JP2000019879A - Heating roller for fixing, fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve physical property such as the heat conductivity and the wear resistance of a mold-released layer and to restrain the backward scattering phenomenon of toner by providing the mold-released layer consisting of plural layers formed of the mixed material of the fluorinated resin and filler on the outer peripheral surface of a nearly cylindrical core bar. SOLUTION: A heating roller for fixing 56 has constitution where the mold- released layer 70 having about 50 μm film thickness is formed to enhance releasing property from paper on the surface of the cylindrical iron core bar 57 having about 3 mm thickness. The layer 70 is formed of 1st and 2nd fluorinated resin layers 72 and 74 having the same film thickness (25 μm) including granular silicon carbide (SiC) 80 whose average particle size is 5 μm by about 9 wt.% as the filler. In such a case, resistance is generated on a boundary between two layers 72 and 74, so that a resistance value is made higher all the more. Therefore, insulating property is enhanced, charge having a reverse polarity to the toner transferred to paper is restrained from moving to the core bar 57, and the backward scattering phenomenon of the toner is restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a heat fixing roller,
Regarding a fixing device and an image forming apparatus, particularly, an electrostatic copying machine,
The present invention relates to a heat fixing roller, a fixing device, and an image forming apparatus using an electrostatic transfer process, such as an electrostatic copying printer.

[0002]

2. Description of the Related Art Printers using an electrophotographic process,
In a copier or the like, as a fixing method of fixing an unfixed toner image formed on a recording medium such as a recording sheet and forming a permanent image, a pressure fixing method, a flash fixing method, a pressure heating fixing method, and the like have been proposed. I have.

[0003] The pressure fixing method and the flash fixing method are superior in terms of quick printing and energy saving as compared with the pressure heating fixing method. There are problems such as the toner image being disturbed and the recording medium being deformed. For this reason, the pressure heating fixing method is generally widely used.

This pressure-heating fixing device has a nip portion composed of a heat-fixing roller having a heat source such as a heater and a pressure roller arranged to face the heat-fixing roller. The unfixed toner image on the recording medium is melted and the unfixed fused toner is fixed on the recording medium by nipping and heating and pressing the recording medium passing between the two rollers by the two rollers.

In general, a release layer for improving the releasability of a recording medium is provided on the surface of the heat fixing roller. Conventionally, a release layer on the surface of the heat fixing roller has been used as a release layer.
Fluororesin coated by electrostatic painting,
There have been proposed ones coated with a fluororesin tube and those coated simultaneously with a mixed material of a fluororesin and a filler.

[0006]

However, when a fluororesin coated by electrostatic coating or a fluororesin tube coated is used as the release layer, the fluororesin has thermal conductivity and abrasion resistance. Therefore, there is a disadvantage that the set temperature must be increased in order to secure the fixing performance. Further, since the wear resistance of the release layer is low, the life of the heat fixing roller is short, and therefore, there is a disadvantage that the heat fixing roller must be replaced frequently.

When the release layer is formed by simultaneously coating a mixed material of a fluororesin and a filler, the release layer may be formed by coating the fluororesin by electrostatic coating or by coating a fluororesin tube. than,
Although it is possible to lower the set temperature and improve the wear resistance to extend the life, there is another problem described below due to the inclusion of the filler.

That is, as a substance used as a filler, for example, Japanese Unexamined Patent Publication (Kokai) No. 60-122977, Japanese Patent Publication No. 4-52955, etc. disclose silicon carbide (SiC),
Japanese Patent Application Laid-Open No. 9-237007 discloses graphite powder, and other fillers include whisker-like single crystal fibers and carbon black. Since these fillers have lower releasability than fluororesin, the release layer containing these fillers is inferior to the release layer containing no filler.

In addition, since the unfixed toner easily adheres to the filler, the unfixed toner adheres to the filler exposed on the surface of the release layer one after another. As a result, the filler exposed on the surface is removed. As a nucleus, there is also a problem that the unfixed toner grows greatly and causes image quality defects such as offset and toner smear on the print surface.

By the way, in addition to the above-mentioned problem, the "toner scattering phenomenon" in which the unfixed toner on the recording medium is blown off in the vicinity immediately before the nip has also been a problem. This phenomenon of toner scattering behind is particularly noticeable in a high-humidity environment, and its cause and its estimation mechanism will be briefly described below.

It is considered that factors behind the phenomenon of the toner scattering behind mainly include an electrical factor and a thermal change factor of air near the nip portion.

As the former electrical elements, the surface of the release layer is charged to the same polarity as the toner and the toner is electrostatically blown off. The charge of the opposite polarity to the toner applied to the recording medium moves to the core of the heat fixing roller, and as a result, the electrostatic attraction of the toner is weakened, and the unfixed toner adhering to the recording medium is removed. The air turbulence generated in the vicinity immediately before the nip portion is likely to be scattered due to local turbulence.

