JPH0430591B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fixing device for heating and fixing an unfixed image, such as a powder image, to an image support material such as paper, and is applicable to an electrophotographic recording device, a laser beam, a facsimile machine, a copying machine, etc. The present invention relates to a fixing device that can be applied to an image forming apparatus.

2. Description of the Related Art Conventionally, a heat fixing method has been employed in a fixing device that fixes an unfixed image (hereinafter referred to as a toner image) formed by an image forming method such as electrophotography onto a recording material such as paper. In this type of heat fixing, a system is often used in which paper carrying a toner image is conveyed between a heating roller equipped with a heat source and a pressure roller that is in pressure contact with the heating roller.

Since an image forming apparatus that performs heat fixing requires a fixing temperature of 150 to 200 degrees, a considerable amount of time, approximately 4 minutes, is required as a wait time after turning on the main switch. In order to reduce this wait time, many technological innovations have been made, such as increasing the output of electrical control means and heating sources, but these have resulted in increased costs, other problems, and increased complexity of the equipment. was.

Furthermore, there are many problems in the roller configurations of the heating roller and the pressure roller. For example, in a heating roller, heat distribution tends to be uneven in the axial direction, and heat dissipates rapidly at the ends of the roller, causing an increase in wait time. Furthermore, during the fixing operation, the temperature may easily increase at the edges due to the fact that recording materials of different widths are used and the length of the roller is longer than the width of the maximum size.

On the other hand, the devices provided on the pressure roller side can be roughly divided into the following three types, each of which has drawbacks as described below.

In the first case, a primer is coated on the core metal and a thick layer of silicone rubber or the like is provided on the surface, that is, a uniform elastic layer is provided on the roller base.
In this type of roller, it is necessary to add oil or additives to reduce the elasticity of the elastic material, such as rubber, and as a result, the mechanical
It changes physical properties. Therefore, the hardness cannot be made too low while maintaining its properties. In addition, the pressure contact area obtained with the support material that supports the toner image formed by electrophotography is small, and the amount of heat that can be applied per unit time is small, and the elastic layer In addition, it requires a large amount of materials such as rubber, which is often used as a rubber material, and is uneconomical. Furthermore, it takes a long time to wait to heat the entire elastic layer, which increases the fall of the initial roller surface. This caused a lack of retention. Moreover, the method of increasing the number of heaters to prevent this is uneconomical.

In the second case, a fixing roller is formed by coating a core with a primer and further providing a porous member made of silicone rubber. The disadvantages of this roller are
The surface smoothness of the fixing roller is poor, which reduces fixing performance, and when a release agent is applied, a large amount of release agent is contained in the porous material, making the porous member itself susceptible to deterioration. Durability is inferior to solid.

In the third case, two elastic layers are added to improve oil resistance.
There are those with multi-layered or triple-layered structures. However, when a large number of elastic layers are provided simply to improve oil resistance, the cost increases significantly due to the use of a large amount of elastic material as described above.

In the first and third cases, the heat capacity becomes extremely large due to several layers or a thick rubber layer, resulting in an increase in waiting time, and the temperature distribution over the entire length tends to be uneven, resulting in poor fixing. The same was true in the case of Furthermore, since it requires a large amount of rubber material, it is expensive and has poor durability.

As mentioned above, in a fixing device having a heating roller and a pressure roller, there are not only problems with the individual components, but also additive problems that arise due to the required configuration, especially an increase in wait time. was causing

The present invention has been made in order to solve the above-mentioned problems that occur when fixing objects to be fixed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device that reduces wait time and has better fixing performance than conventional fixing devices.

Another object of the present invention is to equalize the temperature on the surface of the rotating body while maintaining the physical properties,
Our goal is to provide products with high durability.

Another object of the present invention is to provide a fixing device equipped with a rotating body that is cheaper than the conventional fixing device and achieves resource saving.

Further objects of the invention will become apparent from the description below.

