Patent Application
20170031287
The present invention relates to a fixing device and a fixing method for forming an image on a recording medium by heating a resin toner for forming an image to soften or fluidize the toner and adhere the toner to the recording medium or partly impregnate the recording medium with the toner, particularly to a toner fixing device and a toner fixing method for subjecting an unfixed toner image transferred to the recording medium to heating and fixing to obtain a permanent fixed image in a power saving manner without deterioration of the image.
Electrophotographic recording is used widely for copying machine, a printer, or the like. Electrophotographic recording is performed in a manner as mentioned below. Namely, a toner is attached electrostatically to a photoreceptor (a photoconductor drum, a belt-like photoreceptor, a sheet-like photoreceptor, or the like) by electrostatic charging, exposing and developing and then is moved and transferred to the recording medium by electrostatic attraction. Then, the toner is fluidized by heating with a heating and pressing roller to give rise to adhesiveness of the toner, thereby causing cohesion of toners and adhesion of toner to the recording medium. As a result, the toner will not move freely. In other words, softening, fluidization and adhesion arise and then, by pressing the toner in an adhered state, an image is fixed to the recording medium.
In a method of fixing the toner on the recording medium having a transferred toner thereon, it is known that the recording medium travels, while being pressed, for example, with a heating roller heated with a built-in halogen lamp and a pressure roller located opposite to the heating roller. Namely, pressing and heating are conducted simultaneously. Thus, a recording medium on which the toner has been transferred is moved while rotating the heating roller and the pressure roller, and therefore, the surface of the toner is hardly rubbed. However, since the recording medium is pressed with the pressure roller while the toner is in a completely fluidized state, the softened and fluidized toner attaches to the surface of the heating roller and a part of the toner surface is peeled off. Also, it is necessary to have a halogen lamp built inside the roller. Therefore, there is a problem such that power consumption is high and it takes time until the temperature of the heating roller is elevated sufficiently after turning on a switch. In order to solve this problem, it is necessary to preheat the roller. Thus, further power consumption is required and it is impossible to comply with a demand for energy saving.
Meanwhile, a method of using a ceramic heater, in which a heating element is formed on a surface of a ceramic substrate, has been proposed. However, in this method, in order to efficiently use heat of the ceramic heater, heating and pressing are carried out with the surface of the heater being brought into contact with a portion of a recording medium on which a toner has been transferred. In addition, the ceramic heater cannot be rotated unlike a roller. The recording medium is carried while the surface of the ceramic heater is rubbed with the surface of the recording medium on which a toner has been transferred. As a result, the whole or a part of the toner is apt to be damaged before being fixed. Therefore, as shown, for example, in JP H05-273879 A or “SURF and ODF” (Journal of the Imaging Society of Japan, Vol. 48, No. 5, pp. 411-416, 2009), there is employed a method of disposing a heat-resistant film (sheet) made of polyimide or the like between the ceramic heater and the recording medium and carrying the recording medium by carrying the heat-resistant film synchronously with a transfer speed of the recording medium.
Also as shown, for example, in “Electrophotograph” (Ed. by The Imaging Society of Japan, Issued by Publication Dept. of Tokyo Denki University, Jun. 20, 2008, pp. 67-69), a corona discharge method, a roller transfer method, and the like are known as the method for transferring a toner from a photoreceptor to a recording medium. The corona discharge method has, as shown in
Then, in a developer unit 86, a toner is adhered to the latent image formed on the surface of the photoreceptor 81 while stirring the toner, thus forming a visible image on the surface of the photoreceptor 81. Thereafter, the toner on the photoreceptor 81 is transferred onto the recording medium 80 by giving an electric charge antipolar to the toner onto the back surface of the recording medium 80 through corona discharging by the transfer charger 82. An electric field weaker than that of the transfer charger 82 has been applied to the separate charger 83 so that the recording medium 80 should not be sucked by the photoreceptor 81 and wound on the photoreceptor 81. Namely, in the transfer section, the photoreceptor 81 and the transfer charger 82 are disposed in pairs independently to form a transfer device. Further, in a roller transfer method, as shown in
As mentioned above, in the event of heating and pressing a transferred toner via the heat-resistant film, since the heating is conducted indirectly via the heat-resistant film, much amount of heat is required. As a result, there is a problem that even if a ceramic heater is used, power consumption cannot be reduced sufficiently. Further, there is a problem that since the heat-resistant film needs to be moved coincidently to a transfer speed of the recording medium, a complicated configuration is required.
Furthermore, as mentioned above, if fluidization and adhesion of the toner are carried out simultaneously, the fluidized toner is apt to stick to a heating/pressing roller or an intervening heat-resistant film, and a part of the toner image is lost, thereby causing a problem that the image becomes unclear. In addition, in such heating, since the heating and the pressing are conducted from the surface side of the toner, firstly the toner of the surface side is formed into a fluidized state earlier than the toner at the recording medium side, and the pressing is conducted in such a state. Therefore, there is a problem that the toner is apt to stick to the heat-resistant film (a heating/pressing roller) rather than impregnating into the recording medium.
Further, in the case where the recording medium is a material having hygroscopic property such as paper, for example, as shown in
Also, when heating is performed from the surface side of the transferred toner, even if the surface side of the toner is in a fluidized state, fluidization of the toner at its surface side contacting with the recording medium is delayed compared with the fluidization at the surface side, and therefore, adhesiveness of the toner to the recording medium is apt to insufficient. Further, in a state of the toner being transferred to the recording medium, the toner is only adhered to the recording medium with a week electrostatic force, and the toner is covered with an external additive. Therefore, fine powders of the toner and the external additive are apt to scatter during a period of time until the recording medium reaches the heating roller and the pressure roller, and dust floats in the air, which may result in environmental pollution.
