JPH10149044A - Image thermal fixing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the fixability even when the feeding speed of a recording material is expedited or in the use at a lowered fixing temperature by providing such a structure that a plurality of external heating members are contactable/ retreatable with/from a pair of fixing members. SOLUTION: An external heating roller 53 forming an external heating member is provided on the circumferential surface of a fixing roller 40 in such a manner as to be contactable/retreatable. The external heating roller 53 is moved by a contact/retreat mechanism so as to be brought into contact with/ retreated from the circumferential surface of the fixing roller 40, the external heating roller 53 is pressed by a spring when it makes contact with the fixing roller 40, and driven and rotated by the fixing roller 40. Thus, the heat supplied from the external heating roller 53 is efficiently moved toward a recording material P without laying the inner part of the fixing roller 40 in a low temperature state. Thus, the lowest temperature in continuous paper feeding can be raised by bringing the external heating roller 53 to the fixing roller 40 only in the middle of printing operation, and satisfactory fixability can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image heating and fixing apparatus which is mounted on an image forming apparatus such as a printer, a copying machine, a facsimile or the like and heats and fixes an unfixed image formed on a recording material.

[0002]

2. Description of the Related Art Conventionally, various image forming apparatuses are known. Among them, a photosensitive member is subjected to image exposure with laser light,
An electrophotographic image forming apparatus that develops the image to obtain an image has been widely used. Such an image forming apparatus has advantages such as high image quality and high speed, and is widely used as an output device such as a copying machine, a color laser beam printer, and the like.

For example, an example of a conventional copying machine is shown in FIGS.
This will be described with reference to FIG. The color copying machine shown in FIG. 14 has an image reading means 101 for reading a document image at an upper part thereof, and an electrophotographic photosensitive drum 102 serving as an image forming means is arranged at a lower part thereof. And a recording material supply tray
The recording material P fed from 103 and 104 is a recording material transport system 105
After passing through the photosensitive drum 102 to form an unfixed image t, the unfixed image t is guided to the image heating and fixing device 107 through the conveyor belt means 106.

As shown in FIG. 15, a fixing roller 108 and a pressure roller 109 having halogen heaters 108a and 109a built therein are arranged in the image heating and fixing device 107, respectively. , 109, the recording material P on which the unfixed image t is formed is nipped and conveyed, so that the unfixed image t is fixed on the recording material P by being heated and pressed, and then provided outside the machine. The sheet is discharged to the discharged tray 110.

[0005]

However, in the prior art described above, in the case of a full-color printer, the outer layers of the fixing roller 108 and the pressure roller 109 are relatively thick, and rubber or resin having a low thermal conductivity is used. Therefore, if the speed is further increased in order to improve the throughput (conveyance processing efficiency), for example, the feed speed of the recording material P is increased from 160 [mm / s] to 220 [mm / s]. When raised,
The heat supply from the inside of the fixing roller 108 and the pressure roller 109 is delayed, and as shown in FIG. 16, the surface temperature of each of the rollers 108, 109 decreases, and the recording material P is transferred to each of the rollers 108, 10
The amount of heat supplied per sheet is significantly reduced due to the shorter contact time with the sheet.

As a result, the feed speed (fixing speed) of the recording material P is increased, and as a result, as shown in FIG.
When the temperature of the lowest point of each of the rollers 108 and 109 when the paper is continuously fed falls below the feasible temperature region indicated by the oblique line in FIG.
The fixability at the lowest point temperatures of 108 and 109 cannot be secured, and a cold offset (unfixed due to low temperature) occurs at the rear end of the recording material P.

Further, in order to obtain an image with low gloss (image surface roughness), it is required to lower the fixing temperature. If the temperature control is set low from the beginning, each roller 108, 109 is used when a relatively large-sized recording material P such as A3 size passes through one sheet.
Of the recording material P decreases by about 10 to 20 ° C.
, The temperature rises between the recording materials P before the following recording material P enters and returns. However, when the rear end of the recording material P passes, the surface temperatures of the rollers 108 and 109 are
The temperature deviates from the fixable temperature range indicated by the hatched area 17, resulting in a cold offset.

[0008] The present invention is to solve the above problems,
The purpose is to increase the feeding speed of the recording material, or to use it with a lower fixing temperature.
It is an object of the present invention to provide an image heating / fixing apparatus capable of securing the fixing property and an image forming apparatus having the same.

[0009]

A typical configuration according to the present invention for achieving the above object has a fixing member pair rotatably disposed while being pressed against each other, and the fixing member pair is formed. An image heating and fixing device that heats and fixes an unfixed image on the recording material by nipping and conveying a recording material on which an unfixed image is formed at a nip portion, wherein at least one external heating member is provided for the fixing member pair. The image heating / fixing device is configured to be able to contact / retreat.

The contact / retreat operation of the external heating member with respect to the fixing member pair is performed according to the surface temperature of the fixing member pair or the timing at which the recording material is conveyed to the fixing member pair. It is preferable to configure.

