JP2003076190A - Fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent 'tail-end peeling offsetting' by prescribing the surface property of a heat fixing means in a fixing device in which a cleaning member is not abutted against the surface of the heat fixing means. SOLUTION: The fixing device has a fixing roller 1 which has a heater 3, a pressure roller 2 which is arranged such that it is pressed against the fixing roller 1, and a peeling layer as the surface layer of the pressure roller 2; and the pressure roller 2 has on its surface a low-resistance fluororesin layer of <=10<6> in surface resistance value in 500 V application and the surface of the fixing roller 1 which comes into contact with the an image formation surface of a recording material 6 satisfies Rz.Sm>=400 t/50, where Rz is the 10-point mean roughness (μm) of the surface, Sm is the mean interval (μm) of unevenness of the surface, and t is the thickness (μm) of the heat-fixation surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for developing an electrostatic latent image on an image bearing member in an image forming apparatus and fixing the developed toner image on a recording material, and an image forming apparatus having the fixing device. Regarding the device.

[0002]

2. Description of the Related Art Conventionally, an electrophotographic method has been widely used as an image forming method for forming an image on a recording material. The general method is to charge and expose a photoconductor using a photoconductive material to form an electrical latent image, develop the latent image with colored toner, and then print it on a recording material such as paper. It is melted and fixed on top to obtain a fixed image. Then, the residual toner on the photoconductor is cleaned, and the above steps are repeated.

As a fixing device used in such an image forming apparatus, a roller having a heat source inside or a film-shaped heat fixing means, and an elastic member for contacting the heat fixing means under pressure to convey a recording material. A roller pair consisting of pressure rollers is used. The surface of these heat fixing means is covered with a tube or coating of a material having excellent releasability such as a fluororesin, and is as smooth as possible from the viewpoint of releasability with toner and fixability (10-point average roughness; Rz ≦ It is generally formed to 5 μm).

Conventionally, as means for preventing offset to the recording material, a releasing agent such as silicone oil is applied to the surface of the heat fixing means by a cleaning member such as a web or pad, or offset toner is applied to the cleaning member. The method of collection is taken.

However, recently, in order to solve the offset problem in the fixing device, a potential difference is generated between the pair of rollers in the direction of pressing the unfixed toner image on the recording material against the recording material to prevent the offset on the rollers. There are many things. For example, a bias having the same polarity as the toner is applied to the roller core metal of the heat fixing means (-100 V for negative toner).
~ -2000 V) is applied to induce a potential for repelling toner on the surface, one elastic pressure roller is a medium resistance roller in which a conductive agent is dispersed in the surface layer and the elastic layer, and a diode is connected to the core metal. Therefore, there is a fixing device that maintains a potential difference from the heat fixing means.

An example of a conventional fixing device will be described with reference to FIG. In FIG. 6, the fixing roller 101 has a PFA resin layer 112 of 50 μm provided on an aluminum core metal 111 having a thickness of 1 mm. A heater 103 as a heating unit is provided inside the fixing roller 101, and the fixing roller is pressed from the inside.

On the other hand, the pressure roller 102 is pressed against the fixing roller by a pressure means (not shown) and forms a 6 mm fixing nip N between itself and the fixing roller 101. Pressure roller
102 is an iron core metal 121, on which an elastic layer 122 made of heat-resistant silicon sponge rubber 6 mm, and further PF
A release layer 123 made of A resin is formed. The unfixed toner 107 is fixed on the recording material 106 by being heated and pressed in the fixing nip N.

The entrance guide 104 functions as a guide for stably conveying the recording material 106 on which the unfixed toner image is formed to the fixing nip N. The thermistor 105 is the fixing roller 101.
Is a temperature detection sensor that detects the surface temperature of the fixing roller, which contacts the surface of the fixing roller with a predetermined contact pressure, and turns on / off the power to the heater so that the temperature of the fixing roller surface becomes constant during printing. The electric circuit that turns on and off the energization is not shown). In the fixing device having the cleaning mechanism, the thermistor 105 can be provided in the recording material passage area. However, in the fixing device having no cleaning mechanism as shown in FIG. It is provided in the area.