Furthermore, when the heating and the pressing are conducted simultaneously, the heating and the pressing must be carried out during an interval of a width of a contacting portion (nip width) where the heating and pressing roller comes into contact with the rotation roller. Therefore, when the transfer speed of the recording medium is fast, sufficient fixing cannot be made, and thus there is a restriction in a printing speed.
The present invention has been made to solve such problems as mentioned above, and an object of the present invention is to provide a fixing device and a fixing method, which assure that a vivid fixed image can be obtained by configuring a heating section and a pressing and conveying section separately and maintaining a temperature of the pressing and conveying section at a certain level, without disposing the heat-resistant film between the transferred toner on the recording medium and a heating substrate, thereby causing no damage of the transferred toner, and that a power-saving heating substrate which has a heating element formed on its surface and is capable of quick start can be used.
Another object of the present invention is to provide a fixing device and a fixing method, which assure that scattering of the toner can be prevented by enabling the toner to be heated immediately after the transferring of the toner.
Yet another object of the present invention is to provide a fixing device and a fixing method, which assure that the toner can be fixed to the recording medium at a high speed without damaging the toner surface.
Still another object of the present invention is to provide a fixing device and a fixing method, which assure that even in the case where the recording medium is one having hygroscopic property such as paper, the toner image can be prevented from becoming unclear by evaporation of moisture of the recording medium.
Further object of the present invention is to provide a fixing device and a fixing method, which assure that while scattering of a fine powder is prevented by heating the transferred toner immediately after the transferring, the toner temperature can be decreased at a pressing and conveying section so that the toner can be stuck to the recording medium without allowing the toner to be formed into a fluidized state (into a molten state).
The fixing device of the present invention comprises: a transfer section for transferring a toner formed on a photoreceptor to a recording medium, the toner being attached by developing an electrostatic latent image, a heating section provided at a downstream side of the recording medium from the transfer section, for heating the toner transferred in the transfer section, and a pressing and conveying section provided at a downstream side of the recording medium from the heating section for conveying the recording medium while pressing, with a pressure roller, a surface of the recording medium on which the toner is attached, wherein in the heating section, heating is performed by a first heating substrate from the other side of the recording medium than the surface on which the toner is transferred and/or a second heating substrate from the side of the surface on which the toner was transferred, the second heating substrate being provided apart from the recording medium, and the heating is continued until the toner transferred on the recording medium becomes a softened state or a fluidized state, and in the pressing and conveying section, the recording medium is pressurized at a temperature below a temperature at which the recording medium is in a softened state or in a fluidized state, wherein in the pressing and conveying section, an extension part of the first heating substrate or a fourth heating substrate which is different from the first heating substrate is provided opposite to the pressure roller with the recording medium being disposed therebetween, and the recording medium is subjected to pressing with the pressure roller and the first heating substrate or the fourth heating substrate.
Here, the downstream side means a front in the traveling direction of the recording medium and the roller, namely means a paper discharging side in the case of the recording medium. Reversely upstream side means, in the case of the recording medium, a supply side thereof. Further, a softened state means a state of a toner such that in a viscoelastic property of a toner to be explained infra, the toner is within a temperature range in a rubber region (softening region), and has a resilience in which viscoelasticity of the toner becomes to be lower than in a solid region and the toner is deformed easily by an external force, and a fluidized state means a state of the toner being capable of flowing in a liquid form. It is a matter of course that even in the case of the rubber state, as the temperature is higher, viscoelasticity decreases, and the toner is close to the fluidized state, and even in the case of a fluidized state, as the temperature is higher, flowability increases.
The first heating substrate can be configured to have a structure such that the first heating substrate is extended up to a position where an extended portion of the first heating substrate is located opposed to the pressure roller with the recording medium being disposed therebetween and a heating element is not formed on the extended portion opposed to the pressure roller. The fixing devise further comprises an insulating substrate that is continuously provided throughout the transfer section, the heating section and the pressing and conveying section and comes into contact with a back surface of the recording medium opposed to the surface on which the toner is attached, wherein an electrode for transferring is provided on the insulating substrate for the transfer section, a heating element is provided on the insulating substrate for the heating section, wherein the heating element and the insulating substrate constitute the first heating substrate, and in the pressing and conveying section, the insulating substrate is formed as a support for receiving a pressure of the pressure roller.
Here, “continuously” means that the insulating substrate is not always integrated completely, and connection thereof may be made using an adhesive or the like so as to obtain good heat conductivity along the travelling direction of the recording medium 41. Further, in the vertical direction of the travelling direction of the recording medium, a plurality of heating substrates may be provided apart from each other.
Furthermore, it is preferable that a fifth heating substrate for heating the recording medium is provided at an upstream side of the recording medium from the transfer section, thereby enabling moisture contained in the recording medium to be evaporated beforehand. This fifth heating substrate is used effectively irrespective of the structure of the first heating substrate. Thus the toner can be heated just before the transferring and immediately after the transferring, thereby preventing degradation of an image and scattering of the toner powder.
The fixing method of the present invention is characterized in that a toner is fixed to a recording medium by providing a transfer section for transferring the toner showing an image on one surface of the recording medium, by an electrophotographic process, providing a heating section for changing the toner from a solid state to a softened state or a fluidized state by heating the toner from a side of the toner-transferred surface of the recording medium apart from the surface, and/or from an opposite side of the recording medium while carrying the recording medium, and providing a pressing and conveying section for carrying the recording medium while pressing it, wherein the recording medium having the toner become to a softened state or a fluidized state is conveyed between a pressure roller provided at the toner side of the recording medium and a first heating substrate disposed at an opposite side of the recording medium or a fourth heating substrate different from the first heating substrate, to be pressed at a temperature of the toner which is not higher than a temperature of the toner at the heating section.