The reason why the resistance of the release layer is low is that when a fluorine resin is coated to a thickness of 50 μm or less, a pinhole is formed in the release layer, and the presence of the pinhole causes the release layer to have a small thickness. Is lower than the inherently high resistance value (10 ¹² Ω or more) of the fluororesin.

When a heat-fixing roller is used as a release layer by covering a tube of fluororesin, since the pinhole does not exist, the insulation of the release layer is high, so that the transfer charge leaks. However, it is possible to reduce the scattering of toner behind, but the problem when using only the above-described fluororesin as the release layer, that is, the set temperature must be increased to secure the fixing performance, and However, it is not possible to eliminate disadvantages such as the need to frequently replace the heat fixing roller due to the short length. The same applies to the case where the influence of pinholes is prevented by coating the fluororesin thickly and the electric resistance value is increased.

In order to reduce the toner scattering phenomenon based on electrical elements, an electrode for applying a bias by contacting a part of the recording medium is provided near the nip portion. It is configured to flow to the ground through the heat fixing roller, and the generated electric field enhances the holding force of the toner on the recording medium,
It is disclosed in Japanese Patent Application Laid-Open No. 8-272245.

However, when the resistance value of the heat-fixing roller is low, as in the case where the fluororesin is coated by electrostatic coating, a large amount of current flows and a large-capacity transformer is required, so that the cost of the power supply is greatly reduced. There is a problem of becoming high. Of course, when the fluororesin tube is covered to form a release layer, the current flowing to the ground can be suppressed to a very small amount, so that the cost of the power supply can be reduced. A physical problem that occurs when a resin is used, that is, a problem that the set temperature must be increased in order to secure the fixing performance and that the life of the heat fixing roller is short remains.

In the case where the release layer is formed by simultaneously coating a mixed material of a fluororesin and a filler, the physical problem caused when the fluororesin is used as the release layer can be solved to some extent. Because the resistance value of the release layer is further reduced by the incorporation of the filler, the electrostatic attraction force of the toner is further weakened compared to the case where the filler is not incorporation, and the unfixed toner attached to the recording medium is immediately Is easily scattered due to local turbulence of the air flow generated near the area.

In this case, even if the power for holding the toner on the recording medium is increased by an electric field generated by applying a current caused by the applied bias to the ground via the recording medium and the heat fixing roller, There is a drawback that the current flowing further increases as compared with the case where no agent is mixed, and a transformer with a larger capacity is required, so that the cost of the power supply is greatly increased.

One of the factors that cause the toner to be scattered rearward is as follows, which is the latter factor of the thermal change of air near the nip portion.

That is, when the recording medium containing water is heated in the nip portion, water vapor is generated at that time, and the air expands rapidly. Water vapor may flow back to the side. In the conventional configuration, the pressure of the back-flowing water vapor does not greatly affect the toner on the recording medium, but it has been confirmed that the pressure has an effect in a fixing device with an increased fixing speed.

That is, in a fixing device with an increased fixing speed, the conveying speed of the recording medium is high, so that the time required for the recording medium to pass through the nip portion is shortened, and the fixing property may be deteriorated. To prevent this, the amount of heat applied to the recording medium per unit time is increased, so that the amount of water vapor generated per unit time increases. At the same time, the speed at which the recording medium is introduced into the nip is increased due to the increase in the transport speed of the recording medium, and the spraying speed of water vapor on the toner on the recording medium is relatively increased. Among them, it is considered that the toner having a weak electrostatic holding force is blown backward by the pressure of the water vapor.

The above problems are summarized for the conventional heat fixing roller as shown in Table 1 below.

[0023]

[Table 1] From the above, the present invention provides a heat-fixing roller that can improve the physical properties of the release layer such as thermal conductivity and abrasion resistance and suppress the occurrence of the “toner scatter phenomenon behind”. This is the first purpose.

It is a second object of the present invention to provide a fixing device which requires less replacement of the heat fixing roller, suppresses the occurrence of image quality defects such as offset and toner contamination, and has less disturbance of the image due to the toner scatter. The purpose of.

Further, the number of replacements of the heat fixing roller is small, the occurrence of image quality defects such as offset and toner contamination is suppressed, the image is not disturbed due to the toner scattering phenomenon, and the fixing cost including the power supply is further reduced. It is a third object to provide an image forming apparatus capable of reducing image quality.

[0026]

In order to achieve the above object, the heat fixing roller according to the first aspect of the present invention is provided on the outer peripheral surface of a substantially cylindrical core metal by using a mixed material of a fluororesin and a filler. A release layer including a plurality of formed layers is provided.

That is, in the heat fixing roller according to the first aspect of the present invention, since the release layer is made of a mixed material of a fluororesin and a filler, good heat conductivity and abrasion resistance are secured. Since the release layer has a multilayer structure including at least two layers of the first layer and the second layer, the resistance value of the release layer is higher than that of the release layer having a single-layer structure. Therefore,
The insulating property is enhanced, and the transfer of charges of the opposite polarity to the toner applied on the recording medium to the core metal can be reduced. For this reason, the electrostatic attraction between the recording medium and the toner can be favorably maintained.
It is possible to prevent the toner from scattering behind.

