JP2008064991A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the fixing metal belt from abruptly shrinking even when passing through the contact area heated to a high temperature in a fixing unit built in an image forming apparatus. <P>SOLUTION: The fixing belt is an endless belt made by forming a mold release layer on the surface of a metal base layer and stretched on a fixing roll 31, a releasing roll 35, and tension roll 36 to move around as the fixing roll 31 turns in the arrow r direction as illustrated. The paper sheet carried to the contact area N of the fixing roll 31 and the pressure roll 32 is heated and pressed to stick to the outer surface of the fixing belt 33 by the adhesion of the melted toner. The fixing belt 33 is cooled by the heat radiation regulator 37 before cooled in the open air to an extent not abruptly shrinking when passing through the contact area N with the paper sheet sticking to the surface. Thus, the fixing metal belt 33 is prevented from abruptly shrinking. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

Some electrophotographic image forming apparatuses use a fixing belt as a fixing device for fixing a toner image onto a sheet. For example, in the fixing device disclosed in Patent Document 1, a stainless steel metal belt that is hard to be scratched compared to a resin belt is stretched around two axes of a heating roller and a cooling roller, and a toner image is formed. The sheet is subjected to heat and pressure at the contact portion between the heating roller and the pressure roller, with the recording surface in close contact with the outer peripheral surface of the fixing belt. The sheet to which heat and pressure are applied at the contact portion is cooled by a cooling member while being conveyed toward the sheet discharge port by the fixing belt. As a result, the toner captures and solidifies the smooth surface shape of the metal belt to obtain a highly glossy image, and the releasability when the paper is peeled from the metal belt is improved. Further, the fixing device disclosed in Patent Document 2 brings a heat roller having a circumferential surface formed of a metal annular film into contact with a pressure roller, and heats and pressurizes the paper on the paper introduction side at the contact portion. The paper is cooled on the exit side. Thereby, the releasability of the paper is improved. Further, the fixing device disclosed in Patent Document 3 applies heat and pressure to a sheet at a contact portion between a pressure belt made of a metal such as aluminum or nickel and a fixing roller whose surface is heated, and the contact portion. The paper is cooled at the exit side. Thereby, the peelability of the paper is improved.
JP 2005-292578 A JP-A-4-362833 JP-A-10-254266

However, since all of the fixing devices disclosed in Patent Documents 1 to 3 use a metal belt, when the metal belt passes through a contact portion heated to a high temperature and touches a relatively low temperature outside air. The stored heat is excessively released and contracts abruptly, and the surface becomes wavy. Also, this type of fixing device often forms a high-gloss image by bringing the recording surface of the paper into close contact with the outer peripheral surface of the metal belt and cooling it. When a portion that does not contact the belt is generated, uneven glossiness is generated in the printed surface. Further, since the metal belt suddenly contracts and emits a metal sound, the metal sound may cause discomfort to the user.
The present invention has been made in view of such a background, and an image forming apparatus equipped with a fixing device that does not cause rapid contraction of a metal belt when the metal belt is passed through a contact portion heated to a high temperature. The purpose is to provide.

  An image forming apparatus according to a preferred aspect of the present invention includes: an image forming unit that generates a toner image corresponding to image data on a peripheral surface of a photoconductor, and transfers the toner image to a recording material; and the toner image is transferred. A heating roll that applies heat to the recording material, and a pressure that presses the recording material toward the heating roll when the recording material is supplied between the heating roll and itself. An endless belt-like member made of metal that is stretched by a roll and the heating roll and at least one or more support members, and is moved around by following the rotation of at least one of the heating roll and the support member A fixing belt that conveys the recording material supplied between the heating roll and the pressure roll along the moving direction, and the heating roll among the support members that stretch the fixing belt. in front A cooling unit that is provided between the heating roll and a support member that changes a moving direction of the fixing belt that has passed through a position facing the pressure roll, and that cools the recording material conveyed to the fixing belt; and the heating roll; And a heat absorption means provided between the cooling means and absorbing heat held by the fixing belt.

In this aspect, the heat absorption means may be provided in contact with the cooling means.
In each of the above aspects, the heat absorbing means is provided in contact with the inner peripheral surface of the fixing belt, and has a thermal conductivity λ (W / m · K) between the surface in contact with the fixing belt and the opposite surface. The distance t (m) may satisfy the relationship of 2 × 10 ³ ≦ λ / t ≦ 2 × 10 ⁶ .

