JPH11109779A - Thermal fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thermal fixing device constituted so that leak type offset and offset caused by charge-up are prevented from occurring and productivity is excellent by incorporating an electronic conductive material whose specific resistance is within the range of a specified value in a mold-releasing layer being the outermost layer of a heating member. SOLUTION: In the thermal fixing device for fixing an unfixed image on a recording material as the permanent image, the mold-releasing layer 13c being the outermost layer of the heating member is formed as the layer for preventing toner from being offset with respect to a fixing film by being covered with fluororesin such as PFA, PTFE, FEP or the like whose mold releasing property is excellent by the thickness of about 5 to 15 μm by a coating method such as an electrostatic spraying method or a dipping method. Besides, the electronic conductive material 13d such as carbon black, beryllium oxide, hafnium oxide, magnesium oxide or sodium oxide whose specific resistance is 10<7> to 10<12> Ωcm is mixed in the layer 13c in order to prevent the fixing film from being offset caused by the charge-up.

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 employing an image forming process such as an electrophotographic system or an electrostatic recording system, and more particularly to a recording material (transfer material, printing paper, photosensitive paper) in an image forming process part. A characteristic of the heat fixing device is that the unfixed toner image of the target image information formed and carried on the electrostatic recording paper or the like by the transfer method or the direct method is subjected to a heat fixing process as a fixed image.

[0002]

2. Description of the Related Art Conventionally, a fixing device provided in an image forming apparatus adopting an electrophotographic system, an electrostatic recording system, or the like has a nip portion formed by a fixing roller and a pressure roller which are rotated while being pressed against each other. A so-called heat fixing device, which fixes a permanent image on a recording material by passing the recording material carrying an unfixed toner image, is widely used.

FIG. 6 shows an example of a conventional heat fixing device.

[0006] In FIG. 6, reference numeral 40 denotes a fixing roller which is a heating member provided with a heating element.
A halogen lamp 41, which is a heating element, is disposed inside the inside of the hollow core 42, and heat is applied sufficiently to melt the toner on the recording material from the inside of the hollow metal core 42 by energization from a power supply (not shown).

Further, in order to fix the toner on the recording material without offsetting it, a polytetrafluoroethylene copolymer (PTFE) having excellent releasability is provided outside the hollow metal core 42. ), A release layer 43 such as a perfluoroalkoxytetrafluoroethylene copolymer (PFA) is formed.

The release layer 43 is formed in a tube shape, or is formed by electrostatic spraying, dipping coating or the like.

In some cases, a conductive member such as carbon black is mixed into the release layer in order to prevent offset caused by charging up of the surface of the fixing roller due to conveyance of the recording material.

Further, the hollow core metal 42 of the fixing roller 40 is electrically grounded, detects the temperature of the surface of the fixing roller, and applies heat to the halogen lamp so as to heat the toner image on the recording material at an appropriate temperature. The power supply is on / off controlled.

On the other hand, a pressing roller 50 is a pressing member which is pressed against the fixing roller 40 by a pressing spring (not shown) at both ends in the longitudinal direction of the roller.

The pressure roller 50 includes an elastic layer 52 formed of an elastic layer made of silicon rubber or a sponge elastic layer formed by foaming silicon rubber on the outside of the cored bar 51, and a PTFE similar to the fixing roller formed on the outer layer. Or PF
A release layer 53 such as A or FEP is formed in a tubular shape or by coating.

Therefore, a sufficient nip width can be formed between the two rollers by the elasticity of the pressure roller 50.

The toner image on the recording material nipped and conveyed to the nip can be fixed by heating from a fixing roller.

In addition, a method for minimizing power consumption by not supplying power to the heat fixing device during standby, specifically, fixing a toner image on a recording material via a film between a heater and a pressure roller. Japanese Patent Application Laid-Open No. 63-313182 / 1990
JP-A-157878 / JP-A-4-44075 /
It has been proposed in Japanese Patent Application Laid-Open No. 4-202980.

FIG. 7 shows a schematic configuration of a film heating system.

In FIG. 7, a stay holder (support) is provided.
Heating body (hereinafter referred to as heater) 61 fixedly supported by 62
A thin film (hereinafter, referred to as a fixing film) 63 as a heat-resistant heating member is attached to the heater 61 and the elastic pressing roller 50 as a pressing member pressed by a pressing unit (not shown).
A nip portion (fixing nip portion) having a predetermined nip width is formed with the nip therebetween.

The heater 61 is heated and adjusted to a predetermined temperature by energization.

