Patent Grant
7356298
The present invention relates to an image fixing apparatus and a process for fixing an image in electrophotography utilized in a copying machine, facsimile, or a printer, and more particularly to an image fixing apparatus and a process for fixing an image which is useful in saving energy.
Conventionally, there is an increasing demand for saving resources and energy for the sake of preserving global environment. In a technology utilizing electrophotography, a trend in saving electricity for the purpose of saving energy has been actively pursued, specifically in the technology of image fixing which accompanies rapid consumption of electricity, thereby calling for fixing in low temperatures. In order to achieve a low-temperature fixing, a melting point or a softening point of a toner inevitably needs to be decreased, and when melting point or softening point of a thermoplastic resin contained in the toner is decreased, a melt viscosity of such thermoplastic resin tends to deteriorate. In such thermoplastic resins, the melting point or the softening point is determined by an amount of molecules, distribution in molecular amounts, rate of crystallization, rate of cross-linking, and intermolecular forces. In order to decrease the melting point or the softening point of such resins sharing the same structures, the amount of molecules, the rate of cross-linking, or distribution of molecules need to be reduced among the conditions mentioned above. However, in terms of distribution of molecular amount, there is a limit in order to maintain resin preservability, and accordingly, the bottom line is inevitably determined. Consequently, when amount of molecules is decreased, the distribution of molecular amount is narrowed. Generally, when an amount of molecules is decreased, melt viscosity deteriorates due to weakened bonding force interacting between the molecules owing to shortened molecular chains. The melt viscosity also deteriorates when distribution of molecular amount is narrowed due to the weakened bonding force interacting on molecular chains. Further, melt viscosity deteriorates when the rate of cross-linking between the molecules is reduced, due to easy moving of molecules. However, as disclosed in the Japanese Patent Application Publication (JP-B) No. 51-29825, there is a process for fixing the toners deteriorated in melt viscosity without causing off-settings.
Another technology which utilizes such method is for example, disclosed in the Japanese Patent No. 2,516,886. According to this publication, the heater element in the JP-B 51-29825 is configured as a linear heater element provided with pulse electricity, and having a structure to suppress excess heat exhaustion within the system. By such arrangements, advantages such as unnecessary preheating which contributes to shortened standing time is attained.
However, when heating using unvaried pulse electricity, a temperature in the front edge portion of an image tends to be low due to insufficient heat of the heating body, a supporting body thereof, or a platen roller which remain cool. On the other hand, in the rear edge portion of an image, temperatures of the heating body, the supporting body of the heating body, or the platen roller tends to increase due to heat accumulation, thereby difference in temperature tends to be caused between the front edge portion and the rear edge portion of the image. As a countermeasure to such phenomenon, there is a method in which the temperature in the front edge portion of the image is set higher to avoid defective fixing while area of a rubber region in the toner is determined larger to cope with the temperature increase in the rear edge portion of the image. However, when the melting point of the toner is set low from the stand point of saving energy, it becomes very difficult to retain enough rubber regions, and hence, hot-offsetting is caused, or if not causes hot-offsetting, glossiness in the image tends to be produced due to excessively deteriorated melt viscosity of the toner. Moreover, if the temperature is set higher from the beginning, an effect of saving energy which the method aims to attain may be spoiled, and therefore, a different technological approach to attain saving in energy is pursued.
By carefully reflecting on the drawbacks of the conventional art, the present invention provides a process for fixing a toner image and an image fixing apparatus which further saves energy while maintains stability in operation without causing off-settings and the like.
The first aspect of the present invention provides an image fixing apparatus, comprising: a linear heating body; an endless belt entrained around thereon; means for supplying electricity to the linear heating body with pulse electricity; a pressure body for interposing a subject to be fixed having an image between the endless belt; the image is heated by the linear heating body by way of the endless belt, and thereafter being cooled and removed from the endless belt; wherein the image is formed by a toner comprising a binder containing a resin as a main component, and one of a softening point and a melting point of the toner is in the range of 50 to 160° C., and a viscosity of the toner is in the range of 10 to 1013 centi-poise at temperature of one of a softening point and a melting point or more of the toner.