In FIG. 1, reference numeral 1 denotes a heat fixing roller, which is a thin metal roller 5 having a heating means 4 inside, and a Teflon (trade name) coating layer 6 provided on the surface thereof.
2 is a pressure roller that comes into pressure contact with the heat fixing roller 1;
A primer ₇₂ of one-component RTV silicone rubber is applied onto the core bar 7, which serves as the center axis of rotation, and a sponge layer 8 made of a silicone sponge having many closed cells inside is adhered thereto, and then RTV silicone rubber is applied. It has an elastic coating layer 9 that has a long elasticity. The surface of the pressure roller 2 is generally coated with RTV (room temperature vulcanization type) silicone rubber and then polished to adjust the shape of the roller. In this way, if the elastic sponge layer 8 and the elastic coating layer 9 are made of the same type of material, the bondability will be good and the durability will be improved. Furthermore, in this example, since the same type of material is used for the primer ₇₂ , the bondability to the core metal is improved.

One of the features of this embodiment is that the above-described heat fixing roller has a thin metal roller 5a having a wall thickness d and a coating layer 6 of tetrafluoroethylene resin around the thin metal roller 5a. In this embodiment, the diameter r of the roller 5 is 25 mm.
On the other hand, the wall thickness d is set to 2.5 mm.

The elastic coating layer 9 is thinner than the sponge layer 8, but this is a preferable configuration since it has the effect of stabilizing the temperature rise and its distribution when heated. In this embodiment, the sponge layer 8 has a thickness of 6 mm, and the elastic coating layer 9 has a thickness of 1 mm.

The sponge layer 8 was formed by mixing silicone rubber with a crosslinking material and a foaming material and molding the foaming ratio of 2 times, and had an Asker hardness in the range of 17±2 degrees. Furthermore, the coating layer 9
is 40 degrees in JIS hardness.

As shown in FIG. 2, this pressure roller has its end surface not covered with a silicone rubber layer. That is, the rubber layer is provided only on the circumferential surface of the pressure roller, and the left and right sides have a rubber layer on the circumferential surface and a silicone rubber sponge layer on the inside. This makes the heat distribution more uniform in the longitudinal direction.

Further, the Teflon product name coating layer 6 of the heat fixing roller 1 is provided with a cleaning means such as a cleaning blade 16 and a cleaning device such as that described in JP-A-55-144268.
An anti-offset liquid application means 3 (as shown in the figure, includes a silicone oil impregnated member 10, a damage prevention member 12, and a continuous porous member 11) is in contact with it.

Furthermore, the pressure roller 2 has means for varying the state of pressure contact with the heat fixing roller 1, for example,
An arm 17 that supports the rotation of the core metal 7 and makes these positions variable together with the mounting point 7 ₁ and a point 17 ₁ that is the center of rotation of the arm 17 and the position of the arm 17 as indicated by the broken line arrow. cam means 1
8 are provided as shown in the figure.

In this example, a pressure of about 7 kg is applied between the heat fixing roller 1 and the pressure roller 2 by this pressure adjustment means. The operation of the cam means 18 occurs when the recording material such as the paper P is jammed, and the pressure between the rollers is reduced to 0 to several kg, or the rollers 1 and 2 are separated.

Further, a contact type thermistor 13 ₁ is pressed against the circumferential surface of the heat fixing roller 1 by the elastic force of a leaf spring 24 so as to maintain a predetermined pressure contact force.
The thermistor ₁₃₁ has a resin tape-like material on its surface so as not to damage the surface of the fixing roller 1, and holds a temperature sensing element (not shown) with an elastic sponge material.

Reference numeral 23 separates the paper P from the heat fixing roller 1 with a separating claw. 22 is a guide plate on the pressure roller 2 side;
Together with the separating claw 23, a transport path for the paper P is secured.
Reference numerals 16 ₁ and 16 ₂ are paper discharge rollers that pinch and convey the fixed paper P to the outside of the image forming apparatus or to the stacking section.

In this figure, reference numeral 25 denotes an upper support workpiece that integrally holds the fixing unit (the structure of which was explained in FIG. 1, see FIG. 1), and 26 is a similar lower support workpiece. Reference numeral 27 denotes a guide member within the image forming apparatus that removably supports the support member 26 of the fixing unit. 28 is a fixed part inside the image forming apparatus;
It is spaced apart from the support wall surrounding the thermistor ₁₃₁ with a gap therebetween.