The fixing film 63 is conveyed in the direction of the arrow while being in close contact with and sliding on the surface of the heater 61 and the surface of the pressure roller 50 at the fixing nip by the driving means (not shown) or the rotational force of the pressure roller 50. , A cylindrical or endless belt, or a rolled end web.

In a state where the heater 61 is heated and controlled to a predetermined temperature and the fixing film 63 is transported and moved in the direction of the arrow, the material to be heated is located between the fixing film 63 in the fixing nip portion and the pressure roller 50. When a recording material on which an unfixed toner image is formed and carried is introduced, the recording material is brought into close contact with the surface of the fixing film 63 and is conveyed while holding the fixing nip together with the fixing film 63.

In the fixing nip portion, the recording material / toner image is heated by a heater 61 via a fixing film 63 to heat and fix the toner image on the recording material. It is peeled off from the surface 63 and transported.

In general, a ceramic heater is used as the heater 61 as a heating element.

For example, the surface of a ceramic substrate (e.g., fixing film 6) having electrical insulation, good thermal conductivity, and low heat capacity such as alumina.
3) (silver palladium (Ag / Pd) .Ta2N) along the substrate longitudinal direction (direction perpendicular to the drawing).
Is formed by screen printing or the like, and the surface on which the heat generating resistance layer is formed is further covered with a thin glass protective layer.

The ceramic heater 61 is energized by the current-carrying heat-generating resistor layer to generate heat, so that the entire heater including the ceramic substrate and the glass protective layer is rapidly heated.

The power supply to the heat-generating resistance layer is controlled so that the temperature rise of the heater 61 is maintained at a predetermined substantially constant temperature (fixing temperature) by the temperature detecting means 64 provided on the back of the heater. I do.

That is, the heater 61 is heated and adjusted to a predetermined fixing temperature.

The fixing film 63 has a very small thickness of 20 to 70 μm in order to efficiently apply the heat of the heater 61 to the recording material as the material to be heated in the fixing nip portion.

FIG. 8 shows the structure of the fixing film 63.

The fixing film 63 includes a film base layer 63a,
It has a three-layer configuration of a conductive primer layer 63b and a release layer 63c, with the film base layer 63a side being the heater side and the release layer 63c being the pressure roller side.

The film base layer 63a is made of polyimide, polyamideimide, PEEK or the like having high insulation properties,
It has a high elasticity, is formed with a thickness of about 15 to 60 μm, and maintains the mechanical strength such as the tear strength of the entire fixing film 63. The conductive primer layer 63b has a thickness of 2 to 6 μm.
The fixing film 63 is formed of a thin layer, and is electrically connected to the ground in order to prevent charge-up of the entire fixing film 63.

The releasable layer 63c is a layer for preventing toner offset from the fixing film 63.
A, PTFE, FEP, etc. Fluororesin thickness 5-10μ
m, so that the specific resistance in the release layer is 10 in order to reduce charge-up on the surface of the fixing film 63 and prevent electrostatic offset similarly to the fixing roller.
^-3 to 10 ⁶ [Omega] cm about the electron conductive substance is a conductive member such as carbon black is mixed.

The stay holder 62 is formed of, for example, a heat-resistant plastic member, prevents heat radiation in the direction opposite to the nip, holds the heater 61, and fixes the fixing film 6.
3 also serves as a transport guide.

Further, the fixing film 63 and the heater 61
Therefore, it is necessary to suppress the frictional resistance between the fixing film and the fixing film.
A lubricant such as high heat resistant grease is interposed between the surfaces of the heater 61 and the stay holder 62.

[0032]

However, both the release layer of the fixing roller heating system and the release layer of the film heating system described above are relatively low in particle size such as carbon black in order to prevent charge-up on the surface. Specific resistance (10 ^-3 to 10
⁽ Approximately ⁶ Ωcm) is dispersed substantially uniformly.

The dispersion of the electronic conductive substance from the outer surface in contact with the recording material to the conductive primer layer and the conductive hollow core metal depends on the low specific resistance of the electronic conductive substance. As a result, the surface resistance and the volume resistance of the release layer change significantly.

Further, when the recording material is transported and durable, the release layer is scraped, and when the actual resistance from the surface of the release layer to the conductive primer layer changes, the transfer charge of the recording material becomes conductive. It is difficult to prevent a leak-type offset caused by leaking to the primer layer.

That is, when a large amount of the above-mentioned electron conductive substance is mixed into the release layer, it is easy to prevent charge-up of the surface of the fixing film or the surface of the fixing roller due to the conveyance of the recording material.

