JP3893822B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile machine, and a multifunction machine of these, and more particularly to a pair of conveying rolls that convey a recording sheet after fixing.
[0002]
[Prior art]
Conventionally, a toner image is electrostatically held on a recording sheet, and the recording sheet holding the toner image is nipped and conveyed to a nip portion of a fixing rotating body pair such as a heating roll and a pressure roll. 2. Description of the Related Art Image forming apparatuses that fix a toner image on a recording sheet by the action of applied heat and pressure are widely known. The fixed recording sheet is nipped and conveyed by a pair of conveying rolls and is discharged to the outside of the image forming apparatus.
[0003]
As a material used for this transport roll, for example, POM (polyoxymethylene) is generally used. Furthermore, in order to prevent the toner from adhering to the surface of the transport roll, PFA (tetrafluoroethylene perfluorovinyl ether polymer), PTFE (tetrafluoroethylene resin), etc., which have higher releasability from the toner than POM, are used. in use.
[0004]
[Problems to be solved by the invention]
However, when a conveyance roll made of a material such as POM, PFA, or PTFE is used along with a change in the configuration of the fixing device, image quality may be deteriorated. That is, today, the amount of release agent (oil) supplied to the recording sheet at the time of fixing is smaller for improving the writing property and adhesion to the recording sheet after image formation. Furthermore, there is a so-called oil-less fixing device that does not supply a release agent (oil) to a recording sheet for ease of maintenance, cost reduction, and the like.
[0005]
In such a fixing device, it is general that the toner contains wax so that the toner itself has releasability while reducing the supply amount of the release agent or instead of supplying the release agent. The wax is melted by the fixing process and comes into contact with the transport roll before it is completely solidified. As a result, streaky wax is deposited on the image in contact with the transport roll, resulting in poor image quality.
[0006]
The present invention has been made in view of such problems, and an object thereof is to provide an image forming apparatus capable of preventing image quality defects due to wax or the like contained in toner.
[0007]
[Means for Solving the Problems]
That is, the present invention includes a fixing unit for fixing an unfixed toner image on a recording sheet, an image forming apparatus and a conveying roller pair for conveying nip the recording sheet that has been fixed by the fixing means, the conveying roller pair is the A transport roller pair on the most upstream side with respect to the fixing unit, and the entire surface of the roll in contact with the toner image fixed in the transport roll pair is constituted by a porous member. By configuring the image forming apparatus in this way, even if the melt present on the surface of the recording sheet after fixing comes into contact with the conveyance roll, the melt is held in each hole of the porous member, Does not stain the image.
[0008]
Here, as such a porous member, a foaming member is preferable. Further, since it is in contact with a relatively high-temperature recording sheet immediately after fixing, it is preferably excellent in heat resistance. Examples of the porous member having such conditions include sponges such as silicon, urethane, chloroprene, polyethylene, natural rubber, and nitrile rubber.
[0009]
Further, as the number of such porous cells, the number of cells per roll axial length 25 [mm] is preferably 8 to 100 [Claim 5], more preferably the axial length of the roll. The number of cells per 25 [mm] is in the range of 30 to 80 [pieces].
[0010]
As the melt existing on the surface of the recording sheet after fixing, a toner can be generally used, but the melting point of the toner is relatively high and solidifies immediately after fixing. Therefore, a melt that causes poor image quality has a melting point lower than that of the toner, and a typical one is wax contained in the toner.
[0011]
This wax is generally contained in the toner in order to improve the releasability between the toner and the fixing rotator constituting the fixing unit, so that the fixing unit does not supply a release agent to the recording sheet (oilless Type), a relatively large amount of wax is contained in the toner. Therefore, when the fixing unit does not supply oil to the recording sheet during fixing (claim 3), the effect of the present invention is more remarkably exhibited. The fixing means is generally constituted by a pair of fixing members having a heat source therein, and at least one of the pair of fixing members is a roll-shaped or endless belt-shaped rotating body.
