JPH11174888A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent irregular fixing all over a sheet and to obtain an image showing excellent transparency by controlling the hardness of a first pressurizing roller to be smaller than the hardness of a heating roller and controlling the amt. of an oil to be applied on the heating roller to a specified amt. or smaller. SOLUTION: The heating roller 50 and a first pressurizing roller 60 are arranged so as to satisfy Hr=Hh/Hp>1, wherein Hh and Hp are hardness of the heating roller and the pressurizing roller, respectively, and Hr is the hardness ratio of these rollers. Namely, the hardness Hp of the first pressurizing roller 60 is controlled to be smaller than the hardness Hh of the heating roller 50. Further, an oil coating roller 94 to apply an oil on the surface of the heating roller 50 is disposed on the outer surface of the heating roller 50 so as to assist peeling of a sheet S from the heating roller 50. The oil coating roller 94 is used to apply a release agent such as a silicone oil by <=0.0063 mg/cm<2> on the circumferential surface of the heating roller 50.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet (plain paper, coated paper, OHP (overhead projector) sheet, glossy paper, glossy film, postcard, etc.) in an image forming apparatus such as a printer, a facsimile, a copying machine or the like. Or a fixing device for fixing a toner image carried on an envelope or the like onto a sheet. In particular, the present invention relates to a fixing device in which two pressure rollers are pressed against one heating roller.

[0002]

2. Description of the Related Art Conventionally, a fixing device as shown in FIG. 8 is known in which two pressure rollers are sequentially pressed against one heating roller from the upstream side in the rotation direction. (Japanese Patent Publication No. 58-21262).

In FIG. 1, reference numeral 1 denotes a heating roller, which is driven to rotate in a direction indicated by an arrow by a drive motor (not shown).

On the outer peripheral surface of the heating roller 1, pressure rollers 2, 3 are arranged. The pressure rollers 2 and 3 are supported by the metal plate 4 and are pressed against the heating roller 1 to be driven to rotate.

The heating roller 1 is covered with hard rubber,
The pressure roller 2 is covered with softer rubber, and the pressure roller 3 is covered with rubber harder than the pressure roller 2.

[0006] A sheet (not shown) is supplied to a pressing portion between the heating roller 1 and the pressing roller 2 in a state where the toner image is attached to the upper surface thereof. The toner image is fused to the sheet by passing through the pressing portion with the roller 3.

According to the above publication, the peripheral speed of the pressure roller 3 is higher than the peripheral speed of the pressure roller 2 due to the above-described configuration, whereby a tension is applied to the sheet between the pressure rollers 2 and 3. Works to obtain a contact time longer than the contact time between the sheet and the heating roller in the pressing portion composed of one heating roller and one pressure roller, so that the toner image is effectively fused to the sheet. Can be achieved at reduced operating temperatures and applied pressures.

In general, a heating roller and a pressing roller pressed against the heating roller are provided, and the toner is heated and fused onto the sheet by passing the sheet with the toner between the two rollers. In the fixing device, the sheet may be wound around the surface of the heating roller due to the adhesive force of the melted toner. In particular, when a color image is to be obtained by fusing and fixing a multi-color toner image superimposed on a sheet, it is necessary to sufficiently heat and melt-mix the superposed multi-color toner to obtain transparency. As a result, the sheet easily winds around the heating roller.

Therefore, conventionally, a large amount of oil (for example, 0.015873 mg / cm ² or more) is applied to the surface of the heating roller to prevent the sheet from being wound around the heating roller.

[0010] The above publication does not describe oil application.

[0011]

According to the conventional fixing device shown in FIG. 8, since the peripheral speed of the pressure roller 3 is higher than the peripheral speed of the pressure roller 2, the leading end of the sheet is pressurized. When the sheet passes through the pressure portion between the roller 2 and the heating roller 1 and reaches the pressure portion between the pressure roller 3 and the heating roller 1, tension acts on the sheet between the pressure rollers 2 and 3. The sheet comes into good contact with the heating roller 1, but conversely, the tension does not act until the leading edge of the sheet reaches the pressure portion between the pressing roller 3 and the heating roller 1, and therefore,
The sheet will not come into good contact with the heating roller 1.

