JP7322253B2 - heater and fuser - Google Patents

Description

The present invention relates to a fixing device mounted in an image forming apparatus such as an electrophotographic recording type copier or printer, and a heater mounted in the fixing device.

2. Description of the Related Art As a fixing device installed in an electrophotographic image forming apparatus, a device using a film is known. This fixing device has a tubular film and a heater that contacts the inner surface of the film. Since a fixing device using a film has a low heat capacity, it has advantages such as short warm-up time and low power consumption.

The heater has a substrate made of a material such as ceramic, and a heating resistor (heating element) provided on the substrate. The temperature of the heater is detected by a temperature detection element such as a thermistor, and the controller controls power supply to the heating resistor according to the output of the temperature detection element.

As a configuration of the temperature detection element, there is a configuration in which the temperature detection element provided independently of the heater is pressed against the heater via an insulating sheet. In addition, there is also a heater-integrated configuration in which a temperature detection element and a conductive line electrically connected to the temperature detection element are provided on a substrate of the heater by a coating method such as screen printing. In the heater-integrated type, the temperature detecting element, the conductive line, and the heating element are protected by a glass film for insulation. The heater-integrated type has the advantage that the temperature detection element is printed on the substrate, so there is little variation in responsiveness and the temperature detection accuracy is high.

Furthermore, in order to accurately detect the temperature of the fixing nip portion, there is also a proposal to provide a temperature detection element on the side of the film sliding surface of the heater (Patent Document 1). Also, in order to reduce the size of the heater, it is conceivable to provide the heating resistor on the surface of the substrate opposite to the surface on which the temperature detection element is provided.

JP-A-10-240357

However, in the heater configuration described above, the thickness from the surface of the substrate at the portion where the temperature detection element and the conductive line are provided is greater than the other portions, and there is a possibility that the surface of the heater becomes uneven. According to the studies of the present inventors, it has been found that when the conductive lines on the heater substrate are formed parallel to the conveying direction of the recording material, poor fixing and gloss streaks may occur. The reason for this is that the heat and pressure applied to the toner image are uneven due to the steps on the surface of the heater caused by the conductive lines.

SUMMARY OF THE INVENTION An object of the present invention is to provide a heater and a fixing device capable of suppressing image defects such as poor fixing and gloss streaks.

The present invention for solving the above-described problems is a heater used in a fixing device for fixing an image formed on a recording material to the recording material, comprising: a substrate; a heating element provided on the substrate; A first temperature detection element provided on the surface of the substrate opposite to the surface on which the heating element is provided, and a first temperature detection element provided on the same surface of the substrate on which the first temperature detection element is provided. two conductive lines electrically connected to the first temperature sensing element and on the same surface of the substrate on which the first temperature sensing element is located; a second temperature detection element provided at a position closer to one end of the substrate in the longitudinal direction of the substrate than the position at which the first temperature detection element is provided; and the first temperature detection element of the substrate. two conductive lines electrically connected to the second temperature sensing element, the first temperature sensing element, and the first temperature sensing element. the two conductive lines electrically connected to the sensing element; the second temperature sensing element; and the two conductive lines electrically connected to the second temperature sensing element. and a protective layer covering the heater, wherein, of the two conductive lines electrically connected to the first temperature sensing element, the first conductive line extends from the first temperature sensing element to the substrate. Of the two conductive lines extending toward the one end of the substrate in the longitudinal direction of the substrate and electrically connected to the first temperature sensing element, the second conductive line is the first in the protective layer of the first conductive line extending from the temperature sensing element of toward the other end of the substrate in the longitudinal direction of the substrate and electrically connected to the first temperature sensing element The covered portion includes the first conductive line electrically connected to the first temperature sensing element and the two conductive lines electrically connected to the second temperature sensing element. It extends from a first position where the first temperature sensing element is arranged in the lateral direction of the substrate to a second position different from the first position in the lateral direction so as not to overlap the line. There is an area, and the area extending from the first position to the second position covered with the protective layer has an area inclined with respect to both the longitudinal direction and the lateral direction of the substrate. is characterized in that there is no region parallel to the lateral direction .

According to the present invention, it is possible to provide a heater and a fixing device capable of suppressing image defects such as poor fixing and gloss streaks.

