JPH1195601A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of performing excellent fixation over a long period even if offset of toner occurs on a surface of a fixing roller. SOLUTION: This device is constituted so that the cleaning roller 20 is held in contact with the pressure roller 10 while driven by the rotation of the pressure roller 10, and to make the temp. of the cleaning roller 20 higher than the temp. of glass transition point of the toner, while lower than the temp. of the pressure roller 10, and the temp. on the pressure roller 10 lower than the temp. of the fixing roller 9, at the print starting time. The device is composed so that the toner being offset on the fixing roller 9 is shifted to the surface of the pressure roller 10 whose temp. is lower than the fixing roller 9, in the case of the temp. adjusting time of the fixing device 8, and the toner shifted to the pressure roller 10 is shifted and held to the cleaning roller 20 whose temp. is lower than the pressure roller 10 while higher than the temp. of the glass transition point of the toner.

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 having a fixing device for heating and fixing toner on a transfer material.

[0002]

2. Description of the Related Art Conventionally, an image carrier having an electrostatic latent image on the surface thereof, a developing device for developing the electrostatic latent image on the image carrier with a toner as a developer to visualize the image, and a developed device have been developed. 2. Description of the Related Art An image forming apparatus having a transfer device for transferring a toner image on an image carrier onto a transfer material, a fixing device for fixing the toner on the transfer material by heating and pressing the transfer material on which the toner image has been transferred, and the like are known. The image forming apparatus includes an electrophotographic printer, a copying machine, a facsimile, and the like.

As shown in FIG. 4, a fixing device 59 for forming an image on a transfer material by fixing the toner on the transfer material by heating and pressurizing the toner is brought into contact with the surface of the transfer material carrying the toner. A fixing roller 60 heated by a halogen lamp 62 as a heating member;
In many cases, a thermal fixing system having a pair of rollers with a pressing roller 61 pressed against zero is used.

The fixing roller 60 of the fixing device 59 includes:
The felt member 63 containing the silicone oil is brought into contact with the toner member to prevent the toner on the transfer material from being offset from the toner adhering to the surface of the fixing roller 60. Since the felt member 63 has a function of applying silicone oil to the surface of the fixing roller 60 and removing foreign substances such as toner adhered to the surface of the fixing roller 60, a user or the like periodically removes the felt member 63. I am trying to replace it.

[0005] Further, as shown in FIG.
To the fixing roller 60, for example, by applying a negative voltage to the fixing roller 60 so that the negatively charged toner 68 on the transfer material 67 is not offset to the surface of the fixing roller 60. I have. Further, a diode 65 is also connected to the pressure roller 61 to
The surface of the toner is charged to the positive polarity, and the toner 6 charged to the negative polarity
In some cases, the offset may be more effectively prevented by attracting 8 to the transfer material 67. Recently, the use of a fixing device configured to apply a voltage having a polarity opposite to the polarity of the charged toner to the fixing roller has been increasing, and this effectively offsets the toner without providing the above-mentioned felt member. This is because it is possible to prevent such a problem and to save the trouble of replacing the felt member.

As a transfer material used in these image forming apparatuses, paper made only for electrophotography by adding a sizing agent such as kaolin or rosin to hardwood or softwood pulp is often used. Kaolin and rosin as sizing agents added to pulp are added so as not to adversely affect the electrophotographic process. For example, talc, a sizing agent, adheres to the surface of the image carrier and absorbs moisture in the air or paper to reduce the resistance, so that an electrostatic latent image electrostatically formed on the surface of the image carrier is formed. This causes a phenomenon called "image deletion", thereby deteriorating the quality of the image formed on the transfer material. However, image deletion is prevented by adding kaolin or rosin.

Until now, acid paper has been the mainstream of the above-mentioned specialty paper. However, the use of neutral paper has increased due to the problem of preservability such as severe deterioration of the paper due to long-term storage. I have. As an additive added to neutral paper, which has been increasing recently, calcium carbonate (C
aCO ₃ ) is increasingly used. This is because calcium carbonate is inexpensive and has high whiteness, so if calcium carbonate is added, bleaching does not need to be performed excessively to make the paper white, which clears one environmental problem in the papermaking process. That you can do it. Calcium carbonate may be mixed in paper up to about 25% by weight.

The above-mentioned calcium carbonate includes limestone obtained by crushing limestone into powder, and heavy calcium carbonate originating in paleontology called “chalk”. There is also light calcium carbonate made by crushing limestone, heating it to produce CaO, and pouring it into water to inject carbon dioxide into lime milk.

[0009]

However, in an image forming apparatus using a fixing device configured to apply a voltage having a polarity opposite to the polarity of the charged toner to the fixing roller, the above-mentioned calcium carbonate contains a large amount of calcium carbonate. When using neutral paper,
It has been found that the following problems may occur.

When paper containing calcium carbonate as a transfer material is set in a transfer paper cassette or the like, and is fed from the cassette through a predetermined conveyance path during image formation,
Paper dust is generated by contact with a paper feed roller, a transport roller, a registration roller, a guide surface in the transport path, and the like provided in the transport path. This paper powder contains a large amount of calcium carbonate depending on the content. Calcium carbonate in paper powder generated by transportation or the like is easily charged to a positive polarity by friction with metals and plastics.