Further, since the release layer has a multilayer structure, a low-cost material can be partially used as the release layer depending on the use conditions of the heat-fixing roller, so that the cost can be reduced.

According to a second aspect of the present invention, in the heat fixing roller according to the first aspect, the release layer includes at least two layers having different film thicknesses.

Here, when the release layer is composed of two layers having the same thickness (release layer A), and when the release layer is composed of two layers having different thicknesses ( FIG. 8 shows a graph in which the electric resistance value of the release layer B) was measured. Here, for comparison, the content of the filler in the release layer A and the content of the filler in the release layer B were the same. As is clear from FIG. 8, the release layer B has a 0.5-order higher electrical resistance value than the release layer A,
It can be seen that the electric resistance can be increased only by changing the film thickness.

That is, in the second aspect of the present invention, at least two of the plurality of layers constituting the release layer have different film thicknesses, so that the insulating properties of the release layer are further enhanced, and It is possible to further reduce the movement of charges having a polarity opposite to that of the toner applied on the medium to the metal core. For this reason, the electrostatic attraction between the recording medium and the toner can be maintained more favorably.
It is possible to prevent the toner from scattering behind.

When the release layer has a multilayer structure of three or more layers, the thickness of all the layers may be different.
A small number of layers selected in advance may have different thicknesses, and the number of different layers can be selected each time.

[0033] Further, the invention of claim 3 is based on claim 1 or 2.
In the heat fixing roller according to the above, the film thickness of the first layer provided on the uppermost layer of the release layer is smaller than the film thickness of the second layer provided below the first layer. It is characterized by the following.

That is, by making the thickness of the first layer, which is the uppermost layer, smaller than the thickness of the second layer, for example, the first layer, which is the uppermost layer of the release layer, is released. In the case where the second layer is made of a high-priced material having good properties, the cost can be relatively low. When the thickness of the second layer is larger than that of the first layer, the film of the second layer is formed. Since the amount of the filler included increases as much as the thickness becomes thicker than the film thickness of the first layer, good thermal conductivity can be secured.

According to a fourth aspect of the present invention, there is provided the first to third aspects.
In the heat fixing roller according to any one of the first to third aspects, the content of the filler in the first layer provided on the uppermost layer of the release layer may be the second layer provided on the lower side of the first layer. Characterized in that it is less than the content of the filler in the layer (a).

That is, in the invention of claim 4, the content of the filler in the first layer, which is the uppermost layer of the release layer, is adjusted to the content of the filler in the second layer provided below the first layer. Since the composition is smaller than the content, the number of fillers exposed on the surface of the release layer is reduced. That is, since the surface area ratio of the filler exposed on the surface of the release layer is reduced, not only the release property of the release layer can be made relatively good, but also the offset caused by the growth of the unfixed toner attached to the filler. In addition, the occurrence of poor image quality such as toner contamination can be suppressed.

According to a fifth aspect of the present invention, in the heat fixing roller according to any one of the first to fourth aspects, the filler is substantially granular and is provided on the uppermost layer of the release layer. The average particle size of the filler of the first layer provided is larger than the average particle size of the filler of the second layer provided below the first layer.

That is, in the heat fixing roller according to the present invention, the average particle diameter of the filler in the first layer, which is the uppermost layer of the release layer, is the second layer provided below the first layer. Since the composition is larger than the average particle size of the filler in the layer, even if the content of the filler in the first layer is equal to the content of the filler in the second layer, Even if the content of the agent is slightly higher than that of the second layer, the ratio of the surface area of the filler exposed on the surface of the release layer is reduced as compared with the one having the same average particle size. Therefore, not only the releasability of the release layer becomes relatively good, but also the occurrence of image quality defects such as offset and toner contamination due to the growth of the unfixed toner attached to the filler can be suppressed.

According to a sixth aspect of the present invention, in the heat fixing roller according to any one of the first to fourth aspects, the filler is whisker-shaped, and is provided on the uppermost layer of the release layer. The average length in the longitudinal direction of the filler in the first layer provided is longer than the average length in the longitudinal direction of the filler in the second layer provided below the first layer. I do.

That is, in the heat fixing roller according to the present invention, the average length in the longitudinal direction of the filler in the first layer, which is the uppermost layer of the release layer, is provided below the first layer. Since the configuration is longer than the average length in the longitudinal direction of the filler of the second layer, even if the content of the filler of the first layer and the content of the filler of the second layer are equal, or Even if the filler content of the first layer is slightly higher than that of the second layer, the surface area ratio of the filler exposed on the surface of the release layer is reduced as compared with that of the same average length in the longitudinal direction. . Therefore, not only the releasability of the release layer becomes relatively good, but also the occurrence of image quality defects such as offset and toner contamination due to the growth of the unfixed toner attached to the filler can be suppressed.