Cross-sectional view of an image forming apparatus Cross-sectional view of the fixing device Configuration diagram of heater according to embodiment 1 Configuration diagram of a heater according to a comparative example A diagram showing the locations of image defects The configuration diagram of the heater of Modification 1 of Embodiment 1 The configuration diagram of the heater of Modification 2 of Embodiment 1 The configuration diagram of the heater of Modification 3 of Embodiment 1 Configuration diagram of a heater according to Example 2 The block diagram of the heater of another example based on Example 2. Enlarged view near the conductive line of the heater of Example 2 FIG. 10 is a configuration diagram of a sliding surface of a heater of a modified example of the second embodiment; The block diagram of the back surface of the heater of the modification of Example 2.

[Example 1]
FIG. 1 is a sectional view of an electrophotographic recording type image forming apparatus. A photosensitive drum 1 is rotationally driven in the direction of the arrow, and its surface is uniformly charged by a charging roller 2 . Next, the charged surface of the photosensitive drum 1 is scanned by a laser scanner 3 with a laser beam L according to image information. Thereby, an electrostatic latent image is formed on the surface of the photosensitive drum 1 . The electrostatic latent image is developed with toner supplied from the developing device 4 . The toner image formed on the photosensitive drum 1 is transferred onto the recording material P fed from the paper feeding cassette 6 at the transfer nip portion where the transfer roller 5 and the photosensitive drum 1 are pressed against each other. The recording material P to which the toner image has been transferred is conveyed to the fixing device 7 , and the toner image is heat-fixed on the recording material in the fixing device 7 . After that, the recording material P is discharged onto a paper discharge tray. Toner remaining on the photosensitive drum 1 after transfer is collected by a cleaning device 8 .

(Structure of Fixing Device 7)
Next, the fixing device 7 will be described with reference to FIG. FIG. 2 is a sectional view of the fixing device. The fixing device 7 has a film unit 10 and a pressure roller 20, and a fixing nip portion N for nipping and conveying the recording material P is formed between them. The film unit 10 has a tubular film 11 and a heater 12 provided on the inner surface of the film 11 . The fixing device 7 further includes a heater holder 13 that holds the heater 12 and a metallic stay 14 that is biased by a pressure spring (not shown) to press the heater holder 13 against the pressure roller 20 .

The film 11 has a base layer and a release layer formed on the outside of the base layer. The base layer is made of heat-resistant resin such as polyimide, polyamide-imide, or PEEK, or metal such as SUS (stainless steel). The release layer is a mixture or single layer of fluororesins such as PTFE, PFA, and FEP, and heat-resistant resins having good release properties such as silicone resins. Further, an intermediate layer made of heat-resistant rubber such as silicone rubber may be provided between the base layer and the release layer. The film 11 of this embodiment has a 30 μm thick SUS base layer, a 200 μm thick silicone rubber layer (elastic layer), and a 20 μm thick release layer made of PFA. The outer diameter of the film 11 was 24 mm, and the length in the longitudinal direction (the width direction of the recording material P) was 240 mm.

The heater holder 13 holds the heater 12 and also has a guide function of guiding the rotation of the film 11 . The heater holder 13 is made of heat-resistant resin such as liquid crystal polymer.

The metal stay 14 is a component that reinforces the heater holder 13 . A highly rigid metal such as SUS is used for the metal stay 14 in order to withstand the load when the heater holder 13 is pressed against the pressure roller 20 .

The pressure roller 20 has a core metal 21 and an elastic layer 22 formed outside the core metal. A release layer such as PFA or PTFE may be provided outside the elastic layer 22 . The pressure roller 20 rotates in the direction of the arrow when the core bar 21 receives power from a motor (not shown). As the pressure roller 20 rotates, the film 11 also rotates. The pressure roller 20 of this embodiment has an elastic layer 22 made of silicone rubber with a thickness of 3.5 mm and a release layer made of PFA with a thickness of 70 μm. The pressure roller 20 has an outer diameter of 25 mm and a longitudinal length of 230 mm.

The fixing device 7 fixes the image formed on the recording material P with heat from the heater 12 via the rotating film 11 .

(Structure of heater 12)
Next, the configuration of the heater 12 of this embodiment will be described with reference to FIG. The heater 12 has a substrate 30 and a heating element 31 provided on the substrate 30 . The heater 12 further includes a temperature detection element 33 provided on the surface of the substrate 30 opposite to the surface on which the heating element 31 is provided, and a surface of the substrate 30 opposite to the surface on which the heating element 31 is provided. and a conductive line 34 provided in and electrically connected to the temperature sensing element 33 .