The paper powder containing calcium carbonate adheres to the surface of the negatively charged fixing roller by an electric attraction force or a physical force, and the paper powder containing calcium carbonate adheres to the surface of the fixing roller. Is formed. Since calcium carbonate is positively charged, the transfer paper carrying the toner is transported with calcium carbonate adhered to the surface of the fixing roller, and the toner comes into contact with the fixing roller. Is offset to the surface of the transfer roller.

The toner offset to the surface of the fixing roller is mixed with calcium carbonate and adheres to the surface of the fixing roller. However, when the fixing device warms up, the fixing roller and the pressure roller come into direct contact with each other. While rotating, the offset toner on the fixing roller transfers to the surface of the pressure roller having a lower temperature than the fixing roller. This is a pressure roller with a low surface temperature of 80 to 120 ° C,
When a fixing roller having a high surface temperature of 180 to 200 ° C. is compared with a fixing roller having a low surface temperature, toner is more likely to adhere to a pressing roller having a low surface temperature than a fixing roller having a high temperature.

The phenomenon in which the offset toner on the fixing roller is transferred to the pressure roller occurs little by little. When the number of sheets passing through the fixing device exceeds tens of thousands, the toner transferred to the pressure roller is pressed by the toner. It grows to large flakes on the roller surface. If the transferred toner grows until it becomes flake-like, a part of the flake-like toner comes to adhere to the surface of the fixing roller, causing a problem that the toner image on the transfer material is disturbed.

[0014] The above phenomenon was tested on various transfer papers, and as a result, calcium carbonate contained in the paper was reduced to 10%.
% To 25% (weight ratio), especially 15% to 2%.
At 5% (weight ratio), it frequently occurs. This is because the toner contamination of the fixing roller is not necessarily proportional to the amount of calcium carbonate, and the sizing agent (AK
D, ASA, kaolin, neutral rosin, etc.) and the method of bleaching the transfer paper (chlorine, non-chlorine) can be considered, but in any case, if the amount containing calcium carbonate exceeds 10%, the fixing roller Is caused by the offset toner.

Accordingly, the present invention is directed to a fixing roller, in which a cleaning roller is brought into contact with a pressing roller to transfer toner transferred from the fixing roller to the pressing roller to the cleaning roller and to hold the toner on the surface of the cleaning roller. It is an object of the present invention to provide an image forming apparatus capable of performing good fixing over a long period of time even when toner offset occurs due to calcium carbonate attached to the surface. It is another object of the present invention to provide an image forming apparatus capable of reducing the generation of paper dust from a transfer sheet during the transfer of the transfer sheet.

[0016]

According to a first aspect of the present invention, there is provided an image carrier having an electrostatic latent image on a surface thereof, and developing the electrostatic latent image on the image carrier. Developing device that develops a visible image by developing with toner as a developer, a transfer device that transfers the developed toner image on the image carrier to a transfer material, and a fixing roller that is heated by a heating unit and a pressure contact with the fixing roller. And a fixing device having a pressure roller, wherein the fixing roller and the pressure roller of the fixing device are rotatably arranged and provided at a pressure contact portion between the fixing roller and the pressure roller. In an image forming apparatus for fixing a toner on a transfer material by applying heat and pressure by passing a transfer material onto which a toner image has been transferred, the fixing device includes a cleaning roller that rotates in contact with a pressure roller and prints. At the start, Tona Achieved by making the temperature of the cleaning roller higher than the temperature of the glass transition point of the toner, which is the temperature at which the toner softens, and lower than the temperature of the pressure roller, and the temperature of the pressure roller is lower than the temperature of the fixing roller. Is done.

Further, according to the second invention of the present application, the above object is achieved by forming the cleaning roller into a hollow substantially pipe shape having an outer diameter of 5 to 15 mm using aluminum.

According to a third aspect of the present invention, the above object is attained by providing an image forming apparatus having a fixing device in which an oil applying member for applying silicone oil to a surface of a fixing roller is not provided. Achieved.

According to a fourth aspect of the present invention, there is provided a fixing device, wherein a bias voltage for pressing toner in a transfer material direction is applied to both or one of a fixing roller and a pressure roller. Is achieved.

According to a fifth aspect of the present invention, there is provided a transfer material used in an image forming apparatus.
This is achieved by containing 10% to 25% by weight of calcium carbonate.

Further, according to the sixth aspect of the present invention, the object is to make it easy for the fixing roller, the pressure roller, and the cleaning roller of the fixing device to separate the transfer material from the surface. The surface of each roller is formed so that the releasability of the fixing roller is better than that of the pressure roller and the releasability of the pressure roller is better than that of the cleaning roller. It is achieved by doing.

Further, according to the seventh aspect of the present invention, the above object is achieved by forming the cleaning roller from metal and making the cleaning roller and the pressure roller conductive so as to have the same potential. .

According to an eighth aspect of the present invention, the above object is attained by providing an image forming apparatus having a transport path for transporting a transfer material to a predetermined process of image formation, wherein at least one transport path is provided. This is achieved by the fact that the part is formed in a substantially rectangular shape.