The fixing device is rotated by a driving means (not shown) while controlling the heating so that the surface of the fixing roller reaches a predetermined temperature, and the unfixed image sent to the fixing device is fixed.

Here, in the fixing device having no cleaning mechanism as shown in FIG. 6, the offset is prevented by setting the potential as follows. First, the pressure roller 102
Conductive silicon rubber (volume resistivity: 10 ² to 10 ⁴ Ω · cm) is formed as an elastic layer 122 on an iron cored bar 121, and a roller resistance value of 10 ⁶ to 10 ¹² Ω (500 V of a fluororesin tube is applied thereto). The release layer 123 is coated with a PFA resin tube so as to form a medium resistance pressure roller having a surface resistance of 10 ⁶ to 10 ¹² Ω. A diode 109 is connected to the iron cored bar 121 for self-bias, and -300 V is applied to one fixing roller cored bar 111 by a power supply 108 to form a potential difference of 300 V in a direction to press the negative toner toward the image forming surface side. .

By thus forming the electric potential for repelling the toner, the cleaning member becomes unnecessary, an accident such as oil leakage does not occur, and the user does not have to regularly replace the cleaning member. It became so.

[0012]

However, the following offset phenomenon may occur in a fixing device in which the thermal fixing means is not provided with a cleaning member.

When the recording material is conveyed through the fixing nip formed by the heat fixing means and the pressure roller 102 and the trailing edge of the recording material is separated from the heat fixing means, the recording material is recorded as shown in FIG. It is known that peeling discharge occurs between the material and the fixing nip N, and the potential of the surface of the heat fixing unit is partially lowered (referred to as peeling potential). As a result, the unfixed toner image on the succeeding recording material located after one round (length L) of the heat fixing means is peeled off, and the offset image is left after one round of the heat fixing means (length L). Yes (see FIG. 7 (b)). This phenomenon will be referred to as "rear end peeling offset" to distinguish it from a normal offset. M shown in FIG. 7B is the distance between the recording materials conveyed.

In order to prevent "rear edge peeling offset",
The pressure roller 102 may be made to have a low resistance to reduce the peeling discharge when the recording material is separated so as to prevent the offset toner adhering to the surface of the heat fixing means. If it is changed, peeling discharge is likely to occur due to the recording material, and as shown in FIG. 7A, peeling charges remain on the surface of the heat fixing means, and a sufficient effect cannot be obtained.

An object of the present invention is to provide a "rear end peeling offset" by defining the surface property of the heat fixing means in a fixing device in which the cleaning member is not brought into contact with the surface of the heat fixing means.
To provide a fixing device capable of preventing the above and an image forming apparatus using the same.

[0016]

A typical constitution of the present invention for achieving the above object is a heat fixing means having a heating means, and a pressure means arranged so as to be in pressure contact with the heat fixing means. And a releasing device as a surface layer of the pressing means, the surface of the pressing means has a low resistance fluororesin layer having a surface resistance value of 10 ⁶ Ω or less when 500 V is applied. Then, the surface of the heat fixing means in contact with the image forming surface of the recording material has a ten-point average roughness of Rz (μm), an average spacing of surface irregularities of Sm (μm), and a releasing surface of the heat fixing surface. When the layer thickness is t (μm), Rz · Sm ≧ 40
It is characterized by satisfying the relationship of 0t / 50.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) A first embodiment of the present invention will be described. 1 is a schematic explanatory view of an image forming apparatus, FIG. 2 is a schematic explanatory view of a fixing device, and FIG. 3 is an enlarged schematic view of the surface of a fixing roller. In the description, the features of the present invention are described, followed by a detailed description of the individual devices.

(Characteristics of this Embodiment) In the present invention,
It was considered that the "rear edge peeling offset" was correlated with the surface property of the heat fixing means. That is, if the surface of the heat fixing means is smooth, the contact area between the trailing edge of the recording material and the heat fixing means is large, and peeling discharge is likely to occur. It was thought that the potential V was likely to remain. Here, when the electrostatic capacitance between the substrate of the heat fixing means and the surface release layer is C, the peeling potential V is represented by V = Q / C. Further, if the area where the recording material and the surface of the heat fixing means contact each other is S, the peeling charge Q is Q∝S.