That is, according to the conventional apparatus shown in FIG. 8, the toner on the sheet is separated between the time when the leading edge of the sheet reaches the pressure portion between the pressing roller 3 and the heating roller 1 and the time thereafter. The amount of heat applied to the sheet significantly differs, and as a result, there is a problem that unevenness in fixing (unevenness in fixing strength, coloring, transparency, etc.) occurs between the leading end portion and the central portion of the sheet. The same problem occurs at the trailing end of the sheet, and during the period until the trailing end of the sheet passes through the pressing portion between the pressure roller 2 and the heating roller 1 and the subsequent period, The amount of heat applied to the toner is significantly different, and as a result, fixing unevenness occurs at the center portion and the rear end portion of the sheet.

On the other hand, the present inventor has discovered that applying a large amount of oil to the surface of the heating roller impairs the transparency of the toner image. The reason is that when a large amount of oil is applied to the surface of the heating roller, the toner is heated and melted while being pressed through the large amount of oil. This is because the smoothness of the toner surface after fixing is impaired due to the fact that the smoothness of the heating roller surface is not reflected on the toner surface, and irregular reflection is caused,
it is conceivable that.

An object of the present invention is to solve the above-mentioned problems and to provide a fixing device capable of obtaining an image having excellent transparency without causing fixing unevenness over the entire sheet. .

[0015]

According to a first aspect of the present invention, there is provided a fixing device comprising: a heating roller having a heat source therein; and a heating roller which is sequentially pressed against the heating roller from an upstream side in a rotational direction thereof. A fixing device having a first pressure roller and a second pressure roller, wherein the hardness of the first pressure roller is configured to be smaller than the hardness of the heating roller, and the amount of oil applied to the heating roller is 0.0063 mg / cm. ² or less.

[0016]

[Effects] As described above, the present inventor has discovered that applying a large amount of oil to the surface of the heating roller impairs the transparency of the toner image, and further studies based on this discovery. As a result, it was found that good transparency was obtained by setting the amount of oil applied to the heating roller to 0.0063 mg / cm ² or less.

According to a first aspect of the present invention, there is provided a fixing device including a heating roller having a heat source therein, and first and second pressure rollers which are sequentially pressed against the heating roller from an upstream side in a rotation direction. The hardness of the first pressure roller is configured to be smaller than the hardness of the heating roller, and the amount of oil applied to the heating roller is 0.0063 mg /
Since the configuration is set to not more than cm ^{2, the} following operational effects can be obtained with this device.

That is, if the hardness of the first pressure roller is configured to be smaller than the hardness of the heating roller, the shape of the pressure contact portion (first nip portion) between the heating roller and the first pressure roller is reduced. When viewed from the axial direction, the first pressure roller side has a concave shape, and the sheet that has passed through the first nip portion is curled in a direction in which it is wound around the heating roller including its leading end. For this reason, the leading edge of the sheet is discharged from the first nip portion in a state of being in contact with or close to the heating roller regardless of the presence or absence of toner, and a van der Waals is provided between the sheet and the heating roller. Since the force and the mirror image force are applied, the sheet is easily wound around the heating roller from the leading end.

Further, when the amount of oil applied to the heating roller is 0.0063 mg / cm ² or less, the sheet is more easily wound around the heating roller.

As described above, when the sheet passing through the first nip portion is wound around the heating roller from the leading end, if toner is present at the leading end of the sheet, the melting of the toner proceeds at once, and the heating is performed. A more stable contact state with the roller can be obtained.

Then, while maintaining the heated state of the sheet, the sheet moves toward a pressure contact portion (second nip portion) between the heating roller and the second pressure roller, and the toner is conveyed by the second nip portion while the toner is conveyed. Further, the sheet is heated and pressed to be completely fixed on the sheet.

As described above, the toner image fixed on the sheet becomes an image having excellent transparency because the amount of oil applied to the heating roller is 0.0063 mg / cm ² or less.

As described above, according to the fixing device of the first aspect, an even fixing state can be obtained over the entire sheet, and an image having excellent transparency can be obtained.

[0024]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view showing an essential part of an example of an image forming apparatus using the fixing device according to the present invention, FIG. 2 is an enlarged partial end view taken along the line II-II in FIG. 1, and FIG. It is a partially omitted side view showing one embodiment of an apparatus.

First, an image forming apparatus will be described with reference to FIGS.

This image forming apparatus is designed for yellow, cyan,
This is an apparatus that can form a full-color image using a developing device using magenta and black toners.

In FIG. 1, reference numeral 10 denotes a photosensitive member, which is driven to rotate in a direction indicated by an arrow in FIG.

