JP2003081505A - Sheet feeder and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet feeder and an image forming device that prevent attachment of a waterdrop to a sheet without arranging a special member. SOLUTION: In the sheet feeder for feeding the sheet 108 heated, an ejection guide 110 brought into a contact with the heated sheet thus fed comprises a member with a contact angle θ with water of θ<90 deg.. The used member offers thermal conductivity of the ejection guide of λ<=0.4 [W/mk] to prevent heat transmitted from a heat source and heat from air and the sheet both it receives from escaping to another member and retard attachment of a waterdrop to an ejection member surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet conveying apparatus for conveying a heated sheet and an image forming apparatus using the electrophotographic system such as a facsimile, a printer, a copying machine and the like equipped with the sheet conveying apparatus.

[0002]

2. Description of the Related Art Conventionally, exposure means for exposing a photosensitive drum to form a latent image, developing means for scattering or contacting the latent image with toner to develop the latent image, and developing means for developing the latent image on the photosensitive drum. An image forming apparatus that forms an image using a transfer unit that transfers the formed toner image onto a sheet and a fixing unit that conveys the toner image on the sheet under pressure while conveying the toner image is generally known. There is.

In a fixing device of an image forming apparatus, when a sheet as a recording material is made of a material containing water such as paper,
Moisture in the sheet evaporates due to heating when fixing,
Condensation on the sheet transport path from the fixing device to the discharge port,
There is a possibility that the discharged paper or the sheet guided to the double-sided conveyance path for forming an image on both sides adheres to the sheet and wets the sheet or disturbs the image.

Therefore, conventionally, in order to solve the above problems, measures have been taken such that moisture is released by a fan and heat is intentionally applied to the discharge guide. For example, in Japanese Unexamined Patent Publication No. 7-261585, the discharge guide is made of sheet metal, and a guide cover for covering it with mylar or the like is provided.

[0005]

However, in the above method, the discharge guide is provided with a special device or a fan is attached to the image forming apparatus to reduce the size, cost, and design flexibility. It was difficult to be compatible with.

In the above-mentioned Japanese Patent Laid-Open No. 7-261585, since the metal plate is used for the discharge guide, it is necessary to purposely cover it with the covering means, and the number of parts increases. Furthermore, even if a discharge guide cover with low thermal conductivity such as mylar or plastic molded products is used, there are many that have lower thermal conductivity than metal, and even if the thermal conductivity is low, the discharge guide cover has a low thermal conductivity. If the cover itself is cold, water droplets will not adhere to it. Actually, the trace of water droplets becomes a problem until the entire fixing device including the discharge guide is heated, so that it is not enough to cover the metal plate with mylar or the like.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a sheet conveying apparatus and an image forming apparatus which do not attach water drops to a sheet without providing a special member.

[0008]

A typical structure according to the present invention for achieving the above object is a contact member for contacting a heated and conveyed sheet in a sheet conveying apparatus for conveying a heated sheet. The contact angle θ with water is θ <90
It is characterized in that it is composed of a member having a degree of °.

In the above structure, the water droplets attached to the contact member do not move to the sheet.

The contact member has a thermal conductivity of λ.
If a member with ≤ 0.4 [W / mk] is used, it will not escape to other members when heat from heat source, heat from air or sheet is received, and water droplets will adhere to the surface of contact member. Can be difficult. Further, since the surface tension of water drops tends to decrease with temperature, the wettability of the contact member improves as the contact member warms.

Further, the surface roughness (JIS,
By setting Ra) to 5 μm or more, the contact angle with water can be made smaller, and the water droplets will adhere more strongly to the contact member. However, since the contact member comes into contact with the sheet, if it is too rough, it affects transportability and rubbing.

[0012]

DETAILED DESCRIPTION OF THE INVENTION An image forming apparatus using a sheet conveying apparatus according to an embodiment of the present invention will be described with reference to the drawings.

[First Embodiment] An image forming apparatus according to the present embodiment transfers a toner image onto a sheet by an electrophotographic method, heats and fixes the toner image by a fixing device, and discharges the toner image.

(Image Forming Apparatus) First, the overall structure of the image forming apparatus will be described with reference to FIG. 1. FIG. 1 is an overall schematic explanatory view of the image forming apparatus.

