JP2013171750A - Transparent planar heating element and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transparent planar heating element which is excellent in transparency and visibility, has surface heating characteristics capable of uniform heat generation, and has a curved surface.SOLUTION: The transparent planar heating element of the present invention includes one or more pairs of electrodes in a conductive layer of a conductive substrate and has a curved surface. The conductive substrate is a laminate of a transparent substrate and the conductive layer. The conductive layer has an irregular network structure.

Description

  The present invention relates to a transparent sheet-shaped heating element having a curved surface having excellent sheet transparency and visibility and capable of generating uniform heat, and a method for producing the same.

  Conventionally, refrigeration and refrigeration showcases need to prevent condensation on the glass surface that constitutes the window portion. For this reason, a transparent conductive film is formed on the glass surface, and predetermined power is applied to the window surface. It is done to warm up. In order to prevent fogging and dew condensation in automobile window glass, a defroster using a transparent conductive film is also used, and a transparent sheet heating element is used to prevent illuminance from falling due to snow accumulation or freezing on the light front cover. Consideration is being made. Also, in cold regions, use of a transparent sheet heating element to prevent snow melting and freezing in order to prevent the visibility of road signs and the like due to snow accumulation and freezing on road signs and traffic lights, and in low temperature environments in cold regions The necessity of providing a transparent sheet heating element for temperature control is increasing in order to prevent malfunction of the liquid crystal display element used in the above, and to assist startup.

  As a liquid crystal display element used in a low-temperature environment such as a cold region, for example, as proposed in Patent Document 1, a mesh-like heating resistor is disposed and heated, as in Patent Document 2, and the like. Transparent surface heating using a transparent conductive film such as silver, copper or indium tin oxide (ITO) provided on a transparent substrate as a heating surface, and a pair of metal electrodes for energizing the transparent conductive film The body has been reported. However, in the method of Patent Document 1, it is difficult to uniformly heat the entire liquid crystal element, and a heating resistor made of an opaque metal tends to be an obstacle when viewing a liquid crystal display. Also, in the method of Patent Document 2, it is not always easy to uniformly heat the entire liquid crystal element, and when a heating element made of a transparent conductive film that increases haze and reflection as the thickness increases, It may interfere with viewing the LCD display. In addition, when the thickness is thin enough to ensure transparency, the conductivity is inferior, so that the amount of flowing current is small and the rise of heat generation may be slow. Furthermore, when a sputtering method, a vapor deposition method, or the like is used, the manufacturing cost is high, and the ITO transparent conductive film has a problem that it is poor in bending resistance and easily cracked, so that it can be applied to a member having a curved surface. It's not easy.

  On the other hand, as in Patent Document 3, a three-dimensional curved surface having a mesh pattern having intersections of a large number of lattices formed of conductive metal wiring and electrodes formed at opposite ends of the mesh pattern. However, since the mesh pattern is regular, metal wiring may be seen, which is problematic in terms of visibility.

  Therefore, a transparent sheet heating element having a curved surface, which has high transparency and visibility, has a low resistance value of the conductive portion, and can generate uniform heat, is desired.

JP 58-126517 A JP-A-9-306647 JP 2009-272303 A

  An object of the present invention is to provide a transparent sheet heating element having a curved surface having excellent surface transparency and visibility, and having a surface heating characteristic capable of generating uniform heat.

The present invention employs the following means in order to solve such problems. That is:
1) A transparent planar heating element having a curved surface having one or more electrodes in a conductive layer of a conductive substrate,
The conductive substrate is a laminate of a transparent substrate and a conductive layer,
The transparent layered heating element, wherein the conductive layer has an irregular network structure.
2) The transparent sheet heating element according to 1), wherein a transparent protective layer is provided on the surface of the conductive substrate on the conductive layer side.
3) The transparent sheet heating element according to 1) or 2), wherein the conductive layer has a surface resistivity of 1 to 100Ω / □.
4) The transparent sheet heating element according to any one of 1) to 3), wherein the total light transmittance is 50% or more.
5) The method for producing a transparent sheet heating element according to any one of 1) to 4), wherein the curved surface is formed by thermoforming.

