JPH0854797A - Fixing device for electrophotographic printer - Google Patents

Abstract

PURPOSE:To suppress the curling amount of paper occurring at the time of fixing operation within a certain extent, to deal with the change of factor to cause curling (moisture in paper, and temp., humidity as the atmospheric condition, and printing conditions), and to prevent a curling prevention roll and image from soiling. CONSTITUTION:The opposite side of paper surface dried by a fixing rear side heat roll 1 dried by the curling preventive heat roll 2 after the paper is cooled, thus extension and contraction of the both side can be equalized, therefore the paper curling amount occurring at the fixing time is suppressed within a certain amount. And, since the set temp. of the curling preventive heat roll 2 is changed while monitoring the curling amount, the change of the factor causing curling (moisture in paper, temp., humidity as the atmospheric conditions and printing condition can be respectively dealt with. Moreover, since the resident period from the fixing rear side heat roll 1 to the curling preventive heat roll 2 is taken into consideration, the toner is stuck and completely fixed on the paper, and thereafter brought into contact with the curling preventive heat roll 2, the soiling of either the curling preventive roll 2 or the image is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for an electrophotographic printing machine such as a copying machine, a printing machine or a printer plotter which uses a liquid developer.

[0002]

2. Description of the Related Art In an electrophotographic printer, a fixing device that heats and fixes toner on an adhering surface by a high-temperature flash lamp (for example, an infrared lamp), a fixing device that heats and fixes toner on an adhering surface by a heat roll, and a toner There is used a fixing device or the like that heats and fixes the adhesive surface with a heated film.

A conventional example of an electrophotographic printer using the above-mentioned fixing device will be described with reference to FIG. 6, in which 1 is a fixing back side heat roll, 4 is a nip roll, 5 is a cutter, 7 is paper, 8 is a paper supply roll, 9 is a drive roll, 10 is a paper feed roll, 11a is a blue printing roll, 11b is a red printing roll, 11c is a yellow printing roll, 11d is a black printing roll, and 12a to 12d are the above printing rolls 11a to 11d.
Is a nip roll, and 13 is a paper feed roll.

In the electrophotographic printer shown in FIG. 6, the paper 7 delivered from the paper supply roll 8 passes between the printing rolls 11a to 11d and the nip rolls 12a to 12d via the drive roll 9 and the paper feed roll 10. To do. Then, after passing between these printing rolls 11a to 11d and nip rolls 12a to 12d, the printing surface of the printed printing paper is fixed by the fixing back surface heat roll 1, and enters the paper discharge unit 16 via the cutter 5.

The applicant of the present application has proposed a liquid developer for double-sided heat roll fixing, which is applicable to the electrophotographic printing machine shown in FIG. 6, and a fixing device described in (2), namely, (1) high. In a liquid developer in which toner particles mainly composed of a colorant and a binder resin are dispersed in an insulating low dielectric constant hydrocarbon solvent, the fixing temperature T ₁ of the toner wet with the solvent is A liquid developer for double-sided fixing of hot rolls, which is lower than the heat remelting temperature T ₂ of the dried solid. (2) The paper surface temperature T _R in contact with the heat roll is T ₁ <T _R <
(Wherein, T _1: the toner fixing temperature, T _2: heating remelt temperature of the toner dry product) hot roll so as to T ₂ by controlling the heating value of the heating fixing from the back of the fixing surface in a heat roll A fixing device suitable for the liquid developer for double-sided fixing of hot rolls, wherein: Already proposed.

It is found in the patents of Japanese Patent Application Laid-Open No. 59-117167 and Japanese Patent Application No. 62-155964 that a reheating device is provided again from the direction opposite to the fixing device. However, there is no means for detecting curl, and the biggest difference is that there is no measure for the retention time, that is, the solidification time so that the toner once fixed does not remelt. In each case,
Since the reheating device is of a nip type, it is much better not to apply pressure from the viewpoint of toner peeling.

