JP3319210B2 - Fixing device - Google Patents

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 fixing toner transferred on both sides of a recording material to the recording material.
Things .

[0002]

2. Description of the Related Art As a fixing device for fixing a toner image on both sides of a recording material, a recording material holding unfixed toner on each of the front and back surfaces is passed through a fixing device only once, and the so-called one process is performed on the recording material. A double-sided fixing device that fixes unfixed toner is known. Here, the fixing device includes:
The recording material holding the unfixed toner is radiated and heated in a non-contact state to fix the unfixed toner to the recording material. There is a fixing device based on a contact fixing method in which heating is performed while being nipped and conveyed to fix unfixed toner on a recording material.

[0003]

In the case of a fixing device using a contact fixing method using a fixing roller, the fixing performance is governed by the heat roller temperature, nip pressure and nip width (fixing time). Regarding the nip area, an appropriate nip area is normally secured by configuring at least one of the pair of fixing rollers pressed against each other as a roller having an elastic layer. For example, as shown in FIG. 7, the upper fixing roller 15 is a hard roller, the lower fixing roller 16 is a soft roller having an elastic layer, the roller 15 is a driving roller, and the roller 16 is a driven roller. The fixing roller 15 has a releasable resin layer 20a such as a fluorine-based resin formed on a surface of a metal roller 21a such as aluminum, and a halogen lamp 22a is built in the metal roller 21b. On the other hand, in the fixing roller 16, an elastic layer 23 (thickness h) made of silicon rubber is formed on the surface of a metal roller 21b made of aluminum or the like, and a release layer 20b made of a fluororesin is formed outside the elastic layer 23. The halogen lamp 22b is built in the metal roller 21b. Both pairs of fixing rollers are pressed with a constant load, and a nip region having a width W is formed. Usually, the radius r ₂ of a radius r ₁ and the lower side of the soft roller 16 of the upper hard roller 15 is the same, a hard roller drive side, is configured to the driven side soft roller taken. In the nip region, the lower soft roller is deformed because of having the elastic layer 23, and the effective radius r in the nip region is r.
₂ changes to r2 _' . As a result, the lower soft roller effective radius r _{2 ′} becomes larger than the radius r ₁ of the upper hard roller. Therefore, when the rotational angular velocity of both the fixing roller are the same, the moving velocity υ _2> υ ₁ next to the upper hard roller, the moving speed difference is generated. For this reason, as shown in FIG. 7A, since the lower surface of the recording material has a higher moving speed than the upper surface, stresses Fc and Fe in different directions act on the upper and lower toner images of the paper relatively. For this reason, as shown in FIG. 7B, a problem arises in that the fixed toner images 19a and 19b after passing through the nip portion have character blur. This phenomenon has not been a problem when printing on one side or printing on one side (fixed) and then printing on the other side. In addition, the thermal resistance of the recording material per unit time of the soft roller is smaller than that of the hard roller because the soft roller has the thermal resistance corresponding to the elastic layer. For this reason, the same amount of heat cannot be applied to the front and back surfaces of the recording material when passing through the fixing device, causing a problem that the fixing strength of the toner differs between the front and back surfaces.

Further, in an electrostatic recording apparatus using the above-described fixing device, character blurring and offset occur when retracting and pressing the upper and lower fixing rollers from the recording material at the time of stopping and starting the double-sided printing operation. There was a problem.

It is an object of the present invention to provide a fixing device capable of making the fixing strength of the toner formed on the front surface of the recording material equal to that of the toner formed on the back surface of the recording material .

[0006]

The object of the present invention is to pass a recording material holding an unfixed toner image on the front and back to a nip area formed by a pair of fixing rollers provided with a heating source.
In the fixing device for fixing the unfixed toner image on the recording material, among the fixing rollers, one fixing roller is a hard roller provided with a release resin layer on a metal roller, the other fixing roller, An elastic layer is provided on a metal roller, and a soft roller is further provided with a release resin layer on the elastic layer, and a recording material sent from the nip area is wound around a surface of the soft roller by a predetermined angle. The surface of the recording material that is conveyed
When the fixing strength of the toner is in contact with the hard roller,
The above-mentioned soft
This is achieved by defining the angle at which the recording material is wound around the roller .