It should be noted that the pressure roller 2 can be elastically deformed more greatly than in the past, and the pressure contact portion with the fixing roller 1 can be made much larger than in the past. In this example, the pressure welding width is 3 mm for an outer diameter of 25 mm, and it is approximately 8 g/unit area.
A pressure of 2 mm ² is acting at this pressure contact.

Now, the paper P having the toner image T formed by a predetermined image forming means is conveyed along with the movement of the belt 15 that is applied to the pair of conveyance rollers 14 .
Next, the paper P is transferred from the belt 15 to the guide member 13 and guided to the pressure contact area formed by the heating and pressure rollers 1 and 2. The toner image T is fused and fixed on the paper P at this pressure contact portion, and is discharged together with the paper P.

At this time, most of the heat from the heat source 4 is absorbed by the thin, thick portion of the fixing roller 1. At the same time, the pressure roller 2 is heated by conductive heat from the fixing roller 1 and reaches a surface temperature necessary for immediate fixing. Therefore, the waiting time of conventional heat fixing devices of several minutes can be significantly reduced. The wait time in this example is about 15 seconds, and when the time required for forming a toner image on the paper P when installed in an image forming apparatus is subtracted, the wait time is almost eliminated.

In terms of fixability, the fixing roller and pressure roller are stabilized at a fixable temperature for the reason described later, making it possible to obtain high-quality images.

As described above, the pressure roller 2 has an elastic layer having a large number of closed cells therein, and a surface layer outside the elastic layer. Since this sponge layer 8 has a large volume occupied by gas such as air in addition to sponge components, the thermal conductivity of this sponge layer 8 is much lower than that of the covering layer 9. In other words, the amount of heating required by the heating fixing roller 1 to maintain the entire pressure roller 2 itself at a predetermined temperature may be small compared to the conventional one. In addition, since there is almost no other large amount of wasteful heat consumed, the heat efficiency for fixing in the pressure roller and the fixing roller is also highly efficient.

Therefore, most of the heat capacity heated by the heating means 4 is occupied by only the surface layers of the fixing roller 1 and the pressure roller 2, so the wait time at startup (required until the process can start) is time) can be significantly reduced. At the same time, sponge layer 8
Since appropriate elasticity can be obtained, fixing performance is also improved. Furthermore, even if the apparent hardness of the roller surface is the same, the above embodiment having the sponge layer 8 is more easily deformed than the one made of solid solid.
Furthermore, the pressure contact area between the rollers can be made wider.

During this fixing action, the incidence of wrinkles that tend to occur on the paper P is greatly reduced. Despite the fact that the generally known treatments for wrinkles, such as processing them into an inverted crown shape, were not taken, the occurrence of wrinkles could be prevented to about 1/10 of the conventional rate.

Focusing on the closed cells of this sponge layer 8, the expansion ratio and hardness were studied as follows, and the following conclusions were obtained.

When incorporated into an actual device, the elastic layer having a large number of closed cells may be deformed when fixing an unfixed image to a recording material such as paper P, or may change due to continued exposure to heat or pressure. It was seen. Specifically, it was observed that closed cells within the elastic layer were destroyed during the fixing action, resulting in changes in outer diameter and hardness in some areas.

In view of this point, conditions for eliminating the above-mentioned disadvantages were investigated. When we tried using rubber materials of various hardness before foaming and changing the foaming ratio, we found that if the foaming ratio was less than 1.5 times, there were fewer closed cells and the overall insulation effect was better than a roller made of only rubber. However, the heat capacity increased, which was not preferable. Moreover, when the expansion ratio is made larger than 3 times, the number of bubbles increases and the partition walls forming the closed cells become thinner. Therefore, the closed cells become connected due to pressure load or thermal expansion, which changes their elasticity, which is undesirable. Further, by setting the expansion ratio within the range of 1.5 times or more and 3 times or less, appropriate elasticity and heat insulation properties were obtained, which was preferable.