On the other hand, the transfer charge holding the toner image on the recording material leaks to the conductive primer layer or the conductive hollow core metal in the portion where the electronic conductive material in the release layer is dense. It will be easier.

In particular, when a recording material having a small surface resistance is used, a large amount of electron conductive material is microscopically transferred, and almost all of the transferred charge on the recording material is reduced from the point where the transferred charge is likely to leak. Leaks into the conductive hollow core.

As a result, the toner image on the recording material is no longer electrostatically held on the recording material, and tends to be offset due to a decrease in the toner suction force on the recording material.

When a small amount of the above-mentioned electron conductive substance is mixed in the release layer, the transfer charge can be prevented from leaking, but the difference in the dispersion density of the electron conductive substance in the release layer becomes larger. In a portion where the electron conductive material is sparse, the surface of the release layer is locally charged up, which may lead to an offset.

For example, when the dried recording material is conveyed after being peeled off from the fixing nip portion, when the rear end of the recording material is discharged from the nip portion, the surface of the heating member corresponds to the rear end of the recording material. The part is charged up linearly.

If the toner image of the succeeding recording material is fixed while maintaining this potential, the toner image of the succeeding recording material corresponding to the charged-up position is peeled off (hereinafter referred to as a peeling offset). .

Therefore, when an electron conductive material such as carbon black having a specific resistance of about 10 ^-3 to 10 ⁶ Ωcm is mixed into the release layer, the surface resistance and the volume resistance of the release layer are reduced by the electronic conductivity. Changes rapidly depending on the amount of
Severe management is required to mix the optimal amount of the electronic conductive material and minimize the variation in the amount of the electronic conductive material mixed, as well as the dispersion density of the electronic conductive material in the release layer. However, since the offset phenomenon has a significant effect, it is necessary to make the dispersion density uniform.

However, in the case of the above-mentioned particle-shaped electron conductive material such as carbon black, it is difficult to uniformly disperse them in a minute range because of easy aggregation.

From the above, it is difficult to completely prevent both the offset due to the transfer charge leakage and the offset due to the charge-up, and it is necessary to stably produce a release layer having appropriate resistance characteristics. Was also difficult.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and an object of the present invention is to make it easy to control the amount of an electronically conductive substance to be mixed, and to improve the electronic conductivity in a release layer. An object of the present invention is to provide a heat-fixing apparatus and an image forming apparatus having good productivity by easily making the dispersion density of a conductive substance uniform, thereby preventing a leak-type offset and an offset due to charge-up.

[0046]

According to the present invention, there is provided a fixing member having a heating member.
Between the fixing nips pressed against each other by the pressing member,
In a heat fixing device for fixing the unfixed image as a permanent image on the recording material by passing the recording material on which the unfixed image is formed, a specific resistance is provided in the release layer on the outermost surface of the heating member. Contains an electronic conductive substance of 10 ⁷ Ωcm or more and 10 ¹² Ωcm or less.

Accordingly, since the surface resistance and the volume resistance of the release layer do not extremely change depending on the amount of the electron conductive substance mixed therein, the release layer having a desired resistance value can be easily formed, and the leak type offset and offset can be obtained. The prevention effect is obtained for both of the charge-up offsets.

Further, the outermost release layer of the pressing member contains an electronic conductive substance having a specific resistance of 10 ⁷ Ωcm or more and 10 ¹² Ωcm or less.

Accordingly, the amount of the electron conductive substance mixed in the release layer of the heating member can be reduced as compared with the case where the electronic conductive substance is mixed only in the release layer of the heating member. Even if the release layer surface of the heating member is slightly shaved,
Since the electron conductive substance is unlikely to be locally dense, leakage of transferred charges is less likely to occur, and a leak-type offset prevention effect can be obtained for a long time.

Further, by passing the recording material on which the unfixed image is formed between the fixing member having the heating member and the fixing nip pressed against each other by the pressing member,
In the heat fixing device for fixing the unfixed image as a permanent image on a recording material, when forming the outermost release layer of the heating member, a solution in which a conductive substance is dissolved is converted into a liquid release property. It is characterized by being mixed into a layer material.

Therefore, the formed release layer has a predetermined surface resistance with no local difference due to the uniformly dispersed electron conductive material, and the local potential on the surface of the heating member is suppressed. Prevents offset due to charge-up.

When the outermost release layer of the pressure member is formed, a solution in which a conductive substance is dissolved is mixed into a liquid release layer material.

