JP2003142233A - Heating body, manufacturing method of heat generation body, heating device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heating body rising in temperature rapidly and having PTC characteristics capable of self temperature control, a heating device satisfying on-demand property and energy-saving property by the heating body and also modifying or doing without a non-paper-passing part temperature rise phenomenon and an image forming device equipped with the heating device as an image heating and fixing means. SOLUTION: The heating body 1 is a porous material as a heat generating body 2 having positive temperature resistance coefficient and generating heat by electricity conducting. Also, the heating body 1 has as the heat generating body 2 a porous material of pore volume rate from 10 to 40% generating heat by electricity conducting and having positive temperature resistance coefficient.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a PTC characteristic (Posi
a heating body having a self-temperature control characteristic having a tive temperature coefficient, a method of manufacturing a heating body of the heating body,
The present invention relates to a heating device and an image forming apparatus.

[0002]

2. Description of the Related Art For example, as a heating device (fixing device) for heating and fixing an unfixed toner image formed and carried on a recording material surface as a permanently fixed image in a copying machine such as an electrophotographic system, a printer or a facsimile machine. The heat roller type is widely used.

This heating device of the heating roller system records as a heated material in which an unfixed toner image is formed and carried in a pressure contact nip portion between a heat roller (fixing roller) and an elastic pressure roller which rotate in pressure contact with each other. The material is introduced and nipped and conveyed, and the unfixed toner image is heated and melted by the heat of the heat roller to be fixed on the recording material. The heat roller is a metal cylindrical cylinder whose outer peripheral surface is coated with a good release material such as fluororesin, as a heat roller, and a heater such as a halogen lamp or a xenon lamp is included in the heat roller, so that the heat generated by the heater The heat roller is heated from the inside, and the temperature is controlled by a temperature control system including a roller temperature detection element so that the outer surface temperature of the heat roller is maintained at a predetermined fixing temperature. The elastic pressure roller is, for example, a silicon rubber roller coated with a material having a good mold release property such as a fluororesin.

The heating device of the heat roller type has a small energy saving effect because it is difficult to rapidly raise the temperature, that is, on-demand fixing is difficult because the heat capacity of the heat roller is large and heating is performed to an unnecessary portion.

As a device capable of on-demand fixing, there is a film heating type heating device. This has a fixedly supported heating element and a heat-resistant film (fixing film) that slides in contact with this heating element, and heats the material to be heated by the heat from the heating element via the film. On-demand fixing is possible by using a ceramic heater that is a heating device and has a low heat capacity and can rapidly raise the temperature as a heating body, and a thin film having a low heat capacity. The ceramic heater includes, for example, a ceramic substrate made of alumina or the like having a thickness of about 0.6 to 1 mm, and a conductive heating resistor layer such as silver-paradium which is patterned on the substrate surface by screen printing using a resistor paste. With a basic structure, the overall heat capacity is low and the temperature can be rapidly raised by energizing the energization heating resistor layer.

[0006]

In any of the above heating devices of the heat roller system and the film heating system,
When a material to be heated that is narrower than the material to be heated that has the maximum paper width that can be passed through the device is passed, excess heat accumulates in the part of the heating part where the heated material does not pass (non-paper passing part). That is, a problem of so-called “temperature rise in non-sheet passing portion” has occurred.

For example, even if the temperature of the heat roller or the film in the paper passing portion is controlled at 200 ° C., the temperature of the non-paper passing portion exceeds 250 ° C. (temperature rise in the non-paper passing portion) and the rubber used is It could damage the resin. Alternatively,
The elastic pressure roller has a large diameter expansion in the non-sheet passing portion, and an outer diameter difference in the axial direction is generated, so that the film is twisted or wrinkles are generated in the material to be heated.

In order to solve this problem, it has been practiced to provide a plurality of heating elements to separately generate heat at the center and end portions, or to change the sheet passing interval.

The film heating type heating device can rapidly raise the temperature, but if the ceramic heater, which is a heating body, has a thickness of about 0.6 to 1 mm, the heat transfer in the longitudinal direction is poor, so that the heating is not conducted. It was not possible to continue passing small size paper, such as postcards and envelopes, unless the printing speed was rapidly reduced to raise the temperature of the paper portion. For example, A
Even with a device capable of printing 20 sheets per minute in No. 4, if it becomes an envelope, unless it is reduced to 10 sheets per minute or less, it will be damaged.

In order to eliminate the temperature rise in the non-sheet passing portion, for example, PT is formed on the energization heating resistor layer itself formed in the ceramic heater.
Content that has C characteristics has been proposed. An energization heating resistor having a PTC characteristic heats up due to energization and rises in temperature, but when the temperature reaches a specific temperature (switching temperature), the resistance value suddenly rises and the temperature rise is suppressed. It is an energization heating resistor having a self-temperature control characteristic having a positive resistance temperature characteristic). For example, a semiconductor ceramic obtained by adding a doping material to barium titanate and sintering the same is about 2
It has a PTC characteristic in which the switching temperature is 05 ° C.

By giving the PTC characteristic to the energization heat-generating resistor layer itself, the non-sheet passing portion of the heating body reaches the specific switching temperature even if the temperature of the non-sheet passing portion reaches a certain switching temperature. The energization to the energization heating resistor layer part corresponding to P is P
According to the TC characteristic, the temperature is rapidly reduced, heat generation is suppressed, and the temperature rise in the non-sheet passing portion is eliminated or alleviated.