In the case of pressing with the pressure roller, the pressing can be carried out while heating the recording medium at a temperature equal to or lower than a temperature of the toner in the softened state with interposing the recording medium between the pressure roller and an extending portion, in which a heating element is not provided, of an insulation substrate of the heating substrate of the heating section by using heat conducting through the insulating substrate. An insulating substrate may be continuously provided throughout the transfer section, the heating section and the pressing and conveying section, and an electrode for transferring at the transfer section and a heating element for heating at the heating section are provided respectively on a surface of the insulating substrate, and an extended part of the insulating substrate is formed as a support of the pressing and conveying section.
Another embodiment of the fixing method of the present invention is a method for fixing a toner transferred at a transfer section on a recording medium, while conveying the recording medium successively through the transfer section, a heating section and a pressing and conveying section, the method being characterized in that a fine powder of the toner is prevented from scattering by heating the transferred toner immediately after the transferring at the transfer section.
According to the fixing device and the fixing method of the present invention, the heating section for heating the transferred toner so that the toner is in a softened state or in a fluidized state (in a molten state) and the pressing and conveying section for carrying the recording medium while fixing the toner under pressure are separated from each other so that the heating substrate is not slid on the recording medium with the transferred toner. And, in the heating section, the toner is heated to be in a softened state or in a fluidized state, and is adhered to the recording medium. Therefore, the toners do not move individually and the image is not deteriorated by pressing with the pressure roller in the pressing and conveying section. Accordingly, there is no need of disposing a heat-resistant film between the toners and the pressure roller. Namely, at the pressing and conveying section, a temperature of the toner decreases and viscoelasticity of the toner becomes large. Therefore, possibility of the toner adhering to the pressure roller is decreased to a great extent. In this case, if the temperature of the pressing and conveying section decreases greatly, sufficient adhesion cannot be obtained. Therefore, it is preferable that in the pressing and conveying section, heating is carried out at a temperature equal to or lower than the temperature of the toner in the softened state.
In the pressing and conveying section of the present invention, at a position opposite to the pressure roller via the recording medium is provided, as a support portion, an extended portion of the first heating substrate of the heating section, or a fourth heating substrate disposed separately from the first heating substrate or a part of the continuous insulating substrate having a heating element formed on the substrate. Therefore, the temperature of the toner heated at the heating section does not decrease rapidly and there is no case where the toner does not impregnate into the recording medium. This is because the temperature of the support portion increases due to heat conduction from the heating section even if the extended portion or the insulating substrate does not have a heating element on that portion, when the substrate is continuous up to the pressing and conveying section. Therefore, a properly low temperature is maintained with preventing a sudden temperature drop, and the temperature of the pressing and conveying section is not higher than that of the heating section.
As a result, deterioration of the toner image hardly arises. In addition, since the heating section is heated by the heating substrate composed of the heating element formed on the ceramic substrate, it is possible to conduct on-demand heating assuring good responsibility. Therefore, even if usually the heating section is turned off or is kept at a low preheating temperature, when starting the fixing device, the temperature can be elevated immediately, thus greatly contributing to power saving and enabling an accurate image to be fixed completely.
Further, by separating the heating section from the pressing and conveying section, the toner image can be heated nearly at the same time as the transferring. Therefore, during the carrying of the recording medium, the toner is formed into a softened state, which makes it possible to prevent scattering of a toner powder, and as a result, contributes to prevention of environmental pollution. Also, by increasing a length of the heating section, sufficient heating can be conducted, and in the pressing and conveying section, the pressing is carried out only by pressing mechanically, and therefore, it is possible to conduct the pressing in a short period of time. As a result, the carrying speed of the recording medium can be increased, and it is possible to increase the number of hourly printed matters to a great extent. Furthermore, according to the present invention, since the heating can be done from the back surface side of the recording medium, adhesion of the toner to the recording medium can be easily obtained.
Also, since the fifth heating substrate for heating the recording medium before the transferring is provided, moisture contained in the recording medium can be evaporated, and even if the moisture is not evaporated completely, it is removed easily at the following heating section. Therefore, it is possible to prevent an uneven surface of the toner due to blisters caused by the heating of the toner into a fluidized state as well as the elevation of the temperature of the recording medium. As a result, a very glossy clean image can be fixed to the recording medium. Furthermore, since the temperature of the recording medium has been increased at the time of the transferring, the temperature of the transferred toner increases immediately by the heating after the transferring and the toner becomes a softened state, thereby enabling scattering of the toner powder to be prevented more. Particularly in color printing, in many cases, four-color toner images are overlapped and transferred in a belt-like form, and then finally fixed. In these cases, toners of different colors are overlapped and transferred, and when the recording medium temperature has been increased before the transferring, scattering of the toners and deterioration of the image can be easily prevented, which is very effective.
Furthermore, since the insulating substrate provided with a heating element on its surface is formed continuously at least from the transfer section to the pressing and conveying section, even at the transfer section, where a heating element is not provided on the insulating substrate, temperatures of the insulating substrate and the recording medium have been elevated, and therefore, the toner is heated to a certain extent just after the transfer. However, since it is better not to increase the temperature of the photoreceptor from the viewpoint of its service life, the heating element provided upstream thereof is designed so as to inhibit heat generation and elevation of temperature thereof. Further, since the heating element can be formed in the vicinity of the electrode for transferring, the toner is fully heated immediately after the transferring. As a result, not only a period of time for forming the toner into a softened state of a fluidized state (a molten state) can be decreased but also scattering of the toner can be surely inhibited. In addition, the insulating substrate is provided on the surface (back surface) of the recording media opposite to the surface on which the toner is transferred, and the heating element is formed on the surface of the insulating substrate, and therefore, the heating is conducted from the back surface of the recording medium. As a result, the toner is also softened from the recording medium side to be in a fluidized state. Namely, adhesion of the toner to the recording medium is very good. Thus, when the toner is pressed at the pressing and conveying section, and the toner temperature is decreased and the toner surface becomes not in a fluidized state, it becomes easy to adhere the toner to the recording medium.