Further, to achieve the second object, a fixing device according to a seventh aspect of the present invention includes the heat fixing roller according to any one of the first to sixth aspects. That is, the heat fixing roller according to claim 1 to claim 6 has good thermal conductivity and abrasion resistance, high insulation of the release layer, and furthermore, Since the releasability is relatively good and the surface area of the filler exposed on the surface of the release layer is small, the fixing device equipped with such a heat fixing roller requires less replacement of the heat fixing roller, the offset and the toner. This makes it possible to suppress the occurrence of image quality defects such as dirt, and to suppress the occurrence of image disturbance due to the toner scattering phenomenon.

In order to achieve the third object,
An image forming apparatus according to an eighth aspect of the present invention includes the fixing device according to the seventh aspect. That is, in the fixing device according to the seventh aspect, as described above, the replacement of the heat fixing roller is small, the occurrence of image quality defects such as offset and toner smear can be suppressed, and the image generated due to the toner scattering in the rear direction can be suppressed. Since it is hard to cause disturbance and can reduce the fixing cost including the power supply, the image forming apparatus equipped with such a fixing device requires less replacement of the heat fixing roller, and has poor image quality such as offset and toner stain. Is suppressed, the image is less likely to be disturbed due to the toner scattering, and the fixing cost including the power supply can be reduced.

According to a ninth aspect of the present invention, the image forming apparatus according to the eighth aspect has a surface layer made of a conductive material, and the recording medium is sandwiched together with the heat-fixing roller so as to be undetermined on the recording medium. A pressure roller for forming a nip portion for pressing and fixing the toner at the same time as the toner is melted, and bias applying means for applying a bias having a polarity opposite to the polarity of the toner to the surface of the pressure roller. It is characterized by.

As a result, the unfixed toner on the recording medium can be strongly held on the recording medium by the generated electric field, so that the occurrence of the toner rearward scattering phenomenon is further suppressed, and the image resulting from the toner rearward scattering phenomenon is obtained. Can be prevented.

[0045]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
This will be described with reference to FIG.

(First Embodiment) A first embodiment will be described with reference to FIGS. As shown in FIG. 1, the image forming apparatus 10 according to the first embodiment
And a fixing device 14 having a pressure roller 58. The fixing device 14 is covered with the casing 12 and formed in a substantially box shape.

Below the image forming apparatus 10, a plurality of paper trays 16 (three paper trays 16A, 16B and 16C are shown in the present embodiment) are provided. Each of the sheet trays 16A, 16B, and 16C is provided with sheets 18 having different sizes such as, for example, B5 size, B4 size, A4 size, and A3 size. A half-moon roller 20 is provided in the vicinity of the paper discharge section of the paper tray 16, and the paper 1 is transferred from the designated paper tray 16.
8 are fed one by one, and are transported in a predetermined direction by a plurality of transport roller pairs 22. When the image forming apparatus 10 instructs image formation on both sides (front and back sides) of the sheet 28, the sheet 18 on which image formation on the front side has been completed.
Is provided with a sheet reversing unit 17 for reversing the front and back.

On one side of the image forming apparatus 10, a manual feed tray 24 for manually inserting paper 18 as necessary.
Are arranged. A half-moon roller 20 is provided near the paper discharge section of the manual feed tray 24 in the same manner as the above-mentioned paper tray 16, so that the paper 18 can be sent out one by one.

The fixing device 1 is provided above the image forming apparatus 10.
4 is provided with a discharge tray 26 from which the sheet 18 on which a desired image is fixed is discharged.

Paper tray 16 in image forming apparatus 10
In the upper part of the image data, image data obtained by reading an original with a scanner and performing various image processing (because the image forming apparatus 10 in the present embodiment is for a color image, image processing is performed by yellow, magenta, cyan, (Which is converted into image data of four colors of black)
And an image forming unit 28 including a fixing device 14 for fixing a desired image on the sheet 18 and the like.

The optical scanning device 32 includes a light source, a rotating polygon mirror 3
4. fθ lens, cylindrical mirror, reflection mirror 3
6 and the like. A laser beam emitted from a light source (not shown) is deflected by a rotating polygon mirror 34 and fθ lens, cylindrical mirror, reflection mirror 36
Irradiation is performed on the photoreceptor 30 via the like.

A charger 3 is provided around the photosensitive member 30.
8, a rotary developing device 40, an intermediate transfer member 42 composed of an IBT belt, a photoreceptor cleaner 44, and a static elimination lamp (not shown) are provided.

