JPH04337779A - Pressure roller and fixing device - Google Patents

Abstract

PURPOSE:To prevent a paper with high smoothness and an OHP sheet from winding about a pressure roller by providing a projection on the surface of the pressure roller whose hardness is low. CONSTITUTION:The pressure roller 2 having projections at several spots on its external side press-contacts with a heating roller 1 and is rotated by following the rotation of the roller 1. A nip part is formed at a pressuring part because the roller 2 is deformed, and toner 11 is fixed on a recording material 8 by heat and pressure. At the part of the roller 2 other than the nip part, the recording material 8 contacts with the roller 2 only in the small area of the material 8 and the projection. Thus, the attracting force between the roller 2 and the recording material 8 becomes weak and the recording material 8 does not wind about the pressure roller.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to paper peeling of a fixing roller used in an electrophotographic apparatus or the like.

0002

[Prior Art] Conventionally, a sheet of paper onto which a toner image has been transferred from a photoreceptor is passed between a pair of rollers and fixed by heat and pressure.
The fixing device generally consists of a heating roller and a pressure roller, and the heating roller is made of PTFE on the surface of an aluminum tube.
, PFA, or other so-called Teflon. A halogen lamp is also installed as a heat source. The other pressure roller is an elastic material, that is, a rubber roller, and because it requires stable physical strength at high temperatures, silicone rubber is generally used. However, recently, in order to perform double-sided printing on envelopes, the hardness of the pressure roller has been lowered to prevent wrinkles, and the paper has a two-layer structure. In order to reduce the hardness, the first layer is made of foamed rubber like a sponge, and the second layer is covered with a Teflon tube or RTV type silicone rubber. The thickness is about 50 μm to 300 μm, and the hardness is about Hs 40 to 65°, but the relative hardness is low and wrinkles of the envelope and paper wrinkles do not occur during double-sided printing. However, a phenomenon occurs in which thin paper, OHP sheets, etc. get wrapped around the pressure roller. This is because the surface of the pressure roller is highly smooth, so especially for highly smooth objects such as OHP sheets, the suction force becomes strong and the sheet gets wrapped around. Therefore, Japanese Patent Application No. 63-181229 and Japanese Patent Application No. 63-181
As shown in the illustration of No. 3-181230, peeling claws are provided on both the heating roller and the pressure roller to prevent the rollers from being wrapped around each other. Also, by applying silicone oil, it prevents offset and wrapping around the roller.

0003

[Problems to be Solved by the Invention] The above-mentioned prior art requires a peeling claw and an oil application device, making it expensive. There also arises a problem in maintainability. Further, the provision of a peeling claw causes problems such as damage to the roller and staining of the image due to toner adhering to the claw.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a fixing device that has a simple configuration and can prevent wrapping around a pressure roller.

[0005]

[Means for solving the problem] In order to achieve the above object, the outer diameter of the pressure roller is partially increased to reduce the contact area between the pressure roller and paper (including OHP sheets) after passing through the roller. By reducing the amount, wrapping around the pressure roller can be prevented. Further, by setting the position of the pressure roller with the large outer diameter at the optimum position depending on the paper size, the paper can be peeled off effectively. Furthermore, the difference in the outer diameter of the pressure roller is set to 0.
By setting the thickness to 3 to 4.0 mm, it is possible to reduce variations in fixing strength and to achieve both paper peeling. As an application example, by arranging each roller so that the axis of the heating roller and the axis of the pressure roller intersect at the center, the paper enters the nip section diagonally and is ejected. Since the paper is ejected from the edge of the paper, the area in contact with the pressure roller is small, and the elasticity of the paper makes it easier to peel off from the pressure roller.

[0006]

[Operation] Therefore, by reducing the contact area between the paper discharged from the fixing roller and the pressure roller, the elasticity of the paper prevents the paper from wrapping around.

