JPH01142779A - Heat fixing device - Google Patents

Abstract

PURPOSE:To prevent wrinkling of a toner image carrier by forming a heating roll and press roll to such surface hardness at which the nip part thereof is flattened and providing a prescribed crown to at least one of these rolls. CONSTITUTION:The press roll 1 and the heating roll 2 are constituted respectively by laminating heat resistant elastic material layers 12, 22 and releasable resin layers 12, 24 on arbors 11, 21. The rolls 1, 2 are formed to have the same outside diameter and such surface hardness at which the nip part 3 is flattened. The crown of <=2 times the quantity of the deflection generated when the rolls are brought into pressurized contact with each other by a prescribed pressure is provided on at least one roll. The roll 2 is preferably on a driving side and the crown is preferably provided to the roll 1. The difference in the surface hardness between the two rolls is preferably <=15 deg. Hs and the surface hardness of the two rolls is preferably <=85 deg. Hs.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to an image forming apparatus such as an electrophotographic apparatus or an electrostatic printing apparatus, in which a toner image formed on a carrier such as a toner image is heated on at least one side. The device relates to a heat fixing device that performs fixing between a pair of rolls that rotate in pressure contact with each other, and is capable of preventing wrinkles not only for V-passing paper but also for multi-layer paper carriers such as envelopes. The present invention relates to a heat fixing device that has been improved so as to be able to fix toner images without causing the occurrence of.

[Conventional technology]

The fixing device in an image forming apparatus is a heating roll made of a metal core with good thermal conductivity, which is equipped with a heat source such as an infrared lamp, halogen lamp, or nichrome wire, and coated with a non-adhesive heat-resistant layer. 2. Description of the Related Art A heat roll type heat fixing device is known in which a pressure roll whose surface is coated with a heat-resistant elastic layer is disposed facing each other.

FIG. 6 is a side view of essential parts showing an example of the conventional heat fixing device. In the figure, reference numerals 1 and 2 denote a pressure roll and a heating roll, which are formed so that their axes are substantially parallel and rotatable in the direction of the arrow, and one roll is arranged in pressure contact with the other rolls. In the conventional type, for example, the pressure roll 1 has a heat-resistant elastic layer 12 made of silicone rubber with a hardness of about 25 to 55 inches on the surface of a core metal 11 made of a material with good thermal conductivity such as aluminum alloy or iron. On the other hand, the lump heat roll 2 is coated with tetrafluoroethylene resin (P
It is coated with a releasable resin layer 24 made of a low surface energy resin such as TFE) or perfluoroalkoxy resin (PFA). Therefore, due to the difference in elasticity between the two rolls, the surface of the pressure roll 1 is elastically deformed to form a concave surface at the nip 3 between the pressure roll 1 and the heating roll 2, as shown in FIG.

In the above heat fixing device, when fixing a toner image formed on a carrier (not shown).

First, power is supplied to the heat source 23 to heat the surface of the heating roll 2 to a temperature required for fixing, and the heating roll 2 and pressure roll 1 are brought into pressure contact with each other with an appropriate pressure and rotated to release the carrier carrying the toner image. By passing the toner image in the direction A between both rolls, the toner image can be fixed on the carrier.

On the other hand, as a means of displaying addresses on a large number of envelopes.

Printing directly on envelopes using a printer is being considered. The problem here is that wrinkles occur when the envelope carrying the toner image is fed to the above-described heat fixing device to fix the toner image. When wrinkles occur on an envelope, not only does the envelope become curved or deformed, but the printed address is divided by the wrinkles, and in extreme cases, there are problems such as making it impossible to decipher or read the envelope. That is, an envelope has at least a two-ply part due to its structure, and depending on the part or the overlapped part, the gluing can be triple or quadruple, which increases the maximum paper thickness and causes mutual sliding movement in the two-ply part. The above problem is a unique phenomenon caused by such sliding movement, and is a problem that is not experienced in normal copying.

Considering the causes of paper wrinkles as described above, first of all, as shown in FIG. is forming. For this reason, when a carrier (not shown) such as a toner image carrying member is fed in the direction of arrow A, the carrier is first bent at the entrance 3a of the nip portion 3 with its upper side concave.