Therefore, the unevenness of the surface of the heat fixing means is measured,
When the relationship between the surface property of the heat fixing means and the “rear end peeling offset” was investigated, it was found that the surface of the heat fixing means had a relationship of Rz · Sm ≧ 400 · t / 50 (1) (hereinafter referred to as equation (1)). It has been found that the "rear end peeling offset" can be prevented if satisfied. Here, t is the thickness of the surface release layer of the fixing roller as the heat fixing means, and Rz and Sm are JIS surface roughness (B06, respectively).
01) The ten-point average roughness Rz (μm) and the average spacing Sm (μm) between the convex portions and the convex portions (or the concave portions and the concave portions).
Is.

The area S in contact with the surface of the heat fixing means is Rz.
It is considered to be inversely proportional to Sm, and therefore the peeling charge Q is
It can be expressed as Q∝1 / (Rz · Sm). That is, even with the same Rz, if the average spacing Sm between the convex portions and the convex portions (or the concave portions and the concave portions) is large, the area S in which the recording material comes into contact with the surface of the heat fixing unit becomes small.

(Image Forming Apparatus) A laser beam printer will be described as an example of the image forming apparatus. As shown in FIG. 1, the image forming apparatus includes a feeding cassette 50, a feeding roller 51 (including a pickup roller), and a sheet metal 52 as a feeding unit, and a feeding roller pair 48 as a feeding unit. The image forming unit includes a laser scanner 40 as an exposure unit, a photosensitive drum 41 as an image carrier, and a primary charger.
It has a developing roller 42 and a developing roller 43.
It has a fixing device 60 as a fixing means, and has a conveyance roller pair 61, a discharge tray 70, and a discharge roller pair as a discharge portion.
With 71.

Further, the fixing device 60 has a fixing roller 1 and a pressure roller 2 as a pressure means, and has a fixing drive motor M for driving the fixing roller 1 and a CPU for controlling the drive of the fixing drive motor M. It has a control unit 30, a display unit 20 for displaying information such as warnings and the like judged by the control unit 30 to the user.

The sheet-shaped recording material P stacked and stored in the feeding cassette 50 is a feeding roller which rotates counterclockwise in the drawing.
It is fed by 51 and guided to the transport sheet metal 52, and is transported by the transport roller pair.
It is sent to the nip part of 48. Then, the recording material is sent between the photosensitive drum 41 and the transfer roller 46 by the pair of conveying rollers 48.

The photosensitive drum 41 is rotating clockwise in the figure and is uniformly charged by the primary charger 42. The laser scanner 40 is attached to the outer peripheral surface of the photosensitive drum 41.
An electrostatic latent image is sequentially formed on the photoconductor drum 41 by the laser light L from, and the electrostatic latent image is subsequently developed by the developing roller 43 to form a toner image. Photoconductor drum 41
The toner image on the photosensitive drum 41 is sequentially transferred by the transfer roller 46 onto the recording material sent between the transfer roller 46 and the transfer roller 46.

The recording material on which the toner image has been transferred in this manner is sent to the fixing device 60, where it is heated and pressed to fix the toner image on the recording material. Thereafter, the recording material is sent to the discharge roller pair 71 by the transport roller pair 61, and then discharged onto the discharge tray 70 on the apparatus main body by the discharge roller pair 71.

In this laser beam printer, a process cartridge 45 having a photosensitive drum 41 and process means (laser scanner 40, primary charger 42, etc.) that act on the photosensitive drum 41, a unit of a fixing device 60, The relationship between the feeding roller 51 and the transfer roller 46 is a consumable part and needs to be replaced several times during the life of the product.

(Fixing Device) As shown in FIG.
Has the following configuration. The fixing roller 1 has a surface release layer 12a of PFA resin of 50 μm provided on a core metal 11a of aluminum having a thickness of 1 mm. A heater 3 as a heating unit is provided inside the fixing roller 1 and presses the fixing roller from the inside.