  According to the present invention, it is possible to provide a transparent sheet heating element having a curved surface having high transparency, having a surface heating characteristic capable of generating uniform heat, in which a conductive portion is hardly visible. Since the transparent sheet-shaped heating element in the present invention has the above-mentioned characteristics, for example, assisting activation of a liquid crystal display element having a curved surface in a low-temperature environment such as a cold region, preventing snow melting and freezing of a traffic light, etc., defroster for automobile windows , Etc. can be suitably used.

  The present invention has been intensively studied on the above-mentioned problem, that is, a transparent sheet-shaped heating element having a curved surface having excellent transparency and visibility and capable of uniform heat generation, and is formed from metal fine particles. After forming a curved surface by thermoforming a conductive substrate that is a laminate of a conductive layer having an irregular network structure and a transparent substrate, the above problems can be solved at once by providing the conductive layer with one or more pairs of electrodes. It has been clarified to do. That is, a transparent sheet heating element having a pair of electrodes in a conductive layer of a conductive substrate and having a curved surface, the conductive substrate being a laminate of a transparent substrate and a conductive layer, It is an invention of a transparent planar heating element characterized in that the layer has an irregular network structure.

  It is important that the conductive substrate used in the transparent sheet heating element of the present invention is a laminate of a transparent substrate and a conductive layer. The conductive layer is preferably formed of metal fine particles. Examples of the metal used for the fine metal particles include gold, silver, copper, platinum, iron, aluminum, nickel, cobalt, zinc, tin, palladium, rhodium, ruthenium, bismuth, and the like. Alternatively, two or more kinds may be used in combination. Moreover, even if the metal is not a pure metal, any metal may be used as long as a predetermined conductivity can be finally obtained by a known conductive treatment described later, such as a metal oxide, an organic acid metal salt, a fatty acid metal salt, A metal compound coated and bound with a compound can also be selected.

  The conductive layer is a layer composed of the metal fine particles as described above, and if necessary to form a conductive layer having an irregular network structure, the conductive layer is not limited to the metal fine particles. Various additives such as dispersants, surfactants, protective resins, thermosetting resins, UV curable resins, antioxidants, heat stabilizers, weathering stabilizers, UV absorbers, pigments, dyes, organic or inorganic fine particles Inorganic components such as fillers and antistatic agents, and organic components can be contained. Moreover, in order to use the conductive substrate having the conductive layer as the transparent planar heating element of the present invention, the conductive layer having an irregular network structure is not necessary for forming the conductive layer. When necessary, various additives as described above may be contained.

  As a method of obtaining a conductive substrate in which the transparent substrate and the conductive layer of the present invention are laminated, even if the transparent substrate and the conductive layer are directly laminated, the transparent substrate and the conductive layer are laminated with an adhesive or an adhesive. Also good. In addition, in order to improve the adhesion between the transparent substrate and the conductive layer, a treatment method such as corona discharge treatment, primer treatment, short wavelength ultraviolet irradiation treatment or silane coupling treatment is used on the transparent substrate surface on which the conductive layer is laminated. Then, direct lamination or lamination may be performed, or a transfer method described later can be used.

  Examples of the method for directly laminating the conductive layer on the transparent substrate include a known coating method or printing method for the metal fine particle dispersion on the transparent substrate, such as a die coating method, an applicator method, a comma coating method, and a dipping method. Is preferably used.

  In addition, the metal fine particle dispersion can use water and various organic solvents as a solvent in consideration of the dispersibility of the metal fine particles, the solubility of the various additives described above, and the like. A solvent containing both can also be used.

  A conductive substrate using a transfer method can be obtained by the following steps. That is, a step of applying an ultraviolet curable resin or a thermosetting resin on the surface of the conductive layer of the laminate in which conductive layers having an irregular network structure are laminated, and an ultraviolet curable resin or a thermosetting resin. A step of bonding a transparent substrate after curing, a step of peeling an irregular network structure composed of a base material and metal fine particles in the laminate, and transferring to a transparent substrate, or an ultraviolet curable compound or heat curing The step of bonding and curing the surface coated with the conductive compound and the transparent substrate, the substrate in the laminate in which the conductive layer having an irregular network structure is laminated, and the conductive layer are peeled off and transferred to the transparent substrate The conductive substrate obtained by this transfer method is preferable because it has an advantage of imparting smoothness to the surface of the conductive layer.