Around the photoreceptor 10, along a rotation direction thereof, a charging roller 11 as a charging unit, a developing roller 20 (Y, M, C, K) as a developing unit, an intermediate transfer device 30, and a cleaning unit Means 12 are arranged.

The photosensitive member 10 has a cylindrical conductive substrate 10a.
(See FIG. 2) and a photosensitive layer 10b formed on the surface thereof.

The charging roller 11 contacts the outer peripheral surface of the photoreceptor 10 to uniformly charge the outer peripheral surface. An outer peripheral surface of the uniformly charged photoconductor 10 is subjected to selective exposure L according to desired image information by an exposure unit (not shown), and an electrostatic latent image is formed on the photoconductor 10 by the exposure L. You.

This electrostatic latent image is developed with toner applied by a developing roller 20.

The developing rollers 20Y for yellow, 20C for cyan, 20M for magenta, and 20M for black
K is provided. These developing rollers 20Y, 20
C, 20M, and 20K can selectively contact the photoconductor 10, and when they come into contact, any one of yellow, cyan, magenta, and black is applied to the surface of the photoconductor 10. Then, the electrostatic latent image on the photoconductor 10 is developed.

The developed toner image is transferred onto an intermediate transfer belt 36 described later.

After the transfer, the cleaning means 12
A cleaner blade 13 for scraping off the toner remaining on and adhering to the outer peripheral surface of the photoreceptor 10, and a receiving unit 14 for receiving the toner scraped off by the cleaner blade 13
And

The intermediate transfer device 30 includes a driving roller 31 and
Four driven rollers 32, 33, 34, 35 and an endless intermediate transfer belt 36 stretched around these rollers.
And

The drive roller 31 rotates at substantially the same peripheral speed as the photosensitive member 10 because a gear (not shown) fixed to an end of the drive roller 31 meshes with a drive gear (not shown) of the photosensitive member 10. Driven, and thus the intermediate transfer belt 3
6 is driven to circulate at substantially the same peripheral speed as the photosensitive member 10 in the direction of the arrow shown in the figure.

The driven roller 35 is disposed at a position where the intermediate transfer belt 36 is pressed against the photoreceptor 10 by its own tension between the driven roller 35 and the drive roller 31. In the primary transfer section T1
Are formed. The driven roller 35 is disposed near the primary transfer portion T1 on the upstream side in the circulation direction of the intermediate transfer belt 36.

The driving roller 31 has an intermediate transfer belt 36
A voltage (primary transfer voltage) V1 is applied to a later-described conductive layer 36a of the intermediate transfer belt 36 via the electrode roller 37.

The driven roller 32 is a tension roller, and urges the intermediate transfer belt 36 in the direction of its tension by urging means (not shown).

The driven roller 33 is a backup roller that forms the secondary transfer portion T2. A secondary transfer roller 38 is opposed to the backup roller 33 via an intermediate transfer belt 36. The secondary transfer roller 38
It can be moved toward and away from the intermediate transfer belt 36 by a contacting / separating mechanism (not shown). A secondary transfer voltage V2 is applied to the secondary transfer roller 38.

The driven roller 34 is a backup roller for the belt cleaner 39. Belt cleaner 39
Is a cleaner blade 39 which comes into contact with the intermediate transfer belt 36 and scrapes off the toner remaining and adhering to the outer peripheral surface thereof.
a, and a receiving portion 39b for receiving the toner scraped off by the cleaner blade 39a. The belt cleaner 39 can be moved toward and away from the intermediate transfer belt 36 by a contact / separation mechanism (not shown).

As shown in FIG. 2, the intermediate transfer belt 36 is a multilayer belt having a conductive layer 36a and a resistance layer 36b formed on the conductive layer 36a and pressed against the photosensitive member 10. ing. The conductive layer 36a is formed on an insulating substrate 36c made of a synthetic resin, and the primary transfer voltage V1 is applied to the conductive layer 36a via the above-described electrode roller 37. The conductive layer 36a is exposed in a strip shape by removing the resistive layer 36b in a strip shape at the side edge of the belt 36, and the electrode roller 37 comes into contact with the exposed portion.

In the course of circulating the intermediate transfer belt 36, the toner image on the photoreceptor 10 is transferred onto the intermediate transfer belt 36 in the primary transfer portion T1, and the intermediate transfer belt 3
The toner image transferred onto the sheet 6 is transferred to a sheet S such as a sheet supplied between the secondary transfer roller 38 and the secondary transfer section T2.

