JPH11219055A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain the adhesive strength and additional writing performance of a recording material after fixation without spoiling the color reproducibility, etc., by specifying the surface roughness of the surface base of a fixing rotary body below a specific value and then preventing toner from sticking on the fixing rotary body securely and stably in the beginning and for a long period. SOLUTION: The fixing device 1 consists of a heat roll 11, a pressure roll 13 which is pressed against a fixing roll 11 through an endless belt 12 extended between extension rolls 15a and 15b, and a pressure pad 14. The core part of the heat roll 11 is a cylinder made of aluminum and the surface of the core part is coated with silicone rubber. This endless belt 12 is wound around the pressure roll 13 and extension rolls 15a and 15b to specific tension. The pressure roll 13 is pressed against the heat roll 11 through the endless belt 12. Then the roughness R of the surface base board of the endless belt 12 is not more 200 (nmRz).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine and a printer, and more particularly to an improvement in a fixing device.

[0002]

2. Description of the Related Art Conventionally, as a fixing device of an electrophotographic image forming apparatus such as a copying machine or a printer, a fixing device which performs fixing by a pair of fixing rotations in pressure contact with each other in a roll shape or a belt shape is well known. . That is, the unfixed toner image formed on the recording material by the electrophotographic process is passed through the nibs of the pair of fixing rotators, and at that time, the toner image is formed by the action of heat and pressure from the fixing rotator. The image is fixed thereon to obtain a permanent image. Further, as a fixing rotating body, a roll-shaped one or an endless belt-shaped one is known.

[0003] In such a fixing device, a problem that has conventionally been encountered is the adhesion (offset) of the toner to the fixing rotating body. That is, the unfixed toner is in a molten state when passing through the nip portion of the pair of fixing rotators, and thus easily adheres to the contacting fixing rotator. Therefore, the recording material itself is not peeled from the fixing rotating body, causing a jam,
There has been such a problem that toner adhered to the fixing rotating body contaminates a subsequent recording material.

[0004] Therefore, a releasing agent such as silicone oil is applied to the surface of the fixing rotary member by various releasing agent supply devices. However, if this release agent is applied too much, problems such as image defects, particularly poor color reproducibility of full-color images, and poor light transmittance of the OHP sheet may occur.

[0005] In order to solve these problems, the applicant of the present invention disclosed in Japanese Patent Application Laid-Open No. 5-119659 that the surface roughness of a donor roll and a pickup roll constituting a release agent supply device is fixed to fix the toner. Japanese Patent Application Laid-Open No. 6-308849 discloses a technique for regulating the amount of release agent applied to a rotating body to 15 to 40 [μl / one side of a recording material] by providing a difference in rotation between a donor roll and a pickup roll. A technique has been proposed in which the lower limit of the amount of the release agent applied to the fixing rotating body is restricted to 6 [μl / one side of the recording material].

Further, the present applicant has specified the characteristics of the pickup roll and the surface roughness thereof in order to make it easier for the adhesive tape to adhere to the recording material after fixing and to make it easy to write on the recording material after fixing. A technique has been already filed (Japanese Patent Application No. 9-145532) for stably controlling the amount of release agent applied to a very small amount (2.5 [μl / one side of recording material] or less) over a long period of time.

[0007]

According to this technique, the color reproducibility and the light transmittance of the OHP sheet are not impaired, and the adhesiveness and rewriting property of the recording material after fixing can be maintained. However, if the application amount of the release agent is regulated to such a small amount, it may be difficult to prevent the toner, which is the original purpose of applying the release agent, from adhering to the fixing rotating body.

The present invention has been made based on such a demand, and a purpose of the present invention is to stably prevent toner from adhering to a fixing rotating body for an initial period and for a long period of time, and to improve the color. It is an object of the present invention to provide a fixing device of an image forming apparatus capable of maintaining the adhesiveness and the rewriting property of a recording material after fixing without impairing the reproducibility of the OHP sheet and the light transmittance of the OHP sheet.