According to a ninth aspect of the present invention, the above object is achieved when a transfer sheet is used as a transfer material, and the transfer material in a transport path provided in the image forming apparatus rubs. This is achieved by providing a fluororesin layer at a position.

That is, according to the first aspect of the present invention, the fixing device is provided with the cleaning roller which rotates in contact with the pressure roller, and the glass transition temperature of the toner, which is the temperature at which the toner softens at the start of printing. The temperature of the cleaning roller is higher than the temperature of the cleaning roller and lower than the temperature of the pressure roller, and the temperature of the pressure roller is lower than the temperature of the fixing roller. When the roller and the pressure roller rotate while directly contacting each other, the toner offset to the fixing roller in the fixing process is transferred to the surface of the pressure roller having a lower temperature than the fixing roller, and the toner transferred to the pressure roller. Is transferred to the cleaning roller at a temperature lower than the pressure roller and higher than the glass point transfer temperature of the toner, and is held.
The contamination of the fixing roller with the offset toner is prevented for a long period of time.

Further, according to the second aspect of the present invention, the heat capacity of the cleaning roller is reduced by forming the cleaning roller from aluminum into a hollow substantially pipe shape having an outer diameter of 5 to 15 mm. The roller is heated to a predetermined temperature in a short time.

Further, according to the third aspect of the present invention, when the surface of the fixing roller is not provided with an oil applying member for applying silicone oil and the member for cleaning the surface of the fixing roller is not provided. The cleaning roller is rotatably brought into contact with the pressure roller, thereby preventing the fixing roller from being stained by the offset toner for a long time.

According to the fourth aspect of the present invention, a bias voltage for pressing the toner in the direction of the transfer material is applied to both or one of the fixing roller and the pressure roller of the fixing device. Even when powder from the transfer material adheres to the surface and the toner is offset on the surface, the cleaning roller can be rotatably brought into contact with the pressure roller to prevent the fixing roller from being stained by the offset toner for a long time. Is prevented.

According to the fifth aspect of the present invention, the transfer material used in the image forming apparatus contains 10% to 25% by weight of calcium carbonate. The cleaning roller can be rotated by the pressure roller even when the toner becomes powdery and scatters during transportation, etc., and adheres to the surface of the fixing roller, causing toner to be offset to the fixing roller. The contact prevents the fixing roller from being stained by the offset toner for a long period of time.

According to the sixth aspect of the present invention, the releasability of the fixing roller, the pressure roller, and the cleaning roller of the fixing device is smaller than the releasability of the pressure roller. The surface of each roller is formed so that the releasability of the pressure roller is better than the releasability of the cleaning roller. The transfer of the offset toner to the roller is favorably performed, and the toner transferred to the cleaning roller is reliably held.

According to the seventh aspect of the present invention, since the cleaning roller is made of metal and the cleaning roller and the pressure roller are electrically connected to each other and have the same potential, the cleaning roller is charged. This prevents the potential from being discharged from the surface of the pressure roller.

According to the eighth aspect of the present invention, at least a part of the transfer path of the transfer material provided in the image forming apparatus is formed in a substantially ⊃ shape, and friction between the transfer material and the transfer path is formed. Even if the powder is scattered a lot and the toner adheres to the surface of the fixing roller and causes toner offset, the cleaning roller can be rotatably brought into contact with the pressure roller to fix the fixing roller. Stain due to offset toner is prevented for a long period of time.

According to the ninth aspect of the present invention, when transfer paper is used as the transfer material, the fluororesin is located at the position where the transfer material slides on the transfer path provided in the image forming apparatus. By providing the layer, the friction between the transfer material and the conveyance path is reduced, so that the amount of paper generated from the transfer paper is suppressed, and the cleaning roller is rotatably brought into contact with the pressure roller. The fouling of the fixing roller with the offset toner is prevented for a long period of time.

[0034]

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

(First Embodiment) First, a first embodiment of the present invention will be described with reference to FIGS.

As shown in FIG. 1, an image forming apparatus in which a toner on a transfer material is fixed on the transfer material by heating and pressing with a fixing device is used as an image carrier having an electrostatic latent image on its surface. A photosensitive drum 2, a charging roller 3 as a charging unit for uniformly charging the surface of the photosensitive drum 2,
Exposure means (not shown) for exposing the surface of the photosensitive drum 2 charged by the charging roller 3 with the laser beam 1 to form an electrostatic latent image on the photosensitive drum 2, A developing device 4 that develops the electrostatic latent image with a toner as a developer to make it a visible image; a transfer roller 5 as a transfer device that transfers the developed toner image on the photosensitive drum 2 to a transfer material; A fixing device 8 for heating and pressing the transferred transfer material to fix the toner on the transfer material, a transfer material cassette 19 for storing the transfer material, a paper feed roller 18 for feeding the transfer material, a fed transfer It has a transport path for transporting the material.

In the image formation by the above-described image forming apparatus, first, the surface of the photosensitive drum 2 is uniformly charged to a negative polarity by the charging roller 3. Then, the laser beam 1 corresponding to the image signal is irradiated on the surface of the negatively charged photosensitive drum 2 by a laser unit (not shown) or a scanner unit which is an exposure means provided with a polygon mirror, thereby forming an electrostatic latent image. An image is formed on the surface of the photosensitive drum 2.
Here, the laser beam 1 irradiates a portion corresponding to an image, that is, a so-called image scanning method is used.