According to the present invention, the external heating member is moved to the fixing member pair in accordance with the surface temperature of the fixing member pair or the timing at which the recording material is conveyed to the fixing member pair. By abutting / retracting, the temperature of the fixing member pair can be easily adjusted, thereby increasing the feeding speed of the recording material or reducing the recording temperature even when the fixing material is used at a lower temperature. Heating and fixing of an unfixed image on a material can be reliably performed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, an embodiment in which the present invention is applied to a copying machine as an example of an image heat fixing apparatus according to the present invention and an image forming apparatus provided with the same will be specifically described. FIG. 1 is a diagram showing a configuration of an image forming apparatus provided with an image heat fixing device according to the present invention, FIG. 2 is a diagram showing a configuration of a document reading system, FIG. 3 is a diagram showing a configuration of a CCD color sensor, and FIG. FIG. 5 is a diagram showing a configuration of an image signal processing circuit, FIG. 5 is a schematic cross-sectional view showing a configuration of an image heating / fixing apparatus according to the present invention, and FIG. 6 shows how an external heating member is brought into contact / retreat with a pair of fixing members. FIG. 7 and FIG. 7 are diagrams showing the softening temperature characteristics of the toner, and FIG. 8 is a diagram showing the surface temperature change of the fixing member pair of the first embodiment of the image heating and fixing apparatus according to the present invention.

First, an overall configuration of an image forming apparatus provided with an image heating / fixing apparatus according to the present invention will be described with reference to FIGS. In FIG. 1, an image forming apparatus main body 1 includes a document feed system 2 disposed above the document feed system 2, a document read system 3 disposed below the document feed system 2, and a document read system 3.
, A rotary developing device 5 which is a developing unit disposed in the lower part in the vicinity of the latent image forming unit 4, and the image forming apparatus main body 1 substantially from the right side in FIG. 1. Recording material transport system 6 serving as transport means provided over the central portion
And is configured.

As shown in FIG. 2, the original reading system 3 is provided with a platen glass 8 for supporting the original 7 fixed to the apparatus main body 1, and provided below the platen glass 8. As the optical system unit 9 moves in the direction of the arrow a in FIG. 2, the original surface of the original 7 placed on the platen glass 8 with the original surface facing down is sequentially scanned and recorded on the original surface of the original 7. Read the image information.

That is, when the copy start key of the operation unit (not shown) is pressed, the light emitted from the irradiation light source 10 when the optical system unit 9 moves in the direction of the arrow a in FIG. The reflected light corresponding to the image information passes through the imaging element array 11 and the infrared cut filter 12, and
An image is formed as an original image on a D (contact CCD color sensor) 13.

As shown in FIG. 3, a red R, green G, and blue B filter is regularly attached to each pixel of the CCD 13 so that a document image is formed on the CCD 13 as the document 7 is scanned. When an image is formed, an electric signal is output from the CCD 13, and the electric signal is processed by a signal processing circuit shown in FIG.

In FIG. 4, 13B, 13G and 13R correspond to FIG.
3 shows electric signals from the B, G, and R elements on the CCD 13 shown in FIG. The signals of 13B, 13G and 13R are A / D
The signals are converted into digital signals B, G, and R by a conversion circuit (analog / digital conversion circuit) 14 and converted into Y ₁ , M ₁ , and C ₁ , which are density signals in the form of digital signals, by a density conversion circuit 15.

The Y ₁ , M ₁ , and C ₁ signals are input to a circuit 16 for performing black extraction and UCR (under color removal) processing, and are subjected to arithmetic processing represented by the following equation to perform Y ₂ , M ₂ , C ₂ , and C _{1 processing} . It is generated as bk ₂ signal.

[0019]

(Equation 1)

Here, ｛ _min (Y ₁ , M ₁ ,
C ₁ )｝ is the minimum signal among the signals Y ₁ , M ₁ , and C ₁ , and k ₁ , k ₂ , and k ₃ are predetermined coefficients, respectively.

Next, the _{Y 2, M 2, C 2} , Bk 2 signals are input to the color correction circuit 17 to correct the spectral distribution of the colorant used in the color separation filter and the image forming means CCD13 , The following determinant is applied. Here, the following {a ₁₁ ~a _44} is a masking coefficient of each color correction.

[0022]

(Equation 2)

The operation results Y ₃ , M ₃ ,
Based on the C ₃ and Bk ₃ signals, the latent image forming unit 4 is irradiated with a laser beam E, which will be described in detail later, and visualization is performed.

As shown in FIG. 1, the latent image forming section 4 is provided with an electrophotographic photosensitive drum 18 serving as a latent image carrier as an image forming means rotatable in the direction of arrow b in FIG. Have been. In the vicinity of the outer peripheral surface of the photoconductor drum 18, a charge removing charger 19, a cleaning unit 20, and a primary charger 21 are sequentially arranged from the upstream side to the downstream side in the rotation direction of the photoconductor drum 18, and further, On the outer peripheral surface of the drum 18, image exposure means 22 such as a laser beam scanner for forming an electrostatic latent image and image exposure reflection means 23 such as a mirror are provided.

Therefore, the image exposing means 22 makes the above Y ₃ , M ₃ ,
When the laser beam E is radiated based on the C ₃ and Bk ₃ signals, the laser beam E is radiated on the photosensitive drum 18 via the image exposure / reflection means 23 and is uniformly charged by the primary charger 21. After the electrostatic latent image is formed on the photosensitive drum 18, the image is visualized as a developer image by the rotary developing device 5.

The rotary developing device 5 includes a photosensitive drum 18
Of the apparatus main body 1
The four types of developing devices are mounted at four positions in the circumferential direction in a rotating body 24 formed of a housing rotatable with respect to the developing device.

The four types of developing devices are a yellow developing device 25Y, a magenta developing device 25M, and a cyan developing device 25C, respectively.
And the black developing device 25Bk, and the above Y ₃ , M ₃ ,
Developing is performed with a developer of each color corresponding to an electrostatic latent image based on each signal of C ₃ and Bk ₃ . Then, the developed visible image on the photosensitive drum 18 is transferred onto a recording material P made of paper, synthetic resin, or the like conveyed by the recording material conveyance system 6. In the following description, a case where the recording material P is made of paper will be described.

