JPH11167303A - Image fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image fixing device where toner is prevented from being accumulated on a roller in the fixing device while using developer capable of making developing compatible with fixing even the case of a high-speed machine without making the device complicated. SOLUTION: Relating to this image fixing device, the developer incorporating binding resin and releasing agent is used as the developer for an electrostatic charge image; and the device is equipped with a thermal fixing means fixing transfer material carrying the developer from a nip part and a pressure means arranged to press-contact with the thermal fixing means. The releasing agent exists on the surface of at least either the thermal fixing means or the pressure means. Then, the content of the releasing agent included in the developer is 5-8 pts.wt. based on 100 pts.wt. binding resin, and the releasing agent has a functional group in hydrocarbon as a base body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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 form an electric latent image by charging and exposing a photoreceptor using a photoconductive substance, developing the latent image with a colored toner, and transferring the latent image onto a transfer material such as paper. Then, the toner is melted and fixed on the transfer material by applying heat and pressure together with the transfer material to obtain a fixed image. Then, the residual toner on the photoreceptor is cleaned, and the above steps are repeated.

In recent years, such an image forming apparatus has begun to be frequently used not only in a copying machine but also in the field of a printer or a personal computer as an output device of a computer. Therefore, smaller size, lighter weight, higher speed, and higher reliability have been pursued, and a simpler machine configuration has been demanded. This is the same in the fixing device.

Conventionally, in a fixing device that fixes toner on a recording material by heat, a part of the toner image adheres to and transfers to the roller surface because the roller surface and the toner image come into contact in a molten state. In some cases, a so-called offset phenomenon occurs in which the image is re-transferred onto the recording material at the roller cycle. It is one of the essential conditions of the heat fixing device that the toner does not adhere to the roller.

Conventionally, for the purpose of preventing the toner from adhering to the roller, for example, the roller surface is formed of a material having excellent releasability with respect to the toner, for example, a fluorine resin, and the surface of the roller is formed of silicone oil as an anti-offset agent For example, coating with a liquid having a good releasability, such as, for example, is performed. But,
In order to constantly coat the roller surface with the anti-offset liquid, a device for supplying the anti-offset liquid is required, which not only complicates the device, but also may cause the anti-offset liquid to leak into the machine and become contaminated. was there.

In view of this, instead of supplying the silicone oil to the roller by the apparatus, instead of supplying the offset preventing liquid from the toner during heating, a method of adding a release agent such as low molecular weight polypropylene to the toner is used. Has been proposed.

[0007] Adding a wax as a release agent to the toner is used not only to improve the offset of the toner at low and high temperatures, but also to improve the fixability at low temperatures. An important point when adding a wax to a toner is to highly disperse the wax in the toner. However, as high-speed and high-quality image forming apparatuses have recently required high-temperature fixing properties for toners, binders having low melt viscosity properties and low-melting waxes have been used, and waxes have been used in toners. It is becoming difficult to highly disperse. If the dispersibility of the wax in the toner is insufficient, the fluidity of the toner is remarkably deteriorated, and the developability is affected such as deterioration of fog and inability to achieve high image quality.

In order to cope with the low-temperature fixing property and the anti-offset property at high temperatures, the toner has a wide molecular weight distribution of the binder resin, and an appropriate amount of low-molecular-weight wax is added to the resin to reduce the low-temperature of the fixing device. In addition, both high-temperature offset and developability are achieved.

[0009]

However, in an image forming apparatus using a binder having a low melt viscosity and a low melting point wax, the following problems relating to a fixing device tend to occur. That is, toner does not adhere to the roller at the start of use of the fixing device, but as the frequency of use increases, toner adheres to the roller surface, and the toner-adhered image immediately appears on the recording material as in a conventional offset. Instead, the toner accumulates as a lump on the roller surface, and after the accumulation progresses, a phenomenon occurs in which the lump of the toner appears on the front and back of the recording material.

[0010] Lumps of toner are likely to be generated on the pressure roller having a low roller surface temperature, and lightly adhere to the back surface of the recording material in the early stage of durability. The medium also transfers to the fixing roller side, causing irregular image stains on the image printing surface.