  As the transparent substrate of the conductive substrate used for the transparent sheet heating element of the present invention, a thermoplastic resin film can be used. When the transparent substrate which comprises a conductive substrate is a thermoplastic resin film, it is preferable at points, such as transparency, a softness | flexibility, and workability. The thermoplastic resin film as used in the present invention is a general term for films that are melted or softened by heat, and is not particularly limited, but representative examples include polyolefins such as polyester films, polypropylene films, and polyethylene films. Films, polylactic acid films, polycarbonate films, acrylic films such as polymethyl methacrylate films and polystyrene films, polyamide films such as nylon, polyvinyl chloride films, polyurethane films, fluorine films, polyphenylene sulfide films, and the like can be used.

  Also, in this thermoplastic resin film, various additives such as antioxidants, heat stabilizers, weathering stabilizers, ultraviolet absorbers, organic lubricants, pigments, dyes, organic or inorganic fine particles, fillers Further, an antistatic agent, a nucleating agent, or the like may be added to such an extent that the characteristics are not deteriorated.

  On the surface where the conductive layer of the transparent substrate used in the transparent sheet heating element of the present invention is not laminated, and on the transparent protective layer, various functional layers such as an adhesive layer, a release layer, an adhesion-imparting layer, In addition, a weather resistant layer or the like may be provided.

  It is important that the conductive layer in the transparent sheet heating element of the present invention has an irregular network structure. That is, the conductive substrate is a laminate of a transparent substrate and a conductive layer having an irregular network structure. In the case where the conductive layer has an irregular network structure, the line portion is difficult to be visually recognized, so that the visibility is superior to the conductive layer having a regular mesh structure.

  Here, the network structure of an irregular network structure indicates a structure in which several points are connected by several line segments. That is, the conductive layer having a network structure in the present invention means a structure in which line segments composed of metal fine particles and the above-described various additives are connected at a plurality of points, and the conductive layer is derived from this structure. Expresses sex. Moreover, the part enclosed by this line segment becomes an opening part, and transparency is expressed by this opening part. By configuring such a network structure, the transparency and conductivity of the transparent sheet heating element can be made excellent.

  Irregular network structure irregularity can be identified by an observation image of a differential interference microscope or the like, and the network structure is in a state where the shape and size of the openings are irregular in the shape, that is, the mesh portion, The shape of the linear portion is not a straight line but a state in which the line thickness is uneven.

  In the transparent planar heating element of the present invention, it is important that one or more pairs of electrodes are provided on the conductive layer of the conductive substrate. The transparent sheet heating element of the present invention functions as a heating element by energizing this electrode. The term “one or more pairs of electrodes” means that there are one or more pairs of electrodes for energizing the transparent sheet heating element of the present invention. By providing one or more pairs of electrodes, even when the transparent sheet heating element is enlarged, it is possible to energize electricity from a plurality of locations, so that uneven conduction is less likely to occur. Therefore, temperature unevenness of the entire transparent sheet-shaped heating element hardly occurs, and the temperature can be generated uniformly.

  Any electrode can be used as long as it has conductivity. Examples of preferable electrodes include metal paste, conductive resin, metal foil, metal tape, and metal plating layer. It can be used alone or as a laminate, multilayer or mixed layer and used as an electrode. From the viewpoint of contact resistance, it is preferable to use an electrode having a lower resistance value.

  The thickness of the electrode is not limited as long as the conductive layer having an irregular network structure used for the transparent planar heating element of the present invention functions as a heating surface so that the current necessary for the conduction can be passed. Usually, it is 0.1 μm or more, preferably 0.5 μm to 100 μm, more preferably 1 to 50 μm, and more preferably 5 to 20 μm.

  It is important that the transparent planar heating element of the present invention has a curved surface. A curved surface indicates that the radius of curvature is not infinite, and examples include bowl-like and wave-like shapes. Here, having a curved surface means that at least a part of the transparent planar heating element has a curved surface, and may have a plurality of curved surfaces. The transparent sheet heating element of the present invention may have a curved surface as a whole, but the entire shape of the transparent sheet heating element may be a combination of at least one curved surface and a plane. preferable. In the transparent sheet heating element of the present invention, it is important that any part of the transparent sheet heating element has a curved surface. However, as a preferable aspect, the conductive substrate in the transparent sheet heating element is a curved surface. It is to have.

