JPH0314351B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a fixing device for a copying machine or the like using an electrophotographic process, and particularly to a heating roll type heat fixing device.

[Conventional technology]

Generally, a copying machine using an electrophotographic process is provided with a fixing device that fixes an unfixed toner image on a sheet of paper, and a so-called heated roll type fixing device is widely used as an example of this fixing device.

Conventionally, this type of heat fixing device includes, for example, a heated heating roll a and a pressure roll b that is in pressure contact with the heating roll a and rotates together with the heating roll a, as shown in FIG. 2, for example. By inserting the paper d holding the unfixed toner image c between the pair of rolls a and b, the heating roll a
The unfixed toner image c is fixed on the paper d by applying the heat from the toner and the pressure from the pressure roll b to the toner and the paper d.

In this type, the heating roll a is fitted with a shaft (not shown), for example, and has a cylindrical core e made of metal or the like having mechanical strength that can withstand pressure.
and a heater f disposed inside this cylindrical core e.
and a material that satisfies heat resistance, toner release properties, etc.
For example, HTV silicone rubber (High
Temperature Vulcanization Silicone
and a heat-resistant release layer g formed by coating the surface of the cylindrical core e with polytetrafluoroethylene (PTFE) or polytetrafluoroethylene (PTFE).

On the other hand, the pressure roll b is composed of, for example, a shaft h and an elastic layer fitted onto the shaft h, and when it comes into contact with the heating roll a, it forms a predetermined fixing nip and has heat resistance, etc. Satisfied materials,
Specifically, HTV silicone rubber, fluoro rubber,
EPDA rubber (Ethylene Propylene Diene Acryl)
The elastic layer is formed of a heat-resistant elastic material such as rubber.

By the way, in such a heat fixing device, the toner surface of the paper d comes into direct contact with the surface of the heating roll a, so the sticky nature of the softened toner causes the paper d to wrap around the surface of the heating roll a. bring about a situation. In order to prevent such a situation, a device for peeling off the paper d wrapped around the surface of the heating roll a is usually required.

Conventionally, this type of paper peeling device has a plurality of peeling claws i made of metal or heat-resistant plastic along the length of the heating roll a, as shown in FIG. The base of a peeling claw i with a sharp tip is pivotally supported on a support part (not shown), and the tip of the peeling claw i is pressed against the surface of the heating roll a with a load of several grams to several tens of grams using a biasing spring j or the like. This is what I did.

According to this type, the tip of the peeling pawl i does not lift up from the heating roll a even when the heating roll a rotates or the paper d hits the tip of the peeling pawl i, and the peeling pawl i is stably arranged. has been done. Therefore, the paper d that is being conveyed wrapped around the surface of the heating roll a is effectively peeled off by the tip of the peeling claw i, guided by a guide member k disposed near the peeling claw i, and guided by the discharge roll l.
They are led to the side.

[Issues that the invention attempts to solve]

However, in such a conventional paper peeling device, the sharp tip of the peeling claw i is in pressure contact with the surface of the heating roll a, so that the heat-resistant release layer g of the heating roll a is Since the tip edge is scraped, the heating roll a wears out relatively quickly, which causes a decrease in the durability of the heating roll a.

The above-mentioned tendency is particularly noticeable in the heating roll a using an elastic material such as HTV silicone rubber as the heat-resistant release layer g.

On the other hand, the tip itself of the peeling claw i is also worn and becomes rounded, which is a cause of deterioration of the durability of the peeling claw i.

Therefore, the inventor of the present invention used a heat fixing device equipped with a heating roll a, and as a result of extensive research to solve the above problems, the inventor found that the cause of the paper d being wrapped around the heating roll a during fixing is as follows. It has been found that in addition to the adhesive force of the toner, the adsorption force that acts between the heating roll a and the paper d is also one of them.

In other words, in the nip area between heating roll a and pressure roll b, the air interposed between the surface of heating roll a and paper d is expelled by the pressure action of both rolls a and b, creating a vacuum state. This is because an adsorption force acts between the roll a and the paper d, and due to this adsorption force, the paper d is adsorbed and wound around the heating roll a even if the pressure is released after the nip area.

This adsorption force is determined by the surface roughness of the heating roll a, that is, the surface roughness of the heat-resistant release layer g, and the paper d.
When ordinary paper is used, the average surface roughness of heating roll a
It has also been found that when the value of Ra is 0.3 μm or less, it becomes greater than the adhesive force of the toner.

