JP2002221837A - Image forming apparatus equipped with device for cooling recording sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a cooling effect for a recording sheet. SOLUTION: The recording sheet 5 ejected from the fixing part 10 of the image forming apparatus is cooled so that its surface temperature may be lowered to the almost glass transition point temperature of transferred toner, and further it is cooled by the cooling part 20 of a heat pipe 3. To that end, after the recording sheet is ejected from the fixing part 10, it is carried a distance L>;v×t when it is assumed that the time taken until the surface temperature of the recording sheet attained just after fixing processing reaches the glass transition point temperature of the toner is (t) and the moving (carrying) speed of the recording sheet is (v).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus provided with a cooling device for a recording sheet thermally fixed in electrophotographic image formation.

[0002]

2. Description of the Related Art Conventionally, an electrophotography in which a recording sheet is sandwiched between a heating roller rotating with a built-in heater and a pressing roller pressing the heating roller to thermally fix a toner image transferred to the recording sheet. Thermal fixing devices for image forming apparatuses are well known. The recording sheet on which fixing is performed in this manner accumulates heat and is liable to curl. Further, when the recording sheet is stacked on the discharge tray as it is, the toner on the recording sheet becomes tacky due to heat accumulation between the recording sheets. Then, a so-called offset that is transferred to the back side of the next recording sheet may occur. This is particularly remarkable when high-speed printing is performed, or when the color printing is performed, and the thickness of the toner is increased by color superposition, and when the fixing temperature is increased to fix the entire image. Therefore, in order to prevent this, a cooling device is provided. FIG. 5 shows an example of this type of cooling device. Although the overall view is not shown, the cooling device configured in the image forming apparatus has a front frame 16 and a rear frame 17 fixed by means (not shown) between a front cover 21 and a rear cover 22. The transport roller 12 made of an elastic material is interposed between the front frame 16 and the rear frame 17.
And a cooling roller 13 composed of a heat pipe.
An auxiliary cover 24 is provided on the rear cover 22, and the cooling roller 13 passes through the rear cover 22 and reaches a gap 23 in the auxiliary cover 24. A radiating fin 14 is provided in a portion of the cooling roller 13 located in the gap 23, and a cooling fan 18 is installed so as to be opposed to the fin 14 so as to be surrounded by the auxiliary cover 23. Further, the auxiliary cover 23 is provided with an air supply hole 26 and an exhaust hole 27. The recording sheet (not shown) carried into such a cooling device is sandwiched between the transport roller 12 and the cooling roller 13, cooled by the cooling roller 13, and then discharged to a discharge tray (not shown).
At this time, the cooling roller 13 is supplied with air from the air supply hole 26 by the fin 14 attached to a part thereof and the cooling fan 18 for forcibly cooling the fin 14, and the cooling effect is enhanced by the external air exhausted from the exhaust hole 27. It has become. The recording sheet cooled in this manner was less likely to curl, and the rate of occurrence of offset was reduced.

[0003]

The printing speed of an image forming apparatus has been further increased, and there has been a demand for a further improvement in an environment in which an offset occurs in color printing as the printing speed is improved. However, the conventional cooling system is a system that supplies the heat-fixed recording sheet to the heat pipe without pre-cooling, and there is a limit to removing the heat absorbed by the heat pipe from the radiation fins by blowing. It was difficult to obtain a sufficient cooling effect to prevent offset, and the cooling function was not sufficient depending on the thickness of the sheet material used together with color printing. There was a problem that it was necessary to increase the size of the device.

The present invention has been made in view of the above circumstances, and focuses on the glass transition temperature of the toner fixed on a recording sheet, thereby lowering the temperature to approximately the glass transition temperature in advance, and then further cooling. Accordingly, it is possible to provide a recording sheet cooling device in an image forming apparatus in which a sufficient cooling effect can be obtained with a simple mechanism.

[0005]

According to a first aspect of the present invention, there is provided an image forming apparatus including a recording sheet cooling device for feeding a recording sheet discharged from a heat fixing unit to a cooling unit to cool the recording sheet. First cooling means for cooling the surface temperature of the recording sheet to substantially the glass transition temperature of the toner transferred to the recording sheet; and second cooling for further cooling the recording sheet cooled to the substantially glass transition temperature. And an image forming apparatus provided with a recording sheet cooling device.

