JP2006293134A - Fixing apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately suppress the temperature rise, in a non-paper passing area of a heat-generating part. <P>SOLUTION: The fixing apparatus 2 for fixing an unfixed toner image to a recording paper 25 includes ducts 27, 28 and 29 for guiding cooling air to a fixing roller 22; the ducts 27, 28 and 29 are partitioned into a plurality of sections in the axial direction of the fixing roller 22; gaps are arranged in the intermediate parts of the ducts 27, 28, 29 so that the fixed recording paper 25 crosses the ducts 27, 28 and 29; by making the fixed recording paper 25 cross the ducts 27, 28 and 29, the fixed recording paper 25 is cooled; and in the paper passing area interrupted by the fixed recording paper, cooling air will not be transferred to the heat-generating part, and consequently, the non-paper passing area on the fixing roller 22 is cooled. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a facsimile machine, or a printer, and heats an image made of a heat-meltable developer (toner) formed on the surface of a sheet such as paper to be permanently fixed. The present invention relates to a heat-fixing type fixing device that fixes an image on a sheet and an image forming apparatus including the same.

  In an electrophotographic image forming apparatus, toner as a developer electrostatically transferred from a photosensitive member to a recording paper as a sheet is easily peeled off, so that the toner is permanently applied to the recording paper by heating or pressurizing the toner. It is necessary to fix it. This process is called a fixing process. There are various fixing methods. Among them, the heat fixing method using a heat roller is most widely used because of its high thermal efficiency and safety.

  In the heat fixing method, two rollers are pressed against each other, and at least one of the rollers is heated, and a sheet such as a recording sheet or an OHP sheet that supports an unfixed toner image is supported on the pressure contact portion (nip portion) of the two rollers. In this method, unfixed toner is heated and fixed on a sheet by passing the toner through.

  In such a heat-fixing type fixing device, it is difficult to make the temperature distribution in the sheet width direction (a direction perpendicular to the sheet conveying direction, also referred to as an axial direction) uniform. That is, in an area (sheet passing area) through which a small sheet of B5 or A4 size passes, heat is consumed for heating the sheet (an unfixed toner image and a sheet that supports the unfixed toner image). However, in the area where the sheet does not pass (non-sheet passing area), heat is not consumed for heating the sheet, so heat is stored, and the temperature of the nip portion of the non-sheet passing area is maintained at a predetermined temperature. It becomes higher than the temperature of the nip part.

  For this reason, when a large size sheet is passed after a small size sheet is continuously passed (for example, when an A4 size recording sheet is passed continuously and then an A3 size recording sheet is passed), the large size is passed. Non-fixed toner images may be unevenly fixed or wrinkled, or the toner corresponding to the non-sheet passing area of the unfixed toner image may be melted too much to adhere to the fixing roller and stain the surface of the sheet. In the case of color toner, there are problems such as a difference in gloss.

  Therefore, it has been considered to make the temperature distribution in the sheet width direction uniform by cooling the non-sheet passing region where the temperature is excessively high. This method of cooling the non-sheet passing region that has been overheated can be realized with a relatively simple mechanism and can be reduced in cost. As conventional techniques, there are the following (1) to (3). .

  (1) The overheated portion is air-cooled while controlling the passage of the air flow with a bi-metal variable slit, temperature detecting means, etc. by the air passage window. Alternatively, air is blown from the back side of the sheet on the paper discharge side, and only the portion not blocked by the sheet is air-cooled (see Patent Document 1).

  (2) A cooling fan and a duct are provided, and only the non-sheet passing area is air-cooled using a sheet before fixing (see Patent Document 2).

(3) By wrapping the sheet around the fixing roller and cooling it from above with a cooling means such as cold air / cooling roller, the fixing roller cooling in the outer area where there is no sheet is further compared with the area covered with the sheet. Cooling. Or the same effect is acquired by preheating a sheet | seat with a pressure roller (refer patent document 3).
JP-A-3-139682 JP-A-4-051179 Japanese Patent No. 3451461

  In the prior arts (1) to (3), an apparatus having a configuration that does not require a size detection mechanism and a cooling region changing mechanism is disclosed. In (1), cold air is sent from the back side of a sheet immediately after transfer. Since there is no duct up to the vicinity of the fixing roller portion, there is a weak point that the boundary between sheet passing and non-sheet passing at the sheet end is unclear. In (2), there is a weak point that the sheet is cooled before it is heated. In (3), since the sheet has a curvature along the outer diameter of the fixing roller, a separating means from the roller is essential, or when the transfer paper is preheated, a heating element is required in addition to the fixing roller. There are weaknesses.