As shown in FIG. 1, an opening is formed on the right side of the apparatus main body 1. Removable recording material supply trays 26 and 27 are provided in the opening so as to protrude partially outside the apparatus. ing. Feed rollers 26a and 27a are arranged above the feed side of the recording material feed trays 26 and 27.

On the other hand, a transfer drum 28 which is rotatable in the direction of arrow c in FIG. 1 as a transfer means is provided opposite to the photosensitive drum 18, and the transfer drums 28a and 27a And a conveyance guide 30a, 30 as conveyance means for conveying the recording material P
b is provided.

In the vicinity of the outer peripheral surface of the transfer drum 28, from the upstream side to the downstream side in the rotation direction of the transfer drum 28, a contact roller 31, a gripper 32, a recording material separating charger 33, and a separating claw.
34 are arranged sequentially. On the inner peripheral side of the transfer drum 28, a transfer charger 35 and a recording material separating charger 36 are arranged.

On the surface of the transfer drum 28, a transfer sheet made of polyvinylidene fluoride or the like is adhered to a portion where the recording material P is wound, and the recording material P is electrostatically adhered to the transfer sheet. It is supposed to be. A transfer belt means 37 is provided on the upper right side of the transfer drum 28 in FIG.
An image heating and fixing device 38, which will be described in detail later, is disposed adjacent to the end of the recording material P in the transport direction.

Further, the image heating / fixing device 38 extends to the outside of the apparatus main body 1 further downstream in the transport direction than the image heating / fixing apparatus 38, and
A discharge tray 39 configured to be detachable from the apparatus main body 1 is arranged.

Next, the structure of the image heating and fixing apparatus according to the present invention will be described in detail with reference to FIGS. FIG.
As shown in FIG. 7, the image heating and fixing device 38 includes a fixing roller 40 serving as a fixing member having a halogen heater 40a serving as a heating unit therein, and a pressurizing member serving as a fixing member having a halogen heater 41a serving as a heating unit therein. The roller 41 is configured as a fixing member pair rotatably arranged while being pressed against each other at a total pressure of about 40 [kg] by a pressing mechanism (not shown).

Thermistors 42a and 42b, which are temperature detecting means, are in contact with the fixing roller 40 and the pressure roller 41.
The thermistors 42a and 42b detect the temperatures of the fixing roller 40 and the pressure roller 41, and the control device 43 controls the halogen heaters 40a and 41a based on the detected information, thereby controlling the temperature of the fixing roller 40 and the pressure roller 41. Together about 150
The unfixed image t formed of a developing material such as a sharp melt toner transferred onto the recording material P is fixed to the fixing roller 40 and the pressing roller
The sheet passes through a nip portion 41 and is heated and pressed to be fixed on the recording material P.

The sharp-melt color toner formed on the recording material P has a high affinity and also has the property of being easily offset to the fixing roller 40, and therefore exhibits high releasability over a long period of time. It is necessary. Therefore, an oil application device 44 serving as a release agent applying unit and a cleaning device 45 for removing oil and dirt from the fixing roller 40 are provided near the outer periphery of the fixing roller 40, and the pressure roller is provided near the outer periphery of the pressure roller 41. By providing a cleaning blade 46 for removing oil and dirt 41, the releasability is further improved.

The oil application device 44 is a dimethyl silicone oil 47a (KF96, 300cs manufactured by Shin-Etsu Chemical) in an oil pan 47.
Is applied to the outer peripheral surface of the fixing roller 40 by regulating the oil application amount by the oil application amount adjusting blade 50 via the oil pumping roller 48 and the oil application roller 49, and the application amount will be described later. An amount of {0.08 [g / A4 size]} is applied according to the measurement method.
The oil application roller 49 can be brought into contact with and separated from the fixing roller 40, and applies oil from a position 5 [mm] from the leading end of the recording material P to a position 5 [mm] from the rear end. ing.

The amount of silicone oil applied by the oil application device 44 is determined as follows. First, A
The weight of 50 blank sheets of four sizes is defined as A ₁ [g]. The image is not transferred onto the blank sheet, and the fixing roller 40 is coated without applying silicone oil to the rubber layer of the fixing roller 40 described later. The weight of the 50 blank sheets after passing the nip portion between the white paper and the pressure roller 41 is defined as B [g].

Next, similarly, another A4 size blank paper 50
The weight of the sheet is assumed to be A ₂ [g], and the image on the white paper is not transferred, but the silicone oil is applied to the rubber layer of the fixing roller 40 so that the space between the fixing roller 40 and the pressure roller 41 is The weight of the 50 blank sheets after passing the nip is
[G].

Using the above weights A ₁ , B, A ₂ , and C, A
The coating amount X [g] of the silicone oil per one sheet of white paper of four sizes is obtained by the following equation.

[0040]

(Equation 3)

On the other hand, a cleaning device 45 provided in contact with the fixing roller 40 is provided with a non-woven web 51 made of Nomex (trade name) stretched by winding means (not shown).
Is pressed against the surface of the fixing roller 40 by the pressing roller 52 to perform cleaning. Further, the nonwoven fabric web 51 is appropriately wound by the winding means so that toner and the like do not accumulate on the contact portion with the fixing roller 40.

The fixing roller 40 is composed of an HTV (high temperature vulcanization type) silicone rubber layer on the outer periphery of an aluminum cored bar 40b.
An RTV (room temperature vulcanization type) silicone rubber layer 40d is provided on the outer periphery of the HTV silicone rubber layer 40c as a heat-resistant elastic layer, and has a thickness of 3 [mm] and a diameter of 40 [m].
m].