The sheet S is fed from a sheet feeding device (not shown), and is supplied to the secondary transfer portion T2 at a predetermined timing by a gate roller pair G.

The sheet S to which the toner image has been transferred in the secondary transfer section T2 passes through a fixing device 40, which will be described in detail later, where the toner image is fixed, and is conveyed to a predetermined position.

The operation of the entire image forming apparatus as described above is as follows.

(I) When a print command signal (image formation signal) from a host computer or the like (not shown) (not shown) is input to the control unit of the image forming apparatus,
Photoconductor 10, developing roller 20, and intermediate transfer belt 3
6 is driven to rotate.

(Ii) The outer peripheral surface of the photoconductor 10 is uniformly charged by the charging roller 11.

(Iii) The outer peripheral surface of the uniformly charged photoreceptor 10 is subjected to selective exposure L according to image information of the first color (for example, yellow) by an exposure unit (not shown), so that a yellow electrostatic charge is produced. A latent image is formed.

(Iv) Only the developing roller 20Y for the first color (for example, yellow) comes into contact with the photoconductor 10, whereby the electrostatic latent image is developed, and the toner image for the first color (for example, yellow) is formed. Is formed on the photoconductor 10.

(V) A primary transfer voltage V1 having a polarity opposite to the charging polarity of the toner is applied to the intermediate transfer belt 36, and the toner image formed on the photoconductor 10 is transferred to the primary transfer section, The toner image is transferred onto the intermediate transfer belt 36 at a pressure contact portion T1 with the intermediate transfer belt 36. At this time,
The secondary transfer roller 38 and the belt cleaner 39 are separated from the intermediate transfer belt 36.

(Vi) After the toner remaining on the photoreceptor 10 is removed by the cleaning means 12, the photoreceptor 10 is neutralized by static elimination light from a static elimination means (not shown).

(Vii) The above operations (ii) to (vi) are repeated as necessary. That is, the second color, the third color, the fourth color,
Is repeated on the intermediate transfer belt 36 to form a toner image corresponding to the content of the print command signal.

(Viii) Sheet S at predetermined timing
Is supplied, and immediately before or after the leading end of the sheet S reaches the second transfer portion T2 (that is, at the timing when the toner image on the intermediate transfer belt 36 is transferred to a desired position on the sheet S). When the transfer roller 38 is pressed against the intermediate transfer belt 36 and the secondary transfer voltage V2 is applied, the toner image on the intermediate transfer belt 36 (basically, a full-color image in which four color toner images are superimposed) is formed on a sheet. Transferred to S. Further, the belt cleaner 39 comes into contact with the intermediate transfer belt 36, and the toner remaining on the intermediate transfer belt 36 after the secondary transfer is removed.

(Ix) The toner image is fixed on the sheet S by passing the sheet S through the fixing device 40, and then the sheet S is conveyed to a predetermined position (for example, outside the apparatus).

According to the above-described image forming apparatus, the sheet S to which the full-color toner image on which the four-color toner images are basically superimposed is transferred is supplied to the fixing device 40.

Next, the fixing device 40 will be described.

In FIG. 3, reference numeral 41 denotes a fixing device frame, 50 denotes a heating roller, 60 denotes a first pressure roller, and 70 denotes a second pressure roller.

The heating roller 50 has a heat source 51 at its center.
And has an elastic layer 52 on its surface. Therefore, the heating roller 50 is an elastic roller as a whole. The heating roller 50 is rotatably supported by the side plate 42 of the frame 41 so as to be immovable in the axial direction and the radial direction, and is rotatably driven in a direction indicated by an arrow by driving means (not shown). I have.

The first pressure roller 60 has a metal shaft 61.
And a roller portion 62 fixed thereto, and an elastic layer 62a formed on the surface thereof. Therefore, the first pressure roller 60 is an elastic roller as a whole. The first pressure roller 60 has two ends of a shaft 61 bearing 6.
Lever 64, 64 via 3, 63 (only one shown)
(Only one shown) is rotatably supported. One end of the lever 64 is rotatably supported on the side plate 42 of the frame 41 by a shaft 64a, and a tension spring 65 as a pressing means is provided between the other end 64b and the frame 41. Since the shaft 61 of the first pressure roller 60 is supported at an intermediate portion of the lever 64, the tension spring 65 plays a role as a pressure means. Therefore, the first pressure roller 60 is moved by the action of the tension spring 65 to the heating roller 5.
0, and rotates following the heating roller 50.

