JPH03267975A - Fixing device - Google Patents

Abstract

PURPOSE:To prevent a wrinkle from occurring when toner is fixed to a transfer paper which is composed of two restricted papers by lowering the fixing pressure of a nipping part between two pressurizing rollers and a fixing roller and increasing a nipping time which is enough for obtaining a specified fixing rate. CONSTITUTION:The pressurizing roller is composed of the two pressurizing rollers 2a and 2b. The pressurizing rollers 2a and 2b and the fixing roller 1 lower the fixing pressure of the nipping part formed for the transfer paper 6 which passes through these rollers to such an extent that the wrinkle is not caused, and also the nipping time is increased to obtain the specified fixing rate. Thus, the plural pressurizing rollers 2a and 2b are respectively pressurized to the fixing roller 1 by the low fixing pressure, that means, by pressure by which the wrinkle is not caused on the transfer paper 6 like an envelope and the fixing rate is raised.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a fixing device for an image forming apparatus such as a copying machine, a printer, or a facsimile machine.

2. Description of the Related Art A fixing device that has a fixing roller having a heating device inside and a pressure roller that is pressed against the fixing roller and drives the fixing roller and the pressure roller by the fixing roller is used in a copying machine. It has been conventionally used in image forming apparatuses such as the following.

In general, to improve fixing performance, fixing temperature, fixing pressure,
It is desirable to increase both nip times. On the other hand, there is a problem in that wrinkles occur on the transfer paper during fixing, and in order to prevent wrinkles from occurring, it is desirable to reduce the fixing temperature, fixing pressure, and nip time. Therefore, there are mutually contradictory properties regarding fixing properties and wrinkle prevention.

With normal transfer paper that is cut one by one, the paper will become distorted and wrinkled if the paper does not enter the nip between the fixing roller and the pressure roller evenly due to curling or waving at the leading edge of the paper. . This wrinkle is a problem in mechanical conveyance of paper and can be prevented by controlling the position of the tip of the fixing entrance guide plate, but wrinkles may occur depending on the characteristics of the transfer paper. For example, due to the fixing temperature, the water content in the paper evaporates and the paper contracts, causing distortion and wrinkles. This wrinkling also depends on the fiber direction of the paper.

Recently, envelopes have been used more frequently in the field of image forming apparatuses, especially printers.

- In contrast to the above-mentioned wrinkles in cut paper that is cut into individual sheets, transfer paper that has at least a double layer structure, such as an envelope, has two sheets stacked on top of each other and is regulated by gluing, folding, etc. Wrinkles may occur under different conditions.

(+) In the case of transfer paper such as an envelope, two sheets of paper enter the nip between the fixing roller and the pressure roller, and the paper in contact with the fixing roller is driven by the fixing roller. transported by. At this time, if the fixing roller is a hard roller and the pressure roller is a soft roller, the pressure roller 2 is deformed at the nip portion following the curved surface of the fixing roller l, as shown in FIG. 6(A). Therefore, the two stacked sheets of paper 6a and 6b are the blank paper (back paper) 6b
This precedes the inner paper (front paper) 6a that is in contact with the fixing roller 1. However, in the case of an envelope, the three sides other than the entrance are connected to each other by adhesive or folding, and the circumference is restricted, so the inner paper 6a and the outer paper 6b are connected to each other, as shown in Figure (B). The two sheets of paper 6a cannot be separated from each other.

6b will be absorbed in the form of wrinkles at the trailing edge of the paper being conveyed.

The thickness of each of these two sheets of paper 6a and 6b is 1
00μ, and the diameter of fixing roller 1 is 30M.

The length of the envelope is 190+n+n, and the fixing nip width is 3mm.

Considering an example in which the rotational speed of the fixing roller 1 is Nrpm, the conveyance amount of the envelope surface per second is = N X π
The speed becomes
60 rpm, and the difference between the two is ΔL=NxπX O,2
/60 rpm.

The rotational speed N of the fixing roller l is 72×60/π×30=4
If the speed is 5.84 rpm, then by simple calculation, the fixing roller 1
The linear speed of is 72 mm/see, and the conveyance deviation of both sheets is (πxo
, 2/60) x45.84x190/72=1.26
It becomes mm.