  According to the present invention, even when the metal belt is passed through the contact portion heated to a high temperature in the fixing device mounted on the image forming apparatus, the metal belt is not rapidly contracted.

(First embodiment)
A first embodiment of the present invention will be described.
FIG. 1 is a schematic hardware configuration diagram of an image forming apparatus 1 according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 includes a paper tray 10, an image forming engine 20, and a fixing unit 30.

  The paper tray 10 stores a plurality of sheets cut into a predetermined size such as A4. The paper stored in the paper tray 10 includes a base material layer mainly composed of cellulose and an image receiving layer mainly composed of a thermoplastic resin such as polyester. A toner image is formed on the surface of the base material layer (hereinafter referred to as “recording surface”) among these two layers. The sheets are picked from the sheet tray 10 one by one and are sequentially conveyed on a sheet conveyance path connected to the sheet discharge port via the image forming engine 20 and the fixing unit 30.

  The image forming engine 20 is provided for each of yellow (Y), magenta (M), cyan (C), and black (K), and each of them includes a photosensitive drum, a charging unit, an exposure unit, a developing unit, And a transfer portion. An outline of how each unit is driven is as follows. First, the charging unit uniformly charges the circumferential surface of the photosensitive drum that circulates at a predetermined speed, and then the exposure unit scans the circumferential surface while inputting. An electrostatic latent image is formed by irradiating laser light modulated according to the image data. Further, the developing unit supplies the toner to develop the electrostatic latent image as a toner image, and the developed toner image is transferred to the paper on the paper transport path by the transfer unit.

As shown in FIG. 2, the fixing unit 30 includes a fixing roll 31, a pressure roll 32, a fixing belt 33, a cooling member 34, a peeling roll 35, a tension roll 36, and a heat dissipation suppressing member 37.
The fixing roll 31 is a roll-shaped member in which a release layer made of a PFA tube is formed on the surface of a metal core having high thermal conductivity. A halogen lamp is provided inside the core, and the surface of the fixing roll 31 is heated to a predetermined temperature by the halogen lamp. This predetermined temperature is a temperature at which the heat transmitted from the surface of the fixing roll 31 to the paper melts the toner on the paper and softens the image receiving layer of the paper. The fixing roll 31 is rotated by a motor (not shown) to move the fixing belt 33 in the direction of arrow r in the drawing.

  In the pressure roll 32, the surface of a metal core having high thermal conductivity is coated with an elastic body layer made of silicon rubber having a rubber hardness (JIS-A) of about 40 °, and further fixed on the surface of the elastic body layer. This is a roll-like member in which a release layer similar to the roll 31 is formed. A halogen lamp is provided inside the core, and the surface of the pressure roll 32 is heated by the halogen lamp. The pressure roll 32 is disposed to face the fixing roll 31 with the fixing belt 33 interposed therebetween, and the sheet conveyed to the facing position (hereinafter referred to as “contact portion N”) is fed to the fixing roll 31 side. Press at a predetermined pressure.

As shown in FIG. 3, the fixing belt 33 is an endless belt-like member in which a release layer 33b for imparting release properties is formed on the surface of a base material layer 33a made of metal. In FIG. 2, the fixing belt 33 is stretched around a fixing roll 31, a peeling roll 35, and a tension roll 36, and is rotated in the direction of the arrow r in the figure following the rotation of the fixing roll 31.
Heat and pressure are applied to the sheet conveyed to the contact portion N in a state where the recording surface is in close contact with the outer peripheral surface of the fixing belt 33. In the paper to which heat and pressure are applied at the contact portion N, the toner formed on the recording surface thereof melts to cause stickiness, and adheres to the outer peripheral surface of the fixing belt 33 that is in close contact. The fixing belt 33 conveys the sheet in the direction of the arrow r while the sheet is adhered to the outer peripheral surface by the adhesive force of the toner.

  The peeling roll 35 changes the moving direction of the fixing belt 33 that has passed through the contact portion N while stretching the fixing belt 33 and rotating in accordance with the circumferential movement thereof. When the sheet adhering to the outer peripheral surface of the fixing belt 33 is conveyed to the installation position of the peeling roll 35 as the fixing belt 33 rotates, the sheet is sequentially peeled from the leading end and completely peeled from the fixing belt 33. It is sent to the paper exit.