The second pressure roller 70 has a metal shaft 71.
And a roller portion 72 fixed thereto, and an elastic layer 72a formed on the surface thereof. Therefore, the second pressure roller 70 is an elastic roller as a whole. The second pressure roller 70 has both ends of a shaft 71 rotatably supported by levers 74, 74 (only one is shown) via bearings (not shown). One end of the lever 74 is a shaft 74
As shown in FIG. 3A, the frame 41 is rotatably supported by the side plate 42 of the frame 41, and a tension spring 75 is provided between the other end 74b and the frame 41 as a pressing means. Since the shaft 71 of the second pressure roller 70 is supported at an intermediate portion of the lever 74, the tension spring 75 plays a role as pressure means. Therefore, the second pressure roller 70 is pressed against the heating roller 50 by the action of the tension spring 75 and rotates following the heating roller 50. The second pressure roller 70 is in pressure contact with the heating roller 50 downstream of the first pressure roller 60 in the rotation direction of the heating roller 50.

The heating roller 50 and the first
The pressing roller 60 is configured so as to satisfy the condition of Hr> 1 when the respective hardnesses are Hh and Hp and the hardness ratio between the two is Hr = Hh / Hp. That is, the configuration is such that the hardness Hp of the first pressure roller 60 is smaller than the hardness Hh of the heating roller 50.

On the outer peripheral surface of the heating roller 50, an oil application roller 94 for applying oil to the surface of the heating roller 50 is provided in order to assist the peeling of the sheet S from the heating roller 50. The oil application roller 94 is rotatably supported by a support member 94a attached to the frame 41.
And is driven to rotate. The oil application roller 94 is
The peripheral surface of the heating roller 50, a release agent such as silicone oil, is applied in the range of 0.0063mg / cm ² or less (including the case where 0 mg / cm ^2, i.e. not coated).

As described above, if the amount of oil applied to the heating roller 50 is relatively small, the sheet S
The sheet S that has passed through the pressing portion between the heating roller 50 and the second pressure roller 70 is easily wound around the heating roller 5.
There is a possibility that the film may be wound around the heating roller 50 without being separated from zero.

Therefore, in this embodiment, a second peeling claw 92 for peeling the sheet S from the heating roller 50 is arranged on the outer peripheral surface of the heating roller 50 on the downstream side of the second pressure roller 70. is there.

In this embodiment, a guide body 80 is provided between the first pressure roller 60 and the second pressure roller 70, and the first pressure roller 60 has Although the separation claw 91 is provided, the guide body 80 and the first separation claw 91 may not necessarily be provided for the reason described later.

The above-described fixing device is disposed, for example, after the second transfer portion T2 in the above-described image forming apparatus, and operates as follows.

With the operation of the image forming apparatus, the heating roller 50 is heated by the heat source 51, and the first and second pressure rollers 60 and 70 are pressed against the heating roller 50.
As the heating roller 50 is driven to rotate in the direction of the arrow shown in the figure, the first and second pressure rollers 60 and 70 are driven to rotate.

The sheet S is supplied between the heating roller 50 and the first pressure roller 60 in a state where the toner image has been transferred to the upper surface thereof.

The sheet S thus supplied is firstly
The pressure contact portion between the heating roller 50 and the first pressure roller 60 (first
The toner is wound around the heating roller 50 while being conveyed by the nip portion N1, and the toner is heated and pressed to be temporarily fixed.

Next, the sheet S is maintained at the heated state, and then faces the pressure contact portion (second nip portion) N2 between the heating roller 50 and the second pressing roller 70, and the second nip portion N
The toner is further heated and pressed while being conveyed by the fixing roller 2, and is completely fixed.

The sheet S on which the toner image has been fixed is thereafter
It is peeled off from the heating roller 50 and is conveyed to a predetermined position via the curl correcting roller 93.

According to the fixing device of this embodiment, the following operation and effect can be obtained.

(A) The hardness Hp of the first pressure roller 60 is configured to be smaller than the hardness Hh of the heating roller 50, and the amount of oil applied to the heating roller 50 is 0.006.
Since the configuration is set to 3 mg / cm ² or less, the following operational effects can be obtained with this device.