[0007]

According to the above construction, the recording material sent from the nip area is conveyed by being wound around the surface of the soft roller at a predetermined angle, so that the shortage of the input heat due to the presence of the elastic layer is compensated. As a result, the fixing strength between the front surface and the back surface of the recording material can be made equal.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. (Embodiment 1) In FIG. 1, reference numeral 1a denotes a first photosensitive drum having a photoconductor layer 2a formed on the surface thereof, and a charger 3a.
The photoconductor layer 2a, the surface of which has been given a charge, is irradiated with an image light pattern by the exposure unit 4a to form a latent image, and then developed by the developing unit 5a to form a toner image 6a. In this embodiment, an organic photoconductor (OP) is used as a photoconductor.
C), and a reversal development method using negatively charged toner will be described. The toner image 6a is transferred to the recording material (paper) 1 by the bias roller 12 to which a positive polarity DC voltage is applied.
0 is transferred to the upper surface. 7a is an erase lamp, and 8a is a photoreceptor cleaner. Reference numeral 13 denotes a static eliminator to which an AC voltage or an AC voltage on which a positive DC voltage is superimposed is applied, which reduces the charge of the toner image 6a and further converts the toner image 6a into a reverse polarity (positive polarity). Reference numeral 1b denotes a second photoconductor drum having a photoconductor layer 2b formed on the surface thereof. An organic photoconductor (OPC) is used similarly to the first photoconductor drum, and the toner image 6b is formed on the drum by a reversal development method. Is formed.
The negatively charged toner image 6b is attracted by the positive charge applied to the upper surface of the sheet by the transfer corotron 14, and is transferred to the lower surface of the sheet.

Toner images 6a, 6 formed on both sides of a sheet
b is fixed on the sheet by a fixing device including the fixing rollers 15 and 16 having the configuration shown in FIG. 2, and becomes fixed toner images 19a and 19b, respectively. 17a and 17b are cleaners of the fixing roller. Reference numeral 9 denotes a recording material (paper) feed roller, 11 denotes a paper brake, and 18 denotes an out roller.

In the fixing device of this embodiment, 15 is a hard roller, 16 is an elastic roller, 15 is a driving roller, and 16 is a driven roller. Here, 22a, 22b
Is a PFA resin layer, and 23 is a Si-based rubber layer.

The upper fixing roller 15 is a hard roller and is a driving roller, and the lower fixing roller 16 is a soft roller having an elastic layer and is a driven roller.
Both pairs of fixing rollers are pressed with a constant load, and a nip region having a width W is formed. In this nip region, the lower fixing roller is deformed. Assuming that the area of the deformation region of the elastic layer in the nip portion is ΔS, the effective radius r _{2 ′} of the lower fixing roller is expressed by Expression (1), and is larger than r ₂ .

R _{2 ′} = r ₂ {1 + ΔS / (h × W)} ^1/2 (1)

When the fixing roller 16 is driven by the fixing roller 15, the rotational angular velocity becomes the same ω. If the effective radii of the rollers are the same, the respective rotational speeds U1, U2 are also the same. For this purpose, the effective radius r _{2 ′} of the lower fixing roller may be the same as the radius r ₁ of the upper fixing roller (the same as the effective radius because it is a hard roller). Therefore, r ₂ is as follows.

R ₂ = r ₁ {1 + ΔS / (h × W)} − ^1/2 (2)

Here, △ S is represented by a function of r ₁ , r ₂ , h, and W, and when this is substituted into equation (2), equation (3) is obtained.

R ₂ = r ₁ / {1 + W ² / (16h × r ₁ )} (3)

Also, rewriting equation (3) for W,

W = {16 × h × r ₁ × (r ₁ −r ₂ ) / r ₂ } ^1/2 (4)

From equation (4), since W> 0, r ₁ > r ₂
Must.

Therefore, as a method of making the effective radius of rotation in the nip portion the same, the radius r of the hard roller 15 is used.
₁ , nip width W, thickness h of elastic layer of soft roller 16
If the value is determined, (3) is obtained radius r ₂ of the lower fixing roller from the equation.

On the other hand, when the values of r ₁ , r ₂ , and h are determined, the nip width W satisfying the expression (4) is obtained as follows.
The two rollers may be pressed against each other as described above. Especially for long term fixing
When the elastic property of the elastic layer is reduced by using a roller , the pressing pressure of the fixing roller may be adjusted so that the nip width W becomes a predetermined value.