[0009]

SUMMARY OF THE INVENTION The present invention has a pair of fixing rotators which are pressed against each other and rotate, and a toner image formed on a recording material by an electrophotographic process is pressed against the pair of fixing rotators. In the fixing device of the image forming apparatus in which the fixing is performed by passing through the fixing rotator, the surface roughness R of the surface substrate of the fixing rotator satisfies R <200 [nmRz].

With the fixing device having such a structure, the amount of the release agent applied to the fixing rotating body is, for example, 2.5%.
[Μl / single side of recording material] Even in the following minute amounts, it is possible to reliably prevent the toner from adhering to the fixing rotating body (offset) for an initial period and for a long time. That is, the present inventor has found that the fine surface roughness of the surface of the fixing rotator, which is also the surface of the base, is related to the occurrence of offset, and furthermore, even in the case of a very small amount of the release agent applied, the offset is surely achieved. Succeeded in specifying the fine surface roughness of the base surface which can prevent the occurrence of the surface roughness.

Here, the fixing rotating body includes a shape such as a roll shape and an endless belt shape. The surface substrate of the fixing rotator refers to a portion of the surface of the fixing rotator except for agglomerates of the filler constituting the surface and irregularities due to polishing scratches.

According to the present invention, there is provided a pair of fixing rotators which are pressed against each other and rotate, and a toner image formed on a recording material by an electrophotographic process is passed through a pressing portion of the pair of fixing rotators. In the fixing device of the image forming apparatus for fixing, the initial value of the surface roughness of the surface substrate of the fixing rotating body is R ′ [nmRz], and the cumulative number of recording materials fixed by the fixing device is T [1000 sheets]. Is a fixing device used under the condition of R ′ + 1.33T <R <200 [nmRz].

[0013] With such a configuration of the fixing device, the state of the surface roughness of the surface substrate of the fixing rotating body can be indirectly known from the accumulated number of fixed recording materials. The amount of the release agent applied is, for example, 2.5 [μ
1 / single side of recording material] The product life of the fixing rotating body in which offset does not occur can be predicted even in the following minute amounts. That is, the inventor has succeeded in specifying the relationship between the surface roughness of the surface substrate of the fixing rotating body and the accumulated number of recording materials fixed by the fixing device.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to examples. Embodiment 1 FIG. 1 shows a fixing device according to this embodiment. In FIG. 1, reference numeral 1 denotes a fixing device.
It comprises a heating roll 11, a pressure roll 13 and a pressure pad 14 which are in pressure contact with the fixing roll 11 via an endless belt 12 stretched by stretching rolls 15a and 15b.

The core of the heating roll 11 has an outer diameter of 46 mm.
mm, an aluminum cylinder having an inner diameter of 40 mm. The surface of the core portion is coated with silicon rubber having a thickness of 2 mm and a hardness of 45 °, and the surface is further coated with a 2 μm thick viton rubber (trade name, manufactured by DuPont). The endless belt 12 has a thickness of 75 μm and a width of 300 μm.
mm, polyimide film with a circumference of 188 mm and a thickness of 17
It is coated with 0 μm silicon rubber. This endless belt 12 is made of stainless steel and has a diameter of 23 m.
It is wound with a tension of 49.8 N by a pressure roll of m and tension rolls 15 a and 15 b having diameters of 18 mm and 17 mm, respectively. The pressure roll 13 is pressed against the heating roll 11 via the endless belt 12 with a force of 35.3 N.

The surface roughness R of the surface substrate of the endless belt 12 is R = 100 [nmRz] (<200 [nmRz])
It is. The measurement length is 25 μm. In addition,
The reason why the measurement length is shorter than the general standard reference length (250 μm) is because the surface of the fixing rotating body is polished, and the measurement is performed while avoiding uneven portions due to the polishing. Other points are measured by the method described in the JIS Handbook. The surface roughness was measured using an atomic force microscope (SPM-9500, manufactured by Shimadzu Corporation).
FIG. 2 shows a simulated three-dimensional surface view of the measurement results. As described above, on the surface of the fixing rotator (endless belt 12), there are a convex portion due to an agglomerate of the filler constituting the surface and a concave portion due to polishing scratches generated when polishing the fixing rotator (endless belt 12). However, the roughness of the surface substrate excluding these was measured. According to the atomic force microscope, the projections due to agglomerates, the depressions due to polishing scratches and the surface substrate are distinguished because the measurement surface is displayed on the screen of the television monitor according to the electron force microscope described above. , And can be easily observed and distinguished.