The image forming apparatus of this embodiment is a yellow,
This is a laser beam printer capable of forming a full-color image by using developing means using four color toners of cyan, magenta, and black.

Reference numeral 11 denotes the exterior of the printer. Reference numerals 1 and 2 denote sheet feeding units for feeding sheets, 1 denotes a multi-tray, and 2 denotes a cassette tray. 3 is a photosensitive drum 6 according to an image signal
The latent image is formed on the photoconductive drum 6 by the exposure unit, and the yellow developing device 4a, the magenta developing device 4b, the cyan developing device 4c, and the black developing device 4d of the developing unit 4 form a latent image on the photoconductive drum 6. A toner image is formed on. The toner image on the photosensitive drum 6 is transferred to the intermediate transfer body unit 7 and further transferred to the conveyed sheet by the secondary transfer body 8 (hereinafter, the transfer position of the secondary transfer body 8 onto the sheet). Is referred to as the "transfer part").

The unfixed image on the sheet passing through the transfer section is
The sheet is heated and pressed by the film heating type fixing device 5 to be fixed. The sheet that has passed through the fixing device 5 is conveyed to the face-up discharge unit 13 or the face-down discharge unit 12, or the traveling direction is reversed by the switchback mechanism 9, passes through the automatic double-sided conveyance path 10, and is transferred to both sides. The image is formed.

FIG. 2 is a schematic cross-sectional explanatory view showing a cross-sectional view of the fixing device 5, in which the toner image 109 on the sheet 108 has a ceramic (AlN, Al2O2, etc.) heater substrate 106 and a heating element 107.
While the heat from the heater consisting of is applied through the film 101, it is being conveyed while being pressed by the pressure roller 105. Here, 102 is a film guide that is made of a resin such as liquid crystal polymer (LCP) and guides the film 101, and inside thereof is a T stay 104 made of metal that transmits a pressing force to the film guide. The temperature is controlled by the chip thermistor 103 bonded on the heater substrate 106.
The voltage detected in step 1 is converted into a temperature by a temperature control means (not shown), and the PID control or the like controls energization of the heating element 107 to control the heater to a desired temperature.

(Sheet Conveying Device) Next, a sheet conveying structure for discharging the sheet on which the toner image is heated and fixed by the fixing device 5 will be described.

The toner image transferred onto the sheet 108 is heated and fixed by the fixing device 5 and is discharged. At this time, the discharge guide 110 as a sheet guide for guiding the sheet 108 to the downstream side of the fixing device 5 in the sheet conveying direction and the sheet are conveyed so that the sheet 108 after the toner image fixing is smoothly removed from the fixing nip portion. A discharge roller 113 serving as a conveyance rotating member and a discharge roller 114 that presses a sheet against the roller 113 are provided. The discharge guide 110 is shown in FIG.
2 is a schematic view of the discharge roller 113 when viewed obliquely from above.

The sheet 108 having passed through the fixing nip portion comes into contact with the discharge guide 110 as a contact member at its leading end, but when it is nipped by the fixing nip portion and both the discharge roller 113 and the discharge roller 114, the discharge guide 110. Float from. At this time, when the sheet 108 contains water like paper, it is heated in the nip portion to evaporate the water, and the water vapor becomes water droplets 112 and easily adheres to the discharge guide 110.

When the trailing edge of the sheet 108 passes through the fixing nip and is sandwiched between the discharging roller 113 and the discharging roller 114, the strength of the sheet 108, the curling direction, the conveying direction, etc. The sheet 108 comes into contact with the discharge guide 110 again due to the above factor. At this time, the water droplet 112 adheres to the rear end of the sheet 108.

FIG. 4 is a table showing the relationship between the contact angle and the amount of water droplets deposited on the sheet, which was examined when an image was actually formed. As shown in these results, image disturbance started to appear from the contact angle of 90 °, and good images were obtained when the contact angle was smaller than that.

Here, the "contact angle" means the angle θ of the boundary portion where the discharge guide 110 and the water droplet 112 contact each other, as shown in FIG. In this embodiment, CA-X manufactured by Kyowa Interface Science Co., Ltd. was used for measuring the contact angle. In addition, since it is difficult to directly measure the amount of water droplets attached to the sheet, it was evaluated as image disturbance.