  The transparent sheet heating element of the present invention preferably has a transparent protective layer on the surface of the conductive substrate on the conductive layer side. The resin forming the transparent protective layer is not particularly limited, and examples thereof include an ultraviolet curable resin and a thermosetting resin. Examples of the ultraviolet curable resin include polyester acrylate, urethane acrylate, epoxy acrylate, and the like. Examples of thermosetting resins include unsaturated polyester resins, epoxy resins, urethane resins, and silicone resins. The transparent protective layer may be formed by directly laminating the aforementioned ultraviolet curable resin or thermosetting resin from the conductive layer side of the transparent sheet heating element. Moreover, after providing an adhesive layer or an adhesive layer on the conductive layer, a thermoplastic resin film may be laminated as a transparent protective layer.

  The thermoplastic resin film is not particularly limited, but polyester film, polyolefin film, polylactic acid film, polycarbonate film, acrylic film, polyamide film, polyvinyl chloride film, polyurethane film, fluorine film, polyphenylene A sulfide film or the like can be used.

  The transparent protective layer only needs to be protected so that the conductive layer having an irregular network structure in the present invention is not peeled off or scraped. Further, since the transparent sheet heating element is energized to generate heat, the transparent protective layer also has an effect as an insulator. Therefore, the thickness of the transparent protective layer is not particularly limited as long as the thickness of the transparent protective layer is greater than the thickness of the conductive layer as long as the conductive film can serve as a protection and insulator.

  The surface specific resistance value of the conductive layer of the conductive substrate used for the transparent sheet heating element of the present invention is preferably 1 to 100Ω / □. More preferably, it is 1-30 ohm / square, More preferably, it is 1-10 ohm / square, Especially preferably, it is 1-5 ohm / square. Even if the surface specific resistance value is greater than 100Ω, it is possible to generate heat, but this is not preferable because high power application is required. Although the lower surface specific resistance value is preferable, the lower limit that can be practically achieved is considered to be about 1Ω / □, and therefore, about 1Ω / □ is considered the lower limit.

  When the conductive layer is formed from a metal fine particle dispersion and the conductive layer contains an insulating compound in addition to the metal fine particles, the conductivity is increased by organic solvent treatment, acid treatment, heat treatment, current treatment, etc. In order to increase the conductivity of the conductive layer and reduce the surface specific resistance value, a known method may be used.

  The above-mentioned measurement of the surface specific resistance value of the conductive layer is, for example, in the form conforming to JIS-K-7194 (established in 1994) in the normal condition (23 ° C., relative humidity 65%) after standing for 24 hours. Thus, measurement can be performed using Loresta-EP (manufactured by Mitsubishi Chemical Corporation, model number: MCP-T360). In addition, when the conductive substrate of the present invention has a transparent protective layer on the surface on the conductive layer side, the surface specific resistance value of the conductive layer is measured by removing the transparent protective layer if it can be removed. In the case where it cannot be removed, it is a value measured before laminating the transparent protective layer.

  The total light transmittance of the transparent sheet heating element in the present invention is preferably 50% or more, more preferably 60% or more. If the total light transmittance is less than 50%, there may be a problem in terms of transparency of the transparent sheet heating element. In addition, although the total light transmittance of a transparent planar heating element is so preferable that it is high, since it is difficult to make it higher than 95% practically, an upper limit is considered to be about 95%.

  The curved surface of the transparent sheet heating element of the present invention is preferably formed by thermoforming. Here, thermoforming is a forming method in which a resin film, a sheet, or the like is softened by heating to form a shape, and vacuum forming, pressure forming, press forming, and the like are known methods. The molding method may be appropriately selected in consideration of the types and characteristics of the transparent substrate and the transparent protective layer.