As shown by the arrow in FIG. 2, the measurement is performed in the same direction as the polishing direction regardless of whether the fixing rotator is a belt-shaped or a roll-shaped as in this embodiment. FIG.
Indicates a portion to be measured (measurement unit).
FIG. 3A shows a measuring unit when the fixing rotating body is a belt-shaped one, and FIG. 3B shows a measuring unit when the fixing rotating body is a roll-shaped one. In each of the figures, the measuring unit shows only one point. However, in actuality, the recording material passing paper portion is located on both sides of the recording material in the axial direction, at three places in the center, and three places at 120 ° steps in each circumferential direction. Measurement is performed by averaging nine measurement units.

In this embodiment, there is no regulation on the surface roughness of the pressure roll 13. This is because there is no direct contact with the toner, and the offset does not matter.

The heating roll 11 and the pressure roll 13
Is heated to a predetermined temperature by heaters 8 and 9 housed therein. The fixing device to which the release agent supply device according to the present invention is applied is not limited to the configuration in which such a configuration on the pressing side is configured by an endless belt. It may be performed.

In the vicinity of the heating roll 11, a minute amount of a release agent such as silicone oil (2.5 [μl /
A release agent supply device 2 for applying to one side of a recording material] is provided.

The release agent supply device 2 includes a pickup roll (first roll) 2 whose surfaces rotate in contact with each other.
1 and a donor roll (second roll) 22. Silicon oil (hereinafter simply referred to as “oil”) is supplied to the pickup roll 21, and the oil supplied to the pickup roll 21 is supplied to the donor roll 22.
Is supplied to the surface of the heating roll 11 through
A surface layer 211 is provided on the surface of the pickup roll 21, the surface roughness is set so as to satisfy Ra ≦ 0.23 [μmRa], and at least the surface of the donor roll 22 is formed of an elastic material.

In order to uniformly control the amount of oil applied to the pickup roll 21 to an appropriate amount, a metering blade 23 is pressed with a predetermined pressure in parallel with the pickup roll. Further, an oil supply pipe 24 is provided in parallel with the pickup roll 21 and the like for replenishing the oil, a felt 25 provided in contact with the pickup roll to receive the oil, and a pickup 25 for storing excess oil. An oil pan 26 is provided below the roll 21, the metering blade 23, and the like.

More specifically, the release agent supply device 2
Comprises a pick-up roll 21 and a donor roll 22 whose surfaces rotate in contact with each other. The surface roughness Ra is 0.06 [μ
mRa] (≦ 0.23). The donor roll 22 has a hardness of 51 ° as an elastic layer formed on a stainless steel cylinder.
Silicon rubber layer (surface roughness Ra = 1.5 [μmR
a)) to form a cylinder having a diameter of 20 mm.

If the hardness Hs of the rubber covering the donor roll is too low, the toner roll 22 itself will be damaged if the pickup roll 21 is damaged by paper dust or the like. On the other hand, if it is too high, it becomes difficult to uniformly press the donor roll 22 in the axial direction of the heating or pressure roll. Therefore, the hardness Hs of the coated rubber of the donor roll is preferably 28 ° ≦ Hs ≦ 65 °. The donor roll 22 contacts the surface of the pickup roll 21 and also contacts the heating roll 11 of the fixing device 1.

