JP2006294604A - Planar heater, its manufacturing method, and image fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a planar heater wherein a substrate is prevented from being damaged by thermal impact, the heating value of a resistance heater can be effectively used for fixing treatment since thermal conductivity of a substrate is low, and furthermore, the temperature rise of a paper non-passing part can be controlled. <P>SOLUTION: This planar heater is equipped with an insulating substrate, a heater, an electrode, and a heat resistant insulating layer. The insulating substrate comprises a polyimide resin. The heater is formed from a polyimide resin in which a conductive material is mixed and dispersed, and is provided on the insulating substrate. The electrode is to supply power to the heater. The heat resistant insulating layer is formed so as to cover the insulating substrate and the heater. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sheet heater that thermally fixes a toner image in a copying machine, a laser beam printer, and the like, a manufacturing method thereof, and an image fixing device using the sheet heater. More specifically, the present invention relates to a sheet heater for thermally fixing a toner image via a thin film seamless belt in an image fixing apparatus such as a copying machine or a laser beam printer, and an image fixing apparatus using the sheet heater.

In recent years, in electrophotographic copying machines and laser beam printers, a polyimide resin seamless belt or a metal thin film seamless tube is used as a fixing method to thermally fix unfixed toner images formed on copy paper. The method is becoming mainstream.
In an image fixing apparatus employing such a belt fixing system, for example, a planar ceramic heater is disposed inside a thin-film polyimide resin seamless belt having a thickness of 20 to 80 μm, and the outer surface of the polyimide resin seamless belt serves as a drive source. It is in pressure contact with the pressure roll to be connected. In such an image fixing apparatus, when the copy paper on which the toner image is formed is sequentially fed between the fixing belt and the pressure roll, the toner is heated and melted by the ceramic heater, and the toner image is placed on the copy paper. It is fixed. At this time, the fixing belt is rotationally driven by the driving force of the pressure roll transmitted through the copy paper, and the copy paper is fed and discharged together with the pressure roll.

  By the way, the ceramic heater used in such an image fixing apparatus of the belt fixing type is formed by, for example, forming a resistance heating element made of silver / palladium alloy on an insulating substrate such as ceramic by screen printing or the like, and then extending the length of the heater surface. It is manufactured by forming an electrode for energizing the resistance heating element at both ends in the direction, a signal extracting electrode of the thermistor, and the like. More specifically, as proposed in Patent Document 1 below, a silver / palladium alloy is formed on an alumina ceramic substrate by screen printing and fired at a high temperature, and then a glassy protective layer is provided as a ceramic heater. Yes. Such ceramic heaters have a very fast rise after energization, so there is no waiting time, and power consumption can be significantly reduced (on-demand fixing method) as compared with a fixing roll method using a conventional halogen lamp. For this reason, recently, a laser printer that can thermally fix A4 size copy paper at a high speed of 36 to 40 sheets per minute using such a ceramic heater is also commercially available.

  By the way, when a paper of the same size is inserted into a fixing machine with a belt fixing type image fixing apparatus compatible with A3 paper, the paper passes through the fixing belt in the longitudinal direction through the fixing belt. The entire surface of the paper is heated and normal heat fixing is performed. However, in the case of a small paper such as a postcard, the postcard passes through the central portion or one end of the heater in the length direction, and the amount of heat of the heater is absorbed by the postcard in the portion where the postcard passes. Although predetermined fixing is performed, heat is not consumed in a portion where the postcard has not passed, so that a local temperature difference occurs on the ceramic substrate (referred to as non-sheet passing portion temperature rise). Further, a heater used in a belt fixing type image fixing apparatus is required to have a heat generation capacity for instantaneously obtaining a fixing temperature of about 200 ° C. For this reason, when a ceramic heater is employed as a heater mounted on an image fixing apparatus of a belt fixing system, a local temperature difference occurs on the heater surface, and the ceramic substrate is easily destroyed by these thermal shocks. In order to solve such a problem, it has been proposed that the ceramic substrate material is not alumina but aluminum nitride, silicon nitride, or the like having higher thermal conductivity than alumina. Incidentally, in the following Patent Document 2, it is proposed that the substrate constituting the ceramic heater is formed of a sintered body of an aluminum oxide powder material to which a zirconium oxide powder material is added.

However, in the ceramic substrate improved as described above, since heat generated by the resistance heating element is easily radiated through the ceramic substrate, heat loss is likely to occur. In addition, there is a problem in the uniformity of the temperature of the entire length of the ceramic heater, and fixing failure tends to occur. Furthermore, the zirconium oxide powder material is expensive and has a problem of increasing the heater price.
Therefore, the inventors of the present invention produced a substrate by replacing the ceramic substrate material with polyimide resin powder, and produced a planar heater by laminating and integrating a metal electric resistance heating element on the substrate (see Patent Document 3). . When this planar heater is used as a fixing heater of a belt fixing device, since the substrate is organic, it is possible to prevent damage to the substrate due to thermal shock, maintain the uniform temperature of the entire length of the heater, and make a metal electric resistance heating element The heat generated from the heat can be effectively used for the fixing process.
Japanese Patent Laid-Open No. 03-114755 JP-A-11-143265 JP 2005-26185 A

However, the planar heater made of such a polyimide resin substrate is complicated to produce a metal electric resistance heating element and adjust the resistance value. In addition, since it is necessary to bond a metal electric resistance heating element on a polyimide resin substrate with a heat-resistant adhesive, there is a problem with respect to durability of adhesive strength due to repeated use from a fixing temperature (about 200 ° C.) to room temperature.
The present invention can prevent the substrate from being damaged by thermal shock, can effectively use the heat generation amount of the resistance heating element for the fixing process due to the low thermal conductivity of the substrate, and further increases the temperature of the non-sheet passing portion. It is an object of the present invention to provide a controllable sheet heater, a method for manufacturing the sheet heater, and an image fixing apparatus using the sheet heater.

  The planar heater according to the present invention includes an insulating substrate, a heating element, an electrode, and a heat-resistant insulating layer. The insulating substrate is made of polyimide resin. The heating element is made of a conductive polyimide resin and is provided on the insulating substrate. Here, the “conductive polyimide resin” is a polyimide resin in which conductive materials are mixed and dispersed. The electrode is for supplying power to the heating element. The heat resistant insulating layer is formed so as to cover the insulating substrate and the heating element.

In the planar heater according to the present invention, the conductive polyimide resin is preferably obtained by imide conversion after mixing and dispersing a conductive substance in a polyimide precursor. The “polyimide precursor” mentioned here is (1) a polyimide precursor obtained by reacting at least one tetracarboxylic dianhydride or derivative thereof with at least one diamine or derivative thereof in a polar solvent. Preferably, it is a solution or (2) a non-thermoplastic polyimide precursor solution obtained by reacting an ester compound derived from at least one tetracarboxylic acid with at least one diamine or derivative thereof in a polar solvent. . The “polyimide precursor” is a non-thermoplastic polyimide precursor solution obtained by reacting an ester compound derived from at least one tetracarboxylic acid with at least one diamine or derivative thereof in a polar solvent. If an ester compound derived from a tetracarboxylic acid is represented by the following formula (a) _{wherein, R 1, R 2, R} 3, R 4 are each independently hydrogen, from 1 to 8 carbon atoms hydrocarbon group (aromatic A ring, a functional group such as —O—, —CO—, and —OH), or a phenyl group. R ′ represents chemical formula (A-1) or chemical formula (A-2) (wherein X represents O, S, SO, SO ₂ , CH ₂ , C (CH ₃ ) ₂ , CO, or a direct bond). )] Is preferably an ester compound derived from at least one tetracarboxylic acid selected from the group consisting of ester compounds derived from tetracarboxylic acids represented by the following formula (I): [Wherein R ″ represents a chemical formula (I-1) or a chemical formula (
I-2) (wherein Y represents O, S, SO, SO ₂ , CH ₂ , C (CH ₃ ) ₂ , CO, or a direct bond)] selected from the group consisting of diamines or derivatives It is preferable that at least one kind of diamine or derivative thereof be mixed, and the mixing molar ratio of the ester compound derived from tetracarboxylic acid and the diamine or derivative thereof is preferably 80: 100 or more and 99: 100 or less. .

In the planar heater according to the present invention, the conductive materials are tantalum nitride (TaN), tantalum carbide (TaC), molybdenum trisilicide (Mo ₅ Si ₃ ), rhenium-tungsten alloy, molybdenum disilicide (MoSi ₂ ), It is preferably at least one selected from the group consisting of tungsten (W), molybdenum (Mo), tungsten carbide (WC), titanium carbide (TiC), metal, carbon black, graphite, and carbon nanotube.