FIG. 6 shows the result of observing the state of toner accumulation on the surface of the pressure roller according to the number of endurance sheets. The vertical axis in FIG. 6 is obtained by visually observing the toner accumulation amount on the roller surface.
When the area exceeds the shaded area in the figure, it is shown that a toner-adhered image can be seen on the paper. When the wax content of the toner is 4 parts by weight based on 100 parts by weight of the binder resin,
The toner gradually accumulates on the roller, and once a toner-adhered image is generated on paper.

On the other hand, when the wax content of the toner is 7
If the toner content is on a weight basis, the wax content tends to be the same as 4 parts by weight until the toner-adhered image is generated on the paper, but the toner accumulation amount on the roller once the toner-adhered image is generated on the paper. Was reduced, and no toner-adhered image was generated on the paper thereafter.

As a result of observing the change on the roller surface, when the wax content in the toner is large, the wax layer in the toner is formed on the roller after the toner is once peeled off the paper from the roller. Turned out to be.

In the wax layer, a small amount of fog and offset toner on the recording material is transferred to the roller surface and heated and melted at the fixing nip position, so that the wax component in the toner is separated and precipitated from the toner. It is presumed that the toner was formed, and it is considered that the toner was prevented from sticking to the roller by the releasing action of the wax.

The conditions under which the wax layer is likely to be formed on the roller include not only the amount of the wax added to the toner as described above but also the following tendency.

The resin on the roller surface contains not only a fluororesin but also a conductive agent in the fluororesin.

As wax added to the toner,
Having a functional group at the terminal.

However, if a large amount of wax, which is a release agent, is added to the toner in order to bring out a sufficient effect, filming on the photoreceptor and contamination on the surface of the toner carrier such as the developing sleeve are caused, leading to image deterioration. . Therefore, conventionally, a release agent is added to the toner to the extent that image deterioration does not occur, and a small amount of release oil is supplied to the roller of the fixing device or used together with a device that cleans the offset toner with a winding web or the like. Is being done,
It is still unfavorable in terms of the size, weight reduction, and high reliability of the device.

Based on the above experimental results, it was found that when a wax layer added to the toner was formed on a roller in advance and durability was performed, a good result without toner accumulation on the roller was obtained from the beginning.

Accordingly, an object of the present invention is to use a developer capable of achieving both developability and fixability even in a high-speed machine without complicating the apparatus, and to store toner on a roller in the fixing device. An object of the present invention is to provide an image fixing device that does not generate any image.

[0021]

Means and Action for Solving the Problems In order to solve the above problems, the present inventors have made intensive studies and arrived at the present invention. That is, the present application includes the following inventions and embodiments.

(A) using a developer containing a binder resin and a release agent as a developer for an electrostatic charge image, and a heat fixing means for fixing a transfer material carrying the developer from a nip portion thereof; An image fixing apparatus comprising: a pressing unit disposed so as to be in pressure contact with the heat fixing unit, wherein a release agent is present on at least one surface of the heat fixing unit and the pressing unit. apparatus.

(B) The image fixing device according to (a), wherein the release agent is a release agent contained in the developer.

(C) The content of the release agent contained in the developer is 5 to 8 parts by weight based on 100 parts by weight of the binder resin, and the release agent has a functional group in a hydrocarbon as a base. The image fixing device according to (a) or (b), wherein

(D) At least one surface of the heat fixing means and the pressure means is formed of a resin excellent in releasability in which a release agent contained in the developer is substantially uniformly dispersed. The image fixing device according to (a) or (b), wherein

(E) A coating member impregnated with a release agent contained in a developer is in contact with at least one of the heat fixing means and the pressure means (a) or (b).
The image fixing device as described in the above.

[0027]

Embodiments of the present invention will be described below. As an example of the image forming apparatus to be described, a high-speed printer capable of printing 20 sheets / minute in A4 width will be described. Paper can be passed up to A3 length (297 mm wide) as a recording material, and can be conveyed by the center reference where the center of the recording material coincides with the center of the fixing roller. Further, since a method of forming an unfixed image conveyed to the fixing device is performed by a known electrophotographic technique, a description thereof will be omitted.

The following toners are used for the above-described high-speed printer.