  The tension roll 36 rotates in accordance with the circumferential movement of the fixing belt 33 while stretching the fixing belt 33, and is also biased when the fixing belt 33 is continuously circulated (the fixing belt 33 is one of the tension rolls 36). Correct the phenomenon of moving toward the edge).

  The cooling member 34 is disposed in contact with the inner peripheral surface of the fixing belt 33 in the section between the fixing roll 31 and the peeling roll 35. The cooling member 34 includes an aluminum heat sink and a cooling fan, and a plurality of heat radiation fins are provided on the inner surface of the heat sink that contacts the inner peripheral surface of the fixing belt 33. The heat sink is cooled by air from the cooling fan and cools the sheet conveyed to the fixing belt 33.

  The heat dissipation suppressing member 37 is disposed in contact with the inner peripheral surface of the fixing belt 33 in the section between the fixing roll 31 and the cooling member 34. This heat dissipation suppressing member 37 is a plate-like member made of SUS304 (Steel Use Stainless 304) having a high thermal conductivity, and the distance (thickness) from the surface contacting the fixing belt 33 to the opposite surface is 1 mm, fixing. The length of the belt 33 in the width direction is longer than the width of the fixing belt 33. The material (SUS304) and the thickness forming the heat radiation suppressing member 37 are designed in advance so as to absorb a heat amount that does not cause the fixing belt 33 to rapidly contract from the fixing belt 33 that has passed through the contact portion N.

Next, the operation of the fixing unit 30 will be described.
The sheet on which the toner image is formed by the image forming engine 20 is conveyed to the contact portion N, and heat and pressure are applied in a state where the recording surface is in close contact with the outer peripheral surface of the fixing belt 33. Then, the toner on the recording surface of the paper is melted and the image receiving layer is softened, and the melted toner is embedded in the image receiving layer. The recording surface of the paper adheres to the outer peripheral surface of the fixing belt 33 that is in close contact with the adhesive force of the melted toner. Since the outer peripheral surface of the fixing belt 33 has a smooth shape with no irregularities, the recording surface of the sheet and the outer peripheral surface of the fixing belt 33 are attached with high adhesion. For this reason, the sheet is conveyed in the direction of the arrow r as the fixing belt 33 moves around in a state where the sheet is adhered to the fixing belt 33 with an adhesive force that does not peel off.

  As soon as the fixing belt 33 having the paper attached to the outer peripheral surface passes through the contact portion N, the fixing belt 33 reaches the installation position of the heat dissipation suppressing member 37. Since the heat dissipation suppression member 37 is provided in the vicinity of the contact portion N, the fixing belt 33 that has passed through the contact portion N is heated by the heat dissipation suppression member 37 before being cooled by being exposed to the outside air. Absorbed. As described above, the heat radiation suppressing member 37 is designed so as to absorb a quantity of heat that does not cause the fixing belt 33 to contract rapidly. Therefore, the fixing belt 33 does not rapidly contract due to excessive release of heat. The outer peripheral surface is maintained in a smooth shape. The sheet is conveyed to the installation position of the cooling member 34 while being in close contact with the smooth outer peripheral surface.

  The sheet conveyed to the installation position of the cooling member 34 is cooled to a temperature not higher than the glass transition temperature by the cooling member 34. Then, the melted toner copies the shape of the smooth outer peripheral surface of the fixing belt 33 and solidifies to form a high gloss image. When the paper on which the toner is solidified is conveyed to the installation position of the peeling roll 35 by the fixing belt 33, the paper is peeled in order from the leading end, and the paper peeled off from the fixing belt 33 is discharged as a printed matter from the paper discharge port. Is done.

  Then, the experiment which this inventor performed in order to confirm the installation effect of the heat dissipation suppression member 37 and its experimental result are demonstrated. In this experiment, the number of sheets peeled off from the fixing belt 33 before the paper that passed through the contact portion N reached the peeling roll 35 (the number of sheets dropped out), and the unevenness of the glossiness in the discharged printed matter were observed. The measurement is made with the configuration in which the heat dissipation suppression member 37 is provided and the configuration in which the heat dissipation suppression member 37 is not provided. Both the dropout of the paper and the in-plane unevenness of the glossiness are phenomena that occur when the adhesion between the paper and the fixing belt 33 decreases due to the rapid contraction of the fixing belt 33. That is, the occurrence of these phenomena means that the fixing belt 33 is rapidly contracted.