However, in the method of printing the resistor paste on the ceramic substrate by screen printing, adjustment of the print paste has not been realized.

Further, since the commercially available PTC heating body is a dense (bulk) sintered body, it has a large heat capacity, a slow temperature rising rate, and a large amount of waste in terms of thermal efficiency. Therefore, it has not been possible to meet the demands of the market such as on-demand and energy saving.

Therefore, an object of the present invention is to provide a heating element having a PTC characteristic capable of rapidly heating and controlling its own temperature.

Further, the heating member satisfies the on-demand property and the energy saving property, and eliminates or alleviates the temperature rise phenomenon in the non-sheet passing portion, and an image provided with the heating device as an image heating fixing means. An object is to provide a forming device.

[0016]

The present invention provides a heating element, a method of mainly producing heat, a heating device, and an image forming apparatus characterized by the following constitutions.

(1) A heating element characterized in that a porous material having a positive temperature coefficient of resistance, which generates heat when energized, is mainly composed of heat generation.

(2) A heating body characterized in that the main body of heat generation is a porous material having a pore volume ratio of 10 to 40%, which has a positive temperature resistance coefficient by generating heat when energized.

(3) The heating element according to (1) or (2), characterized in that the porous material which is the main body of heat generation is a porous ceramic material.

(4) The heating element according to any one of (1) to (3), characterized in that the heating element is sandwiched between sandwiches of a power feeding electrode member.

(5) The energization direction to the heat generating main body is parallel to the relative movement direction of the heating body and the material to be heated or is perpendicular to the surface of the material to be heated ( The heating element according to any one of 1) to (4).

(6) Any one of (1) to (5), characterized in that a temperature detecting element for temperature control is provided.
The heating element described in 1.

(7) A plastic mixture obtained by mixing powder of a substance having a positive temperature resistance coefficient, heat resistant fibers, a filler, a water resistant granular organic substance, a binder and water is molded and then molded. A method for producing a heat-generating main body in a heating element according to any one of (1) to (6), characterized by firing.

(8) A heating device for heating a material to be heated by the heat of the heating device, wherein the heating device is the heating device according to any one of (1) to (6). .

(9) A heating device for heating a material to be heated by the heat of the heating member, wherein the heating member is the heating member according to any one of (1) to (6). .

(10) In a heating device having a fixedly supported heating body and a film that slides in contact with the heating body, and heats a material to be heated by heat from the heating body through the film. , The heating element is any one of (1) to (6)
A heating device according to claim 3.

(11) The heating device according to (10), further comprising a pressure rotator that forms a heating nip portion by being pressed against each other with the film interposed therebetween.

(12) Any one of (9) to (11), wherein the material to be heated is a recording material carrying an image.
The heating device described in 1.

(13) In an image forming apparatus having an image forming means for forming and carrying an unfixed toner image on a recording material and an image fixing means for heating and fixing the unfixed toner image on the recording material, the image fixing means is (9) ) To (12), the image forming apparatus.

[Operation] By making the heat-generating main body having the PTC characteristic a porous material, the heat capacity can be lowered and the heating body can be provided with a steep temperature rising property. Can meet.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] (1) Image Forming Apparatus FIG. 1 is a schematic structural model view of an example of an image forming apparatus. The image forming apparatus in this embodiment is a laser beam printer using a transfer type electrophotographic process.

Reference numeral 31 denotes a rotary drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image bearing member, which is rotationally driven in a clockwise direction indicated by an arrow at a predetermined peripheral speed.

Reference numeral 32 denotes a charging roller as a charging means, which uniformly charges the outer peripheral surface of the rotating photosensitive drum 31 to a predetermined polarity and potential. In this example, the charging process is uniformly performed at about -600V.

Reference numeral 33 denotes a laser beam scanner as an information writing means, which outputs a laser beam L modulated in accordance with a time-series electric digital pixel signal of image information to output the uniformly charged surface of the photosensitive drum 31. Scan and expose. Due to this scanning exposure, the potential of the exposed light portion on the uniformly charged surface of the photosensitive drum 31 is attenuated, and an electrostatic latent image corresponding to the scanning exposure pattern is formed on the surface of the photosensitive drum due to the potential contrast with the potential of the exposed dark portion.

A toner developing device 34 is a developing means. In this example, the reversal developing device uses a negative toner having a negative charging polarity, and toner adheres to the exposed bright portion on the surface of the photosensitive drum to develop the electrostatic latent image as a toner image.

Reference numeral 35 denotes a paper feed cassette. A recording material (transfer paper) P stacked and stored in the paper feed cassette is separated and fed by a pickup roller 36, and passes through a sheet path 37 and a registration sensor 38. Then, the toner is fed to the transfer nip portion, which is the contact portion between the photosensitive drum 31 and the transfer roller 39 as the transfer means, at a predetermined control timing. A predetermined transfer bias (plus 1 KV to 5 KV) is applied to the transfer roller 39, and the toner image formed on the surface of the photosensitive drum 31 is electrostatically transferred onto the surface of the recording material P that is nipped and conveyed in the transfer nip portion. It

A fixing device 40 introduces the recording material P separated from the surface of the photosensitive drum 31 through the transfer nip portion, and heats and fixes the unfixed toner image on the surface of the recording material P as a permanently fixed image. The fixing device 40 will be described in detail in the next section (2).

