JPH1027677A - Flat heating unit coated with silica film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To give certain hardness, tensile strength, etc., to a composition without generating a wrinkle and shrinkage in a heating sheet, increase mechanical strength, give waterproof and electric M also stabilize an internal composition, so as to stabilize physical properties of electric resistance value or the like. SOLUTION: Relating to a flat heating unit, a heating sheet 1 of relatively rough composition like carbon fiber mixed making paper or the like is impregnated with a silica solution to be hardened, by forming a silica film 6, the flat heating unit, having electric insulation, waterproof and chemical resistance, is given mechanical, strength, to fix an internal composition and stabilize an electric resistance value. The silica solution is suitably a liquid-state glass precursor with organopolysiloxane as a main material, this solution is infiltrated in a space of the internal composition of the flat heating sheet, also a film is formed in a sheet surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet heating element covered with a cured silica film, and more specifically, to a sheet heating element using a carbon fiber as a conductor to form a flexible thin glass sheet. The present invention relates to a planar heating element which is coated with a silica film to impart electrical insulation and waterproofness, and which fixes and stabilizes a gradual structure inside a sheet.

[0002]

2. Description of the Related Art Heretofore, as a sheet-like heat generating sheet, there have been known a sheet formed by mixing carbon fibers with paper or a nonwoven fabric. Carbon fibers radiate far-infrared rays favorably even at relatively low heat generation temperatures, and are particularly effective in melting snow and ice.Therefore, carbon fiber is expected to be used in this respect. Since there are many gaps in the internal structure and low strength, and there is no so-called "stiffness", not only there is a problem in handling and processing, but also the loose structure and the possibility of floating of the conductive carbon fiber However, there is a problem that physical properties such as electric resistance value are not stable and reliability is low in performance.

[0003] By laminating such a mixed paper or nonwoven fabric with a plastic film, the "stiffness" can be improved and waterproofness and electrical insulation can be imparted, but paper or nonwoven fabric without "stiffness" can be laminated with a laminator. Wrinkles, shrinkage of paper and non-woven fabric, and easy tearing due to low tensile strength. In addition, simply laminating mixed paper and non-woven fabric does not eliminate the floating property of the internal structure composed of carbon fiber and pulp, and thus cannot eliminate the instability of performance such as electrical resistance and physical strength. there were.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a sheet-like heat generating sheet having no "waist" without causing wrinkles or shrinkage to have a certain hardness or tensile strength in the tissue. An object of the present invention is to increase mechanical strength by imparting hardness and the like, impart waterproofness and electrical insulation, and stabilize physical properties such as electric resistance by stabilizing an internal structure.

[0005]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a method for applying a silica solution to a sheet-like heat generating sheet having a relatively coarse structure and having no "stiffness", such as a paper made of carbon fiber mixed paper or a non-woven fabric. By applying by dipping or spraying and curing to form a silica film, it gives mechanical strength to the sheet heating sheet, immobilizes the internal structure, stabilizes physical properties such as electric resistance, and cures the silica film. Thus, a planar heating element having good physical properties such as electrical insulation, waterproofness, chemical resistance, and heat resistance can be realized. Since the silica cured film is initially applied in a liquid or fluid state, it penetrates well into the inside of the heat generating sheet, and when cured, fixes and stabilizes the tissue, improves the mechanical strength such as tear strength, and disperses. Since the floating property of the carbon fiber is fixed, the electric resistance value can be stabilized.

The silica solution used in the present invention is a liquid glass precursor containing organopolysiloxane as a main component. This silica solution has a silicon content of 6 in terms of SiO _2.
0% (by weight) or more and liquid at normal temperature. For application of the silica solution, an appropriate technique such as immersion, roller coating, brush coating, or spraying can be used. When a large amount of impregnation is used, immersion is used. The sheet heating element to which the solution is applied is at room temperature (20 to 2
(5 ° C.) to form a film that is dry to the touch in 2 to 3 hours by drying at room temperature and further to dry for 2 to 3 days to form a cured silica film that covers the inside and the entire surface of the sheet heating element. You.

[0007] Such a cured silica film not only covers the surface of the sheet heating sheet, but also penetrates into the sheet and solidifies, whereby the carbon fiber and pulp or synthetic fiber constituting the sheet are used. Since the internal structure formed with gaps is fixed and the floating carbon fibers are tightly fixed together, the physical "hip" strength is given to improve the handleability and the tear strength etc. And, importantly, stabilizes the electrical resistance through the myriad of carbon fibers dispersed and in contact with each other. In addition, the outer surface is provided with waterproof properties and electrical insulation properties by the silica film, and also has advantageous properties such as heat resistance and chemical resistance. In addition, since the cured silica film has flexibility or flexibility, the sheet-like heat generation sheet can be provided with not only physical hardness but also flexibility. In addition, when copper foil is adhered to the sheet heating sheet as an electrode, oxidation or deterioration due to moisture or chemicals is usually liable to occur, but if the metal part is sealed and covered with a hardened silica film, the durability of the electrode can be improved. Can also be improved.