Next, it is bent at the nip portion 3 with the lower side concave, and further bent again at the outlet 3b of the nip portion 3 so that the upper side is concave. On the other hand, when the carrier has double or more overlapping parts like an envelope, the repeated bending action of the two-pronged part 3 may cause sliding movement between the upper and lower constituent parts, or the difference in paper thickness may result. It is presumed that the difference in moving speed also causes a speed difference between the upper and lower portions of the envelope, causing wrinkles.

Various structures have been proposed to prevent the above-mentioned paper wrinkles. For example, Utility Model Publication No. 54-98226
No. 15818) discloses that even FG-type copy paper can be prevented from curling and wrinkling by bringing a heating roll and a pressure roll into light pressure contact and by making the pressure deformation rates of both rolls the same or similar. There is. Also, JP-A-59-745
No. 78 has a core material to prevent wrinkles even under adverse conditions such as double-sided copying.

It is disclosed that a roll consisting of a heat-resistant elastic layer covering the heat-resistant elastic layer and a fluororesin layer coated thereon is used as both a heating roll and a pressure roll.

Furthermore, in the case of envelope fixing, a method has been proposed in which the fixing pressure is lower than the fixing pressure suitable for fixing plain paper (Japanese Patent Laid-Open No. 61-294475).

[Problem that the invention seeks to solve]

When fixing the toner image formed on the envelope.

The above-mentioned conventional techniques cannot achieve the fully satisfactory result 5, that is, prevent wrinkles while ensuring good fixing performance. That is, according to the invention described in JP-A No. 61-294475, it is possible to prevent wrinkles, but
Since the fixing pressure becomes low, good fixing performance cannot be obtained. Furthermore, the device described in Utility Model Application Publication No. 54-98226 has a structure in which both rolls are brought into "light pressure contact" in order to equalize or approximate the amount of deformation of the pressure contact portion of both rolls, so that sufficient fixing performance can be obtained. With the problem of not having one. Furthermore, in the apparatus described in JP-A-59-74548, the thickness of the elastic layer of the heating roll and the elastic layer of the pressure roll are different.

Under severe conditions where a substantially planar nip is not formed and the toner image on the envelope is fixed, no wrinkle-preventing effect can be expected. Recently, there has been a demand for a fixing device for envelopes that can also perform fixing for plain paper, and there is a problem in that the above-mentioned conventional devices cannot meet this demand.

The present invention solves the problems existing in the prior art described above, and allows high-quality paper to be produced without wrinkles even when carrying not only 9 sheets but also multiple sheets such as envelopes. An object of the present invention is to provide a heat fixing device capable of obtaining a fixed toner image.

[Means for solving problems]

In order to solve the problems existing in the above-mentioned prior art, in the present invention, a heating roll that is in contact with the toner image on the carrier and a pressure contact that forms a nip between the heating roll and the heating roll are provided. In the heat fixing device having a roll, the heating roll and the pressure roll are provided with a heat-resistant elastic layer and a release resin layer around a core metal, and have substantially the same outer diameter; The nip is formed to have a surface hardness that is substantially flat, and at least one of the rolls is provided with a crown that is twice or less the amount of deflection that occurs in the roll when pressed with a predetermined pressure. This technical method was adopted.

In the present invention, if there is no difference in hardness between the pressure roll and the heating roll, no wrinkles will occur on the envelope during envelope fixing. If the hardness difference becomes large, a concave surface appears at the nip portion, which is a cause of wrinkles, which is disadvantageous. Therefore, the hardness difference is Hs 15° or less, preferably Hs 10°
The following shall apply.

If the surface hardness of the pressure roll and heating roll is high, the occurrence of paper wrinkles can be avoided, but the nip width is insufficient and the fixing performance is insufficient, so it is preferable to set the surface hardness to Hs 85° or less. . Note that when the surface hardness is high, it is possible to secure a predetermined nip width by increasing the pressing force.

This is undesirable because it induces deformation of the toner image bearing member, resulting in shortened lifespan, wrinkles, and other undesirable phenomena.

Next, the thickness of the heat-resistant elastic layer provided on the heating roll is 1lIl.
If it is less than 11, the effect as an elastic body will be weakened and it will be difficult to maintain the surface of the 70 to a predetermined hardness uniformly, which is disadvantageous. On the other hand, if the thickness exceeds 21 mm, not only will the temperature distribution in each part of the heating roll become uneven, but it will also inhibit heat conduction, causing unforeseen accidents such as overheating of both ends, which are non-sheet passing parts. Therefore, it is undesirable.