Furthermore, durability was investigated by applying pressure to the elastic layer at this expansion ratio to change its surface hardness. If the Asker hardness is lower than 10, the physical properties of the rubber will be unstable as a whole, the strength will be weak, and thermal stability will not be obtained. Moreover, the degree of deformation becomes too large due to the continuously applied pressure, making it unsuitable as a pressure roller. In order to obtain a predetermined hardness as a pressure roller using an elastic layer having such a low hardness, it is necessary to increase the thickness of the outer surface layer of the elastic layer. However, if the thickness of the surface layer is increased, the elasticity will decrease accordingly and the heat capacity will increase. Therefore, a lot of heat is required to heat the surface layer, which lengthens the waiting time.
The advantage of the elastic layer is lost. When the Asker hardness is greater than 30, the durability of the partition walls between closed cells tends to deteriorate due to continuous pressurization and heating, and elasticity sufficient to absorb the expansion of the cells cannot be obtained. Therefore, when the durability limit was reached, the bubbles sometimes exploded and changed in diameter. On the other hand, when the Asker hardness was in the range of 10 to 30, preferred elasticity and hardness could be maintained, the thickness of the surface layer could be reduced, and high durability could be obtained.

Further, although it is possible to manufacture a product with thick closed cell partition walls by increasing the expansion ratio, the variation in hardness in the circumferential direction and axial direction of the roller becomes large. Therefore, the amount of pressure applied in the axial direction of the pressure roller varies greatly, resulting in a decrease in fixing performance.

Incidentally, the variation in hardness of the elastic layer is preferably about ±2 to ±3 in terms of Asker hardness.

As explained above, the preferable conditions are that the foaming rate is
It is 1.5 times or more and 3 times or less, and the Asker hardness is 10 or more and 30 or less.

In addition, as mentioned above, we can determine the apparent density (weight/volume) of those that provide appropriate elasticity and heat insulation effects, and those that are highly durable, and those that cause other inconveniences.
(g/cm ³ ) and the size of closed cells. In terms of apparent density, the thermal and pressure durability obtained by the proportion of closed cells is 0.36.
It was within the range of 0.42 (g/cm ³ ). Similarly, the closed cells had a minimum diameter of 0.03 mm or more and a maximum diameter of 0.7 mm or less, and in a preferable state, most of the closed cells had a diameter of 0.5 mm.

Furthermore, the present inventor conducted experiments to obtain a more preferable embodiment, and found that one that satisfies the following requirements is even more preferable.

When a roller is formed from a single layer of silicone sponge and used for fixing, the air bubbles may create areas with good fixation and areas with poor fixation, which is undesirable and has a smooth surface. I found this to be preferable. In other words, it is preferable for the surface layer of the pressure roller to have surface smoothness because it can provide a higher level of fixing.

Also, regarding the thickness of the surface layer from another perspective,
Silicone surface layer thickness experiments ranging from 0.3 mm to 5 mm thickness were investigated. As a result, if it is too thick, the effect of the sponge layer, which is rich in elasticity and restorability, cannot be used effectively, and if it is too thin, the strength and manufacturing costs will increase, and stability will be affected.
It was found that the thickness is preferably 0.01 mm to 2 mm, more preferably 0.5 mm to 2 mm, and even more preferably 0.7 mm to 1 mm (however, if the roller diameter is 25φ ).

Considering this comprehensively and other results (not listed), it is preferable for the surface layer to have a thickness that is 1/4 or less of the thickness of the elastic lower layer such as a silicone sponge layer. I understood.

The pressure roller has an elastic layer on the base made of a material with relatively poor thermal conductivity and rich elastic restoring force, such as a silicone sponge layer or a porous layer made of fluororubber, and a thin layer of heat conductive material such as silicone rubber. Any rotating body may be used as long as it has a multi-layer structure and has a heat-resistant layer on its surface. This makes it possible to form a uniform and constant nip width (pressing force) with low contact pressure.