The metering blade 23 for controlling the oil applied to the pickup roll 21 to a uniform and proper amount is made of silicone rubber, and is picked up so as to be pressed against the pickup roller 21 with a predetermined pressing force. The roll is disposed over the entire length in the longitudinal direction of the roll. The metalling blade 23 has a corner portion (edge portion) in which a portion pressed against the surface of the pickup roll 21 is not subjected to a process such as chamfering. The amount of penetration of the corner into the pickup roll 21 is 0.9 mm.

The material of the felt 25 for impregnating the oil supplied from the oil supply pipe 24 is Nomex felt (trade name, manufactured by Chiyoda Integra).
An oil pan 26 for receiving excess oil is provided below the oil supply pipe, the felt 25, and the metering blade 23.

The above-mentioned donor roll 22 is used for the heating roll 11.
And the pickup roll 21 is pressed and driven. Further, in this embodiment, the heating roll 11 and the pickup roll 21 are used as the same rotary drive source.

The operation of the fixing device according to this embodiment will be described below. By driving the heating roll 11 and the pickup roll 21 to rotate, the donor roll 22 rotatably installed between the heating roll 11 and the pickup roll 21 starts rotating following the rotation thereof. Then, the oil soaked in the felt 25 is first applied to the surface of the pickup roll 21. The oil 13 adhering to the surface of the pickup roll 21 is regulated to a certain amount by the surface roughness of the pickup roll 21 and the metering blade 23 to form a film having a predetermined thickness. This oil film is transferred to the surface of the donor roll 22 that comes into contact with the pickup roll 21, and is further transferred to the heating roll 11 that comes into contact with the donor roll 22.
Is applied and supplied to the surface. The amount of oil supplied to the heating roll 11 is 2.5 [μl / one side of the recording material, which is a quantity that prevents adhesion of the toner to the heating roll 11 and does not impair the adhesion to the recording material after fixing and the writing property. ]. The excess oil is returned into the oil pan 26.

The heating roller 11 coated with such an amount of the release agent forms a nip portion between the heating roller 11 and the endless belt 12, and the recording material holding the unfixed toner image in the nip portion is conveyed. Is done. When the toner passes through the nip, the fixing toner is melted by the action of the heat and the pressure, and is fixed on the recording material to form a permanent image. In this case, the heating roll 1
No. 1 defines the surface roughness of the surface substrate, and furthermore, since a film of the release agent is formed, the toner in the molten state is not offset.

Further, even if the circumferential length of the heating roll 11 changes due to thermal expansion and the heating roll 11 rotates at a constant angular velocity, the circumferential speed may change. Even in such a case, since the donor roll 22 is rotatably installed, it rotates following the changed peripheral speed, so that an error does not easily occur in the peripheral speed between the heating roll 11 and the donor roll 22. Even if the amount of supplied oil is small, phenomena such as stick clip and backlash do not occur, and as a result, defects in image quality hardly occur.

Further, since the heating roll 11 and the pickup roll 21 are driven to rotate by the same drive source, the number of parts is reduced, and such a fixing device and its releasing agent supply device can be provided at low cost. Can be.

In this embodiment, the fixing rotator (heating roll 1)
By defining the surface roughness of the surface substrate of 1), it is possible to reliably prevent offset even in a state where only a small amount of the release agent is applied, but it is necessary to specify the surface roughness. An experiment was performed. Although the surface roughness is measured by the atomic force microscope as described above, it is difficult to measure the surface roughness of the fixing rotating body during use. Therefore, an experiment was conducted to determine the relationship between the accumulated number of fixed recording materials and the surface roughness.

Next, the contents of the above experiment and the results thereof will be described.

Experiment 1 (Specification of Surface Roughness) The surface roughness of the surface substrate of the fixing rotating body was 100 to 300.
Eight types of fixing rotators up to [nmRz] were prepared, and an experiment was performed on the occurrence of offset at that time. In addition,
The configuration of the fixing device is the same as that described in the embodiment. The fixing rotator was prepared by a roll surface polishing apparatus called a sanding machine, which has been conventionally known.