In the planar heater according to the present invention, the heating element preferably has temperature self-control characteristics.
Further, in the planar heater according to the present invention, the insulating substrate is a powder molded body obtained by imide conversion after molding the polyimide precursor powder or while molding the polyimide precursor powder, and includes a filler made of an inorganic insulating material. preferable.

  Such a planar heater is preferably manufactured through a filler mixing step, a powdering step, an insulating substrate manufacturing step, an electrode installation step, a conductive substance mixing step, a coating step, and a heat-resistant insulating layer forming step. . In the filler mixing step, a filler made of an inorganic insulating material is mixed in the first polyimide precursor solution to prepare a filler-containing polyimide precursor solution. In the powdering step, the filler-containing polyimide precursor solution is pulverized to prepare a filler-containing polyimide precursor powder. In the insulating substrate manufacturing step, after the filler-containing polyimide precursor powder is molded or while the filler-containing polyimide precursor powder is molded, imide conversion is performed to manufacture the insulating substrate. In the electrode installation step, at least a pair of electrodes is provided on the insulating substrate. In the conductive material mixing step, a conductive material is mixed in the second polyimide precursor solution to prepare a polyimide precursor solution containing a conductive material. In the coating step, the polyimide precursor solution containing a conductive substance is partially coated on the insulating substrate so as to overlap a part of the electrode. In the imide conversion step, the conductive material-containing polyimide precursor is imide converted to form a heating element. In the heat resistant insulating layer forming step, the heat resistant insulating layer is formed so as to cover the insulating substrate and the heating element. The first polyimide precursor solution and the second polyimide precursor solution may be the same or different.

Such a planar heater can be used as a heat source of a fixing device of the image forming apparatus.
In addition, in such an image fixing apparatus having a fixing belt and a pressure roll, such a planar heater can exhibit its function by being disposed on the pressure roller side inside the fixing belt. The pressure roll is for pressing copy paper against the fixing belt. When the copy paper on which the toner image is formed is sequentially fed between the sheet heater and the pressure roll, the toner is heated and melted, and the toner image is fixed on the copy paper at the nip point.

  When the planar heater according to the present invention is used as a substrate for a planar heater used in an image fixing apparatus of a belt fixing type, since the insulating substrate material is polyimide and organic, a rapid temperature increase immediately after energization, etc. The conventional problem that the substrate is damaged can be solved without the thermal shock caused by the temperature and the damage due to the temperature difference (non-sheet passing temperature rise) on the heating element that occurs when the copy papers of different sizes are passed. . Further, the polyimide powder molded substrate can be easily molded even at a complicated shape, and can be manufactured at a low price. Further, in the planar heater according to the present invention, polyimide powder is used as the insulating substrate material and polyimide resin is used as the matrix material of the heating element. Therefore, the insulating substrate and the heating element can be firmly integrated and have excellent durability. Yes. In addition, since the polyimide powder molded substrate has a low thermal conductivity, the amount of heat radiated from the substrate side is small, and the amount of heat generated by the heating element can be effectively used for improving the fixability. Further, since the composition for forming the heating element is in a paste form, a desired shape and size can be easily obtained by a printing method or a coating method. For this reason, in the planar heater according to the present invention, the resistance value can be adjusted with high accuracy. The resistance value can also be defined by selecting the type and amount of conductive material to be mixed and dispersed in the polyimide precursor.

  In the planar heater according to the present invention, an optimal conductive material is selected, and mixed and dispersed in the polyimide precursor, whereby a temperature self-control type heating element, that is, a PTC (Positive Temperature Coefficient) characteristic or NTC ( A heating element exhibiting negative temperature coefficient characteristics can be prepared. Further, the planar heater according to the present invention can control the temperature rise of the non-sheet passing portion, which is a problem in the belt fixing method. Further, the imide conversion temperature of the polyimide precursor is at most 400 to 450 ° C., and can be manufactured without a large production line at a sintering temperature exceeding 800 to 1200 ° C. as in the case of a conventional ceramic heater. . For this reason, manufacturing cost can be suppressed low.

The planar heater according to the embodiment of the present invention is mainly composed of an insulating substrate, a heating element, an electrode, and a heat-resistant insulating layer.
As the insulating substrate, a film made of a heat-resistant resin such as a polyimide resin, a molded body such as a sheet, or a plate can be used. In the embodiment of the present invention, a more preferable insulating substrate is a polyimide powder-molded substrate obtained by press-molding a polyimide precursor powder and imide-converted, and a substrate containing a filler made of an inorganic insulating material. The polyimide powder molded substrate has a low thermal conductivity and is the most preferable insulating substrate that can suppress heat radiation from the substrate and effectively use the heat generated by the heating element for improving the fixing property.

  The polyimide powder molded substrate is molded from a polyamic acid powder having an average particle diameter of 0.1 to 50 μm, and is completed through imide conversion. This polyimide powder molded substrate is excellent in mechanical properties such as strength and dimensional stability. The molding of the powder compact is influenced by the particle diameter of the polyamic acid powder, the conditions such as the powder molding method and the pressing pressure, or the properties of the filler added to the polyamic acid powder, but the average particle diameter of the polyamic acid powder is more preferably 1. The range is ˜30 μm.

  The particle diameter of the polyamic acid powder can be optimized by adjusting the mixing molar ratio of the wholly aromatic diamine and the wholly aromatic tetracarboxylic dianhydride in the production process of the polyimide precursor solution. For example, when 4,4′-diaminodiphenyl ether (DDE = oxydianiline (ODA)) and pyromellitic anhydride (PMDA) are polymerized in an N-methyl-2-pyrrolidone solvent, PMDA is added to 100 mol% of DDE. When 94 mol% or more is blended, the particle diameter of the polyamic acid powder purified by the solvent coprecipitation method or the like increases rapidly, and the substrate molded with this powder has low mechanical strength and is easily damaged. Moreover, when PMDA is 70 mol% or less, the molecular weight is reduced, the mechanical strength is lowered, and it cannot be used as a substrate for a planar heater. In this way, by appropriately setting the blending ratio of the wholly aromatic diamine and the wholly aromatic tetracarboxylic dianhydride, the molecular weight at the time of polymerization can be changed, and the optimal polyamic for molding a polyimide powder molded substrate The acid powder can be purified. Also, polyamic acid powders with different particle diameters can be purified by the combination of monomers and powder purification method, and the method for producing polyamic acid should be selected appropriately according to the intended use of the powder and the required properties of the powder compact. Can do.

Moreover, when the filler which consists of an inorganic insulating material is contained in a polyimide powder molding board | substrate, it is preferable that the mixing amount of a filler is the range of 43-900 weight part with respect to 100 weight part of polyimide powder. The purpose of adding an inorganic insulating material is to adjust the linear expansion coefficient of the insulating substrate, and the level of the linear expansion coefficient of the heating element formed on the insulating substrate or the metal electrode for supplying power to the heating element. It is for adjusting. The linear expansion coefficient of a general polyimide resin is 1.0 to 2.5 × 10 ⁻⁵ cm / cm / ° C., but the polyimide powder molded substrate is increased by powder molding, and the linear expansion coefficient is 5 to 6 × 10 ⁻⁵ cm / cm / ° C. In addition, when nickel foil is employ | adopted as a metal electrode, since the linear expansion coefficient of nickel foil is 1.69 * 10 < ^-5 > cm / cm / degreeC, it is 2.9- of the linear expansion coefficient of a polyimide powder molding board | substrate. 3.5 times. Therefore, when the sheet heater using the polyimide powder molded substrate not mixed with the inorganic insulating filler is energized, the sheet heater is warped like a bimetal due to heat generation. In order to solve such a problem, it is preferable to mix a filler made of an inorganic insulating material having a small linear expansion coefficient in a polyimide powder molded substrate so as to match the linear expansion coefficient of a metal electrode or a heating element. That is, the inorganic insulating filler used in the embodiment of the present invention is not particularly limited as long as the linear expansion coefficient is small.

  A particularly preferable blending amount of the inorganic insulating material filler is in the range of 100 to 700 parts by weight with respect to 100 parts by weight of the polyimide powder. This is because an insulating substrate having both the adjustment of the linear expansion coefficient and the mechanical properties of the polyimide powder molded substrate can be obtained within this range. The inorganic insulating filler preferably has an average particle diameter in the range of 0.5 to 15 μm, and a fine one having a small particle diameter can easily change the linear expansion coefficient. Moreover, the shape of the inorganic insulating filler may be any shape such as a particle shape or a fiber shape. In order to improve thermal shock, it is also preferable to add acicular crystal powder.

