JP2813297B2 - Fixing device for electrophotographic 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 an electrophotographic apparatus used for fixing a toner on a recording medium by fusing and pressing.

[0002]

2. Description of the Related Art As a fixing device for an electrophotographic apparatus, a so-called heating roller system has been conventionally used in many cases. This is accomplished by providing a heating source inside a pair of rollers provided with a coating made of a non-adhesive substance on the surface, and rotating the roller while applying an appropriate pressure between the two rollers, so that the recording medium on which the toner has been transferred is described above. The fixing is performed by passing between a pair of rollers.

On the other hand, recently, a belt has been wound between one of the pair of rollers and a third roller,
A technique has been developed in which the toner on the recording medium is pressed by the belt surface. For example, (a) JP-A-4-508
In No. 83 (FIG. 5), a heat-conductive fixing belt c is wrapped around a heat-resistant elastic fixing roller a and a heat supporting roller b, and a pressure roller d pressing the fixing roller a from below through the fixing belt c is provided. The toner image is fixed between the fixing belt c and the pressure roller d with the toner e 'and the recording medium e therebetween, and the heat-resistant elastic layer of the fixing roller a is not peeled off by heating the heater f.

[0004] Further, in the (b) JP-A-4-273274 (FIG. 6), a heat fixing roller a ₁ and the support roller b
_The fixing belt c ₁ wrapped around for _one time is heated to the fixing roller a _1.
The heating and pressing roller d ₁ for pressing from below provided for,
Conveying the recording medium e after fixing the toner e 'with the fixing belt c ₁ while cooling by the cooling device h on guide g, a fixing belt c the image support e after the cooling
By separating from _{1, the} fixed image without offset transfer can be obtained without using a release agent such as silicone oil.

(C) In Japanese Patent Application Laid-Open No. 5-11651 (FIG. 7), heating of the fixing roller a ₂ , the supporting roller b ₂ , the fixing belt c ₂ , the pressure roller d ₂ and the fixing belt c ₂ is performed. in the configuration consisting of use heater f, provided the transfer device i of the recording medium e parallel state of the lower fixing belt c ₂ preheating the toner, thereby can set low fixing temperature, the fixing device is simplified, compact And lower prices are possible.

(D) In Japanese Utility Model Application Laid-Open No. 4-124267, even if the fixing belt is made of metal and the speed of belt fixing is increased, the heat conductivity is good and the heating and cooling becomes smooth. And good image quality can be obtained.

In the above-mentioned prior art, the prior art (a) has no technical idea of preheating the toner e 'and the recording medium e by the heated fixing belt c.
In the prior art (c), have been described for the preheating of the fixing belt c _2, in particular a technique relating to use of the capsule toner for low-temperature fixing, the place to suggest any way for preventing the offset that occurs when the toner used in the high-temperature fixing Absent.

Further prior art (b) are those forced cooling of the fixing belt c ₁ which moves along with the image recording medium e about after the fixing operation, the prior art (d) shows the fixing belt itself cooled in the mobile stroke It is self-cooling depending on the configuration.

[0009]

In the present invention, the temperature of the nip is set low by preheating the toner and the recording medium via a fixing belt, and the nip is formed by using a belt having a small heat capacity as the fixing belt. The purpose is to obtain an image without offset by oilless or trace amount oil application by rapidly cooling the fixing belt at the time of passing through the section and suppressing the temperature of the toner on the recording medium that separates from the fixing belt at the nip exit. Is what you do.

[0010]

In order to achieve the above object, according to the present invention, an endless fixing belt having a release layer on the surface of a belt main body is stretched between a fixing roller and a heating roller. A pressure roller that presses the fixing roller from below via a fixing belt is provided to form a nip portion between the fixing belt and the pressure roller, and a nip portion between the heating roller and the nip portion below the fixing belt. A recording medium support is provided at the close position to form a substantially linear heating path between the fixing belt and the fixing belt, and the heat capacity per 1 cm ² of the fixing belt is 0.002 to 0.025 cal / ° C. Features.

