JPH06260265A - Transparent surface heating element - Google Patents

Abstract

PURPOSE:To uniform the current distribution or heat generation on a conductive film, and improve the connecting property or connecting work property with an external wire by constituting an electrode from a conductive resin layer laminated on a metal foil stuck to the side end of a conductive film, and a terminal part on the foil. CONSTITUTION:In an electrode 4, a metal foil 7 consisting of copper foil is stuck on each side end of the conductive film 3 of a transparent conductive sheet 1 with an adhesive 8, and a conductive resin layer 9 consisting of silver ink is integrally laminated on the foil 7 and the film 3 near it by screen printing. A transparent protective film 5 is stuck to the whole surface with an adhesive 6. The middle part of each metal foil 7 is exposed from the film 5 and the layer 9 as a terminal 10. When an external wire is connected to each terminal 10 by soldering, and a voltage is applied, the foil 7 and the layer 9 in the electrode 4 have substantially equal potentials over the whole length, the current distribution on the film 3 between both electrodes are uniformed over the whole surface, and the heating value can be also uniformed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent sheet heating element used for a back heater of a liquid crystal display, a dew condensation preventing heater of a window glass or the like.

[0002]

2. Description of the Related Art In general, a liquid crystal display has a low response characteristic at a low temperature. Therefore, a liquid crystal display incorporated in a device used at a low temperature, for example, an instrument panel of an automobile, a television set, a navigation system or the like has the response characteristic of Heating means are required to prevent degradation.

As the heating means, a transparent conductive sheet having a conductive film formed on an insulating base material is provided with electrodes made of a conductive resin layer in a band shape on both sides of the conductive film by printing or the like, and a voltage is applied between both electrodes. There is known a transparent sheet heating element that heats a conductive film. However, in the case of this well-known technique, since the electric resistance of the electrode made of the conductive resin layer is significantly higher than that of the conductive film, a relatively large voltage drop occurs in the length direction of the electrode when a voltage is applied, and The conductive film cannot be uniformly heated over the entire surface.
When such a transparent sheet heating element is attached to the glass of the liquid crystal display, the glass will be distorted or cracked due to the difference in the coefficient of thermal expansion between the two.

On the other hand, in order to solve the above-mentioned problem, in JP-A-4-289685 and the like, a metal foil is attached on the conductive resin layer and the conductive resin layer is formed on the metal foil and the conductive resin layer around the metal foil. There has been proposed an electrode structure formed by integrally laminating. However, in the case of this conventional technique, the external electric wire for applying a voltage is connected to the conductive resin layer of the electrode by crimping or the like as in the case of the above-mentioned known technique, so that the connectivity between the external electric wire and the electrode and In addition to poor connection workability, it is difficult to heat the conductive film uniformly over the entire surface because a large amount of current still remains in the conductive film in the conductive resin layer near the connection with the external electric wire. There is a problem that the metal foil and the conductive resin layer are easily stuck in the electrode.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to make the current distribution on the conductive film uniform and to allow the conductive film to generate heat evenly over the entire surface, and moreover, the connectivity and connection between the external electric wire and the electrode. It is to provide a transparent sheet heating element having excellent workability.

[0006]

A transparent sheet heating element according to the present invention has a transparent conductive sheet formed by forming a conductive film on an insulating base material, in which strip-shaped electrodes are provided on both side ends of the conductive film. In a transparent planar heating element in which a voltage is applied to the conductive film to heat the conductive film, each electrode is a metal foil adhered in a strip shape on the end of the conductive film and a metal foil and a conductive film in the vicinity thereof. It is characterized in that it is composed of a conductive resin layer integrally laminated and a terminal portion formed by partially exposing the metal foil from the conductive resin layer.

A transparent film or transparent sheet made of polyester or other plastic can be used as the insulating base material, and gold, silver, indium tin oxide, aluminum or the like can be selected as the material of the conductive film. Furthermore, as the metal foil, a metal foil having good electrical conductivity such as gold foil, silver foil, copper foil, aluminum foil is preferable, and a known silver ink or carbon ink having excellent printability can be preferably used for the conductive resin layer. .