That is, since a binder resin having a wide molecular weight distribution is preferable as a binder resin in order to cope with low-temperature fixing property and anti-offset property at high temperature, a styrene copolymer having two molecular weight peaks is used.

The wax as a release agent to be mixed with the binder resin contains a wax having a functional group in a hydrocarbon as a base (hereinafter referred to as a polar wax). Examples of the functional group include a hydrogen group, a carboxyl group, an amino group, an ester group, and an amide group, and any functional group having a polarity that reacts with a conductive agent such as carbon black may be used. Charging stability to the above binder resin,
By adding other inorganic fine powder for the purpose of improving developability and fluidity, the developability in a high-speed machine can be stabilized.

First, details of the fixing device according to the present invention will be described with reference to FIG.

In FIG. 7, reference numeral 1 denotes a fixing roller as a recording material conveying means, and a PFA resin layer 12 is provided on a 1 mm thick aluminum core. A heater 3 as a heating unit is provided inside the fixing roller, and heats the fixing roller from the inside.

On the other hand, reference numeral 2 denotes a pressure roller which is pressed by a fixing roller (not shown) and forms a 6 mm fixing nip N. The pressing roller 2 has an elastic layer 22 made of heat-resistant silicon sponge rubber 6 mm on an iron core 21 and a release agent layer 23 made of PFA resin formed thereon.

The unfixed toner 7 is fixed on the recording material by being heated and pressed in the fixing nip.

An entrance guide 4 serves as a guide for stably transporting the recording material 6 on which the unfixed toner image is formed to the fixing nip.

Reference numeral 5 denotes a thermistor which is a temperature detecting sensor for detecting the surface temperature of the fixing roller, which is in contact with the surface of the fixing roller at a predetermined contact pressure so that the temperature of the surface of the fixing roller becomes constant during printing. The power supply to the heater is turned on and off (an electric circuit for turning the power supply on and off is not shown). In a fixing device having a cleaning mechanism, a thermistor can be provided in the recording material passage area. However, in a fixing device having no cleaning mechanism as shown in FIG. Provided.

In a conventional roller fixing device, a predetermined potential difference may be provided between the fixing roller and the pressure roller for the purpose of preventing offset, and the transfer of toner to the surface of the fixing roller may be prevented. Reference numeral 8 in FIG. 7 denotes a DC power supply that applies a bias having the same polarity as the toner 7 to the fixing roller core 11.
Is a diode connected to the core of the pressure roller 2 in order to keep the surface potential of the pressure roller 2 opposite to that of the toner.

The fixing device is rotated by driving means (not shown) while heating the fixing roller so that the surface of the fixing roller has a predetermined temperature, thereby fixing the unfixed image sent to the fixing device. At this time, as described above, a DC bias of -600 V is applied to the core of the fixing roller to form a potential difference between the fixing roller and the pressure roller, thereby preventing toner offset.

[0039]

Embodiment 1 As an embodiment which is most easily implemented in the present invention, a case where wax added to toner is applied to the surface of a pressure roller will be described as an example.

The pressing roller has an outer diameter of φ30 and a hardness of 50.
゜ (Asker C 500g load), conductive silicone rubber sponge layer 6mm around iron φ15 core metal and 5
A press roller having a PFA resin tube containing a conductive agent having a thickness of 0 μm and having a wax layer added to the toner used in the image forming apparatus main body formed on the surface of the press roller was prototyped.

An example of a method for manufacturing the pressure roller of this embodiment will be described below with reference to FIG. First, a raw material unvulcanized rubber 31 obtained by adding a vulcanizing agent to a silicone rubber composition comprising a silicone rubber, a reinforcing filler, a heat resistant agent, and the like is extruded using an extruder.
Wind around 0 to make an unvulcanized extruded product. Next, a metal hollow pipe 32 for vulcanization molding is prepared, a fluororesin tube 33 on the inner surface of the metal hollow pipe 32 is mounted, and the above-mentioned unvulcanized extruded product is mounted further inside. By heating these simultaneously with the metal pipe 32, vulcanization,
At the same time as firing, bonding between the core metal and sponge and between the sponge and fluororesin tube is performed simultaneously.