[0011]

Since the fixing belt has a small heat capacity, the toner and the recording medium take heat away from the nip portion to cool down itself, so that the temperature of the molten toner is not raised unnecessarily. And the toner is peeled off, and offset is prevented.

[0012]

DETAILED DESCRIPTION FIG. 1 is a fixing device of a color copying machine, R ₁
Is a fixing roller, R ₂ is a pressure roller, R ₃ is a heating roller,
B denotes a fixing belt, H ₁ and H ₂ denote heating sources, S ₁ and S ₂ denote thermistors as temperature control means, G denotes a guide plate, and P denotes a heating path of a recording medium onto which toner has been transferred.

The fixing roller R ₁ is formed by providing a heat-resistant elastic coating layer 2 made of silicone rubber having a thickness of 3 mm on an aluminum core 1 having a diameter of 34 mm, and a pressure roller R ₂ is provided on an aluminum core 3 having a diameter of 40 mm. Is provided with a heat-resistant elastic coating layer 4 of 50 μm silicone rubber. The surface hardness of the heat-resistant elastic coating layer 2 is set equal to or softer than the hardness of the heat-resistant elastic coating layer 4.

The heating roller R ₃ has a Teflon coating layer 6 having a thickness of 30 μm on an aluminum core 5 having a diameter of 40 mm, and a step portion having a thickness larger than the thickness of the fixing belt B at both ends in the axial direction for preventing the fixing belt B from shifting. 7 (see FIG. 2).

The tension roller R ₄ is formed of an aluminum material having a diameter of 20 mm, and its shape can be arbitrarily selected from a straight, an inverted crown, or a regular crown, and can perform both cleaning and application of a small amount of oil.
The fixing belt B is one configured to provide a thickness of 45μm release layer B ₂ according to 50μm silicone rubber on the outer peripheral surface of the endless belt mainly B ₁ of metallic nickel by electroforming, or thickness 55μm polyimide resin Endless belt main body B
Those formed by providing a release layer B ₂ with silicone rubber 130μm on the outer circumferential surface of ₁ a (see FIG. 3).

Heating roller R_ThreeInside the main heating source H₁But
Provided, a pressure roller R_TwoInside the auxiliary heating source H_TwoBut
Provided, and a fixing roller R₁Inside as needed
An auxiliary heating source can be provided. Heating roller R_ThreeOutside
On the side, the main heating source H₁To control the temperature of the thermistor
Star S₁Is provided in contact with the fixing belt B, and a pressure roller
R_TwoIn contact with thermistor S _TwoIs provided.

A guide plate G made of a metal material as a recording medium support is provided below the fixing belt B at a position below the fixing belt B from near the heating roller R ₃ to just before the nip portion N.
Distance between is disposed substantially parallel state and the fixing belt B in the range of 0.5 to 10 mm, extending substantially linearly toward the front of the nip portion N from the vicinity of the heating roller R ₃ between the fixing belt B, A heating path P for preheating the toner C ₁ and the recording medium C is formed.

The pressure roller R ₂ is pressurized toward the fixing roller R ₁ through pressure lever 9 by a pair of springs 8, the fixing pressure in the nip portion N is set to 66 kg. During operation, the fixing belt B is linearly moved toward the nip portion N between the fixing roller R ₁ and the pressure roller R ₂ from the heating roller R ₃ at a linear velocity of 100 mm / s, the recording medium C at this same speed Is fed into the heating passage P on the guide plate G by the transport means T, and the guide accumulating thermal energy with the fixing belt B when moving through the heating passage P on the guide plate G in a non-contact state with the fixing belt B. Preheated by plate G. As preferable heating conditions, the temperature of the heating roller R ₃ is 150 to 170 ° C., and the fixing belt B in the heating space P is
Temperature one hundred and forty-five to one hundred and sixty-five ° C., is set by the thermistor S ₁ such that the temperature one hundred and eight to one hundred and twenty-three ° C. of the pressure roller R ₂ at the nip portion N, the toner C for forming an unfixed image when moving heating passage P ₁ softens.