  An object of the present invention is to accurately suppress the temperature rise in the non-sheet passing region of the heat generating portion.

In order to achieve the above object, the present invention adopts the following configuration. That is,
In a fixing device for fixing an unfixed developer image on a sheet,
It has an air passage that guides cooling air to the heat generating part,
The air passage is partitioned into a plurality of sections in the sheet width direction, and a gap through which the sheet after fixing crosses the air passage is provided in the middle of the air passage,
Since the sheet after fixing crosses the air path, the sheet after fixing is cooled and the paper passing area blocked by the sheet after fixing does not allow the cooling air to reach the heat generating part, and the heat generating part is not passed. The fixing device is characterized in that the paper region is cooled.

  According to the present invention, the temperature rise in the non-sheet passing region of the heat generating portion can be accurately suppressed.

(First embodiment)
The first embodiment will be described with reference to FIGS.

  The image forming apparatus will be described with reference to FIG. FIG. 1 is a cross-sectional view of an image forming apparatus 100 in which the fixing device 2 is incorporated. The image forming apparatus 100 includes an electrophotographic photosensitive drum (image carrier) 101. The photosensitive drum 101 is uniformly charged by the charging roller 102, and an electrostatic latent image is formed on the photosensitive drum 101 by being irradiated with laser light from the exposure device 103. Next, the electrostatic latent image is developed as a visible image by supplying toner onto the photosensitive drum 101 from the developing device 104 filled with toner as a developer, and the developer image is formed on the photosensitive drum 101 as a developer image. A toner image is formed. The photosensitive drum 101, the charging roller 102, the exposure device 103, the developing device 104, and the like that form the toner image constitute image forming means. A transfer roller 105 is installed adjacent to the photosensitive drum 101, and the toner image formed on the photosensitive drum 101 is transferred onto a recording sheet as a sheet conveyed by the action of the transfer roller 105. The recording paper is stored in a cassette 106, picked up one by one by a feeding roller 107, and supplied between a photosensitive drum 101 and a transfer roller 105 through a conveying roller pair 108 and a registration roller pair 109. Further, the unfixed recording sheet onto which the toner image has been transferred is fixed by heating and pressurizing in the fixing device 2, and then discharged to the discharge tray 110 outside the apparatus through the discharge roller pair 26 as a recorded image.

  The fixing device 2 will be described with reference to FIGS. 2 and 3 are cross-sectional views showing a schematic configuration when the fixing device 2 of the present embodiment is viewed from the axial direction of the fixing roller 22. FIG. 4 is a diagram showing the positional relationship in the longitudinal direction of the duct, the recording sheet, the fixing roller, and the heat source, and the duct portion is a cross section cut by a line along the flow of the cooling air.

  In FIG. 2, reference numeral 21 denotes a heat source for heating the fixing roller 22, and reference numeral 22 denotes a fixing roller having the heat source 21 therein. The heat source 21 is a heating element such as a halogen lamp, and is disposed in the axial direction of the fixing roller 22 (the same direction as the sheet width direction) with a length substantially equal to the entire length of the fixing roller 22. The inner surface can be heated uniformly in the axial direction. For this reason, the fixing roller 22 generates heat, and the fixing roller 22 itself is a heat generating portion. A pressure roller 23 is pressed against the fixing roller 22 by a pressure contact mechanism (not shown). A sheet entrance guide 24 guides the recording sheet 25 (a copy sheet on which toner is placed (a toner image is formed)) to a nip portion between the fixing roller 22 and the pressure roller 23. A discharge roller pair 26 sends out the recording paper 25 that has passed through the nip portion to the outside of the fixing device 2.