Furthermore, this pressure roller has the effect of helping to conduct heat in the axial direction in the heat fixing roller and making the heat distribution in the axial direction uniform. As mentioned above, since the inside of the pressure roller is a porous elastic layer that is difficult to conduct heat, the main heat is quickly transmitted to the surface layer, and the temperature becomes high in a short period of time. Therefore, it is possible to compensate for the heat distribution on the surface of the heating fixing roller at the pressure contact portion.
Therefore, the heat distribution of the heat fixing roller can be made uniform when the roller pair rotates in pressure contact with each other. This makes it possible to further shorten the wait time and prevent the sudden temperature drop and fall phenomenon during the fixing operation.

Next, using FIGS. 2 and 3, heat fixing roller 1
We will mainly explain the characteristics of . In FIG. 2, the fixing roller 1 ₁ and the pressure roller 2 ₁ are separated from each other, but normally they are in pressure contact as shown in FIG. 1.

In FIGS. 2 and 3, the fixing roller ₁₁ has a cylindrical shape. This roller ₁₁ is made by coating the surface of a thin aluminum pipe ₅₁ with a 25-30 μm polytetrafluoroethylene resin layer ₆₁ as an offset prevention layer. A notch 30a is provided at the end of the fixing roller ₁₁ , and serves as a fitting groove for a drive gear (described later). In addition, A in the figure
is an area through which B5 size sheets pass, B is an area through which A4 size sheets pass, and both ends thereof are sheet non-passage areas C.

31a and 31b are rolling bearings that rotatably support the fixing roller ₁₁ . Note that this bearing 31a,
31b is attached to a support frame (not shown) of the fixing device. In addition, 30 is a drive gear, and the notch portion 3
It is fitted and fixed to the fixing roller 1 ₁ at 0a,
Drive from a drive source 33 on the copying machine main body side is transmitted via a gear 29 on the main body side to rotate the fixing roller ₁₁ . Furthermore, 4 ₁ is a support member 4 that also serves as an electrode.
A halogen heater as a heat source is held by a and 4b, and the amount of heat generated at both ends is greater than the amount of heat generated at the center. This configuration is intended to compensate for the decrease in surface temperature due to the amount of heat radiated from both ends of the fixing roller ₁₁ . The fixing roller 1 ₁ is controlled on and off by a temperature sensing element 13 ₁ in contact with the surface and a control circuit (not shown) so as to maintain the surface of the fixing roller 1 ₁ at a predetermined temperature. Note that the drive gear 30 is fitted into the notch 30a to prevent the fixing roller ₁₁ from slipping with respect to the bearings 31a and 31b using screws or the like.

A pressure roller 2 ₁ has the same configuration as the pressure roller 2 described above, and faces the fixing roller 1 ₁ under pressure. A heat-resistant porous elastic layer 8 ₁ is provided around the stainless steel core 7, and its surface is further covered with a very thin elastic layer 9 ₁ of silicone rubber. This core metal 16 is also rotatably supported by rolling bearings 17a and 17b.

In this embodiment as well, the above-mentioned effects are obtained, and the uniformity of the surface temperature of the fixing roller 1 ₁ is further promoted by the action of the elastic layer 9 ₁ of the pressure roller 2 ₁ , and the characteristics of each roller are A certain reduction in wait time can be further improved reciprocally.

In this embodiment, the fixing roller 1 ₁ and the pipe 5 ₁
is a cylinder that is open at both ends and has approximately the same diameter. Therefore, in this embodiment, the excess heat is efficiently released to the outside, so that it is possible to effectively prevent the temperature increase in the sheet non-passing area C on the roller circumferential surface. Moreover, since the amount of heat transferred to the roller support portion during heating is reduced, the circumferential surface of each roller 1 ₁ , 9 ₁ can quickly reach a predetermined uniform temperature. Furthermore, in this embodiment, the pipe ₅₁ is located in the sheet passage area (A or B).
and the bearing portion to which the bearing supporting the pipe ₅₁ is attached are both on the same generatrix. Therefore, there is no risk of uneven thickness of the roller, which may occur when conventional fixing rollers (particularly the example shown in Figure 2) are manufactured using methods such as bulge pressing or cold tube forging. Even so, the heat distribution on the circumferential surface of the roller became uniform, and the temperature was raised to a uniform temperature.