The electrostatic latent image formed on the photosensitive drum 2 is
The toner image is developed by the toner stored in the developing device 4 and is visualized. The developing device 4 uses a jumping development method by reversal development in which a negative one-component magnetic toner adheres to a portion of the photosensitive drum 2 exposed to the laser beam 1. The toner image developed on the photosensitive drum 2 by the developing device 4 is transferred to the photosensitive drum 2 at a predetermined timing.
The image is transferred by the transfer roller 5 to a transfer material conveyed to a position opposite to the transfer roller 5 and the transfer roller 5.

Paper as a transfer material to which the toner image is transferred is stored in a paper cassette 19,
The sheet is picked up by a sheet feeding roller 18 provided in the printer 9 and is fed one by one to a first guide 16 for conveyance by a pair of rollers 17 rotating in the same direction. The transfer paper fed to the first guide 16 is guided upward by the first guide 16, and is transported by an intermediate roller pair 15 provided downstream of the first guide 16 in the transport direction of the transfer paper. The paper is conveyed in the direction of the second guide 14.

The transfer direction of the transfer paper conveyed into the second guide 14 is changed by guide members 13a and 13b provided near the outlet of the second guide 14. At the positions of the guide members 13a and 13b provided on the second guide 14, the transfer paper rubs against the surfaces of the guide members 13a and 13b when the transfer direction of the transfer paper is changed.

A registration roller pair 12 is provided on the downstream side of the second guide 14 in the transfer paper transfer direction.
The transfer paper conveyed through the guide 14 is conveyed by the registration roller pair 12 to a position where the photosensitive drum 2 and the transfer roller 5, which are transfer positions, oppose each other so as to correspond to an image signal. The transfer paper conveyed in one transfer direction by the pair of registration rollers 12 is accurately moved to the transfer position by the pair of pre-transfer guides 11 arranged between the pair of registration rollers 12 and the transfer position. . When the transfer paper is conveyed to the transfer position, +1.5
When a voltage of +5 KV is applied, a negatively charged toner image carried on the photosensitive drum 2 is transferred to a transfer material. The transfer paper on which the toner image has been transferred is guided by the transfer guide 6 and the fixing entrance guide 7 after the transfer, and is conveyed in the direction of the fixing device 8, and the toner on the transfer paper is fixed on the transfer paper by the fixing device 8, and the transfer paper is transferred. An image is formed on the image.

Fixing device 8 for fixing toner on transfer paper
As shown in FIG. 2, a fixing roller 9 provided with a halogen lamp 9a as a pressing means and rotatably disposed, and a fixing roller 9 provided by a pressing means (not shown).
And a pressure roller 10 that is pressed against the fixing roller 9 and rotates in accordance with the rotation of the fixing roller 9. The pressure roller 10 is heated to a predetermined temperature by a halogen lamp 9 a and is in contact with the pressure roller 10. By passing the transfer paper, the toner on the transfer paper can be heated and pressed to melt and fix the toner on the transfer paper.

The fixing roller 9 is formed, for example, by bonding a PFA tube 31 to the outer periphery of a substantially cylindrical core 30 made of aluminum with a primer layer interposed therebetween. Are arranged along the line, and the surface of the fixing roller 9 is heated to a predetermined temperature by the two halogen heaters 9a. Note that a pipe having a thickness of 2.5 mm is used for the core metal 30 of the fixing roller 9 and the PFA tube 31 is used.
Uses a tube of insulating PFA resin having a thickness of 50 μm.

The pressure roller 10 pressed against the fixing roller 9 has an elastic layer made of a conductive sponge rubber layer 33 adhered to the outer periphery of a substantially bar-shaped core 32 via a primer layer. A PFA tube 34 is adhered to the outer periphery of the fixing roller 33 via a primer layer, and is rotated by the rotation of the fixing roller 9 heated to a predetermined temperature by each halogen heater 9a. The surface is heated to a predetermined temperature by the fixing roller 9. The pressure roller 10 has a predetermined heat capacity due to the above configuration, and the temperature at the start of printing of the pressure roller 10 heated by being driven and rotated by the fixing roller 9 is equal to the temperature of the fixing roller 9. Lower than that. The core metal 32 of the pressure roller 10 is made of an iron rod having a diameter of 14 mm.
3 is a sponge-shaped member made of conductive silicone rubber having a thickness of 8 mm, and the outermost PFA tube 3 is used.
No. 4 is a PFA resin tube having a thickness of 50 μm and made semiconductive by mixing carbon.

The power supply 40 is connected to the core metal 30 of the fixing roller 9 and a voltage of -700 V having the same polarity as the toner is applied, so that the surface of the fixing roller 9 has a negative polarity. The anode side of the diode 41 is connected to the metal core 32 of the pressure roller 10 and is self-biased so that the surface of the pressure roller 10 has a positive polarity, so that the negative toner on the transfer paper is pressed against the transfer material. This prevents the negatively charged toner on the surface of the fixing roller 9 from offsetting to the fixing roller 9. The power supply connected to the fixing roller or the diode connected to the pressure roller may be only one of them.