On the other hand, the pressure roller 2 is pressed against the fixing roller by a pressure means (not shown) and forms a fixing nip N of 6 mm between itself and the fixing roller 1. Pressure roller 2
On an iron cored bar 21, an elastic layer 22 made of heat-resistant silicon sponge rubber 6 mm and a release layer 23 made of PFA resin are further formed. Unfixed toner 7
Is heated and pressed in the fixing nip N, so that it is fixed on the recording material 6.

The entrance guide 4 serves as a guide for stably conveying the recording material 6 on which the unfixed toner image is formed to the fixing nip N. The thermistor 5 is a temperature detection sensor that detects the surface temperature of the fixing roller 1. The thermistor 5 is in contact with the surface of the fixing roller with a predetermined contact pressure, and a heater is provided to keep the temperature of the fixing roller surface constant during printing. Is turned on / off (the electric circuit that turns on / off the current is not shown). In the fixing device having the cleaning mechanism, the thermistor 5 can be provided in the recording material passage area. However, in the fixing device having no cleaning mechanism as shown in FIG. It is provided in the area.

The fixing device is rotated by a driving means (not shown) while controlling the heating so that the surface of the fixing roller reaches a predetermined temperature, and the unfixed image sent to the fixing device is fixed.

(Manufacturing Method of Fixing Roller 1) Next, the fixing roller 1 whose surface is coated with PFA resin satisfying the expression (1)
I will describe the production method. An aluminum cylinder cut into a predetermined shape is coated with a conductive primer in which polyamide and a fluororesin component are mixed at a constant ratio and dried.
Then insert it into the aluminum cylinder and fix the tube. By placing this in an electric furnace and heating and firing it, the tube can be thermally shrunk and at the same time adhered to the aluminum cylinder. Then, the roller is taken out of the electric furnace and cooled to form the fixing roller 1.

By the way, with the primer and PFA resin,
Since the primer has a higher melting point, the PFA resin on the surface is in a molten state at the highest temperature reached in the electric furnace (about 400 ° C.). When this is cooled, it is crystallized into islands on the surface of the fixing roller 1 to form irregularities as shown in FIG. Each of these crystals is called a "spherulite."

In this embodiment, the size of the "spherulite" is adjusted as a means for defining the surface roughness of the fixing roller 1. The specific method will be described below.

First, as the PFA resin, PFA450HP-J manufactured by DuPont Mitsui Chemicals Co., Ltd. is used to prepare a tube having a thickness of 50 μm. This is inserted into and attached to an aluminum cylinder coated with a primer in advance, and then heated and baked at 400 ° C. for 1.5 hours in an electric path. Next, cold air at 15 ° C. is uniformly blown onto the fixing roller 1 immediately after firing for about 10 minutes to rapidly cool the fixing roller 1 to accelerate the growth of spherulites.

The fixing roller 1 manufactured in this way is referred to as Example 1. In order to compare with the fixing roller 1 of Example 1, a fixing roller that is calcined and then gradually cooled in the open air at 23 ° C. (Comparative Example 1), and a PFA resin in which spherulites hardly grow in the cooling process. A fixing roller (Comparative Example 2) manufactured using PFA451HP-J manufactured by Mitsui DuPont Chlorochemical Co., Ltd. was prepared. The surface of these fixing rollers was measured with the surface roughness measuring device and the measuring conditions shown in Table 1.

[0036]

[Table 1]

Further, as the pressure roller 2, three kinds of conductive PFA resin tubes having different surface resistances were manufactured, and conductive silicon rubber (volume resistivity: 10 ² to 10 ⁴ ) was formed on an iron cored bar.
Ω · cm) was coated on a molded rubber roller.

These fixing roller and pressure roller were installed in a fixing device so that the nip width was 6 mm, and the image of "rear end separation offset" was evaluated by a laser beam printer with a process speed of 150 mm / s. Image evaluation and determination were performed as follows.