As for the degree of image disturbance, a solid black image is formed on both sides of the entire paper having a moisture content of 7 to 8%, and the face-down discharge section
Eject from 12. When discharged from the face-down discharge unit 12, as shown in FIG. 1, since the sheet 108 passes through the discharge guide 110 and is bent immediately, the rear end of the sheet 108 is easily rubbed against the discharge guide 110. That is, in the case of double-sided recording, water drops adhere to the solid black image on the first side. Immediately after being discharged, the part where the water drops adhere is rubbed with a rough sheet to compare the difference with other parts. did.

In FIG. 4, "○" indicating the degree of "image disturbance" indicates a state in which there is no image disturbance, "△" indicates a state in which the image is slightly disturbed, and "x" indicates image disturbance. Is clear, and the larger the number of “x”, the larger the image disturbance.

The discharge guide 110 is provided by a facsimile, a printer, a printer, or the like in order to make the contact angle with the water droplet 112 various angles.
Liquid crystalline polymer (LCP), polyamide (PA), polybutylene terephthalate (PBT), polycarbonate (PC), acrylonitrile butadiene styrene (ABS), polyethylene (PE), which are standard resins used in copying machines. Polyethylene terephthalate (PE
T), polymethylmethacrylate (PMMA), polyoxymethylene (POM), polypropylene (PP), modified polyphenylene ether, polyphenylene sulfide (PPS), polystyrene (PS), polysulfone (PSU), etc. A surfactant, a silicon film, or a fluorine film was mixed or coated before use.

Generally, the adhesion force of a liquid to a solid surface is Wa.
= γL (1 + Cosθ) This is Young's formula γ
S = γSL + γLCosθ is expressed by Dupre's formula Wa = γS + γL−
It is obtained by substituting for γSL. θ is the contact angle (0 to 180
°), γSL is the interfacial tension, γL is the surface tension of the liquid, γS
Is the surface tension of the liquid.

The adhesive force corresponds to the work of separating the liquid from the member. That is, if the value of Cos θ is increased, the wettability is improved and the water droplets are more easily held by the discharge guide 110. As shown in FIG. 4, water droplets 1 on the discharge guide 110
12 adheres to the sheet 108 when the contact angle is smaller than 90 °. This indicates that if the adhesion force of the water droplets to the discharge guide 110 is smaller than the contact angle of 90 °, the amount of adhesion to the sheet 108 will be small. FIG. 6 shows a state in which the water droplet 112 is hard to adhere to the sheet 108 because the contact angle is smaller than 90 °. On the other hand, FIG. 7 shows a state in which the discharge guide 110 has a contact angle of 90 ° or more, so that the water droplets 112 attached to the discharge guide 110 are easily transferred to the sheet 108.

As described above, if the discharge guide 110 having a contact angle with the water droplet 112 smaller than 90 ° is used, even if the water vapor generated from the sheet 108 containing water becomes a water droplet on the discharge guide 110, It becomes difficult to adhere to the conveyed sheet 108, and a good image can be obtained.

[Second Embodiment] In the above-described first embodiment, when the contact angle with water is smaller than 90 °, the discharge guide 11
Although it has been shown that the water droplets 112 adhered to the upper part of the sheet hardly move to the sheet 108, in the present embodiment, the surface roughness of the discharge guide is increased so that the water droplets adhered to the discharge guide do not move to the sheet. Here is an example. The discharge guide of this embodiment has the same shape as the discharge guide 110 of the first embodiment. As the surface roughness in this embodiment, the arithmetic average surface roughness Ra, which is a method defined by JIS, is used as a number indicating the surface roughness.

FIG. 8 shows a discharge guide as an example of the discharge guide.
This is a list of the results of examining the degree of image disorder and transportability by actually using a member made of resin as the main material for 110 and changing the surface roughness to actually pass the paper. The surface roughness R
a is the arithmetic average surface roughness determined by JIS standard (B0601-1994).

The degree of image disturbance was examined in the same manner as in the first embodiment. The contact angle between the discharge guide 110 and the water drop used in this experiment is 88 °. Ejection guide in the first embodiment
It has been shown that if the contact angle of the water droplet with respect to 110 is smaller than 90 °, the adhesion of the water droplet to the sheet 108 can be suppressed.
It was not perfect near 0 °.