FIG. 3( a ) is a diagram showing the back side of the heater 12 , that is, the surface of the heater 12 opposite to the sliding surface with the film 11 . A heating resistor (heating element) 31 and electrodes 32 are formed on an alumina substrate 30 by screen printing, and the heating resistor 31 is covered with a rear protective layer 35 (made of glass). A connector (not shown) is connected to the electrode 32, and the heating resistor 31 generates heat by electric power supplied from the power supply. The material of the substrate 30 may be a ceramic material such as aluminum nitride, or a metal whose surface is covered with an insulating layer.

FIG. 3(b) is a diagram showing the sliding surface side of the heater 12. As shown in FIG. A thermistor 33 as a temperature detecting element and a conductive line 34 are formed on the sliding surface side of the heater 12 by screen printing. The temperature detected by the thermistor 33 can be known by connecting the conductive line 34 to the control circuit 9 in the image forming apparatus via a connector (not shown). This embodiment is characterized in that the conductive line 34 has a region 34a that is inclined with respect to both the longitudinal direction D1 and the lateral direction D2 of the substrate 30. FIG. Although the details will be described later, by forming the conductive lines 34 in an oblique direction, it is possible to suppress the occurrence of image defects. A line X indicates the center of the heater 12 in the lateral direction D3.

The thermistor 33 and the conductive line 34 are also covered with a sliding surface side protective layer 36 (made of glass). Since the protective layer 36 on the sliding surface side also plays a role of protecting the thermistor 33 and the conductive line 34 from abrasion due to rubbing against the film 11, a glass material having better wear resistance than the protective layer on the back surface side is used. Using. The material of the heating resistor 31 is Ag/Pd, and the material of the electrode 32 and the conductive line 34 is Ag. The heater 12 of this example has three thermistors 33, one in the center in the longitudinal direction D1 and one at each end, but the number of thermistors may be one or more.

(Effect of this embodiment)
A comparative example to be compared with this embodiment will be described. FIG. 4 is a diagram showing the sliding surface side of the heater 120 of the comparative example. Since the conductive line 34 has a region 34b parallel to the lateral direction D2, a local step occurs in a part of the surface of the heater 120 (the surface of the protective layer 36) in the longitudinal direction D1. The step in the comparative example (the step in the thickness direction of the heater 120) was 20 μm. The back side of the heater of the comparative example is the same as that of the first example shown in FIG. 3(a).

The effects of this example were verified under the following conditions. First, as the recording material P, plain paper and glossy paper were prepared. "HP Laser Jet 90g" was used as plain paper, and "HP Brochure Paper 200g" was used as glossy paper. An unfixed toner image was formed on each of plain paper and glossy paper. Then, these recording materials P were fixed by the fixing device 7 equipped with the heater 12 of this embodiment. Similarly, these recording materials P were fixed by a fixing device equipped with a heater of Comparative Example 120. FIG. A toner image after being fixed by the fixing device of this example and a toner image after being fixed by the fixing device of the comparative example were compared. The transport speed was set to 300 mm/sec when fixing plain paper, and was set to 75 mm/sec when fixing glossy paper. Both the control target temperature of the heater 12 and the control target temperature of the heater 120 were set to 160°C.

Table 1 shows the results. When the heater 120 of the comparative example was used, image defects occurred on both plain paper and glossy paper. In the comparative example, as shown in FIG. 5, at the position where the region 34b (see FIG. 4) parallel to the width direction exists, there is an adverse effect of insufficient fixation of the toner image T, or a gloss streak due to a decrease in glossiness. Td occurred.

As described above, by using the heater of this embodiment, it is possible to suppress the occurrence of image defects. The reason is explained below.

First, the reason why the image defect occurs in the comparative example is that the stepped portion of the heater sliding surface (surface of the protective layer) caused by the conductive line 34 locally generates an area where the heat and pressure applied to the toner image are insufficient. Because it does. By forming the conductive lines 34 obliquely as in the present embodiment, the steps on the sliding surface side are not concentrated in a part of the longitudinal direction, and heat and pressure are not generated in localized regions as in the comparative example. shortage does not occur. As a result, the fixability of the toner becomes substantially uniform over the entire length, and image defects do not occur.

Also, in order to show the effective range of this embodiment, an experiment was conducted by changing the arrangement of the conductive lines 34 . As shown in FIG. 3B, an angle A is an angle formed by a conductive line formed obliquely with respect to a parallel line drawn parallel to the longitudinal direction of the heater at a position X at the center of the substrate 30 in the lateral direction. A was changed and the images after fixing were compared. In the "configuration of this embodiment" in Table 1 above, the angle A was set to 45°.