[0022]

[Table 1]

Table 1 shows the shape of a soft roller that does not cause character blur when it is used in combination with the hard roller 15 having a different radius according to equation (3). Release layer 2
Since the thickness of 0a and 20b is usually 0.1 mm or less, it is extremely thin (1/10 to 1/100) compared to the radius of the metal rollers 21a and 21b and the thickness of the elastic layer 23. Since it can be neglected, r ₁ and r ₂ are approximately calculated by setting the radius r ₁ of the hard roller 15 to the radius of the metal roller 21 a and the radius r ₂ of the soft roller 16 to the metal roller 21.
The sum of the radius b and the thickness h of the elastic layer 23 was used.

On the other hand, the nip width W and the thickness h of the elastic layer 23
When determined, the radius r ₂ is obtained in decreasing (2), resulting in it determines the radius of the metal roller 21b. In Table 1 is the radius r ₁ of the hard roller 15 showed a case of 50,30,15Mm, radius r ₂ is about 0.3~0.5mm smaller than the radius r _1. By setting this value, the effective radii of the hard roller 15 and the elastic roller 16 in the nip state become equal, and the speed when the paper passes through the nip area becomes the same on the upper surface and the lower surface, so that no character blur occurs. .

(Second Embodiment) In the first embodiment, the upper fixing roller 15 has a hard roller and the lower fixing roller 16 has an elastic roller. In the second embodiment, the upper and lower fixing rollers as shown in FIG. Reference numerals 15 and 16 both denote the case of elastic rollers. Recently, the amount of recycled paper used as printing paper has tended to increase due to environmental problems. However, recycled paper, also called rough paper, has large irregularities on the surface as compared with high-quality paper, and some have a difference in irregularities close to 50 μm. is there. For this reason, the hard roller cannot follow the unevenness of the paper and cannot sufficiently fix the toner to the paper, so that the fixing strength is reduced. For this reason, in the case of recycled paper, a soft roller having an elastic layer is preferable. For this purpose, by using the same structure and the same radius for both 15 and 16 and using one as a drive roller and the other as a follower, the speed at which the paper passes through the nip area becomes the same on the upper surface and the lower surface. Occurrence can be prevented.

The fixing roller may have exactly the same diameter as the metal roller and the same material and thickness of the elastic layer and the releasable resin layer. The thickness of the layers may be different for both. Further, a feed roller for returning the sheet to the upstream side by a predetermined distance (about 1 inch) is provided on the upstream side of the recording material conveyance brake mechanism, and an out roller for applying tension to the recording material is provided on the fixing device in preparation for printing resumption. Provided downstream.

The thickness h of the elastic layers 23a and 23b is
In consideration of high-speed fixing, the thinner is better in consideration of the heat conduction from the lamps 22a and 22b. However, if it is too thin, the effect of the elastic roller is lost. As a result of the experiment, the elastic layers 23a, 23
It was found that the thickness h of b was desirably at least 50 μm.

Soft rollers having exactly the same shape may be used as the upper and lower fixing rollers, or the thickness of one of the elastic layer and the release resin layer may be changed.

(Embodiment 3) FIG. 4 is a view showing another embodiment. In the fixing device configuration, the upper fixing roller 15 is a hard roller, and the lower fixing roller 16 is an elastic roller. In order to secure the fixing strength, it is necessary to make the fixing energy given to the toner on the upper and lower surfaces of the paper the same. In the elastic roller, the thermal resistance is increased by the amount of the elastic layer, and the amount of heat energy applied to the sheet per unit time is reduced. For this reason,
There are two methods for applying the same amount of heat to the toner on the upper and lower surfaces of the paper when passing through the fixing device.

(A) Heater lamp 2 of soft roller 16
The power of 2b is applied to the heater lamp 22a of the hard roller 15.
To be greater than the power of.