[0007]

The electrophotographic printing machine shown in FIG. 6 has the following problems. That is, if (a) the liquid developer for double-sided fixing of the heat roll of (1) and the fixing device of (2) are used, the toner can be sufficiently fixed on the adhering surface, but the paper after print fixing is In cutting into A4 size, there is a problem that the printing paper curls in the same direction as the curvature of the fixing back side heat roll 1. (B) The curled printing paper is difficult to bind and is unsuitable as a printing machine. (C) In order to prevent curling, as a result of testing by changing the set temperature of the fixing back side heat roll 1, the wrapping angle and the tension of the paper, the fixing and the curl are in a mutually contradictory relationship, and the fixing is easy. That is, the smaller the tape peelability and the smaller the solvent content in the paper, the larger the curl. On the contrary, under the condition that curl is almost suppressed,
The fixing was insufficient and the toner tended to peel off when rubbed by hand. (D) The degree of curl depends on the set temperature and printing conditions of the fixing back side heat roll 1 (how many colors are printed and the amount of solvent per unit area)
It is necessary to control the curl according to each condition.

The present invention has been proposed in view of the above problems, and its object is to suppress the curl amount of paper generated during a fixing operation within a certain range. Moisture, atmospheric conditions such as temperature and humidity
It is an object of the present invention to provide a fixing device for an electrophotographic printing machine, which can cope with changes in printing conditions) and can prevent curl prevention and image contamination.

[0009]

In order to achieve the above object, a fixing device for an electrophotographic printing machine of the present invention comprises a fixing back side heat roll for heating the printing paper after transfer from the back side,
A curl-preventing heat roll which is arranged on the downstream side of the heat roll and has a heating means provided inside to wind and convey the printing paper in the opposite direction to the back heat roll, and the back heat roll and the curl prevention. And a cooling section or a cooling means for the printing paper provided between the heat roll and the heat roll.

In the fixing device of the electrophotographic printing machine,
The curl amount is detected by detecting the curl of the printing paper, and the curl amount is compared with the reference curl amount. Based on the result, the temperature of the curl prevention heat roll is calculated and the temperature of the roll is controlled. And a temperature control means for controlling the temperature.

[0011]

The fixing device of the electrophotographic printer according to the present invention is constructed as described above, and has the following functions. The reason why the curl occurs is that the bimetal, which is formed by laminating two kinds of metals having different expansion coefficients as shown in FIG. 2, is warped when heated or cooled. Paper is similar, and if one side is moistened or one side is dried, curling occurs. Therefore, in the present invention, the opposite side of the paper surface dried by the fixing back side heat roll is dried by the curl prevention heat roll to make the expansion and contraction of both sides to the same level. However, if the set temperature of the curl prevention heat roll is kept too high, curl occurs in the opposite direction to the curl generated by the first fixing back heat roll. The curl is affected by moisture in the paper, atmospheric conditions, printing conditions, and the like. Therefore, it is necessary to detect the curl situation with a sensor and determine the curl prevention heat roll temperature. In addition, FIG. 3 shows the peeling of the toner surface when the residence time between the fixing back side heat roll and the curl prevention heat roll is used as a parameter in terms of print density (measured by an optical densitometer). Three
Indicates that the lower the print density, the greater the amount of toner peeled off by the curl prevention heat roll. The residence time is 2 seconds or longer, preferably 3.5 seconds or longer, and the best is 4 seconds or longer. The above description is based on the dwell time as a means for cooling the paper surface after fixing until the curl prevention heat roll, but in consideration of the compactness of the device, cooling stability, etc., the fixing back heat roll and curl prevention A cooling section is provided between the heat roll and the heat roll. Further, the same effect can be obtained by installing cold air blowing means or a roll having a cooling means inside thereof.