In the second aspect of the present invention, there is provided a process for fixing an image, comprising: a process for interposing a subject to be fixed having an image between a pressure body and an endless belt entrained around a linear heating body which receives pulse electricity from means for supplying pulse electricity, in an image fixing apparatus; a process for heating the image by the linear heating body by way of the endless belt; a process for separating the subject for fixing image from the endless belt after the image is cooled, wherein the image is formed by a toner comprising a binder containing a resin as a main component, and one of a softening point and a melting point of the toner is in the range of 50 to 160° C., and a viscosity of the toner is in the range of 10 to 1013 centi-poise at temperature of one of a softening point and a melting point or more of the toner.
The present invention will be described hereinafter in detail. The present invention provides an image fixing system which is a system for fixing a toner image, comprising: a linear heating body, an endless belt entrained around thereon, a pressure body for interposing a subject to be fixed having an image between the endless belt, and means for supplying pulse electricity to the heating body, wherein an image on the subject to be fixed is heated by the linear heating body by way of the endless belt, and separates the subject to be fixed from the endless belt following a step for cooling, and the image is formed by a toner comprising a bonding agent in which the main ingredient is a resin, the softening point or the melting point of the toner is in the range of 50 to 160° C., and the viscosity in the range of 10 to 1013 cm-P (centi-poise) at temperatures on or greater than the softening point or the melting point. The image fixing system of the present invention successfully solved shortcomings of the conventional art by altering widths of the electric pulse provided to the heating body, or by varying the number of electric pulses supplied to the heating body per prescribed time unit during a process for fixing the image on a single subject to be fixed.
In general, a toner image is fixed by fusing the image, specifically a binder resin which is a fusing component of the toner in the toner image, with heat and pressure onto a subject to be fixed. From the viewpoint of achieving a satisfying fusion, the toner image preferably is exerted a strong pressure, and in order to give strong pressure, the subject to be fixed having a toner image on the substrate preferably is exerted a continuous pressure one after another by a heated thin pressure body disposed in a ridge line in the MD (mechanical direction). The “linear heating body” as referred in the present invention defines a very thin heated pressure body in a rigid line, and does not refer to a heating body such as a nichrome line or the like. The linear heating body may be furnished within the guide roller or may be provided separately from the guide roller. The linear heating body does not necessarily rotate. An example of the linear heating body includes a thermal head or the like. The linear heating body of the present invention may be heated by any known suitable heating methods such as resistance heating, induction heating, high frequency vibration heating, or a laser heating. Further, waveforms of an electric pulse is not limited and may be anything from square, triangle, or sinusoidal. Also, the intervals between the pulses do not necessarily have to be an off-state.
That is, by reducing frequency of electric pulses, or by reducing width of the pulse electricity during the start of fixing to the end of fixing corresponding to a region of an image on a single subject to be fixed, energy for supplying electricity is gradually reduced, and the surface temperature of the heating body is not excessively increased, the temperature of the toner may be maintained generally uniform, thereby generation of hot-offsettings, and irregular glossiness in the image may be inhibited.
In practice, if a ratio of electric supply at the time of starting and ending of the fixing process when converted in the MD (mechanical direction) having length of 420 mm (if the subject to be fixed is applied in a longitudinal direction of A3 as defined in JIS P 0138), is 10:9 to 10:1, fixing was proved to be carried out stably in a manner of the present invention, and when accounting for fluctuation in actual condition of use, preferably is in the range of 10:8 to 10:2, and more preferably is 10:8 to 10:3, and most preferably is 10:7 to 10:4, all of which extremely surpass energy savings accomplished in the conventional art. Here, decrease in electric supply (amount of electricity) may be carried out continuously, or in a step-down approach, as far as gradual decrease is maintained. However, allowing for minor fluctuations under various operating conditions, a step for cooling as furnished in the present invention may be necessary after the step for heating.
Generally, fixing of toners is carried out under a state so-called “rubber region of the resin” which refers to a phenomenon in which, as the temperature of the toner increases, resin in the toner begins to intenerate, and leads to deterioration in viscosity of the resin. Note that “rubber-like region” herein does not refer to an elastic restoring force when a power is exerted to deform a high polymer material and released thereafter, but rather to a factor for decrease in stress (or creep factor) of the material itself. The toner in the conventional roller fixing system has an extremely high viscosity in the resin contained in the toner, exhibits high self cohesion in a so-called rubber-region which covers from inteneration to a complete melting, thus hardly causes off-setting meaning a portion of the toner adheres on the fixing roller. However, when the toner is complete melted, the viscosity of the toner remarkably drops to cause deterioration in self-cohesion, and causes portion of the toner to adhere to the fixing roller.