Further, in a conventional method for performing heating and pressing simultaneously, the heating and pressing of the toner are carried out only at a contact portion (a nip portion) of a heating/pressing roller with a rotation roller. Therefore, a passing time during which a recording medium passes through the nip portion is short, and minute adjustment is required for a heating temperature and a pressure. In such a conventional device for printing 40 sheets of recording mediums per minute, the passing time at a 5 mm long nip portion is about 25 ms at a conveying speed of 200 mm per sec. However, in the present invention, the heating section is separated from the pressing and conveying section and only pressing is required on the pressure roller. Therefore, the recording medium can be carried, for example, in as very short period of time as about 10 ms. Thus, 2.5 times increase in speed can be achieved. Namely, a printing speed can be increased greatly. For fluidization of a toner at the heating section, even if a conveying speed of the recording medium is fast, heating is carried out by increasing a heating distance. Therefore, a printing speed can be increased.
Next, the fixing device and the fixing method of the present invention are explained in detail by referring to the drawings. As shown in
Namely, in conventional fixing devices, as mentioned above, when aiming at power saving without using a halogen lamp, the fixing must be carried out by heating and pressing with a heat-resistant film being disposed between a ceramic heater and a surface of a recording medium on which a toner was attached so that the toner-transferred surface should not be rubbed directly with the ceramic heater. Therefore, there is a problem that heat from the ceramic heater is not conducted directly to the toner-transferred surface and thus there is much loss of heat. Further, not only the heat-resistant film becomes a heat resistance but also its temperature decreases during the rotation of the heat-resistant film. Therefore, re-heating the heat-resistant film is necessary, which results in further power consumption. Furthermore, the heat-resistant film must be carried synchronously to a speed of the recording medium, resulting in complicated mechanism.
The present invention is characterized in that by changing a conventional idea of performing both heating and pressing of the toner simultaneously, the heating section 1 for heating the toner transferred to the recording medium to change the toner from a solid state to a softened state or a fluidized state (molten state) is separated from the pressing and conveying section 2 for pressing the toner 42 to the recording medium 4 while cooling the toner 42; thereby the heating substrate 10 mainly composed of a ceramic heater being used, and the recording medium 41 being carried while being pressed directly with a rotation roller (the pressure roller 21). The pressing and conveying section 2 is configured such that the extended part of the first heating substrate 10a or the fourth heating substrate 10d is used at a position opposite to the pressure roller 21 with the recording medium 41 disposed between the heating substrate and the pressure roller 21, thereby allowing the recording medium 41 to be pressed.
By using such a configuration, the toner 42 is heated in the heating section 1 to be changed from the solid state to a softened state or a fluidized state and impregnated into the recording medium 41, and then is subjected to pressing by the pressure roller 21 in the pressing and conveying section 2, resulting in decrease in its temperature and fixing the toner to the recording medium. In this case, since the first heating substrate 10a or the fourth heating substrate 10d is provided as a support at a position opposite to the pressure roller 21 with the recording medium 41 disposed between the heating substrate and the pressure roller 21, the temperature of the toner 42 does not decrease rapidly and the toner is not solidified. As a result, the toner hardly sticks to the pressure roller 21 side and deterioration (loss) of the toner 42 hardly arises. In addition, in the pressing and conveying section 2, it is sufficient to apply a force instantly, and also sufficient heating can be performed by increasing the travelling distance in the heating section 1, which makes it possible to increase the conveying speed of the recording medium 41 and enables the number of sheets to be treated per minute to be increased.
In the above-mentioned example, the fourth heating substrate 10d is provided at a position opposed to the pressure roller 21 with the recording medium 41 disposed between the heating substrate 10d and the pressure roller 21. Meanwhile, as shown in
Here, the softened state or the fluidized state (molten state) of the toner 42 in the heating section 1 is explained. The toner is prepared by mixing various components. For example, a main component is an acryl-styrene copolymer, and its mixing ratio can be set at various ratios. Also other components such as a plastic, a pigment, a dye, a plasticizer (for adjusting hardness) and a wax (related to starting of softened state or fluidized state) are mixed. Further, an external additive (small particles comprising titanium oxide, silica and the like and having a size of not more than 1 μm are adhered to the outside of the toner particles so that the toner particles do not adhere to each other) is also mixed. Therefore, though it is difficult to show characteristics of the toner unconditionally, an example of a change of viscoelasticity of the toner 42 to a temperature is illustrated as a general characteristic in
Also, in color printing, if toner particles are very small, it is possible to carry out mixed printing by pressing the toner particles. However, in general terms, a temperature region suitable for monochrome printing is applied to such mixed printing. If the temperature is further increased, there appears a point C of temperature change where lowering of viscoelasticity becomes abrupt again (212° to 265° C. in the case of PET, and about 200° C. in the case of an acryl-styrene copolymer). However, absolute values of these temperatures change according to a composition of the toner and are not stable. The temperature of this point C is a point where the toner changes from a rubber region to a fluidization region and is generally called a temperature where melting or fusion begins. In the region from the point B to the point C of temperature change, the toner is in a state softened to an extent so as to be impregnated between paper fibers by applying a pressure to the toner as explained above. As mentioned above, in this region, monochrome printing can be made without any problem, and the temperature range between the points B and C is called a softened state.