The pressure roller 9 is provided with a cleaning roller 20 which comes into contact with the pressure roller 10 and rotates according to the rotation of the pressure roller 10. The cleaning roller 20 is brought into contact with an arbitrary outer peripheral surface of the pressure roller 10 other than the pressure contact portion with the fixing roller 9, and the fixing roller 9
The temperature of the pressure roller 10 is lower than the temperature of the pressure roller 10 by being rotated following the rotation of the pressure roller 10 heated to a predetermined temperature, and the used toner is softened from a solid state by being heated. The glass is heated to a temperature higher than the glass transition temperature, which is the temperature at which the state transitions.

That is, the fixing roller 9, the pressure roller 10,
The temperature decreases in the order of the cleaning roller 20, and the toner offset to the fixing roller 9 transfers to a member having a lower temperature, so that the offset toner on the fixing roller 9 transfers to the pressure roller 10, The toner transferred to the pressure roller 10 can be transferred to the surface of the cleaning roller 20.

Here, in order to make the temperature of the cleaning roller 20 higher than the temperature of the glass transition point of the toner by the amount of heating from the pressure roller 10, the cleaning roller 20
Needs to be smaller than the heat capacity of the pressure roller 10. Note that the outer diameter of the cleaning roller 20 is 5
By setting the thickness to about 15 mm, the heat capacity of the cleaning roller is reduced, and the cleaning roller 20 can be easily heated to a predetermined glass transition point of the toner during warm-up of the fixing device.

When the cleaning roller 20 is formed to have a low heat capacity in this manner, the pressure roller 10
This is effective when a sponge-like silicone rubber elastic layer is used. This is because the pressure roller having the sponge-like elastic layer is easily heated by the amount of heating from the fixing roller, but may have insufficient heat capacity to heat the cleaning roller.

In order to transfer the toner on the fixing roller and clean the fixing roller (transfer the toner from the pressing roller to the cleaning roller), only before the image formation (before starting printing), the cleaning with the pressing roller is performed. It is sufficient to raise the temperature of the roller to a predetermined temperature.In order to raise the temperature of the pressure roller and the cleaning roller to the predetermined temperature in a short time before image formation, the pressure roller is made of a silicone rubber sponge. It is particularly effective to form the cleaning roller in the shape of a small-diameter pipe while having the elastic layer.

The cleaning roller 20 in contact with the pressure roller 10 is, for example, an aluminum pipe having a thickness of 1 mm and an outer diameter of 10 mm. The cleaning roller 20 is arranged so that the distance from the center of rotation is constant, and the cleaning roller 20 can rotate following the rotation of the pressure roller 10. Note that a pressure unit may be provided on the cleaning roller so that the cleaning roller is pressed against the pressure roller 10 at a predetermined pressure.

Since the cleaning roller 20 has a small diameter and a thin roller shape, it has a small heat capacity,
This eliminates the need for extra warm-up rotation of the fixing device before the printing operation. Further, since the cleaning roller 20 is formed of metal, the cleaning roller 20 is electrically connected to the pressure roller 10 with which the cleaning roller 20 is in contact, and can be set to the same potential as the pressure roller 10. Pressure roller 10
Is prevented from being discharged from the surface of the substrate.

During standby of the fixing device 8 having the above configuration,
The driving of the two halogen heaters 9a is controlled so that the temperature of the fixing roller 9 is maintained at 170 to 180 ° C, and the temperature during fixing is maintained at 190 to 200 ° C. In the present embodiment, when a print signal is issued from a control unit (not shown) of the image forming apparatus in the standby state of the fixing device 8, the fixing roller is fixed for about 15 seconds until the transfer paper enters the fixing device 8. The idle rotation 9 heats the pressure roller 10 to about 130 ° C. At this time, the temperature of the cleaning roller 20, which moves following the pressure roller 10, rises to about 110 ° C.

When the temperature of the cleaning roller 20 rises to the temperature of the steam, if the contaminated toner transferred from the fixing roller 9 adheres to the surface of the pressure roller 10, the pressure roller 1
The toner is transferred from the surface of the cleaning roller 20 to the surface of the cleaning roller 20, and the toner is fixed and held on the surface of the cleaning roller 20. Since the pressure roller 10 in contact with the cleaning roller 20 does not reach a temperature lower than the temperature of the cleaning roller 20, the toner adhered to the cleaning roller 20 does not peel off from the cleaning roller 20 without being removed. 20 will remain on the surface. The toner used in the present embodiment had a glass transition temperature of about 82 ° C., which is the temperature at which the toner softens.

Further, when the toner offset to the fixing roller 9 is transferred to the pressure roller 10 while the fixing process is repeated, the next toner is stacked on the toner transferred to the surface of the cleaning roller 20. .

As described above, when the temperature of the fixing roller, the pressure roller, and the cleaning roller is decreased in this order, and the temperature of the lowest cleaning roller is higher than the temperature of the glass transition point of the toner, The toner offset to the fixing roller sequentially moves to the pressure roller and the cleaning roller according to the temperature gradient of each roller, and is stacked on the cleaning roller having the lowest temperature, thereby fixing the toner for a long time. Even if the fixing is performed, no smear due to the offset toner is generated on the fixing roller, so that a good image can be formed over a long period of time.