That is, if the hardness Hp of the first pressing roller 60 is configured to be smaller than the hardness Hh of the heating roller 50, as shown schematically in FIG.
(First nip) N1 between the pressure roller 60 and the first pressure roller 60
The shape of the first pressure roller 6 as viewed from the axial direction of the roller is
The sheet S that has passed through the first nip portion N1 has a shape that is concave on the 0 side, and is curled in a direction in which the sheet S including the leading end Sa is wound around the heating roller 50. For this reason, the leading end Sa of the sheet S is discharged from the first nip portion N in a state of being in contact with or close to the heating roller 50 regardless of the presence or absence of the toner. Since a van der Waals force and a mirror image force act between the sheets, the sheet S is easily wound around the heating roller 50 from the leading end Sa.

Further, when the amount of oil applied to the heating roller 50 is 0.0063 mg / cm ² or less,
The sheet S is more easily wrapped around the heating roller 50.

As described above, when the sheet S passing through the first nip portion N1 is wound around the heating roller 50 from the leading end Sa, if toner is present at the leading end of the sheet S, the toner is melted. At a glance, a more stable contact state with the heating roller 50 can be obtained.

Then, while the heated state of the sheet S is maintained, the sheet S is directed to a pressure contact portion (second nip portion) between the heating roller 50 and the second pressure roller 70, and is conveyed by the second nip portion. The toner is further heated and pressed to be completely fixed on the sheet S.

As described above, the toner image fixed on the sheet S becomes an image having excellent transparency because the amount of oil applied to the heating roller 50 is 0.0063 mg / cm ² or less. .

As described above, according to the fixing device of this embodiment, an even fixing state can be obtained over the entire sheet, and an image having excellent transparency can be obtained.

In particular, when the sheet is an OHP sheet and a color image is to be obtained by fusing and fixing a plurality of color toner images superimposed on the OHP sheet, the superposed plurality of color toner images are required. Is required to be sufficiently heated and melt-mixed to obtain transparency. According to the fixing device of this embodiment, an image having excellent transparency can be obtained.

As described above, if the amount of oil applied to the heating roller 50 is relatively small, the sheet S is likely to be wound around the heating roller 50, so that the heat roller 50 and the second pressure roller 70 Sheet S that has passed through clamping portion N2
Is not peeled off from the heating roller 50 and easily winds around the heating roller 50. In this embodiment, on the downstream side of the second pressure roller 70, on the outer peripheral surface of the heating roller 50,
Since the second peeling claw 92 for peeling the sheet S from the heating roller 50 is provided, the sheet S that has passed through the pressure portion N2 between the heating roller 50 and the second pressure roller 70 is Peeled off reliably.

(B) In an apparatus such as the image forming apparatus shown in FIG. 1 for fixing a multi-color toner image collectively transferred on the sheet S collectively, stable color developing property and excellent in the OHP sheet are obtained. In order to ensure transparency, it is necessary to sufficiently melt and mix the multi-layered toner to fix it.

On the other hand, according to the fixing device of this embodiment, as described above, the toner image of the sheet S is firstly pressed by the pressure contact portion (the first contact portion) between the heating roller 50 and the first pressure roller 60. 1 nip portion) is temporarily fixed by N1,
Next, the toner is continuously heated by being wound around the heating roller 50 as described above, and a pressure contact portion (second nip portion) between the heating roller 50 and the second pressure roller 70 while the heated state is maintained. Since the toner is further heated and pressed by N2 and is secondarily fixed, even if the toner has a multilayer structure, the toner can be sufficiently melted and mixed and fixed.

Accordingly, it is possible to obtain stable color development of the color toner image and excellent transparency in the OHP sheet.

Further, as described above, since the amount of oil applied to the heating roller 50 is 0.0063 mg / cm ² or less, a color image excellent in transparency can be obtained, particularly in an OHP sheet.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and can be appropriately modified within the scope of the present invention.

For example, in the above embodiment, the first and second pressure rollers 60 and 70 are
Although only the pressure contact is provided, the present invention can also be applied to a configuration in which a guide pressure roller is provided between the first and second pressure rollers 60 and 70. is there. Further, in the above-described embodiment, an elastic roller is used as the heating roller 50, but the present invention can be applied to a case where a rigid roller is used.