[0012]

EXAMPLES Next, a fixing device for an electrophotographic printing machine according to the present invention will be described with reference to one example shown in FIGS. 1 to 5. 1 in FIG. 1 is a fixing back side heat roll, 2 is a curl preventing heat roll, and FIG. 3a and 3b are paper feed rolls, 4 is a nip roll, 5 is a cutter, 6 is a laser type displacement sensor, 7 is paper,
Reference numeral 14 is a paper discharge unit, 15 is a thermocouple, and 16 is a temperature control device (temperature control means: computer). (1) In order to correct the curl, it is necessary to evaporate the water from both the front and back sides of the paper 7, and the curl prevention heat roll 2 is used to evaporate the water on the front surface of the paper after the fixing back heat roll 1. It is installed. (2) The degree of curl depends on printing conditions. This is because there is a difference in the evaporation amount of the solvent by the fixing back surface heat roll 1, and the evaporation amount of the moisture on the back surface side is also affected. It was found that the degree of this curl changes if the temperature of the curl prevention heat roll 2 is controlled. Therefore, the state of curl is detected by the laser displacement sensor 6, and the temperature of the curl prevention heat roll 2 is controlled. (3) If the curl prevention heat roll 2 is provided immediately after the fixing back surface heat roll 1, the fixed toner tends to peel off, and it is necessary to set a certain residence time after fixing and before fixing. For that purpose, a roll extension system and a web cooling means are provided. (4) The following toner was used. Aliphatic hydrocarbon Isobar G (Exxon): 216 parts, aromatic hydrocarbon toluene (Katayama Chemical): 144 parts, aliphatic alcohol ethanol (in a container equipped with a stirrer, a thermometer, a reflux condenser, and a vacuum degassing device. (Katayama Chemical): 90 parts, modified ethylene / vinyl acetate copolymer Dumilan C-2280 (Takeda): 6 parts, colorant Brilliant Carmine 6B (Dainichi Seika): 1.2 parts and 60 at 70 ° C. After stirring for a minute to completely dissolve the dumilan, while maintaining the temperature of the liquid at 40 ° C. (at this time, the dumilan was in a dissolved state), the container was vacuum degassed to remove toluene and ethanol from the solvent. A red toner particle dispersion liquid having a volume-based 50% particle diameter of 1.95 μm was obtained.

The mixed solvent of this toner particle dispersion was replaced with Isobar G, and a conventional additive such as a charge control agent was added to prepare a liquid developer for electrophotography (solid content: 2%). The fixing temperature of this toner in a solvent wet state was 80 ° C., and the dry solid heat-melting temperature was 130 ° C. Next, the operating state of the fixing device of the electrophotographic printing machine shown in FIG. 1 will be described.

(Operation state 1) Web speed 100 mm /
sec, a high-quality paper 7 having a paper width of 1 m and a thickness of 80 μ was used, and the average amount of adhering solvent was 6.324 kg / Hr and the amount of adhering toner was 0.812 kg / Hr. Further, as the fixing backside heat roll 1, a roll having a diameter of 40 mmφ and a surface of fluorine was used.

Paper inlet temperature is 25 ° C., tension is 2 kg
When f / m, the temperature of the fixing back side heat roll 1 is set to 22.
It was set to 5 ° C. Then, the paper passes through the cutter 5 and the paper output unit 1
The end portion and the central portion of the paper 7 which reached 4 were measured by the laser displacement type sensor 6 (when the curl amount was measured), and h = 5 mm. Therefore, when the set temperature of the curl prevention heat roll 2 was set to 110 ° C., the curl amount became 0.5 mm or less, and there was no problem in practical use.

The curl prevention heat roll 2 is made of the same material as the fixing back heat roll 1 and has the same size. In addition, the residence time of the paper passing through the fixing back side heat roll 1, the nip roll 4 and the feed roll 3a to the curl prevention heat roll 2 was set to 4.5 seconds. (Operating state 2) When the tension was set to 5 kgf / m and the curl amount of the paper 7 which reached the paper discharge section 14 through the cutter 5 was measured, it was about 9 mm. Therefore, when the set temperature of the curl prevention heat roll 2 was set to 125 ° C., the curl amount became 0.5 mm or less.

The temperature control device (computer) shown in FIG.
16 captures the values of the two laser displacement type sensors 6,
The set temperature of the curl prevention heat roll 2 is changed. At the same time, the thermocouple 15 is used for the curl prevention heat roll
The surface temperature is monitored and input to the temperature controller 16. FIG. 4 is a block diagram of the temperature control device 16.

