JPH077233B2 - Heat fixing device - Google Patents

Description

The present invention relates to an image forming apparatus such as an electrophotographic apparatus or an electrostatic printing apparatus, in which at least one of a toner image formed on a carrier such as paper is heated. The present invention relates to a heat fixing device that is provided with a means and that fixes between a pair of rolls that rotate in a state of being pressed against each other, and in particular, even with a multiple-layered carrier such as an envelope, a toner image can be formed without wrinkling. The present invention relates to a heat fixing device improved so that fixing can be performed.

[Conventional technology]

As a fixing device in the image forming apparatus, a heating roll in which a non-adhesive heat-resistant layer is coated on the surface of a metal core having good heat conductivity, which internally has a heat source such as an infrared lamp, a halogen lamp, or a nichrome wire, is used. There is known a heat roll type heat fixing device in which a pressure roll having a surface coated with a heat resistant elastic material layer is disposed so as to face each other.

In the above heat fixing device, when fixing the toner image formed on the carrier, first, the heat source is fed to heat the surface of the heating roll to a temperature necessary for fixing, and the heating roll and the pressure roll are separated. The toner image can be fixed on the carrier by pressing and rotating the carrier with an appropriate pressure and passing the carrier carrying the toner image between both rolls.

In such a heat fixing device, it is particularly important that an offset does not occur and a wrinkle does not occur on the carrier in order to obtain a good quality fixed image.

In order to prevent offset, a heating roll whose surface is coated with a resin with good releasability such as polytetrafluoroethylene (PTFE) or perfluoroalkoxy-tetrafluoroethylene copolymer (PFA) is used. However, since such a heating roll has a low elasticity, it cannot be said to be sufficient in terms of fixing property and has a drawback that the surface is likely to be scratched. In order to eliminate this drawback, a heating roll has been proposed in which a mixed layer of fluororubber and fluororesin is formed on the roll surface, and then firing is performed to form a fluororesin layer as the outermost layer. (Usp4,568,275).

However, this heating roll has a problem of poor durability. That is, since the fluororesin layer on the surface has a thickness of only a few μm, the fluororesin layer is worn by tens of thousands of copies due to contact with a cleaning member or the like.

Therefore, a heating roller provided with a fluororesin layer on the surface of the above mixed layer has been proposed (JP-A-59-217010).

On the other hand, various structures have been proposed to prevent paper wrinkles. For example, Jitsukai Sho 54-98226 (Jitsuko Sho 62-15818)
Discloses that the heating roller and the pressure roller are brought into light contact with each other, and the pressure deformation rates of both rollers are made equal to or close to each other, whereby curling and wrinkling can be prevented even on thick copy paper. Further, Japanese Patent Laid-Open No. 59-74578 discloses a core material, a heat-resistant elastic layer covering the core material, and a fluororesin layer coated thereon in order to prevent wrinkles even under adverse conditions such as thin double-sided copying. It is disclosed that the roller composed of the above is used as both the heating roller and the pressure roller.

By the way, as a means for writing addresses on a large number of envelopes, printing directly on the envelopes by a printer is being considered.
The problem here is that wrinkles are generated when the envelope carrying the toner image is fed to the above-described heat fixing device to fix the toner image. If the envelope is wrinkled,
Not only is the envelope curved or deformed, but the printed address is divided by wrinkles, and in extreme cases, it cannot be read or read. That is,
The envelope has at least two stacking parts due to its construction, and depending on the glue part or the stacking part, it becomes triple or quadruple, and the maximum paper thickness becomes thicker, and the two stacking parts mutually slide and move. The above-mentioned problem is a peculiar phenomenon caused by such sliding movement, and is a problem that is not experienced in ordinary copying. As a countermeasure against this, in the case of envelope fixing, a means such as lowering the fixing pressure below the fixing pressure suitable for fixing plain paper has been proposed (JP-A-61-294475).
issue).

[Problems to be solved by the invention]

When fixing the toner image formed on the envelope, the above-mentioned conventional technique cannot sufficiently prevent the result, that is, it is not possible to prevent wrinkles while securing good fixing property.
That is, according to the invention described in JP-A-61-294475, it is possible to prevent wrinkles, but the fixing pressure becomes low, so that good fixing properties cannot be obtained. See also
The device described in Japanese Patent No. 98226 also has a problem that sufficient fixing property cannot be obtained because both rollers have a structure of "light pressure contact" in order to make the deformation amounts of the pressure contact portions of both rollers equal or close to each other. Further, in the apparatus described in JP-A-59-74548, since the elastic layer of the heating roller and the elastic layer of the pressure roller have different thicknesses, a substantially flat nip is not formed, and the toner image on the envelope is not formed. The anti-wrinkle action cannot be expected under the severe conditions such as fixing of wrinkles.