A drum cleaning device 41 cleans the surface of the photosensitive drum by removing contaminants such as transfer residual toner and paper dust remaining on the surface of the photosensitive drum 31 after the recording material is separated.

The recording material that has passed through the fixing device 40 is discharged to a discharge tray 43 through a sheet path 42.

(2) Fixing Device 40 FIG. 2 is a schematic cross-sectional model view of the main part of the fixing device 40 in this embodiment. The fixing device 40 of this example is basically a pressure roller driving type film heating type heating device disclosed in Japanese Patent Laid-Open No. 4-44075 to 44083, and a porous ceramic heating having PTC characteristics as a heating body. I am using my body.

Reference numeral 1 is a porous ceramic heating body having PTC characteristics (hereinafter referred to as PTC porous heating body),
It is a laterally long member having a longitudinal direction in a direction (perpendicular to the drawing in FIG. 2) orthogonal to the moving direction A of the recording material P in the recording material conveying surface. In this example, it is an elongated prismatic member having a length of 230 mm, a width of 6 mm, and a height (thickness) of 3 mm, which generates heat when energized and is temperature controlled to a predetermined temperature by a temperature control system. Details of the PTC porous heating body 1 will be described in the following item (3).

Reference numeral 11 denotes a heating body support (heating body holder) which heat-insulates and supports the PTC porous heating body 1 by exposing its heating surface side downward.

Reference numeral 12 denotes a cylindrical (endless) heat resistant film (hereinafter referred to as a fixing film), which has the above-mentioned PT.
Heating body support 11 on which the C porous heating body 1 is fixedly supported
It is loosely fitted on. In this example, the cylindrical fixing film 12 is a seamless polyimide film having a diameter of 24 mm and a thickness of 45 μm and a fluororesin coat having a thickness of 10 μm coated on the surface thereof.

The fixing film 12 has a film thickness of 100 μm or less, and preferably 10 to 10 μm in order to enhance the heat transfer property, reduce the heat capacity, and improve the quick start property.
PTFE, PFA, FEP with heat resistance of about 50 μm
Single layer, or polyimide, polyamideimide, PE
PTFE, PF on the outer surface of EK, PES, PPS, etc.
A composite layer film in which A, FEP and the like are mixed and coated can be used.

Reference numeral 13 denotes a rigid pressure stay (iron stay) made of a metal such as iron, which is inserted into the cylindrical fixing film 12 and positioned inside the heating body support 11. . The upper surface of the rigid pressure stay 13 is in contact with or close to the inner surface of the fixing film and also serves as a film inner surface guide member for supporting the fixing film 12 from the inside.

Reference numeral 14 denotes an elastic pressure roller having an outer diameter of 20 mm. In this example, an iron or aluminum core metal 15 having an outer diameter of 14 mm and a silicon rubber layer 16 having a thickness of 3 mm and an Asker C hardness of 50 degrees are provided. , A surface coating layer 17 of fluororesin having a thickness of 300 μm.

The pressure roller 14 is arranged such that both ends of the cored bar 15 are rotatably supported by bearings between the side plates (not shown) and the front side of the fixing device. Above the pressure roller 14, the PTC porous heater 1 and the heater support 1 are provided.
1. The assembly assembly of 1, the fixing film 12, the pressure stay 13, and the like is arranged in parallel with the pressure roller 14 with the PTC porous heating body 1 side facing downward, and the pressure stay 13 is resistant to the elasticity of the pressure roller 14. Then, by applying a predetermined pressing force downward with an urging means (not shown) to apply a pressure urging state, P
The lower surface of the TC porous heating element 1 is sandwiched with the fixing film 12 and pressed against the pressure roller 14 to form the fixing nip portion N having a predetermined width. In this example, the total pressure is 150N
Was added. As a result, the width of the fixing nip portion N became 6 mm.

The pressure roller 14 is rotationally driven in a counterclockwise direction indicated by an arrow at a predetermined peripheral speed by the rotational driving force transmitted by a driving means (not shown) via a power transmission system. The rotational force of the pressure roller 14 acts on the fixing film 12 by the frictional force between the roller 14 and the outer surface of the fixing film 12 in the fixing nip portion N (the recording material P is introduced into the fixing nip portion N). The rotational force indirectly acts on the fixing film 12 via the recording material P), the fixing film 12
However, the inner surface of the PTC porous heating body 1 is rotationally driven in the clockwise direction indicated by the arrow while sliding in pressure contact with the downward surface of the PTC porous heating body 1 in the fixing nip portion N. The pressure stay 13 which also serves as a film inner surface guide member facilitates rotation of the fixing film 12.

Since the fixing film 12 always rotates in a tension-free state (a state in which no tension is applied) for at least a part of its circumference, the displacement force of the fixing film 12 in the axial direction due to the rotation is small. Therefore, although not shown in the figure, a simple member such as a flange member that simply receives the end portion of the fixing film is sufficient as the deviation movement restricting means of the fixing film 12.

The rotation of the pressure roller 14 of the fixing device 40 and the energization of the PTC porous heater 1 are carried out based on the pressing of the copy button of the image forming apparatus or the print command signal, or the unfixed image to be fixed. The start of the recording material P supporting the toner image t is started based on a signal detected by a sensor (not shown) provided on the front side of the fixing device.