[0035]

[Table 1]

Table 1 shows the results of the experiment. When an offset does not occur, a circle is provided, and when an offset occurs, a cross is provided. Thus, when the surface roughness of the surface substrate of the fixing rotator was 200 [nmRz] or more, an offset was generated, and when the surface roughness was less than 200 [nmRz], no offset was generated.

Experiment 2 (Relationship with the number of sheets fixed) The initial value R 'of the surface roughness of the surface substrate was R' = 100 [n
mRz], and the accumulated number of fixed recording materials is represented by T [100
0] and T is 10, 20, 30, 40, 50, 6
The surface roughness R of the surface substrate of the fixing rotating body at 0 and 75 was measured sequentially, and as shown in FIG. 4, a relational expression of R = R ′ + 1.33T was obtained.

According to this experiment, the surface roughness R [nmRz] of the surface substrate of the fixing rotator and the cumulative number of fixings T [1000]
Sheets] has a linear relationship, and its proportional coefficient is 1.3.
3, the life of the fixing rotator is actually measured by an atomic force microscope or the like based on the initial value R 'of the surface roughness of the surface substrate and the accumulated number of sheets fixed. You can predict without doing. For example, a fixing rotator having an initial value R ′ = 100 [nmRz] is (200-100) /1.33≒7.52, which is about 7500.
It can be seen that up to sheets, even if the amount of the release agent applied is very small, the offset can be reliably prevented and the fixing can be performed.

For comparison, the surface roughness of the surface substrate of the conventional fixing rotator was measured and plotted on the graph of FIG.
It was plotted as a ₁ ~P _4. These conventional ones all exceed 200 [nmRz], and it is understood that a small amount of the release agent may cause offset.

[0040]

As described above in detail, according to the first aspect of the present invention, even when the amount of the release agent applied to the fixing rotating body is very small, the toner adheres to the fixing rotating body. (Offset) can be reliably prevented both initially and for a long time. As a result, the amount of the release agent applied can be limited to a very small amount, so that the color reproducibility and the light transmittance of the OHP sheet are not impaired. Can be kept.

According to the second or third aspect of the present invention, the state of the surface roughness of the surface substrate of the fixing rotating body can be indirectly known from the accumulated number of recording materials fixed by the fixing device. Even if the amount of release agent applied to the rotating body is very small,
It is possible to predict the product life of the fixing rotating body in which no offset occurs.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a fixing device according to an embodiment.

FIG. 2 is a schematic diagram of a three-dimensional surface of a fixing rotating body.

FIG. 3 is a diagram illustrating a measurement unit of a fixing rotating body. .

FIG. 4 is a graph showing the relationship between the surface roughness of the surface substrate of the fixing rotating body and the number of sheets fixed.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fixing device, 11 ... Heating roll, 12 ... Endless belt (fixing rotating body), 13 ... Pressure roll, 14 ... Pressure pad, 15a, b ... Stretch roll, 2 ... Release agent supply device, 2
DESCRIPTION OF SYMBOLS 1 ... Pickup roll, 211 ... Surface layer, 22 ... Donor roll, 24 ... Oil supply pipe, 25 ... Felt,
26 ... Oil pan measuring unit Fixing rotating body (belt shape) (a)

Claims (2)

[Claims] 1. An image which has a pair of fixing rotators which are pressed against each other and rotate, and which is fixed by passing a toner image formed on a recording material by an electrophotographic process to a pressing portion of the pair of fixing rotators. In the fixing device of the forming device, the surface roughness R of the surface substrate of the fixing rotating body is R <200.
A fixing device characterized by [nmRz]. 2. An image which has a pair of fixing rotators which are pressed against each other and rotate, and which is fixed by passing a toner image formed on a recording material by an electrophotographic process to a pressing portion of the pair of fixing rotators. In the fixing device of the forming device, the initial value of the surface roughness of the surface substrate of the fixing rotator is R ′.
[NmRz], the cumulative number of recording materials fixed by the fixing device is T
A fixing device characterized in that R '+ 1.33T <200 [nmRz] as [1000 sheets].