As the filler made of an inorganic insulating material, an optimum filler such as the type, particle diameter, shape or blending amount can be selected depending on the material, shape, and heat generation amount of the electrode or the heating element. Boron nitride, aluminum nitride, silicon carbide, aluminum oxide, quartz, glass powder, magnesium oxide, and the like are preferable materials that can be used alone or in combination.
The method of mixing the polyimide powder and the inorganic insulating filler is preferable because the method of mixing the inorganic insulating filler in the polyimide precursor solution in advance can be mixed in the solution and can be uniformly dispersed. Through a subsequent powder purification step, a powder in which polyimide / inorganic insulating filler is uniformly mixed and dispersed can be obtained. Alternatively, polyimide powder or polyamic acid powder alone may be purified in advance, and then the inorganic insulating filler may be mixed in powder form. Examples of the method for purifying the powder from the polyimide precursor solution include a solvent coprecipitation method, an emulsion polymerization method, and a precipitation polymerization method. Here, the solvent coprecipitation method, which is a general purification method of polyamic acid powder, will be described. The solvent coprecipitation method is a method in which a polyimide precursor solution is a solvent having low solubility in a polyimide precursor such as ethyl alcohol (poor This is a method in which a precipitate is formed by dropping into a solvent, and then separated from a poor solvent. The purification method can be appropriately selected in consideration of the use and characteristics of the powder such as an emulsion polymerization method and a precipitation polymerization method as described above.

  Moreover, when manufacturing a polyimide powder molding board | substrate from a polyamic acid powder, it can heat and manufacture to the imide conversion temperature of a polyamic acid after press molding with the shaping | molding die of a predetermined size. In addition, polyamic acid powder can be imide converted while being molded with a mold, and the shape and dimensions are determined according to the required characteristics of the polyimide powder molded substrate, and conditions such as press pressure and imide conversion temperature are set. Can do.

  A polyimide precursor solution that is a basis for producing a polyimide powder molded substrate can be obtained, for example, by reacting an aromatic tetracarboxylic dianhydride and an aromatic diamine in an organic polar solvent. Representative examples of such aromatic tetracarboxylic acids include 3,4,3 ′, 4′-benzophenonetetracarboxylic dianhydride, pyromellitic anhydride, 3,4,3 ′, 4′-biphenyltetracarboxylic acid. Dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 3,4,3 ′, 4′-diphenylsulfoxide tetracarboxylic dianhydride, 2,3,3 ′, 4 ′ -Diphenyl ether tetracarboxylic dianhydride, 3,4,3 ', 4'-diphenyl sulfide tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, 1,2,5, 6-naphthalenetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) ether dianhydride, 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride, 2,3 , 3 ', 4 -Diphenylmethanetetracarboxylic dianhydride, 3,4,3 ', 4'-diphenyl (2,2-isopropylidene) tetracarboxylic dianhydride, 2,3,3', 4'-diphenylsulfoxide tetracarboxylic acid A dianhydride etc. are mentioned, These can be used individually or in mixture. Moreover, these aromatic tetracarboxylic acids may be made into tetracarboxylic acid ester. That is, there is no limitation as long as the above-described characteristics of the insulating substrate can be obtained.

  On the other hand, the aromatic diamine is not particularly limited and includes paraphenylenediamine, metaphenylenediamine, 4,4-diaminodiphenyl ether, 4,4-diaminodiphenylmethane, benzidine, 3,3-diaminodiphenylmethane, 3,3-dimethoxybenzidine, Examples include 4,4-diaminodiphenylpropane, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, and these can be used alone or in combination.

  Organic polar solvents include N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N-methyl Caprolactam, hexamethylphosphoric triamide, 1,2-dimethoxyethane, diglyme, triglyme, tetrahydrofuran, 1,4-dioxane, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, diethoxyethane, dimethyl sulfoxide And sulfolane. These solvents can be used alone or as a mixture or mixed with other solvents such as toluene, xylene, acetone, ie, aromatic hydrocarbon, methanol, ethanol, ie, alcohol.

  The heating element is made of a polyimide precursor composition in which metal powder having general conductivity characteristics is mixed and dispersed, and a polyimide precursor composition in which conductive materials for obtaining PTC or NTC characteristics are mixed and dispersed. Can do. That is, in the embodiment of the present invention, a planar heater can be produced by combining two types of insulating substrates and two types of polyimide precursor compositions. These combinations can be selected in accordance with the use and characteristics of the planar heater.

  The polyimide precursor composition is preferably a paste-like composition in which conductive substances are mixed and dispersed in a polyimide precursor solution. The polyimide precursor solution can be prepared from raw materials such as an aromatic tetracarboxylic dianhydride, an aromatic diamine, and an organic polar solvent used to produce the polyimide powder molded substrate described above. A composition using biphenyltetracarboxylic dianhydride “BPDA” and paraphenylenediamine “PPD” has high heat resistance and excellent mechanical properties, and is a preferred composition for producing a heating element.

  Furthermore, the most preferable heating element in the embodiment of the present invention is a heating element whose matrix material is substantially made of a polyimide resin, and has a temperature self-control characteristic (PTC or NTC characteristic) simultaneously with the heating characteristic as an electric resistor. It is what you have. For example, when the heating element has PTC characteristics, a pair of electrodes is provided along the longitudinal direction of the heating element so that a current flows between the electrodes (in the width direction of the heating element). When a predetermined voltage is applied to the heating element having the PTC characteristic, the temperature of the heating element gradually rises, and when the predetermined temperature is reached, the resistance value of the heating element rapidly increases and the current is controlled. At the same time, the temperature is self-controlled, and so-called temperature self-control characteristics are developed. When the heating element has NTC characteristics, electrodes are provided at both ends in the longitudinal direction of the heating element, and a current flows between the electrodes (longitudinal direction of the heating element). When a part of the heat generating area in the longitudinal direction is hotter than the other part, the resistance value of the part becomes lower than that of the other part. As a result, the amount of heat generated in this region is reduced, and excessive temperature rise can be suppressed. In the heating element having these characteristics, it is possible to prevent the temperature rise of the non-sheet passing portion.

  A heating element having such temperature self-control characteristics is an ester compound derived from at least one tetracarboxylic acid (hereinafter referred to as a tetracarboxylic acid ester compound), a diamine or a derivative thereof (hereinafter referred to as a diamine compound). , A polar solvent, and a conductive powder. The mixing molar ratio of the tetracarboxylic acid ester compound and the diamine compound is preferably 80: 100 to 99: 100. The mixing molar ratio of the tetracarboxylic acid ester compound and the diamine compound will determine the molecular weight of the polyimide resin, and the highest molecular weight polyimide when the mixing molar ratio of the tetracarboxylic acid ester compound and the diamine compound is 1: 1. A resin can be obtained. Even if such a polyimide resin has a rigid molecular chain and exhibits a glass transition temperature, it does not melt and flow. Therefore, a heating element obtained by mixing and dispersing conductive powder in such a polyimide resin has sufficient mechanical properties and dimensional stability. However, according to the experiments by the present inventors, the temperature self-control characteristic is poor in reproducibility and the change rate of the resistance value is large. Such a phenomenon tends to appear particularly when the mixing molar ratio of the tetracarboxylic ester acid compound and the diamine compound is 1: 1. When the mixing molar ratio of the tetracarboxylic ester compound and the diamine compound is 1: 1, the polyimide resin has the highest molecular weight, so that rigid molecular chains are entangled and dispersed in the polyimide resin repeatedly from room temperature to the fixing temperature. This is probably because the movement of the conductive material is fixed. For this reason, the inventors of the present application reduced the molecular weight of the polyimide by setting the mixing molar ratio of the tetracarboxylic ester acid compound and the diamine compound to a specific molar ratio other than 1: 1. As a result, it was possible to obtain a heating element having a small change rate of resistance value, that is, high reproducibility even when heat generation was repeated. In other words, in a heating element with a small molecular weight of polyimide, when energized to generate heat, the polyimide moves more easily than a rigid polyimide with a high molecular weight, and the conductive material mixed in the polyimide resin also moves the polyimide thermally. It is considered that regular contact, divergence, or movement can be repeated in this. In order to improve temperature self-control characteristics and to obtain sufficient mechanical characteristics as a heating element, the mixing molar ratio is preferably in the range of 80: 100 to 99: 100. The mixing molar ratio may be any of the tetracarboxylic acid ester compound or the diamine compound. More preferably, the mixing molar ratio of the diamine compound to the tetracarboxylic acid ester compound is in the range of 85: 100 to 95: 100. When the mixing molar ratio of the tetracarboxylic acid ester compound and the diamine compound is less than 80: 100, the molecular weight of the polyimide is lowered, and at the same time, the strength as a heating element is remarkably lowered. No cracks or cracks occur in the heating element. On the other hand, when the mixing molar ratio is larger than 99: 100, the polyimide becomes rigid and the temperature self-control characteristic is deteriorated.