The present invention was completed based on the results of such research, and its object is to make the surface roughness of the pressure roll smaller than that of the heating roll so that the pressure roll acts between the pressure roll and a sheet such as paper. It is an object of the present invention to provide a heat fixing device in which the adsorption force is made larger than the adsorption force acting between the heating roll and the sheet and the adhesive force of the toner, thereby preventing the sheet from wrapping around the heating roll.

[Means to solve the problem]

That is, the present invention includes a heating roll coated with a heat-resistant release layer and heated by a heat source, and a pressure roll coated with a heat-resistant elastic layer, and unfixed particles are formed between these rolls that rotate while being in pressure contact with each other. Assuming a heat fixing device that fixes the unfixed toner image by inserting the sheet on which the toner image has been formed with the unfixed toner image side toward the heating roll side, the heat-resistant elastic layer of the pressure roll is heated. It is characterized in that it is made of a heat-resistant elastic material whose average surface roughness Ra is smaller than the surface roughness of the heat-resistant release layer in the roll and is 0.3 μm or less.

Generally, pressure rolls are manufactured by polishing the surface of a heat-resistant elastic material, but it is difficult to reduce the average surface roughness Ra of the roll surface to 0.3 μm or less using this polishing method.

Therefore, the pressure roll used in the present invention is
A thin film layer of a heat-resistant mold release agent is further formed on the surface of the roll finished by the polishing method by spraying or dipping to reduce the average surface roughness Ra.
0.3μm or less or surface roughness
By using a molding method in which a roll mold with a diameter of 0.3 μm or less is used and a heat-resistant material such as HTV silicone rubber is poured into the mold and cured, the average surface roughness Ra of the roll after molding can be reduced to 0.3. It was obtained with a size of less than μm.

[Effect]

According to the above-mentioned technical means, the heat-resistant elastic material layer of the pressure roll is a heat-resistant elastic material whose surface roughness is smaller than that of the heat-resistant release layer of the heating roll and whose average surface roughness Ra is 0.3 μm or less. The adsorption force that acts between the sheet and the pressure roll covered with the heat-resistant elastic layer is the adsorption force that acts between the sheet and the heating roll covered with the heat-resistant release layer, as well as the adhesion of the toner. Since the force is larger than the force, the sheet is attracted to the pressure roll side, making it possible to prevent the sheet from being wrapped around the heating roll.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG.
and peeling members 3 and 4 disposed near the paper discharge side of each roll 1 and 2.

First, the heating roll 1 consists of a cylindrical core metal 5 with a diameter of 40 mm and a length of 350 mm, which is rotatably supported in the direction of arrow A by power (not shown), the surface of the core metal 5 is coated with a wall thickness of 0.35 mm, and the core metal 5 is polished. Average surface roughness by method
It consists of a heat-resistant release layer 6 made of RTV silicone rubber whose Ra value is adjusted to 1.2 μm, and a heater 7 for heating the surface of the heating roll 1 is disposed within the core bar 5, as shown in the figure. The surface temperature of the heating roll 1 is controlled at 180° C. by a temperature controller (not shown), and an appropriate amount of silicone oil is supplied to the surface by an oil supply device (not shown).

On the other hand, the pressure roll 2 is provided below the heating roll 1, and has a diameter of 25 mm like the heating roll 1.
It consists of a cylindrical core bar 8 with a length of 320 mm, and a heat-resistant elastic layer 9 of HTV silicone rubber that covers the surface of the core bar 8 with a wall thickness of 8 mm. A load of 40 kg is applied between the heating roll 1 and the pressure roll 2 by a mechanism not shown in the drawings. A nip is formed.

The heat-resistant elastic layer 9 of the pressure roll 2 is manufactured by a molding method, and its average surface roughness is
The value of Ra was adjusted to 0.1 μm.

Also, on the paper ejection side of heating roll 1, a thickness of 0.15
Three peeling members 3 made of stainless steel plates with a width of 10 mm and a length of 15 mm are arranged at approximately equal intervals along the length of the heating roll 1, and each tip is 0.5 mm from the surface of the heating roll 1. are placed apart.

On the other hand, on the paper exit side of the pressure roll 2, four identical peeling members 4 are arranged at approximately equal intervals along the length direction of the pressure roll 2, and each tip is separated by a mechanism (not shown). The heat fixing device according to the embodiment is constructed by pressing the pressure roller 2 onto the surface thereof with a load of 10 g.

Next, to explain the operation of the heat fixing device according to the embodiment, as shown in FIG.
The toner is inserted between the pressure rolls 2 and 2, and the toner is melted by heat transfer from the heating roll 1, poured into the fibers of the paper 11, cooled, and fixed.