  Reference numeral 27 denotes a duct having a plurality of partition walls parallel to a plane orthogonal to the axis of the fixing roller 22, and has an opening 27 a having one end opened to the fan 12 side, and the other end is conveyed. The opening 27b is opened to the passing area side of the recording paper 25. The partition wall of the duct 27 is provided corresponding to the position of the width (each size) of the conveyed recording paper 25. Similarly to the duct 27, the duct 29 has a partition wall. One end is an opening 29 a that opens to the passing area side of the recording paper 25, and the other end is open to the outer peripheral side of the fixing roller 22. It is set as the made opening part 29b. The duct 29 has a shape that draws an arc along the outer periphery of the fixing roller 22. Similarly to the duct 27, 28 is a duct having a partition wall, and is formed so as to connect the opening 27b of the duct 27 and the opening 29a of the duct 29 at a position sandwiching the recording paper 25 being conveyed. .

  Here, the ducts 27, 28, and 29 form an air passage that guides cooling air from the outside of the apparatus to the fixing roller 22 as a heat generating portion. The fact that the air passage is divided into three parts such as ducts 27, 28, and 29 indicates that the air passage is divided into three parts by having a gap in the middle, and this duct 27, 28, The recording paper 25 is conveyed into the gap between 29 and the recording paper 25 crosses the air path twice. The ducts 27, 28, and 29 have partition walls corresponding to the positions of the width (each size) of the recording paper 25, and the ducts 27, 28, and 29 (air passages) are axially (sheet width) by this wall. In the direction).

  Reference numeral 12 denotes a fan for sending wind outside the apparatus to the opening 27a of the duct 27 as cooling air. A unit cover member 13 covers the fixing device 2. Reference numeral 14 denotes a fan for exhausting the inside of the apparatus.

Next, the partition walls of the ducts 27, 28 and 29 will be described. In FIG. 4, the length of the fixing roller 22 is Lr (in FIG. 4, only the roller is shown, but the bearing / drive gear portion may be included), and the length of the heat source 21 is Lh (usually the length of the heat source 21). (Lh is set to be approximately equal to or larger than the maximum sheet width), and the minimum sheet width that can be conveyed is Ls.
The width L2 of the duct wall is Lh <L2 ≦ Lr,
The width L1 of the duct wall has a relationship of L1 ≦ Ls− (1 to 6 mm + (duct wall thickness × 2)).

Further, the width of the duct wall between L2 and L1 is substantially equal to the width of the paper of each size to be conveyed, or from the paper width (1-6 mm + (duct wall thickness × 2) as in the above formula. )) It is desirable to set a smaller amount. However, when the width of adjacent duct walls is small, the widths of the duct walls may be determined by grouping the paper widths of the respective sizes together to arrange the number of duct walls.

  In the present embodiment of FIG. 4, the duct wall does not exist inside the duct wall width L <b> 1, or the wall of the duct 27 between the openings 27 a to 27 b in the duct 27 has a curved shape. , A wall may be added between L1 or a flow straightening plate may be provided after the fan 12 to make the air volume distribution from the fan 12 to the fixing roller 22 uniform.

  Next, the case where the recording paper 25 reaches the duct portion will be described. The state of FIG. 3A is a case where the recording paper 25 has not arrived at the gaps between the ducts 27, 28, and 29. In the state of FIG. 3A, the flow of the wind (cooling air) from the fan 12 reaches the fixing roller 22 from the opening 29b through the ducts 27, 28, and 29 in the entire axial direction region, and is fixed. The roller 22 is cooled.

  On the other hand, the state of FIG. 3B is a case where the recording sheet 25 being conveyed passes through the gaps between the ducts 27, 28 and 29 and crosses a part of the duct. In the state of FIG. 3B, the wind flow from the fan 12 is blocked by the recording paper 25. Here, the partition walls of the ducts 27, 28, 29 are provided corresponding to the positions of the width (each size) of the recording paper 25 to be conveyed. In the intermediate portion, the flow of the wind from the fan 12 is blocked by the recording paper 25, and in the outer portion of the width of the recording paper 25, that is, the non-sheet passing region where the fixing roller 22 is heated, the fan 12 The fixing roller 22 is cooled by the wind flow.