In the embodiment of the present invention, a preferred tetracarboxylic acid ester compound is represented by the following chemical formula (A): wherein R ₁ , R ₂ , R ₃ and R ₄ are each independently hydrogen and carbon atoms having 1 to 8 carbon atoms. A hydrogen group (which may have a functional group such as an aromatic ring, —O—, —CO—, and —OH) or a phenyl group is represented. R ′ represents chemical formula (A-1) or chemical formula (A-2) (wherein X represents O, S, SO, SO ₂ , CH ₂ , C (CH ₃ ) ₂ , CO, or a direct bond). ] An ester compound derived from at least one tetracarboxylic acid selected from

In the embodiments of the present invention, preferred diamines or derivatives thereof are represented by the following chemical formula (I)
[Wherein R ″ represents a chemical formula (I-1) or a chemical formula (I-2) (wherein Y represents O, S, SO, SO ₂
, CH ₂ , C (CH ₃ ) ₂ , CO, or a direct bond)].

In addition, the tetracarboxylic acid ester compound used in the embodiment of the present invention can be obtained very simply by esterifying the corresponding tetracarboxylic dianhydride with an alcohol. The esterification is preferably performed at a temperature of 50 to 150 ° C.
Examples of the tetracarboxylic dianhydride for inducing formation of the tetracarboxylic acid ester compound include 3,4,3 ′, 4′-benzophenonetetracarboxylic dianhydride, pyromellitic anhydride, 3,4,3 ′, 4 ′. -Biphenyltetracarboxylic dianhydride, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, 3,4,3', 4'-diphenyl sulfoxide tetracarboxylic dianhydride, 2,3 3 ′, 4′-diphenyl ether tetracarboxylic dianhydride, 3,4,3 ′, 4′-diphenyl sulfide tetracarboxylic dianhydride, 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride 2,3,3 ′, 4′-diphenylmethanetetracarboxylic dianhydride, 3,4,3 ′, 4′-diphenyl (2,2-isopropylidene) tetracarboxylic dianhydride, 2,3,3 ', 4'- Diphenyl sulfoxide tetracarboxylic dianhydride, 3,4,3 ′, 4′-diphenyl ether tetracarboxylic dianhydride, 3,4,3 ′, 4′-diphenylsulfone tetracarboxylic dianhydride, 2,3, 3 ′, 4′-diphenylsulfonetracarboxylic dianhydride, 2,3,3 ′, 4′-diphenylsulfide tetracarboxylic dianhydride, 3,4,3 ′, 4′-diphenylsulfanetetracarboxylic acid Dianhydrides, 2,3,3 ′, 4′-benzophenonetetracarboxylic dianhydride, 2,3,3 ′, 4′-diphenyl (2,2-isopropylidene) tetracarboxylic dianhydride and the like These can be used alone or in combination.

  Examples of the alcohol for induction-forming the tetracarboxylic acid ester compound include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, and 2-methyl-2. -Propanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 2-methyl-2-butanol, 3-methyl-2-butanol, 2,2-dimethyl-1-propanol, 1-hexanol, 2-methyl-1-pentanol, 4-methyl-2-pentanol, 2-ethyl-1-butanol, cyclohexanol, 2-methoxyethanol, 2- Ethoxyethanol, 2- (methoxymethoxy) ethanol, 2-isopropoxyethanol 2-butoxyethanol, phenol, 1-hydroxy-2-propanone, 4-hydroxy-2-butanone, 3-hydroxy-2-butanone, 1-hydroxy-2-butanone, 2-phenylethanol, 1-phenyl-1- Hydroxyethane, 2-phenoxyethanol and the like, and 1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2,3 -Butanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, glycerol, 2-ethyl-2- (hydroxymethyl) -1,3-propanediol, 1,2,6-hexanetriol 2,2′-dihydroxydiethyl ether, 2- (2-methoxyethoxy) ethanol, Polyhydric alcohols such as 2- (2-ethoxyethoxy) ethanol, 3,6-dioxaoctane-1,8-diol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol and dipropylene glycol are also exemplified. be able to. These alcohols can be used alone or in admixture of two or more.

The tetracarboxylic acid ester compound can also be produced by other methods such as direct esterification of tetracarboxylic acid.
Examples of the diamine used in the embodiment of the present invention include 4,4′-diaminodiphenyl sulfone, 4,4′-diaminodiphenyl ether, 4,4′-diaminophenyl sulfone, 4,4′-diaminodiphenylpropane, p-phenylenediamine, m-phenylenediamine, 1,5-diaminonaphthalene, 3,3'-dichlorobenzidine, 3,3'-dimethyl-4,4'-biphenyldiamine, 4,4'-diaminodiphenyl sulfide-3 , 3'-diaminodiphenylsulfone, benzidine, 3,3'-dimethylbenzidine, m-xylylenediamine, hexamethylenediamine, diaminopropyltetramethylene, 3-methylheptamethylenediamine 1,4-diaminobenzene, 1,3- Diaminobenzene, 2,2'-dimethyl-4,4'-di Minobiphenyl, 2,4-diaminotoluene, 3,4'-biphenyldiamine, 3,4'-diaminodiphenyl sulfoxide, 2,2-bis (3-aminophenyl) propane, 4,4'-diaminobenzophenone, 3, 3'-biphenyldiamine, 2,6-diaminotoluene, 4,4'-biphenyldiamine, 3,3'-diaminodiphenylsulfone, 3,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 4,4 ' -Diaminodiphenylmethane, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-bis (4-aminophenyl) sulfide, 2,2-bis (4-aminophenyl) propane, 2,2 -(3-aminophenyl) (4-aminophenyl) propane, 3,3'-diaminobenzofe 3,3′-dimethyl-4,4′-diaminobiphenyl, 3,3′-bis (4-aminophenyl) sulfide, 4,4′-diaminodiphenyl sulfoxide, 3,4′-diaminobenzophenone, 3, 3'-diaminodiphenyl sulfoxide, 3,4'-diaminodiphenyl sulfone, 2,5-diaminotoluene, 3,3'-diaminodiphenyl ether, 4,4'-bis (4-aminophenyl) sulfide, 2,2'- Dimethyl-4,4′-diaminobiphenyl, 3,4′-bis (4-aminophenyl) sulfide, 3,3′-bis (4-aminophenyl) sulfide, 4,4′-diaminodiphenyl sulfoxide, 3,3 '-Diaminodiphenyl sulfoxide, 3,4'-diaminodiphenyl sulfone, 2,5-diaminotoluene, 3,3'-hydroxy-4 4,4'-diaminobiphenyl and the like, and these can be used alone or in combination.

  Examples of the polar organic solvent useful in the embodiment of the present invention include N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, N-methyl-2-pyrrolidone, 1, 3-dimethyl-2-imidazolidinone, N-methylcaprolactam, hexamethylphosphoric triamide, 1,2-dimethoxyethane, diglyme, triglyme, tetrahydrofuran, 1,4-dioxane, γ-butyrolactone, dimethyl carbonate, diethyl carbonate , Ethylene carbonate, propylene carbonate, diethoxyethane, dimethyl sulfoxide, sulfolane and the like. Among these, a particularly preferred solvent is N-methyl-2-pyrrolidone (NMP). These solvents can be used alone or as a mixture or mixed with other solvents such as toluene, xylene, ie, aromatic hydrocarbon, methanol, ethanol, ie, alcohol.

  In the embodiment of the present invention, a preferred polyimide precursor for forming a heating element is 3,4,3 ′, 4′-benzophenone tetra of the following chemical formula (A-3) as an aromatic tetracarboxylic dianhydride. Carboxylic dianhydride (BTDA) is used. Specifically, the BTDA is heated and stirred at a temperature of 50 to 150 ° C. in an alcohol, preferably ethanol and a polar solvent, preferably N-methyl-2-pyrrolidone, to obtain a tetracarboxylic acid ester compound solution. Then, 80 to 99 mol%, more preferably 90 mol% of a diamine, preferably 4,4′-diaminodiphenylmethane (MDA) of the following chemical formula (I-3) is added to this solution in a molar fraction of the tetracarboxylic acid component. Stir at room temperature to 150 ° C., and finally add the conductive material.