The present invention solves the above-mentioned problems existing in the prior art, and it is possible to obtain a high-quality fixed toner image without causing wrinkles even in the case of a carrier composed of a plurality of layers such as an envelope. An object is to provide a heat fixing device.

[Means for solving problems]

In order to solve the above-mentioned problems existing in the prior art, in the present invention, a heating roll in contact with the toner image on the carrier and a pressurizing member so as to form a nip between the heating roll and the heating roll. In a heat fixing device having a roll, the heat roll and the pressure roll are provided with an elastic layer having heat resistance and a resin surface layer having releasability around a core bar, and have substantially the same outer surface. And the surface hardness of the heating roll and the pressure roll is less than Hs85 ° and the difference in surface hardness between both rolls is within Hs10 °, the elastic layer of the heating roll has a thermal conductivity of 0.2 × 10 ^-3 cal / cm ・ sec ・
A material having a temperature of ℃ or more is formed to have a thickness of 1 to 2 mm, and the heating roll and the pressure roll are pressed with a linear pressure of 0.8 to 2.0 kg / cm to form the nip so as to be substantially flat. It adopted the technical means.

[Action]

With the above-described structure, the nip portion between the pressure roll and the heating roll forming the heat fixing device, that is, the passage portion of the toner image carrier can be made substantially flat, so that the toner image carrier is wrinkled. It is considered that there is an action to prevent

Further, by making the shape of the nip substantially flat, the action of preventing the carrier after fixing from winding around the surface of the heating roll can be expected. This eliminates the need for a separating claw and eliminates damage to the roll surface due to contact between the separating claw and the roll surface.

〔Example〕

 The details of the present invention will be described below with reference to the accompanying drawings.

First, the basic configuration of the present invention will be described in comparison with a conventional example.

FIG. 1 and FIG. 3 are explanatory views of a pressure contact state between a pressure roll and a heating roll according to the present invention and the related art, respectively. In both figures, 1 and 2 are a pressure roll and a heating roll, respectively, whose axes are formed substantially parallel to each other and are rotatable in the direction of the arrow, and both rolls are arranged in a pressure contact state. In the conventional one, for example, the pressure roll 1 has a heat-resistant elastic layer 12 made of silicone rubber having a hardness of about 25 to 55 ° on the surface of a cored bar 11 made of a material having good thermal conductivity such as aluminum alloy and iron. On the other hand, the heating roll 2 is coated with a heat source 23, and the surface of a cored bar 21 made of a material having good thermal conductivity is coated with a low surface energy resin such as tetrafluoroethylene resin (PTFE) or perfluoroalkoxy resin (PFA). It is formed by covering the heat-resistant release layer 24 of. Therefore, due to the difference in elasticity between the two rolls, the surface of the pressure roll 1 is elastically deformed to form a concave surface in the nip portion 3 between the pressure roll 1 and the heating roll 2 as shown in FIG. Therefore, when a carrier (not shown) such as paper carrying a toner image is fed in the direction of arrow A, the carrier is first bent upward at the entrance 3a of the nip portion 3 and then downward at the nip portion 3. It is bent as a concave portion, and at the outlet 3b of the nip portion 3, the upper portion is bent again as a concave portion. On the other hand, when the carrier has double or more overlapping portions like an envelope, sliding movement occurs between upper and lower constituent parts due to repeated bending action in the nip portion 3 or movement due to a difference in paper thickness. It is presumed that the difference in speed also causes a difference in speed between the upper and lower parts of the envelope, causing wrinkles. On the other hand, according to the present invention, for example, heat resistant elastic layers 12 and 22 of substantially the same material and the same thickness are formed on the surfaces of the core metal 11 of the pressure roll 1 and the core metal 21 of the heating roll 2, respectively. Since the surface hardness of the both is within the hardness difference Hs of 15 °, the nip portion 3 becomes a substantially flat surface as shown in FIG. It has the effect of not giving it and making the vertical movement speed of the carrier substantially the same.

The following experiment was conducted in order to confirm the above action.