The photosensitive member 30 rotates at a constant speed in the direction of arrow A shown in FIG. The charging member 38 negatively charges the photoconductor 30 uniformly. The rotary developing device 40 includes four color toners 46Y of yellow, magenta, cyan, and black.
46M, 46C and 46B are supplied. The intermediate transfer body 42 is wound around a plurality of rollers 48, and moves at a constant speed in the direction of arrow B shown in FIG. 1 as the rollers 48 rotate. The photoreceptor cleaner 44 includes:
The toner remaining on the photoconductor 30 without being transferred to the intermediate transfer body 42 is removed. Further, the charge removing lamp removes the charge of the photosensitive member 30 after the residual toner is removed by the photosensitive member cleaner 44.

Further, an image detection sensor 51 and an intermediate transfer member cleaner 50 are disposed around the intermediate transfer member 42. The image detection sensor 51 is provided upstream of the transfer unit 52 in the rotation direction of the intermediate transfer body 42, and detects the presence or absence of a toner image formed on the intermediate transfer body 42. The intermediate transfer body cleaner 50 is provided downstream of the transfer unit 52 in the rotation direction of the intermediate transfer body 42, and after the transfer of the toner image from the intermediate transfer body 42 to the sheet 18 is completed, the intermediate transfer body 42 The toner remaining on the surface is removed.

The photosensitive member 30 rotating in the direction of arrow A is uniformly negatively charged by the charger 38, and
First, a first-color black latent image is formed on the photoreceptor 30 by the laser light emitted from the photoreceptor 2. This latent image is developed with black toner by the black developing device of the rotary developing device 40. The developed black toner image is transferred to the intermediate transfer member 42.
Is transferred to The toner remaining on the photoconductor 30 without being transferred is removed by a cleaner (not shown), and the photoconductor 30 is discharged by a discharge lamp.

Then, the photosensitive member 30 is uniformly negatively charged again by the charger 38, and the second color yellow image is formed. In this manner, a total of four color toner images are sequentially transferred to the intermediate transfer member 26 from the third color magenta to the fourth color cyan. When the transfer of the four color toner images to the intermediate transfer member 42 is completed, a final toner image is formed on the surface of the intermediate transfer member 42.

Below the intermediate transfer member 42, the intermediate transfer member 4
A transfer section 52 for transferring the final toner image formed on the sheet 2 to the sheet 18 is provided. The paper 18 is conveyed from the paper tray 16 provided with the paper 18 of the designated size to the transfer unit 52 by the conveyance roller pair 22 as described above.

The fixing device 14 is provided downstream of the transfer section 52 in the transport direction of the paper 18. In the fixing device 14, a predetermined image is formed on the sheet 18 by subjecting the sheet 34 onto which the final toner image has been transferred to heat and pressure.
Formed on top. The details of the fixing device 14 will be described below.

As shown in FIG. 2, the fixing device 14 heats and fixes the toner 54 transferred onto the sheet 18 to the sheet 18 by fusing and fixing the sheet 18 together with the heat and fixing roller 56. And a pressure roller 58 that forms a nip portion.

The heat fixing roller 56 has a 50 μm-thick release layer 70 (see FIG. 3) formed on the surface of an iron hollow core 57 having a thickness of about 3 mm in order to enhance the release property from paper. Configuration. This release layer 70, as shown in FIG.
First and second two fluororesin layers 72 and 74 of the same film thickness (25 μm) containing about 9 wt% of granular silicon carbide (SiC) 80 having an average particle diameter of 5 μm as a filler (hereinafter the upper layer is the first layer). Fluororesin layer 72, and the lower layer side is referred to as second fluororesin layer 74).

FIG. 4 is a graph showing the measured electric resistance when the release layer 70 is composed of two layers and the electric resistance when the release layer 70 is composed of one layer. As is clear from FIG. 4, the electric resistance value when the release layer 70 is composed of two layers is two orders of magnitude higher than the electric resistance value when the release layer 70 is composed of one layer. I understand. The reason for this is that when the release layer 70 is composed of two layers, resistance is generated at the interface between the two layers, so that the resistance value increases accordingly. Therefore, it can be said that as the number of layers increases, the electric resistance value increases accordingly.

In the first embodiment, the release layer 70 is
The first fluororesin layer 72 as the second layer and the second fluororesin layer 72 as the second layer
Since it has a structure composed of two layers of the fluororesin layer 74, the electric resistance value is higher than that of the release layer composed of one layer, so that the insulating property is improved, and the polarity is opposite to that of the toner 54 transferred onto the paper 18. Of the electric charge to the core metal 57 can be reduced. Therefore, the electrostatic attraction between the sheet 18 and the toner 54 transferred onto the sheet 18 can be maintained satisfactorily, so that the toner can be prevented from scattering backward.

A halogen lamp 62 as a heating element is built in the heat fixing roller 56. The on / off control of the halogen lamp 62 is controlled by a microcomputer. Since this point is a well-known technique, detailed description will be omitted.

Further, a temperature detection sensor 64 is set on the outer peripheral portion of the heat fixing roller 56. The temperature detection sensor 64 detects the surface temperature of the heat fixing roller 56.