  The transparent sheet heating element having a curved surface of the present invention can be obtained by the following steps. First, a conductive substrate is thermoformed according to a molding die having a desired shape to obtain a conductive substrate having a curved surface. Thereafter, it can be obtained by providing one or more pairs of electrodes on a conductive substrate having a curved surface. When a transparent protective layer is laminated on the surface of the transparent sheet heating element on the conductive layer side, the conductive substrate having the transparent protective layer laminated on the surface of the conductive substrate in the conductive substrate is Similarly, after forming a curved surface by thermoforming, it can also be obtained by a method comprising an electrode.

  Hereinafter, although the transparent planar heating element of this invention is illustrated and demonstrated more concretely, this invention is not limited to this. That is, a copper foil having a uniform width was applied in parallel to both ends of a conductive substrate having an irregular mesh structure conductive layer obtained by a known method, a pair of electrodes was taken, and a transparent protective layer was laminated. Later, by vacuum forming, a transparent sheet heating element having a curved surface can be obtained.

[Characteristic measurement method and effect evaluation method]
The method for measuring the characteristics of the conductive substrate prepared in each example and comparative example and the method for evaluating the effect are as follows.
(1) Conductivity The conductivity of the conductive layer of the conductive substrate was evaluated by the surface specific resistance value. The surface specific resistance value is measured in a normal condition (23 ° C., relative humidity 65%) for 24 hours, and in that atmosphere, in compliance with JIS-K-7194 (established in 1994), Loresta-EP (Mitsubishi This was carried out using Chemical Co., Ltd., model number: MCP-T360). The unit is Ω / □. In addition, this measuring device can measure below 1 × 10 ⁶ Ω / □.
(2) Total light transmittance The total light transmittance is determined in accordance with JIS-K-7375 (established in 2008) after leaving the conductive substrate for 2 hours in the normal state (23 ° C., relative humidity 65%). , Using a fully automatic direct reading haze computer “HGM-2DP” manufactured by Suga Test Instruments Co., Ltd. The average value measured three times was defined as the total light transmittance of the transparent sheet heating element. If the total light transmittance is 50% or more, the transparency is good. In the case of a transparent sheet heating element in which a conductive layer is laminated only on one side of the transparent substrate, the transparent sheet heating element is installed so that light enters from the side where the conductive layer is laminated.
(3) Conductive layer observation (shape observation)
The conductive layer of the conductive substrate is observed using a differential interference microscope (LEICA DMLM manufactured by Leica Microsystems) or a scanning electron microscope (S-2100A type Hitachi scanning electron microscope, Hitachi, Ltd.). It was confirmed whether or not a conductive layer having an irregular network structure was formed. In addition, surface observation is carried out on three arbitrarily selected surfaces, and when an irregular network structure is confirmed in any place, the transparent sheet heating element having the observed conductive layer is irregular. It was judged to have a conductive layer having a simple network structure.
(4) Evaluation of exothermicity The exothermic evaluation of the transparent sheet heating element was performed by attaching a copper tape to both ends of the transparent sheet heating element, taking electrodes, and applying current to the center surface 5 minutes later. If the surface temperature of the transparent sheet heating element when the temperature (heating temperature) is measured with a radial temperature sensor (made by KEYENCE, model number FT-H20) is higher than the temperature before energization, it is used as a transparent sheet heating element “○” can be used, and “×” indicates a temperature lower than the temperature before energization.

Next, the present invention will be described based on examples.

(Conductive substrate 1)
On one side of a biaxially stretched polyethylene terephthalate film (Lumirror (registered trademark) T60 manufactured by Toray Industries, Inc.), a metal fine particle solution (XA-9053 manufactured by Fujikura Kasei Co., Ltd.) is formed into an irregular mesh-like line by screen printing. Printing was performed to obtain a laminate having an irregular network structure composed of metal fine particles. Next, as a conductive treatment of this laminate, heat treatment was performed at 150 ° C. for 2 minutes, and then immersed in 1N hydrochloric acid (1N hydrochloric acid manufactured by Nacalai Tesque) for 30 seconds. Thereafter, the laminate was taken out, washed with water, and dried at 100 ° C. for 1 minute to remove moisture, thereby obtaining a conductive substrate 1 having a surface specific resistance value of 30Ω / □ and a total light transmittance of 75%.

