 160 and the halogen heater 120. This increases the heating efficiency of the halogen heater 120 for the nip forming member 130 and suppresses wasteful energy consumption caused by heating the stay member 160 by radiant heat from the halogen heater 120. Instead of providing the reflecting member 140, the same effect can be obtained by insulating or mirror-finishing the surface of the stay member 160 on the halogen heater 120 side.

(Fixing heat source)
The output control of the halogen heater 120 is performed based on the temperature detection result of the belt surface by, for example, a temperature sensor provided on the outer periphery on the upstream side in the belt rotation direction of the fixing belt 110. By controlling the output of the heater in this way, the temperature (fixing temperature) of the fixing belt 110 can be set to a desired temperature.

In this embodiment, the heating portion of the halogen heater 120 is a single heater. Alternatively, a heater having multiple heating portions may be used, for example, one of which has a heating portion in the center in the longitudinal direction corresponding to small size paper, and the other has heating portions at both ends in the longitudinal direction corresponding to large size paper.

The paper P (=transfer paper) fed from the paper feed mechanism has the toner image transferred to it by the transfer mechanism, and is then sent to the fixing nip N of the fixing device 100, where the toner image is fixed to the recording medium by applying heat and pressure.

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

Figure 5 is a perspective view (part 2) showing the configuration of a fixing device according to one embodiment of the present invention, and Figure 6 is a perspective view showing the configuration of a nip forming member according to one embodiment of the present invention.

The nip forming member 130 of this embodiment has a nip portion 132 that forms the fixing nip portion N, and an extension portion 134 provided at the short end of the nip portion 132 along the longitudinal direction of the nip portion 132. In this embodiment, the extension portion 134 extends uniformly along the longitudinal direction of the nip portion 132 on the downstream side in the paper passage direction. However, this is not limited to this, and the extension portion 134 may be provided on the upstream side in the paper passage direction depending on the design concept and layout of the fixing device configuration.

The extension 134 has at least one contact portion where a thermistor 190 or a safety device 200 is provided. In addition, the extension 134 is divided into a contact region 134a that includes the contact portion and a non-contact region 134b that does not include the contact portion by a plurality of slits 136 formed in the short direction.

Each slit 136 may have a depth d1 that reaches halfway along the short side of the extension 134, as shown in FIG. 7(a), or may have a depth d2 that reaches the nip portion 132 (end 132a) as shown in FIG. 7(b).

In this way, the nip forming member 130 of this embodiment has a discontinuous configuration between the contact area 134a and the remaining non-contact area 134b, thereby blocking the transfer of heat from the contact area 134a to the non-contact area 134b.

(Modification)
In such a configuration, the extension 134 of the nip forming member 130 may be folded at either the contact region 134a or the other non-contact region 134b, and the angle it forms with the plane of the nip portion 132 may be determined arbitrarily. In FIG. 8, the contact region 134a of the extension 134 is folded so that the plane of the contact region 134a and the plane of the nip portion 132 are parallel to each other.

The shape of the contact area 134a of the extension 134 is not limited to a rectangle or a square, and may be any shape, such as a semicircular shape, in accordance with the amount of heat stored in the contact area 134a, as shown in FIG. 9. Furthermore, the protrusion amount S1 of the contact area 134a may be set in accordance with the amount of heat stored in the contact area 134a, as shown in FIG. 10.

Another characteristic feature of the nip forming member 130 of this embodiment is that the area and thickness of the contact region 134a are adjusted to make the heat storage capacity of the contact region 134a lower than that of the non-contact region 134b.

Here, the heat storage capacity HS is defined as HS = V·c/L, where V (m ³ ) is the volume defined by the contact area 134a (or the non-contact area 134b), c (J/g·K) is the specific heat of the extension portion 134, and L (m) is the longitudinal length of the contact area 134a (or the non-contact area 134b).

As shown in FIG. 11, the contact area 134a (or the non-contact area 134b) is
(1) Both sides of the region are slits;
(1-1) When the base of the slit 136 is a corner, the area is defined by the slits 136 on both sides and a line connecting the bases of the slits 136 on both sides,
(1-2) When the root of the slit 136 is rounded, the slit 136 further includes an area that is separated by a tangent line between the rounded shapes (see the right part of FIG. 11 ); and
(2) When one end of the region is the first slit 136a and the other end is the end 134c of the extension portion 134, the slit adjacent to the first slit 136a is defined as the second slit 136b, and the region is defined by the extension line of the line connecting the roots of the first and second slits 136a, 136b, the end 134c of the extension portion, and the first slit 136a (see the left part of Figure 11).