In a state where the driven peripheral speed of the fixing film 12 is stabilized by the rotational driving of the heating roller 14 and the temperature of the PTC porous heater 1 rises to a predetermined level,
The fixing film 12 and the pressure roller 14 in the fixing nip portion N
A recording material P to be image-fixed as a material to be heated is introduced between and, and the fixing nip portion N is nipped and conveyed together with the fixing film 12, whereby the heat of the PTC porous heating body 1 causes the fixing film 12 to move. The unfixed toner image t applied to the recording material P via the recording material P is heated and fixed on the surface of the recording material P. The recording material P passing through the fixing nip portion N is the fixing film 1
It is separated from the second surface and conveyed. The area of the fixing nip N is an area where pressure and temperature are applied between the pressure roller 14 and the PTC porous heating body 1.

(3) PTC Porous Heating Body 1 FIG. 3 is an enlarged cross-sectional model view of the PTC porous heating body portion in the fixing device of this embodiment, and FIG. 4 (a) is the rear surface of the PTC porous heating body 1 with the middle portion omitted. Side plan view, (b)
Similarly, it is a plane model drawing of the surface side with the middle part omitted.

The PTC porous heating element 1 of the present example comprises: A porous ceramic material that has PTC characteristics, that is, generates heat when energized and has a positive temperature resistance coefficient, as the heat generating main body 2; First and second power supply electrode layers 3a provided on the two side surfaces of the heat generating body 2 on the upstream side and the downstream side in the recording material moving direction A.
3b ,. An overcoat layer (protective layer) provided on the surface of the heating body 2 where the sliding surface of the fixing film is the surface of the heating body
The slidable glass layer 4 as a. The heating main body 2 has a side opposite to the sliding surface side of the fixing film as a heating body rear surface side, and a thermistor 5 as a temperature detecting element provided on the rear surface side.

The porous ceramic material having PTC characteristics as the heat generating main body 2 is a laterally elongated member having a length in the direction orthogonal to the moving direction A of the recording material P in the recording material conveying surface, and in this example, the length is long. It is an elongated prismatic member having a width of 230 mm, a width of 6 mm, and a height (thickness) of 3 mm.

The first and second power supply electrode layers 3a and 3b are conductive material layers having a thickness of several tens of μm. For example, a silver paste layer is applied by screen printing or the like to the two side surfaces of the heat generating main body 2 on the upstream side and the downstream side in the recording material moving direction A by screen printing or the like, and the silver paste layer is baked. The electrode formation direction is
It is provided upstream and downstream in the direction in which the recording material is passed. As a result, when the current becomes parallel to the sheet passing direction of the recording material and a temperature rise occurs in the non-sheet passing portion, the resistance value of the heat generating main body 2 in that portion rises and the current is suppressed, Heat generation in the non-sheet passing portion is suppressed.

The slidable glass layer 4 is also a thin layer of about 10 to several tens of μm. For example, a glass paste layer is entirely applied to the sliding surface side of the fixing film of the heat-generating body 2 by screen printing or the like and baked.

In the PTC porous heating body 1 of this example,
Since the first and second power feeding electrode layers 3a and 3b and the glass layer 4 are thin layers as described above, the length, width, and height (thickness) of the PTC porous heating body 1 are determined by the heat generation. The above length of the porous ceramic material having PTC characteristics as the main body 2,
It is substantially the same as the width and height (thickness).

The thermistor 5 as a temperature detecting element is provided in contact with the back surface of the heating element corresponding to the minimum sheet passing width area. In this example, the recording material P is conveyed with the center as a reference, and the thermistor 5 is arranged on the back surface of the heating body at a substantially central portion in the longitudinal direction of the heating body.

Reference numeral 100 is a control circuit section, and 101 is a power supply circuit section (AC power supply). From the power supply circuit unit 101 to the first and second
Power is supplied between the power supply electrode layers 3a and 3b of the
The longitudinal portions of the element generate heat when energized. In the present example, the energization direction in each longitudinal portion of the heat generating main body 2 is parallel to the moving direction A of the film 12 and the recording material P which are the material to be heated in the fixing nip portion N.

The temperature of the heating element 2 is detected by the thermistor 5, and the detected temperature information is input to the control circuit section 100.
The control circuit unit 100 controls the power supplied from the power supply circuit unit 101 to the first and second power supply electrode layers 3a and 3b so that the temperature detected by the thermistor 5 is maintained at a predetermined fixing temperature. The temperature control of the heating element 1 is performed.

The porous ceramic material having PTC characteristics as the heat generating main body 2 of this example has a porosity volume ratio of 2 containing barium titanate as a main component as a substance having PTC characteristics.
0% porous sintered material, length 230mm, width 6m
A m-shaped column having a height of 3 mm was used. The electric resistance value is 1 between the first and second power supply electrode layers 3a and 3b.
It is 8Ω. By connecting to a 120V AC power source, a maximum of 800W of power can be taken out.

FIG. 5 shows the PTC characteristics of the PTC porous heating element 1 in this example, with a switching temperature of 205.
℃.

The barium titanate bulk sintered body has a density of about 5 g / cm ³ and a specific heat of about 0.8.
J / K · g, which is 1 cm ³ obtained by this multiplication
The heat capacity per unit is 4 J / K.

On the other hand, the pore volume ratio in this example is 20%.
The barium titanate porous sintered material has a density of about 0.
7 g / cm ³ , specific heat is about 1.93 J / K · g, and the heat capacity per 1 cm ³ obtained by this multiplication is 1.35 J / K, which is about 1/3 of the bulk sintered body of barium titanate. And, the easiness of warming is about 3 times.