In general, when a thermoplastic resin is heated, it usually remains solid up to the softening point, and then becomes soft to exhibit viscosity above the softening point, and reaches a state of viscous liquid when further heated above the melting point. The conditions such as range of temperature between the softening point and the melting point, viscosity of the toner from the softening point to the melting point and above the melting point, are subject for change with respect to molecular amount of the resin, distribution of molecular amount, rate of crystallization, rate of cross-linking, and intermolecular forces. Accordingly, resins which exhibit 10 to 1013 cm-P (centi-poise) in between the softening point and the melting point may be used in the present invention from on or above the softening point, and apparently on or above the melting point. Therefore, the term “rubber-like region” used herein does not refer to an elastic restoring force when a power is exerted to deform a high polymer material and released thereafter, but rather to a factor for decrease in stress (or creep factor) of the material itself.
When the melt viscosity of the toner is low, apparently the deterioration in viscosity in a state of rubber-like region becomes intense, and accordingly, such toners are not qualified for use in the heat roller fixing system of the conventional art due to off-setting caused if used without coating silicone oil on the surface of the roller. However, when viscosity of the oil is extremely low, a method for coating oil tends to be expensive and becomes a burden to the user.
Consequently, in an actual fixing process utilizing the heat-rollers, the fixing is performed within the range of viscosity under the rubber region. However, as disclosed in the Japanese Patent Publication (JP-B) No. 51-29825, immediately after heating, without removing the subject to be fixed from the fixing member, removing is carried out after the step for cooling, thereby removing is performed after the toner is cooled and solidified. Accordingly, under this method, compared to other conventional methods, toners do not adhere to the fixing member even when viscosity of the toner at the time of melting is low, and thus leaving much room for allowance.
In
The guide roller (G1) and the guide roller (G2) may either be a drive roller and the other a driven roller, or either one of the rollers may be a cooling roller. In this example, the guide roller (G2) acts as the cooling roller for the image (P1) on the subject to be fixed (P3) which is conveyed in the direction of advance from left to right on the endless belt (B) as indicated by an arrow in the figure. In the apparatus in
The controlling system of the image fixing apparatus in this example includes: means for controlling supply of electricity (A1) for a heater which is the heating body (H1) including means for switching supply of electricity, and means for controlling the rotation (A2) of a pulse motor (M) for driving the guide roller (G1) which also acts as drive roller, and these means for controlling (A1) and (A2) receives an image signal from the image position sensor (S) which monitors a location of the image (P1) on the subject to be fixed (P3). These means for controlling (A1) and (A2) are controlled by the controller (B1) connected to the RAM (B2) and ROM (B3), and controls supply of electricity from the electricity source (A3). The guide roller (G3), which also acts as heat fixing roller, is furnished with a thermal sensor such as thermistor (SM), and an output signal from the thermistor is sent to the means for controlling (A1) and used for switching operation to switch supply of electricity in the means for switching electricity (not shown in the drawings). In heating the toner image for fixing, the supply of electricity does not necessarily be a pulse electricity, and when the subject for controlling which is, for instance, a voltage and/or a electric current, is provided in an amount defined in analogue, it is not impossible to control the analogue amount using a digital signal as the subject to be controlled. However, in this example, supply of electricity is used as an amount of pulse electricity which is not only the amount for controlling, but also an amount to be controlled (subject for controlling). Needless to say the merit of such controlling system is well known by the ones skilled in the art.
When the number of pulses in a series of electric pulses is defined as Nn, frequency of the pulses as Cn, and a length of time as Pn, the respective data for Nn, Cn, and Pn are initially stored in the ROM (Read Only Memory) (B3) in advance in a manner to allow reading out. Next, triggered by an address signal provided to the ROM (B3) from the controller (B1), the retrieved data (Nn, Cn, and Pn) are sequentially sent to a register (B4) and to a data latch unit (B5), both of which are controlled by the controller (B1). In the controller, the data Nn is sent to N pulse counter (B6), while data (Cn and Pn) are sent to the counter for determining length of time in supplying electricity (B7).
The counter for determining length of time in supplying electricity (B7) determines a length in time for electric supply per one pulse data (Cj, Pk), and feeds the data to the queue driver (A11) of the means for controlling supply of electricity (A1). The queue driver (A11) outputs prescribed pulses in accordance with the sequential order of the data representing time of electric supply, and drives the heater (H1). At the same time, the N Pulse counter (B6) counts the number of output electric pulses, and sends signal to the controller (B1) after counting reaches the data Ni.
