JPS61296377A - Fixing device - Google Patents

Abstract

PURPOSE:To obtain an excellent image without soiling a backup roller by using a PFA and a specific non-ground silicone rubber as the coat material of a heat roller and the backup roller, respectively. CONSTITUTION:The PFA and the injection-molded non-ground silicone rubber with a rubber hardness 40 deg.HS or below are used as the coat material of the heat roller and the backup roller, respectively. In terms of a fixing device, the set temperature of the heat roller at fixing is set to 170 deg.C or above, and a pressure load holding a transfer paper is set to 1.3kg/cm or below. Thus the roller will not develop toner soil for many hours, and can stand the use without cleaning and oil.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a fixing device for heating and fixing an unfixed image, such as a powder image, to an image support such as paper, and relates to an electrophotographic recording device, an intelligent copier, etc. The present invention relates to a fixing device that can be applied to image forming apparatuses such as laser printers and copying machines.

[Prior Art] Conventionally, an unfixed image (hereinafter referred to as a toner image) formed by an image forming apparatus using electrophotography or the like is fixed onto an image support such as paper (hereinafter referred to as transfer paper). The fixing device uses a heat fixing method.

In this type of heat fixing, a transfer paper carrying a toner image is conveyed and fixed between a heat roller equipped with a heat source and a backup roller in pressure contact with the heat roller, which is often used.

FIG. 7 shows a sectional view of a general heating roller type fixing device. There is a cylindrical metal roller 12 having a heating means such as a heater 11 inside, a heat roller A having a surface coating layer 13 such as FEPSPTFE on its surface, and a silicon core 20 on the circumferential surface opposite thereto. There is a backup roller B that is formed and polished by wrapping rubber 21 or the like around it. During fixing, the heat roller A and the backup roller B are in pressure contact and are rotated in the direction of the arrow by power. The transfer paper P conveyed on a guide plate 31 provided on the right side of the fixing device is held and conveyed between a heat roller A and a backup roller B, during which time the toner is fused onto the transfer paper P. The fixed image is output from the fixing device.

The commonly used heat roller A has a thickness of approximately 2 to 5 m.
A pipe of AQ of about m is used as the core metal 12, and 25 to 3
The coating layer 13 is coated with a fluororesin having a thickness of 0 μm. Also, backup roller B is approximately 20
The core metal 20 is made of SUS having a diameter of mm, and the core metal 20 is injection-molded and polished so that its peripheral surface is coated with silicone rubber 21 to a thickness of about 5 mm.

When copying is performed for a long time using such a fixing device, toner stains on the roller often occur. The stains on the heat roller during fixing become toner stains on the surface of the transfer paper, and the stains on the backup roller B that is pressed against the heat roller A, resulting in stains on the back surface of the transfer paper. Conventionally, as a countermeasure against dirt on the backup roller, for example, as shown in FIG. 7, a cleaning mechanism in which a cleaning felt 22 is impregnated with silicone oil having an appropriate viscosity is attached to the heat roller or the backup roller to improve mold release properties. At the same time, the attached toner is cleaned. It has also been attempted to coat the backup roller with a substance that exhibits good mold releasability.

[Problems to be Solved by the Invention] Even with a conventional fixing device having a cleaning mechanism, for example, when used for a long time, the cleaning mechanism gets dirty and the backup roller gets dirty, which deteriorates the copy quality. could not be avoided. SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device that can produce good copy images without staining not only the heat roller but also the backup roller, regardless of whether or not a cleaning mechanism is provided.

[Means for Solving the Problems] The present invention aims to achieve the above object, and the present invention involves sandwiching an image support between a heat roller and a back unroller, heating and fixing the image support, and discharging the image support. To provide a fixing device according to the present invention, characterized in that the coating material of the heat roller is PFA, and the backup roller is made of injection molded non-abrasive silicone rubber with a rubber hardness of 40°I-IS or less. It is.

That is, the present invention uses PF with good mold release properties as a heat roller.
A (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) is used as the coating material, and the backup roller is made by injection molding silicone rubber (HTV or RTV) around the core metal, making it a non-abrasive roller that prevents toner from accumulating. (smooth surface).

In the fixing device according to the present invention, the set temperature of the heat roller during fixing is set to 170°C or higher, and the pressing load for nipping the transfer paper (hereinafter referred to as nip pressure) is 1.3 kg/
By setting it below Cm, the effect of the present invention becomes even more remarkable.

[Function] Figure 2 shows the relationship between the coating material of the heat roller and the toner adhesion rate, which was conducted by the inventor of the present invention.
Copying was measured under the conditions of a heat roller temperature of 185° C. and a line speed of 140 mm/sec, and PFA showed better results than PTFE (polytetrafluoroethylene).

Figure 3 shows the offset range (the solid line range is the range where offset occurs) with respect to the heat roller temperature for the heat roller coating materials PFA and PTFE.
The experiment was conducted by maintaining the temperature difference between the backup roller and the heat roller within 10°C. The results showed that the offset phenomenon is less likely to occur in PFA even at high temperatures.