Therefore, in this embodiment, the wall thickness of the pipe 5 ₁ is uniform over both the sheet passage area (A or B) and the bearing portion where the bearing supporting the pipe 5 ₁ is attached, that is, over the entire area of the pipe 5 ₁ . It was possible to form a thin wall, reduce non-uniformity in heat distribution, and maintain a uniform temperature around the roller surface. Furthermore, the manufacturing process could be shortened.

The thickness d of the heat fixing roller 1 will be further explained. Due to the thin wall thickness of such rollers, localized overheating may occur to the extent that the entire surface of the roller cannot retain the same amount of heat, or heat transfer on the roller surface may be slow. In particular, there were cases in which heat mobility in the generatrix direction of the surface of the heat fixing roller could not be obtained. In addition, because of the thin wall thickness, although it can quickly respond to heat, it is easily affected by the heat release characteristics of the heating source, causing problems in heat retention and strength, making it difficult to achieve sufficient fixing. It may not be possible.

In other words, the minimum necessary wall thickness to shorten the weight up time should be a wall thickness that allows for easy transfer of heat in the direction of the fuser roller's generatrix, and a thickness that allows the core metal of that wall thickness to not change over time. It is most effective to bring the pressure roller into contact with pressure.

In the present invention, with respect to this wall thickness d, the outer diameter r of the rotating body is
It has been found that the above-mentioned problem can be solved by one that satisfies the formula 5/r≦d≦r/10 for (mm). Further, in order to make the movement in the generatrix direction more reliable, it is preferable that 15/r≦d≦r/10. Further, the wall thickness d is preferably 3 mm or less in consideration of strength, since the heat capacity increases when it becomes thicker, such as when the outer diameter r is 30 mm or more.

<Specific example> The heat fixing roller 1 is a cylindrical roller with an outer diameter of 25 mm and a length of approximately 280 mm, and a coating layer of tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA) is coated on an aluminum cylindrical roller with a wall thickness of 1.6 mm to a thickness of 25 μm + 10 μm. -5μ thickness.

Pressure roller 2 is a roller with an outer diameter of approximately 24 mm and a length of approximately 230 mm, and has a 6 mm thick HTV (high temperature vulcanization type) silicone sponge layer on a 10φ core metal, and a
It has a 0.7mm to 1mm RTV (room temperature vulcanization type) silicone rubber layer.

A gear is fitted to the surface part of the heat fixing roller 1 that does not contact the pressure roller 2, and a gear of 1.0 mm is fitted inside the gear.
It has a built-in ~1.2KW halogen heater. The heat fixing roller 1 and the pressure roller 2 always have a total pressure of about 7
Kg pressure welded. The width of the pressure welding part is approximately 2.5mm
~3.0mm.

The heat fixing roller 1 is driven, and the pressure roller 2 is caused to follow this.

The hardness of the silicone sponge layer above is Asker.
When measured with a Ctype rubber hardness meter for sponges (manufactured by Koubunshi Kagakusha) with a load of 300g, it was 27° ± 3°.

A process of fixing a powder image onto paper was performed using the fixing device having the above configuration. As a result, the wait time from the time when current was applied to the heater of the heat-fixing roller until the surface temperature of the fixing roller reached 180° was only about 15 seconds. In addition, the pressure roller surface temperature was able to rise to 160°C.
Furthermore, the powder image could be fixed on paper with almost uniform fixability.

This excellent and revolutionary result can be understood by comparing it with the waiting time of any conventional heat fixing device, which takes about 4 to 10 minutes. Furthermore, since the pressure roller of the conventional device has a rubber layer in units of 10 mm, it can only be heated to a maximum temperature of about 70°C. That is, it is understood that the pressure roller of the above specific example can rapidly heat up to 160°, thereby reducing the waiting time, and has sufficient elasticity, thereby improving fixing performance.