At this time, the metal hollow pipe 32
The wax 34 added to the toner is uniformly applied to the inner surface, and the unvulcanized rubber expands and expands, so that the fluororesin tube 33 and the wax 34 come into contact with each other and the wax is applied to the tube surface. The method of uniformly applying the wax 34 in the pipe 32 is as follows.
The solid wax may be brought into contact with the inner surface of the pipe 32 while heating, and then rotated, and then cooled.

Here, since it is difficult to fix and solidify the wax 34 on the surface of the tube 33 by using only the fluororesin as the resin tube 33, it is preferable that the resin contains a conductive agent. Examples of the conductive agent include carbon black such as conductive carbon black, acetylene black, and Ketjen black, but are not limited thereto, and those having conductivity such as metal powder and metal oxide (for example, tin oxide and zinc oxide). Should be fine. As a method of containing a conductive agent in a certain ratio in a tube, a conductive pellet and a fluororesin pure pellet in which the conductive agent is previously added to a pellet-shaped fluororesin are prepared, and the tube is kept at a predetermined resistance within a desired resistance range. May be mixed at the weight ratio described above to form a tube. As the volume resistivity of the tube, if the content of the conductive agent is too large, the releasability of the roller surface is impaired, and if the conductive agent is too small, the roller becomes high resistance and at the same time it becomes difficult to apply wax. 10 ⁶ to 1
0 ^{1 2} (Ω · cm) is preferable.

It is also preferable to add a conductive agent such as carbon black to the raw unvulcanized rubber in advance to make the silicone rubber sponge more conductive than the surface fluororesin. The volume resistivity of rubber is 10 ² to 1 in an unfoamed state.
0 ⁵ (Ω · cm) is better that the low-resistance than the surface layer tube and so on.

The total resistance (product resistance) of the pressure roller manufactured as described above is 10 ⁵ Ω or more (measurement was performed using an R8340A high resistance meter manufactured by Advantest Co., Ltd. while an aluminum roller was brought into contact with a low pressure roller. DC 500 V is applied) to prevent the leakage of the bias applied to the fixing roller.

FIG. 3 shows the result of observing the toner accumulation state on the surface of the pressure roller according to the number of durable sheets when the pressure roller described above is used. The vertical axis in FIG. 3 is obtained by visually observing the amount of accumulated toner on the roller surface, and indicates that when the area exceeds the shaded area in the figure, a toner-adhered image can be seen on paper. The wax content of the toner is 7 parts by weight with respect to 100 parts by weight of the binder resin. In the case where the pressure roller of this embodiment is mounted on the fixing device, even if the durability is advanced, a lump of toner is observed on the pressure roller. No good results were obtained. Further, no image stain on the paper occurred.

Embodiment 2 Next, an example in which wax previously added to the toner is added to the surface fluororesin of the fixing roller or the pressure roller will be described.

When the surface of the roller is coated with a fluororesin, a small amount (about 5 to 20% by weight) of the above wax component may be added to the molten fluororesin and applied to the roller surface. It is preferable to use a fluororesin tube in terms of durability and leak resistance because of its excellent durability.

Of course, this embodiment can also be applied to a case where the roller surface is coated with a fluororesin. Further, two fluororesin layers may be used. For example, as shown in FIG. 4, a silicone rubber sponge layer 41 is formed around a cored bar 40, and a lower fluororesin layer 42 having a low resistance and a release agent resin layer 43 in which wax is dispersed thereon are formed thereon.

In the method of forming a two-layer tube with a tube, it is preferable to form a seamless tube by attaching an annular die to a plurality of extruders and co-extruding the film. Similarly, in the case of coating, the composition may be changed by changing the composition of the fluororesin of the lower layer and the upper layer.

Embodiment 3 As another method for coating the surface of the pressure roller with the wax added to the toner, as shown in FIG.
The elastic roller 53 in which the upper elastic silicone rubber layer 4 mm (51) is impregnated with the wax is brought into contact with the pressure roller 2. The elastic roller 53 is contacted with a total pressure of 5 kgf or less, and is driven to rotate with respect to the pressure roller 2 to apply wax to the surface of the pressure roller. Elastic roller 5
Regarding the amount of the wax to be impregnated in the toner 3, if the amount of the wax added to the toner is large, the wax contained in the toner forms a wax layer on the surface of the pressure roller. There is no need to replenish as long as wax is included. In this apparatus, if the amount of the solid wax impregnated in the elastic roller was 10 g or more, toner adhesion did not occur even when durability was achieved.