In the present embodiment, when the pressure roller 14 is rotated at a peripheral speed of the surface of 200 mm / sec and 100 V is input to the heating element 1 to heat it with the above fixing device specifications, the output of the thermistor 5 is obtained. When measured, it took 5 seconds from room temperature (25 ° C.) to heat to 190 ° C., and a temperature rising rate sufficient to maintain the on-demand property was obtained.

As described above, by making the heat-generating main body 2 having the PTC characteristic a porous material, it is possible to reduce the heat capacity and to provide a steep temperature rise property, and it is possible to satisfy the on-demand property and the energy saving property. .

Further, the switching temperature of the heat generating main body 2 having the PTC characteristic is 205 ° C. (FIG. 5), and when the temperature of the non-sheet passing portion exceeds 205 ° C., the fixing temperature control of the sheet passing portion exceeds 190 ° C. As a result, the resistance value of only the heat-generating main portion corresponding to the non-sheet passing portion increases and the energization is reduced, so that the temperature rise does not stop and the temperature does not rise above 205 ° C. Therefore, the temperature rise phenomenon of the non-sheet passing portion is eliminated, and the sheet passing speed of
It has become possible to continue feeding paper even after the 10th sheet in the state of mm / sec.

(4) Manufacturing Method of Heating Main Body 2 A manufacturing procedure of a porous ceramic material having PTC characteristics as the heating main body 2 will be described.

The porous ceramic material having PTC characteristics as the heat generating main body 2 is a powder of a substance having a positive temperature resistance coefficient such as barium titanate, a heat resistant fiber, a filler if necessary, and a water resistant material. It can be manufactured by molding, drying and then firing a plastic mixture obtained by mixing the organic particulate organic substance, the binder, and water.

A) Heat-resistant fibers include rock wool,
Aluminosilicate fibers, alumina fibers, glass fibers, aramid fibers and the like can be used. The thickness of the heat-resistant fiber used affects the size of the interfiber gap of the product,
In order to obtain large voids, it is advantageous to use a slightly thicker fiber having a fiber diameter of about 2 to 15 μm.

B) If necessary, about 3 for heat resistant fiber
The amount of interfiber voids in the product can be adjusted by using up to 00% by weight of a filler, for example, gairome clay, kibushi clay, kaolin, bentonite, alumina, silica and the like.
That is, the interfiber voids can be reduced by blending the filler and increasing the blending amount thereof. However, the filler content is 300 with respect to the heat resistant fiber.
When the content exceeds 10% by weight, the heat capacity increases, and it becomes difficult to secure the rate of temperature rise as the heating element by the above mechanism.
On the other hand, if it is 50% or less, there are too many voids and the strength as a heating element cannot be obtained.

Further, in order to have electric resistance, PT
Barium titanate particles having C characteristics and other metal oxides (for example, tin oxide, zinc oxide, and titanium oxide), metal powders, and powders such as SiC and carbon are prepared and added.

C) The water-resistant granular organic material is used to generate pores in the product. As this material, materials made of various synthetic resins such as polypropylene, polyethylene, polystyrene and acrylic resin are suitable, and expanded resin particles can also be used. In addition, pulverized products of water-resistant natural organic substances such as wood, carbon powder and the like can also be used. It is necessary for this material to be water resistant in order to maintain the granular state until the raw material mixture is mixed with water, molded, and dried.

The particle size of the water-resistant granular organic material is at least 0.
It needs to be 05 mm, and if it is too fine, it cannot form the pores that serve for the above-mentioned heat insulation and for reducing the heat capacity. Further, the granular material having a particle size of more than 2 mm causes excessive pores to deteriorate the physical properties and uniformity of the product, and also lowers the strength. The compounding ratio of the water-resistant granular organic matter is that of the pores formed in the product. Control the total amount. Therefore, the heat capacity of the product can be changed by changing the compounding ratio of this material.

D) As a binder, methyl cellulose,
In addition to organic binders such as carboxymethyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, phenolic resins, polyacrylic acid esters, sodium polyacrylate, etc., inorganic materials such as colloidal silica, alumina sol, sodium silicate, lithium silicate, glass frit, etc. Binders can be used. However, those that do not react with other additives, or those that have no electrical conductivity and do not change with time, PT
Those having no reactivity with barium titanate particles having C characteristics are selected.

The organic binder develops strength just after the raw material mixture is molded and dried to facilitate the subsequent handling, and most of them increase the viscosity of the raw material mixture to facilitate the molding. It also works. On the other hand, the inorganic binder maintains the binding force without burning even when the raw material mixture is molded and fired at a high temperature reaching 1000 ° C.

Therefore, it is advantageous to use both an organic binder and an inorganic binder in combination, and the raw material mixture is added to the inorganic binder in the required amount to bring the strength and hardness of the final product to the required level. From the viewpoint of ensuring the moldability of and the strength of the molded product before firing, it is desirable to use an organic binder in combination.

E) An appropriate amount of water is added to the above raw materials and mixed to form a uniform plastic mixture. The amount of the binder and water also influences the size and amount of the interfiber microvoids of the product.

The preferable mixing ratio of the raw materials varies depending on the kind of the binder, the heating temperature after molding, the required product characteristics and the like, but when heating to 150 to 400 ° C. to obtain the product, the preferable mixing ratio of the raw materials is Generally within the following range.