(Conductive substrate 2)
A transparent conductive substrate (Toray Film) having a surface specific resistance of 10Ω / □ having an irregular network structure on a biaxially stretched polyethylene terephthalate film (Lumirror (registered trademark) U46 manufactured by Toray Industries, Inc.) and a total light transmittance of 80% A nano silver transparent conductive film TCC-010 manufactured by Processing Co., Ltd. was used as the conductive substrate 2.

(Transparent protective layer forming solution)
As a solution for forming a transparent protective layer, a resin obtained by diluting a commercially available hard coat agent ("OPSTAR" (registered trademark) Z7534, manufactured by JSR Corporation) with methyl isobutyl ketone to a solid content concentration of 40% by weight The solution was used.

Example 1
A copper tape was affixed to 5 mm portions on both ends of the conductive layer side surface of the conductive substrate 1 to provide a pair of electrodes. Thereafter, the transparent protective layer forming solution was applied with a wire bar and laminated on the conductive layer to obtain a transparent sheet heating element having a transparent protective layer. This transparent sheet heating element was formed into a curved surface having a curvature radius of 20 cm by vacuum forming. The conductive layer of the transparent sheet heating element had an irregular network structure, and had a surface resistivity of 30Ω / □ and a total light transmittance of 75%. The exothermic temperature when applying a current of 1 A to the transparent sheet heating element was 30 ° C., and the temperature before energization was 20 ° C., so the exothermic property was “◯”.

(Example 2)
A copper tape was affixed to 5 mm portions at both ends of the conductive layer side surface of the conductive substrate 2 to provide a pair of electrodes. Thereafter, the transparent protective layer forming solution was applied with a wire bar and laminated on the conductive layer to obtain a transparent sheet heating element having a transparent protective layer. This transparent sheet heating element was formed into a curved surface having a curvature radius of 20 cm by vacuum forming. The conductive layer of the transparent sheet heating element had an irregular network structure, and had a surface resistivity of 10Ω / □ and a total light transmittance of 80%. In addition, when the exothermic evaluation of the transparent sheet heating element when a current of 1 A was applied was performed, the exothermic temperature was 40 ° C. and the temperature before energization was 20 ° C. there were.

(Example 3)
A copper tape was affixed to 5 mm portions at both ends of the conductive layer side surface of the conductive substrate 2 to provide a pair of electrodes. Thereafter, the transparent protective layer forming solution was applied with a wire bar and laminated on the conductive layer to obtain a transparent sheet heating element having a transparent protective layer. This transparent sheet heating element was formed into a curved surface with a curvature radius of 5 cm by vacuum forming. The conductive layer of the transparent sheet heating element had an irregular network structure, and had a surface resistivity of 10Ω / □ and a total light transmittance of 80%. In addition, when the exothermic evaluation of the transparent sheet heating element when a current of 1 A was applied was performed, the exothermic temperature was 40 ° C. and the temperature before energization was 20 ° C. there were.

Example 4
When the exothermic evaluation when a current of 2 A was applied to the transparent sheet heating element obtained by the same method as in Example 3 was performed, the heating temperature was 50 ° C., and the temperature before energization was 20 ° C. Therefore, the exothermic property was “◯”.

(Comparative Example 1)
Although vacuum forming was attempted using an ITO film as the conductive substrate, the ITO layer was cracked, and no conductivity and heat generation characteristics were found.

  The present invention relates to a transparent sheet heating element capable of uniformly generating heat, and more particularly to a transparent sheet heating element used for a liquid crystal display element having a curved surface, an automobile defroster, and the like.

Claims (5)

A transparent heating element having a curved surface with one or more pairs of electrodes in a conductive layer of a conductive substrate,
The conductive substrate is a laminate of a transparent substrate and a conductive layer,
The transparent layered heating element, wherein the conductive layer has an irregular network structure.   The transparent sheet heating element according to claim 1, further comprising a transparent protective layer on a surface of the conductive substrate on the conductive layer side.   The transparent sheet heating element according to claim 1 or 2, wherein the conductive layer has a surface specific resistance value of 1 to 100 Ω / □.   The transparent sheet heating element according to claim 1, wherein the total light transmittance is 50% or more.   The method for producing a transparent sheet heating element according to any one of claims 1 to 4, wherein the curved surface is formed by thermoforming.