Each of the fixing roller, the pressure roller, and the cleaning roller has a releasability, which is the ease with which the transfer material is separated from the surface, and a releasability of the fixing roller. The surface of each roller may be formed so that the releasability of the pressure roller is better than the releasability of the cleaning roller. That is, by lowering the releasability of each roller in the order of the fixing roller, the pressure roller, and the cleaning roller, the toner can be more easily transferred to the cleaning roller.

In this embodiment, the surface of the fixing roller 9 is P
The surface of the pressure roller 10 is made of PFA resin which is made semiconductive by mixing carbon, and the cleaning roller 20 is made of only an aluminum pipe rather than the releasability of the fixing roller 9 and the pressure roller 10. By making the releasability of the roller 20 extremely low, the offset toner is easily transferred to the cleaning roller 20 and hardly peeled off. In addition, the surface of the cleaning roller is polished so that 1
Irregularities of about 10 μm to 10 μm may be formed. In this case, the transfer of the toner to the cleaning roller can be further improved and the toner can be hardly peeled off. The cleaning roller may be inspected periodically to remove the toner from the surface of the cleaning roller when the toner adheres and is stacked, or the cleaning roller may be replaced.

The fixing using a transfer paper containing about 20% by weight of calcium carbonate is performed by a printer using a fixing device having a cleaning roller having the above configuration, and the fixing device having no cleaning roller is used. Was compared using a transfer paper containing about 20% by weight of calcium carbonate with a printer using a printer.

The results of the comparison are shown in Table 1 below. As can be seen from Table 1 above, in the fixing device having the cleaning roller according to the present embodiment, the fixing roller is not stained even after passing about 100,000 sheets.

Further, when fixing is performed using a transfer paper containing a predetermined amount of calcium carbonate by a printer using a fixing device having a cleaning roller of the present embodiment,
Table 2 below shows the relationship between the temperature of the cleaning roller and the contamination of the fixing roller when a predetermined number of sheets are passed. The toner used had a glass transition temperature of about 82 ° C. As can be seen from Table 2 above, when the temperature of the cleaning roller is 70 ° C., which is lower than the temperature of the glass transition point of the used toner, the transfer of the toner to the cleaning roller becomes poor, so Toner contamination occurs. This is because the toner adhering to the pressure roller is transferred to the cleaning roller by setting the temperature of the cleaning roller higher than the temperature of the glass transition point of the toner and softening the toner.

The temperature of the cleaning roller is 90 ° C.
In this case, it is considered that the black spots occurred because the toner transferred to the cleaning roller adhered to the pressure roller again while being solidified because the temperature of the cleaning roller was not sufficiently high. Further, when the temperature of the cleaning roller is 110 ° C., which is sufficiently higher than the temperature of the glass transition point of the toner, no toner stain is generated on the fixing roller. From this, it was found that the temperature of the cleaning roller at the start of printing needs to be higher by 10 ° C., and more preferably by about 20 ° C., than the glass transition temperature Tg of the toner.

Further, the fixing device having the cleaning roller of the present embodiment is effective when the weight ratio of calcium carbonate contained in the transfer paper is about 10% to 25%. This is because even if there is no member for cleaning the surface of the fixing roller such as a felt member for applying silicone oil, the offset toner is carried little by little to the transfer material. If the toner does not contain, or the content is less than about 10% by weight, it is considered that the fixing roller is not stained even when 100,000 or more sheets of transfer paper are passed through the fixing device. Table 3 below shows the relationship between the number of fixed toner particles generated by the fixing roller caused by the amount of calcium carbonate contained in the transfer paper when fixing is performed by a fixing device having no conventional cleaning roller. Show the relationship. As can be seen from Table 3, when the amount of calcium carbonate is less than about 10%, the conventional fixing device is at a level where the contamination of the fixing roller with the offset toner is negligible.

In the case where a cleaning roller is provided as in the present embodiment, it is possible to prevent the fixing roller from being stained by offset toner in a fixing device having no oil applying member for applying silicone oil to the fixing roller. Maintenance work such as replacing an oil application member for applying silicone oil can be omitted.

Further, when a bias having the same polarity as that of the toner is applied to the fixing roller or the pressure roller is self-biased, the toner is moved in the direction of the transfer material in order to prevent toner offset and toner scattering. When an image is formed using a transfer material containing a large amount of calcium carbonate in a fixing device to which a pressing bias is applied, when a device in which a cleaning roller is in contact with a pressure roller as in this embodiment is used, effective fixing is performed. The contamination of the roller can be prevented.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIG. According to the present embodiment, in the image forming apparatus according to the first embodiment, the transfer sheet is provided with a fluororesin layer at a position where the transfer sheet and the transfer path rub against each other in the transfer path of the transfer sheet. By suppressing the generation of paper dust due to rubbing, the offset of the toner to the fixing roller can be reduced. The photosensitive drum, the developing device, the fixing device, and the like other than the rubbing portion of the transport path can use the same members and the like as those in the first embodiment, and a detailed description thereof will be omitted.