Furthermore, the thermal conductivity of the material constituting the elastic layer provided on the heating roll is 0.2X10-cal/cm-5ec
・If it is less than ℃, the heat conduction effect within the heating roll will be insufficient, which will not only make the temperature distribution uneven but also cause
This is disadvantageous because it causes local heating.

A more preferable thermal conductivity is 0.6 x 10-”cal/
cn-sec・“C or more.However, the thermal conductivity is 1.
5 X 1O-3cal/am-see ・To make it larger than ℃, a large amount of good heat conductive material 1 is added in the 3 elastic layers.
For example, it is necessary to mix carbon blank, metal oxide such as titanium oxide, etc. However, as a result of the mixing of the above-mentioned good heat conductive substance, on the one hand, the hardness becomes greater than Hs85°, making it impossible to secure a sufficient nip width. Therefore, the thermal conductivity is preferably 1.5 x 104 cal/cm-sec-'c or less.

The contact pressure that should be applied to the pressure roll and heating roll is 0.8
If it is not more than kg/cm, it is inconvenient because the nip width between two rolls cannot be secured, and more preferably 1.2 kg.
/cm or more. However, if the linear pressure is too large, this structure will lead to a reduction in service life due to plastic deformation of the rubber, so it is preferably 2.0 kg/cn+ or less.

In order to ensure good fixing performance especially at a fixing speed of 100 mm/sec or more, the linear pressure needs to be 1.2 kg/cm or more.

[For production]

With the above configuration, the nip between the pressure roll and the heating roll constituting the heat fixing device, that is, the passage area of the toner image carrier, can be formed into a substantially flat surface, thereby preventing wrinkles from forming on the toner image carrier. It is thought that it has the effect of preventing.

Also, by making the shape of the nip approximately flat.

It can also be expected to prevent the carrier after fixing from wrapping around the surface of the heating roll. This eliminates the need for separation claws9.
Damage to the roll surface due to contact between the separating claw and the roll surface is eliminated.

Furthermore, since at least one of the rolls is provided with a crown that is less than twice the amount of deflection that occurs in the roll when pressed with a predetermined pressure, the nip width is constant in the length direction of the roll, and it is possible to hold a particularly thin material. In the case of bodies, this prevents wrinkles caused by roll peripheral speed differences.

〔Example〕

FIG. 1 is a side view of essential parts showing an embodiment of the present invention, and the same parts are designated by the same reference numerals as in FIG. 6. In FIG. 1, 14 is a releasable resin layer, and the releasable resin layer 24
Similarly, it is formed from a low surface energy resin such as PTFE or PF8.

Further, 22 is a heat-resistant elastic material layer, which is adhered to the surface of the core bar 21. It is made by mixing a good heat conductive substance such as carbon black or titanium oxide into an elastic material such as silicone rubber, so that it has a high thermal conductivity. It is preferable to make it large. Next, a releasable oil layer 24 is provided on the outer surface of the heat-resistant elastic layer 22 to prevent offset. Additionally, the surface hardness of the pressure roll 1 and the heating roll 2 should be Hs85' or less, and the difference in surface hardness between the nine rolls should be Hs15' or less, preferably Hsl.
In this case, the surface hardness of the roll (A
Type spring hardness: JTS K 6301) is a value measured using a commercially available hardness meter (manufactured by Kobunshi Keiki, model JA).

With the above configuration, the pressure roll 1 and the heating roll 2 are formed to have an outer diameter of 31 mm, and the thickness of the release resin N14°24 is preferably 10 to 50 μm), and are pressed together at a pressure of 1.2 kg/cm, Fixing was performed at a fixing temperature of 180° C. and a fixing speed of 166 mm/sec. When the state of wrinkles was evaluated using an envelope as a toner image carrier, no wrinkles were observed if there was no difference in hardness between the pressure roll 1 and the heating roll 2. On the other hand, if the difference in hardness between the two rolls is large, most of the wrinkles will occur and the envelope will be deformed. That is, the above hardness difference is within Hs15°, preferably HslO0
If within.