Therefore, since the solution is mixed into the liquid release layer material, it can be uniformly dispersed by simple stirring, and local charges can be suppressed.

The mixed conductive material is preferably dissolved in water.

Therefore, by mixing the aqueous solution into the liquid release layer material, the electronic conductive substance can be uniformly dispersed in the formed release layer.

Further, it is preferable that the release layer is formed of a fluororesin.

Therefore, the releasability is good.

It is preferable that the image forming apparatus comprises an image forming means for forming an unfixed image on a recording material and the heat fixing device for fixing the unfixed image as a permanent image on the recording material.

Accordingly, an effect of preventing both offsets in the image forming apparatus can be obtained.

[0060]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are intended to limit the scope of the present invention only to them unless otherwise specified. Not a thing.

(Embodiment 1) First, the structure of the image forming apparatus of the present invention is such that an unfixed image is formed on a recording material by an image forming means as shown in FIG. It has become so.

In the image forming means, reference numeral 1 denotes a photosensitive drum, on which a photosensitive material such as OPC, amorphous Se, amorphous Si or the like is formed on a cylindrical base such as aluminum or nickel. The photosensitive drum 1 is driven to rotate in the direction of the arrow. First, the surface of the photosensitive drum 1 is uniformly charged by a charging roller 2 as a charging device.

Next, scanning exposure is performed by a laser beam 3 that is ON / OFF controlled according to image information, and an electrostatic latent image is formed. This electrostatic latent image is developed and visualized by the developing device 4. As the developing method, a jumping developing method,
Two-component development, FEED development, and the like are used, and image exposure and reversal development are often used in combination.

The image is transferred from the photosensitive drum 1 onto the recording material P conveyed at a predetermined timing by a transfer roller 5 as a visualized toner image transfer device. At this time, the recording material P is nipped and conveyed to the photosensitive drum 1 and the transfer roller 5 with a constant pressing force.

On the other hand, the transfer residual toner remaining on the photosensitive drum 1 is removed from the surface of the photosensitive drum 1 by the cleaning device 7.

The heat fixing device 6 has a configuration as shown in FIG.

The fixing member 10 comprises the following members.

Reference numeral 13 denotes a fixing film which is a heating member having a small heat capacity. The fixing film has a total pressure of 100 μm or less and has heat resistance and thermoplasticity, such as polyimide, polyamide imide, PEEK, PES, P
It is a film based on PS, PFA, PTFE, FEP, or the like.

In addition, a film having a total pressure of 20 μm or more is required as a film having sufficient strength and excellent durability to constitute a long-life heat fixing device.

Therefore, the total thickness of the fixing film 13 is optimally not less than 20 μm and not more than 100 μm.

Further, in order to prevent toner offset and ensure the separation of the recording material, PFA, PTFE, FE
A heat-resistant resin such as P or a silicone resin having a good release property is mixed or coated alone.

Reference numeral 11 denotes a heating heater provided inside the fixing film 13, which heats a nip portion where the toner image on the recording material is melted and fixed.

The heater 11 is formed on the surface of a highly insulating ceramic substrate made of alumina or the like along the longitudinal direction by applying a current-generating resistor layer made of, for example, Ag / Pd (silver palladium), RuO2 or Ta2N by screen printing or the like. 10μ thickness
m and a width of about 1 to 5 mm.

Further, a temperature detecting element 14 such as a thermistor for detecting the temperature of the ceramic substrate raised in accordance with the heat generated by the current-generating resistance layer is provided on the rear surface of the ceramic substrate.

In accordance with the signal from the temperature detecting element 14, the duty ratio and the wave number of the voltage applied from the electrode (not shown) at the longitudinal end to the energized heat generating resistive layer are appropriately controlled, thereby fixing the image. Keeping the temperature controlled in the nip approximately constant,
Heating necessary for fixing the toner image on the recording material is performed.

The DC power supply from the temperature detecting element 14 to the temperature control unit (not shown) is achieved by a connector (not shown) via a DC power supply unit (not shown) and a DC electrode unit.

Further, a protective layer such as a thin glass coat which can withstand rubbing with the fixing film is provided on the surface of the energizing heat generating resistance layer of the heater 11.

Reference numeral 12 denotes a heat insulating stay holder for holding the heater 11 and preventing heat radiation in the direction opposite to the nip, and includes a liquid crystal polymer, a phenol resin, PPS, and PEEK.
And the like.

The fixing film 13 is loosely fitted to the heat insulating stay holder 12 with a margin, and is disposed rotatably in the direction of the arrow.