Note that thermal expansion of the roller, slippage between sheets of paper, or slip between paper and rollers are not considered here.

When conducting an experiment with two sheets of A4 size (297 mm) cut paper stacked one on top of the other, the paper on the pressure roller side ran first by about 1.5 mm, which roughly matches the theoretical value above.

In this way, with two layers of transfer paper like envelopes,
According to the conventional fixing device, there is a problem in that wrinkles occur at the trailing edge of the paper.

(2) Next, the conventional pressure roller 2 is made of silicone rubber or an inner cylinder made of silicone rubber covered with a Teflon tube.

The problem here is that the density of the silicone rubber is not necessarily uniform over the entire area, but is uneven. As a result, the hardness of the rubber becomes uneven, resulting in non-uniform nip width or non-uniform surface pressure at the nip, which is a major cause of wrinkles in the transfer paper. In addition, silicone rubber has a high density, so when making continuous small-size copies, the temperature at both ends of the fixing roller rises, and the heat is transferred to the pressure roller, causing thermal expansion at both ends to achieve the desired nip width. becomes wider than the value of , and as a result, the trailing edge of the transfer paper springs up,
There is a problem in that images are rubbed against guide plates and the like.

Problems to be Solved by the Invention (a) Therefore, the inventor of the present invention aimed to solve the above problem (1) by providing a fixing roller 1 and a pressure roller 2.
An experiment was conducted on the pressing force between the envelopes, that is, the fixing pressure, the rank of wrinkles generated on the envelope at that time, and the fixing performance, and the results shown in FIG. 7 were obtained. In the figure, a straight line A shown as a solid line indicates adhesion, and a straight line B shown as a broken line indicates the state of occurrence of wrinkles. It is shown that the occurrence of wrinkles decreases from rank 1 to rank 5. The example in the figure shows a fixing temperature of 18°C.
This is a case of a combination of a Teflon (trade name) coated fixing roller 1 with a nip width of 3 mm and a pressure roller 2 made of Si rubber.

From the figure, if we assume that the area with good wrinkle resistance is rank 4 or above, the surface pressure will be approximately 0.7 kg f/cn!
The allowable value for fixing property is 55%.
If it is above, the surface pressure will be approximately 1. It can be seen that more than Okg f/cot is required.

Therefore, in order to obtain a fixing device with less wrinkles on the envelope and satisfactory fixing performance, the fixing pressure of the pressure roller 1 should be set to 0.7 kg.
f/cn! It has been found that it is necessary to manage as follows, and to increase the fixing temperature or increase the nip time by the pressure roller l in order to improve the fixing performance.

Furthermore, at the nip portion between the fixing roller 1 and the pressure roller 2, in order to prevent a difference in conveyance speed between the two sheets of envelope paper 6a and 6b, the fixing roller l' and the pressure roller 2 are arranged as shown in FIG. are both formed as soft rollers, and the fixing roller l
It has been found that the above-mentioned difference in conveyance speed between the two sheets of paper can be eliminated by making the nip portion between the pressure roller 2 and the pressure roller 2 substantially planar (straight in cross section).

(b) Next, regarding the above problem (2), there is an example of using a heat-resistant elastic foam as a pressure roller disclosed in Japanese Patent Publication No. 1-36624 as a way to solve this problem. In the case of foam pressure rollers, the effect of improving wrinkles, especially envelope wrinkles, is insufficient, and the surface pressure at the nip is lower than that of silicone rubber, so in order to obtain the same fixing pressure, it is necessary to use silicone rubber. It is necessary to increase the nip width. For this reason, the diameter of the pressure roller increases, resulting in a problem of high material costs.

Therefore, an object of the present invention is to, by referring to the knowledge described in (a) above, to avoid wrinkles even when using a double-layered transfer paper such as an envelope, and in addition to this, (b)
It is an object of the present invention to provide an inexpensive fixing device that solves the problems mentioned above, provides good fixing performance, and reduces material costs for a pressure roller.