Heat-resistant fiber (total amount with filler when using filler) 100 parts by weight Barium titanate 10-100 parts by weight Carbon 20-100 parts by weight Water-resistant granular organic matter 10-300 parts by weight Binder 2 ˜100 parts by weight Water Appropriate amount (usually 20 to 200% by weight based on the total amount of the above raw materials) The obtained plastic mixture is molded into a predetermined shape such as a rod shape, a cylinder shape, a plate shape or the like according to the intended use of the product. There is no limitation on the molding method, and any molding method such as extrusion molding and press molding can be selected according to the product shape.

Next, the molded body is dried at room temperature or under heating to cure and remove water. Fine communication voids between the fibers are formed at this stage. Further about 150-400
When the particulate organic substance is burnt or decomposed and gasified to be extinguished by raising the temperature to ℃, pores remain after that.

In the step of heating and eliminating the particulate organic matter, it is inevitable that the organic binder also partially carbonizes or burns, but it is desirable to minimize it. Therefore, only organic binders should be used. When using, the heat treatment is often restricted. On the other hand, when an inorganic binder is used as a main binder and an organic binder is used as an auxiliary, a sufficient product strength can be obtained even if the organic binder is completely burned off. It is possible to easily and completely eliminate the particulate organic matter by baking at a high temperature, and to completely cure the inorganic binder, so that its characteristics can be sufficiently exhibited.

In order to prevent the occurrence of cracks due to the rapid disappearance of the granular organic matter due to the firing at a high temperature of 400 ° C. to about 1000 ° C., 150 to 40 prior to the firing at a high temperature.
Preheating at 0 ° C may be performed in some cases. In this case, the preferable mixing ratio of the raw materials is in the range below.

Heat resistant fiber (total amount with filler when using filler) 100 parts by weight Barium titanate 10 to 100 parts by weight Carbon 20 to 100 parts by weight Water-resistant granular organic matter 10 to 300 parts by weight Binder 50 Up to 300 parts by weight Water Appropriate amount (usually 20 to 200% by weight with respect to the total amount of the above raw materials) By the above, it has PTC characteristics, and also has PTC characteristics as a heat-generating main body 2 that is excellent in mechanical strength and durability A porous ceramic material is obtained.

During the molding of the porous ceramic material or after the molding, a paste in which silver or platinum is dispersed in glass is applied to a required portion of the porous ceramic material, and the paste is baked at the same time or in a later step. And the second power supply electrode layer 3a
It is possible to form 3b. The slidable glass layer 4 can also be applied by dipping or printing and firing a glass paste.

The porosity volume ratio of the porous ceramic material having PTC characteristics as the heat generating main body 2 is preferably set to 10 to 40%.

If the pore volume ratio is less than 10%, the heat capacity becomes large and it becomes difficult to warm up, so that a sufficient on-demand effect cannot be obtained. If it is more than 40%, the strength as a molded article decreases, and it becomes difficult to form a flat surface when an electrode layer or a sliding glass layer is formed, which makes it difficult to make a contact.
Alternatively, there is a problem that heat is not easily transferred to the film because of poor contact with the film.

In the present invention, the porosity volume ratio of the porous ceramic material having the PTC characteristic is the volume V derived from the outer dimensions of the porous ceramic material having the PTC characteristic,
A porous ceramic material having PTC characteristics is impregnated with a liquid, and the amount V ′ is measured to obtain V ′ / V × 100.
It is a value calculated by (%).

(5) Comparison with other fixing devices a) Film heating type on-demand fixing device using the PTC porous heating element 1 of the above-mentioned Example 1, and b) Conventional halogen heater-containing heat roller. Table 1 shows a comparison of three fixing devices of the system and c) an on-demand fixing device of the film heating system using a plate-shaped ceramic heater as a heating body.

FIG. 6 is a schematic diagram of a heat roller type heat fixing device used in the above comparison.

Reference numeral 21 denotes a heat roller (fixing roller), which is made of an aluminum pipe (cylinder) having an outer diameter of 25 mm and a wall thickness of 0.8 mm as a substrate, and the outer peripheral surface of which is coated with 25 μm thick PFA. Reference numeral 22 is a 750 W halogen heater inserted and arranged in the heat roller 21. Reference numeral 14 denotes a pressure roller, which is similar to the pressure roller used in the heat fixing device of this embodiment. Heat roller 21 and pressure roller 14 are 150N
The fixing nip portion N having a width of 6 mm is formed by press-contacting with the load. The heat roller 21 and the pressure roller 14 are rotationally driven in the direction of the arrow. The heat roller 21 is heated from the inside by the heat generated by the halogen heater 22, and the halogen heater 22 is heated by a temperature control system including a roller temperature detecting element.
Is controlled so that the outer surface temperature of the heat roller 21 is maintained at a predetermined fixing temperature of 190 ° C. in this example. Then, the recording material P on which the unfixed toner image T is formed and carried is introduced into the fixing nip portion N and is nipped and conveyed to heat and melt the unfixed toner image by the heat of the heat roller 21 to fix it on the recording material. is there.

FIG. 7 is a structural schematic diagram of an on-demand fixing device using a plate-shaped ceramic heater as a heating element used in the above comparison. In comparison with the on-demand heat fixing device of the first embodiment, the difference is that the heating body is not the PTC porous heating body but the plate-shaped ceramic heater 23, and the other device configurations are substantially the same.