Further, since the fixing film 13 rotates while rubbing against the internal heater 11 and the heat-insulating stay holder 12, the frictional resistance between the heater 11 and the heat-insulating stay holder 12 and the fixing film 13 is reduced. There is a need.

Therefore, a small amount of lubricant such as heat-resistant grease is interposed on the surfaces of the heater 11 and the heat insulating stay holder 12. Thus, the fixing film 13 can rotate smoothly.

The pressure roller 20 serving as a pressure member has an elastic layer 22 formed by foaming heat-resistant rubber such as silicon rubber or fluorine rubber or silicon rubber on the outside of the cored bar 21.
, And a release layer 23 of PFA, PTFE, FEP or the like may be formed thereon.

The pressure roller 20 is sufficiently pressed in the direction of the fixing member 10 from both ends in the longitudinal direction by a pressing means (not shown) so as to form a nip required for heat fixing. It is rotationally driven in the direction of the arrow by an unillustrated rotational drive means from the end through the metal core 21.

Thus, the fixing film 13 is driven to rotate on the outside of the stay holder 12 in the direction of the arrow in FIG. Alternatively, a driving roller (not shown) is provided inside the fixing film 13 and the driving roller is rotated to rotate the fixing film 13.

FIG. 3 shows the structure of the fixing film 13.

In FIG. 3, reference numeral 13a denotes a film base layer, and a conductive primer layer 13b has a thickness of 2 to 6 μm on the outside.
m and a releasable layer 1 on the outside.
3c is formed.

Here, when the fixing film 13 is made to be insulative as a whole, the recording material charged in the transfer section of the image forming apparatus passes through the fixing nip, so that the fixing film 13 and the pressure roller The surface potential of 20 rises, causing charge-up.

For this reason, the fixing film 13 and the pressure roller 2
0, an electric field may be generated, and an electrostatic offset may occur in the fixing film 13.

Accordingly, as described above, the primer layer is made conductive by mixing carbon black or the like into the primer layer 13b, which is the intermediate layer of the fixing film 13, and the conductive primer layer 13b is electrically grounded. Connected.

Thus, the primer layer of the fixing film and the ground can be set to the same potential.

The release layer 13c has a structure as shown in FIG. 5, for example.

The releasable layer 13c serves as a toner offset preventing layer for the fixing film 13 and has good releasability.
A, PTFE, FEP or other fluororesin is electrostatically sprayed,
It is formed by coating to a thickness of about 5 to 15 μm by a coating method such as dipping.

In order to prevent offset due to charge-up of the fixing film 13, carbon black, beryllium oxide, hafnium oxide, magnesium oxide, sodium oxide having a specific resistance of 10 ⁷ to 10 ¹² Ωcm is contained in the release layer. 13d is mixed therein.

Incidentally, these are the specific resistance 1 shown in the prior art.
It is a substance having a higher specific resistance than a conductive substance such as carbon black of about 0 ^-3 to 10 ⁶ Ωcm, and by dispersing these in a fluororesin substantially uniformly, a predetermined amount is formed on the release layer 13c. Surface resistance and volume resistance can be provided.

Further, since the surface resistance and the volume resistance of the release layer 13c do not change much with respect to the mixing amount of the electron conductive material 13d, it is not necessary to control the mixing amount so severely.

In the above, the present embodiment mainly describes the heat fixing device of the film heating system, but the same effect can be applied to the fixing roller heating system.

That is, in the fixing roller heating system shown in FIG. 4, the release layer 33 formed outside the aluminum hollow core 32 containing the halogen lamp 31 is also used.
By dispersing an electron conductive substance having a relatively high specific resistance in the fluororesin similarly to the above-mentioned film heating release layer, offset due to charge-up and offset due to leak can be easily prevented at the same time.

Reference numeral 34 denotes a temperature detecting element for keeping the temperature of the outermost layer of the fixing roller 30 constant.

Here, in order to confirm the above effects, the following examination was conducted.

The structure of the heating fixing device is as follows. A conductive primer layer in which carbon black is dispersed on the outer surface of a 50 μm thick polyimide fixing film having an inner diameter of φ24, and magnesium oxide having a specific resistance of 2 × 10 ⁸ Ωcm on the surface thereof
After dispersing in a mixed solution of A and PTFE, a release layer was formed through dipping coating and baking steps.

The heater used was one in which Ag / Pd was screen-printed as a heat generating resistance layer on an alumina substrate and a glass protective layer was formed on the surface thereof.

The pressure roller used was a roller of φ25 in which a PFA tube was covered on silicone rubber.