On the other hand, the pressure roller 41 is a 1 mm thick HTV silicone rubber layer on the outer periphery of the aluminum cored bar 41b.
The HTV silicone rubber layer 41c is further provided with a fluororesin layer 41d on the outer periphery thereof, and has a diameter of 40 [mm].

By combining the fixing roller 40 and the pressure roller 41 having the above-described configuration, the releasability from the sharp melt toner is further improved.

In recent years, with the spread of color copying machines, the speed and convenience of color copying machines are the same as those of black-and-white copying machines, that is, automatic double-sided copying, or the use of paper from postcards to large size, thin paper to thick paper. In addition, it has become necessary to meet various needs such as the use of OHP films and pack print films.

Therefore, in order to fix a double-sided image, not only the fixing roller 40 but also the surface layer of the pressure roller 41 may be made of RTV or LTV (low temperature vulcanization type) silicone rubber having a high toner releasing effect. At the same time, in order to satisfy the high-speed color fixing, the diameter of the roller is increased (for example, a diameter of 60 [mm] or 80 [mm]) to enlarge the nip portion. To improve the fixability.

However, the silicone rubber of the surface layer which is originally used for maintaining the mold releasability and the silicone rubber of the lower layer for forming the nip portion which wraps the sharp melt toner are both the same as the silicone oil used. Because it is very familiar, a large amount of silicone oil enters the silicone rubber depending on its durability, and especially the lowermost layer of silicone rubber contains a large amount of silicone oil, which causes a gap between the core and the core metal interface during heating. Peeling may occur.

Therefore, in a copying machine which is required to make a large number of copies at a high speed, in order to prevent the peeling, both the fixing roller 40 and the pressure roller 41 use the lower silicone rubber and the surface silicone rubber. In many cases, fluorine rubber having an oil-resistant layer that does not absorb and allow the passage of silicone oil is used.

Next, the configuration of the external heating member which is a feature of the present invention will be described. As shown in FIGS. 5 and 6, on the outer peripheral surface of the fixing roller 40, an external heating roller 53 serving as an external heating member is configured to be able to abut / retreat.

The external heating roller 53 is moved by an abutting / retracting mechanism (not shown) to abut / retreat with respect to the outer peripheral surface of the fixing roller 40. When the fixing roller 40 contacts the fixing roller 40, the fixing roller 40 is pressed by a spring (not shown).

For example, the external heating roller 53 is supported by a support rod such as a heat insulating bush. Then, the support rod is moved to apply pressure to and detach from the fixing roller 40. This attachment / detachment is achieved by using a well-known technique such as a spring clutch and a solenoid.

The external heating roller 53 has a halogen heater 53a built therein, and the outer periphery thereof has, for example,
The surface of the metal is coated with a metal having high thermal conductivity, such as aluminum, iron, or stainless steel, or a rubber or resin having a high releasability. And this external heating roller
53 is held at both ends by a heat-insulating bush having high heat resistance.

The thermistors 42a, 42b, 42c are arranged in contact with the fixing roller 40, the pressure roller 41, and the external heating roller 53, respectively. The thermistors 42a, 42b, 42c cause the rollers 40, 41, 53, respectively. Of the halogen heaters 40a and 41 based on the temperature information.
The temperature of each of the rollers 40, 41, 53 is controlled by controlling a, 53a.

As an example of the temperature control, the external heating roller 53 as the external heating member is set to have a higher temperature than the fixing roller 40 and the pressure roller 41 as the fixing member pair. 220 ° C., and the fixing roller 40 and the pressure roller 41 are set at 180 ° C.

The sequence of the entire image forming apparatus configured as described above will be described by taking a full color mode as an example. In FIG. 1, when the photosensitive drum 18 rotates in the direction of arrow b in FIG. 1, the photosensitive member on the photosensitive drum 18 is uniformly charged by the primary charger 21. Note that, in the image forming apparatus shown in FIG.
“Process speed”) is 160 [mm / sec].

When the photosensitive drum 18 is uniformly charged by the primary charger 21, image exposure is performed by the laser beam E modulated by the yellow image signal Y ₃ of the original 7, and the photosensitive drum 18 is exposed. An electrostatic latent image is formed on the rotating body
By the rotation of 24, the electrostatic latent image is developed by the yellow developing device 25Y previously set at the developing position.

On the other hand, the recording material P selectively fed out from the recording material supply trays 26 and 27 by the feeding rollers 26a and 27a and conveyed via the conveying rollers 29 and the conveyance guides 30a and 30b is a predetermined one. It is held by the gripper 32 at the timing, and is electrostatically wound around the transfer drum 28 by the contact roller 31 and the electrode facing the contact roller 31.

The transfer drum 28 rotates in the direction of arrow c in FIG. 1 in synchronization with the photosensitive drum 18 and
The visible image developed at 25Y is transferred by the transfer charger 35 at a portion where the outer peripheral surface of the photosensitive drum 18 and the outer peripheral surface of the transfer drum 28 are in contact. The transfer drum 28 continues to rotate as it is, and prepares for transfer of the next color (magenta in FIG. 1).

The photosensitive drum 18 is neutralized by a neutralizing charger 19, cleaned by a cleaning means 20 using a conventionally known blade method, and then charged again by a primary charger 21 to obtain a next magenta image signal M _3. Receives image exposure in the same manner as described above.

The rotary developing device 5 includes a photosensitive drum 18
Rotates while an electrostatic latent image by the magenta image signal M ₃ is formed by the image exposure above, magenta developing device 25
M is fixed at the above-described predetermined developing position to perform predetermined magenta development.