Means for Solving the Problems In order to achieve the above-mentioned objects, the present invention provides a rotatably supported and driven fixing roller that has a heating device inside, and a transfer paper that is pressed against the fixing roller and driven. In a thermal fixing device having a pressure roller, the pressure roller includes at least two pressure rollers, and the pressure roller and the fixing roller fix the nip formed for the transfer paper to pass through. It is characterized in that the pressure is low enough not to cause wrinkles, and the nip time is increased enough to achieve a predetermined fixing rate.

The diameter of the pressure roller on the transfer paper entrance side is the same as or smaller than the diameter of the pressure roller on the discharge side.

The present invention also provides a thermal fixing device including a rotatably supported and driven fixing roller having a heating device therein, and a pressure roller that presses a transfer paper against the fixing roller and is driven by the pressure roller. It is characterized in that it consists of at least two pressure rollers and is made of heat-resistant elastic foam.

Then, the pressure roller is set such that [pressure force J of the pressure roller on the transfer paper inlet side ≦[pressure force of other pressure rollers] or [hardness of the pressure roller on the transfer paper inlet side]≦[other pressure rollers] hardness].

Operation According to the present invention, each of the plurality of pressure rollers is pressed against the fixing roller with a low fixing pressure, that is, with a pressure that does not cause wrinkles in transfer paper such as an envelope. The transfer paper is conveyed by a fixing roller, and the plurality of pressure rollers are driven by contact with the transfer paper. Sufficient fixing cannot be achieved with the fixing pressure of one pressure roller, but by fixing the transfer paper to the fixing roller under pressure using multiple pressure rollers, sufficient nip time is secured and the fixing rate is also increased. .

Embodiment In the first embodiment shown in FIG. 1, a fixing roller 1 and a plurality of pressure rollers 2a and 2b, for example two pressure rollers 2a and 2b having approximately the same diameter, are provided which are pressed against the fixing roller 1. Fixing roller 1 and pressure roller 2a.

2b are rotatably supported by the casing 3 of the fixing device, respectively, and the fixing roller 1 is driven by a drive device (not shown).

A heating device 49 such as a heater is provided inside the fixing roller 1, and the surface temperature of the fixing roller I is measured by a temperature measuring device 59 such as a thermistor.

Toner image! The transfer paper 6 onto which the image 2 has been transferred is guided by an entrance guide 7 to a first nip portion 8 between the entrance pressure roller 2a and the fixing roller l.

The paper fixed under the pressure of the entrance pressure roller 2a is sent to the second nip portion 9 between the discharge side pressure roller 2b and the fixing roller 1.

After fixing, the transfer paper 6 is separated from the fixing roller 1 by a separating claw 11 and is discharged along a discharge guide 10.

In order to prevent wrinkles from forming on transfer paper, such as envelopes, when fixing, the pressure applied to the fixing roller 1 by pressure rollers 2a and 2b is reduced to such an extent that wrinkles do not occur, for example, to about 1/4 of the normal fixing pressure. do. 0,7 with reference to Figure 3
) cg f / cry or less, and multiple pressure rollers 2 are used to compensate for the decrease in fixing performance due to the decrease in fixing pressure.
a.

2b increases the nip time.

In the first embodiment, it is difficult to provide a paper separation and conveyance guide for separating and conveying the transfer paper 6 to the pressure rollers between the two pressure rollers arranged close to each other. Therefore, the transfer paper 6 that has passed through the first pressure roller 2a is fed without a guide, so when it enters the second nip portion 9 of the next pressure roller 2b, it may be bent or jammed. A possibility arises.

The second embodiment shown in FIG. 2 can prevent such problems, and for this reason, a roller with the smallest possible diameter is used as the pressure roller 2a on the entry side, and the paper is automatically rolled due to its curvature. It is convenient that the paper can be separated, and the pressure roller 2b that follows should have a diameter as large as possible so that the paper can smoothly enter the second nip portion 9.

In this second embodiment and the following third embodiment, the same or equivalent parts as in the first embodiment will be given the same reference numerals and explanations will be omitted, and as mentioned above, only the different parts will be explained. .