[0090]

[Experimental example] A plurality of heating rollers having different hardness and a plurality of pressure rollers having different hardness are prepared. The pressure roller is brought into pressure contact with the heating roller in various combinations, and the amount of oil applied to the heating roller is prepared. To confirm whether the sheet having the toner image around the heating roller is wrapped,
The results of measuring the turbidity (HAZE) as an index of transparency are shown in the tables of FIGS.

When the above experimental results were examined, it was found that the turbidity increased as the amount of oil applied increased, as is clear from, for example, A to F in the table of FIG. In particular, paying attention to G ′ in FIG. 6, D in FIG. 5, and F ′ in FIG.
These conditions were the same except for the amount of oil applied, and the turbidity was increased by increasing the amount of oil applied, so it became clear that the turbidity increased as the amount of oil applied increased. .

In general, if the turbidity is 20 or less, it can be said that the transparency is practically sufficient.
It was roughly found that turbidity of 20 or less can be achieved by controlling the amount to 06349 mg / cm ² or less.

On the other hand, for example, as is clear from F, G, H in the table of FIG. 5 and B ′, A ′, C ′ in the table of FIG.
It was found that the turbidity decreased as the hardness ratio increased. It was also found that as the hardness ratio increased, the sheet was more likely to wind around the heating roller.

Therefore, based on the above experimental results, the results of A to F in the table of FIG. 5 are plotted and connected by a straight line to show the relationship between the hardness ratio, the oil application amount, and the presence or absence of sheet wrapping. Created a graph. Fig. 7 shows the graph.
Shown in In FIG. 7, the right side of the straight line Y is a winding area where the winding of the sheet occurs, and the left side is a peeling area where the winding does not occur. In FIG. 7, a straight line A is a line where the amount of oil is 0.006349.

From the tables of FIGS. 5 and 6 and the graph of FIG.
At least, when the hardness ratio Hr between the heating roller and the pressing roller is Hr> 1 and the oil application amount is 0.0063 or less, the sheet is wound around the heating roller and sufficient transparency is obtained. I understood that.

The heating roller used in the experiment was provided with a silicone rubber layer or a fluorine rubber layer on the surface of an aluminum pipe, and the hardness of the roller was changed by changing the thickness of the rubber layer. In the pressure roller, a silicone rubber layer or a fluorine rubber layer was provided on the surface of a steel pipe, and the hardness of the roller was changed by changing the thickness of the rubber layer. The pressure roller prepared here can be used as both the first pressure roller and the second pressure roller. Therefore, the hardness ratio between the heating roller and the pressure roller in the table, Hr = Hh / Hp is between the heating roller and the first
The hardness ratio Hr (= Hh / Hp) with the pressure roller is
The hardness ratio between the heating roller and the second pressure roller (Hr2 (= H
h / Hp2)). In the above experiment, the maximum amount of oil applied was set to 0.
015873 mg / cm ² (10 mg / a4 in terms of A4 size sheet). If the amount of oil applied exceeds this maximum amount (10 mg / a4), the sheet will absorb too much oil and cannot be used practically.

[0097]

Embodiments Hereinafter, specific embodiments will be described.

<Regarding Heating Roller 50 and the Like> Heating Roller 5
0 means that a silicone rubber layer having a thickness of about 2 mm is provided on the surface of an aluminum pipe having an outer diameter of about 31 mm and an outer diameter of 35 m.
m and hardness of about 48. As the first pressure roller 60, a silicone rubber layer having a thickness of about 2 mm is provided on the surface of a steel pipe having an outer diameter of about 31 mm, and an outer diameter of about 35 mm and a hardness of about 32. The hardness ratio between the two is set to about 1.5 (see fixing device J in FIG. 5).

The second pressure roller 70 has an outer diameter of 11 m.
m, a silicone rubber layer having a thickness of about 2 mm is provided on the surface of a steel pipe having an outer diameter of about 15 mm and a hardness of about 80.
(See the fixing device J ′ in FIG. 6).

In the center of the heating roller 50, a halogen lamp is disposed as a heat source 51.

The pressing force of the first pressure roller 60 and the second pressure roller 70 against the heating roller 50 is 30
It is set appropriately within the range of about 120 kg.

<Regarding the Oil Application Roller 94> The oil application roller 94 has an oil holding layer such as a heat-resistant fiber (for example, felt) or sponge which can be impregnated with oil (silicone oil or the like) having an appropriate viscosity. One having a coating amount regulating layer made of a porous film of ethylene tetrafluoride or the like on the surface is used.