Subsequently, the above-described process is performed for each of the cyan color and the black color. When the transfer of the four colors is completed, the four-color visual image formed on the recording material P is The recording material P is released from the transfer drum 28 by the separation claw 34, and the recording material P is separated from the transfer drum 28 by the separation claw 34. It is fed and fixed by heat and pressure to complete a series of full-color print sequences, and a required full-color print image is formed.

As described above, since a multicolor toner forms two to four layers in a color image, an electrophotographic image forming apparatus capable of forming a color image uses a black and white toner for the color image. It has different features from the device.

That is, since the toner is required to have good meltability and color mixing when heat is applied, a sharp melt toner having a low softening point and a low melt viscosity is used. By using this sharp melt toner, a color copy having a wide color reproduction range of a copy can be obtained.

Such a sharp melt toner is obtained by melting a toner forming material such as a binder resin such as a polyester resin or a styrene-acryl ester resin, a coloring agent (dye, a sublimable dye), and a charge control agent. It is manufactured by kneading, pulverizing and classifying.

If necessary, an external addition step of adding various external additives (for example, hydrophobic colloidal silica) to the toner may be added. As such a color toner, a toner using a polyester resin as the binder resin is particularly preferable in consideration of the fixing property and the sharp melt property. Examples of the sharp melt polyester resin include a polymer compound having an ester bond in the main chain of a molecule synthesized from a diol compound and a dicarboxylic acid.

In particular, the following formula (where R is an ethylene or propylene group, x and y are each a positive integer of 1 or more, and the average value of x + y is 2 to 10) is shown below. A bisphenol derivative or a substituted product thereof as a diol component, and a carboxylic acid component comprising a divalent or higher carboxylic acid or an acid anhydride thereof or a lower alkyl ester thereof (for example, fumaric acid, maleic acid, maleic anhydride, phthalic acid, A polyester resin obtained by at least co-condensation polymerization with terephthalic acid, trimellitic acid, pyromellitic acid, etc. is more preferable because it has sharp melting characteristics.

[0067]

Embedded image

The softening point of the polyester resin is 75 to 15
0 ° C., more preferably 80 ° C.
It is good if it is -120 [° C]. FIG. 7 shows an example of the softening characteristics of a sharp melt toner containing this polyester resin as a binder resin.

The measurement conditions were as follows: a flow tester (CFT-50)
0A type / manufactured by Shimadzu Corporation), and a die (nozzle) having a diameter of 0.2 [mm] and a thickness of 1.0 [mm] is applied with an extrusion load of 20 [kg]. , Preheating time 3
After 00 seconds, when the temperature was raised at a constant speed of 6 [° C./min], a plunger drop amount-temperature curve (hereinafter, referred to as “softening S-shaped curve”) of the drawn toner was obtained.

The toner used as the sample is a fine powder precisely weighed 1 to 3 [g], and the cross-sectional area of the plunger is 1.0 [cm ² ].
And The softening S-shaped curve obtained under such measurement conditions becomes a curve as shown in FIG. 7, and as the temperature rises at a constant speed, the toner is gradually heated and starts to flow out (FIG. 7).
Plunger descent A → B). When the temperature is further increased, the toner in a molten state flows out greatly (plunger descent B → C → D in FIG. 7), and the plunger descent stops and ends (plunger descent D → E in FIG. 7).

In FIG. 7, the height H of the softening S-shaped curve indicates the total outflow, and the temperature T ₀ corresponding to the point C of H / 2 indicates the softening point of the toner.

Whether or not the toner and the binder resin have a sharp melt property can be determined by measuring the apparent melt viscosity of the toner or the binder resin. The toner or the binder resin having such a sharp melt property is defined as a temperature at which the apparent melt viscosity shows 10 ³ poises is T ₁ , 5.
When the temperature at the time of showing × 10 ² poise is T ₂ , it means one satisfying the following conditions.

[0073]

(Equation 4)

The sharp-melt resin having these temperature-melt viscosity characteristics is characterized in that the viscosity decreases sharply when heated. Such a decrease in viscosity causes an appropriate mixing of the uppermost toner layer and the lowermost toner layer, and further sharply increases the transparency of the toner layer itself, thereby causing good color reduction mixing.

In the following, an experiment was conducted to compare the temperature change of the surfaces of the fixing rollers 40 and 108 between the case where the external heating roller 53 of the present embodiment is provided and the conventional example where the external heating roller 53 is not provided (see FIG. 15). FIG. 8 shows the results.

Here, the external heating roller 53 of this embodiment is a hollow aluminum rod having an outer diameter of 40 [mm] and a thickness of 2 [mm]. Are formed so as to have a width of 3 [mm] in the rotation direction.

Further, in the present embodiment, the fixing roller 40 is provided so that the total of the heater wattage (heating power consumption) is equal between the case where the external heating roller 53 of the present embodiment is provided and the conventional example where the external heating roller 53 is not provided. Halogen heater 40a is 400
[W], the halogen heater 53a of the external heating roller 53 is set to 2
In the conventional example, the halogen heater 108a of the fixing roller 108 is 600 [W], and the external heating roller 53 is not attached.

In FIG. 8, the surface temperature curve of the fixing roller 108 of the conventional example is indicated by I, and the surface temperature curve of the fixing roller 40 when the external heating roller 53 of the present embodiment is always in contact with the fixing roller 40 is shown. The curve is indicated by J, and the surface temperature curve of the fixing roller 40 when the external heating roller 53 of this embodiment is brought into contact with the fixing roller 40 only during the printing operation is indicated by K.

