JPS6252580A - Paired fixing roller for fixing device - Google Patents

Abstract

PURPOSE:To feed plural recording materials of different sizes, and to shorten the elevation time of paired rollers for fixation and decrease heat loss by forming a fixing roller for pressing which has an internal elastic sponge layer and a surface elastic layer and is smaller in diameter at a position corresponding to the no-image part of a recording material than at an image part. CONSTITUTION:The pressure roller 2 has small-diameter parts 6 at both ends and a large-diameter part 7 in the center, the length of the large-diameter part 7 is nearly equal to the width I of an image area, and the small-diameter part 6 has such a diameter that it does not contact or contacts the fixing roller 1 slightly. The pressure roller 2 has the internal elastic layer 5 made of silicone sponge around its mandrel 4 and the external layer 5 further made of solid-state silicone rubber around said layer; and both of them form one elastic layer on the whole and the roller is pressed against the fixing roller 1 made of a rigid material to form a proper nip.

Description

Detailed Description of the Invention (1) Purpose of the Invention (Field of Industrial Application) This invention relates to image forming apparatuses that utilize electrostatic processes, such as electrophotographic copying machines and printers, and particularly to fixing devices thereof. be.

(Prior Art and Problems to be Solved) In the above-described image forming apparatus, a pair of rollers heated to a predetermined temperature and pressed against each other transfers a sheet-like transfer material carrying an unfixed toner image. A fixing device configured to fix a toner image on a transfer material by passing the toner image through the transfer material is conventionally well known.

FIG. 6 is a schematic perspective view showing the pair of pressure rollers of such a fixing device, in which an appropriate heat source 3 is arranged inside, and a thin layer of Teflon (trade name) or the like is coated on the surface as a release agent 7. (10
A core bar 4 is attached to a fixing roller 1 which has a silicon sponge layer 5. If necessary, a pressure roller 2 made of solid silicone rubber or the like having appropriate elasticity and heat resistance is brought into pressure contact with the outside of the fixing roller pair to form a nip portion of an appropriate width between the two rollers. Prepared.

A transfer material T carrying an unfixed toner image is inserted into the nip portion of such a pair of rollers in the direction of arrow A, and the toner is fused and fixed to the transfer material.

On the other hand, regarding transfer materials, Japan's JIS and A4 size paper (in the United States, it is letter size, which is almost the same size) is currently widely used not only in Japan but also in Europe and the United States. In order to obtain copies or prints, most needs can be met as long as the image can be formed up to A4 size. However, B4-sized documents, which are much larger than this, are also used quite widely, at least in Japan, mainly in government offices.

Considering these circumstances comprehensively, it is preferable that the size that can be used as a transfer material that can be passed through an image forming apparatus is B4 size, and that the actual copies or prints that are made are limited to A4 or letter size. , a practical device can be obtained that can also use a dog-sized transfer material while avoiding an increase in the size of the image forming device.

However, if the heat-pressure type fixing device with the above-mentioned configuration is applied as is to the above-mentioned image forming apparatus, the fixing roller would be long to allow the dog-sized transfer material to pass through, and the heat capacity would be correspondingly large. Because of this, it takes time to raise the temperature to the specified temperature, and the areas without toner on both sides of the moving transfer material are heated more than necessary, resulting in increased heat loss. However, in the case of dog-sized transfer paper, there was a risk that the accumulation of stress on the paper would cause wrinkles in the transfer material.

Furthermore, if the axial length of the upper and lower pair of rollers is approximately the same as that of the effective image, there will be parts of the transfer paper that are heated and parts that are not, so the paper will stretch differently and the boundaries will be stepped. If this happens, there will be an inconvenience that unevenness will be formed on the transfer paper near the border. Therefore, the effective image area of the transfer paper is heated and sandwiched so that the toner on the transfer paper is fixed, and the non-image area is heated to support the transfer material and is heated moderately without changing the temperature suddenly from the effective image area. It will be necessary to do so.

The present invention has been made in order to cope with such a situation, and is designed to reduce heat loss while making it possible to pass a dog-sized transfer material in a fixing device that uses a heat and pressure method as described above. The object of the present invention is to provide a fixing device that can be made smaller in size and faster in fixing speed, and that does not cause wrinkles even when dog-sized transfer materials are used. (2) Structure of the invention (technical means for solving problems and their effects) A specific example of the invention achieves the above object, and is equipped with a pair of pressure rollers that use a heating and pressing method. In the fixing device,
1. Adopting a heating and pressing method used in an image forming apparatus capable of passing at least two types of recording materials of different sizes and capable of copying or printing within the range of small-sized recording materials; In a fixing device having a pair of fixing rollers, the fixing device includes a fixing roller and a pressure roller that is in pressure contact with the fixing roller, and performs fixing by conveying a recording material to the pair of fixing rollers. A fixing device characterized in that the roller has an internal elastic sponge layer and a surface elastic layer, and a diameter at a position corresponding to a non-image area of a recording material is smaller than a diameter at an image area.