The fixing belt B, the toner because it is smaller the heat capacity, which is easily heated to a temperature necessary for fixing at the heating roller R ₃ moiety reaches the nip portion N, moves the fixing belt B at the same speed with C ₁ and the recording medium C is moved a heating passage P while being in contact with the guide plate G that heat storage, since it is pre-heated by radiant heat of the fixing belt B, melting at a temperature lower than the conventional state of the nip portion N And fixable.

At the time of fixing, the fixing belt B having a small heat capacity heated by the main heating source H ₁ transfers the heat to the toner C _1.
And the fixing belt B is cooled by applying it to the recording medium C, so that the temperature of the toner at the exit of the nip portion N becomes much lower than that in the case of the conventional roller fixing and the like, and the toner and the fixing belt B are separated. getting better separation of the mold layer B _2, fixed image without offset is obtained by the oil-less or trace oil coating.

The heat capacity per 1 cm ^{2 of the} fixing belt B is set in the range of 0.002 to 0.025 cal / ° C. Since low-temperature offset heat capacity that it follows the range is too small is likely to occur, should be set high temperature of the heating roller R _3, large thermal load against the fixing belt B, also becomes more than this range the thermal capacity Becomes too large, the temperature drop at the nip portion N is small, and a large amount of oil application is required to suppress the occurrence of high-temperature offset. The heat capacity per 1 cm ^{2 of the} fixing belt B is preferably 0.005 to 0.01 cal / ° C.

The heat capacity per 1 cm ^{2 of the} fixing belt B is
Specific heat (cal / ℃ · g) × Density (g / cm ³⁾ × thickness (c
m) × 1 (cm ² ), the heat capacity of the fixing belt B used in this embodiment is (heat capacity of 45 μm of Ni electroformed) + (silicone rubber 50 μm).
μm heat capacity) = (0.106 × 8.80 × 0.004)
5) + (0.26 × 1.05 × 0.005) ≒ 0.00
56 cal / ° C. and (heat capacity of polyimide 55 μm) + (silicone rubber 1
30 μm heat capacity) = (0.24 × 1.40 × 0.00)
55) + (0.26 × 1.05 × 0.013) ≒ 0.0
054 cal / ° C.

The surface hardness of the fixing roller R ₁ is determined by
Since than equal to ₂ in surface hardness or it is set soft, become a part of the pressing roller R ₂ bite into the fixing roller R ₁ together with the fixing belt B in the nip N, thus the nip N the tip direction of the recording medium C such as paper out is a downward pressure roller R ₂ side in less horizontally, separation claws of the fixing belt B side is not required (see FIG. 4).

[0024] In cold climates, etc., because it may interfere with the fixing performance and pressure roller R ₂ is too cold immediately after startup, in which case the heating in the auxiliary heat source H _2. The deviation of the fixing belt B is fixed in the fixing belt stepped portion 7 thickness and more comparable belt provided to the force of the heating roller R ₃ of offset generated in the nip portion N by utilizing the rigidity of the B Can withstand well.

EXPERIMENTAL EXAMPLE 1 A fixing device of the present invention having a structure as shown in FIG. 1 and having a fixing belt (Ni electroformed belt 45 μm + silicone rubber 50 μm) was used, and a Minolta camera CF- was used as toner. Using a 70 toner, the set temperature of each part of the apparatus was changed in multiple stages to fix the toner image on plain paper. Table 1 shows the results of the evaluation of the fixing performance. The following conditions were fixed. Linear velocity of fixing belt: 100 mm / s Pressure of pressure roller: 66 kg Distance between fixing belt and guide plate: 3 mm

[0026]

[Table 1]

[Experimental Example 2] A toner image was fixed on plain paper under the same conditions as in Experimental Example 1 except that the fixing device of the present invention equipped with a fixing belt of (polyimide 55 μm + silicone rubber 130 μm) was used. Table 2 shows the evaluation results of the fixing performance.