As shown in FIG. 8, the number of sheets
At about 0 [sheets / minute], the surface temperatures of the fixing rollers 40 and 108 reach the lowest point, and when the number of sheets passed further increases, the surface temperatures of the fixing rollers 40 and 108 rise and return. The heating temperature of the external heating roller 53 is adjusted so as to be equal to the temperature of the fixing roller 40.

In the case of the present embodiment, when the external heating roller 53 is brought into contact with the fixing roller 40 from the initial stage (curve J), the external heating roller 53 is compared with the conventional example (curve I). It has been found that the drop in surface temperature can be suppressed slightly.

In the initial stage, the external heating roller 53 is retracted from the fixing roller 40, and
Is maintained at 220 ° C., and the recording material P is
When the external heating roller 53 is brought into contact with the fixing roller 40 at the same time as it begins to pass through the nip portion between the pressure roller 41 and the pressure roller 41 and is maintained (curve K), the conventional example (curve I) and the aforementioned As compared with the case where the external heating roller 53 is always in contact with the fixing roller 40 from the initial stage (curve J), the lowest point temperature of the surface temperature of the fixing roller 40 is increased by 10 ° C. or more. It has been found that the drop in the surface temperature of the fixing roller 40 can be suppressed considerably.

In the case of the curve K, the lowest temperature at which the surface temperature of the fixing roller 40 falls is the cold offset start temperature (1).
50 [° C.]), the fixed image is not offset.

As described above, the external heating roller 53, which is an external heating member, makes contact / retreat operation with the fixing roller 40, which is a pair of fixing members, at the timing when the recording material P is conveyed (when the fixing roller 40 (The timing of entering the nip portion with the roller 41), the lowermost temperature of the surface temperature of the fixing roller 40 can be increased, and the surface temperature of the fixing roller 40 can be increased. Can be suppressed.

If the temperature of the external heating roller 53 is kept higher than the temperature of the fixing roller 40 as the fixing member pair from the beginning, the response (heat loss) to the decrease in the surface temperature of the fixing roller 40 can be improved. Heat is supplied from the external heating roller 53 to the fixing roller 40 with good sensitivity accuracy.

Here, the external heating roller 53 is connected to the fixing roller 40.
When used in contact with the fixing roller 40, only the surface of the fixing roller 40 is heated and a high temperature state is maintained, so that the signal of the thermistor 42a for detecting the surface temperature of the fixing roller 40 always shows an appropriate value for temperature control. . As a result, only the surface of the fixing roller 40 has a high temperature and the inside thereof has a low temperature without turning on the halogen heater 40a of the fixing roller 40, and the heat supplied from the external heating roller 53 is dispersed and enters the fixing roller 40. May move.

To prevent this, for example, when the external heating roller 53 is in contact with the fixing roller 40, the halogen heater 40a of the fixing roller 40 is always turned on. With such a configuration, the heat supplied from the external heating roller 53 moves to the recording material P efficiently without the temperature inside the fixing roller 40 becoming low.

As described above, by contacting the external heating roller 53 with the fixing roller 40 only during the printing operation, the lowest point temperature during continuous paper feeding can be increased, and good fixing performance can be obtained. It is obtained.

Next, a second embodiment of the image heating and fixing apparatus according to the present invention will be described with reference to FIGS. FIG.
FIG. 10 is a diagram illustrating a temperature change of a fixing member pair of the image heating and fixing device according to the second embodiment. FIG. 10 is a diagram illustrating a temperature change of the fixing member pair when the paper is continuously passed in the conventional image heating and fixing device.
FIG. 11 is a diagram illustrating a temperature change of the fixing member pair in the contact / retreat state of the external heating member of the image heating / fixing apparatus according to the second embodiment. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

As described above, when the external heating roller 53 is brought into contact with the fixing roller 40, the decrease in the temperature of the fixing roller 40 can be reduced. However, if the external heating roller 53 is kept in contact with the fixing roller 40, the curve K 'shown in FIG. As described above, there is a possibility that the surface temperature of the fixing roller 40 rises excessively and overshoots (overheats).

Therefore, in the present embodiment, the curve K ″ in FIG.
As shown in FIG.
When the temperature reaches 0 ° C., the external heating roller 53 is
Evacuate from. As a result, the temperature of the surface of the fixing roller 40 is reduced to about 180 ° C. and is maintained, so that the overshoot (overheating) can be prevented.

That is, an external heating roller as an external heating member
Since the operation of abutting / retreating the fixing roller 53 with respect to the fixing roller 40, which is a pair of fixing members, is performed according to the surface temperature of the fixing roller 40, overshooting (overheating) can be prevented, and In addition, thermal deterioration of the rubber of the pressure roller can be reduced.

Further, in the first embodiment, the external heating roller 53 is brought into contact with the fixing roller 40 only during the printing operation.
This is a case where printing is performed at a relatively high speed of [sheets / minute] and the sheet interval is very narrow.

On the other hand, in the conventional example, as shown in FIG. 10, when the printing operation is performed when the sheet interval is relatively long and the number of sheets passed is 10 [sheets / minute] or less, the surface temperature of the fixing roller 40 during the sheet passing is reduced. However, even if the external heating roller 53 is not provided, the fixing roller 40 almost returns to the original temperature before the next recording material P arrives.