FIG. 7B is an enlarged cross-sectional model view of the plate-shaped ceramic heater 23 as a heating body used here, in which a horizontally long alumina base material having a width of 6 mm and a thickness of 0.6 mm is used as the heater substrate 24. As the heating resistor 25, an electric resistance material such as Ag / Pd (silver-palladium) is formed on the heater substrate 24 so as to have a thickness of 10 to 30 μm and a width of 0.8.
It has a resistance value of 18Ω and is coated and baked by screen printing or the like to ˜3 mm, and is coated with glass or fluororesin as the overcoat layer 26 (protective layer). The plate-shaped ceramic heater 23 is used as the heating body support 1
1 is fitted in a groove provided along the longitudinal direction on the outer lower surface of 1 and is adhered and fixedly supported.

The plate-shaped ceramic heater 23 rapidly rises in temperature when the energization heating resistor 25 generates heat over the entire length of the energization heating resistor 25, and the temperature rise is detected by the temperature detecting element 27. The temperature detection element 27 is fed back to the control system shown in the drawing to heat the image.
The energization to the heating resistor 25 is controlled so that the temperature is maintained at a predetermined set temperature, 190 ° C. in this example. The pressing force is 150 N, and the width of the fixing nip portion N is 6 mm.

[0095]

[Table 1]

As the amount of heat required for fixing monochrome printing,
It took 45 seconds for the heat roller type fixing device to rise to the temperature-controlled temperature of 190 ° C., but the on-demand fixing device of Example 1 started up in 5 seconds and printing was possible. From this, it can be seen that the heat roller type fixing device has a slow start-up and cannot obtain the on-demand property.

The on-demand fixing device using the ceramic heater 23 can raise the temperature in the same time as the on-demand fixing device of the first embodiment.

A commercial 10 size envelope (104.8 mm × 242.3 mm) was continuously attached to one of these devices.
Table 1 also shows the temperature rise in the non-sheet-passing portion when 0 sheets are passed at a sheet-passing speed of 150 mm / sec.

In the heat roller type fixing device, due to the heat capacity and the cross-sectional area of the heat roller 21, the number of sheets is raised to 205 ° C. only.

However, in the case of the on-demand fixing device using the ceramic heater 23, since the heat conduction in the longitudinal direction is poor, the surface temperature of the pressure roller at the non-sheet passing portion is 260.
Since the temperature reaches up to ℃ and exceeds the heat resistant temperature of the fluororesin, the fixing device is damaged. In order to prevent this, it is necessary to widen the sheet passing interval around the sixth sheet.

In the on-demand fixing device of the first embodiment using the PTC porous heating element 1, the non-sheet passing portion is 205
When the temperature reaches ℃, the resistance value of the heating element increases only in the non-sheet passing area and the current flow is reduced.
No more than that. Therefore, the sheet passing speed is 150
It has become possible to continue feeding paper even after the 10th sheet in the state of mm / sec.

As described above, since the heating body which mainly uses the porous material having the PTC characteristic as the heat generating element is used, it is possible to obtain a heating body which is lightweight and capable of heating at a high speed while controlling its own temperature. Was given. Further, in the fixing device using this heating element, it is possible to obtain a device that has both on-demand property and energy saving property and that suppresses the temperature rise in the non-sheet passing portion.

Further, a bulk PTC heating element having the same size as the PTC porous heating element 1 of the fixing apparatus of Example 1 was used to form a fixing apparatus of the same film heating system as that of the fixing apparatus of Example 1, and the same power was used. Was added, room temperature from 25 ℃ to 1
It took 25 seconds to reach 90 ° C.

[Embodiment 2] In the on-demand fixing device using the ceramic heater 23, it is possible to form a heater having a curvature when a metal is used in order to obtain heat conduction in the base material of the film 12. Have difficulty. Because the ceramic material such as alumina or aluminum nitride as the heater substrate 24 has a large dimensional change due to sintering,
The workability after sintering is poor, and if a pattern such as a resistor is printed after forming a curved surface shape, the accuracy of the thickness and width of the resistor pattern deteriorates, so that a desired resistance value can be obtained. It was difficult.

On the other hand, in the case of the PTC porous heating body 1 according to the present invention, the porous material 2 having PTC characteristics, which is the main component of heat generation, is a material with good machinability, and it is a large frame for extrusion molding or die molding. Since it is finished after forming the shape of, the curved surface can be easily made. Moreover, since the whole functions as a heating element, the accuracy of the resistance value can be improved. Figure 8
Is an example of the PTC porous heater 1 having a curved surface on the film sliding side.

[Embodiment 3] FIG. 9 shows a PTC porous heater 1 in which the first and second feeding electrode layers 3a and 3b are taken in different manners.

In the present embodiment, the PTC which is the main body of heat generation
The first and second power feeding electrode layers 3a and 3b are formed on the front surface side which is the film sliding side of the porous material 2 having the characteristics and the back surface side which is the opposite side thereof, and the first surface which is the front surface side. An insulating coating (glass or ceramic coating such as alumina) 4 is formed on the surface of the power feeding electrode layer 3a to form the heating element 1.

In this example, the PTC porous heating element 1 was used.
There are two reasons for changing the way of taking the first and second power feeding electrode layers 3a and 3b.

First, in order to make the sliding surface of the porous material 2 having the PTC characteristic, which is the main component of heat generation, with the fixing film 12 smooth, the coat 4 of glass or the like had to be applied in Example 1. In this embodiment, since the surface of the porous material 2 is sealed with the coat for forming the electrode 3a and the insulating coat 4 is formed, a smooth surface can be formed with a small number of times. it can.