[0012]
The recording sheet after fixing is finally discharged to the outside of the image forming apparatus. However, when the transport path from the fixing unit to the discharge port is relatively long, the pair of transport rolls is moved from the fixing unit to the recording sheet. A plurality of locations are provided from the upstream side to the downstream side on the transport path to the discharge port. In such a case, the melt (for example, wax) on the recording sheet is cooled along with the conveyance, solidifies before reaching the downstream side on the conveyance path, and may not stain the image even if it contacts the conveyance roll. In such a case, if the surface of the roll in contact with the fixed toner image of the pair of conveyance rolls closest to the fixing unit on the most upstream side on the conveyance path is constituted by a porous member. It is sufficient (claim 4).
[0013]
As a specific configuration of the transport roll that comes into contact with the fixed toner image, for example, an axial member that constitutes a rotating shaft, a porous member that constitutes an outer layer of the axial member, and the axial member include It can be provided with a shaft support member that is rotatably supported. And it is preferable that the magnitude | size of the other conveyance roll direction of this axial support member is smaller than the magnitude | size of the other conveyance roll direction of a shaft center member (Claim 6). By configuring in this way, even when the porous member is elastically deformed by being pressed against the other transport roll, the shaft support member is prevented from coming into direct contact with the other transport roll or the recording sheet. This is because the porous member is always in contact with the transport roll and the recording sheet. Note that POM, PFA, PTFE, or the like can be used as the material of the shaft center member.
[0014]
Further, the shaft support member may be configured integrally with the leaf spring member. This leaf spring member is for urging the transport roll to another transport roll that is paired with the transport roll to apply an appropriate nip pressure to the nip portion of both transport rolls, and has an appropriate elasticity, for example. It can be made of metal.
[0015]
[Mode for Carrying Out the Invention]
FIG. 1 shows an image forming apparatus 10 including a fixing device 14 according to the present invention. As shown in FIG. 1, the image forming apparatus 10 is covered with a casing 12 and formed in a substantially box shape.
[0016]
A plurality of recording medium trays 16 (in the present embodiment, three recording medium trays 16A, 16B, and 16C are shown) are disposed below the image forming apparatus 10. Each of the recording medium trays 16A, 16B, and 16C is provided with recording media 18 having different sizes such as B5 size, B4 size, A4 size, and A3 size. A half-moon roller 20 is disposed in the vicinity of the recording medium discharge portion in the recording medium tray 16, and the recording sheets 18 are sent out one by one from the designated paper tray 16 and conveyed in a predetermined direction by a plurality of conveying roller pairs 22. Is done. In addition, when the image forming apparatus 10 instructs to form images on both sides (front and back) of the paper 28, a paper reversing unit 17 is provided for reversing the front and back of the recording sheet 18 that has finished image formation on the front side. ing.
[0017]
On one side surface of the image forming apparatus 10, a manual feed tray 24 for manually inserting the recording sheet 18 is disposed as necessary. Similar to the paper tray 16 described above, a half-moon roller 20 is disposed in the vicinity of the paper insertion portion of the manual feed tray 24 so that the recording sheets 18 can be fed one by one.
[0018]
A discharge tray 26 for discharging a recording sheet 18 on which a desired image is fixed by a fixing device (fixing unit) 14 is provided on the upper portion of the image forming apparatus 10.
[0019]
Image data obtained by reading a document with a scanner and performing various image processing is provided above the paper tray 16 in the image forming apparatus 10 (since the image forming apparatus 10 in this embodiment is intended for color images, image processing is performed. Is converted into image data of four colors of yellow, magenta, cyan, and black), and a fixing device that fixes a desired image on the recording sheet 18. An image forming unit 28 including 14 or the like is provided.
[0020]
The optical scanning device 32 includes a light source, a rotary polygon mirror 34, an fθ lens, a cylindrical mirror, a reflection mirror 36, and the like. Laser light emitted from a light source (not shown) is deflected by the rotating polygonal mirror 34 and applied to the photoconductor 30 through an fθ lens, a cylindrical mirror, a reflection mirror 36, and the like.
[0021]
Further, around the photosensitive member 30, a charger 38, a rotary developing device 40, an intermediate transfer member 42 composed of an IBT belt, a photosensitive member cleaner 44, and a neutralizing lamp (not shown) are disposed.
[0022]
The photoconductor 30 rotates at a constant speed in the direction of arrow A shown in FIG. The charging member 38 uniformly negatively charges the photosensitive member 30. The rotary developing device 40 is supplied with toners 46Y, 46M, 46C, and 46Bk of four colors of yellow, magenta, cyan, and black. The toners 46Y, 46M, 46C, and 46Bk of the respective colors contain wax in order to improve releasability from the heating roller of the fixing device 14 described later.