[0008] The sheet-shaped heating sheet coated with silica is further laminated with a plastic film or a plastic sheet, for example, a polyester film or a polypropylene film, on the outer side thereof, thereby perfecting insulation and waterproofness, and further increasing mechanical strength. be able to. As a plastic for lamination, a film or sheet of a thermoplastic or thermosetting plastic can be widely used.

[0009]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view schematically showing one embodiment of a planar heating element covered with a cured silica film of the present invention.
The sheet-like heat generating sheet 1 is preferably made of a carbon fiber blended paper obtained by blending carbon fibers cut short to about 5 mm with pulp, for example, and cutting the carbon fibers into natural fibers or synthetic fibers by a wet or dry method. Can be used. Such a heat generating sheet has a very coarse structure in which there is a gap between fibers, and does not have a “stiffness” as described above. Electrodes 2 are provided at appropriate positions on such a sheet, for example, on both sides in order to form a current-carrying heating element. In the example shown in the figure, the electrode 2 is formed of a silver powder particle 3 that has penetrated into a rough tissue and has been solidified, and a copper foil 4 stuck thereon. The silver powder particles 3 are formed by rubbing the silver paste into the sheet 1 and drying and solidifying it. A part of the copper foil 4 is extended beyond the edge of the sheet 1 as shown in FIG. This lead part 5
The conductor to be connected to the power supply later is fixed by solder or the like.

[0010] The sheet heating sheet 1 provided with the electrodes as described above.
The cured silica film 6 can be formed on at least the entire heat generating portion, that is, on the entire surface of the heat generating sheet except for the electrodes 2.
Preferably, a cured silica film 6 is formed on the entire surface including the electrode 2 as shown in FIG. The thickness of the film 6 is 0.1
It can be from 5 microns to 5 microns or more (eg, about 1 mm). In the figure, the silica film 6 is shown slightly apart from the heat generating sheet 1 for clarity. However, in actuality, the silica film 6 is in close contact with both the upper and lower surfaces and the four side surfaces (edge portions) of the heat generating sheet. The silica solution permeates into the heat generating sheet 1 and is hardened. As shown in FIG. 2 which is a plan view, the lead portion 5 extends out of the silica film 6, and a lead wire leading to a power supply is connected thereto. Instead of forming the lead portion 5, a part of the copper foil 4 on the heat generating sheet may be masked and a silica solution may be applied.

As described above, the silica film 6 is formed from a liquid glass precursor containing organopolysiloxane as a main material. More specifically, this liquid glass precursor is composed of an organopolysiloxane as a main material, a crosslinking agent, and a curing catalyst. The main material is composed of a liquid organopolysiloxane having a methyl group or a phenyl group. The cross-linking material is composed of an organopolysiloxane having functional side chains such as an alkoxy group, an acyloxy group, and an oxime group. The curing catalyst is Z
It can be a metal-containing organic compound such as n, Al, Co, or Sn, or an inorganic substance such as boron ion or halogen. These three components are mixed to form a one-part type silica solution, which is preferably used without a solvent. However, in some cases, it may be used after being diluted with a solvent such as isopropyl alcohol. Such a solution can be applied to the sheet heating sheet by an appropriate method such as immersion, spraying, or roller coating as described above.

As described above, the silica solution applied in a liquid state to the sheet heating sheet cures naturally when left at room temperature as described above, but its curing mechanism is based on the functional group (methyl group, or methyl group) of the main material organopolysiloxane. Phenyl group) is hydrolyzed by moisture in the air in the first stage to be converted to a hydroxyl group (OH), and in the second stage, a functional group of the crosslinking agent organopolysiloxane acts on the hydroxyl group of this organopolysiloxane,
Further, a dealcoholization reaction occurs under the action of a curing catalyst, and the reaction gradually proceeds to form a high-molecular polysiloxane compound having a three-dimensional structure. In this way, the silica material on the cured sheet-like heating sheet has an appearance like a so-called thin glass film, and this glass substance is formed not only on the surface of the sheet-like heating sheet but also inside thereof.

The mechanism by which the cured silica film or glass film stabilizes the sheet-like heat generating sheet will be described with reference to an enlarged schematic sectional view of FIG. The carbon fiber-mixed heat generating sheet is formed by dispersing a myriad of carbon fibers C in pulp P indicated by hatching. Some of the carbon fibers C are in contact with each other to form a conductive path as indicated by S in the figure, but some are free or floating without contacting each other as shown by circles A or B. There are also things. Such a floating carbon fiber, when energized to the heat generating sheet, sticks to and separates from each other to cause a change in the interelectrode resistance value of the sheet, thereby causing instability.