On the other hand, in this embodiment, since the discharge guide 110 having a contact angle with water of 88 ° is used, the image disturbance is within an allowable range, but it does not completely disappear. . However, even if such a discharge guide 110 is used, as shown in FIG. 8, when the surface roughness of the discharge guide 110 is increased, the image is not disturbed and a good image can be obtained. This is because the surface of the discharge guide 110 is roughened, so that the contact angle with the water droplet is reduced.

Actually, the discharge guide 11 having a surface roughness of about 5 μm
When the contact angle with respect to a water droplet of 0 was measured, it was 79 °. On the other hand, the transportability was evaluated by observing the degree of bending of the leading edge of the sheet that has entered the discharge guide 110 through the fixing nip portion.

In FIG. 8, “◯” indicating the degree of “transportability” indicates a state in which there is no problem in transportability, “Δ” indicates a state of being slightly caught by the discharge guide 110, and “x” indicates the discharge guide. The state is clearly caught by 110 and it is difficult to enter the discharge guide 110. That is, when the surface roughness of the discharge guide 110 is larger than 300 μm, the transportability becomes unacceptable, which is incompatible with the effect of reducing the contact angle. Therefore, the surface roughness Ra is preferably limited to 5 μm ≦ Ra ≦ 300 μm.

As described above, according to the present embodiment, the apparent contact angle can be reduced by increasing the surface roughness of the discharge guide 110, and the effect of preventing water droplets from adhering to the sheet can be obtained. Can be increased.

[Third Embodiment] Next, a third embodiment will be described. The reason why water drops adhere to the discharge guide 110 is
This is because the water is evaporated from the sheet heated by the fixing device 5 and condensed on a member having a relatively low temperature. In general, dew condensation occurs on the downstream side of the fixing device 5 in the sheet conveyance direction, and when the temperature of the discharge guide 110 rises as the sheet is conveyed, eventually, almost no water droplets are condensed regardless of the material. In the present embodiment, in consideration of this, the thermal conductivity λ
An example in which a resin having a low viscosity is used for the discharge guide 110 will be described.
The shape of the discharge guide of this embodiment is the same as that of the first embodiment.

FIG. 9 shows a discharge guide made of materials having different thermal conductivities.
It is a table showing the thermal conductivity of 110, the highest temperature reached when an image is actually formed, and the degree of image disturbance.

The temperature was measured where the thermocouple was in direct contact with the sheet of discharge guide 110. The surface roughness (JIS, Ra) of the discharge guide 110 was unified to Ra = 1 μm. Further, as the material of the discharge guide 110, a resin material having a uniform contact angle with water droplets of about 88 ° was used.

When a resin having a low thermal conductivity is used, heat obtained indirectly by the heating means of the fixing device 5, the sheet, and the air is stored, and the temperature easily rises. When the temperature rises, the water droplets easily evaporate and the surface tension of the water droplets decreases, so that it becomes difficult for the water droplets to move from the surface of the discharge guide 110 to the sheet.

For example, the surface tension of water at 60 ° C. is 66.17 [mN
/ m], but 69.55 [mN / m] at 40 ° C. The smaller the surface tension of the water droplets, the smaller the contact angle between the discharge guide 110 and the water droplets. Further, the temperature of the discharge guide 110 quickly rises, which is effective in preventing condensation of water droplets in the first place.

As shown in FIG. 9, the lower the heat conductivity, the higher the temperature reached by the discharge guide, and the image disturbance is good until the heat conductivity λ is about λ = 0.4 [W / mk]. there were. Then, as the thermal conductivity λ increases, the heat on the surface of the discharge guide 110 is likely to be dissipated, and the water vapor is likely to be condensed. Therefore, the thermal conductivity λ = 0.4 [W / mk] is the limit.

As described above, according to this embodiment,
By using a member having a low thermal conductivity for the discharge guide 110, the temperature of the discharge guide surface easily rises, water droplets are prevented from adhering, and the attached water droplets are quickly evaporated and moved to the sheet. Can be difficult.

For example, even with the same polyethylene (PE),
High-density polyethylene and low-density polyethylene have different thermal conductivities. The higher the density of the polymer resin is, the higher the thermal conductivity becomes. On the contrary, the heat insulating property is remarkably improved by adopting a foam structure. As the discharge guide 110, a resin having a high heat insulating property is desired as much as possible. Therefore, if there is no problem with heat resistance, releasability, strength, expansion coefficient, life, etc., it is preferable to select one having a low thermal conductivity.