[0023]
The intermediate transfer member 42 is wound around a plurality of rollers 48, and moves at a constant speed in the direction of arrow B shown in FIG. 1 as the rollers 48 rotate. The photoreceptor cleaner 44 removes toner remaining on the photoreceptor 30 without being transferred to the intermediate transfer body 42. Further, the static elimination lamp neutralizes the photoconductor 30 after the remaining toner is removed by the photoconductor cleaner 44.
[0024]
Further, an image detection sensor 51 and an intermediate transfer body cleaner 50 are disposed around the intermediate transfer body 42. The image detection sensor 51 is provided upstream of the transfer unit 52 in the rotation direction of the intermediate transfer body 42 and detects the presence or absence of a toner image formed on the intermediate transfer body 42. The intermediate transfer body cleaner 50 is provided downstream of the transfer portion 52 in the rotation direction of the intermediate transfer body 42, and after the transfer of the toner image I from the intermediate transfer body 42 to the recording sheet 18 is finished, the intermediate transfer body. The toner 46 remaining on the surface of 42 is removed.
[0025]
The photosensitive member 30 that rotates in the direction of arrow A is uniformly negatively charged by the charger 38, and first a black latent image of the first color is formed on the photosensitive member 30 by the laser light emitted from the optical scanning device 32. The This latent image is developed with black toner by the black developer of the rotary developer 40. The developed black toner image is transferred to the intermediate transfer body 42. The toner 46 remaining without being transferred onto the photoconductor 30 is removed by a cleaner (not shown), and the photoconductor 30 is neutralized by a static elimination lamp.
[0026]
The photosensitive member 30 is again negatively charged uniformly by the charger 38, and the second color yellow image is formed. In this way, a total of four color toner images I from the third color magenta to the fourth color cyan are sequentially transferred to the intermediate transfer member 26. When the transfer of the four color toner images I to the intermediate transfer body 42 is completed, the final toner image I is formed on the surface of the intermediate transfer body 42.
[0027]
Below the intermediate transfer body 42, a transfer section 52 for transferring the final toner image I formed on the intermediate transfer body 42 to the recording sheet 18 is provided. The recording sheet 18 is conveyed from the paper tray 16 provided with the recording sheet 18 having a specified size as described above to the transfer unit 52 by the conveying roller pair 22.
[0028]
A fixing device (fixing means) 14 is disposed on the downstream side in the conveyance direction of the recording sheet 18 from the position where the transfer unit 52 is disposed. In the fixing device 14, a predetermined toner image I is formed on the recording sheet 18 by performing a fixing process on the paper 34 onto which the final toner image I has been transferred. The recording sheet on which the image is formed is conveyed while being sandwiched between conveyance roller pairs 7, 8, and 22 one after another along a conveyance path indicated by P in the drawing, and is discharged to the discharge tray 26.
[0029]
The fixing device 14 has a heating roller (fixing rotator) 56 for fusing and fixing the toner 46 transferred onto the paper 18 to the paper 18, and for sandwiching and pressing the paper 18 together with the heating roller 56. And a pressure roller (fixing rotator) 58. The heating roller 56 is configured as an iron metal hollow gold having a thickness of about 3 mm. Further, a rubber layer having a thickness of about 2 mm is formed on the contact surface with the sheet 18, that is, the surface of the heating roller 56, and a halogen lamp (heat source) is built in the heating roller 56. The pressure roller 58 is formed with a rubber layer having a thickness of about 1 mm around the core metal such as iron, and a halogen lamp (heat source) is provided inside the pressure roller 58. Built in. The pressure roller 58 presses the heating roller 56 with a constant pressure by a spring. As a result, the recording sheet 18 is nipped and conveyed by the heating roller 56 and the pressure roller 58. Thus, when the recording sheet 18 passes between the heating roller 56 and the pressure roller 58, the toner 46 is pressure-melted and fixed on the paper 18.