(Evaluation method of trailing edge separation offset "environment:
15 ° C / 10% RH ") Using a transparency for OHT as a recording material, a character image on the entire surface is printed on the first sheet, a character image is printed on the second sheet 10 cm at the leading edge, and the rest is output blank. As a set, 5 sets were continuously printed out, and the final 10th blank area was compared. The reason why the entire surface of the first sheet of each set is a character image is to ensure that the toner is peeled off by the rear end peeling by the fixing roller.

(Determination of Rear Edge Peeling Offset) As a result of comparing Example 1 with Comparative Examples 1 and 2, as shown in Table 2, the pressure roller has a surface resistance of 10 ⁶ Ω when 500 V is applied. If the following is the case, for the fixing roller of Example 1 in which the surface roughness of the fixing roller satisfies the expression (1),
Although "rear edge separation offset" was not seen, "rear edge separation offset" was observed in the fixing rollers of Comparative Example 1 and Comparative Example 2 in which the surface roughness of the fixing roller did not satisfy the expression (1). .

[0041]

[Table 2]

From the above, the surface resistance of the pressure roller is 500.
When the voltage is 10 ⁶ Ω or less when the voltage is applied and the surface roughness of the fixing roller satisfies the expression (1), "rear end separation offset"
It turns out that can be reliably prevented.

The case of coating the surface of the fixing roller with the PFA resin tube has been described above, but the same applies to the case of coating the PFA resin. Further, as the release layer on the surface, other PTFE resin, FEP resin or the like may be used.

Furthermore, as the primer for adhering the core metal of the fixing roller as the substrate and the surface release layer, it is preferable that the conductive agent such as carbon is dispersed to give conductivity as in Example 1. The reason is that the magnitude of the peeling potential V can be suppressed by increasing the capacitance C between the core metal and the surface release layer.

Using the fixing device of Example 1,
Since a normal offset image or "rear end separation offset" does not occur, it is not necessary to bring the cleaning member into contact with the fixing roller, and the apparatus does not become complicated. In addition, the user does not have to load the cleaning member regularly.

As described above, the surface of the pressing means is
Surface resistance is 10 when applying 500V ⁶Less than Ω
If it is an anti-fluorine resin layer,
Suppressing peeling discharge due to recording material
The "rear end peeling offset" can be prevented.

In particular, PFA is used as the surface release layer of the heat fixing means.
If a resin is used, the surface can be easily made to have an appropriate roughness by heating and firing on a core metal and then rapidly cooling.
As the surface release layer of the heat fixing means, PTFE resin,
When it is formed of FEP resin or the like, it is excellent in releasability with a toner, abrasion resistance with a recording material, and also has heat resistance, so that it is suitable for a release layer of a thermal fixing device.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to the drawings. Here, the same configurations as those of the above-described embodiment are denoted by the same reference numerals and the description thereof will be omitted. FIG. 4 is a sectional view of the fixing roller of the second embodiment.

(Characteristics of this Embodiment) In order to cope with an image forming apparatus of a higher speed in this embodiment, the thickness of the release layer on the cored bar is made thinner and the thermal conductivity is improved as compared with the first embodiment. It is a thing. Specifically, a primer is applied to a 2 mm aluminum fixing roller core metal 11b as a base,
The PFA tube 30 μm is used as the surface release layer 12b.
A φ50 fixing roller manufactured under the same conditions as in Comparative Example 1 of the embodiment (heating the fixing roller and then gradually cooling it) was manufactured and incorporated into a fixing device. Using this fixing device, an image was output by a laser beam printer with a process speed of 200 mm / s. The method for measuring the surface roughness and the method for evaluating the trailing edge separation offset are the same as in Example 1.

When a fixing roller (Example 2) using a PFA tube having a thickness of 30 μm is used, as shown in Table 3, even if the surface roughness is the same as that of Comparative Example 1, the formula (1) is given by If the surface resistance of the filled and pressure roller was not more than 10 ⁶ Ω when 500 V was applied, “rear end peeling offset” was not observed. As described above, the present invention does not depend on the manufacturing conditions of the fixing roller.