Therefore, there is no need for a device for intermittently supplying a release liquid such as silicone oil onto a roller or a complicated member such as a take-up web as in the prior art.

In the above description, an elastic roller impregnated with wax is brought into contact with the pressure roller 2, but in the case of a fixing device using a fixing roller or a film, it may be brought into contact with the film.
Further, as a member impregnated with the wax to be brought into contact with the pressure roller 2, in addition to the above, for example, a material obtained by adding a wax to a cleaning pad made of wool felt detachable from the roller may be used. With a cleaning pad, the toner on the roller surface can be removed at the same time as the wax is applied to the roller surface, and can be replaced as needed.

Other Examples As another method of forming a wax layer on the surface of a pressure roller using a pressure roller, assembling a fixing device, idling while heating is performed, and solid wax added to the toner is added. May be brought into contact with a roller to form a wax layer. Also in this case, in order to make the polar wax adhere to the roller surface, it is preferable that a conductive agent is added to the inside of the fluororesin tube of the roller surface layer as in the first embodiment.

Since the wax is brought into contact with the fixing device while being rotated, there is an advantage that uniform wax can be applied not only to the surface of the pressure roller but also to the surface of the fixing roller. The idle rotation while heating the fixing device may be performed during the inspection at the time of assembling the device, and does not affect the manufacturing process capability.

[0056]

As described above, a wax layer previously added to the toner is formed on the surface of the fixing roller or the pressure roller, and a sufficient amount of a new wax component is supplied from the toner during the image fixing process. However, since a wax layer was provided on the roller surface, it was possible to prevent image stains that had occurred in the early stage of durability. In addition, there is no need for a complicated structure such as a take-up type release agent applying member used in a conventional copying machine or the like, and there is an advantage that it can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a pressure roller according to a first embodiment in which a polar wax is applied to the surface.

FIG. 2 is a diagram illustrating a method of manufacturing the pressure roller according to the first embodiment.

FIG. 3 is a diagram showing a comparison between toner adhesion due to conventional durability and Example 1;

FIG. 4 is a sectional view of a pressure roller according to a second embodiment.

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

FIG. 6 is a diagram comparing toner adhesion depending on the amount of wax added to the toner.

FIG. 7 is a sectional view of a fixing device used in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing roller 2 Pressure roller 3 Heater 4 Entrance guide 5 Temperature detection sensor (thermistor) 6 Recording material N Fixing nip 7 Toner 11 Fixing roller core metal 12 Releasable resin layer 21, 30 Pressure roller core metal 22, 31 Elasticity Layers 23, 33 Release agent layer 34 Wax coating layer 40 Core metal 41 Silicone rubber sponge layer 42 Lower fluorocarbon resin layer 43 Release agent layer 50 Core metal 51 Elastic silicone rubber layer 53 Elastic roller impregnated with wax

Claims (5)

[Claims] And a heat fixing means for fixing a transfer material carrying the developer from a nip portion thereof, using a developer containing a binder resin and a release agent as a developer of the electrostatic charge image. An image fixing apparatus comprising: a pressure unit arranged to be in pressure contact with a heat fixing unit, wherein a release agent is present on at least one surface of the heat fixing unit and the pressure unit. . 2. The image fixing device according to claim 1, wherein the release agent is a release agent contained in the developer. 3. The content of the release agent contained in the developer is 5 to 8 parts by weight based on 100 parts by weight of the binder resin, and the release agent has a functional group in a hydrocarbon as a base. The image fixing device according to claim 1, wherein: 4. The method according to claim 1, wherein at least one surface of the heat fixing unit and the pressing unit is formed of a resin having excellent releasability, in which a release agent contained in the developer is substantially uniformly dispersed. The image fixing device according to claim 1, wherein: 5. The image fixing device according to claim 1, wherein at least one of the heat fixing unit and the pressure unit is in contact with a coating member impregnated with a release agent contained in a developer. apparatus.