Meanwhile, in the case of color printing, it is necessary that toners having different colors are mixed sufficiently. Therefore, there is a case where clean printed matter cannot be obtained with a normal grain size of a toner only by forming into a softened state. However, when the toner temperature reaches a temperature in the fluidization region of not less than the point C of temperature change as shown in
Therefore, in the heating section 1, the toner is heated until it is in a softened state or in a fluidized state (being suitable for a color fixing region), depending on kind of printing. The fixing in the pressing and conveying section 2 is characterized by adhering the toner pressing while decreasing the toner temperature to a temperature where the toner is in a softened state and is easily impregnated between the fibers or a temperature where the toner is in a fluidized state and the toners having different colors are mixed and impregnated between the fibers.
Low temperature fixing of the toner 42 has progressed because of a demand for processing at a higher speed. Also it is necessary to consider not only printing of characters but also printing of an image on an entire surface of a recording medium. When, for example, an acryl-styrene resin is used as a component for the toner, in the case of a 2 μm thickness, 1.4 of a specific heat and 0.126 g per one A4 size recording medium, an amount of heat required for the toner is 17.6 J/100° C. Meanwhile, in the case of A4 size plain paper of a 70 μm thickness, 1.25 of a specific heat and 4.2 g, an amount of heat required for the paper is 525 J/100° C. Also from this point of view, it is very effective to incline a fixing device for effective use of heat like the fixing method of the present invention, and increase in the number of heating substrates will enable fixing of 60 sheets or more per minute.
In the example shown in
On the other hand, as explained later, when the toner is heated from the toner-transferred surface side by means of the second heating substrate 10b, as shown in
In the case of heating from the back surface side of the recording medium 41, as shown in
The second heating substrate 10b is disposed at the side of the toner-transferred surface of the recording medium 41 in the heating section 1 and is separated from the recording medium 41. Namely, the second heating substrate 10b is configured to be capable of heating the toner 42 without coming into contact with the toner 42 transferred on the recording medium 41. In other words, this second heating substrate 10b is so designed as to heat the toner 42 with radiation heat from the second heating substrate 10b but not by contact with the recording medium 41. Therefore, the toner-transferred surface of the recording medium 41 is not rubbed with the second heating substrate 10b, and a part of un-fixed toner 42 is not peeled off. From this point of view, it is preferable that the second heating substrate 10b has a structure enabling heat radiation to be easily emitted from its surface. For example, as shown in
For example, it is preferable that the second heating substrate 10b has a structure allowing heat radiation to be easily emitted by forming thereon a heat radiation layer made of a material having good heat radiation such as black alumite or glass and by forming an uneven surface of a width of from about 10 to 50 μm and a depth of from about 10 to 50 μm.
Specifically the heat radiation layer is formed by applying a paste mainly comprising a mixture comprising ruthenium oxide (RuO2) and alumina (Al2O3) similarly to the heating element 12 (in the heating element 12, Ag is further mixed to adjust a resistance value) by printing for sintering. Therefore, before the paste has been hardened completely, by pressing the above-mentioned convex/concave structure or the like onto the paste, an uneven surface is formed and thus, a desired rough surface can be formed.
Further, it is known that an amount of heat radiation of an object is proportional to a value of (emissivity)×(the fourth power of an absolute temperature of an object surface (K4)). Therefore, it is preferable to increase a surface temperature of the heat radiation layer 18 in order to increase an amount of heat radiation. From this point of view, it is preferable to concentrate as much heat as possible from the heating element 12 on the heat radiation layer 18 without releasing the heat. Therefore, as mentioned above, it is preferable to form a heat insulating layer, which is not shown in the drawing, between the heating element 12 and the insulating substrate 11 so that transmittance of the heat generated by the heating element 12 to the insulating substrate 11 is reduced as far as possible. However, as mentioned above, in the case of common use with the third heating substrate 10c, heat transmission to the insulating substrate 11 side is necessary, and so it is not preferable to dispose the heat insulating layer between the heating element 12 and the insulating substrate 11.
Further in the example shown in
This third heating substrate 10c is not an essential one. On the other hand, as described below, the third heating substrate 10c is provided with a resistive element for temperature measurement, and a temperature of the outer periphery of the pressure roller 21 is measured via the third heating substrate 10c. In the case of continuous printing, there is a case where a temperature of the outer periphery of the pressure roller 21 coming into contact with the heated toner 42 is elevated, and no heating by the third heating substrate 10c is necessary, or there may be a case where cooling by air cooling or the like is necessary. The structure of the first heating substrate 10a itself, and essential portions of the second heating substrate 10b, the third heating substrate 10c and the fifth heating substrate 10f are nearly the same as the structure of so-called a ceramic heater where a heating element is formed on one surface of conventional ceramic substrate. Therefore, an example of a common heating substrate 10 is described below in reference to
A purpose of the pressing and conveying section 2 is to cohere the toner with the toner temperature having been lowered. However, if the temperature decreases too rapidly, the pressing cannot be carried out surely. Therefore, it is preferable to carry out heating to a certain extent lest the temperature should decrease rapidly. Thus, the pressing of the recording medium 41 is carried out at a temperature equal to or lower than the temperature of the toner in the softened or fluidized state in the heating section 1, namely at a temperature lower than that of the fluidization region. In other words, the pressing is done at a temperature lower than the temperature for heating in the heating section 1. Therefore, when the pressure roller 21 is heated and its temperature becomes too high by continuous printing, as mentioned above, there is a case where the heating is not done and cooling (air cooling) is conducted.