By making the heat storage capacity of the contact area 134a lower than that of the non-contact area 134b, the difference between the heat capacity of the contact area 134a combined with the heat capacity of the thermistor 190 or safety device 200 and the heat capacity of the non-contact area 134b can be reduced. Therefore, the difference between the amount of heat transferred from the nip portion 132 to the contact area 134a and the amount of heat transferred from the nip portion 132 to the non-contact area 134b can be reduced, and temperature unevenness in the longitudinal direction of the nip portion 132 can be suppressed. In addition, the thermistor 190 can accurately detect the temperature of the nip forming member 130.

As an advantageous configuration, it is desirable that the heat storage capacity of the contact area 134a and the thermistor 190 or safety device 200 provided in contact with the contact portion of the contact area 134a be approximately equal to the heat storage capacity of the non-contact area 134b (within a difference of ±15%).

By doing this, it is possible to further suppress temperature unevenness in the longitudinal direction of the nip portion 132. In addition, the difference in heat storage capacity between the contact area 134a and the non-contact area 134b is the amount of heat transferred to the thermistor 190 or the safety device 200.

Figure 12 is a diagram showing the heat capacity of each of the contact area and the non-contact area. As shown in Figure 12 (a), a thermistor 190 is provided in the first contact area 134a', and a safety device 200 is provided in the second contact area 134a''. Here, the heat capacity C1 of the safety device 200 is larger than the heat capacity C2 of the thermistor 190 (C1 > C2).

Figure 12(b) is a bar graph showing the heat capacity per unit area in each of regions (1) to (5). In this embodiment, the area of the contact region 134a is adjusted so that the sum of the heat capacities in each of regions (1) to (5) is approximately equal.

For example, as shown in the bar graph of region (2), the heat capacity of the first contact region 134a' is reduced by the amount of the thermistor 190. Also, as shown in the bar graph of region (3), the heat capacity of the second contact region 134a'' is reduced even more than the heat capacity of the first contact region 134a'.

By adjusting in this way, the sum of the heat capacities of the regions (1) to (5) can be made approximately equal, and therefore the heat capacity can be made approximately equal along the length of the extension portion 134.

Figure 13 is a diagram showing a method for adjusting the area of the contact region. The heat capacity of each of the areas of the first contact region 134a' and the second contact region 134a'' can be adjusted by adjusting the short-side length as shown in Figure 13(a) or the long-side length as shown in Figure 13(b).

Figure 14 is a diagram (part 2) showing a method for adjusting the area of the contact region. Figure 14(a) shows the extension portion (contact region and non-contact region) in a plan view, and Figure 14(b) is a cross-sectional view taken along line A-A' in (a).

As shown in FIG. 14B, by adjusting the thickness _t2 of the first contact region 134a' and the thickness _t3 of the second contact region 134a'', respectively, the sums of the heat capacities of the first contact region 134a' and the second contact region 134a'' can be made substantially equal to each other.

By adjusting it in this way, the heat capacity can be made approximately equal along the length of the extension portion 134.

Next, we will explain an image forming apparatus equipped with the fixing device of the present invention.

Figure 15 is a schematic diagram showing an image forming apparatus according to one embodiment of the present invention. As shown in Figure 15, an image forming unit 40 is provided almost above a paper transport unit 30, and an image reading unit 50 is provided further above that. The paper transport unit 30 includes, as a paper feed unit, a paper feed tray 20 on which paper P is loaded, a pickup roller 2a that feeds paper P on the paper feed tray 20, and a pair of rollers (feed roller 2b and reverse roller 2c) that separate the paper P. The paper transport unit 30 also includes transport rollers 3a, 3b, and registration rollers 4a, 4b. In this way, the paper transport unit 30 is configured to transport paper P sent out from the paper feed tray 20 toward the image forming unit 40.

The image forming unit 40 includes a photoconductor (transfer roller) 14, a charging means 5 arranged around the photoconductor (transfer roller) 14, a developing means 6, a transfer means 7, a cleaning means 8, and a conveyor belt 9 for conveying the paper P after the image has been transferred. The image forming unit 40 also includes a fixing device 100 for fixing the paper P on which the image has been formed, and a writing means 11 for partially exposing the uniformly charged photoconductor (transfer roller) 14 to light to form a latent image.

Next, the process of forming an image on paper P will be explained. When the paper feed signal is turned on, the pickup roller 2a rotates downward and feeds out paper P from the paper feed tray 20. The fed paper P is separated one by one at the nip between the feed roller 2b and the reverse roller 2c and reaches the transport rollers 3a and 3b, and is further transported and abuts against the nip between the registration rollers 4a and 4b for skew correction. It is then sent out at the appropriate time to meet up with the toner image on the drum-shaped photoconductor (transfer roller) 14.

Next, the image forming unit 40 forms an image on the paper P supplied from the paper transport unit 30, and the fixing device 100 fixes the image onto the paper P. After fixing, the paper P is discharged via the paper discharge rollers 16 to the paper discharge tray 13.