[0007]

[Embodiments] Hereinafter, embodiments of the present invention will be explained with reference to the drawings. FIG. 1 shows a sectional view of a fixing device according to the present invention. Reference numeral 1 applies a Teflon coating to the surface of an aluminum tube using a heating roller, and a halogen lamp 3 serving as a heat source is held in the center from both ends. 2 is a pressure roller, and LTV type silicone rubber with a rubber hardness of Hs 10° is formed on the outer periphery of the core bar in the center, and a PF film with a thickness of 150 μm is formed on the outer periphery.
It covers the A tube. The pressure roller 2 is brought into pressure contact with the heating roller 1 by a roller receiving fitting 4 and a push spring 5, and rotates in sliding contact with the heating roller 1. 6 controls the temperature of the outer peripheral surface of the heating roller 1 with a thermistor. Reference numeral 7 denotes a peeling claw for preventing the recording material 8 from being wrapped around the heating roller 1, and applies slight pressure to the heating roller 1 by a tension spring 9.

Reference numeral 10 denotes a guide plate for guiding the recording material 8 between the rollers. 11 indicates toner.

In the above configuration, when the recording material 8 carrying a toner image is passed between the rollers, it generally curls toward the hot roller 1, but unlike an OHP sheet, it is highly smooth and absorbs moisture. The smoother the surface of the pressure roller 2, the more difficult the recording material 8 is to be sucked in and wound around the roller. Therefore, as shown in FIG.
A plurality of convex portions 2a are provided on the surface of the OHP sheet to reduce the contact area with the OHP sheet, thereby weakening the suction force and preventing wrapping. Also, the pressure roller 2 shown in FIG.
Convex portions 2a are provided at several locations on the outer periphery of the OHP sheet to reduce the contact area between the OHP sheet after fixing and the pressure roller 2 to prevent wrapping. In addition, the gap between the convex portions 2a has an efficient position depending on the size of the recording material 8, and is 210 m for A4 size.
In the case of a width of m, it is preferable that the convex portions 2a are set at the center of the paper and at a position of ±50 to 70 mm from the center of the paper to the left and right. In other words, three convex portions 2a are optimal. Furthermore, when supporting up to A3, it is better to add two additional locations at positions of ±50 to 70 mm. Next, the height h of the convex portion 2a varies depending on the hardness of the rubber, but is optimally in the range of 0.3 to 4 mm. If the height is too high, the nip portion will be non-uniform and some areas will not be fixed, and if the height is too low, the adhesion to the pressure roller 2 will be poor, causing wrapping.

FIG. 4 shows an example of application, in which the axis of the heating roller 1 and the axis of the pressure roller 2 are installed so that they intersect at the center of the rollers, and as shown in FIG. By being discharged from the corner portion of No. 8, the corner portion is more easily peeled off than the pressure roller 2.

[0011]

According to the present invention, highly smooth OHP sheets, thin paper, and the like can be highly reliable without being wrapped around the pressure roller, and the structure is simple and inexpensive.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a fixing device showing an embodiment of the present invention.

FIG. 2 is a perspective view of a pressure roller of the present invention.

FIG. 3 is a perspective view of a pressure roller showing an application example.

FIG. 4 is an explanatory diagram showing the axes of a heating roller and a pressure roller.

FIG. 5 is a perspective view of paper being ejected from between the rollers.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Heat roller, 2... Pressure roller, 2a... Convex part, 3... Halogen lamp, 8... Recording material.

Claims (4)

[Claims] [Claim 1] A heating roller having a heat source and a pressure roller that is in pressure contact with the heating roller are provided, a recording material carrying a toner image is passed between the rollers, and the toner image is transferred onto the recording material using heat and pressure. A pressure roller in a fixing device for fixing, characterized in that an uneven portion is provided on an outer circumferential surface of the pressure roller. 2. The pressure roller according to claim 1, wherein the outer diameter of a plurality of locations on the outer circumference of the pressure roller is increased by 0.3 mm to 4 mm. 3. The heating roller according to claim 1, wherein the position of the outer peripheral protruding portion is provided corresponding to each paper size.
Pressure roller as described. 4. A fixing device characterized in that each roller is arranged so that the axis of the heating roller and the axis of the pressure roller according to claim 1 intersect at the center.