In this pressing and conveying section 2, when the temperature of the pressure roller 21 is not more than the temperature of the softened toner, as shown in
From the viewpoint mentioned above, in the pressing and conveying section 2, the heating from the back surface side of the recording medium 41 is preferable rather than elevation of the temperature of the pressure roller 21. Therefore, as shown in
For a heating/pressing roller used for conventional fixing devices, a rubber roller which is easily heated is used, and the pressing is carried out while heating. However, in the present invention, heating is not intended, and the pressing is rather carried out while cooling. Therefore, it is preferable that at least the outer surface of the pressure roller 21 is formed from a material being easily separated from the toner, having releasability and assuring that the toner is not adhered to the pressure roller 21.
Specifically, the pressure roller 21 is made of a relatively hard insulating material such as plastic, and a fluorine-containing resin film for prevention of adhesion of the toner is formed on an outer surface 21a. In the heating of the pressure roller 21, an amount of heat for allowing the toner 42 to be changed into a softened state or a fluidized state is not required, and the heating is done lest the temperature of the toner 42 in the softened state or the fluidized state should lower suddenly, thereby solidifying the toner. Therefore, the toner temperature needs not to be so high, and as shown in
As mentioned above, the purpose of the pressure roller 21 is to press the toner 42 changed into a softened state or a fluidized state in the heating section 1 on the recording medium 41 in order to impregnate the toner 42 into the recording medium 41. However, if the temperature of the toner 42 on the recording medium (paper) 41 carried to the pressing and conveying section 2 lowers suddenly, the toner may not be impregnated sufficiently into the recording medium 41 only by pressing. In consideration of such a case, it is preferable that the temperature of the pressure roller 21 is high enough to a certain extent lest the toner temperature should lower suddenly. Therefore, in the example shown in
As mentioned above, when the transferred toner 42 is heated, its viscoelasticity decreases gradually as shown in
In the transfer section 3, in the same manner as in usual electrophotographic printer, while rotating a photoconductor drum 31 being an example of a photoconductor so that the photoreceptor drum 31 passes through a cleaning section 32, a electric charge removing section 33, an charging section 34, an exposure (optical writing) section 35 and a developing section 36, optical writing is conducted at the exposure section 35 using laser beam or LED light to form an electrostatic latent image on the photoconductor drum 31, and then the toner 42a is adhered to the electrostatic latent image on the photoconductor drum 31 at the developing section 36 to be developed and form a visible image. Then, by transferring the toner 42a from the photoconductor drum 31 to the recording medium 41 with an electric force using a transfer device 37, a photographic image is formed on the recording medium 41. The toner 42a is prepared by mixing various pigments to a resin. This recording medium 41 is then carried via the heating section 1 and the pressing and conveying section 2 in order, thereby fixing the image of the transferred toner 42. In the case of color printing, the any color toners 42 of black (K), cyan (C), magenta (M) and yellow (Y) are transferred in order, and after the transferring the toners of plural colors, the toners are heated in the heating section 1 to be changed to a softened state and then into a fluidized state, followed by pressing. If the toner is carried for a long period of time in a state of being transferred, it may be released and may float in the air. Therefore, it can be considered that soon after the transferring of the toner of each color, the toner is fixed temporarily.
In the transfer section 3 shown in
In other words, as shown in
As mentioned above, it is necessary that the insulating substrate 5 is formed continuously from the heating section 1. The term “continuously” does not mean, as mentioned above, that the insulating substrate 5 is not necessarily integrated. The insulating substrates 5 may be formed separately for the heating section 1, the transfer section 3 and the pressing and conveying section 2, and then connected with an adhesive or by abutting to each other. Namely, the insulating substrates 5 may be connected so as to enable sufficient heat conduction to be obtained. The entire insulating substrate 5 is not necessarily made of an insulating material, and at least surfaces thereof, on which the heating element 12 and the electrode 39 for transferring are provided, may be made of an insulating material. Therefore, the insulating substrate may be a metal plate having an insulating film formed thereon. With such configuration, the insulating substrate 5 is excellent in thermal conductivity.
The insulating substrate 5 may be one which is used as an insulating substrate of the heating substrate to be used in the heating section 1. Namely, unlimited example of a usable insulating substrate is one having excellent thermal conductivity and made of alumina or the like. A shape thereof is preferably rectangular, but is not limited thereto. A width W thereof (see
As described below, the heating element 12, etc. are formed on the surface of the insulating substrate 5, and a protection layer such as a cover substrate is formed on the surface of the insulating substrate. One or more of convex(s) and concave(s) are formed on the surface of the cover substrate, and further suction holes and/or suction grooves are formed on the insulating substrate 5 and the protection layer thereon, and by suction of the recording medium 41, a contact pressure at the convex portions is increased, which enables heat conduction from the heating element 12 to be enhanced more. Such convex and concave are formed, for example, in a shape of chevron (Quonset hut shape; D-shaped) in a height of a portion of the heating element of about 0.2 to 0.3 mm per a 50 mm length of the insulating substrate 5. Examples of a method for forming such convex include a method of forming a plurality of insulating substrates 5 having a D-shaped surface and connecting the substrates, a method of when forming a glazed layer (heat-insulating layer), which is not shown, on the insulating substrate 5, increasing a thickness of a center part of the glazed layer before forming the heating element 12, a method of increasing the thickness of the heating element 12 or the thickness of the protection layer 17, and the like methods. For the suction of the recording medium, it is possible to use an electrostatic chuck method for electrostatic suction by forming an electrode. Anyway, it is preferable to form a convex by swelling a part of the heating element 12.