[0028]

[Table 2]

[Experimental Example 3] OHP was performed in the same manner as in Experimental Example 1.
The toner image is fixed to the paper, and the transmittance of the fixed image is measured.
The following results were obtained as compared with the fixing results obtained by using a −70 actual machine. The total transmittance was almost the same for roller fixing and belt fixing. The transmittance of each color was 2 to 3 times that of the roller fixing value for each color. Turbidity is 1 for belt fixing for each color.
/ 2. In other words, since the surface temperature of the belt and toner at the time of paper ejection is lower than that in the case of roller fixing and the cohesive force of the toner is strong, the toner is not pulled on the fixing belt and a smooth toner image surface is obtained. is there.

[0030]

As described above, according to the present invention, there is provided an endless fixing belt having a release layer on the surface of a belt mainly composed of a heat-resistant metal or resin having a high Young's modulus between a fixing roller and a heating roller. A pressure roller that stretches and presses the fixing roller from below via the fixing belt to form a nip portion between the fixing belt and the pressure roller, and an adjacent position below the fixing belt between the heating roller and the nip portion , A recording medium support is provided to form a substantially linear heating path between the fixing belt and the fixing belt, and the heat capacity per 1 cm ^{2 of} the fixing belt is 0.002.
0.025 cal / ° C., so that in addition to lowering the fixing temperature at the nip due to the preheating effect in the heating passage, the toner temperature is excessively increased due to the self-cooling action at the nip of the fixing belt having a small heat capacity. The releasability from the fixing belt can be improved without increasing the quality of the image, and a fixed image without offset can be obtained by applying an oil-less or trace amount of oil.

[Brief description of the drawings]

FIG. 1 is a side view of an embodiment of a fixing device for an electrophotographic apparatus according to the present invention.

FIG. 2 is a front view of the heating roller in the above.

FIG. 3 is an enlarged sectional view of the fixing belt in the same.

FIG. 4 is an enlarged view showing an operation of a nip portion.

FIG. 5 is an explanatory diagram of a conventional example.

FIG. 6 is an explanatory diagram of another conventional example.

FIG. 7 is an explanatory view of still another conventional example.

[Explanation of symbols]

R ₁ fixing roller R ₂ pressure roller R ₃ heating roller B fixing belt B ₁ belt main body B ₂ release layer G guide plate P heating passage

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-263677 (JP, A) JP-A-2-162383 (JP, A) JP-A-4-50883 (JP, A) JP-A-4-263 122969 (JP, A) JP-A-4-186270 (JP, A) JP-A-4-273274 (JP, A) JP-A-5-11651 (JP, A) JP-A-6-202527 (JP, A) JP-A-6-230599 (JP, A) JP-A-6-295091 (JP, A) JP-A-61-13862 (JP, U) JP-A-2-140555 (JP, U) JP-A-4-124267 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) G03G 15/20

Claims (1)

(57) [Claims] An endless fixing belt having a release layer on the surface of a belt main body is stretched between a fixing roller and a heating roller,
A pressure roller that presses the fixing roller from below through the fixing belt is provided to form a nip portion between the fixing belt and the pressure roller, and a nip portion is provided between the heating roller and the nip portion below the fixing belt. A recording medium support is provided in the vicinity of the fixing belt to form a substantially linear heating passage between the fixing belt and the fixing belt, and the heat capacity per 1 cm ^{2 of the} fixing belt is 0.00
A fixing device for an electrophotographic apparatus, wherein the fixing device has a temperature of 2 to 0.025 cal / ° C.