It has been found that, in addition to calcium carbonate, the amount of paper dust emitted from the transfer paper is a factor that causes the fixing roller to be stained by the offset toner. In the image forming apparatus, as a configuration in which paper dust is likely to be generated from the transfer paper during conveyance, for example, as shown in FIG. 1 of the first embodiment, a transfer paper cassette 1 is provided below the photosensitive drum 2.
9, the transfer path is formed in a substantially ⊃ shape so that the transfer paper is made to make a U-turn during the transfer.

In the transport path configured as described above, the transfer paper has a greater chance of rubbing against the surface of the transport path during transport than in the case where the transport path is linear, and the transfer paper and the transport path Is rubbed strongly and paper powder is easily discharged from the transfer paper. In particular, the positions of the guide members 13a and 13b provided immediately before the registration roller pair 12 of the second guide 14 are in a place where the transfer paper and the surface of the transfer path on the transfer paper side are strongly rubbed and paper powder is likely to be generated. is there.

In this embodiment, as shown in FIG. 3, a fluororesin layer 42 is provided on the surface of the base member 40 of the guide member 13a 'on the side of the conveyance path to reduce the friction of the surface of the guide member 13a' on the side of the conveyance path. , The generation of paper dust due to the rubbing between the guide member 13a 'and the transfer paper is reduced. Further, a fluororesin layer may be provided on the surface of the guide member 13b in FIG. 1 on the side of the transport path.

The fluororesin layer 42 provided on the guide member 13a 'is provided on the surface of the guide member on the conveying path side of the base material, for example, an industrial Teflon tape # 5 manufactured by Sumitomo 3M.
49 (thickness: 0.09 mm). This makes it easy to form the guide member, and also reduces the generation of paper dust from the transfer paper by removing only the guide member and attaching the tape to the existing image forming apparatus. it can. The surface of the guide member on the side of the conveyance path may be coated with a fluororesin. Furthermore, in FIG.
A fluororesin layer may be provided on the surface of the first guide 16 or the second guide 14 on the transport path side.

This embodiment reduces the friction of the surface of the portion of the conveyance path that rubs against the transfer paper, and combines the fixing device having the cleaning roller of the first embodiment with the offset of the fixing roller. It is possible to more effectively prevent toner contamination by toner.

Table 4 below shows an image forming apparatus using a fixing device having a cleaning roller according to the first embodiment,
The guide member according to the present embodiment is provided with a fluororesin layer on the surface of the guide member at a position where the guide member slides against the transfer sheet, and is fixed with a transfer sheet containing 22% by weight of calcium carbonate with an image forming apparatus using a fixing device having a cleaning roller. Indicates the number of sheets on which toner contamination has occurred in the case where. As can be seen from Table 4 above, in the image forming apparatus using a fixing device having a cleaning roller and a fluororesin layer provided on the surface of the guide member of the present embodiment at the position where the guide member rubs against the transfer paper, By suppressing the generation of paper dust and cleaning the dirt toner transferred to the pressure roller by the cleaning roller, it is possible to prevent the dirt due to the offset toner of the fixing device for a longer time than the fixing device of the first embodiment. As a result, the life of the fixing device can be greatly extended.

[0073]

As described above, according to the first aspect of the present invention, the fixing device is provided with the cleaning roller which rotates while being in contact with the pressure roller.
The temperature of the cleaning roller is higher than the temperature of the glass transition point of the toner, which is the temperature at which the toner softens, and is lower than the temperature of the pressure roller, and the temperature of the pressure roller is lower than the temperature of the fixing roller. By doing
When the fixing roller and the pressure roller rotate while directly contacting each other, such as when adjusting the temperature of the fixing device, the toner that has been offset from the fixing roller in the fixing process transfers to the surface of the pressure roller that has a lower temperature than the fixing roller. Since the toner transferred to the pressure roller is transferred to the cleaning roller having a temperature lower than that of the pressure roller and higher than the temperature at which the glass point of the toner is transferred to the cleaning roller, the contamination of the fixing roller by the offset toner is removed for a long time. Thus, the fixing device can have a long service life or a small number of maintenance operations, thereby saving time and effort.

Further, according to the second aspect of the present invention, the heat capacity of the cleaning roller is reduced by forming the cleaning roller in a hollow substantially pipe shape having an outer diameter of 5 to 15 mm by using aluminum. Since the roller can be heated to a predetermined temperature in a short time, the cleaning roller can be easily heated even when the fixing device is normally warmed up.

Further, according to the third aspect of the present invention, even when the surface of the fixing roller is not provided with an oil applying member for applying silicone oil and the surface of the fixing roller is not cleaned, By making the cleaning roller rotatably contact the pressure roller, it is possible to prevent the fixing roller from being stained by the offset toner for a long period of time, and it is possible to eliminate the trouble such as replacing the oil application member. Device.

According to the fourth aspect of the present invention, a bias voltage for pressing the toner in the direction of the transfer material is applied to both or one of the fixing roller and the pressure roller of the fixing device. Even if powder from the transfer material adheres to the surface and the toner is offset on the surface, the cleaning roller can be rotatably brought into contact with the pressure roller to prevent the fixing roller from being stained by the offset toner for a long time. For a long period of time, and good image formation can be performed over a long period of time.