  Eventually, the recording sheet 25 after fixing crosses the ducts 27, 28 and 29, so that the recording sheet 25 after fixing is directly cooled by the cooling air from the duct 27 and is blocked by the recording sheet 25 after fixing. In the sheet passing area, the cooling air does not reach the fixing roller 22, and only the non-sheet passing area of the fixing roller 22 is cooled.

  As described above, in the present embodiment, a special mechanism for detecting the width of the recording paper 25 and changing the cooling region in accordance with the width of the recording paper 25 of any width is not required. In addition, the region where the temperature rises in the non-sheet-passing region can be cooled more strongly than the region that does not (paper passing region), and the temperature rise in the non-sheet-passing region can be accurately suppressed.

  Further, since the duct 29 has an arc shape along the outer periphery of the fixing roller 22, the duct 29 that does not supply wind exhibits a heat insulating effect to cover the fixing roller 22, and the air staying in the duct 29. The heat insulation effect of the layer is exhibited, the heat dissipation of the fixing roller 22 is prevented, the thermal efficiency is increased, and the energy saving effect can be exhibited.

  Further, the recording paper 25 after fixing is cooled by the wind from the duct 27, and the temperature of the recording paper 25 can be lowered when discharged.

  On the other hand, since the recording paper 25 crosses the ducts 27 and 28 and between the ducts 28 and 29 twice, the sealing performance for blocking the cooling air is further improved.

(Second Embodiment)
A second embodiment will be described with reference to FIG. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

The present embodiment is an example applied to the fixing device 2 constituted by a fixing rotating body (heat generating part) composed of a sheet heating element 41 and a heat-resistant film 42 and a driving roller 43. Fixing device 2 having this configuration
Then, since the sheet heating element 41 is compact, the heat capacity is smaller than that of the roller type device, and the sheet heating element 41 is blown when the temperature rise in the non-sheet passing region occurs. For this reason, by adopting the configuration of the present invention using the ducts 27, 28, and 29, it is possible to accurately suppress the temperature rise in the non-sheet passing region and prevent the sheet heating element 41 from fusing.

(Third embodiment)
The third embodiment will be described with reference to FIG. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the present embodiment, a cooling means 51 such as a heat pipe or a cooling water flow path is provided in the duct 29, and the cooling air of the fan 12 is cooled by the cooling means 51. . For this reason, the temperature rise in the non-sheet passing region of the fixing roller 22 can be more accurately suppressed.

(Fourth embodiment)
A fourth embodiment will be described with reference to FIG. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  In this embodiment, a belt conveyance device is used as a lower unit that pressurizes the fixing roller 22 of the fixing device 2. A belt 63 fixes and conveys the recording paper 25. The duct 28 is provided with a valve 61 and a cooling port 62 for sending cooling air to the belt 63 and the recording paper 25 in order to separate the leading end of the recording paper from the belt 63. In addition, the duct 29 is provided with an extension 29c so as to increase the duct length of the distance of the belt 63 and to send the cooling air to the fixing roller 22 without leakage (loss). Also by this, the temperature rise in the non-sheet passing region of the fixing roller 22 can be accurately suppressed.

(Fifth embodiment)
The fifth embodiment will be described with reference to FIG. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the present embodiment, an exhaust heat duct 71 is provided as an exhaust path for exhausting the wind after cooling air from the duct 29 as the air path cools the fixing roller 22. The exhaust heat duct 71 has an opening 71 a in the vicinity of the opening 29 b on the fixing roller 22 side of the duct 29, and an opening 71 b on the fan 72 side that exhausts air inside the apparatus. Here, the exhaust heat duct 71 corresponds to the position of the width (each size) of the recording paper 25 conveyed into the exhaust heat duct 71 in the same manner as the other ducts 27, 28, and 29. A partition wall parallel to a plane orthogonal to the axis is provided. According to this, the exhaust heat duct 71 can exhaust the air that has cooled the temperature rise in the non-sheet passing area of the fixing roller 22 and the flow of the cooling air is improved, so that the cold air is prevented from flowing outside the area. The cooling effect of the area can be increased.