A transparent protective film is usually attached to the entire surface of the conductive film and, if necessary, the electrode except the terminal portion. The terminals may be coated with solder in advance for connection with an external electric wire.

[0009]

In the transparent sheet heating element, when external wires are connected to the terminals of both electrodes by soldering or another method and a voltage is applied between the electrodes, the metal foil in each electrode has a good electrical conductivity. Therefore, the electric potential is almost constant over the entire length without causing a voltage drop in the length direction, and the conductive resin layer that electrically connects the metal foil and the conductive film is also substantially equal electric potential over the entire length. Since a uniform voltage is applied to the conductive film over the entire length of each electrode, the current distribution on the conductive film is uniform over the entire surface and the calorific value of Joule heat is also uniform over the entire surface.

When the transparent sheet heating element is used as a back heater of a liquid crystal display for automobiles, for example, it is necessary to rapidly raise the temperature to a required temperature. For example, a heater for preventing dew condensation on window glass. When it is used by being attached to a glass surface or sandwiched between glass, the temperature may be gradually raised to a temperature at which human body is not burned. The time required to reach the required temperature can be arbitrarily determined by selecting the applied voltage and the surface resistance value of the conductive film. The surface resistance value of the conductive film is, for example, about 3 to 7 Ω / □ for the former use, and 500 to about the latter use.
About 2000Ω / □ can be suitably selected.

[0011]

FIG. 1 is a schematic view of a transparent sheet heating element according to an embodiment of the present invention, (A) is a sectional view, and (B) is a plan view.

In FIG. 1, the transparent conductive sheet 1 is formed by forming a conductive film 3 having a surface resistance value of 7 Ω / □ on an insulating substrate 2 made of a transparent film.
Electrodes 4 are provided in strips at both ends, and the conductive film 3 and the electrodes 4 are provided.
The transparent protective film 5 is adhered to the entire surface with the adhesive 6.

In the electrode 4, a metal foil 7 made of copper foil is provided on each side end of the conductive film 3 in the transparent conductive sheet 1 with an adhesive agent 8.
The conductive resin layer 9 made of silver ink is integrally laminated on the metal foil 7 and the conductive film 3 in the vicinity thereof by screen printing, and the intermediate portion of each metal foil 7 serves as the terminal portion 10. The transparent protective film 5 and the conductive resin layer 9 are exposed.

Each terminal portion 10 of the transparent sheet heating element having the above construction
An external electric wire 11 was connected to the electrode and a DC voltage of 12 V was applied between both electrodes 4 to measure the surface temperature distribution of the conductive film 3 during the temperature rise.
It was confirmed that the temperature distribution was within the range.

[0015]

Since the transparent sheet heating element according to the present invention is constructed as described above, the current distribution on the conductive film can be made uniform, and the conductive film can be uniformly heated over the entire surface. Excellent connectivity and workability between electric wires and electrodes.

[Brief description of drawings]

FIG. 1 is a schematic view of a transparent sheet heating element according to an embodiment of the present invention, (A) is a sectional view, and (B) is a plan view.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent conductive sheet 2 Insulating base material 3 Conductive film 4 Electrode 7 Metal foil 9 Conductive resin layer 10 Terminal part

Claims (1)

[Claims] 1. A transparent conductive sheet formed by forming a conductive film on an insulating base material, in which strip-shaped electrodes are provided at both ends of the conductive film, and a voltage is applied between both electrodes to heat the conductive film. In the planar heating element, each electrode has a metal foil adhered in a strip shape on the end of the conductive film, a conductive resin layer integrally laminated on the metal foil and the conductive film in the vicinity thereof, and the metal foil is a conductive resin. A transparent sheet heating element, comprising a terminal portion partially exposed from the layer.