Therefore, if the external heating roller 53 is kept in contact with the fixing roller 40 during the printing operation when the number of sheets passed is equal to or less than 10 [sheets / minute], the temperature of the fixing roller 40 continues to rise at the sheet interval. In this embodiment, the external heating roller 53 is retracted from the fixing roller 40 at a timing when the preceding recording material P passes through the nip portion between the fixing roller 40 and the pressure roller 41 and escapes, and the subsequent recording material P is fixed. The external heating roller 53 is configured to be brought into contact with the fixing roller 40 at a timing of entering the nip between the roller 40 and the pressure roller 41.

That is, when the number of prints is low, the operation of bringing the external heating roller 53 into contact with the fixing roller 40 at the sheet passing timing and retracting the external heating roller 53 from the fixing roller 40 at the sheet interval is repeated.

Further, the retreat timing of the external heating roller 53 is not limited to immediately after sheet passing as described above, but may be appropriately determined depending on the throughput (sheet passing number [sheets / min]) and the temperature control temperature as shown in FIG. Configure to change.

FIG. 11 shows an example of such a case.
In the case of [sheets / minute], the contact / retreat timing of the external heating roller 53 with respect to the fixing roller 40 during the printing operation of the first to fourth recording materials P is shown in the upper part of FIG. The change in the surface temperature of the fixing roller 40 is shown in the lower part of FIG.

Next, a third embodiment of the image heat fixing apparatus according to the present invention will be described with reference to FIGS. Figure
FIG. 12 is a diagram showing a change in gloss with respect to the temperature of the external heating member of the image heating / fixing apparatus according to the third embodiment, and FIG.
FIG. 13B shows a temperature change of the fixing member pair when the external heating member is retracted from the fixing member pair in the image heating fixing device of the embodiment. FIG. 13B shows the image heating fixing device of the third embodiment. FIG. 7 is a diagram illustrating a temperature change of the fixing member pair when the external heating member is brought into contact with the fixing member pair. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

The present embodiment relates to control of gloss (roughness of the image surface) when the external heating roller 53 is used. FIG. 12 shows the gloss temperature dependence when the fixing speed is 220 [mm / sec]. That is, FIG.
As shown in (1), when low gloss (0 to 10%) is required, the fixing temperature needs to be 150 [° C.] or lower.
[° C.] or higher.

However, the external heating roller 53 is not used, and only the fixing roller 40 and the pressure roller 41 are used.
When the temperature is adjusted to 0 [° C.], when a printing operation is performed on a recording material P made of A3 size paper at a conveyance speed of 220 [mm / sec] and 5 [sheets / min], one recording material P When the recording material P passes through the nip portion between the fixing roller 40 and the pressure roller 41, the leading edge of the recording material P passes through the nip portion, and the trailing edge passes, the curve Q in FIG. As shown in FIG. 13, the temperature of the fixing roller 40 changes (falls) by about 18 ° C.
As shown in FIG. 7A, the area deviates from the fixable area indicated by oblique lines, and a cold offset occurs.

On the other hand, when the external heating roller 53 is brought into contact with the fixing roller 40 and the temperature is similarly controlled to 150 ° C., the recording material P made of A3-size paper is fed at a conveying speed of 220 [mm / sec],
When a printing operation is performed at [sheets / minute], when one recording material P passes through the nip portion between the fixing roller 40 and the pressure roller 41, the leading end of the recording material P passes through the nip portion. At the time and when the rear end passes, as shown by the curve R in FIG. 13B, the heat from the external heating roller 53 is supplied with good response, so that the temperature of the fixing roller 40 is about 10 ° C. However, it does not change (fall) but is always located in the fixable area indicated by the oblique lines in FIG. 13B, and it is possible to prevent cold offset and secure the fixability.

If the distance between the sheets is wide (for example, 10 sheets / min.), If the external heating roller 53 is kept in contact with the fixing roller 40, the subsequent recording material P is Since the surface temperature of the fixing roller 40 continues to rise until the nip portion between the fixing roller 40 and the pressure roller 41 is reached, an external heating roller
It is necessary to retract 53 from fixing roller 40.

When a high gloss image is obtained, it is not necessary to reduce the paper passing speed, as in the case of the low gloss image.
Since a change in the temperature of the fixing roller 40 when the recording material P is passed can be reduced, an image having uniform gloss can be obtained.

Next, as an example of an actual printing operation,
A case in which the user selects the low gloss mode on a control panel (not shown) will be described. First, the fixing roller
It is in a standby state until the temperature of 40 becomes 150 [° C]. In this state, the external heating roller 53 is retracted from the fixing roller 40, and the temperature of the external heating roller 53 is maintained at 220 [° C.].

Then, the temperature of the fixing roller 40 becomes 150
When the temperature reaches [° C.], the printing operation is started, and the leading end of the first recording material P reaches the nip portion between the fixing roller 40 and the pressure roller 41 and contacts the leading end of the recording material P of the fixing roller 40. Reaches the position where the external heating roller 53 faces, and at the same time, the external heating roller 53 comes into contact with the fixing roller 40.

With the above configuration, as shown in FIG. 12, the gloss is about 10%, and the fixability is good.

Then, the succeeding recording material P is applied to the fixing roller 40.
If the surface temperature of the fixing roller 40 returns to 150 [° C.] before reaching the nip portion between the fixing roller 40 and the pressure roller 41, the external heating roller 53 is retracted from the fixing roller 40 and The above operation is repeated for P.

As described above, by using the external heating roller 53, a low gloss image can be obtained without lowering the feeding speed of the recording material P, and the throughput (transport processing efficiency) can be improved.

Although the case where the external heating roller 53 is used as the external heating member has been described, in addition to the roller, a belt made of resin, rubber, metal, or the like, or a non-contact type heat source is used. It is also possible to configure.