According to the fifth aspect of the present invention, the transfer material used in the image forming apparatus contains 10% to 25% by weight of calcium carbonate. The cleaning roller can be rotated by the pressure roller even when the toner becomes powdery and scatters during transportation, etc., and adheres to the surface of the fixing roller, causing toner to be offset to the fixing roller. The contact makes it possible to prevent the fixing roller from being stained by the offset toner for a long period of time, and it is possible to form a good image for a long period of time even when an image is formed using neutral paper or the like.

According to the sixth aspect of the present invention, the releasability of the fixing roller, the pressure roller, and the cleaning roller of the fixing device is smaller than that of the pressure roller. The surface of each roller is formed so that the releasability of the pressure roller is better than the releasability of the cleaning roller. The transfer of the offset toner to the roller can be performed favorably, and the toner transferred to the cleaning roller can be reliably held, so that a good image can be formed over a long period of time.

Further, according to the seventh aspect of the present invention, the cleaning roller is formed of metal, and the cleaning roller and the pressure roller are electrically connected to each other to have the same potential, so that the cleaning roller is charged. This can prevent the potential from being discharged from the surface of the pressure roller, and can reduce the offset of the toner to the fixing roller.

According to the eighth aspect of the present invention, at least a part of the transfer path of the transfer material provided in the image forming apparatus is formed in a substantially ⊃ shape due to the installation area or the like. The cleaning roller is rotatably brought into contact with the pressure roller even when the powder is scattered due to friction between the roller and the conveyance path and the powder adheres to the surface of the fixing roller and causes toner offset. By doing
The fixing roller can be prevented from being stained by the offset toner for a long period of time, and a good image system can be performed for a long period of time even in a compact image forming apparatus.

According to the ninth aspect of the present invention, when transfer paper is used as the transfer material, the fluororesin is located at the position where the transfer material slides on the transport path provided in the image forming apparatus. By providing the layer, the friction between the transfer material and the conveyance path is reduced, so that the amount of paper generated from the transfer paper is suppressed, and the cleaning roller is rotatably brought into contact with the pressure roller. The contamination of the fixing roller with the offset toner can be prevented for a longer period.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus of the present invention.

FIG. 2 is a schematic configuration diagram illustrating a fixing device according to the first embodiment.

FIG. 3 is a perspective view illustrating a guide member according to a second embodiment.

FIG. 4 is a schematic configuration diagram illustrating a fixing device having an oil application member of silicone oil used in a conventional image forming apparatus.

FIG. 5 is a schematic configuration diagram illustrating a conventional fixing device to which a bias for preventing toner offset is applied.

[Explanation of symbols]

 2 Photosensitive Drum (Image Carrier) 4 Developing Device 8 Fixing Device 9 Fixing Roller 10 Pressure Roller 20 Cleaning Roller

Claims (9)

[Claims] An image carrier that carries an electrostatic latent image on a surface thereof;
A developing device that develops an electrostatic latent image on the image carrier with a toner as a developer to make the image visible, a transfer device that transfers the developed toner image on the image carrier to a transfer material, and a heating unit An image forming apparatus provided with a fixing device having a fixing roller heated by the fixing device and a pressing roller pressed against the fixing roller, wherein the fixing roller and the pressing roller of the fixing device are rotatably arranged. In an image forming apparatus in which a transfer material on which a toner image has been transferred is passed through a pressure contact portion between a fixing roller and a pressure roller, the toner on the transfer material is heated and pressed to fix the toner on the transfer material. And a cleaning roller that rotates in contact with the pressure roller. At the start of printing, the temperature of the cleaning roller is higher than the temperature of the glass transition point of the toner, which is the temperature at which the toner softens. Leaning temperature of the roller is lower than the temperature of the pressure roller, and an image forming apparatus, wherein the temperature of the pressure roller is lower than the temperature of the fixing roller. 2. The image forming apparatus according to claim 1, wherein the cleaning roller is made of aluminum and has a hollow substantially pipe shape having an outer diameter of 5 to 15 mm. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus has a fixing device provided with no oil applying member for applying silicone oil to the surface of the fixing roller. 4. The fixing device according to claim 1, wherein a bias voltage for pressing the toner toward the transfer material is applied to at least one of the fixing roller and the pressure roller. The image forming apparatus according to any one of the above. 5. A transfer material used in an image forming apparatus includes:
The image forming apparatus according to claim 1, wherein the content of calcium carbonate is 10% to 25% by weight. 6. A fixing roller, a pressure roller, and a cleaning roller of a fixing device, each of which has a releasability that facilitates separation of a transfer material from a surface, and a releasability of a fixing roller that corresponds to a pressure roller. 2. The roller according to claim 1, wherein the surface of each roller is formed such that the releasability of the pressure roller is better than that of the cleaning roller.
The image forming apparatus according to claim 1. 7. The cleaning roller according to claim 1, wherein the cleaning roller is made of metal, and the cleaning roller and the pressure roller are electrically connected to each other to have the same potential. Image forming apparatus. 8. The image forming apparatus has a transport path for transporting a transfer material to a predetermined process of image formation, and at least a part of the transport path is formed in a substantially ⊃ shape.
The image forming apparatus according to claim 1. 9. When a transfer paper is used as the transfer material, a fluororesin layer is provided at a position on the conveyance path provided in the image forming apparatus where the transfer material rubs.
An image forming apparatus according to claim 1.