The pressure roller 58 is made of a metal core 61 such as iron.
And a rubber layer 6 having a thickness of about 1 mm formed around the cored bar.
0 and a conductive release layer (not shown) on the uppermost layer, and are arranged so as to press the heat fixing roller 56 with a constant pressure by a spring 68. Thus, the sheet 18 is nipped and conveyed by the heat fixing roller 56 and the pressure roller 58. Thus, when the paper 18 passes between the heat fixing roller 56 and the pressure roller 58, the toner 54 is fused and fixed on the paper 18.

The pressure roller 58 has a high voltage power supply 65 for applying a bias having a polarity opposite to that of the toner, and a pressure roller 5.
8 in contact with the surface of the pressure roller 58 along the longitudinal direction,
The bias applied from the high voltage power supply 65 is
And a bias applying means constituted by a brush-like power supply unit 63 applied to the surface of the device.

The pressing roller 5 is driven by the bias applying means.
8, a bias having a polarity opposite to that of the toner is applied to the surface of the sheet 18 between the heat fixing roller 56 and the pressure roller 58.
An electric field acts in a direction to increase the electrostatic attraction force between the toner and the unfixed toner 54. As a result, the force opposing the backflow phenomenon of water vapor near the entrance of the nip is strengthened, so that the phenomenon of the toner scattering backward can be reduced.

Since the release layer on the surface of the heat fixing roller 56 has a two-layer structure, the electric resistance value is large, and a bias having a polarity opposite to that of the toner is applied to the surface of the pressure roller 58 by the bias applying means. Sometimes, the heat fixing roller 56
As a result, the current flowing into the ground through the ground is reduced, so that the operating cost of the high-voltage power supply 65 can be greatly reduced.

In the first embodiment, the first fluororesin layer 72 and the second fluororesin layer 74 are formed of the same fluororesin, but different fluororesins may be used according to the purpose. It can also be used. For example, by using a material having a higher releasability than the second fluororesin layer 74 as the first fluororesin layer 72 forming the surface of the heat fixing roller 56, silicon carbide exposed from the first fluororesin layer 72 ( In the case of an image forming apparatus in which the unfixed toner 54 transferred onto the sheet 18 is less likely to adhere to the (SiC) 80, and the first fluororesin layer 72 is less likely to be completely worn away, the second Even if the material of the fluororesin layer 74 is changed to a low-priced material having inferior releasability, it does not matter much, so that the cost can be reduced.

Of course, the same applies to the filler. In addition to silicon carbide (SiC), for example, graphite powder, whisker-like single crystal fiber, granular carbon black, or the like is selected according to the conditions to obtain unfixed filler. This prevents the toner 54 from adhering, thereby suppressing the occurrence of poor image quality and reducing costs.

In the first embodiment, the shape of the power supply portion 63 is a brush. However, the shape is not limited to this as long as a bias can be applied to the surface of the pressure roller 58. Alternatively, other shapes such as a bulk shape can be adopted.

In the first embodiment, for explanation,
Although the release layer has a two-layer structure with the same film thickness, it is also possible to use two or more layers, such as a three-layer structure with the same film thickness and a four-layer structure with the same film thickness. The same or higher effects as above can be obtained.

(Second Embodiment) The second embodiment is different from the first embodiment in that
As shown in FIG. 5, in the first embodiment, the release layer 70 formed on the surface of the heat fixing roller 56 uses the granular silicon carbide (SiC) 80 having the same average particle size as a filler to form a granular carbonized material. 25 μm-thick first fluororesin layer 71 containing silicon (SiC) 80 at about 4.5 wt%, and 25 μm film thickness containing about 9 wt% of granular silicon carbide (SiC) 80
Of the second fluororesin layer 73.

That is, in the second embodiment, the release layer has a two-layer structure, thereby increasing the electric resistance to prevent the toner from scattering backward, and is provided as the uppermost first layer. By setting the content of the filler in the first fluororesin layer 71 to about half that of the second fluororesin layer 73 provided thereunder, the silicon carbide (SiC) 80 exposed from the surface of the heat fixing roller 56 Is reduced, thereby reducing the possibility that unfixed toner 54 adheres to silicon carbide (SiC) 80 one after another and grows. The rest is the same as the first embodiment, and the description is omitted.

(Third Embodiment) The third embodiment is different from the third embodiment in that
As shown in FIG. 6, in the first embodiment, the release layer 70 formed on the surface of the heat fixing roller 56 contains 9 wt% of granular silicon carbide (SiC) 82 having a large average particle size.
9 wt% of a first fluororesin layer 76 having a thickness of 25 μm and a granular silicon carbide (SiC) 80 having a small average particle size.
It is formed from a second fluororesin layer 78 having a film thickness of about 25 μm including the thickness.