According to a second aspect of the present invention, in the image forming apparatus provided with the recording sheet cooling device according to the first aspect, each of the first cooling means has a surface temperature of the recording sheet after the heat fixing of the toner. When the time to reach the glass transition point temperature is t, the moving speed of the recording sheet is v, and the distance from the position of the fixing unit to the cooling unit is L, the recording sheet is conveyed by a distance such that L> v × t, An image forming apparatus including a recording sheet cooling device, which is a cooling unit that performs natural cooling.

According to a third aspect of the present invention, in the image forming apparatus provided with the recording sheet cooling device according to the first aspect, the first cooling unit is a cooling unit that performs forced cooling while conveying the recording sheet. An image forming apparatus including a recording sheet cooling device.

According to a fourth aspect of the present invention, in the image forming apparatus having the recording sheet cooling device according to any one of the first to third aspects, the second cooling means is a contact type cooling means. An image forming apparatus provided with a cooling device for a recording sheet.

[0009]

Embodiments of the present invention will be described below. FIG. 1 is a diagram showing the relationship between the temperature and the viscosity of the toner. The horizontal axis represents the temperature, and the vertical axis represents the viscosity. The toner is
It is a solid at normal temperature and has a very high viscosity, but begins to soften when the temperature exceeds a certain temperature T1 (glass transition temperature) and liquefies when it reaches a certain temperature T2 (melting temperature). Usually, the temperature used for fixing the recording sheet is the temperature T
1 and below the temperature T2. In FIG.
Is the temperature between More specifically, generally, T
1 is about 60 to 70 ° C., and T2 is about 130 ° C. FIG.
Is a diagram showing the time required for the surface temperature immediately after the fixing process of the recording sheet to reach the glass transition point temperature of the toner in the case of natural cooling and forced cooling, in which the horizontal axis represents time, the vertical axis represents temperature, and The change of the time until the transition point temperature T1 is reached is shown depending on the presence or absence of the blowing means. Now, if it is attempted to lower the surface temperature of the recording sheet immediately after the fixing process to the glass transition temperature T1 of the toner, it takes t1 hours in a natural state without air blowing or the like. , Shorter t
Reach in 2 hours. Of course, in the case of blowing air, the curve in FIG. Accordingly, the present invention provides a cooling method in which the recording sheet is fed to a contact-type cooling device such as a heat pipe and cooled in a state in which the surface temperature of the recording sheet in a high temperature state is previously reduced to a temperature equal to or lower than the glass transition temperature of the toner by the fixing process. It is to make.

FIG. 3 is a diagram schematically showing a fixing unit and a cooling unit in an electrophotographic image forming apparatus according to an embodiment of the present invention. The heating unit is made of iron or aluminum with a built-in heater (not shown). A fixing unit 10 including a roller 1 and a pressure roller 2 formed of silicone rubber or the like.
Then, the recording sheet 5 to which the toner image has been transferred is carried in from the right side of the paper, and heat fixing is performed. The recording sheet 5 on which the heat fixing has been performed is first cooled to approximately the glass transition temperature in advance by natural cooling means. That is, the time when the surface temperature of the recording sheet 5 immediately after the thermal fixing reaches the glass transition point temperature of the toner is t1, the moving (conveying) speed of the recording sheet is v, and the fixing portion position (the heating roller 1 and the pressure roller 2 When the distance from the erosion position) to the cooling unit position (the erosion position between the cooling roller 3 and the transport roller 4) is L, the fixing unit 10 and the cooling unit 2
Between 0 and 0, a passing path having a distance L> v × t1 is formed.
The recording sheet 5 passing through this path is naturally cooled in the course of passing, and drops to substantially the glass transition temperature before reaching the entrance of the cooling unit 20. Next, the recording sheet 5 in such a temperature state is further forcibly cooled by the cooling unit 20 constituted by the heat pipe 3 rotating at substantially the same speed as the conveying speed v of the sheet. Therefore, the toner thermally fixed on the recording sheet 5 is sufficiently solidified.

The pressure roller 2 and the transport roller 4 in the embodiment of the present invention may be of a belt transport type instead of being transported by rollers.