If the sliding surface is not smooth, heat transfer is poor and the fixability is poor, and the sliding of the fixing film 12 is bad, and there is a risk of slippage.

The surface roughness of the insulating coat 4 is R
The z is preferably 1 micron or less, more preferably 0.5 micron or less.

[Others] 1) The heating element of the present invention is not limited to a film heating type heating apparatus, but a heating apparatus for directly heating a heating element supported by a heating element support to a material to be heated. Of course, it can also be applied to.

The heating element of the present invention can be used, for example, as a heating element for a mosquito repellent mat, a heating element such as a fan using a far infrared ray heater, a hair dryer, or the like.

2) In a film heating type heating device, an endless belt-shaped film may be tensioned and stretched so as to be rotatably driven. It is also possible to use a long end film wound in a roll and to make the device run at a predetermined speed from the delivery shaft side to the winding shaft side via a heater.

3) Further, the heating device of the present invention is not limited to an image heating and fixing device, but other than that, for example, an image heating device for heating a recording material carrying an image to modify the surface properties such as gloss, and a post-fixing treatment. It can be widely used as an image heating device for heating, a heating device for feeding a sheet-like material for drying treatment, laminating treatment, heat sealing treatment, wrinkle removing treatment, a heating device for drying used in an inkjet printer, and the like.

[0116]

As described above, according to the present invention, it is possible to obtain a heating element having a PTC characteristic capable of controlling the self-temperature while increasing the temperature at a high speed.

Further, the heating member satisfies the on-demand property and the energy saving property and eliminates or alleviates the temperature rising phenomenon in the non-sheet passing portion, and an image provided with the heating device as the image heating and fixing means. A forming device can be provided.

[Brief description of drawings]

FIG. 1 is a schematic configuration model diagram of an image forming apparatus according to a first embodiment.

FIG. 2 is a schematic cross-sectional view of the fixing device.

FIG. 3 is an enlarged cross-sectional model view of a PTC porous heating body portion.

FIG. 4 (a) is a plan view of the back side of the PTC porous heating body with the middle part omitted, and FIG. 4 (b) is a top side plan view of the PTC porous heating body with the middle part omitted.

FIG. 5 PTC characteristic diagram

FIG. 6 is a schematic configuration diagram of a heat roller type fixing device as a comparative example.

FIG. 7 is a schematic configuration diagram of an on-demand fixing device using a ceramic heater as a comparative example.

FIG. 8 is an enlarged cross-sectional model view of a PTC porous heating body portion according to the second embodiment.

FIG. 9 is an enlarged cross-sectional model view of a PTC porous heating body portion according to the third embodiment.

[Explanation of symbols]

1 ... PTC porous heating element, 2 ... PTC porous material as the main body of heat generation, 3a, 3b ... First and second power feeding electrode layers, 4 ... Sliding glass layer, 5 ... Temperature detection Element, 1
1 ... Heating body support, 12 ... Fixing film, 13 ...
Rigid pressure stay, 14 ... Pressure roller, N ... Fixing nip part, P ... Recording material (heated material), t ... Toner image

Continued front page    (72) Inventor Jun Asami             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2H033 AA03 AA23 AA30 AA32 BA25                       BA26 BA27 BA32 BE03 CA51                 3K058 AA02 AA13 AA81 BA18 CA12                       CA22 CA61 CB10 DA04                 3K092 PP18 QA05 QB21 QB30 QB37                       QB74 RF11 UA06 VV16 VV21

Claims (13)

[Claims] 1. A heating body comprising a porous material having a positive temperature coefficient of resistance as a main body of heat generation by generating heat when energized. 2. A heating body comprising a porous material having a pore volume ratio of 10 to 40% and having a positive temperature resistance coefficient as a main body of heat generation by generating heat when energized. 3. The heating element according to claim 1, wherein the porous material that is the main body of heat generation is a porous ceramic material. 4. The power supply electrode member is provided with the main body of heat generation being sandwiched between the power supply electrode members.
The heating element according to any one of 1. 5. The heating element is energized in a direction parallel to the relative movement direction between the heating body and the material to be heated or a direction perpendicular to the surface of the material to be heated. The heating element according to any one of 1 to 4. 6. The heating element according to claim 1, further comprising a temperature detecting element for controlling temperature. 7. A plastic mixture obtained by mixing powder of a substance having a positive temperature resistance coefficient, heat resistant fibers, water resistant granular organic matter, a binder and water is molded, dried and then fired. The method for producing a heat-generating main body in the heating element according to claim 1, wherein 8. The method for producing a heat-generating main body in a heating element according to claim 7, wherein a filler is blended in the plastic mixture. 9. A heating device for heating a material to be heated by heat of a heating body, wherein the heating body is the heating body according to any one of claims 1 to 6. 10. A heating device having a fixedly supported heating body and a film that slides in contact with the heating body, and heats a material to be heated by heat from the heating body through the film, A heating device, wherein the heating member is the heating member according to any one of claims 1 to 6. 11. The heating device according to claim 10, further comprising a pressure rotator that forms a heating nip portion by being pressed against each other with the film interposed therebetween. 12. The heating device according to claim 9, wherein the material to be heated is a recording material carrying an image. 13. An image forming apparatus comprising: an image forming unit that forms and carries an unfixed toner image on a recording material; and an image fixing unit that heat-fixes the unfixed toner image on the recording material. 13. The image forming apparatus according to any one of items 1 to 12.