The sensor unit measures the values of h _An and h _Bn , and the curl amount calculation unit calculates the curl amount. The absolute value of the curl amount is compared with one curl amount reference by the curl amount comparison unit to determine whether or not the temperature of the heat roll is controlled. When n = 1 and 2, Δ from the reference data storage unit
The standard data of h and T is called, the temperature calculation for correcting the temperature of the heat roll is performed, and the temperature control of the heat roll is performed. The curl amount and the temperature of the heat roll at this time are stored in the storage unit.

When n ≧ 3, the previous value (for example, n = 2) and the previous previous value (for example, n =) of the curl amount and the heat roll temperature are set.
1) is called from the storage unit, the corrected temperature of the heat roll is calculated, and the temperature of the heat roll is controlled. The curl amount and the temperature of the heat roll at this time are also stored in the storage unit.
FIG. 5 shows the control flow of the temperature control device 16 in more detail. It takes in sensor inputs h _{A, n} and h _{B, n} . n indicates that it is the n-th data. The curl amount is calculated _{. If} the absolute value of Δh _n = h _{B, n} −h _{A, n} is 0.5 mm or more, the temperature of the curl prevention heat roll 2 is changed. ,It does not change.

In the case of n = 1 and the second time, the temperature of the curl prevention roll 2 is adjusted using a predetermined curl amount oh and a reference curve of the surface temperature of the curl prevention roll 2. On the other hand, when n ≧ 3, correction is performed using the following equation.

[0021]

[Equation 1]

Here, the symbols are as follows. T _n : curl prevention heat roll temperature to be corrected this time T _n-1 : previous curl prevention heat roll temperature T _n-2 : previous curl prevention heat roll temperature Δh _n-1 : previous curl amount Δh _{n- 2} : Curling amount before last M: Weighting factor (usually 0.5)

[0023]

As described above, the fixing device of the electrophotographic printing machine of the present invention has the opposite side of the paper surface dried by the fixing back side heat roll as described above, and after the paper is cooled, it is dried by the curl preventing heat roll to form a double-sided sheet. Since the expansion and contraction of
The amount of curl of the paper generated during the fixing operation can be suppressed within a certain range.

Since the set temperature of the curl preventing heat roll can be changed while monitoring the curl amount, factors causing curl (water content in paper, temperature / humidity
It can respond to changes in printing conditions. In addition, the dwell time from the fixing back heat roll to the curl prevention heat roll is taken into consideration.Because the toner adheres to the paper and is completely fixed, it contacts the curl prevention heat roll. And image contamination can be prevented.

[Brief description of drawings]

FIG. 1 is a side view showing an embodiment of a fixing device of an electrophotographic printing machine according to the present invention.

FIG. 2 is an explanatory diagram showing a mechanism of occurrence of a curl phenomenon.

FIG. 3 is an explanatory diagram showing a relationship between a dwell time and a residence time from a back side heat roll to a curl prevention heat roll.

FIG. 4 is a control block diagram of a temperature control unit of the fixing device.

FIG. 5 is a control flow chart of a temperature control unit of the fixing device.

FIG. 6 is a side view showing a conventional electrophotographic printing machine.

[Explanation of symbols]

 1 Backside heat roll for fixing 2 Curling prevention heat roll 3a, b Paper feed roll 4 Nip roll 5 Cutter 6 Laser displacement sensor 7 Paper 8 Supply roll 9 Drive roll 10 Paper feed roll 11a-d Printing roll 12a-d Nip roll 13 Sending Paper roll 14 Paper discharge section 15 Thermocouple 16 Temperature control means (computer)

Claims (2)

[Claims] 1. A fixing back side heat roll that heats the transferred printing paper from the back side, and a heating means provided inside the fixing back side heat roll to provide the printing paper to the back side heat roll. An electronic device comprising a curl prevention heat roll wound in the opposite direction and conveyed, and a cooling section or a cooling means for the printing paper provided between the back heat roll and the curl prevention heat roll. Fixing device for photo printer. 2. A curling amount is detected by detecting the curl of the printing paper, and the curl amount is compared with a reference curl amount, and the temperature of the curl prevention heat roll is calculated based on the result. The fixing device for an electrophotographic printing machine according to claim 1, further comprising temperature control means for controlling the temperature of the roll.