With this configuration, recording materials of multiple sizes can be passed through, the rising time of the pair of fixing rollers can be shortened, and heat loss can be reduced. It can also prevent wrinkles that tend to occur on dog size recording materials.

(Description of Embodiments) FIG. 1 is a plan view showing an application of the present invention to an image forming apparatus using a laser beam, in which an optical image forming means 1
The optical image formed in step 9 is converted into a transferable toner image by the image carrier 14, and the transfer materials So to S traveling from the bottom to the top in the figure contact or come close to this toner image and carry it, and further It is assumed that the image travels upward in the figure and is fixed by a fixing device F.

The optical image forming means 19 includes an optical casing 20, and a laser beam L is projected from a laser unit 21 onto the mirror surface of a polygon mirror 15 that is located inside the optical casing 20 and rotates at high speed. The laser beam L is swung horizontally in the drawing and reaches the image carrier 14 via the imaging lenses 16 and 17. Although not shown, a portion of the laser beam is distributed to a detifter placed at an appropriate location, and after a predetermined period of time from the time when the detector receives the light, the laser beam is driven by a recording signal to detect the code on the surface of the image carrier. 30
．． It is assumed that the combing image is written during the period 31.

A latent image formed on the photoconductive layer on the surface of the image carrier 14 by writing with a laser beam is converted into a transferable toner image by a developing device (not shown), and then transferred to a transfer site equipped with a transfer charger (also not shown). In this step, the toner image is transferred to the transfer material So or S that reaches the position.

In any case, as can be seen from FIG. 1, the image carrier, and therefore the image area on the transfer material, is the transfer material S. .

Regardless of the size of S (S. is shown as A4 size and S as B4 size in Figure 1), it is a width. S so that a margin of appropriate width is formed. The work is determined.

The transfer material So or S carrying the unfixed toner image reaches the fixing roller pair F formed by pressing the fixing roller 1 and the pressure roller 2, passes through the pressure contact portion of both rollers, and during this time the toner image is transferred. It is assumed that the image is fused and fixed to the transfer material and the fixing is completed.

FIG. 2 is a perspective view showing the structure and relationship between the transfer material and the pair of fixing rollers.

In the figure, the cross-sectional configurations of the fixing roller 1 and the pressure roller that are in pressure contact with each other are the same as those of the above-mentioned known structure (see FIG. 6).

Further, as can be seen from FIGS. 1 and 2, the pressure roller 2 has small diameter portions 6 on both sides and a large diameter portion 7 at the center, and the length of the large diameter portion 7 is equal to the length I in the image area. The diameter of the small diameter portion 6 is such that it does not come into contact with the fixing roller 1 or only slightly contacts the fixing roller 1.゛The length of the large diameter portion does not necessarily have to exactly match the image area I, and in the case of a transfer material of approximately A4 size, the former is better than the latter, preferably 1. Om
It is actually preferable to make the roller 1 and the roller 2 larger. With this structure, the contact area between the roller 1 and the roller 2 is smaller than that of the conventional one, and only the toner image passes through it. The time required for the surface of the fixing roller to reach a predetermined temperature can be shortened, and since the margin area where no toner is not actively heated, the heat dissipation effect is small, so it is possible to increase the fixing speed.

Furthermore, when a pair of rollers configured as described above are brought into pressure contact with each other, it is common to apply force to the bearing portions at both ends of at least one of both rollers in order to apply pressure, so the pressure at both ends tends to increase. As a result, there was a risk that strain would be concentrated on the transfer material being held and wrinkles would occur.However, in the case of the present invention, such defects can be avoided because the non-image areas at both ends are not pressed too hard. .

FIG. 3 shows the luminescence distribution in the axial direction of the fixing roller according to the present invention when a halogen lamp is used as the light source, and the luminescence distribution curve for the output distribution light source as indicated by the symbol (Hl)K is shown. As shown in the diagram, the high temperature region is concentrated only on the width of the A4 size transfer material that covers the image area I.
A state is obtained in which the transfer material is not heated unnecessarily in the non-image area. The non-image area may also be appropriately heated as a light source, as shown by (H2), so that the light emission distribution curve becomes as shown by H2, thereby compensating for the heat dissipation from the end of the fixing roller.