The primer layer of all fixing films was 4 μm.
m, the surface layer is coated with a fluororesin of 8 μm, and the magnesium oxide of the electronic conductive substance dispersed in the fluororesin is 5 to 3 with respect to the fluororesin which is a mixed solution of PFA and PTFE.
0 vol%.

As a conventional technique, a comparison was made using a fluororesin layer in which carbon black having a specific resistance of 10 ⁴ Ωcm was dispersed in the fluororesin in an amount of ^{4 to} 10 vol%.

As a comparative example, the case where no conductive substance was dispersed in the release layer was also evaluated.評 価 Evaluation items (1) Leak-type offset: Three sheets of recording material having low surface resistance were continuously passed, and occurrence of offset was confirmed. (2) Charge-up: Potential measurement on the surface of the fixing film and occurrence of offset were confirmed when a recording material having a high surface resistance was continuously conveyed.

The evaluation results are shown below. In the table, 表 indicates a level without any problem, Δ indicates an allowable level, and X indicates a poor level (the same applies to the following tables).

In the following table, evaluation 1 indicates the leak type offset, evaluation 2-1 indicates the potential of the film surface, and evaluation 2-2 indicates the evaluation of the offset due to charge-up.

[0109]

[Table 1] From the above results, when forming a release layer of a fixing film in which a conductive material having a low specific resistance is mixed in a fluororesin as in the prior art, the surface resistance and the volume of the release layer Since the resistance changes rapidly depending on the amount of the conductive material, the resistance changes rapidly, so it is necessary to mix a desired amount of the conductive material, and it is difficult to minimize the variation in the mixed amount of the conductive material as much as possible. Need to be managed,
This has led to a decline in productivity.

Further, since the offset phenomenon also severely affects the dispersion density of the conductive substance, it is necessary to improve the dispersion density.

Therefore, it can be seen that it is difficult to completely prevent both the leak type offset and the offset due to charge-up.

On the other hand, in this embodiment, since the mixed electronic conductive substance has a specific resistance of 10 ⁷ Ωcm or more, the surface resistance and the volume resistance of the release layer depend on the mixed amount of the electronic conductive substance. Because of a small change rate of the electronic conductive material, which does not change significantly, a suitable amount can be easily mixed, and a large difference in resistance value does not occur even if the dispersion density is agglomerated in a minute range.

In the case of an electronic conductive substance having a specific resistance exceeding 10 ¹² Ωcm, productivity is poor because a large amount of the conductive substance is required.

Therefore, the specific resistance of the present embodiment is 10 ⁷ Ωc
When an electron conductive material having a length of not less than m and not more than 10 ¹² Ωcm is mixed, there is no point where the transfer charge leaks locally, and the local potential on the surface is also suppressed. Are prevented, and the process can be performed without deteriorating the productivity of the fixing film.

(Embodiment 2) Embodiment 2 will be described below.

The configuration of the entire apparatus is the same as that shown in FIG. 1 described in the first embodiment, and the configuration inside the heat fixing device is also the same as that shown in FIG. 2 described in the first embodiment.

In this embodiment, a water-soluble conductive material having a relatively high specific resistance is applied to the release layer forming the outermost surface of the fixing film in order to obtain an electronic conductive material that is more uniformly dispersed. In a state of an aqueous solution, it is mixed into a liquid fluororesin which is a liquid release layer.

That is, potassium chloride, nickel chloride,
Titanium chloride, iron chloride, lithium chloride, zinc chloride, cobalt chloride, potassium chromate, sodium bromide, potassium hydroxide, sodium hydroxide, potassium carbonate, sodium iodide, aluminum sulfate, thorium oxychloride, molybdenum oxychloride, etc. After a conductive substance soluble in water is mixed with a liquid fluorocarbon resin such as PFA, PTFE or FEP in the form of an aqueous solution, the film is formed by a coating method such as spraying or dipping. A release layer as an outer layer is formed.

Here, there is an ion conductive substance as a water-soluble conductive substance. In the case of an ion conductive substance, the release layer is formed depending on the use environment of temperature and humidity and the amount of water vapor evaporated from the recording material. Since the surface resistance changes significantly, it is difficult to control the potential on the surface of the release layer.

By forming the release layer as described above, the electron conductive substance having a relatively high specific resistance can be uniformly dispersed in the fluororesin layer, so that the surface resistance of the formed release layer can be improved. In addition, the volume resistance is hardly biased, and as described in the first embodiment, an appropriate amount of the conductive substance can be easily mixed. Therefore, by mixing with the liquid fluororesin in the form of an aqueous solution, it is possible to uniformly disperse the mixture by simple stirring, thereby preventing both the leak-type offset and the offset due to the charge-up of the surface of the release layer. It becomes possible.