Figure 4 shows the relationship between the heat roller temperature and the amount of toner adhesion when the coating material of the heat roller is PFA.The amount of toner adhesion at 185°C is approximately 120% of the amount of toner adhesion at 210°C. It was obtained through experiments that

Figure 5 shows the relationship between the nip pressure and the toner adhesion rate to the heat roller when the heat roller coating material is PFA and the heat roller temperature is constant. Experiments have shown that the toner adhesion rate tends to increase.

If the coating material of the heat roller is PFA and the backup roller is made of silicone rubber as described above, the toner stains on the heat roller will migrate to the backup roller side, and the toner stains on the backup roller will be larger than the toner stains on the heat roller. becomes much larger.

Figure 6 shows the relationship between the toner transfer rate from the backup roller to the transfer paper and the nip pressure.
, 3 kg/cm or less, the toner transfer rate decreases and experimental results show that it is preferable.

Furthermore, due to the roughness of the roller surface, toner accumulates in the recesses of the backup roller, and toner adhesion to the recesses tends to further develop into roller stains. Conventionally, backup rollers have been molded and then polished. However, it is not easy to obtain a good smooth surface by polishing a rubber material, and if you examine the surface under magnification, you will often find that it has serrated irregularities. It has been experimentally found that the backup roller as it is is less likely to become dirty.

In addition, if the backup roller is not polished, processing constraints on rubber hardness are removed, and comparative experiments were conducted with backup rollers that were simply molded for various hardnesses. If the rubber hardness is low, the nip width will be wide for the same nip pressure (so the same line speed,
Under the same roller temperature conditions, it is possible to lower the nip pressure by lowering the rubber hardness.

In the experiment shown in FIG. 4, when the rubber hardness of the backup roller was lowered and the nip pressure was correspondingly lowered, the amount of toner adhering to the heat roller tended to decrease.

Based on these experimental results, the inventors of the present invention have provided a fixing device that reduces toner stains on the heat roller and backup roller and allows good fixing of toner images onto transfer paper. must satisfy the following four conditions.

(1) There is little toner adhesion to the heat roller.

(2) Good toner transfer from the heat roller to the backup roller.

(3) It is difficult to accumulate toner on the backup roller.

(4) Appropriate toner transferability from the backup roller to the transfer paper (back side).

That is, by using PFA as the coating material of the heat roller, condition (1) is satisfied from FIG.

Condition (2) is also satisfied by using PFA as the coat material of the heat roller and silicone rubber as the backup roller.

Furthermore, silicone rubber is injection molded as a coating layer for the backup roller, and condition (3) is achieved by not performing post-processing such as polishing.
) is satisfied.

In addition, the rubber hardness of the backup roller should be 40°HS or less.
The fourth rule is to keep the nip pressure at 1.3 kg/0m or less.
From the figure and Figure 5, condition (1) is not met.

Similarly, setting the nip pressure to 1.3 kg/0m or less satisfies condition (4) from FIG.

It has been experimentally revealed that these conditions mentioned above have a mutual correlation and have a synergistic effect to obtain good results.

In addition, PTFE and FEP used in this specification below.

The structural formula etc. of PFA are shown.

[Example 2] Comparative experiments were conducted under eight fixing conditions described below.

The test was carried out by modifying a copying machine U-B ix3300 MR (manufactured by Konishiroku Photo Industry Co., Ltd.), and attaching separately manufactured heat rollers and backup rollers to the roller fixing section. However, the outer diameter of the rollers is 40mm.
φ, and in order to clarify the comparison of cleaning effects, the cleaning mechanism was removed and a comparison test was conducted under the following common conditions.

1. Copy speed: 33 sheets/min (using A4 paper) 2. Conveyance speed: 220 mm/sec 3. Developer: Contains 7% by weight of carbon black dispersed in styrene acrylic resin and is hydrophobic. A mixture of 5% by weight of toner having an average particle diameter of 12 μm to which 0.4% by weight of silica was externally added and 95% by weight of a carrier consisting of ferrite particles was used.

(1) FIG. 1 shows a sectional view of a heat roller and a backup roller according to the present invention. Heat roller A has an outer diameter of 40
An Aρ hollow cylinder with a wall thickness of t=5 mm is used as the core metal 12A, and a layer of PFA (Mitsui Fluorochemical product MP-10) with a layer thickness of t=25 to 30 μm is applied to the upper surface via an adhesive undercoat layer brimer. ) was coated and fired to form a coating layer 13A.

Backup roller B was made by injection molding silicone rubber (Shin-Etsu Chemical Co., Ltd.) having a thickness of 5 mm on the circumferential surface of a core bar 20A made of SUS with a diameter of 30 mm.

The elastic layer 21A had a rubber hardness of 35°I (S).

This backup roller B has been injection molded and has not been subjected to any post-processing such as polishing. Therefore, the inner surface of the mold was finished with a mirror finish, and special care was taken to avoid eccentricity during molding.