The concave surface of the nip portion 3 as shown in FIG. 3 can be avoided. In this case, if the hardness of one pressure roll and/or heating roll exceeds Hs85°, no wrinkles will occur, but the nip width will be insufficient and the fixing performance will be insufficient. - If the fixing pressure is increased in order to secure the crab width, the plastic deformation of the rubber or resin depending on heat and pressure becomes large, resulting in a shortened lifespan of both rolls.

Next, using the above-mentioned apparatus, nine sheets of paper were used as toner image carriers, and fixing was carried out under the above-mentioned fixing conditions. As a result, although no wrinkles were observed, waving was observed at both edges of the paper 4, as shown in FIG. We will discuss the mechanism of this waving phenomenon.

FIG. 3 is a plan view schematically showing a nip portion 3 formed between the pressure roll I and the heating roll 2. As shown in FIG. In the figure, when a pressure roll 1 and a heating roll 2 are brought into pressure contact with each other at both ends thereof, for example, via a spring (not shown), a two-tube part 3 as shown by diagonal lines is formed. And this two-tube part 3
This is because the pressure roll 1 and/or the heating roll 2 are bent.

Usually, the width at the center appears smaller than the width at both ends. That is, both the rolls 1.2 in the nip part 3
The radius of is Re, where the center is Rc and both ends are Re.
>Re. On the other hand, since the rotational speed of both the rolls 1 and 2 is constant, the circumferential speed at the nip portion 3 is
, if both ends are Ve, then Vc>Ve, and the circumferential speed at the center is greater than the circumferential speed at both ends. Since there is a difference in the circumferential speed, that is, the paper feeding speed, it is recognized that the waving phenomenon shown in FIG. 2 occurs.

Here, as shown in FIG. 4, when the above-mentioned pressure roll l and heating roll 2 are formed into a cylindrical body with a uniform diameter in the axial direction, and a load (W) is applied to both ends of one roll, The roll of one car will be deflected. The amount of deflection δ is the sum of the amount of deflection δ1 of the pressure roll and the amount of deflection δ2 of the heating roll.

δ1. δ2 is 5Wβ'/384 E I (B: longitudinal elastic modulus of roll, ■: second moment of area of roll W
:Contact pressure (linear pressure) per unit length of both rolls.

l: roll length).

In the present invention, this amount of deflection δ is compensated for by, for example, attaching a crown to the pressure roll 1 as shown in FIG. Make it as follows.

In the pressure roll shown in Fig. 5, the crown amount Cr is Dt
(Dt +D:+)X% but 1 usually D2#D
3, so here we will explain as Cr = D ID z. To compensate for the above deflection, δ=D
I-D! /2 is required.

The crown amount cr=2δ. When Cr>2δ, contrary to FIG. 3, the nip width at the center becomes narrower than the nip width at both ends, making wrinkles more likely to occur. Theoretically, when Cr=26, the nip width at both ends and the nip width at the center are the same, but considering other conditions 1, such as wrinkles and fixability, it is preferable that Cr is 1.7δ or less. Understood. Further, when Cr is 0.2δ or more, it is effective in preventing waviness, but it is preferably 0.5δ or more.

Next, the results of fixing on plain paper using the pressure roll 1 provided with the crown shown in FIG. 5 are shown in the table. Please use 8M75 as plain paper.

Pressure pressure 1.8kg/c+n, 29℃, 49%RH
It was established in this environment. What is a crown here?

The pressure roll 1 is formed to have a larger diameter at the center than at both ends.

The following margins are used for the core metal that forms the heating roll and pressure roll.
Aluminum alloy (E = 7.3 x 103kg/
cd) with an outer diameter of 27.2 mm and 28 m, respectively.
2.5 m and 4 cm in thickness, respectively, and the body length of both was 24311+m.

As is clear from the table, when the crown amount is 0, it is disadvantageous because the waving phenomenon appears as described above. By increasing the crown amount, the difference in nip width between both ends and the center portion is reduced and the waving phenomenon disappears, but if it is increased too much, paper wrinkles will occur. That is, if a crown is provided that exceeds the amount of deflection that occurs in the pressure roll 1 due to pressure welding, the nip width at the center of the roll 5 will be larger than the nip width at both ends, and the relationship between the roll radii will be reversed.