The silicone sponge layer in the above specific example was formed by a tubing method or an injection molding method using a paper tube. In the tubing method, high-temperature vulcanized silicone rubber compound is poured out from a container with a ring-shaped opening, and then the cylindrical rubber tube is placed inside a cylindrical heater and heated from the surrounding area to foam and form a sponge tube. It is something. The shape of the sponge tube is determined by the inner diameter of the ring-shaped opening and the inner diameter of the cylindrical heater. The pressure roller was molded using the following procedure. This sponge tube has a skin layer on its surface, so
The inner diameter of the layer is expanded by suctioning from the surrounding area.
A core bar whose surface is coated with a silicone primer for adhesion is inserted into this inner diameter. After this, the suction is released and the sponge tube is glued to the core metal. Furthermore, the skin layer on the surface of the sponge tube is scraped to form a sponge layer of a predetermined thickness. On the surface of this sponge layer
Laminate RTV silicone rubber to a specified thickness. Thereafter, final polishing was performed to obtain the above-mentioned pressure roller.

In the injection method using a paper tube, a primer-treated core metal is inserted into a cylindrical paper tube of a predetermined diameter, and a high-temperature vulcanized silicone rubber compound is injected between the paper tube and the core metal and heated. to form a spongy silicone rubber layer. Furthermore, after this, the paper tube is removed and polished. Such a process is called an injection method using a paper tube. Hereinafter, the pressure roller may be molded using the above-mentioned RTV silicone rubber laminate coating.

Further, as another example of the above pressure roller example,
In addition to the method of covering the silicone sponge layer with a sponge tube, it is also possible to use a general method of spreading rubber around a core metal, allowing it to swell, and then heating it.

In addition, an inexpensive method is to cover each tube with a silicone rubber tube and then place it in a mold.
NVR (low-temperature vulcanization type) using the injection method
Silicone rubber may be poured between the sponge layer and the mold. In this case, due to the precision of the release surface of the mold, there is no need for final polishing and it is suitable for mass production.

Furthermore, in order to further reduce variations between products and unstable hardness in the method for manufacturing the pressure roller, we have invented the following manufacturing method that is novel and has excellent effects. Its features include a process in which a cylindrical mold with a precisely finished inner surface is rotated to form a surface rubber layer of a predetermined thickness on the inner surface, and a foaming agent-containing rubber layer temporarily molded inside the cylindrical mold as a core. The method includes the step of heating the material containing the roller base from the periphery.

The processed roller thus manufactured can have a uniform surface layer thickness. Furthermore, since the surface accuracy is determined by the inner surface accuracy of the cylindrical shape, final polishing is no longer necessary, and the process can be simplified. Furthermore, since the surface layer of the elastic layer having closed cells can be made uniform, variations in the hardness of the roller can be almost eliminated.

Specific examples will be given below for comparison with conventional methods.

<Specific example> An appropriate amount of liquid low-temperature vulcanizing silicone rubber (LTV) is poured into the inner surface of a metal mold whose inner surface has been finished with a surface roughness of 0.1 μm or less, and the mold is heated at high speed so that the center of the roller axis is centered. Rotate to create a surface rubber layer of uniform thickness on the inner surface.

Next, high-temperature vulcanization (HTV) silicone rubber mixed with a vulcanizing material, a crosslinking material, and a foaming material is temporarily molded into a cylindrical shape on the roller core bar, and then the surface rubber layer is placed in the mold that has already been made. Insert the core and mold so that their axes align with each other in the center and fix the positions of the core and mold. These rubber layers are simultaneously heated in an oven to vulcanize them so that heat is evenly applied to the rubber layers, the mold, and the core metal to cause temporary vulcanization and foaming. After that, after the mold is cooled, the part formed on the core metal is removed and secondary vulcanization is performed in an atmosphere of about 140°.

The pressure roller manufactured in this way has very little variation in hardness as described above, and the effect of the surface layer and the effect of the inner elastic layer having closed cells can be more stabilized.

Now, when creating a surface layer after forming the sponge layer as described above, there are (a) casting method and (b) casting method.
In case (a), final polishing is required, and in case (b),
It is sometimes difficult to make the thickness of the surface layer uniform due to the cylindrical nature and elastic deflection of the sponge layer.