That is, in the third embodiment, the release layer has a two-layer structure, thereby increasing the electric resistance to prevent the toner from scattering backward, and is provided as the uppermost first layer. By setting the average particle size of the filler mixed into the first fluororesin layer 76 to be larger than the second fluororesin layer 78, the content of the filler in the first fluororesin layer 76 is reduced to the second fluororesin layer 78. The same can reduce the total surface area of the filler exposed on the surface. Therefore, the possibility that the unfixed toner 54 adheres and grows one after another on the granular silicon carbide (SiC) 82 while ensuring good thermal conductivity and abrasion resistance is reduced. The rest is the same as the first embodiment, and the description is omitted.

If the content of the filler in the first fluororesin layer 76 is not so much a problem as to be less than that of the second fluororesin layer 78, if the content of the filler in the first fluororesin layer 76 does not become a problem. The content may be lower than that of the second fluororesin layer 78. In this case, the cost can be reduced in addition to the above-described effects.

(Fourth Embodiment) The fourth embodiment is different from the first embodiment in that
As shown in FIG. 7, in the first embodiment, the release layer 70 formed on the surface of the heat fixing roller 56 uses the granular carbon carbide (SiC) 80 having the same average particle size as a filler to form a granular carbonized material. A first fluororesin layer 77 having a thickness of 10 μm containing about 3 wt% silicon (SiC) 80 and a second fluororesin layer 79 having a thickness of 40 μm containing about 9 wt% granular silicon carbide (SiC) 80 are formed.

That is, in the fourth embodiment, the release layer has a two-layer structure, thereby increasing the electric resistance to prevent the toner from scattering backward, and is provided as the uppermost first layer. By making the thickness of the first fluororesin layer 77 smaller than the thickness of the second fluororesin layer 79, the electric resistance value is further increased.

Therefore, in the fourth embodiment, the film thicknesses of the first fluororesin layer 77 and the second fluororesin layer 79 forming the release layer 70 are changed. Since the electric resistance value is further increased in comparison with the
And the toner 54 transferred onto the sheet 18 can be maintained in a good electrostatic attraction force, and the effect of preventing the toner from scattering backward can be further enhanced. This is the same when the thickness of the second fluororesin layer 79 is smaller than that of the first fluororesin layer 77. Further, the same applies to a case of a multi-layer structure of three or more layers instead of the two-layer structure.

Further, by increasing the electric resistance value, when a bias having a polarity opposite to that of the toner is applied to the surface of the pressure roller 58 by the bias applying means, the current flowing to the ground through the heat fixing roller 56 is further reduced. Since it can be reduced, the operating cost of the high-voltage power supply 65 can be further reduced.

Further, in the fourth embodiment, since the first fluororesin layer 77 as the uppermost layer is made thin, for example,
Even if the first fluororesin layer 77 is formed of a material having good releasability and a high material cost, the cost can be suppressed because the film thickness is small.

As another example, when the peeling claw and the temperature sensor are in contact with each other in the paper passing portion, the abrasion proceeds to that extent, and streak-like fixing unevenness may occur on the image surface. In this case, if the thickness of the first fluororesin layer 77 is reduced,
The degree of uneven wear can be reduced. That is, since the second fluororesin layer 79 contains a sufficient amount of filler, it has high abrasion resistance. The traveling speed can be slowed, and the occurrence of streak-like fixing unevenness can be minimized. In addition, since the part which was unevenly worn by the peeling claw and the temperature sensor is always in a polished state,
Even if the second fluororesin 79 having a high filler content is exposed, there is no fear that the toner 54 grows with the filler on the surface as a nucleus.

In the fourth embodiment, the content of silicon carbide (SiC) in the first fluororesin layer 77 is smaller than the content of silicon carbide (SiC) in the second fluororesin layer 79. Therefore, the total surface area of the silicon carbide (SiC) 80 exposed on the surface of the heat fixing roller 56 is reduced, thereby reducing the possibility that the unfixed toner 54 adheres to the silicon carbide (SiC) 80 one after another and grows. Reducing.

In some cases, the content of silicon carbide (SiC) in the first fluororesin layer 77 and the content of silicon carbide (SiC) in the second fluororesin layer 79 may be substantially equal.

As an application of the fourth embodiment, as shown in FIG. 9, the average particle size of silicon carbide (SiC) 82 contained in the first fluororesin layer 77 is contained in the second fluororesin layer 79. A configuration in which the average particle diameter is larger than the average particle diameter of silicon carbide (SiC) can also be employed. In this case, by adjusting the filling rate of silicon carbide (SiC) according to the conditions, the total surface area of silicon carbide (SiC) 80 exposed on the surface of heat fixing roller 56 can be adjusted. The rest is the same as the first embodiment, and the description is omitted.

[0087]

As described above, according to the first to sixth aspects of the present invention, it is possible to improve the physical properties such as the thermal conductivity and the abrasion resistance of the release layer. This achieves the effect of obtaining a heat fixing roller capable of suppressing the occurrence of the phenomenon.