  In order to facilitate handling of the polyimide precursor solution, the solid content concentration in the solution is preferably 30 to 80% by weight, more preferably 40 to 70% by weight. When the solid content concentration is low, the viscosity of the polyimide precursor solution is extremely low, and the mixed and dispersed conductive material is settled, making it difficult to obtain characteristics as a heating element. On the other hand, if the solid content concentration is too high, the fluidity of the polyimide precursor is remarkably lost, so that mixing and dispersion of the conductive material and molding are extremely difficult.

In addition, the polyimide precursor solution according to the embodiment of the present invention may contain an additive such as an antioxidant as long as the temperature self-control characteristic is not adversely affected.
As the conductive material used in the embodiment of the present invention, tantalum nitride (TaN), tantalum carbide (TaC), molybdenum trisilicide (Mo ₅ Si ₃ ), rhenium-tungsten alloy, molybdenum disilicide (MoSi ₂ ), Tungsten (W), molybdenum (Mo) tungsten carbide (WC), titanium carbide (TiC) and metal powder, carbon black, graphite, carbon nanotubes and the like can be mentioned, and these can be used alone or in combination. In addition, although a thing with shapes, such as a fibrous form and a needle-like crystal form, can be used for an electroconductive substance, A particulate powder is easy to mix and disperse | distribute to a polyimide precursor solution, and is preferable. Tungsten carbide powder is one of the more preferable conductive powders. Although the compounding quantity of electroconductive powder changes with selection of electroconductive powder material, it is 20 weight%-90 weight% with respect to solid content concentration of a polyimide precursor solution.

  Such a planar heater is preferably manufactured through a filler mixing step, a powdering step, an insulating substrate manufacturing step, an electrode installation step, a conductive substance mixing step, a coating step, and a heat-resistant insulating layer forming step. . In the filler mixing step, a filler made of an inorganic insulating material is mixed in the polyimide precursor solution to prepare a filler-containing polyimide precursor solution. In the powdering step, the filler-containing polyimide precursor solution is pulverized to prepare a filler-containing polyimide precursor powder. In the insulating substrate manufacturing step, after the filler-containing polyimide precursor powder is molded or while the filler-containing polyimide precursor powder is molded, imide conversion is performed to manufacture the insulating substrate. In the electrode installation step, at least a pair of electrodes is provided on the insulating substrate. Specifically, the electrode can be formed of a conductive paint such as a silver paste or a metal foil. In the conductive substance mixing step, a conductive substance is mixed in the polyimide precursor solution to prepare a polyimide precursor solution containing a conductive substance. In the coating step, the polyimide precursor solution containing a conductive substance is partially coated on the insulating substrate so as to overlap a part of the electrode. In this coating step, the heating element can be formed by a known method such as bar coating or screen printing on the surface of a polyimide powder molded substrate or a polyimide sheet with a conductive polyimide precursor solution. In the imide conversion step, the conductive material-containing polyimide precursor is imide converted to form a heating element. In this imide conversion step, it is preferable that the polyimide precursor solution containing the conductive material applied in the coating step is heated stepwise in an oven or the like to remove the polar solvent and the imide conversion is performed sequentially or simultaneously. Also, the polyimide precursor solution containing a conductive material was applied on an insulating substrate, dried at a temperature of 80 to 120 ° C. for 30 to 120 minutes, and then heated at a temperature of 200 ° C. for 10 to 180 minutes. After that, it is more preferable that it is imidized by heating at a temperature of 250 to 400 ° C. for 30 to 120 minutes. In the heat resistant insulating layer forming step, the heat resistant insulating layer is formed so as to cover the insulating substrate and the heating element. At this time, the electrode and the heating element except for the contact portion with the external terminal for power supply are coated with a polyimide precursor solution by a well-known method, and imidization is completed by heating to form a heat-resistant insulating layer. preferable. In addition, as a material of the heat resistant insulating layer, polyimide resin is particularly preferable in view of characteristics such as adhesion to the substrate and the heating element, heat resistance, and electric insulation. Moreover, as a heat-resistant insulating material other than the polyimide resin, an inorganic coating material obtained by a sol-gel method or the like, a fluorine-based material, a silicone-based material, or the like can be used. By the way, in the fixing heater of the image fixing apparatus, the surface of the heating element is in contact with the inner surface of the polyimide tubular material. For this reason, it is preferable to reduce the frictional resistance with respect to the inner surface of the polyimide tubular body of the heating element. For this purpose, it is preferable to form the heat-resistant insulating layer from a fluororesin alone or a polyimide resin in which fluororesins are mixed and dispersed.

FIG. 1 is a top view and a longitudinal sectional view in a longitudinal direction of a planar heater according to an embodiment of the present invention. FIG. 2 is a longitudinal sectional view in the width direction of the planar heater according to one embodiment of the present invention. As shown in FIGS. 1 and 2, this planar heater is mainly composed of a polyimide powder molded substrate 1, a heating element 3, an electrode portion 2, and a heat-resistant insulating layer 4.
FIG. 5 is a longitudinal sectional view of a fixing device according to an embodiment of the present invention. The fixing device 10 mainly includes a fixing belt 11, a support 12, a sheet heater 13, and a pressure roll 14. A support 12 is disposed on the inner side of the fixing belt 11, and the shape of the fixing belt 11 is maintained by the support 12. In addition, a planar heater 13 is disposed inside the fixing belt 11 so as to be sandwiched by the support 12. A thermistor 15 is disposed on the upper surface of the planar heater 13. Based on the temperature data output from the thermistor 15, the heat generation temperature of the planar heater 13 is controlled. The pressure roll 14 is a core metal 16 provided with a rubber layer, and is pressed against the planar heater 13 via the fixing belt 11. When the copy paper 17 on which the toner image is formed is sequentially fed between the sheet heater 13 and the pressure roll 14, the toner 18 is heated and melted by the sheet heater 13, and on the copy sheet at the nip point N. The toner image 19 is fixed.

Hereinafter, the contents of the present invention will be described more specifically with reference to examples. In the present embodiment, the planar heater was evaluated under the following conditions and measuring instrument.
(1) Linear expansion coefficient Linear expansion coefficient measuring device: manufactured by Shimadzu Corporation, thermomechanical analyzer TMA-50
Temperature range: room temperature to 300 ° C., heating rate 10 ° C./min, load: 2 g (tensile load)
Distance between chucks: 10mm
The same sample was measured twice in succession and the second value was adopted.

(2) Thermal conductivity Thermal conductivity measuring device: QTM-500 manufactured by Kyoto Electronics Industry Co., Ltd.
(3) Average particle size Particle size distribution measurement: LA920 manufactured by Horiba, Ltd.

(1) Preparation of polyimide powder molded substrate After dissolving 25.74 g (0.129 mol) of 4,4′-diaminodiphenyl ether (DDE) in 249 g of N-methyl-2-pyrrolidone (NMP), the solution was stirred. Then, 25.26 g (0.116 mol) of pyromellitic anhydride (PMDA) was added to the solution in 3 portions and stirred at room temperature for 12 hours. As a result, a polyimide precursor solution having a solid content of 17% by weight and an acid-amine mixing molar ratio of 90: 100 was obtained.

Next, 18.67 g of aluminum oxide powder (Nippon Light Metal Co., Ltd .: A32) having an average particle diameter of 1 μm was added to 32.94 g of NMP, and the mixture was stirred for 15 minutes while applying ultrasonic waves. 47.06 g of the polyimide precursor solution was added to the aluminum oxide dispersion and stirred for 5 minutes to obtain a mixed slurry.
Subsequently, the mixed slurry was added dropwise to 800 mL of ethanol that was vigorously stirred with a stirrer over 45 minutes, and stirred for another 30 minutes after completion of the dropwise addition. The resulting precipitate was collected by suction filtration, washed with ethanol, and then dried under reduced pressure for 6 hours and at atmospheric pressure of 80 ° C. for 1 hour to obtain a mixed powder of polyimide precursor and aluminum oxide. In addition, the average particle diameter at the time of powderizing only a polyimide precursor in the state which does not add aluminum oxide powder was about 30 micrometers.