Furthermore, when creating a thin surface layer, air bubbles were introduced, and the rubber layer often did not have a uniform thickness due to the flow and pressure of the rubber during casting.

The pressure roller produced by this method solves these problems.

In the above embodiment, the total pressure applied between the fixing roller and the pressure roller is preferably 20 kg or less,
In order to further improve durability and maintain good fixing properties,
More preferably, it was 5 g/mm ² to 50 g/mm ² .

The surface layer in the above embodiments may be a skin layer used to form a sponge that has been smoothed and has the thickness described above, but preferably an elastic layer with a substantially uniform thickness as described above. It is preferable to provide a new one because thermal stability can be achieved.

As explained in the above embodiment, the pressure roller is
It has an elastic layer with a predetermined hardness and a predetermined number of closed cells, and a thin elastic layer on the outside. Effective use can be maintained.

Further, when the porous elastic layer has closed cells, the pressure roller tends to become crown-shaped due to thermal expansion of air, and therefore wrinkles tend to occur in the paper.

Therefore, in the present invention, this problem is solved by making the heat distribution of the halogen heater, which is the heating means, larger at both ends than at the center.

As described above, based on the technical concept of the above-mentioned fixing device, there is a thin rotary body and a heat-resistant rotary body, and the inner layer has a porous elastic layer such as a sponge, and the surface thereof has a thin heat-resistant surface layer such as silicone rubber. By using a heat fixing device that has a heat fixing mechanism, it is possible to obtain an ideal device with extremely short wait time due to the mutual action of both rotating bodies, and uniform heat fixation of the object to be fixed during the fixing action. was completed.

Furthermore, by having a thin rotating body, it was possible to significantly reduce the wait time during startup.

As explained above, this fixing device has good fixing performance during start-up, allows free elastic deformation, maintains high image quality resulting from exceptional fixing performance, and has an extremely high wrinkle prevention effect, unlike conventional fixing devices. It is an economical and resource-saving fixing device that eliminates the need to add a filler, does not deteriorate the physical properties of the elastic layer structure itself, and is easier to manufacture.

The terms "sponge" and "sponge layer" above mean ceuars ayer (bubble layer) in English, and specifically, it has a large amount of gas-containing bubbles, most of which are They are closed cells (expanded foams or expanded ces) in which each cell is independent and isolated from others. Therefore, the silicone rubber mentioned above is the most preferable material, but polyethylene synthetic materials with closed cells, soft rubber (foamed at room temperature), hard rubber (press foamed), and hard polyurethane (chemical reaction method) are also available.
Various methods such as the following can be applied.

However, even if this "sponge" contains some open cells (sponge) whose cells communicate with each other, it is included in the present invention as long as the desired elasticity and desired heat insulation properties are obtained. .

ceuar in this example and the following examples
Ayer is mostly composed of closed cells containing gas (for example, air or vaporized additives in rubber), and has a resin film such as silicone rubber as a partition wall. This has the advantage that closed cells have a higher heat insulating effect than open cells, have more elasticity, and are easier to obtain a predetermined pressure.

The present invention relates to the configuration of a fixing device for heating and fixing an unfixed image, such as a powder image, to an image support material such as paper. Even when a pressure roller having a porous elastic layer containing air bubbles is used, wrinkles do not occur in the image support material.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention, FIG. 2 is an explanatory diagram of another embodiment of the invention, and FIG. 3 is an explanatory diagram of the main part of FIG. 1 is a heating fixing roller, 1 ₁ is a fixing roller, 2,
2 ₁ is a pressure roller, 4 is a heating means, 8 is a sponge layer, 9 is an elastic coating layer, r is a radius, and d is a wall thickness.

Claims (1)

[Scope of Claims] 1. A pressure roller having a fixing roller heated by a heating means, a porous elastic layer in pressure contact with the fixing roller, and a resin layer provided on the porous elastic layer. In the heat fixing device, the porous elastic layer has a large number of closed cells,
A heat fixing device characterized in that the heating means has a larger heat distribution at both ends than at the center.