(B) Heater lamp 2 of soft roller 16
2b power and heater lamp 22a of hard roller 15
After passing through the nip as shown in FIG. 4, the paper is wound around the elastic roller 16 by the winding roller 24.
And apply the amount of the insufficient heat to the toner on the lower surface of the sheet. Here, θ is the winding angle of the paper, and the thermal conductivity of the silicone rubber used as the elastic layer is large,
The smaller the thickness of the elastic layer, the smaller θ can be. In addition,
Reference numeral 18 denotes an out roller, which applies tension to the paper to eliminate paper thickening in the paper winding area and prevent occurrence of character blur. With the above measures, the fixing strength of the toner on the upper and lower surfaces of the paper can be made the same.

(Embodiment 4) FIG. 5 is a view for explaining another embodiment. The operation of the fixing system when printing is interrupted in a double-sided simultaneous fixing device using a heat roller will be described. The axes of the upper and lower heat rollers are respectively a spring 25a,
The upper and lower heat rollers are press-fitted by the cams 26a and 26b during printing to form a nip portion. The fixing operation is performed when the paper on which the toner image is formed passes. When printing is interrupted, the recording material conveyance brake device 11 operates to stop the running of the paper and
By the operations of a and 26b, the upper and lower heat rollers are separated from the sheet. Further, the out roller 18b is a scuff roller, and the sheet is stretched by a tensile stress that does not break, so that the sheet does not sag. Further, the sheet is backed up by a predetermined distance (for example, 1 inch) by the transport roller 9 in preparation for the restart of printing.

As a result, it is possible to prevent hot offset of the toner due to an increase in the heating time when the printing is interrupted, and character blur due to a press contact failure of the upper and lower heat rollers when the printing is resumed.

(Embodiment 5) FIG. 6 is a view showing another embodiment. The difference from FIG. 5 is the method of separating the upper and lower heat rollers from the paper when printing is interrupted. Here, the shafts of the lower heat rollers are respectively attached to arms 27 to which springs 25 are connected.
8 is connected to the shaft of the lower heat roller. During printing, the lower fixing roller 16 and the out roller 18 are
b is pushed up and pressed against the upper fixing roller to form a fixing nip, and the paper 10 is
It is held and transported by 8a and 18b. In this case, only the lower fixing roller needs to be moved.

[0035]

According to the present invention, it is possible to provide a fixing device capable of making the fixing strength of the toner formed on the front surface of the recording material equal to that of the toner formed on the back surface thereof.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of an electrostatic recording apparatus using a fixing device of the present invention.

FIG. 2 is an explanatory diagram illustrating a structure of a fixing roller of the fixing device of the present invention.

FIG. 3 is an explanatory view showing another embodiment of the present invention.

FIG. 4 is an explanatory view showing another embodiment of the present invention.

FIG. 5 is an explanatory diagram illustrating a configuration of a retracting mechanism of the fixing roller.

FIG. 6 is an explanatory diagram illustrating a configuration of a retracting mechanism of the fixing roller.

FIG. 7 is an explanatory diagram showing a fixing state.

[Explanation of symbols]

10: recording material, 15: fixing roller, 16: fixing roller,
20 ... release layer, 21 ... metal tube, 22 ... lamp, 23 ...
Elastic layer.

Continuation of front page (56) References JP-A-3-68965 (JP, A) JP-A-1-142779 (JP, A) JP-A-3-231786 (JP, A) JP-A-4-306668 (JP, A) JP-A-2-28677 (JP, A) JP-A-7-5785 (JP, A) JP-A-4-273274 (JP, A) JP-A-7-160137 (JP, A) 4-97187 (JP, A) JP-A-3-72390 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 13/20 G03G 15/20 G03G 15/00 106

Claims (1)

(57) [Claims] A fixing device for fixing the unfixed toner image to the recording material by passing the recording material holding the unfixed toner image on the front and back through a nip area formed by a pair of fixing rollers provided with a heating source; In the apparatus, among the fixing rollers, one of the fixing rollers is a hard roller having a releasable resin layer provided on a metal roller, and the other fixing roller is provided with an elastic layer on a metal roller. and a soft roller having a releasing resin layer on the material layer, the recording material fed from the nip region, when transported by wind around a predetermined angle to the surface of the soft roller DOO
In addition, the toner of the recording material surface in contact with the soft roller is determined.
The adhesion strength of the toner on the recording material surface in contact with the hard roller
So that it is equivalent to the fixing strength of
A fixing device wherein a winding angle of a recording material to be formed is specified .