Therefore, if a silica solution is applied and penetrates into the inside, and if the carbon fibers in the circle A are wrapped around each other so as to be closely adhered so as to eliminate the gap, the carbon fiber in this portion is obtained. No longer stick to each other or separate from each other, and a conductive path having a stable resistance value is obtained. Conversely, if the silica solution enters the gap between the carbon fibers in the circle B and solidifies, for example, electricity will no longer flow in this portion, so that the resistance value is also stabilized.

In the sheet heating sheet 1 to which the silica film 6 is applied, the silica substance applied in a liquid state penetrates into the inside of the sheet and hardens to fix a coarse structure. The mechanical strength is increased, and the positions of the randomly dispersed carbon fibers, which are conductors, are also fixed, so physical properties such as electrical resistance are stabilized.In addition, when a silica solution is applied including the electrode portion, silver is applied. -Since the electrode material such as copper foil is prevented from being oxidized and deteriorated, the performance as a current-carrying planar heating element is improved. On the outer surface of the sheet, the silica film 6 provides electrical insulation and waterproofness, and also provides heat resistance and chemical resistance, so that the sheet can be used for various outdoor and indoor applications as it is.

However, more preferably, an organic film 7 such as a saturated or unsaturated polyester film or an epoxy resin sheet is formed on the outer surface of the cured silica film as shown in FIG.
Are laminated, a sheet heating element having greater mechanical strength and insulation / waterproofness can be obtained. FIG.
The heating element shown in (1) has a composite composition of organic and inorganic substances in which a heating sheet 1 such as carbon fiber mixed paper is impregnated with an inorganic silica substance, and is formed into a film 6, and an organic film 7 is applied to the outer surface thereof. It can be said that it is a new heating element. In the figure, although a certain thickness is shown for clarity, actually, even if the organic film 7 is included, it is 1 mm or less, more specifically, about 600 to 7 mm.
A very thin heating element having a thickness of about 00 microns can be obtained.

[0017]

According to the present invention, a sheet having a rough texture is fixed and strengthened by impregnating and coating a sheet-like heat generating sheet with a silica film, so that the sheet is mechanically thin despite being a thin heat generating sheet. Strength is improved, subsequent processing and handling become easier, and electrical properties such as resistance are stabilized.
A reliable heating element can be manufactured.
Due to the nature of the silica, the sheet-like heat generating sheet is provided with the oxidation resistance and chemical resistance of the electrode, and the outer surface of the sheet is also provided with insulation and waterproofness. Since the heating element can be given flexibility or flexibility by applying a thin silica film,
There is an effect that it is possible to develop an unusually thin sheet heating element having a new function.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing an embodiment of a sheet heating element coated with a silica film of the present invention.

FIG. 2 is a schematic plan view of the heating element shown in FIG.

FIG. 3 is an enlarged schematic sectional view illustrating a mechanism of stabilization by applying a silica film according to the present invention.

FIG. 4 is a schematic cross-sectional view of a sheet heating element in which an organic film is further applied on a cured silica film.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Surface heating sheet 2 ... Electrode 3 ... Silver powder 4 ... Copper foil 5 ... Lead part 6 ... Hardened silica film 7 ... Organic film P ... Pulp C ... Carbon fiber S ... Contact point A, B ... Free point

Claims (7)

[Claims] An electrode (2) is provided on a sheet heating sheet (1),
A sheet heating element in which at least the entire heating portion of the sheet heating sheet is covered with a hardened silica film (6) so that electrodes can be connected to a power source as appropriate. 2. The sheet heating element according to claim 1, wherein the cured silica film covers the entire sheet heating sheet including a power source. 3. The cured silica film is formed by applying a liquid glass precursor containing an organopolysiloxane as a main material in a liquid state to a sheet heating sheet and curing the liquid glass precursor.
2. The sheet heating element according to item 1. 4. The sheet heating sheet is formed by dispersing short cut carbon fibers in paper or nonwoven fabric,
4. The sheet heating element according to claim 3, wherein the heating element has a relatively coarse internal structure having many gaps. 5. The silica film is applied to a sheet-like heat generating sheet in a liquid state, penetrates into gaps in the internal structure of the sheet, and is also placed on the surface, and is hardened inside and on the surface. The planar heating element according to claim 4, which is formed. 6. An electrode (2) is provided on a sheet heating sheet (1),
The entire sheet-like heat generating sheet including the electrodes was covered with a cured silica film (6), and a plastic film or sheet was laminated on the outer surface of the silica film so that a power supply could be connected outside the plastic film or sheet. Sheet heating element. 7. The sheet-like heat generating sheet is formed by dispersing a short cut carbon fiber in paper or nonwoven fabric.
The silica film has a relatively coarse internal structure with many gaps, and the silica film applies a liquid glass precursor containing an organopolysiloxane as a main material to the sheet-like heat generating sheet in a liquid state, and penetrates the gaps in the internal structure of the sheet. The sheet heating element according to claim 6, wherein the sheet heating element is a glass having a film formed on the sheet surface.