In the transfer section 3, as mentioned above, the electrode 39 for transferring is formed on the surface of the insulating substrate 5. The electrode 39 for transferring is one formed by adhering a stainless alloy to the insulating substrate 5 with an elastic adhesive, and the surface and corner portions thereof are finished smooth with a metal film of about 30 to 50 μm thick and about 8 mm wide. A voltage of, for example, about 500 V to 1000 V which is reverse potential to a potential of the charged toner 42a is applied via an electrode terminal not shown in the drawing for electrically charging the recording medium 41 to transfer the charged toner 42a from the surface of the photoconductor 31. If an electric potential of the electrode 39 for transferring is too high, the transferred toner 42 is charged with a reverse electric potential, and is attracted to an electric potential of the photoconductor 31 when the recording medium 41 separates from the transfer section 3. Therefore, in the case where the recording medium 41 is not a continuous sheet of paper, but cut paper of A4 and B5 sizes, since the recording medium 41 is wound on the photoconductor 31, it is necessary to set the toner 42 to have an electric potential which allows the recording medium 41 not to be wound on the photoreceptor by separating the toner 42 from the photoconductor 31. The electrode 39 for transferring can also be fixed to the surface of the insulating substrate 5 by increasing its width to be extended toward the upstream side of the transfer section 3 or by connecting separate electrode parts on the insulating substrate. In the case where the fifth heating element 12e described below is provided, the electrode 39 for transferring can be provided on the surface thereof via an insulating layer.
In this embodiment, the substrate, on which the electrode 39 for transferring of the transfer section 3 is disposed, is formed by extending the insulating substrate 5 of the heating section 1 having the heating element 12 thereon or is connected to the insulating substrate of the heating section 1. Therefore, also in the transfer section 3, the temperature of the insulating substrate 5 is increased and the recording medium 41 is also heated. As a result, since the transferred toner 42 is heated immediately after the transferring, it is easily adhered to the recording medium 41, thereby not only inhibiting scattering of fine powders of the toner 42, deterioration of an image and winding of the recording medium 41 on the photoconductor 31 but also reducing a period of time for changing the toner 42 into a softened state or a fluidized state. As shown in
In the example shown in
The fifth heating substrates 10f can also be formed in the same manner as in the first heating substrate 10a, and as shown in
From the viewpoint of heating the recording medium 41 for evaporating moisture and effectively heating each heating part, for example, as shown in
From the viewpoint of effective use of heat, it is preferable that an angle of the inclination of the fixing device with respect to a horizontal plane is as large as possible. However, since the transferred toner 42 is only attached to the surface of the recording medium 41 such as paper, if the inclination is too large, the toner 42 may slip down. The same may arise in the case of heating until the toner 42 becomes a fluidized state in the heating section 1. From this point of view, a smaller inclination is preferred. In consideration of the above-mentioned points, the inclination is preferably from 20° to 60°, further preferably from about 30° to 45°. As mentioned above, since the fixing device is enclosed with the cover case 7 and is inclined, the recording medium 41 can be dried even with weak heat in the recording medium heating section 4, and the toner 42 can be heated to be changed into the softened state or the fluidized state in the heating section 1, which as a whole, can reduce energy consumption, and contributes to prevention of global warming.
In the embodiment shown in
The above-mentioned first to fifth heating substrates 10a to 10f are of the same structure and are explained simply as a heating substrate 10. The heating substrate 10 has the same structure as conventional heating head which is used for recording and erasing of a card and the like. For example,
More specifically, the heating substrate has a structure such that the heating element 12 and the resistive elements 13 (13a, 13b) for temperature measurement are provided on one surface of the insulating substrate 11 made of ceramic such as alumina. The shapes and arrangement thereof may be selected optionally. In the embodiment shown in
In the case where the heating substrate 10 is formed using one long insulating substrate 11, the heating substrate is controlled to enable the temperature of the entire insulating substrate 11 to be always uniform by forming a plurality of electrodes 14 and temperature measurement terminals 15 in the midst of the heating elements 12 and the resistive elements 13 for temperature measurement to allow a voltage to be applied dividedly or allow temperatures of each region of the insulating substrate 11 to be set independently.
In the embodiment shown in
The heating element 12 is formed by selecting, for example, Ag, Pd, RuO2, Pt, metallic oxide, glass powder and the like, mixing them to make a temperature coefficient, resistance value and the like most suitable, forming the mixture into a paste-like shape, and then subjecting the mixture to printing and baking. A sheet resistance value of the heating element 12 formed by the baking can be changed by an amount of a solid insulating powder. The resistance value and the temperature coefficient can be changed by a ratio of the amounts of mixed components. A similar paste-like mixture prepared by increasing a ratio of Ag and decreasing a ratio of Pd is used as a material for the conductors (electrode 14, temperature measurement terminal 15, connecting conductor 16), thereby making it possible to form the conductors by printing in the same manner as in the heating element 12. There is a case where the mixing ratios need to be changed depending on a working temperature of the heating element in relation to terminal connection. When the ratio of Ag increases, the resistance value can be decreased. A positive higher temperature coefficient of the resistance of the heating element 12 is preferable, and it is preferable to use a material of from 1000 to 3500 ppm/° C. Further, though it is not shown in the drawing, the electrodes are provided at suitable positions along a current flowing direction of the heating element 12, thereby enabling a voltage to be applied partly and enabling the respective temperatures of the heating elements to be changed.
The positive higher temperature coefficient of the resistance means that if the temperature is elevated, increase of the resistance value is large. Therefore, by measuring the resistance value in a state of heat generation, detection of actual heat generation temperature can be made easily accurately from a deviation from a reference resistance value, and a deviation from the desired heat generation temperature can be corrected easily by adjusting an effective applied power. In the case of a fixing device, commercial AC power source is used as a power source for the heating element 12 in many cases, and there are many cases where the commercial AC power source is used as it is, for example, in the form of half-wave rectification or full-wave rectification without changing to a direct current. In that case, an effective value is controlled with a pulsating current as it is. It should be noted that a two-way thyristor (brand name: TRIAC) is used for control, and the control is done using an effective value. The temperature measurement is also done using an effective value, and the temperature control is done using TRIAC. Further, when the temperature coefficient of the resistance is positive, in the case of excessive elevation of the temperature, the resistance value increases, a current value decreases, an amount of heat generated decreases, and the temperature reaches to a saturated state earlier. Therefore, temperature stability at high temperatures is excellent, and overheating due to thermal runaway can be prevented. In addition, a standard width of the heating element 12 may be set such that a given temperature is obtained according to application, and a plurality of heating elements 12 may be arranged in parallel.