As shown in Table 2, no image defects occurred at angles A=45° and A=60°. When the angle A was increased to 75°, the configuration of the heater 120 approached that of the comparative example, so a slight image defect occurred although it was slighter than that of the comparative example.

From the results of this example, it was found that image defects are less likely to occur if the conductive lines 34 are formed so that the angle A is 60° or less. However, the condition of angle A=60° is affected by the type of film, the thickness of the conductive line, the type of recording material, and the conveying speed, and is not a unique condition. However, if the angle A is made smaller than 90°, it becomes difficult for the steps on the sliding surface side to be concentrated in a part of the longitudinal direction, as described above. Therefore, providing the conductive line with an area inclined with respect to both the longitudinal direction and the lateral direction of the substrate without providing an area parallel to the lateral direction has the effect of suppressing the occurrence of image defects.

(Modification 1)
As a modification 1 of this embodiment, a heater as shown in FIG. 6 may be used. In FIG. 6, there is also a region in which the conductive lines 34 are formed parallel to the lateral direction, but if the length of this region is short, image defects are less likely to occur. In this example, if the length of the region parallel to the lateral direction was 1.5 mm or less, no image defect occurred. As with the condition of the angle A, this condition is not unambiguously determined, but the shorter the length of the conductive line 34 formed in the lateral direction, the better.

(Modification 2)
Modification 2 of this embodiment will be described. As shown in FIG. 7, the conductive line of the heater of Modification 2 has a region parallel to the longitudinal direction of the substrate and a region parallel to the lateral direction of the substrate. Regions parallel to the direction are alternately connected to form a staircase shape. In this modified example as well, if the length of the region formed in the lateral direction is short (1.5 mm or less in this embodiment), image defects are less likely to occur.

(Modification 3)
As shown in FIG. 8, the shape of the thermistor 33 as a temperature detecting element may be a shape that is not parallel to either the longitudinal direction or the lateral direction. If the thermistor 33 has a region parallel to the width direction, there is a possibility that an image defect will occur as in the case where the conductive line 34 extends parallel to the width direction. This modification can be said to be a more preferable example because it is possible to avoid concentration of steps in a part of the longitudinal direction, including the thermistor 33, and to suppress image defects.

(Example 2)
Next, Example 2 of the present invention will be described. A feature of the present embodiment is that the steps themselves caused by the conductive lines are reduced, and image defects are suppressed.

The basic configuration and operation of the fixing device 7 are the same as those of the first and second embodiments. Only the shape of the sliding surface side of the heater 12 mounted on the fixing device 7 is different between the two.

(Structure of heater)
The configuration of the heater of this embodiment will be described with reference to FIG. FIG. 9A shows the back side of the substrate 30, which has the same shape as in the first embodiment. FIG. 9(b) shows the sliding surface side, and the thermistor 33 and the conductive line 34 are formed in the same manner as in FIG. However, in this embodiment, a convex portion 37 electrically insulated from the conductive line is provided on the surface of the substrate on which the conductive line is provided. The material of the convex portion 37 in this example is Ag. The thermistor 33, the conductive line 34, and the projection are covered with a protective layer 36 (made of glass).

The convex portion 37 reduces the step that occurs in the comparative example of the first embodiment. In this embodiment, the convex portion is formed at a position where the step is 10 μm or less, the reason for which will be described later.

(Effect of this embodiment)
The effects of this embodiment will be shown. The experiment was conducted under the same conditions as in Example 1, and only the heater mounted in the fixing device of this example was used for comparison with the comparative example. In order to show the effective range of this example, the distance D between the conductive line and the convex portion was changed, and the image after fixing was evaluated. As shown in the enlarged view of the heater sliding surface side in FIG. 11, a step of 20 μm is generated in the comparative example. A step of 10 μm was generated when the distance D between the surface and the convex portion was 0.50 mm.

Table 3 shows the results. The results of the comparative example are the same as those of the first example. When the level difference was reduced to 15 μm, fixing failure did not occur on plain paper, but slight glossy streaks occurred. On the other hand, if the steps could be reduced to 10 μm, no image defects occurred. This is because if the step is 10 μm or less, the area that is difficult to receive heat and pressure is reduced, and sufficient fixability can be obtained.