FIG. 4 also shows the temperature distribution curve as seen in the axial direction of the fixing roller, where the symbol A is the distribution curve in a steady state where no transfer material is inserted, and the symbol C is the distribution curve in a steady state where the transfer material is not inserted. As shown, the overall temperature decreases, but as seen in relation to the paper size shown on the horizontal axis,
It can be seen that the fixing temperature is maintained even at the edge of the image area.

Reference numeral B indicates the temperature distribution during paper feeding in a conventional fixing device, and the temperature drop of the fixing roller is large at both ends of the image area.

FIG. 5 shows the configuration of the pressure roller of the pair of rollers shown in FIG. 2, in which an elastic inner layer 5 made of silicone sponge is formed around a core metal 4 made of iron, stainless steel, etc. Further, an outer layer 5a made of solid silicone rubber is formed on its outer periphery, and both of them together form one elastic layer, which is pressed against the fixing roller 1 made of a rigid material to form an appropriate nip.

Furthermore, a large diameter part 72 is formed in the center of the pressure roller 2, and a small diameter part 6 is formed at both ends thereof, and the difference in level between the two is preferably 0.1 to 1, preferably 0.3 to 0.8. good.

If the step is made smaller, the thermal efficiency will deteriorate and wrinkles will tend to occur more easily.If the step is made larger, the thermal efficiency will be improved and wrinkles will be less likely to occur. There is a tendency for it to become easier.

The above-mentioned pressure roller is manufactured by applying a liquid silicone rubber primer to the surface of the core metal 4, adhering unvulcanized silicone rubber thereon, and heating and foaming it at a temperature of 60° to 110°C.
After vulcanizing at 130° to 150°C to form a spongy inner layer, an elastic coating 5 such as RTV silicone rubber is applied.
form a.

The hardness of the elastic layer is preferably an ASKERC hardness of 45° or less, preferably in the range of 1 or 25° to 40'.

Since the fixing roller pair according to the present invention uses such a pressure roller, both ends of the roller do not contact the opposing fixing roller or contact with the opposing fixing roller with slight pressure. Therefore, it is possible to obtain the desired nip width with low pressure. Even if the core metal is made thinner, uneven pressure distribution in the axial direction will occur due to bending.
It is also possible to prevent wrinkles from forming on the transfer material. Therefore, the heat capacity of the pair of fixing rollers as a whole is small and the fixing temperature can be quickly reached.

In the above example, silicone rubber sponge was used for the elastic layer, but materials other than silicone rubber can also be used as long as they have the desired heat resistance, and solid elastic materials other than sponge can also be used to ensure the hardness described above. Of course, you can use it if you can.

(3) As described in detail of the invention, in the present invention, a fixing roller,
In the fixing roller pair using the pressure fixing roller that is in pressure contact with the fixing roller, since the pressure roller has the above-mentioned configuration, the heat capacity of the fixing roller pair is small and the predetermined temperature can be quickly reached, so the image can be started quickly. A forming device is obtained, and power consumption can be reduced even during fixing work because the transfer material is not actively heated to the non-image area where no toner is present. Furthermore, this can prevent defects such as distortion and wrinkles, especially when using wide transfer materials, making it possible to use recording materials that were previously unusable. , the allowable range of materials can be expanded.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view showing an example of application of the present invention to an image forming apparatus, FIG. 2 is a perspective view showing a pair of fixing rollers according to the present invention, FIG. 3 is the light emission distribution of the above, and FIG. 5 is a graph showing the temperature distribution, FIG. 5 is an axial sectional view showing the structure of the pressure roller, and FIG. 6 is a perspective view showing a known pair of fixing rollers. DESCRIPTION OF SYMBOLS 1... Fixing roller, 2... Pressure roller, 3... Heat source, 4... Core metal, 5... Sponge elastic layer, So, S
...Transfer material. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure D; 36-

Claims (1)

[Scope of Claims] A fixing device that includes a fixing roller and a pressure roller that presses against the fixing roller, and performs fixing by conveying a recording material to a pair of fixing rollers, wherein the pressure fixing roller has an internal elastic sponge. 1. A fixing device comprising a layer and a surface elastic layer, and a diameter of a position corresponding to a non-image area of a recording material is smaller than a diameter of an image area.