JP2908478B2 - Fixing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a roller fixing device.

(Prior Art) As one of fixing devices for fixing a toner image formed on a paper to be fixed (transfer paper) by electrophotography, there is a fixing device including a pair of rollers which are pressed against each other and rotated. In FIG. 1, a transfer paper 5 on which a toner image is formed is guided by a guide plate 4 and fed between a fixing roller 2 and a pressure roller 3. The fixing roller 2 has a heat source inside, and its outer surface is formed of an elastic layer such as rubber.
The fixing roller 2 comes into contact with the toner image forming surface of the transfer paper, and a so-called offset phenomenon occurs in which the molten toner is transferred to the peripheral surface of the roller. In order to avoid this, an anti-offset liquid supply roller 1 is pressed against the surface of the fixing roller 2 so that an appropriate amount of an anti-offset liquid such as silicon oil stored in this roller is applied. I have. The anti-offset liquid of the anti-offset liquid supply roller 1 is supplied as the fixing roller 2 rotates. The outer diameter of the anti-offset liquid supply roller 1 is equal in the axial direction, and both ends thereof are pressed against the fixing roller 2 by being pressed with equal pressure.

(Problems to be Solved by the Invention) However, the conventional anti-offset liquid supplied in a press-contact manner between the anti-offset liquid roller and the fixing roller is uniformly supplied in the axial direction of the fixing roller. by the way,
The fixing roller has a length that allows the maximum usable transfer paper to pass through. Then, when the small-sized transfer paper to be fixed is continuously passed, the offset preventing liquid in the portion through which the transfer paper passes adheres to the transfer paper and is consumed, but in the portion through which the transfer paper does not pass. Since the offset prevention liquid is not consumed, it is accumulated on the surface of the fixing roller, and when a large-size transfer sheet is passed, there is a problem that a large amount of this prevention liquid adheres to the paper and impairs copy quality. As a measure to cope with this, a member such as a blade or a felt is brought into contact with the end of the fixing roller to scrape off the excess offset prevention liquid. Have left.

Accordingly, an object of the present invention is to provide a fixing device capable of supplying an appropriate amount of an offset preventing liquid without causing a scraping member to contact a fixing roller.

(Means for Solving the Problems) A fixing device to which the present invention is applied is a fixing device comprising a pair of rollers which rotate while being pressed against each other. An anti-offset member for supplying a liquid to the surface of the fixing roller, and a first pressure application for pressing a reference end of the anti-offset member located on the reference side of the conveyance path of the sheet to be fixed against the fixing roller with pressure P1. Means, and a second pressure applying means for pressing the non-reference end opposite to the reference end of the offset prevention member to the fixing roller with a pressure P2, wherein the pressure P1 is larger than the pressure P2. It is characterized by having done.

(Operation) When the pressure for pressing the offset preventing liquid supply roller against the fixing roller is changed, a relatively large amount of the offset preventing liquid is supplied to the end of the fixing roller located on the reference side of the transfer path of the transfer sheet. Since the amount of the preventive liquid is always carried away by the transfer paper that is passed through and supplied to the end opposite to the reference side, the preventive liquid does not become excessively supplied over the entire length of the roller.

Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

Offset prevention liquid supply roller 1A shown in FIG.
Has a tapered structure suitable for transporting the transfer paper by a center reference method using the center of the fixing roller 2 (see FIG. 1) in the axial direction as the reference for transporting the transfer paper. That is, the offset prevention liquid supply roller 1A has an outer diameter of a central portion 1Aa that is a reference of the transport path as D1, and an outer diameter of both ends 1Ab and 1Ab farthest from the reference side as D2, D1> D2
The outer diameter is finished so that In other words, the offset prevention liquid supply roller 1A is
It is formed in a tapered outer shape that gradually becomes narrower from a toward both ends. When a uniform pressure is applied to both ends of the offset prevention liquid supply roller 1A to press the fixing roller 2 against the fixing roller 2, the portion where the two rollers come into contact, the so-called nip shape 1A2, becomes as shown in FIG. 4 (a). In addition, the width of the central portion is wide and gradually narrows toward both ends.

Offset prevention liquid supply roller 1B shown in FIG. 2 (b)
This is also a tapered external structure suitable for transferring the transfer paper by the center reference method. In the roller 1B, a predetermined length portion of the central portion 1Ba in the axial direction has an outer diameter D1, and both ends of the central portion 1Ba gradually become thinner toward both end portions 1Bb, 1Bb of the outer diameter D2 (<D1). It has a tapered shape. In this case, the shape of the nip portion is denoted by reference numeral in FIG.
As shown by 1B2, the width of the central portion, which is the reference side, is wide over a predetermined length, and gradually narrows toward both end portions away from the reference side.