Further, irrespective of the specific resistance value, a solution in which a conductive substance is dissolved can be mixed therein, and not only a conductive substance soluble in water but also a substance soluble in an acid or the like is included.

(Embodiment 3) Embodiment 3 will be described below.

The configuration of the entire apparatus is the same as that shown in FIG. 1 described in the first embodiment, and the configuration inside the heat fixing device is also the same as that shown in FIG. 2 described in the first embodiment.

In this embodiment, the electron conductive substance dispersed in the release layer forming the outermost surface of the fixing film is also dispersed in the release layer formed as the outermost layer of the pressing member.

[0125] Release layer 2 of pressure roller in this embodiment
3 (FIGS. 2 and 4) is formed by forming a fluororesin such as PFA, PTFE, FEP or the like in a tubular shape or by coating. High electron conductive material is mixed.

Since the electron conductive substance is also mixed in the release layer of the pressing member, even if the amount of the electronic conductive substance mixed in the release layer of the heating member is reduced, the charge is locally increased. Thus, the offset due to charge-up can be prevented in the same manner as in the first embodiment. In particular, even with respect to local charging that occurs when the rear end of the recording material peels from the fixing nip portion, a tanning effect of both the fixing member and the pressing member can be obtained, so that even when the image forming apparatus speeds up. Since the potential is not locally held, a sufficient effect can be obtained for the stripping offset.

Further, since the amount of the electron conductive substance mixed into the release layer of the heating member is reduced, even if the release layer of the fixing member is slightly scraped due to, for example, the durability of the recording material, the recording material may be removed. The number of durable sheets until the above transfer charge leaks to the conductive primer layer can be increased, and the effect of preventing a leak-type offset can be extended.

In order to confirm the above, the following examination was conducted.

The heat fixing device is constituted by a fixing film having an inner diameter of φ24, a conductive primer layer in which carbon black is dispersed on the outer surface of polyimide having a thickness of 50 μm, and magnesium oxide having a specific resistance of 2 × 10 ⁸ Ωcm on the surface thereof.
8 for fluororesin, which is a mixture of A and PTFE
After dispersing by vol%, a release layer was formed through a dipping coating and baking process.

The heater used was one in which Ag / Pd was screen-printed as an exothermic resistance layer on an alumina substrate, and a glass protective layer was formed on the surface thereof.

The pressure roller is 2 × 10 on silicone rubber.
A φ25 tube covered with a PFA tube mixed with 5 vol% of magnesium oxide having a specific resistance of ⁸ Ωcm was used.

The primer layer of all fixing films was 4 μm.
m, the surface layer was coated with a fluororesin at 8 μm.

As a comparative example, a pressure roller of φ25 in which a pure PFE tube was covered on silicone rubber,
Magnesium oxide with specific resistance of 2 × 10 ⁸ Ωcm is PFA
10 with respect to fluororesin which is a mixture of PTFE and PTFE
The case where a fixing film in which vol.% was dispersed was used was compared.

As a conventional technique, a comparison was made using a fluororesin layer in which carbon black having a specific resistance of 10 ⁴ Ωcm was dispersed at 5 vol% with respect to the fluororesin.

As the conventional pressure roller, a roller having a diameter of φ25 in which a pure PFA tube was covered on silicone rubber was used.

In the above-described embodiment, comparative example, and conventional technique, the initial stripping offset is of the same level, and the leak-type offset does not occur at all in the initial stage.

As an evaluation, a leak type offset before and after endurance was confirmed by continuously passing three recording materials having a low surface resistance.

The evaluation results are shown below.

[0139]

[Table 2] From the above results, when the electronic conductive material is mixed only in the release layer of the heating member, the initial stripping offset is within the allowable range, so that a certain amount of the electronic conductive material is required. However, when the recording material was transported and durable, the surface of the heating member was gradually scraped, so that the leakage of the transfer charge of the recording material from the locally dense portion of the electronic conductive material to the conductive primer layer was observed. Occurs.

In particular, when an electronic conductive material having a low specific resistance is used as in the prior art, the number of sheets having a long life is reduced.

On the other hand, when an electron conductive substance is mixed in the release layer of the pressing member as in the present embodiment,
Since the amount of the electron conductive substance mixed into the release layer of the heating member can be reduced, the density is hardly locally increased, and a leak-type offset hardly occurs even after the durability.