FIG. 4 is a diagram schematically showing a fixing section and a cooling section in an electrophotographic image forming apparatus according to another embodiment of the present invention. Reference numeral 6 denotes a blower fan for blowing air to a recording sheet. is there. In the drawing, the same components as those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted. According to the above embodiment, the cooling of the recording sheet to the glass transition point temperature is performed by natural cooling in the process of passing through the transport path, so that the transport distance L may need to be increased. Therefore, in the present embodiment, a blower fan 6 that cools the surface of the recording sheet 5 in a non-contact manner is provided in the passage, and the cooling is forcibly performed. Due to this cooling, the time required for the surface temperature of the recording sheet after thermal fixing to reach the glass transition point temperature of the toner is represented by t2, and the moving (conveying) speed of the recording sheet is represented by v. If the distance from the contact point of the pressure roller 2) to the cooling unit position (the contact point of the cooling roller 3 and the transport roller 4) is L ′, then L ′>
v × t2 (where t2 <t1), and the distance of the passing path can be shortened as compared with the case where no forced cooling means is provided. The recording sheet 5 whose surface temperature has decreased to the glass point transfer temperature in this way is further cooled by the cooling unit 20.
The toner is cooled by forced cooling that comes into contact with the heat pipe, so that the toner is sufficiently solidified.

The pressure roller 2 and the transport roller 4 in the embodiment of the present invention may be of a belt transport type instead of being transported by rollers.

[0014]

According to the first aspect of the present invention, the surface temperature of the recording sheet discharged from the heat fixing section of the image forming apparatus of the image forming apparatus is lowered to the glass transition point temperature in advance, and then the next forcing is performed. Since cooling is performed by the cooling means, a sufficient cooling effect can be obtained without increasing the size of the cooling device.
Therefore, it is possible to prevent occurrence of an offset as in the related art. Effect corresponding to the second aspect of the present invention: Since natural cooling is used, cooling to the glass transition temperature can be performed without requiring special equipment. According to the third aspect of the present invention, since the recording sheet is forcibly cooled while being conveyed, the conveying distance can be shortened, the space of the image forming apparatus can be saved, and the image forming apparatus can be reduced in size. Helps According to the fourth aspect of the present invention, since the recording sheet that has been cooled in advance is forcibly cooled, the recording sheet can be sufficiently cooled.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between temperature and viscosity of toner.

FIG. 2 is a diagram illustrating a time required until a recording sheet surface temperature reaches a glass transition temperature of a toner.

FIG. 3 is a diagram schematically illustrating a fixing unit and a cooling unit in the electrophotographic image forming apparatus according to one embodiment of the present disclosure.

FIG. 4 is a diagram schematically illustrating a fixing unit and a cooling unit in an electrophotographic image forming apparatus according to another embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of a conventional cooling device.

[Explanation of symbols]

1. Heat roller, 2. Press roller, 3. Heat pipe,
4 ... conveying roller, 5 ... recording sheet, 6 ... conveying roller, 7
… Transport guide

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hideki Kosugi 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2H033 AA09 AA15 AA21 BA02 BA10 BA29 2H072 AB20 CA01 JA02 3F049 AA10 CA11 DA11 LA01 LB03

Claims (4)

[Claims] 1. An image forming apparatus comprising a recording sheet cooling device for feeding a recording sheet discharged from a heat fixing unit to a cooling unit to cool the recording sheet, and transferring a surface temperature of the recording sheet to the recording sheet. A first cooling means for cooling the toner to a temperature substantially equal to the glass transition point of the toner, and a second cooling means for further cooling the recording sheet cooled to the temperature substantially equal to the glass transition point. An image forming apparatus provided with a cooling device. 2. An image forming apparatus provided with a recording sheet cooling device according to claim 1, wherein said first cooling means comprises:
When the time required for the surface temperature of the recording sheet after thermal fixing to reach the glass transition temperature of the toner is t, the moving speed of the recording sheet is v, and the distance from the position of the fixing unit to the cooling unit is L, An image forming apparatus provided with a recording sheet cooling device, which is a cooling unit that conveys the recording sheet by a distance of> v × t and performs natural cooling. 3. An image forming apparatus provided with a recording sheet cooling device according to claim 1, wherein said first cooling unit is a cooling unit that performs forced cooling while conveying the recording sheet. An image forming apparatus including a recording sheet cooling device. 4. The recording sheet cooling apparatus according to claim 1, wherein said second cooling means is a forced cooling means. An image forming apparatus provided with a cooling device.