In FIG. 1, the pressure roll 1 and the heating roll 2 are formed on the outside of the core bars 11 and 21 made of aluminum alloy, respectively, and coated with HTV silicone rubber or perfluoroalkoxy (PFA) resin to have an outer diameter of 31 mm. The pressure was 1.2 kg / cm and the fixing was carried out. Fixing speed is 160mm / sec, fixing temperature is 18
It was 0 ° C. In this case, the hardness of silicone rubber was changed in various combinations, and the envelope was used as a toner image bearing member by combining with a roll coated with PFA resin, and 100 envelopes were produced for each combination. The condition was evaluated. The results are shown in FIG.
In this case, the surface hardness of the roll (A type spring hardness: JIS K
6301) is a value measured by a commercially available hardness tester (manufactured by Kobunshi Keiki, model JA). As is clear from Fig. 4,
If there is no difference in hardness between the pressure roll and the heating roll, the envelope will not wrinkle at all. On the contrary, when the hardness difference between the two rolls is large, almost all wrinkles occur and the envelope is deformed. That is, if the hardness difference is within Hs 15 ° (within the range of parallel chain lines), preferably within Hs 10 ° (within the range of parallel solid lines), it is possible to avoid the concave surface of the nip portion 3 as shown in FIG. it can. In this case, when the hardness of the pressure roll and / or the heating roll exceeds Hs85 °, paper wrinkles do not occur, but the nip width (W in Fig. 1) is insufficient and the fixability is insufficient. On the other hand, if the fixing pressure is increased in order to secure the nip width, the plastic deformation of the rubber or resin depending on the heat and the pressure becomes large, resulting in a cause of shortening the life of both rollers.

Further, FIG. 5 is a diagram showing a wrinkle generation state of the toner image bearing member when the outer diameters of the pressure roll and the heating roll are variously changed and combined, and under the same fixing conditions as those shown in FIG. It depends. As is apparent from FIG. 5, when there is no difference in outer diameter between the pressure roll and the heating roll, no wrinkles are observed in the envelope as the toner image carrier. On the other hand, when the difference in outer diameter between the two rolls is large, almost all wrinkles occur and the envelope is deformed. That is, when the outer diameter difference is within 5 mm (within the range of parallel chain lines), and preferably within 2 mm (within the range of parallel solid lines), it is possible to prevent the envelope from wrinkling. Particularly when the outer diameters of both rolls are formed to be substantially the same, extremely good results can be obtained.

As described above, the heating roll and the pressure roll are made to have a surface hardness such that the nip formed between the rolls becomes a substantially flat surface, and the outer diameters of the rolls are made as close as possible to each other, so that the envelope is wrinkled. Can be prevented.

However, if the structure shown in FIG. 1 is applied to an actual machine as it is, a problem of offset occurs. A structure for solving this problem is shown in FIG.

In FIG. 2, on the surface of the heat resistant elastic body layer 12 formed on the surface of the core metal 11 of the pressure roll 1, the release resin layer 14 made of the above-mentioned fluororesin is further formed, and the heating roll 2 A releasable resin layer 24 is further formed on the surface of the heat resistant elastic body layer 22 formed on the surface of the core metal 21. Since the outer surface of the heating roll 2 is the releasable resin layer, the occurrence of offset can be prevented. Since the outer surface of the pressure roll 1 is also a releasable resin layer, the surface hardness of both rolls can be made uniform and wrinkles can be prevented. The releasable resin layer may have a thickness of about 10 to 50 μm.

In order to perform good fixing with the apparatus shown in FIG. 2, it is necessary to consider the following conditions.

In the conventional device shown in FIG. 3, the pressure roll has a structure that is easily elastically deformed. Therefore, if the contact pressure between both rolls is about 1 kg / cm in linear pressure, good fixability can be obtained. A nip width (usually 3-5 mm) can be secured. However, this device cannot be put to practical use because wrinkles occur in the envelope even with a linear pressure of 0.1 to 0.2 kg / cm.

On the other hand, in the apparatus shown in FIG. 2, since the pressure roll has a higher rigidity than the conventional one, it is necessary to press both rolls so as to generate a contact pressure larger than the conventional one in order to secure the nip width. As a specific condition, it is desirable that the contact pressure between both rolls be 0.8 kg / cm or more in linear pressure,
It is more preferably 1.2 kg / cm or more. However, if the linear pressure is too large, this structure will also shorten the life due to plastic deformation of the rubber, so 2.0 kg / cm or less is preferable. Especially 100 mm / sec
In order to secure good fixing properties at the above fixing speeds, the linear pressure must be 1.2 kg / cm or more.

The conditions regarding the roll for achieving the object of the present invention also include the following. When the surface hardness of the pressure roll and the heating roll exceeds Hs85 °, it is inconvenient because the predetermined nip width cannot be secured even if a predetermined pressure contact force is applied. The preferred surface hardness is 80 ° or less. In this case, even if the pressure contact force is increased to secure the nip width, the toner image carrier is deformed, the life is shortened, and wrinkles and other undesired phenomena occur, which is not preferable.

Next, if the thickness of the heat resistant elastic layer provided on the heating roll is less than 1 mm, the effect as an elastic body is weakened, and it becomes difficult to keep the roll surface at a predetermined hardness and uniformly, which is inconvenient. . On the other hand, when the thickness exceeds 2 mm, not only the temperature distribution of each part of the heating roll becomes non-uniform, but also the both ends which are the non-sheet-passing parts are overheated to prevent heat conduction.
It is not preferable because it causes an unexpected accident.