(1-1) The fixing temperature on the heat roller surface of the heat roller and backup roller explained in (1) is 200℃.
Set the nip pressure (linear pressure) to 1 kg/cm.
I adjusted it so that it was and tested it.

A test was conducted by setting the heat roller and backup roller described in (1-201) so that the fixing temperature on the heat roller surface was 160°C, and adjusting the nip pressure (linear pressure) to 1 kg/cm. .

(1-3) The heat roller and backup roller explained in (1) are heated to a temperature of 200
°C, set the nip pressure (linear pressure) to 1,
The weight was adjusted to 5 kg/cm and tested.

(L-4) The heat roller and backup roller explained in (1) are heated to a temperature of 160
℃, and set the nip pressure (linear pressure) to 1,5
kg/cm, and a test was conducted.

(2-1) The same heat roller as explained in (1) was used. For backup roller, 30mm
Rubber hardness 35°H is applied to the circumferential surface of the core metal made of φ SUS material.
An elastic layer of S was provided, and the peripheral surface was polished to a diameter of 40 mm.

A test was conducted using this roller at a fixing temperature of 200° C. and a nip pressure (linear pressure) of 1 kg/cm.

(2-2) The same heat roller as explained in (1) was used. For backup roller, 30mm
Rubber hardness 45°H is applied to the circumferential surface of the core metal made of φ SUS material.
S silicone rubber was injection molded to a thickness of t=5 mm, and no post-processing was performed.

A test was conducted using this roller at a fixing temperature of 2QO<0>C and a nip pressure (linear pressure) of 1.5 kg/cm.

(2-3) The same heat roller as explained in (1) was used. For backup roller, 30a+
Rubber hardness 45° on the circumferential surface of the core metal made of mφ SUS material.
An elastic layer of HS was provided, and the peripheral surface was polished to a diameter of 40 mm. Using this roller, a test was conducted at a fixing temperature of 200° C. and a nip pressure (linear pressure N, 5 kg/am).

(3-],) A heat roller with a PTF'E coating layer was used. The test was otherwise conducted under exactly the same conditions as (1-1).

The durability test of 10,000 copies of A4 paper was conducted under the above conditions and the results were as follows.

(t-i) Even after 10,000 copies, no significant toner stains were observed on the roller surface, and no difference in copy image quality was observed from the initial level.

(1-2) Toner stains began to be observed on the roller surface after about 50,000 copies. However, the toner staining did not progress, and even after 100,000 copies, no difference in copy image quality was observed compared to the initial copy.

(1-3) Toner stains began to be observed on the roller surface after about 80,000 copies. However, even after 100,000 copies, the toner staining did not progress.

(1-4) Toner stains began to be observed on the roller surface after about 40,000 copies, and the toner stains progressed slowly until offset occurred at 60,000 copies. However, when a cleaning mechanism was added and the test was performed again, the same result as (+-1) was observed.

(2-1) Toner stains began to be observed on the roller surface after about 20,000 copies, and the toner stains gradually progressed until offset occurred at 30,000 copies.

(2-2) Toner stains began to be observed after around 30,000 copies. Toner staining progressed slowly, and offset occurred after 50,000 copies.

(2-3) Toner stains began to be observed after 10,000 copies, and the toner stains progressed until offset occurred at 20,000 copies.

(3-1) Toner stains became visible after about 8,000 copies, and the toner stains progressed until offset occurred after 20,000 copies.

[Effects of the Invention] As is clear from the comparison test, the fixing device using the roller according to the present invention has excellent fixing performance in terms of durability, and the roller does not become stained with toner over a long period of time. Therefore, a fixing device that can be used satisfactorily even when it is cleaning-free and oil-free has been developed.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a roller portion according to the present invention. FIGS. 2 and 3 are characteristic comparison diagrams when the roller coating layer is made of PFA and PTFE. FIG. 4 is a graph showing the relationship between fixing temperature and toner adhesion amount. FIG. 5 is a graph showing the relationship between nip pressure and toner adhesion rate. FIG. 6 is a graph showing the relationship between nip pressure and toner transfer rate. FIG. 7 is a sectional view of a conventional roller fixing device. 12A... Core metal 13A... Covering layer 20A
... Core metal 21A ... Elastic layer A ... Heat roller B ... Backup roller Applicant: Konishiroku Photo Industry Co., Ltd. Figure 5 Figure 6

Claims (2)

[Claims] (1) In a fixing device in which an image support material is sandwiched between a heat roller and a backup roller, heat-fixed and discharged, the coat material of the heat roller is PFA, and the backup roller has a rubber hardness of 40°HS. A fixing device characterized by being made of the following injection molded non-abrasive silicone rubber. (2) The set temperature of the heat roller is 170°C or higher,
2. The fixing device according to claim 1, wherein the pressure bonding load for sandwiching the image supporting material is 1.3 kg/cm or less.