[0051]

[Table 3]

(Third Embodiment) A third embodiment of the present invention will be described with reference to the drawings. Here, the same configurations as those of the above-described embodiment are denoted by the same reference numerals and the description thereof will be omitted. FIG. 5 is a schematic explanatory view of the fixing device according to the third embodiment.

(Characteristics of this Embodiment) In this embodiment, the surface of the film base of the heat fixing means is coated with a fluororesin layer in which roughening particles are dispersed, and the roughness of the film surface satisfies the expression (1). Thus, the peeling discharge is reduced.

(Fixing Device) As shown in FIG. 5, in the fixing device of this embodiment, a heat-resistant film (fixing film) 80 as an endless belt-like heat fixing means is a semi-circular film guide member 83 ( (Stay) is covered with a shape with a margin in the circumference. The fixing film 80 has a thickness of 100 μm or less, preferably 20 to 60 μm in order to reduce the heat capacity and improve the quick start property.
PTF on a film of polyimide, polyamide, PEEK, PES, etc., which has excellent heat resistance, releasability, strength, and durability
It is a composite layer film coated with a release layer such as E / PFA / FEP.

The pressure roller 81 comprises an elastic layer made of silicon rubber on a cored bar made of iron, aluminum or the like, and a PF on the surface.
The A tube is formed and is rotated by drive means (not shown). A guide member 84 is provided to guide the recording material smoothly to the fixing nip N.

In FIG. 5, the fixing film 80 is brought into close contact with the surface of the heating body 82 in the direction shown by the arrow by the rotation of the pressure roller 81, and is rotated at a predetermined speed while sliding on the surface of the heating body 82. To do. The predetermined speed is substantially the same as the conveying speed of the recording material 6 carrying the unfixed toner image T.

The heating element 82 has an energization heating element 82a as a heating means for generating heat by supplying electric power.
The nip portion is heated by the heat generated in a. Unfixed toner image T
The recording material 6 carrying C is conveyed to the fixing nip N, and the recording material 6 and the film come into close contact with each other and pass through the fixing nip N.

In this type of fixing device, since the electric heating element 82a and the fixing film 80 are close to each other, the fixing film 80
It is difficult to apply a bias voltage to the. Further, since it is structurally difficult to clean the surface of the fixing film 80, it is common not to bring the cleaning member into contact.

Therefore, when the trailing edge of the recording material is separated from the film, the peeling potential is likely to remain, and the unfixed toner image on the succeeding recording material is peeled off, and "rear edge peeling offset" is likely to occur.

In the present embodiment, the power supply brush is provided on the surface of the pressure roller 81 in the non-passage area of the end portion of the recording material.
85 is in contact, and a bias of +300 V is applied by the power supply 86. Also, the roughening particles have an average particle size of 5 μm.
It is preferable to melt-disperse inorganic particles of m to 30 μm in a fluororesin and spray-coat the surface of the fixing film 80.
The roughening particles include, for example, inorganic particles such as carbon black, silica and titanium oxide.

In order to confirm the effect of this embodiment,
A fixing film 80 having the following structure was produced. A polyimide film of 50 μm coated with a PTFE resin of 8 μm (Comparative Example 4) and a resin of 8 μm obtained by mixing PTFE resin with silica powder having an average particle size of 10 μm (Example 3). Also, as the pressure roller 81, three kinds of conductive PFA resin tubes having different surface resistances were manufactured, and 5 m of silicon rubber was placed on the iron cored bar.
m was coated on a molded rubber roller. The hardness is 56 ° in each case.

The fixing film 80 and the pressure roller 81 are pressed against the heating body 82 at a pressure of 10 kgf, assembled into a fixing device so as to obtain a width of the fixing nip N of 6 mm, and a laser beam printer having a process speed of 100 mm / s is used. Image comparison was performed. The method for measuring the surface roughness and the method for evaluating the trailing edge separation offset are the same as in Example 1. Comparative example Table 4
Shown in.

[0063]

[Table 4]

As described above, even in a fixing device using an endless film to which it is difficult to apply a bias, roughening particles are added to the surface release layer, and the pressure roller 81 has a surface resistance of 10 ⁶ Ω or less when 500 V is applied. In this case, by defining the film surface roughness, the "trailing edge separation offset" can be prevented.

(Other Embodiments) In the above-described embodiments, the printer has been described as an example of the image forming apparatus, but the present invention is not limited to this, and a facsimile machine or a copying machine may be used.

[0066]

As described above, according to the present invention, the surface of the pressing means has a surface resistance value of 1 when 500 V is applied.
The surface of the heat fixing means having a low-resistivity fluororesin layer of 0 ⁶ Ω or less and in contact with the image forming surface of the recording material is Rz.
In order to satisfy the relationship of Sm ≧ 400t / 50, in a fixing device in which the cleaning member is not brought into contact with the surface of the heat fixing unit, by defining the surface property of the heat fixing unit, it is possible to prevent “rear end peeling offset”. It is possible to provide a fixing device that can be used and an image forming apparatus using the fixing device.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of an image forming apparatus.

FIG. 2 is a schematic explanatory diagram of a fixing device.

FIG. 3 is an enlarged schematic view of the surface of a fixing roller.

FIG. 4 is a cross-sectional view of a fixing roller according to a second exemplary embodiment.

FIG. 5 is a schematic explanatory view of a fixing device according to a third embodiment.

FIG. 6 is a schematic explanatory view of a conventional fixing device.

FIG. 7 is an explanatory diagram of a trailing edge separation offset.

[Explanation of symbols]

M: Fixing drive motor N: Fixing nip T: unfixed toner image 1 ... Fixing roller 2 ... Pressure roller 3 ... Heater 4 ... Entrance guide 5 ... Thermistor 6 ... Recording material 7 ... Unfixed toner 11a ... Fixing roller core metal 11b ... Fixing roller core metal 12a ... Surface release layer 12b ... Surface release layer 20 ... Display 21… Iron core 22 ... Elastic layer 23… Release layer 30… Control means 40… Laser scanner 41… Photosensitive drum 42 ... Primary charger 43… Developing roller 45… Process cartridge 46… Transfer roller 48… Conveyor roller pair 50… Feed cassette 51… Feeding roller 52… Conveying sheet metal 60… Fixing device 61… Conveyor roller pair 70… Ejection tray 71… Ejection roller pair 80… Fixing film 81… Pressure roller 82 ... Heating body 82a ... Electric heating element 83… Film guide member 84… Guide member 85… Power supply brush 86… Power

Continued front page    F term (reference) 2H033 AA09 BA25 BB03 BB04 BB12                       BB13 BB14 BB18 BB29 BB30                       BB34 BE03                 3J103 AA02 AA61 AA85 BA02 FA16                       GA27 GA66 HA04 HA20 HA41                       HA43                 3K058 AA22 BA18 DA04

Claims (6)

[Claims] 1. A fixing device comprising: a heat fixing unit having a heating unit; a pressure unit arranged in pressure contact with the heat fixing unit; and a release layer as a surface layer of the pressure unit. The surface of the pressure means has a low resistance fluororesin layer having a surface resistance value of 10 ⁶ Ω or less when 500 V is applied, and the surface of the heat fixing means in contact with the image forming surface of the recording material is
When the ten-point average roughness of the surface is Rz (μm), the average spacing of the surface irregularities is Sm (μm), and the thickness of the release layer on the heat fixing surface is t (μm), Rz · Sm ≧ 400t / A fixing device characterized by satisfying a relationship of 50. 2. The fixing device according to claim 1, wherein the surface release layer of the heat fixing means is PFA resin. 3. The fixing device according to claim 1, wherein the primer for adhering the substrate of the heat fixing means and the surface release layer is electrically conductive. 4. The fixing device according to claim 1, wherein the fixing means is an endless belt-shaped film in which roughening particles are added to a surface release layer on the surface. 5. The fixing device according to claim 1, wherein a member for cleaning the developer is not in contact with the surface of the heat fixing means. 6. An image forming apparatus, comprising: an image bearing member; and a development formed on the image bearing member transferred to a recording material, and the transferred image is fixed by a fixing unit to form an image. The image forming apparatus is the fixing device according to any one of claims 1 to 5.