(Demonstration experiment)
The present inventors conducted a demonstration experiment to evaluate the image quality (fixability, gloss unevenness, etc.) of the image forming apparatus according to the embodiment described above. Specifically, a plurality of nip forming members 130 with different heat storage properties of the contact area 134a were prepared, and images were actually formed (printed) using each nip forming member 130. Then, the paper P on which the image was formed was visually inspected to examine the effect of the temperature difference ΔT between the contact area 134a and the non-contact area 134b on the image quality.

Here, the temperature difference ΔT was calculated as ΔT = T1 - T2 from the temperature (T1) at the longitudinal center position of the contact area 134a near the end of the nip portion 132 while the paper is passing, and the temperature (T2) at the longitudinal center position of the non-contact area 134b. Note that the temperatures (T1, T2) were each measured with a non-contact temperature sensor.

As a result, it was found that if the temperature difference ΔT (= T1 - T2) is 5°C or less, good fixing properties and good image quality without uneven gloss can be obtained. This demonstrated the effectiveness of the present invention.

The present invention has been described in detail above using an embodiment. This embodiment is merely an example, and can be modified in various ways without departing from the spirit of the invention. In addition, any configuration can be adopted as the image forming device as long as the present invention is applicable. The image forming device is not limited to a copier or printer, but may also be a facsimile or a multifunction device with multiple functions.

2a Pick-up roller 2b Feed roller 2c Reverse roller 3a, 3b Conveying roller 4a, 4b Registration roller 5 Charging means 6 Developing means 7 Transfer means 8 Cleaning means 9 Conveying belt 10 Nip member 11 Writing means 12 Nip portion 13 Paper discharge tray 14 Detected portion 16 Paper discharge roller 20 Paper feed tray 30 Paper conveying section 40 Image forming section 50 Image reading section 100 Fixing device 110 Fixing belt 120 Halogen heater 130 Nip forming member 132 Nip portion 134 Extension portion 134a Contact area 134b Non-contact area 136 Slit 140 Reflecting member 150 Pressure roller 160 Stay member 170 Flange 180 Side plate 190 Thermistor 200 Safety device F Pressure N Fixing nip P Paper

JP 2016-071333 A JP 2016-164590 A JP 2008-292551 A JP 2015-75562 A

Claims (10)

A nip forming member that forms a fixing nip portion of a fixing device,
The nip forming member has at least one contact type temperature detecting means for detecting the temperature of the nip forming member,
the nip forming member has a nip portion that forms the fixing nip portion, and an extension portion that is provided at an end portion in a short side direction of the nip portion along a long side direction of the nip portion,
the extension portion has at least one contact portion with which the temperature detection means comes into contact;
A nip forming member characterized in that the extension portion is divided into a contact area including the contact portion and a non-contact area that does not contact the temperature detection means by a slit formed in the transport direction of the recording medium. The nip forming member according to claim 1, characterized in that the longitudinal length of the contact area is shorter than the longitudinal length of the non-contact area. The nip forming member according to claim 1 or 2, characterized in that either the contact area or the non-contact area is bent relative to the nip portion to provide an angle. The heat storage HS of the contact area or the non-contact area is
Let V be the volume defined by the contact area or the non-contact area.
The specific heat of the extension portion is c;
The longitudinal length of the contact area or the non-contact area is L,
4. The nip forming member according to claim 1, which is determined by the formula HS=V·c/L. The nip forming member according to any one of claims 1 to 4, characterized in that the heat storage capacity of the contact area and the temperature detection means provided in contact with the contact portion of the contact area is substantially equal to the heat storage capacity of the non-contact area. The contact area or the non-contact area is
(1) Both sides of the region are the slits,
(1-1) When the root of the slit is a corner, the area is defined by the slit on both sides and a line connecting the roots of the slit on both sides,
(1-2) When the root of the slit is rounded, the slit further includes a region that is bounded by a tangent to the rounded shape; and
(2) A nip forming member as described in any one of claims 1 to 5, characterized in that when one end of the area is a first slit and the other side is the end of the extended portion, the slit adjacent to the first slit is a second slit, and the area is bounded by an extension line of a line connecting the roots of the first and second slits, the end of the extended portion, and the first slit. The nip forming member according to any one of claims 1 to 6, characterized in that the nip portion and the extension portion are formed of metal. A cylindrical fixing member;
a pressure member disposed opposite to the outer circumferential side of the fixing member;
a fixing heat source that is disposed on the inner peripheral side of the fixing member and heats by radiation;
A fixing device comprising: the nip forming member according to claim 1 , the nip forming member being disposed on an inner circumferential side of the fixing member. An image forming apparatus equipped with the fixing device according to claim 8. During image formation,
The temperature of the longitudinal center position of the contact area near the end of the nip portion during paper passing is defined as T1, and the temperature of the longitudinal center position of the non-contact area near the end of the nip portion during paper passing is defined as T2.
10. The image forming apparatus according to claim 9, wherein the temperature difference ΔT (=T1-T2) is 5° C. or less.

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