[0030]
By the way, in this image forming apparatus 10, in order to prevent the toner image I from being soiled by wax (melt) contained in the toner 46 constituting the toner image I, the fixing device 14 supplies the discharge tray (discharge port) 26. Among the transport roll pairs 7 and 8 and 22 provided in the transport path P up to, various countermeasures are taken in the transport roll pairs 7 and 8 on the most upstream side. Hereinafter, these will be described.
[0031]
FIG. 2 is a cross-sectional view showing a configuration around the conveying roll pair 7 and 8 closest to the fixing device 14. FIG. 3 is a perspective view of the configuration around the conveying roll pair 7 and 8 closest to the fixing device 14 from the direction of the arrow V in FIG. As shown in these drawings, of the pair of conveyance rolls 7 and 8, the conveyance roll 7 that comes into contact with the toner image I fixed on the recording sheet 18 is attached to a conveyance plate 90 that forms a part of the conveyance path. The other conveyance roll 8 is attached to a guide plate 80 that guides the recording sheet 18 discharged from the nip portion N of the fixing device 14. In addition, the other conveyance roll 8 is comprised by POM.
[0032]
Then, four pairs (7a to d, 8a to d) of these conveying roll pairs 7 and 8 are arranged at right angles to the conveying direction of the recording sheet 18 (see FIG. 3). Note that both the guide plate 80 and the transport plate 90 have a large number of ribs 81 and 91 extending in the transport direction for reducing the transport resistance with the recording sheet 18.
[0033]
FIG. 4 is a perspective view of one transport roll 7. As shown in the figure, the transport roll 7 includes a shaft center member 71 that constitutes a rotation shaft, a porous member 70 that constitutes an outer layer of the shaft center member 71, and a shaft member that rotatably supports the shaft center member. The shaft support member 72 has both a role as a leaf spring member and a role as an attachment member to the transport plate 90. In addition, the dashed-dotted line in the figure shows the rotating shaft S (hereinafter the same).
[0034]
5 to 7 are perspective views of components of the transport roll 7 shown in FIG. 4. FIG. 5 shows a shaft member 71, FIG. 6 shows a porous member 70, and FIG. 7 shows a shaft support member 72. A perspective view is shown.
[0035]
The shaft center member 71 shown in FIG. 5 is made of POM and has a substantially cylindrical shape with the rotation axis S as the center. Substantially at the axial direction end side of the cylindrical shape has a diameter diameter portion 711 and 712 for holding the porous member 70, the diameter of the thick diameter portion 711, 712 and 2R _1. Further, the length of the central portion 710 sandwiched between the large diameter portions 711 and 712 in the direction of the rotation axis S is L ₁ .
[0036]
The porous member 70 shown in FIG. 6 is made of a sponge and has a substantially cylindrical shape. The cylindrical inner diameter (diameter) is 2R ₀ (inner), and the outer diameter (diameter) is 2R ₀ (outer). Here, the relationship between the diameters 2R _{1 of the} large-diameter portions 711 and 712 of the shaft member 71 is 2R ₀ (inner) <2R ₁ <2R ₀ (outer), that is, R ₀ (inner) <R ₁ < R ₀ (outside). If the length S of the porous member 70 in the rotational axis direction is L ₀ , the relationship with the length L ₁ in the rotational axis S direction of the central portion 710 of the previous shaft center member 71 is L ₀ ≈L ₁ . .
[0037]
The shaft support member 72 shown in FIG. 7 is made of stainless steel, and has an attachment shape 723 for attachment to the transport plate 90 at the top, and the shaft center member 71 at both ends of the rotation axis S direction. The shaft support shapes 721 and 722 for rotatably supporting the shaft are provided. A circular hole centered on the rotation axis S is formed at the center of each of the shaft support shapes 721 and 722. Further, each of the shaft support shapes 721 and 722 is formed substantially on the side of the transport roll 8 with the rotation axis S as the center. Is a semicircle. When the radius of the semicircle is R ₂ , the relation between the diameters 2R _{1 of the} large diameter portions 711 and 712 of the shaft member 71 is R ₂ <R ₁ .