[Other Embodiments] In each of the above-described embodiments, the discharge guide 110 has been described. However, for the sake of design, when only the discharge roller 113 is provided without the discharge guide 110, the discharge roller 113 is not provided. A problem is that water droplets attached to the shaft 115 attach to the sheet 108. In this case as well, the shaft of the discharge roller 113, which is a contact member that comes into contact with the sheet, has a contact angle of 90 ° with respect to water droplets or a surface roughness
S, Ra) is 5 μm ≦ Ra ≦ 300 μm, and the thermal conductivity is 0.4
The member set to [W / mk] may be used.

Although not mentioned in the above embodiment, the process of manufacturing the discharge guide 110 using the resin material includes the step of wiping off the mold release agent such as silicone having a relatively low surface tension. It is preferable that the effects of the present invention can be sufficiently exerted.

The discharge guide 110 and the discharge roller 113 are also provided.
However, the same effect can be obtained by configuring the contact member, which is a member to which water vapor from the heated sheet is attached and which is in contact with the conveyed sheet, as described above.

[0049]

As described above, according to the present invention,
Without providing a special device, it is possible to retain the water droplets attached to the member that comes into contact with the heated sheet and prevent it from moving to the sheet.

Further, the contact member is made of a material having a predetermined thermal conductivity to promote re-evaporation of water droplets adhering to the member, so that a good image can be obtained even in a low temperature environment where dew condensation easily occurs. Can be formed

[Brief description of drawings]

FIG. 1 is an overall cross-sectional schematic view of an image forming apparatus having a discharge guide according to a first embodiment.

FIG. 2 is a schematic cross-sectional view of a fixing device and a discharge guide according to the first embodiment.

FIG. 3 is a schematic perspective view of a discharge guide.

FIG. 4 is a table showing experimental results of the first embodiment.

FIG. 5 is a schematic diagram showing a contact angle.

FIG. 6 is a schematic diagram showing an example in which water droplets are difficult to attach to a sheet.

FIG. 7 is a schematic diagram showing an example in which water droplets easily attach to a sheet.

FIG. 8 is a table showing experimental results in the second embodiment.

FIG. 9 is a table showing experimental results in the third embodiment.

[Explanation of symbols]

1 ... Multi-tray 2 ... Cassette tray 3 ... Exposure unit 4 ... Development unit 4a ... Yellow developing device 4b ... Magenta developing device 4c ... Cyan developing device 4d ... Black developing device 5 ... Fixing device 6 ... Photosensitive drum 7 ... Intermediate transfer unit 8 ... Secondary transfer body 9… Switchback mechanism 10… Automatic double-sided transport path 11… Exterior 12… Face-down discharge part 13… Face-up discharge part 101… Film 102… Film guide 103… Chip thermistor 104… Stay 105… Pressure roller 106… Heater substrate 107… Heating element 108… Sheet 109 Toner image 110… Ejection guide 112 ... water drops 113… Ejection roller 114… Ejection roller 115… Axis

Claims (6)

[Claims] 1. A sheet conveying device for conveying a heated sheet, wherein a contact member for contacting the heated and conveyed sheet is constituted by a member having a contact angle θ with water of θ <90 °. Characteristic sheet conveying device. 2. The contact member has a thermal conductivity λ of λ ≦ 0.4.
It is configured by a member having [W / mk].
The sheet conveying device described. 3. The sheet conveying apparatus according to claim 1, wherein the contact member is a conveying rotating body that conveys a sheet. 4. The sheet conveying apparatus according to claim 1, wherein the contact member is a sheet guide that guides a conveyed sheet. 5. The sheet guide has a surface roughness (JIS,
5. The sheet conveying apparatus according to claim 4, wherein Ra) is 5 μm ≦ Ra ≦ 300 μm. 6. An image forming apparatus for heating and fixing a sheet on which an image has been formed and discharging the sheet, wherein the sheet conveying apparatus for discharging the sheet on which the heat and fixing have been performed is described in any one of claims 1 to 5. An image forming apparatus using the sheet conveying device.