From the above results, it is possible to suppress image defects by forming the convex portions so that the step on the surface of the protective layer can be reduced to 10 μm or less. That is, the step between the protective layer on the conductive line, the protective layer on the protrusion, and the protective layer positioned between the conductive line and the protrusion is set to 10 μm or less. Thus, image defects can be suppressed. Since the conductive line 34 or the convex portion 37 exists over a wide area on the heater, the present embodiment has the advantage that the thermal resistance approaches uniformity, and is preferable to the first embodiment.

Moreover, although the same material (Ag) is used for the conductive line 34 and the projection 37 in this embodiment, different materials may be used. However, when the same material is used, the heat resistance of the conductive line portion and the convex member portion becomes uniform as described above, so that it is easier to suppress the occurrence of image defects.

In FIG. 9B, the convex portion 37 is formed parallel to the longitudinal direction of the heater. By reducing , the same effect as the above embodiment can be obtained.

(Modification)
As a modification of this embodiment, as shown in FIG. 12, a conductive line 34 may be formed obliquely on a substrate 30 and a convex portion 37 may be formed insulated from the conductive line 34 . This is a more preferable example because the conductive line 34 in the oblique direction can avoid a situation in which the step is concentrated in a part of the longitudinal direction as in the first embodiment, and the step itself can be reduced by the projecting member 37 . Further, the protrusions 37 may be formed on the heater having the conductive line shape shown in the modified example of the first embodiment.

It should be noted that the shape of the heating resistor 31 is not limited to that used in the present embodiment and modified examples. For example, as shown in FIG. 13, a plurality of heating resistors 31 may be provided in the longitudinal direction, and the temperature of each may be controlled independently. The heating resistor 31 shown in FIG. 13 is divided into five regions, each of which can be independently controlled. In the case of independent temperature control, a thermistor is required for each region, and a large number of conductive lines connecting the thermistors are also required, so that the effect of the present invention can be further obtained.

11 Film 12 Heater 30 Substrate 31 Heating Resistor 33 Thermistor 34 Conductive Line 37 Projection

Claims (4)

A heater used in a fixing device that fixes an image formed on a recording material to the recording material,
a substrate;
a heating element provided on the substrate;
a first temperature sensing element provided on the surface of the substrate opposite to the surface on which the heating element is provided;
two conductive lines on the same side of the substrate as the first temperature sensing element and electrically connected to the first temperature sensing element;
provided on the same surface of the substrate as the surface on which the first temperature detection element is provided, and at one end of the substrate in the longitudinal direction of the substrate from the position on which the first temperature detection element is provided. a second temperature sensing element provided at a close position;
two conductive lines on the same side of the substrate as the first temperature sensing element and electrically connected to the second temperature sensing element;
The first temperature sensing element, the two conductive lines electrically connected to the first temperature sensing element, the second temperature sensing element, the second temperature sensing element and an electrical a protective layer overlying the two electrically connected conductive lines;
In a heater having
Of the two conductive lines electrically connected to the first temperature sensing element, the first conductive line is located at the one end of the substrate in the longitudinal direction of the substrate from the first temperature sensing element. extends towards
Of the two conductive lines electrically connected to the first temperature sensing element, the second conductive line extends from the first temperature sensing element to the other end of the substrate in the longitudinal direction of the substrate. extends towards
The portion of the first conductive line electrically connected to the first temperature sensing element covered with the protective layer includes the first temperature sensing element electrically connected to the first temperature sensing element. The first temperature sensing element is arranged in the lateral direction of the substrate such that one conductive line does not overlap the two conductive lines electrically connected to the second temperature sensing element. There is a region extending from the first position in the lateral direction to a second position different from the first position in the lateral direction,
The region covered with the protective layer and extending from the first position to the second position includes a region inclined with respect to both the longitudinal direction and the lateral direction of the substrate. A heater characterized in that there are no areas parallel to the direction . 2. The heater according to claim 1 , wherein said heater has a plurality of independently controllable heating elements along the longitudinal direction of said substrate. a tubular film;
a heater in contact with the inner surface of the film;
and fixing an image formed on a recording material to the recording material by heat from the heater through the rotating film,
The heater is the heater according to claim 1 or 2,
A fixing device, wherein the surface of the heater on which the first temperature detection element is provided is arranged so as to be in contact with the inner surface of the film. 4. The fixing device according to claim 3, further comprising a pressure roller forming a fixing nip for nipping and conveying the recording material together with the heater via the film.

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