  FIG. 4 is a diagram showing the results of this experiment. The number of sheets dropped out in the drawing is the fixing belt before reaching the peeling roll 35 when every ten sheets are continuously passed through the contact portion N. The number of sheets peeled off (separated) from 33 is shown. In addition, the in-plane unevenness of glossiness in the figure is an item indicating the variation in glossiness of a predetermined part on the recording surface of the printed matter, ○ indicates that the variation in glossiness is within the reference range, and Δ indicates the glossiness It shows that the variation of is slightly over the reference range.

  As shown in the figure, when the heat dissipation suppressing member 37 is not provided, eight sheets out of the ten sheets that have been passed through fall off before reaching the peeling roll 35. Further, in-print unevenness exceeding the reference range was observed in the discharged printed matter. Based on these results, when the heat dissipation suppressing member 37 is not provided, the fixing belt that has passed through the contact portion N may come into contact with the relatively low temperature outside air, causing heat to be excessively released and rapidly contracting. Recognize.

  On the other hand, when the heat dissipation suppressing member 37 was provided, the number of sheets dropped out was zero, and the uneven glossiness of the printed material was also within the reference range. That is, it can be seen that the provision of the heat dissipation suppressing member 37 prevents the fixing belt 33 from rapidly contracting.

(Second Embodiment)
A second embodiment of the present invention will be described. The hardware configuration of the image forming apparatus 1 according to the present embodiment is the same as that of the first embodiment described above except for the arrangement position of the heat dissipation suppressing member 37.
As shown in FIG. 5, the heat dissipation suppressing member 37 is disposed in contact with the surface on the fixing roll 31 side of the cooling member 34 and the inner peripheral surface of the fixing belt 33. Since the heat radiation suppressing member 37 is in contact with the cooling member 34, the absorbed heat is cooled by the cooling member 34, and the temperature is always close to the cooling member 34. As a result, even when the paper is continuously passed through the contact portion N, the same action as in the first embodiment described above can be obtained.

Then, the experiment and the experimental result which were performed in order to confirm the effect when the inventors of the present application brought the heat radiation suppressing member 37 into contact with the cooling member 34 will be described. In this experiment, the glossiness of a printed material when 100 sheets of paper are continuously passed through the contact portion N is measured with a configuration in which the heat dissipation suppression member 37 is in contact with the cooling member 34 and in a configuration in which the gloss is not in contact with each other. It is a thing.
FIG. 6 is a diagram showing the results of this experiment, where the horizontal axis of the figure indicates the number of sheets to be printed (sheets) indicating how many sheets have been passed, and the vertical axis indicates the glossiness (Gs) of the printed materials. (20 °)). As shown in the figure, while the number of sheets to be passed is small, the glossiness is similar in both configurations, but as the number of sheets to be passed increases, the printed matter in a configuration in which the heat dissipation suppression member 37 is not brought into contact with the cooling member 34. The glossiness of is low. That is, it can be seen that, by bringing the heat dissipation suppressing member 37 into contact with the cooling member 34, good glossiness can be obtained even when continuous printing is performed.

(Other embodiments)
The present invention can be modified in various ways.
In the said embodiment, although the heat dissipation suppression member 37 was a member with a thickness of 1 mm made of SUS304, the material and thickness thereof are not limited to this.

FIG. 7 is a diagram showing experimental results in an experiment conducted by the inventors of the present application in order to obtain a relationship between the thermal conductivity (λ) and the thickness (t) of a material suitable for the heat dissipation suppressing member 37. In this experiment, whether or not the glossiness of the printed matter is good and whether or not the sheet is dropped are determined by changing the thermal conductivity (λ) and thickness (t) of the material forming the heat dissipation suppression member 37 (λ / t (× 10 ³ )). The glossiness shown in the figure is an item indicating whether the glossiness of the printed material satisfies the target value of Gs (20 °) ≧ 80, and ◯ indicates the glossiness of the printed material of the target value Gs (20 °) ≧ 80. X indicates that the glossiness of the printed material is below the target value Gs (20 °) ≧ 80. Further, the sheet dropout is an item indicating whether or not the sheet has dropped out, ○ indicates that all 10 sheets continuously passed through the contact portion N have reached the peeling roll 35 and have been peeled off, and x represents Of the ten sheets that have been continuously passed through the contact portion N, at least one sheet has dropped from the fixing belt 33 before reaching the peeling roll 35.