Since Rc<Re, the one circumferential speed becomes Vc<Ve, causing wrinkles, which is inconvenient. For this reason, pressure roll 1
It is preferable that the amount of crown to be provided is 40 to 180 μm. Here, the amount of deflection of the roll (calculated value, however, the elastic layer and resin layer of the roll are extremely small compared to the outer diameter of the core metal, so it was calculated by ignoring these) is the amount of deflection of the pressure roll 1. 56.7 μm, heating roll 2 is 32.5 μm, and the total deflection amount of both is 89.2 μm.

In this example, an example was shown in which the crown was provided on the pressure roll, but it may be provided on the heating roll or both rolls. It should be selected appropriately taking into consideration the dimensions, shape, rigidity, etc. of the rolls, but in short, it is sufficient to select an amount corresponding to the amount of deflection that occurs in both rolls when they are pressed together with a predetermined pressure. Furthermore, the elastic layers of the heating roll and pressure roll are not limited to silicone rubber, but may be made of other known materials.

For example, it may be fluororubber or a mixture of fluororubber and fluororesin. Further, there are two elastic layers. For example, a fluororubber layer (which may contain a fluororesin) may be formed on the silicone rubber layer. Although such a structure is disadvantageous in terms of cost, it is advantageous in terms of the strength of the roll. In other words, if a silicone rubber layer is formed on the surface of the core metal, a fluororesin-containing fluororesin layer is formed on it, and then a two-surface fluororesin layer is formed after firing, the fluororesin layer appears on the surface of the fluororesin layer. Because of this, peeling of the 9-surface fluororesin layer is less likely to occur.

〔Effect of the invention〕

Since the present invention has the structure and operation as described above, 1) Even if the toner image bearing member is composed of multiple layers, such as an envelope, it is possible to produce a normal toner image with good image quality without wrinkles. It has the effect of being able to fix the problem. Also especially.

By making both the heating roll and the pressure roll have a roll structure in which a heat-resistant elastic layer and a heat-resistant release layer or a release resin layer are formed on a core metal, an envelope-like carrier can be created without wrinkles. The upper toner image can be fixed well even under high speed conditions. Furthermore, even if the carrier is not only the above-mentioned envelope but also thin plain paper, the desired fixing can be carried out without causing any waving or creases.

The same heat fixing device can be used for both envelope fixing and plain paper fixing. Further, it is possible to prevent the carrier from being wrapped around the heating roll without using a separating claw.

[Brief explanation of the drawing]

Fig. 1 is a side view of the main part showing an embodiment of the present invention, Fig. 2 is a perspective view showing the undulating phenomenon that occurs on both edges of paper, and Fig. 3 is a waving phenomenon formed between the pressure roll and the heating roll. FIG. 4 is a diagram illustrating the deflection of a pair of rolls, FIG. 5 is a diagram illustrating a roll provided with a crown,
FIG. 6 is a side view of essential parts showing an example of a conventional heating device. 1: Pressure roll, 2: Heating roll, 3: Nip part.

Claims (7)

[Claims] (1) In a heat fixing device having a heating roll in contact with a toner image on a carrier, and a pressure roll brought into pressure contact with the heating roll to form a nip, the heating roll and the pressure roll are provided. are provided with a heat-resistant elastic layer and a mold release resin layer around the core metal, and have substantially the same outer diameter and a surface hardness such that the nip is substantially flat. A heat fixing device characterized in that at least one of the rolls is provided with a crown that is twice or less the amount of deflection that occurs in the roll when pressed with a predetermined pressure. (2) The heat fixing device according to claim 1, wherein the heating roll is on the driving side, the pressure roll is on the driven side, and the pressure roll is provided with a crown. (3) The difference in surface hardness between the heating roll and the pressure roll is Hs1
The heat fixing device according to claim 1 or 2, wherein the angle is 5° or less. (4) The surface hardness of the heating roll and pressure roll is Hs8
The heat fixing device according to any one of claims 1 to 3, wherein the angle is 5° or less. (5) The heat fixing device according to any one of claims 1 to 4, wherein the elastic layer of the heating roll has a thickness of 1 to 2 mm. (6) Any one of claims 1 to 5, wherein the thermal conductivity of the material forming the elastic layer of the heating roll is 0.2 x 10^-^3 cal/cm・sec・℃ or more. The heat fixing device described. (7) The contact pressure between the heating roll and the pressure roll is 0.8k
The heat fixing device according to any one of claims 1 to 6, which has a linear pressure of g/cm or more.