The polyimide precursor / aluminum oxide mixed powder is uniformly placed in a mold having a length of 320 mm, a width of 10 mm, and a depth of 10 mm, and a pressure of 2.058 × 10 ⁷ Pa (210 kg / cm ² ) is applied at room temperature using a press. The operation of releasing the pressure after applying was repeated 2-3 times, and finally a pressure of 9.8 × 10 ⁷ Pa (1000 kg / cm ² ) was applied for 10 minutes. Thereafter, the molded product was taken out from the mold, heated from 80 ° C. to 200 ° C. over 5 hours in a drying furnace, and heated at 200 ° C. for 1 hour as it was. Further, a polyimide powder molded substrate having a total length of 310 mm, a width of 9.7 mm, and a thickness of 1 mm after baking at 300 ° C. for 1 hour and at 400 ° C. (polyimide / aluminum oxide mixed powder molded substrate: aluminum oxide content 70% by weight) Got.

In order to measure the linear expansion coefficient of the polyimide powder molded substrate, a test piece having a length of 13 mm, a width of 3.5 mm, and a thickness of 0.75 mm was cut out from the molded body. In addition, this test piece was cut out so that a longitudinal direction might correspond with the longitudinal direction of a molded object. As a result of the measurement, the linear expansion coefficient was 1.84 × 10 ⁻⁵ cm / cm / ° C. (average expansion coefficient of 100 ° C. to 250 ° C.). In addition, a test piece having a width of 100 mm, a length of 150 mm, and a thickness of 1.0 mm was prepared under the conditions of Example 1 for measuring the thermal conductivity, and the thermal conductivity was measured. As a result, the result was 0.44 W / m · k. .

(2) Production of electrode In order to produce an electrode for supplying power to the heating element, a linear expansion coefficient of 1.69 × 10 ⁻⁵ cm / cm / ° C. (100 μm), a thickness of 50 μm, a length of 300 mm, a width of 110 mm One side of a nickel foil (manufactured by Toyo Seifaku Co., Ltd.) having a temperature of from [deg.] C. to 250 [deg.] C. was polished with sandpaper and washed. Thereafter, a polyimide varnish (RC5019 manufactured by IST Corporation) is coated on the polished surface of the nickel foil to a thickness of 200 μm and heated at 120 ° C. for 30 minutes, 200 ° C. for 30 minutes, and further heated at 300 ° C. for 60 minutes. did. As a result, an electrode material film in which a polyimide film having a thickness of 20 μm was laminated was produced.

  Next, an electrode pattern is printed on the nickel foil of the electrode material with an etching resist ink, and after the ink is dried, the portion where the etching resist ink is not printed with an etching solution (ferric chloride solution: manufactured by Sanhayato Co., Ltd.) Etched. Then, after the etching process was completed, the etching resist ink was removed. By this etching treatment, an electrode circuit having an electrode portion having a width of 1 mm and a width of 1 mm formed between the electrodes in parallel with the longitudinal direction and a power supply terminal portion was obtained. And the film in which this electrode circuit was formed was cut into width 10mm and length 300mm.

(3) Adhesion of electrode circuit to polyimide powder molded substrate A polyimide adhesive (SKYBOND 703 manufactured by IS Corporation) is applied to a thickness of 10 μm on a polyimide powder molded substrate (polyimide / aluminum oxide mixed powder molded substrate). Then, the polyimide film in which the electrode circuit was formed was affixed so that the polyimide film surface might become an adhesive surface. Then, a pressure of 100 N was applied to the entire surface, and the mixture was heated at 120 ° C. for 30 minutes, 200 ° C. for 30 minutes, and further at 300 ° C. for 60 minutes, and then slowly cooled to bond the electrode circuit onto the polyimide powder molded substrate.

(4) Preparation of heating element (a) Preparation of polyimide precursor A 500 mL three-necked flask was equipped with a stirring rod equipped with stirring blades made of polytetrafluoroethylene to obtain a synthesis container. Then, in the synthesis container, 3,4,3 ′, 4′-benzophenone tetracarboxylic dianhydride (BTDA) manufactured by ALLCO as an acid component so that the solid content of the polyimide precursor solution is 55 mass%. 667 g (0.1014 mol) as a solvent, 30.326 g of N-methyl-2-pyrrolidone (NMP) manufactured by Mitsubishi Gas Chemical Co., Ltd., and 14.011 g (0.01 g) of ethanol manufactured by Wako Pure Chemical Industries, Ltd. as an esterifying agent. 3041 mol) was added, heated to 60 ° C. and stirred for 2 hours to obtain an ester compound of BTDA. Thereafter, 21.333 g (0.1126 mol) of 4,4′-diaminodiphenylmethane (MDA) manufactured by Ciba-Geigy was added so that the number of moles of the tetracarboxylic acid component was 0.9 times the number of moles of the diamine component. Furthermore, it stirred at 60 degreeC for 1 hour, and obtained the polyimide precursor solution.

(B) Blending of conductive powder Next, 277 parts by weight of tungsten carbide powder (WC10 manufactured by Allied Material Co., Ltd.) having an average particle size of 1.0 μm as the conductive powder is obtained with respect to 100 parts by weight of the solid content of the polyimide precursor solution. The polyimide precursor composition was mixed with the polyimide precursor solution and stirred and mixed with a stirrer for 30 minutes while applying ultrasonic waves to obtain a polyimide precursor composition in which tungsten carbide was uniformly mixed and dispersed. The polyimide precursor composition was pasty.

(C) Application and firing of polyimide precursor composition On the polyimide powder molded substrate on which the electrode circuit is laminated, the polyimide precursor composition is 5 mm wide, 222 mm long, and 20 μm thick (based on solid content) by screen printing. And evenly applied. Then, the polyimide powder molded substrate is put in an oven, 20 minutes at 80 ° C., 30 minutes at 110 ° C., 30 minutes at 120 ° C., 20 minutes at 150 ° C., 20 minutes at 200 ° C., then 1 hour at 300 ° C. Thereafter, heating was performed at a temperature of 400 ° C. for 20 minutes to obtain a heating element.

(D) Formation of heat-resistant insulating layer Polyimide precursor solution (Pyre-ML RC5063: BPDA-PPD type polyimide precursor solution manufactured by IST Corporation) as a material for forming the heat-resistant insulating layer, solid content concentration 18 % By weight). Subsequently, a polyimide precursor solution is applied on the heating element so as to cover the entire substrate except for the power supply terminal portion, and is heated and imidized as usual, and a polyimide insulating layer having a thickness of 20 μm is provided. The heater was completed. The resistance value between the electrodes of the planar heater was 25Ω at room temperature (23 ° C.) (digital multimeter Model 17562 manufactured by Yokogawa Electric Corporation was used). Although this planar heater was heated to 300 ° C., no deformation such as warping was observed. In addition, this planar heater has a positive temperature resistance characteristic as shown in FIG. 3, and exhibits a PTC characteristic in which when the heat is generated up to about 300 ° C., the resistance value suddenly increases and no current flows to suppress heat generation. (See FIG. 3). Incidentally, the graph of FIG. 3 shows the temperature − when the lead wire is connected to the electrode of the planar heater and the temperature is gradually increased from room temperature to 350 ° C. after being inserted into the thermostatic bath, and the change in electrical resistance value as the temperature rises is measured. It is a resistance curve. At this time, the change in the resistance value with increasing temperature rose very sharply around 250 ° C., and the resistance value at 350 ° C. increased to 15 times the resistance value at room temperature. Further, the temperature raising / cooling operation from room temperature to 350 ° C. was repeated 10 times, but stable PTC characteristics were obtained.

  Assuming the phenomenon of temperature rise in the non-sheet-passing area that occurs in laser beam printers, etc., an aluminum heat sink is applied to the central part of the longitudinal direction of the heating element of this planar heater, voltage is applied to the heating element, and thermocouple The temperature rise of the heat dissipating part (surface on which fixing was performed by paper passing) and the non-heat dissipating part (non-paper passing part) were measured. FIG. 4 is a comparison diagram showing the temperature rise of the heat dissipating part and the non-heat dissipating part. FIG. 4 shows that the temperature continues to rise in the heat radiating section. On the other hand, in the non-heat dissipating part, the temperature rises rapidly, but it can be seen that the temperature becomes constant due to temperature self-control characteristics around 300 ° C. and does not rise. Therefore, it has been clarified that this sheet heater can suppress an abnormal temperature rise such as a temperature rise in a non-sheet passing portion of a laser beam printer or the like.

  Then, this planar heater was mounted on a laser beam fixing machine 10 shown in FIG. 5 to perform a fixing test. In the fixing test, the fixing belt 11 is “a composite tubular material in which a fluororesin mixed with an ion conductive anti-offset agent is coated on the surface of a polyimide resin seamless tube (a fixing belt manufactured by IST Corporation, 24 mm, thickness 62 μm, length 232 mm), and the toner 18 is heated and melted while sequentially feeding the copy paper 17 on which the toner image is formed between the fixing belt 13 and the pressure roll 14. A toner image 19 was fixed on the copy paper. As a result of setting the A4 size paper so that 16 sheets could be fixed per minute and performing a fixing durability test, a good image was stably obtained.

  Biphenyltetracarboxylic dianhydride (BPDA) 28.384 g (0.0965 mol) was added to a mixed solvent of NMP 35.727 g and methanol 9.273 g (0.2894 mol), and then stirred at 80 ° C. for 2 hours to give tetracarboxylic acid. An ester compound was prepared. Then, 26.616 g (0.1072 mol) of 4,4′-diaminodiphenylsulfone (44DDS) is added so that the tetracarboxylic acid ester compound component has a mixing molar ratio of 90: 100 with respect to the diamine component, and at 80 ° C. The mixture was stirred for 1 hour to obtain a polyimide precursor solution for preparing a heating element. Next, 277 parts by weight of tungsten carbide powder was blended with respect to 100 parts by weight of the solid content of the polyimide precursor solution, and a planar heater was produced under the same conditions as in Example 1. Then, the planar heater was evaluated in the same manner as in Example 1. This sheet heater showed a PTC characteristic in which when the heat was generated up to about 280 ° C., the resistance value rose sharply and no current flowed to suppress heat generation. This planar heater was mounted on the same laser beam fixing machine 10 as in Example 1 and a fixing test was performed. As a result, the temperature rise of the non-sheet passing portion could be controlled and a good image was stably obtained.

  As a polyimide precursor solution for producing a heating element, I. Co., Ltd. S. Pyre-ML RC5063 (BPDA-PPD based polyimide precursor solution) manufactured by Tei was employed. The solid content concentration of the polyimide precursor solution was adjusted to 18% by mass. Next, nickel powder having an average particle size of 1.0 μm (Ni-Flake 94 manufactured by Fukuda Metal Industry Co., Ltd.) was added to the polyimide precursor solution, and the nickel powder was 257 wt. It mixed so that it might become a part. Then, while stirring this mixture, pyromellitic anhydride (PMDA) was added to adjust the viscosity to 1000 poise to prepare a nickel powder mixed polyimide precursor solution. And the nickel powder mixed polyimide precursor solution was uniformly apply | coated on the same board | substrate as Example 1 by the screen-printing method similarly to Example 1. FIG. Next, a polytetrafluoroethylene resin powder having an average particle size of 3.0 μm (trade name “Zonyl MP1200” manufactured by DuPont) in the same polyimide precursor solution (Pyre-ML RC5063 manufactured by I.S. T. Co., Ltd.) as before. ) (Hereinafter abbreviated as PTFE powder) was added to 100 parts by mass of the polyimide precursor solution and stirred so that the ratio of PTFE powder was 20 parts by mass to prepare a PTFE powder mixed polyimide precursor solution. Thereafter, the PTFE powder mixed polyimide precursor solution was passed through a 250 mesh stainless steel wire mesh to filter coarse foreign matters in the PTFE powder mixed polyimide precursor solution. Subsequently, the filtered PTFE powder mixed polyimide precursor solution was applied onto the substrate and the heating element so as to cover the entire substrate except for the power supply terminal portion. And after drying at 120 degreeC for 30 minutes, it heated up to 200 degreeC in 40 minutes, and heated at the same temperature for 20 minutes. And after heating for 10 minutes at 250 degreeC as a final imidation process, it heated up to 400 degreeC in 15 minutes, heated for 10 minutes at the same temperature, and completed the planar heater provided with the 20-micrometer heat-resistant insulating layer. . The resistance value between the electrodes of the heating element was 25Ω at room temperature (23 ° C.) (digital multimeter Model 17562 manufactured by Yokogawa Electric Corporation was used). And although this planar heater was heated to 300 degreeC, deformation | transformation, such as curvature, was not recognized. As a result of mounting this planar heater on the laser beam fixing machine 10 shown in FIG. 5 and setting so that 16 sheets of A4 size paper can be fixed per minute, and performing a fixing durability test, a good image is stably obtained. It was.

  438 parts by weight of tantalum carbide powder (Wako first grade) was blended with 100 parts by weight of the solid content of the polyimide precursor solution prepared for heating element preparation in Example 1, and a planar heater was prepared in the same manner as in Example 1. . And the temperature resistance characteristic of this planar heater was measured similarly to Example 1. When the change in the electrical resistance value accompanying the temperature rise was measured, the resistance value sharply rose in the vicinity of 200 ° C., and the resistance value increased 2.5 times by 265 ° C. Further, the temperature raising / cooling operation from room temperature to 265 ° C. was repeated 10 times, and the change rate of the resistance value of the test specimen at this time was + 10% (see FIG. 6). In addition, as a result of performing a fixing durability test by mounting this planar heater on the laser beam fixing machine 10 shown in FIG. 5 so that 16 sheets of A4 size paper can be fixed per minute, a good image is stably obtained. Obtained.

  51.5 parts by weight of filamentous nickel powder (Type 210 manufactured by INCO) was blended with 100 parts by weight of the solid content of the polyimide precursor solution prepared for producing the heating element in Example 1, and the surface was the same as in Example 1. A heater was prepared. And the temperature resistance characteristic of this planar heater was measured similarly to Example 1. When the change in the electrical resistance value accompanying the temperature rise was measured, the resistance value sharply rose in the vicinity of 300 ° C., and the resistance value increased to 2.2 times by 350 ° C. Further, the temperature raising / cooling operation from room temperature to 350 ° C. was repeated 10 times, and the change rate of the resistance value of the test specimen at this time was −3% (see FIG. 7). In addition, as a result of performing a fixing durability test by mounting this planar heater on the laser beam fixing machine 10 shown in FIG. 5 so that 16 sheets of A4 size paper can be fixed per minute, a good image is stably obtained. Obtained.

  29.627 g (0.0922 mol) of BTDA as an acid component, 43.408 g of NMP as a solvent, and 6.292 g (0.1014 mol) of ethylene glycol as an esterifying agent were stirred at 60 ° C. for 2 hours to obtain a tetracarboxylic acid ester compound. A polyimide precursor for producing a heating element in the same manner as in Example 1 except that MDA 20.303 g (0.102 mol) was used so that the mixing molar ratio of the ester compound component and the diamine component was 90: 100. A solution was synthesized. 189 parts by weight of titanium carbide powder (OP10 manufactured by Allied Material) was blended with 100 parts by weight of the solid content of this polyimide precursor solution, and a planar heater was produced in the same manner as in Example 1. And the temperature resistance characteristic of this planar heater was measured similarly to Example 1. When the change in the electrical resistance value accompanying the temperature rise was measured, the resistance value sharply rose in the vicinity of 250 ° C., and the resistance value increased to 33 times by 300 ° C. Further, the temperature raising / cooling operation from room temperature to 300 ° C. was repeated 10 times, and the change rate of the resistance value of the test specimen at this time was + 2% (see FIG. 8). In addition, as a result of performing a fixing durability test by mounting this planar heater on the laser beam fixing machine 10 shown in FIG. 5 so that 16 sheets of A4 size paper can be fixed per minute, a good image is stably obtained. Obtained.

  BTDA 32.180 g (0.0999 mol) as an acid component, NMP 43.181 g as a solvent, and ethylene glycol 6.819 g (0.1099 mol) as an esterifying agent were stirred at 60 ° C. for 2 hours to obtain a tetracarboxylic acid ester compound. A polyimide precursor for producing a heating element in the same manner as in Example 1 except that MDA17.820 g (0.0899 mol) was used so that the mixing molar ratio of the ester compound component and the diamine component was 100: 90. A solution was synthesized. 151 parts by weight of titanium carbide powder was blended with 100 parts by weight of the solid content of this polyimide precursor solution, and a planar heater was produced in the same manner as in Example 1. And the temperature resistance characteristic of this planar heater was measured similarly to Example 1. When the change in the electrical resistance value accompanying the temperature rise was measured, the resistance value sharply rose in the vicinity of 250 ° C., and the resistance value increased up to 17 times by 300 ° C. Further, the temperature raising / cooling operation from room temperature to 300 ° C. was repeated 10 times, and the change rate of the resistance value of the test specimen at this time was −5% (see FIG. 9). In addition, as a result of performing a fixing durability test by mounting this planar heater on the laser beam fixing machine 10 shown in FIG. 5 so that 16 sheets of A4 size paper can be fixed per minute, a good image is stably obtained. Obtained.

As a polyimide precursor solution used for forming a heat-resistant insulating layer, I. S. Pyre-ML RC5063 made by Tei Co. was prepared. And boron nitride powder (Mitsui Chemicals Co., Ltd. MBN-010T) was mixed with this polyimide precursor solution so that boron nitride powder might be 20 mass parts with respect to 100 mass parts of fixed parts of a polyimide precursor solution. A planar heater was completed under the same conditions as in Example 1 except that a boron nitride mixed polyimide precursor solution was prepared. This planar heater has high thermal conductivity by mixing boron nitride in the insulating layer and low sliding resistance with the inner surface of the fixing belt. As a result of performing a fixing test in the same manner as in Example 1, a good image was obtained.
(Comparative Example 1)
A polyimide precursor solution was synthesized in the same manner as in Example 1 except that the mixing molar ratio of the tetracarboxylic acid ester compound and the diamine was 1: 1 in the polyimide precursor solution for producing the heating element. In addition, 277 parts by weight of tungsten carbide powder was blended with respect to 100 parts by weight of the solid content of the polyimide precursor solution, and a planar heater was produced in the same manner as in Example 1 to evaluate the characteristics. This planar heater developed PTC characteristics near 300 ° C. as the temperature increased. However, the temperature at which the PTC characteristics developed was large in repeated heat tests, and could not be used as a temperature self-control heating element.
(Comparative Example 2)
After 6.903 g (0.0348 mol) of MDA, which is a diamine component, was added to 83.0 g of NMP and MDA was completely dissolved in NMP, the acid diamine component was adjusted to a molar ratio of 100: 90 with respect to the diamine component. BTDA 10.097 g (0.0313 mol), which is an anhydrous component, was added as a solid over 5 minutes and reacted at room temperature for 12 hours to obtain a polyimi precursor solution. In addition, the solid content of this polyimide precursor solution is adjusted to be 17% by mass. Thereafter, 277 parts by weight of tungsten carbide powder was blended with respect to 100 parts by weight of the solid content of the polyimide precursor solution, and an attempt was made to produce a planar heater under the same conditions as in Example 1, but cracking occurred during heating imidization. Occurred. It was revealed that the polyimide composition prepared with only the mixing molar ratio of the acid component and the diamine component being 90: 100 without bridging the tetracarboxylic dianhydride was brittle and could not be molded.
(Comparative Example 3)
A planar heater was produced under the same conditions as in Example 1 except that aluminum oxide was not added in the production of the polyimide powder molded substrate of Example 1. Note that the linear expansion coefficient of the heating element of this planar heater was 5.3 × 10 ⁻⁵ cm / cm / ° C., and when heated by energization, the heating element was warped inside.

It is the upper side figure and longitudinal cross-sectional view of the longitudinal direction of the planar heater which concerns on one Embodiment of this invention. It is a longitudinal cross-sectional view of the width direction of the planar heater which concerns on one Embodiment of this invention. It is a figure which shows the temperature and resistance characteristic of the heat generating body shown by Example 1. FIG. It is a figure which shows the temperature self-control characteristic of the heat generating body shown by Example 1. FIG. It is a longitudinal cross-sectional view of the laser beam fixing machine which concerns on one Embodiment of this invention. It is a figure which shows the temperature and resistance characteristic of the heat generating body shown by Example 4. FIG. It is a figure which shows the temperature and resistance characteristic of the heat generating body shown by Example 5. FIG. It is a figure which shows the temperature and resistance characteristic of the heat generating body shown by Example 6. FIG. It is a figure which shows the temperature and resistance characteristic of the heat generating body shown by Example 7. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polyimide powder shaping | molding board | substrate 2 Electrode terminal part 3 Heat generating body 4 Heat-resistant insulating layer 5 Adhesive layer 10 Image fixing apparatus 11 Fixing belt 12 Support body 13 Heater 14 Pressure roll 15 Thermistor 16 Core metal of pressure roller 17 Copy paper 18 Toner 19 Toner image N Nip

Claims (13)

An insulating substrate made of polyimide resin;
A heating element provided on the insulating substrate and formed from a conductive polyimide resin that is a polyimide resin in which conductive substances are mixed and dispersed;
An electrode for supplying power to the heating element;
A heat-resistant insulating layer formed to cover the insulating substrate and the heating element;
A sheet heater comprising: The conductive polyimide resin is obtained by imide conversion after mixing and dispersing the conductive material in a polyimide precursor,
The planar heater according to claim 1. The insulating substrate is a powder molded body obtained by imide conversion while molding the polyimide precursor powder or while molding the polyimide precursor powder, and includes a filler made of an inorganic insulating material.
The planar heater according to claim 1 or 2. The polyimide precursor is a polyimide precursor solution obtained by reacting at least one tetracarboxylic dianhydride or derivative thereof with at least one diamine or derivative thereof in a polar solvent.
The planar heater according to claim 2. The polyimide precursor is a non-thermoplastic polyimide precursor solution obtained by reacting an ester compound derived from at least one tetracarboxylic acid and at least one diamine or derivative thereof in a polar solvent.
The planar heater according to claim 2. The mixing molar ratio of the ester compound derived from the tetracarboxylic acid and the diamine or derivative thereof is 80: 100 or more and 99: 100 or less.
The planar heater according to claim 5. The ester compound derived from the tetracarboxylic acid has the following chemical formula (A) [wherein R ₁ , R ₂ , R ₃ , R ₄ are each independently hydrogen, a hydrocarbon group having 1 to 8 carbon atoms (aromatic A ring, a functional group such as —O—, —CO—, and —OH), or a phenyl group. R ′ represents chemical formula (A-1) or chemical formula (A-2) (wherein X represents O, S, SO, SO ₂ , CH ₂ , C (CH ₃ ) ₂ , CO, or a direct bond). ] An ester compound derived from at least one tetracarboxylic acid selected from the group consisting of ester compounds derived from the tetracarboxylic acid represented by:
The planar heater according to any one of claims 4 to 6.

The diamine or a derivative thereof has the following chemical formula (I) [wherein R ″ is a chemical formula (I-1) or a chemical formula (I-2) (where Y is O, S, SO, SO ₂ , CH ₂ , C (CH ₃ ) ₂ , CO, or represents a direct bond)], or at least one diamine selected from the group consisting of the derivatives described above or a derivative thereof.
The planar heater according to any one of claims 4 to 6.

The conductive material is tantalum nitride (TaN), tantalum carbide (TaC), molybdenum trisilicide (Mo ₅ Si ₃ ), rhenium-tungsten alloy, molybdenum disilicide (MoSi ₂ ), tungsten (W), molybdenum (Mo). , At least one selected from the group consisting of tungsten carbide (WC), titanium carbide (TiC), metal, carbon black, graphite, and carbon nanotubes.
The planar heater according to any one of claims 1 to 8. The heating element has temperature self-control characteristics,
The planar heater according to any one of claims 1 to 9. The sheet heater according to any one of claims 1 to 9 is provided as a heat source.
Fixing machine for image forming apparatus. A fixing belt,
A pressure roll for pressing copy paper against the fixing belt;
The planar heater according to any one of claims 1 to 9, which is disposed on the inner side of the fixing belt and on the pressure roll side,
An image fixing device comprising: A filler mixing step of preparing a filler-containing polyimide precursor solution by mixing a filler made of an inorganic insulating material in the first polyimide precursor solution;
A powdering step of preparing a filler-containing polyimide precursor powder by pulverizing the filler-containing polyimide precursor solution;
After forming the polyimide precursor powder with filler or after forming the polyimide precursor powder with filler, imide conversion to produce an insulating substrate,
An electrode installation step of providing at least a pair of electrodes on the insulating substrate;
A conductive substance mixing step of preparing a polyimide precursor solution containing a conductive substance by mixing a conductive substance in the second polyimide precursor solution;
A coating step of partially coating the conductive material-containing polyimide precursor solution on the insulating substrate so as to overlap a part of the electrode;
An imide conversion step in which the polyimide precursor containing the conductive substance is converted into an imide to form a heating element;
A heat-resistant insulating layer forming step of forming a heat-resistant insulating layer so as to cover the insulating substrate and the heating element;
A method for manufacturing a planar heater.

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