(Sixth embodiment)
The sixth embodiment will be described with reference to FIG. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

In the present embodiment, two ducts 81 and 83 are provided with the conveyance path of the recording paper 25 interposed therebetween. The duct 81 is a duct having a plurality of partition walls parallel to a surface orthogonal to the axis of the fixing roller 22, and has an opening 81 a with one end opened to the fan 82 side, and the other end is conveyed. The opening 81b is opened to the passing area side of the recording paper 25 after fixing. The duct 81 has an arc shape along the outer periphery of the pressure roller 23, and the unfixed recording sheet 25 is adsorbed by a fan 82 that sucks air from the inside of the apparatus. The duct 83 is a duct having a partition wall similarly to the duct 81, and one end portion is an opening portion 83 a opened to the passing region side of the recording paper 25 after fixing, and the other end portion is the fixing roller 22. It is set as the opening part 83b opened to the outer peripheral side. The duct 83 has a shape that draws an arc along the outer periphery of the fixing roller 22.

  Here, the ducts 81 and 83 form an air passage that guides cooling air from the inside of the apparatus to the fixing roller 22 as a heat generating portion. The fact that the air passage is divided into two, such as the ducts 81 and 83, indicates that the air passage is divided into two by having a gap in the middle, and the gap between the ducts 81 and 83 is Then, the recording paper 25 is conveyed and the recording paper 25 crosses the air path once. The ducts 81 and 83 have partition walls corresponding to the position of the width (each size) of the recording paper 25, and the ducts 81 and 83 (air passages) are arranged in the axial direction (sheet width direction). It is divided into sections.

  In the configuration of the present embodiment as described above, similarly to the first embodiment, the temperature rise in the non-sheet passing region of the fixing roller 22 can be accurately suppressed.

  Although not shown, if the exhaust duct as in the fifth embodiment is provided from the opening 83b which is a cool air discharge port of the duct 83, the cooling effect can be further increased.

  Also, the opening 81a of the duct 81 sucks the unfixed recording paper 25, and thus sucks air from the inside of the apparatus. However, the present invention is not limited to this, and for example, opens to the lower part of the apparatus and sucks air from outside the apparatus. You may do it.

Sectional drawing which shows the image forming apparatus incorporating the fixing device which concerns on 1st Embodiment. Sectional drawing which shows the fixing device which concerns on 1st Embodiment. Sectional drawing of the part in the axial direction of the fixing roller of the fixing device which concerns on 1st Embodiment. Schematic showing the longitudinal direction of the fixing device according to the first embodiment Sectional drawing which shows the fixing device which concerns on 2nd Embodiment. Sectional drawing which shows the fixing device which concerns on 3rd Embodiment. Sectional drawing which shows the fixing device which concerns on 4th Embodiment. Sectional drawing which shows the fixing device which concerns on 5th Embodiment. Sectional drawing which shows the fixing device which concerns on 6th Embodiment.

Explanation of symbols

2 Fixing device 12 Fan 21 Heat source 22 Fixing roller 23 Pressure roller 25 Recording paper 26 Discharge roller pair 27 Duct 28 Duct 29 Duct 29c Extension part 41 Planar heating element 42 Heat-resistant film 43 Driving roller 51 Cooling means 61 Valve 62 Cooling port 63 Belt 71 Waste heat duct 72 Fan 81 Duct 82 Fan 83 Duct

Claims (4)

In a fixing device for fixing an unfixed developer image on a sheet,
It has an air passage that guides cooling air to the heat generating part,
The air passage is partitioned into a plurality of sections in the sheet width direction, and a gap through which the sheet after fixing crosses the air passage is provided in the middle of the air passage,
Since the sheet after fixing crosses the air path, the sheet after fixing is cooled and the paper passing area blocked by the sheet after fixing does not allow the cooling air to reach the heat generating part, and the heat generating part is not passed. A fixing device in which a paper region is cooled.   The fixing device according to claim 1, wherein the gap is provided at two places, and the sheet after fixing crosses the air path twice. It has an exhaust passage that exhausts air from the heat generating part,
The fixing device according to claim 1, wherein the exhaust path is partitioned into a plurality of sections in the sheet width direction in the same manner as the air path. Image forming means for forming a developer image on the sheet;
The fixing device according to claim 1, wherein the developer image formed by the image forming unit is fixed to a sheet.
An image forming apparatus comprising:

Images