According to the seventh aspect of the present invention, there is little replacement of the heat-fixing roller, the occurrence of image quality defects such as offset and toner contamination can be suppressed, and the image is less disturbed by the toner scattering phenomenon. The effect that a device is obtained is achieved.

Further, according to the inventions of claims 8 and 9, the replacement of the heat-fixing roller is small, the occurrence of image quality defects such as offset and toner smear can be suppressed, and the image caused by the toner scattering in the rear direction can be suppressed. This achieves an effect that an image forming apparatus that can reduce the fixing cost including the power supply can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram illustrating details of a fixing device.

FIG. 3 is a schematic configuration diagram illustrating a part of a release layer formed on the surface of the heat fixing roller according to the first embodiment of the present invention.

FIG. 4 is a graph showing measured electric resistance values when the release layer 70 is composed of two layers and electric resistance values when the release layer 70 is composed of one layer.

FIG. 5 is a schematic configuration diagram illustrating a part of a release layer formed on a surface of a heat fixing roller according to a second embodiment of the present invention.

FIG. 6 is a schematic configuration diagram illustrating a part of a release layer formed on a surface of a heat fixing roller according to a third embodiment of the present invention.

FIG. 7 is a schematic configuration diagram illustrating a part of a release layer formed on a surface of a heat fixing roller according to a fourth embodiment of the present invention.

FIG. 8 is a graph showing the relationship between the electric resistance of the release layer A in which the release layer 70 is composed of two layers having the same thickness and the thickness of the release layer 70 having different thicknesses.
5 is a graph showing the measured electrical resistance of a release layer B composed of two layers.

FIG. 9 is a schematic configuration diagram showing a part of a release layer 70 formed on the surface of a heat fixing roller 56, which is an application example of the fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Image forming apparatus 14 Fixing device 18 Paper 54 Toner 56 Heat fixing roller 57 Hollow core metal 58 Pressure roller 60 Rubber layer 62 Halogen lamp 63 Power supply part 64 Temperature detection sensor 65 High voltage power supply 68 Spring 70 Release layer 72 First fluororesin Layer 74 Second fluororesin layer 80 Silicon carbide (SiC)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Yasuo Suzuki, Inventor 3-7-1, Funai, Iwatsuki-shi, Saitama Prefecture Fuji Xerox Co., Ltd. Iwatsuki Office (72) Keiichi Fujimori 3-7-1, Fuuchi, Iwatsuki-shi, Saitama Prefecture No. Fuji Xerox Co., Ltd. Iwatsuki Office (72) Inventor Osamu Shimizu 3-7-1, Fukui, Iwatsuki City, Saitama Prefecture Fuji Xerox Co., Ltd. Iwatsuki Office F-term (reference) 2H033 AA09 AA16 BB03 BB05 BB13 BB14 3J103 AA02 AA14 AA23 AA51 EA13 FA01 FA02 FA13 FA15 FA30 GA02 GA57 GA58 GA66 HA03 HA12 HA20 HA22 HA43

Claims (9)

[Claims] 1. A heat fixing roller comprising: a substantially cylindrical core metal; and a release layer comprising a plurality of layers each formed of a mixed material of a fluororesin and a filler on an outer peripheral surface of the core metal. 2. The heat fixing roller according to claim 1, wherein the release layer includes at least two layers having different film thicknesses. 3. A film thickness of a first layer provided on an uppermost layer of the release layer is smaller than a film thickness of a second layer provided below the first layer. Claim 1 or Claim 2
2. The heat fixing roller according to 1. 4. The content of the filler in the first layer provided on the uppermost layer of the release layer is the content of the filler in the second layer provided below the first layer. The heat fixing roller according to claim 1, wherein the number of the heat fixing rollers is less. 5. The filler according to claim 1, wherein the filler has a substantially granular shape, and an average particle size of the filler in the first layer provided on the uppermost layer of the release layer is provided below the first layer. 2. The method according to claim 1, wherein the average particle size of the filler in the second layer is larger than the average particle size.
The heat fixing roller according to any one of claims 1 to 4. 6. The filler has a whisker shape, and the average length in the longitudinal direction of the filler of the first layer provided on the uppermost layer of the release layer is lower than the first layer. The heat fixing roller according to any one of claims 1 to 4, wherein the length of the filler in the second layer provided is longer than the average length in the longitudinal direction. 7. A fixing device comprising the heat fixing roller according to claim 1. 8. An image forming apparatus comprising the fixing device according to claim 7. 9. An image forming apparatus according to claim 8, further comprising a surface layer made of a conductive material, wherein the image forming apparatus sandwiches the recording medium together with the heat fixing roller to melt unfixed toner on the recording medium. An image forming apparatus further comprising: a pressure roller for forming a nip portion for pressing and fixing; and a bias applying unit for applying a bias having a polarity opposite to the polarity of the toner to the surface of the pressure roller. .