In this manner, the controller (B1) outputs address signals for the next cycle, and also controls the register (B4) and the data latch unit (B5). For example, in the present invention, values for the respective data may be determined at Cn=10 ms constant, Pc=9 ms and Nc=30 at the time of temperature rise, P1=2 ms and N1=in the range of 213 to 215 at the time of controlling temperature isothermally. Here, the length of time for electric supply, number of pulses for each mode is defined based on the data collected in advance.
Therefore, such means for controlling supply of electricity (A1) may be varied in the fixing process for each of the image (P1) on a single subject to be fixed (P3). Further, in the figure, the means for controlling supply of electricity (A1) of the heater (H1) is shown as a mode having extended supply of electricity per pulse (P) in which the number of pulse electricity cycle is dense (C), and a normal (constant) mode which comes thereafter. When the heater (H1) has an excellent heat-blocking property, the temperature of the heater as the heating body may gradually increase, pulse width per unit time or the number of pulses provided to the heater (H1) preferably is reduced during the process for fixing from the start of heating until the end of heating for all of the images in a single subject to be fixed (B3).
Therefore, it is preferable to configure the means for controlling supply of electricity (A1) of the present invention to hold off supply of electricity to the heating body (H1) before the front edge of the image (P1) reaches the position of the heating body which is a heater (H1), and/or the means for supplying electricity (A1) to stop the supply of electricity immediately after the rear-edge of the image (P1) passes through the position of the heating body even if the rear-end of the substrate (2) bearing the image (P1) is still on its way to pass the position of the heating body.
The self-active multivibrator is devised to conduct the primary coil (L11) of the transformer when one transistor (TR11) turns to be conductive. Consequently, while the secondary inductive output voltage is outputted to the secondary coil (L21) after a short while and then used as a heater source, the third inductive output voltage generated after a short while is output to the primary coil (L11) due to this secondary output voltage. Then, this third inductive output voltage generated after a short while is fed back to the other transistor (TR12) to render it conductive, and the transistor (TR12) functions in the same way as the transistor (TR11). Then, this operation is repeated alternatively to operate the multi-vibrator. A condenser (C1) is used to set a time constant (that is, a frequency of the pulse electricity) at the time of electrically conducting both transistors by cooperating with the primary coil (L11) of the circuit. Further, a direct current component from a rectifier (D) is given as the power supply to this circuit.
Therefore, this self-active multivibrator is used to determine the lowest and the highest limits in the temperatures during heating by the heater (H1) of the fixing device of the present invention. Hence, it determines the range of temperatures as illustrated in
Further, it is possible to combine a conventional method for protecting circuit elements from surge voltage. For example, a Zener diode which turns electrically conductive at the time of reaching zener break voltage is connected parallel to the resist (R3) plus rectifier (D) to protect the rectifier (D) from a sudden over voltage current, thus it is possible to provide an over current bypass path at the portion of a resist (R3) for the rectifier (D). In the case of such circuit, not only having a merit of pulse electricity output, but also leaves out a back electromotive force absorption circuit having a general high time constant, which includes the diode and the resistance.
As shown in
In
In
The present invention will be described in detail using examples. In the present invention, amount of electric supply as the subject to be controlled acquires a shape of pulse waveform. When such pulse electricity is applied to the heater (H1), in the heat fixing roller as a heating body which directly performs fixing, the amount of heat is diffused multi-dimensionally, and as shown in chart representing output amount of the heat from the roller (G3) in
Further, by using a toner having relatively low melt viscosity of 10 (superscript: 4) to print out three lines of solid images disposed 2 centimeters apart having 2 centimeters in width in the direction of advance, problems such as image expansion or off-setting was not caused due to an effect of controlled integral waveforms of the present invention, and for all three lines, a uniform solid images in quality were obtained.
As clearly understood from a concrete as well as thorough descriptions in the foregoing, the present invention brings an explicit effect of stability in actual operation without causing off-settings and the like, and attains further energy savings using a process for fixing toner images and an image fixing apparatus of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2001-290062 | Sep 2001 | JP | national |
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| Number | Date | Country | |
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| 20060159477 A1 | Jul 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10247631 | Sep 2002 | US |
| Child | 11384496 | US |