In forming the release layer of the heating member and the release layer of the pressing member according to the second embodiment,
A similar effect can be obtained by using a conductive material having a high specific resistance to dissolve, including the water-soluble conductive material shown in FIG.

[0143]

As described above, according to the present invention,
An image forming apparatus for fixing the unfixed image as a permanent image on the recording material by passing the recording material on which the unfixed image is formed through a nip portion between the fixing member having the heating member and the pressure member. Since the outermost release layer of the heating member contains an electronic conductive substance having a specific resistance of 10 ⁷ Ωcm or more and 10 ¹² Ωcm or less, a release layer having a target resistance value is uniformly formed. This makes it easier to perform the operation, and eliminates a point where the transfer charge leaks locally, thereby preventing a leak-type offset. In addition, since a local charge on the surface is suppressed, an offset due to charge-up can be prevented.

Further, since the outermost release layer of the pressing member also contains an electronic conductive substance having a specific resistance of 10 ⁷ Ωcm or more and 10 ¹² Ωcm or less, the heating member is made to be durable by the paper passing durability of the recording material. Even when the surface of the release layer is scraped, the transfer charge of the recording material is unlikely to leak to the conductive primer layer or the conductive hollow core of the heating member, and a leak-type offset prevention effect can be obtained for a long time.

Further, since the solution in which the conductive substance is dissolved is mixed into the liquid release layer material when forming the outermost release layer of the heating member, the conductive substance is uniformly dispersed. Since it has a predetermined surface resistance with no local difference, the local potential on the surface of the heating member can be suppressed, thereby making it possible to prevent offset due to charge-up.

Further, when forming the outermost release layer of the pressing member, the solution in which the conductive substance is dissolved is mixed into the liquid release layer material, so that only one of the release layers is used. It is possible to uniformly disperse the mixture while reducing the amount of each mixture rather than the amount of mixture.

Since the mixed conductive substance dissolves in water,
It is mixed with a liquid release layer material in the state of an aqueous solution.

Since the release layer is formed of a fluororesin, it has good release properties.

The image forming apparatus may include an image forming means for forming an unfixed image on a recording material and a heat fixing device for fixing the unfixed image as a permanent image.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an image forming apparatus according to the present invention.

FIG. 2 is a configuration diagram of a heat fixing device according to the present invention.

FIG. 3 is a sectional view of a fixing film according to an embodiment of the present invention.

FIG. 4 is a configuration diagram of a heat fixing device according to the present invention.

FIG. 5 is a cross-sectional view of a release layer according to one embodiment of the present invention.

FIG. 6 is a configuration diagram of a heat fixing device according to a conventional technique.

FIG. 7 is a configuration diagram of a heat fixing device according to a conventional technique.

FIG. 8 is a sectional view of a fixing film according to a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Heater 12 Heat insulation stay holder 13 Fixing film 13c Release layer 13d Electronic conductive material 20 Pressure roller

Claims (7)

[Claims] An unfixed image is recorded by passing a recording material on which the unfixed image is formed between a fixing member having a heating member and a fixing nip pressed against each other by a pressing member. In a heat fixing device for fixing a permanent image on a material, a specific resistance of 10 ⁷
A heat fixing device comprising an electronic conductive substance having a resistance of Ωcm or more and 10 ¹² Ωcm or less. 2. The method according to claim 1, wherein the outermost release layer of the pressing member contains an electronic conductive substance having a specific resistance of 10 ⁷ Ωcm or more and 10 ¹² Ωcm or less. The fixing device according to claim 1. 3. An unfixed image is recorded by passing a recording material on which an unfixed image is formed between a fixing member having a heating member and a fixing nip pressed against each other by a pressure member. In a heat fixing device for fixing a permanent image on a material, when forming the outermost release layer of the heating member, the solution in which the conductive substance is dissolved is mixed into the liquid release layer. Characteristic heat fixing device. 4. The liquid releasable layer according to claim 3, wherein a solution in which a conductive substance is dissolved is mixed into the liquid releasable layer when forming the outermost releasable layer of the pressing member. The fixing device according to claim 1. 5. The heat fixing device according to claim 3, wherein the mixed conductive material is dissolved in water. 6. The heat fixing device according to claim 1, wherein the release layer is formed of a fluororesin. 7. The heat fixing device according to claim 1, wherein an image forming means for forming an unfixed image on the recording material, and fixing the unfixed image as a permanent image on the recording material. An image forming apparatus comprising: