JP6019761B2 - Planar heating element and manufacturing method thereof - Google Patents

Description

  The present invention relates to a planar heating element comprising at least a base material and a resistor, wherein the resistor includes a conductive substance and a fibrous polysaccharide having a carboxyl group.

  Conventionally, as a planar heating element, carbon particles such as carbon black, conductive inorganic fillers, and conductive materials such as metal compounds are mixed in resin as a binder, and this paste-like material is molded on an insulating substrate. Thus, a structure using a Joule heat generated by energizing the resistor is used. The temperature can be controlled by controlling the applied voltage after designing and producing the conductivity of the conductive material, the thermal conductivity of the binder, the shape of the resistor, and the like. Such a heating element can be applied to a device having a relatively wide plane or curved surface, such as a floor surface or a wall surface heating device.

JP 2009-256617 A JP 2005-11651 A Japanese Patent Application No. 2009-547135

  When dispersing a conductive material in a binder, it is difficult to uniformly disperse due to the formation of agglomerates or uneven distribution due to the size of the specific surface area and the affinity of the surface state. There is. Alternatively, when a substance having a large specific gravity such as metal particles is used, it separates and precipitates in the binder during storage and is difficult to redisperse. Thus, it is difficult to control the dispersion of the conductive material. On the other hand, the conductive characteristics and heat generation characteristics are greatly affected by the dispersibility, and many of the functions are efficiently exhibited in a well-dispersed state.

Various attempts have been made in the past to solve the above problems.
Patent Document 1 discloses a method of adsorbing a synthetic polymer having an imide group on the surface of carbon particles. However, when this method is used, the heat resistance and compatibility with the resin are improved, but agglomeration of carbon particles cannot be sufficiently suppressed, and it is difficult to sufficiently exhibit electrical and mechanical properties. It is. Patent Document 2 discloses a method of mounting a soaking plate in order to make the in-plane temperature of the heating element uniform. However, when this method is used, the manufacturing process becomes complicated and thinning becomes difficult. Patent Document 3 discloses a method for improving the dispersibility of carbon nanotubes by adding a surfactant to a dispersion medium. However, when this method is used, the dispersibility in the dispersion state is good, but since the carbon nanotubes form aggregates during the drying process, it is difficult to fully exhibit the electrical characteristics.

  The present invention has been made in consideration of the background art as described above. The environmental load from manufacturing to disposal is extremely low, the manufacturing process is simple, the productivity is high, and the electrical and mechanical characteristics are high. An object is to provide a planar heating element.

The present invention has been made to solve the above problems, the present onset Ming, at least the substrate, electrodes for energizing resistors formed on one surface of the substrate, and to a resistor The sheet heating element is characterized in that the resistor includes a conductive substance and a fibrous polysaccharide having a carboxyl group. And the fibrous polysaccharide which has the said carboxyl group is a cellulose fiber, It is characterized by the above-mentioned. And the fiber width of the said cellulose fiber is 2 to 50 nm, The length of the said cellulose fiber is 0.5 to 50 micrometer, It is characterized by the above-mentioned.

This onset Ming is a planar heating element you wherein at least part of the carboxyl groups of the cellulose fibers is a carboxylic acid salt.

This onset Ming, the conductive material is a planar heating element you characterized in that it consists of carbon particles.

This onset Ming is a planar heating element you wherein the conductive material is a metal particle.

This onset Ming is a planar heating element you wherein the particle size of the conductive material is 1nm or more 100nm or less.

This onset Ming is a planar heating element you wherein a thickness after curing of the resistor is 0.5μm or more 10μm or less.

This onset Ming, and a step of providing an electrode on the step and on the resistor to form a resistor by printing on one side of the substrate, the fibrous the resistor is electrically conductive material and a carboxyl group polysaccharide Is a manufacturing method of the planar heating element characterized by including. And the fibrous polysaccharide which has the said carboxyl group is a cellulose fiber, It is characterized by the above-mentioned. And the fiber width of the said cellulose fiber is 2 to 50 nm, The length of the said cellulose fiber is 0.5 to 50 micrometer, It is characterized by the above-mentioned.

  According to the present invention, it is possible to provide a planar heating element that has an extremely low environmental load from manufacture to disposal, a simple manufacturing process, and high productivity. According to this method, a dispersion liquid in which a conductive substance is simply dispersed can be obtained, and the resistor formed by this dispersion liquid has sufficient electrical and mechanical characteristics.

It is a top view of one embodiment of the planar heating element of the present invention. It is a sectional side view of one embodiment of the sheet heating element of the present invention.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an upper view of a planar heating element in the present invention. The planar heating element 10 according to the present invention includes at least a resistor 11 and an electrode 12 provided on the resistor 11. The resistor 11 includes at least a conductive substance and a fibrous polysaccharide having a carboxyl group. Here, the shape and arrangement of the electrode 12 are appropriately designed according to the shape and arrangement of the resistor 11 and the use of the planar heating element, and are not particularly limited.

  2 is a cross-sectional side view taken along line A'-A of the planar heating element of the present invention shown in FIG. In the planar heating element 20 in the present invention, at least a resistor 21 is formed on at least one surface of a substrate 23, and an electrode 22 is provided on the resistor 21. Here, the resistor 21 and the electrode 22 may be formed on both surfaces of the substrate. The resistor 21 may be formed on a part or the entire surface of the substrate. The shape of the resistor 21 includes, for example, a strip shape, a bellows shape, and an uneven shape, but is appropriately designed depending on the use of the planar heating element, and is not particularly limited.

  Examples of the fibrous polysaccharide used in the present invention include cellulose, chitin, chitosan and the like, and cellulose fibers having a regular structural arrangement and a rigid skeleton are particularly preferable. Wood pulp, non-wood pulp, cotton, bacterial cellulose, and the like can be used as cellulose that is a raw material for cellulose fibers.

  As a method for introducing a carboxyl group into cellulose, several chemical treatment methods are currently reported. However, as in the present invention, in order to have a structure that is fibrous and has good dispersibility, and the conductive material can efficiently interact with the carboxyl group of cellulose, the carboxyl group is maintained while maintaining the crystal structure of cellulose as much as possible. It is desirable that the carboxyl group is regularly present on the fiber surface.

Specifically, the following method is desirable. 2,2,6,6-tetramethyl-1-pipedinyloxy radical (TEMPO) is used as a catalyst, and an oxidizing agent such as sodium hypochlorite and bromide such as sodium bromide are used while adjusting pH. To process. According to this method, only the primary hydroxyl group at the cellulose C6 position existing on the surface of microfibril which is the smallest fiber unit having crystallinity is selectively oxidized to a carboxyl group due to steric hindrance of TEMPO. Since the binding of microfibrils is weakened by the electrostatic repulsion of the introduced carboxyl group, a fibrous cellulose having high crystallinity highly dispersed by mechanical treatment with low energy input can be obtained.
Furthermore, when this method is used, since the molecular weight reduction of the obtained cellulose fiber is suppressed, high mechanical strength is maintained.

Hereinafter, a specific method of the chemical treatment will be described.
While adding nitroxy radical and sodium bromide to cellulose dispersed in water and stirring at room temperature, an aqueous sodium hypochlorite solution is added to oxidize the cellulose. An alkaline solution such as sodium hydroxide is added during the oxidation reaction to control the pH in the reaction system to 9-11. At this time, the hydroxyl group at the C6 position on the surface of the cellulose fiber is oxidized to a carboxyl group. Thoroughly washing with water and the obtained cellulose dispersed in a fibrous form is used as the constituent material of the dispersion. In addition, as an oxidizing agent, hypohalous acid or its salt, and halogenous acid or its salt can be used, and sodium hypochlorite is especially preferable. Examples of the bromide include lithium bromide, potassium bromide, sodium bromide and the like, and sodium bromide is particularly preferable.

  Furthermore, a part of the carboxyl group is a carboxylate. For example, the cation serving as a counter ion of the carboxyl group includes alkali metal ions (lithium, sodium, potassium, etc.), alkaline earth metals (calcium, etc.), ammonium ions, organic oniums (various aliphatic amines, aromatic amines, diamines, etc.) Amines such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetra-n-butylammonium hydroxide, benzyltrimethylammonium hydroxide, 2-hydroxyethyltrimethylammonium hydroxide, and the like. Or a phenyl group or a hydroxyalkyl group, and four Rs may be the same or different.) Ammonium hydroxide compound, a phosphonium hydroxide compound such as tetraethylphosphonium hydroxide, Beam compounds include counterions such as hydroxide sulfonium compounds). Two or more of these may be mixed to form a salt.

  Furthermore, it is preferable to include a fibrous polysaccharide having a fiber width of 2 nm to 50 nm and a length of 0.5 μm to 50 μm. The dispersibility mechanism of the conductive substance in the present invention is not clear, but the fibrous polysaccharide in this range can ensure dispersion stability by electrostatic repulsion between fibers. In addition, since the conductive substance is captured by the entangled structure between the cellulose fibers, it is difficult to be lost and the yield can be improved. On the other hand, when the fiber width exceeds 50 nm, the ratio of the surface area to the total volume of the cellulose fibers becomes relatively small, and the number of sites capable of interacting with the conductive material is reduced. Therefore, the conductive material can be efficiently dispersed. In addition to this, the interaction between the conductive substances cannot be increased, leading to a decrease in the conductive efficiency. On the other hand, if the length is less than 0.5 μm, the cellulose fibers cannot be sufficiently entangled with each other, which causes a decrease in the film strength of the resistor, which is not preferable. Furthermore, when the length exceeds 50 μm, the entanglement between the cellulose fibers increases, so that the fibers are difficult to disperse and precipitates are easily formed, so that the dispersion stability decreases. The width and length of the fiber is measured with AFM, TEM, etc. in the state of dispersion in which the fiber diluted with water or other solvent to a solid content concentration of about 0.1% is spread on glass and dried. can do.

  The dispersion method of the cellulose having a carboxyl group and the dispersion method when preparing a dispersion by mixing a conductive substance are not particularly limited, but use of various pulverizers, mixers, agitators, ultrasonic waves, etc. To disperse. For example, a processing method using shearing force or collision such as a mixer, a high-speed rotating mixer, a shear mixer, a blender, an ultrasonic homogenizer, a high-pressure homogenizer, a ball mill, a Waring blender, a flash mixer, and a turbulizer can be used. You can also combine them. The conductive material may be mixed after cellulose is previously dispersed in a dispersion medium, or a mixture of cellulose and a conductive material may be dispersed. As a result, cellulose is dispersed to form nano-order fibers, and the conductive material efficiently interacts with the dispersed fibers, thereby preparing a dispersion having good dispersibility.

  A resistor having low conductivity is formed by printing this on a substrate and heating and firing. An electrode is provided on the formed resistor and Joule heat is generated by passing an electric current, and the resistor generates heat.

In the present invention, the dispersibility and dispersion stability of the conductive material include a hydroxyl group inherent to the fibrous polysaccharide present in the dispersion and a carboxyl group imparted by chemical treatment, and the individual conductive materials. In addition, since the carboxyl groups of the fibrous polysaccharide are partially ionized, they are electrostatically repelled from each other, so that they are easily dispersed, and the stability in the dispersed state is considered good. Furthermore, when this method is used, by including fibrous polysaccharides, the film-forming property due to the entanglement of the fibers, the heat resistance of the polysaccharides, the conductivity of the conductive material captured by the nano-order fibers Ancillary effects such as improvement in yield and improvement in conductivity due to ionization of carboxyl groups contained in the polysaccharide can be obtained.
Further, as can be seen in papermaking, since the polysaccharide fibers in the dry state have good film-forming properties due to strong hydrogen bonding, heating at a high temperature is not required when the resistor is produced. Further, since the chemical or mechanical load is small when the conductive material is dispersed, the original characteristics of the conductive material can be exhibited. In addition, fibrous polysaccharides have a high aspect ratio and are dispersed in a dispersion medium while maintaining molecular weight to some extent, so that they have viscosity even at a low concentration and are easy to adjust the film thickness in printing.
In consideration of the above-described effects, the present invention can be used in various fields and applications.

  The conductive substance used in the present invention is preferably composed of carbon particles. The particle diameter is preferably 1 nm or more and 100 nm or less, and more preferably 1 nm or more and 50 nm or less. Carbon particles include all carbon blacks (furnace black, channel black, thermal black, acetylene black, ketjen black, lamp black), fullerenes, carbon nanotubes, carbon nanohorns, carbon nanofibers, and graphite. Any of materials obtained by physically or chemically treating these may be used.

  Further, the carbon particles may be subjected to a surface treatment as a pretreatment. Examples of the surface treatment include oxidation treatment, graft polymerization reaction, coupling treatment, mechanical treatment, plasma treatment, graphitization, activation treatment, and the like. By applying pretreatment, the surface state of the carbon particles is changed to introduce various functional groups, and by forming an organic layer, the reaction and compatibility with the matrix resin is improved, and the carbon particles themselves aggregate. Dispersibility can be improved by inhibiting.

  It is further desirable to use metal particles as the conductive substance. The particle diameter is preferably from 1 nm to 100 nm, more preferably from 1 nm to 20 nm. When the particle diameter is smaller than 1 nm, the cohesive force due to the surface tension of the nanoparticles is strong, and it is difficult to uniformly disperse, so that uniform conductivity cannot be obtained on the surface. Further, when the particle diameter is larger than 100 nm, the interaction between the particles becomes relatively small, so that aggregation does not easily occur and the effect of dispersion by this method is hardly exhibited.

Regarding the metal particles as the conductive substance in the present invention, a method of depositing metal particles in the dispersion medium using an oxidation-reduction reaction can be used in addition to a method of adding the metal particles in the dispersion medium. Specifically, the following method is desirable. (Reference: Chem. Commun., 2010, 46, 8567-8568)
A water-soluble inorganic metal salt is added to a dispersion containing cellulose fibers having a carboxyl group and stirred at a low temperature. At this time, an ionized metal is coordinated as a counter ion of a carboxyl group or a carboxylate salt present on the cellulose fiber. Thereafter, by adding an excessive amount of a reducing agent, the metal is reduced and deposited due to a difference in ionization tendency. The particle size of the metal particles thus obtained can be controlled by the reaction temperature, reaction time, and concentration of inorganic metal salts, and metal particles of 1 to 100 nm can be obtained. As the metal of the inorganic metal salt, metals such as gold, silver, copper, iron, lead, platinum, alloys thereof, oxides, chlorides, and the like can be used. Note that. The particle size of the metal particles can be determined by diluting the dispersion of metal particles to a solid content concentration of about 0.05%, developing on glass or the like, and observing the dried particles using a TEM or the like.

  The metal particles obtained by the above method cannot be isolated from cellulose fibers. Therefore, it is evaluated by the particle diameter obtained by observation and the amount of deposited metal calculated from the charged inorganic metal salts.

  Unlike the method of adding metal particles to the dispersion medium, when the above method is used, the metal particles are not unevenly distributed because the metal particles are formed in a straight line along the rigid cellulose fiber. In addition, since the inter-particle distance is uniform, uniform conductivity can be obtained in the resistor. Furthermore, since metal particles form a network with the entanglement of cellulose fibers, the efficiency in electrical connection is good, and high conductivity can be exhibited with a small amount of metal, so the amount of metal used is greatly reduced. be able to.

  In the range where aggregation and precipitation do not occur, water-soluble high water content is used to increase the electrostatic repulsion between fibers, to control the viscosity of the dispersion, or to provide functionality such as coatability and wettability. Various additives including saccharides and various resins may be included. For example, chemically modified cellulose typified by carboxymethyl cellulose, carrageenan, xanthan gum, sodium alginate, agar, solubilized starch, silane coupling agent, leveling agent, antifoaming agent, water-soluble polymer, synthetic polymer, inorganic System particles, organic particles, lubricants, and the like can be used.

  About the resistor in this invention, the resistor which has low electroconductivity can be formed by printing the dispersion liquid of an electroconductive substance on the substrate partially or on the whole surface, and heating and baking this. The printing method is not particularly limited, and flexographic printing, offset printing, gravure printing, screen printing, ink jet printing, bar coater, spin coater, and the like can be used. After printing, by heating and firing, the dispersion medium is vaporized, and the fibrous polysaccharides in the dispersion medium or the fibrous polysaccharide and the substrate mainly form physical crosslinks due to hydrogen bonding to form the conductive substance. An encapsulated resistor is formed. As the heating and baking method, any one of resistance heating, infrared heating, dielectric heating, microwave heating, induction heating, or a combination of these two or more heating methods may be used.

  If the thickness of the resistor after curing is smaller than 0.5 μm, the resistor does not sufficiently follow the unevenness of the substrate surface and the substrate is partially exposed, so that the conductivity as designed is obtained. In addition, there is a possibility that uniform conductivity cannot be obtained on the surface of the resistor. Moreover, when the thickness after hardening becomes larger than 10 micrometers, it will become easy to produce problems, such as crack generation, in a resistor at the time of handling.

  As a base material used for this invention, what is necessary is just to have insulation, A thermoplastic resin, a thermosetting resin, paper, glass etc. can be used.

  For the purpose of protecting the resistor surface and suppressing moisture absorption, a resin layer may be provided after the resistor is formed. The resin layer is not particularly limited, but a thermoplastic resin may be directly formed, or a sheet-like resin may be laminated via an adhesive.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. Various evaluation results are summarized in Table 1.

<Reagents / Materials>
Silver paste: (Asahi Chemical Laboratory, LS-453)
Cellulose: Bleached Kraft Pulp (Fletcher Challenge Canada “Machenzie”)
TEMPO: Commercial product (Tokyo Chemical Industry Co., Ltd., 98%)
Sodium hypochlorite: Commercial product (Wako Pure Chemical Industries, Ltd., Cl: 5%)
Sodium bromide: Commercial product (Wako Pure Chemical Industries, Ltd.)
Carbon black: commercial product (Mitsubishi Chemical, # 40)
Silver nitrate aqueous solution: Commercial product (Wako Pure Chemical Industries, Ltd.)
Sodium borohydride: Commercial product (Wako Pure Chemical Industries, Ltd.)
Carboxymethylcellulose sodium salt (substitution degree 1.2): Commercially available product (Wako Pure Chemical Industries, Ltd.)

<Example 1>
A glass substrate was used as the substrate. A silver paste was applied by screen printing, a T-shaped electrode having a line width of 1 mm and an electrode pad were formed to have an electrode width of 10 mm, and cured at 100 ° C. for 30 minutes. Next, cellulose (carboxyl group amount 1.5 mmol / g) to which a carboxyl group was imparted by TEMPO oxidation treatment was prepared. The pH was adjusted to 10 using 1M sodium hydroxide while adding ion-exchanged water so that the solid content concentration of cellulose was 4% as a whole. These were processed for 1 hour using a mixer (Osaka Chemical, Absolute Mill, 14,000 rpm) to prepare a preparation liquid containing cellulose fibers. The obtained cellulose fiber had a fiber width of 3 nm and a fiber length of 1.6 μm. 5 ml of the above preparation solution, 400 mg of carbon black and 5 ml of ion-exchanged water were mixed and stirred with a desktop stirrer to prepare a carbon black dispersion. The dispersion was coated on the electrode so as to be 10 mm square by screen printing, and then dried at 100 ° C. for 30 minutes to form a 10 μm thick resistor.

<Example 2>
In the same manner as in Example 1, a preparation liquid containing cellulose fibers was prepared so as to have a solid content concentration of 4%. The same amount of 5 mM silver nitrate was added, and after stirring for 30 minutes with a desktop stirrer, 50 mM sodium borohydride was further added twice the amount of the preparation and stirred for 90 minutes to prepare a dispersion. From TEM observation of the dispersion, formation of silver particles having a particle diameter of 5 to 7 nm was confirmed. A resistor was formed on the glass substrate in the same manner as in Example 1.

<Comparative Example 1>
It formed similarly using the carboxymethylcellulose (CMC) aqueous solution (4% of solid content) using the carboxymethyl which is a non-fibrous polysaccharide as a binder instead of the preparation liquid in Example 1. FIG.
<Comparative example 2>
It formed similarly using the CMC aqueous solution (solid content 4%) instead of the preparation liquid in Example 2. FIG.

  In Examples 1 and 2 and Comparative Examples 1 and 2, resistance values between the electrodes were measured with a digital multimeter. Further, in the planar heating element, the applied voltage was 20 to 80 V, and the temperature after 60 seconds at the center of the heating element was measured with a thermocouple (Table 1). Moreover, the temperature change for every 10 seconds was measured in Example 1 and the comparative example 1 using the applied voltage 50V (Table 2).

  As shown in Tables 1 and 2, it can be seen that when a cellulose fiber having a carboxyl group is present in a dispersion of carbon particles or metal particles, an electric current flows and a highly responsive heating element is obtained.

According to the present invention, it is possible to manufacture a conductive substrate that has an extremely low environmental load from manufacturing to disposal and low manufacturing costs. When the present invention is used, by including fibrous polysaccharide, film forming property due to entanglement of fibers, heat resistance of polysaccharide, dimensional stability under heat load, conductivity due to ionization of carboxyl group contained in polysaccharide Accompanying effects such as improvement in adhesion and adhesion to the substrate by nano-order fibers can be obtained.
In consideration of the above-described effects, if the present invention is used, it is possible to develop various uses such as foods, pharmaceuticals, and electronic members.

DESCRIPTION OF SYMBOLS 10 ... Planar heating element 11 ... Resistor 12 ... Electrode 20 ... Planar heating element 21 ... Resistor 22 ... Electrode 23 ... Base material

Claims (7)

At least a base material, resistor formed on one surface of the substrate, and is composed of electrodes for energizing the resistor, seen including a fibrous polysaccharide said resistor having a conductive material and a carboxyl group ,
The fibrous polysaccharide having the carboxyl group is a cellulose fiber,
A planar heating element , wherein a fiber width of the cellulose fiber is 2 nm or more and 50 nm or less, and a length of the cellulose fiber is 0.5 μm or more and 50 μm or less . Sheet heating element according to claim 1, wherein at least a part of carboxyl groups of the cellulose fibers is a carboxylic acid salt.   2. The planar heating element according to claim 1, wherein the conductive substance is made of carbon particles.   The planar heating element according to claim 1, wherein the conductive substance is metal particles. The planar heating element according to claim 3 or 4 , wherein the conductive substance has a particle size of 1 nm or more and 100 nm or less.   The planar heating element according to claim 1, wherein a thickness of the resistor after curing is not less than 0.5 µm and not more than 10 µm. And a step of the step of forming the resistor by printing on one side of a substrate provided with electrodes on the resistor, seen including a fibrous polysaccharide said resistor having a conductive material and a carboxyl group,
The fibrous polysaccharide having the carboxyl group is a cellulose fiber,
A method for producing a planar heating element, wherein the cellulose fiber has a fiber width of 2 nm to 50 nm and a length of the cellulose fiber of 0.5 μm to 50 μm .

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