At this time, the paper 11 normally tends to wrap around the heating roll 1 side due to the adhesive force of the toner, but in the heat fixing device according to the embodiment, the pressure roll 1
The average surface roughness Ra of the heat-resistant elastic layer 9 in the heating roll 1 is 0.1 μm, which is smaller than the average surface roughness Ra of the heat-resistant release layer 6 in the heating roll 1, which is 1.2 μm. Since the suction force acting between the pressure rolls 2 is larger, the paper 11
has a strong tendency to be adsorbed to the pressure roll 2 side.

Therefore, the leading edge of the paper 11 is connected to the heating roll 1.
Since the sheet 11 is discharged floating above the surface, the paper 11 can be smoothly peeled off from the heating roll 1 even if the tip of the peeling member 3 is not in pressure contact with the heating roll 1.

Therefore, in the heat fixing device according to the embodiment, there is no need to press the release member 3 against the surface of the heating roll 1, and wear of the heat-resistant release layer 6 of the heating roll 1 and the release member 3 can be prevented. Durability can be significantly improved.

Note that if the adsorption force acting between the paper 11 and the pressure roll 2 is significantly greater than the adhesive force of the toner, the paper 11 will wrap around the pressure roll 2. Therefore, in the heat fixing device according to the embodiment, The tip of the peeling member 4 disposed on the pressure roll 2 is brought into pressure contact with the surface of the pressure roll 2 to prevent it from being wrapped around the pressure roll 2.

Therefore, the heat-resistant elastic layer 9 of the pressure roll 2 wears out due to contact with the peeling member 4, but the thickness of the heat-resistant elastic layer 9 of the pressure roll 2 is usually smaller than the heat-resistant release layer 6 of the heating roll 1. Moreover, since the heat-resistant elastic layer 9 contacts only the back side of the paper 11, even if the heat-resistant elastic layer 9 is slightly abraded, it will not adversely affect copy image quality.

Therefore, compared to conventional heat fixing devices, the interval between replacing the roll or the peeling member 4 can be extended, and maintenance management thereof can be significantly reduced.

Here, using this heat fixing device, copy paper without toner, copy paper with an unfixed toner image, and special paper with excellent smoothness such as coated paper or art paper are inserted. When we examined the peeling state of each paper, we found that copy paper without toner had a strong tendency to wrap around the pressure roll 2 side, whereas copy paper with a toner image had less of this tendency. It was confirmed that the leading edge of the paper was lifted off the surface of the heating roll 1 when it was ejected.

On the other hand, regarding the special paper, it was confirmed that the adsorption force with the pressure roll 2 was significantly increased, and there was no tendency for the paper to wrap around the heating roll 1 side at all.

〔Effect of the invention〕

According to the present invention, the adsorption force acting between the sheet and the pressure roll covered with the heat-resistant elastic layer is equal to the adsorption force acting between the sheet and the heating roll covered with the heat-resistant release layer, as well as the adhesion force of the toner. Since the size of the sheet is larger, the sheet is adsorbed to the pressure roll side, thereby making it possible to prevent the sheet from being wrapped around the heating roll.

Therefore, it is no longer necessary to press the tip of the peeling member against the surface of the heating roll as in the past, so the heat-resistant release layer and peeling member of the heating roll are less likely to wear out, reducing the replacement life of the heating roll and peeling member. It becomes possible to extend the length significantly, and has the effect of improving the stability of the heat fixing device.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of a heat fixing device according to an embodiment of the present invention, and FIG. 2 is a side sectional view of a conventional heat fixing device. Description of symbols, 1... Heating roll, 2... Pressure roll, 3, 4... Peeling member, 5, 8... Core bar, 6...
...Heat-resistant release layer, 7...Heater, 9...Heat-resistant elastic layer, 10...Unfixed toner image, 11...Paper.

Claims (1)

[Claims] 1. A heating roll coated with a heat-resistant mold release layer and heated by a heat source, and a pressure roll coated with a heat-resistant elastic layer, and between these rolls rotating while being pressed against each other. In a heat fixing device that fixes the unfixed toner image by inserting the sheet on which the unfixed toner image is formed with the unfixed toner image side toward the heating roll side, the heat-resistant elastic layer of the pressure roll is heated. 1. A heat fixing device comprising a heat-resistant elastic material having an average surface roughness Ra of 0.3 μm or less, which is smaller than the surface roughness of a heat-resistant release layer in a roll.