[0038]
FIG. 8 illustrates the operation of such a pair of transport rolls 7 and 8 (Note: Write an arrow indicating the transport direction of the recording sheet 18 in FIG. 8). As described above, since the surface of the conveying roll 7 that is in contact with the toner image I on the recording sheet 18 is constituted by the porous member 70, the wax in the toner 46 is melted immediately after fixing. Further, it is possible to maintain a good image quality without contaminating the portion of the image that is in contact with the transport roll 7. In particular, when the toner image I is full-color, when the toner image I is formed on substantially the entire surface of the recording sheet 18, and when the type of the recording sheet 18 is an OHP sheet, coated paper, or glossy paper, wax or the like is generally used. Therefore, it is preferable to apply the present invention. Further, since the wax does not affect the image quality, the degree of freedom in designing the toner and the wax is increased, and the effect of contributing to the stabilization of the image quality and the reduction in the manufacturing cost of the toner.
[0039]
Further, as shown in the figure, the porous member 70 of the conveying roll 7 is urged toward the other conveying roll 8 by the shaft support member 72 and is pressed against the recording sheet 18 and the other conveying roll 8 to be elastically deformed. To do. A hatched portion indicated by reference numeral 700 in FIG. 8 indicates elastic deformation of the porous member 70. Even when the porous member 70 is elastically deformed in this way, the size of the shaft support member 72 (721, 722) in the other transport roll 8 direction is the other transport roll 8 of the shaft center member 71 (711, 712). Since it is smaller than the size in the direction (R ₂ <R ₁ <R ₀ (inside): see FIGS. 5, 6, and 7), the metal shaft support members 72 (721, 722) are directly connected to the recording sheet 18 and others. The transport roll 8 is not contacted.
[0040]
In addition, although the material of the porous member 70 and the size of each part can be selected as appropriate, in this embodiment, the porous member 70 uses urethane sponge and the number of cells is 50 [pieces / 25 mm]. Yes, R ₂ = 2 [mm], R ₁ = 2.5 [mm], R ₀ (inside) = 2 [mm], R ₀ (outside) = 4 [mm], L ₀ = L ₁ = 13 [ mm].
[0041]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide an image forming apparatus capable of preventing image quality defects due to wax or the like contained in toner.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of an image forming apparatus to which the present invention can be applied.
FIG. 2 is a cross-sectional view around a pair of transport rolls according to an embodiment.
FIG. 3 is a perspective view of the periphery of a pair of conveyance rolls according to the embodiment.
FIG. 4 is a perspective view of a transport roll according to an embodiment.
FIG. 5 is a perspective view of a shaft member that constitutes the transport roll shown in FIG. 4;
FIG. 6 is a perspective view of a porous member constituting the transport roll shown in FIG.
7 is a perspective view of a shaft support member that constitutes the transport roll shown in FIG. 4; FIG.
FIG. 8 is a cross-sectional view showing a usage state of the pair of transport rolls according to the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 14 ... Fixing device (fixing means) 7, 8 ... Conveying roll, 70 ... Porous member, 71 ... Shaft center member, 711, 712 ... Large diameter part, 72 ... Shaft support member, 721, 722 ... Shaft support shape, S ... rotating shaft, I ... toner image, 18 ... recording sheet

Claims (6)

In an image forming apparatus comprising: a fixing unit that fixes an unfixed toner image on a recording sheet; and a pair of conveying rolls that sandwich and convey the recording sheet fixed by the fixing unit.
The conveying roll pair is the most upstream conveying roll pair with respect to the fixing unit, and the entire surface of the roll contacting the toner image fixed in the conveying roll pair is constituted by a porous member. .   The image forming apparatus according to claim 1, wherein the toner constituting the unfixed toner image contains wax.   The image forming apparatus according to claim 1, wherein the fixing unit does not supply a release agent to the recording sheet during fixing.   A plurality of the transport roll pairs are provided on the transport path from the fixing unit to the recording sheet discharge port, and the surface of the roll that comes into contact with the fixed toner image in the transport roll pair closest to the fixing unit is a porous member. The image forming apparatus according to claim 1, comprising:   The image forming apparatus according to claim 1, wherein the multi-material member has 8 to 100 cells / 25 mm.   The transport roll that contacts the fixed toner image includes a shaft member that constitutes a rotation shaft, a porous member that constitutes an outer layer of the shaft member, and a shaft support portion that rotatably supports the shaft member. The image forming apparatus according to claim 1, wherein a size of the shaft support member in the other transport roll direction is smaller than a size of the shaft member in the other transport roll direction.

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