Further, the external heating roller 53 as the external heating member is brought into contact with the fixing roller 40 as the fixing member pair.
The case where the external heating roller 53 is configured to be retractable has been described. However, as another configuration, the external heating roller 53 may be configured to be able to contact / retract with the pressure roller 41 as a fixing member pair. Further, although the fixing member pair is constituted by two roller systems including the fixing roller 40 and the pressure roller 41, it may be constituted by using a belt system in addition to the rollers.

[0111]

Since the present invention has the above-described configuration and operation, it is possible to reduce a temperature change during continuous passage due to an increase in the feeding speed of the recording material, and further, it is possible to reduce the fixing temperature. Even when used, good fixability can be secured.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of an image forming apparatus including an image heating and fixing device according to the present invention.

FIG. 2 is a diagram illustrating a configuration of a document reading system.

FIG. 3 is a diagram illustrating a configuration of a CCD color sensor.

FIG. 4 is a diagram illustrating a configuration of an image signal processing circuit.

FIG. 5 is a schematic sectional view illustrating a configuration of an image heating and fixing device according to the present invention.

FIG. 6 is a diagram illustrating a state in which an external heating member is brought into contact / retreat with a fixing member pair.

FIG. 7 is a diagram illustrating a softening temperature characteristic of a toner.

FIG. 8 is a diagram showing a change in surface temperature of a fixing member pair of the first embodiment of the image heating / fixing apparatus according to the present invention.

FIG. 9 is a diagram illustrating a temperature change of a fixing member pair of the image heating fixing device according to the second embodiment.

FIG. 10 is a diagram illustrating a temperature change of a fixing member pair when a sheet is continuously passed in a conventional image heating and fixing apparatus.

FIG. 11 is a diagram illustrating a temperature change of a fixing member pair in an abutting / retreating state of an external heating member of the image heating / fixing apparatus of the second embodiment.

FIG. 12 is a diagram illustrating a change in gloss with respect to a temperature of an external heating member of the image heating / fixing apparatus according to the third embodiment.

13A is a diagram illustrating a temperature change of the fixing member pair when the external heating member is retracted from the fixing member pair in the image heating and fixing device of the third embodiment, and FIG. 13B is a diagram illustrating the third embodiment. FIG. 6 is a diagram showing a temperature change of the fixing member pair when the external heating member is brought into contact with the fixing member pair in the image heating and fixing apparatus according to the embodiment.

FIG. 14 is a diagram illustrating a conventional example.

FIG. 15 is a diagram illustrating a conventional example.

FIG. 16 is a diagram illustrating a conventional example.

FIG. 17 is a diagram illustrating a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus main body, 2 ... Document feeding system, 3 ... Document reading system, 4 ... Latent image forming unit, 5 ... Rotary developing device, 6 ... Recording material conveyance system, 7 ... Document, 8 ... Platen glass, 9 ... Optical system unit, 10 ... Irradiation light source, 11 ... Imaging element array, 12 ...
Infrared cut filter, 13: CCD, 14: A / D conversion circuit, 15: density conversion circuit, 16: black extraction / UCR processing circuit,
17: color correction circuit, 18: photoreceptor drum, 19: charger for removing static electricity, 20: cleaning means, 21: primary charger, 22: image exposure means, 23: image exposure reflection means, 24: rotating body, 25Y ... Yellow developing device, 25M: Magenta developing device, 25C: Cyan developing device, 25Bk: Black developing device, 26, 27: Recording material supply tray, 26a, 27a: Feed roller, 28: Transfer drum, 29: Transport roller, 30a, 30b: conveyance guide, 31: contact roller, 32: gripper, 33: charger for separating recording material,
34 ... separation claw, 35 ... transfer charger, 36 ... recording material separation charger, 37 ... conveyor belt means, 38 ... image heating and fixing device, 39
... Ejection tray, 40 ... Fixing roller, 40b ... Core, 40c ...
HTV silicone rubber layer, 40d RTV silicone rubber layer, 41 pressure roller, 40a, 41a halogen heater, 42
a, 42b, 42c: Thermistor, 43: Control device, 44: Oil application device, 45: Cleaning device, 46: Cleaning blade, 47: Oil pan, 48: Oil pumping roller, 49: Oil application roller, 50: Oil application Amount adjusting blade, 51: nonwoven fabric web, 52: pressing roller, 53: external heating roller, 53a: halogen heater, E: laser beam,
P: recording material, t: unfixed image

Claims (5)

[Claims] 1. A fixing member pair rotatably disposed while being pressed against each other, wherein a recording material on which an unfixed image is formed is nipped and conveyed by a nip portion formed by the fixing member pair to convey the recording material onto the recording material. An image heating / fixing apparatus for performing heat fixing of an unfixed image according to claim 1, wherein one or more external heating members are configured to be able to contact / retreat with respect to the fixing member pair. 2. The image according to claim 1, wherein the contact / retreat operation of the external heating member with respect to the fixing member pair is performed according to the surface temperature of the fixing member pair. Heat fixing device. 3. The fixing device according to claim 1, wherein the contact / retreat operation of the external heating member with respect to the fixing member pair is performed in accordance with a timing at which a recording material is conveyed to the fixing member pair. The image heating and fixing device according to claim 1. 4. An image heating and fixing apparatus, wherein the temperature of the external heating member is set to be higher than that of the fixing member pair. 5. A conveying means for conveying a recording material, an image forming means for forming an unfixed image on the recording material conveyed by the conveying means in accordance with image information, and a recording medium formed by the image forming means. An image forming apparatus, comprising: an image heating and fixing device according to claim 1, which heats and fixes an unfixed image.