Further, the electrodes 14 comprising a good electric conductor such as a silver-palladium alloy having a small palladium ratio or an Ag—Pt alloy are formed by printing at both ends of the heating element 12. As shown in
Similarly to the heating element 12, the resistive elements 13 (13a, 13b) for temperature measurement are formed on the surface of the insulating substrate 11 in the vicinity of the heating element 12. It is preferable that the resistive elements 13a, 13b for temperature measurement are formed along the heating element 12 as shown in
The resistive elements 13 for temperature measurement may be formed using the same material as in the heating element 12, however, a material having a large absolute value (%) of the temperature coefficient is preferred. The resistive elements 13 for temperature measurement are those which do not generate heat but detect the temperature of the insulating substrate 11 and allow the toner 42 to reach a softened state or a fluidized state. For example, a width of the resistive element for temperature measurement is 0.5 mm, and a length thereof is somewhat smaller than the heating element 12. An applied voltage of the resistive element for temperature measurement is as low as possible so as not to cause heat generation of the resistive element 13 for temperature measurement itself, and for example, about 5 V is applied thereto. Namely, since the resistive element 13 for temperature measurement is disposed directly on the insulating substrate 11, the temperatures of the both are nearly the same, and by measuring the resistance value of the resistive element 13 for temperature measurement, the temperature of the surface of the insulating substrate 11 can be known. Therefore, the temperature of the insulating substrate 11 for heating the recording medium 41 is adjusted so as to change the toner into a softened state or a fluidized state is obtained. Namely, generally the resistance value of the material of the resistive element for temperature measurement varies as its temperature varies, and therefore, the temperature of the resistive element for temperature measurement is measured by measuring variation of its resistance value. While the temperature detection means is described later, by detecting a voltage variation at both ends of the resistive element 13 for temperature measurement, a resistance value of the resistive element 13 for temperature measurement is detected, when a current is constant, and a temperature of the resistive element 13 for temperature measurement is obtained from the detected resistance value and a temperature coefficient (which varies depending on the material thereof and is known beforehand). When the temperature coefficient is larger, a measurement error can be minimized. In that case, the temperature coefficient may be either plus or minus.
The resistive element 13 for temperature measurement can be formed by printing or the like, and its material is not limited to the same one as that of the heating element 12, but is selected according to application. Namely, when a minute temperature difference is needed, it is possible to use a material having a different mixing ratio of Ag and Pd or a completely different material having a large temperature coefficient for the resistive element 13 for temperature measurement. The temperature measurement terminals 15 of the resistive element 13 for temperature measurement are also formed using a material having good conductivity and prepared by increasing a ratio of Ag and decreasing a ratio of Pd in the same manner as in the electrodes 14 of the heating element 12. The temperature measurement terminals 15 are not necessarily formed at the ends of the resistive element 13 for temperature measurement. For example, as shown in
While in
In the embodiment shown in
A size (diameter) of the through-hole 19a is about 0.3 to 0.5 mm, a width of the groove 19b is about 0.3 to 0.5 mm, and a depth of the groove 19b is about 0.2 to 0.3 mm. A small size blower or a small size vacuum pump (a vacuum chuck for semiconductor wafer) can be used as a suction tool. Reclamation of heat from the sucked heated air can be considered at a preheating section (preheating of the recording medium before and after the transferring). Further, as shown in
On the surfaces of the heating element 12 and the resistive element 13 for temperature measurement, the above-mentioned protection layer 17 is provided, and comes into direct contact with the back surface of the recording medium 41, which allows the temperature of the recording medium 41 to rise fast and is advantageous from the viewpoint of power saving. Further, the number of heating elements 12 is increased or decreased properly depending on a temperature of generated heat and a conveying speed of the recording medium 41 (in the case of a 70 μm thick paper of A4 size, by heating with an amount of heat of about 6 J during conveying of a sheet of paper, the toner 42 can be molten). In addition, in the example shown in
In the examples shown in
In the embodiment shown in
The embodiment shown in
In the example shown in
As mentioned above, if the temperature for heating the toner 42 is too low, the toner cannot be changed into a softened state or a fluidized state and cannot be fixed sufficiently. Further, if it is too high, a part of the toner 42 adheres to the pressure roller 21 in the pressing and conveying section 2, which is not preferable. Therefore, the temperatures of the heating substrates 10 need to be controlled accurately. Temperature control means (drive circuit) of the fixing device shown in
The temperature of the insulating substrate 11 can be detected by measuring a voltage V between both ends of the resistive element 13 using a constant electric current supplied from a constant current circuit 350 with an electric current of a power source 310, and by obtaining a resistance value of the resistive element 13 for temperature measurement at that time. Namely a temperature of the insulating substrate 11 (see
This theory of temperature measurement will be explained below in more detail by referring to
In the above-mentioned example, the power source for the heating element 12 is separated from the power source for the resistive element 13 for temperature measurement. However, by sharing the power source for the both, a commercial power source of, for example, AC 100 V to 240 V can be used. A circuit diagram of the example is shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-148106 | Jul 2015 | JP | national |
| 2015-257395 | Dec 2015 | JP | national |
| 2016-026299 | Feb 2016 | JP | national |
| 2016-095626 | May 2016 | JP | national |