Next, the offset prevention liquid supply roller shown in FIG.
The transfer path of the transfer paper is based on one side, and the offset prevention liquid supply roller 1C shown in FIG. 3A has the outer diameter of one end 1Ca on the reference side as D1 and is furthest from the reference side. When the outer diameter of the other end 1Cb is D2, its outer dimensions are finished so that D1> D2. In other words, the offset prevention liquid supply roller 1C is moved from one end 1Ca to the other end 1Ca.
It is formed in a tapered shape that gradually becomes thinner toward Cb. When an even pressure is applied to both ends of the offset prevention liquid supply roller 1C and the offset prevention liquid supply roller 1C is pressed against the fixing roller 2,
As shown in FIG. 5 (a), the shape 1C2 of the nip gradually narrows from the reference end to the other end.

Offset prevention liquid supply roller 1D shown in FIG. 3 (b)
This is also a tapered structure suitable for transferring transfer paper in a one-sided reference system. This roller 1D has a reference end 1Da
Is the outer diameter D1 and the outer diameter D2 from the end.
(<D1) has a tapered shape that gradually narrows toward the other end 1Db. In this case, as shown by reference numeral 1D2 in FIG. 5B, the shape of the nip portion is such that the width on the reference side is wide over a predetermined length and becomes gradually narrower as the distance from the predetermined length portion increases.

As described above, when the outer shape of the offset prevention liquid supply roller is formed in a tapered shape, the nip portion when pressed against the fixing roller has a wider width on the reference side of the transfer path of the transfer paper and gradually narrows as the distance from the reference side increases. Therefore, the amount of the anti-offset liquid supplied to the fixing roller increases on the reference side and decreases as the distance from the reference side increases. Therefore, even if the transfer paper smaller in size than the maximum usable transfer paper is continuously passed, the offset preventing liquid does not accumulate on the peripheral surface of the fixing roller remote from the reference side.

Next, FIG. 6 shows another embodiment of the present invention. The outer diameter of the offset prevention liquid supply roller 1E is formed to be equal over the entire length. Both ends of the roller 1E are rotatably supported by bearings 10 and 11. Pressures are applied to the bearings 10 and 11 by the pressure applying means 12 and 13 so as to press the offset preventing liquid supply roller 1E against the fixing roller 2. When the end supported by the bearing 10 is set as the reference side, between the pressure P1 by the pressure applying means 12 and the pressure 2 by the pressure applying means 13 pressing the bearing 11 farther from the reference side. , Each pressure applying means is configured so that the relationship of P1> P2 is satisfied. When such a pressure is applied to the offset preventing liquid supply roller 1E, the nip formed between the roller and the fixing roller 2 has a shape 1E2 shown in FIG.
, The width gradually decreases from the reference side to the non-reference side. Therefore, the amount of the offset prevention liquid supplied to the fixing roller 2 is large on the reference side and decreases as the distance from the reference side increases. Therefore, even if the transfer paper smaller in size than the maximum usable transfer paper is continuously passed, the offset preventing liquid does not accumulate on the peripheral surface of the fixing roller remote from the reference side.

(Effect of the Invention) As described above, according to the present invention, the supply amount of the offset preventing liquid can be reduced as the distance from the reference side of the transfer path of the transfer paper is reduced, and the small-size transfer paper can be continuously passed. Even if the paper is used, the offset prevention liquid does not remain excessively. Even if a large-sized transfer paper is subsequently passed, a large amount of the offset prevention liquid does not adhere to the transfer paper, and the copy quality is not impaired.

[Brief description of the drawings]

FIG. 1 is a schematic structural view of a fixing device to which the present invention is directed, and FIG.
FIGS. 3 and 3 are front views showing only the anti-offset liquid supply roller according to different embodiments of the present invention. FIGS. 4 and 5 are views showing the shape of a nip formed by the roller and the fixing roller. FIG. 6 is a front view showing another embodiment of the present invention. 1 ... Offset prevention liquid supply roller, 2 ... Fixing roller.

Claims (1)

(57) [Claims] A fixing device comprising a pair of rollers which rotate while being pressed against each other, wherein an offset preventing member which is pressed against a surface of the fixing roller and supplies an offset preventing liquid stored therein to the surface of the fixing roller. First pressure applying means for pressing a reference end of the offset prevention member, which is located on the reference side of the conveyance path of the sheet to be fixed, to the fixing roller with pressure P1, and the reference end of the offset prevention member. A second pressure applying means for pressing a non-reference end opposite to the fixing roller to the fixing roller with a pressure P2, wherein the pressure P1 is larger than the pressure P2.