In the third embodiment shown in FIG.
A fixing roller made of Teflon (trade name of polytetrafluoroethylene) or silicone rubber with a built-in
In order to reduce material costs, the fixing roller 1 is comprised of a plurality (in this example, two) pressure rollers 2a and 2b made of heat-resistant elastic foam and having a diameter smaller than that of the fixing roller 1. This pressure roller is determined by the following conditions: [pressure force of pressure roller 2a on transfer paper entrance side]≦[pressure force of other pressure roller 2b], or [hardness of pressure roller 2a on transfer paper entrance side]≦[other pressure roller 2
hardness b], and particularly preferably both relationships. Specifically, the hardness is suitably 20H3 (degrees) or less according to JIS.

In addition, in this embodiment, the back side of the copy image is stained due to toner adhering to the pressure rollers 2a and 2b, and the pressure rollers 2a and 2b are
In order to prevent uneven fixing due to surface smoothing of 2b, the fourth
As shown in the figure, it is preferable to coat the surface of the heat-resistant elastic foam 15 with a thin releasable resin (silicone rubber, PFA (perfluoroalkoxyethylene resin) tube, etc.). Note that 13 indicates a conveyor belt, and 14 indicates a pair of paper discharge rollers.

Next, the pressure rollers 2a and 2b with respect to the diameter of the fixing roller 1
The influence on the transfer paper depending on the diameter of the paper will be explained with reference to FIG. In FIG. 5(A), the diameters of the pressure rollers 2a and 2b are larger than the diameter of the fixing roller l (for example, the diameter of the pressure rollers 2a and 2b is 45 m + 111 m compared to the diameter 401 of the fixing roller 1.
) In the fixing device, and in the same figure (B), the pressure roller 2a.

The diameter of the transfer paper 6 is smaller than the diameter of the fixing roller l (for example, the diameter of the pressure rollers 2a and 2b is 16 mm while the diameter of the fixing roller 1 is 40 mm). Indicates the condition. In FIG. 5(A), since the pressure rollers 2a and 2b have larger diameters, the first nip portion 8
Since the distance from the second nip portion 9 to the second nip portion 9 is long, paper jams are likely to occur in front of the pressure roller 2b as shown in the figure.

On the other hand, in FIG. 5(B), since the pressure rollers 2a, 2b have smaller diameters, the distance between the first nip part 8 and the second nip part 9 becomes shorter. Paper jams do not occur even with transfer paper such as wet paper. Note that the pressure roller diameter is preferably made as small as possible within a range that satisfies fixing performance.

Next, a fixing device consisting of a Teflon fixing roller l with a diameter of 40 mm and various pressure rollers 2a and 2b shown in Table 1 was set as shown in Figure 3, and the fixing speed (linear speed) was 120 m/
Fixing was performed at a fixing temperature of 185° C. and the fixing performance on the main transfer paper 6 and the occurrence of wrinkles were tested, and the results are shown in the same table. Fixability (%) is measured by the clock method, and envelope wrinkles are evaluated using a 5-level evaluation method, with rank 5 being ``no wrinkles'' and rank 1 being ``extremely bad wrinkles'' (however, ranks 4 and above are based on the standard). Value) was evaluated.

In addition, the paper is 30'C-90%R so that wrinkles may easily occur.
) (conditioned for 4 hours).

(The following is a margin) The NCLI combination is a combination of ordinary silicone rollers, and has a high wrinkle occurrence rate, and in particular, envelope wrinkles are the lowest at rank 1. Magnet 2 has the configuration disclosed in Japanese Patent Publication No. 1-36624 in which the pressure roller is made of foamed silicone, and has good fixing properties and wrinkle generation. However, the envelope wrinkles are ranked 3, and some wrinkles occur. Floor 3 uses two foamed silicone pressure rollers with a small diameter of 16 mm.
Everything is good, but there is still room for improvement. Therefore, if the pressing force of the entrance side pressure roller is lowered as in the case of 4, wrinkles will completely disappear, but the fixing performance will deteriorate. Therefore, if the hardness of the pressure roller on the entrance side is further lowered as in point 5, both wrinkles and fixing properties can be satisfied.