As shown in the figure, when the value of the heat dissipation suppression parameter λ / t (× 10 ³ ) is 1.1, 4220, and 6000, the glossiness of the printed matter is insufficient, and the heat dissipation suppression parameter λ / t Further, when the value of (× 10 ³ ) was 4220 and 6000, the sheet also dropped out. That is, if the value of the heat dissipation suppression parameter λ / t (× 10 ³ ) of the heat dissipation suppression member 37 is a value within the range of 2 to 2000 × 10 ³ , a printed matter that does not drop out and has good glossiness is obtained. can get. As the heat dissipation suppression member 37 having the heat dissipation suppression parameter in this range, for example, a member made of aluminum and having a thickness of 1 mm may be used.

  The heat radiation suppressing member 37 in the above embodiment may be disposed so that the side surface on the fixing roll 31 side is provided in a round shape along the circumference of the fixing roll 31 and closer to the fixing roll 31.

  In the above-described embodiment, the fixing belt 33 has a release layer 33b for imparting releasability formed on the surface of the base material layer 33a made of metal. However, as shown in FIG. The structure which provided the elastic layer 33c between the base material layer 33a and the mold release layer 33b may be sufficient.

  In the second embodiment, the heat dissipation suppressing member 37 is always at a temperature close to the cooling member 34, and cools the paper that has passed through the contact portion N to a glass transition temperature or lower. Therefore, even if the length of the cooling member 34 in the circumferential movement direction of the fixing belt 33 is shortened, the section for cooling the sheet to the glass transition temperature or less secures the same length as in the configuration of the above-described embodiment. be able to. As a result, the same cooling action as in the above embodiment can be obtained, and the apparatus can be miniaturized.

2 is a schematic hardware configuration diagram of the image forming apparatus 1. FIG. FIG. 2 is a schematic configuration diagram of a fixing unit 30 (first embodiment). FIG. 3 is a cross-sectional view of the fixing belt 33 (first embodiment). It is a figure which shows the installation effect of the heat dissipation suppression member. FIG. 3 is a schematic configuration diagram of a fixing unit 30 (second embodiment). It is a figure which shows the effect at the time of making the heat dissipation suppression member 37 contact the cooling member 34. FIG. It is a figure which shows the optimal range of a heat dissipation suppression parameter. It is sectional drawing of the fixing belt 33 (other embodiment).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Paper tray, 20 ... Image forming engine, 30 ... Fixing part, 31 ... Fixing roll, 32 ... Pressure roll, 33 ... Fixing belt, 33a ... Base material layer, 33b ... Release layer, 33c ... elastic layer, 34 ... cooling member, 35 ... peeling roll, 36 ... tension roll, 37 ... heat dissipation suppressing member.

Claims (3)

Image forming means for generating a toner image corresponding to the image data on the peripheral surface of the photoreceptor and transferring the toner image to a recording material;
A heating roll for applying heat to the recording material onto which the toner image has been transferred;
A pressure roll that is provided facing the heating roll and presses the recording material toward the heating roll when a recording material is supplied between the heating roll and itself,
A metal endless belt member stretched by the heating roll and at least one or more support members, wherein the endless belt-like member is rotated by the rotation of at least one of the heating roll and the support member. A fixing belt that conveys the recording material supplied between the heating roll and the pressure roll along its moving direction;
Among the supporting members that stretch the fixing belt, the fixing belt is provided between the supporting member that changes the moving direction of the fixing belt that has passed the position where the heating roll and the pressure roll face each other, and the heating roll. Cooling means for cooling the recording material conveyed to
An image forming apparatus comprising: a heat absorbing unit that is provided between the heating roll and the cooling unit and absorbs heat held by the fixing belt. The image forming apparatus according to claim 1.
The image forming apparatus, wherein the heat absorbing means is provided in contact with the cooling means. The image forming apparatus according to claim 1, wherein
The heat absorbing means is provided in contact with the inner peripheral surface of the fixing belt, and has a thermal conductivity λ (W / m · K) and a distance t (m from the surface in contact with the fixing belt to the opposite surface thereof. ) Satisfy the relationship of 2 × 10 ³ ≦ λ / t ≦ 2 × 10 ⁶ .

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