The amount of oil applied (discharged amount) can be adjusted by adjusting the oil viscosity, the hole diameter of the porous film, the density, and the like.

More specifically, the oil used is dimethyl silicone oil and has a viscosity (cst) of 10
Approximately 00. Amount applied to the surface of the heating roller 50 (mg
/ Cm ² ) is about 0.005.

<Regarding Toner> As the toner, a color toner having a softening point temperature of 130 ° C. or less is used.

More specifically, a high-concentration pigment toner having a particle size of about 7 μm is used. Regarding the amount of the external additive of the toner, the amount of the external additive having a large particle diameter is set to 0.5 to 4.0% by weight (more preferably about 0.7% by weight), and the amount of the external additive having a small particle diameter is determined. 1.5 to 4.0 wt% (more preferably about 2.0 wt%). The external additive having a large particle size is necessary mainly for improving the durability stability of the toner. In this regard, the larger the amount, the better, but if it exceeds 4.0 wt%, the fluidity of the toner becomes poor. This is because it is not preferable because it affects hollow holes and the like. The external additive having a small particle size is necessary mainly for improving the transferability of rough paper. From this point, the more the additive, the better. However, when the content exceeds 4.0 wt%, the floating silica becomes a trigger. This is because the photoconductor 10 and the intermediate transfer belt 36 are likely to be filmed, which is not preferable. Also,
Regarding the fluidity of toner, A.I. D is about 0.35 g / cc, and the charge amount is −10 μC / g or more.

The toner amount before the secondary transfer, that is, the toner amount on the intermediate transfer belt 36 is set to 1.5 mg / cm ² or less.

<Regarding Guide Body 80> As shown in FIG. 3, the guide body 80 includes a pair of substantially C-shaped side plates 81, 81.
(Only one is shown), a back plate 82 connecting these side plates 81, 81, and the heating roller 50 from the back plate 82.
And a guide surface 84 formed as a front end surface of the guide portion 83.

The guide body 80 has its side plates 81, 81 rotatably supported by the bearing 63 of the first pressure roller 60, so that the shaft 6 of the first pressure roller 60 can rotate.
1 is rotatably supported. Guide body 80
A tension spring 85 is provided between the frame and the frame 41 as urging means. Therefore, the guide body 8
0 is urged by the action of the spring 85 in a direction in which the guide surface 84 approaches the heating roller 50, that is, clockwise in FIG. 3. Part (outside of the image area) is regulated, and as a result, the guide body 80
Has been positioned. In such a state, the starting end of the guide surface 84 is close to the outer peripheral surface of the first pressure roller 60, and the pressure contact portion (first nip portion) between the heating roller 50 and the first pressure roller 60 is provided. Even if the leading end of the sheet that has passed through N1 does not wind around the heating roller 50 for some reason, this is reliably performed by the heating roller 50 and the second
It is guided toward a pressure contact portion (second nip portion) N2 with the pressure roller 70. Also, the guide surface 84
The interval between the heating roller 50 and the outer peripheral surface 50 is inclined in such a direction that it gradually narrows as the sheet advances.

[0110]

According to the fixing device of the present invention, an even fixing state can be obtained over the entire sheet, and an image having excellent transparency can be obtained.

[0111]

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a main part of an example of an image forming apparatus using a fixing device according to the present invention.

FIG. 2 is an enlarged partial end view of II-II in FIG. 1;

FIG. 3 is a partially omitted side view showing an embodiment of the fixing device according to the present invention.

FIGS. 4 (a) and 4 (b) are operation explanatory diagrams.

FIG. 5 is a table showing an experimental example.

FIG. 6 is a table showing an experimental example.

FIG. 7 is a graph showing an experimental example.

FIG. 8 is an explanatory diagram of a conventional technique.

[Explanation of symbols]

 Reference Signs List 40 fixing device 50 heating roller 51 heat source 60 first pressure roller 70 second pressure roller

Claims (1)

[Claims] 1. A fixing device comprising: a heating roller having a heat source therein; and first and second pressure rollers which are sequentially pressed against the heating roller from an upstream side in a rotation direction thereof, wherein the heating roller A fixing device, wherein the hardness of the first pressure roller is configured to be smaller than the hardness of the first pressure roller, and the amount of oil applied to the heating roller is 0.0063 mg / cm ² or less.