From the above, it can be said that the fixing section should be divided into two parts, the entrance side should be used as a preliminary fixing section to reduce the surface pressure as much as possible, and the transfer paper should enter the nip section on the exit side softly to avoid wrinkles. On the other hand, the exit side is set as the main fixing section, and the exit side nip section performs complete fixing. This increases the level of wrinkle generation compared to the Nch2 combination.

Furthermore, the major advantage of dividing the fixing section into two is that
Since the pressure roller can be made small in diameter, material costs can be reduced.

The pressure rollers actually used in the above test were 5mm thick for the φ40mm one, 3mm thick for the φ16mm one, and the one using two φ16+nm rollers was φ
It requires about half the materials compared to one using one 40mrn.

Effects of the Invention The present invention is as described above, has at least two pressure rollers, lowers the fixing pressure at the nip between the pressure roller and the fixing roller to an extent that does not cause wrinkles, and maintains a predetermined level. Since the nip time has been increased to the extent that the fixing rate can be increased, when toner is fixed on a transfer paper made of two sheets of paper bound together, such as an envelope, wrinkles do not occur as with conventional fixing devices.
The diameter of the pressure roller on the entry side is smaller than the diameter of the pressure roller on the discharge side, allowing the transfer paper to enter the nip portion smoothly, and the pressure roller is made of heat-resistant elastic foam. Since the pressure roller is made of In addition to the low occurrence of , the fixing performance is also good, especially if [pressure roller pressure on the transfer paper entrance side] ≦ [other pressure roller pressure] or [pressure roller hardness on the transfer paper entrance side] ] ≦ [Hardness of other pressure rollers] (Hardness is 20 in JIS
The fixing section is divided into a pre-fixing section and a main fixing section, and the transfer paper enters the fixing section softly, which prevents wrinkles on the transfer paper, especially envelope wrinkles. There is an effect that it can completely prevent the problem and also satisfy the fixing performance.

[Brief explanation of drawings]

Fig. 1 is a front view of the first embodiment of the invention, Fig. 2 is a front view of the second embodiment, Fig. 3 is a front view of the third embodiment, and Fig. 4 is a front view of the third embodiment. End view of pressure roller, Figure 5 (A)
(B) is an explanatory diagram of the operation of a fixing device in which a pressure roller with a diameter different from that of the fixing roller is arranged, and FIG. 6 (A)
(B) is an explanatory diagram of the fixing state of an envelope by a conventional fixing device, FIG. 7 is a diagram showing the relationship between the fixing pressure by a pressure roller, the occurrence of wrinkles, and the fixing property of an envelope, and FIG. FIG. 3 is an explanatory diagram showing a state of a nip portion in the case of a fixing roller. 1...Fixing rollers 2a, 2b...Pressure rollers 4...Heating device 6...Transfer paper 8.9...Nip part horse figure 3Σ horse 2 figure horse 8 figure

Claims (1)

[Scope of Claims] 1. In a fixing device having a rotatably supported and driven fixing roller having a heating device therein, and a pressure roller that presses a transfer paper against the fixing roller and follows the fixing roller, The pressure roller is composed of at least two pressure rollers, and the pressure roller and the fixing roller lower the fixing pressure at the nip formed for the transfer paper passing through to a level that does not cause wrinkles, thereby achieving a predetermined fixation level. A fixing device characterized in that the nip time is increased as much as possible. 2. The fixing device according to claim 1, wherein the diameter of the pressure roller on the entrance side of the transfer paper is equal to or smaller than the diameter of the pressure roller on the discharge side. 3. In a thermal fixing device having a rotatably supported and driven fixing roller having a heating device inside, and a pressure roller that presses the transfer paper against the fixing roller and is driven, the pressure roller has at least two Consists of pressure rollers,
A fixing device characterized in that it is made of a heat-resistant elastic foam. 4. If the pressure roller is [pressure force of the pressure roller on the transfer paper entrance side] ≦ [pressure force of other pressure rollers] or [hardness of the pressure roller on the transfer paper entrance side] ≦ [other pressure rollers] 4. The fixing device according to claim 3, wherein the fixing device has a hardness of .