Further, if the thermal conductivity of the material forming the elastic layer provided on the heating roll is less than 0.2 × 10 ^-3 cal / cm · sec · ° C, the heat conduction effect in the heating roll will be insufficient and the temperature distribution will be insufficient. Is not only uneven, but also causes local heating, which is inconvenient. A more preferable thermal conductivity is 0.6 × 10 ^-3 cal / c
m / sec / ° C or higher. However, the thermal conductivity is 1.5 × 10 ^-3 cal
In order to make it higher than / cm · sec · ° C, it is necessary to mix a large amount of a good heat-conducting substance, for example, a metal oxide such as carbon black or titanium oxide, into the elastic layer. However, the result of mixing the above good thermal conductive material is that the hardness is Hs
It becomes larger than 80 °, and it becomes impossible to secure a sufficient nip width. Therefore, the thermal conductivity should be 1.5 × 10 ^-3 cal / cm · sec · ° C or less.

In addition to the above, the device of the present invention is significantly different from the conventional device in the following points.

In a normal heating roll type fixing device, the nip is the third
Because of the shape shown in the figure, the carrier after passing through the nip tends to wind around the heating roll. As a countermeasure against this, a separation claw has conventionally been brought into contact with a heating roll. However, the use of separation claws damages the surface of the heating roll and shortens the roll life. In addition, the separation claws themselves are deteriorated and deformed by heat during long-term use, and the separation function deteriorates, so replacement of claws is also necessary. .

On the other hand, in the apparatus of the present invention, since the nip has a substantially flat shape as shown in FIG. 2, the carrier after passing through the nip is discharged to the outside of the fixing device without being wound around the heating roll. It That is, the apparatus of the present invention has a function of separating the carrier passing through the nip from the heating roll without using the separating claw.

The present invention is not limited to the above embodiment, and the following modifications are possible. That is, the elastic layers of the heating roll and the pressure roll are not limited to silicone rubber, but may be other known materials such as fluororubber or a mixture of fluororubber and fluororesin. In addition, a fluororubber layer (which may include a fluororesin) may be formed on the silicone rubber layer, for example, with two elastic layers. Although such a structure is disadvantageous in terms of price, it is advantageous in terms of roll strength. That is, when a silicone rubber layer is formed on the surface of a core metal, a fluororesin-containing fluororubber layer is formed on the core rubber, and then the surface fluororesin layer is formed after firing, the fluororesin layer appears on the surface of the fluororubber layer. Therefore, peeling of the surface fluororesin layer is less likely to occur.

〔The invention's effect〕

Since the present invention has the configuration and operation as described above, a toner image carrier having a normal and good image quality does not cause wrinkles even if the toner image carrier is composed of a plurality of layers such as an envelope. The effect is that it can be fixed. Moreover, in particular, both the heating roll and the pressure roll have a roll structure in which a heat-resistant elastic layer and a heat-resistant release layer or release resin layer are formed on a core metal, so that an envelope-like structure can be obtained without wrinkling. A toner image on a different carrier can be fixed well even under high speed conditions. Further, it is possible to prevent the carrier from being wound around the heating roll without using the separating claw.

[Brief description of drawings]

FIG. 1 is a view showing a pressure contact state between a pressure roll and a heating roll for explaining the principle of the present invention, FIG. 2 is a sectional view of a heat fixing device according to an embodiment of the present invention, and FIG. FIG. 4 is an explanatory view of a pressure contact state in a conventional one, FIG. 4 is a view showing a wrinkle generation state of an envelope when surface hardness of a pressure roll and a heating roll in FIG. 1 is changed, and FIG. It is a figure which shows the wrinkle generation | occurrence | production state of an envelope when each outer diameter of a roll and a heating roll is changed. 1: Pressure roll, 2: Heating roll, 3: Nip part.

Claims (1)

[Claims] 1. A heating and fixing device comprising a heating roll in contact with a toner image on a carrier and a pressure roll pressed against the heating roll so as to form a nip between the heating roll and the heating roll. The pressure roll is provided with an elastic layer having heat resistance and a resin surface layer having releasability around the core metal, and is formed to have substantially the same outer diameter. The surface hardness is less than 85 s and the difference in surface hardness between the two rolls is within 10 s, and the thermal conductivity of the elastic layer of the heating roll is 0.2 × 10 ^-3 cal / cm ・ sec ・
Formed to a thickness of 1 to 2 mm with a material of ℃ or higher, and press the heating roll and pressure roll with a linear pressure of 0.8 to 2.0 kg / cm to form the nip to be substantially flat. A heat fixing device characterized by: